Patent Publication Number: US-2022226946-A1

Title: Rotary table device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2021-005681 filed on Jan. 18, 2021, the contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a rotary table device. 
     BACKGROUND ART 
     There is known a rotary table device that includes a distributor and distributes with the distributor a fluid such as air or oil to a rotary table that fixes a workpiece or a device for processing a workpiece (for example, JP2014-161995A). The distributor includes a fixed center sleeve, a center shaft that rotates relative to the center sleeve, a plurality of annular recesses axially provided on an inner periphery of the center sleeve, a first path hole that radially communicates with the recesses on an outer diameter side, and a second path hole that radially communicates with the recesses on an inner diameter side. In the rotary table device, the fluid flows from a fluid flow path provided in the center sleeve into the recesses through the first path hole, and is supplied to a fluid flow path formed in the center shaft through the second path hole. The center shaft is connected to the table, and the fluid supplied to the fluid flow path in the center shaft is fed to the table to drive a device on the table such as a chuck device. Examples of the fluid include liquid such as oil and coolant, and gas such as air. To prevent fluid leakage between the plurality of recesses on a boundary surface between the center sleeve and the center shaft, O-rings are provided on two sides of each of the recesses in the axial direction. 
     SUMMARY OF INVENTION 
     However, when the amount of air or oil distributed by the distributor increases, the number of recesses increases, and the number of O-rings also increases. When the number of O-rings increases, dynamic resistance due to the O-rings increases during rotation of the center shaft. When the center shaft rotates, the center sleeve is twisted by the dynamic resistance. Although not described in JP2014-161995A, when an encoder for detecting rotation of the rotary table is provided between the center sleeve and the center shaft on one end side in the axial direction, a rotation non-detection zone of the encoder is generated due to the twist of the center sleeve, and a lost motion of the rotary table occurs. As a result, it is expected that rotation control performance and rotation positioning accuracy deteriorate. Therefore, there is a demand for a configuration that prevents deterioration in the rotation control performance and the rotation positioning accuracy due to dynamic resistance of the O-rings. 
     The present disclosure can be implemented in the following aspects. 
     According to a first aspect of the present disclosure, a rotary table device includes: a rotary table; a case supporting the rotary table rotatably around a rotation axis; a center shaft erected toward the rotary table in a position of the case corresponding to the rotation axis; a housing fixed to the case and spaced apart from the center shaft to surround the center shaft, the housing including an inner peripheral surface having a circular cross section over a predetermined range along the rotation axis; a center sleeve disposed outside the center shaft and inside the housing, the center sleeve being fixed to the rotary table, the center sleeve including an outer peripheral surface having a circular cross section corresponding to the inner peripheral surface, and the outer peripheral surface being configured to rotate concentrically with the inner peripheral surface; a rotary encoder disposed on the center shaft and the rotary table, the rotary encoder being configured to detect a rotation angle of the rotary table; a plurality of recesses formed in at least one of the inner circumferential surface and the outer circumferential surface to form a flow path of a fluid; a plurality of O-rings disposed to be sandwiched between the inner peripheral surface and the outer peripheral surface to prevent a leakage of the fluid from the plurality of recesses; an in-housing fluid flow path formed inside the housing and each communicating with the plurality of recesses; and a plurality of in-sleeve fluid flow paths formed inside the center sleeve and each communicating with the plurality of recesses to supply the fluid into the flow path provided in the rotary table. According to the rotary table device of the first aspect, even when the rotary table and the center sleeve rotate relative to the housing and dynamic resistance of the O-rings is generated between the center sleeve and the housing, the center shaft is not affected by the dynamic resistance of the O-rings since no O-ring is provided between the center sleeve and the center shaft. As a result, neither a rotation non-detection zone of the encoder provided on the center shaft occurs nor a lost motion of the rotary table occurs. As a result, it is possible to prevent deterioration of rotation control performance and rotation positioning accuracy due to the dynamic resistance of the O-rings. 
     According to a second aspect of present disclosure, the plurality of recesses may have an annular groove shape. According to the rotary table device of the second aspect, the recesses each have an annular groove shape, and thus the fluid can be stably supplied from the housing to the center sleeve regardless of a rotation position of the center sleeve. 
     According to a third aspect of present disclosure, the plurality of recesses may be formed on the inner circumferential surface of the housing. According to the rotary table device of the third aspect, no recess is provided in the center sleeve, and thus the thickness of the center sleeve can be reduced. 
     According to a fourth aspect of present disclosure, the rotary table device may further include: a rotary support portion arranged between the center shaft and the center sleeve. According to the rotary table device of the fourth aspect, a distance between the center shaft and the center sleeve is kept constant, and the center sleeve can be prevented from being misaligned. 
     According to a fifth aspect of the present disclosure, the rotary support portion may include a bearing device or a dry bush. According to the rotary table device of the fifth aspect, friction between the center shaft and the center sleeve can be reduced. 
     The present disclosure can also be implemented in various forms other than the rotary table device. For example, the present disclosure can be implemented in a form of a machining device, a machining center, or the like. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic view of a five-axis machining center including a rotary table device. 
         FIG. 2  is a schematic view of a configuration of the rotary table device. 
         FIG. 3  is an enlarged view of a region III in  FIG. 2 . 
         FIG. 4  is a schematic view of a configuration of a rotary table device according to a second embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
       FIG. 1  is a schematic view of a five-axis machining center  10  including a rotary table device  30 . The five-axis machining center  10  includes a bed  20 , the rotary table device  30 , a turning spindle  70  including a chuck device, a column  80 , and a saddle  90 . The five-axis machining center  10  is of a horizontal type, in which a vertical direction is referred to as a y-axis direction, and horizontal directions intersecting the y-axis direction are referred to as an x-axis direction and a z-axis direction. 
     The bed  20  includes a pair of rails  21  extending along the z-axis, and a work table  25  extending in the −z direction of the rails  21 . The work table  25  is provided with a pair of rails  26  extending along the x-axis. The rotary table device  30  is disposed above the rails  26 . The rotary table device  30  is movable along the x-axis above the rails  26  by a servo motor (not illustrated). 
     The rotary table device  30  includes a rotary table  31  rotatable around a B-axis. The turning spindle  70  including a chuck device is disposed above the rotary table  31 . The turning spindle  70  is also referred to as a turning main shaft. The turning spindle  70  can grip a workpiece  100  and rotate the workpiece  100  around an A-axis by a motor (not illustrated). A force used for gripping the workpiece  100  is provided by hydraulic pressure supplied via the rotary table device  30 . A supply route thereof will be described later. 
     The column  80  is disposed above the rails  21  and is movable along the z-axis above the rails  21  by a servo motor (not illustrated). The column  80  is provided with a pair of rails  81  extending along the y-axis. The saddle  90  is disposed above the rails  81 . The saddle  90  is movable along the y-axis above the rails  81  by a servo motor  82 . The saddle  90  is provided with a spindle  91  to which a tool for machining a workpiece is attached. The spindle  91  is also referred to as a main shaft. When a motor (not illustrated) rotates the spindle  91 , the tool rotates and processes the workpiece  100 . When a skiving tool is used as the tool, the rotation of the tool and the rotation of the workpiece  100  are linked, and a tooth surface of the workpiece  100  is skived when the tool is moved in the axial direction relative to the workpiece  100 . By using the rotary table device  30 , the machining accuracy of the tooth surface is improved. 
       FIG. 2  is a schematic view of a configuration of the rotary table device  30 . The rotary table device  30  includes rotary components that rotate and stationary components that do not rotate. The rotary table device  30  includes, as the rotary components, the rotary table  31  (see  FIG. 1 , not illustrated in  FIG. 2 ), a center sleeve  40 , a first rotor  51 , a second rotor  52 , a rotor magnet  54  of a built-in motor, an inner ring  55  of a rolling bearing, a first coupling portion  56  that couples the center sleeve  40  with a second coupling portion  57 , the second coupling portion  57 , and a rotor portion  63   a  inside an encoder. The rotary table device  30  further includes, as the stationary components, a case  60 , a center shaft  61 , an encoder mounting portion  62  that couples the center shaft  61  with a casing  63   b , the casing  63   b  on an outer diameter side of the encoder, a housing  64 , a housing support portion  65 , a stator coil  66  of the built-in motor, and an outer ring  67  of the rolling bearing. 
     The case  60  includes a disk portion  60   b  serving as a bottom surface of the rotary table device  30  and a cylindrical portion  60   a  rising from an outer periphery of the disk portion  60   b . Here, the disk portion  60   b  side is referred to as “lower”, and a direction in which the cylindrical portion  60   a  rises is referred to as “upper”. The disk portion  60   b  has an opening  60   c  in the center. A cable and other signal lines (not illustrated) for sending an output from the casing  63   b  on the outer diameter side of the encoder to an external control device (not illustrated) pass through the opening  60   c . A B-axis OB, which is the center of the case  60 , passes through the center of the opening  60   c . The B-axis OB is a rotation axis of the rotary table  31 . The center shaft  61  having a cylindrical shape with the B-axis OB as a center axis is erected on the disk portion  60   b . A fixing portion  61   a  having a flange shape is formed at a lower end of the center shaft  61 . The fixing portion  61   a  is fixed to the disk portion  60   b  of the case  60  by a screw (not illustrated). In  FIG. 2 , screws for fixing members are not illustrated. The encoder mounting portion  62  is fixed to the center shaft  61  by a screw on a side (upper side in  FIG. 2 ) of the center shaft  61  opposite to the disk portion  60   b . The encoder mounting portion  62  has a cylindrical shape and includes a flange  62   a  on a side opposite to the center shaft  61 . A central portion  62   b  of the flange  62   a  on the side opposite to the center shaft  61  is recessed, and the casing  63   b  on the outer diameter side of the encoder is fixed to the recessed central portion  62   b  by a screw. The casing  63   b  on the outer diameter side of the encoder has a cylindrical shape. The rotor portion  63   a  rotates integrally with the rotary table  31 . The rotor portion  63   a  and the casing  63   b  are provided in a rotary encoder  63  that detects a rotation angle of the rotary table  31 . In the present embodiment, a magnetic or optical rotary encoder can be used as the rotary encoder. 
     The center sleeve  40 , which is a rotary component, is disposed outside the center shaft  61  with a slight gap therebetween. The center sleeve  40  has a cylindrical shape concentric with the B-axis OB. The center sleeve  40  includes a flange  40   a  on a side opposite to the case  60 . The cylindrical first rotor  51 , which is concentric with the B-axis OB, is disposed on an outer periphery of the flange  40   a . The cylindrical second rotor  52 , which is concentric with the B-axis OB, is disposed on an outer peripheral side of the first rotor  51 . The rotor magnet  54  is disposed on the case  60  side of the second rotor  52 . The built-in motor which is a direct drive motor includes the rotor magnet  54  and the stator coil  66  that is a stationary component. The inner ring  55  of the rolling bearing is disposed on an outer periphery of the second rotor  52 . A three-way bearing includes the inner ring  55  of the rolling bearing and the outer ring  67  of the rolling bearing that is a stationary component, and the three-way bearing supports vertically and radially the outer ring  67 . The first coupling portion  56  is fixed with a screw on a side of the flange  40   a  opposite to the case  60 . The first coupling portion  56  includes a cylindrical portion  56   a  concentric with the B-axis OB, and a disk portion  56   b  formed with a hole  56   c  at a central portion of the cylindrical portion  56   a  on the rotary table  31  side (upper side in  FIG. 2 ). The second coupling portion  57  is fitted into and fixed to the hole  56   c.    
     The center sleeve  40  has an outer peripheral surface having a circular cross section, and the housing  64  is disposed outside the outer peripheral surface with a slight gap therebetween. The housing  64  is fixed to the case  60  by a screw. That is, the center sleeve  40  and the housing  64  are spaced apart from each other. The housing  64  has a cylindrical shape concentric with the B-axis OB. The housing support portion  65  is disposed on an outer peripheral side of the housing  64 , and is fixed to the case  60  by a screw. The housing support portion  65  supports the housing  64  from the outer peripheral side. 
     The stator coil  66  is disposed inside the cylindrical portion  60   a  of the case  60 . As described above, the stator coil  66  is included in the direct drive motor together with the rotor magnet  54 . 
     The housing  64  has an inner peripheral surface having a circular cross section over a predetermined range along the B-axis OB. A plurality of recesses  64   a  each having an annular groove shape are formed on the inner peripheral surface. Between the inner peripheral surface of the housing  64  and the outer peripheral surface of the center sleeve  40 , O-rings  68  are disposed above and below each of the recesses  64   a  in a direction along the B-axis OB. The O-rings  68  are sandwiched between the inner circumferential surface of the housing  64  and the outer circumferential surface of the center sleeve  40 , and prevent leakage of a fluid supplied to the recesses  64   a . The O-rings  68  generate dynamic resistance when the center sleeve  40  rotates, and thus the number of the O-rings  68  is preferably small. Here, since the O-rings  68  can be shared by two adjacent recesses  64   a , the number of the O-rings  68  may be “n+1” pieces if the number of the recesses  64   a  is “n” pieces. The plurality of recesses  64   a  and a plurality of in-housing fluid flow paths  64   b  respectively communicating thereto are formed inside the housing  64 . Each of the fluid paths  64   b  includes a radial path hole communicating with the corresponding recess  64   a , and an axially extending passage. 
     A plurality of in-case fluid flow paths  60   d  are formed in the cylindrical portion  60   a  and the disk portion  60   b  of the case  60 , and are respectively connected to the plurality of in-housing fluid flow paths  64   b  of the housing  64 . Fluid supply pipes  69  respectively connected to the plurality of in-case fluid flow paths  60   d  are connected to the cylindrical portion  60   a  and the disk portion  60   b.    
     Inside the center sleeve  40 , a plurality of in-sleeve fluid flow paths  40   c  are respectively connected to the plurality of recesses  64   a . Each of the fluid flow paths  40   c  includes a radial path hole communicating with the corresponding recess  64   a  and an axially extending passage. The in-sleeve fluid flow paths  40   c  are connected to fluid flow paths (not illustrated) of the rotary table  31  via a plurality of in-rotor fluid flow paths  51   a  formed inside the first rotor  51 . The fluid flow paths of the rotary table  31  are connected to the turning spindle  70  including a chuck device via a tube (not illustrated). The housing  64  and the center sleeve  40  serves as a so-called distributor that distributes a fluid. The number of the recesses  64   a  is the distribution number of the distributor. 
       FIG. 3  is an enlarged view of a region III in  FIG. 2 . As indicated by arrows, the fluid is supplied from the fluid flow path  64   b  formed in the housing  64  to a space defined by the recess  64   a , the center sleeve  40 , and two O-rings, and is further supplied to the fluid flow path  40   c  formed in the center sleeve  40 . The O-rings  68  prevent leakage of the fluid in the vertical direction. 
     In the present embodiment, no O-ring is provided between the center shaft  61 , to which the encoder  63  is coupled at one end in the axial direction, and the center sleeve  40 , and the O-rings are disposed between the center sleeve  40  and the housing  64 . Therefore, even if dynamic resistance is generated in the O-rings  68  between the center sleeve  40  and the housing  64  when the center sleeve  40  rotates, the dynamic resistance does not act on the center shaft  61 , so that the center shaft  61  would not be twisted. As a result, neither a rotation non-detection zone of the encoder  63  nor a lost motion of the rotary table  31  occurs. 
     In the above embodiment, the recesses  64   a  are formed in the housing  64 . Alternatively, the recesses may be formed in the center sleeve  40 , or be formed in both the housing  64  and the center sleeve  40 . That is, the recesses may be formed in at least one of the housing  64  and the center sleeve  40 . When the recesses  64   a  are formed in the housing  64 , the thickness of the center sleeve  40  can be reduced. 
     When the recesses  64   a  each have an annular groove shape, the fluid can be stably supplied from the housing  64  to the center sleeve  40  regardless of a rotation position of the center sleeve  40 . 
     Second Embodiment 
       FIG. 4  is a schematic view of a rotary table device according to a second embodiment. In the first embodiment, a slight gap is provided between the center sleeve  40  and the center shaft  61 . In the second embodiment, a rotary support portion  42  is disposed in the gap. A distance between the center shaft  61  and the center sleeve  40  is kept constant, and the center sleeve  40  can be prevented from being misaligned. Examples of the rotary support portion  42  include a bearing device such as a roller bearing, or a dry bush. 
     The present disclosure is not limited to the above-described embodiments, and can be implemented by various configurations without departing from the gist of the present disclosure. For example, the technical features in the embodiments corresponding to the technical features in the aspects described in the summary may be replaced or combined as appropriate to solve a part or all of the above-described problems or to achieve a part or all of the above-described effects. One of the technical features may be omitted as appropriate unless described as essential in the present specification.