JP2006335009A - Thermal printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable a printing density to be controlled without spoiling the gradation in a gradation controlling type thermal printer. <P>SOLUTION: The thermal printer expresses a gradation by changing the printing density by the unit of a dot in such a manner that 4 bit tone data or 8 bit tone data or the like is converted into a plurality of continuous 1 bit data, and the 1 bit data is rewritten several times during a 1 dot printing process. In the thermal printer, a strobe signal is turned on/off synchronously with a latch signal which latches off every time when the 1 bit data is transferred to a shift register of the thermal printing head. At the same time, a means for controlling the duty ratio of the strobe signal is provided. The strobe pulse is turned on/off for each 1 bit data, and the duty ratio is controlled, and in this way, the overall printing density can be controlled without spoiling the gradation. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a thermal printer, and more particularly to a gradation control type thermal printer.

  In the thermal printer, the print density varies depending on the environmental temperature and the temperature of the thermal print head, and it is necessary to control the heat generation energy of the thermal print head to obtain an appropriate print density. Other than the gradation control type thermal printer capable of multi-tone photo printing, it is easy to automatically control the print density. Usually, the temperature is detected by a temperature sensitive element such as a thermistor, and 1 dot is detected according to the detected temperature. The print density is controlled by changing the duty ratio of the corresponding strobe signal (Patent Documents 1 and 2, etc.).

  Fig. 3 shows an example of print density control based on the duty ratio of the strobe pulse. When dot data is transferred to the shift register of the line-type thermal print head and latched by the latch circuit, transfer of dot data for one line is completed. In addition to the latch-off, the strobe signal is output and the heating element generates heat while the strobe signal continues, and printing for one line is performed.

  Fig. 3 (a) shows the case where the duty ratio of the strobe signal is 100%, and Fig. 3 (b) shows the case where the duty ratio of the strobe signal is 50%, and heat is generated in proportion to the duty ratio of the strobe signal. The heat generation energy of the element changes, and the printing density also changes according to the heat generation energy.

  On the other hand, a gradation control type that expresses multiple gradations by modulating the print density in dot units by representing one dot as multi-bit multi-gradation data such as 8 bits and controlling the energization time for each dot in multiple steps. The above technique cannot be applied to a thermal printer (eg, Patent Document 3).

  Fig. 4 shows a timing chart of a thermal print head that controls gradation by converting 4-bit 16-gradation data into 1-bit x 16-data as an example of gradation control. 16 bits of 1-bit data for one dot The lower part shows a latch signal that is turned on / off in synchronization with the data clock, the lower part shows a strobe signal for one dot, and the lower part shows the heat generation timing of the heating element.

Thus, during the printing process for one dot, for example, in 4-bit gradation control, 1-bit data is rewritten 16 times, and the gradation changes in proportion to the number of on-bits in 16 1-bit data. Therefore, the strobe signal must be continued during the print processing time for one dot. If the duty ratio of the strobe signal is reduced to less than 100%, some of a plurality of 1-bit data composing one dot will be discarded, and gradation expression as the data cannot be performed.
Japanese Patent Laid-Open No. 5-238043 JP 5-309860 (paragraph 0002) JP-A-5-008427

  Conventional gradation control type thermal printers are not equipped with means to control the overall print density without losing gradation according to the environmental temperature, the heat generation history of the thermal print head, and the like. There is a problem of changing. Therefore, a technical problem to be solved in order to improve the gradation accuracy of the gradation control type thermal printer arises, and the present invention aims to solve the above problem.

  The present invention is proposed in order to achieve the above-mentioned object, and converts image data expressing gradation for each dot by a plurality of bits into a plurality of continuous 1-bit data, and dot based on the 1-bit data. A latch signal that latches off each time 1-bit data is transferred to the shift register of the thermal print head in a thermal printer that expresses gradation by changing the print density in dots by controlling the heating element energization time in units. A thermal printer is provided which includes a means for controlling the duty ratio of the strobe signal by changing the duty ratio by turning on and off the strobe signal in synchronization with the strobe signal. Is.

  The present invention also provides the thermal printer configured to control the duty ratio in accordance with temperature information via a temperature sensitive element such as a thermistor and heat generation history information of the heat generation element.

  The present invention controls a duty ratio by turning on / off a strobe pulse for each 1-bit data in a thermal printer that expresses gradation by dividing 1-dot printing time and rewriting 1-bit data multiple times. With this configuration, the overall print density can be controlled without losing the gradation.

  The present invention converts image data expressing gradation for each dot by a plurality of bits into a plurality of continuous 1-bit data, rewrites the one-bit data a plurality of times during a one-dot printing process, In a thermal printer that expresses gradation by changing the print density according to the on / off ratio, the strobe signal is turned on in synchronization with a latch signal that is latched off each time 1-bit data is transferred to the shift register of the thermal print head, and By providing means for controlling the duty ratio of the strobe signal, it is possible to control the print density in the gradation control type thermal printer.

  FIG. 1 shows a thermal printhead drive circuit unit of a thermal printer, and 1 is a CPU that controls the entire thermal printhead drive circuit unit. Multi-bit gradation image data transferred from the host computer is read into the line buffer 2, and each dot constituting one line is converted into 1-bit data corresponding to the gradation by the multi-bit / 1-bit data conversion circuit 3. The data is written into the energization data buffer 4 and sequentially transferred to the shift register 10 of the thermal print head 9 in synchronization with the clock timing of the clock generator 5.

  Based on the clock timing of the clock generator 5, the latch signal generator 6 sets the thermal print head latch circuit 11 to the latch-off state when 1-bit data for one line of the thermal print head is transferred to the shift register 10. At the same time, the strobe signal generator 7 outputs a strobe signal in synchronization with the latch-off, and the power source 13 is energized to the heating element 12 to execute printing.

  When printing for one line is executed, 1-bit data for the next line is transferred from the energization data buffer 4 to the shift register 10 by the signal of the energization counter 8, and the 1-bit data of the shift register 10 is rewritten. Each time rewriting is completed, the latch circuit 11 is latched off by the latch-off signal, a strobe signal is output, the line-type heating element 12 is energized, and 1-bit data is rewritten a plurality of times during 1-dot printing. Gradation control is performed.

  Unlike the conventional thermal printer, in the thermal printer of the present invention, the CPU generates a strobe signal in synchronization with the data transfer frequency and the latch operation frequency. In other words, the strobe signal is generated each time 1-bit data is transferred and latched off, and the duty ratio of the strobe signal is controlled.

  Figure 2 shows the operation timing of a thermal print head that performs 16 gradation printing by rewriting 1-bit data per dot 16 times as an example, but even with 256 gradation processing (8-bit gradation), etc. The principle is the same. The number corresponding to the number of dots in the line direction (the number of heating elements) of the line-type thermal print head, that is, 1-bit data for one line is transferred to the shift register and latched. 1 line is printed when power is turned on.

 The strobe signal generation frequency matches the data transfer frequency of one line and the latch signal generation frequency, and the print density when the pulse width of the strobe signal is maximum (duty ratio 100%) as shown in Fig. 2 (a). Is the highest concentration. Then, the duty ratio is controlled in accordance with the feedback signal of the environmental temperature and the head temperature by a temperature sensitive element such as a thermistor, and the duty ratio decreases as the temperature rises. FIG. 2 (b) shows a state where the strobe signal has a duty ratio of 20%.

  Further, the duty ratio may be manually adjusted by an operation of a key or a dial. For example, if the initial duty ratio is manually set to 90%, the duty ratio can be set within a range from 90% to less during operation. The duty ratio is automatically controlled. In addition, if the heat generation history control is also performed, the duty ratio is gradually decreased according to the ON history of one heating element or the heating element and the left and right heating elements, and the level due to heat storage is increased. Tone modulation can be suppressed, and more accurate gradation representation can be obtained.

  In this way, in a thermal printer that expresses gradation by dividing the printing time of 1 dot and rewriting the data multiple times, the strobe pulse is turned on and off for each 1-bit data, and the duty ratio is controlled. Thus, the overall print density can be controlled without losing the gradation.

  The present invention is not limited to the above-described embodiment, and various modifications are possible within the technical scope of the present invention, and it is natural that the present invention extends to those modifications.

The block diagram of a thermal print head drive circuit. 4 is a timing chart of a one-dot printing operation of the thermal print head in the gradation control type thermal printer of the present invention. The conventional example is shown, and (a) and (b) are timing charts of the 1-dot printing operation of the thermal print head, respectively. The timing chart of the 1 dot printing operation of a gradation control type thermal print head which shows a conventional example.

Explanation of symbols

1 CPU
2 line buffer
3 Multi-bit / 1-bit data conversion circuit
4 Energized data buffer
5 Clock generator
6 Latch signal generator
7 Strobe signal generator
8 Energizing counter
9 Thermal print head
10 Shift register
11 Latch circuit
12 Heating element
13 Power supply

Claims (2)

By converting the image data expressing the gradation for each dot with a plurality of bits into a plurality of continuous 1-bit data, and controlling the heating element energization time in units of dots based on the 1-bit data, the print density is set in dots. In a thermal printer that expresses gradation by changing the
A means for turning on and off the strobe signal in synchronization with a latch signal that is latched off each time 1-bit data is transferred to the shift register of the thermal print head, and for controlling the duty ratio of the strobe signal, and changing the duty ratio; A thermal printer characterized in that the printing density is controlled by the above. The thermal printer according to claim 1, wherein the duty ratio is controlled in accordance with temperature information via a temperature sensitive element such as a thermistor and heat generation history information of the heat generation element.

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