JPH0970998A - Method and device for correcting thermal accumulation of thermal head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To apply optimum shading correction to each of thermal heads by obtaining a parameter for the shading correction by each of the thermal heads. SOLUTION: When assembling and adjusting this device in a factory, test printing in colors of yellow, magenta and cyan in respective prescribed densities is executed. In the test printing, temperatures of a thermal head and an ambient temperature are measured by means of an ambient temperature sensor 22 and a head temperature sensor 21. After the test printing, densities of the three colors at the two measuring points are measured. Two parameters of a head voltage calculation equation for calculating a head voltage are determined by each of colors by utilizing the three densities and the ambient temperature and head temperature at the measuring points in the recording. In the actual printing, the head voltage is calculated based on the two kinds of temperatures by utilizing the head voltage calculation equation including the parameters of the predetermined color to be printed. The calculation of the head voltage is executed every prescribed time interval, then the head voltage is adjusted via a regulator 35 in accordance with the calculation result.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat storage correction method and apparatus for a thermal head used in a thermal printer.

[0002]

2. Description of the Related Art In a thermal printer, a thermosensitive recording paper having a thermosensitive coloring layer formed on a support is used. An image is recorded on the thermosensitive coloring layer by pressing and heating the thermosensitive recording paper with a thermal head, and then ultraviolet rays are applied. Irradiate to fix the image. Further, a color thermosensitive recording paper in which a cyan thermosensitive coloring layer, a magenta thermosensitive coloring layer, and a yellow thermosensitive coloring layer are sequentially formed on a support is also known.

In color thermosensitive recording paper, the uppermost yellow thermosensitive coloring layer has the highest thermal sensitivity and the lowermost cyan thermosensitive coloring layer has the lowest thermal sensitivity. Utilizing this difference in thermal sensitivity, the thermal recording paper is pressed and heated by a thermal head while moving, and the respective thermal coloring layers are recorded in order from the uppermost layer. Immediately after recording, the yellow thermosensitive coloring layer and the magenta thermosensitive coloring layer are fixed by irradiating ultraviolet rays in a wavelength range specific to each thermosensitive coloring layer. By this fixation, the uncolored coloring components are photolyzed, and the coloring ability is lost.

In the thermal printer, since the thermal head is cold at the start of recording, even if each heating element is driven with desired electric energy, it is not possible to develop a desired density of color. As a result, so-called shading occurs, in which the density at the beginning of the recording area is generally low, and the overall density increases as recording proceeds.

In order to prevent the occurrence of shading due to heat accumulation in the thermal head, a method is known in which the temperature of the thermal head is measured and the electric energy supplied to each heating element is controlled in accordance with this temperature (Japanese Patent Laid-Open No. 2000-242242). 54-1
50136). This electric energy control is performed by adjusting the voltage applied to the thermal head or
This is done by adjusting the pulse width of the pulse that drives the element.

A thermal printer is also known in which correction data for the energy applied to the thermal head is created according to the substrate temperature distribution of the thermal head, and the energy applied to each heating element is individually controlled according to the correction data. (JP-A-60-143980).

Further, a thermal printer that includes a constant value parameter (coefficient) and obtains a head voltage using an arithmetic expression in which the temperature of the thermal head is a variable and adjusts the head voltage to prevent the occurrence of shading has already been used. It is commercially available. In this thermal printer, all products use the same parameter value.

[0008]

All thermal printers are designed so that the measurement accuracy of a temperature sensor such as a thermistor, the pressure contact state between the thermal head and the thermal recording paper, and the heat radiation state of the thermal head are the same. However, in the actual product, the pressure contact state and heat dissipation state are slightly different. Therefore, there is a problem that shading correction varies depending on each thermal printer.

It is an object of the present invention to provide a thermal head heat storage correction method and apparatus capable of performing optimum shading correction for each thermal printer.

[0010]

In order to achieve the above object, in the thermal storage correction device for a thermal head according to claim 1, a temperature sensor for measuring the temperature of the thermal head,
At least the density measuring means for measuring the density of at least one measurement point after creating a test print for recording the thermosensitive recording paper at a predetermined density, the density information at the measurement point, and the thermal head temperature information during recording of the measurement point. A calculation means for determining one parameter, a storage means for storing the obtained at least one parameter, and an arithmetic expression including the at least one parameter read from the storage means are used to measure with a temperature sensor during actual printing. The calculation means for calculating the heat storage correction data of the thermal head according to the thermal head temperature information and the adjusting means for adjusting the electric energy supplied to each heating element according to the heat storage correction data are provided.

In the thermal head heat storage correction method according to the third aspect, the temperature of the thermal head at at least one measurement point is measured during the production of the test print, and the density at the measurement point is measured after the test print. At least one parameter is determined from the thermal head temperature information and the density information, and in actual printing, an arithmetic expression including this parameter is used, and the thermal storage heat correction data of the thermal head is obtained according to the thermal head temperature information measured by the temperature sensor. It is calculated and the electric energy supplied to each heating element of the thermal head is adjusted.

According to the second or third aspect of the invention, the electric energy supplied to each heating element is adjusted by adjusting the head voltage applied to the thermal head.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG.
0, a heating element array 10a in which a large number of heating elements are arranged in a line is formed. This thermal head 1
0 is swingable about a shaft 11 as a fulcrum, and swings between a print position for pressing the color thermosensitive recording paper 12 on the platen roller 13 and a retracted position separated from the platen roller 13.

The color thermosensitive recording paper 12 is, as is well known,
On the support, a cyan thermosensitive coloring layer, a magenta thermosensitive coloring layer,
Yellow thermosensitive coloring layers are sequentially layered. The yellow thermosensitive coloring layer, which is the uppermost layer, has the highest heat sensitivity and develops yellow with a small amount of heat energy. The cyan thermosensitive coloring layer, which is the lowermost layer, has the lowest thermal sensitivity and develops cyan with a large amount of heat energy. Further, the yellow thermosensitive coloring layer is 420
When it is irradiated with nm near-ultraviolet rays, the coloring ability disappears. The magenta thermosensitive coloring layer loses its coloring ability when irradiated with ultraviolet rays of 365 nm.

A transport roller pair 15 is disposed downstream of the thermal head 10 and is rotated by a pulse motor 16 in both forward and reverse directions. The transport roller pair 15 reciprocates by nipping the color thermosensitive recording paper 12.

The fixing device 17 has an emission peak of 420 nm.
An ultraviolet lamp 18 for yellow which generates near ultraviolet light,
A magenta ultraviolet lamp 19 that emits ultraviolet light having an emission peak of 365 nm. A reflector 20 is arranged behind these ultraviolet lamps 18 and 19.

A densitometer 21 for measuring the yellow density, magenta intensity and cyan density of the recorded color thermosensitive recording paper 12 is provided in the paper discharge passage. As is well known, the densitometer 21 is composed of a white light source section for illuminating a measurement point of the color thermosensitive recording paper 12 and a photometric section for measuring the reflected light from the measurement point in three colors.

An environmental temperature sensor 22 for measuring the environmental temperature of the thermal head 10 is arranged near the thermal head 10. A thermistor or the like is used as the environmental temperature sensor 22. The reference numeral 23 is
A position sensor for detecting the front end of the color thermosensitive recording paper 12.

In FIG. 2, the heating element array 10a is
It is formed on a ceramic substrate 25. The substrate 25 is also provided with a drive circuit and the like for driving the heating element array 10a. The substrate 25 is fixed on the head holder 26.

The head holder 26 is made of aluminum and is provided with a plurality of fins 26a for improving heat dissipation. Further, a recess is formed on the upper surface of the head holder 26, and the head temperature sensor 2 is formed in the recess.
7 are stored. As the head temperature sensor 27, for example, a thermistor is used, and in order to accurately measure the temperature of the substrate 25, it is fixed with an adhesive 28 having a good thermal conductivity.

In FIG. 3, signals from the environmental temperature sensor 22 and the head temperature sensor 25 are A / D converters 30 and 3.
1 is converted into digital data and sent to the controller 32 as thermal head temperature information. Also, densitometer 2
The signals of three color densities from 1 are also digitally converted by the A / D converter 3 and sent to the controller 32 as three color density information.

The controller 32 determines the parameters of the head voltage calculation formula during assembly and adjustment. In the actual printing by the user, the head voltage is calculated using the temperature information. This head voltage information is sent to the regulator 35 to adjust its output voltage.

The image memory 36 stores one frame of yellow image data, magenta image data, and cyan image data fetched from a video camera or a scanner. These image data are read line by line according to the color to be printed, and the drive data generation circuit 37
Sent to The drive data generation circuit 37 processes the image data for one line in parallel and converts one image data into serial drive data of the number corresponding to the number of gradations. For example, in the case of 256 gradations, it is converted into 256-bit drive data.

Each drive data is ANDed in a predetermined cycle.
It is sent to the circuit array 38. This AND circuit array 38
When the drive data is "H" and the strobe signal of "H" is input from the controller 32, each of the AND circuits turns on the corresponding transistor of the driver circuit 39.

In each transistor of the driver circuit 39,
Each heating element (resistance element) constituting the heating element array 10a is connected. The head voltage from the regulator 35 is applied to each heating element, and when the corresponding transistor is turned on, it is energized to generate heat.

FIG. 4 shows functional blocks of the controller. The parameter calculator 40 is for determining the parameters used in the calculation formula of the head voltage. The determination of this parameter allows the production of test prints during factory assembly adjustments, on the basis of which the optimum shading correction for individual thermal printers is possible. The head voltage calculation formula is used in common for each color, although the parameters are different for each color. This arithmetic expression is as follows.

[0027]

[Equation 1]

Here, each symbol is as follows. V: Head Voltage R: Average of the heating element resistance value E _0: absolute zero thermal energy required to record a predetermined concentration in T _A: environmental temperature of the thermal head T _H: the thermal head temperature K _1, K ₂ : Parameter

As shown in FIG. 5, a test print 41 is created by each thermal printer when the parameters are determined. The test print 41 has a gray color because yellow, magenta, and cyan are uniformly recorded at a predetermined density in the recording area 41a. In the recording area 41a, the densities DA and DB for the three colors of the two predetermined measurement points A and B, and the environmental temperature T _A and the head temperature T _H during this recording are input to the parameter calculator 40. .

As shown in FIG. 6, the parameter calculating section 40 separately stores table data showing the relationship between the concentration (D) and the thermal energy (V ² / R). There are three types of table data for yellow, magenta, and cyan. Two thermal energies are obtained from the densities DA and DB of the two measurement points A and B using the table data corresponding to the color to be determined. The two thermal energies, the two temperatures (T _A , T _H ), and the constant thermal energy E ₀ are substituted into the above-described head voltage arithmetic expression to obtain, for example, yellow parameters K ₁ and K ₂ . The obtained parameters K ₁ and K ₂ are written in the ROM 43.

The head voltage calculation unit 44 calculates a head voltage calculation formula at a predetermined time interval during printing by the user to calculate the head voltage V of the color being printed. In this calculation, the parameters K ₁ , K ₂ , and E ₀ read from the ROM 43 are used, and the head voltage value capable of preventing the occurrence of shading from the environmental temperature T _A and the head temperature T _H during printing. Calculate V.
The information on the head voltage value V is sent to the regulator 35 so that the head voltage V is applied to the heating element array 10a. Since the calculation of the head voltage value V is performed every predetermined time, the head voltage V is adjusted each time.

Next, the operation of the above embodiment will be described. Color heat-sensitive recording paper 12 when assembling and adjusting at the factory
Then, each color is recorded at a predetermined density to prepare a test print 41, from which the parameters K ₁ and K ₂ of each color are determined.

This test print is performed as follows. First, the controller 32 writes predetermined yellow image data, magenta image data, and cyan image data for one frame into the image memory 36. Further, the controller 32 controls the regulator 35 to output a voltage for test printing.

Next, the controller 32 operates the paper feeding device to feed the color thermosensitive recording paper 12 from the paper feeding cassette (not shown). During this paper feeding, the thermal head 10
Is set to a retracted position away from the platen roller 13. The color thermal recording paper 12 is the thermal head 10.
And the platen roller 13 and the conveying roller pair 1
Nip to 5.

After the nip of the conveying roller pair 15, the pulse motor 16 is rotated to convey the color thermosensitive recording paper 12.
During this conveyance, when the leading end of the color thermosensitive recording paper 12 is detected by the position sensor 23, the yellow printing process is started. First, the thermal head 10 swings clockwise to move to the printing position where the color thermosensitive recording paper 12 is pressed.

The controller 36 reads the yellow image data for one line from the image memory 36 and sends it to the drive data generating circuit 37. This drive data generation circuit 37
1 converts the yellow image data into, for example, 256 pieces of driving data and sends the driving data one bit at a time.
The data is sent to the corresponding AND circuit of the D circuit array 37.

The controller 32 uses the AND circuit array 3
The strobe signal is sent to the AND circuit array 38 in synchronism with the output of the drive data to 7. As a result, the output of the AND circuit to which the drive data of “H” is input while the strobe signal is input becomes “H”, and the corresponding heating element is energized to generate heat. The heating element is pulse-driven a number of times corresponding to the yellow image data for test printing, and applies a predetermined heat energy to the color thermosensitive recording paper to develop a color.

In this way, the heating element array 10a
Records a yellow image having a constant density line by line in the recording area of the color thermosensitive recording face 12. During the recording of the yellow image, the temperatures T _A and T _H measured by the environmental temperature sensor 22 and the head temperature sensor 27 are taken into the controller 32. The controller 32
The temperatures T _A and T _H during recording of the two predetermined measurement points A and B are stored in the RAM.

When recording a yellow image, the controller 32 turns on the yellow ultraviolet lamp 18.
Then, when the portion in the recording area where the yellow image is recorded comes, the near-ultraviolet ray having a light emission peak of 420 nm emitted from the yellow ultraviolet lamp 18 is irradiated and fixed.

The carrying amount of the color thermosensitive recording paper 12 is measured by counting the drive pulses of the pulse motor 16. When it is detected from this count value that the rear end of the color thermosensitive recording paper 12 has reached the return start position near the conveying roller pair 15, the printing process of the yellow image ends.

Next, the controller 32 turns off the yellow ultraviolet lamp 18 and turns the thermal head 1 on.
Swing 0 counterclockwise to move to the retracted position. At the same time, the reverse rotation of the pulse motor 16 is started, and the leading edge of the color thermosensitive recording paper 12 is returned to the print start position detected by the position sensor 23.

When the color thermosensitive recording paper 12 is returned to the print start position, the pulse motor 16 starts forward rotation, and the thermal head 10 moves to the print position.
The magenta printing process starts. In this magenta printing process, similarly to the yellow printing process, a magenta image having a constant density is recorded line by line in the recording area.

While the portion on which the magenta image is recorded passes through the magenta ultraviolet lamp 19, the magenta image is fixed by the ultraviolet rays having an emission peak of 365 nm emitted from the magenta ultraviolet lamp 19. The magenta ultraviolet lamp 19 is lit until the paper discharge is completed. Even in the magenta printing process, the temperature at the time of recording the measurement points A and B is taken into the controller 32.

When the printing process of the magenta image is completed, the pulse motor 16 is rotated in the reverse direction to return the color thermosensitive recording paper 12 to the print start position. Next, when the cyan printing process is started, the pulse motor 16 again rotates in the forward direction to convey the color thermosensitive recording paper 12 at a constant speed. During this conveyance, the thermal head 10 records a cyan image having a constant density line by line in the recording area. Again,
The temperature at the time of recording the measurement points A and B is taken into the controller 32.

The color thermosensitive recording paper 12 on which a full-color image is recorded in a three-color frame sequential manner is used as a test print 41.
It is ejected to a paper ejection tray (not shown) while being irradiated with magenta ultraviolet rays. During this discharge, the densitometer 21 measures the three-color densities along the line passing through the two measurement points A and B in the recording area 41a. During the measurement of the density, the controller 32 specifies the amount of conveyance of the test print 41 by 2
Take in the three color densities of one measurement point A and B.

After the test print 41 is discharged, the parameter calculation unit 40 uses the three color densities of the measurement points A and B and refers to the table data of each color to determine the thermal energy (V ² / R).
Is calculated for each color. Next, in the head voltage calculation formula, the thermal energy at the measurement points A and B and the temperature (T _A , T _H ) at the time of recording
And the thermal energy E ₀ are substituted to obtain the parameters K ₁ and K ₂ for each color, and these are written in the ROM (EEPROM).

In the printing by the user, the image data of three colors taken in from the skier or the video camera is written in the image memory 36. When the print key is operated, a full-color image is recorded on the color thermosensitive recording paper 12 by three-color frame sequential recording in the same manner as the above-described test print.

At a predetermined time interval during the printing process of each color
The controller 32 uses the environment from the environment temperature sensor 22.
Temperature T_AAnd the head temperature from the head temperature sensor 27
T_HTake in and. The head voltage calculation unit 44 prints
Color parameter K₁, K ₂, E₀From ROM 43
read out. And the head voltage including these parameters
From the pressure calculation formula, find the head voltage V of the color being printed,
The regulator 35 so that the head voltage V is output.
Control. Therefore, the regulator 35 is
In consideration of the heat storage of the thermal head 10, the head voltage
To prevent shading. The number
The head voltage may be controlled for each line.

In the above-described embodiment, the densitometer 21 is built in the thermal printer, but it may be omitted to reduce the cost. In this case, a densitometer 21, a dedicated measuring instrument equipped with an arithmetic unit incorporating the table data shown in FIG. 6, a display or a printing unit is used, and the densities of the measurement points A and B of the test print are measured with this dedicated measuring instrument. Measured, 2
The thermal energy (V ² / R) at the two measurement points A and B is obtained. Then, these two thermal energies are input to the thermal printer, the parameters K ₁ and K ₂ of each color are calculated and written in the ROM 43.

Although the electric energy of each heating element is collectively corrected by changing the head voltage by using the head voltage calculation formula, the correction value of the electric energy supplied to each heating element may be obtained. Then, this correction value is added to or subtracted from each image data to correct each image data.

Although a constant head voltage is used during test printing, the head voltage may be adjusted by using default values common to each printer as parameters K ₁ and K ₂ . In this case, the arithmetic expression for obtaining the parameter only changes.

Since the reliability increases as the number of measurement points increases, it is preferable to increase the number of measurement points. Then, a large number of parameters K ₁ and K ₂ are obtained by combining two measurement points, and the average value of these is used. Furthermore, although the accuracy of shading correction is somewhat deteriorated, the number of parameters may be set to one by considering the environmental temperature as a constant value.

A platen drum having a large size may be used, and a color thermosensitive recording paper may be wound around the platen drum to record one color for each rotation. Further, a thermal head may be provided for each color, and a full-color image may be recorded by one transfer. Further, the color thermosensitive recording paper may have a four-layer structure in which a black thermosensitive coloring layer is provided in addition to the yellow thermosensitive coloring layer, the magenta thermosensitive coloring layer and the cyan thermosensitive coloring layer. Of course, a thermosensitive recording paper on which a thermosensitive coloring layer of one color is recorded can be used.

[0054]

According to the present invention having the above-mentioned structure, a test print is prepared by an individual thermal printer, and the thermal head temperature information at the time of recording the measurement point on the test print and the density information at the measurement point are used to determine the thermal print. Since the parameters of the arithmetic expression for calculating the heat storage correction data of the head are determined, it is possible to perform the optimum shading correction for each thermal printer. Further, by controlling the head voltage, the shading correction of each heating element is collectively performed, so that the correction is simple.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a color thermal printer of the present invention.

FIG. 2 is a cross-sectional view of a thermal head.

FIG. 3 is a block diagram showing an electrical configuration.

FIG. 4 is a functional block diagram of a head voltage control system.

FIG. 5 is an explanatory diagram of a test print.

FIG. 6 is a graph of table data showing the relationship between the density of test prints and thermal energy.

[Explanation of symbols]

 10 Thermal Head 10a Heating Element Array 12 Color Thermal Recording Paper 21 Densitometer 22 Environmental Temperature Sensor 27 Head Temperature Sensor

Claims (4)

[Claims] 1. A thermal printer, comprising: a thermal head having a plurality of heating elements arranged in a line; and the thermal head heats a thermal recording paper for color recording; and a thermal sensor for measuring the temperature of the thermal head; At least 1 from the density measuring means for measuring the density of at least one measurement point after creating a test print for recording the recording paper at a predetermined density, and the density information of this measurement point and the thermal head temperature information during recording of the measurement point. Using a calculation means for determining one parameter, a storage means for storing the obtained at least one parameter, and a calculation formula including at least one parameter read from the storage means,
Calculation means for calculating the thermal storage correction data of the thermal head according to the thermal head temperature information measured by the temperature sensor during actual printing, and adjustment for adjusting the electric energy supplied to each heating element according to the thermal storage correction data And a heat storage correction device for a thermal head. 2. The heat storage correction apparatus for a thermal head according to claim 1, wherein the adjusting unit is a regulator that adjusts a head voltage applied to the thermal head according to the heat storage correction data. 3. At least one during the creation of the test print.
The temperature of the thermal head at one measurement point is measured, the density at the measurement point is measured after test printing, and at least one parameter is determined from these thermal head temperature information and density information. The thermal head is characterized by calculating the thermal storage correction data of the thermal head according to the thermal head temperature information measured by the temperature sensor, and adjusting the electric energy supplied to each heating element of the thermal head using an arithmetic expression including Heat storage correction method. 4. A thermal storage correction method for a thermal head, wherein the electric energy is adjusted by adjusting a head voltage applied to the thermal head.