Rotational dobby
FIELD OF THE INVENTION 
     This invention relates to a driving coupling for a rotationally driven dobby and, more particularly, to such a driving coupling which includes an eccentric ring supported freely rotatably on a drive shaft for controlling a heddle frame of a weaving machine, a connecting rod freely rotatably supported on the eccentric ring, a pivotally supported controlling switching arm having an indexing ring with a controlling cam, which indexing ring is approximately concentric with respect to the drive shaft and can be swung back and forth with respect to and in a radial plane of the drive shaft, and two pawls which can engage the same groove in the drive shaft and are each supported swingably on the eccentric ring, wherein one pawl is a driving pawl which serves to take along the eccentric ring with the shaft and the other pawl serves to hold back the eccentric ring so as to maintain the driving pawl in play-free engagement in the groove of the drive shaft. 
     BACKGROUND OF THE INVENTION 
     Such rotational dobbies have become well-known both in technical literature and also in reality, wherein for the coupling, different radially movable and controlled driving keys which can engage a groove of the drive shaft have been provided, for example as disclosed in U.S. Pat. No. 3 180 366, German Pat. No. 1 535 258 and German Offenlegungsschrift No. 30 01 310, and on the other hand pawls have been provided which are supported on the eccentric ring, are controlled in any manner and engage a groove of the drive shaft. Examples of such a driving coupling are for example illustrated and described in Swiss Pat. No. 473 253,  German Offenlegungsschrift No. 29 09 131 and French Pat. No. 1 201 358. 
     In all of the aforementioned conventional rotational dobbies, the drive shaft rotates intermittently in successive steps of 180°. It is common to effect the control of the coupling during the phase when the drive shaft stands still, wherein such standstill phase in the case of weaving machines which run with a high speed is relatively short or is limited in time. There thus resulted during the development of high-speed rotational dobbies the problem of carrying out the entire control during this limited time or constructing the coupling so that the effective duration for the control, including the reading of the pattern card and also the giving of impulses and safe adjusting of the coupling members, is expanded without limiting the working speed of the connected weaving machines. 
     It has proven to be disadvantageous to have control mechanisms in which the important controlling function is carried out by a spring, because an instability factor with respect to a constant timely control sequence develops and such mechanism are unreliable when viewed over a long term, which is not the case in mechanical control mechanisms which do not have a spring. During the initial tensioning of springs in anticipatorily controlled arrangements, a considerable reserve force must be produced by the control apparatus, which requires a stronger type of construction of the control apparatus. Finally, it is decisive that the thickness of the coupling elements depends on the width defined by the heddle-frame separation. 
     Important for the coupling operation is furthermore the safe and certain engagement of the pawls in the groove of the drive shaft. The members for the engaging operation are advantageously tapered at their ends. It is thereby disadvantageous that, during a great load on a wedge or pawl, for example upon a quick shaft start during the intermittent shaft operation, the tapered ends facilitate a pressing of the coupling parts out of the shaft groove. For example, German Offenlegungsschrift No. 30 01 310 shows a locking system which, within the given conditions, is designed short pitched and for this reason does not assure the demanded functional safety. 
     A further condition which is requested from a modern machine is a universally usable coupling, that is a coupling which operates both during forward and also during reverse operation of the machine. The possibility of turning the shaft or the weaving back for pick finding must be assured in dobbies. 
     A goal of the invention is thus a driving coupling for rotational dobbies which works in both directions of rotation, which can be anticipatorily controlled without the help of a spring, which effects a play-free coupling, and which has in the coupled condition an automatic self-block. In addition, this coupling is to be able to be installed within the heddle-frame spacing of a weaving machine and is to work error-free at a high speed. 
     SUMMARY OF THE INVENTION 
     This is achieved by providing a rotational dobby of the above-mentioned type, in which respective plates of a toggle-lever joint are each pivotally coupled to a respective pawl and the swivel axle of the toggle-lever joint is guided slidably in the controlling cam of the switching arm, wherein to prevent rotation of the pawls and the eccentric ring about the drive shaft in the disengaged condition of the pawls, two stationary catch openings which are diametrically opposed one another are provided for receiving the swivel axle of the togglelever joint when it is in a bent-out position, and wherein the plates of the toggle-lever joint, in the extended condition thereof, serve to block movement of the pawls away from engagement with a groove of the drive shaft. 
     The connecting of the two pawls, which are arranged in a mirror-image relationship, by a toggle-lever system permits, on one hand, a staggered or simultaneous controlling and engaging thereof and, on the other hand, an automatic blocking in a coupled condition thereof in which the two plates and the joint lie in a straight line, that is, in an extended dead-center position. An anticipatory control is thus possible with a staggered control and engagement. 
     For controlling and switching the coupling or the toggle joint, a switching arm is arranged approximately concentrically around the drive shaft and is swung back and forth by the reading members of the pattern card. Such switching arms, which have an annular ring or enlargement, have become known through U.S. Pat. No. 3,724,511, U.S. Pat. No. 3,730,231, and U.S. Pat. No. 4,614,211 and have thereon 360° collars or grooves which, according to the invention, are connected to the swivel axle of the toggle joint. 
     For holding the eccentric ring against rotation when the pawls are disengaged, a part of the swivel axis of the toggle joint is moved into a stationary catch opening formed preferably by ends of two semicircular guide rails which are arranged coaxially around the eccentric ring on the connecting rod. These can be supported resiliently and can additionally hold the toggle joint in its locked condition during its rotational movement with the engaged pawls and the eccentric ring. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Two exemplary embodiments of the invention are illustrated in the drawings, in which: 
     FIG. 1 diagrammatically illustrates a lift unit of a dobby which is connected to a weaving machine and which works according to the principle of the rotational drive; 
     FIG. 2 is a side view of an inventive rotational lift unit in an engaged condition; 
     FIG. 3 is a cross-sectional view taken along the line III--III in FIG. 2; 
     FIG. 4 is a cross-sectional view similar to FIG. 3 but showing a different operational position; 
     FIG. 5 is a side view similar to FIG. 2 showing the lift unit of FIG. 2 in a disengaged condition; 
     FIG. 6 is a similar view of the lift unit in a position between its engaged and disengaged conditions; 
     FIG. 7 is a longitudinal cross-sectional view of a toggle-lever joint which is in an extended position and which is a component of the lift unit of FIG. 2; and 
     FIG. 8 is a view similar to FIG. 2 of a modified embodiment of the rotational lift unit of FIG. 2. 
    
    
     DETAILED DESCRIPTION 
     In FIG. 1, a dobby 2 is secured on the frame 1 of a weaving machine 10, and the drive shaft 3 of the dobby 2, through an eccentric ring which is not illustrated in FIG. 1, movably supports a connecting rod 4 which, through a linkage 40, effects movement of a heddle frame 100. 
     Referring to FIG. 2, the eccentric ring 5 is freely rotataly but axially nonmovably supported in a bore or bearing opening 45 through the connecting rod 4, and is rotatably supported on the intermittently rotating drive shaft 3, which has two longitudinal grooves 30 and 31 arranged diametrically opposite one another. 
     The movement of the connecting rod 4 is transmitted by a bolt or pin 41 to a driving arm 43 which is pivotally supported on a stationary pin 42 and which is pivotally coupled at a location spaced radially from the pin 42 to the linkage 40 which moves the heddle frame of the weaving machine. 
     Two pawls 7 and 70 have arm extensions 71 and 72 that make them two-arm levers which are swingably supported on the ring 5 by two pins 57 and 75 which extend parallel to the shaft 3. Depending on the control, the free ends 73 and 74 of the pawls can engage the grooves 30 or 31 in the drive shaft 3. Plates 81 and 82 of a toggle-lever joint 8 are pivotally coupled to a respective one of the arm extensions 71 and 72, and are pivotally coupled to each other by a swivel axle 80 which forms the swivel axis of the toggle-lever joint. 
     To control the coupling, or rather the toggle-lever joint, a switching arm 9 is supported swingably with respect to and in a radial plane of the drive shaft 3 on a housing-fixed or stationary bolt 92, and movement of the switching arm 9 is effected by a conventional control system 90 which preferably includes a not-illustrated and conventional pattern card. The switching arm 9 has in its center region an annular enlargement or ring 91, through which the drive shaft 3 of the dobby extends. The ring 91 of the switching arm 9 has in the side thereof facing the eccentric ring 5 an annular guide groove 98, which is also called a controlling cam, or alternatively a 360° collar similar to that disclosed in U.S. Pat. No. 3,730,231, the disclosure of which is hereby incorporated herein by reference. The guide groove 98 is operatively coupled to the swivel axle 80 of the toggle-lever joint 8 and controls the driving coupling by means of a member or roller 89 which slides or rolls in the groove 98 and, in the exemplary embodiment, is supported on the swivel axle 80. 
     In the preferred embodiment of FIG. 2, two arcuate guide rails 6 and 60 are fixedly secured on the connecting rod 4 in a diametrically opposed relationship so as to be adjacent to and concentric with respect to the opening 45 in the connecting rod 4. The guide rails 6 and 60 have adjacent ends 46 and 47 which serve as blocks having a gap or catch opening 48 between them, and a gap 49 is provided between the other ends of the guide rails 6 and 60. If desired, the rails 6 and 60 can be resiliently supported to yieldably permit a small amount of radially outward movement in a manner similar to that disclosed in U.S. Pat. No. 3,724,511, the disclosure of which is hereby incorporated herein by reference. 
     Starting out from the engaged position of the driving coupling according to FIG. 2, in which the pawls 7 and 70 engage the groove 30 in the drive shaft 3 during or approximately during a standstill of the drive shaft 3, the switching arm 9 can be moved to the right to the position according to FIG. 5. The swivel axle 80 and thus the pivot joint of the toggle-lever joint 8 are thereby moved radially outwardly into the catch opening 48 between the two blocks 46 and 47, which results in a bending of the toggle-lever joint. The two arm extensions 71 and 72 are thereby pivoted toward one another by the two plates 81 and 82 of the toggle-lever joint, thereby causing the pawls 7 and 70 to be swung outwardly out of the groove 30 to the position according to FIG. 5. A disk 88, which can engage the blocks 46 and 47 to effect a catching of the toggle-lever joint 8 in the catch opening 48, is provided on the swivel axis 80. In FIG. 5, the drive shaft 3 rotates without taking along or in other words effecting rotation of the eccentric ring 5. The toggle-lever joint remains caught in the catch opening. The toggle-lever joint 8, the pawls 7 and 70, and the eccentric ring 5 remain at a standstill in the positions shown in FIG. 5, which in turn holds the heddle frame stationary. 
     If a positional change of the heddle frame is now supposed to occur in response to the pattern card and under control of the control system 90, the switching arm 9 is pivoted by the system 90, shortly before reaching a standstill of the drive shaft, from the position A of FIG. 5 toward the position B, and cooperation of its guide groove 98 wit h the roller 89 causes the swivel axle 80 to be moved into the position according to FIG. 6. Since the groove 30 in the drive shaft 3 is already angularly aligned with the upper pawl 7, the pawl 7 can engage the groove 30, while the lower pawl 70 still rests on the drive shaft 3. In order to assume this asymmetrical position, the swivel axle 80 moves away from the normal symmetry axis Y of the toggle-lever joint 8 by a distance X. Upon further rotation of the drive shaft, the pawl 7 is taken along rotationally by the edge 32 of the groove 30. The pawl 70 moves into engagement with the groove 30 and thus prevents play in the coupling. Upon reaching this position, the switching arm 9 can swing the rest of the way to position B (FIG. 5), so that the mechanism is in the position according to FIG. 2. The two plates 81 and 82 of the toggle-lever joint thus move to an extended position in which they form a straight line and produce a toggle effect which blocks pivotal movement of the pawls 7 and 70 about pins 57 and 75. The eccentric ring 5 is taken along rotationally by the pawls 7 and 70 due to the bearing pins 57 and 75 which are secured to the ring 5. The member or roller 89 slides or rolls in the guide groove 98, and the entire toggle-joint mechanism rotates 180° along with the ring 5 to the next standstill position of the drive shaft 3, and carries out further 180° movements until the next control movement of the switching arm 9 occurs. The heddle frame 100 of the weaving machine 1 is moved between its upper and lower positions by the connecting rod 4 and the linkage 40 as the ring 5 rotates. 
     For releasing the coupling between the ring 5 and shaft 3, the switching arm 9 is moved by the system 90, during or approximately during a standstill of the drive shaft 3, from position B (FIG. 5) into one of the positions A and C (FIG. 5), as appropriate. The groove 98 in the ring 91 of the arm 9 thus moves the roller 89 and axle 80 radially outwardly, causing the automatic block of the toggle-lever joint to be released and the pawls 7 and 70 to move out of the groove in the drive shaft. 
     The described switching operations, which are effected by movement of the switching arm 9 between three positions, can occur both in the region of the right catch opening 48 and also in the region of the left catch opening 49. The right catch opening 48 receives the disk 88 during movement of the arm 9 from the position B into the position A, and the left catch opening 49 receives the disk 88 during movement of the arm 9 from the position B into the position C. 
     The free ends 73 and 74 of the pawls 7 and 70, and also the edges 32 and 33 of the grooves 30 and 31 in the drive shaft 3, are ccnstructed so that, when the driving coupling is engaged (FIG. 2), they are approximately parallel to a line which extends between the two swivel points 57 and 75 of the pawls, and the pawls in the position of FIG. 2 extend approximately tangentially with respect to the outer surface of the drive shaft. This results in a troublefree engagement of the pawls and ensures, during the fast starting of the drive shaft after a standstill and the associated flank pressure applied to the locking surfaces 73 and 74, that the pawls are not moved out of the shaft groove, the engaging surfaces of the pawl ends 73 and 74 and groove edges 32 and 33 being held against relative movement by friction. 
     FIG. 8 shows a double modification of an inventive rotational lift unit. The pawls 7 and 70 are in engagement with the groove 30 in the drive shaft, so that the eccentric ring 5 carries out a rotary movement of 180° with the drive shaft. All elements correspond with those of FIG. 2. In addition, as a supplement, two spring arrangements are provided, namely a single tension spring 67 which pulls the two pawls 7 and 70 pivotally toward one another and two leaf springs 76 which are each secured on a respective pawl 7 or 70 and which each have an end which extends into the space between the drive shaft and indexing ring and which, in the engaged condition of the pawls, is spaced a small distance from the inner circumference of the indexing ring 91 so that, during rotation of the eccentric ring 5 and the pawls 7 and 70 with the drive shaft 3, friction does not occur between the springs 76 and the ring 91. When the pawls are in a disengaged position and the disk 88 of the toggle joint 8 is in one of the catch openings 48 and 49 so that the eccentric ring is held against rotation about the shaft 3, then the free ends of the leaf springs 76 are each supported on the inner circumference of the indexing ring 91 and support through their resilient spring action a subsequent movement of the pawls into engagement with a groove in the drive shaft. 
     It is expressly pointed out that the springs 67 and 76 do not themselves control the movement of the pawls 7 and 70 and the toggle-lever joint components 71, 81, 80, 72 and 82, but instead only assist or support their controlled movement in certain directions in the sense of a certain acceleration. 
     It is also emphasized that the springs 67 and 76 achieve essentially the same result, and it is thus possible to provide only the spring 67 or only the springs 76. 
     The boundary surfaces 61 and 62 which form the catch openings 48 can be provided on two or four blocks or, as explained above, can be provided on blocks 46 and 47 which are the ends of guide rails 6 and 60 which are each semicircular and concentric to the bore 45 in the connecting rod 4 for the eccentric ring 5. The joint of the toggle-lever joint 8 can slide along these guide rails 6 and 60 to provide an additional safety factor against a bending of the toggle-lever joint, wherein the disk 88 on the swivel axis 80 is preferably the part which slidably engages the rails 6 and 60 and can also be a cam on the swivel axle itself or a separate plate. The catch openings 48 and 49 can if desired be arranged on a stationary part of the machine housing instead of on the connecting rod, and have entry widths which are larger than the largest diameter of the joint of the toggle-lever joint, for example larger than the diameter of the disk 88. With this, funnel-shaped catch openings to effect a catching of the toggle joint are assured. Through the already described two-part asymmetrical position of the swivel axle 80 with respect to the catch opening 48 or 49, there results a controllable control path and a play-free support. 
     The pawls 7 and 70, the toggle-lever joint 8, and the catch openings 48 and 49 preferably lie symmetrically with respect to the radially extending centerline y of the connecting rod 4. 
     In place of the connecting rod 4, it is possible to provide, for transferring movement of the eccentric ring 5 through the linkage 40 to the heddle frame 100, a roller lever, which can consist of a rocking lever which is arranged on a stationary axle, which on one side engages with a roller the periphery of the eccentric ring, and which on the other side is connected to the linkage 40. The heddle frame, under control of the rocking lever, is moved up and down during the rotation of the eccentric ring. The blocks 46 and 47 of the guide rails 6 and 60 which form the catch openings 48 and 49 are thereby secured on the housing or on the frame of the dobby 2. 
     The described driving coupling makes possible an anticipatory control of the actual coupling with a controlled forced engagement at the moment of the standstill of the drive shaft. No spring-controlled operations take place, and the individual structural parts are not subjected to wear through friction. The coupling, in spite of this, operates safely and quickly with a simple automatic lock in the coupled position. 
     Although particular preferred embodiments of the invention have been disclosed in detail for illustrative purposes, it will be recognized that variations or modifications of the disclosed apparatus, including the rearrangement of parts, lie within the scope of the present invention.