Image forming apparatus, image forming method and program

Abstract

To provide an image formation apparatus which can detect a relative conveyance amount deviation between a recording medium and a head in a conveyance direction.SOLUTION: An image formation apparatus comprises: a head which includes a first nozzle 601 that discharges colored ink, a second nozzle 602 that discharges underlayer ink and a third nozzle 603 that is arranged at a position different from the first nozzle in the conveyance direction of a recording medium and discharges the colored ink; a control unit which controls the relative movement between the recording medium and the head along the main-scanning direction, the relative movement by a prescribed conveyance amount between the recording medium and the head along the conveyance direction and the discharge of the colored ink and the underlayer ink; and a reading unit which reads a test pattern formed with the colored ink. The image formation apparatus forms a first test pattern by the discharge from the first nozzle, forms a second test pattern by the discharge from the third nozzle, and forms a mask image M3 so as to overlap the upper side or lower side of the first and second test patterns with the underlayer ink discharged from the second nozzle.SELECTED DRAWING: Figure 16

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus, an image forming method, and a program. [Background technology]

[0002] Conventionally, there has been known an image forming device that forms an image on a recording medium by controlling the relative movement between a head and the recording medium along both the main scanning direction and the recording medium transport direction that intersects with the main scanning direction, and the ejection of ink by the head.

[0003] As the image forming device, a configuration has been disclosed in which an actual distance of misalignment corresponding to the amount of misalignment in an image captured by an imaging unit is calculated, and the transport distance of an object is corrected for each direction of carriage movement (see, for example, Patent Document 1). This image forming device forms a pair of first markers with a head, images a test pattern in which a second marker is formed with a head tilted differently from when the pair of first markers were formed, calculates the ratio between the distance between the first markers and the amount of misalignment of the second marker from the captured image, calculates the actual distance of misalignment of the second marker based on that ratio, and adjusts a parameter related to the transport distance. Summary of the Invention [Problem to be solved by the invention]

[0004] However, with the configuration of Patent Document 1, if the recording medium is transparent, for example, it may not be possible to detect the test pattern formed on the recording medium, and it may not be possible to detect the deviation in the relative transport amount between the recording medium and the head in the transport direction.

[0005] SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of detecting a deviation in the relative transport amount between a recording medium and a head in the transport direction. [Means for solving the problem]

[0006] An image forming apparatus according to one aspect of the present invention has a head including a first nozzle that ejects colored ink, a second nozzle that ejects undercoat ink, and a third nozzle that is disposed at a position different from the first nozzle in a transport direction of a recording medium and ejects the colored ink; a control unit that controls relative movement between the recording medium and the head along a main scanning direction that intersects the transport direction, relative movement between the recording medium and the head along the transport direction by a predetermined transport amount, and ejection of each of the colored ink and the undercoat ink by the head; and a reading unit that reads a test pattern formed on the recording medium by the colored ink ejected from the head, the head has, in order from upstream in the transport direction, the first nozzle, the second nozzle, and the third nozzle; the control unit controls to form a first test pattern on the recording medium using the colored ink ejected from the first nozzles, to form a second test pattern on the recording medium using the colored ink ejected from the third nozzles, and to form mask images using the base ink ejected from the second nozzles so as to overlap above or below the first test pattern and the second test pattern, respectively; after forming a part of the first test pattern with the colored ink ejected from the first nozzles, the head and the recording medium are moved relatively in the transport direction by the predetermined transport amount, the mask image is formed so as to be superimposed on the first test pattern with the base ink ejected from the second nozzles, and thereafter the head and the recording medium are further moved relatively in the transport direction by the predetermined transport amount, and the second test pattern is formed on the mask image with the colored ink ejected from the third nozzles; The reading unit reads the positions of the first test pattern and the second test pattern. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an image forming apparatus capable of detecting a deviation in the relative transport amount between the recording medium and the head in the transport direction. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a perspective view showing the inside of an image forming apparatus according to an embodiment; [Figure 2] FIG. 2 is a top view illustrating an example of the internal configuration of the image forming device according to the embodiment. [Figure 3] FIG. 2 is a diagram illustrating an example of the configuration of a carriage according to an embodiment. [Figure 4] FIG. 2 is a perspective view showing an example of the configuration of an imaging unit according to the embodiment. [Figure 5] FIG. 2 is an exploded perspective view showing an example of the configuration of an imaging unit according to the embodiment. [Figure 6] 5 is a longitudinal cross-sectional view of the imaging unit as seen from the X1 direction in FIG. 4. [Figure 7] 5 is a longitudinal sectional view of the imaging unit as seen from the X2 direction in FIG. 4. [Figure 8] FIG. 2 is a plan view of an imaging unit according to the first embodiment. [Figure 9] FIG. 10 is a diagram illustrating a reference chart. [Figure 10] FIG. 10 is a vertical cross-sectional view of an imaging unit that does not have a reference chart. [Figure 11] 11 is a plan view of the imaging unit of FIG. 10 as viewed from the X2 direction. [Figure 12] FIG. 2 is a diagram illustrating an example of a configuration around a conveying roller. [Figure 13] FIG. 2 is a diagram illustrating an example of a hardware configuration of an image forming apparatus according to an embodiment. [Figure 14] FIG. 2 is a diagram illustrating an example of a functional configuration of a CPU according to the embodiment. [Figure 15] FIG. 10 is a diagram illustrating an example of a test pattern formed on a recording medium. [Figure 16] 1A to 1C are diagrams illustrating a method for forming a test pattern according to an embodiment. [Figure 17] 10 is a diagram illustrating an example of a method for calculating the ratio between the distance between a pair of second markers and the amount of positional deviation of a first marker in a captured image. FIG. [Figure 18] FIG. 1 is a first diagram illustrating an example of the operation of the image forming apparatus according to the embodiment. [Figure 19] FIG. 2 is a second diagram illustrating the operation of the image forming apparatus according to the embodiment. [Figure 20] FIG. 3 is a third diagram illustrating the operation of the image forming apparatus according to the embodiment. [Figure 21] FIG. 4 is a fourth diagram illustrating the operation of the image forming apparatus according to the embodiment. [Figure 22] FIG. 10 is a diagram illustrating the function of a mask image. [Figure 23] FIG. 10 is a diagram showing a first modified example of a head arrangement. [Figure 24] FIG. 10 is a diagram showing a second modified example of a head arrangement. [Figure 25] FIG. 10 is a diagram showing a third modified example of a head arrangement. [Figure 26] FIG. 10 is a perspective view illustrating a configuration of an image forming apparatus according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes the preferred embodiments of the present invention with reference to the accompanying drawings. In the drawings, the same components are designated by the same reference numerals, and redundant explanations may be omitted.

[0010] Furthermore, the embodiments shown below are examples of image forming apparatuses that embody the technical concepts of the present invention, and the present invention is not limited to the embodiments shown below. The dimensions, materials, shapes, relative locations, etc. of the components described below are intended to be illustrative and not to limit the scope of the present invention unless otherwise specified. Furthermore, the sizes and positional relationships of components shown in the drawings may be exaggerated for clarity.

[0011] [Embodiment] <Configuration Example of Image Forming Apparatus 100> The configuration of an image forming apparatus 100 according to an embodiment will be described with reference to Fig. 1 to Fig. 3. Fig. 1 is a perspective view showing the interior of the image forming apparatus 100 in a see-through manner. Fig. 2 is a top view showing an example of the internal configuration of the image forming apparatus 100. Fig. 3 is a diagram showing an example of the configuration of a carriage 5.

[0012] As shown in Figure 1, the image forming apparatus 100 has a carriage 5 that moves back and forth in the main scanning direction (the direction of arrow A in the figure). The carriage 5 is supported by a main guide rod 3 that extends along the main scanning direction. The carriage 5 is also provided with a connecting piece 5a. The connecting piece 5a engages with a sub-guide member 4 that is provided in parallel with the main guide rod 3, stabilizing the posture of the carriage 5.

[0013] The carriage 5 is connected to a timing belt 11 that is stretched between a drive pulley 9 and a driven pulley 10. The drive pulley 9 is rotated by the drive of a main scanning motor 8. The driven pulley 10 has a mechanism for adjusting the distance between itself and the drive pulley 9, and has the function of applying a predetermined tension to the timing belt 11.

[0014] The carriage 5 moves back and forth in the main scanning direction as the timing belt 11 is driven by the main scanning motor 8. The movement amount and movement speed of the carriage 5 are controlled based on the encoder value output by a main scanning encoder sensor 131 provided on the carriage 5 upon detecting marks on an encoder sheet 14, as shown in FIG.

[0015] 3, carriage 5 is equipped with heads 6A, 6B, and 6C. Each of heads 6A, 6B, and 6C includes a first nozzle that ejects colored ink, a second nozzle that ejects base ink, and a third nozzle that ejects colored ink and is positioned differently from the first nozzle in the sub-scanning direction. The sub-scanning direction is a direction that intersects with the main scanning direction and is an example of a transport direction.

[0016] Head 6A has a nozzle row 6Ay with a large number of nozzles that eject yellow (Y) ink, a nozzle row 6Ac with a large number of nozzles that eject cyan (C) ink, a nozzle row 6Am with a large number of nozzles that eject magenta (M) ink, and a nozzle row 6Ak with a large number of nozzles that eject black (K) ink. Similarly, head 6C has one each of nozzle rows 6Cy, 6Cc, 6Cm, and 6Ck. Head 6B has four nozzle rows 6Bw1, 6Bw2, 6Bw3, and 6Bw4 with a large number of nozzles that eject white (W) ink.

[0017] Hereinafter, these heads 6A, 6B, and 6C will be collectively referred to as head 6. Head 6 is supported by carriage 5 so that its ejection surface (nozzle surface) faces downward (toward recording medium P).

[0018] The cartridge 7, which is an ink supply body for supplying ink to the head 6, is not mounted on the carriage 5 but is placed at a predetermined position within the image forming apparatus 100. The cartridge 7 and the head 6 are connected by a pipe, and ink is supplied from the cartridge 7 to the head 6 via this pipe.

[0019] As shown in FIG. 2, the image forming apparatus 100 has a platen 16 positioned opposite the ejection surface of the head 6. The platen 16 supports the recording medium P when ink is ejected from the head 6 onto the recording medium P. The platen 16 has many through-holes that penetrate in the thickness direction, and has rib-like protrusions that surround each through-hole. The image forming apparatus 100 can prevent the recording medium P from falling off the platen 16 by operating a suction fan provided on the side of the platen 16 opposite the surface that supports the recording medium P.

[0020] The image forming apparatus 100 sandwiches the recording medium P between conveying rollers driven by a sub-scanning motor 12 (see FIG. 13), and conveys the recording medium P intermittently over a platen 16 in the sub-scanning direction (the direction of arrow B in FIG. 2).

[0021] The image forming apparatus 100 has a head 6 with a large number of nozzles arranged in the sub-scanning direction. In this embodiment, the image forming apparatus 100 intermittently transports the recording medium P in the sub-scanning direction, and while the transport of the recording medium P is stopped, the image forming apparatus 100 selectively drives the nozzles of the head 6 in accordance with image data while moving the carriage 5 back and forth in the main scanning direction, and ejects ink from the head 6 onto the recording medium P on the platen 16, thereby forming an image on the recording medium P.

[0022] The image forming apparatus 100 also has a maintenance mechanism 15 for maintaining the reliability of the head 6. The maintenance mechanism 15 cleans and caps the ejection surface of the head 6, discharges unnecessary ink from the head 6, and so on.

[0023] As shown in FIG. 3, the carriage 5 has an imaging unit 20 for capturing an image of a test pattern TP (see FIG. 15) formed on the recording medium P.

[0024] The imaging unit 20 is an example of a reading unit that reads the test pattern TP formed on the recording medium P with colored ink ejected from the head 6. In particular, in this embodiment, the imaging unit 20 reads the positions of the first test pattern and the second test pattern included in the test pattern TP.

[0025] The image forming apparatus 100 has the above-described components inside an exterior body 1. The exterior body 1 has an openable and closable cover member 2. When the image forming apparatus 100 is undergoing maintenance or when a jam occurs, the cover member 2 can be opened to perform work on the components provided inside the exterior body 1.

[0026] 3 may or may not have a reference chart that is imaged simultaneously with the test pattern TP. The reference chart is used to calculate the colorimetric values ​​of the test pattern TP using, for example, the RGB values ​​of each reference patch (see FIG. 9).

[0027] <First example of imaging unit 20> Specific examples of the imaging unit 20 having a reference chart will be described with reference to Figs. 4 to 8. Fig. 4 is a perspective view showing the appearance of the imaging unit. Fig. 5 is an exploded perspective view of the imaging unit 20. Fig. 6 is a vertical cross-sectional view of the imaging unit 20 as seen from the X1 direction in Fig. 4. Fig. 7 is a vertical cross-sectional view of the imaging unit 20 as seen from the X2 direction in Fig. 4. Fig. 8 is a plan view of the imaging unit 20.

[0028] The imaging unit 20 has, for example, a rectangular box-shaped housing 51. The housing 51 has, for example, a bottom plate 51a and a top plate 51b that face each other with a predetermined gap between them, and side walls 51c, 51d, 51e, and 51f that connect the bottom plate 51a and the top plate 51b.

[0029] Bottom plate 51a and side walls 51d, 51e, and 51f of housing 51 are integrally formed by, for example, molding, while top plate 51b and side walls 51c are detachable. Figure 5 shows the state in which top plate 51b and side walls 51c have been removed.

[0030] The image forming apparatus 100 has the imaging unit 20 in a transport path of the recording medium P on which the test pattern TP is formed, for example, in a state where a part of the housing 51 is supported by a predetermined support member. As shown in Figures 6 and 7, the image forming apparatus 100 supports the imaging unit 20 by a predetermined support member so that the bottom plate portion 51a of the housing 51 faces the transported recording medium P in a substantially parallel state with a gap d between them.

[0031] The imaging unit 20 has an opening 53 in the bottom plate 51a of the housing 51 facing the recording medium P on which the test pattern TP is formed, so that the test pattern TP outside the housing 51 can be imaged from inside the housing 51. The imaging unit 20 also has a reference chart 300 on the inner surface of the bottom plate 51a of the housing 51, adjacent to the opening 53 via a support member 63. The reference chart 300 is imaged together with the test pattern TP by the sensor unit 26 when measuring the color of the test pattern TP and acquiring the RGB values.

[0032] The imaging unit 20 also has a circuit board 54 on the side of the top plate 51b inside the housing 51. As shown in Fig. 8, the circuit board 54 is fixed by fastening members 54b, and the housing 51 has a rectangular box shape with the surface on the circuit board 54 side open. Note that the shape of the housing 51 is not limited to a rectangular box, and may be, for example, a cylindrical box shape or an elliptical cylindrical box shape having a bottom plate 51a in which an opening 53 is formed.

[0033] Furthermore, imaging unit 20 has sensor unit 26 for capturing an image, located between top panel 51b of housing 51 and circuit board 54. As shown in Fig. 6, sensor unit 26 has two-dimensional sensor 27, such as a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal Oxide Semiconductor) sensor, and imaging lens 28 for forming an optical image of the imaging range of sensor unit 26 on the light receiving surface (imaging area) of two-dimensional sensor 27. Two-dimensional sensor 27 is a light receiving element array in which light receiving elements that receive reflected light from a subject are arranged two-dimensionally.

[0034] The imaging unit 20 holds the sensor unit 26 by means of a sensor holder 56 formed integrally with, for example, the side wall 51e of the housing 51. The sensor holder 56 has a ring portion 56a provided in a position facing a through hole 54a formed in the circuit board 54. The ring portion 56a has a through hole of a size following the outer shape of the protruding portion of the sensor unit 26 on the imaging lens 28 side. By inserting the protruding portion on the imaging lens 28 side into the ring portion 56a of the sensor holder 56, the imaging unit 20 holds the sensor unit 26 by means of the sensor holder 56 such that the imaging lens 28 faces the bottom plate 51a side of the housing 51 through the through hole 54a of the circuit board 54.

[0035] 6 is approximately perpendicular to the bottom plate 51a of the housing 51, and the opening 53 and a reference chart 300 (described later) are included in the imaging range. This allows the sensor unit 26 to capture an image of the test pattern TP outside the housing 51 through the opening 53 in a part of the imaging area of ​​the two-dimensional sensor 27. In addition, the sensor unit 26 can capture an image of the reference chart 300 placed inside the housing 51 in another part of the imaging area of ​​the two-dimensional sensor 27.

[0036] The sensor unit 26 is electrically connected to a circuit board 54, on which various electronic components are mounted, via, for example, a flexible cable. The circuit board 54 also has an external connection connector 57 to which a connection cable for connecting the imaging unit 20 to the main control board of the image forming apparatus 100 is attached.

[0037] The imaging unit 20 has a pair of light sources 58 on the circuit board 54, which are located on a center line OA in the sub-scanning direction that passes through the center of the sensor unit 26 and are spaced apart by a predetermined amount in the sub-scanning direction from the center of the sensor unit 26. The light sources 58 illuminate the imaging range substantially uniformly when the sensor unit 26 captures an image. An LED (Light Emitting Diode) or the like is suitable as the light source 58, for example, as it is space-saving and advantageous for power saving.

[0038] As shown in Figures 7 and 8, the imaging unit 20 has a pair of LEDs as light sources 58 that are evenly arranged in a direction perpendicular to the direction in which the opening 53 and the reference chart 300 are aligned, with the center of the imaging lens 28 as the reference.

[0039] The two LEDs used as light source 58 are mounted, for example, on the surface of circuit board 54 on the bottom plate portion 51a side. However, light source 58 need not necessarily be mounted directly on circuit board 54 as long as it is positioned so that the imaging range of sensor unit 26 can be illuminated approximately uniformly with diffused light. Furthermore, by arranging the two LEDs in symmetrical positions with respect to two-dimensional sensor 27, it is possible to capture an image of the imaging surface under the same illumination conditions as on the reference chart 300 side.

[0040] In this embodiment, an LED is used as the light source 58, but the type of light source 58 is not limited to an LED. For example, the light source 58 may be an organic EL or the like. When an organic EL is used as the light source 58, illumination light having a spectral distribution close to that of sunlight can be obtained, and therefore, improvement in color measurement accuracy can be expected.

[0041] 8, sensor unit 26 includes light absorber 55c directly below light source 58 and two-dimensional sensor 27. Light absorber 55c reflects or absorbs light from light source 58 in directions other than two-dimensional sensor 27. Light absorber 55c has an acute-angled shape and is formed so that incident light from light source 58 is reflected to the inner surface of light absorber 55c, and is structured so as not to be reflected in the incident direction.

[0042] The housing 51 also has an optical path length changing member 59 inside it in the optical path between the sensor unit 26 and the test pattern TP outside the housing 51 that is imaged by the sensor unit 26 through the opening 53 .

[0043] The optical path length changing member 59 is an optical element with a refractive index n that has sufficient transmittance for the light from the light source 58. The optical path length changing member 59 has the function of moving the imaging plane of the optical image of the test pattern TP outside the housing 51 closer to the imaging plane of the optical image of the reference chart 300 inside the housing 51.

[0044] The imaging unit 20 changes the optical path length by placing an optical path length changing member 59 in the optical path between the sensor unit 26 and the subject outside the housing 51. As a result, the imaging unit 20 aligns the imaging plane of the optical image of the test pattern TP outside the housing 51 and the imaging plane of the reference chart 300 inside the housing 51 with the light receiving surface of the two-dimensional sensor 27 of the sensor unit 26. Therefore, the sensor unit 26 can capture images in focus of both the test pattern TP outside the housing 51 and the reference chart 300 inside the housing 51.

[0045] 6, the optical path length changing member 59 is supported at both ends of its surface facing the bottom plate 51a by a pair of ribs 60 and 61. A pressing member 62 is disposed between the surface of the optical path length changing member 59 facing the top plate 51b and the circuit board 54, preventing the optical path length changing member 59 from moving inside the housing 51. The optical path length changing member 59 is disposed so as to close the opening 53 provided in the bottom plate 51a of the housing 51. Therefore, the optical path length changing member 59 also functions to prevent impurities such as ink mist and dust that enter the housing 51 from the outside through the opening 53 from adhering to the sensor unit 26, the light source 58, the reference chart 300, etc.

[0046] The mechanical configuration of the imaging unit 20 described above is merely an example and is not limited to this. The imaging unit 20 may be configured to capture an image of the test pattern TP outside the housing 51 through the opening 53 using the sensor unit 26 provided inside the housing 51 at least while the light source 58 provided inside the housing 51 is turned on. The imaging unit 20 can be modified or changed in various ways with respect to the above configuration.

[0047] For example, the imaging unit 20 according to this embodiment has the reference chart 300 on the inner surface of the bottom plate 51a of the housing 51. However, an opening separate from the opening 53 may be provided at the position where the reference chart 300 is to be placed on the bottom plate 51a of the housing 51, and the reference chart 300 may be attached from outside the housing 51 at the position where this opening is provided. In this case, the sensor unit 26 captures an image of the test pattern TP formed on the recording medium P through the opening 53, and also captures an image of the reference chart 300 attached from outside to the bottom plate 51a of the housing 51 through the opening separate from the opening 53. This example has the advantage that the reference chart 300 can be easily replaced if it becomes dirty or otherwise defective.

[0048] <Configuration example of Reference Chart 300> A specific example of the reference chart 300 arranged on the housing 51 of the imaging unit 20 will be described with reference to Fig. 9. Fig. 9 is a diagram showing a specific example of the reference chart.

[0049] The reference chart 300 shown in FIG. 9 has a plurality of color measurement patch rows 310 to 340 in which color measurement patches for color measurement are arranged, a distance measurement line 350, and a marker 360 for specifying the chart position.

[0050] The colorimetric patch arrays 310 to 340 include a colorimetric patch array 310 in which colorimetric patches of primary colors YMCK are arranged in gradation order, a colorimetric patch array 320 in which colorimetric patches of secondary colors RGB are arranged in gradation order, a colorimetric patch array (achromatic gradation pattern) 330 in which grayscale colorimetric patches are arranged in gradation order, and a colorimetric patch array 340 in which colorimetric patches of tertiary colors are arranged.

[0051] The distance measurement line 350 is a substantially rectangular frame formed to surround the plurality of color measurement patch rows 310 to 340. The chart position specifying markers 360 are provided at the four corners of the distance measurement line 350 and function as markers for specifying the position of each color measurement patch. By identifying the distance measurement line 350 and the chart position specifying markers 360 at its four corners from the image of the reference chart 300 captured by the sensor unit 26, the position of the reference chart 300 and the position of each color measurement patch can be specified.

[0052] Each of the colorimetry patches constituting the colorimetry patch arrays 310-340 functions as a reference for color tones that reflects the imaging conditions of the sensor unit 26. The configuration of the colorimetry patch arrays 310-340 arranged on the reference chart 300 is not limited to the example shown in FIG. 9 , and any colorimetry patch array can be applied. The image forming apparatus 100 may use colorimetry patches that can identify as wide a color range as possible, or the colorimetry patch array 310 of the primary colors of YMCK and the colorimetry patch array 330 of the grayscale may use patches of colorimetry values ​​of color materials used in the image forming apparatus 100. The colorimetry patch array 320 of the secondary colors of RGB may be composed of patches of colorimetry values ​​that can be produced by the color materials used in the image forming apparatus 100, or may use a reference color chart with defined colorimetry values, such as Japan Color.

[0053] In this embodiment, the reference chart 300 is used, which has color measurement patch arrays 310 to 340 in the shape of general patches (color charts), but the reference chart 300 does not necessarily have to have such color measurement patch arrays 310 to 340. The reference chart 300 may have a configuration in which multiple colors that can be used for color measurement are arranged so that their respective positions can be identified.

[0054] Because the reference chart 300 is disposed adjacent to the opening 53 on the inner surface of the bottom plate 51a of the housing 51, the sensor unit 26 can capture an image of the test pattern TP outside the housing 51 in parallel. Note that, in this case, "parallel capture" means acquiring one frame of image data including the test pattern TP outside the housing 51 and the reference chart 300. In other words, even if there is a time lag in acquiring data for each pixel, acquiring image data including the test pattern TP outside the housing 51 and the reference chart 300 in one frame will result in the test pattern TP outside the housing 51 and the reference chart 300 being captured in parallel.

[0055] <Second Example of Imaging Unit 20> 10 and 11, a specific example of an imaging unit 20 that does not have a reference chart will be described as a second example of the imaging unit 20. Fig. 10 is a vertical cross-sectional view of the imaging unit. Fig. 11 is a plan view of the imaging unit of Fig. 10 as viewed from the X2 direction.

[0056] As shown in FIG. 10, the imaging unit 20 has a light source 42 and a sensor unit 26 on a substrate 41 fixed to the carriage 5.

[0057] The light source 42 includes, for example, an LED, and irradiates illumination light onto a test pattern TP formed on a recording medium P, which is the subject. Light reflected from the test pattern TP (diffuse reflection light or regular reflection light) is incident on the sensor unit 26. As shown in FIG. 11 , four light sources 42 are arranged to surround the test pattern TP formed on the recording medium P, and irradiate the test pattern TP with uniform illumination light.

[0058] Sensor unit 26 has a two-dimensional sensor 27 such as a CCD sensor or a CMOS sensor, and imaging lens 28. Sensor unit 26 causes reflected light of illumination light emitted from light source 42 onto test pattern TP to enter two-dimensional sensor 27 through imaging lens 28. Two-dimensional sensor 27 converts the incident light into an analog signal by photoelectric conversion, and outputs the signal as a captured image of test pattern TP.

[0059] <Configuration example of the conveying roller 152 and its surroundings> The configuration for transporting the recording medium P, which is the object to be transported, will now be described. Fig. 12 is a diagram showing an example of the configuration around the transport roller 152. As shown in Fig. 12, the recording medium P is transported intermittently in a sub-scanning direction (direction of arrow B in the figure) perpendicular to the main scanning direction (direction of arrow A in the figure), which is the direction of movement of the carriage 5. At this time, an encoder 35 provided coaxially with the transport roller 152 is read by a sub-scanning encoder sensor 132 provided on a side plate (not shown).

[0060] Based on the information thus read, the transport amount of the recording medium P is controlled by a sensor control unit 124 (see FIG. 13) electrically connected to the sub-scanning encoder sensor 132. In this example, the encoder 35 is configured as a rotary encoder, in which an optical grating is arranged in a disk shape, and is configured to be able to detect the angle, amount of rotation, rotation speed, etc.

[0061] <Example of Hardware Configuration of Image Forming Apparatus 100> Next, the hardware configuration of the image forming apparatus 100 of this embodiment will be described with reference to Fig. 13. Fig. 13 is a diagram showing the hardware configuration of the image forming apparatus of the first embodiment.

[0062] As shown in FIG. 13, the image forming apparatus 100 includes a control unit 130, a head 6, a main scanning encoder sensor 131, an imaging unit 20, a main scanning motor 8, a conveying unit 150, and a sub-scanning motor 12.

[0063] The control unit 130 includes a CPU 110, a ROM 102, a RAM 103, a head driver 104, a main scanning driver 105, a sub-scanning driver 106, and a control FPGA (Field-Programmable Gate Array) 120.

[0064] The control unit 130 is mounted on a main control board. The head 6, main scanning encoder sensor 131, and imaging unit 20 are mounted on the carriage 5. The sub-scanning encoder sensor 132 and conveyance rollers 152 are mounted on the conveyance unit 150.

[0065] The control unit 130 controls the relative movement between the recording medium P and the head 6 along the main scanning direction, the relative movement between the recording medium P and the head 6 by a predetermined transport amount along the sub-scanning direction, and the ejection of each of the colored inks and the base ink by the head 6.

[0066] In particular, in this embodiment, the control unit 130 controls the formation of a first test pattern on the recording medium P using colored ink ejected from the first nozzle, the formation of a second test pattern on the recording medium P using colored ink ejected from the third nozzle, and the formation of a mask image using base ink ejected from the second nozzle so as to overlap above or below the first test pattern and the second test pattern, respectively.

[0067] The CPU 110 is responsible for overall control of the image forming apparatus 100. For example, the CPU 110 uses the RAM 103 as a work area to execute various control programs stored in the ROM 102 and outputs control commands for controlling various operations in the image forming apparatus 100.

[0068] In this embodiment, the image forming apparatus 100 uses the CPU 110 to realize functions such as forming a test pattern TP, functioning as a distance measurement device, and function of adjusting parameters related to the conveyance amount of the recording medium P based on the distance. The test pattern TP formed by the image forming apparatus 100 includes a first test pattern, a second test pattern, and a mask image.

[0069] A head driver 104, a main scanning driver 105, and a sub-scanning driver 106 are drivers for driving the head 6, the main scanning motor 8, and the sub-scanning motor 12, respectively.

[0070] The control FPGA 120 cooperates with the CPU 110 to control various operations in the image forming apparatus 100. The control FPGA 120 has, as functional components, for example, a CPU control unit 121, a memory control unit 122, an ink ejection control unit 123, a sensor control unit 124, and a motor control unit 125.

[0071] The CPU control unit 121 communicates with the CPU 110 to transmit various pieces of information acquired by the control FPGA 120 to the CPU 110 and also receives control commands output from the CPU 110 .

[0072] The memory control unit 122 performs memory control for the CPU 110 to access the ROM 102 and the RAM 103 .

[0073] The ink ejection control unit 123 controls the operation of the head driver 104 in response to a control command from the CPU 110 , thereby controlling the timing of ink ejection from the head 6 driven by the head driver 104 .

[0074] The sensor control unit 124 performs processing on sensor signals such as encoder values ​​output from the main scanning encoder sensor 131 and the sub-scanning encoder sensor 132. For example, the sensor control unit 124 performs processing to calculate the position, movement speed, movement direction, etc. of the carriage 5 based on the encoder value output from the main scanning encoder sensor 131. Furthermore, for example, the sensor control unit 124 performs processing to calculate the rotation speed, rotation direction, etc. of the conveyance roller 152 that conveys the recording medium P based on the encoder value output from the sub-scanning encoder sensor 132.

[0075] The motor control unit 125 controls the operation of the main scanning driver 105 in response to a control command from the CPU 110, thereby controlling the main scanning motor 8 driven by the main scanning driver 105 and controlling the movement of the carriage 5 in the main scanning direction. The motor control unit 125 also controls the operation of the sub scanning driver 106 in response to a control command from the CPU 110, thereby controlling the sub scanning motor 12 driven by the sub scanning driver 106 and controlling the movement (conveyance) of the recording medium P in the sub scanning direction by the conveyance roller 152.

[0076] Note that the above-described units are examples of control functions realized by the control FPGA 120, and various other control functions may be realized by the control FPGA 120. Also, all or part of the above control functions may be realized by a program executed by the CPU 110 or another general-purpose CPU. Also, part of the above control functions may be realized by dedicated hardware such as another FPGA or ASIC (Application Specific Integrated Circuit) different from the control FPGA 120.

[0077] The head 6 has multiple nozzles that eject ink to form an image (see Figure 3), and is driven by a head driver 104 whose operation is controlled by the CPU 110 and the control FPGA 120, and ejects ink onto a recording medium P on the platen 16 to form an image.

[0078] The main scanning encoder sensor 131 detects the marks on the encoder sheet 14 and outputs the obtained encoder value to the control FPGA 120. This encoder value is used by the sensor control unit 124 of the control FPGA 120 to calculate the position, movement speed, and movement direction of the carriage 5. The position, movement speed, and movement direction of the carriage 5 calculated by the sensor control unit 124 from the encoder value are sent to the CPU 110. The CPU 110 generates a control command for controlling the main scanning motor 8 based on the position, movement speed, and movement direction of the carriage 5 and outputs the control command to the motor control unit 125.

[0079] The imaging unit 20, which is controlled by the CPU 110, captures an image of a test pattern TP formed on a recording medium P and performs various processes on the captured image, and includes a two-dimensional sensor CPU 140 and a two-dimensional sensor 27.

[0080] Two-dimensional sensor 27 is a CCD sensor, a CMOS sensor, or the like, and captures an image of test pattern TP and frame line F under predetermined operating conditions based on various setting signals sent from two-dimensional sensor CPU 140. Two-dimensional sensor 27 then sends the captured image to two-dimensional sensor CPU 140.

[0081] Two-dimensional sensor CPU 140 controls two-dimensional sensor 27 and processes images captured by two-dimensional sensor 27. Specifically, two-dimensional sensor CPU 140 sets various operating conditions for two-dimensional sensor 27 by sending various setting signals to imaging unit 20. Two-dimensional sensor CPU 140 also realizes the function of detecting markers of test pattern TP from a captured image of test pattern TP, and the function of calculating the ratio between the distance in the captured image and the actual distance.

[0082] Furthermore, imaging unit 20 is provided with RAM and ROM, and two-dimensional sensor CPU 140 uses, for example, RAM as a work area to execute various control programs stored in ROM and output control commands for controlling various operations in imaging unit 20. Two-dimensional sensor CPU 140 also has a built-in function of AD converting the analog signal obtained by photoelectric conversion of two-dimensional sensor 27 into digital image data, and performing various image processing on the image data such as shading correction, white balance correction, gamma correction, and image data format conversion. Note that the various image processing on the captured image may be configured to be performed in part or in whole outside imaging unit 20.

[0083] The sub-scanning encoder sensor 132 reads the encoder 35 and outputs the obtained encoder value to the control FPGA 120. This encoder value is used in the sensor control unit 124 of the control FPGA 120 to calculate the rotation speed and rotation direction of the conveyance roller 152 that conveys the recording medium P. The rotation speed and rotation direction of the conveyance roller 152 calculated by the sensor control unit 124 from the encoder value are sent to the CPU 110. The CPU 110 generates a control command for controlling the sub-scanning motor 12 based on the rotation speed and rotation direction of the conveyance roller 152 and outputs it to the motor control unit 125.

[0084] The conveyance roller 152 rotates at the rotation speed and in the rotation direction based on the control command received from the motor control unit 125, thereby conveying the recording medium P by a predetermined conveyance amount.

[0085] In the image forming apparatus 100 of the present embodiment, an image forming unit that forms an image on the recording medium P is configured by the head driver 104, the main scanning driver 105, and the sub-scanning driver 106 controlled by the above-described CPU 110 and control FPGA 120, and the head 6, the main scanning motor 8, and the sub-scanning motor 12 driven thereby.

[0086] In FIG. 13, the two-dimensional sensor CPU 140 and the imaging unit 20 were mounted on the carriage 5, but the two-dimensional sensor CPU 140 and the imaging unit 20 only need to be arranged so that they can appropriately image the test pattern TP formed on the recording medium P, and do not necessarily have to be mounted on the carriage 5.

[0087] <Functional configuration example of CPU 110> Referring to FIG. 14, the functions mainly realized by the CPU 110 of the control unit 130 will be described. FIG. 14 is a block diagram showing an example of the functional configuration of the CPU 110.

[0088] The CPU 110 has a pattern forming unit 111, an actual distance calculation unit 114, an adjustment unit 115, and a transport control unit 116. The CPU 110 uses, for example, the RAM 103 as a work area and executes a control program stored in the ROM 102 to realize the functions of the pattern forming unit 111, the actual distance calculation unit 114, the adjustment unit 115, the transport control unit 116, etc.

[0089] In this embodiment, a configuration in which these functions are realized by the CPU 110 is exemplified, but at least some of these functions may be realized by components other than the CPU 110, such as the control FPGA 120 or the imaging unit 20. Alternatively, at least some of the above functions may be realized by distributed processing performed by the CPU 110 and components other than the CPU 110.

[0090] In addition, the two-dimensional sensor CPU 140 of the imaging unit 20 uses, for example, RAM as a working area to execute a control program stored in ROM, thereby realizing functions such as a position detection unit 142 and a ratio calculation unit 143.

[0091] The transport control unit 116 controls the transport rollers 152 of the transport unit 150 that transport the recording medium P. For example, the transport control unit 116 determines the rotation speed and rotation direction of the transport rollers 152 based on the encoder value output from the sub-scanning encoder sensor 132, and controls the transport of the recording medium P by the transport rollers 152 by sending control commands indicating the rotation speed and rotation direction to the transport rollers 152 of the transport unit 150 via the control FPGA 120.

[0092] The pattern forming unit 111 reads pattern data stored in advance in, for example, the ROM 102, and causes the image forming unit to perform an image forming operation according to the pattern data, thereby forming a test pattern TP on the recording medium P. The imaging unit 20 images the test pattern TP formed on the recording medium P by the pattern forming unit 111.

[0093] The pattern forming unit 111 uses the image forming unit to form a first marker M1 and one of a pair of second markers M2a and M2b on the recording medium P, and after the recording medium P is transported by a predetermined transport distance, forms a mask image M3 made of white ink on top of the previously formed image. Note that the first marker M1, the pair of second markers M2a and M2b, and the mask image M3 are components included in the test pattern TP.

[0094] After forming a mask image M3 using white ink, the pattern forming unit 111 again transports the recording medium P by a predetermined transport amount, and then forms the first marker M1 and the other of the pair of second markers M2a and M2b that were not formed before the transport.

[0095] In this embodiment, an example will be given in which the pattern forming unit 111 forms a first marker M1 on the recording medium P, and after the recording medium P is transported by a predetermined transport amount, forms a mask image M3 on top of the first marker M1 using white ink, and after the recording medium P is transported again by a predetermined transport amount, forms a pair of second markers M2a and M2b.

[0096] The order in which the first marker M1 and the pair of second markers M2a and M2b are formed can be any order, and the pattern forming unit 111 may form the pair of second markers M2a and M2b on the recording medium P, form a mask image M3 using white ink, and then form the first marker M1 after the recording medium P has been transported by a predetermined transport distance.

[0097] <Example of test pattern TP> The test pattern TP will be described with reference to Fig. 15. Fig. 15 is a diagram showing an example of the test pattern TP formed on the recording medium P.

[0098] As shown in FIG. 15, the test pattern TP includes a set of markers MM including at least a first marker M1 and a pair of second markers M2a and M2b, and a mask image M3 formed with white ink.

[0099] 15 has a first marker M1 midway between a pair of second markers M2a and M2b. The first marker M1 and the pair of second markers M2a and M2b are formed by dots and are formed along the sub-scanning direction (the direction of arrow B in the figure).

[0100] The mask image M3 made of white ink is formed on top of the first marker M1 after it has been formed. In other words, the mask image M3 is formed so as to overlap the first marker M1. A pair of second markers M2a and M2b are formed on top of the mask image M3 made of white ink.

[0101] <Test pattern TP formation method> A method for forming the test pattern TP will be described with reference to Fig. 16. Fig. 16 is a diagram showing an example of the method for forming the test pattern TP. Fig. 16(a) is a diagram showing the first marker M1, Fig. 16(b) is a diagram showing the actual transport amount L1, and Fig. 16(c) is a diagram showing the second markers M2a and M2b formed on the mask image M3.

[0102] As shown in Figures 16(a), 16(b), and 16(c), the head 6 includes a first nozzle 601, a second nozzle 602, and a third nozzle 603. The first nozzle 601 ejects colored ink. The second nozzle 602 ejects base ink. The third nozzle 603 is disposed at a different position from the first nozzle 601 in the sub-scanning direction, and ejects colored ink. The head 6 has, in order from upstream in the sub-scanning direction, the first nozzle 601, the second nozzle 602, and the third nozzle 603.

[0103] The first marker M1 is an example of a first test pattern formed on the recording medium P by colored ink ejected from the first nozzle 601. The second markers M2a and M2b are an example of a second test pattern formed on the recording medium P by colored ink ejected from the third nozzle 603. The mask image M3 is an example of a mask image formed by base ink ejected from the second nozzle 602 so as to overlap above or below the first marker M1 and the second markers M2a and M2b, respectively.

[0104] 16(a), the pattern forming unit 111 forms a first marker M1 on the recording medium P. Next, as shown in FIG. 16(b), the conveyance control unit 116 causes the conveyance roller 152 to convey the recording medium P in the sub-scanning direction (the direction of arrow B in the figure) by an actual conveyance amount L1.

[0105] The pattern forming unit 111 then forms a mask image M3 formed with white ink so as to overlay the first marker M1, in other words, so that the mask image M3 is superimposed on the first marker M1. Then, as shown in Fig. 16(c), after transport by the actual transport amount L2, the pattern forming unit 111 forms second markers M2a and M2b on top of the mask image M3 formed with white ink.

[0106] This pair of second markers M2a and M2b are formed by two third nozzles 603 (designated nozzles) that are spaced a distance e on both the front and rear sides in the sub-scanning direction, with the nozzle spaced an ideal carry amount L3 from the first nozzle 601 that ejected colored ink to form the first marker M1 as a reference. The ideal carry amount L3 is an example of a predetermined carry amount.

[0107] In the following, this reference nozzle will be referred to as the reference nozzle, and the two nozzles located a distance e in front and behind the reference nozzle in the sub-scanning direction will be referred to as the designated nozzles. The number of third nozzles 603 is not limited to two, and may be one nozzle.

[0108] If the actual transport amount L1+L2 and the ideal transport amount L3 are the same, a test pattern TP is formed in which the first marker M1 is formed at an ideal position that is the midpoint in the sub-scanning direction between the pair of second markers M2a and M2b. On the other hand, if the actual transport amount L1+L2 and the ideal transport amount L3 are different, a test pattern TP is formed in which the first marker M1 is formed at a position close to either of the pair of second markers M2a and M2b, for example.

[0109] Then, by photographing this test pattern TP and calculating the relative positional relationship between the first marker M1 and the pair of second markers M2a and M2b, it is possible to detect the deviation between the ideal conveyance amount L3 and the actual conveyance amount L1+L2. Note that, in this embodiment, an example is described in which the ideal position of the first marker M1 is the intermediate position between the pair of second markers M2a and M2b, but it does not have to be the intermediate position between the pair of second markers M2a and M2b. In other words, as long as the first marker M1 can be photographed together with the pair of second markers M2a and M2b and is formed at a predetermined position, the ideal position of the first marker M1 may be a position close to either one of the pair of second markers M2a and M2b, and does not have to be between the pair of second markers M2a and M2b.

[0110] The mask image M3 constituting the test pattern TP is formed by the base ink ejected from the second nozzle 602. If the recording medium P is transparent, the presence of through-holes formed in the thickness direction of the platen 16 or ink stains deposited during the image formation operation at positions overlapping the test pattern TP when photographing the test pattern TP may interfere with calculation of the relative positional relationship between the first marker M1 and the second markers M2a and M2b. The mask image M3 has the function of hiding the through-holes and stains, preventing them from interfering with the calculation.

[0111] <Example of correction process for transport amount based on transport amount deviation calculation result> The position detection unit 142 (see Figure 14) of the CPU 140 for the two-dimensional sensor detects the first marker M1 and a pair of second markers M2a and M2b from the captured image by performing predetermined processing such as binarization processing on the captured image captured by the imaging unit 20.

[0112] The ratio calculation unit 143 of the CPU 140 for the two-dimensional sensor calculates the ratio between the distance between the pair of second markers M2a and M2b in the captured image and the amount of positional deviation of the first marker M1 in the captured image based on the positions of the first marker M1 and the pair of second markers M2a and M2b in the captured image.

[0113] A method for calculating the ratio will be specifically described with reference to Fig. 17. Fig. 17 is a diagram illustrating a method for calculating the ratio between the distance between a pair of second markers M2a and M2b in a captured image and the amount of positional deviation of the first marker M1.

[0114] 17, the ratio calculation unit 143 calculates the distance h between the pair of second markers M1a and M1b in the captured image from the positions of the detected pair of second markers M2a and M2b, and then calculates the positional deviation amount s of the first marker M1 in the captured image from the difference between the detected first marker M1 and the ideal position of the first marker M1.

[0115] In this embodiment, the ideal position of the first marker M1 is a position corresponding to the midpoint between the pair of second markers M2a and M2b, i.e., a position that is half the distance between the pair of second markers M2a and M2b from the respective positions of the second markers M2a and M2b. In Fig. 17, this is a position that is an equal distance h / 2 from the respective positions of the second markers M2a and M2b (the position at a distance a1 in Fig. 17).

[0116] Therefore, the positional deviation amount s of the first marker M1 in the captured image is the difference between the distance a1 between the ideal positions of the second marker M2a and the first marker M1 and the distance a between the second marker M2a and the first marker M1. Then, the positional deviation amount s of the first marker M1 in the captured image is divided by the distance h between the pair of second markers M2a and M2b in the captured image to calculate a ratio (s / h). The ratio calculated by the ratio calculation unit 143 is passed to the actual distance calculation unit 114.

[0117] The actual distance calculation unit 114 (see FIG. 14) of the CPU 110 calculates the actual distance of the positional shift amount of the first marker M1 based on the actual distance between the pair of second markers M2a and M2b and the ratio calculated by the ratio calculation unit 143. That is, the actual distance calculation unit 114 multiplies the actual distance between the pair of second markers M2a and M2b by the ratio calculated by the ratio calculation unit 143 (the ratio s / h in FIG. 17) to calculate the actual distance of the positional shift amount s of the first marker M1 relative to the pair of second markers M2a and M2b. The actual distance calculated by the actual distance calculation unit 114 is passed to the adjustment unit 115.

[0118] The adjustment unit 115 of the CPU 110 calculates a correction amount for a parameter related to the transport amount of the recording medium P by the transport control unit 116 for each scanning direction of the carriage 5 based on the positional deviation amount s of the first marker M1 calculated by the actual distance calculation unit 114, and performs adjustment using the calculated correction amount. The parameter related to the transport amount of the recording medium P is, for example, a parameter for controlling the rotation speed of the transport roller 152. The adjustment unit 115 transmits the adjustment values ​​of these parameters to the control FPGA 120, thereby adjusting the control operation of the transport roller 152 by the transport control unit 116, etc. This makes it possible to improve the accuracy of the ink landing position even when the inclination of the head 6A differs between the forward and backward passes.

[0119] <Example of Operation of Image Forming Apparatus 100> The operation of image forming apparatus 100 will be described with reference to Fig. 18 to Fig. 22. Fig. 18 to Fig. 21 are diagrams illustrating the operation of the image forming apparatus, with Fig. 18 being Fig. 1, Fig. 19 being Fig. 2, Fig. 20 being Fig. 3, and Fig. 21 being Fig. 4. Fig. 22 is a diagram explaining the effect of mask image M3.

[0120] When the user of the image forming apparatus 100 sets the type of recording medium P using the image forming apparatus 100 main body and selects a specific type, the CPU 110 causes the pattern forming unit 111 to output the test pattern TP in accordance with the procedure for forming the test pattern TP described in Fig. 16. Note that the switching to output the test pattern TP may be performed by the user using the operation unit to select whether the recording medium P is transparent or not and instructing the image forming apparatus 100 to do so.

[0121] As shown in Figure 18, the image forming apparatus 100 forms first markers M1, M1', M1'', and M1''' using a nozzle array 6AK arranged in a head 6A located upstream of the recording medium P in the sub-scanning direction. Note that the first marker M1 is a collective term for the first markers M1, M1', M1'', and M1'''.

[0122] Next, the image forming apparatus 100 intermittently conveys the first markers M1, M1', M1'', and M1''' formed on the recording medium P by dividing the actual conveyance amount L1 into N1 times, and conveys them to the position of the head 6B.

[0123] Next, as shown in FIG. 19, the image forming apparatus 100 transports the first marker M1 to the position of the head 6B, and then uses the nozzle rows 6Bw1, 6Bw2, 6Bw3, and 6Bw4 arranged in the head 6B to form a mask image M3 using white ink so that it overlaps the first markers M1, M1', M1'', and M1'''.

[0124] Next, the image forming apparatus 100 forms a mask image M3 in white ink so that it overlaps the first markers M1, M1', M1'', and M1''', and then transports the actual transport amount L2 intermittently in N2 steps to the position of the head 6C.

[0125] Next, the image forming apparatus 100 transports the first markers M1, M1', M1'', and M1''', which are formed so as to overlap the mask image M3, to the position of the head 6C, and then forms pairs of second markers M2a, M2a', M2a'', M2a''', M2b, M2b', M2b'', and M2b''', and a frame F on the mask image M3. Note that the second markers M2a and M2b are a collective term for M2a', M2a'', M2a''', M2b, M2b', M2b'', and M2b''',.

[0126] As shown in FIG. 20, the nozzles used to form pairs of second markers M2a, M2a', M2a'', M2a''', M2b, M2b', M2b'', and M2b''' are nozzles whose positional relationship with respect to the first markers M1, M1', M1'', and M1''' is equal to the distance e when the first markers M1, M1', M1'', and M1''' are transported by the ideal transport amount L3.

[0127] Next, the image forming apparatus 100 uses the head 6C to form a pair of second markers M2a, M2a', M2a'', M2a''', M2b, M2b', M2b'' and M2b''', and a frame line F, completing the test pattern TP, and then transports the test pattern TP a distance L4 and moves it to an area that can be imaged by the imaging unit 20.

[0128] Next, as shown in FIG. 21, the image forming apparatus 100 moves to the imaging area of ​​the imaging unit 20, then images the test pattern TP using the imaging unit 20, and calculates the relative positional relationship between the first markers M1, M1', M1'', and M1'''' and the pair of second markers M2a, M2a', M2a'', M2a'''', M2b, M2b', M2b'''', and M2b''''.

[0129] 22(a), when the image forming apparatus 100 captures an image of the test pattern TP using the imaging unit 20, the positions of the through-holes H formed in the platen 16 may overlap with the test pattern TP. If the through-holes H overlap with the first markers M1, M1', M1'', and M1''', or with the pairs of second markers M2a, M2a', M2a'', M2a''', M2b, M2b', M2b'', and M2b''', it may not be possible to correctly calculate the relative positional relationship.

[0130] 22(b), in this embodiment, first markers M1, M1', M1" and M1'", or pairs of second markers M2a, M2a', M2a", M2a'", M2b, M2b', M2b" and M2b'", are formed above or below mask image M3. As a result, even when first markers M1, M1', M1" and M1"', or pairs of second markers M2a, M2a', M2a", M2a'", M2b, M2b', M2b" and M2b'", overlap with through-hole H, image forming apparatus 100 can correctly calculate the relative positional relationship because through-hole H is hidden by mask image M3.

[0131] In this embodiment, black ink is used to form the first markers M1, M1', M1'', and M1''', and the pairs of second markers M2a, M2a', M2a'', M2a''', M2b, M2b', M2b'', and M2b''', of the test pattern TP, but ink of another color may be used. Also, different colors may be used for the first markers M1, M1', M1'', and M1''' and the pairs of second markers M2a, M2a', M2a'', M2a''', M2b, M2b', M2b'', and M2b''',.

[0132] In addition, in this embodiment, white ink is used as the mask image M3 of the test pattern TP, but ink other than white may be used as long as it has a contrast difference between the first markers M1, M1', M1'', and M1'''' and the pair of second markers M2a, M2a', M2a'', M2a'''', M2b, M2b', M2b'' and M2b''''.

[0133] <Operational Effects of Image Forming Apparatus 100> 2. Description of the Related Art Conventionally, there has been known a technique for detecting deviation in the amount of conveyance of a recording medium by an image forming apparatus based on a test pattern formed on the recording medium.

[0134] Furthermore, as an example of the above technology, Patent Document 1 discloses a configuration in which an actual distance of misalignment is calculated according to the amount of misalignment in an image captured by an imaging unit, and the transport distance of an object is corrected for each direction of carriage movement. This image forming device forms a pair of first markers with a head, captures an image of a test pattern in which a second marker is formed with a head tilted differently from when the pair of first markers were formed, calculates the ratio between the distance between the first markers and the amount of misalignment of the second markers from the captured image, calculates the actual distance of misalignment of the second marker based on that ratio, and adjusts parameters related to the transport distance.

[0135] However, with the technology of Patent Document 1, when the recording medium is transparent, it is affected by the condition of the transport surface on the back of the recording medium, and therefore, it may not be possible to detect the test pattern formed on the recording medium, and the deviation in the transport amount may not be detected correctly.

[0136] In this embodiment, the image forming apparatus 100 has a head 6 including a first nozzle 601 that ejects colored ink, a second nozzle 602 that ejects base ink, and a third nozzle 603 that ejects colored ink and is positioned differently from the first nozzle 601 in the sub-scanning direction (the transport direction of the recording medium P). The image forming apparatus 100 also has a control unit 130 that controls the relative movement between the recording medium P and the head 6 in the main scanning direction, the relative movement between the recording medium P and the head 6 by an actual transport amount L1 (predetermined transport amount) in the transport direction, and the ejection of each of the colored ink and base ink by the head 6. The image forming apparatus 100 also has an imaging unit 20 (reading unit) that reads the test pattern TP formed on the recording medium P with the colored inks ejected from the head 6.

[0137] The control unit 130 performs control so that a first marker M1 (first test pattern) is formed on the recording medium P using colored ink ejected from the first nozzle 601, second markers M2a and M2b (second test pattern) are formed on the recording medium P using colored ink ejected from the third nozzle 603, and a mask image M3 is formed so as to overlap above or below the first marker M1 and the second markers M2a and M2b using base ink ejected from the second nozzle 602. The imaging unit 20 reads the positions of the first marker M1 and the second markers M2a and M2b.

[0138] With the above configuration, the image forming apparatus 100 can read the first marker M1 and the second markers M2a and M2b, which are arranged at different positions in the relative transport direction of the head 6 and the recording medium P, with the mask image M3 as the background, using the imaging unit 20. As a result, in this embodiment, the first marker M1 and the second markers M2a and M2b can be correctly detected without being affected by the state of the transport surface behind the recording medium P, and an image forming apparatus 100 can be provided that can detect deviations in the relative transport amount between the recording medium P and the head 6 in the sub-scanning direction.

[0139] In this embodiment, in order to determine the deviation in the transport amount in the sub-scanning direction, it is sufficient that at least the first nozzle 601 and the third nozzle 603 are positioned at different positions in the sub-scanning direction, and the positional relationship with the second nozzle 602 is not particularly important.

[0140] In this embodiment, a configuration in which the carriage 5 moves in the main scanning direction and the recording medium P moves in the sub-scanning direction has been exemplified, but the present invention is not limited to this. As long as the recording medium P and the carriage 5 can move relative to each other, a configuration in which the recording medium P or the carriage 5 moves in both the main scanning direction and the sub-scanning direction, or a configuration in which the recording medium P moves in the main scanning direction and the carriage 5 moves in the sub-scanning direction, may also be used.

[0141] In this embodiment, the head 6 has, in order from upstream in the sub-scanning direction, a first nozzle 601, a second nozzle 602, and a third nozzle 603. In other words, in this embodiment, the first nozzle 601 and the third nozzle 603 used to detect the test pattern TP are arranged apart in the sub-scanning direction, sandwiching the second nozzle 602 that forms the mask image. This makes it possible to increase the transport distance by which the recording medium P is relatively moved from when the first marker M1 is formed on the recording medium P until the second markers M2a and M2b are formed on the recording medium P. Since the image forming apparatus 100 can ensure a longer transport distance, it can increase the deviation in the transport distance and more accurately detect the deviation in the transport distance.

[0142] In this embodiment, the control unit 130 controls the head 6 and the recording medium P to relatively move by the actual transport amount L1 in the sub-scanning direction after forming a portion of the first marker M1 using colored ink ejected from the first nozzle 601, form a mask image M3 using base ink ejected from the second nozzle 602 so that it overlaps the first marker M1, and then further relatively move the head 6 and the recording medium P by the actual transport amount L1 in the sub-scanning direction to form second markers M2a and M2b on the mask image M3 using colored ink ejected from the third nozzle 603. This allows the image forming apparatus 100 to form and read the test pattern TP without rewinding the recording medium P, i.e., without relatively moving the recording medium P in the direction opposite to the sub-scanning direction. As a result, the image forming apparatus 100 can accurately read the test pattern TP using the imaging unit 20 without being affected by skew of the recording medium P that occurs during the rewinding operation or changes in the relative transport amount due to slippage at the transport roller 152.

[0143] The control unit 130 may also perform control such that a portion of the first marker M1 is formed using colored ink ejected from the first nozzle 601, and a mask image M3 is formed using base ink ejected from the second nozzle 602 so as to overlap the first marker M1 with a density that prevents the portion of the first marker M1 from disappearing. The image forming apparatus 100 can form the mask image M3 with a density that prevents the portion of the first marker M1 formed on the recording medium P with colored ink ejected from the first nozzle 601 from disappearing, and thus the test pattern TP can be correctly read by the imaging unit 20 while maintaining the background effect of the mask image M3.

[0144] Alternatively, the head 6 may include multiple heads, and the control unit 130 may perform control to detect a deviation in the relative transport control amount between the recording medium P and the head 6 in the sub-scanning direction without rewinding the recording medium P. Since the image forming apparatus 100 can form and read the test pattern TP without rewinding the recording medium P, the image capturing unit 20 can accurately read the test pattern TP without being affected by skew of the recording medium P that occurs during the rewinding operation or changes in the deviation in the relative transport amount due to slippage at the transport roller 152.

[0145] In this embodiment, the undercoat ink is white ink, which makes it easier to increase the contrast between the test pattern TP and the mask image.

[0146] The base ink may be an ink of a color other than white that provides a predetermined contrast between the first marker M1 and the mask image M3. In this case, it is also easy to increase the contrast between the test pattern TP and the mask image.

[0147] <Modification> The embodiment can be modified in various ways, and modifications will be described below. (Head 6 placement) Modified examples of the arrangement of the head 6 will be described with reference to Figures 23 to 25. Figures 23 to 25 are diagrams showing modified examples of the arrangement of the head 6, with Figure 23 showing a first modified example, Figure 24 showing a second modified example, and Figure 25 showing a third modified example.

[0148] 23 to 25, head 6A has first nozzles 601 that eject colored ink, head 6B has second nozzles 602 that eject base ink, and head 6C has third nozzles 603 that eject colored ink.

[0149] 23, head 6A ejects colored ink to form a first marker M1 on the recording medium P, and head 6C ejects colored ink to form second markers M2a and M2b on the recording medium P. Thereafter, head 6B ejects base ink to form a mask image M3 so as to overlap both the first marker M1 and the second markers M2a and M2b.

[0150] 24, head 6A ejects colored ink to form a first marker M1 on the recording medium P, and head 6C ejects colored ink to form second markers M2a and M2b on the recording medium P. Then, head 6B ejects base ink to form a mask image M3 so that it overlaps both the first marker M1 and the second markers M2a and M2b. Heads 6C and 6B form the second markers M2a and M2b and the mask image M3 on the recording medium P by moving the carriage 5 in the same direction in the main scanning direction.

[0151] In the third modified example shown in FIG. 25, head 6A ejects colored ink to form a first marker M1 on the recording medium P, and then head 6B ejects base ink to form a mask image M3 so that it overlaps the first marker M1. Heads 6A and 6B form the first marker M1 and mask image M3 on the recording medium P by moving carriage 5 in the main scanning direction at the same time. Thereafter, head 6C ejects colored ink to form second markers M2a and M2b on the recording medium P. The mask image M3 is formed below the second markers M2a and M2b.

[0152] Alternatively, for example, in the third modified example, the length of head 6B in the sub-scanning direction may be set to a length that overlaps with heads 6A and 6C.

[0153] In the embodiment, a configuration has been exemplified in which colored ink and base ink are ejected when the carriage 5 moves in only one direction along the main scanning direction, but a configuration in which colored ink and base ink are ejected during each of the reciprocating movements may also be used.

[0154] In the second and third variants, when colored ink and base ink are ejected during each of the reciprocating movements, the order in which the second markers M2a and M2b and the mask image M3 are formed is reversed between the forward movement and the return movement, but the second markers M2a and M2b can be read by the imaging unit 20 in either order.

[0155] (Modification of Image Forming Apparatus) FIG. 26 is a perspective view illustrating an example of the overall configuration of an image forming apparatus 100a according to a modified example.

[0156] The image forming apparatus 100a includes a carriage 200 and a stage 13 on which a recording medium P is placed. The carriage 200 is equipped with a plurality of heads each having a plurality of nozzles, and forms an image by ejecting color inks and base ink from the nozzles of the heads. The nozzles are provided on the surface facing the stage 13.

[0157] An irradiation unit 400, which is a light source that irradiates ultraviolet light, is provided on the surface of the carriage 200 facing the stage 13. The irradiation unit 400 irradiates light with a wavelength that hardens the liquid ejected from the nozzles.

[0158] A guide rod 19 is hung between the left and right side plates 18a and 18b, and the guide rod 19 holds a carriage 200 so that the carriage 200 is movable in the X direction (main scanning direction).

[0159] The carriage 200, guide rod 19, and side plates 18a and 18b are integrally movable in the Y direction (sub-scanning direction) along guide rails 29 provided at the bottom of the stage 13. Furthermore, the carriage 200 is held so as to be movable in the Z direction (up and down direction).

[0160] In the configuration of Figure 26, the image forming apparatus 100a forms an image by alternately performing a main scanning operation in which ink is ejected from the nozzles onto the recording medium P while moving the head in the main scanning direction, and a sub-scanning operation in which the head is moved in the sub-scanning direction.

[0161] Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes are possible within the scope of the gist of the embodiments of the present invention described in the claims.

[0162] The embodiments also include an image forming method. For example, the image forming method is an image forming method using an image forming apparatus, in which the image forming apparatus ejects the colored inks and the undercoat ink using a head having a first nozzle that ejects colored inks, a second nozzle that ejects undercoat inks, and a third nozzle that is disposed at a position different from the first nozzle in a transport direction of the recording medium and ejects the colored inks, and a control unit controls relative movement between the recording medium and the head in a main scanning direction that intersects the transport direction, relative movement between the recording medium and the head by a predetermined transport amount along the transport direction, and ejection of the colored inks and the undercoat ink by the head. and controls a reading unit to read a test pattern formed on the recording medium using colored ink ejected from the head, the control unit controls to form a first test pattern on the recording medium using colored ink ejected from the first nozzle, form a second test pattern on the recording medium using colored ink ejected from the third nozzle, and form mask images using base ink ejected from the second nozzle so as to overlap above or below the first test pattern and the second test pattern, respectively, and the reading unit reads the positions of the first test pattern and the second test pattern. This image forming method can achieve the same effects as the image forming apparatus described above. Note that this image forming method may be implemented using a CPU, a circuit such as an LSI, an IC card, a standalone module, or the like.

[0163] The embodiments also include a program. For example, the program may include a head having a first nozzle that ejects colored ink, a second nozzle that ejects undercoat ink, and a third nozzle that ejects colored ink and is disposed at a position different from the first nozzle in a transport direction of the recording medium, and a control unit that controls relative movement between the recording medium and the head along a main scanning direction that intersects with the transport direction, relative movement between the recording medium and the head along the transport direction by a predetermined transport distance, and the ejection of each of the colored ink and the undercoat ink by the head, and a reading unit that reads the ink ejected from the head. The program reads a test pattern formed on the recording medium with colored ink, the control unit controls the image forming apparatus to form a first test pattern on the recording medium with colored ink ejected from the first nozzles, form a second test pattern on the recording medium with colored ink ejected from the third nozzles, and form mask images with base ink ejected from the second nozzles so as to overlap above or below the first test pattern and the second test pattern, respectively, and the reading unit reads the positions of the first test pattern and the second test pattern. Such a program causes the image forming apparatus to execute processing to obtain the same effects as the image forming apparatus described above.

[0164] Furthermore, all ordinal numbers, quantitative numbers, and other figures used in the description of the embodiments are merely examples for specifically explaining the technology of the present invention, and the present invention is not limited to the exemplified figures. Furthermore, the connection relationships between the components are merely examples for specifically explaining the technology of the present invention, and the connection relationships for realizing the functions of the present invention are not limited to these.

[0165] The division of blocks in the functional block diagram is merely an example, and multiple blocks may be realized as a single block, one block may be divided into multiple blocks, or some functions may be moved to another block.Furthermore, the functions of multiple blocks having similar functions may be processed in parallel or in time-sharing by a single piece of hardware or software.

[0166] Furthermore, each function of the above-described embodiments can be realized by one or more processing circuits. Here, the term "processing circuit" in this specification includes a processor programmed to perform each function by software, such as a processor implemented by an electronic circuit, as well as devices such as an ASIC (Application Specific Integrated Circuit), a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), and conventional circuit modules designed to perform each of the above-described functions. [Explanation of symbols]

[0167] 5,200 carriages 6, 6A, 6B, 6C head 601 No. 1 nozzle 602 Second Nozzle 603 3rd nozzle 20 Imaging unit (example of reading unit) 26 Sensor section 27 Two-dimensional sensor 28 Imaging lens 100, 100a Image forming apparatus 110 CPU 111 Pattern forming section 114 Actual distance calculation unit 115 Adjustment section 116 Transport control unit 130 control section 140 CPU for two-dimensional sensor 142, 212 Position detection unit 143, 213 Ratio calculation section H through hole 150 Conveyor L1, L2 Actual transport amount L3 Ideal transport amount (example of specified transport amount) M1 First marker M2a, M2b Second marker M3 mask image MM Set P Recording medium TP Test Pattern [Prior art documents] [Patent documents]

[0168] [Patent Document 1] Patent No. 6911335

Claims

1. a head including a first nozzle that ejects colored ink, a second nozzle that ejects base ink, and a third nozzle that ejects colored ink and is disposed at a position different from the first nozzle in the transport direction of the recording medium; a control unit that controls relative movement between the recording medium and the head along a main scanning direction that intersects with the transport direction, relative movement between the recording medium and the head by a predetermined transport amount along the transport direction, and ejection of each of the color inks and the undercoat ink by the head; a reading unit that reads a test pattern formed on the recording medium by colored ink ejected from the head, the head includes, in order from upstream in the transport direction, the first nozzle, the second nozzle, and the third nozzle; The control unit controlling the ink jetting method so that a first test pattern is formed on the recording medium by the colored ink ejected from the first nozzles, a second test pattern is formed on the recording medium by the colored ink ejected from the third nozzles, and mask images are formed by the base ink ejected from the second nozzles so as to overlap above or below the first test pattern and the second test pattern, respectively; after forming a part of the first test pattern with the colored ink ejected from the first nozzles, the head and the recording medium are moved relatively in the transport direction by the predetermined transport amount, the mask image is formed so as to be superimposed on the first test pattern with the base ink ejected from the second nozzles, and thereafter the head and the recording medium are further moved relatively in the transport direction by the predetermined transport amount, and the second test pattern is formed on the mask image with the colored ink ejected from the third nozzles; The reading unit reads the positions of the first test pattern and the second test pattern.

2. a head including a first nozzle that ejects colored ink, a second nozzle that ejects base ink, and a third nozzle that ejects colored ink and is disposed at a position different from the first nozzle in the transport direction of the recording medium; a control unit that controls relative movement between the recording medium and the head along a main scanning direction that intersects with the transport direction, relative movement between the recording medium and the head by a predetermined transport amount along the transport direction, and ejection of each of the color inks and the undercoat ink by the head; a reading unit that reads a test pattern formed on the recording medium by colored ink ejected from the head, the head includes, in order from upstream in the transport direction, the first nozzle, the second nozzle, and the third nozzle; The control unit controlling the ink jetting method so that a first test pattern is formed on the recording medium by the colored ink ejected from the first nozzles, a second test pattern is formed on the recording medium by the colored ink ejected from the third nozzles, and mask images are formed by the base ink ejected from the second nozzles so as to overlap above or below the first test pattern and the second test pattern, respectively; controlling the mask image to be formed by the colored ink ejected from the first nozzles so as to form a part of the first test pattern, and the mask image to be formed by the base ink ejected from the second nozzles so as to overlap the first test pattern with a density that does not erase a part of the first test pattern; The reading unit reads the positions of the first test pattern and the second test pattern.

3. a head including a first nozzle that ejects colored ink, a second nozzle that ejects base ink, and a third nozzle that ejects colored ink and is disposed at a position different from the first nozzle in the transport direction of the recording medium; a control unit that controls relative movement between the recording medium and the head along a main scanning direction that intersects with the transport direction, relative movement between the recording medium and the head by a predetermined transport amount along the transport direction, and ejection of each of the color inks and the undercoat ink by the head; a reading unit that reads a test pattern formed on the recording medium by colored ink ejected from the head, The head includes a plurality of heads, The control unit controlling the ink jetting method so that a first test pattern is formed on the recording medium by the colored ink ejected from the first nozzles, a second test pattern is formed on the recording medium by the colored ink ejected from the third nozzles, and mask images are formed by the base ink ejected from the second nozzles so as to overlap above or below the first test pattern and the second test pattern, respectively; a control unit that detects a deviation in the relative transport amount between the recording medium and the head in the transport direction without performing an operation of relatively moving the recording medium in a direction opposite to the transport direction; The reading unit reads the positions of the first test pattern and the second test pattern.

4. The image forming apparatus according to claim 3 , wherein the head includes, in order from upstream in the transport direction, the first nozzle, the second nozzle, and the third nozzle.

5. 5. The image forming apparatus of claim 2, wherein the control unit controls the head and the recording medium to move relative to each other in the transport direction by the predetermined transport amount, form the mask image using base ink ejected from the second nozzle so as to overlap the first test pattern, and then further move the head and the recording medium relative to each other in the transport direction by the predetermined transport amount, and form the second test pattern on top of the mask image using colored ink ejected from the third nozzle.

6. 6. An image forming apparatus according to claim 3, wherein the control unit controls the mask image to be formed so that a portion of the first test pattern is formed using colored ink ejected from the first nozzle, and the mask image is formed so that the mask image is superimposed on the first test pattern using base ink ejected from the second nozzle at a density that does not erase a portion of the first test pattern.

7. The head includes a plurality of heads, 7. The image forming apparatus according to claim 4, wherein the control unit controls the head to detect a deviation in the relative transport amount between the recording medium and the head in the transport direction without performing an operation to move the recording medium relatively in a direction opposite to the transport direction.

8. 8. The image forming apparatus according to claim 1, wherein the undercoat ink is a white ink.

9. 8. The image forming apparatus according to claim 1, wherein the undercoat ink is an ink of a color other than white that has a predetermined contrast between the first test pattern and the mask image.

10. An image forming method using an image forming apparatus, the image forming apparatus comprising: ejecting the color ink and the undercoat ink using a head having a first nozzle that ejects the color ink, a second nozzle that ejects the undercoat ink, and a third nozzle that ejects the color ink and is disposed at a position different from the first nozzle in the conveyance direction of the recording medium; a control unit controls relative movement between the recording medium and the head along a main scanning direction intersecting the transport direction, relative movement between the recording medium and the head by a predetermined transport amount along the transport direction, and ejection of each of the color inks and the undercoat ink by the head; a reading unit reading a test pattern formed on the recording medium by the colored ink ejected from the head; the head includes, in order from upstream in the transport direction, the first nozzle, the second nozzle, and the third nozzle; The control unit controlling the ink jetting method so that a first test pattern is formed on the recording medium by the colored ink ejected from the first nozzles, a second test pattern is formed on the recording medium by the colored ink ejected from the third nozzles, and mask images are formed by the base ink ejected from the second nozzles so as to overlap above or below the first test pattern and the second test pattern, respectively; after forming a part of the first test pattern with the colored ink ejected from the first nozzles, the head and the recording medium are moved relatively in the transport direction by the predetermined transport amount, the mask image is formed so as to be superimposed on the first test pattern with the base ink ejected from the second nozzles, and thereafter the head and the recording medium are further moved relatively in the transport direction by the predetermined transport amount, and the second test pattern is formed on the mask image with the colored ink ejected from the third nozzles; The image forming method, wherein the reading unit reads the positions of the first test pattern and the second test pattern.

11. ejecting the color ink and the undercoat ink using a head having a first nozzle that ejects the color ink, a second nozzle that ejects the undercoat ink, and a third nozzle that ejects the color ink and is disposed at a position different from the first nozzle in the conveyance direction of the recording medium; a control unit controls relative movement between the recording medium and the head along a main scanning direction intersecting the transport direction, relative movement between the recording medium and the head by a predetermined transport amount along the transport direction, and ejection of each of the color inks and the undercoat ink by the head; a reading unit reading a test pattern formed on the recording medium by the colored ink ejected from the head; the head includes, in order from upstream in the transport direction, the first nozzle, the second nozzle, and the third nozzle; The control unit controlling the ink jetting method so that a first test pattern is formed on the recording medium by the colored ink ejected from the first nozzles, a second test pattern is formed on the recording medium by the colored ink ejected from the third nozzles, and mask images are formed by the base ink ejected from the second nozzles so as to overlap above or below the first test pattern and the second test pattern, respectively; after forming a part of the first test pattern with the colored ink ejected from the first nozzles, the head and the recording medium are moved relatively in the transport direction by the predetermined transport amount, the mask image is formed so as to be superimposed on the first test pattern with the base ink ejected from the second nozzles, and thereafter the head and the recording medium are further moved relatively in the transport direction by the predetermined transport amount, and the second test pattern is formed on the mask image with the colored ink ejected from the third nozzles; The reading unit reads the positions of the first test pattern and the second test pattern.

Images