Abstract:
A workpiece clamping system with a machine spindle and a clamping chuck has a bayonet lock with projections. The bayonet lock is closed by insertion and turning. The bayonet lock can be clamped or locked, whereby parts of the projections are movable and exert a locking force on the other projections. A bayonet lock can be placed internally or externally on the workpiece clamping system.

Description:
FIELD OF APPLICATION AND PRIOR ART  
       [0001]     The invention relates to a workpiece clamping system having a machine spindle and a clamping means for clamping a workpiece, the clamping means being fixable to the machine spindle. It is in particular replaceable and ensures a rapid change with respect to the most varied clamping systems or clamping means.  
         [0002]     In the case of machining by cutting, the parts to be machined must be fixed to a machine. For this purpose use is made of different clamping devices or clamping systems. The clamping device must correspond to the configuration of the part and the machining task. If different parts are made on the same machine, the specific devices must be changeable rapidly and with a high positioning accuracy. This set problem is solved in the case of so-called machining centres by the replacement of complete device ranges with so-called zero clamping systems, such as are e.g. described in De 297 22 730 U1 and DE 101 23 268 A1. Such zero clamping systems usually have a permanent clamping force or power implemented by spring action. The positioning and introduction of the necessary clamping or retaining force takes place by means of a draw-in nipple. The clamping systems fixed to these zero clamping devices are generally manually operated or are equipped with additional hydraulic or pneumatic connections. The retaining or draw-in force of the individual zero clamping devices is very limited, so that several clamping devices are used for one workpiece clamping range.  
         [0003]     In the case of machines where the workpiece is fixed to a machine spindle for machining purposes, it is only possible to fit one quick-change device to the spindle. The retaining forces necessary for machining and the necessary rigidity effects are much higher in such machines, such as e.g. hobbing machines. In addition, power-operated clamping systems cannot be fixed to the commercially available zero clamping systems because there is no interface to a power operation, such as e.g. a cylinder. Therefore the known systems are not suitable for machine tools, which have a power-operated clamping device at the spindle end. In addition, the known zero clamping systems have a very complicated construction.  
       PROBLEM AND SOLUTION  
       [0004]     The problem of the invention is to provide an aforementioned workpiece clamping system, in which the fixing and in particular the replacement of a clamping means on a machine spindle can on the one hand take place rapidly and on the other with high positioning accuracy, whilst giving the system a very simple construction.  
         [0005]     This problem is solved by a workpiece clamping system having the features of claim  1 . Advantageous and preferred developments of the invention form the subject matter of further claims and are explained in greater detail hereinafter. By express reference the wording of the claims is made into part of the content of the description.  
         [0006]     According to the invention a bayonet catch or bayonet lock is constructed on the workpiece clamping system and can be closed by attaching the clamping means to the machine spindle and by a rotary movement or actuation. However, locking means are provided so as to bring about a higher fixing force with a resulting more accurate positioning compared with a conventional bayonet lock. As a result the bayonet lock is locked so as to give a stronger and more release-protected fixing.  
         [0007]     Thus, the advantage of a rapid, simple fixing by means of a bayonet lock can be used, which normally does not require tool use. Through the combination with locking by the locking means, it is also possible to ensure that the bayonet lock does not of its own accord become loosened or even released. Moreover as a result of locking, the connection between the clamping means and machine spindle can be given an even more accurate fit and more precise positioning. It is advantageously possible that on locking the bayonet lock the clamping means is drawn or pressed more strongly against or into the machine spindle. Locking should also take place very simply and in an easy to release manner. Advantageous developments of the invention are directed at this. The device also has a simple construction, so as to prevent maintenance work to the greatest possible extent. With the joining of the workpiece clamping system there can be a coupling to a machine power clamping device.  
         [0008]     According to an embodiment of the invention, the bayonet lock has on the one hand projections on the clamping means and on the other projections on the machine spindle. These projections correspond to one another in such a way that they permit the function of a per se known bayonet lock. In the fixed state, i.e. when the bayonet lock is functioning, the projections are in engagement with one another by contact faces. These contact faces are inclined to the attachment direction, i.e. the direction in which the clamping means are moved up to or attached to the machine spindle. In the case of a rotating machine spindle said attachment direction is generally the rotation axis, so that the contact faces are also inclined to the machine spindle rotation axis. Advantageously at least one of the projections is movable in a direction inclined to the contact faces or inclined to the attachment direction. It is particularly advantageously movable perpendicular to the attachment direction, i.e. roughly precisely in the radial direction. Thus, through the movement of the projection the corresponding projection in the attachment direction is tightened, which permits the aforementioned intensification of fixing with increased retaining force or power.  
         [0009]     The movable projection or the locking means of the bayonet lock are advantageously provided on the machine spindle. This offers the advantage that on the machine spindle it is possible to provide other devices, such as tension tubes or those which can bring about locking. This is frequently the case on machine spindles. It is also possible to fix to in each case one machine spindle different clamping means, particularly chucks, which have a simple construction and no movable parts or projections, without the clamping means requiring modifications with respect to the rigid projections in their part of the bayonet lock.  
         [0010]     It is admittedly possible to give a complete projection a movable construction. However, advantageously only part of such a projection is movable, so that the projection is actually fixed and only a part is movable. Such projections can e.g. be made relatively wide and a central part is movable. Thus, in all cases there is a certain bayonet lock retaining force, even if the movable part does not move or fails, because e.g. the mobility is restricted by a dirtying effect or the like.  
         [0011]     For the movement of the projection and part thereof it is possible to provide a force, particularly a clamping force, which acts against a clamping ring. Such a clamping ring is advantageously loosely mounted or received and revolves in such a way that it engages on several projections, particularly on all the projections of part of the workpiece clamping system, i.e. so-to-speak on one side of the bayonet lock. Preferably it either runs inside or outside the projections. In a preferred development there are several movable projections or several movable parts, namely one on each projection, all engaging in a similar manner with the same clamping ring.  
         [0012]     For clamping purposes a screw can produce the power means between a movable projection or part thereof and the clamping ring. Advantageously the screw is mounted in a corresponding thread in the clamping ring and presses against the projection. Advantageously there is only a single clamping screw for such a clamping ring. If all the movable projections engage on the clamping ring, a very uniformly distributed clamping force is produced, as is generally known with such clamping rings. Such a clamping ring and which also ensures a good centring is e.g. known from DE 103 23 662 A, to which express reference is made here.  
         [0013]     It is possible for the bayonet lock part constructed on the clamping means to engage in the machine spindle or project into the same. On the inwardly projecting portion are provided radially protruding projections, which in particular protrude radially outwards. They are surrounded by corresponding projections fixed to the machine spindle and forming the part of the bayonet lock which is constructed on the machine spindle. Preferably and as indicated hereinbefore the movable projections are constructed on the machine spindle.  
         [0014]     In an alternative development of the invention a bayonet lock is so constructed that only part of it, particularly the part constructed on the clamping means is rotatable or has to be rotated for fixing purposes. Both during fixing and on locking relative to the machine spindle, the clamping means does not have to be rotated or moved. This has the major advantage that with large, cumbersome clamping means there is no need for a movement and they can consequently be gripped and secured to the machine spindle. This e.g. permits the interlocking of continuous hydraulic lines, which are interconnected by corresponding connections between the machine spindle and clamping means. Moreover further functional passages are possible, if rotation is not necessary.  
         [0015]     On the clamping means can be provided a rotary retaining ring which forms the bayonet lock part constructed on the clamping means. The retaining ring can have radially positioned projections with which cooperate corresponding projections on the machine spindle. As stated hereinbefore, the projections engage with one another by contact faces inclined to the attachment direction. Here again the attachment direction advantageously coincides with the machine spindle rotation axis. Here again the locking of the bayonet lock is brought about in that one of the projections or a part thereof is movable in a direction inclined to the contact face, advantageously perpendicular to the attachment direction. Reference should be made to the earlier description for details thereof.  
         [0016]     A projection can be moved by a force acting against a revolving force distributing element or a clamping ring, as described hereinbefore. It is also possible to provide a locking screw or the like, which moves the projection or part thereof for locking the bayonet lock. Alternatively to such a clamping ring, it is possible to provide on a force distributing element an inclined face with which it engages on the movable projection. The inclined face is inclined to the movement direction of the movable projection or its part. The angle between the inclined face and the attachment direction is preferably smaller than 90°, advantageously between 45° and 90°. The force distributing element can e.g. be moved in the attachment direction. Through the engagement of the inclined surface on the movable projection the latter is moved, said movement being in the form of a locking of the bayonet lock. As described for the clamping ring, it is advantageous if all the movable projections engage on the force distribution element. Thus, with a movement of the force distribution element it is possible to move all the projections or their parts.  
         [0017]     Advantageously in this development of the invention the bayonet lock is provided in the outer area of the workpiece clamping system/machine spindle and clamping means or surrounds the same. A rotary retaining ring can be positioned externally or form part of the circumference of the clamping means or machine spindle. It is advantageously accessible at its outer circumferential surface, so that it can be easily gripped and rotated.  
         [0018]     It can be advantageous if the force locking the bayonet lock acts permanently To this end a power or energy storage device can be provided, e.g. in the form of a spring mechanism. By means of a release device and a release force it is possible to cancel out the locking of the bayonet lock for closing or opening purposes. Without this release force the bayonet lock is automatically locked again.  
         [0019]     It is advantageously possible to provide for the movable projections or their parts permanently applied restoring forces and e.g. restoring springs can be used for this purpose. The restoring forces press the projections or their parts counter to the locking direction. In this way it is possible to ensure that in the absence of the locking force the movable projections are automatically released. Within the scope of the invention it is possible both to permanently apply the bayonet lock locking force and simultaneously allow the restoring forces to act on the movable projections. However, the restoring forces are overcome by the locking force.  
         [0020]     In order to bring about an adequate and very effective positioning and fixing, the bayonet lock is constructed uniformly or symmetrically. For this purpose the projections are uniformly distributed on the machine spindle and/or clamping means. They should have a rotational symmetry in such a way that equally large projections, in certain circumstances with in each case movable parts, are provided with equal angular spacings. Preferably there are in each case three projections displaced by 120° to one another.  
         [0021]     To increase the positioning accuracy of the clamping means in the machine spindle, it is possible to provide a conical portion which engages in said machine spindle. It engages there on a corresponding conical face, so that a precise positioning or centring is obtained. As a result of a drawing in force, which can e.g. also be applied by the force or locking of the bayonet lock, said conical faces are pressed into one another. It is also possible to provide between the conical portion and conical face circumferentially distributed rolling members. They can be in the form of balls or rollers, which in certain circumstances can be embedded in an elastic mounting. This is e.g. described in DE 102 34 210 A1, to which express reference is made. This ensures a high positioning accuracy.  
         [0022]     It is also possible to provide a snapping or latching device, so that through snapping or latching a predetermined position is provided between the clamping means and work spindle, in which the bayonet lock is closed to such an extent that subsequently locking can take place. Alternatively to such a snapping device marks can be provided for indicating to an operator when the bayonet lock can be locked.  
         [0023]     The clamping screw for a clamping ring or a force distributing element can be constituted by a screw with a so-called differential thread. It engages on the one hand with a threaded portion in the clamping ring and on the other with another threaded portion in the movable projection or part. As a result of different pitches or different pitch directions, either there can be an increase in the force or an increase in the operating path covered during each rotation. The thread pitch in the projection can e.g. exceed that in the clamping ring.  
         [0024]     These and further features can be gathered from the claims, description and drawings and the individual features, both individually or in the form of sub-combinations, can be implemented in an embodiment of the invention and in other fields and can represent advantageous, independently protectable constructions for which protection is claimed here. The subdivision of the application into individual sections and the subheadings in no way restrict the general validity of the statements made thereunder. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]     The invention is described in greater detail hereinafter relative to embodiments of the invention and the attached drawings, wherein show:  
         [0026]      FIG. 1 A  lateral section through a first embodiment of a machine spindle with inserted chuck and internal bayonet lock.  
         [0027]      FIG. 2 A  section through a view of the arrangement of  FIG. 1  from above.  
         [0028]     FIGS.  3  to  5  Variants of the bayonet lock in views similar to  FIG. 1  in detail form.  
         [0029]      FIG. 6 A  variant of the arrangement of  FIG. 1  with external bayonet lock and internal locking.  
         [0030]      FIG. 7  An inclined view of the arrangement of  FIG. 6 . 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0031]      FIGS. 1 and 2  show a conventionally constructed machine spindle  11   a  having a spindle body  12   a  to which is connected from the front an attachment area  13   a . As is conventionally the case with machine spindles, a tension tube  14   a  runs in a longitudinal recess of machine spindle  11   a  in spindle body  12   a.    
         [0032]     To the machine spindle  11   a  is attached a chuck  30   a , which is not shown here, but corresponds to a conventional chuck such as is e.g. described in DE 102 34 210 A. Chuck  30   a  has a central conical shoulder  31   a , which engages in the attachment area  13   a . Around the conical outer face on conical shoulder  31   a  runs a ball mat  32   a , which is known from DE 102 34 210 A.  
         [0033]     An area with radially protruding projections  34   a  is connected at the bottom to conical shoulder  31   a . As can be gathered from  FIG. 2 , there are three projections  34   a , which form part of the bayonet lock as yet to be described. The top of the projection  34   a  is slightly bevelled so as to form the inclined contact faces  34   a  of the projections of chuck  30   a.    
         [0034]     An elongated tension tube adapter  37   a  projects through the conical shoulder  31   a . By means of a projection-like tension connection  38   a  the tension tube adapter  37   a  engages in the tension tube  14   a  of machine spindle  11   a  or corresponding projections. The production or locking of the tension connection  38   a  takes place in advantageous manner in the same way as for the bayonet lock as yet to be described.  
         [0035]     In the attachment area  13   a  machine spindle  11   a  has a base plate  16   a , which on the outer area has an upright, circumferential edge  17   a . From above is inserted or engaged a cover plate  18   a , which roughly terminates with edge  17   a  and forms a closed connection. There are three pawls  21   a  between base plate  16   a  and cover plate  18   a  and have inwardly protruding projections  22   a . As is apparent from the plan view of  FIG. 2 , these projections  22   a  form a small area of wider projections  22   a ′ forming part of cover plate  18   a . It can be seen that the movable projections  22   a  are positioned roughly centrally on the fixed projections  22   a′.    
         [0036]     By means of a guide pin  24   a  and a return spring  25   a , which engage in a recess on the top of pawl  21   a , there is a guidance of the pawls and they are automatically pressed radially outwards and this will be explained in greater detail hereinafter.  
         [0037]     Between base plate  16   a  and cover plate  18   a , a mechanically stable, closed clamping ring  26   a  passes round the pawls  21   a . In a thread in clamping ring  26   a  there is a clamping screw  27   a  which is accessible from the outside. Adjusting screws  28   a  screwed into clamping ring  26   a  engage on the other two pawls  21   a.    
       Function of the Embodiment of FIGS.  1  and  2   
       [0038]     A connection between machine spindle  11   a  and chuck  30   a  according to  FIGS. 1 and 2  is brought about in the following way:  
         [0039]     With the tension tube adapter  37   a  at the front the chuck  30   a  is introduced into machine spindle  11   a . The ball mat  32   a  engages with the bearing surfaces  19   a  on cover plate  18   a , which leads to a precise centring and positioning. The projections  34   a  of chuck  30   a  pass between and beyond the projections  22   a ′ of machine spindle  11   a  and this also applies to the tension connection  38   a.    
         [0040]     The chuck  30   a  is then turned somewhat to the extent that the projections  34   a  are positioned precisely centrally to projections  22   a  or pawls  21   a . This means that they simultaneously engage beneath projections  22   a ′. As projections  34   a  are much wider than projections  22   a , as is illustrated by the broken line representation in  FIG. 2 , the thus formed bayonet lock is locked in all cases. This applies to the not shown tension connection  38   a  in the same way. In order to find the precise end position on rotating chuck  30   a  following insertion into machine spindle  11   a , it is possible to provide stops, snapping means or alternatively markings.  
         [0041]     During insertion the clamping screw  27   a  is unscrewed, so that the pawl  21   a  is pressed outwards against pin  24   a  by return spring  25   a . The same applies to all the pawls  21   a , which have similar return springs. For locking the bayonet lock the clamping screw  27   a  is screwed into the clamping ring  26   a  and engages with the outside of pawl  21   a , so that the latter is pressed radially inwards. The inclined contact faces  35   a  of projections  22   a  and  34   a  brings about a clamping or locking of the connection. So that said locking does not impair the precise positioning or centring of the conical shoulder  31   a  in machine spindle  11   a , the circumferential clamping ring  26   a  is provided. Through the tightening of clamping screw  27   a , clamping ring  26   a  is drawn outwards to the right. This means that simultaneously by means of adjusting screws  28   a  it engages with the outsides of the two other pawls  21   a  and consequently presses them or their projections  22   a  against the corresponding projections  34   a  of chuck  30   a . This leads to a locking of all three projections  34   a  of chuck  30   a . Said locking also takes place uniformly so that it does not change the centring or positioning of chuck  30   a  on machine spindle  11   a . An adjustment for adapting machine spindle  11   a  can e.g. be brought about by adjusting screws  28   a.    
         [0042]     Following the tightening of clamping screw  27   a  to a certain predetermined force the bayonet lock is not only closed, but also locked. Chuck  30   a  or conical shoulder  31   a  is drawn by a small amount further into bearing surface  19   a  of machine spindle  11   a , which further intensifies fixing.  
       Detailed Description of the Further Embodiments  
       [0043]      FIG. 3  shows in detail form a variant restricted to the attachment area  13   b  of machine spindle  11   b . A differently constructed cover plate  18   b  is placed on a base plate  16   b , constructed in similar manner to  FIG. 1 , with marginal areas  17   b  on spindle body  12   b . Here there is no separate, free, floating mounted clamping ring. For this purpose cover plate  18   b  has a downwardly drawn area, where there is a thread for a clamping screw  27   b  engaging on a pawl  21   b . The latter is constructed like that of  FIG. 1 . In such a construction there is either only a single movable pawl  21   b , which is moved by clamping screw  27   b  and brings about a locking of the bayonet lock at a single location. Alternatively there can be several movable pawls  21   b  with in each case a clamping screw  27   b  in a downwardly drawn area. Chuck  30   b  with conical shoulder  31   b  and projections  34   b  have an identical construction to  FIG. 1  and this also applies in  FIGS. 4 and 5 .  
         [0044]      FIG. 4  shows a further alternative construction of attachment area  13   c . Compared with  FIG. 3  base plate  16   c  and cover plate  18   c  have an identical construction. However, movable pawl  21   c  has a thread smaller than that in cover plate  18   c  and a different pitch. A clamping screw  27   c  is screwed into both the threads in cover plate  18   c  and pawl  21   c . It is constructed as a so-called differential screw and has two different threaded areas  27   c ′,  27   c ″. This makes it possible to exert an increased force for locking the bayonet lock or moving the pawl  21   c . It also permits the pawl  21   c  to be drawn outwards in a planned manner even in the case that it jams and the force of a return spring similar to FIGS.  1  to  3  would not be adequate. Here again there is a clamping screw  27   c  for each movable pawl  21   c.    
         [0045]     It is also possible to have a construction in which a differential screw is used for a pawl in the case of a clamping ring according to  FIG. 1 . If the other movable pawls are also connected in fixed manner to the clamping ring, e.g. in that screws, similar to the adjusting screws, firmly engage in the pawls, it is here again possible to bring about a force-caused release of the locking by retracting all the pawls.  
         [0046]     In a further alternative according to  FIG. 5  base plate  16   d  and cover plate  18   d  once again form a type of closed housing for the attachment area  13   d . The movable pawls  21   d  once again have guide pins  24   d  and return springs  25   d . On the right-hand outside they have inclined sides  23   d , which become wider in the downwards direction.  
         [0047]     A locking element  40   d  is provided for moving or locking pawls  21   d . It has an inclined portion  41   d  engaging on the inclined side  23   d  of pawl  21   d . By means of a compression spring  43   d  locking element  40   d  is pressed downwards, so that inclined portion  41   d  runs downwards on inclined side  23   d  and presses same radially inwards for locking the bayonet lock on projections  22   d  and  34   d . Obviously the compression spring  43   d  must have a relatively strong construction.  
         [0048]     For releasing the locking effect between locking element  40   d  and base plate  16   d  is provided a pressure chamber  45   d  into which can be introduced a fluid, e.g. compressed air or hydraulic fluid. This fluid forces the locking element  40   d  upwards and consequently permits a movement of pawl  21   d  in the radially outwards direction brought about by return spring  25   d.    
         [0049]     In place of compression spring  43   d  and pressure chamber  45   d  use can be made of other clamping means. It is e.g. possible from above to screw a screw through cover plate  18   d  and press the locking element  40   d  downwards. This screw can also be constructed like the differential screw of  FIG. 4  so as to bring about a movement of locking element  40   d  in both the upwards and downwards direction.  
         [0050]      FIG. 6  shows a fundamentally different construction of a bayonet lock. A chuck  30   e  is attached to a spindle body  12   e  of a machine spindle  11   e , which has no inner tension device. Once again the spindle body  12   e  has a mounted base plate  16   e  closed by a cover plate  18   e . Both are screwed, as can be seen to the left in  FIG. 6 . Between base plate  16   e  and cover plate  18   e  there are movable pawls  21   e , advantageously three uniformly distributed pawls. They are guided by a guide pin  24   e  and return springs can be provided, as in the previous embodiments.  
         [0051]     The pawls  21   e  have radially outwardly protruding projections  22   e , which have downwardly directed, inclined contact faces  35   e , with inclined sides  23   e  on the radially inner end.  
         [0052]     Centrally in attachment area  13   e  is mounted a locking element  40   e  having inclined portions  41   e , which engage on the inclined sides  23   e  of pawl  21   e . If locking element  40   e  is forced downwards by compression spring  43   e , i.e. into machine spindle  11   e , the inclined portion  41   e , via inclined side  23   e , presses the pawl  21   e  radially outwards. Resetting of the locking element  40   e  can e.g. take place by means of a pressure chamber  45   e , as described relative to  FIG. 5 . Alternatively other resetting means can be provided.  
         [0053]     Chuck  30   e  is widened in its lower area and has a circumferential bayonet ring  50   e , which is circumferentially completely closed and mounted in rotary manner. It can engage by projections  51   e  over chuck  30   e.    
         [0054]     At the lower end of bayonet ring  50   e  are formed projections  34   e , corresponding to the moving pawls  21   e . Projections  34   e  have inclined contact faces  35   e , on which can correspondingly engage projections  22   e  of pawls  21   e . With respect to the parts forming the bayonet lock, the arrangement according to  FIG. 6  is constructed similar to that of  FIG. 2 . For mounting chuck  30   e  on spindle body  12   e  bayonet ring  50   e  is brought into a position in which with its projections  34   e  is runs past corresponding projections  22   e ′ of spindle body  12   e . Through the rotation of bayonet ring  50   e , its projections  34   e  engage behind projections  22   e ′ and projections  22   e  on pawls  21   e . If for locking purpose pressure is drawn off from pressure chamber  45   e , locking element  40   e  is forced downwards and simultaneously pawls  21   e  are forced outwards. Through the outward movement of pawls  21   e  a locking of the bayonet lock takes place.  
         [0055]     The circumferential bayonet ring  50   e  can be particularly clearly seen in the inclined view of  FIG. 7 . The section in  FIG. 7  also takes place along two movable pawls  21   e , the guide pin  24   e  only being visible for the right-hand pawl.  
         [0056]     Similar to the projections according to  FIG. 2 , the projections  34   e  of  FIGS. 6 and 7  are limited to a specific inscribed angle range. This also applies to projections  22 ′ e  and movable parts  22 ′.  
         [0057]     The arrangement of  FIGS. 6 and 7  offers the advantage that for producing the bayonet lock chuck  30   e  does not have to be rotated relative to machine spindle  11   e  and spindle body  12   e  and instead only bayonet ring  50   e  is turned. This makes it possible, e.g. similar to the screw coupling shown to the left, to have continuous hydraulic lines or the like which are connected on installation. Thus, a chuck  30   e  can be coupled not only mechanically to machine spindle  11   e , but simultaneously can be provided with continuous functions or controls.