JPH0639178B2 - Printing control device for thermal printer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a print control device 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 the print control device of the thermal printer,
There is one that stores the past driving history of the heating elements and controls the thermal history to determine the next printing energy of each heating element.

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 basic energization time fluctuated, and good print quality could not be obtained against temperature changes and voltage fluctuations. It was

The object of the present invention is to eliminate such drawbacks of the prior art,
Provided is a thermal printer control device which constantly keeps a good print quality by keeping the ratio of the applied energy to be reduced even when the applied energy to the heating element is changed depending on the temperature and the voltage condition during the thermal history control. To do.

[Means for Solving Problems] The print control device for a thermal printer according to the present invention has the following means for solving these problems.

a. Thermal head or heating resistance element that detects ambient temperature b. A resistance network including the heat-sensitive resistance element c. An amplifier circuit for amplifying the potential at a predetermined voltage dividing point of the resistor network d. Multiple CR circuits with capacitors and resistors connected in series e. A plurality of voltage comparison circuits for converting the charge / discharge time of the capacitor into a pulse width with reference to the output voltage of the amplifier circuit f. Discharge circuit for simultaneously discharging the plurality of capacitors connected to the voltage comparison circuit. The discharge circuit has the above means, one of the voltage comparison circuits is used for setting the reference energization time of the heating element, and the other is used as a driving history. Accordingly, the control device is used to determine the reduction amount when the energization time of the heating element is reduced.

[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 circuit network including the thermistor 1, 17 and 18 are resistors, and 34 is a capacitor, respectively. The capacitor 34 is for preventing noise and has nothing to do with the characteristics.

Reference numeral 3 is 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 20 as inputs of the operational amplifier. The operational amplifier 10 also has a feedback resistor 22, a diode 23, and an input resistor 24. The voltage dividing circuit 30 is composed of resistors 19 and 21 and a variable resistor 20, and forms a reference input section of the operational amplifier 10.

Reference numerals 11, 12, and 13 denote voltage comparison circuits, which are commonly connected to the output terminal of the operational amplifier 10 as a reference input.
Also, the CR circuits 31, 32, and 3 are input as compared inputs, respectively.
3 is connected. 4, 5, 6 are resistors, 7, 8,
Reference numerals 9 and 9 respectively indicate capacitors. 27, 28,
Reference numeral 29 is a discharging transistor, and a discharging circuit is formed by using the transistors 27, 28, 29 and the input resistors 37, 38, 39 as main constituent elements.

35 is a trigger input terminal, 36 is a power input terminal, 14, 1
Reference numerals 5 and 16 respectively represent output terminals of this energization width control circuit.

(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 20 ° C using the B constant.
The value R (20) and the absolute temperature T are expressed by the following equation.

Rt = R (20) expB (1 / T (t) -1 / T (20)) ...
Formula 1 T (t) = Absolute temperature at any temperature T (20) = Absolute temperature at 20 ° C. Looking at Formula 1, since the term of exp is included, the reciprocal of temperature is log 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 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, where the horizontal axis is the absolute temperature and the vertical axis is the resistance value Rt and the minute. The voltage at the pressure point A and the output voltage Vop of the operational amplifier are shown.

41 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 43 is a characteristic curve showing the temperature characteristic of the output voltage Vop of the operational amplifier. The thermistor has a negative characteristic with respect to temperature change as shown by the characteristic curve.

The following items can be cited as features of performing such correction.

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

2. Linearity is given over a relatively wide range.

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

The amplifier circuit 3 uses the corrected temperature characteristic to partially expand the voltage. Therefore, the voltage dividing point A for obtaining the characteristic curve 42 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.

When the value of the resistor 24 is R24 and the value of the resistor 22 is R22, the magnification K is K = (R24 + R22) / R24.

The functions of the diode 23 are: Since the abrupt rise of the reference potential at low temperature is suppressed, the output pulse width of the voltage comparison circuits 11, 12, 13 is prevented from increasing at low temperature as a result.

2. The inflection point of partial enlargement can be changed.

Various characteristic curves can be created by changing or eliminating the number of diodes by utilizing the characteristics of 1 and 2.

The variable resistor 20 in the voltage dividing circuit 30 adjusts Vop without changing the rate of change of the output voltage Vop of the operational amplifier with respect to temperature change, and sets the output pulse width of the voltage comparison unit in the subsequent stage to a predetermined value. It is a thing.

The time constants of the CR circuits 31, 32 and 33 have the following relationship.

If the values of the resistors 4, 5, 6 are R4, R5, R6 and the values of the capacitors 7, 8, 9 are C7, C8, C9, then C7 * R4> C8 * R5> C9 * R6.

FIG. 3 is an explanatory diagram showing input / output waveforms of the voltage comparison circuit of the conduction width control circuit of FIG.

Reference numeral 51 is a trigger input waveform given to the input terminal 35 of the discharge circuit, and its pulse width tg is extremely small, so that it can be ignored in terms of characteristics. 52 shows the waveform of the output terminal 14, 53 shows the waveform of the output terminal 15, and 54 shows the waveform of the output terminal 16. Each pulse width is TW14, T
It is shown by W15 and TW16, and has the following relationship.

TW14>TW15> TW16 FIG. 4 is a characteristic diagram showing the temperature characteristics of the pulse widths of the output waveforms 52, 53 and 54. Due to the operation of the thermistor 1 and the amplifier circuit, the voltage on the non-inverting input side of the voltage comparison circuit decreases as the temperature rises. Therefore, the voltage on the inverting input side of the voltage comparison circuit has a time constant specific to the CR circuits 31, 32, 33. The time from the discharge state until the voltage rises and exceeds the voltage on the non-inverting input side, that is, the output pulse width becomes shorter.

The values of the output pulse widths TW14, TW15, and TW16 at 20 ° C. become t1, t2, t3 in order from the largest value, and become t4, t5, t6 at 0 ° C. in order. At this time, the following relationship is established.

t2 / t1≈t5 / t4 t2 / t3≈t5 / t6 Such characteristics are possessed over the entire temperature range.

This is based on the following theoretical formula.

When the output voltage of the operational amplifier 10 is 20 ° C., Vop (20),
When the power supply voltage is Vc, the output pulse width TW14 of the voltage comparison circuit 11 is expressed by the following equation.

ln: As natural logarithm, TW14 = −C7 × R4ln (1-Vop (20) / Vc) Similarly, TW15 is TW15 = −C8 × R5ln (1-Vop (20) / Vc).

At this time, the ratio of both pulse widths becomes TW14 / TW15 = (C7 × R4) / (C8 × R5), the term relating to temperature disappears, and the ratio of time constants is obtained.

By controlling the thermal history of the thermal printer using the energization width control circuit having such characteristics, it is possible to realize extremely good printing quality.

FIG. 5 is a schematic diagram showing an embodiment of the printing control device according to the present invention. Reference numeral 40 is a conduction width control circuit (hereinafter abbreviated as CTCC) shown in FIG. 1, and 46 is a thermal device having a plurality of heating elements 45. Heads and 47 are head drivers, respectively. The thermistor 1 in the CTCC is arranged in contact with the thermal head 46.

Reference numeral 44 is a power supply control transistor that turns on and off the power supply terminal of the head driver 47, and reference numeral 50 is a CPU that integrally controls the entire thermal printer. The CPU 50 outputs a head data 48 corresponding to each heating element to the head driver 47 at the time when a trigger is output to the trigger input terminal 35 of the CPCC 40 at each head energization timing in response to the print data input. The head driver 4 is used to energize the heating element.
This is done when the power is supplied to 7 and the head data is in the active state. Therefore, printing of a desired dot is realized by setting the head data corresponding to the heating element on which this dot is to be printed to the active state and the head data corresponding to the other heating elements to the inactive state.

Reference numeral 43 is an inverter connected to the output terminal 14 of the CTCC 40. The transistor 44 determines the operating time of the head driver and the reference energizing time of the heating element 45.

Pulse signals output from the output terminals 15 and 16 of the CTCC 40 and having pulse widths of TW15 and TW16, respectively, are input to the CPU 50.

FIG. 6 is an explanatory diagram showing the energization state of one heating element of the thermal head according to the history control method of this embodiment.
This is an example in the case of ° C. Hereinafter, a method of setting the reduction amount from the reference energization time according to the past driving history in the CPU will be described with reference to this drawing.

Reference numeral 61 indicates a state when the energization is continuous, that is, when the heating element is energized in the energization section immediately before the energization section in which the reduction time is to be set. Different reduction times are set depending on the presence or absence of energization in the immediately preceding energization section. That is, the reduction time is TW15 when the current is applied and TW16 when the current is not applied. Since it is an example in the case of 20 ° C., the values of TW15 and TW16 are t2 and t3, respectively.

Reference numeral 62 indicates that when power is supplied every other dot, that is, the power is not supplied in the power supply section immediately before the power supply section in which the reduction time is to be set, and the current is supplied immediately before the current supply section in which the reduction time is to be set. The state when the power is supplied in the power supply section is shown, and the reduction time is TW16. T3 at 20 ° C
Is.

61 and 62 are energizing pulse waveforms for explaining the case where the reduction time is provided. However, when the conduction pulse waveform does not belong to either of these cases, the reduction time is zero like the first pulse of 61 and 62. It is said that

In this way, the CPU 50 controls the heating element 45 of the thermal head.
A head corresponding to a heating element to be energized from the head data output terminal in synchronization with the pulse signals from the output terminals 15 and 16 of the CTCC by setting a reduction time from the reference energization time according to the past driving history of The data 48 is output.

This operation will be described in more detail with reference to FIG. 5 by taking an energization waveform 61 shown in FIG. 6 as an example. Here, when the head data 48 is at a high level (hereinafter abbreviated as “H”), energization to the corresponding heating element is permitted, and when it is at a low level (hereinafter abbreviated as “L”). Shall stop energization. In the energization section on the left side of the energization waveform 61, CP
As described above, U50 outputs a trigger to the trigger input terminal 35 and simultaneously outputs the head data 48 to the head driver 47.
"H" is output as. As a result, the output terminal 14 of the CTCC 40 becomes "H", and the power feeding control transistor 4
No. 4 is turned on, power supply to the head driver 47 is started, and at the same time, energization to the corresponding heating element is permitted, and thus energization is started. In the central energization section of the energization waveform 61, the CPU 50 sets the reduction time to TW16 as described above, so that the head data 48 is set to "L" at the same time as the trigger output. At this point, power supply to the head driver is started, but power supply to the corresponding heating element is not performed. And after 16 hours of TW, CT
When the output terminal 16 of the CC 40 changes from "H" to "L", the CPU 50 outputs the head data 48 at this timing.
Is set to "H", and energization to the corresponding heating element is started.
Similarly, in the energization section on the right side of the energization waveform 61, C
Since the PU 50 sets the reduction time to TW15 as described above, the head data "L" is output at the same time as the trigger output, and the output terminal 15 of the CTCC 40 changes from "H" to "L" after TW15 hours have elapsed. Sometimes head data "H"
By outputting, the energization to the corresponding heating element is started.

In this way, the reference energization time is the output terminal 1 of the CTCC.
It is set by setting the power supply time to the head driver by using the output pulse width TW14 from No. 4, and the reduction time from the reference energization time is selected from TW15 or TW16 or zero according to the drive history of the heating element. The current-carrying time is therefore determined as the difference between them.

Note that the number of voltage comparison circuits is not limited to three, and by increasing the number, more detailed thermal history control can be performed.

Further, by making the CR circuits 31, 32, 33 common to the power supply to the thermal head 46, it is possible to compensate the energization width even for power fluctuation of the thermal head.

Further, the heat-sensitive resistance element has not only the thermistor but also an element having a positive characteristic with respect to temperature change, which has the same effect.

FIG. 7 is a schematic view showing another embodiment of the print control device for the thermal printer according to the present invention, and the same parts as those in FIG.

Reference numerals 71, 72 and 73 are LS-374 of TTL, that is, a latch circuit similar to the 8-circuit 3-state D-type flip-flop, which temporarily holds head energization data. 7
Reference numerals 4 and 75 are differentiating circuits connected to the output terminal of the CTCC 40. Reference numeral 76 is a decoder for latching the address information simultaneously with the output of the head energization data 48. Reference numeral 77 is a CPU WR.
A terminal, 78 is a gate for synchronizing the address information and the WR signal, and 79 is a gate for compounding the signals of the differentiating circuits 74, 75 and the gate 78 to obtain the clock signals of the latch circuits 71, 72, 73, respectively.

This embodiment will be described in detail below with reference to FIG.

Differentiating circuits 74 and 75 obtain a trigger output synchronized with the falling timing of the output waveform shown in FIG.
At the same time, the differentiating circuit 74 generates a trigger output, and similarly, at the same time as the time TW16 elapses, the differentiating circuit 75 generates a trigger output.

First, the CPU 50 outputs the energization data 48 including the history data three times. Gate 78 in synchronization with data output
Outputs a clock signal from the latch circuits 71, 72,
The respective data are stored in 73. Next, at the same time as the energization timing, a trigger is output to the input terminal 35 to operate the head driver 47, and the predetermined heating element is energized based on the data stored in the latch circuit 73.

When TW16 hours have passed, a trigger output is generated at the gate 79, and the data of the latch circuit 72 is moved to the latch circuit 73 by using this as a clock, and predetermined energization is performed.
After 15 hours, the gate 79 similarly outputs a trigger output, and the last data is sent to the head driver. After that, when a predetermined dot is formed, the transistor 44 is closed and the energization is completed after 14 hours have passed.

In the embodiment shown in FIG. 7, since the CPU does not participate in the timing of transmitting the history data, the processing speed can be increased and the thermal printer can be applied at high speed.

[Effects of the Invention] As described above, the print control device of the thermal printer according to the present invention properly operates even when the reference energization time to the heating element is changed depending on the environmental temperature condition and the voltage change of the heating element. You can set the applied energy during thermal history control,
It is possible to achieve extremely good print 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 characteristic diagram showing the relationship between the resistance value of the thermistor, the voltage dividing point of the resistor network and the output potential of the operational amplifier. FIG. 3 is an explanatory diagram showing input / output waveforms of the energization width control circuit of the present invention. FIG. 4 is a characteristic diagram showing the temperature characteristic of the output waveform of the energization width control circuit of the present invention. FIG. 5 is a schematic view of an embodiment of a print control device according to the present invention. FIG. 6 is an explanatory diagram of a thermal head printing control method using the present invention. FIG. 7 is a schematic view of another embodiment of the print control device according to the present invention. 1 ... Thermistor 2 ... Resistor circuit network 3 ... Amplifier circuit 11, 12, 13 ... Voltage comparison circuit 31, 32, 33 ... CR circuit 46 ... Thermal head

Claims (1)

[Claims] 1. A thermal printer for forming dots by a plurality of heating elements and printing directly on thermal paper or on plain paper via a transfer film, and a storage means for storing the driving history of each heating element. A thermal head drive circuit that energizes and drives the heating elements, and a control unit that sets the energization time to each heating element when printing the next dot or subsequent dots based on the stored driving history. In the thermal printer as described above, a. A heat sensitive resistance element for detecting the temperature of the thermal head in which the heating element is arranged or the ambient temperature of the thermal head, b. A resistance circuit network including the heat sensitive resistance element, c. an amplifier circuit that amplifies the potential at a predetermined voltage dividing point of the resistor network, and d. a plurality of integrator circuits that have different time constants and whose output potential rises over time. , E. A plurality of voltage comparison circuits for comparing the output potential of the amplifier circuit with the output potential of the integrator circuit and converting the output potential of the amplifier circuit into a pulse width; and f. Initializing the plurality of integrator circuits at the same time. An initialization circuit for resetting the voltage, g. A reference energization time setting circuit for setting a reference energization time of the thermal head drive circuit using an output of one voltage comparison circuit among the plurality of voltage comparison circuits, and h. Reduction time setting means for setting the energization stop time in the reference energization time by using the output of another voltage comparison circuit of the plurality of voltage comparison circuits based on the drive history stored in the storage means, A print control device for a thermal printer, which has: