Limit cycle characterization, existence and quenching in the control of a high performance hydraulic actuator

The characteristics and the nonlinear dynamics of a high performance hydraulic actuator produced by ASI Inc. are described and modeled. When a feedback is applied for the regulation of output force, a limit cycle is observed. The existence of the limit cycle can a priori be attributed to one, or to a combination of, the four dominant nonlinear effect that were identified in these actuators. In order to pinpoint its origin, successive approximations are made to apply the describing function principle, so as to predict the onset of the limit cycle as function of the feedback gain. Given the experimental data, this method allows us to attribute beyond any doubt its origin to the electromagnetic hysteresis in the valve, which is based on jet-pipe technology. A multiple term lead-lag controller is designed and implemented to quench the limit cycle and improve the rise time of the force control by more than an order of magnitude