Reduction of quantisation noise in position servosystems

The performance of a digital position servo system is analyzed. In particular, the bandwidth limitation due to finite position resolution (or quantization) is discussed. The principal consequences of finite position resolution are: (1) torque pulsation and attendant speed ripple; (2) excessive current ripple leading to additional machine and power converter losses; and (3) acoustic noise in the machine. Two controller structures are presented which minimize these objectionable effects: the oversampling digital filter and the state observer. The oversampling digital filter is proposed as a simple, parameter-free, cost-effective solution. The state observer offers potentially superior performance but is parameter dependent and more complex. Simulation and measurement results are presented for both methods, and potential pitfalls in their implementation are discussed