JPH0478548A - Control circuit of thermal head - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a control circuit for a thermal head installed in a facsimile machine, a printer, etc.

[Conventional technology]

Conventionally, for example, in a thermal head of a facsimile machine, data to be transferred is compressed, so the printing time for one line changes depending on the content of the data. Therefore,
It is also necessary to change the energy applied to the thermal head, but with conventional technology, these processes are handled on the facsimile machine side, that is, in the external peripheral circuit of the thermal head, without having this function in the circuit inside the thermal head. was being done.

In such conventional devices, when the printing speed of the previous line is fast or the printing rate (black rate) is high, the temperature of the resistor of the thermal head is rising, and no control is applied to it. When energy is added to the next line, the resistor temperature may continue to rise, causing problems such as the output print density changing even when the same data is input.

In order to prevent such problems, the above-mentioned external peripheral circuit of the thermal head has been used.

More specifically, the problem was addressed on the system side that uses the thermal head as a component.

FIG. 3 shows the configuration when external peripheral circuits are used. In order to obtain high-quality images, this circuit requires a large memory circuit to refer to data from several lines before, and the recording control section also becomes complicated.

On the other hand, some thermal heads have a thermal history control function to solve the above problem.

FIG. 4 shows a configuration diagram of a thermal history control thermal head, and FIG. 5 shows an example in which an IC is used in the data conversion circuit section. As is clear from FIG. 5, although this method also provides high image quality, it is very complicated and is not used in facsimile machines below intermediate level due to cost issues.

[Problem to be solved by the invention]

As mentioned above, conventional thermal heads do not have the function to control the applied energy, and the peripheral circuitry has to take over that function, making the peripheral circuitry complex and requiring time and effort to make adjustments. It is difficult to obtain the desired print quality and the cost is high. Furthermore, those having a control function on the thermal head side require a complicated circuit, which is also problematic in terms of high cost.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a thermal head that can simplify the peripheral circuits of a facsimile machine and the like and improve printing quality.

(Means for Solving the Problems) A thermal head according to the present invention charges a capacitor in synchronization with a latch signal, controls discharging of the capacitor using a data signal, and generates a printing energy control signal. to drive.

(Function) The thermal head according to the present invention utilizes the discharge phenomenon of a capacitor to control printing speed and printing rate by turning on a switch.
By using it for OFF control, it outputs a reference voltage, that is, a print energy control signal, which is approximately correlated with the temperature of the thermal head.

[Embodiments of the invention]

The present invention is a type of thermal history thermal head shown in FIG. Conventionally, the data conversion circuit section shown in FIG. 4 was composed of a dedicated IC, as shown in FIG. 5. The present invention simplifies this without sacrificing functionality.

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, Vo is the reference voltage for charging the capacitor Co, and SWI is a switch controlled by the LAT (:H signal) externally applied to the thermal head. This is the printing speed itself.Resistance R is one of the time constants that determines the discharge time of capacitor CO.(1) is an AND gate, (2) is inverter 1, and DATA and CL
D while reading DATA using two types of OCK signals.
When the ATA signal is "H", SW2 is turned OFF. (3
)'s inverter 2, resistor R4, and capacitor C0 are also set to SW3.
5If3 turns OFF while reading DATA.

Resistor R7 and resistor R3 are SW2 and 5113, respectively.
When turned on, the capacitor Co is discharged with a time constant determined by the resistor R1. V out is taken out as a signal for controlling the energy applied to the thermal head.

Next, the operation will be explained. In Fig. 2 (A), the SWI
, SW2, and SW3 are controlled and the discharge state of the capacitor Co is shown in FIG. 2(B).

First, when LATf':H is input, 5w1 turns ON.
Since SW2 and SW3 are OFF, the capacitor Co is charged with the reference voltage VO. After charging, SWI
is turned OFF. After that, during the DATA reading period, DATA is "L", that is, in the case of white printing, SW2
turns ON and discharges the capacitor CO with a time constant determined by τ=(R+ +R2)xCo. When DATA is "H", that is, black is printed, SW2 is turned off and the discharge of the capacitor CO is temporarily stopped.

That is, in the case of DATA with a high printing rate (black rate), the Vout voltage is maintained high because the discharge is temporarily stopped.

When the DATA reading is completed, the next L A T C
SW2 is OFF and SW3 is OFF until 11 is input.
N, and the capacitor Co is discharged with a time constant determined by τ=(R+ +R3)xCo. SWI resets the capacitor, SW2 depends on the printing rate (black rate),
SW3 controls the discharge of the capacitor Co by the interval (printing speed) of LAT[l:H. Therefore, new 1.
The level of V out immediately before ATCH is manually input has a low printing rate (black rate), and the lower the printing speed is, the lower it becomes. The level of VouL is the same as the voltage application state to the resistor of the thermal head, that is, the temperature state. Therefore, if V out is taken out as a signal, the temperature state of the thermal head resistor can be inferred based on the level of the signal, and it can be used as a control signal for applied energy. For example, if V out is high, the temperature of the resistor of the thermal head is considered to be high, and unless the applied energy is lowered, problems such as density unevenness, burn-in, etc. will occur.

Further, in the above embodiment, the case where the Vout voltage is taken out to the outside has been explained, but the Vout voltage is taken out inside the thermal head.
The t voltage is fed back to the common voltage (voltage applied to the resistor), and the common voltage, which is normally constant, is
The applied energy may be controlled by changing it according to the height of t. In this case, an external applied energy control circuit is not required.

〔Effect of the invention〕

As described above, according to the present invention, since the reference voltage (Vout) obtained from the printing speed and printing rate is output to the outside, the applied energy control circuit of the external circuit can be simplified and the printing quality can be improved. This has the effect of providing a thermal head with a simple configuration.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are diagrams according to one embodiment of the present invention.
The figure is a circuit diagram for determining the reference voltage (Vout). Figure 2 (A) shows CLOCK-DATA-t, ATCH
FIG. 2(B) is a timing chart showing the input signal of 5W1, SW2, and ON/OFF timing of 5W3, and FIG. 2(B) is a diagram showing the discharge state of the capacitor Co. 3 to 5 show conventional examples; FIG. 3 is a configuration diagram of a circuit for controlling energy applied to a thermal head on the facsimile machine side; FIG. 4 is a configuration diagram of a thermal history control thermal head;
FIG. 5 is a configuration diagram of the data conversion circuit section of the thermal history control thermal head. (1) is an AND gate, and (2) and (3) are inverters. In Figure 1, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] A reference voltage, a latch signal that provides a printing speed specified by a time interval, and a data signal that indicates a printing rate are input, and the capacitor is charged in synchronization with the latch signal.
A control circuit for a thermal head, characterized in that the control circuit for a thermal head generates a printing energy control signal by controlling discharge of the capacitor using the data signal of the printing rate.