JPS59127782A - Driving controller for thermal recording head - Google Patents

Abstract

PURPOSE:To record with favorable and uniform image quality at high speed, by a method wherein heating element input energy satisfying a predetermined condition is calculated, and control is performed in accordance with the calculation result. CONSTITUTION:The lapse of time (t) from the preceding-time driving of the heating element in the thermal recording head is measured by a counter, while a temperature rise DELTATp of a machine body of the head after the lapse of time (t) is measured through a thermometer, and a required input energy Ein satisfying the condition of formula I (wherein C1 and R1 the capacitance and the resistance of the machine body of the head; E0 is input energy with which a favorable print quality can be secured when the machine body is in a standard condition; e is the base of natural logarithm; A is a constant) is determined through calculation by a calculator. The driving of the thermal recording head is controlled on the basis of the energy Ein thus determined. Accordingly, recording is conducted with a favorable and uniform image quality, and the recording can be performed at high speed.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a thermal recording head drive control device, more specifically,
The present invention relates to a thermal recording head and a drive control device that use a thermal recording method to thermally record information on a recording medium by applying energy to a heating element.

In conventional techniques, such as thermal transfer recording and thermal recording using a thermal recording medium, heat remains in the structure of the thermal recording head, that is, the thermal head, depending on the previous driving state of the heating element. This heat storage effect decays exponentially over time. Thermal recording basically allows good recording to be obtained by appropriately controlling the thermal conditions of the thermal head and disk depending on the image information to be recorded. However, if the heat storage effect from the previous drive remains in the thermal head, it will appear as noise in the next new recording. For example, in a recorded image, in a portion with a high density of black pixels, the pixels are mutually blacked out, resulting in a decrease in resolution. Therefore, if the amount of heat generated is lowered, the black part with low pixel density will be missing. Therefore, high-speed recording in which driving is performed at such short intervals that the influence of the previous driving does not sufficiently disappear cannot be performed.

In order to improve this drawback, there is a method (Japanese Unexamined Patent Publication No. 55-142675) in which the interval between the previous drive and the previous drive in recording is measured and the width of one drive or pulse of the heating element is controlled accordingly. A method has been proposed in which additional printing is performed when the recording signal is a space signal (Japanese Unexamined Patent Publication No. 55831/1983).

There is also a method (Japanese Patent Publication No. 55-47980) in which the next driving time of the heating element is controlled in proportion to the length of one driving element stop period.

However, in either method, the energy to be applied to the heating element is not controlled according to the nature of the image information to be recorded or the state of heat storage in the head, so it is difficult to obtain recorded images of uniformly good quality. Can not. This tendency is particularly noticeable in Japanese 70 links, which contain a mixture of various fonts and characters of various sizes, and facsimiles, which transmit various images, and are therefore not suitable for high-speed recording.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a thermal recording head drive control device that eliminates the drawbacks of the prior art and can perform high-speed recording with good image quality.

Configuration The configuration of the present invention will be described below based on one embodiment.

In thermal recording using a thermal recording head (thermal head), that is, recording that uses a thermal recording medium, or thermal transfer recording, that is, recording that transfers pigments such as ink to a normal recording medium such as plain paper using heat, the recording speed is As the speed increases, the image quality, that is, the quality of recorded images such as characters and images, is greatly influenced by the image information and the heat storage state of the head.

For example, in thermal transfer recording, as shown in FIG. 1, in a thermal recording head or thermal recording head, a Y-type structure or substrate 10 is disposed facing a flatten roller 12, and a recording medium 14 such as plain paper and a An ink sheet 16 is interposed.

In this example, the thermal head structure 10 is arranged in a line, with nine heating elements and one
8 to form a heating element array 180 (FIG. 5). Therefore, as the flatten roller 12 rotates in the direction of the arrow A, the recording medium 14 and the ink sheet 16 are fed in the sub-scanning direction B, and ink is transferred from the ink sheet 16 to the recording medium 14 in accordance with the heat generated by the heating element 18. Line recording is performed by transferring the image to the image plane.

FIGS. 2A and 2B show an example of a recorded image using a conventional recording method, that is, a method in which the energy applied to the heating element 18 of the thermal structure 10 is not controlled in accordance with the image information to be recorded. In these examples, each character is formed by a number of dots or pixels, 0.8 in Figure 2A.
In FIG. 2B, an energy of 0.4 millinonyl/dot is applied to the heating element 18.

FIG. 2A shows an example in which the heat storage state of the heating element 18 becomes too high at a location where images are densely packed, resulting in a part of the image being collapsed. If the applied energy is lowered regardless of the image information in order to avoid overheating of the heating element 18, part of the image will be missing, as shown in the example shown in FIG. 2B.

As shown in detail in FIG. 3A, the thermal transfer system is a heat-generating system that melts a portion 164 of the ink layer 162 on the ink sheet base 160 of the ink sheet 16 by heat generated by the heat generating element 18 and transfers it onto the recording medium 14. It is. However, heating element 1
A portion of the thermal energy applied to the ink layer 162 flows into the ink layer 162, particularly a portion 164 thereof, through various thermal resistances, and also leaks to the head substrate 1o and the surrounding atmosphere.

This heat generation system is treated as a thermal model system and analyzed by replacing it with an electrical equivalent circuit model.

This equivalent circuit is shown in FIG. 3B. Here, each element is as follows.

C1: Heat capacity of the heating element 18 C2: Heat capacity of the thermal head substrate 1o C3: Heat capacity when the ink 164 to be transferred is raised to its melting temperature C4: Heat capacity of the surrounding atmosphere R1: Heat capacity from the heating element 18 to the thermal head substrate (heat dissipation R2: Thermal resistance from the thermal head substrate 1o to the atmosphere R3: Thermal resistance from the heating element 18 to the ink layer 1624 via the air layer 3o and the ink sheet base 160, etc. R4: Thermal resistance from the heating element 18 to air layer 3o and ink 7-t1
Thermal resistance R5 when heat leaks to the substrate 1o and the platen 12 through 6, etc.: Heat capacity when heat is absorbed by the ink 164 to be transferred Dl: Zener diode that indicates the melting temperature T: Heat storage temperature of the thermal head substrate 1o In the equivalent circuit of FIG. 3B, the heat capacity c2 is much larger than C1, and at the level of the time when the heating element 18 is driven, the temperature T of the heat capacity c2.

It can be assumed that there is no change. Although the thermal resistance R3 is sufficiently thicker than R1, the temperature T of the heat capacity C at the time t has elapsed after giving the temperature To to the heat capacity c1 is (1
) can be approximated by the formula.

However, e is the base of natural logarithm.

The melting energy of the ink 164 is several hundred times greater than the energy that raises the temperature of a unit amount of ink by the equivalent of 1°C, so in a practical temperature range, the energy to store heat capacity C3 in the melting temperature range is necessary for transfer. It can be ignored from the point of view of energy.

The melting temperature Tk of the ink is sufficiently higher than T, and
Considering that the ink sheet 16 moves according to the linear velocity during recording, the temperature of the heating element 18 that contributes to melting the ink is the temperature of the portion exceeding the melting temperature Tk. That is, as shown in FIG. 4, if the horizontal axis represents the elapsed time t after the temperature T is given to the heat capacity C1, and the vertical axis represents the temperature T of the heat capacity C, the curve 40 becomes the above-mentioned (1). According to the formula, the shaded part 42
is a portion that contributes to melting of the ink 164.

In order to avoid complication of calculation, the shaded area 42 is set at a temperature T.
. , the energy Q flowing through the thermal resistance R5 and therefore absorbed by the ink 164 to be transferred is approximated by equation (3).

The temperature T that makes Q constant is (Irrespective of the image information or the heat storage state of the thermal head 10, in order to give a predetermined energy of Q to the ink 164 to be transferred,
It is necessary to give the heat of T8 obtained by the formula 5) to the heating element 18.

T8=To-T=(To-'rp)(1-e C+R
+) (10) In equation (5), equation (1) was substituted for T, and equation (4) was substituted for T.

By the way, the thermal energy to be input to the heating element 18 of the substrate 1o, that is, the heat capacity C1, that is, the input energy E + n is given by equation (6).

Ein2c, 'I'5 (6) When the temperature T of the substrate 10 is held at an arbitrary reference temperature and the heat capacity CI of the heating element 18 is the same temperature as this temperature T,
E is the input energy required to obtain a good record. Then, the long-term energy conditions for recording image information satisfactorily are expressed by equations (5) and (6) to equation (7).

-tuny in = ”'o (1-AΔTp X 1 e
C+R1) (7) However, A is a constant expressed by the following formula (8), ΔT.

is the increase in the temperature of the substrate 10 from the reference temperature. Referring to FIG. 5, the thermal energy applied to the heating element 18 is expressed as (7)
The control circuit 100 that controls according to the formula basically consists of two random access memories (RAM) 102 and 10.
4, Shift Reno Star 106, AND key
G 108, RAM 1 1. 0,
Latch 112, counter 114, read-only memory (RO
M) 116, as well as a latch multiplexer 118
It consists of etc.

In this example, the thermal destructure lO is 2.048
It forms a line head of 2, 04-8 bits, and has a 7-bit register 182 and a latch 184 for holding the state of each bit. In other words, one recording line (row) consists of 2.048 bits. In this embodiment, as shown in No. 6, l line period τ for recording one line,
The heating element 18 is driven by dividing the period into N sub-periods τ8. - For example, τ1 is approximately 25 milliseconds, τ8 is approximately 300 microseconds, and N is 8. Therefore, for example, when recording white on the recording medium 14, no pulse is applied to the stage of the input star 182 corresponding to the white bit, as shown by reference numeral 322 in FIG. 6(E), but black is recorded. In this case, the stage of the shift register 182 corresponding to the black bit has n pieces (n is 1
.about.8 natural number) is applied. This corresponds to each sub-period τ.

184 in response to the signal LOAD which is activated every time.
is held only during each subperiod τ8, during which the corresponding transistor 186 is conductive.

Therefore, one line period τ1. Overall, it is equally economical.
TB's i-drive Yarus 32 (same figure (F))
) is formed.

In this embodiment, the time nτ8 (driving the heating element 18 during the line period τ1), that is, the ratio n/N is determined according to the equation (7), that is, the length of the rest period from the previous drive and the head substrate 10. controlled according to the temperature.

RAM 1.02 and 104 are 2 bits (2,0
It is a 48-bit random access memory that stores input data I DATA as image information to be recorded.
Either RAM 1 alternately bit by bit from 20 to 2
．． 02t or 104 in a toggle manner. Its storage address is specified by IADD. One RA
When the M 102 size or 104 is full, the data is output bit serially from the lead 122 and input to the shift register 1.06. Its speed is one line period τ. 08 times, and is performed eight times during one line period τ.

Its output address is designated by 0ADD.

FIG. 6 shows signal waveforms in each part of the circuit in FIG. 5, but the period axes are the same in FIG.
One line period τ1 is expanded by (B), which is not shown. Same figure (A)
When the image information data IDATA to be recorded is input,
The same data is repeatedly output to the output 122 eight times at eight times the speed. (C) - (Each left half shows the waveform focused on bit O of line O, each right half shows the waveform focused on bit O of line I.
, 047 are omitted with waveform symbols.

RAMs 102 and 104 thus function as toggle buffers, which are performed by the toggle buffer control 130.

The 2-bit delay output QB of the shift register 106 is AND
It is input to one input 124 of the gate 108 ((C) in the same figure. In synchronization with each bit, the heating element 18 for 1 bit and A signal determining the width of the laser pulse 32 to be driven ((F) in the same figure) is supplied from the multiplexer 118 ((D) in the same figure).When this signal is significant, it is sent to the thermal signal. The data transferred to the card 1o is valid, and invalid when unexpected.

Therefore, as mentioned above, if one line of recording data is transferred 8 times and is significant n times, then 1 drive pulse 32 is 1
Line period τ1. The width is n/8 ((F) in the same figure).

The circuit 110°11 is for determining the width of this Q line.
2. formed by 114, 116 and 118.

The RAM i 10 has a storage capacity of 2 x 4 bits and 1- bits, and is addressed by an address line 132 in synchronization with data output from the toggle section and the front section in the upper half of FIG. The storage in the RAM 110 is performed by the signal WE for the last one of the eight data transfers described above for each bit.
This is done by NA or example, and the counter 1
The state of output QA' Q+ (and Q.14) is written to the address corresponding to that bit via data line 134.

The counter 114 has a heating element 18 corresponding to each bit.
Line period τ is the elapsed time since the last time the line was driven. In this example, the driving state of each bit, that is, the previous history, is monitored up to eight line periods ago. More specifically, the output address 0ADD
One bit of image information data is read out eight times from the address of RAM 102t or 104 specified by and transferred to the iPad through the shift register 106 (Fig. 6 (B) and (C)). However, in synchronization with the eighth and final transfer, the contents of the memory location in RAM 110 specified by the same address are read out to output 136, and the contents are read out to output 136.
Protected at 12. 1 is applied to the address input 138 of the ROM 116, and is also applied to inputs A, B, and C of the counter 114. Incidentally, the signal ELCLK is a pixel clock signal that is maintained for each bit of image information data.

The counter 114 responds to the signal CNTLOAD applied in synchronization with bit 1 of the image information data to
- Load the values A, B and C, and also the same 1 bit,
The counted clock signal CNTCLK is divided by CNTCLK, that is, it is stepped from 1 to values A, B, and C, and the values are outputted to outputs QA, QB, and Qo. This output is transferred to the RAM 110 through the lead 134 and written to the corresponding address. This count anomaly 7° operation is performed in response to a signal CNTENA synchronized with the last of the eight transfers of 1 bit, 1. image information data.

Incidentally, the same image information data (FIG. 6(C)) as the other output QB is output to one output QA of the shift register 106, and this is supplied to one input 142 of the NAND gate 140. . If the 1-bit picture information data to be recorded is black as shown by bit-0 on line 0, the NAND gate 140 is activated in synchronization with the signal CNTENA, and the counter 114 is activated by the reset terminal R. is reset to "all O". Hence the outputs QA, QB and Q. "All O's" of "0" are stored in the RAM 110 at the corresponding address.

In this way, the RAMll0 and the counter 114 monitor the previous history of each bit in one line up to eight lines before the drive state.

The ROM i 16 contains addresses AO to A2 given from the lead 138 corresponding to the rest period t of the heating element 18 (formula (7) described above), and a signal T (ERM) indicating the temperature of the substrate 10. The driving force 32 n (FIG. 6 (F)) corresponding to the appropriate input energy E calculated in advance according to equation (7) is stored in the storage location specified by the addresses A3 to A7 given by the phase given by . The pulse width is 320 (same figure).
F,))) is stored as the number n. signal THER
M is a temperature detector 2 such as a thermistor that measures the temperature of the substrate 10.
2 (Fig. 1) and detects it using analog/digital (A/D).
) converted signal and is related to ΔT in equation L(7).

The data indicating the iE pulse number n is read out to the outputs QO to Q7 of the ROM 116, and each time the signal MP Any of the outputs QO-Q7 of the ROM 116 is sequentially output to the lead 126 through the multiplexer 118, and is applied to the AND gate 108 (in FIG. 6) as data for determining the pulse width described above. It should be noted that such feeding of the temperature of the thermal head substrate 10 may be performed with respect to the power supply voltage that supplies the applied voltage HD to the heating element 18 from the sensor 22 on the substrate 10.

In this way, a driving pulse 3'2 with a pulse width of 1/2 times corresponding to the input energy E determined according to equation (7) for each line is applied to the heating element 18.

In this embodiment, when black level recording is performed by dividing one line period τ1 into eight pulses 320, the first n pulses 320 are activated, but the present invention is not limited to this. Instead, n pulses 320 including the last one may be energized, and n pulses 320 including the last one may be energized.
0 may be energized randomly. Note that these numerical values are merely illustrative examples and do not limit the present invention in any way. In addition, although the input energy to the heating element 18 is controlled by increasing or decreasing the number n1 of the pulses 320, that is, the pulse width of the driving pulse 32 of the transistor 186, other methods such as It will be appreciated that this may be accomplished by increasing or decreasing the height of pulse 32, ie, the magnitude of the energizing voltage or current of a switching element such as transistor 186.

An experiment was conducted using an ink sheet 16 with a melting point of 63 DEG C. and a 2048-bit thin film type thermal head as the thermal head 10, and the results of determining the energy applied to the heating element 18 are shown in FIG. This is an approximate formula (
The data satisfies item 7). An image sample under this control condition is shown in Figure 2C, and
It can be seen that the drawbacks of the conventional example shown in FIGS. 2A and 2B have been improved.

Although the explanation so far has focused on thermal transfer recording, the above control conditions can also be applied to thermal recording.

The melting energy of the ink in the circuit shown in Figure 3B is replaced by the coloring energy, and the value of thermal resistance R3 can be considered to be different. , the reference temperature of the substrate temperature Tp is set to 2, although it varies depending on various conditions such as the RAD configuration.
If it is 0℃, the existing 8X8 tot/wn
In the thermal transfer recording system of No. 2, values in the following ranges are generally considered to be advantageous.

EO = 0.5-10 millinoyules/dot A = 1.
0X10 ~2. OX 10-2CIR1=2. O
X 10 ~1. OX I Q-2 The recording example shown in FIG. 2C was obtained under the following condition values.

Eo 20.9 millijoules/dot A = 1.5 x 10-2 C, R1 = 5 x 10-3 Reference temperature = 20°C Effect According to the present invention, the heat storage state of the thermal head heating element can be determined based on its previous driving history and the head Since the substrate temperature is monitored and the driving energy is controlled accordingly, good recording quality can always be obtained regardless of the image information to be recorded. Furthermore, since the driving interval of the heating element can be shortened, thermal recording can be achieved much faster than in the past. Therefore, the present invention is particularly advantageously applied to facsimiles and high-speed solinters.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of a thermal transfer recording system according to the present invention, which cannot be explained in detail, FIGS. 2A to 2C are views showing recording samples according to the prior art and the present invention, respectively, and FIG. 3A is a thermal transfer system. Fig. 3B is a circuit diagram showing an equinodal circuit using the thermal transfer system shown in Fig. 3A as an electrical model; Graphs showing examples; FIG. 5 is a block diagram showing an embodiment of a control circuit of a thermal recording head drive control device according to the present invention; FIG. 6 is a timing diagram showing waveforms appearing in the circuit of FIG. 5; FIG. 1 is a graph showing an example of experimental results of a thermal recording head and a drive control device according to the present invention. Explanation of symbols of main parts 1O...Thermal head structure, 18...Heating element, 2
2...Temperature detector, 1oo...Control circuit, 102°104.110...Random access memory, 108
...AND dart, 114...counter, 116.
... Read-only memory, 13o... Toggle buffer control, 182... Shift reno star. Patent applicant Rico Co., Ltd. Figure 7 True 3A Hole 38 Figure Collection 2, 4 [2] Insect 28 Figure Ice 2C (
21

Claims (1)

[Scope of Claims] In a thermal recording head drive control device for a recording apparatus that performs recording on a recording medium by applying input energy to a heating element of a thermal recording head to drive it, the drive control device comprises: a heating element in front of the heating element; a time counting means for counting the elapsed time t from the driving of the heat recorder; a temperature detection means for detecting the temperature of the structure of the heat recorder; The thermal resistance to the structure is R1z, the input energy required to obtain good recording quality when the structure is at the reference temperature is Eo, the constant is A, the base of the natural logarithm is e, and the time t has elapsed. When the temperature of the structure increases by ΔT, the input energy E1n required to obtain good recording image quality is approximately expressed by the following formula: E,=Eo(1-AΔTp)(16c+n
+ )n. A thermal recording head and a drive control device, comprising: drive control means for controlling the input energy in response to the time counting means and the temperature detection means so as to satisfy the following: