Abstract:
A clamping device for machine tools, the device provided with a power-operated chuck, an electrical drive motor, and a movement converter, with force accumulator. An output element is rotatably mounted on the output shaft of the drive motor, and is in driving connection with the movement converter. The output element is adapted to be connected to the output shaft by a servo device, and the movement converter can be interlocked with the spindle of the machine tool by a second servo device. 
     It is thus possible to clamp or unclamp a workpiece. During working procedures, the drive motor is stopped. There is no need for elaborate control functions, rather the servo devices are actuated to make a driving connection between the drive motor and the movement converter, or to release this connection, and to block the movement converter during working procedures by means of its connection to the spindle of the machine tool.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a clamping device for machine tools the device being provided with a power-operated chuck for holding a workpiece, clamping jaws of which can be actuated using the clamping device by means of an axially moveable to draw rod, in which the clamping device possesses an electric drive motor with a changeover function for triggering clamping movements, a movement converter for converting the adjustment movements of the rotor shaft of the drive motor into the axial adjustment movements of the draw rod required for actuating the clamping jaws, as well as a force accumulator for maintaining the clamping force and which is comprises preloaded spring packs supported on a spindle nut of the movement converter, as well as to a process for operating a clamping device of this kind. 
         [0003]    2. Description of the Prior Art 
         [0004]    A clamping device of this kind is disclosed in EP 2103368 A1. The design structure of this clamping device is such that an externally arranged drive motor is connected, via a belt drive, to a bell housing in a driving connection, and the bell housing acts on a draw rod via a movement converter. 
       SUMMARY OF THE INVENTION 
       [0005]    In order to exclude an unwanted axial movement of the draw rod, the drive motor, together with the spindle of the machine tool, must be driven synchronously. The control function to achieve this synchronisation is extremely elaborate. Also, if there is a change of direction of rotation of the machine tool, the drive motor must continuously retain the direction of rotation with a high torque to the point of standstill, and after a change of direction of rotation, the direction of rotation and torque must be reversed. Furthermore, it is a disadvantage that the particular required high torque has to be transferred across the entire speed range of the machine tool by means of the belt drive. Damage to the belt drive often results from this, and the high load on the transmission element must be secured by additional measures so as to avoid downtimes and damage to the clamping devices to a large extent. The object of the present invention is, therefore, to create a clamping device for machine tools of the aforementioned type, such that an elaborate control function for adapting to the particular operating status of the machine tool is not required, rather no drive energy should be taken from the drive motor during working procedures. Instead, the drive motor should be at a standstill. Furthermore, a change of direction of rotation of the rotor shaft of the drive motor should not be required when there is a change of direction of rotation of the machine tool, and the load on the transmission elements between the drive motor and the movement converter should be kept at an extremely low level, with the effect that damage to these elements, especially breakage of the belt drive, is excluded to a large extent. Nevertheless, possible damage should not influence the safety of the clamping procedures. Furthermore, it should be possible for the clamping force to be changed at any speed during the working procedure. 
         [0006]    In accordance with the present invention, this is achieved in a clamping device for machine tools of the aforementioned type in that an output element is mounted on a rotating arrangement on the output shaft of the rotor, and is continuously in a driving connection with the movement converter, that the output element can be connected to the output shaft of the rotor by means of a first servo device, and that the movement converter can be interlocked with the spindle of the machine tool by means of a second servo device, either directly or via intermediate elements. 
         [0007]    In this case, it is advantageous for the movement converter and the force accumulator to be inserted in a bell-shaped housing which is in a driving connection with the output element of the rotor, in which case the housing should be connected in a positive connection to the spindle nut of the movement converter, for example, by cam-shaped drivers or gearing. 
         [0008]    In accordance with a different design configuration, the drive energy can also be transferred to the spindle nut of the movement converter by providing an intermediate element that is connected via the belt drive to the output element of the drive motor and, possibly, in a positive connection with the spindle nut via a driver, preferably arranged at the side next to the movement converter. 
         [0009]    In order to provide a driving connection between the output element and the housing of the movement converter, it is possible to provide a belt drive, in particular a toothed belt drive or a gear connection, in which case the driving connection between the output element of the drive motor and the housing of the movement converter can be configured with a step-down, step-up or 1:1 ratio. 
         [0010]    The first and/or second servo device can be configured in each case as an electromagnetically, or pneumatically, or hydraulically operated clutch. In an electromagnetically operated servo device, the engageable components can be connected by means of friction elements, toothed discs preferably provided with pointed gearing, or discs, equipped with fluting and knurling. It is also advantageous for the armature of the electromagnetically operated clutch to be supported against the output element by one or more return springs. 
         [0011]    Furthermore, it is appropriate for the second servo device to be equipped with an adjusting ring connected to the housing of the movement converter in a rotationally fixed arrangement, in which case on the side of the adjusting ring facing the spindle of the machine tool, the adjusting ring is provided with gearing, or a friction lining, that interacts with mating gearing, or another friction lining, provided on the spindle, in which case the adjusting element of the second servo device should be in a driven connection with the adjusting ring by means of one or more radially aligned pins preferably provided with anti-friction bearings, or by means of an angle piece. 
         [0012]    In the configuration of the first servo device as an electromagnetically operated clutch, it should consist of a first housing component located in a fixed arrangement and holding the magnetic coil, and a second housing component mounted so as to be adapted to turn in relation to the first housing component, in which case the second housing component is in a permanent connection with the rotor shaft of the drive motor. Furthermore, the armature of the electromagnetically operated clutch should be coupled to the output element of the drive motor in a rotationally rigid but axially movable arrangement, and the first servo device should be arranged in a housing together with the output element of the drive motor, with the drive motor flange-mounted on the outside of the housing. Furthermore, when the first servo device is configured as an electromagnetically operated clutch, the housing facing the drive motor should be provided with an insert configured as a hub upon which the output element is mounted in a rotating arrangement. 
         [0013]    According to a further configuration variant, there is provision for the housing accommodating the movement converter to be mounted in a rotating arrangement on an intermediate piece in a permanent connection with the spindle of the machine tool. 
         [0014]    According to a further embodiment, however, the rotor of the drive motor can also be mounted in a rotating arrangement directly on the housing accommodating the movement converter, in which case the armature of the electromagnetically operated servo device should be axially movable directly on the rotor of the drive motor and the components, including the magnetic coil, should be supported on an intermediate piece attached to the housing of the movement converter. 
         [0015]    The drive motor, the first servo device, as well as the second servo device, should be jointly controllable by means of a central computing unit, for which purpose it is possible for a distance measuring device, and/or one or more limit switches, to be allocated to the adjusting element of the movement converter, the signals from which can be picked off outside the housing of the movement converter. Also, a distance measuring device can be allocated to the draw rod, preferably arranged in its end area facing away from the machine tool. 
         [0016]    The first servo device and the second servo device in this clamping device can be interconnected in the same direction, or in parallel, or alternately, by means of a common computing unit, by straightforward means depending on the operating status of the clamping device, such that when the first servo unit is activated to transfer drive energy to the movement converter, the rotor shaft of the drive motor is connected to its output element and the second servo device is also activated, meaning that the interlock between the housing and the spindle of the machine tool is released, and that when there is a modification in the working procedure of the machine tool, for example when clamping or unclamping the workpiece, the first servo unit is depressurised, the second servo device is also depressurised or, in a double-action servo device, activated, and the housing of the movement converter is in a driving connection with the spindle of the machine tool. 
         [0017]    If a clamping device for machine tools is configured according to the present invention wherein the drive motor is in a driving connection with the movement converter and this converter can be activated or deactivated, then it is possible in a straightforward way to supply energy to the clamping device for clamping or unclamping a workpiece, while however, stopping the drive motor during working procedures. There is no need for elaborate control functions for this purpose, instead the two servo devices are to be actuated accordingly in each case so as to connect the drive motor to the movement converter in a driving connection or to release this connection, and to block the movement converter during working procedures through a connection to the spindle of the machine tool. 
         [0018]    The components involved in energy transmission are thus only exposed to load for a short period; damage to them is thus practically excluded during operation. Nevertheless, the clamping device is always secured without the need for particular precautions to be taken, because during working procedures the movement converter is permanently connected to the spindle of the machine tool, thereby preventing the workpiece from coming unclamping by itself. As a result, high operational safety is provided over a long service life. 
         [0019]    Furthermore, the clamping device configured in accordance with the invention has a straightforward design and can thus be manufactured economically; furthermore, it only takes up a small amount of space, meaning that versatile use is guaranteed advantageously and with a high level of reliability. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    The drawings show the clamping device for machine tools configured in accordance with the present invention, as well as variations, the details of which are explained below. In the drawings, 
           [0021]      FIG. 1  shows a clamping device mounted on a machine tool in an axial section during a machining procedure, 
           [0022]      FIG. 2  shows the clamping device in accordance with  FIG. 1  in a partial section and magnified view, during the transmission of drive energy to the clamping device, 
           [0023]      FIG. 3  shows a sample embodiment of the clamping device in a partial section during a machining procedure, 
           [0024]      FIG. 4  shows another sample embodiment of the clamping device in accordance with  FIG. 1 , with different kinds of servo devices, also during a machining procedure, 
           [0025]      FIG. 5  shows a clamping device in accordance with  FIG. 1 , with a drive motor arranged directly on the movement converter, also during a machine procedure, and 
           [0026]      FIG. 6  shows a further embodiment of the clamping device in accordance with  FIG. 1 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    The clamping device illustrated in  FIGS. 1 to 6 , and identified by  1 ,  1 ′,  1 ″ or  1 ′″, is used for actuating a power-operated chuck  5  arranged on a machine tool  2  equipped with an electric motor  4 , by means of radially adjustable clamping jaws  6  by which a workpiece  10  to be machined, can be clamped in the chuck  5 . The clamping jaws  6  of the power-operated chuck  5  in this case can be actuated via relay levers  8  by an axially adjustable, two-part draw rod  7 ,  7 ′ in a driving connection with an electric drive motor  11  or  101  that has a changeover function, by means of a movement converter  51 . The movement converter  51  converts the rotational adjustment movements of the drive motor  11  into axial feed movements of the draw rod  7 ,  7 ′. 
         [0028]    The drive motor  11  in this case comprises a stator  12  in a fixed location located with its axis in parallel to the lengthways axis A of the clamping device  1 , and of a rotor  13  with an output element  15  arranged on the output shaft  14  of the rotor  13 , with the output element  15  in a rotating mounting, and in a permanent driving connection, with the movement converter  51 . For this purpose, in the embodiment shown in  FIGS. 1 ,  2  and  4 , there is a belt drive composed of the output element  15  which is configured as a belt pulley  16 , as well as a belt pulley  17  attached to a housing  19  that accommodates the movement converter  51 , and a flat or toothed belt  18 . 
         [0029]    The output element  15  can be connected in a driving connection with the output shaft  14  of the drive motor  11  by means of a first servo device  21 . Using a second servo device  41 , the housing  19  can be connected to a spindle  3  of the machine tool  2  by means of an adjusting ring  48  so that, as shown in  FIG. 2 , when the first servo device  21  is activated and energy is transferred to the second servo device  41  from the drive motor  11  on the servo device  41 , and from this to the draw rod  7 ,  7 ′, with the result that the clamping jaws  6  of the power-operated chuck  5  can be adjusted for opening and closing the power-operated chuck  5 . 
         [0030]    If, on the other hand, as shown in  FIG. 1 , the first servo device  21  is depressurised and the second servo device  41  is also depressurised, the housing  19  is connected to the spindle  3  of the machine tool by means of the adjusting ring  48 . By means of the belt pulley  17  and the belt drive  18 , the output element  15 , in a rotating mounting forming the belt pulley  16 , is also driven. The drive motor  11  is stopped in this operating position, i.e. in the working procedures to be undertaken on the machine tool  2 . 
         [0031]    In the embodiments shown in  FIGS. 1 ,  2  and  3 , as well as  5 , the first servo device  21  is configured as an electromagnetically actuated clutch consisting of two housing components  22  and  23 , a magnetic coil  24 , as well as an armature  25 . The housing component  22 , accommodating the magnetic coil  24  in this case, is in a rotating mounting on the housing component  23  by means of an anti-friction bearing  31 , in which case the housing component  23  is firmly connected to the rotor shaft  14  by means of a wedge  36  as well as a screw  37 . In addition, a friction lining  28  is inserted in the housing component  23  on the end and, as shown in  FIG. 2 , the armature  25  makes contact with the friction lining  28 , against the force of return springs  26 , when the servo device  21  is actuated. 
         [0032]    In this case, the armature  25  is held in an axially movable arrangement on pins  27  that are inserted into the output element  15 , as a result of which a rotationally rigid connection is created between them. Furthermore, the housing component  23  is provided on an attachment in the form of a hub  29  extending in the direction of the drive motor  11 , with the output element  15  in a rotating mounting on the hub  29  by means of anti-friction bearings  30 . This means that the armature  25 , friction lining  28 , and housing component  23  connect the output element  15  to the rotor shaft  14  when the servo device  21  is activated, as a result of which there is a driving connection between the drive motor  11  and the motion converter  41 , and via this, to the draw rod  7 ′. 
         [0033]    In the embodiment shown in  FIGS. 1 to 3 , the first servo device  21  and the output element  25  are inserted in a two-part housing  32  on which the drive motor  11  is flange-mounted at the side in parallel with the lengthways axis A of the clamping device  1 . Screws  34  attach the housing component  22  of the first servo device firmly to the housing  32 . A signal line  35  carries both electrical energy for excitation and control signals to the magnetic coil  24  of the first servo device  21 . 
         [0034]    The second servo device  41  is also configured as an electromagnetically operated clutch, with a magnetic coil  43  and an armature  44  interacting with the magnetic coil  43  inserted in a housing  42 . In this embodiment, an attachment  44 ′ is formed onto the armature  44 , with anti-friction bearings  47  supported on pins  46  attached to the attachment  44 ′. The anti-friction bearings  47  allow the armature  44  to act on the adjusting ring  48  when electrical energy is supplied via a signal line  45 , as a result of which the adjusting ring  48  is pushed against the force of return springs  49  to the right-hand limit position as shown in  FIG. 2 . By means of pins  59 , the adjusting ring  48  is connected to the housing  19  accommodating the movement converter  41  in a rotationally fixed arrangement, but can be moved axially in relation to it. 
         [0035]    If, however, as shown in  FIG. 1 , the second servo device  41  is depressurised, then the force of the return springs  49  pushes the adjusting ring  48  to the left. Gearing  65  attached to the side of the adjusting ring  48  engages in this case in mating gearing  66  worked onto an intermediate element  56 , as a result of which the housing  19  of the movement converter  41  attached via the adjusting ring  48  in a rotationally fixed arrangement to the intermediate element  56  attached by screws  60  to the spindle  3  of the machine tool  2  is connected in a rotationally fixed arrangement to the spindle  3  and rotates together with it during working procedures. 
         [0036]    Furthermore,  FIG. 5  shows that the adjusting ring  48  can also be supported via friction linings  67  and  68  in a non-positive arrangement on the intermediate element  56  that is attached to a flange  9  of the machine spindle  3 . 
         [0037]    In all embodiments, the movement converters  51  each comprise a spindle nut  52  and anti-friction bodies  53 . The anti-friction bodies  53  engage in threads  54  or  55  worked onto the spindle nut  52  and the draw rod  7 ′, and the threads  54  or  55  provide a driving connection for the spindle nut  52  and the draw rod  7 ′, so that when the spindle nut  52  is turned by the drive motor  11 , the draw rod  7 ′ is moved axially for clamping or unclamping the power-operated chuck  5 . 
         [0038]    Bearings  57  and  58  mount the movement converter  51  and the housing  19  accommodating a force accumulator  61  in a rotating arrangement on the intermediate element  56  that is in a rotationally fixed connection with the machine spindle  3 . During working procedures, this means the housing  19  of the movement converter  41  arranged within it, as well as the force accumulator  61 , which comprises spring packs  62  and  63  made up of cup springs  64 , are driven by the spindle  3  of the machine tool  2 . Also, because the input element is mounted in a rotating arrangement on the rotor shaft  14 , it also rotates when the drive motor  11  is stationary. 
         [0039]    A signal line  72  connects the drive motor  11  to a central computing unit  71 . In addition, the first servo device  21  is connected to the computing unit  71  via the signal line  35 , and the second servo device  41  is connected to the computing unit  71  via the signal line  45 . Also, the adjustment travel of the spindle nut  52  is recorded by means of a setting ring  73  that is attached to the machine spindle  52  and passes through its by means of a slot  20 ; by means of a limit switch  74  attached to the setting ring  73 , it is possible to record positions of the spindle nut  52 . 
         [0040]    In accordance with  FIG. 2 , instead of the limit switch  74 , it is also possible to provide a distance measuring device  74 ′. A further distance measuring device  76  allocated to the draw rod  7 ′ and interacting with a setting ring  75  also makes it possible to ascertain the particular position of the draw rod  7 ′. Control lines  77 ,  78  or  79  also carry the signals obtained from the limit switch  74  or the distance measuring devices  74 ′ and  76  to the computing unit  71  where they are evaluated, as a result of which the particular operating position of the clamping device is known. 
         [0041]    In accordance with  FIG. 4 , the first servo device  81  and the second servo device  91  can also be configured as hydraulically or pneumatically actuated clutches. Adjustment pistons  83  or  93  are inserted in a cylinder  82  or  92  in this case, and can be acted on by a pressurised fluid. 
         [0042]    In the servo device  81 , a pressurised chamber is provided in the cylinder  82 . The piston  83  that can be moved against the return springs  49  acts on an actuator  85  in this case which is provided with spur gearing  86  that can be inserted into mating gearing  87  attached to the output element  15  when the adjustment piston  83  is pressurised by a supply line  88 . When the gearing  86 ,  87  is engaged, the output element  15  is in a rotationally fixed connection with the rotor shaft  14  of the drive motor  11  by means of the actuator  85  and a carrier  90  connected to it, in which case the carrier  90  has a hub  90 ′ formed onto it and is in a driving connection with the rotor shaft  14 . 
         [0043]    In the servo device  81 , on the other hand, the adjustment piston  93  is equipped with a piston rod  94  and two pressure chambers  97  and  98  are provided in a cylinder  92  with the effect that the adjustment piston  93  can be pushed to the right when pressurised fluid is supplied via connection  96  in order to disengage the gearing  65  and  66 , and can be pushed to the left by the force of the return springs  49  in order to disengage the gearing  65  and  66 . 
         [0044]    In the embodiment of the clamping device  1 ″ according to  FIG. 5 , the rotor  13  of the drive motor in  11  is rotatably mounted directly on the housing  19  that accommodates the movement converter  51 . The armature  25 ′ of the servo device  21 ′ in this case is attached in an axially movable arrangement to the rotor  13 , and the housing components  22 ′ and  23 ′ including the magnetic coil  24 ′ are supported on an intermediate piece  19 ′ that is attached to the housing  19 . In this way, a compact design is produced with a large usable internal diameter for the clamping device  1 ″. 
         [0045]    In the clamping device  1 ′″ shown in  FIG. 6 , the drive motor  101  does not act on the housing  19  accommodating the movement converter  51 , but rather acts directly on its spindle nut  52 . To achieve this, an intermediate element  111  is mounted on the draw rod  7 ′ in a rotating arrangement at the side next to the housing  19 , and the intermediate element  111  is connected to the spindle nut  52  in a positive connection via cams  113 ,  114 . In addition, a belt drive  106  is connected to the intermediate element  111 , as the result of which the drive energy taken from a rotor shaft  104  of the drive motor  101  comprising a stator  102  or a rotor  103  for adjusting the clamping jaws  6  of the power-operated chuck  5  is input into the spindle nut  52  of the movement converter  51  when the first servo device  21  is closed, by means of an output element  105 , the belt drive  106 , and the intermediate element  111 , and the drive energy is transmitted from there to the draw rod  7 ′. 
         [0046]    An adjustment element  115  is to be actuated by means of the second servo device  41 , with the adjustment element  115  allowing the gearing  116  and  117  provided on it, and on the spindle nut  52 , to be engaged and disengaged. The adjustment element  115  is connected by pins  118  in a rotationally fixed connection to the housing  19  attached to the machine spindle  3 , which means the clamping device  1 ′″ is blocked for working procedures when the gearing  116  and  117  is engaged.