JP2007021780A - Printer and method for printing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printer capable of suppressing variation in density. <P>SOLUTION: This printer comprises a correction section for correcting a printing gradation value designated within a prescribed range determined by designatable minimum and maximum gradation values. The printer further comprises a head which has an element for performing an operation to eject ink and ejects ink whereby a drive signal corresponding to a size of a dot to be formed is applied to the element. The printer is equipped with a drive signal generation section that generates a drive signal for forming a dot with a size different from that of a dot which can be formed in the case where a post-correction printing gradation value is within the prescribed range when the post-correction printing gradation value corrected by the correction section exceeds the prescribed range. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a printing apparatus and a printing method.

  Examples of so-called inkjet printing apparatuses that perform printing by discharging ink from a head include printers, plotters, and facsimiles. In this type of printing apparatus, there is an apparatus that controls the operation of an element included in a head by a drive signal and ejects ink by varying the amount for each gradation (for example, see Patent Document 1). In this apparatus, control is performed with four gradations including non-dot formation, small dots, medium dots, and large dots. For this reason, four types of drive signals are generated and applied to the element.

Also, there is a printing apparatus that samples an image with a CCD sensor and outputs digitized data with an inkjet printer (see, for example, Patent Document 2). In order to correct density unevenness, the characteristics of gain unevenness of the CCD sensor are stored as coefficients, and the characteristics of density unevenness of the head are stored as coefficients, and binarization processing is performed in consideration of these coefficients. .
Japanese Patent Laid-Open No. 10-193857 Japanese Patent Laid-Open No. 2-54676

  In the above-described printing apparatus, variations in the processing accuracy of the nozzles may cause an abnormality in the ink ejection amount, and the flight direction of the ink ejected from the nozzles may cause landing deviation in the paper feed direction. In some areas, dots are formed such that the density is high and the density appears to be low in some areas, resulting in density unevenness. In such a case, it may be possible to suppress the density unevenness by correcting the print gradation value within a predetermined print gradation value range for a specific area where the density unevenness occurs. When there is a large influence of density, density unevenness may not be suppressed.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a printing apparatus capable of suppressing density unevenness that occurs even when correction is performed within a predetermined printing gradation value range. It is in.

The main invention for achieving the object is as follows:
(A) a head that has an element that operates to eject ink, and that applies a drive signal corresponding to the size of a dot to be formed to the element, thereby ejecting ink;
(B) a correction unit for correcting a print gradation value designated within a predetermined range determined by a minimum gradation value and a maximum gradation value that can be designated;
(C) When the corrected print gradation value corrected by the correction unit exceeds the predetermined range, the size is different from the dots that can be formed when the corrected print gradation value is within the predetermined range. A drive signal generation unit that generates a drive signal for forming the dots of
Is a printing apparatus.

  Other features of the present invention will become apparent from the description of this specification and the accompanying drawings.

=== Summary of disclosure ===
At least the following matters will become apparent from the description of this specification and the accompanying drawings.

It has an element that operates to eject ink, and a drive signal corresponding to the size of the dot to be formed is applied to the element, whereby a head that ejects ink, a minimum gradation value and a maximum that can be specified A correction unit for correcting a printing gradation value designated within a predetermined range determined by the gradation value, and when the corrected printing gradation value corrected by the correction unit exceeds the predetermined range, A printing apparatus comprising: a drive signal generation unit configured to generate a drive signal for forming a dot having a size different from a dot that can be formed when the corrected print gradation value is within the predetermined range.
According to such a printing apparatus, when the gradation is outside the range of the print gradation value due to the correction of the print gradation value, a dot having a size corresponding to the print gradation value outside the range is generated. Density unevenness can be suppressed.

In such a printing apparatus, the drive signal generation unit is disposed between an original drive signal generation unit that generates an original drive signal having a plurality of waveform units that operate the element, and the original drive generation unit and the element. Preferably, a switch for generating a drive signal to be applied to the element from the original drive signal and a switch controller for controlling the operation of the switch based on the corrected print gradation value are provided.
According to such a printing apparatus, the drive signal generation unit can be configured using the original drive signal generation unit, the switch, and the switch controller.

In the printing apparatus, the drive signal generation unit further includes a switch operation information storage unit that stores switch operation information for determining the operation of the switch, and the switch controller includes the corrected print tone value. Preferably, a selection unit that selects corresponding switch operation information is provided.
According to such a printing apparatus, the switch operation information can be selected based on the corrected print gradation value.

In the printing apparatus, the drive signal generation unit may include a first dot, a second dot larger than the first dot, and the second dot when the corrected print gradation value is within the predetermined range. A drive signal for forming a third dot larger than the second dot is generated, and when the corrected print gradation value exceeds the predetermined range, a dot larger than the third dot, or It is preferable to generate a drive signal for forming a dot smaller than the first dot.
According to such a printing apparatus, when the corrected print gradation value exceeds a predetermined range, a dot larger than the third dot or a dot smaller than the first dot is formed, and density unevenness is formed. Can be suppressed.

In this printing apparatus, it is preferable that the minimum gradation value that can be specified is 0 and the maximum gradation value that can be specified is 255.
According to such a printing apparatus, the predetermined range can be determined with the minimum gradation value that can be specified as 0 and the maximum gradation value that can be specified as 255.

In the printing apparatus, the head discharges the ink when the drive signal is applied to the element while the head is moving in a predetermined direction. It is preferable that the print gradation value is corrected based on correction data that is configured by a plurality of unit regions arranged in a predetermined direction and that is prepared for each row region aligned in another predetermined direction that intersects the predetermined direction.
According to such a printing apparatus, density unevenness can be suppressed by correcting the print gradation value based on the correction data prepared for each row region.

In the printing apparatus, it is preferable that the correction unit includes a memory that stores a correction program and a CPU that operates according to the correction program.
According to such a printing apparatus, the correction unit can be realized by executing the correction program on the CPU.

Also, a printing apparatus having the following configuration can be realized. That is, it has an element that performs an operation for ejecting ink, and while moving in a predetermined direction, a drive signal corresponding to the size of a dot to be formed is applied to the element, whereby the ink is discharged. A correction unit for correcting a printing gradation value designated within a range defined by an ejection head, 0 that is a minimum gradation value that can be designated, and 255 that is a maximum gradation value, and a correction program And a CPU that operates according to the correction program, and is prepared for each row region that is configured by a plurality of unit regions arranged in the predetermined direction and that is arranged in another predetermined direction intersecting the predetermined direction. A correction unit that corrects the print gradation value based on the corrected data, and the corrected printing when the corrected print gradation value corrected by the correction unit exceeds the range. A drive signal generation unit that generates a drive signal for forming a dot having a size different from a dot that can be formed when the gradation value is within the range, and includes a plurality of waveform units that operate the element. An original drive signal generator for generating a drive signal, a switch disposed between the original drive generator and the element, and for generating a drive signal applied to the element from the original drive signal; and the switch A switch operation information storage unit that stores switch operation information for determining the operation of the printer, and a selection unit that selects corresponding switch operation information based on the corrected print gradation value, and controls the operation of the switch A switch controller, and when the corrected print tone value is within the range, the first dot, the second dot larger than the first dot, and the second dot Drive signal for forming a third dot that is larger than the first dot, and when the corrected print tone value exceeds the range, the dot that is larger than the third dot or the first dot It is also possible to realize a printing apparatus including a drive signal generation unit that generates a drive signal for forming small dots.
According to such a printing apparatus, since almost all the effects described above are exhibited, the object of the present invention is achieved most effectively.

A step of correcting a print gradation value designated within a predetermined range determined by a minimum gradation value and a maximum gradation value that can be designated; and the corrected print gradation value subjected to the correction is within the predetermined range. Generating a drive signal for forming a dot having a size different from a dot that can be formed when the corrected print gradation value is within the predetermined range when exceeding, and a size of the dot to be formed A printing method including a step of ejecting ink by applying a drive signal according to the above to the element can also be realized.
According to such a printing method, when the gradation is outside the range of the printing gradation value due to the correction of the printing gradation value, a dot having a size corresponding to the printing gradation value outside the range is generated. Density unevenness can be suppressed.

=== Configuration of Printing Apparatus 100 ===
<About the overall configuration>
First, a printing apparatus 100 according to the present embodiment will be described with reference to FIG. The illustrated printing apparatus 100 includes a printer 1 as a printing apparatus main body and a computer 110 as a printing control apparatus. Here, the printing apparatus main body forms an image by actually ejecting ink. The print control apparatus outputs print data and the like to the printing apparatus main body.

  Specifically, the printing apparatus 100 includes a printer 1, a computer 110, a display device 120, an input device 130, and a recording / reproducing device 140. The printer 1 prints an image on a medium such as paper, cloth, or film. In the following description, a sheet S (see FIG. 3A), which is a typical medium, will be described as an example. The computer 110 is communicably connected to the printer 1. In order to cause the printer 1 to print an image, the computer 110 outputs print data corresponding to the image to the printer 1. Computer programs such as application programs and printer drivers are installed in the computer 110. The display device 120 has a display. The display device 120 is for displaying a user interface of a computer program, for example. The input device 130 is a keyboard 131 or a mouse 132, for example. The recording / reproducing device 140 is, for example, a flexible disk drive device 141 or a CD-ROM drive device 142.

=== Computer 110 ===
<Configuration of Computer 110>
FIG. 2 is a block diagram illustrating configurations of the computer 110 and the printer 1. First, the configuration of the computer 110 will be briefly described. The computer 110 includes the recording / reproducing device 140 and the host-side controller 111 described above. The recording / reproducing apparatus 140 is communicably connected to the host-side controller 111, and is attached to the housing of the computer 110, for example. The host-side controller 111 performs various controls in the computer 110, and the display device 120 and the input device 130 described above are also connected to be communicable. The host-side controller 111 includes an interface unit 112, a CPU 113, and a memory 114. The interface unit 112 is interposed between the printer 1 and exchanges data. The CPU 113 is an arithmetic processing unit for performing overall control of the computer 110. The memory 114 is used to secure an area for storing a computer program used by the CPU 113, a work area, and the like, and includes a RAM, an EEPROM, a ROM, a magnetic disk device, and the like. As described above, computer programs stored in the memory 114 include application programs and printer drivers. The CPU 113 performs various controls according to the computer program stored in the memory 114. The host-side controller 111 operates as a correction unit when the CPU 113 executes a printer driver (that is, a correction program) stored in the memory 114 (described later).

The print data is data in a format that can be interpreted by the printer 1, and includes various command data and dot formation data SI (see FIG. 6). The command data is data for causing the printer 1 to execute a specific operation. The command data includes, for example, command data for instructing paper feed, command data for indicating the carry amount, and command data for instructing paper discharge. The dot formation data SI is data relating to dots of an image to be printed. Here, the dots are formed on the paper S so as to correspond to virtual grids (hereinafter also referred to as unit areas) virtually defined. The dot formation data SI is composed of 2-bit gradation data indicating four gradations. The dot formation data SI includes gradation data [00] (gradation data corresponding to no dot), gradation data [01] (gradation data corresponding to formation of a small dot), and gradation data [ 10] (gradation data corresponding to formation of medium dots) and gradation data [11] (gradation data corresponding to formation of large dots or extra large dots described later). For the gradation data [11], a large dot or an extra large dot is selected by a selection signal S _slct (see FIG. 14) described later.

=== Printer 1 ===
<About the configuration of the printer 1>
Next, the configuration of the printer 1 will be described. Here, FIG. 3A is a diagram illustrating a configuration of the printer 1 of the present embodiment. FIG. 3B is a side view illustrating the configuration of the printer 1 of the present embodiment. In the following description, FIG. 2 is also referred to. As shown in FIG. 2, the printer 1 includes a paper transport mechanism 20, a carriage moving mechanism 30, a head unit 40, an original drive signal generation circuit 50, a detector group 60, and a printer-side controller 70. The original drive signal generation circuit 50 and the printer-side controller 70 are mounted on a common controller board CTR. The head unit 40 includes a head control unit HC and a head 41. In the printer 1, the control target unit, that is, the paper transport mechanism 20, the carriage moving mechanism 30, the head unit 40 (head control unit HC, head 41), and the original drive signal generation circuit 50 are controlled by the printer-side controller 70. That is, the printer-side controller 70 controls the control target unit based on the print data received from the computer 110 and prints an image on the paper S. At this time, each detector of the detector group 60 detects the state of each part in the printer 1 and outputs the detection result to the printer-side controller 70. Upon receiving the detection results from each detector, the printer-side controller 70 controls the control target unit based on the detection results.

  In the printer 1, the original drive signal generation circuit 50, the printer-side controller 70, and the head controller HC correspond to the drive signal generator, and the piezo element PZT included in the head 41 (see FIGS. 4A and 4B). ) Is generated. In addition, each part which comprises a drive signal production | generation part, and the drive signal produced | generated are demonstrated in detail later.

<Regarding the paper transport mechanism 20>
The paper transport mechanism 20 corresponds to a medium transport unit that transports a medium. The paper transport mechanism 20 feeds the paper S as a medium to a printable position, or transports the paper S by a predetermined transport amount in the transport direction. This transport direction is a direction (corresponding to another predetermined direction) that intersects the carriage movement direction described below. 3A and 3B, the paper transport mechanism 20 includes a paper feed roller 21, a transport motor 22, a transport roller 23, a platen 24, and a paper discharge roller 25. The paper feed roller 21 is a roller for automatically feeding the paper S inserted into the paper insertion opening into the printer 1 and has a D-shaped cross section in this example. The carry motor 22 is a motor for carrying the paper S in the carrying direction, and its operation is controlled by the printer-side controller 70. The transport roller 23 is a roller for transporting the paper S sent by the paper feed roller 21 to a printable area. The platen 24 is a member for supporting the paper S from the back side. The paper discharge roller 25 is a roller for carrying the paper S that has been printed.

<About the carriage moving mechanism 30>
The carriage moving mechanism 30 is for moving the carriage CR to which the head unit 40 is attached in the carriage moving direction. The carriage movement direction includes a movement direction from one end side to the other end side and a movement direction from the other end side to the one end side. The head unit 40 has a head 41. Therefore, the carriage movement direction corresponds to the head movement direction (predetermined direction) in which the head 41 moves. The carriage moving mechanism 30 corresponds to a head moving unit that moves the head 41 in a predetermined direction. The carriage moving mechanism 30 includes a carriage motor 31, a guide shaft 32, a timing belt 33, a drive pulley 34, and an idler pulley 35. The carriage motor 31 corresponds to a drive source for moving the carriage CR. The operation of the carriage motor 31 is controlled by the printer-side controller 70. A drive pulley 34 is attached to the rotation shaft of the carriage motor 31. The drive pulley 34 is disposed on one end side in the carriage movement direction. An idler pulley 35 is disposed on the other end side in the carriage movement direction on the opposite side to the drive pulley 34. The timing belt 33 is an annular member whose end is fixed to the carriage CR, and is spanned between a drive pulley 34 and an idler pulley 35. The guide shaft 32 supports the carriage CR in a movable state. The guide shaft 32 is attached along the carriage movement direction. Accordingly, when the carriage motor 31 operates, the carriage CR moves along the guide shaft 32 in the carriage movement direction. Along with this, the head 41 also moves in the head moving direction.

  An ink cartridge IC (see FIG. 3A) for storing ink is mounted on the carriage CR. This ink cartridge IC corresponds to an ink storage container. The ink cartridge IC of the present embodiment includes a black ink cartridge ICk that stores black ink and a color ink cartridge ICc that stores a plurality of color inks.

<About the head unit 40>
The head unit 40 is for ejecting ink toward the paper S. The head unit 40 includes a head 41 and a head controller HC. Here, FIG. 4 is a cross-sectional view for explaining the structure of the head 41. FIG. 5 is a diagram illustrating the arrangement of nozzle rows. For convenience, the head 41 will be described here, and the head controller HC will be described later.

<About the head 41>
The head 41 includes a case 411, a flow path unit 412, and a piezo element PZT. Here, for simplification of description, a portion necessary for ejecting ink from one nozzle Nz will be described.

  The flow path unit 412 includes a flow path forming plate 412a, an elastic plate 412b bonded to one surface of the flow path forming plate 412a, and a nozzle plate 412c bonded to the other surface of the flow path forming plate 412a. . The flow path forming plate 412a is formed with a groove portion serving as a pressure chamber 412d, a through hole serving as a nozzle communication port 412e, a through port serving as a common ink chamber 412f, and a groove portion serving as an ink supply path 412g.

  An adhesive substrate 413 is fixed to the case 411. The bonding substrate 413 is a rectangular plate, and a piezo element PZT is bonded to one surface. An island portion 412j is joined to the tip of the piezo element PZT, and an elastic region is formed by an elastic film 412i around the island portion 412j.

  The piezo element PZT is deformed by applying a potential difference between opposing electrodes. In this example, it expands and contracts in the longitudinal direction of the element. The amount of expansion / contraction is determined according to the potential of the piezo element PZT. The potential of the piezo element PZT is determined by the applied drive signal (portion indicated by a solid line in FIGS. 20A and 20B). Accordingly, the piezo element PZT expands and contracts according to the potential of the applied drive signal.

  When the piezo element PZT expands and contracts, the island portion 412j is pushed toward the pressure chamber 412d or pulled in the opposite direction. At this time, since the elastic film 412i around the island portion is deformed, ink can be efficiently discharged from the nozzle Nz. Such a piezo element PZT corresponds to an element that is charged and discharged by a drive signal and performs an operation for ejecting ink. When the piezo element PZT is used for the head 41, the amount and speed of the ejected ink can be variously controlled according to the shape of the applied drive pulses PS1 to PS4.

  The nozzle plate 412c described above is provided on the sheet facing surface of the head 41. The nozzle plate 412c is provided with a plurality of nozzle rows composed of a plurality of nozzles Nz corresponding to the type of ink. As described above, since this printer 1 can eject four types of ink, four nozzle rows are also provided. In the example shown in FIG. 5, a black ink nozzle row Nk, a cyan ink nozzle row Nc, a magenta ink nozzle row Nm, and a yellow ink nozzle row Ny are provided from the left side of the drawing. Each nozzle row is formed in a state of being aligned in the carriage direction along the transport direction.

<About the head controller HC>
Next, the head controller HC will be described. Here, FIG. 6 is a block diagram for explaining the configuration of the head controller HC. As described above, the head controller HC constitutes a part of the drive signal generator. The head controller HC in this embodiment includes a shift register 81, a latch circuit 82, a control logic 83, a decoder 84, a gate circuit 85, and a head-side switch 86. Each part excluding the control logic 83, that is, the shift register 81, the latch circuit 82, the decoder 84, the gate circuit 85, and the head side switch 86 are provided for each piezo element PZT, that is, for each nozzle Nz. The head controller HC is provided for each ink type. As described above, since this printer 1 can eject four types of ink, four blocks shown in FIG. 6 are provided. Hereinafter, each part which comprises the head control part HC is demonstrated.

  The shift register 81 is for setting the dot formation data SI from the printer-side controller 70. The latch circuit 82 latches the dot formation data SI set in the shift register 81.

  The control logic 83 corresponds to a switch operation information storage unit, and stores switch operation information (q0 to q3 and q3 ') for determining the operation of the head-side switch 86. Then, the stored switch operation information is output while being switched at a timing defined by the latch signal LAT and the change signal CH (see FIG. 7). That is, it outputs in time series. The control logic 83 stores switch operation information for each gradation for each type of dot formation data SI. The switch operation information stored in the control logic 83 will be described later.

The decoder 84 selects the switch operation information for each gradation output from the control logic 83 according to the dot formation data SI latched by the latch circuit 82. That is, the decoder 84 corresponds to a selection unit that selects corresponding switch operation information based on the gradation value indicated by the dot formation data SI. Further, the decoder 84 selects switch operation information based on the selection signal S _slct, and outputs the selected switch operation information to the head side switch 86 through the gate circuit 85. As described above, the switch operation information applied to the head-side switch 86 is selected by the decoder 84. Therefore, it can be said that the decoder 84 outputs the switch operation information corresponding to the dot formation data SI from the plural types of pre-selection switch operation information output simultaneously from the control logic 83 as the post-selection switch operation information.

  The gate circuit 85 is for applying the switch operation information from the decoder 84 and the N-charge signal N_CHG from the printer-side controller 70 to the head-side switch 86. Here, the N-charge signal N_CHG is a forced application signal for applying the original drive signal COM (see FIG. 7) to all the piezo elements PZT belonging to the block, and the potential of the piezo element PZT is expressed as follows. Used to adjust. The N-charge signal N_CHG is an effective signal at the L level. Therefore, when the N-charge signal N_CHG is at the H level, the output level of the gate circuit 85 changes depending on the switch operation information from the decoder 84. On the other hand, when N-charge signal N_CHG is at L level, its output level is at H level regardless of the switch operation information from decoder 84.

  The head-side switch 86 is a switch that operates in accordance with switch operation information input through the gate circuit 85 and the N-charge signal N_CHG. The head-side switch 86 is disposed between the supply line of the original drive signal COM and the piezo element PZT, applies the original drive signal COM to the piezo element PZT in the on state, and blocks the original drive signal COM in the off state. . The supply line for the original drive signal COM is connected to the original drive signal generation circuit 50. For this reason, it can be said that the head-side switch 86 is disposed between the original drive signal generation circuit 50 and the piezo element PZT. When the N-charge signal N_CHG is at the H level, the head-side switch 86 is turned on / off according to the switch operation information selected by the decoder 84, and a necessary portion (that is, the drive signal) in the original drive signal COM is piezo element. Apply to PZT. Therefore, the head side switch 86 corresponds to a switch for generating a drive signal applied to the piezo element PZT from the original drive signal COM.

  Further, the part for controlling the operation of the head-side switch 86, specifically, the shift register 81, the latch circuit 82, and the decoder 84 correspond to a switch controller. The switch controller generates post-selection switch operation information from the dot formation data SI (gradation data) and the pre-selection switch operation information. Note that the shift register 81, the latch circuit 82, the control logic 83, and the decoder 84 will be described later.

<Regarding the Original Drive Signal Generation Circuit 50>
The original drive signal generation circuit 50 generates an original drive signal COM and corresponds to an original drive signal generation unit. Here, the original drive signal COM is a signal that is the basis of the drive signal for driving the piezo element PZT, as can be seen from the above description.

  As shown in FIG. 7, the original drive signal COM is repeatedly generated every repetition period T. This repetition period T can be divided into four periods T1 to T4. The original drive signal COM is generated in the first period signal SS1 generated in the first period T1, the second period signal SS2 generated in the second period T2, and the third period T3 generated in the third period T3. It has a section signal SS3 and a fourth section signal SS4 generated in the fourth period T4. The first section signal SS1 has a drive pulse PS1. The second interval signal SS2 has a drive pulse PS2, the third interval signal SS3 has a drive pulse PS3, and the fourth interval signal SS4 has a drive pulse PS4. These drive pulses PS1 to PS4 correspond to a waveform portion for operating the piezo element PZT, and the shape thereof is determined based on the operation performed by the piezo element PZT.

  The drive pulse PS1, the drive pulse PS3, and the drive pulse PS4 are waveform portions used when ink is ejected from the nozzle Nz. Among these, the drive pulse PS1 and the drive pulse PS4 have the same waveform. When one of the drive pulses PS1 and PS4 is applied to the piezo element PZT, an amount of ink corresponding to the medium dot is ejected from the nozzle Nz. When this ink lands on the paper S, medium dots are formed in the unit area of the paper S. Further, when the drive pulses PS1 and PS4 are applied to the piezo element PZT, an amount of ink corresponding to a large dot is ejected from the nozzle Nz, and a large dot is formed on the paper S. .

  For convenience, the drive pulse PS1 and the drive pulse PS4 are also referred to as medium dot pulses. Further, the drive pulse PS1 is also referred to as a first medium dot pulse, and the drive pulse PS4 is also referred to as a second medium dot pulse.

  The drive pulse PS3 is a drive signal applied to the piezo element PZT when forming a small dot. That is, when this drive pulse PS3 is applied to the piezo element PZT, an amount of ink corresponding to a small dot is ejected from the nozzle Nz. When this ink lands on the paper S, small dots are formed. For convenience, the drive pulse PS3 is also referred to as a small dot pulse.

  On the other hand, the drive pulse PS2 is a pulse for finely vibrating the meniscus (the free surface of the ink exposed at the nozzle portion). That is, when the drive pulse PS2 is applied to the piezo element PZT, a pressure fluctuation that does not eject ink occurs in the ink in the pressure chamber 412d. Thereby, the meniscus is displaced in the nozzle Nz, and the ink near the nozzle Nz is agitated. For convenience, the drive pulse PS2 is also referred to as a fine vibration pulse.

  Such an original drive signal COM is output from the original drive signal generation circuit 50 based on drive signal generation information from the printer-side controller 70. Hereinafter, an operation of generating the original drive signal COM by the original drive signal generation circuit 50 will be described. FIG. 8 is a conceptual diagram for explaining the operation of generating the original drive signal COM.

  The printer-side controller 70 obtains an output voltage for each update cycle τ based on a parameter for generating the original drive signal COM. When generating the original drive signal COM, the printer-side controller 70 obtains a DAC value corresponding to the output voltage (for example, information representing the output voltage as a 10-bit digital value), and the obtained DAC value is described above. The drive signal generation information is output to the original drive signal generation circuit 50 every update cycle τ. In the example of FIG. 8, the DAC value corresponding to the voltage V1 is output at the timing t (n) defined by the clock. Thus, the output of the original drive signal generation circuit 50 becomes the voltage V1 in the update cycle τ (n). Since the DAC values corresponding to the voltage V1 are sequentially output until the update period τ (n + 4), the original drive signal generation circuit 50 continues to output the voltage V1. At the timing t (n + 5), a DAC value corresponding to the voltage V2 is output. As a result, the output of the original drive signal generation circuit 50 drops from the voltage V1 to the voltage V2 in the update cycle τ (n + 5). Similarly, at the timing t (n + 6), the DAC value corresponding to the voltage V3 is output. As a result, in the update cycle τ (n + 6), the output of the original drive signal generation circuit 50 drops from the voltage V2 to the voltage V3. Similarly, since the DAC value is output in the same manner, the voltage output from the original drive signal generation circuit 50 gradually decreases. Then, in the update cycle τ (n + 10), the output of the original drive signal generation circuit 50 becomes the voltage V4. In the original drive signal generation circuit 50, the non-output side terminal is grounded. For this reason, the terminal on the output side has a potential corresponding to the output voltage.

<Regarding the detector group 60>
The detector group 60 is for monitoring the status of the printer 1. As shown in FIGS. 3A and 3B, the detector group 60 includes a linear encoder 61, a rotary encoder 62, a paper detector 63, and a paper width detector 64. The linear encoder 61 is for detecting the position of the carriage CR in the carriage movement direction. The rotary encoder 62 is for detecting the rotation amount of the transport roller 23. The paper detector 63 is for detecting the paper S to be printed. The paper width detector 64 is for detecting the width of the paper S to be printed.

<About the printer-side controller 70>
The printer-side controller 70 controls each unit included in the printer 1. For example, the printer-side controller 70 alternately performs an operation of transporting the paper S by a predetermined transport amount and an operation of intermittently ejecting ink while moving the carriage CR (head 41). Is printing an image. Therefore, the printer-side controller 70 controls the conveyance of the paper S by controlling the rotation amount of the conveyance motor 22. The printer-side controller 70 controls the movement of the carriage CR by controlling the rotation of the carriage motor 31. Further, the dot formation data SI is output to the head control unit HC to perform control for ejecting ink. As described above, the dot formation data SI is used when the drive signal applied to the piezo element PZT is generated from the original drive signal COM. In addition, the printer-side controller 70 also performs control to output a DAC value as voltage designation information to the original drive signal generation circuit 50. As described above, the printer-side controller 70 performs control for generating the original drive signal COM and control for generating the drive signal applied to the piezo element PZT from the original drive signal COM. Therefore, it can be said that the printer-side controller 70 constitutes a drive signal generation unit together with the original drive signal generation circuit 50, the head side switch 86, and the head control unit HC.

As shown in FIG. 2, the printer-side controller 70 includes an interface unit 71, a CPU 72, a memory 73, and a control unit 74. The interface unit 71 exchanges data with the computer 110 which is an external device. The CPU 72 is an arithmetic processing unit for performing overall control of the printer 1. The memory 73 is for securing an area for storing a program of the CPU 72, a work area, and the like, and is configured by a storage element such as a RAM, an EEPROM, or a ROM. Then, the CPU 72 controls each control target unit in accordance with the computer program stored in the memory 73. For example, the CPU 72 controls the paper transport mechanism 20 and the carriage movement mechanism 30 via the control unit 74. For example, control signals for the transport motor 22 and the carriage motor 31 are output. The CPU 72 corresponds to a head control signal (for example, a clock CLK, dot formation data SI, a latch signal LAT, a change signal CH, an N-charge signal N_CHG, and a selection signal S _slct for controlling the operation of the head 41. 6 is output to the head controller HC, and a DAC value for generating the original drive signal COM is output to the original drive signal generation circuit 50.

<About printing operation>
When an image is printed on the paper S by the exemplified printing apparatus 100, a process for generating print data and a process for printing on the paper S based on the print data are performed. A process for generating print data is performed by the computer 110 included in the printing apparatus 100. That is, the CPU 113 included in the host-side controller 111 operates according to the computer program stored in the memory 114 and executes this process. Therefore, this computer program has a code for executing each process. Further, the process for printing on the paper S is performed by the printer 1 included in the printing apparatus 100. That is, the CPU 72 included in the printer-side controller 70 operates according to the computer program stored in the memory 73 and executes this process. Therefore, this computer program has a code for executing each process.

<Processing for generating print data>
First, processing for generating print data will be described. Here, FIG. 9 is a flowchart for explaining processing for generating print data. As shown in FIG. 9, in the processing for generating print data, resolution conversion processing (S901), color conversion processing (S902), gradation value correction processing (S903), halftone processing (S904), rasterization processing ( S905) is performed.

In the resolution conversion process (S901), image data (text data, image data, etc.) is converted into a resolution for printing an image on the paper S (the interval between dots when printing, also referred to as print resolution). It is processing.
The color conversion process (S902) is a process of converting each RGB pixel data of the RGB image data into data having gradation values of multiple levels (for example, 256 levels) represented by the CMYK color space. This color conversion processing is performed by referring to a table (color conversion lookup table) in which RGB gradation values and CMYK gradation values are associated with each other.
In the gradation value correction process (S903), the gradation value of each pixel data (corresponding to the pre-correction printing gradation value) is used as the correction value (corresponding to correction data) of the column region to which the pixel data belongs. ) To obtain a corrected tone value (corresponding to a corrected print tone value). The tone value correction process will be described later.
The halftone process (S904) is a process for converting CMYK pixel data having multi-stage gradation values into small-stage gradation data that can be expressed by the printer 1. That is, this is processing for obtaining dot formation data SI from CMYK pixel data having multi-stage gradation values. By this halftone processing, for example, 2-bit dot formation data SI indicating four gradation values is obtained from CMYK pixel data indicating 256 gradation values.
The rasterization process (S905) is a process for changing the dot formation data SI obtained by the halftone process in the order of data to be transferred to the printer 1. The rasterized dot formation data SI is output to the printer 1 as print data together with the command data described above.

<Processing for Printing on Paper S>
Next, processing performed by the printer 1 to print on the paper S will be described. Here, FIG. 10 is a flowchart for explaining processing performed during printing.

As shown in FIG. 10, in the process for printing on the paper S, a print command reception operation (S1001), a paper feed operation (S1002), a dot formation operation (S1003), a transport operation (S1004), and a paper discharge determination ( S1005), paper discharge processing (S1006), and print end determination (S1007) are performed.
In the print command reception operation (S 1001), the printer-side controller 70 receives a print command from the computer 110 via the interface unit 71. This print command is included in print data transmitted from the computer 110.
The paper feeding operation (S1002) is an operation for moving the paper S to be printed and positioning it at a printing start position (so-called cueing position). In this paper feeding operation, the printer-side controller 70 rotates the paper feeding roller 21 and sends the paper S to be printed to the transport roller 23. Subsequently, the printer-side controller 70 rotates the transport roller 23 to position the paper S sent from the paper feed roller 21 at the print start position.
The dot forming operation (S1003) is an operation for forming dots on the paper S by intermittently ejecting ink from the head 41 moving in the carriage movement direction. The printer-side controller 70 drives the carriage motor 31 to move the carriage CR in the carriage movement direction. Further, the printer-side controller 70 ejects ink from the head 41 (nozzles Nz) based on the head control signal while the carriage CR is moving. When the ink ejected from the head 41 lands on the paper S, dots are formed on the paper S as described above. The dot forming operation will be described in detail later.
The transport operation (S1004) is an operation of moving the paper S relative to the head 41 along the transport direction. The printer-side controller 70 rotates the transport roller 23 to transport the paper S in the transport direction. By this transport operation, the head 41 can form dots at positions different from the positions of the dots formed by the previous dot formation operation.
The paper discharge determination (S1005) is a process for determining whether or not to discharge the paper S being printed. This determination is made based on the presence or absence of print data. That is, the printer-side controller 70 determines whether or not there is print data for the paper S being printed, and determines that the paper is not discharged if the print data remains. In this case, the printer-side controller 70 alternately repeats the dot formation operation and the conveyance operation until there is no print data, and gradually prints an image composed of dots on the paper S.
The paper discharge process (S1006) is a process for discharging the paper S. In this processing, the printer-side controller 70 determines that the paper is discharged if there is no print data, and rotates the paper discharge roller 25 to discharge the printed paper S to the outside. Note that whether or not to discharge paper may be determined based on a paper discharge command included in the print data.
The print end determination is a determination as to whether or not to continue printing. In this determination, the printer-side controller 70 (S1007) determines whether there is print data. If printing is to be performed on the next paper S, a paper feeding operation for the next paper S is performed. On the other hand, if printing is not performed on the next sheet S, the printing operation is terminated.

  As described above, the image is printed by repeatedly performing the dot formation operation (S1003) and the conveyance operation (S1004). In the dot forming operation, ink is intermittently ejected from the head 41 (nozzle Nz) that moves in the head moving direction (predetermined direction). When the ink ejected from the head 41 lands on the surface of the paper S, dots are formed on the paper S. Since the ink is intermittently ejected while the head 41 is moving, a plurality of dots are formed on the paper S in a state of being aligned along the head moving direction. That is, on the paper S, a dot row (hereinafter also referred to as a raster line) composed of a plurality of dots along the head moving direction is formed. Since the dot forming operation and the carrying operation are repeated, a plurality of raster lines are formed adjacent to the carrying direction (another predetermined direction). Therefore, it can be said that the image printed on the paper S is composed of a plurality of raster lines adjacent in the transport direction.

=== Image correction by correction value ===
<About correction values for each row area>
By the way, this type of printer is required to improve the quality of a printed image. In order to meet such a demand, in this printer 1, a correction value is set for each row region where a raster line is formed, and the gradation value of each pixel constituting the raster line is set by a printer driver (correction program). The correction is made based on this correction value. More specifically, the CPU 113 of the host-side controller 111 executes the printer driver (correction program) stored in the memory 114.

  Here, the “row region” refers to a region composed of a plurality of unit regions arranged in the moving direction of the head 41. For example, when the print resolution is 720 dpi × 720 dpi, the row region is a band-like region having a width of 35.28 μm (≈ 1/720 inch) in the transport direction. When ink is ejected in an ideal state from the nozzle Nz moving in the head moving direction, dots are formed at positions suitable for this row region, and a raster line is formed.

  Such gradation value correction is performed, for example, in order to suppress density unevenness caused by ink landing deviation or the like. Hereinafter, this density unevenness will be described. FIG. 11A is an explanatory diagram of a state where dots are formed at ideal positions with respect to each row region (unit region). In this state, since there is no dot size defect due to landing deviation in the transport direction and nozzle failure, dots are accurately formed in each unit area, and printing is performed so as to have a constant density. . Therefore, the raster line is also accurately formed with respect to the row region.

  FIG. 11B is an explanatory diagram of the influence of variation due to nozzle processing accuracy and the like. Here, the raster line formed in the second row region is formed on the third row region side (upstream side in the transport direction) due to the variation in the flight direction of the ink ejected from the nozzles. Further, the amount of ink ejected toward the fifth row region is smaller than the reference, and the dots formed in the fifth row region are small. Originally, although image pieces having the same density should be formed in each row region, due to variations in processing accuracy, shading occurs in the image pieces according to the row region. For example, the image piece in the second row region is relatively light and the image piece in the third row region is relatively dark. Further, the image piece in the fifth row region becomes relatively light. When the print image composed of such raster lines is viewed macroscopically, stripe-shaped density unevenness along the moving direction of the carriage is visually recognized. This density unevenness causes a reduction in image quality of the printed image.

  FIG. 11C is an explanatory diagram of the correction of the gradation value that is performed when the above-described density defect occurs. In this gradation value correction, the pixel data (256-level CMYK pixel data) of the pixel corresponding to the row area is formed so that a dark image piece is formed in the dark and easily visible row area. Correct the key value. Further, the gradation value of the pixel data of the pixel corresponding to the row region is corrected so that a dark image piece is formed in a row region that is easily viewed. For example, in each row area, the dot generation rate is high for the second row region, the dot creation rate is low for the third row region, and the dot creation rate is high for the fifth row region. The gradation value of the pixel data of the corresponding pixel is corrected. As a result, the dot generation rate of the raster lines in each row area is changed, the density of the image pieces in the row area is corrected, and density unevenness of the entire print image is suppressed.

  By the way, in FIG. 11B, the reason why the density of the image piece formed in the third row region is high is not due to the influence of the nozzles forming the raster line in the third row region, but the adjacent second row. This is due to the influence of nozzles that form raster lines in the region. For this reason, when a nozzle that forms a raster line in the third row region forms a raster line in another row region, the image piece formed in that row region is not always dark. That is, even if the image pieces are formed by the same nozzle, the density may be different if the nozzles that form adjacent image pieces are different. In such a case, the density unevenness cannot be suppressed with the correction value simply associated with the nozzle. Therefore, in this embodiment, the gradation value of the pixel data is corrected based on the correction value set for each row area.

  This correction value is stored in the memory 73 of the printer controller 70, for example. Further, it may be stored in a storage medium such as a CD-ROM attached together with a printer driver or the like. Then, at the manufacturing factory of the printer 1, a correction value is set for each printer 1 and shipped. In this setting step, for example, the correction pattern is printed on the target printer 1. Next, the correction pattern is read by a scanner to obtain density data. Thereafter, the density of each column area in the correction pattern is acquired based on the obtained density data, and the correction value corresponding to each column area is acquired based on the density of each column area. As described above, the acquired correction value is stored in the memory 73 of the printer-side controller 70 or stored in the attached CD-ROM. This correction value reflects the characteristic of density unevenness in each printer. In this embodiment, the gradation value before correction and the gradation value after correction have a correspondence relationship as shown in FIG. 12, for example. Here, FIG. 12 is an explanatory diagram for the gradation value correction processing in a certain column region, and shows how the gradation value S_in of the pixel data of the pixels belonging to this column region is corrected. Note that the corrected gradation value is S_out. The row area shown in this figure tends to be printed with a lighter density, so that the gradation value after correction is set to be higher than the gradation value before correction. The pre-correction gradation value in the range of 0 to 255 is associated with the gradation value in the range of 0 to 255. This correspondence is determined for each row region. Furthermore, it is determined for each ink color.

  When the user who has purchased the printer 1 installs the printer driver in the computer, the printer driver corrects the gradation value of each pixel data using the correction value indicating this correspondence, and uses the corrected gradation value. The image is printed.

=== About density correction ===
<Problems in density correction>
In the printing apparatus 100 that performs such correction, there is a possibility that the gradation value of the pixel data exceeds the specifiable range as a result of performing the correction using the correction value described above. It is assumed that the minimum gradation value that can be specified when forming dots is 1, and the maximum gradation value is 255. In this case, the maximum gradation value may exceed 255 due to the correction described above.

Here, FIG. 13A is an explanatory diagram when white streaks occur. FIG. 13B is a diagram for explaining the relationship between the gradation value before correction and the gradation value after correction in that case.
For example, the impact of ink landing deviation is extremely large, and a situation in which correction cannot be completed within the gradation range of 0 to 255 may occur. For example, as shown in FIG. 13A, even if large dots are formed at a formation rate of 100%, white stripes may occur due to the impact of landing deviation.
In this case, as shown in FIG. 13B, the corrected gradation value does not fall within the range of 0 to 255 and exceeds 255. In such a case, even if correction is performed in the same gradation value range (0 to 255) as the gradation value before correction, the range exceeding the maximum gradation value cannot be corrected. That is, since the corrected gradation value is limited to a maximum of 255 (indicated by a dotted line in FIG. 13B), a large dot can only be formed at a formation rate of 100%, and white stripes are generated.

  In view of such circumstances, the printing apparatus 100 of the present embodiment allows correction exceeding 255, which is the maximum gradation value that can be specified, as shown in FIG. 13B. When the gradation value after correction exceeds 255, extra large dots are used instead of large dots to suppress density unevenness such as white stripes. In other words, when the corrected gradation value exceeds the specifiable range, a dot having a size different from that of a dot that can be formed when the corrected gradation value is within the specifiable range (outside the range) Dots of a size corresponding to the gradation value) are formed. In short, a drive signal for forming dots of different sizes is generated and applied to the piezo element PZT. As a result, density unevenness that cannot be corrected by the conventional apparatus can be improved.

As described above, in the printer 1 of this embodiment, when the corrected gradation value exceeds 255, an extra large dot is formed. Hence, the switching operation information q0 to q3, q3 ', these switches operation information q0 to q3, q3' decoder 84 for selecting a selection signal _{S slct} used in the decoder 84, and sets the selection signal _{S slct} etc. The halftone process (S904) is characterized. Hereinafter, these characteristic parts will be described.

<About Decoder 84>
First, the configuration of the decoder 84 will be described. Here, FIG. 14 is a diagram for explaining the configuration of the decoder 84.

  The decoder 84 selects and outputs one corresponding to the latched dot formation data SI from the switch operation information q0 to q3, q3 '. The decoder 84 has seven AND circuits 831 to 837 and one OR circuit 848. The AND circuits 831 to 835 have three input terminals and one output terminal, one switch operation information of switch operation information q0 to q3, q3 ′, upper bit data of the dot formation data SI, Lower-order bit data of the dot formation data SI is input. The AND circuits 831 to 835 are different in the way of inputting the upper bit data and the lower bit data of the dot formation data SI.

  That is, the switch operation information q0 without dots, the inverted data of the upper bits of the dot formation data SI, and the inverted data of the lower bits are input to the first AND circuit 841. For this reason, when the dot formation data SI is data [00], the output from the first AND circuit 841 is in accordance with the switch operation information q0 without dots. The second AND circuit 842 receives small dot switch operation information q 1, inverted data of upper bits of dot formation data SI, and lower bit data. For this reason, when the dot formation data SI is data [01], the output from the second AND circuit 842 has contents according to the switch operation information q1 of the small dot (first dot). In addition, the third AND circuit 843 includes switch operation information q2 for medium dots (second dots larger than the first dots), upper bit data of dot formation data SI, and inverted data of lower bits. Have been entered. For this reason, when the dot formation data SI is data [10], the output from the third AND circuit 843 is in accordance with the medium dot switch operation information q2. The fourth AND circuit 844 also receives switch operation information q3 for large dots (third dots larger than the second dots), upper bit data and lower bit data of the dot formation data SI. Has been. For this reason, when the dot formation data SI is data [11], the output from the fourth AND circuit 844 is the content according to the large dot switch operation information q3. The fifth AND circuit 845 receives switch operation information q 3 ′ of extra large dots (dots larger than the third dot), upper bit data of dot formation data SI, and lower bit data. For this reason, when the dot formation data SI is data [11], the output from the fifth AND circuit 845 has contents according to the extra large dot switch operation information q3 '.

One of the output from the fourth AND circuit 844 and the output from the fifth AND circuit 845 is selected by the sixth AND circuit 846 and the seventh AND circuit 847. That is, the sixth AND circuit 846 and the seventh AND circuit 847 constitute a specific selection unit 2001. The specific selection unit 2001 selects a plurality of switch operation information assigned to the same dot formation data SI ([11] in the present embodiment) based on the selection signal S _slct . The sixth AND circuit 846 and the seventh AND circuit 847 have two input terminals and one output terminal. Then, the output from the fourth AND circuit 844 is input to one input terminal of the sixth AND circuit 846, and the inverted signal of the selection signal S _slct is input to the other input terminal. The output from the fifth AND circuit 845 is input to one input terminal of the seventh AND circuit 847, and the selection signal S _slct is input to the other input terminal. Therefore, when the selection signal S _slct is at the L level, the output of the sixth AND circuit 846 is the same as the output of the fourth AND circuit 844, and the output of the seventh AND circuit 847 maintains the L level. On the other hand, when the selection signal S _slct is at the H level, the output of the sixth AND circuit 846 maintains the L level, and the output of the seventh AND circuit 847 is the same as the output of the fifth AND circuit 845. In short, depending on the level of the selection signal S _slct , either the large dot switch operation information q3 or the extra large dot switch operation information q3 ′ is valid.

The selection signal S _slct is a signal having a level corresponding to the content of the selection bit. This selection bit is information for selecting either a large dot or an extra large dot, and is determined by halftone processing (S904) according to the corrected gradation value. The selection signal S _slct is an H level signal when the selection bit is [1], and an L level signal when the selection bit is [0]. The selection bit setting process will be described later.

The OR circuit 848 has five input terminals and one output terminal. The outputs of the first AND circuit 841, the second AND circuit 842, the third AND circuit 843, the sixth AND circuit 846, and the seventh AND circuit 847 are input to each of the five input terminals. From the OR circuit 848, the switch operation information q0 to q3, q3 ′ corresponding to the latched dot formation data SI and the selection signal S _slct is output.

The dot formation data SI, the switch operation information q0 to q3, q3 ′, and the application control of the original drive signal COM to the piezo element PZT by the selection signal S _slct will be described later.

<About halftone processing>
The dot formation data SI and the selection signal S _slct described above are generated by halftone processing (S904). Here, the halftone process will be described in detail. FIG. 15 is a flowchart of halftone processing by the dither method, and the following steps are executed according to the flowchart.

  First, in step S1500, CMYK image data is acquired. This CMYK image data is composed of image data represented by the above-described corrected printing tone values for the respective ink colors of C, M, Y, and K. That is, the CMYK image data includes C image data related to cyan (C), M image data related to magenta (M), Y image data related to yellow (Y), and image data related to black (K). These C, M, Y, and K image data are respectively composed of C, M, Y, and K pixel data indicating the gradation value of each ink color.

  The following description applies to any of C, M, Y, and K image data, and therefore K image data will be described as a representative of these.

Next, for all K pixel data in the K image data, the processing from step S1501 to step S1513 is executed while sequentially changing the K pixel data to be processed. It is converted into 3-bit data indicating any one of “None”, “Small dot formation”, “Medium dot formation”, “Large dot formation”, and “Extra large dot formation”. In the present embodiment, this data is referred to as dot identification data for convenience. The most significant bit in the dot identification data is a selection bit that is the basis of the selection signal S _slct , and the lower 2 bits are gradation data. As described above, the selection bit plays a role of selecting whether to form a large dot or an extra large dot. For this reason, the dot identification data is assigned [000] when “no dot formation”, “001” when “small dot formation”, and [010] when “medium dot formation”. ] Is assigned. Also, [011] is assigned for “large dot formation”, and [111] is assigned for “extra-large dot formation”. In short, the dot identification data for the large dots and the extra large dots has the same low-order 2-bit gradation data [11]. The selection bits of the upper 1 bit are different. When the content is [0], a large dot is selected, and when the content is [1], an extra large dot is selected.

  First, in step S1501, it is determined whether or not the corrected gradation value exceeds 255. Here, the state where the corrected gradation value exceeds 255 means that the dot size is insufficient even when the large dot generation rate is 100%. Therefore, the dot identification data is set to “111” so as to form extra large dots instead of large dots (S1512). In the dot identification data setting step (S1308 to S1312) in FIG. 15, these data are separately shown so that the selected bits in the dot identification data can be distinguished from the gradation data.

  On the other hand, when the corrected gradation value is 255 or less, the process proceeds to step S1502. In step S1502, large dot level data LVL is set as follows according to the gradation value of the K pixel data to be processed. FIG. 16 is a diagram showing a generation rate table used to determine level data for each of large, medium, and small dots. In the figure, the horizontal axis is the gradation value (0 to 255), the left vertical axis is the dot generation rate (%), and the right vertical axis is the level data (0 to 255). Here, the “dot generation rate” means the proportion of pixels in which dots are formed among pixels in a region when a uniform region is reproduced according to a certain gradation value. . In FIG. 16, a profile SD indicated by a thin solid line indicates a generation rate of small dots, a profile MD indicated by a thick solid line indicates a generation rate of medium dots, and a profile LD indicated by a dotted line indicates generation of large dots. Each rate is shown. The level data refers to data obtained by converting the dot generation rate into 256 levels from 0 to 255.

  In step S1502, the level data LVL corresponding to the gradation value is read from the large dot profile LD. For example, as shown in FIG. 16, if the gradation value of the K pixel data to be processed is gr, the level data LVL is obtained as 1d using the profile LD. Actually, this profile LD is stored in a memory (not shown) such as a ROM in the computer 1100 in the form of a one-dimensional table, and the printer driver obtains level data by referring to this table. .

  Next, in step S1503, it is determined whether or not the level data LVL set as described above is larger than the threshold value THL. Here, dot on / off determination is performed by the dither method. The threshold value THL is set to a different value for each pixel block of a so-called dither matrix. In the present embodiment, a matrix in which values from 0 to 254 appear in a 16 × 16 square pixel block is used.

  FIG. 17 is a diagram showing a state of dot on / off determination by the dither method. For the sake of illustration, FIG. 17 shows only some K pixel data. First, as shown in the drawing, the level data LVL of each K pixel data is compared with the threshold value THL of the pixel block on the dither matrix corresponding to the K pixel data. When the level data LVL is larger than the threshold value THL, the dot is turned on, and when the level data LVL is smaller, the dot is turned off. In the figure, shaded pixel data is K pixel data for turning on a dot. That is, in step S1503, if the level data LVL is larger than the threshold value THL, the process proceeds to step S1511. Otherwise, the process proceeds to step S1504. When the process proceeds to step S1511, the printer driver records dot identification data “011” indicating a large dot in association with the K pixel data to be processed, and the process proceeds to step S1513. In step S1513, it is determined whether or not the process has been completed for all the K pixel data. If the process has been completed, the halftone process is terminated. If the process has not been completed, the process target is determined. The process proceeds to unprocessed K pixel data, and the process returns to step S1501.

  On the other hand, if the processing proceeds to step S1504, the printer driver sets medium dot level data LVM. The medium dot level data LVM is set by the above-described generation rate table based on the gradation value. The setting method is the same as that for setting the large dot level data LVL. That is, in the example shown in FIG. 16, the level data LVM is obtained as 2d.

  In step S1505, the medium dot level data LVM and the threshold value THM are compared to determine whether the medium dot is on or off. The on / off determination method is the same as that for large dots, but the threshold THM used for determination is different from the threshold THL for large dots as shown below. That is, when ON / OFF determination is performed using the same dither matrix for large dots and medium dots, the pixel blocks where the dots are likely to be turned on coincide with each other. That is, when a large dot is turned off, there is a high possibility that a medium dot is also turned off. As a result, the production rate of medium dots may be lower than the desired production rate. In order to avoid such a phenomenon, in this embodiment, the dither matrix is changed for both. In other words, the pixel blocks that are likely to be turned on are changed between large dots and medium dots, thereby ensuring that each is appropriately formed.

  FIG. 18A is a diagram showing a dither matrix used for determination of large dots. FIG. 18B is a diagram showing a dither matrix used for medium dot determination. In this embodiment, the first dither matrix TM of FIG. 18A is used for large dots, and the second dither matrix UM of FIG. 18B in which each threshold value is moved symmetrically about the center in the transport direction for medium dots. Is used. In this embodiment, as described above, a 16 × 16 matrix is used, but for convenience of illustration, FIG. 18 shows a 4 × 4 matrix. Note that dither matrices that are completely different for large dots and medium dots may be used.

  If the medium dot level data LVM is greater than the medium dot threshold value THM in step S1504, it is determined that the medium dot should be turned on, and the process proceeds to step S1510. The process proceeds to S1506. If the process proceeds to step S1510, the printer driver records dot identification data “010” indicating a medium dot in association with the K pixel data to be processed, and the process proceeds to step S1513. In step S1513, it is determined whether or not the process has been completed for all the K pixel data. If the process has been completed, the halftone process is terminated. If the process has not been completed, the process target is determined. The process proceeds to unprocessed K pixel data, and the process returns to step S1501.

  On the other hand, if the processing proceeds to step S1506, the small dot level data LVS is set in the same manner as the setting of the level data for large dots and medium dots. The dither matrix for small dots is preferably different from that for medium dots and large dots in order to prevent a decrease in the generation rate of small dots as described above.

  In step S1507, if the level data LVS is greater than the small dot threshold THS, the printer driver proceeds to step S1509. Otherwise, the printer driver proceeds to step S1508. If the process proceeds to step S1509, dot identification data “001” indicating a small dot is recorded in association with the K pixel data to be processed, and the process proceeds to step S1513. In step S1513, it is determined whether or not the processing has been completed for all the K pixel data. If not, the processing target is moved to unprocessed K pixel data, and the process returns to step S1501. On the other hand, if it has been completed, the halftone process for the K image data is terminated, and the halftone process is similarly performed for the image data of other colors.

  On the other hand, if the process proceeds to step S1508, the printer driver records dot identification data “000” indicating no dot in association with the K pixel data to be processed, and the process proceeds to step S1513. In step S1513, it is determined whether or not the processing has been completed for all the K pixel data. If not, the processing target is moved to unprocessed K pixel data, and the process returns to step S1501. On the other hand, if it has been completed, the halftone process for the K image data is terminated, and the halftone process is similarly performed for the image data of other colors.

<Application of the original drive signal COM to the piezo element PZT>
The dot identification data set in the above-described halftone process is changed in the data order in the rasterizing process (S905) and sent to the printer 1 as the print data described above. In the printer 1, processing for printing on the paper S is performed based on the print data. The dot identification data described above is used in the dot formation operation (S1003) in this process. That is, it is used when the original drive signal COM is applied to the piezo element PZT.

  Here, application of the original drive signal COM to the piezo element PZT will be described. First, switch operation information that defines a portion applied to the piezo element PZT in the original drive signal COM will be described. Here, FIG. 19A is a diagram for explaining switch operation information when forming no dots or large dots. FIG. 19B is a diagram for explaining switch operation information when an extra large dot is formed. As shown in FIG. 19A, the switch operation information includes switch operation information q0 corresponding to gradation data [00] (gradation data without dots) composed of [0100], and gradation data [01] (small dot Switch operation information q1 corresponding to (tone data) is configured with [0010]. Further, the switch operation information q2 corresponding to the gradation data [10] (medium dot gradation data) is composed of [1000], and the switch operation corresponding to the gradation data [11] (large dot gradation data). The information q3 is composed of [1001]. Further, the gradation data “11” (the gradation data of the extra large dot) further corresponds to the switch operation information q3 ′ constituted by the data [1011]. The switch operation information is stored in the control logic 83, but the contents are transferred from the printer-side controller 70. This switch operation information is set with the dot formation data SI described above and is updated every repetition period T. Each of T1, T2, T3, and T4 in the switch operation information of FIGS. 19A and 19B corresponds to each period of T1, T2, T3, and T4 in the repetition period T in FIG. For example, in the period of T1, the leading 0 of [0100] constituting the switch operation information q0, the leading 0 of [0010] constituting the switch operation information q1, and the switch operation information q2 [ 1000], the first 1 of [1001] constituting the switch operation information q3, and the first 1 of [1011] constituting the switch operation information q3 ′ are respectively controlled. It is sent from the logic 83 to the decoder 84.

This switch operation information is selected by the decoder 84. That is, the decoder 84 selects the switch operation information q0 when the gradation data from the latch circuit 82 is [00], and selects the switch operation information q1 when the gradation data is [01]. Similarly, the switch operation information q2 is selected in the case of gradation data [10], and the switch operation information q3 or q3 ′ is selected in the case of gradation data [11]. Among these, in the case of the gradation data [00], [01], [10], the switch operation information q0, q1, q2 is selected regardless of the content of the selection signal S _slct . In the case of the gradation data [11], as described above, either the switch operation information q3 or the switch operation information q3 ′ is selected according to the content of the selection signal S _slct .

  Next, application of the original drive signal COM to the piezo element PZT according to the selected switch operation information will be described. The selected switch operation information is output to the head-side switch 86. Thereby, as shown in FIGS. 20A and 20B, the section signals SS1 to SS4 constituting the original drive signal COM are selectively applied to the piezo element PZT.

  In the case of the switch operation information q0, the second section signal SS2 generated in the period T2 is applied to the piezo element PZT. That is, the second section signal SS2 corresponds to a drive signal. As a result, the drive pulse PS2 (fine vibration pulse) is applied to the piezo element PZT, and the meniscus is finely vibrated. In the case of the switch operation information q1, the third section signal SS3 generated in the period T3 is applied to the piezo element PZT as a drive signal. As a result, the drive pulse PS3 (small dot pulse) is applied to the piezo element PZT, and an amount of ink necessary for forming a small dot is ejected from the nozzle Nz. In the case of the switch operation information q2, the first section signal SS1 generated in the period T1 is applied to the piezo element PZT as a drive signal. As a result, the drive pulse PS1 (first medium dot pulse) is applied to the piezo element PZT, and an amount of ink necessary for forming the medium dot is ejected from the nozzle Nz.

  In the case of the switch operation information q3, the first section signal SS1 generated in the period T1 and the fourth section signal SS4 generated in the period T4 are applied to the piezo element PZT as drive signals. Accordingly, the drive pulse PS1 (first medium dot pulse) and the drive pulse PS4 (second medium dot pulse) are applied to the piezo element PZT. Then, an amount of ink necessary to form a large dot is ejected from the nozzle Nz. In the case of the switch information q3 ′, the first section signal SS1 generated in the period T1, the third section signal SS3 generated in the period T3, and the fourth section signal SS4 generated in the period T4 are the piezo elements PZT. To be applied. Accordingly, the drive pulse PS1, the drive pulse PS3, and the drive pulse PS4 are applied to the piezo element PZT. Then, an amount of ink necessary to form an extra large dot is ejected from the nozzle Nz.

  As described above, in this embodiment, when the corrected gradation value exceeds the maximum value 255 that can be specified, dot formation using extra large dots is performed, and thus a high-quality image is printed. Can do.

  By the way, the first embodiment has described the printer 1 that uses extra large dots for density unevenness that cannot be corrected by large dots. This printer 1 has an advantage that, when large white dots cannot be filled and white lines are generated, white lines can be suppressed by printing with extra large dots instead. However, it is not limited to this configuration. Hereinafter, other embodiments will be described.

=== About the Second Embodiment ===
Next, a second embodiment will be described. In the first embodiment, white stripes that are not completely filled with large dots are printed instead of extra large dots to adjust density unevenness. However, in the second embodiment, it is possible to discharge extremely small dots, and small dots can be ejected. It is possible to print with a small dot instead. Then, density unevenness can be suppressed by expressing gradation that is not within the predetermined range.
At this time, the original drive signal is composed of a signal capable of forming a very small dot, a small dot, a medium dot, and a large dot in the combination of the section signals. When the corrected print gradation value is in a range larger than 0 and smaller than 1, which is a gradation value that cannot be expressed by a small dot, a minimal dot (from the first dot) is used instead of the small dot. Small dots) are formed. The selection bit and the selection signal described above are used to select the small dot and the minimal dot.

=== About Other Embodiments ===
Each of the above-described embodiments is mainly described for the printer 1, but includes disclosure of a printing apparatus, a printing method, and the like. Moreover, although the printer 1 as an embodiment has been described, the above embodiment is for facilitating the understanding of the present invention, and is not intended to limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and it is needless to say that the present invention includes equivalents thereof. In particular, the embodiments described below are also included in the present invention.

<About drive signal>
In each of the above-described embodiments, different driving signals are generated by using a common original driving signal COM and changing a selection pattern of driving pulses (waveform portions). In this regard, a plurality of original drive signal generation circuits 50 may be provided to generate a plurality of types of original drive signals COM.

<Regarding the correction unit for print gradation values>
In the above embodiment, the print gradation value correction unit is realized by the CPU 113 executing the printer driver in the memory 114. However, the printer driver is stored in the ROM in the printer 1 and has a copy function and the like. It can also be configured in a composite printer. Then, the printer-side CPU 72 may be caused to execute a printer driver in the ROM to realize a print gradation value correction unit.

<About printing devices>
In the above-described embodiment, the single-function printer 1 that exclusively performs printing has been described as an example. However, the printing apparatus is not limited to this embodiment. For example, a set of a plotter or facsimile apparatus and the computer 110 may be used. In this case, a plotter or a facsimile machine corresponds to the printing apparatus main body.
In addition, color filter manufacturing equipment, dyeing equipment, fine processing equipment, semiconductor manufacturing equipment, surface processing equipment, 3D modeling machines, liquid vaporizers, organic EL manufacturing equipment (especially polymer EL manufacturing equipment), display manufacturing equipment, You may apply the technique similar to this embodiment to the various printing apparatuses which applied inkjet technology, such as a film | membrane apparatus and a DNA chip manufacturing apparatus. These methods and manufacturing methods are also within the scope of application.

<Elements of the head 41>
In each of the above-described embodiments, the piezo element PZT is exemplified as an element included in the head 41, that is, an element that performs an operation for ejecting ink, but is not limited to the piezo element PZT. For example, an electrostatic actuator, a magnetostrictive element, and a heating element can be elements that the head 41 has.

It is a figure explaining the structure of a printing apparatus. It is a block diagram explaining the structure of a computer and a printer. FIG. 3A is a diagram illustrating a configuration of the printer according to the present embodiment. FIG. 3B is a side view illustrating the configuration of the printer according to the present embodiment. It is sectional drawing for demonstrating the structure of a head. It is a figure explaining arrangement | positioning of a nozzle row. It is a block diagram for demonstrating the structure of a head control part. It is a figure explaining an original drive signal. It is a conceptual diagram for demonstrating the production | generation operation | movement of an original drive signal. 6 is a flowchart for explaining processing for generating print data. It is a flowchart explaining the process performed at the time of printing. FIG. 11A is an explanatory diagram of a state when dots are ideally formed. FIG. 11B is an explanatory diagram of the influence of variations in nozzle processing accuracy. FIG. 11C is an explanatory diagram showing a state when dots are formed by the printing method of the present embodiment. It is explanatory drawing for the gradation value correction process in a certain row area. FIG. 13A is an explanatory diagram when white streaks occur. FIG. 13B is a diagram for explaining the relationship between the gradation value before correction and the gradation value after correction in the case of FIG. 13A. FIG. 14 is a diagram for explaining the configuration of the decoder. It is a flowchart of a halftone process. It is a figure which shows the generation rate table of a dot. It is a figure which shows the mode of the dot ON / OFF determination by a dither method. FIG. 18A is a diagram showing a dither matrix used for determination of large dots. FIG. 18B is a diagram showing a dither matrix used for medium dot determination. FIG. 19A is a diagram for explaining switch operation information when forming no dots or large dots. FIG. 19B is a diagram for explaining switch operation information when an extra large dot is formed. FIG. 20A is a diagram for explaining drive signals when forming no dots or large dots. FIG. 20B is a diagram for explaining a drive signal when an extra large dot is formed.

Explanation of symbols

1 printer, 20 paper transport mechanism, 21 paper feed roller, 22 transport motor,
23 transport roller, 24 platen, 25 paper discharge roller,
30 Carriage moving mechanism, 31 Carriage motor, 32 Guide shaft,
33 timing belt, 34 drive pulley, 35 idler pulley,
40 head units, 41 heads,
50 original drive signal generation circuit, 60 detector group, 61 linear encoder,
62 rotary encoder, 63 paper detector, 64 paper width detector,
70 printer side controller, 71 interface unit, 72 CPU,
73 memory, 74 control unit, 81 shift register,
82 latch circuit, 83 control logic, 84 decoder, 85 gate circuit,
86 Head side switch,
100 printing device, 110 computer, 111 host side controller,
112 interface unit, 113 CPU, 114 memory,
120 display device, 130 input device, 131 keyboard, 132 mouse,
140 recording / reproducing apparatus, 141 flexible disk drive apparatus,
142 CD-ROM drive device,
S paper, SI dot formation data, HC head controller, PZT piezo element,
CR carriage, IC ink cartridge,
ICk black ink cartridge, ICc color ink cartridge,
Nz nozzle, Nk black ink nozzle row, Nc cyan ink nozzle row,
Nm magenta ink nozzle row, Ny yellow ink nozzle row,
LAT latch signal, CH change signal, q0 to q3 ′ switch operation information,
N_CHG N-charge signal, COM original drive signal,
SS1 first section signal, SS2 second section signal, SS3 third section signal,
SS4 4th section signal, PS1 to PS4 drive pulse

Claims (9)

(A) a head that has an element that operates to eject ink, and that applies a drive signal corresponding to the size of a dot to be formed to the element, thereby ejecting ink;
(B) a correction unit for correcting a print gradation value designated within a predetermined range determined by a minimum gradation value and a maximum gradation value that can be designated;
(C) When the corrected print gradation value corrected by the correction unit exceeds the predetermined range, the size is different from the dots that can be formed when the corrected print gradation value is within the predetermined range. A drive signal generation unit that generates a drive signal for forming the dots of
A printing apparatus comprising: The printing apparatus according to claim 1,
The drive signal generator is
An original drive signal generating unit for generating an original drive signal having a plurality of waveform parts for operating the element;
A switch disposed between the original drive generation unit and the element, for generating a drive signal applied to the element from the original drive signal;
A switch controller for controlling the operation of the switch based on the corrected print gradation value;
A printing apparatus comprising: The printing apparatus according to claim 2,
The drive signal generator is
A switch operation information storage unit storing switch operation information for determining the operation of the switch;
The switch controller
A printing apparatus comprising: a selection unit that selects corresponding switch operation information based on the corrected print tone value. The printing apparatus according to any one of claims 1 to 3,
The drive signal generator is
When the corrected print tone value is within the predetermined range, a first dot, a second dot larger than the first dot, and a third dot larger than the second dot are formed. Drive signal for
A printing apparatus that generates a drive signal for forming a dot larger than the third dot or a dot smaller than the first dot when the corrected print gradation value exceeds the predetermined range . The printing apparatus according to any one of claims 1 to 4,
The minimum gradation value that can be specified is 0, and the maximum gradation value that can be specified is 255. The printing apparatus according to any one of claims 1 to 5,
The head is
During the movement in a predetermined direction, the drive signal is applied to the element to eject the ink,
The correction unit is
A printing apparatus that corrects the print gradation value based on correction data that is configured by a plurality of unit regions arranged in the predetermined direction and is prepared for each row region arranged in another predetermined direction that intersects the predetermined direction. The printing apparatus according to any one of claims 1 to 6,
The correction unit is
A memory storing a correction program;
A CPU that operates according to the correction program;
Having a printing device. (A) It has an element that performs an operation for ejecting ink, and a drive signal corresponding to the size of a dot to be formed is applied to the element while moving in a predetermined direction, whereby the ink is A head for discharging,
(B) a correction unit for correcting a print gradation value designated within a range defined by 0 which is a minimum gradation value which can be designated and 255 which is a maximum gradation value;
A memory that stores a correction program; and a CPU that operates according to the correction program;
A correction unit configured to correct the print tone value based on correction data prepared for each of the row regions arranged in a predetermined direction intersecting the predetermined direction and configured by a plurality of unit regions arranged in the predetermined direction;
(C) When the corrected print gradation value corrected by the correction unit exceeds the range, the dot has a size different from that that can be formed when the corrected print gradation value is within the range. A drive signal generation unit for generating a drive signal for forming
An original drive signal generating unit for generating an original drive signal having a plurality of waveform parts for operating the element;
A switch disposed between the original drive generation unit and the element, for generating a drive signal applied to the element from the original drive signal;
A switch operation information storage unit that stores switch operation information for determining the operation of the switch;
A switch controller that includes a selection unit that selects corresponding switch operation information based on the corrected print gradation value, and that controls the operation of the switch;
To form a first dot, a second dot larger than the first dot, and a third dot larger than the second dot when the corrected print tone value is within the range Drive signal, and when the corrected print tone value exceeds the range, the drive signal for forming a dot larger than the third dot or a dot smaller than the first dot A drive signal generation unit for generating
A printing apparatus comprising: Correcting the print gradation value designated within a predetermined range defined by the minimum gradation value and the maximum gradation value that can be designated;
When the corrected print tone value after the correction exceeds the predetermined range, a dot having a size different from that which can be formed when the corrected print tone value is within the predetermined range is formed. Generating a drive signal for:
Applying a drive signal to the element according to the size of the dot to be formed and discharging the ink;
Including printing method.

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