Method for improved range accuracy in laser range finders

• US 6,842,231 B2
• Filed: 09/30/2002
• Issued: 01/11/2005
• Est. Priority Date: 09/30/2002
• Status: Expired due to Term

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Johnson, Scott C., Sakamoto, Colin N., Brown, Stanley D., Nourrcier, Charles E., Wirtz, Karen D., Martinez, Angela K.
• Primary Examiner(s): Wong, Don
• Assistant Examiner(s): Nguyen, Phillip
• Application Number:
  US10/260,736
• Publication Number:
  US 20040066501A1
• Time in Patent Office: 834 Days
• Field of Search: 356 401- 51
• US Class Current: 356/5.01
• 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 7/4865 Time delay measurement, e.g. time-of-flight measurement, time of arrival measurement or determining the exact position of a peak peak detection in noise, signal conditioning G01S7/487

Abstract

The range of a threshold detection laser range finder is increased by adding a low cost Analog-to-Digital converter and sampling a portion of a reflected laser pulse. The slope of the sampled reflected laser pulse is calculated and the shape of the reflected laser pulse is inferred from known shapes. The center point of the inferred shape is approximated using a lookup table, and a correction value is calculated based on the center point of the inferred shape and the sampled portion. The correction value is applied to an uncorrected range estimate to arrive at an accurate estimate of the range of the object of interest.

Claims

1. A laser range finder for determining a range of an object of interest, comprising:

a laser source for generating a plurality of laser pulses and for directing the plurality of laser pulses toward the object of interest;

a laser for detecting a reflected laser pulse, and

generating an analog signal representative of a shape of the laser pulse;

an analog-to digital converter for converting a portion of the analog signal into a digital signal; and

a processor for inferring a shape of the reflected laser pulse from the digital signal,

calculating a range correction value from the inferred shape of the reflected laser pulse, and

applying the range correction value to an uncorrected range value to obtain the range of the object of interest.

2. A laser range finder in accordance with claim 1, wherein the signal is proportional to the strength of the reflected laser pulse.

3. A laser range finder in accordance with claim 1, wherein the processor calculates a slope from the sampled portion of the signal.

4. A laser range finder in accordance with claim 3, wherein the slope is calculated from a first point and a second point, the first point being a predetermined threshold level, and the second point being sampled a predetermined delay after the magnitude of the signal exceeds the first point.

5. A laser range finder in accordance with claim 4, further comprising a memory.

6. A laser range finder in accordance with claim 5, wherein a shape of the reflected laser pulse is inferred from the slope and from a plurality of known slopes of reflected laser pulse shapes.

7. A laser range finder in accordance with claim 6, wherein the plurality of known slopes of reflected pulses are stored in the memory.

8. A laser range finder in accordance with claim 7, wherein the memory is ROM.

9. A laser range finder in accordance with claim 6, wherein a center point of the shape of the reflected laser pulse is approximated based on the inferred shape.

10. A laser range finder in accordance with claim 9, wherein the center point is approximated from a lookup table.

11. A laser range finder in accordance with claim 10, wherein the lookup table is stored in memory.

12. A laser range finder in accordance with claim 11, wherein the memory is ROM.

13. A laser range finder in accordance with claim 10, wherein a range correction value is determined from a distance between the second point and the center point of the shape of the reflected laser pulse.

14. A laser range finder in accordance with claim 13, wherein the predetermined delay is adjustable.

15. A method for calculating the range of an object using a laser range finder, comprising the steps of:

pulsing a laser at an object of interest;

starting a range counter at the initiation of the laser pulse, the range counter accumulating an uncorrected range value;

detecting a reflected laser pulse;

generating a signal indicative of the reflected laser pulse;

latching the uncorrected range value when the signal exceeds a predetermined threshold level;

inferring a shape of the reflected laser pulse from a portion of the signal;

calculating a range correction value from the shape of the reflected laser pulse; and

applying the range correction value to the latched uncorrected range value to obtain the range of the object of interest.

16. A method in accordance with claim 15, wherein the shape of the reflected laser pulse is inferred from a slope of the signal and from a plurality of known slopes of reflected laser pulse shapes.

17. A method in accordance with claim 16, wherein the slope is calculated from a first point and a second point, the first point being the predetermined threshold level, and the second point being a delayed sample of the signal.

18. A method in accordance with claim 17, wherein a center point of the shape of the reflected laser pulse is approximated from a lookup table.

19. A method in accordance with claim 18, wherein the range correction value is calculated from the center point and the delayed sample of the signal.

20. A laser range finder for determining a range of an object of interest, comprising:

a laser source for pulsing a laser at an object of interest;

a range counter started at the initiation of the laser pulse, the range counter accumulating an uncorrected range value;

a laser receiver for detecting a reflected laser pulse;

generating a signal indicative of the reflected laser pulse; and

latching the uncorrected range value when the signal exceeds a predetermined threshold level; and

a processor for inferring a shape of the reflected laser pulse from a portion of the signal,

calculating a range correction value from the shape of the reflected laser pulse, and

applying the range correction value to the latched uncorrected range value to obtain the range of the object of interest.

21. A method for calculating the range of a laser range finder, comprising the steps of:

pulsing a laser at an object of interest;

detecting a reflected laser pulse;

generating an analog signal representative of a shape of the reflected laser pulse;

converting a portion of the analog signal into a digital signal;

inferring a shape of the reflected laser pulse from the digital signal;

calculating a range correction value from the inferred shape of the reflected laser pulse; and

applying the range correction value to an uncorrected range value to obtain the range of the object of interest.

22. The method in accordance with claim 21, further comprising the step of calculating a slope of the reflected laser pulse from the digital signal.

23. A method in accordance with claim 22, wherein the slope is calculated from a first point and a second point, the first point being the predetermined threshold level, and the second point being a delayed sample of the signal.

24. A method in accordance with claim 22, wherein a center point of the shape of the reflected laser pulse is approximated from a lookup table.

25. A method in accordance with claim 21, wherein the range correction value is calculated using the center point of the inferred shape and the delayed sample of the signal.