Incremental printing of symbolic information – Thermal marking apparatus or processes – Multicolor
Reexamination Certificate
2000-02-14
2001-08-28
Le, N. (Department: 2861)
Incremental printing of symbolic information
Thermal marking apparatus or processes
Multicolor
Reexamination Certificate
active
06281919
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to heat history control for a thermal head, and particularly to histogram control for a stencil-making device for making stencils used in multi-color printing using a thermal head, for every color used in printing.
2. Description of the Related Art
Conventionally, stencil making devices for stencil printing apparatus where thermo-sensitive stencils are perforated by a thermal head are well known.
In these stencil making devices, original images are read out by image scanners or given by computers connected to the stencil making devices, and stencil materials are perforated using a thermal head operated according to the signals representing the images from the scanners or computers. The perforated stencil is then wrapped around a printing drum and printing paper is inserted between the printing drum and a press roller that presses against this printing drum and rotates around its axis. Ink within the printing drum is then pressed onto printing paper through perforations in the perforated stencil and transferred to the printing paper.
The thermal head employed as an output head for making stencils has a plurality of heating elements corresponding to pixels arranged in a straight line. Perforations are then opened up in the stencil materials by heating just desired heating elements corresponding to the image data so as to form a perforated image on the stencil. When stencils are made using this kind of thermal head at an accelerated speed, thermal energy is gradually accumulated at the heat generating elements, since the perforating for the next line is started before thermal energy applied to the heat generating element is sufficiently diffused and emitted. As a result, heat is accumulated at each heating element according to its heat history. This causes unevenness in energy states and deterioration in image quality.
In order to solve this problem of deterioration of image quality caused by heat history in high-speed stencil-making devices, it is necessary to control the energy applied to the current line according to the heat history of the thermal head, i.e. to carry out heat history control. Conventionally, there is a method where heat history data (for, for example, a number of previous lines in a sub-scanning direction) for each heating element and its surrounding heating elements is stored in heating element units and the energy applied to the current line is controlled based on this heat history data so as to control the amount of heat generated by the heating elements (for example, refer to Japanese Unexamined Patent Publication No. 60(1985)-16113, and Japanese Unexamined Patent Publication No. 2(1990)-8065). There is a further method where heating data corresponding to the total amount of heat for a previous number of lines is added up and the heating amount for the thermal head is controlled block-by-block for the block units arranged in the main scanning direction or collecting up all of the blocks in the main scanning direction based on the heating data. Heating data corresponding to the total amount of heating of the head is added up by a method of providing a thermistor at a prescribed location on the thermal head and detecting the temperature of the thermal head using the sensor and adding up the heating data, or a method of adding up heating data based on perforation data for a method such as, for example, counting a number of black pixels of perforation data (binary data), calculating a black pixel ratio corresponding to a printing ratio. The heating data is then added up based on the perforation data. The carrying out of thermal history control based on this added up heating data is then referred to as “histogram control” and the heating data employed in this control is referred to as “histogram data”.
This histogram control controls energy applied to a thermal head according to the heat history of the thermal head. Therefore, with stencil-making devices for multicolor printing involving a plurality of stencils, when stencils are used for each color, it is preferable for histogram control to be carried out based on histogram data obtained for each color.
However, when histogram control is carried out based on histogram data obtained for each color in this manner, there are cases where the hue of regions that are printed in an overlaid manner is inappropriate even when the colors of regions of printed matter where colors are printed independently are appropriate.
The cause of this was investigated, but no definite cause was found. On the other hand, when histogram control is carried out for stencils for other colors based on histogram data for a color for which the printing density is greatest of the colors of ink used in printing, or when histogram control is carried out for stencils for each color based on histogram data for the color of the greatest printing density (for example, black when the color of the printing inks are yellow, cyan and magenta) and of a different hue to all of the inks used in printing, improvement in the inappropriateness of hues of regions where printing overlaps can be discerned.
It is therefore the object of the present invention, based on the above knowledge, to provide a stencil-making device for use in multi-color printing, for carrying out histogram control in such a manner that regions printed in an overlapping manner do not have inappropriate hues.
SUMMARY OF THE INVENTION
A stencil-making device, for making stencils used in multi-color printing using a thermal head, comprises energy control means for subjecting energy to be applied to the thermal head to histogram control based on heating data for a number of previous lines in a sub-scanning direction of the head. The energy control means obtains the heating data for a prescribed color of a density greater than the density of ink used in printing with a stencil and subjects at least a stencil for one color to applied energy control based on the obtained heating data.
“Histogram control” refers to adding up heating data based on perforation data and then performing heat history control based on this added up heating data. Counting of the number of black pixels for the perforation data, calculating the black pixel ratio and adding up the heating data can be performed while adding up the heating data based on the perforation data. This is by no means limited to calculating the black pixel ratio, providing that the heating data for the previous number of lines in the sub-scanning direction of the thermal head is added up based on the perforation data.
The “prescribed color” can be the same hue as any of the inks used in printing or can be a different hue to any of the inks used in printing. When the hue is different, the ink having this color is imaginary.
A stencil-making device, for making stencils used in multi-color printing using a thermal head, comprises energy control means for subjecting energy to be applied to the thermal head to histogram control based on heating data for a number of previous lines in a sub-scanning direction of the head. The energy control means obtains the heating data for a color of a different color and hue to and greater density than any color of ink used in the printing and subjects stencils for all of the colors used in the printing to applied energy control based on the heating data.
An ink having “a different hue to an ink of any color used in the printing and a greater density than the color of any ink” is also imaginary.
A stencil-making device, for making stencils used in multi-color printing using a thermal head, comprising energy control means for subjecting energy to be applied to the thermal head to histogram control based on heating data for a number of previous lines in a sub-scanning direction of the head. The energy control means obtains the heating data for the densest color of the colors of inks used in the printing, and subjects the stencils for all of the colors used in the printing to applied energy control based on this heating data.
It is pre
Feggins K.
Le N.
Nixon & Peabody LLP
Riso Kagaku Corporation
Studebaker Donald R.
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