Printer, printing method of printer, program

Abstract

To improve printing quality than before in making a thermal head perform printing on a printing medium.SOLUTION: A printer according to an aspect of the present invention performs printing on a printing medium having a thermosensitive color developing layer. The printer comprises: a thermal head having a plurality of heater elements arranged linearly; a pulse setting part that sets a first application period for an energization pulse for applying heat energy to cause the thermosensitive color developing layer to develop colors to the plurality of heater elements in a printing cycle of one line; an application period correcting part that corrects the length of the first application period set by the pulse setting part on the basis of an image of an object to be printed; and a printing speed determining part that determines a printing speed at the time of printing the whole of the image at a constant speed by lengthening the printing cycle so that the maximum length of the first application period corrected by the application period correcting part falls within the printing period.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a printer, a printing method of a printer, and a program.

Background Art

[0002] Generally, a thermal head generates heat by independently passing a predetermined current through a plurality of heating elements arranged in a line, and prints information by forming a dot pattern on a printing medium having a heat-sensitive color-developing layer. At this time, the presence or absence of color development of the dot corresponding to the heating element is controlled by the time during which current is passed through the heating element (that is, the energization pulse width). When printing on a printing medium using a thermal head, a method of variably controlling the printing speed for each line to be printed is known. For example, Patent Document 1 discloses a detection means for detecting the ratio of the printing area for each line in the direction orthogonal to the conveyance of the recording medium from print data, a storage means for storing a conveyance speed table associating the printing density, the ratio of the printing area, and the conveyance speed, and a conveyance means for determining the conveyance speed by referring to the conveyance speed table from the value of the ratio of the printing area detected by the detection means and conveying the recording medium.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a conventional printing control method, where the printing speed is changed line by line from a plurality of preset printing speeds (for example, the speeds set in the conveyance speed table of Patent Document 1) within one page, it is impossible to uniformize the printing density within one page, and there is a problem that the printing quality is likely to deteriorate. That is, in the method of changing the printing speed, the printing density when the printing speed is constant and the printing density while the printing speed is being changed do not become uniform, and the overall printing quality of one page may decrease.

[0005] Therefore, an object of the present invention is to improve the printing quality more than before when printing on a printing medium by a thermal head.

Means for Solving the Problems

[0006] One aspect of the present invention is a printer having a printing medium with a thermosensitive coloring layer. Print the entire page at a constant printing speed This printer is equipped with a thermal head having a plurality of heating elements arranged in a line, For one page an image to be printed Analyze , A printing analysis unit that estimates the maximum length of the energization pulse application period for the plurality of heating elements in one line printing cycle and a printing speed determination unit that determines Marking the printing speed such that the maximum length of the preheating period Within the printing cycle fits within Determine whether or not, and if it does not fit, the printing cycle, which is lengthened Before printing, decelerate the printing to Before printing, decelerate the printing accommodate the printing speed. An application period correction unit that corrects the length of the application period so that the difference in the ratio of the application period to the printing cycle is equal to or less than a predetermined value before and after lengthening the printing cycle by the printing speed determination unit It is provided with.

Advantages of the Invention

[0007] According to one aspect of the present invention, when printing on a printing medium by a thermal head, the printing quality can be improved more than before.

Brief Description of the Drawings

[0008]

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Best Mode for Carrying Out the Invention

[0009] Hereinafter, a printer according to an embodiment will be described. A printer according to an embodiment is a thermal printer that prints on a printing medium having a heat-sensitive color layer. The printing medium may contain any material as a base material, and is not limited to the case where the base material is paper. For example, a film can also be used as the base material. A printer according to an embodiment includes a thermal head having a plurality of heating elements arranged in a line, and a pulse setting unit. The pulse setting unit sets an application period (first application period) of an energization pulse for applying thermal energy to cause the heat-sensitive color layer to develop color with respect to the plurality of heating elements of the thermal head in one line printing cycle. A strobe signal described later is an example of the energization pulse.

[0010] In a printer according to an embodiment, based on an image to be printed, the length of the first application period set by the pulse setting unit is corrected, and the printing cycle is lengthened so that the maximum length of the corrected first application period is within a limit, thereby determining the printing speed when printing the entire image at a constant speed. As a result, since the printing speed does not change throughout the period of printing the image, unevenness in printing density can be avoided, and the overall printing quality of one page can be improved.

[0011] In a printer according to an embodiment, before printing on the printing medium, the printing speed when printing is corrected so as to decelerate from a preset printing speed. Further, the printing speed after correction and / or the length of the first application period are corrected so that the difference in the ratio of the first application period of the energization pulse to the printing cycle is equal to or less than a predetermined value before and after the correction of the printing speed. As will be described later, according to the findings obtained by the inventors, since the printing density is determined according to the ratio of the first application period of the energization pulse to the printing cycle, fluctuations in the printing density can be suppressed by not greatly changing the difference in the ratio before and after the correction. Hereinafter, the printer according to the embodiment will be described in more detail with reference to the drawings.

[0012] FIG. 1 illustrates a printer 1 according to an embodiment. The printer 1 is a thermal printer that prints on a label having a heat-sensitive coloring layer on one side. As shown in FIG. 1, the printer 1 includes a roll paper storage chamber 9, a platen roller 10, a thermal head 15, a printer cover 25, a coil spring 29, etc. The roll paper R can be loaded into the roll paper storage chamber 9 by opening and closing the printer cover 25. The roll paper R is formed by winding a strip-shaped continuous paper P in a roll shape. Although not shown, in one embodiment, the continuous paper P has, for example, a strip-shaped backing paper and a plurality of labels temporarily attached at predetermined intervals on the backing paper. The label attachment surface of the backing paper is coated with a release agent such as silicone so that the labels can be easily peeled off. In another embodiment, the continuous paper P may be a label without a backing paper.

[0013] As shown in FIG. 1, in the printer 1, the platen roller 10 is supported in a state where it can rotate in both forward and reverse directions. The platen roller 10 is a conveying means for conveying the continuous paper P drawn from the roll paper R, and is formed in a state of extending along the width direction of the continuous paper P. A gear (not shown) is provided at one end of the platen shaft of the platen roller 10, and this gear is mechanically connected to a stepping motor (not shown) for driving the roller. The platen roller 10 rotates in response to the rotation of the stepping motor that operates based on a signal transmitted from a circuit board (not shown).

[0014] The thermal head 15 is, for example, a printing means for printing information such as characters, symbols, figures, or codes on the labels on the continuous paper P. The thermal head 15 includes a plurality of heating elements (heating resistors) arranged along the width direction of the continuous paper P, and performs printing by selectively energizing the plurality of heating elements based on a signal transmitted from a circuit board. The thermal head 15 is arranged to face the platen roller 10 when the printer cover 25 is in the closed state, and sandwiches the continuous paper P together with the platen roller 10. The coil spring 29 is a biasing means for biasing the thermal head 15 toward the platen roller 10, and generates an appropriate nip pressure for printing between the thermal head 15 and the platen roller 10. In the following description, the direction orthogonal to the conveyance direction of the continuous paper P (that is, the direction in which the heating elements are arranged) is referred to as the "main scanning direction", and the same direction as the conveyance direction of the continuous paper P is referred to as the "sub-scanning direction". The thermal head 15 will be described in more detail later.

[0015] Next, with reference to FIG. 2, the internal configuration of the printer 1 will be described. FIG. 2 is a block diagram showing the internal configuration of the printer 1. As shown in FIG. 2, the printer 1 includes, for example, a control unit 11, a storage 12, a drive circuit 13, a motor 14 mechanically connected to the platen roller 10, a thermal head 15, and a communication interface (I / F) 16.

[0016] The control unit 11 includes a controller and a memory, and controls the operation of the printer 1. The processor reads and executes the firmware stored in the ROM when the printer 1 is started up. The controller includes a CPU (Central Processing Unit) as will be described later, and controls the thermal head 15 to print predetermined information on the label by executing the firmware. The storage 12 is a storage device such as an SSD (Solid State Drive). The storage 12 stores, for example, a printing file acquired from a host computer via the communication interface 16. The storage 12 may store information on the printing format when printing information on each label.

[0017] The drive circuit 13 is a circuit that drives a motor 14 that controls the rotation of the platen roller 10 in response to a conveyance request from the control unit 11. The motor 14 is, for example, a stepping motor. The conveyance request includes, for example, information on the conveyance direction (forward or reverse direction) and the conveyance amount (for example, the number of steps).

[0018] The control unit 11 executes a printing process by controlling to selectively pass a current through each of a plurality of heating elements included in the thermal head 15 based on the image data to be printed. The image data is data obtained by drawing a print file as bitmap data. When the heating element of the thermal head 15 heated by the current is pressed against a label on the continuous paper P conveyed by the platen roller 10, information is printed on the label by the heat-sensitive coloring layer of the label against which the heating element is pressed coloring.

[0019] The communication interface 16 includes, for example, a communication circuit for communicating with an external device such as a host computer.

[0020] Next, with reference to FIGS. 3 and 4, the printing operation of the printer 1 will be described. FIG. 3 is a functional block diagram focusing on the control unit and the thermal head in the printer 1 according to one embodiment. FIG. 4 is a schematic circuit diagram of the thermal head 15 according to one embodiment.

[0021] As shown in FIG. 3, the control unit 11 includes a CPU 111, a head controller 112, and a memory 113, and is configured such that each unit can communicate via a bus 114. The CPU 111 controls the overall printing operation in the control unit 11. The head controller 112 supplies various signals for performing printing on the thermal head 15 under the control of the CPU 111. The signals supplied to the thermal head 15 by the head controller 112 include a clock pulse CLK, a latch pulse LATCH, a data signal DATA, and a strobe signal STB.

[0022] The memory 113 (an example of a storage unit) is, for example, a RAM (Random Access Memory), and has a FIFO (First In First Out) configured image buffer, a line buffer, a heat history data table, and a reference strobe table.

[0023] In one embodiment, the CPU 111 performs heat history control to execute printing. Heat history control is control for adjusting the length of a strobe application period, which is a conduction pulse width, based on data that has been conducted to the heating element in the past and / or data that is scheduled to be conducted to the heating element, and making the thermal energy applied to the heating element constant. To perform heat history control, the CPU 111 generates data obtained by changing the original image data (hereinafter referred to as "heat history reflected data") based on the print data of a dot of interest and the print data of dots around the dot in the original image data to be printed. The heat history reflected data is stored in the image buffer. In the following description, "image data" means the original image data before being changed to heat history reflected data.

[0024] In heat history control, a plurality of data signals and a plurality of strobe signals corresponding to each data signal are generated during one printing cycle (that is, one line printing cycle). In the example described later, four data signals and strobe signals are generated during one printing cycle. In this case, for example, if M heating elements are arranged in a line in the thermal head 15 and the data of one line of the image data (line data) is M bits, then the data of one line of the heat history reflected data (line data) is M × 4 bits of data.

[0025] The line data of the image data includes print data indicating whether printing is to be performed for each dot. The print data is either "print" or "non-print". On the other hand, the data for each dot of the line data of the heat history reflection data corresponding to one-line data of the image data corresponds to a plurality of data signals and is data indicating either "energized" or "not energized".

[0026] Line data of the heat history reflection data is sequentially stored in the line buffer. As described above, the heat history data table is referred to when generating the heat history reflection data. The heat history data table shows the relationship between the applied data of the dot to be processed (hereinafter referred to as "target dot") in the printing target line (hereinafter referred to as "target line") in the image data, and the printing data of the dots corresponding to the target dot in the lines before and after the target line (that is, past printing data, future printing data), and the strobe level for the target dot during the printing cycle.

[0027] Here, the strobe level indicates the level (high level or low level) of each data signal in a plurality of strobe application periods for the heating element corresponding to the target dot. The level of the data signal indicates the presence or absence of the application of an energization pulse in each strobe application period. The strobe level indicates the length of time during which current flows through the heating element substantially during the printing cycle. The higher the strobe level, the longer the current flows through the heating element during the printing period, so that a large amount of heat energy is applied to the heating element.

[0028] The CPU 111 refers to the heat history data table and determines the level of each data signal (high level indicating "energized" or low level indicating "not energized") in a plurality of strobe application periods for each dot of the target line. Thereby, considering the current printing data of the target dot and the printing data before and after it, the heat energy applied to the heating element corresponding to the current target dot is appropriately controlled.

[0029] In the thermal history data table of another embodiment, it further includes the relationship between the printing data of each dot adjacent to the dot of interest and the strobe level for the dot of interest during the printing cycle. By referring to the printing data of the dots adjacent to the left and right of the dot of interest, since the thermal energy received by the heating element corresponding to the dot of interest from the adjacent heating elements is also considered, the thermal energy applied to the heating element corresponding to the current dot of interest is more appropriately controlled.

[0030] The head controller 112 generates the data signal DATA based on the line data sequentially transferred from the line buffer, and generates the strobe signal STB at a predetermined timing. Note that the transfer of the line data from the line buffer to the head controller 112 is performed, for example, by DMA (Direct Memory Access).

[0031] As shown in FIG. 3, the thermal head 15 includes a drive circuit 2, a heating element group 3, and a thermistor 4 (an example of a temperature detection unit). The heating element group 3 is composed of a plurality of heating elements (heating resistors) arranged on a line. The drive circuit 2 selectively passes current through each heating element of the heating element group 3 based on various signals supplied from the head controller 112 to generate heat. The thermistor 4 detects the temperature of the thermal head 15 (thermal head temperature). A detailed configuration example of the drive circuit 2 and the heating element group 3 will be described later.

[0032] As shown in FIG. 4, the drive circuit 2 of one embodiment includes at least a shift register (S / R) 21 for temporarily storing the data signal DATA for one line, a latch circuit (L) 22, a gate circuit group 23, and a transistor group 24. The heating element group 3 includes heating elements (heating resistors) 31_1 to 31_M.

[0033] The drive circuit 2 operates based on the data signal DATA, the clock pulse CLK, the latch pulse LATCH, and the strobe signal STB. These data and signals are input or transferred from the head controller 112. To shorten the transfer time, the transfer of the data signal DATA for one line may be divided and transferred using a plurality of line buffers. In that case, a divided part of the data signal DATA for one line is stored in each line buffer, and serial transfer is performed from each line buffer.

[0034] Note that in the drive circuit 2 of FIG. 4, the strobe signal STB is of positive logic (current flows through the heating element and generates heat when at a high level). In another embodiment, the strobe signal STB may be of negative logic (current flows through the heating element and generates heat when at a low level).

[0035] The shift register 21 receives and holds the data signal DATA for one line in synchronization with the clock pulse CLK. Note that the data signal DATA (an example of an energization pulse) is composed of a bit string where the "energized" case is at a high level and the "non-energized" case is at a low level. The latch circuit 22 is connected in parallel to the shift register 21 and transfers and holds the bit string on the shift register 21 in a simultaneous parallel manner. The transfer timing of data from the shift register 21 to the latch circuit 22 is controlled by the latch pulse LATCH.

[0036] The gate circuit group 23 includes gate circuits (AND circuits) 23_1, 23_2, …, 23_M corresponding to the first to Mth dots of one line respectively. The strobe signal STB is supplied to one input terminal of each gate circuit, and the other input terminal of each gate circuit is connected to the output of the latch circuit 22. Each gate circuit of the gate circuit group 23 outputs the logical product of the corresponding data signal DATA and the strobe signal STB. The transistor group 24 includes MOS transistors 24_1 to 24_M. Each MOS transistor turns on / off according to the output of the corresponding gate circuit.

[0037] While the strobe signal STB is at a high level, the logic level of the output terminal of each gate circuit in the gate circuit group 23 coincides with the output level of the latch circuit 22. For example, when the output level of the latch circuit 22 is a high level indicating "energized", the output of the corresponding gate circuit becomes a high level, so that the corresponding MOS transistor is turned on and current flows through the heating element 31. Conversely, when the output level of the latch circuit 22 is a low level indicating "non-energized", the output of the corresponding gate circuit becomes a low level, so that the corresponding MOS transistor is turned off and no current flows through the heating element 31.

[0038] When the strobe signal STB is of negative logic, it may be configured as follows. That is, in FIG. 4, each gate circuit in the gate circuit group 23 is a NAND circuit, and the inverted signal of the strobe signal STB is input to the NAND circuit. Thereby, when the strobe signal STB is at a low level, the NAND circuit outputs the inverted signal of the output of the latch circuit 22. The corresponding MOS transistor is configured to turn on and current flows through the heating element when the output of the NAND circuit is at a low level.

[0039] When heat history control is not performed, one data signal DATA is sent to the drive circuit 2 of the thermal head 15 once during the printing period for one line of line data. On the other hand, when heat history control is performed, a plurality of data signals DATA (for example, data signals DATA1 to DATA4 described later) are sent to the drive circuit 2 of the thermal head 15 during a plurality of periods within the printing period for one line of line data.

[0040] In one embodiment, the head controller 112 supplies four data signals DATA1 to DATA4 to the drive circuit 2 at a predetermined timing synchronized with the clock pulse CLK during the printing period. When the one-line data of the image data is M bits, the corresponding line data of the thermal history reflection data is data of M×4 bits. Each M-bit of this M×4-bit data is supplied to the drive circuit 2 as data signals DATA1 to DATA4 in four divisions.

[0041] The head controller 112 supplies a latch pulse LATCH and strobe signals STB1 to STB4 to the drive circuit 2 of the thermal head 15 at a predetermined timing synchronized with the clock pulse CLK. The relationship between the transfer timing of the data signal and the application timing of the strobe signal in one printing cycle when performing thermal history control will be described later.

[0042] Fig. 5 shows the relationship between the strobe level (STB level) and the timing (strobe pattern) at which current substantially flows through the heating element in each period (hereinafter, appropriately referred to as the "strobe period") during which the strobe signals STB1 to STB4 are applied during the printing cycle in the thermal history control according to one embodiment. In the case of a thermal head with positive logic, the fact that current substantially flows through the heating element means that the corresponding data signals DATA1 to DATA4 are at a high level. That is, the data signals DATA1 to DATA4 are associated with the strobe level. For example, the data signals DATA1 to DATA4 corresponding to the dot of interest are 4-bit data corresponding to the strobe level. For example, the data signals DATA1 to DATA4 are "0000" when the strobe level is "0", "0110" when the strobe level is "6", and "1111" when the strobe level is "15".

[0043] In one embodiment, when the strobe level is 4 or more, heat energy for changing the color of the heat-sensitive coloring layer of the label is given to the heating element, and when the strobe level is less than 4, heat energy for changing the color of the heat-sensitive coloring layer of the label is not given to the heating element, but a preheating effect on the heating element is exhibited.

[0044] In one embodiment, as shown in FIG. 5, four strobe signals STB1 to STB4 corresponding to four data signals in a printing cycle are set in the order from the longest period to the shortest period. That is, assuming the lengths (strobe lengths) of the four strobe signals STB1 to STB4 are L1 to L4 respectively, L1 > L2 > L3 > L4 is satisfied. Preferably, the ratio of the lengths of the four strobe signals STB1 to STB4 is 8:4:2:1. By setting the ratio of the lengths in this way, the number of combinations of the time (i.e., the strobe length) for applying thermal energy to the heating element during one printing cycle can be maximized as much as possible, and precise setting of the applied energy becomes possible. The ratio of the lengths of the four strobe signals STB1 to STB4 is not limited to 8:4:2:1, but by making each length different, 16 (= 2 4 ) different patterns of strobe lengths can be set.

[0045] The CPU 111 determines the strobe level by referring to the thermal history data table for each target dot of the target line data. The CPU 111 generates thermal history reflection data by assigning 4-bit data corresponding to the strobe level to each target dot. The head controller 112 assigns the data of the 1st bit to the 4th bit to the data signals DATA1 to DATA4 respectively for each target dot of the line data of the thermal history reflection data.

[0046] Next, a method for determining a preferable printing speed and strobe length will be described. In one embodiment, the CPU 111 determines the strobe lengths L1 to L4 of the strobe signals STB1 to STB4 according to the printing speed and printing density by referring to the reference strobe table. FIG. 6 shows a configuration example of the reference strobe table. As illustrated in FIG. 6, the reference strobing table describes strobing lengths L1 to L4 (i.e., 50 strobing patterns) for combinations of printing speeds (e.g., 2 to 6 IPS (inch per second)) and printing densities (1A to 10A). Hereinafter, the printing speed and printing density defined in the reference strobing table are referred to as “speed setting value” and “density setting value”, respectively. The reference strobing table serves as a reference for density correction described later. The thermal head temperature is 25° C., the battery voltage is the maximum voltage V MAX and it shows the strobing length when the number of dots printed simultaneously is 1.

[0047] In the reference strobing table, the density setting values are density setting values that are darker (i.e., higher density) in the order from 1A to 10A. Although the number of each of the speed setting value and the density setting value is not limited, in the example shown in FIG. 6, since there are 5 levels of speed setting values and 10 levels of density setting values, 50 strobing lengths L1 to L4 are set. The strobing lengths L1 to L4 are not limited, but can be in the ratio of 8:4:2:1 as described above. The 5-level speed setting value is an example of a plurality of printing speeds. Note that the printing cycle is described in the reference strobing table shown in FIG. 6 for reference, but it is not essential to include the printing cycle in the reference strobing table. Since the length of one line of the label to be printed is known, the printing cycle is uniquely determined according to the speed setting value. As shown in FIG. 6, the higher the speed setting value, the shorter the printing cycle. Therefore, in order to fit all the strobing lengths L1 to L4 within the printing cycle, each strobing length becomes shorter. Also, the higher the density setting value, the greater the required thermal energy, so each strobing length becomes longer.

[0048] In the reference strobe table, the density setting value is a relative setting value for lightness and darkness at a predetermined speed setting value. Therefore, if the speed setting value is different, even if the density setting value is the same, the actually obtained printing density (that is, the degree of lightness and darkness when actually printed on the label) is different. For example, the printing density obtained by the density setting value of 5A is different between the case where the speed setting value is 2IPS and the case where the speed setting value is 3IPS.

[0049] FIG. 7 shows the transfer timings of data signals DATA1 to DATA4 and the application timings of strobe signals STB1 to STB4 when performing printing with thermal history control in one embodiment. FIG. 7 is a timing chart showing the transfer timings of data signals and the application timings of strobe signals in the printing cycle SLT. As shown in FIG. 7, a waiting time WT is set between consecutive strobe application periods. In one embodiment, the CPU 111 refers to the reference strobe table and determines the timings illustrated in FIG. 7 before printing. Here, the printing cycle SLT is determined by the speed setting value. As shown in the reference strobe table of FIG. 6, in the case of "density setting value: 1A", compared with the case of "density setting value: 5A" (default setting), the strobe lengths of the four strobe signals STB1 to STB4 become shorter. On the other hand, in the case of "density setting value: 10A", compared with the case of "density setting value: 5A" (default setting), the strobe lengths of the four strobe signals STB1 to STB4 become longer.

[0050] Next, a method for determining the printing speed of the printer 1 according to one embodiment will be described. In one embodiment, instead of setting the actual printing speed to any one of a plurality of speed setting values in the reference strobe table, the printing speed is changed from the speed setting value based on the image to be printed and the operating environment (for example, battery voltage) (that is, variable speed). In one embodiment, the printing speed is adjusted with a speed range (an example of the second speed range; for example, 1 mm / second) smaller than the speed range (an example of the first speed range; 1 IPS in the example of FIG. 6) of a plurality of speed setting values defined in the reference strobe table. The image to be printed is printed at a constant speed according to the adjusted printing speed. That is, one page including the image to be printed is printed at a constant speed according to the adjusted printing speed. As a result, although the actual printing speed may be different from the speed setting value and thus it is a best-effort type printing speed, there is an advantage that the printing quality of the entire label is improved. Hereinafter, this method of determining the printing speed is referred to as the "continuously variable speed method".

[0051] In the continuously variable speed method, the adjustment of the printing speed is performed before the start of printing, and the printing speed does not change during printing. As will be described later, in one embodiment, density correction is performed so that the printing quality does not deteriorate depending on the operating environment of the printer 1, the layout of the image to be printed, etc. In this density correction, the strobe length is corrected for each line according to the operating environment such as the battery voltage and the thermal head temperature, and the number of dots printed simultaneously in one line in the image to be printed. At that time, the image to be printed is analyzed before printing, and the printing speed is adjusted so that the strobe signal fits within the printing cycle of one line even when the strobe length becomes maximum after correction.

[0052] The advantages of determining the printing speed by the continuously variable speed method will be described with reference to FIGS. 8A and 8B while comparing with the conventional printing speed determination methods. FIG. 8A shows a part of an exemplary image, and FIG. 8B shows the change in the printing speed in different printing speed determination methods when printing the image shown in FIG. 8A according to the passage of time (that is, in the main scanning direction). Here, as the conventional printing speed determination methods, the "stepwise constant speed method" and the "stepwise variable speed method" are given. The stepwise constant speed method is the simplest speed determination method, and it is a method of determining the printing speed according to a speed setting value previously set by the user from among a plurality of speed setting values, or a speed setting value set by default. The step-variable speed method is a method of changing the printing speed in line units to any one of a plurality of preset speed setting values according to the stoke length required as a result of density correction. In FIG. 8B, the printing speed in the case of the step-constant speed method is indicated by M1, the printing speed in the case of the step-variable speed method is indicated by M2, and the printing speed in the case of the continuously variable speed method is indicated by M3.

[0053] In FIG. 8A, the image to be printed includes image portions IM1 to IM3 having a relatively large number of dots printed simultaneously in one line. For example, the image portions IM1 to IM3 include a straight line, which is a typical example having a large number of dots printed simultaneously in the sub-scanning direction. Referring to FIG. 8B, in the step-constant speed method (M1), printing of all lines is performed at a preset speed setting value (4 IPS in FIG. 8B). Therefore, in order to make the printing density uniform throughout the image, the user must select in advance an optimal speed setting value according to the operating environment such as the image to be printed and the battery voltage. However, this is not realistic and results in a deterioration of the printing quality. For example, even when it is necessary to increase the stoke length to ensure the required printing density by density correction, if the increased stoke length does not fit within the printing cycle corresponding to the preset speed setting value, the necessary thermal energy cannot be applied to the heating element, resulting in a decrease in the printing density.

[0054] In the step-variable speed method (M2), for lines with a large number of simultaneously printed dots in one line, such as the image portions IM1 to IM3, the speed is relatively low, and for other image portions (i.e., image portions consisting of lines with a small number of simultaneously printed dots in one line), it is controlled to be relatively high. For example, for lines with a relatively small number of simultaneously printed dots, printing is performed at a high speed by batch printing, and for lines with a relatively large number of simultaneously printed dots, printing is performed at a low speed by divided printing. Divided printing is a method of dividing one line into a plurality of parts and printing. When one line is divided into two parts, the printing speed is halved in simple calculation. Therefore, in the step-variable speed method (M2), depending on the layout of the entire image to be printed, the throughput may decrease significantly (i.e., the time required to print the entire image becomes long). Also, when there are few blank portions in the main scanning direction, the printing speed may not be restored, and printing may be performed during the speed change. Since the balance between the printing speed and the stroke length is lost during this speed change (in other words, the balance between the on (heat addition) and off (cooling) times is lost), the printing density is not uniform, and the printing quality deteriorates. In summary, the problem with the step-variable speed method is that the throughput and image quality may deteriorate depending on the printing layout.

[0055] The continuously variable speed method (M3) according to one embodiment is a method that, unlike the conventional step-constant speed method and step-variable speed method, can equalize the printing density throughout the image and improve the printing quality of the label. Hereinafter, this continuously variable speed method will be described in detail.

[0056] First, with reference to FIGS. 9 and 10, the density correction of one embodiment will be described. As described above, in density correction, the stroke length is corrected for each line according to the operating environment such as the battery voltage and the number of simultaneously printed dots in one line in the image to be printed.

[0057] In one embodiment, the density correction includes battery voltage correction that corrects the stroke length based on the battery voltage. Since the applied power to the heating element 31 of the thermal head 15 decreases due to the decrease in the battery voltage, battery voltage correction is performed to compensate for the decrease in the applied power by increasing the stroke length. The battery voltage correction is performed, for example, with reference to the battery voltage correction table shown in FIG. 9.

[0058] As shown in FIG. 9, in the battery voltage correction table, the battery voltage and the voltage correction ratio are described in association with each other. The voltage correction ratio is a value to be multiplied with respect to the stroke length described in the reference stroke table in the battery voltage correction. The reference battery voltage is the maximum voltage V MAX At this time, with the voltage correction ratio (“100%”), no change is made to the stroke length described in the reference stroke table. In the battery voltage correction table, it is described such that the voltage correction ratio increases as the battery voltage decreases. Therefore, in the battery voltage correction, as the battery voltage becomes lower, the stroke length is corrected to be longer than the value described in the reference stroke table. In a non-limiting example, the maximum voltage V MAX is about 16 to 17 V, and the minimum voltage V MIN is about 12 to 13 V, and is set, for example, in increments of 0.01 V to 0.05 V. In addition, in the battery voltage correction, it is not always necessary to refer to the battery voltage correction table, and the voltage correction ratio may be calculated using a known function that defines the relationship between the battery voltage correction and the voltage correction ratio. In that case, the function defines the relationship between the battery voltage and the voltage correction ratio so as to compensate for the applied heat amount corresponding to the difference between the maximum voltage V MAX and the current battery voltage by extending the stroke time.

[0059] In one embodiment, the density correction includes head voltage drop correction and power supply voltage drop correction that correct the stroke length based on the number of dots printed simultaneously. In the thermal head 15, as the number of simultaneously printed dots in one line (printing rate in one line) increases, the applied power to the heating element 31 decreases due to the voltage drop caused by the ON resistance in the circuit (e.g., the ON resistance of the MOS transistor in FIG. 4), the conduction resistance, etc. Therefore, head voltage drop correction is performed to compensate for the decrease in the applied power by increasing the strobe length. On the other hand, as the number of simultaneously printed dots in one line increases, the peak current flowing through the thermal head 15 increases, resulting in a decrease in the power supply voltage and a decrease in the applied power to the heating element 31. Therefore, power supply voltage drop correction is performed to compensate for the decrease in the applied power by increasing the strobe length.

[0060] The head voltage drop correction and the power supply voltage drop correction are performed, for example, with reference to the dot number correction table shown in FIG. 9. In one embodiment, individual dot number correction tables are prepared for each of the head voltage drop correction and the power supply voltage drop correction.

[0061] As shown in FIG. 9, in the dot number correction table, the number of simultaneously printed dots and the dot number correction ratio are described in association with each other. The dot number correction ratio is a value to be multiplied with respect to the strobe length described in the reference strobe table in the head voltage drop correction and the power supply voltage drop correction. The reference number of simultaneously printed dots is "1", and at this time, the voltage correction ratio ("100%") does not change the strobe length described in the reference strobe table. In the dot number correction table, it is described such that the dot number correction ratio increases as the number of simultaneously printed dots increases. Therefore, in the head voltage drop correction and the power supply voltage drop correction, as the number of simultaneously printed dots increases, the strobe length is corrected to be longer than the value described in the reference strobe table.

[0062] In one embodiment, the density correction includes head temperature correction that corrects the strobe length based on the thermal head temperature. The thermal head temperature is detected by the thermistor 4 (FIG. 3). In order to suppress fluctuations in printing density due to temperature fluctuations of the thermal head 15 as much as possible, head temperature correction is performed. The head temperature correction is performed, for example, with reference to the temperature correction table shown in FIG. 10.

[0063] As shown in FIG. 10, in the temperature correction table, the thermal head temperature and the temperature correction ratio are described in association with each other. The temperature correction ratio is a value to be multiplied with respect to the stroke length described in the reference stroke table in head temperature correction. The reference thermal head temperature is 25°C, and at this time the temperature correction ratio (“100%”), no change is made to the stroke length described in the reference stroke table. In the temperature correction table, it is described such that the temperature correction ratio increases as the thermal head temperature decreases, and the temperature correction ratio decreases as the thermal head temperature increases. Therefore, in head temperature correction, depending on the thermal head temperature, the stroke length may be made longer or shorter than the value described in the reference stroke table. Note that in head temperature correction, it is not always necessary to refer to the temperature correction table, and a function assuming a linear relationship between the thermal head temperature and the temperature correction ratio may be defined. For example, the temperature correction ratio may be defined in advance as a linear function with respect to the difference between the reference value of the thermal head temperature (25°C in the example of FIG. 10) and the current value (measured value) of the thermal head temperature.

[0064] Note that the density correction in one embodiment includes at least any one of battery voltage correction, head voltage drop correction, power supply voltage drop correction, and head temperature correction. When performing density correction as described above, if the strobing length is made longer than the value described in the reference strobing table, the strobing length may not fit within the current printing cycle. Therefore, in the continuously variable speed method, a simulation of density correction is performed before printing, and control is performed to decelerate the printing speed from the speed setting value so that it fits within the printing cycle even in the case of the maximum strobing length due to density correction. That is, it is ensured that there is no variation in print quality caused by the strobing length not fitting within the printing cycle due to the operating environment such as battery voltage or the layout of the image to be printed.

[0065] Furthermore, as a result of the earnest research by the inventor of the present application, the following findings (I) and (II) were obtained. (I) The printing density is generally determined by the ratio (hereinafter referred to as "density ratio") of the continuous pulse time within the printing cycle. Here, the "continuous pulse time" is the length of the strobing period for applying thermal energy to cause the heat-sensitive coloring layer to color. In the example shown in FIG. 5, it is the length of the period from the rising edge timing of the strobing signal STB1 to the falling edge timing of the strobing signal STB2 (an example of the first application period).

[0066] (II) Even with the same density ratio, the lower the printing speed, the higher the tendency for the printing density to become darker. For example, in the reference strobing table shown in FIG. 6, even when the density ratio in the case of a density setting value of 5A (reference) is made to have little difference among a plurality of speed setting values, the lower the speed setting value, the darker the actual printing density obtained. Therefore, in order to keep the printing density unchanged when decelerating the printing speed from the speed setting value, it is necessary to lower the density ratio in accordance with the deceleration of the printing speed.

[0067] Based on the findings of (I) and (II) above, in the continuously variable speed method, a deceleration correction process for the printing speed according to the execution result of the density correction simulation before printing is executed, and a density ratio correction process according to the corrected printing speed is executed. The deceleration correction process and the density ratio correction process will be described with reference to FIG. 11. FIG. 11 is a diagram for explaining the deceleration correction process and the density ratio correction process in the continuously variable speed method.

[0068] Referring to FIG. 11, state ST1 shows the strobe signals STB1 to STB4 at the speed setting value and density setting value set immediately before printing in the reference strobe table. The printing cycle SLT1 is determined according to the speed setting value. In FIG. 11, the continuous pulse time CP including the application periods of the strobe signals STB1 and STB2 in state ST1 is shown.

[0069] State ST2 in FIG. 11 is the result of performing a density correction simulation on the strobe signals STB1 to STB4 shown in state ST1, and shows the strobe signals STB1_max to STB4_max when the strobe length of each of the strobe signals STB1 to STB4 is maximized by density correction. In one embodiment, the strobe length of each of the strobe signals STB1_max to STB4_max is the value obtained by multiplying the maximum value of the voltage correction ratio (FIG. 9) × the dot number correction ratio (FIG. 9) with respect to the strobe length of each of the reference strobe signals STB1 to STB4. Note that this maximum value varies depending on the layout of the image to be printed and the battery voltage at that time.

[0070] The purpose of this density correction simulation is to estimate in advance the maximum value of the strobe length due to density correction during printing in order to determine the printing speed before printing. When density correction is performed during printing, the strobe length of the applied strobe signal varies for each line between the reference strobe signals STB1 to STB4 and the strobe signals STB1_max to STB4_max in the case of the maximum strobe length according to the number of dots printed simultaneously in each line of the image to be printed and the thermal head temperature.

[0071] In the state ST2 of FIG. 11, it shows a case where the strobing signals STB1_max to STB4_max when the strobing length is maximized by density correction do not fit within the printing period SLT1 determined by the speed setting value. Therefore, in the deceleration correction process, the printing speed is corrected so that the strobing signals STB1_max to STB4_max fit within the printing period. As described above, it is adjusted with a speed width (for example, 1 mm / second) smaller than the speed width (1 IPS in the example of FIG. 6) of the plurality of speed setting values defined in the reference strobing table. Therefore, while making it possible to accommodate the strobing signals STB1_max to STB4_max, it is possible to limit the speed reduction to a minimum with respect to the preset speed setting value.

[0072] The state ST3 in FIG. 11 shows a state where the deceleration correction process is executed on the strobing signals STB1 to STB4 in the state ST1, and the printing period is extended from SLT1 to SLT2. By extending the printing period in this way, no matter which line of the image to be printed (that is, even when printing the line with the maximum number of simultaneously printed dots in the image), the situation where the strobing signal does not fit within the printing period due to density correction does not occur.

[0073] As described above, the printing density is generally determined by the density ratio (the above (I)), but when comparing the state ST3 with the state ST1, by extending the printing period from SLT1 to SLT2, the density ratio of the reference strobing signals STB1 to STB4 changes (decreases). Specifically, in FIG. 11, the density ratio decreases from CP / SLT1 to CP / SLT2. Therefore, a density ratio correction process is executed on the strobing signals STB1 to STB4 in the state ST3 so that the density ratio before and after the deceleration correction process is the same. The state ST4 in FIG. 11 shows the strobing signals STB1_c to STB4_c after the density ratio correction process. Here, assuming that the continuous pulse time after the concentration ratio correction process is CP_c, the strobe signals STB1_c to STB4_c are determined so that the following equation (1) holds. As a result, as shown in FIG. 11, the continuous pulse time increases by Δt. CP_c = (SLT2 / SLT1) · CP …(1)

[0074] Although not shown in FIG. 11, in one embodiment, the deceleration correction process may be executed at least once from the strobe signals STB1_c to STB4_c in the state ST4 of FIG. 11. That is, as described above, even with the same concentration ratio, the lower the printing speed, the darker the printing concentration tends to be ((II)). Therefore, in the state ST4, although the concentration ratio is the same as that in the state ST1, the printing concentration is set to be darker than that in the state ST1 by the amount by which the printing speed has decreased. Therefore, it is preferable to execute the deceleration correction process on the strobe signal in the state ST4 so as to approach the printing concentration by the strobe signal in the state ST1.

[0075] In one embodiment, the deceleration correction process and the concentration ratio correction process may be repeatedly executed a predetermined number of times. As shown in the state ST4 of FIG. 11, the strobe length of each of the strobe signals STB1_c to STB4_c after the concentration ratio correction process is extended with respect to the strobe length of each of the strobe signals STB1 to STB4 in the original state ST1. Therefore, a density correction simulation is performed on the strobe signals STB1_c to STB4_c to check whether the strobe signal when each strobe length becomes maximum due to density correction fits within the printing cycle SLT2. If it does not fit, the second deceleration correction process is executed. As a result of executing this second deceleration correction process, the concentration ratio fluctuates before and after the execution of the second deceleration correction process. Therefore, a second concentration ratio correction process is executed to adjust the concentration ratio. Thus, in one embodiment, by repeating the deceleration correction process and the density ratio correction process a predetermined number of times, a desired strobe signal can be determined. As will be described later, the number of executions of each of the deceleration correction process and the density ratio correction process can be set as appropriate.

[0076] As described above, for the strobe pattern determined by the speed setting value and the density setting value in the reference strobe table, in order to ensure the printing quality, density correction according to the print layout and the operating environment is performed. However, this density correction alone is not sufficient, and it is necessary to consider the printing speed and the density ratio based on the findings of (I) and (II) above. Therefore, in the continuously variable speed method, when determining the printing speed before printing, while adjusting the printing speed so that the density correction functions properly, the deceleration correction process and the density ratio correction process are executed at least once. Thereby, the printing quality can be made good for the entire image to be printed (the printing density can be made uniform throughout the image).

[0077] In one embodiment, the control unit 11 of the printer 1 functions as the following pulse setting unit, print period correction unit, and printing speed determination unit. This corresponds to the change from SLT1 to SLT2 of the printing cycle in FIG. 11. (a1) A pulse setting unit that sets a first strobe period (for example, a period during which a strobe signal STB1 and / or STB2 is applied; an example of a first application period) for applying thermal energy to cause the heat-sensitive coloring layer of the label to color with respect to a plurality of heating elements of the thermal head 15 in the printing cycle of one line. (a2) A print period correction unit that corrects the length of the first strobe period set by the pulse setting unit based on the image to be printed (for example, based on the number of dots printed simultaneously in one line of the image). (a3) A printing speed determination unit that determines the printing speed when printing the entire image at a constant speed by increasing the printing cycle so that the maximum length of the first strobe period after correction by the print period correction unit is within the limit.

[0078] By the control unit 11 of the printer 1 functioning as each of the parts (a1) to (a3), even when the above density correction is performed, the first strobe period can be within the printing cycle, and the density correction during printing can exhibit its effect. Also, by making the printing speed constant over the entire image, compared with the conventional step-variable speed method, it is possible to suppress a decrease in throughput due to acceleration and deceleration of the printing speed during printing, and there is an advantage that a decrease in print quality due to a change in the printing speed during printing can be avoided. Furthermore, when compared with the conventional step-low speed method of printing at a constant speed according to the speed set value, the throughput decreases by lengthening the printing cycle (decelerating the printing speed), but by making it possible to finely adjust the printing speed with a small speed range (for example, 1 mm / second), it is possible to minimize the decrease in throughput.

[0079] In one embodiment, the printer 1 executes thermal history control. In this case, the pulse setting unit sets, in addition to the first strobe period, a second strobe period (for example, a period during which the strobe signals STB3 and / or STB4 are applied; an example of the second application period) for applying thermal energy to a plurality of heating elements of the thermal head 15 so as not to cause the heat-sensitive coloring layer of the label to develop color. The printing period correction unit corrects the lengths of the first strobe period and the second strobe period, and the printing speed determination unit determines the printing speed when printing the entire image at a constant speed by lengthening the printing cycle so that the maximum lengths of the corrected first strobe period and second strobe period are within the limit.

[0080] In one embodiment, the control unit 11 of the printer 1 further functions as a second application period correction unit that further corrects the length of the first strobe period corrected by the application period correction unit so that the difference in density ratio is equal to or less than a predetermined value before and after lengthening the printing cycle. This corresponds to the density ratio correction process from state ST3 to state ST4 in FIG. 11. By executing the density ratio correction process, the density ratio is maintained within a predetermined range, so that the printing density is uniformized and the print quality of the entire image is further improved. Note that in FIG. 11, as shown in Equation (1), the density ratio correction was performed so that the density ratios in state ST1 and state ST4 were the same, but this is not the only case. It is sufficient that the difference in the density ratio before and after the density ratio correction process is equal to or less than a predetermined value that does not substantially affect the printing density.

[0081] Next, with reference to FIGS. 12 to 16, a series of processes for realizing a continuously variable speed method will be described. FIGS. 12 to 15 are flowcharts corresponding to the pre-printing process performed before printing. FIG. 16 is a flowchart corresponding to the in-printing process performed during printing. The flowchart of each figure is executed by the control unit 11 (CPU 111 and head controller 112).

[0082] Hereinafter, the pre-printing process of one embodiment will be described. FIG. 12 shows the overall flow of the pre-printing process of one embodiment. As described above, this overall flow shows the flow in the case where the deceleration correction process and the density ratio correction process are repeated a predetermined number of times. First, the control unit 11 sets a deceleration correction counter CTR_1 that defines the upper limit number of times to perform the deceleration correction process (step S2), and sets a density ratio correction counter CTR_2 that defines the upper limit number of times to perform the density ratio correction process (step S4). For example, the value (set value) set in the deceleration correction counter CTR_1 is 2, and the value (set value) set in the density ratio correction counter CTR_2 is 1. The set values of each counter are not limited, but are set so as to satisfy CTR_1 > CTR_2.

[0083] Steps S6 to S14 in FIG. 12 are configured to execute the deceleration correction process (step S6) and the density ratio correction process (step S12) for the number of times of the set values in steps S2 and S4, respectively. The deceleration execution flag is a flag indicating whether or not the deceleration of the printing speed (that is, the extension of the printing cycle) has been executed in the deceleration correction process, and becomes "1" when the deceleration of the printing speed is executed.

[0084] As described below, in the deceleration correction process, when the printing speed is decelerated because the strobe signal does not fit within the printing cycle, the deceleration execution flag becomes "1" and the deceleration correction counter CTR_1 is decremented by 1. In the deceleration correction process, when the strobe signal fits within the printing cycle, the deceleration execution flag remains "0". Also, each time the density ratio correction process is executed, the density ratio correction counter CTR_2 is decremented by 1. Therefore, in the flow of FIG. 12, as a result of executing the deceleration correction process (step S6), when the deceleration execution flag is "0" (that is, when the strobe signal fits within the printing cycle) (step S8: NO), the control unit 11 ends the pre-printing process. When the deceleration execution flag is "1" (step S8: YES), it is determined whether or not to execute the density ratio correction process (step S12) based on whether the density ratio correction counter CTR_2 is "0" (step S10).

[0085] After the execution of the density ratio correction process, it is determined whether the deceleration correction counter CTR_1 is "0" (step S14). The control unit 11 ends the pre-printing process when the deceleration correction counter CTR_1 is "0", and returns to step S6 to execute the deceleration correction process when it is not "0". As described above, the deceleration correction process and the density ratio correction process are executed the number of times of the set value of each counter.

[0086] Next, the details of the deceleration correction process will be described with reference to FIG. 13. Referring to FIG. 13, in the deceleration correction process, the control unit 11 first initializes the deceleration execution flag to "0" (step S20). Next, the control unit 11 generates a first corrected strobe table based on the reference strobe table (step S22). More specifically, the control unit 11 refers to the battery voltage correction table (FIG. 9) to identify the voltage correction ratio corresponding to the current battery voltage, and multiplies each strobe length of the reference strobe table by the identified voltage correction ratio to generate the first corrected strobe table. Note that in step S22, instead of generating a first corrected strobe table corresponding to all strobe patterns in the reference strobe table, it is also possible to calculate the corrected strobe length corresponding to the strobe pattern of the current speed setting value and concentration setting value in the reference strobe table.

[0087] Next, the control unit 11 generates a dot number correction table (step S24). In one embodiment, individual dot number correction tables (FIG. 9) are prepared for each of the head voltage drop correction and the power supply voltage drop correction. In that case, the control unit 11 multiplies the dot number correction ratios corresponding to each battery voltage in the dot number correction table corresponding to the head voltage drop correction and the dot number correction table corresponding to the power supply voltage drop correction, thereby generating a dot number correction table combining the head voltage drop correction and the power supply voltage drop correction.

[0088] Next, the control unit 11 executes a density correction simulation shown in detail in FIG. 14 (step S26). As described above, the purpose of the density correction simulation is to estimate in advance the maximum value of the strobe length due to density correction during printing in order to determine the printing speed before printing. In other words, the density correction simulation is a process of estimating the maximum value of the corrected strobe length before printing so that even when the strobe length (corrected strobe length) becomes maximum due to density correction during printing, the maximum corrected strobe length fits within the printing cycle.

[0089] Referring to FIG. 14, the density correction simulation is performed as follows. First, the control unit 11 refers to the first corrected strobe table generated in step S22 and specifies the strobe length of each strobe signal corresponding to the current speed setting value and concentration setting value (step S42). Here, the specified strobe length is the strobe length in which the battery voltage correction is reflected with respect to the corresponding value in the reference strobe table. Next, the control unit 11 analyzes the image to be printed, identifies the maximum value among the number of dots printed simultaneously for each line in the image (step S44), and executes dot number correction (step S46). That is, the control unit 11 identifies the dot number correction ratio corresponding to the maximum value of the number of dots printed simultaneously identified in step S44 by referring to the dot number correction table generated in step S42.

[0090] Next, the control unit 11 executes temperature correction (step S48). More specifically, the control unit 11 refers to the temperature correction table (Fig. 10) to identify the temperature correction ratio corresponding to the current thermal head temperature. When referring to the temperature correction table, when the thermal head temperature is lower than the current value, the temperature correction ratio increases and correction is performed during printing so that the stroke length becomes longer. However, such correction does not need to be considered in density correction simulation. This is because the thermal head temperature during printing is higher than the thermal head temperature at the time of density correction simulation execution.

[0091] Finally, the control unit 11 determines the maximum value of the corrected stroke length (step S50). In step S50, the control unit 11 multiplies the stroke lengths of the strobe signals STB1 to STB4 identified in step S44 by the dot number correction ratio identified in step S46 and the temperature correction ratio identified in step S48 to determine the maximum value of the corrected stroke length.

[0092] Return to the description of Fig. 13. After executing the density correction simulation, the control unit 11 determines whether or not the maximum value of the corrected stroke length fits within the printing cycle (step S28). If the maximum value of the corrected stroke length fits within the printing cycle, there is no need to change the printing speed, so the deceleration correction counter CTR_1 is set to 0 (step S30). In this case, since the deceleration execution flag remains "0", the control unit 11 ends the pre-printing process (step S8: NO in Fig. 12).

[0093] When the maximum value of the corrected stroke length does not fit within the printing cycle (step S28: NO), the control unit 11 extends the printing cycle so that the maximum value of the corrected stroke length fits (that is, decelerates the printing speed) (step S32). At this time, preferably, it is adjusted with a speed width (for example, 1 mm / second) smaller than the speed width (1 IPS in the example of FIG. 6) of the plurality of speed setting values defined in the reference stroke table. The control unit 11 sets the deceleration execution flag to "1" in response to the deceleration of the printing speed (step S34), and subtracts 1 from the deceleration correction counter CTR_1 (step S36).

[0094] Next, the details of the density ratio correction process will be described with reference to FIG. 15. Referring to FIG. 15, in the density ratio correction process, the control unit 11 first obtains the continuous pulse time CP (refer to state ST1 in FIG. 11) corresponding to the current speed setting value and density setting value from the reference stroke table (for example, FIG. 6) (step S60), and calculates the density ratio (step S62). The density ratio is a value obtained by dividing the continuous pulse time CP by the printing cycle corresponding to the speed setting value.

[0095] Next, the control unit 11 calculates the continuous pulse time after deceleration correction (that is, after the execution of step S32 of the deceleration correction process performed immediately before) (step S64), and generates a new reference stroke table (step S66). Here, as shown in the above formula (1), the continuous pulse time is corrected so that the density ratio is the same before and after deceleration correction, and a new reference stroke table is generated based on the corrected continuous pulse time. This new reference stroke table serves as a reference when generating the first corrected stroke table when the deceleration correction process is executed later. Finally, the control unit 11 subtracts 1 from the density ratio correction counter CTR_2 (step S68). Note that in step S66, instead of generating a new reference stroke table corresponding to all stroke patterns, it is also possible to calculate a new stroke length corresponding to the stroke pattern of the current speed setting value and density setting value.

[0096] The above is the pre-print processing of one embodiment. By repeating the deceleration correction process and the density ratio correction process a predetermined number of times, the printing speed, the printing cycle, and the first corrected strobe table used in the in-print processing are determined before printing.

[0097] Next, the in-print processing will be described with reference to FIG. 16. Printing is performed at a constant speed according to the printing speed determined in the pre-print processing for the entire image of the printing target. In the in-print processing, a series of processes shown in FIG. 16 are performed line by line. In the following description, the line to be printed is referred to as the "target line". Referring to FIG. 16, the control unit 11 first acquires the thermal head temperature from the thermistor 4 (step S70), and refers to the temperature correction table (FIG. 10) to acquire (specify) the temperature correction ratio corresponding to the acquired thermal head temperature (step S72). As described above, the temperature correction ratio may be calculated based on the reference value and the current value of the thermal head temperature.

[0098] Next, the control unit 11 corrects the first corrected strobe table generated in the pre-print deceleration correction process (step S22 in FIG. 13) by the temperature correction ratio acquired in step S72 to generate a second corrected strobe table (step S74). The first corrected strobe table reflects the battery voltage correction. Since the battery voltage during printing is considered to be substantially the same as the battery voltage before printing, it is also used in the in-print processing. Each strobe length described in the second corrected strobe table is a value obtained by multiplying the corresponding strobe length of the first corrected strobe table by the temperature correction ratio.

[0099] Next, the control unit 11 acquires the number of simultaneously printed dots on the target line (step S76), and acquires a dot number correction ratio corresponding to the acquired number of simultaneously printed dots by referring to a dot number correction table (Fig. 9) (step S78). Further, the control unit 11 multiplies the stroke length of each strobe signal corresponding to the current speed setting value and density setting value in the second corrected strobe table by the dot number correction ratio acquired in step S78, thereby determining the stroke length of each strobe signal to be applied to the target line (step S80). In the deceleration correction process before printing (step S22 in Fig. 13), when calculating the corrected stroke length corresponding to the stroke pattern of the current speed setting value and density setting value instead of generating the first corrected strobe table, in step S74, the corrected stroke length is calculated as the stroke length corrected by the temperature correction ratio acquired in step S72. This process is equivalent to the process in step S80.

[0100] The above is the processing during printing in one embodiment. For each target line, density correction based on the thermal head temperature and the number of simultaneously printed dots is executed to determine the stroke length of each strobe signal during the printing cycle. In the pre-printing process, since the printing speed is adjusted based on the maximum corrected stroke length by density correction, the stroke length of each strobe signal determined in step S80 fits within the printing cycle for all lines of the image to be printed.

[0101] In one embodiment, an example in which the stroke application period is provided 4 times during the printing cycle in the thermal history control has been described, but it is not limited thereto, and it may be 3 times or 5 times or more. By increasing the number of times of the stroke application period, more stroke levels can be set, enabling more precise control.

[0102] As described above, the flowcharts in FIGS. 12 to 16 are executed by the control unit 11 (CPU 111 and head controller 112). At this time, in one embodiment, the control unit 11 of the printer 1 functions as the following pulse setting unit, first correction unit, and second correction unit. (b1) A pulse setting unit that sets a first strobe period (for example, a period during which a strobe signal STB1 and / or STB2 is applied; an example of a first application period) for applying thermal energy to cause the heat-sensitive coloring layer of the label to develop color with respect to a plurality of heating elements of the thermal head 15 in the printing cycle of one line. (b2) A first correction unit that corrects the printing speed when printing so as to decelerate from the speed setting value before printing on the label. (b3) A second correction unit that corrects the printing speed after correction by the first correction unit and / or the length of the first strobe period so that the difference in density ratio is equal to or less than a predetermined value before and after the correction of the printing speed by the first correction unit.

[0103] Here, the first correction unit corresponds to the first deceleration correction process. The second correction unit corresponds to the density ratio correction process performed after the first deceleration correction process and / or the deceleration correction process for the second time and later. The second correction unit may include at least one of the correction process of the printing speed and the correction process of the length of the first strobe period, or both processes. That is, since the density ratio can change depending on the printing speed and / or the first strobe period, the density ratio can be adjusted to a desired range by performing the correction of the printing speed and the correction of the length of the first strobe period individually or both. At this time, the method of adjusting the density ratio to a desired range is not limited to the method based on the pre-printing correction process in FIG. 12.

[0104] With the above configuration, when changing the printing speed from the speed setting value before printing on the label, it is possible to suppress a decrease in print quality (that is, suppress fluctuations in the printing density during printing). In other words, when printing at a printing speed different from the plurality of speed setting values defined in the reference strobe table, it is possible to suppress a decrease in print quality. As a result, from the user's perspective, as long as the speed setting and density setting for the printer 1 are the same, there is an advantage that the same level of print quality can always be obtained regardless of the operating environment of the printer 1 and the layout of the image to be printed.

[0105] Also, the strobe length of each strobe pattern described in the reference strobe table has been determined in advance through trial and error so as to obtain a predetermined printing density (that is, verified). Therefore, when changing the printing speed from the speed setting value defined in the reference strobe table, it is a condition where what kind of print quality will be obtained has not been verified. By executing the deceleration correction process and the density ratio correction process described above even under such conditions, it becomes possible to adjust the printing density to be approximately the same as the verified level.

[0106] In one embodiment, the second correction unit includes the following ratio correction unit and printing speed correction unit. (c1) A ratio correction unit that executes a process of correcting the length of the first strobe period so that the density ratio becomes substantially the same before and after the correction of the printing speed by the first correction unit (density ratio correction process) (c2) A printing speed correction unit that executes a process of correcting the printing speed so as to further decelerate from the printing speed after correction by the first correction unit (deceleration correction process) That is, as shown in FIG. 12, when controlling both the printing speed and the density ratio, the strobe length can be determined efficiently by continuously performing the density ratio correction process and the deceleration correction process. The number of executions of each process can be defined by the set value of the counter corresponding to each process, as described with reference to FIG. 12.

[0107] In one embodiment, the printer 1 performs thermal history control. In this case, in addition to the first strobe period, the above-described pulse setting unit sets a second strobe period (for example, a period during which the strobe signals STB3 and / or STB4 are applied; an example of the second application period) for applying thermal energy to a plurality of heating elements of the thermal head 15 such that the heat-sensitive coloring layer of the label is not colored. The above-described first correction unit corrects the printing speed so that the first strobe period and the second strobe period are within the printing cycle. The second correction unit corrects the printing speed after correction by the first correction unit, and / or the lengths of the first strobe period and the second strobe period so that the difference in density ratio is equal to or less than a predetermined value before and after the correction of the printing speed by the first correction unit.

[0108] In one embodiment, printing is performed without performing the above-described thermal history control. Even in this case, the above-described continuously variable speed method can be applied. FIG. 17 is a diagram corresponding to FIG. 11 and shows a continuously variable speed method when thermal history control is not performed. When thermal history control is not performed, a single strobe signal STB is set during the printing cycle of one line. In this case, the length of the strobe period for applying thermal energy to cause the heat-sensitive coloring layer to color is equal to the strobe length L of the strobe signal STB.

[0109] The state ST2 in FIG. 17 is the result of performing density correction simulation on the strobe signal STB shown in the state ST1, and shows the strobe signal STB_max when the strobe length L of the strobe signal STB is maximized by density correction. In one embodiment, the strobe length of the strobe signal STB_max is the value obtained by multiplying the reference strobe length L by the maximum value of the voltage correction ratio (FIG. 9) × the dot number correction ratio (FIG. 9).

[0110] The state ST2 in FIG. 17 shows a case where the strobe signal STB_max when the strobe length is maximized by density correction does not fit within the printing cycle SLT1 determined by the speed setting value. The state ST3 in FIG. 17 indicates a state where a deceleration correction process is executed on the strobe signal STB in the state ST1, and the printing cycle is extended from SLT1 to SLT2. By extending the printing cycle in this way, even when printing a line where the number of dots printed simultaneously in the image is maximum, it does not occur that the strobe signal does not fit within the printing cycle due to density correction.

[0111] The result of performing the density ratio correction process on the strobe signal STB in the state ST3 is the strobe signal STB_c in the state ST4. Here, assuming that the strobe length L after the density ratio correction process is L_c, the strobe signal STB_c is determined so that the following formula (2) holds. As a result, as shown in FIG. 17, the continuous pulse time increases by Δt. L_c=(SLT2 / SLT1)·L …(2)

[0112] In one embodiment, a printing method for a printer having the following steps is disclosed. (d1) A step of setting a first strobe period of a strobe signal for applying thermal energy to cause the heat-sensitive coloring layer of the label to color with respect to a plurality of heating elements of the thermal head 15 in a printing cycle of one line (d2) A step of performing correction on the length of the set first strobe period based on the image to be printed (d3) A step of determining the printing speed when printing the entire image at a constant speed by increasing the printing cycle so that the maximum length of the corrected first strobe period fits

[0113] In one embodiment, a printing method for a printer having the following steps is disclosed. (e1) A step of setting a first strobe period of a strobe signal for applying thermal energy to cause the heat-sensitive coloring layer of the label to color with respect to a plurality of heating elements in a printing cycle of one line (e2) A step of correcting the printing speed when performing printing so as to decelerate from the speed setting value before performing printing on the label correcting the printing speed after correction, and / or the length of the first strobe period, so that the difference in density ratio is equal to or less than a predetermined value before and after the correction of the printing speed

[0114] A program according to an embodiment is a program that causes a computer to execute the printing method of the printer. For example, when the CPU 111 included in the control unit 11 of the printer 1 executes the program, the printing method of the printer is executed. In one embodiment, this program may be recorded on a non-transitory computer-readable recording medium.

[0115] As described above, the embodiments of the printer, the printing method of the printer, and the program of the present invention have been described in detail. However, the scope of the present invention is not limited to the above embodiments. Further, various improvements and changes are possible within the scope not departing from the gist of the present invention.

Explanation of Signs

[0116] 1... Printer 9... Storage chamber 10... Platen roller 11... Control unit 111... CPU 112... Head controller 113... Memory 114... Bus 12... Storage 13... Drive circuit 14... Motor 15... Thermal head 2... Drive circuit 21... Shift register 22... Latch circuit 23... Gate circuit group 23_1~23_M... AND circuit 24... Transistor group 24_1~24_M... MOS transistor 3... Heat generating element group 31_1~31_M... Heat generating element 4... Thermistor 16…Communication interface 20…Issuing port 25…Printer cover 29…Coil spring DATA1~DATA4…Data signal STB1~STB4…Strobe signal L1~L4…Pulse width WT…Standby time P…Continuous paper R…Roll paper

Claims

1. A printer that prints an entire page of a printing medium having a heat-sensitive color-developing layer at a constant printing speed, comprising: a thermal head having a plurality of heating elements arranged in a line; a printing analysis unit that analyzes an image to be printed for one page and estimates the maximum length of the application period of an energization pulse to the plurality of heating elements in one line printing cycle; a printing speed determination unit that determines before printing whether the maximum length of the application period fits within the printing cycle, and if it does not fit, decelerates the printing speed by lengthening the printing cycle; an application period correction unit that corrects the length of the application period so that the difference in the ratio of the application period to the printing cycle is equal to or less than a predetermined value before and after the printing cycle is lengthened by the printing speed determination unit. Printer.

2. It includes a storage unit that stores data on the length of the application period of the energization pulse in one line printing cycle corresponding to each of a plurality of set values of printing speeds set at a predetermined first speed width, The printing speed determination unit determines the printing speed with a second speed width smaller than the first speed width based on any one of the set values of the plurality of printing speed set values. The printer according to claim 1.

3. The printing analysis unit estimates the maximum length of the application period based on the maximum value of the number of dots printed simultaneously for each line in the image. The printer according to claim 1 or 2.

4. It includes a battery that supplies power to the thermal head, The printing analysis unit estimates the maximum length of the application period based on the voltage of the battery. The printer according to any one of claims 1 to 3.

5. It includes a temperature detection unit that detects the temperature of the thermal head, The printing analysis unit estimates the maximum length of the application period based on the temperature of the thermal head. The printer according to any one of claims 1 to 4.

6. The application period includes a first application period for applying thermal energy to cause the heat-sensitive color-developing layer to develop color for the plurality of heating elements, and a second application period of an energization pulse for applying thermal energy to such an extent that the heat-sensitive color-developing layer does not develop color for the plurality of heating elements. The printer according to any one of claims 1 to 5.

7. A printing method in a printer having a thermal head with a plurality of heating elements arranged in a line and printing an entire page of a printing medium having a heat-sensitive coloring layer at a constant printing speed, comprising: Analyzing an image to be printed for one page, estimating the maximum length of the application period of the energization pulse to the plurality of heating elements in one line printing cycle; Determining before printing whether the maximum length of the application period fits within the printing cycle, and if not, decelerating the printing speed by lengthening the printing cycle; Correcting the length of the application period so that the difference in the ratio of the application period to the printing cycle before and after lengthening the printing cycle is equal to or less than a predetermined value; A printing method for a printer. **Claim 8** A program for causing a computer to execute a predetermined method in a printer having a thermal head with a plurality of heating elements arranged in a line and printing an entire page of a printing medium having a heat-sensitive coloring layer at a constant printing speed, the method comprising: The method includes: Analyzing an image to be printed for one page, estimating the maximum length of the application period of the energization pulse to the plurality of heating elements in one line printing cycle; Determining before printing whether the maximum length of the application period fits within the printing cycle, and if not, decelerating the printing speed by lengthening the printing cycle; Including correcting the length of the application period so that the difference in the ratio of the application period to the printing cycle before and after lengthening the printing cycle is equal to or less than a predetermined value; A program.

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