Abstract:
A device for connecting a tool to a mechanical drive contains as the coupling element a spring washer coupling or clutch, which is made in one piece from metal and at least in the rotation direction has a limited resilience. Use is made thereof for preventing torque peaks in the case of a sudden deceleration of the tool, e.g. if a screw strikes a wood surface.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a device for connecting a tool to a mechanical rotary drive. The tool can e.g. be a bit or also drilling/cutting tools such as e.g. countersinking cutters, taps or reamers. With tools of this type the problem arises that the alignment between the workpiece to be rotated, e.g. a screw, and tool is not always correct. Numerous proposals for solving this problem exist. 
     For example a flexible socket wrench is known (DE 36 24 686), where the pivotability is ensured by pins at right angles to the longitudinal axis of the tool. 
     A screwdriver with an articulated head part is also known (DE 94 03 845), where use is made of a tubular rubber spring. 
     A device for connecting screwdriver inserts to a drive mechanism is known (DE 41 43 218), where a torsion coupling is provided, which allows an angular movement between the driving part and the driven part. 
     In the case of socket wrenches a further problem arises in that very high torques can occur on stopping the screwing movement and which can lead to the destruction of the tool or also the screw. If on turning a screw into hard wood the screw head reaches the wood surface, a sudden torque occurs and a release clutch on the drive is no longer able to immediately flatten the torque peaks. 
     The problem of the invention is to provide a device for connecting a tool to a mechanical rotary drive, which compared with the prior art offers advantages with respect to the service life of the tool and/or screw. 
     SUMMARY OF THE INVENTION 
     The invention relates to a device for connecting a tool to a rotary driving apparatus through a spring disc coupling, also referred to herein as a spring washer coupling. 
     The spring washer coupling or clutch is a component built up in one piece from a plurality of parallel, ring-shaped washers, which are interconnected with the aid of webs. The webs pass along a diameter. The webs between two washers are displaced by 90ø with respect to the webs between the next two washers. Such a spring washer coupling is e.g. known from EP 318 669 and is intended to compensate any alignment errors of the axes which occur and these can be both angle errors and displacement errors. 
     According to a further development of the invention the drive element and driven element are mounted in such a way that they are always positioned coaxially. In this case the spring washer coupling is not used for compensating alignment errors of rotation axes. Instead it serves exclusively to bring about in the rotation direction a slight flexibility or resilience of the coupling element and to reduce the aforementioned impacts when the screwing movement is suddenly stopped. 
     However, it is also possible to mount the drive element and driven element in such a way that an angle compensation of their rotation axes is possible. 
     In order to bring the coupling element in a particularly simple manner into rotary engagement with the drive element and/or driven element, according to the invention it is possible for the at least one entry end of the coupling element to have a polygonal, e.g. hexagonal shape, which engages in a complimentary recess of the drive element and/or driven element. 
     The spring washer coupling also has resilience characteristics in the axial direction. According to the invention the coupling element can have an end clearance. 
     A possible tool, which can be connected to the rotary drive by the device is a bit for a mechanical screwdriver. Here it is mainly a question of reducing sudden torque peaks. 
     However, according to the invention the device can also be used with a drill, where it is appropriate to integrate the described coupling element e.g. into a drill chuck. 
     According to a further development of the invention the coupling element is constructed in one piece with the drive element and the driven element. As a result the number of components of the connecting element is reduced. In addition, the device then has a simpler construction. 
     According to a further development of the invention the gaps between the parallel, ring-shaped washers of the spring washer coupling are filled, e.g. extruded completely or partly with a relatively hard or rigid elastomer material. Extrusion with a soft elastomer material does not modify the resilience characteristics of the spring washer coupling, but can prevent the penetration of dirt. Extrusion can take place in such a way that also the outside is covered with an elastomer coating, so that it is no longer possible to see the slits. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features details and advantages of the invention can be gathered from the following description of a preferred embodiment thereof and with reference to the attached drawings, wherein show: 
     FIG. 1 Diagrammatically a longitudinal section through a device according to the invention. 
     FIG. 2 A section along line II—II in FIG.  1 . 
     FIG. 3 A part axial sectional view of another embodiment. 
     FIG. 4 A representation corresponding to FIG. 3 of an embodiment with a drill chuck. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows in a highly diagrammatical, simplified form a device with which a tool, e.g. a bit, can be connected to an electric screwdriver. The device contains a drive part  1  with a shank  2 , which can either be fixed in a chuck or can be directly connected to the drive. The drive part  1  has an inner recess  3  open to one face and which in the vicinity of the bottom  4  of the recess  3  has a hexagonal cross-section. The recess  3  has a circular construction in the area located further towards the open face. 
     Coaxially to the drive part  1  is provided a driven part  5 , which also has an inner recess  6  open to one face. The two inner recesses  3 ,  6  are arranged in reciprocal extension and pass into one another when the parts are assembled. The inner recess  6  has in the vicinity of its bottom  7  a hexagonal cross-section, to which is connected an area with a circular cross-section. 
     On the axial face  8  of the driven part  5  remote from the recess  6  is formed a hexagonal receptacle  9  for the bit. By means of an outer sleeve  10 , which is only shown in simplified form, the two parts  1 , 5  are held in such a way that they are axially aligned, but separated by an axial gap  17 . 
     In the two inner recesses  3  and  6 , which pass into one another, is inserted a coupling element  11  to be described in greater detail hereinafter. The axial extension of the coupling element  11  is somewhat smaller than the spacing of the bottoms  4 ,  7  of the two inner recesses  3 ,  6 , so that the coupling element  11  has a certain end clearance. 
     The upper end of the coupling element  11  in FIG. 1 has a hexagonal cross-section corresponding to the cross-section of the corresponding area of the inner recess  3 . By means of said engagement end  12  the coupling element  11  engages in the inner recess  3  of the drive part  1  in the rotation direction. 
     At the opposite end the coupling element  11  also has an engagement end  13  with a hexagonal cross-section, which is adapted to the hexagonal cross-section of the inner recess  6  in this area. The coupling element  11  also engages with this engagement end  13  in non-rotary manner in the driven part  5 . 
     Between the upper engagement end  12  and the lower engagement end  13  the coupling element has a cylindrical body, which forms or represents a spring washer coupling or clutch. The spring washer coupling has an axial bore  14 , cf. FIG.  2 . It comprises a plurality of spring washers  15 , which have a small mutual spacing in the axial direction. The spring washers are interconnected by webs  16 , cf. the section of FIG. 2, which run in the radial direction from the axial bore  14  to the edge. In other words the webs  16  pass along a diameter. The webs  16  between two washers are displaced by 90ø with respect to the webs between one of the two washers and the in each case next spring washer  15 . In this way a resilience or flexibility is obtained in the axial direction, together with a deflectability. However, no use is made thereof in the arrangement according to FIG.  1 . What is important for the application case shown here is the slight, but very controlled flexibility in the rotation direction. The coupling element here acts as a torsion spring. 
     Through the choice of the thickness of the spring washers  15 , the width of the webs  16  and the number thereof, the material and diameter of the central bore  14 , it is possible to bring about a desired spring characteristic of the spring washer coupling. 
     FIG. 3 shows an embodiment of a connecting element in which the drive part, driven part and coupling element are constructed in one piece. The drive part  21  is constructed as a hexagonal shank, which is inserted in a corresponding receptacle of a tool and can be locked there by a clamping element, which engages in a constriction  22  of the shank  21 . 
     To the shank  21  is then connected the coupling element  23  constructed as a spring washer coupling. The construction has already been described in connection with FIG.  1 . To the coupling element  23  is connected the driven part  24 , which is constructed as a cylindrical body with an axial recess  26  open to the face  25 . The recess  26  has a hexagonal cross-section, so that a bit can be inserted in it. 
     In the bottom  27  of the recess  26  is inserted a magnet  28  serving to magnetize the bit, so that in this way a screw is held on the bit. 
     For locking the bit the recess  26  can have a circumferential groove in which is inserted an O-ring  29 . On inserting the bit it is compressed in such a way that it non-positively fixes the bit. 
     In an embodiment of the connecting element according to the invention the gaps  30  between the individual spring washers can be extruded with a plastics material, e.g. elastomer. As a result no dirt, chips or the like can penetrate the gaps of the spring washer coupling, which might influence the characteristics thereof. For simplification reasons the extrusion with the plastics material is not illustrated. Extrusion can also take place in such a way that the entire outer contour of the coupling element  23  is covered. 
     FIG. 4 shows another embodiment, where it is part of an automatic drill. On the outer end of the connecting element is placed a drill chuck  31  with the aid of which a drill can be clamped between several jaws  32 . The drill chuck is connected by means of a coupling element  33 , constructed as a spring washer coupling, to a plate  34 . On the plate  34  are constructed three journals  35 , which can serve to mount gearwheels. These gearwheels form part of a planetary gear with which the drill chuck  31  is driven in rotary manner. 
     In the case of this connecting element once again between the drive part, in this case the washer  34 , the coupling element  33  and part of the drill chuck in which the jaws  32  are mounted a one-piece formation exists. 
     Whereas in the embodiment according to FIG. 1 the coupling element with the spring washer coupling serves exclusively to flatten torque peaks on reaching an end stop, the spring washer coupling in the embodiments of FIGS. 3 and 4 can also allow an angle compensation and/or an axial displacement.