GB1584707A

GB1584707A - Control equipment for welding

Info

Publication number: GB1584707A
Application number: GB2973077A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-05-30
Filing date: 1978-05-30
Publication date: 1981-02-18

Description

(54) CONTROL EQUIPMENT FOR WELDING (71) I, FRANZ HIRSCHMANN, 93 High View Road, London, W.13, a British subject, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention refers to means for control ling the position of a welding torch relative to the prepared seam, with the aim of achieving a high quality weld. Such seam tracking devices are required for automatic welding machines, which use for the joining process a gas flame, an arc between the workpiece and a refractory or a consumable electrode, a laser, electron, light or ultrasonic beam or other means serving as a source of energy producing the required heat.

Known devices use an electromagnetic field produced by one or more coils to sense the path of the junction between two pieces of metal, which may or may not be ferromagnetic. The most common method is to use a differential transformer with an E core having an alternating voltage applied to the centre section and comparing the two secondary voltages of the two outer coils.

When the secondary voltages are equal, the central primary coil is directly above the seam since the two inductance paths are equal. Such a device, although accurate with the right seam preparation, fails to give the correct signal if the two pieces to be welded are not flat, or one is proud of the other; the central limb of the E core will then be displaced from its position above the seam centre line when the secondary voltages are equal. Object of the invention is a device, which gives the correct signal for the control of the torch position, even if one edge of the seam is proud of the other, or the shape of a groove prepared for the seam varies, or the seam preparation is not consistent in other ways. Another object of the invention is a device, which gives signals available for controlling the welding procedure so as to compensate for the otherwise detrimental influence of an inconsistent seam preparation.

According to the invention means are provided for sensing the heights of the two sides of the seam to be welded in the proximity of an electromagnetic seam tracking device, these means bemg used to keep the mean height of the seam tracking device from the seam approximately constant, with electrical signal derived from the difference in output from the said height sensing means being applied to compensate for the errors in the signals of said seam tracking device.

By using the fact that the said seam tracking device is kept approximately at a constant height and that the same compensating signal is applied to the said seam tracking device to keep it above the seam, means can also be provided for the extraction of an electrical signal in the neutral position from the seam tracking device which will be a function of the shape and dimension of the groove of the said seam. The said electrical signal can be used to alter the welding characteristics by changing the welding current, welding speed, welding voltage, weld ing current pulsing, welding torch weaving, welding gun height or filler wire steed, or any combination of the individual characteristics such that a uniform weld may be produced irrespective of changes in the workpiece preparation.

The invention will now be more fully described by means of an example.

With reference to the accompanying drawings, in Fig. 1, 1 is a plate on the left hand side of the workpiece, 2 is a plate on the right hand side of the workpiece; 3 is the seam to be welded. 4 is a potentiometric linear displacement transducer which is used to measure the height of the E core 6 of the seam tracking device from 1. 5 is a potentiometric linear displacement transducer which is used to measure the height of 6 from 2. 7 is a supporting member to hold 4, 5 and 6 together. 8 is the primary coil of the seam tracking device, 9 is the secondary coil sensing the magnetic flux in the left hand side of the E core, 10 is the secondary coil sensing the magnetic flux in the right hand side of the E core. 11 is a servo which controls the height of 7, and 12 is a servo which controls the lateral position of 7. In Fig. 2, 13 is an oscillator, feeding the primary coil 8. 14 and 15 are precision rectifiers giving direct voltage outputs proportional to the outputs of the secondary voltages of coils 9 and 10 respectively. 16 is a differential amplifier. 17 is a humming amplifier which sums the outputs of amplifiers 16 and ] 9 and has an adequate gain and output to drive the servo 12. 18 is a direct voltage signal which is proportional to the mean of the outputs of secondaries 9 and 10 and is used to control the welding characteristics. 1 9 is a differential amplifier which compares the outputs of the transducers 4 and 5. 20 is a differential amplifier which compares the mean outputs of 4 and 5 which are obtained using summing amplifier 21, with a substantially fixed voltage derived from the potential divider 22. The differential amplifier 20 drives the height controlling servo 11.

In operation. if the plates 1 and 2 of the workpiece are level and at the correct distance from the supporting member 7, the outputs of transducers 4 and 5 will be equal, and equal to the voltage at the potential divider 22; consequently the outputs of amplifiers 19 and 20 will be zero. If the central limb of the E core 6 is nearer to plate 1 of the workpiece, the output of secondary 9 will be greater than that of secondary 10.

The output of amplifier 16 will be positive, causing amplifier 17 to have a positive output. The servo 12 therefore operates causing the seam tracking device to move to the right until the central limb of the E core 6 is directly above the seam 3. The signal 18 gives a voltage proportional to the gap in the seam 3 and is very nearly independent of the out of balance voltages of the secondaries 9 and 10. If the height of the supporting member 7 from the workpiece 1 and 2 is too great, the output of amplifier 21 will be more positive than the potential of the potential divider 22 and the output amplifier 20 will be positive, causing servo 11 to lower the supporting member 7 until it is at the correct height. If the level of plate 2 is higher than that of 1, but the average height of the supporting member 7 above the workpiece is correct and the centre of the E core 6 is above the seam 3, the output of coil 10 will be greater than that of coil 9 causing the output amplifier 16 to be slightly negative. Because the output of transducer 5 is more positive than 4, the output of amplifier 19 will be slightly positive. The output of amplifier 17 is then zero and compensation has thus been achieved. It will be appreciated that any form of magnetic or eddy current seam tracking device could be used instead of the simple E core type shown in the example. A single I core could be used sensing changes of inductance or phase shift.

A double I core could be used sensing phase shift, a double U core could be used in the same way as a double I core or an E core. A standard inductive proximity detector could also be used.

Th.- linear potentiometric transducers 4 and 5 could be replaced by any distance measuring device such as an inductive proximity detector or by U cores with primary and secondary coils working in a similar manner to the seam tracking device itself. I cores could be used; E cores could be used to give the device information about the gradient of the workpiece in conjunction with a suitable servo amplifier for servo 11.

The potentiometric transducers can be defined as electromechanical height sensing means, whereas inductive proximity detectors are, like the seam tracking device, electromagnetic means.

The device following the seam can be mounted on the welding torch or gun and move together with it, provided the distance between tracking device and welding gun can be large enough so that the heat produced by the gun does not interfere with the working of the tracking device, but on the other hand is not so great that the position of the tracking device differs substantially from the position of the gun. With curved seams tracking device and welding gun have to be controlled by separate servo motors, with the tracking device entering its position into a suitable memory device, which is read by the controls of the welding gun when it arrives at the recorded position of the tracking device.

The vertical distance of the welding gun from the workpiece can be made to differ from the distance of the tracer head, making use of the signal 18, if for instance a tack weld makes it advisable to increase the torch distance by a suitable amount. Such a tack weld may be sensed and introduced into other control circuits if the signal 18 exceeds a certain value, caused, for instance, by a reduced magnetic resistance between the legs of the E core. The amplitude of the signal 18 is determined with a ferromagnetic material by the magnetic resistance between the legs which carry coils 9 and 10, and the leg which carries coil 8. With a nonferromagnetic material varying voltages are induced in the coils 9 and 10 by the eddy currents in the plates 1 and 2, which have been produced by coil 8.

With a workpiece on which the two plates 1 and 2 are on a different level a compensation of their influence on to the seam centering can alternatively be achieved by tilting the supporting member 7; where inductive transducers are used for measuring the dis tance between the tracer head and the two plates 1 and 2, instead of potentiometric transducers shown in Fig; 2, such inductive transducers may be combined with the inductive transducers indicating the seam centre in a single assembly.

The output of amplifier 19 could be fed into a function generator, prior to adding the compensation voltage to that of the output of amplifier 16, in order to achieve more accurate compensation. This function generator could receive a signal from the output of amplifier 16 or the signal 18 or both. As a further alternative a multiplier instead of the summing amplifier 17 or any combination can be used to give the most accurate compensation. The usefulness of these additional circuit elements which increase the cost and complexity of the whole device would depend on the quality of the workpiece preparation and the required accuracy of the seam tracking; in most cases the additions would not be required.

WHAT I CLAIM IS:- 1. Equipment for controlling the position of a welding torch relative to the prepared seam, with means sensing the heights of the two sides of the seam to be welded in the proximity of an electromagnetic seam tracking device and keeping the mean height of said seam tracking device from the seam approximately constant, and with electrical signals derived from the difference in output of said heights sensing means applied to compensate for errors in the signals of said seam tracking device.

2. Control equipment according to Claim 1, with a signal derived in the neutral position from the seam tracking device applied to means for altering at least one of the variables of the welding characteristics.

3. Control equipment according to Claim 2, with the signal from the seam tracking device changing the distance of a welding gun from the seam preparation.

4. Control equipment according to Claim 1 to 3, with the seam tracking device receiving the compensating signals over a function generator.

5. Control equipment according to Claim 1 to 4, with means for tilting the electromagnetic seam tracking device according to signals derived from the heights sensing means.

6. Control equipment according to Claim 1 to 4, with an electromagnetic seam tracking device and electromagnetic height sensing means.

7. Control equipment according to Claim 1 to 4, with an electromagnetic seam tracking device and electromechanical height sensing means.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. centre in a single assembly. The output of amplifier 19 could be fed into a function generator, prior to adding the compensation voltage to that of the output of amplifier 16, in order to achieve more accurate compensation. This function generator could receive a signal from the output of amplifier 16 or the signal 18 or both. As a further alternative a multiplier instead of the summing amplifier 17 or any combination can be used to give the most accurate compensation. The usefulness of these additional circuit elements which increase the cost and complexity of the whole device would depend on the quality of the workpiece preparation and the required accuracy of the seam tracking; in most cases the additions would not be required. WHAT I CLAIM IS:-

1. Equipment for controlling the position of a welding torch relative to the prepared seam, with means sensing the heights of the two sides of the seam to be welded in the proximity of an electromagnetic seam tracking device and keeping the mean height of said seam tracking device from the seam approximately constant, and with electrical signals derived from the difference in output of said heights sensing means applied to compensate for errors in the signals of said seam tracking device.