JPH10305607A - Method for controlling thermal head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel method for controlling a thermal head which eliminates a lot of control of the thermal head and a special hardware conventionally required to reproduce good gradations, compensate for an insensitive part of a thermal transfer ink and correct influences by accumulated heat, and can record good gradational images without losing natural gradational feature of image data and correct a shear in the reproduction of gradations due to the accumulated heat. SOLUTION: Although a hardware constitution may be maintained the same as a general thermal head-driving circuit, a driving signal is adapted to supply printing pulses of a fixed time length of a count to each heat-generating body which is determined by image data, a rise sensitivity correction pulse count obtained from a rise sensitivity characteristic of an ink ribbon obtained beforehand by experiments or the like, and an accumulated heat correction pulse count preliminarily obtained similarly by experiments or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for recording an image by controlling a thermal head based on image data and transferring a thermal transfer ink containing a color material onto a desired medium. The method of controlling the thermal head to reproduce the tones on the recorded image, especially the correction to reproduce well without deteriorating the gradation of the underlying image data and the reproduction error due to the heat storage of the thermal head And a control method capable of easily realizing the correction of.

[0002]

2. Description of the Related Art As a method of performing gradation recording by thermal transfer recording, a so-called dye transfer ribbon is used as a recording material, and the amount of dye sublimation or diffusion transfer onto a recording medium is changed in accordance with the amount of heat generated by a thermal head. To perform gradation recording by using
And a method of performing gradation recording by changing the size of a dot transferred to a recording medium using a special thermal head called a heat concentration head or a concentrated heating head and a heat fusion transfer ribbon. Have been.

In any case, in order to perform image recording with gradation based on digital image data having gradation, the image data is supplied to a thermal head as a recording head in accordance with the gradation of the image data. It is necessary to control the recording energy by an appropriate method. In this case, in view of the characteristics of thermal transfer recording, it is known that good gradation reproduction cannot be obtained by simply associating the data value of an image with the recording energy in a linear relationship. I have.

The first characteristic that causes this is that the relationship between the recording energy and the recorded image density is not linear due to the characteristics of the recording material, and a particular problem is that the recording material is insensitive to the applied recording energy. There is an area, and the output image density cannot be obtained until the recording energy reaches a certain level or more. As a result, no image output is obtained for the gradation image data associated with the level up to the certain level, and the number of gradations of the resulting image output is essentially equal to the gradation of the image data. It is less than the key. Specifically,
As shown in FIG. 2, the original gradation number of the image data is 256.
Even if the gradation is used, there is an insensitive part, and the actual number of gradations recorded as an image is smaller than 256 gradations.

[0005] The second characteristic that causes the above is that the thermal head, which is a recording head, gradually accumulates heat due to the heat generated during recording and rises in temperature. This means that the recording is superimposed on the energy and affects the recording, so that the actual recording density becomes higher than the original recording density. As a result, when printing is continuously performed on a number of media, the heat storage in the long-term mode, in which the image density is higher on the medium on which printing is performed at the end than on the medium on which printing is performed first, is one. When recording is performed on a single medium, two types of heat storage phenomena occur, namely, heat storage in the short-term mode in which a density difference occurs between the recording start portion and the end portion.

[0006] In order to solve such a characteristic, a conventionally adopted solution is as follows. For the first characteristic, as shown in an example in FIG. 3, the dead zone is detected before the timing when a recording pulse is applied. A method such as applying a bias pulse by a control method different from the normal gradation control pulse for compensating for the portion, or transferring the head even in a portion where the transfer ink of the transfer ribbon does not record due to its temperature, so-called For example, a method of providing some kind of heating means such as an external heater and preheating to a temperature just before the occurrence of fog is performed.

With respect to the second characteristic, a thermistor or the like is provided on the thermal head for detecting the temperature of the thermal head main body for the heat storage in the long-term mode. A method of cooling a thermal head by a cooling mechanism particularly provided such as a pipe or a Peltier element is employed. Alternatively, conversely, a method is known in which recording is performed while the entire head is heated to a level at which the amount of heat stored by recording and the amount of heat radiated from the head are balanced, but a special heating mechanism is required for that. In addition, since thermistors cannot follow the heat storage in the short-term mode, a control circuit for adjusting the applied voltage on the control circuit side of the thermal head to compensate for the concentration change due to the heat storage is experimentally grasped. To establish
As a countermeasure, a method of equipping a special control circuit for finely adjusting the recording pulse length, which is originally a fixed length, has been taken.

A drive circuit for driving the thermal head based on image data and control signals supplied from the outside is mounted on the thermal head itself, and the mounted drive circuit is an example of the configuration shown in FIG. Is a gate circuit that controls ON / OFF of the heating element based on a control signal and an image data signal supplied in synchronization with a clock signal supplied from an external controller. Since it cannot be implemented, special circuits must be provided externally. In addition, since these controls are affected by the material characteristics, the actual control circuit configuration and the contents of constants must be determined according to the material characteristics.

As described above, in the prior art, special control circuits are prepared by different methods for the two types of correction elements, that is, the correction of the sensitivity of the thermal transfer material and the correction of the influence of the heat storage of the thermal head. However, there is a problem that the hardware configuration is complicated or the control software is complicated because the control method is incorporated or a special control method is incorporated. Another problem is that when the material properties are changed, the hardware must be redesigned and manufactured in accordance with the change.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned prior art, and has as its object to reproduce good gradation in the prior art, to compensate for the insensitive portion of the thermal transfer ink, and Corrects the effects of heat storage, without the need to use multiple types of thermal head controls and special hardware required to perform all of them, and without degrading the gradation inherent in the image data. It is an object of the present invention to provide a novel thermal head control method which enables not only to record a gradation image but also to correct deviation of gradation reproduction due to heat storage of a thermal head.

[0011]

A feature of the means provided by the present invention to solve the above-mentioned problems is that these corrections can be performed without adding any special device or circuit to the thermal head and its surroundings. Therefore, the thermal head drive circuit shown in FIG. 4 may be used as it is as a hardware configuration. On the other hand, as a signal for driving this drive circuit, image data and the number of rise sensitivity correction pulses obtained from the rise sensitivity characteristics of the ink ribbon obtained experimentally in advance can be obtained experimentally in advance. What is necessary is just to supply the number of printing pulses of a fixed time length obtained from the number of pulses for correcting the heat storage to each heating element.

More specifically, as set forth in claim 1,
In a thermal head control method for recording an image with gradation on a desired medium using a thermal head and thermal transfer ink, the number of pulses of a pulsed output having a fixed time length is determined according to the number of gradations of each pixel of an image. By controlling the recording energy of each heating element of the thermal head by outputting the number of pulses, the number of pulses to be output is adjusted to the number corresponding to the number of gradations of each pixel and the pulse for correcting the rising sensitivity of the ink ribbon. A method for controlling a thermal head, characterized in that the number is a sum of the number of pulses for correcting the degree of heat storage of the thermal head.

Preferably, the control method of the thermal head according to the first aspect is based on a pulse for correcting the rising sensitivity of the ink ribbon and a heat storage degree of the thermal head. It is characterized in that whether or not to apply a pulse for compensating for is determined by the presence or absence of the first gradation data of the data of each pixel.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The rising sensitivity of an ink ribbon can be known from the result of recording beforehand without any correction, and the number of pulses required for correction can be determined from the result. May be incorporated into the control software. Also, the number of pulses to correct the heat storage is
As for the results of experimentally printing various patterns without correction in advance, the degree of correction of the number of pulses can be obtained based on the result of measuring the rise in density due to heat storage and the model of heat storage, etc. It is possible to determine the number of correction pulses in accordance with the printing conditions. Although the specific method of obtaining the number of correction pulses differs depending on the heat storage model, any value obtained by any method can be applied to the present invention.

Which heating element is to be provided with these correction pulses can be easily determined by whether or not the heating element performs image recording even for only one gradation. That is, it is not necessary to perform the heat storage correction and the rise correction for the heating element that does not perform any recording at a certain point, and conversely, for the point where the recording is performed at one gradation, it is possible to reliably perform the recording for one gradation. It is necessary to make each correction. Therefore, the recording signal of the first gradation can be used as a determination signal as to whether to add a correction pulse.

According to the above-described recording method, as shown in FIG. 1, the correction pulse for the insensitive portion and the heat storage correction pulse, which have been obtained in advance, are controlled by the same control method as that for the normal printing pulse. Data is applied to the heating element, and then a pulse corresponding to the gradation of the image is applied, so that image recording can be performed without losing the original number of gradations of the image data, and at the same time, a special control circuit Necessary correction can be performed without providing.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specifically, the thermal head driving circuit of FIG.
And a timing chart shown in FIG.
First, the data of the first gradation is input from the data input terminals Data1 to Data4 in synchronization with the Clock signal, and is provided with a shift register function and a gate circuit function.
C1 to IC8 are stored. Thereafter, the data is latched up by the Latch signal, and ON / OFF of the gate circuit corresponding to each heating element is set. Thereafter, by supplying the strobe signal a number of times corresponding to the number of correction pulses, a necessary number of correction pulses can be applied only to the heating element whose first gradation is on. Next, after the completion of the application of the correction pulse, the data of the second gradation is supplied from the data input terminal, and the Latch signal and the Strobe signal are sequentially added once each to perform the recording of the second gradation. In the third and subsequent gradations, image recording is performed by sequentially applying recording signals in the same manner.

[0018]

According to the thermal head control method of the present invention, in the above-mentioned thermal transfer recording, when recording an image having gradation, good reproduction of gradation and good thermal transfer ink can be obtained by the conventional technique. Compensation for insensitive parts and correction of the effects of heat storage, a thermal head control consisting of multiple types and a simple thermal head control method without the need for special hardware to perform all of these. Thus, not only is it possible to express the gradation of the image well, but it is also possible to correct the deviation of the gradation reproduction due to the heat storage of the thermal head, and the above-mentioned problem was solved.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a gradation control method according to one embodiment of a thermal head control method of the present invention.

FIG. 2 is a diagram illustrating a control method when no correction is performed according to an example of the related art.

FIG. 3 is a diagram illustrating a heat storage correction method according to an example of the related art.

FIG. 4 is a block diagram illustrating a control section of a thermal head according to an embodiment of the thermal head control method of the present invention.

FIG. 5 is a timing chart illustrating control of a thermal head according to an embodiment of the present invention;

Claims (2)

[Claims] In a method of controlling a thermal head when an image having a gradation is recorded on a desired medium using a thermal head and a thermal transfer ink, the number of pulses of a pulsed output having a fixed time length is determined for each pixel of the image. The recording energy of each heating element of the thermal head is controlled by outputting the number corresponding to the number of gradations, and the number of pulses to be output is controlled by the number corresponding to the number of gradations of each pixel and the rising sensitivity of the ink ribbon. A method of controlling a thermal head, wherein the number of pulses for correction and the number of pulses for correcting the degree of heat storage of the thermal head are added. 2. A method according to claim 1, wherein a pulse for correcting the rising sensitivity of the ink ribbon and a pulse for correcting the degree of heat storage of the thermal head are applied. The method according to claim 1, wherein the method is determined based on the presence or absence of the thermal head.