Incremental printing of symbolic information – Thermal marking apparatus or processes – Preheating
Reexamination Certificate
2002-08-06
2003-12-30
Tran, Huan H. (Department: 2861)
Incremental printing of symbolic information
Thermal marking apparatus or processes
Preheating
C400S120080
Reexamination Certificate
active
06670976
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of and an apparatus for controlling a thermal head, for instance, in a heat-sensitive plate making apparatus, and more particularly to a method of and an apparatus for controlling heater elements in such a thermal head.
2. Description of the Related Art
There has been known a heat-sensitive plate making apparatus which makes a plate (e.g., a stencil) by thermally perforating a plate material by selectively energizing some of heater elements of a thermal head arranged in a main scanning direction while moving the plate material in a sub-scanning direction relatively to the thermal head. In such a plate making apparatus, heat history control, in which the time for which each heater elements is energized is controlled according to its heat history, is carried out. For example, when a square area of the plate material is to be perforated in order to print a square such as shown in
FIG. 21A
, imperforation can occur at an upper edge portion
72
and left and right side edge portions
71
of the square area as shown in
FIG. 21B
if the heater elements of the thermal head corresponding to the square area is uniformly energized without performing the heat history control. This is probably because the heater elements corresponding to the left and right side edge portions
71
cannot be sufficiently heated since heater elements on the outer sides of the left and right side edge portions
71
are not at an elevated temperature and because the heater elements corresponding to the upper edge portion
72
are not heated at the preceding perforating timing. On the other hand, if all the heater elements corresponding to the square area are energized for a longer time so that even the heater elements corresponding to the upper edge portion
72
and the left and right edge portions
71
are heated to a temperature sufficient to perforate the plate material, the perforations corresponding to the area
73
in
FIG. 21B
will become too large in size though imperforation at the edge portions
71
and
72
can be prevented.
When the heat history control is performed so that when a certain pixel (will be referred to as “a pixel of current interest”, hereinbelow) is a black spot which involves perforation of the plate material and at least one of the pixels adjacent to the pixel of current interest on opposite sides thereof and a pixel immediately preceding to the pixel of current interest is a white spot which does not involve perforation of the plate material, the heater element corresponding to the pixel of current interest is energized for a longer time, the heater elements corresponding to the edge portions
71
and
72
can be heated to a temperature equivalent to that of the heater elements corresponding to the area
73
, whereby the perforations in the square area can be uniform in size as shown in FIG.
21
C.
However such a heat history control is disadvantageous in that particular heater elements are repeatedly energized for a longer time than the other heater elements and the particular heater elements deteriorate in durability. For example, the heater elements corresponding to the edge portions
71
and
72
are energized for a longer time than the other heater elements during several perforations, and when a plurality of perforations arranged in a row in the sub-scanning direction are formed to print a thin line, one of the heater elements is continuously energized for a longer time. Durability of particular heater elements deteriorates also in a heat history control where such particular heater elements are not energized for a longer time but are applied with a larger power per unit time. In other words, when power applied to particular heater elements is increased in order to prevent defective perforation due to fluctuation in heating temperature of the heater elements (the temperature to which the heater element is heated when energized), there is a fear that the thermal head can deteriorate in durability.
SUMMARY OF THE INVENTION
In view of the foregoing observations and description, the primary object of the present invention is to provide a method of and an apparatus for controlling a thermal head comprising a plurality of heater elements arranged in one direction so that fluctuation in heating temperatures of the heater elements can be suppressed and defective perforation can be prevented without deteriorating the durability of the thermal head.
In accordance with a first aspect of the present invention, there is provided a method of controlling a thermal head provided with a plurality of heater elements which are arranged in a main scanning direction, the method comprising the step of selectively energizing the heater elements according to black and white information for the pixels to be formed by the respective heater elements, wherein the improvement comprises
the step of an auxiliary heating control in which each heater element corresponding to a pixel the black and white information for which is white is heated to an auxiliary temperature according to the black and white information for pixels adjacent to the pixel in the main scanning direction.
In accordance with a second aspect of the present invention, there is provided an apparatus for controlling a thermal head provided with a plurality of heater elements which are arranged in a main scanning direction, the apparatus comprising a heater control means which selectively energizes the heater elements according to black and white information for the pixels to be formed by the respective heater elements, wherein the improvement comprises that
the heater control means is provided with an auxiliary heater control means which performs an auxiliary heating control in which each heater element corresponding to a pixel the black and white information for which is white is heated to an auxiliary temperature according to the black and white information for pixels adjacent to the pixel in the main scanning direction.
For example, when the thermal head is used in a heat-sensitive printer, the “black and white information” represents whether the pixel is to be black or white, and when the thermal head is used in a heat-sensitive plate making apparatus, the “black and white information” represents whether the pixel is to be perforated. In the former case, that the black and white information for the pixel is white means that the pixel should not be printed and in the latter case, that the black and white information for the pixel is white means that the pixel should not be perforated.
The heater control means may be further provided with a preheating heater control means which performs a preheating control in which each heater element corresponding to a pixel the black and white information for which is white is heated to a preheating temperature according to the black and white information for pixels adjacent to the pixel in a sub-scanning direction substantially perpendicular to the main scanning direction.
The auxiliary temperature or the preheating temperature means a temperature lower than a temperature at which the heater element can accomplish the expected objected, that is, a temperature at which the heater element cannot form a perforation through which the ink can pass (including the case where the plate material is not perforated at all) in the case where the thermal head is used in a heat-sensitive plate making apparatus and a temperature at which the heater element cannot form a black spot in the case where the thermal head is used in a heat-sensitive printer.
The heater control means may be further provided with a heat history heater control means which performs a heat history control in which each heater element corresponding to a pixel the black and white information for which is black is additionally heated on the basis of the black and white information for pixels adjacent to the pixel in the main scanning direction and/or a sub-scanning direction substantially perpendicular to the main scanning direction.
The auxiliary heater c
Nixon & Peabody LLP
Riso Kagaku Corporation
Studebaker Donald R.
Tran Huan H.
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