Apple Inc.
Mass displacement estimation using back EMF and magnetic reference crossing

Abstract:

In an embodiment, a single-sided or double-sided moving magnet haptic engine comprises: a frame; one or more magnetic field sources mounted to the frame and operable to generate a magnetic field and a back electromotive force (EMF) voltage; a magnetic mass positioned within the frame and operable to move within the frame along a movement axis; a comparator mounted to the frame, the comparator operable to detect the magnetic field and to generate a signal indicating a crossing of one or more magnetic references by the magnetic field; and a processor coupled to the one or more sensors and operable to estimate a displacement of the magnetic mass on the movement axis based on the back EMF voltage and the signal. Other embodiments are directed to a single-sided or double-sided moving coil haptic engine.