Abstract: A linear force motor has an elongated body provided with an annular chamber therewithin. An armature is arranged within the chamber for axial movement relative thereto. Two axially-spaced permanent magnets, with their like poles arranged to face one another, are arranged within the body radially inwardly of the chamber, and are separated by a common polepiece. The force motor has four axially-spaced active air gaps, arranged in various reciprocal pairs and various parallel pairs. When the armature is shifted one direction relative to the body, the majority of each magnet's static flux passes through one parallel pair of air gaps. When the armature is shifted in the other direction relative to the body, the majority of each magnet static flux passes through the other parallel pair of air gaps. The motor has one or more coils operatively arranged to generate control flux in a path which passes through at least one reciprocal pair of air gaps.

Abstract: A method of providing a torque motor with air gaps of equal length between an armature interposed between two spaced polepieces, comprises the steps of: assembling the torque motor so that the armature is roughly positioned between the polepieces, positioning an electrode so that two spaced portions thereof of equal width are arranged proximate the air gaps, providing a plurality of repetitious pulses of electrical energy between the electrode and the torque motor assembly, moving the electrode and torque motor assembly relative to one another, and removing proximate material from the armature and polepieces, as necessary, by electrical discharge between the electrode and torque motor assembly, thereby to provide air gaps of equal length between the armature and the polepieces.