The principle of coordinate measuring needle calibration is analyzed

The principle of coordinate measuring needle calibration is analyzed

The measurement accuracy and efficiency of CMM are closely related to the calibration and selection of measuring needle. Before measurement, the measuring needle must be reasonably selected and calibrated, because the measuring ball of the measuring needle has its own size, and the different directions of the measuring parts may be in contact with the different directions of the measuring ball. Therefore, the measurement data contains the value of the ball itself, and the needle calibration is the process of measuring the size of the ball itself. Especially in the calibration of different length and direction of the measuring needle the sphericity error of the measuring ball calibration results is very important to the measurement results.

1. Measuring needle calibration principle

During the measurement and sampling process, when the measuring needle touches the surface of the measured part, the measuring head system will display the signal as the target signal of the measurement, and then tell the computer the coordinate value of the measured point to collect data.

In addition, because the CMM is measured through the probe system, the obtained point coordinate value is the coordinate value of the center of the probe ball. To obtain the actual size of the workpiece under test, add or subtract the dynamic diameter value of the test ball. After entering the probe calibration procedure, measure the standard ball, measurement method and the ball measurement method in the geometric element measurement procedure - sample. When the number of sampling points reaches the requirement, the measuring program will automatically calculate the measuring points, and the processed probe calibration results will be automatically returned to the probe calibration dialog box interface. When the back button is pressed, the calibrated probe data will be used as a correction for subsequent use data processing. The datum data includes the probe radius and sphericity errors, as well as the coordinates between the center of the probe and the center of the zero probe.

2. The following problems should be paid attention to when calibrating the measuring needle:

(1) Preparation before measurement: according to the measurement scale of the workpiece and the direction and orientation to be measured, first confirm the required measurement needle combination, including the diameter, number and direction of the measurement needle and whether to install the long rod, and try not to replace it in the measurement process.

(2) Detection and calibration: Measuring needle calibration time, the selected measuring needle should be in the axis of the standard ball maximum diameter separation contact measurement, in order to improve the accuracy of needle calibration. Note that the diameter of the calibrated needle and the shape errors during calibration are investigated. If there is a big change, you need to find out why. It is necessary to calibrate more than 6 times, investigate the duplicate data of calibration results, and find out the standard deviation for analysis according to the statistical principle.