| dc.description.abstract | An approach for self-sensing is proposed for voice-coil actuators that have an invertible, position-dependent inductance. Actuators with these properties are denoted as position-invertible, variable-inductance (PIVI) actuators. The self-sensing methodology is based on tracking the inductance of a PIVI actuator from the oscillation frequency of a modified Pierce oscillator. By extension, the oscillation frequency provides a measurement of the actuator position without an external position sensor.
An electrical model for PIVI voice-coil actuators is first derived to aid in analysis. Oscillator theory is then introduced and applied to the analysis of a typical Pierce oscillator. The modified Pierce oscillator is then introduced and analyzed under the assumption of low-frequency actuator motion and driving current relative to the oscillation frequency. The effects of parasitic capacitance from the actuator current source are then discussed along with a mitigation method. A test circuit, including the modified Pierce oscillator and a transconductance amplifier, is then presented. Due to time constraints, the modified Pierce oscillator was constructed with a variable inductor rather than an actual PIVI actuator. This was considered acceptable since the variable inductor mimics a PIVI actuator operating under the low-frequency assumption. Modifications to the transconductance amplifier were presented that allowed parasitic impedance to be increased by a minimum factor of three.
The modified Pierce oscillator circuit was tested under conditions that simulated a powered PIVI actuator. Results showed the oscillation frequency was an invertible function of the core-insertion distance of the variable inductor. It was also observed that the oscillation frequency varied less than 3% in the presence of various disturbance currents through the variable inductor. The tested conditions simulated a powered PIVI actuator, so it was considered likely that these two behaviors would also be observed if the modified Pierce oscillator was used with an actual PIVI actuator. While these results are not definitive, they suggest that the modified Pierce oscillator could be used as a self-sensing methodology for PIVI type voice-coil actuators. However, more work will be needed to verify this behavior with an actual PIVI type voice-coil actuator. | |
