JPH031602B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a workpiece surface shape measuring method for optically detecting the period of periodic irregularities of a surface shape shown on a workpiece in cutting processing.

Conventionally, various methods have been proposed for determining the periodic component of the unevenness of the surface shape shown on the workpiece, including methods of measuring the surface shape of the workpiece and determining it from the shape signal thereof.

The main method is to measure the cross-sectional shape of the workpiece surface with a stylus-type detector, and then frequency-analyze the electrical output signal using a computer system to determine the periodic component of the surface.

This frequency analysis method using a computer system is not suitable for easily determining the periodic components of the workpiece surface shape at the processing site and using it to judge the quality of the workpiece because the computer system is expensive. .

In view of the above, the present invention is characterized in that the period of irregularities on the surface of a workpiece can be easily measured while the workpiece is installed on a machine tool.

The present invention will be described in detail with reference to the accompanying drawings.

As a result of conducting milling experiments under various cutting conditions and measuring the surface shape of the workpiece, we found the following.

The surface of the workpiece shows irregularities in the pitch of feed marks (marks of cutting edges caused by the amount of table feed per milling cutter blade);
In relation to the phase difference between the spindle rotation period and the spindle system natural vibration period, it is several times the feed mark (often 4 to 5 times).
In some cases, irregularities with a period having a pitch equal to the width of the length are shown.

The unevenness that appears at several times the length of the feed mark is considered to be the effect of vibrations in the mechanical system. If only a feed mark is shown, the surface shape is good, whereas if periodic irregularities several times the length of the feed mark are shown, the surface shape is poor. If periodic irregularities several times the length of this feed mark can be detected during machining,
It is very effective in monitoring defects in workpieces.

For this purpose, we investigated a simple detection method for determining the period of surface irregularities using a light source device that can flicker at an arbitrary period within the range of 1/2 to 1/5 times the table feed rate per blade.

The principle of detection is shown in Figure 1 A, B and Figure 2 A, B.
Shown below. If there is periodicity in the unevenness of the workpiece surface as shown in Figure 1A, if there is a certain relationship with the blinking cycle of the table, the light intensity value at each measurement point will be similar as shown in Figure 1B. Then, the difference in light intensity between adjacent measurement points is determined, the magnitude of the variation is calculated using a microcomputer to determine the standard deviation, and the presence or absence of periodicity is confirmed by comparing the magnitude with a threshold value.

On the other hand, when there is no periodicity as shown in Figure 2A, the change in the light intensity difference between adjacent measurement points is large as shown in Figure 2B, so a certain threshold value should be set for the value of the light intensity difference between adjacent measurement points. Confirm that there is no periodicity.

If the workpiece has periodic irregularities, in order to detect them, it is necessary to match the period of the detected irregularities with the blinking cycle of the light source when the table on which the workpiece is placed moves at a constant speed. be. This includes the number of vibrations transferred to the workpiece by one blade, which is determined from the natural frequency f (Hz) of the machine spindle system, the spindle rotation speed n (rpm), and the number of cutting edges z, which are determined by calculation or measurement.
60・f/(n・z)=N±α (N is an integer, α is a fraction, and is a value related to the phase difference between the spindle rotation period and the spindle system natural vibration period. In the experiment, the value was between 0.1 and 0.5. , and periodic irregularities with a pitch of 1/α x feed mark width are shown on the workpiece.) Using the value of α found from 1/α x feed mark width, set the blinking cycle of the light source from this and the table feed speed. , set value in 1/10 cycle increments of 5/10
Shift sequentially up to the period and check for periodicity. When there is periodicity on the workpiece, if the flickering period of the light source and the period of the irregularities on the workpiece match, the period of the irregularities can be determined from the flickering period value.

The measurement method of the present invention described in detail above eliminates the need for an expensive computer system in the conventional frequency analysis method, and can easily determine the quality of the surface shape of a workpiece at the processing site without contact. Therefore, it can be effectively used as a sensing method for automation technology in cutting.

[Brief explanation of the drawing]

1A and 2B and 2A and 2B are explanatory diagrams of the measurement principle of the present invention, respectively, and FIG. 3 is a configuration diagram of an apparatus for implementing the present invention. 1...Machine tool feed table, 2 ...Work material,
3... Microcomputer, 4... Light source blinking cycle setting device, 5... Reflected light amount detector, 6... Display device, 7... Table feed speed detector.

Claims (1)

[Claims] 1. Detects the cutting feed rate during cutting, and illuminates the workpiece surface by blinking the fiber light source at a cycle of 1/2 to 1/5 of the feed cycle calculated based on the machining conditions and machine vibration characteristics. A method for measuring the surface shape of a workpiece, characterized in that the amount of reflected light on the workpiece is measured, and based on the measured value, the presence or absence of periodic irregularities on the workpiece surface and the value of the period are detected.