Incremental printing of symbolic information – Thermal marking apparatus or processes – Density control
Reexamination Certificate
2000-07-21
2002-11-05
Tran, Huan (Department: 2861)
Incremental printing of symbolic information
Thermal marking apparatus or processes
Density control
C347S176000
Reexamination Certificate
active
06476839
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
Our invention relates to a thermal printer for imparting onto a recording medium a different color or tone of color according to the level of heat energy imparted to the recording medium.
2. Description of the Related Art
Line thermal printers and other types of thermal printers have numerous independently heat-driven thermal elements arranged in line, and print by selectively driving these thermal elements to impart heat to the corresponding position of an oppositely positioned heat sensitive paper, thereby causing the heat sensitive paper to change color. The color produced in the heat sensitive paper by this type of printer differs according to the amount of heat energy imparted by the thermal element. As a result, actual print results, such as the color density, will also differ according to whether or not a selected thermal element was driven immediately before, i.e. whether or not a selected thermal element has residual heat.
A typical method of avoiding such problems and improving print quality has been to store past printed pixel data as a print history. This print history is then used to vary the next pulse width applied to a particular thermal element and adjust the thermal element drive time.
FIG. 10
is a control block diagram of a conventional line thermal printer in which this print history is used as noted above. One dot line unit of print pixel data received from a host is temporarily stored in a print buffer
1
, and sent to a print head unit
10
by way of selector
4
. When a next dot line of print pixel data is stored in the print buffer
1
, the current data in the print buffer
1
is first moved to a history buffer
2
. The data stored in history buffer
2
and data stored in print buffer
1
are then operated on bit by bit by logic circuit
3
, and output to selector
4
. The selector
4
is a type of sequencer and sequentially outputs data from print buffer
1
and data from logic circuit
3
according to a data selection signal from control circuit section
5
. More specifically, the strobe period is divided into a part (period
1
) for passing data from print buffer
1
, and a part (period
2
) for passing data from the logic circuit
3
During period
1
the data selection signal applies data from the print buffer
1
to the print head unit
10
, and during period
2
applies data from the logic circuit
3
to the print head unit
10
.
Another technique for color printing with a thermal printer is taught, for example, in Japanese Patent 2836584. In this technique the heat sensitive paper is manufactured with layers of different colors, and a particular color is printed by changing the heat energy applied by a particular thermal element. To print one color in this type of printer, the pulse width of the thermal element drive circuit is lengthened so that a high level of heat energy is applied, and to print another color, the pulse width is shortened so that a low level of energy is applied. While this technology can also be used for single color printing with multiple gradations, it is still necessary vary the pulse width according to the desired gradation.
Considering these problems with multigradient thermal printing using a print history as described above, it is very difficult to directly apply this heat history control technique to printing in many colors or many tones in single color printing because of the increasing complexity of the print history. A line thermal printer that can switch between high quality single color printing using a print history, and printing in multiple colors, is also desirable. Achieving such a line thermal printer requires technology for flexibly controlling a buffer for storing history data for each print pixel, and particularly requires technology for efficiently sharing the buffer between single color printing and printing in multiple colors (multicolor printing).
OBJECTS OF THE INVENTION
An object of our invention is to provide a method for easily realizing heat history control even in a printing method for producing multiple colors.
A further object is to provide a line thermal printer capable of switching between high quality single color printing considering the print history, and multicolor printing.
Yet a further object is to provide a method for efficiently sharing a buffer storing print pixel data for use in single color printing and multicolor printing in a line thermal printer of this type.
SUMMARY OF THE INVENTION
To achieve the above objects, we provide in a thermal printer that prints on a recording medium in which plural colors can be produced depending upon the heat energy applied to the recording medium: a thermal element for producing the plural colors; a thermal element drive circuit that drives the thermal element; a receiving circuit for receiving color data specifying either no color or one of the plural colors; memory for storing the color data received by the receiving circuit; and a drive control circuit for supplying a particular drive signal to the thermal element drive circuit based on the current color data received by the receiving circuit, and previous color data stored in memory.
This thermal printer further preferably has in its memory a first storage part for storing presence or absence of first color data based on color data received by the receiving circuit, and a second storage part for storing presence or absence of second color data based on color data received by the receiving circuit.
Yet further preferably, the first and second storage parts of the memory respectively store the presence or absence of current and previous first color data, and the presence or absence of current and previous second color data.
Yet further preferably, the drive control circuit is divided into plural parts and defines a strobe period of the drive circuit, and has a logic circuit for determining whether, current is applied to the thermal element during the plural strobe period parts based on at least presence or absence of current first color data, presence or absence of previous first color data, presence or absence of current second color data, and presence or absence of a previous second color data.
Yet further preferably, the thermal printer in this case also has a color mode setting circuit for setting a color mode, and a memory allocation circuit for determining the color data to be stored in memory according to the color mode set by the color mode setting circuit. In this case the drive control circuit supplies a different control signal to the thermal element drive circuit according to the color mode set by the color mode setting circuit.
Further preferably in this case, when a dual color mode is set, the memory allocation circuit stores in memory the presence or absence of first color data, and the presence or absence of the second color data, based on color data received by the receiving circuit. When a single color mode is set, the memory allocation circuit stores the presence or absence of only the first color data in memory based on the color data received by the receiving circuit.
Further preferably, when the dual color mode is set, the memory allocation circuit stores in memory the presence or absence of current and previous first color data, and the presence or absence of current and previous second color data, based on color data received by the receiving circuit. When the single color mode is set, the memory allocation circuit stores the presence or absence of previous first color data in memory instead of storing the presence or absence of current and previous second color data.
The drive control circuit of this thermal printer further preferably has a first strobe period dividing circuit for dividing the drive circuit strobe period into first specific plural parts, a first logic circuit, a second strobe period dividing circuit for dividing the drive circuit strobe period into second specific plural parts, and a second logic circuit. This first logic circuit determines whether current is applied to the thermal element durin
Imai Satoru
Nakajima Satoshi
Seiko Epson Corporation
Tran Huan
Watson Mark P.
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