GB506654A - Improvements in feeding apparatus for sound films and strip sound records - Google Patents

Abstract

506,654. Sound-film speed controlling devices. KOLB, O. K. (Beer, P. F.) Dec. 1, 1937, No. 33214. [Class 40 (ii)] [Also in Group XXXV] Relates to devices for controlling the speed of a film or like sound record, which is fed over a flywheel roller at or near the soundreproduction point, and consists in driving the roller by a synchronous motor supplied with current from an A.C. generator, the frequency of which is controlled by means dependent upon variations in the speed of the film. In the arrangement shown in Fig. 1, the film is driven by sprocket wheels geared to a driving motor (not shown), over a flywheel roller V, which is directly coupled to a synchronous motor M. The motor is driven by current from an oscillation generator G, the frequency of which is determined by the constants of an oscillation circuit K, and is normally such that the motor M drives the flywheel at a speed at which the peripheral velocity of the roller V corresponds exactly to the mean velocity of the film. Rollers R, R<2>, coupled by a spring, bear upon bights in the film, the roller R being connected through a spring F to a slider arm A which controls the resistance r in the circuit K. A dashpot or the like B damps the motion of the roller R. If the speed of the driving motor is suddenly reduced, the lower film bight is shortened, and the spring F is compressed. No action on the arm A takes place if the speed variation is momentary, but if it is of long duration (due, for example, to shrinkage of the film), the arm A is moved downwards, reducing the effective resistance r, and consequently the motor M runs more slowly. In a modification, Fig. 2 (not shown), rollers which engage bights in the film on opposite sides of the roller V are mounted on an arm pivoted on the axis of the roller, which arm is connected at its outer end through a spring to the slider arm of the controlling resistance. In order to facilitate synchronism between the generator and the motor M when the film is started, it is preferable that reaction should take place, in such a manner that whilst the motor is running at a slower speed than that corresponding to the frequency of the generator the current supplied to the motor will retard the frequency of the generator. For this purpose, the said reaction may be provided by inserting the stator of the motor in the generator circuit in such manner that the self-induction of the stator influences the frequency of the generator. Two such arrangements are shown in Figs. 3 and 4, in each of which S is the stator of the motor, and G is a valve generator. A further arrangement is described, Fig. 5 (not shown), in which the generator is an ordinary buzzer, the frequency of which is mainly determined by the natural frequency of the contactspring. Specification 249,627, [Class 40 (ii)], is referred to.