JPS61266269A - Thermal printer - Google Patents

Abstract

PURPOSE:To enable energy impressed on a thermal head to be appropriately selected, by determining the energizing time of a heating element by an output from a pulse-generating circuit. CONSTITUTION:When a thermal head comes to a printing position, a trigger pulse is inputted to IN1, a discharging transistor 7 is instantaneously turned ON, charging is immediately started through the second resistor means 5, and a predetermined pulse width tw is outputted by a comparing circuit 10. A dot pattern is outputted from a CPU 13, and appropriate electric power is supplied to a heating element 3 selected by a signal from the circuit 10. When printing a character with a generally used density, a low-level signal is impressed on IN2 to turn ON a short-circuiting transistor 8. When printing a character with high density, velocity of a thermal head 2 is reduced, and the transistor 8 is turned OFF, charging of a capacitor 6 is conducted through the first resistor means 4, and the pulse width tw is enlarged.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a thermal printer with an improved driving method.

[Prior art]

The fourth @ is part of a constant temperature control circuit of a conventional thermal pen, and is a circuit known in Japanese Patent Publication No. 53-15578. By slightly modifying the circuit shown in Figure 4, it is possible to apply it to a thermal printer.
4452 also proposes a method for driving a thermal printer using a similar principle.A conventional example will be briefly described below.

51 is a power supply having a variable element, a resistor 32 and a capacitor 35 constitute a charging circuit, 34 is a discharging circuit for the capacitor 55, 35 is a reference voltage source that generates a reference voltage E, and 36
57 is a resistor that determines the bias current of a Zener diode used as a reference voltage source, and 57 is a comparison circuit. In operation, after being instantaneously discharged by the discharge circuit 54, charging is started via the resistor 62, and when the reference voltage E is reached, the comparator circuit 37 provides an output with a pulse width t. The characteristic of the conventional example is that the pulse width is increased or decreased in response to fluctuations in the power supply voltage.When the voltage is low, the pulse width is increased and when the voltage is high, the pulse width is decreased. This stabilized the heat generation temperature relative to the power supply voltage.

[Problem that the invention seeks to solve]

However, in the conventional method, it has been impossible to increase or decrease the pulse width t depending on the print mode of the thermal printer or the like. In general, with thermal printers, it is possible to freely select the character width and print density, and it is possible to achieve high print quality by increasing or decreasing the energy applied to the heat generating head according to such print density. becomes.

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermal printer equipped with a drive circuit that can appropriately select energy applied to a heat generating head in accordance with character width and print density.

[Means for solving problems]

The thermal printer of the present invention has a plurality of heating elements,
In a thermal printer that selectively energizes the heating element to print on printing paper, a charging circuit including a first resistance means, a second resistance means, and a capacitor connected in series; a) circuit for opening and closing both ends of the resistor means, and a pulse generating circuit that converts the time required for the capacitor to reach a predetermined charge level into a pulse width or period and outputs the pulse width or period, and the output of the pulse generating circuit The energization time to the heating element is determined by:

〔Example〕

Therefore, details of the present invention will be explained below based on illustrated embodiments.

FIG. 2 shows the mechanism of a dot-to-matrix thermal printer to which the present invention is applied, and reference numeral 14 in the figure is a step motor for driving the head attached to a base 114, which is connected via a gear train 115. and is connected to the timing belt 118. Reference numeral 117 denotes a carriage on which the thermal hect 2 and the ink ribbon cartridge 118 are mounted, and is guided by guide rods 119-α and 119-b, and configured to reciprocate in the axial direction of the platen 120 by a timing belt 116.

Reference numeral 2 in the figure is the aforementioned thermal head mounted on the carriage, which in this embodiment includes a plurality of heating elements 5, 5.
... are arranged in a hierarchical relationship.

Each heating element 5 making up this thermal head
．． 5. . . . are commonly connected, and the other terminal of each heat generating element is connected to a drive circuit 12 driven by a pattern signal from the 0PU 13.

FIG. 2 shows an embodiment of a drive circuit used in the mechanism of the thermal printer shown in FIG.

Reference numeral 1 denotes a power source, which is a driving source for the thermal head 2 . A heating element 5 is installed in the thermal head 2.

First resistance means4. Second resistance means5. A charging circuit is formed with the capacitor 6. The second resistance means 5 includes a variable resistor 51 and a heat-sensitive resistance element 52 whose resistance value changes significantly depending on temperature. 7 is a discharging transistor which is a type of discharging circuit that instantly discharges the capacitor 6. 8 is a shutter transistor which is a type of short circuit that opens and closes both ends of the first resistor means 4. Reference numeral 9 denotes a Zener diode for a reference voltage source used in the comparator circuit 10. The above-described charging circuit, discharging circuit, shorting circuit, and comparison circuit constitute the pulse generating circuit 50.

Reference numeral 11 denotes a switching transistor that turns on and off the power supply terminal of the transistor array 12 in accordance with the output of the comparator circuit 10, and allows the heating element 5 to be energized for only the output pulse width tW of the comparator circuit 10. 15 is an OPU that controls the thermal printer, inputs printing data,
Correspondingly, in addition to controlling the various transistors and outputting print data from the thermal head as already described, it also drives various motors and inputs data from the PhosF combinator (not shown) and the like. 14 is a step motor that moves the thermal head 2, and 15 is a transistor array that supplies power to this step motor.

〔motion〕

When the thermal head comes to the printing position, a trigger pulse is input to step N1, the discharging transistor 7 is turned on instantaneously, and charging starts immediately through the second resistor means 5, and the comparison circuit i'
? 510, the predetermined pulse width tW is outputted. 0
Dot pattern data is output from the PU 13, the switching transistor is turned on by a signal from the comparison circuit 10, an ITT source is supplied to the transistor array 12, and excessive power is supplied to the selected heating element 3.

In dot printers, it has been common practice to change the moving speed of the dot head depending on the character width and dot density. However, in a thermal printer, the print density changes depending on the moving speed of the thermal head, so the applied energy must be adjusted depending on the moving speed of the thermal head.

In FIG. 1, the first resistance means 4 is installed to switch the applied energy, and when printing characters with the most commonly used density, a low level signal is applied to IN2. When the printing transistor 8 is turned on and high-density characters are to be printed, the moving speed of the thermal head 2 is reduced, and the printing transistor 8 is turned off and the first resistance means 4 is turned off. Power is generated to the capacitor 6 through the pulse, and the pulse width tW increases.

The pulse width at this time, when the shutter transistor 8 is turned on, is expressed as follows.

tW1 = Pulse width when transistor is on R = Value of second resistor means 5 Vc = Voltage of power supply 1 0 = Value of capacitor 6 B Reference voltage of wealth comparison circuit 10, then tW1 = -O
Rum(1-■)・・・・・・・・・1, Equation Also, when the gate transistor 8 is turned off, the pulse width tW2 is the first
Letting the value of the resistance means 4 be r, the following will be obtained.

tW, =-0-(R+r)t%(1-l)・-・-
-2 type % type % By appropriately selecting the value of the first resistance means 4, it is possible to obtain the optimum print density for each print mode.

FIG. 3 shows another embodiment of the invention, in which the same parts as in FIG. 1 are designated by the same numbers.

Reference numeral 20 designates a type of comparator circuit, which uses the transistor emitter-to-emitter voltage VBI as a reference voltage.

A waveform shaping transistor 21 has an output terminal and is input to the discharging transistor 7, forming an oscillation circuit 118 type pulse generating circuit as a whole. The period T of this output has characteristics similar to the pulse width tW shown in FIG.

When a low level input is applied to IN, the period T is reduced.

Reference numeral 25 denotes a switch that shimmies a part of the second resistance means, and is used to slightly vary the applied energy depending on the resistance value of the heating element. This is a switch for changing ranks.

By inputting the output of the transistor 21 to a counting circuit that counts predetermined pulses, it is possible to determine the energization time to the heating element.

Note that in the above explanation, printing is a concept that includes not only characters such as numbers and alphabets, but also graphs, images, and the like.

〔Effect of the invention〕

The effects of the present invention will be described below.

According to the present invention, it is possible to easily convert the applied energy depending on the printing mode or the like.

Furthermore, by adding a heat-sensitive resistance element to one of the components of the second resistance means 5, it is possible to use the second resistance means 5 in common with the temperature compensation circuit of the thermal head.

Furthermore, by making the power supply of the pulse generation circuit according to the present invention the same as the power supply of the thermal head, the pulse width can be increased or decreased in response to fluctuations in the power supply voltage, so that it can also be used in common with the power supply voltage compensation circuit. . - In recent years, thermal printers have also been used as thermal transfer printers using thermal ribbons.

However, the generally available plain paper with low smoothness has poor printing quality, which has been an obstacle to its widespread use. By using the drive circuit according to the present invention, the moving speed of the thermal head can be reduced and the applied energy can be increased to improve print quality for such low-smooth paper, and for thermal transfer paper, the moving speed of the thermal head can be reduced. Control such as increasing the printing speed, decreasing the applied energy, and controlling the printing speed becomes easily possible.

The thermal printer drive circuit according to the present invention is capable of consolidating all the temperature information necessary for controlling the thermal head and the information for the rank of the resistance value of the thermal head into one circuit, and the configuration of the thermal printer can be changed. The program software for operating the OPU is simplified. Furthermore, unlike the conventional method of varying the power supply voltage depending on the temperature, a fixed power supply can be used, and it can be shared with a power supply used for a motor or the like.

As described above, the present invention is a drive circuit that always obtains an appropriate print density depending on the print mode of a thermal printer, and is extremely useful because it can reduce the difference in print quality depending on the print paper of a thermal transfer printer. be.

(c) 37... Comparison circuit

[Brief explanation of drawings]

FIG. 1 shows an embodiment of a driving circuit for a thermal printer according to the present invention. FIG. 2 is a perspective view showing an embodiment of the mechanical part of the thermal printer used in the present invention. FIG. 5 shows another embodiment of the drive circuit used in the thermal printer of the present invention. FIG. 4 shows a part of a conventional thermal pen constant temperature control circuit. 1......Power supply 2...Thermal head 4...First resistance means 5...Second Resistance means 8......Short-circuit transistor 10...
... Comparison circuit 20 ... Comparison circuit 30 ... Pulse generation circuit 32 ... Resistor 55 ... Capacitor 54 ... Discharge More than circuits 3rd 4th cause

Claims (1)

[Claims] having a plurality of heating elements, selectively energizing the heating elements;
In thermal printers that print on printing paper, the first
A charging circuit including a resistor means, a second resistor means, and a capacitor connected in series, and a short circuit that opens and closes both ends of the first resistor means reach a predetermined charging level of the capacitor. A thermal printer comprising a pulse generation circuit that converts time into a pulse width or period and outputs the result, and the time for energization of the heating element is determined by the output of the pulse generation circuit.