Constraint Error Analysis for Three DOF Pure Translational Parallel Robot

Many uncertain factors influence the accuracy and repeatability of robots. These factors include manufacturing and assembly tolerances and deviations in actuators and controllers. The effects of these uncertain factors must be carefully analyzed to obtain a clear insight into the manipulator performance. In order to ensure the position and orientation accuracy of a robot end effector as well as to reduce the manufacturing cost of the robot, it is necessary to quantify the influence of the uncertain factors. This involves a study of the direct and inverse kinematics of robot end effectors in the presence of uncertain factors. From perspective of structure synthesis, certain special geometric constraints, such as joint axes intersecting at one point or perpendicular to each other, are necessary in realizing the end-effector motion of kinematically parallel robots along individual motion axes. These requirements are difficult to achieve in the actual system due to assembly errors and manufacturing tolerances. An approach to evaluate the effects of constraint errors on parallel robot is proposed. This approach is illustrated by a 3-DOF parallel robot with translation. The results show that the proposed evaluation method is effective to guide design and assembly.