GB1568054A - Contactsensing probe - Google Patents

Description

(54) CONTACT-SENSING PROBE (71) We, ROLLS-ROYCE LIMITED, a British Company of 65 Buckingham Gate, London SWIE 6AT (formerly known as Rolls-Royce (1971) Limited, and of Norfolk House, St. James's Square, London, SWIY 4JR) and RENISHAW ELECTRICAL LIMITED, a British Company of Gloucester Street, Wotton-under-Edge, Gloucestershire Gel 12 7DN, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a contact-sensing probe for use in machines, e.g. inspection machines, adapted to signal the coordinate position of the probe when it makes contact with the workpiece.

This invention is an improvement in or modification of the invention described in our Patent No. 1,445,977 wherein is claimed a probe for use in measuring apparatus, comprising a fixed member, a movable member having a stylus, either two or three locating elements provided on one of the members at spaced apart locations thereon, each element being disposed between a respective pair of mutually convergent surfaces provided on the other member, a bias means arranged to act on the movable member into a position in which each element engages both surfaces of the respective said pair, the movable member being movable against the action of the bias means to break engagement at at least one of said surfaces, and means for detecting a said engagement-breaking movement of the movable member.

It is an object of this invention to provide an improvement in or modification of the organisation of the surfaces supporting said movable on said fixed member.

According to this invention there is provided a contact-sensing probe for use in measuring apparatus wherein the probe is movable relative to a workpiece and a stylus provided on the probe is engageable with the workpiece; the probe comprising: a movable member engageable with a fixed member at first, second and third surface means provided on the members, the first surface means being arranged to oppose movement of the movable member in one sense of a given direction, the second surface means being arranged to oppose movement of the movable member in the opposite sense of said direction, the movable member being tiltable on the first and/or second surface means, the third surface means being arranged to oppose said tilting, bias means for urging the movable member into engagement with the fixed member at each said surface means, the movable member being disengageable, in opposition to the bias means, from said first or second surface means by movement respectively in said opposite or said one sense of direction or from said third surface means by said tilting, and the movable member including a said stylus having a portion extending away from the fixed member in said given direction and having at its end remote from the fixed member a portion extending transversely to said direction for application to said end of a force away from said fixed member.

An example of a probe according to this invention will now be described with reference to the accompanying drawing wherein: Figure 1 is a partly sectioned elevation of the probe, Figure 2 is a section on the line Il-Il in Figure 1, Figure 3 is a section on the line Ill-Ill in Figure 1, and Figure 4 is a detail of a modification.

In the following description reference is made to directions X, Y, Z being the mutually perpendicular directions of the rectangular co-ordinate system as indicated in Figures 1, 2.

Referring to Figures 1 to 3, a movable member 9 comprises a stylus 10 connected to a rod-shaped body 11 elongate along an axis I Ia normally extending in the direction Z being a first or given direction. The stylus has at the free or sensing end thereof a disc 12 whereby to contact a workpiece 13. The body 11 is supported on a fixed member or housing 14 provided with a spigot 15 for fixed attachment to the head of a measuring machine (not shown) supporting the probe for three-dimensional movement relative to the workpiece.

The member 9 is supported in the housing 14 at two locations A, B spaced apart in direction Z. At location A the member 9 embodies a spherical element 16 engaging a complementary recess 17 constituted by mutually convergent surfaces 20 of three equi-spaced balls, being a ball 18 and two balls 18a, secured to the housing. The recess 17 has an axis 17a lying in the direction X being a second direction. The centres of the balls lie in a plane 19 extending in the directions Y, Z, the direction Y being a third direction. It is clear that the balls 18, l8a engage the element 16 at three points thereon.

At location B the member 9 has a cylindrical element 21 concentric with the axis 11 a and engaging a complementary recess 22 constituted by mutually convergent surfaces 23 of two balls 24 whose centres lie in the plane 19 on a line perpendicular to the axis 17a. It is clear that the balls 24 engage the element 21 at two points thereon.

The recesses 17, 22 are convergent in the second direction X, i.e. a direction transverse to the first direction Z.

The member 9 is biased into engagement with the balls 18, 18a, 24 by a spring 25 arranged between the housing 14 and the body 11 in a position intermediate between the locations A, B. When engaged with all five balls, then, taking into account the bias of the spring 25, the member 9 is positively constrained by the balls 18 and 18a for universal pivotal motion about the centre of the element 16 and by the balls 24 against movement such as would enable the disc 12 to move in the third direction Y, i.e.

transversely to the first and second directions Z, X. When thus constrained the member 9 is said to be in a rest position.

More specifically the bias created by the force of the spring and the convergence of the ball surfaces, causes the elements 16, 21 to slide into the lowest possible position in the recesses 17, 22. As will be explained, the member 9 is displaceable from the rest position in opposition to the force of the spring by a force applied to the disc 12 by engagement thereof with the work piece and the member 9 will be returned to the rest position by said bias on cessation of the latter force.

Any movement of the member 9 relative to the housing 14 is detectable by a metal proximity sensor 26 provided in a nonmetallic part of the housing. For the purpose of detecting such movement use is made of the fact that movement of the disc 12 in any of the directions X, Y, Z must result in tilting of the member 9 such that axis 1 la thereof moves out of parallelism with the Y-Z plane. Thus, movement in the direction Y causes the cylindrical part 21 to slide up one or other of the surfaces 23 and so pivot member 9 about the axis 17a and out of the Y-Z plane. Similarly movement in the direction Z causes the ball 16 to slide up at least one of the three balls 18, 18a and tilt the member 9 on the balls 24.

Movement in the direction X causes the member 9 to rock on the balls 18, 18a or the balls 24. Any of these movements is effectively detectable at a portion 27 of the body 11 substantially medially between the locations A, B and the sensor 26 is mounted accordingly in a position adjacent the portion 27 and such as to detect movement thereof perpendicular to the Y-Z plane.

It will be seen that movement in any of the directions X, Y, Z may take place in either sense of direction. For example, movement of the disc 12 in the direction Z may take place towards or away from the housing. The latter situation applies when the machine is used to raise the disc 12 against an undercut surface 13a of the work piece.

When, after contact with work piece, the probe is moved so that contact with the work piece is disestablished and the force on the disc 12 ceases, the bias created by the spring and the convergent surfaces causes the elements 16, 21 to slide back into the lowest position in the recesses 17, 22 so that the member 9 is returned to the rest position.

To ensure good sliding action and high repeatability in attaining the rest position the elements 16, 22 and the balls 18, 18a 24 are made of hardened and polished steel.

Commercial ball bearing finishes are sufficient for this purpose.

The sensor 26 is known per se as comprising for example a pair of electromagnetic induction coils 28, 29 connected in a bridge circuit 30 such that a change in the reactance of one of the coils, as may be produced by a change of position of the stylus, varies the bridge output, e.g., away from zero. The bridge output is taken through an amplifier 31 to a suitable indicating means, e.g. a volt meter.

The measuring machine referred to is known per se and generally comprises a said head supported by carriages movable respectively in the directions X, Y and Z respectively. The carriages are provided with means for measuring the co-ordinate position of the head and thus of the probe attached thereto. A work piece is measured by measuring the position of the head at the instant when, on contact between the disc 12 and the work piece 13, the output of the sensor 26 changes.

It will be clear that in the absence of provision to the contrary the member 9 is rotatable about the axis 11 a. This is no disadvantage because of the sensing end of the stylus is rotationally symmetrical about the axis l la, e.g. as in the case of the disc 12, the angular position of the member 9 about latter axis is immaterial. However if the sensing end of the stylus is laterally off-set from the axis l la, as shown by a lateral arm 32 and spherical end 33, (Figure 4) the need arises for inhibiting rotation of the member 9 about the axis 11 a. To this end, Figures 1, 3 the member 9 has secured thereto a lateral arm 34 the free end 35 of which is provided with a convex surface resting at a single point location C, on a flat surface 36 on the housing 14.The location C lies with the locations A and B at three corners of a triangle extending in a plane including the directions Y, Z. The spring 25 is connected between the arm 34 and the housing in a position relatively closer to the end 35 than the axis 11 a because the bias pressure required at the locations A, B is smaller than at the location C. However, two springs may be provided, one at the location C and one directly intermediate between the locations A, B.

A conical recess may be used instead of the recess formed by the balls 18 and 18a. At each location A or B the recess 17 or 23 may be provided on either one of the members 9, 14, the element being provided on. the corresponding other one of the members 9, 14. Instead of the one sensor 26 shown, two such sensors may be provided respectively adjacent the locations A, B.

In the context of the member 9 in either sense of any of the directions X, Y, Z, and of the movement of the disc 12 or the arm 32 toward or away from the housing 14, it may be said that the surface of the one ball 18 and the complementary surface of the element 16 define a first surface means at which the movable member 9 is engageable with the housing 14 and which is arranged to oppose movement of the member 9 in the sense of the direction Z involving movement of the disc 12 or arm 32 toward the housing 14; that the surfaces of the two balls 18a and the complementary surface of the element 16 define a second surface means at which the member 9 is engageable with the housing 14 and which is arranged to oppose movement of the member 9 in the sense involving movement of the disc 12 or arm 32 in the sense of the direction away from the housing 14; that the member 9 is tiltable on the ball 18 and/or the balls 18a in the sense of becoming disengaged from at least one of the balls 24; and that the surfaces of the balls 24 and the complementary surface of the element 21 define a third surface means at which the member 9 and the housing 14 are engageable and which opposes said tilting movement of the member 9.

This application is a divisional of Application No. 40718/75, Serial No.

1,568,053.

WHAT WE CLAIM IS: 1. Contact-sensing probe for use in measuring apparatus wherein the probe is movable relative to a workpiece and a stylus provided on the probe is engageable with the workpiece; the probe comprising: a movable member engageable with a fixed member at first, second and third surface means provided on the members, the first surface means being arranged to oppose movement of the movable member in one sense of a given direction, the second surface means being arranged to oppose movement of the movable member in the opposite sense of said direction, the movable member being tiltable on the first and/or second surface means, the third surface means being arranged to oppose said tilting, bias means for urging the movable member into engagement with the fixed member at each said surface means, the movable member being disengageable, in opposition to the bias means, from said first or second surface means by movement respectively in said opposite or said one sense of direction or from said third surface means by said tilting, and the movable member including a said stylus having a portion extending away from the fixed member in said given direction and having at its end remote from the fixed member a portion extending transversely to said direction for application to said end of a force away from said fixed member.

2. Probe according to Claim 1 comprising means for supporting the movable member against movement transversely to said given direction.

3. Probe according to Claim 2 wherein one of said members comprises an element situated between convergent surfaces provided on the other one of said members and co-operating therewith to support the movable member against movement transversely to said given direction.

4. Probe according to Claims 1, 2 or 3 including means constraining said movable member against rotation about an axis lying in said given direction.

5. Probe according to any one of Claims 1 to 4, said movable member being supported on the fixed member at two locations spaced apart in said given direction being a

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. by measuring the position of the head at the instant when, on contact between the disc 12 and the work piece 13, the output of the sensor 26 changes. It will be clear that in the absence of provision to the contrary the member 9 is rotatable about the axis 11 a. This is no disadvantage because of the sensing end of the stylus is rotationally symmetrical about the axis l la, e.g. as in the case of the disc 12, the angular position of the member 9 about latter axis is immaterial. However if the sensing end of the stylus is laterally off-set from the axis l la, as shown by a lateral arm 32 and spherical end 33, (Figure 4) the need arises for inhibiting rotation of the member 9 about the axis 11 a. To this end, Figures 1, 3 the member 9 has secured thereto a lateral arm 34 the free end 35 of which is provided with a convex surface resting at a single point location C, on a flat surface 36 on the housing 14.The location C lies with the locations A and B at three corners of a triangle extending in a plane including the directions Y, Z. The spring 25 is connected between the arm 34 and the housing in a position relatively closer to the end 35 than the axis 11 a because the bias pressure required at the locations A, B is smaller than at the location C. However, two springs may be provided, one at the location C and one directly intermediate between the locations A, B. A conical recess may be used instead of the recess formed by the balls 18 and 18a. At each location A or B the recess 17 or 23 may be provided on either one of the members 9, 14, the element being provided on. the corresponding other one of the members 9, 14. Instead of the one sensor 26 shown, two such sensors may be provided respectively adjacent the locations A, B. In the context of the member 9 in either sense of any of the directions X, Y, Z, and of the movement of the disc 12 or the arm 32 toward or away from the housing 14, it may be said that the surface of the one ball 18 and the complementary surface of the element 16 define a first surface means at which the movable member 9 is engageable with the housing 14 and which is arranged to oppose movement of the member 9 in the sense of the direction Z involving movement of the disc 12 or arm 32 toward the housing 14; that the surfaces of the two balls 18a and the complementary surface of the element 16 define a second surface means at which the member 9 is engageable with the housing 14 and which is arranged to oppose movement of the member 9 in the sense involving movement of the disc 12 or arm 32 in the sense of the direction away from the housing 14; that the member 9 is tiltable on the ball 18 and/or the balls 18a in the sense of becoming disengaged from at least one of the balls 24; and that the surfaces of the balls 24 and the complementary surface of the element 21 define a third surface means at which the member 9 and the housing 14 are engageable and which opposes said tilting movement of the member 9. This application is a divisional of Application No. 40718/75, Serial No. 1,568,053. WHAT WE CLAIM IS:

1. Contact-sensing probe for use in measuring apparatus wherein the probe is movable relative to a workpiece and a stylus provided on the probe is engageable with the workpiece; the probe comprising: a movable member engageable with a fixed member at first, second and third surface means provided on the members, the first surface means being arranged to oppose movement of the movable member in one sense of a given direction, the second surface means being arranged to oppose movement of the movable member in the opposite sense of said direction, the movable member being tiltable on the first and/or second surface means, the third surface means being arranged to oppose said tilting, bias means for urging the movable member into engagement with the fixed member at each said surface means, the movable member being disengageable, in opposition to the bias means, from said first or second surface means by movement respectively in said opposite or said one sense of direction or from said third surface means by said tilting, and the movable member including a said stylus having a portion extending away from the fixed member in said given direction and having at its end remote from the fixed member a portion extending transversely to said direction for application to said end of a force away from said fixed member.

2. Probe according to Claim 1 comprising means for supporting the movable member against movement transversely to said given direction.

3. Probe according to Claim 2 wherein one of said members comprises an element situated between convergent surfaces provided on the other one of said members and co-operating therewith to support the movable member against movement transversely to said given direction.

4. Probe according to Claims 1, 2 or 3 including means constraining said movable member against rotation about an axis lying in said given direction.

5. Probe according to any one of Claims 1 to 4, said movable member being supported on the fixed member at two locations spaced apart in said given direction being a

first direction, at each said location there being an element provided on one of the members situated between convergent surfaces provided on the other member, the convergent surfaces at each said location being convergent in a second direction transverse to said first direction, the convergent surfaces at one of said locations defining an axi-symmetric recess comprising said first and second surface means, the convergent surfaces at the other one of said locations comprising said third surface means and being arranged to constrain the movable member against movement in a third direction transverse to said first and second directions, said bias means urging the movable member into engagement with said fixed member so that at each said location the element slides on said surfaces into a positive engagement therewith thereby to provide a rest position for the movable member.

6. Contact-sensing probe substantially as describe herein with reference to the accompanying drawings.