JPH06134653A - Method for machining curved surface symmetrical to axis of revolution - Google Patents

Abstract

PURPOSE:To machine with a high efficiency a curved surface which is excellent in the shape precision and symmetrical to the axis of revolution by modifying the original point of the locus, the radius and the position of the tool based on the results of the shape measurement, and executing the following machining by using the tool while executing a relative movement of the tool along the tool locus to be modified based on these modified values. CONSTITUTION:The error DELTAC when the tool original point is set, the mounting positional error DELTAR of a tool 6, and the original point error DELTAtheta of the tool position are obtained by a computation processing device 17 by using the errors of the shape of the surface to be machined which are measured by an electric displacement gauge and obtained from the shape of the surface to be machined. These values are received by a numerical control device 17, the tool original point, the tool mounting position and the original point of the tool position control are modified, and an objective shape of the surface to be machined can be obtained while an ideal tool locus being described by re-machining.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a machining method suitable for highly precisely machining a machined surface, which is involved in grinding a curved surface symmetrical with respect to a rotation axis.

[0002]

2. Description of the Related Art Conventionally, when a rotationally axisymmetric curved surface is machined on a work piece, the attitude of the tool is such that the rotation axis of the work piece and the tool (for example, a grinding wheel) are always in contact with the work surface vertically. The position where the center axis of rotation for controlling is intersected is set as the tool origin, and the coordinate system from this tool origin is used to perform the machining by moving the tool on the relative locus by numerical control.

However, the error at the time of setting the tool origin and the error of the tool radius, and the change of the tool contact point at the time of setting the tool origin and during machining (for example, whirling due to thermal expansion and centrifugal force of the grinding wheel shaft or the grinding wheel drive spindle) ) Caused deterioration in shape accuracy.

In order to prevent this deterioration, for example, as described in Japanese Patent Laid-Open No. 60-114445, some of the errors at the time of setting the origin of the tool are considered, but the error of the tool radius is considered. We did not consider the origin of the tool or the tool attitude control function.

When the method described in Japanese Patent Laid-Open No. 60-114445 is not applied, the machining surface shape error obtained from the measurement of the machining surface shape is corrected to a tool locus with respect to the machining surface rotation center, and this is repeated. It took a very long time to process it.

[0006]

As described above, when machining a rotationally axisymmetric curved surface, the rotation axis of the workpiece and the rotation center axis for controlling the attitude of the tool are intersected, and this position is set in the radial direction of the tool. Set as the origin. Further, at this time, the attitude in which the grindstone and the contact point of the workpiece are on the axis of rotation of the workpiece is the tool origin of the tool posture control function. However, the error in setting the tool origin causes an error in the relative trajectory of the tool with respect to the rotation axis. In addition, due to an error in mounting the tool to the attitude control function, too much or uncut part of the surface to be machined was caused in the normal direction.

In the prior art described in Japanese Patent Laid-Open No. 60-114445, although some of the errors at the time of setting the tool origin are taken into consideration, the errors in attaching the tool to the attitude control function are taken into consideration. Therefore, in order to obtain a predetermined shape accuracy, it took a long time for the correction, and the working efficiency was not sufficient.

The present invention can solve the above-mentioned problems of the prior art and efficiently process a rotationally axisymmetric curved surface having excellent shape accuracy on a workpiece.

[0009]

In order to solve the above-mentioned problems, a structure of a method for machining a rotationally axisymmetric curved surface according to the present invention is configured so that a workpiece is rotated and a tool attached to a tool attitude control device is used. , While controlling the tool posture so as to always come into contact with the surface to be machined perpendicularly, the rotation axis of the machined object is relatively moved along a predetermined tool locus with the tool origin, and the machined object is moved by the tool. In the method of machining a rotationally axisymmetric curved surface, after performing machining once, the machining surface shape of the workpiece is measured. If this machining surface shape error is less than the target value, the machining is finished If so, a tool origin setting error, a tool mounting error, and a tool posture origin setting error are calculated based on the machining surface shape error, and the tool origin, the tool mounting, and the tool posture origin are corrected according to the calculation results. So While relatively moving the tool along the modified tool path is obtained by the repeated operations of running the next machining by the tool.

The details are as follows.

When the target cross-sectional shape of the rotational axis symmetric curved surface is given by a certain function, the machining surface shape error at a point at an arbitrary distance from the rotation axis of the workpiece is referred to as the error at the time of setting the tool origin. It is expressed as a function of the tool mounting error, the error in setting the origin of the tool posture, and the distance from the rotation axis. By substituting the machining surface shape error at each measurement point obtained by the shape measurement into this function formula, the error when setting the tool origin, the tool mounting error, and the error when setting the tool attitude origin are calculated by the multiple regression analysis method. To do. This calculation result is input to the numerical control device to correct the tool origin, the tool attachment position, and the attitude control origin, and then the machining is repeated to obtain the target machined surface shape.

[0012]

The error in setting the tool origin, the tool mounting position error, and the tool attitude control origin error are major factors in the deterioration of the shape accuracy and must be minimized. However, it is difficult to accurately grasp the shape of a tool such as a grinding wheel, and an error occurs due to wear, thermal expansion, whirling, etc. during processing. So, for example, using the machining surface shape error obtained from the shape of the machining surface measured with an electric displacement meter,
The calculation processor calculates the error when setting the tool origin, the tool mounting position error, and the tool orientation origin error, and inputs these to the numerical controller to correct the tool origin, tool mounting position, and tool orientation control origin. By performing the machining again, it is possible to obtain the target machined surface shape while drawing an ideal tool path.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a processing procedure diagram of a method for processing a rotationally axisymmetric curved surface according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram showing an example of a processing apparatus used for carrying out the processing method according to FIG. FIG. 3 is a cross-sectional view showing an error in setting the tool origin, a tool mounting error, and an origin setting error in the tool attitude control of the grinding wheel in FIG. Figure 4
Is XY indicating the relationship between the error and the deterioration of the accuracy of the machined surface shape
It is a schematic diagram in a plane.

The processing apparatus used in this embodiment is a general two-dimensional (XY plane) control processing apparatus, the configuration of which will be described with reference to FIG.

Reference numeral 1 denotes a processing apparatus main body, on which Y
The shaft table 2 is supported so as to be movable in the Y-axis direction. 3 is an X-axis table, and Y-axis table 2
It is supported so that it can move freely in the X-axis direction. Numeral 4 is fixed on the rotary table West X-axis table 3, and an XYZ stage 5 is fixed on the rotary table 4. The grinding spindle 7 supporting the grinding wheel 6 so that it can rotate is fixed to an XYZ stage 5 that can be finely adjusted in the X-axis, Y-axis, and Z-axis directions. A spindle 8 is fixed to a spindle 9 that can be rotated as a workpiece, and the spindle 9 is driven by a spindle motor 10. 11 is a numerical controller,
It is possible to control the X-axis table drive motor 12, the Y-axis table drive motor 13, and the rotary table drive motor 14 to control the grinding wheel to any tool posture at any position in the XY plane. Reference numeral 16 is an electric displacement gauge capable of measuring the shape of the machined surface, and this electric displacement gauge 16 is fixed to the Y-axis table 3 via an arm 15. 17
Is a calculation processing device, and the calculation processing device 17 is electrically connected to the numerical control device 11.

By using the processing apparatus configured as described above,
A method of processing a rotationally symmetric curved surface according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2.

The work piece 8 is attached to the spindle 9. The workpiece 8 is roughly machined into a shape similar to the machined surface shape y = f (x). The grinding wheel 6 rotates the grinding wheel 6, and the spindle motor 10 rotates the spindle 9 and the workpiece 8 around the rotation axis.

The target machining surface shape, that is, the rotationally axisymmetric curved surface y = f (x), the coordinates of the origin of the tool, and the coordinates of the origin of the tool posture are input to the numerical controller 11. Calculation processing device 1
In FIG. 7, an error calculation formula (equation (5) described later) for calculating a tool origin setting error ΔC, a tool mounting error ΔR, and a tool attitude origin setting error Δθ from the machining surface shape error Δy is shown. Input (I in FIG. 1). The numerical control device 11 calculates a tool trajectory from the machining surface shape (II in FIG. 1). The origin when designating this tool locus is the point when the rotation axis of the workpiece 8 and the rotation axis of the rotary table 4 for controlling the tool posture are in the same YZ plane. The grinding wheel 6 is mounted on the rotary shaft of the rotary table such that the points at which the grinding wheel 6 contacts the workpiece 8 coincide with each other. However, in reality, the alignment of the axes at the tool origin and the attachment of the grinding wheel are not always accurate, and have errors.

Next, along the designated tool path, X
The table 3 and the Y table 2 are moved, the grinding surface 6 is used to process the processed surface shape on the workpiece 8, and the first processing is finished (III in FIG. 1).

Here, the workpiece 4 is processed by the electric displacement gauge 10.
The machined surface shape is measured on the rotation center axis of, ie, the plane including the rotation axis (IV in FIG. 1). The measurement result is input to the calculation processing device 17, and the machining surface shape error is calculated by comparison with the coordinates of the target machining surface shape (V in FIG. 1).

Then, it is judged whether or not the machining surface shape error is equal to or less than the target value (VI in FIG. 1), and if it is less than the target value, the machining is completed. However, if the target value is not reached, the setting error ΔC in the X-axis direction of the tool origin, the tool mounting error ΔR, and the tool attitude origin setting are made from the above-mentioned machining surface shape error using the equation (5) described later. The error Δθ is calculated by the calculation processing device 17 (VII in FIG. 1).
The errors ΔC, ΔR, and Δθ obtained by this calculation are input to the numerical controller 11 to correct the tool origin and the tool attitude origin (VIII in FIG. 1), and then the tool path is calculated again (I in FIG. 1).
After returning to I), the same operation as above is repeated, and when the processed surface shape becomes equal to or less than the target value, the processing is completed. Then, by removing the work piece 8 from the main shaft 9, a work piece having a target rotationally axisymmetric curved surface y = f (x) is obtained.

The above is the procedure of the processing method. Next, details of the error calculation formula (Formula 5) will be described with reference to FIGS. FIG. 3 shows the setting error ΔC (X-axis direction) of the tool origin, the tool mounting error ΔR, and the origin setting of the tool posture when the grinding wheel 6 sets the tool origin at the position shown in the figure with respect to the workpiece 8. The error .DELTA..theta. Is shown, where 18 is the rotation axis of the workpiece, that is, the rotation center, 19 is the rotation center axis of the rotary table 4, and 20 is the contact point between the grinding wheel 6 and the workpiece 8. Ideally, the contact point 20 between the grinding wheel 6 and the workpiece 8 is on the rotation center axis 19 of the rotary table 4, and the rotation center axis 19 of the rotary table 4 is on the rotation axis 18 of the workpiece. It is in.

FIG. 4 is a schematic diagram on the XY plane showing the relationship between the above-mentioned error and the deterioration in accuracy of the machined surface shape. Reference numeral 23 is a target processed surface shape y = f (x), and 21 is an ideal grinding wheel for processing this. However, since there is a tool origin setting error ΔC (X axis direction), a tool mounting error ΔR, and a tool attitude origin setting error Δθ, the position of the grinding wheel is 22 and the surface shape machined by this is 24. . If the target machining surface shape 23 is represented by y = f (x), machining at a distance x _i from the rotation center 18 of the workpiece (corresponding to the Y axis in FIG. 4) in the X axis direction. The surface shape error Δy _i is a tool origin setting error Δ by a geometric method.
C (X axis direction), tool mounting error ΔR, and position error ΔE in the grindstone axis direction due to the origin setting error Δθ of the tool attitude are expressed by the following (Equation 1).

[0025]

[Equation 1]

However, θ _i is the angle formed by the tangent line of the target machined surface shape 23 to the X axis at the distance x _i from the center of rotation in the X axis direction. Further, the following expression (Formula 2) is established between θ _i and the first derivative y ′ = f ′ (x) of y = f (x).

[0027]

[Equation 2]

Therefore, the formula (1) can be replaced with the form of the formula (3).

[0029]

[Equation 3]

Therefore

[0031]

[Equation 4]

From the equation (4), the tool origin setting error ΔC,
The tool mounting error ΔR and the tool position error ΔE can be obtained from the following determinant (Equation 5) by the multiple regression analysis method.

[0033]

[Equation 5]

However, n is the number of measurement points, which is theoretically 3 or more, preferably 30 or more.

In this way, the tool origin setting error ΔC,
Tool mounting error ΔR and position error in the grindstone axis direction Δ
E is obtained, and using this, the origin setting error Δ of the tool posture
Tool mounting error ΔR 'after correcting θ and tool attitude
Is geometrically determined by the equations (6) and (7).

[0036]

[Equation 6]

[0037]

[Equation 7]

By substituting the measurement result Δy _i of the machining surface shape error in this way, the tool origin setting error ΔC, the tool mounting error ΔR ′, and the tool posture origin setting error Δθ can be obtained.

A specific example will be shown. Workpiece 8 is cemented carbide K0
5 is a raw material having a diameter of 30 mm, and the workpiece 8 is rotated at 50 r / min by the main shaft 9, and the Y-axis table 2,
While moving the tool at a speed of 0.5 mm / min using the X-axis table 3, the diamond electrodeposition grindstone No. 400 grinding tool 6 (rotation speed 18000 r / min)
A rotationally axisymmetric curved surface of an aspherical surface represented by the following (Equation 8) was processed.

[0040]

Y = Cx ² / (1 + √1− (K + 1) C ² y ² )
+ A ₄ y ⁴ + A ₆ y ⁶ + A ₈ y ⁸ + A ₁₀ y ¹⁰ However, C = 3.2504 × 10 to ² K = −5.0503 × 10 to ¹ A ₄ = −6.8765 × 10 to ⁶ A ₆ = 3.3117399 × 10 to ⁹ A ₈ = −3.8984728 × 10 to ¹¹ A ₁₀ = −1.314145 × 10 to ¹³ −14 ≦ y ≦ 14 Tool origin, tool mounting position and tool attitude origin are once corrected. The accuracy of the shape is ± 0.2μ.
m, the processing time was about 12 hours.

On the other hand, when the conventional processing method (the number of corrections was 3 times) was applied, the shape accuracy was ± 1 μm.
m, the processing time was about 32 hours.

The following effects can be obtained by selecting the embodiment described above. The processing accuracy of the rotationally symmetric curved surface is improved, and the processing efficiency is improved by 60% or more as compared with the conventional one. In the above embodiments, the case where the grinding wheel is used as the tool has been described, but the present invention can be applied to the case where the cutting is performed by using another tool, for example, a cutting tool.

[0043]

As described in detail above, according to the present invention, there is provided a method of processing a rotationally symmetric curved surface capable of efficiently processing a rotationally symmetric curved surface having excellent shape accuracy on a workpiece. can do.

[Brief description of drawings]

FIG. 1 is a processing procedure diagram of a method of processing a rotationally axisymmetric curved surface according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram showing an example of a processing apparatus used to carry out the processing method according to FIG.

FIG. 3 is a cross-sectional view showing an error in setting a tool origin, a tool mounting error, and a tool attitude control origin setting error of the grinding wheel in FIG.

FIG. 4 is a schematic diagram on an XY plane showing a relationship between the error and deterioration in accuracy of a machined surface shape.

[Explanation of symbols]

 1 ... Machining apparatus main body, 2 ... Y-axis table, 3 ... X-axis table, 4 ... Rotating table, 5 ... XYZ stage, 6 ... Grinding grindstone, 7 ... Grinding spindle, 8 ... Workpiece, 9 ... Spindle, 10 ... Spindle motor, 11 ... Numerical control device, 12 ... X-axis table drive motor, 13 ... Y-axis table drive motor, 14 ... Rotation table drive motor, 15 ... Arm, 16 ... Electric displacement meter, 17 ... Calculation processing device , 18: rotation axis of the work piece, 19: center axis of rotation of the rotary table 4, 20: contact point between the grinding wheel 6 and the work piece 21, 21: ideal grinding wheel, 22: actual position of the grinding wheel , 23 ... Target processed surface shape, 24 ... Actually processed surface shape.

Claims (1)

[Claims] 1. A machine tool that rotates a rotationally symmetrical surface by rotating a workpiece and causing the tool to move on a relative trajectory with respect to the axis of rotation of the workpiece, thereby numerically controlling the tool trajectory. A numerical control means capable of, and a tool attitude control means for constantly contacting the tool perpendicularly to the target machining surface shape, shape detecting means for measuring the machining shape of the workpiece,
Provided is arithmetic means for obtaining the shape error of the workpiece and the error at the time of tool setting based on the data obtained from the detecting means,
After performing the machining once, measure the machining surface shape, correct the origin of the tool locus, the tool radius, and the tool posture based on this shape measurement result, and perform the tool along the modified tool locus based on these modified values. A method for processing a rotationally axisymmetric curved surface, characterized in that the next processing is executed by the tool while relatively moving.