Multi-fiber cylinder position sensor using time-of-flight technique

• US 6,769,349 B2
• Filed: 06/04/2001
• Issued: 08/03/2004
• Est. Priority Date: 06/04/2001
• Status: Expired due to Term

• Current Assignee: Blue Leaf IP Incorporated (CNH Industrial N.V.), CNH America Llc (CNH Industrial N.V.)
• Original Assignee: Case Corporation (CNH Industrial N.V.)
• Inventors: Arshad, Mohammad Javaid, Berger, Alan D., Maierhafer, Daniel L., Chan, Danley C.
• Primary Examiner(s): Look, Edward K.
• Assistant Examiner(s): LESLIE, MICHAEL S
• Application Number:
  US09/872,874
• Publication Number:
  US 20020180461A1
• Time in Patent Office: 1,156 Days
• Field of Search: 92/5.R, 91/1
• US Class Current: 92/5.00R
• CPC Class Codes: G01S 17/10 using transmission of interrupted, pulse-modulated waves determination of distance by phase measurements G01S17/32
• CPC Class Codes: G01S 17/88 Lidar systems specially adapted for specific applications
• CPC Class Codes: G01S 7/4818 using optical fibres

Abstract

A hydraulic actuator is disclosed having a cylinder with a piston that is moved by hydraulic fluid. A light guide in one end of the cylinder directs a laser beam into the cylinder, and off the piston where the beam is reflected. The beam then exits the cylinder through at least two light guides connected to two corresponding optical fibers. Each of the optical fibers are joined together into one fiber that carries the reflected beam of light to a photo-diode located remote from the cylinder. A control circuit measures the time of flight of the laser beam.

Claims

1. A fluid actuated cylindrical actuator is provided comprising:

a cylinder having first and second end;

an end cap fixed to the first end of the cylinder and having a rod opening;

a piston disposed in the cylinder;

a rod coupled to the piston and extending from inside the cylinder to outside the cylinder and passing through the rod opening;

a first light guide extending from inside the cylinder to outside the cylinder and adapted to transmit at least a first beam of laser light at a first frequency from outside the cylinder to inside the cylinder and to bar the passage of the fluid;

and a plurality of second light guides having first ends extending from inside the cylinder to outside the cylinder and distal second ends that are coupled to at least one light detector, wherein each of the plurality of second light guides is configured to substantially simultaneously transmit at least a first reflected portion of the beam of laser light from inside the cylinder to outside the cylinder.

2. The actuator of claim 1, wherein the first light guide is disposed to transmit the first beam of laser light substantially along a longitudinal axis of the cylinder such that the first beam impinges on a reflective portion of the piston over substantially an entire range of piston travel.

3. The actuator of claim 2, wherein each of the second light guides is disposed on opposing sides of the first light guide such that they both receive a reflected portion of the light beam.

4. The actuator of claim 3, wherein each of the second light guides is disposed substantially equidistantly from the first light guide.

5. The actuator of claim 4, wherein the plurality of second light guides includes at least three light guides that are disposed along a semicircular arc about the first light guide.

6. The actuator of claim 5, wherein the second ends of the plurality of second light guides are optically coupled to a single light detector and wherein the light detector has an electrical output that is produced by light carried by at least two of the plurality of second light guides.

7. A hydraulic actuator for an agricultural or construction vehicle comprising:

a cylinder having a substantially circular internal diameter and a longitudinal cylindrical axis;

a piston having a substantially circular outer diameter and configured to be received in and hydraulically sealed against the inner diameter of the cylinder;

a piston rod with a substantially circular outer rod diameter that is fixed to the piston and extends from the piston inside the cylinder, through a first end wall of the cylinder to a location outside the cylinder, wherein the first end wall is disposed to enclose and seal a first end of the cylinder and is substantially perpendicular to the longitudinal axis of the cylinder;

a second end wall fixed to the cylinder and disposed to seal a second end of the cylinder substantially perpendicular to the longitudinal axis of the cylinder, the second end wall including a first optical path configured to transmit a beam of laser light through the second end wall to a reflective surface fixed to the piston and further including a plurality of second optical paths returning from the reflective surface to transmit the reflected beam of laser light back through the end wall in a plurality of return paths;

a first optical fiber optically and mechanically coupled to the second end wall to transmit the beam of laser light from a remote laser light source to the first optical path; and

a plurality of second optical fibers optically and mechanically coupled to the second end wall to transmit the reflected beam of laser light to at least one remote laser light receiver.

8. The hydraulic actuator of claim 7, wherein the first optical path and the plurality of second optical paths includes at least one hermetically sealed fiber optical feed-through or connector extending through the second end wall.

9. The hydraulic actuator of claim 8, wherein the first optical fiber and the plurality of second optical fibers are multi-modal optical fibers.

10. The hydraulic actuator of claim 9, further comprising a first photo-diode configured to receive light transmitted through at least one of the plurality of second optical fibers.

11. The hydraulic actuator of claim 10, wherein the first photodiode is disposed to receive light from at least two of the plurality of second optical fibers.

12. The hydraulic actuator of claim 11, further comprising a second photodiode configured to receive light transmitted through at least another of the plurality of second optical fibers.

13. A method of determining the position of a piston in a hydraulic cylinder includes the steps of:

generating a beam of laser light;

reflecting the beam of laser light off a surface fixed to move axially with the piston;

receiving a first portion of the reflected beam by a first reflected light guide and a second portion of the reflected beam by a second reflected light guide;

conducting the first and second portions of the reflected beam through first and second optical fibers to at least one remotely located light detector; and

calculating a first time of flight of the beam based at least upon the first and second portions of reflected light.

14. The method of claim 13, further comprising the step measuring a second time of flight of the beam by moving the piston to a second location in the cylinder while simultaneously increasing the optical path length of both the first and second portions of the beam an equal amount.

15. The method of claim 14 the step of moving the piston to the second location may include the step of filling a chamber of the cylinder through which the beam passes while simultaneously moving the cylinder.

16. The method of claim 15, wherein step of generating the beam may include the step of generating the beam with a wavelength of between 500 and 1700 nanometers.

17. The method of claim 16, wherein step of generating the beam may include the step of generating the beam with a wavelength in the range of 840 and 980 nanometers.

18. The method of claim 16 wherein the step of generating the beam may include the step of generating the beam with a wavelength in the range of 700 and 1150 nanometers.

19. The method of claim 18 wherein the step of generating the beam may include the step of generating the beam with a wavelength in the range of 700 and 900 nanometers.

20. The method of claim 18 wherein the step of generating the beam may include the step of generating the beam with a wavelength in the range of 950 and 1025 nanometers.

21. The method of claim 18 wherein the step of generating the beam may include the step of generating the beam with a wavelength in the range of 1030 and 1150 nanometers.

22. The method of claim 16 wherein the step of generating the beam may include the step of generating the beam with a wavelength of between 1250 and 1400 nanometers.

23. The method of claim 16 wherein the step of generating the beam may include the step of generating the beam with a wavelength in the range of 1450 and 1650 nanometers.

24. The method of claim 17, wherein step of generating the beam may include the step of generating a sequence of individual pulses of light, and the step of calculating the first and second times-of-flight may include the step of determining the time-of-flight of at least one pulse in the sequence of individual pulses of light.

25. The method of claim 18, further comprising the step of simultaneously transmitting the sequence of pulses through the first and second optical fibers to arrive at the first photodiode at substantially the same time.