GB2090661A

GB2090661A - Guiding device for joining tools

Info

Publication number: GB2090661A
Application number: GB8036880A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-06-16
Filing date: 1980-11-18
Publication date: 1982-07-14
Also published as: DE3123096A1

Abstract

Sensing device for guiding a joining tool along a seam preparation, includes a coil connected to a medium frequency circuit and wound on a rectangular non-magnetic coil former, the longer side of the former being at least twice as long as the shorter side. In a first embodiment, two coils 1, 2 having parallel axes are mounted with their longer sides touching, the line of their longer sides being arranged parallel to the length of the seam. In a second embodiment, (Fig. 3) three coils are mounted in staggered formation, each having one longer side coincident with a common line of travel. In a third embodiment (Fig. 4) a single coil is arranged for oscillation transverse to its line of travel, so that one and the other of its longer sides are alternately aligned with the line of travel. <IMAGE>

Description

SPECIFICATION Guiding device for joining tools The invention refers to guiding devices, which sense the area of a seam preparation and keep the joining tool in its centre.

Welding processes with high heat concentration, like tungsten-inert gas arc welding and laser beam welding, require high accuracyforthe guiding of the heat source. Known accurate sensing devices, in par ticular those of the so-called electro-magnetic type, have to be kept very near to the workpiece surface, at a distance not exceeding 2mm, sometimes 1 mm or less, if they are required to signal a deviation of the centre of the seam preparation by a small fraction of a millimeter.

The sensing devices are subject to the heat of the joining process, e.g. that of the welding arc, as well as to the heat radiation of a hot workpiece. The varying temperature ofthe sensing organ can cause a serious error, which often cannot be fully compensated by special circuitry. A tracer head may under these circumstances have to lead the welding torch by a considerable distance, and this may necessitate the insertion of a memory device which records the position tracked by the tracer head, with the recorded data read by the welding torch when it arrives at the previously recorded tracer head position.

Object of the invention is an electromagnetic sensing device which can be subjected to changing high temperatures, without influencing its signals or their high accuracy. Another object of the invention is a sensing device, which due to its small dimensions can observe the seam area near to the joint, although it is kept well away from the workpiece surface.

A sensing device according to the invention includes 2 coils connected to a medium frequency circuit, wound on a rectangular coil former of non-magnetic material with the ratio of at least 1 to 2 of the sides of the rectangle, the coils mounted with the longer sides touching and kept in the direction of the seam preparation and with the coil axis perpen dicular to the workpiece surface, the axial length of the coils and the build-up of the windings being of the same order as the shorter side of the rectangle, and means comparing the inductance ofthe coils.

Examples of the invention are shown in the drawing.

The coils 1 and 2 of figure 1 and 2 are connected in series to a supply of 60 kHz, with their inductance compared in a bridge circuit and utilised for the control of a servomotor, not shown, applying known circuitry. The coils are wound of anodised aluminium wire, with 200 turns, on ceramic cores 3 with the cross section of 3mm x 6mm; the axial length ofthe coils, and the build-up of the windings is again near 3mm. The coils are mounted tight together, so that the surface opposed to the workpiece components 4 and 5 is only about 12 by 18mm. Ceramic material protects the outside of the assembly.

It was possible to control with such a device the position of a welding torch towards the centre line of the seam preparation with an accuracy better than 0.1 mm, at a gap varying between nil and abt 5mum, and with the bottom of the sensing coils 1 Omm away from the workpiece. The material of the workpiece could be mild steel, stainless or aluminium, with a wide range of thickness tested successfully. The anodised aluminium wire and the ceramic core will stand temperatures of several hundred degree C.

Fig 3 shows an alternative arrangement with 3 coils, 11,12 and 13, where coils 11 and 12 or coils 12 and 13 are alternatively used in short intervals as signal sources; this arrangement, although larger, offers advantages with curved seams.

In fig 4 a single coil 21 is mounted on an arm 22 and oscillated across the seam line, with the width of the oscillation equal to the width of the coil, so that the extreme positions of the single coil 21 correspond to the stationary positions of coils 1 and 2.

Optical or other switches, not shown can be used to indicate, whether the coil has reached a position right or left of the centre line. The signals received in the two areas are integrated and compared, and can then be used for adjusting the position of a welding torch keeping it in the seam centre; alternatively, the signals may be entered in a memory device.

It is known to use rectangular coils for electromagnetic sensing, and the possibility of using coils without magnetic cores has been mentioned.

But it has been considered necessary so far to use magnetic cores, which make the device temperature sensitive, in order to achieve a sensitivity even one ortwo orders of magnitudes belowthatwhich could be obtained by following the rules given by the invention.

The sensing device as described will deviate from the seam preparation if the workpiece surface is not at a right angle to the sensing device, or if one side of the workpiece is proud of the other. The specification of my British Patent (Application 29730/77) describes a method which reduces the said deviation by means of summing the output of a differential height transducer with the output of the sensing device such that the resultant signal remains essentially constant when either of the two sides of the seam to be welded in the proximity of the sensing device becomes proud of the other.

The device shown in figure 5 and 6 makes use of that method. The capacity sensing plates 6 and 7 are mounted on the coil assembly consisting of the coils 1 and 2 and the cores 3, so that they are opposite the workpiece components 4 and Son both sides of the seam. The plates 6 and 7 are C shaped, open towards the seam centre line, with the result that the differential height signal changes with the angle of tracking, and is a maximum when the seam follows the axis of the coil assembly, but is a minimum where the tracking signal from the seam received by the coils 1 and 2 is also low.

The coil assembly with the capacitor plates may be The drawings originally filed were informal and the print here reproduced is taken from a later filed formal copy surrounded by a guard ring, which will act as an electrical and a mechanical shield.

Claims

1. Sensing device for guiding a joining tool along a seam preparation, including 2 coils connected to a medium frequency circuit, wound on a rectangular non-magnetic coil former with the ratio of at least 1 to 2 of the sides of the rectangle, the coils mounted with the longer sides touching and kept in the direction of the seam preparation, and with the coil axis perpendicular to the workpiece surface, the axial length of the coils and the build-up of the windings being of the same order as the shorter side of the rectangle, and means comparing the inductance of the coils in a medium frequency circuit.

2. Sensing device according to claim 1, with the 2 coils mounted on opposite sides of the seam replaced by a single coil, oscillated over its width across the seam, with switches indicating when the single coil reaches the positions of the replaced coils.

3. Sensing device according to claim 1 or 2, with coils of anodised aluminium wire on a ceramic coil former.

4. Sensing device according to claim 1 to 3, designed according to the data given in the specification.

5. Sensing device according to claim 1 to 4 with capacity sensing plates mounted on the coil assemby on both sides of the seam, and means for summing the signals obtained from the coils with the difference of signals from the plates.

6. Sensing device according to claim 5, with the differential signal changed with the angle of track ing.

7. Sensing device according to claim 6, with C shaped sensing plates, open towards the seam centre line.

8. Sensing device according to claim 7, with a guard ring surrounding the coil assembly as an electrical and mechanical shield.

9. Sensing device according to claim 1 to 8, with the two separate coils replaced by a single coil, oscillated across the seam line with the width of oscillation equal the width of the coils, and means for comparing the signals received in a position right and left of the seam line.

10. Sensing device according to claim 1 to 8, with more than 2 coils transposed along the seam line.