US 5,675,416 AGranted

Apparatus and method for detecting and sorting plastic articles having a preferred axis of birefringence

AssigneeSRC Vision, Inc.

InventorsDuncan B. Campbell, Carl D. Christy, H. Parks Squyres, Steven D. Lancaster

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Abstract

A sorting system (10) propels a stream of randomly arranged PET and PVC articles (12, 14) through an inspection zone (20) including a first light polarizer/analyzer combination (24, 26), an article-detecting gap (G), and a second light polarizer/analyzer combination (28, 30). The first and second polarizer/analyzer combinations are oriented to extinguish normally incident light in the absence of articles in the inspection zone and are offset 45 degrees relative to each other such that at least one polarizer/analyzer combination detects a principal axis of birefringence of PET articles. The gap is employed to detect the presence of an article in the inspection zone. A video camera (22) includes first, second, and third CCD arrays (58, 60, 62) positioned to receive respective light rays (48, 64, 50) from the first light polarizer/analyzer combination, the gap, and the second light polarizer/analyzer combination and to generate first, second, and third video signals representative of the light each receives. A video signal processor (68) processes the second video signal to identify the presence of multiple articles in the inspection zone, processes the first and third video signals to determine whether each of the multiple articles is made from PET, and selectively activates air ejectors (70) to separate the PET articles from the other articles.

Claims43

Dependent claims

An apparatus for detecting an article having a principal axis of birefringence, comprising:

a light source positioned to emit first and second light rays that propagate through respective first and second portions of an inspection zone having a length;
a first light polarizer spaced apart from a first light analyzer to form between them the first portion of the inspection zone, the first light ray striking the first light polarizer and exiting the first light analyzer, the first light polarizer having a first polarization axis and the first light analyzer having a first analyzer axis, the first polarization and analyzer axes oriented to cause the first light ray to exit the first light analyzer at a predetermined intensity;
a second light polarizer spaced apart from a second light analyzer to form between them the second portion of the inspection zone, the second light ray striking the second light polarizer and exiting the second light analyzer, the second light polarizer having a second polarization axis and the second light analyzer having a second analyzer axis, the second polarization and analyzer axes oriented to cause the second light ray to exit the second light analyzer at a second predetermined intensity, the second polarization axis being angularly offset relative to the first polarization axis;
a conveyor causing the article to move at a predetermined speed and in a substantially constant arbitrary orientation along the length of the inspection zone such that the principal axis of birefringence of the article has an orientation that causes a change in intensity of at least one of the first light ray intersecting the article and exiting the first light analyzer and the second light ray intersecting the article and exiting the second light analyzer;
and
first and second light detectors positioned to detect, respectively, changes in intensity of the first and second light rays from their respective first and second predetermined intensities, a change in intensity of at least one of the first and second light rays indicating that the article has a principal axis of birefringence.

3 more elements

A method for detecting an article having a principal axis of birefringence, comprising:

propagating light rays through an inspection zone;
spacing apart a first light polarizer and a first light analyzer to form a first portion of the inspection zone therebetween, the first light polarizer having a first polarization axis and the first light analyzer having a first analyzer axis, the first polarization and analyzer axes oriented to transmit an intensity of a first light ray entering the first light polarizer, propagating through the first portion of the inspection zone, and exiting the first light analyzer;
spacing apart a second light polarizer and a second light analyzer to form a second portion of the inspection zone therebetween, the second light polarizer having a second polarization axis and the second light analyzer having a second analyzer axis, the second polarization and analyzer axes oriented to transmit an intensity of a second light ray entering the second light polarizer, propagating through the second portion of the inspection zone, and exiting the second light analyzer;
offsetting angularly the second polarization axis relative to the first polarization axis;
conveying the article at a predetermined velocity and in a substantially constant arbitrary orientation along a length of the inspection zone such that the principal axis of birefringence of the article has an orientation that causes a changed intensity of at least one of the first light ray intersecting the article and exiting the first light analyzer and the second light ray intersecting the article and exiting the second light analyzer;
and
detecting the changed intensity of at least one of the first light ray exiting the first light analyzer and the second light ray exiting the second light analyzer.

4 more elements

Dependencies are inferred from the claim text.