GB2086980A - Universal joints - Google Patents

Abstract

In a universal (three axis) joint for a tool plate 10 of the manipulator mechanisms of automatic handling equipment, there are two third members (23a, 23b) each pivotally supported by a second member (22), and wherein each third member (23a, 23b) a) is essentially U-shaped, having a base portion with two free edges upstanding therefrom between which extends a third axis (C-C), b) carries thrust member attachment means located upon the face of the base portion opposing the free ends and nearer one such end than the other, whereby there may be affixed thereto a thrust member (24a, 24b), and c) is supported about the third axis (C-C) with its free ends interleaved with those of the other third member, so that the two attachment means (and, when affixed thereto, the two thrust members) are coplanar with first (A-A) and second (B-B) axes, and any forces transmitted therethrough intersect with the three axis intersection point. A U-shaped first member 21 is pivotally supported upon the tool plate 10 by a spindle 31. <IMAGE>

Description

SPECIFICATION Universal joints This invention relates to universal joints, and concerns in particular such joints useful as part of the manipulative structure of a robot or other automatic machinery.

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 from a number of individual 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 part - the portion that "manipulates" the parts referred to herein as the manipulator mechanism.

The design of the manipulator mechanisms of present automatic handling equipment of this type tends to be based upon that of the human arm.

The mechanism has a grasping device (a "hand") attached by a first joint (a "wrist") to a first extender member (a "fore-arm") itself attached, either directly or via a second joint (an "elbow") to a second extender member (an "upper arm"), by a third joint (a "shoulder") to the body of the machine which itself may be mounted by a fourth joint (a "waist") on the floor. However, while the human arm is a superb piece of manipulative machinery, its robot imitations are not; indeed, it has become evident that "humanoid" robot structures of this general type are far from ideal for the task, particularly when they are to be used in equipment for the rapid assembly of small components. Such structures are deficient in speed, stiffness (both structural and servomechanical), and dynamic control, and thus an alternative approach is required to produce a suitable manipulator mechanism.

In a complex assembly process it may be possible - and, indeed, desirable - for the manipulative capability of the equipment to be shared between the assembly carrier and the main component manipulator. It is then possible to restrict the latter's range of movement to less than a conventional "robot arm" - an arm-angle controlled five- or six-axis robot.This eases the task of designing the alternative mechanism, and opens up the way for such mechanisms which do not copy the structure of the human arm, and in the Specification of our copending Application for Letters Patent No. 80/29,667 (l/6451/M) there is described and claimed just such an alternative design of manipulator, which design provides a manipulator mechanism comprising a support member (for whatever tool it is intended the mechanism should operate and/or position) connected, by universal joints at at least three positions triangularly disposed thereon, to at least six rods longitudinally slideably supported in hexagonally-disposed universal bearings, such that the position and attitude of the support member in space relative to the universal bearings is fully defined by the lengths of the rods between the respective joints and bearings.The universal joints by which the rods are connected to the support member are three axis joints, and may be any such that enable each rod to pivot and twist in any direction relative to the support member. A three axis joint may for convenience here be defined as the combination of a first member with mounting means whereby it may be pivotally supported upon a chosen object about a first axis, a second member with mounting means whereby it may be pivotally supported by the first member about a second axis, and a third member with mounting means whereby it may be pivotally supported by the second member about the third axis, the three axes being mutually at right angles and intersecting at a point.If this joint is connected between two objects (one thus being pivotally connected to the first member by the latter's mounting means, and the other being rigidly connected to the third member) then the two will be freely pivotable with respect to each other about any of the three axes.

There are many conventional varieties of three axis joints, but few (if any) of them permit really large angular movements about all three axes, or truly allow the connection of three objects one to another such that all the forces between the objects pass through a single point. It is, however, this very sort of joint that is especially preferred for the manipulator mechanism of the aforementioned Application No. 80/29,667 and the present invention seeks to provide just this sort of joint.

In one aspect, therefore, this invention provides a three axis joint as hereinbefore defined, wherein there are two third members each pivotally supported by the second member, and wherein each third member a) is essentially U-shaped, having a base portion with two free ends upstanding therefrom between which extends the third axis, b) carries thrust member attachment means located upon the face of the base portion opposing the free ends and nearer one such end than the other, whereby there may be affixed thereto a thrust member; and c) is supported about the third axis with its free ends interleaved with those of the other third member, so that the two attachment means (and, when affixed thereto, the two thrust members) are coplanar with the first and second axes, and any forces transmitted therethrough intersect with the three axis intersection point.

The manner in which any one member is pivotally supported may be any that is convenient having regard to the shape of each member. For example: the first member may be a U-shaped bracket pivotally supported upon the chosen object (usually the manipulator mechanism's tool plate) by a spindle rigidly secured to the base of the first member and extending away therefrom into engagement with bearing surfaces mounted on or in the object; the second member may be a flat plate mounted longitudinally within a U-shaped bracket first member and pivotally supported upon the first member by conical pivots in its opposed edges co-operating with adjusting screws threaded through the upstanding free ends of the bracket; each third member may be pivotally supported upon a plate-like second member by a pin extending laterally on either side of the plate second member and passing through apertures in the third members' free ends.

Each third member is essentially U-shaped. It may be described, alternatively, as "forked" (in the manner of a bicycle fork).

Each third member carries thrust member attachment means, by which it may be connected to one rod of the manipulator mechanism of the aforementioned Application No. 80/29,667. These attachment means may in fact be "notional", in the sense that the thrust member is actually either integral with or, say, welded to the third member, though in practice it is more likely that the attachment means will be a socket into which the thrust member is securely fitted (by, for example, screw thread action). These attachment means (notional or real) are offset to one side of the third member. This is so that, by choosing the correct amount of offset depending upon the dimensions of the member, when the two third members are pivotally supported in the required interleaved manner the two thrust members (when attached) will be in the same plane.

The two third members are pivotally supported upon the second member in an interleaved fashion. Where the second member is a flat plate, and because the lateral dimension of the third member/plate/third member combination is small, it is much preferred that all three should be pressed into sideways (face-to-face) engagement with each other. This may be achieved using a suitably stepped pivot pin and locking collar (described in more detail hereinafter) which can be tightened up to draw each "inside" third member free end into engagement with its face of the second member plate.

The invention extends, of course, to a manipulator mechanism as described and claimed in the aforementioned Application No. 80/29,667, whenever using a universal joint as described and claimed herein.

An embodiment of the invention is now described, though only by way of illustration, with reference to the accompanying drawings in which: Figure 1 is a diagrammatic perspective view of a manipulator mechanism generally of the aforementioned Application No. 80/29,667, but using universal joints according to the present invention; Figures 2A and B are respectively diagrammatic side sectional and exaggerated top plan views of a universal joint according to the invention.

Where possible, similar parts in the Figures have been given the same reference numerals.

The mechanism of Figure 1 comprises a tool plate (10) having upon its upper face three universal joints (as 1 - as provided by the invention; suitable such joints are shown in Figures 2A and 2B) disposed in an equilateral triangle and to each of which are attached the lower ends of two rods (as 12) the upper ends of which are slideably mounted in ball joints (as 13) disposed at the points of a regular hexagon in a planar mainframe upper platform (14) supported by corner pillars (as 15) above a work surface (16).

Each ball joint 13, through which the rod 12 slides longitudinally, carries upon its upper surface the working parts of a jacking system (as 20) by which an electric motor (not shown) drives the rod 12 up or down by any chosen, measured, amount: so driving the tool plate 10 into any chosen position and attitude relative to the platform 14 carrying the ball joints 13.

In this embodiment, the ball joints 13 are regularly placed on a circle in the same overhead plane (14) to give the maximum degree of triangulation in the nominal centre of the work volume. Within a sphere of diameter equal to the height of the platform 1 4 the lengths of the rods determine the position, tilt (up to 450 in any direction) and twist about a vertical axis of the tool plate 10. The tilt is progressively restricted, as the working volume is increased, from a sphere to an oblate spheroid about twice the height across.

The three axis joint of the invention is shown in Figures 2A and 2B. The joint comprises a Ushaped first member (21) pivotally mounted upon the tool plate 10 (not shown in Figure 2B), a flat plate second member (22) pivotally supported between the upturned ends of the U-shaped first member 20, and two "upside down" U-shaped third members (23a, 23b) pivotally supported upon the plate second member 22. Each U-shaped third member 23a, 23b has attached to it (by means not shown) a rod-like thrust member (24a, 24b).

The U-shaped first member 21 is pivotally supported upon the tool plate 10 by a spindle (31) affixed centrally to the underside of the U base, this spindle being held by the two angular contact bearings (as 32) pressed from either side into an aperture (33) in the tool plate. Any end float is taken up by a retaining nut (34) screwed onto the end of the spindle. The first axis A-A passes axially of the spindle 31.

The flat plate second member 22 is pivotally supported between the ends of the U-shaped first member 21 by two conically-tipped lockable adjusting screws (as 36) co-operating with correspondingly shaped recesses (as 37) in either end face of the second member. The second axis B-B passes between the points of the adjusting screws 36; it is coplanar with the first axis A-A, and crosses it centrally of the flat plate second member 22.

Each inverted U-shaped third member 23a, 23b is pivotally supported by a pin (39) passing between its face ends and through an experture located centrally of the flat plate second member 22 (and thus where the first and second axes cross). The third axis C-C passes axially of this pin 39, and cross the first and second axes at their central crossing point. All three axes therefore intersect at a point.

The two U-shaped third members 23a, 23b are mounted upon the pin 39 in an interleaved fashion (as is seen clearest from Figure 2A), and their respective rod-like thrust members 24a, 24b are mounted offset (each by an amount equal to half the thickness of the flat plate second member 22) and in the opposite sense one to the other. This means that the line of any thrust transmitted through the bearing along each rod 24a, 24b (which line is here coincident with the rod axis) is coplanar one with the other and with the first and second axes.As a result, all forces exerted on the joint via either one or both of the rods 24a, 24b or the tool plate 10 intersect at a point (the intersection point of the three axes), and there are no distorting couples acting to displace the joint (or tool plate) in any unpredictable fashion.

Since the plate second member 22 is quite narrow, and the length of pin 39 engagement small, added stability is given to the assembly by pressing the inside face of one of the free ends of each U-shaped third member 23a, 23b against the plate. To exert this pressure the pin 39 is stepped (41) with the outside diameter of the flange passing through the free end remote from the plate 22 to press on the inner free end of the other fork third member 23a, 23b. Similarly a collar (42) is fitted to the pin 39 on the opposite side to engage with the inner free end of the third member 23a, 23b that is pressed against the other side of the plate. A nut (43) on the outside of the collar 42 applies the pressure, and to allow large angular movements of the plate 22 it is convenient to make the coller 42 and nut 43 a single item.

Claims (5)

1. A three axis joint as hereinbefore defined, wherein there are two third members each pivotally supported by the second member, and wherein each third member a) is essentially U-shaped, having a base portion with two free ends upstanding therefrom between which extends the third axis, b) carries thrust member attachment means located upon the face of the base portion opposing the free ends and nearer one such end than the other, whereby there may be affixed thereto a thrust member; and c) is supported about the third axis with its free ends interleaved with those of the other third member, so that the two attachment means (and, when affixed thereto, the two thrust members) are coplanar with the first and second axes, and any forces transmitted therethrough intersect with the three axis intersection point.

2. A joint as claimed in claim 1, wherein: the first member is a U-shaped bracket pivotally supported upon the chosen object by a spindle rigidly secured to the base of the first member and extending away therefrom into engagement with bearing surfaces mounted on or in the object; the second member is a flat plate mounted longitudinally within the U-shaped bracket first member and pivotally supported upon the first member by conical pivots in its opposed edges cooperating with adjusting screws threaded through the upstanding free ends of the bracket; and each third member is pivotally supported upon the plate-like second member by a pin extending laterally on either side of the plate second member and passing through apertures in the third members' free ends.

3. A joint as claimed in either of the preceding claims, wherein, where the second member is a flat plate, the two third members and the plate are pressed into sideways (face-to-face) engagement with each other.

4. A three-axis joint as claimed in any of the preceding claims and substantially as described hereinbefore.

5. A manipulator mechanism as described and claimed in the Specification of the aforementioned Application No. 80/29,667, whenever using a universal joint as claimed in any of the preceding claims.