Research On The Design Of Joint Motors For Legged Robots

Legged robots have been developed rapidly in recent years,and the electric drive method has become the mainstream drive method for legged robots with the advantages of simple mechanical structure and high control accuracy.The permanent magnet synchronous motor has the advantages of high torque density,high power density and high efficiency,and is the power source of the electrically driven legged robots.In this paper,the following work is carried out to study the joint modular motors for legged robots.The paper introduces three types of joint modular motors: direct-drive motors,quasi-direct drive motors and series elastic motors,their respective structures,advantages and disadvantages and applicable scenarios.The domestic and foreign products of electric drive legged robots and their adopted joint modular motor solutions are summarized,and their differences in motor ontology and control are analyzed.The paper discusses the electromagnetic design method of the motor from the perspective of improving the torque density of the motor.In the selection of topology,the structural characteristics,advantages and disadvantages of radial flux,axial flux,transverse flux and new structure permanent magnet motor are compared;in the selection of pole/slot combination,its influence on electromagnetic performance such as torque output capability,flux weakening capability,cogging torque and inductance of the motor is analyzed;in the optimization of permanent magnet,its influence on motor performance is explained from two aspects: shape of permanent magnet and magnetizing method.The quasi-direct drive joint motor has a stronger torque output capability due to its reduction mechanism.The paper designs a quasi-direct drive joint motor,with an overall scheme of an outer rotor,an embedded planetary gearbox and a rear integrated controller.The paper analyzes the influence of pole/slot combination and stator/rotor parameters on the electromagnetic performance of the motor,extracts the key feature parameters with high parameter sensitivity,combines multi-objective genetic algorithm to obtain the optimal solution of the electromagnetic design,and calibrates it by finite element method.Compared to quasi-direct drive joint motors,direct drive joint motors have advantages in terms of cost,noise,backlash,mechanical friction and mechanical complexity.With the same package size as the quasi-direct drive motor,the paper designs a direct-drive motor.The design study is carried out in terms of topology selection,optimization of permanent magnet magnet magnetization method,sensitivity analysis of stator and rotor parameters,and calibration by finite element method.A prototype of a quasi-direct drive joint motor and a direct drive joint motor were completed according to the design plan,and the problems of stator and rotor core processing and permanent magnet assembly were solved in the fabrication process.A test platform was built to test the motor characteristics parameters,no-load and load conditions,and the results were compared with the calculated values and the sources of errors were analyzed to verify the accuracy of the electromagnetic design.Finally,the electromagnetic performance of quasi-direct drive and direct-drive joint motors are compared and analyzed,and their respective advantages and applications are summarized.