Determining reflectance of a target using a time of flight ranging system

Patent metadata

Field	Value
Publication number	US-2017031007-A1
Application number	US-201514809384-A
Country	US
Kind code	A1
Filing date	Jul 27, 2015
Priority date	Jul 27, 2015
Publication date	Feb 2, 2017
Grant date	—

Abstract

An electronic device includes a ranging light source and a reflected light detector. A logic circuit causes the ranging light source to emit ranging light at a target. Reflected light from the target is detected using the reflected light detector, with the reflected light being a portion of the ranging light that reflects from the target back toward the reflected light detector. An intensity of the reflected light is determined using the reflected light detector. A distance to the target is determined based upon time elapsed between activating the ranging light source and detecting the reflected ranging light. Reflectance of the target is calculated, based upon the intensity of the reflected light and the distance to the target.

First claim

1 . An electronic device, comprising:
a ranging light source; a reflected light detector; a logic circuit configured to
cause the ranging light source to emit ranging light at a target,
detect reflected light from the target using the reflected light detector, the reflected light being a portion of the ranging light that reflects from the target back toward the reflected light detector,
determine an intensity of the reflected light using the reflected light detector,
determine a distance to the target based upon time elapsed between activating the ranging light source and detecting the reflected ranging light, and
calculate reflectance of the target, based upon the intensity of the reflected light and the distance to the target.

2 . The electronic device of claim 1 , wherein the logic circuit is further configured to determine a color of the target based upon the reflectance of the target.

3 . The electronic device of claim 1 , wherein the logic circuit is configured to calculate the reflectance by:
calculating an intensity of the reflected light at a surface of the target as a product of the intensity of the reflected light at the reflected light detector and a square of the distance to the target; and determining the reflectance of the target based on the intensity of the reflected light at the surface of the target.

4 . The electronic device of claim 1 , wherein the logic circuit calculates the reflectance as a function of a quotient of first and second exponential functions, the first exponential function having the intensity of the reflected light as an offset and having the distance as an exponent of Euler's number, the second exponential function having an offset and having the distance to the target and a coarse reflectance as exponents of Euler's number.

5 . The electronic device of claim 1 , wherein the logic circuit is further configured to calculate a coarse reflectance as:

Coarse



Reflectance

=

(

Intensity





of



the



reflected



light

-

A
*



B
*
Distance

)

C
+

D
*



E
*
Distance

,

where A, B, C, D, and E are coefficients.

6 . The electronic device of claim 5 , wherein A is between −50 and −30, wherein B is between −0.01 and −0.1, wherein C is between 0.01 and 0.2, wherein D is between 1 and 3, and wherein E is between −0.01 and −0.1.

7 . The electronic device of claim 5 , wherein the logic circuit is configured to calculate the reflectance as:

Reflectance
=

Intensity





of



the



reflected



light

-

A
*



B
*
Distance

C
+

D
*



(

F
+

G
*
Coarse



Reflectance

)

*
Distacne

where A, B, C, D, F, and G are coefficients.

8 . The electronic device of claim 7 , wherein A is between −50 and −30, wherein B is between −0.01 and −0.1, wherein C is between 0.01 and 0.2, wherein D is between 1 and 3, wherein F is between −0.01 and −0.1, and wherein G is between 0.0001 and 0.0005.

9 . The electronic device of claim 1 , wherein the logic circuit is configured to calculate the reflectance as:

Reflectance
=

Intensity

1
-



-

(

H
*

Assignees

• St Microelectronics Inc
• Stmicroelectronics (Research & Development) Ltd

Inventors

• Winterton Darin K
• Lee Sam

Classifications

• G01S7/4865

  Time delay measurement, e.g. time-of-flight measurement, time of arrival measurement or determining the exact position of a peak (peak detection in noise, signal conditioning G01S7/487) · CPC title

• G01S7/4861 Primary

  Circuits for detection, sampling, integration or read-out · CPC title

• G01S7/4802

  using analysis of echo signal for target characterisation; Target signature; Target cross-section · CPC title

• G01S17/08 Primary

  for measuring distance only (indirect measurement G01S17/46; active triangulation systems G01S17/48) · CPC title