Patent GB-760887-A (GB)
Title: Testing device for motion picture film
IPC: G03D15/00
Filed: 1954-10-25
Abstract: 760,887. Kinematograph apparatus. GRUNWALD, R., and WHITE, D. K. Oct. 25, 1954, No. 30671/54. Class 97(1) A film inspecting device comprises a pair of rollers urged together to define a nip through which the film passes, electrical contacts operated in response to the roller movement produced by abnormal film thickness and indicating means actuated by operation of the contacts. In the form shown in Fig. 1 the film is wound by a capstan 34 from a spool 24 over a roller on a spring-loaded arm 28, past a detecting head 30 and an inspection device 32 where it passes over an illuminated panel and may be viewed through a lens and also spliced. From the capstan the film passes cleaning pads 36, which may comprise bands driven oppositely to the film, and a measuring wheel 38 to the spool 36. The film may be rewound over a roller 27 and another spring-loaded arm 29. The arms 28, 29 may be coupled to switches to stop winding if the film breaks or runs out. The detecting head is shown in Fig. 5. The film passes first between rollers 42. 44, the latter being flanged and carried on a fixed axis, the former being carried on a spring-loaded arm 54 pivoted at 56. The arm carries an adjustable contact 58 cooperating with a fixed contact 60. The contacts are adjusted so that a film of normal thickness does not open the contacts but that they are opened by a splice or film portion which has been punched by sprocket teeth out of register with the perforations. The film then passes over the roller 46 of the cross-section shown in Fig. 11 which supports the film only at 46a, 46b leaving the perforated margin unsupported. A pivot 68 supports a mounting for a pair of contacts 50a, 50b, the mounting being rotated by a spring round the pivot so that contact 50b bears, by a jewelled tip, on the film with sufficient pressure to hold the contacts open. The jewelled tip is aligned with the film perforations and is sufficiently long not to enter a normal perforation. A torn perforation however allows the tip to enter and the contacts to close. Of a similar pair of contacts, 52a, 52b (not shown in Fig. 5), mounted alongside on the same support one 52b, Fig. 11, bears on the film outside the perforations. Any crack in the film outwards from a perforation to the edge.will weaken the film sufficiently to allow these contacts to close. The contacts may be lifted from the film for film threading by pressure on the arm 78 to rotate the pivot 68 which, by a projecting pin 69 acting on the end of the arm 54, also separates the rollers 42, 44. Closure of either of the pairs of contacts 50a, 50b or 52a, 52b, as a result of a film defect, applies a positive voltage from a source 154 to the grid of a thyratron 144, overriding the normal negative bias provided by the source 150. Firing of the thyratron actuates a relay 142 to stop the film drive. The opening of the normally closed contacts 58, 60 by a film splice passing between the rollers 42, 44 causes a positive voltage to be applied to the grid of the thyratron 102 from the source 106, overriding the normal negative bias provided by the source 108, to fire the thyratron to operate a counter 102 which opens the anode circuit to reset it for counting the next signal. Repeated closures of the contacts 58, 60, as by a portion of film which has been punched by sprocket teeth, cause successive charges to be passed to a capacitor 136 through a rectifier 138, the resulting cumulative voltage firing the thyratron to operate a relay 124 to stop the film drive after a number of successive operations of the contacts 58, 60 adjustable by varying a resistance 140. The relay also breaks the circuit of the counter 100 to prevent a single long splice being counted more than once by the counter 100 after its circuit has been reset.