Laser diode liquid-level/distance measurement

• US 5,257,090 A
• Filed: 11/27/1991
• Issued: 10/26/1993
• Est. Priority Date: 11/27/1991
• Status: Expired due to Fees

• Current Assignee: dbi Corp.
• Original Assignee: United Technologies Corporation (Raytheon Technologies Corporation d/b/a RTX)
• Inventors: Zepke, Bruce E., Meinzer, Richard A.
• Primary Examiner(s): Turner, Samuel A.
• Assistant Examiner(s): Keesee, LaCharles
• Application Number:
  US07/800,336
• Time in Patent Office: 699 Days
• Field of Search: 250/205, 250/576, 356/3, 356/4, 356/4.5, 356/5, 356/345, 356/356, 356/358, 356/349
• US Class Current: 356/498
• CPC Class Codes: G01F 23/292 Light , e.g. infrared or ultraviolet
• CPC Class Codes: G01F 23/686 using opto-electrically actuated indicating means
• CPC Class Codes: G01S 17/32 using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
• CPC Class Codes: G01S 17/88 Lidar systems specially adapted for specific applications

Abstract

A laser diode distance measurement device includes a laser diode assembly 10, comprising a laser diode and photodiode, which emits light 17 to a lens 19 which provides collimated light 20 incident on a float 22 which is covered with reflective tape on its top surface 24. The light 20 is reflected from the float 22 back to the laser diode assembly 10 which causes the assembly 10 to provide a signal having magnitude pulses (due to coherent interference) on a line 15 to a liquid level measurement circuit 14 related to the distance L to the float 22. Use of the collimated beam 20 and reflective tape on the float 22 minimizes speckle while providing adequate optical intensity feedback. The laser assembly 10 is driven by a sawtooth waveform signal that reduces electronic processing. The distance measurement circuit 14 blanks-out the feedback signal during discontinuities of the laser diode drive signal to minimize associated noise from distorting the distance measurement. Alternatively, the float may be omitted and the tube 11 made small enough to provide a meniscus effect curvature at a liquid surface 250 which provides a curved reflective surface to reflect the incident light 20, in a consistent fashion, back to the laser assembly 10.

Claims

1. A laser-based distance measuring device for measuring the distance to a cooperative target having predetermined highly reflective properties, comprising:

a laser assembly, having a laser with a variable optical operating frequency, emitting an output light toward the target;

collimating means, disposed in the path of the output light, for providing a collimated light, the collimated light being incident on the target and being reflected by the target back into said laser assembly;

said laser assembly also providing a feedback signal having a magnitude related to the distance from said laser assembly to the target based on coherent interference within said laser between light reflected from the target and light within said laser;

the collimated light from said collimating means together with the highly reflective properties of the target providing reduced speckle noise and substantially constant speckle noise floor over the travel range of the target;

laser drive means, for providing a variable laser drive signal to said laser assembly for varying the optical operating frequency of said laser; and

distance measurement means, responsive to said feedback signal from said laser assembly, for providing a distance signal indicative of the distance to the target.

2. Apparatus of claim 1 wherein said laser drive signal comprises a sawtooth waveform.

3. Apparatus of claim 1 wherein the target is covered with reflective tape.

4. Apparatus of claim 1 wherein said distance measurement signal is related to the number of pulses of said feedback signal.

5. Apparatus of claim 1 wherein said laser comprises a laser diode.

6. Apparatus of claim 1 wherein the target is disposed on a liquid, the level of which is related to the distance.

7. Apparatus of claim 6 further comprising a tube for confining the target to an area near the collimated light and containing the liquid to be measured.

8. Apparatus of claim 6 wherein said distance measurement means comprises means for providing a liquid level signal indicative of the level of the liquid.

9. A laser-based distance measuring device for measuring the level of a liquid, comprising:

a tube, for containing a portion of the liquid to be measured, having a size and material composition so as to cause a meniscus effect at a surface of the liquid in said tube;

a laser assembly, having a laser with a variable optical operating frequency, emitting an output light toward the liquid;

calibrating disposed in the path of the output light, for providing a collimated light, the collimated light being incident on the liquid and being reflected by the liquid back into said laser assembly;

laser drive means, for providing a variable laser drive signal to said laser assembly for varying the optical operating frequency of said laser;

said laser assembly also providing a feedback signal having a magnitude related to the distance from said laser assembly to the liquid based on coherent interference within said laser between the reflected light from the liquid and light within said laser; and

distance measurement means, responsive to said feedback signal from said laser assembly, for providing a liquid level signal indicative of the level of the liquid.

10. Apparatus of claim 9 wherein said laser drive signal comprises a sawtooth waveform.

11. Apparatus of claim 9 wherein said liquid level signal is related to the number of pulses of said feedback signal.

12. Apparatus of claim 9 wherein said laser comprises a laser diode.

13. A laser-based distance measuring device for measuring the distance to a target, comprising:

a laser assembly, having a laser with a variable optical operating frequency, emitting an output light toward the target, the output light from said laser assembly being incident on the target and being reflected by the target back into said laser assembly;

laser drive means, for providing a variable laser drive signal to said laser assembly for varying the optical operating frequency of said laser;

said laser assembly also providing a feedback signal having a magnitude related to the distance from said laser assembly to the target based on coherent interference within said laser between light reflected from the target and light within said laser; and

signal processing means, responsive to said feedback signal from said laser assembly, for blanking-out a portion of said feedback signal coincident wit discontinuities of said laser drive signal.

14. Apparatus of claim 13 wherein said laser drive signal comprises a sawtooth waveform.