System and method of magnetically sensing position of a moving component

• US 7,259,553 B2
• Filed: 04/13/2005
• Issued: 08/21/2007
• Est. Priority Date: 04/13/2005
• Status: Active Grant

• Current Assignee: SRI International, Inc.
• Original Assignee: SRI International, Inc.
• Inventors: Arns, Jr., Donald C., Garcia, Pablo
• Primary Examiner(s): LEDYNH, BOT L
• Application Number:
  US11/104,740
• Publication Number:
  US 20060232268A1
• Time in Patent Office: 860 Days
• Field of Search: 324/207.25, 324/213
• US Class Current: 324/207.25
• CPC Class Codes: F15B 15/2846 using detection of markings, e.g. markings on the piston rod
• CPC Class Codes: F15B 15/2861 using magnetic means
• CPC Class Codes: G01D 5/00 Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable G01D3/00 takes precedence; specially adapted for apparatus giving results other than momentary value of variable G01D1/00
• CPC Class Codes: G01D 5/24423 Mounting means or means for restraining during shipping G01D5/24442 takes precedence
• CPC Class Codes: G01D 5/24438 Special design of the sensing element or scale
• CPC Class Codes: G01D 5/24447 by energy backup
• CPC Class Codes: G01D 5/24476 Signal processing G01D5/2448 - G01D5/24495 take precedence

Abstract

A position-sensing system magnetically senses the position of a piston rod moving with respect to a cylinder. A magnetically hard layer on the piston rod provides a recording medium. Information is magnetically recorded in regions of the magnetically hard layer. These regions provide a relative encoding scheme for determining the position of the piston rod. Magnetic-field sensors are positioned over redundant tracks of magnetically recorded regions. Each magnetic-field sensor positioned over a given track senses the same magnetized regions while the piston rod moves with respect to the cylinder. Other magnetic-field sensors can sense ambient fields for use in performing common-mode rejection. A write head can dynamically repair damaged or erased regions detected by the magnetic-field sensors. Energized by a battery-backup power source, the magnetic-field sensors and associated circuitry can continue to track movement of the piston rod when the machinery is off.

Claims

1. A position-sensing system, comprising:

a cylinder;

a piston rod movably coupled to the cylinder for movement with respect thereto;

a magnetically hard layer formed on the piston rod to provide a recording medium, a plurality of regions of the magnetically hard layer being magnetized to provide an encoding scheme for determining a position of the piston rod relative to the cylinder; and

a plurality of magnetic-field sensors coupled to the cylinder in proximity of the magnetically hard layer to sense the magnetized regions while the piston rod is moving with respect to the cylinder, at least two of the magnetic-field sensors being axially positioned to sense the same set of magnetized regions in succession and to generate signals in response to the sensed magnetized regions that can be used to determine a position of the piston rod.

2. The position-sensing system of claim 1, wherein at least one given magnetic field sensor is positioned at a greater distance from the magnetically hard layer than the magnetic field sensors positioned to sense the magnetically recorded regions, the given magnetic field sensor sensing an ambient field used to perform common-mode rejection.

3. The position-sensing system of claim 1, further comprising a power source supplying electrical power to the plurality of magnetic field sensors and associated read-head electronics when equipment using the position-sensing system is off so that the magnetic field sensors can sense movement of the piston rod with respect to the cylinder while the equipment is off.

4. The position-sensing system of claim 1, wherein the plurality of magnetically recorded regions are disposed in spatially separated tracks extending along in a direction of the motion of the piston rod, with at least two magnetic field sensors for each track of magnetically recorded regions.

5. The position-sensing system of claim 1, wherein the piston rod is cylindrically shaped and the magnetically recorded regions include rings around a circumference of the piston rod.

6. The position-sensing system of claim 1, wherein the piston rod is made of a ferromagnetic material and the magnetically hard layer is disposed adjacent to an outer surface of the ferromagnetic material without any intervening non-magnetic layer, and wherein the plurality of regions of the magnetically hard layer are longitudinally recorded.

7. The position-sensing system of claim 1, further comprising a flux concentrator near each magnetic field sensor of the plurality of magnetic field sensors, to improve sensing of magnetically recorded regions.

8. The position-sensing system of claim 1, further comprising a second plurality of magnetically recorded regions for providing an absolute measurement associated with movement of the piston rod.

9. The position-sensing system of claim 1, further comprising a write head, integrated with the plurality of magnetic field sensors, for repairing damaged or erased magnetically recorded regions.

10. The position-sensing system of claim 1, further comprising means for computing and storing positional information based on output signals produced by the plurality of magnetic field sensors, wherein the positional information can be displayed or used to control movement or position of a machine or of a component thereof.

11. 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.

12. The method of claim 11, further comprising sensing an ambient field for use in performing common-mode rejection.

13. The method of claim 11, further comprising supplying electrical power to the plurality of magnetic field sensors and associated read-head electronics when a machine integrated with the cylinder and piston rod is off so that the magnetic field sensors can detect movement of the piston rod with respect to the cylinder while the machine is off.

14. The method of claim 11, wherein the step of magnetically recording includes magnetically recording regions in spatially separated tracks extending in a direction of the motion of the piston rod, and further comprising reading each track of magnetically recorded regions with at least two magnetic field sensors.

15. The method of claim 11, wherein the step of magnetically recording includes longitudinally recording information in the plurality of regions of the magnetically hard layer;

and wherein the piston rod is made of a ferromagnetic material and the magnetically hard layer is disposed adjacent to an outer surface of the ferromagnetic material without any intervening non-magnetic layer.

16. The method of claim 11, further comprising concentrating flux near each of the plurality of magnetic field sensors to improve the reading of magnetically recorded regions.

17. The method of claim 11, further comprising sensing a damaged or erased magnetically recorded region and dynamically repairing this region.

18. The method of claim 11, further comprising computing and storing positional information based on output signals produced by the plurality of magnetic field sensors, wherein the positional information can be displayed or used to control movement or position of a machine or of a component thereof.

19. 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.

20. The apparatus of claim 19, further comprising a write head positioned over a track of magnetically recorded regions for dynamically repairing damaged or erased magnetically recorded regions detected by the first plurality of magnetic field sensors.

21. The apparatus of claim 19, further comprising a power source supplying electrical power to the pluralities of 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.

22. The apparatus of claim 19, wherein the piston rod is made of a ferromagnetic material and the magnetically hard layer is disposed adjacent to an outer surface of the ferromagnetic material without any intervening non-magnetic layer, and wherein the plurality of regions of the magnetically hard layer are longitudinally recorded.

23. The apparatus of claim 19, further comprising a flux concentrator near each magnetic field sensor of the first plurality of magnetic field sensors, to improve sensing of the magnetized regions of the magnetically hard layer.

24. The apparatus of claim 19, further comprising means for computing and storing positional information based on output signals produced by the pluralities of magnetic field sensors, wherein the positional information can be displayed or used to control movement or position of a machine or of a component thereof.

31. The apparatus of claim 19, wherein the plurality of magnetically recorded regions are disposed in spatially separated tracks extending along in a direction of the motion of the piston rod, with at least two magnetic field sensors for each track of magnetically recorded regions.

32. The apparatus of claim 19, wherein the piston rod is cylindrically shaped and the magnetically recorded regions include rings around a circumference of the piston rod.

33. The apparatus of claim 19, further comprising a second plurality of magnetically recorded regions for providing an absolute measurement associated with movement of the piston rod.

25. 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.

26. The apparatus of claim 25, wherein the piston rod is cylindrically shaped and the magnetically recorded regions include rings around a circumference of the piston rod.

27. The apparatus of claim 25, wherein the piston rod is made of a ferromagnetic material and the magnetically hard layer is disposed adjacent to an outer surface of the ferromagnetic material without any intervening non-magnetic layer, and wherein the information magnetically recorded in the plurality of regions of the magnetically hard layer is longitudinally recorded.

28. The apparatus of claim 25, further comprising a flux concentrator near one or more of the magnetic field sensors, to improve sensing of magnetically recorded regions.

29. The apparatus of claim 25, further comprising a second plurality of magnetically recorded regions for providing an absolute measurement associated with movement of the piston rod.

30. The apparatus of claim 25, further comprising means for computing and storing positional information based on output signals produced by the pluralities of magnetic field sensors, wherein the positional information can be displayed or used to control movement or position of a machine or of a component thereof.