JPS60203472A - Pulse width controller for drive pulse of heating resistor - Google Patents

Abstract

PURPOSE:To compensate for the deterioration of picture quality by controlling effects of the variation in the voltage of power source and also in the temperature of a recording head with varying loads by a method in which a drive power source is supplied to heating resistors on the basis of pulse width from comparison of the output levels of an integrator and a temperature detector. CONSTITUTION:Terminal voltage Vt of a thermister 1 is applied to the plus (+) side input terminal of a comparator 3. An integrator 10 to integrate power source voltage E for driving the thermal head is made up of a resistor 4 and a condenser 5, and its integration output SI is applied to the minus (-) side input terminal of the comparator 3. A transistor 6 forms a discharge circuit to reset the integrator 10 and is driven by trigger pulse PT. The pulse width of drive pulse PD sent out from the comparator 3 is greater, the lower the power source voltage E becomes, but the pulse width is smaller, the higher the voltage E becomes. The pulse width tau is longer, the lower the voltage E becomes, and also the pulse width is shorter, the lower the output voltage Vt of the thermister 1 becomes with the rise of the temperature of the base plate. In the opposite case, opposite actions result.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a thermal recording device, and more particularly to a resistance heating element drive, movement, pulse width control device for controlling the drive pulse of a recording head in a thermal recording device.

In the recording section of conventional technology facsimile 7mm machines, thermal transfer printers, etc.
Thermal head (
Some devices record images, characters, etc. on paper using a recording head (recording head).

For example, a standard facsimile IJ device is equipped with a thermal guide having a width of about 216 mm IJ meters so that it can record on A4 size thermal paper. Recording pixel density: 8 dots/
In terms of millimeters, this thermal head has 172 mm.
Eight heating resistors are arranged.

Each heating resistor is connected to a driving power source via a switching element such as a transistor, and each switching element is turned on and off by a recording control section. In this way, one line is recorded one after another. Therefore, since an arbitrary number of thermal heads from 1 to 1728 are driven at a time, the load on the thermal head power source fluctuates significantly.

To compensate for this load fluctuation, a load capacitor can be attached to the power supply, but such a load capacitor must have a very large capacity, for example, about 56,000 microfarads, which increases the cost of the power supply. This caused an inconvenience.

For example, the recording apparatus described in Japanese Patent Application Laid-Open No. 54-161949 controls the width of the pulse for driving the recorder so that the integral value of the recording power becomes constant. However, this configuration requires a power integration circuit and a multiplication circuit, making the configuration complicated, and it is not possible to cope with temperature changes in the thermal head substrate only by controlling based on the power integral value.

Purpose The present invention eliminates the drawbacks of the prior art, suppresses the effects of fluctuations in power supply voltage due to changes in load over time, large current drive, etc., and changes in temperature of the recording head, and compensates for deterioration in image quality. The object of the present invention is to provide a guru width control device with a simple configuration.

Configuration The configuration of the present invention will be described below based on one embodiment.

FIG. 1 shows an embodiment in which the present invention is applied to drive pulse control of a recording head of a thermal recording device. In the same figure,
l is a thermistor that detects the substrate temperature of the thermal head (path shown), 2 is a current limiting resistor, and the terminal voltage Vt of thermistor l (see Figure 2 (b)) is applied to the + side input terminal of comparator 3. ing. In addition, the resistor 4 and capacitor 6 are connected to the power supply voltage E for driving the thermal head.
Configure an integrator IO that integrates and its integral output SI (
(see FIG. 2(b)) is applied to one side input terminal of the conducer 3. The transistor 6 forms a discharge circuit that resets the integrator lO. )).

Therefore, the drive nors P output from the controller and the rotor 3
D is the trigger virus P as shown in Figure 2 (C).
The logic level is H from the time when T is received until the integral output SI becomes larger than the voltage Vt. This drive pulse PD controls the ON period τ of the thermal head. The resistance value of resistor 4 is R, and the capacitance of capacitor 5 is C.
Then, with this pulse width, r--CRtn (IVt/E) (1) By the way, as is well known, the temperature of the thermal substrate is proportional to the applied energy supplied to the thermal head. . Further, the terminal voltage V of the thermistor I is configured to change linearly with a negative slope with respect to changes in substrate temperature. Therefore, when the applied energy (power supply voltage E in this case) supplied to the thermal head changes, the terminal voltage vt of the thermistor 1 changes with a negative slope. That is, as the applied energy decreases, the terminal voltage vt of the thermistor l increases, and conversely, as the applied energy increases, the terminal voltage vt of the thermistor l decreases.As a result, the + side input of the comparator 3 is It increases, and changes to decrease as the power supply voltage E increases.

On the other hand, the integral output SI of the integrator IO has a gradual rising slope when the power supply voltage E becomes low, and a rising slope becomes steep when the power supply voltage E becomes high.

Therefore, the pulse width of the driving d' pulse PD outputted by the converter 3 becomes larger as the power supply voltage E becomes lower, and conversely becomes smaller as the power supply voltage E becomes higher. As a result, one recording cycle (one cycle of Triganoculus PT)
The total amount of applied energy supplied to the thermal head in , remains approximately constant regardless of fluctuations in the power supply voltage E. In other words, in the range of 2V and (E), from equation (1),
Approximately negative 1 is the width of the drive pulse with respect to the substrate temperature.
We will take the following proportional relationship. This slope depends on the value of CR.

Therefore, as shown in FIG. 2, if the power supply voltage E decreases, the pulse width τ increases, and if the substrate temperature increases and the output voltage vt of the thermistor I decreases, the pulse width τ decreases. Of course, for the reverse of this and that, the movements are reversed.

'Therefore, even if a large number of heat-generating resistors are driven at once by the thermal head, such as in an all-black or horizontally ruled image, and a large current flows, or if voltage fluctuations occur due to changes in the device over time, etc., the specified level will always be maintained. energy can be supplied to the thermal head.

To give a specific example, the resistance R1 of the thermal head heating element is set to 2.
000, recording voltage E is IIV, driver saturation voltage Vs
If at is 1v, it becomes O, Smi.

Assuming that the recording voltage is reduced by 10 degrees, in the case of the conventional method without pulse width compensation, the applied energy is reduced by 20 degrees compared to 0.5 millijoules.

However, in the circuit of this embodiment, the thermistor voltage Vt
=5V, when the recording voltage E75 is decreased by 10 degrees, the pulse width τ increases as follows.

Therefore, the applied energy is 04 millijoules x 116
times = 0.464 millijoules, which indicates that the 20% decrease in applied energy is compensated for by approximately 7%.

Effects As explained above, according to the present invention, when a power supply voltage fluctuation occurs, it is approximately compensated for by an integrating circuit and a comparator circuit with a simple configuration. etc., and has the effect of preventing deterioration of image quality with a simple configuration.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment in which the nosol width control device according to the present invention is applied to the thermal recording head drive grooveless control of a thermal recording device. FIG. 2 is an explanation of the operation of the device shown in FIG. 1. It is a waveform diagram used. One sign of the main part, one link...Thermistor 2.4...Resistor 3...Comparator 5...Capacitor 6...Transistor

Claims (1)

[Scope of Claims] A pulse width control device that supplies drive power to a resistive heating element in a pulsed manner and controls the pulse width, the device comprising: a pulse width control device that is reset by a timing signal that indicates the driving timing of the resistive heating element; , an integrator that integrates the voltage of the drive power source, and a temperature detector that detects the temperature of the resistive heating element.The output level of the integrator and the output level of the temperature detector are compared to determine whether the former is higher than the latter. a comparator that outputs an output signal indicating that the current is low, and supplies the driving power to the resistive heating element with a pulse width corresponding to the output signal of the comparator. Noculus width control device for drive pulses.