JPH03261815A - Measuring method of coordinate measuring machine - Google Patents

Abstract

PURPOSE:To measure the shape or the like of an object by a method wherein the force in a direction of each axis generated when a probe is shifted in the direction of each axis per unit amount is obtained beforehand, and both the force per unit amount of shift and the force acting on a stylus in the direction of each axis are obtained. CONSTITUTION:Supposing that the displacement of a probe when a stylus 30 is brought into contact with a contact point P on the surface of an object 32 to be measured is x, y, and the pressing force of the stylus 30 to the object 32 when the probe is shifted per unit amount is kx, ky, the force acting on the stylus 30 at the contact point P is as presented by formulae I, II. The force Fx, Fy assumes the directional ratios of a normal vector N to the surface of the object 32, and therefore, the directional cosines lambda, mu of the normal vector N are as indicated by formulae III, IV, making it possible to determine the normal vector N. Accordingly, if the displacement x, y of the probe is converted to the pressing force kx, ky of the stylus 30 resulting from the displacement, the normal vector N of the surface of the object 32 at the contact point P is obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a measuring method using a coordinate measuring machine, and in particular, the present invention relates to a measuring method using a coordinate measuring machine, and in particular, a stylus that is in contact with an object to be measured is moved along the surface of the object to be measured. The present invention relates to a measuring method using a coordinate measuring machine for determining the coordinates or shape of.

[Conventional technology]

When measuring the shape of an object to be measured with a stylus, it is necessary to find the point of contact between the stylus and the surface of the object to be measured, and for this purpose it is necessary to find the normal vector of the surface of the object to be measured at the point of contact P. The following two methods have been adopted as examples of this means.

The first method is as shown in Figure 3, at three points near the contact P (
C1+ SO2, Qs ) or (P, Q, Q2
The normal vector N of the plane extending from > is substituted as the normal vector of the object to be measured at the contact point P.

In addition, the second method can be applied when the stylus lO shown in FIG. This is a method of regarding it as vector N.

[Problem to be solved by the invention]

However, the first method has the problem of requiring extra time because it is necessary to measure three points (Q, , Q2, Q,) that are not directly necessary to find the normal vector. Furthermore, there is a problem that the error becomes large when the distribution of the three points is extremely narrow or when the curvature of the surface of the object to be measured is small.

In addition, in the second method, it is good if the pressing force of the stylus lO on the surface of the object to be measured 12 per unit displacement of the probe body is applied equally in the three axial directions, but if a different pressing force is applied for each axis. , the normal vector is N' as shown in Figure 4.
There is a problem that an error occurs.

The present invention has been made in view of the above circumstances, and provides a measuring method that can determine a normal vector with little error at a contact point P in a coordinate measuring machine using a probe capable of three-dimensionally detecting displacement. The purpose is to

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention moves a stylus of a probe that is provided in the main body of the measuring device and is capable of three-dimensionally detecting displacement along the surface of the object to be measured. In a measurement method using a coordinate measuring machine that moves by moving the probe to measure the shape of the object to be measured, the force in each axis direction that occurs when the probe is displaced by a unit displacement amount in each axis direction is determined in advance, and the force in each axis direction is calculated in advance. Find the contact force and the force applied to the stylus in each axis direction, find the normal vector at the point of contact between the stylus and the surface of the object to be measured from the withdrawal force, and use this normal vector to measure the shape of the object, etc. It is characterized by

[Effect]

According to the present invention, the pressing force in each axial direction that occurs when the probe is displaced by a unit displacement amount in each axial direction is determined, and the pressing force in each axial direction is calculated from the pressing force per unit displacement and the displacement of the probe in each axial direction. The pressing force of the working stylus is determined, and from this pressing force, the direction ratio of the normal vector at the contact point between the stylus and the surface of the object to be measured can be determined.

Therefore, even in the case of a probe that can detect displacement three-dimensionally with different pressing forces per unit displacement for each axis, the normal vector can be accurately determined, so the contact point between the stylus and the object to be measured can be accurately determined. be able to.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a measuring method using a coordinate measuring machine according to the present invention will be described in detail below with reference to the accompanying drawings.

As shown in FIG. 1, the probe (not shown) when the stylus 30 is brought into contact with the contact point P on the surface of the object to be measured 32
Let the displacement of be xS'l. Further, it is assumed that the pressing force of the stylus 30 on the object to be measured 32 in each axial direction that occurs when the probe is displaced by a unit displacement in each axial direction is kX. From this condition, the forces F, , F, which are applied to the stylus 30 at the contact point P on the object to be measured 32 can be obtained from the following equation.

F, l=, I-x F, =, ·y (In this case, k and k are calculated in advance) The force F applied to the stylus 30 is calculated from the above formula.

, FY are the directional ratios of the normal vector N to the surface of the object to be measured 32 at the contact point P, so the directional cosines λ and μ of the normal vector N are determined by the following equations.

This allows the normal vector to be determined.

This method is characterized by determining the normal vector N of the surface of the object to be measured 32 at the contact point P by converting the displacement XS'l of the probe into the pressing force f, fy of the stylus generated from the displacement. be.

In this way, determining the normal vector is especially essential when measuring points on the surface of an object having a free curve or free-form surface using a stylus of a significant diameter.

Although the above embodiments have been described in terms of two dimensions, the present invention can also be applied to probes that are displaced not only in two dimensions but also in three dimensions.

By the way, when measuring the coordinates of a point on the surface of the object to be measured 32, the shape of the tip of the stylus 30 used for measurement is mostly spherical, and the measured value obtained at that time is the shape of the stylus 300 balls. The center coordinates are C,,C,. Therefore, in order to convert into the value of the contact point P between the stylus 30 and the surface of the object to be measured 32, it is necessary to find the contact point P. In this case, if the normal vector to the surface of the object to be measured 32 at the contact point P is known, the coordinate PNP of the contact point P can be determined by the following equation.

p, =c, -λ・T P, =C, -μ・T As a result, the coordinates of the contact point P can be determined from the measured value of the center coordinates of the stylus 30, and the surface shape of the object to be measured 32 can be measured. be able to.

In the embodiment described above, the coordinates of the contact point P are determined on the condition that the normal vector of the contact point P is known, but if the coordinates of the contact point P are known, the normal vector of the contact point P can also be determined.

〔Effect of the invention〕

As described above, according to the measuring method of the coordinate measuring machine according to the present invention, a logically accurate normal vector can be determined by converting displacement into force. In other words, in a displacement probe, the force generated per unit displacement is generally different for each axis, but with this method, it is logically accurate regardless of whether the force generated per unit displacement is different or not. The normal vector can be found. Therefore, the coordinates of the contact point between the stylus and the object to be measured can be accurately determined.

Further, since the direction ratio of the normal vector can be obtained only by multiplication, the calculation is easy and the calculation time can be shortened.

Therefore, there is an advantage in that the control cycle can be shortened when attempting to control a machine using software using information on normal vectors.

[Brief explanation of drawings]

Figure 1 is a diagram showing the positional relationship in the probe coordinate system when the stylus is in contact with the object to be measured, Figure 2 is an enlarged view showing the state in which the stylus is in contact with the object to be measured, and Figures 3 and 4 are The figure shows a conventional measuring method using a coordinate measuring machine for determining a normal vector. 30... Stylus, 32... Measured object. jI 1 Figure

Claims (1)

[Claims] Coordinate measurement in which a stylus of a probe that is provided in the main body of the measuring device and is capable of three-dimensionally detecting displacement is moved along the surface of the object to be measured to measure the shape, etc. of the object to be measured. In the machine measurement method, the force in each axis direction that occurs when the probe is displaced by a unit displacement amount in each axis direction is determined in advance, and the force per unit displacement and the force applied to the stylus in each axis direction are determined. A measuring method for a coordinate measuring machine, characterized in that a normal vector at the contact point between the stylus and the surface of the object to be measured is determined from the force, and this normal vector is used to measure the shape, etc. of the object to be measured.