Thermal printer with sensor for leading edge of receiver sheet

A thermal printer (10) is useful for printing onto a receiver sheet (22, 24, 26) having a leading edge and a trailing edge and includes an elongated rotatable platen (34); an elongated thermal print head (30) positioned parallel to the platen; a pathway (12, 14, 16) for receiving a receiver sheet in a printing direction from the platen, the platen being positioned for rotation in the printing direction with at least a portion of the platen in the pathway to engage a receiver sheet or a dye donor web (31); a supply roll (28) of dye donor web positioned upstream of the print head; a mechanism (76-112, 132-142) for moving the print head into the pathway opposite the portion of the platen to press the print head into engagement with the dye donor web, the dye donor web into engagement with the receiver sheet, and the receiver sheet into engagement with the platen; a mechanism (180-188) for rotating the platen in the printing direction to move either the dye donor web or both the dye donor web and the receiver sheet between the print head and the platen; a mechanism (36-42) for sensing when the leading edge of the receiver sheet has reached a predetermined location downstream of the print head and for producing a signal; a controller (212), responsive to the signal, for activating the print head to cause dye transfer between the dye donor web and the receiver sheet; and a mechanism (18 , 166-174) for moving the receiver sheet in the pathway for successive thermal transfers of different dyes from the dye donor web.