JPH01205971A - Grinding machine for non-roundness machining - Google Patents

Abstract

PURPOSE:To stabilize the grinding capability of a machining means within a certain region by detecting the rotating electric power of a machining means and providing a rotation control means for increasing or decreasing the rotational speed of a workpiece corresponding to the detected value. CONSTITUTION:NC data SNC entered from an NC data preparation part is converted and corrected in a conversion part 42 in respect of a value at the time of the rough machining and finish machining of a workpiece 9. The value is converted into an analog signal S1 at a D/A converter 43 and then inputted to a subtracter 45. On the other hand, the detected value of the rotating electric power for a grindstone drive motor 14 is inputted to the subtracter 45 as a signal S2. In the subtracter 45, the signal S2 is subtracted from the signal S1 and the result of the subtraction is amplified and outputted to a feed pulse part 46 as a signal S3. A command pulse CP outputted from a pulse generator 57 in the feed pulse part 46 is inputted to a C-axis servo amp 47. This amp 47 drives a C-axis servomotor 7 for the rotation thereof and reduces the rotational speed of the workpiece 9, thereby stabilizing the grinding capability of a grindstone 15.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is for non-perfect circular machining, in which the circumferential surface of a workpiece is machined into a non-α circular shape while moving and rotating the workpiece relative to a rotating processing tool. Regarding grinding machines.

[Prior art and its problems] When machining non-perfect circular shapes such as the cam ring of a cobane type hydraulic pump, while rotating a processing tool such as a grindstone at a predetermined position,
In addition, there is a method of moving and rotating the workpiece relative to the nipping tool to process the peripheral surface of the workpiece.

As an apparatus for grinding a workpiece by the above method, there is a numerically controlled (so-called NC) grinding machine for non-perfect circular machining. This grinding machine is equipped with data on the ideal non-perfect circular shape of the workpiece, and from this data and data such as the transmission characteristics of the grinding machine, the following error is calculated, and the following error is determined by the amount of movement of the workpiece to be corrected and The amount of rotation, operating speed, etc. are calculated, and the workpiece is moved and rotated based on the calculations. As a result, the workpiece is ground while errors in the actual machined shape are corrected.

That is, in the grinding machine for non-round machining as described above, the workpiece is attached to a predetermined support base, and the processing tool is operated at a predetermined position. The control device of the grinding machine moves and rotationally drives the support base of the workpiece based on the movement amount, rotation amount, operating speed, etc. of the workpiece determined from the non-perfect circular shape data and the data of the transmission characteristic 1 of the grinding machine. Controls the servo system. The workpiece is ground by being moved and rotated by the support table mentioned above by the servo system.

Note that the workpiece can be brought closer to the ideal shape by feedback of correction data obtained from the measured values of the shape and dimensions after the completion of machining or during machining. Further, such workpiece processing is usually performed by rotating a processing tool at a constant predetermined speed.

However, since there is a considerable difference in the grinding ability (so-called sharpness) of the grindstone used as a processing tool and before dressing, the processing tool is rotated at a constant speed to grind the workpiece. If this is done, there is a problem in that errors due to changes in the grinding ability become large, leading to a decrease in the finishing accuracy of the workpiece. In other words, in addition to form errors caused by the quantity and quality of the non-circular shape data themselves, which affect the finishing accuracy of the workpiece, the influence of machining errors caused by grindstones and the like as a machining tool becomes large.

For this reason, as disclosed in Japanese Patent Publication No. 50-21182, the optimum grinding force (contact pressure between the workpiece and the grinding wheel) etc. is memorized for each material of the workpiece, and Based on this, some methods control the speed at which the grinding wheel is applied to the workpiece so that the grinding force during actual machining is optimized.

[Objective of the Invention] The present invention has been made in view of the above-mentioned background, and it is an object of the present invention to eliminate the influence on the machining accuracy of a workpiece due to the grinding ability of a grindstone, etc. used as a machining tool, and to achieve high finishing accuracy. The purpose is to provide a grinding machine for machining non-perfect circles.

[At of the Invention] In order to achieve the above object, a grinding machine for non-round processing according to the present invention includes a processing means that rotates at a predetermined position and grinds a workpiece that is brought into contact with it, and a grinding machine that is represented by a series of points. The movement of the workpiece f
1, a control data creation stage for creating control data such as rotation amount and operating speed; a drive means for moving and rotationally driving the workpiece; and controlling the drive means based on control data by the control data creation means. (1) A power detection means for detecting the rotational power of the processing means, and increasing or decreasing the rotational speed of the workpiece in accordance with the power value detected by the power detection means. The rotation control means is configured to include rotation control means.

(2) a grinding speed detection means for detecting the speed of the grinding process from the amount of dimensional displacement of the workpiece per predetermined time; The present invention includes a co-rotating iVJ control means for increasing/decreasing the rotation speed.

With the above configuration, (1) ""( is the grinding capacity of the processing means or the power value is detected by the power detection means, and the rotational speed of the workpiece is controlled to increase or decrease accordingly. It is possible to stabilize the grinding ability within a certain range.

(2) The grinding force of the processing means is detected as the grinding speed by the grinding speed detection means, and the rotational speed of the workpiece is controlled to increase or decrease accordingly. It is possible to stabilize it.

Therefore, both (1) and (2) above, 7J
It is possible to eliminate the influence on the machining accuracy of the workpiece due to fluctuations in the grinding ability of the rJ machining means, and it is possible to improve the finishing accuracy of the workpiece.

[Embodiments of the Invention] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a perspective view showing the main parts of a mechanism in an embodiment of a grinding machine for non-round machining according to the present invention. In the figure, l is the base of the main mechanism of the grinder, 2 is the X-axis table, 3 is the Y-axis table, 4 is the rotary table, 5 is the X-axis servo motor, 6 is the Y-axis servo motor, and 7 is the C-axis servo motor, 8 is a dresser. Further, GM indicates the entire grinding machine for non-perfect round processing.

On the base l of the grinding iGM for non-perfect circular machining, there is a simultaneous 3-axis controller a that controls the movement of the workpiece that will be described later.
A section IO is provided. This simultaneous three-axis control mechanism section lO is
X axis cheatle 2. It is composed of a Y-axis table 32, a rotary table 4, and each drive mechanism that drives each of these chifurs. By the way, the axes that are orthogonal to each other are the X axis, the Y axis,
Let's call it the Z axis.

The X-axis table 2 moves on the base l in a predetermined direction (X-axis direction)
It is installed so that it can reciprocate, and its movement is controlled by an X-axis drive mechanism including an X-axis servo motor 5.

The Y-axis table 3 can reciprocate in the Y-axis direction.

It is installed on the upper surface of the X-axis table 2 so that its full surface is parallel to the table surface of the X-axis full 2. The movement of this Y-axis table 3 is controlled by a Y-axis drive mechanism including a Y-axis servo motor 6.

The rotary table 4 can be rotated around Z@.

J9 is placed on the upper medium heat portion of the Y-axis full 3 so that its chiffle surface is parallel to the chiffle surfaces of the X-axis full 2 and Y-axis full 3. The rotation axis of this rotary diffle 4 will be referred to as the C-axis. Note that the rotation of this rotary cheatle 4 is controlled by a rotation drive mechanism including a C-axis servo motor 7. Further, a workpiece to be described later is removably fixed to the center of the upper surface of the rotary chiffle 4.

The dresser 8 is installed on the Y-axis table 3, and grinds and shapes the surface of a rotatable grindstone, which will be described later, by coming into contact with the surface.

1, 11 is a column erected in the Z-axis direction on a base L, 12 is a Z-table, 13 is a U-axis table, 14 is a grindstone drive motor, 15 is a grindstone, and 16 is a Z-axis table. Axis servo motor 17 is a U-axis servo motor.

The Z-axis chiffle 12 has a table surface that is a plane that includes the Z-axis, and is installed in front of the column 11 so as to be able to reciprocate in the Z-axis direction. The movement of this Z vehicle differential 12 is controlled by a Z-axis drive mechanism including a Z-axis servo motor 16.

The U-axis full 13 reciprocates in the U-axis direction, which is parallel to the X-axis, and moves the Z-axis table 1 so that its full surface is parallel to the table surface of the Z-axis table 12.
It is installed on the -F side of 2. The movement of this U-axis table 13 is controlled by a U-axis drive mechanism including a C-axis servo motor 17.

The whetstone drive motor 14 has a whetstone 15 attached to the tip of its rotating shaft, and the whetstone 15 is rotated so that the rotating shaft is parallel to the Z-axis.
It is installed on the upper surface of the shaft table 13. Therefore, the grindstone 15 can be moved in a predetermined direction by the Z-axis table 12 and the U-axis table 13, and rotated at a high speed at a predetermined position.

FIG. 2 is an enlarged perspective view showing the peripheral portion of the rotary table 4 shown in FIG. 1. In the figure, reference numeral 9 indicates a workpiece whose periphery is to be ground, and P indicates a contact point of the grindstone 15 with the workpiece 9.

The workpiece 9 is a cam link of a vane-type hydraulic pump whose inner circumferential surface is oval, for example, and whose processed circumferential surface is non-circular. This work 9 is fixed to the center of the upper surface of the rotary table 4 so that it can be attached and removed, so that
Axis table 2. The position of the Y-axis table 39 is controlled by the operation of the rotary table 4. Therefore, the inner circumferential surface of the work 9 is ground by moving and rotating the work 9 relative to the grindstone 15 which is rotating at a high speed at a predetermined position.

FIG. 3 is a block diagram showing the numerical control (NC) system of the grinding machine GM for non-round machining shown in FIG. In the figure, 9' is a processed workpiece, 30 is a grinding machine control section, 31 is an NC data creation section, 32 is an NC unit, and 34
is form data of a non-perfect circular shape, and 36 is a shape measuring section that measures the non-perfect circular shape of the workpiece 9'.

As shown in FIG. 4, the grinding machine control section 30 is connected to the simultaneous 3-axis control mechanism section IO of the grinding machine GM for non-perfect round processing, and is composed of an NC data creation section 31 and an NC unit 32. .

The NC data creation unit 31 determines whether the shape is a non-perfect circle, the angle θ and the radius vector R.
Form data 3 shown as a series of point cloud data by
The amount of movement in the X-axis direction based on 4.

N of a non-perfect circular shape consisting of the amount of movement in the X-axis direction and the rotation angle of the C-axis
The C data is calculated and the NC data is output to the NC unit 32. In this example, as disclosed in Japanese Unexamined Patent Publication No. 62-34765 by the applicant, the i-stone 1
The machining action direction at the contact point P of No. 5 to the workpiece 9 is a specific - direction, and the passing speed V of the inner circumferential surface of the workpiece 9 at the contact point P. The movement and rotational speed of the workpiece 9 are controlled so that the rotational speed is constant, and highly accurate machining is performed. Therefore, the NC data creation unit 31 creates an X-axis movement amount, an X-axis movement amount, and a C value that satisfy the above conditions.
The amount of feed pulses (foot time) for each axis is calculated in order to keep the shaft rotation angle and passage speed v6 constant.

The NC unit 32 generates control pulses for the simultaneous three-axis control mechanism section 10 based on the NC data input from the NC data creation section 31, and outputs the control pulses to the three-axis control mechanism section 10 at the time of L times. . As a result, the inner circumferential surface of the workpiece 9 of the grinding machine GMI for non-perfect round processing is subjected to grinding based on the form data 34 of the non-perfect circular shape.

The shape of the processed workpiece 9' is measured by the shape measuring section 36. Then, the measured value is fed back to the NC data creation section 31 as correction data.

FIG. 4 is a block diagram of a portion of the grinding machine control section 30 shown in FIG. 3 related to control of the rotary table 4. In addition, X
The control of the axes, Y-axis, etc. is the same as in the conventional case, so a description thereof will be omitted.

In the figure, 41 is a sequencer that controls the sequence of the grinding machine control unit 30, and 42 is an NC input from the NC data creation unit 31 during rough machining and finishing machining of the workpiece 9.
an override conversion unit for converting and correcting data S, lc; 4;
3 is a D/A converter, 44 is a power detection unit that detects the rotational power of the grindstone drive motor 14, 45 is a subtracter, 46 is a foot pulse unit, and 47 is a C-axis servo amplifier.

NC data SHc input from the NC data creation section 31
is converted and corrected by the override/conversion unit 42 during rough machining and finishing machining of the workpiece 9, and D/
The A converter 43 inputs it to the subtracter 45 as an analog signal S. - On the other hand, from the power detection section 44,
The detected value of the rotational power of the grindstone drive motor 14 is input to the g calculator 45 as a signal S2. In the subtracter 45, the signal S,
The signal S2 is subtracted from the signal S2, and the subtraction result is amplified and outputted to the foot pulse section 46 as a signal S3. Note that the subtracter 45 is a well-known differential amplifier circuit composed of an operational amplifier 51 and resistors R1 to R4.

The foot pulse unit 46 stores the output values from the F/F converter 55 and the A/F converter 55 for converting the signal S3 from the subtracter 45 into a digital value, and generates a driving command pulse CP corresponding to the value. The operation of the pulse generator 57 is controlled by the sequencer 41.

Command pulse CP output from pulse generator 57 is input to C-axis servo amplifier 47, and C-axis servo amplifier 47 rotates C-axis servo motor 7 based on this command pulse CP. Note that the rotation position and speed of rotation F relative to the workpiece 9 (rotary table 4) by the C-axis servo motor 7 are fed back to the C-axis servo amplifier 47, thereby controlling the C-axis servo system in a stable direction. .

The power detection unit 44 includes the above-mentioned grindstone drive motor 14, current detector 61. Voltage detector 621 Multiplier 63, Filter 64
．． It is composed of an amplifier 65. The current and voltage of the grindstone drive motor 14 are detected by a current detector 61 and a voltage detector 62, respectively. Then, each output (detection) signal of the current detector 61 and voltage detector 62 is output to a multiplier 63. As a result, the multiplier 63°C calculates the electric power of the grindstone drive motor 14. The output signal of the multiplier 63 is filtered to remove its noise component by a filter 64, appropriately amplified by an amplifier 65, and then outputted to the subtracter 45 as a signal S2.

FIGS. 5(a), (b), and (c) are conceptual diagrams in which examples of output signals from each part of the block diagram shown in FIG. 4 are graphically displayed. In the figure, (a) shows the output signal S1 of the D/A converter 43, and (b) shows the output signal S2 of the power detection section 44.
and (c) respectively show the output signal S3 of the subtracter 45.

The signal S shown in FIG. 5(a) is the override converter 4.
2, the voltage value is converted and corrected to Vn during rough machining of the workpiece 9, and to v8 during finishing machining.

On the other hand, the signal S2 shown in FIG. 5(b) increases or decreases in inverse proportion to fluctuations in the grinding ability of the grindstone 15. In other words, when the grinding capacity of the grinding wheel 15 is low, such as immediately after or immediately before dressing, the voltage value of the signal S2 increases as shown on the left side of FIG. 5(b) because the power consumption of the grinding wheel drive motor 14 increases. When the grinding wheel 15 is free from clogging and has a high grinding ability, the power consumption of the grinding wheel drive motor 14 decreases and becomes smaller as shown on the right side of FIG. 5(b).

The signal S3 shown in FIG. 5(c) is obtained by subtracting the signal S2 from the signal S1 by the subtracter 45 and amplifying it.
If the voltage values shown on the left side of the figure are lower overall, the grinding ability of the grindstone 15 is low, and if the voltage values shown on the right side of the figure are higher overall, the grinding ability of the grindstone 15 is high. This signal S3
Depending on the voltage value, the rotational speed of the C4dl servo motor 7, that is, the workpiece 9, is relatively increased or decreased.

In other words, when the grinding ability of the grinding wheel 15 is low, the C-axis servo motor 7 is rotated relatively slowly due to the signal S3 shown on the left side of the figure, which has a lower voltage value overall, and the grinding wheel 15 is rotated relatively slowly. This control will improve the grinding ability of No. 15. In addition, when the grinding tooth force of the grindstone 15 is high,
The C-axis servo motor 7 is rotated relatively quickly by the signal S3 whose voltage value is generally higher as shown on the right side of the figure, and this is also a control that improves the grinding ability of the grindstone 15 for the workpiece 9. becomes.

That is, according to such a configuration, the grinding ability of the grinding wheel 15 is detected by the power detection unit 44, and the rotational speed of the workpiece 9 is controlled to increase or decrease accordingly, so that the grinding ability of the grinding wheel 15 is stabilized within a certain range. becomes possible. As a result, it is possible to eliminate the influence of fluctuations in the grinding ability of the grindstone 15 on the machining accuracy of the workpiece 9, and it is possible to improve the finishing accuracy of the workpiece 9.

Now, an embodiment of a grinding machine for non-perfect circular machining according to Patent Claim 94(2) will be described.

FIG. 6 is a block diagram showing only the changed parts in the control section of the rotary table 4 shown in FIG. 4. 3 in the same figure
44' is a grinding speed detector for detecting the speed of grinding the workpiece 9, and 45' is an adder.

The grinding speed detection section 44' includes a dimensional displacement detector 66 for detecting the amount of dimensional displacement of the workpiece 9, a synchronous rectifier 67, and an amplifier 68.
．． The 0-dimensional displacement detector 66 constituted by the differential calculation processing circuit 69 is a detector using a so-called differential transformer, and the amount of dimensional displacement of the workpiece 9 is detected as an alternating current voltage. The output signal of the dimensional displacement detector 66 is rectified by a primary stage synchronous rectifier 67, appropriately amplified by an amplifier 68, and then input to a differential calculation processing circuit 69.

The differential calculation processing circuit 69 is a circuit that performs differential calculation on the input signal by sampling the input signal for a predetermined period of time. Therefore, the output signal 82' of the differential calculation processing circuit 69 is the amount of dimensional displacement of the workpiece 9 per predetermined time,
In other words, it is the amount of grinding of the work 9 per predetermined time, that is, the speed of grinding the work 9.

The adder 45' includes a well-known addition circuit including an operational amplifier 52 and resistors R5 to R8, and an operational amplifier 53 and resistors R9 to R8.
It is composed of a well-known inverting amplifier circuit based on II. The operational amplifier 52 adds the signal 82' from the grinding speed detection section 44' mentioned above and the signal S1 from the D/A converter 43 shown in FIG. 4, and outputs the addition result to the operational amplifier 53. Ru. Note that the operational amplifier 52 is an addition circuit with an inverted output. Therefore, the operational amplifier 53 inverts the signal from the operational amplifier 52 again.
A signal S3 that is in phase with the signal S is output.

FIGS. 7(a), (b), and <c) are conceptual diagrams in which examples of output signals from each part of the block diagram shown in FIG. 6 are graphically displayed in the same manner as FIG. 5. In the figure, (a) shows the output signal SI of the D/A converter 43 shown in FIG. 4, (b) shows the output signal S2' of the grinding speed detector 44', and (c) shows the output signal S2' of the adder 45'. The output signal S1 is shown in each case.

The voltage value of the signal S1 shown in FIG. 7(a) is corrected by the override converting section 42 as described above by converting it into V□ during rough machining of the workpiece 9 and V8 during finishing machining.

On the other hand, the signal S2' shown in FIG. 7(b) increases or decreases in proportion to fluctuations in the grinding force of the grindstone 15. In other words, the signal S2'
If the grinding ability is low, such as immediately after or immediately before dressing, the voltage value of
The amount of dimensional displacement, in other words, the amount of grinding of the workpiece 9 per predetermined time, that is, the speed of grinding the workpiece 9, decreases as shown on the left side of FIG. 7(b), and the grindstone 15 becomes clogged. If the grinding ability is high and there is no such problem, the speed of grinding the workpiece 9 increases, as shown on the right side of FIG. 7(b).

The signal S:l shown in FIG. 7(C) is obtained by adding the signal 82' to the above signal S by the adder 45' and amplifying it. When the grinding ability of the grindstone 15 is low, the voltage value shown on the right side of the figure is generally higher, or the grinding ability of the grindstone 15 is high. Depending on the voltage value of this signal S1, the rotational speed of the C-axis servo motor 7, that is, the workpiece 9, is relatively increased or decreased.

In other words, when the grinding ability of the grinding wheel 15 is low, the C-axis servo motor is rotated relatively slowly by the signal S shown on the left side of the figure, which has a lower voltage value overall, and the grinding wheel 15 is rotated relatively slowly. This will improve the grinding ability of the machine. Moreover, when the grinding ability of the whetstone 15 is high,
The C@ servo motor 7 is rotated relatively quickly by the signal S3 whose voltage value is generally higher as shown on the right side of the figure, and this is also a control that improves the grinding ability of the grindstone 15 for the workpiece 9. becomes.

That is, according to such a configuration, the grinding capacity of the grinding wheel 15 is detected by the grinding speed detection section 44', and the rotational speed of the workpiece 9 is controlled to increase or decrease accordingly.
It is possible to stabilize the grinding ability of the machine within a certain range.

As a result, it is possible to eliminate the influence on the machining accuracy of the workpiece 9 due to fluctuations in the grinding speed of the grindstone 15, and
It is possible to improve the finishing accuracy.

In the above two embodiments, the case where the inner circumferential surface of the workpiece 9 is ground is explained, but the present invention is not limited to this, and the present invention is also applicable to the case where the non-circular outer circumferential surface of the workpiece 9 is ground. Needless to say, it is also applicable.

[Effect of the invention] As explained above, according to this invention, the patent claims (
In the grinding machine for non-perfect round machining (1), the grinding capacity of the processing means is detected as a power value by the power detection means, and the rotational speed of the workpiece is controlled to increase or decrease accordingly. can be stabilized within a certain range.

In addition, in the grinding machine for non-round machining of patent claim (2), the grinding capacity of the processing means or the speed of the grinding process is detected by the grinding speed detection means, and the rotational speed of the workpiece is controlled to increase or decrease accordingly. Therefore, it is possible to stabilize the grinding ability of the processing means within a certain range.

Therefore, the grinding machine for non-round machining in the above direction can also eliminate the influence on the machining accuracy of the workpiece due to fluctuations in the grinding ability of the machining means, and improve the finishing accuracy of the workpiece. I can do it.

[Brief Description of the Drawings] Figure 1 is a perspective view showing the main parts of the mechanism in an embodiment of the grinding machine for non-round processing according to the present invention, and Figure 2 is the peripheral part of the rotary table 4 shown in Figure 1. FIG. 3 is a block diagram showing the numerical control system for grinding @GM for non-round machining shown in FIG. 1, and FIG. 4 shows the inside of the grinding machine control section 30 shown in FIG. The block diagrams and ms diagrams (a), (b), and (c) of the parts related to the control of the rotary table 4 shown in FIG. The figure is a block diagram showing only the changed parts in the control section of the rotary table 4 shown in FIG. 4, and FIGS. 5 is a conceptual diagram showing an example in a graph similar to FIG. 5. FIG. GM-...Grinding machine for non-perfect round processing 9...Work (workpiece) lO...Simultaneous 3-axis control mechanism section (drive means) 14...
Grinding wheel drive motor 15... Grinding wheel (processing means) 31... NC data creation section (control data creation means) 32... NC unit (controlling means) 34... Form data (shape data) 44-.・
Power detection section (power detection means) 44'... Grinding speed detection section (grinding speed detection means) 45... Subtractor (rotation control means) 45'... Addition base (rotation control means) 51.52. 53... Operational amplifier R8 to R11... Resistor 61... Current detector 62... Voltage detector 63... Multiplier 64... Filter 65. 68... Amplifier 66... Dimensions Displacement detector 67...Synchronous rectifier 69...Differential calculation processing circuit Patent applicant Mazda Motor Corporation

Claims (2)

[Claims] (1) Processing means that rotates at a predetermined position and grinds the workpiece that comes into contact with it, non-perfect circular shape data represented by a series of points, and the shape and dimensions of the workpiece that has been processed or is currently being processed. control data creation means for creating control data such as the movement amount, rotation amount, and operating speed of the workpiece from correction data obtained from the measured values; a drive means for moving and rotationally driving the workpiece; and the drive means. A grinding machine comprising: a control means for controlling the rotational power of the processing means based on control data from the control data creation means; a power detection means for detecting the rotational power of the processing means; A grinding machine for non-perfect round machining, characterized in that it is equipped with a rotation control means for increasing and decreasing the rotation speed of a workpiece. (2) Processing means that rotates at a predetermined position and grinds the workpiece that comes into contact with it, non-perfect circular shape data represented by a series of points, and the shape and dimensions of the workpiece that has been processed or is currently being processed. control data creation means for creating control data such as the movement amount, rotation amount, and operating speed of the workpiece from correction data obtained from the measured values; a drive means for moving and rotationally driving the workpiece; and the drive means. A grinding machine comprising: a control means for controlling the grinding speed based on control data from the control data creation means; A grinding machine for non-round machining, comprising: rotation control means for increasing or decreasing the rotation speed of a workpiece in accordance with the speed of grinding detected by the grinding speed detection means.