Analysis and Design of a Novel Magnetic Levitation Gravity Compensator With Low Passive Force Variation in a Large Vertical Displacement

This paper presents a novel magnetic levitation gravity compensator and its design philosophy by which the nearly constant levitation force performance within a relatively large vertical displacement can be easily obtained. Generally, the absolute levitation is desired in many ultraprecision positioning systems, because the vibration disturbance can be effectively isolated. However, it is very difficult to obtain the low stiffness performance due to the serious nonlinearity of the passive force between two permanent magnets. The proposed magnetic levitation gravity compensator is combined with two passive magnetic levitation units owning the opposite levitation force characteristics. Based on the design principle of stiffness counteraction, the two levitation forces from the two units are superimposed but the resultant levitation force variation is very low. The stiffness counteraction effect is finally verified by experiments. The prototype testing data shows that the maximum levitation force variation of the proposed magnetic levitation gravity compensator within ±5 mm is only 0.72 N, which is 2.4% of the rated passive levitation force 30 N.