JP2005144755A - Thermal printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a heating element of a thermal head from sinking too much in a recording sheet. <P>SOLUTION: A head position adjusting mechanism 35 consisting of a head support 37 for supporting the thermal head 18, an adjusting screw 39 screwed in a screw hole 38 formed at the head support 37 so as to adjust a distance between the heating element 18a and a platen roller 19, and a motor 42 for rotating the adjusting screw 39 is set at a color thermal printer. A data table for correction in which a total application energy amount calculated from line data sent from a DSP 52, and a rotation angle of the motor 42 such that the heating element 18 is prevented from sinking too much into the recording sheet 11 are made to correspond to each other is stored in an LUT 53 connected to a system controller 50 of the color thermal printer. The system controller 50 rotates the motor 42 with reference to the data table for correction at the time of printing, so that the heating element 18a can be prevented from sinking too much in the recording sheet 11. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a thermal printer including a thermal head that performs thermal recording by heating.

  Thermal printers including thermal printers that use thermal recording paper are provided with thermal heads that perform image printing (thermal recording). The thermal head is provided with a partial glaze in which a highly heat-storing glazed glass is layered on a head substrate, and a part of this is bulged into a cylindrical ridge. A heating element array in which a plurality of heating elements are arranged in a line along the main scanning direction is provided near the apex of the partial glaze. The thermal printer presses the heating element array against the thermal recording paper, and in that state, the thermal recording paper is conveyed in the sub-scanning direction orthogonal to the main scanning direction, and the line images in the main scanning direction are sequentially colored and recorded on one screen. Get an image of the minute. In the heating element array, for example, one heating element corresponds to one pixel, and each heating element is colored according to the density of the corresponding pixel based on image data. A platen roller that supports the thermal recording paper from its back surface is disposed at a position facing the heating element array, and the thermal recording paper is conveyed in a nipped state by the platen roller and the thermal head.

  When the thermal recording paper is nipped, the vicinity of the apex of the partial glaze that includes the heating element array sinks into the recording surface of the thermal recording paper. However, if the amount of the heating element array is too small, the heat transfer efficiency is poor, and conversely. If it is too large, plastic deformation will occur on the recording paper, causing streaky deformation on the recording surface. Since the nip force for sandwiching the thermal recording paper changes depending on the position of the thermal head at the time of printing, for example, at the time of shipment, the head position is adjusted so as to obtain an appropriate amount of penetration.

  Further, even if the thermal head or the platen roller bends in the main scanning direction, the amount of entrainment of each heat generating element changes, and color unevenness occurs along the main scanning direction. For such problems, as described in the following Patent Documents 1 and 2, the thermal head is prevented from being bent by a plurality of screws arranged in the main scanning direction, and also described in the following Patent Document 3. As described above, there has been developed a technique for adjusting the amount of entrainment of each heating element by bending a platen roller by pressing a spring. With such a thermal head flatness adjustment technique, it is possible to obtain a good print image without color unevenness in the main scanning direction.

Japanese Patent Laid-Open No. 9-201991 Japanese Patent Laid-Open No. 10-100459 Japanese Patent Laid-Open No. 9-290522

  As described above, the amount of indentation of the heating element array is adjusted by adjusting the nip force at the time of shipment. However, it is known that the density of the heating element array varies depending on the density of the image, that is, the temperature change of the heating element array. . For example, when a high density image is printed, the heating element array reaches a high temperature, so that the recording surface is softened by heating the heating element array, and the amount of squeezing increases. On the other hand, when printing a low density image, In this case, since the temperature of the heating element array is lowered, the amount of penetration is reduced.

  The change in the amount of embedding causes a plastic deformation at the boundary between the high density part and the low density part in the case of an image with a sharp change in shading, and it seems as if a relief has been applied. In the case where there is a sudden change in shading across the entire area in the main scanning direction, such as when the first half of the screen is white and the second half is black, the thermal recording paper may be creased. Such streak-like deformations and creases deteriorate the quality of the print image quality. In recent years when the demand for higher print quality has become more severe, as represented by higher resolution, these problems can no longer be ignored, and effective countermeasures are desired. It was rare.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a thermal printer that prevents a deterioration in print image quality due to a change in the amount of heat-generating element array that is inserted into a recording sheet according to an image.

  The thermal printer of the present invention includes a platen roller and a thermal head that is disposed at a position facing the platen roller and includes a heating element array extending in the main scanning direction, and recording is performed by the platen roller and the thermal head. In the thermal printer that nips the paper and heats the heating element array based on image data to thermally record the image while conveying the recording paper in the sub-scanning direction orthogonal to the main scanning direction in the state, the image Nip force control means for predicting the amount of the heating element array to be inserted into the recording surface of the recording paper based on the data, and controlling the nip force for sandwiching the recording paper based on the prediction result. To do. The nip force control means is preferably a head position adjusting mechanism that adjusts the head position of the thermal head to change the distance between the thermal head and the platen roller during thermal recording.

  Further, it is preferable that the head position adjusting mechanism moves the heat generating element array in a direction to move away from the platen roller from a standard position when the predicted amount of indentation is larger than a reference value. Furthermore, it is preferable that the head position adjusting mechanism moves the heat generating element array in a direction closer to the platen roller than the standard position when the predicted amount of penetration is smaller than a reference value.

  The thermal printer of the present invention predicts the amount of the heat generating element array to be inserted into the recording surface of the recording paper based on the image data to be printed, and controls the nip force for sandwiching the recording paper based on the prediction result. Therefore, it is possible to prevent streak-like deformation or creases on the recording surface of the recording paper, and there is an advantage that a high-quality printed image can be obtained.

  FIG. 1 is a schematic view showing a color thermal printer (hereinafter simply referred to as a printer) 10 embodying the present invention. The printer 10 is a color thermal printer that uses a long color thermal recording paper (hereinafter simply referred to as recording paper) 11 as a recording medium. The recording paper 11 is set in the printer 10 in the form of a recording paper roll 12 wound in a roll shape.

  A paper feed roller 13 is in contact with the outer peripheral surface of the recording paper roll 12. The paper feed roller 13 is driven by a transport motor (not shown). When the paper feed roller 13 rotates in the clockwise direction in the figure, the recording paper roll 12 is rotated in the counterclockwise direction in the figure, and the recording paper 11 is sent out from the recording paper roll 12. Conversely, when the paper feed roller 13 is rotated counterclockwise in the figure, the recording paper roll 12 is rotated clockwise in the figure, and the recording paper 11 is rewound onto the recording paper roll 12.

  As is well known, the recording paper 11 has a cyan thermosensitive coloring layer, a magenta thermosensitive coloring layer, and a yellow thermosensitive coloring layer sequentially provided on a support. The yellow thermosensitive coloring layer, which is the uppermost layer, has the highest thermal 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 large heat energy. Further, the yellow thermosensitive coloring layer, which is the first thermosensitive coloring layer, loses its coloring ability when irradiated with yellow fixing light that is blue-violet light having a wavelength of about 420 nm. The magenta thermosensitive coloring layer, which is the second thermosensitive coloring layer, develops magenta with intermediate thermal energy between the yellow thermosensitive coloring layer and the cyan thermosensitive coloring layer, and is irradiated with magenta fixing light having a near ultraviolet wavelength of about 365 nm. The color developing ability disappears.

  In the vicinity of the recording paper roll 12, a conveying roller pair 16 that sandwiches and conveys the recording paper 11 is disposed. The transport roller pair 16 includes a capstan roller 16a that is rotationally driven by a transport motor (not shown), and a pinch roller 16b that presses the capstan roller 16a. Then, it is reciprocated in the rewind direction on the left side of the figure.

  A thermal head 18 and a platen roller 19 are disposed downstream of the conveyance roller pair 16 in the paper feeding direction so as to sandwich the conveyance path of the recording paper 11. The thermal head 18 is disposed above the conveyance path of the recording paper 11, and has a heating element array (hereinafter simply referred to as a heating element) 18a in which a large number of heating elements are arranged in a line along the main scanning direction. ing. As described above, the heating elements 18a are arranged on a partial glaze layer (not shown) bulged on the cylindrical ridges on the head body 22 made of an alumina substrate or the like. The thermal head 18 nips the recording paper 11 with the platen roller 19 and moves between a printing position where the heating element 18a is pressed against the recording surface and a retracted position away from the recording surface. This movement is performed by a shift mechanism 21 including a cam, a spring, a solenoid and the like. At the time of printing, the thermal head 18 is moved to the printing position, the recording paper 11 is nipped with the platen roller 19, and each heating element 18a is heated to a predetermined temperature corresponding to the image data, thereby recording. Each thermosensitive coloring layer of the paper 11 is colored to perform printing. Further, the platen roller 19 is driven to rotate in accordance with the conveyance of the recording paper 11.

  An optical fixing device 28 is disposed on the downstream side of the thermal head 18 in the paper feeding direction so as to face the recording surface of the recording paper 11. The optical fixing unit 28 includes a yellow fixing lamp 29, a magenta fixing lamp 30, a reflector 31, and the like. The yellow fixing lamp 29 emits blue-violet light having an emission peak of 420 nm to fix the yellow thermosensitive coloring layer of the recording paper 11. The magenta fixing lamp 30 emits near-ultraviolet light of 365 nm to fix the magenta thermosensitive coloring layer.

  A cutter 32 and a paper discharge port 33 are sequentially arranged on the downstream side in the paper feeding direction of the optical fixing device 28. The cutter 32 cuts the long recording paper 11 for each recording area. The recording paper 11 cut into a sheet shape by the cutter 32 is discharged from the paper discharge port 33.

  The thermal head 18 is movable between a printing position where the recording paper 11 is nipped with the platen roller 19 by the shift mechanism 21 and a retracted position away from the recording surface. The thermal head 18 is provided with a head position adjusting mechanism 35 for finely adjusting the head position at the time of printing according to the image density. Then, the nip force for sandwiching the recording paper 11 is controlled in accordance with the density of the image to be thermally recorded. Especially when the density of the image to be thermally recorded is high, the amount of the heat generating element 18a is reduced by reducing this nip force. I try not to get too big.

  The head position adjusting mechanism 35 moves the thermal head 18 in a direction toward the platen roller 19 (downward in the figure) and in a direction retracting from the platen roller 19 (upward in the figure). As a result, the distance between the heating element 18a of the thermal head 18 at the printing position and the platen roller 19 can be arbitrarily adjusted. As a result, the nip force (the pressing force of the heating element 18a on the recording surface) is reduced. It becomes possible to adjust. For example, if the thermal head 18 is moved in the upward direction in the figure, the distance between the heating element 18a and the platen roller 19 is increased, so that the nip force is weakened. On the contrary, if the head is moved downward in the figure, the distance between the heating element 18a and the platen roller 19 becomes narrow, so that the nip force becomes strong. As a matter of course, if the nip force becomes too strong, the recording surface will be indented or the heating element 18a itself will be damaged. Conversely, if the nip force becomes too weak, the print image will be blurred. Since there is a twist, the head position adjusting mechanism 35 adjusts the head position of the thermal head 18 so that the nip force is within a predetermined amount. The configuration of the head position adjusting mechanism 35 will be described with reference to FIGS. 2 is a cross-sectional view of the thermal head 18, and FIG. 3 is a schematic view of the thermal head 18 viewed from the side.

  As shown in FIGS. 2 and 3, the head position adjusting mechanism 35 is screwed into a head support base 37 that supports the head main body 22 and a screw hole (female screw) 38 that is formed substantially at the center of the head support 37. The adjustment screw 39 for adjusting the distance between the heating element 18a and the platen roller 19 and the screw head 39a provided at the approximate center of the upper surface of the head body 22 and formed at the lower end of the adjustment screw 39 in the figure. A gripping member 41 that rotatably grips the motor and a motor 42 that rotates the adjusting screw 39 via a gear (not shown) or the like. Therefore, the thermal head 18 can be moved in the vertical direction in the figure by turning the adjusting screw 39 clockwise or counterclockwise using the motor 42, so that the nip force, that is, the recording surface of the heating element 18a is applied. The amount of sinking can be controlled. Since the screw head 39b is formed at the other end (upper end in the figure) of the adjustment screw 39, the thermal head 18 is shown by using a screw having a predetermined length as the adjustment screw 39. The amount of movement to move in the middle-down direction can be regulated. Further, the amount of movement for moving the thermal head 18 upward in the drawing can be regulated by adjusting the height of the gripping member 41.

  Since the springs 45 are fixed to both ends of the thermal head 18 and the other ends of the springs 45 are fixed to the head support 37, the thermal head 18 always faces the head support 37 (upward in the figure). ). Thereby, the flatness of the thermal head 18 can be maintained, or the flatness of the thermal head 18 can be adjusted according to the bending of the platen roller 19 when the head is pressed, as described in Patent Document 3. . In this embodiment, only two springs 45 are provided, but three or more springs 45 may be provided as necessary.

  As the motor 42, for example, a stepping motor (registered trademark) is used. As is well known, a stepping motor (registered trademark) rotates by an angle corresponding to the number of pulse signals input via a motor driver 47 that controls driving of the motor 42. Therefore, by controlling the number of pulses of the pulse signal output to the motor 42, the rotation angle of the motor 42 can be controlled. Therefore, the amount of movement for moving the thermal head 18 in the vertical direction in the figure is controlled. Can do. In this embodiment, the thermal head 18 moves upward in the figure when the rotation angle of the motor 42 is increased, and moves downward in the figure when the rotation angle is decreased.

  The number of pulses of the pulse signal output to the motor 42 via the motor driver 47 is controlled by the system controller 50. Although not shown, the system controller 50 includes a CPU, a work ROM, a work RAM, and the like, and comprehensively controls the operation of the entire printer. In addition to the motor driver 47, the system controller 50 includes a DSP (Digital Signal Processor) 52 for controlling various image processing of the printer 10, and control information for controlling the rotation angle of the motor 42, which will be described in detail later. The stored LUT 53, a head driver for driving the heat generating element 18a, a transport motor driver for driving the transport motor, a lamp driver for driving the fixing lamps 29 and 30, an operation panel, etc. are connected, although not shown. The system controller 50 controls the operation of each unit of the printer 10 based on an input signal from the operation panel.

  Connected to the DSP 52 are an image memory 54 that stores image data to be printed, a data memory 55 that stores frame data obtained by separating the image data into RGB colors by the DSP 52, and the like. At the time of printing, the DSP 52 sequentially sends line data read line by line from the frame data stored in the data memory 55 to the system controller 50.

  Based on the line data sent from the DSP 52, the system controller 50 drives the head driver to cause the heating element 18a to generate heat and prints line by line. At this time, the system controller 50 rotates the motor 42 based on the rotation angle control information stored in the LUT 53. Therefore, in order to prevent the heating element 18a from being excessively embedded in the recording surface during printing, for example, as shown in FIG. 4, the total applied energy amount obtained from the line data sent from the DSP 52 and the total applied energy amount The relationship between the amount of the heat generating element 18a and the amount of indentation into the recording surface when the voltage is applied is measured in advance. Here, the total applied energy amount is a cumulative amount of applied energy (power amount) applied to each heating element 18a when printing for one line. As a matter of course, the higher the density of the image to be printed, the larger the applied energy amount, and the higher the applied energy, the higher the temperature of each heating element 18a. Therefore, the amount of sinking tends to increase as the total applied energy amount increases.

  By obtaining the relationship between the total amount of applied energy and the amount of penetration as shown in FIG. 4, the amount of penetration of the heating element 18a when any arbitrary amount of applied energy is applied can be known. Therefore, for example, the reference value of the amount of squeezing that gives a high-quality print image that does not cause streak-like deformation or indentation on the recording surface and does not cause blurring is h1, and the total applied energy amount corresponding to h1 is E1. When the total applied energy amount of the line data sent from the DSP 52 is E2, if E2> E1, the amount of concavity h2 corresponding to E2 is naturally h2> h1. In this case, if the rotation angle of the motor 42 is increased by an amount corresponding to the magnitude of the difference between h2 and h1, the thermal head 18 moves upward (see FIGS. 2 and 3) as described above. The amount of dip into the recording surface is h1. Conversely, when E2 <E1, h2 <h1, so the rotation angle of the motor 42 may be reduced by an amount corresponding to the magnitude of the difference between h1 and h2. As a result, a high-quality print image can be obtained. Therefore, for example, as shown in FIG. 5, a graph or the like is created in which the total amount of applied energy is associated with the rotation angle of the motor 42 that corrects the amount of the heating element 18a to be inserted into the recording surface.

  As shown in FIG. 5, by associating the total amount of applied energy with the rotation angle of the motor 42, for example, when the rotation angle of the motor 42 corresponding to E1 is θ1, all of the line data sent from the DSP 52 is displayed. When the applied energy amount E2 is E2> E1 or E2 <E1, the rotation angle of the motor 42 may be increased or decreased from θ1 to θ2 corresponding to E2. Therefore, a rotation angle correction data table (hereinafter simply referred to as correction) or an arithmetic expression in which the total applied energy amount and the rotation angle of the motor 42 are associated with each other is created from the graph of FIG. A table or the like is stored in the LUT 53 (see FIG. 2) as rotation angle control information. As a result, as shown in FIG. 2, when the line data is sent from the DSP 52, the system controller 50 calculates the total thermal recording energy from the line data, and uses the correction data table stored in the LUT 53. The rotation angle of the motor 42 is obtained with reference to the reference. Then, the system controller 50 corrects the amount of the heat generating element 18a by rotating the motor 42 based on the obtained rotation angle. By repeating this correction operation until the printing of all lines is completed, it is possible to prevent excessive heat sinking on the recording surface of the heating element 18a when an image having a high density is printed.

  As shown in FIG. 1, the printer 10 according to the present embodiment is a three-pass color thermal printer that performs thermal recording by causing the recording paper 11 to reciprocate three times with respect to one thermal head 18. As described above, since the thermal sensitivities of the thermosensitive coloring layers of the recording paper 11 are different, the total amount of energy applied to the recording surface is high during cyan image printing and low during yellow image printing. Therefore, it is preferable to correct the difference in thermal sensitivity by, for example, multiplying the rotation angle of the motor 42 obtained from the correction data table by an arbitrary coefficient uniformly for each thermosensitive coloring layer. Further, in the printer 10, when performing thermal recording on a plurality of types of recording paper 11 having different thicknesses, a correction data table corresponding to each type is created and stored in the LUT 53. It is preferable to correct the amount of indentation using a correction data table corresponding to the product type.

  Next, the operation of the present embodiment will be described with reference to the flowchart shown in FIG. 6 and FIGS. When the printer 10 receives a print instruction from the user, the paper feed roller 13 starts rotating by driving a transport motor (not shown). The paper feed roller 13 rotates in the clockwise direction in the figure and feeds the recording paper 11 from the recording paper roll 12. At the same time, the system controller 50 calculates the total applied energy amount from the line data sent from the DSP 52, and obtains the rotation angle of the motor 42 with reference to the correction data table stored in the LUT 53.

  When the recording paper 11 fed from the recording paper roll 12 is nipped by the transport roller pair 16, the capstan roller 16a of the transport roller pair 16 is rotated in the paper feeding direction by the transport motor, and the recording paper 11 is moved to the recording paper. It is pulled out from the roll 12 and conveyed in the paper feeding direction. When the leading end of the recording area of the recording paper 11 reaches the heating element array 18 a of the thermal head 18, the system controller 50 moves the thermal head 18 to the printing position using the shift mechanism 21, and the platen roller 19. The recording paper 11 is nipped and the motor 42 is rotated by the calculated rotation angle to correct the amount of the heat generating element 18a to be inserted into the recording surface. Next, the heat generating element 18a generates heat according to the yellow image, and one line of yellow image is printed on the yellow thermosensitive coloring layer. Next, based on the line data sequentially sent from the DSP, the indentation amount correction operation and the printing operation are repeated until the printing of all the lines is completed. At this time, the platen roller 19 is pressed from below to stabilize the contact state between the recording paper 11 and the thermal head 18. When printing of all lines is completed, the thermal head 18 is moved to the retracted position.

  Further, the yellow fixing lamp 29 of the optical fixing device 28 is turned on during the printing of the yellow image. Then, the printed recording paper 11 is sequentially conveyed by the conveyance roller pair 16, and the conveyance is stopped when the trailing edge of the recording area passes through the optical fixing device 28. At the same time, the yellow fixing lamp 29 is turned off. Thereby, the yellow image is fixed. When fixing of the yellow image is completed, the system controller 50 conveys the recording paper 11 in the rewind direction. Thereafter, similar to the above-described printing and fixing of the yellow image, printing and fixing of the magenta image and printing of the cyan image are performed. For each line data sent from the DSP 52, the amount of indentation of the heat generating element 18a onto the recording surface is corrected, so that it is possible to prevent streaky deformation or creases on the recording surface.

  When the printing of the cyan image is completed, the recording paper 11 is further conveyed in the paper feeding direction, separated at a predetermined position by the cutter 32, and discharged from the paper discharge port 33. Thereafter, the system controller 50 conveys the leading edge of the recording paper 11 to a position where the conveyance roller pair 16 nips, and enters a standby state for the next printing process. If there is no next input even after a certain time has elapsed, the power is turned off after the recording paper 11 is rewound onto the recording paper roll 12.

  In this embodiment, the head position adjusting mechanism 35 moves the thermal head 18 in the direction toward the platen roller 19 and in the direction away from the platen roller 19 in order to control the amount of the heating element 18a to be inserted into the recording surface. However, the present invention is not limited to this, and instead of providing the head position adjusting mechanism 35, the platen roller 19 is directed toward the thermal head 18. A roller position adjusting mechanism that moves in a direction away from the thermal head 18 may be provided. Even in this case, by moving the platen roller 19, the distance between the heating element 18a of the thermal head 18 at the printing position and the platen roller 19 can be arbitrarily adjusted, so that the nip force is controlled. Can do.

  In the present embodiment, the amount of indentation onto the recording surface of the heating element 18a is corrected when printing each image of yellow, magenta, and cyan. However, the present invention is not limited to this, and the amount of applied energy is not limited to this. The amount of indentation may be corrected only when the largest cyan image is printed.

  In this embodiment, when the amount of stagnation predicted from the image data (line data) is larger than the reference value (h1), the thermal head 18 is moved away from the platen roller 19, and the reference value is reached. Is smaller, the thermal head 18 is moved in the direction toward the platen roller 19 to correct the amount of indentation. However, the present invention is not limited to this. Since the thermal head 18 is adjusted to a head position at which an appropriate amount of indentation can be obtained at the time of shipment from the printer, the amount of indentation is hardly less than the reference value. Therefore, the amount of sinking may be corrected only when the amount of sinking predicted is larger than the reference value.

  Further, in this embodiment, the description has been given of the three-pass type color thermal printer that performs printing by reciprocating the color thermal recording paper three times with respect to one thermal head. The present invention can also be applied to a one-pass color thermal printer that performs printing by passing the color thermal recording paper once.

  In this embodiment, a long recording paper is used and cut after printing to create a sheet-like color print. However, the present invention also applies to a color thermal printer that prints on a recording paper cut into a sheet. Can be applied. In this embodiment, a color thermal printer has been described as an example. However, a monochrome thermal printer, or a thermal melting type in which an ink ribbon is heated from behind and melted or sublimated ink is transferred to recording paper to record an image. The present invention can also be applied to various thermal printers that perform printing using a thermal head such as a sublimation type thermal transfer printer.

It is the schematic of the color thermal printer which implemented this invention. It is sectional drawing of the thermal head of the printer. It is the schematic which looked at the thermal head of the printer from the side. 6 is a graph showing the relationship between the total amount of energy applied to the heating element of the thermal head of the printer and the amount of sinking of the heating element. 6 is a graph showing the relationship between the total amount of energy applied to the heat generating element of the thermal head of the printer and the rotation angle of a motor that controls the amount of heat element inserted. 3 is a flowchart showing print processing of the printer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Printer 11 Recording paper 18 Thermal head 18a Heating element 35 Head position adjustment mechanism 37 Head support stand 39 Adjustment screw 42 Motor 50 System controller 52 DSP
53 LUT
54 Image memory 55 Data memory

Claims (4)

A platen roller, and a thermal head that is disposed at a position facing the platen roller and includes a heating element array extending in the main scanning direction, and the recording paper is nipped by the platen roller and the thermal head. In a thermal printer that heats the heating element array based on image data and thermally records an image while conveying the recording paper in a sub-scanning direction orthogonal to the main scanning direction,
Nip force control means for predicting the amount of the heating element array to be inserted into the recording surface of the recording paper based on the image data and controlling the nip force for sandwiching the recording paper based on the prediction result. Features a thermal printer.   2. The head position adjusting mechanism according to claim 1, wherein the nip force control means is a head position adjusting mechanism that adjusts a head position of the thermal head to change a distance between the thermal head and the platen roller during thermal recording. Thermal printer.   The head position adjusting mechanism moves the heating element array in a direction away from the platen roller from a standard position when the predicted amount of indentation is larger than a reference value. Thermal printer.   The head position adjusting mechanism is configured to move the heating element array in a direction closer to the platen roller than the standard position when the predicted amount of indentation is smaller than the reference value. The thermal printer according to 2 or 3.

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