Design of a High Torque Density Robot Joint and Analysis of Force Control Method Applied for a Light Exoskeleton

Abstract

In many robotic applications, the joint is required to have a small volume, low weight and high torque output. In this paper, based on the finite element analysis (FEA), a 36-slot 40-pole outer rotor surface-mounted permanent magnet (OR-SPM) motor with concentrated winding is designed for the exoskeleton robot. The fractional slot concentrated winding (FSCW) is employed to reduce end winding height, leading better portability. Since the motor is relatively flat, the 3D end effect is critical to the electromagnetic performances. Special attention is paid to 3D end effect during the multi-objective optimization of the OR–SPM motor. In order to increase the ending torque output, the planetary reducer is located between OR–SPM motor and load, and then system level optimization covering motor and reducer is carried out to achieve best torque output. In addition, the force impendence control method with parameter self-adaptive capability is proposed to improve user experience of the exoskeleton robot, where the key parameters in the algorithm vary according to different actions of the exoskeleton. In addition, the inertia of load is calculated using the parameter identification based on least squares method. Finally, the prototype of the joint is fabricated and tested to validate the above FEA results and control method. The user experience of the exoskeleton robot is also covered.

Optimizing Exoskeleton Design with Evolutionary Computation: An Intensive Survey

“…Specifically, we observed that 48 studies did not include any optimization method, 35 studies claimed to have implemented an optimization algorithm without giving further details, 57 studies focused on control and trajectory optimization rather than mechanical design, and 1 study used a trivial brute force algorithm rather than a proper optimization method [21]. Among the remaining studies, six optimized the mechanical design through finite element analysis (FEA) [22][23][24][25][26][27]. FEA is mostly embedded with current computeraided design software to analyze how a given design reacts under real-world conditions rather than offering an exact solution that would correspond to a desired constraint or requirement.…”

“…Out of the 38 research studies focusing on the mechanical optimization of exoskeletons, we eliminated 6 using FEA as the optimization method [22][23][24][25][26][27]. FEA is a computerized method for predicting how a product reacts to real-world forces, vibration, heat, fluid flow, and other physical effects, showing whether a product will break, wear out, or work the way it was designed.…”

Toward Inherently Safer Human-Robot Interaction Using Compliant Actuators With High Torque-to-Inertia Ratios and Low Torque-to-Stiffness Ratios

“…Motors with large-diameter hollow rotors have higher inertia than those with small-diameter solid rotors. Geartrains [8], belt drives [9], and cable drives [10] with low transmission ratios have been developed to reduce the reflected inertia of an actuator. The frictional loss of the actuator can also be reduced, allowing the actuator to be back-drivable.…”