JP2002205420A - Thermal printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent lowering of a coloring density at a portion in the vicinity of a side edge of a recording paper. SOLUTION: A line sensor having CCD elements 14a arranged at a pitch roughly the same as that of heating elements 15a is disposed at an upstream side of a thermal head 15. The line sensor 14 detects a side edge 20a of a color thermal recording paper 20. The heating element array 15d is made in a non- driving condition based on the edge position data from the line sensor 14. The image data corresponding to the heating elements 15a at a portion in the vicinity of each of the side edges 20a, 20b of the heating element array 15c is replaced with non-printing data. When an image is printed on a whole width of the color thermal recording paper 20, lowering of the coloring density at a portion in the vicinity of each of side edges 20a, 20b is suppressed, thereby achieving the desired coloring density.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal printer, and more particularly, to a thermal printer that records an image almost to a side edge of a recording sheet.

[0002]

2. Description of the Related Art A recording paper is transported in a sub-scanning direction perpendicular to a thermal head in which a large number of heating elements are arranged in a line in a main scanning direction. There is a thermal printer that generates heat to perform thermal recording. This thermal printer has a thermal transfer recording type that heats an ink sheet sandwiched between a thermal head and recording paper to transfer the ink on the ink sheet to the recording paper, and a thermosensitive coloring layer that develops color by heat. There is a thermal recording type using recording paper.

[0003] In any of the above thermal printers, it has been desired to perform printing over the entire width of the recording paper to eliminate margins at the side edges. Then, Japanese Patent Application Laid-Open No. 9-27221
As described in Japanese Patent Laid-Open No. 7, a thermal printer using a thermal head in which heating elements are arranged longer than the width of a recording sheet has been proposed. In this thermal printer, a sensor for detecting the side edge of the recording paper is provided so that a heating element located outside the side edge of the recording paper does not overheat,
The heating elements located outside the side edges of the recording paper are forced to be in a non-driving state.

[0004]

However, in the above-described thermal printer, the color density of the print image gradually decreases from the desired color density as the recording paper approaches the side edge of the recording paper, and the print quality of the print image decreases. There is a problem of lowering.

On the other hand, when the side edge of the recording paper is over the heating element, there is a problem that the gradually reduced density rapidly increases at the position of the heating element, and the side edge becomes black.

The present invention has been made to solve the above-mentioned problem, and prevents a decrease in color density near the side edge of a recording sheet.
An object of the present invention is to provide a thermal printer that prevents print quality from deteriorating.

[0007]

In order to achieve the above object, a thermal printer of the present invention uses a thermal head in which a plurality of heating elements are arranged in a line longer than the width of a recording sheet in a main scanning direction. In a thermal printer that records an image on a recording sheet conveyed in the sub-scanning direction, a detecting unit that detects a side edge position of the recording sheet, and a recording sheet based on the side edge position of the recording sheet detected by the detecting unit. And a data correction unit for performing a predetermined correction process on image data corresponding to the heating element located near the side edge of the heating elements facing.

The data correction means prints image data corresponding to a predetermined number, for example, N, of heating elements located in the vicinity of the side edge of the printing data in which the heating energy of the heating element gradually increases as approaching the side edge of the recording paper. Replace with In addition, the non-printing data is given to the heating element facing the side edge, thereby preventing a sharp increase in the density of the side edge. The data correction means comprises several,
For example, image data corresponding to M (M <N) heating elements is replaced with non-print data.

The detecting means is a plurality of line sensors arranged at substantially the same pitch as the plurality of heating elements in the main scanning direction. Further, the detecting means, a temperature measuring means for measuring the temperature of each of the plurality of heating elements, and a heating time measuring means for measuring the heating time until each heating element reaches a predetermined temperature using this temperature measuring means, And a side edge position calculating means for calculating the position of the side edge of the recording paper from the respective heating times of the heating elements.

[0010]

FIG. 1 is a schematic diagram showing the configuration of a color thermal printer embodying the present invention. The color thermal printer 10 includes first, second, and third transport roller pairs 11, 1
2, 13, a line sensor 14, a thermal head 15, a photo sensor 16, an optical fixing device 17, a system controller 18, and the like. The first, second, and third transport roller pairs 11, 12, and 13 are rotationally driven in both forward and reverse directions by a pulse motor 19, and transport the thermosensitive recording paper 20 wound in a roll in a reciprocating manner. Pulse motor 19
Is controlled by the system controller 18 via the motor driver 21.

The drive pulse to the pulse motor 19 is counted by a pulse counter 22, and based on this, the system controller 18 specifies a print start position, a recording paper return position, a cut position, and the like. Pulse counter 22
Counts up the drive pulse when the pulse motor 19 rotates forward, and counts down the drive pulse when the pulse motor 19 rotates backward.

The color thermosensitive recording paper 20 is, as is well known,
On the support, a cyan thermosensitive coloring layer, a magenta thermosensitive coloring layer, and a yellow thermosensitive coloring layer are sequentially provided. The yellow thermosensitive coloring layer, which is the uppermost layer, has the highest thermal sensitivity and develops yellow with small heat energy. The cyan thermosensitive coloring layer, which is the lowermost layer, has the lowest thermal sensitivity and develops cyan with large thermal energy. The yellow thermosensitive coloring layer loses its coloring ability when irradiated with near-ultraviolet light having a peak emission wavelength of 420 nm. The magenta thermosensitive coloring layer develops a magenta color with a thermal energy intermediate between the yellow thermosensitive coloring layer and the cyan thermosensitive coloring layer, and has a peak emission wavelength of 365 nm.
When the ultraviolet rays are irradiated, the coloring ability is lost.

A thermal head 15 is disposed between the first and second transport roller pairs 11 and 12. As shown in FIG. 2, the thermal head 15 has a large number of heating elements 15.
heating element array 1 in which a is arranged in a line in the main scanning direction
5b. The heating element array 15b is formed slightly longer than the width of the recording paper in order to print an image having no margin on the color thermosensitive recording paper 20. Then, one end of the heating element array 15b and the side edge 20b of the color thermosensitive recording paper 20 guided by a guide member described later coincide with each other.

In FIG. 1, a platen roller 2 for supporting the color thermosensitive recording paper 20 is located at a position facing the heating element array 15b with the conveyance path of the color thermosensitive recording paper 20 interposed therebetween.
4 are arranged. The thermal head 15 is swingable with the shaft 25 as a fulcrum, and is moved between a print position where the color thermosensitive recording paper 20 on the platen roller 24 is pressed and a retract position where the thermal recording paper is retracted upward away from the platen roller 24. Rocks.

When the color thermosensitive recording paper 20 is conveyed in the paper feeding direction via the head driver 26, the system controller 18 controls each heating element 15 of the heating element array 15b.
a is heated to a predetermined temperature in accordance with print data to be described later, and thermal energy is supplied to the color thermosensitive recording paper 20 to cause each thermosensitive coloring layer to selectively develop a color. Platen roller 2
Reference numeral 4 rotates in accordance with the conveyance of the color thermosensitive recording paper 20, and stabilizes the contact state between the color thermosensitive recording paper 20 and the heating element array 15b.

In FIG. 2, an urging member 27 for pressing one side edge 20a of the color thermosensitive recording paper 20 is provided around the thermal head 15. The urging force of the urging member 27 causes the other side edge 20 of the color thermosensitive recording paper 20 to move.
b is constantly pressed against the guide member 28. Further, a line sensor 14 for detecting the side edge of the color thermosensitive recording paper 20 is arranged on the upstream side of the thermal head 15 in the paper feeding direction and on the side edge 20a side of the color thermosensitive recording paper 20. As the line sensor 14, a CCD array 14b in which a plurality of CCD elements 14a are arranged at substantially the same pitch as the heating elements 15a arranged in the thermal head 15 is used. The line sensor 14 detects the position of the side edge 20 a of the color thermosensitive recording paper 20 being conveyed at a predetermined timing, and sends the side edge position data to the system controller 18.

In FIG. 1, a photo sensor 16 and an optical fixing device 17 are provided between the second and third conveying roller pairs 12 and 13.
And are arranged. The photosensor 16 is a light emitting element 16 disposed below the transport path of the color thermosensitive recording paper 20.
a, and a light receiving element 16b disposed at a position above and facing the light emitting element 16a. Color thermal recording paper 2
When 0 is conveyed and enters between the light emitting element 16a and the light receiving element 16b, the light emitted from the light emitting element 16a is blocked by the color thermosensitive recording paper 20 and does not enter the light receiving element 16b. The light receiving element 16b sends a detection signal to the system controller 18 when the light stops entering.

The optical fixing device 17 comprises a reflector 30, an ultraviolet lamp 31 for yellow, and an ultraviolet lamp 32 for magenta. The yellow UV lamp 31 emits near-ultraviolet light having an emission wavelength peak of 420 nm, and the magenta ultraviolet lamp 32 emits ultraviolet light having an emission wavelength peak of 365 nm. And these ultraviolet lamps 31 and 3
2 is the system controller 18 via the driver 33
Respectively, and fix the recorded yellow thermosensitive coloring layer and the magenta thermosensitive coloring layer so as not to develop a color even if heated again.

FIG. 3 is a block diagram showing an electrical configuration of the color thermal printer 10. System controller 1
8, each of the sensors 14 and 16 and each driver 2
A memory controller 35, a print data forming unit 36, and the like are connected in addition to the components 1, 26 and the pulse counter 22.

Although not shown, the color thermal printer 10 is provided with an I / O port to which various external devices can be attached, and this I / O port has an I / O circuit 3.
7 is connected. The I / O circuit 37 includes a digital camera 38 and a computer 39 connected to the I / O port.
For example, R, G, and B color image data are input. The input image data is stored in the frame memory 40 via the I / O circuit 37. The I / O port is also provided with a video output terminal.
To display the print image.

As shown in FIG. 2, the system controller 18 controls the color thermosensitive recording paper among the heating elements 15a based on the side edge position data of the side edge 20a of the color thermosensitive recording paper 20 detected by the line sensor 14. 20 side edges 20
a, a heating element array 15c positioned inside the thermosensitive recording paper 20 facing the color thermosensitive recording paper 20, and a heating element array 1 positioned outside the side edge 20a and not facing the color thermosensitive recording paper 20.
5d.

Each color image data stored in the frame memory 40 is read and written by the memory controller 35 controlled by the system controller 18 in the print data forming section 36 as appropriate. Print data forming unit 3
6 forms print data of each color of yellow (Y), magenta (M), and cyan (C) for driving each heating element 15a of the thermal head 15 based on each color image data. The print data includes the non-printing data in which the image data that does not cause the heat-sensitive coloring layers to develop a color is "0" without causing the heating element 15a to generate heat exceeding the bias heat energy, and the heating element 15a in accordance with the image data. The print data includes print data for generating heat at a predetermined temperature and corrected print data obtained by performing a predetermined data correction process on image data.

The print data forming section 36 prepares non-print data for each heating element 15a of the heating element row 15d based on the side edge position data detected by the line sensor 14, and generates each heating element of the heating element row 15c. Print data is created for the element 15a. Further, the color thermosensitive recording paper 20
Then, corrected print data is created by performing data correction processing for preventing a decrease in color density on image data assigned to a predetermined number (N) of heating elements near the side edges 20a and 20b of the image forming apparatus.

For example, when recording a uniform solid image having image data of "128", as shown in FIG.
Five heating elements 15a (address-
1-5), non-print data is created and the side edge 2
0a, 12 heating elements 15a (address 0 to 0)
For (11), corrected print data is generated such that the heat generation energy gradually increases toward the heat element at address 0. Since the thermal energy is gradually increased toward the end as described above, the concentration is prevented from decreasing toward the end.

The print data formed from these print data, corrected print data and non-print data is shown in FIG.
Are input to the head driver 26 as shown in FIG. The head driver 26 is controlled by the system controller 18 to cause each of the heating elements 15a of the thermal head 15 to generate heat in accordance with the input print data, thereby performing thermal recording on each of the thermosensitive coloring layers of the color thermosensitive recording paper 20. In this manner, the image is printed over the entire width of the color thermosensitive recording paper 20, and the color density 46 near the side edges 20a and 20b is prevented from lowering.

Next, the operation of the above configuration will be described.
When performing thermal recording on the color thermal recording paper 20 using the color thermal printer 10 of the present invention, first, the digital camera 3
8 or computer 39 or the like. The input image data is stored in the frame memory 40 via the I / O circuit 37 for each color.

When the printing operation of the color thermal printer 10 is started, the system controller 18 drives the pulse motor 19 through the motor driver 21 in the normal direction. The pulse motor 19 includes first, second, and third transport roller pairs 11,
The color thermosensitive recording paper 20 is transported in the paper feeding direction by rotating the recording papers 12 and 13 in the paper feeding direction. At this time, the thermal head 15 is set at the retracted position so as not to hinder the conveyance of the color thermosensitive recording paper 20. In addition, the urging member 27
, The side edge 20b of the color thermosensitive recording paper 20 is always conveyed while being pressed against the guide member 28.

The line sensor 14 is a color thermosensitive recording paper 2
The position of the 0 side edge 20a is detected, and the side edge position data is sent to the system controller 18. The system controller 18 specifies the heating element row 15c facing the color thermosensitive recording paper 20 and the heating element row 15d not facing the color thermosensitive recording paper 20 based on the side edge position data. Color thermal recording paper 20
Is detected by the photo sensor 16, the thermal head 15 is set at the printing position, and thermal recording of the yellow thermosensitive coloring layer is started.

In the print data forming section 36, based on each color image data from the frame memory 40, yellow print data for heating each of the heating elements 15a of the heating element row 15c to a predetermined temperature, and a side edge of the color thermosensitive recording paper 20 20
a, correction print data of yellow which has been subjected to a correction process for preventing the color density from gradually decreasing toward a and 20b, and bias thermal energy (thermal energy for heating up to immediately before coloring) for each of the heating elements 15a of the heating element row 15d. And the non-printing data of yellow. The yellow print data formed from the print data, the corrected print data, and the non-print data is input to the head driver 26.

The head driver 26 causes each of the heat generating elements 15a to generate heat in accordance with the inputted yellow print data, thereby causing the yellow thermosensitive coloring layer to develop a desired density. 1
When the recording of the line is completed, the color thermal recording paper 20 is conveyed by one line, and the thermal recording of the next line is performed in the same manner. Thus, the thermal recording and the transport of the color thermosensitive recording paper 20 are repeated until the recording of the yellow image is completed. When the portion where the yellow image is thermally recorded reaches the optical fixing device 17, the yellow thermosensitive coloring layer is optically fixed by the yellow ultraviolet lamp 31 turned on by the system controller 18 via the driver 33.

After the light fixing of the yellow thermosensitive coloring layer is completed,
The first, second, and third transport roller pairs 11, 12, and 13 rotate in reverse to transport the color thermosensitive recording paper 20 in the returning direction to the magenta image recording start position. Then, in the same manner as during the thermal recording of the yellow image, the print data forming section 36 performs the correction processing of the print data based on the side edge position data, forms the print data, and inputs the magenta print data to the head driver 26.

The head driver 26 causes each heating element 15a to generate heat in synchronization with the feeding of the color thermosensitive recording paper 20 in accordance with the input magenta print data, and records a magenta image on the magenta thermosensitive coloring layer. When the portion where the magenta image is thermally recorded reaches the optical fixing device 17, the magenta ultraviolet lamp 32 is turned on by the system controller 18 via the driver 33.
The magenta thermosensitive coloring layer is light-fixed.

When the light fixing of the magenta thermosensitive coloring layer is completed,
The first, second, and third transport roller pairs 11, 12, and 13 are again rotated reversely, and transport the color thermosensitive recording paper 20 in the returning direction to the recording start position of the cyan image. Then, in the same manner as during the thermal recording of the yellow image, the print data forming unit 36 performs the correction processing of the print data based on the side edge position data, forms the print data, and inputs the cyan print data to the head driver 26.

The head driver 26 causes each of the heating elements 15a to generate heat in accordance with the input cyan print data and thermally records the cyan image in the same manner as the magenta image. The cyan thermosensitive coloring layer is configured so as not to develop a color in a normal storage state, and thus does not have light fixing properties. However, also during cyan recording, the magenta ultraviolet lamp 32 is turned on in the same manner as during magenta recording, and the unrecorded area having a yellow tint is bleached.

The color thermosensitive recording paper 20 is conveyed even after the thermal recording and light fixing to each thermosensitive coloring layer are completed, and when the cut position of each print image reaches a cutter (not shown), the cutter operates to print the print image. Disconnected every time. Here, the color thermosensitive recording paper 20 is transferred to each of the transport roller pairs 11, 12, and 13.
Since the print image is conveyed while being pinched, a margin is generated at the leading end and the trailing end of the print image. Therefore, the system controller 18 sets the leading end and the trailing end position of each print image to the cut position and performs color thermal recording. The paper 20 is positioned on the cutter, and these margins are also cut. In this way, a borderless print without margins is obtained. The cut thermal recorded print image is discharged outside the printer.

When the side edge of the color thermosensitive recording paper 20 does not coincide with the end of the heating element, the side edge passes over the heating element. In this case, it was confirmed by an experiment that when the heating element with which the side edge was in contact was driven by the corrected print data, the density of the side edge was extremely increased, resulting in black streaks. Since the thermosensitive coloring layers of three colors are exposed on the end face of the color thermosensitive recording paper 20 by cutting during manufacturing, the thermal sensitivity of this portion is higher than the original value. Further, since the side edges are curled, a part of the end face is likely to come into contact with the heating element. For these reasons, it is presumed that the three-color heat-sensitive coloring layers on the end face portions develop color and become black.

In the embodiment shown in FIG. 5, the side edge 20a of the color thermosensitive recording paper 20 is located on the heating element of the address "-1". In this case, the non-printing data is given to the heating element of the address “−1” to prevent the occurrence of black stripes on the side edge 20a. Of course, the address "1
Correction printing data whose thermal energy gradually increases are given to the heating elements of “1” to “0”.

The color thermosensitive recording paper 20 is cut into a predetermined width at the time of manufacture. Due to this cutting, the position of the side edge slightly changes even for one color thermal recording sheet.
On the other hand, the width of the heating element is about 120 to 150 μ.
Therefore, the position of the side edge slightly changes during recording on one color thermal recording sheet. Therefore, in order to reliably prevent the occurrence of black streaks on the side edges, it is preferable to apply non-print data to the heating element of address "0" as shown in FIG. That is, the heating element of address “0” is located entirely inside the side edge, but in consideration of safety,
Non-print data is provided.

Although the non-print data is given to one heating element, the number is determined as appropriate. In any case, if the number of heating elements located near the side edge of the color thermosensitive recording paper 20 is N, and the number M of heating elements near the side edge is M, then N> M. In the example shown in FIG. 6, N is the 12 heating elements of addresses “11” to “0”,
M is one heating element of address “0”.

In the above embodiment, the color thermosensitive recording paper 20
Is pressed by the urging member 27 and the other side edge 20b is pressed against the guide member 28 to perform positioning. Then, the position of the side edge 20a is detected by the line sensor 14, and the image data is corrected based on the side edge position data. However, as shown in FIG. 7, the line sensors 50 and 51 are
May be provided on both side edges 20a and 20b, respectively, and the data correction processing of the image data may be performed based on the respective side edge position data.

In the above embodiment, the color thermosensitive recording paper 20
A line sensor is used to detect the position of the side edge of the recording paper 20. However, there is a difference in the energization time until the target temperature is reached between the heating element that is in contact with the color thermal recording paper 20 and the heating element that is not in contact. Therefore, the side edge position may be detected based on the difference in the energization time. FIG. 8 is a schematic diagram showing a main configuration of the color thermal printer in this case.

Each heating element 60 has a current detecting resistor 61,
The transistor 62 and the AND gate 63 are connected, and a constant head voltage Vth is applied.
The print data of the serial signal formed by the print data forming unit 64 is input to the shift register 65 in synchronization with a clock signal (Clock). Shift register 6
In step 5, the input print data is converted into a parallel signal and output to the latch circuit 66. The latch circuit 66 stores this in synchronization with the latch signal (Latch). When the latch signal (Latch) is input to the strobe circuit 67, the strobe circuit 67 outputs an “H” level strobe signal to one input terminal of the AND gate 63. The drive pulse width of the strobe signal is changed for each color recording. When the other input terminal of the AND gate 63 goes to "H" level by the output signal of the latch circuit 66, the AND terminal of these input terminals causes the output terminal of the AND gate 63 to go to "H" level, and the transistor 62
Is turned on, the heating element 60 is energized and generates heat.

The connection point between the heating element 60 and the current detection resistor 61 is connected to an A / D converter 69 via a selector 68. The temperature of each heating element 60 is detected by a change in voltage value due to a change in electrical resistance from the temperature dependence of the resistance value of the heating element 60. That is, each heating element has a characteristic that the resistance decreases as the temperature increases. For this reason,
The voltage at the connection point decreases as the temperature of the heating element 60 increases. The voltage at the connection point is converted into a digital signal by the A / D converter 69 and then input to the comparator 70.

In the setting register 71, a target voltage value E0 obtained by converting the attained temperature of each heating element 60 into a voltage value is set. Comparator 70 compares voltage value E with target voltage value E0, and when E <E0, sets the output signal to “L” level, and when E ≧ E0, sets the output signal to “H” level. This output signal is output from the strobe circuit 67 and the counter 7.
2 is input. Current detection resistor 61, selector 6
8, the A / D converter 69, the comparator 70, and the setting register 71 constitute a temperature measuring section 75 for each heating element.

The strobe circuit 67 turns on the heating element 60 to be measured and, at the same time, starts the start signal (St).
art) to the counter 72. This counter 72
Count the clock signal and start measuring the energization time,
When the stop signal (Stop) is input from the comparator 70, the measurement ends. In this way, the heating elements are measured one by one while switching the selector 68. The measured energization time of each heating element 60 is input to the system controller 76. In the system controller 76, each heating element 60
From the difference in the energizing time of the color thermosensitive recording paper 20
The positions of a and 20b are calculated and specified. That is, since the heat is transmitted to the color thermosensitive recording paper 20 at the heating element 60 that is in contact with the color thermosensitive recording paper 20, the energization time until the temperature reaches a certain temperature is longer than that of the heating element 60 that is not in contact. . From the difference in the energization time, the color thermosensitive recording paper 2
The positions of the 0 side edges 20a and 20b are specified.

The detection of the side edge position of the color thermosensitive recording paper 20 is performed before printing is started. That is, 1
Before the recording position of the line, place a dummy print line
Lines are provided, and dummy print data that does not cause the yellow thermosensitive coloring layer to develop color is sent to the shift register 65 with respect to this dummy print line, and the energizing time until each heating element 60 reaches a certain temperature is set for each heating element. Ask for.
Then, the heating element portion where the energization time switches is detected,
The boundary of the switching heating element is defined by the color thermosensitive recording paper 20.
Are specified as the positions of the side edges 20a and 20b. For this reason, in the detection processing of the side edge position of the color thermosensitive recording paper 20, the strobe circuit 67 sets the "H" level for each AND gate 63 so as to sequentially drive the heating elements 60 one by one at the time of dummy printing. And outputs the strobe signal. Then, the energization time until each heating element 60 reaches a certain temperature at this time is sequentially obtained for each heating element.

The side edge position data obtained in this manner is
The data is input to the print data forming unit 64, and based on this, the same data correction processing as in the above embodiment is performed on the image data of the first and subsequent lines.

In the above embodiment, the dummy print line is provided, and the side of the recording paper is detected by heating to a temperature range in which the yellow thermosensitive coloring layer does not develop a color. The side edge position of the recording paper may be detected from the difference in the energization time required to reach a certain temperature during the recording of the first line.

The heating element records one dot by bias driving and gradation driving. The bias driving is to generate thermal energy just before color development, and the gradation driving is to apply gradation thermal energy according to the color density. In the present invention, as the non-printing data, data that only performs bias driving is used, but printing data that becomes inactive without bias driving may be used.

In the above embodiment, the image is printed using a long recording paper. However, a cut recording paper that has been cut in a sheet shape in advance may be used. The color thermosensitive recording paper may have a four-layer structure in which a black thermosensitive coloring layer is provided in addition to a yellow thermosensitive coloring layer, a magenta thermosensitive coloring layer, and a cyan thermosensitive coloring layer.

In the above-described embodiment, a thermal printer in which thermal recording of each color is performed by one thermal head is described as an example. However, a thermal head is provided for each color, and a full-color image is recorded on recording paper by one transport. The present invention may be applied to a thermal printer that prints an image.

[0052]

As described above, according to the thermal printer of the present invention, the line sensor for detecting the side edge position of the recording paper,
Data correction means for performing a predetermined correction process on image data corresponding to a heating element located near the side edge of the heating elements facing the recording sheet based on the side edge position of the recording sheet detected by the line sensor. With this configuration, even when printing an image over the entire width of the recording paper, the color density near the side edge does not gradually decrease from the desired color density toward the side edge, and the deterioration of print quality is suppressed. Can be

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of a thermal printer of the present invention.

FIG. 2 is a plan view showing a configuration around a thermal head.

FIG. 3 is a block diagram illustrating an electrical configuration of the thermal printer.

FIG. 4 is a graph showing a data correction processing method according to the first embodiment.

FIG. 5 is a graph illustrating a data correction processing method according to a second embodiment.

FIG. 6 is a graph showing a data correction processing method according to a third embodiment.

FIG. 7 is a plan view showing a method for detecting both side edge positions of the color thermosensitive recording paper using two line sensors.

FIG. 8 is a schematic diagram showing a method for detecting the positions of both side edges of the color thermosensitive recording paper based on the difference in the energization times to the heating elements.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 color thermal printer 14 line sensor 15 thermal head 16 photo sensor 17 optical fixing device 18 system controller 19 pulse motor 20 color thermal recording paper 22 pulse counter 27 biasing member 28 guide member 35 memory controller 36 print data forming section 40 frame memory 45 , 47, 48 Image data 46 Color density

Claims (6)

[Claims] 1. A thermal printer that uses a thermal head in which a plurality of heating elements are arranged in a line shape longer than the width of a recording sheet in a main scanning direction and records an image on the recording sheet conveyed in a sub-scanning direction. Detecting means for detecting a side edge position of the recording sheet, and corresponding to a heating element located near the side edge among the heating elements facing the recording sheet based on the side edge position of the recording sheet detected by the detecting means. And a data correction unit for performing a predetermined correction process on the selected image data. 2. The data correction means converts image data corresponding to a predetermined number of heating elements located in the vicinity of a side edge into print data in which the heating energy of the heating element gradually increases as approaching the side edge of the recording paper. 2. The thermal printer according to claim 1, wherein the thermal printer is replaced. 3. A thermal printer according to claim 2, wherein said data correction means replaces the image data of the heating element whose side edge of the recording paper faces with non-printing data. 4. The thermal printer according to claim 2, wherein said data correction means replaces image data corresponding to several heating elements near the side edge with non-printing data. 5. A thermal printer according to claim 1, wherein said detecting means comprises a plurality of line sensors arranged at substantially the same pitch as said plurality of heating elements in a main scanning direction. . 6. The temperature detecting means for measuring a temperature of each of the plurality of heating elements, and a heating means for measuring a heating time until each of the heating elements reaches a predetermined temperature using the temperature measuring means. 5. The thermal printer according to claim 1, further comprising: a time measuring unit; and a side edge position calculating unit configured to calculate a position of a side edge of the recording paper from a heating time of each heating element.