WO1981001974A1

WO1981001974A1 - Welding head adjusting device

Info

Publication number: WO1981001974A1
Application number: PCT/SE1980/000356
Authority: WO
Inventors: J Johansson
Original assignee: Torsteknik Ab; J Johansson
Priority date: 1980-01-09
Filing date: 1980-12-30
Publication date: 1981-07-23
Also published as: SE8000182L; SE419952B; FR2473380A1

Abstract

In welding machines a relative movement between the workpiece (2) and a machine part (7) serving as a support for a welding head (13) along a predetermined path corresponding to an estimated course of the joint (16) to be welded is somehow caused to take place but for various reasons there is most frequently a discrepancy between this estimated course and the actual one. In order to compensate deviations between the two courses a welding head adjusting device is used which comprises a holder (9) adapted to be secured to the machine part (7), a carrier (10) for the welding head (13) which carrier is adjustably connected to the holder, and a sensor member (15) which is intermittently extensible from the carrier towards the workpiece (2) to thereby establish the actual position of the joint (16) and to correspondingly adjust the position of the welding head (13) relative to the machine part (7).

Description

WELDING HEAD ADJUSTING DEVICE

This invention relates to a welding head adjusting device for use in a welding machine of the kind in which during the welding operation a relative movement between the workpiece and a machine part serving as a support for the welding head along a predetermined path corresponding to an estimated course of the joint to be welded is caused to take place, the device being adapted to compensate deviations occurring between the actual course of the joint and the estimated one.

In automatic welding machines, which most commonly but not necessarily produce the welding seam by electric arc welding carried out with or without a protective gas supply, the welding head or its equivalent is caused to follow the joint either by moving the head supporting machine part only, such as by means of a so-called industrial robot, by moving the workpiece only, such as by some suitable conveyor means, or by moving both the workpiece and the head supporting machine part by means of some suitable combination of co-ordinated mechanisms.

For various reasons it is objectional in such welding machines to control the relative movement between the welding head and the workpiece by means of some sort of mechanical joint follower which during the entire welding process continuously remains in physical contact with a region of the workpiece lying close to the welding seam to be produced. Therefore, it is common practice to use some kind of equipment, such as an industrial robot or a conveyor system, which in one way or the other can be programmed or otherwise adapted to produce a relative movement between a fixture for the workpiece and the head supporting machine part along an estimated path which is as close as possible to the desired one. However, in practice this estimated path can only be approximately correct, because several unpredictable factors, such as varying dimensional tolerances of the workpiece parts, deformations of these parts resulting from welding stresses and insufficient accuracy in securing the workpiece to the fixture, will result in deviations between the two paths, which most frequently are only small, perhaps at most some tens of millimeters, but which can nevertheless hazard the welding result. In order to compensate such deviations between the actual course or line of the joint and the estimated one it is previously known per se to intermittently detect the actual position of the joint and, when required, to correct the path of relative movement between the welding head support and the workpiece accordingly. However, so far this has required a complicated and expensive supplementa tion of the welding machine with further moving mechanisms operative in two planes at right angles to one another.

The present invention has for its object to offer a much simpler but nevertheless entirely satisfactory alter native to the previously known art, which alternative per mits the estimated and preselected path of relative movement between the fixture of the workpiece and the machine part supporting the welding head to remain unchanged during the entire welding operation, whereas instead any deviation of the actual course of the joint from the estimated one is compensated by correcting the position of the welding head in relation to its support at rather close time intervals. With this object in view the device according to the invention presents the characterizing features set forth in the following claims. For further elucidation of the invention a preferred embodiment thereof will now be described with reference to the accompanying drawings, in which

Fig. 1 is a side view of a welding machine provided with a device according to the invention,

Fig. 2 is a slightly simplified and partial perspective view illustrating the welding head adjusting device in operation,

Fig. 3 is a longitudinal sectional elevation of the device showing its details in an inoperative position, and

Figs, 4 to 9 inclusive are simplified longitudinal sectional elevations of the device illustrating various stages in its operation. The welding machine illustrated in Fig. 1, which is an extremely simple variant of the type of automatic welding machine in which the device according to the invention is intended to be used, comprises a table 1 on which a workpiece 2 is secured in a predetermined position by well known fixture means not shown. A stationary stand 3 is secured to the table 1 and supports a guide 4 for a slide member 5 which by means of a driving mechanism, not shown, can be reciprocated along a rectilinear path relative to the guide and, hence, to the table 1. Connected to the free end portion of the rod 5 by means of a coupling piece 6 is a machine part 7 serving as a support for a welding head adjusting device 8 according to the invention. This device 8 comprises a holder 9 secured to the machine part 7 and a welding head carrier 10 which is adjustably connected to the holder and has an externally cylindrical portion 11. Clamped to this carrier portion 11 and embracing the same is a radially projecting bracket 12 for a welding head 13 which may thus be adjusted both axially and circumferentially in relation to the carrier 10. To the upper end of the welding head 13 are connected a. cable for current supply and conduits for the supply of electrode material and, if required, a protective gas, which cable and conduits in a manner known per se are all enclosed in a common prote ctive sheath 14. The carrier 10 has a sensor member 15 which is extensible in a direction towards the clamped workpiece 2 on the table 1 as will be more closely described in the following. The workpiece 2 is composed of at least two parts which are to be welded together. By way of example, these parts may have the form and be put together in the manner illustrated in Fig. 2, where they are designated by 2a and 2b, respectively, so as to form between them an elongate joint lβ located between two surface portions 17 and 18 converging towards the joint. It is to be understood that in practice the parts of the workpiece most frequently are of a considerably more complex design than that shown in Fig. 2, but the conditions within the region of the joint may never theless be substantially the same as here shown for illustrative purpose only. Of course, during the welding opera tion in the machine of Fig. 1 the workpiece 2 must be fixed to the working table 1 in such a position that the joint 16 will extend at least generally parallel to the rectilinear path of movement of the machine part 7 as determined by the guide 4. However, as the joint is rarely perfectly rectilinear or at least will scarcely remain so during the weld ing operation, it is almost impossible in practive to assure a perfect agreement between the course of the joint and the path of the machine member 7 even if the dimensional accuracy of the parts of the workpiece is high. In order to substantially eliminate the detrimental effect of this fact on the welding result, the holder 9 together with the carrier 10 and its sensor member 15 form a device which makes possible a correction of the position of the welding head 13 in relation to the machine member 7 at close time intervals most suitably corresponding to a welding seam length of 10-15 millimeters.

The construction of the device 8 more clearly appears from Fig. 3. In the upper portion of the holder 9 there is a cylindrical chamber 20, the upper end of which is closed by a lid-like member 21 immovably connected by means not shown to the aforesaid machine part 7 for thereby reliably attaching the holder 9 thereto. In the lower portion of the holder 9 there is an open-ended bore 22 which is concentric with but smaller in diameter than the chamber 20. The upper end of the bore 22 opens into the chamber 20 and is surrounded by a shoulder 23 having seats for an annular series of supporting balls 24. The lower end of the bore 22 opens through the lower end face of the holder 9 where a yieldable sealing member 25 is provided.

The carrier 10 in its turn comprises a substantially cylindrical body having at its upper end a circular, disklike head or piston member 26 the circumferential surface of which is generally spherical. The piston member 26 is axially movable within the chamber 20 of the holder 9. with a sliding fit and is also tiltable therein within certain limits, and it is provided with a kind of piston ring 27 which may be radially expanded by supplying air under pressure to a hose connection 28 on the carrier 10 in order to thereby lock the piston member 26 in its given position within the chamber 20 and thus retain the carrier 10 in any desirable position relative to the holder 9. A shaft-like portion 29 of the carrier 10 extends downwardly from the piston member 26 and passes with a radial play out through the bore 22 in the lower portion cf the holder 9 , whereby it will be possible to tilt the entire carrier 10 a limited angle in all directions relative to the holder. The shaft-like carrier portion 29 is provided on opposite sides thereof with axially extending grooves 30 , in which corresponding guiding projections 31 engage with a sliding fit in order to prevent all rotational movement between the holder 9 and the carrier 10. It is to be ncted that, although the drawing figures 3 to 9 show only one of these grooves 30 and its related guiding projection 31 there is in practice a corresponding groove and projection opposite to the one shown. Thanks to these grooves and projections the carrier 10 will only be able to pivot relative to the holder 9 about an axis 32 which, as illustrated in Fig. 2, is at least approximately parallel to but remote from the joint 16 to be welded. It is to be noted that this pivot axis 32 does not remain stationary in relation to the hol der 9 but will move vertically when the carrier 10 is correspondingly moved upwards or downwards.

In the upper carrier portion 29 there is provided a cylinder bore 33 opening centrally on the upper side of the piston member 26 and housing a counter piston 34 which has an upper, spherical end 35 adapted to be pressed against a supporting surface 36 on the lower side of the holder lid 21 when air under pressure is supplied to a hose connection 37 at the lower end of the bore 33. The counter piston 34 thereby urges the carrier 10 downwardly in relation to the holder 9 and towards a lowermost end or starting position which is defined by the engagement of the piston member 26 against the supporting balls 24. In the lower portion of the carrier 10 there is provid ed another bore 40, in which a piston 41 is movable. The bore 40 is coaxial with and has in this case the same dia meter as the cylinder bore 33 for the counter piston 34. The piston 41 is attached to the upper end of a rod 42 which forms part of the sensor member 15 mentioned herein before and extends through a guide member 43 mounted within the lower end portion of the bore 40 so as to project centrally at the lower end of the carrier 10. The piston 4l is movable in a downward direction against the action of a return spring 44 when air under pressure is supplied to a hose connection 45 at the upper end of the bore 40. The downward movement of the piston 4l is limited by an upward ly extending, tubular extension 46 of the guide member 43 At its lower end the rod 42 is provided with a replaceable tip 47 which in the case shown is substantially cylindrical and has a generally semispherical free end.

From the foregoing it should be understood that the carrier 10 is adjustable relative to the holder 9 on one hand by moving axially thereto and on the other hand by tilt ing or pivoting about the axis 32. Hence, the welding head 13 attached to the carrier 10 is correspondingly adjustable in relation to the machine part 7 which moves along the path determined by the guide 4. According to the invention this fact is utilized in such manner that the position of the carrier 10 relative to the workpiece joint 16 is checked at suitable time intervals and, when necessary, corrected by means of the sensor member 15, it being in most cases suitable although not always entirely necessary to temporarily interrupt the welding process during each such procedure. How this sensing and adjusting procedure is actually effected by the device is illustrated by the diagrammatic figures 4-9. In Fig. 4 the carrier 10 is in its starting position, i.e. the position shown in Fig. 3, relative to the holder 9- However, as can be seen, this means that the welding head 13 occupies a slightly incorrect working position relative to the joint of the work piece 2. Now, air from a suitable source is supplied under a slightly reduced pressure through the connection 37 to the cylinder bore 33 and- under unreduced or in other words a somewhat higher pressure through the connection 45 to the bore 40, whereby the sensor member 15 is projected in a direction towards the work piece 2 in such manner that its tip 47 impinges against one of the inclined surface portions of the workpiece adjacent to the joint 16 as illustrated in Fig. 5 . At the same time the connection 28 on the carrier 10 is opened to the atmosphere whereby the carrier 10 will be. free to move relative to the holder 9. The result will be that the sensor tip 47 under the influence of the air pressure acting on the piston 41 seeks itself towards the joint thereby primarily causing the carrier 10 and the welding head 13 to move into a laterally corrected position as illustrated in Fig. 6.

When the sensor tip 47 finally abuts both the two converging surface portions of the workpiece 2 as in Fig. 6 no further lateral movement of the welding head carrier 10 will take place, and now the sensor member 15 is in a position which is representative for the actual position of the joint l6 only a short distance ahead of the point where the forward end of the welding seam is. However, in the case illustrated, the position of the welding head 13 is still not entirely correct, because in fact it is located a little too close to the joint. This error is corrected in the next stage, in which the carrier 10 under the influence of the air pressure acting on piston 41 is pressed upwards in relation to the holder 9 against the action of the yielding counter piston 34 until the upper end of the tubular extension 46 abuts the bottom side of the piston 41. When this is accomplished the sensor member 15 as well as the carrier 10 will be in the position relative to the holder 9 illustrated in Fig. 1 wherein a full correction of the position of the welding head 13 has been reached. Under the entire adjusting procedure thus described the counter piston 34 yieldingly urges the carrier 10 downwards relative to the holder 9 with a force which is considerably less than, and e.g. only half as great as, the force acting between the carrier 10 and the piston 41 of the sensor member 15.

In practice the entire adjustment procedure just described takes place very rapidly and practically continously and, as soon as this procedure has been completed, air under pressure is again supplied to the connection 28 in order to cause the piston ring 27 of the piston member 26 to expand and to thereby lock the carrier 10 in its new position relative to the holder 9. Then the sensor member 15 is immediately caused to retract as shown in Fig. 8 by the air pressure on the piston 41 being relieved. Preferably at the same time the pressure in the cylinder 33 is also relieved. Now the welding head 13 will be in a position which is entirely correct in relation to the joint of the work piece 2 and the welding operation can start again. After a short time interval the joint sensing procedure is repeated and, if now the position of the welding head rela tive to the joint has changed, for example as illustrated in a slightly exaggerated manner in Fig. 9, a new adjustment will be carried out. As will be readily understood by the man skilled in the art several modifications in details in the device shown and described are feasible without hazarding the result aimed at. Thus for instance the counter piston 34 instead of being actuated by a lower air pressure than the sensor piston 41 may be given a correspondingly smaller diameter, in which case the bores of the two pistons may openly communicate and have a common single connection, such as connection 45 It is also possible to let the counter piston 34 be actuated solely by a spring. Furthermore the releasable locking of the carrier 10 in relation to the holder 9 may be accomplished by other means than those shown in the illustrated example. This is particularly true if the welding head carrier does not have the piston member 26 as shown and described but is instead swingably mounted on a slide member which in turn is movable towards and away from the workpiece along a guide member serving as a holder. Of course, the configuration of the sensor tip may also be varied within wide limits in order to fit the workpiece or, more specifically, the environment of the joint to be welded. For example, the sensor tip may be forked or Y-shaped in order to straddle with its prongs a portion of the workpiece in case the joint to be welded follows an external edge on the latter, because the essential thing is that the sensor tip when being caused to impinge against the workpiece, somehow seeks itself into a well defined workpiece abutting position which serves as an indication of the actual position of the joint.

Claims

1. A welding head adjusting device for use in a welding machine of the kind in which during the welding operation a relative movement between the workpiece (2) and a machine part (7) serving as a support for the welding head (13) along a predetermined path corresponding to an estimated course of the joint (16) to be welded is caused to take place, the device being adapted to compensate deviations occuring between the actual course of the joint and the estimated one, c h a r a c t e r i z e d in that it comprises a holder (9) adapted to be secured to the machine part (7), a carrier (10) for the welding head (13), which carrier is connected to the holder (9) in a manner to permit adjustment thereof relative to the holder in a direction towards and away from the joint (16) to be welded as well fas in a direction transverse to the joint in order to thereby change the position of the welding head (13) relative to the machine part (7), a sensor member (15) movably connected to the welding head carrier (10) and operative to intermittently impinge against the workpiece (2) in a manner to seek itself, when being actuated, into a workpiece abutting position which serves as an indication of the actual position of the joint (16), and means for forcing the welding head carrier (10) into a predetermined position relative to the sensor member (15) at the time when the latter has reached its workpiece abutting position, whereby any necessary correction of the position of the carrier (10) relative to the holder (9) and, hence, of the welding head (13) relative to the workpiece (2) will be effected in the event of a discrepancy between the actual position of the joint (l6) and the estimated position there of.

2. A welding head adjusting device according to claim 1 c h a r a c t e r i z e d in that the welding head carrier (10) is adjustable relative to the holder (9) in the trans verse direction of the joint (16) by being pivoted about an axis (32) which generally follows the joint but is remote therefrom.

3. A welding head adjusting device according to claim

1 or 2 c h a r a c t e r i z e d in that means (27) are provided for positively locking the welding head carrier (10) in all its feasible positions relative to the holder (9), the locking means being releasable in each sensing operation.

4. A welding head adjusting device according to claim 3 c h a r a c t e r i z e d in that the welding head carrier

(10) comprises a circular piston member (26) which is radially expansible by supplying a pressure medium thereto, and that the holder (9) comprises a cylindrical chamber

(20) in which the piston member (10) is movable in a direction towards and away from the workpiece (2) and also tiltable to a limited extent in a direction transverse to the joint (16) to be welded, the carrier (10) being lockable relative to the holder (9) by expanding the piston member

(26) within the chamber (20).

5 A welding head adjusting device according to any one of the preceding claims c h a r a c t e r i z e d in that the sensor member (15) comprises a rod (42) which is guided relative to the welding head carrier (10) and extensible therefrom towards the workpiece (2), and a tip

(47) on the rod having such configuration that, when the rod (42) is extended, it will seek the workpiece abutting position representative of the actual position of the joint

(l6) by engaging surface portions (17, 18) on the workpiece

(2) forming an angle to one another.

6. A welding head adjusting device according to claim 5 c h ar a c t e r i z e d in that the sensor rod (42) is connected to a piston (41) which, in a bore (40) provided in the welding head carrier (10) and under the influence of a pressure medium supplied to one end of the bore, is movable to push the rod (42) into a predetermined end position relative to the carrier (10), the piston (41) preferably being so moved against the action of a return spring (44).

7. A welding head adjusting device according to any one of the preceding claims c h ar a c t e r i z e d in that between the welding head carrier (10) ahd the holder (9) there is provided a piston-cylinder-mechanism (33-35) which, under the influence of a pressure medium supplied thereto, urges the carrier (10) to move towards the workpiece (2) in relation to the holder (9).

8. A welding head adjusting device according to claims 6 and 7 c h a r a c t e r i z e d in that the pistoncylinder-mechanism (33-35) comprises a cylinder bore (33) in the welding head carrier (10) which is coaxial with the bore (40) of the piston (41) connected to the sensor rod (42), and a counter piston (34) movable in the cylinder bore (33) and having an end portion (35) abutting a supporting. surface (36) in the holder (9).

9. A welding head adjusting device according to any one of the preceding claims c h a r a c t e r i z e d in that the welding head carrier (10) has an externally cylindrical portion (11), and that the welding head (13) is connected to the carrier (10) by means of a bracket (12) adjustably embracing the cylindrical carrier portion (11) and adapted to be fixed thereon by clamping.