JPS6351104B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal recording apparatus that corrects non-uniformity of images recorded by a thermal recording head.

A thermal recording apparatus using a thermal recording head is equipped with a drive circuit for selectively driving a large number of heating resistors on the thermal recording head in accordance with image signals.

FIG. 1 shows an example of a drive circuit, and in order to simplify the explanation, the number of heating resistors arranged on the thermal recording head 1 is shown to be much smaller than the actual number. A voltage for causing each heating element to generate heat is applied from a constant voltage power source (not shown) to the voltage supply terminal V _ps of this drive circuit, and two source driver signal terminals S 1 and S ₂ are connected to two source driver signal terminals S ₁ and S 2 . A pulse signal is supplied to alternately turn on the common terminal switch elements Q ₁ and Q ₂ . Furthermore, the five sync driver signal terminals D ₁ to _{D 5} are supplied with image signals for pixels corresponding to the heating resistors R ₁ to R ₁₀ arranged on the thermal recording head. Each sink driver signal terminal _D1 to _D5 is connected to a corresponding control terminal (base of a transistor) of a data terminal switch element _Q3 to _Q7 , respectively. Therefore, when a pulse signal is supplied to the source drive signal terminal S ₁ and the common terminal switch element Q ₁ is conductive, the sink driver signal terminals D ₁ to _{D 5} of the data terminal switch elements Q ₃ to _{Q 7} are printed. The element corresponding to the terminal to which the desired image signal is supplied becomes conductive. Then, among the five heat generating resistors R ₁ to _{R 5} whose one end is connected to the common terminal switch element Q ₁ , the heat generating resistor whose other end is connected to the conductive data terminal switch element is energized and generates heat. While the pulse signal is supplied to the other source driver signal terminal _S2 ,
Similarly, among the other five heat generating resistors _R6 to _R10 , the heat generating resistor corresponding to the image signal is energized and generates heat.

In such a drive circuit, the common terminal switch element Q ₁ ,
The current flowing through Q ₂ changes. Accordingly, the degree of voltage drop due to the impedance of these common terminal switch elements Q ₁ and Q ₂ and the line changes accordingly, and the amount of heat generated by the heating resistors R ₁ to _{R 10} changes. For the above reasons, if the number of heating resistors that are energized at the same time differs, the recording characteristics such as recording density and the size of printed dots will differ, resulting in non-uniformity of the recorded image.

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 recording device that can correct non-uniformity of recorded images.

The present invention achieves the above object by detecting the voltage applied to the heating resistor and changing the width of the pulse applied to the heating resistor accordingly.

The present invention will be explained in detail with reference to Examples below.

FIG. 2 shows the electric circuit of the thermosensitive recording device. In this device, pulse voltages 3 and 4 alternately output from two common terminal switch elements (Q ₁ and Q ₂ in FIG. 1) in the applied pulse generator 2 are applied to the heating resistor of the thermal recording head 1. Supplied to the common terminal of each group. The recorded data 5 is supplied to a signal terminal controller (Q ₃ to _{Q 7} in FIG. 1) 6, and the signals outputted from there are respectively supplied to the other ends of heating resistors whose one ends are connected to the common terminal.

Pulse voltages 3 and 4 outputted from the applied pulse generator 2 are also supplied to a voltage controlled oscillator 7, respectively. The voltage controlled oscillator 7 samples each pulse voltage at the rising point, holds it, and changes the oscillation frequency based on the voltage value. The frequency divider 8 divides this oscillation frequency appropriately to create a pulse signal with a predetermined pulse width. A constant voltage power supply 9 is supplied to the application pulse generator 2, and generates a pulse voltage having the same pulse width as the pulse signal described above.

FIG. 3 shows the relationship between the voltage drop ΔV applied to the heating resistor and the pulse width τ in this thermosensitive recording device. When only a small number of heating resistors of the thermal recording head 1 are energized, the constant voltage power supply 9 outputs, for example, 15V.
The voltage is applied to the heating resistor with almost no drop. At this time, the voltage controlled oscillator to which a voltage of approximately 15V is applied oscillates at 20KHz. The frequency divider 8 divides this signal at a constant frequency division ratio to create a pulse signal having a pulse width of 0.5 msec. Therefore, in this case, the heating resistor is energized with a voltage of 15V for 0.5msec and generates heat.

On the other hand, when a group of heating resistors arranged in a line are all energized at the same time, such as when printing black ruled lines, the constant voltage power supply 9
The 15V voltage output from the 15V voltage drops by, for example, 4V and is applied to each heating resistor. At this time, the voltage controlled oscillator 7 to which a voltage of 11V is applied is
Oscillates at 10KHz. The frequency divider 8 divides this signal at a constant frequency division ratio to create a pulse signal having a pulse width of 10 msec. Therefore, in this case, the heating resistor is
A voltage of 11V is applied for 1.0msec, and the uniformity of the recording density is similarly maintained.

In this manner, according to the present invention, the pulse width of the applied pulse is varied in accordance with the drop in voltage applied to the heating resistors of the thermal recording head 1, so that the pulse width of the applied pulse is varied regardless of the number of heating resistors that are energized at the same time. The recording density of each heating resistor can be kept uniform. In addition, in the present invention, since the width of the pulse applied to the thermal recording head is changed, if the width of the change is compensated according to the temperature of the substrate of the thermal recording head and the temperature of the outside air, it can be used under any environment. It becomes possible to make the recording density of the recording paper uniform.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an outline of a drive circuit for a thermal recording head, FIG. 2 is a block diagram showing the main parts of a thermal recording device in an embodiment of the present invention, and FIG. 3 shows a pulse width τ plotted on the vertical axis. FIG. 3 is a characteristic diagram of the device of the above embodiment in which the voltage drop ΔV is plotted and the oscillation frequency of the voltage controlled oscillator is plotted on the horizontal axis. DESCRIPTION OF SYMBOLS 1...Thermal recording head, 2...Applying pulse generator, 6...Signal terminal controller, 7...Voltage controlled oscillator.

Claims (1)

[Claims] 1 A thermal recording head equipped with a large number of heat generating resistors, a drive circuit that selectively energizes the heat generating resistors at the same timing according to an image signal, and a voltage applied to the heat generating resistors from this drive circuit. a detection means for detecting the voltage drop; and a pulse width setting means for increasing the pulse width of the pulse signal for driving the heating resistor input to the drive circuit in accordance with the voltage drop detected by the detection means. A thermal recording device comprising: