JPS61286168A - Drive circuit for thermal printer - Google Patents

Abstract

PURPOSE:To obtain a drive circuit for low-cost thermal printers capable of being driven by cells by a method in which time of reaching charging levels is converted into pulse width, and the time of electrifying to heating elements is determined by the output. CONSTITUTION:When charging to a condenser 7 is started, charging time till reference voltage E is sent out as a pulse waveform with pulse width (t) to the output terminal of a comparison circuit 11. The pulse width (t) determins electrifying time of heating elements, and a characteristic curve 31 is for the case of reference voltage E=0.7V by a pulse generating circuit 18. The range approximated to the straight line becomes from J-point to K-point, and the range of x=5.7-9.2 at x-axile results. From the viewpoint of voltage values, the range becomes the range of 4.6V-6.4V since xXE=vc, showing the expansion of isoenergy characteristics to great extent. In short, even when the voltage of a power source 1, e.g., cells, etc., is lowered, proper recording density can be secured.

Description

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

[Prior art]

FIG. 5(b)) is a part of a conventional constant temperature control circuit for a thermal pen, and is a circuit known in 1% Publication No. 53-15378. By slightly modifying the circuit shown in Fig. 5), it is possible to apply it to a thermal printer, and the problems at this time will be described in detail below. 101t
A voltage VCft is generated by a power source that has a variable element such as an i-battery. 102 resistors, 103 a capacitor, the capacitors are connected in series to the power supply 101K via the resistor 102, a switch 104 is connected in parallel to the capacitor 103, and the above circuit forms a charging/discharging circuit 111.

Reference numeral 105 indicates a switch drive circuit that opens and closes the switch 104 at regular intervals, 106 a voltage comparison circuit, 107 a reference power supply, and 108 a variable voltage divider. 109
is the switch of the thermal pen 109, which is turned on and off by the output of the voltage comparator circuit 106, and the thermal pen 1
09 is maintained at a constant temperature regardless of fluctuations in the power supply voltage VC. In order to apply Fig. 5 (b) to a thermal printer, the number of heating elements corresponding to the thermal pen 109 is increased, and a circuit for selectively controlling the switch 110f, etc.
t Required hZ - The principle of heating to a constant temperature to stabilize the next print quality remains the same. Switch 1 in Figure 5 6)
04, the capacitor 03 is instantly turned on and the capacitor 03 is discharged, the charging time t until the voltage of the reference power supply 107 reaches the voltage E divided by the variable voltage divider 108 is taken out by the voltage comparator circuit 106, and the heating time t is fixed at a constant cycle T. Each time, the switch 110 is turned on to control the temperature of the thermal pen.

If the resistance value of the thermal pen is fr, the heating time is t, and the heating cycle is T, then the energy per unit time applied to the thermal pen (P
LI)) is expressed by the following formula (1).

In order for the temperature hZ to be constant, it is sufficient that the energy is approximately constant, so the relationship between t and VC at this time may be as follows: t = τ7 Song... Song Interval (2).

Such a relationship will be referred to as isoenergetic characteristics or isotemperature characteristics.

For the heating time t of the circuit shown in Fig. 5 (α), capacitor 1
If the resistance value of C1 resistor 102 is R, then
It is expressed by equation (5).

t=-CIIRln (1-possible)... Between songs (3) Vc/E with this as two axes! , tloRf is plotted on the y-axis, and is plotted on a logarithmic scale (in FIG. 5). 121 is (3)
The ratio characteristic curve divided by the formula fOR, the slope of 122 is -2
is a straight line. The relational expression of the locus of points parallel to this straight line 122 is expressed by linear equation (4).

y=αP α=constant...Song・-(43In other words, the relational expression (2) between t and V of the isothermal characteristic is the same as the expression (4), and the temperature is constant on the trajectory parallel to the straight line 122. The part of the characteristic curve 121 that can be approximated in parallel to the straight line 122 is from point P to point Q, and if the value is 2, z = 13 to 1.6.
That's about it. If we assume that the power source is four manganese batteries, the initial value is about 6.5V, and at this time, Z = V
C/m = 1.6, so IC = 4.06 (7)%
If =4.06 when z=t5, then v(H
approximately 5.3 (T4), i.e. 6.5 (V)
This means that constant temperature driving is only possible at about ~5.3 (v).

Generally, manganese batteries have an EIUM of 0.5 at EIUM 3.
There is an internal resistance hZ of about Ω, and when there are multiple heat generating elements corresponding to the thermal pen 109, such as in a thermal printer, and they are energized at the same time, the voltage drop is significant. A circuit h having: is necessary. Also, in a method such as a thermal printer, which instantly converts the applied energy into heat to form dots.

Even if the difference in energy is minute, it has a strong influence on print quality, so characteristics closer to the straight line 122 are required. In addition, if the direction of curvature of the characteristic curve 121 is in a direction in which there is too much energy for both high and low voltages,
It is unsuitable to be busy 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 also possible to use a constant voltage circuit to drive the thermal printer.b''-1 When the power source is driven by a battery, the power consumption by the power circuit is large.

Not suitable for battery operation.

[Problem that the invention seeks to solve]

An object of the present invention is to provide a drive circuit that significantly improves the characteristics of conventional constant temperature control circuits and enables, for example, a thermal printer to be driven by a manganese battery. Another object of the present invention is to provide a thermal printer drive circuit that consumes less power and is inexpensive.

[Means to try to solve problems]

A driving circuit for a thermal printer according to the present invention includes two resistor means for dividing the voltage of the power source of the heating element, a constant voltage means connected in parallel to one of the resistor means, and a voltage dividing point of the resistor means and one end of the power source. A charging circuit is configured with at least one capacitor, and a pulse generating circuit is configured to convert the time required to reach the charging level into a pulse width or cycle, and the output of the pulse generating circuit is used to energize the heating element. It determines the time. Examples below? I will explain using

〔Example〕

FIG. 1 shows an embodiment of an actual operating circuit of a thermal printer according to the present invention.

Reference numeral 1 indicates a power source, and reference numeral 2 indicates a thermal head in which a plurality of heating elements 3 are disposed. 4 and 5 are resistor means for dividing the voltage of the power supply, Zener diodes which are a type of constant voltage means are connected in parallel to the six-digit resistor means 4, and 7 is a resistor means 4.
．． 5 is a capacitor inserted between the voltage dividing point S and the O (minus) terminal of the power supply, and resistor means 8.9? - connected through. Incidentally, the capacitor 7 may be inserted between the (+) terminal of the power supply h'--in this case, the word "charge" is interpreted to mean "discharge", and conversely, "discharge" is interpreted as "charge". The charging circuit 10 is formed by the above. The resistance means 8.9 are adjusting resistors.

17 Discharge transistor that instantaneously discharges capacitor 7, 11 turns on and off depending on the charge level of the capacitor.
12 indicates a Zener diode that determines the reference voltage of the comparison circuit 110.

Reference numeral 13 denotes a head drive IC in which an inverter and 14 transistors for driving heating elements are integrated. 20 is CP
U, which processes print data from a host computer, etc., and controls the thermal head 2, etc. When the pattern data 16 from the CPU 20 is sent out, the strobe terminal 15 in the head drive area 014
Electricity is applied to each heating element only for the time when bt becomes low level.

〔motion〕

When a trim input is applied to the INN terminal of the discharging transistor 17, charging of the capacitor 7 is started, and the charging time up to the reference voltage E is outputted to the output terminal of the comparison circuit 11 as a pulse waveform having a pulse width of 11.

The charging circuit 10, the discharging transistor 17, and the comparison circuit 11'f constitute a pulse generating circuit 18 as main components.

[Effect]

The operation of the present invention will be explained in detail using FIGS. 2 and 5.

FIG. 2 is a diagram showing the relationship between the power supply voltage VC and the potential v8 at the voltage dividing point S. - As an example, the lightning voltage of the constant voltage means 6, the voltage Vz
h'-2,5V, ratio of resistance means 4.5+! lt1:2
It shows the characteristics when . The characteristic of this characteristic curve 30 is that when the potential of VC is high, v8 is approximated by the following equation.

v5 = vc, -vz ・・・・・・・・・・・・
(5) Also, as VC decreases, the following will occur.

vs = engineering (6) (-E-knee =-
)5 R4+R53 R4 and R5 indicate the resistance value of the resistance means 4.5.

At this time, when the output pulse width of the pulse generation circuit is t, and equation (5) is satisfied.

t = −0−RtnCl−−)・−・−・−(7) Vc
-Vz, and when formula (6) is used, it is approximated as follows.

Medium-〇-RIJL(1-”)・・・・・・・・・・・・
...(8)C (C) In both equations (8), R represents the combined resistance value of the adjustment resistor 7.8, and the value of the resistance means 4.5 is.

Assuming that R is sufficiently smaller than the above R, its influence on R is ignored.

Figure 3 shows the pulse width of the pulse generation circuit 18 and the power supply voltage VQ.
This is a characteristic diagram showing the relationship between the two and the same scale as in FIG. 5 is used. Components that are the same as those in FIG. 3 are designated by the same numbers. Reference numeral 31 shows a characteristic curve of the noxle generating circuit 18 according to the present invention, and is an example of the characteristic curve when the reference voltage is 0.7V. 32 is a straight line with a slope of -2, and the range approximated by this straight line is from 3 points to 1 point. On the X axis, z =
The range is from 5.7 to 9.2. If you look at this in terms of voltage value!
Since XF: = VC, 4.6 (V) ~ 6.
4 (7), which significantly expands the range of equal energy characteristics compared to conventional circuits.

That is, even if the voltage of the power source 1, such as a battery, decreases, appropriate power is applied to the heating element over a wide voltage range, and an appropriate concentration/l'- is maintained.

[Other Examples]

FIG. 4 shows another embodiment of the pulse generating circuit.

Components that are the same as those in FIG. 1 are designated by the same numbers, and descriptions thereof will be omitted.

61F! This is another embodiment of the constant voltage means, 71 is a transistor, 72 and 73 are resistors, and by adjusting the variable resistor 73, the constant voltage value Vzf can be freely selected. It is a type of 62-digit comparison circuit and is a transistor. A reference voltage source is no longer required, and the base-emitter voltage of the transistor is used instead. 63 is /<+1177 for waveform shaping. It is a 64-digit inverter,
With this configuration, an oscillation circuit having a period T that is almost equal to the pulse width t is obtained. By using this as an input to a counter or the like, it is possible to create a time period for energizing the thermal head, and a similar effect can be expected.

〔effect〕

In this way, the thermal printer drive circuit according to the present invention can control the energization time to one heating element in response to fluctuations in power supply voltage, and can always maintain appropriate print density, as well as directly converting voltage into energization width. It has the feature of no power loss car.

Furthermore, the reference voltage source 12 is an element having temperature-sensitive characteristics.

For example, by using a silicon diode or the like, it is possible to maintain a temperature compensation characteristic in which the pulse width t is shortened when the temperature is higher than K, and the inverse Kt is lengthened when the temperature is lower.

As described above, the present invention can be widely applied to drive circuits for thermal printers.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an embodiment of a driving circuit for a thermal printer according to the present invention. 1...Power supply 4.5...Resistance means 2...Thermal head 6...
Constant voltage means 7... Capacitor 11...
Comparison circuit FIG. 2 is a diagram showing the relationship between the potential at the voltage dividing point S of the pulse generation circuit used in the drive circuit of the thermal printer according to the present invention and the power supply voltage. Figure 3 shows the pulse width t of the pulse generation circuit and the power supply voltage VC.
FIG. 2 is a characteristic diagram showing the relationship between VC and VC. FIG. 4 is a circuit diagram showing another embodiment of the pulse generating circuit. gXS diagram (c)) is a schematic diagram of a constant temperature control circuit of a conventional thermal pen. 101... Power supply 103... Capacitor 106... Voltage comparator circuit FIG. 5(b) is a diagram showing the characteristics of a conventional constant temperature control circuit. that's all

Claims (1)

[Claims] having a plurality of heating elements, selectively energizing the heating elements;
In a thermal printer that prints on printing paper, a power source for the heating element, at least two resistance means for dividing the voltage of the power source, a constant voltage means connected in parallel to one of the resistance means, and voltage dividing by the resistance means and at least one capacitor inserted into one end of the power source, and a pulse generation circuit that converts the time required for the charging circuit to reach a predetermined charge level into a pulse width or period, A drive circuit for a thermal printer, which determines the duration of energization of the heating element based on the output of a pulse generation circuit.