Printing device

Abstract

To provide a printing device that can suppress a printing quality from deteriorating, while suppressing the device from enlarging in size and a printing medium from deforming.SOLUTION: Inkjet heads 21 have a plurality of nozzles arranged in a main scanning direction orthogonal to a conveying direction of a printing medium P that is conveyed on a conveying belt 11, which discharge ink from the plurality of nozzles to the conveyed printing medium P to print an image on the medium. A biaxial encoder 5 detects variation of a position in the main scanning direction of the printing medium P being conveyed on the conveying belt 11. A control part 6 controls correspondence relation between each pixel of the image printed by the inkjet heads 21 and the nozzle discharging ink to each pixel, in response to the variation of the position in the main scanning direction of the printing medium P detected by the biaxial encoder 5.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a printing device. [Background technology]

[0002] Printing devices are known that print by ejecting ink from an inkjet head onto a print medium such as paper transported by a transport mechanism such as a transport belt. In such printing devices, the inkjet head has multiple nozzles arranged in a nozzle arrangement direction perpendicular to the transport direction of the print medium, and ejects ink from these nozzles to print an image.

[0003] In such printing devices, fluctuations in the transport speed of the print medium and fluctuations in the position of the print medium in the nozzle array direction can occur. For example, in a transport mechanism that holds and transports the print medium on a circular transport belt wound around rollers, fluctuations in the transport speed of the print medium by the transport belt can occur due to unevenness in the thickness of the transport belt or eccentricity of the rollers. Furthermore, meandering of the transport belt can cause fluctuations in the position of the print medium in the nozzle array direction.

[0004] Fluctuations in the transport speed of the printing medium and fluctuations in the position of the printing medium in the nozzle arrangement direction cause the landing position of ink ejected from the inkjet head on the printing medium to deviate from the desired position (landing deviation), resulting in a deterioration in print quality.

[0005] The following techniques are known as techniques for reducing ink landing deviation in the transport direction due to fluctuations in the transport speed of the print medium: For example, in the transport mechanism that transports the print medium using the transport belt described above, a roller that rotates in response to the transport belt is installed, an encoder is attached to this roller, and the timing of ink ejection is controlled based on the output pulse signal of the encoder.

[0006] Furthermore, a technology for reducing ink landing deviation in the nozzle arrangement direction due to fluctuations in the position of the printing medium in the nozzle arrangement direction is disclosed in Patent Document 1. The technology in Patent Document 1 detects the position of the transported object (printing medium) in an orthogonal direction (nozzle arrangement direction) that is perpendicular to the transport direction of the transported object, and moves the head unit in the orthogonal direction using an actuator based on the detection result.

[0007] Another technique for reducing ink impact deviation in the nozzle arrangement direction due to fluctuations in the position of the printing medium in the nozzle arrangement direction is to physically restrict the position by abutting the printing medium against a guide member such as a metal plate, thereby suppressing the fluctuations. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2018-158574 Summary of the Invention [Problem to be solved by the invention]

[0009] However, the technology of Patent Document 1 requires the provision of an actuator, which leads to an increase in the size of the device.

[0010] Furthermore, with the technique of abutting the print medium against a guide member, it is difficult to sufficiently suppress fluctuations in the position of the print medium, and if the fluctuations in the position of the print medium become too great, there is a risk that the print medium will become deformed.

[0011] The present invention has been made in view of the above, and has an object to provide a printing device that can reduce degradation of print quality while suppressing an increase in size of the device and deformation of the print medium. [Means for solving the problem]

[0012] In order to achieve the above object, the printing device of the present invention is characterized by comprising: an ejection unit having a plurality of nozzles arranged in a nozzle arrangement direction perpendicular to the transport direction of a printing medium transported by a transport mechanism, and ejecting ink from the plurality of nozzles onto the transported printing medium to print an image; a detection unit that detects fluctuations in the position of the transported printing medium in the nozzle arrangement direction; and a control unit that controls the correspondence between each pixel of an image printed by the ejection unit and the nozzles that eject ink to each pixel in accordance with the fluctuations in the position of the printing medium in the nozzle arrangement direction detected by the detection unit. [Effects of the Invention]

[0013] According to the printing device of the present invention, it is possible to reduce degradation of print quality while suppressing an increase in the size of the device and deformation of the print medium. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic configuration diagram of a printing device according to an embodiment. [Figure 2] FIG. 2 is a schematic diagram illustrating the configuration of an inkjet head of the printing device shown in FIG. [Figure 3] FIG. 2 is a schematic diagram illustrating the configuration of a two-axis encoder of the printing device shown in FIG. [Figure 4] FIG. 2 is a control block diagram of the printing apparatus shown in FIG. [Figure 5] FIG. 4 is a diagram showing an example of an output pulse signal of a two-axis encoder. [Figure 6] 10 is a flowchart illustrating offset control in the main scanning direction. [Figure 7] 10 is a flowchart illustrating offset control in the main scanning direction. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The same or equivalent parts and components are designated by the same or equivalent reference numerals throughout the drawings.

[0016] The following embodiments are examples of devices that embody the technical idea of ​​the present invention, and the technical idea of ​​the present invention does not limit the materials, shapes, structures, arrangements, etc. of each component to those described below. The technical idea of ​​the present invention can be modified in various ways within the scope of the claims.

[0017] FIG. 1 is a schematic diagram of a printing device according to an embodiment of the present invention. FIG. 2 is a schematic diagram of an inkjet head of the printing device shown in FIG. 1. FIG. 3 is a schematic diagram of a two-axis encoder of the printing device shown in FIG. 1. FIG. 4 is a control block diagram of the printing device shown in FIG. 1. In FIG. 1, the direction perpendicular to the paper surface is the front-to-rear direction, and the front direction of the paper surface is the forward direction. In addition, the up-down and left-right directions of the paper surface in FIG. 1 are the up-down and left-right directions.

[0018] As shown in FIGS. 1 and 4, a printing device 1 according to this embodiment includes a transport unit 2, a paper feed sensor 3, a head unit 4, a two-axis encoder 5 (corresponding to a detection unit), and a control unit 6.

[0019] The transport unit 2 transports a print medium P such as paper. The transport unit 2 includes a transport belt (corresponding to a transport mechanism) 11, a drive roller 12, a driven roller 13, and a transport motor .

[0020] The conveyor belt 11 holds and conveys the printing medium P. The conveyor belt 11 is a circular belt stretched over a drive roller 12 and a driven roller 13. The conveyor belt 11 is driven to circulate clockwise in FIG. 1, thereby conveying the printing medium P placed on the conveyor surface 11a in a conveying direction (sub-scanning direction) from left to right. The conveyor surface 11a is the upper surface of the conveyor belt 11 that is horizontal between the drive roller 12 and the driven roller 13.

[0021] The drive roller 12 rotates the conveyor belt 11 in the clockwise direction in FIG.

[0022] The driven roller 13 supports the conveyor belt 11 together with the drive roller 12. The driven roller 13 is disposed spaced apart from the drive roller 12 in the left-right direction. The driven roller 13 is rotated by the conveyor belt 11 as it rotates.

[0023] The conveying motor 14 drives the driving roller 12 to rotate.

[0024] The paper feed sensor 3 detects the printing medium P fed from a paper feed unit (not shown) to the conveying unit 2. The paper feed sensor 3 is disposed at a predetermined position on the upstream end of the conveying belt 11, which is a predetermined position upstream of the head unit 4 in the conveying direction of the printing medium P.

[0025] The head unit 4 prints on the print medium P transported by the transport unit 2. The head unit 4 includes a plurality of inkjet heads (corresponding to ejection units) 21 and a head holder 22.

[0026] The four inkjet heads 21 print an image by ejecting ink of a different color (for example, black, cyan, magenta, or yellow) onto the print medium P. The four inkjet heads 21 are arranged side by side in the left-right direction (sub-scanning direction). The four inkjet heads 21 have the same configuration except for the inks they eject.

[0027] As shown in Fig. 2, the inkjet head 21 has a plurality of nozzles 26 that eject ink. Fig. 2 is a view of the inkjet head 21 as seen from below.

[0028] The multiple nozzles 26 are arranged along a main scanning direction (corresponding to the nozzle arrangement direction), which is a direction (front-rear direction) perpendicular to the transport direction (sub-scanning direction) of the print medium P. The nozzles 26 open to a nozzle surface 21a, which is the lower surface of the inkjet head 21.

[0029] The head holder 22 holds the four inkjet heads 21 and the two-axis encoder 5 .

[0030] The biaxial encoder 5 detects fluctuations in the position of the printing medium P transported by the transport belt 11 in the front-to-rear direction (main scanning direction), while also detecting the transport speed of the printing medium P by the transport belt 11. The biaxial encoder 5 is disposed adjacent to the upstream side of the most upstream inkjet head 21. The biaxial encoder 5 is held at the upstream end of the head holder 22.

[0031] As shown in FIGS. 3 and 4, the two-axis encoder 5 includes a ball portion 31, a main scanning direction encoder 32, a sub-scanning direction encoder 33, and a riding sensor .

[0032] The ball portion 31 is formed in a spherical shape. The ball portion 31 is located near the upstream side of the most upstream inkjet head 21. The ball portion 31 is biased downward by a biasing member (not shown) made of an elastic body such as a spring. As a result, when there is no printing medium P at the position of the ball portion 31, the ball portion 31 abuts against the conveyor belt 11 and rotates in accordance with the conveyor belt 11. When the printing medium P reaches the position of the ball portion 31, the ball portion 31 rides up onto the printing medium P, abuts against the printing medium P, and rotates in accordance with the printing medium P. In other words, the ball portion 31 abuts against the printing medium P passing by the inkjet head 21 and rotates in accordance with the printing medium P, and when there is no printing medium P passing by the inkjet head 21, the ball portion 31 abuts against the conveyor belt 11 and rotates in accordance with the conveyor belt 11.

[0033] The main scanning direction encoder 32 detects fluctuations in the position of the print medium P transported by the transport belt 11 in the front-to-rear direction (main scanning direction).

[0034] The main scanning direction encoder 32 includes a roller 41 , a shaft 42 , a rotary slit plate 43 , a fixed slit plate 44 , and a sensor unit 45 .

[0035] The roller 41 abuts against the ball portion 31 from one side in the front-rear direction (the front side in the example of FIG. 3), and rotates following the rotation of the ball portion 31 about a rotation axis A1 that is parallel to the left-right direction. The roller 41 is attached to a shaft 42.

[0036] The shaft 42 extends in the left-right direction and rotates together with the roller 41 .

[0037] The rotary slit plate 43 is a disk with many slits. Many slits are formed at a predetermined pitch around the entire circumference of the rotary slit plate 43. The rotary slit plate 43 is attached to the shaft 42 and rotates together with the shaft 42.

[0038] The fixed slit plate 44 has two slits, one for an A-phase signal and one for a B-phase signal. The fixed slit plate 44 is arranged in parallel with the rotary slit plate 43.

[0039] The sensor unit 45 has a light-emitting element and a light-receiving element (neither of which is shown) that are arranged opposite each other with the rotary slit plate 43 and the fixed slit plate 44 in between. The light-emitting element emits light toward the light-receiving element. When the rotary slit plate 43 rotates, light from the light-emitting element that passes through the two slits of the fixed slit plate 44 either passes through the slits of the rotary slit plate 43 or is blocked by the rotary slit plate 43. The light-receiving element receives light from the light-emitting element that has passed through each slit of the rotary slit plate 43 and the two slits of the fixed slit plate 44, and outputs an A-phase signal and a B-phase signal that are pulse signals with a predetermined phase difference.

[0040] In the main scanning direction encoder 32 described above, the relationship between the output timing of the A-phase signal pulse and the B-phase signal pulse with a predetermined phase difference changes depending on the rotation direction of the shaft 42. Therefore, the rotation direction of the ball portion 31 around the rotation axis A1 can be detected based on the relationship between the output timing of the A-phase signal pulse and the B-phase signal pulse with a predetermined phase difference.

[0041] Furthermore, the rotation angle of the ball portion 31 around the rotation axis A1 can be detected based on the number of pulses of the A-phase signal and the B-phase signal output by the main scanning direction encoder 32.

[0042] When the ball portion 31 is in contact with the printing medium P, the rotation direction of the ball portion 31 about the rotation axis A1 indicates the movement direction of the printing medium P in the front-to-rear direction. When the ball portion 31 is in contact with the conveyor belt 11, the rotation direction of the ball portion 31 about the rotation axis A1 indicates the movement direction of the conveyor belt 11 in the front-to-rear direction.

[0043] Furthermore, the rotation angle of ball portion 31 about rotation axis A1 indicates the movement distance of print medium P in the front-to-rear direction when ball portion 31 is in contact with print medium P. When ball portion 31 is in contact with conveyor belt 11, the rotation angle of ball portion 31 about rotation axis A1 indicates the movement distance of conveyor belt 11 in the front-to-rear direction.

[0044] Therefore, the rotation direction and rotation angle of ball portion 31 about rotation axis A1 when ball portion 31 is in contact with print medium P indicate fluctuations in the front-to-rear position of print medium P. Also, the rotation direction and rotation angle of ball portion 31 about rotation axis A1 when ball portion 31 is in contact with conveyor belt 11 indicate fluctuations in the front-to-rear position of conveyor belt 11 due to meandering, etc.

[0045] From the above, the main scanning direction encoder 32 detects fluctuations in the position of the printing medium P in the front-to-rear direction from the rotation direction and rotation angle of the ball portion 31 about the rotation axis A1 when the ball portion 31 is in contact with the printing medium P. Also, the main scanning direction encoder 32 detects fluctuations in the position of the conveyor belt 11 in the front-to-rear direction from the rotation direction and rotation angle of the ball portion 31 about the rotation axis A1 when the ball portion 31 is in contact with the conveyor belt 11.

[0046] Here, fluctuations in the position of the conveyor belt 11 in the front-to-rear direction cause fluctuations in the position of the printing medium P in the front-to-rear direction. Therefore, when the ball portion 31 is in contact with the conveyor belt 11, the main scanning direction encoder 32 can be said to detect fluctuations in the position of the printing medium P in the front-to-rear direction by detecting fluctuations in the position of the conveyor belt 11 in the front-to-rear direction.

[0047] Therefore, the main scanning direction encoder 32 detects the fluctuation in the position of the transported printing medium P in the front-to-rear direction (main scanning direction) from the rotation direction and rotation angle of the ball portion 31 around the rotation axis A1, as described above.

[0048] Here, when the ball portion 31 is in contact with the printing medium P, even if slippage occurs between the conveying belt 11 and the printing medium P, it is possible to detect fluctuations in the position of the printing medium P in the forward and backward directions with high accuracy.

[0049] The sub-scanning direction encoder 33 detects the speed at which the print medium P is transported by the transport belt 11 .

[0050] The sub-scanning direction encoder 33 includes a roller 51, a shaft 52, a rotary slit plate 53, a fixed slit plate 54, and a sensor unit 55. The roller 51, shaft 52, rotary slit plate 53, fixed slit plate 54, and sensor unit 55 of the sub-scanning direction encoder 33 have the same configurations as the roller 41, shaft 42, rotary slit plate 43, fixed slit plate 44, and sensor unit 45 of the main scanning direction encoder 32, respectively, and therefore detailed description thereof will be omitted.

[0051] The roller 51 of the sub-scanning direction encoder 33 contacts the ball portion 31 from one side in the left-right direction (the left side in the example of FIG. 3) and rotates following the rotation of the ball portion 31 around a rotation axis A2 parallel to the front-rear direction.

[0052] This allows the rotational speed of the ball portion 31 around the rotation axis A2 to be detected from the pulse period of the A-phase signal or B-phase signal output by the sensor portion 55 of the sub-scanning direction encoder 33, and from this rotational speed, the transport speed of the printing medium P by the transport belt 11 can be detected.

[0053] Here, when the ball portion 31 is in contact with the printing medium P, even if slippage occurs between the conveying belt 11 and the printing medium P, it is possible to detect the conveying speed of the printing medium P with high accuracy.

[0054] The ride-up sensor 34 detects that the ball portion 31 rides up on a print medium P that is held and transported on the transport surface 11a of the transport belt 11 and has a thickness equal to or greater than a predetermined thickness.

[0055] The control unit 6 controls the overall operation of the printing device 1. The control unit 6 is configured with a CPU, RAM, ROM, a hard disk, and the like.

[0056] Specifically, the control unit 6 controls the inkjet heads 21 to eject ink onto the print medium P being transported by the transport unit 2, based on image data of the print target, to print an image.

[0057] During printing, the control unit 6 controls the timing at which ink is ejected from each nozzle 26 of each inkjet head 21 in accordance with the speed at which the print medium P is transported by the transport belt 11, as detected by the sub-scanning direction encoder 33.

[0058] The control unit 6 also performs offset control in the main scanning direction, which controls the correspondence between each pixel of an image printed by each inkjet head 21 and the nozzles 26 that eject ink onto each pixel, in accordance with fluctuations in the front-to-rear position of the print medium P detected by the main scanning direction encoder 32.

[0059] Next, the operation of the printing device 1 will be described.

[0060] The control unit 6 controls the ink jet heads 21 to eject ink onto the printing medium P, which is fed from a paper feed unit (not shown) and transported by the transport unit 2, based on image data to be printed, to print an image.

[0061] At this time, the control unit 6 controls the timing at which ink is ejected from each nozzle 26 of each inkjet head 21 in accordance with the transport speed of the print medium P detected by the sub-scanning direction encoder 33.

[0062] Specifically, the control unit 6 controls the timing at which ink is ejected from each nozzle 26 of each inkjet head 21 based on the timing of the rising edge of the output pulse signal (A-phase signal or B-phase signal) of the sub-scanning direction encoder 33.

[0063] Here, if there is a fluctuation in the transport speed of the print medium P by the transport belt 11, there will be a fluctuation in the pulse period and pulse width of the output pulse signal (A-phase signal in the example of FIG. 5) of the sub-scanning direction encoder 33, as shown in the upper part of Fig. 5. Even in such a case, it is possible to reduce deviation in the ink landing position by controlling the timing of ink ejection from each nozzle 26 of each inkjet head 21 as described above.

[0064] The control unit 6 also performs offset control in the main scanning direction. This offset control in the main scanning direction will be described with reference to the flowcharts of FIGS.

[0065] In step S1 of Fig. 6, the control unit 6 determines whether or not the printing medium P has been fed to the transport unit 2. Here, when the leading edge of the printing medium P is detected by the paper feed sensor 3, the control unit 6 determines that the printing medium P has been fed to the transport unit 2. If it is determined that the printing medium P has not been fed to the transport unit 2 (step S1: NO), the control unit 6 repeats step S1.

[0066] If it is determined that the print medium P has been fed to the transport unit 2 (step S1: YES), the control unit 6 sets the offset correction value C to "0" in step S2.

[0067] Here, the offset correction value C indicates the amount and direction of offset in the main scanning direction for shifting (offsetting) the correspondence between each pixel in the image to be printed and the nozzles 26 that eject ink to each pixel. A positive value for the offset correction value C indicates that the pixel corresponding to each nozzle 26 is shifted to one side in the main scanning direction. A negative value for the offset correction value C indicates that the pixel corresponding to each nozzle 26 is shifted to the other side. The absolute value of the offset correction value C indicates the amount of offset.

[0068] Next, in step S3, the control unit 6 determines whether the printing medium P has reached the head unit 4 (whether it has started passing through the inkjet head 21). Here, when the riding-up sensor 34 detects that the ball portion 31 has run up on the printing medium P, the control unit 6 determines that the printing medium P has reached the head unit 4.

[0069] In addition, if the printing medium P is less than a predetermined thickness and the ball portion 31 cannot be detected by the climbing sensor 34 as having climbed onto the printing medium P, for example, the control unit 6 determines whether the printing medium P has reached the head unit 4 based on the number of output pulses from the sub-scanning direction encoder 33 after the leading edge of the printing medium P is detected by the paper feed sensor 3.

[0070] If it is determined that the printing medium P has not reached the head unit 4 (step S3: NO), in step S4, the control unit 6 determines whether or not it has detected a pulse of the A-phase signal and a pulse of the B-phase signal with a predetermined phase difference from the main scanning direction encoder 32.

[0071] Here, the rotation of ball portion 31 about rotation axis A1 due to the movement of conveyor belt 11 (printing medium P) in the front-to-back direction causes A-phase signal pulses and B-phase signal pulses with a predetermined phase difference to be output from main scanning direction encoder 32, as shown in the middle and bottom diagrams of Fig. 5. The output timing relationship of the A-phase signal pulses and B-phase signal pulses changes depending on the rotation direction of ball portion 31 about rotation axis A1, which corresponds to the movement direction of conveyor belt 11 (printing medium P) in the front-to-back direction.

[0072] Returning to FIG. 6, if it is determined that the pulse of the A-phase signal and the pulse of the B-phase signal with a predetermined phase difference have not been detected (step S4: NO), the control unit 6 returns to step S3.

[0073] If it is determined that a pulse of the A-phase signal and a pulse of the B-phase signal with a predetermined phase difference have been detected (step S4: YES), in step S5, the control unit 6 determines whether or not the pulse of the A-phase signal has been detected first, among the pulses of the A-phase signal and the B-phase signal with a predetermined phase difference that have been detected.

[0074] If it is determined that the pulse of the A-phase signal has been detected first (step S5: YES), the control unit 6 adds "1" to the offset correction value C in step S6.

[0075] If it is determined that the pulse of the B-phase signal has been detected first (step S5: NO), the control unit 6 subtracts "1" from the offset correction value C in step S7.

[0076] After steps S6 and S7, in step S8, the control unit 6 offsets the pixels corresponding to each nozzle 26 of each inkjet head 21 by the amount of the addition or subtraction of the offset correction value C in steps S6 and S7.

[0077] Specifically, if "1" is added to the offset correction value C in step S6, in step S8, the control unit 6 shifts the pixels corresponding to each nozzle 26 to one side in the main scanning direction by a predetermined number of pixels (predetermined offset amount).

[0078] Also, if "1" is subtracted from the offset correction value C in step S7, in step S8, the control unit 6 shifts the pixels corresponding to each nozzle 26 of each inkjet head 21 to the other side in the main scanning direction by a predetermined number of pixels (predetermined offset amount).

[0079] Here, for example, by setting the resolution of the main scanning direction encoder 32 so that the distance traveled in the front-to-back direction of the conveyor belt 11 (printing medium P) for one pulse of the main scanning direction encoder 32 is the same as the interval between adjacent pixels in the main scanning direction of the image to be printed, the above-mentioned predetermined number of pixels becomes "1." This makes it possible to easily control the offset, since the pixel corresponding to each nozzle 26 is shifted by one pixel in the main scanning direction in response to an increase or decrease of "1" in the offset correction value C.

[0080] After step S8, the control unit 6 returns to step S3. If it is determined in step S3 that the print medium P has reached the head unit 4 (step S3: YES), the control unit 6 determines in step S9 of FIG. 7 whether the absolute value of the offset correction value C exceeds the specified value Ck.

[0081] Here, the specified value Ck is set so that the image printed by the inkjet head 21 moves by an offset amount corresponding to the absolute value of the offset correction value C, but the amount of movement does not exceed a threshold. In other words, the specified value Ck is set to a value corresponding to the threshold value of the offset amount corresponding to the absolute value of the offset correction value C. The specified value Ck corresponding to the threshold value of the offset amount is set to a value that prevents ink from being ejected onto the conveyor belt 11 outside the printing medium P and prevents the margins of the printing medium P from being insufficient, for example, within the expected range of fluctuation of the printing medium P in the front-to-rear direction.

[0082] If it is determined that the absolute value of the offset correction value C exceeds the specified value Ck (step S9: YES), the control unit 6 stops the printing operation due to an error in step S10.

[0083] If it is determined that the absolute value of the offset correction value C is equal to or less than the specified value Ck (step S9: NO), the control unit 6 proceeds to step S11. The processes of steps S11 to S14 are the same as the processes of steps S4 to S7 described above.

[0084] After step S13 and after step S14, in step S15, the control unit 6 determines whether or not the absolute value of the offset correction value C exceeds the specified value Ck.

[0085] If it is determined that the absolute value of the offset correction value C exceeds the specified value Ck (step S15: YES), the control unit 6 proceeds to step S10 and stops the printing operation due to an error.

[0086] If it is determined that the absolute value of the offset correction value C is less than or equal to the specified value Ck (step S15: NO), in step S16, the control unit 6 offsets the pixels corresponding to each nozzle 26 of each inkjet head 21 by the amount of the addition or subtraction of the offset correction value C performed in steps S13 and S14.

[0087] After step S16, or if it is determined in step S11 that a pulse of the A-phase signal and a pulse of the B-phase signal with a predetermined phase difference have not been detected (step S11: NO), the control unit 6 determines in step S17 whether printing on the fed print medium P has finished. If it is determined that printing has not finished (step S17: NO), the control unit 6 returns to step S11. If the control unit 6 determines that printing has finished (step S11: YES), the series of processes ends.

[0088] As described above, in the offset control in the main scanning direction, when the main scanning direction encoder 32 outputs an A-phase signal pulse and a B-phase signal pulse with a predetermined phase difference, the control unit 6 adds or subtracts the offset correction value C according to the order of the output timing of these pulses (steps S4 to S7, S11 to S14).The control unit 6 then offsets the pixels corresponding to each nozzle 26 of each inkjet head 21 by the amount of the addition or subtraction of the offset correction value C (steps S8 and S16).

[0089] In this way, the control unit 6 controls the correspondence between each pixel of the image printed by each inkjet head 21 and the nozzles 26 that eject ink to each pixel, in accordance with the fluctuation in the position of the printing medium P in the front-to-rear direction detected by the main scanning direction encoder 32 from the rotation direction and rotation angle of the ball portion 31 around the rotation axis A1.

[0090] This control of the correspondence between each pixel and the nozzles 26 that eject ink to each pixel is started when the printing medium P is fed (step S1: YES) by setting the offset correction value C to "0" (step S2). Before the printing medium P reaches the head unit 4 (begins passing by the inkjet head 21) (step S3: NO), printing is not performed, but the correspondence between each pixel of the image printed by the inkjet head 21 after the printing medium P arrives and the nozzles 26 that eject ink to each pixel is controlled in accordance with fluctuations in the position of the printing medium P in the front-to-back direction. After the printing medium P reaches the head unit 4 (step S3: YES), the image is printed, and the correspondence between each pixel of the image and the nozzles 26 that eject ink to each pixel is controlled in accordance with fluctuations in the position of the printing medium P in the front-to-back direction.

[0091] Furthermore, if the absolute value of the offset correction value C exceeds the specified value Ck (steps S9, S15: YES) after the printing medium P reaches the head unit 4 (starts passing through the inkjet head 21), the control unit 6 stops the printing operation due to an error (step S10).

[0092] In this way, after the printing medium P starts passing through the inkjet heads 21, if the offset amount from the initial correspondence between each pixel printed by each inkjet head 21 and the nozzles 26 that eject ink to each pixel exceeds a threshold value, the control unit 6 stops printing by each inkjet head 21.

[0093] As described above, in the printing device 1, the control unit 6 controls the correspondence between each pixel of the image printed by each inkjet head 21 and the nozzles 26 that eject ink onto each pixel, in accordance with fluctuations in the position of the printing medium P in the front-to-rear direction detected by the main scanning direction encoder 32 of the two-axis encoder 5. This reduces deviations in the ink landing position due to fluctuations in the position of the printing medium P in the front-to-rear direction, thereby reducing degradation in print image quality.

[0094] The printer 1 does not require a mechanism for moving the inkjet head 21 back and forth, which helps prevent the device from becoming too large. Also, since there is no need to provide a guide member for guiding the printing medium P, the printing medium P will not collide with the guide member and become deformed.

[0095] Therefore, according to the printing device 1, it is possible to suppress an increase in the size of the device and deformation of the printing medium P, while mitigating degradation of print quality.

[0096] Furthermore, in the printing device 1, the two-axis encoder 5 detects fluctuations in the front-to-rear position of the printing medium P transported by the transport belt 11, while also detecting the transport speed of the printing medium P by the transport belt 11. The control unit 6 controls the timing of ejecting ink from each nozzle 26 of each inkjet head 21 in accordance with the transport speed of the printing medium P detected by the sub-scanning direction encoder 33 of the two-axis encoder 5.

[0097] This reduces misalignment of ink landing in the front-to-back and left-to-right directions without the need to provide separate detectors for detecting fluctuations in the position of the printing medium P in the front-to-back direction and the conveying speed of the printing medium P by the conveyor belt 11. As a result, it is possible to reduce degradation of print quality while minimizing the complexity of the device configuration.

[0098] The biaxial encoder 5 also has a ball portion 31 that comes into contact with the print medium P as it passes through the inkjet head 21 and rotates in response to the print medium P. The biaxial encoder 5 detects fluctuations in the front-to-rear position of the transported print medium P from the direction and angle of rotation of the ball portion 31 about rotation axis A1, and detects the transport speed of the print medium P from the rotation speed of the ball portion 31 about rotation axis A2. This makes it possible to detect fluctuations in the front-to-rear position of the print medium P and the transport speed of the print medium P with high accuracy, even if slippage occurs between the transport belt 11 and the print medium P. As a result, degradation of print quality due to misaligned ink droplets can be further reduced.

[0099] Furthermore, in the printing device 1, after the printing medium P starts passing the inkjet heads 21, if the amount of offset from the initial correspondence between each pixel printed by each inkjet head 21 and the nozzles 26 that eject ink onto each pixel exceeds a threshold, the control unit 6 stops printing by each inkjet head 21. This reduces the risk of ink being ejected onto the conveyor belt 11 outside the printing medium P or of insufficient margins on the printing medium P.

[0100] In the above-described embodiment, the two-axis encoder 5 detects the positional fluctuation of the printing medium P in the front-to-rear direction while detecting the transport speed of the printing medium P. However, a configuration in which the detection of the positional fluctuation of the printing medium P in the front-to-rear direction and the detection of the transport speed of the printing medium P are performed by separate detection units may also be used. For example, a detection unit configured by removing the sub-scanning direction encoder 33 from the two-axis encoder 5 shown in FIG. 3 may detect the positional fluctuation of the printing medium P in the front-to-rear direction, and the transport speed of the printing medium P may be detected by a roller that rotates following the transport belt 11 and an encoder attached to this roller.

[0101] Furthermore, in the above-described embodiment, a printing device 1 equipped with a conveying unit 2 was described, but the present invention can also be applied to a printing device that prints by ejecting ink onto a printing medium conveyed by an existing conveying mechanism.

[0102] The present invention is not limited to the above-described embodiments, and the components can be modified and embodied in practice without departing from the spirit of the invention. Furthermore, various inventions can be created by appropriately combining multiple components disclosed in the above-described embodiments. For example, some components may be omitted from all the components shown in the embodiments.

[0103] [Note] The present application discloses the following inventions.

[0104] (Appendix 1) an ejection unit that has a plurality of nozzles arranged in a nozzle arrangement direction perpendicular to the transport direction of the print medium transported by the transport mechanism, and ejects ink from the plurality of nozzles onto the transported print medium to print an image; a detection unit that detects a change in the position of the transported print medium in the nozzle arrangement direction; a control unit that controls the correspondence between each pixel of an image printed by the ejection unit and the nozzles that eject ink onto each pixel, in accordance with a change in the position of the print medium in the nozzle arrangement direction detected by the detection unit; A printing device comprising:

[0105] (Appendix 2) the detection unit detects a positional fluctuation of the transported print medium in the nozzle arrangement direction, and detects a transport speed of the print medium by the transport mechanism; 2. The printing device according to claim 1, wherein the control unit controls the timing at which ink is ejected from the plurality of nozzles in accordance with the transport speed detected by the detection unit.

[0106] (Appendix 3) The detection unit a ball portion that contacts the print medium passing through the ejection portion and rotates in response to the print medium; detecting a change in the position of the print medium in the nozzle arrangement direction from a rotation direction and a rotation angle of the ball portion about a rotation axis along the transport direction; 3. The printing device according to claim 2, wherein the transport speed of the print medium is detected from the rotation speed of the ball portion about a rotation axis along the nozzle arrangement direction.

[0107] (Appendix 4) The printing device described in any one of Appendixes 1 to 3, characterized in that, after the printing medium begins to pass through the ejection section, the control section stops printing by the ejection section when an offset amount from an initial correspondence between each pixel of the image printed by the ejection section and the nozzles that eject ink to each pixel exceeds a threshold value. [Explanation of symbols]

[0108] 1 Printing device 2. Conveyor section 3 Paper feed sensor 4 Head Unit 5 2-axis encoder 6 Control Unit 11 Conveyor belt 12 Drive roller 13 Driven roller 14 Transport motor 21 Inkjet head 26 nozzles 31 Ball section 32 Main scanning direction encoder 33 Sub-scanning direction encoder 34 Climbing sensor 41,51 Laura 42,52 axes 43,53 Rotating slit plate 44,54 Fixed slit plate 45,55 Sensor section A1, A2 rotation axis

Claims

1. an ejection unit that has a plurality of nozzles arranged in a nozzle arrangement direction perpendicular to the transport direction of the print medium transported by the transport mechanism, and ejects ink from the plurality of nozzles onto the transported print medium to print an image; a detection unit that detects a change in the position of the transported print medium in the nozzle arrangement direction; a control unit that controls the correspondence between each pixel of an image printed by the ejection unit and the nozzles that eject ink onto each pixel, in accordance with a change in the position of the print medium in the nozzle arrangement direction detected by the detection unit; A printing device comprising:

2. the detection unit detects a positional fluctuation of the transported print medium in the nozzle arrangement direction, and detects a transport speed of the print medium by the transport mechanism; 2. The printing apparatus according to claim 1, wherein the control unit controls the timing at which ink is ejected from the plurality of nozzles in accordance with the transport speed detected by the detection unit.

3. The detection unit a ball portion that contacts the print medium passing through the ejection portion and rotates in response to the print medium; detecting a change in the position of the print medium in the nozzle arrangement direction from a rotation direction and a rotation angle of the ball portion about a rotation axis along the transport direction; 3. The printing device according to claim 2, wherein the transport speed of the print medium is detected from the rotation speed of the ball portion about a rotation axis along the nozzle arrangement direction.

4. The printing device according to any one of claims 1 to 3, characterized in that, after the printing medium begins to pass through the ejection section, the control section stops printing by the ejection section if an offset amount from an initial correspondence between each pixel of the image printed by the ejection section and the nozzles that eject ink to each pixel exceeds a threshold value.

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