What are the roundness measurement methods of the image measuring instrument?

What are the measurement methods of roundness of the image measuring instrument? Roundness is the shape error in geometric tolerances. In addition to the roundness meter, there are many roundness measurement methods, such as the two-point method, the V-block method and the universal display method. However, these methods have too few points, the measurement results are not strict enough, and the data processing is cumbersome. Even with a roundness meter, it is impossible to measure larger workpieces. Single-point measurement: As some discrete points are obtained, a single-point touch method is used for calculation and evaluation using the smaller square method. When calculating with the smaller square method, the sampling points are usually even numbers and the average value is taken. When using the single-point method for roundness measurement, the number of sampling points should not be too small, otherwise the true situation of roundness cannot be reflected. Generally, if you want to grasp a tighter shape, you can reflect the basic contour shape of the measured circle after 16 o'clock. The number of measurement points can be increased, such as 24, 32, etc. Automatic measurement is usually used for sampling, because manual sampling is inconvenient to control the vector direction. The single-point touch measurement method is characterized by high measurement efficiency and low wear on the ball. Scanning measurement: If you want to master the complete shape, you can use the scanning method. When scanning, you can obtain a complete outline and evaluate it using the smaller contained area method. The scanning method is characterized by slightly lower efficiency, but it can analyze the contour of the part in detail. Both of these methods can accurately measure roundness and can be selected according to actual requirements. The influence of surface roughness on roundness error: Surface roughness has a great influence on roundness error. According to the characteristics of roundness, the surface roughness and waviness of roundness should be removed. The method is to use filtering in the roundness meter. In the middle, it is equipped with a dedicated electronic filter and set some cut-off frequencies, such as 1 to 15, 1 to 45, 15 to 450 cycles/revolution, etc., indicating the number of sine waves that appear per revolution. Among the three coordinates, the corresponding coordinates are also provided. The digital filter instruction performs the same function, and the frequency is represented by the measurement point. The purpose of selecting the cutoff frequency is to suppress the surface roughness and waviness of the higher harmonic components. The cut-off frequency is mainly selected according to the process requirements, that is, whether the influence of surface roughness and waviness on the part is important. Generally speaking, when it is necessary to analyze the components of roughness, the image measuring instrument usually takes 15 and chooses a wider cut-off frequency, such as 50, 150, 500, etc.