Kinematic analysis for a six-degree-of-freedom 3-PRPS parallel mechanism

A Stewart-platform-based six-degree-of-freedom parallel mechanism is presented that can be used as a general-purpose spatial manipulator arm. The system consists of an output platform which is connected to a fixed base by means of three PRPS (parameters P, R, and S denote the prismatic, revolute, and spherical joints) subchains. All prismatic joints in this mechanism are active inputs which control the platform's motion. The author provides a detailed investigation describing the mechanism and analyzing its forward and reverse position functions. A closed-form solution is presented to obtain the required inputs for a desired position and orientation of the output platform. A forward position analysis of this mechanism is formulated which can be solved numerically to determine the platform's position and orientation for a set of given inputs. The author examines the workspace and uses screw theory to identify the geometric singularities of the manipulator in order to avoid undesirable robot configurations. >