Printing apparatus with mechanism precisely defining printing start

Abstract

A color printer is provided in which a paper sheet is wrapped about a rotatable platen and three colors are printed on the sheet, to obtain an image, by a thermal head and a color ribbon during three rotations of the platen. In a paper feeding device for the printer, a sheet of paper is fed by a feeding roller, from the bottom of a stack of paper sheets in a paper tray through, a feeding guide to the platen. The tray has an opening in its bottom plate so as to expose the lowermost paper sheet stored therein. The feeding roller is provided under the tray and lifts up toward the opening of the tray so as to come in engagement with the lowermost paper sheet, the feeding roller rotating to feed it to the platen. The width of the platen is less than that of the sheet and the circumference thereof is less than the length of the sheet. Therefore, when the sheet is wrapped about the platen, it extends laterally outward from the ends thereof, and its ends overlap. Accordingly, during printing, the sheet is securely wrapped about the platen and its position does not shift and the extension of the sheet from the edges of the platen allows a sensor to determine a print starting position by sensing a mark of the edge of the sheet. Thus, a fixed print starting position is obtained during all three rotations of the platen during the print cycle.