Trajectory Planning of a 3-DOF Under-constrained Cable-suspended Parallel Robot
Cable-suspended parallel robot is a special type of parallel robot that belongs to the category of flexible robots.The end-effector is driven by cables instead of rigid rods to achieve the change of its pose.A three-degree-of-freedom(3-DOF)under-constrained cable-suspended parallel robot was studied.The cable mast could rotate along a circular guide rail,that is,the angle of the cable mast is variable,which realizes the reconfiguration of the robot and reduces the probability of collision between cable and cable as well as between cable and obstacles.The inverse kinematics equation of the robot was established based on the vector closed-loop principle.The dynamics equation of the robot was established according to the Lagrange formula.Given the motion trajectory of the robot's end-effector,and the quintic polynomial was adopted to plan the motion trajectory of the robot.The unplanned and planned position,velocity and acceleration curves in the X,Y and Z directions were obtained.At the points where the velocity changed abruptly,the planned velocity and acceleration curves achieved smooth transition to avoid vibration and impact during the robot's movement,so as to smooth the motion trajectory of the end-effector.The experimental curves of the length and tension of three cables were basically consistent with the planned expected curves,and the camera tracking trajectory was basically consistent with the motion trajectory after the quintic polynomial planning.Numerical simulation and experimental results validated the correctness of the inverse kinematics and dynamics analysis of the 3-DOF under-constrained cable-suspended parallel robot,as well as the effectiveness of the quintic polynomial planning.
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