JP2001099641A - Surface shape measurement method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To immediately read the surface coordinates of three or more points around a probe at the time of measuring center coordinate of a contact type probes and obtain a normal to surface near a contact point. SOLUTION: Three or more non-contact displacement meters are attached to a contact type coordinate measurement probe concentrically to the axis of the probe to measure three or more coordinate values around the probe tip end and at the same time of measuring the center coordinate of the contact type probe, three or more surface coordinates around the probe are read to obtain a normal to surface near the contact point and the coordinate of contact point is immediately obtained by offsetting by the probe radius.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface shape measuring method for measuring three-dimensional coordinates and generating an object shape from a set of coordinates of the measurement points.

[0002]

2. Description of the Related Art A method of measuring three-dimensional coordinates and generating an object shape from a set of coordinates of the measurement points is well known. In many cases, a three-dimensional measuring machine 20 having three linearly moving parts orthogonal to each other as shown in FIG. 7 is used. If the contact probe 21 for three-dimensional coordinate measurement is shaped as shown in FIG. 8, it comes into contact with the object surface at the measurement points a ₁ , a ₂ , a ₃ as shown in FIG.
A fitted surface 22 is generated as shown in FIG. 11, and an offset surface 23 as shown in FIG. 12 is generated. The coordinates of the contact portion at the time of contact are obtained as in Expression 1. (Equation 1) P = P _a + R · n P: coordinates of contact point R: radius of probe pa: center coordinates of probe sphere n: unit normal vector at contact point The normal vector of the shape can be easily obtained. On the other hand, in the case of a shape composed of a free-form surface, it is necessary to increase the number of measurement points and capture the surface shape in order to reproduce the shape. From these measurement points, the normal direction of the surface is estimated, and the three-dimensional shape is restored as a set of coordinates of the contact portion.

[0003]

However, in the case of a complex shape, it is necessary to measure more than tens of thousands of points, and manual measurement requires a great deal of labor. Further, in order to reproduce an accurate surface shape, it is necessary to generate an offset curved surface or the like in consideration of a probe shape and a contact point. In general, a normal vector required to generate an offset curved surface from a large number of measurement points is generated as follows. First, a curved surface to be fitted is generated from a large number of measurement points (center coordinates of the probe) by the least square method or the like. Next, a curved surface is generated which is offset by the radius of the probe toward the inside of the measured object along the normal vector of the generated curved surface.
Assuming that this curved surface matches the surface shape of the object, the measured value is used as the measured value. As described above, the measurement of the free-form surface shape by the conventional contact type three-dimensional measuring machine requires software capable of generating a free-form surface and an offset surface. In addition, the probe cannot be manually operated to move to an arbitrary measurement point, come into contact with the work surface, and immediately obtain a coordinate value. That is, when real-time measurement is required, there is a problem in that measurement and software processing for generating an offset curved surface are required, so that the method cannot be applied.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and to provide a probe for contact-type coordinate measurement with a probe.
At least three non-contact displacement gauges are mounted on a concentric circle with respect to the probe axis to measure coordinate values at three or more points around the probe tip. By reading the surface coordinates of three or more surrounding points, the surface normal near the contact point is obtained, and the coordinates of the contact point are immediately obtained by offsetting by the probe radius.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described in detail with reference to one embodiment shown in FIGS. Three or more non-contact displacement gauges are provided on the contact coordinate measuring probe 1,
3 and 4 are attached concentrically to the axis of the probe 1,
This figure shows a configuration in which coordinate values at three or more points around the tip of the probe are measured. At the same time as measuring the center coordinates of the contact probe 1, the surface coordinates at three or more points around the probe 1 are read to determine the surface normal near the contact point, and the coordinates of the contact point are immediately offset by the radius of the probe 1. Can be sought.

The normal direction near the probe contact point is determined by the following procedure. When three non-contact displacement meters 2, 3, and 4 shown in FIGS. 4 to 6 are arranged on concentric circles, and the measured coordinate values are m ₁ , m ₂ , and m ₃ , 2
Two vectors a and b are obtained. The normal direction of the plane containing these two vectors is determined by the outer product a × b, where a = m ₂ −m ₃ b = m ₃ −m ₁ . When this is divided by a scalar and normalized, n = a × b / | a × b | Therefore, from the measured values, the coordinate values of the shape surface are as follows. P = P _a + Rn The arrangement of the non-contact displacement meter may be such that the tip of the probe is inside the triangle formed by the measurement points, and does not need to be a regular triangle. Also, the probe tip shape can be applied to cases other than spherical.

[0007]

According to the present invention, three or more non-contact displacement gauges are attached to a contact coordinate measuring probe on a concentric circle with respect to the axis of the probe, and three or more coordinate values around the tip of the probe are measured. Measure the center coordinates of the contact probe and simultaneously read the surface coordinates of three or more points around the probe to find the surface normal near the contact point, offset the probe radius and immediately set the coordinates of the contact point This eliminates the need for curved surface processing software required when measuring a three-dimensional complex shape, and simplifies the measurement because the data processing step can be omitted. Since it is not necessary to perform multi-point measurement for obtaining the normal direction, an accurate surface shape can be reproduced with a smaller number of measurement points than the conventional method.

[Brief description of the drawings]

FIG. 1 is a front view of one embodiment of the present invention.

FIG. 2 is an external perspective view of FIG.

FIG. 3 is a front view for explaining the operation of FIG. 1;

FIG. 4 is a top view of the probe and measurement points of FIG. 3;

FIG. 5 is an operation explanatory plan view of FIG. 4;

FIG. 6 is a plan view for explaining the operation of FIG. 5;

FIG. 7 is an external perspective view of a conventional three-dimensional measuring machine having a three-axis linearly moving portion.

FIG. 8 is a front view of the wobble of FIG. 7;

FIG. 9 is a diagram showing a measurement probe and a measurement surface.

FIG. 10 is a diagram illustrating a method of correcting a measured value.

[Explanation of symbols]

1 Contact-type coordinate measuring probe 2, 3, 4 Non-contact type displacement meter P Coordinate of contact point R Probe radius P ₁ Center coordinate of probe sphere n Unit normal vector at contact point

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Claims (1)

[Claims] At least three non-contact displacement gauges are attached to a contact type coordinate measuring probe on a concentric circle with respect to an axis of the probe, and coordinate values at three or more points around a tip of the probe are measured. By reading the surface coordinates of three or more points around the probe at the same time as measuring the center coordinates of the probe, the surface normal near the contact point is obtained, and the coordinates of the contact point are immediately obtained by offsetting by the probe radius. Surface shape measurement method.