JPH0323956A - Multivalue drive device of thermal head - Google Patents

Abstract

PURPOSE:To enable recording density level to be accurately controlled over an extensive ambient temperature range by generating a recording pulse signal to be applied to a thermal element in accordance with a signal of recording density, pulse width value and misalignment value. CONSTITUTION:A drive LSI circuit transfers misalignment value D to a latch 1 and density gradation level value G to a latch 2 prior to the start of recording in each line, and a counter counts a clock for application pulse. Consequently, the width of an application pulse is equivalent to the sum of 'time T0 required for a counter output to coincide with the density gradation level value G after the initialization of recording in a single line' and 'time D'. FF is set by a line start signal which indicates the initiation of recording in a single line and then is reset by a comparator output which detects the coincidence of the counter output with the density gradation level value G to obtain the T0. Next, if the misalignment value is 'positive', reset timing is delayed by D, and if the value is 'negative', the set timing of FF is delayed and consequently, a FF output becomes a specified application pulse.

Description

[Detailed Description of the Invention] [Summary] This invention relates to a multi-value drive device for a thermal head in a thermal printer, and is capable of accurately controlling each density level of halftones to be recorded over a wide thermal head ambient temperature range, regardless of the recording density characteristics of the recording medium. In a thermal printer that applies a thermal recording signal to a heating element of a thermal head and continuously controls the recording density on a recording medium according to the heat generation temperature of the heating element, A recording pulse width table that uses temperature as a parameter and stores the width of a recording pulse that should be applied to the heating element in order to obtain a predetermined halftone recording density on the recording medium; a conversion means for converting into a pulse width value and deviation amount at the median value of;
(1) and (2) recording pulse generating means for generating a recording pulse signal to be applied to the heating element in accordance with the density signal to be recorded, the pulse width value, and the deviation amount.

[Industrial application field]

The present invention relates to a multi-value driving device for a thermal head in a thermal printer, and in particular, to accurately control each density level of halftones to be recorded over a wide range of ambient temperature of the thermal head, regardless of the recording density characteristics of the recording medium. The present invention relates to a thermal head multi-value drive device capable of.

Thermal printers that use heat to record information such as characters include a thermal recording method and a thermal transfer recording method. The former is a method that records by bringing the thermal head into direct contact with a recording paper that changes color due to heat and heating the heating element of the thermal head to change the color of the recording paper, while the latter heats the ink with the thermal head to melt or melt the ink. This is a method of sublimating and transferring it to recording paper for recording. Furthermore, based on the heating element scanning method, there are two main types: line recording method and serial recording method. A line recording method is used for high-speed recording, and a serial recording method is used for low-speed recording.

In these thermal printers, there is a need for means for compensating for recording density fluctuations caused by changes in the ambient temperature of the thermal head.

[Conventional technology]

FIG. 6 shows an outline of a line recording type thermal transfer recording device, and FIG. 7 shows the structure of a thermal head.

The thermal head 51 has an ink sheet 52 and a recording paper 53.
It faces the platen 54 via. ink sheet 5
The ink sheet 52 is heat-fusible, and the ink sheet 52 is heated by the thermal head 5■.
The ink No. 2 is melted and transferred to the recording paper 53, and recording is performed. The thermal head 51 has heating elements for one line arranged along the direction perpendicular to the plane of the paper, and records for one line are performed almost simultaneously. When one line of recording is completed, the recording paper 53 and the ink sheet 52 are simultaneously transported in the direction of the arrow.

The thermal head 51 has a multilayer structure as shown in FIG. That is, a glaze layer 64, a heating element 63, and an electrode 62 are provided in a layered structure on a substrate 65, and a protective layer 61 is provided on the surface that contacts the recording paper. In addition,
66 is a heat sink.

Such thermal heads accumulate heat within them.

That is, first, a high-speed heat accumulation phenomenon on the order of milliseconds in the glaze layer 64; second, a medium-speed heat accumulation phenomenon on the order of seconds in the glaze layer 64 and the substrate 65; and third, a heat accumulation phenomenon on the order of seconds at the glaze layer 64. , there is a slow heat accumulation phenomenon on the order of minutes in the entire thermal head including the substrate 65 and the heat sink 66. The first of these poses a major problem when characters and the like are recorded in binary format at high speed. Normally, the line recording period is about 1 to 2 milliseconds, which is shorter than the time constant of high-speed heat storage, so it is greatly affected. However, in the halftone recording that is the object of the present invention, the line recording period is usually 30 milliseconds or more, and even the fastest one is more than ten milliseconds, so the first high-speed heat accumulation can be ignored.

In halftone recording, the influence of the second and third heat storage phenomena is large, and especially when the line recording cycle is as fast as 10-odd milliseconds, highly accurate compensation for the second medium-speed heat storage is essential. .

This heat accumulation is a phenomenon inside the thermal head board, so it cannot be detected with high precision from the outside with a sensor, etc.
As already proposed, a method of predicting and compensating for the amount of heat storage based on the history of recorded data using calculations is effective.

Regarding the third type of slow heat storage, since it is a slow phenomenon on the order of minutes, it can be detected with high precision using a temperature detection element (thermistor, etc.) attached to the heat sink, and the sum with the second predicted result can be integrated. By using it as the amount of heat storage, the second and third can be corrected at the same time. The influence of changes in the ambient temperature of the thermal head is also included as a third factor, and is corrected with high precision.

Specifically, the relationship between the pulse width applied to the thermal head and the recording density changes depending on the amount of heat storage, as shown in FIG. 3, and the density recorded for the same pulse width increases with the amount of heat storage. On the other hand, if the applied pulse width is changed according to the amount of heat storage (5) (6), for example, the heat storage temperature is T.

By setting to, TI, t1, T2, t2, the recording density can be set to D8 regardless of the amount of heat storage.

In this way, by using the medium-speed heat storage prediction calculation circuit and the thermal head heat sink temperature detection circuit together, and increasing or decreasing the thermal head application pulse width according to the calculated total heat storage amount, all the heat storage in the thermal head can be eliminated. Can be corrected with high precision.

[Problem to be solved by the invention]

However, in order to realize this, there is a problem in that, as described below, a thermal head having an extremely large number of data input lines and a data transfer frequency of each data line being extremely high is required.

Taking the case of the most common A4 size with a dot density of 300 tot/inch as an example, the number of heating elements in one line of the thermal head is 2560. The drive LSI mounted on the thermal head latches the data and directly drives the heat generating elements (hereinafter referred to as drive LSI).One drive LSI can drive 64 heat generating elements, so for 2560 heat generating elements, 40 A number of driving LSTs are installed. Data transfer frequency is 4M
flz, and the time required to serially transfer data for 2560 heating elements is
bit) then 2560X 1/ (4 X106) = 0.64X10
-3, which is sufficiently smaller than the line recording period. Therefore, data for all heating elements can be transferred serially. That is, 40 driving LSIs were connected in series as shown in FIG. 8, and the data power line to the thermal head could be reduced to one.

However, in halftone recording, the data is usually 4 to 6 bits (
16 to 64 gradations), and in order to stably record halftones, it is necessary to precisely control the applied pulse width for each heating element according to the amount of heat storage at medium and low speeds. Since the heat accumulation compensation characteristics are completely different depending on the recording medium (thermal paper, melt type thermal transfer ink sheet, sublimation type thermal transfer ink sheet), heat accumulation compensation processing cannot essentially be performed by the driving LSI on the thermal head. Further, the heat storage prediction calculation is very complicated and cannot be processed by a driving LSI due to the circuit scale.

Therefore, the thermal head control circuit determines the pulse width of each dot so that the recorded density is a predetermined value (usually 16 to 64 dots) regardless of the amount of heat storage, generates a pulse, and sends it to the thermal head. A method is used to transfer the information to

Specifically, the method shown in FIG. 910 has been conventionally used. As shown in the figure, in order to make the pulse width resolution as high as possible, a dedicated data input line is prepared for each driving LSI. That is, 40 data power lines are required. At a data transfer frequency of 4 MHz, data is serially transferred to 64 heating elements driven by one LSI. The time required for one transfer is 64X 1/ (4 XIO6) - ↓ 6X]. 0-'6
becomes. Normally, even when recording 64 gradations with a line recording period of 15 ms, sufficient accuracy can be obtained with this method, since heat accumulation can be compensated with high precision with a time resolution of 20 to 30 μs. However, because the number of data signal lines is as large as 40, and it is necessary to guarantee a high data transfer frequency of 4 Mtlz for each line, there is a problem that the yield of the thermal head is reduced and it becomes very expensive.

Further, the signal waveform transferred to the thermal head is complicated as shown in FIG. 10, and there is a problem in that the thermal head control circuit is also complicated.

The object of the present invention is to provide a thermal head multi-value drive that can accurately control each density level of the halftone to be recorded over a wide range of thermal head ambient temperature ranges based on the amount of pulse width deviation, regardless of the recording density characteristics of the recording medium. The goal is to provide equipment.

[Means to solve the problem]

According to the present invention, in a thermal printer that applies a thermal recording signal to a heating element of a thermal head and continuously controls the recording density on a recording medium based on the heat generation temperature of the heating element, the ambient temperature of the heating element is set as a parameter. a recording pulse width table (A) storing the width of a recording pulse to be applied to the heating element in order to obtain a predetermined halftone recording density on the recording medium; a converting means (B) for converting into a pulse width value and deviation amount at the median value; and generating a recording pulse signal to be applied to the heating element according to the density signal to be recorded and the pulse width value and deviation amount. Recording pulse generating means (C
) and.

[For production]

16 to 16 to over the entire operating temperature range of thermal printers
In order to perform halftone recording of 64 gradations, more than several thousand types of pulse width data are required. However, since the temperature of the thermal head changes overall, only 128 to 1024 of them are required at the same time, and it is sufficient to have at most 10 types of temperature. In such a narrow temperature range, the applied pulse width corresponding to each gray level varies directly with temperature and gray level;
All data can be generated from data in the middle of the temperature range.

The present invention focuses on such points and provides pulse width information (16 to 64 gradations) corresponding to each gradation level for a certain amount of heat storage.
is transferred to the thermal head as shown in Fig. 2 on one signal line as shown in Fig. 3, and the thermal head corrects this signal according to the gradation level to generate an applied pulse. By reducing the number of data signals (from 40 to 3) and the data transfer frequency (from 4 Mllz to several KHz), the yield of thermal heads can be significantly improved. In addition, the data transferred to the thermal head includes the "pulse width for a certain heat storage amount" data that is common to each heating element, and the "gradation level," data of each heating element.
and the amount of deviation from the pulse width value in the amount of heat storage.The former is only one type, and the latter only needs to be serially transferred for all heating elements, and no unnecessary data format conversion is required. The head control circuit has a very simple structure.

(l1) (12) The drive LSI needs to receive the signals shown in Figure 3 and generate pulses to be applied to each heating element, so it is somewhat complicated, but the same circuit can be used for 40 circuits per printer. The mass production effect is significant because it also uses the same material, and the cost increase is almost negligible.

〔Example〕

In the block diagram of the embodiment shown in FIG. 2, the circuit diagram and time chart of the clock generation circuit for applied pulses are shown in FIGS. The circuit diagram and time chart are shown in Figures 5(a) and (b).

First, for the applied pulse clock generation circuit l1 shown in FIG. 2, a reference clock corresponding to the required resolution of the applied pulse width is prepared as shown in FIG. The number of output pulses of the clock is multiplied by a counter 2. The interval between each pulse of the applied pulse clock is expressed by the number of reference clocks (hereinafter referred to as
(denoted as time) are stored in the ROM in order from address 0, and if the count 2 output is used as the address, the ROM
The output is the time at which the applied pulse clock should be output.

Since the output of the counter 1 is the time, the clock for application pulses can be obtained by detecting the coincidence between this and the ROM output. In order to adjust the waveform, the comparator output and the reference clock are input to the AND gate in the circuit shown in FIG. 4(a).

In addition, in Figure 2, all necessary original clocks (128 to
024 type) is prepared, and the pulse width at the median value is selected from among them according to the variable range of the amount of heat storage at each point, but in this example, it is necessary to prepare all the original clocks. Instead, only the circuit shown in FIG. 4(a) is prepared, and the upper address of the ROM is switched according to the amount of heat storage.

Next, the drive LSI equipped with the thermal head shown in Fig. 5(a)
In this circuit, first, before starting recording of each line, the shift amount D1 is transferred to latch 1 and the gradation level value G is transferred to latch 2 via the data line (1 bit) (13) (↓4). Data lines are connected serially for all LSIs.

The counter counts the clocks for applied pulses.

Therefore, the width of the applied pulse is the sum of "time T from the start of recording of the l line until the count output matches the gradation level value G" and "time D."

First, by setting the FF with a line start signal indicating the start of recording one line and resetting it with a comparator output that detects the coincidence of the count output and the gradation level value G, To can be obtained. Next, if the amount of deviation is positive, the reset timing is delayed by D, so that the FF output becomes the desired applied pulse. If the amount of deviation is negative, the reset timing delay amount cannot be made negative, so conversely, F
By delaying the cent timing of F, the width of the applied pulse can be shortened by D. As a result, the FF output becomes the desired applied pulse.

In the circuit of FIG. 5(a), the deviation iD and the human output signals of the selector 1.2 and FF are as follows, and the operation described above can be obtained.

〔Effect of the invention〕

As explained above, according to the present invention, the recording density level can be adjusted over a wide ambient temperature range, regardless of the recording density characteristics of the halftone recording medium used, without increasing the data signal line of the thermal head and the data transfer frequency. can be precisely controlled over the entire range.

(■5) (1G) As a result, it becomes possible to construct a high-quality image printer at low cost without density fluctuation or color shift.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the principle structure of the present invention, FIG. 2 is a block diagram of an embodiment of the present invention, FIG. 3 is a diagram showing the relationship between the applied pulse width and the recording density, and the relationship between the applied pulses. Figure (a) is a block diagram of one embodiment of a clock generation circuit for applied pulses, Figure 4 (b) is a time chart of Figure 4 (a), and Figure 5 (a) is a block diagram of an LSI equipped with a thermal head. 5(b) is a time chart of FIG. 5(a), FIG. 6 is a schematic diagram of a thermal transfer recording device using a line recording method, FIG. 7 is a structural diagram of a thermal head, and FIG. 8 is a diagram of a thermal head. FIG. 9 is a data input line connection diagram of the thermal head, FIG. 9 is a data input line connection diagram of the thermal head during conventional multi-value driving, and FIG. 10 is a signal waveform diagram of the data input line in FIG. (Explanation of symbols) A... Recording pulse width table, B... Pulse width, deviation amount conversion means, C... Pulse generation means, D... Thermal head, 11... Clock generation circuit for applied pulses .

Claims (1)

[Claims] 1. Applying a thermal recording signal to a heating element of a thermal head,
and a thermal printer in which the recording density on the recording medium is continuously controlled by the heat generation temperature of the heating element, wherein the ambient temperature of the heating element is used as a parameter to obtain a predetermined halftone recording density on the recording medium. a recording pulse width table (A) that stores the width of the recording pulse to be applied to the heating element; and a conversion means (B) that converts the recording pulse width value into a pulse width value and deviation amount at the median of the ambient temperature range. , a recording pulse generating means (C) for generating a recording pulse signal to be applied to the heating element according to the density signal to be recorded, the pulse width value and the deviation amount; Head multivalue drive device.