In addition to the positioning error, straightness error, angular motion error and perpendicularity error, the CMM also has errors caused by force deformation, thermal deformation, measuring system, probe system, control system, data recording and processing system:

1. Force deformation error

As a precision measuring instrument, the CMM should have high rigidity, so that the force deformation will not become an important factor affecting the measuring accuracy of the CMM. However, with the acceleration of production rhythm in various industries, the requirements for the efficiency of CMM measurement have also been improved, including higher movement speed and detection speed, which requires its moving parts to be light in weight, but this contradicts with the improvement of component stiffness.

2. Thermal deformation error

To understand the thermal deformation of the CMM, first measure the temperature of the instrument, the measured object and the environment. In order to realize thermal deformation error compensation, it is necessary to stick temperature measuring elements on the three scales and the measured piece, and place temperature measuring elements in the air to check whether the ambient temperature and temperature gradient meet the requirements. Only when the ambient temperature meets the requirements, it is meaningful to test the performance of the measuring instrument, and the measurement accuracy error of the CMM will be greatly reduced. If conditions permit, we suggest you place the instrument in a constant temperature room and control the temperature and humidity in the room.

In order to realize error compensation, in addition to measuring temperature, it is also necessary to know the equivalent linear expansion coefficient of the scale and the measured piece. The so-called equivalent linear expansion coefficient refers to that in the actual machine, it is not only related to the material, but also to the fixing mode. Therefore, the equivalent linear expansion coefficient obtained through actual measurement can better reflect the use state of the scale and the current situation of thermal deformation error, and also conforms to the principle of consistency. Because the same temperature measuring element is used to determine the equivalent linear expansion coefficient and make error compensation, the influence of temperature calibration error of the temperature measuring element is eliminated.

3. Error of measuring head and accessories

The displacement z of the CMM is the sum (external dimension) or difference (internal dimension) of the measured dimension L and the equivalent diameter d of the measuring end, so the calibration of the equivalent diameter of the measuring end is of great significance. The calibration method of the equivalent diameter of the measuring end is to use the measuring head to measure the calibrated standard ball or gauge block. The difference between the instrument movement and the size of the standard ball or gauge block is the equivalent diameter of the measuring end. It should be pointed out that since the elastic deformation of the measuring rod has a great impact on the equivalent diameter of the measuring ball, the equivalent diameter of the measuring end should be recalibrated after replacing the measuring rod, adding an extension rod, connecting the adapter or the rotation angle of the rotary body.