DETECTION AND RANGING METHODS AND SYSTEMS

• US 20100277713A1
• Filed: 12/19/2008
• Published: 11/04/2010
• Est. Priority Date: 12/21/2007
• Status: Active Grant

• Current Assignee: LeddarTech, Inc.
• Original Assignee: LeddarTech, Inc.
• Inventors: Mimeault, Yvan
• Granted Patent: US 8,310,655 B2
• Time in Patent Office: Days
• 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 7/4861 Circuits for detection, sampling, integration or read-out
• 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
• CPC Class Codes: G01S 7/487 Extracting wanted echo signals , e.g. pulse detection

Abstract

There is provided a system and a method for acquiring a detected light optical signal and generating an accumulated digital trace The method comprises providing a light source for illumination of a field of view, an optical detector, an analog-to-digital converter (ADC), emitting one pulse from the light source in the field of view, detecting a reflection signal of the pulse by the optical detector, acquiring j points for the detected reflection signal by the ADC, storing, in a buffer, the digital signal waveform of j points, introducing a phase shift of 2pi/P, repeating, P times, the steps of emitting, detecting, acquiring, storing and introducing, to store, in the buffer, an interleaved waveform of P×j points, accumulating M traces of interleaved P×j points for a total of N=M×P acquisition sets, N being a total number of pulses emitted, creating one combined trace of the reflected signal of j×P points by adding each point of the M traces Additionally, the combined trace can be compared to a detected reference reflection signal of the pulse to determine a distance traveled by the pulse

Claims

1. A method for acquiring a detected light optical signal and generating an accumulated digital trace, the method comprising:

providing

a light source for illumination of a field of view;

an optical detector;

an analog-to-digital converter (ADC) with a sample rate of F Hz and B bits of resolution;

emitting one pulse from said light source in said field of view;

detecting a reflection signal of said pulse by the optical detector;

acquiring j points for said detected reflection signal by said ADC by acquiring one of said j points at each 1/F second thereby converting said optical reflection signal into a digital signal waveform of j points;

storing, in a buffer, said digital signal waveform of j points;

introducing a phase shift of 2π

/P between said emission of said light pulse and a beginning of said acquisition of said j points by the ADC;

repeating, P times, said steps of emitting, detecting, acquiring, storing and introducing, to store, in said buffer, an interleaved waveform of P×

j points, said interleaved waveform being equivalent to a single acquisition with a temporal resolution of 1/(F×

P) second;

accumulating M traces of interleaved P×

j points for a total of N=M×

P acquisition sets, N being a total number of pulses emitted;

using the N sets, creating one combined trace of the reflected signal by adding each point of the M traces, point per point, to generate one accumulated digital trace of j×

P points, each point in the combined trace being an accumulation of M=N/P sets and an effective time resolution of the combined trace being 1/(F×

P) second;

wherein a length of said buffer is at least j×

P and a number of bits of each element in said buffer is B+2^M;

wherein said sample rate of said ADC is virtually increased thereby allowing a low cost ADC having a low sample rate F to be used.

2. The method as claimed in claim 1, wherein j equals 1, thereby acquiring only one point per pulse.

3. The method as claimed in claim 1, wherein at least one of P and M is adjusted as a function of j.

4. The method as claimed in claim 1, further comprising:

convoluting a reference signal with said combined trace.

5. The method as claimed in claim 1, further comprising:

detecting a reference reflection signal of said pulse by a reference optical detector at said emission of said pulse thereby acquiring a reference zero value and a reference trace for said pulse;

comparing said reference trace for said pulse to said combined trace;

determining a distance traveled by said pulse based on said comparison.

6. The method as claimed in claim 1, further comprising:

providing a timer;

triggering said timer to calculate a time elapsed between said emission of said pulse and said detection of said reflection signal;

determining a distance traveled by said pulse based on said time elapsed.

7. The method as claimed in claim 1, wherein said introducing a phase shift comprises delaying a clock of the ADC by a fraction of a period.

8. The method as claimed in claim 1, wherein said introducing a phase shift comprises delaying a driver of the light source.

9. The method as claimed in claim 1, wherein said lighting system comprises several light sources being driven sequentially using at least one sensor, a frequency of acquisition is a frequency of the optical source multiplied by the number of optical sources.

10. The method as claimed in claim 1, further comprising:

determining a time at which said emitting occurred;

choosing a filter based on a frequency of a transition;

filtering the reflection signal using said filter;

detecting at least one of rising and falling edges for said filtered reflection signal and locating at least one of a rising and a falling slope;

acquiring samples in said at least one of a rising and a falling slope to memorize a digital waveform of the slope;

calculating a linear regression on said digital waveform of the slope;

calculating an intercept point in said linear regression;

calculating a difference in time between said emitting and said intercept point to estimate a distance to an object causing said reflection.

11. The method as claimed in claim 10, wherein said determining a time comprises sampling said signal from said source.

12. The method as claimed in claim 11, wherein said determining a time comprises using an electrical synchronization signal.

13. The method as claimed in claim 11, further comprising determining different weights in the calculation as a function of the level of the noise.

14. The method as claimed in claim 11, further comprising:

providing a threshold; and

determining the presence of an object at a predetermined target distance using said threshold.

15. The method as claimed in claim 11, further comprising diminishing a level of noise using at least one of an averaging and a filtering technique.

16. The method as claimed in claim 11, further comprising using a shifting technique to acquire more points.

17. A powered lighting system for acquiring a detected light optical signal and generating an accumulated digital trace, the powered lighting system comprising:

at least one light source for illumination of a field of view and emitting a pulse in said field of view;

an illumination driver for driving said light source;

an optical detector for detecting a reflection signal of a reflection of said pulse;

an analog-to-digital converter (ADC) with a sample rate of F Hz and B bits of resolution for acquiring j points for said detected reflection signal by acquiring one of said j points at each 1/F second thereby converting said optical reflection signal into a digital signal waveform of j points;

a buffer for storing said digital signal waveform;

a processor for

controlling said illumination driver and said optical detector;

sending information for storage in said buffer, wherein a length of said buffer is at least j×

P and a number of bits of each element in said buffer is B+2^M;

introducing a phase shift of 2π

/P between said emission of said light pulse and a beginning of said acquisition of said j points by the ADC;

causing to repeat, P times, said emitting, detecting, acquiring, storing and introducing, to obtain an interleaved waveform of P×

j points, said interleaved waveform being equivalent to a single acquisition with a temporal resolution of 1/(F×

P) second;

accumulating M traces of interleaved P×

j points for a total of N=M×

P acquisition sets, N being a total number of pulses emitted;

creating one combined trace of the reflected signal using the N sets, by adding each point of the M traces, point per point, to generate one accumulated digital trace of j×

P points, each point in the combined trace being an accumulation of M=N/P sets and an effective time resolution of the combined trace being 1/(F×

P) second;

wherein said sample rate of said ADC is virtually increased thereby allowing a low cost ADC having a low sample rate F to be used.

18. The system as claimed in claim 17, wherein j equals 1, thereby acquiring only one point per pulse.

19. The system as claimed in claim 17, wherein at least one of P and M is adjusted as a function of j.

20. The system as claimed in claim 17, further comprising:

a memory for providing a reference signal;

said processor convoluting said reference signal with said combined trace.

21. The system as claimed in claim 17, further comprising:

a reference detector for detecting a reference reflection signal of said pulse at said emission of said pulse thereby acquiring a reference zero value and a reference trace for said pulse;

said processor comparing said reference trace for said pulse to said combined trace and determining a distance traveled by said pulse based on said comparison.

22. The system as claimed in claim 17, further comprising:

a timer;

said processor triggering said timer to calculate a time elapsed between said emission of said pulse and said detection of said reflection signal and determining a distance traveled by said pulse based on said time elapsed.

23. The system as claimed in claim 17, wherein said introducing a phase shift comprises delaying a clock of the ADC by a fraction of a period.

24. The system as claimed in claim 17, wherein said introducing a phase shift comprises delaying a driver of the light source.

25. The system as claimed in claim 17, wherein said lighting system comprises several light sources being driven sequentially using at least one sensor, a frequency of acquisition is a frequency of the optical source multiplied by the number of optical sources.

26. A method for detecting a distance to an object, comprising:

providing a lighting system having at least one pulse width modulated visible-light source for illumination of a field of view;

emitting an illumination signal for illuminating said field of view for a duration of time y using said visible-light source at a time t, said time t typically being a center of a transition from a non-illuminated state to an illuminated state of said field of view, for at least one pulse;

starting an optical sensor for integrating a reflection energy captured by said visible-light source, of a reflection of said illumination signal, for a first time period at a time t−

x of a first one of said at least one pulse;

stopping said optical sensor for said first time period at a time t+x for said first one of said at least one pulse and determining a first integration value for said first time period;

starting said optical sensor for integrating said reflection energy captured by said visible-light source, of said reflection of said illumination signal, for a second time period at a time t+y−

x for a second one of said at least one pulse, said second one being one of said first one and another one of said at least one pulse, y being greater than x;

stopping said optical sensor for said second time period at a time t+y+x for said second one of said at least one pulse and determining a second integration value for said second time period;

calculating a difference value between said first integration value and said second integration value;

determining a propagation delay value proportional to said difference value;

determining said distance to said object from said propagation delay value.

27. A method as claimed in claim 26, further comprising:

providing a threshold distance to a pre-identified object;

comparing said distance to said object with said threshold distance;

determining said object to be said pre-identified object if said comparison is positive.

28. A method as claimed in claim 26, further comprising:

measuring a background integration value for non-negligible illumination background from other lighting sources during an integration time t−

x to t+x when said source is not emitting;

subtracting from each said first integration value and said second integration value said background integration value prior to said calculating a difference.

29. A method as claimed in claim 26, further comprising, when said x is greater than said y, said integrating being larger than a width of the pulse,

switching a synchronisation of said illumination signal with said starting said optical sensor.