1. Field of the Invention
The present invention relates to a transfer sheet guiding device for use in electrophotographic imaging apparatus, and more particularly to a device for separating a transfer sheet from a photosensitive drum, the sheet bearing an image transferred thereto, and for guiding the sheet.
2. Description of the Prior Art
Generally in imaging apparatus utilizing electrophotography such as an electrophotographic copying apparatus, it is necessary to separate a transfer sheet from the photosensitive drum after a powder image formed thereon is transferred to the sheet. Separating means for this purpose include one for forcibly separating one lateral side of the transfer sheet from the drum.
FIG. 1 is a perspective view of a conventional separating device of the type mentioned above. Referenced by 101 in FIG. 1 is a photosensitive drum. A powder image formed on the drum 101 is transferred at the transfer position to a transfer sheet P fed to the drum 101, whereupon one lateral side of the sheet P is forcibly separated from the drum 101 by a separating belt 104. The transfer sheet P is then nipped at this separated side between rollers 105, 106 and is transported onto a guide plate 102. In this way, the transfer sheet P is completely separated from the photosensitive drum 101.
The separating device thus separates one lateral side of the transfer sheet P from the drum 101 and therefore fails to smoothly separate the other side of the sheet P from the drum side of the drum where no separating belt is provided. At this side where the separating belt 104 is not provided, the transfer sheet P tends to travel with the rotation of the drum 101 because such is attracted to the drum 101. Consequently, the other side of the sheet P becomes raised off the guide plate 102 as shown in FIG. 1, is positioned along the guide plate 102 later than the above-mentioned one side thereof and curls up. As the transfer sheet P is transported by the pair of separating rollers 105, 106 in this state, the rear end of the sheet P passes transported means for feeding the sheet P to the drum 101 (e.g. a pair of timing rollers), whereupon a force acting to eliminate the curl from the sheet P acts in a direction opposite to the direction of transport which results in the sheet P being transported obliquely.
If the transfer sheet P is thus fed to the fixing unit as curled, the sheet develops defects such as creases on fixing. Furthermore when the transfer sheet P is obliquely fed due to uncurling, the image transferred to the sheet P at the transfer position will be displaced or deformed.
The degree of curl of the transfer sheet varies with the ambient condition (e.g. humidity), the properties (e.g. strength) of the sheet, etc., consequently varying the obliqueness of transport of the sheet due to the curling. To obviate these defects, consideration needs to be given to every ambient condition, and the properties of the sheet, etc.