Comparative Efficiency Study of Two Proposed Designs Tested in Water and Air Cooling Conditions for a High Power Humanoid Robot Hollow Joint

Abstract

When a robot is designed, usually the weight of the same motors limits the maximum payload of the robot. While the designer tries to increase the power of the motors to give the robot better payload capacity, by doing so, it also makes the robot itself heavier and then the improvement in payload capacity is lost in lifting the robot itself. Many approaches to improve payload capacity consist in using an existing commercial electric motor and modifying it by adding external accessories to avoid non-safe motor internal heat. They usually use a mechanic reduction to increase payload capacity, but they lose maximum speed at the same time. Currently, there are no proper solutions for a motor in a humanoid robot application that manages to lift very heavy objects at high speed and that at the same time the motors are small and lightweight. In order to obtained more power from the robot joint actuator, in this paper we propose and compared a new thermal channel and thermal sealed jacket design for a permanent magnet electric motor to solve this problem. The design takes advantage of the fractional-slot concentrated-winding motor configuration and its fill factor to force liquid and air directly to the winding separately, in order to examine their head extradition to increase its performance in a specify scenario. The propose design shows an improvement in relation to the head extraction of the sealed jacket design with respect to the thermal channels when forcing liquid through them. Both designs are simulated assuming an extreme scenario where the winding reaches 100 °C for validation purposes. The experiments were carried out in the Ansys CFD Software to evaluate their heat transfer behavior.