Sensorless position control of voice-coil motors for needle-free jet injection

This paper demonstrates a simple method for sensorless position estimation and control of a linear voice-coil actuator. Such actuators are currently used in needle-free jet injector prototypes. The sensorless method makes use of the position dependent impedance of the voice-coil at high frequencies to produce an estimate of coil position. This is achieved through the addition of a high frequency signal to the motor´s driving signal. The position and frequency dependence of the voice-coil impedance is presented. Also the ability of this sensorless position estimation method to control position to a square set point is demonstrated using PID control. A jet injection is performed in order to observe the ability of this position sensing method to track position in such a high speed application.