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

Lyndon S. Stephens, Dae Gon Kim

Research output: Contribution to journalArticlepeer-review

40 Scopus citations


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.

Original languageEnglish
Pages (from-to)1764-1773
Number of pages10
JournalIEEE Transactions on Magnetics
Issue number4
StatePublished - Jul 2002

Bibliographical note

Funding Information:
Manuscript received December 11, 2000; revised March 19, 2002. This work was supported by Airex Corporation, Dover, NH, and the United States Air Force under contract F04701-97-C-0014. The authors are with the Department of Mechanical Engineering, University of Kentucky, Lexington, KY 40506-0108 USA (e-mail: stephens@engr. Publisher Item Identifier S 0018-9464(02)06369-0.


  • Magnetic bearings
  • Permanent magnet motors
  • Self-bearing motors
  • Servomotors

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Electrical and Electronic Engineering


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