Abstract: A position control and monitoring circuitry is provided for an electric motor having a plurality of coils and a movable element. A drive circuit generates a square wave drive signal of variable mark/space ratio to drive the coils to position the movable element. A monitoring circuit modulates square wave transitions at a sub-harmnonic of the drive signal frequency and generates a monitoring signal for injection into the coils. A sensor senses the monitoring signal from the coils to determine the position of the movable element. A difference circuit drives the drive circuit with a difference between an input signal and an output signal of the sensor.

Abstract: A linear permanent magnet electric motor whose poles are extended by pole-pieces of high permeability material to provide the armature or moving element of the assembly. Two groups of two windings are positioned symmetrically about the nominal geometric center of each of the pole-pieces and hence nominal center of magnetic saliency. Thus, the device is capable of being a combined motor and position sensor as well as a device capable of combining linear velocity and linear position sensing.