Abstract: The present invention encompasses a scanning optical system such as internal drum photoplotters that has a raster scanner for advancing a circularly polarized optical beam across a substrate surface in a first direction to form a scan line and for advancing the optical beam in a second direction substantially perpendicular to the first direction. There is a curved platen for receiving a substrate and an apparatus for switching the optical beam polarization between first and second directions in response to polarization control signals;. An encoder generates signals indicative of the position of the optical beam along a current scan line. There is a controller that receives the encoder signals and generates the advancement signals and the modulator control signals. The controller further provides the optical beam polarization switching signals in dependence on the encoder signals such that the optical beam polarization is switched after the completion of the current scan line.

Abstract: A photoplotting apparatus is provided. The apparatus comprises an internal drum plotter and a media sheet handling apparatus for sequentially delivering a photosensitive media sheet to the photoplotter for exposure from a stack of such sheets. The photoplotter has reduced turbulence within the drum during exposure of the media sheet, and the sheet handling apparatus includes means for separating the sheets in the stack from interleaves disposed between adjacent sheets in the stack.

Abstract: An apparatus includes a media handler which is capable of processing a supply of media sheets which can take the form of plates, aluminum or plastic used in lithographic printing presses or the like, or can be film which is advanced to a drum and scanned by a scanning process and thereafter removed from the drum surface by appropriate handling means.

Abstract: An optical beam generator system for use in an imaging system that forms an image in a substrate comprises a beam generator, a mode filter and a state selector. The optical beam has a first power level above an exposure level that exposes the image in the substrate and a second power level below the exposure level which does not expose the substrate. The beam generator generates a near single mode coherent optical beam in response to received command signals corresponding to an "on" state and generates a multimode incoherent optical beam in response to received command signals corresponding to an "off" state. The filter is optically coupled to the beam generator and attenuates an optical component of the received optical beam which is not single mode to a magnitude below the exposure level.

Abstract: An apparatus includes a media handler which is capable of processing a supply of media sheets which can take the form of plates, aluminum or plastic used in lithographic printing presses or the like, or can be film which is advanced to a drum and scanned by a scanning process and thereafter removed from the drum surface by appropriate handling means.

Abstract: A method and apparatus used with a printed circuit board (PCB) defect detection system generates a reference database image of the PCB having tolerances for each individual PCB feature, The invention is characterized by a tolerance database of at least three states in which each color is weighted and adjacent pixels are grouped into arrays or "bins". An error signal is generated when the sum of the pixel weights in a bin exceeds a preselected threshold.

Abstract: A method and apparatus used with a printed circuit board (PCB) defect detection system generates a reference database image of the PCB having tolerances for each individual PCB feature wherein a tolerance database of at least three states in which each color is weighted and adjacent pixels are grouped into arrays or "bins". An error signal is generated when the sum of the pixel weights in a bin exceeds a preselected threshold.

Abstract: A method and apparatus for compensating substrate distortion in automatic optical inspection (AOI) systems eliminates false error signals during printed circuit boards (PCB) defect detection. The present invention is used in feature edge transition AOI systems that employ pixel to pixel comparison between CAD and scanned PCB feature databases. The present invention divides the substrate into a plurality of regions or "tiles". A distortion vector for each tile is calculated and is used to generate a shift of pixels within each tile which removes any variation between the preferred pixel location and the actual pixel location, thereby enabling the AOI system to avoid generating error signals when features are only misplaced on the substrate.

Abstract: An apparatus for use in improving the accuracy of optical systems such as internal drum photoplotters includes a raster scanner responsive to control signals for advancing relative to a substrate an optical beam across a substrate surface in a first direction forming a scan line and for cooperatively advancing relative to the substrate the optical beam in a second direction substantially perpendicular to the first direction. A signal generator provides a clock signal configured to control the advancement of the optical beam in a first direction. There is a memory for storing error signals indicative of deviations of the curved surface from a preferred value of curvature. The apparatus is characterized by a controller for generating control signals in dependence on the error signals such that the phase of the clock signal is adjusted, thereby removing the curvature error for a segment of the scan line.

Abstract: An image buffer for use with laser imagers is configured to receive image signals from a raster image processor (RIP). The image buffer comprises a two by two data switch and two memories for storing image data signals as generated by the RIP. The stored image data signals are presented to the laser imager in accordance with command signals provided by an image buffer controller. The image buffer controller utilizes a video interface that includes a SCSI controller and line buffer to reformat the stored image data signals before presentation to the laser imager, thereby allowing for independent operation of the RIP and laser imager.

Abstract: A method and apparatus used with a printed circuit board (PCB) defect detection system generates a reference data base image of the PCB having tolerances for each individual PCB feature. The invention includes a transitional data base having three states, black, white and gray corresponding to areas where the PCB features respectively must appear, must not appear and may or may not appear.

Abstract: A novel laser raster scanner that scans, in response to control signals from a controller, an exposure beam across a substrate by means of a rotating polygonal mirror having a plurality of reflective facets provides passive facet tracking by means of a plurality of glass windows configured with the polygonal mirror to cooperate with corresponding ones of the reflective facets. A first beam steering mechanism provides the laser beam to a window at a first surface thereof. A second beam steering mechanism receives the laser beam from an opposed second window surface and provides an illumination beam to the corresponding reflective facet. Each window is positioned to displace the laser beam from the incident axis so as to produce a corresponding displacement of the illumination beam on the facet in the direction of mirror rotation.

Abstract: A method and apparatus that provides skip line asynchronous imaging is characterized by a controller that computes pixel signals in a sequence of arrays and stores those arrays in a buffer. A controller will adjust the rate advancement of the write platen and synchronize therewith the presentation of a signal array to a mirror facet should the controller determine that the next line of data is not ready for imaging.

Abstract: A novel method and apparatus for determining the accuracy of artwork produced from a laser direct imaging system employs a calibration substrate which has images of opposed, perpendicular scales and registration marks thereon. The overall system dimensional error is determined directly from substrate measurements, as is the magnitude of the mechanical and processing errors.

Abstract: A novel apparatus for use in generating a scan timing signal in a laser raster scanner includes an optical diffuser positioned to receive a scanned reference beam through a reference mask. The diffused, modulated reference beam is presented to an array of photodetectors. The number of photodetectors in the array is selected to be sufficient so that at least two photodetectors receive the diffused modulated reference beam simultaneously as the reference beam is scanned along the reference mask.

Abstract: A novel method and apparatus for improving the overall accuracy and repeatability of an optical photoplotter which is characterized by a controller which determines an image position error from interferometric feedback signals and position command signals and subsequently provides displacement of the image in dependence thereon.