Inspection apparatus

• US 4,737,650 A
• Filed: 04/13/1987
• Issued: 04/12/1988
• Est. Priority Date: 09/24/1984
• Status: Expired due to Term

• Current Assignee: Siram SPA (Veolia Environnement SA)
• Original Assignee: Siram SPA (Veolia Environnement SA)
• Inventors: West, Robert N.
• Primary Examiner(s): NOT, DEFINED
• Application Number:
  US07/038,487
• Time in Patent Office: 365 Days
• Field of Search: 250/571, 356/243, 356/431, 356/237, 356/446, 356/445
• US Class Current: 250/559.07
• CPC Class Codes: G01N 21/8901 Optical details; Scanning details per se G02B

Abstract

A beam of radiation is scanned across a sheet 13 and is either reflected therefrom or transmitted therethrough. Faults in the sheet 13 deflect, scatter or alternate the beam which is then passed to a retroreflector screen 24 where it forms an image 15. Analysis of the image 15 is carried out via the scanning means 22 to determine the faults in the sheet 13.

Claims

1. Inspection apparatus for inspecting an object, comprising:

means for forming a narrow beam of radiation for transmission along a first optical path;

a rotatable mirror drum comprising a plurality of facets, said mirror drum being disposed in said first optical path for scanning said beam of radiation across an object under test that is located across said first optical path and is radiation transmissive;

reflective screen means in said first optical path for receiving the beam of radiation after the beam has been transmitted by said object, said beam forming an image on said reflective screen means, said reflective screen means reflecting said image along a second optical path back toward said object and said rotatable mirror drum;

focusing means located on said second optical path for bringing said image into focus after further transmission of said reflected image by said object;

a detector means located on said second optical path for receiving said focused image, the detector means being sensitive to changes in (a) the position in any direction;

(b) the size, and (c) the intensity of the image formed thereon caused by the influence of the object;

the detector means and the reflective screen being at conjugate points with respect to the focusing means; and

means for analyzing the focused image and thereby inspect the object.

2. Apparatus as claimed in claim 1 in which the reflection screen means for receiving the beam of radiation comprises a radiation scattering screen.

3. Apparatus as claimed in claim 2 in which the reflection screen means for receiving the beam of radiation comprises a retro-reflective screen.

4. Apparatus as claimed in claim 3 in which said detector means includes two areas, one of which influences the focused image in a different way to the other, the focused image being passed to one of the areas when the object under test is normal and being deflected to or toward the other area when the focused image is influenced by faults in the object under test.

5. Apparatus as claimed in claim 4 in which one of the two areas has at least one dimension which generally corresponds to the outer dimension of the focused image where it strikes the area so that any deflection of the focused image away from that first area causes the focused image to pass into the second area.

6. Apparatus as claimed in claim 5 in which one of the areas is the same shape as the cross section of the focused image and the other of the areas surrounds the first area.

7. Apparatus as claimed in claim 6 in which one area has a different opacity with respect to the other area so that, if the detector means is arranged behind the two areas, the radiation received by the detector means varies as the focused image is moved from one area to the other by a fault or flaw in the object under test.

8. Apparatus as claimed in claim 7 in which one area has a transmission characteristic whereby it transmits or reflects half the intensity of the focused image striking it, the other area transmitting or reflecting substantially all of the focused image striking it.

9. Apparatus as claimed in claim 8 in which said areas are defined by optical fibres.

10. Inspection apparatus for inspecting an object transparent to radiation, comprising:

a laser for producing radiation along a first optical path;

first lens means in the first optical path for focusing the radiation from the laser and thereby forming a narrow beam;

a beam splitter means on said first optical path, said beam splitter means comprising a mirror on a first surface thereof and having a central aperture through which the beam from the laser passes and emerges from said first surface;

a mirror drum on said first optical path, said mirror drum comprising a plurality of flat mirror facets arranged so as to be rotatable about an axis, said mirror drum forming a scanner which, upon rotation about said axis, scans the beam formed by the first lens means across and through the object under inspection;

means for mounting said object under inspection on said first optical path;

a retro-reflecting sheet being arranged both as to position and extent so as to receive the beam of radiation after it has been transmitted through the object under inspection to form an image on said retro-reflecting sheet; and

to reflect said image in the form of radiation along a second optical path that is substantially coincident with said first optical path;

second lens means for bringing said reflected image into focus, said second lens means receiving radiation in the form of said image along said second optical path and via said mirror drum and via the first surface of said beam splitter means, said beam splitter means causing said second optical path to depart from coincidence with said first optical path;

a target apparatus comprising a plurality of separate portions on said second optical path and adapted to receive the reflection from said beam splitter means;

the target apparatus and the retro-reflecting sheet being at conjugate points with respect to the second lens means;

separate detector means connected to each of said portions of said target apparatus, said separate detector means being arranged in conjunction with each other so as to be sensitive to changes in the position in any direction of the focused image, to the size of said focused image, and to the intensity of said focused image.

11. Inspection apparatus as claimed in claim 10 in which said first and second lens means each comprises multiple element lenses.