Patent ID: 7309932

Claim:
A voice coil motor apparatus for positioning, comprising: a voice coil motor to generate a motion force to drive a load; a position feedback sensor to measure relative displacement of a movable part of the voice coil motor, the position feedback sensor including: a photo interrupter that uses a light emitting diode to transmit light signals, and a phototransistor to receive reflected light signals; a light reflector that is installed with a reflective surface facing the photo interrupter, so that displacement of the movable part of the motor results in changes of light intensity of the reflected light signals; and a bias circuit that receives the reflected light signals from the photo interrupter and converts the light signals to voltage signals accordingly; and a positioning controller that uses the voltage signals representing the displacement to perform mathematical operations, so that a motion force on the movable part can be manipulated to achieve positioning; wherein the bias circuit comprises: an op amp having a positive terminal and a negative terminal, the positive terminal being connected to a steady voltage source and the negative terminal being connected to a collector of the phototransistor; and a resistor in which one end is connected to the negative terminal of the op amp, and another end is connected to an output of the op amp, so that a collector current is converted to the voltage signals.