M.S. Thesis Presentation by Joel Christopher Miller
Wednesday, May 13, 1998

(Dr. Thomas Kurfess, advisor)

"Modulating Dynamic Stiffness of a Brushless DC Linear Motor"


The goal of this research is to modulate the dynamic stiffness profile of a brushless linear DC motor.  There exists a large pool of research attesting to the critical role the dynamic stiffness of a machine tool plays in the quality of its finished parts and efficiency of the machining process.  Depending on the operation performed and the material of the machined part, different profiles of dynamic stiffness result in varying work piece surface finish and process efficiency.  Currently, the dynamic stiffness of a machine tool has been strictly dependent on its physical composition.  Consequently, the machining process is designed around a machine tool’s existing dynamic stiffness.  The ability to change the dynamic stiffness of linear drives employed as main feed mechanisms will provide tremendous flexibility to machine tools by allowing the dynamic stiffness to be designed around the desired process.

This research includes performing comprehensive system identification of the motor controller, amplifier and motor system, developing analytical results varying controller parameters to change resonant frequencies and amplitudes of the stiffness profile.  Experimental data are obtained for comparison to predicted results.  The resultant stiffness of the controlled system is analyzed to determine the relative success of the control system.  In addition, several alternative controller designs are developed and analytically studied for possible future implementation.