Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
1999-05-28
2001-11-27
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S235000, C250S216000
Reexamination Certificate
active
06323503
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to optical scanning systems. More particularly, this invention relates to a system and method capable of imaging targets in the presence of specular reflection.
2. Description of Related Art
Coded symbologies are being used in an increasingly diverse array of applications. The ability to track a large amount of items quickly and efficiently has led coded symbologies to be used in applications such as retail checkout, warehousing, inventory control and document tracking. As the volume of items tracked by coded symbologies has increased, the need for optical scanners which operate at high speeds has likewise increased.
Various optical scanning systems have been developed for reading and decoding coded symbologies. Scanning systems include optical laser scanners and optical charge-coupled device (CCD) scanners. Optical laser scanners generally employ a laser diode, a multifaceted polygonal mirror, focusing optics and a detector. The scanning rate of an optical laser scanner is limited by the number of facets on the mirror and the available motor speed.
CCD scanners may incorporate a non-laser light source and a CCD light detecting means, such as a CCD linear sensor. A portion of the light which is reflected from the coded symbology is detected by the CCD linear sensor and converted into an electrical signal which is the basis for a digital image of the coded symbology that has been scanned. The digital image is then processed and decoded according to the specific type of coded symbology.
One disadvantage with current CCD scanners is that they are susceptible to specular reflection which saturates areas of the CCD linear sensor and prohibits the detection of a portion of the optically coded information. This is particularly a problem when the coded symbology is printed under a highly reflective surface, such as a plastic coating.
Specular reflection is only a problem at a single angle, known as the “critical angle”, between the light source, the reflective surface and the CCD linear sensor. Current methods of coping with specular reflection include placing separate scanners at different angles with respect to the surface. However, providing duplicate CCD scanners for this purpose is extremely expensive. Techniques involving light polarizers have also been used. However, due to the light losses introduced by the materials used to make light polarizers, they are extremely inefficient.
Accordingly, there exists a need for an efficient and inexpensive scanning system with the speed of a CCD scanner that can accurately read and decode coded symbologies in the presence of specular reflection.
SUMMARY OF THE INVENTION
The present invention utilizes two CCD linear sensors and a bandpass means to improve the ability of an optical scanner to discriminate against specular reflection. A coded symbology is illuminated by a noncoherent light source and light reflected from the coded symbology travels along a first path and strikes the front face of the bandpass means. The bandpass means, functioning as a notch filter, transmits a select bandwidth of light while reflecting all other light onto a first CCD linear sensor. Simultaneously, light reflected from the bar code symbol travels along a second path, at a different angle with respect to the plane of the coded symbology than the first path, and is reflected from a mirror onto the back face of the bandpass means. The bandpass means transmits the select bandwidth of light onto a second CCD linear sensor and reflects all other light. The CCD linear sensors each have a notch filter which permits the detection of only a select bandwidth. Since specular reflection is only experienced at a single angle with respect to the plane of the coded symbology, and each CCD linear sensor detects an image at a different angle with respect to the plane of the coded symbology; a complete image of the coded symbology is obtained by one or both of the CCD linear sensors, or can be reconstructed by combining information obtained from both CCD linear sensors.
Accordingly, it is an object of the invention to provide a CCD scanner which can read and decode coded symbologies in the presence of specular reflection.
Other objects and advantages will become apparent to those skilled in the art after reading the detailed description of a presently preferred embodiment.
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Accu-Sort Systems, Inc.
Le Que T.
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