GB2283797A

GB2283797A - Linkage drive mechanism

Info

Publication number: GB2283797A
Application number: GB9421834A
Authority: GB
Inventors: Gregory Vines
Original assignee: BRUNEL UNIVERSITY OF WEST LOND
Current assignee: BRUNEL UNIVERSITY OF WEST LOND
Priority date: 1993-11-15
Filing date: 1994-10-28
Publication date: 1995-05-17
Also published as: GB9421834D0

Abstract

A drive linkage for translating rotary motion from an output shaft (10) of a motor to swinging movement of 8 driven arm comprises a housing (14), an input member (11) having a surface oblique to the output shaft (10) and connected to the shaft and is about a first axis (A), a first axle perpendicular to the oblique surface (11), an intermediate member (12) mounted to the first axle and rotatable about a second axis (D) of the first axle, and an output member (13) coupled by a second axle to the intermediate member (12) to rotate relative thereto about a third axis (B) perpendicular to the second axis (D). The output member (13) is coupled to the housing (14) by a third axle and rotatable relative about a fourth axis (C) perpendicular to the first axis (A). The output member (13) is in use connected to the driven arm so as to cause it to swing about the fourth axis (C). The drive linkage is suitable for use with robots and enables the motor to be located remote from the driven arm, simplifying the design without disadvantages of prior art arrangements. <IMAGE>

Description

LINKAGE MECHANISM DRIVE This invention concerns a drive linkage mechanism.

In the field of robots, a major concern is the provision of controllable driving forces to the linked members of a robot arm to achieve movement and positioning of the final 'hand'.

There are two approaches to this: either individual drive motors are located actually at the 'shoulder', 'elbow' and 'wrist' (so-called 'direct drive'); or the drive motors are remote, e.g. on a fixed base, and there is a transmission linkage to the respective driven member. The former is generally favoured, but is expensive and subject to a number of other technical disadvantages. The latter has disadvantages which have been up to now greater than those of direct drive.

It is the aim of the invention to provide an improved drive linkage mechanism which will make remote motors the more attractive and advantageous option.

According to an aspect of the present invention, there is provided a drive linkage for translating rotary motion of a rotating member to swinging movement of a driven arm comprising support means; an input member connectable to a rotating member and rotatable about a first axis relative to the support means; first axle means disposed at an angle to the input member to provide rotation about a second axis at an angle to the first axis; an intermediate member mounted to the first axle means and rotatable about the second axis; and an output member coupled by second axle means to the intermediate member so as to be rotatable relative thereto about a third axis, the output member being coupled to the support by third axle means and rotatable relative to the support about a fourth axis substantially perpendicular to the first axis, the output member being connectable to a driven arm and operative to provide swinging movement about the fourth axis.

Preferably, the input member includes a surface oblique to the first axis, the first axle means extending substantially perpendicular to the oblique surface.

Advantageously, the first axle means includes first bearing means between the intermediate member and the oblique surface.

The second and third axle means are preferably disposed such that the third and fourth axes are substantially perpendicular to one another.

In the preferred embodiment, the output member encircles the intermediate member, the second axle means including a pair of axles at opposing sides of the output member coupling the output member to the intermediate member. The third axle means may include a pair of axles at opposing sides of the output member coupling the output member to the support means at two points of support, the axles of the second and third axle means lying substantially perpendicular to one another.

Bearing means are preferably fixed to the support means for locating the rotating member relative to the support.

The present invention is also directed to an automated device including a motor having an output shaft, an arm member and a drive linkage of the type specified coupling the output shaft to the arm member.

Accordingly the invention proposes a drive linkage mechanism in which rotation of an input shaft is converted into swinging movement of a driven arm. The arm may be mounted on a gimbal-like frame supported between a fixed bearing, the axes of which intersect the axis of the input shaft, and the input shaft.

Such a mechanism (hereinafter referred to as a 'gimbal drive') allows the efficient use of remote motors in robots, the mechanism being located with the respective drive motor on a fixed base. The 'direct drive' approach previously favoured is no longer so advantageous, and the balance is tipped in favour of remote drives.

In order that the invention shall be clearly understood, an exemplary embodiment thereof will now be described with reference to the accompanying drawings, in which: Fig. 1 shows a mechanism according to the invention in front view, with the input shaft at 0 relative to the housing; Fig. 2 shows the mechanism of Fig. 1 in side view; Fig. 3 shows a section centrally through Fig. 2 in the plane of the paper; Figs. 4 to 6 show view corresponding to Figs. 1 to 3 but with the input shaft twined through 90 relative to the housing; Fig. 7 shows the output motion of an arm fixed to the outer ring; Fig. 8 shows a schematic diagram of a robot arm using 'gimbal drives' to transmit motion from fixed motors.

A gimbal drive is a novel mechanism which transfers rotation of an input shaft to swinging of an output link with a perpendicular axis. It has a non-linear transfer characteristic with limited output travel. Devised as an output actuator relocation device for use within the design of robots, it can markedly reduce the size of the motors required.

The gimbal drive fills the gap between conventional transmissions (which suffer from high friction loss, compliance, backlash, and require regular maintenance) and direct-drive (which overcomes those problems but cannot be made cost effective due to its extreme motor requirements). It can be considered as a "direct" transmission.

A gimbal drive consists of 3 moving parts: an input shaft 10 with an oblique end face 11; an inner ring 12; an outer ring 13; and a housing 14, see Figures 1 to 6.

The oblique end face 11 has significant diameter and is cut off at some non-zero angle 6c The shaft 10 is mounted in the housing and is free to turn about its axis (axis A).

The inner ring 12 and outer ring 13 form a gimbal arrangement, with the outermost axles going into the housing 14.

This gimbal is positioned onto the cut-off surface 11 of the shaft 10 such that axes A, B, C, and D intersect at point P.

More specifically, the inner ring 12 provides two axes of rotation. The first axis D is provided by shaft 20 which is fixed to the oblique shaft 11 and extends substantially perpendicular to the oblique surface thereof. This axis D is the axis about which the inner ring 12 rotates during rotation of the input shaft 10.

The second axis B is provided by drive point bearings 22 which are located at the outer perimeter of the inner ring 12 in opposing relationship. The drive point bearings 22 couple the outer ring 13 to the inner ring 12 such that the outer ring 13 can pivot relative to the inner ring 12 about axis B.

The outer ring includes a second axis of rotation, namely axis C, which is perpendicular to its other axis of rotation, that is axis B. Axis C is provided by bearings 24 located at opposite sides of the outer ring 13 and extending into the housing 14. The bearings 24 cause the outer ring 13 to rotate around a single axis of rotation (axis C) relative to the housing.

The input shaft 10 forms the input axle of the device and the output is. provided by the outer ring 13. In use, the input would be driven directly by the motor for that joint.

The outer ring would be bolted to/integral with one of the links of the arm. To achieve the maximum benefit, the motor would be a low speed torque motor, involving no gearing within it.

The gimbal drive may be considered to be an end cam with a large number of followers (=number of rolling elements within the main thrust bearing).

The retaining bearing and shaft are not essential to the operation of the drive but they improve the drive's stiffness by enforcing contact between the oblique shaft and inner ring, thereby providing a direct means of preloading the main thrust bearing.

In operation, turning the input shaft causes the cut-off surface 11 to describe a path normal to a conic (with apex at point P). This motion is composed of 3 components: a simple rotation about axis D, and rotary oscillations about axes B and C.

The main thrust bearing absorbs the rotation about axis D and transmits the 2 rotary oscillations to the inner ring.

The driving point bearings absorb the component about axis B, transmitting the final component to the outer ring which rotates cyclically about axis C, which is the output axis.

The motion of the outer ring (for a continuous input rotation) is shown in figure 7. The output travel is from -ec to +etc.

There are two main novel features of gimbal drives which makes their use beneficial within robots: Actuator Relocation to a Perpendicular Axis: As the gimbal transfers motion to a perpendicular axis, it is possible to site the 3 main motors on the base of a robot arm so that they remain stationary. (Fig. 8). This greatly reduces the loading on the motors, hence allowing them to be smaller and cheaper. Existing actuator relocation mechanisms, of comparable directness, transfer torque to a distant but parallel axis. It is envisaged that the output shafts of the elbow and shoulder transmissions would have the same axis so as to allow a parallel linkage to be used to drive the elbow, thereby simplifying kinematics.

Non-constant Mechanical Advantage: As can be seen in figure 9, a gimbal drive reflects less of the link torque back to the actuator as the extremes of link travel are approached.

This increased mechanical advantage may be arranged to coincide with the link angles where the gravity loading is the largest, thereby reducing peak torque requirement. A reduction of 20W is expected for the shoulder joint of the proposed topology. Transmissions used within existing robots exhibit constant mechanical advantage.

Both of these benefits may be harvested simultaneously. The topology shown in figure 8 achieves this.

The drive is simple and rugged, with no rubbing contacts, so it will be reliable and require little maintenance. It possesses low compliance and no backlash. Furthermore, as it is antagonistic in nature, structural stiffness may be enhanced and bearing play reduced by means of preloading.

Finally, it requires no intricate fabrication techniques.

All the relocation devices in use within current directdrive arms relocate motion to a parallel axis, precluding 3 degrees of freedom relocation.

The use of gimbal drives will enable the production of new robot design which out-perform current models in real terms.

By reducing the motor costs, direct transmission arms will be able to offer direct-drive qualities at significantly lower product cost. The lower torque demands improve efficiency, thereby reducing operating costs.

The invention may also find application in flexible automation equipment.

Claims

1. A drive linkage for translating rotary motion of a rotating member to swinging movement of a driven arm comprising support means; an input member connectable to a rotating member and rotatable about a first axis relative to the support means; first axle means disposed at an angle to the input member to provide rotation about a second axis at an angle to the first axis; an intermediate member mounted to the first axle means and rotatable about the second axis; and an output member coupled by second axle means to the intermediate member so as to be rotatable relative thereto about a third axis, the output member being coupled to the support by third axle means and rotatable relative to the support about a fourth axis substantially perpendicular to the first axis, the output member being connectable to a driven arm and operative to provide swinging movement about the fourth axis.

2. A drive linkage according to claim 1, wherein the input member includes a surface oblique to the first axis, the first axle means extending substantially perpendicular to the oblique surface.

3. A drive linkage according to claim 2, wherein the first axle means includes first bearing means between the intermediate member and the oblique surface.

4. A drive linkage according to claim 1, 2 or 3, wherein the second and third axle means are disposed such that the third and fourth axes are substantially perpendicular to one another.

5. A drive linkage according to any preceding claim, wherein the output member encircles the intermediate member, the second axle means including a pair of axles at opposing sides of the output member coupling the output member to the intermediate member.

6. A drive linkage according to claim 5, wherein the third axle means includes a pair of axles at opposing sides of the output member coupling the output member to the support means at two points of support, the axles of the second and third axle means lying substantially perpendicular to one another.

7. A drive linkage according to any preceding claim, comprising bearing means fixed to the support means for locating the rotating member relative to the support.

8. A drive linkage substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

9. An automated device including a motor having an output shaft, an arm member and a drive linkage according to any preceding claim coupling the output shaft to the arm member.

10. An automated device according to claim 9, wherein the device is a robot.