Linear motor velocity sensor

Abstract

A velocity sensing method and apparatus to be used in conjunction with a linear motor having a moveable voice coil. More particularly, an apparatus is disclosed whereby a velocity sensing loop is positioned on a surface defined by wire windings of a linear motor voice coil. The velocity sensing loop is configured so that an end portion is perpendicular to the longitudinal axis of the voice coil and two side portions are parallel to the longitudinal axis of the voice coil. As the end portion of the velocity sensing loop traverses a magnetic field with which the voice coil reacts for positioning thereof, a voltage is induced within the velocity sensing loop which is proportional to the velocity of the loop as it passes through the magnetic field. This voltage can be used in conjunction with a feedback loop to control current through, and thus velocity of, the voice coil, thereby providing a means by which velocity of the voice coil can be maintained within predetermined limits during the time that the velocity sensing loop is passing through the magnetic field. The apparatus is believed to be especially useful for head positioning in magnetic disk memory systems by providing a means whereby velocity of the head as it approaches a disk surface can be controlled without use of an external velocity transducer.