GB2053060A - A positioning device for a workpiece welding or re-lining head - Google Patents

Abstract

A positioning device for positioning a workpiece welding or relining head 40 with respect to a conical or, as shown, cylindrical surface comprises a positioning arm 1 together with a head carrier arm 2, and a drive system 3 capable of moving the head carrier arm 2 in three perpendicular directions to allow three dimensional displacement of the head 40. The positioning arm 1 is pivotally mounted on a support block 31 on the free end of an arm 30 and, upon actuation of a jack 17, pivots under gravity from an upper, rest position to a lower working position in which rollers 11 on the arm 1 engage the workpiece internal surface. A means 12 locating the head axially of the workpiece is held against a workpiece abutment 43 by a spring 14. <IMAGE>

Description

SPECIFICATION Positioning device for a workpiece welding or re-lining head THIS INVENTION relates to a positioning device for accurately and continuously positioning a welding or re-lining head at the end of a relatively long arm.

A positioning problem of this kind arises, for example, in connection with the welding or steel tubes on the mountings of a nuclear reactor vessel. Tubes for a vessel of this kind generally have an inside diameter of about 1 metre, and if tubes of this kind are to be welded on the vessel mountings the welding head has to be introduced inside the tube and the hollow journal of a manipulator for a length of some 7 to 8 metres. Another example of an application for a positioning device is in the re-lining of the inside of a tube using strip metal.

Known devices for positioning a working head under such circumstances use a control loop by means of which a relative offset of the working head in relation to its correct position produces a correction signal which controls the device for moving the head, so that it is brought into a correct position with respect to the work to be carried out. A system of this kind operates by alternate movements with play, and not only has a considerable response and displacement time, but also a minimum operating threshold beyond which the system does not respond. The accuracy of positioning carried out with such a control system is therefore limited.This lack of accuracy is further aggravated and becomes unacceptable when bevelled edges requiring to be welded have radii of curvature of some metres, and this situation deteriorates still further if significant temperature variations are taken into account.

The invention aims to solve the problem of providing a positioning device capable of positioning a re-lining or welding head continuously and rapidly with high accuracy, irrespective of the three-dimensional irregularities of the workpiece.

The principle on which the device according to the invention is based is that the device vertically follows the workpiece by gravity, thus avoiding any oscillatory movement and providing the required accuracy at all times without any delay and without any limit. For horizontal movement, gravity is replaced by a considerable pneumatic force of spring force, operating in only one direction.

In the case of the particular applications in mind, the problems to be solved in providing a suitable positioning device are as follows: (a) The play due to diameter differences (wear) or temperature variations, for example, must be taken up automatically; and (b) Any vibration which would reduce the accuracy of positioning must be avoided.

The positioning device according to the invention is adapted to solve these problems, thus providing a remarkably accurate continuous positioning in every possible case.

According to the invention, there is provided a positioning device comprising: an arm carrying at a free end thereof a working head; a support block on which the head-carrier arm is mounted; a positioning arm mounted on the support block parallel to the head-carrier arm so as to be pivotable in a vertical plane, the positioning arm carrying at least two positioning rollers at its free end; a retaining device connecting the support block and the positioning arm, said device having a first stage in which said positioning arm is held in a raised position when the positioning device is in a rest position, and having a second state in which said positioning arm is released or pushed to increase the gravity effect; a return device connecting the positioning arm and the support block in order to hold said positioning arm in the working position by a tractive force when the retaining device is in its second state.

In an embodiment of the invention, the head-carrier arm is connected adjacent said head to the positioning arm by coupling means exerting a thrust or tractive force on the head-carrier arm irrespective of the relative movements of the head-carrier arm and the positioning arm in the three directions in spece.

In order that the invention may be readily understood, embodiments thereof will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is an elevation of one embodiment of the positioning device according to the invention in a rest position; Figure 2 is an end view of the device in the rest position; Figure 3 is an elevation of the device according to Fig. 1 in a working position on a cylindrical surface; Figure 4 is an end view of the device in the working position; and Figures 5 and 6 are respectively an elevation and plan view showing another embodiment of the positioning device according to the invention.

Referring to Figs. 1 to 4, a positioning device 10 embodying the invention is equipped with a welding head 40. In Figs. 1 and 2 the positioning device 10 is shown in a rest position, partially engaged inside a cylindrical tube 20 which is to be welded on a mounting formed on the body of a nuclear reactor vessel (not whosn). The positioning device 10 is fixed to the end of an arm 30 which conventionally is extremely long (e.g. 7 to 10 metres). The welding head 40 delivers a welding wire 41.

The positioning device 10 comprises a posi tioning arm 1, a head-carrier arm 2, and a drive system 3 to move the arm 2 in three directions: the axial direction of the tube 20, the direction in the plane of the drawing perpendicular to the axial direction, and the direction perpendicular to the plane of the drawing. The positioning arm 1 has a free end carrying two positioning rollers 11 and a stop device 12, the functions of these parts being described hereinafter. At its other end, the positioning arm 1 is mounted on a support block 31 fixed to the end of the arm 30. The arm 1 is mounted on block 31 through the agency of a pivot 13, an articulation arm 15 and a second pivot 16. Pivot 13 is connected to the support block 31 by a spring 14 (or a pneumatic jack if required), which pulls arm 1 towards arm 30.Arm 1 is also connected to the support block 31 by a hydraulic jack 17 which, in the rest position, holds the point 18 of the arm 1 pulled towards the arm 30 thus locking arm 1 in a slightly upwardly inclined position.

The head-carrier arm 2 is connected to the positioning arm 1 through the agency of a pneumatic jack 21 which is so actuated as to maintain the application of a force to the arm 2, whereby the latter is in a state of prestressing under flexure. This prestressed state of the arm 2 takes up all the play of the guides and nuts for the three-dimensional movement, thus preventing any vibration of the arm and hence of the head 40, while allowing three-dimensional displacement of the head 40 with respect to the positioning arm 1.

In the rest position shown in Fig. 1 the positioning device 10 is introduced axially into the tube 20 requiring to be welded, lined or re-lined. In this rest position of the positioning device, arm 1 is inclined with its head upwards and the rollers 11 together with the stop device 12 are suspended in the air as shown in Fig. 2. The positioning device 10 is introduced into the tube in this way until the head 40 reaches just beyond the working zone 42 in Fig. 3. The positioning device is then put into the working position shown in Fig. 3.

To bring the positioning device 10 into the working position, jack 17 is actuated to release the arm 1 so that it pivots about pivot 13 by gravity. Jack 17 may also be designed to push the arm 1 in order to augment the effect of gravity. During this pivoting movement, the rollers 11 and the stop device 12 are lowered until they rest freely on the inner wall of the tube 20 as shown in Fig. 4. By withdrawing the arm 30 in a sense to retract the positioning device from the tube 20, the spring 14 is caused to exert a tractive force on the pivot 13 and on the positioning arm 1 and the stop device 12 comes into engagement with an abutment 43 provided in the tube 20, thus holding the positioning device 10 perfectly in the desired axial position. In a nuclear reactor tube, abutment 43 is normally the edge of the rust-proof lining provided on the inner surface.Compression of the spring 14 allows axial movements of the abutment 43 and enables the stop device 12 to follow these movements axially, device 12 being continually applied against the abutment 43 by the spring 14. A limit contact 19 stops the withdrawal movement when the tube 20 has reached half its axial displacement. The jack 21 applying a force to the arm 2 holds the welding head 40 in a stable and rigid position with respect to the connection between the arms 2 and 1. It is then an easy matter for the operator to control the three-dimensional movement of the arm 2 with respect to the arm 1 when the progress of the weld so requires. The accuracy and stability of positioning of the welding head 40 enable the operator to carry out accurate adjustment, for example, of the lowest point of the weld, this being an important factor as regards weld quality.

In the example described above, the tube 20 has a cylirldrical inner surface but the positioning device 10 can, of course, equally well be used with a tube having a conical inner surface.

Figs. 5 and 6 show another embodiment of the positioning device intended more particularly for the positioning of a strip re-lining head for cases in which the successive relining positions extend over a certain length.

Reference 51 denotes the re-lining strip guided by the head 50. The difference between the embodiment shown in Figs. 5 and 6 and the embodiments shown in Fig. 3 is the addition of a double-parallelogram articulation system 52 and 53 by means of which the positioning arm 1 is mounted on the support block 31. Parallelogram 53 is connected to the retaining device 17 and parallelogram 52 is connected to the return device 14. This system provides accurate positioning of the strip 51 despite the relatively considerable axial movements of the tube for relining and hence of the stop device 12, head 50 then perfectly following the movement of the roller 12 on the abutment 43.

The positioning device 10 embodying the invention provides accurate positioning of the welding or re-lining head. The radial displacement is provided by the movement of the rollers 11, which accurately define the centre of the tube 20, the inner surface of which is finished with high precision. The axial displacement is provided by the displacement of the stop device 12. The overall transverse displacement is provided by rotation of the released arm 30 about a vertical axis.

Claims (8)

1. A positioning device comprising: an arm carrying at a free end thereof a working head; a support block on which the headcarrier arm is mounted; a positioning arm mounted on the support block parallel to the head-carrier arm so as to be pivotable in a vertical plane, the positioning arm carrying at least two positioning rollers at its free end; a retaining device connecting the support block and the positioning arm, said device having a first state in which said positioning arm is held in a raised position when the positioning device is in a rest position, and having a second state in which said positioning arm is released or pushed to increase the gravity effect; a return device connecting the positioning arm and the support block in order to hold said positioning arm in the working position by a tractive force when the retaining device is in its second state.

2. A positioning device according to claim 1, wherein the positioning arm is mounted on the support block by means of a doubleparallelogram articulated device, a first parallelogram being connected to the retaining device and a second parallelogram being connected to the return device.

3. A positioning device according to claim 1 or 2, wherein the end of the head-carrier arm adjacent said head is connected to the positioning arm by a coupling means exerting a tractive or thrust force on the head-carrier arm irrespective of the relative movements of the head-carrier arm and the positioning arm in the three directions in space.

4. A positioning device according to any one of claims 1 to 3, comprising a drive system to drive the head-carrier arm in three directions.

5. A positioning device according to any one of claims 1 to 4, wherein the positioning arm bears a stop device adapted to co-operate with a stop means provided on the surface of the workpiece.

6. A positioning device substantially as hereinbefore described with reference to, and as illustrated in, Figs. 1 to 4 of the accompanying drawings.

7. A positioning device substantially as hereinbefore described with reference to Figs.

5 and 6 of the accompanying drawings.

8. Any novel feature or combination of features herein described.