JPH02231156A - Thermal printer - Google Patents

Abstract

PURPOSE:To obtain printing of uniform density at all times by providing a plurality of heat generating resistors and a plurality of signal lines provided to be selectively cut to alter conditions for heating heat generating resistor in response to the grade of the resistance value of the resistor. CONSTITUTION:A print signal P is received from a controller 1, and a printing head 3 having a plurality of heat generating resistors D1-D7 is driven. Since a thermistor TM is connected to the base side terminal (d) of a transistor Tr3, the bias voltage Vd of the terminal (d) is altered in response to a peripheral temperature, a heat application voltage Ve for obtaining a suitable printing density is output to the emitter side of a current supply transistor Tr4, currents flowing to the resistors D1-D7 become substantially constant to print in a suitable density. Further, since resistors R2, R3 are connected in the grade to the terminal (d), signal lines L1, L2 are selectively cut at the grade of the resistance value of the head 3, the composite resistance of the bias resistor group of the transistor Tr3 is altered to change the bias voltage Vd of the terminal (d), thereby obtaining a suitable head application voltage Ve.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal printer, and more particularly to a thermal printer that arranges a plurality of heating resistors and prints by causing the resistors to generate heat by passing a printing pulse signal through the resistors. Since the thermal head is composed of multiple heating resistors, the resistance value of the heating elements will vary to some extent due to manufacturing process, just like general resistance elements. Therefore, in order to eliminate the difference in printing density due to the difference in resistance between thermal heads, it is necessary to make the resistance as uniform as possible, but the heating resistors of thermal heads are graded according to a certain resistance value range ( A compensation circuit or gating circuit is required to change the printing conditions (printing pulse width or printing voltage) depending on each grade (grading or quality). However, adjustment of such a compensation circuit is extremely difficult and requires specialized knowledge and equipment. SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks and provide a thermal blink whose resistance value is automatically corrected simply by attaching a thermal head with signal lines cut according to the grade of resistance value. Embodiments of the present invention will be described in detail below based on the drawings. As shown in FIG. A print head 3 consisting of a plurality of heat generating resistors D1 to DA is driven. The control circuit l is provided inside an electronic device such as a calculator, and the pulse width is set to T according to the information to be printed, as shown in Figure 2a.
．． generates a signal. The drive circuit has a transistor T r + functioning as an inverter, by which the phase of the print signal P applied from the control circuit is inverted as shown in FIG. 2b. This print signal whose phase has been inverted is connected to one terminal a of the capacitor C. The other terminal b of this capacitor C is a resistor R. Trz is connected to the power supply voltage VH via the terminal Trz, and is also connected to the base side of the transistor Trz. This capacitor 〇 and resistor R0 form an exponential waveform circuit, and the output of this exponential waveform circuit, that is, the signal appearing at connection point b, has a waveform as shown in Figure 2C. Note that the emitter sides of transistors T r + and Trz are each grounded. The output of the transistor Tr2, that is, the collector is the transistor Tr. is connected to the base of. A bias resistor R is connected to the collector side terminal d of this transistor Tr. via the power supply voltage V. is applied. Furthermore, the collector side terminal d has a thermistor TM,
gray? Dividing resistance R2. R3 is connected, the other end of the thermistor TM is grounded via an adjustment resistor R4, and a grading resistor R*. Signal lines L, . L. It is similarly grounded via .
The signal waveform appearing at the collector d of this transistor T r x is as shown in FIG. 2 d. The output of the drive transistor Trs is the current supply transistor Tr. connected to the base of this transistor T r
A power supply voltage VH is applied to the collector side of T.a, and its emitter side terminal e is connected to a switching transistor T. ．． ．． T ■．・・・． The heating resistors D, D2 . of the thermal head 3 are connected via T■. -...D, and the other ends of the heating resistors of these thermal heads are each grounded. The waveform appearing at the output terminal e of the transistor Tr4 is illustrated in FIG. 2e. When the switching ton radiator "rat. Toy" is activated and current flows through the heating resistor, the resistor generates heat (about 300℃).
, When this heating element is pressed onto thermal recording paper, printing is performed on the recording paper according to the shape of the resistor. As is generally well known, these heat generating resistors are arranged in a line at predetermined intervals, and the predetermined heat generating resistors are driven in synchronization with the head movement, and the driven resistors cause The composed dots are recorded on the recording paper. Next, the operation of the thermal head driving device of the present invention constructed as described above will be explained with reference to the signal waveforms shown in FIG. First, when a printing pulse signal P with a pulse width of T is output from the Ill m circuit l, this signal is transmitted through the transistor T r
The phase is inverted by I, and the waveform shown in FIG. 2b appears at terminal a. The signal appearing at terminal a is passed through an exponential waveform circuit consisting of a capacitor C and a resistor R0 to obtain an exponential waveform as shown in FIG. 2C. The shape of this exponential waveform is determined by the capacitance of capacitor C and the resistance value of resistor R0. Let V0 be the voltage appearing at terminal b when the print pulse signal ends,
This voltage V. is equal to the conduction voltage of the transistor Trz《
Capacitor C and bias resistor R so that If you set the value of , the voltage appearing at terminal b will be V. When this happens, the transistor T r a becomes conductive, so that the signal appearing at the output d of the transistor Trz becomes a rectangular wave with a pulse width Tp as shown in FIG. 2d.

Even if the control circuit l breaks down for some reason and a printing pulse signal with a pulse width TP' that is abnormally longer than the predetermined pulse width is output as shown on the right side of Fig. 2a, the voltage appearing at terminal b changes exponentially and rises,
Since the transistor Trz is already conductive when the voltage reaches v0, a rectangular wave with an appropriate pulse width Tp is always obtained at the terminal d, and a safety circuit function that protects against failure of the control circuit is obtained. Next, since the thermistor TM is connected to the base side terminal d of the transistor Tr3, the bias voltage Vd of the terminal d can be changed according to the ambient temperature, and the emitter side of the current supply transistor Tr4 is connected to the thermistor TM. The head applied voltage Ve for obtaining a proper print density is output regardless of the current density. That is, the value of the head applied voltage Ve is equal to the bias voltage V
The voltage drop of the transistor Tr3 and the current supply transistor Tr4 is subtracted from d, and the current flowing through the heating resistors D, to D7 becomes a nearly constant current value without being affected by the ambient temperature, and printing with an appropriate density is performed. You will get it. In this way, the function of the temperature correction circuit is obtained.

Furthermore, a grading resistor R2. Since R3 is connected, the signal lines L, . By selectively cutting off L2, the combined resistance of the bias resistance group of the transistor T r 3 is changed, and the bias voltage Vd at the terminal d is changed, thereby obtaining an appropriate head applied voltage Ve. That is, this provides a compensation circuit or a grading circuit that automatically determines the head applied voltage Ve for an appropriate print density for each thermal head. In some cases, it is possible to create even more grades by providing more grading resistors and selectively cutting the corresponding signal lines. It becomes possible to keep the temperature constant.

In the embodiment described above, all of the thermal head safety circuit, temperature compensation circuit, and grading circuit are provided, but even if the heating resistor is driven through any two circuits, the conventional thermal A printer with better print quality and higher reliability than those using a head drive device can be obtained. As explained in detail above, in the present invention, a plurality of signal lines are provided to compensate for the grades of the plurality of heating resistors of the thermal head, and one of the signal lines is selected in advance according to the grade of resistance value. Since it uses a configuration in which the signal line is cut according to the resistance value of the heating resistor, simply attaching the thermal head will automatically compensate for the resistance value of the heating resistor, ensuring that the signal line is always uniform. Dark? You will get a printout of .

[Brief explanation of the drawing]

FIG. 1 is an electrical circuit diagram schematically showing the thermal head driving device of the present invention, and FIGS. 2(a) to 2(e) are signal waveform diagrams for explaining the operation of the circuit shown in FIG. 1, respectively. l...1 control circuit 2...drive circuit 3...1 print head P...print pulse signal vl. l...
Power supply voltage TM...Thermistor R2. R. −・
-Grading resistance L. ．． L. - One signal line Trz... One drive transistor Tr4. One current supply transistor T, I1. T.R.
■~T RT...-Switching transistor D. ．．
D. ．． ～D,... Heating resistor procedure amendment (voluntary) February 1990, Figure 2, 2. Name of invention Recording head 3. Relationship with the case of the person making the amendment

Claims (1)

[Scope of Claims] 1) A thermal printer that has a plurality of heating resistors and performs printing by selectively generating heat from the resistors, comprising: a plurality of heating resistors and resistance values of these heating resistors; A thermal head is provided with a plurality of signal lines in order to compensate for the grade of the heating element, and the signal line is selectively cut in advance according to the grade of the resistance value of the heating element, and a printing pulse signal is applied to the thermal head. A drive circuit that causes the heat-generating resistor to generate heat, a safety circuit that limits the pulse width to a predetermined value or less when the pulse width of the print pulse signal changes, and a safety circuit that keeps the current supplied to the thermal head constant. 1. A thermal printer comprising: a temperature correction circuit that controls bias according to changes in ambient temperature so as to control bias. 2) The thermal printer according to claim 1, wherein the thermal head has a temperature detection signal line connected to a temperature detection element in addition to the signal line. 3) The thermal printer according to claim 2, wherein the temperature detection signal line also serves as a ground connection line for the thermal head.