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EP-3798678-B1 - TIME-OF-FLIGHT INDEPENDENT OF OBJECT REFLECTIVITY

EP3798678B1EP 3798678 B1EP3798678 B1EP 3798678B1EP-3798678-B1

Inventors

  • NGUYEN, THUC-UYEN

Dates

Publication Date
20260506
Application Date
20200925

Claims (12)

  1. A method comprising: flashing an object (110) with a first illumination pulse at a first illumination power level; flashing the object (110) with a second illumination pulse at a second illumination power level different from the first illumination power level; integrating at least a portion of a first return pulse which is the first illumination pulse returning from the object (110) to determine a first return time; integrating at least a portion of a second return pulse which is the second illumination pulse returning from the object (110) to determine a second return time; using the first and second return times to determine distance to the object (110) independent of reflectivity of the object (110); characterized in that using the first and second return times to determine the distance to the object (110) includes using a look up table (LUT) (124) to correlate the first and second return times to distance to the object (110), wherein the first and second return times are input to the LUT and wherein the actual travel time to the object is output from the LUT and is used to calculate the distance to the object.
  2. The method as recited in claim 1, wherein the LUT (124) is limited to an operational space; optionally wherein the LUT (124) is limited to an operational space ranging from 5 meters to 10 meters.
  3. The method as recited in any preceding claim, wherein the second illumination power level is 80% of the first illumination power level.
  4. The method as recited in any preceding claim, wherein the first and second illumination pulses each conform to a Gaussian temporal profile.
  5. The method as recited in any preceding claim, wherein using the LUT (124) includes using two sub-tables, one for each pulse, wherein each sub-table correlates respective measured travel time to predetermined actual travel times, and wherein using the LUT (124) includes locating predetermined actual travel times in each of the sub-tables that closest match each other, which actual travel time can be used for calculating actual distance to the object (110).
  6. The method as recited in any preceding claim, further comprising updating distance to the object (110) by repeating flashing the object (110) with the first and second illumination sources, integrating the first and second return pulses, determining the temporal difference, and determining distance to the object (110).
  7. A system (100) comprising: an illuminator (102) configured to flash a scene with two different levels of illumination power; a sensor (104) that is sensitive to illumination from the illuminator (102); and a controller (108) operatively connected to the illuminator (102) and to the sensor (104), the controller (108) being configured to use the sensor (104) and the illuminator (102) at two different levels of illumination power to find range to an object (110) independent of reflectivity of the object (110); wherein the controller (108) includes machine readable instructions configured to cause the controller (108) to: use the illuminator (102) to flash an object with a first illumination pulse at a first illumination power level; use the illuminator (102) to flash the object with a second illumination pulse at a second illumination power level lower than the first illumination power level; use the sensor (104) to integrate at least a portion of a first return pulse which is the first illumination pulse returning from the object (110) to determine a first return time; use the sensor (104) to integrate at least a portion of a second return pulse which is the second illumination pulse returning from the object (110) to determine a second return time; and use the first and second return times to determine distance to the object (110) independent of reflectivity of the object (110), characterized in that using the first and second return times to determine the distance to the object (110) includes using a look up table (LUT) (124) to correlate the first and second return times to distance to the object (110), ), wherein the first and second return times are input to the LUT and wherein the actual travel time to the object is output from the LUT, and is used to calculate the distance to the object.
  8. The system as recited in claim 7, wherein the LUT (124) is limited to an operational space.
  9. The system as recited in claim 8, wherein the LUT (124) is limited to an operational space ranging from 5 meters to 10 meters.
  10. The system as recited in any one of claims 7-9, wherein the second illumination power level is 80% of the first illumination power level.
  11. The system as recited in any one of claims 7-9, wherein the first and second illumination pulses each conform to a Gaussian temporal profile.
  12. The system as recited in claim any one of claims 7-11, wherein using the LUT (124) includes using two sub-tables, one for each pulse, wherein each sub-table correlates respective measured travel time to predetermined actual travel times, and wherein using the LUT (124) includes locating predetermined actual travel times in each of the sub-tables that closest match each other, which actual travel time can be used for calculating actual distance to the object (110).

Description

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT This invention was made with government support under contract number 40010791 awarded by the NIGHT VISION LAB AND ELECTRONIC SENSOR DIRECTORATE (US ARMY). The government has certain rights in the invention. BACKGROUND 1. Field The present disclosure relates to imaging, and more particularly to time of flight imaging such as in range finder and LIDAR systems. 2. Description of Related Art In flash time-of-flight (ToF) depth sensing applications, the depth or range information is calculated based on the traveled time of a light pulse. As the retuned pulse is integrated and exceeds a threshold value, a receiving pixel will mark the receipt of the returned light. Objects of unknown reflectivity can significantly undermine the system's depth accuracy. A more reflective object appears to be closer than a less reflective object at the same distance. DE 102014117097B3 discloses a distance measuring device and a method for determining a distance with the distance measuring device. The conventional techniques have been considered satisfactory for their intended purpose. However, there is an ever present need for improved systems and methods for time-of-flight determinations. This disclosure provides a solution for this need. SUMMARY According to a first aspect, there is provided a method as claimed in claim 1. The LUT can be limited to an operational space such as an operation space ranging from 5 meters to 10 meters. The second illumination power level can be 80% of the first illumination power level. The first and second illumination pulses can each conform to a Gaussian temporal profile. Using the LUT can include using two sub-tables, one for each pulse, wherein each sub-table correlates respective measured travel time to predetermined actual travel times, and wherein using the LUT includes locating predetermined actual travel times in each of the sub-tables that closest match each other, which actual travel time can be used for calculating actual distance to the object. The method can include updating distance to the object by repeating flashing the object with the first and second illumination sources, integrating the first and second return pulses, determining the temporal difference, and determining distance to the object. According to a second aspect, there is provided a system as claimed in claim 7. The controller includes machine readable instructions configured to use the illuminator and sensor to implement methods as disclosed above. These and other features of the systems and methods of the subject disclosure will become more readily apparent to those skilled in the art from the following detailed description of the preferred embodiments taken in conjunction with the drawings. BRIEF DESCRIPTION OF THE DRAWINGS So that those skilled in the art to which the subject disclosure appertains will readily understand how to make and use the devices and methods of the subject disclosure without undue experimentation, preferred embodiments thereof will be described in detail herein below with reference to certain figures, wherein: Fig. 1 is a schematic perspective view of an embodiment of a system constructed in accordance with the present disclosure, showing the illuminator, sensor, and controller;Fig. 2 is a diagram showing a method in accordance with the present disclosure, showing a process for using the system of Fig. 1; andFig. 3 is a diagram showing more detail about the LUT procedure shown in Fig. 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, a partial view of an embodiment of a system in accordance with the disclosure is shown in Fig. 1 and is designated generally by reference character 100. Other embodiments of systems in accordance with the disclosure, or aspects thereof, are provided in Figs. 2-3, as will be described. The systems and methods described herein can be used to find range to an object, such as in laser range finding or LIDAR (Light Detection and Ranging), that is independent the object's reflectivity. The system 100 includes an illuminator 102 configured to flash a scene with two different levels of illumination power. The flash cone 106 in Fig. 2 indicates the illumination from the illuminator 102. The system 100 also includes a sensor 104 that is sensitive to illumination from the illuminator 102. As indicated by the dashed line in Fig. 1, the sensor can detect a return of a pulse of illumination from the illuminator 102 that is reflected off of an object 110. The timing of the return of the reflected pulse is used to determine rage between the object 110 and the system 100. A controller 108 is operatively connected to the illuminator 102 and to the sensor 104. The controller 108 is configured to use the s