JPH03261817A - Controlling method for stylus of coordinate measuring machine - Google Patents

Abstract

PURPOSE:To realize measurement with a fixed measuring pressure even when a stylus is flexible by obtaining the displacement of a probe in a direction of each axis of a probe coordinate system when the probe is shifted a predetermined amount because of the reaction in the direction of each axis. CONSTITUTION:In the case of profiling measurement, the scalar when the force obtained by combining the reaction force generated in a direction of a normal vector to the surface of an object 22 to be measured and the frictional force generated when a stylus 20 traces the surface of the object 22 is represented by a vector is used as the force F acting on the stylus 20. Moreover, the directional cosine of the combined force is used as direction cosines lambda, mu. In order to put the object 22 in contact with the stylus 20 at a contact point P with the measuring force F, a zero point of the probe is controlled so that the displacements xd, yd of the probe becomes the value expressed by a formula when Ku, Ky are constants. Accordingly, even a flexible stylus can measure with the constant measuring pressure.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for controlling a stylus capable of three-dimensionally detecting displacement of a coordinate measuring machine, and in particular, the present invention relates to a method for controlling a stylus capable of three-dimensionally detecting displacement of a coordinate measuring machine. The present invention relates to a stylus control method for a coordinate measuring machine that moves along a surface to determine the coordinates or shape of an object to be measured.

[Conventional technology]

Generally, when measuring the coordinates or shape of the object to be measured,
A stylus provided on the probe is moved while pressing against the surface of the object to be measured, thereby measuring the surface shape of the object to be measured.

[Problem to be solved by the invention]

However, in a probe that can detect displacement three-dimensionally in -a, the force generated per unit displacement differs depending on the axis of displacement, so as shown in FIG. Even if you try to touch it, the object to be measured 12
The problem is that the stylus lO is slid and positioned at a point P' where the force resulting from the displacement of the probe and the normal to the surface of the probe are balanced, which causes a deviation from the surface to be measured, resulting in a measurement error.

Furthermore, if the stylus 10 has a large deflection per unit force, it is not possible to control the force applied to the object to be measured 12 or the absolute displacement of the probe, and especially in the case of scanning measurement, it is difficult to control the scanning direction. There may be a problem that it cannot be done.

Furthermore, if the coordinate system of the measurement device body (for example, a coordinate measuring machine) to which the probe is attached is not parallel to the coordinate system of the probe, it is necessary to install the probe and the coordinate system of the device body to which it is attached mechanically parallel. The problem may arise that there is.

The present invention has been made in view of the above circumstances, and it is possible to position a stylus at a predetermined position on the surface of an object to be measured, and even in the case of a stylus that is easily bent, it is possible to control the scanning direction especially in scanning measurement. To provide a stylus control method for a coordinate measuring machine, which can measure an object to be measured even if the coordinate system of a measuring device main body to which a probe is attached and the coordinate system of the probe are not kept parallel. With the goal.

[Means to solve problems]

In order to achieve the above object, the present invention moves a stylus of a probe that is movably provided on the main body of a measuring device and is capable of three-dimensionally detecting displacement along the surface of the object to be measured. In a measurement method for measuring the shape, etc. of a body, the transformation matrix from the body coordinate system to the probe coordinate system given in advance and the direction of the body coordinate system of the normal to the surface of the workpiece at the point of contact between the workpiece surface and the stylus. Based on the cosine value, convert the direction cosine value of the normal line to the direction cosine value in the probe coordinate system, and then calculate the per unit displacement of the probe acting in each axis direction of the probe coordinate system given in advance. Based on the pushing force of Based on the balance condition and the value of the direction cosine of the normal line of the probe coordinate system, the reaction force in each axis direction of the probe coordinate system is determined, and from the reaction force in each axis direction, the reaction force of the probe in each axis direction of the probe coordinate system is calculated. The method is characterized in that the amount of displacement is determined and the probe is moved based on the determined amount of displacement of the probe.

[Effect]

According to the present invention, the value of the direction cosine in the body coordinate system of the normal to the workpiece surface at a predetermined fixation point between the workpiece surface and the stylus is converted into the direction cosine value in the probe coordinate system. Next, calculate the pressing force of the stylus acting in each axis direction of the probe coordinate system when the probe is displaced by a predetermined amount, and calculate the balance condition between this pressing force and the reaction force that the stylus receives from the surface of the object to be measured, and the probe coordinates. The reaction force in each axis direction of the probe coordinate system is determined based on the value of the direction cosine of the normal to the surface to be measured in the system, and the probe coordinate system when the probe is displaced by the predetermined amount from the reaction force in each axis direction is calculated. The displacement of the probe in each axis direction can be determined.

Therefore, by moving the probe based on the determined displacement of the probe, misalignment of the stylus can be prevented.

In addition, based on the determined displacement of the probe in each axis direction, the movement of the probe can be controlled so that the measurement pressure generated from the displacement of the probe remains constant, so the measurement pressure can be kept constant even with a stylus that is easily bent. be able to.

Furthermore, the amount of deflection of the stylus in each axis direction of the probe coordinate system when the probe is displaced by a predetermined amount is determined, and the center coordinates of the stylus in each axis direction of the probe coordinate system are determined from this amount of deflection and the predetermined amount of displacement. Based on the given transformation matrix from the body coordinate system to the probe coordinate system, the zero points of all axes of the probe can be found in the body coordinate system, so the probe coordinate system becomes parallel to the body coordinate system. It is necessary to arrange it like this.

〔Example〕

Preferred embodiments of the stylus control method for a coordinate measuring machine according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows the relationship between the coordinate system 0-X, IYIl of the measuring device main body (hereinafter referred to as "main body"), not shown, and the coordinate system c-xy of the probe (not shown).

First, the displacement of the probe without causing displacement of the stylus 20 is determined.

Here, assuming that the following information (1) to (6) is given in advance, (1) A transformation matrix for the coordinate system OXXYN of the main body to the coordinate system c-xy of the probe: M (2) The main body The coordinates of the point of contact P between the stylus 20 and the surface of the object to be measured 22 in the coordinate system o - x, y: Xp
% Vp (3) Directional cosine of the normal to the surface of the object to be measured 22 at the contact point P: λ1, μ.

(4) Crab k generated per unit displacement in each axis direction of the probe
Xk.

(5) Amount of deflection of the stylus 20 per unit force on each axis of the probe: ρ8 ρ.

(6) Radius of stylus 20: "In FIG. 1, the zero points of all axes of the probe are controlled to be positioned at point C (xc yc) in the body's coordinate system ox, y.

In addition, the stylus 20 is connected to the contact point P on the surface of the object to be measured 22.
When they touch, the center coordinates of the stylus 20 are Xs, yi
Now, if the displacement of the probe that occurs when the zero point of the probe is positioned at point C on the device is Xd, y, then the forces F,, F, that occur in each axis direction of the probe coordinate system C-XY are , (However, F-, high77 lower 717n-) The displacement of the probe from above is Xa'Jd.

Furthermore, the direction cosine of the normal line to the surface of the object 22 at the contact point P on the surface of the object to be measured 22 is expressed as the probe coordinate c-
It can be converted into direction cosines λ and μ in xy.

It can be expressed as.

In the case of scanning measurement, the force F applied to the stylus 20 is
Substituting the sum of the reaction force generated in the direction of the normal vector of the surface of the object to be measured 22 and the frictional force generated when the stylus 20 traces the surface of the object to be measured 22 expressed as a vector, Moreover, the direction cosine of the vector of the synthesized force may be substituted for λ and μ.

From the above, in order for the object to be measured 22 and the stylus 20 to come into contact at the contact point P with the measurement pressure F, the probe displacement X
The device may be controlled so that the zero point of the probe is located at the position where ds yd becomes the value determined by equation (4).

As described above, according to the present invention, the object to be measured 22 and the stylus 20 can be moved along the surface of the object to be measured 22 at the contact point P so that the stylus 20 does not become misaligned.

Next, in the case of control to keep the absolute displacement d of the probe constant,
From equation (4), the direction cosine of the displacement vector of the probe in each arm radius λ6, μm in the coordinate system c-xy of the probe is as follows.

Here, since a=,G;7-]7=constant, the probe displacements xd and yd may be positioned as follows.

Thereby, even with a stylus that is easily bent, measurement can be performed under uniform conditions with a constant measurement pressure or a constant probe displacement.

Next, the relationship between the body coordinate system ox, y and the zero point C of the probe coordinate system c-xy is determined.

When displacements X,1, V' occur in the probe, the amount of deflection B, , By of each axial direction of the stylus 20 in the coordinate system c-xy of the probe is as follows.

Therefore, the center coordinates Xs, ys' of the stylus 20 in the coordinate system c-xy of the lobe can be calculated using equation (4) or (
6) and equation (7), and therefore, the zero point of the probe is 3' to the coordinate XC of the point C at the seat aOXM Yll of the device to be positioned.
c is calculated by ).

This eliminates the need to arrange the probe in the device so that the coordinate system of the probe is parallel to the coordinate system of the main body.

Note that the stylus control method for a coordinate measuring machine according to the present invention can be applied to both point-to-point measurement and scanning measurement.

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

〔Effect of the invention〕

As described above, according to the stylus control method for a coordinate measuring machine according to the present invention, the stylus can be positioned without positional deviation even if the forces generated per unit displacement differ in each axis of the probe. Therefore, the point of contact between the stylus and the object to be measured can be controlled, and especially when measuring the cross section of a three-dimensional shape, the point of contact can be controlled so that the point of contact always exists on the cross section.

Furthermore, even a stylus that is easily bent can be measured under uniform conditions with a constant measurement pressure or constant probe displacement.

Furthermore, since the zero points of all axes of the probe's coordinate system can be determined, it is not necessary to attach the probe to the apparatus so that the probe's coordinate system is parallel to the coordinate system of the main body.

[Brief explanation of drawings]

Figure 1 shows the relationship between the body's coordinate system and the probe's coordinate system when the stylus is in contact with the surface of the object to be measured, and Figure 2 shows the relationship between the stylus and the probe's surface in the probe's coordinate system. FIG. 3 is a diagram showing a state in which a conventional stylus moves on the surface of an object to be measured when the pressing force of a conventional stylus is not equal in each axial direction. 10.20...Stylus, 12.22...Object to be measured.

Claims (4)

[Claims] (1) In a measurement method in which a stylus of a probe that is movably attached to 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. , based on the transformation matrix from the body coordinate system to the probe coordinate system given in advance and the value of the direction cosine of the body coordinate system of the normal to the object surface at the point of contact between the object surface and the stylus. The value of the direction cosine of the line is converted to the value of the direction cosine in the probe coordinate system, and then the probe is Determine the pressing force acting on the stylus in each axis direction of the probe coordinate system when the stylus is displaced by a predetermined amount, and determine the balance condition between the pressing force of the stylus and the reaction force that the stylus receives from the surface of the object to be measured, and the method of the probe coordinate system. Based on the value of the direction cosine of the line, find the reaction force in each axis direction of the probe coordinate system, find the displacement of the probe in each axis direction of the probe coordinate system from the reaction force in each axis direction, and calculate the probe displacement in each axis direction of the probe coordinate system. A stylus control method for a coordinate measuring machine, characterized in that a probe is moved based on the amount of displacement of the coordinate measuring machine. (2) The coordinate measuring machine according to claim (1), wherein the movement of the probe is controlled so that the amount of displacement of the probe is constant based on the determined displacement of the probe in each axial direction. Stylus control method. (3) The coordinate system according to claim (1), wherein the movement of the probe is controlled based on the determined displacement of the probe in each axial direction so that the measured pressure generated from the displacement of the probe is constant. How to control the stylus of the measuring machine. (4) Determine the amount of deflection of the stylus in each axis direction of the probe coordinate system when the probe is displaced by a predetermined amount, and determine the center coordinates of the stylus in each axis direction of the probe coordinate system from the amount of deflection and the predetermined amount of displacement; The coordinate system according to claim 1, characterized in that zero points of all axes of the probe are determined in the body coordinate system based on the center coordinates and a conversion matrix from the body coordinate system to the probe coordinate system given in advance. How to control the stylus of the measuring machine.