Abstract
Though ‘repetitive control’ can provide for significantly accurate operations, its performance in turn degrades dramatically when the reference period is not equal to the dead time in the repetitive controller. This paper proposes, bearing its application to path control in mind, an extension of repetitive control which can adapt itself to dynamical changes in the reference period.
First, the dead time is driven by a PLL circuitry to statically track the reference period. The scheme is then refined by reducing transient errors by
(1) switching the controllers, in which control variable waveforms are previously formed by enough number of repetitions, according to changes in the period,
(2) forcing the state variables, with a feedforward operation, to fit itself to the new period.
Also proposed is a practical scheme for cases where speed changes more than once a cycle. Since the cases cannot enjoy the effect of repetition, the compensator is thus excluded from the loop and repetitive control is made use of offline to form the control variable waveform.
An application of the proposed method is then described: path control of a deburring robot which changes its path speed according to the cutting load. The experimental results show that the accuracy remains same as the case of constant speed.
