JPS61118268A - Thermal serial type video printer - Google Patents

Abstract

PURPOSE:To stabilize the density and tonality of printing by a method in which applied power to a head in a comparatively short period is corrected, applied power to the head in a comparatively long period is corrected by detecting the heating condition of resistors by a thermister for finely controlling the density of printing by double correcting functions. CONSTITUTION:The output 8 of a head voltage control circuit 7 is supplied through a detection circuit 9 for applied current to the head to the head 1. The current value detected as voltage is fed back as the output signal 10 of the circuit 9 to a head voltage control circuit 7. The output 11 of a thermister set adjacently to resistors is also fed back to the circuit 7. Short-period temperature rise or change of the heating resistor of the head is detected by average values integrated in the range of about 1 second of current amount to the head 1. The long-period temperature rise or change is detected by the resistance value of the thermister. These detected outputs are fed back to the circuit 7 to regulate applied voltage to the head 1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a thermal serial type video printer that is suitable for obtaining hard copies of television screens and is capable of imparting stable gradation to the print density of copies.

[Background of the invention]

In recent years, there has been an increasing demand for an inexpensive notebook computer for selecting a specific television screen and making a hard copy of it.

A home notebook copying device that can print television broadcast screens with density gradations is already on the market, using a heat-sensitive line head that spans the entire horizontal width of the television screen, similar to facsimile devices. There is.

This device uses a thermistor attached to the back of the head to stabilize the printing density against increases in line head temperature, and utilizes the fact that the resistance value of the thermistor changes as the head temperature increases. The printer is designed to adjust the voltage pulse width applied to the head to stabilize the print density even in the face of changes in ambient temperature or increases in the temperature of the head itself due to continuous printing. However, this device has some problems in terms of price because the line head that spans the entire width of the screen in the horizontal direction is relatively expensive.

In other words, so-called home appliances must first be inexpensive, have excellent performance, and be designed to be suitable for mass production. An inexpensive printing method uses a thermal serial head, which is used in printers for small personal computers, but when this method is used as a video printer, the temperature rise of the head must be controlled more precisely. Without it, it would be difficult to stabilize the printing density to maintain correct density gradation, and it would be impossible to increase the printing speed.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a small, low-noise, low-cost video printer for home use that uses a heat-sensitive serial system, has stable print density, and can maintain correct print density gradation.

[Summary of the invention]

In order to achieve the above object, the present invention connects a resistor in series to the head application power supply circuit, and detects the short-term average power applied to the head from the voltage across this resistor. In addition to correcting the power applied to the head over a relatively long period of time by detecting the angular heating state of the resistor using a thermistor, these dual correction functions allow fine control of print density. In this way, the print density and gradation are stabilized against head temperature changes caused by various causes.

Print density wIl with thermal serial video printer
! In order to maintain the ll stably, it is necessary to appropriately control the power applied to the head in response to changes in ambient temperature and the heat storage characteristics of the head itself due to head energization. When a 7-real head is used, it is not possible to take a long time when the head is not energized, so it has become particularly important to precisely and appropriately control the power applied to the head.

Therefore, in order to detect the current applied to the head, a resistor is connected in series to the power supply circuit to the head, the average current flowing to the head is detected from the voltage across this resistor, and the result is sent to the head voltage control circuit. The system returns to the system by predicting short-term (about 1 second) changes in the heat storage state of the heat-generating resistor portion of the head due to the power applied to the head, and changing the voltage or pulse width applied to the head to generate a relatively short-term change. In addition to stabilizing the printing density, a thermistor is placed close to the resistor, and the resistance change of the thermistor due to the heat generated by this resistor is fed back to the head voltage control circuit, and the power applied to the head is adjusted. The aim was to stabilize the printing density.

[Embodiments of the invention]

FIG. 1(a) is a circuit block diagram of one embodiment of the present invention. The thermal head 1 is composed of several to dozens of heating resistor dots arranged in the vertical direction of the printing screen.

The image printing function control circuit 2 processes the image signal input from the terminal 3, and applies the voltage to the heating resistor of the head so that the desired print density is obtained by the corresponding head corresponding to each position of the image. Power is controlled via signal line 4.

Although not shown, there is a storage device that stores a specific screen that is designated to be taken as a hard copy, and the density tone of the screen stored at the address corresponding to each pixel of this device is used as an image signal. It is entered as . In addition to controlling the pulse voltage applied to the head, the image printing function control circuit 2 also has functions such as driving paper and setting print density conditions, but this figure only shows the function of controlling the voltage applied to the head. The output 6 of the head power supply circuit section 5 is inputted to the head voltage control circuit 71C. Output 8 of head voltage control circuit 7
is supplied to the head 1 via a current detection circuit 9 applied to the head. In the applied current detection circuit 9, the current value detected as the voltage across the resistor connected in series to the above-mentioned power supply is fed back to the head voltage control circuit 7 as an output signal 10 of the applied current detection circuit 9. is input. In addition, the thermistor (according to resistance change) installed close to the resistor
The output 11 is also fed back into the head voltage control circuit 7. Short-term temperature rises or changes in the head heating resistor caused by energizing the head for printing operations are detected by averaging the amount of current flowing to the head integrated over a range of approximately 1 second, and , for long-term head temperature increases or changes,
Detection is performed based on the resistance value of the thermistor, and the respective detection outputs are fed back into the head voltage control circuit 7 to adjust the voltage applied to the head. It can be corrected. In other words, a thermistor alone cannot capture the ever-changing tendency of minute temperature changes in the head, which has a small but inevitable heat storage capacity (temperature inertia).
The idea is to compensate for this point by detecting the average value of the current flowing to the head within a short period of time.

FIG. 1(b) shows a specific example of internal connections of the head voltage control circuit 7, the current detection circuit 9 applied to the head, etc. in one embodiment of the present invention. The head voltage control circuit 7 includes an output transistor 12 and a voltage control transistor 13.
and its peripheral elements, and by changing the base voltage of the voltage control transistor 13, the voltage of the output 8 can be changed. The circuit 9 for detecting the current applied to -\rad has a resistor 16 and a transistor 17 connected in parallel to the current detecting resistor 14, and obtains a detection signal on the collector side of the transistor 17 in proportion to the current flowing to the head. The diode 15 is a diode for correcting the voltage between B and 1 of the transistor 17. In order to obtain a value obtained by integrating the current applied to the head over a range of approximately 1 second, the output of the transistor 17 is
A resistor 18 and a capacitor 19 are connected. The output 10 is a voltage control transistor 13 of the head voltage control circuit 7.
In order to control the base voltage of the transistor 13, the base voltage of the transistor 13 is applied superimposed on the ground side voltage of the setting resistor, and the pace voltage of the transistor 17 is increased in response to a change (increase) in the current applied to the head. 13 to lower the voltage applied to the head and adjust the power applied to the head. In addition, a thermistor 2 is placed close to the current detection resistor 14.
0 is connected and placed, and the thermistor 2 is
Let the temperature of 0 rise. The base voltage of the transistor 13 is controlled by the resistance change due to the temperature rise of the thermistor 20. Here, the conditions for correcting the change in print density caused by the temperature rise of the head due to head energization are set by the resistor 14, the thermistor 2o, the heat conduction conditions between them, and the base voltage control 1] condition of the voltage control transistor 13. By setting a constant according to the relationship, it is possible to stabilize changes in print density caused by head temperature rise due to the head's ambient temperature and current supply.

In this embodiment, the voltage applied to the head is controlled to finely adjust the printing density. The print density can also be adjusted by connecting to the peripheral circuit and changing the pulse width for controlling the power applied to the head.

〔Effect of the invention〕

As explained above, according to the present invention, the heat generation temperature of the head heating resistor rises in a short time due to printing operation (a temperature change of about 1 second, which is within a time period that cannot be detected by a temperature detection element such as a thermistor attached to the head). It is possible to correct the print density change due to K (temperature change of K), and it is also possible to detect the heat generation state of the resistor for detecting the current applied to the head at the same time, instead of detecting the actual temperature rise of the head. As a result, there is no need to attach a temperature sensing element to the head itself, and it can be integrated in the power supply circuit and control circuit (separated from the head), improving productivity and helping to reduce costs. .

[Brief explanation of the drawing]

FIG. 1(a) is a circuit block diagram of one embodiment of the present invention.
Figure (b) is a diagram showing a specific example of internal connections of the main parts of the embodiment. 1...Thermal head 2...Image printing function control circuit 3...Image signal input terminal 5...Head power supply circuit section 7... Head voltage control circuit 8... Head applied voltage output 9... Current applied to the head detection circuit 10...
... Head current detection signal output 11 ... Thermistor output 12 ... Head applied voltage control output transistor 13 ... Head applied voltage control transistor 14
...Head current detection resistor 15...Voltage correction diode 16...Current detection circuit resistor 17...Current detection transistor 18...
...Current detection circuit resistor 19...Current detection circuit capacitor 20...
...Thermistor. X 1 Figure (b)

Claims (1)

[Claims] In a thermal serial video printer that has a density gradation control function, a resistor is connected in series to the head application power supply circuit, and the short-term average power applied to the head is detected from the voltage across this resistor. In addition to correcting the head applied power, a thermistor detects the heat generation state of the resistor to perform relatively long-term head applied power correction.These dual correction functions control the printing density to correct the short-term head A thermal serial type video printer that is characterized by being able to stabilize printing density even in the face of minute temperature changes.