Causes and solutions of thermal deformation error in CMM

The size of the object varies with the temperature, which is a fixed characteristic. There are two main factors causing thermal deformation error: firstly, the temperature deviation of the measured object and the CMM from 20 0C;Second, the size of the measured object and the performance of the instrument vary with the temperature.For the measured object, the main reason is that its size changes with temperature, that is, it has a non-zero linear expansion coefficient;For CMM, it may be the size change of its structure or its other performance changes, such as the gain of the amplifier changes with temperature.The current of the photocell increases with the temperature.If the CMM has a uniform temperature field and is made of materials with the same linear expansion coefficient, then the CMM only generates simple thermal deformation, and the thermal error generated is equal to the difference between the thermal deformation error of the workpiece and the thermal deformation error of the scale.However, in reality, there is a temperature gradient in the instrument, and the linear expansion coefficient of each part is different, resulting in complex deformation, and for larger workpiece length, the error will be greater.For the grating ruler system, the temperature error is more likely to occur because the glass grating is far from the expansion coefficient of the steel line of the mechanism.The reading head of the grating ruler after a long time of light source irradiation, the temperature will be greatly increased, the reading may appear a great deviation, the actual measurement has been wrong data, therefore, the temperature caused by the error should be given very high attention.In order to solve the above problems, we require that: (1) CMM should be installed in a fixed place, the ambient temperature should not be too high, and the ventilation conditions should be good;(2) In the three-coordinate software, thermal deformation coefficient is used to compensate;(3) After the CMM works for a period of time, the machine should be shut down to cool down, and generally the work should not exceed one hour, and the power supply of the microcomputer should be turned off;In our practical application, if the above points are taken into account, the errors caused by the linear expansion coefficient of CMM data should be controllable under general room temperature conditions.