Rangefinder and method for collecting calibration data

• US 7,414,707 B2
• Filed: 05/03/2006
• Issued: 08/19/2008
• Est. Priority Date: 11/26/2003
• Status: Expired due to Fees

• Current Assignee: Meade Instruments Corporation
• Original Assignee: Meade Instruments Corporation
• Inventors: Baun, Kenneth W., LaBelle, John, Szczuka, Steven
• Primary Examiner(s): EVANS, FANNIE L
• Application Number:
  US11/417,423
• Publication Number:
  US 20060215149A1
• Time in Patent Office: 839 Days
• Field of Search: 356/6
• US Class Current: 356/6
• CPC Class Codes: G01C 3/08 Use of electric radiation detectors
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating

Abstract

An apparatus and method for calibrating range measurements are provided wherein calibration data is collected with each range measurement or group of range measurements. The calibration data comprise a plurality of simulated range measurements. In one embodiment, the simulated range measurements are used to analyze errors that vary with time and environmental conditions. Range measurements are calibrated by correlating a measured flight time of a transmitted and reflected laser beam with the simulated range measurements and a relationship between laser beam flight times and target ranges based on the speed of the laser beam.

Claims

1. A method for estimating a range to a target using a rangefinder, the rangefinder comprising a transmitter and a receiver, the method comprising:

emitting a beam from the transmitter towards the target;

detecting a reflected beam from the target in the receiver, wherein a flight time comprises a time between emitting the beam and the detecting the reflected beam;

accumulating counts at least during the flight time;

determining the range to the target from the counts;

using calibration data at least responsive to dynamic factors to correct measurement error in the determined range; and

outputting a calibrated range measurement.

2. The method of claim 1, wherein the counts are accumulated in a high speed counter.

3. The method of claim 1, wherein accumulating the counts includes generating the counts from a time base.

4. The method of claim 1, wherein the dynamic factors comprise electronic characteristics of the rangefinder.

5. The method of claim 1, wherein the dynamic factors comprise environmental conditions.

6. A method for estimating a range to a target using a rangefinder, the rangefinder comprising a transmitter and a receiver, the method comprising:

emitting a beam from the transmitter towards the target;

detecting a reflected beam from the target in the receiver, wherein a flight time comprises a time between emitting the beam and the detecting the reflected beam;

accumulating counts at least during the flight time;

determining the range to the target from the counts;

calibrating the rangefinder, the calibration including;

determining a first relationship between said flight time and said range, the first relationship including a first slope;

generating a first simulated range measurement for a first calibration flight time;

generating a second simulated range measurement for a second calibration flight time; and

determining a second relationship between said flight time and said range based on the first and second calibration flight times and the first and second simulated range measurements, the second relationship including a second slope;

correlating the counts to the first relationship using the second relationship; and

determining the range to the target using the correlation.

7. The method of claim 6, wherein correlating the counts to the first relationship comprises:

correlating the counts to the second relationship;

determining a calibrated time; and

correlating the calibrated time to the first relationship to determine a calibrated range.

8. The method of claim 6, wherein the first slope is proportional to a speed of the beam.

9. The method of claim 6, wherein the second slope is proportional to a ratio of a difference between the first and second simulated range measurements and a difference between the first and second calibration flight times.

10. The method of claim 6, further comprising:

selecting a range calibration value; and

shifting the first relationship by the range calibration value.

11. The method of claim 10, wherein selecting the range calibration value comprises measuring a strength of a detected beam.

12. The method of claim 10, wherein selecting the range calibration value comprises choosing the range calibration value from a range of values stored in a memory.

13. A method for estimating a distance to a target using a rangefinder, the rangefinder comprising an emitter and a receiver, the method comprising:

emitting a beam from the emitter towards the target;

detecting a reflected beam from the target in the receiver;

at least between the emitting and the detecting, acquiring processor data representative of time;

determining the distance to the target using the processor data;

correcting measurement error in the determined distance using calibration data responsive to at least one of environmental factors and electronic characteristics of the rangefinder; and

outputting a calibrated range measurement.

14. A method for estimating a range to a target, the method comprising:

emitting a beam towards a target;

after emitting, starting a timer;

detecting a reflected beam from the target;

after detecting, stopping the timer; and

determining the range to the target using data acquired from the timer and calibration data responsive to simulated range measurements, wherein a flight time comprises time between at least the emitting and the detecting, wherein the timer runs at least during the flight time, and wherein the timer comprises a processor.

15. The method of claim 14, wherein determining the range comprises at least one of:

adjusting a completed flight time calculation, changing a value within a flight time calculation, and modifying the timer data.

16. A rangefinder configured to determine a range to a target, the rangefinder comprising:

a transmitter configured to emit a beam towards the target;

a receiver configured to detect a reflected beam from the target;

timing circuitry including a high speed counter configured to accumulate counts, the timing circuitry configured to measure a flight time between at least the emission of the beam from the transmitter and the detection of the reflected beam by the receiver; and

a calibration section configured to correct error in the measured flight time using calibration data responsive to dynamic factors.

17. The rangefinder of claim 16, wherein the flight time is proportional to the counts.

18. The rangefinder of claim 16, wherein the timing circuitry includes an oscillator.

19. The rangefinder of claim 16, wherein the transmitter comprises a laser diode configured to emit a pulsed laser beam.

20. The rangefinder of claim 16, wherein the calibration section is configured to perform at least one of:

correcting a completed flight time calculation, adjusting a value within a flight time calculation, and modifying the counts.

21. A rangefinder configured to determine a range to a target, the rangefinder comprising:

a transmitter configured to emit a beam towards the target;

a receiver configured to detect a reflected beam from the target; and

timing circuitry including a high speed counter configured to accumulate counts, the timing circuitry configured to measure a flight time between at least the emission of the beam from the transmitter and the detection of the reflected beam by the receiver;

a calibration section configured to determine calibration data related to dynamic factors; and

a processor configured to adjust the flight time based on the calibration data.

22. The rangefinder of claim 21, wherein the calibration section is further configured to simulate first and second range measurements.

23. The rangefinder of claim 22, wherein the processor is further configured to correlate the flight time to the first and second simulated range measurements.

24. The rangefinder of claim 21, wherein the dynamic factors comprise range measurement errors that vary with environmental conditions.

25. The rangefinder of claim 21, wherein the processor is further configured to adjust the flight time based on inherent delays of the rangefinder.

26. The rangefinder of claim 21, wherein the processor is further configured to adjust the flight time according to a strength of a detected beam.

27. The rangefinder of claim 21, further comprising a memory, the memory including at least two range calibration values.

28. The rangefinder of claim 27, wherein the processor is further configured to adjust the flight time based on a calibration value between the at least two range calibration values.

29. A system for measuring a range to a target, the system comprising:

a means for transmitting a beam towards a target;

a means for detecting a beam reflected from the target;

a means for measuring data during the flight time, the flight time comprising time at least between transmission of the beam and detection of the reflected beam;

a means for determining calibration data related to dynamic factors; and

a means for adjusting the flight time based on the calibration data.

30. The system of claim 29, wherein the measuring means comprises a high speed counter driven by a time base and wherein the data comprises counts.

31. The system of claim 30, wherein the time base comprises an oscillator.

32. The system of claim 29, wherein the calibration data determining means comprises a calibration section and wherein the dynamic factors comprise electronic characteristics of the system.

33. The system of claim 29, wherein the calibration data determining means comprises a calibration section and wherein the dynamic factors comprise environmental conditions.

34. The system of claim 29, wherein the flight time adjusting means comprises a processor.