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The working principle of three coordinate measuring machine

1. The basic composition and maintenance specifications of the CMM


1. Mechanical system: It is mainly composed of a worktable and a three-axis guide rail. The material is composed of granite with good temperature stability. It adopts air-floating guide rail, DC servo motor, and synchronous belt drive. The air-floating block is suspended on the guide rail, and the distance from the guide rail is very narrow, so pay attention to keeping the guide rail clean. The diameter of the small hole of the air float block is very small, and it is easy to be blocked by the dust in the gas, so it is necessary to ensure the cleanness of the machine's air intake. When loading and unloading the workpiece, pay attention to the guide rail surface not to be scratched or collide with the workpiece.


2. Grating scale and reading head: each axis has a pair, which is a length measuring element, which is a photoelectric element. The dust attached will affect the normal operation. Unless you make a mistake in reading, don't wipe it.


3. Probe system: It is mainly a trigger probe, which is the only part in contact with the workpiece. The probe sensor has a "contact-bias-transmit-response" process every time a point is measured. Severe collision of the probe will result in reduced life or damage, and long-term use will make the probe easy to fatigue and reduce sensitivity.


4. Computer and electrical system: it is a part of machine control and data processing. Mainly pay attention to the loose phenomenon of the plug-in and the stability of the power supply.


 The measuring machine is mainly affected by the following 3 aspects of the external environment:


1. Power supply: This is the most influential part of the electrical system of the machine. Unstable voltage and pollution of the power supply will cause system failure. Therefore, voltage stabilizing equipment with voltage stabilization and filtering functions is needed. UPS uninterruptible power supply is also recommended.


2. Gas supply: In order to prevent the gas from blocking the air flotation block, the gas source must be clean.


3. Environmental vibration, dust, temperature and humidity: vibration will affect the accuracy of the machine when it is working, temperature has a great effect on length measurement, and humidity will cause electrical and mechanical failures!



Principle of Coordinate Measuring Machine


The coordinate measuring machine is a universal digital measuring device based on coordinate measurement. It first converts the measurement of each measured geometric element into the measurement of the coordinate positions of some point sets on these geometric elements. After the coordinate positions of these points are measured, they are calculated by mathematical operations based on the spatial coordinate values of these points. Size and shape error. To measure the diameter of a cylindrical hole on the workpiece, you can touch three points (points 1, 2, 3) on the inner wall of the hole in the section I perpendicular to the axis of the hole, and then calculate according to the coordinate values of these three points The diameter of the hole and the center coordinate OI; if more points are touched in the section (points 1, 2, ..., n, n is the number of measuring points), the section can be calculated according to the least square method or the minimum condition method The roundness error of the circle; if you measure multiple cross-sectional circles perpendicular to the axis of the hole (I, II,..., m, m are the number of measured cross-sectional circles), the cylinder of the hole can be calculated according to the coordinate value of the measured point The position of the hole axis can be calculated according to the coordinate value of the center of each circle and the center coordinates of the circle of each section. If three points are touched on the hole end face A, the position error of the hole axis to the end face can be calculated. It can be seen that this working principle of CMM makes it very versatile and flexible. In principle, it can measure any parameter of any geometric element of any workpiece.