JPS61205072A - Thermal head driving circuit - Google Patents

Abstract

PURPOSE:To increase the overall processing speed of a system and also to simplify software by performing automatic temperature/pulse width control with a trigger signal given once from the outside and at the same time delivering automatically print signals of the 1st-N-th blocks. CONSTITUTION:The temperature of the heat discharge part of a thermal head is detected by a temperature detecting output terminal 1. Then the signals are converted by a temperature converting circuit 3 and supplied to a pulse width modulation circuit. Then a print command signal is given to a print command input terminal 2 from a control circuit MPU and therefore the pulse width modulation circuit delivers the pulse width signal proportional to the temperature of the thermal head. At the same time, a timer 5 delivers a signal of the pulse width set previously. Then an AND is secured by an AND gate 13 between the output pulse width signal of the pulse width modulation circuit and the output pulse width signal 4 of the timer 5. This AND is delivered for execution of temperature control. At the same time, it is possible to obtain the pulse width signal protected with the maximum rating of the thermal head as the 1st strobe signal. Thus the strobe signals are delivered successively to output terminals 23-27.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a drive circuit for a thermal head that has a large number of heat generating resistors and is divided into several blocks and is driven. The present invention relates to a thermal head drive circuit suitable for a printing method that requires signal temperature control.

[Background of the invention]

In recent years, thermal heads (thermal line heads), which have a large number of heat-generating resistors arranged in a straight line, have been widely used as printing mechanisms in facsimile machines, printers, etc. because they have a simple mechanism, are popular, and are highly reliable. .

Tome name &'s base, folding, pickled right - salary If mother-in-law 4 - - - - Rad's internal circuit r, j: Generally, it is J in Figure 1. ■(, 1 H I (, 640ri heating resistor shown, DATA terminals are serial data input terminal f, CLO Input terminal 'i LAfCH end f-r
U, serially transferred f--data (1) latch input terminal F, S'rt(, (,)l 1-3T[I, 0BE
5 is the print signal input terminal L7, Vnl'i
Source terminal for heating resistor, ICI・-, r C5
is the driver of M1 passion resistance, ′? ). Print ti, first j'-take turn, latch shift, then print signal (x (
o ), the driver is fully driven and corresponds to the data. Also, apply +♂ heat to the heating resistor, heat sensitive paper, etc., and color it.
Do it with J゛. In this case, the print signal is divided into 5 parts.For example, if you try to print all black data, if you print all of them at once, the consumption current of the heat generation source will peak. This is to reduce the load on the power supply section by dividing the load, which sometimes reaches several 1 OA. In addition, this printing signal is generally a pulse signal of several milliseconds, and in order to obtain good printing image quality, the temperature of the heat dissipation part of the di-full head is detected and the pulse of the printing pulse signal is changed to four corners. 1.-(
, It is normal to do ``l'' of printing L energy.

The mark of this thermal head is 1. In recent years, the microprocessor (hereinafter referred to as M'P) has become widely used.
(abbreviated as TJ) 4:1 history is common, and the control circuit of RLT had the entire configuration shown in Figure 2.

The entire operation of the circuit shown in FIG. 2 will now be explained. , First, sir ,
It is installed in the radiator 1 part of the -2 ref. ) circuit converts it into a digital signal and imports it into the IX4P. In short, +nP [
The parallel/serial conversion circuit is fully activated under the control of J. Print data is transferred to the full head. So “r, ST
J Niji printing is performed p times on the signal of OBgl = 5, but at this time, the printing pulse width is 1fLsfl from the temperature signal taken into the VLP U before, and the pulse width is 1fLsfl for the determined pulse width.
Output from 10 circuits and print. An example of the strobe signal output at this time is shown in FIG. When the thermal head is controlled using this conventional circuit system, the MPU software is interposed in the 110 circuit that performs A/D conversion and full output of the strobe No. 11, reducing the efficiency of the MPU. This is because in A/I conversion, the time from the start to the end of the conversion is a waiting time by the software, and the time t during which the Stroop signal is output is also a waiting time by the software, and at that time, lI5 is the number IQ. m 3 and several ms
It is. These times are full power and dead time, and for iJPU, which also processes ponds, it is a factor that hinders Akane speed processing. In addition, since 1VfP U is interposed in the speed control and print signal output, if an MPU runaway occurs, it may cause printing errors or burnout of the thermal head, so reliability is reduced. It lacks. Currently, thermal heads are very expensive, so it is essential to protect them from burnout and the like. The conventional technology had drawbacks such as "dual series", which hindered high-speed processing and had poor reliability.

[Embodiments of the invention]

The present invention is intended to improve these drawbacks, and its implementation is shown in FIG. In Figure 4,
1. 2 is a temperature detection terminal, 2 is a print command input terminal, 3 is a temperature conversion circuit, 4 is a pulse modulation circuit with an edge trigger input, 5-9 is a timer circuit with an edge trigger input,]
, 1 and 12 are OR gates, 13 to 17 are AND gates, 18 to 22 are inverters, and 23 to 27 are strobe signal output terminals. The entire operation will be explained below. At this time,
It is assumed that the print data has already been transferred to the thermal head. First, the temperature of the heat dissipation part of the thermal head is detected by the temperature detection terminal 1, and the temperature is converted into a signal by the sub-circuit and input to the pulse width fJ circuit. Next, the control circuit (MP
When a print command signal is input from U) to the print command input terminal 2, the pulse width KAl path outputs a pulse width signal proportional to the temperature of the thermal head. At the same time, since the timer 5 is being activated by the print command signal, it outputs a signal with a preset pulse width (for example, the maximum pulse width defined by the thermal head). and,
The logic of the output pulse width signal of the pulse one corner modulation circuit and the output pulse width signal of timer 5,
3, and by outputting this, a pulse width signal that is temperature controlled and protected to the maximum rating of the thermal head can be obtained as the first strobe signal. In addition, this output is inputted to the trigger input of the timer 10 via the timer 6 and the OR gate, and the s
・Start at the trailing edge of the raoag signal, then the output of the timer IO is input to the pulse 1 @ modulation circuit via the AND gate 11, and the same operation as the previous time is performed.
A second strobe signal is output at 4. In this way, strobe signals are sequentially output to the output terminals 23-27. Incidentally, the inverters 18 to 22 are used to keep the strobe signal level the same as that in FIG. 3.

According to the present invention, by inputting a print command signal from the control circuit (Mpσ) only once, everything is automatically set to ``temperature control'' and print strobe signals are sequentially output to perform printing operations, so software is not required. It is possible to use the MPU efficiently without the need to set timers 5 to 9.
By setting the time to the maximum rating of the thermal head, even if the MPU goes out of control, the pulse width will be limited by that time - the thermal head will not be destroyed.

〔Effect of the invention〕

Non-invention has an effect below μ.

1. In a system equipped with tVPU and having thermal-\rad as a printing mechanism, the LdPU is not involved in the thermal head printing operation, so the processing speed of the entire system can be completely improved and the software can be simplified. I can do it.

λ In the above system, since the N1PU is not involved in the printing operation of the thermal head, it is possible to prevent printing errors due to malfunction of the MPU, damage to the thermal head, etc., and improve the reliability of the system. .

[Brief explanation of drawings]

Figure 1 is an internal circuit diagram that plays a role in the thermal head, Figure 2 is a conventional drive circuit diagram for the thermal head, and Figure 3 is printed with S.
A time chart of the TOBg signal, FIG. 4, is a diagram showing an embodiment of the present invention.

Claims (1)

[Claims] 1. In a thermal head drive circuit that has a large number of heat generating resistors and is driven by dividing the heat generating resistors into N blocks, a voltage or current/pulse width modulation circuit that generates a pulse in response to a trigger input and a plurality of A timer circuit is provided, which applies a voltage or current expressed as a function of the temperature of the heat radiation part of the thermal head to the voltage or current/pulse width modulation circuit, and generates a pulse expressed as a function of the temperature by an external trigger input. Obtain a pulse width signal, add this pulse width signal to the trigger input of a first timer circuit, use the AND signal of the output of this timer circuit and the pulse width signal as a print signal for the first block of the thermal head, and further add this pulse width signal to the trigger input of a first timer circuit. The printing signal of the first block is added to the trigger input of the voltage or current/pulse width modulation circuit and the trigger input of the second timer circuit, and the output of the voltage or current/pulse width modulation circuit and the output of the second timer circuit are The AND signal of
4th...Obtain the printing signal for the Nth block. Automatically control the temperature/pulse width by one external trigger signal, and print the 1st, 2nd...Nth block. A thermal head drive circuit characterized by automatically outputting signals in sequence.