GB2051418A

GB2051418A - Control of tool movement

Info

Publication number: GB2051418A
Application number: GB7920761A
Authority: GB
Original assignee: BOC Ltd Australia
Current assignee: BOC Ltd Australia
Priority date: 1979-06-14
Filing date: 1979-06-14
Publication date: 1981-01-14
Also published as: ZA803419B; AU5935880A

Abstract

A device for controlling automatically the movement of a tool head during a working pass e.g. of a welding electrode along a seam to be welded includes an infra-red height sensor unit and an infra-red line follower unit both contained within a sensor housing. Deviation of the welding head from the weld seam or from a predetermined height above it causes a feedback signal to be generated which corrects the deviation. The infra-red radiation source may be pulsed at a predetermined frequency.

Description

SPECIFICATION A device for controlling automatically the movement of tools The present invention relates to devices for controlling automatically the movement of a tool during a working operation and in particular to devices for controlling automatically the movement of a welding electrode during a working pass along a welding path.

It is frequently necessary to ensure that during a manufacturing process the desired path of a tool relative to a work piece is maintained. For example, when seam welding a workpiece, it is known to use a device which includes both a height sensor unit and a line follower unit. The height sensor unit maintains the welding electrode at a predetermined distance from the workpiece to be welded, whilst the line follower unit ensures that the welding electrode follows the seam to be welded. The line follower unit can comprise one or more photocells which follow a line on the workpiece at a constant distance from the centre of the intended seam to ensure that the welding electrode follows automatically along the centre of the seam. The photocells each form part of a light sensor unit which includes a light source which illuminates a portion of the guide line.The photocells generate a signal corresponding to the amount of light entering the cell after reflection from the guide line.

This known line follower unit suffers from the disadvantage that frequently the signals generated by the photocells are affected adversely by ambient light and also the light emanating from the welding arc.

A device for controlling automatically the movement of a welding electrode should seek to meet the following requirements: (a) the height sensor and line follower sensor should be small in size; (b) they should be rugged and have a fast response for frequency modulation; and (c) it should be simple to pulse electronically the light emanating from the sensors without the need of an external light chopper.

It is an aim of the present invention to meet the above desiderata.

According to the present invention, a device for controlling automatically the movement of a tool during a working operation along a desired path, comprises a height sensor unit including an emitter for directing infra-red light onto a surface and a receiver for receiving the infra-red light reflected from the surface, the receiver generating a signal corresponding to the infra-red light received and means for comparing this signal with a signal representing the desired height of the tool above the path and means for driving the height sensor and with it the tool incrementally towards or away from the path according to the compared signals; and a line follower unit including an emitter for directing infra-red light onto a small area of a surface on which the line to be followed is located and a receiver for receiving the infra-red light reflected from the surface, the receiver generating a signal corresponding to the infra-red light received, means for driving the line follower unit and with it the tool incrementally in a direction transversely to the desired path in accordance with the signal so as to keep the signal at a predetermined level.

Throughout this specification the word "line" in the expression "line follower unit" is intended to embrace a line dividing two areas of contrasting reflectivity. For example, the line between abutting black and white tapes or the line defined by the edge produced when two surfaces of a workpiece meet at an angle.

An embodiment of the invention will now be described, by way of example, reference being made to the Figures of the accompanying diagrammatic drawings in which: Figure 1 is an end view of a welding machine to which a device for controlling automatically the movement of the welding electrode along a Figure 2 is a block diagram of the electronic circuitry forming part of the device shown in Fig. 1.

As shown in Fig. 1, an electric arc welding machine 10 includes a welding torch 3 with an electrode 13 mounted above the seam between two workpieces 11, 12 to be welded on a vertical slide 1 driven by a motor 7. The vertical slide 1 is mounted on a horizontal slide 2 driven by a motor 8. The assembly comprising the vertical and horizontal slides and the components mounted on them is mounted for movement with a carrier (not shown) in the general direction of the seam between the workpieces 11, 12.

Attached to the workpiece 11 is a tape 13 one half of the upper (as shown) surface of which is highly reflective to infra-red light whilst the opposite half is comparatively nonreflective to infra-red light. The two halves define between them a line which is arranged substantially parallel to but spaced from the seam to be welded.

A sensor housing 4 is mounted immediately above the line on a vertical fine adjustment slide 6 which in turn is mounted on a horizontal fine adjustment slide 5. The fine adjustment slides 5, 6 are carried on the vertical slide 1.

Referring also to Fig. 2, the sensor housing 4 contains a height sensor unit and a line follower unit. The height sensor unit includes an emitter 20 for directing infra-red light onto the highly reflective half of the upper surface of the tape 13 and receiver 21 for receiving the infra-red light reflected from the said highly reflective half of the upper surface of the tape 13. The infra-red light emanating from the emitter 20 is pulsed at a predetermined frequency by an oscillator 30.

An electrical signal corresponding to the infra-red light received is passed by the receiver 21 to an amplifier 22. From the amplifier 22 the signal is passed through a filter network 23 and a DC converter 24 to a motor logic network 25 where it is compared with an electrical signal representing the desired height of the welding electrode 13 above the seam to be welded. The signal resulting from this comparison is fed via motor drive 27 to the motor 7, the operation of which causes the vertical slide to move vertically and with it the sensor housing 4 with the height sensor unit and concomitantly the welding electrode 13.

The line follower unit is the same combination of parts as for the height sensor unit in that it includes an emitter and a receiver and the electronic circuitry as illustrated in Fig. 2 and described above with reference to the height sensor unit. However, in the case of the line follower unit, infra-red emanating from the emitter will fall either wholly on the highly reflective surface of the tape giving a "black" signal or between the different reflective surfaces in which case it will give a "grey" signal. When the area of infra-red light emitted by the emitter is bisected by the line this will give rise to the optimum grey signal from the amplifier 22. However, should the line follower ever become spaced by such a distance from the line that the area of infrared light lies wholly within the highly reflective surface then the amplifier 22 produces a maximum white signal.Alternatively, should the area of infra-red light enamating from the emitter lie wholly within the adsorbent surface, then it will cause the amplifier 22 to emit a maximum black signal.

The signal received by the motor 8 will cause the motor to move the horizontal slide 2 to the right or left until the optimum grey signal is received. The movement of the horizontal slide 2 will cuase the sensor housing 4 with the line follower unit and concomitantly the welding electrode 13 to move transversely of the line being followed until the optimum grey signal is received.

In operation, the tape 13 is placed on the upper surface of the workpiece 11 with its two contrasting reflective surfaces uppermost (as shown). The tape is arranged so that the line defined by the two contrasting reflective surface is a facsimile of the seam between the workpieces 11, 12 to be welded. Next, the welding electrode 13 is arranged immediately above the seam at the height required for the welding operation. The sensor housing 4 is then adjusted by means of the horizontal and vertical fine adjustment slides 5, 6 so that the optimum grey signal is generated by the amplifier 22.

The welding operation is then commenced and it will be apparent that both the height and the position of the welding torch 3 transversely of the welding path will be sensed and adjusted automatically by the height sensor and the line follower during a welding pass along the seam.

A particular advantage of the device described above is that both the height sensor and the line follower sensor are contained within the sensor housing 4. A further advantage is that by using infra-red light the signals generated by the amplifier are not adversely affected by ambient or the arc light during the welding operation. Furthermore, the emitters are simple to pulse electronically by means of oscillators without the need for an external light chopper.

Claims

1. A device for controlling automatically the movement of a tool during a working operation along a desired path, comprising a height sensor unit including an emitter for directing infra-red light onto a surface and a receiver for receiving the infra-red light reflected from the surface, the receiver generating a signal corresponding to the infra-red light received and means for comparing this signal with a signal representing the desired height of the tool above the path and means for driving the height sensor and with it the tool incrementally towards or away from the desired path according to the compared signals; and a line follower unit including an emitter for directing infra-red light onto a small area of a surface on which the line to be followed is located and a receiver for receiving the infra-red light reflected from the surface, the receiver generating a signal corresponding to the infra-red light received, means for driving the line follower unit and with it the tool incrementally in a direction transversely to the desired path in accordance with the signal so as to keep the signal at a predetermined level.

2. A device for controlling automatically the movement of a welding electrode during a working pass along a desired welding path, comprising a height sensor unit including an emitter for directing infra-red light onto a surface and receiver for receiving the infra-red light reflected from the surface, the receiver generating a signal corresponding to the infrared light received, means for comparing the signal with a signal representing the desired height of the welding electrode above the welding path and means for driving the height sensor and with it the welding electrode incrementally towards or away from the welding path according to the compared signals; and a line follower unit including an emitter for directing infra-red light onto a small area of a surface on which the line to be followed is located and a receiver for receiving the infrared light reflected from the surface, the re ceiver generating a signal corresponding to the infra-red light received, means for driving the line follower unit and with it the welding electrode incrementally in a direction adversely to the welding path in accordance with the signal so as to keep the signal at a predetermined level.

3. A device as claimed in claim 2, in which the height sensor unit and the line follower unit are contained within a sensor housing which is adjustably mounted on a slide carrying the welding electrode.

4. A device as claimed in claim 3, in which the sensor housing and the welding electrode are each mounted on a vertical slide which in turn is mounted on a horizontal slide, the vertical and horizontal slides each being driven individually by a motor controlled by the signals produced from the height sensor unit and the line follower unit respectively.

5. A device as claimed in any one of claims 1 to 4, in which the infra-red light emanating from each emitter is pulsed at a predetermined frequency by an oscillator.

6. A device for controlling automatically the movement of a tool during a working operation along a desired path, constructed, arranged and adapted to operate substantially as hereinbefore described with reference to and as illustrated in the Figures of the accompanying drawings.