GB2103966A

GB2103966A - Work head assembly

Info

Publication number: GB2103966A
Application number: GB08220527A
Authority: GB
Inventors: Robert Alexander Shore; Joseph Roger Topping; John David Jones
Original assignee: British Aerospace PLC
Current assignee: BAE Systems PLC
Priority date: 1981-07-17
Filing date: 1982-07-15
Publication date: 1983-03-02
Also published as: DE3226605C2; JPS5828488A; GB2103966B; IT1148369B; FR2509648B1; FR2509648A1; DE3226605A1; IT8248849A0

Abstract

A workhead assembly 10 for machine tool apparatus - for example a robot having a movable arm - includes a mounting member 11 for attachment to the machine tool apparatus and a tool head 18. The tool head includes at spaced positions two tool arrangements 19 and 20, the tool head being pivoted on the mounting member by means of shaft 16, for movement between a position in which one of the tool arrangements 19 is in registration with a predetermined operating axis A and a position in which the other tool arrangement 20 is in registration therewith. <IMAGE>

Description

SPECIFICATION Work head assembly This invention relates to a work head assembly for attachment to machine tool apparatus and which includes at least two tool arrangements adapted alternately to be operable on a work piece.

In this Specification the term "machine tool apparatus" includes industrial machines such as robots, lathes, drilling machines etc.

By the term "robot" in this Specification is meant apparatus which includes a computer control system which enable the apparatus to be taught automatically to move an arm to a number of locations at predetermined orientations.

According to this invention, there is provided a work head assembly for machine tool apparatus, which assembly includes a mounting member to allow the assembly to be attached to the machine tool apparatus and a tool head, the tool head including at spaced positions at least two tool arrangements, the tool head being mounted on the mounting member by coupling means allowing displacement of the tool head relative to the mounting member between a position in which one of the tool arrangements is in registration with a predetermined operating axis and a position in which the other of the tool arrangements is in registration with said axis, there being drive means to effect displacement of the tool head between said positions.

Preferably, said drive means includes a vane actuator mechanism.

By way of example only, one specific embodiment of work head assembly of this invention will now be described in detail, reference being made to the accompanying drawing which is a schematic, part-sectioned side view of a work head assembly.

The embodiment of work head illustrated is intended to be attached to the roll plate or terminal flange of the arm of a Cincinnati Milacron T3 Industrial Robot for applications where a series of at least two machining operations are to be performed one after the other at a number of taught locations around the work piece. By way of example only, a series of operations may be the drilling and subsequent clipping of an aircraft skin to an associated sub-frame; the drilling and subsequent blind rivetting of an aircraft skin and associated sub-frame or the drilling and subsequent reaming of a hole. In each of the cited series, it is essential that the operating axes of the first and second operations are precisely aligned.

It is possible to teach a conventional robot to move its arm to a number of locations in sequence on a workpiece and whilst, when in a given position, the arm may be kept precisely in that position, it is found that the repeatability of positioning of the robot arm in the same location may not be sufficiently precise to allow the robot to perform the first operation of the series with one tool at one location, move its arm to a toolchanging location and change its tool and then return the arm to the same location with sufficient accuracy to allow the second operation properly to be performed. Moreover, the machine time involved in locating the arm for the first operation, performing the first operation, effecting tool change, repositioning the tool and performing the second operation for each taught location over the whole workpiece is relatively high.

In the following embodiment, two tool arrangements are mounted on a tool head which is movably mounted on a mounting member which is secured to a robot arm; in operation the arm is moved to a taught location and kept in that position whilst the two operations are performed one after the other, tool changing being effected by pivotting the tool head with respect to the mounting member. In this manner precise alignment of the operating axes of the first and second operations is ensured.

The embodiment of work head illustrated is adapted for use in the drilling and clipping of an aircraft skin to an associated subframe, and thus will be programmed to drill and countersink a hole and then to insert a clip into the hole to pull the skin against the subframe. This cycle of operations will be repeated for a number of locations and orientations about the work-piece and the robot previously will have been programmed to move its arm to each of these operating positions in turn.

The work head assembly 10 includes a mounting member in the form of a base plate 1 1 adapted to be secured to the roll plate of the arm of a robot. The base plate 11 includes a pair of lugs 12 (only one of which is shown) between which is secured the body housing 13 of a vane actuator 14. The vane 1 5 of the actuator is secured to a shaft 16 which is attached at each of its ends to one of a pair of lugs 17 provided on a rocking mount assembly 18. On operation of the vane actuator 14, the vane 1 5, together with the rocking mount assembly, are together displaced angularly with respect to the base plate 11. The rocking mount assembly 18 is provided with two tool assemblies, a drill head assembly 19 and a nut running assembly 20, spaced angularly by 67 2 about shaft 16.The rocking mount assembly includes a pair of steel inserts 21 and limit microswitches 22 which co-operate with adjustable stops 23 provided on the base plate 1 1 to limit the arc of movement of the rocking mount assembly between a position in which the drill head assembly 19 is aligned with an operating axis A (i.e. the position shown in the Figure) and a position in which the nut running assembly 20 is aligned with the operating axis A. It will be seen that the lines of action of drill head assembly 19 and nut running assembly 20, when each assembly is in its operating position, pass through the centre line of shaft 16, and the centre of base plate 11.

The drill head assembly 19 comprises a base support bracket 24 which is secured to the rocking mount assembly 18 and fixedly carries a pair of pillars 25 (only one of which is shown). A drill support bracket is mounted for sliding movement on the pillars 25 by means of a pair of bores.

Sliding movement is effected by means of a pair of pneumatic rams 27 acting between the base support bracket 24 and the drill support bracket 26, there being a micro-switch 24' to sense when the two are fully contracted.

A pneumatically-operated drill 28 is carried on the drill support bracket 26 by forward and rearward compliant mountings 29, 29' respectively, which allow a compliance of approximately 40. The compliant mountings each comprise mating spherical surfaces coated with a fluorocarbon. The compliant mountings may be preloaded to a desired degree by means of hollow bolt 30 secured to the rear end of the drill 28. The forward end of the drill 28 includes a drill head housing 31.

The nut running assembly 20 comprises a generally C-shaped bracket 32 which is secured to the rocking mount assembly 18. A pair of pillars 33 (only one of which is shown) extend between the limbs of the bracket 32 and slidably support a pneumatically-operated nut-runner 34. Sliding movement of the nut-runner 34 is effected by a pneumatic ram 35 housed in an extension of bracket 32, there being a micro-switch 34' to sense when the nut-runner 34 is fully retracted.

The nut-runner 34 may hold a skin clip, insert it into a drilled hole, and then run up the nut of the skin clip and tighten it to a desired torque locally to clamp the aircraft skin to the subframe at pressures of, typically 50-1 00 psi, and then release the clip.

In this specification, the term "skin-clip" is used to mean a device including a body portion having a longitudinal bore in which is slidably mounted a clip element. The clip element has a bifurcated portion the limbs of which are biassed apart and carry abutments which engage the lip of a drilled hole, and a threaded shaft portion. The limbs of the bifurcated portion extend through one end of the bore of the body portion whilst the threaded portion extends through the other end and carries a nut. Tightening of the nut causes the bifurcated portion to be retracted into the body portion.

A typical sequence of operation will now be described. At the starting position, the rocking mount assembly 18 is positioned so that the drill head assembly 19 is aligned with operating axis A.

The drill head assembly 19 is fully retracted with the drill motor stationary, and the nut runner assembly 20 is fully retracted. All these positions are electrically sensed and may be displayed on a panel.

The robot arm is automatically driven to its taught commencement position which aligns the drill assembly at a computed angle normal to the aircraft skin. It positions the assembly with the drill tip standing off from the skin by 10 mm. Once this position has been established, the control system for the work head assembly 10 is activated. Pneumatic rams 27 are activated to bring the pneumatically-operated drill 28 forward and thus bringing the tip of the drill and its housing 31 into contact with the aircraft skin, the housing 31 clamping the skin securely against the supporting sub-frame. When this has been achieved, the pressure in the pneumatic supply line to the pneumatic rams 27 rises to a stall condition and this is sensed by the control system which causes the pneumatically-operated drill to be activated.Once a hole has been drilled in the skin and the sub-frame, the drill is stopped and pneumatic rams 27 contracted to retract the drill assembly 1 9. Full retraction of the drill head assembly 1 9 is electrically sensed by means of a micro switch 24'.

The control system for the work head assembly 10 then activates the vane actuator 14 to rotate the rocking mount assembly 18 through 6730 SO that the nut running assembly 20 is aligned with the operating axis A. This action is assisted by means of the relevant insert 21 contacting associated stop 23 on the base plate 11 and causing the associated microswitch 22 to be operated. The nut running assembly 20, together with a skin clip is thus positioned directly over the previously drilled and countersunk hole but 10 mm away from the aircraft skin. Rams 35 are then actuated to drive the nut runner and the skin clip to move forward. This motion will continue until the skin clip has been fully entered into the previously drilled hole and the static nose of the nut runner has clamped the aircraft skin against its sub-frame.In this position, the pressure applied to the pneumatic rams 35 rises to the stall condition and this is sensed by the control system for the work head assembly 10. The control system subsequently causes the nut running assembly to be operated to run the nut up the skin clip up to the desired torque, thus tightening the skin clip into position. Once this has been achieved, the nut running assembly 19 is retracted to its starting position.

The robot is then driven until the nut running assembly is positioned in communication with a skin clip magazine, and a further skin clip then transferred to the nut runner 20.

The vane actuator 14 is then actuated to return the work head assembly 10 to its starting position.

The robot arm is then driven by its control system to its next pre-programmed location and the cycle repeated.

The above embodiment has been described with specific reference to a drilling and clipping operation. It should be emphasized that the invention extends to work head assemblies for performing any series of operations which require alignment of the first and second operating axes, for example drilling and rivetting.

Whilst the above embodiment has been described with reference to use of the work head on a Cincinnati Milacron T3 Industrial Robot, the work head may be used with other industrial machinery, for example a lathe.

The angular spacings of the two tool assemblies may be different from 6730, as convenient.

Claims

1. A workhead assembly for machine tool apparatus which assembly includes a mounting member to allow the assembly to be attached to the machine tool apparatus and a tool head, the tool head including at spaced positions at least two tool arrangements, the tool head being mounted on the mounting member by coupling means allowing displacement of the tool head relative to the mounting member between a position in which one of the tool arrangements is in registration with a predetermined operating axis and a position in which another tool arrangement is in registration with said predetermined axis, there being drive means to effect displacement of the tool head between said positions.

2. A workhead assembly according to Claim 1, wherein said coupling means are in the form of pivot means.

3. A workhead assembly according to Claim 2, wherein the tool head includes two tool arrangements, and stop means are provided to limit pivotting movement of the tool head between a position in which one of the tool arrangements is in registration with said predetermined operating axis and a position in which the other tool arrangement is in registration therewith.

4. A workhead assembly according to any of the preceding Claims, wherein said drive means include a vane actuator mechanism.

5. A workhead assembly according to any of the preceding Claims, wherein one of the tool arrangements comprises a drilling device and another tool arrangement comprises a rivetting device.

6. Robot apparatus including a movable arm, computer control means for moving the arm to a series of predetermined locations, mounting means attached to said arm and pivotally carrying a tool head, the tool head including at spaced locations two tool arrangements, the tool head being pivotable with respect to the mounting member between a position in which one of the tool arrangements is in registration with a predetermined operating axis with respect to the mounting member and a position in which the other tool arrangement is in registration with said predetermined axis.

7. A workhead assembly substantially as hereinbefore described, with reference to and as illustrated in, the accompanying drawing.

8. Robot apparatus, substantially as hereinbefore described, with reference to and as illustrated in, the accompanying drawing.