Importance

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Abstract

A pair of referencing coils are mounted in direct association with a rotatable scale having a reference position index and a code strip. A reference position sensor generates a signal in response to alignment of the reference position sensor with the reference position index, and magnetic members are operative to normally align the scale with magnetic north. An electrical drive is provided for alternately energizing the reference coils disposed at predetermined angles to one another and to the magnetic members which respond to the energization of each coil and advance the reference position index toward the reference position sensor. Preferably alignment coils are positioned at equal angles to either side of the reference position sensor so that drive requirements are such that the current applied to each coil is only necessary to draw the magnets and associated scale through an angle which is just greater than one-half the total included angle between the coils.

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First Claim