Radiant energy – Photocells; circuits and apparatus – With circuit for evaluating a web – strand – strip – or sheet
Reexamination Certificate
1992-12-03
2001-07-17
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
06262432
ABSTRACT:
RELATED APPLICATIONS
This patent application is related to three other U.S. patent applications entitled: “High Speed Optical Inspection Apparatus and Method”, “High Speed Optical Inspection Apparatus for a Transparent Disk and Method Therefor”, and “High Speed Optical Inspection Apparatus for a Transparent Flat Panel and Method Therefor” which are assigned to the same assignee as this patent application and which are filed on the same date as the date of this patent application.
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 a flat, polished reflective disk, such as those commonly used as platters for hard disk drives. This apparatus inspects with high resolution at high speed with automatic handling of the disk to allow the apparatus to be used effectively in a production inspection environment.
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. Some optical inspection systems have been used with limited success in inspecting reflective disks, 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 in their hands and move the disk 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 reflective disks in a production environment. This inspection system includes automatic handling of the disks, high speed inspection, and high resolution to detect defects smaller that the spot size of the beam and/or more shallow than 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 reflective disks.
It is another 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 a further object of this invention to provide a high speed optical inspection apparatus and method with surface defect detection which has a high speed optical scanner to provide linear movement of the beam across a radius of the disk, and a disk actuator to rotate the disk, thereby positioning each portion of the disk in the path of the linear movement of the beam, thereby completely inspecting the entire face surface of the disk.
It is still another object of this invention to provide a high speed optical inspection apparatus and method with edge inspection using a light source and linear Charge-Coupled Device (CCD) cameras which scan the edge of the disk as it is rotated during surface inspection.
It is yet another object of this invention to provide a high speed optical inspection apparatus and method which has an Automatic Disk Handler for automatically loading the disks into the apparatus and for automatically unloading the disks 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 preferred embodiment of the present invention, an optical inspection apparatus for inspecting a reflective disk 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. The Surface Inspection Assembly nominally comprises a laser light source which transmits a light beam, a high-speed Optical Scanner, Scanning Optics, a beam splitter, optional Detection Optics, and a Parallel Detector Array within a Detector. In this configuration the light beam in the Surface Inspection Assembly originates in the laser, is transmitted through a filter, and is transmitted to the Optical Scanner, which reflects the light beam off the moving polygonal scanner head, causing the light beam to sweep across the Scanning Optics.
In the preferred embodiment of the present invention, the inspection apparatus is used to inspect both sides of the reflective disk within the same scan. This is accomplished by placing the reflective disk near the center of the scanning beam sweep, with its face normal to the direction of the sweep. Two mirrors are placed at 45 degree angles with respect to the two faces of the disk such that the Optical Scanner beam is reflected onto the two faces. The Scanning Optics and the mirrors focus the Optical Scanner beam on the two faces of the reflective disk. As the Optical Scanner beam begins its scan, the first mirror reflects the beam to the outer edge of the first face of the disk. The reflective face of the disk reflects the beam back to the mirror, which reflects the beam back to the Optical Scanner. This reflected beam is distinguished from the transmitted beam using a beam splitter between the laser and the Optical Scanner. The reflected beam is then projected on the Parallel Detector Array, which detects defects in the disk above a programmable threshold. 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 disk 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, which changes correspond to surface defects an a reflective disk.
As the Optical Scanner beam moves, the beam on the disk moves from outside to inside on this first side of the disk. The first side of the disk is completely scanned when th
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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