Linear motor with angularly indexed magnetic poles

Abstract

A motor for rectilinear stepping over a multiplicity of fine steps, or controlled synchronous reciprocation over a relatively long stroke. Electric coils are arranged in what is preferably an outer stator having two sections separated by an axially poled permanent magnet. Each section is formed by a series of magnetic-pole-defining members, successive members being indexed angularly by the angle between adjoining slots. A displacer has an axially extending series of magnetizable ring surfaces, separated by circumferential gaps having an axial length preferably equal to two displacer members. Operating as a stepping motor, energization of one stator coil increases magnetic flux in those stator members of a section having the same angular alignment, and attracts displacer teeth into alignment with those stator members. For the next step, another coil set is energized, to increase magnetic flux in pole faces in the axially adjoining stator members, indexed one angular position, so that the displacer moves a step equal to the axial length of the displacer member. In a preferred embodiment the displacer is made as a thin tube of alternating magnetizable and nonmagnetizable portions, with the return path formed by an inner stator having teeth aligned opposite the outer stator pole forming teeth. For the same coil current, this configuration can provide greater force while at the same time reducing the displacer mass.