Spot welding tongs for robotic applications in resistance welding or workpieces

This application is a divisional application of U.S. patent application Ser. No. 10/563,528 filed on Jan. 3, 2006, wherein the disclosure of this application is hereby incorporated herein by reference in its entirety, and wherein the \'528 application is a national stage application and claims priority from international Application Serial No. PCT AT/04/00151 filed on May 4, 2004, and wherein the international application claims priority from Austrian Application Serial no. A1023/2003 filed on Jul. 3, 2003, wherein the disclosures of the \'528 application, the PCT application, and the Austrian application are hereby incorporated herein by reference.

The invention relates to spot welding tongs for robotic applications for the resistance welding of workpieces and, in particular, sheet metals, of the type including tong arms which are each pivotally mounted on a base body and adjustable by an actuating means and to which electrode holders for the electrodes are fastened, and further including winding means comprising a wind-off roller and a wind-up roller for winding off and on a strip for the protection of at least one electrode. The tong arms pivotally mounted on the base body are pivoted relative to each other in order to produce a spot weld and again pivoted away from each other after completion of said spot weld.

The invention further relates to spot welding tongs for robotic applications for the resistance welding of workpieces and, in particular, sheet metals, of the type including tong arms which are each pivotally mounted on a base body and adjustable by an actuating means and to which electrode holders for the electrodes are fastened.

From DE 197 54 546 C1, a spot welding tool comprising a winding device for winding on and off a film strip transversely contacting the electrode tip of the spot welding electrode is known. The spot welding tool is equipped with an annular wind-off coil for winding off the film strip and an annular wind-up coil for winding up the film strip, and comprises an annular driving means for the clocked rotation of the wind-up coil. The wind-off coil, the wind-up coil and the driving means are adjacently arranged, coaxially with one another, around the electrode shaft or electrode holder of the spot welding electrode. A first setting roller is arranged obliquely to the electrode shaft and at a radial distance from the wind-off coil to deflect the film strip from the wind-off coil towards the electrode tip and place it in a transverse position. Furthermore, a second setting roller is arranged obliquely to the electrode shaft and at a radial distance from the wind-up coil to deflect the film strip from the electrode tip towards the wind-up coil and place it in a transverse position, wherein the two setting rollers are arranged in an opposed relationship laterally of the electrode shaft.

A similar configuration is also known from JP 05 192 774, in which the wind-up and wind-off coils are likewise arranged on the electrode shaft or electrode holder, respectively.

The previously mentioned designs involve the disadvantage that the accessibility of the spot welding tool is strongly limited because of the arrangement of the wind-up and wind-off coils in the region of the electrode shaft or electrode holder, which calls for a substantial enlargement of the spot welding tongs in the end region and, in particular, in the welding zone.

As a result, only easily accessible workpieces can be spot-welded by a spot welding tool of this type.

Other constructions of spot welding devices including strips for the protection of the electrodes are known from JP 10 029 071 A, JP 08 118 037 A, JP 04 322 886 A or JP 05 192 774 A. In those spot welding tools, the strip, which is supplied and discharged via a winding device, is positioned above the electrode, likewise as a protection against any contact of the electrode with the workpiece or structural component, so that the strip will contact the workpiece or structural component during a spot welding process. In doing so, the wind-up and wind-off coils are arranged and fixed independently of the spot welding tool.

U.S. Pat. No. 5,961,854 A discloses spot welding tongs including a winding device for winding on and off an electrode protection strip, yet no details can be taken as to the arrangement of the winding device and the course of the electrode protection strip. The spot welding tongs are relatively voluminous, thus affecting the accessibility of workpieces.

U.S. Pat. No. 4,481,401 A discloses spot welding tongs including winding means for winding on and off an electrode protection strip, with a ring being arranged upstream of the electrode for the guidance of the electrode protection strip. Yet, the strip extends at an angle relative to the tong arm from that ring to the winding device, for which reason relatively much space is required again.

SU 1 206 038 A discloses spot welding tongs in which the winding means for the electrode protection strip is fastened to the tong arm and carried at an angle of about 45.degree. relative to the electrode. That arrangement requires an especially large space, for which reason those spot welding tongs are merely suitable for welding flat workpieces. Their use in the automated sector and, in particular, with welding robots is feasible only to a limited extent.

GB 571 401 A and JP 55141387 A too show spot welding tongs including winding means for electrode protection strips, which occupy relatively large spaces, for which reason an application with welding robots is practically impossible.

Finally, DE 199 48 043 A1 shows robot welding tongs according to the present application, yet does not disclose any winding means for winding on and off a strip for the protection of at least one electrode.

There, it is disadvantageous that a very large space is required such that the direct application is only feasible with flat workpieces. An automatic use, particularly with robots, is therefore not possible.

Another, very essential disadvantage of the above-mentioned prior art devices resides in that the strip is pulled over the electrode during conveyance, thus causing an elevated electrode wear on account of the friction occurring between the electrode and the strip.

One object of one embodiment of the present invention, therefore, resides in providing spot welding tongs for robotic applications for the resistance welding of workpieces, with which the accessibility is not substantially affected and this results in a very simple and a compact design of the spot welding tongs including an electrode protection strip. In addition, an exchange of the strip is to be feasible as simply and rapidly as possible.

According to another object of one embodiment of the present invention, the structure of the tong arm is to be as light-weight and compact as possible.

The first object of one embodiment of the invention is achieved in that the wind-off roller and the wind-up roller of the winding means are arranged on the base body or on the tong arm, and that at least one guiding groove is provided on the tong arm and/or on the electrode holder for the guidance of the strip along the tong arm.