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.

What is claimed is: 
     
       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.