This paper presents a hybrid method for the optimum kinematic design of two-degree-of-freedom (2-DOF) parallel manipulators with mirror symmetrical geometry. By taking advantage of both local and global approaches, the proposed method can be implemented in two steps. In the first step, the optimal architecture, in terms of isotropy and the behavior of the direct Jacobian matrix, is achieved, resulting in a set of closed-form parametric relationships that enable the number of design variables to be reduced. In the second step, the workspace bounded by the specified conditioning index is generated, which allows only one design parameter to be determined by optimizing a comprehensive index in a rectangular workspace. The kinematic optimization of a revolute-jointed 2-DOF parallel robot has been taken as an example to illustrate the effectiveness of this approach.

A novel and plug-and-play robot wrist with three rotational degrees of freedom (DOF) is proposed in this paper. The wrist is composed of three independent kinematic chains, each of which rotates with respect to the fixed reference frame. Thus, the output of the wrist is the resultant of the differential motions of the three kinematic chains. The structure of the mechanism is simple and compact with a relatively large orientation capability. Various end-effectors, CCD camera for instance, can be mounted on the wrist through standard interface. The working principle and mechanical structure are described and the mathematical models for inverse and forward analyses are developed. The singularity of the wrist is also obtained.