JP2005246694A - Thermal printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal printer in which variation in density due to the temperature of a carry roller can be prevented. <P>SOLUTION: A recording sheet 11 fed to a thermal printer is thermally recorded with an image by means of a thermal head 22 while being carried in the returning direction by means of a carry roller 16. The carry roller 16 consists of a capstan roller 14 and a pinch roller 15. In the vicinity of these rollers 14 and 15, temperature sensors 46 and 47 are arranged in order to measure the surface temperature of each roller. Since the temperature of the carry roller 16 is lower than the surface temperature of the recording sheet 11 immediately after printing an image thereon, temperature of the recording area lowers in the region where the carry roller 16 passes and the density thereat lowers as compared with that at other part. Based on the temperature measured by the temperature sensors 46 and 47, a correction amount calculating section 38 determines the correction amount of print energy of the thermal head 22 to compensate for decrease in density. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a thermal printer that heat-records an image by heating the thermal recording paper with a thermal head, and more specifically, thermal recording that performs thermal recording while conveying the thermal recording paper by a conveyance roller disposed downstream in the printing direction. It relates to printers.

  The thermal printer uses a thermal transfer printer that heats an ink sheet with a thermal head and transfers the ink onto a recording paper to record an image, and a thermal recording paper that self-colors when heated, and this thermal recording paper is used as a thermal head. There are two types of thermal printers that record images by heating.

  The thermal printer performs line recording of an image with a thermal head while the recording paper is conveyed by a conveyance roller. The thermal head is provided with a heating element array in which a plurality of heating elements corresponding to pixels are arranged in a line. Images are thermally recorded by causing each heating element to generate heat according to the density of each pixel. The At a position facing the thermal head, a platen roller for supporting the recording paper pressed against the thermal head from the back side is disposed.

  The heat generated by the thermal head is also transmitted to the platen roller via the recording paper and is accumulated on the platen roller. When a plurality of images are continuously recorded, the temperature of the platen roller is cumulatively increased due to this heat accumulation. As a result, the heat storage of the platen roller generates heat energy higher than the thermal energy applied by the thermal head, and the image may be recorded at a density higher than the desired density. Therefore, a thermal printer that measures the temperature of the platen roller and corrects the heat generation energy of the thermal head according to this temperature is known (Patent Document 1 below). Further, in the thermal printer of Patent Document 2 below, the platen roller is cooled to prevent density fluctuation due to heat storage of the platen roller.

JP-A-5-193180 JP-A-8-072275

  A thermal recording paper that self-colors by heating continues to develop color for a while after being heated by the heat accumulated in the recording paper itself. The thermal recording paper is transported while being tensioned by a transport roller disposed downstream of the thermal head in the transport direction during printing, and the temperature of the transport roller is lower than the surface temperature of the recording area. For this reason, when a part of the recording area comes into contact with the conveyance roller during the color development period, there is a problem that the portion is cooled by the conveyance roller and the density is lowered as compared with other portions. In the above-described conventional thermal printer, only density fluctuation due to heat storage of the platen roller is considered, and measures against density fluctuation caused by the conveyance roller are not taken into consideration.

  An object of the present invention is to provide a thermal printer capable of preventing density fluctuations caused by the temperature of a conveyance roller.

  The thermal printer of the present invention is a thermal printer that thermally records an image by heating the thermal recording paper by the thermal head while conveying the thermal recording paper by a conveyance roller disposed downstream in the printing direction of the thermal head. A roller temperature sensor for measuring the temperature of the conveying roller, and a surface temperature of the recording area immediately after printing based on the roller temperature measured by the roller temperature sensor, and a surface temperature of the recording area after passing the conveying roller And a correction means for correcting the printing energy of the thermal head in accordance with the temperature difference.

  The temperature difference may be obtained by estimating the surface temperature of the recording paper immediately after printing or may be obtained by actual measurement.

  The present invention relates to the thermal roller in which the thermal recording paper is heated by the thermal head to thermally record an image while the thermal recording paper is conveyed by a conveyance roller disposed on the downstream side in the printing direction of the thermal head. The temperature of the roller temperature sensor for measuring the temperature of the recording area, the surface temperature of the recording area immediately after printing based on the roller temperature measured by the roller temperature sensor, and the temperature of the surface temperature of the recording area after passing the conveying roller Since the difference is obtained and the correction means for correcting the printing energy of the thermal head according to the temperature difference is provided, the density fluctuation due to the temperature of the conveying roller can be prevented.

  A color thermal printer 10 shown in FIG. 1 is loaded with a recording paper roll 12 in which a long recording paper 11 is wound in a roll shape. 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. In addition, the yellow thermosensitive coloring layer loses its coloring ability when irradiated with yellow fixing light which is blue-violet visible light having an emission wavelength peak of about 420 nm. The magenta thermosensitive coloring layer develops magenta with intermediate thermal energy between the yellow thermosensitive coloring layer and the cyan thermosensitive coloring layer, and develops color when irradiated with magenta fixing light having a peak emission wavelength of about 365 nm. The ability is lost.

  The paper feed roller 13 abuts on the recording paper roll 12 and rotates the recording paper roll 12, thereby pulling out the leading end of the recording paper 11 from the roll 12 to the conveyance path. A conveyance roller 16 including a capstan roller 14 and a pinch roller 15 is disposed on the downstream side of the paper feed roller 13. The pinch roller 15 is in a retracted position with a gap between the pinch roller 15 and the capstan roller 14 at the time of paper feeding. The recording paper 11 is nipped together with the capstan roller 14. The conveying roller 16 conveys the recording paper 11 in the feeding direction and the returning direction in a nipped state. The transport path is constituted by a guide member (not shown), and the recording paper 11 is transported while being guided by the guide member along the path.

  The paper feed roller 13 and the transport roller 16 are driven to rotate in both forward and reverse directions by the transport motor 17. The conveyance motor 17 is controlled by the controller 21 through a motor driver (not shown). As the carry motor 17, for example, a stepping motor whose rotation amount is determined according to the given number of pulses is used, and the controller 21 counts the drive pulse given to the carry motor 17 to thereby determine the recording start position, The position of the recording paper 11 such as the cutting position and the conveyance amount thereof are specified.

  A thermal head 22 is disposed on the downstream side of the transport roller 16. As is well known, the thermal head 22 is provided with a heating element array 22a in which a large number of heating elements are arranged in the main scanning direction, and each heating element is placed in a state where the heating element array 22a is pressed against the recording paper 11. Heat is generated and thermal energy corresponding to the gradation value of the image data is given to the recording paper 11. The thermal head 22 is controlled by a head control unit 24.

  The image data captured by the printer 10 is subjected to gamma correction processing, YC conversion processing, and the like by the image processing unit 41 and is written to the frame memory 42. Image data is transferred line by line from the frame memory 42 to the line memory 43. The head controller 24 generates drive data based on the image data for one line in the line memory 43, converts this into drive signals, and drives the thermal head 22.

  A platen roller 23 that supports the recording paper 11 from the back surface is disposed at a position facing the heating element array 22a. The platen roller 23 is driven and rotated in accordance with the conveyance of the recording paper 11, and stabilizes the contact state between the recording paper 11 and the heating element array 22a. The recording paper 11 is sandwiched between the thermal head 22 and the platen roller 23 to be brought into pressure contact with the heating element array 22a.

  The thermal recording by the thermal head 22 is performed while the recording paper 11 is transported in the returning direction after once passing through the thermal head 22 through the recording area of one screen of the recording paper 11 at the time of paper feeding. Thus, by performing printing while transporting in the return direction, a front tension is applied to the recording paper 11 by the transport roller 16 disposed downstream of the thermal head 22 in the return direction (printing direction). Since the printing is performed in a state where the recording paper 11 is pulled by the front tension, the positional deviation of the image is prevented.

  The thermal head 22 is swung by a shift mechanism (not shown) between a retreat position where a gap is formed between the heating element array 22a and the platen roller 23 and a pressing position where the heating element array 22a is pressed against the recording paper 11. The When feeding paper, the thermal head 22 is in the retracted position, and a paper feed path for the recording paper 11 is secured between the heating element array 22 a and the platen roller 23. At the time of recording, the thermal head 22 moves to the press contact position, and the heating element array 22a is pressed against the recording paper 11.

  An optical fixing device 26 is disposed downstream of the thermal head 22 in the feeding direction. The optical fixing device 26 includes a yellow fixing lamp 27 that emits yellow fixing light and a magenta fixing lamp 28 that emits magenta fixing light. The light fixing of the yellow image is performed while the yellow fixing lamp 27 is turned on after the thermal recording of the yellow image is completed, and the recording area is conveyed in the feeding direction as opposed to the thermal recording. Thereafter, thermal recording of the magenta image is started while the recording area is conveyed in the returning direction. At this time, the yellow fixing lamp 27 is turned off. When the thermal recording of the magenta image is completed, the magenta fixing lamp 28 is turned on, and magenta light fixing is started while conveying the recording area in the feeding direction. After the recording area passes through the optical fixing device 26, the conveyance direction is reversed to the return direction, and thermal recording of the cyan image is started.

  A cutter 32 is disposed downstream of the optical fixing device 26 in the feeding direction. The cutter 32 cuts a margin generated at the leading end of the recording paper 11 and cuts a recorded portion of the recording paper 11 that has been subjected to thermal recording and fixing into one sheet. The cut sheet is discharged out of the printer from the discharge outlet. The unrecorded portion of the recording paper 11 is rewound onto the recording paper roll 12.

  A platen temperature sensor 36 that measures the surface temperature of the platen roller 23 is disposed in the vicinity of the platen roller 23. Since the platen roller 23 is in contact with the recording paper 11, the temperature affects the color density of the recording paper 11. Therefore, in the printer 10, the printing energy generated by the thermal head 22 is corrected according to the surface temperature of the platen roller 23. As the platen temperature sensor 36, for example, a radiation thermometer that measures temperature by capturing infrared rays emitted from a measurement object is used. The radiation thermometer is suitable for measuring the surface temperature of a rotating body such as the platen roller 23 because it measures the temperature without contacting the measurement object.

  The analog temperature signal output from the platen temperature sensor 36 is converted into digital temperature data by the A / D converter 37 and input to the controller 21. The controller 21 sends this temperature data to the correction amount calculation unit 38. The correction amount calculation unit 38 calculates the correction amount of the printing energy generated by the thermal head 22 based on the input temperature data. The correction amount calculation unit 38 is provided with a table memory that stores the relationship between the platen temperature and the correction amount. By referring to this table memory, a correction amount corresponding to the platen temperature is obtained. Of course, the relational expression between the platen temperature and the correction amount may be stored, and the correction amount may be obtained by calculation.

  The platen temperature is first measured before recording the first line, and then measured every time one line is recorded. A correction amount of printing energy for one line to be recorded is calculated according to the measured temperature. The head control unit 24 generates drive data by adding the correction amount input from the correction amount calculation unit 38 to the image data for one line read from the line memory 43, and generates a drive signal corresponding to the drive data. Output to the thermal head 22 to drive the thermal head 22.

  Further, the conveyance roller 16 disposed downstream in the conveyance direction (return direction) at the time of printing of the thermal head 22 has a temperature lower than the surface temperature of the recording paper 11 immediately after printing. The recording paper 11 is printed by its own heat storage and continues to develop a color reaction for a while. However, when the recording paper 11 passes through the conveyance roller 16, the recording paper 11 is cooled and the color development becomes dull. According to experiments, the surface temperature of the recording area immediately after printing is about 50 ° C., and after passing through the conveying roller 16, the temperature drops to about 20 ° C.

  As shown in FIG. 2, when a part of the recording area passes through the conveyance roller 16, the density of the passage area that has passed through the conveyance roller 16 is lower than that of the non-passage area. Approximately 0.05 to 0.1 (OD).

  For this reason, the printer 10 measures the temperature of the conveying roller 16 so that the density difference does not occur, and corrects the printing energy generated by the thermal head 22 based on the temperature. In the vicinity of each of the capstan roller 14 and the pinch roller 15 constituting the conveying roller 16, roller temperature sensors 46 and 47 are arranged, respectively. As these roller temperature sensors 46 and 47, for example, radiation thermometers are used in the same manner as the platen temperature sensor 36.

  The analog temperature signals output from the roller temperature sensors 46 and 47 are converted into digital temperature data by the A / D converter 37 and output to the controller 21. The controller 21 sends this to the correction amount calculation unit 38. The correction amount calculation unit 38 calculates the correction amount of the printing energy generated by the thermal head 22 based on the input temperature data. Each roller temperature is measured before recording the first line, and thereafter measured every time one line is recorded. A correction amount of printing energy for one line to be recorded is calculated according to the measured temperature. The head control unit 24 generates drive data by adding the correction amount input from the correction amount calculation unit 38 to the image data for one line read from the line memory 43, and generates a drive signal corresponding to the drive data. Output to the thermal head 22 to drive the thermal head 22.

  First, the correction amount calculation unit 38 causes the surface temperature of the recording paper 11 immediately after being heated by the thermal head 22 to pass through the conveying roller 16 based on the temperature measured by each of the roller temperature sensors 46 and 47. Is predicted (temperature difference between the surface temperature of the recording paper 11 immediately after printing and the surface temperature after passing through the conveying roller 16). Then, a density decrease due to the predicted temperature difference is obtained, and an energy correction amount for compensating for it is obtained. The head controller 24 corrects the printing energy obtained based on the image data in accordance with the energy correction amount, and drives the thermal head 22 so that the corrected printing energy is applied to the recording paper 11.

  The correction amount calculation unit 38 is provided with a table memory that stores the relationship between the temperature difference and the correction amount. By referring to this table memory, the correction amount corresponding to the temperature difference is obtained. Of course, the relational expression between the temperature and the correction amount may be stored, and the correction amount may be obtained by calculation.

  In the recording area, the passing area through which the conveyance roller 16 passes is determined according to the length of the recording area. The controller 21 causes the correction amount calculation unit 38 to correct the density fluctuation caused by the transport roller 16 until the recording of the passage area is completed. Such correction eliminates density fluctuations between the passing area and the non-passing area in the recording area, so that a high-quality image without unevenness is recorded.

  Hereinafter, the operation of the above configuration will be described with reference to the flowchart shown in FIG. When a print instruction is given, the recording paper 11 is fed to the transport path. The fed recording paper 11 is conveyed in the feeding direction by the conveying roller 16. When the recording area passes through the thermal head 22, the conveyance of the recording paper 11 is stopped. The printing of the yellow image is started by the thermal head 22 while the conveyance motor 17 is reversed and the recording paper 11 is conveyed in the returning direction.

  At this time, the correction amount calculation unit 38 obtains the correction amount of the printing energy based on the platen temperature measured by the platen temperature sensor 36. At the same time, as shown in the flowchart of FIG. 3, the correction amount calculation unit 38 calculates the temperature difference between the temperature of the conveying roller 16 measured by the roller temperature sensors 46 and 47 and the surface temperature of the recording paper 11 immediately after printing. The correction amount of the printing energy corresponding to this temperature difference is obtained.

  The thermal head 22 applies the corrected printing energy to the recording paper 11 and records the first line image for one line. When recording the next line image, the correction amount calculation unit 38 obtains the correction amount of the printing energy of the next line image based on the platen temperature and the temperature of the conveying roller in the same procedure as described above, and the head The control unit 24 drives the thermal head 22 so as to generate corrected printing energy. The correction based on the temperature of the conveying roller 16 is repeated until the recording in the passing area is completed.

  When the recording in the passage area is completed, the correction amount calculation unit 38 performs only correction based on the platen temperature. Thus, an image for one screen is recorded. The passing area is provided with printing energy that allows for a decrease in density due to cooling by the transport roller 16, so that there is no density fluctuation between the non-passing area and density unevenness over the entire recording area. It is possible to record an image without any image.

  After the yellow image recording is completed, the recording paper 11 is conveyed in the feeding direction, and the yellow image is optically fixed. Thereafter, the magenta image is thermally recorded by the thermal head 22 while being conveyed again in the returning direction. Even during the printing of the magenta image, the printing energy is corrected based on the platen temperature and the temperature of the conveying roller in the same procedure as described above. When the thermal recording of the magenta image is completed, the recording paper 11 is conveyed in the feeding direction, and the magenta image is optically fixed. Thereafter, a cyan image is printed while the recording paper 11 is conveyed in the returning direction. Even when the cyan image is printed, the printing energy is corrected. As described above, since the correction is performed even when printing with magenta and cyan, a full-color image without density unevenness can be obtained over the entire recording area. The recording paper 11 on which the cyan image has been printed is sent to the cutter 32, and the recorded portion is cut into a sheet and discharged.

  In the above embodiment, the surface temperature of the recording paper immediately after being heated by the thermal head is predicted, and based on the difference between the surface temperature and the surface temperature of the recording paper after passing through the conveying roller, the printing energy Although the example of calculating the correction amount has been described, the correction amount may be obtained by actually measuring the surface temperature of the recording paper immediately after printing with a temperature sensor. In this way, an accurate correction amount can be obtained, but the measured temperature cannot be measured unless an image is recorded once, so that correction cannot be performed from the first line.

  Moreover, although the said embodiment demonstrated the example using a non-contact type radiation thermometer as a temperature sensor, you may use contact-type temperature sensors, such as a thermistor.

It is a block diagram of the color thermal printer of this invention. It is explanatory drawing of a passing area and a non-passing area. 6 is a flowchart illustrating a printing energy correction procedure based on the temperature of a conveyance roller.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Color thermal printer 11 Color thermal recording paper 14 Capstan roller 15 Pinch roller 16 Conveyance roller 21 Controller 22 Thermal head 22a Heating element array 23 Platen roller 24 Head control part 36 Platen temperature sensor 38 Correction amount calculation part 46, 47 Roller temperature sensor

Claims (3)

In a thermal printer that heat-records an image by heating the thermal recording paper with the thermal head while conveying the thermal recording paper with a conveyance roller disposed downstream in the printing direction of the thermal head,
A roller temperature sensor for measuring the temperature of the conveying roller, and a surface temperature of the recording area immediately after printing based on the roller temperature measured by the roller temperature sensor, and a surface temperature of the recording area after passing the conveying roller And a correction means for correcting the printing energy of the thermal head in accordance with the temperature difference.   2. The thermal printer according to claim 1, wherein the correction unit estimates a surface temperature of the recording paper immediately after printing, and obtains the temperature difference based on the estimated surface temperature.   2. The thermal printer according to claim 1, wherein the correction unit obtains the temperature difference based on an actual measurement value of the surface temperature of the recording paper immediately after printing.

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