GB2268900A

GB2268900A - A process and a device for setting the insertion speed (welding arm movement speed) during welding using welding studs

Info

Publication number: GB2268900A
Application number: GB9313118A
Authority: GB
Inventors: Wolfgang Gauger
Original assignee: Obo Bettermann OHG
Current assignee: Obo Bettermann OHG
Priority date: 1992-07-23
Filing date: 1993-06-24
Publication date: 1994-01-26
Anticipated expiration: 2013-06-24
Also published as: FR2693932A1; DE4224274C1; GB2268900B; GB9313118D0; FR2693932B1

Abstract

In welding using welding studs (5) or similar constructional components in the course of a capacitor discharge welding procedure employing tip ignition, the welding stud is held in a driven stud holder (4) and advanced into the welding position by pneumatic actuation of the holder, e.g. by means of cylinder 1. The speed of advance of the stud holder is maintained constant regardless of the orientation of the direction of advance. This is achieved by suitable control of the pneumatic medium in cylinder 1 eg by control of its delivery pressure or exit throttling. The system allows consistent welding at different angles e.g. on a robot arm. <IMAGE>

Description

268900 A PROCESS AND A DEVICE FOR SETTING THE INSERTION SPEED (WELDING ARM

MOVEMENT SPEED) DURING WELDING USING WELDING STUDS The invention relates to a process for setting the insertion speed during welding using welding studs or similar constructional components in the course of a capacitor discharge welding procedure employing tip ignition, wherein the welding stud is held in a driven stud holder and is inserted into a welding position by a pneumatically actuated holder.

During welding of welding studs by means of the so-called capacitor discharge welding procedure employing tip ignition (Graham process) it is necessary, depending on the material, to set different speeds of insertion of the studs in the melting bath. In the case of stationary welding installations this insertion speed is established only one time and then during the numerous succeeding welding processes is not altered again. Good welding results can be obtained with stationary installations in this manner. However, if the welding head of the welding unit is attached not to a stationary device but to a robot which can deliver welding studs to different welding points and weld them there, then, if these different points are located at different three-dimensional angles, a difference in speed occurs depending on.the angle. This results because the force of gravity has different effects on the operating element comprising stud, stud holder and drive element, depending on the threedimensional angle of this functional element. Consequently completely different insertion speeds are attained depending on whether the stud is delivered to the welding position in the direction of the force of gravity or if, for example, it should be delivered to a welding position against the force of gravity.

Starting from this state of the art, the aim of the invention is to provide a process and a device with which the desired uniformly constant insertion speed can be achieved even with different angles of-delivery of the studs to the welding position relative to the direction of the force of gravity.

To achieve this objective it is proposed that the welding stud together with the stud holder, as an element of a welding robot or a 3-axis MCmachine having a rotatable welding head, is delivered to the welding position alternatively at different three-dimensional angles and the welding studs are inserted at the latter angles at a constant speed, where the insertion speed is held constant in dependence on the direction of insertion relative to the direction of the force of gravity as a result of the fact that in dependence on the relative three-dimensional angle of the insertion direction, the pneumatic medium is delivered or removed at a different pressure and/or with appropriately throttled exhaust air.

A preferred device for performing the process, comprising a welding robot or a 3-axis MC-machine having a rotatable welding head and a longitudinally movable welding stud holder which is rotatably or pivotably driven on or by it and which has a welding stud receiver on itsfront face, is characterized in that the positioning element for the longitudinal displacement of the stud holder is a pneumatic operating cylinder which is permanently fixed, in particular to the robot, in that a control valve, especially a proportional pressure control valve, is connected in the compressed air delivery pipe to the positioning element, the extent of opening of which is determined by a setting device coupled to it, by means of which the relative angular setting of the stud holder or its set direction can be measured and which assigns a predetermined pressure to this angular setting, taking into account the direction of the force of-gravity relative to the set direction of the stud holder, andlor that a,motor controlled throttle valve or a plurality of alternatively connectable throttle valves having different -restriction cross-sections is or are connected to the exhaust air outlet of the operating cylinder so that the speed of positioning the stud holder and consequently the insertion speed of the welding stud held by the latter is at least substantially constant independently of the set direction relative to the direction of the force of gravity.

Basically the process and device relate to pneumatically operated welding heads. Such a welding head comprises a pneumatic operating cylinder which is connected through a coupling to a drive shaft for the stud holder, where the stud holder comprises a stud receiver at its front face. This stud head is fixed to an appropriate welding robot and can be moved by the latter into selected positions. The pressure of the pneumatic medium is raised or lowered in dependence o n the relative direction of insertion of the welding stud, and thus in dependence on the relative directional setting of the stud holder, according to whether the insertion direction extends in the direction of the gravitational force or in the opposite direction to gravity. Alternatively, or additionally, the exhaust air from the pneumatic element can also be throttled in dependence on the relative angular position of the insertion direction in order to achieve the desired constant insertion speed independent of the direction of movement.

A preferred further development envisages that a proportional pressure control valve is connected to the operating cylinder on its inlet side, which valve can be actuated by a setting device and an electronic drive unit, where the setting device allocates a defined pressure to each angular position of the setting direction of the stud holder and by means of the electronic drive unit sets the proportional pressure control valve accordingly.

In an embodiment of this kind a proportional pressure control valve is connectedto the inlet of the operating cylinder, which valve is actuated by means of an electronic drive unit which in turn is connected to a setting device. The relative angular setting of the-set direction is detected by the setting device and a defined pressure is assigned to each angular setting which is then established in theproportional pressure control valve by means of the electronic drive unit and which is then applied to the operating cylinder. In this manner it is possible to adjust the piston driving force of the pneumatic operating cylinder in every case to compensate for the accelerating force of gravity acting on the mass moved (guide element, stud holder, stud), and so the end result is that for every welding position the same constant speed of insertion of the stud in the melting bath can be acheived.

An alternative arrangement, which can also be provided in addition to the measures described above, envisages that a plurality of throttle valves having switching valves, in particular electromagnetic switching valves, connected after them are connected to the output side of the operating cylinder, where the throttle valves can be actuated in dependence on the relative set position of the stud holder, in particular by means of an element which detects this angular setting.

This embodiment is particularly advantageous if there are only alimited number of angular settings. With this limited number of angular settings a corresponding throttle valve with an associated electromagnetic switching valve can be assigned to each angular setting. Depending on the relative angular setting, the flow of exhaust air from the pneumatic cylinder is then restricted by means of the throttle valve associated with this angular setting so that with a constant input pressure the amount of exhaust air flowing through is altered, which causes an effect on the speed of movement of the piston and consequently to an effect on speed of insertion of the welding stud into the melting bath. It is also possible in this manner to obtain the same constant insertion speed for every welding.position of the different angular settings.

In another a'lternative-arrangement, which can also be provided in addition to the measures described above, it is envisaged that an adjustable throttle valve with an associated adjustment motor is connected tothe output side of the operating cylinder, where the adjustment motor can be controlled by an element which detects the relative angular setting of the stud holder.

In this embodiment the relative angular setting of the direction of approach of the stud holder is detected by an appropriate positioning element and a defined flow rate through the throttle valve is allocated to each angular setting to which rate the throttle valve is set by means of the adjustment motor. Again it is possible in this manner to maintain the insertion speed equally high and constant for every angular setting.

Embodiments of the invention are described, by way of example only, with reference to the following drawings in which:

Figure 1 shows the principles of construction of a welding head; Figure 2 shows a first embodiment for maintaining the insertion speed constant; and Figures 3 and 4 schematically show two other alternative embodiments.

Figure 1 shows a pneumatic operating cylinder 1 which is connected through a coupling 2 to a drive shaft 3 which is held in a guide. A stud holder 4, which holds a welding stud 5 with an ignition tip 6, is attached to the drive shaft 3. The total assembly shown in Figure 1 is referred to as a welding head and the said welding head is a constituent element of a welding robot by means of which the welding head can-be rotated,-pivoted and-moved linearly so that the welding head can bemoved towelding positions arranged three-dimensionally at will. In the case of the embodiment shown in Figure 2 a proportional.pressure control valve 7 which can be controlled by an electronic drive unit 8, which in turn is coupled to a setting device 9, is connected to the inlet side of the operating cylinder 1. The relative angular setting or orientation of the set direction of the stud holder 4 is detected by the setting device 9 and a defined pressure value is assigned to it. By means of the electronic drive unit 8 this pressure value is established in the proportional pressure control valve 7 and the operating cylinder 1 is subjected to this pressure on its inlet side. The exhaust air flows unrestricted from the operating cylinder 1 at 10.

In the embodiment shown in Figure 3 a plurality of throttle valves 12 having different restriction characteristics are connected to the outlet side of the operating cylinder 2, the compressed air inlet to which is indicated by 11. These throttle valves 12 are each assigned to a defined angular setting of the set direction of the stud holder 4, so that at the appropriately set angular setting the corresponding throttle valve 12 is opened by the actuation of an electromagnetic switching valve 13. Consequently the exhaust air 10 can flow out of the operating cylinder 2, restricted to a greater or lesser extent depending on the angular setting of the set direction of the stud holder 4, so that an appropriately constant movement of the pneumatic positioning element is obtained adapted to the relative angular setting.

In the embodiment shown in'Figure 4 an adjustable throttle valve 14, through which the exhaust air can escape from the operating cylinder 2, is connected to the outlet side of the operating cylinder 21. Depending on the angular setting of the set direction of the stud holder 4, the flow rate through the throttle valve is set by means of an adjustment motor 15 coupled to the throttle valve 14. For this purpose the adjustment motor 15 is actuated by an electronic control unit 16, which in turn is connected to a setting device which detects the relative angular setting of the set direction of the stud holder 4 and transmits an appropriate signal to the electronic control unit 16 so that the adjustment motor 15 can be actuated by the latter.

With all the alternative embodiments shown it is possible to maintain the speed of insertion of the we] ding stud into the melting bath at the same value and constant, quite independently of the relative angular setting or orientation of the set direction of the stud holder, in other words of the direction of delivery of the welding stud to the appropriate welding position.

The invention is not limited to the embodiment examples shown, but can be modified in many ways within the scope of the invention.

j 8

Claims

1. A process for setting the insertion speed during welding using welding studs or similar constructional components in the course of a capacitor discharge welding procedure employing tip ignition, wherein the welding stud is held in a driven stud holder and is inserted into the welding position by the holder which is pneumatically actuated, characterized in that the welding stud together with the stud holder, as an element of a welding robot or a 3-axis MC-machine having a rotatable welding head, is delivered to the welding position at a selected three-dimensional angle whilst the welding studs are inserted at the angle at a constant speed, where the insertion speed is held constant in dependence on the direction of insertion relative to the direction of the force of gravity as a result of the fact that in dependence on the relative three-dimensional angle of the insertion direction, the pneumatic medium is delivered or removed at a different pressure and/or with appropriately throttled exhaust air.

2. A device for performing the process according to claim 1 comprising a welding robot or a 3-axis MC-machine having a rotatable welding head and a longitudinally movable welding stud holder which is rotatably or pivotably driven on or by it and which has a welding stud receiver on a front face thereof, characterized in that the positioning element for the longitudinal displacement of the stud holder (4) is a pneumatic operating cylinder (1) which is permanently fixed, in particular to the robot, in that a control valve, especially a proportional pressure control valve (7), is connected in the compressed air delivery pipe (11) to the positioning element, the extent of opening of which is determined by a setting device (9) coupled to it, by.means of which the relative angular setting of the stud holder (4) or its set direction can be measured and which assigns a predetermined pressure to this angular setting, taking into account the direction of the force of gravity relative to the set direction of the stud holder (4), and/or that a motor controlled throttle valve (14) or a plurality of alternatively connectable throttle valves (12) having different restriction cross-sections is or are connected to the exhaust air outlet (10) of the operating cylinder (1) so that the speed of positioning the stud holder (4) and consequently the insertion speed of the welding stud (5) held by the latter is at least substantially constant independently of the set direction relative to the direction of the force of gravity.

3. A device according to claim 2, characterized in that a proportional pressure control valve (7) is connected to the operating cylinder (1) at its inlet side which valve can be actuated by a setting device (9) and an electronic drive unit (8), where the setting device (9) assigns defined pressures to angular settings of the set direction of the stud holder (4) and by means of the electronic drive unit (8) sets the proportional pressure control valve (7) accordingly.

4. A device according to claim 2 or claim 3, characterized in that a plurality of throttle valves (12) having switching valves (13), in particular electromagnetic switching valves, connected after them are connected to the output side of the operating cylinder (1), where the throttle valves (12) can be actuated in dependence on the relative set position of the stud holder (4), in particular by means of an element which detects this angular setting.

5. A device according to any one of claims 2 to 4, characterized in that an adjustable throttle valve (14) with an associated adjustment motor (15) is connected to the output side of the operating cylinder (1), where the adjustment motor (15) can be controlled by an element (e.g. 16) which detects the relative angular setting of the stud holder (4).

6. A device for setting the invention speed of a welding stud during welding substantially as hereinbefore described and illustrated in Figure 1 in combination with Figures 2, 3 or 4 of the accompanying drawings.