Radiant energy – Photocells; circuits and apparatus – With circuit for evaluating a web – strand – strip – or sheet
Reexamination Certificate
1992-12-03
2001-06-26
Allen, Stephone B. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
With circuit for evaluating a web, strand, strip, or sheet
C356S239100
Reexamination Certificate
active
06252242
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to optical apparatus and methods, and relates, more specifically, to an optical inspection apparatus and method for detecting faults in flat, polished transparent and reflective media, which inspects with high resolution at high speed with automatic handling of the media to allow the apparatus to be used effectively in a production inspection environment. The apparatus of the present invention is well-suited to the inspection of transparent and reflective disks used as platters for hard disk drives, and to the inspection of transparent flat panels such as those commonly used in Liquid Crystal Display (LCD) panels.
DESCRIPTION OF THE PRIOR ART
Disks for hard disk drives require a surface that is flat to a high degree of accuracy, and that is free from defects such as scratches and chips. Likewise, flat panels also have requirements for flatness and absence of defects. Some optical inspection systems have been used with limited success in inspecting media such as disks and flat panels, but do not provide the accuracy or speed that is needed in a production environment.
Dark field microscopes and scatterometers are inspection apparatus well-known in the art. A dark field microscope can somewhat accurately locate surface defects, but takes too long to inspect to be effectively used in a production environment. A scatterometer is faster than a dark field microscope, but has less accuracy (detects fewer defects). Both the dark field microscope and the scatterometer have low detection sensitivity to shallow defects or defects that have a depth less than the wavelength of the light used, which cause a phase shift in the light beam but do not diffuse (scatter) the light in different directions. An interferometer, which is well-known in the art, is suitable to detecting phase shifts, but takes substantial time and effort to set up, limiting its use to laboratory environments.
The inherent limitations of the prior art inspection systems have limited their use in industrial production environments. Indeed, the most common inspection method used in a production environment is a manual, visual inspection by human inspectors, which hold the disk or flat panel in their hands and move it in ambient or special light looking for the presence of scratches, chips and other defects. This inspection method is labor intensive, relatively slow, and subject to human errors such as missed defects which the human eye cannot easily distinguish.
Therefore, there existed a need to provide a high speed optical inspection system and method which has a high sensitivity to defects which can be used to inspect both transparent and reflective media in a production environment. This inspection system includes automatic handling of the media, high speed inspection, and high resolution to detect defects smaller that the spot size of the beam and/or more shallow that the wavelength of light used. The increased speed of this apparatus increases throughput of the production system, and assures that any mistakes or defects introduced by human inspectors is eliminated.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a high-speed optical inspection apparatus and method suitable for production testing of transparent disks.
It is another object of this invention to provide a high speed optical inspection apparatus and method suitable for production testing of reflective disks.
It is a further object of this invention to provide a high speed optical inspection apparatus and method suitable for production testing of transparent flat panels.
It is a still further object of this invention to provide a high speed optical inspection apparatus and method which is computer-controlled using an IBM PC-AT computer or equivalent.
It is still another object of this invention to provide a high speed optical inspection apparatus and method with surface inspection which has a high speed optical scanner to provide linear movement of the beam across the width of the media, and a media actuator to position each portion of the media in the path of the linear movement of the beam, thereby completely inspecting the entire face surface of the media.
It is yet another object of this invention to provide a high speed optical inspection apparatus and method with edge inspection (if required) using a light source and linear Charge-Coupled Device (CCD) cameras which scan the edge of the media as it is moved as needed during surface inspection.
It is still another object of this invention to provide a high speed optical inspection apparatus and method which has an automatic media handler for automatically loading the media into the apparatus and for automatically unloading the media from the apparatus.
It is a still further object of this invention to provide a high speed optical inspection apparatus and method which detects both phase and amplitude changes of the light beam using multiple detectors to sense changes in the nominal Gaussian distribution of the light beam.
It is yet another object of this invention to provide a high speed optical inspection apparatus and method which has a trigger detector within the path of the scanning light beam to provide a signal to synchronize the controlling computer to the scan of the light beam.
According to the present invention, an optical inspection apparatus is provided. This inspection apparatus is controlled by an IBM PC-AT computer or equivalent, and has a typical color monitor, printer and keyboard. An Optical Inspection Assembly is provided which comprises a Surface Inspection Assembly and an Edge Inspection Assembly (if required). The Surface Inspection Assembly nominally comprises a laser light source which transmits a light beam, a high-speed Optical Scanner, Scanning Optics, Detection Optics, and a Parallel Detector Array within a Detector. The computer controls the automatic loading and unloading of the media by sending appropriate control signals to the Automatic Media Handler. The computer also controls the movement of the media across the linear scan of the Optical Scanner within the Surface Inspection Assembly to assure the entire surface of the media is inspected. While the media is being moved, both the Surface Inspection Assembly and the Edge Inspection Assembly (if present) simultaneously perform their respective inspections. Surface defects are detected by changes in the nominal light level or in the two-dimensional Gaussian distribution of the detected light beam as explained in more detail below. Edge defects are detected using cameras to monitor the illuminated edges of the media. Any defect detected that exceeds a programmable threshold is reported to the computer, causing the inspection to fail.
The Optical Scanner causes a linear scan of the light beam across one axis of the media. After contact with the media the light beam goes to a Parallel Detector Array. This array is typically a matrix of photodiodes or Charge-Coupled Devices (CCDs) upon which the light beam is projected. This matrix configuration provides a two dimensional Gaussian response with respect to light intensity (amplitude). Any defect in the media deflects light from the Parallel Detector Array (causing a change in the nominal light level) or shifts its phase (causing a change in the Gaussian distribution), both of which are detected by the processing electronics coupled to the Parallel Detector Array. Thus the processing electronics simply look for changes in the nominal level or distribution of the Gaussian response provided by the Parallel Detector Array in response to a nominal light beam. Any defect that exceeds a programmable threshold value is reported to the computer, which causes the inspection to fail. Note that the Automatic Media Handler sorts the tested media according to the pass or fail results of the inspection.
In the first embodiment of the present invention, the inspection system is used to inspect transparent disks. In this configuration the light beam in the Surface Inspection Assembly originates in the laser, is tran
Brunfeld Andrei
Laver Ilan
Pekel Ely
Shamir Joseph
Singher Liviu
Allen Stephone B.
Brown & Sharpe Surface Inspection Systems, Inc.
Wolf Greenfield & Sacks P.C.
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