A spherical two-degree-of- freedom wrist adapting the structure of the spatial parallelogram is proposed. A U type extended link out of three UU type limbs of the spatial parallelogram is selected as an output link. As a result, the wrist can be interpreted as being formed by combination of a U type limb and a (2-UU)+U type hybrid limb. Screw theory is employed to analyze its first-order kinematic model. Then a compact wrist prototype suitable for wrist module supporting the robot hand is designed and implemented. Finally, experiments with the prototype confirm that the wrist has a very high potential application for wrist modules in terms of dexterity and maximum load handling capacity.

This paper presents a new antagonistic tendon-driven joint (TDJ) which has an advantage of enhanced stiffness characteristics. Detailed mathematical analyses on the stiffness of typical TDJs are worked out to compare the stiffness among them. Prototypes of the proposed TDJ design are introduced in the form of packaged modular structure that merges two TDJs generating a combined roll-pitch motion or similar ones. Numerical examples are given to confirm the superior stiffness of the proposed TDJ design.

In this paper, we propose an in-hand motion planning algorithm for 3D objects under rolling contacts. By assuming the in-hand motion is quasi-static, we apply the concept of independent contact region (ICR) to determine stable boundaries of finger contact points during the in-hand motion. A specified level of grasp quality margin representing the ability to bear external load is guaranteed. The overall scheme contains two motion planning phases: one is the motion planning with fingers simultaneously rolling over the object surface, and the other is the planning associated with switching fingers of contact and non-contact. Simulation/experimental results are provided to show the feasibility of the proposed algorithm.

In this paper, we present a practically useful and intuitive grasp quality measure that takes into account the shapes of object geometries and the torque limits of finger actuators. The proposed grasp quality measure is defined by the distance between the convex hulls of the absolute grasp wrench space (a-GWS) and the object wrench space (OWS), where a-GWS and OWS are, respectively, created by the active wrenches from the robot fingers with limited torque bounds and the uniform distribution of unitary normal disturbances on the surface of a polyhedral object. The computational algorithm for the grasp quality measure also yields the information of which spots of the object are fatal under the disturbance, which makes the algorithm practically useful. We demonstrate the validity of the proposed measure through numerical examples.