Development of a New High Speed Cable-Based Planar Parallel Manipulator
Sun, Nan Nan
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Industrial robots and automation technology have advanced rapidly in the last several decades. New types of manipulators that uses parallel mechanisms are becoming more popular due to their high speed and high stiffness. This thesis focuses on a sub-class of parallel manipulators that uses cables to replace rigid links for further increase in speed. The design strategies in this study were expanded from research works by Khajepour. Behzadipour, and Edmon Chan. This thesis presents analysis and development of a new cable-based planar parallel manipulator that is based on a previous prototype built by Edmon Chan. The new manipulator design added a new rotational DOF to the end-effector, and the number of cables are doubled in order to increase the stiffness. New methods for kinematics and dynamics analysis are formulated to make the procedure more systematic. A new mathematical formulation for stiffness matrix of the end-effector is presented. The resultant stiffness matrix is equivalent to the stiffness matrix formulated by Behzadipour. Additional stiffness analysis is conducted on valid range of stiffness calculation and comparison of different cable configurations. A multi-objective optimization problem is formulated in order to search for the best set of design parameters for the manipulator, and it is solved with an exhaustive complete search method. A physical prototype of the manipulator is modelled and manufactured with the help of partners from Conestoga college. Experiments with the manipulator show that more powerful motors are needed to run the robot at full speed. Motor torque measurements show that the dynamics analysis of the manipulator is valid. Stiffness of the manipulator is measured by applying external force to the end-effector, and it is shown to be strong. The manipulator is able to demonstrate a sort and pick-and-place operation at 60 cycles per minute while running at 70% of the maximum speed, with an acceleration of 2.8 g and velocity of 4 m/s.