Intelligent controller for robust orientation control of smart actuator based parallel manipulator

Abstract

Flexible parallel manipulators can be used as an orienting device due to its precise positioning ability. The flexibility demands the use of non-conventional actuators and noncontact type/flexible sensors for feedback measurement. This study proposes a novel 2 Degree of Freedom (DoF) parallel manipulator actuated by shape memory alloy springs (SMA) which could be used as an orienting device for a table top Cartesian robot. To mitigate the use of contact type sensor, model based feedback is proposed to obtain SMA length for the feedback control. The inclusion of SMA actuators to parallel mechanism imposes control challenges due to nonlinearities, coupling effects, and disturbances. This work also proposes a novel control scheme based on concept of partition control law to control the SMA spring position without the use of any complex mathematical model. The proposed controller is a combination of two parts Fuzzy PID servo control and the time delay estimation (TDE) based auxiliary control. The fuzzy PID control handles the error tracking and the auxiliary control tries to cancel the nonlinearities and disturbances, thus enhancing the robustness. The performance of the proposed controller is tested for a complex trajectory under disturbances and the results are compared with existing nonlinear controllers which proves superior nature of the proposed controller.