JP2000006459A - Thermal printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal printer capable of taking in the concept of printing efficiency to accurately obtain objective density and to prevent that the irregularity of the resistance value of a heating resistor is displayed as the irregularity of detection temp. SOLUTION: A thermal printer is equipped with a thermal head 1 having a large number of heating resistors R1-Rg6 having characteristics changed in electric resistance value in dependence on temp., a resistance detection part 3 supplying a current to the heating resistors successively in a printing process to obtain detection values for temp. measurement and a printing data forming/ control part 2 obtaining correction values from the correction value groups of the respective heating resistors classified into a plurality of groups with a prepared predetermined temp. range to correct the detection values and estimating printing efficiency on the basis of the start temp. (corrected value) of the heating resistors in the present row obtained in the printing process and the current supply time to the heating elements in a front row to determine the current supply time to the respective heating resistors of the present row on the basis this predetermined efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal printer having a serial or line type thermal head.

[0002]

2. Description of the Related Art FIG. 38 is a perspective view showing a main part of a general serial head type thermal printer. The thermal printer includes a transport roller 101 for transporting recording paper (not shown), a platen 102 disposed near the transport roller 101, and a motor (not shown) that rotates a predetermined angle in response to a pulse. A gear group 103 for transmitting the rotational force of the motor to the transport roller 101; a serial head 104 for printing on recording paper; a head support 105 for instructing the serial head 104; And a paper feed tray 108 for guiding the recording paper in the lateral direction of the recording paper.

FIG. 34 is an explanatory view showing a printing mechanism. The recording paper 110 is located between the serial head 104 and the platen 102. And this recording paper 11
The ink ribbon 106a of the ink ribbon cassette 106 is interposed between the serial head 104 and the serial head 104. Serial head 104 and ink ribbon cassette 106
Moves to the left (carriage scanning direction) in FIG.
The ink ribbon 106a is unwound from the supply roll 106b and is taken up by the take-up roll 106c.
Then, when one line is printed, the transport roller 101 is driven, and the recording paper 110 is moved by the line feed width.

FIG. 35 is a schematic view showing a state in which three lines and approximately one third of the next line are printed on the recording paper 110 by the above-described printing principle.

[0005]

By the way, in the thermal head 201 as shown in the perspective view of FIG. 36, the ink characteristics and the recording paper characteristics are good and the head pressing force at the time of printing and the head and the recording paper Is uniform across all the heating resistors, and the printing density tends to be non-uniform despite the heating resistors being heated during the same energizing time. It is considered that the cause is that the maximum temperature of the heating resistor at the time of heat generation is non-uniform. The non-uniformity is considered to be a difference in a change in temperature rise within an energizing time of each heating resistor, and is considered to be secondary to a difference in a heat storage amount. Specifically, the following elements are included.

[0006] The resistance value of each heating resistor is non-uniform. That is, if the resistance value is different, the amount of generated heat is different and the maximum temperature is different. Non-uniformity of power supply to each heating resistor. That is, the thermal head 20 shown in the perspective view of FIG.
In 1, if the width of the common electrode 202 (only one side is shown in the figure, but actually exists on both sides of the head) is narrow, the voltage drop occurs toward the center, and the supplied power becomes uneven, and Make a difference. This phenomenon is called common drop. Presence or absence of adjacent heating resistors That is, the heating resistor at the end of the heating resistor row has a heating resistor on only one side. Is unlikely to occur. Non-uniform thickness of the heat insulating layer below the heat generating resistor. That is, if the heat insulating layer is thin, the temperature rise gradient slows down quickly and the maximum temperature decreases.

In order to eliminate the influence of the common drop, a thermal head 205 having a folded electrode structure as shown in FIG. 37 is provided. However, in such a thermal head 205, one printing dot is formed by the two heating resistors 206, so that it is not suitable for high resolution.

When the driver IC mounted on the serial head substrate is brought to the flexible cable, the angle formed between the serial head and the platen plate can be reduced, so that the distance from the heating element to the end of the head substrate is reduced. Can be lengthened, thereby increasing the width of the common electrode and reducing the effect of the common drop. However, if the angle formed between the serial head and the platen plate is too small, it becomes inappropriate for the fusion heat transfer to plain paper using resin ink. Here, for printing on plain paper having a rough surface, it is preferable to use resin ink. When the resin ink is heated to a molten state, it adheres to only a plurality of convex vertices on the recording paper surface in a microscopically uneven state, and the resin ink does not break even on a concave portion between the vertices. Therefore, it is possible to transfer a desired area of ink to the recording paper. However, if the base film is to be peeled off in a state where the ink has cooled and hardened, the ink is peeled off from the recording paper while remaining attached to the base film. Therefore, the ink needs to be in a molten state at the time when the base film is peeled off. For this, the time from heating to peeling must be shortened,
If the angle between the serial head and the platen plate is reduced and the width of the common electrode is increased, the contact time between the head and the recording paper increases, and it becomes difficult to shorten the time from heating to peeling.

If the temperature rise of the heating resistor is not uniform,
The non-uniformity of heat storage is promoted by continuous printing, and the degree of non-uniformity of the maximum temperature is increased. Such a problem,
This also occurs in printing with a uniform energization time, but the actual printed image is various. For example, the first half of one line is printed with half of all heating resistors, and the second half is all heating resistors. In the case where printing is performed in the first printing, the unevenness of the heat storage amount generated in the first printing is large, and greatly affects the second printing.

There is known a method of simply determining a correction value of the energization time from a density distribution. This method measures the density distribution generated by printing with a uniform energizing time, and shortens the energizing time for high density parts and prolongs the energizing time for low density parts to obtain a desired uniform density. The way to do it. In other words, this is a method in which an energization time is prepared in advance so that a uniform target density is obtained for each target gradation. According to this method, when the printed image has a uniform gradation, a uniform density distribution is obtained, and even when the printed image is not a uniform gradation, the influence of the common drop and the heat radiation tends to be the same.
Although it has some degree of correction effect, it is not suitable for mass production of a printing apparatus because it is necessary to actually print and measure the density.

From the printing history information of the heating resistor to be controlled and the surrounding heating resistor, the energization time expected to obtain the density of the target gradation is determined in consideration of the heat storage condition and the influence of the common drop. Methods are known. However, a large amount of memory is consumed to store printing history information for a long time and a wide range, and a relatively large-scale and high-speed integrated circuit is required to calculate the energizing time based on the history information. Is required.

JP-A-8-169133 (IPC)
In B41J 2/355), a heating resistor whose electric resistance changes depending on the temperature is used, and the temperature of the heating resistor is repeatedly detected in the process of raising the temperature of the heating resistor by conducting heat. Thus, there is disclosed a method of stopping the energization of the heating resistor when it is detected that the heating resistor has reached a predetermined temperature. Since the maximum temperature of the heating resistor during printing is detected, the density control is performed accurately, but there is a problem that the printing time is delayed. In other words, in this method, during one line printing period,
A plurality of dispersed pulse energizing periods for printing and a plurality of measurement periods for temperature detection are required, and each dispersed pulse energizing period and the measuring period are set alternately. For example, assuming that 64 heating resistors are used, the measurement cycle is 1 μs, and a dispersion pulse is performed 255 times for 255 gradation printing, 1 × 64 × 255 = 1 × 64 × 255 =
About 16 ms is required.

SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide a thermal printer which can obtain a target density without excessively lengthening a one-line printing cycle by incorporating the concept of printing efficiency. And Further, even if there is a variation in the resistance value of the heating resistor, it is prevented from appearing as a variation in the detected temperature.

[0014]

SUMMARY OF THE INVENTION A thermal printer according to the present invention includes a thermal head having a plurality of heating resistors each having a characteristic in which an electric resistance value changes depending on temperature, and a thermal head having a plurality of heating resistors in a printing process. A detection value obtaining means for obtaining a detection value for temperature measurement by sequentially energizing, and a correction value from a correction value group for each heating resistor classified into a plurality of classes within a predetermined temperature range prepared in advance. Means for acquiring and correcting the detection value.

[0015] A provisional temperature of the heating resistor is obtained from the detection value obtained by the detection value obtaining means and the characteristic, and then a correction value is obtained from the correction value group to correct the detection value. You may be able to.

Under the first temperature condition, each heating resistor is not energized for printing but is energized for measurement, and is calculated based on each detected value obtained by energizing for measurement, the average detected value, and the characteristic. The first correction value for each heating resistor for each temperature class obtained in the above may be obtained, and the first correction value may constitute the correction value group. According to such a correction value group, even if there is a resistance value variation in the heating resistor, it can be prevented from appearing as a detected temperature variation.

The detected values of the respective heating resistors are obtained by energizing the respective heating resistors after the second temperature condition higher than the first temperature condition, and the detected values are obtained under the first temperature condition. Each heating resistor is not energized for printing, and each heating value for each temperature class obtained by calculation based on each detection value, average detection value, and the characteristic obtained by energizing for measurement. The detection value is corrected by the first correction value obtained for the resistor, an average curve of the corrected values that are the corrected values is obtained, and a difference between the corrected values with respect to the average curve is defined as a variation. The process of obtaining the variation is performed under one or more temperature conditions different from the second temperature condition, and the plurality of variations under the different temperature conditions obtained for each heating resistor is used to calculate each heating resistance for each temperature class. The variation of the body is determined and this is used as the first correction value. Obtains a second correction value by taste may constitute the correction value group by the second correction value. According to such a correction group, even if each heating resistor has a variation in the resistance change rate, or even if the resistance change rate changes with temperature, it can be prevented from appearing as a detected temperature variation. .

The one or more temperature conditions different from the second temperature condition may be obtained during a natural cooling period after the second temperature condition.

The one or more temperature conditions different from the second temperature condition may be set separately from the second temperature condition.

The second temperature condition or a temperature condition set separately from the second temperature condition may be realized by energizing the heating resistor. Here, the above-mentioned temperature condition can be realized by placing the head in a constant temperature chamber, but in this case, it takes time until the temperature is changed and the temperature is stabilized. Therefore, it is not suitable for obtaining individual correction values of mass-produced heads.

Efficiency estimating means for estimating the printing efficiency based on the starting temperature of the heating resistor in the current row and the energizing time to the heating resistor in the front row obtained in the printing process, and based on the printing efficiency. Print data generation control means for determining the energization time to each heating resistor in the current row.

The efficiency estimating means corrects the printing efficiency based on the energizing time of the front row of the target heating resistor and the energizing time of the front row on both sides adjacent to the target heating resistor. Is also good.

A correction means is provided for correcting a temperature difference due to a detection time shift from the first heating resistor to the last heating resistor by natural cooling when a heating value is sequentially supplied to obtain a detection value for temperature measurement. You may. Here, when printing is performed for a uniform energizing time, all the heating resistors reach the peak temperature at the same time, and then are naturally cooled. Temperature detection is performed before energization for printing. That is, since the detection is performed during the cooling period, the earlier the detection time is, the higher the detected temperature is. Therefore, for example, the detection value of the heating resistor whose detection time is early is corrected to a small value, and the detection value of the heating resistor whose detection time is late is corrected to a large value.

The correcting means may be realized by a correction value group in which a correction value is added to a correction value group for each heating resistor classified into a plurality of classes within a predetermined temperature range prepared in advance. According to this, the correction for the variation in the detection time is performed simultaneously with the correction for the variation in the resistance value of each heating resistor. Assuming that the temperature detection value at room temperature detected in the non-printing state is corrected by a correction value group of a higher temperature class, a linear approximation of the distribution in which the corrected values are plotted in the order of temperature detection. The slope of the straight line has a positive value.

[0025] The correction value may be set in consideration of the energizing time of front row printing. Here, in natural cooling, the slope of the temperature drop slows down with time. The longer the energization time, the shorter the cooling time, and the steeper the slope of the temperature drop at the temperature detection time. In this case, since the difference between the detection values due to the difference in the detection time becomes large, the tendency to gradually increase the correction value in the detection order is increased. If the energization time is short, the reverse is true.

[0026] The correction value may be set in consideration of the starting temperature of the current row printing. When the front row energizing time is long, the start temperature of the next row increases with the peak temperature. Therefore, the temperature of the current row can be used instead of referring to the energization time of the front row. Here, if a correction table is prepared for each energization time, a large amount of memory will be consumed.
With this configuration that takes into account the starting temperature of the current row printing, the correction value for each temperature class only needs to take into account the correction value according to that temperature (the tendency of the correction value gradually increases with temperature). Only one correction table is required.

The table for estimating the printing efficiency is shared by the thermal heads, and the average resistance of the heating resistors of the employed thermal head is taken into account in consideration of the difference in the amount of heat generated by the difference in the average resistance of each thermal head. Control means may be provided for adjusting the response to the heat value by the value, not by the applied voltage, but by the ratio of the ON time to the cycle of a plurality of dispersed pulses constituting the energization time. Here, the average resistance values of the heating resistors in the two heads are X ₀ and X ₁ (X ₀ <X ₁ ), respectively.
Assume that If the applied voltage of the head are the same, often the amount of heat generated towards the head of average resistance value X average resistance value X ₁ of the head of _0, setting to both the same energization time that corresponds to the same target density However, the printing densities of the two differ from each other. If the adjustment for such a difference is performed with the voltage applied to the head, the actual measurement is performed at a voltage different from the head voltage at the time of acquiring the correction value table, and the correction value becomes meaningless. The adjustment value table can be utilized by adjusting the ON time with respect to the cycle of the plurality of dispersed pulses constituting the energization time.

A motor drive control means for stopping the operation of the motor during energization of each heating resistor for temperature detection in the printing process may be provided. According to this, it is possible to prevent noise from the motor from being mixed into the digital value which is the temperature detection value, and to obtain an accurate temperature detection value.

[0029]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a main part of a printing data control system of a thermal printer according to an embodiment of the present invention. This thermal printer includes a serial type thermal head 1. The serial type thermal head 1 has a plurality of heating resistors (R1 to R96) arranged in a line in a vertical direction (recording paper conveyance direction: sub-scanning direction), and supplies print data to the heating resistors. The one-line printing is performed, and the one-line printing is repeated while scanning the thermal head 1 in the horizontal direction (main scanning direction) of the recording paper, thereby forming one scanning recording line. The image is formed on the recording paper by repeating the printing. In addition, each of the heating resistors (R1 to R96) constituting the thermal head 1 has a resistance (for example, a characteristic called NTC, which lowers a resistance value with respect to a temperature rise called a NTC) that changes a resistance value in response to a temperature change. ). Therefore, data (AD_OUT described later) obtained by measuring the resistance value of each heating resistor is also temperature data of each heating resistor.

The basis of the printing data control in this embodiment is to determine the temperature of each heating resistor at the time of performing one-line printing, that is, to start the one-line printing. That the temperature of the heating resistor is several times,
The printing efficiency is estimated based on the actual energizing time in the previous one-line printing, and the energizing time to each heating resistor is controlled from the printing efficiency. Here, the printing efficiency is constant despite the fact that a constant head voltage is applied and printing is performed with the same energizing time.
Depending on the position of the heating resistor, the number of simultaneously energized dots, or the degree of heat storage, when the printing density differs, it is assumed that the printing efficiency is good when the high density comes out, and the printing efficiency is bad when the low density comes out only. Can be defined as

When the starting temperature of one-line printing is ascertained by using the resistance value of each heating resistor, since the resistance value varies between the heating resistors, an error occurs in the measured temperature based on the resistance value. included. In order to eliminate this error, it is necessary to create a temperature correction table for each heating resistor. In this embodiment, the temperature of the heating resistor is divided into several classes, and a temperature correction table is created for each class.

The host control circuit 14 performs various controls in the thermal printer, a carriage motor 16,
Control (excitation ON / OFF) of the motor drive circuit 15 that drives the ink motor 17 and the LF (line feed) motor 18, that is, the resistance value (temperature) of each heating resistor
Is detected, the excitation of the motor is turned off, and in the actual printing process after the detection, control is performed to turn on the excitation of the motor. Further, when the data generation / control unit 2 detects the resistance value (temperature) of each heating resistor according to a predetermined sequence, the transistor Tr1 is turned off. In the actual printing process after the detection, the transistor Tr1 is turned off. O
N is controlled.

The data generation / control section 2 generates printing data (SDATA) to be given to the thermal head 1 based on image data (DATA) given from outside (not shown). In addition, as will be described later, resistance value measurement data (SDATA) for measuring the resistance value (temperature) of each of the heating resistors R1 to R96 of the thermal head 1 is generated. Further, after the resistance value (temperature) of the thermal head 1 is measured, the printing data (SDA) based on the printing efficiency is obtained.
TA) is corrected.

The thermal head 1 includes 96 heating resistors R1 to R96, a shift register section 6, a latch output gate section 7, and a driver section 8. A data generation / control unit 2 is connected to the thermal head 1 and print data (SD) supplied to each of the heating resistors R1 to R96.
ATA), resistance measurement data (hereinafter, may be simply referred to as printing data including resistance measurement data), and various control signals. Also thermal head 1
Is connected to a resistance value measuring unit 3.

The shift register 6 provided in the thermal head 1 is constituted by cascading, for example, 96 D-type flip-flops. This shift register 6 includes:
Printing data (SDATA) and a head clock signal (HCLK) supplied from the data generation / control unit 2 to each of the heating resistors R1 to R96 are provided. The printing data (SDATA) is a head clock signal (HCLK)
Is given serially in synchronization with

In the latch section 7, for example, 96 latch circuits are provided corresponding to the D-type flip-flops constituting the shift register 6, respectively. Each latch circuit receives a latch signal (/ LA) from the data generation / control unit 2.
TCH: / indicates negative logic), and the printing data (SDATA) stored in the shift register 6 is output to the driver unit 8 in parallel based on the latch signal (/ LATCH). You.

In the driver section 8, for example, 96 AND circuits are provided corresponding to the 96 latch circuits constituting the latch section 7, respectively. Each AND circuit receives a strobe signal (/ ST) from the data generation / control unit 2.
B) are provided, and the strobe signal (/ ST
Based on B), the printing data (SDATA) given from the latch unit 7 is given to each of the heating resistors R1 to R96.

The heating resistors R1 to R96 are formed of resistors whose electric resistance changes depending on the temperature, and are connected in parallel to a head voltage supply line to which the head voltage Vh is supplied. Outputs from the respective AND circuits included in the driver unit 8 are provided to terminals of the heating resistors R1 to R96 opposite to the terminals to which the head voltage supply lines are connected, respectively. It has become.

The resistance value measuring section 3 includes a transistor Tr1,
The thermal head 1 is configured to include a resistor Ra, a differential amplifier 10 and an analog / digital converter (hereinafter, referred to as an AD converter) 11, and measures resistance values of the heating resistors R1 to R96 of the thermal head 1.

The transistor Tr1 has its ON / OFF
Is used to switch between the resistance value measurement operation and the normal printing operation.
It is turned on / off in A). This transistor Tr1
Is constituted by a PNP-type bipolar transistor or the like in this embodiment, the collector terminal is grounded,
The emitter terminal is connected to the common (GND) of the driver section 8 of the thermal head 1. Then, the measurement control signal (EN) from the data generation / control unit 2 is supplied to the base terminal.
A) is given.

The resistor Ra has a preset resistance value, one end is grounded, and the other end is connected to the transistor Tr1.
And the driver section 8 of the thermal head 1, and when the transistor Tr1 is OFF, the head voltage Vh is divided by the selected one heating resistor and the resistor Ra. .

The differential amplifier 10 includes an amplifier 13 and four resistors r1 to r having arbitrary resistance values.
4 is included. The inverting input terminal of the amplifier 13 is supplied with a preset reference voltage Vref, and the non-inverting input terminal is connected to each of the heating resistors R1 to
Connected between R96 and resistor Ra. The differential amplifier 10 amplifies the difference between the divided value of the head voltage Vh divided by the selected one heating resistor and the resistor Ra and the reference voltage Vref.

The AD converter 11 has an input terminal IN,
An output terminal OUT and a chip select terminal (/ CS) are provided. The output voltage Vo output from the differential amplifier 10 is applied to the input terminal IN, and the applied output voltage V
o is subjected to analog / digital conversion. From the output terminal OUT, the analog / digital converted output voltage Vo is
It is output as a digital detection value (AD_OUT). The data generation / control unit 2 also supplies an analog / digital conversion instruction signal (/ A) to a chip select terminal (/ CS).
D_CS).

A memory 4 constituted by a RAM or the like stores digital detection values (AD_OUT) of the respective heating resistors R1 to R96 of the thermal head 1 measured by the resistance measuring section 3. In addition, the power supply time data to each heating resistor corresponding to the detection correction value (Dh), the temporary efficiency (temporary η), the efficiency correction value (ηh), and the corrected efficiency (η), which are temperature correction tables, are stored. . Further, it is also used as a work area for performing various controls in the thermal printer.

FIG. 2 shows the timing of various signals in the operation of measuring the resistance (temperature) of the heating resistor at the start of one-line printing and the subsequent actual printing operation. In addition,
When the detection correction value (Dh), which is the temperature correction table, is obtained, the same processing as the processing in the “resistance measurement period” in FIG. 2 is performed. Hereinafter, the operation of measuring the resistance (temperature) of the heating resistor at the time of starting one-line printing based on FIG. 2 will be described, and then the detection correction value (D
Specific contents for obtaining h) will be described.

[Resistance (Temperature) Measuring Operation] When a low level measurement control signal (ENA) is supplied from the data generation / control section 2 to the base terminal of the transistor Tr1 (FIG. 2).
(See (e)), the collector-emitter of the transistor Tr1 conducts, the heating resistors R1 to R96 are grounded via the transistor Tr1, and an operation state for forming an image on recording paper is set. On the other hand, the transistor Tr1
When a high-level measurement control signal (ENA) is supplied from the data generation / control unit 2 to the base terminal of the transistor Tr1 (see FIG. 2E), the collector and the emitter of the transistor Tr1 are cut off, and each heating resistor is turned off. R1 to R96 are grounded via a resistor Ra, and each heating resistor R1 constituting the thermal head 1
An operation state for measuring the resistance values of R96 to R96 is set. Hereinafter, the operation of measuring the resistance (resistance measurement period) will be described.

With the rise of the measurement control signal (ENA) applied to the base terminal of the transistor Tr1 to the high level, the data generation / control unit 2 outputs resistance measurement data (SDATA), for example, "100... (Indicating that only the heating resistor R1 is energized) is supplied to the shift register 6 of the thermal head 1 based on the head clock signal (HCLK) (see FIGS. 2A and 2B). This resistance measurement data (SDATA) “100
.. 0 ”is resistance measurement data for energizing only one of the 96 heating resistors R1 to R96. In this case,
This is resistance value measurement data for energizing only the heating resistor R1. The transfer of the resistance value measurement data (SDATA) requires time td. As the ENA rises, the pulse motors 16, 17, and 18 are de-energized by the processing of the host control circuit and the motor drive circuit.

After the transfer of the resistance value measurement data (SDATA) is completed, that is, after a lapse of time td from the rise of the measurement control signal (ENA) to the high level, the falling of the latch signal (/ LATCH) occurs. The resistance measurement data (SDATA) stored in the shift register 6 is latched by each of the 96 latch circuits of the latch unit 7 (FIG. 2).
(C)). When the strobe signal (/ STB) falls to a low level after the resistance measurement data (SDATA) is latched in the latch unit 7, the driver unit 8
, Data for resistance value measurement (SDATA) is given to each of the heating resistors R1 to R96, the head voltage Vh is applied only to the heating resistor R1 to be measured, and only the heating resistor R1 is energized. (See FIG. 2D).

At this time, the other heating resistors R2 to R96
, The head voltage Vh is divided by the heating resistor R1 and the resistor Ra, and the divided voltage is supplied to the non-inverting input terminal of the amplifier 13 of the differential amplifier 10. The differential amplifier 10 outputs the output voltage Vo by subtracting the reference voltage Vref from the divided voltage (see FIG. 2F). In this case, the output voltage Vo is set within a predetermined range by the respective resistance values of the four resistors r1 to r4 constituting the differential amplifier 10.

The output voltage Vo is supplied to the AD converter 11
And an AD converter select signal (/ AD_C) supplied from the data generation / control unit 2
Analog / digital conversion is performed with the fall of S) (see FIG. 2 (g)). In the AD converter 11,
The digitized output voltage Vo is output from the output terminal OUT as an output signal (AD_OUT) and stored in the memory 4 via the data generation / control unit 2 (FIG. 2 (h)).
reference).

As described above, the resistance value of the heating resistor R1 is measured. During or after the measurement, the data generation / control section 2 outputs a one-pulse head clock signal (HCLK) rising to a high level to the shift register 6 as shown in FIG. 2 (FIG. 2B). reference). The shift register 6 receives the 1 of the head clock signal (HCLK).
The resistance measurement data (SDA) that is supplied only to the heating resistance element R1 stored in the shift register 6 by a pulse.
TA). For example, the measured resistance value data (SDATA) is “100...
If it is “0”, it is shifted right by one, and the resistance value measurement data (SDATA) becomes “010... 0” that energizes only the heating resistor R2. As a result, the next latch signal (/ LATCH) Strobe signal after falling (/
With the fall of STB) (see FIGS. 2C and 2D), the heating resistor R2 is energized, and the above-described processing is performed to measure the resistance value of the heating resistor R2. .

Each time the resistance value of each heating resistor is measured as described above, the shift processing of the resistance measurement data (SDATA) stored in the shift register 6 is performed, and the measured heating resistor is measured. Heating resistors R2 to R9 different from R1
The resistance measurement data for measuring the resistance of No. 6 is created. After the resistance value of the last heating resistor R96 is measured, the measurement control signal (ENA) falls to a low level (see FIG. 2 (e)), and an operation state for forming an image on recording paper is set. The shooting operation is started. When this printing operation is started, the pulse motors 16, 17, and 18 are excited by the processing of the host control circuit 14 and the motor drive circuit 15.

[Detection correction value (D
h) Acquisition Method] The acquisition method of the detection correction value (Dh) will be described with reference to FIGS. 6 to 19 based on the flowcharts of FIGS.
Will be described with reference to the above as appropriate. First, as described above, the detected value (AD_OU) of each heating resistor at normal temperature is used.
T) and an average detection value thereof is obtained (step S81). Next, the detected value and the average detected value are converted into a resistance value (step S82). Then, the NTC value (NT
Assuming that the resistance change rate of the C-characteristic resistor) is -1200 ppm, each resistance value and average resistance value with respect to the temperature of each heating resistor are calculated by calculation (step S8).
3). Here, if the resistance at room temperature is 1150 Ω, 1100 Ω, and 1050 Ω, the results of a, b, and c shown in FIG. 13 are obtained. Can be regarded as an average resistance value of 1100Ω.

The above resistance values and average resistance values are converted into detection values. By this conversion, a, as shown in FIG.
The results of b and c are obtained. Further, the average detected value (detected value of a standard heating resistor having an average resistance (b in FIG. 12)) with respect to the temperature obtained by this conversion is taken on the X axis, the detected value of each heating element is taken on the Y axis, and the NTC value is calculated. A detection value graph (table) assumed to be constant is created (step S84). That is, a correction graph when the NTC value is assumed to be constant is created. Specifically, as shown in FIG.
25 ° C for a heating resistor having an average characteristic of
If the detection value of (60) is obtained at the time of (2), the value of (32) is changed to the detection value of (92) at 25 ° C. for the heating resistor having the characteristic of a. Subtraction correction is required. When the heating resistor having the characteristic of c is at 25 ° C., (3
Since the detection value becomes 1), a correction for adding the value of (29) is required. When the heating resistor having the average characteristic of b is at 75 ° C., (10
If the detection value is 2), the detection value of (136) is obtained for the heating resistor having the characteristic of a when the temperature is 75 ° C. Therefore, the correction of subtracting the value of (34) is necessary. It is. In addition, when the temperature of the heating resistor having the characteristic of c is 75 ° C., the detected value becomes (72), so that a correction of adding a value of (30) is necessary. The correction graph shows such a correction relationship.

As described above, the correction value of the detection value for each heating resistor is prepared for the temperature. In order to reduce the number of data, the temperature is divided into 16 classes, and a table as shown below is prepared. 1 is created (step S85). This correction table (numbers in non-brackets) is referred to as a first correction value table. here,
In this correction table and the following description, of the 96 heating resistors, the first to forty-eighth heating resistors have the characteristic of a, and the forty-ninth to ninety-sixth heating resistors. The heating resistor is shown as having the characteristic of c. In Table 1 below, the numbers in parentheses indicate the values after correction due to the detection time shift described later. This correction will be described later.

[0056]

[Table 1]

Next, an experiment is conducted in which all the heating resistors are heated in several stages of energization time (step S91). Here, the entire head portion of the thermal head is, for example, 50 ° C.
Alternatively, in a case where the temperature is substantially uniform at a temperature other than the normal temperature such as 70 ° C., even if the detected value obtained in this state is corrected using the first correction value table, the corrected value is 50 ° C. Or, it is a small variation centered on a value such as 70 ° C. Therefore, a second correction value table is created based on the results of an experiment in which all heating resistors are heated during the several stages of energization time (steps S92 to S92).
96, steps S101 to S105).

First, a heat generation experiment will be described. In this embodiment, the heating resistor is repeatedly energized until 300 to 400 cycles (rows) at which the temperature change is saturated at the same cycle as normal printing. FIG. 6 shows a case where all the heating resistors are heated during the three stages of energization time. The first stage is a case where 167 times of energization are performed for each heating resistor for 28 μs in the printing of one row for a duration of 28 μs, and this is repeated for n rows. The energization is performed 107 times with 28 μs energization time for each heating resistor in the printing, and this is repeated for n columns. The third stage is energization for 28 μs for each heating resistor in one row of printing. This is a case where current is supplied for 47 times in time, and this is repeated for n columns. Note that this temperature experiment does not need to be an actual printing with an ink ribbon or recording paper.

FIG. 8 shows that in a three-stage experiment, 36
When energization is stopped after energization of 0 rows (period),
This shows how the temperature of the head portion decreases. Immediately after the energization is stopped, the heat is unevenly distributed due to the variation in the resistance value of each heating resistor, but as time passes, the heat moves from the higher side to the lower side, and the temperature distribution becomes smooth. The state of the temperature drop after the temperature distribution becomes smooth is detected. For this reason, in FIG. 8, the measurement is started not from the 361st column immediately after the energization but from the next 362th column. Of course, the measurement may be started after several cycles (rows).

The temperature measurement of the heating resistors in each row is performed in the same process as the temperature detection at the start of printing in each row in actual printing. Here, as shown in FIG. 7, 6 m of one cycle (time allocated to one column printing)
In s, there are a measurement period (0.768 ms) and an energization period (the maximum is 28 μs × 167 = 4.68 ms).
In the temperature detection during the temperature decrease in this heat generation experiment, no current is supplied to the heat generating resistor during the current supply period.

FIG. 9 shows one measurement period (0.768 m
In s), the manner in which the detection values of each of the 96 heating resistors in one row are obtained is shown. The temperature gradually decreases when the detection values of the 96 heating resistors in one row are obtained.

Next, a first provisional correction process of adding a normal temperature correction value (Dh (normal temperature) i) in the first correction value table to each detected value is performed (step S92). Here, AD_OUTi is a detection value by detection, and AD_OUi
Tmean is used as a detection value by the calculation in FIG.

Here, among the 96 heating resistors, the first to forty-eighth heating resistors have the characteristic a (low resistance at normal temperature) and the forty-ninth heating resistor. Assuming that the 96th heating resistor from the body has the characteristic of c (high resistance value at room temperature), if it is at room temperature, FIG.
A result like 0 (a) will be obtained. Also, as shown in FIG. 11, if the 96th heating resistor from the first heating resistor has a temperature distribution of 75 ° C. to 125 ° C., the result shown in FIG. become. If the resistance change rates (NTC values) of the seventeenth and eighty-first heating resistors are smaller than -1200 ppm, the projection-like detection results shown in FIG. 10B are obtained. Then, when the first temporary correction process is performed on this result, as shown in FIG. 14, the corrected value of the detected value of the first heating resistor at 75 ° C. is 136-32.
Is (104), the corrected value of the detection value of the forty-eighth heating resistor is (129) at 161-32, and the corrected value of the detection value of the forty-ninth heating resistor is (124) at 95 + 29.
And the corrected value of the detection value of the 96th heating resistor at 125 ° C. is 118 + 29, which is (147). Here, since the temperature distribution is simply assumed as shown in FIG. 11, the change in the resistance value and the change in the detected value of each heating element can be predicted as shown in FIGS. 13 and 12, but the temperature is actually unknown. For,
The changed detection value is unknown, and no correction value is obtained.
Therefore, a known correction value at normal temperature is used as the correction value of the first provisional correction. The validity is described below. In the first place, the correction value is a value obtained by adding a correction value to a detection value that varies for each heating resistor at a certain temperature to be the same value as a detection value of a virtual standard heating element having an average resistance value. Therefore, the correction value varies with the variation in the resistance value, and the distribution shape is similar at any temperature. Focusing on a certain heating resistor, the change in the correction value for various temperatures is small compared to the variation in the resistance value at a certain temperature. For example, in FIG. 12, the normal temperature 25 ° C. correction values of the heating resistors a and c are −32, +29,
The difference is 29 − (− 32) = 61, whereas the difference between the correction values at room temperature 25 ° C. and 125 ° C. is 3 for a.
There are only 6-32 = 4 and 32-29 = 3 for b.
Therefore, it can be said that the error is small even if a known correction value at normal temperature is used instead of the unknown correction value at unknown temperature.

Next, AD_OUT after the first temporary correction
The distribution of i is obtained, and the average curve (temporary θi) is obtained (step S93). That is, in the case of FIG. 14, this is the corrected value of the detection value of the forty-eighth heating resistor (129).
And the corrected value of the detection value of the 49th heating resistor (1
24) and a curve (see the dashed line in the figure) passing through the middle (126.5). (126.5)
Is -34 for the characteristic a and -30 for the characteristic c (see FIG. 12). Note that acquisition of the average curve (temporary θi) is performed by Fourier transform and inverse Fourier transform. That is, the distribution of the provisionally corrected detection values fluctuates finely, and this fluctuation is captured as a wave to perform Fourier analysis. By this Fourier analysis, the wave is separated into sine waves of each partial period when the entire distribution is one period. By removing high-frequency components from these sine waves and performing inverse Fourier transform on the rest, an average curve passing through the center of the variance after provisional correction that fluctuates finely can be obtained.

Next, a second provisional correction is performed (step S9).
4). First, a temperature class is selected from the temporary θi, and a temporary Dhi is obtained from the first correction value table. Then, the temporary Dhi is added to the detected value. That is, in the case of FIG.
The detected value 136 of the first heat generating resistor of the above is added to the provisional Dh of 75 ° C.
i = −34 [the detected value 1 of the first heating resistor at 75 ° C. 1
36 is (104) after the first provisional correction,
In the temperature class 7 of Table 1, -34 is obtained. ], The value after the second provisional correction becomes (102), and the value after the second provisional correction of the forty-eighth heating resistor is 161-34.
[As described above, the provisional θi for the temperature class of (126.5) is -34 for the characteristic a] and becomes (127),
The value of the forty-ninth heating resistor after the second provisional correction is 95 + 30.
[As described above, the temporary θi for the temperature class of (126.5) is +30 for the characteristic c] and becomes (125),
The value of the 96th heating resistor after the second provisional correction is 118 + 3
The value after the first provisional correction for the detected value 118 of the 96th heating resistor at 2 [125 ° C. is (147), and +32 is obtained in the temperature class 12 of Table 1. ], The value after the second provisional correction becomes (150). And
By such processing, the second temporary correction result shown in FIG. 15 is obtained.

Next, the second temporarily corrected value AD_OU
By taking the distribution of Ti, an average curve θi is obtained (step S9)
5). The acquisition of the average curve (θi) is also performed by Fourier transform and inverse Fourier transform. Then, the above correction processing is performed n times (step S96). In this embodiment, three rows are measured at each of the three stages (see FIG. 8).

Next, the second temporarily corrected value AD_OU
The average curve θi is subtracted from Ti (step S101).
As a result, a variation i is obtained. For example, the variation from the first heating resistor to the entire 96th heating resistor in one measurement is as shown in FIG. As a result of this processing, as shown in FIG. 18, a data pair of the average curve θi and the difference (variation i) is obtained for each heating resistor (column 362, column 363,...). This process is performed n (9) times (step S10)
2).

Next, in each heating resistor, the variation i =
An approximate expression is created in the form of fi (θi) (step S10)
3). That is, for each heating resistor, the average curve value is plotted on the horizontal axis and the variation i is plotted on the vertical axis, so that the correlation of the variation with the temperature substitute value (the value of the average curve) in each heating resistor is known. . FIG. 17 shows the variation i = fi (θi) for the seventeenth heating resistor.

Next, based on the above approximation equation, the variation i = fi (θ center value of each class) corresponding to the center value (θ center value) of the temperature substitute value of each temperature class in the first correction value table ) Is obtained (step S104). For example, in the case of the temperature class 7, since the temperature substitution range is 101 to 109, a variation i of each heat generation resistance value with respect to the central value 105 is obtained, and is set as the variation in the temperature class 7.

Next, a second correction value table is created by subtracting the variation i = fi (θ center value of each class) from the correction value of each heating resistance value of each temperature class in the first correction value table ( Step 105). The second correction value table is conceptually shown in Table 2 below.

[0071]

[Table 2]

FIG. 20 is a diagram showing the concept of an overall table using the second correction value table as a detection correction value (Dh).

The acquisition of the second correction value table described above is performed by the configuration shown in FIG. 19 at the time of shipping the printer. That is, the control board 53 is connected to a measurement printer 52 having a thermal head (measured head 51) to be measured. The control board 53 is a circuit corresponding to the circuit in FIG. The detected value (digital value) from the A / D converter of the control board 53 is arranged and stored in the logic analyzer 54. Personal computer 55
Inputs the detection value (digital value) from the logic analyzer 54 and executes the processing for creating the above-described second correction value table. The created second correction value table is stored in the memory as text data.

[Method of Correcting Detected Resistance Value (Temperature) with Detection Correction Value (Dh)] For a certain heating resistor (for example, the R-th heating resistor), as shown in the flowchart of FIG. In the second correction value (detection correction value (Dh)) stored in the memory, the first temperature class to the Rth
Read the correction value Dh of the th heating resistor (step S
61). Then, provisional correction is performed (step S62). The temporary θ obtained by the temporary correction is obtained by adding a correction value of the first temperature class to the actually detected value AD_OUT. Next, from the second correction value table, the temporary θ
Is selected, and the correction value Dh of the R-th heating resistor is read (step S63). And
This temporary correction is performed (step S64). Θ obtained by the main correction is obtained by adding the correction value Dh (the corresponding class) of the corresponding temperature class to the actually detected value AD_OUT.

That is, in order to formally correct each detected value, the correction must use a correction value corresponding to the temperature class. However, it is not possible to immediately select the temperature class from the detected values. Can not. For example, for the heating resistor having the characteristic of FIG.
, The correction value at that temperature (75 ° C.) must be corrected to (102) by adding -34, which is a correction value at the first temperature class, since this cannot be performed immediately. -32 is added, and (10
A temporary correction value of 4) is obtained, and this value is read out from the second correction value table to read out a correction value of -34 to perform the main correction.

[Estimation Processing of Printing Efficiency] (Tentative Estimation of Printing Efficiency) The printing efficiency will be described again, although a constant head voltage is always applied and printing is performed with the same energizing time. When the printing density differs depending on the position of the heating resistor, the number of simultaneously energized dots, or the degree of heat storage, the printing efficiency is good when the high density appears, and the printing efficiency is poor when the low density appears only. , Can be defined as

Here, the distribution of the starting temperature when printing is performed for a thermal head having a common electrode (see FIG. 36) for a uniform energizing time is high near the left and right sides of the head as shown in FIG. Low at left and right ends and center. In particular, when a head having a narrow common electrode is used, the voltage drop at the center of the head becomes large, so that the power supply becomes smaller, the calorific value decreases, the temperature decreases, and the printing density decreases at the center. . This phenomenon is called common drop.
Further, since the left and right ends have only one heating resistor on one side, the escape of heat at the time of temperature rise or temperature drop becomes large, and the temperature becomes low. The density distribution in printing using such a head has the same shape as the temperature distribution in FIG. 32 described above (FIG. 31).
Reference: density distribution without correction). In other words, even if the same amount of current is applied to each heating resistor, the printing efficiency of the heating resistor near the left and right of the head is high, and the printing efficiency is low at the left and right ends and the center.

In the temperature distribution in printing where the same amount of current is applied to each heating resistor, the temperature is made dimensionless with reference to the highest temperature and the lowest temperature. This dimensionless temperature is substituted for the printing efficiency. If a certain temperature is obtained as a result of imprinting during a certain energizing time, the data is organized so that it can be understood how much the dimensionless temperature is compared with the reference temperature at the energizing time. Then, at each energizing time, a data pair of the print density with respect to the dimensionless temperature is acquired. By rearranging the group of these data pairs, it is sufficient to know how long the energization time should be to obtain an arbitrary target concentration at an arbitrary dimensionless temperature.

For example, FIG. 32 shows that the eleventh heating resistor to the eighth heating resistor among the 96th heating resistor from the first heating resistor.
6 is a detection value after temperature correction when a predetermined time is supplied to the heating resistor 6 in a heat-saturated state (see FIG. 6). In FIG. 32, for example, the detection value after correction is 11
The printing efficiency of about 5 (approximately the center of the heating elements) is "5", and the printing efficiency of the corrected detection value of about 132 (near the left and right of the heating elements) is "60". Then, if the printing efficiency is obtained for each energizing time of 0 to 255, the table shown in FIG. 21 is obtained.

The above-mentioned printing efficiency is based on how many times the temperature of the heating resistor at the time of starting one-line printing and what the actual energizing time was in the preceding one-line printing. However, the temperature of the heating resistor at the time of starting the one-line printing is obtained several times by detecting the resistance value of each heating resistor and correcting the detected value. Can be On the other hand, the actual energization time in the preceding one-line printing can be obtained by writing the energizing time in the front row in the memory and reading it out when printing the current row.

If the printing efficiency is known and the printing density data at each printing efficiency is prepared, if a certain target density is to be obtained, the target efficiency is obtained from the prepared data based on the efficiency at that time. What is necessary is just to search for the energizing time at which the temperature is obtained.

FIG. 23 is a table showing the relationship between the printing efficiency and the target gradation (printing data). Based on this table, the energizing time for obtaining the target temperature at the printing efficiency at that time is searched. You can come. The printing efficiency in this table is the corrected printing efficiency, and the correction will be described below.

(Correction to Provisional Estimated Value) According to the above-described printing data correction control using the printing efficiency, a substantially desired density could be obtained. However, stripe-shaped density non-uniformity may occur in the direction in which the head carriage scans, that is, in the direction perpendicular to the row of heating resistors. Analysis of the cause revealed the following. The printing efficiency of the heating resistor to be controlled is determined by the temperature at the start of the heating resistor and the energizing time in the front row. When the energization time on both sides is long, since the starting temperature of the heating resistor to be controlled is high, the dimensionless temperature is high, and it is estimated that the heating resistor has high printing efficiency. . Then, a shorter energizing time is allocated, and the actual printing density becomes lower than the target density. Conversely, if the energizing time of the heating resistor in the front row is long but the energizing time on both sides thereof is short, the temperature at the start of the heating resistor to be controlled is low, and thus the dimensionless It is presumed that the heating resistor has a low temperature and a low printing efficiency. Then, a longer energizing time is allocated, and the actual printing density becomes higher than the target density.

Therefore, the printing efficiency of the heating resistor to be controlled is corrected in consideration of the energization time in the front row of the heating resistor adjacent to the heating resistor to be controlled. In this embodiment, the energization time of the heating resistor to be controlled is subtracted from each of the energization times of the left and right heating resistors in the front row, and the sum is taken. The larger the total value, the lower the estimation efficiency. Correction is performed so that the smaller the total value, the higher the estimation efficiency.

FIG. 22 shows a table of the provisional efficiency correction value (ηh) in the above correction. FIG. 33 is a graph showing the table of FIG.
In FIG. 33, instead of “sum of the difference between the front row energizing time and both sides”, “sum of the difference between the front row energizing time and both sides” +
64 ". Originally, the “sum of the difference between the front row energizing time and both sides” takes a value of ± 64, but in order to make the total value correspond to the address of the look-up table, add 64 so as not to take a negative value. I have.

[Print Data Correction Control Using Printing Efficiency]
For example, for the r-th heating resistor, as shown in the flowchart of FIG.
The energization time (TIME (r, row-1)) of 1) is read (step S71). Next, the stored current column start temperature (θ (r, row)) is referred to (step S7).
2). Next, using the table of FIG.
The provisional printing efficiency (η (r, row-1)) is obtained from (r, row-1) and θ (r, row) (step S7).
3).

Next, the energization time (TIME (r-1, row-
1) is read (step S74). Furthermore, the energization time (TIME) of the heating resistor (r + 1) adjacent to the front row from the memory is
(R + 1, row-1) is read (step S7)
5). Then, in the energization time in the front row, the sum of the differences from the heating resistors on both sides (ΣΔTIME (r, row-1))
Is obtained (step S76). Next, referring to FIG.
TIME (r, row-1) and ΣΔTIME (r, ro
w-1) and the correction value (ηh (r, row)
-1)) is obtained (step S77). Then, the printing efficiency is corrected, and the printing efficiency (η (r, row)) is obtained by substituting the current row efficiency with the front row efficiency (step S78). Using this η (r, row), the energization time (TIME) for the target density (image data DATA) is obtained by referring to the table of FIG.

Here, in the temperature measurement of the current row, the detection time from the first heating resistor to the last heating resistor by natural cooling when obtaining a detection value for temperature measurement by sequentially supplying current to the heating resistors. The difference causes a temperature difference. Therefore, it is desirable to correct the temperature difference due to the detection time shift. That is, it is desirable to use a value that would have been obtained if the temperatures of all the heating resistors were detected simultaneously at a certain moment. The correction of the temperature difference may be performed after correcting the detected value using the second correction value table (Table 2). However, the correction value is reflected in the second correction value table itself. Is also good. For example, the first correction table based on the first correction table
Referring to the correction value table (Table 1), the numbers in parentheses in the first correction value table correspond to the corrected values.

The temperature detection is performed in order from the first heating resistor. By using the corrected value (numerical value in parentheses) of the first correction value table, the heating resistor whose detection time is earlier is detected. The temperature is corrected to be low, and the temperature of the heating resistor whose detection time is late is corrected to be high.

Further, in natural cooling, the slope of the temperature drop becomes slower as time elapses, so that the longer the front row energization time, the steeper the slope of the temperature drop at the temperature detection time. In this case, since the difference between the detection values due to the difference in the detection time becomes large, it is desirable to increase the gradient of the value for correcting the correction value in the detection order in order to gradually increase. The reverse is true for short energization times. That is, the correction value may be increased when the energization time in the front row is long, and the correction value may be decreased when the energization time in the front row is short.

When the energization time in the front row is long, the start temperature in the next row becomes higher as well as the peak temperature. Therefore, instead of correcting the correction value with the energization time in the front row, the correction value may be corrected using the temperature in the current row. The corrected values in parentheses in the first correction value table (Table 1) take this temperature into account. For example, the corrected value of the first heating resistor in the third temperature class is (−3).
In contrast to 3), the corrected value of the first heating resistor in the twelfth temperature class is (-39).

FIG. 30 shows a case where the target gradation is uniform.
9 is a graph showing the result of detecting the density of ink when actual printing is performed using the printing data control based on the printing efficiency described above. On the other hand, FIG. 31 is a graph showing the result of detecting the ink density when actual printing is performed without performing printing data control based on printing efficiency when the target gradation is uniform. is there. As can be seen by comparing these figures, a uniform density can be obtained by using the printing data control based on the printing efficiency. 30 and 31 are as follows.
This is a representation of the reflection density obtained by sampling each dot when printing 360 rows with 76 dots.

Although the detection correction value (Dh) in FIG. 20 is prepared for each head, the tables relating to the printing efficiency in FIGS. 21 to 23 can be used in common for each head. Here, assuming that the applied voltage (Vh in FIG. 1) is constant and the resistance value of the heating resistor is different, the power consumption is different and the amount of generated heat is also different. This appears as a difference in printing efficiency, and the energization time is determined accordingly.
That is, in order to use the printing efficiency tables of FIGS. 21 to 23 in common for each head, even if the average resistance value between the heads is different, the amount of heat generated when energized for a certain energizing time is calculated for each head. Need to be almost the same. If the processing for this is to change the applied voltage (Vh in FIG. 1) according to the difference in the average resistance value of the head, FIG.
Is controlled by a value different from the partial pressure value based on the resistance value Ra at the time when the detection correction value (Dh) is obtained.
Therefore, the applied voltage is set to be the same, and the ratio (duty) of the ON time to the cycle of the plurality of dispersed pulses constituting the energizing time is adjusted according to the difference in the average resistance value of the head. That is, printing control is performed by determining the duty according to the average resistance value for each head.

In this embodiment, the above control for the difference in the average resistance value is realized by setting the duty ratio according to the average resistance value. The average resistance value of each head is obtained when obtaining the second correction table. The setting of the duty is, for example, to increase the duty when the average resistance value is higher than a certain reference resistance value, and to decrease the duty when the average resistance value is lower.

Next, the overall flow of processing in one color printing will be described with reference to the flowchart of FIG. First, the recording paper is supplied to the printing unit (step S
1). The printing of a certain row (L) is performed by one-line printing of yellow, one-line printing of magenta, and one-line printing of cyan (steps S2, S3, S4, and S5). It is determined whether or not a predetermined line has been printed (step S6). If the predetermined line has been printed, the sheet is discharged (step S7). If there is an unprinted line, a line feed is performed (step S8), and L = L + 1 processing. (Step 9), and then proceed to Step 3.

The printing of one line is performed by executing the printing of one column a predetermined number of times, as shown in the flowchart of FIG. 25 (steps S11, S12, S13, S14).

The printing of one line is performed as shown in the flowchart of FIG. First, the image data of each heating resistor is transferred to the memory 4 (step 21). Next, a command to print one column is issued from the upper control circuit 14 to the data generation / control section 2 (step S22). It is determined whether or not the ENA signal has risen (step S23). When the ENA signal rises, the resistance value (temperature) of each heating resistor is measured (see the measurement period in FIG. 7).
The excitation of the pulse motors 16, 17, 18 is turned off (step S24).

In the case of printing using a serial head, a pulse motor is driven to move the carriage during printing, and a pulse motor for winding the ink ribbon is driven. In the case of printing using a line head, a pulse motor for conveying a recording sheet is driven, and a DC motor or a pulse motor for winding an ink sheet is driven. If the motor drive is excited during the temperature detection period, noise is added to the detection value which is a digital value, which adversely affects the temperature detection. By stopping the excitation of the motor during the detection period, it is possible to prevent such noise from being mixed. In this embodiment, the detection period is 1 ms or less (see FIG. 7). During this period, even if the excitation of the motor is interrupted, the operation of the carriage and the ink winding operation is not adversely affected.

Next, the transistor Tr1 is turned off (step S25), and the process proceeds to a measurement and control subroutine (step S26). Next, it is determined whether or not the ENA signal has fallen (step S27). If the ENA signal falls, one-row printing (refer to the energizing time in FIG. 7) is performed, so that the excitation of the pulse motor is turned ON and motor control necessary for one-row printing is started (step S28). ,
S30, S31PS33). And the transistor Tr
1 is turned on (step S29), and power is simultaneously supplied to all the heating resistors for the power supply time determined for each heating resistor in the above-described measurement and control subroutine (step S3).
2).

Measurement and control subroutine (step S2
In 6), as shown in FIG. 27, first, "1" is set at the position of the first heating resistor of the shift register 6, and "0" is set at other positions (step S4).
1). Then, r = 1 is set as the number of the heating resistor to be detected (step S42), a latch signal is set, and only one (r-th) heating resistor is energized by the driver unit 8 (step S42). S43). The resistance value measuring unit 3 obtains the divided voltage Va of the measured resistance Ra, subtracts the reference voltage Vref from the voltage Va, and amplifies the subtracted value with the amplification factor α by the amplifier 13 to obtain the voltage value Vo (step S45).
The voltage value Vo is converted into a digital value by the A / D converter 11 to obtain (AD_OUT) (step S4).
6). Then, the detection value correction subroutine (step S
47) and a subroutine for estimating the printing efficiency (step S
Go to 48). The specific contents of steps S47 and S48 have already been described with reference to the flowcharts of FIGS. 28 and 29, and will not be described here.

Next, the energizing time TIME is determined from the printing efficiency η and the image data DATA by using the table of FIG. 23 (step S49). Then, in order to perform the next column printing, the process of r = r + 1 is performed (step S50), and it is determined whether or not r exceeds 96 which is the total number of the heating resistors (step S51). Returns, NO
If so, the contents of the shift register 6 are shifted by 1 bit (step S52). Then, the process proceeds to step 43.

In the above description, the case where a serial head is used has been described. However, the present invention can be applied to a line head.

[0103]

As described above, according to the present invention, it is possible to accurately detect the temperature of each heating resistor at the start of current row printing of a thermal head (not only a serial type but also a line type). it can. Then, since the printing efficiency of each heating resistor is determined based on the temperature at the start of the current row printing and the front row energizing time for each heating resistor, even in various heat storage situations based on various printing data. The target density can be obtained.

In particular, even when a serial head having a common electrode is used, accurate temperature detection is performed by eliminating the influence of the variation in the resistance value of each heating resistor, the variation in the rate of change in resistance, and the effect of the common drop. Since control can be realized, head yield can be improved and cost can be reduced, and streak in the carriage scanning direction, which is a problem unique to serial heads, can be prevented. Image quality can be realized, and high resolution can be easily achieved because there is no need to use a serial head having a folded electrode structure. Furthermore,
As described above, the effect of the common drop can be eliminated, so the width of the common electrode can be reduced, shortening the time from heating the ink sheet to peeling it off, making it easier to use resin ink. it can.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a main part of a thermal printer according to an embodiment of the present invention.

FIG. 2 is a timing chart for explaining an operation of measuring a resistance value (temperature) of a thermal head in the thermal printer of FIG. 1;

FIG. 3 is a flowchart showing a part of a process for obtaining a correction value table according to the embodiment of the present invention.

FIG. 4 is a flowchart showing a continuation of FIG. 3;

FIG. 5 is a flowchart showing a continuation of FIG. 4;

FIG. 6 is a diagram illustrating a part of a process for obtaining a correction value table according to the embodiment of the present invention, in which a three-stage saturation temperature state is realized by energizing a heating resistor. FIG.

FIG. 7 is an explanatory diagram showing a relationship between a resistance value (temperature) measurement period and a power-on time for printing in the thermal head in the thermal printer of FIG. 1;

FIG. 8 is an explanatory diagram showing a state in which temperature measurement is performed at the timing of FIG. 7 during a natural cooling period after the three-stage saturation temperature condition of FIG. 6;

FIG. 9 is an explanatory diagram showing one measurement period of FIG. 8 in an enlarged manner.

FIG. 10A is a graph showing a difference in detection value due to a difference in the normal temperature resistance value of the heating resistors when all the temperatures of the 96 heating resistors are at room temperature, and FIG. 12) is a graph showing the difference in the detected value due to the difference in the room temperature resistance value of the heating resistor when the temperature distribution of FIG. 11 is shown.

FIG. 11 is a graph tentatively assuming the temperatures of 96 heating resistors to show FIG. 10 (b).

FIG. 12 is a graph showing a relationship between a temperature and a detection value obtained by calculation with a constant resistance change rate for three heating resistors having different normal temperature resistance values.

FIG. 13 is a graph showing a relationship between a temperature and a resistance value obtained by calculation with a constant resistance change rate for three heating resistors having different normal temperature resistance values.

FIG. 14 is an explanatory diagram illustrating a first temporary correction.

FIG. 15 is an explanatory diagram illustrating a second temporary correction.

FIG. 16 is an explanatory diagram showing a variation.

FIG. 17 is a graph showing a first-order approximation curve of a variation of a seventeenth heating resistor.

FIG. 18 is an explanatory diagram showing a relationship between an average curve and a difference obtained to obtain the first-order approximation curve in FIG. 17;

FIG. 19 is a configuration diagram for obtaining correction data.

FIG. 20 is an explanatory diagram of a second correction value table.

FIG. 21 is an explanatory diagram of a temporary efficiency table.

FIG. 22 is an explanatory diagram of an efficiency correction value table.

FIG. 23 is an explanatory diagram of a table in which the energization time is determined based on the corrected efficiency and the target gradation.

FIG. 24 is a flowchart showing the flow of processing for printing one sheet.

FIG. 25 is a flowchart showing an operation during one-line printing.

FIG. 26 is a flowchart showing the contents of a subroutine for one-column printing.

FIG. 27 is a flowchart showing the contents of a measurement and control subroutine.

FIG. 28 is a flowchart showing the contents of a detection value correction subroutine.

FIG. 29 is a flowchart showing the contents of a printing efficiency estimation subroutine.

FIG. 30 is a graph showing an experimental result by correction based on printing efficiency.

FIG. 31 is a graph showing an experimental result when correction based on printing efficiency is not performed.

FIG. 32 is a graph showing a relationship between a heating resistor and a corrected temperature.

FIG. 33 is a graph showing a correction value of the efficiency determined by the relationship between the front row energizing time of the target heating resistor and the front row energizing time of the heating resistor on both sides thereof.

FIG. 34 is an explanatory diagram showing a main part of a printing mechanism using a thermal head and an ink ribbon.

FIG. 35 is an explanatory diagram showing a state in which three lines and approximately one-third of lines are printed on a recording sheet.

FIG. 36 is a perspective view of a serial type thermal head including a common electrode.

FIG. 37 is a perspective view of a serial type thermal head having a folded electrode.

FIG. 38 is an explanatory view showing substantially the entirety of a printing mechanism using a thermal head and an ink ribbon.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Thermal head 2 Data generation / control part 3 Resistance value measurement part 4 Memory 6 Shift register part 7 Latch part 8 Driver part 11 AD converter 14 Upper control circuit 15 Motor drive circuit

Claims (15)

[Claims] 1. A thermal head having a plurality of heating resistors having a characteristic in which an electric resistance value varies depending on temperature, and a detection value for temperature measurement by sequentially energizing the heating resistors in a printing process. And a means for correcting the detection value by obtaining a correction value from a correction value group for each heating resistor classified into a plurality of classes in a predetermined temperature range prepared in advance. A thermal printer comprising: 2. A method of obtaining a temporary temperature of a heating resistor from the detection value obtained by the detection value obtaining means and the characteristic, obtaining a correction value from the correction value group, and obtaining the detection value. A thermal printer characterized in that the thermal printer is corrected. 3. A method according to claim 1, wherein the heating element is not energized for printing under the first temperature condition, but is based on each detected value, average detected value, and the characteristic obtained by energizing for measurement. 2. The thermal correction device according to claim 1, wherein a first correction value for each heating resistor for each temperature class obtained by calculation is obtained, and the first correction value constitutes the correction value group. Printer. 4. A detection value of each heating resistor is obtained by energizing each heating resistor after a second temperature condition higher than the first temperature condition, thereby obtaining a first temperature condition. Each heating resistor is not energized for imprinting for printing below, and for each temperature class obtained by calculation based on each detected value, average detected value, and the characteristic obtained by energizing for measurement. The detection value is corrected by the first correction value obtained for each heating resistor,
An average curve of the corrected values that are the corrected values is obtained, a difference between the corrected values with respect to the average curve is set as a variation, and a process of obtaining the variation is performed by one or more processes different from the second temperature condition. Performed under temperature conditions, a variation for each heating resistor for each temperature class is obtained from a plurality of variations under different temperature conditions obtained for each heating resistor, and this is added to the first correction value. 2. The thermal printer according to claim 1, wherein a second correction value is obtained, and the correction value group is configured by the second correction value. 5. The thermal according to claim 4, wherein one or more temperature conditions different from the second temperature condition are obtained during a natural cooling period after the second temperature condition. Printer. 6. The apparatus according to claim 4, wherein one or a plurality of temperature conditions different from the second temperature condition are set separately from the second temperature condition. Thermal printer. 7. The method according to claim 4, wherein the second temperature condition or the temperature condition set separately from the second temperature condition is realized by energizing a heating resistor. The thermal printer according to claim 6. 8. Efficiency estimating means for estimating the printing efficiency based on the starting temperature of the heating resistor in the current row obtained in the printing process and the energization time to the heating resistor in the front row, and the printing efficiency. The thermal printer according to any one of claims 1 to 7, further comprising: a print data generation control unit that determines an energization time to each of the heating resistors in the current row based on the print data. 9. The printing apparatus according to claim 6, wherein the efficiency estimating unit corrects the printing efficiency based on the energizing time of the front row of the target heating resistor and the energizing time of the front row on both sides adjacent to the target heating resistor. The thermal printer according to claim 8, wherein 10. A correcting means for correcting a temperature difference due to a detection time lag from a first heating resistor to a last heating resistor by natural cooling when a detection value for temperature measurement is obtained by sequentially energizing a heating resistor. The thermal printer according to claim 8, further comprising: 11. The correction means according to claim 1, wherein said correction value group is realized by adding a correction value to a correction value group for each heating resistor classified into a plurality of classes within a predetermined temperature range prepared in advance. The thermal printer according to claim 10, wherein: 12. The thermal printer according to claim 11, wherein the correction value is set in consideration of an energization time of front row printing. 13. The thermal printer according to claim 11, wherein the correction value is set in consideration of a start temperature of current row printing. 14. A table for estimating the printing efficiency is common to each thermal head, and taking into consideration the difference in the amount of heat generated due to the difference in the average resistance value of each thermal head, the table of the heating resistor of the adopted thermal head is used. 9. A control means for adjusting a response to a heat value based on an average resistance value by a ratio of an ON time to a cycle of a plurality of dispersed pulses constituting an energization time instead of an applied voltage. 14. The thermal printer according to any one of 13). 15. The apparatus according to claim 1, further comprising motor drive control means for stopping operation of the motor during energization of each heating resistor for temperature detection in a printing process. The thermal printer according to any one of the above.