JPS60233512A - Method for detecting angle with high accuracy in measuring three-dimensional coordinate value - Google Patents

Abstract

PURPOSE:To detect an angle with high accuracy by reducing friction in a contact point of a measuring ball and an object to be measured, which occurs when an automatic approach function of a profile machine tool has been used. CONSTITUTION:A measuring ball 12 is approached to an object to be measured automatically by fixing one shaft of X, Y and Z shafts, displacement quantities Ex, Ey and Ez of a measuring point T are read, and a direction vector of reaction from the inclined surface of the measuring point T by an internal operation of an NC, but due to the presence of a frictional force (f), the reaction turns to the N direction. Subsequently, the measuring ball 12 is separated from an inclined surface 11, and simultaneously moved by a triaxial NC automatic feed. Next, the measuring ball 12 is positioned simultaneously at an approach end point by the triaxial NC automatic feed, displacement quantities E'x, E'y and E'z are read again, a direction vector of a reaction from the inclined surface 11 in this state is derived, and the measuring ball 12 is moved along its direction vector until it is separated from the inclined surface 11. In this way, displacement quantities of the approach end point by the measurment of said two times are compared, the measuring procedure is repeated until its difference enters prescribed range, an angle of a contact point in the final time point is derived, and a coordinate of the contact point is calculated.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to an angle detection method for measuring the coordinate values of a three-dimensional free-form surface. This is an angle detection method that performs highly accurate angle detection by reducing the friction at the point of contact between the measuring ball and the object to be measured that occurs when using the automatic approach function of .

Regarding conventional technology, the recent trend is that demand is changing from cutting to molding, and moreover, higher precision and shorter delivery times are required. Among molding processes, it is particularly difficult to measure the highly accurate outer shape of a mold with a three-dimensional free-form surface using anything other than a three-dimensional measuring machine. However, three-dimensional measuring machines are expensive, and many small and medium-sized mold manufacturers cannot afford them.

Based on the above circumstances, we investigated the possibility of high-precision measurement on the machine using a simple tracer on a copying machine tool. The three-dimensional coordinate measurement principle of a known copying machine tool uses a single-axis fixed automatic approach function to approach the object to be measured, and then calculates the measurement sphere and surface to be measured from the vector of the resultant displacement of the measurement at the end point of the approach. Calculate the angle at the contact point, and calculate the coordinates in the x, ySz axis direction at the end of the approach,
Based on the measured sphere diameter and the angle obtained by calculation, x, y
, the coordinates in the z-axis direction are corrected to obtain the coordinates of the contact point between the object to be measured and the measurement sphere.

FIG. 1 is a plane cut along a plane including the center of the measurement sphere (0) and the point of contact (T) between the object to be measured (2) and the measurement sphere (1). In Figure 1, the measurement sphere (1) is fixed at the X and Y axes and
The ball descends in the axial direction and first contacts the object to be measured (2) at point T', and the ball center position at this time is set to 0'. Furthermore, measuring ball (1)
continues its approach, descends to the virtual sphere center □l l, and stops. In reality, by contacting the object to be measured, the center of the measurement sphere moves to point 0 on the normal line of the surface of the object to be measured including the contact point T. 5 is the displacement corresponding to the diameter of the measurement sphere, and o o'' is detected as the actual displacement of the measurement sphere.The coordinates of the virtual sphere center point 0° are expressed as (X,
Y, Z), to calculate the coordinate values of the contact point T between the measurement sphere and the object to be measured, from (X, Y, Z''), the correction amount shown in the shaded area (Hx, Hy, Hz).The correction amount can be determined by Hz=R・□−Ex +Ey +Ez, where R is the radius of the measurement sphere.

However, ExsDisplacement in the X-axis direction EyrDisplacement in the Y-axis direction EzsDisplacement in the Z-axis direction Figure 2 shows the basic structure of the tracer head that satisfies the above performance, and the measurement sphere is normal to the smooth surface to be measured. To displace and stop the measurement sphere in the three-dimensional direction,
It is necessary to have equal displacement-load characteristics (spring constant) in the x, y, and z directions.

In FIG. 2, the measuring sphere (1) is supported by a plurality of cylindrically distributed elastic ribbons (3) and a flange (5) at right angles thereto. The elastic ribbon ensures movement in the XY plane, and the linear ball (6) between the flange and the tracer axis (8) ensures movement in two axes, and the tracer axis always maintains a vertical direction and is elastically displaced in parallel. It is a mechanism. Displacement detection is xS
Differential transformers (7) are provided in each of the y- and z-axis directions for detection. (4) is a weight adjuster.

By the way, in the needle side method described above, as shown in FIG. 3, the simultaneous one-axis automatic approach function of the copying machine tool is used to detect the angle θ and calculate the coordinates of the contact point. In this simultaneous 1-axis automatic approach, the measuring ball (1) comes into contact with the object to be measured, and while inputting the axial displacement Ex, Ey, Ez, the measuring ball (1)
moves along the object to be measured, and the resultant displacement (E=Ex2+
The process ends when Ey2+Ez2) reaches the set value. However, at this time, the object to be measured and the measuring ball (1
) Due to the influence of the frictional force (f) between the measurement ball (1) and the object to be measured, the drag force (N) caused by the object to be measured does not point in the normal direction of the surface at the measurement point (T). For this reason, the axial displacement (Ex, By, Ez
) is different from the actual value, and an error proportional to the diameter of the measurement sphere intervenes in the coordinates of the measurement point in which this angle is involved.

Purpose of the Invention The present invention uses a tracer of a copying machine tool to eliminate the influence of frictional force between a measurement ball and a measured object, improve angle detection accuracy, and perform highly accurate three-dimensional coordinate value measurement. That's true.

200 Invention Structure This invention uses a copying machine tool having an automatic approach function and a simultaneous 3-axis control function, performs an automatic approach with one axis fixed, and calculates the contact point from the object to be measured from the displacement amount at the automatic approach end point. The first measurement procedure involves determining the direction vector of the drag force and then moving the measuring ball in the vector direction using simultaneous 3-axis NC automatic feeding until the measuring ball and the object to be measured are completely separated; Position to the end point of the previous approach, read the displacement again, determine the direction vector of the drag force from the object to be measured, and then use simultaneous 3-axis NC automatic feed to completely separate the measuring ball from the object in the direction of that vector. A second measurement procedure in which the measuring ball is moved up to the point where the displacement amount at the end of the previous approach and the amount of displacement at the end of the current approach are compared until the difference falls within a certain range. A third measurement procedure takes in the amount of displacement at the end of the final approach, and an internal calculation of the NC calculates the angle of the contact point from the amount of displacement at the end of the final approach obtained in the third measurement procedure. , and a fourth measurement procedure of calculating the coordinates of the contact point based on the requested angle and the measurement sphere diameter.

E. In Examples 4 to 8, the shaded area is the measurement slope (11
), the circle indicates the measurement sphere (12) of the copying machine tool, the dashed-dotted line (C) indicates the surface normal at the measurement point (P), and the arrow (
D) indicates the direction of movement of the measuring ball, and arrow (N) indicates the direction of the drag force based on the calculation result.

Hereinafter, the angle detection method in three-dimensional measurement according to the present invention will be explained with reference to FIGS. 4 to 8.

First measurement procedure: The measurement ball (12) is automatically approached to the object to be measured with the -axis fixed among the x, y, and z axes, and the displacement E at the end point of the automatic approach, that is, the measurement point (T) is measured. ” ,'E
y % E z is read and the direction vector of the drag force from the slope at the measuring point (T) is determined by internal calculation of the NC (Figure 4). Theoretically, the direction vector of the drag force determined by this calculation should point in the direction of the T-0 line in Figure 1, but in reality, due to the presence of frictional force (f), the direction vector of the drag force Slightly counterclockwise from the normal at (T), for example, arrow (
N) (Figure 5). Therefore, the measurement ball (12) is placed in the direction of the direction vector of the above-mentioned drag force by calculation.
The measurement ball (12) is moved by simultaneous 3-axis NC automatic feed by a distance that completely separates the ball and the slope (FIG. 6).

2nd measurement procedure Simultaneous 3-axis NC to the approach end point determined in the 1st measurement procedure
Position the measuring ball (12) by automatic feed (Fig. 7), read the displacement Ex', Eyl, Ez'' again,
In this state, the direction vector of the drag force from the slope is determined, and then the measurement ball (12) is moved along the direction vector of the drag force by simultaneous three-axis NC automatic feed until the measurement ball (12) is completely separated from the slope.

Third measurement procedure The amount of displacement at the approach end point according to the first measurement procedure and the second
The second measurement procedure is repeated until the difference is within a certain range (FIG. 8).

Fourth measurement procedure The third measurement procedure captures the amount of displacement at the end of the final approach, and calculates the angle of the contact point by internal calculation of the NC. Then, the coordinates of the contact point are calculated from the determined angle and the measured sphere diameter.

9 Effects of the Invention In the first to fourth measurement procedures described above, the third measurement procedure reduces the friction caused by the approach direction,
It becomes possible to bring the drag force from the slope closer to the surface normal direction of the contact point.

The present invention can be applied not only to measurement using a tracer of a copying machine equipped with a simultaneous three-axis control function and an automatic approach function, but also to an analog three-dimensional coordinate measuring machine.

[Brief explanation of the drawing]

Figure 1 shows the actual three-dimensional coordinate measurement using the tracer of a copying machine tool, Figure 2 shows the internal structure of the tracer, and Figure 3 shows the force relationship between the measuring ball and the slope at the end point of the automatic approach. 4 to 8 are explanatory diagrams of the measurement procedure of the present invention. (11) -Measuring slope, (12)--Measuring sphere, (T)
- Measurement point, (N) - Surface normal at measurement point (T). 1st WJ 1 (1000th Figure 8)

Claims (1)

[Claims] (11 Using a copying machine tool with automatic approach function and simultaneous 3-axis control function, perform automatic approach with one axis fixed, calculate the direction vector of the drag force from the slope of the contact point from the displacement amount at the automatic approach end point, Next, the first measurement procedure involves moving the measuring ball in the vector direction using simultaneous 3-axis NC automatic feeding until the measuring ball and the slope are completely separated, and positioning to the previous approach end point using simultaneous 3-axis NC automatic feeding. A second measurement procedure in which the amount of displacement is read again, the direction vector of the drag force from the slope is determined, and then the measurement ball is moved in the direction of the vector by simultaneous three-axis NC automatic feed until the measurement ball and the slope are completely separated; Compare the amount of displacement at the end of the previous approach with the amount of displacement at the end of this approach, repeat the second measurement procedure until the difference is within a certain range, and calculate the amount of displacement at the end of the final approach. The angle of the contact point is determined by the internal calculation of the NC from the third measurement procedure to be imported and the displacement amount at the end of the final approach obtained in the third measurement procedure, and the angle of the contact point is determined based on the requested angle and the measurement sphere diameter. A highly accurate angle detection method in three-dimensional coordinate value measurement comprising a fourth measurement procedure for calculating the coordinates of a contact point.