In the programming of cnc machining, the proper use of methods and techniques is of great significance to ensure and improve the machining accuracy of NC machine tools.So what determines CNC machining accuracy?The machining accuracy of NC machine tool is determined by the position detection element, which is composed of the detection element (sensor) and signal processing device and is an important part of the closed-loop servo system of NC machine tool.Its function is to detect the actual value of the position and speed of the table, and send feedback signal to the CNC 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 velocity.The position detecting element is divided into direct measuring element and indirect measuring element according to the detecting method.Linear detection element is generally used in linear motion measurement of machine tools, which is called direct measurement, and the position closed-loop control constituted by it is called full closed-loop control.The measuring precision mainly depends on the measuring element precision and is not affected by the machine tool transmission precision.Since the linear displacement of the machine tool table has a precise proportional relation with the rotation Angle of the drive motor, the method of driving to detect the rotation Angle of the motor or lead screw can be used to indirectly measure the moving distance of the table. This method is called indirect measurement, and the position closed-loop control formed by it is called semi-closed-loop control.The measurement precision of NC machining depends on the precision of the measuring element and the feed chain of the machine tool.The machining accuracy of closed-loop NC machine tools is largely determined by the accuracy of the position detection device. Nc machine tools have very strict requirements on the position detection elements, and their resolution is usually between 0.001 — 0.01mm or less.The probability of failure detection components compared with the NUMERICAL control device is still relatively high, often report cable damage, component fouling, collision deformation phenomenon.If it is suspected that the fault of the detection component should first check whether there is cable broken, dirt, deformation, etc., you can also measure its output to determine the quality of the detection component, which requires a good command of the working principle of the detection component and output signal.Here are some examples of what to do when, for example, a device is failing to detect mechanical oscillations (acceleration/deceleration).
1) Failure of pulse encoder.At this point, check whether the voltage of the feedback line terminal on the speed unit drops at certain points. If any drop indicates that the pulse encoder is defective, 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. The coupling should be replaced.
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