Printing device, printing method, and detection method

Abstract

The present invention more appropriately irradiates a medium with ultraviolet rays.　A printing device 10 uses an ultraviolet curable ink to perform printing on a three-dimensional medium 50 held by a holding jig 40 which is a holding member. The printing device 10 includes an inkjet head 102, a sub-scanning drive part 18, and a control part 30. The holding jig 40 includes a rotation mechanism, an ultraviolet irradiator, and a cover. The control part 30 causes the inkjet head 102 to perform a main scanning operation by causing the inkjet head 102 to discharge the ink while causing the rotation mechanism to rotate the medium 50 and causes the inkjet head to perform a sub-scanning operation within a range such that the position of a nozzle row in the sub-scanning direction remains within an opposing position medium range when the range from one end to the other end of the medium 50 in the sub-scanning direction at a position opposing the nozzle row is defined as the opposing position medium range.

Description

Printing device, printing method, and detection method

[0001] The present invention relates to a printing device, a printing method, and a detection method.

[0002] Conventionally, there has been known a printing device that performs inkjet printing on the outer surface of a cylindrical body (see, for example, Patent Document 1). The printing device disclosed in Patent Document 1 mounts a cylindrical body that does not absorb ink on a mandrel that is rotatable about a central axis and movable in the axial direction and in a direction perpendicular to the axial direction, and then sprays ultraviolet-curable ink of each color onto the outer surface of the cylindrical body from inkjet heads of an inkjet head group that is composed of a plurality of nozzles that spray each color of ink, thereby performing a desired decorative print and curing the decorative print by irradiating it with ultraviolet light.

[0003] JP 2010-143200 A

[0004] When printing using UV-curable ink using an inkjet system, if the UV light irradiated to cure the ink hits the inkjet head, the ink may harden at the nozzle position of the inkjet head, causing the nozzle to clog. Furthermore, when printing while rotating the medium (media, workpiece) to be printed on, UV light may be irradiated onto the side of the medium at a position in the rotation direction from the ink landing position (the position where the medium has rotated). In this case, UV light leaking from around the medium may be more likely to reach the inkjet head. Therefore, when printing with such a configuration, it is desirable to more appropriately irradiate the medium with UV light. Therefore, an object of the present invention is to provide a printing device, printing method, and detection method that can solve the above problems.

[0005] Furthermore, when printing on a target medium using an inkjet method, ink is typically ejected from the inkjet head while the inkjet head is moved relative to a position on the medium facing the inkjet head. Furthermore, ink droplets ejected from the inkjet head travel between the inkjet head and the medium before reaching the medium. To achieve high-quality printing, it is desirable to eject ink from the inkjet head at a timing that matches the distance (head gap) between the inkjet head and the medium.

[0006] In addition, when printing on a three-dimensional medium (a three-dimensional medium) using an inkjet method, for example, misalignment of the inkjet head relative to the medium can make it difficult to achieve high-quality printing. For example, when printing on a flat medium such as paper or film, even if the inkjet head is misaligned relative to the medium, the head gap does not change. However, with a three-dimensional medium, the head gap changes depending on the position of the medium. Therefore, if the inkjet head is misaligned relative to the medium, the head gap also changes. Furthermore, as a result, when performing color printing using multiple different ink colors, the misalignment of the ink landing positions can vary depending on the ink color, potentially resulting in reduced print quality. Therefore, there has been a demand for more appropriate printing on three-dimensional media. Therefore, an object of the present invention is to provide a printing device and adjustment method that can solve the above problems.

[0007] The inventors of the present application conducted extensive research into a configuration for inkjet printing while rotating a three-dimensional medium and irradiating the outer surface of the medium with ultraviolet light. They came up with the idea of ​​installing a cover between the ultraviolet irradiator that irradiates ultraviolet light and the inkjet head to cover at least the ultraviolet irradiator. This configuration makes it possible to reduce UV exposure to the inkjet head. When using such a cover, for example, a cover with an opening that matches the shape of the medium can be considered. However, even in this case, a gap may occur between the edge of the medium in the axial direction of rotation and the cover, and UV light may leak through the gap. When printing on the outer surface of a medium, the inkjet head is caused to perform a main scanning operation (scan) and a sub-scanning operation (feed) to eject ink to various positions on the outer surface. Here, the sub-scanning operation refers to movement relative to the medium in a predetermined sub-scanning direction. In this case, for example, when attempting to print over a wide area on the outer surface of the medium, the inkjet head may pass through the gap between the cover and the medium during one of the sub-scanning operations. As a result, ultraviolet rays leaking through the gaps may hit the inkjet head, causing the ink to harden near the nozzles, potentially resulting in clogging of the nozzles.

[0008] In response to this problem, the inventors of the present application came up with a solution to the problem of changing the relative movement of the inkjet head during at least some of the sub-scanning operations from a typical sub-scanning operation, so that the inkjet head does not pass through the gap between the cover and the medium. This configuration prevents ultraviolet light from reaching the inkjet head in the gap between the cover and the medium. This also makes it less likely for the nozzles in the inkjet head to become clogged.

[0009] Furthermore, the inventors of the present application have conducted further intensive research and have found the characteristics necessary to obtain such effects, which have led to the present invention.In order to solve the above-mentioned problems, the present invention provides a printing device that uses ultraviolet curable ink to print on a three-dimensional medium held by a holding member that holds a medium to be printed on, the printing device comprising: an inkjet head having a nozzle row in which a plurality of nozzles are arranged at different positions in a predetermined nozzle row direction; a sub-scanning driver that causes the inkjet head to perform a sub-scanning operation to move the inkjet head relatively to the medium in a sub-scanning direction parallel to the nozzle row direction; and a control unit that controls the operation of the inkjet head and the sub-scanning driver, the holding member comprising: a rotation mechanism that rotates the medium while holding the medium at a position opposite the nozzle row; an ultraviolet irradiator that irradiates ultraviolet light onto an outer surface of the medium; and a cover that covers at least the ultraviolet irradiator from the side of an upper surface of the holding member that is the surface facing the inkjet head, the cover having an opening that faces the nozzle row and that covers the upper surface of the holding member while opposing the nozzle row to the medium at the position of the opening, and the rotation mechanism that rotates the medium while holding the medium at a position opposite the nozzle row. the control unit further controls the rotational operation of rotating the medium using the rotation mechanism, and causes the inkjet head to eject ink while rotating the medium using the rotation mechanism, thereby causing the inkjet head to perform a main scanning operation of ejecting ink onto the rotating medium, and causes the inkjet head to perform the sub-scanning operation between at least some of the main scanning operations and perform the main scanning operation a plurality of times, thereby causing the inkjet head to eject ink onto a printing range in the sub-scanning direction that is wider in the sub-scanning direction than a nozzle array length, which is the length of the nozzle array in the sub-scanning direction, and when a range from one end to the other end of the medium arranged at a position opposite the nozzle array in the sub-scanning direction is defined as an opposing position medium range, the inkjet head is caused to perform the sub-scanning operation within a range that does not cause the position of the nozzle array in the sub-scanning direction to go outside the opposing position medium range.

[0010] This configuration prevents the inkjet head from passing through the gap between the cover and the medium during the sub-scanning operation, thereby preventing ultraviolet light from reaching the inkjet head at the gap between the cover and the medium. This reduces the likelihood of clogging of the inkjet head nozzles. In this configuration, the control unit causes the inkjet head to perform all main scanning operations while the nozzle array position in the sub-scanning direction is within the opposing position medium range. In this case, the control unit causes the inkjet head to perform sub-scanning operations between at least some of the main scanning operations, thereby causing the inkjet head to print on the entire side of the medium at most.

[0011] In this configuration, the ultraviolet irradiator irradiates the medium with ultraviolet light from a position farther from the inkjet head than the position on the medium closest to the inkjet head (the top of the medium). This configuration allows the ultraviolet irradiator to be easily and appropriately covered with a cover. In this case, it is desirable for the ultraviolet irradiator to irradiate ultraviolet light toward a position downstream in the direction of rotation of the medium from the position where the ink lands on the medium, and at a rotation angle of 90 to 180 degrees from the position of impact.

[0012] In addition, with this configuration, the printing device may perform multi-pass printing, in which the main scanning operation is performed multiple times while one position on the medium faces the nozzle array. In this case, the control unit causes the inkjet head to perform main scanning operations a number of times corresponding to a preset number of passes while aligning one end (front end) of the medium in the sub-scanning direction with one end (front end) of the nozzle array in the sub-scanning direction. After causing the inkjet head to perform main scanning operations a number of times corresponding to the number of passes, the control unit causes the inkjet head to perform a sub-scanning operation in which the inkjet head moves in the sub-scanning direction relative to the medium a distance corresponding to the length of the nozzle array divided by the number of passes before causing the inkjet head to perform the next main scanning operation. This configuration allows the inkjet head to properly perform the first number of main scanning operations without performing a sub-scanning operation in which the inkjet head passes through the gap between the cover and the medium on the one end of the medium side. This also more appropriately prevents ultraviolet light from irradiating the inkjet head at the gap between the cover and the medium. This type of operation can also be considered as starting the initial main scanning operation (the main scanning operation for the first scan) with one edge of the medium and one edge of the inkjet head aligned. The pass number corresponding distance is also an example of a standard movement amount (feed amount) in a sub-scanning operation.

[0013] In this case, it is also possible to perform sub-scanning operations over a distance shorter than the distance corresponding to the number of passes while performing main scanning operations for the first number of passes. For example, the printing device may increase the printing resolution in the sub-scanning direction beyond the resolution corresponding to the nozzle pitch in the nozzle row. The nozzle pitch is the distance between nozzles in the nozzle row in the sub-scanning direction. By performing multi-pass printing, the printing resolution in the sub-scanning direction can be increased beyond the resolution corresponding to the nozzle pitch. For example, during at least a portion of the intervals between the main scanning operations corresponding to the number of passes performed while aligning one edge of the medium with one edge of the nozzle row, the sub-scanning driver may move the inkjet head in the sub-scanning direction relative to the medium by a distance less than the nozzle pitch. This configuration allows for high-resolution printing while preventing ultraviolet light from reaching the inkjet head in the gap between the cover and the medium.

[0014] Furthermore, with this configuration, the control unit causes the inkjet head to perform main scanning and sub-scanning operations so as not to perform a sub-scanning operation that positions the inkjet head in the gap between the cover and the medium, even on the other end (rear end) of the medium and the inkjet head. More specifically, during a sub-scanning operation in which the position of the other end of the nozzle array exceeds the position of the other end of the medium in the sub-scanning direction when the movement distance of the inkjet head relative to the medium is set to the pass number distance, the control unit causes the inkjet head to perform a sub-scanning operation so that the inkjet head moves relative to the medium by the movement distance until the other end of the nozzle array reaches the position of the other end of the medium. This configuration prevents a sub-scanning operation in which the other end of the nozzle array exceeds the position of the other end of the medium. This more appropriately prevents ultraviolet light from hitting the inkjet head in the gap between the cover and the medium. Furthermore, the control unit causes the inkjet head to perform a sub-scanning operation in which the other end of the nozzle array reaches the other end of the medium in the sub-scanning direction, and then causes the inkjet head to perform multiple main scanning operations while the other end of the medium and the other end of the nozzle array are aligned. This configuration allows the inkjet head to perform the required number of main scanning operations over an area including the other end of the medium. Furthermore, the control unit causes the inkjet head to perform main scanning operations for the number of passes while the other end of the medium and the other end of the nozzle array are aligned. The state in which the other end of the medium and the other end of the nozzle array are aligned may be a state in which the distance between the other end of the medium and the other end of the nozzle array is equal to or less than the nozzle pitch. In this case, the control unit may cause the inkjet head to perform sub-scanning operations in which the inkjet head moves relatively a distance less than the nozzle pitch between multiple main scanning operations performed in this state.

[0015] Furthermore, when controlling the printing operation, it is also possible to treat the range on the medium where printing is performed (the print target area) as the range of the medium. In this case, one end (leading end) of the medium is a position corresponding to one end of the print range in the sub-scanning direction. The other end (trailing end) of the medium is a position corresponding to the other end of the print range in the sub-scanning direction. Aligning the positions of one end of the medium with one end of the nozzle row corresponds to aligning the position corresponding to one end of the print data in the sub-scanning direction with the position of one end of the nozzle row in the sub-scanning direction. Aligning the positions of the other end of the medium with the other end of the nozzle row corresponds to aligning the position corresponding to the other end of the print data in the sub-scanning direction with the position of the other end of the nozzle row in the sub-scanning direction.

[0016] Furthermore, in this configuration, if a gap occurs between the cover and the medium due to, for example, misalignment of the cover, unintended leakage of ultraviolet light may occur, resulting in exposure of the inkjet head to ultraviolet light. Therefore, it is preferable to be able to confirm whether the cover is properly covering the ultraviolet irradiator in a predetermined state. In this case, for example, a sensor may be used to detect the state of the gap. More specifically, the printing device may further include a sensor used to detect the position of the upper surface of the holding member and a sensor moving means for moving the sensor relative to the holding member. Here, the holding member may further include a cover moving means for moving the cover in a direction that changes the distance between the inkjet head and the cover. The control unit may then further control the sensor and the sensor moving means to detect the state of the gap between the cover and the medium based on the sensor output acquired while the sensor moving means moves the sensor along a path that passes through the edge of the opening of the cover. This configuration makes it possible to detect the state of the gap between the cover and the medium. This also makes it possible to appropriately prevent unintended leakage of ultraviolet light due to, for example, misalignment of the cover. In this case, the control unit moves the sensor along multiple paths in a direction intersecting the nozzle row direction. The plurality of paths include a one-end path that passes near one end of the medium in the sub-scanning direction, an other-end path that passes near the other end of the medium, and an intermediate path that passes over the medium between the one-end path and the other-end path. This configuration allows for more appropriate detection of the state of the gap between the cover and the medium.

[0017] A photo sensor that detects light can be used as such a sensor. In this case, for example, a light-reflective member can be attached to at least a portion of at least one of the medium and the cover. In this case, the control unit moves the sensor along a path that allows the sensor to detect light reflected from the light-reflective member on at least one of the medium and the cover. This configuration allows for more appropriate detection of the state of the gap between the cover and the medium. For example, a light-reflective tape, such as white, can be used as the light-reflective member. Furthermore, when a photo sensor is used as the sensor, it is also possible for the sensor to directly detect UV rays leaking through the gap. In this case, while the UV irradiator irradiates the outer surface of the medium with UV rays, the control unit further detects UV rays leaking through the gap between the edge of the cover opening and the medium based on the output of the sensor. This configuration allows for more appropriate detection of unintended UV leakage due to misalignment of the cover, etc. Furthermore, a printing method or the like having the same characteristics as described above can also be used as a configuration of the present invention. In this case, the same effects as described above can also be obtained.

[0018] The features of the present invention can also be considered by focusing on the configuration using such a sensor. In this case, the present invention is a printing device that prints on a three-dimensional medium held by a holding member that holds a medium to be printed using ultraviolet curable ink, the printing device comprising: an inkjet head having a nozzle row in which a plurality of nozzles are arranged at different positions in a predetermined nozzle row direction; a sensor used to detect the position of an upper surface of the holding member that is the surface of the holding member that faces the inkjet head; sensor moving means that moves the sensor relative to the holding member; and a control unit that controls operations of the inkjet head, the sensor, and the sensor moving means, the holding member rotating the medium while holding the medium at a position facing the nozzle row. the inkjet head and the cover are provided with a rotation mechanism for rotating the inkjet head, an ultraviolet irradiator for irradiating ultraviolet rays onto the outer surface of the medium, a cover which is a member covering at least the ultraviolet irradiator from the side of the upper surface of the holding member and has an opening at a position opposite the nozzle row, and which covers the upper surface of the holding member while opposing the nozzle row and the medium at the position of the opening, and a cover moving means for moving the cover in a direction that changes the distance between the inkjet head and the cover, and the control unit detects the state of the gap that occurs between the cover and the medium based on the output of the sensor obtained while moving the sensor by the sensor moving means along a path that passes through the edge of the opening of the cover.

[0019] This configuration allows the state of the gap between the cover and the medium to be properly detected. This also properly prevents unintended leakage of ultraviolet light due to misalignment of the cover, etc. Therefore, this configuration allows for more proper irradiation of ultraviolet light onto the medium. It is also conceivable to use a detection method or the like having the same characteristics as described above as a configuration of the present invention. In this case, the same effects as described above can also be obtained.

[0020] The present inventors also conceived a method for detecting the position of an inkjet head relative to the medium when printing on a three-dimensional medium using an inkjet method and adjusting it as necessary. To achieve this, they devised a method for causing the inkjet head to draw patterns that overlap on the medium when the inkjet head's relative position is correct, but do not overlap when the inkjet head's relative position is deviated from the correct position. Through extensive research, the present inventors also conceived a method for using, as such patterns, a first pattern drawn by a nozzle row (a nozzle row in the inkjet head) that is positioned at a first relative position relative to the medium, and a second pattern drawn by nozzles that is positioned at a second relative position. This configuration allows the position of the inkjet head relative to the medium to be detected and the position of the inkjet head to be appropriately adjusted as necessary.

[0021] Furthermore, the inventors of the present application have conducted further intensive research and have found the characteristics necessary to obtain such effects, which have led to the present invention. In order to solve the above-mentioned problems, the present invention provides a printing device for printing on a three-dimensional medium, the printing device comprising: an inkjet head having a nozzle array in which a plurality of nozzles are arranged in a predetermined nozzle array direction; a main scanning drive unit that causes the inkjet head to perform a main scanning operation in which the inkjet head moves along a predetermined main scanning direction on a printing surface of the medium while ejecting ink; and a control unit that controls the operation of the inkjet head and the main scanning drive unit, wherein the control unit, when adjusting the position of the inkjet head, causes the inkjet head to draw a first pattern and a second pattern, and when the relative position of the inkjet head with respect to the medium is at a predetermined reference position, the first pattern and the second pattern are drawn at the same position in the main scanning direction on the medium, and the inkjet head draws the first pattern with ink ejected from the nozzles of the nozzle array when the relative position of the nozzle array with respect to the medium is at a first position, and draws the second pattern with ink ejected from the nozzles of the nozzle array when the relative position of the nozzle array with respect to the medium is at a second position different from the first position.

[0022] According to this configuration, when the relative positions of the inkjet heads having nozzle rows are aligned with a reference position, the first pattern and the second pattern are drawn at the same position in the main scanning direction on the medium. Furthermore, when the relative positions of the inkjet heads are deviated from the reference position, a deviation occurs in the positions (positions in the main scanning direction) at which the first pattern and the second pattern are drawn on the medium. This makes it possible to properly detect whether the relative positions of the inkjet heads are aligned with the reference position. Furthermore, this makes it possible to properly adjust the relative positions of the inkjet heads, etc., as necessary. Therefore, this configuration allows for more appropriate printing on three-dimensional media.

[0023] In this configuration, the relative position of the nozzle row with respect to the medium (relative position of the nozzle row) can be considered to correspond to the relative position of the inkjet head with respect to the medium. With respect to the relative position of the inkjet head, the reference position can be considered to be a predetermined correct position. Furthermore, drawing the first pattern and the second pattern at the same position in the main scanning direction can be considered to mean drawing them at substantially the same position with accuracy according to the quality required for printing, etc. Drawing the first pattern and the second pattern at the same position in the main scanning direction can also be considered to mean that the first pattern and the second pattern overlap in the main scanning direction.

[0024] In this configuration, the medium is held by a holding member disposed opposite the inkjet head. The holding member includes a rotation mechanism that rotates the medium while holding it opposite the nozzle row. The main scanning drive unit rotates the medium using the rotation mechanism, thereby moving the inkjet head in the main scanning direction relative to the position on the medium that faces the nozzle row. This configuration allows the inkjet head to perform the main scanning operation appropriately when a three-dimensional medium is used. This also allows appropriate printing on the three-dimensional medium. A cylindrical (cylindrical) medium, for example, can be suitably used as the medium held by the holding member. A cylindrical medium is an example of a medium shaped like a rotating body. The holding member can also be used to hold a medium shaped like a rotating body other than a cylindrical shape, such as a conical or truncated conical medium. When the medium is rotated by the holding member, the fact that the first pattern and the second pattern are drawn at the same position in the main scanning direction can also be considered as the fact that the first pattern and the second pattern are drawn at the same position in the rotation direction.

[0025] In this configuration, it is also conceivable to draw the first pattern and the second pattern using multiple nozzle arrays included in a single inkjet head. In this case, the inkjet head has multiple nozzle arrays that are positioned differently in the main scanning direction. These multiple nozzle arrays are an example of multiple nozzle arrays whose relative positions with respect to each other are known. For multiple nozzle arrays, "the positions of the multiple nozzle arrays in the main scanning direction are different from each other" means that, when the inkjet head is positioned to eject ink onto a medium, the positions of the multiple nozzle arrays in the inkjet head in the main scanning direction are different from each other. In this case, it is also conceivable to draw the first pattern by ejecting ink from nozzles in a first nozzle array among the multiple nozzle arrays in a single inkjet head, and then draw the second pattern by ejecting ink from nozzles in a second nozzle array different from the first nozzle array. This makes it possible to appropriately detect whether the positions of the inkjet head having these nozzle arrays are aligned with the reference position.

[0026] Furthermore, when an inkjet head having multiple nozzle rows is used and the above-mentioned holding member is used, it is possible to fix the inkjet head so that the first nozzle row and the second nozzle row are arranged on opposite sides of the position of the center of rotation of the medium in the main scanning direction, and have the first nozzle row and the second nozzle row draw the first pattern and the second pattern. In this case, it is possible to align the center position of the first nozzle row and the second nozzle row in the inkjet head with the position of the rotation axis of the medium in the main scanning direction. Furthermore, the control unit of the printing device ejects ink from the nozzles of the first nozzle row and the nozzles of the second nozzle row in this state, causing the inkjet head to draw the first pattern and the second pattern.

[0027] In this configuration, the first pattern and the second pattern may be patterns whose overlapping pattern changes depending on the degree of deviation of the relative position of the inkjet head with respect to the medium when the relative position of the inkjet head deviates from a reference position. This configuration allows for easier and more appropriate adjustment of the relative position of the inkjet heads. In this configuration, the printing device may include multiple inkjet heads. In this case, for example, in addition to the first pattern and the second pattern, the inkjet heads may be caused to draw a pattern for detecting deviation in the distance between the inkjet heads. Such a pattern may be a pattern whose state changes depending on the distance between the multiple inkjet heads. In this case, the control unit of the printing device causes the multiple inkjet heads to further draw a pattern whose state changes depending on the distance between the multiple inkjet heads. The first pattern and the second pattern are patterns for adjusting deviation in landing positions that occurs between multiple nozzle rows whose relative positions are known, such as multiple nozzle rows in a single inkjet head. In contrast, the pattern for detecting deviation in the distance between the inkjet heads is a pattern for adjusting deviation in landing positions that occurs between the inkjet heads.

[0028] Furthermore, when printing is performed while holding a medium by a holding member and rotating the medium, it is also possible to draw the first pattern and the second pattern with different rotation directions of the medium. In this case, a feature of the present invention can also be considered by focusing on the configuration of a printing device that prints on a three-dimensional medium held by a holding member. The present invention relates to a printing device that prints on a three-dimensional medium held by a holding member that holds a medium to be printed, the printing device comprising: an inkjet head having a nozzle row in which a plurality of nozzles are arranged in a predetermined nozzle row direction; a main scanning drive unit that causes the inkjet head to perform a main scanning operation in which ink is ejected while moving relatively over the printing surface of the medium in a predetermined main scanning direction; and a control unit that controls the operation of the inkjet head and the main scanning drive unit, the holding member having a rotation mechanism that rotates the medium while holding the medium in a position opposite the nozzle row, and the main scanning drive unit that rotates the medium using the rotation mechanism to eject the ink onto the printing surface of the medium. The inkjet head is moved relative to the medium in the main scanning direction, and the control unit adjusts the position of the inkjet head to draw a first pattern and a second pattern. When the relative position of the inkjet head with respect to the medium is at a predetermined reference position, the first pattern and the second pattern are drawn at the same position on the medium in the main scanning direction. The inkjet head draws the first pattern while rotating the medium in a first rotation direction using the rotation mechanism, and draws the second pattern while rotating the medium in a second rotation direction opposite to the first rotation direction. This configuration also makes it possible to properly detect whether the relative position of the inkjet head is aligned with the reference position. This also enables more appropriate printing on three-dimensional media. The present invention may also be configured using an adjustment method or the like having the same characteristics as described above. In this case, the same effects as described above can be obtained.

[0029] According to the present invention, ultraviolet light can be irradiated onto a medium more appropriately. Also, according to the present invention, printing can be performed more appropriately on a three-dimensional medium.

[0030] [Correction based on Rule 91 03.09.2024] This figure explains a printing device 10 according to one embodiment of the present invention. FIG. 1(a) shows an example of the configuration of the main components of the printing device 10. FIG. 1(b) shows an example of the configuration of the head unit 12. This figure shows an example of the configuration of a holding jig 40. FIGS. 2(a) and 2(b) are a cross-sectional view and a top view, respectively, showing a simplified example of the configuration of the holding jig 40. This figure shows an example of the configuration of the holding jig 40. FIG. 3(a) is a cross-sectional view showing a more specific example of the configuration of the holding jig 40. FIG. 3(b) is a perspective view showing an example of the configuration of the ultraviolet irradiator 208 in the holding jig 40. This figure explains the magnet sheet 224 in the holding jig 40. This figure shows an example of main scanning and sub-scanning operations that are the same as or similar to those in a conventional method. This figure shows an example of main scanning and sub-scanning operations in this example. This figure shows another example of main scanning and sub-scanning operations in this example. FIG. 7( a) shows an example of the position of the inkjet head 102 during the Nth and (N+1)th main scanning operations performed on a medium 50 of a predetermined size. FIG. 7( b) shows an example of the position of the inkjet head 102 during the (N-1)th and Nth main scanning operations performed on a medium 50 of a predetermined size different from that shown in FIG. 7( a). This figure shows an example of an operation for detecting the state of a gap using the sensor 20. This is a flowchart showing an example of an operation for detecting the state of a gap in the printing device 10. This figure explains how to print on the side of the medium 50. FIGS. 10( a) and 10(b) show examples of how to print on the side of the medium 50. This figure explains the targets of adjustments to be made to the printing device 10. FIG. 11( a) shows an example of a correct state that does not require adjustment. FIG. 11( b) shows an example of a state that requires adjustment. This figure explains the pattern to be drawn by the printing device 10 during adjustment. FIG. 12( a) is a diagram explaining patterns 302 a and 302 b to be drawn by the inkjet head 102. 12B shows an example of the state of patterns 302a and 302b that are drawn when there is no misalignment in the relative position of the inkjet head 102 with respect to the medium 50. This figure explains the patterns that are drawn by the printing device 10 during adjustment.13(a) and 13(b) show examples of the state of patterns 302a and 302b that are drawn when there is a deviation in the relative position of the inkjet head 102 with respect to the medium 50. These figures explain adjustment of the distance between the inkjet heads 102. FIGS. 14(a) and 14(b) explain problems that arise when there is a deviation in the distance between the inkjet heads 102. FIG. 14(c) shows examples of patterns 304a and 304b that are used when adjusting the distance between the inkjet heads 102. These figures show modified examples of adjustment operations for the printing device 10. FIGS. 15(a) and 15(b) show examples of adjustment operations.

[0031] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating a printing device 10 according to an embodiment of the present invention. FIG. 1(a) shows an example of the configuration of the main parts of the printing device 10. Except as described below, the printing device 10 and each part of the printing device 10 may have the same or similar features as known printing devices and their respective parts.

[0032] The printing device 10 of this example is an inkjet printer that uses ultraviolet-curable ink (UV ink) to print on a three-dimensional medium 50 held by a holding jig 40. UV-curable ink is ink that is fixed to the medium 50 by being irradiated with ultraviolet light. The medium 50 can also be considered a workpiece (workpiece) that is the target of printing processing in the printing device 10. The holding jig 40 of this example is an example of a holding member that holds the medium 50. The holding jig 40 holds the medium 50 rotatably around a predetermined rotation axis at a position facing the inkjet head 102, and rotates the medium 50 according to control of the printing device 10. The position facing the inkjet head 102 refers to a position facing the nozzle array of the inkjet head 102. Holding the medium 50 at a position facing the inkjet head 102 means holding the medium 50 at a position facing the inkjet head 102 when ink is ejected from the inkjet head 102 onto the medium 50. The holding jig 40 of this example is also equipped with an ultraviolet irradiator, and irradiates ultraviolet rays onto the outer surface of the medium 50. The configuration of the holding jig 40 will be described in more detail later.

[0033] The printing device 10 of this example also includes a head unit 12, a base unit 14, a main scanning driver 16, a sub-scan driver 18, a sensor 20, a sensor moving means 22, and a control unit 30. The head unit 12 has an inkjet head that ejects ink onto a medium 50. The configuration of the head unit 12 will be described in more detail later. The base unit 14 is a platform-shaped member that holds a holding jig 40 in a position facing the head unit 12. The base unit 14 of this example holds the holding jig 40 by placing the holding jig 40 on its upper surface so that the inkjet head of the head unit 12 faces the medium 50 held by the holding jig 40. The main scanning driver 16 is a driver that causes the inkjet head of the head unit 12 to perform a main scanning operation. The main scanning operation is an operation in which ink is ejected while moving relative to the medium 50 in a predetermined main scanning direction (Y direction in the figure). Furthermore, the main scanning drive unit 16 in this example rotates the medium 50 using the holding jig 40 in accordance with the control of the control unit 30, thereby moving the opposing position between the medium 50 and the nozzle row in the circumferential direction. This can also be considered as the inkjet head moving in the main scanning direction relative to the medium 50 as the medium 50 rotates. The main scanning operation in this example can also be considered as the operation of ejecting ink onto the rotating medium. The main scanning operation can also be considered as the operation of ejecting ink onto the medium 50 while fixing the position of the inkjet head relative to the medium 50 in the sub-scanning direction.

[0034] The sub-scanning driver 18 is a driver that causes the inkjet head of the head unit 12 to perform a sub-scanning operation. The sub-scanning operation is an operation of moving relative to the medium 50 in a sub-scanning direction (X direction in the figure) that is perpendicular to the main scanning direction. The sub-scanning operation can also be considered a feeding operation that changes the area of ​​the medium that faces the inkjet head by moving relatively in the sub-scanning direction. The main scanning direction in this example is an example of a predetermined first direction. The sub-scanning direction is an example of a second direction that is perpendicular to the first direction. The main scanning operation is an example of a first scan in which ink is ejected while moving in the first direction relative to each position on the medium 50. The sub-scanning operation is an example of a second scan in which ink is moved relative to the medium 50 in the second direction.

[0035] The sensor 20 is a detection means used to detect the state of the holding jig 40. In this example, the sensor 20 is a photosensor that detects ultraviolet light leaking from the opening of the holding jig 40. The sensor 20 can detect whether the medium 50 is properly installed relative to the holding jig 40. More specifically, the sensor 20 can detect ultraviolet light leakage caused by misalignment of the cover of the holding jig 40 or the medium 50, thereby detecting misalignment of the cover or the medium 50. It is also possible to detect the state of the gap between the cover of the holding jig 40 and the medium 50 based on the detection results of the sensor 20. The sensor moving means 22 is a means for moving the sensor 20 relative to the holding jig 40, and moves the sensor 20 to match the location where the sensor 20 will perform detection. The control unit 30 is, for example, a part including a CPU of the printing device 10, and controls the operation of each part of the printing device 10 in accordance with programs such as firmware (FW) of the printing device 10.

[0036] Next, the configuration of the head unit 12 will be described in more detail. FIG. 1B shows an example of the configuration of the head unit 12. The head unit 12 of this example has multiple inkjet heads 102 that eject ultraviolet-curable ink. The head unit 12 of this example has four inkjet heads 102, as distinguished by the reference numerals 102a to 102d in the figure. Of these, the inkjet heads 102a to 102c are aligned in the main scanning direction with their positions in the sub-scanning direction aligned. The inkjet head 102d is aligned in a position offset in the sub-scanning direction from the inkjet heads 102a to 102c. This can be considered to mean that at least some of the inkjet heads 102 of the head unit 12 are aligned in the main scanning direction with their positions in the sub-scanning direction aligned, or that some of the inkjet heads 102 are aligned in a position offset in the sub-scanning direction from the other inkjet heads 102.

[0037] Furthermore, as shown in the figure, the inkjet head 102 denoted by reference numeral 102a is distinguished by reference numerals 112a and 112b. The inkjet head 102 of this example has multiple nozzle rows 112 (two nozzle rows 112). The nozzle rows 112 are rows in which multiple nozzles are arranged at different positions in a predetermined nozzle row direction. In this example, the nozzle row direction is a direction parallel to the sub-scanning direction. The multiple nozzle rows 112 are also positioned at different positions in the main scanning direction. In this example, the multiple nozzle rows 112 in the same inkjet head 102 are an example of multiple nozzle rows 112 in which the relative positions of one nozzle row to the other are known. The inkjet head 102 ejects multiple colors of ink from the multiple nozzle rows 112. The inkjet head 102 ejects a first color of ink from a first nozzle row 112 and ejects a second color of ink, different from the first color, from a second nozzle row 112 that is different from the first nozzle row 112. Furthermore, depending on the desired printing content, the inkjet head 102 may eject ink of the same color from multiple nozzle rows 112 .

[0038] The printing device 10 of this example performs printing using a multi-pass method. The multi-pass method is a method in which a main scanning operation is performed multiple times at one position on the medium 50. When printing is performed by the printing device 10 of this example, the control unit 30 moves the head unit 12 relative to the medium 50, thereby sequentially moving the inkjet heads 102 of the head unit 12 directly above the rotating medium 50 and facing the medium 50. The control unit 30 then causes the multiple inkjet heads 102 to sequentially eject ink onto the medium 50. With a first inkjet head 102 facing the medium 50, the control unit 30 causes that inkjet head 102 to eject ink onto the entire printing range on the side of the medium 50. Then, after causing the first inkjet head 102 to eject ink onto the medium 50, the control unit 30 causes a second inkjet head 102, different from the first inkjet head 102, to face the medium 50, and in this state, causes the inkjet head 102 to eject ink onto the side surface of the medium 50 in the same manner as described above. By repeating the same operation thereafter, the control unit 30 causes the multiple inkjet heads 102 of the head unit 12 to eject ink onto the medium 50.

[0039] Next, the configuration of the holding jig 40 used in the printing apparatus 10 of this embodiment will be described in more detail. FIGS. 2 and 3 show an example of the configuration of the holding jig 40. FIGS. 2(a) and 2(b) are a cross-sectional view and a top view, respectively, showing a simplified example of the configuration of the holding jig 40. FIG. 3(a) is a cross-sectional view showing a more specific example of the configuration of the holding jig 40. FIG. 3(b) is a perspective view showing an example of the configuration of the ultraviolet irradiator 208 in the holding jig 40. As described above, the holding jig 40 of this embodiment rotatably holds the medium 50. The holding jig 40 also irradiates the outer surface of the medium 50 with ultraviolet light. To perform these functions, the holding jig 40 of this embodiment includes a housing 202, a cover 204, a rotation mechanism 206, an ultraviolet irradiator 208, a light source holder 210, and a cover moving mechanism 212.

[0040] The housing 202 is a housing portion of the holding jig 40 that constitutes the bottom and side surfaces of the holding jig 40, and houses a rotation mechanism 206, an ultraviolet irradiator 208, a light source holder 210, etc. between the housing 202 and the cover 204. The cover 204 is a member that covers the top surface of the holding jig 40. The top surface of the holding jig 40 is the surface of the holding jig 40 that faces the inkjet head 102 (see FIG. 1 ). The cover 204 can also be considered a member that covers at least the ultraviolet irradiator 208 from the top surface side of the holding jig 40. Furthermore, the cover 204 in this example has an opening 220 at a position facing the nozzle row of the inkjet head 102, and covers the top surface of the holding jig 40 while arranging the nozzle row and the medium 50 facing each other at the position of the opening 220. Having the opening 220 at a position facing the nozzle row means that when one of the inkjet heads 102 is opposed to the medium 50 during printing, the opening 220 is positioned facing the nozzle row of that inkjet head 102. The opening 220 can also be thought of as opening on the top surface of the holding jig 40 so that ink ejected from the nozzle row of the inkjet head 102 can reach the medium 50.

[0041] The cover 204 of this example also has a base portion 222 and a magnet sheet 224. The base portion 222 is a plate-shaped portion that constitutes the base of the cover 204 and holds the magnet sheet 224 between the inkjet head 102 and the medium 50. The magnet sheet 224 is a removable portion of the cover 204 and is processed to a shape that matches the shape of the medium 50. As described above, the cover 204 of this example has an opening 220. The opening 220 is preferably shaped to match the shape of the medium 50 so as to prevent an unnecessary gap from forming between the cover 204 and the medium 50. Therefore, in this example, the opening 220 is formed in the magnet sheet 224 and the base portion 222 holds the magnet sheet 224, thereby shaping the opening 220 of the cover 204 to match the shape of the medium 50. As shown in the figure, the base portion 222 has an opening that is larger than the opening 220 of the cover 204 and holds the magnet sheet 224 so as to cover a portion of this large opening. With this configuration, the opening 220 can be appropriately formed in the cover 204 to match the shape of the medium 50. The magnetic sheet 224 of the cover 204 can also be considered a member shaped to match the shape of the medium 50. The base portion 222 can also be considered a portion with a fixed shape that is independent of the shape of the medium 50.

[0042] The rotation mechanism 206 rotates the medium 50 while holding it at a position facing the nozzle row of the inkjet head 102. The rotation mechanism 206 of this example also includes a shaft 226 and a rotation drive unit 228. The shaft 226 is a part that rotatably holds the medium 50, and rotatably holds the medium 50 at one end and the other end of the axial direction of the rotation shaft of the medium 50. A chuck or the like suited to the medium 50 can be suitably used as the shaft 226. The rotation drive unit 228 is a drive unit that rotates the shaft 226, and by rotating the shaft 226, the medium 50 rotates together with the shaft 226. As described above, in the printing device 10 of this example (see FIG. 1 ), the inkjet head 102 moves relative to the outer surface of the medium 50 by rotating the medium 50 during the main scanning operation. The control unit 30 (see FIG. 1) of the printing device 10 controls the operation of the rotation drive unit 228, thereby controlling the rotation operation of the rotation mechanism 206 to rotate the medium 50. The control unit 30 also controls the operation of the inkjet head 102 and the rotation mechanism 206 via the main scanning drive unit 16 (see FIG. 1), causing the rotation mechanism 206 to rotate the medium 50 while causing the inkjet head 102 to eject ink. In this way, the control unit 30 causes the inkjet head 102 to perform a main scanning operation. Furthermore, the rotation mechanism 206 in this example rotates the medium 50 so that the direction of movement of the outer surface of the medium 50 at a position facing the nozzle row of the inkjet head 102 is the main scanning direction.

[0043] The ultraviolet irradiator 208 is an ultraviolet light source (UV light source) that irradiates the outer surface (side surface) of the medium 50 with ultraviolet light. The ultraviolet irradiator 208 is disposed adjacent to the medium 50 in the housing 202 of the holding jig 40, thereby irradiating the outer surface of the rotating medium 50 with ultraviolet light. This causes the ultraviolet irradiator 208 to cure ink (UV-curable ink) adhered to the medium 50. The ultraviolet irradiator 208 in this example also includes a lighting unit 242 and a canopy 244, as shown in FIG. 3B . The lighting unit 242 is a part of the ultraviolet irradiator 208 that generates ultraviolet light and includes, for example, multiple UVLEDs. The UVLEDs are light-emitting diodes that emit ultraviolet light. The lighting unit 242 lights up in response to control by the control unit 30. The canopy 244 is a light-shielding member (light-shielding unit) that blocks some of the ultraviolet light generated by the lighting unit 242. The canopy 244 of this example is disposed between the inkjet head 102 and the lighting unit 242, thereby blocking ultraviolet light traveling in the direction toward the inkjet head 102. By using such a canopy 244, stray light traveling toward the inkjet head 102 can be appropriately reduced.

[0044] Furthermore, the ultraviolet irradiator 208 of this example irradiates the medium 50 with ultraviolet light from a position farther from the inkjet head 102 than the top of the medium 50. The top of the medium 50 is the position on the medium 50 closest to the inkjet head 102. This configuration allows the ultraviolet irradiator 208 to be easily and appropriately covered by the cover 204. This also more appropriately reduces stray light traveling from the ultraviolet irradiator 208 toward the inkjet head 102. Furthermore, the ultraviolet irradiator 208 of this example irradiates ultraviolet light downstream in the direction of rotation of the medium 50 from the impact position where the ink lands on the medium 50, and toward a position that is 90 to 180 degrees from the impact position in the rotation direction. Furthermore, it is preferable to install the ultraviolet irradiator 208 in a position where reflected light from the medium 50 is directed away from the inkjet head 102 (e.g., downward).

[0045] The light source holding unit 210 is a platform-shaped member that holds the ultraviolet irradiator 208. In this example, the light source holding unit 210 holds the ultraviolet irradiator 208 on its upper surface, thereby holding the ultraviolet irradiator 208 in a position where ultraviolet light can be irradiated toward the outer surface of the medium 50. The cover moving means 212 is a means for moving the cover 204 vertically. The vertical direction here refers to the direction in which the distance between the inkjet head 102 and the cover 204 changes. The cover moving means 212 in this example is a means for moving the cover 204 manually by a user. For example, the base portion 222 of the cover 204 is moved vertically by rotating a manual handle, thereby moving the magnetic sheet 224 together with the base portion 222. The cover moving means 212 can move the cover 204 to match the size of the medium 50, etc. In order to appropriately reduce stray light traveling from the ultraviolet irradiator 208 toward the inkjet head 102, it is important to avoid a large gap between the cover 204 and the medium 50. To prevent such a gap from occurring, it is preferable to bring the edge of the opening 220 of the cover 204 sufficiently close to the medium 50. To achieve this, it is preferable to move the cover 204 vertically as needed, depending on the size of the medium 50, etc. In this example, the gap between the cover 204 and the medium 50 can be sufficiently reduced by moving the cover 204 using the cover moving means 212. Sufficiently reducing the gap between the cover 204 and the medium 50 can be thought of as essentially eliminating the gap in the lateral direction of the medium 50. The gap in the lateral direction of the medium 50 refers to the gap in the direction perpendicular to the rotation axis of the medium 50. Substantially eliminating the gap in the lateral direction means reducing the gap to a level that does not affect the rotation of the medium 50 and does not cause problematic stray light.

[0046] Next, the countermeasures against stray light implemented in the printing device 10 of this embodiment will be described in more detail. As described above, the cover 204 of this embodiment has a base portion 222 and a magnetic sheet 224. The magnetic sheet 224 is processed to a shape that matches the shape of the medium 50, etc. By using such a magnetic sheet 224, it is possible to appropriately and sufficiently reduce the lateral gap of the medium 50, as shown in FIG. 4, for example. FIG. 4 is a diagram illustrating the magnetic sheet 224 in the holding jig 40. The upper left diagram of FIG. 4 shows an example of a state in which the magnetic sheet 224 is installed. The lower right diagram shows an example of a state in which the magnetic sheet 224 has been removed. As can be seen from the state illustrated in FIG. 4, in this embodiment, the magnetic sheet 224 can appropriately and sufficiently reduce the lateral gap of the medium 50, as described above.

[0047] However, even if a magnetic sheet 224 shaped to match the shape of the medium 50 is used, if the cover 204 is not positioned properly in the vertical direction, an unintended gap may occur between the cover 204 and the medium 50, potentially allowing problematic stray light to reach the inkjet head 102. Therefore, the printing device 10 of this example uses a sensor 20 (see FIG. 1 ) to detect the state of the gap between the cover 204 and the medium 50. The sensor 20 can be considered to be used to detect the position of the top surface of the holding jig 40. In this example, to facilitate detection by the sensor 20, white tape 232 is affixed to a predetermined position on the magnetic sheet 224. The tape 232 is an example of a light-reflective member affixed to at least a portion of at least one of the medium 50 and the cover 204. Tape of a light-reflective color other than white may be used as the tape 232. Furthermore, a material other than the tape 232 may also be used as the light-reflective member. The tape 232 in this example can also be considered to indicate the location where detection by the sensor 20 is performed. The operation of detecting the gap state using the sensor 20 will be described in more detail later.

[0048] Furthermore, as described above, in this example, by using the magnet sheet 224 and adjusting the position of the cover 204 in the vertical direction, it is possible to sufficiently reduce the gap in the lateral direction (main scanning direction, left-right direction) of the medium 50. In this case, the edge of the cover 204 overlaps the medium 50 in the vertical direction at the edge of the cover 204 in the horizontal direction, thereby appropriately preventing stray light. However, even in this case, if the gaps are eliminated at one end and the other end (front and back) in the horizontal direction and the front-to-back direction (sub-scanning direction), the medium 50 will rotate with the cover 204 and the medium 50 in contact, making the medium 50 more susceptible to scratches. Therefore, at these positions, gaps that are not blocked by either the cover 204 or the medium 50 are likely to occur. Furthermore, as a result, for example, when the inkjet head 102 is caused to perform main scanning and sub-scanning operations using a conventional method, stray light leaking from the front-to-back edges can reach the inkjet head 102, potentially causing problems such as nozzle clogging. In contrast, in this example, the inkjet head 102 is caused to perform main scanning and sub-scanning operations so that the inkjet head 102 does not pass through the gap between the cover 204 and the medium 50 in the front-to-rear direction, thereby making it less susceptible to the effects of such stray light. The main scanning and sub-scanning operations performed by the inkjet head 102 in this example will be described in more detail below. For ease of explanation, an example of main scanning and sub-scanning operations that are the same as or similar to conventional methods will first be described.

[0049] FIG. 5 is a diagram showing an example of main scanning and sub-scanning operations that are the same as or similar to conventional methods, and shows an example of main scanning and sub-scanning operations in which one inkjet head 102 ejects ink onto each position on the medium 50. The illustrated operation is an example of a two-pass operation in which two main scanning operations are performed onto each position on the medium 50. Furthermore, in FIG. 5, the areas indicated by letters A to D are areas whose width in the sub-scanning direction corresponds to the number of passes. These areas can also be thought of as band areas corresponding to one pass. Below, these areas will be referred to as areas A to D. Furthermore, the operation will be described with the lower side of the figure as the front side and the upper side as the back side.

[0050] In the first main scanning operation (first scan) of the illustrated operation, the inkjet head 102 ejects ink in a first pass onto area A. In this case, the inkjet head 102 is moved forward from a position corresponding to the front edge of the print data, and ink is ejected onto the medium 50 using only a portion (half) of the rear side of the inkjet head 102. In addition, in a second main scanning operation (second scan), the inkjet head 102 ejects ink in a second pass onto area A, and ejects ink in a first pass onto area B. In this case, for example, as shown in the figure, the entire inkjet head 102 is used to eject ink onto the medium 50. When the second scan is completed, the image drawn by the inkjet head 102 on the front edge (leading end portion) of the medium 50 corresponding to area A is completed.

[0051] Thereafter, by performing a main scanning operation while performing a sub-scanning operation between main scanning operations, the inkjet head 102 ejects ink to each position on the medium 50. In the fourth main scanning operation (fourth scan), which is one before the last main scanning operation (final scan) in the illustrated operation, the inkjet head 102 ejects ink in a second pass onto region C and ejects ink in a first pass onto region D. In this case, too, as shown in the figure, the entire inkjet head 102 is used to eject ink onto the medium 50. In contrast, in the fifth main scanning operation (fifth scan), which is the final scan, the inkjet head 102 is moved further to the back by a sub-scanning operation and then the main scanning operation is performed, ejecting ink in a second pass onto region D. In this case, only a portion (half) of the front side of the inkjet head 102 is used to eject ink onto the medium 50. As a result, during some main scanning operations, such as the first and fifth scans, the inkjet head 102 passes over the gap between the cover 204 and the medium 50 in the front-to-back direction. This gap makes it easier for stray light to strike the inkjet head 102. As a result, nozzle clogging is more likely to occur in the inkjet head 102. In contrast, in this example, by having the inkjet head 102 perform main scanning operations and sub-scanning operations as shown in FIG. 6, for example, this type of problem is less likely to occur.

[0052] FIG. 6 is a diagram showing an example of the main scanning operation and the sub-scanning operation in this example, in which one inkjet head 102 ejects ink to each position on the medium 50. As shown in the figure, in this example, for at least some of the main scanning operation and the sub-scanning operation, the way the inkjet head 102 is moved during the sub-scanning operation and the portion of the inkjet head 102 onto which ink is ejected during the main scanning operation are different from those shown in FIG. 5. This also eliminates the main scanning operation and the sub-scanning operation in which the inkjet head 102 passes over the gap between the cover 204 and the medium 50 in the front-to-rear direction. This operation can also be considered as an operation in which the nozzle array of the inkjet head 102 does not extend beyond the front and rear ends of the print data.

[0053] The operation shown in FIG. 6 , like the operation shown in FIG. 5 , is also an example of a two-pass operation. Regions A to D have a width in the sub-scanning direction corresponding to the number of passes. In the first scan of this example, the inkjet head 102 is moved to a position where the leading edge of the medium 50 overlaps with the leading edge of the inkjet head 102, which is the front end in the sub-scanning direction, and the inkjet head 102 performs a main scanning operation. In controlling the printing operation, it is also possible to treat the printing range (target printing area) on the medium 50 as the range of the medium 50. In this case, the leading edge of the medium 50 can be considered to correspond to the leading edge of the printing range on the medium 50. Aligning the leading edge of the medium 50 with the leading edge of the inkjet head 102 can also be considered to align the position of the leading edge of the inkjet head 102 with the position corresponding to the leading edge of the print data. In the first scan, as shown in the figure, only a portion (half) of the inkjet head 102 on the front side is used to eject ink onto the medium 50. As a result, the inkjet head 102 in the first scan ejects ink onto the region A in the first pass.

[0054] Furthermore, after the first main scan, as shown in the figure, the second main scan is performed without substantially changing the position of the inkjet head 102 in the sub-scanning direction. Not substantially changing the position of the inkjet head 102 in the sub-scanning direction means not changing the position of the inkjet head 102 by more than a small distance required to increase resolution in the sub-scanning direction. By performing multi-pass printing, the printing device 10 can increase the print resolution in the sub-scanning direction beyond the resolution corresponding to the nozzle pitch of the nozzle array. The nozzle pitch is the distance between nozzles in the nozzle array in the sub-scanning direction. For example, between the first and second scans, the inkjet head 102 can be moved relative to the medium 50 by a distance less than the nozzle pitch. Even when the inkjet head 102 is moved by such a short distance relative to the medium 50, it can be considered that the position of the inkjet head 102 in the sub-scanning direction is not substantially changed.

[0055] Furthermore, in the second scan, as shown in the figure, the entire inkjet head 102 is used to eject ink onto the medium 50. As a result, in the second scan, the inkjet head 102 performs a second pass of ink ejection onto region A, and a first pass of ink ejection onto region B. When the second scan is complete, the image drawn by the inkjet head 102 on the leading edge portion of the medium 50 corresponding to region A is completed.

[0056] Thereafter, the inkjet head 102 ejects ink to each position on the medium 50 by performing sub-scanning operations while performing main scanning operations between main scanning operations until the rear end (trailing end) of the inkjet head 102 reaches the rear end (trailing end) of the medium 50. The rear end of the inkjet head 102 reaching the rear end of the medium 50 can be considered to mean that the rear end of the inkjet head 102 reaches the rear end of the medium 50 when a sub-scan operation is performed at a standard movement amount (feed amount) in any sub-scan operation. The rear end of the inkjet head 102 reaching the rear end of the medium 50 during a sub-scan operation can also be considered to mean that the rear end of the inkjet head 102 and the rear end of the medium 50 overlap during or at the end of the sub-scan operation. Furthermore, the standard movement amount in a sub-scan operation is a movement amount determined according to the number of passes. The movement amount determined according to the number of passes is a movement amount corresponding to the distance obtained by dividing the nozzle row length by the number of passes. The nozzle row length is the length of the nozzle row in the sub-scanning direction. In this example, the standard movement amount in the sub-scanning operation is the movement distance corresponding to the distance obtained by dividing the nozzle row length by the number of passes (the distance corresponding to the number of passes). As described above, in controlling the printing operation, it is possible to treat the printing range as the range of the medium 50. In this case, the rear end of the medium 50 is the position corresponding to the other end of the printing range in the sub-scanning direction.

[0057] In the example shown in FIG. 6 , in the sub-scanning operation performed immediately before the fourth scan, the far end of the inkjet head 102 comes to the position of the far end of the medium 50. In this example, after the main scanning operation for the second scan is performed, a sub-scanning operation is performed using the standard movement amount for each main scanning operation until the main scanning operation for the fourth scan is performed. In the main scanning operations for the second scan to the fourth scan, the entire inkjet head 102 is used to eject ink onto the medium 50. In this case, in the third scan, the inkjet head 102 ejects ink in a second pass onto region B, and ejects ink in a first pass onto region C. In the fourth scan, the inkjet head 102 ejects ink in a second pass onto region C, and ejects ink in a first pass onto region D.

[0058] Here, if a sub-scanning operation is performed at the standard movement distance after the fourth main scanning operation, the rear edge of the inkjet head 102 will exceed the rear edge of the medium 50. If such a sub-scanning operation is performed, the inkjet head 102 will pass over the gap between the cover 204 and the medium 50 in the front-to-rear direction during this sub-scanning operation and the next main scanning operation. Stray light will then strike the inkjet head 102 at this gap, making nozzle clogging more likely. Therefore, in this example, the subsequent main scanning operation is performed without performing a sub-scanning operation in which the rear edge of the inkjet head 102 exceeds the rear edge of the medium 50. More specifically, after the fourth main scanning operation, the fifth main scanning operation is performed without substantially changing the position of the inkjet head 102 in the sub-scanning direction. During this main scanning operation, as shown in the figure, only a portion (half) of the rear side of the inkjet head 102 is used to eject ink onto the medium 50. This prevents the inkjet head 102 from passing through the gap (gap in the front-to-rear direction) between the cover 204 and the medium 50. This also makes it possible to properly perform multi-pass printing on the medium 50 without performing a main scanning operation with the inkjet head 102 positioned above the gap in the front-to-rear direction between the cover 204 and the medium 50. Therefore, according to this example, it is possible to prevent stray light (ultraviolet rays) from hitting the inkjet head 102 at the gap between the cover 204 and the medium 50. This also makes it less likely for the nozzles of the inkjet head 102 to become clogged.

[0059] As can be seen from the illustrated operations, in this example, printing is performed on a printing range whose width in the sub-scanning direction is wider than the length of the nozzle array. Furthermore, when focusing on the control performed by the control unit 30 in the printing device 10 regarding this printing operation, it can be thought of as the control unit 30 causing the inkjet head 102 to eject ink on a printing range whose width in the sub-scanning direction is wider than the length of the nozzle array by causing the inkjet head to perform multiple main scanning operations while performing sub-scanning operations between at least some of the main scanning operations.

[0060] 6 is an example of an operation in which the inkjet head 102 is always above the medium 50. The inkjet head 102 always above the medium 50 means that, during a series of printing operations, the inkjet head 102 is not positioned above the gap between the cover 204 and the medium 50, regardless of the timing of the main scanning operation or the sub-scanning operation performed with the ultraviolet irradiator 208 turned on. The function of the printing device 10 performing such a printing operation can also be considered to be a function of completing printing without the inkjet head 102 extending beyond the medium 50. Furthermore, if the range from one end to the other end of the medium 50 in the sub-scanning direction at a position facing the nozzle row of the inkjet head 102 is defined as the facing position medium range, then the printing device 10 can also be considered to cause the inkjet head 102 to perform the sub-scanning operation within a range in which the position of the nozzle row in the sub-scanning direction does not extend beyond the facing position medium range. Furthermore, with regard to such operations, when focusing on the control of the control unit 30, the control unit 30 in this example causes the inkjet head 102 to perform all main scanning operations while the position of the nozzle array in the sub-scanning direction is within the opposing position medium range. Furthermore, the control unit 30 causes the inkjet head 102 to perform sub-scanning operations between at least some of the main scanning operations, thereby causing the inkjet head 102 to print on the entire side surface of the medium 50 at most. Printing on the entire side surface of the medium 50 with the inkjet head 102 can be considered to be ejecting ink from the inkjet head 102 to positions on the entire side surface of the medium 50 where ink needs to be ejected, depending on the image to be printed, etc. Furthermore, printing on the entire side surface of the medium 50 can also be considered to mean that the entire side surface of the medium 50 constitutes a substantial printing range. The term "the entire side surface constitutes a substantial printing range" means that the printing range is an area that an observer perceives as the entire surface, depending on the purpose of printing, etc.

[0061] Furthermore, the print range in this example is the print range indicated by the print data. Furthermore, when considering the relationship between print data and printing operations, as can be understood from the above explanation, the printing operation shown in FIG. 5 corresponding to the conventional method starts printing from the front side of the print data and ends printing from the back side of the print data. Furthermore, when printing on the entire side of the medium 50 or a print range close to it, using print data corresponding to a print range approximately the same size as the medium 50 increases the risk of stray light hitting the inkjet head 102 at the gap in the front-to-back direction. In contrast, this example can appropriately prevent such problems from occurring even when using print data corresponding to a print range approximately the same size as the medium 50.

[0062] As can be seen from the first and second scans in the operation shown in FIG. 6 , the control unit 30 of this example causes the inkjet head 102 to perform main scanning operations a number of times corresponding to the number of passes, while aligning one end (front end) of the medium 50 in the sub-scanning direction (front-rear direction) with one end (front end) of the inkjet head 102 in the sub-scanning direction at a position facing the nozzle row. Aligning one end of the medium 50 with one end of the inkjet head 102 can be thought of as aligning one end of the medium 50 with one end of the nozzle row in the inkjet head 102. The number of times corresponding to the number of passes refers to the number of main scanning operations that need to be performed at that position depending on the number of passes. In the case of the operation shown in FIG. 6 , this number is two. Furthermore, in this example, after causing the inkjet head 102 to perform main scanning operations a number of times corresponding to the number of passes in this state, the control unit 30 causes the inkjet head 102 to perform a sub-scanning operation at a standard movement amount (feed amount) before causing the inkjet head 102 to perform the next main scanning operation. With this configuration, it is possible to properly perform the first number of main scanning operations for the number of passes performed without performing a sub-scanning operation in which the inkjet head 102 passes through the gap between the cover 204 and the medium 50 on one edge side of the medium 50. This also prevents ultraviolet light from hitting the inkjet head 102 at this gap during any of the sub-scanning operations or main scanning operations. This operation can also be considered as starting the first main scanning operation (the main scanning operation for the first scan) with one edge of the medium 50 and one edge of the inkjet head 102 aligned.

[0063] Furthermore, as described above, for example, if the printing resolution in the sub-scanning direction is to be higher than the resolution corresponding to the nozzle pitch, it is also possible to move the inkjet head 102 relative to the medium 50 by a distance less than the nozzle pitch between the first and second scans. For example, it is possible to perform sub-scanning operations a distance shorter than the standard movement amount in the sub-scanning direction while performing main scanning operations for the first number of passes. More specifically, the sub-scanning driver 18 (see FIG. 1 ) moves the inkjet head 102 in the sub-scanning direction relative to the medium 50 by a distance less than the nozzle pitch during at least a portion of the main scanning operations corresponding to the number of passes performed while one edge of the medium 50 is aligned with one edge of the inkjet head 102. As can be seen from the fourth and fifth scans in the operation shown in FIG. 6 , the control unit 30 of this example controls the inkjet head 102 to perform main and sub-scanning operations so as not to perform sub-scanning operations that would position the inkjet head 102 in the gap between the cover 204 and the medium 50, even at the other end (rear end, innermost end) of the medium 50 and the inkjet head 102. This allows for high-resolution printing while more appropriately preventing ultraviolet light from reaching the inkjet head 102 in the gap between the cover 204 and the medium 50. For ease of illustration and explanation, FIG. 6 illustrates an example of main and sub-scanning operations performed by the inkjet head 102 when the width of the medium 50 in the sub-scanning direction is an integral multiple (four times) of the standard movement amount in the sub-scanning operation. However, the size of the medium 50 may differ from that shown in FIG. 6 , as in the example shown in FIG. 7 , for example.

[0064] FIG. 7 shows another example of the main scanning operation and sub-scanning operation in this embodiment, illustrating an example in which a medium 50 larger in size in the sub-scanning direction than the example shown in FIG. 6 is used. FIG. 7( a) shows an example of the position of the inkjet head 102 during the Nth and (N+1)th main scanning operations performed on a medium 50 of a predetermined size. FIG. 7( b) shows an example of the position of the inkjet head 102 during the (N-1)th and Nth main scanning operations performed on a medium 50 of a predetermined size different from that shown in FIG. 7( a). The width of the medium 50 in FIG. 7( a) in the sub-scanning direction is larger than the width of the medium 50 in FIG. 6 by an integer multiple of the standard movement amount of the sub-scanning operation. Then, during the sub-scanning operation performed immediately before the Nth (N is a predetermined integer) main scanning operation, the rear end (trailing edge) of the inkjet head 102 reaches the rear end position of the medium 50. After the Nth main scanning operation has been performed, the inkjet head 102 is caused to perform the necessary number of main scanning operations thereafter without substantially changing the position of the inkjet head 102 in the sub-scanning direction, as shown as the N+1th main scanning operation in the figure. In this case, as in the case of the fifth main scanning operation in Figure 6, for example, only a portion (half) of the inkjet head 102 on the far side is used to eject ink onto the medium 50. Also in this case, between the multiple main scanning operations performed in this state, the inkjet head 102 is caused to perform sub-scanning operations, as necessary, in which the inkjet head 102 moves relatively a distance less than the nozzle pitch.

[0065] FIG. 7B shows an example in which the width of the medium 50 in the sub-scanning direction is slightly smaller than that of the medium 50 shown in FIG. 7A. In FIG. 7B, area F is smaller than that shown in FIG. 7A. The width of the medium 50 in the sub-scanning direction shown in FIG. 7B is not an integer multiple of the standard movement amount in the sub-scanning operation. In this case, if the inkjet head 102 is caused to perform a sub-scanning operation at the standard movement amount after the main scanning operation at the (N-1)th scan shown in the figure, the rear edge of the inkjet head 102 will exceed the position of the rear edge of the medium 50. Therefore, in the sub-scanning operation after the main scanning operation at the (N-1)th scan, the inkjet head 102 is caused to perform a sub-scanning operation at a movement amount smaller than the standard movement amount, so that the position of the rear edge of the inkjet head 102 is aligned with the position of the rear edge of the medium 50. This configuration appropriately prevents the inkjet head 102 from moving outside the range facing the medium 50. Furthermore, in subsequent main scanning operations from the Nth scan onwards, ink is ejected onto the area to be targeted for ink ejection using only a portion of the inkjet head 102. With this configuration, even if the width in the sub-scanning direction is not an integral multiple of the standard movement amount in the sub-scanning operation, ink can be ejected onto the medium 50 without the inkjet head 102 extending beyond the range facing the medium 50.

[0066] 6 and 7 , the sub-scanning operation performed near the rear edge of the medium 50 can also be considered in terms of the control of the control unit of the printing device 10. In the following description, the edge of the inkjet head 102 may be considered to refer to the edge of the nozzle array of the inkjet head 102. More specifically, assuming that the movement amount of the sub-scanning operation is the standard movement amount, the control unit 30 either moves the inkjet head 102 by an amount that causes the rear edge of the nozzle array to reach the rear edge of the medium 50 during the sub-scanning operation in which the rear edge (other end) of the nozzle array passes the rear edge (other end) of the medium 50, or does not move the inkjet head 102 at all. This prevents the end of the inkjet head 102 from passing the edge of the medium 50 on the rear side. This also more appropriately prevents ultraviolet light from reaching the inkjet head 102 at the gap between the cover 204 (see FIG. 2 ) of the holding jig 40 and the medium 50. Furthermore, as described above, the control unit 30 causes the inkjet head 102 to perform a sub-scanning operation in which the rear end of the nozzle array reaches the position of the rear end of the medium 50 in the sub-scanning direction, and then causes the inkjet head 102 to perform multiple main scanning operations as necessary while aligning the rear end of the medium 50 with the rear end of the nozzle array. This allows the necessary number of main scanning operations to be performed over an area including the rear end of the medium 50. The state in which the rear end of the medium 50 is aligned with the rear end of the nozzle array may be a state in which the distance between the rear end of the medium and the rear end of the nozzle array is equal to or less than the nozzle pitch. Furthermore, the rear end of the medium 50 may be the rear end of the printing range. In this case, aligning the rear end of the medium 50 with the rear end of the nozzle array can be considered to be aligning the position of the end of the print data on the rear side of the medium 50 with the position of the rear end of the nozzle array. In this state, the control unit 30 causes the inkjet head 102 to perform main scanning operations for the number of passes. For ease of illustration and explanation, the above description has primarily focused on operations for performing two-pass printing. However, the number of passes for printing may be a number other than two.In this case, too, by performing an operation according to the number of passes in the same or similar manner as described above, it is possible to appropriately eject ink onto the medium 50. Furthermore, by appropriately changing the number of main scanning operations performed without substantially changing the position of the inkjet head 102 in the sub-scanning direction on the front or back side of the medium 50, it is possible to appropriately perform an operation according to the number of passes even when the number of passes is greater than two.

[0067] As described above, in this example, by performing the main scanning and sub-scanning operations of the inkjet head 102 at positions that correspond to the size of the medium 50, stray light leaking from the holding jig 40 can be appropriately prevented from hitting the inkjet head 102. Furthermore, even when printing is performed to the full size of the medium 50, nozzle clogging due to stray light is less likely to occur, making it possible to more appropriately print using large-sized print data. This also allows for more appropriate printing on the entire side of the medium 50. Furthermore, the effects of stray light can be appropriately reduced by controlling the main scanning and sub-scanning operations by the control unit 30 without adding any new components to the printing device 10. To more appropriately reduce the effects of stray light, it is preferable to prevent stray light from leaking outside the holding jig 40. As described above, it is important to prevent a large gap from occurring between the cover 204 of the holding jig 40 and the medium 50. In this example, the sensor 20 is used to detect the state of the gap between the cover 204 and the medium 50. The operation of detecting the state of the gap using the sensor 20 will be described in more detail below.

[0068] FIG. 8 is a diagram showing an example of an operation for detecting the state of a gap using the sensor 20, and shows an example of a path along which the sensor 20 moves when detecting the state. As described above, in this example, the holding jig 40 has white tape 232 attached to a predetermined position on the magnetic sheet 224 that constitutes the cover 204. The tape 232 increases the light reflectivity, thereby enabling more appropriate detection using the sensor 20. The tape 232 indicates the location where detection by the sensor 20 is performed. The tape 232 can also be attached to the medium 50 as needed. For example, when using a medium 50 with a color that does not reflect light well, it is possible to attach the tape 232 to the medium 50.

[0069] The control unit 30 (see FIG. 1 ) of the printing device 10 moves the sensor 20 along a path capable of detecting light reflected from the cover 204 and the tape 232 of the medium 50. The control unit 30 moves the sensor 20 by controlling the operation of the sensor moving means 22 (see FIG. 1 ). In this example, the control unit 30 moves the sensor 20 along multiple paths indicated by arrows in the figure. These multiple paths include a front path, a rear path, and a center path on the medium 50. The front path is an example of a one-end path that passes near one end of the medium 50 at a position facing the nozzle row of the inkjet head 102 (see FIG. 1 ) during printing. The rear path is an example of an other-end path that passes near the other end of the medium 50 at a position facing the inkjet head 102 during printing. The center path is an example of an intermediate position path that passes over the medium 50 between the one-end path and the other-end path. These paths extend in a direction intersecting the nozzle row direction. Furthermore, as can be understood from the illustrated configuration, these paths can also be considered as paths that pass through the edge of the opening 220 of the cover 204. The multiple paths along which the sensor 20 is moved may include other paths. Furthermore, the control unit 30 of this example moves the sensor 20 along these paths and detects the state of the gap between the cover 204 and the medium 50 based on the acquired output of the sensor 20. This makes it possible to appropriately prevent unintended leakage of ultraviolet light due to misalignment of the cover 204, etc.

[0070] As described above, the control unit 30 in this example detects the state of the gap between the cover 204 and the medium 50 based on the output of the sensor 20. The control unit 30 detects the state of the gap by detecting a change in the output of the sensor 20 that occurs at the position of the gap. As described above, the cover 204 in this example uses a magnetic sheet 224 shaped to match the shape of the medium 50, making it less likely for an unnecessary gap to form between the opening 220 and the medium 50. However, even in this case, a certain degree of step will occur at the edge of the opening 220. Therefore, when the sensor 20 is moved along a path that passes the edge, a change in output corresponding to the step will occur at the edge. This allows the control unit 30 to detect the position of the edge of the opening 220. In this case, if the gap at the edge becomes larger due to, for example, a misalignment in the height of the cover 204, the output of the sensor 20 will change depending on the size of the gap. This change in output reflects the state of the gap. The control unit appropriately detects the state of the gap based on the output of the sensor 20 and its change. In this example, the sensor 20 detects reflected light from the cover 204 and the medium 50. The control unit 30 then detects the gap status based on the light detected by the sensor 20. The control unit 30 determines that the gap is large when the reflectance at the edge of the opening 220 is smaller than a predetermined reference value. The reflectance detected by the sensor 20 can also be considered to reflect the distance between the cover 204 and the medium 50. Therefore, the control unit 30 can also be considered to be detecting this distance. In this example, the sensor 20 is moved along the front, back, and center paths as described above. This allows the gap status to be properly detected over a wide range of the medium 50. This also allows proper confirmation that the medium 50 and cover 204 are properly installed.

[0071] It is also possible to turn off the ultraviolet irradiator 208 (see FIG. 2) of the holding jig 40 while using the sensor 20 to detect the gap condition. This configuration allows for more accurate detection of changes in reflectance occurring at the edge of the opening 220. In a modified version of the gap condition detection operation, the sensor 20 may perform detection while the ultraviolet irradiator 208 is turned on. To more reliably prevent unintended leakage of ultraviolet light from the gap between the cover 204 and the medium 50, it is also possible to directly detect the actual leaking ultraviolet light. For example, while the ultraviolet irradiator 208 irradiates the outer surface of the medium 50 with ultraviolet light, the control unit 30 may further detect ultraviolet light leaking from the gap between the edge of the opening 220 of the cover 204 and the medium 50 based on the output of the sensor 20. This configuration allows for more accurate detection of unintended leakage of ultraviolet light due to misalignment of the cover 204, etc. In this case, it is also possible to move the sensor 20 along the same path as when detecting the gap condition. Alternatively, when detecting the actual leaking ultraviolet light, the sensor 20 may be moved along a different path than when detecting the state of the gap. Furthermore, it is preferable to detect the actual leaking ultraviolet light not only at a position corresponding to the gap between the cover 204 and the medium 50 in the lateral direction of the medium 50, but also at a position corresponding to the gap in the front-to-rear direction.

[0072] Next, the operation of detecting the gap between the cover 204 and the medium 50 will be described in more detail. FIG. 9 is a flowchart illustrating an example of the operation of detecting the gap in the printing device 10. The operation illustrated in FIG. 9 is an example of a detection method for detecting the state of the printing device 10. Detecting the state of the printing device 10 refers to detecting the state of the printing device 10 and the holding jig 40 used in the printing device 10. The operation illustrated in FIG. 9 can also be considered an example of a work set detection operation. Work set detection is detecting whether the medium 50 is properly installed relative to the holding jig 40. Proper installation of the medium 50 relative to the holding jig 40 means that the medium 50 is properly installed, and the height of the cover 204 of the holding jig 40 and the position of the magnetic sheet 224 on the cover 204 are appropriate to match the position (height, etc.) of the medium 50. In this example, the control unit 30 of the printing device 10 initiates control related to work set detection in response to a user instruction. In this case, for example, a menu (for example, a work set detection execution selection screen) is displayed on the monitor of the printing device 10 or the computer (control PC) that controls the operation of the printing device 10 to accept user instructions.

[0073] In the control operation for workpiece set detection, the control unit 30 receives a user's designation of a detection position for detecting the gap condition (S102). The control unit 30 receives user instructions, for example, by having the user operate an input device (e.g., an LED pointer, up / down keys, etc.) that inputs information to the printing device 10. The control unit 30 in this example also receives user designation of detection positions corresponding to the front, back, and center paths shown in FIG. 8 . This configuration allows for appropriate setting of a preferred detection position even when the printing range changes depending on the chuck used as the shaft 226 in the rotation mechanism 206 of the holding jig 40 or the medium 50. After receiving the user's designation of the detection position, the control unit 30 controls the operation of the sensor moving unit 22 to move the sensor 20 along the path corresponding to the detection position. The control unit 30 then executes a detection operation to acquire the output (sensor value) of the sensor 20 (S104).

[0074] The control unit 30 also detects the state of the gap between the cover 204 and the medium 50 based on the output of the sensor 20 detected in step S104, and determines whether there is a problem with the state of the gap (S106). As described above, the control unit 30 in this example determines that the gap is widening if the reflectance at the edge of the opening 220 is smaller than a predetermined reference value. Therefore, in step S106, the control unit 30 determines that there is a problem with the state of the gap if the output of the sensor 20 is below a predetermined threshold at any position.

[0075] If the output of the sensor 20 is not below the threshold value along any of the paths, the control unit 30 determines that there is no problem with the gap condition (Yes in S106) and terminates the work set detection operation. On the other hand, if the output of the sensor 20 is below the threshold value at any position along any of the paths, the control unit 30 determines that there is a problem with the gap condition (No in S106). In this case, the control unit 30 displays an error message on the monitor of the printing device 10 or the computer that controls the operation of the printing device 10 (S108). In this example, after the user confirms the error message, the control unit 30 displays a screen on the monitor or the like that prompts the user to install the cover 204 again (cover set) (S110), and terminates the work set detection operation.

[0076] In this example, the operation of step S104 may be affected by errors. Therefore, if it is determined in step S106 that the output of sensor 20 is below the threshold at any position on any path, the process may return to step S104 and acquire the output of sensor 20 again. In this case, in step S106, the control unit 30 determines that there is a problem with the gap condition if the output of sensor 20 is still below the threshold at any position even after a preset number of times (e.g., about three times). This configuration allows the work set detection operation to be performed more appropriately.

[0077] Next, supplementary explanations will be given regarding the various components described above. As described above, the printing device 10 of this example prints on the medium 50 while rotating the medium 50. A cylindrical (cylindrical) medium, for example, can be suitably used as the medium 50. A cylindrical medium is a medium shaped like a body of revolution whose cross section in a plane perpendicular to the axis of rotation is circular. Furthermore, media 50 having shapes other than a cylindrical shape can also be used. A medium shaped like a body of revolution can also be suitably used as a medium shaped like a body of revolution. Examples of such media include conical and truncated conical media. Furthermore, when a conical or truncated conical medium is used, the holding jig 40 holds the medium so that the height of the medium is constant at a position facing the inkjet head 102 (the position where the ink lands). In this case, for example, it is possible to hold the medium so that the generatrix of the conical or other shaped medium at the position facing the inkjet head 102 is horizontal by appropriately tilting the rotation axis that rotates the medium relative to the horizontal direction.

[0078] Furthermore, when printing on the medium 50 while rotating the medium 50 as in this example, it is conceivable that a seam 302a of the image will occur on the side of the medium 50, as shown in Fig. 10. Fig. 10 is a diagram illustrating how to print on the side of the medium 50. Figs. 10(a) and 10(b) show examples of how to print on the side of the medium 50.

[0079] As can be seen from the seam 302a shown in FIG. 10 , the seam 302a of the image on the side surface of the medium 50 can be considered to be, for example, the boundary between the position where ink is first ejected onto the side surface during main scanning (the drawing start position) and the position where ink is last ejected onto the side surface during main scanning (the drawing end position). The seam 302a is typically formed in a straight line, as shown in FIG. 10A , for example. The straight seam 302a is a seam where ink dots formed by ink ejected at the drawing start and drawing end positions during main scanning are aligned in a straight line. In this case, to prevent the background color of the medium 50 from being visible at the seam 302a, for example, ink dots are overlapped at the seam 302a, drawing a dark line corresponding to the seam 302a and making the seam 302a more noticeable. In order to make the seam 302a less noticeable, it is possible to form a non-linear seam 302a, as shown in FIG. 10B. A non-linear seam 302a is a seam where the ink dots formed by ink ejected at the start and end positions of the main scanning operation are not aligned in a straight line. In this case, it is possible to form a jagged seam 302a, as shown in the figure, for example. This configuration can more appropriately prevent the seam 302a from being noticeable. This also allows for appropriate printing on the side of the medium 50 with higher quality.

[0080] Next, the adjustments made to the printing device 10 in this example will be described. FIG. 11 is a diagram illustrating the target of adjustment in one example of adjustment made to the printing device 10. FIG. 11( a) shows an example of a correct state in which no adjustment is necessary. The state shown in FIG. 11( a) can also be considered a state in which appropriate adjustment has been made. FIG. 11( b) shows an example of a state in which adjustment is necessary. As described above, the inkjet head 102 in this example has two nozzle rows 112. As shown in FIG. 11( a), with one inkjet head 102 facing the medium 50, ink is ejected from the multiple nozzle rows 112 onto the medium 50. The main scanning driver 16 (see FIG. 1) ejects ink from each nozzle row 112 at a timing adjusted to match the differences in the positions of the nozzle rows 112, thereby causing the inkjet head 102 to eject ink to ejection positions set according to the printing resolution. The inkjet head 102 also ejects ink of different colors from the multiple nozzle rows 112. 11 , the inkjet head 102 has a nozzle row 112 indicated as row A in the figure and a nozzle row 112 indicated as row B. The inkjet head 102 ejects magenta (M) ink from the nozzle row 112 in row A, and ejects black (K) ink from the nozzle row 112 in row B. If the position of the inkjet head 102 relative to the medium 50 is correctly adjusted, the magenta and black inks ejected into the same printing range will overlap in the same range, as shown in the right part of FIG. 11A , for example.

[0081] However, the positions of the holding jig 40, the inkjet head 102, etc. may be subject to, for example, mechanical dimensional errors (mechanical dimensional errors). As a result, the position of the inkjet head 102 relative to the medium 50 (the relative position of the inkjet head 102) may deviate from the reference position. The reference position here refers to a position that corresponds to a predetermined correct position. Such positional deviations include, for example, a deviation between the center of the inkjet head 102 and the center of the medium 50 in the left-right direction (main scanning direction) in the figure. The left-right direction here is an example of a direction perpendicular to the rotation axis of the medium 50.

[0082] In this regard, when printing on a flat medium such as paper or film, rather than a three-dimensional medium 50 as in this example, even if a misalignment occurs in the relative position of the inkjet head 102 with respect to the medium 50, only the area printed on the medium 50 is misaligned, and the printed content itself typically remains unchanged. In contrast, when printing on a three-dimensional medium 50 as in this example, if a misalignment occurs in the relative position of the inkjet head 102 with respect to the medium 50, an unintended misalignment occurs in the head gap, which is the distance between the inkjet head 102 and the medium 50 when ejecting ink. As a result, the printed content itself also changes. As described above, in this example, the inkjet head 102 is caused to eject ink by aligning the midpoint between row A and row B of the inkjet head 102 with the rotation axis of the medium 50 in the left-right direction. If there is no misalignment in the relative position of the inkjet head 102 with respect to the medium 50, the head gap at the positions of the nozzle rows 112 of row A and row B will be the same distance, as shown, for example, in the left portion of FIG. 11A . In contrast, if there is a deviation in the relative position of the inkjet head 102 with respect to the medium 50, the head gap at the position of one of the nozzle rows 112 of row A and row B will be larger than in the case shown in FIG. 11( a), and the head gap at the position of the other nozzle row 112 will be smaller than in the case shown in FIG. 11( a). For example, in the left part of FIG. 11( b), the head gap at the position of the nozzle row 112 of row A, which ejects magenta ink, is larger, and the head gap at the position of the nozzle row 112 of row B, which ejects black ink, is smaller. In this case, the ink ejected from one nozzle row 112 travels a longer distance to land on the medium 50, while the ink ejected from the other nozzle row 112 travels a shorter distance to land on the medium 50, resulting in a deviation in the landing positions. In the case shown in FIG. 11( b), the magenta ink will land to the right of the intended design position. Furthermore, the black ink will land to the left of the intended design position.As a result, even when magenta and black inks are ejected onto the same print area by design, there will be a discrepancy in the area onto which the inks are ejected, as shown on the right side of FIG. 11B, for example.

[0083] Therefore, in order to more appropriately print on the three-dimensional medium 50, it is desirable to perform adjustments to the printing device 10 to prevent the above-mentioned deviation in the ink ejection range. In this example, an example of such an adjustment is to adjust the relative position of the inkjet head 102 with respect to the medium 50, as described below. Another example of such an adjustment is to align the center position of the inkjet head 102 with the center position of the medium 50 in the left-right direction. This adjustment can also be considered as an adjustment to reduce deviation in the landing position of each nozzle row 112 for the multiple nozzle rows 112 in a single inkjet head 102 (adjusting the landing deviation for each nozzle row within one head). In this example, this adjustment is performed by having the printing device 10 print the patterns shown in FIGS. 12 and 13 and appropriately changing the position of the inkjet head 102 according to the state of the printed pattern.

[0084] 12 and 13 are diagrams illustrating patterns that are drawn by the printing device 10 when the printing device 10 is adjusted. These patterns are examples of patterns that the control unit 30 (see FIG. 1) draws on the inkjet head 102 when the printing device 10 is adjusted. FIG. 12( a) is a diagram illustrating patterns 302a and 302b that are drawn by the inkjet head 102 when the control unit 30 (see FIG. 1) draws on the inkjet head 102. FIG. 12( b) shows an example of the state of patterns 302a and 302b that are drawn when there is no misalignment in the relative position of the inkjet head 102 with respect to the medium 50. FIGS. 13( a) and 13(b) show an example of the state of patterns 302a and 302b that are drawn when there is a misalignment in the relative position of the inkjet head 102 with respect to the medium 50.

[0085] During the adjustment, the control unit 30 of this example causes the multiple nozzle rows 112 of one inkjet head 102 to draw predetermined patterns 302a and 302b. The inkjet head 102 draws pattern 302a by ejecting ink from one of the two nozzle rows 112. Then, it draws pattern 302b by ejecting ink from the other nozzle row 112. In this example, pattern 302a is an example of a first pattern. Pattern 302b is an example of a second pattern. Furthermore, one nozzle row 112 that draws pattern 302a is an example of a first nozzle row. The other nozzle row 112 that draws pattern 302b is an example of a second nozzle row that is different from the first nozzle row. Furthermore, in this case, the position of one nozzle row 112 that draws pattern 302a is an example of a first position. The position of the other nozzle row 112 that draws pattern 302b is an example of a second position that is different from the first position. Furthermore, with regard to the operation of the inkjet head 102, the operation of drawing pattern 302a with one nozzle row 112 is an example of an operation of drawing a first pattern with ink ejected from the nozzles of the nozzle row 112 when the position of the nozzle row 112 relative to the medium 50 is at a first position. The operation of drawing pattern 302b with the other nozzle row 112 is an example of an operation of drawing a second pattern with ink ejected from the nozzles of the nozzle row 112 when the position of the nozzle row 112 relative to the medium 50 is at a second position. The inkjet head 102 shown in Figure 12(a) draws pattern 302a with nozzle row A 112 that ejects magenta ink. Then, pattern 302b is drawn with nozzle row B 112 that ejects black ink.

[0086] For ease of illustration and explanation, the right side of Fig. 12(a) shows the magenta pattern with a dashed line and the black pattern with a solid line to indicate the difference in ink color. Furthermore, although the patterns 302a and 302b are depicted with offset positions in Fig. 12(a), during actual adjustment, the control unit 30 causes the inkjet head 102 to draw the patterns 302a and 302b so that, as designed, the patterns 302a and 302b overlap on the medium 50 in the main scanning direction corresponding to the left-right direction in Fig. 12(b), for example. Here, "the patterns 302a and 302b overlap as designed" means that the patterns 302a and 302b overlap when the relative position of the inkjet head 102 with respect to the medium 50 is aligned with a reference position (not deviated from the reference position). Furthermore, the multiple patterns 302a and 302b are an example of patterns that are drawn at the same position in the main scanning direction on the medium 50 when the relative position of the inkjet head 102 with respect to the medium 50 is a reference position. Drawing the patterns 302a and 302b at the same position in the main scanning direction can be considered to mean that they are drawn at substantially the same position with a precision according to the quality required for printing, etc. Furthermore, when the medium 50 is rotated by the holding jig 40 (see FIG. 1 ) as in this example, drawing the patterns 302a and 302b at the same position in the main scanning direction can also be considered to mean that the patterns 302a and 302b are drawn at the same position in the rotation direction of the medium 50.

[0087] In this example, the positions of the medium 50 and the nozzle arrays A and B of the nozzle array 112 are in the relationship shown in the left portion of FIG. 12A . Specifically, the relative position of the inkjet head 102 is fixed so that the nozzle arrays A and B of the nozzle array 112 are positioned on opposite sides of the rotation center of the medium 50 in the main scanning direction. In this state, the control unit 30 ejects ink from the nozzles of the nozzle arrays A and B, causing the inkjet head 102 to draw patterns 302a and 302b. This configuration allows the patterns 302a and 302b to be properly drawn using multiple nozzle arrays 112 included in a single inkjet head 102. Furthermore, in this case, it is possible to align the central positions of the nozzle array A and the nozzle array B in the main scanning direction with the rotation axis of the medium 50, as in the example shown in FIG. 11A . This configuration allows the head gaps of the multiple nozzle arrays 112 to be aligned when the relative position of the inkjet head 102 with respect to the medium 50 is aligned with the reference position. This also allows the inkjet head 102 to easily and appropriately write the overlapping patterns 302a and 302b on the medium 50 when the relative position of the inkjet head 102 is aligned with the reference position.

[0088] Furthermore, in this example, if the relative position of the inkjet head 102 with respect to the medium 50 is deviated from the reference position, a deviation in the impact position occurs, resulting in a deviation in the positions (positions in the main scanning direction) where patterns 302a and 302b are drawn on the medium 50, as shown in Figures 13(a) and 13(b). For example, when the medium 50 is rotated in the rotation direction indicated by the arrow in the figure, if the head gap becomes smaller due to a deviation in the relative position of the inkjet head 102, the amount of rotation of the medium 50 before the ink lands becomes smaller, resulting in a deviation in the impact position toward the left in the figure, which is downstream in the rotation direction of the medium 50. Furthermore, if the head gap becomes larger, the amount of rotation of the medium 50 before the ink lands becomes larger, resulting in a deviation in the impact position toward the right in the figure, which is upstream in the rotation direction of the medium 50. Figure 13(a) shows an example in which the relative position of the inkjet head 102 with respect to the medium 50 is deviated to the right in the figure, as shown in the left part of the figure. In this case, as shown in the right part of the figure, the state of the patterns 302a and 302b is such that the pattern 302a corresponding to the nozzle row A 112 is shifted to the left relative to the pattern 302b corresponding to the nozzle row B 112. Therefore, in this case, an adjustment is made to move the position of the inkjet head 102 to the left based on the state of the patterns 302a and 302b. Also, FIG. 13B shows an example in which the relative position of the inkjet head 102 with respect to the medium 50 is shifted to the left, as shown in the left part of the figure. In this case, as shown in the right part of the figure, the state of the patterns 302a and 302b is such that the pattern 302a is shifted to the right relative to the pattern 302b. Therefore, in this case, an adjustment is made to move the position of the inkjet head 102 to the right based on the state of the patterns 302a and 302b. This example makes it possible to properly detect whether the relative position of the inkjet head 102 with respect to the medium 50 is aligned with the reference position. This also makes it possible to properly adjust the relative position of the inkjet head 102 as necessary.

[0089] Here, the state in which the patterns 302a and 302b in this example overlap indicates a state in which there is no problem with the relative position of the inkjet head 102. By adjusting the relative position of the inkjet head 102 so that the patterns 302a and 302b overlap, the relative position of the inkjet head 102 can be appropriately adjusted. By appropriately adjusting the relative position of the inkjet head 102, printing can be performed more appropriately on the three-dimensional medium 50. Furthermore, the multiple nozzle rows 112 of the inkjet head 102 in this example have known relative positions and are formed at predetermined positions on the inkjet head 102. Adjusting the relative position of the inkjet head 102 with respect to the medium 50 corresponds to adjusting the relative position of the nozzle rows 112 with respect to the medium 50. In this case, the patterns 302a and 302b can also be considered as patterns for adjusting the deviation in landing position that occurs between the multiple nozzle rows 112 with known relative positions. In addition, adjusting the relative position of the inkjet head 102 can also be thought of as adjusting the relative position of the nozzle rows 112 with respect to the medium 50 without changing the relative positional relationship between the nozzle rows 112 for multiple nozzle rows 112.

[0090] Furthermore, as can be understood from the above description, if the relative position of the inkjet head 102 with respect to the medium 50 in this example is misaligned, the patterns 302a and 302b will be misaligned in a direction corresponding to the direction of the misalignment of the inkjet head 102. Therefore, the patterns 302a and 302b can also be considered as patterns for detecting the direction of the misalignment of the relative position of the inkjet head 102. In this example, the greater the misalignment of the inkjet head 102, the greater the misalignment of the patterns 302a and 302b. Therefore, the patterns 302a and 302b can also be considered as patterns whose overlapping pattern changes depending on the degree of misalignment when the relative position of the inkjet head 102 is misaligned from the reference position. Furthermore, in a modified example of the adjustment operation for the printing device 10, if the relative position of the inkjet head 102 is adjusted with higher precision, it is also possible to use additional patterns for detecting the magnitude of the misalignment of the relative position of the inkjet head 102. For example, in addition to the patterns 302a and 302b described above, it is also possible to use patterns that overlap when the magnitude of the misalignment of the inkjet head 102 is a predetermined magnitude. As such patterns, for example, it is conceivable to use a plurality of sets of patterns each having a different magnitude of overlapping deviation between the patterns. With this configuration, it is possible to appropriately detect the magnitude of deviation in the relative position of the inkjet head 102.

[0091] As described above, the printing device 10 of this example includes multiple inkjet heads 102. The relative position of any of the inkjet heads 102 with respect to the medium 50 can be adjusted. In this case, it is also possible to adjust the positions of the other inkjet heads 102 with respect to the inkjet head 102 whose relative position with respect to the medium 50 has been adjusted. In this case, the control unit 30 of the printing device 10 causes the multiple inkjet heads 102 to draw patterns for detecting deviations in the distance between the inkjet heads 102. Such patterns are an example of inter-head distance adjustment patterns used to adjust the distance between the inkjet heads 102. In this case, the control unit 30 causes the multiple inkjet heads 102 to draw inter-head distance adjustment patterns in addition to the above-described patterns 302a and 302b.

[0092] FIG. 14 is a diagram illustrating a method for adjusting the distance between the inkjet heads 102. FIGS. 14( a) and 14(b) are diagrams illustrating problems that arise when the distance between the inkjet heads 102 is misaligned. FIG. 14(a) illustrates a state in which there is no misalignment in the distance between the inkjet heads 102. FIG. 14(b) illustrates an example of a state in which there is a misalignment in the distance between the inkjet heads 102. As described above, in this example, the multiple inkjet heads 102 are moved in sequence to directly above the rotating medium 50 so as to face the medium 50. The control unit 30 causes the multiple inkjet heads 102 to eject ink onto the medium 50 in sequence. At this time, the control unit 30 moves the head unit 12 (see FIG. 1) having the multiple inkjet heads 102 according to the designed distance between the inkjet heads 102.

[0093] If the inkjet heads 102 are attached to the head unit 12 in the correct positions and there is no deviation in the distance between the inkjet heads 102, the inkjet heads 102 will always face the medium 50 correctly, even if the inkjet head 102 facing the medium 50 is changed, as shown in FIG. 14A, for example. More specifically, if the relative position of the leftmost inkjet head 102 with respect to the medium 50 is correctly adjusted, the inkjet heads 102 from the second left (the second, third, and fourth) can also be sequentially moved appropriately to directly above the medium 50. This allows the central positions of all inkjet heads 102 in the main scanning direction to be aligned with the center position of the medium 50, thereby ejecting ink. However, if there is a deviation in the distance between the inkjet heads 102 at any position on the head unit 12, as shown in FIG. 14B, for example, the inkjet head 102 that is newly placed facing the medium 50 will not face the medium 50 correctly. More specifically, in the case shown in Figure 14(b), the distance Lh between the leftmost inkjet head 102 in the figure and the inkjet head 102 adjacent to it (the second inkjet head 102) is greater than the correct distance (the original distance). In this case, since it is impossible to know the actual distance Lh, the control unit 30 moves the head unit 12 based on the designed distance between the inkjet heads 102. As a result, the positions of the second and subsequent inkjet heads 102 are shifted from directly above the medium 50. If printing is performed in this state, the ink landing position will be shifted, preventing proper printing.

[0094] In contrast, in this example, the distance between the inkjet heads 102 is further adjusted by causing the multiple inkjet heads 102 to draw patterns 304a and 304b shown in Fig. 14(c). Fig. 14(c) shows an example of patterns 304a and 304b used when adjusting the distance between the inkjet heads 102. The patterns 304a and 304b are patterns for adjusting the variation in the distance between the inkjet heads 102. The patterns 304a and 304b can also be considered as patterns for detecting deviations in landing positions that occur between the inkjet heads 102.

[0095] As described above, the inkjet head 102 in this example has two nozzle rows 112. The control unit 30 draws the pattern 304a with ink ejected from the nozzles of one of the nozzle rows 112 of one of the inkjet heads 102. The control unit 30 also draws the pattern 304b with ink ejected from the nozzles of one of the nozzle rows 112 of the other inkjet head 102. The control unit 30 sets one of the inkjet heads 102 in the head unit 12 as the reference inkjet head 102 and causes that inkjet head 102 to draw the pattern 304a. Then, the control unit 30 selects one inkjet head 102 to be aligned with the reference inkjet head 102 and causes that inkjet head 102 to draw the pattern 304b. In this case, it is preferable to use different patterns as the patterns 304a and 304b, as shown in the figure, for example. This configuration makes it possible to easily and appropriately distinguish between the patterns 304a and 304b. Furthermore, patterns 304a and 304b can be suitably used that at least partially overlap on the medium 50 when the distance between the inkjet heads 102 is correct. In this example, pattern 304a includes vertical lines extending in the up-down direction and horizontal lines extending in the left-right direction. In contrast, pattern 304b includes only vertical lines, not horizontal lines. When the distance between the inkjet heads 102 is correct, the vertical line portions of pattern 304a overlap the vertical line portions of pattern 304b on the medium 50. This configuration makes it possible to properly detect whether the distance between the inkjet heads 102 is correct. Based on the detection results, the distance between the inkjet heads 102 can be adjusted.

[0096] FIG. 14C shows an example of patterns 304a and 304b when the distance between the inkjet heads 102 is off and requires adjustment. In FIG. 14C, pattern 304b drawn by the inkjet head 102 to be adjusted is drawn to the left of pattern 304a drawn by the reference inkjet head 102. This indicates that the distance between the inkjet heads 102 is wider than the correct distance, causing the ink ejected by the inkjet head 102 to be adjusted to be off to the left of the correct position. Conversely, if pattern 304b were drawn to the right of pattern 304a, this would mean that the distance between the inkjet heads 102 is narrower than the correct distance. In this example, adjustment of the distance between the inkjet heads 102 can be achieved by, for example, adjusting the movement distance of the head unit 12 when changing the inkjet head 102 facing the medium 50. For example, if the distance between the inkjet heads 102 is wider than the correct distance, adjustment to increase the movement distance can be performed. Furthermore, if the distance between the inkjet heads 102 is narrower than the correct distance, adjustment may be made to shorten the movement distance.

[0097] The patterns 304a and 304b in this example are an example of a pattern whose state changes depending on the distance between the multiple inkjet heads 102. As a modified example of the adjustment operation for the printing device 10, it is also possible to use a pattern for detecting the magnitude of deviation in the distance between the inkjet heads 102 in order to adjust the distance between the inkjet heads 102 with higher accuracy. For example, in addition to the above-described patterns 304a and 304b, it is also possible to use a pattern that overlaps when the magnitude of deviation in the distance between the inkjet heads 102 is a predetermined magnitude. It is also possible to use multiple sets of patterns such that the magnitude of deviation in the overlap of the patterns differs from one another. With this configuration, it is possible to appropriately detect the magnitude of deviation in the distance between the inkjet heads 102.

[0098] Next, supplementary explanations and explanations of modified examples regarding the above-described components will be provided. As described above, in this example, adjustments to the printing device 10 are made by causing the inkjet heads 102 to eject ink under the control of the control unit 30 of the printing device 10. Furthermore, these adjustments include adjustments to the relative positions of the inkjet heads 102 with respect to the medium 50 and adjustments to the distance between the inkjet heads 102. This can be considered to be an adjustment function of the printing device 10. Furthermore, this adjustment can also be considered to be adjustments to the landing positions of ink of each color ejected from the multiple inkjet heads 102. The pattern drawn by the inkjet heads 102 during adjustment is an example of an adjustment pattern used to adjust the landing positions. Furthermore, according to this example, if a deviation occurs in the landing position of ink ejected from any of the inkjet heads 102, the deviation in the landing position can be clearly presented to the user (adjuster) performing the adjustment. Furthermore, in the printing device 10 of this example, at least some of the multiple inkjet heads 102 can be considered to be aligned in a direction perpendicular to the direction of the rotation axis of the medium 50. In order to properly align the landing positions of ink ejected from all nozzle rows 112 of all inkjet heads 102, it is necessary to align the center of each inkjet head 102 in the left-right direction (main scanning direction) with the center of the medium 50. Furthermore, a function for adjusting the distance between the inkjet heads 102 is also required for the multiple inkjet heads 102. In contrast, as described above, this example makes it possible to properly implement these adjustment functions. This also enables more appropriate printing on the three-dimensional medium 50.

[0099] Furthermore, in the above, an example has been described in which the relative position of the inkjet head 102 with respect to the medium 50 is adjusted using multiple nozzle rows 112 of one inkjet head 102. However, as a modified adjustment operation, it is also possible to perform adjustment using only one nozzle row 112 of the inkjet head 102. In this case, for example, it is possible to use any one nozzle row 112 of the inkjet head 102 having multiple nozzle rows 112. Furthermore, as a modified configuration of the printing device 10, it is also possible to use an inkjet head 102 having only one nozzle row 112 instead of an inkjet head 102 having multiple nozzle rows 112. More specifically, it is possible to perform adjustment of the relative position of the inkjet head 102 with respect to the medium 50 using, for example, the operation shown in FIG. 15 .

[0100] FIG. 15 is a diagram illustrating a modified adjustment operation in the printing device 10, illustrating an example of an operation for adjusting the relative position of the inkjet head 102 with respect to the medium 50 using one nozzle row 112 of the inkjet head 102. As described above, when an inkjet head 102 having multiple nozzle rows 112 is used to adjust the relative position of the inkjet head 102 with respect to the medium 50, it is possible to draw patterns 302a and 302b (see FIG. 12 ) by ejecting ink from nozzles of the multiple nozzle rows 112 that are located at different positions, as in the operation shown in FIG. 12( a), for example. In contrast, in the modified example shown in FIG. 15( a), the control unit 30 of the printing device 10 causes the inkjet head 102 to draw a pattern corresponding to pattern 302a while the relative position of the inkjet head 102 with respect to the medium 50 is set to a first position, as shown in the left part of the figure. Then, as shown in the right part of the figure, the control unit 30 moves the inkjet head 102 relative to the medium 50, and sets the relative position of the inkjet head 102 with respect to the medium 50 to a second position different from the first position. At that position, the control unit 30 then causes the inkjet head 102 to write a pattern corresponding to the pattern 302b. Even with this configuration, the deviation in the relative position of the inkjet head 102 with respect to the medium 50 can be detected appropriately.

[0101] It is also possible to detect a change in the landing position caused by a shift in the relative position of the inkjet head 102 with respect to the medium 50 by, for example, changing the rotation direction of the medium 50, as shown in FIG. 15B . That is, the control unit 30 detects a shift in the relative position by causing the inkjet head 102 to write patterns corresponding to patterns 302a and 302b while rotating the medium 50 in different directions. More specifically, as shown on the left side of the figure, the control unit 30 causes the inkjet head 102 to write a pattern corresponding to pattern 302a while rotating the medium 50 in a first rotation direction using the rotation mechanism 206 (see FIG. 2 ) included in the holding jig 40. Then, as shown on the right side of the figure, the control unit 30 causes the inkjet head 102 to write a pattern corresponding to pattern 302b while rotating the medium 50 in a second rotation direction opposite to the first rotation direction. This configuration also allows for appropriate detection of a shift in the relative position of the inkjet head 102 with respect to the medium 50. This also allows printing on the three-dimensional medium 50 to be performed more appropriately.

[0102] In a further modification of the adjustment operation in the printing device 10, it is also possible to adjust the relative positions of the inkjet heads 102 with respect to the medium 50 using multiple inkjet heads 102 whose relative positions have been appropriately and sufficiently adjusted. In this case, for example, it is possible to use a head group in which the positions of the multiple inkjet heads 102 are already fixed. This can be thought of as performing the operation described with reference to FIGS. 12 and 13 using multiple nozzle rows 112 in the multiple inkjet heads 102. More specifically, in this case, the control unit 30 causes a first inkjet head 102 of the multiple inkjet heads 102 to write a pattern corresponding to pattern 302a, and causes a second inkjet head 102 different from the first inkjet head 102 to write a pattern corresponding to pattern 302b. Even with this configuration, it is possible to appropriately detect the deviation in the relative position of the inkjet heads 102 with respect to the medium 50.

[0103] As described above, the printing device 10 of this embodiment prints on the medium 50 while rotating the medium 50. A cylindrical (cylindrical) medium, for example, can be used as the medium 50. A cylindrical medium is a medium shaped like a body of revolution whose cross section in a plane perpendicular to the rotation axis is circular. Furthermore, media 50 of shapes other than a cylindrical shape can also be used. A medium shaped like a body of revolution can also be used. Examples of such media include conical and truncated conical media. When using a conical or truncated conical medium, the holding jig 40 holds the medium so that the height of the medium is constant at the position facing the inkjet head 102 (the position where the ink lands). In this case, for example, the axis of rotation that rotates the medium can be appropriately tilted relative to the horizontal direction to hold the medium so that the generatrix of the conical or other shaped medium is horizontal at the position facing the inkjet head 102.

[0104] Furthermore, when printing on media of various shapes as described above, the printing device 10 uses the multiple nozzle arrays 112 of the inkjet head 102 when using at least some of the media shapes. For example, when using a medium 50 having a shape with a constant or substantially constant cross-sectional shape in a plane perpendicular to the rotation axis, such as a cylindrical or substantially cylindrical medium, printing can be performed using the multiple nozzle arrays 112 of the inkjet head 102. In this case, the relative position of the inkjet head 102 with respect to the medium 50 can be easily and appropriately adjusted, for example, by the operations described with reference to FIGS. 12 and 6 . On the other hand, when using a medium with a more complex shape than a cylindrical medium, such as a conical or truncated conical medium, and higher quality printing is desired, it may be preferable to use only one nozzle array 112 of the inkjet head 102. In such a case, printing can be performed using only one of the multiple nozzle arrays 112 of the inkjet head 102. In this case, the position of the nozzle array 112 to be used can be aligned with the position of the rotation axis in the main scanning direction. Furthermore, depending on the method of controlling the printing operation, the position of the nozzle row 112 to be used may be shifted from the position of the rotation axis as necessary. In this case, too, the relative position of the inkjet head 102 with respect to the medium 50 can be adjusted using the multiple nozzle rows 112 of the inkjet head 102 through the operations described with reference to Figures 12 and 6. Furthermore, it is also possible to adjust the relative position of the inkjet head 102 with respect to the medium through the operations described with reference to Figures 15(a) and 15(b), for example, depending on the required accuracy of adjustment, etc.

[0105] Furthermore, with respect to a three-dimensional medium 50, the problem of head gap change due to a shift in the relative position of the inkjet head 102 with respect to the medium 50 also occurs when the medium 50 is not rotated. Therefore, even when the medium 50 is not rotated, the same or similar adjustment as described above may be made to the relative position of the inkjet head 102 with respect to the medium 50. In this case, too, the relative position of the inkjet head 102 with respect to the medium 50 can be appropriately adjusted by drawing patterns corresponding to patterns 302a and 302b using nozzle rows arranged at different positions. Furthermore, when adjusting the relative position of the inkjet head 102 with respect to the medium 50, for example, when the medium is rotated, the positional relationship between the rotation axis of the medium and the inkjet head 102 becomes important. Therefore, it is preferable to make an adjustment by moving the inkjet head 102 relative to the medium 50 so that the position of the inkjet head 102 with respect to the rotation axis becomes a predetermined position. On the other hand, when printing on a three-dimensional medium 50 without rotating the medium 50, it is also possible to adjust the relative position of the inkjet head 102 with respect to the medium 50 without moving the inkjet head 102 relative to the medium 50. In this case, it is possible to make an adjustment, for example, by changing the timing at which the inkjet head 102 ejects ink.

[0106] The present invention can be suitably used in, for example, a printing device.

[0107] 10...printing device, 102...inkjet head, 112...nozzle array, 12...head unit, 14...base unit, 16...main scanning drive unit, 18...sub-scanning drive unit, 20...sensor, 202...casing unit, 204...cover, 206...rotation mechanism, 208...ultraviolet irradiator, 210...light source holding unit, 212...cover moving means, 22...sensor moving means, 220...opening, 222...base unit, 224...magnetic sheet, 226...shaft unit, 228...rotation drive unit, 232...tape, 242...lighting unit, 244...canopy, 30...control unit, 302a...seam, 302...pattern, 304...pattern, 40...holding jig, 50...medium

Claims

1. A printing device that uses ultraviolet curable ink to print on a three-dimensional medium held by a holding member that holds a medium to be printed on, the printing device comprising: an inkjet head having a nozzle row in which a plurality of nozzles are arranged at different positions in a predetermined nozzle row direction; a sub-scanning drive unit that causes the inkjet head to perform a sub-scanning operation to move the inkjet head relative to the medium in a sub-scanning direction parallel to the nozzle row direction; and a control unit that controls the operation of the inkjet head and the sub-scanning drive unit, the holding member comprising: a rotation mechanism that rotates the medium while holding the medium at a position opposite the nozzle row; an ultraviolet irradiator that irradiates ultraviolet light onto an outer surface of the medium; and a cover that is a member that covers at least the ultraviolet irradiator from the side of an upper surface of the holding member, which is the surface facing the inkjet head, the cover having an opening at a position opposite the nozzle row and covering the upper surface of the holding member while opposing the nozzle row to the medium at the position of the opening, the rotation mechanism rotates the medium such that a direction of movement of an outer surface of the medium at a position facing the nozzle row is a main scanning direction perpendicular to the sub-scanning direction, and the control unit further controls a rotation operation of rotating the medium by the rotation mechanism, and causes the inkjet head to perform a main scanning operation of ejecting ink onto the rotating medium by rotating the medium with the rotation mechanism, and causes the inkjet head to perform the main scanning operation multiple times while performing the sub-scanning operation between at least some of the main scanning operations, thereby causing the inkjet head to eject ink onto a printing range that is wider in the sub-scanning direction than a nozzle row length, which is the length of the nozzle row in the sub-scanning direction, Furthermore, when the range from one end to the other end in the sub-scanning direction of the medium arranged in a position opposite the nozzle row is defined as the opposing position medium range, the printing device is characterized in that the inkjet head is caused to perform the sub-scanning operation within a range that does not cause the position of the nozzle row in the sub-scanning direction to go outside the opposing position medium range.

2. A printing device as described in claim 1, characterized in that printing is performed using a multi-pass method in which the main scanning operation is performed a plurality of times while one position on the medium is facing the nozzle row, and the control unit causes the inkjet head to perform the main scanning operation a number of times corresponding to a preset number of passes while aligning the positions in the sub-scanning direction of one end of the medium, which is positioned opposite the nozzle row, with one end of the nozzle row, which is the end on the same side in the same direction, and after causing the inkjet head to perform the main scanning operation a number of times corresponding to the number of passes, before causing the inkjet head to perform the next main scanning operation, causes the inkjet head to perform the sub-scanning operation in which the inkjet head moves in the sub-scanning direction relative to the medium a distance corresponding to the number of passes, which is a moving distance corresponding to the distance obtained by dividing the length of the nozzle row by the number of passes.

3. The printing device described in claim 2, characterized in that, when the spacing between the nozzles in the nozzle row in the sub-scanning direction is defined as a nozzle pitch, by performing printing using the multi-pass method, the printing resolution in the sub-scanning direction is made higher than the resolution corresponding to the nozzle pitch, and printing is performed on the medium, and during at least a portion of the main scanning operations performed a number of times corresponding to the number of passes while one end of the medium is aligned with one end of the nozzle row, the sub-scanning drive unit moves the inkjet head in the sub-scanning direction relative to the medium by a distance less than the nozzle pitch.

4. A printing device as described in claim 2, characterized in that during the sub-scanning operation when the position of the other end of the nozzle row exceeds the position of the other end of the medium in the sub-scanning direction when the movement distance of the inkjet head relative to the medium is set to the pass number corresponding distance, the control unit causes the inkjet head to perform the sub-scanning operation so that the inkjet head moves relative to the medium by the movement distance until the other end of the nozzle row reaches the position of the other end of the medium.

5. The printing device described in claim 4, characterized in that the control unit causes the inkjet head to perform the sub-scanning operation in which the other end of the nozzle row reaches the position of the other end of the medium in the sub-scanning direction, and then causes the inkjet head to perform the main scanning operation multiple times while aligning the position of the other end of the medium with the other end of the nozzle row.

6. The printing device described in claim 1, further comprising a sensor used to detect the position of the upper surface of the holding member, and a sensor moving means for moving the sensor relative to the holding member, wherein the holding member further comprises a cover moving means for moving the cover in a direction that changes the distance between the inkjet head and the cover, and the control unit further controls the sensor and the sensor moving means, and detects the state of the gap between the cover and the medium based on the output of the sensor obtained while moving the sensor by the sensor moving means along a path that passes through the edge of the opening of the cover.

7. A printing device as described in claim 1, characterized in that printing is performed using a multi-pass method in which the main scanning operation is performed a plurality of times while one position on the medium is facing the nozzle row, and the control unit causes the inkjet head to perform the main scanning operation a number of times corresponding to a preset number of passes while aligning a position corresponding to one end of the print data in the sub-scanning direction with one end of the nozzle row, which is the end on the same side in the sub-scanning direction, and after causing the inkjet head to perform the main scanning operation a number of times corresponding to the number of passes, before causing the inkjet head to perform the next main scanning operation, causes the inkjet head to perform the sub-scanning operation in which it moves in the sub-scanning direction relative to the medium a distance corresponding to the number of passes, which is a moving distance corresponding to the distance obtained by dividing the length of the nozzle row by the number of passes.

8. A printing device as described in claim 7, characterized in that during the sub-scanning operation when the position of the other end of the nozzle row exceeds a position corresponding to the other end of the print data in the sub-scanning direction when the movement distance of the inkjet head relative to the medium is set to the pass number corresponding distance, the control unit causes the inkjet head to perform the sub-scanning operation so that the inkjet head moves relative to the medium a movement distance until the other end of the nozzle row reaches a position corresponding to the other end of the print data.

9. A printing device that uses ultraviolet curable ink to print on a three-dimensional medium held by a holding member that holds a medium to be printed on, the printing device comprising: an inkjet head having a nozzle row in which a plurality of nozzles are arranged at different positions in a predetermined nozzle row direction; a sensor used to detect the position of an upper surface of the holding member, which is the surface of the holding member that faces the inkjet head; sensor moving means for moving the sensor relatively to the holding member; and a control unit for controlling the operation of the inkjet head, the sensor, and the sensor moving means, the holding member comprising: a rotation mechanism that rotates the medium while holding the medium at a position facing the nozzle row; an ultraviolet irradiator that irradiates ultraviolet rays onto the outer surface of the medium; a cover that is a member that covers at least the ultraviolet irradiator from the side of the upper surface of the holding member, has an opening at a position facing the nozzle row, and covers the upper surface of the holding member while facing the nozzle row at the position of the opening; and cover moving means for moving the cover in a direction in which the distance between the inkjet head and the cover changes. A printing device characterized in that the control unit detects the state of the gap between the cover and the medium based on the output of the sensor obtained while moving the sensor by the sensor moving means along a path passing through the edge of the opening of the cover.

10. The printing device described in claim 9, characterized in that the control unit moves the sensor along multiple paths in a direction intersecting the nozzle row direction, and the multiple paths include, in the nozzle row direction, a one-end side path that passes near one end of the medium, an other-end side path that passes near the other end of the medium, and an intermediate position path that passes over the medium between the one-end side path and the other-end side path.

11. The printing device described in claim 9, characterized in that the sensor is a photosensor that detects light, and detects reflected light from the cover and the medium with a light-reflective material attached to at least a portion of at least one of the medium and the cover, and the control unit moves the sensor along a path that allows the sensor to detect reflected light from the light-reflective material on at least one of the medium and the cover.

12. The printing device described in claim 9, characterized in that the sensor is a photosensor that detects light, and when the ultraviolet irradiator irradiates ultraviolet light onto the outer surface of the medium, the control unit further detects ultraviolet light leaking through the gap between the edge of the opening of the cover and the medium based on the output of the sensor.

13. A printing method for printing on a three-dimensional medium held by a holding member that holds a medium to be printed on, using ultraviolet curable ink, the method comprising: causing an inkjet head having a nozzle row in which a plurality of nozzles are arranged at different positions in a predetermined nozzle row direction to perform a sub-scanning operation of moving the inkjet head relative to the medium in a sub-scanning direction parallel to the nozzle row direction; the holding member comprising: a rotation mechanism that rotates the medium while holding the medium at a position opposite the nozzle row; an ultraviolet irradiator that irradiates ultraviolet light onto an outer surface of the medium; and a cover that is a member that covers at least the ultraviolet irradiator from the side of the top surface of the holding member, which is the surface facing the inkjet head, the cover having an opening at a position opposite the nozzle row and covering the top surface of the holding member while opposing the nozzle row to the medium at the position of the opening; the rotation mechanism rotates the medium such that the direction of movement of the outer surface of the medium at the position opposite the nozzle row is a main scanning direction perpendicular to the sub-scanning direction; a printing method comprising: controlling a rotation operation for rotating the medium with the rotation mechanism, causing the inkjet head to eject ink while rotating the medium with the rotation mechanism, thereby causing the inkjet head to perform a main scanning operation of ejecting ink onto the rotating medium; causing the inkjet head to perform the sub-scanning operation between at least some of the main scanning operations, while causing the inkjet head to perform the main scanning operation a plurality of times, thereby causing the inkjet head to eject ink onto a printing range that is wider in the sub-scanning direction than a nozzle array length, which is the length of the nozzle array in the sub-scanning direction; and causing the inkjet head to perform the sub-scanning operation within a range that does not cause the position of the nozzle array in the sub-scanning direction to go outside the opposing position medium range, when a range from one end to the other end of the medium arranged at a position opposite the nozzle array in the sub-scanning direction is defined as an opposing position medium range.

14. A detection method for detecting the state of a printing device that uses ultraviolet curing ink to print on a three-dimensional medium held by a holding member that holds a medium to be printed on, the printing device comprising: an inkjet head having a nozzle row in which a plurality of nozzles are arranged at different positions in a predetermined nozzle row direction; a sensor used to detect the position of an upper surface of the holding member, which is the surface of the holding member that faces the inkjet head; and a sensor moving means for moving the sensor relative to the holding member, the holding member comprising: a rotation mechanism that rotates the medium while holding the medium at a position facing the nozzle row; an ultraviolet irradiator that irradiates ultraviolet rays onto the outer surface of the medium; a cover that is a member that covers at least the ultraviolet irradiator from the side of the upper surface of the holding member, has an opening at a position facing the nozzle row, and covers the upper surface of the holding member while opposing the nozzle row to the medium at the position of the opening; and a cover moving means for moving the cover in a direction in which the distance between the inkjet head and the cover changes. A detection method characterized by detecting the state of the gap between the cover and the medium based on the output of the sensor obtained while moving the sensor by the sensor moving means along a path passing through the edge of the opening of the cover.

15. A printing device for printing on a three-dimensional medium, comprising: an inkjet head having a nozzle row in which a plurality of nozzles are aligned in a predetermined nozzle row direction; a main scanning drive unit that causes the inkjet head to perform a main scanning operation in which the inkjet head ejects ink while moving relatively over the printing surface of the medium in a predetermined main scanning direction; and a control unit that controls the operation of the inkjet head and the main scanning drive unit, wherein the control unit, when adjusting the position of the inkjet head, causes the inkjet head to draw a first pattern and a second pattern, and when the relative position of the inkjet head with respect to the medium is at a predetermined reference position, the first pattern and the second pattern are drawn at the same position in the main scanning direction on the medium, and the inkjet head draws the first pattern with ink ejected from the nozzles of the nozzle row when the relative position of the nozzle row with respect to the medium is at a first position, and draws the second pattern with ink ejected from the nozzles of the nozzle row when the relative position of the nozzle row with respect to the medium is at a second position different from the first position.

16. A printing device as described in claim 15, characterized in that the medium is held by a holding member, the holding member has a rotation mechanism that rotates the medium while holding the medium in a position facing the nozzle row, and the main scanning drive unit moves the inkjet head relatively in the main scanning direction with respect to the printing surface of the medium by rotating the medium using the rotation mechanism.

17. A printing device as described in claim 16, characterized in that the inkjet head has a plurality of nozzle rows that are positioned differently in the main scanning direction, and the first pattern is drawn by ejecting ink from nozzles of a first nozzle row, and the second pattern is drawn by ejecting ink from nozzles of a second nozzle row that is different from the first nozzle row.

18. A printing device as described in claim 17, characterized in that, with the inkjet head positioned so that the first nozzle row and the second nozzle row are positioned on opposite sides of the boundary defined by the position of the center of rotation of the medium in the main scanning direction, the control unit causes the first nozzle row and the second nozzle row to write the first pattern and the second pattern.

19. A printing device as described in claim 15, characterized in that when the relative position of the inkjet head with respect to the medium deviates from the reference position, the manner in which the first pattern and the second pattern overlap changes depending on the degree of deviation.

20. A printing device as described in claim 19, further comprising a plurality of said inkjet heads, wherein the control unit further causes the plurality of inkjet heads to write a pattern whose print result changes depending on the distance between the plurality of inkjet heads in the main scanning direction.

21. A printing device that prints on a three-dimensional medium held by a holding member that holds a medium to be printed, comprising: an inkjet head having a nozzle row in which a plurality of nozzles are arranged in a predetermined nozzle row direction; a main scanning drive unit that causes the inkjet head to perform a main scanning operation of ejecting ink while moving relatively on the printing surface of the medium along a preset main scanning direction; and a control unit that controls the operation of the inkjet head and the main scanning drive unit, wherein the holding member has a rotation mechanism that rotates the medium while holding the medium at a position opposite the nozzle row, and the main scanning drive unit moves the inkjet head relatively in the main scanning direction with respect to the printing surface of the medium by rotating the medium with the rotation mechanism, and the control unit causes the inkjet head to draw a first pattern and a second pattern when adjusting the position of the inkjet head, and when the relative position of the inkjet head with respect to the medium is at a predetermined reference position, the first pattern and the second pattern are drawn at the same position in the main scanning direction on the medium, The inkjet head is characterized in that it draws the first pattern while rotating the medium in a first rotation direction by the rotation mechanism, and draws the second pattern while rotating the medium in a second rotation direction opposite to the first rotation direction.

22. A method for adjusting a printing device that prints on a three-dimensional medium, comprising the steps of: causing an inkjet head provided in the printing device to draw a first pattern and a second pattern; the inkjet head has a nozzle row in which a plurality of nozzles are arranged in a predetermined nozzle row direction; causing the inkjet head to perform a main scanning operation in which it ejects ink while moving relatively along a predetermined main scanning direction over the printing surface of the medium; when the relative position of the inkjet head to the medium is at a predetermined reference position, the first pattern and the second pattern are drawn at the same position in the main scanning direction on the medium; and causing the inkjet head to draw the first pattern when the relative position of the nozzle row to the medium is at a first position, and to draw the second pattern when the relative position of the nozzle row to the medium is at a second position different from the first position.

23. A method for adjusting a printing device that prints on a three-dimensional medium held by a holding member that holds a medium to be printed, comprising the steps of: causing an inkjet head provided in the printing device to draw a first pattern and a second pattern; the inkjet head has a nozzle row in which a plurality of nozzles are arranged in a predetermined nozzle row direction; causing the inkjet head to perform a main scanning operation in which the inkjet head ejects ink while moving relatively along a preset main scanning direction on the printing surface of the medium; the holding member has a rotation mechanism that rotates the medium while holding it at a position opposite the nozzle row; during the main scanning operation, the inkjet head is moved in the main scanning direction relative to the printing surface of the medium by rotating the medium with the rotation mechanism; and when the relative position of the inkjet head with respect to the medium is at a predetermined reference position, the first pattern and the second pattern are drawn at the same position on the medium in the main scanning direction; an adjustment method comprising: rotating the medium in a first rotation direction by the rotation mechanism; causing the inkjet head to draw the first pattern; and rotating the medium in a second rotation direction opposite to the first rotation direction; and causing the inkjet head to draw the second pattern.

Images