Patent Publication Number: US-2010126308-A1

Title: Angular indexing apparatus for machine tool

Description:
TECHNICAL FIELD 
     The present invention relates to an angular indexing apparatus for a machine tool, and, more particularly, to an angular indexing apparatus used in, for example, a 5-axis machining apparatus (machining apparatus capable of simultaneous 5-axis control) or a rotating table apparatus. 
     BACKGROUND ART 
     As an example of an angular indexing apparatus for a machine tool, a series supporting type is known. In this type, a fifth servo motor that indexes an angle is built in the lower portion of a head; a lower head is provided directly below a vertical rotating shaft, which is rotated by the fifth servo motor, so as to be branched facing downward in a U shape; and an oscillating head for mounting a tool is rotatably supported. (Patent Document 1) 
     As a different example of an angular indexing apparatus for a machine tool, a parallel supporting type is known. In this type, a rotating drive motor that indexes an angle is built in a head supporting member; the lower portion of a vertical head is connected to the lower portion of an oblique drive shaft, which is rotated by the rotating drive motor; and a vertical tool main shaft is rotatably supported in the head. In addition, the angular indexing apparatus is known as using a rotating drive motor including a rotor and a stator, that is, as singly using what is called a DD motor (that is, using one DD motor). (Patent Document 2) 
     In the machine tool, the characteristics required of the DD motor differ depending upon a processing method or a processing object. In addition, when a torque that is larger than a present torque is required, in order to increase the torque using one DD motor, the outside diameter of the DD motor itself must be increased. When this is done, the outside diameter of a head surrounding the DD motor is also increased, which is not desirable. Ordinarily, the angular indexing apparatus is mounted to a predetermined mounting position of the existing machine tool. If the outside diameter of the head is made larger than a present outside diameter, the angular indexing apparatus cannot be mounted as it is to the existing machine tool, thereby making it necessary to modify the machine tool itself. 
     For a bearing that supports the rotating shaft, a roller gear cam (crobodile cam) (Patent Document 1) or a cross roller bearing (Patent Document 2) is used. 
     When a torque that is larger than a related torque is transmitted to the rotating shaft, it is necessary to increase support rigidity of the bearing and to prevent a reduction in indexing precision. 
     [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2006-26835 (paragraph numbers 0010, 0011; FIGS. 1 and 3) 
     [Patent Document 2] Japanese Unexamined Patent Application Publication No. 2-116437 (page 3, lower left column; page 9, lower column; FIG. 16) 
     DISCLOSURE OF INVENTION 
     Problems to be Solved by the Invention 
     The present invention is created considering the aforementioned circumstances. The present invention aims at providing at a rotating shaft a torque that is larger than a present torque without increasing the outside diameter of a component that is built in a motor. An object to be achieved when a torque that can be output at the rotating shaft is increased is to increase support rigidity of a bearing. 
     Means for Solving the Problems 
     The present invention presupposes the following: an angular indexing apparatus for a machine tool, including a rotating shaft, a housing, a bearing, and driving means, the rotating shaft having a member that is rotationally driven secured to one end thereof, the housing at least surrounding an outer periphery of the rotating shaft for supporting the rotating shaft, the housing being mountable to and removable from the machine tool, the bearing being accommodated between the housing and the rotating shaft, the driving means being provided between the housing and the rotating shaft, the driving means rotationally driving the rotating shaft to index an angular position thereof, wherein, as the driving means, a drive motor, including a motor rotor and a motor stator, is used, the motor rotor and the motor stator being concentrically disposed around the rotating shaft in the housing. 
     The following solving means is provided. In the solving means, the driving means is such that a plurality of the drive motors are disposed in series so as to be separated from each other in the axial direction of the rotating shaft. 
     Due to disposing the plurality of drive motors in series in the axial direction, the rotating shaft becomes long in the axial direction. One bearing that supports the rotating shaft may be used. However, in order to increase support rigidity and rotational precision, it is desirable to use the following solving means. In the solving means, a plurality of the bearings for supporting the rotating shaft are separated from each other in the axial direction; a multiple-row roller bearing capable of supporting an axial load and a radial load is used for the bearing that is closest to a side of a member that is rotationally driven among the bearings; and at least one bearing among the other bearings is disposed between the plurality of the drive motors. 
     ADVANTAGES 
     Since a plurality of the drive motors are disposed in series so as to be separated from each other in the axial direction of the rotating shaft, it is possible to provide a torque that is larger than that of one drive motor. Therefore, compared to a case in which a torque equivalent to that of one drive motor is obtained, the outside diameters of the drive motors can be reduced. As a result, it is possible to reduce the size of the housing, and, thus, to reduce the outside diameter of the entire indexing apparatus. Further, if a plurality of the drive motors having outside diameters equal to those of the drive motors of an existing indexing apparatus are used, the outside diameter of the housing also becomes equal to that of the existing housing, thereby facilitating a mounting operation. 
     When the rotating shaft that becomes long due to dispositions of the drive motors is supported by a plurality of bearings, it is possible to increase the support rigidity and the rotational precision. In addition, since a multiple-row roller bearing capable of supporting an axial load and a radial load is used for the bearing that is closest to the side of the member that is rotationally driven, the rotating shaft can be supported with even higher rigidity. Further, instead of disposing a plurality of bearings at respective end portions of the rotating shaft, at least one bearing among the bearings other than that closest to the side of the member that is rotationally driven is disposed between the plurality of drive motors, so that the distance between the bearings is reduced. When the distance between the bearings is large, the rotational precision is reduced due to flexing of the rotating shaft. By virtue of the aforementioned structure, such a problem can be overcome. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a sectional view of an embodiment of an angular indexing apparatus for a machine tool. 
         FIG. 2  is a sectional view of another embodiment of an angular indexing apparatus for a machine tool. 
         FIG. 3  is an enlarged sectional view of a multiple-row roller bearing. 
         FIG. 4  is a schematic front view of a processing head. 
         FIG. 5  is a perspective view of the entire machine tool. 
     
    
    
     REFERENCE NUMERALS 
     
         
         
           
               1  machine tool 
               2  head 
               3  column 
               4  cross rail 
               5  saddle 
               6  ram 
               7  table 
               8  processing head 
               9  spindle 
               10  spindle unit 
               11  first support head 
               12  base 
               13  casing 
               14  leg 
               20  second support head 
               30  housing 
               31  first housing member 
               31   a  body 
               31   b  first housing sleeve 
               31   c  outwardly facing window 
               32  second housing member 
               32   a  body 
               32   b  second housing sleeve 
               32   c  engagement stopping sleeve 
               32   d  spacer sleeve 
               32   e  outwardly facing window 
             c 1  connector 
             c 11  cable 
             H 1  cable wiring hole 
             c 2  connector 
             c 21  cable 
             H 2  cable wiring hole 
             c 3  connector 
             c 31  cable 
             H 3  cable wiring hole 
               40  rotating shaft 
               40   a  rotation detection shaft member 
               41  first shaft member 
               42  second shaft member 
               42   a  body 
               42   b  recessed portion 
               42   c  second shaft sleeve 
               42   d  connecting member 
               42   e  flange member 
               43  third shaft member 
               50  clamping mechanism 
               51  clamp sleeve 
               51   a  thick-walled portion 
               51   b  thin-walled portion 
               52  pressure-receiving member 
               53  pressure chamber 
               54  fluid path 
               54   a  exit portion 
             R rotary joint 
             R 1  distributor 
             R 1   a  flange portion 
             R 2  shaft 
             R 2   a  first shaft sleeve 
             R 0  annular groove 
             R 11  fluid path 
             R 21  fluid path 
             B 1  bearing 
             B 2  bearing 
             B 2   a  inner ring 
             B 2   b  outer ring 
             B 2   c  circular cylindrical roller 
             M 1  drive motor 
             M 1   a  motor rotor 
             M 1   b  motor stator 
             M 1   c  stator sleeve 
             M 2  drive motor 
             M 2   a  motor rotor 
             M 2   b  motor stator 
             M 2   c  stator sleeve 
               60  rotation detector 
               61  detector stator 
               62  detector rotor 
           
         
       
    
     BEST MODES FOR CARRYING OUT THE INVENTION 
     In an example of a machine tool  1  to which the present invention is applied, as shown in  FIG. 5 , a gate-type machine tool (machining center) is used as a composite machining apparatus, such as a 5-axis machining apparatus or a multi-axis machining apparatus. The illustrated machine tool  1  is a machining apparatus capable of simultaneous 5-axis control; and includes, as a machine tool body, left and right columns  3  and  3 , a cross rail  4 , a saddle  5 , a ram  6 , and a table  7 . The left and right columns  3  and  3  stand from respective sides of a head  2 . The cross rail  4  is disposed at the columns  3  and  3  and moves vertically (in the direction of a Z axis) along one of front and back surfaces of each column  3 . The saddle  5  moves horizontally towards the left and right (in the direction of a Y axis) along the front surface of the cross rail  4  (that is, along a side that is the same as that where the cross rail  4  is provided with respect to the columns  3 ). The ram  6  moves along the front surface of the saddle  5  in the direction of the Z axis. The table  7  moves along the upper surface of the head  2  in a front-back direction. In addition, a processing head  8  is removably mounted to the ram  6  of the machine tool body. A spindle unit  10  including a spindle  9  to which a tool is mounted is provided as one component of the processing head  8 . 
     In such a machine tool  1 , during processing of a workpiece, by numerical-value control based on a preset program, the table  7 , the cross rail  4 , the saddle  5 , and the ram  6  are moved, and the processing head  8  indexes the angular position (rotation position) of the spindle unit  10 . By this, in the gate-type machine tool, it is possible to abut the tool upon each processing surface of the workpiece at a suitable angle and to process the workpiece, and to, for example, cut and process the workpiece having a complicated shape. 
     As shown in  FIG. 4 , the processing head  8  includes the spindle unit  10 , a first support head  11 , and a second support head  20 . The spindle unit  20  is provided with the spindle  9  to which a tool is mounted. The first support head  11  rotatably supports the spindle unit  10  in a state allowing angular adjustment. The second support head  20  rotatably supports the first support head  11  at a side opposite to the spindle unit  10 . In addition, the first support head  11  (a base  12  of the first support head  11 ) corresponds to what is called a member that is rotationally driven in the invention of the application, and the second support head  20  corresponds to what is called the angular indexing apparatus in the invention of the application. 
     The spindle unit  10  is a spindle head having a motor built therein, and rotationally drives at a high speed the spindle  9 , rotatably supported in a casing  13  thereof, by the built-in motor (not shown). 
     The first support head  11  rotatably supports the spindle unit  10  with an A axis as center, and, with a built-in motor, causes the spindle unit  10  to rotate around the axis (hereunder referred to as “A axis”) that is orthogonal to an axial direction corresponding to a vertical direction (hereunder referred to as “C-axis direction”) to index the angular position thereof. The C axis is parallel to a Z axis of the machine tool  1 . 
     The first support head  11  has the shape of a fork in which a pair of legs  14  and  14  are mounted to the base  12  (portion at the side of the second support head  20 ) so as to be spaced apart (separated) from each other. The spindle unit  10  is supported between the pair of legs  14  and  14 . More specifically, a pair of support shafts (not shown), rotatably supported in the interiors of the respective legs  14  and disposed so that their rotational axes match the A axis, are mounted to the respective side surfaces of the spindle unit  10 . By the support shafts, the spindle unit  10  is rotatably supported between the pair of legs  14  and  14 . In addition, by rotationally driving the support shafts by a motor built in the leg  14 , the spindle unit  10  is rotated around the A axis as center, to index its angular position. 
     The second support head  20  supports the first support head  11  so that the first support head  11  rotates around the C axis as center, rotates the first support head  11  by a built-in driving means, and indexes its angular position, to index the angular position of the spindle unit  10 . The second support head  20  is mounted to the ram  6  of the machine tool  1 , and has the first support head  11  mounted to one end thereof. In the description below, each part of the second support head  20  basically has a cylindrical shape or an annular shape with the C axis as the axis. In addition, the term “connect” means that fastening and securing with, for example, screws or bolts. 
     As shown in  FIG. 1 , the second support head  20  includes a housing  30 , a rotating shaft  40 , bearings B 1  and B 2 , driving means M 1  and M 2 , and a clamping mechanism  50  (which holds the rotating shaft  40  so as to be incapable of rotating). The rotating shaft  40  is rotatably supported in the interior of the housing  30 . The bearings B 1  and B 2  are interposed between the housing  30  and the rotating shaft  40 . The driving means M 1  and M 2  are similarly interposed between the housing  30  and the rotating shaft  40 . The clamping mechanism  50  is similarly interposed between the housing  30  and the rotating shaft  40 . The driving means M 1  and M 2  and the bearings B 1  and B 2  are plural in number, and are disposed in series so as to be spaced apart from each other in the C axis direction. In the embodiment, a cross roller bearing is used for the bearing B 1  at a side (upper side) opposite to the member that is rotationally driven, and a multiple-row roller bearing capable of supporting an axial load and a radial load is used for the bearing B 2  at the side of the member that is rotationally driven (lower side). 
     The driving means M 1  and M 2  rotationally drive the rotating shaft  40  with respect to the housing  30  secured to the machine tool  1 , and driving motors M 1  and M 2  are used therefor. Each of the driving motors M 1  and M 2  is a type that is operated by directly connecting it to a load without using a decelerator such as a gear (this type is popularly called a direct-drive motor/DD motor). The drive motors M 1  and M 2  include motor stators M 1   b  and M 2   b , motor rotors M 1   a  and M 2   a , and stator sleeves M 1   c  and M 2   c , respectively, all of which are concentrically disposed. The motor stators M 1   b  and M 2   b  are formed by winding coils around fixed iron cores. In the motor rotors M 1   a  and M 2   a , a plurality of opposing magnets disposed close to the inner peripheral surfaces of the respective motor stators M 1   b  and M 2   b  are disposed in a peripheral direction. The stator sleeves M 1   c  and M 2   c  hold the motor stators M 1   b  and M 2   b , respectively. 
     The housing  30  primarily includes housing members  31  and  32 , and a distributor R 1  of a rotary joint R. The housing  30  can be divided in the C axis direction, and includes the housing member  31  and the housing member  32  in the figure. Regarding the housing members  31  and  32 , the illustrated upper housing member  31  is a first housing member, and the lower housing member  32  is a second housing member. The outside diameter of the distributor R 1  is less than the inside diameter of the first housing member  31 . The first housing member  31  and the second housing member  32  are connected to each other in the form of a vertically long cylinder. The distributor R 1  is concentrically disposed so as to be spaced apart from the inner peripheral side of the first housing member  31 . An outer peripheral portion of a flange portion R 1   a , which projects radially outward from the upper end of the distributor R 1 , is connected to an upper end portion of the first housing member  31 . By this, a space is formed between the first housing member  31  and the distributor R 1 , a space is formed at the inner peripheral side of the distributor R 1 , and a space is formed at the inner peripheral side of the second housing member  32  for communication therewith. The rotating shaft  40 , the bearings B 1  and B 2 , and the drive motors M 1  and M 2  are disposed in these spaces. 
     A body  31   a  of the first housing member  31  has an L shape in cross section at one side thereof, the L shape being formed by inwardly bending a lower end portion of the body  31   a . A first housing sleeve  31   b , which projects radially inward towards the distributor R 1 , is connected to an upper end portion of the body  31   a . The cross section at one side of the body  31  has overall a U shape that opens inwardly. 
     The rotary joint R includes the cylindrical distributor R 1  and a cylindrical shaft R 2  having different diameters. The distributor R 1  and the shaft R 2  are rotatably fitted to each other in the form of a double tube. Here, the shaft R 2  is fitted to the outer side of the distributor R 1 . A plurality of fluid paths R 11  and R 21  are formed at the distributor R 1  and the shaft R 2 , respectively, so that they are positionally shifted from each other in a circumferential direction. Annular grooves R 0 , which communicate with the fluid paths R 11  and R 21 , are formed in a fitting peripheral surface between the distributor R 1  and the shaft R 2 . By virtue of this structure, even if the distributor R 1  and the shaft R 2  rotate relative to each other, the state of communication between the fluid paths R 11  of the distributor R 1  and the fluid paths R 21  of the shaft R 2  is maintained. The fluid paths R 11  of the distributor R 1  are formed so as to communicate with the outside at the flange portion R 1   a , and the flow paths R 21  of the shaft R 2  are formed so as to communicate with the first support head  11 . 
     A second housing sleeve  32   b , which projects radially inward, is connected to an upper end portion of a body  32   a  of the second housing member  32 , and an engagement stopping sleeve  32   c , which projects radially inward, is connected to a lower end portion of the body  32   a  of the second housing member  32 . In addition, the second housing member  32  is secured to the first housing member  31  by connecting the second housing sleeve  32   b  to the lower portion of the first housing member  31 . 
     The rotating shaft  40  primarily includes cylindrical shaft members  41 ,  42 , and  40   a , and can be divided in the C-axial direction at locations corresponding to a dividing location of the housing  30 . In the figure, the rotating shaft  40  can be divided in two in the C-axis direction. The shaft member  41 , disposed in the space between the first housing member  31  and the distributor R 1 , is a first shaft member. The shaft member  41 , disposed in the space at the inner peripheral side of the second housing member  32 , is a second shaft member. The shaft member  40   a , disposed in the space at the inner peripheral side of the distributor R 1 , is a rotation detection shaft member. In addition, the rotation detection shaft member  40   a  and the first shaft member  41 , which are disposed at the inner and outer sides of the distributor R 1 , respectively, are abutted upon and connected to the upper end of the second shaft member  42  with the C axis as center. The first shaft member  41  and the second shaft member  42  can be divided at a location corresponding to the dividing location of the housing  30 . 
     The body of the first shaft member  41  corresponds to the shaft R 2  of the rotary joint R. The first shaft member  41  is formed so that the lower portion of the shaft R 2  projects radially outward so as to face the lower portion of the first housing member  31 , and so that a first shaft sleeve R 2   a , which projects radially outward, is connected to the upper portion of the shaft R 2 . In addition, one drive motor M 1  and one bearing B 1  are disposed in a cylindrical space between the first shaft member  41  and the first housing member  31 , and the bearing B 1  is disposed beneath the drive motor M 1 . That is, the upper bearing B 1  is disposed between the upper drive motor M 1  and the lower drive motor M 2 . 
     An outer peripheral portion (outer ring) of the upper bearing B 1  (cross roller bearing) is connected to the lower portion of the first housing member  31 , and an inner peripheral portion (inner ring) of the upper bearing B 1  is connected to the lower portion of the first shaft member  41 . 
     In the upper drive motor M 1 , the motor stator M 1   b  is secured to the inner peripheral side of the first housing member  31  through the stator sleeve M 1   c , and the motor rotor M 1   a  is secured to the outer peripheral side of the first shaft member  41 . More specifically, the motor stator M 1   b  is concentrically fitted and secured to an inner peripheral surface of the stator sleeve M 1   c , and the stator sleeve M 1   c  is connected to the lower side of the first housing sleeve  31   b  to secure the motor stator M 1   b  to the first housing member  31 . The motor rotor M 1   a  is fitted to the outer peripheral surface of the first shaft member  41  (the shaft R 2  of the rotary joint R), and is connected to the lower surface of the first shaft sleeve R 2   a , to secure the motor rotor M 1   a  to the first shaft member  41 . 
     A cable c 11  is connected to the upper drive motor M 1  through a connector c 1 . The cable c 11  is, for example, a current supply cable for a U phase, a V phase, or a W phase for supplying current to a coil built in the motor stator; a ground wire; or a detection wire for detecting abnormality of the drive motor M 1 . For disposing the connector c 1 , a space that is locally recessed in a portion of the lower surface of the first housing sleeve  31   b  is formed. The connector c 1  is disposed in the recessed space. A cable wiring hole H 1  extending vertically through the first housing sleeve  31   b  is provided therein for passing the cable c 11  therethrough. 
     In the second shaft member  42 , a recessed portion  42   b  is formed in the center portion of the upper end surface of a body  42   a , and the lower portion of the distributor R 1  and the lower portion of the rotation detection shaft member  40   a  are disposed in the recessed portion  42   b . The recessed portion  42   b  has a stepped form in which the inside diameter of the upper portion thereof is larger than that of the lower portion thereof. An outer peripheral surface of the lower portion of the distributor R 1  contacts the inner peripheral side of the upper portion of the recessed portion  42   b , and an outer peripheral surface of the lower portion of the rotation detection shaft member  40   a  contacts the inner peripheral side of the lower portion of the recessed portion  42   b . The second shaft member  42  is provided with a second shaft sleeve  42   c  connected to the upper portion of the body  42   a  thereof and projecting radially outward. The second shaft sleeve  42   c  is connected to the first shaft member  41  provided on the second shaft sleeve  42   c.    
     The second shaft member  42  includes a flange member  42   e , disposed at the lower side of the body  42   a , and a connecting member  42   d , disposed so as to sandwich the flange member  42   e ; and is formed so that, along with the flange member  42   e , the connecting member  42   d  is connected to the lower surface of the second shaft member  42 . The lower end surface of the connecting member  42   d  and the upper end surface of the base  12  of the first support head  11  are positioned with respect to each other by fitting a recess and a protrusion to each other. 
     By projecting the second shaft member  42  and the second housing member  32  inwardly and outwardly at proper locations, three annular spaces are formed between the members  42  and  32  so as to be vertically spaced apart from each other. The lower drive motor M 2 , the clamping mechanism  50 , and the lower bearing B 2  are separately disposed in the three spaces, respectively. 
     The lower drive motor M 2  is disposed in the upper space among the three spaces. Similarly to the upper drive motor M 1 , the lower drive motor M 2  includes a motor rotor M 2   a , motor stator M 2   b , and a stator sleeve M 2   c , which are similarly secured to the second housing member  32  through the second housing sleeve  32   b  or to the second shaft member  42  through the second shaft sleeve  42   c.    
     A plurality of cables c 21  are also connected to the lower drive motor M 2  through a connector c 2 . For disposing the connector c 2 , a space that is locally recessed is formed in the lower surface of the second housing sleeve  32   b . In addition, a cable wiring hole H 2  for passing the cables c 21  therethrough is formed so as to communicate with the interior of the second housing sleeve  32   b , the interior of the first housing member  31 , and the interior of the first housing sleeve  31  along the axial direction. Further, an outwardly facing window  31   c  opening to the cables c 21  is formed in the outer periphery of the lower end portion of the first housing member  31 . The outwardly facing window  31   c  is used when passing the cables c 21  through the cable wiring hole H 2  after connecting the first housing member  31  and the second housing sleeve  32   b  to each other. 
     The clamping mechanism  50  is disposed in the middle space among the three spaces. The clamping mechanism  50  includes a clamp sleeve  51 , which relatively compresses the rotating shaft  40  so that the rotating shaft  40  is incapable of rotating relatively, and a pressure-receiving member  52 , which guides fluid for deforming the clamp sleeve  51 . The pressure-receiving member  52  and the clamp sleeve  51  are successively concentrically disposed at the inner peripheral side of the second housing member  32  so as to be connected to each other. The clamp sleeve  51  has a groove at its outer periphery. By the groove, a deformable thin-walled portion  51   b  is formed between an upper thick-walled portion  51   a  and a lower thick-walled portion  51   a . By the groove and the pressure-receiving member  52 , a pressure chamber  53  is formed between the outer side of the thin-walled portion  51   b  and the pressure-receiving member  52 . The clamp sleeve  51  is disposed by disposing the thin-walled portion  51   b  near the second shaft member  42 . Further, a fluid path  54  communicating with the pressure chamber  53  is formed in the interior of the pressure-receiving member  52 . An exit portion  54   a  of the fluid path  54  opens into the pressure chamber  53 . The fluid path  54  is formed in the housing members  31  and  32 , and communicates with a fluid path (not shown) that communicates with the outside at the housing sleeve  31   b . By supplying fluid into the fluid path  54 , the thin-walled portion  51   b  is deformed in a small-diameter direction and the second shaft member  42  is compressed to keep the rotating shaft  40  in a state in which it is incapable of rotating. 
     The lower bearing B 2  is specifically a triplex-row roller bearing (also called a triplex-row circular cylindrical roller bearing/axial radial roller bearing). More specifically, as shown in  FIG. 3 , the bearing B 2  (triplex roller bearing) includes an inner ring B 2   a , an outer ring B 2   b , and a plurality of circular cylindrical rollers B 2   c  interposed between the inner ring B 2   a  and the outer ring B 2   b . By assembling a plurality of parts, the inner ring B 2   a  is formed so as to have a U shape in cross section at one side and so as to open outwardly. An inner peripheral portion of the outer ring B 2   b  is disposed at an intermediate portion in a height direction of a grooved portion of the inner ring B 2   a  that opens. The inner ring B 2   a  and the outer ring B 2   b  are connected to the rotating shaft  40  and the housing  30 , respectively. The circular cylindrical rollers B 2   c  are disposed at the upper side, the lower side, and the inner side of the outer ring B 2   b , respectively. An axial load is supported by the upper and lower circular cylindrical roller B 2   c  and B 2   c , and a radial load is supported by the inner circular cylindrical roller B 2   c . The inner circular cylindrical roller B 2   c  is held by a holding member (not shown). 
     A rotation detector  60  for detecting an amount of rotation of the rotating shaft  40 , that is, an angular position of the first support head  11  is secured to the upper end of the rotating shaft  40  (rotation detection shaft member  40   a ) and the housing  30  (distributor R 1 ) through, for example, bearings. In the rotation detector  60 , a detector stator  61  is secured to the distributor R 1 , and a detector rotor  62  is secured to the upper end portion of the rotation detection shaft member  40   a . A detection signal of the rotation detector  60  is transmitted to a controlling device of the machine tool  1 , and is used to control the rotation of the first support head  11 . 
       FIG. 2  shows a second support head  20  according to another embodiment. This is an embodiment in which three drive motors, that is, drive motors M 1 , M 2 , and M 3  are disposed in series between a housing  30  and a rotating shaft  40  so as to be spaced apart from each other in a C-axis direction. Even in this embodiment, the housing  30  and the rotating shaft  40  can be divided in three in the C-axis direction in accordance with the locations where the drive motors M 1 , M 2 , and M 3  are disposed. That is, in the second support head  20  shown in  FIG. 2 , three housings members, that is, housing members  31 ,  32 , and  33  or the first housing member  31 , the second housing member  32 , and third housing member  33  are linearly connected to each other in the C-axis direction. The drive motors M 1 , M 2 , and M 3 , and a first shaft member  41 , a second shaft member  42 , and a third shaft member  43  are disposed in correspondence with each other at the inner sides of the respective housing members  31 ,  32 , and  33 . The first shaft member  41 , the second shaft member  42 , and the third shaft member  43  are connected to each other in a straight line along the C-axis direction. 
     The second shaft member  42  and the third shaft member  43  in this case are provided by dividing the second shaft member  42  according to the previous embodiment at the intermediate portion in the axial direction and connecting the divided portions to each other through a spacer shaft member  42   f . The second housing member  32  and the third housing member  33  are formed by dividing the second housing member  32  according to the previous embodiment in the axial direction and connecting the divided portions to each other through a spacer sleeve  32   d.    
     In the lowest drive motor M 3 , the disposition of a motor rotor M 3   a , a motor stator M 3   b , and a stator sleeve M 3   c  is similar to that in the other drive motors M 1  and M 2 . A connector c 3 , a cable c 31 , and a cable wiring hole H 3  for the lowest drive motor M 3  are provided similarly to those in the previous embodiment. A wiring hole H 2  for the intermediate cable, and the wiring hole H 3  for the lowest cable are positionally shifted from each other in a circumferential direction. An outwardly facing window  32   e  at the lower end portion of the second housing member  32  is provided similarly to an outwardly facing window  31   c  of the first housing member  31 . 
     Further, the present invention is not limited to the above-described embodiments, so that various modifications can be made without departing from the scope of the claims. 
     The multiple-row roller bearing for the bearing B 2  at the lowest side (side of the member that is rotationally driven) is not limited to the aforementioned triplex circular cylindrical roller bearing. Other types of multiple-row roller bearings, such as a multiple-row conical roller bearing, which can support an axial load and a radial load may be used. 
     In the embodiment shown in  FIG. 2 , although a bearing is not disposed between the upper drive motor M 1  and the intermediate drive motor M 2 , a bearing may be disposed between the drive motors M 1  and M 2 . In addition, a bearing may be disposed above the upper drive motor M 1 . That is, although the number of bearings is set as appropriate in accordance with the length of the rotating shaft  40  and load applied to the rotating shaft  40 , in the present invention, at least one bearing among the plurality of bearings other than the bearing closest to the side of the member that is rotationally driven may be disposed between the drive motors that are disposed in series so as to be separated from each other. For example, when three bearings are used, at least one of the two bearings other than the bearing that is closest to the side of the member that is rotationally driven may be disposed between the drive motors; and, when three or more drive motors are used, the remaining one bearing may be disposed between the drive motors or may be disposed at an end portion of the rotating shaft  40  at the side opposite to the member that is rotationally driven. When three or more drive motors are used, it goes without saying that the support rigidity is further increased if bearings are disposed between all of the drive motors. 
     The bearing B 1 , which is a bearing other than the lowest bearing, is not limited to the aforementioned cross roller bearing, so that other bearing types may be used. The cross roller bearing can support an axial load and a radial load. However, the bearing need not be one that can support loads in both directions. The bearing may be one that is in accordance with the form of the machine tool  1  to which the processing head  8  is mounted. For example, when the machine tool  1  is a horizontal machining center, the C-axis direction of the rotating shaft  40  becomes a horizontal direction. Therefore, a bearing that can support only a radial load (a radial bearing, more specifically, a radial needle bearing, a radial ball bearing, a radial roller bearing, etc.) may be used. 
     When the machine tool  1  is a vertical machining center, the C-axis direction of the rotating shaft  40  becomes a vertical direction. Therefore, a bearing that can support only an axial load (an axial bearing or a thrust bearing, more specifically, a thrust needle bearing, a thrust ball bearing, a thrust roller bearing, etc.) may be used. 
     The application of the angular indexing apparatus according to the present invention is not limited to, for example, the aforementioned 5-axis machining apparatus. For example, the angular indexing apparatus may be applied to a rotating table apparatus that rotationally drives a circular table on which a workpiece is placed and that indexes its angular position. When the angular indexing apparatus is used as a rotating table apparatus, the aforementioned circular table corresponds to what is called a member that is rotationally driven in the present invention. 
     Further, according to the angular indexing apparatus of the present invention, the number of drive motors that are used is not limited to those mentioned above, so that four or more drive motors may be disposed in series so as to be separated from each other in the axial direction.