JPH0630898B2 - Printing control device for thermal printer - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a print control device for a thermal printer having a thermal head in which a plurality of heat generating elements are arranged, and more particularly to thermal history control.

[Conventional technology]

Conventionally, in thermal printers, in order to prevent deterioration of print quality due to heat accumulation during continuous use of the thermal head,
Various methods have been used. Among them is the special public Sho5
A method of memorizing the previous data for each dot to determine the energization time as in JP-A-5-48631, and JP-B-57-185.
A method such as 07 in which the energization time is changed depending on the driving cycle is used. These are generally called history control methods.

As still another method, a method of detecting the temperature of the surface of the thermal head and determining the energy applied to the head has been used.

[Problems to be solved by the invention]

In these conventional examples, the serial type thermal head is insufficient, and it is impossible to actually suppress the heat storage of the thermal head.

This is because in the history control method, even if the applied energy is determined while checking the history for each heat generating element, there is heat diffusion to the adjacent heat generating elements. The conventional method of processing was overwhelming.
Further, in a serial type thermal head that requires high speed, such complicated processing results in a high processing time.

Further, in the method of detecting the temperature of the surface of the thermal head with the heat-sensitive element, in the serial printer, it is practically impossible to exert its effect in the first line because of the delay in the detection time from the heat generating element. It was

An object of the present invention is to eliminate these problems of the prior art and to provide a control method most suitable for printing control of a serial type thermal printer which is high speed and excellent in printing quality.

[Means for solving problems]

The print control device for a thermal printer according to the present invention includes, as means for solving the problems, a heat-sensitive resistance element mounted on a thermal head, a resistance circuit network including the heat-sensitive resistance element, and a predetermined voltage division of the resistance circuit network. Reference energization width control circuit consisting of an amplification circuit that amplifies the potential of the point, and a voltage comparison circuit that uses the output potential of the amplification circuit as a reference potential and outputs a reference energization pulse of a width that corresponds to the charge and discharge time of the capacitor, and a reference A power supply control circuit that sets the pulse width of the power supply pulse to a common reference power supply time to a plurality of heat generating elements,
Measuring means for measuring the pulse width of the reference energizing pulse; and section signal generating means for synchronizing with the reference energizing pulse and for generating a section signal having a time width proportional to the pulse width of the reference energizing pulse obtained by the measuring means. , A storage unit that stores the drive history of each of the plurality of heat generating elements, and a combination of section signals corresponding to each heat generating element is selected from the section signals based on the drive history and print data, and the reference energization time is selected. And an applied energy setting means for setting the energization prohibition time.

Further, the section signal generation means is configured to generate the section signal for each printing of a predetermined amount.

Further, the voltage comparison circuit is characterized in that the pulse width of the reference energizing pulse can be switched between two or more kinds.

[Action]

The output of this operational amplifier, which corrects the temperature characteristics of the thermistor with a resistor network that includes a type of thermistor that detects the thermal head or its ambient temperature, and amplifies this with an operational amplifier that is an amplifier circuit. The potential is used as the reference potential, and the charging time to the reference potential of the capacitor is output as the pulse width by the voltage comparison circuit,
By setting this pulse width as the reference energization time of the heat generating element on the thermal head, the optimum pulse width is always added to the temperature fluctuation.

Further, the reference energization time is measured, and the reduction amount from the reference energization time is determined according to the storage result of the driving history of each heat generating element, and the heat accumulation during continuous energization is suppressed to obtain good print quality. .

〔Example〕

FIG. 8 is a schematic view showing the structure of the thermal head of the print control device of the thermal printer according to the present invention. FIG. 8 (a) is a perspective view and FIG. 8 (b) is a sectional view. Reference numeral 81 is a base material made of ceramics, 82 is a glass glaze part in which a part of the base material is projected, 83 is a heating element, 84 is a flexible substrate on which an electrode 87 of the heating element is arranged, 82
Is a thermistor which is a kind of heat-sensitive resistance element arranged in contact with the back surface of the base material on the opposite side of the glass glaze portion, and 8
Reference numeral 6 denotes a resin agent that prevents the thermistor 85 from contacting with the air, and allows the temperature in the immediate vicinity of the glass glaze portion 82 to be accurately detected. A heat dissipation member may be further installed on the back surface.

9 (a), (b), and (c) are explanatory views showing the difference in temperature detection characteristics due to the difference in the installation site of the thermistor arranged in contact with the thermal head.

FIG. 9 (a) shows a circuit for checking the resistance value change of the thermistor by a voltage change, 91 is a fixed resistor which is not affected by temperature, and 92 is a thermistor.

FIG. 9B shows the mounting position of the thermistor in the conventional example, in which the thermistor 85 is attached to the surface of the thermal head 81.
Is installed. Reference numeral 83 is a heat generating element.

FIG. 9 (c) shows the difference in resistance value change of the thermistor between the thermal head used in the print control apparatus according to the present invention shown in FIG. 8 and the conventional example, with the horizontal axis representing time and the vertical axis representing time. The voltage of the check terminal is taken. To is the time during which the same applied pulse as for printing is applied to the thermal head, and Tf
Is the downtime. 93 is the characteristic curve in the conventional example,
Even after the energization pulse ends, the temperature of the thermistor further rises, and the delay time td ₁ at that time reaches nearly 0.5 seconds. Reference numeral 94 denotes a characteristic curve according to the present invention. Since the influence of the outside air temperature is small, it is possible to detect the temperature in the vicinity of the heat generating element well, and the detection delay time td ₂ is about 30 ms. Therefore, conventionally, when printing is continuously performed, the effect of the thermosensitive resistive element such as the thermistor is hardly exhibited in the first line, but the thermal head used in the present invention has an extremely small response delay, and therefore the effect of the thermosensitive element can be obtained from one line. It can be used.

However, due to the effect of heat storage on the glass glaze portion installed on the surface of the thermal head and the heat conduction time to the back surface, a response delay remains for a minute time. The glass glaze portion is installed for the purpose of responding to paper, and has a heat storage effect instead of serving to locally and rapidly increase the temperature of the heat generating element. For this reason, when the same heat generating element is continuously energized, the temperature of the glass glaze surface rises before the thermistor can detect it, a tailing phenomenon occurs, the dot shape is disturbed, and print quality deteriorates. Conventional thermal printers using a thermistor have left such problems.

In the present invention, in order to correct not only the temperature of the base material of the thermal head but also the temperature rise of the glass glaze part, the energizing pulse width is changed according to the driving history of the heating element that has already been driven. A variable method is used.
The correction based on the drive history is sufficient at most within one character as a basic character. For example, in the case of vertical n dots × horizontal m dots, a storage means for storing within m dot columns may be prepared.

〔Example〕

FIG. 2 is a schematic circuit diagram showing an embodiment of the reference energization width and control circuit of the print control apparatus according to the present invention.

Reference numeral 1 denotes a resistance circuit network including a thermistor 7 which is a kind of a thermal head or a thermal resistance element for detecting an ambient temperature, 11, 12 and a resistor, and 13 a capacitor for noise prevention. The capacitor 13 has nothing to do with the characteristics.

Reference numeral 2 is an amplifier circuit having an operational amplifier 8, which has a predetermined voltage dividing point of the resistor network and a predetermined voltage dividing point of the voltage dividing circuit 14 having the variable resistor 16 as inputs of the operational amplifier. . The operational amplifier 8 also has a feedback resistor 19, a diode 20, and an input resistor 18. The voltage dividing circuit 14 is composed of resistors 15 and 17 and a variable resistor 16 and forms a reference input section of the operational amplifier 8.

3 is a voltage comparison unit, which is a voltage comparison circuit 9, a capacitor 10,
It has resistors 23 and 24 and transistors 21 and 22 as basic constituent elements.

Reference numeral 4 is a power supply control circuit, which is composed of a buffer 25, a head driver 26, and a switching transistor 27.

Reference numeral 5 is a thermal head having a heating resistor 30 which is a heating element.

Reference numeral 6 denotes a CPU that controls the thermal printer.

〔motion〕

The resistance network 1 is a curve correction unit that compensates for the temperature characteristics of the thermistor.

The resistance value Rt of the thermistor is generally 20 using the B constant.
The value in degrees Celsius is represented by R (20) and the absolute temperature T is represented by the following equation.

T (t) = absolute temperature at arbitrary temperature T (20) = absolute temperature at 20 ° C. Looking at Equation 1, since the term of exp is included, the reciprocal of temperature is 1 og linear. That is, the resistance value decreases as the temperature rises, and the rate of change is smaller on the high temperature side.

In the case of the thermal head, it is better to reduce the applied energy as the temperature is higher, the printing quality is better, and the heat generating element is safer, and it is necessary to compensate the characteristics of the thermistor.

FIG. 5 is a graph showing the characteristics of the resistance value Rt of the thermistor, the output voltage of the voltage dividing point A of the resistor network 1 and the output voltage of the amplifier circuit 2, where the horizontal axis represents the absolute temperature and the vertical axis represents the resistance value Rt. The voltage dividing point A and the output potential of the amplifier circuit 2 are shown.

51 is the temperature characteristic of the resistance value Rt of the thermistor,
Is a characteristic curve showing the temperature characteristic of the potential of the voltage dividing point A, and 53 is a characteristic curve showing the temperature characteristic of the output potential of the amplifier circuit 2.

The following items are listed as features of such compensation.

 Fewer peripheral elements and less variation such as variations.

 Linearity can be provided in a relatively wide range.

The change in the output voltage with respect to the temperature outside the operating temperature range, for example, 0 ° C. or less, 40 ° C. or more, can be reduced, and the thermal head can be protected from destruction.

The amplifier circuit 2 uses the compensated temperature characteristic to partially expand the voltage. Therefore, the voltage dividing point A for obtaining the characteristic curve 52 is used as one input and the voltage dividing circuit using a resistor is used as the other input.

The magnification of this circuit is expressed below.

If the value of the resistor 18 is R18 and the value of the resistor 19 is R19, the magnification ρ is Becomes

The function of the diode 20 is to suppress a rapid rise of the reference potential at low temperature, and as a result, prevent an increase in the output width of the voltage comparison circuit 9 at low temperature.

 The inflection point of partial enlargement can be changed.

By using the characteristics of and, various characteristic curves can be created by changing the number of diodes.

The variable resistor 16 in the voltage dividing circuit 14 adjusts the output potential Vop without changing the rate of change of the output potential with respect to the temperature, and sets the output pulse width of the voltage comparison unit in the subsequent stage to a predetermined value to prevent thermal change. The initial value of the energy applied to the head is set.

The voltage comparison circuit 9 is formed by the resistance circuit network 1 and the amplification circuit 2.
Forming a reference voltage generating circuit.

The voltage comparison unit 3 is a circuit unit that converts the charging time up to the output voltage Vop of the reference voltage generation circuit of the capacitor 10 into a pulse width, and the transistor 21 is a discharge transistor that instantaneously discharges the capacitor 10 by a trigger input. ,
Reference numeral 27 is a coupling capacitor for input.

FIG. 6 is an explanatory diagram showing an input signal and an output waveform of the voltage comparison unit, and 61 is a trigger signal sent from the CPU 6. Reference numerals 62 and 63 denote output waveforms, and 62 denotes an output when the pulse width switching transistor 22 is off,
Reference numerals 63 indicate outputs when the switch is on. The pulse width TW1 of the output waveform 62 is larger than the pulse width TW2 of the output waveform 63. The pulse width is switched when the optimum energy is obtained by changing the energy applied to the thermal head according to the characteristics of the ink ribbon, the surface condition of the printing paper, and the like.

In this pulse width TW, the values of the resistor 23 and the resistor 24 are R23 and R24, respectively, and the value of the capacitor 10 is C1.
If the output potential of the operational amplifier is 0 and the output potential of the operational amplifier is Vop, the following is represented when the transistor 22 is off. At this time, the pulse width of the trigger input is so small that it is ignored.

Also, when the transistor 22 is on, Since Vc is a circuit voltage which is generally constant at 5V, the pulse width TW is determined by the potential of Vop. C10, R2
By selecting the values of R3 and R24 and the value of the amplifier circuit 2 of the preceding stage, it is possible to realize the characteristic having the linear change rate of the pulse width in the limited temperature range. On the contrary, it is also possible to freely change the temperature characteristic.

The output of the voltage comparison circuit 9 is transmitted to the switching transistor 27 via the inverter buffer 25.

The transistor 27 is connected to the power supply terminal 26a of the head driver 26, the head driver becomes operable for the pulse width TW time, and the reference energization time of the heat generating element 30 is determined.

The resistance circuit network 1, the amplifier circuit 2, and the voltage comparison circuit 9 described above form a reference conduction width control circuit. This output pulse width TW serves as the reference energization time of the heat generating element, and mainly determines the end of energization.

The coupling capacitor 27 is installed so that the output pulse width TW is output only for a predetermined time even if the trigger input goes high due to a malfunction of the CPU 6. For this reason, the thermal head is safe because it is energized only for a predetermined time in any case.

Generally, in the heat history control or the like, when the heating element 30 is continuously energized, the energization time of the heating element is reduced by a predetermined time from the pulse width TW.

In this case, when the head driver 26 is in an operable state, C
The data output signal 6a from the PU side is used to reduce the energization time.

In addition, Vc is a circuit power supply, and Vh is a thermal head power supply.

Further, the diode 20 may not be necessary and may be a Zener diode.

Furthermore, although the heat-sensitive resistance element has been described using the thermistor,
A posistor having a positive characteristic with respect to temperature can be used. At this time, the characteristics may be inverted by changing the input direction of the operational amplifier.

FIG. 77 is a characteristic diagram showing the relationship between the applied energy of the thermal head and the temperature, which is obtained by the print control device according to the present invention.

The applied energy E is represented by the following equation, where Rh is the resistance value of the thermal head and Vs is the saturation voltage of the head driver.

The vertical axis of FIG. 7 represents this applied energy, the horizontal axis represents the temperature of the thermistor 7, 71 is a characteristic curve when the transistor 22 is off, and 72 is a characteristic curve when the transistor 22 is on. It represents.

In this way, it is possible to provide a linear characteristic with respect to temperature change, and the characteristic that the rate of change of applied energy with respect to temperature is approximately the same even when the transistor 22 is turned on and off. It is possible to stabilize the print density against temperature changes.

FIG. 1 is a schematic block diagram showing the construction of an embodiment of a print control device for a thermal printer according to the present invention. Second
The same parts as those in the figure are indicated by the same reference numerals and the description thereof is omitted.

Reference numeral 5 is a thermal head in which a thermistor is placed in contact with the back surface as shown in FIG. 8, 31 is a third buffer, and 32 is a third buffer.
Indicates a second buffer, and 33 indicates a first buffer, which is formed by a latch circuit for temporarily storing data for thermal head. A measuring unit 34 measures the output pulse width TW of the reference energization width control circuit 40. Reference numeral 37 denotes a ROM (read only memory) having a control program for controlling the CPU 6 and a kind of applied energy judgment table of applied energy judgment means, and 44 a RAM (random access memory) including a storage means for storing the driving history of the heat generating element. ), 41 is the next print data, 42 is the current print data, 4
Reference numeral 3 denotes a register that stores the previous print data.

36 is a motor for moving the thermal head 5 relative to the printing paper, 35 is motor control means for controlling the moving speed of the motor 36, and 39 is a switch for selecting a printing mode including the motor speed. .

FIG. 3 is an embodiment of an applied energy judgment table which is a kind of applied energy judgment means showing the relationship between the degree of driving history and the energization time to the heat generating element.

TW is the output pulse width of the reference energization width control circuit 40,
This is multiplied by a coefficient K to calculate the pulse width. This coefficient K is recorded in the applied energy judgment table 38 in the ROM 37. The coefficient K is not limited to this table, and the optimum value is determined according to the actual print quality.
Further, the value of the coefficient K and the number of data to be stored also change depending on how many times the past history is stored. This table is ROM37
To remember.

〔motion〕

FIG. 4 is an explanatory diagram showing the operation of the print control device of the thermal printer of the present invention. As an example, an actual driving method when the four types of history shown in FIG. 3 are stored in the storage means 44. It is shown.

Reference numeral 45 represents past print data stored in the storage means 41, 42, 43 for storing the driving history of each heat generating element when the number of heat generating elements is eight. In the print data, 1 indicates printing, that is, energization, and 0 indicates non-printing, that is, non-energization. For example, in the heating element of the third dot, the previous and next print data is 1, the current print data is 0, and
In the dot heating element, the previous print data is 0, and the current and next print data is 1.

47, 48, 49 are the first dot, the second dot,
The energization waveform of the 3rd dot is shown. The rising portions t ₀ , t ₁ , t ₂ of the energization waveform indicate the energization start timings of the previous time, the current time, and the next time, respectively, and the shaded portion in the waveform indicates the energization prohibited section.

Reference numeral 50 is an explanatory diagram showing details of the energizing pulse. r1, r
2 and r3 are timings at which the data of the first, second and third buffers, which are latch circuits for temporarily storing the data for the thermal head, are sent to the head driver, and r4 is the reference energization width control circuit 40. The end of the power supply to the determined head driver, that is, the end time of the energization time is shown. r1 is also the energization start timing, and is generated by the CPU in synchronization with the rising of the reference energization pulse.

T1, T2, and T3 represent respective energization sections, and in the embodiment of FIG. 4, their values satisfy the relationship of the following equation.

TW = T1 + T2 + T3 T1 = 0.2 × TW T2 = 0.15 × TW T3 = 0.65 × TW The energization time shown in FIG. 3 can be realized by using the section signal having such a width. That is, 47 and 4 in FIG.
As shown in FIG. 9, when the current is supplied at two continuous power supply timings, the power supply in the section T1 is prohibited, so that the power is supplied only in the section of r2 to r4, that is, the time of T + T3. From the above equation, this energization time is 0.8 × TW. 47, there is an example in which power is supplied at three consecutive power supply timings, but at this time, sections T1 and T2
Energization is prohibited in the section from r3 to r4,
That is, energization is performed only for the time T3, and the time is 0.65.
× TW.

Further, as shown at 48, the energization timing of 1 is stopped,
When energizing at the energizing timing before and after that, energizing in the section T2 is prohibited, and the energizing time is T1.
It becomes + T3, that is, 0.85 × TW.

In this way, by realizing the relationship between the energization history and the energization time in FIG. 3, T3 <T2 + T3 <T1 + T3 is established, so that the appropriate energization width control is performed corresponding to the past energization history of each heat generating element. Therefore, it is possible to make the print density constant in a minute print section during one-line print, and improve the print quality.

As shown in FIG. 1, the CPU 6 is provided in the first to third buffers.
The strobe signal line is further wired, and the CPU outputs the strobe signal to output the third, second and first strobe signals.
The data in the buffer can be simultaneously shifted to the second, first and head drivers, respectively. Therefore, if the CPU outputs this strobe signal at the timing of r1, the data in the first buffer is output to the head driver, and at the same time, the data in the third and second buffers are shifted to the second and first buffers, respectively. To be done. Next, when the CPU outputs the strobe signal at the timing of r2, the data originally stored in the second buffer and shifted to the first buffer at the timing of r1 is output to the head driver. Further, if the CPU outputs a strobe signal at the timing of r3, similarly, the data originally stored in the third buffer becomes
It is output to the head driver.

Therefore, the data in the first buffer is output to the head driver during the period from r1 to r2, that is, the time T1, and similarly, the data in the second and third buffers is output to the head driver during the time T2 and T3. Become. In other words, T
When energizing each section of T1, T2, and T3, the data of the corresponding first, second, and third buffers may be set to 1.

Reference numeral 46 indicates data stored in the first to third buffers 33, 32, 31 prior to the energization timing t2. For the data of the first, second and third buffers, an appropriate combination is selected from the sections T1 to T3 according to the procedure of the above technique so as to satisfy the relationship of FIG. It is stored in the buffer. That is, since the first dot is energized only at T3,
Since only the buffer is set to 1 and the third dot is energized by T1 + T3, the data in the first and third buffers is 1. A latch circuit or a shift register is generally used for the first to third buffers, but the first to third buffers can be built in the RAM, and the CPU may sequentially read from the RAM at a predetermined timing and send the data to the head driver.

As described above, r ₄ is the end of the energizing pulse determined by the reference energizing width control circuit 40. The reference energization width control circuit 40 accurately detects the temperature of the thermal head which gradually rises even by the above-described history-based driving method, determines the reference energization time, further prevents heat generation, and print quality. It is installed to help improve

Although the TW is slightly reduced due to the temperature rise of the thermal head 5 even in the case of printing one line, it is difficult to measure the TW for each energization timing due to the limitation of the processing capacity of the CPU and the like. . In the present invention, in order to solve this, prior to printing, the TW is measured and stored using the measuring unit 34, and during printing of one line, the TW is used to determine the pulse width according to the driving history. . Further, in printing such as screen copy, if the print duty is small, it is possible to measure the TW only at the beginning of one screen.

In the present embodiment, the method of storing the heat history up to two dots before is described. However, the number is increased to 3 dots and 4 dots and the number of times of data transmission is set to 4 times and 5 times. The effect is even more remarkable. However, the printing speed and C
There is a limit depending on the processing time of PU, and normal characters, n ×
With the letters m-dots tomato, it is possible to sufficiently exert the effect within m-dots rows. That is the first
As shown in the figure, the thermistor placed in contact with the base material immediately after the glass glaze part with a heating element detects the temperature in the immediate vicinity of the glass glaze part very accurately and quickly, and the feedback energy is applied to the energy applied to the thermal head. This is because

In thermal transfer printers, plain paper printing is possible,
Unlike conventional thermal paper, it has to cover various types of paper. Especially, the printing quality depends on the smoothness of the surface. In order to solve this, in the present invention, it is possible to select a low speed printing mode or a high speed printing mode. When the low speed printing mode is selected by the switch 39, the motor control means 35 decelerates the motor 36 to about 1/2 of that at high speed. In conjunction with this, the reference energization width control circuit 4
0 transistor 22 turns off and output pulse width is about 1.5
It will be double to double. By controlling in this way, clear printing is possible even on low-smoothness paper such as bond paper generally used in offices in the United States.

This is because the ink can sufficiently permeate into the fibers of the paper by decreasing the moving speed of the thermal head and increasing the applied energy.

At this time, it was confirmed that the printing speed was about ½ and the applied energy was about 1.5 to 2 times the effect as compared with the transfer-only paper. Further, since the print density at this time also changes according to the pulse width, the history control can be similarly performed by using the coefficient of the applied energy determination table as it is even if the print speed is different.

In the present embodiment, the applied energy determination table is stored as a coefficient, but the numerical values of T1, T2 and T3 with respect to the numerical value of TW may be stored as time.

The measuring means 34 can also be realized by a timer built in the CPU 6 or software means.

〔The invention's effect〕

 The present invention has the following effects.

A print control device for a thermal printer according to the present invention includes a thermal resistance element mounted on a thermal head, a resistance circuit network including the thermal resistance element, and an amplification circuit for amplifying a potential at a predetermined voltage dividing point of the resistance circuit network. Since the output potential of the amplifier circuit is used as a reference potential and a reference current supply width control circuit including a voltage comparison circuit that outputs a reference current supply pulse having a width corresponding to the charge / discharge time of the capacitor is provided, the temperature of the thermal head is detected. A pulse width corresponding to this, that is, a signal having a shorter pulse width as the temperature of the thermal head becomes higher is generated as a reference energizing pulse, so that the standard energizing adapted to the usage state and the environmental temperature averaged for each heating element of the thermal head. The pulse can be generated automatically. As a result, it is possible to solve the problem of heat storage of the thermal head, which is a drawback of the conventional print control method using only history control.

Further, since it has a power supply control circuit that makes the pulse width of the reference power supply pulse a common reference power supply time to a plurality of heat generating elements,
By setting a common reference energization time for each heat generating element by using a pulse width suitable for the usage state and the ambient temperature that averages each heat generating element of the above reference energization pulse, each heat generating element can It is possible to set a reference energization time that reflects the influence of the environmental temperature in common for each heat generating element.

Further, a measuring means for measuring the pulse width of the reference energizing pulse, and a section signal generation for generating a section signal in synchronization with the reference energizing pulse and having a time width proportional to the pulse width of the reference energizing pulse obtained by the measuring means. Unit, a storage unit that stores the driving history of each of the plurality of heat generating elements, and based on this driving history and print data, a combination of section signals corresponding to each heating element is selected from among the section signals and the reference is selected. Since there is an applied energy setting means for setting the energization prohibition time in the energization time, the above-mentioned operation is performed according to the drive history indicating the individual usage state of each heating element and the presence or absence of print data corresponding to the heating element. By combining the section signals, the energization prohibition time in the reference energization time can be calculated without considering the change in the reference energization time. Kekimekomakaku can and be appropriately set. In other words, if the energization prohibition time is set according to the individual energization history of each heat generating element by the combination of the above-mentioned section signals, the energization prohibition time is automatically proportional to the reference energization time. It can reflect the influence of the heat generating element or the environmental temperature. As a result, it is possible to solve the problem of print density unevenness, which is a drawback of the conventional print control method using only the heat sensitive element. Further, by supplying such an optimum applied energy, it becomes possible to reduce the power consumption and greatly extend the life of the thermal head.

Further, since the section signal generation unit is configured to generate the section signal for each predetermined amount of printing, it is not necessary to generate the section signal at every energization timing, and the section signal generation unit can be relatively operated. It can be realized by a low-priced, low-function CPU or the like. In addition, since a section signal is generated prior to printing of a predetermined amount, when an abnormal high temperature state of the thermal head is detected, recovery processing such as providing a pause for cooling the thermal head is performed. It is possible to normally print the predetermined amount. As a result, damage to the thermal head can be prevented and the reliability of printing can be improved.

Further, since the voltage comparison circuit is configured to be able to switch two or more types of pulse widths of the reference energizing pulse, the reference energizing time can be set according to the characteristics of the ink ribbon, the type of printing paper, and the like.

As described above, the present invention has excellent features and effects and is extremely useful for a thermal printer.

[Brief description of drawings]

FIG. 1 is a schematic block diagram showing the construction of an embodiment of a thermal printer of the present invention. FIG. 2 is a circuit diagram of an embodiment of the reference energization width control circuit of the present invention. FIG. 3 is an explanatory view showing an embodiment of the applied energy judging means of the present invention. FIG. 4 is an explanatory view showing the operation of the print control device of the thermal printer of the present invention. FIG. 5 is a characteristic diagram showing temperature characteristics of the resistance value of the thermistor, the voltage dividing point of the resistance network having the thermistor, and the potential of the output of the amplifier circuit. FIG. 6 is an explanatory diagram showing an input signal and an output waveform of the voltage comparison unit. FIG. 7 is a characteristic diagram showing characteristics of the print control device according to the present invention. FIG. 8 is a schematic diagram showing the structure of the thermal head used in the present invention. FIG. 9 is an explanatory diagram of the temperature detection characteristics of the thermistor placed in contact with the thermal head. 1 ... Resistor circuit network 2 ... Amplification circuit 4 ... Feed control circuit 9 ... Voltage comparison circuit 10 ... Capacitor 5 ... Thermal head 6 ... CPU 7 ... Thermistor 44 ... Storage means 38 ... Applied energy Judgment table

Claims (3)

[Claims] 1. A thermal printer using a thermal head having a plurality of heat generating elements and performing printing while moving relative to plain paper via a thermal paper or a transfer film, wherein: a. A mounted heat-sensitive resistance element, b a resistance circuit network including the heat-sensitive resistance element, c an amplification circuit for amplifying the potential at a predetermined voltage dividing point of the resistance circuit network, and d an output potential of the amplification circuit as a reference A voltage comparison circuit that outputs a reference energization pulse having a width according to the charge / discharge time of the capacitor, and a reference energization width control circuit consisting of: e The pulse width of the reference energization pulse is common to the plurality of heat generating elements. A power supply control circuit for setting a reference energization time of: f, a measuring unit that measures the pulse width of the reference energizing pulse, g the reference that is synchronized with the reference energizing pulse, and is obtained by the measuring unit. Section signal generating means for generating a section signal having a time width proportional to the pulse width of the electric pulse, h storage means for storing the driving history of each of the plurality of heat generating elements, and i for the driving history and print data. On the basis of the section signals, applied energy setting means for selecting a combination of section signals corresponding to respective heat generating elements from the section signals and setting an energization prohibition time in the reference energization time. Print control device for thermal printer. 2. The print control device for a thermal printer according to claim 1, wherein the section signal generation means is configured to generate the section signal each time a predetermined amount of printing is performed. . 3. The thermal printer according to claim 1, wherein the voltage comparison circuit is configured so that two or more types of pulse widths of the reference energizing pulse can be switched. Control device.