JPS5952074B2 - Voltage compensation control method for thermal printer - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for controlling a thermal printer.

SUMMARY OF THE INVENTION An object of the present invention is to provide a control method for a thermal printer that changes the energization time to a heat generating element of the thermal printer in accordance with the power supply voltage, thereby achieving stable printing quality against fluctuations in the power supply voltage.

Another object of the present invention is to change not only the heating element of the thermal printer but also the power supply time to the power source of the paper feeding device according to the power supply voltage, thereby effectively extracting the capacity of the power supply and making it possible to operate for a long time. An object of the present invention is to provide a method of controlling a thermal printer with low power consumption.

Still another object of the present invention is to provide a protection circuit for a heat generating element of a thermal printer, which shortens the energization time and prevents thermal destruction of the heat generating element when an abnormally high voltage is applied to the heat generating element of the thermal printer. be.

Still another object of the present invention is to provide a power source control method that suppresses abnormal temperature rises in the power source of a paper feeding device of a thermal printer and ensures stable operation with respect to power supply voltage.

FIG. 1 is a block diagram of an electronic desktop calculator using a conventional thermal printer control method.

1 is a power source, which may be a dry battery, a nickel-cadmium battery, or the like, or a rectified commercial AC power source.

2 is a regulator for obtaining a constant voltage in response to power fluctuations; 3 is a power transistor of the regulator 2; 4 is a heating element mounted on the thermal head of the thermal printer;
5 is a power supply transistor that energizes the heating element; 6 is a calculation clock pulse oscillator (hereinafter referred to as OSC); 7 is a central processor unit (hereinafter referred to as CPU); 8
9 is a read-only memory (hereinafter referred to as ROM), 9 is a flip-flop (hereinafter referred to as FF) that determines the energization time to the heating element 4, 10 is a printer control unit (hereinafter referred to as PCU), and 11 is a paper feeding device. (PF),
12 each indicates a keyboard (KB).

The heating element 4 and the paper feeding device 11 are connected to a thermal printer 13.
It is a component of Signals entered manually through the keyboard 12 are subjected to calculations and other processing by the θCPU 7, and pre-prepared character patterns are stored in the ROM 8.
It is read from and sent to PCUIO. PCUIO is
It controls the power supply transistor 5 and the paper feed device 11, and performs the printing process of predetermined characters, symbols, etc. '5 Figure 2 is a diagram showing the structure of a thermal head in which a plurality of heating elements are arranged.

Reference numeral 21 denotes a base material made of an insulating material such as ceramic or glass, on which heating elements 4 are arranged in a line.

22 is a common electrical conductor to which one end of the power supply is connected.

23 is a signal supply electrical conductor connected to the power supply transistor.

24 is a group of heating elements that are the basics of forming one character, and in this case, the character is formed by arranging a plurality of five dots vertically.

FIG. 3 is a schematic diagram of characters formed by the thermal head.

It is constructed using an Mxn matrix. If the number of digits is one, the number of heat generating elements is Mxl, and in the thermal head of FIG. 2, since m=5 and l=8, 40 heat generating elements are required. As shown in FIG. 3, when a character is composed of a 5.times.7 matrix, if the head shown in FIG. 2 is used, seven steps are required to print one line.

Conventionally, the 0SC6 employs a circuit with a relatively stable frequency, and the frequency is divided by the FF9, and the heating element 4
The time to turn on electricity was determined.

Therefore, when the power source 1 has a variable element, for example, when a dry battery is used as the power source, it is essential to use a regulator to stabilize the heat amount of the heat generating element 4 to a constant value. For dry batteries, generally 1.5 [] to 1
It is necessary for the device to work normally within the range [ ], and if eight dry batteries are connected in series to the power supply 1 in Figure 1, the power supply voltage V1 can vary from 12 [V] to 8 [V]. I will do it. Considering this voltage fluctuation, the set voltage V2 on the secondary side of the regulator is set to 5 [V] with a margin of 8 [V].
It has to be moderate. When the regulator 2 is used, power is wasted due to the collector loss of the power transistor 3. If the power loss is large, it is extremely disadvantageous when using a power source with limited capacity such as a battery, and this cannot be ignored when considering portability. Furthermore, if the regulator 2 is damaged due to some abnormality, a voltage of several volts in addition to the normal voltage will be applied to the heating element 4, and the heating element 4 will be burned out in an instant. I was concerned about safety.

In addition, when the printer manufacturer and the calculator manufacturer are different, there are many disadvantages such as differences in print quality due to differences in the set voltage V2 of the regulator 2 and variations in the energization time. The present invention eliminates these various conventional drawbacks,
It suppresses power loss and extracts power effectively, making it possible to make battery-powered calculators with printers more portable. It also provides stable printing quality against power fluctuations, and eliminates heat-generating elements in the event of power supply abnormalities, especially high voltage. This is an extremely ideal thermal printer control method that reduces the energization time and also functions as a thermal head protection circuit. An embodiment of the present invention will be shown and described in detail from FIG. 4 onwards.

FIG. 4 is a block diagram of an electronic desktop calculator according to an embodiment of the present invention.

31 is a power supply, 32 is a pulse generation circuit (hereinafter referred to as PG) that detects the power supply voltage and has a period or pulse width according to the voltage.
), 34 is a heating element on the thermal head, 35 is a power supply transistor that supplies electricity to the heating element 34, 36 is an arithmetic clock pulse oscillator (hereinafter referred to as 0SC), 39 is a flip-flop (hereinafter referred to as FF), 4] indicate paper feed devices (PF), respectively.

The heating element 34 and paper feed device 41 are a thermal printer 43
It becomes a component of Central processor unit (
(hereinafter referred to as CPU) 37 is the keyboard (KB) 42
It receives the input signal obtained from the printer, performs arithmetic processing, etc., reads out the necessary character pattern from the read-only memory (hereinafter referred to as ROM) 38, and sends it to the printer control unit (
(hereinafter referred to as PCU) 40. The processing functions up to this point are exactly the same as those of the conventional embodiment shown in FIG.
PG32 is a pulse generating circuit whose cycle changes as the voltage changes, and converts the signal of PG32 into a signal specifying the energization time, energizes the heating element 34 appropriately, and controls printing quality. In the end, the clock pulse of PCU4O became PG.
32 will be in charge. FIG. 5 shows an embodiment of the circuit of the PG32.

51 is a varistor which is one of the resistance elements, 52 is a capacitor, 53 is a resistor, and 54 is a capacitor.

Resistance value R5l of varistor 51 and value C5 of capacitor 52
2 determines one time constant τ1-C52·R5l, and the other time constant τ2=C54·R53 is determined by the value R53 of the resistor 53 and the value C54 of the capacitor 54, respectively. At a period determined by the above time constant, the transistors 55 and 56 alternately turn on and off. Repeat 0FF. The sixth is a diagram showing the characteristics of the varistor.

The varistor 51 has a characteristic in which the resistance value decreases as the voltage E increases, as shown in the characteristic curve of FIG. 6, where E is the voltage applied to the varistor and I is the current flowing through the varistor. By using a varistor with these characteristics as one of the components of the resistor that determines the period of the pulse generation circuit, the period is short when the voltage is high, and the period is long when the voltage is low. This is a pulse generation circuit that generates a pulse. or,
By using a thermistor in R5l or R53, the period can also be changed depending on the temperature.
Thermal printers are generally affected by ambient temperature, so
By using a negative characteristic thermistor and appropriately combining it with a fixed resistor, when the temperature is high, the period of the pulse generation circuit is short, and when the temperature is low, the period becomes long.
The time during which electricity is applied to the heat generating element 34 is adjusted, and appropriate print quality can be obtained. FIG. 7 shows a time chart of the thermal printer 43 of the calculator shown in FIG.

a is the output waveform of the pulse generating circuit PG32 which oscillates at a period of 1T according to the voltage, b is the frequency-divided waveform by the FF39, C is a print command to start printing in response to a signal from the keyboard 42, etc., and d is a print command to start printing in response to a signal from the keyboard 42, etc. A head energization control pulse that sets the energization time and position on the time axis for energizing the heat generating element 34.
For each heat generating element 34, a signal that is the basis of each energization signal, e indicates a power energization control pulse that sets the energization time and position on the time axis of the power source of the paper feeding device 41, respectively. . The head energization control pulse 61 in d determines the energization time Wd for the first row of the Mxn matrix in FIG. occurs, and the series of printing processes ends. The power energization control pulse 64 of e determines the energization time We to the power source of the paper feed device 41 and the position on the time axis in order to move the printed paper from the first line to the second line. The power source generally uses a plunger or step motor. In the time chart shown in FIG. 7, both the head energization control pulse d and the power energization control pulse e are synchronized with the output waveform a of the PG 32.

Therefore, as the period T of the PG 32 changes depending on the voltage, the printing speed also changes. FIG. 8 is another embodiment of the power source of the present invention, which is a schematic diagram of a common step motor.

65 is a rotor, 66 and 67 are drive coils with intermediate taps, which constitute 4-phase coils A, B, C, and D.
The rotor 65 rotates by a predetermined rotation angle by sequentially applying electricity in the direction of the arrow 68 from B to C-)D.

FIG. 9 shows a time chart when driving the step motor.

f is the output waveform of the PG 32, g is a head energization control pulse that controls the energization time to the heating element 34, and h is a step motor energization control pulse. Since the step motor has four phases, h requires four types of energization control pulses. The major difference between the time chart in FIG. 7 and the time chart in FIG. 9 is that e is the energization control pulse for a single-phase driven plunger or a special step motor.
As shown in FIG. 9, the driving coils 66 and 67 are energized by
After power is applied to A, power is applied to B, and after power is applied to B, power is applied to C, and so on. Also, in relation to the paper feed amount, D
If the amount of paper feed is insufficient even after turning on the power up to
All you have to do is turn on the power again. Conventionally, the time during which electricity was applied to the paper feed reblancher or the step motor was kept constant, but the present invention has a feature in which the time during which electricity is applied to the moving motor changes as the power supply voltage changes.

Plungers and step motors generally have a property that the higher the power supply voltage, the faster the response speed. Therefore, if the voltage is high, most of the electrician's energy will be lost as heat even if the energization is extended for a certain period of time. If heat dissipation from step motors, plungers, etc. is not sufficient, the temperature rise at high voltage may cause equipment burnout. In the present invention, in order to eliminate such problems, the energization time for the 7 motive power is also changed according to the power supply voltage, and the temperature rise at high voltage of the motive power is suppressed, thereby improving the reliability and safety of the equipment. It's extremely expensive. In addition, by changing the energization time according to the power supply voltage, the energization time is short at high voltages and the power can be extracted effectively, and at low voltages, the energization time is lengthened to eliminate malfunctions. This drive method is suitable for long-term operation with low power consumption, and is an extremely effective control method for devices that use power sources with limited capacity, such as batteries. Two points P and q in FIG. 6 indicate arbitrary two points on the characteristic curve, and the current values at that time are respectively Ip and Iq, and the voltage values are Ep and Eq.

Generally, the characteristics of the varistor 51 are expressed by the following [Formula-1]. When β is expressed using the voltage values and current values at the two points P and q described above, it becomes [Formula-2].

The relationship between the period T and the voltage V of the pulse generation circuit shown in FIG. 5 is shown in a graph using a varistor 51 of approximately β=0.3 to 0.38 and a voltage of 24 V as an example, as shown in FIG. 10. The characteristic curve 71 shows the characteristic.

Some variation in the characteristic curve appears due to variation in the capacitor. Let Vr be the center value of the operating voltage of the thermal printer 43, let r be the point on the characteristic curve 71 at that time, and let Tr be the period. If the Joule heat when the heat generating element 34 is energized is J, and the resistance value of the heat generating element 34 is R34, then J is expressed by the following [Formula-3]. (Wd is proportional to the period T) Theoretically, if J=constant, the amount of heat applied to the heating element 34 will be constant even if the voltage fluctuates, and the printing quality will also be constant.

In the circuit of PG32 shown in FIG.
It has been confirmed through experiments that the J constant of [Formula-1] is satisfied by using a material with a diameter of about 0.3 to 0.38. When Js/Jr is graphed with an arbitrary point on the characteristic curve 71 as S and the Joule line at this time as Jr, it shows a nearly linear characteristic as shown in the characteristic curve 72. It is presumed that if the energization time to the heating element 34 is varied according to this characteristic, a constant amount of heat will always be supplied, and that a constant quality of characters and symbols printed on thermal paper will be obtained. It has been found that when the voltage is higher than Vr, the print becomes darker, and when the voltage is lower than Vr, the print becomes lighter.
When determining Js/Jr to correct this shading, characteristic curve 73
The longer the period T is, the larger Js/Jr becomes. The reason why such a phenomenon occurs is considered to be that the longer the current application time Wd is, the greater the amount of heat that escapes to the base material 21 and the like. Period T and voltage V that satisfy Js/Jr characteristic curve 73
A characteristic curve 74 is shown in a graph. 11th
The figure is a circuit diagram of an embodiment of the PG 32 configured to satisfy the characteristic curve 74.

81 is a varistor, 82 is a capacitor, 83 is an adjustment resistor, 84 is a capacitor 85, and 86 is a transistor, respectively.

The circuit configuration up to this point is exactly the same as the circuit shown in Figure 5, but the feature of the circuit in Figure 11 is that the Zener diode 89 and the resistor section 90 are connected in series to the voltage terminal V4. That's true. Other components that do not affect the characteristics include a waveform shaping transistor 87, an output terminal 88, and the like. The resistance section 90 has a fixed resistor 91 and a thermistor 92 in a parallel circuit. There is no particular reason to use a parallel circuit, and various combinations can be considered depending on the temperature characteristics, such as using only a thermistor, or using a series circuit of a thermistor and a fixed resistor. Furthermore, if temperature compensation is not particularly required, the resistor section 90 may be omitted. The pulse generating circuit shown in FIG. 5 has a characteristic in which the amount of change in period is determined in accordance with the amount of change in voltage. The circuit shown in FIG. 11 makes good use of this characteristic to create the characteristic curve 74, and its principle will be described below.
By inserting the Zener diode 89 between the V3 terminal and the V4 terminal, the rate of change in voltage at the voltage terminal V4 can be increased. As an example, the thermal printer 43
The center value of the working voltage is Vr, and the Zener voltage of the Zener diode is Vz, Vr = 20 [], Vz = 10 [V
], if the voltage V3 when it fluctuates is 18 [V], it can be expressed as follows, with the rate of change of voltage being ρ1.
However, when there is no Zener diode, the rate of change is ρ2
It can be seen that the rate of change is clearly greater for ρ1.

If the rate of change in voltage is large, the rate of change in the period of the pulse generation circuit shown in FIG.
You can move in 4 directions. As is clear from [Formula-4], in order to increase the rate of change in the period, it is sufficient to increase the zener voltage Vz. Using such characteristics, the Zener voltage Vz and the resistance value R9O of the resistor section 90 are determined so as to match the characteristic curve 74 in FIG. 10. FIG. 12 shows the temperature characteristics of the output of the PG 32 shown in FIG.

101 is a characteristic curve at 50° C. When the voltage Vr (7) is applied, the r point at room temperature moves to the t point, and the period becomes Tt, which is smaller than Tr.

Similarly, it becomes smaller than the characteristic curve 74 at any point. 102 is the characteristic curve at 0°C, and contrary to 101, the overall
point r moves to point u, and the period becomes Tu.

Providing the PG 32 with such characteristics has the following advantages.

In other words, when the temperature is high, the energizing time to the heating element 34 is reduced, and when the temperature is low, the energizing time is expanded, thereby changing the energizing time with respect to the temperature and stabilizing the printing quality. can do. The resistance section 90 including the thermistor 92 can also be included in the adjustment resistor 83. Further, by placing the thermistor 92 on the base material 21 shown in FIG. 2, the static temperature of the heat generating element can be accurately detected. Conventionally, in order to improve the printing quality of thermal printers, when LSI manufacturers create clock pulse oscillators,
There were many difficulties, as it was necessary to increase the accuracy of the oscillation period of the clock pulse oscillator, and it was also necessary to increase the accuracy of the power supply of electronic equipment such as calculators into which thermal printers were incorporated. However, if a thermal printer has a pulse generation circuit according to the present invention inside, calculator manufacturers and L.
It is possible to supply a thermal printer that guarantees appropriate print quality without requiring any intervention from the SI manufacturer, and the marketability of thermal printers becomes extremely large. Also PG
By incorporating a pulse generation circuit using a thermistor into the printer, the temperature of the thermal printer can be detected and the printing quality can be controlled, and by attaching the thermistor to the thermal head as shown in Figure 1, it is possible to accurately control the temperature of the thermal printer.
The temperature of the heating element 34 can be detected, and a thermal printer with good printing quality can be realized.

In the past, thermal printer manufacturers had problems with yield due to variations in the resistance value of the thermal head, but PG32 at the standard voltage (or center voltage Vr)
By adjusting the cycle of the heat generating element 34 according to the average value of the resistance value R34 of the heating element 34, variations in the resistance value between the thermal heads can be absorbed, making it easy to supply thermal printers with uniform printing quality. There are many advantages to having a built-in printer clock generation circuit in a printer. In the present invention, in order to make it easier to understand, a flip-flop (FF) 39 is used based on the output of the PG32, but the FF
39 is included in PCU4O and is common. CPU3
7. PCU4O is usually integrated using LSI, and conventionally 0SC36 was also included in LSI.
The PG32 of the present invention can also achieve C by selecting the material of the varistor.
It is also possible to include it in the PU 37 and convert it into an IC. Also, Mx
Although the character structure uses an n matrix, other structure methods such as segment type can also produce the same effect. The Zener diode in the circuit exhibits similar characteristics even when a plurality of general diodes are connected in the forward direction. The present invention can be widely applied to electronic devices that use a thermal printer as a printing means, and in the detailed explanation, an electronic desktop calculator is used as an example.As described above, the thermal printer according to the present invention This control method is an extremely innovative method that simplifies and stabilizes the print quality of thermal printers, realizes low power consumption, increases the reliability of the thermal head, and expands the marketability of thermal printers. It can be widely applied to controlling thermal printers.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of an electronic desk calculator using a conventional thermal printer control method, where 1 is a power supply, 2 is a regulator,
Reference numeral 4 indicates a heat generating element, and reference numeral 6 indicates a calculation clock pulse oscillator. FIG. 2 is a diagram showing a heat head in which heat generating elements 4 are arranged.
1 is a base material, 22 is a common electrical conductor, and 23 is a signal supply electrical conductor. FIG. 3 is a schematic diagram showing an example of the structure of characters printed using the thermal head of FIG. 2. FIG. FIG. 4 is a schematic diagram of a calculator using the thermal printer control method according to the present invention, in which 31 represents a power source, 32 represents a pulse generation circuit, and 34 represents a heat generating element. FIG. 5 is a circuit diagram showing the configuration of the PG 32 shown in FIG. 4, where 51 indicates a varistor, and 55 and 56 indicate transistors. FIG. 6 is a diagram showing the voltage-current characteristics of the varistor 51, which is one of the components shown in FIG. FIG. 7 is a time chart of the control method of the thermal printer of the present invention, where T is the period of the output waveform of PG32;
Wd indicates the time period during which the heat generating element 4 is energized, and We indicates the time period during which the plunger or step motor is energized. FIG. 8 is a schematic diagram of a step motor that serves as a power source for the thermal printer, with reference numeral 65 representing a rotary shaft, and numerals 66 and 67 representing drive coils, respectively. FIG. 9 is a time chart of the control system of the thermal printer when the step motor shown in FIG.
Wh indicates the time during which the step motor is energized. FIG. 10 is a diagram showing the characteristics of the pulse generating circuit shown in FIG. 5, in which the horizontal axis represents the period T, the left vertical axis represents the power supply voltage, and the right vertical axis represents the heat ratio. 7] shows the characteristic curve of the pulse generating circuit of FIG. 5, and 74 shows the characteristic curve required by the thermal printer. FIG. 11 shows an embodiment of a pulse generating circuit that satisfies the characteristic curve 74 shown in FIG.
2 is a thermistor, 81 is a varistor, and 85 and 86 are transistors. FIG. 12 is a graph showing the temperature characteristics of the pulse generating circuit shown in FIG. 11, in which the vertical axis represents voltage and the horizontal axis represents period. 101 is at high temperature, ]02
show the characteristic curves at low temperatures.

Claims (1)

[Claims] 1. A thermal printer that has a heat-generating head and a paper feeding device and prints on thermal paper has a pulse generation circuit that changes the pulse width or cycle depending on the power supply voltage applied to the thermal printer, A voltage compensation control method for a thermal printer, in which the pulse generating circuit determines a time period for energizing a heat generating element on the heat generating head and a time period for energizing a power source of the paper feeding device.