GB2063133A - A pneumatically operated welding machine control system - Google Patents

Abstract

The control system causes the electrodes to approach the workpiece under low pressure until the electrodes have reached a position too close to the workpiece for an operator's finger or hand to be trapped therebetween. This is achieved by having a throttled discharge to the atmosphere during the initial advancing stroke of the electrode actuator. In one embodiment pressure is initially applied to the drive side (12a) of the actuator (11) via pressure reducing valves (23,27) and the delivery line is open to the atmosphere via a high pressure valve (19) muffler; when the electrodes have advanced to a safe position, a limit switch (16) is tripped to energize the high pressure valve (19) which then communicates full welding pressure to the actuator (11). In another embodiment the actuator is caused to move initially by the weight of the electrode and associated equipment and this movement is resisted by a throttled discharge of air from the lower chamber of the actuator, the discharge is controlled by restrictor valves in a circuit which ensures that there is always some pressure resisting movement of the actuator even in the event of leaky seals. <IMAGE>

Description

SPECIFICATION A pneumatically operated welding machine control system The present invention relates to a pneumatically operated welding machine control system for causing the approach and return movement of the electrodes of a welding machine.

Pneumatically operated welding machines have electrodes which are advanced, along a working stroke, to a working position where they contact the workpiece to be welded. When the electrode is in contact with the workpiece it is necessary for it to be pressed into contact therewith at high pressure, partly to ensure adequate electrical contact, partly for the purpose of obtaining good mechanical contact of component parts to be welded.

One of the problems which have been experienced with such welding equipment, however, is that an operator manipulating the workpiece or workpieces can sometimes get a part of his anatomy such as a hand or finger, trapped between the workpiece and the electrode, particularly with machines which have foot operated switches for setting the machine into operation since these may be operated inadvertantly causing the electrodes to be advanced along their working stroke before the operator has had an opportunity to finish positioning the workpiece and remove his hands.Accidents can also happen even when the control switch is operated deliberately since, because the electrodes have to be pressed against the workpiece at high pressure, this high pressure is applied to close the electrodes, moving them along their working stroke, and this results in a rapid movement of the electrodes along the working stroke.

The present invention seeks to provide a control system for a pneumatically operated welding machine which, whilst permitting the electrodes to be pressed against the workpiece at the same high pressure as known machines, allows the working stroke to be performed at low pressure, at least up to a point too close to the workpiece for the operator's hand or fingers to be trapped between them, after which the high pressure is applied to clamp the electrodes against the workpiece.

According, therefore, to one aspect of the present invention there is provided a pneumatically operated welding machine control system, in which the electrodes of the machine are displaced along a working stroke in which the electrodes are caused to approach one another, and a return stroke in which they are caused to move apart, by a pneumatic actuator, wherein during the working stroke the movement of the actuator is controlled by a low pressure which is applied to the actuator and also able to discharge through a throttled passage.

In one embodiment of the invention the low pressure applied to the actuator causes the displacement thereof along the working stroke, and in another embodiment of the invention the low pressure is applied in a sense such as to resist the movement of the actuator, the movement being caused by the weight of the component parts of the machine supported by the actuator.

In the first mentioned embodiment the throttled passage may be the muffler of a high pressure valve operable, when energised, to apply high pressure from a source thereof to the pneumatic actuator whereby to close the electrodes for a welding operation. The high pressure valve is preferably controlled by switching means sensitive to the position of the pneumatic actuator and operative to energise the high pressure valve when the actuator has reached a predetermined position close to the end of its working stroke. The distance between the electrode and the workpiece when the actuator has reached the said predetermined position is preferably in the region of one quarter of an inch which is certainly too small a gap for an operator's hand or fingers to be trapped between the electrode and the workpiece.

In the event of such an accident, that is if the operator's hand or fingers get trapped between the work-piece and the electrode being displaced along its working stroke by the actuator, the low pressure will not cause serious damage, and the low pressure can, in any event, discharge to the atmosphere through the throttled passage. The high pressure valve remains de-energised.

According to another aspect of the present invention, there is provided a pneumatically operated welding machine control system, in which the electrodes of the machine are displaced by a pneumatic actuator and initial closing of the electrodes on to a workpiece is effected by allowing the pressure in the actuator to discharge through a throttled opening.

Preferably the actuator, or an element displaced therewith, is provided with engagement means for operating a limit switch to cause full closing pressure to be applied by the actuator after the electrodes have been closed to a predetermined spacing.

Two embodiments of the present invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a pneumatic circuit diagram of a first embodiment of the invention; and Figure 2 is a pneumatic circuit diagram of a second embodiment of the invention.

Referring now to Figure 1 the circuit shown includes a pneumatic actuator, generally indicated 11, comprising a cylinder 12 housing a piston 13 which separates the cylinder into an upper chamber 1 2a and a lower chamber 1 2b. A piston rod 14 attached to the piston 13 is also connected to a welding electrode (not shown) of the machine and upon movement of the piston rod 14 in the direction of the arrow A of Figure 1 the welding electrode is moved along a working stroke from its fully withdrawn position (shown in Figure 1)to an advanced position in contact with the workpiece to be welded.

In contact with the piston rod 14 is a roller 17 of a limit switch 16 which switches when a shoulder 15 of the piston rod 14 passes the location of the limit switch. This limit switch is mounted in an adjustable manner so that its precise position along the stroke of the piston rod 14 can be adjusted in accordance with the requirements of any particular welding operation being conducted, in particular in dependence on the shape and dimensions of the workpiece being welded.

The upper chamber of the cylinder 12 is fed, along a line 18, via a high pressureairvalve 19 which, in turn, is fed from an adjustable pressure restrictor valve 20 supplied from an air supply along a line 21.

The high pressure air valve 19 is of a switch-over type used, in this circuit, to interrupt communication between the restrictor valve 20 and the upper chamber 12a of the cylinder 12 when not energised, establishing communication between these when energised.

A branch line 22 connects the air supply line 21 with a second restrictor valve 23 which leads to a low pressure air valve 24 having two output lines 25,26.

When the valve 24 is not energised the restrictor valve 23 communicates with the line 25 which leads to the lower chamber 12b of cylinder 12 and causes the actuator 11 to retract, making a return stroke of the electrodes. When the air valve 24 is energised, on the other hand, the restrictor valve 23 communicates with the line 26 which leads, via a further low pressure restrictorvalve 27 and a unidirectional valve 28 into the high pressure air line 18 leading to the upper chamber 12a of the actuator.

The circuit described above operates as follows: When the two air valves 19,24 are both de-energised air at a pressure determined by the setting of the adjustable restrictor valve 23 is fed to the lower chamber 12b causing the electrodes to be displaced along their return stroke to an open or spaced apart position allowing the workpiece to be located in position. When satisfactory positioning of the workpiece has been effected the air valve 24 is energised, for example by means of a foot pedal switch, and upon commuting to its second position delivers air along the line 26 to the upper chamber 12a of the actuator 11 at a pressure determined by the adjustment of the low pressure restrictor valve 27.Of course, this air will also escape through the high pressure air valve 19 which, at this stage, is not energised so that the line 18 is open to the atmos pherethrough the high pressure air valve muffler; however, there is sufficient surge upon switching to ensure that the piston 13 starts to move and sufficient back pressure due to the resistance of the high pressure air valve muffler to ensure that the actuator 11 continues to advance under low pressure until the electrode is within about one quarter of an inch from the workpiece, at which position the limit switch 16 is set to throw thereby energising the high pressure air valve 19 which commutes to its second position immediately, delivering air at a pressure determined by the adjustment of the restrictor valve 20 along the line 18 into the upper chamber 12a pressurising the actuator strongly and clamping the electrode against the workpiece with the high force which is required during welding. The unidirectional valve 28 prevents escape of the high pressure air through the restrictor valve 27.

With energisation of the low pressure air valve 24 when the initial advance of the actuator is started, the line 25 which communicates with the lower chamber 12b of the cylinder 12 is connected to atmosphere allowing the chamber 12b to discharge freely.

At the end of a welding operation both valves 19 and 24 are de-energised and thus return to the original position shown in Figure 1, the actuator being supplied via the line 25 with pressure into the lower chamber 12b causing it to retract.

In the second embodiment illustrated in Figure 2 components which are the same or fulfil a similar function to corresponding components in Figure 1 have been indicated with the same reference numerals and are not further discussed in detail.

The embodiment of Figure 2 is suitable for use with a welding machine in which the movable electrode will fall under its own weight towards the workpiece, this weight being supported by the actuator 11 during its return stroke.

The adjustable restrictor valve 23, in this embodiment leads via a line 30, to one input of a five port control valve 31 which, in the de-energised state connects it with the line 25 leading to the lower chamber 12b of the actuator 11. When the valve 31 is energised the line 25 is put into communication with a line 35 leading to a further adjustable restrictor valve 33 open to the atmosphere so that the pressure within the chamber 12b is discharged gradually. This allows the piston 30 to advance in the direction of the arrow A under the weight of the equipment associated with the electrode (the high pressure valve 19 being de-energised and the line 18 being in communication with the atmosphere). When the critical position is reached, and the limit switch 16 trips, the high pressure valve 19 is energised and puts the line 18 in communication with the high pressure source along the line 21 via the pressure regulator valve 20 thereby applying clamping pressure to the electrodes carried by the piston rod 14.

In order to ensure that leaky seals or other worn parts in the system do not result in a too rapid movement of the piston 13 upon energisation of the valve 31, a further regulator valve 32 is connected between the discharge line 35 and a port in the valve 31 to which a line 36 is connected when the valve is energised. The further regulator valve 32 supplies a pressure just below the relief pressure of the valve 33 thereby ensuring adequate resistance to the movement of the piston 13.

Claims (15)

1. A pneumatically operated machine control system, wherein the electrodes of the machine are displaced by a pneumatic actuator alternately along a working stroke in which the electrodes are caused to approach one another and along a return stroke in which they are caused to move apart, and wherein during a part of the working stroke the movement of the actuator is controlled by a low pressure which is applied to the actuator and also able to discharge through a restricted passage.

2. A control system as claimed in Claim 1, in which full working pressure is applied to the actuator at a preselectable position along the stroke.

3. A control system as claimed in Claim 2, in which application of the full working pressure is controlled by a switching device operated by the pneumatic actuator itself.

4. A control system as claimed in Claim 3, in which the switching device is an electrical switch operated by mechanical interaction with the actuator arm.

5. A control system as claimed in Claim 4, in which the actuator arm is provided with engagement means for operatively engaging a mechanical operating member of the said electrical switch.

6. A control system as claimed in any preceding claim, in which the application of full working pressure or the said low pressure to the pneumatic actuator is controlled by a solenoid operated valve.

7. A control system as claimed in any preceding Claim, in which the application of the said low pressure to the pneumatic actuator effects displacement thereof along the said working stroke.

8. A control system as claimed in any of Claims 1 to 6, in which the application of the said low pressure to the pneumatic actuator resists displacement thereof, which displacement is caused by the weight of the equipment carried by the actuator.

9. A control system as claimed in any preceding Claim, in which there are provided means for applying a predetermined low pressure to the discharge side of the pneumatic actuator during the working stroke thereof, whereby to maintain the pressure therein at a positive value greater than zero.

10. A pneumatically operated welding machine control system, in which the electrodes of the machine are displaced by a pneumatic actuator, and initial closing of the electrodes onto a workpiece is effected by allowing the pressure in the actuator to discharge through a restricted opening.

11. A control system as claimed in Claim 10, in which the restricted opening is the muffler of a high pressure valve operable when energised, to apply high pressure from a pressure source to the pneumatic actuator whereby to close the electrodes for the welding operation.

12. A control system as claimed in any of Claims 1 to 9, in which the low pressure is applied to the actuator via a pressure regulating valve fed by a high pressure source, the pressure regulating valve being bypassed by a solenoid operated pneumatic valve energised by the said switching device.

13. A control system as claimed in any preceding Claim, in which the pressure for the return stroke of the actuator is applied thereto by a solenoid operated commutating valve.

14. A control system as claimed in Claim 13, in which the said solenoid operated commutation valve is the same valve as that through which the high pressure for final closure of the electrodes is applied.

15. A pneumatically operated welding machine control system substantially as hereinbefore described with reference to Figure 1 or Figure 2 of the accompanying drawings.