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.
16-MM SOUND-FILM PROJECTION 373
be maintained as long as possible if undue strain is to be avoided.
It is therefore necessary to employ an intermittent mechanism capable of moving the film forward during 60° of the cycle when silent films are projected and, when sound films are projected, to employ a mechanism which only completes this movement after rotating through approximately 90° of the complete cycle. The mechanism shown at 'E', Figure 160, consists of a main lever 'F', connected to an eccentrically rotating pin 'G' and constrained by a second lever *H\ Lever 'H' is connected by a pin joint to the main claw lever 'F' and, at its other extremity, by an eccentrically rotating pin * J' to a wheel rotating at twice the speed at which wheel 'K' rotates. By this combination of finks and eccentric pins the path shown at *L' will be traced out by the claw tips, the 'pulldown' will be accomplished within 60° of the complete cycle and over that portion of the path shown to the left of the vertical dotted line. This mechanism is, therefore, one of many which is suitable for use in silent projectors and in conjunction with the shutter shown at 'C, Figure 160.
If links are replaced by one solid plate, which is then driven by suitable cams instead of eccentric pins, a mechanism as shown at 'M', Figure 160, will be produced. This arrangement may be used in conjunction with shutter 'D' to satisfy the requirements met with in sound projection. In the design shown in the figure, the location of the main claw lever 'N' is controlled by two cams one to move the claw into and away from the film whilst the other causes vertical motion to move the film forward. The shaft which supports the rear cam T' is extended to pass through a horizontal slot cut in a cover plate *Q\ Lever 'N' is therefore variably pivoted about the extended shaft so that it may move towards or away from the film gate and also rotate about this shaft. Cam 'R' rotates within a housing so that contact is only made between the cam and the upper and lower horizontal walls of this housing cam 'R' is therefore only capable of imparting a vertical motion to the claw lever. The combination of these movements causes the claw pin to trace out the path shown to the left of the figure so that the vertical movement, to the left of the dotted line, will be substantially straight and will take place over one-quarter of the complete cycle of operations.
Some projectors may be operated either at the silent speed of 16-frames per second or the sound speed of 24-frames per second. Unless provision is made to interchange certain sections of the mechanism when operating at the different film speeds it is not