Surface distance determination using reflected light

• US 9,562,966 B1
• Filed: 06/17/2015
• Issued: 02/07/2017
• Est. Priority Date: 03/07/2013
• Status: Expired due to Fees

• Current Assignee: Amazon Technologies, Inc. (Amazon.com, Inc.)
• Original Assignee: Amazon Technologies, Inc. (Amazon.com, Inc.)
• Inventors: Degges, Ronald Joseph Jr., Liu, Qiang
• Primary Examiner(s): Ratcliffe, Luke
• Assistant Examiner(s): Rodriguez, Vicente
• Application Number:
  US14/742,218
• Time in Patent Office: 601 Days
• 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 comprising:

a light source to emit pulses of light at a predetermined frequency;

a sensor housing including at least two light sensors to detect light emitted from the light source and light reflected off of a surface of an object, the two light sensors including;

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

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

determine a variance of at least the ratio and a prior ratio determined from prior measured intensity values;

compare the variance to baseline variance data that associates the variance with a distance range, the distance range including a minimum distance and a maximum distance defined by a distance of light travel during one cycle of the predetermined frequency;

select the distance range to indicate candidate distances for a distance between the sensor housing and the surface; and

determine the distance between the sensor housing and the surface based at least in part on the ratio and the candidate distances included in the distance range.

2. The system of claim 1, wherein determining the variance from at least the ratio and the prior ratio further comprises:

accessing additional first measured intensity values obtained by the first light sensor, and

determining the variance based at least in part on the additional light intensity values.

3. The system of claim 2, wherein light associated with the additional measured intensity values is captured within a predetermined amount of time before the first time interval.

4. The system of claim 1, wherein determining the variance includes determining measurement inconsistencies attributed to the distance being within the distance range, the measurement inconsistencies causing at least part of the variance.

5. The system of claim 1, wherein:

the two light sensors measure intensity of light reflected off of the surface located at a first predetermined distance from the sensor housing;

the two light sensors measure intensity of light reflected off of the surface located at a second predetermined distance from the sensor housing; and

the one or more processors store the measured intensity of light for at least the first and second predetermined distances as the baseline variance data.

6. The system of claim 1, wherein:

the first light sensor takes multiple measurements of an intensity of light reflected from the surface located a predetermined distance from the sensor housing; and

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

7. The system of claim 1, further comprising:

determining a first distance between a first portion of the surface and the sensor housing;

determining a second distance between a second portion of the surface and the sensor housing; and

determining that the first and second distances are within a threshold variance for the surface.

8. The system of claim 1, wherein the one or more processors determine that the surface has moved relative to the two light sensors based at least in part on a comparison of the determined distance with a previously determined distance.

9. The system of claim 1, further comprising:

determining a first distance between a first portion of the surface and the sensor housing;

determining a second distance between a second portion of the surface and the sensor housing;

determining that the first and second distances are outside of a threshold variance for the surface; and

determining a new distance range associated with the first portion or the second portion of the surface, the new distance range used to determine a new distance for the first distance or the second distance.

10. A method comprising:

emitting light in pulses;

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

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

determining a variance of at least the first measured intensity value of light and a prior measured intensity value of light;

comparing the variance to baseline variance data that associates the variance with a distance range, the distance range including a minimum distance and a maximum distance defined by a distance of light travel during one cycle of the frequency;

selecting the distance range to indicate candidate distances for a distance between the sensor device and the surface; and

determining the distance based at least in part on the comparing the first measured intensity value of light to the second measured intensity value of light and the distance range, the distance being within the distance range.

11. The method of claim 10, further comprising measuring an intensity of a prior pulse of light to determine the prior measured intensity value within a predetermined amount of time before the measuring of the intensity of the pulse of light.

12. The method of claim 10, further comprising dividing the surface into a plurality of surface areas, and wherein the determining the distance range for a surface area is based at least in part on determined distance ranges of other surface areas of the plurality of surface areas that are adjacent to the surface area.

13. The method of claim 10, further comprising calculating the variance as a standard deviation.

14. The method of claim 10, further comprising:

determining a first distance between a first portion of the surface and the sensor device;

determining a second distance between a second portion of the surface and the sensor device; and

determining that the first and second distances are within a threshold variance for the surface.

15. The method of claim 10, further comprising storing measured light using one or more capacitors that store energy from a photodiode connected to the one or more capacitors.

16. A method comprising:

emitting light in pulses;

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

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

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

determining a variance of at least the first measured intensity value of light and the third measured intensity value of light or from at least the second measured intensity value of light and the fourth measured intensity value of light;

comparing the variance to baseline variance data that associates the variance with a distance range, the distance range including a minimum distance and a maximum distance defined by a distance of light travel during one cycle of the frequency;

selecting the distance range to indicate candidate distances for a distance between the sensor device and the surface; and

determining the distance based at least in part on the comparison between the first measured intensity value of light and the second measured intensity value of light, the distance being within the distance range.

17. The method of claim 16, wherein measuring the third measured intensity value of light occurs within a predetermined amount of time after the first measured intensity value of light.

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 range is further based at least in part on a distance range of another surface that is adjacent to the surface.

20. The method of claim 16, further comprising:

determining a first distance between a first portion of the surface and the sensor device;

determining a second distance between a second portion of the surface and the sensor device;

determining that the first and second distances are outside of a threshold variance for the surface; and

determining a new distance range associated with the first portion or the second portion of the surface, the new distance range used to determine a new distance for the first distance or the second distance.