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What Will Determine the Precision of CNC Machining?

In the preparation of CNC machining programs, proper use of methods and techniques is of great significance to ensure and improve the machining accuracy of CNC machine tools. So what determines the machining accuracy of CNC services?


The machining accuracy of CNC service machine tools is determined by the position detection element


The position detection element is composed of detection elements (sensors) and signal processing devices, and is an important part of the closed-loop servo system of CNC machine tools. Its function is to detect the actual value of the position and speed of the workbench, and send a feedback signal to the numerical control device or servo device, thus forming a closed-loop control. The detection element generally uses the principle of light or magnetism to complete the detection of position or speed.


The position detection element is divided into direct measurement element and indirect measurement element according to the detection method. Linear detection elements are generally used for linear movement measurement of the machine tool, which is called direct measurement, and the formed position closed-loop control is called fully closed-loop control. The measurement accuracy mainly depends on the accuracy of the measuring element and is not affected by the transmission accuracy of the machine tool.


Since the linear displacement of the aluminium CNC service machine tool table has an accurate proportional relationship with the rotation angle of the driving motor, the method of driving the detection motor or the rotation angle of the screw can be used to indirectly measure the moving distance of the table. This method is called indirect measurement. The formed position closed-loop control is called semi-closed-loop control.


The measurement accuracy of CNC service processing depends on the accuracy of the detection components and the machine tool feed transmission chain


The machining accuracy of the closed-loop CNC machine tool is largely determined by the accuracy of the position detection device, and the service CNC machine tools materials has very strict requirements on the position detection element. Compared with the numerical control device, the probability of failure of the detection element is still relatively high, and the phenomenon of cable damage, component contamination, and collision deformation often occurs.


If it is suspected that the detection element is faulty, first check whether the cable is broken, stained, deformed, etc., and can also determine the quality of the detection element by measuring its output, which requires mastering the working principle of the detection element and the output signal. . The following is an example to illustrate, for example, what should be done when the detection device malfunctions and the mechanical oscillation (during acceleration/deceleration)?


(1) The pulse encoder is faulty. At this time, check whether the voltage of the feedback line terminal on the speed unit drops at a certain point. If the voltage drops, it indicates that the pulse encoder is defective, and the encoder should be replaced.


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

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