JPH01128852A - Heat accumulation detector for thermal head - Google Patents

Abstract

PURPOSE:To accurately detect the quantity of heat accumulated, by providing a detecting resistance for detecting a recording current passed through a group of het generating elements of a thermal head, a differential amplifier for obtaining the detected voltage, an integrator to be charged with the output of the differential amplifier and discharged, and a comparator for outputting a heat accumulation detection signal based on an output from the integrator. CONSTITUTION:Heat accumulation in a thermal head 1 is proportional to consumption of electric power by the head 1. The power consumption can be detected by a recording current passed through each of heat generating elements 10a-10n, and is obtained by integrating the voltage acorss a detecting resistor 2. A voltage waveform obtained through the detecting resistor 2 is amplified by a differential amplifier 3, and is inputted to an integrator 4, which is charged when the recording current is flowing and which is discharged when the recording current is not flowing, under the control of a charging/discharging controlling circuit 5. This operation is repeated, and when an output from the integrator 4 is detected to be more than a predetermined value by a comparator 6, it is judged that a limit of heat accumulation is exceeded, and a heat accumulation detection signal TS is outputted. By this, it is possible to perform accurate detection of heat accumulation following up to printing patterns or gradational recording, and a construction for the detection is made easy and inexpensive.

Description

[Detailed description of the invention] [Table of contents] Overview Industrial field of application Prior art (Figure 4) Problems to be solved by the invention Means for solving the problems (Figure 1) Working examples (a ) Description of one embodiment (Figures 2 and 3) (bl Description of other embodiments Effects of the invention [Summary] Regarding a heat accumulation detection device that detects the heat accumulation state of a thermal head driven in multiple gradations, printing pattern The purpose of this system is to accurately detect the amount of heat stored in response to changes in temperature and gradation, and includes a detection resistor to detect the recording current flowing through the heating element group of the thermal head, and a differential amplifier to determine the detection voltage of the detection resistor. an integrator that charges and discharges the output of the differential amplifier; a charge/discharge control circuit that controls charging and discharging of the integrator based on the output of the differential amplifier; and a heat accumulation detection signal output from the output of the integrator. It has a comparator.

[Industrial application field]

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

A thermal transfer printer or a thermal printer uses a thermal line head in which a large number of heating resistive elements are arranged in a negative row.

When a thermal line head performs continuous recording such as solid printing for a long time, the head accumulates heat.

When the head accumulates heat, print quality deteriorates such as density changes and resolution deterioration, especially when performing multi-gradation printing by changing the peak value or pulse width of the recording current pulse.

Heat storage is proportional to the amount of power consumed by the head, so if heat storage that adversely affects printing occurs, lower the peak value of the recording current pulse or narrow the pulse width to reduce the power consumed by the head. It is necessary to perform control to reduce the amount of heat and then return the current pulse to its original state when the amount of accumulated heat decreases.

Therefore, there is a need for a heat accumulation 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 constructed by connecting n heat generating resistors 10a to 10n and drive transistors lla to 1lrt in series in parallel to a power supply +VE.

Each transistor lla to lln has an individual drive signal D.
Driven by V a % D V n, current flows through desired heat generating resistors 10a to 10n, generating heat.

The conventional N heat detection device charges a divided voltage of power supply +V=ε (by resistor r and Zener diode ZD) with an integrator of resistor R1 and capacitor C, and generates drive signals DVa to DV.
A structure is known in which the transistor Tr is turned on and discharged by the OR output of n (for example, the patent application publication number 62-
(See Publication No. 38150, etc.).

In this prior art, capacitor C is charged without printing,
When the capacitor C is discharged and printed continuously, the charging voltage E of the capacitor C decreases, thereby detecting heat accumulation.

In addition, as another conventional technique, a method has been known in which the density of current pulses is totaled by arithmetic processing by a processor from the drive signal D V a '' D V n of each heating resistor 102 to 10 n, and the amount of heat storage is calculated.

[Problem that the invention attempts to solve]

However, in the former prior art, the drive signal D
Since the charging and discharging characteristics are constant regardless of the V a = D V n pattern (i.e. print pattern) or gradation (pulse width or current value), the amount of heat storage can be accurately detected based on changes in the print pattern or gradation recording. The problem was that I couldn't do it.

Furthermore, with the latter conventional technology, in order to obtain an accurate amount of heat storage for changes in print patterns and gradation recording, it is difficult to create a program, it takes a lot of calculation time, and a high-speed processor is required. be.

SUMMARY OF THE INVENTION An object of the present invention is to provide a heat storage detection device for a thermal head that can accurately detect the amount of heat storage with respect to print patterns and gradation changes.

[Means for solving problems]

FIG. 1 is a diagram explaining the principle of the present invention.

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

[Effect]

Heat storage in 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 changed by integrating the voltage across the detection resistor 2.

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

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

When this is repeated and the comparator 6 detects that the output of the integrator 4 exceeds a certain value, it is determined that the heat storage has exceeded the limit and a heat storage detection signal TS is output.

This makes it possible to accurately detect heat accumulation that follows print patterns and gradation recording, and to realize a simple and inexpensive configuration.

〔Example〕

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

In the figures, the same parts as those shown in FIGS. 1 and 4 are indicated by the same symbols.

The integrator 4 includes an adjustment resistor r and a first analog switch 4.
0, 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 v
It is comprised of a comparator 51 that compares the charging pulse with h and generates a charging pulse, and an inversion circuit 52 that inverts the charging pulse and generates a discharging pulse.

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

Each of the heating elements 10a-10n is supplied with current from the power supply +Vεε via the detection resistor 2.

Therefore, the current flowing through the detection resistor 2 corresponds to the recording current of the head l, that is, the sum of the currents flowing through the heating elements 102 to 10n.

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

When a recording current flows through the head 1 according to the drive signals DVa to DVn, voltages are generated at three points on both ends of the detection resistor 2, and at point b.

The potential at point a is Va in Figure 3, and the potential at point b is V in Figure 3.
It becomes b.

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

This output potential is amplified by the amplifier 50 of the charge/discharge control circuit 5, resulting in the amplified output shown in FIG.

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

In the comparator 51, the amplified output is at the slice level vh
When the voltage is higher than that, a charging pulse (potential at point e) that becomes high level is output.

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

Further, an inverting circuit 52 inverts the charging pulse to create a discharging pulse as shown in FIG.

Therefore, when the recording current flows, the charging pulse becomes high, turning on the first analog switch 40 of the integrator 4, and turning off the second analog switch 41, so that the detected potential from the differential amplifier 3 is r and is charged to capacitor C.

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

When the recording current does not flow, the charging pulse is at a low level and the first analog switch 4o is turned off, and the discharge pulse is at a high level and the second analog switch 41 is turned on, so that the capacitor C is charged. Voltage is resistance R
discharge through °.

Since charging of the integrator 4 corresponds to heat storage in the head 1, by adjusting the values of the resistor r and the capacitor C, the heat storage characteristics and the charging characteristics 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, the heat radiation characteristics and the discharge characteristics can be made proportional.

The output of the integrator 4 (g-point potential) 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 storage in the head 1 has increased, The output of 6 becomes high level as the potential at point h in FIG. 3 1, and the width of drive signals DVa-DVn is controlled to be small as described above by this heat storage detection signal TS.

When the potential at point g becomes smaller than the limit level Vs again, it means that the heat storage in the head l has become smaller, and the heat storage detection signal TS
becomes low level, and the drive signal [)V a %
Return the width of DV n.

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 the signal to a /D converter and inputting this output to the CPU.

In this way, it is possible to integrate the detection potential according to the print pattern and gradation, and it is possible to accurately detect heat accumulation.

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

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

fb) Description of other embodiments In the above embodiments, a line thermal head used in a thermal transfer printer was explained, but it may also be used in a thermal printer, and the thermal head may also be a resistance line type, a thin H9 type, or a thick film type. No matter the type.

Furthermore, although the explanation has been given by taking gradation recording by controlling the current supply time as an example, the present invention can be similarly applied to gradation recording by controlling the current value.

Although the present invention has been described above using examples, the present invention can be modified in various ways according to the gist of the present invention, and these are not excluded from the present invention.

〔Effect of the invention〕

As explained above, the present invention has the effect of accurately detecting heat accumulation by following changes in print patterns and gradation recording, contributes to stabilizing recording quality, and is simple and compact. It also has the effect of being able to be constructed at low cost, and such functions can be easily implemented in a printer.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the principle of the present invention, FIG. 2 is a configuration diagram of an embodiment of the present invention, FIG. 3 is an operational waveform diagram of an embodiment of the present invention, and FIG. 4 is an explanatory diagram of the prior art. In the figure, 1: thermal head, 10a-10n: heating element, 2: detection resistor, 3: differential amplifier, 4: integrator, 5: charge/discharge control circuit, 6: converter.

Claims (1)

[Claims] A detection resistor (2) for detecting the recording current flowing through the heating element group (10a to 10n) of the thermal head, and a differential amplifier (2) for determining the detection voltage of the detection resistor (2). 3
), an integrator (4) that charges and discharges the output of the differential amplifier (3), and a charge/discharge control circuit ( 5) and the integrator (4
) outputs a heat storage detection signal from the output of the comparator (6
) A heat accumulation detection device for a thermal head, comprising: