Method for calibrating camera measurement system

Patent metadata

Field	Value
Publication number	US-9996931-B2
Application number	US-201214361361-A
Country	US
Kind code	B2
Filing date	Feb 24, 2012
Priority date	Dec 26, 2011
Publication date	Jun 12, 2018
Grant date	Jun 12, 2018

Abstract

In a calibration method a ring-shaped jig is disposed on a machine tool workpiece. The optical axis of a camera is aligned parallel to an axis of the machine tool. The jig is photographed with the horizontal or the vertical direction of the camera aligned with an axial direction other than the signal direction of the machine tool. The circumferential shape of the jig in the photograph is extracted as a contour. The center position of the jig in the image is calculated from the contour while all distortion correction coefficients in tangential and radial directions are ignored and set to zero. The displacements of the main point of the camera are set to zero. The translation distance, which is an external parameter of calibration, is calculated based on the center position of the jig in the image and the known three-dimensional center position of the jig.

First claim

The invention claimed is:

1. A method for calibrating a camera measurement system having a single camera comprising:
setting a ring-shaped calibration jig at a workpiece on a machining tool;
aligning an optical axis of said camera parallel to a single axis of a coordinate system of said machining tool and also aligning a horizontal direction or a vertical direction of said camera with an axial direction other than a direction of said single axis of said machining tool wherein an image of said calibration jig is aligned at a central portion of an image and photographed using said camera;
extracting a circumferential shape of said calibration jig in said central portion of said image as a contour;
calculating a center position (U Ring , V Ring ) of said calibration jig in said image from said contour; and
calculating a translation distance (tx, ty, tz) as an external parameter of calibration on the basis of said center position (U Ring , V Ring ) of said calibration jig in said central portion of said image and a known three-dimensional center position (X r , Y r , Z r ) of said calibration jig, wherein all the distortion correction coefficients in a tangential direction of said camera and all the distortion correction coefficients in a radial direction of said camera are ignored and set to zero and displacement of the main point of a camera are all set to zero and are included in the translation distance of the camera as

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Assignees

• Yamamoto Hideaki
• Mitsubishi Heavy Ind Machine Tool Co Ltd

Inventors

• Yamamoto Hideaki

Classifications

• G06T2207/30244

  Camera pose · CPC title

• G06T7/0018 Primary

  Physics · mapped topic

• H04N17/002

  for television cameras · CPC title

• B23Q17/2428

  for measuring existing positions of tools or workpieces · CPC title

• B23Q17/249

  using image analysis, e.g. for radar, infrared or array camera images · CPC title