Thermal printer

Abstract

To provide a thermal printer capable of easily preventing the occurrence of a density difference in the width direction of a thermal film.SOLUTION: A thermal printer according to an aspect of the present disclosure is a thermal printer that performs printing by heating a thermal head, the thermal printer including a control unit that controls heating of the thermal head based on a predetermined print request to print a print content related to the print request, in which the control unit increases or decreases a heating amount of the thermal head with respect to a heating amount based on the print request in order to reduce a density difference in a width direction of a medium.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a thermal printer that performs printing using, for example, a thermal head. [Background technology]

[0002] A thermal printer has a thermal head and a platen roller. The platen roller determines the printing position of the thermal head, and the thermal head is positioned opposite the platen roller. In the thermal printer of Patent Document 1, long thermal paper is loaded in a roll paper storage compartment and is pulled out and transported to the printing position. In the thermal printer of Patent Document 1, the thermal head is biased toward the platen roller by the biasing force of a compression coil spring, and the thermal head is pressed against the thermal paper at the printing position. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-208761 Summary of the Invention [Problem to be solved by the invention]

[0004] In the thermal printer of Patent Document 1, if the thermal head is not uniformly biased toward the platen roller by the biasing force of the compression coil spring, density variations across the width of the thermal paper can occur, and differences in print length can occur on the left and right sides of the print area when printing. These differences in print length are caused by friction between the thermal head and the thermal paper, thermal head pressure, inconsistent flatness, and different energies being applied to the thermal paper on the left and right sides. Furthermore, the thermal paper can become more humid due to the temperature and humidity around it, which increases friction and exacerbates the problem. This problem is not limited to thermal printers that print on thermal paper unwound from a long roll of paper, but also occurs in thermal printers that print on thermal paper cut to a specified length.

[0005] As shown in Figure 8(a), an appropriate print range is set for each sheet of paper of a specified length, and the print lengths on both sides of the appropriate print range are length A. In contrast, as shown in Figure 8(b), if the print length at the right end of the print area is longer (A+a) than the print length at the left end of the print area (A), the print area is not positioned within the appropriate appropriate print range, and therefore is outside the specifications.

[0006] Previously, problems such as density variations across the width of thermal paper and differences in print length between the left and right sides of the print area were controlled by fine-tuning the pressure of the thermal head. The thermal head pressure is determined by the left and right compression coil springs that urge the thermal head toward the platen roller, and fine-tuning the thermal head pressure requires adding washers to the compression coil springs. Since thermal head pressure varies between machines, fine adjustments are required for each machine, which creates the problem of requiring a huge amount of work.

[0007] The present invention was made with an eye on such problems, and its main purpose is to provide a thermal printer that can easily prevent density differences across the width of the thermal film and differences in printing length between the left and right sides of the printing area. [Means for solving the problem]

[0008] In other words, the thermal printer of the present invention is a thermal printer that prints by heating a thermal head, and is equipped with a control unit that prints a printing area related to a specified printing request by controlling the heating of the thermal head based on the specified printing request, and is characterized in that the control unit increases or decreases the amount of heating of the thermal head relative to the amount of heating based on the printing request in order to reduce density differences across the width of the medium.

[0009] Therefore, in the thermal printer according to the present invention, the heating amount of the thermal head is increased or decreased based on the printing requirements to reduce density differences across the width of the thermal film. Therefore, even if the biasing forces of the left and right compression coil springs that bias the thermal head toward the platen roller are not uniform, there is no need to add washers to the compression coil springs to fine-tune the pressure of the thermal head. This makes it easy to prevent density differences across the width of the thermal film. Furthermore, by correcting the heating amount of the thermal head to reduce density differences across the width of the thermal film, it may be possible to reduce the difference in print length between the left and right sides of the print area.

[0010] In the thermal printer of the present invention, it is preferable that the printer has a density sensor that detects the density of a printed area printed at two locations separated in the width direction of the medium, and that the control unit has a density correction table that shows the relationship between the density difference of the printed area detected by the density sensor and the amount of increase or decrease in the heating amount of the thermal head to reduce the density difference.

[0011] Therefore, in the thermal printer according to the present invention, the density correction table makes it possible to easily detect the amount of increase or decrease in the amount of heat of the thermal head in order to reduce density differences across the width of the thermal film.

[0012] In the thermal printer of the present invention, it is preferable that the printer has a sensor that detects the difference in printing length between the left and right sides of the printing area, and the control unit has an image cutting correction table that shows the relationship between the difference in printing length detected by the sensor and the amount of increase or decrease in printing length on either the left or right side of the printing area to reduce the difference in printing length.

[0013] Therefore, in the thermal printer according to the present invention, the image cut correction table makes it easy to detect the amount of increase or decrease in the printing length on either the left or right side of the printing area in order to reduce the difference in printing length between the left and right sides of the printing area.

[0014] In the thermal printer according to the present invention, it is preferable that the control unit increases or decreases the print length on either the left or right side of the print area by increasing or decreasing the number of dots included in the print area.

[0015] Therefore, in the thermal printer according to the present invention, the print length on either the left or right side of the print area can be easily increased or decreased by increasing or decreasing the number of dots included in the print area.

[0016] In the thermal printer according to the present invention, it is preferable that the printer has a sensor that detects at least one of temperature and humidity, and the control unit has the image cut correction table for each detection result detected by the sensor.

[0017] Therefore, in the thermal printer of the present invention, regardless of the temperature and humidity around the thermal printer, it is possible to easily detect the amount of increase or decrease in the printing length on either the left or right side of the printing area in order to reduce the difference in printing length between the left and right sides of the printing area. [Effects of the Invention]

[0018] According to the present invention, it is possible to easily prevent density differences in the width direction of the medium and differences in print length between the left and right sides of the print area. [Brief explanation of the drawings]

[0019] [Figure 1]1 is a configuration diagram that schematically illustrates a thermal printer 1 according to an embodiment of the present invention. [Figure 2] 2 is a plan view of the essential parts, schematically showing the relationship between the thermal head 3 and the thermal film 2 of the thermal printer 1 of FIG. [Figure 3] FIG. 2 is a functional block diagram of the thermal printer 1 of FIG. [Figure 4] 4 is a flowchart showing a method for adjusting the left and right print lengths of the print area in the thermal printer 1 of FIG. [Figure 5] FIG. 5(a) is a diagram showing a state where there is a difference in print length between the left and right sides of the print area, and FIG. 5(b) is a diagram showing a state where the print lengths on the left and right sides of the print area have been corrected. [Figure 6] 2A to 2C are diagrams illustrating a method for printing by increasing or decreasing the number of dots included in a printing area in the thermal printer 1 of FIG. [Figure 7] FIG. 10 is a diagram illustrating a configuration of a thermal printer 101 according to a modified example of the present invention. [Figure 8] FIG. 8(a) is a diagram for explaining the appropriate print range of the paper, and FIG. 8(b) is a diagram for explaining a state in which print lengths occur on the left and right sides of the print area. DETAILED DESCRIPTION OF THE INVENTION

[0020] A thermal printer 1 according to an embodiment of the present invention will now be described with reference to the drawings.

[0021] 1, the thermal printer 1 has a thermal head 3, an elevating means 8 for raising and lowering the thermal head 3, and a paper feed drive unit 5 for feeding the thermal film 2 below the thermal head 3. The resolution of the thermal printer 1 is, for example, 500 dpi.

[0022] As shown in Fig. 2, the thermal head 3 has a heating region 3c extending along the width direction of the thermal film 2, and a predetermined number of heating elements 3a are arranged in the heating region 3c. The heating elements 3a are elements that generate heat when energized, and are provided corresponding to each pixel (dot) arranged in a row along the main scanning direction. When energized, the heating elements 3a generate heat, which heats the thermal film 2, thereby printing dots. As in Patent Document 1, which is a conventional technique, the thermal head 3 is urged toward the platen roller 5c by the urging force of multiple compression coil springs (not shown) arranged at intervals along the width direction of the thermal film 2.

[0023] The paper feed drive unit 5 has a feed roller 5a and a pinch roller 5b that sandwich the thermal film 2, and is configured to position the thermal film 2 sandwiched between them between the thermal head 3 and the platen roller 5c. The rolled thermal film 2 is held in the paper feed unit 6, and the feed roller 5a is rotated by a rotation drive source (not shown), which rotates the paper feed unit 6 and transports the thermal film 2.

[0024] In the thermal printer 1, the thermal film 2 is moved in the sub-scanning direction so as to be wound around the paper feed unit 6 and supplied to between the thermal head 3 and the platen roller 5c, thereby printing pixels line by line in the main scanning direction while printing pixels sequentially along the sub-scanning direction.

[0025] The thermal printer 1 has a temperature sensor 10, a humidity sensor 11, three density sensors 12a to 12c, and two transmission sensors 13a and 13b.

[0026] The temperature sensor 10 detects the temperature around the printer, and the humidity sensor 11 detects the humidity around the printer.

[0027] The three density sensors 12a to 12c detect the density of the print areas (dots) printed on the thermal film 2 by the thermal head 3. The three density sensors 12a to 12c are arranged downstream of the thermal head 3 in the transport direction of the thermal film 2, spaced apart in the width direction of the thermal film 2. For example, when test printing including print areas of the same density along the width direction of the thermal film 2 is performed in the thermal printer 1, the three density sensors 12a to 12c each detect the density of the areas printed as print areas of the same density.

[0028] The two transmissive sensors 13a and 13b detect the rear end of the printing area printed on the thermal film 2 by the thermal head 3. The two transmissive sensors 13a and 13b are arranged downstream of the thermal head 3 in the transport direction of the thermal film 2 and spaced apart in the width direction of the thermal film 2. In this embodiment, the two transmissive sensors 13a and 13b are arranged near both ends in the width direction of the thermal film 2. The two transmissive sensors 13a and 13b are arranged equidistant from the thermal head 3 in the transport direction of the thermal film 2.

[0029] The transmissive sensor 13a has a light-emitting element 13a1 located below the transport path of the thermal film 2 and a light-receiving element 13a2 located above the transport path of the thermal film 2. The light-receiving element 13a2 is located opposite the light-emitting element 13a1 and can receive light emitted by the light-emitting element 13a1. The amount of light received by the light-receiving element 13a2 when the light emitted by the light-emitting element 13a1 passes through the print area printed by the thermal head 3 differs from the amount of light received when the light emitted by the light-emitting element 13a1 does not pass through the print area printed by the thermal head 3. Therefore, by detecting the amount of light received by the light-receiving element 13a2, the rear end of the print area printed by the thermal head 3 (the end of the print area downstream in the transport direction of the thermal film 2) can be detected. The transmissive sensor 13b has the same configuration as the transmissive sensor 13a, and therefore a detailed description thereof will be omitted.

[0030] In the thermal printer 1, the two transmissive sensors 13a and 13b are disposed near both ends of the thermal film 2 in the width direction, and are disposed equidistant from the thermal head 3 in the transport direction of the thermal film 2. Therefore, when the rear end of the printing area is aligned with the width direction of the thermal film 2, the two transmissive sensors 13a and 13b simultaneously detect the rear end of the printing area. On the other hand, when the ends of the printing area are inclined with respect to the width direction of the thermal film 2, the two transmissive sensors 13a and 13b do not simultaneously detect the rear end of the printing area. In this case, the difference in printing length between the left and right sides of the printing area can be detected based on the timing when the rear end of the printing area is detected by the transmissive sensor 13a, the timing when the rear end of the printing area is detected by the transmissive sensor 13b, and the transport speed of the thermal film 2.

[0031] The control unit 50 is configured with a normal microcomputer equipped with a CPU, memory, and interface, similar to well-known thermal printers, and programs are written in the memory. The CPU calls up and executes the necessary programs as appropriate, thereby working in cooperation with peripheral hardware resources to achieve the desired transport and printing operations.

[0032] The control unit 50 has a print control unit 51, a paper feed drive control unit 52, and a memory unit 53. The control unit 50 is also connected to the thermal head 3, the paper feed drive unit 5, a temperature sensor 10, a humidity sensor 11, three density sensors 12a to 12c, and two transmission sensors 13a and 13b.

[0033] The print control unit 51 controls the power supply to the heating elements 3a of the thermal head 3 to perform printing based on a print request (including a normal print request and a test print request) input from the outside.

[0034] The paper feed drive control unit 52 controls the driving of the paper feed drive unit 5 .

[0035] The storage unit 53 stores print content to be printed when a normal print request is made and test print content (test pattern) to be printed when a test print request is made. The storage unit 53 of this embodiment also stores various correction tables, including a temperature and humidity correction table 54, a density correction table 55, and an image cut correction table 56.

[0036] The temperature and humidity correction table 54 will now be described.

[0037] When the temperature and humidity around the thermal printer 1 change, the print length of the print area changes accordingly. There is a specific relationship between the temperature and humidity around the thermal printer 1 and the print length of the print area. For example, in a high-temperature, high-humidity environment, the thermal film 2 absorbs moisture, increasing friction and shortening the print length of the print area. Therefore, if the temperature and humidity around the thermal printer 1 are known, it is possible to detect the increase or decrease in the print length of the print area when printing at that temperature and humidity. Furthermore, the greater the heat output (output energy) of the heating element 3a of the thermal head 3 when printing on the thermal film 2, the longer the print length of the print area.

[0038] That is, if the temperature and humidity around the thermal printer 1 are known, the amount of increase or decrease in the printing length of the printing area at that time can be detected, and by adjusting the heat output of the heating element 3a of the thermal head 3 when printing on the thermal film 2 so that the amount of increase or decrease in the printing length of the printing area is zero, the printing length of the printing area can be made to match the appropriate printing range set for the paper. For example, if the printing length of the printing area becomes shorter in a high-temperature and high-humidity environment, the thermal head 3 can increase the heat output (output energy) of the heating element 3a when printing on the thermal film 2, thereby reducing friction, thereby lengthening the printing length of the printing area.

[0039] The temperature and humidity correction table 54 is a correction table that shows the relationship between the temperature and humidity around the thermal printer 1 and the correction amount for the heat generation (output energy) of the heating element 3a of the thermal head 3 to prevent the print length of the print area from increasing or decreasing when printing is performed at that temperature and humidity. In other words, when printing is performed with the thermal printer 1, if the temperature and humidity around the thermal printer 1 are detected and printing is performed after correction based on the correction amount for the heat generation of the heating element 3a of the thermal head 3 that corresponds to that temperature and humidity, the print length of the print area will match the appropriate print range set on the paper.

[0040] The density correction table 55 will now be described.

[0041] As described above, in the thermal printer 1, if the thermal head 3 is not uniformly biased toward the platen roller 5c by the biasing force of the compression coil spring, density variations in the width direction of the thermal film 2 and differences in print length between the left and right sides occur. A conventional solution to this problem is to fine-tune the pressure of the thermal head 3, but this requires a huge amount of work. Therefore, in this embodiment, the density variations in the width direction of the thermal film 2 that occur when the thermal head 3 is not uniformly biased toward the platen roller 5c by the biasing force of the compression coil spring are reduced by adjusting the heat generation (output energy) of the heating element 3a of the thermal head 3 during printing. The greater the heat generation of the heating element 3a of the thermal head 3 during printing, the denser the density of the print area (dots) printed by the heating element 3a.

[0042] The density correction table 55 is a correction table showing the relationship between a density difference between two areas (dots) of the same density printed at two locations separated in the width direction of the thermal film 2 and the correction amount for the heat generation amount of the heating element 3a of the thermal head 3 to reduce the density difference. In other words, if a density difference occurs between two areas of the same density printed at two locations separated in the width direction of the thermal film 2, the density difference between the two areas of the same density printed at two locations separated in the width direction of the thermal film 2 can be eliminated by increasing the heat generation amount (output energy) of the heating element 3a when printing the lighter density area by an amount corresponding to the density difference.

[0043] The image cut correction table 56 will now be described.

[0044] As described above, in the thermal printer 1 of this embodiment, the density difference in the width direction of the thermal film 2 that occurs when the thermal head 3 is not uniformly urged toward the platen roller 5c by the urging force of the compression coil spring is reduced by adjusting the heat generation amount (output energy) of the heating element 3a of the thermal head 3 during printing. Therefore, in the thermal printer 1, the state in which the thermal head 3 is not uniformly urged toward the platen roller 5c by the urging force of the compression coil spring remains unchanged.

[0045] If printing is performed when the thermal head 3 is not uniformly biased toward the platen roller 5c by the biasing force of the compression coil spring, a difference in print length will occur between the left and right sides of the print area. The thermal printer 1 uses transmission sensors 13a and 13b to detect the difference in print length between the left and right sides of the print area, and adjusts the print length of the left and right sides of the print area printed in the print area to eliminate the difference. In the thermal printer 1 of this embodiment, the print length of either the left or right side of the print area is increased or decreased by increasing or decreasing the number of dots included in the print area.

[0046] For example, if there is a difference in print length between the left and right sides of the print area, the number of dots is reduced at equal intervals from the longer side to the shorter side of the print length. Also, if the temperature and humidity around the thermal printer 1 change, the print length of the print area changes accordingly, so when adjusting the number of dots included in the print area to eliminate the difference in print length between the left and right sides of the print area, different adjustments are required depending on the temperature and humidity around the thermal printer 1. When the number of dots included in the print area is adjusted to eliminate the difference in print length between the left and right sides of the print area, the print length of the print area will match the appropriate print range set on the paper.

[0047] The image cut correction table 56 is a correction table that shows the relationship between the difference in print length between the left and right sides of the print area detected using the transmission sensors 13a and 13b and the increase or decrease in the number of dots included in the print area that is adjusted to reduce or eliminate the difference in print length between the left and right sides. The image cut correction table 56 is created for each temperature and humidity around the thermal printer 1. In other words, when printing with the thermal printer 1, if the difference in print length between the left and right sides is detected and the number of dots corresponding to the difference in print length is corrected and printing is performed, the print length of the print area will match the appropriate range set for the paper.

[0048] The procedure for printing on the thermal film 2 in the thermal printer 1 will be described with reference to FIG.

[0049] <Step S1> In step S1, the control unit 50 measures the temperature and humidity around the thermal printer 1 using the temperature sensor 10 and humidity sensor 11.

[0050] <Step S2> In step S2, the control unit 50 determines, based on the temperature and humidity correction table 54, the correction amount to eliminate the difference in printing length between the left and right sides of the printing area, i.e., the correction amount for the heat generation (output energy) of the heating element 3a of the thermal head 3 when printing on the thermal film 2.

[0051] <Step S3> In step S3, the control unit 50 performs printing while correcting the amount of heat (output energy) generated when the thermal head 3 prints on the thermal film 2 based on the correction amount determined in step S2.

[0052] <Step S4> In step S4, the control unit 50 determines whether there is a density difference between two areas (dots) of the same density that are printed at two locations separated in the width direction of the thermal film 2. If it is determined that there is a density difference between the two areas separated in the width direction of the thermal film 2, the process proceeds to step S5. If it is determined that there is no density difference between the two areas separated in the width direction of the thermal film 2, the process proceeds to step S7.

[0053] <Step S5> In step S5, the control unit 50 determines, based on the density correction table 55, the correction amount for eliminating the density difference between two areas separated in the width direction of the thermal film 2, i.e., the correction amount for the heat generation amount (output energy) of the heating element 3a of the thermal head 3 when printing on the thermal film 2.

[0054] <Step S6> In step S6, the control unit 50 performs printing while correcting the heat generation amount (output energy) of the thermal head 3 when printing on the thermal film 2 based on the correction amount determined in step S5.

[0055] <Step S7> In step S7, the control unit 50 determines whether there is a difference in print length between the left and right sides of the print area. If it is determined that there is a difference in print length between the left and right sides of the print area, the process proceeds to step S8. If it is determined that there is no difference in print length between the left and right sides of the print area, the process ends.

[0056] <Step S8> In step S8, the control unit 50 determines the amount of correction for the left and right print lengths of the print area to eliminate the difference between the left and right print lengths of the print area, i.e., the amount of increase or decrease in the number of dots included in the print area, based on the image cut correction table 56. Note that the image cut correction table 56 used corresponds to the temperature measured by the temperature sensor 10 and the humidity measured by the humidity sensor 11 at that time.

[0057] <Step S9> In step S9, the control unit 50 performs printing while increasing or decreasing the number of dots included in the print area to eliminate the difference in print length between the left and right sides of the print area based on the correction amount determined in step S8.

[0058] A method for printing by increasing or decreasing the number of dots included in the printing area in the thermal printer 1 will be described with reference to Fig. 5. In Fig. 5(a) and Fig. 5(b), the dot rows N1 to N5 are described as including 54 dots each.

[0059] In this embodiment, we will explain the case where printing is not performed by increasing or decreasing the number of dots included in the printing area, and the printing length at the right end of the printing area is (A+a) longer than the printing length (A) at the left end of the printing area, as shown in Figure 8(b).

[0060] 5(a) shows five dot rows N1 to N5 printed near the rear edge of the print area. Dot row N1 is positioned closest to the rear edge of the print area, and dot rows N2 to N5 are positioned in order of increasing distance from dot row N1.

[0061] In Figure 5(a), the print length at the right end of the print area is longer by a length a than the print length A at the left end of the print area, resulting in a difference in print length a between the left and right sides of the print area. Therefore, if the left and right print lengths are not corrected, as shown in Figure 5(a), the rear end of the print area will be inclined with respect to the width direction of the thermal film 2. As shown in Figure 5(a), the difference in print length a between the left and right sides of the print area corresponds to the length of 3 dots at the right end of the print area.

[0062] In the thermal printer 1, the control unit 50 detects the difference a in print length between the left and right sides of the print area using the transmission sensors 13a and 13b, and reduces the number of dots printed on the longer side of the print length to match the shorter side of the print length, for example. In this embodiment, the allowable range of the difference in print length between the left and right sides of the print area (allowable print length range a1) is described as the range of one row of dots N, for example. In this case, the range (print adjustment range a2) obtained by subtracting the allowable print length range a1 from the difference in print length a between the left and right sides of the print area is set as the range for increasing or decreasing the number of dots to be printed. (Difference in print length between left and right a) = (Print length tolerance a1) + (Print adjustment range a2)

[0063] Therefore, the print length tolerance range a1 refers to the range in which the left and right print lengths are not allowed to increase any further, and the print adjustment range a2 refers to the range in which dots that fall even slightly within this range are not printed. In Figure 5(b), the upper end of the print adjustment range a2 coincides with the boundary between the print length tolerance range a1 and the print adjustment range a2, and "dots within the print adjustment range a2" refers to dots that are at least partially contained within the print adjustment range a2. For example, as shown in Figure 5(b), if dots at least partially within the print adjustment range a2 are not printed, the difference in left and right print lengths will fall within the print length tolerance range a1.

[0064] As shown in FIG. 5(b), by reducing the number of dots included in the two dot rows N1-N2 printed near the rear end of the print area, the difference in print length a between the left and right sides of the print area is reduced to a1 (where a > a1), thereby reducing the inclination of the rear end of the print area relative to the width direction of the thermal film 2. In FIG. 5(a), the difference in print length a between the left and right sides of the print area is three dots, whereas in FIG. 5(b), the difference in print length a1 between the left and right sides of the print area is reduced to within one dot. For example, when the difference in print length a between the left and right sides of the print area is three dots, the image cut correction table 56 can detect how to reduce the number of dots included in the two dot rows N1-N2 so that the difference in print length between the left and right sides of the print area is reduced to within one dot. The thermal printer 1 of this embodiment is configured to not print dots within a print adjustment range a2, which is calculated by subtracting the print length tolerance range a1 from the difference in print length a between the left and right sides of the print area. The print length tolerance a1 is set appropriately depending on the tolerance for the difference in print length between the left and right sides of the print area.

[0065] That is, when printing five dot rows N1 to N5 near the rear end of the printing area, the control unit 50 reduces the number of dots included in the two dot rows N1 to N2 as shown in FIG. (1) When printing dot row N1, the dots in portion n1 on the left side of the printing area of ​​dot row N1 are printed because the entire area of ​​each dot is outside the print adjustment range a2, whereas the dots outside portion n1 are not printed because at least a portion of each dot is within the print adjustment range a2. (2) When printing dot row N2, the dots in portion n2 on the left side of the printing area of ​​dot row N2 are printed because the entire area of ​​each dot is outside the print adjustment range a2, whereas the dots outside portion n1 are not printed because at least a portion of each dot is within the print adjustment range a2. (3) When printing dot row N3, all dots in portion n3 of dot row N3 are printed because the entire area of ​​each dot is outside the print adjustment range a2. (4) When printing dot row N4, all dots in portion n4 of dot row N4 are printed because the entire area of ​​each dot is outside the print adjustment range a2. (5) When printing dot row N5, all dots in portion n5 of dot row N5 are printed because the entire area of ​​each dot is outside the print adjustment range a2.

[0066] As described above, the thermal printer 1 of this embodiment is a thermal printer that prints by heating the thermal head 3, and is equipped with a control unit 50 that controls the heating of the thermal head 3 based on a specified printing request to print the printing area related to the printing request, and the control unit 50 increases or decreases the heating amount of the thermal head 3 relative to the heating amount based on the printing request in order to reduce the density difference in the width direction of the thermal film 2.

[0067] As a result, in the thermal printer 1 of this embodiment, the amount of heat applied by the thermal head 3 is increased or decreased based on the printing request to reduce density differences across the width of the thermal film 2. Therefore, even if the biasing forces of the left and right compression coil springs that bias the thermal head 3 toward the platen roller 5c are not uniform, there is no need to add washers to the compression coil springs to fine-tune the pressure of the thermal head 3. This makes it easy to prevent density differences across the width of the thermal film 2. Furthermore, by correcting the amount of heat applied by the thermal head 3 to reduce density differences across the width of the thermal film 2, it may be possible to reduce the difference in print length across the left and right of the print area.

[0068] The thermal printer 1 of this embodiment has density sensors 12a to 12c that detect the density of the printed area printed at three locations spaced apart in the width direction of the thermal film 2, and the control unit 50 has a density correction table 55 that shows the relationship between the density difference of the printed area detected by two of the density sensors 12a to 12c and the amount of increase or decrease in the heating amount of the thermal head 3 to reduce the density difference.

[0069] As a result, in the thermal printer 1 of this embodiment, the density correction table 55 can easily detect the increase or decrease in the amount of heat of the thermal head 3 to reduce density differences in the width direction of the thermal film 2.

[0070] The thermal printer 1 of this embodiment has transmission sensors 13a and 13b that detect the difference in printing length between the left and right sides of the printing area, and the control unit 50 has an image cutting correction table 56 that shows the relationship between the printing length difference detected by the transmission sensors 13a and 13b and the amount of increase or decrease in printing length on either the left or right side of the printing area to reduce the printing length difference.

[0071] As a result, in the thermal printer 1 of this embodiment, the image cut correction table 56 can easily detect the amount of increase or decrease in the print length on either the left or right side of the print area to reduce the difference in print length between the left and right sides of the print area.

[0072] In the thermal printer 1 of this embodiment, the control unit 50 increases or decreases the print length on either the left or right side of the print area by increasing or decreasing the number of dots included in the print area.

[0073] As a result, in the thermal printer 1 of this embodiment, the print length on either the left or right side of the print area can be easily increased or decreased by increasing or decreasing the number of dots included in the print area.

[0074] The thermal printer 1 of this embodiment has a temperature sensor 10 that detects temperature and a humidity sensor 11 that detects humidity, and the control unit 50 has an image cut correction table 56 for each detection result detected by the temperature sensor 10 and the humidity sensor 11.

[0075] As a result, in the thermal printer 1 of this embodiment, regardless of the temperature and humidity around the thermal printer 1, it is possible to easily detect the increase or decrease in the number of dots included in the printed content to reduce the difference in printing length between the left and right sides of the printing area.

[0076] Although the embodiments of the present invention have been described above, the specific configuration of each part is not limited to the above-described embodiments. The specific configuration of each part is not limited to the above-described embodiments, and various modifications are possible within the scope of the present invention.

[0077] For example, in this embodiment, the thermal printer 1 is described as printing on a roll of thermal film 2, but this is not limiting. The present invention may also be applied to a thermal printer 101 that prints on a thermal film 2 that has been cut to a predetermined length, as shown in FIG. 7 . In the thermal printer 101, the paper feed drive unit 105 includes feed rollers 105a1-105a3 that sandwich the thermal film 2 and pinch rollers 105b1-105b3, and is configured to position the thermal film 2 sandwiched between them between the thermal head 3 and the platen roller 105c. The thermal film 2 cut to a predetermined length is held flat in the paper feed unit 106, and the stacked thermal film 2 is pressed from above by roller 105n. The feed roller 105a1 and pinch roller 105b1 are rotated by a rotary drive source (not shown) to transport the thermal film 2 held in the paper feed unit 106 one sheet at a time. The feed rollers 105a2, 105a3 and the pinch rollers 105b2, 105b3 are located downstream of the thermal head 3 and the platen roller 105c in the transport direction, and transport the thermal film 2 downstream in the transport direction. In the thermal printer 101, the medium leading edge detection sensor 113a is located upstream of the thermal head 3 and the platen roller 105c in the transport direction. Like the transmissive sensor 13a, the medium leading edge detection sensor 113a has a light-emitting element 113a1 located below the transport path of the thermal film 2 and a light-receiving element 113a2 located above the transport path of the thermal film 2. Therefore, the leading edge of the thermal film 2 can be detected by detecting light emitted from the light-emitting element 113a1 with the light-receiving element 113a2. Similar to the thermal printer 1, the thermal printer 101 has a temperature sensor 10, a humidity sensor 11, three density sensors 12a to 12c, and two transmission sensors 13a and 13b.

[0078] In the above embodiment, when the printing length at the right end of the printing area is longer than the printing length at the left end of the printing area, the number of dots printed on the longer side of the printing length is reduced to match the shorter side of the printing length, but this is not limited to this. When the printing length at the right end of the printing area is longer than the printing length at the left end of the printing area, the number of dots printed on the shorter side of the printing length may be increased to match the longer side of the printing length. A similar correction can be made when the printing length at the left end of the printing area is longer than the printing length at the right end of the printing area.

[0079] In the above embodiment, the medium is a thermal film 2, but is not limited to this. Thermal paper (thermal paper) may also be used as the medium. The present invention is also directed to a thermal printer that prints by heating a thermal head, and may also be one that prints on a medium using, for example, an ink ribbon.

[0080] In the above embodiment, the printing operation of thermal printer 1 ends when printing is performed while increasing or decreasing the number of dots included in the print area in step S9, but this is not limited to this. For example, after printing while increasing or decreasing the number of dots included in the print area in step S9, the process may return to step S7 to check whether the left-to-right length of the print area is within the appropriate print range, and if it is not within the appropriate print range, the process may proceed to step S8, and if it is within the appropriate print range, the printing operation may end. In other words, the printing operation of thermal printer 1 may include a step of reconfirming whether the left-to-right length of the print area is within the appropriate print range after printing while increasing or decreasing the number of dots included in the print area. [Explanation of symbols]

[0081] 1. Thermal printer 2 Thermal film 3 Thermal head 10 Temperature Sensor 11 Humidity sensor 12a~12c Concentration sensor 13a, 13b Transmission sensors 50 control section 54 Temperature and Humidity Correction Table 55 Density correction table 56 Image cut correction table

Claims

1. A thermal printer that prints by heating a thermal head, a control unit that controls heating of the thermal head based on a predetermined print request to print a print area related to the print request, The control unit increases or decreases the amount of heat applied to the thermal head based on the print request in order to reduce density differences across the width of the medium.

2. The printer has density sensors that detect the density of print areas printed at two locations separated in the width direction of the medium, 2. The thermal printer according to claim 1, wherein the control unit has a density correction table indicating the relationship between the density difference in the printing area detected by the density sensor and the amount of heat increase or decrease of the thermal head to reduce the density difference.

3. It has a sensor that detects the difference in print length between the left and right sides of the print area, A thermal printer according to claim 1 or 2, characterized in that the control unit has an image cut correction table that indicates the relationship between the print length difference detected by the sensor and the amount of increase or decrease in print length on either the left or right side of the print area to reduce the print length difference.

4. 4. The thermal printer according to claim 3, wherein the control unit increases or decreases the print length on either the left or right side of the print area by increasing or decreasing the number of dots included in the print area.

5. a sensor for detecting at least one of temperature and humidity; 4. The thermal printer according to claim 3, wherein the control unit has the image cut correction table for each detection result detected by the sensor.

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