JPH07164280A - Straightness correcting device - Google Patents

Abstract

PURPOSE:To provide a straightness correcting device which can be easily automatized, conform to a large load and precisely correct the straightness. CONSTITUTION:A work 25 to be machined is rotated by a workpiece spindle 20, pressed to a cylindrical grinding wheel 10 reciprocating (arrow A) while being rotated by the movement (arrow B) of a cutting table 21, and ground. At this time of grinding, a straightness correction value I(X) corresponding to the position (X) measured by a table position measuring instrument 17 is supplied from a memory device 53 to an adder 57, wherein the adding processing with a standard signal S is carried out. The control part 34 of a magnetic bearing part 33 feedback-controls the exciting currents of electromagnets 35, 36 with the signal processed by the adder 57 as a reference. A rotating shaft 19 is moved by the straightness error portion by this control, whereby the straightness in the reciprocation of the cylindrical grinding wheel 10 is corrected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a straightness correcting device, and more particularly, to a straightness correcting device for correcting the straightness of an ultra-precision table using static pressure guide of oil, air, or the like.

[0002]

2. Description of the Related Art In a machine tool, for example, a reciprocating table on which a tool spindle or the like is mounted is linearly reciprocated by using static pressure guides, and a grindstone is reciprocally moved to cut into a workpiece. By doing so, the surface of the workpiece is ground.

In such machining, the relative positional relationship between the tool (grinding stone) being machined and the workpiece directly determines the machining accuracy. Therefore, in ultra-precision machining that requires machining accuracy that exceeds the motion accuracy of the reciprocating table,
It is necessary to improve (correct) the straightness by minimizing the vertical displacement (straightness error) in the reciprocating motion of the reciprocating table. Conventionally, the straightness is corrected by the following method and device.

That is, in the first example, since the straightness error is related to the shape error such as the minute distortion and the unevenness of the guide surface which guides the reciprocating table, the shape error of the guide surface is measured by the laser measuring instrument or the like. Is measured, and there is a method of improving the straightness by correcting the guide surface with a lap or the like based on the measured data.

As a second example, there is a device for correcting the straightness by moving the reciprocating table side in the vertical direction of the reciprocating movement by the straightness error. In this device, a sub-table supported by springs is installed on the reciprocal table so that it can be translated in the horizontal direction.
The tool rest, spindle, etc. are fixed on this sub-table. Further, on the sub-table, a sensor that measures a straightness error during reciprocating movement is fixed on the basis of a reference device installed on the fixed side. Then, an actuator such as a piezo element is used to move the sub-table by the amount of the measured straightness error, thereby correcting the straightness.

As a third example, there is a device for correcting the straightness by directly moving the diamond bite or the like itself by a straightness error by a piezo element when cutting is performed by the diamond bite or the like. In this device, a reciprocating table that reciprocates has a diamond bite supported by a leaf spring or parallel spring so that it can move in the vertical direction of reciprocating motion. Correct the straightness by moving the bite etc.

Further, as a fourth example, a slitting table which feeds perpendicularly to the reciprocating motion of the reciprocating table is moved in the feeding direction or the opposite direction by a straightness error by using a numerical controller. There is a method of correcting the straightness. That is, the numerical control device controls the driving force of the drive motor that moves the cutting table via a ball screw or the like based on the straightness error data of the reciprocating table, and the straightness error is moved by moving the cutting table by the straightness error. Degree correction.

[0008]

However, in the first example, it is difficult to automate because the correction of the guide surface requires skill and is laborious. Further, in the second example, since the sub-table is supported by the spring, the rigidity is low, and the response speed of the sub-table becomes slow due to the weight of the sub-table and the tool rest mounted on the upper surface thereof. Correction is not accurate.

In the third example, since the piezo element is used as a driving source, it is difficult to use it for a tool having a small driving force and a large load such as a tool spindle, and a cutting tool. Limited to the example. Further, in order to increase the driving force to move the grindstone spindle or the like, there is a problem that it becomes a large-scale device.

In the fourth example, since the cutting table is moved by controlling the driving force of the drive motor, there are many error factors such as the shape error of the ball screw, and the moving amount of the cutting table, that is, the correction value. Error occurs. Further, since the table is moved, the response is poor and the straightness correction cannot be performed accurately.

Therefore, an object of the present invention is to provide a straightness correction device which is easy to automate, can cope with a large load, and can correct straightness accurately.

[0012]

According to a first aspect of the present invention, a magnetic bearing is used as a bearing for holding a rotary shaft to which either one of a machining tool and a workpiece is fixed at a reference position and receiving a load in a cutting direction. Spindle, a first table on which the spindle is placed, a second table on which the other one of the machining tool and the workpiece is placed, and at least one of the first table and the second table Cutting means for moving the cutting tool to the workpiece by moving the cutting tool in a cutting direction, and moving means for reciprocating at least one of the first table and the second table in a direction perpendicular to the cutting direction. , The relative positional change amount in the cutting direction between the workpiece and the machining tool at each moving position when the table is reciprocated by the moving means is erroneous in the straightness of the table. Straightness error storing means for storing the reference position changing means for changing the reference position held by the magnetic bearing in the cutting direction by the straightness error amount stored in the straightness error storing means at each moving position of the table. The straightness correction device is equipped with and to achieve the above object.

According to a second aspect of the present invention, the straightness correction apparatus according to the first aspect is provided with straightness error measuring means for measuring a straightness error of the table during the reciprocating motion, and the straightness error storage is provided. The means achieves the above object by storing the straightness error measured by the straightness error measuring means.

According to a third aspect of the present invention, the straightness correcting device according to the first aspect is provided with cutting speed detecting means for detecting the cutting amount per unit time of the machining tool by the cutting means, and the reference position. The changing means starts the changing process of the reference position when the cutting speed detected by the cutting speed detecting means becomes smaller than the maximum value of the straightness error stored in the straightness error storage means. Achieve the purpose.

According to a fourth aspect of the present invention, the straightness correction device according to the first aspect is provided with a cutting amount detecting means for detecting a cutting amount of the working tool per one reciprocating motion of the table. The reference position changing means is
When the cutting amount per one round trip detected by the cutting amount detecting means becomes smaller than the maximum value of the straightness error stored in the straightness error storing means, by starting the changing process of the reference position, Achieve the purpose.

In the invention described in claim 5, claims 3 and 4 are provided.
In the straightness correction apparatus described above, the moving means achieves the object by slowing the reciprocating speed at a time point when the process of changing the reference position by the reference position changing device is started.

[0017]

In the straightness correcting device according to the first aspect of the present invention, the rotary shaft held at the reference position by the magnetic bearing rotates, and at least one of the first table and the second table is perpendicular to the cutting direction by the moving means. The workpiece is machined by reciprocating in the direction and moving in the cutting direction by the cutting means. The reference position changing means changes the reference position held by the magnetic bearing in the cutting direction by the straightness error amount stored in the straightness error storage means at each moving position during the reciprocating movement, thereby correcting the straightness. To be done.

In the straightness correcting device according to the second aspect, in the straightness correcting device according to the first aspect, the straightness error measuring means measures the straightness error when the table reciprocates, and stores the straightness error. The means stores the straightness error measured by the straightness error measuring means. Then, the reference position changing means corrects the straightness based on the straightness error stored in the straightness error storage means.

In the straightness correcting device according to the third aspect, in the straightness correcting device according to the first aspect, the cutting speed detecting means detects the cutting amount per unit time of the machining tool by the cutting means and changes the reference position. The means starts the straightness correction when the cutting speed detected by the cutting speed detecting means becomes smaller than the maximum value of the straightness error stored in the straightness error storage means.

In the straightness correcting device according to a fourth aspect of the present invention, in the straightness correcting device according to the first aspect, the cutting amount detecting means detects the cutting amount of the machining tool per one reciprocating motion of the reciprocating motion of the table to obtain a reference value. The position changing means starts the straightness correction when the cut amount per round trip detected by the cut amount detecting means becomes smaller than the maximum value of the straightness error stored in the straightness error storage means.

In the straightness correcting apparatus according to the fifth aspect, in the straightness correcting apparatus according to the third and fourth aspects, the moving means reciprocates the table when the straightness correction by the reference position changing means is started. Slow down.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a straightness correcting device of the present invention will be described in detail below with reference to FIGS. Figure 1
3 shows the overall configuration of the straightness correction device according to the first embodiment.

The straightness correction device comprises a reciprocating table 12 on which a tool spindle 11 for rotating a cylindrical grindstone 10 which is a working tool is mounted. The reciprocating table 12 is guided by a static pressure guide surface (not shown) and driven by a reciprocating motor 15 to reciprocate linearly as indicated by an arrow A in FIG. On the left side in the figure of the reciprocating table 12, the reciprocating table 1 is shown.
A table position measuring device 17 for measuring the position of the two in the reciprocating direction at predetermined time intervals is installed. The position of the reciprocating table 12 may be measured by an encoder attached to the reciprocating motor 15.

Further, the straightness correction device is used for the work 25
It has a cutting table 21 on which a workpiece spindle 20 for rotating the workpiece is mounted. The cutting table 21 is moved at a predetermined speed in a direction perpendicular to the reciprocating motion of the reciprocating table 12 (direction shown by an arrow B) by driving the cutting motor 23, and presses the work 25 against the cylindrical grindstone 10. It is designed to let you.

The work spindle 20 has a rotary shaft 19 to which a workpiece 25 is fixed at its tip, and the rotary shaft 1
9 has a radial bearing 27 that supports 9 in the radial direction. As the radial bearing 27, for example, a hydraulic or pneumatic static pressure bearing, a dynamic pressure bearing, or a magnetic bearing is used. The rotary shaft 19 is rotated at a high speed by driving a rotary motor 29 for the workpiece spindle. Although not shown, the tool spindle 11 is also provided with a motor for rotationally driving the tool spindle 11.

Further, the rotary shaft 19 is provided with a disk-shaped thrust bearing rotor portion 31, and before and after that,
A magnetic bearing portion 33 is arranged to hold this magnetically in a non-contact manner. The magnetic bearing portion 33 detects a positional displacement of the thrust bearing rotor portion 31 in the axial direction and a pair of electromagnets 35 and 36 before and after applying a magnetic force in the axial direction to the thrust bearing rotor portion 31. Displacement sensor 3
8 and 39 are provided.

Further, the straightness correction device is composed of the displacement sensor 3
A control unit 34 is provided for performing feedback control of the exciting currents of the electromagnets 35 and 36 based on the sensor outputs of 8 and 39, and holding the axial position of the thrust bearing rotor unit 31 at a predetermined position. The control unit 34 controls the thrust bearing rotor unit 3 from the sensor outputs of the displacement sensors 38 and 39.
Sensor signal adjuster 41 for obtaining a signal corresponding to position 1
And an adder 43 for subtracting the signal from the sensor signal adjuster 41 from a predetermined reference signal for instructing the holding position (reference position) of the thrust bearing rotor unit 31, and the signal from the adder 43 P that performs processing such as advancing the phase
The ID compensator 45, the phase inverter 47 which inverts the phase of the signal from the PID compensator 45 and outputs the result, and the signal is amplified to a predetermined exciting current based on the output signal from the phase inverter 47. It is composed of power amplifiers 50 and 51 for supplying to the electromagnets 35 and 36. This control unit 34
A thrust magnetic bearing is constituted by the magnetic bearing portion 33 and the magnetic bearing portion 33.

The straightness correction device is a table position measuring device 1.
Each position X1, X of the reciprocating table 12 measured by 7
2. ． ． A value to correct the straightness error in Xn, that is, straightness correction values I (X1), I (X2). ． ． I (Xn)
Is stored in a RAM (random access memory), a ROM (read only memory), or the like.

The straightness correction value I (X) is a straightness error value measured by a laser length measuring device or the like before the straightness correction device is operated, for example, when the device is shipped. The storage device 53 stores the measured value (position X) from the table position measuring device 17.
Is supplied, the straightness correction value I (X) at the position X is output. This output signal is converted into an analog signal by the D / A converter 55 and is then added to the adder 57. It is being supplied.

The adder 57 is supplied with a reference signal S for instructing a predetermined holding position (reference position) of the thrust bearing rotor portion 31, that is, a neutral point between the electromagnets 35 and 36. A signal obtained by subtracting the straightness correction value I from S is finally supplied to the adder 43 as a reference signal for instructing the holding position of the thrust bearing rotor portion 31.

Next, the operation of the embodiment thus constructed will be described. First, the work piece 25 and the cylindrical grindstone 1
In a state where 0 is not in contact with the electromagnet 35 by the control unit 34,
The thrust bearing rotor unit 31 is held at a predetermined position by feedback control of the exciting current of the motor 36, and the rotary shaft 19 is rotationally driven by the workpiece spindle rotary motor 29. At this time, the table position measuring device 17 has not started measuring the position of the reciprocating table 12. Therefore, the storage device 53 does not output the straightness correction value I (X), and the reference signal S is supplied to the adder 43.

Next, the cylindrical grindstone 10 is attached to the tool spindle 11
Is rotated by a motor (not shown) and the reciprocating table 12 is reciprocated by the reciprocating motor 15. Then, the cutting table 23 is moved in the direction of arrow B at a predetermined speed by the cutting motor 23,
The cylindrical grindstone 10 is cut into the rotating workpiece 25.

As a result, the surface of the work 25 is ground by the cylindrical grindstone 10. At this time, the table position measuring device 17 starts measuring the position of the reciprocating table 12 and stores the measured position X in the storage device. Send to 53. Then, the storage device 53 sequentially supplies the straightness correction value I (X) at the position X to the adder 57. As a result, the reference signal to the adder 43 is supplied to the adder 43 as a signal for instructing the holding position deviated by the straightness error occurring at the position X, and the control unit 34 outputs this changed reference signal. Based on the reference, the exciting currents of the electromagnets 35 and 36 are feedback-controlled.

Therefore, the electromagnets 35 and 36 move the rotating shaft 19 in the axial direction by an amount corresponding to the straightness error in accordance with each position X of the reciprocating table 12 (in this specification, this magnetic force is referred to as "correcting magnetic force"). (Referred to as “1” is generated), and the cylindrical grindstone 1 is reciprocally moved by the movement of the rotary shaft 19 by the correction magnetic force.
A change in position of 0 in the axial direction with respect to the workpiece 25 is offset. That is, the straightness is corrected.

In the first embodiment, the work piece spindle 20.
The thrust bearing is composed of a magnetic bearing, and the straightness is corrected by canceling the straightness error in the cutting direction at the neutral position (reference position) of the magnetic bearing. However, the bearing that receives a load in the cutting direction of the tool spindle 11 may be a magnetic bearing, and this magnetic bearing may be operated in the same manner as in the first embodiment to correct the straightness. For example, when the cylindrical grindstone 10 is used as a tool as in the first embodiment, the radial bearing of the tool spindle 11 is a magnetic bearing, and when the cup grindstone is a working tool, the thrust bearing of the tool spindle is a magnetic bearing. , Straightness correction operation is performed with this bearing.

FIG. 2 shows the entire structure of the straightness correction device according to the second embodiment of the present invention. The first
The same reference numerals are given to the same components as those of the embodiments, detailed description thereof will be appropriately omitted, and the same applies to the following embodiments. In the present embodiment, a straightness measuring device 61 for measuring the straightness error of the reciprocating table 12 is fixed to the side of the tool spindle 11 on the reciprocating table 12 with the reference device 60 installed on the fixed side as a reference. There is. As the reference device 60, for example, a reflection mirror or an optical straight is used, and a straightness measuring device 61 is used.
For this, for example, a non-contact sensor such as a laser length measuring device or a capacitance type displacement meter is used.

The straightness measuring device 61 converts the measured straightness error value into a straightness correction value as a digital signal and supplies it to the storage device 53. Storage device 53
Then, the straightness correction value from the straightness measuring device 61 is sequentially stored in a predetermined area as a straightness correction value I (X) corresponding to the position X measured by the table position measuring device 17. .

The other structure is similar to that of the first embodiment.
Next, the operation of the second embodiment configured as described above will be described. First, when the device is started, the reciprocating table 1
By reciprocating 2, the straightness measuring device 61 measures the straightness error at each position X measured by the table position measuring device 17. This measured value is stored in the storage device 53 as the straightness correction value I (X).

Then, the grinding of the work 25 is started,
Thereafter, each straightness correction value I stored in the storage device 53
Based on (X), straightness correction is performed as in the first embodiment. The measurement of the straightness error by the straightness measuring device 61 may be performed several times at every predetermined time during grinding, and in this case, the data in the storage device 53 is sequentially rewritten to correct the straightness.

The straightness correction value measured by the straightness measuring device 61 is supplied to the adder 57 as it is without being temporarily stored in the storage device 53, and the straightness error is measured and the straightness correction is performed in real time. May be. As described above, in this embodiment, since the straightness error can be appropriately measured, the straightness correction value I at each position X can be adjusted by using the device.
Even when (X) changes, it is possible to perform correction with the straightness correction value corresponding to the change. Therefore, accurate straightness correction can always be performed.

FIG. 3 shows a straightness correction device according to a third embodiment of the present invention. The straightness correction device according to the present embodiment includes a dimension measuring device 71 that measures the thickness of the workpiece 25. A cut amount calculator 73 that calculates the cut amount per unit time for the workpiece 25 from the measured value is connected to the dimension measuring device 71.
The value calculated by the cut amount calculator 73 is supplied to the comparator 75.

The comparator 75 is connected to a maximum correction value memory 77 for storing the maximum correction value among the straightness correction values I '(X') output from the storage device 53,
The maximum correction value from the maximum correction value memory 77 is compared with the cut amount from the cut amount calculator 73.

Further, in this embodiment, a switch 78 for opening / closing according to the comparison result of the comparator 75 is arranged between the D / A converter 55 and the adder 57. The switch 78 is normally open, and is closed when the result of comparison by the comparator 75 is that the maximum correction value (maximum straightness error) ≧ unit time cut amount (cut speed).

A table speed switching device 79 is connected to the comparator 75, and the comparison result is also supplied to the table speed switching device 79. Although not shown, the table speed changer 79 is connected to the reciprocating motor 15, and when the result of the comparison by the comparator 75 is that the maximum correction value ≧ the unit time cut amount, the reciprocating speed of the reciprocating table 12 is set. The driving force of the reciprocating motor 15 is switched so as to slow down.

In this embodiment also, the storage device 53
The straightness correction value I '(X') of is measured in advance, but this is the data measured for the position X'of a finer pitch than in the first embodiment, and the data amount is , Which is larger than that in the first embodiment.

The other structure is similar to that of the first embodiment. Next, the operation of the third embodiment configured as described above will be described. First, the reciprocating table 12 is moved at a relatively high cutting speed to perform rough grinding. At this time, the cutting amount calculator 73 calculates the cutting amount per unit time from the measurement value of the dimension measuring device 71, and calculates it by the comparator 7
Supply to 5. At the same time, the storage device 53 outputs the straightness correction value I '(X') corresponding to the position X'measured by the table position measuring device 17 to the adder 57, and the maximum correction value memory 77 outputs this output. Straightness correction value I'from data
The maximum value of (X ') is stored.

The comparator 75 uses the maximum correction value memory 77.
The maximum correction value of is compared with the cut amount from the cut amount calculator 73. If the result of comparison is that the maximum correction value ≦ unit time cut amount, the switch 78 remains open. Therefore, the straightness correction value I ′ output from the storage device 53
The data of (X ') is not supplied to the adder 57. That is, straightness correction is not performed.

When the work 25 is ground by a predetermined amount,
This time, the cutting speed of the cutting table 21 is reduced to perform fine grinding. When fine grinding is started and the comparison in the comparator 75 shows that the maximum correction value ≧ unit time cut amount,
The switch 78 closes the circuit, and the table speed selector 79 slows down the reciprocating speed of the reciprocating table 12. Due to the decrease in the reciprocating speed, the interval between the positions X'measured by the table position measuring device 17 every predetermined time becomes smaller than that in the first embodiment, and the switch 78 is closed to close the position X '. The straightness correction value I ′ (X ′) corresponding to “′” is sequentially supplied to the adder 57.

FIG. 4 shows the configuration of a straightness correction device according to the fourth embodiment of the present invention. In this embodiment,
Cutting amount calculator 73 'for calculating the cutting amount of the cutting table 21 when the reciprocating table 12 makes one reciprocation.
Is provided. Further, instead of the maximum correction value memory 77 in the third embodiment, a straightness correction process setting device 80 that stores (sets) the cutting amount in the final processing process such as during fine grinding or spark out is provided. ing. In addition,
The cut amount set in the straightness correction process setting device 80 is equivalent to the maximum correction value in the third embodiment. The straightness correction process setting device 80 supplies the set cutting amount to the comparator 75, and in the comparator 75, one of the cutting amount from the straightness correction process setting device 80 and the cutting amount calculator 73 'is set. It is designed to compare the cut amount per round trip.

When the depth of cut per reciprocation is smaller than the depth of cut set in the straightness correction process setting device 80, that is, during fine grinding or spark-out, the switch is pressed. 78 is designed to close. Therefore, in this embodiment, the straightness correction is started at the time of entering the final processing step. Further, in the table speed changer 79, as a result of the comparison by the comparator 75, the straightness correction process setting device 8 is the cut amount per reciprocation.
When the cut amount becomes smaller than 0, the reciprocating speed of the reciprocating table 12 is reduced.

Other configurations and operations are similar to those of the third embodiment. In the above third and fourth embodiments, the straightness correction is performed only in the final machining process such as fine grinding for determining the final shape accuracy of the machined work 25 or spark out. The correction efficiency is good. Also,
Since the straightness correction is started when the cutting amount per unit time becomes small to some extent, when the cutting amount is large, the tool spindle 11 is pressed by the pressing force.
Although the accuracy of the correction may decrease due to the bending of the lens, such a decrease in the accuracy can be prevented.

Further, in the third and fourth embodiments, the reciprocating speed of the reciprocating table 12 is slowed down at the time of starting the straightness correction so that the pitch is finer than that in the first and second embodiments. Straightness correction value I'corresponding to the measured position X '
Since the straightness is corrected by (X '), the correction accuracy can be further improved.

In the third and fourth embodiments, the reciprocating speed of the reciprocating table 12 is slowed down at the start of straightness correction. However, even if the straightness correction pitch in the reciprocating direction is rough, the reciprocating speed of the reciprocating table 12 may be kept constant if a sufficient straightness correction accuracy can be obtained.

In each of the above embodiments, the cylindrical grindstone 10 is used.
Although the side reciprocates, the cutting table 21 side may reciprocate to perform the machining.
In this case, the straightness of the reciprocating motion of the cutting table 21 is corrected. Further, as a processing tool, a cylindrical grindstone 10
However, other processing tools such as a cup grindstone or a cutting tool such as a diamond bite may be used.

In each of the above embodiments, the command value of the reference signal supplied to the adder 43 is changed to generate the correction magnetic force for moving the rotary shaft 19 in the straightness error axis direction. However, separately from the control unit 34, the electromagnet 35 based on the straightness correction value I (X) of the storage device 53,
A circuit for increasing / decreasing the exciting current of 36 may be provided, and the correction magnetic force may be generated by this circuit.

[0056]

According to the first aspect of the present invention, since the straightness is corrected by utilizing the magnetic force of the magnetic bearing, the structure is simple without using a special mechanism, and automation is easy. Further, by increasing the rigidity of the magnetic bearing, it is possible to deal with a heavy load such as a spindle.

Further, since the correction is performed by directly moving the reference position of the magnetic bearing in the cutting direction of the spindle,
There are few error factors and good responsiveness. Therefore, the straightness can be accurately corrected. According to the invention of claim 2,
Since the straightness correction is performed according to the measured straightness error, in addition to the above effect, there is an effect that the correct straightness correction can be performed even when the straightness error changes.

According to the third and fourth aspects of the invention, the straightness correction is further started when the cutting speed by the cutting means or the cutting amount per one round trip of the table becomes smaller than the maximum correction value. Therefore, the correction can be efficiently performed.

According to the fifth aspect of the present invention, the straightness correction can be performed at a fine pitch because the reciprocating speed of the moving means is slowed down when the straightness correction by the reference position changing means is started. Further, it is possible to perform straightness correction with higher accuracy.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an overall configuration of a straightness correction device according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an overall configuration of a straightness correction device according to a second embodiment of the present invention.

FIG. 3 is an explanatory diagram showing an overall configuration of a straightness correction device according to a third embodiment of the present invention.

FIG. 4 is an explanatory diagram showing an overall configuration of a straightness correction device according to a fourth embodiment of the present invention.

[Explanation of symbols]

 10 Cylindrical grindstone 11 Tool spindle 12 Reciprocating table 14 Linear scale 15 Reciprocating motor 17 Table position measuring device 19 Work spindle 21 Cutting table 23 Cutting motor 25 Machining work 29 Work spindle rotating motor 31 Thrust bearing rotor part 33 Magnetic Bearing unit 34 Control unit 35, 36 Electromagnet 38, 39 Displacement sensor 41 Sensor signal adjuster 43 Adder 45 PID compensator 47 Phase inverter 50, 51 Power amplifier 53 Storage device 57 Adder 60 Reference device 61 Straightness measuring device 71 Dimension measuring device 73, 73 'Cutting depth calculator 75 Comparator 77 Maximum correction value memory 79 Table speed selector 80 Straightness correction process setting device

Claims (5)

[Claims] 1. A spindle comprising a magnetic bearing as a bearing for holding a rotary shaft to which one of a machining tool and a workpiece is fixed at a reference position and receiving a load in a cutting direction, and a spindle mounted on the spindle. A first table, a second table on which the other one of the machining tool and the workpiece is placed, and at least one of the first table and the second table is moved in the cutting direction to move the machining tool. A cutting means for cutting a work, a moving means for reciprocating at least one of the first table and the second table in a direction perpendicular to the cutting direction, and the table for reciprocating movement by the moving means. And a straightness error storage means for storing the relative position change amount of the workpiece and the machining tool in the cutting direction at each moving position as a straightness error of the table. A straight position changing means for changing the reference position held by the magnetic bearing in the cutting direction by the straightness error amount stored in the straightness error storing means at each moving position of the table. Degree correction device. 2. A straightness error measuring unit for measuring a straightness error of the table during the reciprocating movement, wherein the straightness error storage unit stores the straightness error measured by the straightness error measuring unit. The straightness correction device according to claim 1, wherein 3. A cutting speed detecting means for detecting a cutting amount of the machining tool per unit time by the cutting means, wherein the reference position changing means has a cutting speed detected by the cutting speed detecting means as the straightness. 2. The straightness correction apparatus according to claim 1, wherein the process of changing the reference position is started when the straightness error stored in the error storage means becomes smaller than the maximum value. 4. A cutting amount detecting means for detecting a cutting amount of the working tool per one reciprocating movement of the table in a reciprocating motion is provided, and the reference position changing means detects the cutting amount per one reciprocating movement detected by the cutting amount detecting means. 2. The straightness correction apparatus according to claim 1, wherein the processing for changing the reference position is started when the cut amount becomes smaller than the maximum value of the straightness error stored in the straightness error storage means. 5. The straightness according to claim 3, wherein the moving means slows down the speed of the reciprocating movement at a time point when the reference position changing means starts the process of changing the reference position. Correction device.