JPH03230966A - Thermal printer - Google Patents

Abstract

PURPOSE:To correct variation of printing density in a feed direction by heat accumulation by a method wherein correction for a printing signal is performed in a form corresponding to variation in temperature peculiar to each component of a thermal head. CONSTITUTION:In order to correct a heat accumulation effect due to concurrent heating, a concurrent heating data storage part 3 varies concurrent heating data according to a line data from a line counter 7 which counts a line pulse. That is, a concurrent heating period is decreased quickly after start of printing and thereafter, becomes almost constant. Besides a gradation pulse length data gives a fixed printing period to each gradation, and appears in a printing data as an electrification period of each gradation. In order to correct a heat accumulation effect due to this gradation printing, a correction data preparation table 14 varies the gradation pulse length data which a reference pulse length table 13 generates according to a counting value of a gradation counter 10, depending on a temperature data which a temperature data preparation circuit 2 generates according to output of a temperature measuring thermistor 22 detecting the line data from the line counter 7 and temperature of a thermal head.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention 1. Field of the Invention The present invention relates to a thermal printer, and more particularly to a thermal printer that corrects changes in print density due to heat storage effects.

[Prior art] Conventional thermal printers of this type include a thermal printer (Japanese Patent Application Laid-Open No. 11374/1983) that uses heater control to maintain a constant density, and a thermal printer that uses preheating before starting printing to reduce the rise in the rising part. A thermal printer (Japanese Unexamined Patent Application Publication No. 49867/1983) is known that attempts to achieve uniform density.

[Problems to be Solved by the Invention] In the printer disclosed in JP-A-60-11374, when adjusting the printing density by controlling a heater that forcibly heats the thermal head, it is difficult to adjust the print density from temperature detection. The reaction speed until the heating element is actually heated is slow, and there is a delay in the rise in print density that can be seen at the start of printing,
It is difficult to deal with the increase in density due to heat accumulation that occurs in the latter half of printing.

In addition, with the method disclosed in Japanese Patent Application Laid-open No. 61-49867, in which a preheating pulse is applied to the heating element before printing starts, the delay in the rise at the start of heat generation can be corrected, but the concentration due to heat accumulation. It is not possible to prevent second elevation.

The present invention has been made in view of the above problems, and an object of the present invention is to correct changes in print density due to heat accumulation.

[Means for Solving the Problems] In order to achieve this object, the thermal printer of the present invention outputs an image onto a recording medium by moving a thermal head relative to the recording medium in the sub-scanning direction. Thermal printers that form images include a temperature measuring element that detects the temperature near the heating element of the thermal head, a pulse width control means that controls the printing pulse width in response to the temperature measured by the temperature measuring element, and the current technology. The image data processing apparatus is configured to include a calculation means for correcting the value of the current image data by taking into account the history of past image data.

[Operation] In the thermal printer configured as described above, the print signal is corrected in response to temperature fluctuations specific to each component of the thermal head. Thereby, changes in print density in the sub-scanning direction due to heat accumulation can be corrected.

[Example] Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of a thermal printer according to the present invention.

In FIG. 1, according to address data from an address counter 8, image data is sent as parallel data from a data storage section 9 to a data comparison circuit 12 via a thermal history data calculation circuit 11. This data is data comparison circuit 1
2, it is compared with the Curran I data from the gradation counter 10, and is stored in the shift register 1 as serial image data.
Sent to 7. The output of the shift register 17 is latched by the latch circuit 16 by the carry signal of the address counter 8, and the output of the latch circuit 16 is sent to the NOR circuits G1 and G.
2,... Can be supplied to Gn as data signal B.

In the NOR circuits Gl, G2, ... Gn, a strobe signal A for setting the print pulse width supplied from the print pulse generation circuit 15 and a data signal B from the latch circuit 16
A transistor drive signal C obtained by ANDing the inverted signals of each of the transistors is output to the bases of the transistors T1, T2, . . . Tn. Heat generating resistors R1 to Rn are connected to the collectors of the transistors T1, T2, φ...Tn, respectively, and when the transistors T1, T2,..., Tn are turned on, the heat generating resistors R1 to Rn are connected to the collectors of the transistors T1, T2, φ...Tn. Printing is performed by generating heat. In Fig. 2, strobe signal A1
A timing chart of data signal B1 and transistor drive signal C is shown. The strobe signal A and the data signal B are corrected as described later, and changes in print density due to heat storage effects can be corrected.

Next, with reference to FIG. 3, density fluctuations in the sub-scanning direction (direction from the first line to the last line of the page to be printed) when the same data is printed in solid form will be explained.

The thermal head of the thermal printer is constructed such that a heating resistor 25 is formed on a ceramic base 24, and the ceramic base 24 is fixed with an aluminum base 23, as shown in a cross-sectional view in FIG. 3(a). The heating resistor 25 corresponds to the heating resistors R1 to Rn in FIG.

The heater 21 in FIG. 3(a) is used to heat the aluminum base 23, and the fan 20 is used to cool the aluminum base 23.

The temperature of each part of the thermal head changes with its own time constant with respect to heat storage.

That is, each part P1, R2 of the aluminum base 23, ceramic base 24, and heating resistor 25 shown in FIG. 3(a)
, and R3 each exhibit a temperature change with a unique time constant, and these temperature changes affect the concentration change in a combined manner. When the density correction is not performed, the density increases as the number of printed lines increases, as shown in FIG. 3(b).

By the way, temperature changes specific to each part of Pl, R2, and R3 are shown in FIGS. 3(c) to 3(e), respectively. In the 21st part, there is almost no temperature change between the print start position and print end position. On the other hand, in the R2 part,
The temperature gradually rises as time passes, and in the 23rd part, the temperature rises suddenly at the start of printing, and then becomes almost constant.

Among these, temperature fluctuations of 11 parts are corrected by temperature management using the heater 21 for heating and the fan 20 for cooling. Temperature changes at position P2 are dealt with by correction using strobe signal Δ (see FIG. 2). The strobe signal A is generated by the printing pulse generation circuit 15 in response to the reheating data sent from the reheating data storage section 3 and the gradation pulse length data sent from the reference pulse length table 13 via the correction data creation table 14. Created. The reheating data corresponds to the amount of heat required for the lowest gradation printing to be applied to the heating resistor 25, and appears in the print signal as the reheating period shown in FIG. 2(a).

In order to correct the heat storage effect due to this reheating, the reheating data storage section 3 stores the reheating data in a fourth manner according to the line data from the line counter 7 that counts line pulses (LP).
Change as shown in the figure.

That is, the reheating period is suddenly reduced after printing starts, and thereafter remains almost constant. Due to heat replenishment during this reheating period,
The print density near the lowest gradation is kept constant.

On the other hand, the gradation pulse length data gives a unique printing period for each gradation, and appears in the print signal as the energization period for each gradation shown in FIG. 2(f). In order to correct the heat storage effect due to this gradation printing, the correction data creation table 14 is such that the reference pulse length table 13 is
The gradation pulse length data generated corresponding to the count value of
The temperature data generated by the temperature data generation circuit 2 corresponds to the output shown in FIG.

The operation of the correction data creation table 14 will be explained with reference to FIG.

As shown in FIG. 5(a), correction data creation table 1
4 is composed of two tables 14a and 14b. The contents of the table 14a are shown in FIG. 5(b). Further, the contents of the table 14b are shown in FIG. 5(c).

The table 14a creates intermediate data for the temperature data. Intermediate data increases as temperature data increases. This relationship between temperature data and intermediate data changes depending on the line data. That is, as the line data increases, the intermediate data values for the same temperature increase. This is to remove the element of temperature increase only due to supplementary heat included in the temperature data. The relationship between temperature data and intermediate data can be set for each color, and intermediate data corresponding to each color is generated in response to a color code.

The table 14b creates corrected gradation pulse length data for the reference gradation pulse length data. The corrected grayscale pulse length data is increased in proportion to the reference grayscale pulse length data. Further, as the intermediate data increases, the corrected gray scale pulse length data for the same reference gray scale pulse length data is decreased.

Assume that when the intermediate data value is the intermediate value MID, the following relationship holds true: standard grayscale pulse length data SD9- = corrected grayscale pulse length data RD. At this time, the reference gradation pulse length data generated from the reference pulse length table 13 is sent to the print pulse generation circuit 15 without being corrected, and printing energization is performed with the gradation pulse width in accordance with the reference value.

next, Intermediate value data value> Intermediate value MID When , Standard gradation pulse length data SD 〉Corrected gradation pulse length data RD Therefore, the gradation pulse width decreases from the reference value.

Also, Intermediate value data value <Intermediate value MID When , Standard gradation pulse length data SD <Corrected gradation pulse length data RD Therefore, the gradation pulse width increases from the reference value.

With the combination of the above tables 14a and 14b, the gradation pulse width is corrected in response to the parameters of the temperature data, line data, and color code 0-, and the temperature fluctuation in the 22 section shown in FIG. 3 is corrected. I do.

The temperature change at section 23 shown in FIG. 3 is dealt with by correcting the image data signal. The image data output from the data storage section 9 passes through a thermal history data calculation circuit 11 having the configuration shown in FIG. 6(a), for example. The image data that has been output from the data storage section 9 is input to the table 11a through two routes.

On the other hand, data D (Fig. 6(b)) is directly stored in table lla.
), and the other is a low-pass filter (LPF)
It is input as data E to table Ila via llb. As a result, for example, as shown in FIG. 6(b),
Data D that changes from a predetermined value to another predetermined value and then returns to its original value becomes data E with blunted rising and falling edges, as shown in FIG. 6(C). Table lla creates data F (FIG. 6(d)) that is corrected from data D and data E in a direction that emphasizes data change portions.

Therefore, for example, when data D is data of a predetermined value from beginning to end (data for solid printing) as shown in FIG. 6(e), data E and F are as follows.
As shown in FIGS. 6(f) and (g), respectively.

Table lla creates correction data F by calculating data F = (data D - data E) G + data D for a certain gain value G setting.

In this way, the image data is corrected by passing it through the thermal history data calculation circuit 11, thereby correcting the print density fluctuation caused by the unique temperature fluctuation component in the 23rd section shown in FIG. 3(e).

As described above, it is possible to correct the unique temperature fluctuation components at each portion of Pl, P2, and P3 shown in FIG. 3, and suppress fluctuations in print density.

The density measurement results of the print samples after this correction are shown in FIGS. 7 to 9. The horizontal axis represents the number of lines in the sub-scanning direction, and the vertical axis represents the optical reflection density. The samples are solid prints using the same data.

-12= FIG. 7 shows the density measurement results of the printed sample when only the temperature of the aluminum base 23 was controlled. 8th
The figure shows the density measurement result of the print sample when the strobe signal A is corrected using the correction data creation table 14.

FIG. 9 shows the density measurement results of the printed sample after further correction by the thermal history data calculation circuit 11. The number of gradations was 256 in all cases, and four colors of sublimation ink, yellow, magenta, cyan, and black, were printed in layers.

According to the embodiments described above, concentration fluctuations due to the heat storage effect of the thermal head can be corrected for each element of temperature fluctuation, and the correction effect is large.

Further, since the correction is performed by processing the printing pulses using a table in memory, the circuit is simplified, and the correction can be easily adjusted by rewriting the data in the table.

[Effects of the Invention] As described above, according to the thermal printer of the present invention, the print signal is corrected in accordance with the temperature fluctuations specific to each component of the thermal head, so that the side effects caused by heat accumulation are reduced. It becomes possible to correct changes in print density in the scanning direction on a page-by-page basis.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the thermal printer according to the present invention, and FIGS. 2(a) to (C) are waveform diagrams illustrating the operation of the embodiment of the thermal printer according to the present invention. FIGS. 2(d) to (f) are partially enlarged views of FIGS. 2(a) to (c), and FIG. 3(a) is a cross-sectional view of the thermal head. ) is a characteristic diagram explaining the change in density of the thermal head when not corrected, Figure 3(c)
Characteristic diagrams illustrating temperature changes at each position of the thermal head, FIG. 4 a characteristic diagram illustrating data contents of the reheating data storage section, and FIG. 5(a) depicting correction data creation. Figure 1099 and Figure 5 (
b) and (C) are characteristic diagrams explaining the operation of the correction data creation table 14, FIG. 6(a) is a block diagram explaining the configuration of the thermal history data calculation circuit, and FIG.
-) to (g) are waveform diagrams explaining the operation of the thermal history data calculation circuit, and Figs. 7 to 9 are density characteristic diagrams showing the operation results of an embodiment of the υ--multi printer according to the present invention. It is. 2... Temperature data creation circuit, 3... Reheating data storage section, 4+ 5+ 6... Input terminal, 7... Line counter, 8... Address counter, 9... Data storage section, 10 ... Gradation counter, 11 - Heat history data calculation circuit, 12 - Data comparison circuit, 13 - Reference pulse table, 14 - Correction data creation table, 15 -
・Print pulse generation circuit, 16...Latch circuit, 17...
Shift register, 20...Fan, 21 - Heater,
22... Thermistor for temperature measurement, 23... Aluminum heath, 2
4...Ceramic base, 25...Fever low antibody.

Claims (1)

[Claims] In a thermal printer that forms an output image on a recording medium by moving a thermal head relative to the recording medium in a sub-scanning direction, a temperature measuring element that detects a temperature near a heating element of the thermal head. a pulse width control means for controlling a printing pulse width in accordance with the temperature measured by the temperature measuring element; A thermal printer having calculation means for correcting values.