Nonlinear control strategy development for asymmetric actuators

We develop a nonlinear control method for asymmetric actuators. Asymmetric actuators do not generate symmetric power during an application. Thrusters and shape memory alloy wires are examples of this class of actuators that produce only unidirectional forces. Hydraulic and pneumatic cylinders are generally asymmetric because, under constant pressure, the generated force in the forward direction is different than that in the reverse direction. Existing control methods assume a symmetric actuation, and therefore, application of asymmetric actuators calls for new control schemes. Current control techniques implement a bias in utilizing asymmetric actuators. However, the amount of the bias depends on the control effort and is not constant. Also, the use of a bias changes the system equilibrium point and introduces a steady-state error. We propose a control scheme capable of producing any biased input. The controller is a second-order system coupled to the system through quadratic terms. The application of quadratic terms for the control input enables us to generate any biased control input, which can be utilized by asymmetric actuators.