JPS63985B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal recording method in which an image is formed by applying thermal energy to a recording medium by raster scanning.

In image recording devices using conventional thermal recording methods, such as facsimiles, the sub-scanning line density is determined by the recording time, so a change in the recording time immediately appears as a difference in the sub-scanning line density. This directly affected image quality as a difference in density between recorded images. That is, at a certain recording time T,
If the image shown in Figure 1b is obtained, if the recording time is reduced to T/2, that is, the sub-scanning line density is reduced to half, the resulting image will be as shown in Figure 1b. It will be like that. As can be seen from the comparison of the two qualities, when the sub-scanning line density is high, the overall density is high, and when it is low, the image is formed at a low density.

In order to suppress the density difference caused by such a difference in sub-scanning density, a method has been proposed in the past, as shown in FIG. However, with this method, the sense of discontinuity in the strabismus part is emphasized, and the number of main lines to be interpolated is one or two.
Since it is a digital quantity such as n books, the original scanning line density ratio is 1:2, 1:3, etc.
It had drawbacks such as being applicable only to cases with a specific proportional relationship such as 1:n.

The present invention aims to eliminate these conventional drawbacks, to provide a thermal recording method that maintains constant image density even when the density of sub-scanning lines changes and has excellent image reproducibility.

In the method according to the present invention, when the sub-scanning line density is low, by changing at least one of the amplitude and duration of the pulse applied to the thermal head in advance in accordance with the sub-scanning line density. This gives more energy to the heat-sensitive head, and gives less energy when the density is high. In other words, by controlling the density of the recorded line itself according to the sub-scanning line density, the overall density difference or density unevenness in the image is suppressed, and even if the sub-scanning line density or recording time is changed, the overall density is almost the same. The aim is to obtain images of Since the energy supplied to the heat-sensitive head is determined by the duration and amplitude of the applied pulse, in the present invention at least one of them is varied depending on the recording time or the sub-scanning line density.

The present invention will be described in detail below with reference to the drawings.

FIG. 2 is a block diagram of a first embodiment of the present invention in which the amplitude of the electric pulse supplied to the heat-sensitive head is constant, and its duration becomes smaller as the sub-scanning line density increases; 2 is a direct/parallel conversion circuit using a shift register, etc.; 3 is a pulse width setting circuit that generates a pulse for the energization time corresponding to the sub-scanning line density; 4 is a specific block of the thermal head. 5 is a block designation switch for selecting each of the above-mentioned components 1 to 4.
A timing generation circuit 6 that generates various timing clocks for synchronizing the operations of the This is a thermal head that can record minute amounts of information.

Now, when video information 7 is sent from outside the recording apparatus, the input buffer 1 samples it using a clock 11 according to its transmission speed. Next, the shift clock 12 transfers this information to the serial/parallel conversion circuit 2 at a timing suitable for the recording apparatus. The serial/parallel conversion circuit 2 transmits the serial signal transferred at each timing indicated by the output instruction clock 13 to the head electrode as a parallel signal 8. Meanwhile, in synchronization with this, a trigger signal 15 for applying energy to the head is transmitted to the pulse width setting circuit 3.
From there, an energization instruction signal 10 having a pulse width corresponding to the value of the sub-scanning line density instruction signal 22 is generated. During the period specified by the energization instruction signal 10, the block designation switch 4 connects the circuit connected to a specific block of the head and supplies energy to the head. When the recording of the specific block is completed, the block designation switch 4 prepares to connect the circuit connected to the next block by the switching instruction clock 14, and waits for the signal 10. In this way, by controlling the energy applied to the thermal head 6 using the energization instruction signal generated in the pulse width setting circuit 3, the recording density of each scanning line becomes smaller as the sub-scanning line density increases, and the entire image is The apparent density felt by humans when looking at the image can be made constant regardless of the sub-scanning line density.

FIG. 3 is a block diagram showing a part of the circuit in FIG. 2 in detail, and 16 ₁ to 16 _o are trigger signals whose pulse widths are the time constants determined by C ₁ to _Co and R ₁ to _Ro . This is a multivibrator generated by 15. 17 ₁ to 17 _o are AND gates, and 18 is an OR gate, and by this combination, among the output pulses of each of the multivibrators 16 ₁ to 16 _o , the output pulses correspond to the sub-scanning line density designated by the sub-scanning line density instruction signal 22. Only the output pulse is passed through the AND gate and the OR gate and is transmitted to the block designation switch 4 as signal 10. Reference numeral 19 denotes a counter, which is sequentially counted up by the switching instruction clock 14. A decoder 20 decodes the output of the counter 19 and connects a specific block so that it is energized only for the period indicated by the energization instruction signal 10, thereby making it possible to supply energy.

In Figure 4, the pulse amplitude is constant, and the pulse width PW
This is a diagram showing an example of the relationship between the sub-scanning line density and the scanning line recording density when the parameter is taken as a parameter, and from this it is possible to easily obtain the relationship between the sub-scanning line density and the pulse width to keep the density constant. can.

Figure 5 shows that the width of the energizing electric pulse is kept constant;
This is a block diagram of another embodiment of the present invention in which the amplitude is made smaller as the sub-scanning line density becomes larger.
The same symbols as in Fig. 2 indicate the same parts, and 2
Reference numeral 3 denotes a pulse amplitude setting circuit that controls the amplitude so that electrical energy corresponding to the sub-scanning line density is supplied to the head.

Now, when video information 7 is sent from outside the recording device,
Parallel video signals 8 are applied to thermal head 6 in a manner similar to that described with respect to FIG. On the other hand, in synchronization with the clock signal 13, the circuit connected to the specific block of the block designation switch 4 is activated by the energization instruction signal 1.
Pulse 2 is closed for a period indicated by 0 and has an amplitude set by the pulse amplitude setting circuit 23.
5 is supplied to the thermal head 6. This completes the recording of the specific block, and preparations for recording the next block are then made in the same manner as in the case of FIG.

FIG. 6 is a partially detailed block diagram of FIG. 5.
28 is a constant voltage power supply, and one of the resistors R ₁ to R _o is selected by a switch 26 that is switched according to the sub-scanning line density specified by the sub-scanning line density instruction signal 22, and this resistor is Feedback is provided via the As a result, the voltage of the pulse signal 25 supplied to the block designation switch 4 is set to a predetermined value. Thereafter, as in the case of the first embodiment, electrical energy is sequentially supplied to the designated blocks to perform thermal recording. It will be obvious that this embodiment achieves the same effects as the first embodiment. Figure 7 shows the relationship between sub-scanning line density and scanning line recording density when the pulse width is constant and the pulse amplitude PH is used as a parameter.
FIG. 3 is a diagram showing an example, from which the relationship between sub-scanning line density and pulse amplitude for keeping the density constant can be easily obtained.

It goes without saying that the invention can be used in combination with schemes for controlling the energy supplied to heat sensitive elements for other purposes. As an example, the present invention can be combined with a temperature compensation energy control system aimed at correcting density unevenness due to temperature rise of a heat sensitive head. FIG. 8 shows one example of this, which includes a temperature sensor 32 such as a thermistor that detects the temperature of the heat-sensitive head or its substrate;
A circuit 33 that performs temperature compensation by controlling the power supply characteristics according to the output of the sensor 32 is combined with the circuit shown in FIG. It will be understood very easily that the same effects as those of the first and second embodiments described above are thereby achieved.

In general, thermal recording requires a long recording time and the maximum value of power applied to the head is also subject to regulations, but sufficient measures can be taken by combining the two compensation methods as described above.

In the above, an example has been explained in which one of the amplitude and duration of the electric pulse supplied to the thermal head is controlled, but it is easy to understand that both may be controlled simultaneously according to the number of sub-scanning lines. It will probably be done.

As described above, according to the present invention, the energy supplied to the thermal head is controlled by the pulse width and/or its amplitude to change the recording line density, thereby controlling the recording time, that is, the sub-scanning line density. Even when switched to , it is possible to obtain a high-quality image in which the density of the image is kept constant.

Furthermore, since the energy applied to the thermal head can be continuously controlled, even when the sub-scanning line density is continuously changed, the effect of keeping the image density constant can be sufficiently achieved. Furthermore, since the arrangement of the recording dots does not change, the sense of discontinuity in the shaded area is not emphasized as in the conventional example.

Note that if the supplied energy is reduced in accordance with an increase in the sub-scanning line density, not only the recording density of the line will decrease, but also its width, and in the opposite case, both the recording density and the width will increase. The effect of this will be further strengthened.

[Brief explanation of the drawing]

Fig. 1 is a diagram for explaining the difference in image density due to the difference in sub-scanning line density, Fig. 2 is a block diagram of an embodiment of the present invention, and Fig. 3 shows a part of Fig. 2 in detail. 4 and 7 are graphs showing examples of the relationship between sub-scanning line density, pulse width, pulse amplitude, and recording density. FIG. 5 is a block diagram of another embodiment of the present invention, and FIG. The figure is a partially detailed block diagram, and FIG. 8 is a block diagram showing an example of application in which the recording methods of FIGS. 5 and 6 are combined with a temperature compensation circuit. 1...Input buffer, 2...Series-parallel switching circuit, 3
...Pulse amplitude setting circuit, 4...Block designation switch, 5...Timing generation circuit, 6...Thermal head, 23...Pulse amplitude setting circuit.

Claims (1)

[Claims] 1. In a thermal recording method in which energy is supplied to a thermal head by electric pulses, the amplitude of the electric pulses is adjusted such that the higher the sub-scanning line density, the smaller at least one of the line width and density of the recording line. and a duration width, the thermal recording method is characterized in that at least one of the duration width and the duration width is controlled to become smaller as the sub-scanning line density increases.