An Experimental Study on Control of a Pneumatic 6-DoF Gough-Stewart Robot Using Backstepping-Sliding Mode and Geometry-Based Quasi-Forward Kinematic Method

In this paper, the trajectory tracking control problem is addressed for a pneumatically actuated 6- DoF Gough-Stewart parallel robot. At first, dynamic model of the pneumatic system of each link of the robot which comprises a pneumatic actuator and a proportional electrical control valve is extracted. Unknown parameters of the obtained dynamic model consisting friction force, viscous coefficient and the parameters of the valve are identified by employing an evolutionary algorithm. Then, position control of the robot's pneumatic actuator is investigated based on designing Backstepping-Sliding Mode controller according to the nonlinear dynamic model of the pneumatic system. Moreover, kinematic equations of the 6- DoF parallel robot are achieved and a novel method is proposed, the so-called Geometry-based Quasi-Forward Kinematic, which calculates position of the end-effector of the robot without using expensive position sensors. Accordingly, kinematically closed-loop control of the parallel robot, which is based on simultaneous joint space and task space control, is investigated for trajectory tracking using potentiometers, a rotation sensor and based on the computed position of the end-effector by the proposed method. Desired sinusoidal pure rotations and translations are tracked in which root mean square error of the pure translations and rotations are lower than 1.3 (cm) and 2.6 (deg), respectively. The experimental results reveal that trajectory tracking control of the pneumatic 6-DoF Gough-Stewart parallel robot performs properly based on the proposed control strategies and the novel method for calculating position of the end-effector.