The T-ROBOT: a Parasitic Motion Free 1T2R Parallel Manipulator

Abstract

Parallel manipulators are a lower degree of freedom (DoF) type when they cannot have all motions in ？6 because of the restrictions imposed by branches connecting the fixed and moving plates. This class of manipulators' motion is usually described using independent parameters that are the DoF of the manipulator, and the rest of the parameters are constrained and are assumed to have not occurred. However, in some cases, a small amplitude-dependent (parasitic) motion occurs along the direction of the constraint. This unexpected parasitic motion refers to a dependent motion in the task space that occurs along with other main motions of the manipulator, and it usually introduces an undesired movement that leads to low accuracy or control/calibration difficulty. However, from the manipulator's perspective, it must be included in the kinematics analysis to satisfy the structural constraint. Thus, this phenomenon must be well understood and removed from the workspace to avoid complications caused by it [1]. Thus, this paper introduces the T-ROBOT, a 1T2R parasitic free manipulator. The manipulator has two identical limbs with revolute-revolute-spherical (RRS) joints and one limb with revolute-revolute-revolute- universal (RRRU) joints,. The three (two spherical and one universal) joints on the moving plate are collinear and this configuration is used as a condition to remove the parasitic motion. Consequently, all the dependent motion becomes zero in the entire workspace.