Patent GB-984767-A (GB)
Title: Film projection apparatus using a removable cassette
IPC: G03B21/54
Filed: 1961-05-19
Abstract: 984,767. Sound-film projection apparatus: cassettes: films. A. W. KINGSTON. May 15, 1962 [May 19, 1961; Aug. 15, 1961], Nos. 18439/61 and 29436/61. Headings G2C and G2E. [Also in Division G5] A cassette holding a film having two picture tracks arranged to run in opposite directions and a magnetic sound track associated with each picture track comprises, as shown, two bobbins 13, 14 on which the film 19 is coiled, a film gate 30 and a single sprocket 86 in engagement with the film for feeding the same to and away from the gate 30. The cassette is removably mounted on the deck 11 of a projection apparatus which is provided with a drive spindle 38 for the sprocket 86, driving spindles 17, 18 for engagement with the internally splined central holes of the bobbins 13,14 a film traction device 36 and a prism 33 received in an aperture 32 of the cassette for directing light through the gate 30 and towards a projection lens 34. The deck 11 is also provided with a driving capstan 52 a pressure roller 55, a magnetic head 51 a pressure pad 53 and rollers 57, 57<SP>1</SP>, all of which members are accommodated within an operating 49 in the cassette across which the film 19 passes on its way to and from the sprocket 86. The rollers 57, 57<SP>1</SP> and 55 and the pressure pad 53 are slidable towards the rectilinear film section, 47,47<SP>1</SP> during operation of the projection apparatus to ensure free running of the film in the region and to draw the film past the magnetic head 51 against which it is pressed by the pad 53. Film tensioning devices in the form of guides 40,41 and 40<SP>1</SP>, 41<SP>1</SP> respectively on spring-urged levers 42, 42<SP>1</SP> are provided in the cassette together with a spring-urged slide member 59 having two posts 60, 60<SP>1</SP> for locking the film in position against rollers 48, 62 and 481, 62<SP>1</SP> respectively. This locking device is automatically released during operation of the projector by movement of a peg 64 projecting from the deck 11. The rollers 62,62<SP>1</SP> may be replaced by fixed gripping surfaces. A pin, engageable with the perforations of the film when the cassette is removed from the deck may also be provided. After projection of one of the two associated picture and sound tracks, the cassette may be removed, inverted and replaced on the deck 11 to bring the other picture track into alignment with the optical system 33, 34 and the other sound track into alignment with the magnetic head 51 and pad 53. In a modified embodiment, in which inversion of the cassette is not necessary when changing from a first to a second set of picture and sound tracks, an additional head 71 and slidable pressure pad 73 is provided together with a further pressure roller 75 moving in a slot 76. After projection of the first set of tracks the elements 51, 53 and 55 are rendered inoperative and replaced in operation by elements 71, 73 and 75. The direction of drive of spindles 38, 17 and 18 is reversed and the elements 33 and 34 are wound into alignment with the second set of tracks. The gate 30 is provided with a shutter for obscuring the picture tracks not being projected. In this modified embodiment the openings in the cassette (for spindle 38 &c.) may be provided in one wall only, in this case the bottom wall 10. Further, only a single magnetic head may be provided if it is movable into alignment with the two sound tracks. Known means for sensing the ends of the film may be arranged to switch off the apparatus. Corner pieces 77-80 are provided on the deck for locating the cassette in position. All guide rollers and surfaces may be arranged to engage only the edges of the film. Many of the details of the projection apparatus are as disclosed in Specification 645,485. The film may be formed with central perforations, a picture track on each side of the perforated strip and a magnetic sound track at the side of each picture track strip remote from the central strip. Alternatively, perforations may be provided along each edge of the film, a picture track adjacent each row of perforations and a magnetic sound track adjacent each picture track. For use with the non-reversible cassette mentioned above an assymmetrical arrangement may be used, with perforations along one edge,two picture tracks side by side and two magnetic sound tracks side by side at the other edge. The magnetic stripes may be made thicker than necessary for recording purposes and may be duplicated on the back of the film to protect the same from scratching. The stripes on the back may be of non-magnetic material. In this case the special shaping of the guide rollers and surfaces referred to above would be unnecessary. In the case of a film with central perforations, raised stripes may also be provided on both sides between the perforated strip and the picture tracks.