Device in camera shutter for maintaining separate blades in intimate contact with each other
BACKGROUND OF THE INVENTION 
     This invention relates to a device in a camera shutter for maintaining shutter separate blades in intimate contact with each other. 
     It is highly desirable to provide a plurality of shutter separate blades for covering a shutter aperture for the purpose of reducing the size of the shutter. However, the separate blades are constructed generally of thin metal plates and can not satisfactorily maintain themselves in intimate contact with each other and such blades require high precision machining in order to provide the necessary high degree of lightproof characteristics needed for the shutter. This invention makes it possible to manufacture a shutter with ease and without high precision machining and which shutter is simple in construction and has a high degree of lightproof characteristics achieved by maintaining the blades in intimate contact with each other. 
     A difficulty attendant with conventional shutters of this type is that sufficient flatness of the surfaces of each shutter separate blade constructed of a thin plate can not be achieved while the blade is being manufactured whereby a small clearance is formed between adjacent blades. The clearance prevents the blades from being held in intimate contact with each other thereby rendering the lightproof characteristics poor and insufficient. This has led to the drawback that providing the sufficient flatness of the blade surfaces requires skillful high precision machining which in turn makes it difficult to produce less costly shutters. 
     With the construction according to the invention, the blades can be maintained in intimate contact with one another even if there are employed separate blades having surfaces of insufficient flatness. This is accomplished by providing at set of projections for urging the respective blades together when in their open and closed positions. 
     According to the invention, the respective blades are held in intimate contact with each other by using an extremely simple structure. Accordingly, conventional high precision machining is no longer necessary to produce blades having a tendency to maintain themselves in close contact with each other nor to impart sufficient flatness to the surfaces of respective blades. The prior art type blades with such a tendency are held in frictional engagement with one another and the frictional forces between the blades prevent their smooth movement. The present invention eliminates the above prior art shortcoming. 
    
    
     BRIEF DESCRIPTION OF THE INVENTION 
     FIG. 1 is a plan view of a first embodiment of this invention; 
     FIG. 2 is a plan view of a second embodiment of this invention; 
     FIG. 3 is a cross-sectional view taken along lines III--III of FIGS. 1 and 2 and; 
     FIG. 4 is a view similar to FIG. 3 but showing a conventional prior art type device. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In FIG. 1, a shutter base plate (1) has an exposure aperture (1a) defined therein. A subsidiary plate (2) substantially identical in shape with the base plate (1) is supported over the base plate (1) (See FIG. 3). Between these base plates, there are provided an opening group of shutter blades (3) for starting or initiating an exposure operation and a closing group of shutter blades (6) for finishing or completing the exposure, these groups each being supported on one end of the base plate (1) and being movable between a first closed position where they cover or close the aperture and a second open position where they uncover or open the aperture. 
     Each of the groups of shutter blades (3), (6) is composed of a plurality of separate, small size blades. The structure and mode of operation of the separate blades are fully disclosed in Utility Model No. 49-63948 laid open to public inspection and therefore, their explanation is omitted herein. 
     FIG. 2 shows another arrangement of the separate blades which is similar in structure to that shown in FIG. 1. The mode of operation of the FIG. 2 arrangement is similar to that of the blade groups disclosed in Utility Model No. 48-111133 laid open to public inspection and therefore, its explanation is omitted herein. 
     FIG. 3 is a cross-sectional view taken along line lines III--III of FIGS. 1 and 2. As shown, the base plate (2) has formed thereon downwardly projecting projections (2b), (`c) which are engageable with an upwardly projecting projection (4d) on an opening member (4) and an upwardly projecting projection (7d) on a closing member (7), respectively, when these projections (4d), (7d) come to the first position where the blades cover or close the shutter aperture (1a) whereupon the projections (2b), (2c) bias the opening group of shutter blades (3) and the closing group of shutter blades (6) toward the base plate (1). The base plate (1) has an upwardly projecting projection (1b) formed thereon which is positioned so as to be engageable with a separate covering blade (3b) of the opening group of shutter blades (3) or a separate covering blade (6b) of the closing group of shutter blades (6), whereupon blade (3b) or (6b), when held in the aperture covering position, is urged into contact with blade (3a ) or (6a) adjacent to and upwardly of the blade (3b) or (6b). 
     FIG. 4 illustrates the conventional type base plates and shutter blades in the position corresponding to that shown in FIG. 3. In FIG. 4, since there are no downwardly projecting projections on the subsidiary plate (2), the groups of shutter blades are movable relatively freely. Further, with no upwardly projecting projection (1b), the separate covering blade (3b) slides beneath the closing group of shutter blades (6) when the shutter is set thereby forming clearances or gaps in the group of shutter blades (3) which in turn have reduced lightproof characteristics. 
     Thus, it will be understood that the maximum lightproof characteristics can be obtained when adjacent shutter blades are held in planes parallel and close to each other. 
     While the above embodiments have been described with respect to the focal-plane shutter, the invention is also applicable to the lens shutter having one or two sets of blades in which case the base plates have formed thereon projections projecting in a direction to hold the blades in close contact with one another only when the aperture is closed. Furthermore, it is possible to provide projections corresponding to succeeding respective blades. Still further, the respective blades can have projections which operate in the same way as in the disclosed embodiments. What is claimed is: