JPS60151073A - Thermal head driving circuit - Google Patents

Abstract

PURPOSE:To prevent image quality from being lowered due to broken characters or the like, by a method wherein the change of the resistance of each heating element to a predetermined resistance is detected, and the temperature of the heating element is prevented from being raised beyond an appropriate printing temperature. CONSTITUTION:When the temperature of each of the heating elements R1-Rn reaches the appropriate printing temperature T0, a switching circuit for the element is turned OFF to forcibly stop the passage of an electric current to the element. For this purpose, the system is provided with measuring resistors r0 having the same resistance (which is sufficiently lower than the resistance of the heating element) and provided between each heating element and each switching circuit, and driving circuits 1-n each of which detects the change of the temperature of each of the elememts R1-Rn to the appropriate temperature T0 by monitoring the voltage between the ends of the resistor and performs ON-OFF control for the relevant switching circuit. Accordingly, when the temperature of the heating element Rn reaches the appropriate temperature T0, a signal of logic level ''1'' is outputted from a comparator n1, and the change of the temperature of the element Rn to the appropriate temperature T0 is detected.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a drive circuit for a thermal head used in a thermal recording device, and particularly to a drive circuit that can be miniaturized to the extent that it can be incorporated into the thermal head itself, and The present invention relates to the realization of a circuit that can effectively drive the thermal head while correcting heat accumulation in the thermal head.

[Prior art]

The thermal head used for thermal recording usually has multiple heating elements to correspond to the number of image collections in the main scanning direction of the thermal recording medium (for example, it is necessary when recording image information on Japanese Industrial Standards A column No. 4 recording paper). The number of heating elements is 1728, B row 4
By generating heat from only the necessary heating elements corresponding to the image information, the heat-sensitive red paper, ink donor sheet, etc. that comes into sliding contact with the heating element can be The heat recording material is colored.

By the way, when recording using such a thermal head, the recording period of one line in particular is 10 m sec.
If you try to achieve speed drive in the following manner, (2) For example, when the same heat generating element generates heat continuously [, due to the influence of heat accumulation, the next row of confectionery will start before the heat generating confectionery cools down completely. Data had to be recorded, causing variations in recording density and deteriorating image quality.

For this reason, recording devices that use the same thermal head
It is essential to correct the heat accumulation and adopt a driving mode according to the temperature situation of each heating element.

In the past, attempts have been made to develop a circuit to drive the thermal head while correcting the heat accumulation described above, but the following problems arise: The H1 recording device itself becomes complicated and has a single cylinder.

○ Recording devices become larger.

There were still many problems in practical application.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermal head drive circuit that is inexpensive and has a simple configuration suitable for integration, and is capable of effectively driving a thermal head including the above-mentioned heat accumulation correction.

[Structure of the invention]

In this invention, as long as each heat-generating confectionery can be prevented from being heated above a predetermined temperature appropriate for printing, the heat accumulation correction described above can be substantially achieved, and each of these heat-generating elements Since the change in temperature corresponds to the change in the resistance value of the heat generating element, the appropriate predetermined temperature for the above printing can be determined accurately by detecting the transition to the corresponding predetermined resistance value for each heat generating confectionery. Focusing on this fact, we developed a switch circuit that selectively energizes each of the above-mentioned heat-generating confectioneries commonly connected to a power supply circuit and each of these heat-generating elements based on a drive signal corresponding to image information. In addition to providing an appropriate resistor between each of the heating elements, the voltage across the resistor is such that the resistance value corresponds to a predetermined temperature that is appropriate for the printing of the heating confectionery. The first value corresponding to the value of f is compared with the second value indicating the resistance value transition of the heat generating element, that is, the actual voltage value between both ends of the resistor, and this second value is A converter is provided which outputs a predetermined detection signal indicating this when the current becomes lower than 1 of 1, and an appropriate logic circuit outputs the corresponding signal of the drive signal at the time this detection signal is output. Try to block it. As a result, even if the heat-generating elements that have stored heat are driven again, the temperature of these heat-generating elements will not rise above the above-mentioned appropriate printing temperature, and deterioration of image quality due to characters being crushed etc. can be effectively avoided. Ru. Furthermore, since such a circuit can be integrated and made extremely compact, it can also be directly incorporated into the thermal head itself), which instantly eliminates the various problems previously encountered. Ru.

〔Effect of the invention〕

As described above, according to the thermal head drive circuit according to the present invention, it is possible to effectively drive the thermal head with heat accumulation correction using a simple configuration that is inexpensive and suitable for integration.

In particular, if the drive circuit is integrated as described above and incorporated directly into the thermal head, it will be possible to simply apply a drive signal corresponding to the image information to the thermal head, similar to the original thermal recording device. With just this, the drive of the thermal head and the correction of heat accumulation can be realized simultaneously and automatically.

〔Example〕

FIG. 1 shows a pulse width of 1 ms for one heating element of a thermal head to be driven in this invention.
The following shows the temperature response, resistance value change, and supply power change when driven by a drive signal (hereinafter simply referred to as a drive signal following the previous description).

In other words, as shown in FIG. 1, the temperature T of the heating element increases exponentially at the same time as the drive signal is applied, and the resistance value R also increases accordingly. Become. In particular, the temperature T and the resistance value R are in a nearly proportional relationship as shown in FIG. 2, and if the change in the resistance value R of the heating element can be detected, the temperature T can also be automatically determined.

FIG. 3 shows an embodiment of the drive circuit of the present invention constructed in consideration of these characteristics of the heating element. Finally, the structure of the circuit of this embodiment will be explained.

In FIG. 3, R1, Rn+R3r"'Rn-1+Rn, which are commonly connected to the power supply circuit 10, are
The above-mentioned heating elements of the thermal head are shown isometrically, and these heating elements R,, R2゜R3, .
...Rn-1r Rn is each corresponding switch circuit s, l
When "'2 Hs3+" and "8n-1+Sn are turned on, they are respectively energized and driven.

Now, in this example circuit, each of the heating elements R1°R2,
Rs, -Rn-j t The change in temperature T is monitored for each Rn, and when the same temperature T becomes an appropriate temperature for printing (this is set as To), the above-mentioned switch circuit corresponding to the element in question is activated at this point. The heating elements R1+R2 are
+ R3+ "' Rn-1+ In order to monitor the temperature change of Rn, a measuring resistor 76 having the same resistance value is connected between these valley elements and each of the switch circuits (this resistance value is the resistance value of the heating element). )
and the appropriate temperature T of the heating element mentioned above by monitoring the voltages across these resistors rQ. Drive circuits 1, 2, 3゜...(n
-1) and n.

Hereinafter, taking as an example the operation of the drive circuit n arranged corresponding to the n-th heating element Rn, these drive circuits 1, 2, 3
．． ...(n-1), the operation related to the above detection and control of n will be described in detail. Note that FIG. 4 is a time chart showing an example of the operation of these heating elements Rn and drive circuit n.
In this explanation, FIG. 4 will also be referred to.

Assuming that the value of the voltage applied from the power supply circuit 10 to the heating element Rn is vl, and the value of the voltage extracted by the drive circuit is 9, the value of this extracted voltage can be increased by arranging the measuring resistor r6. The value υ is expressed in the form ■Sa:'-'r6Rn. In other words, this value τ increases as the heating element Rn is heated and its temperature rises (see FIG. 4 (h)), and therefore its resistance value Rn (the same sign is used for convenience) increases. becomes smaller (4th
(See Figure (1)).

Now, the comparator n1 of the drive circuit n receives such a voltage ν at the inverting terminal, and sets the voltage -vQ corresponding to the same voltage τ corresponding to the appropriate temperature To of the heating element Rn at the non-inverting terminal. The comparator outputs a signal of logic level "0#" when the voltage V is higher than the set voltage vQ, and outputs a signal of logic level "'1" when the voltage τ becomes lower than the set voltage vo. If the heating element Rn reaches the appropriate temperature To, a signal of logic level ``1#'' will be output from the comparator n1 (the fourth Figure (j
), as long as the output of the comparator n1 is monitored, the transition of the heating element Rn to the appropriate temperature To can be monitored. Note that the value of the set voltage v6 is determined at the appropriate temperature T depending on the voltage division mode of the externally applied voltage VDD by the resistors r1 and r2.

is empirically set to a value corresponding to Further, the resistor r3 connected to the inverting terminal of the comparator (9), the parator n1, is a protection resistor.

The output of the comparator n1 is applied to the AND gate n2 as an appropriate temperature detection signal GT of the heat generating element Rn, and in the AND gate R2, the drive signal DSn (fourth
(See Figure (C)). If this AND condition is satisfied, the heating release command signal CS (see FIG. 4(d)) is further applied to the flip-flop n4 via the OR gate n3, setting the flip-flop n4 in the set state (the fourth (See figure (e)). This flip-flop n4 is constituted by a toggle-type frig-flozzo, and receives a set signal 5Sn (see FIG. 4(b)) transmitted from the drive signal generation circuit 20 when the thermal header finishes the previous printing. The print start signal PRn (
4(a)), and is further set when the heating release command signal C8 is applied (10), based on the application timing of each of these signals (10). 4(a) and (b) and (d) and (e)).

Note that the drive signal generation circuit 20 is a well-known circuit in thermal recording apparatuses that generate the above-mentioned various timing signals based on the received image information VD, and a detailed explanation thereof will be omitted.

Now, flip-flop n4 is set by the heating release command signal C8, and this output FO is at a logic level.
1#, the inverter n5 inverts this and outputs a signal IO having a logic level of 0# (see FIG. 4(f)). And this inverter output IO
and the drive signal DSn are finally ANDed by AND/DART n6, and at this time, the signal whose logic level is "1#" is the actual drive signal TDSn (see FIG. 4G) of the heating element Rn. is added to the switch circuit Sn, and this switch circuit Sn is turned on only during the time when the logic level is "1".In other words, this switch circuit Sn
The heating element Rn is kept in the ON state only for the time from when the drive signal DSn is generated from the drive signal generation circuit 20 until the heating release command signal CS is generated, and the heat generating element Rn is also switched off only during this time. It is actually driven (see Fig. 4(h)).

In this way, if this drive circuit n is used, the heat generating element Rn will always be at the appropriate printing temperature T when driven, regardless of whether heat is stored or not. It is heated to 1, and this temperature 1
Since it is not heated above 0, the image (cumulative) printed on the recording paper by the heating element Rn is always maintained at a constant size and density and is of high quality.

In this embodiment circuit, temperature detection and drive control as described above are performed for each heating element R1r R2+R3.

... Rn1 * This is performed separately for each Rn, and as a result, the same heating cord R1 + R2 + R
3, . . . Rn-1+ The above-mentioned high-quality image recording can be performed on all Rn.

By the way, in this example circuit, each of the above heating elements "1 r
Although this circuit is constructed on the assumption that the resistance values of R2+R3H""'n-j + Rn are all equal, the same embodiment circuit can also be applied to thermal heads in which there are variations in the resistance values of these heating elements. Of course it is. In other words, if there is variation in the resistance value of each heating element, the value of the voltage corresponding to the appropriate printing temperature To will also be different for each heating element. As shown in Figure 5, the relationship between the temperature response and the change in resistance value of a heating element is the same for each heating element, and the resistance value of each heating element under the same temperature condition is For example, each drive circuit 1, 2, 3 . ...If the value of the reference setting voltage υ0 at (n-")+n is adjusted based on the measured resistance value of the heating element, variations in these resistance values can also be corrected well. Of course, this correction method is optional.For example, the value of the voltage may be calculated and corrected based on the measured resistance value, or the resistance value of the measuring resistor ro may be corrected based on the measured resistance value. The value may be set based on the resistance value obtained.

(13) Further, each drive circuit 1, 2, 3 . ...(n-1).

The configuration of the logic circuit in n is not limited to the above-mentioned embodiment, but is arbitrary, and the drive signal DS1 is determined based on the output of the comparator, which is a printing appropriate temperature detection circuit for each heating element.
, DS2, DS3, -DSn-4, and any configuration that can block the corresponding signals of DSn may be used.

Furthermore, in the same embodiment, as shown in FIG. 3, each of the drive circuits 1, 2, 3 . ...(n-1), the overall configuration was designed assuming that n would be directly incorporated into the thermal head itself (a configuration that is fully possible with this invention), but this does not meet the actual situation. Depending on the situation, the drive signal generating circuit 20 can be configured as desired by incorporating the drive circuits up to each comparator into the thermal head and converting each subsequent logic circuit to the drive signal generation circuit 20.
The combination can be freely selected, such as a combination of the above drive circuits and the drive signal generation circuit 20.

[Brief explanation of drawings]

Figure 1 shows a line showing the relationship between temperature response, resistance value change, and supply power change when one heat generating element (14) of a thermal head is driven with a drive signal with a pulse width of 1 ms. 2 is a diagram showing the correspondence between temperature response and resistance value change in the heating element, FIG. 3 is a circuit diagram showing an embodiment of the thermal head drive circuit according to the present invention, and FIG. FIG. 3 is a time chart showing an operation example of the embodiment circuit shown in FIG. 3, and FIG. 5 is a diagram showing the correspondence between each temperature response and resistance value change in three heating elements having different resistance values at room temperature. 1, 2, 3, ”・(n −1), n =・
Drive circuit, nl... comparator, R2, R6...
And dirt, R3...or dirt, R4...flip-flop, R5...inverter, 10...power supply circuit, 20...drive signal generation circuit, R1+R2s
RB p ”' Rn-1+ Rn...Heating element, r
o...Measuring resistor, sl l s21S,...S
nl, sn...Switch circuit (15) 'E4%l5Jrr-'d7 Special order son-in-law αq

Claims (1)

[Claims] A switch circuit is provided between each heating element of the thermal head commonly connected to a power supply circuit and the ground, and the switch circuit is turned on by a drive signal formed in accordance with received image information. In a thermal head drive circuit that energizes and drives the heating element by doing so, a resistor is interposed between each of the heating elements and each of the switch circuits, and each of the heating elements is The resistor corresponding to the appropriate printing temperature of the corresponding heating element compares the first value corresponding to the voltage across the resistor with the second value which is the actual voltage across the resistor, and calculates the second value.
A comparator that outputs a detection signal when the value of xD becomes lower than the first *xD, and a logic circuit that quickly cuts off the corresponding signal of the drive signal at the time when the detection signal is output. Thermal head drive circuit. (1)