Distance detection method and system

Abstract

There is provided a system and method for detecting a distance to an object. The method comprises 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 the field of view for a duration of time y using the visible-light source at a time t; integrating a reflection energy for a first time period from a time t−x to a time t+x; determining a first integration value for the first time period; integrating the reflection energy for a second time period from a time t+y−x to a time t+y+x; determining a second integration value for the second time period; calculating a difference value between the first integration value and the second integration value; determining a propagation delay value proportional to the difference value; determining the distance to the object from the propagation delay value.

Description

where c represents the velocity of light, INT represents the integration time, P1 represents the integration value synchronized with the rising edge of the optical pulse and P2 represents the integration value synchronized on the falling edge of the optical pulse.

When an illumination background from other lighting sources is not negligible, measurement of the background B during an integration time INT when the optical source of the system is off can be made and subtracted from each integration value P1 and P2. The relationship with non negligible background is:
Distance=c×(INT/4)*((P2−B)−(P1−B))/(P2+P1−2B),
where B is the integration value of the optical background level when the optical source of the system is off.

In the case where the integration time is larger than the width of the pulse of the optical source, the same technique can be used by switching the synchronisation of the signal of the optical source and the signal to the sensor integration time. The result becomes:
Distance=c×(INT/4)*(P1−P2)/(P2+P1),
where c represents the velocity of light, INT represents the integration time, P1 represents the integration value when optical pulse is synchronized with the rising edge of integration and P2 represents the integration value when the optical pulse is synchronized with the falling edge of integration.

When an illumination background from other lighting sources is not negligible, the relationship is:
Distance=c×(INT/4)*((P1−B)−(P2−B))/(P2+P1−2B).

Values from the signal integration are memorized. In the case of an array of sensors, each “pixel” is memorized. Several integrations can be performed and an averaging process can be done to improve signal to noise ratio. In the case of an array, we also can improve signal to noise ratio by using a groups of pixel and combining them to form a larger pixel (binning)

In summary, with reference to FIG. 17, the main steps of the method for acquiring a detected light optical signal and generating an accumulated digital trace are shown. The method comprises providing a light source with an optical detector for illumination of a field of view 1700; providing an analog-to-digital converter (ADC) 1702; emitting one pulse from the light source in the field of view 1704; detecting a reflection signal of the pulse by the optical detector 1706; acquiring j points for the detected reflection signal by the ADC 1708; storing, in a buffer, the digital signal waveform of j points 1710; introducing a phase shift of 2π/P 1712; repeating, P times 1714, the steps of emitting 1704, detecting 1706, acquiring 1708, storing 1710 and introducing 1712 to store 1710, in the buffer, an interleaved waveform of P×j points; accumulating 1716 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 1718.

Additionally, the combined trace can be compared 1720 to a detected reference reflection signal of the pulse to determine 1722 a distance traveled by the pulse.

Alternatively, a timer can be triggered to calculate a time elapsed 1724 between the emission of the pulse and the detection of the reflection signal to determine a distance traveled 1722 by the pulse based on the time elapsed.

In summary, with reference to FIG. 18, the main steps of the method for detecting a distance to an object are shown. The method comprises providing a lighting system 1800 having at least one pulse width modulated visible-light source for illumination of a field of view; emitting an illumination signal 1802 for illuminating the field of view for a duration of time y using the visible-light source at a time t; integrating a reflection energy for a first time period from a time t−x to a time t+x 1808; determining a first integration value for the first time period 1810; integrating the reflection energy for a second time period from a time t+y−x to a time t+y+x 1812; determining a second integration value for the second time period 1814; calculating a difference value between the first integration value and the second integration value 1816; determining a propagation delay value proportional to the difference value 1818; determining the distance to the object from the propagation delay value 1820.

While illustrated in the block diagrams as groups of discrete components communicating with each other via distinct data signal connections, it will be understood by those skilled in the art that the illustrated embodiments may be provided by a combination of hardware and software components, with some components being implemented by a given function or operation of a hardware or software system, and many of the data paths illustrated being implemented by data communication within a computer application or operating system. The structure illustrated is thus provided for efficiency of teaching the described embodiment.

Claims

1. 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 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;

measuring a background integration value for non-negligible illumination background from other lighting sources during an integration time 2x when said visible-light source is not emitting;

subtracting from each said first integration value and said second integration value said background integration value to obtain background compensated first integration value and second integration value;

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

determining a propagation delay value proportional to said difference value;

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

2. A method as claimed in claim 1, 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.

3. A method as claimed in claim 1, 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.

4. A ranging system, comprising:

a) a driver circuit configured to produce a driving signal for causing a light source to emit pulsed light toward a scene containing an object;

b) an optical detector configured to collect pulsed light emitted from the light source and back-scattered from the object and to produce an output signal conveying acquisitions of light pulses;

c) a signal processing system coupled to the optical detector, configured for:

i. sampling the output signal to obtain sampled acquisitions of light pulses;

ii. performing an accumulation of a number of the sampled acquisitions of light pulses to define an accumulated digital signal;

iii. obtaining a distance measurement from the accumulated digital signal;

iv. detecting in the output signal a pattern comprising low frequency signals and spikes;

v. outputting an indication of a weather condition correlated to the pattern of low frequency signals and spikes; and

vi. causing the driver circuit to vary an intensity of the light source based on the detected weather conditions.

5. The ranging system of claim 4, wherein the pulsed light is non-visible light.

6. The ranging system of claim 4, further comprising a lens through which light from the light source passes towards the scene, wherein the signal processing system is further configured for monitoring reflection from the lens from the light source, determining the condition of the lens based on the monitoring and further adjusting the intensity of the light source based on the determined condition of the lens.

7. The ranging system of claim 4, wherein processing the sampled acquisitions to detect the patterns comprises digital correlation.

8. The ranging system of claim 4, further comprising a database, wherein the patterns are predetermined patterns stored in the database.

9. The ranging system of claim 4, wherein the signal processing system further comprises an analog-to-digital converter (ADC).

10. The ranging system of claim 4, wherein the optical detector comprises at least one of an avalanche photodiode (APD), a photomultiplier (PMT) and a complementary metal-oxide semi-conductor (CMOS) and charged-coupled device (CCD) array sensor.

11. The ranging system of claim 4, wherein the signal processing system is further configured for varying the number of accumulated sampled acquisitions based on a parameter of the object.

12. The ranging system of claim 11, wherein the parameter of the object includes a distance to the object, the processing of the output signal comprises increasing the number of the accumulated sample acquisitions to obtain a distance measurement with an increasing distance to the object.

13. The ranging system of claim 11, wherein the parameter of the object includes a distance to the object, the processing of the output signal comprises decreasing the number of the accumulated sample acquisitions to obtain a distance measurement with a decreasing distance to the object.

14. The ranging system of claim 4, wherein the optical detector comprises an array of pixels, each pixel associated with a respective output signal produced based on light detected at that pixel.

15. The ranging system of claim 14, wherein the array is a 1D array.

16. The ranging system of claim 14, wherein the array is a 2D array.

17. A signal processing method, comprising:

sampling an output signal from an optical detector to obtain sampled acquisitions of light pulses emitted from a light source and back-scattered from one or more objects in a scene;

performing an accumulation of a number of the sampled acquisitions of light pulses to define an accumulated digital signal;

obtaining a distance measurement from the accumulated digital signal;

detecting in the output signal a pattern comprising low frequency signals and spikes;

outputting an indication of a weather condition correlated to the pattern of low frequency signals and spikes; and

varying an intensity of the light source based on the detected weather conditions.