Gravity compensation design of Delta parallel robots using gear-spring modules

This paper presents the gravity compensation for Delta parallel robots by adding a gear-slider mechanism with a compression spring, namely the "gear-spring module," onto each robot leg. The major significance of the proposing design is that it suggests a compact mechanical solution for gravity compensation of the Delta robot without a compromise of the compensation performance and the robot workspace. The design parameters are determined to approximate the theoretical perfect balancing at a set of targeted configurations. Torque- and energy-reduction criteria are employed to evaluate the performance of gravity compensation. Design examples are implemented through a theoretical design model and a real industrial Delta robot, the FANUC M-3iA/12H. For the theoretical design model, the motor torques of the robot can be effectively reduced within 86 percent of its kinematic workspace. For the industrial Delta robot example, the theoretical peak torque and energy consumption are decreased by up to 38.4% and 55.4% for a pick-and-place task, for which a 10-kgf moving platform is traveling within a range of 1.32 m and a varying speed between 0 and 0.72 m/s. Last, a comparison between the uses of the gear-spring modules, torsion springs, and tension springs for gravity compensation is provided. (C) 2020 Elsevier Ltd. All rights reserved.