JPS60151074A - Thermal head driving circuit - Google Patents

Abstract

PURPOSE:To prevent trailing or printing of broken images from occurring, by a method wherein the width and the repetition period of an impressed pulse for driving each unit heating element of a thermal head is determined in accordance with the heat accumulation level of the head, thereby controlling the temperature of the unit heating element. CONSTITUTION:Predetermined data 23, 24 read from a 6-line buffer 12 and an interval memory 18 are supplied to a calculating circuit 25 for the heat accumulation level to calculate the heat accumulation level of each unit heating element of the thermal head. A calculating circuit 22 for a heating element driving pulse width (Ti) calculates the driving pulse width (Ti) for each unit heating element, and the Ti data 32 obtained by the calculation are supplied to a thermal head controlling circuit 14 to be used as printing information. A period-discriminating circuit 34 in a calculating circuit 21 for the heating element driving conditions calculates the repetition period T, and the data 37 obtained by the calculation are supplied to the circuit 14 to control the repetition period T of printing.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thermal head drive circuit used in a thermal recording device or a display device using a magnetized latent image.

[Prior art]

The thermal head, which is formed by arranging a large number of unit heating elements usually in rows, can selectively cause these unit heating elements to generate heat in accordance with image information. The heat pulses thus generated are used to record an image in a thermal recording device or a thermal transfer recording device, and are used to form a magnetized latent image in some types of display devices.

By the way, since recording devices and display devices using thermal heads perform recording or display (hereinafter simply referred to as recording) using thermal energy, if there is an excess or deficiency in this energy, it will affect the image quality. It will affect you. Therefore, various types of thermal head drive circuits have been proposed in the past that control the heat generation temperature of each unit heating element by changing the time width and voltage value of the drive pulse applied to each unit heating element.

As an example, FIG. 1 shows the operation of a circuit that controls the width of a drive pulse. Among them, Δ in the figure shows the change in the heat generation temperature of the unit heating element. The temperature of the unit heating element rises periodically by the applied pulse 11, which is not shown in FIG. The repetition period of the applied pulse 11 is T. However, the application time width is different, and the maximum temperature T MAX of the unit heating element is controlled to always be a predetermined value.

However, with such conventional temperature control, heat accumulation in the thermal head may progress temporarily.

In such a case, even if the time width of the applied pulse 11 is controlled, the temperature at the pulse application starting point 12 of each period increases. As a result, a phenomenon occurs in which each unit heating element is maintained at a considerably high temperature even in a section where power supply to the thermal head is stopped. In such a section 14, even a slight temperature change causes printing to occur even in the background area, which is not normally printed, resulting in so-called "collapse". Furthermore, in a recording apparatus using a thermal transfer recording method, not only the ink in the printed area but also the surrounding ink is transferred to the recording paper in a trailing manner, resulting in so-called paper trailing. Such "collapse" and "tailing" occur at a repetition period T. This can be prevented by selecting a larger value than a certain value.

However, in this case, it is impossible to achieve high-speed recording and high-speed display. That is, in the current recording devices or display devices, it has been insufficient to realize heat storage correction aimed at high speed and high image quality.

[Purpose of the invention]

In view of the above circumstances, an object of the present invention is to provide a thermal head drive circuit that can sufficiently control cooling of a thermal head.

[Structure of the Invention] In the present invention, the heat storage level of the thermal head is calculated, and the width of the applied pulse and the repetition period of the applied pulse for driving each unit heating element of the thermal head are determined according to this level. As a result, the temperature of the unit heating element is appropriately controlled, and trailing and crushing are effectively prevented.

〔Example〕

The present invention will be described in detail below with reference to Examples.

Outline of Circuit FIG. 2 shows an outline of the thermal head drive circuit of this embodiment. A recording apparatus equipped with this thermal head drive circuit is designed to perform recording using a rask scan method. One line (1 line) from a data source (not shown)
The latest 6 lines of the image information 11 sent for each rask are sequentially written into the 6-line buffer 12.

On the other hand, a thermal head control circuit 14 that controls the driving of the thermal head outputs a line synchronization signal 15 every time recording of one line is started. The line synchronization signal 15 is input to the interval counter 16,
The recording intervals of each line are counted. The interval data 17 thus obtained is supplied to an interval memory 18, where the latest six lines of data are also stored.

Of the image information 11 written in the 6-line buffer 12, the latest one line of image information 19 is supplied to the heating element drive pulse width calculation circuit 22 in the heating element drive condition calculation circuit 21, and is used as information for printing. used as. Further, predetermined data 23 and 24 read from each of the 6-line buffer 12 and the interval memory 18 are supplied to a heat storage level calculation circuit 25, and the heat storage level of each unit heating element of the thermal head is calculated. X and data 26 as a result of this calculation become input data to the heating element drive pulse width calculation circuit 22. This heating element drive pulse width calculation circuit 2
2, temperature data 27 from the thermistor which will be explained after being placed on the substrate of the thermal head, resistance value data 28 representing the resistance value of each unit heating element from the thermal head, and further from the thermal history memory 29. The thermal history data 31 is manually input. The heating element driving pulse width calculating circuit 22 calculates the driving pulse width of each unit heating element from the above various data.

The T1 data 32 obtained as the calculation result is supplied to the thermal head control circuit 14 and used as print information. This T data 32 is also supplied to the thermal history memory 29, where the thermal history data 31 is created with a time delay of one line.

The heating element drive condition calculation circuit 21 is provided with a period determination circuit 34 for determining the repetition period of printing. The cycle determination circuit 34 determines the repetition cycle based on three types of data: X, data 26, temperature data 27, and thermal history data 3100. The cycle determination data 35 as the determination result is supplied to a cycle calculation circuit 36, and a repetition cycle T is calculated. The T data 37 as the calculation result is supplied to the thermal head control circuit 14, and the printing repetition period T is controlled.

Next, the main parts of the device will be explained in detail.

Heat storage level calculation circuit First, the calculation of the heat storage level calculation circuit 25 will be explained.

The heat storage level calculation circuit 25 is a part that calculates the heat storage state of each unit heat generating element by taking into consideration the recording interval.

The principle of calculation will be explained based on FIG. The data row L1 located at the bottom in the figure represents data on the line to be recorded from now on. Also, the data string 1 above this. ．． 2 represents data that is one line past in time. Similarly, the topmost data string L6 represents data from the past five lines. Each of these data is stored in a 6-line buffer 12.

<Direct heat generation and interval heat storage of unit heating elements> Now, in the data string L1, arbitrary data D is shaded in the figure. Focus on. This data D. corresponds to the unit heating element for which printing processing is to be performed.

In this case, a total of 11 pieces of data D are hatched in the figure.
2, D3, D7-D9, DI4-D16, DI
11 to D21 are used to calculate the thermal history when the recording interval is short based on the pulse width when printing was performed in the past. In this thermal head drive circuit, three intervals of 2.4 msec/line, 3.6 msec/line, and 4.8 msec/line are selectively set. When the ink-pulse of recording is short, the interval is 2.4 ms/second according to the interval data 16.
This is a case where it is determined that it is a line. Data D in this case.

Assuming that the heat storage state for is X, this can be determined by adding the black data (print data) of the 11 surrounding data with a predetermined weighting.

Weighting is data D. This is done so that the data D8 has the greatest thermal influence. Specifically, the values are set as shown in the table below.

Table 1 On the other hand, as the recording interval becomes longer, the sampled data becomes different. For example, if the interval is 4.8 msec/line, which is twice the interval of 2.4 msec/line, a total of 6 data D2 thinned out one line at a time,
D3, D14 to D 1 B, D20 (Fig. 4).

The weighting of each data remains unchanged. That is, the total data in this case is as shown in Table 2 below.

(The following is a blank space) 0 Table 2 Heat storage due to leakage current of unit heating element> The unit heating element of the thermal head generates heat not only by applying voltage between adjacent electrodes, but also by so-called leakage current. The heat generated in this way is also stored and does not affect printing.

First, the manner in which leakage current occurs will be briefly explained with reference to FIG. A single elongated heating resistor 51 is formed on the substrate of the thermal head, and two types of electrodes 52 and 53 are attached alternately to this at predetermined intervals. One of the electrodes 5, 522, . . . is grounded via a switching element that is turned on and off according to image data. The other electrode 53. ．． 532 , .
It is connected to the second common line C2 via. Print pulses are supplied to these common lines CI and C2 from a power supply circuit 57 via a switch circuit 58 during a printing operation.

For example, assume that a print pulse is supplied with the switch circuit 58 selecting the first common line CI as shown in the figure. Now, let's focus on a specific electrode 533. If the two adjacent electrodes 522 and 523 are grounded by the switching element described above, current will flow through both of them and the unit heating elements e4 and C5 will generate heat. If only one side is grounded, current flows only in that direction, and the corresponding unit heating element generates heat. If both switching elements are turned off, neither of the unit heating elements e4 and C5 generates heat. This is the original energization control of the thermal head.

By the way, when the voltage is applied to the electrode 533, the second electrode 523 is not grounded, and the adjacent electrode 524
Suppose that is grounded. In this case, it is natural that the unit heating element e8 generates heat via the electrode 535. However, in this case, from the electrode 53 to the unit heating element 05
A current also flows to the electrode 52 via ~e7, and these unit heating elements e5~e! 7 also generates a slight fever. This is heat generation due to leakage current. This heat generation is relatively small. Therefore, in this example, as data considering the influence of heat storage,
Data D shown in FIG. , D8, and Dl.

Figure 6 shows each of these data D. , De, and Dl5. The double light ◎ in the figure indicates one of these data, and the black circle/
represents the bit to be printed. Data D. ,
Regarding DaND15, a weight of "11" is added each time a leakage current occurs. Each data D
. Judgment as to whether or not leakage current is occurring in N Da and Dl5 is based on the 10 data D1, D, ~D shown in FIG.
6, D1o to 3 D I 3, Dl7, is performed by determining the state of D+e.

Calculation by the heat storage level calculation circuit> The heat storage level calculation circuit 25 adds the above various weights to each data D1 to D21, and supplies the result to the heating element drive pulse width calculation circuit 22 as X and data 26. do.

Temperature data FIG. 7 shows the relationship between the substrate temperature of the thermal head and the temperature data 27. A thermistor is attached to the substrate of the thermal head, one end of which is grounded, and the other end connected to a power supply line via a pull-up resistor (not shown). The potential at the connection point between this pull-up resistor and thermistor changes depending on the temperature.

This potential is changed from 0 to 0 by an A/D converter (not shown).
It is converted into temperature data 27 in the range up to 40. The temperature data is supplied to a heating element drive pulse width calculation circuit 22.

Resistance Value Data 4 FIG. 8 shows the relationship between the actual resistance value of each unit heating element of the thermal head and the resistance value data 28. The resistance value data 28 is calculated by an arithmetic circuit (not shown). This arithmetic circuit has a built-in read-only memory.
If the resistance value of each unit heating element is used as address information, 0
A value in the range from 0.30 to 0.30 is output as resistance value data.

FIG. 9 shows the principle of measuring the resistance value of each unit heating element. In this figure, the heating resistor 51 has many unit heating elements e1, e2, .
It is divided into... Now, the first common line C
1 and the power supply circuit 57, and the second
A second ammeter 6 is connected between the common line C2 and the power supply circuit 57.
2 are placed respectively. In this state, the power supply circuit 57
A voltage is applied to both the two common lines CI and C2 from the first switching element 63- connected to the electrode 52.
Turn on 1. Other switching elements 63-2.63
-3, . . . are turned off at this time. In this state, only the two unit heating elements e1 and 5e2 are energized. Other unit heating elements e3, e4,
There is no leakage current.

The output voltage of the power supply circuit 57 is ■. Let IIT be IIT, and the current values detected by each ammeter 6162 be I5 and I2, respectively. If the voltage drop of the line and switching element 63-1 is ignored, the resistance value r of unit heating elements e1 and e2,
, I2 are respectively expressed by the following formulas.

r + -VOLIT / T + r2 = VOUT / 12 If the print data in the shift register (not shown) is shifted by one stage and the same operation is performed, only the second switching element 63-2 will be turned on. . Then, the resistance values rs and r4 for the unit heating elements e3 and e4 are equal. Hereinafter, the resistance values of all unit heating elements can be determined in the same manner. Such resistance value measurement is automatically performed, for example, when the power is turned on to a thermal recording device using this thermal head drive circuit, and the above-mentioned arithmetic circuit calculates the daily resistance value data for each unit heating element. 28 is calculated. Similarly, the resistance value data 28 is supplied to the heating element drive pulse width calculation circuit 22.

Heating element drive pulse width calculation circuit The heating element drive pulse width calculation circuit 22 is equipped with an adder, and after weighting X, data 26, temperature data 27, and resistance value data 28 in a predetermined manner, Add to. The added data is divided into 16 stages by a built-in decoder. On the other hand, from the thermal history memory 29, five steps (from 0.5 msec to 1.2 msec) for each unit heating element (
0, 5, 0, 6, 0, 8, 1, 0 and 1.2 seconds) is supplied. The heating element drive pulse width calculation circuit 22 uses the above-mentioned addition data and thermal history data 31 as address information, and calculates the drive pulse width T1 using a built-in read-only memory.

FIG. 10 shows the input/output relationship of this read-only memory. In this figure, the horizontal axis represents the addition data as input, and the vertical axis represents the drive pulse width TI (unit: m seconds) as output. Five curves 71 to 75 each represent the human output characteristics when the pulse width in the previous line is the value shown in the figure. - As an example, assume that the addition data for certain print data is 10. In this case, the time width of the drive pulse applied to the unit heating element of the previous line is 1.2 m.
If it is seconds, this time it will be shortened to 1.05 msec.

Further, if the previous pulse width is 1.0 msec, it is shortened to 0.9 msec, and if it is 0.5 msec, it is increased to 0.55 msec. Such TI data 32 obtained in bits corresponding to the print data is supplied to the thermal head control circuit 14.

Cycle Determination Circuit On the other hand, the cycle determination circuit 34 determines the repetition cycle based on three types of data: X+ data 26, temperature data 27, and thermal history data 31.

Judgment is made based on the contents written in the built-in read-only memory.

FIG. 11 shows a part of the contents 8 of this read-only memory. To make the contents easier to understand, the thermal history data 31 is expressed in m seconds, the temperature data 27 is expressed in degrees Celsius ('C), and the X data 26 is expressed as O (%) for the minimum value of heat storage and 100 (%) for the maximum value. ) Each is expressed as a percentage. Temperature data 27 is classified in units of 5°C.
X, Data 26 is classified into three stages according to heat storage.

The figure shows the case where the driving pulse T+-+ of the previous line is 1.0 msec, but the thermal head substrate temperature (
The higher the ambient temperature) or the more advanced the heat storage, the more positive the period determination data 35 becomes. The cycle determination data 35 is configured to take one of three values -1, 0, and +1. Although not shown in this figure, the shorter the drive pulse T + -1 of the previous line, the more the period determination data 3
5 leans towards the positive side. For example, the drive pulse T of the previous line,
When -1 is 0.6 msec, when the ambient temperature of the thermal head becomes high, the period determination data 35 always becomes +1 regardless of the heat storage state. Also, if heat storage is progressing,
Even if the ambient temperature is low, the period determination data 35 is +1.

9 Period Calculation Circuit The period determination data 35 is supplied to the period calculation circuit 36, and the repetition period T is calculated. The period calculation circuit 36 is
Three types of cycles can be set: 2.4 msec, 3.6 msec, and 4.8 msec. Initially, a period of 2.4 msec is set. If the cycle determination data 35 is O, the next cycle will be the same as the previous cycle, if it is +1, it will be one step longer, and if it is -1, it will be one step shorter. ”-1 consecutively, the period is fixed to 4.8 msec,
Heat dissipation will be promoted. Similarly, in a case where -1 is consecutive, the period is fixed to 2.4 msec, and heat storage is promoted. T data 37 specifying the repetition period T is supplied to the thermal head control circuit 14.

Thermal Head Control Circuit FIG. 12 shows the main parts of the thermal head control circuit. The pulse width determining circuit 81 of the thermal head control circuit 14 outputs T and data 3 in synchronization with the clock signal 82.
2 for each pixel, and output 0 from the output terminals O2 to 0. Gate control signals 83-1 to 83-5 are output according to the pulse width. As described above, the pulse width determining circuit 81 sets the time width of the drive pulse in five steps (0,
5, 0, 6, 0, 8, 1, 0, and 1.2 msec) to adjust the heat generation amount of the unit heating element. Pulse width is 085
At m seconds, only the first gate control signal 83-1 is high.
(high) level. At 0.6 msec, the first and second gate control signals 83-1.83-2 are at H level. At 0.8 msec, the first to third gate control signals 83-1 to 83-3 are at H level. When the time is 1.0 msec, the first to fourth gate control signals 83-1 to 83
-4, or 1 or 2 msec, all gate control signals 83-1 to 83-5 become I] level.

These gate control signals 83-1 to 83-6 are used to control five corresponding two-man-powered AND gates 84-1 to 84-, respectively.
5 is input. These anime games) 81-1 to 84
-5 is delayed by a delay port (not shown) and is supplied with a pulse width signal 62 and image information 19 associated with each unit heating element. Therefore, for example, when the signal "1" is supplied as the image information 19, if the driving pulse width is 0.8 msec, the first to
From the third AND gates 84-1 to 84-3, the signal
' is output, and the remaining AND gate 84-4.84-5
A signal ``'0'' is outputted from the terminal.These output signals are input to five buffer memories 86-1 to 86-5 arranged corresponding to each of the analog games 84-1 to 84-5. When all 1547 pieces of image information 19 are supplied to each AND gate 811-1 to 84-5, one line of image information is stored in each buffer memory 86-1 to 86-5 with a pulse width will be stored as data.

The data thus stored is supplied as pulse width control data 87 to a shift register/latch circuit of a thermal head (not shown). In the shift register/latch circuit, two contents of the first buffer memory 66-1 are first set in the shift register, and printing is performed with an applied voltage of 0.5 msec, as shown in FIG. 13a. Next, the second buffer memory 86
-2 contents to the shift register described above, and
As shown in Figure 3, printing is performed with an applied voltage of 0.1 msec. Similarly, the third to fifth buffer memo IJ
The contents of 86-3 to 86-5 are set in the shift register one after another, and voltage is applied for 0.2 msec each (
Figure 13c-e). As a result, for example, in a unit heating element that performs printing with a pulse width of 0.8 msec, the current is applied three times as shown in FIGS. 13a to 13c, and the heating element is heated to a desired temperature.

A counter (not shown) for presetting the T data 37 is arranged in the thermal head control circuit 14.
As mentioned above, when printing for one line is completed, the next printing start timing is determined. In this way, the repetition period T and the time width T1 of the drive pulse are controlled for each line, and the printing operation progresses.

[Effects of the Invention] 3. As explained above, according to the present invention, the heat storage unit heating element of the thermal head is monitored as a unit, and the print cycles are temporarily changed each time before the heat storage unit heating element of the thermal head progresses to the extent that the image quality deteriorates. It is set long to dissipate heat from the thermal head. Therefore, the image quality can be improved without substantially reducing the time required for recording or displaying.

[Brief explanation of drawings]

Figure 1 is an indispensable diagram for explaining the state of control by a conventional thermal head drive circuit. Figure <A) is a characteristic diagram showing the temperature change of a unit heating element of a thermal head, and Figure 1 (B) is a characteristic diagram showing the temperature change of a unit heating element of a thermal head.
2 is a waveform diagram of a drive pulse, and FIGS. 2 to 13 are for explaining one embodiment of the present invention. Of these, FIG. 2 is a block diagram showing the main part of the thermal head drive circuit, and FIG. is a data arrangement diagram showing the arrangement of reference data in the image information stored in the 6-line buffer, Fig. 4 is a data arrangement diagram showing the arrangement of sampled data when the recording interval is the longest, and Fig. 5 is a data arrangement diagram showing the arrangement of the sampled data in the case of the longest recording interval. Figure 6 shows various pattern explanatory diagrams showing patterns in which leakage current occurs, and Figure 7 shows memory contents showing the relationship between thermal head substrate temperature and temperature data. An explanatory diagram, Fig. 8 is a memory content explanatory diagram showing the relationship between the resistance value of a unit heating element and resistance value data, Fig. 9 is a principle diagram showing the principle of measuring the resistance value of each unit heating element, and Fig. 10 The figure is an explanatory diagram of the memory contents showing the input/output characteristics of the heating element drive pulse width calculation circuit, Figure 11 is an explanatory diagram of the memory contents showing part of the human output characteristics of the period determination circuit, and Figure 12 is the thermal head control diagram. FIG. 13 is a block diagram showing a part of the circuit that controls the application of drive pulses, and FIG. 13 is a various timing chart showing the application timing of drive pulses. 21... Heating element drive condition calculation circuit, 25...
...Heat storage level calculation circuit, 26...X+ data, 27...Temperature data, 28...Resistance value data, 34...Period determination circuit, 5 36... Period calculation circuit, 37... T data, e... Unit heating element. Applicant Fuji Xerox Co., Ltd. Representative Patent Attorney Umeo Yamauchi 6 4 @ 1 To Revisit 11 To

Claims (1)

[Scope of Claims] (1) In a recording device or display device that is equipped with a plurality of unit heating elements and performs thermal recording or display by selectively driving these units according to image information, image information to be recorded or displayed can be manually recorded or displayed. a heat storage level calculation circuit that calculates the heat storage level of the thermal head; and a unit heating element that determines the width of an applied pulse for driving each of the unit heating elements and the repetition period of the applied pulse according to the calculated heat storage level. A thermal head drive circuit comprising a drive condition calculation circuit. 2. A patent claim characterized in that the heat storage level calculation circuit calculates from image information for recording or display and history information consisting of the width of applied pulses already applied to the unit heat generating elements and their repetition period. The thermal head drive circuit according to item 1. 3. The unit heating element drive condition calculation circuit performs calculations based on the heat storage level calculated by the heat storage level calculation circuit, the ambient temperature of the thermal head, and image information for recording or display. A thermal head drive circuit according to claim 1.