The moving platform of a conventional parallel mechanism is typically connected to the ground link via serial kinematic chains or limbs. When interconnections are created among the limbs, they form coupling sub-chains that can provide additional constraints to the motion of the platform. The resulting complex mechanism offers the potential for improved performance and functionality of the overall mechanism. The basic building block of the parallel mechanism with coupling sub-chain is found to be a two-loop mechanism. This paper presents a screw theory based general method for synthesizing two-loop mechanism by adding an open chain on top of an existing closed chain for a specified combination of rotational and translational degrees of freedom of the end-effector. A comprehensive set of two-loop mechanisms have been presented for various combinations of rotational and translational degrees of freedom.

The dynamic behavior of electro-hydraulic driven parallel manipulators is highly nonlinear system, the nonlinear behavior arising from load friction as well as the valve flow-pressure drop relationship. This paper is concerned with the robust tracking control of electro-hydraulic driven parallel manipulators with the model uncertainties. An adaptive fuzzy controller is used to estimate the uncertainties of electro-hydraulic system, including the payload variation and stiffness etc. Adaptive fuzzy logic and adaptive backstepping method are employed to provide the solution to the control problem. Simulation results from a electro-hydraulic driven 4-SPS (PS) type parallel manipulator demonstrate its strong robustness against a large of parameters variations and load disturbance and its capability of the trajectories tracking performance.

This paper presents a neural-adaptive sliding mode control for the tracking control of 4-SPS(PS) type parallel manipulator. The neural-adaptive controller is introduced to modify the coefficients of sliding manifold in sliding control strategy, which solve the problem that the equivalent control can not be obtained accurately because of the uncertain and fixed coefficients of sliding manifold and external disturbances of the system. So the controller can be designed without depend on fixed sliding manifold as general design method. Accordingly, it can be more effectively to solve the chattering in sliding mode control. The nonlinear controller, which guarantees the stability of the proposed control system based on Lyapunov stability theory, is also developed. Simulation results show that the control approach can decrease the tracking error, enhance the system's robustness and restrain the chattering effectively in the sliding mode control.

This paper designs a robust controller with modeling uncertainties and external disturbance for stable dynamic walking of biped robot. The method of multibody dynamics is applied to construct the equations of motion for the complicated biped robot system with both structured and unstructured uncertainties, and the normal model of the system was taken into account. Then, the optimized trajectories were obtained using the improved hereditary algorithm. Finally, trajectory tracking of dynamic walking robot is controlled by robust control method. It is proved by simulation result that robust control method can effectively restrain the effect of model uncertainties and external disturbance acting on biped robot, and can provide a powerful safeguard for the robot system

The theory of reciprocal screws is used for the enumeration of the feasible limb structures of a class of 3-degree-of-freedom (DOF) rotational parallel manipulators. Geometric conditions for the moving platform to possess finite spherical motion are described. A table of feasible limbs that can be used for the construction of 3-DOF rotational parallel manipulators is developed.