Electromagnetic force motors having extended linearity

Claim 1

In an electromagnetic force motor having a pair of pole pieces spaced apart to provide an airgap therebetween; an armature positioned with a portion thereof in said airgap, said armature being adapted to move in said airgap from a null position thereof thereby more closely approaching one of said pole pieces; a magnetic circuit in said motor including said pole pieces and said armature and including permanent magnetic means for providing polarizing flux and a frame member securing said pole pieces to said permanent magnet means; electrical signal receiving means disposed on said magnetic circuit to establish magnetic flux therein of a strength proportional to a received electrical signal; the improvement of apparatus for extending the linearity of the force versus input signal characteristic of said force motor, comprising: at least one discrete member of magnetically saturable material disposed between said frame member and said permanent magnetic means and having an induction/magnetic force characteristic different from the induction/magnetic force characteristic of said frame member so as to define a magnetic saturation path thereat; said permanent magnet polarizing flux being sufficient to magnetically saturate said discrete member at a preselected armature position other than its null position within said airgap but being insufficient, at said preselected armature position to magnetically saturate frame member material of the same configuration as said discrete member.