Abstract: Singularity is the common characteristics of mechanisms. The force/torque output capability of the moving platform will be obviously reduced, nearby the singular points of a parallel mechanism. So how to evaluate the distance from a point in workspace to singularity becomes an important issue in parallel mechanism design. Aiming at the above problem, two indexes are presented to measure the closeness to position singularity and orientation singularity. A quasi-singularity space is defined by the indexes which includes all points close to singular points. The actuator forces/torques can be guaranteed not to exceed output capacity of motors while the end-effector is outside the quasi-singularity space. An example of a 3-RRR parallel mechanism is given to formulate the method to calculate the two indexes, the quasi-singularity space and the task space.

Key words: 3-RRR mechanism, Closeness measure to singularity, Parallel mechanism, Quasi-singularity space, Singularity analysis