Abstract
The position control arithmetic is crucial to the rapidity, stability and accuracy of CNC system. After analyzing the shortcoming that the conventional PED position controller only is difficult to eliminate system steady-state error, the feedforward control in position controller is researched in detail. If the speed feedforward coefficient and acceleration feedforward coefficient can be computed exactly, the feedforward control approach can remarkably minish steady-state tracking error, enhance servocontrol precision and not change the primary servosystem stability. A nonlinear PED position controller model is developed subsequently to overcome the shortcoming of conventional linear PED position controller which is difficult to obtain rapid response and satisfied overshoot at the same time in the paper, where the expression of proportional control quantity U <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> , the integral control quantity U <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</sub> , and the differential control quantity U <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> is adjusted automatically along with the tracking error variation. The control simulation shows that the developed nonlinear PID position controller can reduce the overshoot to zero, get rapid response and enhance the tracking performance of the CNC system in the meantime. The conclusion is significant to high speed and high accuracy CNC machining.
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