Incremental printing of symbolic information – Thermal marking apparatus or processes – Block driving
Reexamination Certificate
1998-07-27
2001-02-27
Le, N. (Department: 2861)
Incremental printing of symbolic information
Thermal marking apparatus or processes
Block driving
C347S180000, C347S181000
Reexamination Certificate
active
06195110
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thermal printing method and a thermal printer. More particularly, the present invention relates to a thermal printing method and a thermal printer with high fidelity in gradation reproduction of an image.
2. Description Related to the Prior Art
There are plural types of thermal printers, including a thermal transfer type and a direct thermal recording type. The thermal transfer type is either a wax-transfer type or a thermal sublimation type. Ink film is superposed on a recording material or a sheet. A thermal head presses the ink film against the recording material and applies heat to it, so that the ink of the ink film is transferred to the recording material. In the direct thermal recording type, the recording material with a thermosensitive characteristic is heated by the thermal head to develop color of the recording material with an image. The thermal head is constituted by an array of heating elements, which respectively consist of a resistor and are arranged in line. The heating elements are driven by a driver.
In the thermal recording with the thermal head including the heating elements being numerous, a peak voltage of a power source increases considerably when all the heating elements are driven simultaneously. Such an increase in the voltage causes an instantaneous drop in the voltage, and thus irregularity in a reproduced image.
There is a suggestion of decreasing the number of the heating elements being driven simultaneously. The heating elements are grouped into plural groups. Starts of applying heat from the heating elements are set different between the groups. JP-A 3-39262 discloses an idea in which the time of applying heat to the heating elements is divided to plural sections, and the sections are changed over between the respective groups for application of heat energy. This is for the purpose of printing an image with a small capacity of the power source. The heating elements are alternately or cyclically driven between the groups. But the width of drive pulses is divided to plural smaller units. If the printing operation is effected at a high speed, the width of the drive pulses is decreased. Differences in the time of turning on and off the heating elements will remain in results of the printing in a form of irregularity in gradation reproducibility, which will be degraded remarkably.
SUMMARY OF THE INVENTION
In view of the foregoing problems, an object of the present invention is to provide a thermal printing method and a thermal printer with high fidelity in gradation reproduction of an image without irregularity in density.
Another object of the present invention is to provide a thermal printing method and a thermal printer in which occurrence of irregularity in the feeding speed and the density is prevented by reducing changes in the friction coefficient between the recording material and the heating elements.
In order to achieve the above and other objects and advantages of this invention, a thermal head has plural heating elements arranged in line in a main scan direction, the heating elements are supplied with at least one drive pulse while the thermosensitive recording material is conveyed in a sub scan direction crosswise to the main scan direction, for thermal recording to the recording material by one line. The heating elements are grouped into first and second groups. The drive pulse for the first group of the heating elements is determined by starting the drive pulse at a start of the one line. The drive pulse for the second group of the heating elements is determined by ending the drive pulse at an end of the one line.
In a preferred embodiment, the heating elements are arranged cyclically in the main scan direction in relation to the first and second groups.
The heating elements are arranged cyclically by repetition of a predetermined arranging pattern, the arranging pattern is constituted by n of the heating elements included in the first group, and n of the heating elements disposed adjacent thereto and included in the second group, and n≧1.
A number of heating elements included in the first group among the heating elements is substantially equal to a number of heating elements included in the second group among the heating elements.
Furthermore, first comparison data is generated for the first group of the heating elements, the first comparison data being predetermined to step up serially from a minimum. Second comparison data is generated for the second group of the heating elements, the second comparison data being predetermined to step down serially from a maximum. The at least one drive pulse comprises plural drive pulses. The first and second comparison data are compared with heating-element drive data of the one line, the heating-element drive data being determined in accordance with image data, so as to generate a train of the drive pulses.
Consequently the thermal printing method and thermal printer can have high fidelity in gradation reproduction of an image without irregularity in density.
In another preferred embodiment, the thermal head is supplied with at least one bias pulse and at least one image pulse, for thermal recording to the recording material by one line, the bias pulse applies bias heat energy directly short of coloring the coloring layer, and the image pulse applies image heat energy in accordance with coloring density. To drive the thermal head, the heating elements are grouped into first to Nth groups, where N≧2. First to Nth sub-line recording periods are set by dividing N into a line recording period adapted for recording of the one line. During a Kth of the sub-line recording periods, the bias pulse is applied to the heating elements of a Kth of the first to Nth groups, so as to apply the bias heat energy in the thermal head during any of the first to Nth sub-line recording periods. Directly before or directly after the Kth sub-line recording period and during the first to Nth sub-line recording periods, the image pulse is applied to the heating elements of the Kth group.
The heating elements are arranged cyclically in the main scan direction in relation to the first to Nth groups.
Consequently, an occurrence of irregularity in the feeding speed and the density is prevented by reducing changes in the friction coefficient between the recording material and the heating elements.
Moreover, the heating elements are arranged cyclically by repetition of a predetermined arranging pattern, the arranging pattern is constituted by n of the heating elements included in a Kth of the first to Nth groups, and n of the heating elements disposed adjacent thereto and included in a (K+1)th of the first to Nth groups, and n≧1.
Numbers of heating elements included in the first to Nth groups among the heating elements are substantially equal.
The thermal head is used with plural driver ICs, each one of the driver ICs is connected with a of the heating elements, for driving the a heating elements, and the a heating elements are included in one of the first to Nth groups.
The at least one coloring layer comprises first to third coloring layers arranged in sequence from a recording surface of the recording material, the first to third coloring layers are colorable respectively in first to third colors, and the first to third colors include yellow, magenta and cyan. The heating elements are arranged cyclically by repetition of a predetermined arranging pattern, the arranging pattern is predetermined by arranging at least N of the heating elements, and the at least N heating elements are respectively associated with the first to Nth groups. The arranging pattern is different between the first to third colors.
N=N
1
for the first color, N=N
2
for the second color, and N=N
3
for the third color, and N
3
<N
1
.
As an example of the preferred embodiment, the heating elements are grouped into first to fourth groups, the heating elements being arranged cyclically in the main scan direction in relation to the
Kokubo Hideyuki
Nishimura Tomoyoshi
Fuji Photo Film Co. , Ltd.
Le N.
Pham Hai C.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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