Surface distance determination using time-of-flight of light

• US 9,127,942 B1
• Filed: 09/21/2012
• Issued: 09/08/2015
• Est. Priority Date: 09/21/2012
• Status: Active Grant

• Current Assignee: Amazon Technologies, Inc. (Amazon.com, Inc.)
• Original Assignee: Amazon Technologies, Inc. (Amazon.com, Inc.)
• Inventors: Haskin, Menashe, Coley, Christopher D., Zehr, Gregg Elliott, Degges, Ronald Joseph Jr.
• Primary Examiner(s): RATCLIFFE, LUKE D
• Application Number:
  US13/624,611
• Time in Patent Office: 1,082 Days
• Field of Search: 356 301- 285
• US Class Current: 1/1
• CPC Class Codes: G01C 3/08 Use of electric radiation detectors
• CPC Class Codes: G01S 17/10 using transmission of interrupted, pulse-modulated waves determination of distance by phase measurements G01S17/32
• CPC Class Codes: G01S 17/36 with phase comparison between the received signal and the contemporaneously transmitted signal
• CPC Class Codes: G01S 17/50 Systems of measurement based on relative movement of target
• CPC Class Codes: G01S 17/894 3D imaging with simultaneous measurement of time-of-flight at a 2D array of receiver pixels, e.g. time-of-flight cameras or flash lidar
• CPC Class Codes: G06F 3/011 Arrangements for interaction with the human body, e.g. for user immersion in virtual reality blind teaching G09B21/00
• CPC Class Codes: G06F 3/017 Gesture based interaction, e.g. based on a set of recognized hand gestures interaction based on gestures traced on a digitiser G06F3/04883

Abstract

In some embodiments, a distance between the at least one light sensor and the surface may be calculated using a ratio representative of the phase difference using time-of-flight of light. The distance may be within a distance range defined by a distance of light travel during a modulation period of the predetermined frequency. The distance may be based on the ratio defined by an amount of energy stored from captured light during a first time interval and a second time interval, and a comparison of an amount of light stored from captured light during at least a third time interval. The first, second, and third time intervals are different, but may overlap in some instances. In some embodiments, the amount of ambient light may be identified and subtracted from the inputs of the ratio. A switch may be used to prevent oversaturation of a storage element storing the stored energy.

Claims

1. A system comprising:

a light emitter to emit light in pulses having a predetermined frequency;

at least one light sensor to capture, using a plurality of storage elements, energy from the light that is emitted from the light emitter and reflected off of a surface over a period of time including at least four time intervals, the plurality of storage elements including;

a first storage element to store energy from light captured during a first time interval that occurs for a length of time substantially equal to a duration of one of the pulses of light,

a second storage element to store energy from light captured during a second time interval that occurs for a length of time substantially equal to an amount of time between each of the pulses,

a third storage element to store energy from light captured during a third time interval that occurs during a portion of the first time interval, and

a fourth storage element to store energy from light captured during a fourth time interval that occurs during a portion of the second time interval; and

one or more processors to calculate a distance between the at least one light sensor and the surface, the distance being within a distance range defined by a distance traveled by the light during a cycle of the predetermined frequency, the one or more processors calculating the distance based at least in part on;

a ratio of a measurement of the light stored during the first time interval and a measurement of the light stored during the second time interval, and

a comparison of a measurement of the light stored during the third time interval and a measurement of the light stored during the fourth time interval.

2. The system of claim 1, wherein the at least one light sensor comprises a photodiode, and wherein the plurality of storage elements receive energy from the photodiode.

3. The system of claim 2, further comprising a switch to at least temporarily disconnect the plurality of storage elements from the photodiode to prevent oversaturation of any of the plurality of storage elements, wherein activation of the switch initiates a process comprising determining the ratio by the one or more processors.

4. The system of claim 1, wherein the one or more processors further operate to determine a measurement of ambient light as a measurement of light captured during a time period when the light emitter is not emitting light.

5. The system of claim 4, further comprising adjusting the ratio by subtracting the measurement of the ambient light from the measurement of light captured during the first time interval and the measurement of light captured during the second time interval.

6. The system of claim 1, further comprising using the distance to track, within the distance range, movement of the surface.

7. A method comprising:

emitting, by at least one light emitter, light in pulses having a predetermined frequency;

detecting, by at least one light sensor, the light after the light is reflected off a surface, the detecting being performed during at least three time intervals including;

a first time interval that occurs for a length of time substantially equal to a duration of one of the pulses of light,

a second time interval that occurs for a length of time substantially equal to an amount of time between each of the pulses, and

a third time interval defined as occurring during a portion of the first time interval or during a portion of the second time interval, and

calculating, by at least one processor, a distance associated with the surface, the distance being within a distance range defined by a distance traveled by light during a cycle of the predetermined frequency, the distance calculated based at least in part on;

a ratio of a measurement of the light detected during the first time interval and a measurement of the light detected during the second time interval, and

a comparison of a measurement of the light detected during the third time interval and a measurement of ambient light.

8. The method of claim 7, wherein the detecting the light is performed by at least three light sensors.

9. The method of claim 7, wherein the detecting the light is performed by at least three capacitors that store energy from a photodiode connected to the at least three capacitors, each of the at least three capacitors storing energy during a different time interval.

10. The method of claim 7, further comprising determining the measurement of the ambient light by detecting light prior to the emitting the light in the pulses.

11. The method of claim 10, further comprising determining that the distance is within a predetermined subset of the distance range based at least in part on the measurement of the light detected during the third interval.

12. The method of claim 7, wherein the duration of each of the pulses of light and the amount of time between each of the pulses are substantially equal in length of time.

13. The method of claim 7, wherein the predetermined frequency is selected based at least in part on the distance range.

14. The method of claim 7, further comprising determining that the distance is within a predetermined subset of the distance range based at least in part on the measurement of the light detected during the third interval being substantially equal to the measurement of the ambient light.

15. The method of claim 7, further comprising segmenting the surface into a plurality of surface locations.

16. The method of claim 15, further comprising aggregating a plurality of distances from the plurality of surface locations to identify a surface profile within the distance range, the surface profile including the surface location having the calculated distance.

17. A system comprising:

a light emitter to emit light in pulses having a predetermined frequency;

at least one light sensor to detect the light that is emitted from the light emitter and reflected off a surface, the light sensor to detect the light that is emitted from the light emitter and reflected off of the surface during a period of time having at least n discrete time intervals of substantially equal length of time that occur during a cycle of the predetermined frequency, wherein n is an integer greater than or equal to three; and

one or more processors to calculate a distance between the at least one light sensor and the surface, the distance being within a distance range defined by a distance traveled by the light during the cycle of the predetermined frequency, the one or more processors calculating the distance based at least in part on;

a ratio of a measurement of the light detected during a first group of the time intervals and a second group of the time intervals, and

a determination of which one of the discrete time intervals has a lowest measurement of detected light.

18. The system of claim 17, wherein n is equal to four and each of the discrete intervals is equal to one-quarter of one cycle of the predetermined frequency.

19. The system of claim 18, wherein the ratio is defined by a measurement of the light detected during a first two time intervals and a measurement of the light detected during a last two time intervals.

20. The system of claim 17, wherein the determination of which one of the discrete time intervals has the lowest measurement of detected light indicates that the distance is within a predetermined subset range within the distance range.

21. The system of claim 17, further comprising determining a measurement of ambient light based at least in part on the lowest measurement of light detected in any of the n number of the discrete time intervals.

22. The system of claim 21, further comprising adjusting the ratio by subtracting the measurement of the ambient light from the measurement of light detected during each of the discrete time intervals.

23. The system of claim 17, wherein the at least one light sensor includes a plurality of storage elements where each storage element stores energy resulting from detection of light during a different one of the n discrete time intervals, the energy created by a photodiode shared by each of the plurality of storage elements.

24. The system of claim 23, wherein the one or more processors calculate the distance using the ratio of the energy stored in each storage element after a plurality of cycles.

25. The system of claim 24, wherein the at least one light sensor includes a comparator and limiter circuit that at least temporarily prevents further storage of energy by the plurality of storage elements when a fill level of energy of one of the plurality of the storage elements reaches or exceeds a threshold level.

26. A method comprising:

emitting, by at least one light emitter, light in pulses having a predetermined frequency;

detecting, by at least one light sensor, the light after the light is reflected off a surface, the detecting being performed during at least n discrete time intervals of substantially equal length of time that occur during a cycle of the predetermined frequency, wherein n is an integer greater than or equal to three; and

calculating, by at least one processor, a distance between the at least one light sensor and the surface, the distance being within a distance range defined by a distance traveled by the light during the cycle of the predetermined frequency, the one or more processors calculating the distance based at least in part on;

a ratio of a measurement of the light detected during a first group of the time intervals and a second group of the time intervals, and

a determination of which one of the discrete time intervals has a lowest measurement of detected light.