Voice Coil Motor Displacement Sensor Using Impedance

The patent applies periodic measurement signals at specific frequencies (e.g., 25 kHz) to the voice coil motor to determine displacement. By using periodic signals at frequencies well above the motor's resonance frequency (50-150 Hz), the system achieves accurate displacement measurements through impedance variations while the periodic nature of the signal prevents cumulative errors and allows for continuous monitoring without disrupting normal motor operation.

The patent utilizes changes in electrical parameters (impedance, inductance) of the voice coil motor in response to alternating measurement signals to determine displacement. By monitoring how the motor's electrical parameters change with position, the system achieves precise displacement measurement without mechanical contact or additional sensors that could interfere with motor operation.

The patent makes the voice coil motor self-servicing by using its own electrical properties (impedance, inductance) to determine its position. The motor's inherent electrical characteristics vary with displacement, allowing the system to measure position without external sensors. This self-service approach eliminates the need for additional Hall sensors, position sensors, or encoders, thereby reducing device complexity and cost while maintaining measurement precision.

The patent makes the voice coil motor multi-functional by enabling it to serve both as the actuator and as the position sensor. The same voice coil motor that provides mechanical displacement also provides the electrical signal characteristics needed for position measurement. This universal approach eliminates the need for separate sensing components and integrates measurement functionality into the motor itself.

The patent uses periodic measurement signals at frequencies well above the motor's resonance frequency (e.g., 25 kHz versus 50-150 Hz resonance). By operating at such high frequencies, the measurement signal period is much shorter than the motor's mechanical response time, preventing the signal from causing resonant vibrations or unwanted motion while still allowing accurate impedance measurements to be taken during each cycle.

The patent exploits the frequency-dependent electrical parameters of the voice coil motor, particularly inductance, which varies with displacement. By measuring impedance at high frequencies where the motor's mechanical response is negligible, the system accurately captures the displacement-dependent inductance variations without inducing harmful mechanical motion, as the electrical measurements occur too rapidly to drive the mechanical system.