JPS5856873A - Thermal printer drive circuit - Google Patents

Abstract

PURPOSE:To make the printing density uniform, by comparing the voltage of a charging circuit comprising a resistor and a first capacitor that are connected across a power source with the voltage of a charging circuit comprising a second capacitor through a constant voltage circuit, and controlling the width of the current conduction in correspondence with a power supply voltage. CONSTITUTION:The constant voltage means 76 is constituted by a transistor 71 and resistors 72 and 73. At least a series circuit of the resistor 78 and the first capacitor 44 is connected across the connecting point between constant voltage means 76 and a resistor 74 and one terminal of the power source 41. A discharge transistor 47 is connected in parallel with the capacitor 44. The second capacitor 80 and a discharge transistor 82 are connected in parallel with a Zener diode 49 through a resistor 79. Thus a reference voltage generating circuit is formed. The charging levels of the first capacitor 44 and a second capacitor 80 are comapred by a voltage comparing circuit 51, and a heating element is driven.

Description

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

FIG. 1 shows a part of a conventional constant temperature control circuit for a thermal pen, which is known from Japanese Patent Publication No. 55-15578. By slightly modifying the circuit shown in FIG. 1, it is possible to apply it to a thermal printer, and the problems in this case will be described in detail below. 1 generates a voltage vo with a power source having a variable element such as a battery. 2 is a resistor, 3 is a capacitor, the capacitor is connected in series to the power supply 1 via the resistor 2, and a switch 4 is connected in parallel to the capacitor 3, so that the above circuit forms a charging/discharging circuit 11 65 Reference numeral 6 indicates a switch drive circuit that opens and closes the switch 4 in constant synchronization, 6 indicates a voltage comparator circuit 7, and 8 indicates a variable voltage divider. 9 is a thermal pen; 10 is a switch of the thermal pen 9, which is turned on and off by the output of the voltage comparison circuit 6, and is operated so as to maintain the temperature of the thermal pen 9 at a constant fmlf regardless of fluctuations in the power supply voltage V. In order to apply Fig. 1 to a thermal printer, it is necessary to increase the number of heating elements corresponding to the thermal pen 9 and to provide a circuit that selectively controls the switch 10, but it is necessary to heat the device at a constant temperature fK to achieve stable printing quality. The principle of obtaining remains unchanged. Switch 4 in the diagram 5lK1 is turned on instantaneously to discharge the capacitor 3, and the charging time t until the voltage of the reference power supply 7 reaches the voltage K divided by the variable voltage divider 8 is obtained by the voltage comparison circuit wr6. The temperature of the thermal pen is controlled by turning on the switch 10 at regular intervals T for a heating time t.

Figure 2 is a diagram showing the relationship between heating time t and power supply voltage 7c, and shows that charging time is faster in section 7 where the power supply voltage is higher;
The heating time is short t, and when the power supply voltage is low V,
Heating time is long 1. becomes.

Assuming that the resistance of the thermal pen is 1[t''r, the energy (pw) per unit time applied to the thermal pen is expressed by the following equation (1).

l T In order for the temperature to be constant, the energy only needs to be constant n, so the relationship between t and Vll at that time should be V'' OX tz constant... (2).Such voltage and pulse The characteristic of a circuit having a width will be called an equal energy characteristic.

The heating time t of the circuit shown in FIG. FIG. 5 shows this on a logarithmic scale. 12 CR formula (5)
13 is a straight line with a slope of -2. The relational expression of the locus of points parallel to this straight line 13 is the following formula (4
).

y = (1-a constant ...... (4) In other words, the relational expression (2) between t and v6 of the isotemperature characteristic is also the same as the expression (4), and on the trajectory parallel to the straight line 15, the temperature Constant.41
The portion of the sex curve 12 that can be approximated in parallel to the straight line 15 is nine points from point P, and the value of X is about 1.5 to 1.6 Nm. If we assume that the power source is four manganese batteries,
The initial value is about &5V, which is 1! l! At this time, x-/II! Since the wealth is t6, Nm4.0
6 (V). 1 mj, S, if Nm is 4.06, then va. will be approximately aS (V). That is,
This means that constant temperature driving is possible only at about 45 (V) to 5 B (V). Generally, manganese batteries have 5UN3
There is an internal resistance of about α5Ω, and when there are multiple heat-generating elements corresponding to the thermal pen 9, such as in a thermal printer, and they are energized at the same time, the voltage drop is significant, so a wide voltage range is required. A circuit with isoenergetic properties over a range is required. In addition, in systems such as thermal printers, which instantly convert applied energy into heat to form dots, even a small difference in energy can greatly affect printing quality, so it is difficult to print straight lines52. Requires characteristics close to . In addition, the direction of curvature of the characteristic line 51 is in a direction that produces too much energy for both high and low voltages, making it unsuitable for controlling a heating element that is easily destroyed, such as the heating element of a thermal printer. . In order to solve these problems, it is possible to use a constant voltage circuit to drive the thermal printer, but if the power source is powered by a battery, the power loss due to the power circuit is large, making it difficult to use battery power. Not suitable.

Also, in many serial type thermal printers, due to the power storage effect of the heating head, characters are written lightly at the beginning and become darker as the head moves.9. In some cases, the dots became difficult to see due to K dust. The present invention attempts to solve these various problems.

An object of the present invention is to provide a thermal printer drive circuit that greatly improves the characteristics of conventional constant temperature control circuits and enables the thermal printer to be driven by manganese batteries. Another object of the present invention is to provide a thermal printer drive circuit that eliminates variations in the shading of characters from digit to digit and enables uniform print density in a serial drive system for a thermal printer. Still another object is to provide a thermal printer drive circuit that consumes less power and is inexpensive.

A driving circuit for a thermal printer according to the present invention will be described in detail below.

FIG. 4 is a schematic diagram of a conventionally used serial drive type thermal printer. Column 4 (A) The figure is a front view of the thermal printer, and 21 is a heat generating element 22.
This is a heat generating head with a

Reference numeral 24 includes a platen, 25 a carriage for fixing the heat generating head 21, and 27 a groove cam 2. By means of the groove cam and the protrusion provided on the carriage 25, the carriage 25 is fixed.
29 is a motor that is a sliding source that operates the drive shaft; 52 is a motor 29;
Each series represents the rotation of . Figure 4C5) shows
It is a @ side view of the thermal printer, 25 is printing paper, 2
Reference numeral 6 indicates a platen presser spring that presses the platen 24 against the heat generating head 21, 50 indicates a paper feed roller, and 51 indicates a paper presser roller. The roller rotates and the paper is fed. In a serial drive type thermal printer, the heat generating element 22 generally has a heat generating element of 5 dots vertically and 7 dots. Form a 5x7 matrix of characters. In such conventional thermal printers, when printing on the same line, there is often a difference in shading between the characters in the starting digit and the characters in the last digit. This is because heat accumulates in the heat generating head 21, and to eliminate this, measures such as reducing the printing speed are required, which inevitably leads to a decrease in the value of the piece. The present invention eliminates these disadvantages.

FIG. 5 is a schematic circuit diagram of an embodiment of an electronic desktop calculator (hereinafter abbreviated as a calculator) using the basic circuit of the drive circuit of a thermal printer according to the present invention. 41 indicates the voltage V. 42 is a Zener diode which is a type of constant voltage means; 45 is an adjustment resistor; 44
is a capacitor. Zener diode 42, resistor 4
5. Series circuit 4 with capacitor 44 as the basic component
6 and a resistor @45 provided to add the Zener voltage Vx of the Zener diode together form a charging circuit, which is inserted in series with the power supply 4141C.

The connection point between the Zener diode 42 and the adjustment resistor 43 is defined as a voltage dividing point S. Reference numeral 47 denotes a transistor which is a type of switch means for instantly discharging the electric charge of the capacitor 44.
4 are connected in parallel. The transistor 47 and resistor 48 form a discharge circuit. A diode 49 is a type of constant voltage means, and forms a reference voltage generation circuit 57 through a series circuit with a resistor 50 to generate a reference voltage E. 51 is a voltage comparison circuit and a capacitor 44
Turns on and off depending on the charge level. 21 is a nine heat generating head shown in FIG. 4, and 652 is a heat generating head 414322 where the heat generating element 22 is arranged: +t! 1'vt, and is turned on for the energization time determined by the gate circuit 52 between the output of the voltage comparison circuit 51 and the output of the character signal generator 54, and enables printing of a predetermined character. do. Reference numeral 55 denotes a timing signal generating device for controlling the discharge transistor 47, which generates a signal to instantaneously turn on the discharge transistor 47 in synchronization with the printing position. The discharge time may be several tens of μm.

The charging circuit, the discharging circuit, the reference voltage generating circuit and the voltage comparing circuit 51 control the energization width control surface il! 58 is formed. The pulse width of the output waveform of the energization width control circuit 58, that is, the energization time to the heating element is assumed to be t.

Next, the operation of the electrical damage control circuit 5B will be described in detail using Figure @6.

If the potential of the 8 voltage dividing points in FIG.
Narrowed by the expression.

E ′ t = −06RAn (1−vo−v□)−・・
(6) C is the value of the capacitor 44, and R is the value of the adjustment resistor 43.

Figure m6 is a graph showing the relationship between the pulse width t of the width control circuit 5B and the power supply voltage Vc, and uses the same scale as Figure 3. Draw a characteristic curve by applying the y1 value obtained from the actual photoelectric potential V4i when x-ImvC/hole. For example, the reference voltage Ii:
- (17 (V)), and the zener voltage Vts of the zener diode 42 is 2.5 (V) at maximum.
Components that are the same as those in Figure R3 are designated by the same numbers. The characteristic shown by the solid line 61 shows the characteristic of the width control circuit shown in FIG. 5, and 62 is a straight line with a slope of -2.

The range approximated by the direct M162 of characteristic -@61 is from 1 point to 2 points, and the value of X is &6 to 92. Converting this to power supply voltage is 44 (V) to 4.6 (V),
The range of equal energy characteristics is significantly expanded compared to conventional circuits. Generally, the longer the current is applied to the heating element 22, the greater the heat dissipation, so it is necessary to input more energy.Adjustment of such characteristics can be done by changing the constant voltage value of the zener diode 42, This can be easily corrected by adjusting the reference voltage tile.

FIG. 1@7 shows an embodiment of a driving circuit for a thermal printer according to the present invention, and the same parts as in FIGS. 4 and 5 are designated by the same numbers. The transistor 71 and the resistors 72 and 73 constitute a constant voltage means 76 that exhibits characteristics similar to the zenata diode 42 in FIG. 4. 75 is a transistor, which is a type of constant voltage means; A series circuit of this transistor 75, the constant voltage means 76, and the resistor 74 is connected between the terminals of the power supply 41. Constant voltage means 76
A series circuit including at least the resistor 7B and the first capacitor 44 is inserted between the connection point between the resistor 7B and the resistor 74 and one terminal of the power supply 41. A charging circuit whose main components are the constant voltage means 76, the resistor 78, and the first capacitor 44 is formed. , and a discharging transistor 47 is connected in parallel to the capacitor 44 of m1, making the circuit t--generally referred to as a charging/discharging circuit. diode 77
is inserted when you want to adjust the characteristics.

50 is a resistor, and 49 is a Zener diode which is a type of constant voltage means. A second continuum 80 is connected in parallel to this Zener diode 49 via a resistor 79. In addition, a discharge transistor 82 is connected in parallel with the capacitor of series 2 through a resistor 81, and a series circuit of the resistor 50 and the constant voltage means 49 is connected in parallel with the constant voltage means 49. A reference voltage generation circuit is formed using the capacitor as the main component. 51 is a voltage comparison circuit that compares the charge levels of the first capacitor 44 and the second capacitor 80.

83 is a permanent magnet fixed on the shaft of the motor 29, and together with a head 90 containing a coil, it constitutes a tacho generator 86 (hereinafter abbreviated as TG86). 85 instantaneously turns on the transistor 47 that discharges the waveform of τG8A. It is a timing signal generator that converts into a waveform. Upper 77G86
and the timing signal generator 85 constitute a position detector 87. The heat generating head 21 is arranged separately into a heat generating element a and a heat generating element b# which are shifted in position, reducing the number of dots 86 that are energized at the same time and reducing the voltage drop of the manganese battery. .

FIG. 8 shows the change in the reference voltage E on the time axis, where 91 shows the change in the reference voltage E, and 92 shows the transistor 82.
The signal from the CPU 57 to the CPU 57 is shown. Va is the maximum value of the reference voltage E, which is equal to the voltage of the Zener diode 49, and the final fast potential of Vt is the value of the resistor 79 as RI,
If the resistance value of the resistor 81 is R1, it is expressed by the following equation (7).

R9 tp indicates the time of the printing process, tr indicates the time of the return process of returning the heating head 21 to the home position, and when printing is started, C! An H level signal is output from the PU 57, the charge in the capacitor 80 starts to discharge, and the reference voltage Z gradually decreases. Since the time for energizing the heating head 21 is determined by the time for charging the capacitor 44,
As the heat-generating head 21 moves, the energization time is reduced, preventing heat from accumulating in the heat-generating head 21, and eliminating shading in printing for each digit. The value of capacitor 80, resistor 79 .
Determine the value of 81. In the above explanation, the transistor 82 is turned on continuously during the printing process, but there is also a method of turning on the transistor 82 at the same time when 3111tIL is actually applied to the heating head 21, which is better. It's practical.

As described above, the present invention is an extremely useful thermal printer drive circuit that eliminates the drawbacks of conventional thermal printers and eliminates the difference in printing 111f for each digit. Furthermore, it is possible to realize a low power consumption thermal printer drive system that suppresses the power consumption of the power supply.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional constant temperature control circuit for a thermal pen, in which 1 is a power supply, 3 is a capacitor, 6 is a voltage comparison circuit, and 9 is a circuit diagram of a constant temperature control circuit for a thermal pen.
indicate a thermal pen, respectively. FIG. 2 shows the relationship between the heating time t and the power supply voltage Vc for the circuit shown in FIG. Figure 3 shows '#L' of the conventional constant temperature control circuit shown in Figure 41.
It is a characteristic diagram showing the relationship between source voltage and voltage time, where the horizontal axis is
Vc/I is plotted on the vertical axis, and t/CR is plotted on the scale. Figure 4 is a schematic diagram of a thermal printer, in which numeral 21 indicates a heat generating head and numeral 29 indicates a motor. FIG. 5 is a schematic diagram of a calculator using the basic circuit of the thermal printer drive circuit according to the present invention, 42 is a constant voltage means, 44 is a capacitor, 49 is a constant voltage means, 51 is a voltage comparison circuit, 22 Reference numeral 58 indicates a heating element, and 58 indicates an energization width control circuit. Figure 6 is a graph showing the relationship between the power supply and pulse 1 of the current width control circuit according to the present invention. FIG. 7 shows an embodiment of a drive circuit for a thermal printer according to the present invention, where 44 is a first capacitor, 80 is a 42
and 76 represent constant voltage means. FIG. 8 is a diagram showing changes in the reference voltage of the driving circuit of the thermal printer according to the present invention. Above Figure 2 Figure 6 Figure 8

Claims (1)

[Scope of Claims] 'Li: In a drive circuit for a thermal printer that has a plurality of heat generating elements and selectively energizes the heat generating elements to print on printing paper, the power of the heat generating elements is controlled. It has an energization control means that turns on and off, and an energization width control circuit that changes the on time of the energization control means in accordance with the voltage of the power supply applied to the heat generating element. The energization width control circuit includes a charging circuit whose minimum component is a series circuit of at least one resistor and a capacitor @1 inserted across the power supply, and at least a charging circuit inserted across the power supply. It consists of a series circuit of one resistor and a constant voltage means, and a reference voltage generation circuit having a second capacitor tMk connected in parallel with the constant voltage means as a small component,
A driving circuit for a thermal printer, comprising a voltage comparison circuit that compares the photoelectric level of the @1 capacitor and the charge level of the second capacitor. 2) A drive circuit for a pirated thermal printer as claimed in claim 1, in which a constant voltage means is inserted into a charging circuit including a capacitor of @distribution@1.