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. an adaptive signal processing system coupled to the optical detector, configured to perform an adaptive processing of the output signal, including:
 (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 varying with time, the accumulation of the number of the sampled acquisitions of light pulses including performing integration over time of the number of sampled acquisitions of light pulses, 
 (iii) varying the number of accumulated sampled acquisitions of light pulses to obtain a modified accumulated digital signal, based on a parameter of the object, 
 (iv) obtaining a distance measurement from the modified accumulated digital signal. 
   
     
     
       5. The ranging system of claim 4, wherein the accumulated digital signal defines a signal trace with a pulse-shaped segment. 
     
     
       6. The ranging system of claim 5, wherein the signal processing system is configured for adjusting an intensity of the driving signal based on the estimated distance to the object. 
     
     
       7. The ranging system of claim 5, wherein the light is non-visible light. 
     
     
       8. The ranging system of claim 4, wherein the parameter of the object includes a distance to the object, the processing of the output signal comprises increasing the number of accumulated sampled acquisitions of light pulses to obtain a distance measurement, with an increasing distance to the object. 
     
     
       9. The ranging system of claim 4, wherein the parameter of the object includes a distance to the object, the processing of the output signal comprises decreasing the number of accumulated sampled acquisitions of light pulses to obtain a distance measurement, with a decreasing distance to the object. 
     
     
       10. The ranging system as defined in claim 4, wherein the optical detector comprises an array of pixels, each pixel outputting a respective output signal. 
     
     
       11. The ranging system as defined in claim 10, wherein the array is a 2D array. 
     
     
       12. The ranging system as defined in claim 11, wherein the array is a 1D array. 
     
     
       13. The ranging system as defined in claim 4, wherein the sampled acquisitions of light pulses include respective sets of j points, the accumulation of the number of sampled acquisitions of light pulses including adding the number of sets of j points, point by point to generate the accumulated digital signal. 
     
     
       14. The ranging system as defined in claim 13, wherein the processing of the output signal includes phase-shifting the sampled acquisitions of light pulses.