Method of calibrating a detector and calibration sphere for the same

• US 7,055,363 B2
• Filed: 02/11/2004
• Issued: 06/06/2006
• Est. Priority Date: 02/11/2004
• Status: Expired due to Fees

• Current Assignee: Acushnet Company (FILA Holdings Corp.)
• Original Assignee: Acushnet Company (FILA Holdings Corp.)
• Inventors: Furze, Paul A., Laprade, Donald
• Primary Examiner(s): RAEVIS, ROBERT R
• Application Number:
  US10/776,429
• Publication Number:
  US 20050172695A1
• Time in Patent Office: 846 Days
• Field of Search: 73/10.1, 738/658, 738/656, 734/321, 356/243.1, 352/428, 702/94, 702/95
• US Class Current: 73/1.01
• CPC Class Codes: G01B 21/042 Calibration or calibration artifacts G01B3/30, G01B9/02072 take precedence
• CPC Class Codes: G01N 21/951 Balls
• CPC Class Codes: G01N 33/008 Sport articles, e.g. balls, skis or rackets
• CPC Class Codes: G06T 7/80 Analysis of captured images to determine intrinsic or extrinsic camera parameters, i.e. camera calibration

Abstract

A method of calibrating a detector using a calibration object having a rounded surface and indicia is disclosed. The calibration object, when coupled with a detector and analyzer, assists in minimizing image distortion caused by misalignment of the detector relative to the calibration object. A calibration object is also disclosed.

Claims

1. A method of calibrating a detector, comprising:

providing a calibration object that mimics a golf ball having an indicium and an axis of rotation;

making an image of the indicium with a detector;

comparing the image with a predetermined image; and

adjusting the detector so that a subsequent image of the indicium more-closely matches the predetermined image.

2. The method of claim 1 wherein the detector is adjusted to minimize a rotational misalignment of the detector.

3. The method of claim 2 wherein the detector is a line scan camera and the indicium indicates whether a scan line of the camera is parallel to the axis of rotation.

4. The method of claim 1 wherein the detector is adjusted to minimize a horizontal misalignment of the detector.

5. The method of claim 4 wherein the detector is a line scan camera and the indicium indicates whether a scan line of the camera is in front of the axis of rotation.

6. The method of claim 1 wherein the detector is adjusted to minimize a vertical misalignment of the detector.

7. The method of claim 6 wherein the detector is a line scan camera and the indicium indicates whether a scan line of the camera is vertically aligned.

8. The method of claim 6 wherein the calibration object comprises latitudinal indicia that indicate whether the scan line is vertically aligned.

9. The method of claim 1 wherein the indicium indicates whether the detector is out of focus.

10. The method of claim 1 wherein the indicium comprises a longitudinal line.

11. The method of claim 1 wherein the calibration object has a surface, a portion of which is spherically shaped.

12. The method of claim 1 wherein the step of comparing the first indicium image with the predetermined image is performed using a display device.

13. The method of claim 1 wherein the detector is automatically adjusted using a shift mechanism.

14. The method of claim 13 wherein the calibration object has at least two indicia that have a known distance apart from each other, which indicate a scale factor that relates a detected distance to the known distance when detected by the detector.

15. The method of claim 14 wherein the at least two indicia are part of one indistinct marking.

16. A method for calibrating a detector, comprising:

positioning a calibration sphere at a position on a golf ball production line occupied by a golf ball during golf ball inspection;

imaging the calibration object using a line scan camera detector to produce an image;

comparing the image with an predetermined image; and

adjusting the detector.

17. The method of claim 16 wherein the detector is adjusted to minimize horizontal misalignment of the detector.

18. The method of claim 16 wherein the detector is adjusted to minimize rotational misalignment of the detector.

19. The method of claim 16 wherein the detector is adjusted to minimize vertical misalignment of the detector.

20. The method of claim 16 wherein the detector is adjusted to focus the detector.

21. A method for calibrating an image of a calibration object rotatable by a device comprising the steps of:

rotating the calibration object with the device;

providing at least two indicia that make a first angle with each other;

obtaining a digital image of the calibration object;

determining a second angle between the corresponding indicia on the image;

determining an adjustment factor from the first and second angle;

applying said adjustment factor to images of other objects rotated by said device.

22. The method of claim 21 wherein the device is a stepper motor.

23. The method of claim 21 wherein the calibration object is a cylindrical shaped object.

24. The method of claim 21 wherein the at least two indicia comprises linear-lines.