CALIBRATION OF TIME-OF-FLIGHT MEASUREMENT USING STRAY REFLECTIONS

• US 20140291491A1
• Filed: 06/12/2014
• Published: 10/02/2014
• Est. Priority Date: 03/22/2012
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: PrimeSense Ltd (Apple Inc.)
• Inventors: Shpunt, Alexander, Erlich, Raviv
• Granted Patent: US 9,335,220 B2
• Time in Patent Office: Days
• US Class Current: 250/214.1
• CPC Class Codes: G01J 11/00 Measuring the characteristics of individual optical pulses or of optical pulse trains
• CPC Class Codes: G01S 17/89 for mapping or imaging
• CPC Class Codes: G01S 7/4817 relating to scanning
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating
• CPC Class Codes: G02B 26/101 with both horizontal and vertical deflecting means, e.g. raster or XY scanners colour television using laser beams scanning a display screen H04N9/3129
• CPC Class Codes: G02B 5/1814 structurally combined with one or more further optical elements, e.g. lenses, mirrors, prisms or other diffraction gratings G02B5/189 takes precedence

Abstract

Sensing apparatus includes a transmitter, which emits a beam comprising optical pulses toward a scene, and a receiver, which receives reflections of the optical pulses and outputs electrical pulses in response thereto. Processing circuitry is coupled to the receiver so as to receive, in response to each of at least some of the optical pulses emitted by the transmitter, a first electrical pulse output by the receiver at a first time due to stray reflection within the apparatus and a second electrical pulse output by the receiver at a second time due to the beam reflected from the scene, and to generate a measure of a time of flight of the optical pulses to and from points in the scene by taking a difference between the respective first and second times of output of the first and second electrical pulses.

Claims

1. Sensing apparatus, comprising:

a transmitter, which is configured to emit a beam comprising optical pulses toward a scene;

a receiver, which is configured to receive reflections of the optical pulses and to output electrical pulses in response thereto; and

processing circuitry, which is coupled to the receiver so as to receive, in response to each of at least some of the optical pulses emitted by the transmitter, a first electrical pulse output by the receiver at a first time due to stray reflection within the apparatus and a second electrical pulse output by the receiver at a second time due to the beam reflected from the scene, and to generate a measure of a time of flight of the optical pulses to and from points in the scene by taking a difference between the respective first and second times of output of the first and second electrical pulses.

2. The apparatus according to claim 1, and comprising a scanner, which is configured to scan the beam over a scene, wherein the optical pulses are emitted and received at multiple angular positions of the scanner.

3. The apparatus according to claim 1, wherein the processing circuitry is configured to generate a depth map of the scene responsively to the time of flight of the optical pulses.

4. The apparatus according to claim 1, wherein the first time is indicative of an inherent delay of the receiver in generating the electrical pulses in response to the arrival of the optical pulses, and wherein the processing circuitry is configured to calibrate the time of flight in order to correct for the inherent delay.

5. The apparatus according to claim 4, wherein the processing circuitry is configured to compute a moving average of the difference between the respective first and second times over a sequence of the optical pulses, and to calibrate the time of flight using the computed average.

6. A method for optical sensing, comprising:

transmitting a beam comprising optical pulses from a sensing device toward a scene;

receiving reflections of the optical pulses in the sensing device and outputting electrical pulses from the sensing device in response to the received reflections, the electrical pulses comprising, in response to each of at least some of the transmitted optical pulses, a first electrical pulse output by the sensing device at a first time due to stray reflection within the sensing device and a second electrical pulse output by the sensing device at a second time due to the beam reflected from the scene; and

generating a measure of a time of flight of the optical pulses to and from points in the scene by taking a difference between the respective first and second times of output of the first and second electrical pulses.

7. The method according to claim 6, and comprising scanning the beam over a scene, whereby the optical pulses are emitted and received at multiple angular positions relative to the scene.

8. The method according to claim 6, and comprising generating a depth map of the scene responsively to the time of flight of the optical pulses.

9. The method according to claim 6, wherein the first time is indicative of an inherent delay of the sensing device in generating the electrical pulses in response to the arrival of the optical pulses, and wherein generating the measure comprises calibrating the time of flight in order to correct for the inherent delay.

10. The method according to claim 9, wherein calibrating the time of flight comprises computing a moving average of the difference between the respective first and second times over a sequence of the optical pulses, and calibrating the time of flight using the computed average.