JP2008032475A - Surface shape measuring apparatus and method for detecting anomaly of stylus load - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a stylus and a pickup from being broken due to excessive loads acting on the stylus by detecting anomalies of loads acting the stylus in a surface shape measuring apparatus having the stylus which comes into contact with surfaces of objects to be measured. <P>SOLUTION: The surface shape measuring apparatus 1 includes a speed detection part 64 for detecting the rotating speeds of motors (51 and 52) which relatively move the stylus 11 and an object to be measured W or a relative traveling speed between the stylus 1 and the object to be measured W; current detection parts (53 and 54) for detecting a driving current flowing through the motors (51 and 52); and a stylus-load-anomaly detection part 64 for determining that an anomalous load is acting on the stylus 11 when the rotational speeds of the motor (51 and 52) or the relative traveling speed is slower than a prescribed threshold speed Tv and when the driving current exceeds a prescribed threshold current Ti. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  In the present invention, the stylus is moved relative to the surface of the object to be measured, and at this time, a displacement signal is generated by detecting the displacement of the stylus caused by the undulation of the surface of the object to be measured, The present invention relates to a surface shape measuring apparatus for measuring a shape, and more particularly, to a technique for preventing damage to the stylus or a pickup unit that detects displacement of the stylus.

  The surface shape measuring device moves the stylus and the object to be measured while pressing the stylus against the surface of the object to be measured with a predetermined measurement pressure, and the displacement of the stylus caused by the undulation of the surface of the object to be measured at that time. The amount is converted into an electrical signal, the displacement signal converted into an electrical signal is read by a computer or other computer, and the height information of the contact point between the stylus and the surface of the object to be measured obtained from the amount of displacement is obtained. The surface shape data of the object to be measured is created by sequentially arranging on the moving path (for example, Patent Document 1 below). FIG. 1 shows a basic configuration of the surface shape measuring apparatus.

The surface shape measuring apparatus 1 is provided with a table 2 along the XY plane for placing the workpiece W to be measured. A column 3 is erected on the table 2. A Z-direction movable part 4 is attached to the column 3. A motor 51 is built in the column 3, and when the motor 51 is driven, the Z-direction movable portion 4 moves up and down along the column 3 (that is, along the Z direction).
The Z-direction movable portion 4 is provided with an X-direction movable portion 5, an arm portion 10 is attached to the X-direction movable portion 5, and a pickup 6 is attached to the tip of the arm portion 10. The Z-direction movable unit 4 also includes a motor 52, and when the motor 52 is driven, the X-direction movable unit 5 is driven in the X direction.

A measuring element (pickup) 6 for measuring the surface roughness of the object to be measured placed on the table 2 is provided at the tip of the arm 10, and the pickup 6 has a stylus at one end. A cantilever 7 provided with 11 is attached.
When measuring the surface shape of the workpiece W on the measurement surface 103, first, the calculation unit 40 such as a computer moves the Z-direction movable unit 4 via the motor drive circuit 70 and the X-direction movable unit. 5 is driven, and the stylus 11 is positioned at the measurement start position on the measurement surface 103.
Then, the calculation unit 40 drives the motor 52 with the stylus 11 pressed against the measurement surface 103 to move the X direction driving unit 4 at a constant speed. When the stylus 11 moves up and down along the contour of the measurement surface, the cantilever 7 swings. This swing amount is converted into an electric signal by a differential transformer or a differential inductance in the pickup 6. FIG. 2 shows the internal structure of the pickup.

  The pickup 6 has a fulcrum 21 that supports the cantilever 7 in a swingable manner with a direction perpendicular to the longitudinal direction of the cantilever 7 and the protruding direction of the stylus 11 as a rotation axis, and urges the cantilever 7 to keep the stylus 11 constant. And an urging means 22 that is an elastic body such as a spring for pressing against the measurement surface 103 of the workpiece W with the measurement pressure.

When the stylus 11 is displaced along the undulation of the measurement surface 103 (that is, when the stylus 11 is displaced in the vertical direction with respect to a predetermined reference surface of the illustrated Z-direction movable portion 4), the displacement of the stylus 11 causes The cantilever 7 swings, and the swing amount is converted into an electric signal by a differential transformer in the pickup 6.
In the illustrated configuration example, the differential transformer is configured to include an excited primary coil 23, two secondary coils 25, and a magnetic core 26 inserted in the center thereof. It is fixed to the cantilever 7. When the cantilever rotates in accordance with the displacement of the stylus 11, the magnetic core 26 moves in the coil accordingly, and the mutual inductances of the two secondary coils 25 with respect to the primary coil 23 change. For this reason, a difference occurs between the induced voltages of the two secondary coils 25, and an output voltage corresponding to the amount of movement of the core, that is, the amount of displacement of the stylus 11 can be obtained. A differential inductance, a laser interferometer, or an optical encoder may be used instead of the differential transformer.

  The output signal of the pickup 6 is input to an analog / digital conversion circuit (ADC) 30. The analog / digital conversion circuit 30 converts the analog signal into a digital displacement signal string at a predetermined sampling period. The digital displacement signal sequence is input to the calculation unit 40. The calculating unit 40 moves the X-direction movable unit 5 at a constant speed and moves the stylus 11 on the surface of the object to be measured 103, and sequentially reads the values of the displacement signals and the stylus 11 at the respective positions. The Z coordinate of the contact point with the surface 103 to be measured is obtained, and this is sequentially arranged on the movement path of the stylus 11 to create surface shape data of the object to be measured.

JP 2002-107144 A JP 2005-127934 A JP 2005-297127 A

  In the surface shape measuring apparatus 1 for bringing the stylus 11 into contact with the object to be measured as described above, if there is a hole or a step on the surface of the object to be measured, the stylus 11 is caught there, and an excessive load is applied to the stylus 11. May work. However, since the conventional surface shape measuring apparatus 1 does not have a load detecting means acting on the stylus 11, the X-direction movable portion 5 and the Z-direction movable portion 4 are continuously moved while an excessive load is applied to the stylus 11. As a result, the stylus 11 may be damaged.

For example, as shown in FIG. 3A, when measuring the surface shape of the inner surface of the horizontal hole 101 of the workpiece W, when moving the stylus to the measurement start point indicated by the dotted line in the figure, The stylus 11 hits the back of the hole 101 and is easily damaged.
Further, as shown in FIG. 3B, when the hole 102 is present on the surface of the workpiece W, the stylus 11 falls into the hole 102 and may be caught by the stylus 11 to be damaged. .

Further, in the surface shape measuring apparatus 1, when the stylus 11 that is not being measured is moved, for example, when the stylus 11 is moved to the measurement start point, the Z-direction movable unit 4 or the X direction is kept with the stylus 11 being hit against an obstacle. The movable part 5 may be moved, and the stylus 11 and the pickup 6 may be damaged.
In view of the above problems, the present invention is a surface shape measuring device having a stylus that contacts the surface of an object to be measured. The purpose is to prevent damage to the stylus and pickup due to excessive load.

In order to achieve the above object, in the present invention, when the stylus and the object to be measured are relatively moved by the motor, the relative movement speed between the stylus and the object to be measured by the motor and the driving current of the motor are calculated. Each is monitored to detect an abnormality in the load acting on the stylus when the relative movement speed decreases and the drive current exceeds a predetermined threshold.
In order to determine whether or not an abnormal load is acting on the stylus due to an obstacle, the movement by the motor stops while the motor is driven, which increases the drive current of the motor, or the stylus and the object to be measured. In the present invention, both the relative movement speed and the motor driving current are monitored.

  This prevents erroneous detection of a stylus load abnormality even when, for example, the sliding resistance of the measurement surface changes and only the drive current temporarily increases. When the stylus is slid on the measurement surface at low speed, the movement called “stick slip”, that is, the movement of the stylus for a moment and then stopping is repeated, but the drive current should also be monitored at this time. Thus, it is possible to prevent erroneous detection of the stylus load when only the relative movement between the stylus and the object to be measured is temporarily reduced.

The relative moving speed between the stylus and the object to be measured may be directly measured by measuring the relative moving speed or indirectly by measuring the rotational speed of the motor.
When an abnormality in the stylus load is detected, the motor that moves the stylus and the object to be measured is stopped to prevent the stylus and the pickup that supports the stylus from being damaged.

Furthermore, even during normal measurement, the sliding resistance temporarily increases, so that the motor drive current temporarily increases and the relative movement speed decreases simultaneously. . In such a case, if the stylus load abnormality is detected and the motor is stopped, the measurement work may be hindered.
For this reason, when detecting an abnormality in the stylus load due to an increase in the drive current, it is determined that an abnormal load is acting on the stylus only when the drive current exceeds the predetermined threshold for a predetermined time or more. May be.

  In the surface shape measuring apparatus having a stylus that contacts the surface of the object to be measured, the present invention makes it possible to detect an abnormality in the load acting on the stylus, so that when the abnormality is detected, It is possible to prevent the stylus and the pickup from being damaged due to an excessive load acting on the stylus and stopping the movement.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 4 is a schematic configuration diagram of a surface shape measuring apparatus according to an embodiment of the present invention. In the present embodiment, motor current detectors 53 and 54 for detecting drive currents of the motor 51 for moving the Z-direction movable unit 4 and the motor 52 for moving the X-direction movable unit 5 are provided.
In addition, in order to detect the rotational speeds of the motor 51 and the motor 52, rotational speed instruction signals that change in accordance with the respective rotational speeds are input to the calculation unit 40. The rotation speed instruction signal may be, for example, a pulse signal output from an encoder built in the motor 51 and the motor 52, or an output signal from a speed generator having a voltage having a magnitude corresponding to the motor rotation speed. May be.
Since the other components of the surface shape measuring apparatus according to the embodiment of the present invention are the same as those of the surface shape measuring apparatus 1 shown in FIGS. 1 and 2, the description thereof will be omitted in order to prevent duplication of description. Unless otherwise specified, the same function is assumed.

  FIG. 5 is a diagram illustrating a schematic configuration example of the calculation unit 40 illustrated in FIG. 4. The calculation unit 40 realized by a computer or the like includes a CPU 41 that executes a control program for the surface shape measuring apparatus 1 and a program that processes output signals from the pickup 6 to create surface shape data, and each program by the CPU 41. A main storage device 42 such as a RAM and a ROM for storing data necessary for the execution, a sub storage device 43 for storing each program executed by the CPU 41 and the created surface shape data, and a sub storage device 43. And an interface 44 for exchanging data between the CPU 41 and the CPU 41.

  The calculation unit 40 inputs a displacement signal obtained by converting the output signal from the pickup 6 into a digital signal by the analog-to-digital conversion circuit 30, and inputs a control signal for controlling the operation of the motors 51 and 52 to the motor. A motor current value for driving the motors 51 and 52 detected by the motor current detectors 53 and 54, respectively, which is output to the circuit 50 and inputted with rotational speed instruction signals detected by the motors 51 and 52. An interface unit (I / F) 45 for inputting an instruction signal is provided.

  FIG. 6 is a functional block diagram realized by the calculation unit 40 shown in FIG. The calculation unit 40 executes at least a moving mechanism control unit 61, a surface shape data creation unit 62, a speed detection unit 63, and a stylus load abnormality detection by executing a predetermined program stored in the secondary storage device 43 by the CPU 41. Each functional block of the unit 64 and the timer 65 is realized.

The movement mechanism control unit 61 supplies a motor control command for driving the motors 51 and 52 to the motor drive circuit 50. The movement mechanism control unit 61 sends the stylus 11 to a predetermined measurement start position on the surface of the workpiece W by giving a motor control command to the drive circuit 50, and the Z-direction movable unit 5 is moved during the measurement. Move at a constant speed.
Upon receiving the motor control command, the motor control circuit 50 moves the X direction movable unit 5 and the Z direction movable unit 4 by the amount of movement instructed at the moving speed instructed from the moving mechanism control unit 61. 52 is driven. At this time, the motor control circuit 50 controls the drive current to the motors so that the rotational speeds of the motors 51 and 52 are constant by performing servo control.
Further, the moving mechanism control unit 61 supplies the surface shape data creating unit 60 with data such as the movement amount and coordinate values of the Z-direction movable unit 5 necessary for creating the surface shape data.

The surface shape data creation unit 62 sequentially receives a sequence of displacement signals output from the pickup 6 as the stylus 11 moves along the surface of the workpiece W. And from this displacement signal, the height information of the contact point between the stylus 11 and the surface of the workpiece W at each measurement point is obtained.
Then, the surface shape data creation unit 62 obtains a movement path along which the stylus 11 has moved from the movement amount and coordinate value of the Z-direction movable unit 5 obtained from the movement mechanism control unit 61. Then, the surface shape data of the object to be measured is created by sequentially arranging the height information of each measurement point on this movement path.

The speed detector 63 receives the rotation speed instruction signals output from the motors 51 and 52, detects the rotation speeds of the motors 51 and 52, and outputs them to the stylus load abnormality detector 64.
The stylus load abnormality detection unit 64 receives an operation signal indicating that the movement mechanism control unit 61 is driving the motors 51 and 52. While these motors are being driven, the motor currents of the motors 51 and 52 detected by the motor current detectors 53 and 54 and the rotational speeds of the motors 51 and 52 detected by the speed detector 63 are monitored. Using the information on the motor current and the rotational speed, it is detected that there is an abnormality in the load acting on the stylus 11 according to a detection method described later.
The timer 65 will be described later.

  With reference to FIG. 7, a method for detecting abnormality of the stylus load by the stylus load abnormality detection unit 64 will be described. FIG. 7 is a graph showing temporal changes in the motor current Im and the motor rotation speed Vm when the motors 51 and 52 are driven. In FIG. 7, the solid line indicates the motor rotation speed Vm, and the alternate long and short dash line indicates the motor current Im. As shown in the figure, when the motor control circuit 50 performs servo control, the rotation speeds of the motors 51 and 52 are constant until time t0.

At time t0, as described with reference to FIG. 3A, when the stylus 11 hits the back of the lateral hole 101 of the workpiece W, an excessive load is applied to the motor 52, and the speed decreases. Therefore, the motor control circuit 50 increases the motor current in order to maintain the rotation speed of the motor 52, but the motor 52 comes to a stop at time t1.
As shown in FIG. 3B, when the stylus 11 falls into the hole 102 on the surface of the workpiece W and is caught, the motor 52 stops and the motor current increases.
Therefore, the stylus load abnormality detection unit 64 monitors the motor current Im of the motors 51 and 52 detected by the motor current detection units 53 and 54 and the rotation speed Vm of the motors 51 and 52 detected by the speed detection unit 63. When the motor current Im exceeds a predetermined threshold current Ti and the rotational speed Vm becomes lower than the predetermined threshold speed Tv, it is detected that there is an abnormality in the load acting on the stylus 11; A motor stop command signal for stopping the motors 51 and 52 is output to the moving mechanism control unit 61.

Hereinafter, it will be described that the stylus load abnormality detection method according to the present invention is superior to the method of monitoring only the motor current Im and detecting the stylus load abnormality. Considering that the motor current Im is excessive only as a sign of an abnormality in the stylus load, for example, when the stylus 11 is scanning a region where the sliding resistance is large, the abnormality in the stylus load is erroneously detected. It is possible to detect.
In other words, when the stylus 11 scans an area where the sliding resistance is large, even if the stylus 11 moves at a constant speed as shown in FIG. This is because the upper limit Ti may be exceeded or the upper limit Ti may be exceeded for a certain period of time.
In the stylus load abnormality detection method according to the present invention, since the motor speed is also monitored at the same time, it is possible to prevent erroneous detection that may occur when only the motor current Im is monitored.

Next, it will be described that the stylus load abnormality detection method according to the present invention is superior to the method in which only the rotation speed of the motor is monitored to detect the stylus load abnormality.
In particular, when the stylus 11 is slid on the measurement surface at a low speed, the stylus 11 repeats a movement called “stick slip”, that is, a movement that stops for a moment. At this time, the motor rotational speed is temporarily lower than the lower limit value Tv as shown in FIG. 8B despite the normal measurement operation, and the stylus load abnormality may be erroneously detected. obtain.
In the stylus load abnormality detection method according to the present invention, since the motor current is also monitored at the same time, it is possible to prevent erroneous detection that may occur when only the motor rotation speed Vm is monitored.

FIG. 9 is a flowchart of a first example of a stylus load abnormality detection method according to an embodiment of the present invention.
In step S11, the moving mechanism control unit 61 shown in FIG. 6 transmits a motor control command to the motor drive circuit 50, thereby driving the motors 51 and 52. At this time, the stylus load abnormality detection unit 64 receives an operation signal indicating that the moving mechanism control unit 61 is driving the motors 51 and 52, and monitors the motor current and the motor rotation speed of the motors 51 and 52. start.
In step S12, motor currents Im of the motors 51 and 52 are detected by the motor current detectors 53 and 54 shown in FIG. In step S13, the stylus load abnormality detection unit 64 determines whether the detected value of the motor current Im exceeds a predetermined current threshold Ti.

  If it is determined in step S13 that the motor current Im does not exceed the threshold value Ti, the stylus load abnormality detection unit 64 determines that there is no abnormality in the stylus load in step S14, and the process proceeds to step S11. return. If it is determined in step S13 that the motor current Im exceeds the threshold value Ti, the process proceeds to step S15.

In step S15, the speed detector shown in FIG. 6 detects the rotational speed Vm of the motors 51 and 52 from the rotational speed instruction signals of the motors 51 and 52. In step S16, the stylus load abnormality detection unit 64 determines whether or not the detected value of the motor rotation speed Vm is slower than a predetermined speed threshold value Tv.
If it is determined in step S16 that the motor rotation speed Vm is faster than the threshold value Tv, the stylus load abnormality detection unit 64 determines in step S14 that there is no abnormality in the stylus load, and the process proceeds to step S11. return.

  If it is determined in step S16 that the motor rotational speed Vm is slower than the threshold value Tv, it is determined in step S17 that there is an abnormality in the stylus load, and in step S18, a motor stop command signal is sent to the moving mechanism control unit. 61 to stop the motors 51 and 52.

The stylus load abnormality detection unit 64 executes steps S11 to S18 regardless of whether measurement is being performed while receiving the operation signals of the motors 51 and 52 from the movement mechanism control unit 61. The motor currents and rotational speeds of the motors 51 and 52 are monitored. When the abnormality of the load acting on the stylus 11 is detected, the motors 51 and 52 are stopped.
Accordingly, not only during measurement, but also when the stylus 11 moves (for example, when the stylus 11 moves to the measurement start point), the stylus 11 or the pickup 6 is damaged by hitting the stylus 11 against an obstacle. To prevent.

FIG. 10 is a flowchart of a second example of the stylus load abnormality detection method according to the embodiment of the present invention.
Even during normal measurement, the sliding resistance temporarily increases, so that the increase in motor driving current and the decrease in relative movement speed may occur simultaneously. In such a case, if the stylus load abnormality is detected and the motor is stopped, the measurement work may be hindered.

  For this reason, in this embodiment shown in FIG. 10, in addition to the flowchart shown in FIG. 9, when it is determined in step S13 that the motor current Im exceeds the threshold value Ti, the motor current is once again after a certain period Δt has elapsed. By detecting Im, it is determined whether or not the period during which the motor current Im exceeds the threshold value Ti is equal to or longer than a certain period ΔT.

  That is, in the flowchart shown in FIG. 10, when it is determined in step S13 that the motor current Im exceeds the threshold value Ti, the timer 65 shown in FIG. After that, in steps S21 and S22, it is determined again whether or not the motor current Im exceeds the threshold value Ti. If the motor current Im does not exceed the threshold value Ti during the lapse of ΔT, the process proceeds to step S14. It is determined that there is no abnormality in the stylus load.

  On the other hand, if it is determined in S22 that the motor current Im exceeds the threshold value Ti, it is determined that the motor current Im has exceeded the threshold value Ti during the period ΔT, and the process proceeds to step S15 where the motor rotation speed Vm is checked. To migrate.

In the above embodiment, the stylus 11 and the workpiece W are moved relative to each other by moving the stylus 11 with a motor. However, the present invention is not limited to this and is opposite to the above embodiment. In addition, the present invention can be used in an aspect in which the stylus 11 and the object to be measured W are relatively moved by moving the object to be measured W by a motor, and such an aspect is also included in the scope of the present invention.
Further, in the above embodiment, the rotational speeds of the motors 51 and 52 are detected in order to indirectly measure the relative moving speed between the stylus 11 and the object W to be measured. Without limitation, the present invention can also be used for an aspect in which the relative movement speed between the stylus 11 and the object W to be measured is directly measured by, for example, a laser length meter or an ultrasonic distance measuring device. Are also included within the scope of the present invention.

  In the present invention, the stylus is moved relative to the surface of the object to be measured, and at this time, a displacement signal is generated by detecting the displacement of the stylus caused by the undulation of the surface of the object to be measured, The present invention can be used for a surface shape measuring device for measuring a shape.

It is a basic lineblock diagram of a surface shape measuring device. It is the schematic which shows the internal structure of a pick-up. (A) is a figure which shows a mode that a stylus collides in the back of the horizontal hole of a to-be-measured object, (B) is a figure which shows a mode that a stylus is caught in the hole of a to-be-measured object. It is a schematic block diagram of the surface shape measuring apparatus by the Example of this invention. It is a figure which shows the example of schematic structure of the calculation part shown in FIG. It is a functional block diagram implement | achieved by the calculation part shown in FIG. It is explanatory drawing (the 1) of the abnormality detection method of the stylus load by the Example of this invention. (A) is explanatory drawing (the 2) of the abnormal detection method of the stylus load by the Example of this invention (the 2), explanatory drawing (the 3) of the abnormal detection method of the stylus load by the Example of this invention of (B) ). It is a flowchart of the 1st example of the abnormality detection method of the stylus load by the Example of this invention. It is a flowchart of the 2nd example of the abnormality detection method of the stylus load by the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Surface shape measuring apparatus 2 Table 3 Column 4 Movable part 6 Pickup 7 Cantilever 10 Arm part 11 Stylus

Claims (6)

A surface shape measuring device for detecting the displacement of the stylus when the stylus is moved relative to the surface of the object to be measured and measuring the surface shape of the object to be measured,
A speed detector that detects a rotational speed of a motor that relatively moves the stylus and the object to be measured or a relative movement speed between the stylus and the object to be measured;
A current detector for detecting a drive current flowing through the motor;
A stylus load abnormality that determines that an abnormal load is applied to the stylus when the rotational speed of the motor or the relative movement speed is slower than a predetermined threshold speed and the drive current exceeds a predetermined threshold current A detection unit;
A surface shape measuring apparatus comprising:   The stylus load abnormality detection unit further determines that an abnormal load is applied to the stylus when the drive current exceeds the predetermined threshold for a predetermined time or more. The surface shape measuring apparatus according to 1.   The surface shape measuring apparatus according to claim 1, wherein when the stylus load abnormality detection unit detects the abnormality of the load, the motor is stopped. A load acting on the stylus in surface shape measurement for measuring the surface shape of the object to be measured by detecting the displacement of the stylus when the stylus is moved relative to the surface of the object to be measured. An abnormality detection method of a stylus load for detecting an abnormality of
A speed detection step of detecting a rotational speed of a motor that relatively moves the stylus and the object to be measured or a relative movement speed between the stylus and the object to be measured;
A current detection step of detecting a drive current flowing through the motor;
A stylus load abnormality that determines that an abnormal load is applied to the stylus when the rotational speed of the motor or the relative movement speed is slower than a predetermined threshold speed and the drive current exceeds a predetermined threshold current A determination step;
An abnormality detection method characterized by:   5. The stylus load abnormality determination step further determines that an abnormal load is applied to the stylus when the drive current exceeds the predetermined threshold for a predetermined time or more. The abnormality detection method described in 1.   6. The abnormality detection method according to claim 4, wherein the motor is stopped when the load abnormality is detected.

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