Study of limit cycle in antagonistically coupled magneto-rheological actuators

In this paper, the presence of limit cycles in the behaviour of antagonistically coupled magneto-rheological (MR) actuators is investigated. The actuator considered in this paper offers high torque-to-mass and torque-to-inertia ratios, for inherent safe actuation. While the antagonistic arrangement is beneficial in improving the actuator performance and eliminating backlash, it may result in limit cycles when the actuator operates in a position control loop. The occurrence of a limit cycle depends on the parameters of the actuator as well as the controller. An in-depth analysis is carried out in this paper to establish a connection between the system parameters and the limit cycle occurrence. Moreover, sufficient conditions for avoiding limit cycles are derived specifically for a proportional-derivative (PD) controller. Simulations and experimental results validate the analysis and provide insights into conditions under which limit cycles are observed in the operation of antagonistic MR actuators.