Force and torque characteristics for a slotless Lorentz self-bearing servomotor

A new type of self-bearing motor is presented that uses Lorentz-type forces to produce both bearing force and motoring torque. The design eliminates the tradeoff between motoring torque and bearing force with respect to permanent-magnet thickness found in many previous designs. The self-bearing motor layout and servo control are described including alternative winding schemes. Permeance and flux models are presented and used to derive expressions for torque and force production. As with conventional magnetic bearings, these expressions are quadratic with both rotor position and control current. A linearized force-current-displacement relationship is then derived for a general operating point. Experimental results are presented for a prototype servomotor. These results show good agreement with theory and, hence, validate the permeance and flux models, and the linearized force-current relationship. The prototype servomotor, 152 mm in outer diameter and 25.4 mm in length, was a peak bearing force capacity of 213.6 N and a peak torque capacity of 24 N·m, which is limited by power amplifier saturation.