Automated radiographic inspection system

• US 4,415,980 A
• Filed: 03/02/1981
• Issued: 11/15/1983
• Est. Priority Date: 03/02/1981
• Status: Expired due to Term

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Space Operations Company (Martin Marietta Corporation)
• Inventors: Buchanan, Robert A.
• Primary Examiner(s): Wise, Edward J.
• Application Number:
  US06/239,611
• Time in Patent Office: 988 Days
• Field of Search: 364/414, 364/515, 364/521, 364/522, 364/525, 364/527, 358/111, 358/166, 378/2, 378/44, 378/51, 378/58, 378/62, 378/98, 250/323, 250/321
• US Class Current: 378/58
• CPC Class Codes: G01N 23/083 the radiation being X-rays
• CPC Class Codes: G01N 23/18 Investigating the presence of flaws defects or foreign matter
• CPC Class Codes: G06T 2207/10116 X-ray image
• CPC Class Codes: G06T 2207/20224 Image subtraction
• CPC Class Codes: G06T 2207/30164 Workpiece; Machine component
• CPC Class Codes: G06T 7/001 using an image reference approach

Abstract

In an automated real-time radiographic inspection system for detecting flaws, defects or inhomogeneities in manufactured objects, the objects (10, 11, 12, . . . ) to be tested are moved on a conveyor (20) in succession past an X-ray source (30). Penetrating X-ray radiation is transmitted through the objects (10, 11, 12, . . . ) to cause an image to be formed for each object in succession by an electronic imaging system (40). The imaging system (40) generates digital signals representative of the image for each object, and transmits the digital signals to a data processor/comparator (50). One of the objects (10, 11, 12, . . . ) may be considered as a reference object against which the other objects are compared for structural homogeneity. Thus, the electronic images of the objects (11, 12, . . . ) could be compared with the electronic image of, for example, the object (10). Alternatively, the electronic images of the test objects could be compared with an electronic reference image programmed into the data processor/comparator (50), the programmed reference image. The comparison performed by the data processor/comparator (50) is a subtraction process, which eliminates background features common to test and reference images. Thus, any flaw appearing in a test image, but not present in the reference image, stands out in sharp detail. When a flaw occurs in a test image, the subtractive process results in a non-null signal, which activates a conveyor control mechanism (70) for stopping the conveyor (20) so as to enable rejection of the flawed test object.

Claims

1. A method of determining structural conformity of a test object to a reference object for quality control of manufactured objects, said method comprising the steps of:

(a) transmitting X-ray radiation through said reference object to phosphor means for generating an optical signal, which is converted to an electronic image of said reference object;

(b) transmitting x-ray radiation through said test object to phosphor means for generating an optical signal, which is converted to an electronic image of said test object; and

(c) subtracting one of the aforesaid electronic images from the other to produce a subtractive image in which any significant structural difference between said test object and said reference object appears in sharp detail.

2. The method of claim 1 wherein said electronic images of said reference and test objects are digitized representations of said reference and test objects, and wherein the subtracting of one of said electronic images from the other is performed by computer means.

3. The method of claim 2 wherein the electronic image of said reference object is stored in a memory device, and the electronic image of said test object is compared with said image of said reference object by a process wherein one said images is subtracted from the other.

4. The method of claim 1 wherein a separate electronic image is formed of each one of a plurality of test objects, and wherein a control signal is generated whenever any significant difference appears between a particular one of the test objects and said reference object, said control signal activating means for rejecting said particular one of said test objects as not being in structural conformity with said reference object.

5. A method of detecting a substantial inhomogeneity in a test object, said method comprising the sequential steps of:

(a) forming a first image of said test object by causing penetrating electromagnetic radiation from a radiation source to pass through said test object and impinge upon a detector;

(b) causing displacement of one relative to another of said radiation source, test object and detector;

(c) forming a second image of said test object by causing penetrating electromagnetic radiation from said radiation source to pass through said test object and impinge upon said detector; and

(d) subtracting one of said first and second images from the other to produce a subtractive mage in which any substantial inhomogeneity in said test object appears.

6. The method of claim 5 wherein a control signal is generated whenever any inhomogeneity in said test object appears in said subtractive image, said control signal activating means for rejecting said test object.

7. The method of claim 5 wherein said test object is moved relative to said radiation source and detector after said first image has been formed.

8. The method of claim 7 wherein said first and second images are formed by causing X-ray radiation that has passed through said test object to impinge upon phosphor means for generating corresponding first and second optical signals, and by converting said optical signals to digital electronic signals constituting said first and second images.

9. The method of claim 8 wherein digital signal constituting said first image are stored in a memory device, and digital signals constituting said second image are compared with said digital signals constituting said first image by a process wherein one of said first and second images is subtracted from the other by computer means.

10. A system for determining structural conformity of a test object to a reference object for quality control of manufactured objects, said system comprising:

(a) means for transmitting X-ray radiation through said reference object to phosphor means for generating an optical signal, which is converted to an electronic image of said reference object;

(b) means for transmitting X-ray radiation through said test object to phosphor means for generating an optical signal, which is converted to an electronic image of said test object; and

(c) means for subtracting one of said electronic images from the other to produce a subtractive image in which any significant structural difference between said test object and said reference object appears in sharp detail.

11. A system for detecting a substantial inhomogeneity in a test object, said system comprising:

(a) means for forming a first image of said test object by causing penetrating electromagnetic radiation from a radiation source to pass through said test object and impinge upon a detector;

(b) means for causing displacement of one relative to another of said radiation source, test object and detector;

(c) means for forming a second image of said test object by causing penetrating electromagnetic radiation from said radiation source to pass through said test object and impinge upon said detector; and

(d) means for subtracting one of said first and second images from the other to produce a subtractive image in which any substantial inhomogeneity in said test object appears.