A precise speed tracking control of ultrasonic motors via sampled-data H∞ control

In this paper we consider synthesis problems for precise speed control systems of ultrasonic motors. In the previous work, it has been empirically known that in continuous-time H_∞ control based synthesis, conservative evaluation of modeling error is needed to avoid speed fluctuation in high frequency range. However, this conservativeness should be reduced unless the speed fluctuation in high frequency range occurs, since too large conservativeness causes tracking performance degradation in low frequency range. In this paper, it is shown that desirable control experiment results are directly obtained by sampled-data H_∞ control synthesis without such conservativeness in modelings.