JPH0829597B2 - Print control device for thermal printer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a print control apparatus for a thermal printer, such as a thermal paper which is energized by a heating element to print on a thermal paper or a plain paper via a transfer film, and more particularly to a thermal head. It relates to heat history control.

[Prior Art] Conventionally, in a print control device of a thermal printer,
There is a method in which the past drive history of the heating elements is stored and the next applied energy to each heating element is determined to control the thermal history.

In these conventional examples, the next energization time is reduced by a certain amount of time according to the past heat history.

[Problems to be Solved by the Invention] In these conventional techniques, when the conditions such as the ambient temperature and the temperature of the thermal head and the conditions of the supply voltage to the heating element are changed, the energization time to the heating element is generally corrected. , The energization time is adjusted to suit the conditions. However, since the energization time reduced by the thermal history control was constant, the ratio of the applied energy obtained by the reference energization time fluctuated, and good print quality could not be obtained due to temperature changes and voltage fluctuations.

An object of the present invention is to eliminate such drawbacks of the prior art and reduce the ratio of applied energy to be reduced even when the applied energy to the heating element is changed according to temperature and voltage conditions when performing thermal history control. It is an object of the present invention to provide a control device for a thermal printer that keeps the constant value and always obtains good print quality.

[Means for Solving the Problems] In order to achieve such an object, the print control device of the thermal printer of the present invention forms dots by a plurality of heating elements arranged in the print head, and directly or directly on the thermal paper. A thermal printer that prints on plain paper via a transfer film, stores the driving history of each heating element, and the energization time for each heating element of the next dot or subsequent dots is stored according to the stored driving history. In a print control device of a thermal printer for reducing the charge and discharge circuit having at least a capacitor, the operation of which is started from an initial state corresponding to dots, and a heat-sensitive resistance element for detecting the temperature of the print head or its surroundings, Based on a reference potential generation circuit that generates a potential corresponding to the resistance value of this thermosensitive resistance element and the potential generated by this reference potential generation circuit, The voltage dividing circuit that generates a plurality of reference comparison potentials and the charge level of the capacitor are compared with each of the plurality of reference comparison potentials that the voltage division circuit generates, and the timings from the start of the operation of the charge / discharge circuit are different from each other. A plurality of voltage comparison circuits for obtaining a plurality of timings, and the latest timing among these timings is used for setting the reference conduction time of the heating element, and the others are used for reducing the conduction time according to the drive history. It is characterized by having a conduction width control circuit used for setting the reduction amount.

In this case, the reference potential generation circuit includes a resistance circuit network including at least a first resistor connected in parallel with the heat-sensitive resistance element and a second resistor connected in series with the first resistor. , And an amplifier circuit for amplifying the voltage at the connection point of the first and second resistors of this resistor network.

The charge / discharge circuit may be configured to have a constant current circuit for charging the capacitor. In this case,
The constant current circuit may be composed of a constant voltage circuit and a resistor connected between the output of the constant voltage circuit and the power supply used to drive the print head.

[Embodiment] FIG. 1 is a circuit diagram of an embodiment of an energization width control circuit of a print controller for a thermal printer according to the present invention.

Reference numeral 1 is a thermistor which is a kind of heat-sensitive resistance element, 2 is a resistance network including the thermistor 1, 27 and 28 are resistors, and 29 is a capacitor. Capacitor
29 is for noise prevention and has nothing to do with the characteristics.

Reference numeral 3 denotes an amplifier circuit having an operational amplifier 10, which has a predetermined voltage dividing point of the resistor network and a predetermined voltage dividing point of a voltage dividing circuit 30 having a variable resistor 31 as inputs of the operational amplifier. The operational amplifier 10 also has a feedback resistor 9, a capacitor 33, and an input resistor 8. The voltage dividing circuit 30 forms the reference voltage portion of the operational amplifier 10.

Reference numeral 4 is a voltage dividing circuit that divides the output of the amplifier circuit by resistors, and 41, 42, 43, and 44 are resistors that are its constituent elements. The resistance circuit network 2 and the amplifying circuit 3 and the voltage dividing circuit 4 constitute a reference potential generating circuit.

Reference numeral 5 is a constant current circuit with a resistor 3 centered around the operational amplifier 50.
The main components are 4, 35, 36, 39, transistors 37, 40, and capacitor 38, and it is possible to set two kinds of current values by turning on and off the transistor 37.

A capacitor 6 is connected to the constant current circuit 5, is charged by the constant current circuit 5, and is discharged by the transistor 7. Reference numeral 51 is an operational amplifier that forms a buffer circuit that transmits this charging potential to the subsequent stage.

Reference numerals 11, 12, 13, and 14 denote voltage comparison circuits, which serve as reference inputs to divide the output of the operational amplifier 10 into voltage dividing points K and L of the voltage dividing circuit 4.
Each of M and N is used as a reference potential, and the output of an operational amplifier 51 that outputs the charging potential of the capacitor 6 is connected as an input to be compared, and the charging time of the capacitor 6 is converted into a pulse width. When the potentials of the voltage dividing points K, L, M, and N are Vk, Vl, Vm, and Vn, respectively, the following relationships are established.

Vn>Vm>Vl> Vk 15, 16, 17, and 18 are AND gates, one of which is connected to each of the voltage comparison circuits 11 to 14, and the other is connected to the inverting output of the input terminal 20. 52 is an inverter for obtaining this inverted signal.

Reference numeral 19 is a pulse width switching input terminal for switching the output pulse width of the voltage comparison circuit.

 The constant current circuit is connected to the head power supply terminal Vh.

[Operation] The resistance network 2 is a curve correction unit that corrects the temperature characteristic of the thermistor.

The resistance value Rt of the thermistor is generally expressed by the following equation using the B constant as a value of 20 ° C. as R (20) and an absolute temperature T.

Rt = R (20) expB (1 / T (t) -1 / T (20) ... Equation 1 T (t) = absolute temperature at any temperature T (20) = absolute temperature at 20 ° C Looking at Equation 1, the exponent term is included, so the reciprocal of the temperature is log-linear, that is, the resistance value decreases with increasing temperature, and the rate of change is smaller on the high temperature side.

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

FIG. 2 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 resistance network 2 and the output voltage of the operational amplifier 10, where the horizontal axis is the absolute temperature and the vertical axis is the resistance value Rt. And the potential of the voltage dividing point A and the output of the operational amplifier.

Reference numeral 61 is a temperature characteristic of the resistance value Rt of the thermistor, 62 is a temperature characteristic of the potential of the voltage dividing point A, and 63 is a characteristic curve showing the temperature characteristic of the output of the operational amplifier.

The resistance value Rt of the thermistor has a negative characteristic with respect to temperature change, and as shown by the characteristic curve 61 in FIG. 2, the rate of change with respect to temperature is very large. By correcting this characteristic with the resistance circuit network 2, it becomes possible to reduce the rate of change with respect to the temperature change as shown by the characteristic curve 62. The following items are listed as features of the circuit configuration.

1. Fewer peripheral elements and less variation such as variations.

2. Linearity is given in a relatively wide range.

3. The change in output voltage with respect to temperature outside the operating temperature range, for example, 0 ° C or lower, 40 ° C or higher, etc. can be reduced, and the thermal head can be protected from damage.

The amplifying circuit 3 uses the corrected temperature characteristic to partially expand the voltage. Therefore, the voltage dividing point A for obtaining the characteristic curve 62 is used as one input, and the voltage dividing circuit using a resistor is used as the other input.

The operational amplifier 10 amplifies and inverts the potential of the voltage dividing point A and outputs the amplified potential. A characteristic curve 63 shows the characteristic of the output potential V _op at this time.

The variable resistor 31 in the voltage dividing circuit 30 adjusts V _op without changing the rate of change of the output potential V _op of the operational amplifier with respect to temperature change, and sets the output pulse width of the voltage comparator in the subsequent stage to a predetermined value. To be set to. Moreover, in order to adjust the characteristics,
It is also possible to install a variable resistor in the resistance network 2.

The capacitor 33 is installed for noise prevention and has almost no influence on the input / output potential.

The constant current circuit 5 can select two kinds of current values by turning on and off the transistor 37.

A constant current Ir generated by dividing the constant voltage Vr generated across the capacitor 38 by the resistance value of the resistor 39 is generated.

Set the values of resistors 34, 35, 36, 39 to R34, R35, R3 respectively.
6. If R39 is set, the voltage Vr and the current Ir can be calculated by the following equations.

When transistor 37 is on Ir1 = Vr1 / R39 When transistor 37 is off Ir2 = Vr2 / R39 This is because the operation of the operational amplifier 50 controls the voltage across the resistor 39 to always be the same as Vr.
The capacitor 38 is installed to stabilize the power supply. If the power supply of the constant current circuit 5 has variability, the resistors 34, 35
May be constant voltage diodes having different values.

FIG. 3 is an explanatory diagram showing the charging characteristics of the capacitor 6, where the vertical axis represents the charging level and the horizontal axis represents the charging time.

When the transistor 7 is turned off, charging of the capacitor 6 is started. The voltage at this time is calculated by the following formula. The value of the capacitor 6 is C, Now, since the charging current is constant at Ir, Becomes

For this reason, the charging characteristic is represented by a straight line 64 when the transistor 37 is off, and by a straight line 65 when the transistor 37 is on.

This charge potential is directly transmitted to the voltage comparison circuits 11 to 14 by the operational amplifier 51 for buffer. Time t1 to t4 sliced by the reference potentials Vn, Vm, Vl, and Vk of the voltage comparison circuit
u1 to u4 are output as pulse widths from the voltage comparison circuit.

The reference potential fluctuates due to temperature change as described above, for example, if it changes from 20 ° C to 40 ° C, Vn to Vk all change at the same ratio, and if the temperature rises, the pulse width is generally small, On the contrary, if the temperature drops, the pulse width becomes large as a whole.

FIG. 4 is an explanatory diagram of input / output waveforms of the energization width control circuit showing the input waveform of the input terminal 20 and the output waveforms of the output terminals 21 to 24 that output the pulse width of the voltage comparison circuit.

Reference numeral 70 denotes an input waveform to the input terminal 20, and the transistor 7 is turned off for the time of the pulse width TW20 of the L level input, and the charging of the capacitor 6 is started. By limiting the pulse width, it is possible to suppress the energization time to the thermal head in any case, and AND gates 15 to 18 are provided for protection for this purpose.

71 is the output terminal 21, 72 is the output terminal 22, 73 is the output terminal
Reference numeral 23 and 74 indicate the waveform of the output terminal 24, and the pulse widths are indicated by TW21 to TW24, respectively.

 The output pulse width always has the following relationship.

TW21 / TW22 = Vn / Vm TW21 / TW23 = Vn / Vl TW21 / TW24 = Vn / Vk Such a relationship is maintained over the entire temperature range and is always maintained regardless of whether the transistor 37 is on or off. It is a characteristic.

This is because the charging potential rises along the straight line by the constant current circuit 5, and the constant current circuit is indispensable for producing such characteristics.

A variable resistor may be installed in the voltage dividing circuit 4 so that the ratio of the pulse widths can be adjusted and varied for convenience, and can also be used for adjusting the print density of the thermal head.

The constant current circuit 5 is connected to the head power supply terminal. However, if the head power supply has voltage variability of a battery or the like, not only the temperature fluctuation but also the print density can be applied to the head power supply. It is possible to adjust the energization time so as to compensate for the above. When the voltage is high, the pulse width is short, and conversely, when the voltage is low, the pulse width is long, and the print density of the thermal head is corrected. At this time, the reduction time of history control also works at a constant ratio, which is extremely convenient.

When using a semi-fixed power source of a type that changes the voltage conveniently with respect to the average resistance value of the thermal head, connect it to a constant voltage source so that the current value of the constant current circuit does not change accordingly. The resistors 34 and 35 may be replaced with Zener diodes.

In this embodiment, the method of outputting the charging time of the capacitor as the pulse width has been described. However, the discharging time can be converted into the pulse width depending on the circuit configuration, and the ON time of the transistor 7 is included in the pulse width. Both the charging time and the discharging time can be changed to the pulse width. At this time, the shorter the discharge time is, the ideal direction is because the ratio of the pulse widths is always constant.

The transistor 37 is installed to switch the output pulse width of the energization width control circuit. For this purpose, the energy applied to the thermal head is changed depending on the type of thermal paper, the type of ink ribbon, etc. This is to change.

An embodiment of the print control device of the thermal printer using the energization width control circuit having such characteristics will be described in detail below.

FIG. 5 is a schematic diagram showing an embodiment of a printing control device according to the present invention, and 60 is the energization width control circuit (hereinafter referred to as the conduction width control circuit shown in FIG.
Abbreviated as CTCC), 84 is a thermal head in which a plurality of heating elements 85 are arranged, and 82 is a head driver. The thermistor 1 in the CTCC is arranged in contact with the thermal head 84.

86 is a power supply control transistor for turning on / off the power supply terminal of the head driver 82, and 80 is a CPU for controlling the entire thermal printer as a whole, and outputs an L level signal to the input terminal 20 at each head energization timing in response to print data input. The head data 81 is sent to the head driver 82.

Reference numeral 83 is an inverter connected to the output terminal 21 of the CTCC 60, and the transistor 86 determines the operating time of the head driver and the reference energization time of the heating element 85. 87
Is a power input terminal.

Output terminals 22, 23, 24 of CTCC60 are input to CPU80,
Determines the amount of reduction from the reference energization time according to the past drive history of the heating element 85, and outputs the reduced data from the head data output 81 in synchronization with the timing of the output terminals 22, 23, 24.

FIG. 6 is an explanatory diagram showing the energized state of the thermal head history control method using the present invention. As an example, description will be given based on the characteristic straight line 65 of FIG.

Reference numeral 91 indicates a state when power is continuously applied, and the reduction time when two dots are continuous is reduced by t4, when three dots are continuously reduced by t3, and when four dots are continuously reduced by t2.

Reference numeral 92 indicates energization when intermittently applied every other dot, and the reduction time at that time is (t3−t4).

93 indicates a time when the dots are intermittent every two dots, and the reduction time is (t2-t3).

With this configuration, the reduction time is always
A constant ratio to the reference energization time, even if the reference energization time changes according to temperature changes, or if the reference energization time is changed by matching the type of thermal transfer ink ribbon, etc. Since it changes according to this, optimum heat control can always be performed.

Although the present invention has been described using the thermal printer having a heating element, the present invention can be similarly applied to an electric thermal transfer printer having an electrode as a heating element and heating a resistive layer on the back surface of the thermal transfer ribbon. It is possible.

As described above, in the print control device of the thermal printer of the present invention, the charging / discharging circuit included in the energization width control circuit has at least a capacitor, and the initial state corresponding to the dot to be printed is set. The operation is started from, and the charge level of this capacitor is compared with a plurality of reference comparison voltages by a plurality of voltage comparison circuits. On the other hand, the plurality of reference comparison voltages are generated by the voltage dividing circuit based on the potential corresponding to the resistance value of the heat sensitive resistance element that detects the temperature of the print head or its surroundings generated by the reference voltage generation circuit. As a result, the plurality of timings from the start of the operation of the charge / discharge circuit obtained by the plurality of voltage comparison circuits and different from each other correspond to the temperature of the print head or its surroundings, and at the same time, are substantially constant. Can have a ratio of Therefore, by using the latest of these timings for setting the reference energization time of the heating element and the other for setting the amount of reduction when reducing the energization time according to the drive history, the print head Alternatively, the reference energization time and its reduction amount corresponding to the ambient temperature can be obtained, and the ratio between the reference energization time and the reduction amount can be set to be substantially constant.

In this case, the reference potential generation circuit includes a resistance circuit network including at least a first resistor connected in parallel with the heat-sensitive resistance element and a second resistor connected in series with the first resistor. It is possible to compensate for the linearity of the temperature characteristic of the heat-sensitive resistance element by including the amplification circuit that amplifies the voltage at the connection point of the first and second resistors of the resistance circuit network. Therefore, the temperature correction of the reference energization time and the reduction amount thereof can be performed more reliably.

Further, the charge / discharge circuit may be configured to have a constant current circuit for charging the capacitor. By configuring in this way, it is possible to further improve the linearity of the change in the charge level of the capacitor with respect to the charge time. As a result, it becomes possible to further reduce the change in the ratio of the reference energization time to the temperature change of the print head or the like and the reduction amount thereof. Further, by configuring the constant current circuit with a constant voltage circuit and a resistor connected between the output of the constant voltage circuit and the power supply used to drive the print head, the voltage of the power supply fluctuates. In that case, a current corresponding to the fluctuation is supplied to the capacitor, and therefore the reference energization time and the reduction amount thereof are appropriately set according to the fluctuation of the power supply voltage. Even in this case, the ratio of the reference energization time and the reduction amount thereof is kept substantially constant, as described above. Therefore, not only the fluctuation of the environmental temperature condition but also the fluctuation of the voltage of the print head driving power supply Even so, it is possible to properly set the applied energy during the heat history control, and it is possible to realize extremely good printing quality.

Further, by increasing the number of voltage comparison circuits, it becomes possible to easily perform detailed thermal history control.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of an energization width control circuit of a print control device for a thermal printer according to the present invention. FIG. 2 is a graph showing a resistance value of the thermistor, a potential at a voltage dividing point of a resistance network including the thermistor, and a temperature characteristic of an output potential of an operational amplifier for amplifying the potential. FIG. 3 is an explanatory diagram showing the charging characteristics of the capacitor. FIG. 4 is an explanatory diagram of input / output waveforms of the conduction width control circuit according to the present invention. FIG. 5 is a schematic view showing an embodiment of a print control device for a thermal printer according to the present invention. FIG. 6 is an explanatory diagram showing the energized state of the thermal head history control method using the present invention. 1 ... Thermistor 2 ... Resistor network 3 ... Amplifier circuit 11-14 ... Voltage comparison circuit 4 ... Voltage dividing circuit 5 ... Constant current circuit 6 ... Capacitor 84 ... Thermal head

Claims (4)

[Claims] 1. A thermal printer which forms dots by a plurality of heating elements arranged in a print head and prints directly on a thermal paper or on a plain paper via a transfer film. In a print control device of a thermal printer that stores the electricity and reduces the energization time to each heating element of the next dot or subsequent dots according to the stored drive history, at least a capacitor is provided and A charging / discharging circuit whose operation is started from a state, a thermosensitive resistance element that detects the temperature of the print head or its ambient temperature, and a reference potential generation circuit that generates a potential corresponding to the resistance value of the thermosensitive resistance element, A voltage dividing circuit for generating a plurality of reference comparison potentials based on the potential generated by the reference potential generating circuit; A plurality of voltage comparison circuits for obtaining a plurality of different timings from the start of the operation of the charging / discharging circuit by comparing with each of the plurality of reference comparison potentials generated by the circuit, Among them, it has a conduction width control circuit that uses the latest timing for setting the reference conduction time of the heating element and the other for setting the reduction amount when reducing the conduction time according to the driving history. Print control device for thermal printer. 2. The reference potential generating circuit according to claim 1, wherein the first resistor connected in parallel to the thermosensitive resistance element and the second resistor connected in series to the first resistor. A print control device for a thermal printer, comprising: a resistance circuit network having at least the following: and an amplifier circuit that amplifies the voltage at the connection point of the first and second resistors of the resistance circuit network. . 3. The print control device for a thermal printer according to claim 1, wherein the charge / discharge circuit includes a constant current circuit for charging the capacitor. 4. The constant current circuit according to claim 3, comprising a constant voltage circuit and a resistor connected between an output of the constant voltage circuit and a power source used to drive the print head. A print control device for a thermal printer, which is characterized by: