JP4407393B2 - Adjusting the recording position deviation during bidirectional printing using the reference correction value and the relative correction value - Google Patents

Description

  The present invention relates to a technique for printing an image on a print medium while performing main scanning in both directions in a reciprocating manner, and more particularly to a technique for correcting a recording position shift between an outward path and a return path.

  In recent years, color printers that eject several colors of ink from a head have become widespread as output devices for computers. As such a color printer, in recent years, a multi-value printer capable of recording one pixel with a plurality of types of dots having different sizes has been proposed. In a multi-value printer, a relatively small dot is formed in a region of one pixel by a relatively small amount of ink droplets, and a relatively large dot is formed in a region of one pixel by a relatively large amount of ink droplets. Even in such a multi-value printer, so-called “bidirectional printing” can be performed to improve the printing speed, as in other conventional printers.

  In bidirectional printing, there is a problem that the recording position in the main scanning direction in the forward path and the backward path is shifted due to backlash of the driving mechanism in the main scanning direction, warpage of the platen that supports the printing medium below, and the like. It is likely to occur. As a technique for solving such misalignment, for example, a technique described in Japanese Patent Laid-Open No. 5-69625 disclosed by the present applicant is known. In this prior art, a positional deviation amount (print deviation) in the main scanning direction is registered in advance, and the recording positions in the forward path and the backward path are corrected based on this positional deviation amount.

  However, conventionally, little consideration has been given to the positional deviation between the forward path and the return path when bidirectional printing is performed by a multi-value printer. In addition, even if the positional deviation is corrected for a specific one of the plurality of inks, the positional deviation of the other inks may not be corrected. In this case, the image quality of the color image is corrected by the positional deviation correction. There was a problem of not improving much. Such a problem is particularly serious in a halftone region where the influence on the image quality due to the positional deviation is large.

  The present invention has been made to solve the above-described problems in the prior art, and improves the image quality by reducing the shift in the recording position in the main scanning direction between the forward pass and the return pass when performing bidirectional printing. For the purpose.

In order to solve at least a part of the above-described problems, according to the present invention, there is provided a print head having a plurality of nozzle rows for recording dots at each pixel position on the print medium, each nozzle row having a plurality of black inks and a plurality of nozzles. A print head configured to eject one kind of each of the color inks is used. Then, with respect to a specific reference dot formed by a specific nozzle row of the print head, a reference correction value for correcting a shift in the recording position in the main scanning direction in the forward pass and the return pass is set, and at least the reference correction value is used. Then, an adjustment value for reducing the shift of the recording position in the main scanning direction between the forward path and the backward path is determined. Then, using this adjustment value, the recording position in the main scanning direction in the forward path and the backward path is adjusted. The adjustment mode includes a first adjustment mode in which the reference correction value is corrected with a relative correction value prepared in advance to correct the reference correction value, and a second adjustment mode in which the reference correction value is used as an adjustment value as it is. There is. Among these, when color printing is performed using black ink and a plurality of chromatic color inks, the adjustment value determined according to the first adjustment mode is common to the dots of the black ink and the dots of the chromatic color ink. Is used as a common adjustment value to be applied to the print position, and the print position deviation is corrected. When performing black and white printing using black ink, the adjustment value determined according to the second adjustment mode is applied to the black ink dots. Then, the recording position deviation is corrected. The relative correction values are: (i) a linear pattern in which dots are recorded continuously or intermittently by simultaneously ejecting ink from the plurality of nozzle rows for each of the black ink and the plurality of chromatic color inks. And (ii) determining the measurement position by measuring the position of the linear pattern of each chromatic color ink with reference to the linear pattern of the black ink, and (iii) the position of the nozzle row of the black ink The position of the nozzle row of each chromatic ink based on the above is regarded as the design position of the linear pattern of each chromatic ink, and the amount of deviation between the measurement position of the linear pattern of the chromatic ink and the design position is determined. And (iv) a value obtained by averaging the deviation amounts of the plurality of chromatic color inks.

  In this way, the adjustment value for the positional deviation correction can be determined using the reference correction value and the relative correction value, so that the deviation of the recording position in the main scanning direction in the forward path and the backward path is performed in a manner suitable for various printing conditions. Can be relaxed to improve the image quality. Further, the recording position deviation of each nozzle array is reduced as a whole during color printing, while only the recording position deviation of the reference nozzle array (in this case, the black nozzle array) is reduced during monochrome printing. Accordingly, it is possible to effectively reduce the shift of the recording position in each of color printing and monochrome printing.

  When the print head has a plurality of nozzle rows, the reference correction value is a correction for correcting the shift of the recording position in the main scanning direction in the forward pass and the return pass with respect to a specific reference nozzle row in the plurality of nozzle rows. Further, the relative correction value may be a correction value for correcting a shift of the recording position relative to the reference nozzle row with respect to the nozzle rows other than the reference nozzle row among the plurality of nozzle rows. By so doing, it is possible to reduce the displacement of the recording position with respect to the nozzle rows other than the reference nozzle row.

  The reference nozzle row is a black nozzle row for discharging black ink, and the other nozzle rows other than the reference nozzle row preferably include a color nozzle row for discharging color ink.

  The relative correction value may be commonly applied to other nozzle rows other than the reference nozzle row.

  Alternatively, as the relative correction value, an independent value may be applied for each nozzle row with respect to other nozzle rows other than the reference nozzle row. In this way, it is possible to reduce the displacement of the recording position more effectively for each nozzle row.

  In addition, as a relative correction value, an independent value may be applied to each group of nozzle rows that eject the same ink. Since the relative shift amount of the recording position depends on the physical property value of the ink, the shift of the recording position can be more effectively reduced by applying an independent value of the relative correction value for each ink.

  When the print head can form at least N types of dots having different sizes (N is an integer of 2 or more), the reference dot is a dot selected from the N types of dots, and the first adjustment is performed. In the mode, the adjustment value may be commonly applied to N types of dots. In this way, it is possible to improve the image quality by reducing the shift in the recording position in the main scanning direction between the forward path and the backward path regarding N types of dots.

  The reference dot is preferably the largest dot among the N types of dots. For example, when setting a reference correction value by observing a test pattern for positional deviation adjustment, if the test pattern is recorded using the largest dot, it is easy to recognize the positional deviation in the test pattern. Is easy to set.

  Further, the relative correction value may be a value that substantially represents a difference between a positional deviation amount relating to at least one target dot including a dot smaller than the reference dot among the N types of dots and a positional deviation amount relating to the reference dot. . In this way, it is possible to reduce the amount of positional deviation for target dots that have a large effect on image quality.

  The target dot may be the smallest dot among N types of dots. Normally, image quality deterioration tends to be noticeable in an image region where the image density is relatively low. Also, when the image density is relatively low, a minimum size dot is often used. Therefore, if the minimum dot is selected as the target dot whose amount of positional deviation is reduced, the image quality in the low density region can be improved.

  Alternatively, when the target dot includes a plurality of dots having different sizes, an average value of the positional shift amounts related to the plurality of dots can be used as the positional shift amount related to the target dot. In this way, it is possible to reduce the displacement of the recording position for a plurality of dots that have a relatively large influence on the image quality, and as a result, it is possible to improve the image quality.

  The reference dot may be a dot formed with black ink, and the target dot may be a dot formed with chromatic ink. For example, if a test pattern for setting a reference correction value is created with reference dots formed of black ink, it is easy to recognize a positional shift in the test pattern, and therefore, setting of the reference correction value is easy. In a color image, chromatic color ink dots can have a significant effect on image quality. Therefore, the image quality of a color image can be improved by reducing the displacement of the recording position with respect to the chromatic color ink dots.

  Note that the reference correction value may be determined according to correction information indicating a preferable correction state selected from the positional deviation inspection patterns printed on the print medium using the reference nozzle row. In this way, the reference correction value can be easily determined.

  When the printing apparatus can perform main scanning at a plurality of main scanning speeds, it is preferable to apply an independent value to each of the plurality of main scanning speeds as the relative correction value. Since the relative shift amount of the recording position depends on the main scanning speed, the shift of the recording position can be more effectively reduced by applying an independent value of the relative correction value for each main scanning speed.

  Also, when the printing device can eject ink in a plurality of dot ejection modes with different ink ejection speeds, an independent value is applied to each of the plurality of dot ejection modes as a relative correction value. It is preferable to do. Since the relative shift amount of the recording position also depends on the ink discharge speed, the shift of the print position can be more effectively reduced by applying an independent value of the relative correction value for each ink discharge speed. .

  The memory for storing the relative correction value is preferably a non-volatile memory provided in the printing apparatus.

  The memory for storing the relative correction value is preferably fixed to the print head so that it can be attached to and detached from the printing apparatus together with the print head. In this way, even when the print head is replaced, it is possible to correct the shift of the recording position using a relative correction value suitable for the print head.

  The present invention relates to a printing method, a printing apparatus, a computer program for realizing the function of the printing method or the printing apparatus, a recording medium recording the computer program, and data embodied in a carrier wave including the computer program. It can be realized in various modes such as a signal.

Next, embodiments of the present invention will be described in the following order based on examples.
A. Device configuration:
B. Occurrence of misregistration between nozzle rows:
C. First Example (Recording Position Deviation Correction 1 between Nozzle Rows):
D. Second Embodiment (Recording Position Deviation Correction 2 between Nozzle Rows):
E. Third Example (Correction of recording position deviation between dots of different sizes):
F. Modified example

A. Device configuration:
FIG. 1 is a schematic configuration diagram of a printing system including an inkjet printer 20 as a first embodiment of the present invention. The printer 20 includes a sub-scan feed mechanism that transports the printing paper P in the sub-scan direction by the paper feed motor 22 and a main scan feed that reciprocates the carriage 30 in the axial direction (main scan direction) of the platen 26 by the carriage motor 24. Mechanism, a head drive mechanism that drives a print head unit 60 (also referred to as a “print head assembly”) mounted on the carriage 30 to control ink ejection and dot formation, and these paper feed motor 22, carriage motor 24, a control circuit 40 that controls the exchange of signals with the print head unit 60 and the operation panel 32. The control circuit 40 is connected to the computer 88 via the connector 56.

  The sub-scan feed mechanism for transporting the printing paper P includes a gear train (not shown) that transmits the rotation of the paper feed motor 22 to the platen 26 and a paper transport roller (not shown). Further, the main scanning feed mechanism for reciprocating the carriage 30 has an endless drive belt 36 between the carriage motor 24 and a slide shaft 34 that is installed in parallel with the axis of the platen 26 and slidably holds the carriage 30. And a position sensor 39 for detecting the origin position of the carriage 30.

  FIG. 2 is a block diagram showing the configuration of the printer 20 with the control circuit 40 as the center. The control circuit 40 is configured as an arithmetic and logic circuit including a CPU 41, a programmable ROM (PROM) 43, a RAM 44, and a character generator (CG) 45 that stores a dot matrix of characters. The control circuit 40 further includes an I / F dedicated circuit 50 dedicated to interface with an external motor and the like, and a head that is connected to the I / F dedicated circuit 50 and drives the print head unit 60 to eject ink. A drive circuit 52 and a motor drive circuit 54 for driving the paper feed motor 22 and the carriage motor 24 are provided. The I / F dedicated circuit 50 incorporates a parallel interface circuit and can receive a print signal PS supplied from the computer 88 via the connector 56.

  FIG. 3 is an explanatory diagram showing a specific configuration of the print head unit 60 and the ink ejection principle. As shown in FIG. 3, the print head unit 60 has a substantially L shape, can be mounted with a black ink cartridge and a color ink cartridge (not shown), and a partition plate that partitions both cartridges so that they can be mounted. 31 is provided.

  A head ID seal 100 indicating head identification information (also referred to as “head ID”) assigned in advance according to the characteristics of the print head unit 60 is attached to the upper end surface of the print head unit 60. The contents of the head ID displayed on the head ID seal 100 will be described later.

  The entire configuration of FIG. 3 including the print head 28 and the ink cartridge mounting portion is referred to as a “print head unit 60” because the print head unit 60 is attached to and detached from the printer 20 as one component. . That is, when the print head 28 is to be replaced, the print head unit 60 is replaced.

  At the bottom of the print head unit 60, introduction pipes 71 to 76 that guide ink from the ink container to the print head 28 are provided upright. When the black ink cartridge and the color ink cartridge are mounted on the print head unit 60 from above, the introduction tubes 71 to 76 are inserted into the connection holes provided in the respective cartridges.

  FIG. 4 is an explanatory diagram for explaining a mechanism for ejecting ink. When the ink cartridge is attached to the print head unit 60, the ink in the ink cartridge is sucked out through the introduction pipes 71 to 76, and is provided at the lower part of the print head unit 60 as shown in FIG. Guided to the print head 28.

  The print head 28 includes a plurality of nozzles n provided in a line for each color, and an actuator circuit 90 that operates the piezoelectric element PE provided in each nozzle n. The actuator circuit 90 is a part of the head drive circuit 52 (FIG. 2), and controls on / off of a drive signal supplied from a drive signal generation circuit (not shown) in the head drive circuit 52. That is, the actuator circuit 90 latches data indicating ON (discharges ink) or OFF (does not discharge ink) for each nozzle in accordance with the print signal PS supplied from the computer 88, and drives only the ON nozzle. A signal is applied to the piezo element PE.

  FIG. 5 is an explanatory diagram showing the principle of driving the nozzle n by the piezo element PE. The piezo element PE is installed at a position in contact with the ink passage 80 that guides ink to the nozzle n. In this embodiment, by applying a voltage having a predetermined time width between the electrodes provided at both ends of the piezo element PE, the piezo element PE rapidly expands as shown in FIG. The one side wall is deformed. As a result, the volume of the ink passage 80 contracts according to the expansion of the piezo element PE, and the ink corresponding to the contraction becomes particles Ip and is ejected from the tip of the nozzle n at high speed. Printing is performed by the ink particles Ip soaking into the paper P mounted on the platen 26.

  FIG. 6 is an explanatory diagram showing a correspondence relationship between a plurality of nozzles provided in the print head 28 and a plurality of actuator chips. The printer 20 performs printing using six colors of ink of black (K), dark cyan (C), light cyan (LC), dark magenta (M), light magenta (LC), and yellow (Y). It is an apparatus, and is provided with a nozzle row for each ink. Note that dark cyan and light cyan are cyan inks having substantially the same hue and different densities. The same applies to dark magenta ink and light magenta ink.

  The actuator circuit 90 includes a first actuator chip 91 for driving the black nozzle row K and the dark cyan nozzle row C, a second actuator chip 92 for driving the light cyan nozzle row LC and the dark magenta nozzle row M, and a light A magenta nozzle row LM and a third actuator chip 93 for driving the yellow nozzle row Y are provided.

  FIG. 7 is an exploded perspective view of the actuator circuit 90. The three actuator chips 91 to 93 are adhered to the laminated body of the nozzle plate 110 and the reservoir plate 112 with an adhesive. Further, the connection terminal plate 120 is fixed on the actuator chips 91 to 93. At one end of the connection terminal plate 120, an external connection terminal 124 for electrical connection with an external circuit (specifically, the I / F dedicated circuit 50 in FIG. 2) is formed. In addition, an internal connection terminal 122 for electrical connection with the actuator chips 91 to 93 is provided on the lower surface of the connection terminal plate 120. Further, a driver IC 126 is provided on the connection terminal plate 120. In the driver IC 126, a circuit for latching a print signal given from the computer 88, an analog switch for turning on / off a drive signal in accordance with the print signal, and the like are provided. The wiring between the driver IC 126 and the connection terminals 122 and 124 is not shown.

  FIG. 8 is a partial cross-sectional view of the actuator circuit 90. Here, only the cross section of the first actuator chip 91 and the connection terminal plate 120 on the first actuator chip 91 is shown, but the other actuator chips 92 and 93 have the same structure as the first actuator chip 91.

  In the nozzle plate 110, nozzle openings for each ink are formed. The reservoir plate 112 is a plate-like body for forming an ink storage part (reservoir). The actuator chip 91 includes a ceramic sintered body 130 that forms the ink passage 80 (FIG. 5), a piezoelectric element PE disposed above the ceramic channel 130 via a wall surface, and a terminal electrode 132. When the connection terminal plate 120 is fixed on the actuator chip 91, the connection terminal 122 provided on the lower surface of the connection terminal plate 120 and the terminal electrode 132 provided on the upper surface of the actuator chip 91 are electrically connected. Is done. The wiring between the terminal electrode 132 and the piezo element PE is not shown.

B. Occurrence of misregistration between nozzle rows:
In the first and second embodiments, which will be described later, a recording position shift that occurs between nozzle rows during bidirectional printing is adjusted. Therefore, before describing these embodiments, first, the occurrence of a shift in the recording position between the nozzle rows will be described.

FIG. 9 is an explanatory diagram showing positional misalignment during bidirectional printing regarding different nozzle arrays. The nozzle n moves horizontally in both directions above the printing paper P, and forms dots on the printing paper P by ejecting ink in the forward path and the backward path, respectively. Here, the case where the black ink K is ejected and the case where the cyan ink C is ejected are shown in an overlapping manner. The black ink K is assumed to be ejected vertically downward at the ejection speed V _K , while the cyan ink C is assumed to be ejected at a lower ejection speed V _C than the black ink. The combined velocity vectors CV _K and CV _{C for} each ink are a combination of the downward discharge velocity vector and the main scanning velocity vector Vs of the nozzle n. Since the black ink K and the cyan ink C have different downward discharge speeds V _K and V _C , the combined speeds CV _K and CV _C have different sizes and directions.

In this example, black dots are corrected so that the misalignment in bidirectional printing becomes zero. However, since the combined velocity vector CV _C of cyan ink C is different from the synthetic speed vector CV _K of black ink K, when ejecting the cyan ink C at the same timing as the black ink K, the printing paper P with respect to the recording position of the cyan dots A large deviation will occur on the top. It can also be seen that the relative positional relationship (left-right relationship) between the black dots and cyan dots in the forward path is opposite to that in the backward path.

  FIG. 10 is an explanatory diagram showing a plan shift of the recording position shown in FIG. Here, a case is shown where vertical ruled lines along the sub-scanning direction y are recorded in the forward path and the backward path using the black ink K and the cyan ink C, respectively. The vertical ruled lines recorded on the forward path using black ink coincide with the vertical ruled lines recorded on the return path in the main scanning direction x. On the other hand, the vertical ruled line recorded in the forward path using cyan ink is recorded on the right side of the black vertical ruled line, and the vertical ruled line recorded in the return path is recorded on the left side of the black vertical ruled line.

  As described above, when the misalignment between the print positions of the forward pass and the return pass is corrected only for the black nozzle row, the misalignment of the print position may not be corrected well for the other nozzle rows.

The ejection speed of ink droplets ejected from each nozzle row varies depending on various factors as described below.
(1) Manufacturing error of the actuator chip.
(2) Physical properties of the ink (for example, viscosity).
(3) Weight of ink droplet.

  When the main factor of the ink droplet ejection speed is an actuator chip manufacturing error, the ink droplet ejection speed ejected from the same actuator chip is substantially the same. Therefore, in this case, it is preferable to correct the recording position shift in the main scanning direction for each group of nozzle rows driven by different actuator chips.

  On the other hand, if the physical properties of the ink and the weight of the ink droplets have a large effect on the ejection speed, the dot recording position deviation in the main scanning direction should be corrected for each ink or for each nozzle row. Is preferred.

C. First Example (Recording Position Deviation Correction 1 between Nozzle Rows):
FIG. 11 is a flowchart showing the entire processing in the first embodiment of the present invention. In step S1, the printer 20 is assembled on the production line, and in step S2, a relative correction value is set in the printer 20 by the operator. In step S3, the printer 20 is shipped from the factory, and in step S4, the user who purchased the printer 20 sets a reference correction value for correcting a positional deviation during use, and executes printing. Hereinafter, the contents of steps S2 and S4 will be described in detail.

FIG. 12 is a flowchart showing the detailed procedure of step S2 of FIG. In step S11, the printer 20 is used to print a test pattern for determining a relative correction value (relative positional deviation inspection pattern). FIG. 13 is an explanatory diagram illustrating an example of a test pattern for determining a relative correction value. In this test pattern, six vertical ruled lines L _K , L _C , L _LC , L _M , L _LM , and L _Y extending on the printing paper P in the sub-scanning direction y are inks K, C, LC having six colors. , M, LM, and Y, respectively. These six vertical ruled lines are recorded by simultaneously ejecting ink from six sets of nozzle rows while scanning the carriage 30 at a constant speed. Ink ejection in one main scan can only form dots separated by the nozzle pitch in the sub-scanning direction y. Therefore, in order to record vertical ruled lines as shown in FIG. Ink is ejected at the same timing.

  As the test pattern, a linear pattern in which dots are intermittently recorded can be used instead of the vertical ruled line. The same applies to a test pattern for determining a reference correction value described later.

In step S12 of FIG. 12, the mutual shift amount of the six vertical ruled lines shown in FIG. 13 is measured. This measurement is performed, for example, by reading an image of a test pattern with a CCD camera and measuring the positions of the vertical ruled lines L _K , L _C , L _LC , L _M , L _LM , and L _{Y in} the main scanning direction by image processing. Realized. The positions of the six vertical ruled lines are formed by simultaneously ejecting ink from the six sets of nozzle rows. Therefore, if the ink discharge speeds by the six sets of nozzle rows are the same, the six vertical ruled lines are set. The spacing of should be equal to the spacing of the nozzle rows.

X-coordinate value x _K shown in FIG. _{13, x C, x LC,} x M, x LM, x Y is the x-coordinate value x _K of vertical ruled lines L _K of the black ink when the reference, the other five The coordinate values of the respective vertical ruled lines when the vertical ruled lines are arranged according to the design value of the interval between the nozzle rows are shown. Therefore, the positions indicated by these x coordinate values x _K , x _C , x _LC , x _M , x _LM , and x _Y are also referred to as “design positions” below. In step S12, deviation amounts δ _C , δ _LC , δ _M , δ _LM , δ _Y between the design position and the actual vertical ruled line position are measured for five vertical ruled lines other than the black vertical ruled line. At this time, when the position is shifted to the right side from the design position, the shift amount δ is set to a positive value. When the position is shifted to the left side from the design position, the shift amount δ is set to a negative value.

In step S <b> 13, the operator determines an appropriate head ID from the amount of deviation thus measured, and sets the head ID in the printer 20. The head ID is information indicating an appropriate relative correction value for correcting the measured shift amount. As an appropriate relative correction value Δ, for example, as given by the following formula (1), the sign of the average value δave of the deviation amount of all the vertical ruled lines other than the reference vertical ruled line L _K is used. Inverted ones can be used.
Δ = −δave = −Σδi / (N−1) (1)
Here, Σ represents an operation for taking the sum of the deviation amounts δi of all vertical ruled lines other than the black ruled vertical ruled line, and N represents the total number of vertical ruled lines (that is, the number of nozzle rows). .

  FIG. 14 is an explanatory diagram showing the relationship between the relative correction value Δ and the head ID. In this example, the head ID is set to 1 when the relative correction value Δ is −35.0 μm, and the value of the head ID increases by one every time the relative correction value Δ increases by 17.5 μm. Here, 17.5 μm is the minimum value (minimum adjustable value) of the shift amount in the main scanning direction that can be adjusted in the printer 20. As this minimum adjustable value, a value equal to the dot pitch along the main scanning direction can be used. For example, when the resolution in the main scanning direction is 1440 dpi, the dot pitch is about 17.5 μm (= 25.4 mm / 1440), and this value is used as the minimum adjustable value. Note that a value smaller than the dot pitch can be set as the minimum adjustable value.

  The head ID thus determined is stored in the PROM 43 (FIG. 2) in the printer 20. In this embodiment, a head ID seal 100 indicating a head ID is further attached to the upper surface of the print head unit 60 (FIG. 3). Alternatively, a non-volatile memory (for example, a programmable ROM) may be provided in the driver IC 126 (FIG. 7) provided in the print head unit 60, and the head ID may be stored in the non-volatile memory. If the head ID seal 100 is attached to the print head unit 60 or the head ID is stored in the nonvolatile memory in the print head unit 60, the print head unit 60 can be used for another printer 20 as well. There is an advantage that a head ID suitable for the print head unit 60 can be used.

  The determination of the relative correction value in step S2 can also be executed in a state in which the print head unit 60 is incorporated in a dedicated inspection device in a process before the print head unit 60 is incorporated in the printer 20. In this case, the head ID is registered in the PROM 43 in the printer 20 when the print head unit 60 is incorporated into the printer 20 in the subsequent printer assembly process. As a method of registration in the PROM 43, for example, a method of reading the head ID seal 100 with a dedicated reading device or a method of inputting a head ID from a keyboard by an operator can be employed. Alternatively, the head ID stored in the nonvolatile memory in the print head unit 60 may be transferred to the PROM 43 in the printer 20.

The relative correction value Δ may be an average value of the deviation amounts of light cyan and light magenta, as given by the following equation (2).
Δ = − (δ _LC + δ _LM ) / 2 (2)

  Light cyan and light magenta are inks that are most frequently used in a halftone area of a color image (particularly, the image density of cyan or magenta is in the range of about 10% to about 30%). Accuracy has a significant effect on image quality. Therefore, if the head ID is determined from the average value of the shift amounts of light cyan and light magenta, these positional shift amounts can be reduced, so that the image quality of the color image can be improved.

  Note that when the above equation (2) is used, it is sufficient to measure the deviation amount δ from the black ink only for the light cyan ink and the light magenta ink.

  As shown in the flowchart of FIG. 11, the printer 20 is shipped after the head ID is set in the printer 20. When the user uses the printer 20, the deviation of the recording position during bidirectional printing is adjusted as follows using this head ID.

  FIG. 15 is a flowchart showing a procedure for adjusting the deviation during use by the user. In step S21, a test pattern for determining a reference correction value (reference position deviation inspection pattern) is printed using the printer 20. FIG. 16 is an explanatory diagram illustrating an example of a test pattern for determining a reference correction value. This test pattern is composed of a plurality of vertical ruled lines that are printed on the forward path and the backward path using black ink. In the forward pass, vertical ruled lines are recorded at regular intervals, but in the return pass, the positions of the vertical ruled lines in the main scanning direction are sequentially shifted in units of one dot pitch. As a result, a plurality of sets of vertical ruled line pairs are printed on the printing paper P such that the relative positions of the forward and reverse vertical ruled lines are shifted by one dot pitch. A number of misalignment adjustment numbers is printed under a plurality of pairs of vertical ruled lines. The deviation adjustment number has a function as correction information indicating a preferable correction state. Here, the “preferred correction state” means that the positions of the dots formed in the forward path and the backward path in the main scanning direction when the recording position (or recording timing) in the forward path or the backward path is corrected with an appropriate reference correction value. A state that matches. Therefore, a preferable correction state is realized by an appropriate reference correction value. In the example of FIG. 16, a pair of vertical ruled lines having a shift adjustment number of 4 indicates a preferable correction state.

  Note that the test pattern for determining the reference correction value is formed by the reference nozzle row used when determining the relative correction value. Therefore, when the magenta nozzle row is used as the reference nozzle row in place of the black nozzle row when determining the relative correction value, the test pattern for determining the reference correction value is also formed by the magenta nozzle row. .

  The user observes this test pattern and inputs the shift adjustment number of the vertical ruled line pair with the least shift on the user interface screen (not shown) of the printer driver of the computer 88 (FIG. 2). The deviation adjustment number is stored in the PROM 43 in the printer 20.

  Thereafter, when the execution of printing is instructed by the user in step S23, bidirectional printing is executed in step S24 while performing misalignment correction using the reference correction value and the relative correction value. FIG. 17 is a block diagram illustrating a main configuration related to misalignment correction during bidirectional printing in the first embodiment. The PROM 43 in the printer 20 is provided with a head ID storage area 200, an adjustment number storage area 202, a relative correction value table 204, and a reference correction value table 206. In the head ID storage area 200, a head ID indicating a preferred relative correction value is stored. In the adjustment number storage area 202, a shift adjustment number indicating a preferred reference correction value is stored. The relative correction value table 204 is a table that stores the relationship between the head ID and the relative correction value Δ shown in FIG. The reference correction value table 206 is a table showing the relationship between the deviation adjustment number and the reference correction value. The reference correction value table 206 is a table that stores the relationship between the shift amount (that is, the reference correction value) of the recording position of the vertical ruled line on the return path and the shift adjustment number in the test pattern shown in FIG.

  The RAM 44 in the printer 20 stores a computer program having a function as a positional deviation correction execution unit (adjustment value determination unit) 210 for correcting positional deviation during bidirectional printing. The positional deviation correction execution unit 210 reads the relative correction value corresponding to the head ID stored in the PROM 43 from the relative correction value table 204 and reads the reference correction value corresponding to the deviation adjustment number from the reference correction value table 206. When the positional deviation correction execution unit 210 receives a signal indicating the origin position of the carriage 30 from the position sensor 39 (FIG. 1) in the return path, the positional deviation correction execution unit 210 performs a head correction according to the total correction value of the relative correction value and the reference correction value. A signal (delay amount setting value ΔT) for instructing the recording timing is supplied to the head driving circuit 52. In the head drive circuit 52, the same drive signal is supplied to the three actuator chips 91 to 93, and the return path is set according to the recording timing (that is, the delay amount setting value ΔT) given from the position deviation correction execution unit 210. Adjust the recording position. As a result, in the return path, the recording positions of the six nozzle arrays are adjusted with a common correction amount. As described above, since both the relative correction value and the reference correction value are set to an integral multiple of the dot pitch in the main scanning direction, this recording position (that is, the recording timing) is also in units of dot pitch in the main scanning direction. Adjusted. The comprehensive correction value is a value obtained by adding the reference correction value and the relative correction value.

FIG. 18 is an explanatory diagram showing the contents of positional deviation correction using the reference correction value and the relative correction value. FIG. 18A shows that vertical ruled lines formed with black dots are printed at positions shifted in the forward path and the backward path when the positional deviation is not adjusted. FIG. 18B shows a result of adjusting the positional deviation of the black dots using the reference correction value. When the correction using the reference correction value is performed, the positional deviation of the black dots is eliminated during bidirectional printing. FIG. 18C shows a case where vertical ruled lines formed with cyan dots are printed in addition to the vertical ruled lines formed with black dots in the same adjustment state as in FIG. 18B. FIG. 18C is the same as FIG. 10 and there is no black dot misalignment, but the cyan dot misalignment is quite large. FIG. 18D shows a black dot ruled line and a cyan dot ruled line in the case where the shift adjustment by the relative correction value Δ (= −δ _C ) for cyan dots is performed in addition to the shift adjustment by the reference correction value. ing. In FIG. 18D, the positional deviation of the cyan dots is reduced, but the positional deviation of the black dots is slightly increased. As a result, the positional deviation between the black dots and the cyan dots is reduced to approximately the same level. Yes. This is because the recording positions of the six nozzle rows in the return path are corrected with a common correction amount. The example of FIG. 18D is an example in which two types of dots, black dots and cyan dots, are selected as the target dots for positional deviation adjustment, and positional deviation adjustment for these two types of dots is performed.

FIG. 19 is an explanatory diagram showing the contents of positional deviation correction when only cyan dots are targeted for positional deviation adjustment. The adjustment by the reference correction value shown in FIGS. 19A to 19C is the same as that in FIGS. 18A to 18C, and FIG. 19D is different from FIG. In FIG. 19D, as the relative correction value Δ, a value twice the cyan dot shift amount δ _{C in} the relative correction value determination test pattern (FIG. 13) (precisely, a value with a minus sign added thereto). Is used. By doing so, the positional deviation of the black dots becomes large, but the cyan dot can make the positional deviation of the reciprocation almost zero.

As can be understood from the examples of FIGS. 18 and 19, when the deviation amount δ of a specific dot in the relative correction value determination test pattern is used as the relative correction value Δ, the specific dot and the reference dot (black Both the dot and the dot correspond to the target dots for positional deviation adjustment, and the positional deviation regarding these target dots can be reduced. On the other hand, when twice the deviation amount δ of a specific dot in the relative correction value determination test pattern is used as the relative correction value Δ, only that specific dot corresponds to the target dot for positional deviation adjustment. It is possible to reduce the positional deviation regarding the dots. Specifically, when the relative correction value Δ (= − (δ _LC + δ _LM ) / 2) given by the above-described equation (2) is used, 3 of black dots, light cyan dots, and light magenta dots are used. It is possible to reduce the positional misalignment regarding the types of dots to almost the same extent. Further, when the double value is used as the relative correction value, the positional deviation regarding the two types of dots of the light cyan dot and the light magenta dot can be reduced to substantially the same level. Similarly, when the relative correction value Δ (= −δave) given by the above-described equation (1) is used, the positional deviation regarding all six types of dots can be reduced to substantially the same level. In addition, when the double value is used as the relative correction value, the positional deviation regarding the five types of dots other than the black dots can be reduced to substantially the same level.

  As can be seen from FIGS. 18D and 19D, when the positional deviation adjustment is performed based on the reference correction value and the relative correction value, the positional deviation of the color ink dots may become excessively large. Therefore, the quality of the color image is improved.

  In black-and-white printing, since color ink is not used, there is no need to perform positional deviation correction using relative correction values as shown in FIGS. 18D and 19D. Therefore, in black and white printing, positional deviation correction using only the reference correction value as shown in FIG. 18B is preferable. Therefore, when the control circuit 40 of the printer 20 (specifically, the positional deviation correction execution unit 210 in FIG. 17) is notified from the computer 88 (FIG. 1) that monochrome printing is performed, only the reference correction value is used. It is configured to correct misalignment during bidirectional printing, and to correct misregistration during bidirectional printing using a reference correction value and a relative correction value when notified of color printing. It is preferable.

  By the way, there are cases where it is desired to replace the print head unit 60 for reasons such as deterioration of the print head unit 60 over time. When the print head unit 60 is replaced, the head ID of the replaced print head unit 60 is written in the PROM 43 in the control circuit 40 of the printer 20. There are several methods for executing the writing of the head ID as follows. The first method is a method in which the user inputs the head ID displayed on the head ID sticker 100 attached to the print head unit 60 from the computer 88 and writes it to the PROM 43. The second method is a method in which the control circuit 40 reads the head ID from the nonvolatile memory provided in the driver IC 126 (FIG. 7) of the print head unit 60 and writes it to the PROM 43. Thus, if the head ID is stored in the PROM 43 after the print head unit 60 is replaced, the head ID (that is, the relative correction value) suitable for the print head unit 60 after the replacement is used for bidirectional printing. It is possible to correct the positional deviation.

  As described above, in the first embodiment, the relative correction value for correcting the misalignment during bidirectional printing with respect to the other nozzle rows is set on the basis of the black nozzle row, and the relative correction value and the black nozzle row are set. The positional deviation at the time of color bi-directional printing is corrected according to the reference correction value. As a result, it is possible to improve the image quality of color printing. In particular, the user only needs to adjust the positional deviation with respect to the reference nozzle row, and there is an advantage that the image quality during color bidirectional printing can be improved without adjusting the positional deviation of all ink. It should be noted that, when monochrome printing is performed, the positional deviation during bidirectional printing is corrected using only the reference correction value, so that there is an advantage that monochrome printing is not deteriorated.

  FIG. 20 is an explanatory diagram illustrating another configuration of the nozzle row of the print head 28. The print head 28a is provided with three sets of nozzle rows K1 to K3 for black (K), and one set of nozzle rows for cyan (C), magenta (M), and yellow (Y). It has been. In monochrome printing, high-speed printing is executed using all three sets of black nozzle rows K1 to K3. On the other hand, during color printing, the two black nozzle rows K1 and K2 of the first actuator chip 91 are not used, and the black nozzle row K3 and the cyan nozzle row C of the second actuator chip 92 are used. And a magenta nozzle row M and a yellow nozzle row Y are used.

When performing color printing using such a print head, for example, as given by the following equations (3a) and (3b), an average value of the deviation amount between cyan and magenta, or a value that is twice that value is obtained. , And used as a relative correction value Δ during color bidirectional printing.
Δ = − (δ _C + δ _M ) / 2 (3a)
Δ = − (δ _C + δ _M ) (3b)

The deviation amounts δ _C and δ _M between cyan and magenta are measured with reference to the vertical ruled line formed by the black nozzle row K3 used for color printing in the relative correction value determination test pattern (FIG. 13). Relative amount of deviation.

  Thus, in the case of four-color printing that does not use light ink, it is possible to improve the image quality of a color image by determining the head ID from the average value of the amount of deviation between cyan and magenta. Here, yellow is excluded because the yellow dots are not so noticeable, and even if the yellow dots are slightly shifted during bidirectional printing, the image quality is not greatly affected. However, the head ID may be determined from the average value of the shift amounts of cyan, magenta, and yellow. That is, the relative correction value may be determined using the average value of the deviation amounts for all the nozzle rows other than the reference nozzle row among the plurality of nozzle rows used for color printing.

Note that the relative correction value ΔK of the other black nozzle rows K1, K2 with respect to the reference black nozzle row K3 may be obtained. This relative correction value ΔK can be obtained according to the following equation (4).
ΔK = − (δ _K1 + δ _K2 ) / 2 (4)
Here, δ _K1 is a shift amount related to the first black nozzle row K1, and δ _K2 is a shift amount related to the second black nozzle row K2.

  At the time of monochrome printing, using the relative correction value ΔK for the two sets of black nozzle rows K1 and K2 and the reference correction value (determined in FIG. 15) for the black nozzle row K3 used as a reference, If the positional deviation correction is performed, it is possible to reduce the positional deviation of bidirectional printing in black and white printing using three sets of nozzle rows. That is, when a plurality of black nozzle arrays are used in black and white printing, bidirectional printing is performed using a reference correction value related to a specific reference black nozzle array and relative correction values related to other black nozzle arrays. It is preferable to correct the positional deviation of the hour.

D. Second Embodiment (Recording Position Deviation Correction 2 between Nozzle Rows):
FIG. 21 is a block diagram showing a main configuration related to misalignment correction during bidirectional printing in the second embodiment. The difference from the configuration shown in FIG. 17 is that head drive circuits 52a, 52b, and 52c for driving the three actuator chips 91, 92, and 93 are independently provided. That is, the three head drive circuits 52a, 52b, and 52c drive the three actuator chips 91, 92, and 93 independently. Therefore, the recording timing instruction from the positional deviation correction execution unit 210 can also be given independently to each of the head drive circuits 52a, 52b, and 52c. Therefore, positional deviation correction during bidirectional printing can also be executed for each actuator chip.

  Also in the second embodiment, the black nozzle row K of the first actuator chip 91 is used as the reference nozzle row. Accordingly, the reference correction value is determined from the test pattern recorded using the black nozzle row K, as in the first embodiment.

On the other hand, the relative correction value is determined for each actuator chip in the second embodiment. That is, as the relative correction value Δ ₉₁ of the first actuator chip 91, the positive / negative sign of the shift amount δ _C of the vertical ruled line formed by the dark cyan nozzle row C is given by the following equation (4a). The inverted value is adopted.
Δ ₉₁ = −δ _C (4a)

The relative correction values Δ ₉₂ and Δ ₉₃ of the second and third actuator chips ₉₂ and ₉₃ are related to the nozzle rows of the actuator chips as given by the following expressions (4b) and (4c), respectively. A value obtained by inverting the sign of the average value of the deviation amounts is adopted.
Δ ₉₂ = − (δ _LC + δ _M ) / 2 (4b)
Δ ₉₃ = − (δ _LM + δ _Y ) / 2 (4c)

Note that the relative correction values Δ ₉₂ and Δ ₉₃ for the second and third actuator chips ₉₂ and ₉₃ may be determined based on the shift amount of the recording position from the reference nozzle row for one nozzle row. At this time, instead of the above (4b) and (4c), for example, the following equations (5b) and (5c) can be used.
Δ ₉₂ = −δ _LC (5b)
Δ ₉₃ = −δ _LM (5c)

The PROM 43 in the printer 20 stores head IDs representing these three relative correction values Δ ₉₁ , Δ ₉₂ , Δ ₉₃ . Also, relative correction values Δ ₉₁ , Δ ₉₂ , Δ ₉₃ are supplied to the positional deviation correction execution unit 210 according to the head ID. Instead of the above equations (4a) to (5c), a value twice the value on the right side of these equations can be used as the relative correction value.

  The second embodiment described above is characterized in that the relative correction value can be set independently for each actuator chip. In this way, the relative positional deviation from the reference nozzle row can be corrected for each actuator chip, so that the positional deviation during bidirectional printing can be further reduced. Note that in a printer of a type in which three sets of nozzle rows are driven by one actuator chip, the relative correction value can be set independently for each of the three sets of nozzle rows.

  From the viewpoint of improving the image quality of the halftone area, it is preferable to select light cyan dots or light magenta dots as dots to be adjusted for positional deviation, and to reduce the positional deviation of these dots. However, the principle of the first and second embodiments described above is that when performing color printing using M types of ink (M is an integer of 2 or more), a specific density having a relatively low density among the M types of inks. This is applicable when ink (that is, a specific ink other than black) is selected as a target dot for positional deviation adjustment and the positional deviation of the target dot is reduced.

E. Third Example (Correction of recording position deviation between dots of different sizes):
In the first and second embodiments described above, the recording position deviation between the nozzle rows is corrected. In the third embodiment described below, the recording position deviation between a plurality of types of dots having different sizes is corrected. .

  FIG. 22 is an explanatory diagram showing the waveform of the original drive signal ODRV supplied from the head drive circuit 52 (FIG. 2) to the print head 28 in the third embodiment. In the original drive signal ODRV, in the forward path, a large dot waveform W11, a small dot waveform W12, and a medium dot waveform W13 are generated in this order during one pixel period. In the return path, a medium dot waveform W21, a small dot waveform W22, and a large dot waveform W23 are generated in this order during one pixel interval. By selectively using any one of the three waveforms in the forward pass and the return pass, any one of a large dot, a small dot, and a medium dot can be recorded at each pixel position. .

  The order of generation of the waveform for large dots, the waveform for medium dots, and the waveform for small dots in the forward path and the backward path is different in order to substantially match the recording positions of the dots in the main scanning direction in the forward path and the backward path. It is. FIG. 23 is an explanatory diagram showing three types of dots formed using the original drive signal ODRV of FIG. A grid in FIG. 23 indicates a boundary between pixel areas, and one rectangular area divided by the grid corresponds to an area for one pixel. The dots in each pixel area are recorded by ink droplets ejected by the print head 28 when the print head 28 (FIG. 3) moves along the main scanning direction. In the example of FIG. 23, odd-numbered raster lines L1, L3, and L5 are recorded in the forward path, and even-numbered raster lines L2 and L4 are recorded in the backward path. At this time, by adjusting the amount of ejected ink for each pixel, one of three types of dots having different sizes can be formed at each pixel position.

  The small dot is formed at the approximate center of the area of one pixel in both the forward pass and the return pass. The medium dot is formed at a position on the right side of the one-pixel region, and the large dot is formed over almost the entire one-pixel region. As described above, by using the original drive signal ODRV shown in FIGS. 22A and 22B, it is possible to substantially match the landing positions of the ink droplets in the forward path and the backward path. Of course, in reality, there is a possibility that some misalignment may occur during bidirectional printing with respect to each dot, so that misalignment adjustment is necessary.

  FIG. 24 is a graph showing a gradation reproduction method using three types of dots. The horizontal axis in FIG. 24 indicates the relative value of the image signal level, and the vertical axis indicates the dot recording density of three types of dots. Here, “dot recording density” means a ratio of pixel positions where dots are formed. For example, when dots are formed at 40 pixel positions in an area including 100 pixels, the dot recording density is 40%. The image signal level corresponds to a gradation value indicating the density gradation (density level) of the image.

  In the graph of FIG. 24, in the gradation range where the image signal level is 0% to about 16%, the dot recording density of small dots increases linearly from 0% to about 50% as the image signal level increases. As a result, in the image portion where the image signal level is about 16%, small dots are formed at about half the dot positions. In the gradation range where the image signal level is about 16% to about 50%, the dot recording density of small dots linearly decreases from about 50% to about 15% as the image signal level increases. The dot recording density of medium dots increases linearly from 0% to about 80%. In the gradation range where the image signal level is about 50% to 100%, the dot recording density of small dots and medium dots decreases linearly until reaching 0% as the image signal level increases. The dot recording density increases linearly from 0% to 100%. Thus, according to the image signal level of each image portion, the image portion is recorded with one or two types of dots, so that the density gradation of the image is smoothly and linearly reproduced.

  The deviation in the recording position between the forward pass and the return pass is easily noticeable in a halftone area having a gradation range of about 50% or less (about 10% to about 50%). In particular, deviations in the recording positions of the forward and return passes for medium dots and small dots that are frequently used in the halftone area tend to be noticeable in the image in the halftone area.

  By the way, when a test pattern for adjusting the bidirectional recording position deviation is created with medium dots and small dots, there arises a problem that it is difficult for the user to recognize the position deviation in the test pattern. Therefore, it is desirable to use a test pattern formed with large dots as a test pattern for user adjustment. In the third embodiment, in consideration of these circumstances, a reference deviation correction value for positional deviation is set using a test pattern recorded with large dots during adjustment by the user. Further, when printing is performed, this reference correction value is corrected with a predetermined relative correction value, so that the positional deviation adjustment is performed so that the recording positional deviation regarding small dots or medium dots is reduced.

  The processing procedure in the third embodiment is the same as that described in FIGS. 11, 12, and 15 in the first embodiment. However, the pattern for determining the relative correction value is different from that of the first embodiment.

  FIG. 25 is an explanatory diagram showing an example of a test pattern for determining a relative correction value. This test pattern is formed on the printing paper P and includes a large dot test pattern TPL, a small dot test pattern TPS, and a medium dot test pattern TPM. The three test patterns TPL, TPS, and TPM are composed of a pair of vertical ruled lines formed on the forward path and the return path, respectively, and are recorded using black ink. Each vertical ruled line is preferably a straight line having a width of 1 dot so that the position of the vertical ruled line can be measured as accurately as possible.

  In the third embodiment, in step S12 (FIG. 12), deviation amounts δL, δS, and δM of the recording positions of the forward path and the backward path in the three test patterns TPL, TPS, and TPM shown in FIG. 25 are measured. This measurement is realized, for example, by reading an image of a test pattern with a CCD camera and measuring the positions in the main scanning direction X of the vertical ruled line pairs of the three test patterns by image processing.

In step S13, a relative correction value is determined from the deviations δL, δS, and δM thus measured, and set in the PROM in the printer 20. The relative correction value is a difference between the shift amount related to the reference dots and the shift amount related to dots other than the reference dots. When the large dot is the reference dot, the relative correction value ΔS for the small dot and the relative correction value ΔM for the medium dot are given by the following equations (6a) and (6b), respectively.
ΔS = (δS−δL) (6a)
ΔM = (δM−δL) (6b)

  Instead of the relative correction values ΔS, ΔM, the operator may set three deviation amounts δL, δS, δM in the test pattern in the PROM 43 in the printer 20. That is, information that substantially represents the relative correction value may be set in the PROM in the printer 20. Further, it is not necessary to set a relative correction value for all dots other than the reference dot in the PROM 43 in the printer 20, and it is sufficient that at least one relative correction value (for example, ΔS) is set.

  As a test pattern for each dot, a pattern composed of a plurality of pairs of vertical ruled lines may be used. In this case, an average value of the reciprocal recording position deviations in a plurality of pairs of vertical ruled lines for each dot is adopted as the deviation of the recording position for that dot. Moreover, it is also possible to use a linear pattern in which dots are recorded intermittently instead of the vertical ruled lines.

  Furthermore, a part of the test pattern may be recorded with chromatic ink (magenta, light magenta, cyan, light cyan, etc.) other than black ink. In this case, the large dot test pattern TPL may be formed of black ink, and the small dot test pattern TPS and the medium dot test pattern TPM may be formed of chromatic ink. In a color image, small dots and medium dots of chromatic ink have a great influence on the image quality in the halftone area. Therefore, if small dots and medium dots are formed with chromatic color ink and a relative correction value is set for these, the image quality of the halftone area of the color image can be improved.

  In the third embodiment, the test pattern for determining the reference correction value (reference position shift inspection pattern) shown in FIG. 16 is printed on each of the forward pass and the return pass using large black ink dots (that is, reference dots). It consists of multiple pairs of vertical ruled lines.

  Note that the test pattern for determining the reference correction value is formed using the reference dots used when determining the relative correction value. Therefore, when a large magenta ink dot is used as a reference dot instead of a black ink large dot when determining the relative correction value, the test pattern for determining the reference correction value also has a large magenta ink size. Formed with dots.

  Note that it is preferable to select the largest dot as the reference dot used when recording a test pattern for adjusting the deviation by the user. In this way, the user can easily recognize the positional deviation in the test pattern, so that there is an advantage that the positional deviation can be adjusted more accurately.

  Also in the third embodiment, the positional deviation adjustment is executed by the configuration shown in FIG. 17 or FIG. FIG. 26 is an explanatory diagram showing the contents of the positional deviation adjustment in the third embodiment. FIG. 26A shows that vertical ruled lines formed with large dots (reference dots) are printed at positions shifted in the forward path and the backward path when the positional deviation is not adjusted. FIG. 26B shows the results when it is assumed that the positional deviation of the large dots has been adjusted using the reference correction value. When the correction using the reference correction value is performed, the positional deviation for large dots is eliminated during bidirectional printing. FIG. 26C shows a case where vertical ruled lines formed with small dots are printed in addition to the vertical ruled lines formed with large dots in the same adjustment state as FIG. In FIG. 26C, the positional deviation of the large dots has been eliminated, but the positional deviation of the small dots has not been eliminated. On the other hand, in a color image, the image quality is particularly important in a halftone area, and the positional deviation related to small dots has a greater influence on the image quality than large dots. In FIG. 26D, vertical ruled lines formed with large dots and vertical ruled lines formed with small dots when the shift adjustment with the small dot relative correction value ΔS is performed in addition to the shift adjustment with the reference correction value. Is shown. In FIG. 26D, the positional deviation of the small dots is reduced, but the positional deviation of the large dots is slightly increased. As can be seen from FIG. 26D, when the positional deviation adjustment is performed based on the reference correction value and the relative correction value, the positional deviation of the small dots can be reduced, so that the image quality of the halftone area of the color image is improved. improves.

In the case where the influence of the medium dot on the image quality is larger than that of the small dot, the positional deviation may be adjusted using the medium dot relative correction value ΔM. When the influence on the image quality of the small dots and the medium dots is approximately the same, the positional deviation may be adjusted using the average value Δave of the relative correction values of the small dots and the medium dots. At this time, the average value Δave of the relative correction values is given by the following equation (7).
Δave = {(δS−δL) + (δM−δL)} / 2
= {(ΔS + δM) / 2} −δL (7)

  As can be seen from the equation (7), the average value Δave of the relative correction values is a difference between the average value of the shift amounts δS and δM related to the small dots and the medium dots shown in FIG. 25 and the shift amount δL related to the reference dot.

  As can be understood from this example, the relative correction value may not be related to one type of target dot having a specific size, and an average relative correction value related to a plurality of target dots may be used. . Note that the term “target dot” in this specification means “one or more dots to be subjected to positional deviation correction”. The reference dot may be included in the “target dot”.

  By the way, in black-and-white printing, the positional deviation of large dots may have a larger influence on image quality. Therefore, in black and white printing, it may be preferable to perform positional deviation correction using only the reference correction value as shown in FIG. Therefore, when the control circuit 40 of the printer 20 (specifically, the misregistration correction execution unit 210 in FIG. 17) is notified from the computer 88 (FIG. 2) that monochrome printing is performed, only the reference correction value is used. The positional deviation at the time of bidirectional printing is adjusted, and the positional deviation at the time of bidirectional printing is adjusted using the reference correction value and the relative correction value when it is notified that color printing is being performed. It is preferable.

  In addition, even in the case of non-monochrome printing, when the positional deviation of the reference dots is particularly noticeable, it is preferable to adjust the positional deviation using the reference correction value as an adjustment value as it is. That is, the positional deviation correction execution unit (adjustment value determination unit) 210 uses the first adjustment mode in which the adjustment value is determined by correcting the reference correction value with the relative correction value, and the reference correction value is used as the adjustment value as it is. The adjustment value may be determined according to one of the two adjustment modes.

  As described above, in the third embodiment, the reference correction value for the large dot is corrected with the relative correction value prepared in advance, so that the adjustment value for positional deviation adjustment for the small dot and the medium dot is determined. It is possible to improve the image quality of the halftone area. In particular, when adjusting the positional deviation for the user, the test pattern formed with large dots is used, so that there is an advantage that the user can easily adjust the positional deviation accurately.

F. Variations:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

F1. Modification 1:
In a type of printer in which a plurality of values can be used as the main scanning speed (carriage moving speed) when correcting the positional deviation during bidirectional printing using the reference correction value and the relative correction value, it is related to the nozzle array. It is preferable to set a relative correction value for each main scanning speed. As can be seen from the description of FIG. 9 described above, when the main scanning speed Vs is different, the relative positional deviation amount between the nozzle rows also changes. Therefore, if the relative correction value is set for each different main scanning speed, it is possible to further reduce the positional deviation during bidirectional printing.

F2. Modification 2:
In a multi-value printer of a type that can form a plurality of dots of different sizes with the same ink at each pixel position when correcting the positional deviation during bidirectional printing using the reference correction value and the relative correction value, It is preferable to set a relative correction value for each dot size. When the dot size is different, the ink droplet ejection speed also changes. Therefore, if a relative correction value is set for each different dot size, it is possible to further reduce the positional deviation during bidirectional printing. In a multi-value printer, only one dot of the same size may be formed by one nozzle row during one main scan. In this case, since the dot size is selected for each main scan, an appropriate value corresponding to the dot size is selected for each main scan as the relative correction value used for correcting the positional deviation.

  Note that the printing operation for ejecting dots of different sizes can be considered as a printing mode in which the ink ejection speeds are different from each other. Therefore, the above-described modification means that a relative correction value is set for each of a plurality of dot ejection modes having different ink ejection speeds.

F3. Modification 3:
In the first and second embodiments, it is preferable to set the relative correction value independently for each nozzle row other than the reference nozzle row. By doing so, it is possible to further reduce the positional deviation compared to the first and second embodiments described above. Alternatively, the relative correction value may be set independently for each group of nozzle rows that eject the same ink. For example, when two sets of nozzle rows for ejecting specific ink are provided, the same relative correction value may be applied to the two sets of nozzles.

F4. Modification 4:
In the first to third embodiments, the black nozzle row is selected as the reference nozzle row when determining the reference correction value and the relative correction value. However, any nozzle row other than the black nozzle row is selected as the reference nozzle row. Is possible. However, since ink with low density (light cyan or light magenta) cannot easily recognize the test pattern when the user determines the reference correction value, ink with relatively high density (black, dark cyan, dark magenta) is ejected. It is preferable to use the nozzle row as the reference nozzle row.

F5. Modification 5:
In the first to third embodiments, the positional deviation is corrected by adjusting the dot recording position (or recording timing). However, other means may be used to correct the positional deviation. . For example, it is also possible to correct the positional deviation by delaying the drive signal to the actuator chip or adjusting the frequency of the drive signal.

F6. Modification 6:
In the third embodiment, three types of dots having different sizes can be recorded in one pixel area with one nozzle. However, the idea of this embodiment is that one nozzle is generally used for at least one type of ink. Therefore, the present invention can be applied to a printing apparatus in which N types of dots (N is an integer of 2 or more) having different sizes can be recorded at each pixel position. In this case, at least one dot including dots other than the largest dot among the N types of dots can be selected as the target dot for adjusting the positional deviation. The adjustment value of the deviation regarding the target dot is commonly applied to N types of dots.

  As the target dot, for example, the smallest dot among the N types of dots or the medium size dot among the N types of dots can be selected. It is expected that the image quality in the halftone area can be improved by selecting such target dots.

  Note that “N types of medium-sized dots” means a dot having (N + 1) / 2nd size when N is an odd number, and when N is an even number. It means a dot having an N / 2th or (N / 2 + 1) th size. Instead of this, as a dot having a medium size, the most frequently used dot may be used when the image signal shows 50% gradation.

F7. Modification 7:
In each of the above embodiments, the positional deviation is corrected by adjusting the recording position (or recording timing) of the return path. However, the positional deviation may be corrected by adjusting the recording position of the forward path. Further, the positional deviation may be corrected by adjusting both the forward and backward recording positions. That is, in general, the positional deviation may be corrected by adjusting at least one of the recording positions of the forward path and the backward path.

F8. Modification 8:
In each of the above embodiments, an ink jet printer has been described. However, the present invention is not limited to an ink jet printer, and is generally applicable to various printing apparatuses that perform printing using a print head. Further, the present invention is not limited to a method and apparatus for ejecting ink droplets, but can also be applied to a method and apparatus for recording dots by other means.

F9. Modification 9:
In each of the above embodiments, a part of the configuration realized by hardware may be replaced by software, and conversely, a part of the configuration realized by software may be replaced by hardware. . For example, a part of the function of the head drive circuit 52 shown in FIG. 12 can be realized by software.

1 is a schematic configuration diagram of a printing system including a printer 20 according to a first embodiment. FIG. 3 is a block diagram illustrating a configuration of a control circuit 40 in the printer 20. FIG. 3 is a perspective view illustrating a configuration of a print head unit 60. FIG. 3 is an explanatory diagram illustrating a configuration for ejecting ink in each print head. Explanatory drawing which shows a mode that the ink particle Ip is discharged by expansion | extension of the piezo element PE. FIG. 4 is an explanatory diagram illustrating a correspondence relationship between a plurality of nozzles in a print head and a plurality of actuator chips. The exploded perspective view of the actuator circuit 90. FIG. FIG. 4 is a partial cross-sectional view of an actuator circuit 90. Explanatory drawing which shows the position shift at the time of bidirectional | two-way printing of the dot recorded by a different nozzle row. Explanatory drawing which shows the position shift shown by FIG. 9 planarly. The flowchart which shows the whole process of 1st Example. The flowchart which shows the detailed procedure of step S2 of FIG. Explanatory drawing which shows an example of the test pattern for relative correction value determination. Explanatory drawing which shows the relationship between relative correction value (DELTA) and head ID. The flowchart which shows the detailed procedure of step S4 of FIG. Explanatory drawing which shows an example of the test pattern for a reference | standard correction value determination. FIG. 3 is a block diagram illustrating a main configuration related to misalignment correction during bidirectional printing in the first embodiment. Explanatory drawing which shows the content of the position shift correction using the reference | standard correction value and relative correction value when black dot and cyan dot are selected as object dot. Explanatory drawing which shows the content of the position shift correction using the reference | standard correction value and relative correction value when only a cyan dot is selected as an object dot. FIG. 6 is an explanatory diagram showing another configuration of the print head 28a. The block diagram which shows the structure of the control circuit 40a used in 2nd Example. Explanatory drawing which shows the waveform of the original drive signal ODRV in 3rd Example. Explanatory drawing which shows three types of dots formed in 3rd Example. The graph which shows the gradation reproduction method using three types of dots. Explanatory drawing which shows an example of the test pattern for relative correction value determination in 3rd Example. Explanatory drawing which shows the content of the position shift correction | amendment in 3rd Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 ... Inkjet printer 22 ... Paper feed motor 24 ... Carriage motor 26 ... Platen 28 ... Print head 30 ... Carriage 31 ... Partition plate 32 ... Operation panel 34 ... Sliding shaft 36 ... Drive belt 38 ... Pulley 39 ... Position sensor 40 ... Control Circuit 41 ... CPU
43 ... PROM
44 ... RAM
DESCRIPTION OF SYMBOLS 50 ... I / F exclusive circuit 52 ... Head drive circuit 54 ... Motor drive circuit 56 ... Connector 60 ... Print head unit 71-76 ... Introducing pipe 80 ... Ink passage 88 ... Computer 90 ... Actuator circuit 91-93 ... Actuator chip 100 ... Head ID seal 110 ... Nozzle plate 112 ... Reservoir plate 120 ... Connection terminal plate 122 ... Internal connection terminal 124 ... External connection terminal 130 ... Ceramic sintered body 132 ... Terminal electrode 200 ... Head ID storage area 202 ... Adjustment number storage area 204 ... Relative correction value table 206 ... Reference correction value table 210 ... Position displacement correction execution unit (adjustment value determination unit)

Claims (15)

A bidirectional printing apparatus having a bidirectional printing function for printing an image on a printing medium according to a printing image signal while performing main scanning in a bidirectional manner in both directions,
A print head having a plurality of nozzle arrays for recording dots at each pixel position on the print medium, wherein each nozzle array ejects one type of ink among black ink and a plurality of chromatic inks. A configured print head ; and
A main scanning drive unit that performs bidirectional main scanning by moving at least one of the print medium and the print head;
A sub-scanning drive unit that performs sub-scanning by moving at least one of the print medium and the print head;
A head drive unit that applies a drive signal to the print head to cause printing on the print medium;
A control unit for controlling bidirectional printing,
The controller is
A recording position adjustment unit that adjusts the recording position in the main scanning direction in the forward path and the backward path, using an adjustment value for reducing the deviation of the recording position in the main scanning direction in the forward path and the backward path,
The recording position adjustment unit
A first memory for storing a reference correction value for correcting a shift in the recording position in the main scanning direction in the forward pass and the return pass with respect to a specific reference dot formed by a specific nozzle row of the print head;
A second memory for storing a relative correction value prepared in advance for correcting the reference correction value;
An adjustment value determining unit that determines the adjustment value using at least the reference correction value;
With
The adjustment value determining unit includes a first adjustment mode that determines the adjustment value by correcting the reference correction value with the relative correction value, and a second adjustment that uses the reference correction value as the adjustment value as it is. With mode,
The adjustment value determination unit determines the adjustment value determined according to the first adjustment mode when the color printing is performed using black ink and a plurality of chromatic color inks. When the print position deviation is corrected using a common adjustment value commonly applied to dots and black and white printing is performed using black ink, the adjustment value determined according to the second adjustment mode is used as the black ink. It has the function of correcting the recording position deviation by applying to the dots of
The relative correction value is
(I) By simultaneously ejecting ink from the plurality of nozzle rows, a linear pattern in which dots are recorded continuously or intermittently is formed for each of the black ink and the plurality of chromatic inks,
(Ii) determining the measurement position by measuring the position of the linear pattern of each chromatic ink based on the linear pattern of the black ink;
(Iii) Considering the positions of the nozzle rows of the chromatic inks based on the positions of the nozzle rows of the black ink as the design positions of the linear patterns of the chromatic inks, the linear patterns of the chromatic inks Find the amount of deviation between the measurement position and the design position,
(Iv) averaging the deviation amounts for the plurality of chromatic inks;
A bidirectional printing device that is a value obtained by The bidirectional printing apparatus according to claim 1,
The print head can form at least N types of dots having different sizes (N is an integer of 2 or more),
The reference dot is a dot selected from the N types of dots,
In the first adjustment mode, the adjustment value is commonly applied to the N types of dots. The bidirectional printing apparatus according to claim 2, wherein
The bidirectional printing apparatus, wherein the reference dot is the largest dot among the N types of dots. The bidirectional printing apparatus according to any one of claims 1 to 3 ,
The bi-directional printing apparatus, wherein the reference correction value is determined according to correction information indicating a preferable correction state selected from a misregistration inspection pattern printed on a print medium using the reference dots. The bidirectional printing apparatus according to any one of claims 1 to 3 ,
The bidirectional printing apparatus can perform main scanning at a plurality of main scanning speeds,
The bi-directional printing apparatus, wherein the second memory stores a value that is independently applied to each of the plurality of main scanning speeds as the relative correction value. The bidirectional printing apparatus according to any one of claims 1 to 3 ,
The bidirectional printing apparatus can eject ink in a plurality of dot ejection modes having different ink ejection speeds,
The bi-directional printing apparatus, wherein the second memory stores a value that is independently applied to each of the plurality of dot ejection modes as the relative correction value. The bidirectional printing apparatus according to any one of claims 1 to 3 ,
The bi-directional printing apparatus, wherein the second memory is a non-volatile memory provided in the bi-directional printing apparatus. The bidirectional printing apparatus according to any one of claims 1 to 3 ,
The bi-directional printing apparatus, wherein the second memory is fixed to the print head so that the second memory can be attached to and detached from the bi-directional printing apparatus together with the print head. As a print head having a plurality of nozzle rows for recording dots at each pixel position on the print medium , each nozzle row is configured to eject one type of ink among black ink and a plurality of chromatic color inks. A bidirectional printing method for printing an image on the print medium in response to a print image signal while performing a main scan in a bidirectional manner using a printing apparatus including a print head,
(A) a step of setting a reference correction value for correcting a shift in the recording position in the main scanning direction in the forward pass and the return pass with respect to a specific reference dot formed by a specific nozzle row of the print head ;
(B) determining an adjustment value for reducing a shift in the printing position in the main scanning direction in the forward path and the backward path using at least the reference correction value;
(C) adjusting the recording position in the main scanning direction in the forward path and the backward path using the adjustment value,
The step (b)
When performing color printing using black ink and a plurality of chromatic color inks, it is determined according to a first adjustment mode for correcting the reference correction value with a relative correction value prepared in advance to correct the reference correction value. The correction value is used as a common adjustment value that is commonly applied to the black ink dots and the plurality of chromatic color ink dots.
When performing black and white printing using black ink, the adjustment value determined according to the second adjustment mode that uses the reference correction value as the adjustment value as it is is applied to the dots of the black ink to correct the recording position deviation. viewing including the step of running the,
The relative correction value is
(I) By simultaneously ejecting ink from the plurality of nozzle rows, a linear pattern in which dots are recorded continuously or intermittently is formed for each of the black ink and the plurality of chromatic inks,
(Ii) determining the measurement position by measuring the position of the linear pattern of each chromatic ink based on the linear pattern of the black ink;
(Iii) Considering the positions of the nozzle rows of the chromatic inks based on the positions of the nozzle rows of the black ink as the design positions of the linear patterns of the chromatic inks, the linear patterns of the chromatic inks Find the amount of deviation between the measurement position and the design position,
(Iv) averaging the deviation amounts for the plurality of chromatic inks;
Is a value obtained by
Bidirectional printing method. The bidirectional printing method according to claim 9 , wherein
The print head can form at least N types of dots having different sizes (N is an integer of 2 or more),
The reference dot is a dot selected from the N types of dots,
In the first adjustment mode, the adjustment value is commonly applied to the N types of dots. The bidirectional printing method according to claim 10 , wherein
The bidirectional printing method, wherein the reference dot is the largest dot among the N types of dots. The bidirectional printing method according to any one of claims 9 to 11 ,
The bi-directional printing method, wherein the reference correction value is determined according to correction information indicating a preferable correction state selected from a misregistration inspection pattern printed on a print medium using the reference dots. The bidirectional printing method according to any one of claims 9 to 11 ,
The printing apparatus is capable of performing main scanning at a plurality of main scanning speeds;
The bidirectional printing method, wherein the relative correction value is independently applied to each of the plurality of main scanning speeds. The bidirectional printing method according to any one of claims 9 to 11 ,
The printing apparatus can eject ink in a plurality of dot ejection modes having different ink ejection speeds,
The bidirectional correction method, wherein the relative correction value is independently applied to each of the plurality of dot ejection modes. As a print head having a plurality of nozzle rows capable of recording N types of dots of different sizes (N is an integer of 2 or more) in each pixel area on the print medium , each nozzle row is composed of black ink. a plurality of computers having a printing device having a respective one of the ink configured print head to discharge of the chromatic inks, while performing main scanning in both directions in a reciprocating, in accordance with print image signals A computer-readable recording medium recording a computer program for printing an image on the printing medium,
A first correction for correcting a reference correction value for correcting a shift in the recording position in the main scanning direction in the forward pass and the return pass with respect to a specific reference dot formed by a specific nozzle array of the print head is a first correction for correcting a reference correction value. The adjustment value for reducing the shift of the recording position in the main scanning direction in the forward pass and the return pass is determined in accordance with any one of the adjustment mode and the second adjustment mode in which the reference correction value is used as the adjustment value. A computer-readable recording medium recording a computer program for causing the computer to realize the function of adjusting the recording position in the main scanning direction in the forward path and the backward path using the adjustment value,
When performing color printing using black ink and a plurality of chromatic inks, the computer program sets the adjustment values determined in accordance with the first adjustment mode to the black ink dots and the plurality of chromatic ink dots. When the black position is corrected using the black ink, the adjustment value determined according to the second adjustment mode is used as the common adjustment value that is commonly applied to the black ink dots. applying running correction of the recording position shift in,
The relative correction value is
(I) By simultaneously ejecting ink from the plurality of nozzle rows, a linear pattern in which dots are recorded continuously or intermittently is formed for each of the black ink and the plurality of chromatic inks,
(Ii) determining the measurement position by measuring the position of the linear pattern of each chromatic ink based on the linear pattern of the black ink;
(Iii) Considering the positions of the nozzle rows of the chromatic inks based on the positions of the nozzle rows of the black ink as the design positions of the linear patterns of the chromatic inks, the linear patterns of the chromatic inks Find the amount of deviation between the measurement position and the design position,
(Iv) averaging the deviation amounts for the plurality of chromatic inks;
Is a value obtained by
Computer-readable recording medium.

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