Sensorless position detection of a linear actuator using the resonance frequency

This paper presents a method to detect the position of a linear actuator without any position sensor. The actuator winding has a resonance frequency that is very related to the position of the linear actuator moving part. A sinusoidal scan voltage is superposed to the main voltage. Its frequency is close to the resonance frequency and therefore it is possible to measure the resulting scan current amplitude that allows position detection.