Liquid droplet discharge device

Abstract

To provide a liquid droplet discharge device capable of suppressing erroneous determination of a discharge failure of a nozzle even when manufacturing variations of components, performance variations of optical elements, or manufacturing variations due to component assembly are present.SOLUTION: A liquid droplet discharge device comprises: a discharge head in which a plurality of nozzle rows arranged in parallel in a predetermined direction are formed and which has a plurality of nozzles that discharge liquid droplets onto a print medium; a light source which emits light toward a flight space in which liquid droplets discharged from the nozzles fly; a light receiving unit which detects a received light amount associated with light emitted from the light source after passing through the liquid droplets in flight and outputs a detection signal; and a control device. The control device executes: processing of acquiring, for each nozzle, a parameter value indicating a predetermined feature of the detection signal; and processing of determining whether a distribution of the parameter values relative to positions of the respective nozzles becomes linear, and determining a nozzle corresponding to a parameter value that is not distributed linearly as a nozzle having a discharge failure.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present disclosure relates to a droplet ejection device that is provided in a printing device such as an inkjet printer. [Background technology]

[0002] There are conventional techniques for detecting ejection defects in ink droplets ejected from an ejection head. For example, Patent Document 1 discloses a technique in which light emitted from a light source and passing through an ink droplet is received by a light receiving unit, and ejection defects are detected based on whether or not the amount of light received by the light receiving unit has decreased. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-151816 Summary of the Invention [Problem to be solved by the invention]

[0004] However, due to manufacturing variations in parts, performance variations in optical elements, or manufacturing variations due to assembly of parts, the positional relationship between the nozzles of the ejection head and the optical axis of the light may deviate from the design value. Therefore, if the amount of deviation in this positional relationship is large compared to the amount of deviation in the landing of the ink droplets to be detected, there is a risk that an erroneous determination result will be output.

[0005] Therefore, the present disclosure aims to provide a droplet ejection device that can suppress erroneous determination of nozzle ejection defects even when there is manufacturing variation in parts, performance variation in optical elements, or manufacturing variation due to assembly of parts. [Means for solving the problem]

[0006] The droplet ejection device disclosed herein comprises an ejection head having a plurality of nozzle rows arranged in a predetermined direction and a plurality of nozzles that eject droplets onto a printing medium; a light source that emits light toward a flight space into which the droplets ejected from the nozzles fly; a light receiving unit that detects the amount of light received after the light emitted from the light source passes through the droplets in flight and outputs a detection signal; and a control device, wherein the control device performs a process of acquiring parameter values ​​that indicate predetermined characteristics of the detection signal for each nozzle, and a process of determining whether the distribution of each parameter value with respect to the position of each nozzle is linear or not, and determining that a nozzle corresponding to a parameter value that is not distributed linearly is a nozzle with an ejection defect.

[0007] According to the present disclosure, a conventional determination method determines whether or not there is a discharge defect by comparing a detection signal with a reference signal that serves as a determination standard. In this determination method, even if the actual nozzle position deviates from the designed nozzle position due to manufacturing variations in components, even if the droplets land within the allowable landing range for the actual nozzle position, the droplets will be determined to be discharge defect if they are outside the allowable landing range for the designed nozzle position. In contrast, according to the present disclosure, by determining whether each parameter value is linearly distributed in accordance with the perspective of image quality, the linearity of the landing positions of droplets from the nozzles can be evaluated, thereby preventing erroneous determination of a nozzle discharge defect, even in the presence of manufacturing variations in components, performance variations in optical elements, or manufacturing variations due to component assembly. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide a droplet ejection device that can suppress erroneous determination of nozzle ejection defects even when there is manufacturing variation in parts, performance variation in optical elements, or manufacturing variation due to assembly of parts. [Brief explanation of the drawings]

[0009] [Figure 1]1 is a perspective view illustrating a printing device provided with a droplet ejection device according to an embodiment of the present disclosure. [Figure 2] 1 is a plan view illustrating a droplet ejection device according to an embodiment of the present disclosure. [Figure 3] FIG. 2 is a cross-sectional view showing the configuration of the ejection head of FIG. [Figure 4] FIG. 2 is a block diagram showing components of the printing device of FIG. 1. [Figure 5] 10A and 10B are diagrams illustrating how ink droplets ejected from an ejection head and flying are irradiated with laser light. [Figure 6] FIG. 2 is a diagram showing an optical axis and a detection axis in a cross section of a laser beam. [Figure 7] FIG. 2 is a diagram showing a beam waist portion of a laser beam. [Figure 8] FIG. 10 is a diagram showing a coordinate system used when calculating a distance from the optical axis as a converted value. [Figure 9] 10A and 10B are diagrams illustrating an example of the positional relationship between an optical axis and a distance from the optical axis as a converted value. [Figure 10] 10A and 10B are diagrams illustrating examples of values ​​of distances from the optical axis as converted values ​​corresponding to peak signal intensities in detection signals. [Figure 11] FIG. 2 is a diagram showing a nozzle row in the ejection head. [Figure 12] FIG. 10 is a diagram illustrating an example of a reference line determined based on a conversion value. [Figure 13] FIG. 10 is a diagram showing deviation in a direction away from a reference line. [Figure 14] 10A and 10B are diagrams illustrating a state in which the ejection head moves in the movement direction while tilted at a predetermined angle in the ejection defect detection process. [Figure 15] 10 is a table showing the order in which each nozzle arrives above the sensing axis. [Figure 16] Figure 16A shows the maximum distance in the movement direction among the variations in the position of each nozzle depending on the arrangement angle of the ejection head, and Figure 16B shows the minimum distance among the separation distances in the movement direction between two nozzles that are successively crossed by the laser light. [Figure 17]FIG. 10 is a diagram showing the ejection timing of ink droplets at each detection time. [Figure 18] FIG. 10 is a diagram showing the maximum distance among the distances between a plurality of nozzles successively crossed by the detection axis in the movement direction. DETAILED DESCRIPTION OF THE INVENTION

[0010] A droplet ejection device according to an embodiment of the present disclosure will be described below with reference to the drawings. The droplet ejection device described below is merely one embodiment of the present disclosure. Therefore, the present disclosure is not limited to the following embodiment, and additions, deletions, and modifications are possible within the scope of the present disclosure.

[0011] (First embodiment) 1 is a perspective view showing a printing device 1 provided with a droplet ejection device 1a according to an embodiment of the present disclosure. In the following, an example is disclosed in which an inkjet printer capable of printing on a print medium W, which is a three-dimensional object, is used as the image forming position 1, but the printing device 1 also includes inkjet printers that can print only on paper. In other words, the embodiment of the printing device 1 in FIG. 1 is an example and is not limited to this embodiment.

[0012] 1, directions that are orthogonal to each other are referred to as a first direction Ds, a second direction Df, and a third direction Dz. In this embodiment, for example, the first direction Ds is the movement direction of a carriage 3 (described later), the second direction Df is the transport direction of a print medium W (described later), and the third direction Dz is the up-down direction. In the following description, Ds will be referred to as the movement direction, Df will be referred to as the transport direction, and Dz will be referred to as the up-down direction.

[0013] As shown in Fig. 1, the printing device 1 includes a housing 2, operation keys 4, a display unit 5, a platen 6 on which a print medium W is placed, and an upper cover 7. The printing device 1 also includes a droplet ejection device 1a shown in Fig. 2, which includes an ejection head 10 and a controller unit 19 including a control device 20 (Fig. 4). The ejection head 10 is an inkjet head that ejects droplets, for example, ultraviolet-curable ink droplets Id (Fig. 5).

[0014] The housing 2 is formed in a box shape. The housing 2 has an opening 2a. Operation keys 4 are provided on the housing 2. A display unit 5 is also provided near the operation keys 4. The operation keys 4 accept operation inputs from the user. The display unit 5 is configured, for example, as a touch panel, and displays predetermined information. A part of the display unit 5 also functions as an operation key. The controller unit 19 realizes a printing function and controls the display of the display unit 5 based on inputs from the operation keys 4 or external inputs via a communication interface (not shown).

[0015] The platen 6 is configured so that the print medium W can be placed on it. The platen 6 has a predetermined thickness and is made of, for example, a rectangular plate material with the transport direction Df as its longitudinal direction. The platen 6 is removably supported by a platen support base (not shown). The platen support base is configured so that it can be moved in the transport direction Df between a printing position where printing is performed on the print medium W and a detachment position where the print medium W is detached from the platen 6 by driving a transport motor 33 (FIG. 4). As a result, the platen 6 moves the print medium W in the transport direction Df relative to the ejection head 10. During printing, the platen 6 moves in the transport direction Df, so that the print medium W placed on the platen 6 is transported along the transport direction Df. In addition, the upper cover 7 is configured so that it rotates upward when its end is lifted, exposing the interior of the housing 2.

[0016] As shown in FIG. 2, the droplet ejection device 1a includes a storage tank 62, a carriage 3 on which are mounted, for example, two ejection heads 10 (10A, 10B) and two ultraviolet irradiation devices 40 (40A, 40B), and a pair of guide rails 67. In this embodiment, the carriage 3 and a carriage motor 34 (described later) correspond to the moving device. Note that, although two ejection heads 10 and two ultraviolet irradiation devices 40 are provided, this is not limiting, and one ejection head 10 and one ultraviolet irradiation device 40 may also be provided. Furthermore, if the ejection head 10 ejects normal ink droplets that are not ultraviolet-curable ink droplets, the ultraviolet irradiation device 40 is not necessary.

[0017] The carriage 3 is supported by a pair of guide rails 67 extending in the movement direction Ds, and moves back and forth in the movement direction Ds along the guide rails 67. This allows the two ejection heads 10 (10A, 10B) and the two ultraviolet irradiation devices 40 (40A, 40B) to move back and forth in the movement direction Ds. The ejection head 10 is also connected to a storage tank 62 via a tube 62a.

[0018] In this embodiment, for example, the ejection head 10A ejects ink droplets Id of each of the colors yellow (Y), magenta (M), cyan (C), and black (K), which are sometimes collectively referred to as color inks. The ink droplets Id of these four colors are ejected onto the print medium W, thereby printing a color image on the print medium W. Meanwhile, the ejection head 10B ejects white (W) ink droplets Id and clear (Cr) ink droplets Id. When printing a color image on, for example, fabric as the print medium W, white ink droplets Id are ejected first as a base ink to reduce the effect on the color and material of the fabric, and then color ink droplets Id are ejected on top of the white ink droplets Id. Clear ink droplets Id are ejected to impart gloss or protect the printed area.

[0019] Ink is stored in the storage tanks 62. A storage tank 62 is provided for each type of ink. For example, six storage tanks 62 are provided, each storing black, yellow, cyan, magenta, white, and clear ink.

[0020] The droplet discharge device 1a further includes a purge unit 50 and a receiving unit 54. The receiving unit 54 is disposed on one side of the pair of guide rails 67 in the movement direction Ds so as to overlap with the movement area of ​​the carriage 3. The purge unit 50 is disposed on the other side of the pair of guide rails 67 in the movement direction Ds so as to overlap with the movement area of ​​the carriage 3.

[0021] The purge unit 50 has a cap 51, a suction pump 52, and an unillustrated lifting mechanism that lifts and lowers the cap 51 between a suction position and a standby position. The suction pump 52 is connected to the cap 51. At the standby position, the nozzle surface NM (FIG. 3) is separated from the cap 51. At the suction position, the nozzle surface NM is covered by the cap 51, forming a sealed space. When the suction pump 52 is driven while the cap 51 is in the suction position, a purge process is performed in which the sealed space is suctioned and ink is discharged from the nozzle holes 121a (FIG. 3). In addition, the receiver 54 receives ink droplets Id ejected from the ejection head 10 during the flushing process.

[0022] Next, the structure of the ejection head 10 will be described. As shown in FIG. 3, the ejection head 10 has a plurality of nozzles 121 that eject ink droplets Id using ink from a storage tank 62. The ejection head 10 has a laminated body of a flow path forming body and a volume changing unit. An ink flow path is formed inside the flow path forming body, and a plurality of nozzle holes 121a open in the nozzle surface NM, which is the lower surface of the flow path forming body. The volume changing unit is driven to change the volume of the ink flow path. At this time, the meniscus vibrates in the nozzle holes 121a, causing ink to be ejected.

[0023] The flow path forming body of the ejection head 10 is a laminate of a plurality of plates, and the volume changing section includes a vibration plate 155 and an actuator (piezoelectric element) 160. A common electrode 161, which will be described later, is connected to the top of the vibration plate 155.

[0024] The multiple plates are stacked, including, from bottom to top, a nozzle plate 146, a spacer plate 147, a first flow path plate 148, a second flow path plate 149, a third flow path plate 150, a fourth flow path plate 151, a fifth flow path plate 152, a sixth flow path plate 153, and a seventh flow path plate 154.

[0025] Each plate has holes and grooves of various sizes formed therein. Inside the flow path forming body where the plates are stacked, the holes and grooves are combined to form a plurality of nozzles 121, a plurality of individual flow paths 164, and a manifold 122 as ink flow paths.

[0026] The nozzles 121 are formed to penetrate the nozzle plate 146 in the stacking direction. In the nozzle surface NM of the nozzle plate 146, a plurality of nozzle holes 121a, which are the tips of the nozzles 121, are aligned in the transport direction Df to form a nozzle row NL (see FIG. 11, which will be described later).

[0027] The manifold 122 supplies ink to the pressure chambers 128 to which an ejection pressure is applied. The manifold 122 extends in the transport direction Df, and is connected to one end of each of the individual flow paths 164. That is, the manifold 122 functions as a common flow path for the ink. The manifold 122 is formed by through-holes that penetrate the first flow path plate 148 to the fourth flow path plate 151 in the stacking direction and recesses that are recessed from the lower surface of the fifth flow path plate 152, which are overlapped in the stacking direction.

[0028] The nozzle plate 146 is disposed below the spacer plate 147. The spacer plate 147 is formed of, for example, stainless steel. The spacer plate 147 has a recess 145 formed by, for example, half-etching, recessing the surface on the nozzle plate 146 side in the thickness direction of the spacer plate 147, whereby a thin portion constituting the damper portion 147a and a damper space 147b are formed. As a result, the damper space 147b is formed as a buffer space between the manifold 122 and the nozzle plate 146.

[0029] A supply port 122a communicates with the manifold 122. The supply port 122a is formed, for example, in a cylindrical shape and is provided at one end in the transfer direction Df. The manifold 122 and the supply port 122a are connected by a flow path (not shown).

[0030] Each individual flow path 164 is connected to the manifold 122. The upstream end of each individual flow path 164 is connected to the manifold 122, and the downstream end is connected to the base end of the nozzle 121. Each individual flow path 164 is composed of a first communication hole 125, a supply throttle path 126 which is an individual throttle path, a second communication hole 127, a pressure chamber 128, and a descender 129, and these components are arranged in this order.

[0031] The first communication hole 125 has a lower end connected to the upper end of the manifold 122, extends upward in the stacking direction from the manifold 122, and penetrates an upper portion of the fifth flow path plate 152 in the stacking direction.

[0032] The upstream end of supply throttle path 126 is connected to the upper end of first communication hole 125. Supply throttle path 126 is formed by half etching, for example, and is configured as a groove recessed from the lower surface of sixth flow path plate 153. Furthermore, second communication hole 127 has its upstream end connected to the downstream end of supply throttle path 126, extends upward in the stacking direction from supply throttle path 126, and is formed to penetrate sixth flow path plate 153 in the stacking direction.

[0033] The upstream end of the pressure chamber 128 is connected to the downstream end of the second communication hole 127. The pressure chamber 128 is formed to penetrate the seventh flow path plate 154 in the stacking direction.

[0034] The descender 129 is formed by penetrating the spacer plate 147, the first flow path plate 148, the second flow path plate 149, the third flow path plate 150, the fourth flow path plate 151, the fifth flow path plate 152, and the sixth flow path plate 153 in the stacking direction. The descender 129 has an upstream end connected to the downstream end of the pressure chamber 128 and a downstream end connected to the base end of the nozzle 121. The nozzle 121 overlaps the descender 129 in the stacking direction, for example, and is disposed at the center of the descender 129 in the width direction.

[0035] The vibration plate 155 is laminated on the seventh flow path plate 154 and covers the upper openings of the pressure chambers 128 .

[0036] The actuator 160 includes a common electrode 161, a piezoelectric layer 162, and an individual electrode 163, which are arranged in this order. The common electrode 161 covers the entire surface of the vibration plate 155. The piezoelectric layer 162 covers the entire surface of the common electrode 161. The individual electrode 163 is provided for each pressure chamber 128 and is arranged on the piezoelectric layer 162. One individual electrode 163, the common electrode 161, and the portion of the piezoelectric layer 162 sandwiched between the two electrodes constitute one actuator 160.

[0037] The individual electrodes 163 are electrically connected to a head driver IC. The head driver IC receives a control signal from the control device 20, generates a drive signal (voltage signal), and applies it to the individual electrodes 163. In contrast, the common electrode 161 is always maintained at ground potential. In this configuration, the active portion of the piezoelectric layer 162 expands and contracts in the planar direction together with the common electrode 161 and the individual electrodes 163 in response to the drive signal. In response, the vibration plate 155 deforms in cooperation with the drive signal, and changes in the direction of increasing or decreasing the volume of the pressure chamber 128. As a result, an ejection pressure is applied to the pressure chamber 128, causing the ink droplet Id to be ejected from the nozzle 121.

[0038] In the ejection head 10, ink flows into the manifold 122 via the supply port 122a, then flows from the manifold 122 into the supply throttle passage 126 via the first communication hole 125, and then flows from the supply throttle passage 126 into the pressure chamber 128 via the second communication hole 127. The ink then flows through the descender 129 and into the nozzle 121. When an ejection pressure is applied to the pressure chamber 128 by the actuator 160, an ink droplet Id is ejected from the nozzle hole 121a.

[0039] 4, in addition to the above-mentioned components, the printing device 1 also includes a controller unit 19, a reading device 26, motor driver ICs 30 and 31, a head driver IC 32, a transport motor 33, a carriage motor 34, an irradiation device driver IC 35, a purge driver IC 36, a light source driver IC 37, a detection driver IC 38, and motor driver ICs 39 and 70. In addition to the above-mentioned components, the droplet ejection device 1a also includes a light source 65, a detection element 67, and rotation motors 69 and 72. The detection element 67 corresponds to a light receiving unit.

[0040] The controller unit 19 has a control device 20 configured by a CPU, storage units (ROM 21, RAM 22, EEPROM 23, HDD 24), and an ASIC 25. The control device 20 is connected to the storage units and controls the driver ICs 30 to 32, 35 to 39, and 70 and the display unit 5.

[0041] The control device 20 performs various functions by executing predetermined processing programs stored in the ROM 21. The control device 20 may be implemented as a single processor in the controller unit 19, or may be implemented as multiple processors cooperating with each other. The processing programs are read by the reading device 26 from a computer-readable recording medium KB such as a magneto-optical disk or a USB flash memory, and stored in the ROM 21. The RAM 22 stores image data received from the outside and calculation results of the control device 20. The EEPROM 23 stores various initial setting information input by the user. The HDD 24 stores specific information, etc.

[0042] The ASIC 25 is connected to motor driver ICs 30, 31, 39, and 70, a head driver IC 32, an irradiation device driver IC 35, a purge driver IC 36, a light source driver IC 37, and a detection driver IC 38. When the control device 20 receives a print job from a user, it outputs an image recording command to the ASIC 25 based on a processing program. The ASIC 25 controls the driver ICs 30-32, 35-39, and 70 based on the image recording command. The control device 20 moves the platen 6 in the conveyance direction Df by driving the conveyance motor 33 using the motor driver IC 30. The control device 20 moves the carriage 3 in the movement direction Ds by driving the carriage motor 34 using the motor driver IC 31. The control device 20 also controls a rotation motor 69 using the motor driver IC 39. Controlling the rotation motor 69 allows the ejection head 10 to rotate around an axis perpendicular to the nozzle surface NM. Furthermore, the control device 20 controls a rotation motor 72 by a motor driver IC 70. By controlling the rotation motor 72, a frame 71 (described later) can be rotated around an axis perpendicular to the frame 71. This makes it possible to change the optical axis direction (irradiation direction) DL of laser light Lz emitted by a light source 65 (described later).

[0043] The control device 20 converts image data acquired from an external device or the like into ejection data for ejecting ink droplets Id onto the print medium W. The control device 20 causes the head driver IC 32 to eject ink droplets Id from the ejection head 10 based on the converted ejection data. The control device 20 also causes the irradiation device driver IC 35 to irradiate ultraviolet light from each light-emitting diode chip of the ultraviolet irradiation device 40. The control device 20 drives the purge unit 50 with the purge driver IC 36. The control device 20 controls the light source 65 with the light source driver IC 37 and the detection element 67 with the detection driver IC 38.

[0044] 5 is a diagram showing how a laser beam Lz is irradiated onto an ink droplet Id in flight after being ejected from the ejection head 10. The laser beam Lz corresponds to light.

[0045] As shown in FIG. 5, the light source 65 irradiates a laser beam Lz in a specific wavelength region toward a flight space Sh into which ink droplets Id ejected from the nozzles 121 fly. Examples of the light source 65 include a light-emitting diode (LED) and a semiconductor laser (LD). The light source 65 is disposed on one side of the optical axis direction DL of the optical axis La of the laser beam Lz emitted from the light source 65, relative to the position of the ejection head 10. In this case, for example, the nozzle row direction Dn (FIG. 11) of the nozzle row NL (FIG. 11) in the ejection head 10, which will be described later, may be parallel to the optical axis direction DL. The light source 65 is disposed in a box-shaped light source housing 65a. The light source housing 65a has a slit 65b on the side of the emission direction of the laser beam Lz emitted from the light source 65. A lens 65c is disposed in the light source housing 65a so as to cover the slit 65b from the inside of the light source housing 65a. One or more lenses may be provided in addition to the lens 65c.

[0046] The detection element 67 is disposed on the other side of the optical axis direction DL with respect to the position of the ejection head 10. The detection element 67 generates a current based on the received laser light Lz. The current signal from the detection element 67 is converted into a voltage signal by a current-voltage conversion circuit (not shown), and the voltage signal is amplified by an amplifier circuit (not shown). The amplified voltage signal is used in a process to detect ejection defects of the nozzle 121.

[0047] The light source 65 and the detection element 67 are supported by a frame 71 extending in the optical axis direction DL of the laser light Lz. The frame 71 is configured to be rotatable by a rotary motor 72 with the light source 65 as a base point so that the laser light Lz traverses the flight space Sh and the irradiation direction of the laser light Lz changes.

[0048] In this configuration, the laser light Lz emitted from the light source 65 passes through the lens 65c, and is then emitted from the ejection head 10 and irradiated onto the ink droplets Id flying through the flight space Sh. The detection element 67 detects the amount of received light of the laser light Lz emitted from the light source 65 after it has passed through the flight space Sh. The control device 20 detects ejection defects using the signal output from the detection element 67.

[0049] Fig. 6 is a diagram showing the optical axis La and detection axis Da in the cross section of the laser beam Lz. As shown in Fig. 6, the laser beam Lz has the optical axis La at the center of the cross section of the laser beam Lz. In this embodiment, the detection axis Da is an axis that is parallel to the optical axis La and is located at a certain distance from the position of the optical axis La in the radial direction of the laser beam Lz, and that includes the center position of the vertical line segment at which the sensitivity is maximized in the cross section of the laser beam Lz. The process of detecting ejection defects using the detection axis Da will be described later.

[0050] The process of determining whether or not there is a discharge defect by the control device 20 in this embodiment will be described in detail below with reference to the drawings.

[0051] FIG. 7 is a diagram showing the beam waist portion BW of the laser light Lz. FIG. 8 is a diagram showing a coordinate system used when calculating the radial distance from the optical axis La as a converted value CV. FIG. 9 is a diagram showing an example of the positional relationship between the optical axis La and the radial distance from the optical axis La as a converted value CV. FIG. 10 is a diagram showing an example of the value of the radial distance from the optical axis La as a converted value CV corresponding to the peak signal intensity in the detection signal from the detection element 67. FIG. 11 is a diagram showing the nozzle row NL in the ejection head 10. FIG. 12 is a diagram showing an example of a reference line Lb determined based on the converted value CV. FIG. 13 is a diagram showing the deviation Dr in the direction away from the reference line Lb.

[0052] First, we will explain the nozzle rows NL in the ejection head 10. As shown in Figure 11, the ejection head 10 has multiple nozzle rows NL, each consisting of a plurality of nozzles 121 arranged side by side at predetermined intervals in a predetermined nozzle row direction Dn. That is, each nozzle row NL extends in the nozzle row direction Dn. Each nozzle row NL is arranged at predetermined intervals in the movement direction Ds.

[0053] In the process of determining whether or not an ejection defect has occurred, first, the control device 20 rotates the frame 71 using the rotation motor 72 so that the optical axis direction DL of the laser light Lz forms a first angle with respect to the ejection head 10. In this state, the control device 20 causes the light source 65 to emit the laser light Lz, and ejects ink droplets from all of the nozzles 121 while moving the ejection head 10 in the movement direction Ds, thereby acquiring detection signals for all of the nozzles 121 from the detection elements 67. Then, the control device 20 executes a process of acquiring, for each nozzle 121, parameter values ​​that indicate predetermined characteristics of the detection signals.

[0054] The control device 20 then determines whether the distribution of each parameter value corresponding to the position of each nozzle 121, specifically, for example, the distribution of each parameter value for each nozzle row NL, is linear.The control device 20 then executes a process to determine that the nozzles 121 in the nozzle row NL corresponding to parameter values ​​that are not linearly distributed are nozzles with ejection defects.This will be explained in detail below.

[0055] In this embodiment, an example of the parameter value is peak signal strength, as shown in Fig. 10. The control device 20 stores each acquired peak signal strength in the storage unit. Note that the parameter value is not limited to peak signal strength.

[0056] The above parameter values ​​may be used as they are, but the control device 20 executes a process of converting each parameter value to obtain a predetermined converted value CV. As an example of the predetermined converted value CV, the control device 20 acquires the distance from the optical axis La in the radial direction of the cross section of the laser beam Lz, as shown in FIG. 10. The control device 20 stores the acquired converted value CV in a storage unit. A detailed method for acquiring the converted value CV will be described later.

[0057] The control device 20 does not execute the process of obtaining the conversion value CV when the parameter value exceeds the threshold value. On the other hand, the control device 20 executes the process of obtaining the conversion value CV when the parameter value is equal to or less than the threshold value. Note that the threshold value is a value that takes into account the amount of variation between the coordinates of the nozzles 121 in the ejection head 10 and the coordinates on the optical axis La that can be considered in design.

[0058] Next, the control device 20 reads out from the storage unit the converted values ​​CV for each nozzle 121 that form the same nozzle row NL, which is an example of a nozzle group arranged in the same straight line. The data group of the read converted values ​​CV is referred to as the first data group. Note that in the case where the nozzle row direction Dn of the nozzle row NL in the ejection head 10 is perpendicular to the optical axis direction DL, the converted values ​​CV for all of the nozzles 121 that are aligned in a row in the direction perpendicular to the nozzle row direction Dn correspond to the first data group.

[0059] Next, the control device 20 executes a process of determining the reference line Lb using the first data group. In this case, the control device 20 determines the reference line Lb as a predetermined line obtained using the converted values ​​CV for all nozzles 121 among the converted values ​​CV for each nozzle 121 forming the same nozzle row NL, i.e., the entire first data group. Specifically, as shown in FIG. 12, the control device 20 may acquire, for example, an approximate straight line Ln1 as the reference line Lb, an approximate curve Ln2, or a moving average line. Note that the nozzle coordinates in FIG. 12 and FIG. 13 (described later) refer to the coordinates of the nozzle 121 in the movement direction Ds.

[0060] Alternatively, the control device 20 may determine the reference line Lb using only the converted values ​​CV for one or more nozzles 121 located at one end of the nozzle row NL and the converted values ​​CV for one or more nozzles 121 located at the other end of the nozzle row NL, out of all the converted values ​​CV included in the first data group.

[0061] After the reference line Lb is determined in this manner, the control device 20 determines whether the converted value CV for each nozzle 121 is within the allowable range Tr (FIG. 9) relative to the reference line Lb. If the converted value CV is not within the allowable range Tr, the control device 20 determines that the nozzle 121 corresponding to that converted value CV is a nozzle having a discharge defect. In the example of FIG. 9, the converted value CV1 is within the allowable range Tr, but the converted value CV2 is not within the allowable range Tr. Therefore, the control device 20 determines that the nozzle 121 corresponding to the converted value CV2 has a discharge defect. The allowable range Tr is predetermined as a range that is considered to be free from white streaks and misaligned lines and to have no effect on image quality, for example.

[0062] Similarly to the above, the discrimination process is performed on all data groups from the second data group onwards. After the discrimination process is completed on all data groups, the control device 20 then causes the rotation motor 72 to rotate the frame 71 so that the optical axis direction DL of the laser light Lz forms a second angle with respect to the discharge head 10 that is different from the first angle. This can change the irradiation direction of the laser light Lz from the light source 65. In this state, the discrimination process is performed on all data groups in the same manner as above.

[0063] Here, if the number of converted values ​​CV that do not fall within the allowable range Tr for the reference line Lb is less than a predetermined value, the control device 20 determines the nozzle 121 corresponding to the converted value CV that does not fall within the allowable range Tr as a nozzle having an ejection defect. On the other hand, if the number of converted values ​​CV that do not fall within the allowable range Tr for the reference line Lb is equal to or greater than a predetermined value, the control device 20 redetermines the reference line Lb using a different method. The control device 20 then determines whether the converted value CV for each nozzle 121 falls within the allowable range Tr for the redetermined reference line Lb. If the converted value CV does not fall within the allowable range Tr, the control device 20 determines the nozzle 121 corresponding to that converted value CV as a nozzle having an ejection defect.

[0064] Next, a detailed method for obtaining the converted value CV will be described. First, the beam waist portion BW of the laser beam Lz will be described. As shown in Fig. 7, the laser beam Lz emitted from the light source 65 has a beam waist portion BW, which is the portion where the beam diameter is smallest in the optical axis direction DL. The radius of the cross section at this beam waist portion BW is defined as the beam waist radius ω0.

[0065] The detection signal intensity V of an ink droplet ejected from the nozzle 121 at any coordinate (Xn, Yn, Zn) can be calculated using the following formula 1. In formula 1, E(x, y, z) is the light illuminance at the ink droplet position, S is the cross-sectional area of ​​the ink droplet, AEI is the light-to-current conversion sensitivity, AIV is the current-to-voltage conversion sensitivity, and A is the detection circuit amplification. Also, in formula 1, x is the coordinate in the movement direction Ds in Figure 8 (in other words, the coordinate in the radial direction of the laser beam cross section centered on the optical axis La), y is the coordinate in the direction perpendicular to the movement direction Ds in Figure 8, and z is the distance in the optical axis direction from the beam waist portion BW.

[0066]

number

[0067] From Equation 1, the following Equation 2 is obtained.

[0068]

number

[0069] Considering that the laser light Lz is a beam whose intensity distribution in a plane perpendicular to the optical axis direction DL is close to a Gaussian distribution, the illuminance E of the Gaussian beam at an arbitrary position away from the focusing position can be calculated using the following formula 3. In the following formula 3, E0 is the central illuminance, z is the distance from the beam waist BW in the optical axis direction DL, ω(z) is the laser light radius at an arbitrary coordinate in the optical axis direction DL, and ω0 is the beam waist radius.

[0070]

number

[0071] The light illuminance at the ink droplet passing position is converted into the ink droplet passing coordinate (x, z) using Equation 3. In this case, when converting the light illuminance at the ink droplet passing position into the ink droplet passing coordinate (x, z) using Equation 3, for simplicity, the z coordinate of the nozzle 121 corresponding to the ink droplet is used as the z component of the ink droplet passing coordinate. As a result, the radial distance from the optical axis La corresponding to the nozzle 121 is acquired as a converted value CV.

[0072] Conventionally, the presence or absence of ejection defects was determined by comparing the detection signal with a reference signal serving as a judgment standard. With this determination method, even if the actual nozzle position deviates from the designed nozzle position due to manufacturing variations in components, and ink droplets land within the allowable landing range for the actual nozzle position, the ejection defect is determined if the ink droplets land outside the allowable landing range for the designed nozzle position. In contrast, the droplet ejection device 1a disclosed herein determines whether each parameter value (or the converted value CV from the parameter value) is linearly distributed in accordance with the viewpoint of image quality. As a result, even if there are manufacturing variations in components, performance variations in optical elements, or manufacturing variations due to component assembly, erroneous determination of ejection defects in the nozzle 121 can be suppressed by evaluating the linearity of the landing position of ink droplets from the nozzle 121.

[0073] Furthermore, in this embodiment, the control device 20 determines whether the converted value CV for each nozzle 121 is within the allowable range Tr relative to the reference line Lb. In this way, by using the technical concepts of the reference line Lb and the allowable range Tr relative to the reference line Lb, it is possible to determine ejection defects with high accuracy.

[0074] Furthermore, in this embodiment, the control device 20 does not execute the process of obtaining the conversion value CV when the parameter value exceeds a threshold value. As a result, for example, when the amount of deviation in the landing position of ink droplets is large relative to the variation between the nozzle coordinate and the optical axis coordinate, it is possible to determine whether or not there is a discharge defect without obtaining the conversion value CV. This simplifies the process.

[0075] Furthermore, in this embodiment, the control device 20 executes a process to obtain a conversion value CV when the parameter value is equal to or less than a threshold value. As a result, for example, when the amount of deviation in the impact of ink droplets is small relative to the variation between the nozzle coordinate and the optical axis coordinate of the light, the conversion value CV can be used to accurately determine whether or not there is a discharge defect.

[0076] Furthermore, in this embodiment, the control device 20 acquires the approximate line Ln1, the approximate curve Ln2, or the moving average line as the reference line Lb, thereby further reducing erroneous determinations in determining ejection defects.

[0077] Furthermore, in this embodiment, the control device 20 may determine the reference line Lb using only the converted values ​​CV for one or more nozzles 121 located at one end of the nozzle row NL and the converted values ​​CV for one or more nozzles 121 located at the other end of the nozzle row NL, out of all the converted values ​​CV included in the first data group, thereby simplifying the processing.

[0078] Furthermore, in this embodiment, if the number of converted values ​​CV that do not fall within the tolerance range Tr for the reference line Lb is less than a predetermined value, the control device 20 determines that the nozzles 121 corresponding to the converted values ​​CV that do not fall within the tolerance range Tr are nozzles with ejection defects. As a result, if the number of converted values ​​CV that do not fall within the tolerance range Tr is less than a predetermined value, it is possible to regard the reference line Lb as having been determined relatively without being affected by the converted values ​​CV for the nozzles 121 with ejection defects. As a result, it is possible to determine that the nozzles 121 corresponding to converted values ​​CV that do not fall within the tolerance range Tr are nozzles with ejection defects.

[0079] Furthermore, in this embodiment, on the other hand, if the number of converted values ​​CV that do not fall within the tolerance range Tr for the reference line Lb is equal to or greater than a predetermined value, the control device 20 redetermines the reference line Lb using a different method. The control device 20 then determines whether the converted values ​​CV for each nozzle 121 fall within the tolerance range Tr for the redetermined reference line Lb. As a result, if the number of converted values ​​CV that do not fall within the tolerance range Tr is equal to or greater than a predetermined value, it can be assumed that the reference line Lb was determined with a significant influence from the converted values ​​CV for the nozzles 121 with ejection defects. Therefore, in such cases, the reference line Lb is redetermined using converted values ​​CV that are different from some or all of the converted values ​​CV used when initially determining the reference line Lb (or, in the case of a moving average line, a different interval is set). Then, by using the redetermined reference line Lb, ejection defects can be identified with high accuracy.

[0080] Furthermore, in this embodiment, even if the converted value CV for the same nozzle 121 falls within the tolerance range Tr multiple times during a predetermined period, if the converted value CV has a deviation Dr in the direction away from the approximate curve Ln2, which is an example of the reference line Lb, as shown in Figure 13, the control device 20 may determine that the nozzle 121 corresponding to that converted value CV is a nozzle that is likely to have a discharge defect. This makes it possible to quickly detect nozzles 121 that are likely to have a discharge defect due to deviation in the future.

[0081] Furthermore, in this embodiment, the control device 20 may determine that the ejection head 10 needs to be replaced if the number of times that the same nozzle 121 is determined to have an ejection defect exceeds a predetermined number within a predetermined period. This makes it possible to appropriately determine the timing for replacing the ejection head 10 when the ejection defect cannot be resolved by maintenance.

[0082] (Second embodiment) Next, a second embodiment of the present disclosure will be described. Fig. 14 is a diagram showing a state in which the ejection head 10 moves in the movement direction Ds while tilted at an arrangement angle α during the ejection defect detection process. Fig. 15 is a table showing the order in which each nozzle 121 arrives above the detection axis. Note that Fig. 14 shows the ejection head 10 as seen from below.

[0083] In the second embodiment, the control device 20 rotates the ejection head 10 using the rotary motor 69 so that the ejection head 10 forms an angle α with the direction perpendicular to the optical axis direction DL in a plan view, as shown in FIG. 14 . In this state, the control device 20 moves the ejection head 10 using the carriage 3 in the movement direction Ds at a predetermined movement speed Vx. As a result, the ejection head 10 is moved in the movement direction Ds at the movement speed Vx so that the detection axis Da crosses the nozzles 121 in a plan view along the ink droplet ejection direction. The control device 20 executes the ejection defect detection process by ejecting ink droplets from the nozzles 121 in the order in which the nozzles 121 arrive above the detection axis Da, in other words, in the order in which the nozzles 121 cross the detection axis Da in a plan view. In FIG. 15 , the coordinate of each nozzle 121 in the ejection head 10 arranged to form the angle α on the P axis parallel to the movement direction Ds is defined as the P coordinate, and the coordinate on the Q axis perpendicular to the P axis is defined as the Q coordinate. It should be noted that, although the ejection head 10 is moved in the movement direction Ds so that the detection axis Da crosses the nozzle 121, the present invention is not limited to this, and the optical axis La may be used instead of the detection axis Da. The same applies to the third embodiment described below.

[0084] In this way, when the ejection head 10, which is arranged so that the ejection head 10 forms an angle α with the direction perpendicular to the optical axis direction DL, moves in the movement direction Ds at a movement speed Vx, the order in which the nozzles 121 cross the detection axis Da in a plan view and the time at which they cross the detection axis Da are determined, as shown in Fig. 15. Therefore, the time difference between the time for the nozzle 121 that crosses the detection axis Da last and the time for the nozzle 121 that crosses the detection axis Da first is obtained. The control device 20 calculates this time difference in advance and stores it in the memory unit before starting the ejection defect detection process.

[0085] At this time, if there are no nozzles with the same arrival order that cross the detection axis Da, that is, if there is the above-mentioned time difference for all nozzles 121, the control device 20 ejects ink droplets from the nozzles 121 in the order of arrival, and performs ejection failure detection processing for all nozzles 121 based on the detection signal corresponding to the ink droplets.

[0086] On the other hand, if there are multiple nozzles with the same arrival order across the detection axis Da, i.e., if there are nozzles 121 with no time difference as described above, the control device 20 ejects ink droplets from one of the nozzles with the same arrival order (referred to as the k-1th nozzle 121), and then immediately ejects ink droplets from the other nozzle 121 (referred to as the kth nozzle 121) at the maximum frequency fmax of the ejection head 10. In this case, even if the ink droplet ejected from the kth nozzle 121 is ejected normally, it will land at a position shifted from the detection axis Da by (1 / fmax) × the moving speed Vx. When the ink droplet is ejected at such a shifted position, the change in the detection signal strength of the kth nozzle 121 relative to the detection signal strength of normal ejection can be determined in advance. Therefore, a table showing the correction amount for the detection signal strength of the kth nozzle 121 relative to the detection signal strength of normal ejection is stored in advance in the storage unit. The control device 20 then uses the value obtained by multiplying the detection signal for the k-th nozzle 121 by the correction amount in the ejection defect detection process.

[0087] Alternatively, the following may be adopted. When there are multiple nozzles with the same arrival order that intersect the detection axis Da, the control device 20 ejects ink droplets from one nozzle 121 of the nozzles with the same arrival order, and simultaneously ejects ink droplets from another nozzle 121 of the nozzles with the same arrival order. In this case, the detection signal obtained by the detection element 67 is a composite waveform based on the ink droplets ejected from one nozzle 121 and the ink droplets ejected from the other nozzle 121. Therefore, the control device 20 can determine the presence or absence of a discharge defect based on the detection signal of this composite waveform in the discharge defect detection process. Note that if there is a discharge defect nozzle among the nozzles with the same arrival order that simultaneously eject ink droplets, it is not possible to identify which nozzle 121 is the discharge defect nozzle from the composite waveform. Therefore, after the discharge defect detection process is completed, the one nozzle 121 and the other nozzle 121 are moved and stopped above the detection axis Da, and ink droplets are ejected from these nozzles 121 in order. This makes it possible to identify the discharge defect nozzle based on the detection signal based on the ink droplets.

[0088] Furthermore, in this embodiment, the control device 20 may change the movement speed Vx of the ejection head 10 in the movement direction Ds in accordance with the separation distance in the movement direction Ds between two nozzles 121 that are successively crossed by the detection axis Da.

[0089] Furthermore, in FIG. 14, the width of the ejection head 10, specifically the distance between the nozzles 121 at one end and the nozzles 121 at the other end in a direction perpendicular to the nozzle row NL, is represented by W, and the length of the ejection head 10, specifically the distance between the nozzles 121 at one end and the nozzles 121 at the other end in the nozzle row, is represented by L. In FIG. 14, the distance between the nozzles 121 at one end and the nozzles 121 at the other end in the movement direction Ds is represented by the scan length. Therefore, the scan length is calculated by W×cosα+Lsinα. In this case, when the minimum value of the time difference in FIG. 15 is Δtmin, it is preferable to determine the movement speed Vx and the arrangement angle α so that the scan time t for all nozzles 121, (W×cosα+Lsinα) / Vx, is minimized within a range where (1 / Δtmin) is smaller than or equal to fmax. This reduces the total time required for the ejection defect detection process for all nozzles 121.

[0090] In this embodiment, the discharge head 10 is moved in the movement direction Ds, but this is not limiting. The light source 65 may be moved in the movement direction Ds so as to approach the discharge head 10, or both the discharge head 10 and the light source 65 may be moved in the movement direction Ds so as to approach each other.

[0091] As described above, in this embodiment, immediately after causing one nozzle 121 of the simultaneous nozzles to eject ink droplets, the control device 20 causes the other nozzle 121 of the simultaneous nozzles to immediately eject ink droplets at the maximum frequency fmax of the ejection head 10. This makes it possible to prevent erroneous determination of ejection defects even when simultaneous nozzles with overlapping nozzle arrival orders occur. Furthermore, when using a high-density ejection head 10 with a narrow nozzle pitch, there may not be an arrangement angle α at which simultaneous nozzles do not occur, and therefore, a determination process can be performed to accommodate such cases.

[0092] Furthermore, in this embodiment, the control device 20 ejects ink droplets from one of the nozzles 121 of the simultaneous deposition sequence nozzles while simultaneously ejecting ink droplets from the nozzle 121 of the simultaneous deposition sequence nozzles. This makes it possible to determine whether or not there is a discharge defect based on the detection signal of the composite waveform. Furthermore, when using a high-density discharge head 10 with a narrow nozzle pitch, there may not be an arrangement angle α at which simultaneous deposition sequence nozzles do not occur, and therefore, a determination process can be performed to deal with such cases.

[0093] Furthermore, in this embodiment, the control device 20 may change the movement speed Vx of the ejection head 10 in the movement direction Ds depending on the separation distance in the movement direction Ds between two nozzles 121 that are successively crossed by the detection axis Da. This allows for a relatively long time interval between when one nozzle 121 crosses the detection axis Da first and when another nozzle 121 crosses the detection axis Da, by increasing the movement speed Vx during that time interval. For example, the distance between the position in the movement direction Ds of the other nozzle 121 that crosses the detection axis Da later and the position in the movement direction Ds of the first nozzle 121 that crossed the detection axis Da first is ΔXk. In this case, the movement speed Vx can be changed within a range in which the distance traveled by the ejection head 10 in the movement direction Ds during (1 / fmax) is equal to or less than ΔXk. This maximizes the speed of the detection process.

[0094] (Third embodiment) Next, a third embodiment of the present disclosure will be described. Fig. 16A is a diagram showing the maximum distance ΔF in the movement direction Ds among the distances of the variation in the position of each nozzle 121 according to the arrangement angle α of the discharge head 10, and Fig. 16B is a diagram showing the minimum distance ΔXmin among the separation distances in the movement direction Ds between two nozzles 121 that are successively crossed by the detection axis Da of the laser light Lz.

[0095] In the third embodiment, as in the second embodiment, the control device 20 rotates the ejection head 10 using the rotary motor 69 so that the ejection head 10 forms an angle α with the direction perpendicular to the optical axis direction DL in a plan view, as shown in Fig. 14. In this state, the control device 20 moves the ejection head 10 using the carriage 3 in the movement direction Ds at a predetermined movement speed Vx. As a result, the ejection head 10 is moved in the movement direction Ds at the movement speed Vx so that the detection axis Da intersects the nozzles 121 in a plan view along the ink droplet ejection direction. Then, the control device 20 ejects ink droplets from each nozzle 121 while moving the ejection head 10 in the movement direction Ds, thereby executing an ejection defect detection process.

[0096] Here, the interval of variation in the position of each nozzle 121 according to the variation in the arrangement angle α, that is, the interval of variation in the movement direction Ds when the position of each nozzle 121 varies in the movement direction Ds, is stored in advance in a storage unit based on a design value, etc. The control device 20 acquires the above intervals from the storage unit before starting the discharge defect detection process. Next, the control device 20 acquires the maximum interval ΔF shown in FIG. 16A from the acquired intervals.

[0097] Then, before starting the discharge defect detection process, the control device 20 calculates the separation distances (FIG. 15) in the movement direction Ds of two nozzles 121 (shown as nozzle 121a and nozzle 121b in FIG. 16B) that are successively crossed by the detection axis Da. In this case, the control device 20 can calculate the separation distances based on the time difference and movement speed Vx described above in FIG. 15. Next, the control device 20 obtains the minimum distance ΔXmin shown in FIG. 16B from among the separation distances.

[0098] In this configuration, the control device 20 determines the arrangement angle α so that the maximum spacing ΔF is smaller than the minimum distance ΔXmin when the ejection head 10 is moved in the movement direction Ds by the carriage 3. This makes it less likely that the arrival order of the nozzles 121 will change when they cross the detection axis Da.

[0099] Alternatively, in order to suppress fluctuations in the arrival order of the nozzles 121, the control device 20 may thin out the nozzles 121 to be detected in the ejection defect detection process. In other words, the control device 20 may limit the nozzles 121 to be detected. In this case, for example, the nozzles 121 that eject ink droplets may be limited to every other nozzle 121 in the movement direction Ds. This increases the minimum distance ΔXmin and the width of the maximum allowable interval ΔF.

[0100] The above-described method is a method for preventing fluctuations in the arrival order of the nozzles 121, but below we will explain a method for properly performing the ejection defect detection process even if fluctuations in the arrival order occur. Figure 17 is a diagram showing the ejection timing of ink droplets at each detection time. Figure 18 is a diagram showing the maximum distance ΔXmax among the separation distances in the movement direction Ds of multiple nozzles 121 that are successively crossed by the detection axis Da.

[0101] In this embodiment, the laser light Lz from the light source 65 has a detection width in which the signal strength of the detection signal is equal to or greater than a predetermined value, that is, the detection axis Da has a detection width Wd in which ejection defects can be properly detected, as shown in Fig. 14. As a result, the time (detection time) required to detect the ink droplet ejected from the nozzle 121 that is nth in the arrival order when crossing the detection axis Da has a certain width.

[0102] Therefore, the control device 20 acquires information about the simultaneous arrival nozzles, which are nozzles 121 that are estimated to simultaneously cross the detection axis Da of the laser light Lz depending on the variation in the arrangement angle α, using the method described in the second embodiment. Then, when the ejection head 10 moves in the movement direction Ds, the control device 20 causes each of the simultaneous arrival nozzles to eject ink droplets in sequence, starting with each nozzle 121 that could be nth in the arrival order within the detection time corresponding to the nth nozzle based on the detection width Wd, as shown in FIG. 17. Similarly, the control device 20 causes each of the simultaneous arrival nozzles to eject ink droplets in sequence, starting with each nozzle 121 that could be n+1th in the arrival order within the detection time corresponding to the n+1th nozzle based on the detection width Wd. The same applies hereinafter.

[0103] Here, the control device 20 determines whether or not there is an ejection defect based on the detection width Wd and the maximum distance ΔXmax (Figure 18) among the separation distances in the movement direction Ds of the multiple nozzles 121 that are successively crossed by the detection axis Da, and whose order of crossing the detection axis Da can change depending on the variation in the arrangement angle α when the ejection head 10 moves in the movement direction Ds.

[0104] The maximum distance ΔXmax will be described using an example. For example, consider a case where the arrival order of the three nozzles 121a, 121b, and 121c shown in FIG. 18 fluctuates. Examples of patterns of arrival order fluctuation include a pattern in which nozzle 121a, nozzle 121b, and nozzle 121c arrive at the detection axis Da in this order (the pattern in the upper position in FIG. 18), a pattern in which nozzle 121a, nozzle 121c, and nozzle 121b arrive at the detection axis Da in this order (the pattern in the middle position in FIG. 18), and a pattern in which nozzle 121c, nozzle 121b, and nozzle 121a arrive at the detection axis Da in this order (the pattern in the lower position in FIG. 18). In this case, of the distances between the nozzles in the movement direction Ds, the distance between nozzle 121c and nozzle 121a is the maximum distance ΔXmax.

[0105] To explain in detail the method for determining discharge defects in this embodiment, if the maximum distance ΔXmax is smaller than the detection width Wd, discharge defects can be detected by the detection axis Da having the detection width Wd even if the arrival order changes.

[0106] On the other hand, when the maximum distance ΔXmax≧detection width Wd, it may happen that the discharge is judged to be defective even though it is actually normal. In this case, when the designed arrival order is nozzle 121c, nozzle 121b, and nozzle 121a, it is judged that there is no discharge defect in the arrival order pattern of nozzle 121c, nozzle 121b, and nozzle 121a, the arrival order pattern of nozzle 121a, nozzle 121b, and nozzle 121c, and the simultaneous arrival order pattern of nozzle 121c, nozzle 121b, and nozzle 121a. On the other hand, if there is an arrival order pattern other than those mentioned above, or if normal discharge is not achieved at any time, it is judged that there is a discharge defect.

[0107] As described above, in this embodiment, when the carriage 3 moves the ejection head 10 in the movement direction Ds, the control device 20 determines the arrangement angle α so that the maximum spacing ΔF is smaller than the minimum distance ΔXmin. This makes it less likely that the arrival order of the nozzles 121 will change when they cross the detection axis Da, even if there is variation in the arrangement angle α. This makes it possible to prevent erroneous determination of ejection defects in the nozzles 121.

[0108] Furthermore, in this embodiment, the control device 20 may limit the nozzles 121 to be detected. In this case, the minimum distance ΔXmin increases, and the allowable maximum spacing ΔF increases. This makes it possible to increase the allowable variation in the arrangement angle α.

[0109] Furthermore, in this embodiment, when the ejection head 10 moves in the movement direction Ds, the control device 20 ejects ink droplets in order from each nozzle 121 that has the potential to be nth in the arrival order within the detection time corresponding to the nth nozzle based on the detection width Wd for each of the nozzles in the same arrival order. This makes it possible to prevent erroneous determination of ejection defects in the nozzles 121 even if variations in the arrival order occur when the nozzles 121 cross the detection axis Da due to variations in the arrangement angle α.

[0110] Furthermore, in this embodiment, the control device 20 determines whether or not there is a discharge defect based on the detection width Wd and the maximum distance ΔXmax. This makes it possible to prevent erroneous determination of a discharge defect in the nozzle 121 even if the arrival order of the nozzles 121 changes when they cross the detection axis Da due to variations in the arrangement angle α. [Explanation of symbols]

[0111] 1a Droplet discharge device 3 Carriage 10 Discharge head 20 Control device 34 Carriage motor 65 Light source 67 Detector element 121 nozzle DL optical axis direction Ds moving direction ID ink drops La optical axis Lb reference line Ln1 Approximate straight line Ln2 approximate curve Lz laser light NL nozzle row NM nozzle surface Sh flight space Tr tolerance W Printing medium α Placement angle ΔF Maximum distance in the direction of movement ΔXmin Minimum distance among the separation distances ΔXmax Maximum distance among the separation distances

Claims

1. a discharge head having a plurality of nozzles that form a plurality of nozzle rows arranged in a predetermined direction and discharge droplets onto a print medium; a light source that emits light toward a flight space in which the droplets ejected from the nozzle fly; a light receiving unit that detects the amount of light received after the light emitted from the light source has passed through the droplet in flight and outputs a detection signal; a control device; The control device A process of acquiring, for each nozzle, a parameter value indicating a predetermined characteristic of the detection signal; a process of determining whether the distribution of each of the parameter values ​​with respect to the position of each of the nozzles is linear, and determining that the nozzles corresponding to the parameter values ​​that are not distributed linearly are nozzles having ejection defects.

2. The control device A process of converting each of the parameter values ​​to obtain a predetermined converted value; a process of determining a reference line using the converted values ​​for each of the nozzles forming the same nozzle row; 2. The droplet ejection device according to claim 1, further comprising: a process for determining whether the conversion value for each nozzle is within an acceptable range relative to the reference line; and, if the conversion value is not within the acceptable range, determining that the nozzle corresponding to the conversion value is a nozzle having an ejection defect.

3. The droplet ejection device according to claim 2 , wherein the control device does not execute the process of obtaining the converted value when the parameter value exceeds a threshold value.

4. The droplet ejection device according to claim 2 , wherein the control device executes a process for obtaining the converted value when the parameter value is equal to or smaller than a threshold value.

5. The droplet ejection device according to claim 2 , wherein the control device sets the reference line as a moving average line or an approximation line obtained using the converted values ​​for all of the nozzles among the converted values ​​for the nozzles forming the same nozzle row.

6. The droplet ejection device described in claim 2, wherein the control device determines the reference line using, among the conversion values ​​for each of the nozzles forming the same nozzle row, a conversion value for one or more nozzles located at one end of the nozzle row and a conversion value for one or more nozzles located at the other end of the nozzle row.

7. The droplet ejection device according to claim 2, wherein the control device determines that the nozzle corresponding to the converted value that does not fall within the acceptable range is a nozzle having an ejection defect when the number of the converted values ​​that do not fall within the acceptable range relative to the reference line is less than a predetermined value.

8. The droplet ejection device described in claim 2, wherein if the number of converted values ​​that do not fall within the tolerance range for the reference line is equal to or greater than a predetermined value, the control device redetermines the reference line using a different method, determines whether the converted value for each nozzle falls within the tolerance range for the redetermined reference line, and if the converted value does not fall within the tolerance range, determines the nozzle corresponding to the converted value as a nozzle with an ejection defect.

9. The droplet ejection device according to claim 1, wherein the control device determines that a nozzle is at risk of ejection failure if there is a deviation in the direction away from the reference line, even if the conversion value for the same nozzle is within the tolerance range multiple times within a predetermined period.

10. The droplet ejection device according to claim 1 , wherein the control device determines that the ejection head needs to be replaced when the number of times that the same nozzle is determined to have the ejection defect within a predetermined period of time exceeds a predetermined number.

11. a moving device that moves the ejection head or the light source in a predetermined moving direction so that the light crosses the nozzle in a plan view along the ejection direction of the droplets, the ejection head and a direction intersecting with the optical axis direction of the light form an arrangement angle α in the plan view, 2. The droplet ejection device of claim 1, wherein when the ejection head or the light source is moved in the movement direction by the moving device, if there are multiple simultaneous nozzles that are nozzles that the light crosses simultaneously, the control device ejects the droplet from one of the simultaneous nozzles and then ejects the droplet from the other of the simultaneous nozzles at the maximum frequency of the ejection head immediately after ejecting the droplet from the other of the simultaneous nozzles.

12. a moving device that moves the ejection head or the light source in a predetermined moving direction so that the light crosses the nozzle in a plan view along the ejection direction of the droplets, the ejection head and a direction intersecting with the optical axis direction of the light form an arrangement angle α in the plan view, 2. The droplet ejection device according to claim 1, wherein when the ejection head or the light source is moved in the movement direction by the moving device, if there are multiple simultaneous nozzles that are nozzles that the light crosses simultaneously, the control device ejects the droplet from one of the simultaneous nozzles and simultaneously ejects the droplet from the other of the simultaneous nozzles.

13. The droplet ejection device according to claim 11 or 12, wherein the control device changes the speed at which the ejection head or the light source is moved in the movement direction by the moving device depending on the separation distance in the movement direction between two nozzles that are successively crossed by the light.

14. a moving device that moves the ejection head or the light source in a predetermined moving direction so that the light crosses the nozzle in a plan view along the ejection direction of the droplets, the ejection head and a direction intersecting with the optical axis direction of the light form an arrangement angle α in the plan view, The droplet ejection device described in claim 1, wherein the control device determines the placement angle α so that when the ejection head or the light source is moved in the movement direction by the moving device, the maximum distance in the movement direction among the intervals of variation in the position of each nozzle according to the variation in the placement angle α is smaller than the minimum distance among the separation distances in the movement direction between two nozzles that are successively crossed by the light.

15. The droplet ejection device according to claim 14 , wherein the control device limits the nozzles to be detected.

16. a moving device that moves the ejection head or the light source in a predetermined moving direction so that the light crosses the nozzle in a plan view along the ejection direction of the droplets, the ejection head and a direction intersecting with the optical axis direction of the light form an arrangement angle α in the plan view, the light from the light source has a detection width in which the signal intensity of the detection signal is equal to or greater than a predetermined value; 2. The droplet ejection device according to claim 1, wherein the control device ejects the droplets in sequence within a predetermined detection time based on the detection width for each of the simultaneous arrival nozzles, which are nozzles that are estimated to cross the light simultaneously depending on the variation in the placement angle α when the ejection head or the light source is moved in the movement direction by the moving device.

17. The droplet ejection device described in claim 16, wherein the control device determines whether or not there is an ejection defect based on the detection width and the maximum distance among the separation distances in the movement direction of the multiple nozzles that are successively crossed by the light, the order in which the light crosses the multiple nozzles changing depending on the variation in the placement angle α when the ejection head or the light source is moved in the movement direction by the moving device.

Images