Rangefinder and method for collecting calibration data

• US 20060215149A1
• Filed: 05/03/2006
• Published: 09/28/2006
• Est. Priority Date: 11/26/2003
• Status: Active Grant

• Current Assignee: John Labelle, Kenneth W. Baun, Steven Szczuka
• Original Assignee: John Labelle, Kenneth W. Baun, Steven Szczuka
• Inventors: Szczuka, Steven, Baun, Kenneth W., LaBelle, John
• Granted Patent: US 7,414,707 B2
• Time in Patent Office: Days
• US Class Current: 356/5.80
• 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; and

determining the range to the target from the counts.

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, further comprising:

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;

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 with the second relationship; and

determining the range to the target using the correlation.

5. The method of claim 4, 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.

6. The method of claim 4, wherein the first slope is proportional to a speed of the beam.

7. The method of claim 4, 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.

8. The method of claim 4, further comprising:

selecting a range calibration value; and

shifting the first relationship by the range calibration value.

9. The method of claim 8, wherein selecting the range calibration value comprises measuring a strength of a detected beam.

10. The method of claim 8, wherein selecting the range calibration value comprises choosing the range calibration value from a range of values stored in a memory.

11. 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; and

determining the distance to the target using the processor data.

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

emitting a beam towards a target;

starting a timer;

detecting a reflected beam from the target;

stopping the timer; and

determining the range to the target using data acquired from the timer, 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.

13. 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 processor, 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.

14. The rangefinder of claim 13, wherein the flight time is proportional to the counts.

15. The rangefinder of claim 13, comprising an oscillator.

16. The rangefinder of claim 13, wherein the transmitter comprises a laser diode configured to emit a pulsed laser beam.

17. The rangefinder of claim 13, further comprising:

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.

18. The rangefinder of claim 17, wherein the calibration section is further configured to simulate first and second range measurements.

19. The rangefinder of claim 18, wherein the processor is further configured to correlate the flight time to the first and second simulated range measurements.

20. The rangefinder of claim 17, wherein the dynamic factors comprise range measurement errors that vary with environmental conditions.

21. The rangefinder of claim 17, wherein the processor is further configured to adjust the flight time based on inherent delays of the rangefinder.

22. The rangefinder of claim 17, wherein the processor is further configured to adjust the flight time according to a strength of a detected beam.

23. The rangefinder of claim 17, further comprising a memory, the memory including at least two range calibration values.

24. The rangefmder of claim 23, wherein the processor is further configured to adjust the flight time based on a calibration value between the at least two range calibration values.

25. 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; and

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.

26. The system of claim 25, wherein the measuring means comprises a high speed counter driven by a time base and wherein the data comprises counts.

27. The system of claim 26, wherein the time base comprises an oscillator.