In this study, we develop some control algorithms for trajectory tracking of two DOF closed-chain mechanical systems separately driven by two servomotors (closed-chain robot), as well as by one CV motor and the other servomotor (so-called hybrid machine) based on their dynamic model. For the former, the exponential stability and validation of PD computed-torque control algorithm are verified for trajectory tracking of both joints and the end-effector of the system. For the latter, a complex PD computed-torque control algorithm with a closed-loop feedback for the servomotor and an open-loop feedforward for the CV motor is proposed. Simulation studies show that the complex PD computed-torque control algorithm is effective when the velocity fluctuation of the CV motor is reduced to 5% by attaching a flywheel on the CV motor shaft.

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