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10/09/2021 09:10

CNC machining accuracy is determined by what?

In CNC machining programming, methods and techniques used properly to ensure and improve the machining accuracy of CNC machine tools is of great significance. Then CNC machining accuracy is determined by what? The author has accumulated some programming experience in long-term practice, to share.


CNC machine tools in processing accuracy is determined by the position detection element, position detection element is composed of detection elements (sensors) and signal processing devices, is an important part of the CNC machine tool closed-loop servo system. Its role is to detect the actual value of the position and speed of the table, and send feedback signals to the CNC device or servo device, thus constituting a closed-loop control. The detection element generally uses the principle of light or magnetic to complete the detection of position or speed.


Position detection elements in accordance with the detection method is divided into direct measurement elements and indirect measurement elements. The machine tool for linear movement measurement is generally used when the linear detection element, called direct measurement, the position of the closed-loop control is called full closed-loop control. Its measurement accuracy depends mainly on the accuracy of the measuring element, not affected by the accuracy of the machine drive.

Since the linear displacement of the machine table has a precise proportional relationship with the rotation angle of the drive motor, the distance moved by the table can be measured indirectly by using the method of driving the rotation angle of the detection motor or screw, which is called indirect measurement, and the closed-loop control of the position constituted is called semi-closed-loop control.


CNC machining measurement accuracy depends on the accuracy of the detection element and the machine feed drive chain. Closed-loop CNC machine tool processing accuracy is largely determined by the accuracy of the position detection device, CNC machine tools have very strict requirements for the position detection element, its resolution is usually between 0.001 - 0.01mm or less.


The probability of failure of the detection element is still relatively high compared with the CNC device, often out of the cable damage, component defacement, collision deformation phenomenon. If you suspect that the failure of the detection element to first check whether the cable is broken, defaced, deformed, etc., but also by measuring the output to determine the good or bad detection elements, which requires a good grasp of the working principle of the detection element and the output signal. Here we will give an example, for example, when the detection device failure mechanical oscillation (acceleration / deceleration), what should be done?


1) The pulse encoder is faulty. In this case, check whether the voltage of the feedback line terminal on the speed unit drops at certain points, if there is a drop, it indicates that the pulse encoder is not good, and the encoder should be replaced.


(2) The pulse encoder cross coupling may be damaged, causing the shaft speed to be out of sync with the detected speed, so the coupling should be replaced.


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