Nonlinear controller design for asymmetric actuators

This paper deals with the development of a nonlinear control strategy for a symmetric actuators. In asymmetric actuators, the generated force/torque is not symmetric in push and pull. Examples of asymmetric actuators are thrus ters, shape memory alloy wires, and in general, cables and long rods that c annot be used for compression forces. These actuators are called unidirecti onal. More complex asymmetric actuators are those that generate uneven push and pull forces. Examples of these actuators are double acting hydraulic a nd pneumatic cylinders in which the area of the piston is not the same in f orward and reverse directions. Since in the existing control techniques the actuator is assumed to be symmetric, the application of asymmetric actuato rs requires new control schemes. In this paper, we propose a nonlinear cont rol method capable of producing any biased input that can be used by asymme tric actuators. The controller is based on quadratic coupling terms with wh ich positive, negative, and any biased input can be generated. We study the stability of the system along with a method to select the controller gains for tuning the output of the controller to match the actuator type. The no rmal form method and perturbation techniques are used to study the controll er design.