JP2008155337A - Indexing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an indexing device which exerts high indexing accuracy even if a workpiece has a large size. <P>SOLUTION: According to the structure of the indexing device, an indexing table 11 is rotatably supported on a base 10 by a radial bearing 14, an upper thrust bearing 15, and a lower thrust bearing 17 which are all formed of fluid bearings. Then the size of a bearing gap in the upper thrust bearing 15 is detected by a sensor 25, and pressure of pressure fluid supplied to the upper thrust bearing 15 is adjusted by a pressure and flow rate adjusting means 18, so that the size of the bearing gap is maintained to a predetermined value or more at least during rotation of the indexing table 11. Thus an activation torque and a rotation torque of the indexing table 11 are reduced to small values, and the indexing accuracy is enhanced. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an indexing device used for a machine tool for ultra-precise machining such as a mold, and more particularly to handling of a large workpiece and improvement of indexing accuracy.

Conventionally, as shown in Patent Document 1, the indexing device rotatably supports an indexing table by a rolling bearing such as a ball bearing, and this indexing table is rotated by a predetermined angle by a worm / worm wheel mechanism or the like. Many of them are used.
JP-A-6-344244

  As described above, the indexing table is supported by rolling bearings, and the worm / worm wheel mechanism provides a specified angle of rotation, especially when supporting large workpieces, the shaft rigidity is low due to the structure and indexing accuracy. There is a disadvantage that can not be increased.

  In general, a structure in which a scale such as an angle encoder for indexing is placed at the center of the indexing table is used. The larger the workpiece, the more the position shifts at the outer periphery. This is because it becomes larger.

  On the other hand, if the indexing table is supported by a fluid bearing such as an air bearing, the starting torque of the indexing table can be kept small, resulting in increased shaft rigidity and higher indexing accuracy. it can. However, in the case of an air bearing that can suppress the starting torque to a smaller extent, there is no reduction in shaft rigidity, but the bearing rigidity is lowered and cannot support a heavy object such as a large workpiece. There are problems such as weakness in load, and fluid bearings are generally used for light-weight indexing devices.

  An object of the present invention is to provide an indexing device capable of obtaining a high indexing accuracy even for a large workpiece.

  In order to achieve the above object, an indexing device according to the present invention is provided with a base, an indexing table rotatably attached to the base via a fluid bearing, and provided between the base and the indexing table. A sensor for measuring the size of the bearing gap of the bearing, a pressure / flow rate adjusting means for adjusting the pressure / flow rate of the pressure fluid supplied to the fluid bearing to change the size of the bearing gap, And a control unit that operates the pressure / flow rate adjusting means so as to keep the size of the bearing gap at or above a predetermined value at least when the indexing table rotates.

The indexing table may be arranged horizontally, and the sensor may be configured to measure the size of the bearing gap of the upper thrust bearing on which the load of the indexing table acts. The control unit maintains the size of the bearing gap of the upper thrust bearing at a predetermined value or more when the indexing table rotates, and eliminates the bearing gap of the upper thrust bearing when the indexing table stops. Desirably, the flow rate adjusting means is configured to operate.
In addition to the bearing gap sensor, the control unit may be used with other types of sensors including at least a sensor for detecting the pressure or flow rate of the pressure fluid, and the indexing table bearing gap may be manually or The indexing device according to claim 2, wherein the indexing device is configured to automatically maintain a predetermined value.
Furthermore, the fluid bearing is preferably an air bearing.

  As described above, the present invention supports the indexing table rotatably with a fluid bearing, measures the size of the bearing gap with a sensor, and at least rotates the indexing table when the indexing table rotates. Since the pressure of the pressure fluid supplied to the fluid bearing is adjusted so as to maintain the fluid bearing, even a heavy object such as a large workpiece can be rotatably supported by providing a bearing gap of a predetermined size, In particular, even in the case of an air bearing having a smaller starting torque, a heavy load such as a large workpiece can be accurately supported and rotated with a small torque, thereby obtaining an effect of improving the indexing accuracy.

  An embodiment of the present invention will be described below with reference to FIG. In FIG. 1, 10 is a base and 11 is an indexing table. The indexing table 11 is horizontally arranged, and a rotor 12A constituting a direct drive (DD) motor 12 described later is provided at the lower center of the indexing table 11, and an annular boss 13 is integrally provided so as to surround the rotor 12A. ing.

  An outer peripheral surface of the annular boss 13 is rotatably engaged with a radial bearing 14 provided on the base 10 and made of a hydrodynamic bearing such as a static pressure type. Further, the lower surface of the indexing table 11 is rotatably supported by an upper thrust bearing 15 which is provided on the base 10 and is composed of a hydrodynamic bearing such as a static pressure type. Further, a ring-shaped receiving plate 16 is attached to the lower end of the annular boss 13, and the upper surface of the receiving plate 16 is also connected to a lower thrust bearing 17 formed of a hydrodynamic bearing such as a hydrostatic type provided on the base 10. It is close to each other so that it can rotate freely.

  The radial bearing 14, the upper thrust bearing 15 and the lower thrust bearing 17 are each divided into a plurality of parts on the circumference, and the upper thrust bearing 15 to which the load of the indexing table directly acts out of the three bearings 14, 15, 17. Each of the divided bearings is provided with pressure / flow rate adjusting means 18 corresponding to each bearing, and pressure fluid such as pressurized air or pressurized oil is supplied to each bearing through these pressure / flow rate adjusting means 18. To be supplied. The radial bearing 14 and the lower thrust bearing 17 are also divided into a plurality of parts like the upper thrust bearing 15 and supplied with a pressure fluid of a predetermined pressure via a pressure / flow rate adjusting means (not shown).

  The DD motor 12 includes a rotor 12A provided on a projecting portion 11A integrally formed at the lower center of the indexing table 11, and a stator 12B attached to the base 10, and is operated by a motor driving portion 19. Then, the indexing table 11 is rotated.

  An angle encoder 20 is attached between the lower end of the DD motor 12, that is, between the lower end of the protruding portion 11 </ b> A of the indexing table 11 and the base 10, detects the rotational angle position of the indexing table 11, and its output is the control unit 21. Sent to. The control unit 21 operates the motor drive unit 19 by a command given from the outside and the output of the angle encoder 20 to rotate the index table 11 by a predetermined angle, and stops and holds the index table 11 at a predetermined angular position.

  The indexing table 11 is provided with a flow path 22 for vacuum-sucking the workpiece W, and this flow path 22 is vacuumed via a rotary joint 23 provided at the center of the lower end of the protruding portion 11A of the indexing table 11. It is connected to the device 24. The vacuum device 24 is operated by a command from the control unit 21 and selectively switches the flow path 22 between a negative pressure and an atmospheric pressure.

  A plurality of preferably non-contact sensors 25 are arranged on the base 10 so as to face the lower surface of the indexing table 11 at intervals of, for example, 90 ° in the circumferential direction of the indexing table 11. The change in the vertical position of the lower surface or the distance from the sensor 25 is detected, and the output is sent to the control unit 21.

  The control unit 21 obtains the size of the bearing clearance of each of the divided bearings of the upper thrust bearing 15 from the output of each sensor 25, operates each pressure / flow rate adjusting means 18 provided for each bearing, A pressure fluid such as pressurized air or pressurized oil is supplied to each bearing of the upper thrust bearing 15 at a pressure capable of keeping the size of the bearing gap of each bearing at a predetermined value or more. The control unit 21 is configured to operate the pressure adjusting means 18 so as to reduce the pressure of the pressure fluid while the indexing table 11 is stopped, thereby eliminating the bearing gaps of the respective bearings. When a rotation command for the indexing table 11 is issued, the pressure adjusting means 18 is operated to make the size of the bearing gap larger than a predetermined value, and when the size of the bearing gap becomes larger than the predetermined value. The index table 11 is configured to rotate.

  Next, the operation of this apparatus will be described. While the indexing table 11 is stopped as described above, the pressure / flow rate adjusting means 18 lowers the pressure of the pressure fluid supplied to the upper thrust bearing 15 to eliminate the bearing clearance of the upper thrust bearing 15, and the indexing table 11 is moved upward. It is directly supported by the thrust bearing 15. As a result, the indexing table 11 reliably maintains a stopped state in a predetermined posture without causing an inclination or the like due to a change in the bearing gap.

  The radial bearing 14 and the lower thrust bearing 17 are supplied with a pressure fluid of a predetermined pressure even while the indexing table 11 is stopped, hold the center position of the indexing table 11 by the radial bearing 14, and lower thrust. The indexing table 11 is pushed downward by the bearing 17 to eliminate the bearing gap of the upper thrust bearing 15 more completely, and the indexing table 11 is fixedly held.

  When a rotation command for the indexing table 11 is issued in the stop state, the control unit 21 firstly outputs the sensor 25 at a predetermined value or more, that is, the size of the bearing clearance of each of the divided bearings of the upper thrust bearing 15. The pressure / flow rate adjusting means 18 is actuated to increase the pressure of the pressure fluid supplied to the bearings of the upper thrust bearing 15 so that each becomes equal to or greater than a predetermined value.

When the output of the sensor 25 reaches a predetermined value or more, the control unit 21 issues a start command to the motor drive unit 19 to operate the DD motor 12 and rotate the index table 11. The rotation angle position of the indexing table 11 is detected by the angle encoder 20, and when this reaches a predetermined value,
The control unit 21 issues a stop command to stop the rotation of the index table 11.

  The indexing operation of the indexing table 11 is performed while maintaining the size of the bearing clearance of the upper thrust bearing 15 to which the load is applied directly as well as the radial bearing 14 and the lower thrust bearing 17 at a predetermined value or more. 11 starting torque and rotational torque can be kept small. For this reason, the index table 11 is prevented from stick-slip or overrun, and is stopped at an accurate index position.

  When the indexing table 11 is completely stopped, the control unit 21 operates the pressure / flow rate means 18 so as to eliminate the bearing clearance of the upper thrust bearing 15 and reliably holds the indexing table 11 as described above.

  In the above-described embodiment, the example in which the index table 11 is horizontally arranged has been shown. However, the present invention is not limited to this, and the index of the system in which the axis of the index table 11 is horizontally arranged is shown. Even if it is an apparatus, the same effect can be obtained. In addition, various well-known bearings can be used as the fluid bearing, and in particular, a fluid bearing using a gas such as static pressure type air can be used in an air pipe prepared in the factory. It is preferable because it is easy. Furthermore, in the above-described embodiment, an example in which the non-contact sensor 25 opposed to the lower surface of the indexing table 11 is used as a sensor for measuring the size of the bearing gap is shown. However, the present invention is not limited to this, and various modifications such as various sensors such as a capacitance type sensor that can be incorporated in the bearing can be used.

Furthermore, in the above-mentioned embodiment, the example using the sensor 25 for measuring the size of the bearing gap is shown, but the present invention is not limited to this example, and another example of the embodiment includes a table. The position may be used in combination with a sensor having other properties such as a position sensor, a pressure sensor, a flow rate sensor, or the like. In particular, values such as a pressure sensor that is normally provided in the pressure fluid adjustment means, which is a pressure fluid adjustment means, and a flow rate sensor provided in the fluid flow path are input to the control device 21 and are combined together. It is convenient to use for. In this case, the control unit 21 can also use information such as pressure and flow rate obtained from sensors other than these bearing gap sensors. When such a plurality of sensors are used, control is possible while monitoring the bearing gap and detecting the pressure and flow rate of the fluid. That is, the fluid pressure and flow rate values set in advance are controlled manually or automatically using the flow rate control means 18 while monitoring the values of these other sensors provided in the bearings and fluid flow paths. The relationship between the workpiece weight and the bearing gap can be controlled while monitoring so as to maintain an optimum situation under predetermined processing conditions or according to the situation. Furthermore, using the position sensor as another sensor, for example, measuring the position of the upper surface of the table, etc., estimating the bearing gap from the calculation, controlling the pressure / flow rate adjusting means manually or automatically, It is also possible to take an embodiment in which the bearing gap is controlled to an optimum desired position. However, in such a case, the configuration becomes more complicated.

  The present invention is effective for an indexing device used for a machine tool for machining a large workpiece, for ultra-precision machining of a mold or the like, but is not limited thereto, and is not limited to a small workpiece or a machine tool. The present invention can be widely applied to indexing devices for various machines.

The outline block diagram of the indexing device to which this invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Base 11 Indexing table 11A Protrusion part 12 Direct drive (DD) motor 12A Rotor 12B Stator 13 Annular boss 14 Radial bearing 15 Upper thrust bearing 16 Receiving plate 17 Lower thrust bearing 18 Pressure / flow rate adjustment means 19 Motor drive part 20 Angle Encoder 21 Control unit 22 Flow path 23 Rotary joint 24 Vacuum device 25 Sensor W Workpiece.

Claims (5)

Base and
An indexing table rotatably attached to the base via a fluid bearing;
A bearing gap sensor provided between the base and the indexing table for measuring the size of the bearing gap of the fluid bearing;
Pressure / flow rate adjusting means for adjusting the pressure / flow rate of the pressure fluid supplied to the fluid bearing to change the size of the bearing gap;
A controller that takes in the output of the bearing gap sensor and operates the pressure / flow rate adjusting means so as to keep the size of the bearing gap in a desired state at least during rotation of the indexing table;
An indexing device comprising:   The index table is arranged horizontally, and the bearing gap sensor is configured to measure the size of the bearing gap of the upper thrust bearing on which the load of the index table acts. The indexing device according to claim 1.   The control unit maintains the size of the bearing gap of the upper thrust bearing at a predetermined value or more when the indexing table rotates, and eliminates the bearing gap of the upper thrust bearing when the indexing table stops. The indexing device according to claim 2, wherein the indexing device is configured to operate the flow rate adjusting means. In addition to the bearing gap sensor, the controller further uses other types of sensors including at least a sensor for detecting the pressure or flow rate of the pressure fluid to manually determine the index table bearing gap. The indexing device according to claim 1, wherein the indexing device is configured to automatically maintain a desired state.   5. The indexing device according to claim 1, wherein the fluid bearing is an air bearing.

Images