GB2088987A - Drive Systems - Google Patents

Abstract

A drive system for driving longitudinally slideably supported rods back and forth in their mountings, comprises: an elongate slotted slider (12); an open-ended recessed support body (24) within which the slider (12) is mounted with its slot (32) projecting beyond one end of the recess; a motor-drivable rotatable drum (33) mounted upon the support body (24); and a flexible connector (21) in the form of a taut closed loop wound around the drum (33) and extending between the ends of the support body's recess wherein it is attached to the slider (12); such that in operation rotary oscillatory motion of the drum (33) causes the connector (21) to be wound on and off the drum (33) thus driving the slider (12) in linear reciprocatory motion within the support body's recess. <IMAGE>

Description

SPECIFICATION Drive Systems This invention relates to drive systems, and concerns in particular systems for driving rod-like members longitudinally slideable in bearings, which systems may be 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 the human arm.

The mechanism has a grasping device ta "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 co-pending Application for Letters Patent No. 80/29,667 (l/6451/M) there is described and claimed 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 purpose of the manipulator mechanism of the aforementioned Application is to allow the support member to be positioned and orientated in a manner which is fully defined with reference to the universal bearings (which effectively constitute a datum plate with reference to which the position and attitude of the support member is defined). Moreover, in practice the mechanism is to be used automatically to position a tool carried by the support member under the driving control of, say, some suitably programmed microprocessor.Accordingly, very preferably the manipulator mechanism has associated with it drive means for each of the rods, whereby each rod may independently be slid longitudinally through its bearing, so causing the support member connected thereto to take up any desired position and attitude within the possible ranges thereof, and it is said that the drive means may be any suitable "motor"-for example, a hydraulic motor or an electric motor-appropriately operatively connected to the rod, and that it is envisaged that in one embodiment the drive means be external to but supported by the universal bearings, the rod/drive means combination perhaps being a screw jack system.

The present invention is concerned with a novel drive system which is of use for driving a longitudinally slideably supported rod-like member back and forth in its mounting, which system is especially suitable for use with the manipulator mechanism of the aforementioned Application.

In one aspect, therefore, this invention provides a device for converting rotary reciprocatory motion into linear reciprocatory motion, and suitable for use, together with a motor, as the driving means for a manipulator mechanism of the aforementioned Application No. 80/29,667, which device comprises: an elongate slide member having a longitudinally orientated slot open at the slide member's surface and extending in depth inwards at least to the slide member's longitudinal axis; a support body containing an open-ended elongate recess within which the slide member is mounted for linear reciprocatory motion with its slot projecting beyond one end of the recess; a drum member mounted for rotary reciprocatory motion upon the support body and connectable to a motor for driving it in such motion; and a flexible connector element, effectively in the form of a taut closed loop, wound around the drum member and extending between the ends of the support body's recess wherein the connector element is attached to the slide member, lying within the slot therein on at least the side whereat the slot projects beyond the recess end, and wherein the connector element is so disposed that any forces exerted by it upon the slide member are substantially co-axial with the longitudinal axis of the slide member; such that in operation rotary reciprocatory motion of the drum member causes the connector element to be wound on and off the drum thus driving the slide member in linear reciprocatory motion within the support body's elongate recess.

The device of the invention is intended primarily for use, together with a motor, as the driving means for a manipulator mechanism of the aforementioned Application No. 80/29,667.

As such, either the elongate slide member (hereinafter referred to as the slider) is in effect the rod, or it is adapated to be secured, by any suitable means, to the rod. In the latter case it is convenient if the slider matches in general size and shape the rod. Accordingly, the slider is preferably circularly cylindrical, advantageously a hollow tube, with an external diameter equal to that of the rod and a length somewhat greater than the distance it travels from end to end of its reciprocatory linear motion.

Where the slider is solid, then the slot therein is indeed a slot. An alternative, however, is for the slider to be a hollow tube, and in such a case the slot therein is comprised by a suitably slot-shaped aperture in the tube wall, this aperture opening up the centre of the tube to provide what is in effect the desired "slot" extending between the tube's exterior surface and its longitudinal axis.

The support body (hereinafter referred to as the body) is in effect no more than a hollow "tube" matching the slider (so that the latter is a sliding fit within the former) in both shape and crosssection dimensions. Indeed, while it could be a framework, or a series of mounting blocks secured together with a suitable spacing, the body preferably is actually little more than a hollow tube within which the slider moves and upon which the drum member is mounted.

When the device is used with the aforementioned manipulator mechanism the body is that part by which the device is mounted on the universal bearing. The mechanical connection between the body and the bearing may be achieved in any convenient way, but it is preferred that the device be mounted at the side of the bearing distant from the tool plate, and therefore the connection is conveniently made via an extension of the body beyond that recess "open" end past which the slider's slot projects (it will be seen that in such a case this "open" end of the recess is in practice merely a through aperture in the wall of the body). However, it is in practice most advantageous to so mount the rod/drive system motor combination in relation to the universal bearing that the centre of gravity of the whole lies within the bearing.This will usually require the drive system itself to be mounted in the bearing, part of it projecting on one side, part of it projecting on the other side, with the motor and drum member as close as possible to the centre of the bearing. If the bearing is large enough, then the flexible connector element can also pass within the bearing; otherwise it will pass through a suitably positioned aperture in the datum plate supporting the bearing.

The drum member (hereinafter referred to as the drum) is advantageously mounted for rotary motion (about the drum axis) in a plane within which lies the slider's longitudinal axis, though it is not impossible for an operative device to have the drum mounted otherwise-for example, with its axis normal to and intersecting the slider's longitudinal axis.

As is discussed in more detail hereinafter, the drum is preferably fairly thin (from end face to end face), and is internally slotted to allow the flexible connector element to pass within the drum from adjacent one end face to adjacent the other.

The drum may be drivably connectable to a motor in any suitable manner, though it is preferred to drive it via a coaxial spindle rather than in some other way (such as via a friction or cogged drive to its periphery).

Wound around the drum, and operatively connected to the slider, is the flexible connector element (hereinafter referred to as the connector).

When in position, the connector, which is conveniently an inextensible wire cable, is a taut loop interconnecting the drum and the slider. At least part of the loop lies within the slider's slot, and on either side of the slider the connector extends up to each end of the body's recess and coaxially of the slider so that any forces exerted between connector and slider are also coaxial of the slider. In order to avoid frictional and other problems, bearing surfaces are very preferably provided at each end of the body's recess, the connector then passing over these between slider and drum.Suitable bearing surfaces are simple pulley wheels appropriately mounted upon the body, each wheel conveniently being coplanar with the drum plane; naturally, the pulley wheel at the recess end beyond which projects the slider's slot extends down into the slot (so as to enable the connector to be aligned with the slider's longitudinal axis), and indeed it is convenient to utilize this fact to ensure that the slider (and the manipulator mechanism rod to which it is connected) is unable to rotate about its longitudinal axis.

The invention extends, of course, to a manipulator mechanism as described and claimed in the aforementioned Application No.

80/29,667, whenever using a drive system as described and claimed herein.

One 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 of the general type of the aforementioned Application No. 80/29,667, but using a drive device according to the invention.

Figure 2 is a part cut-away perspective view of a drive device according to the invention; Figure 3 is a sectional side view of the device of Figure 2; and Figures 4 and 5 are perspective and part-end views respectively showing details of the connector element arrangement used in the device of Figures 2 and 3.

Where possible, similar parts in the Figures (which are not to scale) have been given the same reference numeral.

The manipulator mechanism of Figure 1 comprises a tool plate (10) having upon its upper face three universal joints (as 11) 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 drive system according to the invention (19-shown in detail in the remaining Figures) by which an electric motor (as 20) drives a drum-wound connector element which is attached via pulleys (as 22, 23) to the upper end of and to a point lower down on the rod 12 (which slides within support body 24).

The motors can thus drive their rods 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 14 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 device of the invention is shown in more detail in Figures 2 to 5, and is perhaps the most clearly shown in Figure 3.

The device consists in essence of two concentric tubes with the inner tube 12 (the slider, part of the manipulator mechanism rod) sliding inside the outer tube 24 (the body). Force causing sliding movement is applied to the inner tube 12 by a multi-stranded twisted steel wire 21 passing up the bore of the tube to an anchor plug (31) at its top end (the right end as viewed).At the lower end (the left as viewed) the wire 21 is brought out through a slot 32 in the wall of the inner tube 12 and an aperture in the wall of the outer tube 24 to pass over an idler pulley 23 to a driving pulley (33-the drum) attached to the shaft of a drive assembly consisting of an electric motor and gearbox 20. After circling the drive pulley 33 three turns, the wire passes up to the opposite end of the outer tube 24 where it turns round a second idler pulley 22 back to a slotted screw wire tensioning device (34) which is part of the anchorage plug 31. The wire 21 thus in effect forms a taut endless loop linking the drive pulley 33 to the inner tube 12.

The three pulleys are supported by two blocks (35, 36) which are held by clamps and screws to the outer tube 24. Slots are provided in the outer tube 24 for the two idler pulleys, and it will be seen that the lower one 23 also engages with the slot 32 in the inner tube 12, so both stopping the inner tube from rotating and also determining the orientation of the whole device in its spherical bearing 13.

The inner tube 12 has an outside diameter somewhat smaller than the bore of the outer tube 24, so giving clearance between them; the anchor plug 31 at the top end of the inner tube is of a larger diameter so as to be a tighter sliding fit within the bore of the outer tube. At the lower end of the outer tube 24 a bearing (37) is provided to fit the outside diameter of the inner tube 12.

The position of the inner tube 12 is given by an encoder (41) driven directly from the drive pulley 33 with the datum being given by one of the end stops (at 42) in the form of L.E.D. and photo diodes; these are interrupted by a small blob (43) fixed to the free part of the wire 21. The wire terminations within the anchor plug 31 are simple blobs (44) of hard solder (or brazing metal) attached to the ends of the wire. These blobs 44 engage with female cones, one in the anchor plug 31, the other in the end of the adjusting screw 34.

The routing of the wire 21 round the drive pulley 33 is shown in Figures 4 and 5. The wire, being continuous at this point, first enters a slot (51) cut diagonally in the wall of the pulley in such a manner that it is deeper at one end that the other. This allows the wire to cross from one edge of the pulley to the other by passing beneath the windings on the periphery. The wire, after emerging from the slot, circles the pulley three times winding back towards the front edge before passing to the rear idler pulley 23. This method of winding causes the wire which is being wound on to take the same track as the wire that is being wound off, and allows a reduction in the width of the pulley to only 4 track widths. It also allows easy clamping of the wire by a screw (52) at the shallow part of the slot 51.

Claims (10)

Claims

1. A device for converting rotary reciprocatory motion into linear reciprocatory motion, and suitable for use, together with a motor, as the driving means for a manipulator mechanism as claimed in the Specification of Application for Letters Patent No. 80/29,667, which device comprises: an elongate slide member having a longitudinally orientated slot open at the slide member's surface and extending in depth inwards at least to the slide member's longitudinal axis; a support body containing an open-ended elongate recess within which the slide member is mounted for linear reciprocatory motion with its slot projecting beyond one end of the recess; a drum member mounted for rotary reciprocatory motion upon the support body and connectable to a motor for driving it in such motion; and a flexible connector element, effectively in the form of a taut closed loop, wound around the drum member and extending between the ends of the support body's recess wherein the connector element is attached to the slide member, lying within the slot therein on at least the side whereat the slot projects beyond the recess end, and wherein the connector element is so disposed that any forces exerted by it upon the slide member are substantially coaxial with the longitudinal axis of the slide member; such that in operation rotary reciprocatory motion of the drum member causes the connector element to be wound on and off the drum thus driving the slide member in linear reciprocatory motion within the support body's elongate recess.

2. A device as claimed in claim 1, wherein the slide member is a circularly cylindrical hollow tube with a length somewhat greater than the distance it travels from end to end of its reciprocatory linear motion.

3. A device as claimed in either of the preceding claims, wherein the support body is in effect no more than a hollow "tube" matching the slide member, so that the latter is a sliding fit within the former, in both shape and cross-section dimensions.

4. A device as claimed in any of the preceding claims, wherein the drum member is mounted for rotary motion (about the drum axis) in a plane within which lies the slide member's longitudinal axis.

5. A device as claimed in any of the preceding claims, wherein the drum member is fairly thin (from end face to end face), and is internally slotted to allow the flexible connector element to pass therewithin from adjacent one end face to adjacent the other.

6. A device as claimed in any of the preceding claims, wherein the drum member is drivably connectable to a motor via a coaxial spindle.

7. A device as claimed in any of the preceding claims, wherein, in order to avoid frictional and other problems, bearing surfaces are provided at each end of the support body's recess, the connector element then passing over these between slide member and drum member.

8. A device as claimed in claim 7, wherein the bearing surfaces are simple pulley wheels appropriately mounted upon the support body, each wheel being coplanar with the drum member plane.

9. A motion converting device as claimed in any of the preceding claims and substantially as described hereinbefore.

10. A manipulator mechanism as claimed in the Specification of Application for Letters Patent No. 80/29,667, whenever using a drive system as claimed in any of the preceding claims.