Abstract:
The rotary workhead device, which is loaded on the table of a machine tool and onto which a workpiece to be machined is rotatably mounted, is equipped with: a base plate that is attached to the table of the machine tool; two rotary workheads that are provided on the base plate and disposed so that the axes of rotation coincide and the workpiece-fixing parts face each other; a guide means that is provided so as to be capable of moving at least one of the rotary workheads back and forth in the direction of the rotation axes; and an impelling means for impelling the one rotary workhead in a direction that separates or brings together the two rotary workheads. The rotary workhead device applies a tensile force or a compressive force on a workpiece, the respective ends of which are fixed between the two rotary workheads.

Description:
REFERENCE TO RELATED APPLICATION 
       [0001]    This application is the national stage application under 35 USC 371 of International Application No. PCT/JP2011/066772, filed Jul. 15, 2011, the entire contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to a rotary workhead for machine tools which process workpieces with tensile or compressive force applied on the workpieces. 
       BACKGROUND OF THE INVENTION 
       [0003]    Conventionally, in order to produce curved surfaces on workpieces, machine tools having a plurality of feed axes are used. When a thin and fragile workpiece, such as turbine blades for steam or gas turbines is processed, it is necessary to prevent deformation of the workpiece due to machining force and vibrations generated from the contact between the tool and the workpiece. 
         [0004]    Patent Document 1 describes a method and an apparatus for machining turbine blades. In the invention of Patent Document 1, one end of a workpiece is secured to a fixture and the other end is supported by a center piece of a tail stock. A tension member of the tailstock is engaged with a stepped part of the end of a turbine blade, and axially moved by a hydraulic cylinder, which is provided in the tail stock, in order to apply a tensile force to the turbine blade whereby the turbine blade is processed under the condition that the apparent rigidity of the turbine blade is increased. 
         [0005]    In a machine tool for a turbine blade disclosed in Patent Document 2, one end of a turbine blade is secured by a main chuck, and the other end is held by a pressure chuck provided in a sub-chuck head. Compressive force is applied to the turbine blade by pressing the end of the turbine blade with the pressure chuck whereby the turbine blade is processed under the condition that the apparent rigidity of the turbine blade is increased. 
         [0006]    Patent Document 1: Japanese Unexamined Patent Publication No. S57-15609 
         [0007]    Patent Document 2: Japanese Unexamined Patent Publication No. H10-76437 
       SUMMARY OF THE INVENTION 
       [0008]    In the invention of Patent Document 1, the hydraulic cylinder for axially moving the tension member is provided in the tailstock, resulting in complex configuration. In addition, a special tail stock, incorporated with a hydraulic cylinder, must be produced, resulting in remarkably increased cost. 
         [0009]    Further, similar to the invention of Patent Document 1, in the invention of Patent Document 2, a pressing mechanism is incorporated in the sub-chuck head, resulting in complex configuration and increase in the production cost. 
         [0010]    The invention is directed to solve the problems in the prior art, and the objective of the invention is to provide a rotary workhead device for a machine tool, which processes a workpiece under tensile or compressive force applied, improved to have a simple configuration whereby the production cost is reduced. 
         [0011]    According to the invention, there is provided a rotary workhead device, disposed on a table of a machine tool, for rotatably mounting a workpiece to be processed, including a base plate adapted to be secured to the table of the machine tool, two opposing rotary workheads disposed on the base plate so as to align the respective rotational axes with each other, guide means for allowing at least one of the rotary workheads to reciprocally move in the direction of the rotational axes; and biasing means for biasing one of the rotary workheads in the direction away from or toward the other of the rotary workheads, wherein a tensile or compressive force is applied to the workpiece secured at its ends between the two rotary workheads. 
         [0012]    According to this feature, a workpiece can be processed while tensile or compressive force is applied to the workpiece whereby the rigidity of the workpiece is apparently increased. Therefore, even a thin and low rigidity workpiece, such as a turbine blade, can be successfully processed because the bending is very small and vibrations are not generated. 
         [0013]    It is not necessary to form a hydraulic cylinder in a tailstock, as described in patent document 1, because the means for biasing one of the two rotary workheads in the direction away from or toward the other rotary workhead can be disposed outside of the movable rotary workheads. This avoids the necessity of a hydraulic cylinder formed in a narrow space of the tailstock whereby the configuration is simplified and the cost can be reduced. 
         [0014]    Further, commercial products can be used as the rotary workheads, which remarkably reduces production cost. This is further advantageous for users, because a special operation is not required. Further, when a problem occurs, it can be quickly fixed by replacing the broken rotary workhead with a commercial product, and therefore the downtime of the machine tool can be reduced. 
         [0015]    According to the invention, the biasing means includes a fluid pressure operated cylinder provided between one of the rotary workheads and the base plate, and a pressure control device for varying the fluid pressure supplied to the fluid pressure operated cylinder. 
         [0016]    According to this feature, suitable tensile or compressive force can be applied depending on the dimension and material of the workpiece by varying the fluid pressure supplied to the fluid pressure operated cylinder with the pressure control device. 
         [0017]    Further, according to the invention, the guide means includes a lever device for allowing manual operation of the reciprocal movement of one of the rotary workheads when a biasing force of the biasing means is not applied. 
         [0018]    In the invention, when a workpiece is mounted to the rotary workhead device, it is necessary to reciprocally move the rotary workhead along the guide means depending on the length of the workpiece or the shapes of the fixtures. According to the feature, this operation can be carried out with the lever device, when the biasing means does not apply the biasing force to one of the rotary workheads. 
         [0019]    According to the invention, the guide means includes a brake device for clamping the reciprocal movement of one of the rotary workheads. 
         [0020]    According to this feature, the brake device clamps the reciprocal movement of one of the rotary workheads, after a biasing force is applied to a rotary workhead. The biasing force is kept applied to the one of the rotary workheads if the biasing means is deactivated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a front view of a machine tool with a rotary workhead device according to an embodiment of the invention. 
           [0022]      FIG. 2  is a side view of the machine tool of  FIG. 1 . 
           [0023]      FIG. 3  is a plan view of the rotary workhead device. 
           [0024]      FIG. 4  is an end view of the rotary workhead device in the direction of arrow lines IV-IV in  FIG. 3 . 
           [0025]      FIG. 5  is a plan view similar to  FIG. 3  a rotary workhead device according to a second embodiment. 
           [0026]      FIG. 6  is an illustration of an alternative embodiment of the fixtures. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    With reference to  FIGS. 1-4 , an embodiment of the rotary workhead device according to the present invention will be described below.  FIG. 1  is a front view of a machine tool with a rotary workhead device according to an embodiment of the invention,  FIG. 2  is a side view of the machine tool of  FIG. 1 ,  FIG. 3  is a plan view of the rotary workhead device and  FIG. 4  is an end view of the rotary workhead device in the direction of arrow lines IV-IV in  FIG. 3 . 
         [0028]    With reference to  FIG. 1 , a machine tool  100 , provided with a rotary workhead device  10  according the embodiment of the invention, is a horizontal machine tool comprising a bed  102  adapted to be secured to a factory floor, a column  104  mounted to the top face of a rear part of the bed  102  for moving in the left-right direction (X-axis direction) by an X-axis feed mechanism, a spindle head  106  mounted to the front surface of the column  104  for moving in the vertical direction (Y-axis direction) by a Y-axis feed mechanism and a saddle  110  mounted to the top face of a front part of the bed  102  for moving in the front-rear direction (Z-axis direction) by a Z-axis feed mechanism. A spindle  108  is supported by the spindled head  106  for rotation about a rotational axis extending in the front-rear direction. A tool T is attached to the end of the spindle  108 . A rotary table  112  is rotatably supported by the saddle  110  for angular range of ± 180  degrees about a vertical axis (B-axis). 
         [0029]    The X-axis feed mechanism may include a pair of X-axis guide rails  102   a  horizontally extending in the left-right direction in the top face of the bed  102 , guide blocks (not shown) mounted to a bottom face of the column  104  for sliding along the X-axis guide rails, an X-axis ball screw (not shown) extending in the X-axis direction in the bed  102 , a nut (not shown) mounted to the lower end portion of the column  104  so as to engage the X-axis ball screw and a servomotor, connected to an end of the X-axis ball screw, for driving the X-axis ball screw. 
         [0030]    Similarly, the Y-axis feed mechanism may include a pair of Y-axis guide rails (not shown) vertically extending in the column  104 , guide blocks (not shown) mounted to the spindle head  106  for sliding along the Y-axis guide rails, a Y-axis ball screw (not shown) extending in the Y-axis direction in the column  104  a nut (not shown) mounted in the spindle head  106  so as to engage the Y-axis ball screw and a servomotor, connected to an end of the Y-axis ball screw, for driving the Y-axis ball screw. 
         [0031]    Similarly, the Z-axis feed mechanism may include a pair of Z-axis guide rails  102   b  horizontally extending in the top face of the bed  102  perpendicularly to the X-axis guide rails  102   a,  guide blocks (not shown) mounted to a bottom face of the saddle  110  for sliding along the Z-axis guide rails, an Z-axis ball screw (not shown) extending in the Z-axis direction in the bed  102 , a nut (not shown) mounted to a bottom face of the saddle  110  so as to engage the Z-axis ball screw and a servomotor, connected to an end of the Z-axis ball screw, for driving the Z-axis ball screw. 
         [0032]    The machine tool  100  further comprises a pallet changer  120  mounted to the front end of the bed  102  and a pallet stocker  114  disposed in front of the pallet changer  120 . In this embodiment, the machine tool  100 , including the pallet changer  120  and the pallet stocker  114 , is enclosed by a splash guard  116 . The pallet changer  120  comprises a changing arm  124  which can rotate about and vertically move along a vertical axis O, and a revolving door  122  which can rotate about and vertically move along the axis O together with the changing arm  124 . The revolving door  122  divides the space within the splash guard  116  into a machining chamber  126  between the revolving door  122  and the column  104  and a preparation chamber  128 , where the pallet stocker  114  is disposed, in front of the revolving door  122 . A front door  116   a , provided in a front panel of the splash guard  116 , allows an operator to access the preparation chamber  128 . 
         [0033]    In this embodiment, a workpiece W is mounted to the rotary workhead device  10  and processed with the tool T. The rotary workhead device  10  comprises a base plate  12  forming a pallet, stationary and movable rotary workheads  14  and  16  mounted to the top face of the base place  12  at either end thereof. Direct drive servomotors (not shown) are respectively provided in the stationary and movable rotary workheads  14  and  16  for rotation about a horizontal rotational axis (A-axis). Face plates  14   a  and  16   a  are secure to the respective shafts of the servomotors. The face plates  14   a  and  16   a  are provided with fixtures  14   b  and  16   b  for fixing a workpiece W. The stationary rotary workhead  14  is secure to the top face of the base plate  12  at one end thereof with a spacer  18  having a suitable thickness allowing the axes of the servomotors of the stationary and movable rotary workheads  14  and  16  to coincide with each other whereby a horizontal rotational feed axis, i.e., A-axis is formed. The movable rotary work head  16  is mounted to the top face of the base plate  12  at the opposite end for liner motion by guide rails, which extend parallel to the common rotational axis (A-axis) of the stationary and movable rotary workheads  14  and  16  and the servomotors, and slider  22  mounted to a bottom face of the movable workhead  16  for sliding along the guide rails  20 . 
         [0034]    Accordingly, the machine tool  100  is a machine tool having five feed axes of three orthogonal liner feed axes, i.e., X-axis, Y-axis and Z-axis, and two rotational feed axes, i.e., A-axis and B-axis. 
         [0035]    The rotary workhead device  10  further comprises, in order to displace the movable rotary workhead  14  along the guide rails  20 , lever  32 , cam  34  attached to the end of the lever  32  and a cam follower  38  mounted to the slider  22  so as to engage the cam  34 . The lever  32  is mounted the base plate  12  for rotation about a vertical axis  32   a.  In the embodiment of  FIG. 3 , by rotating the lever  32  in the counter clockwise direction, the movable rotary workhead  16  moves (to the right in  FIG. 3 ) away from the stationary rotary workhead  14 . 
         [0036]    The rotary workhead device  10  further comprises a hydraulic cylinder  42  for biasing the movable rotary workhead  14  in the direction away from the stationary workhead  14  and a pressure plate  43  attached to the slider so that a piston  42   a  of the hydraulic cylinder  42  can abut thereagainst, a hydraulic pressure source  44  for supplying hydraulic pressure to the hydraulic cylinder  42  and an on-off valve  46  for controlling the on and off of the hydraulic pressure supply to the hydraulic cylinder  42 . The hydraulic pressure source  44  may include for example a reservoir (not shown) for accumulating the working oil, a pump for supplying the working oil to the hydraulic cylinder  42 . The hydraulic cylinder  42  is preferably a one-way cylinder which works effectively in the extending direction of the piston  42   a.    
         [0037]    The rotary workhead device  10  is further provided with a seating sensor  50 . The seating sensor  50  may comprise for example a sensor block  52  attached to the base plate  12 , a pneumatic port  54  formed in the sensor block  52  so as to face the end of the slider  22  and a pressure sensor (not shown), fluidly communicating with the pneumatic port  54 , for detecting the pressure in the pneumatic port  54 . When the end of the slider  22  contacts the sensor block  52 , the port  54  is closed by the end of the slider  22  whereby the pressure sensor detects the increase in the pressure in the pneumatic port  54 . When a workpiece is mounted between the fixers  14   b  and  16   b,  the end of the slider  22  does not contact the sensor block  52 . However, if the pressure sensor detects an increase in the pressure in the pneumatic port  54 , it means that the end of the slider contacts the sensor block  52 . This may be judged that the tension applied to the workpiece W and may trigger a warning. 
         [0038]    In order to supply electric power to the servomotors of the stationary and movable rotary workheads respectively, and to supply the working oil to the hydraulic cylinder  42 , the machine tool  100  comprises a cable and conduit assembly  36  and a central relay  118  for connecting the cable and conduit assembly  36  to an electric source (not shown) and the hydraulic pressure source  44 . The cable and conduit assembly  26  is connected to the servomotors and the hydraulic cylinder  42  through the relay  24  provided on the movable rotary workhead  16 . 
         [0039]    The functional operation of this embodiment will be described below. 
         [0040]    When a machining operation in the machining chamber  126  is completed, a machine controller (not shown) of the machine tool sends a pallet changing command to the pallet changer  120 . This moves the changing arm  124  upwardly along with the revolving door  122  along the axis O whereby either end of the changing arm  124  engage the rotary workhead device  10 , to which the processed workpiece W is mounted in the machining chamber  126 , and the rotary workhead device  10 ′, to which a non-processed workpiece is mounted in the preparation chamber  128 , so as to simultaneously lift them from the rotary table  112  and the pallet stocker  114 , respectively. Further, the pallet changer  120  rotates the changing arm  124  over 180 degrees about the vertical axis O together with revolving door  122 , whereby the processed workpiece W and the non-processed workpiece, respectively attached to the rotary workhead devices  10  and  10 ′, are replaced with each other. After the rotation of the changing arm  124  over 180 degrees, the pallet changer  120  lowers the changing arm  124  with the revolving door  122 , whereby the rotary workhead device  10 ′, to which the non-processed workpiece is mounted, and the rotary workhead device  10 , to which the processed workpiece W is mounted, are respectively placed onto the rotary table  112  and the pallet stocker  114 . 
         [0041]    When a workpiece W is processed in the machining chamber  126  of the machine tool  100 , an operator of the machine tool  100  can open the front door to access the preparation chamber  128  in order to remove a processed workpiece from and to mount a new and non-processed workpiece to the rotary workhead device  10 . For this purpose, the operator closes the on-off valve  46  to block the hydraulic pressure applied to the hydraulic cylinder  42  from the hydraulic pressure source  44 . Then, the workpiece W is removed from the rotary workhead device  10  by loosening the fixtures  14   b  and  16   b,  e.g., chucks. 
         [0042]    Thereafter, a new and non-processed workpiece is mounted to the fixtures  14   b  and  16   b.  At that time, the lever  32  can be rotated in clockwise or counter-clockwise direction to move the movable rotary workhead  16  along the guide rails  20  so as to adjust the distance between the movable and stationary rotary workheads  16  and  14  to the length of the non-processed workpiece. An operator can directly hold and move the movable rotary workhead device, even if the lever  32  is not provided. However, the provision of the lever  32  allows fine adjustment of the positioning of the movable rotary workhead device  16 , and facilitates the mounting operation of a workpiece W. After a non-processed workpiece is secured to the fixers  14   b  and  16   b,  the on-off valve  46  is opened so as to apply the hydraulic pressure to the hydraulic cylinder  42  from the hydraulic pressure source  44 , whereby the piston  42   a  of the hydraulic cylinder  42  abuts the pressure plate  43  so that the movable rotary workhead  16  is biased in the direction away from the stationary rotary workhead  14 , resulting in application of tension in the workpiece. 
         [0043]    Now, with reference to  FIG. 5 , a second embodiment of the invention will be described below.  FIG. 5  is a plan view, similar to  FIG. 3 , of a rotary workhead device according to the second embodiment. 
         [0044]    The rotary workhead device  50  according to the second embodiment can be mounted, similar to the rotary workhead device  10  according to the first embodiment, to the machine tool  100 , and has generally the same configuration. Accordingly, only the configurations different from the rotary workhead device  10  according to the first embodiment will be described below to avoid redundant explanations. 
         [0045]    A hydraulic cylinder  62  is mounted to a base plate  12  of the rotary workhead device  50 , and is oriented so that a piston  62   a  extends and retracts in the direction of an axis A. The piston  62   a  is secured to a slider  22  of a movable rotary workhead  16 . The movable rotary workhead  16  can reciprocally move in the direction of axis A along with the piston  62   a.  The hydraulic cylinder  62  is fluidly connected to a hydraulic pressure source  64  through a pressure control valve  66  and a directional control valve  68 . The directional control valve  68  may be a three-position directional control valve having a first position for extending the piston  62   a,  a second position for retracting the piston  62   a  and a third neutral position, at which the movable rotary workhead  16  can be manually moved along guide rails  20 . Although this embodiment is not provided with a lever device similar to the lever  32  of  FIG. 3 , a lever may be provided. The pressure control valve  66  is an element for adjusting the hydraulic pressure from the hydraulic pressure source  64  to the hydraulic cylinder  62  according to requirements of machining processes, and may be switched between a plurality of positions for different tensile or compressive forces, for example 0 kg, 35 kg, 70 kg and 100 kg applied to the a workpiece to be processed, or may continuously adjust the tensile or compressive force. 
         [0046]    Further, air brakes  72  are provided in a bottom face of the movable rotary workhead  16 . A pneumatic pressure source  74  is fluidly connected to the air brakes  72  through an on-off valve  76 . The air brakes  72  insert wedge shaped members between the slider  22  and the guide rails  20  by the pneumatic pressure from the pneumatic pressure source  74  so as to clamp the slider relative to the guide rails  20 . 
         [0047]    Further, when a workpiece is applied a compressive force, the fixers  14   b  and  16  may be replaced with centering couplings  14   c  and  16   c,  as shown in  FIG. 6 , having features complementary to the end shapes of the workpiece W. 
         [0048]    The functional operation of the second embodiment will be described below. 
         [0049]    Similar to the first embodiment, when a workpiece W is processed in the machining chamber  126  of the machine tool  100 , an operator of the machine tool  100  can open the front door to access the preparation chamber  128  in order to remove a processed workpiece from and to mount a new and non-processed workpiece to the rotary workhead device. For this purpose, the operator closes the on-off valve  76  to block the pneumatic pressure applied to the air brakes  72  from the pneumatic pressure source  74  so that the air brakes are unclamped. This allows the rotary workhead  16  to be manually moved along the guide rails  20 . Then, the workpiece W is removed from the rotary workhead device by loosening the fixtures  14   b  and  16   b,  e.g., chucks. 
         [0050]    Thereafter, a new and non-processed workpiece is mounted to the fixtures  14   b  and  16   b.  At that time, an operator can manually move the movable rotary workhead  16  along the guide rails  20  so as to adjust the distance between the movable and stationary rotary workheads  16  and  14  to the length of the non-processed workpiece. 
         [0051]    After a non-processed workpiece is secured to the fixers  14   b  and  16   b,  the directional control valve  68  is moved to one of the first and second positions so as to apply tensile or compressive force to the non-processed workpiece. Then, the on-off valve  76  is opened in order to clamp the slider to the guide rails  20  by the air brake  72 . This allows the non-processed workpiece to be applied with tensile or compressive force even if the directional control valve  68  is moved to the neutral position and the hydraulic pressure to the hydraulic cylinder  62  is blocked. Accordingly, the air brake  72  allows the supply of the hydraulic pressure to the hydraulic cylinder  62  to be blocked, and thus contributes to energy saving. 
         [0052]    According the above-described first and second embodiments, a workpiece can be processed by controlling the three orthogonal liner feed axes, i.e., X-axis, Y-axis and Z-axis, and the two rotational feed axes, i.e., A-axis and B-axis with tensile or compressive force applied to the workpiece so as to increase apparently the rigidity of the workpiece. Therefore, even a thin and low rigidity workpiece, such as a turbine blade, can be successfully processed because the bending is very small and vibrations are not generated. 
         [0053]    Further, according to the above-described first and second embodiments, it is not necessary to form a hydraulic cylinder in a tailstock, as described in patent document  1 , because the hydraulic cylinder  42 , providing means for biasing the movable rotary workhead  16  in the direction away from the stationary rotary workhead  14 , or the hydraulic cylinder  62 , providing means for biasing the movable rotary workhead  16  in the direction away from or toward the stationary rotary workhead  14 , can be disposed outside of the movable rotary workhead  16 . This avoids the necessity of a hydraulic cylinder formed in a narrow space of the movable rotary workhead  16  whereby the configuration is simplified and the cost is reduced. 
         [0054]    Further, rotary workheads available in the market can be used as the stationary and movable rotary workheads  14  and  16 , which remarkably reduces the production cost. If commercial products are used for the stationary and movable rotary workheads  14  and  16 , it is advantageous for users, because a special operation is not required. Further, when a problem occurs, it can be quickly fixed by replacing the broken rotary workhead with a commercial product, and therefore the downtime of the machine tool  100  is reduced. 
         [0055]    Furthermore, according to the first and second embodiment, during the process of the workpiece W, a workpiece for the next process can be prepared, and therefore, the total processing time can be reduced compared with the invention of patent document 2. 
         [0056]    Furthermore, by using the centering couplings  14   c  and  16   c  as the fixtures, when a workpiece is remounted to the rotary workhead device  50  after the workpiece has been once removed, the workpiece can be placed precisely in the previous position before the removal.