Design of a 3-DOF Spatial Manipulator: Torque Minimization for Static and Dynamic Modes

Minimizing robots' energy consumption is essential to address environmental and economic challenges. This can be achieved by optimizing the mechanism's architecture and components to lower motor torques. Static balancing approaches, such as the redistribution of moving masses with counterweights, are effective but face limitations in dynamic regimes, particularly during high-speed movements. This study introduces a novel three-degrees-of-freedom manipulator inspired by the Scott-Russell mechanism, with an optimum design both in static and dynamic operating modes. For the manipulator's static mode, a single counterweight redistributes its moving masses so that the system's center of mass moves along a straight horizontal path. This maintains a constant potential energy in the system, consequently leading to the cancellation of the input torques. Then, for the manipulator's dynamic mode, an optimal design approach is proposed. By carefully selecting the parameters of the specified counterweight, the input torques are minimized for "Pick-and-Place" trajectories executed according to the "Bang-Bang" motion control law. This design approach reduces energy consumption and minimizes peak torques during dynamic operation. The results clearly demonstrate the transition between static and dynamic modes, along with a significant reduction in the manipulator's input torques in both scenarios. The method is adaptable to other applications, offering an optimal solution to maximize the energy performance of manipulators.