System and method of magnetically sensing position of a moving component

A method for sensing a position of a piston rod moving relative to a cylinder, the method comprising:

• forming a magnetically hard layer on the piston rod to provide a recording medium for storing information;
• magnetically recording information at a plurality of regions of the magnetically hard layer along a direction of motion of the piston rod;
• reading, by a plurality of magnetic field sensors, the same magnetically recorded regions of the magnetically hard layer while the piston rod is moving relative to the cylinder;
• and
• generating output signals by the plurality of magnetic field sensors from which a position of the piston rod with respect to the cylinder can be determined.

An apparatus, comprising:

• a cylinder;
• a piston rod movably coupled to the cylinder for movement with respect thereto;
• a magnetically hard layer formed on a surface of the piston rod to provide a recording medium, information being magnetically recorded in a plurality of regions of the magnetically hard layer to provide an encoding scheme for determining a position of the piston rod relative to the cylinder;
• a first plurality of magnetic field sensors positioned over one or more tracks of magnetically recorded regions to sense the magnetically recorded regions while the piston rod moves with respect to the cylinder;
• and
• a second plurality of magnetic field sensors for sensing ambient fields near the first plurality of magnetic field sensors for use in performing common-mode rejection.

An apparatus, comprising:

• a cylinder;
• a piston rod movably coupled to the cylinder for movement with respect thereto;
• a magnetically hard layer formed on a surface of the piston rod to provide a recording medium, information being magnetically recorded in a plurality of regions of the magnetically hard layer to provide an encoding scheme for determining a position of the piston rod relative to the cylinder;
• a first plurality of magnetic field sensors positioned over redundant tracks of magnetically recorded regions, at least two magnetic field sensors being positioned over each track to sense the magnetically recorded regions while the piston rod moves with respect to the cylinder;
• a second plurality of magnetic field sensors for sensing ambient fields near the first plurality of magnetic field sensors for use in performing common-mode rejection;
• a write head for dynamically repairing damaged or erased magnetically recorded regions detected by one or more magnetic field sensors of the first plurality of magnetic field sensors;
• and
• a power source supplying electrical power to the magnetic field sensors and associated read-head electronics when the apparatus is off so that the magnetic field sensors can continue to sense movement of the piston rod with respect to the cylinder while the apparatus is off.