JP2512033B2 - Thermal head heat storage detector - Google Patents

Description

Detailed Description of the Invention [Table of Contents] Outline Industrial field of application Conventional technology (Fig. 4) Problems to be solved by the invention Means for solving the problems (Fig. 1) Operation Example (a) ) Description of one embodiment (FIGS. 2 and 3) (b) Description of another embodiment [Outline of the invention] [Outline] A heat storage detecting device for detecting a heat storage state of a multi-gradation-driven thermal head, and a print pattern And a differential amplifier for detecting the recording current flowing in the heating element group of the thermal head and the detection voltage of the detection resistor for the purpose of accurately detecting the amount of accumulated heat in response to changes in gradation. An integrator that charges and discharges the output of the differential amplifier; a charge and discharge control circuit that controls the charge and discharge of the integrator by the output of the differential amplifier; and a heat storage detection signal that is output from the output of the integrator. And a comparator.

[Industrial applications]

The present invention relates to a heat storage detection device that detects a heat storage state of a thermal head that is driven in multiple gradations.

In a thermal transfer printer or a thermal printer, a thermal line head in which a large number of heating resistance elements are arranged in a line is used.

In the thermal line head, when continuous recording such as solid printing is performed for a long time, the head accumulates heat.

When the head accumulates heat, print quality deterioration such as density deterioration and resolution deterioration occurs especially when multi-tone printing is performed by changing the peak value or pulse width of the recording current pulse.

The heat storage is proportional to the amount of power consumed by the head, so
When heat accumulation that adversely affects printing occurs, the peak value of the recording current pulse is reduced or the pulse width is narrowed to reduce the power consumed by the head, and when the heat accumulation is low, the current pulse is restored. Need to do.

Therefore, there is a demand for a heat storage detection technique that is simple and has excellent followability.

[Conventional technology]

 FIG. 4 is an explanatory diagram of the prior art.

The thermal head 1 is a power source + V with n heating resistors 10a to 10n and driving transistors 11a to 11n connected in series.
It is configured by connecting in parallel to _EE .

Each transistor 11a-11n has an individual drive signal DVa-D
Driven by Vn, current flows through the desired heating resistors 10a to 10n to generate heat.

The conventional heat storage detection device charges the divided voltage of the power supply + V _EE (by the resistor r and the Zener diode ZD) with the integrator of the resistor R and the capacitor C, and turns on the transistor Tr with the OR output of the drive signals DVa to DVn. There is known a structure in which the electric discharge is performed (see, for example, Japanese Patent Application Publication No. Sho 62-38150).

In this conventional technique, the capacitor C is charged without printing and discharged with printing. When printing is continuously performed, the charging voltage E of the capacitor C is reduced to detect heat storage.

Further, as another conventional technique, a method has been known in which the density of current pulses is totaled by the arithmetic processing of the processor from the drive signals DVa to DVn of the heating resistors 10a to 10n to calculate the heat storage amount.

[Problems to be solved by the invention]

However, in the former conventional technique, the drive signal DV
Since the charge / discharge characteristics are constant regardless of the pattern of a to DVn (that is, the print pattern) and gradation (pulse width and current value), it is possible to accurately detect the heat storage amount for changes in the print pattern and gradation recording. There was a problem that I could not.

Further, in the latter conventional technique, in order to obtain an accurate heat storage amount for a change in a print pattern or gradation recording, it is difficult and time consuming to create the program, and a high-speed processor is required. is there.

An object of the present invention is to provide a heat storage detection device for a thermal head that can accurately detect the heat storage amount with respect to a print pattern or gradation change.

[Means for solving problems]

 FIG. 1 is an explanatory view of the principle of the present invention.

In the figure, the same components as those shown in FIG. 4 are designated by the same symbols, 2 is a detection resistor for detecting the recording current flowing through the heating element groups 10a to 10n of the thermal head, 3 is a differential amplifier, which determines the detection voltage of the detection resistor 2, 4 is an integrator, which charges and discharges the output of the differential amplifier 3, 5 is a charge and discharge control circuit, and the differential amplifier 3 That controls the charge and discharge of the integrator 4 by the output of
6 is a comparator, which is the output of the integrator 4 (integrated voltage)
From which the heat storage detection signal TS is output.

[Action]

The heat storage of the thermal head 1 is proportional to the power consumed by the head 1.

This power consumption can be detected by the recording current of each heating element 10a to 10n, and the power consumption can be obtained by integrating the voltage across the detection resistor 2.

Therefore, the voltage waveform of the detection resistor 2 is amplified by the differential amplifier 3 and input to the integrator 4.

The integrator 4 is charged by the charge / discharge control circuit 5 when the recording current is flowing, and is discharged when the recording current is not flowing.

When this is repeated and the output of the integrator 4 is detected by the comparator 6 to exceed a certain value, the heat storage detection signal TS is output because the heat storage has exceeded the limit.

As a result, it is possible to accurately detect the accumulated heat following the print pattern and gradation recording, and the configuration can be simple and can be realized at low cost.

〔Example〕

 (A) Description of one embodiment FIG. 2 is a configuration diagram of one embodiment of the present invention.

In the figure, the same components as those shown in FIGS. 1 and 4 are denoted by the same symbols.

The integrator 4 includes an adjusting resistor r and a first analog switch.
40, a capacitor C, a resistor R, and a second analog switch 41.

The charge / discharge control circuit 5 includes an amplifier 50 and a slice level Vh.
And a inverting circuit 52 that inverts the charging pulse and emits a discharging pulse.

FIG. 3 is an operation waveform diagram of one embodiment of the present invention, and the operation of the configuration shown in FIG. 2 will be described with reference to FIG.

A current is supplied to each of the heating elements 10a to 10n from the power source + V _EE through the detection resistor 2.

Therefore, the current flowing through the detection resistor 2 corresponds to the recording current of the head 1, that is, the sum of the currents flowing through the heating elements 10a to 10n.

That is, even when gradation recording is performed by pulse width control (energization time control), a current proportional to time can be detected, and even if the print pattern changes, a current proportional to this can be detected.

When a recording current flows in the head 1 by the drive signals DVa to DVn, a voltage is generated at both ends a and b of the detection resistor 2.

The potential at point a is Va in Fig. 3, and the potential at point b is Vb in Fig. 3.
Becomes

The potentials at points a and b are input to the differential amplifier 3, and an amplified waveform is output with SG (signal ground) shown in the detection potential (potential c) in FIG. 3 as a reference.

This detected potential is amplified by the amplifier 50 of the charge / discharge control circuit 5 and becomes the amplified output of FIG.

This amplified output is input to the comparator 51 and sliced at the slice potential Vh of a constant level.

The comparator 51 outputs a charging pulse (potential e) which becomes high level when the amplified output is higher than the slice level Vh.

This charging pulse becomes high level only when the recording current is flowing.

Further, the inversion circuit 52 inverts the charging pulse to create a discharge pulse as shown in FIG.

Therefore, when the recording current flows, the charging pulse becomes high, the first analog switch 40 of the integrator 4 is turned on, and the second analog switch 41 is turned off. Therefore, the detection potential from the differential amplifier 3 is a resistance. The capacitor C is charged through r.

 That is, the integrated value of the recording current is output to the integrator 4.

When the recording current does not flow, the charge pulse is at a low level, the first analog switch 40 is off, and the discharge pulse is at a high level and the second analog switch 41 is on, so that the capacitor C is charged. The voltage discharges through the resistor R.

Since the charge of the integrator 4 corresponds to the heat storage of the head 1,
By adjusting the values of the resistor r and the capacitor C, the heat storage characteristic and the charging characteristic can be made proportional.

Further, since the discharge of the integrator 4 corresponds to the heat radiation of the head 1, by adjusting the values of the resistor R and the capacitor C,
It is possible to make the heat dissipation characteristic and the discharge characteristic proportional.

The output (g-point potential) of the integrator 4 is input to the comparator 6 and compared with a predetermined limit level Vs. When the g-point potential becomes higher than the limit level Vs, it means that the heat accumulation in the head 1 becomes large, The output of 6 becomes high level like the potential at point h in Fig. 3, and by this heat storage detection signal TS,
As described above, the widths of the drive signals DVa to DVn are controlled to be small.

When the potential at the point g becomes smaller than the control level Vs again, the heat storage of the head 1 becomes small, the heat storage detection signal TS becomes low level, and the widths of the drive signals DVa to DVn are restored.

Note that instead of the comparator 6, the output of the integrator 4 is
The width of the drive signal may be controlled by inputting it to the A / D converter and inputting this output to the CPU.

In this way, the detected potential according to the print pattern and gradation can be integrated, and the heat storage can be accurately detected.

Further, the circuit configuration is simple and small, and it can be realized at a low cost and without requiring a space.

 Furthermore, real-time detection is possible, and followability is good.

(B) Description of Other Embodiments In the above embodiments, the line thermal head used in the thermal transfer printer has been described. However, the line thermal head may be used in a thermal printer, and the thermal head may also be a resistance wire type, a thin film type, or a thick film type. Any type.

Also, the gradation recording by controlling the energization time has been described as an example.
The same can be applied to gradation recording by current value control.

Although the present invention has been described with reference to the embodiments, the present invention can be variously modified according to the gist of the present invention, and these modifications are not excluded from the present invention.

〔The invention's effect〕

As described above, according to the present invention, there is an effect that the heat accumulation can be accurately detected by following the change of the print pattern and the gradation recording, which contributes to the stabilization of the recording quality, and is simple and small. There is also an effect that it can be constructed at a low cost, and such a function can be easily realized in the printer.

[Brief description of drawings]

 FIG. 1 is an explanatory view of the principle of the present invention, FIG. 2 is a configuration diagram of an embodiment of the present invention, FIG. 3 is an operation waveform diagram of an embodiment of the present invention, and FIG. 4 is an explanatory diagram of a conventional technique. In the figure, 1; thermal head, 10a to 10n; heating element, 2; detection resistor, 3; differential amplifier, 4; integrator, 5; charge / discharge control circuit, 6; converter.

Claims (1)

(57) [Claims] 1. A heating element group (10a to 10n) of a thermal head.
Detection resistor (2) for detecting the recording current flowing through
A differential amplifier (3) for obtaining the detection voltage of the detection resistor (2); and an integrator (4) for charging and discharging the output of the differential amplifier (3).
A charge / discharge control circuit (5) for controlling charge / discharge of the integrator (4) by the output of the differential amplifier (3), and a comparator (5) for outputting a heat storage detection signal from the output of the integrator (4). 6) The heat storage detecting device for a thermal head, characterized in that