Surface distance determination using reflected light

• US 9,062,969 B1
• Filed: 03/07/2013
• Issued: 06/23/2015
• Est. Priority Date: 03/07/2013
• Status: Expired due to Fees

• Current Assignee: Amazon Technologies, Inc. (Amazon.com, Inc.)
• Original Assignee: Rawles, LLC (Amazon.com, Inc.)
• Inventors: Liu, Qiang, Degges, Ronald Joseph Jr.
• Primary Examiner(s): Ratcliffe, Luke
• Assistant Examiner(s): RODRIGUEZ, VICENTE M
• Application Number:
  US13/789,516
• Time in Patent Office: 838 Days
• Field of Search: 356/5.01
• US Class Current: 1/1
• CPC Class Codes: G01C 3/00 Measuring distances in line of sight; Optical rangefinders tapes, chains or wheels for measuring length G01B3/00; active triangulation systems, i.e. using the transmission and reflection of electromagnetic waves other than radio waves, G01S17/48
• CPC Class Codes: G01S 17/003 Bistatic lidar systems; Multistatic lidar systems
• CPC Class Codes: G01S 17/08 for measuring distance only indirect measurement G01S17/46; active triangulation systems G01S17/48
• CPC Class Codes: G01S 17/36 with phase comparison between the received signal and the contemporaneously transmitted signal
• CPC Class Codes: G01S 17/88 Lidar systems specially adapted for specific applications
• CPC Class Codes: G01S 17/89 for mapping or imaging
• CPC Class Codes: G01S 7/481 Constructional features, e.g. arrangements of optical elements
• CPC Class Codes: G01S 7/4865 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 Class Codes: G01S 7/4915 Time delay measurement, e.g. operational details for pixel components signal extraction and conditioning G01S7/493; Phase measurement
• CPC Class Codes: G01S 7/493 Extracting wanted echo signals

Abstract

A distance between a light source and a surface may be determined by emitting pulses of light from the light source and measuring an intensity of the light after the light reaches the surface. To determine a true distance, aliased distances, which are outside of a known distance segment, are disregarded. The distance segment may be defined by a modulation period of light emitted by the light source. The distance segment may be determined based on a ratio of a measured intensity of light captured during a first time interval and a second time interval, and a comparison of other types of evidence data that identifies a correct distance segment. The evidence data may include data associated with the amplitude (intensity) of the light captured, temporal variations in data, and/or analysis data collected from other surfaces that are adjacent to the surface.

Claims

1. A system to measure distances, the system comprising:

a light source to emit pulses of light, the pulses emitted at a frequency;

two light sensors to detect light that is emitted from the light source and reflected off of a surface, the two light sensors including;

a first light sensor to measure an intensity of light detected during a first time interval to determine a first measured value, and

a second light sensor to measure an intensity of light detected during a second time interval, equal to the first time interval, to determine a second measured value, wherein the first light sensor is off during the second time interval and the second light sensor is off during the first time interval; and

one or more processors to;

determine a ratio of the first measured value to the second measured value;

select a distance segment from a plurality of equal distance segments defined by a distance of light travel during one cycle of the frequency, the distance segment spanning between two different distances, wherein a distance between the two light sensors and the surface is between the two different distances, the distance segment selected based at least in part on at least one of;

comparing the first measured value or the second measured value of the intensity of light to baseline light intensity data stored in reference data, the baseline light intensity data being associated with one of the plurality of equal distance segments, or

comparing a variance in at least the ratio and a second ratio to baseline variance data stored in the reference data, the baseline variance data being associated with one of the plurality of equal distance segments; and

determine the distance between the two light sensors and the surface based at least in part on the ratio and the selected distance segment.

2. The system of claim 1, wherein:

the two light sensors measure intensity of light reflected off of the surface when the surface is located at each of a number of predetermined distances from the two light sensors; and

the one or more processors store the measured intensity of light for each of the predetermined distances as the baseline light intensity data.

3. The system of claim 1, wherein:

the two light sensors take multiple measurements of an intensity of light reflected from the surface, the measurements occurring when the surface is located a predetermined distance from the two light sensors; and

the one or more processors determine a variance of the multiple measurements and store the variance and the predetermined distance as one of multiple entries in the baseline variance data.

4. The system of claim 1, wherein

the first light sensor measures an intensity of light detected during a third time interval to determine a third measured value,

the second light sensor measures an intensity of light detected during a fourth time interval to determine a fourth measured value, and

the one or more processors determine the second ratio based on the third measured value and the fourth measured value.

5. The system of claim 1, wherein the one or more processors are further to compare the determined distance with a previously determined distance to determine whether the surface has moved relative to the two light sensors.

6. A method comprising:

emitting light in pulses;

measuring an intensity of a pulse of light after the pulse of light is reflected off a surface, the measuring providing a first measured value of light associated with a first interval and a second measured value of light associated with a second interval;

comparing the first measured value of light to the second measured value of light;

determining a distance segment associated with a location of the surface, the distance segment selected from a plurality of equal distance segments defined by a distance traveled by the pulse of light, the distance segment spanning between two different distances, the distance segment determined based at least in part on a comparison of the intensity of the pulse of light to baseline light intensity data that is associated with one of the plurality of equal distance segments; and

determining a distance associated with the surface based at least in part on the comparing and the determined distance segment, the distance being within the determined distance segment.

7. The method of claim 6, further comprising accessing the baseline light intensity data from a look up table.

8. The method of claim 6, wherein the baseline light intensity data further includes a value of light absorption for different types of surfaces including a type of the surface.

9. The method of claim 6, wherein the distance segment is further selected based at least in part on (i) a variance in the comparison and (ii) a second comparison to baseline variance data that is associated with one of the plurality of equal distance segments.

10. The method of claim 9, wherein the variance is a standard deviation of the ratio.

11. The method of claim 9, wherein the second comparison is based on measuring an intensity of a second pulse of light immediately following the pulse of light.

12. The method of claim 6, wherein the surface is divided into a plurality of surface areas, and wherein the determining the distance segment for a surface area is based at least in part on determined distance segments of other surface areas of the plurality of surface areas that are adjacent to the surface area.

13. The method of claim 6, wherein the measuring the light is performed by one or more capacitors that store energy from a photodiode connected to the one or more capacitors.

14. The method of claim 6, wherein the light is infrared light.

15. The method of claim 6, wherein a frequency of the pulses is selected based at least in part on an estimated depth of an environment that includes the surface.

16. A method comprising:

emitting light in pulses;

measuring an intensity of a pulse of light after the pulse of light is reflected off a surface, the measuring providing a first measured value of light associated with a first interval and a second measured value of light associated with a second interval;

performing a comparison between the first measured value of light to the second measured value of light;

selecting a distance segment from a plurality of equal distance segments defined by a distance of light traveled by the pulse of light, the distance segment selected based at least in part on a variance of the comparison and a second comparison to baseline light intensity data that is associated with one of the plurality of equal distance segments; and

determining a distance associated with the surface based at least in part on the comparison and the selected distance segment, the distance being within a bounds of the selected distance segment.

17. The method of claim 16, wherein the second comparison is performed within a predetermined amount of time after the comparison.

18. The method of claim 16, wherein the variance is based on consecutive measurements of the intensity of light within a predetermined amount of time.

19. The method of claim 16, wherein the selecting the distance segment is further based at least in part on a distance segment of another surface that is adjacent to the surface.

20. A method comprising:

emitting light in pulses;

measuring an intensity of a pulse of light after the pulse of light is reflected off a surface, the measuring providing a first measured value of light associated with a first interval and a second measured value of light associated with a second interval;

determining a ratio based on the first measured value of light and the second measured value of light;

determining a distance segment from a plurality of equal distance segments defined by a distance of light traveled by the pulse of light, the distance segment spanning between two different distances, the distance segment determined based at least in part on;

a comparison of the intensity of the pulse of light to baseline light intensity data that is associated with one of the plurality of equal distance segments;

or

a variance of the ratio and a second ratio to baseline light intensity data that is associated with one of the plurality of equal distance segments; and

determining a distance associated with the surface based at least in part on the determined distance segment.