Optimal DC motor design for constant voltage seek motion

Abstract

The seek motion (load moved between two stationary positions) performance is analyzed in terms of move time, power dissipation, and gear coupling ratio between the load and motor shafts of mechanical systems driven by DC motors. The motors considered are operated under constant voltage during acceleration, and then the voltage is reversed for deceleration. This analysis is applicable to any kind of DC motor if the electrical time constant is very short compared with the mechanical time constant and the move time. A contour plot of the normalized move time shows the seek speed limitation under any load and power dissipation, and indicates the region for optimal design. The system designer can decide immediately what motor size, in terms of power rate, and gear ratio should be chosen to meet the specified move time with minimal power. The designer can also establish the move time specification under a given power limit. There is no iteration required in the process. An optimal DC voice coil motor (VCM) design based on the analysis result is then described. The load is a rotary actuator for accessing both sides of a 3.5 in. diameter magnetic hard disk. Test results indicate that the specification of 7 ms move time for the average length track seek was met while using minimum power. >