| In 2015,our country has issued the "Made in China 2025" strategic plan to raise the development of the robotics industry to a strategic level.Robotics incorporates many high-tech technologies and its applications not only move from manufacturing to non-manufacturing areas,but also continue to expand at the non-industrial areas such as military,aerospace,medical,service,transportation and entertainment at an astonishing rate.Along with continuous expansion of robot applications,requirements for robot intelligence are also increasing.As a result,it is very important to equip intelligent bionic eyes for robots so that they can perceive and acquire environmental information like humans and quickly and accurately identify and track targets.The motor is the driving part for the robot's bionic eye,and the development of robot intellectualization has raised higher requirements for bionic-eye motor,such as small size,light weight,compact structure,high positioning accuracy,large operating range,large output torque,simple mechanical structure,etc.Obviously,the 2-degree-of-freedom(2-DOF)hybrid stepping motor that can achieve high-precision position control without position sensors is ideal for bionic-eye drives.However,the currently proposed 2-DOF hybrid stepping motors are too complex in structure and too large in size to meet the bionic-eye drive requirements.On the other hand,it is difficult to meet the innovative,analytical and optimized requirements for the bionic-eye-used 2-DOF hybrid stepping motor in terms of present theoretical analysis method as well as standard rotor-magnet motor structure.Therefore,based on the investigation of bionic-eye-used 2-DOF hybrid stepping motor,this paper makes innovation for the analysis method and magnet structure of hybrid stepping motor and for the operation principle and structure of 2-DOF hybrid stepping motor,and carries out performance analyses for the novel stator-permanent-magnet hybrid stepping motor(SHSM)and 2-DOF hybrid stepping motor.The main contents are as follows:1.Presentation,theoretical proof and verification of the tooth-layer calculated torque method and 2-dimensional equivalent finite element analysis method for the hybrid stepping motorFirstly,in order to improve the tooth-layer specific permeability method,most commonly used field-circuit coupling analysis method for hybrid stepping motors,a novel method for the analysis and calculation of electromagnetic torque is proposed in this paper,which is called the tooth-layer calculated torque method.This new method avoids the derivation process of motor's total coenergy with respect to rotor position,which is characterized by simple and high calculating accuracy.Since the stepping motor is a complex closed magnetic circuit system composed of multi-tooth layer,multi-magnetomotive force(MMF)source and other magnetic circuits connected in series and in parallel with each other,this paper starts with simplified stepping motor and gradually transforms to the actual one to propose the tooth-layer calculated torque method,with theoretical proof and finite element analysis verification carried out.The nonlinear equations with vector magnetic bits as variables are established,by solving which the magnetic voltage at each node and MMF drop in each magnetic circuit can be obtained,and then the tooth-layer calculated torque is checked for the calculation and analysis of motor's electromagnetic torque and other parameters.Secondly,taking into account of the fact that the three-dimensional finite element method(3-D FEM)is time-consuming and inefficient for analyzing hybrid stepping motor,a novel 2-dimensional equivalent finite element analysis method is proposed,which has advantages of convenient model establishment,high calculation accuracy and high calculation speed,and which is suitable for solving the static and transient problems.The established two-dimensional equivalent finite element analysis model is obtained from the actual motor's three-dimensional model via structural equivalent transformation,and therefore has correctness in principle.In addition,the established two-dimensional equivalent model can take into account of the influence of insulating layer magnetic resistance between stator and rotor core laminations on the permanent magnetic field distribution in axial direction,and thus has high calculation accuracy.Correctness of this method is verified by 3-D FEM calculation.2.Presentation,structural topology,operation principle and performance analysis of the novel stator-permanent-magnet hybrid stepping motorTo eliminate the structural defects and improve the performance of traditional rotor-permanent-magnet hybrid stepping motor(RHSM),a novel stator-permanent-magnet hybrid stepping motor(SHSM)is proposed in this paper.Basic structure of the SHSM is obtained by structural equivalent transformation from RHSM,and thus the two motors have the same working principle.A prototype of 2-phase 8-pole 50-tooth SHSM is designed and manufactured,and the FEM simulation and experimental study is conducted to validate the feasibility of motor's operation principle and verify the accuracy of theoretical analysis.Four types of SHSM are put forward via the analysis of motor topology,namely,the 1-pair-magnet SHSM,2-pair-magnet SHSM,enhanced 1-pair-magnet SHSM and enhanced 2-pair-magnet SHSM.Comparison models corresponding to each structured SHSM are established,based on which,comparative analysis of motor performance is performed in terms of no-load and load characteristics,with the theoretical analysis verified by FEM simulations.3.Analyses of performance comparison between SHSM and RHSMThe stator-permanent-magnet hybrid stepping motor(SHSM)is a new kind of hybrid stepping motor,which has the same operation principle as traditional RHSM,whereas superiorities such as simpler rotor structure,higher mechanical robustness,higher torque and power density,easy PM dissipation,and simple design and analysis.To evaluate the performance of SHSM,comparative analysis is carried out in terms of the PM air-gap flux density,optimal core length,PM torque,detent torque and torque ripple,stator core flux density,output torque and power density,PM leakage flux and utilization rate.Basic analytical analysis is firstly given,and then the FEM simulation models of the two motors are built,with the FEM comparison analysis conducted to verify the theoretical analysis.4.Presentation,structural topology,operation principle and electromagnetic coupling analysis of the novel 2-degree-of-freedom(2-DOF)hybrid stepping motorTo meet the requirements of bionic-eye-used motor,such as small size,light weight,compact structure,high positioning accuracy,large operating range,large output torque,simple mechanical structure,etc.,three kinds of novel 2-DOF hybrid stepping motor is proposed in this paper,namely,the spherical orthogonal structured 2-DOF hybrid stepping motor,the non-spherical orthogonal structured 2-DOF hybrid stepping motor and the non-spherical structured 2-DOF hybrid stepping motor.Either stator-permanent-magnet or rotor-permanent-magnet hybrid stepping motor can be used for the sub-motors of each 2-DOF motor.To learn more about the characteristics of different structured 2-DOF hybrid stepping motors,so as to select the right model for practical application in different situations,comprehensive comparison analyses in terms of operation principle,operating range,positioning accuracy,torque density and unbalanced force regarding to the three kinds of 2-DOF motors are carried out.In addition,study on electromagnetic coupling between two sub-motors that constitute a 2-DOF motor is performed.Reasons leading to electromagnetic coupling are firstly analyzed,and then the measures to suppress coupling magnetic fields is proposed,in order to improve the performance and simplify the analysis of the 2-DOF motor,in this case,the 2-DOF motor can be divided into two electromagnetically independent sub-motors for analysis.5.Performance analysis and prototype's experimental verification of the novel 2-DOF hybrid stepping motorTaking the spherical orthogonal structured 2-DOF hybrid stepping motor for instance,the 2-dimensional(2-D)equivalent finite element analysis model,including 2-D static coupling equivalent model and 2-D non-coupling equivalent model,is built.Based on which,comprehensive analysis of motor's no-load and load characteristics,positioning accuracy,unilateral magnetic pull force and electromagnetic coupling magnetic field effects are carried out.Prototypes of the proposed three novel 2-DOF hybrid stepping motors are designed and manufactured,and the FEM simulation and experimental results validate the feasibility of motor's operation principle and verify the accuracy of theoretical analysis. |
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