JP2014168903A - Thermal printer and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal printer and a program in which efficient print control can be implemented and energy saving can be realized.SOLUTION: The thermal printer includes: a thermal head in which plural exothermic elements that generates heat by electrification are arranged linearly and printing on a recording medium is implemented by the heat of the exothermic elements; calculation means which calculates a printing ratio indicating the ratio of electrified exothermic elements to the plural exothermic elements from printing data; and control means which, in a case that the printing ratio calculated by the calculation means is in a high printing ratio zone among printing ratio zones which are provided as at least three divided zones, transports the recording medium in the sub scanning direction at a first constant speed lower than the speeds in the other printing ratio zones.

Description

  Embodiments described herein relate generally to a thermal printer and a program.

  2. Description of the Related Art Conventionally, a thermal printer using a thermal head ensures printing quality by variably controlling the printing speed (conveyance speed) of paper according to the number of print dots of print data. However, since the conventional print control aims at both ensuring the print quality and improving the print speed, the print control tends to be complicated, and the energy required for printing tends to increase.

  The problem to be solved by the embodiments of the present invention is to provide a thermal printer and a program capable of performing efficient printing control and saving power.

  The thermal printer of the embodiment includes a thermal head, calculation means, and control means. In the thermal head, a plurality of heating elements that generate heat when energized are arranged in a line, and printing is performed on a recording medium by the heat generated by the heating elements. The calculating means calculates a print rate indicating a ratio of energized heat generating elements among the plurality of heat generating elements from print data. When the printing rate calculated by the calculation unit is in a high printing rate zone of at least three printing rate zones, the control unit sets the conveyance speed in the sub-scanning direction of the recording medium to another printing rate. It is conveyed at a constant first speed that is slower than the belt.

FIG. 1 is a perspective view illustrating an appearance of a thermal printer according to an embodiment. FIG. 2 is a perspective view showing the external appearance of the thermal printer with the cover open. FIG. 3 is a diagram schematically illustrating a sheet conveyance path. FIG. 4 is a block diagram illustrating a control system of the thermal printer according to the embodiment. FIG. 5 is a diagram schematically illustrating the first table data. FIG. 6 is a diagram schematically showing the second table data. FIG. 7 is a diagram for explaining the printing speed control by the printing control unit. FIG. 8 is a diagram illustrating the relationship between the printing speed and the printing energy. FIG. 9 is a diagram illustrating the relationship between the printing speed and the printing energy. FIG. 10 is a flowchart illustrating an example of the operation of the thermal printer according to the embodiment. FIG. 11 is a transparent perspective view illustrating an example of the information processing apparatus.

  Hereinafter, embodiments of a thermal printer and a program will be described in detail with reference to the accompanying drawings. The embodiment described below is an embodiment of a thermal printer and a program, and does not limit the configuration, specifications, or the like. In the present embodiment, a thermal type thermal printer in which a paper roll on which paper is wound is housed and printing is performed by a thermal head is illustrated.

  A schematic structure of the thermal printer according to the present embodiment will be described with reference to FIGS. FIG. 1 is a perspective view showing an appearance of a thermal printer 1 according to the present embodiment. FIG. 2 is a perspective view showing an appearance of the thermal printer 1 with the cover 104 opened.

  The thermal printer 1 has a rectangular parallelepiped housing 101. The housing 101 has an internal structure that accommodates a paper roll PR around which a paper PT that is a recording medium is wound, and an opening 102 is formed on the upper surface so that the paper roll PR can be accommodated therein. In addition, a paper storage portion 103 capable of detachably storing the paper roll PR is formed inside the opening 102.

  The opening 102 is opened or closed by opening and closing a cover 104 that is rotatably provided. The cover 104 is rotatably attached to a back side 105 of the housing 101 that forms one side of the opening 102. In a state where the cover 104 is closed, a paper discharge port 108 for taking out the printed paper PT is provided between the outer side 106 which is the tip of the cover 104 and the front side 107 which is one side of the opening 102. It is formed.

  The cover 104 includes a platen roller 109, a sheet pressing roller 110, and a driven gear 111. The platen roller 109 is provided at a position in contact with the line thermal head 114 in the housing 101 in a state where the cover 104 is closed. The sheet holding roller 110 is provided in the vicinity of the platen roller 109 and contacts the head cover 115a with the cover 104 closed. The platen roller 109 and the sheet restraining roller 110 are both rotatable about the width direction of the thermal printer 1 as a rotation axis.

  A driven gear 111 that rotates integrally with the platen roller 109 is provided on one end side of the platen roller 109. A drive gear 112 is provided at a position corresponding to the driven gear 111 inside the housing 101. The driven gear 111 meshes with the drive gear 112 with the cover 104 closed. The drive gear 112 rotates using a stepping motor 126 (see FIGS. 3 and 4) as a drive source. The driven gear 111 is driven by the drive gear 112 to rotationally drive the platen roller 109 connected to the driven gear 111. In the present embodiment, the driven gear 111 and the drive gear 112 constitute a transmission 128 (see FIG. 4) described later.

  The paper roll PR is stored in the paper storage unit 103 with the roll axis facing the width direction of the thermal printer 1. The paper PT of the paper roll PR is pulled out by the platen roller 109 and conveyed toward the paper discharge port 108 (sub-scanning direction). In the present embodiment, the paper roll PR is detachably stored between the pair of guide fences 113 in the paper storage unit 103.

  The line thermal head 114 is disposed inside the housing 101 at a position facing the platen roller 109 of the cover 104. The head bracket 115 is fixed to the housing 101 and urges the line thermal head 114 upward on the back side of the thermal printer 1. The head cover 115a is attached to the housing 101 as necessary. The head cover 115a urges the line thermal head 114 to prevent vibration.

  Here, the line thermal head 114 has a plurality of heating elements 114a arranged in a line. The heating elements 114a are heating elements that generate heat when energized, and each corresponds to a pixel for one dot. The line thermal head 114 heats the sheet PT and performs printing for each line when the heating element 114a generates heat based on the control of the head control unit 132 (see FIG. 4). In the vicinity of the line thermal head 114, a temperature sensor (temperature detection means) 127 (see FIGS. 3 and 4) for detecting the temperature of the line thermal head 114 is provided.

  In addition, a connection connector portion 116, a battery storage portion 117, and a power input portion 118 are provided on one side surface of the housing 101. The connection connector part 116 is a connection terminal for connecting to an external device. The battery storage unit 117 is a space for storing the rechargeable battery 117a (see FIG. 4). The power input unit 118 is a connection terminal for inserting the plug 201 of the AC adapter 200. The AC adapter 200 is inserted into an external commercial power outlet and supplies DC power from the plug 201.

  As a device for supplying DC power from the power input unit 118, a car adapter, a DC-DC converter, or the like may be used in addition to a general-purpose AC adapter. By connecting the plug 201 to the power input unit 118, DC power is supplied to the thermal printer 1, and the thermal printer 1 can be driven and the rechargeable battery 117a can be charged.

  The housing 101 also includes a display / operation unit 119. The display / operation unit 119 includes a power switch 120, a paper feed button 121 for a user to instruct paper feed and the like, a pause button 122 for a user to instruct a pause of paper feed, and the rechargeable battery 117a. Are provided with an indicator 123 for informing the user of the state of charge, an LCD (Liquid Crystal Display) 124, and a communication window 125 for infrared communication.

  The thermal printer 1 transmits / receives various data to / from external devices connected via the communication window 125 and the connection connector unit 116. For example, the thermal printer 1 receives print data to be printed from an external device through this data transmission / reception, stores it in the storage unit 131 (see FIG. 4), and prints it. Here, the external device is an information processing apparatus such as a personal computer (PC), a POS terminal, a mobile phone, and a handy terminal.

  Next, the conveyance path of the sheet PT will be described with reference to FIG. Here, FIG. 3 is a diagram schematically illustrating the conveyance path of the sheet PT.

  As shown in FIG. 3, in the thermal printer 1, when the paper roll PR is stored in the paper storage unit 103, the paper PT is pulled out and the cover 104 is closed, the pulled paper PT is transferred to the platen roller 109, the line thermal head 114, and the like. Be held between.

  In this state, when a printing mode described later is entered, the stepping motor 126 is driven by the control of the printing control unit 134 (see FIG. 4). As a result, the sheet PT is conveyed in the sub-scanning direction from the sheet roll PR to the sheet discharge port 108 via the line thermal head 114. A head controller 132 (see FIG. 4), which will be described later, prints predetermined content on the conveyed paper PT by causing the line thermal head 114 (heat generating element 114a) to generate heat based on the control of the head controller 132. .

  Next, the control system 130 of the thermal printer 1 will be described. Here, FIG. 4 is a diagram showing the control system 130 of the thermal printer 1. As shown in FIG. 4, the thermal printer 1 includes a storage unit 131, a head control unit 132, a motor control unit 133, a print control unit 134, a communication control unit 135, and a display control unit 136 as a control system 130. And a power control unit 137. In addition, as the printing mechanism 140 according to the present embodiment, the platen roller 109, the line thermal head 114 (heating element 114a), the stepping motor 126, the temperature sensor 127, and the transmission 128 (driven gear 111, driving gear 112) described above are described. doing.

  The storage unit 131 is a storage medium such as a flash memory. The storage unit 131 stores various setting information such as first table data 131a and second table data 131b related to printing speed control, in addition to a program related to control of the thermal printer 1.

  FIG. 5 is a diagram schematically showing the first table data 131a. As shown in FIG. 5, the first table data 131a stores the printing speed (mm / s) in the sub-scanning direction of the line thermal head 114 in association with the printing rate (%). Here, the printing rate indicates the ratio of the heat generating elements 114a that are actually energized by the print data out of the heat generating elements 114a.

  The first table data 131a in FIG. 5 defines that printing is performed at a constant printing speed Vmax when the printing rate R is a low printing rate band where 0 ≦ R <33. Further, it is determined that printing is performed at a constant printing speed Vmin lower than the printing speed Vmax when the printing ratio R is in a high printing ratio band where 73 ≦ R ≦ 100. In the case of the medium printing rate band where the printing rate R is 33 ≦ R <73, it is determined that printing is performed in the range of printing speeds V1 to V2 that is lower than the printing speed Vmax and higher than the printing speed Vmin. .

  Here, the printing speed in the middle printing rate band is dynamically determined in the range of printing speeds V1 to V2 depending on conditions other than the printing rate. A method for determining the printing speeds V1 to V2 is not particularly limited, and a known technique may be used. For example, as shown in FIG. 6, by using the second table data 131b in which each temperature of the line thermal head 114 is associated with the printing speed at that temperature, the printing speed in the medium printing rate band is dynamically set. It may be derived. Here, FIG. 6 is a diagram schematically showing the second table data 131b, where the vertical axis represents the printing speed (mm / s) and the horizontal axis represents the temperature (° C.). The print speed may be derived using a relational expression that defines the relationship between the temperature of the line thermal head 114 and the print speed without using the second table data 131b.

  Returning to FIG. 4, the head controller 132 supplies printing energy (electric power) to the line thermal head 114 in order to cause the heating element 114 a to generate heat under the control of the printing controller 134.

  The motor control unit 133 outputs a drive pulse signal to the stepping motor 126 under the control of the print control unit 134, thereby controlling the conveyance speed of the sheet PT in the sub scanning direction of the line thermal head 114, that is, the print speed.

  The print control unit 134 is a functional unit that comprehensively controls each unit of the thermal printer 1. Specifically, the print control unit 134 operates the thermal printer 1 in various operations depending on the user operation input via the display / operation unit 119 and the situation such as whether external DC power is supplied. Set to mode. Examples of the operation mode include a printing mode in which printing is performed by the line thermal head 114, a charging mode in which the rechargeable battery 117a is charged, and the like.

  The print control unit 134 controls the print operation of the print mechanism 140 by cooperating with the head control unit 132 and the motor control unit 133 in the print mode. Specifically, the print control unit 134 calculates, for each line, the print rate indicating the ratio of the heat generating elements 114a to be energized among all the heat generating elements 114a constituting the line thermal head 114 (calculation means). . Here, the print data is data to be printed input from an external device or the like. Note that the print data may be stored in the storage unit 131.

  In addition, the print control unit 134 specifies a print speed corresponding to the calculated print rate from the first table data 131a. The print control unit 134 controls the printing speed of the line thermal head 114 in the sub-scanning direction by cooperating with the motor control unit 133 based on the specified printing speed (control unit). Hereinafter, the printing speed control performed by the printing control unit 134 will be described.

  FIG. 7 is a diagram for explaining the printing speed control by the printing control unit 134. 7 conforms to the setting contents of the first table data 131a shown in FIG. In FIG. 7, the vertical axis represents the printing speed (mm / s), and the horizontal axis represents the printing rate (%). In the present embodiment, it is assumed that the energization time per dot of the print data is constant.

  In the high printing rate zone where the printing rate R is 73 ≦ R ≦ 100, the number of heat generating elements 114a to be heated is larger than in other printing rate zones. In this case, the total amount of power supplied to the line thermal head 114, that is, power consumption is higher than that in other print rate bands. Therefore, the printing control unit 134 performs printing at a constant printing speed Vmin that is slower than other printing rate bands by cooperating with the motor control unit 133 based on the definition of the first table data 131a.

  As a result, the time for printing one line is longer than in other printing rate bands, but the energization time per dot is constant, so the proportion of energization time per line decreases. Therefore, the printing energy required for printing per line can be reduced. In addition, by reducing the printing speed, the peak value of the printing energy accumulated in the line thermal head 114 can also be reduced. Here, the relationship between the printing speed and the printing energy will be described with reference to FIGS.

  8 and 9 are diagrams showing the relationship between the printing speed and the printing energy. Here, FIG. 8 shows the state of printing energy when the printing speed is V3. FIG. 9 shows the state of printing energy when the printing speed is Vmin (where Vmin <V3). The printing position shown on the vertical axis corresponds to the line of the heating element 114a, and the heating element 114a (dot) that performs printing is represented by a rectangle. The printing energy shown on the vertical axis represents the magnitude of printing energy supplied to the line thermal head 114. The horizontal axis represents the time axis. It is assumed that the printing interval (pitch) on the paper PT output as a printing result is controlled to be substantially the same.

  The head controller 132 supplies electric power (printing energy) to the line thermal head 114 in order to cause the heating element 114a related to the printing to generate heat during the printing period t1 during which printing is performed. The magnitude of the supplied printing energy is proportional to the number of heating elements 114a (rectangles) that actually perform printing. Further, the head controller 132 stops the supply of printing energy during the non-energization period (t2, t3). Then, the head control unit 132 repeatedly supplies and stops printing energy according to the printing period t1 and the non-energization periods t2 and t3. Further, due to the capacitive behavior of the line thermal head 114, the printing energy (corresponding to the amount of heat) is accumulated in the line thermal head 114 during the printing period t1, and is attenuated during the non-energization period (t2, t3).

  Here, since the energization time per dot is constant, the non-energization period t3 at the printing speed Vmin is longer than the non-energization period t2 at the printing speed V3. Therefore, as is clear from FIGS. 8 and 9, the amount of print energy attenuation is greater when printing is performed at a slower printing speed Vmin than when printing is performed at the printing speed V3. Therefore, by performing printing at a slower printing speed Vmin, the peak value of the printing energy accumulated in the line thermal head 114 can be reduced. In the case of printing in a high printing rate band, it is preferable to drive the line thermal head 114 in a divided manner.

  Further, in the low printing rate band where the printing rate R is 0 ≦ R <33, the number of heating elements 114a to be heated is smaller than in other printing rate bands. In this case, the printing energy supplied to the line thermal head 114 is lower than other printing rate bands. For this reason, even if the printing speed is set higher than other printing rate bands, the peak value of the printing energy accumulated in the line thermal head 114 becomes a relatively low value. Therefore, the printing control unit 134 performs printing at a constant printing speed Vmax that is faster than other printing rate bands by cooperating with the motor control unit 133 based on the definition of the first table data 131a. In the case of printing in a low printing rate zone, it is preferable to drive the line thermal head 114 at once.

  Further, in the medium printing rate band where the printing rate R is 33 ≦ R <73, the number of heat generating elements 114a to be heated is varied. In this case, printing speed control according to the temperature of the line thermal head 114 is effective. Therefore, the printing control unit 134 performs printing in the range of the printing speeds V1 to V2 by cooperating with the motor control unit 133 based on the definition of the first table data 131a (second table data 131b). In the case of printing in the medium printing rate band, it is preferable to drive the line thermal head 114 in a divided manner.

  By the way, when the thermal printer 1 according to the present embodiment is used as a receipt printer such as a POS terminal, for example, numbers and characters (characters) are mainly printed. Therefore, the print rate is a low print rate band of 33% or less. Often. However, there is a case where a store name or a logo is printed in white at the end of the receipt. In this case, the printing rate may exceed 74% at the end. Therefore, by applying the above-described printing speed control, it is possible to print at a higher printing speed Vmax with normal receipt printing. In the case of receipt printing including a white logo, the portion other than the white logo is printed at a higher printing speed Vmax, and the white logo portion is printed at a lower printing speed Vmin. Thereby, it is possible to perform printing with reduced power consumption while considering the total printing time.

  Returning to FIG. 4, the communication control unit 135 transmits and receives various data to and from an external device connected through the connection connector unit 116, the communication window 125, and the like, using a communication interface (not shown). The communication interface is, for example, infrared communication such as IrDA, USB, wireless LAN (Local Area Network), RS-232C, Bluetooth (registered trademark), or the like.

  The display control unit 136 controls display on the LCD 124 of the display / operation unit 119 (remaining battery level, radio wave reception status, etc.). The power control unit 137 controls the supply / cutoff of power from an external commercial power outlet or power from the rechargeable battery 117a via the AC adapter 200 or the like according to ON / OFF of the power switch 120 of the display / operation unit 119. .

  Specifically, the power control unit 137 supplies power of a predetermined voltage value and current value to each unit of the thermal printer 1. Further, the power control unit 137 supplies the power input from the AC adapter 200 to the rechargeable battery 117a under the charging mode of the print control unit 134. For example, when the rechargeable battery 117a is a lithium ion rechargeable battery, the CC / CV charging method, that is, the external DC voltage is stepped down to perform constant current voltage charging.

  The thermal printer 1 includes a computer configuration such as a CPU, a ROM, and a RAM (all not shown). Note that some or all of the functional units other than the storage unit 131 in the control system 130 described above may have a software configuration realized by cooperation between a CPU (not shown) and a program stored in the storage unit 131. Alternatively, a hardware configuration realized by a dedicated chip or the like may be used.

  Next, with reference to FIG. 10, the printing speed control operation performed by the thermal printer 1 will be described. FIG. 10 is a flowchart illustrating an example of the procedure of the printing speed control process.

  When printing by the line thermal head 114 is started by setting the print mode or the like, the print control unit 134 acquires the print rate in the line thermal head 114 based on the input print data (step S11). More specifically, the print control unit 134 sets, for each line, a print rate that is a ratio of the number of heating elements 114a that actually perform printing based on print data and the total number of heating elements 114a among the plurality of heating elements 114a. calculate.

  Next, the print control unit 134 refers to the first table data 131a (step S12), and specifies the print speed corresponding to the print rate acquired in step S11 (step S13). When the acquired printing rate R belongs to the middle printing rate band, the printing speed is obtained based on the temperature of the line thermal head 114 detected by the temperature sensor 127.

  Subsequently, the print controller 134 controls the printing speed in the sub-scanning direction of the line thermal head 114 by driving the stepping motor 126 based on the printing speed specified in step S13 (step S14).

  Next, the print control unit 134 determines whether or not the print data has been terminated, such as a print termination operation by the display / operation unit 119 (step S15). Here, when printing is continued (step S15; No), the print control unit 134 returns the process to step S11. If the printing is to be ended (step S15; Yes), the printing control unit 134 ends the printing mode and ends the process.

  As described above, when the printing rate calculated from the print data is in the high printing rate zone, the thermal printer 1 according to the present embodiment sets the printing speed in the sub-scanning direction of the recording medium, that is, the conveyance speed, to other printing rates. It is conveyed at a constant Vmin that is slower than the belt. Further, when the printing rate calculated from the printing data is in the low printing rate zone, the printing speed of the recording medium in the sub-scanning direction is conveyed at a constant Vmax that is higher than the other printing rate zones. Further, when the printing rate calculated from the printing data is in the middle printing rate band, the printing speed of the recording medium in the sub-scanning direction is variably controlled within the range of V1 to V2 which is larger than Vmin and smaller than Vmax.

  As a result, printing can be performed while suppressing the printing energy accumulated in the line thermal head 114 in each printing rate band, so that power saving can be achieved. In the high printing rate zone and the low printing rate zone, power saving can be achieved by simple printing control, and thus efficient printing control can be realized.

  As mentioned above, although embodiment of this invention was described, the said embodiment was shown as an example and is not intending limiting the range of invention. The above embodiment can be implemented in various other forms, and various omissions, replacements, changes, additions, and the like can be made without departing from the scope of the invention. Moreover, the said embodiment and its deformation | transformation are included in the range of the invention, the summary, and the invention described in the claim, and its equal range.

  For example, in the above embodiment, the low print rate band, the medium print rate band, and the high print rate band of the print rate R are set to 0 ≦ R <33, 33 ≦ R <73, and 73 ≦ R ≦ 100, respectively. The range of the printing rate band is not limited to this. In this embodiment, the print rate band is divided into three, but the present invention is not limited to this, and the print rate band may be divided into three or more. Even in this case, it is preferable that the high printing rate band and the low printing rate band be set to the constant printing speeds Vmin and Vmax as in the present embodiment.

  In the above embodiment, the low printing rate band and the high printing rate band are set to a constant printing speed. However, the present invention is not limited to this, and one printing rate band is set to a constant printing speed, and the other printing rate band is set to be the same. The printing speed control similar to that in the middle printing rate band may be used. In the printing speed control of the present embodiment, it is preferable to set the high printing rate band to a constant printing speed Vmin because power consumption in the high printing rate band can be more efficiently reduced.

  In the above-described embodiment, the present invention is applied to the independent thermal printer 1. However, the present invention is not limited thereto, and is applied to an information processing apparatus such as a POS terminal including the control system 130 and the printing mechanism 140 of the thermal printer 1 described above. May be. Here, FIG. 11 is a transparent perspective view illustrating an example of the information processing apparatus.

  The information processing apparatus 300 is, for example, a POS terminal or the like, and includes a touch panel display / operation unit 301 having an LCD panel, a rechargeable battery 302, a printing unit 303, a CPU, a ROM, a RAM, a storage unit, and the like (not shown). A control system 304 is provided. Here, the printing unit 303 includes the control system 130 and the printing mechanism 140 of the thermal printer 1 and performs printing control similar to that of the thermal printer 1. In the case of this configuration, the control system 304 of the information processing apparatus 300 may perform printing control of the printing unit 303.

  In addition, the program executed by the thermal printer 1 of the above embodiment is provided by being incorporated in advance in a storage medium (ROM or storage unit) provided in the thermal printer 1, but is not limited to this and can be installed in an installable format or An executable file may be recorded and provided on a computer-readable recording medium such as a CD-ROM, a flexible disk (FD), a CD-R, or a DVD (Digital Versatile Disk). Furthermore, the storage medium is not limited to a medium independent of a computer or an embedded system, but also includes a storage medium that downloads and stores or temporarily stores a program transmitted via a LAN, the Internet, or the like.

  Further, the program executed by the thermal printer 1 of the above embodiment may be stored on a computer connected to a network such as the Internet and provided by being downloaded via the network. It may be configured to be provided or distributed via.

DESCRIPTION OF SYMBOLS 1 Thermal printer 109 Platen roller 114 Line thermal head 114a Heating element 115 Head bracket 126 Stepping motor 127 Temperature sensor 128 Transmission 130 Control system 131 Memory | storage part 131a 1st table data 131b 2nd table data 132 Head control part 134 Print control part 135 Communication control unit 136 Display control unit 137 Power control unit 140 Printing mechanism PT paper

JP 2010-221436 A

Claims (6)

A plurality of heating elements that generate heat when energized are arranged in a line, and a thermal head that prints on a recording medium by heat generation of the heating elements;
A calculating means for calculating a printing rate indicating a ratio of a heating element to be energized among the plurality of heating elements from print data;
When the printing rate calculated by the calculating means is in a high printing rate zone divided into at least three printing rate zones, the conveyance speed of the recording medium in the sub-scanning direction is lower than other printing rate zones. Control means for conveying at a constant first speed;
Thermal printer equipped with.   When the printing rate calculated by the calculating unit is in a low printing rate zone of the printing rate zone, the control unit sets the conveyance speed of the recording medium in the sub-scanning direction to be higher than that of other printing rate zones. The thermal printer according to claim 1, wherein the thermal printer is transported at a constant second speed.   The control means has a sub-scanning direction of the recording medium when the printing rate calculated by the calculating means is in a medium printing rate zone other than the high printing rate zone and the low printing rate zone of the printing rate zone. The thermal printer according to claim 1, wherein the conveyance speed is variably controlled within a predetermined speed range that is larger than the first speed and smaller than the second speed. A temperature detecting means for detecting the temperature of the thermal head;
The control unit conveys the recording medium in the sub-scanning direction at a speed corresponding to the temperature detected by the temperature detecting unit when the printing rate calculated by the calculating unit is in the middle printing rate band. The thermal printer according to claim 3.   The thermal printer according to any one of claims 1 to 4, wherein the control unit supplies printing energy to the thermal head so that an energization time per dot of the print data is constant. A thermal printer computer provided with a thermal head in which a plurality of heating elements that generate heat when energized are arranged in a line and prints on a recording medium by the heat generation of the heating elements,
A calculating means for calculating a printing rate indicating a ratio of a heating element to be energized among the plurality of heating elements from print data;
When the printing rate calculated by the calculating means is in a high printing rate zone divided into at least three printing rate zones, the conveyance speed of the recording medium in the sub-scanning direction is lower than other printing rate zones. Control means for conveying at a constant first speed;
Program to make it function.

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