| Robot reducers and servo motors are the key parts of robots.In recent years,researchers and technical developers at home and abroad are committed to the development of robot modular joints with compact structure,small volume,light weight and various control modes.The core technology of robot modular joint is to integrate the servo motor and reducer into a compact integrated module.However,the motor and reducer in existing robot modular joint are still two independent components,and the reducers such as planetary reducer,harmonic reducer and RV reducer,etc.are fabricated by using mechanical gears.The contact meshing of mechanical gears inevitably produces friction,heating,noise,precision degradation and failure,etc.This paper explores the application of contactless magnetic-geared machine(MGM)technology in robot to build the magnetic-geared joint motor(MGJM).The MGJM realizes the integration of robot motor and reducer in real sense.The research of MGJM can lay a theoretical foundation for the design and application of novel modular joints.This paper investigates the key technologies of MGJMs on torque capability,gear ratio and cogging torque issues.A novel dual-flux modulated coaxial magnetic gear(DFM-CMG)is designed.Based on the investigation of mechanism of the torque capability improvement in dual-flux modulated structure,a DFM-MGJM is established.A dual-stage MGJM(DS-MGJM)is proposed and designed to improve the gear ratio without increasing the complexity of existing MGM structure.The coupling characteristics in MGJM are investigated,and the recessive-CMG which increases the cogging torque is revealed.The methods to suppress/eliminate the recessive-CMG and decrease the cogging torque are presented,the stationarity of MGJM output torque is improved effectively.The main research contents are as follows.1.The transmission mechanism of the magnetic coupling is discussed.The torque,speed and overload characteristics of the magnetic coupling prototype are tested.The matching principles of pole-pair number and speed for magnetic force transmission are summarized.Based on the magnetic coupling,the operation principle,design method,torque transmission and electromagnetic characteristics of CMG are discussed.For dual-stage CMG design,the matching of torque capability is discussed.2.A novel DFM-CMG with two modulators is presented.Based on the flux-modulation theory,the operation principle and torque transmission of the proposed DFM-CMG are analyzed.The DFM-CMG can be de-composited into two CMG units.The two modulators are related to the two CMG units,respectively.The influence of the relative position of the two modulators on DFM-CMG torque capability is investigated,and the optimal relative position is zero.By using finite-element method(FEM),the dimensions of inner modulator are optimized.The influence of gear ratio on DFM-CMG torque capability is analyzed.The torque capability of DFM-CMG is higher than that of conventional CMGs under the same active size and PM volume.The DFM-CMG is suit for high gear ratio application.A DFM-CMG prototype is fabricated and tested.The improvement of torque capability in DFM-CMG is verified by experiment.The ratio of input speed to output speed is close to theoretical gear ratio.3.The influence of stator structure on cogging torque of pseudo direct-drive(PDD)machine is analyzed.The recessive-CMG in PDD with modulating stator is revealed.It results in high cogging torque and asymmetric flux linkages.Based on DFM-CMG,the structure of the PDD with modulating stator is improved,and a DFM-MGJM is proposed.The DFM-MGJM suppresses the cogging torque caused by recessive-CMG effectively.The DFM-MGJM breaks through the limitation of the outer stator on the torque capability of the inner CMG,makes the stator participate in CMG transmission to improve the torque capability.The DFM-MGJM can be decomposited into two motor units,the superposition characteristics of air gap flux density,no-load back electromagnetic force(EMF)and output torque of the DFM-MGJM are revealed.4.A novel DS-MGJM is proposed.The first stage of the DS-MGJM is a permanent magnet vernier machine(PMVM),and the second stage is a CMG.For the inner PMVM,to reduce the consumption of PM material effectively,the PM arc ratio of consequent-pole interior PM VM(CP?IPMVM)is optimized.The air-gap flux density,back EMF and electromagnetic torque of the CP?IPMVM are theoretically derived by using the equivalent magnetic circuit method.The optimization factor related to the PM arc ratio is extracted.The optimal PM arc ratio is calculated theoretically,and verified by simulation.Compared with conventional PMVM,the back-EMF and electromagnetic torque of the CP?IPMVM with PM arc ratio 0.64 are improved.5.The coupling characteristics in DS-MGJM is analyzed.A recessive-CMG due to the flux partially coupling is extracted.The influence of the recessive-CMG on cogging torque and torque ripple is investigated.The failure mechanism of a DS-MGJM prototype is revealed.The thickness of common rotor yoke controls the portion of flux penetrating the inner air-gap due to the flux partial coupling feature in DS-MGJM.The small thickness of common rotor yoke results in worse cogging torque due to the magnetic gear effect of the recessive-CMG.The improvement methods for DS-MGJM structure are presented.The cogging torques of improved DS-MGJMs are greatly decreased.6.A DS-MGJM is designed.The recessive-CMG in the structure is suppressed.The electromagnetic characteristics of the DS-MGJM are analyzed.A DS-MGJM prototype is fabricated.The no-load back EMF of the prototype is measured,and the evaluated gear ratio is very close to the design value.The DS-MGJM can be equivalent to a dual-inertia system.The DS-MGJM prototype is driven by using sensorless control method.The output speed and torque of the prototype are tested.The ratio of common rotor speed to output speed is close to the gear ratio of outer CMG.The DS-MGJM prototype can runs smoothly.The torque ripple is 2.95% under steady-state torque of 4.74 Nm. |
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