Fibre-optic photoelectric beam device having a transmitting optical unit for detecting a moving object through a control district

• US 5,739,526 A
• Filed: 04/29/1996
• Issued: 04/14/1998
• Est. Priority Date: 05/02/1995
• Status: Expired due to Fees

• Current Assignee: Deutshe Forschungsanstalt Fur Luft-Und Raumfahrt EV
• Original Assignee: Deutshe Forschungsanstalt Fur Luft-Und Raumfahrt EV
• Inventors: Furstenau, Norbert, Jungbluth, Werner
• Primary Examiner(s): LE, QUE TAN
• Application Number:
  US08/639,628
• Time in Patent Office: 715 Days
• Field of Search: 250/227.14, 250/227.19, 250/227.21, 250/222.1, 250/222.2, 250/227.12, 250/559.4, 250/559.32, 250/559.12, 250/227, 250/17, 250/221, 385/4, 385/34, 385/36, 385/41, 385/42
• US Class Current: 250/227.14
• CPC Class Codes: G01B 11/043 for measuring length
• CPC Class Codes: G01P 13/045 with speed indication
• CPC Class Codes: G01P 3/68 using optical means, i.e. using infrared, visible, or ultraviolet light G01P3/80 takes precedence ; by reflection of waves G01S17/58

Abstract

A photoelectric beam device comprises a light source, a monomode optical fibre, a transmitting optical unit, a reflector and a photodetector, where the transmitting optical unit comprises a collimation optical unit, e.g. in the form of a graded index lens or rod lens and a beam expansion optical unit e.g. in the form of a telescopic optical unit. A fibre-optic directional coupler, arranged between the light source and the monomode fibre, conducts to the photodetector the optical signal reflected back from the reflector to the transmitting optical unit and refocused into the fibre.

Claims

1. A photoelectric beam device for detecting a moving object through a control district having first and second ends, said device comprising:

a light source for generating a beam of rays;

a monomode fiber connected at one end thereof to the light source;

a transmitting optical unit having a collimation optical unit connected to said monomode fiber at an opposite end of the monomode fiber, a beam expansion optical unit located at the first end of the control district, and a retro reflector located at the second end of the control district; and

a photo detector at the first end of the control district for tracing a part of the beam of rays reflected from the retro reflector via the transmitting optical unit and the monomode fiber.

2. A photoelectric beam device as set forth in claim 1, said collimation optical unit having one of a graded index lens and a rod lens.

3. A photoelectric beam device as set forth in claim 2 further comprising a guide tube surrounding the opposite end of the monomode fiber for coupling the monomode fiber to one of the graded index lens and rod lens.

4. A photoelectric beam device as set forth in claim 3, said beam expansion optical unit comprising a telescopic optical unit.

5. A photoelectric beam device as set forth in claim 1 further comprising a fiber-optic directional coupler for conducting to the photo detector an optical signals reflected back from the retro reflector to said transmitting optical unit and refocused to said monomode fiber.

6. A photoelectric beam device as set forth in claim 1, said light source comprising a heavy-duty infra-red diode.

7. A photoelectric beam device as set forth in claim 1, said light source comprising a super luminescence diode.

8. A photoelectric beam device as set forth in claim 1, said retro reflector embodying a triple mirror.

9. A photoelectric beam device as set forth in claim 1 further comprising a second transmitting optical unit having a second collimation optical unit connected to another monomode fiber, a second beam expansion optical unit located at the first end of the control district, and a second retro reflector located at the second end of the control district, wherein the direction of movement and speed of the moving object through the control district and the linear length (L) of the moving object is determined by light intensity differences (l₁, l₂).

10. A photoelectric beam device as set forth in claim 9 further comprising a directional coupler having a pair of outlets, said two collimation optical units being connected to the outputs of the directional coupler by said monomode fibers, each fiber carrying two separate light beams of unequal intensity (l₁, l₂).

11. A photoelectric beam device as set forth in claim 10 further comprising a neutral filter disposed within the transmitting optical unit for attenuating the light intensity.