JPH02263663A - Thermal printer - Google Patents

Abstract

PURPOSE:To contrive a rapid and correct resistance measurement by conducting the resistance measurement of heating elements based on the voltage drop amounts of the heating elements changing in level in accordance with a plurality of voltage values. CONSTITUTION:A control circuit 6 supplies control signals Vc to a drive circuit 5 correspondingly to an operation and, simultaneously, determines the voltage level of a power source to, e.g. Ea for the first measurement. The drive circuit 5 successively generates strobe pulses SP correspondingly to the control signals Vc to feed them to switching transistors Q. As a result, an electric current I corresponding to the resistance values of heating elements (r) passes through a resistance R. A voltage Va at this time changes to a level determined by Ea-IR. In the second measurement, the control circuit 6 determines the voltage level of the power source to En. When the resistance measurement is similarly conducted in this state, a voltage Vb at thin time changes to a level determined by En-IR. On the basis of these two measurement results, the resistance values of the heating elements can be measured without being affected by the characteristics of the transistors Q driving the heating elements.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a thermal printer that measures the characteristics of a thermal head that is often used in various printers. The present invention relates to a measuring device for measuring resistance value with high accuracy when energized.

[Prior Art] A thermal head is widely used in printing printers, image recording printers, etc., and an example of its usage and internal structure will be described with reference to FIGS. 4 to 6.

FIG. 4 shows an example of application to a color image recording printer, in which an ink paper 2 is provided so as to be in contact with a plate-shaped thermal head 1 and run, for example, in the six directions of arrows. Incidentally, the ink paper 2 has a cassette structure and is wound in the six directions of arrows while being wound from a bobbin 2a to a bobbin 2b.

The ink paper 2 is coated with sublimable dyes of yellow Y, magenta M, cyan C, and these sublimable dyes are heated by the thermal head 1 to create a color image on the recording paper 4 that is wound around the platen drum 3 and runs. transcribe.

As shown in FIG. 5, the circuit configuration of the thermal head 1 includes a plurality of heating resistance elements (hereinafter referred to as heating elements).
, a switching transistor Q1 that controls energization of these heating elements r, and a drive circuit 5 that selectively drives the switching transistor Q. The number of heating elements r is determined by the device to which this thermal head 1 is applied, as well as the resolution, etc., but when applied to an image recording printer, it may be a large number such as 512 or 1024. It is.

When recording an image, the switch means Sw is selected to the a side.

A power source 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.

Then, 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 5 to each switching transistor Q to turn it on. As a result, a pulsed current flows through the selected heating element r, generates heat corresponding to the amount of current, and heats the sublimable dye as described above.
It records images.

On the other hand, when measuring the resistance value of each heating element r, SW
is set to the b side, power is supplied through the reference resistor R set to a predetermined resistance value, and the strobe pulse SP is supplied as described above, so that a pulse current flows through the series circuit of the heating element r and the transistor Q.

As a result, a current I flows from the power source E through the reference resistor R, and a voltage V corresponding to the amount of current is generated across the series circuit of the heating element r and the transistor Q. That is,
The voltage V is a voltage divided based on the resistance ratio between the resistor R and the heating element r. Therefore, by measuring the voltage V, the resistance value of the heating element r can be determined by r=(V/(E-V))R.

Note that the capacitance C is for reducing fluctuations in the power supply voltage when electricity is applied to the heating element r, and is from several tens of μFD to 10 μFD.
The capacitance value is set to about 0μFD.

[Problems to be Solved by the Invention] When the resistance value of the heating element r varies or changes over time, the amount of heat generated naturally fluctuates, and this causes defects such as color unevenness in the recorded image. The desired phenomenon occurs.

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 values of each heating element r.

Therefore, the resistance of the heating element r is measured as described above, but this measuring method has the following problems.

In other words, electric current! The saturation voltage of the transistor Q is also involved in the amount of current and the voltage V, and the voltage V has a voltage value that is related to the collector-emitter voltage VcB of the transistor Q. Even if the color unevenness is corrected based on measured values including such uncertain factors, it is not possible to record a good image. Therefore, when measuring the resistance of the heating element r, it is necessary to accurately measure the resistance of the heating element itself without being influenced by the characteristics of the transistor Q.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a thermal head measuring device that can quickly and accurately measure the resistance of a heating element that constitutes a thermal head.

[Means for Solving the Problems] In order to achieve such an object, the present invention provides a voltage setting circuit that sets the voltage level of a power source that drives a thermal head to a plurality of voltage levels, and also provides a voltage setting circuit that sets the voltage level of a power source that drives a thermal head to a plurality of voltage levels. The resistance value of the heating element is measured based on the voltage drop across the heating element whose level changes correspondingly.

[Operation] According to the thermal head measuring device configured as described above, the resistance of the heating element can be measured under different conditions, and based on the measurement results, the resistance value of the heating element and the transistor driving the heating element can be determined. Q and Vce can be measured independently.

[Example] An embodiment of the present invention will be described below with reference to FIG.

It should be noted that FIG. 1 is a circuit diagram of a thermal head and its measuring device, and parts common to those in the conventional example are designated by common reference numerals, and explanations thereof will be omitted.

The thermal head 1 includes N heating elements r connected in series.
, a switching transistor Q1, and a drive circuit 5 that sequentially supplies a strobe pulse SP to the switching transistor Q to selectively drive the heating element r.

A pair of power supplies are supplied to both ends of each heating element r and each transistor Q via a resistor R, and the voltage levels are varied from Ea to E by the control circuit 6.
It is made to be variable to n.

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

The control circuit 6 is configured to be program-controllable by a CPU or the like, and switches the control circuit 6 to a resistance measurement mode by operating an operation mechanism (not shown). Control circuit 6
corresponds to the above-mentioned operation, supplies the control signal Vc to the drive circuit 5, and at the same time sets the voltage level of the power supply to, for example, Ea for the first resistance measurement.

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 Va at this time changes to a level determined by E-IR.

Assuming that the VcB of the transistor Q at the time of the first resistance measurement is VcBa for convenience of explanation, and the measured voltage value is Va, the resistance value of the heating element r is as follows: Va - Vcear = x R-° (1) Ea - V
It is found by a.

In the second resistance measurement, the control circuit 6 sets the voltage level of the power supply to En. In this state, the resistance is measured in the same manner as above, but the Vc of the transistor Q at the time of the measurement is
For convenience of explanation, B is set to VcBb, and the measured voltage value is set to vb.
Then, the resistance value of the heating element r is Vb −Vcebr = x R−−−−(2)En −
It is determined by Vb.

By the way, when a transistor is generally driven to a saturated state, the collector-emitter resistance is approximately several ohms, which is sufficiently small compared to the resistance of heating element r (approximately 500 ohms to 3 to 3 ohms). Therefore, when changing the measurement conditions as described above, Vcf! The change in can be ignored.

Therefore, from equations (1) and (2) above, the resistance value of heating element r is: It can be found by

By determining the resistance value of the heating element r under such different conditions, the resistance value of the heating element r itself can be determined without being influenced by the manufacturing quality of the transistor Q.

Next, a second embodiment of the present invention will be described with reference to FIG. The difference between this embodiment and the first embodiment lies in the method of setting the reference resistance. Therefore, parts common to those in the first embodiment are denoted by common reference numerals, and explanation thereof will be omitted.

In this embodiment, the control circuit 6 is configured to switch the switch S to select the voltages Ea and Eb.

By switching to the voltage Ea and performing the first resistance measurement as described above, the resistance value of the heating element r can be determined in the same manner as in equation (1).

On the other hand, the control circuit 6 switches the switch S, and the voltage E
When b is selected, the resistance value of the heating element r is determined as explained in relation to equation (2) above. By measuring the resistance under these different conditions and substituting the measurement results into (3) above, the resistance value of the heating element r can be determined in the same manner as described above. By the way, in each of the above embodiments, the heating element r
A capacitor C is connected between the pair of power supplies in order to reduce fluctuations in power supply voltage during energization. Therefore, when the resistance is measured, the voltage V changes in level as shown in FIG. 6(B) by energizing the heating element r. From the standpoint of improving accuracy, etc., it is desirable to respond quickly to the strobe pulse SP. The third embodiment described below achieves this purpose.

FIG. 3 shows a third embodiment of the present invention, in which the capacitance C
is connected between a pair of power supplies via a switch Sa as shown in FIG. 3(A).

In this embodiment, the control circuit 6 switches to the resistance measurement mode and controls the switch Sa to be in the OFF state, so that the capacitance C has no effect between the pair of power supplies, in other words, with respect to the measurement position of the voltage V. . Therefore, when the strobe pulse SP changes in level as shown in FIG. 3(B), the level of the voltage V also changes with a high speed response as shown in FIG. 3(C).

The level of the voltage V rapidly decreases due to the current I 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 capacitance C, it becomes almost flat. Therefore, it becomes possible to speed up the measurement of the resistance value and to perform accurate measurement.

The resistance value of the heating element r is determined as explained in equations (1) to (3) above, and after the resistance measurement is completed, the switch Sa is turned on and the capacitor C is connected between the pair of power supplies. Connecting. Therefore, during normal image recording, the power supply stabilization operation is performed by the capacitor C.

As described above, according to the printer shown in this embodiment, the resistance of the heating element r can be measured at high speed or accurately, and thus the following uses are 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. Taking this situation into consideration, it will be understood that good image recording can be continued if the resistance of the heating element r is appropriately measured and corrected not only during the manufacturing process but also before image recording.

However, with conventional measurement circuits, not only were they affected by the characteristics of the transistor Q as described above, but they also took a long time to measure, making it difficult to easily carry out measurement and correction prior to image recording. Ta.

In contrast, the measuring circuit shown in this embodiment can measure the resistance of the heating element r at high speed and accurately.

Therefore, taking a video printer as an example, resistance measurement and correction can be easily performed prior to image recording, and high quality image recording can be performed.

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 level change of the power supply voltage is not limited to two values, but may be configured to be variable to a larger number of voltage levels.

Further, the application of the measuring device shown in this embodiment is not limited to the video printer, but can be widely used in various printers that apply thermal heads.

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 described above, in the printer according to the present invention, the power supply voltage of the thermal head is set to a plurality of voltage levels, and the resistance value of the heating element changes in accordance with the set voltage level. The device is configured to measure the resistance and determine the resistance of the heating element itself from the measured resistance value.

According to the configuration, the resistance value of the heating element itself can be measured without being affected by the characteristics of the transistor for controlling the driving of the heating element, and the resistance of the heating element can be accurately measured.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a first embodiment of a printer to which the present invention is applied, Fig. 2 is a circuit diagram showing a second embodiment of the present invention, and Fig. 3 is a circuit diagram showing a third embodiment of the present invention. 4 is a perspective view showing an example of application of the thermal head, FIG. 5 is a circuit diagram showing a conventional thermal head measuring device, and FIG. 6 is a waveform diagram illustrating the circuit operation. Q Niswitching transistor S: switch Sp Nistrope pulse VC two control signals. SW: Image recording/resistance measurement mode changeover switch Code l in the diagram: Thermal head 2: Ink paper 3 Nib platen drum 4: Recording paper 5: Drive circuit 6: Control circuit Ea, Eb, En: Power supply R: Reference resistance r : Heating element 1st figure tX 3 figure (A) figure 2 CB) (C) figure figure figure figure figure

Claims (1)

[Scope of Claims] A thermal printer comprising means for successively energizing heating elements constituting a thermal head and measuring a resistance value of the heating element based on a change in voltage across the heating element during energization, comprising: A voltage setting circuit is provided to set the voltage level of a power source that drives the thermal head to a plurality of voltage levels, and a heating element of the thermal head is driven at the plurality of voltage levels, and a resistance value of the heating element is measured. A thermal printer configured as follows.