Method and Apparatus for Detecting Rotational Movement of a Piston Rod

Abstract

A piston rod position sensing system includes a cylinder and a piston rod arranged in the cylinder for movement with respect thereto. A magnetically hard layer is formed on the piston rod to provide a recording medium. A magnetic pattern is recorded in the magnetically hard layer. The magnetic pattern includes tracks recorded in the magnetically hard layer lengthwise of the piston rod. Each track comprises magnetically written regions used to identify a current position of the piston rod. The sensing system also includes a plurality of magnetic field sensors in greater number than the plurality of tracks. Each magnetic field sensor senses the magnetically written regions of one or more of the tracks while the piston rod is moving with respect to the cylinder and generates signals used for detecting rotation of the piston rod in response to the sensed magnetically written regions.

1 . A piston rod position sensing system, comprising:
 a cylinder;   a piston rod arranged in the cylinder for movement with respect thereto;   a magnetically hard layer formed on the piston rod to provide a recording medium, a magnetic pattern being recorded in the magnetically hard layer, wherein the magnetic pattern comprises a plurality of tracks recorded in the magnetically hard layer lengthwise of the piston rod, each track comprising magnetically written regions that are used to identify a current position of the piston rod; and   a plurality of magnetic field sensors in greater number than the plurality of tracks, each magnetic field sensor sensing the magnetically written regions of one or more of the tracks while the piston rod is moving with respect to the cylinder and generating signals used for detecting rotation of the piston rod in response to the sensed magnetically written regions.