JPH044950B2 - - Google Patents

Description

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

BACKGROUND ART FIG. 1 is a block diagram showing the 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 a 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, the 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. The drive circuit 3 inputs the image signal stored in the latch to an internal switching circuit while the signal ENB is on, and energizes the heating element 1 corresponding to the black pixel of the image signal. As a result, heating element 1
selectively generates heat according 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 depending on 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 supply 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. stored in a latch inside. 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.

OBJECTS OF THE INVENTION The present invention solves the above-mentioned conventional problems, and an object of the present invention is 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. do.

Structure of the Invention The present invention is characterized in that the voltage applied to the recording element during the driving period of the recording element is detected two or more times with different detection times, and the driving time of the recording element is controlled according to the detected value. This is intended to eliminate the influence of fluctuations in the voltage applied to the recording element due to load fluctuations, etc., and to achieve the above-mentioned purpose.

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 according to 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 records the output signal of the analog/digital converter 24, and 26 is a ROM that calculates the drive time from the output signal of the latch 25 and the analog/digital converter 24. A timer 27 turns on the signal ENB for the driving time calculated by the ROM 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 the 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 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.

Time t ₁ from input of trigger pulse TRG (Figure 6)
Later, the sampling pulse ADC is connected to the input terminal 33.
The analog/digital converter 24 samples the output voltage Vth of the recording power source 22 and outputs a digital signal corresponding to the voltage value. Immediately after that, the latch pulse LAT is input,
The output of analog/digital converter 24 is stored in latch 25.

Time t ₂ from input of trigger pulse TRG (Figure 6)
At the time when , the sampling pulse ADC is inputted again, and the analog/digital converter
samples the voltage Vth again and outputs a digital signal corresponding to the voltage value. That is, during the recording period of the heating element 21, the output voltage (voltage applied to the heating element) Vth of the recording power source 22 is detected twice, and once
The second detection value is stored in the latch 25, and the second detection value is stored in the latch 25.
The second detected value is the analog/digital converter 24
is output from.

The ROM 26 calculates the drive time according to the output signals of the latch 25 and the analog/digital converter 24, that is, the first and second detection values, and outputs it to the timer 27. When the drive time calculated by the ROM 26 has elapsed from the input time of the trigger pulse TRG, the timer 27 turns off the signal ENB. As a result, the drive circuit 23 stops energizing all the heating elements 21 .

Next, drive time control will be explained in detail with reference to the waveform diagram in FIG.

When an unregulated power source such as a battery is used as the recording power source 22, its output voltage (hereinafter abbreviated as power supply voltage) Vth fluctuates relatively slowly as shown in waveform a during no load. But,
When the heating element is driven, a fluctuation as shown in waveform b occurs, for example. The amount of drop in the power supply voltage and the slope of its waveform during this drive are mainly determined by the magnitude of the load current, that is, the number of heating elements 21 that are simultaneously driven.

In this example, it is assumed that the power supply voltage Vth changes with a constant slope during the driving period of the heating element, and the power supply voltage value V ₁ after time t ₁ has elapsed from the start of driving (t ₀ ) and after time t ₂ have elapsed from the start of drive (t 0 ). The ROM 26 calculates the drive time required to keep the heat generation amount of the heating element 21 constant from the power supply voltage value V ₂ . Then, by turning on the signal ENB by the timer 27 for this driving time and making the heat generation amount of the heating element constant,
This is intended to make the recording density uniform.

Here, the case where the power supply voltage Vth monotonically decreases has been explained as an example, but the same applies to the case where the power supply voltage Vth monotonically increases.

Furthermore, when a stabilized power supply that operates on a commercial AC power supply is used as the recording power supply 22, the power supply voltage Vth fluctuates periodically, but if the heating element driving time is sufficiently short compared to the fluctuation period, the driving period may vary. Since the fluctuation waveform of the power supply voltage can be linearly approximated, the drive time can be calculated in a similar manner, and recording density unevenness can be prevented.

In addition, in Fig. 7, t _nio is the minimum drive time,
_tnax is the maximum drive time. The time t ₂ from the start of driving to the second detection of the power supply voltage is determined to be shorter than t _nax .

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 twice during the drive period, but it may be detected three 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, two latches corresponding to latch 25 in FIG. 5 are provided, and the first detection value is held in one latch, and the second detection value is held in one latch. the outputs of these latches and the output of the analog/digital converter 24 are input to the ROM 26;
In the ROM 26, the power supply voltage waveform is approximated based on the detected values three times, and the drive 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 its output to the ROM 24 or the timer 27, the driving time may also be controlled depending 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 at the initial stage of application and in the vicinity of the minimum drive time, and the drive time is controlled during the drive time of the recording element according to the detection results, so that load fluctuations can be avoided. It is possible to almost completely eliminate recording density unevenness due to sudden voltage fluctuations during driving caused by such factors, 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 supply, 23... Drive circuit, 24... Analog/digital converter, 25... Latch, 26...
ROM, 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 that detects the applied voltage after a predetermined period of time in the initial stage of a load state and a minimum drive time for voltage application in the load state. A second detection point for detecting the applied voltage is provided nearby, and the recording element is driven within a predetermined range from a minimum drive time to a maximum drive time according to the first and second detected values. A recording element drive control method characterized in that control of end time is performed during drive time.