Singular configurations must be avoided in path planning and control of a parallel manipulator. However, most studies rarely focus on an overall singularity loci distribution of lower-mobility parallel mechanisms. Geometric algebra is employed in analysis of singularity of a 3-RPS parallel manipulator. Twist and wrench in screw theory are represented in geometric algebra. Linear dependency of twists and wrenches are described by outer product in geometric algebra. Reciprocity between twists and constraint wrenches are reflected by duality. To compute the positions of the three spherical joints of the 3-RPS parallel manipulator, Tilt-and-Torsion angles are used to describe the orientation of the moving platform. The outer product of twists and constraint wrenches is used as an index for closeness to singularity(ICS) of the 3-RPS parallel manipulator. An overall and thorough perspective of the singularity loci distribution of the 3-RPS parallel manipulator is disclosed, which is helpful to design, trajectory planning and control of this kind of parallel manipulator.
Optimum design of rider-bicycle mechanisms is very important for customizing bicycles and plays a crucial role in the improvement of athletes' performances and in protection of the riders.Since the birth of the first bicycle,people have been keeping optimizing bicycles with respect to physical conditions of human.In modern design,the basic structure of a bicycle has been formulized,while many geographic parameters remain uncertain.In this paper,the bicycle and the human body are considered as a kinematic mechanism,called rider-bicycle mechanism.The optimum design is implemented from the perspective of mechanism.Effort-saving and comfortableness are considered at the same time.The corresponding performance charts are drawn and the relationship between the performances and parameters of seat height,crank length and body parameters are discussed.By using these charts,the optimal design method of bicycle's parameters for a specified person is then founded.Optimum solutions to get suitable seat height and crank length for a person are obtained accordingly.The research is of significance for customizing bicycles and design of bicycle robot.
Parallel robots are widely used in the academic and industrial fields. In spite of the numerous achievements in the design and dimensional synthesis of the low-mobility parallel robots, few research efforts are directed towards the asymmetric 3-DOF parallel robots whose end-effector can realize 2 translational and 1 rotational(2T1R) motion. In order to develop a manipulator with the capability of full circle rotation to enlarge the workspace, a new 2T1 R parallel mechanism is proposed. The modeling approach and kinematic analysis of this proposed mechanism are investigated. Using the method of vector analysis, the inverse kinematic equations are established. This is followed by a vigorous proof that this mechanism attains an annular workspace through its circular rotation and 2 dimensional translations. Taking the first order perturbation of the kinematic equations, the error Jacobian matrix which represents the mapping relationship between the error sources of geometric parameters and the end-effector position errors is derived. With consideration of the constraint conditions of pressure angles and feasible workspace, the dimensional synthesis is conducted with a goal to minimize the global comprehensive performance index. The dimension parameters making the mechanism to have optimal error mapping and kinematic performance are obtained through the optimization algorithm. All these research achievements lay the foundation for the prototype building of such kind of parallel robots.
