CALIBRATION AND SELF-TEST IN AUTOMATED DATA READING SYSTEMS

• US 20140034731A1
• Filed: 07/22/2013
• Published: 02/06/2014
• Est. Priority Date: 07/31/2012
• Status: Active Grant

• Current Assignee: Datalogic Adc, Inc. (Datalogic S.p.A.)
• Original Assignee: Datalogic Adc, Inc. (Datalogic S.p.A.)
• Inventors: Gao, WenLiang, Hoskinson, Jeffrey J.
• Granted Patent: US 9,519,810 B2
• Time in Patent Office: Days
• US Class Current: 235/438
• CPC Class Codes: G06K 7/015 Aligning or centering of the sensing device with respect to the record carrier
• CPC Class Codes: G06K 7/10811 Focalisation
• CPC Class Codes: G06K 7/10861 sensing of data fields affixed to objects or articles, e.g. coded labels postal sorting B07C3/14, conveying articles B65G47/48
• CPC Class Codes: G06K 7/1443 locating of the code in an image
• CPC Class Codes: G06K 7/146 the method including quality enhancement steps
• CPC Class Codes: G06T 7/80 Analysis of captured images to determine intrinsic or extrinsic camera parameters, i.e. camera calibration

Abstract

Calibrating extrinsic parameters of an imaging system in an automated data reading system includes obtaining, from the imaging system, image data representing an imaged portion of a planar calibration target. The target is coupled to a housing of the automated data reading system and superimposed on a surface thereof. For example, the calibration target is placed on a conveyer surface, or it is printed on the housing of the automated data reading system. The imaged portion of the planar calibration target includes spaced-apart optical codes disposed at positions that coincide with predetermined locations of the automated data reading system to define known calibration-control points for the surface. Optical codes represented in the image data are decoded to obtain observed calibration-control points used for calibrating the extrinsic parameters based on differences between the known and observed locations of the calibration-control points.

Claims

1. A method of calibrating position and orientation parameters of an imaging system in an automated data reading system, the method comprising:

obtaining, from the imaging system, image data representing an imaged portion of a planar calibration target that is superimposed on a surface of the automated data reading system, the imaged portion of the planar calibration target including spaced-apart optical codes disposed at predetermined positions on a surface of the automated data reading system to define known locations of calibration-control points on the surface;

identifying the optical codes from the image data to obtain observed locations of the calibration-control points represented by the image data; and

calibrating position and orientation parameters of the imaging system based on differences between the known and observed locations.

2. A method according to claim 1, in which the calibration target is coupled to a housing of the automated data reading system.

3. A method according to claim 1, in which the step of calibrating comprises:

determining the position and orientation parameters of the imaging system based on a camera model that fits the known locations to the observed locations in accordance with a forward-projection model.

4. A method according to claim 1, in which the step of calibrating comprises:

determining the position and orientation parameters of the imaging system based on a camera model that fits the observed locations to the known locations in accordance with a back-projection model.

5. A method according to claim 4, further comprising:

refining the camera model iteratively.

6. A method according to claim 5, in which the step of refining comprises:

adjusting estimated position and orientation parameters of the camera model;

determining, based on the camera model, a value of a cost function representing spatial differences between the known and observed locations; and

repeating the steps of adjusting and determining until the value of the cost function is within a desired limit.

7. A method according to claim 6, further comprising:

initializing the estimated position and orientation parameters to predetermined values based on a specified installation location of the imaging system in the automated data reading system.

8. A method according to claim 1, in which the imaging system comprises multiple imaging systems including a top-side imaging system with a first field of view configured to project toward a conveyor system, a bottom-side imaging system with a second field of view configured to project via a gap in the conveyor system, and opposing sidewall imaging systems with corresponding and partly overlapping fields of view configured to project laterally, and in which the planar calibration target comprises a multi-plane calibration target having first and second opposing sides that respectively confront the first and second fields of view, and having third and fourth confronting sides that respectively confront the partly overlapping fields of view, the method further comprising:

contemporaneously performing the step of calibrating for the multiple imaging systems.

9. A method according to claim 1, in which the automated data reading system includes optics configured to subdivide a field of view of the imaging system to establish a discontiguous field of view with multiple projection centers having associated position and orientation parameters, the method further comprising:

performing the step of calibrating for the multiple projection centers.

10. A method according to claim 2, in which the housing includes the optical codes affixed thereto to define the planar calibration target that is superimposed on the surface of the housing, the method further comprising:

configuring the automated data reading system to transition from a first mode in which the optical codes are not decodable to a second mode in which the optical codes are decodable.

11. A method according to claim 10, in which the first and second modes comprise exposure control settings, the step of configuring comprising:

transitioning from a first exposure control setting in which the optical codes are not represented in the image data to a second exposure control setting in which the optical codes are represented in the image data.

12. A method according to claim 1, further comprising:

producing an indication that the step of calibrating is concluded.

13. A method according to claim 12, in which the planar calibration target comprises a freestanding template with keyed portions configured to engage corresponding portions of a housing of the automated data reading system while the template is superimposed on a conveyor surface of the automated data reading system, the method further comprising:

notifying a user to uncouple and remove the freestanding template away from the conveyor surface in response to the step of producing an indication.

14. A method according to claim 1, further comprising:

determining bounding boxes for the optical codes from the image data;

determining centroids of the bounding boxes; and

determining a region of interest based on bounding boxes and centroids.

15. A calibration system for calibrating position and orientation parameters of an imaging system in an automated data reading system, the calibration system comprising:

a planar calibration target configured to be coupled to a housing of the automated data reading system and superimposed on a surface of the automated data reading system, the planar calibration target including spaced-apart optical codes disposed at predetermined positions on a surface of the automated data reading system to define known locations of calibration-control points;

an optical code decoder configured to receive, from the imaging system, image data representing an imaged portion of the planar calibration target that includes the optical codes, and further configured to determine from the image data observed locations of the calibration-control points; and

a computing device configured to calibrate the position and orientation parameters based on differences between the known and observed locations.

16. A calibration system according to claim 15, in which the planar calibration target includes two-dimensional optical codes.

17. A calibration system according to claim 15, in which the planar calibration target comprises a freestanding template with keyed portions configured to engage corresponding grooves of the housing of the automated data reading system while the freestanding template is superimposed on a conveyor surface of the automated data reading system.

18. A calibration system according to claim 15, in which the planar calibration target comprises multiple optical codes on confronting sidewalls of the housing that border a read zone of the automated data reading system.

19. A calibration system according to claim 15, in which the optical codes represented in the image data are undecodable in a normal mode and decodable in a calibration mode.

20. A calibration system according to claim 19, in which modules of the optical codes are color-inversed, mirrored, infrared reflective, transposed, or a combination of the four.

21. A calibration system according to claim 19, in which the optical codes represented in the image data are underexposed in the normal mode and sufficiently exposed in the calibration mode to decode the optical codes from the image data.

22. A calibration system according to claim 15, in which the planar calibration target includes optical codes with void areas to inhibit duplicate decodes from a bottom-surface imaging system.

23. A calibration system according to claim 15, in which the imaging system has a consistent focal length adjustment throughout a calibration process.

24. A multi-plane calibration system configured to provide contemporaneous calibration of multiple imaging systems positioned around a read zone of an automated data reading system, the multi-plane calibration system including:

a freestanding template having calibration optical codes on its opposing sides, the freestanding template configured to mechanically engage a housing of the automated data reading system to position the calibration optical codes at known locations with respect to the automated data reading system; and

calibration optical codes printed on sidewalls of the housing at locations that are known with respect to the automated data reading system.