JP2006043779A - Free curved surface shape measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure the free curved surface shape efficiently and with high accuracy without complicated axis control. <P>SOLUTION: A displacement measuring device is fitted to an orthogonal 3-axis machining tool having a work spindle and a tool spindle, and 3-axis control of the orthogonal 3-axis machining tool is performed so that the angle α made between a vector PO→ connecting a measuring point P of a work W and an intersection O of a perpendicular dropped from the measuring point P to the probe central axis St of a displacement measuring device and a normal vector PQ→ of a free curved surface in the measuring point P is constant, thereby measuring and machining the shape of the free curved surface Wf of the work W. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for measuring a free curved surface shape of a workpiece (work), and more particularly to a free curved surface shape measuring method for measuring a curved surface shape using a displacement measuring device attached to a processing machine (machine tool).

  A free-form surface such as a lens mold is processed by a numerically controlled processing machine. In recent years, for a small-diameter aspherical lens that has been in increasing demand, in order to avoid interference between the machine configuration and the grindstone, oblique axis grinding has been proposed in which the grindstone axis is inclined with respect to the workpiece rotation axis (for example, Patent Documents 1 and 2).

  In recent years, normal control has been proposed in which machining is performed while maintaining the inclination vector of the grindstone axis and the free-form surface tangent angle constant (for example, Patent Document 3). Specifically, machining by normal control is performed by setting the tool spindle on the B-axis table and aligning the tool axis with the tangential angle, and simultaneously using the X-axis, Z-axis, and B-axis (swing axis around the Y-axis). Normal control processing by three-axis control is performed.

  In addition, a displacement measuring instrument having a probe (probe) is attached to a tool spindle of a processing machine, and the shape accuracy of a workpiece processing surface is measured on the machine (for example, Patent Document 4). Further, a correction program is created using the measurement data, and finishing is also performed.

  Displacement measuring instruments used for measuring shape accuracy are generally direct-acting, and the angle formed by the displacement detection direction, which is the same axial direction as the central axis of the probe, and the normal direction of the measurement surface If the (contact angle) exceeds a certain angle (maximum contact angle), highly accurate measurement cannot be performed.

  On the other hand, in the conventional on-machine measurement, the center axis of the probe is aligned with the Z axis on the plane defined by the X axis and the Z axis, and the machining surface is scanned by simultaneous biaxial control of the XZ axis By doing so, the shape accuracy of the machined surface is measured.

For this reason, when the radius of curvature of the machining surface (measurement surface) is small, such as a molding die for a small-diameter aspheric lens, the contact angle of the probe becomes large on the outer peripheral side of the machining surface (for example, about 60 degrees). ), It becomes difficult to measure accurately.
Japanese Patent Laid-Open No. 8-229792 JP 2003-11057 A JP-A-7-1000075 JP 2002-267438 A

  The problem to be solved by the present invention is that, when measuring the shape of a free-form surface by a displacement measuring instrument having a measuring element, the contact angle of the measuring element is kept at a small value (for example, 45 degrees or less) even on a machined surface with a small radius of curvature. Thus, it is to measure the free-form surface shape with high accuracy.

  The free curved surface shape measuring method according to the present invention is a free curved surface shape measuring method for measuring the shape of a free curved surface of a workpiece attached to the processing machine using a displacement measuring device attached to the processing machine having three orthogonal control axes. A measurement point at an arbitrary coordinate position of the free-form surface of the workpiece, and a vector that connects an intersection of the measurement point and a line perpendicularly lowered from the measurement point to the central axis of the measuring element of the displacement measuring device; The shape of the free-form surface is measured by performing three-axis control of the processing machine so that the angle formed by the normal vector of the free-form surface at the measurement point is constant.

  In the free-form surface shape measuring method according to the present invention, preferably, the processing machine has an X axis, a Y axis, a Z axis control axis orthogonal to each other, and a work spindle rotating around the Z axis, A stylus of the displacement measuring instrument is disposed on an axis inclined with respect to the rotation axis of the work spindle in a plane defined by two of the three orthogonal axes, and is a free curved surface of the work attached to the work spindle. By performing the axis control of the other axis in synchronization with the simultaneous two-axis control according to the shape of the workpiece, the intersection of the measurement point of the workpiece and the line vertically lowered from the measurement point to the central axis of the probe The shape of the free-form surface is measured on the processing machine while keeping the angle formed by the vector connecting the two and the normal vector of the free-form surface at the measurement point constant.

  In the free curved surface shape measuring method according to the present invention, preferably, the processing machine can rotate around the Z axis, the X axis, the Y axis, and the Z axis orthogonal to each other, and the rotation angle can be controlled as C axis control. A stylus of the displacement measuring instrument having a work spindle and including the measuring element is disposed on an axis inclined with respect to the rotation axis of the work spindle in a plane defined by two of three orthogonal axes; By performing the axis control of the other axis in synchronization with the simultaneous three-axis control including the C axis according to the shape of the free-form surface of the workpiece attached to the workpiece spindle, the measurement point of the workpiece and the measurement point The shape of the free-form surface on the processing machine is kept constant by keeping the angle formed by the vector connecting the intersection point with the line perpendicular to the central axis of the probe and the normal vector of the free-form surface at the measurement point. Performs constant.

  According to the method for measuring the free-form surface according to the present invention, the intersection of the workpiece measurement point and the line perpendicularly lowered from the measurement point to the central axis of the probe of the displacement measuring instrument is connected by the three-axis control of the orthogonal three-axis machine. Normal control is performed to keep the angle formed by the vector and the normal vector of the free-form surface at the measurement point constant.

  As a result, the contact angle of the measuring element of the displacement measuring instrument does not change and the contact angle of the measuring element can be kept small even when the machining surface (measurement surface) has a small radius of curvature. Can be performed with high accuracy.

  First, an orthogonal three-axis machine used for implementing the method for measuring a free-form surface according to the present invention will be described with reference to FIG.

  In this embodiment, the orthogonal triaxial processing machine is an NC super-precision aspherical grinding machine with three-axis control of the XYZ axes. This grinding machine includes a Z-axis table 13 on a horizontal VV type guide surface 12 in the Z-axis direction on a machine base 11 and an X-axis table 15 on a horizontal VV-type guide surface 14 in the X-axis direction. Have

  The Z-axis table 13 is guided by the V-V guide surface portion 12 and can move linearly in the Z-axis direction, and the X-axis table 15 is guided by the V-V-type guide surface portion 14 and can move linearly in the X-axis direction. ing. The Z-axis table 13 is driven in the Z-axis direction by a Z-axis servo motor 27, and the X-axis table 15 is driven in the X-axis direction by an X-axis servo motor 28.

  A work spindle unit 16 is mounted on the Z-axis table 13. The work spindle unit 16 includes a work spindle 17 that can be rotated around the Z-axis by an air bearing, and a C-axis servo motor (work spindle motor) 18 that rotates the work spindle 17. The workpiece W is held by a vacuum chuck or the like.

  A Y-axis column 19 is fixedly mounted on the X-axis table 15. The Y-axis column 19 supports the Y-axis table 20 so as to be movable in the vertical Y-axis direction. The Y-axis table 20 is driven by a ball screw (not shown) by a Y-axis servo motor 21.

  A tool spindle unit 23 is mounted on the Y-axis table 20 with a mounting bracket 22 at an angle. The tool spindle unit 23 includes a tool spindle 25 using an air bearing and a tool spindle motor 26 that rotationally drives the tool spindle 25.

  The tool spindle 25 has an oblique axis arrangement arranged on an axis inclined at a predetermined angle, for example, 45 degrees on a plane defined by the Y axis and the Z axis, and a tool (grinding stone) is attached to the cross grinding method. Oblique axis grinding at.

  The mounting bracket 22 integrally has a horizontal displacement measuring device mounting piece 24. A direct-acting displacement measuring instrument 40 is attached to the displacement measuring instrument mounting piece 24. As shown in FIG. 2, the displacement measuring device 40 has a spherical probe (probe) 42 at the tip of a stylus 41 that forms the central axis of the displacement measuring device 40, and moves the stylus 41 in the axial direction. The displacement sensor 43 detects the amount of movement in the probe center axis St direction.

  The displacement measuring device 40 is attached to the horizontal displacement measuring device mounting piece 24, so that a predetermined angle with respect to the rotation axis (Z-axis direction) of the work spindle 17 in a horizontal plane defined by the X axis and the Z axis. For example, it is an oblique axis arrangement arranged on an axis inclined by 45 degrees.

  The numerical control device 30 is of a microcomputer type and performs simultaneous three-axis control of the Z-axis servomotor 27, the X-axis servomotor 28, and the Y-axis servomotor 21 according to the NC machining program.

  Although not shown, the X axis, Y axis, and Z axis control axes are provided with a linear scale or the like, and position feedback control by a fully closed system is performed.

  When the workpiece W is like an aspherical lens molding die, the free curved surface thereof has an axisymmetric shape around the rotation center axis (Z axis) of the workpiece spindle 17 as shown in FIG. The rotation surface (free-form surface) Wf.

In the free curved surface shape measuring method according to the present invention, as shown in FIG. 3, the measuring element 42 of the displacement measuring device 40 is brought into contact with the free curved surface Wf of the workpiece W, and the measuring point (the measuring element 42 on the free curved surface Wf) is measured. Of the free curved surface Wf at the measuring point P and a vector PO ^→ connecting the intersection point O between the measuring point P and the line perpendicular to the probe center axis St of the displacement measuring device 40. Measure the shape of the free curved surface Wf by scanning the free curved surface Wf by controlling the X axis, Y axis, and Z axis of the orthogonal triaxial machine so that the angle α formed by the vector PQ ^→ is always constant. I do. In this specification, a vector is indicated by a symbol ^→ . Point Q is the center point of the spherical probe 42.

In this embodiment, in measuring the shape of a rotational surface (free-form surface) Wf having an axisymmetric shape around the rotation center axis (Z axis) of the work spindle 17, the work W is rotated around the Z axis by the work spindle 17. In addition to simultaneous X-axis and Z-axis control according to the shape of the free-form curved surface Wf, the Y-axis synchronous axis control is performed, so that the measurement point P and the measurement point P of the workpiece W are moved to the probe center axis St. The shape of the free-form surface Wf is measured while keeping the angle α formed by the vector PO ^→ connecting the intersection point O with the line drawn vertically and the normal vector PQ ^→ of the free-form surface Wf at the measurement point P constant.

Thus, normal control is performed to maintain the normal vector PQ ^→ in the normal direction of the free-form surface Wf, the contact angle of the contact 42 (45 degrees in this embodiment) does not change, and the measurement surface (free-form surface Wf ) Is small, the contact angle of the probe 42 is kept at a small value (45 degrees), and the shape of the free-form surface can be measured with high accuracy. Here, the small value of the contact angle of the measuring element 42 refers to an angle equal to or smaller than the maximum contact angle at which the shape can be measured with the required accuracy.

  The shape measurement of the free curved surface Wf is performed by a so-called in-process method in a state where the workpiece W is mounted on the workpiece spindle 17 of a processing machine that performs the shape processing of the workpiece W.

  Next, normal control for making the contact angle of the displacement measuring device 40 constant in measuring the shape of the rotational surface Wf having an axisymmetric shape will be described in detail with reference to FIG.

When considering normal control in the displacement measuring instrument-workpiece positional relationship shown in FIG. 3, the vector PO ^→ and the measurement point normal vector PQ ^→ When the condition is satisfied, the scanning trajectory Tr (see FIG. 4) of the measuring element 42 is calculated.

^{PQ → · PO → = │PQ →} ││PO → │cos45 ° ( constant) ... (1)
PQ ^→ // N ^→ … (2)
N ^→ is a normal vector of the machining surface obtained from the free-form surface shape data.

  A scanning trajectory Tr that satisfies this condition is obtained, an NC program based on the obtained scanning trajectory is created, and the machining surface 42 is scanned by the above-mentioned NC ultra-precision aspherical grinding machine with three-axis control of the XYZ axes. Measure the shape.

  The spindle motor that rotationally drives the workpiece spindle 17 is a C-axis servo motor 18 that can control the position, and the workpiece spindle 17 is controlled as the C-axis so that the free-form measurement method according to the present invention is applied to a workpiece with a free-form surface. It becomes possible to do.

In this case, in addition to the simultaneous 3-axis control of the X-axis, the Z-axis, and the C-axis according to the shape of the free-form surface of the workpiece, the synchronous axis control of the Y-axis is performed, which is shown in FIG. In the same manner, the vector PO ^→ that connects the measurement point P of the workpiece W and the intersection point O of the line perpendicular to the probe center axis St from the measurement point P and the normal vector PQ ^→ of the free-form surface Wf at the measurement point P are The shape of the free-form surface is measured while keeping the formed angle α constant.

  In this case, due to the axial asymmetric shape, the measurement point on the workpiece is calculated as a general normal vector as shown below.

{Nx, Ny, Nz} = {− (δf / δX ′), − (δf / δY ′), 1} (3)
Assuming that the rotation angle of the C-axis for satisfying the requirement for performing normal control is Θc, the normal vector at the measurement point at that time is expressed as follows.

n ^→ = {p, q, r} (4)
p = Nxcos Θc + Nycos Θc (5)
q = −NxsinΘc + NysinΘc (6)
r = Nz (7)
That is, by using the result obtained from the conditions of the above formulas (1) and (2) as the above formula, the coordinates and workpiece (C) for measuring an arbitrary point on the free-form surface by normal control The rotation angle of the shaft can be calculated.

It is a perspective view which shows the orthogonal triaxial processing machine (NC super-precision aspherical grinding machine) used for implementation of the free-form surface shape measuring method by this invention. It is explanatory drawing which shows the relationship between the workpiece | work and the displacement measuring device in the free-form surface shape measuring method by this invention. It is explanatory drawing which shows the vector relationship of the workpiece | work and the measuring element of a displacement measuring device in the free-form surface shape measuring method by this invention. It is explanatory drawing which shows the relationship between the workpiece | work and the measuring element of a displacement measuring device in the free-form surface shape measuring method by this invention.

Explanation of symbols

11 Machine 13 Z-axis table 15 X-axis table 16 Work spindle unit 17 Work spindle 18 C-axis servo motor 19 Y-axis column 20 Y-axis table 21 Y-axis servo motor 25 Tool spindle 26 Tool spindle motor 27 Z-axis servo motor 28 X Axis servo motor 30 Numerical control device 40 Displacement measuring instrument 41 Stylus 42 Measuring element

Claims (3)

A free curved surface shape measuring method for measuring the shape of a free curved surface of a workpiece attached to a processing machine using a displacement measuring device attached to a processing machine having three orthogonal control axes,
The measurement point is an arbitrary coordinate position of the free-form surface of the workpiece, and the measurement point and a vector connecting the intersection point of the measurement point and a line perpendicularly lowered from the measurement point to the central axis of the measuring instrument of the displacement measuring device, and the measurement point The free-form surface shape measuring method for measuring the shape of the free-form surface by performing three-axis control of the processing machine so that the angle formed by the normal vector of the free-form surface is constant. The processing machine has an X axis, a Y axis, and a Z axis control axis orthogonal to each other, and a work spindle that rotates around the Z axis,
Arranging the stylus of the displacement measuring instrument including the measuring element on an axis inclined with respect to the rotation axis of the work spindle in a plane defined by two of three orthogonal axes;
By performing the axis control of the other axis in synchronization with the simultaneous two-axis control according to the shape of the free curved surface of the workpiece attached to the workpiece spindle, the measurement point of the workpiece is measured from the measurement point of the workpiece and the measurement point. The shape measurement of the free curved surface is performed on the processing machine while maintaining a constant angle formed by a vector connecting an intersection with a line perpendicular to the central axis and a normal vector of the free curved surface at the measurement point. The method of measuring a free-form surface according to 1. The processing machine has an X-axis, Y-axis, and Z-axis control axes that are orthogonal to each other, a work spindle that rotates around the Z-axis and can be controlled in rotation angle as C-axis control,
Arranging the stylus of the displacement measuring instrument including the measuring element on an axis inclined with respect to the rotation axis of the work spindle in a plane defined by two of three orthogonal axes;
By performing axis control of another axis in synchronization with simultaneous 3-axis control including the C axis according to the shape of the free-form surface of the workpiece attached to the workpiece spindle, the workpiece measurement point and the measurement point are Measuring the shape of a free-form surface on the processing machine while maintaining a constant angle between the vector connecting the intersection point with the line perpendicular to the central axis of the probe and the normal vector of the free-form surface at the measurement point The method of measuring a free curved surface shape according to claim 1.

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