JPH044951B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a recording element drive control method for a recording element in a thermal recording apparatus or the like.

Structure of a conventional example and its problems FIG. 1 is a block diagram showing a general structure of a conventional thermal recording apparatus. In this figure, reference numeral 1 denotes heating elements (recording elements) arranged in a row on the thermal head, one end of which is connected to the recording power source 2.
It is connected to the. Reference numeral 3 denotes a drive circuit that drives the heating element 1 according to the image signal, including a shift register for accumulating image signals for one line, and a switching circuit that controls energization of the heating element 1 according to the image signal. It is composed of etc. A timer 4 determines the driving time of the heating element 1 and generates a signal ENB. 5 is a temperature sensor that detects the temperature of the thermal head. 6 is the input terminal for the image signal PIX, 7
is the input terminal of the transfer clock CLK, 8 is the input terminal of the strobe pulse STB, and 9 is the trigger pulse.
This is the input terminal of TRG.

FIG. 2 is a timing chart showing the operation of this thermal recording apparatus.

Next, the operation will be explained. The image signal PIX inputted to the input terminal 6 is taken into the shift register inside the drive circuit 3 at the timing of the transfer clock CLK inputted to the input terminal 7, and is sequentially shifted. When the image signal for one line is transferred, the input of the transfer clock CLK is stopped, the strobe pulse STB is input to the input terminal 8, and the image signal for one line accumulated in the shift register inside the drive circuit 3 is transferred. The signal is stored in a latch provided inside the drive circuit 3.

Next, a trigger pulse TRG is input to the input terminal 9, the timer 4 is activated, and the signal ENB is turned on for a time determined by the temperature indicated by the output signal of the temperature sensor 5. While the signal ENB is on, the drive circuit 3 inputs the image signal stored in the latch to an internal switching circuit, and energizes the heating element 1 corresponding to the black pixel of the image signal. As a result, the heating element 1 selectively generates heat in response to the image signal, and dots are recorded on recording paper (not shown).

Now, not only when an unregulated power source such as a battery is used as the recording power source 2, but also when using a stabilized power source that operates on commercial AC voltage, the output voltage will vary due to load fluctuations, etc. , which varies to some extent. Moreover, since the number of black pixels varies considerably from line to line, the load current of the recording power source 2 also varies considerably.

However, in the case of the above thermal recording device, even if the output voltage of the recording power source 2 changes, the driving time of the heating element 1, that is, the energization time is constant, so the amount of heat generated by the heating element 1 varies from line to line. . As a result, there was a problem in that density unevenness occurred in the recorded image.

To solve this problem, a method has been proposed in which the driving time of the heating element is changed in accordance with fluctuations in the output voltage of the recording power source.

FIG. 3 is a block diagram of such a thermal recording device, and FIG. 4 is a timing diagram thereof.

In FIG. 3, 10 is an analog/digital converter that detects the output voltage of the recording power source 2 and converts it into a digital signal. The output signal of the analog/digital converter 10 is subjected to voltage-time conversion by the ROM 12 and then input to the timer 4. 13 is analog/digital converter 1
This is the input terminal of the sampling pulse ADC for 0. Other than this, it is the same as in FIG.

Explain the operation. As explained in FIG. 1, when the image signal for one line is accumulated in the shift register inside the drive circuit 3, the strobe pulse STB is input, and the image signal accumulated in the shift register is transferred to the drive circuit 3. is stored in the internal latch. Next, the sampling pulse ADC is input to the input terminal 13, and the analog/digital converter 1
0 samples the output voltage of the recording power supply 2,
A digital signal corresponding to the voltage value is output. A time signal corresponding to this digital signal is input from the ROM 12 to the timer 4. Next, trigger pulse TRG is input, and timer 4
A signal is generated only for a time determined by the time signal input from the ROM 12 and the output signal of the temperature sensor 5.
Turn on ENB.

In this way, the driving time of the heating element 1 is controlled by the output voltage of the recording power source 2 immediately before driving (at no load) and the temperature of the thermal head.

According to such a system, it is possible to prevent uneven recording density due to slow fluctuations in the output voltage of the recording power source 2. However, it has no effect on sudden voltage fluctuations during driving due to load fluctuations, etc.
This results in uneven recording density.

Purpose of the invention The present invention solves the above-mentioned conventional problems.
It is an object of the present invention to provide a recording element drive control method that can almost completely eliminate recording density unevenness caused by voltage fluctuations of a recording power source in a thermal recording device or the like.

Structure of the Invention The present invention detects the voltage applied to the recording element at least once before and during the driving period of the recording element, and controls the driving time of the recording element according to the detected value. This feature aims to eliminate the influence of fluctuations in the voltage applied to the recording element due to load fluctuations, and to achieve the above-mentioned object.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 5 is a block diagram showing the main part of a thermal recording apparatus according to an embodiment of the present invention. In this figure, 21 is a heating element (recording element) arranged on the thermal head. 22 is a recording power source, and one end (the upper end in the figure) of the heating element 21 is collectively connected to this recording power source 22.

23 is a drive circuit that drives the heating element 21 in accordance with the image signal. This drive circuit 23 includes a shift register that stores image signals for one line, a latch, a switching circuit that switches between the other end (lower end in the figure) of each heating element 21 and ground, and the switching circuit and the above-mentioned latch. It consists of a gate etc. inserted between the

24 is an analog/digital converter for detecting the output voltage Vth of the recording power source 22. 2
5 is a latch that stores the output signal of the analog/digital converter 24, and 26 is an arithmetic circuit that calculates the driving time from the output signal of the latch 25 and the analog/digital converter 24. This calculation circuit 2
6 is constituted by, for example, a ROM. 27
is a timer that turns on the signal ENB for the driving time calculated by the arithmetic circuit 26.

28 is the input terminal for the image signal PIX, 29 is the input terminal for the transfer clock CLK, and 30 is the strobe pulse.
This is the input terminal of STB. 31 is the trigger pulse
The TRG input terminal, 32 is the latch pulse LAT input terminal, and 33 is the sampling pulse ADC input terminal.

Next, the overall operation of the present thermal recording apparatus will be explained.
FIG. 6 is a timing diagram showing the overall operation.

Image signal input serially to input terminal 28
PIX is the transfer clock input to input terminal 29.
At the timing of CLK, the signals are sequentially taken into the shift register inside the drive circuit 23 and shifted. When the image signal PIX for one line is accumulated in the shift register, a strobe pulse is sent to the input terminal 30.
STB is input, and inside the drive circuit 23,
One line of image signals accumulated in the shift register is stored in the latch.

Next, the sampling pulse ADC input terminal 33
The analog/digital converter 24 samples the output voltage Vth (abbreviated as power supply voltage) of the recording power supply 22, and the voltage value corresponds to the power supply voltage value at no load before driving the heating element. Outputs a digital signal. Immediately thereafter, latch pulse LAT is input and the output of analog/digital converter 24 is stored in latch 25.

Next, the trigger pulse TRG is input to the input terminal 31, and the timer 27 is activated to turn on the signal ENB. When this signal ENB is turned on, the drive circuit 23
Inside, the gate between the latch and the switching circuit is opened, and the connection between the heating element 21 corresponding to the black pixel of the image signal and ground is closed, and current flows through the heating element. In other words, the heating element 21 is driven.

After a certain period of time (shorter than the minimum drive time) after inputting the trigger pulse TRG, the sampling pulse
The ADC is input again to the input terminal 33, and the analog/digital converter 24 samples the power supply voltage Vth and outputs a digital signal corresponding to the voltage value, that is, the power supply voltage value when loaded.

The arithmetic circuit 26 has a latch 25 and an analog/
The drive time is calculated according to the output signal of the digital converter 24, that is, the first and second detection values, and is output to the timer 27. When the drive time calculated by the arithmetic circuit 26 has elapsed from the input time of the trigger pulse TRG, the timer 27 turns off the signal END.
As a result, the drive circuit 23 connects all the heating elements 21
energization is stopped.

Drive time control will be further explained with reference to the waveform diagram in FIG. 7.

Not only when an unregulated power source such as a battery is used as the recording power source 22, but also when a stabilized power source is used, when a load current flows, the power supply voltage Vth changes depending on the magnitude of the load current. For example, fluctuations as shown in waveforms a and b occur. Here waveform b
shows a case where the load is larger than waveform a.

In the initial state under load, the voltage value of the power supply voltage Vth decreases according to the load, but as time passes, it returns to the vicinity of the power supply voltage value under no load with a predetermined time constant of the power supply. . In other words, the power supply voltage waveform during driving is uniquely determined by the power supply voltage under no load if the load is constant.

Therefore, at least the power supply voltage value at no load,
Power supply voltage value after a certain period of time from the start of driving (at load)
From this, the power supply voltage waveform during the driving time can be estimated.

In this embodiment, for example, an arithmetic circuit 26 constituted by a ROM or the like in which drive time data corresponding to detected values is stored in advance as a table.
The latched first detection value and the subsequently input second detection value are input as addresses, and the drive time is output as data. As a result, the heating element 21 is given a constant driving energy and is controlled by the necessary driving time, thereby achieving uniform recording density.

Although one embodiment has been described in detail above, the present invention is not limited thereto.

For example, in the above embodiment, the power supply voltage is detected once during the driving period, but it may be detected two or more times. In this way, the power supply voltage waveform during the driving period can be approximated more accurately, so that the driving time can be controlled with high precision. Specifically, if detection is to be performed three times in total, once before driving and twice during driving, two latches corresponding to latch 25 in FIG. 5 are provided,
The first detected value is held in one latch, the second detected value is held in the other latch, and the outputs of these latches and the output of the analog/digital converter 24 are input to the arithmetic circuit 26. The power supply voltage waveform is estimated based on the detected values three times, and the driving time for making the recording density constant is calculated and input to the timer 27.

It is also possible to calculate the drive time by software means.

Furthermore, similar to the conventional example shown in FIG.
By providing a temperature sensor and inputting the output to the ROM 24 or the timer 27, the driving time may also be controlled based on the temperature of the thermal head. Similarly, it is easy to control the driving time based on variations in the resistance value of the heating element and fluctuations in the recording cycle.

Further, as is clear from the above description, the present invention is not limited to heat-sensitive recording devices, but can be similarly applied to electrostatic recording devices and the like.

Effects of the Invention According to the present invention, the voltage applied to the recording element is detected in the linear approximation region of the applied voltage before the recording element is driven and in the loaded state, and the driving time is controlled according to the detection result. Since this is performed during the recording process, it is possible to almost completely eliminate recording density unevenness due to rapid voltage fluctuations during driving due to load fluctuations, etc., and it is possible to record extremely high-quality images.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a conventional example of a thermal recording device, FIG. 2 is a timing diagram showing the operation of the conventional example, FIG. 3 is a block diagram showing another conventional example of a thermal recording device, and FIG. A timing diagram showing the operation of another conventional example, FIG. 5 is a block diagram showing the main part configuration of a thermal recording device according to an embodiment of the present invention, and FIG. 6 is a timing diagram showing the overall operation of the same embodiment device. 7 are waveform diagrams for explaining drive time control in the same embodiment device. 21... Heating element (recording element), 22... Recording power source, 23... Drive circuit, 24... Analog/digital converter, 25... Latch, 26... Arithmetic circuit, 27... Timer.

Claims (1)

[Claims] 1. When applying a voltage to a plurality of recording elements of an image recording device, a first detection point detects the applied voltage in a no-load state, and a second detection point detects the applied voltage after a predetermined time has elapsed in a loaded state. having a detection point, and controlling the driving end time of the recording element within a predetermined range from a minimum driving time to a maximum driving time during the driving time according to the first and second detected values. A recording element drive control method characterized by: