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408
NEW MOTION PICTURE APPARATUS [J. S. M. P. E.
I6mm Film
35mm Rim
differences between positive and negative and variations in negative shrinkage make it impossible to connect the positive and negative film drums rigidly. Printers embodying various devices to reconcile these requirements have been described in the literature from time to time.2'3-4
In the present printer, synchronism is achieved by mounting the sprockets in pairs, a 16-mm. and a 35-mm. sprocket to a pair, each pair on a common shaft. Each sprocket shaft is driven from the flywheel through helical gears. Slippage of the film over the root of the sprocket teeth is prevented by the two-piece construction of the sprockets (Fig. 3) . The film is supported by a cylinder slightly larger than the root-circle of the sprocket and free to rotate upon needle bearings on the sprocket itself, so that the film clears the root circle by approximately 1
mil. This construction enables the film to move over the sprocket, as it
G A /\| [Tj must to accommodate for shrinkage,
yj without sliding contact, thus prevent
ing scratches. In addition, supporting the film over its entire width reduces the strain on the edges of the film and prevents negative breakage.
A massive flywheel and an oil drag drive are employed to insure exact uniformity of motion of the film by a combination of "brute force" and viscous filtering. The large mass of the flywheel makes it impracticable to drive the flywheel by the film. Instead, the driving motor drives the flywheel through the worm and gear shown in Fig. 4. Worm gear A is free to rotate upon the flywheel shaft which it drives through filter springs B. The natural period of oscillation of this assembly is sufficiently low effectively to prevent transmission of any possible motor or gear-tooth disturbances to the flywheel. Each printing drum is independently coupled to the flywheel by oil friction. This coupling consists of an interleaved set of thin plates, alternately connected to flywheel and film drum, and immersed in heavy oil. This coupling permits slow relative motion between the positive and negative films to accommodate for negative shrinkage. There will be a constant uniform relative motion between the two drums in direct proportion to the deviation of the actual negative shrinkage from the shrinkage for which the drums are designed. While permitting this necessary slow relative movement, the viscous coupling completely eliminates any flutter or wow from sprocket teeth, splices, or film imperfections by offering very high resistance to sudden movements. The area of contact and the film tension are sufficient effectively to prevent slipping of either film over its drum.
Tension is maintained by spring-loaded idler rollers between the sprockets and
FIG. 5.