HK1090417B - Motorized orientable measuring head - Google Patents

Description

Motorized orientable measuring head

Reference data

This application claims priority from european patent application No. 2004EP-106226, filed on 12/1/2004, the contents of which are incorporated herein by reference.

Technical Field

The present invention relates to a re-orientatable measuring head for measuring three-dimensional coordinates of a mechanical component and, in particular, although not exclusively, to a re-orientatable measuring head designed for application on a manual or robotic machine for measuring coordinates.

Background

A contact probe is a measuring instrument, for example applied on a mechanical part production line, for checking the dimensions or the surface of a machined part. Contact detectors are also used to record the three-dimensional shape of complex workpieces, for example for reproduction or imitation thereof.

The probe usually comprises a measuring head designed to be fixed on the arm of the measuring machine or on a movable feeler, said measuring head comprising a ball at the end of an elongated rod and being designed to bring it into contact with the workpiece to be measured.

In most applications, the contact detector is fixed to the movable arm of the machine, whose position in space can be accurately determined by means of a manual or automatic measuring system, for example a position encoder placed on the machine axis. The movable arm is moved in space to bring the measuring feeler of the probe into contact with the workpiece or surface to be measured. Upon contact, a deflecting force is then applied to the contact, moving it away from its initial rest position. The sensor reacts to the slightest displacement of the feeler, generating an electrical signal, which is sent either in the form of an optical 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 from the data of the measuring system. For this purpose, electromechanical or optical sensors or movement sensors based on different principles are used in the prior art, for example sensors comprising constraint gauges (constraint gauges).

In the case of three-dimensional contact probes, the connection between the feeler and the fixed part of the measuring head is generally carried out according to the Boys connection Principle, i.e. for example by placing three cylindrical pins on six spheres so as to define six contact points between the fixing means and the feeler. However, two-dimensional and one-dimensional detectors are also known.

When using probes for measuring workpieces having complex shapes, such as cavities and protrusions, it is difficult or even impossible to bring the feeler into contact with the entire surface of the workpiece without the fixed part of the measuring head or the feeler lever interfering with the elements of the workpiece to be measured. In order to remedy this inconvenience, various measuring heads are known which allow the contact tips to be oriented in space in a plurality of directions. Generally, two separate shafts are required in order to achieve all possible orientations. An instrument of this type is described in european patent application No. EP 0392660.

However, the use of this type of devices is not limited to contact tips, and they may also use contactless detectors, such as cameras, for inspection and verification of machined parts.

The spindle is preferably indexed in the sense that a sufficient but limited number of predetermined and precisely repeatable rest positions are provided. This configuration avoids the trouble of having to recalibrate the machine after each change of orientation of the stylus.

The indexing of the contact rotary shaft is obtained by means of respective indexing surfaces which engage one another and define the desired rest position, for example by means of a spherical cap in which three pins engage. An example of this type of indexing mechanism is described in european patent application No. EP 1443299, filed by the present applicant.

In order to measure complex workpieces, it is desirable that the measuring head be motorized so that the feeler of the probe can be automatically oriented according to the instructions of the measuring machine control program. For this purpose, the rotation and locking of the contact shafts is performed by an electromagnetic actuator, for example an engine or a servomotor, which moves the indexing surfaces apart and rotates the shafts.

One limiting factor of known motorized measuring heads is: when the measuring head is unlocked, it is difficult to accurately define the position of the contact, since neither the distance between the indexing surfaces nor the lock execution time can be accurately known. This uncertainty can increase the response time of the measuring machine and can lead to undesirable collisions between the stylus and the workpiece being measured.

Another limiting factor of the known motorized measuring heads is: the locking system may be influenced by the orientation of the measuring head by gravity or its function. When the measuring heads are not vertically oriented, their operation is therefore problematic or impossible.

The inertial forces associated with the mass of the probe feeler can also have a negative effect on the functioning of the measuring head, in particular when heavy feelers and considerable movement speeds are used.

Another limiting factor of the known measuring head is: in the unlocked position, the distance between the indexing surfaces is not strictly defined. During the rotation of the contact shaft, there may be a collision between the indexing ball and the pin. This type of collision will of course have a negative effect on the accuracy of the indexing.

Disclosure of Invention

It is an object of the present invention to propose a measuring head without the various limitations of the known devices, in particular a measuring head in which the trajectory of the feelers is completely controlled even during the locking and unlocking operations.

It is another object of the present invention to provide a motorized measuring head with indexing in which the orientation of the probe tips can be changed for any orientation of the measuring head.

Another object of the invention is to propose a measuring head in which there is no possibility of any undesired collisions between the indexing surfaces.

These objects are achieved by a device comprising a combination of features which are the main technical solution objects, and in particular by a re-orientatable measuring head for orienting a probe tip relative to a measuring apparatus, comprising: a support element; a first movable member connected to the support member and rotatable relative to the support member about a first axis; an automatic actuator capable of being in a locked state and an unlocked state; wherein said automatic actuator is arranged to exert an unlocking force on said first movable element to move said first movable element away from said support element and allow rotation about said first axis when said actuator is in an unlocked state; a locking force is applied to the first movable element to tighten the first movable element onto the support element and prevent rotation about the first axis when the actuator is in a locked state.

Drawings

The invention will be better understood from a reading of the description given by way of example and illustrated by the accompanying drawings, in which:

FIG. 1 is a view of a motorized measurement head according to the present invention;

FIG. 2 is a cross-sectional view of the inventive measuring head in a locked position;

FIG. 3 is a cross-sectional view of an inventive measuring head in an unlocked position;

FIG. 4 is a detail view of the locking/unlocking mechanism of the measuring head of the invention;

FIGS. 5-8 are various views of an actuator responsible for locking and unlocking in accordance with an aspect of the present invention; and

fig. 9 is a detailed view of a crankshaft included in the actuator shown in fig. 5-8.

Detailed description of the preferred embodiments

Referring to fig. 1, a re-orientatable measuring head 10 according to the invention comprises a support 30 designed to be fixed to a measuring horn and able to move, for example, along three coordinate axes X, Y and Z within a measuring volume. The support may be fixed in place, for example, by a rod 20 or any other fixing mechanism.

Hereinafter, for the sake of brevity, the use of the designation "vertical" refers to the direction indicated by axis B in FIG. 1. This pointing direction is the normal orientation in the figures and is also the orientation in which the inventive device is normally used and is generally coincident with the direction of the vertical axis Z of the measuring machine on which the probe is mounted. However, the detector may be used in any orientation in space.

The first mobile element 40 is fixed to the support 30 so as to be able to rotate about a vertical axis B. The first movable element 40 may preferably have a plurality of indexed positions corresponding to a plurality of small predetermined angles, for example 10 degrees. In a known manner, these indexed positions are determined, for example, by an equalizing connection defining six rest points between the positioning elements, the positions of which are determined with high precision.

The second mobile element 50 is free to rotate about the horizontal axis a and is connected to the first mobile element 40. The rotation of the second mobile element 50 about the axis a can be continuous or indexed, motorized or manual, as described above for the first mobile element 40.

A probe tip 60 is fixed to the second movable element 50 and the bearing, at the end of which a ball 70 is designed to contact the workpiece to be measured. A detection mechanism, not shown in the figures, sends an electrical signal to the optical display 35 or to the control software of the machine via a connector (not shown) in response to the slightest displacement of the ball 70 with respect to the rest position.

A shaft locking and unlocking mechanism according to an aspect of the present invention will be described with reference to fig. 2 and 3.

The support 30 carries a series of balls 31 arranged at generally constant angular intervals, for example 10 °, along the circumference so as to define a series of indexed positions generally regularly spaced. Corresponding to said ball 31, the first mobile element 40 is provided with three pins 41 spaced by 120 ° and able to engage the ball 31. In the locking position (fig. 2), the first mobile element 40 is pressed against the fixed element 30 by pulling the rod 66. Each pin 41 then contacts two adjacent balls 31 so as to form a balanced connection between the supporting element 30 and the mobile element 40 according to the principle of the Boys connection method.

In an equivalent manner, within the framework of the invention, it is possible to exchange the positions of the balls and of the pins by arranging the former on the mobile element and the latter on the supporting element. The ball and pin may also be replaced by other positioning elements capable of defining six points of contact between the supporting element 30 and the mobile element 40.

One end of the vertical rod 66 is fixed in an articulated manner to the supporting element 30, while the other end of the rod 66 is fixed in an articulated manner to an arm of a lever 62, which is able to pivot about an axis 65, fixed with respect to the first mobile element 40. The lever 66 is preferably aligned with the axis of rotation B.

In the locked condition shown in figure 2, the lever 66 is pulled taut and pulls the first movable element 40 upwards, thereby engaging the indexing pin 41 with the ball 31 on the support 30. In this condition, any rotation about the axis B is not possible and the mobile element 40 is locked in an indexed position.

The force exerted by the lever 66 is applied to the relative centre of the point of contact between the ball 31 and the pin 41, and in the direction of the axis B. In this way, an even distribution of the contact force between the ball 31 and the pin 41 is obtained with maximum indexing accuracy.

The second mobile element 50 is also held against the first mobile element 40 by tensioning the horizontal bar 67 aligned with the axis a. On the one hand, the rod 67 is hinged to the mobile element 50, and on the other hand, the rod 67 is hinged to the lever 62.

A second set of balls 43 and pins 42 placed between the first and second movable elements allows the second movable element 50 to rotate so as to be locked in the indexed position.

Optionally, the rods 66 and 67 comprise resilient elements (not shown), such as metal springs, in order to ensure that there is a constant indexing force between the pins 41, 42 and the balls 31, 43. In an equivalent manner, the elastic element may be included in the lever 62 or in the first and second movable elements.

Referring to fig. 5-9, the position of the lever 62 is determined by a crankshaft 59, shown in detail in fig. 9, which is driven in rotation about an axis 75 by an electric motor 45 and toothed wheels 46, 51. In an equivalent manner, the crankshaft 59 may be driven directly by a motor disposed on the same axis 75 of the crankshaft 59 or by any mechanical transmission, such as a pulley system.

One arm of the lever 62 comprises a fork whose two branches 63 and 64 contact two opposite sides of the crank pin 55 of the crankshaft 59 in order to move the lever 62 from the locking position to the unlocking position when the crankshaft 59 rotates by 180 °. Optionally, a ball bearing is interposed between the crank pin 55 and the fork to reduce friction during locking and/or unlocking. In the embodiment shown in the figures, the bearing 54 is provided only in correspondence with the fork-shaped part 63 which transmits the locking force. The force required for the other branch 64 of the fork, which corresponds to the fork responsible for unlocking, is small and a simple antifriction bearing can be used.

The rotation of the crankshaft 59 about the axis 75 is limited by the sector 53 and the pin 55 associated with the first mobile element 40 to an angle of rotation slightly greater than 180 °. The stop position of the pin 55 against the end of the sector 53 is set so as to hit the equilibrium points and thus define stable rest positions corresponding to the locked condition and to the unlocked condition, respectively.

Fig. 3 and 4 show a measuring head according to the invention in an unlocked state. In this case, the lever 62 is inclined and the rods 66 and 67 press on the supporting element 30 and the second movable element 50, respectively, so as to move the indexing elements 31, 41 and 42, 43, respectively, apart by a predetermined distance d1, d2, respectively.

In a different embodiment, the rods 66 and 67 may be driven by a pinion/rack unit.

Since the dual action of the levers 66 and 67 results in the movement of the indexing surfaces apart and closed, the action is independent of the direction of gravity and inertial forces, and there is no need to use springs or resilient elements. The inventive mechanism thus ensures reliable and rapid functioning regardless of the orientation of the measuring head.

In the unlocked position, the rotation about the two axes a and B is ensured by a servomotor (not shown), controlled by the software of the measuring machine, or by other equivalent automatic actuators.

The embodiments described herein include a single actuator for simultaneously locking and unlocking both axes a and B. The invention also includes variations in which each axis of rotation is locked and unlocked by a separate actuator.

In one embodiment, the inventive measuring head comprises only one axis of rotation, for example the horizontal axis a.

Claims (12)

1. A re-orientatable measuring head (10) for orienting a probe tip (60) relative to a measuring device, comprising:

a support element (30);

a first mobile element (40) connected to the support element (30) and able to rotate about a first axis (B) with respect to the support element (30);

an automatic actuator capable of being in a locked state and an unlocked state;

wherein the automatic actuator is arranged to

-exerting an unlocking force on said first movable element (40) so as to move said first movable element (40) away from said supporting element (30) and allow a rotation about said first axis (B) when said automatic actuator is in the unlocked condition;

-exerting a locking force on the first movable element (40) so as to tighten the first movable element (40) onto the supporting element (30) and prevent rotation about the first axis (B) when the automatic actuator is in the locked condition, -the measuring head further comprising a first rigid rod (66) having two ends, one end of which is fixed in an articulated manner to the supporting element (30) and the other end of which is fixed in an articulated manner to the automatic actuator so as to transmit the locking and unlocking forces.

2. The measurement head of claim 1, comprising:

a plurality of movable positioning elements (41) connected to said first movable element (40);

a plurality of fixed positioning elements (31) connected to said supporting element (30) and engageable with said movable positioning elements (41) to define a plurality of predetermined orientations of said first movable element (40) with respect to said supporting element (30).

3. The measuring head of claim 1, wherein the first movable element (40) is moved apart from the support element (30) by a predetermined distance (d2) when the automatic actuator is in an unlocked state.

4. The measuring head of claim 1, wherein the automatic actuator comprises an electric motor (45).

5. The measuring head according to claim 1, wherein the first rigid rod is arranged for tensioning the first movable element (40) when the automatic actuator is in the locked state; -pushing the first movable element (40) when the automatic actuator is in the unlocked state.

6. The measuring head of claim 1, wherein the automatic actuator comprises an electric motor (45) and a lever (62), one arm of which is hinged to one end of the first rigid rod, and the motor (45) acts on a crankshaft (59) to oscillate the lever between the locked and unlocked positions.

7. The measurement head of claim 1, wherein the locking and unlocking are independent of an orientation associated with gravity.

8. The measurement head of claim 1, comprising a rotary actuator for rotating the first movable element (40) relative to the support element (30) when the automatic actuator is in an unlocked position.

9. The measurement head of claim 1, comprising:

a second mobile element (50) connected to said first mobile element (40) so as to be rotatable with respect to said first mobile element about a second axis (A);

wherein the automatic actuator is arranged to

-exerting an unlocking force on said second movable element (50) so as to move said second movable element (50) away from said first movable element (40) and allow rotation about said second axis (a) when said automatic actuator is in the unlocked condition;

applying a locking force to engage the second movable element (50) with the first movable element (40) when the automatic actuator is in a locked state.

10. The measuring head of claim 9, comprising a second rigid rod (67) one end of which is fixed in an articulated manner to the second movable element (50) and the other end of which is fixed in an articulated manner to the automatic actuator, and the automatic actuator comprises an electric motor (45) and a lever (62), one arm of which is articulated to one end of the first rigid rod, and the motor (45) acts on a crankshaft (59) to oscillate the lever between a locking position and an unlocking position.

11. The measuring head of claim 10, wherein the first rigid bar (66) and the second rigid bar (67) are substantially perpendicular to each other and aligned with the first axis of rotation (B) and the second axis of rotation (a), respectively.

12. The measurement head of claim 9, comprising a rotation actuator for rotating the first movable element when the automatic actuator is in an unlocked state.