JP2019171594A - Ink jet printer - Google Patents

Abstract

To make it possible to simplify an operation for correcting a dot position and shorten a time required to correct the dot position.SOLUTION: An ink jet printer comprises: a carriage; a recording head Hdi; a carriage drive processing unit Pr3 that reciprocally moves the carriage; a carry processing unit Pr2 that carries a recording medium; a head drive processing unit Pr1 that forms a test pattern image on a recording medium by driving each recording head Hdi; an image detection processing unit Pr4 that detects a dot and image density of the test pattern image by using an image density detection unit and calculates a correction value for correcting a dot position; and a head drive condition setting unit Pr5 that sets the correction value as a drive condition for the recording head Hdi. The test pattern image is formed from: a reference pattern image formed in only a forward path of the carriage; and a plurality of adjustment pattern images formed in the forward path and a backward path.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an ink jet printer.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a printer, a copier, a facsimile machine, a multifunction machine, for example, an ink jet printer, a carriage is moved in a main scanning direction along a rail, and ink is received from a plurality of recording heads mounted on the carriage. By being ejected and attached to a recording medium, an image such as a character or image composed of a collection of dots is formed, and printing is performed.

  By the way, in a serial type ink jet printer, an image is formed by reciprocating a carriage, but a position where ink ejected from a recording head adheres to a recording medium to form a dot ( Hereinafter, if the “dot position” is different between the forward path and the backward path of the carriage, the image is displaced and the image quality is degraded.

  Therefore, a pattern image for position adjustment is formed on the recording medium, the image density of the pattern image for position adjustment is detected by an optical sensor, and a correction value for correcting the dot position is calculated based on the image density. (For example, refer to Patent Document 1).

JP, 2006-182679, A

  However, in the conventional inkjet printer, there is no image density target value for calculating the correction value, and the correction value is calculated based only on the detected image density. The number of times that the pattern image for adjustment is formed on the recording medium or the image density of the pattern image is increased, and the work for correcting the dot position is troublesome, and the time required for correcting the dot position It will be long.

  The present invention solves the problems of the conventional ink jet printer, simplifies the operation for correcting the dot position, and shortens the time required for correcting the dot position. An object is to provide a printer.

  For this purpose, in the ink jet printer of the present invention, the carriage is reciprocated by driving a carriage arranged to be movable in the main scanning direction, a plurality of recording heads mounted on the carriage, and a carriage moving drive unit. A carriage drive processing unit for moving, a conveyance processing unit for driving a conveyance drive unit to convey a recording medium in the sub-scanning direction, and a head drive for driving each recording head to form a test pattern image on the recording medium A processing unit; an image detection processing unit for detecting a dot and an image density of the test pattern image by the image density detection unit; and calculating a correction value for correcting a dot position based on the dot and the image density; and the image A head driving condition setting unit that sets the correction value calculated by the detection processing unit as the driving condition of the recording head.

  The test pattern image includes a reference pattern image formed only in the forward path of reciprocation of the carriage and a plurality of adjustment pattern images formed in the forward path and the backward path.

  According to the present invention, in an ink jet printer, a carriage arranged to be movable in the main scanning direction, a plurality of recording heads mounted on the carriage, and a carriage moving drive unit are driven to reciprocate the carriage. A carriage drive processing unit for moving, a conveyance processing unit for driving a conveyance drive unit to convey a recording medium in the sub-scanning direction, and a head drive for driving each recording head to form a test pattern image on the recording medium A processing unit; an image detection processing unit for detecting a dot and an image density of the test pattern image by the image density detection unit; and calculating a correction value for correcting a dot position based on the dot and the image density; and the image A head driving condition setting unit that sets the correction value calculated by the detection processing unit as the driving condition of the recording head.

  The test pattern image includes a reference pattern image formed only in the forward path of reciprocation of the carriage and a plurality of adjustment pattern images formed in the forward path and the backward path.

  In this case, based on the adjustment pattern image, the image density of the reference pattern image is set as a target value, and the amount of deviation of the dots in the pattern image that can obtain an image density equal to the image density of the reference pattern image is used to correct the dot position. It can be a correction value.

  Accordingly, since the number of times that the test pattern image is formed on the recording medium and the image density is detected can be reduced, the work for correcting the dot position can be simplified, and the dot position is corrected. The time required for this can be shortened.

It is a control block diagram of the inkjet printer in the embodiment of the present invention. 1 is a perspective view of an ink jet printer according to an embodiment of the present invention. It is a conceptual diagram which shows the principal part of the inkjet printer in embodiment of this invention. It is a figure which shows the example of the basic pattern image in embodiment of this invention. It is a figure which shows the example of the test pattern image in embodiment of this invention. It is an enlarged view of a pattern image in an embodiment of the present invention. 6 is a flowchart showing the operation of the ink jet printer when correcting the dot position in the embodiment of the present invention. It is a figure which shows distribution of the image density of the pattern image in embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In this case, an ink jet printer as an image forming apparatus will be described.

  FIG. 2 is a perspective view of the ink jet printer according to the embodiment of the present invention, and FIG. 3 is a conceptual diagram showing a main part of the ink jet printer according to the embodiment of the present invention.

  In the figure, 10 is a serial type ink jet printer, Fr is a main body of the ink jet printer 10, that is, a frame that supports the apparatus main body, and the frame Fr is a front view of the ink jet printer 10 from the front side (front side in FIG. 2). A receiving plate BP arranged extending from the left end to the right end at the time, a first support portion formed by rising from the receiving plate BP to the right by a predetermined distance from the left end of the receiving plate BP. A frame body PR and a frame body PR as a second support portion formed by rising from the receiving plate BP at a predetermined distance to the left from the right end of the receiving plate BP are provided.

  Between both ends of the receiving plate BP, rails 15 are disposed (constructed) extending linearly, and the carriage 17 extends along the rails 15 in the left-right direction, that is, in the main scanning direction (directions of arrows a and b). It is arrange | positioned so that movement is possible. In the present embodiment, a plurality of recording heads Hdi (i = 1, 2,..., 4) are provided on the carriage 17 on the surface where a plurality of nozzles (not shown) are open, that is, on the nozzle surface. It is mounted toward. In the present embodiment, black, yellow, magenta, and cyan inks are ejected from the nozzles of the recording heads Hdi, and a color image is formed on the recording medium P by the inks.

  A driving pulley 18 is disposed in the vicinity of the left end of the rail 15, and a driven pulley 19 is rotatably disposed in the vicinity of the right end of the rail 15, so that the endless belt 21 can run freely between the pulleys 18 and 19. The carriage 17 is attached to a predetermined portion of the endless belt 21. A carriage motor 22 as a carriage moving drive unit is connected to the pulley 18.

  Accordingly, by driving the carriage motor 22 and running the endless belt 21, the carriage 17 can be moved in the main scanning direction, and each recording head Hdi can be moved in the main scanning direction. At this time, ink of each color is ejected from each nozzle of the recording head Hdi and is attached to the recording medium P conveyed in the direction orthogonal to the moving direction of the carriage 17, that is, in the sub-scanning direction (arrow c direction). As a result, images such as characters and images are formed on the recording medium P, and printing is performed. As the recording medium P, in addition to paper, a resin film such as vinyl chloride or PET can be used.

  A sensor unit 23 is attached to the right side (home position side) of the carriage 17, and a reflective optical sensor 24 as a pixel detection unit and an image density detection unit is disposed on the sensor unit 23. . The optical sensor 24 includes an R detection unit 45 (FIG. 1) as a first color detection unit, a G detection unit 46 as a second color detection unit, and a B detection as a third color detection unit, which will be described later. Section 47, the R detection section 45 converts the image density of the cyan color image, the G detection section 46 sets the image density of the magenta image, and the B detection section 47 converts the image density of the yellow and black colors. Detect the image density.

  A linear scale (not shown) extending along the rail 15 and parallel to the rail 15 is linearly arranged, and a scale of the linear scale is provided by an encoder 35 described later provided on the carriage 17. The position of the carriage 17 is detected based on the optical output and the sensor output of the encoder 35. The moving speed of the carriage 17 can be calculated based on the change in position of the carriage 17 and the time.

  Further, a metal platen 25 having a plate shape is disposed along the rail 15 and extending in parallel with the rail 15. The platen 25 is disposed between the frames PL and PR on the receiving plate BP, and supports the recording medium P conveyed on the platen 25.

  A plurality of suction holes (not shown) are formed in the platen 25, and an air suction device (not shown) for drawing the recording medium P to the platen 25 by negative pressure is disposed below the platen 25. The air suction device includes a suction fan. Air is sucked by the fan through the suction hole, and the recording medium P is supported flat by the platen 25.

  Further, a pre-guide (not shown) as a first medium guide is disposed behind the platen 25. The pre-guide guides the recording medium P fed from a feeding roll (not shown) to the platen 25. For this purpose, a pair of conveyance rollers 30 as a conveyance member is rotatably disposed between the pre-guide and the platen 25 in the conveyance direction of the recording medium P.

  The conveyance roller pair 30 is adjacent to the platen 25 and is rotated at a position above the conveyance roller as a first roller (not shown) as a first roller rotatably disposed at a plurality of locations in the main scanning direction of the carriage 17. It comprises a pinch roller (not shown) as a second roller that is freely arranged and presses the recording medium P against the conveying roller. When a conveyance motor 34 as a conveyance drive unit to be described later is driven and the conveyance roller is rotated, the pinch roller is rotated along with the rotation.

  As a result, the recording medium P is fed from the feed roll while being sandwiched between the transport roller and the pinch roller, transported along the pre-guide, and sent onto the platen 25. Then, the recording medium P and the nozzle surface of the recording head Hdi are opposed to each other, and ink is ejected from each nozzle and adhered to the recording medium P.

  Further, an after guide 33 as a second medium guiding portion for guiding and discharging the recording medium P after printing is disposed in front of the platen 25. The after guide 33 has a curved shape in order to guide the recording medium P discharged from the platen 25 in the horizontal direction downward.

  Therefore, the recording medium P fed out from the feeding roll is guided by the pre-guide and sent to the platen 25, and the ink ejected from each nozzle of the recording head Hdi is adhered onto the platen 25 for printing. After printing, the paper is guided by an after guide 33, sent to a winding device (not shown), and wound.

  Ink adheres to the recording medium P immediately after printing is performed, but when the recording medium P is discharged from the platen 25 before the ink dries and is taken up by the take-up device, the ink spreads. P becomes dirty with ink.

  Therefore, in the present embodiment, in order to dry the ink on the recording medium P and fix it to the recording medium P, a heater (not shown) as a first heating body is embedded in the platen 25, and a pre-guide is provided. Further, heaters (not shown) as second and third heating bodies are respectively attached to the back of the after guide 33, and each heater is covered with an aluminum sheet. Accordingly, the recording medium P conveyed on the pre-guide, the platen 25 and the after-guide 33 is heated by each heater.

  In the present embodiment, the rail 15 is disposed between both ends of the receiving plate BP, and the platen 25 is disposed between the frames PL and PR, so that the carriage 17 is moved on the platen 25. When ink is ejected by each recording head Hdi, that is, recording is performed and the carriage 17 is placed on the left side of the frame body PL, and when the carriage 17 is placed on the right side of the frame body PR, recording is performed by each recording head Hdi. Is not done.

  Therefore, in the present embodiment, the right side from the frame body PR is set to the home position for aligning the origin of the position of the carriage 17, and the left side from the frame body PL is retracted from the platen 25 while being retracted. Therefore, it is in the retracted position.

  A cap unit 43 as a maintenance device is disposed at the home position. The cap unit 43 prevents the ink viscosity from increasing or solidifying in the nozzle by covering the nozzle surface of the recording head Hdi with a cap when the inkjet printer 10 is not used for a long time. Further, the ink is periodically sucked from the recording head Hdi.

  By the way, in the present embodiment, the carriage 17 is reciprocated to form an image. Therefore, if the dot position is different between the forward path and the backward path of the carriage 17, the image shifts and the image The quality will deteriorate.

  Therefore, in the present embodiment, a test pattern image PA (FIG. 5) described later is formed (printed) on the recording medium P, and the image density of the test pattern image PA is detected and detected by the optical sensor 24. Based on the image density, a correction value for correcting the dot position is calculated.

  Next, the control device of the inkjet printer 10 will be described.

  FIG. 1 is a control block diagram of an ink jet printer according to an embodiment of the present invention.

  In the figure, 10 is an ink jet printer, 80 is a control unit that controls the entire sequence of the ink jet printer 10 and performs printing control, 81 is a ROM as a first storage device comprising a nonvolatile memory, and 82 is volatile. A RAM as a second storage device including a memory, 83 is an interface (I / F) control unit that receives print data and control commands from a host computer (not shown) as a host device, 51 is an operation panel, 53 is a sensor group, 24 Is an optical sensor, 45 is an R detector, 46 is a G detector, and 47 is a B detector.

  The control unit 80 includes a CPU (not shown) as an arithmetic unit, an input / output port, a timer, and the like, and performs various processes based on a program recorded in the ROM 81. In addition to the program, the ROM 81 records various initial setting values, data of a basic pattern image Pt (FIG. 4) described later, and the like, and the RAM 82 temporarily records various data. The RAM 82 also functions as a work area when the CPU performs calculations.

  The control unit 80 includes a head drive processing unit Pr1, a conveyance processing unit Pr2, a carriage drive processing unit Pr3, an image detection processing unit Pr4, a head drive condition setting unit Pr5, and the like.

  The head drive processing unit Pr1 generates image data based on print data and control commands sent from the host computer, and drives the recording head Hdi to form an image on the recording medium P. Further, the head drive processing unit Pr1 reads the data of the basic pattern image Pt recorded in the ROM 81, and drives the recording head Hdi based on the data of the basic pattern image Pt so as to write the test pattern image PA on the recording medium P. Form.

  The recording head Hdi is provided with a piezo element 26 as a drive element for each nozzle. When a predetermined voltage is applied between the electrodes arranged at both ends of the piezo element 26, the voltage is increased. Accordingly, the piezo element 26 is driven and expanded and contracted, and the side wall of the flow path for sending ink to the nozzle is deformed. As a result, the cross-sectional area of the ink flow path changes in accordance with the expansion and contraction of the piezo element 26, and an amount of ink corresponding to the change in the cross-sectional area of the ink flow path is ejected from the nozzle as ink droplets.

  The conveyance processing unit Pr2 drives the conveyance motor 34, rotates the conveyance roller pair 30 (FIG. 2), and conveys the recording medium P in the arrow c direction (sub-scanning direction).

  The carriage drive processing unit Pr3 drives the carriage motor 22 by PWM control, causes the endless belt 21 to travel, and reciprocates the carriage 17 in the directions of arrows a and b (main scanning direction). For this purpose, the carriage drive processing unit Pr3 reads the target position and target speed of the carriage 17 from the ROM 81, receives the sensor output of the encoder 35, performs A / D conversion to detect the position of the carriage 17, and uses it as a control value. A PWM control signal is generated and sent to the carriage motor 22. The carriage motor 22 receives the PWM control signal, changes the rotation speed in proportion to the duty of the PWM control signal, and accelerates or decelerates the carriage 17 to move it to the target position at the target speed. Further, the carriage drive processing unit Pr3 sends the position of the carriage 17 to the head drive processing unit Pr1, and the head drive processing unit Pr1 is calculated based on the image data from the nozzles of the recording head Hdi in accordance with the position of the carriage 17. Ink is ejected at the timing.

  The image detection processing unit Pr4 detects the dots and the image density of the test pattern image PA formed on the recording medium P by the optical sensor 24, and corrects the dot position based on the dots and the image density. A correction value Xk described later is calculated.

  The head driving condition setting unit Pr5 sets the correction value Xk as a driving condition for the recording head Hdi in a driving condition dialog formed during printing on a display unit described later.

  In the optical sensor 24, the R detection unit 45, the G detection unit 46, and the B detection unit 47 include a light emitting unit composed of an LED or the like, and a light receiving unit composed of a phototransistor or the like. The red light is generated by the light receiving unit, and the reflected light is received by the light receiving unit to detect the image density of the cyan test pattern image PA. The G detecting unit 46 generates the green light by the light emitting unit, The reflected light is received by the light receiving unit to detect the image density of the magenta test pattern image PA, and the B detecting unit 47 generates blue light by the light emitting unit, and the reflected light is received by the light receiving unit. Thus, the image density of the test pattern image PA of yellow color and the image density of the test pattern image PA of black color are detected.

  Therefore, the head driving condition setting unit Pr5 sets the correction value calculated for each color as the driving condition of the recording head Hdi.

  The operation panel 51 includes an LED screen as a display unit for displaying the state of the inkjet printer 10, a switch, a key, and the like as an operation unit for an operator to give instructions to the inkjet printer 10. When the operation panel 51 is formed by a touch panel, the operation panel 51 functions as a display unit and an operation unit.

  The sensor group 53 detects various printing sensors for monitoring the operation state of the ink jet printer 10, for example, a medium position detecting sensor for detecting the position of the recording medium P, and a printing environment in which the ink jet printer 10 is placed. It consists of a temperature sensor, a humidity sensor, etc.

  Next, the operation of the control unit 80 when printing is performed in the inkjet printer 10 will be described.

  In the inkjet printer 10 according to the present embodiment, when print data and a control command are sent from the host computer to the inkjet printer 10 via the interface control unit 83, the conveyance processing unit Pr2 drives the conveyance motor 34 to convey the conveyance roller. The pair 30 is rotated and the recording medium P is conveyed in the direction of arrow c.

  Subsequently, the carriage drive processing unit Pr3 drives the carriage motor 22 to run the endless belt 21, and moves the carriage 17 in the directions of arrows a and b. At this time, the carriage drive processing unit Pr3 receives the sensor output of the encoder 35, performs A / D conversion to detect the position of the carriage 17, and sends it to the head drive processing unit Pr1. The head drive processing unit Pr1 In accordance with the position 17, the ink is ejected from the nozzles of the recording head Hdi at a timing calculated based on the image data.

  At this time, the conveyance processing unit Pr3 drives the conveyance motor 34 to convey the recording medium P in the direction of the arrow c. Therefore, the ink ejected from the nozzles of the recording head Hdi is attached to the recording medium P, and printing is performed.

  By the way, the test pattern image PA is formed on the recording medium P by forming the basic pattern image Pt by a predetermined method in the forward path and the backward path of the carriage 17.

  4 is a diagram showing an example of a basic pattern image in the embodiment of the present invention, FIG. 5 is a diagram showing an example of a test pattern image in the embodiment of the present invention, and FIG. 6 is a pattern image in the embodiment of the present invention. FIG.

  In the figure, Pt is a basic pattern image formed of a stripe pattern, PA is formed based on the basic pattern image Pt, and in the present embodiment, a plurality of nine pattern images Paj (j = 1, 2). ,..., 9).

  The basic pattern image Pt has a belt-like shape and is formed by ejecting ink. In the present embodiment, the basic pattern image Pt has four image regions Ar1 and a belt-like shape. In the present embodiment, a plurality of non-image areas Ar2 are formed by not discharging, and the image areas Ar1 and non-image areas Ar2 are alternately arranged adjacent to each other. The basic pattern image Pt is created according to the status of the inkjet printer 10 (FIG. 2), for example, the type of the recording medium P used, and is recorded in the ROM 81 (FIG. 1).

  In order to form the test pattern image PA based on the basic pattern image Pt, first, the carriage drive processing unit Pr3 moves the carriage 17 in the direction of arrow a, and the head drive processing unit Pr1 reads the basic pattern image Pt from the ROM 81. Data is read and nine basic pattern images Pt are formed on the recording medium P as first basic pattern images Pt1 in the forward path of the carriage 17.

  Subsequently, the carriage drive processing unit Pr3 moves the carriage 17 in the direction of the arrow b, and the head drive processing unit Pr1 changes the timing at which ink is ejected in the return path of the carriage 17 to differ from each other in the first basic pattern image. Over the Pt1, eight basic pattern images Pt are newly formed on the recording medium P as second basic pattern images Pt2.

  As a result, a test pattern image composed of the pattern image Paj is formed on the recording medium P. Of the pattern images Paj, the pattern image Pa1 is formed as a reference pattern by forming only the first basic pattern image Pt1 in the forward path of the carriage 17, and the pattern images Pa1 to Pa9 are forward paths of the carriage 17. The first basic pattern image Pt1 is formed in step S1, and the second basic pattern image Pt2 is formed so as to overlap the first basic pattern image Pt1 in the return path of the carriage 17, thereby forming an adjustment pattern image.

  That is, when the reference timing for ejecting ink is t0, the pattern image Pa6 is formed by overlapping the second basic pattern image Pt2 at the timing t0, and the second basic pattern at a timing t + 1 that is later by the time τ than the timing t0. A pattern image Pa7 is formed by overlapping the pattern image Pt2, and a pattern image Pa8 is formed by overlapping the second basic pattern image Pt2 at a timing t + 2 that is later by the time 2τ than the timing t0, and a timing that is later by the time 3τ than the timing t0. A pattern image Pa9 is formed by overlapping the second basic pattern image Pt2 at t + 3, and a pattern image Pa5 is formed by overlapping the second basic pattern image Pt2 at timing t-1 that is earlier by time τ than timing t0. The pattern image Pa4 is formed by overlapping the second basic pattern image Pt2 at the timing t-2 that is earlier by the time 2τ than the timing t0, and the second basic pattern image Pt2 at the timing t-3 that is earlier by the time 3τ than the timing t0. The pattern image Pa3 is formed by overlapping the second basic pattern image Pt2 at the timing t-4 that is earlier by the time 4τ than the timing t0, thereby forming the pattern image Pa2.

  Here, the pattern images Pa2 to Pa9 are formed by superimposing the second basic pattern image Pt2 on the first basic pattern image Pt1 at the timing t + 3 to t-4 in the return path of the carriage 17. FIG. As shown in FIG. 5, the dot px1 formed in the image area Ar1 in the first basic pattern image Pt1 and the dot px2 formed in the image area Ar1 in the second basic pattern image Pt2 are formed at the same dot position. Instead, they are formed at different dot positions.

  Accordingly, since the number of dots formed in each image area Ar1 is different in each pattern image Pa2 to Pa9, the image densities of the pattern images Pa2 to Pa9 are different from each other.

  Therefore, in the present embodiment, the image density of each pattern image Pa2 to Pa9 is detected, and a virtual pattern image having the lowest image density is assumed. Correction values for correction are used.

  Next, the operation of the inkjet printer 10 when correcting the dot position will be described.

  FIG. 7 is a flowchart showing the operation of the ink jet printer when correcting the dot position in the embodiment of the present invention. FIG. 8 is a diagram showing the image density distribution of the pattern image in the embodiment of the present invention. In FIG. 8, the horizontal axis represents the dot shift amount X [dot], and the vertical axis represents the image density value V [V].

  First, the carriage drive processing unit Pr3 (FIG. 1) drives the carriage motor 22 to reciprocate the carriage 17, and the head drive processing unit Pr1 detects the type of the recording medium P, refers to the ROM 81, and records the recording medium. Data of the basic pattern image Pt corresponding to P is read, the recording head Hdi is driven, and a test pattern image PA composed of each pattern image Paj is formed on the recording medium P (FIG. 2).

  Next, the image detection processing unit Pr4 uses the optical sensor 24 to detect the dots and image density of the test pattern image PA, that is, the dots and image density of each pattern image Paj. Then, the image detection processing unit Pr4 calculates a dot shift amount Xj (j = 1, 2,..., 9) in each pattern image Paj based on the dots in each pattern image Paj.

  Note that the dot displacement amount Xj is determined based on the positions of predetermined dots formed in the image area Ar1 in the first basic pattern image Pt1 and the predetermined dots formed in the image area Ar1 in the second basic pattern image Pt2. The distance from the dot position corresponding to is represented by the number of dots. Since the image density of each pattern image Paj is detected by the optical sensor 24, the image density value Vj (j = 1, 2,..., 9), which is the sensor output (voltage value) of the optical sensor 24, is the image density. Is small when the image density is low, and small when the image density is high.

  In the present embodiment, the test pattern image PA is formed a plurality of times by the head drive processing unit Pr1, the image density of each pattern image Paj is detected a plurality of times, and the average value of the image density values is the image density. It becomes the value Vj.

  By the way, since the pattern image Pa1 is formed only by the first basic pattern image Pt1 in the forward path of the carriage 17, the dot shift amount X1 is 0 and the image density value V1 is the largest. Therefore, if the pattern image Pa1 is formed by forming the first and second basic pattern images Pt1 and Pt2 similarly to the other pattern images Pa2 to Pa9, the forward path of the carriage 17 In the return pass, each dot is formed at the same dot position.

  Therefore, when there is a pattern image having an image density value equal to the image density value V1 of the pattern image Pa1 among the pattern images Pa2 to Pa9, the dot shift amount of the pattern image is 0. The correction value for correction is 0.

  However, as shown in FIG. 8, since the image density values V2 to V9 of the pattern images Pa2 to Pa9 are smaller than the image density value V1 of the pattern image Pa1, the second basic pattern image is obtained at timing t + 3 to t-4. When Pt2 is formed, the dots are not formed at the same dot position in the forward path and the backward path of the carriage 17. Therefore, it is necessary to correct the dot position.

  Therefore, in the present embodiment, the image detection processing unit Pr4 uses the image density value V1 of the pattern image Pa1 as a target value, the image density is the lowest, and the virtual pattern in which the image density value V is equal to the image density value V1. Assuming the image Pk, the dot shift amount Xk of the virtual pattern image Pk is calculated as a correction value for correcting the dot position.

  For this purpose, the image detection processing unit Pr4 has a pattern image having an image density having a small difference from the image density of the reference pattern image Pa1 among the pattern images Pa2 to Pa9. In the present embodiment, two pattern images are used. Pa5 and Pa6 are selected, and based on the dot displacement amounts X5 and X6 of the pattern images Pa5 and Pa6, the image density values V5 and V6 of the pattern images Pa5 and Pa6, and the image density value V1 of the pattern image Pa1, the virtual image A dot shift amount Xk of the pattern image Pk is calculated.

In this case, since the virtual pattern image Pk is located between the pattern images Pa5 and Pa6, the weight of the pattern image Pa5 for the virtual pattern image Pk is W1, and the weight of the pattern image Pa6 for the virtual pattern image Pk is W2. Then, the weight W1 can be represented by the difference between the image density values V1 and V5, and the weight W2 can be represented by the difference between the image density values V1 and V6.
W1 = V1-V5
W2 = V1-V6
become. Therefore, the dot shift amount Xk of the virtual pattern image Pk is
Xk = W1 / (W1 + W2) × (X2-X1) + X1
Thus, a correction value for correcting the dot position is obtained.

  In the present embodiment, two pattern images Pa5 and Pa6 are selected in order to calculate the dot shift amount Xk of the virtual pattern image Pk, but three or more pattern images are selected. Paj can be selected.

  When the correction value is calculated in this way, the head driving condition setting unit Pt5 sets the head driving condition based on the correction value and adjusts the timing for driving the recording head Hdi. In this way, the dot position can be corrected.

  After the dot position is corrected, the test pattern image PA can be formed again on the recording medium P, and the dot position can be further corrected based on the image density of the test pattern image PA.

  In the present embodiment, the optical sensor 24 includes an R detection unit 45, a G detection unit 46, and a B detection unit 47. The R detection unit 45, the G detection unit 46, and the B detection unit 47 provide the pattern image. Paj dots and image density are detected. Therefore, the image detection processing unit Pr4 uses the dot and image density of each pattern image Paj detected by the R detection unit 45, the G detection unit 46, and the B detection unit 47, and the amount of deviation of the virtual pattern image Pk. Xk is calculated. Accordingly, the timing for driving the recording head Hdi corresponding to each color is adjusted.

  Thus, in the present embodiment, the image density value V1 of the pattern image Pa1 is set as a target value, and an image density value Vk equal to the image density value V1 of the pattern image Pa1 is obtained based on the pattern images Pa5 and Pa6. A virtual pattern image Pk is assumed, and the dot shift amount Xk of the virtual pattern image Pk is used as a correction value for correcting the dot position. Therefore, the test pattern image PA is formed on the recording medium P, and the image density The number of times of detecting can be reduced. Therefore, the operation for correcting the dot position can be simplified, and the time required for correcting the dot position can be shortened.

Next, a flowchart will be described.
Step S1 The head drive processing unit Pr1 forms a test pattern image PA on the recording medium P.
Step S2 The image detection processing unit Pr4 detects the image density of the test pattern image PA.
Step S3 The image detection processing unit Pr4 calculates a correction value for correcting the dot position. Step S4 The head driving condition setting unit Pr5 sets the head driving condition based on the correction value, and ends the process.

  In the present embodiment, one test pattern image PA is created based on the basic pattern image Pt, but the ink used to form the second basic pattern image Pt2 in the return path of the carriage 17 is used. By changing the ejection timing, it is possible to create a plurality of test pattern images and increase the accuracy of the calculated correction value.

  In this embodiment, the dot position when the carriage 17 is reciprocated is corrected. However, when the recording medium P is conveyed, a predetermined test pattern image is formed, and the test pattern image is formed. The dot position can be corrected based on the image density.

  In the above embodiment, the inkjet printer 10 has been described. However, the present invention can be applied to an image forming apparatus such as a copying machine, a facsimile machine, and a multifunction machine.

  In addition, this invention is not limited to the said embodiment, It can change variously based on the meaning of this invention, and does not exclude them from the scope of the present invention.

DESCRIPTION OF SYMBOLS 10 Inkjet printer 17 Carriage 22 Carriage motor 34 Conveyance motor Hdi Recording head P Recording medium Pa1-Pa9 Pattern image PA Test pattern image Pr1 Head drive process part Pr2 Carry process part Pr3 Carriage drive process part Pr4 Image detection process part Pr5 Head drive condition setting Part

Claims (4)

(A) a carriage arranged to be movable in the main scanning direction;
(B) a plurality of recording heads mounted on the carriage;
(C) a carriage drive processing unit that drives the carriage moving drive unit to reciprocate the carriage;
(D) a transport processing unit that drives the transport driving unit to transport the recording medium in the sub-scanning direction;
(E) a head drive processing unit that drives each of the recording heads to form a test pattern image on a recording medium;
(F) an image detection processing unit that detects dots and image density of the test pattern image by the image density detection unit, and calculates a correction value for correcting the dot position based on the dot and image density;
(G) a head driving condition setting unit that sets the correction value calculated by the image detection processing unit as a driving condition of the recording head;
(H) The ink jet printer characterized in that the test pattern image includes a reference pattern image formed only in a forward path of reciprocation of the carriage and a plurality of adjustment pattern images formed in the forward path and the return path.   The correction value is calculated based on the image density value of the reference pattern image, the image density value of two adjustment pattern images having an image density that is small in difference from the image density of the reference pattern image, and the amount of dot displacement. The inkjet printer according to claim 1.   The test pattern image forms a plurality of first basic pattern images on the forward path of the carriage, overlaps the first basic pattern images on the return path of the carriage, and sets a plurality of second basic pattern images at different timings. The ink jet printer according to claim 1, wherein the ink jet printer is formed by forming a basic pattern image. (A) The head drive processing unit forms a plurality of test pattern images corresponding to ink colors,
(B) The image density detection unit detects dots and image densities of the test pattern images by a plurality of color detection units arranged corresponding to the ink colors, and calculates a correction value for each ink color. The inkjet printer according to any one of claims 1 to 3.

Images