JP2011073072A - Fluid holding device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fluid holding device (a static pressure bearing and a static pressure guide) capable of restraining accuracy reduction in a moving body by a disturbance load varying at a high speed. <P>SOLUTION: This fluid holding device includes displacement sensors 9 and 10 for measuring relative displacement by disturbance force of a main spindle 3 and bearings 4 and 5, and land pressure oil supply-suction means 7 and 8 for supplying-sucking pressure oil of a land part of a static pressure pocket, and restrains the accuracy reduction in the fluid holding device by the disturbance force by supplying pressure oil to the land part or sucking the pressure oil of the land part so as to restrain the relative displacement of the bearings 4 and 5 and the main spindle 3 by the disturbance force. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to suppression of accuracy degradation due to a disturbance load of a fluid holding device such as a static pressure bearing or a static pressure guide.

  As a technology for suppressing a decrease in bearing accuracy due to a disturbance load applied to a hydrostatic bearing, a conventional technology for controlling a supply pressure to a fluid bearing according to a displacement due to a disturbance load on the main shaft and suppressing a decrease in accuracy (see, for example, Patent Document 1) In addition, there is a conventional technique (for example, see Patent Document 2) that controls the supply pressure to the fluid bearing according to the pocket pressure fluctuation due to the disturbance load on the main shaft and suppresses the decrease in accuracy.

In the case of the prior art described in Patent Document 1, specifically, in FIG. 4, the main shaft 3 is a hydrostatic bearing in which pressure oil held at a predetermined pressure by a pump 13 and a pressure control valve 14 is supplied via a throttle. 16 and 17 are rotatably supported by the main shaft rotating motor 15, and the relative displacement between the static pressure bearings 16 and 17 and the main shaft 3 is measured by the displacement sensors 9 and 10.
In the static pressure bearing configured as described above, the principle of suppressing the decrease in accuracy is as follows.
When the machining force during steady machining is F, the displacement of the main shaft 3 is E, the bearing rigidity is K, the disturbance force is ΔF, and the displacement increase of the main shaft 3 to which the disturbance force is applied is ΔE, E = F / K, E + ΔE = (F + ΔF) / K is established. Here, if the main shaft rigidity is increased by ΔK and E = (F + ΔF) / (K + ΔK) is established, the displacement amount of the main shaft 3 does not change even when the disturbance force ΔF is applied, so that the main shaft rotation accuracy (bearing accuracy) decreases. do not do. Since the rigidity of the hydrostatic bearing is proportional to the supply pressure, assuming that the initial supply pressure is P and the increased supply pressure is ΔP, (K + ΔK) = K (P + ΔP) / P and ΔK = K · ΔP / P is established. From E = (F + ΔF) / (K + ΔK), ΔK = ΔF / E, and ΔF = K · ΔE, so ΔK = K · ΔE / E holds. Therefore, K · ΔP / P = K · ΔE / E, and the increased supply pressure ΔP becomes ΔP = P · ΔE / E.
From the above, in order to eliminate the increase in displacement of the main shaft 3 due to the disturbance force ΔF, the supply pressure may be increased by ΔP = P · ΔE / E.
A specific action that suppresses a decrease in bearing accuracy due to a disturbance load will be described below.
Based on the displacement increase amount ΔE measured by the displacement sensors 9, 10, the control device 18 increases the increased supply pressure ΔP that becomes bearing rigidity necessary to push back the main shaft to the standard displacement position at the time of steady machining from ΔP = P · ΔE / E. Calculate and command the pressure control valve 14. When the pressure control valve 14 supplies pressure oil whose pressure has been increased by ΔP to the bearings 16 and 17, the rigidity of the bearings 16 and 17 is increased, and the displacement of the main shaft 3 due to the disturbance force is reduced. By continuously performing the above control, a decrease in bearing accuracy due to disturbance force is suppressed.

  In the case of the prior art described in Patent Document 2, at least one of a plurality of throttles of the oil supply pipe line to the static pressure pocket is movably supported, and the terminal end of the supply pipe line is changed according to the fluctuation of the pressure in the pocket due to the disturbance load. Controls the pressure supplied to the throttle to suppress a decrease in bearing accuracy due to disturbance force.

JP 2003-89026 A JP 2002-286037 A

When a disturbance force is applied to the fluid holding device, a displacement determined by the fluid holding device rigidity and the magnitude of the disturbance force is generated, and the fluid holding accuracy is lowered.For example, when used for a spindle device of a machine tool, A decrease in fluid holding accuracy directly leads to a decrease in machining accuracy of the workpiece. In the prior art described in Patent Document 1 and Patent Document 2 described above, the pressure control of the hydrostatic bearing for suppressing the decrease in fluid holding accuracy is performed by controlling the supply pressure to the throttle. There was a limit to the pressure response speed in the pocket, and when the disturbance force fluctuation was high, the response was poor and the deterioration in accuracy could not be suppressed sufficiently.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a fluid holding device that can suppress a decrease in accuracy due to a disturbance force even with a high-speed disturbance force fluctuation.

  In order to solve the above problems, the invention according to claim 1 is characterized in that a static pressure pocket comprising a recess and a land provided around the recess, and a pressure oil supply means for supplying pressure oil to the recess. A land pressure oil supply / suction means capable of supplying pressure oil to the land portion and sucking pressure oil from the land portion; a moving body supported by the pressure oil in the static pressure pocket; and the moving body; Displacement measuring means for measuring the relative displacement of the static pressure pocket, and control for calculating an oil supply / oil suction amount of the land pressure oil supply / suction means according to a displacement amount measured by the displacement measuring means and outputting an operation command And a drive means for driving the land pressure oil supply suction means based on an operation command of the control means, and when the moving body approaches the static pressure pocket, the pressure oil is supplied to the approaching land portion, The moving body is the If away from the pressure pocket is to suck the pressure oil from the land portion away.

  A feature of the invention according to claim 2 is the main shaft on which the movable body rotates in the invention according to claim 1, wherein the static pressure pocket, the land pressure oil supply / suction means, the main shaft, and the static pressure. The displacement measuring means for measuring the relative displacement of the pocket is arranged in a cylindrical shape on the outer periphery of the main shaft.

  The invention according to claim 3 is characterized in that, in the invention according to claim 2, a plurality of the land pressure oil supply / suction means and a plurality of displacement measuring means are provided, and the control means includes a plurality of the displacement measuring means. Calculating an oil supply increase / decrease amount of the plurality of land pressure oil supply / suction means from a displacement amount and outputting an operation command;

  A feature of the invention according to claim 4 is that, in the invention according to any one of claims 1 to 3, a piezoelectric element is provided for driving the land pressure oil supply / suction means.

  According to the invention of claim 1, when a disturbance force acts on the moving body, the relative displacement between the moving body and the static pressure pocket is measured by the displacement measuring means, and the measured displacement amount is sent to the control device. The control means calculates the operating amount of the land pressure oil supply / suction means from the displacement amount, and outputs an operation command to the land pressure oil supply / suction means disposed on the land provided on the outer peripheral portion of the fluid pocket. The land pressure oil supply means supplies pressure oil directly to the land portion or sucks pressure oil from the land portion based on the operation command. When pressure oil is supplied to the land, the oil flow in the static pressure pocket is inhibited and the amount of oil flowing out of the pocket is reduced. Then, the moving body is displaced in the direction away from the pocket. On the other hand, when the pressure oil is sucked in from the land, the outflow of oil in the static pressure pocket is promoted, and the outflow amount from the pocket increases. Decreases and the moving body is displaced in a direction approaching the pocket. By causing the above action to act in a direction that cancels the displacement of the moving body due to the disturbance force, the disturbance displacement of the moving body is suppressed. High-speed disturbance force fluctuation compared to the conventional external supply pressure control method that restricts the flow rate by the restrictor because the oil outflow is controlled directly in the static pressure pocket to suppress disturbance displacement and the response is fast. In addition, it is possible to suppress a reduction in accuracy of the moving body with high accuracy.

  According to the second aspect of the present invention, the moving body is a rotating shaft, and a static pressure pocket is arranged in a cylindrical shape on the outer periphery of the rotating shaft, thereby suppressing deterioration in accuracy of the rotating bearing that is often used at high speed rotation. can do.

  According to the third aspect of the present invention, the control means can calculate using the plurality of displacement amounts measured by the plurality of displacement measurement means, so that the displacement direction and the displacement amount can be determined, and the plurality of land pressure oil supply / suction means Since a predetermined amount can be corrected in any direction by a combination of the increase and decrease amounts of the supplied oil amount, it is possible to suppress a decrease in bearing accuracy against disturbance force fluctuations from any direction on the circumference.

According to the fourth aspect of the invention, since the land pressure oil supply / suction means is driven by the piezoelectric element, high speed operation is possible and the land pressure oil supply / suction means can be configured compactly.

It is the schematic which shows the whole structure of the static pressure bearing apparatus of this embodiment. It is a cross-sectional detail drawing which shows the structure of the static pressure pocket part of this embodiment. FIG. 3 is a detailed view taken from the direction of the arrow A in FIG. FIG. 3 is a cross-sectional view taken along the line BB in FIG. 2 showing the configuration of the land pressure oil supply / suction means of the present embodiment. It is the schematic which shows the whole structure of a prior art.

Hereinafter, an example in which a hydrostatic bearing according to an embodiment of the present invention is used as a main shaft of a machine tool will be described with reference to FIGS.
As shown in FIG. 1, in the hydrostatic bearing device 1 according to this embodiment, a main shaft 3 (corresponding to a moving body of the present invention) that holds a tool 2 is supplied with pressure oil of a predetermined pressure by a pump 13 and a pressure control valve 14. It is rotatably held by the hydrostatic bearings 4 and 5 that are supplied and held by the bearing housing 6, and is driven by the rotary motor 15. The hydrostatic bearing device 1 further includes displacement sensors 9 and 10 that measure relative displacement between the main shaft 3 and the hydrostatic bearings 4 and 5, and a control device 11 that outputs a displacement command based on the displacement amount of the displacement sensors 9 and 10. And a piezoelectric element driver 12 for driving the land pressure oil supply / suction means 7 and 8 based on a displacement command of the control device 11.

Since the static pressure bearing 4 has the same structure as that of the static pressure bearing 5, an example of the static pressure bearing 4 will be described below in detail with reference to FIGS.
The static pressure bearing 4 includes static pressure pockets 20a to 20d including a plurality of lands 42a to 42d and recesses 41a to 41d. The lands 42a to 42d are convex portions provided on the entire outer periphery of the pockets 20a to 20d, and the recesses 41a to 41d are concave portions surrounded by the lands 42a to 42d. Pressure oil supply lines 19a to 19d for supplying pressure oil from the pressure control valve 14 are connected to the recesses 41a to 41d. In the vicinity of the pockets 20a to 20d of the pressure oil supply lines 19a to 19d, A diaphragm is provided. Land pressure oil supply / suction means 7a and land pressure oil supply / suction means 7a 'are arranged on the back surface of the land parallel to the axial direction of the land 42a of the pocket 20a so as to be opposed to the pocket 20a in the circumferential direction. The land pressure oil supply / suction means 7b and the land pressure oil supply / suction means 7b ′ are provided to be opposed to the pocket 20b in the circumferential direction. An oil discharge groove 21 is formed on the outer periphery of the pockets 20a to 20d. The oil discharge groove 21 is disposed at a relative angle of approximately 90 degrees for measuring the relative displacement between the main shaft 3 and the hydrostatic bearing 4. Displacement sensors 9a and 9b are attached. Here, the relative angle of the displacement sensor arrangement is not limited to 90 degrees, and may be any angle other than 180 degrees.

  The land pressure oil supply / suction means 7a has the same structure as the land pressure oil supply / suction means 7a ', 7b, 7b'. An example of the land pressure oil supply / suction means 7b will be described below in detail with reference to FIG. A piezoelectric element driving portion 72b is fixed to the mouth of a radial hole provided on the outer periphery of the hydrostatic bearing 4, and a piston 71b sealed with a seal 73b is slidably joined to the hydrostatic bearing 4 to the piezoelectric element driving portion 72b. The hydraulic pressure chamber 74b is formed between the static pressure bearing 4 and the piston 71b, and the hydraulic pressure chamber 74b is provided with a plurality of supply holes 75b communicating with the land 42b.

  During normal use, the pressure oil maintained at a predetermined pressure by the pump 13 and the pressure control valve 14 is supplied to the recesses 41a to 41d via the pressure oil supply pipes 19a to 19d provided with throttles, and the recesses 41a to 41d. The oil inside flows out from the gap between the lands 42 a to 42 d and the main shaft 3. The main shaft 3 is held at a predetermined position by a pocket internal pressure that balances the inflow oil amount from the pressure oil supply pipes 16a to 16d and the outflow oil amount from the gap between the lands 42a to 42d and the main shaft 3.

The following is a description of the bearing accuracy lowering suppressing action when a disturbance force F0 such as machining load fluctuation and external vibration transmission acts on the main shaft 3.
When a disturbance force is applied to the main shaft 3 in the pocket 20b direction, the main shaft 3 is displaced in the pocket 20b direction, the gap between the land 42b of the pocket 20b and the bearing 3 is reduced by the amount corresponding to the displacement, and the amount of oil outflow from the pocket 20b is reduced. Therefore, the pressure in the pocket 20b increases. On the other hand, in the pocket 20d at a position facing the pocket 20b, the gap between the land 42d and the bearing 3 increases corresponding to the displacement, and the pressure in the pocket 20d decreases. The sum of the increased holding force F1 due to the pressure increase of the pocket 20b and the reduced holding force F2 due to the pressure decrease of the pocket 20d is balanced in the land gap where the disturbance force F0 is equal. Here, when the pressure oil is supplied to the land 42b by the pressure oil supply / suction means 7b, 7b ', the amount of oil flowing out of the pocket 20b from the land portion supplying the pressure oil decreases. In order to make the total amount of oil spilled from the pocket 20b constant while keeping the pressure in the pocket constant, it is necessary to increase the gap between the land 42b and the main shaft 3. That is, the main shaft 3 is pushed back and the main shaft 3 is displaced by disturbance force. Decrease

  On the contrary, when a disturbance force in the pocket 20d direction acts on the main shaft 3, the main shaft 3 is displaced in the pocket 20d direction, and the gap between the land 42b of the pocket 20b and the main shaft 3 increases by the amount corresponding to the displacement. At this time, when the pressure oil is sucked from the land 42b by the land pressure oil supply / suction means 7b, 7b ', the amount of oil flowing out of the pocket 20b from the land that sucks the pressure oil increases. In order to keep the total amount of oil spilled from the pocket 20b constant while keeping the pressure in the pocket constant, the gap between the land 41b and the main shaft 3 needs to be reduced. That is, the main shaft 3 is pulled back toward the pocket 20b, and the disturbance force Reduce the displacement of the spindle 3 due to

Supply and suction of land pressure oil are performed as follows.
In the land pressure oil supply / suction means 7b, 7b 'provided on the back surface of the land portion 42b of the hydrostatic bearing 4, the land pressure oil is supplied to the pistons 71b, 71b' by the piezoelectric element driver 12 based on the command of the piezoelectric element driver 12. Is driven forward by the portions 72b and 72b ′, and the oil in the hydraulic chambers 74b and 74b ′ is supplied to the land portion through the supply holes 75b and 75b ′, and the land pressure oil suction is performed based on the command of the piezoelectric element driver 12. 71b and 71b ′ are driven backward by the piezoelectric element driving portions 72b and 72b ′ at the rear, and the oil in the land portion is sucked into the hydraulic chambers 74b and 74b ′ through the supply holes 75b and 75b ′.

Hereinafter, a description will be given of a spindle accuracy lowering suppressing action by a specific disturbance force.
The displacement due to the disturbance force of the main shaft 3 is measured by the displacement sensors 9a and 9b, the displacement amounts are transferred to the control device 11, and the displacement amounts and the displacement directions of the main shaft 3 are calculated by combining the respective displacement amounts. Next, the main shaft displacement is decomposed and converted into a radial displacement at the circumferential center position of the pockets 20a and 20b, and the disturbance-induced displacements of the pocket 20a and the main shaft 3, and the pocket 20b and the main shaft 3 are calculated. Next, the land pressure oil supply / suction amount that minimizes the displacement due to the disturbance force between the pocket 20a and the main shaft 3 is calculated, and the piston 71a, 71a ′ drive amount command value of the land pressure oil supply / suction means 7a, 7a ′ is calculated. decide. Similarly, the pistons 71b and 71b ′ drive amount command values are determined for the pocket 20b.

Based on the driving amount command value of the pistons 71a and 71a ′ calculated by the control device 11, the piezoelectric element driving portions 72a and 72a ′ are driven via the piezoelectric element driver 12, and the land portion pressure oil supply / suction amount of the pocket 20a is set. Increase / decrease and suppress the disturbance-induced displacement of the pocket 20a and the main shaft 3. Similarly, in the pocket 20b, the displacement due to the disturbance force between the pocket 20b and the main shaft 3 is suppressed.
As a result, the displacement caused by the disturbance force of the main shaft 3 with respect to the static pressure bearing 4 can be suppressed, and the same control is performed on the static pressure bearing 5 to suppress the displacement caused by the disturbance force. By minimizing the main shaft displacement caused by the disturbance force in the hydrostatic bearings 4 and 5, the accuracy of the bearing is reduced due to the disturbance force in the translation of the two shafts excluding the axial direction of the main shaft 3 and the pitching and yawing of the main shaft 3. Can be suppressed.

  According to the above structure, the land portion pressure oil supply / suction amount of the pockets 20a, 20b is directly increased and decreased by the pistons 71a, 71a ′, 71b, 71b ′ in the vicinity of the lands, thereby suppressing disturbance displacement of the main shaft 3. There is no response delay due to flow restriction by restriction as in the conventional external supply pressure control system. Therefore, it is possible to suppress spindle displacement with high accuracy following high-speed disturbance force fluctuations compared to the conventional technology, and it is possible to suppress deterioration in bearing accuracy even when high-frequency vibrations or high-speed fluctuations in machining force occur, and high accuracy and high speed. Processing can be realized.

The displacement due to the disturbance force of the main shaft 3 is measured by the two displacement sensors 9a and 9b, thereby measuring the displacement amount and the direction of the main shaft 3, and the circumferences of the pockets 20a and 20b provided with the land pressure oil supply / suction means. Since the displacement suppression control of the pockets 20a and 20b is performed in terms of the radial displacement at the center position in the direction, it is possible to suppress a decrease in bearing accuracy against disturbance force fluctuations from any direction on the circumference.
Since the land pressure oil supply / suction means 7a, 7a ′, 7b, 7b ′ are driven by a small piezoelectric element that can operate at high speed, the land pressure oil supply / suction means can be reduced in size and operated at high speed.

<Deformation of this embodiment>
Next, a modified aspect of the present embodiment will be described. The main shaft 3 of the above-described embodiment may be a translational moving body and a static pressure guide in which static pressure pockets are arranged in a planar shape.
A high-pass filter may be added to the displacement sensor output of the above embodiment to suppress only the high-frequency component of the disturbance force.
Further, the piezoelectric element driving units 72a, 72a ′, 72b, 72b ′ may be replaced with other driving means such as an electromagnetic solenoid or a motor.
When the disturbance force-induced displacement suppression direction can be substantially limited, the displacement sensors 9 and 10 may be configured to include only one set capable of detecting the displacement in that direction.
When the disturbance force-induced displacement suppression direction can be substantially limited, the land pressure oil supply / suction means 7 and 8 may be configured to include only one set in the static pressure pocket located in that direction.

1: Static pressure bearing device 3: Main shaft 7, 8: Land pressure oil supply / suction means 9, 10: Displacement sensor 11: Control device 12: Piezoelectric element driver 13: Pump 14: Pressure control valve 20a-20d: Static pressure pocket 72a 72a ', 72b, 72b': Piezoelectric element drive units 41a-41d: Recesses 42a-42d: Lands

Claims (4)

  A static pressure pocket comprising a recess and a land provided around the recess; pressure oil supply means for supplying pressure oil to the recess; supply of pressure oil to the land portion; and pressure oil from the land portion Land pressure oil supply / suction means capable of suctioning, a moving body supported by the pressure oil in the static pressure pocket, a displacement measuring means for measuring relative displacement between the moving body and the static pressure pocket, and the displacement measurement Control means for calculating the oil supply / oil suction amount of the land pressure oil supply / suction means according to the displacement amount measured by the means and outputting an operation command; and the land pressure oil supply / suction means based on the operation command of the control means. Driving means for supplying the pressure oil to the land portion approached when the moving body approaches the static pressure pocket, and pressure oil from the land portion leaving when the moving body leaves the static pressure pocket. Suck Fluid holding device which is characterized in that.   The main shaft on which the movable body rotates, the static pressure pocket, the land pressure oil supply / suction means, and the displacement measuring means for measuring the relative displacement between the main shaft and the static pressure pocket are arranged on the outer periphery of the main shaft. The fluid holding device according to claim 1, wherein the fluid holding device is arranged in a cylindrical shape.   A plurality of the land pressure oil supply / suction means and a plurality of the displacement measurement means are provided, and the control means calculates an oil supply increase / decrease amount of the plurality of land pressure oil supply / suction means from a displacement amount of the plurality of displacement measurement means. 3. The fluid holding device according to claim 2, wherein the fluid holding device calculates and outputs an operation command.   The fluid holding device according to any one of claims 1 to 3, further comprising a piezoelectric element for driving the land pressure oil supply / suction means.

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