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

Patent metadata

Field	Value
Publication number	US-10067223-B2
Application number	US-201514809384-A
Country	US
Kind code	B2
Filing date	Jul 27, 2015
Priority date	Jul 27, 2015
Publication date	Sep 4, 2018
Grant date	Sep 4, 2018

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

The invention claimed is:

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;
the reflectance being calculated 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.

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 , further comprising a printing mechanism configured to attempt to print output on a piece of paper; wherein the piece of paper is the target; and wherein the logic circuit is further configured to determine whether the printing mechanism successfully printed the output on the piece of paper based upon the reflectance of the piece of paper.

4. The electronic device of claim 3 , wherein the logic circuit is further configured to determine an ink level of the printing mechanism based upon the reflectance of the piece of paper.

5. The electronic device of claim 1 , further comprising a camera mechanism with an autofocus function; wherein the target is in a field of view of the camera mechanism; and wherein the logic circuit is further configured to determine a maximum autofocus distance between the camera mechanism and the target based upon the reflectance of the target.

6. The electronic device of claim 1 , wherein the ranging light source comprises a vertical cavity surface emitting laser configured to emit the ranging light; wherein the reflected light detector comprises a Geiger mode photodetector configured to detect the reflected light.

7. 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;

calculate a coarse reflectance as:

Coarse
⁢

⁢
Reflectance

=

(

Intensity
⁢

⁢

⁢
of
⁢

⁢
the
⁢

⁢
reflected
⁢

⁢
light

-

A
*

e

B
*
Distance

)

C
+

D
*

e

E
*
Distance

where A is between −50 and −30, B is between −0.01 and −0.1, C is between 0.01 and 0.2, D is between 1 and 3, and E is between −0.01 and −0.1.

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

Reflectance
=

Intensity
⁢

⁢

⁢
of
⁢

⁢
the
⁢

⁢
reflected
⁢

⁢
light

-

A
*

e

B
*
Distance

C
+

D
*

e

(

F
+

G
*
Coarse
⁢

⁢
Reflectance

)

*
Distacne

Assignees

• St Microelectronics Inc
• St Microelectronics Res & Dev Ltd

Inventors

• Winterton Darin K
• Lee Sam

Classifications

• 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

• G01S7/4861 Primary

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