Patent GB-965768-A (GB)
Title: Holder for material in sheet form,especially for light-sensitive material in photographic projection printing apparatus
IPC: G03B27/60
Filed: 1960-12-08
Abstract: 965,768. Holders for sheet material. AGFA A.G. Dec. 8, 1960 [Dec. 9, 1959], No. 42351/60. Heading G2A. A holder for material in sheet form having a supporting surface provided with means for holding said material thereon by suction has an operating element for said suction means so arranged within the area of said surface to be covered by said material that it is operable to establish the' suction by placing the material in its required position upon the surface. The holder is primarily intended for supporting light-sensitive sheet material on the easel of photographic projection printing apparatus. As shown (Figs. 1 and 2) such a holder preferably comprises a transparent or translucent block 4 having a surface 5 for supporting said sheet material and an operating element 36 projecting therebetween and controlling a microswitch 31 by way of linkage 33-35. On positioning a sheet of printing paper on the surface 5, an electromagnet 26 is energized by means of the switch 31 and the element 36 and, by way of its armature 25, a valve slide 21 of a valve 15 is moved from the position shown in Fig. 5 towards the right, whereby a tube 20 from a suction pump (not shown) is connected by way of a passage 13 and one or both of passages 9, 10 in the block 4 to either a series of suction apertures 11 or to both this series and a further series 12, depending on the setting of a cock 18 (Fig. 4). The holder is provided with an angled stop 43 for centring different sizes of paper on the surface 5, said stop being mounted by means of crank arms 44-46 on the upper surface 6 of the housing 1 and being adjustable by a knob 51 on the crank-shaft 50, which knob bears an index 52 co-operating with a paper size scale 53. In the case of small paper sizes which do not extend as far as the apertures 12, by means of a pin 55 projecting downwards from the stop 43 and engaging eccentrically in a disc 42 connected to spigot 40 of the cock 18, said spigot 40 is turned so that the series of apertures 12 and passages 10 and 16 are isolated from the passage 13, thereby preventing suction being applied to their apertures. The holder also includes means for ejecting a printing sheet after an exposure, said means comprising a slide 56 (Figs. 1 and 6) mounted by means of pins 57, 58 on the underside of the stop 43, and being coupled by way of a pin and slot connection 63, 64 to the armature 62 of an electro-magnet 61. This magnet 61 is itself mounted so as to slide on bars 67 and is coupled by way of a pin and slot coupling 69, 70 (Figs. 2 and 6) to the stop 43 so as to partake in the adjustment movements of the stop. Exposure time regulation is effected in that light penetrating a printing sheet on the surface 5 is reflected from the diffusely reflecting lower and side walls of the block 4 through a transparent side window in said block 4 to a photo-cell 3 of an exposure time regulating device. A circuit diagram for this device is given (Fig. 7, not shown) and functions in that during exposure said photo-cell operates to charge a condenser which eventually triggers a thyratron valve, which triggering switches off the exposure light, de-energizes the magnet 26 to open the passage 13 to the atmosphere by way of an opening 23 in valve 15, and energizes the magnet 61 to eject the sheet of printing paper. Switches are provided whereby operation of the magnet 26 and 61 may be over-ridden if it is not required to eject the sheet immediately after exposure. In the case of small paper sizes, parts of the surface 5 not covered by a sheet should be covered by a mask to prevent erronious exposure time measurement by photo-cell 3. The block 4, magnets 26 and 61 and other parts of the holder may be exchangeably mounted in a well 2 of the housing 1, a disconnectible contact bar 98 being provided for the exposure time control device. The surface 5 may be matted or provided with a light diffusing layer (e.g. paper) for focusing purposes. The operating element 36 may be in the form of a push-button and also may be positioned outside the area defined by the suction apertures (but a latching device for the element would in this case be necessary). The supporting surface may be opaque.