1. Field of the Invention
The present invention relates to a thermal printer control and a computer readable medium for printing an image on a printable medium such as a thermal paper by heat generated from a thermal printer head, and particularly relates to a thermal printer control and a computer readable medium by which printing quality may be improved by controlling timings at which an image is printed on a thermal paper even when sticking occurs between a thermal printer head and the thermal paper.
2. Description of Related Art
Heretofore, there is known a thermal printer apparatus for printing an image on a thermal paper serving as a printable medium by discoloring (blackening) the thermal paper with an application of heat generated from a thermal printer head including a heating element. If the thermal paper that has been discolored in the previous printing operation of one line does not advance and remains at the position of the previous printing as shown by the dotted line in FIG. 8A while a feeder roller is in a paper feeding motion as shown by the solid line, the discolored layer of the melted thermal paper is cooled and the thermal paper sticks to the heating element of the printer head. As a result, as shown in FIG. 8B, although an image of the next line is printed, the thermal paper 10 does not advance to the next position and the next image is not printed on the next position, thereby resulting in an image of each line 52 being printed on the same position repeatedly. This produces a void (whitening or printed image dropout) on the thermal paper.
It is proposed to prevent this sticking by lowering the quantity of heat of the printer head. However, according to this method, as the heat is not sufficiently applied to thermal paper, an image cannot be printed on the thermal paper with proper density. For this reason, there are also proposed various apparatuses which prevents sticking between a thermal paper and a printer head so that an image can be reliably printed on the thermal paper without lowering the quantity of heat of the printer head when an image is printed on the thermal paper.
Japanese Examined Patent Publication No. Hei 6-83344 proposes that, in a printing mode of a long printing cycle in which sticking tends to occur, after printing of an image of a predetermined amount is finished, a printer head and a thermal paper are immediately moved relatively to prevent sticking.
Japanese Unexamined Patent Publication No. Hei 7-227990 proposes that, in a low speed thermal paper feeding mode in which sticking ends to occur, an image is printed after image data of predetermined lines is accumulated in a memory. In actual practice, the thermal paper is advanced at a comparatively high speed, thereby preventing occurrence of sticking.
However, the conventional apparatuses are unable to control timings at which an image is printed on the thermal paper. Therefore, if sticking occurs for some reason, then the printing timing becomes inappropriate. Thus, a printed image dropout occurs and a printing quality is lowered.