JP2010208346A - Thermal printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make so as not to generate printing density difference and not to bring about printing deviation at divided places even in case of printing by STB splitting. <P>SOLUTION: In a thermal printer in which a line type thermal head composed by disposing a large number of heating elements in a line state is divided into a predetermined number of printing blocks to print, a means for variably changing times t1', t2', and t3' of applying respective strobe signals STB1 to STB3 for turning on the divided respective printing blocks are provided. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

Embodiments described herein relate generally to a thermal printer that divides a line thermal head into a plurality of print blocks by a strobe signal and performs printing.

  In general, in order to print using a line-type thermal head, it is necessary to prepare a power source capable of supplying a large current for energizing all the printing dots of one line simultaneously. However, in a small printer, a large-sized power source cannot be built in the main body, and thus a small-sized and small-capacity power source is incorporated. Then, one line of the thermal head is divided into a plurality of printing blocks corresponding to the power source, the current is divided for each printing block, and the current flowing at one time is limited to drive the thermal head. ing.

  Further, since power is supplied from the battery in the portable printer, the power supply capacity that can be supplied is limited, and thus the thermal head is divided and energized. Note that dividing one line of the thermal head into a plurality of printing blocks and applying power is generally “dividing and applying with a strobe (STB) signal”, or simply “STB dividing” or “applying a plurality of STBs”. Also called.

  However, when printing is performed by applying power by STB division in this way, even if the energization time of each divided STB application is the same, there is a difference in print density for each divided printing dot group was there. For example, as shown in FIG. 11, when power is applied by STB division when printing the number “12345”, there is a difference in print density at the middle part of the number “3” in the middle. There was a case that occurred. This is due to the following reason.

  Each print dot of the thermal head is a heating element of a resistor, and printing is performed by applying heat generated by heating each resistor to the thermal paper to cause color development. The heat generation energy P is obtained by the product of the applied voltage V, the current I, and the energization time t. In the case of a portable printer, the power supply voltage is supplied from the battery, the applied voltage V is small, and the supplyable current I is Since it is limited, it is necessary to lengthen the energization time t by STB application in order to supply sufficient printing energy. As a result, since the printing speed is slow, a difference in printing density is likely to occur between printing blocks.

  As described above, in a printer with a low printing speed, the difference in printing density tends to appear more as the printing speed becomes slower. In addition, when the printing speed is slow, the printing density is greatly affected by the behavior of the stepping motor used for transporting the paper, and a difference may appear in the printing density. That is, when the paper is conveyed by one step by the stepping motor, each print dot group divided into a plurality of times is in contact with the paper when STB is applied. Since a difference appears in the amount of heat transferred from the paper to the paper, a difference appears in the print density. This will be specifically described below.

  FIG. 12A is a diagram showing the relationship between the elapsed time from the start of application and the moving distance of the thermal head when printing is performed by applying STB by dividing one line of the thermal head into three. As shown in (B) of the figure, each of the three divided STB signals respectively from time T0 to T1 (time t1), time T1 to T2 (time t2), and time T2 to T3 (time t3), respectively. STB1, STB2, and STB3 which are negative logic STB signals (overline is added in FIG. 12B for negative logic) are sequentially applied. Then, as is clear from the movement distance when each STB signal is applied, the movement of the paper when the first STB signal STB1 is applied is actually a very slight movement of the paper. The speed is different from the movement when the subsequent STB signals STB2 and STB3 are applied.

  Also, comparing the paper transport speed when STB1 is applied and when STB3 is applied, the movement distance varies greatly when STB1 is applied, and the paper moves at a high speed, but the movement distance varies when STB3 is applied. There are few and it is almost a stop state. Therefore, at this time, printing is performed at substantially the same location on the sheet. The amount of heat applied to the same portion of the paper is greater in the latter when it is applied during the movement of the paper (when STB1 is applied) and when it is applied during the stop (when STB3 is applied). For this reason, even if STB is applied with the same printing energy supplied, a difference in print density results, and the print density becomes higher when STB3 is applied than when STB1 is applied.

  When STB1 is applied, printing is started from the moving distance 0, and when STB2 is applied, printing is started from the moving distance X. When STB is divided and one line is printed, the first STB application (STB1) is performed. Then, there is a problem in that the sheet moves between the application of STB and the next application of STB (STB2), thereby causing a printing deviation when printing is performed by applying each STB. Therefore, there is a problem that printing cannot be performed on the same line with respect to the sheet, and the printing line is shifted to cause a step as shown in FIG.

  The embodiment of the present invention has been made to solve the above-described problems. In a printer having a thermal head that performs STB division printing, even if printing is performed by STB division, the divided portions are divided. It is an object to prevent a difference in print density and a print deviation from occurring.

  The thermal printer of the embodiment includes a delay unit, a variable unit, and a thermal printer that divides and prints a line-type thermal head in which a large number of heating elements are arranged in a line by a strobe signal. Is provided. The delay means delays the timing of applying the first strobe signal with respect to the drive timing of the paper feed motor when the line-type thermal head is driven by applying a strobe signal to each of the divided print blocks. The variable means applies a strobe signal to each of the divided print blocks so that a print cycle for printing one print line is not delayed for a time delayed by a timing for applying the first strobe signal. Variable application time.

FIG. 1 is a block diagram illustrating a configuration of an embodiment of a thermal printer. FIG. 2 is a block circuit diagram showing the internal configuration of the thermal head. FIG. 3 is a timing chart showing application timing of each strobe signal to each printing block of the thermal head shown in FIG. FIG. 4 is a timing chart for explaining a first example of strobe signal application control in the thermal printer according to the present embodiment. FIG. 5 is a timing chart for explaining a second example of strobe signal application control. FIG. 6 is a timing chart for explaining a third example of strobe signal application control. FIG. 7 is a timing chart for explaining a fourth example of strobe signal application control. FIG. 8 is a timing chart for explaining a fifth example of strobe signal application control. FIG. 9 is a timing chart for explaining an example of strobe signal application control when a highly sensitive supply is used. FIG. 10 is a timing chart showing an example of strobe signal application control when control is performed to delay the application timing of the first STB signal STB1. FIG. 11 is a diagram illustrating an example of printing by a conventional thermal printer. FIG. 12 is a timing chart for explaining an example of strobe signal application control in a conventional thermal printer.

  Hereinafter, the present embodiment will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing the internal configuration of the thermal printer. The thermal printer according to the present embodiment includes a microprocessor unit (MPU) 1, a motor drive circuit 2, a paper transport motor 3, an STB application time control circuit 4, an STB division control circuit 5, an image transfer circuit 6, a thermal head 7, an image. The memory 8 and the program memory 9 are included.

  The MPU 1 is an ultra-compact processing device that controls the entire thermal printer according to the present embodiment. The MPU 1 executes processing according to a control program stored in the program memory 9 and relates to the application of the strobe signal in the present embodiment. Also fulfills the control function.

  The motor drive circuit 2 is a circuit for inputting a motor phase signal from the MPU 1 and step-driving the paper transport motor 3. The paper transport motor 3 is a stepping motor and is step-driven by the motor drive circuit 2 to transport the paper.

  The STB application time control circuit 4 is a timer circuit that controls the timing of applying the strobe signal and the applied pulse width to each print block of the thermal head 7 divided into a predetermined number of print blocks by the strobe signal. The STB division control circuit 5 is a circuit that divides the strobe signal applied to each print block of the thermal head 7 into a plurality of parts on the time axis and controls the division.

  The image transfer circuit 6 is a circuit that reads out image data stored in the image memory 8 and transfers it to the thermal head 7. The thermal head 7 is a line type thermal head in which a large number of heating elements are arranged in a line, and the internal configuration will be described in detail later.

  The image memory 8 is a memory that stores image data to be printed by the thermal head 7, and the program memory 9 is a memory such as an EPROM that stores a control program executed by the MPU 1.

  As shown in FIG. 2, the thermal head 7 has a plurality of print blocks to which strobe signals are respectively applied, and a shift register 13 is connected to each print block via a latch register 12. The number of printing blocks is six. Moreover, it has the thermistor 14 which detects temperature.

  Each printing block has one end connected to the voltage application terminal VH, and controls the heating resistor groups 11a to 11b at the other ends of the heating resistor (heating element) groups 11a to 11f that form printing dots. The NAND gates 10a to 10f are connected to each other, and each of the NAND gates 10a to 10f is connected to one input terminal of each of the STB signals STB1 to STB6 (in FIG. 2, an overline is attached for negative logic). Are input via a NOT circuit (inverter), and the output of the latch register 12 is input to the other input terminal.

Each of the heating resistor groups 11a to 11f includes only one heating resistor in FIG. 2, but actually includes a plurality of heating resistors. Normally, 2 ⁿ heating resistors such as 64 dots or 128 dots, where n is a natural number, are energized.

  The latch register 12 is a circuit that holds the data of each bit input to the shift register 13 at the input timing of the latch signal LAT (indicated by an overline in FIG. 2 for negative logic). The shift register 13 is a shift register for inputting print data DI to be printed by the thermal head 7 from the image transfer circuit 6 shown in FIG. 1, and receives the print data DI in synchronization with the clock signal CLK. Is output.

  Next, the printing operation in the thermal printer having the above configuration will be specifically described. In the above thermal printer, the thermal head 7 has a plurality of printing blocks divided for each STB signal. Therefore, when printing is performed by the thermal head 7, the timing for applying the STB signal to each printing block is divided and ordered. The STB signal is applied to. A timing chart in that case is shown in FIG.

  In FIG. 3, after print data DI for printing is inputted to the shift register 13 in synchronization with the clock signal CLK, the data for all the dots of one line of the thermal head is inputted, and then the latch signal LAT is inputted to the latch register 12 of FIG. Entered. Subsequent to the input of the latch signal LAT, negative logic STB signals STB1 to STB6 are sequentially input. Corresponding to the input of each STB signal, the NAND gates 10a to 10f of each print block are opened for a predetermined time when each STB signal is input, and can be energized, and the print data held in the latch register 12 is changed. Accordingly, the heating resistors 11a to 11f forming the respective printing blocks are sequentially and selectively heated to perform printing.

  At this time, the STB signals STB1 to STB6 are controlled by the STB application time control circuit 4 based on the behavior of the paper according to the driving state of the paper transport motor 3 shown in FIG. 1 at the timing of applying the STB signal to each print block. However, the application times ta to tf of the STB signals STB1 to STB6 are made variable so that the thermal energy given to the paper to be printed becomes constant, and have different lengths. In FIG. 3, the application times ta to tf appear to be the same, but this shows the case of the reference state, which changes based on this.

  Conventionally, the application time of each STB signal STB1 to STB6 has been set to an equal value, but by making each variable in this way, even when the STB signal is divided and printed, the print density for each print block can be increased. Printing can be performed without changing. Therefore, a first example of STB signal application control by the STB application time control circuit 4 shown in FIG. 1 will be described with reference to FIG. FIG. 4A is a diagram showing the relationship between the elapsed time from the start of application and the movement distance of the thermal head 7 when printing is performed by applying STB to the thermal head 7.

As shown in this figure, during the period from time T0 to time T1 ′, the sheet is moving immediately after the start of movement, and the movement distance is long. ′ Indicates that the moving distance is short and the sheet is substantially stopped. Therefore, the application time t1 ′ is set longer than the application times t2 ′ and t3 ′ as shown in FIG. In this example, the relationship between the lengths of the application times t1 ′, t2 ′, and t3 ′ is as follows.
t1 '>t2'> t3 '

  In this way, when applying STB1 with a long moving distance, the energization time is lengthened so that the print density does not become thin. On the other hand, when applying STB2, STB3 with a short moving distance, the energizing time is shortened and the print density does not become dark. Thus, the print density can be adjusted as described above, and the difference in print density does not occur as a whole.

  Next, a second example of STB signal application control by the STB application time control circuit 4 shown in FIG. 1 will be described with reference to FIG. In this case, the first STB signal STB1 is not applied at time T0 in FIG. 5, and is applied at the timing of time T1 ″.

  That is, the timing of applying the STB signal STB1 applied first is delayed with respect to the timing of driving the paper transport motor 3, and the subsequent STB signals STB2, STB3, etc. are also sequentially delayed. In this way, the first STB signal STB1 is applied to the place where the movement distance is short and the behavior of the paper is settled (where the movement of the paper is substantially stopped).

Therefore, printing by applying each STB signal is performed at substantially the same position in the paper conveyance direction, so that it is possible to prevent the printing dots from shifting. In this case, the relationship between the lengths of the application times t1 ″, t2 ″ and t3 ″ is as follows.
t1 ″ = t2 ″ = t3 ″

  As described above, when the timing of applying the first STB signal STB1 is delayed, the time for printing one print line (printing cycle, indicated by t5 in FIG. 5) delays the application timing of STB1. That is, it becomes longer than the printing cycle t4 (shown in FIG. 4) when the timing of applying STB1 is not delayed. Therefore, the STB application time control circuit 4 may change the application time of each STB signal so that the printing cycle is not delayed.

  In this case, as in the third example shown in FIG. 6, the first STB signal STB1 is applied at the time point T1g when the sheet conveyance speed has slowed to some extent, and then the STB2 and STB3 are sequentially applied. Also in this case, the application times t1g, t2g, and t3g of the first STB signal STB1 and the second and third STB signals STB2 and STB3 are changed.

This is because the timing of applying / STB1 is delayed according to the moving speed of the paper, and the printing cycle until the next printing line is printed is made equal to t4. In this example, the relationship between the lengths of the application times t1g, t2g, and t3g is as follows.
t1g>t2g> t3g

  When FIG. 6A is compared with FIG. 5A, the timing at which STB1 is applied is slightly advanced, and STB1 is applied while the paper movement distance is somewhat longer. The conveyance speed itself is considerably slow, and the sheet has already been conveyed to a position near a predetermined stop position.

  Therefore, even if the first STB signal STB1 is applied at the time T1g, the printing deviation is reduced. In addition, since the times t1g, t2g, and t3g of each STB signal change according to the behavior of the paper, there is no difference in print density, and there is no delay in the print cycle, so the print speed is also affected. There will be no.

  Next, a fourth example of STB signal application control will be described with reference to FIG. This example is executed by the STB application time control circuit 4 and the STB division control circuit 5 in FIG. That is, as shown in FIG. 7B, each STB signal is divided into a plurality (four in this example) on the time axis, and the STB signals STB1 to STB3 divided on the time axis are each printed block. Are applied alternately.

  As shown in FIG. 7, each divided STB signal STB1, STB2, STB3 is applied at each time from time T0 to T6, T7, T8, T9. Therefore, the first STB signals STB1, STB2, and STB3 divided from the time point T0 are sequentially applied with the pulse width t6, and the second STB signal STB1 divided at the pulse width t6 is similarly applied from the next time point T6. , STB2, STB3 are sequentially applied. That is, the time for applying one STB signal is divided into four times.

  For this reason, in the prior art, a print shift corresponding to the elapsed time t1 for applying STB2 has occurred between STB signals STB1 and STB2, but as shown in FIG. By dividing into a plurality of parts, only the printing deviation corresponding to ¼ of the elapsed time t1, that is, the pulse width t6 is sufficient, so the printing deviation width is reduced. In addition, the print density difference is reduced to 1/4 of the print density difference corresponding to the elapsed time t1.

  Next, a fifth example of STB signal application control will be described with reference to FIG. This example is also executed by the STB application time control circuit 4 and the STB division control circuit 5 in FIG. Each STB signal divided by the above-described fourth example can vary the pulse width corresponding to the application time under the control of the STB application time control circuit 4.

  That is, from the time T0 shown in FIG. 8A, the first divided STB signals STB1, STB2, and STB3 shown in FIG. 8B are sequentially applied with the pulse width t7, and the next time T6. ', The divided second STB signals STB1, STB2, STB3 are sequentially applied with a pulse width t8.

  From the next time T7 ', the divided third STB signals STB1, STB2, STB3 are sequentially applied with a pulse width t9, and from the next time T8', the divided fourth STB signals STB1, STB2, STB3 is sequentially applied with a pulse width t10. The magnitude relationship among the pulse widths t7, t8, t9, and t10 is set to satisfy t7 <t8 <t9 <t10.

  This is because immediately after the paper conveyance motor 3 starts moving, the moving speed of the paper is fast, so the pulse width t7 of the divided STB signal applied first is made small (narrow), and as shown in FIG. As in the case, the printing deviation is reduced. This prevents a difference in print density from occurring for each print line as a whole.

  In this case, not only is the magnitude relationship between the pulse widths t7, t8, t9, and t10 set so that t7 <t8 <t9 <t10, but the sum of t7, t8, t9, and t10 is applied to STB1 before division. It is good to set it equal to time t1. As a result, the printing deviation can be reduced and the printing density unevenness can be reduced.

  As described above, the thermal printer according to the present embodiment can change the time for applying the STB signal by the STB application time control circuit 4 and the STB division time control circuit 5 controlled by the MPU 1 shown in FIG. Although the control is performed, a circuit capable of performing all the above-described control is not necessarily mounted because of the limitation on the performance of the MPU 1 or the shortage of the timer circuit. In particular, in the case of a small portable printer, manufacturing cost and size are limited, so that there are many cases where all of them cannot be mounted.

  Therefore, in the case where there is such a restriction, the configuration in which the application time of each STB signal described with reference to FIG. 4 which is easy to control by the STB application time control circuit 4 and has a simple configuration is made variable is described with reference to FIG. A configuration may be adopted in which the timing of applying STB1 that is the first STB signal is delayed.

  Further, the energy applied to the thermal head 7 differs depending on the supply used, and therefore, all of the above-described controls may not necessarily be effective control means. For example, when a highly sensitive supply is used, since the supply is highly sensitive, the STB signal application time may be short. Therefore, as shown in FIG. 9, the STB signal STB1 to STB3 application time t1h is short. Thus, the printing cycle t4h is shorter than in the conventional case. Thus, the printing speed is increased.

  In this case, in order to eliminate the occurrence of the print density difference and the occurrence of the print deviation, if control for delaying the timing of applying the first STB signal STB1 is performed, the timing of applying the STB1 is delayed. As shown in FIG. 10, there is a problem that the printing cycle t4s becomes long. Therefore, if the STB signal application time is varied in order to solve this problem, even if the occurrence of the print density difference can be eliminated, it is difficult to settle the movement of the paper, so that the print deviation cannot be completely eliminated. .

  Therefore, if the control corresponding to the fourth example shown in FIG. 7 or the control corresponding to the fifth example shown in FIG. 8 cannot be performed due to a problem in the control of the MPU 1, the second example shown in FIG. Control corresponding to the first example or the second example shown in FIG. 5 is performed. In this case, even when the application time of the first STB signal STB1 is delayed, when the influence on the printing speed is small, that is, when the printing speed is slow, the control corresponding to the second example is performed and the printing speed is fast. Can perform control corresponding to the first example.

  If a selection means is provided to allow the user of the thermal printer to arbitrarily select the means for performing this control, the selection means can select either one according to the control contents of the MPU 1. it can. For example, when the service man mode (turning on the power while pressing the setting key on the operation panel not shown) is started and “STB control” is selected, the various control modes shown in the above embodiment are expressed. , You can choose any of them.

  For example, when priority is given to the printing speed, the control corresponding to the first example is selected, or even when the printing speed is slow, the printing quality is prioritized by eliminating the printing deviation. The selection corresponding to the second example can be performed. In this way, since printing can be performed by any means according to the content to be printed and the purpose of use, the printer is easy to use and easy to use.

  As described above, according to the present embodiment, in a printer that prints using a line-type thermal head, the application time of each STB signal for energizing each divided print block can be varied. The signal application time can be changed according to the actual paper conveyance speed. Therefore, a print density difference does not occur for each print block divided by each STB signal, and the print quality can be improved.

  Further, by delaying the timing of applying the first STB signal with respect to the driving timing of the paper transport motor, the STB signal can be applied according to the behavior of the paper. Therefore, a print density difference does not occur for each divided print block, and no print misalignment occurs when divided.

  Furthermore, if each STB signal is divided along the time axis and applied alternately to each STB, both the print density difference and the print deviation can be further reduced as compared with the case where the STB signals are applied all at once.

  Then, if it is possible to select whether to vary the application time of each STB signal or to delay the timing to apply the first STB signal with respect to the drive timing of the paper transport motor, the operation status and the print contents Since either one can be selected according to the printing, the printer is easy to use and easy to use.

1 Microprocessing unit (MPU)
DESCRIPTION OF SYMBOLS 2 Motor drive circuit 3 Paper conveyance motor 4 STB application time control circuit 5 STB division | segmentation control circuit 6 Image transfer circuit 7 Thermal head 8 Image memory 9 Program memory 10a-10f NAND gate 11a-11f Heating resistor element group 12 Latch register 13 Shift Register 14 thermistor

Claims (2)

In a thermal printer that prints by dividing a line-type thermal head in which a large number of heating elements are arranged in a line into a predetermined number of print blocks by a strobe signal,
Delay means for delaying the timing of applying the first strobe signal to the drive timing of the paper feed motor when driving the line thermal head by applying a strobe signal to each of the divided print blocks;
The application time for applying the strobe signal to each of the divided print blocks is varied so that the printing cycle for printing one print line is not delayed for the time when the timing for applying the first strobe signal is delayed. Variable means;
A thermal printer characterized by comprising: The moving speed of the paper moved by the paper feed motor within the printing cycle becomes slower with the passage of time from the start of paper movement,
The thermal printer according to claim 1, wherein the variable unit varies the application time according to a moving speed of the sheet.

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