10. Hardware for rapid scanning
Rapid-scanning systems for discussion only. The Manuscript Digitization Demonstration Project included an investigation of hardware and software, with a special attempt to identify options for rapid throughput scanning of manuscript documents. The small scale of the Phase II testbed scanning activity and the high cost of many automated devices precluded the actual use of a rapid-throughput scanner in this project and thus the description of this option must be treated as provisional and preliminary. Readers should note that the survey of scanner manufacturers--which covers both non-automated and automated scanners--is covered in Appendices G, H, and I.
An analytic overview of scanner technology is provided in Appendix B, which reproduces a set of overhead slides used in presentations to the committee and to the staff of the Library's National Digital Library Program by Picture Elements. This presentation discussed the component parts of scanners and why particular types of scanners are suited to different collections. The discussion was broad-ranging and covered not only scanners for manuscripts, but also touched on equipment for brittle books, microfilm, photographs, maps, and card catalogs.
The greatest risk to paper in a high speed or automated scanner comes from the mechanical system for handling the sheets. This mechanical system includes a paper feeder, paper transport, and stacker.
Paper feeders. Automatic feeders, because of their need to perform the "de-doubling" operation and because of their tendency to turn documents around corners with high curvatures (usually to preserve stacking order or to flip for imaging the back side) are notoriously injurious to brittle documents. An alternative is for a person to hand place the pages onto a paper transport, thus avoiding all the autofeed problems. This process may introduce skew but, with sophisticated systems, skew can be detected and corrected in the early grayscale processing of the image (using bi-linear interpolation), prior to the binarization stage--without the introduction of any jaggedness.
Paper transport. The most gentle class of transport mechanisms are those that use vacuum belt transports and move documents in a straight path. As of 1995, BancTec, Photomatrix, Electrocom Automation and Image Trak produced scanners with straight-path vacuum-belt design. By using two digital cameras, no flipping of the document is required as would occur when an autofeeder is attached to a flatbed scanner. Members of the Document Digitization Evaluation Committee viewed and tested documents on both the BancTec and Photomatrix scanners and were impressed by their gentle handling.
Paper stacker. The stacker is typically a simple box with appropriate angles, padding, and static-reduction techniques to allow safe accumulation of the pages. The one drawback of the straight paper path is that the stacker ends up containing the book or manuscript in inverted page order. Most of the scanners described in the survey have an "inverter" option, which corrects the stacking order by flipping the document before placing it on the stack. This is not desirable for brittle sheets and nullifies the advantages of the otherwise straight paper path. This inverted stacking order can be fixed by an operator during a subsequent QA step on the original, while checking the original for lost, damaged, or out of order pages. Alternatively, the operator could "deal from the bottom of the deck" when placing the document pages onto the transport. As is indicated in the preceding description, the consultants and committee agreed that straight-path, vacuum-belt scanners showed great promise for handling brittle or delicate materials without damage. The document is held to the moving belt by a vacuum applied through small holes beneath the belt, thus holding the sheet on the belt. No rollers are used in this design and the paper follows a straight-line path. An example of such a transport is illustrated in Figure 10.1.
Figure 10.1. Vacuum belt transport having straight paper path. DocuScan DS-4500 Scanner Transport (Side View). Copyright 1995, BancTec. Used with permission.
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