JP4537977B2 - Thermal printer and printing method therefor - Google Patents

Description

  The present invention relates to a thermal printer capable of simultaneously printing on the front and back surfaces of a print medium and a printing method thereof.

  A double-sided thermal printer having two platen rollers and two thermal heads has been proposed as a thermal printer capable of simultaneously printing on both front and back sides of a thermal paper (see, for example, Patent Document 1).

In this type of conventional double-sided thermal printer, the first platen roller and the second platen roller are rotated at the same feed speed in synchronization with each other. As the thermal paper passes between the first platen roller and the first thermal head, printing is performed on one surface of the thermal paper by the first thermal head. Further, when the thermal paper passes between the second platen roller and the second thermal head, printing is performed on one surface of the thermal paper by the second thermal head.
Japanese Patent Laid-Open No. 11-286147

  As a thermal head used in this type of thermal printer, a line thermal head in which a large number of heating elements are arranged in a row in a direction orthogonal to the thermal paper transport direction is usually used. The line thermal head prints an arbitrary dot pattern on thermal paper by energizing an arbitrary heating element corresponding to a printing dot to apply electric energy and generating heat by the arbitrary heating element.

  For this reason, in a double-sided thermal printer using two thermal heads, if the two thermal heads are controlled to be energized at the same time, the energy consumption (in comparison with a single-sided thermal printer using only one thermal head) The peak value of (current) is approximately doubled. In order to cope with this, an appropriate power source is required, which hinders the cost reduction and miniaturization of the apparatus.

  The present invention has been made based on such circumstances, and the object of the present invention is to be necessary when energizing each thermal head in a double-sided thermal printer that performs printing on both sides of a sheet using two thermal heads. The purpose is to suppress the peak value of the current substantially the same as in the case of a single-sided thermal printer that prints on one side of a sheet using a single thermal head.

A thermal printer according to a first aspect of the present invention is disposed so as to be in contact with one surface of a sheet, and prints dot image data on the one surface by energizing a plurality of heating elements, and A second thermal head that is disposed in contact with the other surface of the paper and that prints dot image data on the other surface by energizing a plurality of heating elements; A reception buffer for storing print data received from the host device; a first image buffer for storing dot image data for printing on one side of the paper; and a print buffer for printing on the other side of the paper. A second image buffer for storing dot image data, and the print data in the reception buffer are sequentially developed from the top into dot image data, and a certain amount thereof is stored in the first image buffer. After this storage, First control means for sequentially developing the remaining print data in the reception buffer into dot image data and storing it in the second image buffer; the number of energized pixels of the dot image data stored in the first image buffer; whether the sum of the number of energizing pixels in the dot image data stored in the image buffer exceeds a threshold value An energized pixel number determining means for determining the asynchronous mode, and when the energized pixel number determining means determines that the sum exceeds the threshold value, the asynchronous mode is set, and when it is determined that the sum is not exceeded, the synchronous mode is set. When the asynchronous mode is set by the setting means and the mode setting means, the energization time required for printing one dot line data by the first thermal head and the energization time required for printing one dot line data by the second thermal head When the synchronous mode is set by the second control means for controlling the energization cycle of the first thermal head and the second thermal head so that they do not overlap, and the mode setting means, the energization time for the first thermal head and the second The first thermal head and the second thermal head are arranged so that at least part of the energization time for the thermal head overlaps. And a third control means for controlling the energization period.

  According to the present invention in which such a measure is taken, the energization time for the first thermal head and the energization time for the second thermal head do not overlap. Therefore, the peak value of the necessary current when energizing each thermal head is obtained as one thermal head. This can be suppressed to the same extent as in the case of a single-sided thermal printer that prints on one side of a sheet using a head.

  The best mode for carrying out the present invention will be described below with reference to the drawings. This embodiment is a case where the present invention is applied to a thermal printer 10 that performs printing on both sides of a thermal paper 1 that has thermal layers on both sides.

  FIG. 1 is a diagram schematically showing an outline of a printing mechanism section in the thermal printer 10 of the present embodiment. The thermal paper 1 wound in a roll shape is accommodated in a paper accommodating portion of a printer main body (not shown). Then, the leading end is pulled out from the paper storage portion and discharged from the paper discharge port of the printer main body to the outside.

  The printer main body is provided with a first thermal head 2 so as to be in contact with one surface of the thermal paper drawn from the paper accommodating portion (hereinafter, this surface is referred to as the front surface 1A). A first platen roller 3 is provided so as to face the first thermal head 2 with the thermal paper 1 interposed therebetween.

  A second thermal head 4 is provided on the upstream side of the first thermal head 2 in the paper feeding direction so as to be in contact with the other surface of the thermal paper drawn from the paper storage portion (hereinafter, this surface is referred to as the back surface 1B). It has been. A second platen roller 5 is provided so as to face the second thermal head 4 with the thermal paper 1 interposed therebetween.

  Further, a cutter mechanism 6 for cutting the thermal paper 1 discharged from the paper discharge port is provided on the downstream side of the first thermal head 2 in the paper feeding direction.

  Thermal layers are formed on the front surface 1A and the back surface 1B of the thermal paper 1, respectively. These heat-sensitive layers are made of a material that develops a desired color such as black or red when heated to a predetermined temperature or higher. As shown in FIG. 1, the thermal paper 1 is wound in a roll shape so that the front surface 1A faces inward.

  Each of the first thermal head 2 and the second thermal head 4 is a line thermal head in which a large number of heating elements are arranged in a row, and the arrangement direction of the heating elements is orthogonal to the conveyance direction of the thermal paper 1. Is attached to the printer body.

  The first platen roller 3 and the second platen roller 5 are formed in a cylindrical shape, and the rotation of a sheet feed motor 23 (to be described later) is transmitted by a power transmission mechanism (not shown) so as to rotate in the directions indicated by the arrows. . As the platen rollers 3 and 5 rotate, the thermal paper 1 drawn out from the paper storage unit is conveyed in the direction of the arrow shown in the figure, and is discharged to the outside from the paper discharge port. Here, the first platen roller 3 and the second platen roller 5 constitute a conveying unit.

  FIG. 2 is a block diagram showing a main configuration including the control circuit of the thermal printer 10. The thermal printer 10 includes a CPU (Central Processing Unit) 11 as a control unit body. The CPU 11 is connected to a ROM (Read Only Memory) 13, a RAM (Random Access Memory) 14, an I / O (Input / Output) port 15, and a communication interface 16 via a bus line 12 such as an address bus and a data bus. , The first and second motor drive circuits 17 and 18 and the first and second head drive circuits 19 and 20 are connected to form a control circuit. Driving power is supplied from the power supply circuit 21 to each part constituting the control circuit.

  Connected to the communication interface 16 is a host device 30 that generates and supplies print data in a timely manner. Signals from various sensors 22 provided in the printer main body are input to the I / O port 15.

  The first motor drive circuit 17 controls on / off of a paper feed motor 23 that is a drive source of a transport unit that transports the thermal paper 1 in one direction. The second motor drive circuit 18 controls on / off of a cutter motor 24 that is a drive source of the cutter mechanism 6.

  The first head drive circuit 19 controls the printing operation of the first thermal head 2. The second head drive circuit 20 controls the printing operation of the second thermal head 4. The correspondence relationship between the first head drive circuit 19 and the first thermal head 2 is shown in the block diagram of FIG. The correspondence relationship between the second head drive circuit 20 and the second thermal head 4 is the same as this, and the description thereof is omitted here.

  The first thermal head 2 includes N (N is a plurality) heating elements arranged in a line, and a line thermal head main body 41 capable of printing one line data consisting of dots of the number of elements N at a time, and the above 1 A latch circuit 42 that latches line data for each line, and an energization control circuit that selectively energizes N heating elements constituting the line thermal head main body 41 according to the one line data latched by the latch circuit 42. 43.

  The first head drive circuit 19 takes in one line data of N dots sequentially input via the bus line 12, outputs a serial data signal DATA to the latch circuit 42 (first-in first-out function), and a latch signal LAT. Is output to the latch circuit 42, and an enable signal ENB is output to the energization control circuit 43.

  The latch circuit 42 latches one line data output from the head drive circuit 19 at the timing when the latch signal LAT becomes active. The energization control circuit 43 energizes the heating element corresponding to the print dot in the one line data latched by the latch circuit 42 while the enable signal ENB is active.

  As shown in FIG. 4, the thermal printer 10 having such a configuration includes a reception buffer 51 for storing print data received from the host device 30, and dot image data of print data to be printed on the surface 1 </ b> A side of the thermal paper 1. Are developed and stored in the RAM 14 and a back image buffer 53 in which dot image data of print data to be printed on the back surface 1B side of the thermal paper 1 is developed and stored.

  Therefore, the CPU 11 controls double-sided printing on the thermal paper 1 according to the procedure shown in the flowchart of FIG. That is, the CPU 11 stands by for receiving print data as ST (step) 1. If the print data is received from the host device 30 and stored in the reception buffer 51, the CPU 11 sequentially develops the print data into dot data from the top and stores it in the front image buffer 52 as ST2. If a certain amount of dot data is stored in the front surface image buffer 52 as ST3, the CPU 11 then sequentially expands the remaining dot of the print data in ST4 and stores it in the back surface image buffer 53. If a certain amount of dot data is stored in the back image buffer 53 as ST5, the CPU 11 proceeds to the process of ST6.

  Even when all the print data in the reception buffer 51 has been expanded into dot data before a certain amount of dot data is stored in the front image buffer 52 or the back image buffer 53, the CPU 11 performs the process of ST6. move on.

  In ST6, the CPU 11 counts the number of print dots in the dot data stored in the front image buffer 52. The number of dots is stored as the number of surface energized pixels p1. In ST7, the number of print dots among the dot data stored in the back image buffer 53 is counted. Then, the number of dots is stored as the number of backside energized pixels p2.

  Next, in step ST8, the CPU 11 adds the front side energized pixel number p1 and the back side energized pixel number p2, and determines whether or not the sum (p1 + p2) exceeds a preset threshold value Q (energized pixel). Number judgment means). Here, the threshold value Q is set based on the specification of the power supply circuit 21.

  When the sum (p1 + p2) of the number of front side energized pixels p1 and the number of backside energized pixels p2 is compared with the threshold value Q, if the sum (p1 + p2) exceeds the threshold value, the CPU 11 performs asynchronous printing mode as ST9. Set to print mode. On the other hand, when the total sum (p1 + p2) does not exceed the threshold value, the CPU 11 sets the print mode to the synchronous print mode as ST10 (mode setting means). After that, the CPU 11 controls each part according to the print mode as ST11 to print the dot data stored in the front image buffer 52 on the front surface 1A of the thermal paper 1 line by line and at the same time stored in the back image buffer 53. Dot data is printed on the back surface 1B of the thermal paper 1 line by line (control means).

  When the printing of the dot data stored in the front image buffer 52 and the back image buffer 53 is finished, the CPU 11 determines whether or not print data remains in the reception buffer 51 in ST12. If print data remains, the processes of ST2 to ST12 are executed again. If no print data remains in ST12, the CPU 11 performs a long feed of the thermal paper 1 and then outputs a drive signal to the cutter motor 24 in ST13 to operate the cutter mechanism 6 so that both the front and back sides are operated. Cut the printed thermal paper. This print processing is finished.

  FIG. 6 shows a timing chart of main signals when the asynchronous print mode is set as the print mode. In the figure, (a) shows an energization cycle (raster cycle) required for printing one dot line data composed of N dots. (B) shows a drive pulse signal for the paper feed motor 23. (C) shows a latch signal LAT1 for the thermal head to be printed on the front surface 1A side of the thermal paper 1, that is, the first thermal head 2. FIG. (D) shows a latch signal LAT2 for the thermal head to be printed on the back surface 1B side of the thermal paper 1, that is, the second thermal head 4. (E) shows an enable signal ENB1 for the first thermal head 2. (F) shows an enable signal ENB2 for the second thermal head 4.

  As shown in the figure, when the asynchronous printing mode is set, a driving pulse signal for the paper feed motor 23 is output at a period of 1/2 of one raster cycle. The latch signal LAT1 for the first thermal head 2 and the latch signal LAT2 for the second thermal head 4 are output at a cycle of one raster cycle. The enable signal ENB1 for the first thermal head 2 is output in synchronization with the pulse signal of the first half of the drive pulse signal that is output in a half cycle of one raster cycle. The enable signal ENB2 for the second thermal head 4 is output in synchronization with the pulse signal in the latter half of the drive pulse signal.

  Note that the pulse widths of the enable signal ENB1 and the enable signal ENB2, that is, the energization time required for printing one dot line data, is set to be shorter than ½ of one raster cycle. In other words, one raster cycle is set to be twice or more the energization time required for printing one dot line data.

  FIG. 8 schematically shows an example of dot printing when the asynchronous printing mode is set. In the drawing, a print example 61 on the left side shows a print example on the front surface 1A side by the first thermal head 2, and a print example 62 on the right side shows a print example on the back surface 1B side by the second thermal head 4. That is, the black circle 63 indicates a printing dot, and the white circle 64 indicates a non-printing dot. The symbol d indicates the dot length of the print dot 63 in the paper transport direction 65.

  The first thermal head 2 enables the heating element corresponding to the print dot 63 among the N-dot one-line data latched by the latch circuit 42 at the timing when the latch signal LAT1 is input (becomes active ON). Energization is performed while ENB1 is input (active ON). As a result, one line of printing dots 63 (dot length = d) is printed on the front surface 1 </ b> A of the thermal paper 1 in a direction orthogonal to the paper transport direction 65.

  On the other hand, the second thermal head 4 generates a heating element corresponding to the print dot 63 out of one line data of N dots latched by the latch circuit 42 at the timing when the latch signal LAT2 is input (becomes active ON). Energization is performed while the enable signal ENB2 is input (active ON). As a result, one line of printing dots 63 (dot length = d) is printed on the back surface 1 </ b> B of the thermal paper 1 in a direction orthogonal to the paper transport direction 65.

  Here, the paper feed motor 23 is turned on in synchronization with the output timing of the enable signal ENB1 and the output timing of the enable signal ENB2, and transports the thermal paper 1 in one direction. The transport amount at this time is d / 2 that is half the dot length d of the print dots 63 in the paper transport direction 65 because the drive pulse signal for the paper feed motor 23 is output in a half cycle of one raster cycle.

  Therefore, as shown in FIG. 8, one line data printed on the front surface 1A of the thermal paper 1 and one line data printed on the back surface 1B are shifted from each other by a half d / 2 of the dot length d. Printed on.

  Thus, when the asynchronous print mode is set as the print mode, the time during which the enable signal ENB1 for the first thermal head 2 is active and the enable signal ENB2 for the second thermal head 2 are active. It is controlled so that it does not overlap with the time. Specifically, the energization cycle of the first thermal head 2 and the second thermal head 4 is set to be twice or more the energization time required for printing one dot line data, and the first thermal head 2 and the second thermal head 4 The energization cycle is controlled to be shifted by approximately ½ cycle.

  Accordingly, since the two thermal heads 2 and 4 are not energized at the same time, the peak value of the required current when the thermal head is energized is suppressed to be substantially the same as that of a single-sided thermal printer having only one thermal head. Can do.

  On the other hand, FIG. 7 shows a timing chart of main signals when the synchronous printing mode is set. Also in this figure, (a) shows the time interval (raster cycle) required for printing one line data of N dots, (b) shows the drive pulse signal for the paper feed motor 23, and (c) shows the first thermal. The latch signal LAT1 for the head 2 is shown. (D) shows the latch signal LAT2 for the second thermal head 4. (e) shows the enable signal ENB1 for the first thermal head 2. (f) shows the second thermal head 4. The enable signal ENB2 is shown.

  As shown in the figure, when the synchronous print mode is set, the drive pulse signal is output to the paper feed motor 23 at a cycle of 1/2 of one raster cycle, similarly to the case where the asynchronous print mode is set. To do. In addition, the latch signal LAT1 for the first thermal head 2 and the latch signal LAT2 for the second thermal head 4 are output at a cycle of one raster cycle. However, one raster cycle in the synchronous printing mode is set to half the time of one raster cycle in the asynchronous printing mode.

  On the other hand, the enable signal ENB1 for the first thermal head 2 and the enable signal ENB2 for the second thermal head 4 are both synchronized with the pulse signal in the first half of the drive pulse signal that is output in a half cycle of one raster cycle. Is output. Note that the pulse widths of the enable signal ENB1 and the enable signal ENB2 are set to be shorter than one raster cycle.

  As described above, when the synchronous print mode is set as the print mode, the time during which the enable signal ENB1 for the first thermal head 2 is active and the enable signal ENB2 for the second thermal head 2 are active. It is controlled so as to coincide with the time. Therefore, although the two thermal heads 2 and 4 are energized simultaneously, the current consumed at that time is within the specification range of the power supply circuit 21 and does not exceed the use range.

  When this synchronous printing mode is set, one raster cycle can be made half of one raster cycle in the asynchronous printing mode. Therefore, since the thermal paper 1 is conveyed at a speed twice as high as that when the asynchronous printing mode is set, high-speed printing can be performed.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage.

  For example, in the above-described embodiment, the energization time for the first thermal head 2 and the second thermal head 4 are increased by shifting the energization period between the first thermal head 2 and the second thermal head 4 by approximately ½ period. Although the energization time is not overlapped, the method of preventing the energization time for the heads 2 and 4 from overlapping is not limited to this.

  FIG. 9 is a timing chart of main signals when the asynchronous printing mode is set in another embodiment. Also in this figure, (a) shows the time interval (raster cycle) required for printing one line data of N dots, (b) shows the drive pulse signal for the paper feed motor 23, and (c) shows the first thermal. The latch signal LAT1 for the head 2 is shown. (D) shows the latch signal LAT2 for the second thermal head 4. (e) shows the enable signal ENB1 for the first thermal head 2. (f) shows the second thermal head 4. The enable signal ENB2 is shown.

  Also in this other embodiment, the enable signal ENB1 for the first thermal head 2 is output in synchronization with the pulse signal of the first half of the drive pulse signal output at a period of 1/2 of one raster cycle. On the other hand, the enable signal ENB2 for the second thermal head 2 is output in synchronization with the fall of the enable signal ENB1. That is, first, energization to the first thermal head 2 is performed, and energization to the second thermal head 4 is started at a timing when energization to the first thermal head 2 is completed.

  Even when such a control method is adopted, the energization time for the first thermal head 2 and the energization time for the second thermal head 4 do not overlap. It can be suppressed to the same level as in the case of a single-sided thermal printer that is only provided.

  In the above embodiment, the energization time for the first thermal head 2 and the energization time for the second thermal head 4 are completely matched when the synchronous printing mode is set. .

  In the above embodiment, the number of print dots (the number of front surface energized pixels p1) among all the dot data expanded in the front surface image buffer 52 and the total of dot data expanded in the back surface image buffer 53. The total of the number of print dots (the number of back side energized pixels p2) was compared with the threshold value Q. The areas of the front image buffer 52 and the back image buffer 53 were divided into a first half and a second half, and each first half It is determined whether the sum of the number of front-surface energized pixels p1 and the number of back-surface energized pixels p2 exceeds the threshold value Q, and the sum of the number of front-surface energized pixels p1 and the number of back-surface energized pixels p2 of each latter half It may be determined whether or not the threshold value Q is exceeded, and the print mode may be changed between the first half and the second half. In this case, the size for dividing the areas of the front surface image buffer 52 and the rear surface image buffer 53 is not limited to ½.

  In the embodiment, the sum of the number of energized pixels p1 of the print data printed by the first thermal head 2 and the number of energized pixels p2 of the print data printed by the second thermal head 4 has the threshold value Q. Asynchronous mode is set when it is determined that it is exceeded, and synchronous mode is set when it is determined that it is not exceeded, but this function is omitted and all thermal printers that print in asynchronous mode are also available. It is included in the invention.

  In the above-described embodiment, the print data is first developed in the front image buffer 52, and if a certain amount is developed, the remaining print data is developed in the back image buffer 53. The method of developing dots in the buffer 52 and the back image buffer 53 is not limited to this.

  In the above embodiment, the thermal paper 1 having the heat-sensitive layers on both sides is used as the paper, but plain paper is used by providing a mechanism for feeding an ink ribbon between the thermal heads 2 and 4 and the paper. The present invention can be similarly applied to a thermal printer.

  In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, the constituent elements over different embodiments may be combined.

1 is a schematic diagram showing an outline of a printing mechanism unit of a thermal printer according to an embodiment of the present invention. The block diagram which shows the principal part structure containing the control circuit of the thermal printer. FIG. 3 is a block diagram showing a main configuration of a thermal head provided in the thermal printer. The schematic diagram which shows the main memory areas formed in RAM of the thermal printer. 3 is a flowchart showing a main part of a control processing procedure executed by the CPU of the thermal printer. The figure which shows the timing example of the main signal when asynchronous printing mode is set as printing mode. The figure which shows one timing example of the main signal when synchronous printing mode is set as printing mode. FIG. 5 is a schematic diagram illustrating an example of dot printing when an asynchronous printing mode is set as a printing mode. The figure which shows the other timing example of the main signal when asynchronous printing mode is set as printing mode.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Thermal paper, 2 ... 1st thermal head, 3 ... 1st platen roller, 4 ... 2nd thermal head, 5 ... 2nd platen roller, 6 ... Cutter mechanism, 11 ... CPU, 21 ... Power supply circuit, 23 ... Paper Feed motor, 24 ... cutter motor, 51 ... reception buffer, 52 ... front image buffer, 53 ... back image buffer.

Claims (8)

A first thermal head that is disposed in contact with one side of the paper and that prints dot image data on the one side by energizing a plurality of heating elements;
A second thermal head that is disposed in contact with the other surface of the paper and that prints dot image data on the other surface by energizing a plurality of heating elements;
A reception buffer for storing print data received from the host device;
A first image buffer for storing dot image data for printing on one side of the paper;
A second image buffer for storing dot image data for printing on the other side of the paper;
The print data in the reception buffer is sequentially developed into dot image data from the beginning, and a certain amount thereof is stored in the first image buffer. After this storage, the remaining print data in the reception buffer is sequentially converted into dot images. First control means for developing the data and storing it in the second image buffer;
Number energized pixels determined the sum of the number of energizing pixels in the dot image data stored number energized pixels of the dot image data stored in the first image buffer and to said second image buffer to determine whether more than a threshold value Means,
A mode setting means for setting an asynchronous mode when the total pixel number is determined to exceed the threshold value by the energized pixel number determining means;
When the asynchronous mode is set by this mode setting means, the energization time required for printing one dot line data by the first thermal head and the energization time required for printing one dot line data by the second thermal head overlap. Second control means for controlling the energization cycle of the first thermal head and the second thermal head so as not to become
When the synchronous mode is set by the mode setting means, the first thermal head and the second thermal head so that at least part of the energization time for the first thermal head and the energization time for the second thermal head overlap. Third control means for controlling the energization cycle of
A thermal printer characterized by comprising: The second control means sets the energization cycle of the first thermal head and the second thermal head to be twice or more the energization time required for printing one dot line data, and the first thermal head and the second thermal head The thermal printer according to claim 1, wherein the energization cycle is shifted by approximately ½ cycle between the thermal printer and the thermal printer. The second control means sets the energization cycle of the first thermal head and the second thermal head to be twice or more the energization time required for printing one dot line data, and the first thermal head and the second thermal head. 2. The thermal printer according to claim 1, wherein energization of one of the thermal heads is performed, and energization of the other thermal head is started at a timing when energization of the one thermal head is completed. The thermal printer according to claim 1, further comprising a fourth control unit configured to increase a sheet conveyance speed when the synchronous mode is set to be higher than a sheet conveyance speed when the asynchronous mode is set. A first thermal head that is disposed in contact with one surface of the paper and that prints dot image data on the one surface by energizing a plurality of heating elements, and is disposed in contact with the other surface of the paper. A second thermal head for printing dot image data on the other surface by energizing a plurality of heating elements, a receiving buffer for storing print data received from the host device, and one surface of the paper A thermal printer printing method comprising a first image buffer for storing dot image data for printing and a second image buffer for storing dot image data for printing on the other side of the paper. And
Expanding the print data in the reception buffer into dot image data sequentially from the top and storing the fixed amount in the first image buffer;
After this storage, the step of developing the remaining print data in the reception buffer sequentially into dot image data and storing it in the second image buffer;
A step of sum of the number of energizing pixels in the dot image data stored number energized pixels of the dot image data stored in the first image buffer and to said second image buffer to determine whether more than a threshold value,
Setting the asynchronous mode when it is determined that the sum exceeds the threshold, and setting the synchronous mode when it is determined that the sum does not exceed the threshold;
When the asynchronous mode is set, the energization time required for printing one dot line data by the first thermal head and the energization time required for printing one dot line data by the second thermal head do not overlap. Controlling the energization cycle of the first thermal head and the second thermal head;
When the synchronous mode is set by the mode setting means, the first thermal head and the second thermal head so that at least part of the energization time for the first thermal head and the energization time for the second thermal head overlap. Controlling the energization cycle of
A printing method for a thermal printer, comprising:   When the asynchronous mode is set, the control is performed such that the energization cycle of the first thermal head and the second thermal head is at least twice the energization time required for printing one dot line data, and the first thermal head By shifting the energization period to the second thermal head by approximately ½ period, the energization time required for printing one dot line data by the first thermal head and the one dot line data by the second thermal head are reduced. 6. The thermal printer printing method according to claim 5, wherein the energization time required for printing does not overlap.   When the asynchronous mode is set, the control is performed such that the energization period of the first thermal head and the second thermal head is at least twice the energization time required for printing one dot line data, and the first thermal head and 6. The energization of one of the second thermal heads is performed, and the energization of the other thermal head is started at the timing when the energization of the one thermal head is finished. Thermal printer printing method.   6. The printing method for a thermal printer according to claim 5, further comprising a step of making the paper transport speed when the synchronous mode is set faster than the paper transport speed when the asynchronous mode is set.

Images