JP2001204167A - Driver and discharge processor utilizing linear motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a driver and a discharge processor utilizing a linear motor in which a main shaft driven with a linear motor is supported with static pressure bearing. SOLUTION: A driver (30) utilizing a linear motor comprises a fixed frame body (21) having the wall portions provided opposed with each other keeping the predetermined interval, a core shaft (10) located and fixed between the wall portions of the frame body (21), a hollow shaft (11) engaged with the core shaft (10) via the static pressure bearing providing therein a collecting route for collecting operation medium and linear motors (15, 23) for applying propulsive force with the hollow shaft (11) to the wall portion of the frame body (21) to move the hollow shaft (11) with the guidance of the core shaft (10). In this case, the hollow shaft is also used as the body to be driven. A discharge processor utilizing the linear motor uses a hollow shaft (11) forming the driver (30) as a quill and is provided with a tool electrode (13) at the end part thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
Also, the present invention relates to a drive device and a discharge machining device using a linear motor driven with high precision.

[0002]

2. Description of the Related Art In recent years, in a precision machine tool, an electric discharge machine, a three-dimensional measuring machine, and the like, a main shaft and a moving shaft are driven and controlled by a linear motor to achieve high speed and high response. . In particular, in the electric discharge machining device, while the minute electric discharge gap between the tool electrode and the workpiece is appropriately maintained, the electric motor is being replaced by a linear motor drive that drives the tool electrode at high speed and with high accuracy. .

As an electric discharge machine for driving a tool electrode by a linear motor, for example, a pair of linear motion bearing rails arranged vertically supports a hollow shaft having a tool electrode attached to a lower end thereof in a vertically movable manner. Means are provided for holding the hollow shaft in a predetermined position while maintaining balance with the weight of the shaft and the tool electrode. Further, a linear motor is provided on opposite sides of the hollow shaft so that magnetic attraction is offset. Are arranged, and the tool electrode is driven and controlled in the Z-axis direction, that is, in the vertical direction using the hollow shaft as a mover. A ball bearing or a cross roller is used as the linear bearing rail.

However, in a bearing using a ball bearing or a cross roller, high precision straightness in the Z-axis motion is slightly inferior to that of a hydrostatic bearing, particularly a hydraulic bearing. In the gap servo control, there is a problem that stick slip occurs and high-response servo controllability over a minute distance deteriorates.

[0005] In order to overcome this problem, it is desirable to use a hydrostatic bearing as the bearing. As an embodiment thereof, there is a voice coil type linear motor disclosed in Japanese Utility Model Laid-Open No. 22082/1990. FIG. 9 is a side view showing a half cross section of the voice coil type linear motor.
21 are provided. The outer periphery of the inner yoke 102 is provided with a porous portion 132 having an ejection hole 131 constituting the inner air bearing portion 103 and an air guide 133. The movable portion 104 is formed in a cup shape, a coil 142 is provided on the tubular portion 141, and the tubular portion 141 is supported by the board-shaped portion 143 so as to face the outer peripheral surface of the inner yoke 102 via a gap, and The load L is attached to the portion 143. The exhaust port 144 is provided in the board-shaped portion 143 so that the inside air bearing portion 103 communicates with the outside air. The stator 105 is provided on the inner surface of the outer yoke 106 provided on the fixed part 101, and is provided opposite to the cylindrical part 141 of the movable part 104 via a gap. Outer air bearing 1
Reference numeral 07 includes a porous portion 172 having an air ejection hole 171 between the surface of the stator 105 and the outer peripheral surface of the cylindrical portion 141, and an air guide 173. The air supply port 108 communicates with the air guides 133 and 173.

Here, when pressurized air is supplied from the air supply port 108, the air passes through the air guides 133 and 173, and is ejected from the air ejection holes 131 and 171. The air is ejected by the inner air bearing portion 103 and the outer air bearing portion 107. , Cylindrical part 14
1 and the movable part 104 is levitated. When the coil 142 is energized, the movable portion 104 moves in the length direction of the inner yoke 102. Since the inner air bearing portion 103 and the outer air bearing portion 107 support the bearing, the bearing rigidity is sufficiently maintained.

[0007] This publication also describes that the cross sections of the inner yoke 102, the cylindrical portion 141, and the outer yoke 106 can be formed in a square or polygon other than a circle.

In addition, Japanese Patent Application Laid-Open No. 61-39845 and Japanese Utility Model Application Laid-Open No.
Japanese Patent No. 9845 and the like.

[0009]

Each of the above-described hydrostatic bearings is merely an example of an air bearing of a drive unit configured in combination with a linear motor, and hydraulic pressure has to be adopted due to the requirement of high bearing rigidity. It cannot be applied to an electric discharge machine that cannot be obtained. In other words, if the drive unit of the tool electrode is configured by using oil instead of air as the working medium of the hydrostatic bearing, the working oil will not be collected, and the oil will flow to the linear motor unit, or around the tool electrode. However, the oil is circulated, and the oil is mixed into the machining fluid, so that it cannot be applied to the electric discharge machine.

In addition, the above-described voice coil type linear motor has a problem in that the coil 142 is mounted between the double cylindrical portions of the movable portion 104, so that the configuration is complicated and maintenance and inspection are difficult.

The present invention has been made in order to solve the above-mentioned problems, and even if a hydraulic static pressure bearing using oil as a working medium is employed, oil can be circulated so as not to leak outside. It is an object of the present invention to provide a drive device and an electric discharge machine using a linear motor that can be made and that can simplify the configuration.

[0012]

The invention according to claim 1 is
A fixed frame having walls facing each other at predetermined intervals,
A core shaft fixed between the wall portions of the frame, a hollow shaft fitted to the core shaft via a hydrostatic bearing having a recovery flow passage therein for recovering the working medium, and a frame; A linear motor that applies a propulsive force to the hollow shaft against the wall of the body and moves the hollow shaft with the core shaft as a guide, and the driving device using the linear motor with the hollow shaft as a driven body. is there.

According to a second aspect of the present invention, there is provided a fixed rectangular frame having walls substantially parallel to each other at a predetermined interval, and a rectangular cross section, the outer surfaces of which are respectively formed on the wall of the frame. The core shaft was fitted to the core shaft via a static shaft bearing fixed at a substantially central portion of the frame so as to be opposed to the core shaft and a recovery flow passage for recovering the working medium therein. A rectangular hollow shaft, a pair of coils wound around a plurality of iron cores,
A plurality of permanent magnets arranged in a row, and a pair of magnet rows, one of the coils and the magnet rows is symmetrically attached to the pair of opposing walls of the frame, and The other is symmetrically mounted on the outer surface of the hollow shaft opposed to the coil, respectively, and a linear motor having a hollow shaft as a mover with a core shaft as a guide, the hollow shaft being a driven body,
Drive device using linear motor.

According to a third aspect of the present invention, in the driving device using the linear motor according to the second aspect, the frame body and the core shaft are fixed so that the core shaft and the hollow shaft are substantially vertical, and the hydrostatic bearing is provided. Is formed by supplying pressure oil to a first communication hole communicating from the end of the core shaft toward the side surface to form an oil film between the outer surface of the core shaft and the inner surface of the hollow shaft. The oil overflowing from the pressure receiving plate is collected at a lower end portion through a second communication hole formed inside the hollow shaft and discharged to the outside of the hollow shaft.

According to a fourth aspect of the present invention, there is provided an electric discharge machining apparatus for machining a workpiece by moving a tool electrode toward the workpiece while generating an electric discharge between the workpiece and the tool electrode. A fixed frame having walls opposed to each other at a predetermined interval, a core shaft fixed between the walls of the frame, and a hydrostatic bearing having a recovery flow passage through which the working medium is recovered. The hollow shaft is fitted to the core shaft, and a propulsive force is applied to the hollow shaft against the wall portion of the frame, and the hollow shaft is moved by using the core shaft as a guide. And an electric discharge machining device using the linear motor, comprising: a linear motor.

According to a fifth aspect of the present invention, in the electric discharge machine using the linear motor according to the fourth aspect, the frame and the core shaft are fixed so that the core shaft and the hollow shaft are substantially vertical. The bearing supplies pressure oil to a first communication hole communicating from an end of the core shaft toward a side surface to form an oil film between an outer surface of the core shaft and an inner surface of the hollow shaft. The oil overflowing from the pressure receiving plate is collected at a lower end portion through a second communication hole formed inside the hollow shaft and discharged to the outside of the hollow shaft.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on preferred embodiments shown in the drawings.

FIG. 1 is a side view showing the configuration of an embodiment of a drive device and an electric discharge machine using a linear motor according to the present invention. In FIG. 1, reference numeral 1 denotes a bed, and a column 2 is provided at a rear portion (right side of the drawing) of the bed 1 when viewed from the front corresponding to the left side of the drawing. Is provided with a saddle 3 as a first movable body that can be moved. Further, a table 4 is provided above the saddle 3 as a second moving body that is movable in the left-right direction (the direction perpendicular to the paper surface), that is, in the X-axis direction. A processing tank 5 filled with an insulating liquid is provided on the table 4, and a workpiece (not shown) is fixed in the processing tank 5.

On the upper part of the front surface of the column 2, a slider 6 as a third moving body movable in the vertical direction, that is, the W-axis direction,
, For example, via a ball screw, and these constitute a sub shaft moving device 8. On the front surface of the slider 6, an inverted "L" composed of a vertical portion 9a and a horizontal portion 9b is provided.
A letter-shaped mounting member 9 is fixed. The vertical portion 9a of the mounting member 9 is fixed to the slider 6 with the free end of the horizontal portion 9b protruding forward.

A horizontal shaft 9b of the mounting member 9 has a core shaft 10
Is substantially vertical and its upper end is firmly fixed. A hollow shaft 11 functioning as a quill is fitted on the core shaft 10 via a hydrostatic bearing (not shown in FIG. 1) so as to be slidable up and down. 12 is fixed, and the tool electrode 13 is gripped by the electrode mounting device 12. Further, a large number of permanent magnet pieces 14 are arranged on the outer walls opposite to each other of the hollow shaft 11, that is, on the left and right outer walls when viewed from the front, while being vertically inclined at a predetermined angle with respect to the horizontal plane. Magnet row 1
5 is attached.

On the other hand, to the vertical portion 9a of the mounting member 9, the back surface of a frame 21 having a square frame-shaped cross section is fixed. In this case, the mounting position of the core shaft 10 with respect to the horizontal portion 9b and the dimensions of the frame 21 are determined so that the hollow shaft 11 is located at the center of the frame 21. Then, window portions 22 are formed on both sides of the frame body 21, and a coil 23 wound around a plurality of iron cores is mounted on each of the window portions 22.

The above-mentioned magnet array 15 and the coil 23 are opposed to each other, whereby the frame 21 on which the coil 23 is mounted is mounted.
Are formed as a stator, and a pair of linear motors are formed using the hollow shaft 11 on which the magnet array 15 is mounted as a moving member, and these constitute a main shaft moving device 24 that can move in the vertical direction, that is, the Z-axis direction. . The main shaft moving device 24 constitutes a drive device 30 of the electric discharge machine together with the electrode mounting device 12 and the air cylinder (not shown in FIG. 1) for balancing the load with the hollow shaft 11. The driving device 30 is not limited to the electric discharge machine, but can be applied to the driving devices of most devices that move tools and products up and down.

FIG. 2 is a front view showing a detailed configuration of the driving device 30, and FIG. 3 is a side view thereof. In the figure, components denoted by the same reference numerals as those in FIG. 1 indicate the same components. In each of these drawings, an attachment member 9 attached to a slider 6 has an end portion of a horizontal portion 9b firmly fixed to an upper end surface of a vertical portion 9a by a bolt or the like, and an upper end portion of a core shaft 10 is connected to the other end of the horizontal portion 9b. It is detachably fixed to the section. As will be described in detail with reference to FIG.
a, a front plate 21b, side plates 21c and 21d are assembled into a square using a number of bolts, and a longitudinally long window 22 for mounting a coil 23 is mounted on the side plates 21c and 21d. Further, a counterbore portion 25 is formed in which both side portions of the window portion 22 are counterbored vertically long from the outside thereof. And the coil 23
Is fitted on the spot facing portion 25 and is fixed to the spot facing portion 25 by a plurality of bolts.

On the other hand, in order to set the mechanical origin in the vertical direction of the hollow shaft 11 driven vertically as a moving member with the core shaft 10 as a guide, the front end of the hollow shaft 11 has A hook-shaped cam dog 26a is attached, and a cam dog 26b whose tip is bent upward in a hook-like manner is attached to a lower front portion of the hollow shaft 11 via an attachment plate 11e. And these cam dogs 26
Limit switches 27a and 27b are provided on the front surface of the front plate 21b, which corresponds to the movement paths of the actuators a and 26b. As described above, the tip of the cam dog 26a is connected to the limit switch 27.
a, and similarly, the tip of the cam dog 26b operates the limit switch 27b. When the hollow shaft 11 moves to the upper limit or the lower limit, the mechanical origin is detected by the operation of the limit switch 27a or 27b. This is set in the control device. The frame 21
A mechanical stopper (not shown) for limiting the movement stroke of the hollow shaft 11 is provided between the shaft and the hollow shaft 11.

A pair of air cylinders 28 are provided between the hollow shaft 11 and the rear plate 21a and the front plate 21b constituting the frame 21 to balance the load with the hollow shaft 11 and the tool electrode 13, respectively. I have.

FIG. 4 is a longitudinal sectional view of the frame 21 for explaining the internal structure of the driving device 30 including the state of attachment of the air cylinder 28, and is the same as FIG. 1 to FIG. Those denoted by reference numerals indicate the same elements. At the lower end of the hollow shaft 11, a flat mounting plate 11e is horizontally mounted integrally. On the other hand, an "L" -shaped bracket 31 is attached to the lower end on the inner side of the back plate 21a constituting the frame 21, and an air cylinder 28 is mounted on the bracket 31 with its axis being vertical. In this case, the lower end of the outer cylinder of the air cylinder 28 with the piston rod 28a protruding downward is fastened to the bracket 31 by a nut or the like. The distal end of the piston rod 28a protruding downward is connected to the rear end of the mounting plate 11e by a shaft joint 32 such as a universal joint. A similar air cylinder 28 (not shown) is fastened to the inside of the front plate 21b constituting the frame 21, that is, a symmetrical position when viewed from the hollow shaft 11, with a similar configuration, and the piston rod is attached to the mounting plate 11e. To the front end.

A position detecting device comprising a linear scale 33 and a sensor 34 is provided inside the frame 21 which is located on the left side of the center of the driving device 30 as viewed from the front, as shown in FIGS. ing. The position detection signal of the sensor 34 is fed back to a linear motor driving device (not shown), and is used for controlling the current of the coil constituting the coil 23 to control the position of the hollow shaft 11.

FIG. 5 is a longitudinal sectional view showing the detailed structure of the hydrostatic bearing of the driving device 30 described above, and FIG.
It is a cross-sectional view in the direction of arrow A. In each of these figures, the hollow shaft 11 is a vertically long plate body 11a, 11b, 11c, 11d.
Are joined together with bolts, for example, with bolts to form a tube having a square cross section. The hollow shaft 11 is arranged coaxially with the frame 21, and a magnet array 15 is mounted on each outer surface of the plates 11 c and 11 d constituting the hollow shaft 11.

Further, the coils 2 are passed through the windows 22 formed on the side plates 21c and 21d constituting the frame 21, respectively.
3 are inserted inward, and the surface of the magnet row 15 and the coil 23
The substrate 23a is fixed to the counterbore portions 25 on both sides of the window portion 22 so as to maintain a predetermined gap, for example, a gap of about 0.6 mm from the surface of the window 22. The position detection device including the linear scale 33 and the sensor 34 described above is provided inside the frame 21 that is located on the left side of the center of the driving device 30 when viewed from the front.

Further, the plate 11 constituting the hollow shaft 11
a, 11b, 11c, and 11d are respectively provided with pressure receiving plates 16a and 1a that are in sliding contact with the outer surface of the core shaft 10 that faces each other.
6b, 16c and 16d are attached. In this case, the pressure receiving plates 16a, 16b, 16c, and 16d are made as wide as possible to increase the pressure receiving area, but gaps are formed at the four corners so that hydraulic oil is collected downward. Also,
Each of the pressure receiving plates 16a, 16b, 16c, and 16d has a gap of about 0.015 mm with respect to the core shaft 10 so that an oil film can be formed between the pressure receiving plates 16a, 16b, 16c, and 16d. On the other hand, the core shaft 10 is provided with an axial hole 10a at the center thereof, and a plurality of communication holes 17 for supplying oil to an outer region thereof. Of these, the communication hole 17 is formed vertically from the upper end surface of the core shaft 10 or vertically from the side surface of the upper end portion. It communicates with a small hole 18 as a nozzle formed in the lateral direction so as to pass through the side surface of the nozzle 10. The open end of the small hole 18 is provided with a counterbore 18a which is counterbored to temporarily store oil therein and form an even oil film around the periphery. And small hole 1
8 are evenly arranged on the four outer surfaces of the core shaft 10, and
It is arranged at equal intervals on each outer surface. In FIG. 5, the hollow shaft 11 is in the ascending position, but even when the hollow shaft 11 is lowered, the small holes 18 remain in the pressure receiving plates 16a, 16b, 16c, 16c.
It is at a position that does not protrude from d. At the entrance of the communication hole 17 formed at the upper end of the core shaft 10, a connection fitting 19 for connecting an oil conduit is mounted.

The lower end of the hollow shaft 11 is closed by a bottom plate 20, and a collection hole 20a and a drain hole 20b are formed on the upper surface of the bottom plate 20.
Accordingly, the outer surface of the core shaft 10 and the pressure receiving plates 16a, 16b, 1
All of the oil leaking from the gaps 6c and 16d travels through the spaces at the four corners inside the hollow shaft 11, falls into the collecting holes 20 of the bottom plate 20, and is discharged from the drain holes 20b. At this time, the oil discharged from the drain hole 20b is collected and supplied again from the connection fitting 19 to the small hole 18 by the pump, thereby forming a hydrostatic bearing having a circulation flow path.

FIG. 8 is a system diagram of a hydraulic control system for operating the hydrostatic bearing. As described above, the communication hole 17 and the small hole 18 are formed in the core shaft 10, and the collection hole 20 a and the drain hole 20 b are formed in the bottom plate 20 of the hollow shaft 11. The oil discharged from the drain hole 20b is stored in the oil storage tank 41. The oil in the oil storage tank 41 is sucked by a pump 42 and sent to another oil storage tank 44 through a filter 43 for removing dust having a particle diameter of 10 μ or more. Further, the oil fed into the oil storage tank 44 is sucked by a pump 45 and sent to a cooler 47 for controlling oil temperature through a filter 46 for removing dust having a particle diameter of 2 μm or more.
The flow control valves 51 to 5n and the check valves 61 to 51 are respectively provided in the pipes branched according to the number of the communication holes 17 formed at 0.
6n are connected, and the outlets of the check valves 61 to 6n are connected to connection fittings 19 formed at the upper end of the core shaft 10 by flexible pipes.

The level detectors 4 are provided at two locations, an upper limit and a lower limit, for confirming that the oil amount in the oil storage tank 41 is within an appropriate range.
8U and 48L are provided, and a level detector 49 is provided in the oil storage tank 44 to generate an alarm when the oil level in the oil storage tank 44 is insufficient.

With the above configuration, high-pressure oil is supplied from the small hole 18 to the gap between the core shaft 10 and the hollow shaft 11, and a hydrostatic bearing is formed between the core shaft 10 and the hollow shaft 11. The hollow shaft 11 can be moved with high precision in the vertical direction using the core shaft 10 as a guide.

In this way, the hollow shaft 11 is guided by the core shaft 10 by the hydrostatic bearing, so that the operation and effect peculiar to the hydrostatic bearing, that is, movement with straightness, low frictional motion, and fine motion without stick slip are achieved. can get. These operating characteristics are particularly effective in a tool such as an electric discharge machine in which a tool electrode and a workpiece face each other via a minute gap and the gap is servoed every moment. In addition, bearings are supported without contact during the life of the bearing,
There is no need to worry about wear and the life is greatly extended.

At this time, since the weight of the hollow shaft 11 and the tool electrode 13 attached thereto is balanced by the air cylinder 28, the hollow shaft 11 can be moved up and down by controlling the coil current of the coil 23. It can be driven and controlled in a vertical direction with high speed and high accuracy only by the necessary minimum thrust. Further, according to this embodiment, there is obtained an advantage that the configuration is significantly simplified as compared with the conventional apparatus shown in FIG.

In the above embodiment, oil is used as the working medium of the hydrostatic bearing. However, the oil travels down the four corner spaces inside the hollow shaft 11 and is collected by the collection hole 20a. Even if a means for sealing the upper end surface of the hollow shaft 11 is not provided, a closed flow path is formed. Of course, when a large bearing stiffness is not required, air can be used as the working fluid.

The upper end of the hollow shaft 11 is closed with a small gap between the hollow shaft 11 and the core shaft 10 so that almost no load is applied to the vertical movement of the hollow shaft 11. Foreign matter such as dust can be prevented from entering.

In the above embodiment, the drive device 30 in which the magnet array 15 is mounted on the hollow shaft 11 and the coil 23 is mounted on the frame 21 has been described.
In this configuration, the hollow shaft 11 can be driven and controlled in a vertical direction with high speed and high accuracy even when the coil 23 is provided and the magnet array 15 is mounted on the frame 21.

The drive device 30 described above is not limited in application to an electric discharge machine, but is applied to a drive device for a machining spindle of a general machine tool or a three-dimensional measuring machine in which a measurement probe is controlled to move in an axis. You can also.

Further, in the above-described embodiment, the electric discharge machining apparatus provided with the auxiliary shaft moving device 8 has been described. However, the electric discharge machining device having the structure in which the auxiliary shaft moving device 8 is removed and the mounting member 9 is directly attached to the column 2 is provided. The present invention can also be applied to the present invention.

[0042]

As is apparent from the above description, according to the present invention, the moving shaft such as the hollow shaft is driven by the linear motor, and the moving shaft is supported by the hydrostatic bearing. Unique high-response servo control is realized without deterioration due to bearing friction or stick slip, and the life of the bearing is greatly extended. In addition, since the working oil is collected in the moving shaft by the configuration in which the static pressure bearing portion merely provides a simple recovery channel, the oil does not leak from the static pressure bearing portion. Further, since the hydrostatic bearing is arranged so as to be built in the hollow shaft, an effect that the entire drive device can be compactly obtained is obtained.

[Brief description of the drawings]

FIG. 1 is a side view showing the configuration of an embodiment of a drive device and an electric discharge machine using a linear motor according to the present invention.

FIG. 2 is a front view showing a detailed configuration of a driving device constituting the embodiment shown in FIG. 1;

FIG. 3 is a side view showing a detailed configuration of a driving device constituting the embodiment shown in FIG. 1;

FIG. 4 is a vertical cross-sectional view of a frame body for explaining an internal configuration of the driving device shown in FIGS. 2 and 3;

FIG. 5 is a longitudinal sectional view showing a detailed configuration of the driving device shown in FIGS. 2 and 3;

FIG. 6 is a cross-sectional view of the drive device shown in FIG.

7 is a partial cross-sectional view illustrating a detailed configuration of a core shaft included in the driving device illustrated in FIG.

FIG. 8 is a system diagram of a hydraulic control system that functions a hydrostatic bearing constituting the drive device shown in FIG. 5;

FIG. 9 is a side view showing a half cross section of a voice coil type linear motor as a conventional driving device.

[Explanation of symbols]

 Reference Signs List 1 bed 2 column 5 processing tank 9 mounting member 10 core shaft 11 hollow shaft 13 tool electrode 15 magnet array 16a to 16d pressure receiving plate 17 communication hole 18 small hole 20 bottom plate 21 frame body 22 window 23 coil 28 air cylinder 30 driving device 41 , 44 Oil storage tank 42,45 Pump 51-5n Flow control valve

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference)

Claims (5)

[Claims] 1. A fixed frame having walls facing each other at a predetermined interval, a core shaft fixed between the walls of the frame, and a recovery flow passage through which a working medium is recovered. A hollow shaft fitted to the core shaft via a hydrostatic bearing having the inside thereof, and a propulsion force acting on the hollow shaft against a wall portion of the frame body; A linear motor that moves the hollow shaft, and a driving device using the linear motor, wherein the hollow shaft is a driven body. 2. A fixed rectangular frame having walls substantially parallel to each other at predetermined intervals, and a rectangular cross-section having an outer surface facing the wall of the frame. A core shaft fixed at a substantially central portion of the frame, and a square shaft fitted to the core shaft via a hydrostatic bearing having a recovery flow passage therein for recovering a working medium. A hollow shaft, including a pair of coils wound around a plurality of iron cores, and a pair of magnet rows in which a plurality of permanent magnets are arranged in a row,
One of the coil and the magnet row is symmetrically attached to the pair of opposing wall portions of the frame, and the other of the coil and the magnet row is symmetrically formed on the outer surface of the hollow shaft facing the coil. A driving device using a linear motor, comprising: a linear motor attached and using the hollow shaft as a movable member with the core shaft as a guide. 3. The first communication means wherein the frame body and the core shaft are fixed so that the core shaft and the hollow shaft are substantially vertical, and the hydrostatic bearing communicates from an end of the core shaft toward a side surface. A pressure oil is supplied to the hole to form an oil film between the outer surface of the core shaft and the inner surface of the hollow shaft, and the oil overflowing from the pressure receiving plate of the hollow shaft enters the inside of the hollow shaft. The driving device using a linear motor according to claim 2, wherein the driving device is collected at a lower end portion through the formed second communication hole and discharged to the outside of the hollow shaft. 4. An electric discharge machining apparatus for machining a workpiece by moving a tool electrode toward the workpiece while generating an electric discharge between the workpiece and the tool electrode. A fixed frame having a wall portion, a core shaft fixed between the wall portions of the frame body, and a static pressure bearing having a recovery flow passage through which a working medium is recovered; A hollow shaft fitted to a shaft and capable of attaching the tool electrode to the lower end thereof, a propulsive force is applied to the hollow shaft against a wall of the frame body, and the hollow shaft is guided using the core shaft as a guide. An electric discharge machine using a linear motor, comprising: a linear motor that moves. 5. The first communication means wherein the frame and the core shaft are fixed so that the core shaft and the hollow shaft are substantially vertical, and the hydrostatic bearing communicates from an end of the core shaft toward a side surface. A pressure oil is supplied to the hole to form an oil film between the outer surface of the core shaft and the inner surface of the hollow shaft, and the oil overflowing from the pressure receiving plate of the hollow shaft enters the inside of the hollow shaft. The electric discharge machine using a linear motor according to claim 4, wherein the linear motor is collected at a lower end portion through the formed second communication hole and discharged to the outside of the hollow shaft.