ABSOLUTE DISTANCE MEASUREMENT FOR TIME-OF-FLIGHT SENSORS

• US 20160124089A1
• Filed: 10/31/2014
• Published: 05/05/2016
• Est. Priority Date: 10/31/2014
• Status: Active Grant

• Current Assignee: Rockwell Automation Switzerland GmbH (Rockwell Automation, Inc.)
• Original Assignee: Cedes Safety & Automation AG (Rockwell Automation, Inc.)
• Inventors: Meinherz, Carl, Hardegger, Martin, Stein, Manfred, Dorizzi, Danilo
• Granted Patent: US 9,823,352 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01C 3/32 by focusing the object, e.g. on a ground glass screen
• CPC Class Codes: G01S 17/08 for measuring distance only indirect measurement G01S17/46; active triangulation systems G01S17/48
• 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 17/48 Active triangulation systems, i.e. using the transmission and reflection of electromagnetic waves other than radio waves
• CPC Class Codes: G01S 17/86 Combinations of lidar systems with systems other than lidar, radar or sonar, e.g. with direction finders
• CPC Class Codes: G01S 17/87 Combinations of systems using electromagnetic waves other than radio waves
• 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: G01S 7/497 Means for monitoring or calibrating

Abstract

A time-of-flight (TOF) sensor device is provided with features for correcting distance measurement offset errors caused by such factors as temperature, dynamic reflectivity ranges of objects in the viewing space, or other factors. In various embodiments, the TOF sensor device generates corrected distance values based on comparison of two different distance values measured for an object by two different measurement techniques, including but not limited to phase shift measurement, pulsed TOF measurement, distance measurement based on the focal length of the TOF sensor'"'"'s lens, and comparison of distance variations with light intensity variations. In addition, some embodiments of the TOF sensor device perform self-calibration using internal waveguides or parasitic reflections as distance references.

Claims

1. A time-of-flight (TOF) sensor device, comprising:

a memory that stores computer-executable components; and

a processor, operatively coupled to the memory, that executes the computer-executable components, the computer-executable components comprising;

an illumination component configured to emit a light beam toward a viewing space;

a first distance determination component configured to generate first distance information for a pixel corresponding to an object in the viewing space based on time-of-flight analysis of reflected light incident on a photo-receiver array;

a second distance determination component configured to generate second distance information for the pixel corresponding to the object; and

a distance adjustment component configured to apply a correction factor to the first distance information based on second distance information.

2. The TOF sensor device of claim 1, wherein the distance adjustment component is configured to generate the correction factor based on a difference between the first distance and the second distance.

3. The TOF sensor device of claim 1, further comprising a receiving lens element configured to receive the reflected light and to direct the reflected light to the photo-receiver array,

wherein the second distance determination component generates the second distance information based on a focal distance of the receiving lens element as the receiving lens element is focused on the object.

4. The TOF sensor device of claim 1, wherein the first distance determination component is configured to generate the first distance information based on measurement of a phase difference between the light beam emitted by the illumination component and the reflected light received at the photo-receiver array.

5. The TOF sensor device of claim 4, wherein the second distance determination component is configured to generate the second distance information based on a measured time duration between emission of a light pulse by the illumination component and receipt of a reflected light pulse at the photo-receiver array.

6. The TOF sensor device of claim 5, wherein the distance adjustment component is configured to add a distance equal to a multiple of a wavelength of the light beam to the first distance information in response to a determination that the second distance information exceeds the first distance information by the multiple of the wavelength.

7. The TOF sensor device of claim 1, wherein the second distance determination component comprises an intensity variation measurement component configured to record a variation of an intensity of the reflected light from the object over time to yield intensity variation information.

8. The TOF sensor device of claim 7, further comprising a distance variation measurement component configured to record a variation of the first distance information for pixel corresponding to the object over time to yield distance variation information,

wherein the distance adjustment component is configured to apply the correction factor in response to a determination that the intensity variation information and the distance variation information do not conform to an inverse-square relationship.

9. The TOF sensor device of claim 1, wherein the second distance determination component comprises at least one of an inductive sensor or a triangulation sensor.

10. The TOF sensor device of claim 1, further comprising:

a light path switching component configured to redirect light from the illumination component to an entrance of a waveguide internal to the TOF sensor device in response to initiation of a calibration sequence, wherein the waveguide is configured to guide the light to the photo-receiver array over a specified distance; and

a calibration component configured to calibrate the first distance determination component based on a difference between the specified distance and a distance value calculated for the light received from the waveguide at the photo-receiver array.

11. The TOF sensor device of claim 1, further comprising:

a light path switching component configured to redirect light from the illumination component to a section of a housing of the TOF sensor device in response to initiation of a calibration sequence, wherein redirection of the light to the section of the housing causes the light to be reflected to the photo-receiver array; and

a calibration component configured to calibrate the first distance determination component based on a difference between a distance value calculated for the light reflected to the photo-receiver array from the section of the housing and a calibration distance comprising a length of the light path from the illumination component to the photo-receiver array via the section of the housing.

12. A method for generating distance information, comprising:

emitting, by a time-of-flight (TOF) sensor comprising at least one processor, a light beam into a viewing area;

generating, by the TOF sensor, a first distance value for a pixel corresponding to an object in the viewing area using a first distance measurement technique, wherein the first distance measurement technique comprises performing time-of-flight analysis of reflected light received at a photo-receiver array of the TOF sensor;

generating, by the TOF sensor, a second distance value for the pixel corresponding to the object using a second distance measurement technique that is different than the first distance measurement technique; and

applying a correction factor to the first distance value based on the second distance value.

13. The method of claim 12, wherein the generating the second distance value comprises generating the second distance value based on a focal length of a receiving lens element of the TOF sensor as the receiving lens element is focused on the object.

14. The method of claim 12, wherein

the generating the first distance value comprises generating the first distance value based on a measured phase shift between the light beam emitted by the TOF sensor and the reflected light received at the photo-receiver array;

and

the generating the second distance value comprises generating the second distance value based on a measured time duration between emission of a light pulse by the TOF sensor and receipt of a reflected light pulse from the object at the photo-receiver array.

15. The method of claim 14, wherein the applying the correction factor comprises:

determining that the second distance value exceeds the first distance value by a multiple of a wavelength of the light beam; and

adding a distance equivalent to the multiple of the wavelength to the first distance value in response the determining.

16. The method of claim 12, further comprising:

monitoring a variation of an intensity of the reflected light received at the photo-receiver array over time to yield an intensity variation;

monitoring the first distance value over time to yield a distance variation; and

generating the correction factor based on a determination that the intensity variation and the distance variation deviate from an inverse-square relationship.

17. The method of claim 12, wherein the generating the second distance value comprises generating the second distance value based on at least one of an inductive measurement or a measurement of an angle of the reflected light beam received at the photo-receiver array.

18. The method of claim 12, further comprising:

redirecting the light beam to an entrance of a waveguide inside the TOF sensor in response to initiation of a calibration sequence;

measuring a third distance value using the first distance measurement technique based on light received at the photo-receiver array from the waveguide; and

calibrating a measurement component used to generate the first distance value based on a difference between the third distance value and a specified length of the waveguide.

19. A non-transitory computer-readable medium having stored thereon instructions that, in response to execution, cause a time-of-flight (TOF) sensor device comprising a processor to perform operations, the operations comprising:

sending a light beam into an area being monitored by the TOF sensor device;

determining a first distance value for a pixel corresponding to an object in the area using a first distance measurement technique, wherein the first distance measurement technique comprises performing time-of-flight analysis of reflected light received at a photo-receiver array of the TOF sensor device;

determining a second distance value for the pixel corresponding to the object using a second distance measurement technique that is different than the first distance measurement technique; and

modifying the first distance value based on the second distance value.

20. The non-transitory computer-readable medium of claim 19, wherein

the determining the first distance value comprises determining the first distance value based on a measured phase shift between the light beam sent by the TOF sensor device and the reflected light received at the photo-receiver array;

and

the determining the second distance value comprises determining the second distance value based on a measured elapsed time between sending of a light pulse by the TOF sensor device and receipt of a reflected light pulse from the object at the photo-receiver array.