JP2010221488A - Method and apparatus for forming image - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To digitally compensate for an individual difference in resistance value between the heating elements of a thermal head. <P>SOLUTION: In a method for forming an image on a medium 3 by use of the plurality of heating elements arranged in a line, at least one of the heating elements which form on-dots forms a main dot 51 and at least one of sub-dots 52a to 52d in series on the medium 3, each sub-dot being smaller than the main dot 51. The number of sub-dots 52a to 52d from which at least one is selected can be changed according to a difference in resistance value between the heating elements, the resistance value being the ability of each of the heating elements to form dot. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method and an apparatus for generating an image using an image generating element such as a thermal head.

  Japanese Patent Application Laid-Open No. 2004-228561 describes that accurate density correction is performed on the basis of resistance value correction and print data actually printed. For this reason, in Patent Document 1, the resistance value of the heating resistor of the thermal head is measured by the resistance value measuring means, and applied according to the resistance value for each dot measured by the resistance value measuring means by the resistance value correcting means. It is described that correction data is calculated so that the energy becomes constant, and the drive signal of the thermal head is corrected with this correction data.

JP 05-008421 A

  In many cases, a DA circuit is required to drive the thermal head in order to control the applied energy to be constant according to the resistance value for each dot by changing the pulse width and voltage of the drive signal. The circuit tends to be large. Therefore, it is desirable that the influence on the image quality due to the variation of the resistance value for each dot can be suppressed digitally.

  One embodiment of the present invention is a method for generating an image on a medium using a plurality of dot generation elements arranged in a line. This method includes that at least one of the plurality of dot generation elements that generate on dots generates a main dot and at least one sub-dot smaller than the main dot in series on the medium. The number of the at least one sub dot is variable depending on the difference in dot forming ability of each of the plurality of dot generation elements. According to this method, the individual difference in dot formation ability of a plurality of dot generation elements, for example, the individual difference in the electrical resistance value of the heating element and the individual difference in the inkjet nozzles are influenced in series before and after the main dot. This can be suppressed by changing the number of subdots generated. The direction in which the main dots and the sub dots are arranged in series is preferably the sub-scanning direction if it is a line head, and is preferably the scanning direction if it is a serial head.

Preferably, the method includes the following steps before the generation in series (the generation in series).
-Measure the dot formation capability of each of the multiple dot generation elements.
The number of sub-dots generated by each of the plurality of dot generation elements together with the main dot is stored in the memory by the dot formation capability of each of the plurality of dot generation elements.

  Dot formation capability of multiple dot generation elements when generating an image by measuring the dot formation capability of multiple dot generation elements and storing the number of subdots in memory according to each dot formation capability It is possible to suppress the influence of the difference in

  The calibrating steps including measuring and storing in memory may be performed at an appropriate timing, for example, at the factory shipment stage, and then repeated periodically. During the image generation job, by repeating the steps including measuring and storing in memory at appropriate intervals, eg, on a page basis, the dot formation capability during image generation The influence on the image quality of the temporal change, for example, the heat history of the heating element can be suppressed.

For a line thermal head including a plurality of heating elements, the step of generating in series desirably includes the following steps.
Supplying a first strobe signal for generating a main dot to a plurality of dot generating elements;
Supplying a plurality of second strobe signals shorter than the first strobe signal to the plurality of dot generating elements for generating at least one sub-dot before and after the first strobe signal.

  One of the different aspects of the present invention is an apparatus having a signal supply unit that supplies a signal for generating an image on a medium to a plurality of dot generating elements arranged in a line. The signal supply unit includes a first signal for generating a main dot in an element that generates an on dot among a plurality of dot generation elements, and at least one sub-dot smaller than the main dot before and after the main dot. A unit for generating a second signal to be generated in series on the medium. The number of the at least one sub dot is variable depending on the difference in dot forming ability of each of the plurality of dot generation elements. Therefore, individual differences in the dot formation ability of a plurality of dot generation elements, for example, individual differences in electrical resistance values of heating elements in the case of a line thermal head, and individual differences in inkjet nozzles in the case of a line inkjet head. Can be suppressed by changing the number of sub-dots generated in series before and after the main dot.

  The apparatus further measures the dot forming ability of each of the plurality of dot generating elements, and the dot forming ability of each of the plurality of dot generating elements allows each of the plurality of dot generating elements to generate sub dots generated together with the main dot. It is desirable to have a calibration unit that stores the number in memory. The dot formation capability of a plurality of dot generation elements can be measured before or during generation of an image, and the number of subdots can be set accordingly. Therefore, it is possible to suppress the influence on the image quality of individual differences in the dot formation capability of the plurality of dot generation elements, including changes with time in dot formation capability, in the on-job.

  The apparatus further includes, for a plurality of dot generation elements, a first strobe signal for generating a main dot, and a first strobe signal for generating at least one subdot before and after the first strobe signal. It is desirable to have a strobe signal generation unit that generates and supplies a plurality of second strobe signals shorter than one strobe signal. The first signal and the second signal of the signal supply unit can be signals for selecting the first strobe signal and the second strobe signal, respectively.

  One of the different aspects of the present invention is an image generation apparatus, for example, a printer, having the above-described apparatus and a plurality of dot generation elements.

FIG. 2 is a diagram illustrating a schematic configuration of a printer. The dot (FIG. 2 (a)) formed in the medium, and the figure which expands and shows it (FIG.2 (b)). The block diagram which shows schematic structure of a thermal head and a control unit. The figure which shows the content of LUT which converts the voltage value corresponding to the resistance value of a heat generating element into the number of subdots. The timing chart which shows the process which measures the resistance value of a heat generating element. The figure which shows the truth table of a decoder. 6 is a timing chart showing a process of forming main dots and sub dots. 6 is a flowchart illustrating a method for generating an image with a printer.

  FIG. 1 shows a schematic configuration of a thermal printer as an example of an image generation apparatus. The printer 1 includes a line-type thermal head 10 in which a plurality of heating elements 11 are arranged in a line, a platen roller 4 for feeding a medium (recording medium) 3, a motor 5 for driving the platen roller 4, and these And a control device 20 for controlling. The control device (control unit) 20 acquires data for printing an image including various contents such as pictures and characters from a host device 9 such as a personal computer, and prints the data on the medium 3 using the thermal head 10. To do.

  FIG. 2A shows a part of the medium 3 printed by the thermal printer 1. On the medium 3, dots 50 for forming an image are generated by the heating elements 11 arranged in a line (L direction). If the medium 3 is thermal paper, the dots 50 are formed on the surface of the medium 3 by the thermal energy supplied from the heating element 11. If the printer 1 is a sublimation type (thermal transfer, sublimation transfer) printer, the dots 50 are generated by the ink discharged from the ink ribbon or the like to the medium 3 by the heat energy of the heating element 11.

  FIG. 2B shows the dot 50 in an enlarged manner. One dot 50 includes one large dot (main dot) 51 and several small dots (subdots) 52 a to 52 d arranged in series with the main dot 51. The number of sub-dots 52a to 52d constituting one dot 50 is arbitrary. In this example, in addition to one main dot 51, one unit of dot 50 is formed by a maximum of four sub-dots 52a to 52d. . In this example, the area of one main dot 51 is drawn approximately equal to the total area of the four sub dots 52a to 52d, but the area ratio or intensity ratio of the main dot 51 and the sub dots 52a to 52d is It can be decided without limitation.

  The sub dots 52a to 52d are for interpolating the dot forming ability of the heat generating element 11 as a dot generating element, that is, the individual difference in the heat generation amount (resistance value). As the heating element 11 has a higher resistance value and is more likely to generate heat, the dot forming ability is higher, and the output of the heating element 11 becomes larger, and a dark black or other color dot 50 can be generated. In this printer 1, the difference in color density due to the difference in resistance value of the heating element 11 is compensated by the spread in the area direction by adding and outputting the sub-dots 52 a to 52 d.

  In the printer 1, data is allocated so that the main dot 51 and the two sub dots 52 a and 52 b are generated by the heat generating element 11 having a standard heat generation amount (resistance value). Therefore, for the heating element 11 having a large resistance value and a large amount of heat generation, data is assigned so that the main dot 51 and one sub dot 52a are generated or only the main dot 51 is generated. On the other hand, data is assigned to the heat generating element 11 having a small resistance value and a small heat generation amount so that the main dot 51 and three or four sub dots 52a to 52c or 52a to 52d are generated. Therefore, in this printer 1, the difference in resistance value of each heating element 11 is compensated by a five-step digital process of “0-4” whether or not to generate the four subdots 52a to 52d. be able to.

  In the line thermal head 10, the heating elements 11 are arranged in the scanning direction L, and the dots 50 are formed by the same heating elements 11 in the sub-scan directions C <b> 1 to C <b> 4. Therefore, in a specific sub-scan direction, for example, in the sub-scan line C4, when the heating element 11 forms an on-dot, the main dot 51 and the sub-dot are set according to the dot formation capability (resistance value) of the heating element 11. When 52a to 52d are always generated and no on dot is formed (OFF), neither the main dot 51 nor the sub dots 52a to 52d are generated.

  FIG. 3 shows the thermal head 10 and the control unit 20 extracted from the printer 1. The thermal head 10 receives and serially generates heating elements (heating elements, dot generation elements) 11 arranged in a plurality of lines and on / off data (energization data) φ1 supplied to each of the plurality of heating elements 11. A shift register (data holding element) 12 for parallel conversion, a latch circuit 13 for latching energization data φ1 supplied to the shift register 12, and an energization data φ1 of the latch circuit 13 by strobe signal φ2 respectively. And a gate circuit 14 for supplying the heating element 11.

  In order to obtain the resistance value of each heating element 11 of the thermal print head, the control unit 20 measures a current value flowing through each heating element 11 and outputs it as a voltage value, and a power source 22 therefor. Based on the AD circuit 23 for converting the voltage value obtained by the current measuring mechanism 21 into a digital value and the resistance value of each heating element 11, the number of sub dots generated by each heating element 11 is set in the memory 75. And a calibration unit 25. In this printer 1, the calibration unit 25 is provided by a program that operates on the LSI 24, but may be provided by an appropriate electronic circuit.

  The calibration unit 25 includes a measurement unit 26 that performs control for measuring the resistance value of each heating element 11, a determination unit 27 that sets the number of subdots based on the measured resistance value (corresponding voltage value), and measurement. And the LUT 28 indicating the assignment of the number of subdots to the corresponding voltage value in this example. As shown in FIG. 4, the LUT 28 stores in advance the number of subdots (variation value) 28b corresponding to the AD converted voltage value 28a.

  The measurement unit 26 includes a measurement data generation unit 26b that outputs data (measurement energization data) φ3 for obtaining a voltage value of the heating element 11, and a strobe signal supply unit 26a that generates a measurement strobe signal φ4. Including. The determination unit 27 refers to the LUT 28 and determines the number of sub-dots 52a to 52d to be generated together with the main dot 51 when it is turned on for each heating element 11 based on the measured resistance value (corresponding voltage value). Then, it is stored in the memory (register) 75 of the energization data generation unit 70 described below.

  FIG. 5 shows measurement energization data φ3 and measurement strobe signal φ4. At time t1, only the 0th (dot 0) heating element 11 is turned on (low potential) and all the other heating elements 11 are turned off (high potential). The latch circuit 13 latches at time t2. At time t3, the low potential strobe signal φ4 is supplied, and only the low potential side gate circuit 14 of the 0th heating element 11 is opened. As a result, power is supplied from the power source 22 only to the 0th heating element 11, and the measurement unit 26 can acquire a voltage value corresponding to the resistance value of the 0th heating element 11. By repeating this process up to the (n-1) th heating element 11, the resistance values of the 0th to (n-1) th heating elements 11 can be obtained. The number of subdots 52 a to 52 d for compensation can be stored in the register 75.

  Returning to FIG. 3, the control unit 20 further includes a signal supply unit 60 that supplies a signal for generating dots on the medium (recording medium) 3 by the thermal head 10 to the thermal head 10. The signal supply unit 60 includes a first signal φ11 for generating a main dot 51 in an element that generates an on dot among a plurality of heating elements (dot generation elements) 11, and a main signal 51 before and after the main dot 51. A unit (energization data generation unit) 70 that generates a second signal φ12 for generating at least one sub-dot 52a to 52d smaller than the dot 51 in series on the medium 3 is included. As described above, in each heating element 11, the number of sub-dots 52 a to 52 d generated before and after the main dot 51 is variable depending on the difference in heating capability (resistance value) of each heating element 11. .

  The signal supply unit 60 further includes at least one sub-dot 52a to 52d before and after the first strobe signal φ21 and the first strobe signal φ21 for generating the main dot 51 by the plurality of heating elements 11. For generating a plurality of second strobe signals φ22a to φ22d shorter than the first strobe signal φ21. The energization data generation unit 70 and the strobe signal generation unit 80 operate under the control of the print control unit 65 mounted on the LSI 24 by software.

  The energization data generation unit 70 includes at least one main register 71 that holds image generation data for generating dots by the first to (n-1) th heating elements 11 for one line (one scan); And a selector 72 for reading on / off data of each dot from the main register 71. The main register 71 stores image data for one line (dot on / off data) from the host 9 via the print control unit 65. The on / off data of the main register 71 becomes the first signal φ11 for generating the main dot 51.

  The energization data generation unit 70 further holds sub data for generating sub dots 52a to 52d by one line (one scan), that is, the 0th to (n-1) th heating elements 11. A register 75, a selector 76 for reading out the compensation data φ5 of each dot from the subregister 75, and a decoder for generating on / off data of the subdots 52a to 52d corresponding to the second strobe signals φ22a to φ22d from the compensation data φ5 of each dot And a selector circuit 77.

  FIG. 6 shows a truth table of the decoder 77 a of the decoder and selector circuit 77. The circuit 77 includes an input side decoder 77a and a selector 77b. The input of the decoder and selector circuit 77 (input of the decoder 77 a) is 3-bit compensation data φ 5, and is input to the sub-register 75 by the resistance value (corresponding voltage value) of each heating element 11 measured by the determination unit 27. Set. The output of the decoder and selector circuit 77 (the output of the selector 77b) is energized to generate subdots that are set in the thermal head 10 before the first to fourth second strobe signals φ22a to φ22d are output. Data (second signal) φ12. The 0th output is data for outputting the main dot 51.

  The energization data generation unit (circuit) 70 further includes a dot number counter 73 that controls the selectors 72 and 76 and a strobe number counter 78 that controls the decoder and selector circuit 77. The energization data generation unit 70 includes a gate circuit 79 that outputs the second signal φ12 that generates the subdots 52a to 52d only when the first signal φ11 that generates the main dot 51 is on. The first signal φ11 for generating the main dot 51 is output through by the 0th output of the decoder and selector circuit 77, and the second signal φ12 for generating the subdots 52a to 52d is the first signal φ11. Output only when on.

  The strobe signal generation unit (circuit) 80 operates based on the data input end signal φ 6 supplied from the print control unit 65. The strobe signal generation unit 80 includes a register 81 in which holding times of the first strobe signal φ21 and four second strobe signals φ22a to φ22b having a holding time shorter than that of the first strobe signal φ21 are set, and a register 81 A selector 82 that selects one of the stored holding times, a strobe number counter 83 that controls the selector 82, a strobe time counter 85, and a comparator 86 that compares the selected holding time with the time counter 85. Including. The strobe signal generation unit 80 includes a buffer 89 that inverts the strobe signal. When the data input end signal φ 6 of the print control unit 65 is output and the energization data φ 1 for generating dots is latched by the latch circuit 13, the strobe time counter 85 is cleared, and the time of the time selected from the register 81 is cleared. A strobe signal φ2 is generated and output.

  FIG. 7 is a timing chart showing how the main dot 51 and the sub dots 52a to 52d are generated. The dots generated in this figure correspond to those in FIGS. 2 (a) and 2 (b). In this thermal head 10, since the low voltage side of the heat generating element 11 is switched, the dot is turned on when the strobe signal φ2 and the energization data φ1 are “0”. In the energization data signal φ1 in FIG. 7, the on-dot signal is shown with a diagonal line, and the off-dot signal is shown without a diagonal line.

  At time t11, a first signal φ11 for generating the main dot 51 is supplied from the signal supply unit 60 of the control unit 20 to the thermal head 10, and is latched by the latch circuit 13 at time t12. At the same time, a first strobe signal φ 21 for generating the main dot 51 is supplied from the signal supply unit 60 to the thermal head 10. Therefore, the main dot 51 is generated on the medium 3 by the heating element 11 to which the first signal φ11 for generating the on-dot is supplied among the plurality of heating elements 11 of the thermal head 10.

  When the first strobe signal φ21 is increased, at time t13, the second signal φ12a for generating the first sub-dot 52a is supplied to the thermal head 10 from the signal supply unit 60 of the control unit 20, and at time t14. Latched by the latch circuit 13. At the same time, a second strobe signal φ 22 a for generating the first sub dot 52 a is supplied from the signal supply unit 60 to the thermal head 10. The second strobe signal φ22a has a shorter holding time than the first strobe signal φ21, and is, for example, about a fraction. For this reason, among the plurality of heating elements 11 of the thermal head 10, the first heating element 11 to which the signal φ12a for generating the ON sub-dot is supplied is smaller than the main dot 51 (small in area). Sub-dots 52a are generated in series in the sub-scan direction following the main dots 51 on the medium 3. Similarly, the second to fourth sub dots 52b to 52d smaller than the main dot 51 are generated, and the process of generating the next main dot 51 is started at time t21.

  FIG. 8 is a flowchart showing a process in which the printer 1 generates an image on the medium 3 using dots. In step 91, it is determined whether a calibration process for measuring the resistance of the heating element 11 and setting the number of subdots is necessary. For example, when it is determined that the calibration process is necessary, for example, when the printer 1 is started, when a new job is started in the printer 1, a certain amount of media, for example, one medium is included in the same job. For example, when printing is performed, or when a predetermined time has elapsed from the start of the job by a timer. In many cases, it is desirable to incorporate a calibration process as an initial process for a job. Further, when the printer 1 is required to print with high image quality and it is necessary to improve the image quality in consideration of changes over time such as thermal history, the calibration process is periodically repeated at an appropriate timing during printing. It is desirable to do.

  If calibration is required, the measurement unit 26 of the calibration unit 25 measures the resistance value of each element 11 in step 92, and the determination unit 27 is suitable for compensating the obtained resistance value in step 93. The number of subdots is set in the register (memory) 75. In step 94, the same processing is repeated for all the heating elements 11 of the thermal head 10.

  If the calibration process is completed or no calibration process is required, an image generation process is performed in step 95. First, the energization data generation unit 70 of the signal supply unit 60 sets image generation data in the thermal head 10 by the first signal (first energization data) φ11. In step 96, the strobe signal generation unit 80 of the signal supply unit 60 generates and supplies the first strobe signal φ 21, whereby the main dot 51 is generated on the medium 3.

  Subsequently, in step 97, the energization data generation unit 70 of the signal supply unit 60 sets the first compensation data in the thermal head 10 by the second signal (second energization data) φ12a. In step 98, the strobe signal generation unit 80 of the signal supply unit 60 generates and supplies the first second strobe signal φ22a. The second strobe signal φ22a has a shorter holding time than the first strobe signal φ21. Accordingly, the first sub-dot 52 a smaller than the main dot 51 is generated on the medium 3. Steps 97 and 98 are repeated until the fourth sub-dot 52d is generated in step 99.

  As described above, according to the image generation method employed in the printer 1, the individual difference in the dot formation ability of the plurality of heating elements (dot generation elements), in this case, the individual difference in the value of the electric resistance is determined as the main dot 51. Can be suppressed by changing the number of sub-dots 52a to 52d generated in series. Therefore, it is possible to compensate for individual differences in the dot formation ability of the dot generation elements with a digital value such as the number of subdots. For this reason, it is possible to compensate for individual differences in dot formation capability with a simple circuit configuration for circuits that need to control analog elements such as pulse width and pulse voltage, and through processing that matches well with software, and to improve image quality. It can be improved. It is also possible to combine the process of compensating for individual differences using subdots with the process of improving image quality using analog elements.

  In the above description, the case where the number of subdots is four is described. However, the number of subdots is not limited to four, and may be three or less or five or more. In addition, the subdots do not have to be generated behind the main dots, the subdots may be generated in front of the main dots, and the subdots may be generated separately in the front and rear with the main dot as the center.

  In addition, the above description is based on a line thermal type printer in which the head does not move in the scan direction, but individual differences are also compensated for by combining the main dot and sub dot for serial printers in which the head moves in the scan direction. Processing to do is applicable. Furthermore, although the thermal printer has been described above, similarly, an ink jet type printer in which individual differences may occur in the amount and direction of ejection due to nozzles (ink jet nozzles) that are dot generation elements, in particular, The image quality of a printed image can be improved by applying the present invention to a line inkjet type printer. Further, the printer is not limited to a personal printer, and may be a multifunction machine or a business printing machine.

1 Printer, 3 Recording media
10 thermal head, 11 heating element 51 main dot, 52a to 52d sub-dot

Claims (10)

A method of generating an image on a medium by a plurality of dot generating elements arranged in a line,
At least one of the plurality of dot generation elements that generate on dots generates a main dot and at least one sub-dot smaller than the main dot in series on the medium;
The method, wherein the number of the at least one sub-dot is variable depending on a difference in dot formation ability of each of the plurality of dot generation elements. In claim 1, prior to generating in series,
Measuring the dot forming ability of each of the plurality of dot generating elements;
The method further comprising: storing, in a memory, the number of sub-dots that each of the plurality of dot generation elements generates together with the main dot according to the dot formation capability of each of the plurality of dot generation elements. In claim 2,
The method further comprising periodically repeating the measuring and storing in the memory. In any one of Claim 1 thru | or 3, These dot production | generation elements are several heat generating elements contained in a line thermal head,
The dot forming ability of each of the plurality of dot generation elements is a value of an electric resistance of each of the plurality of heating elements. In Claim 4, the generating in series includes supplying a first strobe signal for generating the main dots to the plurality of dot generating elements;
Before and after the first strobe signal, a plurality of second strobe signals shorter than the first strobe signal for generating the at least one subdot are supplied to the plurality of dot generation elements. Including a method. An apparatus having a signal supply unit for supplying a signal for generating an image on a medium to a plurality of dot generating elements arranged in a line,
The signal supply unit includes a first signal for generating a main dot in an element that generates an on dot among the plurality of dot generation elements, and at least one smaller than the main dot before and after the main dot. A unit for generating a second signal for generating two subdots in series on the medium,
The apparatus, wherein the number of the at least one subdot is variable depending on a difference in dot formation ability of each of the plurality of dot generation elements.   7. The dot formation capability of each of the plurality of dot generation elements is measured according to claim 6, and each of the plurality of dot generation elements is generated together with the main dot by each dot formation capability of the plurality of dot generation elements. The apparatus further comprising a calibration unit that stores the number of subdots in memory. In Claim 6 or 7, the plurality of dot generation elements are a plurality of heating elements included in a line thermal head,
The dot formation capability of each of the plurality of dot generation elements is an electric resistance value of each of the plurality of heating elements.   9. The signal supply unit according to claim 8, wherein the at least one dot supply element includes a first strobe signal for generating the main dot and a first strobe signal before and after the first strobe signal. An apparatus comprising: a strobe signal generation unit for generating a plurality of second strobe signals shorter than the first strobe signal for generating subdots. An apparatus according to any of claims 6 to 9,
An image generation apparatus comprising the plurality of dot generation elements.

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