JP4204816B2 - Table drive device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a table that requires precise movement, and more particularly to a table drive mechanism that uses a screw shaft and a ball nut and a table drive device that can suppress a three-dimensional motion error of the table caused by a guide portion. .
[0002]
[Prior art]
In a conventional table requiring nanometer-order movement and positioning accuracy, two guide means comprising a precise V-shaped guide groove and a rolling bearing rolling along the guide groove are arranged in parallel. It is composed of a so-called V-V rolling guide provided, or a static pressure guide using an aerostatic bearing. The geometrical error of the guide and the ball nut accompanying the rotation of the screw shaft The rotation and the run-out of the screw shaft induced the three-dimensional motion error of the table.
[0003]
In order to keep the three-dimensional motion error of the table as small as possible, conventionally, the table has been dealt with by improving the processing accuracy and assembly accuracy of the drive mechanism components and guide portions. However, it did not fully satisfy the accuracy actually required.
[0004]
[Problems to be solved by the invention]
In order to further improve the movement accuracy of the table, the present invention does not transmit the mechanical movement error on the drive side to the table as much as possible, apart from the improvement of the processing accuracy and assembly accuracy of the components and guide parts of the table drive mechanism. The object of the present invention is to provide a table driving device that enables precise movement of the table.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, a table driving device according to the present invention is arranged in parallel with the first guide means and a sub table mounted so as to be movable in a predetermined direction by the first guide means provided on the base. A screw shaft rotatably attached to the base side, a ball nut attached to the sub-table and screwed to the screw shaft, a drive source for rotating the screw shaft, and the base to the first A main table mounted so as to be movable in the same predetermined direction as the sub table by a second guide means provided in the same direction as the guide means, and provided between the sub table and the main table. The coupling means transmits the movement of the sub table to the main table. The coupling means is attached to the other end of the coaxial member with one end side fixed to the sub table and fixed to the other end of the coaxial member. A bearing disk having a spherical surface, and a support member that forms a hydrostatic bearing between the front and back partial spherical surfaces of the bearing disk that are fixed to the main table, the center of the partial spherical surface of the sub table It is configured to be set in the vicinity of the starting point of a three-dimensional motion error accompanying driving.
[0006]
According to this configuration, even if the sub table driven by the screw shaft and the ball nut generates a three-dimensional motion error, the three-dimensional motion error of the sub table has a partial spherical surface centered around the starting point. The bearing disk is absorbed by the smooth movement of the hydrostatic bearing, and the movement in the predetermined direction is reliably transmitted from the sub table to the main table. As a result, the main table moves precisely with little influence from the drive side. The center of the partial spherical surface is preferably set near the center of the ball nut or near the center of the sub table in the predetermined direction.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a first embodiment of the present invention will be described in detail with reference to FIGS. FIG. 1 shows a main configuration of a table driving apparatus according to the present invention. In the drawing, first and second guide members 12A and 22A constituting first guide means 12 and second guide means 22 respectively extending in the same direction are provided on a base 10. . A sub table 20 is movably mounted on the first guide member 12A via the first guide means 12, and a workpiece W is mounted on the second guide member 22A to perform measurement, processing, or the like. A main table 24 for performing work is movably mounted via the second guide means 22.
[0011]
FIG. 2 is a side view seen from the Z direction in FIG. 1 and shows the configuration of the second guide means 22. The first guiding means 12 has the same configuration. Two V grooves 22B are formed on the left and right of the upper surface of the second guide member 22A constituting the second guide means 22, and the V groove 22B is formed on the main table 24 along two inclined surfaces of the V groove 22B. A rolling element 22C made up of a roller or a ball that rolls in the longitudinal direction is provided to support the main table 24 so as to be movable in the longitudinal direction of the V-groove 22B. The first and second guide means 12 and 22 are examples, and other known various guide means using a hydrostatic bearing or the like can be used.
[0012]
In FIG. 1, symbol DRV indicates driving means of the sub table 20 in the present invention. The driving means DRV includes a servo motor 16 attached and fixed to the right side surface of the frame 14 erected on the base 10, A screw shaft 18 which is arranged in parallel to one guide means 12 and is rotatably attached to the frame 14 and rotated by a servo motor 16 and a screw shaft provided in the sub table 20 with its axial movement and rotation restricted. 18 and a ball nut 20A that is screwed together. Therefore, when the screw shaft 18 is rotated by the drive of the servo motor 16, the sub table 20 is moved in a predetermined direction, that is, in the left-right direction in FIG. 1, on the first guide member 12A.
[0013]
The right end portion of the shaft member 32 is attached to the left side surface of the sub table 20 in FIG. Further, a bearing disk 30 is attached and fixed to the left end portion of the coaxial member 32. As shown in FIG. 3, the bearing disc 30 has a circular shape, and in FIG. 1, the left surface and the right back surface are respectively formed into partial spherical surfaces. The center positions of the partial spherical surfaces on both the front and back surfaces are the positions of the points P near the center of the ball nut 20A, and the radii of curvature to the spherical surfaces are indicated as R1 and R2, respectively. The spherical center position P is a swing fulcrum of the sub table 20 caused by the swing of the screw shaft 18.
[0014]
A support member 26 having a hydrostatic bearing pad 34 made of a porous body having a partial spherical surface facing a partial spherical surface on the surface side of the bearing disc 30 is attached and fixed to the right side surface of the main table 24 in FIG. A support member 28 having a hydrostatic bearing pad 36 made of a porous body having a partial spherical surface facing the partial spherical surface on the back surface side of the bearing disk 30 is attached and fixed to the support member 26. 34 and 36 are supplied with high-pressure air from a high-pressure air supply unit 38, and a hydrostatic bearing S is configured between the bearing disc 30 and both support members 26 and 28.
[0015]
Therefore, the bearing disc 30 and the shaft member 32 function as a static pressure joint between the sub table 20 and the main table 24. Exhaust from the hydrostatic bearing S is performed from the annular groove 40 provided in the support member 26, the outer peripheral space 42 of the bearing disc 30, and the outer peripheral space of the shaft member 32. In this case, hydraulic pressure can be used instead of the high-pressure air. In the case of this hydraulic pressure, the support member 28 is provided with an annular groove similar to the annular groove 40 to drain the oil. The support members 26 and 28, the bearing disc 30, the shaft member 32, and the hydrostatic bearing pads 34 and 36 constitute a coupling means CPL in the present invention.
[0016]
Next, the operation of this apparatus will be described. When the screw shaft 18 is rotated by the drive of the servo motor 16, the sub table 20 moves along the first guide means 12 through the ball nut 20 </ b> A screwed with the screw shaft 18. The movement of the sub table 20 is transmitted to the main table 24 via the coupling means CPL, and moves the main table 24 along the second guide means 22.
[0017]
By the way, when the auxiliary table 20 is moved via the ball nut 20 </ b> A by the rotation of the screw shaft 18, a rotational force due to the rotation of the screw shaft 18 acts on the ball nut 20 </ b> A, and the auxiliary table 20 is moved around the screw shaft 18. Try to rotate (both rotate). Further, in the nanometer order, the screw shaft 18 has a bend and further bends as it is driven, which causes the ball nut 20 </ b> A to move eccentrically with respect to the ideal center of the screw shaft 18.
[0018]
Due to the accompanying rotation and eccentric movement of the ball nut 20A as described above, the sub table 20 moves in a direction different from the direction in which the first guide means 12 extends starting from the vicinity of the center of the ball nut 20A, so-called three-dimensional movement. An error is generated.
[0019]
The three-dimensional motion error of the sub-table 20 tends to be transmitted to the main table 24 through the coupling means CPL. The coupling means CPL of the present apparatus uses the ball nut 20A that is the starting point of the three-dimensional motion error. Since the bearing disc 30 having a partial spherical surface centered on the point P near the center and the hydrostatic bearing S provided for the partial spherical surface are provided, the three-dimensional motion error, that is, the center of the ball nut 20A is provided. When there is an inclination or a swing of the sub table 20 starting from the vicinity, the bearing disc 30 is moved around the center P by the hydrostatic bearing S and absorbs the tilt or the swing. For this reason, the main table 24 is transmitted only the movement of the sub table 20 in the direction of the second guide means 22 that is the same as the first guide means 12, and a precise movement is performed.
[0020]
The drive means using the screw shaft 18 and the ball nut 20A described above is likely to cause a three-dimensional motion error starting from the vicinity of the center of the ball nut 20A as described above. Therefore, the partial spherical surface of the bearing disc 30 is used as the ball nut 20A. Although an example in which a part of the spherical surface centered on the point P near the center is shown, the present invention is not limited to this, and the center of the partial spherical surface is located near the center of the sub table 20 on the screw shaft 18. The center of the partial spherical surface is preferably determined in accordance with the starting position of the three-dimensional motion error that depends on the configuration of the sub table and its driving means.
[0021]
FIG. 4 is a view showing the coupling means CPL of the reference example , and a sphere 54 is accommodated in the first support members 50 and 52 that are fixedly attached to the sub table 20. Similarly, a sphere 60 is accommodated in second support members 56 and 58 that are fixedly attached to the main table 24. These spheres 54 and 60 are fixedly coupled by a coupling shaft 62. The first and second support members 50, 52, 56, 58 are provided with static pressure bearing pads 64, 66, 68, 70 similar to the static pressure bearing pads 34, 36. It is configured to be supported by the bearing S. 72 and 74 are annular exhaust grooves, and 76 and 78 are exhaust holes. In the case of FIG. 4, since the mechanical motion error is absorbed by the rotation of the spheres 54 and 60 in both the hydrostatic bearings S, the three-dimensional structure of the sub table 20 is compared with the first embodiment. Motion errors are more reliably absorbed.
[0022]
【The invention's effect】
According to the present invention, when the sub table is moved in a predetermined direction by the driving means including the screw shaft and the ball nut, a mechanical motion error on the sub table side including the driving means is formed between the sub table and the main table. The mechanical motion error on the side of the secondary table is not transmitted to the main table, and machining accuracy and assembly accuracy for each component of the drive mechanism that drives the secondary table The main table can be moved with high accuracy without necessarily increasing the accuracy, which is advantageous in terms of manufacturing cost.
[Brief description of the drawings]
FIG. 1 is a partially cutaway front view showing a main configuration of a first embodiment of a table driving apparatus according to the present invention.
FIG. 2 is a side view as seen from the Z direction in FIG.
FIG. 3 is a cross-sectional view taken along line AA in FIG. 1;
FIG. 4 is a view showing a coupling means of a table driving device of a reference example .
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Base 12 First guide means 16 Servo motor 18 Screw shaft 20 Sub table 20A Ball nut 22 Second guide means 24 Main table 26 Support member 28 Support member 30 Bearing disk 32 Shaft members 34 and 36 Hydrostatic bearing pad 50 , 52 First support member 56, 58 Second support member 54, 60 Sphere 62 Coupling shaft 64, 66, 68, 70 Hydrostatic bearing pad CPL Coupling means DRV Drive means P Partial spherical center Q Sphere center S Static pressure Bearing W Workpiece

Claims (3)

A sub-table mounted so as to be movable in a predetermined direction by a first guide means provided on the base, and a screw shaft disposed in parallel with the first guide means and rotatably attached to the base side A ball nut attached to the sub table and screwed into the screw shaft; a drive source for rotating the screw shaft; and a second provided on the base in the same direction as the first guide means. A main table mounted by a guide means so as to be movable in the same predetermined direction as the sub table; and a coupling means provided between the sub table and the main table and transmitting the movement of the sub table to the main table. Become
The coupling means includes a shaft member having one end fixed to the sub-table, a bearing disc attached and fixed to the other end of the coaxial member and having partial spherical surfaces having the same center on the front and back, and the bearing circle fixed to the main table. A support member that forms a hydrostatic bearing between the front and back partial spherical surfaces of the plate, and the center of the partial spherical surface is set in the vicinity of the starting point of the three-dimensional motion error associated with the driving of the sub table. Table drive device characterized. 2. The table driving device according to claim 1, wherein the center of the partial spherical surface is set near the center of the ball nut. The table driving device according to claim 1, wherein the center of the partial spherical surface is set near the center of the sub-table in the predetermined direction.

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