Rangefinder and method for collecting calibration data
View Patent ↗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.
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.