Classification of Measuring Methods of CMM

A Coordinate Measuring Machine (CMM) is a device used to accurately measure the geometry of an object. According to different measurement methods, CMM can be divided into the following categories:

1. Contact Probe measurement coordinate measuring instrument (the most commonly used most common);

2. Visual composite coordinate measuring instrument;

3. Laser composite coordinate measuring instrument (mainly used in product measurement and reverse copy scanning).

Among them, the contact measurement method is often used for the measurement of machined products, pressed products, metal films, etc. In order to analyze the workpiece processing data or provide the original information of the workpiece for reverse engineering, it is often necessary to scan the data points on the surface of the workpiece under test by using a coordinate Measuring Machine. The scanning operation of CMM is to use DMIS program to collect data points in a specific area of the surface of the object to be measured, which can be a line, a surface, a section of the part, a curve of the part or a perimeter line at a certain distance from the edge. The measured object is placed in the coordinate measuring space, the coordinate position of each measuring point on the measured object can be obtained, and the geometric size, shape and position of the measured object can be calculated according to the spatial coordinate values of these points. The basic principle is to obtain the discrete spatial point position of the measured geometric element through the coordination of the detection sensor (probe) and the measurement of the spatial axis movement, and then complete the analysis and fitting of the measured points (point groups) through certain mathematical calculations, and finally restore the measured geometric element, and calculate the deviation between it and the theoretical value (nominal value) on this basis. Thus complete the inspection of the parts under test.

The correct use of CMM should pay attention to the following points:

(1) Before fixing the workpiece, the probe should be returned to the coordinate origin to reserve a large space for the fixing position; The workpiece lifting should be smooth, and can not impact any component of the CMM.

(2) Install the parts correctly, and ensure that the isothermal requirements of the parts and measuring machine are met before installation.

(3) Establish a correct coordinate system to ensure that the built coordinate system meets the requirements of the drawings in order to ensure the accuracy of the measured data.

(4) When the program is automatically run, it is necessary to prevent the interference between the probe and the workpiece, so it is necessary to pay attention to increase the inflection point.

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