HK1084723B - Probe for three-dimensional measurements - Google Patents

Description

Probe for three-dimensional measurement

Technical Field

The present invention relates to a contact probe capable of being oriented in multiple directions in space. Such probes are designed to be used more particularly, but not exclusively, in manual or automatic measuring machines or in machine tools such as milling machines for three-dimensional measurements of parts being machined or during machining.

Background

For example, in order to accurately inspect the dimensions or surfaces of machine parts, contact probes are widely, but not exclusively, used measuring elements in the production line of machine parts. In order to reproduce or model complex-shaped machine parts, contact probes are also used for three-dimensional measurement of complex-shaped machine parts.

A contact probe usually comprises a fixed part designed to fix the fixed part to a measuring machine or machine tool and a movable sensor comprising a ball at the end of an elongated rod and designed to bring the movable sensor into contact with the work piece to be measured.

In most applications, the contact probe is fixed to a movable arm of the machine, the position of which can be accurately determined by means of a manual or automatic measuring system, such as for example a position encoder placed on the shaft of the machine. The movable arm is moved in space until the measuring sensor of the probe is in contact with the work or surface to be measured. During contact, a biasing force is thereby exerted on the sensor, moving it away from its initial rest position. The sensor generates an electrical signal in response to the slightest displacement of the sensor, which is sent as a light signal to the user or to the control software of the machine, which determines therefrom the coordinates of the contact point in a given reference system on the basis of the data of the measuring system. For this purpose, the prior art uses electromechanical or optical sensors or movement sensors based on different principles, for example sensors comprising constraint measurers.

In the case of three-dimensional contact probes, the connection between the sensor and the fixed part of the probe is generally achieved according to the Boys connection principle, i.e. by defining six points of contact between the fixed part and the sensor, for example by means of three cylindrical pins resting on six spheres. However, two-dimensional or one-dimensional probes are also known.

When using a probe for measuring pieces of complex shape with cavities and bulges, it is difficult or even impossible to bring the sensor into contact with the entire surface of the piece to be measured without the fixed part of the probe or the stem of the sensor interfering with the elements of the piece to be measured. To remedy this inconvenience, probes are known that allow orienting the contact sensor in multiple directions within a space. Typically, two separate axes of rotation are required to cover all possible orientations. A probe of this type is described in european patent application EP 0392660.

Preferably, the axis of rotation is indexed (index), meaning that a sufficiently large but limited number of predetermined and accurately repeatable rest positions are provided. This configuration avoids having to recalibrate the measuring machine each time the orientation of the sensor is changed.

During the measurement, the shaft, which allows the above-mentioned prior art probe to be oriented, is locked in one of the positions of the indexing provided. When a different orientation of the probe is required, the operator must manually unlock the shaft by actuating a wheel or lever provided to unlock this action to the shaft, orient the probe as required, and lock the shaft again by returning the wheel or lever into the initial locked position. These operations may lead to positioning errors, which may follow, for example, by inadvertently moving the first axis while positioning the second axis.

Another disadvantage of the above-described feeler is that the locking and unlocking operations require an external torque to be exerted on the locking wheel, which is transmitted to the movable arm of the measuring machine through the feeler and its support. This net torque creates a machine load on the support of the probe and enables the entire probe to move. To avoid this drawback, when the user actuates the locking wheel, he must hold the probe still, which makes it difficult or even impossible to operate with one hand.

Disclosure of Invention

One object of the present invention is to propose a contact probe which can be oriented in a plurality of indexed directions and can be reliably positioned without the risk of positioning errors.

Another object of the invention is to propose a contact probe that is not limited by the prior art.

Another object of the invention is to propose a contact probe that can be oriented in a plurality of indexed directions and that can be operated more easily than prior art probes.

According to the invention, these objects are achieved by a device for orienting a contact probe, which is orientable, of a measuring sensor relative to a measuring apparatus, comprising:

a support element;

a movable element connected to said support element, the movable element being rotatable about an axis relative to said support element;

an axially resilient member for retaining said movable element in a locked position, said member preventing rotation of said movable element;

an indexing element defining six points of contact between said support element and said movable element for defining a plurality of predetermined and repeatable angular positions for said movable element when said movable element is in a locked position;

an actuator against said resilient member for disengaging said movable element from said support element, allowing said movable element to rotate about said axis,

wherein when said movable element is in the locked position, there is no other contact between said support element and said movable element other than said six contact points and said connection to said resilient member.

Drawings

The invention will be better understood from a reading of the description, which is given by way of example and shown by the accompanying drawings.

FIG. 1 shows an embodiment of a contact probe according to the invention;

FIG. 2 shows a cross-section of the contact probe of the present invention depicted in FIG. 1;

figures 3 and 4 show an indexing mechanism and a multiplication mechanism used to disengage the second horizontal axis of the probe of figure 1;

FIG. 5 depicts fixed parts of the probe of FIG. 1;

FIG. 6 shows the movable parts about a first vertical axis of the probe of FIG. 1;

FIG. 7 shows an indexing mechanism and a multiplication mechanism used to decouple the first vertical axis of the probe of FIG. 1;

FIG. 8 depicts the probe of FIG. 1 at a partial stage of assembly of the probe;

FIG. 9 shows a cross-section of the probe of FIG. 1 in a locked position;

FIG. 10 shows a cross-section of the probe of FIG. 1 in a disengaged position of the first vertical rotational axis.

Detailed Description

The first embodiment of the invention depicted in fig. 1 is a contact probe 20 comprising a fixed part 250, the fixed part 250 being depicted in detail in fig. 5, the fixed part 250 being designed to fix the fixed part 250 to a movable arm of a measuring machine by means of a threaded rod 251 or by means of other known fixing means.

The stationary part 250 has on its lower surface 24 spheres 256 regularly spaced along the circumference and projecting partially downward. The sphere 256 defines 24 indexed positions 15 degrees apart for the first rotational axis of the probe, as will be explained further below.

The probe of the present invention can be used in any orientation in space, depending on the application. Referring to fig. 2, for convenience reasons, the term "vertical" will be used hereinafter to indicate a first rotational axis of the probe 211, which corresponds to the geometric axis of the probe, while the term "horizontal" is used for a second axis 212 perpendicular thereto. These terms refer to the conventional orientation used in the drawings, particularly in fig. 2, in which fig. 2 depicts two axes 211 and 212.

For reasons of convenience, the terms "first" and "second" will also be used hereinafter to refer to the two axes and the various elements of the probe. However, since the present invention also includes probes with one, three, or any number of axes of rotation, these terms are not necessarily to be construed in the sense that the present invention is limited to devices with two axes. The terms "first" and "second" also do not imply any kind or order or dependency between elements and are used herein merely as indicators to distinguish between elements of the devices of the invention.

The movable element 210 depicted in fig. 6 and 8 carries three cylindrical pins 217 on its upper surface. The helical spring 235, seen in fig. 9, pulls the movable element 210 against the fixed element 250 via the rod 219. In this case, each of the pins 217 rests on two of the spheres 256, and the six resulting points of contact determine the relative position of the elements 250 and 210 in an accurate and repeatable manner.

In view of the rotational symmetry of the fixed element, the movable element 20 is able to assume 24 indexed positions, separated by 15 degrees about a first axis of rotation 211 corresponding to the geometric axis of the probe. The same result can be achieved by other equivalent constructions, for example by placing a sphere on the movable element and a pin on the fixed element, or by replacing the spherical or cylindrical surface of the pin or sphere with an inclined plane, or also by using six cylindrical pins each having only a single point of contact with one of the spheres. It is also possible to replace the flat spring 235 with an equivalent resilient member, such as a leaf spring, or with an element made of a resilient synthetic material.

The disengagement mechanism 300 depicted in fig. 7, 8, 9 and 10 makes it possible to allow the movable element 210 to rotate about the axis 211. The actuator 300 comprises four levers 306 driven by four push buttons 310 indicated in fig. 7 and four rollers 307 indicated in fig. 7.

When two opposing buttons 310 are pressed, the levers 306 rotate about the pivots 304 and out of the locked position of fig. 9 until they assume a substantially vertical position as depicted in fig. 10, which fig. 10 shows the indexing mechanism of the first shaft 211 in the unlocked position.

In the unlocked position, the rollers 307 push against the supporting ring 314 and move the fixed element 250 axially away from the movable element 210 by means of the ball bearings 313. In the spaced apart position, the ball 256 indicated in fig. 9 and 10 bypasses the pin 217 and does not contact the pin 217, and rotation about the axis 211 is possible.

The seating force of the pin 217 on the sphere 256 must be high enough to avoid any accidental movement of the movable part 210 during the measurement. In this particular embodiment, for example, indexing spring 235 is sized for a total seating force of about 30N, i.e., about 10N for each of the six contact points due to the application of pressure at 60 degrees relative to the shaft.

Applying a force of 30N directly on the button 310 may be difficult. For this reason, the dimensions of the lever 306 and the position of the pivot 304 are chosen to give a sufficient multiplication ratio between the radial force exerted on the button 310 and the axial force opposing the elastic force of the spring 235. For example, a 1: 2 reduction ratio means an actuation force of about 15N, i.e., about 1.5Kgf, at the button 310 that the user can apply without great difficulty. At this reduced ratio, the travel range of the button 310 remains several millimeters.

The numerical values given above must be understood as examples particularly suitable for the present embodiment. Depending on the circumstances, for example, depending on the mass and size of the probe, different values may be selected.

To ensure that the movable element 210 is disengaged around the axis of rotation 211, two opposite buttons 310 need to be actuated simultaneously. In this way, the external forces exerted on the probe are substantially opposite and perpendicular to the axis of rotation 211, the resulting forces and torques are substantially zero, and any unwanted movements of the probe are avoided.

When pushing the button 310 in the radial direction, the operator can rotate the movable element 210 around the axis 211 by actuating the same button in the tangential direction. This operation is very intuitive and can be performed simply with two fingers of one hand. In this case, the distance separating the ball 256 and the pin 217 is sufficient to avoid any contact or rubbing against the indexing surfaces, thereby maintaining positioning accuracy in the indexed positions. Thus, it is not necessary to release the button 310 to go from unlock to probe rotation and then again to probe lock.

The reduction ratio and the coefficient of friction of the materials used are chosen so that the transmission 300 is reversible so that the movable element 210 spontaneously returns to the indexed position once the pressure on the button 310 is released, thereby avoiding accidental use in the disengaged position.

The force generated by the actuator 300 to move the fixed element 250 and the movable element 210 apart is generally in line with and opposite the force applied by the indexing spring 235 and transmitted by the rods 214 and 219 to ensure frictionless rotation in the disengaged position.

Advantageously, a bearing 313, for example a thrust ball bearing, is interposed between the fixed element 250 and the movable element 210, so as to reduce friction during rotation about the first shaft 211. Instead of a thrust ball bearing, another type of bearing, such as a ball or roller bearing, may also be used.

In the locked position visible in fig. 9, the roller 307 is moved away from the support ring 314 by the return spring 336. A small gap (not visible) exists between the roller 307 and the support ring 314 regardless of the orientation of the probe in space.

In this manner, only six contact points between the ball 256 and the pin 217 in the seated position constitute a reaction to the action of the indexing spring 235. Contact between the fixed element 250 and the movable element 210 is maintained without other parts that may cause any kind of constraint that is inevitably negative to accuracy.

Moreover, the force of the indexing spring is applied by the levers 214 and 219 just at the center of gravity of the six contact points and corresponding to the axis of rotation 211 to ensure optimal seating.

In order to be able to use very long springs, which are therefore weak in rigidity, the indexing spring 235 is preferably loaded on the inside of the supporting bar 251, which ensures a constant tension along the entire travel range. The indexing force can be simply adjusted by using screws 218 at the ends of the support rods, or by other equivalent means. The screw 218 is easily accessible from the outside without disassembling the probe, for example simply by opening the cap 252.

The first movable element 210 is connected to a second movable element 220, the second movable element 220 being able to rotate about an axis of rotation 212 perpendicular to a first axis of rotation 211, to which first axis of rotation 211 a trigger 30 of a known type is fixed, as can be seen in figure 2.

The second movable element 220 is urged against the first movable element 210 in the axial direction defined by the axis of rotation 212 by a compression spring 225. The crown of the sphere 226 is made on a vertical face of the movable element 220 and interacts with three cylindrical pins (not depicted in the figures) placed on the face adjacent to the first movable element 210 to define a predetermined number of truly repeatable indexed positions, in a manner similar to that explained above for rotating the first movable element 210.

In a possibly different embodiment, six cylindrical pins with only a single point of contact can be used.

A decoupling and rotation system 400 for the second movable element 220 is depicted in fig. 3 and 4. Disengagement is achieved by applying pressure on the two buttons 411 and 410. The axial force exerted on the button 410 is transmitted by means of the two levers 430 and 450 and the horizontal arm 440, the button 410 being able to slide axially around the part 470, multiplying the axial force exerted on the button 410 and applying it to the spring 225 through the pin 461 and the rod 460, in order to compress the spring 225, which cancels the contact force between 220 and 210. In this embodiment, the dimensions of the arms of the levers 430, 450 are selected so as to achieve a 1: 2 reduction ratio of operating force, for example as for the first movable element 210. A second spring 475, interposed between the button 410 and the part 470, axially pushes the second movable element 220 to the right in fig. 2, allowing it to rotate.

When the button 410 is pushed, the second movable element 220 is moved to the right in figure 2 so that the pin and indexing sphere 226 are no longer in contact and the second movable element 220 can rotate about the shaft 212. Rotation is effected by the operator by means of the button 410, which button 410 is angularly coupled to the part 470 by means of a pin, which is not visible in the figures.

The button 411 opposite the button 410 has the following two functions: the rest surface is provided to the fingers to apply a force opposite to the force applied to the button 410 and to facilitate rotation of the element 220 with two fingers. In fact, the button 411 is angularly coupled to the element 220 and the button 411 is actuated to rotate with it. The use of two forces substantially opposite each other makes it possible to: avoiding the transmission of forces to the support of the probe and avoiding the movement of the whole probe.

The action of the button 410 on the second movable element 220 via the lever 460 is substantially in line with the force exerted by the spring 225 and opposite to the force exerted by the spring 225, which ensures a rectilinear movement without obstruction.

The electrical signal generated by the trigger 30 is transmitted to the user in the form of a light signal emitted by a light emitting diode 50 (fig. 1), or to the control software of the machine, which determines therefrom the coordinates of the contact point within a given reference frame from the data of the measuring system.

In this embodiment, the second movable element 220 is able to assume seven indexed positions 15 degrees apart from each other for a total angle of 90 degrees. In combination with the ability to rotate the first rotational element 210 through 360 degrees, this angle makes it possible to orient the trigger 30 in a number of directions evenly distributed in half-space. However, the device of the present invention can be provided with a common number of indexed positions and any distance between them.

Referring now to fig. 10, the button 310 is surrounded by an annular rubber or elastomer protective membrane 330, the function of which membrane 330 is to protect the internal mechanisms from dirt and dust, and also to prevent heat from the operator's hand from being transferred to the internal indexing mechanism, which heat may have adverse consequences on the accuracy of the indexing. For the same purpose, the buttons 410 and 411 for rotating and disengaging the second shaft 212 are preferably also made of a synthetic material with good heat insulating properties.

As can be seen in fig. 1 and 8, a window 41 is provided on the support element 250, which window 41 allows the angle of rotation relative to the first axis 211 to be read on a scale 47 engraved or printed on the first movable element 210.

The angle of rotation with respect to the second shaft 212 can be read on two windows 40 cut in the outer crown of the button 411. In this case, at least two windows are necessary to allow optimal visibility in all possible orientations of the probe.

The trigger 30 responds to the slightest contact with the work surface to be measured by generating an electrical pulse. The pulses are transmitted via an electronic processing circuit and a connector (not depicted) for connection with the control device of the measuring machine, and to the optical display 50. In this embodiment the display comprises light emitting diodes, but may alternatively comprise other known light emitters, such as for example sheet or line electroluminescent elements. Surrounding the light emitting diodes by an optical light diffuser allows the emitted light to be seen over a wider range of viewing angles.

In an alternative embodiment of the invention, the display 50 is replaced by a number of displays placed at different places on the probe so that at least one display is visible from each possible viewing angle.

In another embodiment of the invention, the display 50 comprises one or several light conductors to emit light generated by one or several light sources from different places of the surface of the probe, so that the light indication is seen from every possible viewing angle.

The invention also includes embodiments in which the rotation and disengagement of the shaft is actuated by an automatic actuator, such as an electric motor and/or a solenoid.

Claims (20)

1. An orientable contact probe (20) for orienting a measurement sensor (30) relative to a measurement device, comprising:

a support element (250);

a movable element (210) connected to said support element (250), the movable element (210) being rotatable about an axis (211) relative to said support element (250);

an axially resilient member (235) for retaining said movable element (210) in a locked position, the member (235) preventing rotation of said movable element (210);

an indexing element (256, 217), the indexing element (256, 217) defining six contact points between the support element (250) and the movable element for defining a number of predetermined and repeatable angular positions for the movable element (210) when the movable element is in the locked position;

an actuator (300) opposing said resilient member (235), said actuator (300) for disengaging said movable element (210) from said support element (250), allowing said movable element to rotate about said axis (211),

wherein, when said movable element (210) is in the locked position, there is no other contact between said support element (250) and said movable element (210) other than said six contact points and said connection to said resilient member (235).

2. The probe according to claim 1, wherein said support element (250) comprises a support rod (251) for fixing said probe to said measuring device, and said elastic member (235) comprises a helical spring axially placed in the internal space of said support rod and connected to said movable element by a rod (219) in line with said axis (211).

3. The probe according to claim 1, comprising a bearing (313) interposed between said support element (250) and said movable element (210) for rotating said movable element (210) with respect to said support element (250).

4. The probe according to claim 3, wherein said actuator (300) comprises a roller (307) for applying a dislodging force between said movable element (210) and said support element (250) through said bearing (313).

5. The probe according to claim 1, wherein said actuator (300) is associated with said movable element (210), and said actuator (300) comprises at least one return means (336), said return means (336) being adapted to return said actuator of said support element (250) when said movable element is in a locked position.

6. The probe according to claim 1, comprising a second movable element (220) connected to the movable element (210) by a second axis (212) for rotating the second movable element (220) relative to the movable element (210);

a second resilient member (225) capable of actuating the second resilient member (225) independently of the resilient member (235) for retaining the second movable element (220) in a locked position preventing rotation of the second movable element (220),

a second actuator (400) opposing the second resilient member (225) for disengaging the second movable element (220) from the movable element (210) allowing the second movable element (220) to rotate about the second axis (212).

7. The probe according to claim 6, wherein the disengagement of the movable element (210) and/or the disengagement of the second movable element (220) is achieved by a movement in the direction of the axis (211), the second axis (212), respectively.

8. The probe according to claim 6, comprising a measurement sensor (30) fixed to said second movable element (220).

9. Probe according to claim 6, wherein the actuator (300) and/or the second actuator (400) respectively disengage the movable element (210) by the action of two substantially symmetrical and opposite external forces applied to the actuator respectively to the second actuator.

10. The probe according to claim 9, wherein said actuator (300) and/or said second actuator (400) respectively drive said movable element (210) and said second movable element (220) in rotation by the action of a pair of external forces respectively applied to said actuator (300) and said second actuator (400).

11. The probe according to claim 9, characterized in that said actuator (300) and/or said second actuator (400) are arranged to stop their action when both said symmetrical and opposite external forces are interrupted.

12. The probe of claim 9, wherein said actuator (300) and/or said second actuator (400) comprises a multiplication mechanism for reducing the intensity of force required to disengage said movable element, said second movable element (220), respectively.

13. The probe of claim 12 wherein said multiplication mechanism includes at least one lever with unequal arms.

14. The probe according to claim 9, wherein said two external forces have a direction substantially perpendicular to said axis (211) and are supported by at least two buttons placed on said probe in diametrically opposite positions with respect to said axis (211).

15. The probe according to claim 6, comprising one or several windows for indicating the angular position of said movable element (210), respectively said second movable element (220).

16. The probe of claim 15, including at least two windows for indicating the position of said second movable element (220).

17. The probe of claim 1, comprising a large-sized light indicator for allowing control of the operation of the probe from any position of the probe.

18. The probe of claim 1, comprising a thermally insulating outer layer for preventing heat conduction from the hand to the probe.

19. The probe according to claim 6, wherein the action of said actuator (300) on said movable element (210) is substantially in line with and opposite to the force exerted by said resilient element (235) on said movable element (210).

20. The probe according to claim 6, wherein the action of said second actuator (400) on said second movable element (220) is substantially in line with and opposite to the force exerted by said second resilient element (225) on said second movable element (220).