An Orientation Measurement System Of The Permanent Magnet Spherical Motor Based On Magnetic Field Measurement

With the rapid development of aerospace,military,industrial intelligence and biomimetic robots,the demand for multi-degree-of-freedom motors has become stronger.The spherical motor has a simple structure,a small size and can realize threedegrees-of-freedom movement.So the spherical motor has attracted wide attention of researchers,and in order to achieve closed-loop control of the spherical motor,the orientation measurement of the rotor is essential.In this paper,a permanent magnet spherical motor for satellite attitude is taken as the research object,and a two-degree-of-freedom orientation measurement method using Hall sensors is proposed.The rotor has eight magnetic poles and is alternately distributes on the vertices of virtual regular hexahedron inscribed in the rotor.The overall spatial magnetic field of the rotor is acquired by rotation transformation and linear superposition,and represented by a spherical harmonic function.Utilizing the characteristics of the overall spatial magnetic field of the rotor along the spherical coordinate system,draw magnetic field contour lines at any magnetic field value,and the approximate fitting ellipses can be obtained.Then,four Hall sensors are formed into a sensor unit,and the position difference between the magnetic pole and the sensor unit is solved according to the geometry intersection relationship between the sensor unit and the magnetic field contour lines.Since there are multiple magnetic poles in the entire rotor space and only one sensor unit cannot cover the entire rotor space,a placement strategy of four sensor units is proposed.Since the existing four sensor units and eight magnetic poles on the rotor,the overall measurement procedure of rotor position are arranged in three steps,firstly determine the magnetic pole position measured by the sensor unit used in the current position,then determine the category of the center of chosen sensors group in the current position,finally subdivide in the horizontal direction and vertical direction to solve the rotor position accurately.Then,a rotor position measurement system including a three-axis rotary table and a Hall sensor measurement device is designed and manufactured.The stepper motor is used to drive the rotor to rotate in the three-axis rotary table.The position of the Hall sensors in the measurement device is designed to ensure that the magnetic field measured by the Hall sensors contains only the radial component.Finally,given a set of angular trajectories,verify the effectiveness of the orientation measurement algorithm through simulation and the rotor position measurement system.This method lays the foundation for the optimization of following orientation measurement methods and the control of spherical motors.