We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.
Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.
Jan., 1945 AIRPLANE VIBRATION REPRODUCER 55
merit is designed in 3 major units : the reproducer assembly which contains all of the elements for film pulling and scanning, an amplifier cabinet containing 14 amplifiers, and a relay rack containing regulated power units to supply the reproducer and amplifiers.
As shown by Fig. 1, the reproducer consists of a cast housing containing the film moving parts. Considering the requirements for film movement and scanning, it was determined that a constant speed sprocket pulling the film across a fixed, curved gate would meet these requirements, provided that the film tension is held very constant. The latter is accomplished by passing the film over a roller located just above the gate, the film being held in contact with the roller by means of a second pressure roller. To this roller is attached an eddy current drag disk of copper, approximately 6 in. in diameter and rotating in a space between 2 sets of permanent magnets. The relative positions of these magnets may be altered in order to change the total magnetic flux and thereby the film tension. A 2-position control is provided with this assembly so that the flux may be altered to give the same effective film tension at either 6 in. or 12 in. per sec, since the drag is proportional to speed for a given flux.
The curved gate is constructed of hardened steel, highly polished on the film contacting surfaces. The abrasive action of the film base serves to maintain a high polish. The contacting surface is relieved over most of the central area and supports the film only in 4 small areas between the sprocket holes where abrasion of the film base will not be in areas useful for scanning. The film is also supported at the edges, permitting a slot to be cut across the gate at its center between the sprocket holes to pass light for scanning.
Film guiding is accomplished by adjustable flanges on the eddy current drag roller. The bearing design is such that end play in the roller shaft may be virtually eliminated. A small roller arm assembly presses the outer race of a ball bearing lightly against the edge of the film at the scanning point, but exerts sufficient pressure to cause the film to run against one guide flange. This minimizes weave even though the film is narrower than standard owing to shrinkage. Feed and holdback sprockets are provided so that there will be free loops of film into the drag roller and out of the sound sprocket. These sprockets are driven by a silent chain which also drives the take-up. The main case contains an opening with guide rollers for passing the film in and out of the case so that long film loops may be run on suitable loop racks.