JPH04168061A - Power control circuit for thermal head - Google Patents

Abstract

PURPOSE:To make it possible to connect to an external control circuit with a small number of signal lines so as to reduce wiring materials and spaces by providing a set/reset means, a pulse generating circuit, a counter, and a distribution circuit in a thermal head and operating a plurality of drivers using these members. CONSTITUTION:A set/reset means 15 is set in accordance with a print start signal. At that set time, a pulse generating circuit 16 outputs print pulses having a predetermined print pulse width by using a temperature detecting means 16a. A counter 17 counts the output of the pulse generating circuit 16 by the number of drivers 13a-13h. In response to the result of the counting, a distribution circuit 18 sends out strobe signals ST to the drivers 13a-13h in turn. Based on the strobe signals ST, each driver energizes a heat generating resistor 14 by a time corresponding to the print pulse width in response to printing data. When the strobe signals are sent out to all drivers, the set/reset means 15 is reset and a printing for 1 line is completed. Thus, functional burden to an external control circuit can be reduced.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a thermal head having a heating resistor for printing characters and images on a thermal recording paper surface, and a thermal head that controls current heating of the heating resistor. The present invention relates to a head energization control circuit.

(Prior Art) Conventionally, as a technology in this kind of field, there has been a technology as shown in FIG. 2, for example. The configuration will be explained below using figures.

FIG. 2 is a 1977 diagram showing a configuration example of a conventional energization control circuit for a thermal head.

This energization control circuit is provided with a plurality of external lead terminals 1 for controlling and driving the thermal head.
The external lead terminals 1 include, for example, a data input terminal 1-1 for inputting print data DT, a clock input terminal 1-2 for inputting a clock signal CL, a latch input terminal 1-3 for inputting a latch signal LT, and a strobe signal ST. Input strobe input terminals 1-4 to 1-11, heating resistor power supply terminal 1-
12.1-13, circuit drive power supply terminal 1-14°1-1
5, and thermistor terminals 1-16.1-17. An external lead terminal 1 made up of these terminals is connected to an external control circuit (not shown).

Furthermore, data input terminal 1-1 and clock input terminal 1
-2 is connected to a latch circuit 3 via, for example, a 2048-bit shift register 2, and its latch circuit n3 is
The latch input terminal 1-3 and the driver section 4 are connected. The driver section 4 is composed of, for example, 256-bit drivers 4a to 4h connected in cascade, and each of the drivers 4a to 4h has strobe input terminals 1-4 to 1-11.
are connected to each. Moreover, each driver 4a~
4h is connected to the power terminal 1-13 and also to the power terminal 1-12 via the heating resistor 5.

A thermistor 6 is connected between the thermistor terminals 1-16 and 1-17.

Next, the operation will be explained.

Based on the synchronization of clock signal CL, data input terminal 1-
1, the print data DT is taken into the shift register 2.

Thereafter, the print data DT in the shift register 2 is stored in the latch circuit 3 at the timing when the latch signal LT switches from the "L" level to the "H'° level."

Subsequently, when the strobe signal ST, which is at "H" level for a certain period of time (print pulse width) under the control of the external control circuit, is sequentially supplied to the strobe input terminals 1-4 to 1-11.
Drivers 4a to 4h corresponding to the respective strobe input terminals 1-4 to 1-11 enable the heating resistor 5 to be energized.

As a result, the heating resistor 5 is energized for the predetermined period of time in accordance with the print data DT in the latch circuit 3. In this way, energization for one line is completed. The print data DT of the next line can be transmitted during printing when each of the drivers 4a to 4h is operating.

Note that the printing pulse width is controlled by converting the ambient temperature of the heating resistor 5 into a resistance value using the thermistor 6, and by an external control circuit based on the resistance value.

(Problems to be Solved by the Invention) However, the thermal head energization control circuit having the above configuration has the following problems.

(1) The external control circuit and the thermal head are connected through the external lead terminal 1 and a large number of signal lines. For this reason, when the distance between the external control circuit and the thermal head is long, a large amount of wiring material and space for the signal line are required, which increases the cost accordingly.

(2) The number of signals propagating between the external control circuit and the thermal head via the signal line increases, and the printing pulse width is controlled by the external control circuit using the thermistor 6 according to the temperature of the thermal head. This placed a heavy functional burden on the external control circuit and required complicated control. This hinders miniaturization and cost reduction of the external control circuit.

The present invention solves the problems of the prior art described above, such as the problem that the number of signal lines between the thermal head and the external control circuit is large, which leads to an increase in the number of signals, and the problem that prevents the miniaturization of the external control circuit. It provides the head.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides a strobe signal having a predetermined print pulse width sent out based on a print start signal to adjust the print pulse width according to print data. In a thermal head energization control circuit comprising: a plurality of drivers for energizing a heat generating resistor for a corresponding time; and a temperature detection means for detecting a temperature near the heat generating resistor in order to control the printing pulse width. , the following measures were taken.

a set/reset means that is set based on the print start signal and is reset when energization to the heating resistor ends; and a print pulse having the print pulse width using the temperature detection means when the set/reset means is set. , a counter that counts the output of the pulse generating circuit, and a distribution circuit that sequentially sends the strobe signal to each of the drivers in accordance with the output of the counter.

(Function) Since the present invention configures the energization control circuit for the thermal head as described above, the set/reset means is set based on the print start signal, and at the time of setting, the pulse generating circuit uses the temperature detecting means. A print pulse having a predetermined print pulse width is output. The counter counts the output of the pulse generation circuit by the number of drivers, and the distribution circuit sequentially sends a strobe signal to each driver according to the count result. Based on this strobe signal, each driver energizes the heating resistor for a time corresponding to the print pulse width according to the print data. When the strobe signal is sent to all drivers, the set/reset means is reset and printing for one line is completed.

Thereby, a strobe signal can be generated within the thermal head, and a constant print density can be obtained in response to temperature changes in the vicinity of the heating resistor.

Therefore, the above problem can be solved.

(Embodiment) FIG. 1 is a configuration block diagram of a thermal head energization control circuit showing an embodiment of the present invention.

This energization control circuit is provided with a plurality of external lead terminals 10 for controlling and driving the thermal head.
The external lead terminals 10 include, for example, a data input terminal 10-1 for inputting print data DT, a clock input terminal 10-2 for inputting a clock signal CL, and a latch/strobe input terminal for inputting a latch signal LT and a print start signal PS. 10
-3, Busy input terminal 10-4 for outputting busy signal BY indicating whether printing is in progress, Power supply terminal 10-5.1 for heating resistor
．． 0-6, and circuit driving power supply terminal 10-7゜10-8
have. An external control circuit (not shown) is connected to an external lead-out terminal 10 made up of these terminals.

Further, the data input terminal 10-1 and the tarlock input terminal 10-2 have, for example, a 2048-bit shift register 1.
A latch circuit 12 is connected through F1, and the latch circuit F
The latch/strobe input terminal 10-3 and the driver section 13 are connected to n12. The driver section 13 includes, for example, cascade-connected 256-bit drivers 13a.
It is composed of 8 divisions of ~13h, and each driver 13
A to 13h are connected to a power terminal 10-6 and also to a power terminal 10-5 via a heating resistor 14.

On the other hand, latch/strobe input terminal 10-3 is set/
A busy input terminal 10 is connected to the input side of an R/S flip-flop 15 (hereinafter simply referred to as F/F) which is a reset means.
-4 are connected to the same output side. Further, a thermistor 16a serving as a temperature detection means is connected to the output power of the F/F 15, and a pulse generation circuit 16 such as an oscillator outputs a print pulse having a predetermined print pulse width when the F/F 15 is set. , an up counter 17 that counts the output of the pulse generation circuit 16, and a distribution circuit 18 that sequentially sends a strobe signal ST to each driver 13a to 13h in accordance with the output of the counter 17 are connected in sequence.

Here, the F/F 15 has a function of being set by a print start signal PS sent from the CPU or the like to indicate the start of printing, and being reset together with the counter 17 when the strobe signal ST is sent to the driver 13h. The drivers 13a to 13h have a function of energizing the heating resistor 14 for a time corresponding to the print pulse width in accordance with the print data DT based on a strobe signal ST having a predetermined print pulse width. Further, the thermistor 16a is installed near a heat sink (not shown) in the thermal head, and has a function of detecting the heat radiation temperature from the heat sink in order to control the printing pulse width.

The operation of the thermal head energization control circuit configured as described above will be explained.

First, print data DT is input to the shift register 11 from the data input terminal 10-1 based on the clock signal CL input to the clock input terminal 10-2. continue,
By latch signal LS, latch/strobe input terminal 1
When 0-3 is switched from the "L'° level to the "H" level, the print data in the shift register 11 is transferred to the latch circuit 12.
is transmitted and stored.

Thereafter, when the input terminal 10-3 is switched from 1189 level to "L" level by the print start signal PS, F/
F15 is set, and the pulse generating circuit 16 starts oscillating and outputs a print pulse.

At this time, the thermistor 16a detects the heat radiation temperature from a heat sink (not shown) provided on the thermal head, and converts the heat radiation temperature into a resistance value. And pulse generation circuit 1
6 sets the oscillation frequency (print pulse width) of the print pulse to be output based on the converted resistance value.

The counter 17 counts the output of the pulse generation circuit 16 and outputs the count result to the distribution circuit 18. In distribution circuit #118, the strobe signal ST is sequentially sent to the drivers L3a to 13h every time the counter 17 counts one. As a result, the drivers 13a to 13h sequentially
It remains on for one cycle of the print pulse. Therefore, the print data D stored in the latch circuit 12
The heating resistor 14 corresponding to T is energized and generates heat.

As a result, printing is performed on the thermal recording paper set in the thermal head in accordance with the print data DT.

Then, after the drivers 13a to 13h are sequentially turned on, the counter 17 and the F/F l 5 are reset, printing for one line is completed, and the printer enters a standby state.

As is clear from the operation timing chart shown in FIG. 3, first, from time T1 to T2, the print data DT of the first line is transmitted to the shift register 11, and at the same time as the transmission is completed, the latch signal LS is used to transmit the data. The print data DT thus obtained is transmitted to the latch circuit 12. Then, printing is started, and print data for the second line is transmitted to the shift register 11 at times T3 to T4 during printing. Thereafter, at time T4 when printing of the first line is completed, the print data DT of the second line is transmitted to the latch circuit 12, and the print data DT of the second line is printed.

Thereafter, new print data DT is transmitted one after another for the third line and the fourth line, and printing is repeated.

During printing, the busy signal BY is at the "H" level, so the external control circuit checks the busy signal BY to determine whether printing has ended or not, and then starts printing the next line.

This embodiment has the following advantages.

As described above, the thermistor 16a installed near the heat sink in the thermal head detects the heat radiation temperature from the heat sink, and adjusts the pulse generation circuit 1 according to the heat radiation temperature.
It functions to control the print pulse width of the print pulse output from 6. As a result, as shown in FIG. 4, the energization time of the heating resistor 14 is automatically increased or decreased, and even if the heat dissipation temperature fluctuates, a nearly constant print density can be obtained.

Note that the present invention is not limited to the illustrated embodiment, and various modifications are possible. For example, there are the following variations.

(I) In the above embodiment, an up counter is used as the counter, but a down counter may also be used.

(n) Although the thermistor 16a is used as the temperature detection means, the present invention is not limited to this, and for example, a temperature sensing diode or an IC temperature sensor may be used.

(Effects of the Invention) As described above in detail, according to the present invention, a set/reset means, a pulse generation circuit, a counter, and a distribution circuit are provided inside the thermal head, and a plurality of drivers are controlled using these. Since the thermal head is driven, the external control circuit and the thermal head can be connected with fewer signal lines. As a result, wiring materials, space, etc. can be significantly reduced, and costs can be reduced accordingly.

Furthermore, the number of signals propagating between the external control circuit and the thermal head via the signal line is reduced, and there is no longer a need to control the printing pulse width with the external control circuit as in the past. It can also reduce the burden on people. Therefore, it is possible to downsize and reduce the cost of the external control circuit.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a configuration of a thermal head energization control circuit according to an embodiment of the present invention, FIG. 2 is a configuration block diagram of a conventional thermal head energization control circuit, and FIG. 3 is an operation timing diagram of FIG. 1. The chart, FIG. 4, is a diagram showing the control of the energization time of the heating resistor in FIG. 1. 13...Driver, 14...Heating resistor, 15...F/F, 16...Pulse generation circuit, 16a...Thermistor , 17...
...Counter, 18...Distribution circuit, ST...
...Strobe signal, DT...Print data, ps...Print start signal.

Claims (1)

[Claims] A strobe signal having a predetermined print pulse width sent out based on a print start signal causes the time of the print pulse width to be
A thermal head energization control circuit comprising: a plurality of drivers for energizing a heating resistor according to print data; and a temperature detection means for detecting a temperature near the heating resistor in order to control the printing pulse width. a set/reset means that is set based on the print start signal and is reset when energization of the heat generating resistors of the plurality of drivers ends; and when the set/reset means is set, the temperature detection means is used to detect the print. a pulse generation circuit that outputs a printing pulse having a pulse width; a counter that counts the output of the pulse generation circuit; and a distribution circuit that sequentially sends the strobe signal to each of the drivers according to the output of the counter. A thermal head energization control circuit is featured.