Abstract:
There is provided a built-in type index table in which a power transmitting means scarcely has backlash and, at the same time, the space and cost can be saved. The index table includes a rotary table for setting a workpiece for a machine tool; a rotary table shaft fixedly provided on the rotary table; a driving motor mechanism, which is a driving source; and a planetary roller speed-reduction mechanism having a sun roller, which is a motor output shaft of the driving motor mechanism, a ring fixed to the speed-reduction mechanism, a plurality of planetary rollers arranged at equal angular intervals between the sun roller and the ring in a pressurized state, and a planetary roller harness that fixedly supports a plurality of planetary roller shafts pivotally supporting the planetary rollers in a rotatable manner and is fixedly provided coaxially with the rotary table shaft.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an index table for a machine tool and, more particularly, to a construction of an index table for indexing the angular position of a workpiece, which index table is suitable for gear cutting and grinding. 
         [0003]    2. Description of the Related Art 
         [0004]    In a conventional gear grinding device, a gear to be machined, which is a workpiece, is set on a rotary index table, which is capable of being moved vertically, by using a collet chuck, the rotary index table is rotationally driven by a servomotor via a gear reducer means, and the rotational speed and the rotational angular position of the index table are detected by an encoder attached concentrically to the index table, the detected values being sent to a control unit and feedback controlled so as to match the preset values of the rotational speed and the rotational angular position of gear grinding. 
         [0005]    A problem with the rotary index table having such a gear reducer means is that since power is transmitted via several gears, the table rotation has an angular position error due to backlash between the gears, which degrades the accuracy of the gear to be machined. 
         [0006]    To solve this problem, the driving means for the conventional index table described in Japanese Unexamined Patent Application Publication No. 2003-159634 (FIG. 1) uses a planetary roller speed-reduction mechanism including a plurality of stages of backlash-less planetary rollers in place of the gear reducer means to obtain a predetermined speed reduction ratio. 
         [0007]    Also, the index table of conventional example described in Japanese Unexamined Patent Application Publication No. 2003-25147 (FIG. 3) has a backlash-less configuration in which a driving motor is housed in a housing that supports the index table, and the output shaft of the motor is connected directly to the table on which the workpiece is set. 
         [0008]    The conventional example described in Japanese Unexamined Patent Application Publication No. 2003-159634 has an advantage that a power transmitting means scarcely has backlash. In this conventional example, however, since a coupling is interposed between a motor and the planetary roller speed-reduction mechanism, many connecting parts such as the output shaft of motor, the coupling, and the planetary roller speed-reduction mechanism are present, so that a power transmitting part lengthens. Therefore, the rigidity decreases as a whole, and therefore an adverse influence may be exerted on the rotation accuracy. 
         [0009]    Also, in the conventional example described in Japanese Unexamined Patent Application Publication No. 2003-25147, a power transmitting means has no backlash and has no problem with the rigidity as in the above-described case. However, since the motor connected directly to the table requires high rotation torque at a low speed, so that the size of device inevitably increases, and therefore the sizes of the housing and peripheral functional parts also increase, which presents a problem of high cost. 
       SUMMARY OF THE INVENTION 
       [0010]    Accordingly, the object of the present invention is to provide a built-in type index table in which a power transmitting means scarcely has backlash and, at the same time, the space and cost can be saved. 
         [0011]    The present invention solves the above-described problems by the means described below. 
         [0012]    (1) A first means provides an index table including a rotary table for setting a workpiece for a machine tool; 
         [0013]    a rotary table shaft fixedly provided on the rotary table; 
         [0014]    a driving motor mechanism, which is a driving source; and 
         [0015]    a planetary roller speed-reduction mechanism having a sun roller, which is a motor output shaft of the driving motor mechanism, a ring fixed to the speed-reduction mechanism housing, a plurality of planetary rollers arranged at equal angular intervals between the sun roller and the ring in a pressurized state, and a planetary roller harness that fixedly supports a plurality of planetary roller shafts pivotally supporting the planetary rollers in a rotatable manner and is fixedly provided coaxially with the rotary table shaft. 
         [0016]    (2) A second means provides an index table, wherein in the index table of the first means, 
         [0017]    a motor of the driving motor mechanism is a servomotor; 
         [0018]    an encoder capable of detecting the rotation angle of the rotary table is provided to feed back the detected values of rotation speed and angular position of the rotary table to a control circuit; and 
         [0019]    control can be carried out so that the rotation speed and angular position of the rotary table take preset values. 
         [0020]    (3) A third means provides an index table, wherein in the index table of the first or second means, 
         [0021]    a bearing interposed between the planetary roller and the planetary roller shaft is an angular contact bearing pressurizing in the axial direction. 
         [0022]    (4) A fourth means provides an index table, wherein in the index table of any one of the first to third means, 
         [0023]    the index table is provided with: 
         [0024]    a rotating shaft center hole formed in the shaft centers of the rotary table shaft, the driving motor mechanism, and the planetary roller harness; and 
         [0025]    a fluid pressure pipe that is disposed in the rotating shaft center hole and is connected to a fluid-operated actuator incorporated in the rotary table. 
         [0026]    (5) A fifth means provides an index table, wherein in the index table of the fourth means, 
         [0027]    a rotary joint for a working fluid is connected to the outside on the driving motor mechanism side of the fluid pressure pipe. 
         [0028]    The inventions of claims  1  and  2  are the index tables of the first and second means, the motor output shaft of the driving motor mechanism is used as the sun roller, and the planetary roller harness is connected directly to the rotary table shaft of the rotary table on which a workpiece is set. Therefore, the whole of device is small in size and low in cost. Also, functional parts and connecting parts thereof have no backlash, and the rotation angle of index table is detected precisely and is feedback controlled so as to match the preset value. Therefore, an effect that the accuracy of rotational angular position of table is improved is achieved. 
         [0029]    The invention of claim  3  is the index table of the third means, and the engagement between the planetary roller, the planetary roller shaft, and the bearing is firm. Therefore, an effect that the accuracy of rotational driving is further improved is achieved. 
         [0030]    Also, the inventions of claims  4  and  5  are the index tables of the fourth and fifth means, and the pipe leading to the fluid-operated actuator capable of operating a clamp for setting and removing the workpiece is allowed to pass through the rotating shaft center hole in the shaft center of the index table and is pulled out to a position distant from the rotary table. Therefore, the size of the rotary joint is small, and the pipe is easy to assemble, so that an effect of reducing cost is achieved. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]      FIG. 1  is a side sectional view of an index table in accordance with an embodiment of the present invention; and 
           [0032]      FIG. 2  is a sectional view showing a detailed construction of a planetary roller in the index table shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0033]    A configuration of an index table in accordance with an embodiment of the present invention will now be described with reference to the accompanying drawings. 
         [0034]      FIG. 1  is a side sectional view of the index table in accordance with the embodiment of the present invention, and  FIG. 2  is a sectional view showing a detailed construction of a planetary roller in the index table shown in  FIG. 1 . 
         [0035]    As shown in  FIG. 1 , an index table  1  includes a rotary table  41  having a workpiece setting surface  41   a  on which a workpiece  2  for a machine tool is set, a rotary table mechanism  40  including a rotary table shaft  42 , which is fixedly provided on the rotary table  41 , or the like, a planetary roller speed-reduction mechanism  20  provided under the rotary table mechanism  40 , a driving motor mechanism  10 , which is a driving source, provided under the planetary roller speed-reduction mechanism  20 , an encoder, and a clamp mechanism working fluid system. 
         [0036]    The rotary table mechanism  40 , the planetary roller speed-reduction mechanism  20 , and the driving motor mechanism  10  are integrated coaxially. 
         [0037]    (Rotary Table Mechanism) 
         [0038]    The rotary table mechanism  40  includes the rotary table  41 , the rotary table shaft  42 , and a table shaft housing  43 . 
         [0039]    The rotary table  41  is attached to the rotary table shaft  42  so that a back surface  41   b  of the table comes into contact with an upper surface  42   c  of the rotary table shaft  42 . 
         [0040]    The table shaft housing  43  and a speed-reduction mechanism housing  34 , described later, are combined with each other integrally in a concentric manner. The table shaft housing  43  and the speed-reduction mechanism housing  34  incorporate bearings  44  and  45 , respectively, so that the rotary table shaft  42  is rotatably supported by the bearings  44  and  45  in such a manner that the axial movement thereof is restricted. 
         [0041]    The index table  1  is attached to an external member  3  via the table shaft housing  43 . 
         [0042]    In the shaft center of the rotary table shaft  42 , a rotating shaft center hole  42   a  that allows hydraulic pipes  53 , described later, to pass through is formed in the axial direction. 
         [0043]    (Planetary Roller Speed-Reduction Mechanism) 
         [0044]    The planetary roller speed-reduction mechanism  20  includes the speed-reduction mechanism housing  34 , a sun roller  21 , which is an output shaft  14  of a servomotor  11  of the driving motor mechanism  10 , described later, a ring  22  fixed to the speed-reduction mechanism housing  34 , a plurality of planetary rollers  25  arranged at equal angular intervals between the ring  22  and the sun roller  21 , and a planetary roller harness  24  (carrier) that pivotally supports the planetary rollers  25  by means of a plurality of planetary roller shafts  23 . 
         [0045]    An inside cylindrical part of the planetary roller speed-reduction mechanism housing  34  accommodates the ring  22 . 
         [0046]    Also, under the planetary roller speed-reduction mechanism housing  34 , an intermediate housing lid  19  is disposed integrally. 
         [0047]    Further, in a lower part of the intermediate housing lid  19 , a bearing  18  on the driving motor mechanism  10  side is supported. 
         [0048]    The ring  22  has an elastic ring shape such that when the ring  22  is pushed from a ring side surface  22   b  at the outer periphery, the diameter of the inner surface of a ring inside diameter part  22   a  decreases. 
         [0049]    The planetary roller harness  24  is attached to the rotary table shaft  42  so that an upper surface  24   a  thereof comes into contact with a lower surface  42   b  of the rotary table shaft  42 . 
         [0050]    In the shaft center of the planetary roller harness  24 , a rotating shaft center hole  24   c  that allows the hydraulic pipes  53 , described later, to pass through is formed in the axial direction. 
         [0051]    In a plurality of harness hollow holes  24   b  arranged at equal angular intervals in the planetary roller harness  24 , the planetary roller shafts  23  are fixedly provided. 
         [0052]    In a tip end part  23   a  of the planetary roller shaft  23 , as shown in  FIG. 2 , the planetary roller  25  is provided via angular contact bearings (hereinafter referred simply to as bearings)  26 A,  26 B,  26 C and  26 D. 
         [0053]    The bearings interposed between the planetary roller  25  and the tip end part  23   a  thereof are the bearings  26 A,  26 B,  26 C and  26 D in which balls are pressurized. 
         [0054]    The four bearings  26 A,  26 B,  26 C and  26 D provided in the axial direction of the planetary roller shaft  23  are configured so as to be pressurized by an axial force caused by a plurality of stages of washers  27  to  31 , a star nut  33  threadedly engaged with the shaft end of the tip end part  23   a  of the planetary roller shaft  23 , and a star washer  32 . 
         [0055]    The force applied to the uppermost washer  27  pushes the side surface of the inner race of the bearing  26 A. The force is transmitted to the outer race of the bearing  26   a  via the ball, and is transmitted from the outer race of the bearing  26 A to the outer race of the bearing  26 B through the washer  28 . 
         [0056]    The force applied to the outer race of the bearing  26 B is transmitted to the inner race of the bearing  26 B via the ball, and is transmitted to the inner race of the bearing  26 C through the washer  29 . 
         [0057]    The force transmitted to the inner race of the bearing  26 C is transmitted to the outer race of the bearing  26 C via the ball, and is transmitted to the outer race of the bearing  26 D through the washer  28 . 
         [0058]    The force transmitted to the outer race of the bearing  26 D is transmitted to the inner race of the bearing  26 D and the lowermost washer  31  in the tip end part  23   a  of the planetary roller shaft  23  via the ball. 
         [0059]    Under the outer race of the bearing  26 D, there is provided the washer  30  for preventing the bearings from dropping. 
         [0060]    The star nut  33  is threadedly engaged with the threads at the tip end of the tip end part  23   a  of the planetary roller shaft  23 , so that the force transmitted through the angular contact bearings  26 A,  26 B,  26 C and  26 D is supported by the star nut  33  via the washer  31  and the star washer  32 . 
         [0061]    At the time of assembly, the rotation angle of the star nut  33  is adjusted to regulate the pressurization force. 
         [0062]    After the rotation angle of the star nut  33  has been determined, one of star protrusions of the star washer  32  the rotation direction of which is restricted with respect to the tip end part  23   a  of the planetary roller shaft  23  is bent, by which the rotation direction of the star nut  33  is restricted. 
         [0063]    (Driving Motor Mechanism) 
         [0064]    As shown in  FIG. 1 , the driving motor mechanism  10  includes a motor housing  15 , a motor housing cover  16 , the intermediate housing lid  19 , and the servomotor  11  (or may be an induction motor the rotation of which is controlled by an inverter or a synchronous motor) including a rotor  12  and a stator  13 . 
         [0065]    On the inside of the motor housing  15 , the stator  13  of the servomotor  11  is fixed. 
         [0066]    Also, on the motor housing cover  16  and the intermediate housing lid  19 , bearings  17  and  18  are incorporated, respectively, so that the motor output shaft  14  integral with the rotor  12  is rotatably supported by the bearings  17  and  18  in such a manner that the axial movement thereof is restricted. 
         [0067]    In the shaft center of the motor output shaft  14 , a rotating shaft center hole  14   a  that allows the hydraulic pipes  53 , described later, to pass through is formed in the axial direction. 
         [0068]    (Encoder) 
         [0069]    At the outer periphery of the rotary table shaft  42 , an encoder drum  57  is fixedly provided to detect the rotation angle. 
         [0070]    On the other hand, on the inner wall of the table shaft housing  43 , an encoder head  58  is fixedly provided at a position facing to the encoder drum  57  to precisely detect the rotation angle of the rotary table  41 , that is, the rotary table shaft  42 . 
         [0071]    The detected values of the rotation speed and angular position of the rotary table  41  detected by the encoder head  58  are fed back to a control circuit, not shown, by which control is carried out so that the rotation speed and angular position of the rotary table  41  take preset values. 
         [0072]    (Clamp Mechanism Working Fluid System) 
         [0073]    Next, the clamp mechanism working fluid system is explained. 
         [0074]    In the upper part in the center of the rotary table shaft  42 , a hole is provided to form a cylinder  50 . This cylinder  50  and the lower part of the rotary table  41  define a cylinder chamber. 
         [0075]    In the cylinder  50 , a piston  51  capable of being moved in the axial direction is provided. 
         [0076]    The piston  51  has an upper piston rod  52   a  and a lower piston rod  52   b . The upper piston rod  52   a  is connected to a clamp mechanism, not shown, for holding the workpiece  2 . In the piston  51  and the lower piston rod  52   b , two fluid passages communicating with oil chambers above and below the piston  51  are formed. 
         [0077]    In the shaft center of the rotary table shaft  42 , the planetary roller harness  24 , and the motor output shaft  14 , the rotating shaft center holes  42   a ,  24   c  and  14   a  are formed, respectively, as described above. 
         [0078]    The inside diameters of these rotating shaft center holes  42   a ,  24   c  and  14   a  are equal, and one axial shaft center through hole is formed by the rotating shaft center holes  42   a ,  24   c  and  14   a  to allow the two hydraulic pipes  53  to pass through. 
         [0079]    The upper ends of the two hydraulic pipes  53  are fixed to the lower surface of the lower piston rod  52   b  under the piston  51  by threaded engagement, press fitting, soldering, or bonding. 
         [0080]    The lower parts of the hydraulic pipes  53  project to the outside through the motor housing cover  16  of the driving motor mechanism  10 . 
         [0081]    To the lower ends of the projecting hydraulic pipes  53 , a rotary joint  54  is connected. 
         [0082]    The rotary joint  54  moves together with the hydraulic pipes  53  in association with the vertical operation of the piston  51 . Therefore, a protrusion  54   a  is provided on the side surface of the rotary joint  54 , and is engaged with a stopper pin  55  fixedly provided on the motor housing cover  16  to prevent the rotary joint  54  from turning. 
         [0083]    Pipes  56 A and  56 B connected to the rotary joint  54  are connected to selector valves, not shown, through flexible pipes, not shown, so that changeover is accomplished from the working fluid side to the discharge tank side and vice versa in the selector valves. 
         [0084]    By the operation (vertical movement) of the piston  51  performed by the working fluid, the clamp mechanism for setting and removing the workpiece  2  can be operated. 
         [0085]    The above is an explanation of one embodiment of the present invention. The present invention is not limited to the above-described embodiment, and, needless to say, the specific construction may be changed variously within the scope of the present invention. 
         [0086]    For example, the hydraulic actuator including the cylinder  50 , the piston  51 , the upper piston rod  52   a , and the lower piston rod  52   b  can be replaced with a fluid-operated actuator such as a pneumatic actuator. 
         [0087]    Also, the hydraulic pipes  53  (or the fluid pressure pipes) is not limited to the above-described pipe having two through holes, and may be a double pipe. 
         [0088]    In this case, the two fluid passages communicating with the upper oil chamber (or fluid pressure chamber) and the lower oil chamber (or fluid pressure chamber) turn to a double hydraulic passage (or a double fluid passage) from an intermediate portion.