In NC machining programming, the proper use of methods and skills is of great significance to ensure and improve the machining accuracy of NC machine tools. So what determines the NC machining accuracy? The machining accuracy of NC machine tool is determined by the position detection element, which is composed of detection element (sensor) and signal processing device. It 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 worktable, and send feedback signals to the NC device or servo device, so as to form a closed-loop control. The detection element generally uses the principle of light or magnetism to detect the position or speed.

The position detection element is divided into direct measurement element and indirect measurement element according to the detection mode. When measuring the linear movement of the machine tool, the linear detection element is generally used, which is called direct measurement, and the position closed-loop control is called full closed-loop control. Its measurement accuracy mainly depends on the accuracy of measuring elements and is not affected by the transmission accuracy of machine tools.

Because the linear displacement of the machine tool workbench has an accurate proportional relationship with the rotation angle of the driving motor, the moving distance of the workbench can be measured indirectly by driving and detecting the rotation angle of the motor or lead screw. This method is called indirect measurement, and the position closed-loop control is called semi closed-loop control.

The measurement accuracy of NC machining depends on the accuracy of detection elements and machine tool feed transmission chain. The machining accuracy of closed-loop NC machine tool is largely determined by the accuracy of position detection device. NC machine tool has very strict requirements for position detection elements, and its resolution is usually between 0.001-0.01mm or less.

The probability of failure of detection components is relatively high compared with numerical control devices, and cable damage, component fouling and collision deformation often occur. If it is suspected that it is the fault of the detection element, first check the broken, dirty and deformed wireless cable, and determine the quality of the detection element by measuring its output, which requires mastering the working principle and output signal of the detection element. Let's give an example, for example, what to do when the detection device fails and the mechanical oscillation (acceleration / deceleration)?

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

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