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