Uncompensatable error of four DOF parallel robot

The design complexity of parallel robots is due to the number of strictly interrelated functional and structural problems. Lower DOF parallel robot rely on strictly geometrical constraints of axis of pairs in and between limbs to obtain the reduced number of DOF. In practice, these constraints will never been perfectly fulfilled due to the inevitability of errors, and hence produce series bad effects and problems. Using screw theory and set theory as mathematical tools, the DOF and constraint system of 4-DOF parallel robot, were systematically summarized and in-depth studied. Kinematic design of a limited DOF parallel robot, is presented that takes into account the error. The errors presented in the paper consist of two kinds. The errors is defined as the position error of rotation center DOF the platform caused by errors in the kinematics constants, such as axis error The above research results provided an insight into the error of 4-dof parallel robot.