A new resonance-based design approach to reduce motor torque requirements in automated machinery

In the last decades, compliant mechanisms have been widely studied but their application has not been widespread due to their susceptibility to fatigue and the lack of systematic design methodologies. In this paper, the authors propose a new approach to be used in the automated machinery mechanism design (the mechanisms are usually subjected to predominant inertial loads) that exploits the capability of the compliant joints to store and release elastic energy in order to reduce the motor torque requirements. Thanks to the carbon-fiber reinforced 3D printing technologies, the compliant joint stiffness can be properly designed to obtain, for the considered mechanism, a resonant condition during its nominal functioning. Moreover, topology optimization can be successfully employed to reduce the mechanism component inertia (keeping the same overall mechanism stiffness) and thus, further diminish the torque requirements. In order to assess the quality of the proposed approach, a pusher mechanism used in a real automated machine has been considered. A prototype has been manufactured to evaluate the effect of the compliant joint introduction and the topology optimization on the motor torque reduction. To validate the results, an experimental campaign has been conducted. Comparison between the standard design approach and the new one emphasizes the superior contribution of compliant joint introduction on the motor torque reduction: a 97% and 96% reduction on the RMS and peak motor torque, respectively, is achieved resorting to the new design approach. Although a high repeatability is achieved, a slight deviation of the trajectory with respect to the ideal one is however registered.