| In the fields of aerospace and ultra-precision processing,the pointing platform in the imaging,positioning and communication device such as space telescopes,remote sensing satellites,and semiconductor lithography systems,is satisfied to the requirements of high-definition imaging and precise positioning by adjusting its posture and position.Traditional pointing and positioning devices are mostly supported by mechanical bearings.The precision is limited by inevitable mechanical friction and wear.Lorentz force-based magnetic levitation technology with the advantages of frictionless,high positioning accuracy,fast response speed,and small inertia,is regarded as the ideal actuator for realizing high precision,large stroke,multiple degrees of freedom,and fast response of the magnetic levitation pointing platform.The research content and status quo of Lorentz pointing platform at home and abroad are introduced,and its development trend is analyzed.On the basis of existing pointing platforms,a novel Lorentz pointing platform with three-degree-of-freedom Lorentz bearing and circular Halbach plane motor is proposed,and its structure and working principle are introduced.This scheme has the characteristics of compact structure,high thrust density,good vibration isolation performance,and large rotation stroke.For the three-degree-of-freedom Lorentz bearing,the mathematical model of radial deflection moment and axial suspension force is derived by the integral method,and the air gap magnetic flux density model is established based on the magnetic circuit method and the reluctance division method.In addition,an optimization method for the air gap magnetic flux density of Lorentz bearing under different working conditions is proposed:(1)When the permanent magnet thickness is constant,the optimal thickness of the magnetic permeable ring is analyzed;(2)When the radial size of the Lorentz bearing and the air gap length are constant,the optimal ratio of the permanent magnet magnetization length to the permeable ring thickness is proposed;(3)When the radial size of the Lorentz bearing is fixed and the air gap length is variable,the optimal values of the permanent magnet magnetization length,the magnetic ring thickness,the air gap size,and the coil winding thickness are analyzed.A novel three-degree-of-freedom Lorentz bearing with dual auxiliary magnetic circuits is proposed.Taking the circular Halbach planar motor as the research object,the mathematical models of its radial translational thrust and axial rotational torque are established,and the air gap flux density model of the Halbach array permanent magnets is established based on the boundary method.Aiming at the comprehensive optimization of the size and uniformity of the air gap magnetic flux density,the finite element analysis of the permanent magnet thickness,the magnetic material thickness,and the magnetization angle of the auxiliary magnetic steel is carried out,which effectively improves the air gap magnetic flux density characteristics.A novel Halbach array planar motor structure is proposed.The six-degree-of-freedom Lorentz pointing platform prototype is developed.a magnetic flux density measurement experiment was carried out,and the proposed performance indicators were verified and analyzed.The results show that the experimental results are in good agreement with the numerical analysis and finite element simulation results,which indicates that this Lorentz pointing platform is promising to meeting the requirement of high-precision positioning in the fields of aerospace and ultra-precision machining. |
