This research has been motivated by the role of dexterous actuators and sensors for measurement and control of high precision dynamic systems and manufacturing automation.  Dr. Lee and his students conducted some of the first detailed study on the creation of a three degrees of freedom (DOF) ball-joint-like variable-reluctance (VR) spherical motor and a means to provide non-contact direct sensing of roll, yaw, and pitch motion in a single joint.  Their results have been the first to provide a rational basis for design, modeling, and control of a three-DOF VR wrist motor as well as the first showing the important differences between the VR spherical motor and the popular three-consecutive-joint wrist or spherical wrist motors of a different kind.

More recently, Lee and his students have investigated the feasibility of designing a spherical wheel motor (SWM) for applications (such as car wheels, propellers for boats, helicopter or underwater vehicle, gyroscopes, and machine tools) where dexterous orientation control of a continuously rotating shaft.   Unlike a VRSM where the  stator permanent magnets (PM) and the rotor electromagnets (EM) are placed on locations following the vertices of a regular polygon, equally-spaced magnetic poles are placed on layers of circular planes for a SWM.  This enables the shaft to spin using a switching controller while allowing the shaft to incline much like a VRSM.  

Lee, K.-M., R. Roth, and Z. Zhou, "Dynamic Modeling And Control of a Ball-Joint-Like Variable Reluctance Spherical Motor,"  ASME Journal Of Dynamics Systems,  Measurements, And Control, Vol. 118, No. 1, March 1996, pp.29-40.

Zhou, Z. and K.-M. Lee, "Characterization of a Three Degrees-of-freedom Variable-Reluctance Spherical Motor," Journal of Systems Engineering, (Special Issue on Motion Control), Vol. 4, pp. 60-69, 1994.  Also presented at the 1994 Japan-U..S. A. Symposium on Flexible Automation, Kobe, Japan, July 11-18, 1994.

Lee, K-M. D. E. Ezenekwe, and T. He, "Design and Control of a Spherical Air Bearing System for Multi-DOF Ball-joint-like Actuators," Mechatronics, 2003, vol. 13, 175-194.

Lee, K.-M. R. A. Sosseh and Z. Wei, “Effects of the Torque Model on the Control of a VR Spherical Motor,” IFAC J. of Control Engineering Practice, 2004, vol. 12/11 pp 1437-1449.

Lee, K.-M., H. Son, and J. Joni, "Concept Development and Design of a Spherical Wheel Motor (SWM)," Proc. of the 2005 IEEE ICRA, April 18-22, Barcelona, Spain, pp. 3652- 3657

Yan L., I. M. Chen, G. L. Yang, W. Lin and K. M. Lee, "Analytical and Experimental Investigation on the Magnetic Field and Torque of a Permanent Magnet Spherical Actuator,” August 2006, IEEE Trans. on Mechatronics, vol. 11, No. 4, pp 409-419.