Energy efficiency is a relevant and challenging topic in the robotic and mechatronic fields. One approach that is investigated to reduce the actuator effort, especially when cyclical and highspeed operations are considered, is the introduction of compliant elements in parallel with the motor shafts. During the robot motion these elements allow for a continuous conversion between elastic potential energy and kinetic one, leading to motor effort reduction. In this paper we present a method for the optimal design of elastic elements, and its application to a 4-DOF parallel robot (4-RUU) performing predefined pick-and-place trajectories. The kinematic and dynamic models of the mechanical system are developed and several scenarios for the springs stiffness and preload are evaluated. Simulation results indicate the feasibility of the proposed approach in reducing the actuators effort and achieving energy efficiency.
