Abstract:
The invention relates to a clamping device for removably mounting a tool ( 3 ) or a tool fixture in a receiving part ( 1 ). Said clamping device comprises several pincers elements ( 33 ) which are concentrically arranged around a central axis ( 32 ) within the receiving part ( 1 ) and are impinged upon by a tension spring ( 39 ) so as to be moved into a clamping position in order to brace the tool ( 3 ) or the tool fixture. In order to be able to automatically replace a tool without using much force and energy, an axially movable closing element ( 17 ) is assigned to the pincers elements ( 33 ). Said closing element ( 17 ) impinges the pincers elements ( 33 ) in a forward position that is advanced in the direction of the pincers elements ( 33 ) for mounting purposes in the clamping position thereof, which is swiveled inward by means of the tension spring ( 39 ), while being movable into a retracted position with the aid of a detaching device ( 12, 16, 45, 46, 47 ) in order to release the pincers elements ( 3 ).

Description:
FIELD OF THE INVENTION 
       [0001]    The invention concerns a clamping device and a clamping system. 
       BACKGROUND OF THE INVENTION 
       [0002]    Clamping devices for removable mounting of tools or tool fixtures in a receiving part generally have a collet chuck arranged in the receiving part, or a clamping set with several pincer elements distributed around the periphery to engage with the tool or tool fixture. In conventional clamping devices, the pincer elements are generally arranged on an axially movable mount or they are activated by an axially displaced clamping cone. In both designs, however, relatively large axial displacements or travel movements of the pincer mount or the clamping cone are required to move the pincer elements between a clamping and a releasing position. Since these travel movements usually occur against the force of a clamping spring when loosening the collet chuck, a relatively high expenditure of force and energy is thereby required. Furthermore, an appropriately large design space must be provided for the necessary travel movements. 
       SUMMARY OF THE INVENTION 
       [0003]    The problem of the invention is to create a clamping device and a clamping system of compact construction to enable an automatic tool changing process even without major expenditure of force and energy, while still safely and reliably mounting the tools. 
         [0004]    This problem is solved by a clamping device and by a clamping system as set forth in the claims. Expedient embodiments and advantageous modifications of the invention are the subject of the dependent claims. 
         [0005]    In the clamping device of the invention, no major axial displacements or travel movements of an activating element are needed to activate the collet chuck. The pincer elements of the collet chuck are axially fixed inside the receiving part and are constantly forced by a clamping spring into a locking position. Moreover, the pincer elements are coordinated with a closing element, which further clamps the pincer elements and holds them in the locking position. Thanks to a loosening mechanism, the closing clement can be pushed into a retracted position and thus releases the pincer elements to swivel into their open position. No major shifting of the closing element is needed for this, nor any major expenditure of force or energy. Thus, instead of a hydraulic activation, there can also be a pneumatic or electrical activation of the clamping device. Even when the closing element is moved into the retracted release position, at first the collet chuck remains closed due to the clamping spring and continues to hold the tool fast. Only when the tool is pushed out from the receiving part, e.g., by the front end of a forcing lever, or pulled out from the receiving part with a corresponding pulling force by an automatic tool changer or by hand, do the pincer elements swivel against the force of the clamping spring into an open position and release the tool. In this way, an unintentional dropping out of the tool is prevented. 
         [0006]    Due to its compact construction, the clamping device of the invention is especially well-suited for installation in a tool fixture or tool-changing head. Such tool-changing heads, thanks to their low weight and small size, enable fast and easy handling. Different tools, even tools for different technologies, can be easily inserted in the tool-changing heads and be changed automatically as needed. In this way, it is also possible to reduce the size of the tool magazines of machine tools, since instead of complete tools one need only provide tool-changing heads. However, the clamping device is not confined to installation in a tool fixture or tool-changing head, but rather it can also be integrated appropriately in a working spindle for the automatic clamping of tool fixtures or tools. 
         [0007]    The loosening mechanism in one expedient embodiment contains a pull rod, which is activated by means of a push rod via a loosening gear and which is connected to the closing element. The loosening gear transforms a forward movement of the push rod into a backward movement of the pull rod and vice versa. The forward movement of the pull rod can thus be used to push out the tools, while the simultaneous backward movement of the pull rod retracts the closing element and thus allows for the opening of the collet chuck. The displacement of the push rod can be achieved, e.g., by a hydraulically operated loosening unit. But the closing element can also be displaced directly by an electrical, pneumatic or other suitable drive system. 
         [0008]    In one expedient embodiment, the closing element is configured in the manner of a bushing with clamping claws projecting in the direction of the pincer elements. The clamping claws have slanted clamping surfaces to bear against the corresponding slanted bearing surfaces of the pincer elements. In this way, the pincer elements can be firmly pushed into the locking position and yet be released for opening with only a slight displacement of the closing element. 
         [0009]    The clamping system of the invention has a first clamping device integrated in a working spindle of a machine toot and a tool-clanging head, removably arranged in the working spindle and removably secured by the first clamping device, with a second clamping device integrated inside it. Both clamping devices can preferably be activated by an activation unit coordinated with the working spindle, so that both an automatic tool change and an automatic changing of tool-changing heads is made possible. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0010]    Further details and benefits of the invention will become clear from the following description of a preferred embodiment example by means of the drawing. It shows: 
           [0011]      FIG. 1 : a tool holder with an integrated clamping device in longitudinal cross section; 
           [0012]      FIG. 2 : the front part of the tool holder shown in  FIG. 1 , in an enlarged cross-sectional view; 
           [0013]      FIG. 3 : the rear part of the tool holder shown in  FIG. 1 , in an enlarged cross-sectional view; 
           [0014]      FIG. 4 : a closing element of the clamping device shown in  FIG. 1 , in a front view and a cross-sectional side view; 
           [0015]      FIG. 5 : a holding element of the clamping device shown in  FIG. 1  in a front view and a cross-sectional side view; 
           [0016]      FIG. 6 : a collet chuck of the clamping device shown in  FIG. 1  in a front view and a cross-sectional side view, and 
           [0017]      FIG. 7 : a clamping system with a work spindle and a tool-changing head. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]      FIG. 1  shows an essentially hollow cylindrical receiving part  1 , in which is integrated a clamping device for the automatic clamping of a tool  3  provided with a tightening bolt  2 . In the embodiment shown here, the hollow cylindrical receiving part  1  is designed as a tool fixture, which can be inserted in a known work spindle of a machine tool, e.g., by an automatic tool changer, and clamped there by a likewise known clamping mechanism. For this purpose, the hollow cylindrical receiving part  1  has, at its right rear end in  FIG. 1 , an outer cone  4  for insertion into a corresponding inner cone  5  at the front end of a work spindle  6 , shown in FIG.  7 . Moreover, on the outside of the receiving part  1  there is a circumferential groove  7  for a tool gripper of the automatic tool changer or the like. 
         [0019]    At the left front end in  FIG. 1 , the hollow receiving part  1  contains an inner cone  8  to receive a corresponding outer cone  9  of the tool  3 . The tool  3  has a continuous central channel  10  for supplying a cooling agent or the like. Inside the hollow receiving part  1 , a movable push rod  12  provided with a continuous borehole  11  is situated. The push rod  12  contains a thin front part  13  and a thick rear part  14 , which is arranged to be axially movable in the receiving part  1 , sealed off by a guide bushing  15  provided with packings. At the thin front part  14  of the push rod  12  is arranged a movable hollow pull rod  16 , coaxial with it. At the front end of the pull rod  16  is fastened a closing element  17 , shown enlarged in the figure. The closing element  17 , designed as a kind of bushing, can move inside a borehole  18  of the receiving part  1  and is sealed radially with an O-ring  19 . The closing element  17  contains forward-projecting clamping claws  20 , which grab a holding element  21  shown enlarged in  FIG. 5  and engaging with a collet chuck  22  shown enlarged in the figure. The pull rod  16  with the closing element  17  attached to it is pressed forward in the direction of the collet chuck  22  by a spring arrangement  23 . In the embodiment shown, the spring arrangement  23  consists of a disk spring pack, in which several disk springs  24  are arranged about the pull rod  16  and clamped between the rear end of the closing element  17  and the front end of a bearing bush  25 , firmly arranged in the receiving part  1 . 
         [0020]    As follows from  FIG. 4 , the closing element  17  which is fastened with interior threads  26  on the front end of the pull rod  16  contains six clamping claws  20  projecting forward in the direction of the collet chuck  22 , having a cross section in the form of a ring segment. Between the forward-beveled clamping claws  20  are provided rectangular slots  27 . On the outside, furthermore, the closing element  17  has an annular groove  28  for the O-ring  19  shown in  FIG. 1 . 
         [0021]      FIG. 5  shows an enlarged view of the holding element  21  which interacts with the closing element  17 . It has a continuous opening  29  and six studs  30  projecting outwardly in a star pattern, between which intermediate spaces  31  are provided for the engagement of the clamping claws  20 . The starlike holding element  21  is fixed inside the receiving part  1  and forms a firm bearing point for the closing element  17 , which is forced forward by the spring arrangement  23 . 
         [0022]      FIG. 6  shows the collet chuck  22  in a cross-sectional view and a front view. In the embodiment shown, it consists of six pincer elements  33  arranged concentrically about a central axis  32  of the receiving part  1 , having a wedge-shaped recess  34  at their inner side, with a forward sloping draw-in surface  35 . At the inner side of the pincer elements  33  an inner annular groove  36  is provided for a lock washer  37 . The pincer elements  33 , furthermore, have an outer annular groove  38  on their outer side for a tension spring  39 , designed here as an annular spring. At the left front end in the cross-sectional view of  FIG. 6 , the pincer elements  33  have a rounded bearing edge  40 , while at the right rear end of the pincer elements  33  a slanted working surface  41  is provided. 
         [0023]    As is especially evident in  FIG. 2 , the pincer elements  33  are arranged in a corresponding recess  42  of the receiving part  1 . The front ends of the pincer elements  33  lie with their rounded front edges  40  against an annular shoulder  43  inside the receiving part  1  and are forced radially outward by the split washer  37 . At their rear ends, the pincer elements  33  are instead forced radially inward by the tension spring  39 , not shown here. The tightening bolt  2  of the tool  3  is thereby enclosed by the wedgelike recesses  34  of the pincer elements  33  and pulled into the receiving part  1  by the slanted draw-in surface  35 . In the clamping position shown in  FIG. 2 , the rear ends of the pincer elements  33  are moreover pushed inwardly by the forward projecting clamping claws  20  of the closing element  17 , which is forced forward by the spring arrangement  23 . For this purpose, the clamping claws  20  have slanted clamping surfaces  44 , identifiable at their front ends in  FIG. 4 , to bear against the slanted working surfaces  41  of the pincer elements  33 . 
         [0024]      FIG. 3  shows a loosening gear for loosening the collet chuck  22 . Thanks to this loosening gear, a forward movement of the push rod  12  is converted into a backward movement of the pull rod  16  and vice versa. The loosening gear contains a clamping cone  45 , which is braced at its front cone surface via balls  46  against a conical bearing surface  47  on the inside of the bearing bush  25  arranged firmly in the receiving part  1 . The clamping cone  45  is braced at the back side by several pressing pins  48  distributed about the circumference against an annular shoulder  49  of the push rod  12 . The pressing pins  48  are screwed in at the rear side of the clamping cone  45  and protrude through continuous holes  50  in an annular flange  51  at the rear end of the pull rod  16 . The rear free ends of the pressing pins  48  lie against the front side of the annular shoulder  49  of the push rod  12 . On the outside of the annular flange  51  are secured forward-projecting pins  52 , which engage with corresponding blind holes  53  at the rear side of a pressing ring  54 . The pressing ring  54  contains alternately forward-projecting and retracted studs  55  and  56 , respectively, while the projecting studs  55  serve as spacers for the balls  46  and the retracted studs  56  lie with their front ends against the balls  46 . 
         [0025]    The mode of operation of the above-described clamping device will now be explained by means of  FIGS. 1 to 3 . In these figures, the clamping device is shown in a clamping position. In the clamping position shown, the pincer elements  33  of the collet chuck  22  are pressed inwardly at their rear ends by the annular spring  29  and by the clamping claws  20  of the closing bush  17 , which is pushed forward via the spring arrangement  23 . In this way, the tightening bolt  2  of the tool  2  [sic;  3 ] is clamped and drawn into the receiving part  1 . The pincer elements  33  are held in the clamping position by the clamping claws  20  of the closing bush  17 , thereby assuring a secure bracing of the tool  3  in the receiving part  1 , which is configured here as a tool fixture. 
         [0026]    To loosen and release the tool  3 , the push rod  12  is pressed forward in the direction of the tool  3  by an activating mechanism, not shown here. In this process, the clamping cone  48  is likewise pushed forward via the pressing pins  48 . In this way, the balls  46  bearing against the conical bearing surface  47  wander radially outward and shove back the pressing ring  54  and the pull rod  16  connected to the latter via the pins  52 . The closing bush  17  secured to the front end of the pull rod  16  is also shoved backward against the force of the spring arrangement  23 , so that the clamping claws  20  of the closing bush  17  are disengaged from the pincer elements  33 . Even when the clamping claws  20  are disengaged from the pincer elements  33 , the rear ends of the pincer elements  33  are still pressed radially inward by the annular spring  39 . Thus, the tool  3  is still held in the receiving part  1 , but it can be removed from the receiving part  1  by an appropriate pulling force. The length of the push rod  12  can be chosen such that the tool  3  is pushed out by its front end. 
         [0027]    The above-described clamping device is not limited to use in an interchangeable too, holder. The clamping device can also be installed accordingly, for example, in a driven rotary spindle of a machine tool for the automatic clamping of tools or tool fixtures. 
         [0028]      FIG. 7  shows a clamping system with a driven rotary work spindle  6  of a machine tool, a first clamping device  57  integrated in the work spindle  6 , a tool-changing head  58  interchangeably arranged in the work spindle  6  and removably secured by the first clamping device  57 , with an integrated second clamping device  59  and a loosening unit  60  for loosening the first and second clamping devices  57  and  59 . The construction and mode of operation of the tool-changing head  58  with the integrated clamping device  59  has been explained above at length. The first clamping device  57  integrated in the work spindle  6  contains a clamping sleeve  61 , which is arranged at the front end of a hollow clamping rod  62 , arranged inside the work spindle  6  and able to move coaxially to its central axis. The clamping sleeve  61  is surrounded by several clamping claws  63 , able to move radially by the axial movement of the clamping sleeve  61 . The clamping claws  63  are guided by a spacer  64  and kept at a distance from each other in the circumferential direction. The clamping sleeve  61  is pulled back by a spring arrangement, not shown here, so that the clamping claws  63  are forced radially outward for the clamping of the tool-changing head  58 . To loosen the tool-changing head  58 , the clamping rod  62  with the clamping sleeve  61  attached to it has to be pushed forward against the force of the spring arrangement, whereby the clamping claws are shoved radially inward and release the tool fixture  58 . The construction and mode of operation of such a clamping device is explained at length in DE 101 59 611 C1. Therefore, the content disclosed in said publication is expressly made to be the subject of the present application. 
         [0029]    In the clamping system shown in  FIG. 7 , a hollow activating rod  65  is led movably inside the clamping rod  62  for moving the push rod  12  inside the tool fixture  58 . The loosening unit  60  is designed so that the clamping rod  62  and/or the activating rod  65  can be pushed forward and thereby loosen the clamping of the tool  3  inside the tool-changing head  58  and/or the clamping of the tool-changing head  58  in the work spindle  6 . For this purpose, the loosening unit  60  can have two separate pushing pistons, which can be deployed separately from each other or jointly.