JPS6087071A - Thermal head driver - Google Patents

Abstract

PURPOSE:To make favorable the yield of a thermal head, appropriately control the generation of heat by the head and enable to prolong the useful life of the head, by controlling the heating value in accordance with the average resistance of heating resistors of the thermal head. CONSTITUTION:Printing data 21 are writen into line buffers 211-214 with a one- line amount as a unit by a selector 23, printing data 251-253 selected by a selector 24 are inputted into a heat accumulation condition calculator 26, which calculates the heat accumulation condition of the thermal head, and inputs it into a pulse width calculator 28. A pulse width for the line in which recording is to be conducted is determined by the calculator 28 on the basis of a calculation output 27 from the calculator 26, a memory output 31 from a pulse width memory 29 storing each pulse width in the preceding line and average resistance information 33 on the heating resistors outputted from a decoder 32, and a pulse width signal 34 is supplied to a pulse voltage impressing circuit for the thermal head. Accordingly, printed density can be corrected in response to the scattering of the heat accumulation condition of the heating elements or the average resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thermal head driving device used in a recording apparatus using a thermal head.

[Prior art]

2. Description of the Related Art Recording devices that perform thermal recording using thermal recording paper or transfer type thermal recording media are widely used in facsimile machines, printers, and the like. Usually, such a recording apparatus uses a thermal head as a recording head, in which heating elements or heating elements are arranged in a row. Since the thermal head generates thermal energy for printing, there is a problem of image quality deterioration caused by this energy.

A typical example of these is heat accumulation during high-speed recording. The heat generated in the heating element by energization is used for printing and is also radiated through the substrate of the thermal head. However, if the thermal head is driven at high speed with a printing cycle of 10 msec or less, for example, the next printing operation will start before sufficient heat radiation has occurred, and heat will accumulate in each heat generating element. As a result, the temperature of each heat generating element becomes non-uniform during recording, resulting in different sizes of printed dots and non-uniform density.

In addition, the average resistance value of the heating element of thermal heads differs among individual thermal heads due to subtle differences in manufacturing conditions. As a result, there is a problem in that the print density differs depending on the recording device. In particular, in a recording apparatus such as the multicolor recording apparatus shown in FIG. 1, in which a plurality of recording units 13 are arranged in parallel orthogonally to the traveling direction 12 of the recording paper 11, the average resistance value of each →normal and -marinal head is If the values were different, the printing density would become unbalanced, resulting in a significant deterioration of the quality of the recording surface.

In order to address this deterioration in image quality caused by thermal energy, attempts have been made to set the optimal amount of thermal energy by adjusting the voltage applied to the sheathal head or the width of the applied pulse. .

FIG. 2 shows one conventional thermal head drive device that performs heat storage control. In this device, the black that occupies in the print data 15 supplied to the thermal head 14, (printing state)
The counter 16 counts the bits of each line. Then, a control signal 17 corresponding to this count value is supplied to a thermal energy control circuit 18. The thermal energy control circuit 18 is, for example, a circuit for setting a pulse voltage or a circuit for setting a pulse width, and when the thermal head 14 records the next line counted by 4 of the counter j6, the applied pulse is applied to each heating element. Adjust 19.

However, with such uniform control over the entire head, it has not been possible to sufficiently correct heat accumulation. However, when focusing on individual heating elements, such control on a line-by-line basis actually causes a local temperature rise or fall, which sometimes leads to deterioration of printing quality.

In addition, when using multiple thermal heads, it has traditionally been necessary to prepare a power supply for each thermal head and adjust the amount of heat generated, or to select and use thermal heads whose heating elements have approximately the same average resistance value. Measures were taken to do so. However, the former measure has the drawback that it uses multiple power sources, making the device larger and more expensive. Moreover, the latter measure has the disadvantage that the yield of thermal heads is poor and the equipment is similarly expensive.

Moreover, conventionally, there has been no device that can simultaneously accomplish heat accumulation correction and correction of print density between individual thermal heads.

[Purpose of the invention]

In view of these circumstances, it is an object of the present invention to provide a thermal head drive device that can correct print density with respect to heat accumulation in a heating element and variations in average resistance value.

[Structure of the invention]

The present invention includes a heat storage state calculating means that calculates the heat storage state of each heating element constituting the thermal head from print data representing printed content, and a pulse width of the voltage applied to the heating element during the previous recording and the heat storage state. heating element individual application energy correction means for correcting the thermal energy to be applied to each heating element based on the heat storage state calculated by the calculation means; A recording apparatus that performs thermal recording is equipped with a thermal head applied energy correction means for correcting the thermal energy to be applied, and the energy corrected by these two correction means is applied to a heating element provided in a thermal head of a recording section. Apply separately. Even in a recording apparatus equipped with a plurality of recording sections, the print density in each recording g+< is appropriately adjusted.

〔Example〕

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

FIG. 3 shows the thermal head driving device of this embodiment. This device has four line buffers 22-1 to 22 into which print data 21 is sequentially written line by line.
~4. The selector 23 receives a line synchronization signal (not shown) and cyclically switches its contact every time two copies of print data for 1947 minutes are supplied. As shown in the figure, the selector 23 is connected to the first line buffer 2.
2-1 is selected, the print data of the line to be recorded is written in the fourth line buffer 22-4. At this time, the third line buffer 22-3
The print data for one line before this is written in the second line buffer 22-2, and the print data for one line before this is written in the second line buffer 22-2.

On the output side of these line buffers 22-1 to 22-4, there is a selector 24 for selecting three line buffers other than the line buffer in which the print data 21 is being written.
is located. In the state shown in this figure, the print data 21 is written in the first line buffer 22-1, so the other three line buffers 22-2 to 22-4
The output side of is selected.

Print data 25-1~ selected by selector 24
25-3 is manually input to the heat storage state calculator 26. The heat storage state calculator 26 is a calculator that calculates the heat storage state of the thermal head. A calculation output 27 of the heat storage state calculation unit 26 is supplied to a pulse width calculation unit 28 .

The pulse width calculator 28 is a calculator that calculates the thermal energy to be applied to each heating element of a thermal head (not shown) and sets the width of the pulse voltage applied to these heating elements accordingly. The pulse width calculator 28 calculates (1) the calculation output 27 and (2) each pulse width one line before. memory output 31 of the pulse width memory 29, and ■decoder 3
Using the data of the three types of resistance value information 33 outputted from 2, the pulse width that can be applied to the line on which recording is currently being performed is determined. The pulse width signal 34 determined individually for each heating element is supplied to a pulse voltage application circuit of the thermal head, which will be described later.

Now, in this thermal head driving device, the heat storage state calculator 26 and the pulse width calculator 280 are used to temporarily determine the pulse width for controlling the heat storage state.

Then, the resistance value information 33 is used to finally determine the pulse width.

The principle of determining the pulse width for heat storage state control will be explained with reference to FIG. The data row L1 located at the bottom in FIG. 4 represents the data on the line to be recorded from now on. Further, the data string L2 that is one line above this represents data that is one line past in terms of time, and the data string L3 that is further above this represents data that is two lines past.

In the data string L1, attention is paid to arbitrary data D hatched in the figure. Let Ti be the optimum pulse width applied to the heating element corresponding to this data, and let xl be the heat storage state at this position. Furthermore, in the data string L2, data corresponding to the same heating element as the data D is assumed to be d. The pulse width applied to this heating element based on this data d is ti
shall be. Note that in this thermal head driving device, the pulse width itself is determined for each heating element, regardless of whether printing is performed or not. That is, the presence of characters 1-11 (11 is 71 depending on whether a pulse voltage is applied to each heating element or not).

In this case, the optimal applied energy to be applied to the heating element corresponding to data D can be expressed by the following equation.

Ti=f(Xi, Li) FIG. 5 shows the principle of calculating the heat storage state x1. In this embodiment, the heat storage state x1 is calculated based on the six data 44-1 to 44-6 shown by solid lines in the figure that exist around the data D. The heat storage state Xi is determined by adding the black data (print data) among the data 44-1 to 44-6 with a predetermined weight.

For example, when the data 44-3 (data d) with the largest thermal influence is set to "lO(1"), the weighting is performed on the line Ll
The data 44-1.44-2 of line L2 is written as '4 []'', and the other data 44-4.44-5 of line L2 is written as par 20.
At °, further data 44-6 of line L3 is '40
” can be expressed as

The following table shows the heat storage state x1 added in this manner in 17 levels from 0 to 16 depending on the printing state. Here, when xl is 0, it means the state where the least amount of heat is stored, and when xl is 16, it means the state where the most amount of heat is stored.

The heat storage state calculator 26 shown in Table 1 and FIG.
4-1 to 44-6 are extracted. Then, using these data as address information, xl is calculated according to the contents of Table 1.

FIG. 6 is a diagram used to explain the operation of the heat storage state calculator that calculates the heat storage state for data D using this table. However, this figure represents a stage in which the selector 23 shown in FIG. 3 is connected to the first line buffer γ22=1. At this stage, three line buffers 22-2
~22-4 receives a tarok signal (not shown),
In synchronization with each other, reading of print data for one line is started bit by bit. Second line buffer 22-2
The print data 25-1 of the previous two lines read out from
After being delayed by one bit, it is manually applied to latch 46 for one bit. Print data 25-2 of the previous line or the line to be recorded read from the third line buffer 22-3 and fourth line buffer γ22-4, respectively
or 25-3 are input to the corresponding 3-bit shift register 47 or 48, respectively.

The data latched in the 1-bit day latch 46 is
One bit at a time is supplied to address terminal A6 of ROM (read only memory) 49. The 3-bit shift register 47 performs serial-to-parallel conversion and supplies the data to address terminals Δ5 to A3 in the ROM 49 in order from the oldest data. The other 3-bit shift register 48 supplies the oldest data to the address terminal Δ2 and the newest data to the address terminal A1.

The table shown in Table 1 is stored in the ROM 49. Address terminals A1 to A6 are data 44 in this table.
-1 to 44-6, respectively. Xi obtained from the table is supplied to a pulse width calculator 28 as a calculation output 27.

The pulse width calculator 28 learns the applied pulse width of each heating element in the previous line from the memory output 31 supplied from the pulse width memory 29. Then, from the Xi determined for each heating element, the pulse width of the line on which recording is currently to be performed is tentatively determined.

FIG. 7 shows how the pulse width is determined by the pulse width calculator 28. In this figure, the horizontal axis represents ×1 as the calculation output, and the vertical axis represents the determined pulse width Ti.
(The unit is m seconds). 5 curves 51-55
These represent the input/output characteristics when the pulse width in the previous line is the value shown in the figure.

As an example, assume that x1 is 10 for certain data. In this case, if the pulse width of the voltage applied to the heat generating element of the previous line is 1.2 msec, this time it is 1.05 msec.
shortened to milliseconds. Also, if the previous pulse width was 1.0 msec, it would be shortened to 0.9 msec, and if it was 0.5 msec, [
], increased to 55 msec.

The determination of the pulse width Ti is performed by the first memory 56 in the pulse width calculator 28, as shown in FIG. That is, the first memory 56 is supplied with the calculation output 27 and the memory output 31 as address information, and the provisional pulse width signal 57 representing the pulse width TI is divided into five levels (0, 5, 0).
, 6, 0, 8° 1.0 and 1.2 msec).

The temporary pulse width signal 57' becomes address information of the second memory 58 together with the resistance value information 33.

Now, at the input end of the decoder 32 (FIG. 3) that creates the resistance value information 33, there are three switches 61 whose one end is grounded.
.about.63 are connected, and a pull-up resistor 64 is connected to the contacts on the non-grounded side. The person assembling the recording device measures the average resistance value of the heating element of the thermal head (not shown) attached to the device, and
Depending on the stage measurement results (minimum, small, medium, large, maximum),
The three switches 61 to 63 are turned on and off as shown in the table below.

Table 2 The second memory 58 (FIG. 8) uses the five-step resistance value information 33 manually inputted from the decoder 32 and the five-step provisional pulse width signal 57 as address information, as shown in the following table. The pulse width signal 34 of 1 ( ) stage is read out.

(Margin below) Table 3 Such a pulse width signal 34 is supplied to the thermal head, and heat generation control is performed with a different pulse width for each unit heating element.

FIG. 9 shows a pulse voltage application circuit that performs such heat generation control. Pulse width determination circuit 68 of this circuit
inputs the pulse width signal 34 one pixel at a time in synchronization with the tarok signal 69, and outputs gate control signals 71-1 to 71-6 according to the pulse width from its output terminals O1 to 06. ing. The pulse width determining circuit 68 sets the pulse width for printing from 0.3 msec to 1.3 msec by O.1.
The heat generation amount of the unit heat generating element is adjusted in 11 steps in millisecond increments.

The pulse width is 0.5, 0.7, 0.9, 1.1 and 1.
When the time is 3 msec, the first gate control signal 71-1<1
-1 (high) level. Also, the width of Noku 117 is 3. '
When the time is 4'm seconds or Q, 5m seconds, the second gate control signal 71-2 becomes the II level.

When the pulse width is 0.6 msec and 0.17 msec, the second and third gate (control signals 71-2, 71-3 are at I' level.Hereinafter referred to as intervals), the response width is 1. .2m
seconds and 1.3 msec, the second to sixth gate control signals 71-2 to 71-6 are at H level.

These gate control signals 71-1 to 71-6 are used to control six two-man powered gamma gates 72-1 to 72-, respectively.
6 will be man-powered. These AND gates 72-1 to 72
-6 shows print data 7 which is delayed by a delay circuit (not shown) and is associated with the pulse width signal 34 and each heating element.
3 are supplied. Therefore, for example, when the signal "1" is supplied as the print data 73, if the pulse width for printing is 0.8 msec, the second to fourth ant games)
? The signals PA1''' are outputted from the AND gates 2-2 to 72-4, and the signal "0°" is outputted from the remaining AND gates 72-1, 72-5, and 72-6. Also, if it is 0.9 msec, then the first to fourth anime games)? The signal "1" is output only from 2-1 to 72-4.

These output signals are output from each AND gate 72-1 to 72-
6 buffer memo IJ 74 arranged corresponding to 6
-1 to 74-6 will be input. When all 1,547 worth of print data 73 is supplied to each of the anime games) 72-1 to 72-6, each buffer memory 74-1 to 74-
6 stores one line of print data as pulse width data.

The data thus stored is supplied as pulse width control data 75 to the driving section of the thermal head. First of all, the first buffer memo in the drive section! The contents of J74-1 are set in the shift register (not shown) of the thermal head, and printing is performed with an applied voltage of 0.1 msec, as shown in FIG. 10a.

Next, the contents of the second buffer memory IJ 74-2 are set in the shift register described above, and printing is performed with an applied voltage of 0.4 msec as shown in FIG.

Similarly, the third to sixth buffer memories 74-3 to
The contents of 74-6 are set in the shift register one after another,
The voltage is applied for 0.2 msec each (FIG. 10c-f). As a result, for example, a heating element that performs printing with a pulse width of 0.8 msec is energized three times as shown in FIG. 10 b to d, and is heated to a desired temperature. As a result, print density is always maintained at a good level.

In this embodiment, the thermal head drive device in one set of recording units has been described above, but in a recording device with a plurality of recording units of 6fti, such as a multicolor recording device, each recording unit has heat storage correction and resistance The value is corrected, and the print density is always kept in a good condition as described above.

〔Effect of the invention〕

As explained above, according to the present invention, the amount of heat generated by the heating element of the thermal head can be adjusted according to the average resistance value of the heating element, so that the yield of the thermal head is improved. Furthermore, since the heat generation of the thermal head is properly controlled, its lifespan is extended and its reliability is improved.

[Brief explanation of drawings]

FIG. 1 is a layout diagram showing the arrangement of the recording section of a multicolor recording device;
FIG. 2 is a block diagram showing an example of a conventional thermal head driving device, and FIGS. 3 to 10 are for explaining an embodiment of the present invention. Of these, FIG. FIG. 4 is an explanatory diagram showing the data string for three lines; FIG. 5 is an explanatory diagram showing the principle of calculating the heat storage state in relation to each data; FIG.
The figure is a block diagram showing the main parts of the heat storage state calculator.
The figure is a data content explanatory diagram that theoretically represents the data written to the first memory in the heat storage state calculator, Figure 8 is a schematic configuration diagram of the pulse width calculator, and Figure 9 is a diagram of the pulse voltage application circuit. The block diagram and FIG. 1 are various timing diagrams showing the application timing of pulse voltages. 13... Recording unit, 26... Heat storage state calculator (heat storage state calculation means)
, 28...Pulse 'l'llll (J)J'
t') device, 29...Pulse width memory, 32...Decoder, 56...First memory (heating element individual applied energy correction means), 58... ...Second memory (thermal head applied energy correction means). Applicant: Fuji Nanakuchi Tsukusu Co., Ltd. Agent: Umeo Yamauchi, Patent Attorney

Claims (1)

[Claims] 1. In a recording device that performs thermal recording by driving a thermal head provided in a recording section, heat storage in each heating element constituting the thermal head is determined from print data representing the printed content. A heat storage state calculating means for calculating the state, and correcting the thermal energy to be applied to each heating element from the pulse width of the voltage applied to the heating element during the previous recording and the heat storage state calculated by the heat storage state calculating means. It is equipped with a heating element individual applied energy correction means and a thermal head applied energy correction means for correcting the thermal energy to be applied to the entire thermal head according to the average resistance value of the heating element of the thermal head. A thermal head driving device characterized in that the generated energy is individually applied to heating elements provided in a thermal head. 2. A heat storage state calculation means that calculates the heat storage state of each heating element constituting the thermal head from the print data representing the printed content, and a heat storage state calculation means that calculates the pulse width of the voltage applied to the heating element during the previous recording and the heat storage state. The heating element individual application energy correction means corrects the thermal energy to be applied to each heating element based on the heat storage state calculated by the heating element, and applies energy to the entire thermal head according to the average resistance value of the heating element of the unidirectional head. 2. The thermal head driving device according to claim 1, wherein each of the plurality of recording sections is provided with a thermal head applied energy correction means for correcting the thermal energy to be applied.