Abstract:
At least one torsion spring is traversely mounted between first and second elements of an overload protector. One end of the spring is elongated to form a pressure arm which bears against the second element.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to robotics, and more particularly relates to overload protectors for robot arms. 
     A device of this type is shown in German Offenlegungsschrift 32 1 132. In this known device, there are two elements, one being secured to the robot arm and the other being secured to the tool or tool holder. These elements are held together by holding bolts, and an axial compression spring holds the elements apart. When sufficient force is exerted on the tool or tool holder, as in the case of an overload, the spring is compressed and the tool axis buckles with respect to the axis of the robot arm. This triggers an internal sensor which halts further operation and thereby protects the robot arm from damage. 
     SUMMARY OF THE INVENTION 
     One object of the invention is to provide a robot arm overload protector which is short and which permits a relatively large excursion between the tool/tool holder and the robot arm itself. 
     Another object is to provide a protector of this type in which the preloading between the elements does not change greatly at different excursions. 
     A further object is, in general, to improve on known devices of this type. 
     In accordance with the invention, an overload protector has two elements which are movable axially towards and away from each other. At least one torsion spring presses the two elements apart. The torsion spring is transverse to the axis of the overload protector and is attached to one of the coupling elements. Each of the springs urges a pressure arm to bear against the other element. 
     Because the springs are torsion springs and are transverse to the axis of the overload protector, they take up little axial height. By manufacturing the torsion springs with a large number of turns, the force exerted by the pressure arm changes only slightly even during large motions of the two elements with respect to each other. One advantageous consequence of this is that it is possible to manufacture an overload protector with a low preloading even for large excursions. 
     Advantageously, the torsion spring is of coiled wire and the pressure arm is a linear extension of the wire. This is simple to manufacture. Further advantageously, the two elements are kept in alignment by mating guide bushings and guide pins. This prevents the two elements from becoming disaligned. 
     In the preferred embodiment, there are a plurality of torsion springs which are arranged symmetrically about the axis. This reduces the transverse forces between the two elements and makes the response of the protector less dependant upon the direction from which the overload occurs. 
     Advantageously, the free end of each torsion spring is supported on a slider which slides along a track in the second element. This linearizes the relationship between the load on the overload protector and the motion of the two elements with respect to each other at the very beginning of motion. In the preferred embodiment, this is further accomplished by mounting the springs on rotatable rollers. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary and non-limiting preferred embodiments of the invention are shown in the drawings, in which: 
     FIG. 1 is a side and partially cross sectional view of a preferred embodiment of the invention; 
     FIG. 2 is a top view of the preferred embodiment; and 
     FIG. 3 is a section through the preferred embodiment along the Plane III--III in FIG. 1. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In the Preferred embodiment, there are two elements, element 1 and element 2. Element 1 is adapted for attachment to a tool or tool holder (not shown) using attachment holes 3, and element 2 is adapted for attachment to a robot arm (not shown) via attachment holes 3. Each of the elements 1 and 2 has an annular centering projection 4 which permits the device to be accurately secured to the robot arm and tool/tool holder. 
     In this example, two symmetrical torson springs 5 made for example of wire are mounted to the element 1. Each spring 5 is mounted on a cylindrical roller 9 which is made for example of plastic, and each roller 9 is secured to the element 1 by a shaft 10, on which the roller 9 rotates freely. 
     One end of each of the torsion springs 5 bears against the underside of the element 1. The other end of each of the torsion springs 5 is elongated in a straight line to form a pressure arm 6. The distal end of each of the pressure arms 6 is inserted into a slide element 7 which is entrained within a corresponding groove 8 in the element 2. 
     When the elements 1 and 2 are urged toward each other, the torsion springs are wound up as the slider elements 7 slide radially outwardly in their grooves 8. To keep the elements 1 and 2 in proper alignment, the element 2 supports guide pins 11 which enter into mating guide bushings 12 that are secured to the element 1. The guide pins 11 and mating bushings 12 are parallel to the axis. Reference numeral 13 indicates a plate which is secured to the end of each guide pin 11. 
     When the elements 1 and 2 are moved towards each other, the springs 5 are torsioned to a comparatively small extent because they have comparatively long pressure arms 6. Additionally, the arms 6 move comparatively freely because of the slider elements 7 and mating grooves 8. As a result, the force exerted by the torsion springs 5 remains relatively low regardless of the excursion of the elements 1 and 2, so that the preferred embodiment is suitable for use in low-force applications such as assembly operations. 
     Those skilled in the art will understand that changes can be made in the preferred embodiments here described, and that these embodiments can be used for other purposes. Such changes and uses are within the scope of the invention, which is limited only by the claims which follow.