Tip Trajectory Tracking of Flexible-joint Manipulators

In this paper a new control strategy is introduced for tip trajectory tracking of flexible-joint manipulators driven by harmonic drives. The proposed controller incorporates friction compensating torque (FCT) and composite controller torque (CCT), which compensate for the friction in the harmonic drives and the flexibility of the joints, respectively. The FCT is a new controller which includes a non-linear one-state LuGre model and a proportional-derivative (PD) controller. The CCT’s design is based on the singular perturbation method and integral manifold concept. An experimental setup of a two-rigid-link flexible-joint (TRLFJ) manipulator was used to verify the proposed controller. The experimental results demonstrated the effectiveness of the controller at slow and fast motions of the manipulator for different trajectories. In particular, the tracking error was reduced significantly by using the proposed controller compared to the results obtained using traditional methods such as the inverse dynamics method for the control of flexible-joint manipulators.