JPS6042073A - Driving method for thermal head - Google Patents

Abstract

PURPOSE:To prevent a heating element from being cooled before a predetermined density is reached and enhance recording speed, by setting the width of a pulse impressed first to be longer than that of the subsequent pulses. CONSTITUTION:Until a thermal recording paper starts forming a color or a predetermined density is reached, a pulse tau with a large width is impressed, and the number of the pulses with small width impressed thereafter is varied to control recorded density. Pulse numbers corresponding to gradation levels are written in a ROM10, signals (a) indicating the gradation levels are address-inputted, and pulse number signals (b) are outputted and are set on a counter 11. An oscillator 13 outputs a pulse (f) with a width tau, while an oscillator 12 outputs the subsequent pulses (d) with a width of smaller than tau. The counter 11 counts down the pulses (d), and when the counted value reaches 0, a resetting signal (c) is outputted by the counter 11 to reset the oscillator 12. An OR gate circuit 15 impresses current-passing pulses (g) on a thermal recording head.

Description

[Detailed description of the invention] 肱亙国亙 The present invention relates to a method for driving a thermal recording head.

A printing density control method is known in which electricity is applied to a heating element in multiple pulses and the number of pulses is controlled according to the output of a temperature sensing element (for example,

(See Japanese Patent Application Laid-Open No. 52-1'43839).

Fig. 1 is a diagram showing the relationship between the number of pulses applied to the heating element and the recording density, and Fig. 2 is a diagram showing the pulse waveform and temperature rise waveform of the heating element at this time. Color development starts at n2 and saturation density is reached at n2. Therefore, even when controlling the recording density, the number of pulses cannot be kept below nl.As mentioned above, A) recording is performed by changing the number of pulses applied to the heating element. In the head driving method that controls the density, the temperature of one heating element increases through repeated heating and cooling cycles, resulting in poor thermal efficiency and, therefore, a drawback that the recording time becomes long.

The present invention has been made to solve the above-mentioned drawbacks,
In particular, this was done with the aim of increasing the speed of recording by continuously supplying electricity until the temperature at which the thermal paper begins to develop color or until a predetermined density is reached.

1-Ichisen The configuration of the present invention will be described below based on one embodiment.

FIG. 3 is a diagram for explaining the operating principle of the present invention. As shown in the figure, a long pulse τ is applied until the thermal paper starts to develop color, and then the number of pulses applied is determined. By changing this, the same effect can be obtained, and the recording speed can be increased.

FIG. 4 is a block diagram for explaining an embodiment of halftone recording according to the present invention, in which 1o is R, OM, 11
is a counter, 12, 13 is an oscillator, 14, ], 5 is a gate circuit, and the signal a indicates the gradation level. For example, if there are 16 gradations, it is a 4-bit signal. The number of pulses corresponding to the gradation level is written in the ROM10, and when address a is input, a pulse number signal s is output. This pulse number signal is set in the counter 11. When a is at gradation level 0, the gate circuit 14 outputs a trigger signal e to the 1 oscillator 13. Oscillator 13 is one shock 1-
It outputs a pulse f having a width τ as shown in FIG.

The oscillator 1.2 is a narrower oscillator of the subsequent pulse d, and starts oscillating by a signal from a controller (not shown). The counter 11 decrements d by one number,
When the count value reaches 0, reset 1-signal C is output,
Reset the oscillator 12.

The gate circuit 15 is an OR gate, and g is a pulse for energizing the thermal recording head. Another example could be concentration compensation for environmental temperature. Even if the energy applied to the heating element is constant, if the environmental temperature changes, the recording density will change as shown in FIG.

To compensate for this, set τ so that a predetermined recording density can be obtained at the highest temperature in the operating environment temperature range, and when the temperature drops, the
Just add more pulses.

In order to realize this, a table of environmental temperature versus the number of additional pulses may be written in the ROM10 shown in FIG. 4, and a signal obtained by AD converting the temperature detected by a thermistor or the like may be used as the address manual a.

Effects As is clear from the above explanation, according to the present invention, thermal efficiency can be improved and recording speed can be increased.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between the number of pulses applied to the heating element and recording density, Figure 2 is a diagram showing the relationship between the pulse waveform applied to the heating element and the temperature rise waveform of the heating element, and Figure 3. A diagram showing the relationship between the applied pulse waveform and the temperature waveform of the heating element according to the present invention, FIG. 4 is an electrical block diagram for explaining one embodiment of the present invention, and FIG. It is a diagram showing the relationship between temperature and recording density. 10...ROM, 11...Counter, 12, 1.3
・Oscillator, 14.15...Gate circuit. Fig. 1 Fig. 2 Fig. 4r71 No. 5ffl Memorial Hall Fee

Claims (1)

[Claims] A method of driving a thermal recording head that changes the number of pulses applied to a heating element, characterized in that recording density is controlled by making the width of the first applied pulse longer than the subsequent pulses. driving method.