Automatic copier show-around erase system

Claim 1

In a copier or copier/printer with a photosensitive imaging surface and a variable magnification optical imaging system with magnification setting means and a copying platen on which various sizes of document sheets may be variably sequentially imaged by the magnification setting of said optical imaging system onto the photosensitive imaging surface as latent images to be developed and transferred to copy sheets, wherein the copier has a fade-out system for preventing the development of areas of the photosensitive imaging surface adjacent the latent images thereon of the document sheets, the improvement comprising: a document sheet transport for transporting the document sheets in a document path onto and over the copying platen of the copier; an array of plural document sensing means integral said document sheet transport and positioned in the document path of said document sheet transport for measuring both the length and width of the document sheets being transported onto the copying platen of the copier; means for indicating the size of the copy sheets on which copies are being made; and fade-out means connecting with and controlled by both said array of plural document sensing means and said magnification setting means of said variable magnification optical imaging system for preventing development of variable areas of said photosensitive imaging surface in response to said length and width measuring of the document sheet being copied and said magnification setting, and wherein said fade-out means is further responsive to said means for indicating the size of the copy sheets on which copies are being made, for automatically preventing development of all areas of said photosensitive imaging surface outside of the smaller of the two of the document latent image areas on the photosensitive imaging surface or said actual copy sheet size indication, by fading out any portions of the document latent image area which will not be engaged for image transfer by the copy sheet, and fading out otherwise developable but nondocument latent image areas of the photosensitive imaging surface even if they are within areas of the photosensitive imaging surface which will be engaged by the copy sheets, so as to provide complete fade-out for a wide range of magnifications, document sizes, and copy sizes, even if the document latent image area is smaller than the copy sheet or the copy sheet is smaller than the document latent image area, to prevent either "show-around" copy defects or undesirable development of portions of the document latent image area which cannot be transferred to the copy sheet, and wherein said fade-out means is operated and controlled in accordance with all of the following parameters: 1. If document width X magnification < copy width, then fade out to the former; 2. If document width X magnification > copy width, then fade out to the latter; 3. If document length X magnification < copy length, then fade out to the former; 4. If document length X magnification > copy length, then fade out to the latter.