Check the needle to pay attention to the problem

Reasons why the calibration value is less than the nominal value:

After understanding the principle of probe calibration, we can easily explain why the needle calibration value is less than the nominal value.

1. Trigger measuring needle is equivalent to lever structure in principle. When touched, the head sensor must be able to trigger (the equivalent of a switch we normally use) in order to send a signal. Because the measuring needle has a certain relation to the standard length, so the ruby ball of the measuring needle needs to run a certain distance after touching the standard ball, so that the sensor triggers the signal. The longer the measuring needle, the greater the distance. Thus, the delay in the touch transmission signal makes the diameter of the fitting sphere less than the sum of the diameters of the ruby sphere and the standard sphere. When the software in the measuring control cabinet subtracts the diameter of the fitting ball from the standard ball (having entered the actual value of the standard ball), the calibrated diameter of the measuring needle is smaller than its nominal value.

2. In the process of contact measurement, the measuring needle will be deformed a little, which increases the delay of the measurement signal, which is also one of the reasons for this phenomenon.

3. When the trigger signal reaches the measuring control cabinet counter, the time required by the head to measure the sensor is fixed. However, during this period, there is a certain relationship between the rate of change of the grating ruler reading and the rate of change of the three standard measuring instruments. When the touch speed is faster, the calibration diameter of the measuring needle is smaller. Conversely, when the touch speed is slower, the calibration diameter of the measuring needle is larger. This is why we usually have to measure the speed and the speed of the needle to measure the same reason the speed has been calibrated

Problems to pay attention to when checking the needle:

The calibration diameter of the needle after calibration is smaller than the nominal value, which will not affect the measuring accuracy of the three standard measuring machines. Instead, it will compensate for the touch delay and deformation of the measuring needle because we are correcting the radius of the ruby ball using CMM measuring software (converting the coordinates of the center point of the ruby ball to the coordinates of the contact point) using the correction diameter instead of the nominal diameter.

When measuring the needle, the following problems should be paid attention to:

1. Measuring base. Head (sensor). Extension rod. Measuring needle. Standard ball shall be installed reliably. Firm, not loose, measuring base. Head (sensor). Extension rod. The measuring needle should not have gaps. Check the safe installation of the measuring needle. After the standard ball is firm, the fingermark and dust on the measuring needle and the standard ball should be wiped, and the measuring needle and the standard ball should be kept clean at any time.

2. When verifying the measuring needle, the measuring speed should be consistent with the speed of the measuring parts. After inspection, observe the diameter of the measuring needle (check whether there is a large deviation from the previous configuration) and check the shape error. If the verification has changed greatly, find out the cause or clean the standard ball and measuring needle. Repeat the calibration 3 to 4 times, observe the duplicate data of the verification results, and check the probe. Measure the needle. Whether the standard ball is firmly installed, but also check the working state of the machine.

3. When multiple needle angles are needed. When checking the position of different measuring needle lengths and measuring needle, the calibration effect must be checked after calibration. The method is: after all the defined measuring needles are calibrated, use the function of the measurement for the standard ball, measure the standard ball with all the calibrated measuring needles, and observe the measurement change of the spherical center coordinates. If there is a change of 1 to 3 microns, it is normal. If the change is significant, recheck the seat. Probe. Extension rod. Measuring needle. Whether the installation of the standard ball is firm is whether the installation of the standard ball is firm, measuring the needle and the handprint and dust on the standard ball.

4. Replace the measuring needle (different CMM has different measuring methods), because the length of the measuring needle is an important parameter for the automatic verification of the measuring head, if there is an error, it will cause abnormal contact collision of the measuring needle, light damage to the measuring needle, heavy damage to the measuring head (sensor).

5. Input the actual diameter of the standard ball correctly. As can be seen from the principle of the verification measuring needle described above, although this is a small generalization, the diameter of the standard ball directly affects the verification value rate event of measuring the gemstone ball, but it is also possible for beginners.