Qiaohong Chen

Kinematic calibration of a 2-DOF translational parallel manipulator

Two types of kinematic calibration method for a 2-DOF (degrees of freedom) translational parallel manipulator are proposed using different error models. A calibration experiment is performed on both methods using an Absolute Laser Tracker and the results are compared. Two error models of the 2-DOF translational parallel manipulator are established using differential method and linear perturbation method, respectively. The two error models are solved using both the least squares method and linear equations. The results for the two different calibration methods show that the error model based on differential method is more effective in improving the accuracy of the 2-DOF translational parallel manipulator. Overall, the absolute position error of the 2-DOF translational parallel manipulator is significantly reduced to 0.13 mm from 0.93 mm after kinematic calibration. Graphical Abstract

Kinematic Analysis of a 3-Axis Parallel Manipulator: The P3

This paper presents kinematic analysis of a 3-axis parallel manipulator, called P3. The P3 parallel manipulator is developed based on a 3-PRRU parallel mechanism, where P denotes prismatic pair, R revolute pair, and U universal joint. The P3 parallel manipulator can undergo two rotations and one translation without parasitic motion. First, a brief description of the P3 is presented. Then, forward and inverse kinematic solutions of the P3 are derived. Parasitic motion is discussed. The Jacobian matrix is obtained based on the velocity equations. Further, singular configurations of the P3 are identified. A special configuration where the actuation fails is also detected based on screw theory. The workspace of P3 is investigated.

Dimensional Synthesis of a 2- P RS- P RRU Parallel Manipulator

This paper deals with the dimensional synthesis of a 2-PRS-PRRU (P, R, S and U standing for actuated prismatic, revolute, spherical and universal joint, respectively) parallel manipulator considering both dexterity and motion/force transmission. First, the inverse kinematic analysis of the parallel robot is presented. Next, the reciprocal of the condition number and the global conditioning index (GCI) based on a dimensionally homogeneous Jacobian matrix are used to evaluate the dexterity. Then, local transmission index (LTI) and good transmission workspace (GTW) are used for evaluation of the motion/force transmissibility of the 2-PRS-PRRU parallel manipulator. Finally, considering the GCI and GTW simultaneously, the parameter-finiteness normalization method is used to produce an optimal design. Both dexterity and motion/force transmission can be improved with the optimized link parameters.

Two Novel Spherical 3-DOF Parallel Manipulators With Circular Prismatic Pairs

Two novel spherical 3-DOF (degrees of freedom) parallel manipulators with circular prismatic pairs are proposed. One is 3-PC (RR)N parallel mechanism, where PC denotes a circular prismatic pair, (RR)N denotes two revolute pairs whose axes intersect at a common point N. The other is 3-PC RN S parallel mechanism. All the revolute axes in three limbs intersect at a common point N. The three circular prismatic pairs can be actuated. Mobility and singularity of this mechanism is analyzed via screw theory. Due to the circular prismatic pair, the rotational DOF of the moving platform about the z axis is decoupled from the other two rotational DOFs.Copyright