HK1066270B - Adjustable probe - Google Patents

Description

Adjustable probe

Technical Field

The present invention relates to a touch activated probe that can be oriented in multiple directions. More precisely, but not exclusively, this probe is concerned with the use in manually operated or automatic measuring machines or machine tools, such as a milling machine, for the three-dimensional measurement of parts that have been or are being machined.

Background

A touch-triggered probe is a widely used, though not absolute, measuring instrument used on a production line of a mechanical part in order to accurately detect the dimensions and surface of the mechanical part. Touch-triggered probes are also used to measure complex-shaped parts in three dimensions in order to duplicate or counterfeit them.

Generally, a touch trigger probe comprises a fixed part for fastening to a measuring machine or machine tool and a movable feeler comprising a ball on the end of an elongated rod and designed to come into contact with the part to be measured.

In most applications, the touch trigger probe is fastened to a movable arm of a machine whose spatial position is accurately determined by a manually operated or actuated measuring system, such as a position encoder provided on a shaft of the machine. The movable arm is moved spatially to bring the measurement probe of the probe head into contact with the surface or part to be measured. During contact, a biasing force is applied to the probe to move the probe out of its initial rest position. A sensor responds to the slight movement of the probe to generate an electrical signal which is sent to the user in the form of an optical signal or to the control software of the machine which determines the coordinates of the point of contact in a given coordinate system based on the data of the measuring system. For this purpose, electromechanical or optical sensors or movement sensors according to different principles, such as sensors comprising strain gauges, are used in the prior art.

In the case of a three-dimensional touch trigger probe, the connection between the stylus and the fixed part of the probe is generally according to the principles of the Boys connection, for example passing through 3 cylindrical pins placed on a sphere, so as to define 6 contacts between the fixture and the stylus. Two-dimensional and one-dimensional probes are also known.

When a probe is used to measure a complex shaped part having cavities and protrusions, it is difficult, if not impossible, to contact the probe with the entire surface of the part, and the fixed portion of the probe or the shaft of the probe will interfere with these elements of the part to be measured. To address this drawback, known probes allow the contact probe to be oriented in a plurality of spatial directions. In general, two independent axes of rotation are required to cover all possible orientations. A probe of this type is described in european patent application EP 0392660a 2.

The rotation axes are preferably indexed in the sense that they provide a sufficiently large but limited number of predetermined and accurately reproducible stop positions. This arrangement avoids having to recalibrate the measuring apparatus after each change in probe orientation.

During the measurement, the axis allowing the orientation of the above-mentioned prior art probe is locked in a given indexed position. When a different orientation of the probe is required, the user must manually unlock the axes by actuating a wheel or a lever provided for this effect, orient the probes as required, and re-lock the axes by returning the wheel or lever to its original locked position. These operations may lead to positioning errors, such as unintended movement of the first axis during positioning of the second axis.

Another disadvantage of the above-described probe is that the locking and unlocking operations require an external torque applied to the locking wheel, which is transmitted by the probe and the carriage of the probe to the movable arm of the measuring machine. This net torque causes mechanical stress on the carrier of the probe and may cause the entire probe to move. To avoid this drawback, the user must keep the probe still while applying the locking wheel, which is difficult or even impossible to perform with one hand.

Disclosure of Invention

It is therefore an object of the present invention to provide a touch trigger probe which can be orientated in a plurality of indexing directions, the operation of which is easier than in the prior art.

It is another object of the invention to propose a touch trigger probe which does not have the limitations of the prior art.

According to the invention, these objects are obtained by means of a device which is the subject of the independent claims and which is notably obtained by means of an adjustable touch-trigger probe for orienting a measuring probe with respect to a measuring apparatus, comprising:

a movable member rotatable about an axis; a resilient means for holding said movable member in a locked position, preventing movement of said movable member; an actuating means linearly displaceable under the influence of an external force, opposite to said resilient means, to disengage said displaceable member by displacement along said axis, allowing said first displaceable member to rotate about said axis; a multiplying device for reducing the magnitude of the external force used to disengage said movable element.

Drawings

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

FIG. 1a shows a first embodiment of a touch trigger probe of the present invention;

FIG. 1b shows a fixed part of the touch trigger probe of the present invention of FIG. 1 a;

figures 1c and 1d show a first axial indexing means of a touch trigger probe according to the invention of figure 1 a;

FIG. 1e shows a multiplication device for decoupling from the first shaft of the probe of FIG. 1 a;

2a, 2b, 2c show cross-sections and front views of the indexing and multiplying device of the second axis of the probe of FIG. 1 a; and

figures 3 and 4, 5a, 5b and 5c show a second embodiment of the probe of the invention.

Detailed Description

The first embodiment of the invention in fig. 1a-1e is a touch trigger probe 20, which probe 20 comprises a fixed part 250, shown in fig. 1b, and is designed to be fastened to the movable arm of a measuring machine by means of the threaded rod 251 or by any other known fastening means.

The fastening part 250 has a plurality of balls 256 on its underside 24, which balls 256 are distributed uniformly along a circumference and project partially downward. The spheres 256 define 24 indexed positions which are spaced 15 degrees apart for the first axis of rotation of the probe, as will be described below. It will be apparent that a different number of spheres may be used depending on the desired number of index positions.

The displaceable member 210 shown in fig. 1c and 1d carries 3 cylindrical pins 217 on its upper side. A flat spring 215 presses the movable element 210 against the indexing element 250. In this case, each pin 217 is located on two spheres 256, and the 6 contact points obtained determine the relative position between the elements 250 and 210 in a precise and reproducible manner.

In view of the rotational symmetry of the fixed element, the movable element 210 can occupy 24 indexed positions that are 15 degrees apart from each other about a first rotational axis 211 corresponding to the coupling axis of the probe. The same result can be obtained by other equivalent structures, such as 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 even by using 6 cylindrical pins each having a single point of contact with one of the spheres. It would also be possible to replace the flat spring 215 by an equivalent elastic means, such as a cylindrical spring or a leaf spring, or by an element made of elastic synthetic material.

The disengagement means 300, shown in fig. 1d and 1e, allow the movable element 210 to rotate about the axis 211. The transmission 300 is constituted by a gear 301, the gear 301 being driven by 4 racks 305 and an inclined helical surface 302.

When two opposite buttons 310 are depressed, the rack 305 drives in rotation the gear 301 and the inclined plane 302 connected thereto, the inclined plane 302 sliding on its bearings (not shown) causing the fixed element 250 to move axially away from the movable element 210. In the position where the ball 256 and pin 217 are separated from each other, the ball 256 protrudes on the pin 217 without contacting the pin 217 and can rotate about the axis 211.

The resting force of the pin 217 on the ball 256 must be high enough to prevent any accidental movement of the movable part during measurement. In this particular embodiment, the spring 215 is machined for a total rest force of about 30N, i.e. about 10N for each of the 6 contact points. Since the pressure is applied at 60 degrees with respect to the axis.

It would be difficult to apply a force of 30N directly on the button 310. Thus, the inclination of the inclined surface 302 is selected 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 216, a 1: 2 reduction ratio meaning that there is a 15N operating force on the button 310, i.e. about 1.5Kgf, which the operator can exert without difficulty. By this decreasing ratio, the movement of the button is kept within a few millimeters.

The values given above must be understood as examples particularly suitable for the given embodiments. Depending on the circumstances, different values will be selectable, for example depending on the mass and size of the probe.

To ensure that the displaceable member 210 is disengaged about the axis of rotation 211, two opposing buttons must be acted upon simultaneously. In this way, the external forces exerted on the probe are substantially opposite each other and perpendicular to the axis of rotation 211, the forces and torques obtained are substantially zero and any unintentional movement of the probe is prevented.

When the button 310 is depressed in a radial direction, the user can rotate the displaceable member 210 about the axis 211 by acting on the same button in a tangential direction. This operation is very intuitive and can be easily performed by two fingers of one hand. In this case, the distance between the ball 256 and the pin 217 is sufficient to avoid any contact and rubbing of these indexing surfaces, thus maintaining the positioning accuracy in the indexed positions. There is no need to release the buttons 310 that enter the rotating probe from the unlock and then lock the probe again.

The reduction ratio and coefficient of friction of the materials used are selected so that the transmission 300 can be reversed so that the displaceable member 210 spontaneously returns to an indexed position upon release of pressure on the button 310, thus avoiding accidental use in the free position.

The first movable element 210 is connected to a second movable element 220, the second movable element 220 being rotatable about a rotation axis 212, the rotation axis 212 being perpendicular to the first rotation axis 211, as shown in fig. 2a for fastening a movable probe 30 of a known type to the first rotation axis 211.

The second movable element 220 is pressed against the first movable element 210 in the axial direction defined by the axis of rotation 212 by a compression spring 225. A spherical crown 226 is provided on the vertical side of the movable element 220 and the spherical crown 226 interacts with 3 pins (not shown) provided on the adjacent side of the first movable element 210 to define a predetermined number of indexed positions which can be accurately reproduced, in a manner similar to that described above, to rotate the first movable element 210.

In a possible variant embodiment, 6 cylindrical pins are used, each with a single contact.

The disengagement and rotation system 400 of the second movable element 220 is shown in fig. 2 b. This disengagement is performed by pressing on the two buttons 411 and 410. The axial force exerted on the button 410, which is able to slide around the piece 470, is transmitted by the two levers 430 and 450 and by the horizontal arm 440, and is doubled by the pin 461 and the rod 460 and is exerted on the spring 225, so as to compress the spring 225, the spring 225 restraining the contact force between the elements 220 and 210. In this embodiment, the dimensions of the arms of the levers 430, 450 will be chosen to obtain a reduction ratio of 1: 2 of the operating force, which reduction ratio is also used for the first movable element 210. A second spring 475, disposed between the button 410 and the feature 470, urges the second movable member 220 axially to the right in fig. 2a while allowing the second movable member 220 to rotate.

When the button is pressed, the second movable element 220 is moved towards the right in fig. 2a, so that the pin and the indexing sphere 226 are no longer in contact, and the second movable element 220 can be rotated about the axis 212. The user applies a rotation by means of the button 410, which button 410 is connected angularly to the piece 470 by means of a pin not shown in the figures.

The button 411 opposite the button 410 has a dual function: giving the fingers a resting surface for exerting a force opposite to the force exerted on the button 410 and facilitating rotation of the element 220 with two fingers. In fact button 411 is angularly connected with element 220 and is rotationally driven with element 220. The use of two forces, which are generally opposed, prevents stresses from being transmitted to the carrier of the probe and prevents movement of the entire probe.

The action of the button 410 on the second displaceable member 220 by the lever 460 is substantially in line and against the force exerted by the spring 225, thus ensuring a rectilinear movement without any interference.

The electrical signals generated by the probe 30 are sent to the user in the form of optical signals emitted by the light emitting diodes 50 (see figure 1a) or to the control software of the machine, which thus determines the coordinates of the contact point in a given coordinate system on the basis of the data of the measuring system.

The lower part of the probe 20 has one or more protective elements 218 protruding from the probe body, the function of the protective elements 218 being to protect the indexing mechanism from vibration against the measurement part or platform. The protective element 218 may be an enlarged portion machined directly into the metal shell 217 or an additional element made of a suitable material that can absorb vibrations, such as rubber or elastomer.

The second movable element 220, in this embodiment, may occupy 7 index positions, the 7 index positions being 15 degrees apart from each other for a total angle of 90 degrees. This angle, in combination with the possible 360 degrees of rotation for the first rotational element 210, allows the probe to be oriented in multiple directions evenly distributed in half space. However, the inventive device can be implemented with a general number of index positions, with any spacing between them.

Fig. 4, 5a and 5b show a second embodiment of the invention in which the uncoupling means 300 of the first shaft 211 are obtained with 4 pairs of identical and symmetrical connecting rods 320.

In this embodiment, each pair of connecting rods 320 is hinged with respect to a central point 323, and when the two ends of the two connecting rods of a central point pair are placed one on the fixed element 250 and the other on the first movable moving element 210, the external force applied to the button 310 is transmitted to said central point 323.

In this design, the reduction ratio between the axial force applied to the movable element 210 and the radial operating force applied to the button 310 is proportional to the tangent of the aperture angle between the connecting rods 320. This results in a reduction ratio that increases as the distance between members 250 and 210 and the angle between connecting rods 320 increases. This variability of the reduced ratio is advantageous because the force required to hold the button pushed at the end of the button operation is minimal, which makes it easier to fine tune the operation of the probe 30.

This advantageous feature may also be provided in this first embodiment by using a non-planar surface instead of the inclined plane 302.

When the button 310 is fully depressed, the distance between the ball 226 and the pin superposed on the ball 226 is maintained, and in any case the ball and the pin cannot come into contact with each other or with other elements of the device of the probe. Under such conditions, wear of the indexing surface is minimized and the indexing accuracy is maintained over its lifetime.

When the user presses on the two opposite buttons 310, the force obtained on the first movable element 210 by the connecting rod 320 is substantially axial with respect to the rotation axis 211, i.e. substantially in a straight line and opposite to the force exerted by the spring 215, thus ensuring a rectilinear movement without interference. On the other hand, if the operator presses asymmetrically on one of the buttons 310, the horizontal component of the force obtained is a high friction between the rod 253 and the bushing 219, which prevents the first movable element 210 from disengaging. This advantageous feature allows avoiding untimely and unintentional operation.

The button 310 is surrounded by a protective ring membrane of rubber or elastomer 330 which serves to protect the internal device from dust and to prevent heat, which would have a dire consequence on the indexing accuracy, from being transferred from the user's hand to the internal indexing means. The buttons 410 and 411, which serve the same purpose of rotating and disengaging the second axis 212, are also preferably made of a synthetic material with good heat insulating properties.

A window 30 is provided on the support member 250 to read the rotation angle with respect to the first axis 211 on a scale engraved or printed on the first movable member 210, as shown in fig. 5a and 5 b.

The angle of rotation with respect to this second axis 212 can be read on two windows 40 provided in the outer crown of the button 411 and visible in fig. 5a and 5 c. Two windows are necessary in this case in order to allow the best visibility of all possible orientations of the probe.

By generating an electrical pulse, the trigger probe 30 is brought into minimal contact with the surface of the component to be measured. The pulse is transmitted by an electronic processing circuit (not shown) to a connector 70 for connection with the control device of the measuring machine and to the light indicator 50. The indicator comprises a light emitting diode in this embodiment, but may alternatively comprise other known light emitting devices, such as sheet or line shaped electronic light emitting elements. The light emitting diode is surmounted by an optical light spreading device to allow the emitted light to be visible over a wide range of viewing angles.

In an alternative embodiment of the invention, the indicator 50 may be replaced by a plurality of indicators disposed at different positions on the probe so that at least one indicator is visible from each possible viewing angle.

In another embodiment of the apparatus of the present invention, the indicator 50 comprises one or more light conductors for emitting light from one or more light sources from different locations on the probe surface, such that the light indicator is visible from each possible viewing angle.

The device of the invention can also be obtained without using an indexing device, but with simple friction means which allow the axis to be locked in an infinite number of orientations.

The invention also includes an embodiment in which the rotation and disengagement of the axis is performed by automatic actuation means, such as an electric motor and/or a solenoid.

In another embodiment of the invention, the rotation of the axis of the probe head is ensured by a servo motor comprising an encoder for measuring the orientation angle of the probe. In this case, the indexing means described above can be retained and removed if the positioning accuracy of the servo motors is sufficient for the application to be performed.

Claims (10)

1. Adjustable touch trigger probe (20) for orienting a measurement probe (30) relative to a measurement device, comprising:

a movable element (210, 220) rotatable about an axis (211, 212);

a resilient means (215, 225) for holding said movable element (210, 220) in a locked position to prevent movement of said movable element (210, 220);

an actuating means (300, 400) opposite said elastic means (215, 225) for disengaging said movable element (210, 220) by moving in the direction of said axis (211, 212) to allow said first movable element to rotate about said axis (211, 212);

a multiplying device for reducing the amount of external force required to manually disengage said movable element.

2. The probe according to claim 1, wherein said actuating means (300, 400) is designed to stop the action of the actuating means (300, 400) when said force is interrupted.

3. The probe according to claim 1, wherein said actuating means (300, 400) are disengaged by the action of two substantially symmetrical and opposite external forces applied to said actuating means.

4. A probe according to claim 3, wherein said multiplying means comprises at least two pairs of symmetrical connecting rods (320), each pair being hinged about a central point (323), said external force being transmitted to said central point.

5. A probe according to claim 3, wherein said multiplying means comprises at least one helical surface forming an inclined plane or an inclined curved surface (302) rotationally driven by at least two racks (305) to which said external force is applied.

6. The probe of claim 1, wherein said multiplying means comprises at least one lever having unequal arms (430, 450).

7. The probe according to claim 3, wherein said actuator means (300) rotationally drives said movable element by the action of a torque of an external force applied to said actuator means (300, 400).

8. The probe of claim 3, wherein said external force is oriented along an axis perpendicular to said probe (20).

9. The probe according to any of the preceding claims, comprising an indexing element (256, 217, 226) for defining a plurality of predetermined and reproducible angular positions of said movable element (210, 220).

10. The probe of any one of the preceding claims 1-10, comprising:

a second movable element (220) connected to said movable element (210) by a second axis (212) for rotating said second movable element (220) relative to said movable element (210);

a second elastic means (225) actuated independently of said elastic means (215) to keep said second movable element (220) in a locking position, preventing said second movable element (220) from moving;

a second actuating means (400) independent of said actuating means (300) to disengage said second movable element (220) allowing said second movable element (220) to rotate about said second axis (212);

-a multiplying device for reducing the amount of force required to disengage said second movable element (220); and

a probe (30) connected to said second movable element (220).