JP2007320087A - Thermal printer and its printing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten the peak value duration time of a current necessary for electrification to a first thermal head and a second thermal head. <P>SOLUTION: The thermal printer is equipped with both the first thermal head which is arranged to be in touch with one surface of a paper and performs printing of dot image data to the one surface through electrification to a plurality of heating elements, and the second thermal head which is arranged to be in touch with the other surface of the paper and performs printing of the dot image data to the other surface through electrification to a plurality of heating elements. In the case of printing character strings of the same size and the same line spacing to both surfaces of the thermal paper by the first thermal head and the second thermal head by dot image data, the printer controls so that a printing starting timing of the character strings by the first thermal head and a printing starting timing of the character strings by the second thermal head shift by at least a time necessary for formation of the line spacing. <P>COPYRIGHT: (C)2008,JPO&INPIT

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

  For this reason, in a double-sided thermal printer using two thermal heads, if the two thermal heads are controlled to simultaneously print the same size and character strings between the same lines on both sides of the thermal paper, only one thermal head is used. Compared to the case of a single-sided thermal printer that is not used, the peak value of energy consumption (current) at the time of printing a character string is approximately doubled and continues. 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 energize both thermal heads as much as possible when printing on both sides of the sheet with the first thermal head and the second thermal head. By shifting so as not to overlap, the peak value duration time of the current required for energization of both thermal heads is shortened.

  The present invention is arranged so as to be in contact with one surface of a sheet, a first thermal head that prints dot image data on one surface by energizing a plurality of heating elements, and is in contact with the other surface of the sheet. And a second thermal head that prints dot image data on the other surface by energizing a plurality of heating elements. When a character string between the same size and the same line is printed with dot image data on both sides of the thermal paper by the first thermal head and the second thermal head, the print start timing of the character string by the first thermal head and the second thermal head Control is performed such that the print start timing of the character string by the head is shifted at least by the time necessary for formation between lines.

  According to the present invention in which such a measure is taken, when the first thermal head and the second thermal head perform printing on both sides of the thermal paper, it is possible to reduce the period in which the energization times of both thermal heads overlap, and the energization of both thermal heads. The peak current duration required for the current can be shortened.

Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings.
In this embodiment, the present invention is applied to a thermal printer 10 that performs printing on both sides of the thermal paper 1.

  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.

  A thermal layer is formed on each of the front surface 1A and the back surface 1B of the thermal paper 1. 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 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 (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.

  A host device 30 is connected to the communication interface 16 to generate and supply print data at an appropriate time. 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 driving 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 driving circuit 19 takes in one line data of N dots sequentially input via the bus line 12 and outputs it as serial data to the latch circuit 42 and outputs the latch signal LAT to the latch circuit 42. And a function of outputting an enable signal ENB to the energization control circuit 43.

  The latch circuit 42 latches 1 dot line data output from the head drive circuit 19 at a timing when the latch signal LAT becomes active. In the energization control circuit 43, the heating element corresponding to the print dot in the 1 dot line data latched by the latch circuit 42 is energized 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. The storage capacities of the front surface image buffer 52 and the back surface image buffer 53 are equal.

  Accordingly, the CPU 11 controls double-sided printing on the thermal paper 1 according to the procedure shown in the flowchart of FIG. 5 (printing control means). 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, then the CPU 11 sequentially develops the remaining dot of the print data in ST4 and stores it in the back image buffer 53. If a certain amount of dot data is stored in the back image buffer 53 in ST5, the CPU 11 proceeds to the printing process in 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 print process in ST6. Proceed to

  This printing process is executed according to the procedure shown in the flowchart of FIG. First, the CPU 11 resets both the front surface line counter A and the rear surface line counter B to “0” as ST11. The front surface line counter A and the rear surface line counter B are formed in the RAM 14, for example.

  Next, in step ST12, the CPU 11 operates the paper feed motor 23 for one step to feed the thermal paper 1 for one line. In ST13, the surface line counter A is incremented by "1". In ST14, the first dot line data of the A line corresponding to the value of the surface line counter A is read from the surface image buffer 52 and transferred to the first head driving circuit 19. As a result, the first dot line data of the A line is latched by the latch circuit 42 of the first thermal head 2 in synchronization with the latch signal LAT. Next, in the first thermal head 2, the heating element corresponding to the print dot in the one dot line data latched by the latch circuit 42 is energized while the enable signal ENB is active. Thus, 1-line dot data for the A-line is printed on the surface 1A of the thermal paper 1.

  Therefore, the CPU 11 determines whether or not the surface line counter A exceeds the first set value P in ST15. The first set value P will be described later. When the surface line counter A does not exceed the first set value P, the CPU 11 returns to the process of ST12. Each time the thermal paper 1 is fed by one line, the front line counter A is incremented by “1”, and the first dot line data of the A line corresponding to the value of the front line counter A is read from the front surface image buffer 52. The process of transferring to the first head drive circuit 19 is repeated.

  Thus, if it is confirmed that the front surface line counter A exceeds the first set value P, the CPU 11 counts up the rear surface line counter B by “1” in ST16. In ST17, the first dot line data of the B line corresponding to the value of the back surface line counter B is read from the back surface image buffer 53 and transferred to the second head drive circuit 20. As a result, the first dot line data of the B line is latched by the latch circuit 42 of the second thermal head 4 in synchronization with the latch signal LAT. Next, in the second thermal head 4, the heating element corresponding to the print dot in the one dot line data latched by the latch circuit 42 is energized while the enable signal ENB is active. Thus, 1-line dot data of the B-th line is printed on the back surface 1B of the thermal paper 1.

  Therefore, the CPU 11 determines whether or not the surface line counter A has reached the second set value Q that is larger than the first set value P in ST18. The second set value Q will also be described later. If the surface line counter A has not reached the second set value Q, the CPU 11 returns to the process of ST12. Each time the thermal paper 1 is fed by one line, the front line counter A is incremented by “1”, and the first dot line data of the A line corresponding to the value of the front line counter A is read from the front surface image buffer 52. And the back line counter B is incremented by “1”, and the first dot line data for the B line corresponding to the value of the back line counter B is obtained from the back image buffer 53. The process of reading and transferring to the second head drive circuit 20 is repeated.

  Thereafter, if it is confirmed that the front surface line counter A has reached the second set value Q, the CPU 11 determines whether the back surface line counter B has reached the second set value Q in ST19. If not reached, the paper feed motor 23 is operated in one step as ST20 to feed the thermal paper 1 by one line, and the process returns to ST15. That is, the back surface line counter B is incremented by “1”, and the first dot line data of the B line corresponding to the value of the back surface line counter B is read from the back surface image buffer 53 and transferred to the second head drive circuit 20. repeat.

  In this way, if it is confirmed that the back surface line counter B has reached the second set value Q, the CPU 11 clears the front surface image buffer 52 and the back surface image buffer 53 as ST21 and ends the current printing process.

  When the printing process of ST6 is completed, the CPU 11 determines whether or not print data remains in the reception buffer 51 as ST7. If print data remains, the processes of ST2 to ST7 are executed again. If no print data remains in ST7, the CPU 11 performs a long feed of the thermal paper 1 and then outputs a drive signal to the cutter motor 24 in ST8 to operate the cutter mechanism 6 so that both the front and back sides are operated. Cut the printed thermal paper. Thus, the process for receiving the print data is completed.

  Now, an example of printing in the present embodiment is schematically shown in FIG. In this example, a character string between the same size and the same line (the contents of the data to be printed need not be the same) is printed in a plurality of lines, and reference numeral 61 in the figure denotes printing on the surface 1A side of the thermal paper 1. An example is shown, and reference numeral 62 indicates an example of printing on the back surface 1B side. In the figure, an arrow 63 indicates the direction in which the thermal paper 1 is conveyed.

  In the figure, the interval indicated by the symbol d indicates the number of lines in the direction parallel to the paper transport direction of the dot line data forming the character string, and one line of character string is formed by 1 dot line data for d lines. It means that it is formed. Similarly, the space | interval shown by the code | symbol h has shown the number of lines required in order to form the space | interval between character strings, and it is line spacing by 1 dot line data (all non-printing dots) for h lines. Means that it is formed. The interval indicated by symbol g is a gap formed by the number of lines ½ (rounded up after the decimal point) of the value obtained by adding the number of lines d corresponding to the size of the character string and the number of lines h corresponding to the space between the lines. Show.

  In this case, the first setting value P used in the process of ST15 of the printing process shown in FIG. 6 is 1 which is a value obtained by adding the number of lines d corresponding to the character string size and the number of lines h corresponding to the line spacing. / 2, that is, a value equal to the number of lines g. The second set value Q used in the process of ST18 of the process is set to the number of lines of dot image data that can be developed in the front image buffer 52 and the back image buffer 53 of the same size.

  By setting the first and second set values P and Q as described above, as shown in FIG. 7, first, the first thermal head 2 is energized from the first line to the g-th line, and thermal The dot data of the first line of the character string is printed on the front surface 1A of the paper 1. At this time, the second thermal head 4 is not energized.

  Next, when the g-th line is printed by the first thermal head 2, the front line counter A exceeds the first set value P, so the printing operation on the back surface 1 </ b> B by the second thermal head 4 is also started. . Thereby, the first thermal head 2 and the second thermal head 4 are energized, respectively, and dot data of a character string is printed on the front surface 1A and the back surface 1B of the thermal paper 1.

  However, the first thermal head 2 is not energized in the line feed section having the number h of lines until the character string having the line number d is printed on the front surface 1A and the next character string is printed. Similarly, the second thermal head 2 is not energized in the line feed section with the number h of lines until the character string with the line number d is printed on the back surface 1B and the next character string is printed.

  Thus, the peak value of the energization current to the first thermal head 2 and the second thermal head 4 changes as shown in FIG. In the figure, reference numeral 71 indicates dot image data printed on the surface 1A by the first thermal head 2, in which hatched portions indicate character strings and unhatched portions indicate line spacing. . Reference numeral 72 indicates dot image data printed on the back surface 1B by the second thermal head 4. Similarly, the hatched portion in the figure indicates a character string, and the non-hatched portion indicates a line spacing. Yes.

  For reference, the change in the peak value of the energization current in the case of single-sided printing in which the same character string is printed on only one side of the paper with one thermal head is shown in FIG. The change of the peak value of the energization current in the case of double-sided printing in which similar character strings are simultaneously printed on both sides is shown in FIG.

  As is apparent from FIG. 8, the period during which both the first thermal head 2 and the second thermal head 4 are energized simultaneously and the peak value of the energization current increases to I2 is the energization time required for printing one line of character strings. The time required for forming a line break is shorter than that. That is, according to the present embodiment, there is an effect that the peak value of the energization current can be suppressed to the same level I1 as in the case of single-sided printing in most periods.

  Incidentally, when the same character string is simultaneously printed on both sides of the paper with two thermal heads (FIG. 8C), the character string is printed in one line during the period when the peak value of the energization current increases to I2. Therefore, the power supply time corresponding to the energization time required is required. For this reason, it has been an obstacle to lowering the price and size of the apparatus, but this embodiment can solve such a problem.

  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, as a method for controlling the character string printing start timing by the first thermal head 2 and the character string printing start timing by the second thermal head 4 to be shifted at least for the time required for formation between the lines, The number of printed dot lines from the start of printing of the character string by the first thermal head 2 is counted by the surface line counter A. The number of printed dot lines is the number of dot lines necessary for forming the character string and the line spacing. When it reaches approximately ½ (= g) of the sum of the number of dot lines required for formation h (= g), the second thermal head 4 is controlled to start printing a character string. Starts printing the character string, counts the number of printed dot lines with the back surface line counter B, and the number of printed dot lines is the dot line necessary for forming the character string. Upon reaching the approximately 1/2 (= g) of the sum of the dot line number h required for the formation of several d and rows, the first thermal head 2 may be controlled so as to start printing the character string.

  Further, the number of print dot lines after the printing of the character string is started by either one of the first thermal head 2 and the second thermal head 4 is counted, and this number of print dot lines is formed between lines. When the number h of dot lines necessary for the above is reached, the other thermal head may be controlled to start printing the character string. That is, the first set value P may be set to a value equal to the number of lines h between rows.

  A printing example of the front surface 1A and the back surface 1B of the thermal paper 1 in this case is schematically shown in FIG. This example is also a case in which a plurality of character strings of the same size and the same line are printed. Reference numeral 81 in the figure indicates a printing example on the front surface 1A side of the thermal paper 1, and reference numeral 82 indicates a printing example on the back surface 1B side. Is shown. In the figure, an arrow 83 indicates the conveyance direction of the thermal paper 1.

  As shown in the figure, first, the first thermal head 2 is energized from the first line to the h-th line, and the dot data of the first line of the character string is printed on the surface 1A of the thermal paper 1. At this time, the second thermal head 4 is not energized.

  Next, when the first thermal head 2 prints the h-th line, the front line counter A exceeds the first set value P, so the printing operation on the back surface 1B by the second thermal head 4 is also started. . Thereby, the first thermal head 2 and the second thermal head 4 are energized, respectively, and dot data of a character string is printed on the front surface 1A and the back surface 1B of the thermal paper 1.

  However, the first thermal head 2 is not energized in the line feed section having the number h of lines until the character string having the line number d is printed on the front surface 1A and the next character string is printed. Similarly, the second thermal head 2 is not energized in the line feed section with the number h of lines until the character string with the line number d is printed on the back surface 1B and the next character string is printed. Therefore, the same operational effects as those of the above embodiment can be obtained.

  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.

  By the way, in the above embodiment, 1-dot line data of a character string is transferred to the first head driving circuit 19 corresponding to the first thermal head 2 and the second head driving corresponding to the second thermal head 4 is performed. Similarly, when 1 dot line data of a character string is transferred to the circuit 20, the enable signal ENB is simultaneously output to the first thermal head 2 and the second thermal head 4, and both heads 2 and 4 are energized simultaneously. There is a problem that the peak value of energy consumption (current) becomes high. Such a problem is that the energization time required for printing one dot line data by the first thermal head 2 and the energization time required for printing one dot line data by the second thermal head 4 do not overlap. 2 and the energization cycle of the second thermal head 4 may be controlled (energization control means).

  Then, next, the first thermal head 2 and the first thermal head 2 are arranged so that the energization time required for printing one dot line data by the first thermal head 2 and the energization time required for printing one dot line data by the second thermal head 4 do not overlap. Another embodiment in which the energization cycle of the second thermal head 4 is controlled will be described with reference to FIGS.

  FIG. 10 is a diagram showing a timing chart of main signals in the other embodiment. 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 surface 1A side of the thermal paper 1, that is, the first thermal head 2. (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, a drive 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.

  An example of dot printing in this case is schematically shown in FIG. In the drawing, a print example 91 on the left side shows a print example on the front surface 1A side by the first thermal head 2, and a print example 92 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 93 indicates a printing dot, and the white circle 94 indicates a non-printing dot. Note that the symbol d indicates the dot length of the print dot 93 in the paper transport direction 95.

  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. 11, 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, the time during which the enable signal ENB1 for the first thermal head 2 is active and the time during which the enable signal ENB2 for the second thermal head 2 is active are controlled so as not to overlap. 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.

  The first thermal head 2 and the second thermal head 2 do not overlap the energization time required for printing one dot line data by the first thermal head 2 and the energization time required for printing one dot line data by the second thermal head 4. The method for controlling the energization cycle of the thermal head 4 is not limited to this.

  FIG. 12 is a diagram showing a timing chart of main signals in still 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 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. FIG. 7 is a flowchart specifically showing a procedure of printing processing in FIG. 6. FIG. FIG. 5 is a schematic diagram showing an example of character string data printed on the front and back surfaces of the thermal paper in the embodiment. The figure which shows the relationship between the peak value of the energization current to the 1st thermal head and the 2nd thermal head, and time in the embodiment compared with the conventional method. The schematic diagram which shows an example of the character string data each printed on the surface and the back surface of the thermal paper in other embodiment of this invention. The figure which shows the example of 1 timing of the main signal in other embodiment of this invention. The schematic diagram which shows the example of dot printing when controlling at the timing of FIG. The figure which shows the other example of timing of the main signal in other embodiment of this invention.

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 (6)

A first thermal head that is arranged 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 disposed so as to be in contact with the other surface of the paper and performing dot image data printing on the other surface by energizing a plurality of heating elements;
In the case where the first thermal head and the second thermal head print character strings of the same size and the same line on both sides of the thermal paper with dot image data, the print start timing of the character strings by the first thermal head and the Print control means for controlling the character string printing start timing by the second thermal head so as to shift at least the time necessary for forming between the lines;
A thermal printer characterized by comprising:   The print control means counts the number of print dot lines after the printing of the character string is started by one of the first thermal head and the second thermal head, and the number of print dot lines is When the sum of the number of dot lines necessary for forming the character string and the number of dot lines necessary for forming between the rows is reached, control is performed so that printing of the character string is started by the other thermal head. The thermal printer according to claim 1.   The print control means counts the number of print dot lines after the printing of the character string is started by one of the first thermal head and the second thermal head, and the number of print dot lines is 2. The thermal printer according to claim 1, wherein when the number of dot lines necessary for forming the line spacing is reached, the other thermal head is controlled to start printing a character string. The first thermal head and the second thermal head are arranged so that the energization time required for printing one dot line data by the first thermal head does not overlap with the energization time required for printing one dot line data by the second thermal head. Energization control means for controlling the energization cycle with the head;
The thermal printer according to claim 1, further comprising: 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 printing method for a thermal printer comprising a second thermal head for printing dot image data on the other surface by energizing a plurality of heating elements,
In the case where the first thermal head and the second thermal head are used to print the character string between the same size and the same line on both sides of the thermal paper with dot image data, whichever of the first thermal head and the second thermal head The number of printed dot lines from the start of character string printing by one of the thermal heads is counted, and this number of printed dot lines is necessary for the number of dot lines necessary for forming the character string and for the formation between the lines. When it reaches 1/2 of the sum of the number of dot lines, printing of the character string is started by the other thermal head, so that the printing start timing of the character string by the first thermal head and the character string by the second thermal head are increased. The starter of printing is shifted at least by the time required for formation between lines Printing method of printer. 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 printing method for a thermal printer comprising a second thermal head for printing dot image data on the other surface by energizing a plurality of heating elements,
When the first thermal head and the second thermal head print character strings of the same size and the same line on both sides of the thermal paper with dot image data, whichever of the first thermal head and the second thermal head The number of printed dot lines after the printing of the character string by one of the thermal heads is counted, and when the number of printed dot lines reaches the number of dot lines necessary for the formation between the lines, the other thermal head By starting the printing of the character string, the printing start timing of the character string by the first thermal head and the printing start timing of the character string by the second thermal head are shifted at least by the time necessary for formation between the lines. A printing method for a thermal printer.

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