Dimension measurement method using projection image obtained by x-ray ct apparatus

Patent metadata

Field	Value
Publication number	US-2020011662-A1
Application number	US-201916455883-A
Country	US
Kind code	A1
Filing date	Jun 28, 2019
Priority date	Jul 4, 2018
Publication date	Jan 9, 2020
Grant date	—

Abstract

In measuring a dimension of an object to be measured W made of a single material, a plurality of transmission images of the object to be measured W are obtained by using an X-ray CT apparatus, and then respective projection images are generated. The projection images are registered with CAD data used in designing the object to be measured W. The dimension of the object to be measured W is calculated by using a relationship between the registered CAD data and projection images. In such a manner, high-precision dimension measurement is achieved by using several tens of projection images and design information without performing CT reconstruction.

First claim

1 . A dimension measurement method using a projection image obtained by an X-ray CT apparatus, the dimension measurement method comprising, in measuring a dimension of an object to be measured made of a single material:
obtaining a plurality of transmission images of the object to be measured by using the X-ray CT apparatus, and then generating respective projection images; registering the projection images with CAD data used in designing the object to be measured; and calculating the dimension of the object to be measured by using a relationship between the registered CAD data and the projection images.

2 . The dimension measurement method according to claim 1 , further comprising:
selecting a representative projection image group for the registered CAD data; obtaining combinations of all projection values in the representative projection image group with transmission lengths estimated from the CAD data; and calculating the dimension of the object to be measured by using a relationship between the obtained projection values and the estimated transmission lengths.

3 . The dimension measurement method according to claim 1 , further comprising:
determining an attenuation coefficient of X-rays by using the registered CAD data so that a difference between a calculated thickness at a measurement point having a known thickness and a design value decreases; and calculating the dimension of the object to be measured by using the attenuation coefficient.

4 . The dimension. measurement method according to claim 1 , wherein the projection images and the CAD data are registered by:
determining barycentric positions of the object to be measured in the respective projection images; calculating a three-dimensional barycentric position of the object to be measured by using the determined barycentric positions of the object to be measured in the respective projection images; determining a barycentric position of the object to be measured on the CAD data; making the barycentric positions of the object to be measured determined from the respective projection images coincide with the barycentric position of the object to be measured on the CAD data; and rotating the CAD data so that orientation of the object to be measured in one of the projection images matches that of the object to be measured on the CAD data.

5 . The dimension measurement method according to claim 4 , wherein the barycentric position of the object to be measured on the CAD data is determined by assuming, for all mesh triangles, a set of triangular pyramids with a given point as apexes and the respective triangles as bases, and taking a weighted average of volumes and barycenters of the respective triangular pyramids.

6 . The dimension measurement method according to claim 4 , wherein the barycentric position of the object to be measured on the CAD data is determined by using a solid model 3D-CAD software.

7 . The dimension measurement method according to claim 4 , wherein orientation alignment rotation of the CAD data is performed by determining orientation about axes of the projection. image by comparing moment of inertial while rotating the CAD data about the axes.

8 . The dimension measurement method according to claim 7 , wherein the axes are a horizontal axis and a vertical axis.

9 . The dimension measurement method according to claim 4 , wherein orientation alignment by rotation of the CAD data is performed by rotating the CAD data so that contours coincide.

10 . The dimension measurement method according to claim 9 , wherein the coincidence of the contours is determined from R=Sa/Sb of a ratio R of an overlapping area Sa to an entire area Sb.

11 . The dimension measurement method according to claim 4 , wherein
orientation alignment by rotation of the CAD data is performed by: initially determining orientation about horizontal and vertical axes of the projection image by comparing moment of inertial while rotating the CAD data about the horizontal and vertical axes, and then rotating the CAD data within a plane of the projection image so that contours coincide.

12 . The dimension measurement method according to claim 11 , wherein the coincidence of the contours is determined from R=Sa/Sb of a ratio R of an overlapping area Sa to an entire area Sb.

Assignees

• Univ Tokyo
• Mitutoyo Corp

Inventors

• Ohtake Yutaka
• Ito Tasuku
• Goto Tomonori
• Kon Masato

Classifications

• G01B15/045 Primary

  by measuring absorption · CPC title

• G01N23/046

  using tomography, e.g. computed tomography [CT] · CPC title

• G01B15/00 Primary

  Measuring arrangements characterised by the use of electromagnetic waves or particle radiation, e.g. by the use of microwaves, X-rays, gamma rays or electrons (characterised by the use of optical techniques G01B9/00, G01B11/00) · CPC title

• G01N2223/401

  image processing · CPC title

• G01B15/02 Primary

  for measuring thickness · CPC title