Study On Transmission Characteristics And The PM Structure Of The LRMG

The Linear-Rotary Magnetic Gear(LRMG)transmit the rotation of screw to the linear motion of nut,or vice versa,through magnetic coupling with no direct mechanical contact.Thus,the problems such as friction,wear,etc.could be eliminated due to the non-contact mechanism.LRMG has the advantages of inherent overload protection,lubrication free,and no lubricant evaporation too.So it can be used to the environment of needing high cleanliness requirements.Now,LRMG is still in basic research phase.Many key theoretical and technical problems haven't been solved.In this paper,the LRMG in which the adjacent spiral poles on screw(or nut)has no air gap was.investigated firstly.The transmission theory,gear ratio and the relationship between the thrust and the structure parameters were analyzed.The static characteristic of it,and the influences of the structure parameters to the stall fore of nut and the stall torque of screw were simulated with FEM.The coupling area between spatial poles of screw and nut is proportional to the axial length of nut and the outer diameter of the screw.Simulation result shows that the stall force and torque increase linearly along with the coupling area increasing.Based on the relational expression of the pole pitch,pole pairs and the gear ratio,the influence of the pole pitch and pole pairs to the stall force and torque was investigated.Result shows that while the pole pitch and pole pairs changes independently(gear ratio changes),the stall force decrease with the pole pairs increasing,but it will get a peak value when pole pitch changes.The stall torque of screw increases along with the pole pitch and pole pairs get larger.When the gear ratio is fixed,the pole pitch and pole pairs will subjects to gear ratio constraint,and an optimal value of pole pairs exists to make the stall force and torque greatest.Orthogonal test method is used to investigate the the influence of several factors which are air gap length,pole thickness and yoke thickness of screw and nut to the stall force and torque.Result shows that air gap legth has the greatest influence,and the followed factor is pole thickness.The yoke thickness almost has no influence.Based on above research,the LRMG in which the adjacent spiral poles on screw(or nut)has air gap was investigated too.The gear ratio expression,and the relationship about gear ratio to rotation speed of screw and translation speed of nut,or to torque of screw and thrust of nut.The influence of several factors such as air gap length,pole pairs,pole thickness,and the yoke thickness to the stall force and torque is simulated.Finally,the LRMG employs nonideal helical magnets was studied.The relationship between the gear ratio and the structure parameters was established,and the influence of radius angle of pole piece to the stall force and torque characteristics,and the gear ratio was investigated.