JP2008030389A - Thermal printer and its printing control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal printer and its printing control method, which suppress a density unevenness generated in printing, and further improve an image quality in a printed matter than the conventional art. <P>SOLUTION: The thermal printer 1 includes a controller 30 which predicts a fluctuation of a friction load between a thermal head 10 and a printing medium RP, to be generated in lines in printing, and makes control to print a dot pattern of image data by turning it by a predetermined angle, based on the prediction result. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a thermal printer that prints a dot pattern of input image data line by line on a print medium by heating a thermal head, and a print control method for the thermal printer.

  In general, when printing with a thermal printer, the ink on the ink ribbon is thermally transferred to a printing medium by heating the thermal head, and the input image data is printed line by line. Also, depending on the thermal printer, there is a case in which the thermal paper is directly used to print the color by heating the thermal header without using the ink ribbon by using the thermal paper as a printing medium. When printing with a thermal printer, it is known that if the density of successive lines changes abruptly, density unevenness along the transport direction of the print medium occurs. For example, as shown in FIG. 1, such density unevenness is obtained by printing a rectangular central portion M of a printing paper 100 as a printing medium on a plain white color (without transferring ink), and removing the central portion M. This occurs when the surrounding outer peripheral portion N is printed with a dark color. In the following, the density unevenness will be briefly described with reference to FIG. 1, taking as an example the case of printing by directly coloring the thermal paper.

  In FIG. 1, a printing paper 100, which is a rectangular thermal paper, is printed in a printing direction X (rightward in FIG. 1). That is, the printing paper 100 is conveyed in the direction opposite to the printing direction X (leftward in FIG. 1), and is a line parallel to the width direction Y by the thermal head 101 arranged along the width direction Y orthogonal to the printing direction X. Printed in units. 2 and 3 are diagrams showing the color densities of the printing paper 100 printed as shown in FIG. 1 along the lines AA and BB parallel to the printing direction X, respectively. 1 to 3, both outer end portions in the printing direction X of the printing paper 100 are indicated by points a and d, and both outer end portions in the printing direction X of the central portion M are indicated by points b and c.

  As shown in FIG. 2, when the printing paper 100 is printed along the printing direction X, the color density is high at a point b where the outer peripheral portion N is switched to the central portion M on the AA line of the printing paper 100. It has fallen sharply from the state. In general, when printing with high density, the temperature of the thermal head 101 is increased, so that the frictional load between the thermal head 101 and the printing paper 100 is reduced. On the other hand, since the temperature of the thermal head 101 is lowered when printing with a low density (including the case of plain white without printing), the frictional load between the thermal head 101 and the printing paper 100 increases. . For this reason, when the printing paper 100 is printed along the printing direction X and passes through a point b where the density rapidly decreases, the frictional load between the thermal head 101 and the printing paper 100 rapidly increases, and the thermal head 101 The conveyance pitch along the printing direction X is temporarily narrowed by being dragged instantaneously in the conveyance direction of the printing paper 100 (that is, the direction opposite to the printing direction X).

  For this reason, as shown in FIG. 3, on the BB line of the printing paper 100, the color density increases instantaneously at the point e immediately after the point b, and then instantaneously at the point f by the recoil returning to the original. To decrease. This phenomenon appears as a density unevenness line along the width direction Y at the positions of the points e and f on the printing paper 100, and deteriorates the image quality of the printed matter. FIG. 4 is an enlarged view in which a corner portion O that is a boundary between the central portion M and the outer peripheral portion N shown in FIG. 1 is enlarged. In FIG. 4, a region surrounded by a dotted line indicates one line at the time of printing. As described above, the color density at the point e shown in FIG. 4 is darker than the surroundings, and the color density at the point f is lighter than the surroundings. This is the density unevenness along the width direction Y. Appears as a line. In the above description, the case where the density passes through the point b where the density rapidly increases has been described. Similarly, when the density passes through the point c where the density increases rapidly, the color density at the point g as shown in FIG. Decreases instantaneously, and then increases instantaneously at the point h due to the recoil returning to the original, so that a line of density unevenness appears.

  In the above description, the case where the thermal printer performs printing by directly coloring the thermal paper without using the ink ribbon has been described as an example. However, the thermal head can also be used when the thermal printer performs printing using the ink ribbon. 101, the same problem occurs due to the frictional load between the ink ribbon and the printing paper 100.

  In the printing control technique described in Patent Document 1, in order to solve the above-described problem of density unevenness, an auxiliary thermal head and an auxiliary roller are provided in a printer, and the thermal head, the printing paper, and the like are provided using the auxiliary thermal head and the auxiliary roller. By keeping the frictional load constant during this period, a sudden change in the frictional load is prevented and density unevenness is suppressed.

  In the print control technique described in Patent Document 2, the energy at the time of printing is calculated for each line of image data to be printed, the friction load is predicted from each calculated energy, and each energy is corrected. By doing so, a sudden change in density load is prevented and density unevenness is suppressed.

JP 2000-177160 A JP 2002-67370 A

  However, in the print control technique described in the above-mentioned Patent Document 1, the configuration of the printer is complicated, the price is increased, and the volume of the installation space is increased. Further, it is very difficult to maintain a constant friction load between the thermal head and the printing paper using the auxiliary thermal head and the auxiliary roller, and density unevenness cannot be appropriately suppressed.

  Further, in the technique described in Patent Document 2, energy for printing is calculated for each line of image data to be printed, and a change in friction load is predicted and correction for this energy is performed. Can only be done in line units. For this reason, for example, when density unevenness occurs in the same line, it is difficult to appropriately suppress the density unevenness.

  The present invention has been made in view of the above problems, and provides a thermal printer, a print control method thereof, and a program capable of suppressing density unevenness occurring during printing and improving the image quality of printed matter as compared with the conventional one. Is the purpose.

  In order to solve the above problems, according to the present invention, a thermal printer that prints a dot pattern of input image data on a print medium line by line by heating the thermal head, the thermal head generated between lines during printing And a control device for controlling the printing so that the dot pattern of the image data is rotated by a predetermined rotation angle based on the prediction result, and fluctuation of the friction load between the printing medium and the printing medium is predicted. A thermal printer is provided.

  In the above thermal printer, printing on the printing medium is performed by thermally transferring the ink on the ink ribbon to the printing medium by heating the thermal head, and when predicting the fluctuation of the friction load, the thermal head, the ink ribbon, and the printing medium You may make it estimate the friction load between.

  In the thermal printer, when the ink ribbon includes a plurality of colors of ink, the control device may predict a change in friction load for at least two of the plurality of colors.

  In the thermal printer, the control device calculates a difference in average gradation values between adjacent lines in the dot pattern of the image data when predicting the variation in the friction load, and calculates the calculated average gradation. You may predict based on the difference of a value.

  In the thermal printer, when the control device rotates the dot pattern of the image data by a predetermined rotation angle, the control device sets the rotation center to the center of the entire dot pattern of the image data, and the predetermined rotation angle. May be set to 1 ° or less.

  In the thermal printer, the control device predicts the friction load variation, the friction load variation when the dot pattern of the image data is rotated by a predetermined rotation angle, and the friction load when the dot pattern is not rotated. Both of the fluctuations may be predicted.

  In the thermal printer, the control device sets a plurality of the predetermined rotation angles when predicting the fluctuation of the friction load, and rotates the dot pattern of the image data for each of the plurality of predetermined rotation angles. The frictional load fluctuation is predicted, one of the plurality of predetermined rotation angles is selected based on the prediction result, and the dot pattern of the image data is rotated by the selected predetermined rotation angle. You may control to print.

  According to the present invention, there is also provided a printing control method for a thermal printer that prints a dot pattern of input image data on a print medium line by line by heating the thermal head, and the thermal head and the print generated between lines during printing. Printing of a thermal printer characterized by predicting a variation in a friction load with a medium and controlling the dot pattern of the image data to be rotated by a predetermined rotation angle based on the prediction result A control method is provided.

  In the printing control method of the thermal printer, printing on the printing medium is performed by thermally transferring the ink on the ink ribbon to the printing medium by heating the thermal head, and when the fluctuation of the friction load is predicted, A friction load between the ribbon and the print medium may be predicted.

  In the printing control method of the thermal printer, when the ink ribbon includes a plurality of colors of ink, a variation in friction load may be predicted for at least two of the plurality of colors.

  In the printing control method of the thermal printer, when predicting the fluctuation of the friction load, each of the average gradation values between adjacent lines in the dot pattern of the image data is calculated, and the calculated average gradation value You may predict based on the difference of these.

  In the printing control method of the thermal printer, when the dot pattern of the image data is rotated by a predetermined rotation angle, the rotation center is set to the center of the entire dot pattern of the image data, and the predetermined rotation angle is set. It may be set to 1 ° or less.

  In the print control method of the thermal printer, when predicting the friction load fluctuation, the friction load fluctuation when the dot pattern of the image data is rotated by a predetermined rotation angle and the friction load when the dot pattern is not rotated are calculated. Both fluctuations may be predicted.

  In the print control method of the thermal printer, a plurality of the predetermined rotation angles are set, and a variation in the friction load when the dot pattern of the image data is rotated for each of the plurality of predetermined rotation angles is estimated. Control may be performed so that one of the plurality of predetermined rotation angles set based on the prediction result is selected, and the dot pattern of the image data is printed by being rotated by the selected predetermined rotation angle.

  According to the present invention, when the dot pattern of the image data input to the thermal printer is printed line by line, the dot pattern of the input image data is rotated by a predetermined rotation angle and printed. It is possible to effectively suppress density unevenness by reducing rapid fluctuations in the frictional load generated between the lines, and to improve the image quality of the printed matter.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the present specification and drawings, elements having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 5 is a configuration diagram showing a configuration of the printer 1 which is an example of the thermal printer according to the embodiment of the present invention. As shown in FIG. 5, the printer 1 is configured such that the ink ribbon R supplied from the ink ribbon supply roller 5 passes through between the thermal head 10 and the platen roller 11 that are arranged to face each other in the housing 2. The take-up roller 15 is configured to be wound up. In addition, a roll paper RP around which a belt-shaped print medium is wound is installed in the lower part of the housing 2 in a replaceable manner. The roll paper RP is sandwiched between the transport roller 25 and the pinch roller 26 via a guide roller 22 that changes the transport direction to a substantially right angle. The roll paper RP sandwiched between the rollers 25 and 26 is transported in a substantially horizontal direction indicated by an arrow in FIG. 5 when the transport roller 25 is driven and rotated by a driving device (not shown). The ink passes through the platen roller 11 together with the ink ribbon R.

  Printing by the printer 1 is performed by applying heat while pressing the thermal head 10 against the platen roller 11 with the ink ribbon R and the roll paper RP sandwiched between the thermal head 10 and the platen roller 11. Is transferred to the roll paper RP line by line in a desired dot pattern (that is, a dot pattern of image data input to the printer 1). The thermal transfer by the thermal head 10 is performed when the roll paper RP is conveyed along with the ink ribbon R in the direction opposite to the arrow shown in FIG. In the present embodiment, the ink ribbon R includes three ink layers of Y (yellow), M (magenta), and C (cyan) that have sublimation properties when heated, and an overcoat layer that serves as a protective layer. It is repeated periodically in a predetermined length unit (for example, 10 inches) along the conveyance direction. At the time of printing, the transport roller 25 repeats normal rotation and reverse rotation to reciprocate the roll paper RP, so that these three color inks are thermally transferred to the roll paper RP in order page by page, and then an overcoat is formed. Done. As a result, the three colors are overlaid, and a high-quality printed material close to a silver salt photograph can be obtained.

  Connected to the thermal head 10 is a control device 30 that controls the output of the ink on the ink ribbon R when it is thermally transferred onto the roll paper RP. An external I / F (interface) 31 is connected to the control device 30. Further, the control device 30 is connected to a mechanism control unit 32 that performs transport control of the ink ribbon R, transport control of the roll paper RP, and the like.

  As shown in FIG. 5, the external I / F 31 has an exposed portion exposed outside the housing 2, and an input port to which a line (not shown) such as a USB cable can be connected to the exposed portion. (Not shown) is provided. Thus, for example, an external device (not shown) such as a personal computer is connected to the printer 1 via a line such as a USB cable, and image data to be printed from the external device to the control device 30 of the printer 1 via the external I / F 31 is transferred. It is possible to input.

  FIG. 6 is a configuration diagram illustrating the configuration of the control device 30 as an example. As shown in FIG. 6, the control device 30 includes a CPU 35, a RAM 36, a ROM 37, and a thermal head control circuit 38 that are connected to each other by a bus line BL. The RAM 36 can record image data input from the external I / F 31. The CPU 35 can control the printer 1 by executing a print control procedure described later based on the program and nonvolatile data recorded in the ROM 37.

  The thermal head control circuit 38 is configured to input an output signal indicating the energy output value of the thermal head 10 to the thermal head 10 based on output data from the CPU 35. The thermal head 10 performs heating based on a signal input from the thermal head control circuit 38 and thermally transfers the dot pattern of the image data to the roll paper RP line by line.

  As shown in FIG. 5, a guide plate 40 for guiding the roll paper RP is provided on the exit side of the thermal head 10 in the transport direction. Further, on the exit side of the guide plate 40 in the transport direction, a roll paper detection sensor 45 that detects whether or not the leading end of the roll paper RP has passed, and a cutting machine that cuts the roll paper RP in the width direction perpendicular to the transport direction. 46 is provided. The roll paper detection sensor 45 can detect that the roll paper RP printed by the thermal head 10 is guided by the guide plate 40 and reaches the roll paper detection sensor 45. The cutting machine 46 can cut the roll paper RP detected by the roll paper detection sensor 45 at a predetermined length along the transport direction. On the exit side of the cutting machine 46 in the conveying direction, another guide plate 47 is provided up to the slit-like discharge port 48 of the housing 2. Thereby, the roll paper RP cut by the cutting machine 46 is guided by the guide plate 47 by its own weight, and is discharged out of the housing 2 from the discharge port 48 as a completed printed matter P.

  A print control method implemented using the printer 1 according to the embodiment of the present invention configured as described above will be described. FIG. 7 is an overall flowchart for explaining the procedure of the print control method according to the embodiment of the present invention.

  As shown in FIG. 7, when printing with the printer 1 is started (step 0), first, for example, image data to be printed is transferred from the external device (not shown) such as a personal computer via the external I / F 31 to the printer 1. (Step 1). The input image data is recorded in the RAM 36 (step 2).

  The CPU 35 reads the image data from the RAM 36, predicts the friction load fluctuation from the read dot pattern of the image data, and rotates the dot pattern of the image data by a predetermined angle with respect to the line based on the prediction result (step). 3). FIG. 8 is a diagram illustrating a dot pattern 51 of C (cyan) image data 50 of the three colors constituting the ink ribbon R as an example of image data read from the RAM 36. FIG. 9 is a flowchart for explaining the procedure of step 3 in detail. Hereinafter, the procedure of step 3 will be described in detail with reference to FIGS. In this case, the C (cyan) image data will be described, but the remaining Y (yellow) and M (magenta) image data of the three colors are also read from the RAM 36 and the same processing is performed.

  In this embodiment, as shown in FIG. 8, the image data 50 is composed of 28 lines (each line is arranged in the horizontal direction in FIG. 8). Each line is composed of 22 pixels arranged in the horizontal direction in FIG. That is, the entire image data 50 is composed of 28 × 22 = 616 pixels. The dot pattern 51 of the image data 50 is obtained by setting gradation values (0 to 255) of the color density of C (cyan) for each of these 616 pixels. In the case of the dot pattern 51 shown in FIG. 8, the gradation value of all the pixels in the 1st to 7th lines from the top and the 22nd to 28th lines from the top is 128. In the 8th to 21st lines from the top, the gradation value of 10 pixels on the left side in FIG. 8 is 128, and the gradation value of 12 pixels on the right side in FIG. 8 is 255. Yes. At the time of printing, the dot pattern 51 of the image data 50 is printed line by line in order from the top.

  When step 3 is started (step 10), as shown in FIG. 9, the CPU 35 first calculates the average gradation value of each line for the dot pattern 51 of the read image data 50 (step 10). 11). More specifically, in the case of the dot pattern 51 shown in FIG. 8, the average gradation value of the first line from the top is 128 (gradation value) × 22 (number of pixels) / 22 (all pixels in the line). Number) = 128. The average gradation value of the eighth line from the top is {128 (gradation value) × 10 (number of pixels) +255 (gradation value) × 12 (number of pixels)} / 22 (total number of pixels in the line). = 197.27. In FIG. 8, the average gradation values for all lines are shown in a table on the right side of the dot pattern 51 of the image data 50.

  Using the average gradation value of each line calculated as described above, the difference of the average gradation value between adjacent lines is calculated for the dot pattern 51 of the image data 50 (step 12). For example, in the dot pattern 51 shown in FIG. 8, the difference in average gradation value between the seventh line from the top and the eighth line from the top is 197.27−128 = 69.27. In FIG. 8, the difference in the average gradation value between adjacent lines for all lines is shown to the right of the average gradation value.

Among the differences in the average gradation values calculated between the adjacent lines as described above, the number F _before of a predetermined threshold value is obtained (step 13). The predetermined threshold is a value determined based on various factors such as the ink ribbon R, the roll paper RP as a printing medium, and the characteristics of the thermal head 10. In this embodiment, the predetermined threshold is set to 64. Yes. In the case of the dot pattern 51 shown in FIG. 8, the number F _before of the difference in the average gradation value between adjacent lines exceeding the threshold value 64 is two.

Here, the contents of step 13 will be briefly described. First, using the fact that there is a strong correlation between the color density (that is, the average gradation value) of the line to be printed and the frictional load among the thermal head 10, the ink ribbon R, and the roll paper RP during printing, The difference between the tone values is regarded as a change in the friction load between lines during printing. Thereby, when the difference of the average gradation value between adjacent lines exceeds a predetermined threshold value, it can be determined that the frictional load fluctuates rapidly between the adjacent lines, so the dot pattern of the image data 50 By calculating the number F _before of the entire 51, it is predicted how rapidly the friction load of the entire dot pattern 51 of the image data 50 varies. Note that a correlation function between the difference between the average gradation values and the friction load may be obtained in advance, and the determination may be made after converting the difference between the average gradation values into the friction load using this correlation function.

Next, when the dot pattern 51 of the image data 50 is rotated with respect to the line by a predetermined rotation angle α (α ≦ 1 °), the same procedure as the above steps 11 to 13 is executed, The number F _after of the average gradation value differences exceeding a predetermined threshold is obtained (step 14). FIG. 10 is an explanatory diagram showing the dot pattern 52 when the dot pattern 51 of the image data 50 shown in FIG. 8 is rotated counterclockwise by a predetermined rotation angle α. In the present embodiment, when the dot pattern 51 of the image data 50 is rotated, the center of the entire dot pattern 51 is set as the rotation center, and the entire dot pattern 51 is rotated. Note that the dot pattern 52 shown in FIG. 10 is shown by being rotated by a rotation angle α of 1 ° or more for the purpose of facilitating the explanation. It is preferable to set it to less than 1 ° which is difficult to recognize.

When calculating the rotated dot pattern 52, for example, the coordinates (x ₂ , y ₂ ) after rotating the point (x ₁ , y ₁ ) on the coordinate xy plane by the rotation angle α The following formula (1) showing the relationship can be used.

10, as in FIG. 8, the average gradation value for all lines and the difference between the average gradation values between adjacent lines are shown in a table on the right side of the dot pattern 52 of the image data 50. . As can be seen from these tables, the number F _after of the average gradation value difference between adjacent lines that exceeds a predetermined threshold is zero.

The number F _before when rotated by the predetermined rotation angle α obtained as described above is compared with the number F _after when not rotated (step 15). As a result of the comparison, when the number F _after is smaller than the number F _before (Yes in step 15), the rotational processing of the rotation angle α causes a rapid change in the friction load between lines during printing to be a state before the rotation. It is determined that the dot pattern 52 is obtained by rotating the dot pattern of the image data 50 to be printed by the rotation angle α (step 16). In this case, the number F _before of the dot patterns 51 shown in FIG. 8 is 2, the number of dot patterns 52 shown in FIG. 10 is 0, and the number F _after is smaller than the number F _before . The dot pattern 52 of the image data 50 to be printed is determined, and printing using this dot pattern 52 is performed.

On the other hand, when the number F _after is the same as or larger than the number F _before (No in Step 15), even if the dot pattern 50 is rotated at the rotation angle α, the frictional load between lines during printing changes rapidly. It is determined that the rotation angle is not reduced from the state before the rotation, the value of the rotation angle α to be set is changed (step 17), and the procedures of steps 14 and 15 are repeated for the changed value of the rotation angle α. Note that a plurality of settable rotation angles α (α ≦ 1 °) are prepared in advance, and when changing the value of the rotation angle α, a predetermined order (for example, the order from the smallest value) Select the values to be set in order of increasing value, such as the order closest to the value to be set first. In the present embodiment, four values (0.25 °, 0.50 °, 0.75 °, 1 °) are prepared in advance as values of the rotation angle α that can be set. Thereafter, the above steps 17, 14, and 15 are repeated until an appropriate value of the rotation angle α that can reduce the rapid fluctuation of the friction load is determined. If the optimum rotation angle α is not determined, it may be determined not to rotate.

  Through the above procedure, the rotation angle α is determined, and step 3 shown in FIG. 7 is completed (step 18).

  The CPU 35 converts the image data 50 rotated at the determined rotation angle α into output data corresponding to the output of the thermal head 10 (step 4), and inputs the converted output data to the thermal head circuit 38 (step). 5). The thermal head circuit 38 sequentially inputs output signals to the thermal head 10 based on the output data (step 6). The thermal head 10 performs thermal transfer by heating based on the output signal, and prints the dot pattern 52 obtained by rotating the C (cyan) ink at the rotation angle α on the roll paper RP line by line (step 7).

  For the remaining Y (yellow) and M (magenta) inks of the three colors, a dot pattern (not shown) of image data (not shown) rotated at the same rotation angle α as C (cyan) is used. Printing is performed on the roll paper RP line by line. In the present embodiment, printing on the roll paper RP is performed in the order of Y (yellow), M (magenta), and C (cyan) according to the arrangement order of the ink ribbons R. In the above description, the rotation angle α is determined based only on C (cyan) of the three colors. However, rapid fluctuations in the frictional load are reduced for Y (yellow) and M (magenta). Such a rotation angle α may be determined. Further, an overcoat layer serving as a protective layer is applied on the roll paper RP on which three colors are printed. Thus, printing by the printer 1 is completed (step 8).

  According to the above embodiment, when the dot pattern 51 of the image data 50 input to the printer 1 is printed line by line, the dot pattern 51 of the input image data 50 is rotated at a predetermined rotation angle with respect to the line. By printing the dot pattern 52 rotated by α (α ≦ 1 °), for example, counterclockwise, abrupt fluctuations in the friction load between lines during printing is reduced, and density unevenness is effectively suppressed, It becomes possible to improve the image quality of the printed matter P as compared with the conventional art. In addition, density irregularities can be dealt with only by image processing without remodeling the main body of the printer 1, so that it can be implemented very easily and the cost can be reduced.

In addition, values F _before and F _after that are used as an index of fluctuations in the friction load between lines when printing the dot pattern 51 of the image data 50 at a predetermined rotation angle α and when the dot pattern 51 is not rotated are calculated. Thus, it is possible to set the rotation angle α that reliably reduces the fluctuation of the friction load. Furthermore, when the dot pattern 51 of the image data 50 is rotated, the center of the entire dot pattern 51 is set as the rotation center, and the rotation process is performed, so that the rotation process is greatly facilitated.

Further, by utilizing the strong correlation between the color density of the line to be printed (that is, the average gradation value) and the frictional load among the thermal head 10, the ink ribbon R, and the roll paper RP, the average gradation value regarded as variation in the frictional load between the lines at the time of printing the difference, the entire dot pattern 51 (52) of the image data 50, the friction load difference of the number _F before the average gradation value exceeds a predetermined threshold _{(F after)} By using the fluctuation index, the calculation is greatly facilitated, and the printing process can be performed efficiently. Furthermore, if a correlation function between the difference between the average gradation values and the friction load is obtained in advance, and the value of the friction load is calculated from this correlation function and used as an index, the rotation angle α can be obtained more appropriately. Become.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, this invention is not limited to the example which concerns. It is obvious for those skilled in the art that various changes or modifications can be conceived within the scope of the technical idea described in the claims, and of course, the technical scope of the present invention is also possible. It is understood that it belongs to.

  In the above-described embodiment, the case where the printer 1 is a thermal printer that performs printing by thermally transferring the ink of the ink ribbon R onto the roll paper RP by heating the thermal head 10 has been described. A thermal printer using paper may be used. In such a thermal printer 1, printing is performed by directly coloring the thermal paper by heating the thermal header 10 without using the ink ribbon R. Therefore, when predicting the friction load, between the lines during printing, The resulting frictional load between the thermal head and the print medium may be predicted.

  In the above-described embodiment, the case where the CPU 35 performs control when the input data is converted into the output data has been described. However, for example, a control program is incorporated into the thermal head control circuit 38, and the input is performed by the thermal head control circuit 30. You may make it perform control at the time of converting data into output data.

  In the above-described embodiment, the case where the control device 30 includes the CPU 35, the RAM 36, the ROM 37, and the thermal head control circuit 38 connected to each other via the bus line BL has been described. However, the control device 30 includes other devices. Or other configurations.

  In the above-described embodiment, when the dot pattern 51 of the image data 50 is rotated, the center of the entire dot pattern 51 is set as the rotation center, and the entire dot pattern 51 is rotated. A position other than the center of the entire 51 may be set as the rotation center. Also, without rotating the entire dot pattern 51, the dot pattern 51 is divided into a plurality of areas (for example, for each line), and each rotation center is set for each of the divided areas, and each of the plurality of areas is rotated. You may make it make it.

In the above-described embodiment, when one rotation angle α that can reduce the rapid fluctuation of the friction load from the state before the rotation is found, the rotation angle of the rotation process is determined as the rotation angle α. As described above, the number F _after is calculated for each of some or all of the plurality of rotation angles α prepared in advance, and the rotation angle α at which the minimum F _after is obtained among the F _after smaller than the number F _{before before} rotation is obtained. May be determined as the optimum rotation angle α.

  In the above-described embodiment, the case where the rotation angle α is determined based only on C (cyan) of the three colors has been described. However, the remaining Y (yellow) and M (magenta) also have a sharp friction load. The rotation angle α may be determined so that the fluctuation is reduced. Note that the human naked eye has low recognition power with respect to density unevenness of Y (yellow). Therefore, considering the processing efficiency, the rotation angle α is determined based on two colors of C (cyan) and M (magenta). preferable.

  In the above-described embodiment, the case where the friction load prediction and the rotation process are performed on the image data of three colors Y (yellow), M (magenta), and C (cyan) included in the ink ribbon R has been described. Frictional load prediction and rotation processing may be performed on image data of a plurality of other colors such as R (red), G (green), and B (blue).

  The present invention will be described using examples and comparative examples.

  FIG. 11 shows data of a comparative example in which predetermined image data is printed by a conventionally known printer, and then the printed matter is read by a scanner and the color density is digitized. The vertical axis indicates the color density and the horizontal axis indicates the print direction. It is the figure shown on the coordinate which is a position along. On the other hand, FIG. 12 is a diagram showing the same predetermined image data printed by the printer of the present invention and the data of the embodiment when the color density is digitized using a scanner in the same coordinates as in FIG. It is. Further, FIG. 13 is an enlarged view showing a part of the data of FIGS. 11 and 12 in an enlarged manner on the same coordinates. In FIG. 13, a dotted line indicates a comparative example, and a solid line indicates an example.

  As shown in FIGS. 11 to 13, when the dot pattern of the image data is rotated at an appropriate rotation angle and printing is performed according to the present invention, the variation range of the color density becomes very small, and the density unevenness is effectively reduced. It was found that the image quality can be improved.

  The present invention is particularly useful for a thermal printer that performs printing in which a dot pattern of input image data is printed on a print medium line by line by heating a thermal head.

It is explanatory drawing at the time of printing the rectangular center part M of the printing paper 100 on white plain, and printing the outer peripheral part N of this center part M with a dark color. FIG. 2 is a diagram showing the color density of the printing paper 100 of FIG. 1 along the line AA. FIG. 3 is a diagram illustrating the color density of the printing paper 100 in FIG. 1 along the line BB. It is the enlarged view to which the corner | angular part O used as the boundary of the center part M and the outer peripheral part N shown in FIG. 1 is a configuration diagram illustrating a configuration of a printer 1 that is an example of a thermal printer according to an embodiment of the present invention. 2 is a configuration diagram illustrating an example of a configuration of a control device 30. FIG. It is a whole flowchart explaining the procedure of the printing control method which concerns on embodiment of this invention. FIG. 4 is a diagram illustrating a dot pattern 51 of C (cyan) image data 50 of three colors constituting an ink ribbon R as an example of image data read from a RAM 36; FIG. 8 is a flowchart for explaining in detail the procedure of step 3 in FIG. 7. FIG. 9 is an explanatory diagram showing a dot pattern 52 when the dot pattern 51 of the image data 50 shown in FIG. 8 is rotated counterclockwise by a predetermined rotation angle α. Data of a comparative example when predetermined image data is printed by a conventionally known printer, and then the printed matter is read by a scanner and the color density is digitized, the vertical axis is the color density and the horizontal axis is the position along the print direction It is the figure shown on the coordinate which is. The same predetermined image data as in the case of FIG. 11 is printed by the printer of the present invention, and the data of the embodiment when the color density is digitized using the scanner is also shown on the same coordinates as in FIG. is there. FIG. 13 is an enlarged view showing a part of the data of FIG. 11 and FIG. 12 on the same coordinates in an enlarged manner.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Printer 2 Case 5 Supply roller 10, 101 Thermal head 11 Platen roller 15 Winding roller 22 Guide roller 25 Transport roller 26 Pinch roller 30 Control device 31 External I / F
32 Mechanism control unit 35 CPU
36 RAM
37 ROM
38 Thermal head control circuit 40, 47 Guide plate 45 Roll paper detection sensor 46 Cutting machine 48 Ejection port 50 Image data 51 Dot pattern before rotation 52 Dot pattern after rotation 100 Printing paper
a to f Point indicating each position along the printing direction AA, BB Line parallel to the printing direction BL Bus line M Center portion N Outer portion O Corner portion P Printed matter R Ink ribbon RP Roll paper X Printing direction Y Width direction α Rotation angle

Claims (14)

A thermal printer that prints a dot pattern of input image data on a print medium line by line by heating a thermal head,
Friction load fluctuation between the thermal head and the print medium that occurs between lines during printing is predicted, and control is performed so that the dot pattern of the image data is rotated by a predetermined rotation angle based on the prediction result and printed. A thermal printer comprising a control device. Printing on the print medium is performed by thermally transferring the ink on the ink ribbon to the print medium by heating the thermal head,
The thermal printer according to claim 1, wherein the friction load between the thermal head, the ink ribbon, and the print medium is predicted when the fluctuation of the friction load is predicted. 3. The control device according to claim 2, wherein when the ink ribbon includes ink of a plurality of colors, the control device predicts a change in friction load for at least two of the plurality of colors. 4. Thermal printer. The control device calculates a difference in average gradation value between adjacent lines in the dot pattern of the image data when predicting a change in the friction load, and based on the calculated difference in average gradation value The thermal printer according to claim 1, wherein the thermal printer is predicted. The control device sets the rotation center to the center of the entire dot pattern of the image data and rotates the predetermined rotation angle to 1 ° or less when rotating the dot pattern of the image data by a predetermined rotation angle. The thermal printer according to claim 1, wherein the thermal printer is set. When the control device predicts the change in the friction load, both the change in the friction load when the dot pattern of the image data is rotated by a predetermined rotation angle and the change in the friction load when the rotation is not performed. The thermal printer according to claim 1, wherein the thermal printer is predicted. The control device sets a plurality of the predetermined rotation angles when predicting the fluctuation of the friction load, and the friction load when the dot pattern of the image data is rotated for each of the plurality of the predetermined rotation angles. And predicting the variation of the image data, selecting one of the plurality of predetermined rotation angles set based on the prediction result, and rotating the dot pattern of the image data by the selected predetermined rotation angle for printing. The thermal printer according to claim 1, wherein the thermal printer is controlled as follows. A thermal printer printing control method for printing a dot pattern of inputted image data on a printing medium line by line by heating a thermal head,
Friction load fluctuation between the thermal head and the print medium that occurs between lines during printing is predicted, and control is performed so that the dot pattern of the image data is rotated by a predetermined rotation angle based on the prediction result and printed. A printing control method for a thermal printer. Printing on the print medium is performed by thermally transferring the ink on the ink ribbon to the print medium by heating the thermal head,
9. The print control method for a thermal printer according to claim 8, wherein the friction load between the thermal head, the ink ribbon, and the print medium is predicted when the fluctuation of the friction load is predicted. The thermal printer printing control according to claim 9, wherein when the ink ribbon includes a plurality of colors of ink, a variation in friction load is predicted for at least two of the plurality of colors. Method. When predicting the fluctuation of the friction load, calculating a difference in average gradation value between adjacent lines in the dot pattern of the image data, and predicting based on the calculated difference in average gradation value The printing control method for a thermal printer according to claim 8, wherein the printing control method is for a thermal printer. When the dot pattern of the image data is rotated by a predetermined rotation angle, the rotation center is set to the center of the entire dot pattern of the image data, and the predetermined rotation angle is set to 1 ° or less. The thermal printer printing control method according to claim 8. When predicting the fluctuation of the friction load, predicting both the fluctuation of the friction load when the dot pattern of the image data is rotated by a predetermined rotation angle and the fluctuation of the friction load when not rotating. The thermal printer printing control method according to claim 8, wherein the printing control method is a thermal printer. When predicting the fluctuation of the friction load, a plurality of the predetermined rotation angles are set, and the fluctuation of the friction load when the dot pattern of the image data is rotated for each of the plurality of predetermined rotation angles is predicted. And selecting one of the plurality of predetermined rotation angles set based on the prediction result, and controlling the dot pattern of the image data to be printed by rotating the selected predetermined rotation angle. The printing control method for a thermal printer according to claim 8, wherein the printing control method is a thermal printer.

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