JPH0113265B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a drive control circuit for a heating resistor array for thermal printing in facsimile machines, printers, and the like.

Thermal recording has been adopted in many recording devices such as facsimiles and printers, and recording paper has also been improved, and the method of melting coloring pigments and coloring agents has excellent stability, so it is being used in more and more applications. It is now being applied. On the other hand, the heat-sensitive head also
Extremely high-density recording has become possible, and even when compared with other electrostatic recording methods, high-quality recording has become possible.

However, in terms of high speed, it still cannot compete with electrostatic recording. This is due to the slow thermal response of the heating resistor. Conventionally, in thermal heads used in medium-speed facsimile machines, the color density is approximately determined by the product of the power normally applied to each heating element and the application time. However, when a thermal head is driven at high speed, the color density changes depending on the driving cycle of each heating resistor, that is, the period from when power is once applied to a certain heating resistor until it is applied again. I end up.

Figure 1 is a characteristic diagram showing the general relationship between the driving period T' of the heating resistor and the coloring density d. According to this diagram, the coloring density is generally a monotonically decreasing function with saturation characteristics with respect to the driving period. I understand that there is something.

Furthermore, Fig. 2 is a characteristic diagram showing the general relationship between the power application time W of the heating resistor and the coloring density d. According to this diagram, the coloring density is generally monotonous with saturation characteristics with respect to the power application time. It can be seen that it is an increasing function. Therefore, in order to obtain a constant color density, generally the driving period T' and the power application time W are
It is only necessary to control the relationship so that it becomes as shown in FIG. However, controlling the power application time for each heating resistor according to each drive cycle requires an enormous amount of control circuitry, and is virtually impossible.

FIG. 2 also shows the general relationship between the peak value P of the power applied to the heating resistor and the coloring density d. Therefore, in order to obtain a constant color density, the relationship between the driving period T' and the peak value P of the applied power can generally be controlled as shown in FIG. However, controlling the peak value of the applied power according to the driving cycle for each heating resistor requires an enormous amount of control circuits, just like controlling the power application time, and is virtually impossible.

On the other hand, various compression methods have been adopted as methods for transmitting image signals such as facsimiles with high efficiency within a limited band. The received compressed image information is normally converted into an original image signal line by line by a decoder, and sent to the recording unit line by line via a buffer memory. The transfer time for one line of image signals from the buffer memory to the recording section corresponds to the printing speed of the recording section, but the printing time for one line is constant with current A4-size high-speed facsimile machines.
5 to 10 ms is normal. For image information with a high compression ratio, such as all black or all white, the image signal is sent from the buffer memory to the recording section without interruption, but for complex image signals with a low compression ratio, the code becomes long, so the image signal is sent from the buffer memory to the recording section without interruption. 100m from sending the image signal of the i line to sending the image signal of the i+1th line
It takes more than s. Print on the i-th line, and print on the i-th line.
The driving cycle of the heating resistor that prints on the +1 line is the time T from the start of printing on the i-th line to the start of printing on the i+1-th line.On the other hand, no printing is performed on the i-th line, but printing is performed on the i-th line. The driving cycle of the heating resistor is longer than the time T. However, in a recorded image where black continues from the i-1st line, the i-th line, and the i+1th line, if the black density of the i-th line is lower than that of the i-1st line and the i+1th line, it is visually Although it is noticeable, when the i-1st line is white and the i-th line or i+1th line is black, or when the i-1st line or i-th line is black and the i+1th line is white, the i-th line is black. Even if the density of black is lower than that of continuous black, it is not visually noticeable.

The present invention has been achieved by utilizing the above-mentioned visual characteristics, and therefore, an object of the present invention is to eliminate density unevenness caused by changes in the driving cycle of the heating resistor in thermal recording. The goal is to visually reduce it.

The above-mentioned object of the present invention is to apply electric power to each heating resistor corresponding to each pixel of a certain line in accordance with an image signal in a drive circuit for a heating resistor array for thermal printing to print in accordance with the image signal. The control means is provided for controlling the application time of the line according to the time from the start of printing of the previous line to the start of printing of the line, and the control means visually detects density unevenness of the recorded image. In a heating resistor array drive control circuit for thermal printing or a driving circuit for a heating resistor array for thermal printing, the heating resistor array corresponding to each pixel in a certain line is controlled according to an image signal. When applying electric power to obtain a print according to the image signal, the control means controls the peak value of the applied electric power to the line according to the time from the start of printing of the previous line to the start of printing of the line. This is achieved by a heating resistor array drive control circuit for thermal printing, characterized in that the control means visually reduces density unevenness in a recorded image. That is, the present invention controls the printing energy of the current line according to the time from the start of printing of the previous line to the start of printing of the current line (line to be printed).

Hereinafter, preferred embodiments of the present invention will be specifically described with reference to the accompanying drawings.

FIG. 4 is a graph obtained by linearly approximating FIG. 3. However, the horizontal axis T in FIG. 4 is the time from the start of printing on the i-th line to the start of printing on the i+1-th line, and corresponds to the horizontal axis T' in FIG. 3, that is, the drive period of the heating resistor. The graph in FIG. 4 explains one embodiment of the present invention, and shows that the power of the heating resistor of the i+1st line is determined by the time T from the start of printing of the ith line to the start of printing of the i+1th line. This means controlling the application time W or the peak value P of the applied power as shown in the graph. In this graph, T ₀ is the minimum time from the start of printing of the i-th line to the start of printing of the i+1-th line.

FIG. 5 is a diagram showing a heating resistor array drive circuit for thermal printing used in the present invention, and shows heating resistors H1 to H1.
This circuit divides a row of heating resistors made of H320 into 4 blocks each having 80 resistors, and drives them through a matrix connection of 4 rows and 80 columns. The drive circuit includes transistors TRB1 to TRB4 and TRB1' to TRB.
4 sets of drive circuits consisting of 4' transistors
Matrix control of all the heating resistors is performed by 80 switching circuits consisting of TRD1 to TRD80, and each heating resistor is driven as follows.

One line of recording is heating resistors H1 to H80, H
81~H160, H161~H240, H241
The process is divided into four times for each block of ~H320. The first record is the heating resistor H1 to H8.
To set it to 0, set the group signal pulse BP1 to logic “1”.
is applied for the time required for recording, transistors TRB1' and TRB1 are turned ON, and a potential of logic 0 or 1 is applied to dot signal pulses DP1 to DP80 in accordance with the image signal, and transistor TRD1 is turned ON. ~Turn TRD80 “on” and “off”. For example, dot signal pulse DP1 is logic “1”
If the potential is , transistor TRD1 is “on”
Therefore, the current printed by the transistor TRB1 from the anode +VR of the recording power source flows through the heating resistor H1 to the cathode of the recording power source by the transistor TRD1. Therefore, the heating resistor H1
generates heat and prints on thermal paper. Other heating resistors are also printed in the same manner. Similarly, transistors TRB2' and TRB2, TRB3' and TRB
3. Turn on TRB4' and TRB4, and turn on and off the transistors of the switching circuit according to the image signal.

When recording the i+1th line by the above method, each group signal pulse is generated according to the time T from the start of printing of the ith line to the start of printing of the i+1th line according to the graph of FIG. BP1～
Controls the pulse width W of the logic "1" potential applied to BP4. An example of controlling the pulse width W is shown in FIG.

FIG. 6D shows the timing at which image signals are transferred line by line from the decoder to the recording section. Figure 6D
In the figures, the time during which the image signal is actually transferred from the buffer memory on the output side of the decoder to the recording section, and the white area indicate the time during which the image signal is not transferred from the buffer memory, respectively. The image signal transfer time for one line from the buffer memory is constant (time
t ₀ ), which is equal to one line recording time of the recording section. Note that the one-line recording time is the time during which the recording section records with the group signal pulse of the maximum width, as will be described later. In this embodiment, the time from the start of image signal transfer of the i-1th line to the start of image signal transfer of the i-th line
_T'0 , which is equal to the time _T0 (= _t0 ) from the start of printing of the i-1th line to the start of printing of the i-th line. Similarly, the time from the start of image signal transfer of the i-th line to the start of image signal transfer of the i+1th line is
T′ ₁ , which is equal to the time T ₁ from the start of printing of the i-th line to the start of printing of the i+1-th line.
The time from the start of image signal transfer of the i+1th line to the start of image signal transfer of the i+2th line is T' ₃ ,
This is equal to the time T ₃ from the start of printing on the i+1th line to the start of printing on the i+2th line. i-th line, respectively, depending on the time of T ₀ , T ₁ , and T ₃ , respectively.
The power printing time of the i+1th line and the i+2th line is controlled according to FIG. That is, in FIG. 4, the power application time W when T=T ₀ is W ₀ , and therefore, as shown in FIG. 6A, the group signal pulses BP1, BP2, BP3 when printing the i-th line are ，
The pulse width of BP4 is _W0 . Similarly,
Group signal pulse of i+1st line and i+2th line
The pulse widths of BP1, BP2, BP, and BP4 are respectively 6th
As shown in Figures B and C. In this embodiment, _the power application time is in the range of W ₀ to W ₂ as shown in FIG. The signal transfer time is also _4W2 .

FIG. 7 is a block diagram showing an embodiment of a recording system of a facsimile receiver using the present invention, and FIG. 9 is a time chart showing the operation of the recording system of FIG. In this embodiment, printing is executed at the timing shown in FIG. 6D. When the coded image signal S is input to the decoder 71, it is changed line by line to the original image signal, and the decoder output _S1 is transferred to the buffer memory 72. At this time, the decoder output _S1 is generated every time the decoder encoded image signal is decoded. Therefore, the time required to complete the transfer of one line's worth of coded image signals to the buffer memory 72 depends on the decoding time of one line's worth of coded image signals. All decoder output for one line is stored in the buffer memory 72.
, a buffer memory output _S2 is generated from the buffer memory 72, stored in the serial-parallel conversion register 78 according to the printing speed of the recording section, and is output by the latch circuit 79 at the "high" timing of the latch signal LATCH. The number of image signals to be simultaneously printed, that is, 80 image signals in the embodiment shown in FIG. 5, are latched at the same time, and the switching circuit 77 is operated. The processing status of the decoder 71 is transmitted to the recording control section 73, and the transfer of the image signal from the buffer memory 72 to the serial-parallel conversion register 78 and the latch timing of the latch circuit 79 are controlled in accordance with the information.

In addition, a frequency dividing circuit 74-1, a drive cycle counter 7
4-2, the drive pulse width W applied to the drive circuit 76 is controlled as shown in FIG. 4 by the latch circuit 74-3 and presettable counter 74-4. In other words, the high frequency pulse HFP is divided into frequency dividing circuit 7
The pulse frequency divided by 4-1 is sent to the drive cycle counter 74.
-2, the period from the time _T0 has elapsed after the start of printing of the i-1th line to the start of printing of the i-th line is counted. That is, the value of T-T ₀ in FIG. 4 is measured. The time T-T ₀ is latched by the latch circuit 74-3 at the start of printing of the i-th line, and
It is held until printing of +1 line starts. The preset pull counter 74-4 controls the drive circuit 7 according to the relationship between the drive period T and the pulse width W shown in FIG.
6 and controls the printing pulse width, and presets the value held in the latch circuit 74-3 at each printing timing.
From the time when the print pulse width reaches _W0 , the high frequency pulse HFP is counted and the print pulse is held until it reaches a preset value. If the HFP is a sufficiently high-frequency pulse and the frequency division ratio of the frequency dividing circuit 74-1 is appropriately set, the printing pulse width of the i-th line can be set as shown in FIG. 4 using the method described above.

The printing pulse width of the i+1st line, the i+2nd line, . . . can also be set in the same manner as described above.

Next, the recording power supply voltage +VR when printing the i-th line is determined by the time T from the start of printing of the i-1th line to the start of printing of the i-th line.
An example in which control is performed to satisfy the -P characteristic will be described. FIG. 8 is a block diagram of an embodiment for implementing this. Common parts between FIG. 8 and FIG. 7 indicate the same configuration. The differences are 74-1, 74-2, 74-3, and 74 in Figure 7.
-4 is 74-5, 74-6, 74- in Figure 8
7, 74-8. That is, in FIG. 7, the drive pulse width W given to the drive circuit 76 is determined by the frequency divider circuit 74-1, drive cycle counter 74-2, latch circuit 74-3, and preset pull counter 74-4 as shown in FIG. T of
-W characteristics, whereas in FIG.
-6, DA converter 74-7, power amplifier 74-
8, the recording power supply voltage of the drive circuit 76 +
VR is controlled as shown in the T-P characteristic shown in FIG. Here, it may be considered that the recording power supply voltage +VR and the peak value P of the power between the heating elements are approximately proportional.

In FIG. 8, the high frequency pulse HFP is counted by a drive cycle counter 74-5 for a period from the time when _T0 has elapsed after the start of printing of the i-1th line until the start of printing of the i-th line. That is, the value of T-T ₀ in FIG. 4 is measured. The time T-T ₀ is latched by the latch circuit 74-6 at the start of printing of the i-th line, and held until the start of printing of the i+1-th line. The DA converter 74-7 is a latch circuit 74-6.
The digital value of is converted into an analog value, and the converted value is amplified by a power amplifier 74-8 to obtain a recording power supply voltage +VR that satisfies the T-P characteristic shown in FIG.

The recording power supply voltages for the i+1st line, the i+2nd line, etc. can also be obtained in the same manner as described above.

In the two embodiments described above, by controlling the time period during which power is applied to each heat generating resistor in the heat generating resistor array and controlling the peak value of the applied power, each of the heat generating resistors from the drive circuit 76 is It controls the energy applied to the heating resistor. As explained in detail above, by using the heating resistor array drive control circuit for thermal printing according to the present invention, it is possible to visually reduce density unevenness caused by changes in the driving cycle of the heating resistors in thermal recording. .

[Brief explanation of drawings]

Fig. 1 is a characteristic diagram showing the general relationship between the driving period T' of the heating resistor and the coloring density d, and Fig. 2 is a characteristic diagram showing the general relationship between the power application time W of the heating resistor and the coloring density d, and the general relationship between the heating resistor's driving period T' and the coloring density d. Peak value P of applied power and color density d
Figure 3 shows the relationship between the driving cycle T' of the heating resistor and the power application time W to obtain a constant color density, and the driving of the heating resistor to obtain a constant color density. FIG. 4 is a characteristic diagram showing the relationship between the period T' and the peak value P of the applied power, and is an explanatory diagram of an embodiment of the present invention. 5th diagram showing the time T, the power application time W of the i+1th line heating resistor, and the peak value P of the applied power to the heating resistor.
The figure is a diagram showing an example of the configuration of a heating resistor row drive circuit for thermal printing used in the present invention, and FIG. FIG. 7 is a block diagram showing a first embodiment of a recording system of a facsimile receiver using the present invention, and FIG. 8 is a recording system of a facsimile receiver using the present invention. FIG. 9 is a block diagram showing the second embodiment of the present invention, and FIG. 9 is a time chart showing the operation of the recording system shown in FIG. T'...driving cycle of the heating resistor, T...time from the start of printing of the i-th line to the start of printing of the i+1th line, d...color density, W...power application time to the heating resistor, P... Peak value of applied power to heating resistor, H1 to H320... Heat generating resistor, BP
1 to BP4...Group signal pulse, DP1 to DP80...
...Dot signal pulse, S...Picture signal, HFP...
High frequency pulse, 71...decoder, 72...buffer memory, 73...recording control section, 74-1...
Frequency dividing circuit, 74-2... Drive cycle counter, 74
-3...Latch circuit, 75-5...Drive cycle counter, 74-6...Latch circuit, 74-7...D
-A converter, 74-8...Power amplifier, 75...
Heating resistor array, 76... Drive circuit, 77...
Switching circuit, 78...Serial-parallel conversion register, 79...Latch circuit.

Claims (1)

[Claims] 1. In a drive circuit for a thermal head that records a line by sequentially supplying image signals for one line to a heating resistor array composed of a large number of heating resistors arranged in one direction, the heating resistor array a driving means capable of supplying the same printing energy to each heating resistor; and means for counting the time from the start of printing of the previous line to the start of printing of the current line;
A heating resistor array drive control circuit comprising: control means for increasing the amount of energy applied from the driving means to each of the heating resistors in accordance with an increase in the counting time when recording the current line. .