Semi closed loop control of the CNC precision machining: it means that an angular displacement detection device is installed on the axis of the open-loop control servo motor, which indirectly detects the displacement of the moving parts by detecting the rotation angle of the servo motor, feeds back to the comparator of the NC device, compares it with the input command, and controls the moving parts with the difference. The machining accuracy is generally about 0.01-0.02MM.
Closed loop control of the CNC precision machining: it is a direct linear or rotary detection device at the corresponding position of the final moving part of the machine tool, which feeds back the directly measured displacement or angular displacement value to the comparator of the NC device for comparison with the input command displacement, and uses the difference to control the moving part, so that the moving part moves strictly according to the actual displacement. The machining accuracy is generally about 0.002-0.01mm.