JPH02248262A - Thermal head and thermal printer using it - Google Patents

Abstract

PURPOSE:To quickly and accurately measure resistance of a heating element by a method wherein a noise absorbing condenser is connected between a pair of power sources driving a thermal head via a switch means and in the case where resistance of the heating element is measured, the above-mentioned switch means is controlled at an open state. CONSTITUTION:When a control circuit 6 is switched to a resistance measuring mode of a heating element (r), the circuit 6 feeds a control signal Vc to a driv ing circuit 5, and the circuit 5 generates successively a strobe pulse SP according to the signal Vc. For instance, a switching transistor Q is driven in an ON state successively from the switching transistor Q on the left side of the figure. Consequently, a current I corresponding to a resistance value of the heating element (r) flows to resistor R, and voltage V is changed to a level to be deter mined by E-IR. In that case, the control circuit 6 controls a switch Sa to an OFF state to perform no operation to a measuring position of the voltage V. Therefore, when a pulse SP is varied by a level, a level of the voltage V responds at high speed to be decreased at high speed. Its time width t becomes flat since there is no time constant with a capacitor C.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a thermal head and a thermal printer using the same, and more specifically to high-speed measurement of the resistance value of a heating element constituting a thermal head. The present invention relates to a thermal head that is capable of printing and a thermal printer using the same.

[Prior Art] Thermal heads are widely used in printing printers, image recording printers, etc., and examples thereof are shown in Figs.
I will explain the 6th episode.

FIG. 4 shows an example of application to a color image recording printer, in which an ink paper 2 is provided so as to run in, for example, six directions of arrows, in contact with a thermal plate 1 formed in a plate shape. Ink paper 2 has yellow Y, magenta M,
A sublimable dye of cyan C is applied, and the sublimable dye is heated by a thermal head 1 to thermally transfer a color image onto a recording paper 4 that is wound around a platen drum 3 and runs.

As shown in FIG. 5, the circuit configuration of the thermal head 1 includes a plurality of heat generating resistive elements (hereinafter referred to as heat generating elements) r, switching transistors Q that control the energization of these heat generating elements r, and a selection of switching transistors Q. It consists of a drive circuit 5 and the like that drive the drive circuit 5 and the like. Note that the heating element r
The number is determined by the device to which this thermal head 1 is applied, resolution, etc., but when applied to an image recording printer, it is a large number such as 512 or 1024.

A power supply voltage E set to a predetermined voltage is supplied to both ends of the heating element r and the switching transistor Q that are connected in series.

When recording an image, a control signal corresponding to the video signal is supplied from the control circuit 6 to the drive circuit 5, and a strobe pulse SP as shown in FIG. 6(A) is applied from the drive circuit 6 to each switching transistor Q. drive to the on state. As a result, a pulsed current flows through the selected heating element, generates heat corresponding to the amount of current, and transfers the sublimable dye as described above.

If a pulsed current flows through the cable that supplies power to the thermal head, harmful unnecessary radiation may occur, so a capacitor C is connected between a pair of power terminals of the thermal head block. Further, since the power supply current is integrated by the capacitor C, there is an effect that the power supply circuit can be one having a small peak current capacity.

The capacitor C has a capacitance value of several tens of μF to about 100 μm7.

[Problem to be solved by the invention] By the way, there may be variations in the resistance value of the heating element r,
Naturally, when aging occurs, the amount of heat generated changes, and this causes undesirable phenomena such as color unevenness in recorded images.

This phenomenon can be prevented and reduced by correcting variations in the heating elements r, but this requires accurate measurement and detection of variations in the resistance value of each heating element r. According to the circuit configuration, a reference resistor R (described later) is inserted between the power source E and the thermal head 1, and the resistance value of the heating element r is determined by measuring the terminal voltage V of the thermal head l. can be found.

That is, the voltage level of the power source E and the resistance value of the reference resistor R are set to predetermined values in advance as described above. Therefore, the resistance value of the heating element r can be determined by measuring the voltage
−(V/ (EV)) ・It is determined by R.

However, since a large-capacity capacitor C is connected in parallel to the series circuit of the heating element r and the switching transistor Q, the time constant of the power supply circuit is large. Therefore, even if the strobe pulse SP has a waveform in which the level changes rapidly as shown in FIG. 6(A), the level change of the voltage ■ will change as shown in FIG. 6(B) due to the time constant i'iii. The waveform begins to change in an exponential curve, resulting in a so-called rounded waveform. Therefore, accurate measurement cannot be performed unless the fall time and rise time of voltage (2) have elapsed after the strobe pulse SP for measurement is supplied.

Moreover, for example, in a thermal head applied to an image recording printer, the heating element r is 51 as described above.
Since there are two or more of them, it would take a lot of time to measure the resistance of the entire thermal head 1.

The present invention has been made in view of the above-mentioned circumstances, and its purpose is to provide a thermal head that can quickly and accurately measure the resistance of a heating element constituting the thermal head, and a resistance measuring function using this thermal head. The objective is to provide a thermal printer with

[Means for Solving the Problems] In order to achieve such an object, the present invention connects a noise absorbing capacitor between a pair of power supplies for driving a smart head via a switch means, and When measuring the resistance of a heating element constituting a thermal head, the switch means is controlled to be in an open state to disconnect the capacitor from the pair of power supplies.

[Function] According to the thermal head configured in this way and the thermal printer using the same, when measuring the resistance of the heating element, no capacitor is connected to the power supply, and the time constant of the power supply path becomes small. , the level of the power supply voltage decreases in response to the resistance value of the heating element at high speed, and by measuring this level drop, the resistance of the heating element can be measured accurately and at high speed.

On the other hand, when performing normal image recording, the switch means is controlled to be in a closed state, the capacitor is connected to the power source, and recording operation can be performed.

[Example] Hereinafter, an example of the present invention will be described with reference to FIGS. 1 to 3. In addition, FIG. 1 is a circuit diagram of the thermal head and its surroundings, FIG. 2 is a waveform diagram for explaining the circuit operation, and FIG. 3 is a circuit diagram showing each side of the switch means, which are common to the conventional example described above. The parts are given the same reference numerals and their explanations are omitted.

The thermal head 1 includes a plurality of N heating elements r connected in series and a plurality of switching transistors Q arranged in parallel, and further supplies a strobe pulse SP to the switching transistors Q in order to control the current of the heating element r. The drive circuit 5 includes a drive circuit 5 and the like.

A power source E set at a predetermined voltage is supplied as a pair of power sources to both ends of each heating element r and each transistor Q via a reference resistor R set to a predetermined resistance value. A switch sb is connected in parallel to the reference resistor R. Further, a capacitor C is connected between the pair of power supplies via a switch Sa.
is connected. The switches Sa and Sb correspond to switch means and resistor insertion means in the present invention, and when measuring the resistance of the heating element r, the control circuit 6
While each is controlled to an open state, that is, an off state, by
When performing image recording, etc., each is controlled to be in the closed state, that is, in the on state.

Next, the resistance measurement operation of the heating element r will be explained.

In this case, an operation mechanism (not shown) controls the control circuit 6.
is switched to the resistance measurement mode, and correspondingly supplies the control signal Vc to the drive circuit 5.

The drive circuit 5 sequentially generates strobe pulses SP in response to the control signal Vc and supplies them to the switching transistor Q. Therefore, for example, the switching transistors Q on the left side shown in FIG. 1 are sequentially driven to the on state, in this case to the saturated state.

As a result, a current (2) corresponding to the resistance value of the heating element r flows through the resistor R, and the voltage V changes to a level determined by E-IR.

What should be noted here is that when the mode is switched to the resistance measurement mode, the switch Sa is controlled to be off by the control circuit 6, and the capacitor C is connected between the pair of power supplies, so that it has no effect on the measurement position of the voltage (3). It is what is done. Therefore, when the strobe pulse SP changes in level as shown in Figure 2 (A), the level of voltage ■ also changes as shown in Figure 2 (B).
), the level changes with a fast response.

The level of the voltage (2) rapidly decreases due to the current (2) corresponding to the resistance value of the heating element r, and since the time width t during which the level decreases has no time constant due to the capacitor C, it becomes almost flat. Therefore, it becomes possible to speed up the measurement of the resistance value and to perform accurate measurement.

Note that the resistance value of the heating element r is r-(V/
(EV)) - Obtained by R. Then, the amount of correction for each heating element r is determined based on the obtained resistance value, and, for example, this correction value is stored in RAM, and this data is read out and corrected when recording an image, thereby achieving good image recording. be able to do so.

On the other hand, when recording an image, the control circuit 6 is switched to recording mode using the operating mechanism. As a result, the control circuit 6 turns off the switches Sa and Sb, connects the capacitor C between the pair of power supplies, shorts the reference resistor R, and sends a control signal ■c corresponding to the video signal.
is supplied to the drive circuit 5. The contents of the control signal Vc include data for selecting the heating element r, controlling the color shading, and previously determined correction data.

The drive circuit 5 supplies strobe pulses SP based on the control signal Vc to the switching transistor Q, but the strobe pulses SP are not supplied sequentially during image recording, but are supplied selectively to form an image.

Next, specific examples of the switch Sa will be sequentially explained with reference to FIG. FIG. 3(A) shows an example in which the switch Sa is composed of a bipolar transistor Qa.

When measuring the resistance of each heating element r, the transistor Qa is controlled to be in an off state by a control signal supplied from the control circuit 6. As a result, the capacitor C is disconnected from the pair of power supplies, and the level change of the voltage (2) responds quickly as described above.

On the other hand, when performing normal image recording, the transistor Qa is controlled to be in an on state by a control signal supplied from the control circuit 6. As a result, the capacitor C is connected between the pair of power supplies, and even if each heating element r is energized, noise can be prevented from being generated.

FIG. 3(B) shows an example in which the switch Sa is composed of an MO3I transistor Qb.

In this example as well, when measuring the resistance of the heating element r, the control circuit 6 controls the MO3I-transistor Qb to be in the off state, and when performing normal image recording, it is controlled to be in the on state.

Figure 3 (C) shows switch Sa and relay switch R)
This example shows an example of the configuration.

It is preferable that the relay switch Ry is turned off when the coil L is energized, and is turned on by a spring or the like when the energization is cut off. That is, measuring the resistance of the heating element r takes a very short time compared to the time required for recording, and the above structure can reduce power consumption during the recording operation, which takes an overwhelmingly long operating time.

By applying the relay switch having the above structure, when measuring the resistance of the heating element r, the relay switch Ry is controlled to be in an OFF state and the capacitor C is disconnected, and when performing normal image recording, power is consumed. The capacitor C can be connected between a pair of power supplies without any trouble.

The switch means is not controlled by the control circuit 6, and the switch means shown in FIG.
The open/close state of the circuit of the capacitor C may be switched using a jumper switch, a solder jumper, etc. as shown in D).

As explained above, according to the thermal head shown in this embodiment and the thermal printer using the same, the resistance of the heating element r can be measured at high speed and accurately, so that it can be used in the following ways. It becomes possible.

For example, even if the resistance value of the heating element r is measured as described above in the manufacturing process of a video printer and correction is made based on the measured value, the resistance value may fluctuate due to aging or other factors. is possible. Considering this situation, it will be understood that if the resistance of the heating element r is measured and corrected not only during the manufacturing process but also before image recording, good image recording can be continued.

However, in the conventional measuring apparatus, as mentioned above, the measurement time is long, and the power supply changes in an exponential curve, so it is difficult to easily carry out measurement and correction at least prior to image recording.

On the other hand, the measurement method using a thermal head and a printer shown in this embodiment can measure the resistance of a heating element at high speed and accuracy. This makes it possible to easily perform corrections and record high-quality images.

With such a configuration, the added value of the video printer can be further improved.

Although the present invention has been described in detail above, the present invention is not limited to the above, and various modifications are possible.

For example, the switches Sa and Sb may be controlled to turn on and off by a timer or the like that takes into account the measurement time of the heating element r.

Further, the application of the thermal head and thermal printer shown in this embodiment is not limited to the video printer, but can be widely used in various printers to which the thermal head is applied.

Furthermore, it can be used as a measuring device for the thermal head itself in the manufacturing process of the thermal head, and can also be used as an after-sales service device for printers.

[Effects of the Invention] As explained above, the thermal head and thermal printer according to the present invention separate the noise absorbing capacitor from between the pair of power supplies when measuring the resistance of the heating element that constitutes the thermal head. Since it is configured to be connected during normal energization, when measuring the resistance of the heating elements, by sequentially energizing the heating elements, the level of the power supply voltage changes in response to the resistance value of the heating elements with a fast response. Then, the resistance value can be measured based on the level of change.

On the other hand, when performing other than the resistor side fixed time, for example, normal recording operation, a capacitor is connected between the pair of power supplies.
Noise is no longer generated even when the heating element is energized, and a stable recording operation is performed.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of a thermal head measuring device to which the present invention is applied, Fig. 2 is a waveform diagram for explaining circuit operation, and Fig. 3 is a circuit diagram showing each side of the switch means. , FIG. 4 is a perspective view showing an application example of the thermal head, FIG. 5 is a circuit diagram of the thermal head, and FIG. 6 is a waveform diagram explaining the circuit operation. Reference numeral 1 in the figure: Thermal head 2: Ink paper 3 Nib platen drum 4: Recording paper 5: Drive circuit 6: Control circuit E: Power supply R: Resistor r: Heat generating element Q Niswitching transistor Sa: Switching means Sb: Resistor Insertion means Sp Nistrope pulse ■c: control signal. -), Figure 1 wealth 2 Figure -3: (A) (C) Figure (B) (D) First cause

Claims (3)

[Claims] (1) A thermal head characterized in that a capacitor is connected via a switch means between a pair of power supply terminals for driving a heating element constituting the thermal head. (2) A thermal head comprising a capacitor connected via a switch means between a pair of power supply terminals for driving a heat generating element constituting the thermal head, and means for controlling an open/closed state of the switch means, the heat generating element 2. A thermal printer according to claim 1, wherein in a mode for measuring the resistance value of the thermal printer, the switch means is opened to speed up the change in the voltage between the terminals. (3) A means for inserting a resistor between the thermal head and a power source that supplies power to the thermal head, and in a mode for measuring the resistance of the heating element, the resistor inserting means and the switch means are simultaneously operated. The thermal printer according to claim 2, characterized in that the thermal printer is configured to control the thermal printer.