DE102011089061B4 - Coordinate measuring machine and method for operating a coordinate measuring machine - Google Patents

Abstract

Method for operating a coordinate measuring machine (11), a mechanism (3) for adjusting a sensor (9) relative to a workpiece support (1) in at least one direction (x) and this mechanism (3) having at least one electric motor (M) has, via which the adjustment of the sensor (9) or the workpiece support (1) is driven in this direction and wherein the method comprises the following steps: a) an electric drive current (Iist) that flows through the electric motor (M) to Movement of the electric motor (M) and in this way a movement of the sensor (9) or the workpiece support (1) is measured, b) an actual position (vist) of the sensor (9) or the workpiece support (1) in the direction (x) driven by the electric motor (M) is measured, c) a control deviation (Ax) between the measured actual position (xist) and a specified target position (xsoll) is determined by determining the difference between the measured actual Position (xist) un d) the specified target position (xsoll) is determined, d) on the basis of the control deviation, a controller (14) determines a manipulated variable (vcontrol) that is used by the electric motor to set the speed of the sensor (9) or the workpiece support (1) (M) is proportional to the driven direction (x), e) depending on the manipulated variable (vcontrol) determined by the controller (14), a current limit value (Imax) or a current limit value band (i.e. H. a range of values for the drive current, which is defined by a lower current limit value Imin and an upper current limit value Imax) determined for the electrical drive current, andf) when the electrical drive current reaches the current limit value (Imax) determined in step (e) and / or if the electrical drive current exceeds the determined current limit value (Imax) or if the current limit value band (Imin, Imax) is left, the movement of the mechanism (3) is stopped at least in the direction driven by the electric motor.

Description

The invention relates to a coordinate measuring machine and a method for operating a coordinate measuring machine. The coordinate measuring machine has a mechanism (see, purely as an example, the mechanism 3 of the portal type in 1 ) to adjust a sensor relative to a workpiece holder in at least one direction, the mechanism having at least one electric motor, via which the adjustment of the sensor or the workpiece holder is driven in this direction. In this case, an electric drive current is measured which flows through the electric motor in order to bring about a movement of the electric motor and in this way a movement of the sensor or the workpiece holder. The measured drive current is compared with a current limit value or a current limit value band and, when the electrical drive current reaches and / or exceeds the current limit value or when the current limit value band is left, the movement of the mechanics is stopped at least in the direction driven by the electric motor.

Such a coordinate measuring machine is from the US patent US 7 627 957 B2 and from its priority application, namely the document DE 10 2006 003 362 A1 , known. A coordinate measuring device of the type mentioned at the beginning and a corresponding method for operating such a coordinate measuring device are shown here. Said current limit value or said current limit value band is determined here as a function of a setpoint speed and / or as a function of a setpoint acceleration with which the movement of the electric motor and thus the movement of the sensor or the workpiece holder should take place in the relevant direction. For this purpose, a functional relationship between the target speed and / or the target acceleration on the one hand and the current limit value of the drive current or the current limit value band of the drive current on the other hand is firmly specified.

This effectively creates a coordinate measuring device that prevents the electric motor from continuing to operate in the event of a collision of moving components of the said mechanics, such as a measuring slide movable in one coordinate direction, or the said sensor or the said workpiece holder with people or objects, even though one Collision has occurred. Due to the dynamic adaptation of the current limit value or the current limit value band as a function of the target speed and / or the target acceleration, it can also be ensured that collisions are recognized at different speeds and accelerations.

Coordinate measuring machines with this type of functionality work reliably. However, the commissioning of the method is sometimes relatively complex because the relationship between the target speed and / or the target acceleration on the one hand and the current flowing through the electric motor on the other hand has to be determined by sometimes complex series of measurements. The controller reacts to a specified target speed and / or a target acceleration with a specific time behavior that must be taken into account when determining the current limit value or the current limit value band. During acceleration processes, for example, the only limited stiffness of the mechanics tends to vibrate, which accordingly leads to a variation in the drive current. Another example is the time offset that lies between the point in time of a new setpoint speed and / or a new setpoint acceleration on the one hand and the point in time of the associated actual change in the drive current on the other.

Another coordinate measuring machine which practically uses exactly the same method as in the document US 7 627 957 B2 and the pamphlet DE 10 2006 003 362 A1 is shown in the document US 2011/0 192 044 A1 shown.

It is also from the pamphlet DE 100 24 976 A1 Generally a torque control device is known which compares an actual drive current of an electric motor with a setpoint drive current of the electric motor and generates a manipulated variable signal as a function of the comparison result. It is ensured that the drive current, based on the comparison with a maximum permitted drive current, is below the maximum permitted value in order to avoid a test element hitting hard against a body.

However, a disadvantage of such a procedure is that the drive current is also limited by the maximum value when the test element is not in the vicinity of the workpiece to be measured. The speed at which the test element can be moved and the acceleration are therefore limited.

From the pamphlet JP 2008 - 32 475 A a surface measuring device is known in which a tactile stylus comes into contact with a surface to be measured. In order to prevent the stylus from breaking off when the load is too high, an anomaly in the loading of the stylus can be detected. For this purpose, a speed determination unit is provided in the surface measuring device for each of the drive motors via which the stylus is moved relative to the surface to be measured relevant drive motor is measured. In addition, a current measuring unit is also provided for each of these drive motors, via which the respective motor current of the drive motor in question is measured. A stylus anomaly determination unit connected to the speed determination units and the current measuring units determines an abnormal load in the stylus if the speed measured for a respective drive motor falls below a predefined threshold value and at the same time the measured current of the drive motor concerned exceeds a threshold value for the current.

It is the object of the present invention to specify a coordinate measuring machine and a method for operating a coordinate measuring machine of the type specified above with a current limit value or current limit value band for the drive current that is adapted to the respective acceleration and / or speed, with which the current limit value or the current limit value band is simpler and easier in particular is adapted more precisely to the drive current.

The object is achieved by the subject matter of the attached independent patent claims 1 and 16.

According to an essential concept of the present invention, an actual position of the sensor or of the measurement support is measured in the direction driven by the electric motor. From this, a control deviation between the measured actual position and a predefined setpoint position is determined by determining the difference between the measured actual position and the predefined setpoint position. On the basis of the control deviation, a controller, which is often referred to as a position controller, then determines a manipulated variable, in particular a manipulated speed variable, which is proportional to the speed to be set for the sensor or the workpiece support in the direction driven by the electric motor. The current limit value or the current limit value band for the electrical drive current is then determined from this manipulated variable.

This is surprising for the following reasons. When considering the method known from the prior art, the person skilled in the art had the expectation that only the setpoint speed and / or the setpoint acceleration would allow a reliable determination of the current limit value for detecting a collision. The reason for this is that the speed and the acceleration of the sensor or the workpiece support in the direction driven by the electric motor are specified by the target speed and the target acceleration, because these variables are derived from the travel commands of the measurement sequence. On the other hand, a manipulated variable determined by a controller, which in particular includes the actual position, is defined by the control behavior of the coordinate measuring machine and is therefore not clearly predetermined by the measurement sequence. In the event of a collision, there were therefore reservations as to whether the evaluation of the manipulated variable of a controller would lead to an early collision detection. What is surprising here is the knowledge that to determine the current limit value or the current limit value band, the functional relationship between the target acceleration and / or the target speed is no longer considered, but the manipulated variable of a controller is used to determine the current limit value or the current limit value band .

The actual position can be determined in different ways. For example, the actual position can be determined from the scale values of a mechanical measuring slide driven by the electric motor. These scale values indicate the current position of the relevant measuring slide in the relevant direction of movement of the respective measuring slide. Alternatively, an acceleration sensor could also be used to determine the actual position, for example, which is attached to the relevant measuring slide or to the sensor. The acceleration sensor in question directly supplies the actual acceleration. The actual position can be obtained from the signal from the acceleration sensor by integrating twice over time.

In principle, the tachometer generator connected to the electric motor for recording the current actual speed can also be used to measure the actual position. Since the actual speed is proportional to the current speed of the driven measuring slide and thus to the speed of the sensor in the relevant direction, the signal supplied by the tachometer generator can itself be used as the actual speed. The actual position can be determined by integrating the signal from the tachometer generator over time.

To determine the current limit value or the current limit value band, an expected drive current can be determined from the manipulated variable determined by the controller, which corresponds to an expected value for the actual electrical drive current that is expected for the current manipulated variable. The expected drive current can generally be determined in different ways. For example, a table can be specified in which values for the expected drive current are stored for a large number of different values of the manipulated variable. If necessary, intermediate values can be determined via interpolation.

The values for such a table can be determined as follows.

As already stated above, the manipulated variable is proportional to a speed to be set for the sensor or the workpiece support in the direction driven by the electric motor. Therefore, the sensor or the workpiece support can simply be moved in the relevant direction driven by the electric motor at different constant speeds and both the manipulated variables that occur and the associated drive currents that occur can be measured. The resulting manipulated variables and the associated drive currents are then stored in a table. An expected drive current can then be read from the table generated in this way, in which the current manipulated variable is determined and the associated drive current is read out from the table.

The drive currents in the electric motor are not only dependent on the speed of the sensor or the workpiece support in the direction driven by the electric motor, but also to a considerable extent on the acceleration of the sensor or the workpiece support in the direction driven by the electric motor. A much more precise determination of the expected drive current in the electric motor can be achieved if a table is provided in which both the manipulated variable and an acceleration are taken into account.

A table in which both the manipulated variable and an actual acceleration are taken into account can be included as follows. The sensor or the workpiece support is moved in the relevant direction driven by the electric motor with a constant actual acceleration. During the acceleration process, the actual speed increases continuously and thus also the manipulated variable proportional to it. During the acceleration process, the associated drive current is then measured for certain values of the manipulated variable. This process is repeated for a large number of different actual accelerations. The measured drive currents depending on the respective actual acceleration and the respective manipulated variable are then stored in the table.

From the table generated in this way, an expected drive current can then be read out in the measuring mode, in which the manipulated variable and the actual acceleration are determined and the associated drive current is read out from the table.

Instead of the measured actual acceleration a _is the expected driving current, a current acceleration a _act are used in the determination generally at least approximately representing the current acceleration of the sensor or the workpiece support in the driven by the electric motor direction. For example, a predefined setpoint acceleration a setpoint can _be used, which is predefined by the control based on the measurement sequence. This is possible because the target acceleration a _supposed relatively similar to the actual actual acceleration _a is.

It may also be the time derivative of the manipulated variable V can be used as a _{tax, tax} actual acceleration a _act. The reason for this is that the said control value V is _controlled in proportion to the adjusted speed of the sensor or the workpiece support in the driven by the electric motor direction in order thus also a time derivative of the manipulated variable V so that _{the control} is proportional to the actual acceleration a _act.

It may also as the current acceleration a _act, an average a _nude - _middle of at least two sizes of said measured actual acceleration a _is given a desired acceleration _to and time derivative of the manipulated variable V are used _controlling a _control.

In measuring mode, the manipulated variable is then V _control and the actual acceleration a _act, either the actual acceleration _a or the target acceleration a _will or the derivative of a _control of the manipulated variable V _control or an average of a _nude - _middle of at least two of the sizes target acceleration a _is to actual acceleration a _is determined and derivative _control are a _control of the manipulated variable V and read from the table of the associated drive current.

However, it is considerably easier if the expected drive current can be calculated from a function. In a very simple form of such a determination of the expected drive _{current only as a function of the manipulated variable V tax} , a variable speed component can simply be taken into account, which is proportional to the current manipulated variable V _tax . The required for this proportionality factor K _v can be easily determined by the sensor or the workpiece support in the respective, driven by the electric motor direction at a high, constant actual speed is moved and the command value V in question determined _tax and the corresponding driving current I _is measured will. The proportionality factor K _v can then be determined as follows: $${\text{K}}_{\text{v}}={\text{I.}}_{\text{is}}/{\text{v}}_{\text{tax}}$$

An expected drive current I _erw can then be obtained after determining the proportionality factor K _v in the regular measuring mode of the coordinate measuring machine can be determined as follows depending on the current manipulated variable V _tax: $${\text{I.}}_{\text{exp}}\left({\text{v}}_{\text{tax}}\right)={\text{v}}_{\text{tax}}·{\text{K}}_{\text{v}}$$

As already explained above, the actual drive current in the electric motor is not only dependent on the speed of the sensor or the workpiece support in the direction driven by the electric motor, but also to a considerable extent on the current acceleration of the sensor or the workpiece support in the direction driven by the electric motor driven direction dependent. The accuracy with which the expected value of the drive _{current I erw} can be determined can therefore be considerably improved if, when determining the expected drive current, a variable acceleration component is taken into account, which is proportional to a current acceleration a _akt .

As already stated above, the measured actual acceleration a _ist can be used _{as the current acceleration a act.} However, a predefined setpoint acceleration a setpoint can also _be used. In addition, the time derivative a _{tax of} the manipulated variable V _tax can also be used. It may also, an average of at least two of the variables measured actual acceleration a _is given a desired acceleration _to and time derivative of the manipulated variable V are used _controlling a _control.

_{An equation that uses} the determined manipulated variable V tax and a measured actual acceleration a _ist or a predetermined target acceleration a _soll or a time derivative a _{tax of} the manipulated variable V _tax or an average value a _akt - _mean of at least two of the measured variables actual acceleration a _is ASON predetermined desired acceleration or time derivative (a _control) of the manipulated variable (V _control) of the drive is current can be calculated, is the following: $${\text{I.}}_{\text{exp}}\left({\text{v}}_{\text{tax}},{\text{a}}_{\text{act}}\right)={\text{v}}_{\text{tax}}·{\text{K}}_{\text{v}}+{\text{a}}_{\text{act}}·{\text{K}}_{\text{a}}$$

• K_v = Proportionalitätsfaktor für den variablen Geschwindigkeitsanteil
• V_steuer = aktuelle Stellgröße des Reglers
• K_a = Proportionalitätsfaktor für den variablen Beschleunigungsanteil
• a_akt = die aktuelle Beschleunigung des Sensors oder der Werkstückauflage in der durch den Elektromotor angetriebenen Richtung, also entweder die gemessene Ist-Beschleunigung a_ist oder die vorgegebene Soll-Beschleunigung a_soll oder eine zeitliche Ableitung a_steuer der Stellgröße V_steuer oder ein Mittelwert a_akt-_mittel aus wenigstens zwei der Größen gemessene Ist-Beschleunigung a_ist, vorgegebene Soll-Beschleunigung a_soll und zeitliche Ableitung a_steuer der Stellgröße V_steuer

Herein mean:

• K _v = proportionality factor for the variable speed component
• V _tax = current manipulated value
• K _a = proportionality factor for the variable acceleration component
• a _akt = the current acceleration of the sensor or the workpiece support in the direction driven by the electric motor, i.e. either the measured actual acceleration a _ist or the specified target acceleration a _soll or a time derivative a _{tax of} the manipulated variable V _tax or an average value a _akt - _middle of at least two of the variables measured actual acceleration a _is given a desired acceleration _to a _controlled and time derivative of the manipulated variable V _tax

In addition to the proportionality factor K _v for the speed component, a proportionality factor K _a for the acceleration component is now also provided in this equation. When determining the two proportionality factors, it is important that the proportionality factor K _v for the speed component is determined first. The determination can be carried out in exactly the same way as was explained above in connection with equation 1 and equation 2. After the current acceleration a _{akt is} equal to zero at a constant actual speed, the acceleration component a _akt • K _a then drops out. As soon as the proportionality factor K _{v has been determined} for the speed component, the proportionality factor for the acceleration component can be determined. _{For this purpose, the sensor or the workpiece support is} accelerated in the relevant direction driven by the electric motor with a high, constant actual acceleration a ist. For a predefined manipulated variable V _control during the acceleration operation, the drive current is then I _is measured. Of the actual acceleration a of the manipulated variable V _{is controlled,} and the measured driving current _I may then be the proportionality factor K _a is determined as follows: $${\text{K}}_{\text{a}}=\left({\text{I.}}_{\text{is}}-{\text{v}}_{\text{tax}}·{\text{K}}_{\text{v}}\right)/{\text{a}}_{\text{is}}$$

Once the proportionality _v K and K _a is determined, then an expected driving current can l _erw during regular measurement operation of the coordinate measuring device depending on the manipulated variable V _control and the actual acceleration a _act (either measurement _is actual acceleration a or determination of the desired acceleration a _soll or determination of the derivative a _control of the manipulated variable V _control or averaging a _nude - _medium through at least two of the variables measured actual acceleration a _is predetermined desired acceleration a _to and calculated derivative a _control of the manipulated variable V _control) calculated by equation 3 will.

It has also been found that _control in addition to the manipulated variable V and the actual acceleration a _act is a further essential parameter, the proportion of drive current that this is necessary to move the sensor or the workpiece support at all in the relevant driven by the electric motor direction . There can be various reasons for this. For example, opposite to the direction of travel, in the one Measuring slide is driven by the electric motor, frictional forces act. Forces can also occur because a cable harness, which contains the power supply lines and / or the signal lines for the mechanics, is deformed by the movement and forces occur as a result. Another reason for a vertically movable measuring slide can be that the weight forces of the measuring slide are absorbed by the electric motor and as a result the weight of the measuring slide counteracts the movement when the measuring slide moves upwards or cooperates with a downward movement in the direction of movement.

It is therefore particularly advantageous if, when determining the expected drive current, a basic component R is taken into account, which corresponds to a drive current when the sensor or the workpiece support is moved in the direction driven by the electric motor at a low constant speed. _{A constant basic component R * that is independent of the speed direction of} the manipulated variable V control can be used as the basic component. However, since this basic component _{can depend on the speed direction of the manipulated variable V tax} , a basic ^{component R ±} _{dependent on the speed direction of the manipulated variable V tax} can particularly advantageously be used as the base component, this direction-dependent basic component R ^± assuming a first constant value R ^{+ if} the measured manipulated variable V _{tax is} positive and assumes a second constant value R ^- when the measured manipulated variable V _{tax is} negative.

This basic component R can be used both in connection with the table described above and in connection with the function just described. If a constant basic component R * is used, the relevant measuring slide is moved in the direction driven by the electric motor at a very low speed and the drive current I act measured here _{is used} as a constant basic component. If a direction-dependent basic ^{component R ±} is to be used, the relevant measuring slide is first moved by the electric motor in the positive ^{direction of speed at a very low speed and the drive current list measured here is taken over as the first constant value R +} and then moved in the negative direction of speed at very low speed and the drive current I measured here _is taken over as the second constant value R ^-.

When using a basic component R, it is essential that it is determined at the very beginning, i.e. before the table described above is created or before the proportionality factors K _v and / or K _{a are determined} in the function. _{The basic component is then} always taken into account when determining the entries in the table or, in the case of the function, when determining the proportionality factor K _v for the variable speed component and / or the proportionality factor K _a for the variable acceleration component, in that the respective measured drive current I ist um the basic portion R is reduced.

An I _exp function (v _tax, a _act), to incorporate a particularly accurate results for the expected driving current I _ext determine, is as follows: $${\text{I.}}_{\text{exp}}\left({\text{v}}_{\text{tax}},{\text{a}}_{\text{act}}\right)=\text{R.}+{\text{v}}_{\text{tax}}\cdot {\text{K}}_{\text{v}}+{\text{a}}_{\text{act}}\cdot {\text{K}}_{\text{a}}$$

• R = der besagte Grundanteil, also entweder der konstante Grundanteil R* oder der richtungsabhängige Grundanteil R^±
• K_v = Proportionalitätsfaktor für den variablen Geschwindigkeitsanteil
• V_steuer = aktuelle Stellgröße des Reglers
• K_a = Proportionalitätsfaktor für den variablen Beschleunigungsanteil
• a_akt = die besagte aktuelle Beschleunigung, also entweder die gemessene Ist-Beschleunigung a_ist oder die vorgegebene Soll-Beschleunigung a_soll oder die Ableitung a_steuer der Stellgröße V_steuer oder ein Mittelwert a_akt-_mittel aus wenigstens zwei der Größen gemessene Ist-Beschleunigung a_ist, vorgegebene Soll-Beschleunigung a_soll und Ableitung a_steuer der Stellgröße V_steuer

Herein mean:

• R = the said basic component, i.e. either the constant basic component R * or the direction-dependent basic component R ^±
• K _v = proportionality factor for the variable speed component
• V _tax = current manipulated value
• K _a = proportionality factor for the variable acceleration component
• a _akt = the said current acceleration, i.e. either the measured actual acceleration a _ist or the specified target acceleration a _soll or the derivative a _{tax of} the manipulated variable V _tax or an average value a _akt - _average of at least two of the measured actual acceleration values _a, given a desired acceleration _to a _control and discharge _control of the manipulated variable V

_Is by determining the actual acceleration a _act and the actual control value V, and substituting these values in Equation 5 can then in a particularly simple manner the correct drive current I are _heated determined.

In the case of a direction-dependent basic component R ^± , the values R ^± , K _v and K _a can be determined as follows. First, the direction-dependent basic component R ^{± is} determined in that the relevant measuring slide is initially moved by the electric motor in the positive direction of speed at a very low speed. The case measured drive current _I ⁺ is accepted as the first constant value R. The measuring slide is then moved in the negative direction of speed at a very low speed and the drive current I act measured here _is taken over as the second constant value R ^-. Thereafter, the proportionality factor K _v is determined for the variable velocity component by the measuring carriage with high constant actual speed is moved and the command value V determined _tax, and the actual driving current I _is measured. After the current Acceleration a _{act is} approximately zero at constant speed, the proportionality factor K _v for the variable speed component can then be determined as follows: $${\text{K}}_{\text{v}}=\left({\text{I.}}_{\text{is}}-\text{R.}\right)/{\text{v}}_{\text{tax}}$$

As already described above, the basic _{component R is taken into account when determining the proportionality factor K v} for the variable speed component, in that the respective measured drive current I _{ist is} reduced by the basic _{component R, i.e. I ist} - R. In the case of a constant basic component, would be set by R, of course, R * and use in case of a direction-dependent basic component R ^± would place of R depending on the direction of the velocity, which is represented by the _control command value V, either R or R ^{+ -} use.

Finally, the proportionality factor for the variable acceleration component is determined by the measuring carriage with high constant actual acceleration _a is moved and _controlled for a time, the manipulated variable V, the actual acceleration a _and the actual driving current _I is measured. The proportionality factor K _a for the variable acceleration component can then be determined as follows: $${\text{K}}_{\text{a}}=\left({\text{I.}}_{\text{is}}-\text{R.}-{\text{v}}_{\text{tax}}\cdot {\text{K}}_{\text{v}}\right)/{\text{a}}_{\text{is}}$$

In equation 7, as already described above, the basic _{component R is also taken into account when determining the proportionality factor K a} for the variable acceleration component, in that the respective measured drive current I _{ist is} reduced by the basic _{component R, i.e. I is} - R. In the case of a of course, instead of R, R * would have to be substituted for a constant basic component, and in the case of a basic component R ^± dependent on the direction of speed, either R ⁺ or R ^- would have to be used instead of R depending on the direction represented by the manipulated variable V _tax .

A current limit value can then be determined very easily from the expected drive _{current I erw by increasing the expected drive current I erw} by a first current value d. Please note the following here. Depending on the direction of the velocity, the _tax results from the control value V, the drive current I _is usually positive or negative. (Note: In the case of vertically movable measuring slides whose weight is not compensated for by a counterweight or a spring, for example, the drive current I _{ist can} also have the same sign for both directions of the actual speed). The increase by a first current value d means in the case of a positive expected drive _{current I exp} that the first current value d is added, while in the case of a negative expected drive current lerw the first current value d must be subtracted. However, one can also simply use the amount of the expected drive _{current I erw} , so that an increase then generally takes place by adding the first current value d.

Instead of a current limit value, however, a current limit value band can also be used, as already explained above, in that a first current value d is added to the expected drive current in order to obtain an upper current limit value and a second current value e is subtracted from the expected drive current to give a lower current limit value obtain. D as far as the first current value and second current value e are the same in magnitude, makes the direction of the velocity, the _control resulting from the control value V, not matter, since the upper current threshold and the lower current limit value far then independent of the velocity direction is always equal to are removed from the expected drive current I _ext.

D as far as the first current value and second current value e are different, must then of course in the opposite direction, the speed, the _control resulting from the control value V, the first constant current value D is subtracted be (this the lower current limit of the current limit value band is then obtained), and the second constant current value e can be added (this then gives the upper current limit value of the current limit value band).

Thus, when determining the current limit value or a first current limit value (upper current limit value for one direction of speed, lower current limit value for the other direction of speed) of the current limit value band, the expected drive current is increased by a first current value in such a way that the amount of the current limit value or the first current limit value of the current limit value band is higher than the amount of the expected drive current.

To determine a second current limit value (lower current limit value for one direction of speed, upper current limit value for the other direction of speed) of the current limit value band, the expected drive current is additionally reduced by a second current value e so that the amount of the second current limit value of the current limit value band is lower than is the amount of expected drive current.

The first current value d and / or the second current value e are constant in the simplest case. Instead of a constant first current value d and possibly a constant second current value e, however, current values can also be used which vary as a function of parameters such as the actual speed and / or the actual acceleration. For example, the magnitude of the first current value d and possibly the second current value e can be greater for low speeds than for high speeds because, in particular for low speeds, there are higher deviations of the measured drive current compared to the expected drive current than at higher speeds.

With regard to the mechanics for adjusting a sensor relative to a workpiece holder, the following should be noted. At the present time there is an abundance of different mechanisms with which a sensor can be adjusted relative to a workpiece holder.

Mechanics in which the workpiece holder is designed as a stationary workpiece table, for example, are common, with the sensor usually being able to be moved in three mutually perpendicular coordinate directions via the mechanics. To this end, such a mechanism has a measuring slide for each of the coordinate directions, which is guided along a linear guide, the relevant measuring slide being driven in the relevant direction via the said electric motor and a scale with an associated reading head being provided via which the current position of the measuring slide can be determined. An exemplary structure of such a coordinate measuring machine is a coordinate measuring machine of the so-called portal type, as described below in connection with 1 is explained in detail.

Coordinate measuring machines are also known in which the relative movement between the sensor and the workpiece support is generated not or not exclusively by adjusting the sensor, but rather by adjusting the workpiece support in one or more coordinate directions. For this purpose, the relevant mechanics then, exactly as described above in connection with the adjustment of the sensor, have a measuring slide for each of the relevant coordinate directions, which is guided along a linear guide, the relevant measuring slide being driven in the relevant direction via the said electric motor and a scale with an associated reading head is provided, via which the current position of the measuring slide can be determined in the relevant direction.

Coordinate measuring machines are also known in which the relative movement between the workpiece support and the sensor is generated by swivel joints. Examples of this are turntables that support the workpiece rotatably along a vertical axis of rotation, swivel joints with which the sensor is rotatably and pivotably attached to the end of the measuring arm, which is movably mounted in three coordinate directions, or robot arms that only have swivel joints. Here, too, an electric motor and a rotary encoder, via which the respective angle of rotation of the rotary joint can be measured, are provided for generating the rotary movement in the swivel joints.

Coordinate measuring machines are also known in which the relative movement between the sensor and the workpiece support is limited to only two coordinate directions. The third coordinate direction is determined, for example, optically using an optical distance sensor. In principle, a mechanism is even conceivable in which the relative movement between the sensor and the workpiece support takes place in only one coordinate direction. For example, the sensor could be a digital camera that records the entire width of the workpiece and that measures the distance to the workpiece, for example through the focus position.

A wide variety of types can be used as sensors.Tactile sensors can be used, such as a measuring probe head, in which the deflection of a probe element touching the workpiece can be measured in three coordinate directions, or a switching probe head which sends a signal when the workpiece touches its probe element gives away. However, optical sensors such as a digital camera or a laser triangulation button or other suitable sensors can also be used, for example.

The invention makes it possible to provide reliable collision monitoring for any course of the speed and thus also any course of the acceleration. In order to achieve high acceleration of the sensor or the workpiece support, a correspondingly high current limit value is required. If only a slow speed is specified and only low acceleration values are allowed, the current limit value can be selected to be low.

1. (a) ein elektrischer Antriebstrom, der durch den Elektromotor fließt, um eine Bewegung des Elektromotors und auf diese Weise eine Bewegung des Sensors oder der Werkstückauflage zu bewirken, wird gemessen,
2. (b) eine Ist-Position des Sensors oder der Werkstückauflage in der durch den Elektromotor angetriebenen Richtung wird gemessen,
3. (c) eine Regelabweichung zwischen der gemessenen Ist-Position und einer vorgegebenen Soll-Position wird durch Ermittlung der Differenz zwischen der gemessenen Ist-Position und der vorgegebenen Soll-Position bestimmt,
4. (d) aufgrund der Regelabweichung wird durch einen Regler eine Stellgröße ermittelt, die zur einzustellenden Geschwindigkeit des Sensors oder der Werkstückauflage in der durch den Elektromotor angetriebenen Richtung proportional ist,
5. (e) abhängig von der durch den Regler ermittelten Stellgröße wird ein Stromgrenzwert oder ein Stromgrenzwertband (d. h. ein Bereich von Werten für den Antriebstrom, der durch einen unteren Stromgrenzwert und einen oberen Stromgrenzwert definiert ist) für den elektrischen Antriebstrom ermittelt,
6. (f) wenn der elektrische Antriebstrom den ermittelten Stromgrenzwert erreicht und/oder wenn der elektrische Antriebstrom den ermittelten Stromgrenzwert überschreitet, oder wenn das Stromgrenzwertband verlassen wird, wird die Bewegung der Mechanik zumindest in der durch den Elektromotor angetriebenen Richtung angehalten.

In particular, a method for operating a coordinate measuring machine is proposed, with a mechanism for adjusting a sensor relative to a workpiece support in at least one direction and this mechanism having at least one electric motor, via which the adjustment of the sensor or the workpiece support is driven in this direction and the method comprising the steps of:

1. (a) an electric drive current that flows through the electric motor in order to cause a movement of the electric motor and in this way a movement of the sensor or the workpiece support is measured,
2. (b) an actual position of the sensor or the workpiece support in the direction driven by the electric motor is measured,
3. (c) a control deviation between the measured actual position and a predetermined target position is determined by determining the difference between the measured actual position and the predetermined target position,
4. (d) on the basis of the system deviation, a controller determines a manipulated variable that is proportional to the speed to be set for the sensor or the workpiece support in the direction driven by the electric motor,
5. (e) depending on the manipulated variable determined by the controller, a current limit value or a current limit value band (i.e. a range of values for the drive current that is defined by a lower current limit value and an upper current limit value) is determined for the electrical drive current,
6. (f) if the electrical drive current reaches the determined current limit value and / or if the electrical drive current exceeds the determined current limit value, or if the current limit value band is left, the movement of the mechanics is stopped at least in the direction driven by the electric motor.

"Exceeding" the current limit value means that the drive current in one case z. B. is greater than the current limit and in another case z. B. is smaller than the current limit value. “Crossing” is to be understood in the sense of “crossing”. The determination of a current limit value and the monitoring of whether the current limit value is reached and / or exceeded also includes the possibility of a current limit value band, i. H. a range of values for the drive current which is defined by a lower current limit value and an upper current limit value. It is then monitored whether the drive current exceeds the current limit value band, i. H. leaves the area, in which case the movement of the mechanics is stopped at least in the direction driven by the electric motor. Leaving the current limit value band is to be understood as meaning that the drive current reaches and / or exceeds the upper current limit value of the current limit value band or reaches and / or “exceeds” the lower current limit value of the current limit value band. Checking whether the current limit value band is left is in fact the same as monitoring whether a current limit value is reached and / or exceeded, only that this monitoring is carried out for an upper current limit value and for a lower current limit value. This feature has been included in the independent claims for the sake of clarity.

The determination of coordinates in a coordinate system is not limited to the fact that the coordinates are Cartesian coordinates. Rather, coordinates of any kind can be determined, for example polar coordinates, cylinder coordinates, etc. A significant advantage of the current monitoring system according to the invention is that the monitoring can remain active even during an accelerated movement of the sensor or the workpiece support in the relevant direction driven by the electric motor. In principle, any high acceleration values can be permitted without the current monitoring having to be switched off.

As shown in detail above, an expected drive current is determined from the manipulated variable determined by the controller and, if applicable, a current acceleration, and the current limit value or the current limit value band is determined from this. In the determination, further parameters can be used to further increase the precision, such as the ambient temperature, the temperature of parts of the coordinate measuring machine, the position of the sensor and / or the workpiece support in a fixed coordinate system, the relative position of the sensor or the workpiece support in relation on the workpiece to be measured or in relation to other parts of the measurement setup and / or through operating states (such as a currently selected gear stage of a multi-stage gearbox, which occurs when the electric motor transmits power to the sensor or to the workpiece support in the relevant the electric motor driven direction is used), be determined. Taking such parameters into account further increases security. In this way, the current limit value can be closer to the current value actually required for operation.

If the current limit value is exceeded or if the current limit value is reached or exceeded or the current limit value band is left, the mechanism is stopped at least in the direction driven by the electric motor. If the mechanics allow the sensor to be adjusted in several directions relative to the workpiece support, the mechanics are preferably stopped in all directions.

The mechanical system can be stopped in the direction driven by the electric motor happen different ways. In the simplest case, the electric drive current of the electric motor provided for driving in the relevant direction is switched off. In order to increase the braking effect, the electric motor can also be activated briefly in such a way that the drive direction is reversed. The electric motor can also be short-circuited. A brake can also be provided, which is then triggered. Furthermore, a coupling can be provided via which the relevant measuring slide, which is provided for adjusting the sensor or the workpiece support in the direction driven by the electric motor, is decoupled from the electric motor so that no more forces are transmitted from the electric motor to the measuring slide. The force and / or the torque of the electric motor can also be limited to a predetermined value. This value can be unchangeable or it can depend on the operating state, the position of the coordinate measuring device and / or on other factors.

The stopping of the mechanics in the direction driven by the electric motor can also be made dependent on the fact that the electric drive current reaches and / or exceeds the determined current limit value continuously over a time interval of a predetermined length or that the electric drive current continuously exceeds the determined current limit value band over a time interval of a predetermined length Length away. As an alternative or in addition, the measured electrical drive current can be subjected to a smoothing of temporal fluctuations by means of a filter. In both cases, it can be ensured that a very brief (in particular caused by a measurement error) exceeding or very brief reaching of the current limit value does not yet have any effects on the operation of the coordinate measuring machine.

A plurality of electric motors of the coordinate measuring machine are preferably provided, which together cause the movement of the sensor and / or the workpiece support. The movements of the electric motors are clearly assigned to movement components of the movement of the sensor or the workpiece support.

For example, at least one electric motor is provided for a linear movement of the sensor or the workpiece support in the relevant direction of the linear movement, each of the linear movements being able to take place exclusively in one of three directions that are perpendicular to one another in pairs. As a result, any desired point can be approached directly within an accessible range of motion. In general, in the case of the plurality of electric motors that jointly cause the movement of the sensor and / or the workpiece support, a current limit value of the electrical drive current is preferably determined separately for each of the plurality of electric motors, this current limit value being dependent on the manipulated variable of the movement component, which is determined by the respective electric motor is effected.

In the case of a coordinate measuring machine with at least one electric motor each for the x-axis, the y-axis and the z-axis in a Cartesian coordinate system, separate current limit values or current limit value bands for the motor currents are determined depending on the determined manipulated variables in the x-direction, in the y- Direction and determined in the z-direction.

In particular, a plurality of electric motors can be provided for at least one of the movement components in order to bring about the movement of the sensor relative to the workpiece support, as is the case, for example, with coordinate measuring machines with a portal design. In this case, the current limit value or the current limit value band is preferably determined for each of the electric motors of the same movement component (in the case of structurally identical electric motors, the same current limit value or the same current limit value band may be used) and it is monitored separately whether the current limit value or one of the two current limit values of the current limit value band is reached and / or exceeded for the electric motor under consideration. In a preferred embodiment, at least one measured value of the electric drive current is compared with an expected value during operation of the coordinate measuring machine, in particular during a movement of the sensor or the workpiece support in the direction driven by the electric motor, in order to check the measurement of the electric drive current for measurement errors to check. The expected value can e.g. B. can be determined using the determined manipulated variable and possibly the measured current acceleration. Provided that the sensor or the workpiece support moves unhindered in the relevant direction driven by the electric motor, the measurement of the electric drive current can be checked for error-free functionality in this way. In the case of devices with more than one motor for one direction of movement (e.g. double drive on a gantry device in portal or bridge design), it is advantageous not to limit the individual motor currents but rather the sum of the motor currents of the two motors of the double drive.

The determination of the current limit value (or the current limit value band), which depends on the manipulated variable of the controller in the relevant direction driven by the electric motor, is preferably carried out by at least one computing device carried out. Alternatively or additionally, the computing device can also initiate and / or control the measures that are required to stop the mechanics in the direction driven by the electric motor when the current limit value is reached and / or exceeded or the current limit value band is left. This functionality of the computing device can be implemented by hardware and / or software.

1. (a) eine Strom-Messeinrichtung, die ausgestaltet ist, einen elektrischen Antriebstrom, der durch den Elektromotor fließt, um eine Bewegung des Elektromotors zu erzeugen und auf diese Weise eine Bewegung des Sensors oder der Werkstückauflage in der betreffenden durch den Elektromotor angetriebenen Richtung zu bewirken, zu messen,
2. (b) eine Ist-Positionsmesseinrichtung, die dazu ausgestaltet ist, die Ist-Position des Sensors oder der Messauflage in der durch den Elektromotor angetriebenen Richtung zu messen,
3. (c) eine Differenzermittlungseinrichtung, die dazu eingerichtet ist eine Regelabweichung zwischen der gemessenen Ist-Position und einer vorgegebenen Soll-Position durch Ermittlung der Differenz zwischen der gemessenen Ist-Position und der vorgegebenen Soll-Position zu bestimmen,
4. (d) einen Regler, insbesondere einen Lageregler, der aufgrund der Regelabweichung eine Stellgröße ermittelt, die zur einzustellenden Geschwindigkeit des Sensors oder der Werkstückauflage in der durch den Elektromotor angetriebenen Richtung proportional ist,
5. (e) eine Stromgrenzwert-Ermittlungseinrichtung, die ausgestaltet ist, abhängig von der durch den Regler ermittelten Stellgröße einen Stromgrenzwert oder ein Stromgrenzwertband (d. h. ein Bereich von Werten für den Antriebstrom, der durch einen unteren Stromgrenzwert und einen oberen Stromgrenzwert definiert ist) für den elektrischen Antriebstrom zu ermitteln, und
6. (f) eine Betätigungseinrichtung, die mit der Strom-Messeinrichtung und mit der Stromgrenzwert-Ermittlungseinrichtung verbunden ist und die ausgestaltet ist, die Bewegung der Mechanik zumindest in der durch den Elektromotor angetriebenen Richtung anzuhalten, wenn der elektrische Antriebstrom den ermittelten Stromgrenzwert erreicht und/oder wenn der elektrische Antriebstrom den ermittelten Stromgrenzwert überschreitet oder wenn der Antriebstrom das Stromgrenzwertband verlässt.

The scope of the present invention also includes a coordinate measuring machine with a mechanism, a workpiece support for receiving a workpiece to be measured and a sensor, the sensor and the workpiece support being adjustable relative to one another in at least one direction by the mechanism, the mechanism having at least one electric motor , via which the adjustment of the sensor or the workpiece support is driven in this direction. The coordinate measuring machine has the following:

1. (A) a current measuring device which is designed to generate an electric drive current which flows through the electric motor in order to generate a movement of the electric motor and in this way to cause a movement of the sensor or the workpiece support in the relevant direction driven by the electric motor , to eat,
2. (b) an actual position measuring device which is designed to measure the actual position of the sensor or the measurement support in the direction driven by the electric motor,
3. (c) a difference determination device which is set up to determine a control deviation between the measured actual position and a predetermined target position by determining the difference between the measured actual position and the predetermined target position,
4. (d) a controller, in particular a position controller, which, based on the control deviation, determines a manipulated variable that is proportional to the speed to be set for the sensor or the workpiece support in the direction driven by the electric motor,
5. (e) a current limit value determination device which is designed, depending on the manipulated variable determined by the controller, a current limit value or a current limit value band (ie a range of values for the drive current that is defined by a lower current limit value and an upper current limit value) for the electrical Determine drive current, and
6. (f) an actuating device which is connected to the current measuring device and to the current limit value determination device and which is designed to stop the movement of the mechanics at least in the direction driven by the electric motor when the electric drive current reaches the determined current limit value and / or if the electrical drive current exceeds the determined current limit value or if the drive current leaves the current limit value band.

For example, the actuating device has a disconnection device which is connected to the current measuring device and to the current limit value determination device and which is designed to switch off the electrical drive current when the electrical drive current reaches the determined current limit value and / or when the electrical drive current reaches the determined value Current limit value exceeds or when the electric drive current leaves the current limit value band.

The coordinate measuring machine is of course set up to also carry out the method according to one of Claims 2 to 15. In particular, to carry out a method according to at least one of claims 2 to 10, the current limit value determination device is set up accordingly so that the method can be carried out.

Insofar as the current limit value determination device is designed so that when determining the expected drive _{current I erw} , a variable acceleration _{component K a} • a _{act is also} taken into account, which is proportional to a current acceleration a _{act of} the sensor or the workpiece support in the direction driven by the electric motor is, additional devices can be present that provide the current acceleration a _act .

As far as the actual acceleration a _act, a target acceleration a _will is used, the target acceleration a _{is to} be used, which is provided by the controller itself as the current acceleration a _act of value.

As far as the actual acceleration a _{act of} a measured actual acceleration a _is to be used, may additionally be provided an actual acceleration measuring device which is adapted to the actual acceleration a _is to the sensor or the measuring pad in the driven by the electric motor direction measure up. The actual acceleration can be determined in different ways. For example, the actual acceleration can be determined from the scale values of a mechanical measuring slide driven by the electric motor, in that the scale values are derived twice according to the time. The scale values are thus derived twice over time. Alternatively, an acceleration sensor can also be used can be used, which is attached, for example, to the relevant measuring slide or to the sensor. The acceleration sensor in question here directly supplies the actual acceleration _a.

If a time derivative a _tax of said manipulated variable V _{tax is} used as the current acceleration a _act , a derivative calculation unit can be provided which is designed to determine _{a time derivative a tax} of said manipulated variable V _tax.

Insofar as a mean value a _akt - _mean of at least two of the variables measured actual speed, specified target speed and determined derivation a _{tax used} for the manipulated variable V _{tax is} used as the current acceleration a _act, a mean value calculation unit can also be provided for this purpose is designed to calculate a mean value a _akt - _mean from at least two of the measured values actual acceleration a _ist , predetermined target acceleration a _soll or time derivative a _{tax of} the manipulated variable V _tax.

With regard to the control-related components, such as the current measuring device, the actual position measuring device, the actual acceleration measuring device, the derivative calculation unit, the difference determination device, the controller, the current limit value determination device, the actuation device or the switch-off device of the coordinate measuring machine, it should be emphasized that these can of course vary in many ways. For example, for reasons of efficiency, several components can be implemented as a common program code on a microcontroller. For example, this is related to below 2 , 3 and 4th this is the case for the difference determination device and the controller, which are summarized in the component with the designation “position controller 14”. In addition, the actual acceleration that is used to determine the current limit value or the current limit value band of the in 2 shown embodiment is required, determined by a double time derivative of the actual position supplied by the reading head of the scale. These temporal derivations of the actual position take place as two procedural steps 40 and 41 in the current limit value determination device 15th instead of (see below on 5 ). In addition, the current limit value determination device calculates 15th also the current limit value or the current limit values of the current limit value band. The current limit value determination device thus includes 15th in addition, components of the actual acceleration measuring device. The acceleration measuring device thus shown thus includes not only the reading head of the linear scale but also parts of the current limit value determination device.

Alternatively, however, individual components could also be executed as separate programs on a common multitasking microcontroller or executed on separate microcontrollers. Furthermore, some or all of the components can also be designed analogously. In addition, analog and digital components can be accommodated on a common module.

In particular, the coordinate measuring machine can have a computer or a microcontroller which contains the current limit value determination device.

The scope of the invention also includes a computer program which, when running on a computer or a microcontroller, determines at least the current limit value or the current limit value band and optionally also initiates the measures to be taken when the current limit value is reached and / or exceeded or when the current limit value band is left and / or controls. In particular, the computer program has program code means which can be stored on a computer-readable data carrier.

In addition, the scope of the invention includes a data carrier on which a data structure is stored which, after being loaded into a working and / or main memory of a computer or a microcontroller, determines at least the current limit value and optionally also that when the current limit value is reached and / or exceeded initiates and / or controls the measures to be taken when leaving the current limit value band.

• 1 ein Koordinatenmessgerät in Portalbauweise,
• 2 rein schematische Darstellung des Antriebes des in x-Richtung beweglichen Querschlittens 7 aus 1 mit einer erfindungsgemäßen Kollisionsüberwachung,
• 3 Ablaufdiagramm zur Ermittlung des Stellwertes V_steuer durch den Lageregler 14 gemäß 2,
• 4 Ablaufdiagramm zur Ermittlung des Stellwertes V_steuer durch den Lageregler 14 gemäß 2 mit einem gegenüber 3 modifizierten Verfahren,
• 5 Ablaufdiagramm zur Ermittlung des oberen Stromgrenzwertes Imax und des unteren Stromgrenzwertes I_min eines Stromgrenzwertbandes in der Stromgrenzwert-Ermittlungseinrichtung 15 aus 2,
• 6 Darstellung des tatsächlich fließenden Antriebsstroms I_ist und des erwarteten Antriebsstroms I_erw und des hieraus ermittelten oberen Stromgrenzwertes Imax und des unteren Stromgrenzwertes I_min eines Stromgrenzwertbandes für einen beispielhaften Verlauf der Soll-Geschwindigkeit v_soll.für den Antrieb aus 2,
• 7 Darstellung des tatsächlich fließenden Antriebsstroms I_ist und des erwarteten Antriebsstroms I_erw und des hieraus ermittelten oberen Stromgrenzwertes Imax und des unteren Stromgrenzwertes I_min eines Stromgrenzwertbandes für einen beispielhaften Verlauf der Soll-Geschwindigkeit V_soll bei einer Kollision des in 2 gezeigten Querschlittens 7 mit einem Gegenstand,
• 8 Darstellung wie in 7, wobei zusätzlich der obere Stromgrenzwert I_max-prior-art eingezeichnet ist, der von einer herkömmlichen Kollisionsüberwachung aufgrund der Soll-Geschwindigkeit und der Soll-Beschleunigung ermittelt würde und der entsprechende Verlauf des gemessenen Antriebsstroms I_{ist-prior-art},
• 9 eine Messkette bei der Verarbeitung eines Messwertes des Antriebsstroms I_ist,
• 10 Darstellung des tatsächlich fließenden Antriebsstroms I_ist und des erwarteten Antriebsstroms I_erw für einen beispielhaften Verlauf der Soll-Geschwindigkeit V_soll des in 2 gezeigten Querschlittens 7,
• 11 Darstellung des erwarteten Antriebsstroms I_erw-_prior-_art für denselben Verlauf der Soll-Geschwindigkeit V_soll gemäß 10, wobei der erwartete Antriebsstrom I_erw-_prior-_art mit einem herkömmlichen Verfahren aus der Soll-Geschwindigkeit und der Soll-Beschleunigung ermittelt wurde,
• 12 Darstellung wie in 12, wobei zusätzlich der tatsächlich gemessene Antriebsstrom I_ist dargestellt ist,
• 13 Ablaufdiagramm zur Ermittlung des oberen Stromgrenzwertes I_max und des unteren Stromgrenzwertes I_min eines Stromgrenzwertbandes in der Stromgrenzwert-Ermittlungseinrichtung 15 aus 2 gemäß einem anderen Ausführungsbeispiel, bei dem die zeitliche Ableitung a_steuer der Stellgröße V_steuer verwendet wird,
• 14 Ablaufdiagramm zur Ermittlung des oberen Stromgrenzwertes Imax und des unteren Stromgrenzwertes I_min eines Stromgrenzwertbandes in der Stromgrenzwert-Ermittlungseinrichtung 15 aus 2 gemäß einem weiteren Ausführungsbeispiel, bei dem die Soll-Beschleunigung a_soll verwendet wird,
• 15 Ablaufdiagramm zur Ermittlung des oberen Stromgrenzwertes Imax und des unteren Stromgrenzwertes Imin eines Stromgrenzwertbandes in der Stromgrenzwert-Ermittlungseinrichtung 15 aus 2 gemäß einem weiteren Ausführungsbeispiel, bei dem ein Mittelwert a_akt-_mittel verwendet wird.

Embodiments of the invention will now be described with reference to the accompanying figures. The individual figures show:

• 1 a coordinate measuring machine in portal design,
• 2 purely schematic representation of the drive of the cross slide movable in the x-direction 7th the end 1 with a collision monitoring according to the invention,
• 3 Flow chart for determining the manipulated _variable V control by the position controller 14th according to 2 ,
• 4th Flow chart for determining the manipulated _variable V control by the position controller 14th according to 2 with one opposite 3 modified procedures,
• 5 Flow chart for determining the upper current limit value Imax and the lower current limit value I _{min of} a current limit value band in the current limit value determination device 15th the end 2 ,
• 6th Representation of the actually flowing drive _{current I ist} and the expected drive _{current I erw} and the determined upper current limit value Imax and the lower current limit value I _{min of} a current limit value band for an exemplary course of the target speed v _soll. For the drive 2 ,
• 7th Representation of the actually flowing drive _{current I ist} and the expected drive _{current I erw} and the determined upper current limit value Imax and the lower current limit value I _{min of} a current limit value band for an exemplary course of the setpoint speed V _soll in the event of a collision of the in 2 shown cross slide 7th with an object
• 8th Representation as in 7th , whereby the upper current limit value I _max -prior-art is also drawn in, which would be determined by conventional collision monitoring on the basis of the setpoint speed and the setpoint acceleration, and the corresponding course of the measured drive _{current I is -prior-art} ,
• 9 a measuring chain in the processing of a measured value of the drive current I _is
• 10 Representation of the actually flowing drive current I _ist and the expected drive current I _erw for an exemplary course of the setpoint speed V _{soll of} the in 2 shown cross slide 7th ,
• 11 Description of the expected driving current I _ext - _prior - _art for the same course of the target velocity V according _to 10 , whereby the expected drive current I _exp - _prior - _{art was determined} with a conventional method from the target speed and the target acceleration,
• 12th Representation as in 12th , whereby the actually measured drive current I _{ist is also} shown,
• 13th Flow chart for determining the upper current limit value I _max and the lower current limit value I _{min of} a current limit value band in the current limit value determination device 15th the end 2 according to another embodiment, in which the time derivative a _{tax of} the manipulated variable V _tax is used,
• 14th Flow chart for determining the upper current limit value Imax and the lower current limit value I _{min of} a current limit value band in the current limit value determination device 15th the end 2 according to a further embodiment in which the target acceleration a _{soll is} used,
• 15th Flow chart for determining the upper current limit value Imax and the lower current limit value Imin of a current limit value band in the current limit value determination device 15th the end 2 according to a further exemplary embodiment, in which an average value a _{akt -mittel} is used.

This in 1 Coordinate measuring machine shown 11 in portal design has a workpiece support in the form of a measuring table 1 on. The coordinate measuring machine 11 includes a mechanism 3 over which a sensor 9 relative to the workpiece support (measuring table 1 ) can be moved in all three coordinate directions x, y and z. In the case of mechanics 3 it is a so-called portal mechanism in which only the sensor 9 is moved in all three coordinate directions x, y and z while the workpiece support (measuring table 1 ) remains in peace. The mechanics 3 comprises a first measuring slide, namely a measuring table 1 spanning portal 4th in the coordinate direction indicated by the arrow y on the workpiece support (measuring table 1 ) is movably guided. A mechanical electric motor, not shown 3 causes the linear movement of this first measuring slide (portal 4th ) the mechanics 3 in y-direction. It is also a linear scale 12th the mechanics 3 provided by a reading head of the mechanism, also not shown in detail 3 is read and thereby the current position of this first measuring slide (portal 4th ) the mechanics 3 supplies.

The mechanics 3 also includes a second measuring slide (cross slide 7th ) running along the the measuring table 1 spanning cross member of the portal 4th is movably guided in the direction indicated by the arrow x. The current position of this second measuring slide (cross slide 7th ) relative to the cross member of the portal 4th can on the basis of a second linear scale 6th the mechanics 3 can also be determined by a reading head 20th the mechanics 3 (only in 2 to see) is read. The movement of the second measuring slide (cross slide 7th ) in the x-direction is controlled by a further electric motor M of the mechanics 3 (only in 2 to see) powered.

It also includes the mechanics 3 a third measuring slide that can be moved in the vertical direction, namely the quill 8th that are attached to the second measuring slide (cross slide 7th ) is mounted movably in the vertical direction indicated by the arrow z. At the bottom of the quill 8th is a sensor 9 attached, which is designed in the present case as a tactile measuring probe head. The third measuring slide (quill 8th ) with the attached sensor 9 can, driven by a further, unspecified electric motor of the mechanics 3 , relative to the second measuring slide (cross slide 7th ) can be moved in the z-direction of the Cartesian coordinate system. Via a third linear scale 10 the mechanics 3 , that of another, not visible reading head of the mechanics 3 is read, the position of the third measuring slide (quill 8th ) can be read out in the direction indicated by the arrow z. With a total of three electric motors in the mechanics 3 can the sensor 9 can therefore be moved in all three coordinate directions x, y and z and thereby moves in all three coordinate directions x, y and z relative to the workpiece support (measuring table 1 ) and thus also relative to a workpiece to be measured 5 that is placed on the workpiece support (measuring table 1 ) is stored. As stated above, the mechanics could 3 but also be designed so that the workpiece support is movably guided in one or more directions. For example, the portal could 4th be immobile in the y-direction and therefore the measuring table 1 be arranged on a measuring slide mounted movably in the y-direction, which is driven by a corresponding electric motor and whose position in the y-direction is determined using a corresponding scale and an associated readout head.

The coordinate measuring machine also includes a controller 2 , and a measuring computer 13th that is in conjunction with the controller 2 stands. The measuring computer 13th hands over to the control 2 Among other things, the predefined measuring processes, for example in the form of points to be measured on the workpiece 5 , with the controller 2 then processes it on the basis of the transferred measurement sequence. The control is available for this 2 in connection with the drives of the mechanics 3 in which also the said electric motors of the mechanics 3 are included. The controls are also in place 2 also in connection with the sensor 9 and the reading heads of the linear scales 6th , 10 and 12th the mechanics 3 . The control 2 then moves the sensor with the drives 9 according to the measuring sequence and thereby scans the workpiece 5 with the sensor 9 away. The controller takes over 2 from the sensor 9 and from the reading heads of the rulers 6th , 10 and 12th the measured values and thereby determines coordinate measured values of the probed points on the surface of the workpiece 5 . The measured values obtained on the basis of the measurement sequence are then used by the control for further evaluation 2 to the measuring computer 13th returned. In order to be able to fulfill said tasks, the control includes 2 one or more real-time capable microprocessors with which the tasks are carried out.

2 shows an abstract representation of the drive for the second measuring slide (cross slide 7th ) the mechanics 3 the end 1 plus control 2 and measuring computer 13th . The drive here comprises in particular an electric motor M, which has a rotating belt 21 drives, on which in turn the cross slide 7th is attached and is thereby moved in the x-direction. Same components as in 1 are denoted by the same reference numerals. It is expressly pointed out that this is a greatly simplified representation in which only a few components of the otherwise very complex system are shown very schematically.

The electric motor M is controlled as follows. From the measuring computer 13th is among other things to the control 2 The specific measuring sequence to be carried out is transferred, this measuring sequence including, among other things, travel commands P (x, y, z) that are sent by the three measuring slides (portal 4th , Cross slide 7th and quill 8th ) Define the position to be approached. Such movement commands P (x, y, z) are sent to a so-called spline interpolator 25th the control 2 to hand over. This spline interpolator 25th based on the current position, calculates a large number of positions to be approached one after the other for the x-direction, the y-direction and the z-direction. The spline interpolator also determines 25th the target speeds for the x-direction, the y-direction and the z-direction by simple temporal derivation of these positions to be approached one after the other for the x-direction, the y-direction and the z-direction, as well as the target by two-fold temporal derivation -Accelerations for the x-direction, the y-direction and the z-direction. In the example shown here only very abstractly, only the target positions for the x-direction X _soll , the target speeds for the x-direction V _soll and the target accelerations for the x-direction a _soll can be seen. The spline interpolator 25th _{sends the x-positions to be} approached one after the other from the move commands P (x, y, z) to a position controller 14th Further. This position controller 14th is also with the one on the cross slide 7th attached reading head 20th connected, and receives from this the one from the linear scale 6th read out actual position x _{is of} the cross slide 7th in X direction. By subtracting from the reading head 20th The actual actual position reported back x _is in the x direction from the set position _{to be} approached X set is calculated by the position controller 14th the control deviation, and calculates therefrom then using an algorithm such as a PID controller or a state regulator, a manipulated variable V _control. This manipulated variable V is adjusted to _control speed of the sensor 9 or the workpiece support 1 in the direction x driven by the electric motor M proportionally. The possible specific processes of the position controller 14th are discussed in more detail below in connection with 3 and 4th shown.

This from the position controller 14th The manipulated variable _Vcontrol is then determined by the position controller 14th the control 2 to a speed controller 18th passed in a digital power level PS. The speed controller 18th in turn, it is also connected to the tachometer generator TG and receives a signal V _{TG from it} , i.e. the current speed of the Electric motor M, which is essentially proportional to the actual speed of the cross slide 7th is in the x-direction. The tachometer generator TG is, for example, a rotary transformer that generates a voltage corresponding to the speed of the electric motor M.

_Control by subtracting the returned by the tachometer generator TG signal V _TG of the command value V, a second control deviation .DELTA.v is generated. The speed controller 18th then uses an algorithm that simulates a PID controller to calculate a second manipulated variable I _a , which corresponds to a drive current to be set, from this second control deviation .DELTA.v. This second manipulated variable I _a is passed on to an actuator SR in the digital power stage PS. On the basis of the drive current I _{a to be set} , the actuator SR then sets the drive current that is supplied via the electrical connections C1 and C2 flows through the electric motor M. The lines C1 and C2 that connect the electric motor M to the actuator SR are via a two-pole relay R2 led, this two-pole relay R2 is switched during normal operation so that along the line C1 and along the line C2 Electricity can flow. Also is a single pole relay R3 between the lines C1 and C2 provided that is open during normal operation. This relay R3 can be switched conductive in the event of a collision, so that the lines C1 and C2 are short-circuited. On the input side, the actuator SR is in the power stage PS via lines C3 and C4 via a two-pole relay R1 connected to a power supply unit EV. This energy supply unit EV can have a transformer and a rectifier, for example. The energy supply unit EV is fed via a network connection PN, which can be connected to an electrical alternating voltage energy supply network. The digital power stage PS also has a current measuring device IM or is combined with such a current measuring device with which the electrical connections C1 , C2 _{and the drive current I ist} flowing through the electric motor M can be measured. Instead of the relay R1 , R2 and R3 Field effect transistors can also be used.

During the operation of the coordinate measuring machine, the digital power level PS thus sets the value of the position controller 14th predetermined manipulated variable V _controlled or more accurately corresponding to the speed control by the 18th from this, the second manipulated variable I _{a determined} the drive current in the electrical connections C1 , C2 and regulates it, the digital power stage PS continuously or quasi-continuously evaluating the _{tachometer signal V TG generated by the tachometer generator TG.} The electric motor M used here is a direct current motor in the exemplary embodiment. Of course, other electric motors can also be used, such as three-phase motors, for example.

In addition, a collision monitoring circuit is implemented in the manner according to the invention, which in the event of a collision of the second measuring slide (that is to say the cross slide 7th ) or the third measuring slide (quill 8th ) or the sensor attached to it 9 with a person or an object automates the entire mechanics 3 brings to a standstill. This is in the control 2 a current limit value determination device 15th provided, on the one hand, the current by the reading head 20th determined actual positions X _is the linear scale 6th reads in the coordinate direction x. In addition, the position controller 14th manipulated variable V determined _tax to the current limit determination means 15th to hand over. The current limit value determination device 15th determined from the control value V and _control from the measured actual position of X _is then an algorithm in detail below in connection with 5 will be explained, an upper current _{limit value Imax and a lower current limit value I min of} a limit value band. The upper current limit value Imax calculated in this way and the calculated lower current limit value I _min are now determined by the current limit value determination device 15th to a comparator 16 transmitted. In addition, the electric drive current I _{ist of} the electric motor M actually measured in the digital power stage PS is sent to the comparator 16 transmitted. The comparator 16 , In turn, a microcontroller, checks now whether the actually measured driving current _I exceeds the upper limit value Imax of the current limit current tape or the lower current limit value I _min of the current limit band "exceeds".

Unless the comparator 16 determines that the actually measured driving current I _is the upper current limit value I _max of the current limit value exceeds band or the lower current limit value I _min of the current limit band "exceeds" transmitted, the comparator 16 to the relay R1 , to the relay R2 and to the relay R3 a signal OFF. This will open both the relay R1 as well as the relay R2 the conductive connection, so that both the power supply of the power stage PS and, in particular, the power supply of the electric motor M is interrupted. Also, the relay will R3 closed, so that the motor M is short-circuited as a result. This brings the second measuring slide (cross slide 7th ) and the third measuring slide (quill 8th ) with the attached sensor 9 very quickly to a standstill. So this is the movement of the mechanics 3 stopped in the x-direction driven by the electric motor M.

The OFF signal is also sent to the drive of the first measuring slide (portal 4th ) for the y-direction and to the drive of the third measuring slide (quill 8th ) for the z-direction. These drives are completely analogous to the one in 2 The shown drive for the second measuring slide, which can be moved in the x-direction (cross slide 7th ) so that the corresponding relays are activated accordingly via the OFF signal. As a result, the drive current for the electric motors of the drive in the y-direction and the drive in the z-direction is switched off and the movement of the mechanics is thereby switched off 3 also stopped in the y-direction driven by the corresponding electric motor and the z-direction driven by the corresponding electric motor.

At this point, for the sake of completeness, it should be noted again that the spline interpolator 25th , the position controller 14th and the current limit value determination device 15th the control 2 can be provided by a single microcontroller. The units are implemented as programs, with each unit (spline interpolator 25th , Position controller 14th , Current limit value determination device 15th is executed by a separate processor core on the microcontroller. Of course, the units (spline interpolator 25th , Position controller 14th , Current limit value determination device 15th ) can also be implemented by separate microcontrollers or constructed as an analog circuit.

The specific function of the position controller 14th the end 2 according to one embodiment is now intended in connection with 3 explained. According to a first step 30th a system deviation Δx is first calculated by the difference between the measured actual position X _{being and} that by the spline interpolator 25th predetermined target position X _{is to be} determined. Herein embodiment, the actual position _is X and the target position X _to the same sign have, the difference that order so as can be determined follows: $$\mathrm{\Delta }\text{x}={\text{x}}_{\text{target}}-{\text{x}}_{\text{is}}$$

From the control deviation .DELTA.x, the said manipulated variable V _{tax is then} calculated from the control deviation .DELTA.x via a digital controller. This digital controller is designed purely by way of example as a PID controller. As is well known to those skilled in the art of control technology, a PID controller is a controller whose manipulated variable is composed of a proportional component, an integral component and a differential component. The proportional component of the manipulated variable V _tax is a component that is proportional to the control deviation. The integral component of the manipulated variable V _tax is a component that is proportional to the time integral over the control deviation. The differential component of the manipulated variable V is _controlled a proportion that is proportional to the time differential (that is, to the time derivative) of the control deviation Ax. Instead of a PID controller, however, other controllers can also be provided, such as only P controllers that only have a proportional component.

4th shows one opposite 3 modified variant of the function of the position controller 14th the end 2 . Exactly as in the embodiment according to 3 takes place in a first step 30th a system deviation Δx is initially calculated by dividing the difference between the measured actual position X _is from that by the spline interpolator 25th predetermined target position X _{is to be} determined. In a second step 32 will then, very similar to step 31 the end 3 _{an intermediate variable V between is} determined from the control deviation Δx via a digital controller. This digital controller is designed purely by way of example as a PID controller. In a final step 33 is then by adding the intermediate _{variable V between} with that of the spline interpolator 25th the end 2 specified target speed V _{is to} calculate the final manipulated variable V _tax: $${\text{v}}_{\text{tax}}={\text{v}}_{\text{between}}+{\text{v}}_{\text{target}}$$

The control value V thus determined is then _controlled by the position controller 14th to the cruise control 18th passed on in the digital power level PS, as described above in connection with 2 has already been explained.

As above in connection with 2 already announced, the specific function of the current limit value determination device is also being announced 15th the end 2 with reference to 5 which shows the individual steps in detail. The current limit value determination device 15th calculated according to step 40 from the read-in actual positions X _{ist of} the sensor 9 in the direction x driven by the electric motor through the time derivative of this actual position x _{, the actual speed V is} after time (i.e. by forming the time differential): $${\text{v}}_{\text{is}}=\mathrm{\Delta }{\text{x}}_{\text{is}}/\mathrm{\Delta }\text{t}$$

In step 41 determines the current limit value determination device 15th by deriving the in step 40 determined actual speed V _is after the time the actual acceleration a _is in x-direction: $${\text{a}}_{\text{is}}=\mathrm{\Delta }{\text{v}}_{\text{is}}/\mathrm{\Delta }\text{t}$$

In order to determine the actual acceleration a _ist , the measured actual position X _is derived twice over time.

In one step 42a is then derived from the actual acceleration a _ist determined in this way and from that of the position controller 14th generated manipulated variable V _tax via a function I _erw (v _tax , a _ist ), which in the illustrated embodiment _{is dependent on the generated manipulated variable V tax} and the determined actual acceleration a, determines an expected drive current I _erw . The function used here as an example is as follows: $${\text{I.}}_{\text{exp}}\left({\text{v}}_{\text{tax}},{\text{a}}_{\text{is}}\right)={\text{R.}}^{\pm }+{\text{v}}_{\text{tax}}\cdot {\text{K}}_{\text{v}}+{\text{a}}_{\text{is}}\cdot {\text{K}}_{\text{a}}$$

• R^± = ein von der Geschwindigkeitsrichtung der Stellgröße V_steuer abhängiger Grundanteil R^±, wobei dieser richtungsabhängige Grundanteil R± einen ersten konstanten Wert R⁺ annimmt, wenn die gemessene Stellgröße V_steuer positiv ist und einen zweiten konstanten Wert R^- annimmt, wenn die gemessene Stellgröße V_steuer negativ ist.
• V_steuer = vom Lageregler 14 nach 2 bereitgestellte Stellgröße
• K_v = Proportionalitätsfaktor für den variablen Geschwindigkeitsanteil, wobei dieser Faktor den Anstieg des Antriebsstroms in Abhängigkeit von der Stellgröße V_steuer beschreibt
• a_ist = gemessene Ist-Beschleunigung
• K_a = Proportionalitätsfaktor für den variablen Beschleunigungsanteil, wobei dieser Faktor den Anstieg des Antriebsstroms in Abhängigkeit von der Ist-Beschleunigung beschreibt

Herein means:

• R ^{± = a basic component R ±} dependent on the speed direction of the manipulated variable V _tax , this direction-dependent base component R ± ^{assuming a first constant value R +} if the measured manipulated variable V _{tax is} positive and a second constant value R ^- if the measured one Manipulated variable V _{tax is} negative.
• V _controlled by the position controller = 14th after 2 provided manipulated variable
• K _v = proportionality factor for the variable rate part, wherein this factor describes the increase of the drive current in dependence on the manipulated variable V _tax
• a _ist = measured actual acceleration
• K _a = proportionality factor for the variable acceleration component, this factor describing the increase in the drive current as a function of the actual acceleration

The constants R ⁺ , R ^- , K _v and K _a can be determined relatively easily. The constant R ⁺ is determined by the cross slide 7th is moved at a very low speed in the positive x-direction and the drive current I _ist flowing here is measured via the drive current sensor IM. The drive current measured here corresponds to the constant R ⁺ . The constant R ^- is determined analogously to this by the cross slide 7th is moved at a very low speed in the opposite direction of travel, that is, in the negative x-direction, and the drive current flowing in this case is measured via the drive current sensor IM. The drive current measured here corresponds to the constant R ^-

The proportionality factor K _v is determined after R ⁺ and R ^{- have been} determined. The cross slide is used for this 7th with an approximately constant speed v _{is moved} either in the positive x-direction or in the negative x-direction. Meanwhile, on the drive current IM of the sensor drive current I flowing in this case _is measured and the control value V determined _tax. Since the speed is constant, the acceleration a _is then zero. When moving in the positive x-direction, the above function must result in the following relationship: $${\text{I.}}_{\text{exp}}\left({\text{v}}_{\text{tax}},{\text{a}}_{\text{is}}\right)={\text{R.}}^{+}+{\text{v}}_{\text{tax}}\cdot {\text{K}}_{\text{v}}$$

By rearranging the equation we get: $${\text{K}}_{\text{v}}=\left({\text{I.}}_{\text{exp}}-{\text{R.}}^{+}\right)/{\text{v}}_{\text{tax}}$$

Since the proportionality factor K _v is determined here, the measured drive current I _ist must of course be used in this equation instead of the drive current I _{exp to be expected, that is to say} $${\text{K}}_{\text{v}}=\left({\text{I.}}_{\text{is}}-{\text{R.}}^{+}\right)/{\text{v}}_{\text{tax}}$$

The proportionality factor K _a is then determined after R ⁺ and R ^- and K _{v have been} determined. The cross slide is used for this 7th with approximately constant actual acceleration a _is either moved in the positive x direction or the negative x direction, during which at a time when the control value V _control, the actual acceleration a _is and the driving current sensor in the case flowing driving current I _is measured. Upon movement in the positive x-direction must be made of the above-mentioned function I _exp (V _control, a _is) yield the following relationship: $${\text{I.}}_{\text{exp}}\left({\text{v}}_{\text{tax}},{\text{a}}_{\text{is}}\right)={\text{R.}}^{+}+{\text{v}}_{\text{tax}}\cdot {\text{K}}_{\text{v}}+{\text{a}}_{\text{is}}\cdot {\text{K}}_{\text{a}}$$

By rearranging the equation we get: $${\text{K}}_{\text{a}}=\left({\text{I.}}_{\text{exp}}-{\text{R.}}^{+}-{\text{v}}_{\text{tax}}\cdot {\text{K}}_{\text{v}}\right)/{\text{a}}_{\text{is}}$$

Since the proportionality factor K _{a is determined here, the measured drive current I ist} must of course be used again in this equation instead of the drive current I _exp to be expected, that is to say $${\text{K}}_{\text{a}}=\left({\text{I.}}_{\text{exp}}-{\text{R.}}^{+}-{\text{v}}_{\text{tax}}\cdot {\text{K}}_{\text{v}}\right)/{\text{a}}_{\text{is}}$$

Now that the constants R ⁺ , R ^- , K _v and K _{a have been} determined, the position controller can, depending on the respective, 14th determined manipulated variable V _tax and the respective actual acceleration a _is an expected value for the drive current I _erw can be calculated from equation 8.

On the basis of the expected drive current I _erw calculated in this way, step 43 an upper current limit value Imax and a lower current limit value I _{min are} determined. To determine the upper current limit value Imax, a constant current value d is added _{to the expected drive current I exp in the simplest case:} $${\text{I.}}_{\text{Max}}={\text{I.}}_{\text{exp}}+\text{d}$$

To determine the lower current limit value I _min , a constant current value e is subtracted from the expected drive _{current I erw in the simplest case:} $${\text{I.}}_{\text{min}}={\text{I.}}_{\text{exp}}-\text{e}$$

In the present exemplary embodiment, the current values d and e are constant and have the same magnitude.

6th shows, purely by way of example, a representation of the actually flowing drive _{current I ist} and the expected drive _{current I erw} and the upper current limit value I _max determined from this and the lower current limit value I _min for an arbitrarily selected exemplary course of the setpoint speed V _soll for the in connection with 2 until 5 explained circuit. Same names as in the 2 , 3 , 4th and 5 have been provided with the same reference numerals. In the exemplary embodiment described here, the target speed V _{soll is} as above in connection with 2 described to be the component of the velocity vector in the x-direction, which is generated by the spline interpolator 25th the control 2 is specified by the actual positions x set _{to be approached one after the other.}

At time t _0, that is to say on the left edge of the diagram, the setpoint speed values v _soll (see dash-dotted line) begin to increase linearly from a first speed value. The linear increase continues until time t _{1 is} reached. Corresponding to the linear increase in the set speed v set _, the set acceleration a set _is constant in the x direction. In order to actually achieve this target acceleration, the associated electric motor M must be supplied with a somewhat higher current. Accordingly, the actual drive current in the motor M (this corresponds to the measured current list (see the dashed line with the reference symbol list) is at a higher level. With the reference symbol I _erw (see solid line with the reference symbol I _erw ), on the other hand, is the expected drive current denotes that of the current limit value determination device 15th _controlled from the actual manipulated variable V and the actual acceleration a _is determined was (see step 42a in 5 ). Starting from this expected drive _{current I erw} , the current limit value determination device was used 15th in addition, the upper current limit value Imax and the lower current limit value Imin of the current limit value band are determined.

The upper current limit value Imax in the time interval [t ₀ ; t ₁ ] is more or less constant at a slightly higher value. The lower current limit value Imin, on the other hand, is even in the negative range. If this upper current limit value Imax of the current limit value band _is exceeded by the actually measured drive current I actual or if this current limit value Imax is reached, appropriate measures are taken. These measures are also initiated when the lower current limit value Imin of the current limit value band _is exceeded by the actual current I act or when this current limit value Imin is reached.

At the end of the first acceleration _{phase, at time t 1} , the actual actual speed vist has reached a value which roughly corresponds to _{the setpoint speed V soll.} In the further course of the movement (or the movement component in the x direction), the setpoint speed V _soll then remains constant until the end of the diagram. Accordingly, the drive current I _ist then drops to a somewhat lower value and then remains approximately constant. Although acceleration no longer takes place from time t ₁ , a relatively high drive current is still required. This must essentially be applied because the movement of the electric motor M and the moving parts driven by the motor, i.e. in particular of the second measuring slide (cross slide 7th ), does not run smoothly. The upper current limit value Imax falls to a lower level than during the acceleration phase in the time interval [to; t ₁ ].

At this point, it should be expressly mentioned again that the procedure described is a purely exemplary embodiment that can vary in many ways, as was explained in detail in the introduction to the description. For example, instead of the in 2 and 5 used current limit value band with an upper current limit value Imax and a lower current limit value Imin, only one current limit value can be used.

In the following, in connection with 7th explains what happens in the event of a collision. 7th shows here very similar to 6th the dash-dotted line with the reference symbol V _{is intended} to indicate the speed profile to be traveled in accordance with the setpoint speed of the one that is movable in the x direction second measuring slide (cross slide 7th ), please refer 1 and 2 . In addition, in 7th the actually flowing current _I of the electric motor M shown as a dashed line. The current limit value determination device is also shown 15th determined expected driving current I _ext, and the upper current limit value Imax and the lower current limit value Imin of the current limit band, the upper current limit value Imax and the lower current limit of the current limit value Imin tape from the current limit determination means 15th to the comparator 16 is delivered.

1. a) Zum einen wird die Ist-Geschwindigkeit des zweiten Messschlittens (Querschlitten 7) stark verringert. Die Stromgrenzwert-Ermittlungseinrichtung 15 ermittelt deshalb aus den Ist-Positionen x_ist eine negative Ist-Beschleunigung a_ist (also eine Bremsbeschleunigung). Hierdurch wird folglich ein verringerter Wert für den erwarteten Antriebsstrom I_erw ermittelt, was gleichzeitig zu einer Absenkung des oberen Stromgrenzwertes Imax und des unteren Stromgrenzwertes Imin des Stromgrenzwertbandes führt.
2. b) Zum Anderen vergrößert sich die Regelabweichung Δx aufgrund der abnehmenden Geschwindigkeit, was zu einem Anstieg der Stellgröße V_steuer führt. Der Geschwindigkeitsregler 18 der digitalen Leistungsstufe PS versucht dabei der vom Lageregler 14 übermittelten Stellgröße V_steuer zu folgen und erhöht zusätzlich die zweite Stellgröße I_a für den Antriebstrom im Elektromotor M, so dass der gemessene Antriebstrom list zusätzlich noch ansteigt.

As can be seen from the diagram _, the second measuring slide (cross slide 7th ) are increased in the x-direction from a first speed value to a maximum speed value, and then remain constant. In the diagram shown here, however, the second measuring slide (cross slide 7th ) at time t _k with an object. This has the following consequences:

1. a) On the one hand, the actual speed of the second measuring slide (cross slide 7th ) greatly reduced. The current limit value determination device 15th therefore determined from the actual positions x _is a negative actual acceleration _a (that is, a deceleration). As a result, a reduced value for the expected drive current I _{erw is} determined, which at the same time leads to a lowering of the upper current limit value Imax and the lower current limit value Imin of the current limit value band.
2. b) On the other hand, the deviation .DELTA.x increased due to the declining rate, resulting in _tax to an increase of the control variable V. The speed controller 18th the digital power level PS is tried by the position controller 14th to follow transmitted manipulated variable V _control and increases additionally the second manipulated variable I _a for the driving current in the electric motor M, so that the measured driving current list additionally increases.

The actual flowing current list thus exceeds the upper current limit value Imax _{at time t s1.} From this point in time t _s1 the comparator goes 16 (see also 2 ) assumes that there is a collision and sends an OFF signal to the relay R1 , the relay R2 and the relay R3 (see also 2 ), whereby, as already described above, the power supply to the power stage PS and in particular to the electric motor M is switched off and the electric motor is short-circuited. In this way, the drive current I _is precipitated from the time t _s1 sharply and the motor M is stopped.

In connection with 8th one of the particular advantages of the method according to the invention over that from the document will now be described in detail US 7 627 957 B2 and the pamphlet DE 10 2006 003 362 A1 known method shown. The representation after 8th corresponds almost identically to the content 7th so the explanations too 7th analog for 8th are valid. Above 7th going beyond is in 8th a dotted curve with the reference Imax-prior-art is also drawn in. This curve shows an example of an upper current limit value based on the target speed V _soll and the target acceleration a _soll according to the method according to the publication US 7 627 957 B2 and the pamphlet DE 10 2006 003 362 A1 could be determined. In addition, the course is shown for the measured drive _{current I ist prior art} , which would result on the basis of the upper current limit value of the drive current Imax prior art. As can be seen from this graph, the upper current limit value Imax-prior-art remains even after the time of the collision t _k unchanged because the upper current limit value precisely not based on the detected actual acceleration _a, and the measured control value V is determined _tax , but on the basis of the unchangeable, from the spline interpolator 25th determined target speed V _soll and the target acceleration a _soll . Thus, according to the conventional solution, the measured drive current Iist prior art would not have exceeded the upper current limit value Imax prior art _{until time t s2.} As this example shows very impressive, the current limit or current limit band from the actual control variable V can by identifying _tax and the actual acceleration actually measured a _is thus a collision be detected much earlier, namely already at time t _s1.

The drive current sensor IM in the digital power level PS in 2 is structured, for example, as in connection with 9 shown. An ammeter MA supplies an analog measurement signal, which is optionally fed to an analog / digital converter AD via an analog filter AF for smoothing the measurement signal over time. In the converter AD, the analog signal is converted into a digital signal and smoothed over time using a further optional digital filter DF. This smoothed, digital measurement signal is, as also in connection with 2 to see the comparator 16 as measured drive current I _is supplied.

As already mentioned above, the embodiment is in connection with a DC motor M (see 2 ) shown. Instead of this, however, other electric motors can of course also be used, such as, for example, three-phase motors or linear motors. In three-phase motors of this type and also in linear motors, all three phases of the AC voltage network are used. The current proportional to the generated torque of the electric motor can be Such electric motors can be easily determined, since the digital power levels made available by the providers of such three-phase motors or linear motors calculate the drive current proportional to the torque actually generated by the electric motor and make it available as a digital value. This provided by the digital power level value of the drive current can be further processed the same way as _is the drive current sensor IM measured drive current I.

In 10 is now a representation of the actually flowing drive current I _ist and the expected drive current I _erw for an exemplary course of the setpoint speed V _soll des in 2 second measuring slide shown (cross slide 7th ) shown. How _to V from the dash-dotted line with the reference number can see the cross slide 7th in the time interval [t _e0 ; t _e1] accelerated constantly from standstill in the positive x-direction, then in the time interval [t _e1 ; t _e2] moves at a constant speed, in the time interval [t _e2 ; t _e3 ] braked to a standstill with a constant negative acceleration. In the time interval [t _e3 ; t _e4] is the cross slide 7th then quiet. In the time interval [t _e4 ; t _e5] becomes the cross slide 7th then from standstill in the opposite direction, ie accelerated constantly in the negative x-direction, then in the time interval [t _e5 ; t _e6 ] moves at a constant speed, and in the time interval [t _e6 ; t _e7] braked again to a standstill with a constant braking acceleration. The one by the current limit value determination device 15th (please refer 2 ) determined drive current I _exp to be expected (see step 42a in 5 ) is shown here as a solid line with the reference symbol I _erw . In addition, the actually measured drive current I _{ist is shown} as a dotted line. The determination of the expected drive _{current I erw} by the current limit value determination device 15th is so good here that the deviations can only be seen very poorly in one and the same diagram. Therefore, in 10 only those points of the actually measured driving current I _is shown as a dotted line, in which significant deviations of the measured drive current I _is compared to the expected driving current I _erw yield. These three deviations (two of them in the time interval [t _e3, t _e4]. And one after the time t _e7 explicitly _with the reference numeral I designates The wavy profile of the expected driving current I _ext and the measured driving current _I is in this case due to the fact that arise, in particular during acceleration oscillations. as the expected driving current I _ext from the manipulated variable V _control and the detected actual acceleration a _is derived, this vibration to flow into the calculation of the expected driving current I _erw with one, so that the correct drive current I _ext mostly corresponds very well to the actually measured drive current I _ist.

In contrast, in 11 for exactly the same course of the target speed v _soll according to 10 an expected drive current lerw-prior-art is shown as a continuous line according to the method from the publication US 7 627 957 B2 and the pamphlet DE 10 2006 003 362 A1 would be determined from the target speed and the target acceleration. How the path of the expected driving current I _ext - _prior - _art looks directly, thereby, in particular the vibrations, which _is the actually measured driving current I has to be not detected. The reason is that this drive is current I _ext - _prior - from the target speed V _{to art} and the target acceleration a _should have been identified thus find, so that actual vibrations not be considered.

12th corresponds to the representation 11 , with the actually measured drive current I _{ist also being} shown. As you can see from this, giving way to the actual measured drive current _{I ext} from the expected driving current I - _prior - _art due to the vibrations from mostly relatively strong. This is unproblematic insofar as the upper and lower current limit values can simply be spaced _{correspondingly far from the expected drive current I exp} - _prior - _art. The inventive calculation of the expected driving current I _ext on the basis of the manipulated variable V _control and the actual acceleration a _is true, the expected driving current I _erw much more accurately _with the actually measured motor current I coincide, so that the upper current threshold and the lower current limit value to closer the expected drive current I _erw can be brought up and a collision can thereby be detected earlier.

With regard to the course of the measured drive current I _, in 10 and 12th the following comments have to be made. In the time interval [t _e0 ; t _e1] , the drive current I _ist initially rises abruptly to a relatively high level and then rises with a smaller slope until the end of this time interval. The reason for this is that the effort required to generate the constant acceleration in this interval increases due to the increasing speed and the resulting increasing frictional forces. In the time interval [t _e1 ; t _e2] , the measured drive current I _{ist is} reduced to a lower level, this drive current being required to overcome the frictional forces occurring at the constant speed in question. In the time interval [t _e2 ; t _e3] , the measured drive current I _is then even negative in order to achieve the necessary constant, negative braking acceleration. The amount of the drive current I _ist increases in the time interval [t _e2 ; t _e3] because the friction forces in the cross slide as the speed decreases 7th lose weight and therefore the Increasing braking acceleration must be generated by the electric motor M. In the time interval [t _e3 ; t _e4] is the cross slide 7th the end 2 quiet again. The particular from 9 clearly visible relatively high drive current shortly after reaching standstill is due to the cross slide 7th is already at a standstill and between that of the spline interpolator 25th specified position x _should and the actually measured actual position x _is a control deviation that the position controller 14th the end 2 in the form of a manipulated variable v control to the speed _controller 18th hands over. This then causes a manipulated variable for the drive current I _a , which is relatively high because it is used to move the cross slide 7th the friction has to be overcome .. The remarks made then apply analogously to the following time intervals, which show practically the same speed profile only in the opposite direction of travel (i.e. in the negative x-direction).

Apart from the different design variants of the position controller 14th according to 3 and 4th the description of the figures relates throughout only to an exemplary embodiment according to FIG 2 In which the drive is current I _ext on the basis of the manipulated variable V _control and based on the detected actual acceleration _a is determined. As already explained in detail in the introduction to the description, instead of the measured actual acceleration aist, another variable can also be used, which is the current acceleration a _{act of} the sensor 9 or the workpiece support 1 describes in the direction x driven by the electric motor.

13th shows here a to 5 alternative flowchart by the determination device 15th the end 2 procedural steps to be carried out to determine the upper current limit value Imax and the lower current limit value I _{min of} a current limit value band. Same process steps as in 5 also have the same reference numerals. The main difference compared to 5 here is to see that instead of the actual acceleration _{a exp} in determining the expected drive current I as the current acceleration a _act of the sensor 9 or the workpiece support 1 in the driven by the electric motor the direction of the time derivative of x a _control of the control variable v _control of the position controller 14th is used. So far are the steps 40 and 41 the end 5 to calculate the actual acceleration a _is no longer in 13th and an additional step instead 45 inserted in the step 44 read-in manipulated variable v _{tax is} derived over time in order to obtain the derivation of this manipulated variable. The derivation takes place via the temporal derivation of the manipulated variable v _tax : $${\text{a}}_{\text{tax}}=\mathrm{\Delta }{\text{v}}_{\text{tax}}/\mathrm{\Delta }\text{t}$$

In step 42b then takes place in the same way as in connection with 5 The calculation of the expected drive current I _{exp was} explained using equation 8. Equation 8 as an equation is in this case almost identical used only with the only difference that instead of the actual acceleration a _is the time derivative of the manipulated variable is a v use _{tax control.} In this respect, the function here is: $${\text{I.}}_{\text{exp}}\left({\text{v}}_{\text{tax}},{\text{a}}_{\text{tax}}\right)={\text{R.}}^{\pm }+{\text{v}}_{\text{tax}}\cdot {\text{K}}_{\text{v}}+{\text{a}}_{\text{tax}}\cdot {\text{K}}_{\text{a}}$$

Because of the slight difference from equation 8 and the corresponding process step 42a in 5 the process step has therefore also been given the slightly changed reference number 42b designated.

14th shows another to 5 alternative flowchart by the determination device 15th the end 2 procedural steps to be carried out to determine the upper current limit value Imax and the lower current limit value I _{min of} a current limit value band. Same process steps as in 5 also have the same reference numerals. The main difference compared to 5 here is to see that instead of the actual acceleration _{a exp} in determining the expected drive current I as the current acceleration a _act of the sensor 9 or the workpiece support 1 in the direction x driven by the electric motor, the predefined setpoint acceleration a setpoint _is used. As already mentioned in connection with 2 explained, this set acceleration a set _{is made} by the spline interpolator 25th determined by two-fold derivation of the target positions in x-direction x _son and is thus in the control 2 to disposal. So far are the steps 40 and 41 the end 5 to calculate the actual acceleration a _is no longer in 14th and instead of that is an additional step 46 inserted, in which the target acceleration a _{soll is} read. In step 42c then takes place in the same way as in connection with 5 The calculation of the expected drive current I _{exp was} explained using equation 8. instead of. Equation 8 as an equation is in this case almost identical used only with the only difference that instead of the actual acceleration a _is the target acceleration a _{is to} be inserted. In this respect, the function here is: $${\text{I.}}_{\text{exp}}\left({\text{v}}_{\text{tax}},{\text{a}}_{\text{target}}\right)={\text{R.}}^{\pm }+{\text{v}}_{\text{tax}}\cdot {\text{K}}_{\text{v}}+{\text{a}}_{\text{target}}\cdot {\text{K}}_{\text{a}}$$

Because of the slight difference from equation 8 and the corresponding process step 42a in 5 the process step has therefore also been given the slightly changed reference number 42c designated.

15th shows another modification of the in 5 flowchart shown. This variant contains method steps from the variant according to 5 and the variant according to 13th . Same process steps as in 5 and 13th also have the same reference numerals. The main difference compared to 5 and 13th can be seen here in the fact that instead of the actual acceleration, a _is (cf. 5 ) or instead of the derivation a _{tax of} the manipulated variable v _tax (cf. 13th ) when determining the expected drive _{current I erw} as the current acceleration a _{act of} the sensor 9 or the workpiece support 1 in the driven direction by the electric motor now x is a mean value of the time derivative of a _control of the control variable v _control of the position controller 14th and the measured actual acceleration a _{ist is} used. The mean value a _{akt --mittel} is calculated using arithmetic averaging as follows from the in step 45 identified a derivative _control of the manipulated variable and out of the step 41 measured actual acceleration a _is calculated: $${\text{a}}_{\text{act}-\text{middle}}=\left({\text{a}}_{\text{is}}+{\text{a}}_{\text{tax}}\right)/2$$

An arithmetic mean was used for this. Of course, other averaging methods can also be used, such as weighted averaging, for example.

In step 42d then takes place in the same way as in connection with 5 The calculation of the expected drive current I _{exp was} explained using equation 8. The equation used here is almost identical to Equation 8, the only difference being that instead of the actual acceleration a _ist, the mean value a _act - _means is used. $${\text{I.}}_{\text{exp}}\left({\text{v}}_{\text{tax}},{\text{a}}_{\text{act}-\text{middle}}\right)={\text{R.}}^{\pm }+{\text{v}}_{\text{tax}}\cdot {\text{K}}_{\text{v}}+{\text{a}}_{\text{act}-\text{middle}}\cdot {\text{K}}_{\text{a}}$$

Because of the slight difference from equation 8 and the corresponding process step 42a in 5 the process step has therefore also been given the slightly changed reference number 42d designated. Instead of averaging over the measured actual acceleration _a, and the derivation of a _control of the control variable v can _{be controlled} as well on the actual acceleration _a, and the target acceleration a _{is to} be averaged or V _control via the outlet a _control of the manipulated variable and the target acceleration a _{is to be} averaged.

Claims (22)

Method for operating a coordinate measuring machine (11), a mechanism (3) being provided for adjusting a sensor (9) relative to a workpiece support (1) in at least one direction (x) and this mechanism (3) having at least one electric motor (M) has, via which the adjustment of the sensor (9) or the workpiece support (1) is driven in this direction and wherein the method comprises the following steps: a) an electric drive current (I _ist ) that flows through the electric motor (M) to a movement of the electric motor (M) and in this way a movement of the sensor (9) or the workpiece support (1) is measured, b) an actual position (v _ist ) of the sensor (9) or the workpiece support (1) ) in the direction (x) driven by the electric motor (M) is measured, c) a control deviation (Ax) between the measured actual position (x _ist ) and a predetermined target position (x _soll ) is determined by determining the difference between the measured actual position n (x _ist ) and the specified target position (x _soll ) is determined, d) on the basis of the control deviation, a controller (14) determines a manipulated variable (v control _{) that corresponds} to the speed to be set for the sensor (9) or the workpiece support ( 1) is driven by the electric motor (M) in the direction (x) proportional to e) of the determined by the controller (14) manipulated variable (V _control) is dependent on a current limit (I _max), or a current limit value band (ie, a range of Values for the drive current, which is defined by a lower current limit value Imin and an upper current limit value Imax) determined for the electrical drive current, and f) if the electrical drive current reaches the current limit value (Imax) determined in step (e) and / or if the electrical Drive current exceeds the determined current limit value (Imax) or if the current limit value band (Imin, Imax) is left, the movement of the mechanism (3) is at least started by the electric motor in the plane direction. Procedure according to Claim 1 Wherein for determining the current limit or power limit band from the determined manipulated variable (V _control), an expected driving current (I _ext) is determined, which corresponds to an expected value for the actual electrical drive current which is expected for the current determined manipulated variable (V _control) . Procedure according to Claim 2 Wherein in determining the expected drive current (I _erw) is a variable speed portion (K _v. V _control) is taken into consideration which is proportional to the determined manipulated variable (V _control). Procedure according to Claim 3 , wherein in the direction (x) driven by the electric motor (M) there is an additional current acceleration (a _act ) of the sensor (9) or of the workpiece support (1) in the through the electric motor (M) driven direction is determined, which _{corresponds either to a measured actual acceleration (a ist} ) of the sensor (9) or the workpiece support (1) or a target acceleration (a _soll ) of the sensor (9) or the workpiece support (1) corresponds or corresponds to a time derivative (asteuer) of the manipulated variable (v _tax ) or an average value (a _act-average ) from at least two of the variables measured actual acceleration (aist), specified target acceleration (a _soll ) or temporal Derivation (asteuer) corresponds to the manipulated variable (v _tax ) and, when determining the expected drive _{current (I erw} ), a variable acceleration _{component (Ka · a act} ) is also taken into account, which is proportional to this current acceleration (aakt). Method according to one of the Claims 2 until 4th , with the determination of the expected drive current (I _erw ) additionally taking into account a basic component (R) which corresponds to a drive current when the sensor (9) or the workpiece support (1) is moved in the direction (x) driven by the electric motor at a low constant speed. Procedure according to Claim 5 , Wherein as a base portion either an independent from the velocity direction constant base part (R ^*) used or a dependent on the speed direction of the manipulated variable (V _control) Base portion (R ^±) is used, and said direction-dependent background component (R ^±) a first constant Assumes value (R ⁺ ) when the manipulated variable (v _tax ) is positive and assumes a second constant value (R ^- ) when the manipulated variable (v _tax ) is negative. Procedure according to Claim 3 , 4th and 6th , whereby the expected drive current (lerw) is determined with the following function Ierw (vsteuer, a _ist ): $${\text{I.}}_{\text{exp}}\left({\text{v}}_{\text{tax}},{\text{a}}_{\text{act}}\right)=\text{R.}+{\text{v}}_{\text{tax}}\cdot {\text{K}}_{\text{v}}+{\text{a}}_{\text{act}}\cdot {\text{K}}_{\text{a}}$$

wherein mean herein: R = the constant base part (R ^*), or the directional base part (R ^±) K determined _v = proportionality factor for the variable velocity component V _control = the controller manipulated variable Ka = proportionality factor for the variable acceleration component A _act = the current acceleration, thus, either the measured actual acceleration _a or the predetermined desired acceleration a _will or the time derivative of a _control of the control variable v _tax or an average AAKT Announcement of at least two of the variables measured actual acceleration a _is predetermined desired acceleration a _should and time derivation a _{tax of} the manipulated variable v _tax . Method according to one of the Claims 2 until 7th , whereby when determining the current limit value (Imax) or a first current limit value of the current limit value band (Imax, Imin), the expected drive _{current (I erw} ) is increased by a first current value (d) in such a way that the amount of the current limit value (I _max ) or the first current limit value of the current limit value band (Imax, Imin) is higher than the amount of the expected drive current (I _erw ). Procedure according to the Claim 8 , whereby to determine a second current limit value of the current limit value band (Imax, Imin) the expected drive _{current (I erw} ) is additionally reduced by a second current value (e) so that the amount of the second current limit value of the current limit value band (Imax, Imin) is lower than the Amount of the expected drive current (I _exp ) is. Procedure according to Claim 8 or 9 , wherein the first current value (d) and / or the second current value (e) are constant. Method according to one of the preceding claims, wherein the electrical drive current is switched off when the electrical drive current _{reaches and / or exceeds the determined current limit value (I max} ) continuously over a time interval of a predetermined length or continuously over the determined current limit value band (I _max , I _min ) leaves a time interval of a predetermined length. The method according to any one of the preceding claims, wherein in step (f) according to Claim 1 a value is used as the electric drive current which has been obtained after smoothing fluctuations over time in the measured value determined in step (a). Method according to one of the preceding claims, wherein a functional relationship between the manipulated variable (V _control) and, optionally, the current acceleration (a _act) on the one hand and the current limit (I _max) on the other hand additionally determined by one or more parameters, by one or more the factors listed below are clearly determined: an ambient temperature, a temperature of parts of the coordinate measuring machine (11), a position of the sensor (9) and / or the workpiece support (1) in a fixed coordinate system, a relative position of the sensor (9 ) or the workpiece support (1) in relation to the workpiece (5) or in relation to other parts of a measurement setup and / or an operating state of the coordinate measuring machine (11). Method according to one of the preceding claims, wherein, before the electrical drive current is switched off, a current direction of the electrical drive current is first reversed. Method according to one of the preceding claims, wherein a plurality of electric motors (M) is provided in order to bring about the movement of the sensor (9) relative to the workpiece support (1), the movements of the electric motors (M) being clearly movement components (x, y, z) can be assigned to the movement of the sensor (9) and / or the workpiece support (1), steps (a) to (f) according to FIG Claim 1 are performed for each of the plurality of electric motors (M) separately, wherein the manipulated variable (V _control) in steps (b) and (c) for each of the components of motion (x, y, z) are measured and wherein, depending on each case, the current limit ( I _max ) or the current limit value band (I _max , I _min ) is determined. Coordinate measuring machine (11), with a mechanism (3), a workpiece support (1) for receiving a workpiece (5) to be measured and a sensor (9), the sensor (9) and the workpiece support (1) from the mechanism (3 ) is adjustable relative to each other in at least one direction (x), the mechanism (3) having at least one electric motor (M), via which the adjustment of the sensor (9) or the workpiece support (1) is driven in this direction (x) , and wherein the coordinate measuring machine (11) comprises: (a) a current measuring device (IM) which is configured to generate an electric drive current (I _ist ) flowing through the electric motor (M) in order to move the electric motor (M ) and in this way to cause a movement of the sensor (9) or the workpiece support (1), to measure, (b) an actual position measuring device (20) which is designed to measure the actual position (x _ist ) of the sensor (9) or the workpiece support (1) in the R driven by the electric motor ichtung (x) to measure, (c) a difference determination unit (14, step 30) which is set up to determine a control deviation (Δx) between the measured actual position (x _ist ) and a predetermined target position (x _soll ) by determining the difference between the measured actual position (x _ist ) and the specified target position (x _soll ) to determine (d) a controller (14, step 31 or 32, 33), which based on the control deviation, a manipulated variable (v _tax ) determined, which is proportional to the speed to be set of the sensor (9) or the workpiece support (1) in the direction (x) driven by the electric motor (M), (e) a current limit value determination device (15, steps 42a, 43 or 42b , 43 or 42c, 43 or 42d, 43) which is designed, depending on the determined by the controller manipulated variable (V _control) a current limit value (I _max), or a current limit value band (ie, a range of values for the drive current flowing through a lower current limit value I _min and e inen upper current limit value I _{max is} defined) for the electrical drive current, and (f) an actuating device (16, R1, R2, R3), which with the current measuring device (IM) and with the current limit value determining device (15, steps 42a, 43 or 42b, 43 or 42c, 43 or 42d, 43) and which is designed to stop the movement of the mechanism (3) at least in the direction driven by the electric motor when the electric drive current exceeds the limit value determination device (15) reached the determined current limit value (I _max ) and / or when the electrical drive current exceeds the current limit value (I _max ) determined by the current limit value determination device (15) or when the drive current leaves the current limit value band (I _min , I _max ). Coordinate measuring machine according to the preceding claim, wherein the actuating device (16, R1, R2, R3) has a switch-off device which is connected to the current measuring device and to the current limit value determining device (15) and which is designed to switch off the electrical drive current when the electrical drive current reaches the determined current limit value (I _max ) and / or if the electrical drive current exceeds the determined current limit value (I _max ) or if the drive current leaves the current limit value band (I _max , I _min ). Coordinate measuring machine according to Claim 16 or 17th , wherein the current limit value determination device (15) is designed, the method according to one of Claims 2 until 10 to execute. Coordinate measuring machine according to Claim 18 , in which the current limit value determination device is designed in such a way that, when determining the expected drive _{current (I erw} ), a variable acceleration _{component (K a} a _act ) is also taken into account, which is proportional to a current acceleration (a _act ) of the sensor (9 ) or the workpiece support (1) is in the direction driven by the electric motor (M). Coordinate measuring machine according to Claim 19 , with an actual acceleration measuring device (20 and 15, steps 40 and 41) being provided which is designed to measure the actual acceleration (a _ist ) of the sensor (9) or the workpiece support (1) in the one driven by the electric motor measuring direction (x) and said measured actual acceleration (a _ist) is used as an actual acceleration (a _act). Coordinate measuring machine according to Claim 19 or 20th , wherein a derivative calculation unit (15, step 45) is additionally provided which is designed to determine a time derivative (a _tax ) of said manipulated variable (v _tax ) and this time derivative (a _tax ) of the manipulated variable (v _tax ) is used as the current acceleration (a _act ). Coordinate measuring machine according to Claim 20 or 21 Wherein an additional average calculating unit (15, step 47) is provided which is adapted to an average value (a _nude-medium) comprised of at least two of the sizes measured actual acceleration (a _ist), predetermined desired acceleration (a _soll ) or time derivative (a _tax ) of the manipulated variable (v _tax ) and this mean value (a _act-average ) being used as the current acceleration (a _act ).

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