JPH04368061A - Thermal transfer recorder - Google Patents

Abstract

PURPOSE:To provide a stable recording characteristic by predicting a recording energy by one line so as to control a recording interval and thereby compensating a coloring density characteristic of recording. CONSTITUTION:When it is expected that a coloring density characteristic is subject to change due to a fluctuation in a voltage applied to a thermal resistance element in a thermal head caused by a change in the recording energy of the entire one recording line depending on a content of a picture (depending whether or not black dot number is more in one recording line), a data arithmetic circuit 9 being a recording energy prediction means predicts a change in the recording energy of one entire line. Then the result of prediction is sent to a reference oscillator in a motor control circuit 2 to control the oscillating frequency. Furthermore, the frequency (oscillating output) controlled from the oscillator is used for deciding number of revolutions of a motor 400 and the drive speed of the motor 400 is controlled in response to the signal. Thus, the coloring density at recording is kept constant regardless of a change in the picture content.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal transfer recording device capable of performing halftone recording by expressing not only black and white binary values but also intermediate shading.
It relates to a thermal transfer recording device that can always record halftones at a stable density without being affected by the content of the image information to be recorded (for example, whether the number of black dots per line is large or small). It is something.

0002

[Prior Art] There have been various methods for recording images and characters used in hard copy output devices for information signals in communication devices and output terminal devices of electronic computers, hard copy devices for image information signals such as video signals, etc. A method has been proposed. Among these recording methods, an intermediate recording medium whose surface is coated with heat-fusible or heat-sublimable ink is used, and this ink is selectively heated using a thermal head or the like to transfer the ink to the surface of the recording medium. Thermal transfer recording method has been put into practical use.

[0003] A recording method has also been put into practical use in which heat-sensitive coloring paper coated with a chemical that changes color or transmittance due to heat is heated by the above-mentioned thermal head or the like to develop color, without using an intermediate recording medium. ing. Among these recording methods, those capable of halftone recording are being put into practical use, in which recording is performed not only in binary gradations of black and white, but also in intermediate densities between white and black.

[0004] In the thermal transfer recording method, a density gradation method is generally used to perform halftone recording, in which the density is controlled for each pixel. In this density gradation method, each heating element arranged in a row in the thermal head corresponds to a pixel, and the density is controlled by increasing or decreasing the amount of ink in accordance with the amount of energy applied to the heating element. There is. Specifically, a method is often used in which resistance elements are used as heating elements and the energization time of each element is controlled in accordance with the gradation (gradation) of the pixel to be recorded.

The structure of a thermal head that performs density gradation recording includes a heat generating resistor element, a switching element individually connected to the heat generating resistor element, and a system that temporarily transmits data (information) for turning on and off the switching element. A latch circuit that stores data, and on/off data that is input from the outside (
and a shift register that stores information.

[0006] The heating resistor element has one terminal connected to a common electrode, and the opposite terminal connected to the other electrode via a switching element. Power is supplied to each heating resistor element by passing current between the common electrode side and the other electrode side via a switching element.

[0007] Controlling the energization time of each heating resistor element
The method to do this is as follows. First, divide the maximum energization time length by the number of shades of light and shade (number of gradations) to be expressed, and divide it into 1.
The step time (time slot) is calculated, and the on/off of each heating resistor element is controlled in units of time slots.

[0008] Since each heating resistor element only needs to be energized for the required energizing time, time slots are used by connecting them to the required length. The on/off control of the heating resistor element in each time slot is controlled by data stored in the latch circuit of the thermal head.
Based on data. Data is input to this latch circuit from the outside via shift registers connected in parallel.

That is, data is transferred to the shift register a number of times corresponding to the number of gradations, energized, and during this energization, image data of the next gradation is transferred, and this operation is performed one after another. This is repeated to obtain an energizing time width for a predetermined number of gradations. When electricity is applied for the duration corresponding to the gradation of the pixel to be recorded, energy corresponding to the energization time is input to the heating resistor element, and this energy is added to the ink paper and photographic paper as heat. , used for sublimation of ink, etc. to perform recording.

The general structure of the part that supplies power to the thermal head is as follows. That is, one terminal of a large number of heating resistive elements arranged in a row is electrically connected to a common power supply line (common electrode), and the other terminal is connected to a different electrode via a switch. ing. When the individual heat generating resistive elements are turned on, current is supplied from a common power supply line (common electrode), and they generate heat and generate thermal energy only while the switch is on.

[0011] At this time, a common power supply line (common electrode)
The problem is the internal impedance (resistance) of the for example,
First, it is assumed that the impedance of a common power supply line (common electrode) is, for example, 1Ω. If the resistance value of each heating resistor element is, for example, 200Ω, and the number of heating resistive elements is, for example, 500, corresponding to the number of scanning lines of an image, if all the heating resistive elements generate heat at the same time (all switches are When turned on), the resistance value of the heating resistor element viewed from the power supply line (common electrode) side is (200/500) since 500 heating resistor elements are connected in parallel.
=0.4Ω.

That is, in this example, the power consumed by the common power supply line (common electrode) is approximately twice or more than the power actually consumed by the heating resistor element, and the recording As a result, the recorded density is lower than the predetermined density.

On the other hand, when one heat generating resistor element generates heat, the resistance of the heat generating resistor element (for example, 200 Ω) is greater than the resistance of the common power supply line (common electrode) of 1 Ω.
are connected in series, the heat loss (power consumption) in the common power supply line (common electrode) is approximately 0.5
% and can be ignored in practice.

[0014] The numerical values exemplified here are just examples, but in an actual thermal head, the impedance of the common electrode is
In terms of order, it is often around 1Ω. The common electrode is manufactured by a manufacturing method that includes a thin film process such as metal vapor deposition, and in principle, the problem of common electrode impedance is an unavoidable problem in thermal heads.

[0015] For the above reasons, the current supplied to each heating resistor element in one line of the thermal head differs greatly between an image part where there is a large proportion of energized heating resistive elements and an image part where there is a small proportion of the number of energized heating resistive elements. It turns out. In other words, in the case of an image in which there are many heating resistive elements that are energized in one line, the loss due to the impedance of the common electrode becomes large, so the power applied to the heating resistive elements decreases, and the recorded density of the image decreases. become.

[0016] Furthermore, in the case of an image in which few heating resistive elements are energized in one line, the loss due to the impedance of the common electrode is small, so the power applied to the heating resistive elements is set to a value close to a predetermined value. Therefore, the recorded density of the image is not impaired. If areas with reduced recording density and areas with lower recording density coexist in one screen of an image in this way, density unevenness will occur within the screen, resulting in deterioration of image quality.

Various attempts have been made to correct the density unevenness caused by the common electrode impedance of the thermal head. For example, JP-A-58-1
As disclosed in Japanese Patent No. 48781, a technique is known in which the width of the energizing pulse is changed in accordance with an increase or decrease in the number of pixels recorded in one line, thereby making the energy supplied to each heating resistor element uniform. ing.

[0018] In this prior art, a binary image of white or black (
For example, in the case of characters (for example, text and line images), the recording density is uniform and it functions satisfactorily; however, for example, halftone images such as natural images that need to be expressed by controlling subtle shading. In some cases, it is necessary to increase the accuracy of correction according to the number of tones to be expressed as a halftone image, and it is well recognized that in cases where there are many tones, it may not be possible to complete the correction. It wasn't.

[0019] In addition, since the coloring characteristics are generally not linear with respect to the energization time, so-called γ correction (non-linear correction) is performed, but it is necessary to make corrections including the γ correction characteristics. However, regarding the points that cannot be corrected by simple operations such as increasing the pulse rate at a uniform rate or a specific width,
Until now, it was little known.

[0020] Another conventional technique, for example, as disclosed in Japanese Unexamined Patent Publication No. 56-86782, is to change the applied voltage or current depending on the number of pixels printed in one line. A technique is known in which the energy supplied to each heating resistor element is made uniform.

[0021] In this conventional technology, it is necessary to finely reset the current and voltage applied to the heat generating resistor element for each line, and the responsiveness of the power supply and the margin of supply capacity must be adjusted when concentration correction is not performed. It is necessary to make the power supply considerably larger than that of the conventional power supply, which increases the cost and size of the power supply, which in turn increases the cost and size of the entire device.

In addition, in the energizing voltage correction method, it is necessary to finely adjust the energizing waveform in units of gradation-by-gradation with higher precision. It was not fully recognized that it would be necessary to make adjustments to the key, making it impossible to make sufficient corrections.

As a conventional technique for changing color density characteristics in accordance with image information to be recorded, for example, Japanese Patent Laid-Open No. 56-70
As is known from Publication No. 976, etc., if there are many heat-generating resistor elements that are energized at the same time and the amount of heat generated by the thermal head is expected to be large, the recording period (interval) may be widened (the recording speed may be slowed down). ), and by increasing the ratio of the cooling period to the heating period, the color development characteristics are changed to be thinner, and a technique is known in which a uniform density is obtained.

[0024] In this conventional technology, the thermal head used is a relatively small so-called "serial head", and the number of heat-generating resistive elements mounted is up to several dozen elements, and the common electrode The voltage drop was mostly normal, and the problem with the common electrode was not recognized.

When this correction according to the prior art is applied to a system using a thermal line head that is relatively large and has a large number of heat-generating resistor elements installed, the recording period (interval ) is set so that it becomes wider and the coloring characteristics become thinner, and the above-mentioned problem that the voltage drop at the common electrode becomes relatively large when the number of heat-generating resistor elements is large is combined, and the desired characteristics are However, there is a problem in that recording is performed with even thinner density characteristics, and the density correction acts in the direction of excessiveness, and this point has not been sufficiently recognized in the past.

[0026]

[Problems to be Solved by the Invention] An object of the present invention is to reduce the density of the entire recording of one line depending on the content of the image information to be recorded (for example, whether the number of black dots per line is large or small). If the voltage drop is large, the voltage drop caused by the common impedance of the thermal head will be relatively large, resulting in a thinner color density, whereas in other areas (lines), the color density will be darker. This prevents fluctuations in recording density and deterioration of image quality at the boundaries, regardless of the content of the image information (such as whether there are many or few black dots per line). However, it is an object of the present invention to provide a thermal transfer recording device that can record images with stable density characteristics.

[0027]

[Means for Solving the Problems] In order to achieve the above object, in the present invention, in a thermal transfer recording apparatus, for the next line to be recorded following the current line being recorded, the next line is a prediction means for predicting the energy required to record the next line based on given image information indicating which element is to be energized and to what degree among a plurality of heat generating resistive elements forming a plurality of heat generating resistive elements; If the energy predicted by A recording interval changing means is provided to speed up the recording operation by narrowing the recording interval.

[0028]

[Operation] When the energy prediction means is given one line of image data, it can calculate and process it to predict the recording energy of the entire line, and at the same time predict the amount of voltage drop due to the common impedance of the thermal head. Therefore, it is possible to predict changes in color density characteristics caused by this.

Further, when the recording interval changing means widens the recording period (interval) (slows down the recording operation), the ratio of the cooling period to the heating period increases in the interval, and the coloring characteristics become lighter. ,
On the other hand, when the recording period (interval) is narrowed (the recording operation is made faster), the ratio of the cooling period to the heating period in the interval becomes smaller, so that the coloring characteristics become darker.

Therefore, when the energy prediction means predicts that the color density characteristics will become lighter, the recording interval changing means narrows the recording period (interval) (speeds up the recording operation) to make the color characteristics darker. When the energy prediction means predicts that the color density characteristics will become darker, the recording interval changing means widens the recording period (interval) (slows down the recording operation) to make the color characteristics thinner. A stable concentration can be maintained.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the internal configuration of a thermal transfer recording apparatus according to a first embodiment of the present invention. In the same figure,
1 is a thermal transfer recording device, 102 is an input terminal for image data to be recorded, 501 is an input interface circuit, 50
2 is an image data memory, 510 is a line memory, 503
3 is a power supply control circuit, 3 is a thermal head, 6 is a power supply, 9 is a data calculation circuit, 500 is a system controller, 2 is a motor control circuit, 400 is a motor, 401 is a deceleration mechanism,
402 is a platen drum.

Inside the thermal transfer recording apparatus, there is a thermal head 3 and a platen drum 402 facing the thermal head 3, and a recording medium (not shown) is placed between them for recording. A current is supplied from the power supply 6 to the heat generating resistor element inside the thermal head 3 to generate heat, thereby performing recording. Furthermore, control of energization to the heating resistor elements in the thermal head 3 is performed by a control signal sent from the energization control circuit 503.

On the other hand, the platen drum 402 receives driving force from the motor 400 via the deceleration mechanism 401 and rotates. This motor 400 is controlled by a motor control circuit 2. The motor control circuit 2 outputs control commands to the motor 400 based on commands from two places, the system controller 500 and the data calculation circuit 9, and returns the control commands to the system controller 500 for subsequent system controller 500. It is reflected in the operation of

In the line memory 510, image data of one line next to the one line of data currently being recorded (hereinafter, this may be referred to as image data of the next line) is stored in the image data memory. It is read out from and stored. In the recording operation for the next line, the image data to be recorded is immediately transferred from the line memory 510 to the energization control circuit 503, and the heat generating resistive elements in the thermal head 3 are classified into those that generate heat and those that do not. Recording is performed by selecting based on data.

On the other hand, image data of the next line is sent to the data calculation circuit 9 from the line memory 510. This image data of the next line is information representing the number of heating resistive elements to be energized in the thermal head 3 and the length of the energization in the recording operation of the next line. The voltage dropped by the common impedance is also represented correspondingly.

That is, the data calculation circuit 9 is given the image data of the next line, and thereby calculates the voltage drop due to the common impedance of the thermal head 3 during the recording operation of the next line, and the color density characteristics during recording. Changes can be predicted.

The prediction result output from the data calculation circuit 9 is sent to the motor control circuit 2 and reflected in the control of the motor 400, and finally controls the operation of the platen drum 402 (specifically, the rotation control speed). That is, the rotational speed of the platen drum 402 is controlled based on the data of the number of energized heating resistive elements in the thermal head 3 and the length of the energized time, thereby stably maintaining color density characteristics during recording. can.

Image data to be recorded is applied from an external device (not shown) to the input terminal 102 in the form of an image information signal such as a video signal, and is then sent to the input interface circuit 50.
1 to the image data memory 502,
Furthermore, the energization control circuit 503
Then, after being converted into an energization waveform used by the thermal head 3, it is sent to the thermal head 3 and recording is performed. Here, each of these parts is controlled by the system controller 500 to perform the intended operation.

FIG. 2 is a perspective view showing the external appearance of the thermal transfer recording apparatus 1 whose internal structure is shown in FIG. 1 for reference. As seen in FIG. 2, the thermal transfer recording apparatus 1 has an input port 110 into which recording paper as a recording medium and ink paper as an intermediate recording medium are input, and the recording paper and ink paper are supplied as consumables from here. do. Also, the recording paper after recording is output from the exit port 1.
11, the recording material is discharged to the outside of the apparatus 1, and the recording operation is thus completed.

FIG. 3 is a perspective view showing the internal mechanical parts of the embodiment shown in FIG. The mechanical section shown in FIG. 3 includes photographic paper 403 as a recording medium on which images are to be recorded.
It is supplied from outside the apparatus and is responsible for recording given image data as an image on the surface of the photographic paper.

In FIG. 3, the thermal head 3 and the platen drum 402 are arranged to face each other, and an ink paper 405 and a photographic paper 403 are sandwiched between these members by means not shown. Then, the heating resistor element in the thermal head 3 is appropriately energized to generate heat according to the given image data to be recorded, so that the ink paper 40
The ink No. 5 is sublimated or thermally melted and adhered to the surface of the photographic paper 403, and if one line is recorded, one line is recorded.

At this time, the platen drum 402 is driven by the motor 400 via the deceleration mechanism 401, and the recording operation for each line is continuously performed. It can be obtained at.

From the line memory on the electric circuit side, the image data of the next line is sent to the data calculation circuit 9, and the prediction result in the data calculation circuit 9 is sent to the motor control circuit 2, and the image data of the next line is sent to the data calculation circuit 9. As described above, the rotational speed of the platen drum 402 is controlled during the recording operation of the next line.

When the platen drum 402 rotates, the photographic paper 403 and the ink paper 405 move in conjunction with the platen drum, and the heating resistor element of the thermal head 3 is heated.
The part of the photographic paper on which no new recording has been made is sent, and 1
As has already been explained many times, line recording is performed continuously and thus a planar recording is obtained.

FIG. 4 shows the relationship between the energy input to the thermal head for recording and the color density obtained at that time corresponding to that energy.
It is a characteristic diagram showing how many heat generating resistive elements are energized at the same time and generate heat among all the heat generating resistive elements constituting the line, according to the proportion thereof.

For example, in FIG. 4, even if the amount of input energy is the same A, the number of heating resistive elements that are simultaneously energized to generate heat among all the heating resistive elements constituting one line in the thermal head is If it is 10%,
Compared to the high coloring density C, the coloring density is low at B when the number of heating resistive elements that are simultaneously energized and heated is 100%. When the number of heating resistive elements is changed from 10% to 100%, the concentration changes significantly from C to B.

[0047] This is because the impedance of the common electrode in the thermal head changes relatively depending on the number of heating resistive elements that are simultaneously energized and generate heat, and as explained in detail earlier. be.

Note that the characteristics shown in FIG. 4 show the case where all images are recorded with the same gradation (same energization time length). In the case of an actual natural image with halftone density, the number of heating resistive elements that are energized at the same time changes during tone control, and the voltage drop at the common electrode of the thermal head is It will continue to change throughout the record.

However, it is possible to calculate the average voltage drop (the amount of voltage drop at the common electrode of the thermal head) to be compensated for based on the entire image data. In other words,
By arithmetic processing such as multiplying the size of the image data by a certain coefficient and performing addition processing, it is possible to process the image data by treating it as a certain amount of voltage drop. That is, the recording energy for one line can be determined from image data through arithmetic processing, and the result of this arithmetic processing corresponds to the occurrence of density unevenness.

In FIG. 4, the voltage applied to the thermal head is constant, and the energization pulse width on the horizontal axis corresponds to the energy input from outside the head to each heating resistor element within the thermal head. Depending on the number of heating resistive elements that are energized simultaneously in the entire thermal head, the actual voltage applied to each heating resistive element changes under the influence of the impedance of the common electrode. The ratio of the number of heating resistor elements that are energized at the same time is gradually decreased from, for example, 100% to, for example, 10%.
%, even if the energy of the energization pulse width shown in A in Figure 4 is input, the concentration obtained from point B to point C will change significantly, as already mentioned. become.

FIG. 5 shows the energy input to the thermal head (the width of the energizing pulse) and the characteristics of the color density obtained in response to that energy for each recording period (interval) per line. be. The characteristics shown in FIG. 5 were obtained under the condition that the number of simultaneously energized heating resistive elements in the thermal head is constant.

Since the heating resistor element is energized with a constant voltage, the energization pulse width on the horizontal axis corresponds to the energy input to the heating resistor element. Even when the same input energy is input to the head, as the recording interval is shortened (the recording speed is increased), the color density becomes darker. For example, if the recording interval is changed in the range of 12 ms to 20 ms/line and the energy of the pulse width shown at point A on the horizontal axis in FIG. 5 is input, the color development obtained from point B to point C on the vertical axis is obtained. The concentration will change significantly.

By combining the characteristics shown in FIG. 4 and the characteristics shown in FIG. 5 explained above, the following control characteristics can be realized. That is, the number of pixels that are simultaneously energized and heated in the thermal head varies depending on the content of the image information (the number of black dots per line is large or small), and as a result, as shown in the characteristics of FIG. The overall density in line recording, that is, the color density characteristics vary. When the overall density of one line of recording increases, it is when the number of pixels that are energized and heated increases, but in this case, the overall image tends to be thinner than the desired density. .

At this time, by shortening the recording interval (increasing the recording speed), the color density characteristics can be increased, as seen in the characteristics shown in FIG. here,
By changing the recording interval, the color density characteristics change in the recording of the next line after the line for which the interval was changed. That is, although the interval is changed for the line being recorded, the amount of change needs to be determined based on the image data of the line next to the line.

[0055] By doing the above, the number of pixels (heating resistor elements) that are simultaneously energized and heated in one line increases, and 1
As the density of the entire recorded line increases, the voltage drop across the common electrode of the thermal head increases, and color density characteristics become thinner accordingly. Therefore, by increasing the recording interval, the color density that is about to become lighter is increased, thereby canceling out the color density characteristics and making it possible to perform recording while maintaining a constant color density characteristic.

On the other hand, if the number of pixels (heating resistance elements) that are simultaneously energized and heated in one line decreases, and the overall recording density of one line decreases, the voltage drop at the common electrode of the thermal head will become smaller. , the color density characteristics become darker accordingly. Therefore, by slowing down the recording interval, the color density that is about to increase is made thinner, thereby canceling out the color density characteristics and making it possible to perform recording while maintaining a constant color density characteristic.

[0057] In actuality, arithmetic processing is performed on image data having intermediate tones to predict the recording energy for one entire line and, by extension, the amount equivalent to the voltage drop at the common electrode of the thermal head, and calculate this by calculating the above-mentioned color density. , is regarded as the required amount that should be made thinner or thicker.

Next, a description will be given of specific hardware for changing the recording interval in response to changes in the amount of recording energy for one line of image data as a whole, and its operation. FIG. 6 shows such hardware as shown in FIG.
FIG. 2 is a block diagram showing details of the motor control circuit 2 and circuits around the motor control circuit 2 in the embodiment shown in FIG.

In FIG. 6, 204 is a reference oscillator;
0 is an oscillator (B), 206 is a changeover switch, 211 is a frequency dividing circuit, and 212 is a motor drive circuit. See FIG. 6. Next 1 read from line memory 510
The image data for the line is sent to the data calculation circuit 9,
Here, information corresponding to the amount of voltage drop at the common electrode to be generated in the thermal head in recording the next line is predicted.

It is assumed that motor 400 is constituted by a step motor. In a step motor, the rotation of the motor itself can be unilaterally controlled only by drive pulses from its drive circuit. Inside the motor control circuit 2,
There is a reference oscillator 204, and the operation of the step motor 400 is controlled based on the oscillation frequency of this reference oscillator.

For example, the step motor drive circuit 21
2, when the step motor 400 is driven by inputting two pulses from the reference oscillator 204 via the changeover switch 206, the motor 400 moves by two steps. motor 4
Since the output of 00 is sent to the platen drum via the deceleration mechanism, the platen drum rotates by a distance corresponding to the number of steps taken by the motor 400.

For example, if the number of steps corresponding to one line of recording is 10, the drive circuit 21
If 10 pulses are input to 0 and the step motor 400 is driven, the platen drum will move by a distance of one line. The pulses output from the reference oscillation circuit 204 are sent to the frequency dividing circuit 211 after passing through the changeover switch 206, and the output of this frequency dividing circuit 211 is sent to the system controller, and the platen drum is connected to one line. Informs you that you have moved the distance.

The frequency dividing ratio in this frequency dividing circuit 211 is set to 1.
If the number of steps is set equal to the number of steps for a line, the system controller 500 can issue a command to record one line each time the platen drum moves by one line. That is, simply by changing the oscillation frequency of the reference oscillator 204, the recording interval can be changed.

Further, a switching control signal is sent from the system controller 500 to the switching switch 206. In addition to the frequency from the reference oscillator 204, the frequency from another oscillator (B) 210 is also sent to the changeover switch 206, and according to a control command from the system controller 500, the changeover switch 206 changes the input frequency to the standard. By switching from the oscillator 204 to another oscillator (B) 210, the frequency sent to the motor drive circuit 212 can be switched.

That is, if the oscillation frequency of the oscillator (B) 210 is set to a much larger value than that of the reference oscillator 204, the recording speed can be changed to the normal recording speed by switching the changeover switch 206. You can switch between high-speed recording and other high-speed recording.

During the recording operation, from the data calculation circuit 9,
The oscillation frequency can be changed (controlled) by inputting into the reference oscillation circuit 204 the results of predicting changes in color density characteristics due to changes in recording energy throughout one line to be recorded. That is, when recording one line, based on the results of predicting changes in recording energy for the entire line,
The recording interval can be changed, and the color density characteristics can be maintained constant by compensating for changes in color density characteristics caused by impedance changes (changes in voltage drop) in the common electrode of the thermal head.

The operations of the motor control circuit 2 and its surrounding circuits, which have been schematically described above, will be described in more detail as follows. In other words, the recording energy for the entire line to be recorded changes depending on the content of the image (in one line to be recorded, if it is black, there are many or few black dots), and the heating resistor element in the thermal head changes. When it is predicted that the coloring density characteristics will change due to a change in the voltage applied to the line, the data calculation circuit 9, which is a recording energy predicting means, predicts the change in the recording energy of the entire line.

The prediction result is then sent to the reference oscillator 204 in the motor control circuit 2 to control its oscillation frequency. Then, the controlled frequency from this oscillator 204 (
The oscillation output) is a signal that determines the rotational speed of the motor 400, and the rotational speed of the motor 400 is controlled according to this signal. That is, when the content of the image changes and the recording energy for each line changes, the motor 400 changes accordingly.
The speed of recording is controlled, and the color density during recording is maintained constant regardless of changes in image content.

FIG. 7 is an explanatory diagram showing an example of an image in which density unevenness is likely to occur due to changes in image content. In the figure, 3 is a thermal head, 403 is a recording paper, and 7 is a thermal head.
01 is an intermediate density area, 702 is a white area, and 703 is a black area.

In FIG. 7, since the thermal head 3 is arranged in the vertical direction of the figure, the heating resistor element array therein also
The lines are lined up in the vertical direction of the diagram, and one line at a time is recorded in the vertical direction of the diagram, and the recording is performed in the right direction indicated by the arrow (along points B, C, D, ......, I, J). As a result, a two-dimensional planar record as shown in the figure is obtained.

In the image seen in FIG. 7, the starting point of recording is B and the ending point is J. During this time, in the order of progress of recording, the area from the recording start point B to point C is a middle density area 701, and the area from point C to point D is a white area 70.
2 and an intermediate density area 701, and from point D to the right, the white area 702 has changed to a black area 703. The length (width) of the black part 703 in the vertical direction becomes shorter at points E, F, G, and H, and after the point H, the black part 703 disappears, and the white part 702
This is a mixed area of a middle density area 701 and an intermediate density area 701.

Therefore, in the image of FIG. 7, point C, point D, and E
At points (hereinafter referred to as points F, G, H, and I), that is, at the transition points of the image, fluctuations in the common impedance in the thermal head 3 occur, resulting in uneven shading of the image. This will be explained in detail below.

In the image example shown in FIG. 7, the recording energy for one line in the vertical direction from point B to point C is an intermediate value, so compared to when recording the maximum density,
The number of heat-generating resistive elements that are energized is small, and the concentration drop due to the voltage drop at the common electrode of the thermal head is moderate.

[0074] Between point C and point D, there is a white area 702, and the recording energy for one line is only in the upper and lower bands of the image (intermediate density area 701), and is small when viewed as one line. value. Therefore, the voltage drop at the common electrode of the thermal head is not so large, and the concentration drop is small. That is, the recording energy per line changes before and after point C.

That is, between points B and C, the voltage drop at the common electrode of the thermal head is medium, so the recorded area at intermediate density becomes thin, and between points C and D, the voltage drop is moderate. Because the drop is small, the recorded area at intermediate density becomes darker, and there is a difference in density (streak) just at point C.
occurs in the direction of the row of heating resistor elements of the thermal head 3. Similarly, at point D, the dark intermediate density part changes to a light intermediate density part (black area 703
), this will appear as a step in concentration. Similarly, density steps (streaks) appear near each point E, F, G, H, and I.

Next, referring to FIG. 8, the results of measuring the difference in density on such an image in the recording progress direction along lines A and A' in FIG. 7 (in the region of the intermediate density portion 701) I will explain. In (a) of FIG. 8, lines A and A in FIG. 7 are plotted on the horizontal axis.
' The distance traveled in the recording direction is taken, and the vertical axis shows the density at that position. In conclusion, 710 in FIG. 8(a) indicates the result of measuring the density level difference on the above-mentioned image.

In FIG. 8(c), the horizontal axis is the same as that in FIG. 8(a), but the vertical axis represents the recording energy of one line at that position. That is, in (c) of FIG.
From recording start point B to point C, the recording energy for one line is medium, from point C to point D, the recording energy for one line decreases (because there is a white area 702), and at point D (black area). 703) becomes maximum, and then
It gradually decreases in a stepwise manner according to the gradual changes in the black part 703,
At point I, it returns to the middle level again.

As is already clear, such fluctuations in the recording energy of one line at each position along the recording progress direction result in similar fluctuations in the voltage drop at the common electrode of the thermal head, and as a result, the recording The density of the image also fluctuates, and the state of the fluctuation is shown in Figure 8(a), which has already been explained.
This is why it is shown as 10. 7 in (a) of Figure 8
11 shows a flat density characteristic that is originally desired.

In FIG. 8(b), the horizontal axis is the same as that in FIG. 8(a), but the vertical axis indicates the recording interval at that position. In FIG. 8(b), if the recording interval (recording speed) is set to a characteristic of 713 (a characteristic that maintains a constant value), the changing density characteristic as seen in 710 of FIG. 8(a) However, the recording interval (
If the recording speed) is set to the characteristic 712 (a characteristic that fluctuates in response to the fluctuation of the recording energy of one line as seen in (c) of FIG. 8), the characteristic 711 in (a) of FIG. 8 is set. This results in a flat (inherently desirable) density characteristic.

As described above, taking the image shown in FIG. 7 as an example, normally C, D, E, F, G, H, I,
Differences in density (streaks) appearing vertically at each point of J
With reference to FIGS. 8(a), (b), and (c), we have quantitatively explained how this problem is solved by the operation of an embodiment of the present invention. .

Next, returning to FIG. 1, the overall operation of the thermal transfer recording apparatus will be explained again. Please refer to FIG. Image data such as a video signal sent from outside the device via the input terminal 102 is sent to the input interface circuit 501, and is once sent to the image data memory 502 and stored therein. The operations of this input interface circuit 501 and image data memory 502 are controlled by a system controller 500.

[0082] After the image data is input to image data memory 502, system controller 500 initiates a recording operation. That is, first, a command is issued to the motor control circuit 2 to start the motor 400 and rotate the platen drum 402 via the deceleration mechanism 401. motor 400
When the motor 400 is started and the number of driving pulses of the motor 400 reaches a certain number, moving distance information (of the platen drum 402) sent from a frequency dividing circuit inside the motor control circuit 2 is sent as a signal to the system controller 500.

Based on this movement distance information, the system controller 500 issues an energization command to the energization control circuit 503. The energization control circuit 503 is connected to the image data memory 5
The image information read from 02 is stored in the line memory 510.
Once the image data for one line is stored,
This is taken out and converted into an energizing waveform for the thermal head 3, and the energizing waveform is sent to the thermal head 3.

In the thermal head 3, the energization control circuit 50
According to the energization waveform signal from 3, the current supplied from the power source 6 is applied to the heating resistor element to generate heat, thereby recording one line. Then, when the motor 400 rotates and the platen drum 402 moves a certain distance, the start signal of one line is sent again from the motor control circuit 2 to the system controller 500, and the recording operation of the next one line is performed. By repeating these recording operations, a two-dimensional screen forming one screen is recorded.

The image data for one line stored in the line memory 510 is used for recording the next line, and the stored image data for one line is subjected to calculation processing in the data calculation circuit 9. By doing so, it is possible to predict the amount of recording energy required by the thermal head in recording the next line, and in turn, it is possible to predict the amount of voltage drop that will occur at the common electrode of the thermal head.

The prediction result is sent to the motor control circuit 2, and the motor 40 is eventually controlled according to the image data to be recorded.
By changing the zero speed, it is possible to perform appropriate recording according to the image data to be recorded. That is, as the recording energy for one line increases, the voltage applied to each heat generating resistor element from the common electrode of the thermal head decreases, which undesirably changes the color density characteristics toward a lower value. On the other hand, the prediction result of the recording energy for this one line is sent to the motor control circuit 2, the recording interval is shortened (the recording speed is fast), and the recording characteristics are set to be dark overall, resulting in the above-mentioned undesirable Characteristic changes will be compensated for and desired constant recording characteristics will be obtained.

FIG. 9 is a block diagram showing the overall configuration of a second embodiment of the present invention. In the embodiment shown in the figure, the inside of the image memory 502 is searched as a means for predicting the recording energy of the next line to be recorded (and, by extension, predicting the amount of voltage drop at the common electrode of the thermal head 3). The configuration uses a data calculation circuit 9 which takes in required image data via a readout line 512 and processes it.

According to this embodiment, image data of any line prior to the recording operation can be read out, and processing can be realized with ample processing time. The prediction result from the recording energy prediction means (data calculation circuit 9) for one line is sent to the motor control circuit 2, and thereafter, the process is carried out in the same manner as in the first embodiment of the present invention shown in FIG. Operate.

FIG. 10 is a block diagram showing the overall configuration of a third embodiment of the present invention. In the embodiment shown in the figure, the recording energy of one line to be recorded next is predicted (
Furthermore, the image data memory 50 serves as a means for predicting the amount of voltage drop at the common electrode of the thermal head 3.
2 to the line memory 510 and sends the data to the line memory 510. The configuration uses a data calculation circuit 9 that takes in required image data from a signal line 513 branching from a line that reads and sends data from the line memory 510 to the line memory 510 and processes the data.

According to this embodiment, the image data memory 5
Image data can be transferred from 02 to line memory 510 and read out to data calculation circuit 9 at the same time, eliminating the need to write image data into line memory 510 and then read it out from line memory 510. This allows processing to be performed with ample time for arithmetic processing. 1-line recording energy prediction means (
The prediction result from the data calculation circuit 9) is sent to the motor control circuit 2, and thereafter the operation is similar to that of the first embodiment of the present invention shown in FIG.

FIG. 11 shows, as a fourth embodiment of the present invention,
1 is a block diagram showing a thermal transfer recording device in which a motor and a motor control circuit are modified. In the figure, 400A is a DC motor, 400B is a FG (frequency generator), 702 is an FG frequency divider circuit, 201 is a motor drive circuit, 206 is a changeover switch, 205 is an F/V converter, 203 is a comparator, 20
4 is an oscillator.

In this embodiment, the motor has a motor main body 40.
0A and the FG (frequency
Generator) 400B,
The rotation speed of the motor body 400A can be detected by the FG 400A. The detection result of the rotation speed of the motor main body 400A by the FG 400B is divided by a specific frequency division ratio by the frequency dividing circuit 702 and sent to the comparator 203.

A reference frequency signal sent from an oscillator 204 is also input to the comparator 203 . and,
This comparator 203 uses the reference frequency and the frequency-divided FG40.
Compare the frequency from 0B, output the error, and
/V converter 205. F/V converter 205
Then, a voltage is output according to the error signal, and the motor body 40
It is output to the 0A drive circuit 201. That is,
When the rotational speed of the motor body 400A fluctuates from a predetermined value, it is compared with the reference frequency in the comparator 203, and the error amount is sent to the drive circuit 201.
The structure is such that fluctuations in the rotational speed of the engine are corrected.

The oscillator 204 has a setting input terminal that can be set externally, so that its oscillation frequency can be set externally. In the setting input terminal part,
The predicted result of the recording energy of one line of the thermal head sent from the data calculation circuit 9 (and the predicted result of the voltage drop amount at the common electrode of the thermal head) is connected, and oscillation is performed according to the predicted measurement result of the recording energy of one line. Frequency can be changed. Thereafter, operations are performed in the same manner as in the first embodiment of the present invention shown in FIG. 1, and an image recorded with uniform color density characteristics can be obtained.

The embodiment shown in FIG. 11 using this DC motor is superior in terms of the overall size and weight of the motor, heat generation, etc., compared to the case where a step motor is used, and in that sense, it is an excellent thermal transfer device. can be provided.

In the above description of the embodiments of the present invention, the ink paper and recording paper to be used have been explained as those using a method using sublimable dyes, but of course other methods such as heat-melting pigments may be used. It is also possible to use a method using heat-sensitive paper coated with a chemical that changes color with heat.
It goes without saying that the present invention can be equally practiced with any recording method using a thermal head.

[0097]

[Effects of the Invention] According to the thermal transfer recording device according to the present invention,
The following effects can be expected. In other words, it is predicted that the recording energy for one line to be recorded will increase or decrease depending on the image information to be recorded, and the voltage drop at the common electrode part in the thermal head will fluctuate, causing the color density characteristics to vary from lighter to darker. When recording, the thermal transfer recording interval (recording cycle) is changed prior to recording based on the predicted recording energy of the one line to be recorded, regardless of changes in the content of the image data to be recorded. It has the advantage of maintaining stable coloring characteristics.

Furthermore, according to the second embodiment of the present invention shown in FIG. 9, one line of data is read out from any desired position inside the image data memory and its recording energy is predicted. The color density can be corrected with sufficient processing time, and thermal transfer recording with even better characteristics can be performed.

According to the third embodiment of the present invention shown in FIG. 10, the image data is simultaneously input to the data calculation circuit at the time of transferring the image data from the image data memory to the line memory, so that the image data is transferred to the line memory again. There is no need to read image data from the image data source, and the color density can be corrected with plenty of processing time.

Furthermore, according to the fourth embodiment of the present invention shown in FIG. 11, since a DC motor is used instead of a step motor as the recording interval changing means, the overall weight of the apparatus, cost, heat generation, etc. In this respect, it has the advantage of providing good performance.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the overall configuration of a thermal transfer recording apparatus according to a first embodiment of the present invention.

FIG. 2 is a perspective view showing the appearance of the embodiment shown in FIG. 1;

FIG. 3 is a perspective view mainly showing a mechanical part of the embodiment shown in FIG. 1;

FIG. 4 is a characteristic diagram showing the characteristics of color density with respect to input energy per recording energy of one line.

FIG. 5 is a characteristic diagram showing the characteristics of color density with respect to input energy for each recording interval.

FIG. 6 is a block diagram showing details of the motor control circuit in FIG. 1;

FIG. 7 is an explanatory diagram showing an example of an image in which density unevenness is likely to occur due to fluctuations in the amount of voltage drop at the common electrode of the thermal head.

8 is a characteristic diagram quantitatively showing the operation and effects of the embodiment of the present invention using the image shown in FIG. 7 as an example; FIG.

FIG. 9 is a block diagram showing the overall configuration of a second embodiment of the present invention.

FIG. 10 is a block diagram showing the overall configuration of a third embodiment of the present invention.

FIG. 11 is a block diagram showing details of a motor control circuit as a main part of a fourth embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1... Thermal transfer recording device, 2... Motor control circuit, 3... Thermal head, 6... Power supply, 9... Data calculation circuit, 204... Reference oscillator, 206... Changeover switch, 210... Oscillator (B
), 211... Frequency divider, 212... Motor drive circuit, 4
00...Motor, 401...Deceleration mechanism, 402...Platen drum, 403...Photographic paper, 405...Ink paper, 500...System controller, 501...Input interface circuit, 502...Image data memory, 503...Electrification control circuit,
510...Line memory

Claims (4)

[Claims] Claim 1: One end of each of a plurality of heating resistance elements arranged in at least one line is connected to a common electrode, each other end is connected to the other electrode via a switching element, and each heating resistance element corresponding to each Continuous recording is performed one line at a time using a thermal line head that controls energization of each heating resistor element by turning on and off switching elements, and records using the heat generated by the energized heating resistor element. In a thermal transfer recording device that obtains two-dimensional surface recording by performing the following steps, regarding the next line to be recorded following the current line being recorded,
A prediction means for predicting the energy required for recording the next line based on given image information indicating how much current should be applied to which element among the plurality of heat generating resistive elements constituting the next line. If the energy predicted by the means is large, the recording interval of the next line required for recording is extended to slow down the recording operation of the next line, and if the predicted energy is small, A thermal transfer recording apparatus characterized by comprising means for narrowing the recording interval of the next line to speed up the recording operation. 2. The thermal transfer recording apparatus according to claim 1, wherein the energy prediction means reads information from a line memory that stores image information of the next line, and calculates the predicted energy by arithmetic processing based on the information. A thermal transfer recording device comprising means. 3. The thermal transfer recording apparatus according to claim 1, wherein the energy estimating means reads out image information in the vicinity of the next line, including the next line, from an image memory that stores the entire image information of the image to be recorded; 1. A thermal transfer recording device comprising a calculation means for calculating predicted energy based on . 4. The thermal transfer recording apparatus according to claim 1, wherein the energy estimating means transfers the energy from an image memory that stores entire image information of an image to be recorded to a line memory that stores image information of the next line. 1. A thermal transfer recording apparatus comprising a calculation means that extracts image information of the next line from the middle of transferring the image information of the line and calculates predicted energy based on the image information through calculation processing.