JPS61235167A - Thermal printer driving circuit - Google Patents

Abstract

PURPOSE:To permit proper selection of an extent of energy application to a heat generating head by corresponding to width of characters and/or printing density, by providing an electrical application width control circuit which consists of a charge circuit and a comparing circuit which has an on-off function, based on a charge level of a discharge circuit and a condenser; and a short-circuiting circuit which opens and closes both ends of a voltage regulating means; and by determining a time for an electrical application to a heat generating element by an output from the comparing circuit. CONSTITUTION:A voltage regulating means 4 is provided for switching of energy to be applied. When a character of an ordinary density is to be printed, a low level signal is applied to IN 2, and a transistor 8 for short-circuiting is turned on; and in case of printing of a high density character, a moving speed of a thermal head 2 is reduced, and at the same time the transistor 8 is turned off and a condenser 6 is charged through the voltage regulating means 4, and a pulse width (tw) is increased. By selecting a proper value of the voltage regulating means 4, the most appropriate printing density is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a drive circuit for a thermal printer.

[Prior art]

The third factor is a part of the constant temperature control circuit of the conventional thermal pen, which is known from Japanese Patent Publication No. 55-15578. By slightly changing W8 in Figure 4, it is possible to apply it to thermal printers rather than VC.
-24432 also proposes a method for driving a thermal printer using the same principle. A conventional example will be briefly described below.

31ij A power supply having a variable element, a resistor 52 and a capacitor 53 constitute a charging circuit, 54 is a discharging circuit for the capacitor 55, 35 is a reference voltage gt-generating reference voltage source,
56 is a resistor that determines the bias current of a Zener diode used as a reference voltage source, and 37 is a comparison circuit. In operation, the battery is instantaneously discharged by the discharge circuit 34, and then 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 @ is increased or decreased in response to fluctuations in the power supply voltage, and when the voltage is low, the pulse @ is increased, and when the voltage is high, the pulse width is decreased, and a thermal pen or thermal head is used. However, in the previous embodiment, the pulse width t
t-, it is impossible to increase or decrease depending on the printing mode of the thermal printer, etc., and it is 6 times. In general, with thermal printers, it is possible to freely select the character width and print density, and depending on the density of the print (including figures and printing tubes),
By increasing or decreasing the energy applied to the heating head,
It becomes possible to achieve high print quality.

[Problem that the invention seeks to solve]

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

[Means for solving problems]

A driving circuit for a thermal printer according to the present invention has a plurality of heat generating elements, and selectively energizes the heat generating elements to print on printing paper. and a capacitor connected in series; a discharging circuit that opens and closes both ends of the capacitor in the charging circuit;

It has an energization width control circuit consisting of a comparison circuit that turns off and a short circuit that opens and closes both ends of the constant voltage means, and determines the energization time to the heating element based on the output of the comparison circuit.

〔Example〕

The present invention will be explained in detail below.

FIG. 1 is a schematic diagram of an embodiment of a drive circuit for a thermal printer according to the present invention.

Reference numeral 1 denotes a power source, which is a driving source for the thermal head 2 . Thermal head 2KFi heating element 3 is the crotch! has been done.

Constant voltage means 4, resistance means 5. A charging circuit is formed with the capacitor 6. The 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 discharge transistor which is a type of discharge circuit that instantly discharges the entire capacitor, and 8 is a short circuit transistor which is a type of short circuit that opens and closes both ends of the constant voltage means 4.

Reference numeral 9 denotes a Zener diode for a reference voltage source used in the comparator circuit 10. 11 corresponds to the output of the comparator circuit 10,
This is a switching transistor that turns on and off the power supply terminal of the transistor array 12, and allows the heating element 3 to be energized only for the time of the output pulse tw of the comparison circuit 10. 1
3 is a CPU that controls the thermal printer, and in addition to controlling the various transistors mentioned above and outputting print data to the thermal head, it also drives various motors and inputs data from a host computer (not shown), etc. conduct.

14 is a step motor for transporting the multi-head 2, and 15 is a transistor array for supplying power to this step motor.

〔motion〕

When the thermal head comes to the printing position, the rN1 pulse is input, the discharging transistor 7 is turned on instantly, and charging is immediately started through the resistor means 5t, and the comparator circuit 10
A predetermined pulse width tv is output. CPT71
3 outputs the dot pattern data, and the comparison circuit 1
The switching transistor is turned on by the signal from 0, power is supplied to the transistor play 12, and appropriate front power is supplied to the selected heating element 3.

In dot printers, the moving speed of the dot head is generally changed depending on the character width and dot density. However, in a thermal printer, the printing density changes depending on the moving speed, so the applied energy must be adjusted by adjusting the moving speed of the thermal head.

In Fig. 1, the constant voltage means 4 is installed to switch the applied energy, and when printing characters with the most commonly used density, apply the IN2 low level signal and When the transistor 8 is turned on and high-density characters are to be printed, the moving speed of the thermal head 2 is reduced, the shorting transistor 8 is turned off, and the capacitor 6 is charged via the constant voltage means 4. , the pulse width tv increases.

At this time, the pulse pulse at 9 o'clock when the shorting transistor 8 is turned on is expressed as follows.

tW1 = Pulse width R when the shorting transistor is turned on =
Value of resistance means 5 Vc = voltage of power supply 1 C = value of capacitor 6 E = comparison circuit 100 reference voltage, then t vl = -ORAn (1-π)...
・・・・・・・・・1 formula Also, when the shorting transistor 8 is turned off and 9 o'clock, the pulse width tY1 is the value t of the constant voltage means 4
−vz, the following will be obtained.

t v z == −CRtn (1−■τ:11−)
--...2 formula % formula % By appropriately selecting the value of the constant voltage means 4, the optimum printing density can be obtained.

FIG. 2 shows another embodiment of the invention, in which the same parts as in FIG. 1 are designated by the same numbers.

The reference numeral 24 is the same as the specific voltage means 4 shown in FIG. This is effective when using one of the resistors as a variable resistor is required for Eri adjustment. Reference numeral 20 denotes a type of comparator circuit, in which the pace emitter voltage VBI of the transistor is used as a reference voltage. 21 is a waveform shaping transistor.

In this operation, a trigger pulse is input to INl to start charging the capacitor 6, and when VBII is reached, the transistor 20 is turned on, and via the transistor 21,
An output pulse having the pulse width of tv is obtained. To IN2,
Similar to FIG. 1, pulse width increase/decrease signals are input.

25 is a switch that shorts out a part of the resistance means, and is used to slightly vary the applied energy depending on the resistance value of the heating element. It is. That is, for heads in a group with a large resistance value, the pulse width is increased and the switch is turned off, and for heads in a group with a small resistance value, the switch is turned off.

〔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 as one of the components of the resistance means 5, it is possible to use it in common with the temperature compensation circuit of the thermal head.

Furthermore, like the conventional embodiments, it is also possible to share the power supply voltage compensation circuit.

Furthermore, as can be seen from Equations 1 and 2 above, the value of the resistance means 5 is related to the pulse width in the same ratio when the constant voltage means is short-circuited and the pulse width is also opened. The temperature change rate of the heat-sensitive resistance element 52 has the advantage that, if the temperature characteristics of the constant voltage means are ignored, the rate of change is always the same, and the rate of temperature compensation also does not change. This also applies to the effect of the t-rank switching switch shown in FIG.

In recent years, thermal printers have begun to be applied to specific thermal transfer printers using thermal ribbons. However, the commonly 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 movement speed of the thermal head can be reduced and the applied energy can be increased to improve the print quality for smooth paper, and for thermal transfer paper, the movement speed of the thermal head can be reduced. Ratio control, characterized by printing speed, can be easily achieved by increasing speed and decreasing applied energy.

The drive circuit of the thermal printer according to the present invention consolidates all the temperature information and the rank of resistance of the thermal head necessary for controlling the thermal head into one circuit, so the configuration of the thermal printer is This simplifies the process and simplifies the program software run by the CPU'i. Also, 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. It is.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a ninth embodiment using a driving circuit for a thermal printer according to the present invention. 1... Power supply 2... Thermal head 4... Constant voltage means 8... Short transistor 10...
- Comparison circuit FIG. 2 is another embodiment of the present invention. 24 . . . Constant voltage means 20 . . . Comparison circuit FIG. 3 is a part of a conventional constant temperature control circuit of a thermal pen. 52... Resistor 35... Capacitor 54... Discharge circuit 37... Comparison circuit and above Page author Epson Corporation Figure 1 2f! 1 Procedural amendment (spontaneous) Patent Application No. 77780 of 1999 and 2003 2 Name of the invention Thermal printer drive circuit 3 Relationship with the person making the amendment Applicant Tokyo 41S Shinjuku-ku 2-441 Nishi-Shinjuku (237) Epson Corporation 4, ft11 Ka Representative Director Tsuneya Nakamura Address: 2-6-21 Kyobashi, Chuo-ku, Tokyo 104 Attached document for amendment to standard procedures (voluntary) 1. The second line from the top of page 9 of the specification: "Head's Lance" should be corrected to "Head's Rank." Z Turn on the 6th line from the top of page 9 of the circular that says "Turn off." ” he corrected. 5. Revise Figure 1 as shown in Attachment 4. Eg diagram

Claims (2)

[Claims] (1) In a drive circuit for a thermal printer that has a plurality of heating elements and selectively energizes the heating elements to print on printing paper, a constant voltage means, a resistance means, and a capacitor are connected in series. a charging circuit that opens and closes both ends of the capacitor in the charging circuit, a comparison circuit that turns on and off depending on the charge level of the capacitor, and a short circuit that opens and closes both ends of the constant voltage means. What is claimed is: 1. A drive circuit for a thermal printer, comprising: an energization width control circuit comprising: a current energization width control circuit; the energization time to the heat generating element is determined based on the output of the comparison circuit. (2) The drive circuit for a thermal printer according to claim 1, wherein a heat-sensitive resistance element is used as a component of the resistance means.