GB2168029A - Alignment devices - Google Patents

Abstract

An alignment device comprises an alignment unit 2 which aligns a tube 1 relative to an external hole. Unit 2 is coupled to an intermediate cage through a pair of mutually opposed bellows 4 and 5. The cage in turn is coupled to an outer fixed cage 6 through a pair of mutually opposed bellows 7 and 8 lying along a line orthogonal to bellows 4 and 5. Differential pressure between the bellows of a pair causes movement of unit 2 in one or other of respective orthogonal directions. Unit 2 includes four pressure chambers located around tube 1 and coupled to the respective bellows. Obstruction of one or more chambers caused by lateral misalignment of tube 1 relative to the external hole causes back pressure in the obstructed chambers which is coupled to the bellows and thus causes movement of unit 2 in a direction to reduce the back pressure. <IMAGE>

Description

SPECIFICATION Alignment devices This invention relates to alignment devices and is concerned with devices designed to align a member relative to an external hole. Such devices have application in robots. An important use of such a device is where the member is itself annular and has a central bore to enable hole-to-hole alignment to be provided. Hole-to-hole alignment is particularly useful where components are required to be fed into a hole in a workpiece or where fluids, whether liquids or gases, are to be supplied to a workpiece.

While many forms of robot have arms which can be aligned by external control, which may be programmed, such alignment is relatively coarse due to the weight of the arm and the lack of stiffness in the structure. Also the position of the workpiece may be ill-defined.

In published UK Patent Application No. 21 25768A there is described a manipulating unit for use with a robot arm comprising a housing in which there are: (a) position sensing means for sensing the position of a member in the housing, which member is coupled locally to tripping means, and (b) actuating means coupled to the sensing means and the member for producing movements of the member within the housing.

As described in the above-numbered specification, the unit is so designed that any movement of the member due to initial mislaignment thereof relative to a datum position in an external workpiece is amplified to tend to eliminate the misalignment. This is achieved in the units which are described by providing pneumatic nozzles as the sensing means, which nozzles are directed towards the member so that movement of the member towards the nozzle generates a back pressure. This back pressure is coupled to an actuating means positioned diametrically opposite the nozzle to move the member towards the nozzle thus amplifying the initial movement due to the misalignment and eliminating it.

Such an arrangement requires physical contact between the member and a workpiece to provide the initial movement which is thereafter amplified by the manipulating unit.

It is an object of the invention to provide an alignment device in which initial physical contact and resulting initial movement is not required.

According to the invention an alignment device comprises an inner member designed to be aligned relative to an external hole, opposed orthogonal pairs of sensors for sensing the lateral alignment of said member relative to a hole in a workpiece which sensors provide sensing signals, actuating means for providing lateral movement to the member in two independent orthogonal directions, coupling means between each pair of sensors and the correspondingly positioned actuating means for causing the actuating means to operate in accordance with the sensing signals to move the inner member in a direction to reduce the magnitude of the sensing signals.

In carrying out the invention the sensors may be pneumatic sensors and may each comprise a cham ber having for example a part annular outlet nozzle directed towards a workpiece, one annular wall of which chamber being constituted by the said inner member, the arrangement being such that an extraneous surface close to the nozzle causes the generation of a back pressure in the chamber.

Preferably also the actuating means are pneumatic actuating means, for example pairs of bellows, and the coupling means comprise air pipes which link the correspondingly positioned chamber to their actuating means so that each actuating means is operated by the back pressure in its associated chamber.

Alternatively the actuating means may be solenoid actuating means and the coupling means then comprise pressure sensors which provide an electrical signal to operate the solenoids.

In one preferred embodiment of the invention one pair of opposed actuating means is coupled between the inner member and an intermediate cage and another pair of opposed actuating means orthogonally disposed relative to said one pair is coupled between the said intermediate cage and an outer fixed cage.

The inner member may be annular and may have a central bore which in operation of the device is aligned coaxially with an external hole in a workpiece.

In order that the invention may be more fully understood reference will now be made to the accompanying drawings in which: Figure 1 is an underneath plan of an alignment device embodying the invention, Figure 1A is an expanded detail of part of Figure 1, Figure 2 is a plan view of the alignment unit, and Figure 3 is a sectional view of the base unit of Figure 2 along the lines AA.

Referring to Figures 1 and 1A an alignment device is illustrated which aligns a central tube 1 positioned within an alignment unit 2 so that tube 1 is coaxially aligned with an external hole in a workpiece (not shown). Alignment unit 2 is coupled to an intermediate cage 3 through a pair of mutually opposed bellows 4 and 5 so that any differential pressure in the bellows causes movement of unit 2 in a direction parallel to a linear axis XX. Intermediate cage is coupled in a similar mannerto an outer cage 6 through a pair of mutually opposed bellows 7 and 8.

Differential pressure between bellows 7 and 8 causes movement of intermediate cage 3 carrying with it alignment unit 2 in a direction YY orthogonal to the line XX. Outer cage 6 is fixed by being rigidly coupled to a robot arm 17. It will thus be seen that it is possible to move unit 2 in either of two mutually orthogonal directions by operation of one or other pair of the mutually opposed pairs of bellows 4,5 and 7, 8. Movement due to differential pressure by any one pair of bellows does not affect movement in the orthogonal direction in any way.

Pressure signals to operate the respective pairs of bellows are obtained by back pressures in two pairs of pressure chambers each supplied with air under pressure. A particular pressure chamber 9 representative of all four of the pressure chambers is shown in section in Figure 3. The chamber is located within alignment unit 2 and has one wall thereof defined by the outer surface of tube 1. Chamber 9 has an inlet orifice 10 through which air is supplied to the chamber and an outlet nozzle 13 in the underneath surface of unit 2. Nozzle 13 is of elongated partannular shape (as shown more clearly in Figure 1A).

If there is any obstruction postioned close to the underneath surface of alignment unit 2 and opposite nozzle 13, a back pressure will build up in chamber 9.

Chamber 9 is positioned close to bellows 4 and is connected thereto by an air coupling through an internal or external pathway. Thus any back pressure in chamber 9 will be communicated to bellows 4.

There is a total of four chambers all similar to chamber 9 and each chamber is positioned close to and is coupled to an associated bellows. Thus if any one chamber of a pair has its nozzle obstructed to a greater degree than the nozzle of the other chamber of a pair, there will be a difference in the back pressures built up in the respective chambers and thus there will be a pressure difference in the two bellows of a pair causing movement of the alignment unit 2.

The alignment device is designed for operation so that it positions alignment unit 2 in a manner two align tube 1 coaxially close to a hole in a workpiece. If unit 2 is properly aligned and tube 1 is coaxial with such a hole, then all four of the nozzles will be equally obstructed and there will be no pressure differential in any pair of bellows. Should, however, there be misalignment, for example in the XX direction, then one of the nozzles of the chambers 9 and its partner chamber 11 will be less obstructed than the other nozzle. There will thus be a difference in back pressure in the two chambers 9 and 11 which will communicate to the corresponding bellows 4 and 5 and thus cause movement of unit 2 in a direction parallel to the axis XX.The direction of movement will be such as to reduce the back pressure in the nozzle facing the obstruction and to increase the back pressure in the chamber the nozzle of which is facing the hole. Thus the movement will cease when the obstructions opposite the two nozzles of a pair are equal and this will occur when the alignment along the XX direction between the bore of member 1 and the hole in the workpiece is exact. A similar alignment will occur independently along the YY direction. Any misalignment is therefore corrected by a motion which tends to reduce the pressure differential.

An alternative actuation force can be provided by the use of two proportional action solenoids, one operating on each cage. The hole detection is still performed using pneumatic sensing, but the outputs from the sensing element are converted to electrical signals and processed by a control algorithm to provide an actuating signal which is outputted to the solenoids to drive the alignment unit. To reduce the cost only two solenoids need be used positioned orthogonally and balanced against return springs.

The solenoid version of the device has the advantage that it provides somewhat larger actuating forces, and highly sophisticated control algorithms can be implemented relatively simply.

Claims (8)

1. An alignment device comprising an inner member designed to be aligned relative to an external hole, opposed orthogonal pairs of sensors for sensing the lateral alignment of said member relative to a hole in a workpiece which sensors provide sensing signals, actuating means for providing lateral movement to the member in two independent orthogonal directions, coupling means between each pair of sensors and the correspondingly positioned actuating means for causing the actuating means to operate in accordance with the sensing signals to move the inner member in a direction to reduce the magnitude of the sensing signals.

2. The device as claimed in Claim 1 in which the sensors are pneumatic sensors.

3. The device as claimed in Claim 2 in which each sensor comprises a chamber having a part annular outlet nozzle directed towards a workpiece, one annular wall of which chamber is constituted by the said inner member and the arrangment being such that an extraneous surface close to the nozzle causes the generation of a back pressure in the chamber.

4. The device as claimed in any one of the preceding claims in which the actuating means are pneumatic actuating means and the coupling means comprise airpipes which link the correspondingly positioned chamber to their actuating means so that each actuating means is operated by the back pressure in its associating chamber.

5. The device as claimed in Claim 1 or Claim 2 in which the actuating means comprises solenoid actuating means and the coupling means comprise pressure sensors which provide an electrical signal to operate the solenoids.

6. The device as claimed in any one of the preceding claims in which one pair of opposed actuating means is coupled between the inner member and an intermediate cage and another pair of opposed actuating means orthogonally disposed relative to said one pair is coupled between the said intermediate cage and an outer fixed cage.

7. The device as claimed in any one of the preceding claims in which the inner member is annular and has a central bore which in operation of the device is aligned coaxially with an external hole in a workpiece.

8. An alignment device substantially as described herein with reference to the accompanying drawings.