Constant-current versus constant-voltage VCM drive analysis

A voice-coil-motor (VCM)-driven actuator is analyzed for both constant-current and constant-voltage drive operation. Through the use of dimensional analysis, the solutions to the two drive methods are directly compared. This allows for quick evaluation of an actuator design. The analysis compares the actuator performance parameters, including seek time, switching time, and maximum angular velocity. The relationship between constant-current and constant-voltage drive is shown to depend on the value of a dimensionless parameter. For actuators with low values of this parameter (<1.43), the current is not back-EMF limited when constant-voltage drive is used. It is shown that such actuators have the same seek time for the same average power dissipated in the coil, regardless of which drive approach is chosen. Therefore, a single equation was derived to describe power generated at the source for both constant-current and constant-voltage drives. The ratio of average power generated at the source average power dissipated in the coil is equal to the ratio of source voltage to stall voltage. A given actuator dissipating the same power in the coil will always have a lower stall voltage and a higher peak voltage if constant-current drive is used instead of constant-voltage drive