GB2238126A - Metrology - Google Patents

Abstract

A measuring probe for continuous form measurement of e.g. cylindrical, conical workpieces in one embodiment has a multiaxis stylus suspended by resilient forces acting in opposition so as to determine an equilibrium rest position. In another embodiment the rest position is determined by the prestressed configuration of a diaphragm 40 on which a stylus assembly 50 is suspended. In another embodiment the linear movement of carriers for armatures of transducers 60 is ensured by a linkage 70 coupled to parallel ligaments/limbs of a pair of resilient means 80A, 80B. Tensioned means (wires 22) may pre-stress both the diaphragm 40 and the limbs/ligaments 80A, 80B. <IMAGE>

Description

METROLOGY This invention relates to a measuring probe, and more particularly a measuring probe capable of responding to multiaxis variations in a workpiece.

An embodiment provides a multi axis continuous measuring probe for use in metrology and more particularly form measurement responsive to three dimensional variations in a workpiece in conjunction with a measuring machine with means for displacing the probe so that the derived data is obtained as a function of both the probe signals and the displacement signals: see European Patent No.

240151A.

Continuous probes for form measurement are distinguished from trigger probes. Continuous probes measure the form of a workpiece by continuous contact therewith. The measurement may take place as a series of measurements each for a given surface area of the workpiece owing to the fact that because of the three dimensional contour of the workpiece, the probe has to be re-positioned between such measurements. Such probes are readily distinguished from trigger probes which make intermittent contact for co-ordinate measurement readings.Furthermore, trigger probes have a rest position which is mechanically defined whereby the rest position defines a fixed datum position from which all displacements occur and which must always be repeatable: the displacement of the stylus triggers an output signal giving the co-ordinates at which the contact was made rather than output signals which are themselves a measure of the probe displacement.

It will be appreciated by those skilled in metrology that measuring probes operate in a defined displacement range and that their accuracy is rated for operation within that range. From GB Patent No.

1499003 it is known to have probes for which provision for stylus movement in X,Y & Z axes is provided by separate sets of resilient suspension means: three orthogonal sets of leaf springs; the rest position of the stylus being the relaxed condition of each set of springs. With these probes, their size imposes limitations on the ability of the probe to access complex workpieces, and their inertia imposes limitations on the rate at which data can be gathered.

The rate at which data can be gathered is directly related to the frequency response of the probe. The frequency response is the parameter related to the speed at which the probe tip can follow variations in the contour - if the frequency is insufficient the probe tip may lose contact with the workpiece and this must be avoided in continuous form measurement. For example in roundness measurement, the workpiece is rotated on a turntable - the maximum speed of rotation is governed mainly by the frequency response of the measuring probe. A probe with a higher frequency response permits a wider range of rotational speeds to be employed and facilitates the ability of the probe to follow contour variations at such rotational speeds.A higher rotational speed thus increases the rate of acquisition of data (the data acquisition rate) and the productivity of a machine used for the inspection of workpieces: adequate frequency response enhances the advantages of multiaxis probes relative to single axis probes, the latter requiring several re-orientations to complete all the measurement data.

GB Patent 2004656 shows another construction of measuring probe with a multiaxis displacement capability, which mounts the stylus relative to a housing by means of a resilient member fixed at one boundary thereof and with the datum position being determined by the resilient member urging a mounting plate for the stylus engaging the housing from which position it is displaced by stylus displacement about several different pivot points. This arrangement also is subject to the aforementioned disadvantages especially in terms of accuracy and repeatability of results (due to the mechanical variations arising from more than one pivot point) and the frequency response.

This invention seeks to overcome these disadvantages and in particular, in embodiments, to provide a probe which has the characteristics of improved accuracy, and repeatability of the results obtained and an increased frequency response. Furthermore, for form measurements carried out on a roundness instrument, the embodiments of the present invention recognise the desirability of the stiffness of the probe in the axial direction of the stylus (Z direction) being of a higher order than the stiffness of the probe in terms of X and Y direction movement of the stylus. This gauging stiffness is related to the gauging force which is applied to the stylus to obtain a displacement.

An embodiment will further provide for the relocation of the stylus in use without deterioration in the repeatability of results.

The present invention has various aspects. According to one aspect there is provided a probe for measuring of workpieces, comprising means for mounting a stylus suspended by resilient forces acting in opposition so as to determine an equilibrium rest position.

According to another aspect there is provided a probe for multi-axis continuous form measurement on workpieces comprising a stylus mounting suspended by resilient forces acting in opposition so as to determine an equilibrium rest position..

This multiaxis probe has freedom of movement, within its measurement range, in the X,Y plane defined by its X,Y axes and along its Z-axis. The rest position is nominally located at the intersection of the X,Y axes (notionally the centre of the X,Y range in the X,Y plane) and at the extremity of outward travel along the Z-axis. After displacement of the stylus in any direction, it will return to the approximate rest position: in practice, this approximate rest position will be within 10 microns of the theoretical centre.

As the probe has continuous axes, this difference between one rest position and the previous rest position, does not result in a measurement error because the exact rest position of the stylus is always known by reading sensor signals.

The stylus movement of such a probe is not limited to discrete translational movement in the X,Y or Z directions, but for instance it can follow an arcuate path in the X,Y plane.

According to another aspect there is provided a probe for multi axis continuous form measurement on workpieces, comprising a housing, a stylus assembly, a resilient diaphragm by which the stylus assembly is mounted on the housing for movement in the X, Y and Z directions, sensors associated with the stylus assembly, said sensors being arranged to produce sensor signals dependent on the movement of the stylus assembly relative to the housing, wherein resilient biassing means and said disphragm are so arranged that said stylus assembly is suspended by resilient forces acting in opposition so as to determine an equilibrium rest position.

Suitable sensors, which are well known in the art, are exemplified herein by inductive transducers.

According to another aspect there is provided a probe for multiaxis form measurement on workpieces, comprising a housing, a stylus assembly, a resilient diaphragm by which the stylus assembly is mounted on the housing for movement in the X, Y and Z directions, sensors associated with the stylus assembly, said sensors being arranged to produce sensor signals dependent on the movement of the stylus assembly relative to the housing, wherein said diaphragm is prestressed in the rest position of the stylus.

According to another aspect there is provided a probe for multiaxis measurement on workpieces, comprising a housing, a stylus assembly, a resilient diaphragm by which the stylus assembly is mounted on the housing for movement in the X, Y and Z directions, transducers linked to the stylus assembly, said tranducers being arranged to produce signals dependent on the movement of the stylus assembly relative to the housing, wherein linkage means are arranged to constrain movement of a movable element of each transducer to substantially linear movement in response to movement of the stylus assembly.

In the preferred embodiment, the sensors are inductive transducers and the movable element is an armature carrier.

The stylus may include a locator plate adapted to be magnetically and displaceably mounted on the mounting plate. The locator plate and the mounting plate may be aligned by spaced elements on one thereof resting in seating means on the other thereof. The spaced elements may be spherical elements (e.g. ball bearings) and the seating means may be a groove or a seat formed by seating elements such as spaced roller bearings. The spaced elements may be arranged with equi-angular spacing.

The embodiments also disclose a stylus assembly with a removably mounted stylus which facilitates stylus replacement without necessitating re-calibration.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which Figure 1 shows an elevation, mainly in section, of a first embodiment of a measuring probe which includes a housing and a stylus assembly; Figure 2 shows an exploded perspective view of the probe of Figure 1 with the stylus removed; Figure 3 shows a section taken on the line A-A of Figure 1; Figures 4 and 5 are plan views of separable parts of the stylus assembly; Figure 6 is a schematic view of a modification to the probe of Figure 1; Figure 7 is a schematic view of another modification of the probe of Figure 1; Figure 8 shows in elevation, mainly in section, a measuring probe according to another embodiment also having a housing and including a stylus assembly; Figure 9 shows an exploded perspective view of the probe of Figure 8 with the stylus removed;; Figure 10 shows a section taken on the line AA of Figure 8; Figure 11 shows an enlarged fragmentary view, partly in section, of part of the stylus assembly of Figure 8; and Figures 12 and 13 show plan views of separable parts of the stylus assembly of Figure 8.

In Figures 1 to 5 of the drawings there is shown a measuring probe 10 for form measurement in conjunction with a measuring machine with a rotatable workpiece table, which comprises a housing 20, a stylus assembly 30 including a resilient diaphragm 40 by which a stylus 50 is mounted on the housing 20 for movement in the orthogonal X, Y, Z directions. This stylus movement is not limited to discrete translational movement in the X,Y or Z directions, but for instance it can follow an arcuate path in the XY plane.

Four transducers 60 (only two of which are shown in Figure 1) mounted in the housing 20 and four linkages 70 connect the stylus assembly 30 to the transducers 60 so that the transducers 60 produce electrical signals dependent on the movement of the stylus assembly 30 relative to the housing 20. Stylus assembly 30 enables the stylus 50 to be mounted on the diagram 40 such that any movement of the stylus 50 is transmitted (as will be explained) to the transducers 60.

The stylus assembly 30 comprises a mounting ring 32 and a mounting plate 34 clamping the diaphragm 40 at its periphery. The diaphragm 40 is centrally attached to the housing 20. As seen from Figure 2, the mounting ring 32 has a peripheral wall 32A and a lower radially extending face 32B. The mounting plate 34 comprises an upper portion 34A for clamping the diaphragm 40 against the face 32B of the mounting ring 32, and a reduced diameter portion 34B with a peripheral wall 34C on which there are mounted four clamp adjusters 36. On the underface 34D of the mounting plate there is a magnet 38 and spherical elements (e.g. ball bearings) 39 for locating the stylus 50. The stylus 50 comprises the locator plate 52 from which the stylus stem 54 depends to the stylus tip 56 which contacts a workpiece for measuring purposes.As will be seen from Figures A and 5 the ball bearings 39 of the mounting plate 34 align with location grooves 58 on the locator plate 52 of the stylus 50. The stylus 50 is demountable from the stylus assembly 30 and it is held in place when in position by the magnet 38. The ball bearings 39, which are fixed to the mounting plate 34, are dimensioned such that there is an air gap between the magnet 38 and the top of the stylus locator plate 52.

The arrangement is such that if the stylus 30 meets undue force or an obstruction it can self-release from the mounting plate 34: this occurs when locking ring 32 abuts the housing 20 which forms a stop limiting upward axial movement of the stylus assembly 30. This arrangement ensures that any one stylus will accurately repeat its fitted position when removed and relocated, thereby avoiding re-calibration.

It will be noted that the ball bearings 39 and location grooves 58 are equiangularly spaced at angles of 1200.

It will be noted from Figure 2 that the mounting ring 32, diaphragm 40 and mounting plate 34 are each provided with assembly apertures 32E, 34E and 40E respectively for their connection by connectors not shown.

The housing 20 is adapted at its lower end for the mounting of the diaphragm 40 and thereby the stylus assembly 30. For this purpose it has a downwardly depending central boss 20A which depends from a radially extending lower face 20B (which proves the aforementioned stop) of the main housing core which is made up of parts 20C, D and E. The diaphragm 40 is centrally clamped to the housing boss 20A by means of a fixing member 24 which has assembly apertures 24A for connectors to pass through the fixing member 24 and the diaphragm 40 to be secured to the housing boss 20A as most clearly apparent from Figure 2. The respective dimensions of the housing boss 20A and the mounting ring 32 in the axial direction of the probe are such that as can be seen from Figure 1 there is a gap between the top of the mounting ring 32 and the housing face 20B, this gap accommodating the measuring range of movement of the stylus assembly 30. As aforesaid, if the stylus assembly 30, over travels upon meeting an obstruction, the face 20B acts as a limit stop and the stylus 30 self-releases.

The housing 20 is further configured so as to provide a central bore 25 for a connector rod 26 to which the fixing member 24 is attached and which extends through the housing thereby to be attachable to a measuring machine. The housing 20 is further configured to provide chambers 27 for the rigid linkages 70 and chambers 28 for the transducers 60. It is best seen from Figure 3 that the housing part 20C with its lower face 20B has a cruciform configuration in which the four linkage chambers 27 are regularly spaced. The linkage chambers 27 have a rectilinear configuration with an inner wall 27A, an outwardly directed walls 27B, walls 27C parallel to the wall 27A, and further outwardly directed walls 27D extending to the parameter of the housing where the chamber 27 opens outwardly from the probe.The chambers 27 are formed by recesses in each of the housing parts 20C, D and E which are contiguous. These three housing parts 20C, D and E clamp between them a pair of ligaments 80A, 80B. The lowermost ligament 80A is clamped centrally between the housing parts 20C and 20D. The ligament 80A has an annular portion, which is clamped between the axial end faces of those housing parts 20C, D, and outwardly and radially projecting limbs 80C, (Figure 3) which have a configuration akin to leaf springs, and leaves 80D. Leaves 80D are also regularly spaced, but offset with respect to the limbs 80C, so as to be clamped between the housing parts 20C, D in those portions thereof which extend to the perimeter as viewed in Figure 3.The ligament 80B is of similar configuration to the ligament 80A and it is mounted between end faces of the housing parts 20D and 20E.

The pair of ligaments 80A, 80B have several functions, one of which is to bias the rest position of the stylus assembly 30, and another of which is to act as guide means for ensuring linear movement of connection means (to be described) between the stylus assembly 30 and the transducers 60, and yet another of which is to place tensioned wires 22 under tension thereby prestressing the diaphragm 40.

The transducers 60 are mounted in four equiangularly spaced bores 20G in the housing part 20E. The transducers 60 comprise coils 60A and armatures 60B carried on armature carriers 60C which extend through passageways 20H in the housing part 20E so as to communicate with the linkage chambers 27. Tensioned wires 22 extend from the mounting plate 34, to which they are clamped by the clamp adjusters 36, to the armature carriers 60C to which they are connected at 60D (Fig.l). Rigid linkages 70 clamp together the pair of ligaments 80A, 80B and are fixedly attached to the armature carrier 60C. It will be seen that the linkages 70 each comprise four parts 70A, B, C and D which are rigidly connected together by connector means (a threaded bolt) 70E (Fig.2). The parts 70A and B clamp the limbs 80C of the ligament 80B and the parts 70C, D clamp the limbs 80C of ligament 80A.

The linkage part 70C carries the means of connection to the armature carrier 60C. As stated, this connection between the rigid linkage 70 and the armature carrier 60C is rigid such that movement of the stylus assembly 30 which is transmitted to the armature carrier 60C by the tensioned wire 22 is also transmitted to the rigid linkages 70 and the ligaments 80A, 80B. As will be understood, the transducers 60 have wiring (not shown) which extends through the upper part of the bores 20G so that the signals of the transducers can be processed by the measuring machine.

The construction of this probe with its stylus assembly 30 mounted by means of the diaphragm 40 and connected by means of the tension wire 26 to the ligaments 80A, 80B is such that, in the rest position of the stylus 50, the ligaments 80A, 80B and the diaphragm 40 and the wires 22 are all pre-tensioned.

In the drawing Figure 1 the relaxed (i.e. unstressed) positions of the diaphragm 40 and the pair of ligaments 80A, 80B are indicated by the lines B, C and D respectively. By the use of the tensioned wires 22 (one for each transducer and each limb 80C) the diaphragm 40 and the ligaments 80A, 80B can be brought into their Figure 1 positions in which they are prestressed. The rest position of the stylus assembly 30 and thereby the stylus 50, is the position in which the opposed resilient members, namely the diaphragm 40 and the pair of ligaments 80A, 80B establish an equilibrium position. In that position the resilient forces exerted by the ligaments 80A, 80B and the resilient forces exerted by the diaphragm 40, which are opposed, are in balance.This means that the rest position of the stylus assembly 30 is one in which the stylus assembly 30 is resiliently held in a position from which it can be displaced in any direction.

From Figure 3 it will be noted that connectors 29 pass through the housing parts 20C, D and E in the regions of the lands thereof which bound the linkage chambers 27 to clamp the parts together in rotational alignment. It will also be noted that the rigid linkages 70 are held in alignment by means of alignment pins 70F which are arranged in parallel on either side of the connectors 70E.

It should be noted that the tensioned wires 22 pass within the aperture defined by the mounting ring 32 and through tensioned wire apertures 40A in the diaphragm and 34F in the mounting plate (Fig. 2). The apertures 34F are aligned with the clamp adjusters 36 whereby at the setting up stage the length of tensioned wire 26 can be adjusted so as to prestress the ligaments 80A, 80B and the diaphragm 40: this is achieved by placing a spacer block in the linkage chamber 27 above the rigid linkage 70 and a further spacer block below the rigid linkage 70 and forcing the mounting ring 42 into contact therewith. This ensures that the correct length of the tensioned wire is determined. Upon release of the spacer blocks (not shown), the gaps between the linkage 70 and on one side thereof the housing part 20E and on the other side thereof the mounting ring 32 are predetermined.

The probe 10 of Figure 1 has the stylus assembly 30 attached to the perimeter of the diaphragm 40, the diaphragm 40 is centrally attached to the housing 20, and the tensioned wires 22 prestress the ligaments 80A, 80B and the diaphragm 40 placing them under tension such that they act resiliently to pull the stylus assembly 30 in opposite directions whereby the rest position of the stylus 60 is at the position in which the opposed forces are in equilibrium.

The latter feature of having the opposed forces in equilibrium at the rest position so as to have a resiliently suspended stylus 30 is an advantageous feature of the present embodiment from which many practical advantages stem. In particular, the gauging force in the Z direction may be made substantially greater than the gauging force in the X,Y directions which is advantageous for form measurements carried out on roundness instruments.Also the accuracy and repeatability of the probe is found in tests to meet a higher standard in comparison with current multiaxis probes and an improved frequency response exhibiting a natural frequency of 50Hz for maximum displacement in the useful displacement range of a 100 mm stylus which has a maximum range of + 2mm displacement in the X,Y directions: even greater frequency capability is exhibited for smaller displacements e.g. in excess of 150 Hz.

Modifications of the probe of Figure 1, which meet the same design criteria, are illustrated schematically in Figure 6, 7 in which like parts have like references.

In the modification of Figure 6, the ligaments 80A, 80B together with the armature carrier 60C, and the stylus assembly 30 are not connected by a tensioned wire 22 but instead by rigid connections 22A (four of them equally spaced as with the tensioned wires 22) comprising the links 22B,C acting on spherical elements (e.g. bearings) 22D which, in turn, sit fixedly in a circumferential groove 34G in mounting plate 34. The link 22C has a radial groove 22E for seating bearing 22D. The radial and circumferential grooves 22E and 34G ensure accurate and automatic positional location for bearings 22D. The diaphragm 40 again is mounted centrally relative to the housing 20 and clamped at its periphery to the stylus assembly 30 by the mounting ring 32 and the mounting plate 34.In order to accommodate this form of rigid connection, diaphragm 40 has apertures 40B through which the bearings 22D can extend freely without encroaching on the active part of the diaphragm 40. This embodiment exhibits the aforementioned resilient suspension of the stylus assembly 30 but with the ligaments 80A, B and diaphragm 40 exerting compression forces.

The modification of Figure 7 is similar to that of Figure 6 in terms of the rigid links 22A between the ligaments 80A, B and the stylus assembly 30. The difference is that the diaphragm 40 is centrally mounted relative to the stylus assembly 30 which now comprises a modified mounting plate 34 (without a mounting ring 32). This mounting plate 34 has a central boss 34H to which the diaphragm 40 is attached (in similar manner to the central attachment of the diaphragm 40 to the housing 20 in the embodiment of Figure 1). The connection between the diaphragm 40 and a depending outer casing 20M of the housing 20 is at the periphery of the diaphragm 40 as shown. Again the rest position is determined by the oppositely acting resilient means, namely the diaphragm 40 and the ligaments 80A, B which in this embodiment exert compression forces.In both Figure 6 and Figure 7 the unstressed positions of the ligaments 80A and 80B and the diaphragm 40 are again illustrated by lines B, C and D.

From the aforegoing, it will be plain that resilient suspension of the stylus can be arranged in a number of different ways other than those illustrated by making use of tension or compression forces which maintain a form of suspension of the stylus in which the stylus rest position is determined by opposed resilient bias means. Likewise, the manner of mounting the diaphragm to the housing, and the diaphragm to the stylus assembly affords a reversible choice of which employs a central mounting and which employs a peripheral mounting. It will be apparent that the advantages of the Figure 1 embodiment can be obtained with such modified embodiments.

Figures 8 to 13 show a second embodiment of a probe for multiaxis form measurement (e.g. with cylindrical or conical workpieces) for use with a measuring machine in which the probe signals and the machine signals are utilised to provide form measurement data for use in measuring workpieces. This probe 110 comprises a housing 120, a stylus assembly 130, a resilient diaphragm 140 by which the stylus assembly 130 (including a stylus 150) is mounted on the housing 120 for movement in the X, Y, Z directions, three transducers 160 (shown in Figure 10) mounted in the housing 120 and directly connected in the stylus assembly 130 so that the transducers 160 produce electrical signals dependent on the movement of the stylus assembly 150 relative to the housing 120.

In the stylus assembly 130, the stylus 150 is releasably connected to a mounting plate 134. The diaphragm 140 is peripherally clamped between a mounting ring 132 and the mounting plate 134. The mounting plate has a peripheral wall 134A (see Figure 11) upstanding from a lower plate 134B and which supports a median member 134C. At three peripherally equi-spaced locations the peripheral wall 134A supports integral bosses 134D (Figure 8) threaded to receive connector members 134E which couple together the mounting plate 134 with the mounting ring 132 to clamp the diaphragm 140. Bosses 134D extend in the axial direction from the median member 134C to the top of the peripheral wall 134A.The median member 134C has apertures 134F which receive sleeves 134G in which the transducers 160 are housed: each sleeve 134G depends from an insert 120H and has an internal portion on which the transducer coil 160A is mounted.

These apertures 134F are equiangularly spaced. The median member 134C on its underside carries a magnet 134H which holds releasably the stylus 150. The median member 134C is further provided with contact elements (e.g. roller bearings) 134J which are fixedly arranged in equiangularly spaced, radially extending locator grooves 134K (Figure 12). The stylus 150 comprises a locator plate 150A on which at three equiangularly spaced locations pairs of spaced spherical elements (e.g. ball bearings) 150B are fixedly mounted. The spacing (Figure 13) between the ball bearings 150B of a pair of ball bearings is such that the ball bearings engage with the roller bearings 134J of the mounting plate 134 so as to radially and axially align the stylus 150 with the mounting plate 134. The ball bearings 150B are fixed relative to the locator plate 150A. The stylus further comprises the stem 150C and the stylus tip 150D.

The lower plate 134B of mounting plate 134 has a central circular recess 134L (Fig.9) which has an axially extending edge 134M defining an aperture to receive the locator plate 150A of the stylus 150.

Further recesses 134N defining axially extending edges 134P communicate with the circular recess 134L so as to define in the material of the lower plate 134B lobes 134Q. The lobes 134Q have at their radially inner extremity the edges 134M. The lobes 134Q are aligned with the apertures 134F for the transducers and these lobes 134Q are provided with axial bores 134R for mounting the transducer armature carrier 160C (to be further described).

The mounting ring 132 has a peripherally extending outer wall 132A and three equiangularly spaced capture members 132B (illustrated in Figure 9) which are of a configuration such as to provide, by means of a respective bore 132C, a cup-like figuration for receiving one end of a respective compression spring 180. Recesses 132D leading to bores 132E are provided to threadedly receive the connectors 134E coupling together the mounting plate 134 with the mounting ring 132 and thereby clamping the diaphragm 140. The diaphragm 140 has assembly apertures 140M for the passage of the connector members 134E and transducer apertures 140B which likewise receive the sleeves 134G. A mounting member 124 is arranged to connect the stylus assembly 130 to the housing 120.It is in the form of a stud which passes through a central aperture 140C in the diaphragm 140 and which threadedly engages a bore 120A (Figure 9) in a boss 120B which downwardly extends from the main core 120C of the housing 120. The housing main core 120C has a lower surface 120D in which there are transducer bores 120E and locator bores 120F which accommodate the compression springs 180. Turning to Figure 8 it will be seen that the locator bores 120F threadedly locate adjustable studs 120G for adjusting the compression of the compression springs 180. The transducer bores 120E are aligned with the transducer sleeves 134G rigidly connected to the housing 120 and displacable relative to apertures 140B in the mounting plate 134.

The transducer bores 120E threadedly receive transducer inserts 120H which provide passageways for wiring associated with the transducers 160 whereby the output of the transducers 160 may be connected to the data gathering equipment. The transducers themselves comprise a coil 160A, an armature 160B, each armature being carried on an armature carrier 1600. The armature carrier 160C being directly and fixedly connected to the mounting plate 134 at the respective bore 134R.

The main core 120C of the housing further comprises a upstanding boss 120J which has a central bore 120K to receive a connector member (not shown) for connecting the probe housing to a measuring machine. The housing further comprises a top plate 120L which seals the interior of the housing and has a depending skirt 120M to guide it into an outer casing 120N surrounding the main core. A bore 120T threadedly connects the top plate with the aforesaid connector member. The outer casing 120N is substantially cylindrical but has a radially inwardly directed flange 120R at the level at which the stylus locator 150A is arranged (see Figure 8). The housing casing flange 120R supports an annular disc 120S which completes the lower side of the housing casing.

This probe 110 has the characteristic in common with the earlier embodiments that the stylus assembly 130, and thereby the stylus 150, is mounted in such manner that the rest position of the stylus, that being the position from which any movement is measured, is determined by the equilibrium position of the mounting assembly in accordance with the balancing of opposed forces of the diaphragm 140 and the compression springs 180. The compression of the springs 180 can be adjusted by means of the adjustable studs 120G.

The diaphragm, which in an unstressed state would be aligned with the plane B (Figure 8), is prestressed by virtue of the fact that it is clamped at its centre by the mounting member 124 in plane B and it is clamped at its perimeter between the mounting plate 134 and mounting ring 132 at a level which prestresses it. It therefore acts under compression with the result that the forces of diaphragm 140 and compression springs 180 are mutually opposed thereby to determine a suspended and equilibrium position of the mounting assembly 130 which determines the rest position for the stylus 150. Movement of the armature carrier 160C in response to any displacement of the stylus 150 is substantially linear with respect to the transducer 160. Any non-linearity components can be compensated for in the calibration.The outputs of the three transducers are calibrated so as to obtain the X, Y and Z measurements. This embodiment does afford a reduction on the number of electronic channels through which the transducer signals must pass and therefore facilitates a reduction in the associated electronics.

As in the embodiment of Figures 1 to 5, this embodiment has a stylus 150 which by virtue of the location means (shown in Figures 12 and 13) is removably connected to the mounting plate 134 where it is held by means of the magnet 134H but from which position it is displacable or replacable. This feature enables the stylus to become displaced if it inadvertently strikes a workpiece causing the mounting ring 132 to contact housing 120 whereby the stylus 150 releases. The housing face 120D and the housing flange 120R provide limit stops for the movement of the stylus assembly 130. It also facilitates replacement of the stylus 150 with repeatability of results when stylii are relocated.

Like the first embodiment, this embodiment also has the advantage when used in form measurement that the gauging force in the Z or axial direction is greater than the gauging force required in the X, Y plane.

This embodiment is found to be particularly advantageous for use in form measurement on roundness instruments.

Features which distinguish this probe 110 from the probe 10 of Figures 1 to 5, are that the location of the transducers 160 and the design of the stylus assembly (in particular the mounting plate 134 and mounting ring 132) reduces the number of moving parts and displaces the centre of mass of those moving parts closer to the rest position of the stylus assembly.

Both embodiments provide a compact design which facilitates use of the probe 110 for following complex workpiece contours as well as an enhancement over the prior art in terms of the frequency response and thereby the rate at which measurement data may be gathered.

In the light of the disclosure herein in which the embodiment of Figures 8 to 13 reduces the number of sensors/transducers from four to three, it will be apparent to those skilled in the art that the embodiment of Figures 1 to 5 may be modified to incorporate three sensors/transducers.

The diaphragm of the embodiments before assembly is disc-shaped and in planar condition (unstressed) so that when prestressed it takes a cone-like configuration. Modifications are possible whereby the diaphragm is pre-formed in a non-planar shape and then prestressed to adopt a different shape.

In each of the embodiments, the diaphragm (40, 140) is in the form of a circular disc of uniform thickness and formed of beryllium-copper alloy which has been fully hardened. In each case the diaphragm is configured so as to permit connection at its centre to the main housing and connection at its periphery to the stylus assembly (as mentioned these could be reversed).

Within the periphery of the circular diaphragm provision is made for other mechanical features of the probe. In the first embodiment, as shown in figure 2, the diaphragm 40 has apertures 40A for the passage therethrough of tensioned wires 22 connecting the linkage 70 to the mounting plate 34, and apertures 40E for assembly purposes. In the second embodiment, as shown in figure 9, the diaphragm 140 has further apertures 140B for the passage therethrough of the sleeves 134G carrying the transducer coils 160A, that is in addition to the apertures 140M - for assembly purposes. The thickness of the diaphragm in the first and second embodiments is 0.003 in. and 0.005 in.

respectively. The thickness is chosen so that given the required diaphragm dimensions and the stylus arm length, and the characteristics of the other part of the probe mechanism, the correct gauging stiffness is achieved in the XY directions at the stylus tip. A typical gauging stiffness in the XY directions for both probes is 100mN per mm displacement when using a lOOmm stylus . Over the relatively small range of movement used, this stiffness remains constant irrespective of displacement and direction.

For the first embodiment (figure 2), the Z-axis gauging stiffness is largely determined by the thickness and design of the diaphragm itself. For the second embodiment (figure 9) the Z-axis gauging stiffness is mainly a function of the biasing system, i.e. the nature of the compression springs and their arrangement.

The properties of beryllium-copper which render it especially suitable for the diaphragm include the facts that: i) it permits higher deflections within its elastic limit than other comparable materials; ii) it has a high endurance limit, i.e. it maintains its elastic properties over a long design life; iii) it exhibits virtually no elastic hysteresis.

A further feature has been incorporated into the probes 10, 110 of the two main embodiments, namely means for damping unwanted stylus movement (including vibration). In the first embodiment, damping means 27F may be provided in the stylus assembly by applying a viscose substance between the linkage 70 and the adjoining linkage chamber walls 27D, as shown in figure 3.

Similarly, in the second embodiment, damping means 132F may be provided in the stylus assembly by applying a viscose substance between the connecting ring 132 and the sleeve 134G (for the transducer coil 160A) as shown in figure 8, 10. By way of example, the damping means 27F and 132F are provided by a charge of viscose substance, such as silicone grease.

Tests have shown that the addition of damping means 27F, 132F to the probe enhances its use on measuring instruments. The damping means provide the following advantages: i) it greatly reduces unwanted stylus movement and vibration during instrument traverse when the stylus is out of contact; ii) it reduces stylus vibration effects when scanning a surface; iii)it allows the stylus to return to a stable rest position in a shorter lapsed time after stylus deflection.

Alternative damping means may be provided in a variety of ways. It is not applicants intention to limit the scope of their claims to the provision of a viscose substance. In addition, different probe applications will require separate rates of damping. For example, a probe used with a roundness instrument requires a lower damping rate than when such a probe is used on a co-ordinate machine.

Claims (45)

1. A probe for measuring of workpieces comprising means for mounting a stylus suspended by resilient forces acting in opposition so as to determine an equilibrium rest position.

2. A probe as claimed in claim 1, wherein provision is made for the adjustment of at least one said resilient force.

3. A probe for multi-axis continuous form measurement on workpieces comprising a stylus mounting suspended by resilient forces acting in opposition so as to determine an equilibrium rest position.

4. A probe as claimed in claim 3, wherein the gauging force in the Z direction is greater by at least an order of magnitude.

5. A probe for multiaxis continuous form measurement on workpieces, comprising a housing, a stylus assembly, a resilient diaphragm by which the stylus assembly is mounted on the housing for movement in the X, Y and Z directions, sensors associated with the stylus assembly, said sensors being arranged to produce sensor signals dependent on the movement of the stylus assembly relative to the housing, wherein resilient biassing means and said diaphragm are so arranged that said stylus assembly is suspended by resilient forces acting in opposition so as to determine an equilibrium rest position.

6. A probe as claimed in claim 5 wherein the resilient biassing means comprises a resilient member defining a plurality of ligament limbs, each ligament limb being associated with a movable element of a said sensor, each said movable element being connected to the stylus assembly.

7. A probe as claimed in claim 6, wherein said resilient biassing means comprises two said resilient members so arranged that radially aligned pairs of ligament limbs from the two resilient members are substantially parallel, rigid linkage means connecting each of said pairs, each said movable element being constrained by said linkage means to ensure substantially linear movement thereof relative to its sensor.

8. A probe as claimed in claim 7, wherein each said movable element is connected to said stylus assembly by tension means.

9. A probe as claimed in claim 8, wherein said tension means is a tensioned wire which prestresses the resilient state of said resilient member and said diaphragm placing them under tension.

10. A probe as claimed in claim 6, wherein each said movable element is rigidly connected to said stylus assembly by rigid means which displace both the resilient member and the diaphragm from their relaxed positions.

11. A probe as claimed in claim 10, comprising a pair of resilient members, associated aligned pairs of ligament limbs being held parallel by said rigid means.

12. A probe as claimed in claim 10 or claim 11, wherein said rigid means co-operate with ball means acting on, and seated in, a groove on the stylus assembly.

13. A probe as claimed in claim 11, wherein one of said rigid means and said stylus assembly has a radially extending groove for locating ball means acting therebetween, and the other thereof has a circumferential groove for receiving said ball means.

14. A probe as claimed in any one of claims 5 to 13, wherein said diaphragm is mounted on said housing at its centre and clamped to the stylus assembly at its periphery.

15. A probe as claimed in any one of claims 5 to 13, wherein said diaphragm is mounted on said housing at its periphery and clamped to the stylus assembly at its centre.

16. A probe as claimed in claim 14, wherein said stylus assembly comprising a mounting plate and a mounting ring to clamp said diaphragm, said mounting plate being adapted to hold a stylus.

17. A probe as claimed in claim 16, wherein said stylus includes a locator plate which is adapted to be magnetically and displacably mounted on said mounting plate.

18. A probe as claimed in either claim 16 or claim 17, wherein said locator plate and said mounting plate are aligned by spaced elements on one thereof resting in seating means on the other thereof.

19. A probe as claimed in any one of claims 5 to 18, wherein said sensors are transducers equiangularly spaced relative to said housing, said transducers being located in transducer bores of said housing, said transducer bores being aligned with linkage chambers, a movable element extending from said transducers towards said stylus assembly and being connected to rigid linkage means to ensure linear motion thereof, said rigid linkage means being associated with said resilient biassing means, said resilient biassing means being configured to ensure said linear motion.

20. A probe as claimed in any one of claims 5 to 18, wherein said sensors comprise transducers and said mounting plate comprises a median member having transducer apertures therein, a sleeve mounted on said housing and associated with each said transducer aperture, each said transducer being carried in a said sleeve, a movable element associated with each said transducer being rigidly connected to the mounting plate for displacement of the armature in dependence on displacement of the stylus assembly.

21. A probe as claim in claim 20 wherein the stylus assembly is provided with means for retaining compression springs arranged between the probe housing and the stylus assembly, said compression springs providing said resilient biassing means.

22. A probe as claimed in claim 21, wherein said springs extend between adjustable studs located in respective stud bores in the main housing and said stylus assembly.

23. A probe for measuring workpieces, arranged, constructed and adapted to operate substantially as hereinbefore described with reference to the embodiment of Figures 1 to 5, or the embodiment of Figures 1 to 5 as modified in either Figure 6 or Figure 7, or the embodiment as described with respect to Figures 8 to 13.

24. A stylus assembly for a probe for measuring workpieces, substantially as hereinbefore described with reference to the embodiments of Figures 1 to 5 or Figures 8 to 13 wherein the stylus is releasably mounted on the stylus assembly.

25. A probe for multiaxis form measurement on workpieces, comprising a housing, a stylus assembly, a resilient diaphragm by which the stylus assembly is mounted on the housing for movement in the X, Y and Z directions, sensors associated with the stylus assembly, said sensors being arranged to produce sensor signals dependent on the movement of the stylus assembly relative to the housing, wherein said diaphragm is prestressed in the rest position of the stylus.

26. A probe as claimed in claim 25, wherein said diaphragm is prestressed into a conical configuration.

27. A probe as claimed in claim 26, wherein said conical configuration is such that the perimeter of the diaphragm is nearer to the sensors in the rest position of the stylus relative to the centre of the diaphragm.

28. A probe as claimed in claim 26, wherein said conical configuration is such that the centre of the diaphragm is nearer to the sensors in the rest position of the stylus relative to the perimeter of the diaphragm.

29. A probe as claimed in any one of claims 25 to 28, wherein the diaphragm is pre-stressed by resilient means acting in opposition to said diaphragm.

30. A probe for multiaxis measurement on workpieces, comprising a housing, a stylus assembly, a resilient diaphragm by which the stylus assembly is mounted on the housing for movement in the X, Y and Z directions, transducers linked to the stylus assembly, said transducers being arranged to produce signals dependent on the movement of the stylus assembly relative to the housing, wherein linkage means are arranged to constrain movement of a movable element of each transducer to substantially linear movement in response to movement of the stylus assembly.

31. A probe as claimed in claim 30, comprising a pair of resilient means arranged to be axially spaced relative to a longitudinal axis of the probe, said resilient means co-operating with rigid linkages individually associated with said transducers, each said rigid linkage being coupled to the movable element of its respective transducer and to said stylus assembly.

32. A probe as claimed in claim 31, wherein resilient means each comprise ligament means, said ligament means having a limb associated with each said rigid linkage means, whereby a parallel pair of said limbs confine a said linkage to substantially linear movement over the measuring range of the probe.

33. A probe as claimed in claim 31 or claim 32, wherein said linkage means is coupled to said stylus assembly by tension means for pre-tensioning the resilient means and said diaphragm.

34. A probe as claimed in claim 33, wherein said tensioning means comprise a tensioned wire and said probe carries tension wire adjusters to permit the length thereof to be adjusted.

35. A probe as claimed in claim 31 or claim 32, wherein said linkage means is coupled to said stylus assembly by ball means, and said ball means engages grooves in each of said rigid linkage means and said stylus assembly.

36. A probe as claimed in claim 35, wherein one of the rigid linkage means and the stylus assembly has radially extending grooves to receive said ball means and the other thereof has a circumferentially extending groove to receive said ball means.

37. A probe for multiaxis measurement on workpieces as claimed in any one of claims 5 to 24, further comprising damping means for damping unwanted stylus assembly movement.

38. A probe as claimed in claim 37, wherein said damping means comprises applying a quantity of a viscose substance at a location which dampens the vibration of the stylus assembly.

39. A probe as claimed in claim 38, when dependent on claim 7, wherein said damping means is juxtaposed said rigid linkage means.

40. A probe as claimed in claim 38, when dependent on claim 20, wherein said damping means is juxtaposed said transducer carrying sleeve.

41. A probe for multiaxis measurement on workpieces as claimed in any one of claims 25 to 29, further comprising damping means for damping unwanted stylus assembly movement.

42. A probe as claimed in claim 41, wherein said damping means comprises applying a quantity of a viscose substance at a location which dampens the vibration of the stylus assembly.

43. A probe for multiaxis measurement on workpieces as claimed in any one of claims 30 to 36, further comprising damping means for damping unwanted stylus assembly movement.

44. A probe as claimed in claim 43, wherein said damping means comprises applying a quantity of a viscose substance at a location which dampens the vibration of the stylus assembly.

45. A probe as claimed in claim 44,- when dependent on claim 31, wherein said damping means is juxtaposed said rigid linkage means.