GB2143498A - Improvements in or relating to assembly robots - Google Patents

Abstract

A robot arm 1 is connected at one end to a support 2 and at the other end to a gripper 3 via pivot 4. The main central portion of the arm 1 consists of a telescopic column 5, which is connected at the support 2 by a ball joint 6, so that the column 5 is free to move in any direction substantially orthogonal to its longitudinal axis. Disposed equiangularly around the column 5, are three extensible screw-threaded rods, two being shown at 7 and 8, within sleeves 9 and 10, respectively. The rods 7 and 8 can be screwed in either direction within their sleeves 9 and 10 by motors. The arm 1 can be extended or retracted in the directions of arrow A by simultaneous and equal extension or retraction of the rods within their sleeves. Furthermore, by extension of only one or two of the three rods, the arm can be caused to move in any direction substantially orthogonal to directions A, such as those shown by arrows B and C. <IMAGE>

Description

SPECIFICATION Improvements in or relating to assembly robots This invention relates to assembly robots and in particular, though not exclusively to an arm for such a robot.

Assembly robots are usually provided with one or more arms, which each have a gripper connected to the end thereof. The arm is capable of being manipulated by driving motors, so that the gripper can pick up and assemble items in accordance with a work sequence which the robot has been programmed to perform.

The robot arm generally comprises an upper portion pivotally connected, at one end, to an end of a lower portion, the upper portion also being capable of rotational movement about its longitudinal axis. The robot gripper is pivotally connected to the other end of the lower portion. Driving motors are provided to manipulate each portion and the gripper of the arm.

However, this rather complex construction can be relatively heavy, which thus requires powerful driving motors and furthermore influences the speed at which the arm can move.

Moreover, a substantial number of highly accurate gearboxes may be required to ensure that sufficiently accurate manipulation of the arm is effected.

It can thus be invisaged that, inter alia, these factors can cause the manufacturing and maintenance costs associated with the robot arm to be considerable.

It is therefore an object of the present invention to provide an improved arm for an assembly robot, which is substantially lighter and simpler in construction and operation than robot arms known heretofore.

According to the invention there is provided an arm for an assembly robot consisting of telescopic means to permit extension and retraction of the arm substantially along a longitudinal axis thereof and actuating means for causing said extension and retraction and for causing movement of the arm in at least one direction substantially orthogonal to said longitudinal axis.

Preferably the telescopic means consists of a telescopic column forming the main central portion of the arm.

One end of the column is preferably connected to the main body of the robot by a ball joint, so that the free end of the column can move without rotation in any direction orthogonal to its longitudinal axis, this free end preferably having a gripper connected thereto.

The actuating means preferably includes at least one motor-driven extensible rod, one end of which is connected to the telescopic column, so that the column is caused to move in a direction substantially orthogonal to its longitudinal axis by extension or retraction of the rod or rods.

The arm is preferably provided with three motor-driven extensible rods disposed at equally-spaced positions around the central column, each rod having a driving motor at one end thereof and being attached to the column at the other end thereof, thereby causing movement of the central telescopic column in substantially all directions orthogonal to its longitudinal axis, as well as extension and retraction thereof along its longitudinal axis.

The arm is preferably provided with further actuating means, consisting of relatively smaller driving motors than those used to move the central column, for causing movement of the end of the column, to which the gripper is attached, and of the gripper itself.

The invention will now be further described by way of example only with reference to the accompanying drawings, wherein: Figure 1 shows a preferred embodiment of the invention, Figure 2 shows a more detailed view of the embodiment shown in Fig. 1, and Figures 3 to 8 show examples of different types of grippers which may be used in conjuction with the embodiment shown in Figs. 1 and 2.

A robot arm is shown generally at 1 in Fig.

1, the arm being connected at one end to a support 2 and a gripper 3 being connected at the other end by a pivot 4. The main central portion of the arm 1 consists of a telescopic column 5, which is connected at the support 2 by a ball joint 6, so that the column 5 is free to move in any direction substantially orthogonal to its longitudinal axis.

Disposed around the column 5, at equally spaced angular intervals, are three extensible screw-threaded rods, two being shown at 7 and 8, within sleeves 9 and 10 respectively.

The rods 7 and 8 are screwed in either direction within their sleeves 9 and 10 by motors accommodated respectively in motor housings 11 and 12, which are connected by pivots 13 and 14 to the support 2. The other ends of the rods 7 and 8 are connected at end 1 5 of the column 5 by ball joints 16 and 1 7, respectively.

The arm 1 can therefore be extended or retracted in the directions of arrow A by simultaneous and equal extension or retraction of the rods within their sleeves, the rods being driven by their respective motors accommodated within their housings.

Furthermore, by extension of only one or two of the three rods, the arm can be caused to move in any direction substantially orthogonal to directions A, such as those shown by arrows B and C.

Fig. 2, wherein like parts are labelled with like references numerals with respect to Fig.

1, shows a more detailed view of the pre ferred embodiment shown in Fig. 1. It can be seen from Fig. 2 that the telescopic column 5 has two motors, 1 8 and 19, disposed therewithin, each being used to power an extensible drive, 20 and 21 respectively which extends therefrom, along the column 5 to the end 1 5. The end 1 5 contains a control mechanism (not shown), which will be described hereinafter. The control mechanism is driven by fast rotation of the drives, 20 and 21, and provides movement of the gripper 3.

The drives 20 and 21, preferably each consist of a rod accommodated within a tube, the rod and tube both having a square cross-section.

An additional motor 22 is also incorporated to provide further movement of the gripper 3.

Motors 18, 19 and 22 are not required to be as large as the other motors, which extend and retract the rods, as they provide relatively small, intricate movements of the gripper 3.

The drives for motors 18, 1 9 and 22 are preferably recirculating ball screws, which have the advantage of reducing backlash of the control mechanism.

It may be preferable to reposition pivots, 1 3 and 14, of the housings, 11 and 12, to a point forward of the housings towards end 1 5 of the column 5, thereby causing the motors in housings, 11 and 12, to act as counterweights against the weight of the end 15, at which the gripper 3 is situated and any item that the gripper is gripping.

It can be seen that the robot arm, in accordance with the present invention, has a number of advantages over conventional arms, one being that it has extra rigidity, thereby allowing the arm to extend further to cover more expansive areas and to provide improved operation at such extensions.

Additionally, the simple construction of the arm enables it to be made considerably lighter than conventional arms, which substantially reduces costs of control circuitry, as well as manufacturing costs, as smaller size motors can be utilised.

Another advantage of the present invention is that the positional geometry required to calculate the lengths of the three rods for any given x, y and z co-ordinate positions, to which the gripper is required to be moved, is substantially simpler than the geometry required for conventional robot arms. Movement of the arm can thus be programmed as linear movements of the rods, rather than angular movements, as required in conventional arms.

Certain regions of the workpiece, which the robot is required to assemble, may be inaccessible by the gripper, due to the rigidity of the arm, but however this problem can be easily overcome by rotating the workpiece on a turntable or by choosing a suitable gripper which is capable of reaching these regions.

Various alternative types of gripper are shown in Figs. 3 to 8, each being capable of being manipulated into different attitudes.

Fig. 3 shows a gripper 3 with a conventional head 23. It can be seen that drive 20 provides rotation in direction D and drive 21 is a worm drive which provides rotation of the head 23 in directions E and F.

Fig. 4 shows a similar gripper which uses the small motor 22 to rotate the gripper 3 in direction G, drive 20 providing rotation in direction H and drive 21 providing rotation in direction I.

Figs. 5 and 6 show a gripper having a linkage driven by a recirculating ball thread, which provides rotation in directions J and K, due to pivots 26 to 29, small motor 22 providing rotation of the gripper 3 in direction L.

Fig. 7 illustrates the use of three rotational axes at 90 to each other, with pivot points at 30 and 31, thereby providing rotation in directions M, N and 0. This arrangement covers substantially all possible attitudes of the gripper 3, but may add considerable complications to the software required for operation of the robot.

Fig. 8 shows a gripper arrangement which makes use of the redundancy which occurs in the other described arrangements, wherein, when the gripper is at a 0, to 90 angle to the horizontal, it covers the same region as when it is at 90 to 180 when rotated through 1 80' about a vertical axis. This use is implemented by two respective 90 rotations about two axes at 45 to the vertical in directions P and Q, thereby dropping the gripper to the position shown by the broken lines at 33. This enables the gripper, which is also pivotted at 32 to provide rotation in direction R, to cover an otherwise inaccessible region.

Other alternative types of gripper will of course be envisaged by persons skilled in the art.

The present invention therefore provides a robot arm of simple, light and relatively rigid construction, which improves the accuracy of operation of the robot and alleviates the need for some of the powerful motors required in conventional arms, thereby substantially reducing the costs of manufacture and operation.

Claims (11)

1. An arm for an assembly robot consisting of telescopic means to permit extention and retraction of the arm substantially along a longitudinal axis thereof and actuating means for causing said extension and retraction and for providing movement of the arm in at least one direction substantially orthogonal to said longitudinal axis.

2. An arm as claimed in Claim 1 wherein said telescopic means consists of a telescopic column forming a central portion of the arm.

3. An arm as claimed in Claim 2 wherin a first end of said column is provided with a ball joint for connection to a main body of the robot, thereby permitting displacement of the free end of said column in any direction orthogonal to said longitudinal axis.

4. An arm as claimed in Claim 2 or 3 wherein a gripper portion is pivotally connected to a second end of said column.

5. An arm as claimed in any preceding claim wherein said actuating means includes at least one motor-driven extensible rod, one end of which is pivotally connected to the telescopic means, so as to cause said extension and retraction and to provide said movement thereof.

6. An arm as claimed in Claim 5 wherein three extensible rods are disposed at substantially equally-spaced angular intervals around said telescopic means, thereby providing said movement in substantially all directions.

7. An arm as claimed in any one of Claims 4 to 6 wherein further actuating means are provided for effecting movement of said gripper portion.

An arm as claimed in Claim 7 wherein said further actuating means includes a control arrangement accommodated within said second end of said column.

9. An arm as claimed in Claim 8 wherein said control arrangement comprises means for effecting rotation of said gripper portion about at least two substantially orthogonal axes.

10. An arm for assembly robot substantially as herein described with reference to the accompanying drawings.

11. An assembly robot provided with at least one arm as claimed in any preceding claim.