The head correction of CMM is the basis to ensure the measurement accuracy. The main factors causing errors in the process of head correction are: the bending deformation of the rod, the contact position and force during head correction. The smaller the force measurement is, the lower the accuracy is. Certain force measurement and velocity measurement should be selected for correction, and the appropriate detection distance should be selected to ensure the correction accuracy.
The verification probe is based on two main reasons.
(1) When CMM measures parts, the end of the measuring needle installed on the measuring sensor is a gemstone ball. After the ball contacts with the surface of the measured part, the measuring signal is triggered. Trigger signals after motion control
The machine sends the current coordinates of the machine to the measuring software, then converts the machine coordinates to the measuring center, and finally offsets the measuring radius according to the touching direction to obtain the correct measuring point coordinates is an important function of the geometric measuring machine software, which can accurately correct the measuring sphere radius value. Due to the error of probe radius size and mounting size, the accuracy of the measuring point may be affected, so the measuring system needs to correct the actual measuring needle radius through the probe verification step.
(2) In the measurement process, it is usually necessary to configure measuring needles with different angles, lengths and diameters to measure different geometric elements. You have to measure these different points
Only through the corresponding transformation can the correct result be calculated under the same coordinates. Because the long rod, sensor and measuring needle will inevitably bring installation errors in the installation process, it is necessary to verify the real position relationship between different probe angles through the probe, so that the software system can be accurately converted.
I. Purpose of probe correction:
a. Obtain the position relationship between the angles of the probe
b. Why the equivalent diameter of the measuring needle is less than the nominal value:
Triggering can only be triggered after contact.
The count lock time after triggering.
The inertia of the measuring machine when it stops.
Measure needle deformation.
The longer the measuring needle, the smaller the equivalent diameter.
C. Calibration probe position:
By using the standard ball to take its spherical coordinates, the relation matrix between different probe positions is obtained, and the elements measured at different probe positions are converted into probe positions.
Measuring points of more than three layers are used to correct the measuring needle.
Check the probe position correction, measure the spherical center of the same ball with each corrected measuring needle, and observe the change of spherical center coordinates.
Three. How to check the probe correction results:
a. Check whether the equivalent diameter of the needle is smaller than the nominal value
b. Check whether the corrected form value is less than 2 microns (actually depends on the machine accuracy)
c. Measure the standard spherical center from different angles to see if there is deviation. Generally, the main check is whether there is deviation ab and the two items must be met at the same time before measurement
4. Factors affecting probe correction results:
a. Environmental factors: temperature, humidity, vibration source, dust
b. If there are foreign bodies in standard ball or ruby, it can be wiped with fine cotton and re-corrected
c. The standard ball and measuring needle are loose
d. The hardware of the machine itself has problems such as air float bearing blockage, loose transmission and electrical reasons.
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