Patent ID: 7711453

Claim:
A positioning control system comprising: a disturbance observer for estimating a disturbance from at least one observed value of a controlled object and feeding back an estimated disturbance; and a saturation element disposed in a feedback loop for feeding back the estimated disturbance from said disturbance observer; said feedback loop having a main loop based on an output value of said controlled object, and a minor loop for performing positive feedback based on a predetermined parameter; said saturation element being disposed in said minor loop, the positioning control system further comprising a saturated value changer for changing a saturated value of said saturation element based on a control deviation, wherein said controlled object comprises a cylinder having a seal on a slidable component thereof, and said saturated value of said saturation element has an absolute value that is greater when said control deviation falls outside of the viscoelastic displacement range of said seal than when said control deviation falls within a viscoelastic displacement range of said seal.