Design Of The Reconfigurable Magnetizing Actuator

Conventional motors reach high efficiency at high speeds,but exoskeleton joint drive or robot joint drive applications typically require low-speed high-torque movements,for which conventional motors are mush less efficient.In particular,when it has to apply torque in a fixed posion,such as while gripping an object or standing upright,the motor at the joint must maintaion torque without rotating,and thus the motor is operating in the zeroefficiency zone.The Typical work-around to this problem has been to use gearboxes.By changing the ratio of speed to torque,gearboxes allow the motor to operate at higher speed,which is more efficient.However,gearboxes introduce now issues such as backlash,additional weight,high reflected inertia during collisions,and sometimes nonbackdriveability.In addition,conventional motors are generally stiff actuators.However,in applications such as exoskeleton joint drive and robot joint drive,it is necessary to interact with human.In view of safety,the motor needs to have compliance.In order to achieve variable stiffness compliance,conventional motors need to add additional elastic elements and complicated mechanical structure.In order to solve these problems,we propose a new type of actuator called the “reconfigurable magnetizing actuator”,which can maintain high efficiency at low speeds and has variable stiffness compliance.The reconfigurable magnetizing actuator uses high transient current pulses to change the magnetization of the permanent magnets on the stator,then change the output torque of the actuator.The number of pulses required at low speeds will be reduced,and at zero speed the permanent magnets can provide torque without any power,so the actuator can maintain high efficiency at low speeds.Besides,the effect of the elastic element can be achieved by the force between the permanent magnets on the stator and the rotor,so the actuator can achieve variable stiffness compliance.