Liquid droplet ejection apparatus

Abstract

To provide a liquid droplet discharge device capable of reducing erroneous detection of discharge failure.SOLUTION: The liquid droplet ejection device includes an ejection head that ejects a liquid droplet to a medium to be printed, an electrode disposed to face the ejection head, a voltage source that generates a potential difference between the ejection head and the electrode, a current detection unit that detects a current flowing between the ejection head and the electrode, and a control device. The controller is configured to execute a process of acquiring a detection waveform based on a current value detected by the current detector when the discharge head discharges a droplet in a state where a potential difference is generated between the discharge head and the electrode by the voltage source, and a process of determining whether or not the detection waveform has a predetermined feature of a normal waveform based on a current value in a case where there is no discharge defect within a detection cycle, and determine that a discharge defect occurs in a case where the detection waveform does not have the predetermined feature within a predetermined period within the detection cycle.SELECTED DRAWING: Figure 6

Description

[Technical Field]

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

[0002] Conventionally, a liquid ejection device is known that drives a head so that liquid is ejected from a nozzle onto an inclined surface of an inclined electrode, and determines the ejection state of the nozzle based on a voltage signal output from the inclined electrode in response to the drive (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-097134 Summary of the Invention [Problem to be solved by the invention]

[0004] However, with the above-mentioned conventional technology, if for some reason the waveform of the voltage signal is identical to or similar to a normal waveform, it may be determined that normal ejection is occurring even when liquid is not being ejected from the nozzle. Possible reasons for this include the bursting of air bubbles in the liquid accumulated on the electrode, or liquid dripping from the nozzle surface onto the electrode. If such an event occurs at the same time as the liquid is being ejected, it can lead to a false detection.

[0005] Therefore, an object of the present disclosure is to provide a droplet ejection device that can reduce false detection of ejection defects. [Means for solving the problem]

[0006] The droplet ejection device disclosed herein comprises an ejection head that ejects droplets onto a printing medium, an electrode arranged opposite the ejection head, a voltage source that generates a potential difference between the ejection head and the electrode, a current detection unit that detects the current flowing between the ejection head and the electrode, and a control device, wherein the control device performs the following processes: a process of acquiring a detection waveform based on a current value detected by the current detection unit when the ejection head ejects droplets while a potential difference is generated between the ejection head and the electrode by the voltage source; and a process of determining whether the detection waveform has predetermined characteristics of a normal waveform based on the current value when there is no ejection defect within a detection period; and determines that the ejection defect has occurred if the detection waveform does not have the predetermined characteristics for a predetermined period within the detection period.

[0007] According to the present disclosure, if the detected waveform does not have a predetermined characteristic of a normal waveform (for example, a maximum value, a minimum value, or a constant value that continues for a predetermined time, etc.) for a predetermined period within the detection cycle, it is determined that a discharge defect has occurred. In this way, the presence or absence of a discharge defect is determined based on whether or not the characteristic of a normal waveform is present, and therefore, false detection of the discharge defect can be reduced. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide a droplet ejection device that can reduce false detection of ejection defects. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a plan view illustrating a droplet ejection device according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a diagram showing nozzle rows in the ejection head of FIG. [Figure 3] FIG. 2 is a cross-sectional view showing the configuration of the ejection head of FIG. [Figure 4] 2 is a block diagram showing an example of components of a printing device having the droplet ejection device of FIG. 1. FIG. [Figure 5] FIG. 10 is a diagram showing a configuration for detecting ejection defects. [Figure 6]10A and 10B are diagrams illustrating examples of a normal waveform and a detected waveform. [Figure 7] 10A and 10B are diagrams illustrating examples of a normal waveform and a detected waveform. 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] FIG. 1 is a plan view showing a droplet ejection device 1a according to an embodiment of the present disclosure. FIG. 2 is a diagram showing a nozzle row NL in the ejection head 10 of FIG. 1. In FIG. 1 and each of the following figures, mutually orthogonal directions 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.

[0012] As shown in FIG. 1, the droplet ejection device 1a includes, for example, two metallic ejection heads 10 (10A, 10B) that are serial heads, two ultraviolet irradiation devices 40 (40A, 40B), a carriage 3 that supports the ejection heads 10 and the ultraviolet irradiation devices 40, a pair of guide rails 67, a storage tank 62, and a controller unit 19 that includes a control device 20 (FIG. 4). The ejection head 10 is an inkjet head that ejects droplets, for example, ultraviolet-curable ink droplets. However, ultraviolet-curable ink droplets are merely an example, and the droplets ejected by the ejection head 10 are not limited to ultraviolet-curable ink droplets. 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.

[0013] 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 causes the discharge head 10 and the ultraviolet irradiation device 40 to move back and forth in the movement direction Ds. The discharge head 10 is also connected to a storage tank 62 via a tube 62a.

[0014] In this embodiment, for example, the ejection head 10A ejects ink droplets of each of the colors cyan (C), magenta (M), yellow (Y), and black (K), which are sometimes collectively referred to as color inks. A color image is printed on the print medium W by ejecting these four color ink droplets onto the print medium W. Meanwhile, the ejection head 10B ejects white (W) ink droplets and clear (Cr) ink droplets. When printing a color image on, for example, fabric as the print medium W, white ink droplets are ejected first as a base ink to reduce the impact on the color and material of the fabric, and then color ink droplets are ejected on top of the white ink droplets. Clear ink droplets are also ejected to impart gloss or protect the printed area.

[0015] 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.

[0016] The print medium W is supported on a platen (not shown). The platen is configured to be movable in a transport direction Df by being driven by a transport motor 33 (FIG. 4) between a printing position where printing is performed on the print medium W and a removal position where the print medium W is removed from the platen. This causes the print medium W to be transported in the transport direction Df.

[0017] The droplet discharge device 1a includes a purge unit 50 and a receiving unit 54. The receiving unit 54 is disposed at one end of the guide rail 67 in the movement direction Ds so as to overlap with the movement area of ​​the carriage 3. The purge unit 50 is disposed at the other end of the guide rail 67 in the movement direction Ds so as to overlap with the movement area of ​​the carriage 3.

[0018] 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) of the ejection head 10 is separated from the cap 51. In contrast, at the suction position, the nozzle surface NM is covered by the cap 51, forming an enclosed 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 enclosed space is suctioned and ink is discharged from the nozzle holes 121a (FIG. 3). The cap 51 is also provided with an electrode 11 (FIG. 5), which will be described later. When the cap 51 is in the suction position, a process of detecting defective ejection is performed. The process of detecting defective ejection will be described in detail later.

[0019] When the flushing process is performed, the ejection head 10 is moved by the carriage 3 to a position above the receiving section 54. In this state, the ejection head 10 performs the flushing process, which forcibly ejects ink droplets. The receiving section 54 receives the ink droplets ejected from the ejection head 10 during the flushing process. Note that a pipe (not shown) is connected to the receiving section 54, and the ink droplets ejected into the receiving section 54 are drained through this pipe.

[0020] As shown in FIG. 2, the ejection head 10 has a plurality of nozzle rows NL, each of which is configured by arranging a plurality of nozzles 121 at predetermined intervals in a predetermined nozzle row direction Dn. That is, each nozzle row NL extends in the nozzle row direction Dn. The nozzle rows NL are arranged at predetermined intervals in the movement direction Ds. For example, the arrangement order of the nozzle rows NL in the ejection head 10A in the movement direction Ds may be, from one side of the movement direction Ds, one or more nozzle rows NL ejecting black ink droplets, one or more nozzle rows NL ejecting cyan ink droplets, one or more nozzle rows NL ejecting magenta ink droplets, and one or more nozzle rows NL ejecting yellow ink droplets. Furthermore, for example, the arrangement order of the nozzle rows NL in the ejection head 10B in the movement direction Ds may be, from one side of the movement direction Ds, one or more nozzle rows NL ejecting white ink droplets, and one or more nozzle rows NL ejecting clear ink droplets. The nozzle row direction Dn is, for example, parallel to the transport direction Df.

[0021] Next, FIG. 3 is a cross-sectional view showing the configuration of the ejection head 10 of FIG. 1. As shown in FIG. 3, the ejection head 10 has a plurality of nozzles 121 that eject ink droplets 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, a meniscus vibrates in the nozzle hole 121a, and ink is ejected.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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 nozzle row direction Dn to form a nozzle row NL.

[0026] 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.

[0027] 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.

[0028] 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).

[0029] 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.

[0030] 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 through an upper portion of the fifth flow path plate 152 in the stacking direction.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] The vibration plate 155 is laminated on the seventh flow path plate 154 and covers the upper openings of the pressure chambers 128 .

[0035] 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.

[0036] The individual electrodes 163 are electrically connected to a head driver IC 32, which will be described later. The head driver IC 32 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 diaphragm 155 deforms in cooperation with the drive signal, and the volume of the pressure chamber 128 changes in a direction that increases or decreases. As a result, an ejection pressure that ejects ink droplets from the nozzles 121 is applied to the pressure chambers 128.

[0037] 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 is ejected from the nozzle hole 121a.

[0038] FIG. 4 is a block diagram showing an example of components of the printing device 1 having the droplet ejection device 1a of FIG.

[0039] 4, the printing device 1 includes operation keys 4, a display unit 5, 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, and a purge driver IC 36. The droplet ejection device 1a also includes a voltage source 37 and a current detection unit 38.

[0040] 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. Part of the display unit 5 also functions as an operation key. The controller unit 19 realizes the printing function based on inputs from the operation keys 4 or external inputs via a communication interface (not shown), and also controls the display of the display unit 5.

[0041] The controller unit 19 includes a control device 20 configured by, for example, 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, and 36 and the display unit 5.

[0042] 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 predetermined information, etc.

[0043] The ASIC 25 is connected to motor driver ICs 30 and 31, a head driver IC 32, an irradiation device driver IC 35, a purge driver IC 36, a voltage source 37, and a current detection unit 38. The ASIC 25 drives the drivers, the voltage source 37, and the current detection unit 38 based on commands from the control device 20.

[0044] The control device 20 moves the platen 6 in the transport direction Df by operating the transport motor 33 using the motor driver IC 30. The control device 20 moves the carriage 3 in the movement direction Ds by operating the carriage motor 34 using the motor driver IC 31.

[0045] The control device 20 converts image data acquired from an external device or the like into ejection data for ejecting ink droplets. The control device 20 causes the head driver IC 32 to eject ink droplets from the ejection head 10 based on the converted ejection data. The control device 20 causes the irradiation device driver IC 35 to irradiate ultraviolet light from a light-emitting diode chip provided in the ultraviolet irradiation device 40. The control device 20 operates the purge unit 50 using the purge driver IC 36.

[0046] The control device 20 generates a potential difference between the ejection head 10 and the electrode 11 (FIG. 5) using a voltage source 37. The control device 20 causes a current detection unit 38 to detect the current flowing between the ejection head 10 and the electrode 11 when a potential difference is generated between the ejection head 10 and the electrode 11.

[0047] Next, we will explain the process for detecting ejection defects in the nozzles 121. Fig. 5 is a diagram showing a configuration for detecting ejection defects. Note that the process for detecting ejection defects is performed with the nozzle surface NM of the ejection head 10 covered by a cap 51, but Fig. 5 shows only the electrode 11 provided on the cap 51, and the cap 51 is not shown.

[0048] When the ejection defect detection process is executed, the control device 20 moves the ejection head 10 to a position above the cap 51 using the carriage 3. Then, the control device 20 raises the cap 51 using an unillustrated lifting mechanism. As a result, the upper edge of the cap 51 comes into contact with the nozzle surface NM of the ejection head 10, and the electrode 11 is positioned opposite the nozzle surface NM of the ejection head 10, as shown in FIG.

[0049] In this state, the control device 20 applies a voltage of, for example, 500 V to the electrode 11 using the voltage source 37, thereby generating a potential difference between the ejection head 10 and the electrode 11. The ejection head 10 is maintained at ground potential. The control device 20 then causes ink droplets to be ejected from the ejection head 10. At this time, charges corresponding to the amount of charge possessed by the ink droplets are induced in the ejection head 10 and the electrode 11, respectively. As a result, a current corresponding to the difference between the amount of charge induced in the ejection head 10 and the amount of charge induced in the electrode 11 flows between the ejection head 10 and the electrode 11. At this time, the current detection unit 38 detects the current flowing between the ejection head 10 and the electrode 11. The control device 20 acquires a detection waveform Wd (described below) based on the current value detected by the utility pole detection unit 38.

[0050] Fig. 6 is a diagram showing an example of a normal waveform Wn and a detected waveform Wd. Note that the normal waveform Wn and the detected waveform Wd in Fig. 6 and Fig. 7, which will be described later, show the correspondence between time and voltage values ​​converted based on current values ​​detected by the utility pole detection unit 38. Note that in Figs. 6 and 7, the detected waveform Wd is shown by a solid line, and the normal waveform Wn is shown by a dashed line.

[0051] The normal waveform Wn is a detection waveform obtained in the past when no ejection defects occur in the nozzle 121. The normal waveform Wn is stored in the storage unit.

[0052] After acquiring the detected waveform Wd based on the current value detected by the current detection unit 38, the control device 20 executes a process to determine whether the detected waveform Wd has predetermined characteristics of the normal waveform Wn during a predetermined period within the detection cycle. In this embodiment, the detection cycle is the period during which ink droplets are ejected from the ejection head 10, and may be, for example, 6 msec. The predetermined period of the detection cycle may also be, for example, the first period of 1 msec or less within the detection cycle.

[0053] To specifically describe the above-mentioned determination process, the control device 20 acquires the maximum value Ma1 during a predetermined period within the detection cycle as the predetermined characteristic of the normal waveform Wn. Note that FIG. 6 shows an example in which only the maximum value Ma1 of the normal waveform Wn appears during the predetermined period, so only the maximum value Ma1 is acquired as the predetermined characteristic, but this is not limited to this. The predetermined period within the detection cycle may be set to include both the maximum value Ma1 and the minimum value Mm1. In this case, the control device 20 acquires not only the maximum value Ma1 of the normal waveform Wn but also the minimum value Mm1 as the predetermined characteristic.

[0054] Next, the control device 20 determines whether the detection waveform Wd has a predetermined characteristic (i.e., a maximum value) during a predetermined period within the detection cycle. In this case, the determination is made as to whether the maximum value Ma2 of the detection waveform Wd appears during the predetermined period within the detection cycle, not whether the maximum value Ma1 of the normal waveform Wn and the maximum value Ma2 of the detection waveform Wd are larger or smaller. In the example of FIG. 6, the maximum value Ma2 of the detection waveform Wd does not appear during the predetermined period within the detection cycle. Therefore, the control device 20 determines that the detection waveform Wd does not have the predetermined characteristic during the predetermined period within the detection cycle. Therefore, the control device 20 determines that a discharge defect has occurred when the detection waveform Wd does not have the predetermined characteristic during the predetermined period within the detection cycle. In this way, the control device 20 determines that a discharge defect has occurred when the maximum value Ma2 of the detection waveform Wd does not appear during the period during which the maximum value Ma1 of the normal waveform Wn appears (i.e., the above-mentioned predetermined period).

[0055] The predetermined period within the detection cycle may be set to include only the minimum value Mm1 of the normal waveform Wn. In this case, the control device 20 determines that a discharge defect has occurred if the minimum value Mm2 of the detection waveform Wd does not appear during the period in which the minimum value Mm1 of the normal waveform Wn appears (i.e., the above-mentioned predetermined period).

[0056] However, for example, if the maximum value Ma2 of the detection waveform Wd appears within a predetermined period within the detection cycle but the minimum value Mm2 does not appear within the predetermined period within the detection cycle, as in the example of Figure 6, using only the maximum value as the predetermined feature cannot properly determine whether there is a discharge defect. For this reason, as described above, it is desirable to set the predetermined period within the detection cycle so that both the maximum value Ma1 and the minimum value Mm1 are included as predetermined features. This allows for proper determination of a discharge defect waveform, for example, when compared with a normal waveform Wn in which both the maximum value Ma1 and the minimum value Mm1 appear within the predetermined period within the detection cycle, in which, for example, the maximum value Ma2 appears within the predetermined period within the detection cycle but the minimum value Mm2 does not appear within the predetermined period within the detection cycle.

[0057] Next, a description will be given of another example of a method for determining whether or not there is a discharge defect by the control device 20. Fig. 7 is a diagram showing another example of the normal waveform Wn and the detection waveform Wd.

[0058] The control device 20 determines that a discharge defect has occurred when the maximum value Ma2 and the minimum value Mm2 in the detected waveform Wd appear in the reverse order of the order in which the maximum value Ma1 and the minimum value Mm1 appear in the normal waveform Wn. In this example, the predetermined period within the detection cycle may be the detection cycle itself. Furthermore, the predetermined characteristic of the normal waveform Wn in this example is the order in which the maximum value Ma1 and the minimum value Mm1 appear.

[0059] Specifically, in this example, the control device 20 acquires the order of appearance of the maximum value Ma1 and the minimum value Mm1 as the predetermined feature of the normal waveform Wn. In the example of Fig. 7, the order of appearance of the predetermined feature is the maximum value Ma1 and the minimum value Mm1.

[0060] Meanwhile, the control device 20 acquires the order of appearance of the maximum value Ma2 and the minimum value Mm2 in the detection waveform Wd. In the example of FIG. 7, the order of appearance in the detection waveform Wd is the minimum value Mm2 followed by the maximum value Ma2. Therefore, the order of appearance of the maximum value Ma2 and the minimum value Mm2 in the detection waveform Wd is reverse to the order of appearance of the maximum value Ma1 and the minimum value Mm1 in the normal waveform Wn. Therefore, the detection waveform Wd does not have the predetermined characteristic during a predetermined period within the detection cycle. Therefore, the control device 20 determines that a discharge defect has occurred.

[0061] 6 and 7 described above, the waveform portion P2 including the maximum value Ma2 and the minimum value Mm2 may appear because air bubbles in the ink accumulated on the electrode 11 burst (example of FIG. 7), or ink droplets drip from the nozzle surface NM onto the electrode 11. When it is determined that an ejection defect is occurring due to such an event, control may be performed to wait until the air bubbles disappear, or the nozzle surface NM may be wiped.

[0062] As described above, according to the droplet ejection device 1a, if the detected waveform Wd does not have a predetermined characteristic of the normal waveform Wn (for example, a maximum value, a minimum value, or a constant value that continues for a predetermined time) during a predetermined period within the detection cycle, it is determined that an ejection defect has occurred. In this way, the presence or absence of an ejection defect is determined based on whether or not the characteristic of the normal waveform Wn is present, and therefore, false detection of the ejection defect can be reduced.

[0063] Furthermore, the detection waveform Wd, which is an abnormal waveform when a discharge defect occurs, differs from the normal waveform Wn in the timing at which the maximum or minimum value appears. According to the present disclosure, by determining that a discharge defect has occurred when the maximum value does not appear when it should appear, or when the minimum value does not appear when it should appear, it is possible to reduce false detections of discharge defects.

[0064] Furthermore, in this embodiment, the detection cycle is the cycle (period) during which ink droplets are ejected from the ejection head 10, so it is easy to determine whether the above-mentioned characteristics appear during a predetermined period within the detection cycle of the detection waveform due to the ejection of ink droplets, which can further reduce false detection of ejection defects.

[0065] Furthermore, for example, in the normal waveform Wn, the maximum value appears before the minimum value, but in the detection waveform Wd, which is an abnormal waveform that occurs when an ink bubble accumulated on the electrode 11 bursts, the minimum value tends to appear before the maximum value. According to the above configuration, it becomes easier to determine whether or not there is a discharge defect based on the above differences between the normal waveform Wn and the detection waveform Wd, which is an abnormal waveform.

[0066] Furthermore, in this embodiment, the normal waveform Wn is a detection waveform obtained in the past when no ejection defects occur in the nozzle 121. This makes it possible to accurately determine whether or not there is an ejection defect by using the detection waveform Wd obtained in the past as an empirical value.

[0067] The present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the gist of the present disclosure.

[0068] In the above embodiment, the maximum value Ma1 and minimum value Mm1 of the normal waveform Wn are used as the predetermined feature of the normal waveform Wn, but the present invention is not limited to this. For example, the predetermined feature may be an intermediate value between the maximum value Ma1 and minimum value Mm1 of the normal waveform Wn, or a constant value that continues for a predetermined period of time.

[0069] In addition, in the above embodiment, the waveform portion P1 of the normal waveform Wn, which includes the maximum value Ma1 and the minimum value Mm1, and the waveform portion P2 of the detected waveform Wd, which includes the maximum value Ma2 and the minimum value Mm2, may be compared using, for example, the sum of the two-line average or a correlation coefficient, and the presence or absence of a discharge defect may be determined based on the degree of difference between them.

[0070] In the above embodiment, the electrode 11 is provided on the cap 51 , but this is not limitative, and the electrode 11 may be disposed separately from the cap 51 .

[0071] Furthermore, in the above embodiment, the ejection head 10 is a serial head, but this is not limiting, and the ejection head 10 may be a line head. [Explanation of symbols]

[0072] 1a Droplet discharge device 10 Discharge head 11 electrodes 20 Control device 37 Voltage Source 38 Current detection unit Ma1 Maximum value of normal waveform Ma2 Maximum value of detected waveform Mm1 Minimum value of normal waveform Mm2 Minimum value of detected waveform W Printing medium Wd detection waveform Wn Normal waveform

Claims

1. a discharge head that discharges droplets onto a print medium; an electrode disposed opposite the ejection head; a voltage source that generates a potential difference between the ejection head and the electrode; a current detection unit that detects a current flowing between the ejection head and the electrode; a control device; The control device a process of acquiring a detection waveform based on a current value detected by the current detection unit when droplets are ejected from the ejection head in a state in which a potential difference is generated between the ejection head and the electrode by the voltage source; and determining whether the detected waveform has predetermined characteristics of a normal waveform based on the current value when there is no ejection defect, during a predetermined period within a detection cycle; The droplet ejection device determines that the ejection defect has occurred when the detection waveform does not have the predetermined characteristic for a predetermined period within the detection cycle.

2. The droplet ejection device according to claim 1, wherein the control device determines that the ejection defect has occurred if the maximum value does not appear in the detected waveform during a period in which the maximum value appears in the normal waveform, and if the minimum value does not appear in the detected waveform during a period in which the minimum value appears in the normal waveform.

3. The droplet ejection device according to claim 1 , wherein the detection period is a period during which droplets are ejected from the ejection head.

4. The droplet ejection device according to claim 1 , wherein the control device determines that the ejection defect has occurred when the maximum and minimum values ​​in the detected waveform appear in a reverse order to the order in which the maximum and minimum values ​​in the normal waveform appear.

5. The droplet ejection device according to claim 1 , wherein the normal waveform is a detected waveform obtained in the past when the ejection failure did not occur.

Images