GB2129086A - Co-ordinate tables - Google Patents

Abstract

Present-day manipulators of the conventional "robot arm" variety are usually not entirely successful; the robot arm, while being capable of performing the gross movement of its human counterpart, is invariably less able to perform the very fine movements increasingly required in modern assembly work. However, fine positioning capability may be achieved by mounting upon the arm, intermediate it and the tool it is to operate, a co-ordinate table (15) able to provide the full range of fine positioning required. The present invention suggests a novel form of coordinate table (15) which comprises: a baseplate 22 having a first eccentrically-bored ring 33 drivably mounted thereon for rotation about the ring's 33 external surface axis; a second eccentrically-bored ring 42 mounted coaxially with the first ring's 33 bore 34 for rotation about that bore's 34 axis, the eccentricity of the second ring's 42 bore 44 matching that of the first ring's 33 bore 34; and a toolplate 62 drivably mounted on the second ring 42 via a cylindrical toolplate support 64 itself mounted coaxially within the second ring's 42 bore 44 for rotation about that bore's 44 axis; there being means 52-54 to prevent uncontrolled relative rotation of the two plates 22, 62 while permitting their relative linear translocation. <IMAGE>

Description

SPECIFICATION Co-ordinate tables This invention concerns co-ordinate tables, and relates in particular to such tables that can be employed for fine positioning of a robot-held tool relative to a workpiece.

On many occasions it is desirable that a physical action be performed by automatic equipment. One such occasion is during the assembly of some object borne upon a carrier from a number of individual component parts, when the machinery handling the parts and performing the assembly should, if possible, be able to pick up each part, orientate it correctly, and then fit it onto the object as so far assembled. That portion of the machinery involved in orientating the component part - the portion that "manipulates" the parts referred to herein as the manipulator mechanism.

Most present-day manipulators are of the conventional "robot arm" variety (in which the machinery emulates, both visually and mechanically, a human arm), and one well-known example of such a manipulator is the PUMA, manufactured by Unimation. Unfortunately, however, the emulation is usually not entirely successful, and the robot arm, while being capable of performing the gross movements of its human counterpart, is invariable less able to perform the very fine movements increasingly required in modern assembly work.

One answer is to redesign completely the manipulator, replacing the conventional arm with something better able to make both gross and fine movement, and such a manipulator is described and claimed in our published British Patent Specification No. 2,083,795A (1/64511MB).

Another answer, more acceptable when - as is commonly the case - existing machinery has to be retained, is to share the manipulative capability of the equipment between the manipulator, effecting gross positioning, and a workpiece carrier, performing the required fine positioning. A carrier for use in such an arrangement is described and claimed in our published British Patent Specification No. 2,085,329A (1/6470/MB).

Unfortunately, there are occasions when it is preferred not to achieve fine positioning by moving the assembly carrier itself; the present invention suggests a third answer to the fine positioning problem in such cases, by providing, for mounting upon the main manipulator intermediate the latter and the tool, a co-ordinate table capable of allowing the full range of fine positioning required.

Co-ordinate tables are themselves well known (the workpiece carrier of our aforementioned Specification No.2,089,329A is such a table, providing fine movement in orthogonal X, Y directions), but generally they are bulky, massive devices needing considerable care in their design and construction to avoid, or deal with, backlash.

The present invention suggests a rather different sort of table, one that operates on what is effectively a polar co-ordinate basis, and that can (partly as a result) be built so as to be small and Jight - and, in particular, light enough to be carried by the main manipulator mechanism without putting too much of a strain on it - and yet have no, or almost no, backlash problem.

In one aspect, therefore, the invention provides a co-ordinate table which comprises: a first plate; a first rotary member mounted on the first plate for rotation about a first axis normal to the plate's plane; there being first driving means for so rotating the first rotary member; a second rotary member mounted on the first rotary member for rotation about a second axis parallel to but spaced from the first axis; a second plate mounted on the second rotary member and parallel to the first plate for rotation about a third axis parallel to but spaced from the second axis, the spacing matching that of the second axis from the first axis, there being second driving means for so rotating the second plate; and means to prevent uncontrolled relative rotation of the first and second plates but permit relative linear translation in any direction parallel to their planes.

The co-ordinate table of the invention may be employed on its own, but is primarily intended for use with a tool-carrying manipulator mechanism, and specifically is to be interposed between the mechanism and the tool, so that coarse positioning of the tool is effected by the manipulator while fine positioning is effected by the table. Naturally, the tool/manipulator mechanism combination may be of any sort where such fine positioning is required, but the table is specifically intended for rotor arm manipulator mechanisms of the type emulating the human arm.

The inventive co-ordinate table includes first and second plates which are driven linearly relative to each other in any direction parallel to their planes. It is on one of these plates that any tool carried by the table is mounted, and by the other of the plates that the table itself is mounted (on, say, a manipulator).For convenience the plate by which the table is mounted, which plate is referred to hereinafter as the baseplate, is identified as the first plate, while the plate on which the tool is mounted, which plate is referred to hereinafter as the toolplate, is identified as the second plate -though it will be appreciated that they could just as easily be the other way round, for the table has no intrinsically correct way up ! The baseplate, then, is simply the plate by which the table may be fixedly (though preferably removably) secured to whatever object - the manipulator mechanism, say - is to support it.

The baseplate may in general be of any appropriate shape or size, and one such is discussed hereinafter with reference to the accompanying drawings.

Mounted on the baseplate is a first rotary member, the mounting being such that the member can rotate about a first axis normal to the baseplate. While in theory the rotary member might take any shape, conveniently it is a thick, planar, annul us (it is referred to hereinafter as the first ring member) with - for reasons that are explained below - an eccentric bore (that is, the cylindrical surfaces defined by its inner and outer periphery are offset, with their axes parallel but spaced one from the other). The ring is in effect a short, stubby, tube with its bore eccentrically but axially-parallelly disposed relative to its outside surface. The mounting of this ring on the baseplate is preferably accomplished using a single circular ball race (of an axial dimension comparable to the ring axial thickness) external of the ring.The ball race is itself mounted roughly centrally of, and with its plane parallel to, the baseplate; most preferably the outside section of the ball race is an interference fit within a ring-like rim or collar upstanding from the baseplate surface, while the inside section of the ball race is an interference fit around the outside surface of the first ring member, and each race is so shaped that when used with oversize balls there is no radial or axial clearance (so that no relative axial or radial movement can occur).

It will be clear that as the preferred first ring member is rotated relative to the baseplate so the eccentric bore thereof rotates around the ring's external surface axis, sweeping out an area that, because of its eccentricity, is larger than it occupies.

The co-ordinate table includes first driving means for rotating the first rotary member relative to the baseplate. These driving means, which are conveniently mounted upon the baseplate, may advantageously include a prime mover on the baseplate driving a gear train of some sort, the final element of this train meshing with a corresponding gear mounted on the first rotary member.In one specifically preferred embodiment (shown in the accompanying drawings) the prime mover is a small electric motor mounted on the baseplate and driving directly a pinion shaft (extending parallel to the plane of the baseplate) meshing with the input of a reduction gear also mounted on the baseplate, and the output of the latter gear (a worm, or a helical gear) engages a gear (a wheel or a helical gear) affixed over a face (that on the side toward the baseplate) of the first ring member; as the motor turns its pinion shaft, so that first ring member is rotated relative to the baseplate.

The driving means conveniently includes feedback means indicating the rotary position of the driving shaft - and thus the rotary position of the first rotary member relative to the baseplate - so that the positioning of the coordinate table may be controlled by some suitable external system (commonly a micro-computer system, which in the most preferred cases is in fact controlling the entire operation of the manipulator mechanism and the tool it is carrying). With a prime mover driving directly a pinion shaft, such feedback means is advantageously a resolver mounted on the baseplate near the end of, and driven by, the shaft.

Mounted on the first rotary member is a second rotary member, the latter being mounted for rotation about a second axis that is parallel to but spaced from the first axis. This second rotary member is also preferably a ring member analogous to the first ring member, and is conveniently mounted within the bore of the first ring member, the mounting being such that the two rings' planes are mutually parallel and the second ring can rotate about its external surface's axis. In essence this second ring member is conveniently simply a version of the first ring member that has a smaller outer diameter (matching the inner diameter of the first ring member) but the same eccentricity - that is to say, it, too, is a short, stubby, tube with its bore eccentrically but axially-parallelly disposed relative to its outside surface.As the first ring member is mounted on the baseplate on a single ball race, so preferably is the second ring member mounted within the first - and thus the second ring ball race is mounted within the first ring's bore, with its outer section fitting within the bore and its inner section fitting around the outside surface of the second ring.

It will be appreciated that, so far as is concerned the most convenient form of ring member, the outer surface of the second ring member is mounted concentrically within the inner surface of the first ring member, while the former's inner surface is eccentric of the latter's outer surface. Thus, as the second ring member is rotated within the first so the former's eccentric bore rotates around its ring's external surface axis, sweeping out an area that is, because of the eccentricity, larger than that it occupies.

Mounted for rotation on the second rotary member is the second plate - the toolplate. The toolplate is in essence merely a platform upon which there may be mounted the tool the manipulator mechanism is to carry (though on occasion the toolplate may be an integral part of the tool), and it may be of any convenient size and shape (one such is described hereinafter with reference to the accompanying drawings). The toolplate is mounted so that it is parallel to the baseplate; thus, however the two move one relative to the other the angle made by the former (and correspondingly, by any tool carried thereby) to a line normal to the latter remains the same.

The toolplate is also mounted so that it can rotate about a third axis parallel to but spaced from the second axis (that about which the second rotary member rotates on the first), and this spacing matches that of the second axis from the first (that about which the first rotary member rotates on the baseplate). When using the preferred ring member the toolplate is conveniently fixedly mounted on a projecting cylindrical toolplate support (in effect, little more than an axle - a short cylinder - at one end of which is secured the toolplate). This support is itself conveniently mounted co-axially within the eccentric bore of the second ring member.

Preferably the support is so mounted for rotation via two small ball races (positoned one near each end of the support), these withstanding the "overturning" forces liable to be experienced in use; conveniently each such ball race has its outer section an interference fit within the second ring member's bore and its inner section an interference fit around the support, and the two sections are tightened (axially) one against the other to pre-load the bearings and eliminate axial and radial clearances.

It will be understood that, the support being mounted within the eccentric bore of the second ring member, it too sweeps out an area greater than it occupies as the second ring member rotates within the first ring member. It will further be understood that the actual position of the support - and thus of the toolplate and any tool carried thereby - relative to the baseplate is determined by the combination of the rotational positions of the two ring members; as is explained in more detail hereinafter with reference to the accompanying drawings, the support axis may be in any position along a radius centred on the first ring member's external wall axis (when the two ring members are so disposed relative one to the other that their matching eccentricities cancel) and of a length equal to both ring's eccentricities added together (when the ring members are so disposed that their eccentricities add), and the radius may be in any direction.

As there are feedback-providing first driving means to rotate the first rotary member relative to the baseplate, so there are feedback-providing second driving means to rotate the toolplate relative to the second rotary member -- and, indeed, much the same considerations apply to this second driving means as to the first.

Preferably, therefore, the second driving means includes a small electric motor prime mover mounted on the toolplate and driving directly a pinion shaft meshing with a reduction gear also mounted on the toolplate, and the latter gear engages a gear wheel affixed over a face (that on the toolplate side) of the second rotary member, there being in addition a resolver mounted on the toolplate near the end of and driven by the shaft.

As the motor turns its pinion shaft, so the toolplate is rotated relative to the second rotary member.

Combining a number of the more convenient forms of the components used in the co-ordinate table of the invention, it can be seen that in a preferred aspect the invention provides a co ordinate table which comprises: a baseplate; a first eccentrically-bored ring member mounted on and parallel to the baseplate for rotation about the ring's external surface axis, with first driving means mounted on the baseplate for so rotating the first ring member; a second eccentrically-bored ring member mounted coaxially with the first ring member's bore for rotation about that bore's axis, the eccentricity of the second ring member's bore matching that of the first ring member's bore; a cylindrical toolplate support mounted coaxially within the second ring member's bore for rotation about that bore's axis;; a toolplate fixedly mounted on the toolplate support and parallel to the second ring member, with second driving means mounted on the toolplate for so rotating the toolplate/support combination; and means to prevent uncontrolled relative rotation of the baseplate and toolplate but permit relative linear translocation in any direction parallel to their planes.

In the absence of any means to restrict, or prevent, relative rotational movement of the toolplate and baseplate the co-ordinate table as so far discussed in detail would freely allow such rotational movement, so that in a short time the angular position of the toolplate, and of any tool carried thereby, would be hopelessly indefinite. It is therefore necessary to prevent uncontrolled mutual rotation of the toolplate and baseplate while, of course, still allowing the two to move linearly with respect to each other in any direction parallel to their planes.One convenient means for preventing any mutual rotation is to employ a parallelogram linkage of the type in which four rigid link arms arranged to follow the sides of a parallelogram itself parallel to the baseplate and toolplate planes are grouped in pairs (one pair is two opposed arms - the left and right ones, say - while the other is the other two opposed arms - the top and bottom ones) one pair to each of the baseplate and toolplate and joined thereto so that each link is pivotally mounted at one end on its plate, the other end of each link being pivotally mounted on a planar framework rigidly joining all these other ends together.Each pair of links joining its plate to the framework allows the two relative movement back and forth to either side of the links and along the general line of the other pair of links, and thus the combination of the two pairs and the framework allows the two plates to move relative to each other in any direction.

When using such a linkage, an embodiment of which is shown in the accompanying drawings, linear translocation of the toolplate relative to the baseplate is permitted but rotation of one relative to the other is prevented.

In certain circumstances, however, a minimal amount of controlled rotation of the toolplate relative to the baseplate may be desirable in order to ease the problem of getting the tool into exactly the right orientation. To do this a different type of linkage is used, specifically one in which one plate is joined by a crank to the other, one end of the crank being drivable so as mutually to rotate the two plates into the desired position (it will be seen that the crank first needs to be driven so as to "cancel" any mutual rotation induced by relative rotation of the ring members, and then further driven so as to impart the desired mutual angular displacement). The driving means employed may conveniently be essentially comparable to the driving means used with each plate/ring member combination.Thus, preferably the crank driving means includes a small electric motor prime mover mounted on the baseplate and driving directly a worm shaft meshing with a gear wheel also mounted on the baseplate, and the latter gear carries pivotally mounted near the periphery of one face the crank arm the other end of which is pivotally mounted near the periphery of the toolplate, there being in addition a resolver mounted on the baseplate near the end of and driven by the shaft. As the motor turns its shaft, so the toolplate is rotated back and forth relative to the baseplate though a small angle the exact size of which depends upon the positions of each end of the crank relative to the rotational axes of the driving gear and the toolplate.

The co-ordinate table of the invention is, at least in its preferred embodiments, a compact light weight assembly giving very accurate offset movements in any angular position. It has a minimum of components, and these may fairly easily be constructed so as to be relatively free of backlash problems.

Naturally, the invention extends to a manipulator mechanism whenever employing a co-ordinate table as described and claimed herein.

Various embodiments of the invention are now described, though by way of illustration only, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a robot arm incorporating a co-ordinate table of the invention; Figures 2A, B and C are respectively underneath plan, section and side elevation views of one embodiment of co-ordinate table of the invention.

Figures 3A and B are the Figure 2b section, and a comparable perspective view, in "exploded" form; Figures 4A, B and C are respectively underneath plan, section and side elevation views (like those of Figures 2A, B and C) of a second embodiment of co-ordinate table of the invention; and Figures 5A, B and C are schematic plan views of the working parts of a co-ordinate table of the invention, showing how the eccentric-mounting of the second ring member and toolplate combine to give radial displacement in any desired direction.

The robot arm of Figure 1 is an arm of the PUMA type, and is in general akin to the human arm. It comprises a body portion (10) on which is pivotally mounted an upper arm portion (11) itself carrying pivotted thereon a lower arm portion (12). At the free end of the lower arm 12 is a wrist joint (13) upon which is normally mounted directly a tool (as the hand-like pincers, 14, shown in dotted outline). In this embodiment, however, there is intermediate the wrist 13 and the pincers 14 a co-ordinate table (generally 15) in accordance with the invention. The table 15 allows the fine movements that the main arm is unable to provide.

One embodiment of co-ordinate table 15 suitable for use with an arm of the type shown in Figure 1 is shown in considerable detail in Figures 2A, B and C and 3A and B (Figure 2B is a section on the line BB of Figure 2A). As can best be seen from the exploded sectional and perspective views of Figures 3A and B (the exploded sectional views of Figure 3A correspond to the unexploded sectional views of Figure 2A), the table has five main portions. The first of these is the baseplate portion (generally 21) comprising the baseplate (22) itself together with electric motor drive means (23) mounted thereon and a circular peripheral wall (24) depending (as viewed) therefrom on the inside surface of which is mounted the outside section (25) of a ball race.

The motor drive means 23 drives a pinion meshing with a reduction gear which in turn drives a pinion on the same shaft that itself drives (see below) the first ring member. This is best understood from the view (of Figure 3B) relating to the corresponding - and similar - drive system for the toolplate.

Fitting within the wall 24, via the ball race inside section (31), is the second of the five portions, namely the first eccentrically-bored ring member portion (generally 32). This comprises the ring member (33) itself, with on its external surface the aforementioned ball race section (31) and on its internal surface the outer section (34) of a second ball race, and secured to the ring member 33 on the face thereof adjacent the baseplate 22 is a gear wheel 35 coaxial with the external ring surface. When the first ring member 32 is fitted within the walls 24 of the baseplate portion 21 the motor pinion/reduction gear combination meshes with, and drives, the gear wheel 35.

The third main portion is the second eccentrically-bored ring member portion (generally 41), which comprises the second ring member (42) itself, the internal section (43) of the ball race with outside section 34, and the internal section of two ball races (44a, b) one of which is within a collar-like extension (45) of the bore surrounds. Mounted externally of this collar-like extension is another gear wheel (46), which is driven by the toolplate motor pinion/reduction gear combination - as best seen in Figure 3B discussed further below. In use, the second ring member 42 fits inside the bore of the first ring member 33.

As shown in Figures 3A and B the next portion is the parallelogram linkage (generally 51) that prevents relative rotation of the baseplate and toolplate. It is convenient, however, first to describe the toolplate portion.

The toolplate portion (generally 61) comprises the toolplate (62) itself, electric motor drive means (63) mounted thereon, and a cylindrical toolplate support (64) having around its external surface the outer sections (65a, b) of the ball race whose inner sections (44a, b) are within the second ring member's bore. When the toolplate and second ring member portions are combined, the drive means 63 meshes with, and drives the ring means via, the gear wheel 46. The perspective view in Figure 3B of the toolplate portion shows clearly how the drive motor 63 drives a reduction gear pair (66, 67) the output end 67 of which drives the second ring member gear wheel 46 via a worm/helical gear (68) mounted on a shaft (69).

This view also shows clearly how the shaft 69 also drives a resolver (70); a similar resolver (26) is similarly driven by the baseplate motor 23.

The parallelogram linkage 51 comprises a rigid framework (52 - in this case a plate) on which are pivotally mounted two pairs of links (53a, b and 54a, b). The links of link pair 53a, b are at their other end pivotally mounted on the baseplate 22, while the links of link pair 54a, b are at their other end pivotally mounted on the toolplate 62.

The arrangement allows the toolplate and baseplate to move in any direction parallel to their planes but prevents them rotating one relative to the other.

In Figures 4A, B and C (Figure 4 is a section on the line BB of Figure 2A, and Figure 4C is partly in section on the line CC of Figure 4A) there is shown a second embodiment of co-ordinate table according to the invention. In this embodiment there is used a different linkage controlling the relative rotation of the toolplate and baseplate. A third electric motor driving means (18), with its own resolver (82), is mounted on the baseplate 22 alongside the first driving motor (26) and drives a crank (83) connected to the periphery of the toolplate 62. It will be evident that the arrangement permits the toolplate and baseplate a small but controlled degree of rotational movement as well as the desired linear movement.

Figures 5A, B and C show how relative rotation of the two ring members of a co-ordinate table like that of Figures 2A, B and C can cause relative linear displacement of the toolplate and baseplate.

Each Figure is purely diagrammatic, and shows in plan view the two ring members 24 and 42 and the toolplate support 64 (ring member 42 nests within the bore of ring member 24, and support 64 nests within the bore of ring member 42).

In Figure 5A (which also includes the outlines of the baseplate 22, shown dashed, and the toolplate 62) the two ring members are so arranged that their external and internal surface axes are in line, with their eccentricities adding. In this disposition all three external surface axes the toolplate support axis (101 - the same as the second ring member bore axis), the second ring member external surface axis (102-the same as the first ring member bore axis) and the first ring member external surface axis (103) - are aligned, with the two ring members so arranged one with respect to the other that their eccentricities add.The displacement distance from the support axis 101 to the first ring external surface axis 103 is at a maximum; in Figure 5A it "points" to the right (as viewed; the same orientation as in Figures 2A, B), but rotation of the first ring member 24 (the second ring member 42 being rotated similarly to stay stationary relative thereto) allows it to point anywhere.

In Figure 5B the two ring members are also arranged with all their axes in line, but here the second ring member 42 has been rotated through 1 800 (relative to its position in Figure 5A), and the eccentricities of the two ring members now cancel. Accordingly, the toolplate support axis coincides with the first ring member external surface axis 103, and the displacement distance is zero.

The situation in Figure 5C is somewhere intermediate those of Figures 5A and 5B, with the second ring member 42 rotated 80 from the former to the latter. In this case the displacement distance D is also intermediate - and in fact is given by the equation D = 2R Cos (8/2) where R is the eccentricity of each ring member (the spacing between each member's external and internal axes). As can be seen, when 0 = O (all the axes are in line, their eccentricities adding) D = 2R, while when 6 = 180 (in line, but cancelling) D = 0.

Claims (19)

1. A co-ordinate table which comprises: a first (or base) plate; a first rotary member mounted on the first, base, plate for rotation about a first axis normal to the plate's plane, there being first driving means for so rotating the first rotary member; a second rotary member mounted on the first rotary member for rotation about a second axis parallel to but spaced from the first axis; a second (or tool) plate mounted on the second rotary member and parallel to the first, base, plate for for rotation about a third axis parallel to but spaced from the second axis, the spacing matching that of the second axis from the first axis, there being second driving means for so rotating the second, tool, plate; and means to prevent uncontrolled relative rotation of the two plates but permit relative linear translation in any direction parallel to their planes.

2. A table as claimed in claim 1, wherein the first rotary member is a first ring, being a thick, planar, annulus with an eccentric bore.

3. A table as claimed in claim 2, wherein the first ring is mounted on the baseplate using a single circular ball race (of an axial dimension comparable to the ring axial thickness) external of the ring, the ball race being itself mounted roughly centrally of, and with its plane parallel to, the baseplate.

4. A table as claimed in claim 3, wherein the outside section of the ball race is an interference fit within a ring-like rim or collar upstanding from the baseplate surface, while the inside section of the ball race is an interference fit around the outside surface of the first ring member, and each race section is so shaped that when used with oversize balls there is no radial or axial clearance.

5. A table as claimed in any of the preceding claims, wherein the first driving means includes a prime mover on the baseplate driving a gear train the final element of which meshes with a corresponding gear mounted on the first rotary member.

6. A table as claimed in any of the preceding claims, wherein the driving means includes feedback means indicating the rotary position of the first rotary member relative to the baseplate.

7. A table as claimed in any of the preceding claims, wherein the second rotary member is a second ring, analogous to the first ring.

8. A table as claimed in claim 7, wherein the second ring is mounted within the bore of the first ring, the mounting being such that the two rings' planes are mutually parallel and the second ring can rotate about its external surface's axis.

9. A table as claimed in claim 8, wherein the second ring is mounted within the first by a single ball race mounted within the first ring's bore, with its outer section fitting within the bore and its inner section fitting around the outside surface of the second ring.

10. A table as claimed in any of the preceding claims wherein, when using a ring as the second rotary member (as defined in Claim 7), the toolplate is fixedly mounted on a projecting cylindrical toolplate support itself mounted coaxially within the eccentric bore of the second ring.

11. A table as claimed in claim 10, wherein the toolplate support is mounted for rotation via two small ball races (positioned one near each end of the support), these withstanding the "overturning" forces liable to be experienced in use, and each such ball race has its outer section an interference fit within the second ring's bore and its inner section an interference fit around the support, and the two sections are tightened (axially) one against the other to pre-load the bearings and eliminate axial and radial clearances.

12. A table as claimed in any of the preceding claims, wherein the second driving means includes a prime mover on the toolplate driving a gear train the final element of which meshes with a corresponding gear mounted on the second rotary member.

13. A table as claimed in claim 12, wherein the driving means includes feedback means indicating the rotary position of the second rotary member relative to the toolplate.

14. A table as claimed in any of the preceding claims, wherein to prevent uncontrolled mutual rotation of the toolplate and baseplate there is employed a parallelogram linkage of the type in which four rigid link arms arranged to follow the sides of a parallelogram itself parallel to the baseplate and toolplate planes are grouped in pairs one pair to each of the baseplate and toolplate and joined thereto so that each link is pivotally mounted at one end on its plate, the other end of each link being pivotally mounted on a planar framework rigidly joining all these other ends together.

15. A table as claimed in any of claims 1 to 13, wherein, to allow a minimal amount of controlled rotation of the toolplate relative to the baseplate, one plate is joined by a crank to the other, one end of the crank being drivable by driving means so as mutually to rotate the two plates into the desired position.

16. A table as claimed in claim 1 5. wherein the driving means includes a prime mover mounted on the baseplate and driving a gear train the final element of which carries pivotally mounted near the periphery of one face a crank arm the other end of which is pivotally mounted near the periphery of the toolplate.

17. A table as claimed in claim 16, wherein the driving means includes feedback means indicating the rotary position of the toolplate relative to the baseplate.

18. A co-ordinate table as claimed in any one of the preceding claims and substantially as described hereinbefore.

19. A manipulator mechanism whenever employing a co-ordinate table as claimed in any of the preceding claims.