Kinematic design of a family of 6-DOF partially decoupled parallel manipulators

Parallel manipulators (PMs) with 6-DOF decoupled motion can simplify the manipulator kinematics and thus facilitate its motion planning and control. This paper studies the kinematic design of a family of partially decoupled parallel manipulators (DPMs) with 3-limb symmetrical structure, in which 3-DOF spatial motion composed of a vertical translation and two horizontal rotations can be independently controlled. The concept of group decoupling (GD) is introduced for classification and synthesis of decoupled motion PMs. Type synthesis of this manipulator family is carried out systematically based on GD and wrench system analysis. As a result, six DPM architectures, five of which are new, are obtained from this exercise. Instantaneous kinematics shows that the order of the Jacobian matrices of the newly found manipulator architectures can be reduced from six to three. The reduction of Jacobian order for the decoupled motion PMs facilitates analysis of manipulator singularity, displacement and statics. Hence, the approach can be utilized for decoupled PMs in other decoupled motion groups.