Droplet ejection device

Abstract

To provide a droplet discharge device which can detect discharge failure with higher accuracy compared to conventional one.SOLUTION: A droplet discharge device comprises: a metal discharge head having a discharge surface where a nozzle hole for discharging droplets to a medium to be printed opens; an electrode moving relatively to the discharge surface; a voltage source which generates an electric potential difference between a discharge head and the electrode; a current detection part which detects electric current flowing between the discharge head and the electrode; and a control device. The control device calculates a droplet flight speed on the basis of a time during which electric flows, when discharging droplets by the discharge head in the state that the electric potential difference is generated between the discharge head and the electrode separated from each by only a first distance by the voltage source, and the first distance, and changes a relative distance between the discharge surface and the electrode so that a distance between the discharge surface and the electrode becomes a second distance longer than the first distance, and calculates a discharge bending amount to a normal flight direction of droplets on the basis of a time until droplets land on the electrode after being discharged.SELECTED DRAWING: Figure 7

Description

[Technical Field]

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

[0002] There are conventional technologies for detecting the ink ejection characteristics of a nozzle provided in a ejection head. For example, Patent Document 1 discloses a droplet ejection device that includes a first electrode that sets a predetermined potential on droplets ejected from the nozzle, a second electrode that sets a potential different from the predetermined potential, and a detection unit that detects a change in potential of the first electrode or the second electrode when droplets are ejected from the nozzle. With this configuration, the flight speed of the droplets ejected from the nozzle is detected based on the detected change in potential. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-131827 Summary of the Invention [Problem to be solved by the invention]

[0004] However, it is difficult to accurately detect defective nozzle ejection based solely on the flight speed of droplets ejected from the nozzle, which can lead to erroneous determination of defective ejection.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a droplet ejection device that can detect ejection defects with higher accuracy than conventional devices. [Means for solving the problem]

[0006] The droplet ejection device of the present invention comprises a metallic ejection head having an ejection surface on which nozzle holes for ejecting droplets onto a printing medium are opened, an electrode that moves relative to the ejection surface, 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 calculates the flight speed of the droplet based on the first distance and the time for which the current flows when the droplet is ejected by the ejection head while a potential difference is generated by the voltage source between the ejection head and the electrode, which are separated by a first distance, and changes the relative distance between the ejection surface and the electrode so that the distance between the ejection surface and the electrode becomes a second distance greater than the first distance, and calculates the amount of ejection deflection of the droplet relative to its normal flight direction based on the time from when the droplet is ejected to when it hits the electrode.

[0007] According to the present invention, it is possible to obtain the flight speed of a droplet and the amount of deflection of the droplet relative to the normal flight direction. This allows for highly accurate detection of defective ejection based on the flight speed and the amount of deflection. In this case, the flight speed is calculated when the distance between the ejection surface and the electrode is a first distance, and the amount of deflection is calculated when the distance between the ejection surface and the electrode is a second distance greater than the first distance. This allows for a larger detectable amount of deflection than when the distance between the ejection surface and the electrode is the first distance, thereby lengthening the detection time (i.e., the time from when the droplet is ejected until it lands on the electrode) due to the magnitude of the deflection. This makes it possible to obtain the amount of deflection with high accuracy while suppressing the influence of noise. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a droplet ejection device that can detect ejection defects with higher accuracy than conventional devices. [Brief explanation of the drawings]

[0009] [Figure 1]1 is a perspective view showing an image forming apparatus provided with a droplet ejection device according to an embodiment of the present invention; [Figure 2] 1 is a plan view showing a droplet ejection device according to an embodiment of the present invention. [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 image forming apparatus of FIG. 1. [Figure 5] 10 is a diagram showing a mode in which ink droplets are ejected from the ejection head in a state in which a potential difference is generated between the ejection head and an electrode, and FIG. 11 is a diagram showing a configuration for detecting a current that flows when ink droplets are ejected. [Figure 6] 10A and 10B are diagrams for explaining deflection of ink droplet ejection; [Figure 7] 10A and 10B are diagrams for explaining a method for calculating the flight speed and the amount of ejection deflection of ink droplets ejected by an ejection head. [Figure 8] 10A and 10B are diagrams illustrating an example of the configuration of an electrode lifting device that lifts and lowers an electrode. [Figure 9] FIG. 10 is a diagram showing a discharge head tilted by a tilting device. [Figure 10] FIG. 10 is a diagram illustrating an example of the configuration of the tilting device of FIG. 9. [Figure 11] FIG. 10 shows electrodes tilted by a driving device. DETAILED DESCRIPTION OF THE INVENTION

[0010] A droplet ejection device according to an embodiment of the present invention will be described below with reference to the drawings. The droplet ejection device described below is merely one embodiment of the present invention. Therefore, the present invention is not limited to the following embodiment, and additions, deletions, and modifications can be made without departing from the spirit of the present invention.

[0011] FIG. 1 is a perspective view showing an image forming apparatus 1 equipped with a droplet ejection device 1a according to one embodiment of the present invention. Hereinafter, an example will be described 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; however, the image forming apparatus 1 also includes inkjet printers capable of printing only on paper. In FIG. 1, mutually orthogonal directions are designated 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 the print medium W (described later), and the third direction Dz is the up-down direction. In the following description, Ds is referred to as the movement direction, Df is referred to as the transport direction, and Dz is referred to as the up-down direction.

[0012] As shown in Fig. 1, the image forming apparatus 1 of this embodiment 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 image forming apparatus 1 also includes a droplet ejection device 1a (Fig. 2) having an ejection head 10, which is, for example, a serial head, and a controller unit 19 including a control device 20 (Fig. 4). The ejection head 10 is an inkjet head that ejects, for example, ultraviolet-curable ink droplets Id (Fig. 5) as droplets.

[0013] 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).

[0014] 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 by driving a transport motor 33 (Figure 4) 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. As a result, the platen 6 moves the ejection surface of the print medium W relative to the ejection head 10 in the transport direction Df. 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.

[0015] The upper cover 7 is configured so that it rotates upward when its end is lifted, thereby exposing the inside of the housing 2.

[0016] 2, the droplet discharge device 1a includes a storage tank 62, a carriage 3 on which are mounted, for example, two metallic discharge heads 10 (10A, 10B) and two ultraviolet irradiation devices 40 (40A, 40B), and a pair of guide rails 67. Although two discharge heads 10 and two ultraviolet irradiation devices 40 are provided, the present invention is not limited to this, and one discharge head 10 and one ultraviolet irradiation device 40 may also be provided.

[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 ejection surface NM (FIG. 3) is separated from the cap 51. On the other hand, at the suction position, the ejection 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, the enclosed space is suctioned, and a purge process is performed in which ink is discharged from the nozzle holes 121a (FIG. 3).

[0022] Here, the electrodes 11, which will be described in detail later, are formed on a cap 51 that covers the ejection surface NM of the ejection head 10 when printing is not being performed on the print medium W. When the ejection surface NM is covered with the cap 51, the cap 51 is rotated by a drive device 58, which will be described later, so that the cap 51 is parallel to the ejection surface NM.

[0023] The receiving portion 54 receives the ink droplets Id ejected from the ejection head 10 during the flushing process.

[0024] Next, the detailed 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 to the ejection 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, and ink is ejected.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] The nozzles 121 are formed to penetrate the nozzle plate 146 in the stacking direction. On the ejection 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.

[0029] 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.

[0030] 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.

[0031] 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).

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] The vibration plate 155 is laminated on the seventh flow path plate 154 and covers the upper openings of the pressure chambers 128 .

[0038] 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.

[0039] The individual electrodes 163 are electrically connected to a driver IC. This 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 to eject an ink droplet Id from the nozzle 121.

[0040] 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.

[0041] Fig. 4 is a block diagram showing the components of the image forming apparatus 1 in Fig. 1. As shown in Fig. 4, the image forming apparatus 1 further 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, lifting device driver ICs 39 and 41, and a tilting device driver IC 42. The droplet ejection device 1a further includes a voltage source 37, a current detection unit 38, a head lifting device 55, an electrode lifting device 56, and a tilting device 57.

[0042] 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, 36, 39, 41, and 42 and the display unit 5.

[0043] 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.

[0044] 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, a current detection unit 38, lifting device driver ICs 39 and 41, and a tilting device driver IC 42 are connected to the ASIC 25. The ASIC 25 drives the drivers, the voltage source 37, and the current detection unit 38 based on commands from the control device 20.

[0045] The control device 20 drives the conveying motor 33 using the motor driver IC 30 to move the platen 6 in the conveying direction Df. The control device 20 drives the carriage motor 34 using the motor driver IC 31 to move the carriage 3 in the movement direction Ds.

[0046] 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 ejection surface. 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 using the purge driver IC 36.

[0047] The control device 20 controls the head lifting device 55 to lift and lower the discharge head 10 using the lifting device driver IC 39. The control device 20 controls the electrode lifting device 56 to lift and lower the electrode 11 (described later) using the lifting device driver IC 41. The control device 20 also controls the tilting device 57 (described later) to tilt using the tilting device driver IC 42.

[0048] The control device 20 generates a potential difference between the ejection head 10 and the electrode 11 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.

[0049] The control device 20 calculates the flight speed of the ink droplet Id based on the time it takes for a current to flow when the ink droplet Id is ejected from the ejection head 10 while a potential difference is generated by the voltage source 37 between the ejection head 10 and the electrode 11, which are separated by a predetermined distance. The control device 20 also calculates the amount of ejection deflection relative to the normal flight direction of the ink droplet Id ejected from the ejection head 10. The calculation of the flight speed and the amount of ejection deflection of the ink droplet Id by the control device 20 will be described in detail later.

[0050] FIG. 5 is a diagram showing a state in which ink droplets Id are ejected from the ejection head 10 in a state in which a potential difference is generated between the ejection head 10 and the electrode 11. As shown in FIG.

[0051] 5, when an ink droplet Id is ejected from the ejection head 10 while a potential difference is generated between the ejection head 10 and the electrode 11 by the voltage source 37, charges corresponding to the amount of charge possessed by the ink droplet Id are induced in the ejection head 10 and the electrode 11. Therefore, 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.

[0052] Here, we will explain the deflection of ink droplets Id ejected from the ejection head 10. As shown in Figure 6, ink droplets Id ejected from a normal nozzle 121 of the ejection head 10 fly along a normal flight direction Dn. In contrast, ink droplets Id ejected from a nozzle 121 with an ejection defect fly along a deflected flight direction Dm that is inclined relative to the normal flight direction Dn.

[0053] FIG. 7 is a diagram for explaining a method for calculating the flight speed and the amount of ejection deflection Rm of the ink droplet Id ejected by the ejection head 10. In FIG.

[0054] 7, when calculating the flight speed of the ink droplet Id, the control device 20 first moves the electrode 11 using the electrode lift device 56 so that the distance between the ejection surface NM of the ejection head 10 and the electrode 11 becomes a first distance L1. The configuration of the electrode lift device 56 will be described in detail later.

[0055] Next, the control device 20 generates a potential difference between the ejection head 10 and the electrode 11 using the voltage source 37. Then, the control device 20 causes the ejection head 10 to eject an ink droplet Id. 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 flowing between the ejection head 10 and the electrode 11 is detected by the current detection unit 38.

[0056] The control device 20 measures the time during which the current detected by the current detection unit 38 is flowing. If the flight speed of the ink droplet Id is v, the distance between the ejection head 10 and the electrode 11 is d (= L1), and the time during which the current is flowing is T, the control device 20 calculates the flight speed of the ink droplet Id using v = d / T.

[0057] The control device 20 can change the volume of the ink droplets Id ejected from the nozzles 121, thereby allowing the ejection head 10 to eject medium-sized or large ink droplets Id. When calculating the flight speed of the ink droplets Id, the control device 20 ejects ink droplets Id with a relatively large volume. Specifically, when calculating the flight speed of the ink droplets Id, the control device 20 ejects ink droplets Id with a volume larger than that of the ink droplets Id during normal printing.

[0058] After calculating the flight speed of the ink droplet Id, the control device 20 determines whether the difference between the calculated flight speed and the normal speed of the ink droplet Id stored in advance in ROM 21 or the like is equal to or greater than a threshold value. If the difference between the calculated flight speed and the normal speed is equal to or greater than the threshold value, the control device 20 calculates the amount of deflection of the ink droplet Id as follows. Note that if the difference between the calculated flight speed and the normal speed is less than the threshold value, it is assumed that no ejection defects have occurred, and the control device 20 does not need to calculate the amount of deflection. Note that the normal speed of the ink droplet Id is, for example, 5 m / s, and the threshold value is, for example, 3 m / s.

[0059] The control device 20 moves the electrode 11 using the electrode lifting device 56 so that the distance between the discharge head 10 and the electrode 11 becomes a second distance L2 that is greater than the first distance L1. Next, the control device 20 causes the voltage source 37 to generate a potential difference between the discharge head 10 and the electrode 11.

[0060] Next, the control device 20 causes the ink droplet Id to be ejected from the ejection head 10. The ejected ink droplet Id flies along a curved flight direction Dm that is inclined relative to the normal flight direction Dn.

[0061] When the ink droplet Id is ejected, a current flows between the ejection head 10 and the electrode 11. At this time, the current flowing between the ejection head 10 and the electrode 11 is detected by the current detection unit 38. The control device 20 measures the time during which the current detected by the current detection unit 38 flows. This time can be considered to be the time required for the ink droplet Id, which has experienced ejection deflection, to fly the flight distance L3 from when it is ejected from the ejection head 10 until it lands on the electrode 11.

[0062] The control device 20 calculates the distance d (i.e., the flight distance L3 of the ink droplet Id in FIG. 7) using the previously calculated flight speed of the ink droplet Id and the measured time for which the current flows, according to the above calculation formula v=d / T.

[0063] This makes the distances L2 and L3 known. Therefore, the angle θ between the normal flight direction Dn for distance L2 and the curved flight direction Dm for distance L3 can be calculated by θ = arccos(L2 / L3). Therefore, the control device 20 acquires the angle θ as the amount of deflection. Alternatively, the amount of deflection may be determined as the distance Rm, which is the difference between the landing position of the ink droplet Id after flying in the normal flight direction Dn and the landing position of the ink droplet Id after flying in the curved flight direction Dm. In this case, the control device 20 can calculate the distance Rm by Rm = L3 × sin θ.

[0064] 8 is a diagram showing an example of the configuration of an electrode lifting device 56 that raises and lowers the electrode 11. The control device 20 changes the distance between the electrode 11 and the ejection surface NM of the ejection head 10 by raising and lowering the electrode 11 using the electrode lifting device 56. Note that the configuration of the head lifting device 55 is the same as the configuration of the electrode lifting device 56, so a description of the head lifting device 55 will be omitted.

[0065] The following configuration is an example and does not limit the configuration of the electrode lifting device 56. As shown in FIG. 8, the electrode lifting device 56 has a motor 56a, which is, for example, an electric motor, a reduction gear 56b including a drive gear and a driven gear, a ball screw 56c, and a movable table 56d. A rotation shaft 56k of the motor 56a is connected to the drive gear of the reduction gear 56b. The ball screw 56c is disposed to extend in the vertical direction Dz. The movable table 56d is connected to the ball screw 56c. The electrode 11 is supported by the movable table 56d.

[0066] When the motor 56a is driven to rotate by the control device 20, the rotational force is transmitted to the ball screw 56c via the reduction gear 56b. This causes the ball screw 56c to rotate about its axis, which in turn moves the movable table 56d in the vertical direction Dz. This makes it possible to move the electrode 11 supported by the movable table 56d in the vertical direction Dz. This allows the distance between the electrode 11 and the ejection surface NM of the ejection head 10 to be changed.

[0067] Fig. 9 is a diagram showing the discharge head 10 tilted by the tilting device 57. Fig. 10 is a diagram showing an example of the configuration of the tilting device 57 of Fig. 9.

[0068] As described above, the distance between the ejection surface NM of the ejection head 10 and the electrode 11 is set to the first distance L1 to calculate the flight speed of the ink droplet Id, and then the ejection head 10 may be tilted when the distance is set to the second distance L2 to obtain the amount of ejection deflection of the ink droplet Id.

[0069] 9, the electrode 11 is arranged horizontally. The tilting device 57 tilts the discharge head 10 in response to an instruction from the control device 20 so that the discharge surface NM of the discharge head 10 is inclined relative to the electrode 11.

[0070] The configuration of the tilting device 57 will be described. The following configuration is an example and is not intended to limit the configuration of the tilting device 57. As shown in Fig. 10, the tilting device 57 includes a motor 57a, which is, for example, an electric motor, a rotating shaft 57k connected to the motor 57a, a disk-shaped rotating plate 57b, a transmission unit 57c, an elevating unit 57d extending in the vertical direction Dz and capable of reciprocating in the vertical direction Dz, and a support unit 57e. A reducer is connected to the motor 57a.

[0071] The rotation shaft 57k is connected to the center of the rotation plate 57b. The transmission part 57c is formed, for example, in a rod shape, and one end thereof is connected eccentrically to the rotation plate 57b, and the other end is connected to the upper end of the lifting part 57d. The support part 57e supports the lifting part 57d so that it can move in the up-down direction Dz. The lower end of the lifting part 57d is fixed to one side of the upper surface of the discharge head 10.

[0072] When the motor 57a is driven by the control device 20, the rotational force is transmitted to the rotating plate 57b via the rotating shaft 57k. This causes the rotating plate 57b to rotate around the rotating shaft 57k. Accordingly, the transmission unit 57c moves the lifting unit 57d upward or downward. As a result, the ejection head 10 is pulled or pressed by the lifting unit 57d, so that the position of one side of the ejection head 10 (i.e., the portion pressed by the lifting unit 57d) becomes higher or lower than the position of the other side. This allows the ejection surface NM of the ejection head 10 to be inclined with respect to the electrode 11. In this way, the distance between the ejection surface NM of the ejection head 10 and the electrode 11 can be changed to the second distance L2 when obtaining the amount of ejection deflection of the ink droplet Id.

[0073] 9, the electrode 11 may include a conductive portion 11a and a non-conductive portion 11b adjacent to the conductive portion 11a. Before calculating the flight speed of the ink droplet Id and the amount of ejection deflection, the control device 20 detects the boundary point 11c between the conductive portion 11a and the non-conductive portion 11b as the origin of the relative movement of the electrode 11 with respect to the ejection surface NM of the ejection head 10, that is, the origin of the movement of the ejection surface NM of the ejection head 10 with respect to the electrode 11 in FIG. 9. This is based on the idea that it is desirable to acquire the origin because a movement error in the ejection head 10 can cause the ejection head 10 to be misaligned with the electrode 11.

[0074] When detecting the boundary point 11c, the control device 20 causes the ejection head 10 to eject an ink droplet Id while generating a potential difference between the ejection head 10 and the conductive portion 11a of the electrode 11 using the voltage source 37. In this case, when the ink droplet Id ejected from the ejection head 10 flies between the ejection head 10 and the non-conductive portion 11b of the electrode 11 or lands on the non-conductive portion 11b, no current is detected by the current detection unit 38. Meanwhile, the control device 20 moves the ejection head 10 using the tilt device 57 to eject the ink droplet Id from the ejection head 10. At this time, the control device 20 completes detection of the boundary point 11c as the origin when the current detection unit 38 detects a current equal to or greater than a threshold value due to the ink droplet Id flying above the boundary point 11c of the electrode 11 and landing on the boundary point 11c. When the ejection head 10 is moved from the conductive portion 11a side to the non-conductive portion 11b side, the detection of the boundary point 11c as the origin is completed at the timing when a current equal to or less than a predetermined threshold is detected.

[0075] In Fig. 9, the distance between the electrode 11 and the ejection surface NM of the ejection head 10 is changed by tilting the ejection head 10, but the distance may also be changed by tilting the electrode 11. Fig. 11 is a diagram showing the electrode 11 tilted by a driving device 58. The configuration of the driving device 58 in Fig. 11 is the same as the configuration of the tilting device 57.

[0076] As described above, after calculating the flight speed of the ink droplet Id by setting the distance between the ejection surface NM of the ejection head 10 and the electrode 11 to a first distance L1, the electrode 11 may be tilted when setting the distance to a second distance L2 to obtain the amount of ejection deflection of the ink droplet Id. In Figure 11, the ejection head 10 is positioned horizontally. In response to instructions from the control device 20, the drive device 58 tilts the electrode 11 so that the upper surface of the electrode 11 is inclined relative to the ejection surface NM of the ejection head 10. As a result, the upper surface of the electrode 11 on the ejection surface NM side is inclined relative to the ejection surface NM.

[0077] When adopting a mode in which the electrode 11 is inclined, an uneven portion 11d is formed on the upper surface of the electrode 11 on the ejection surface NM side, in order to prevent the ink droplets Id from dripping.

[0078] As described above, the droplet ejection device 1a can acquire the flight speed of the ink droplet Id and the amount of deflection of the ink droplet Id relative to the normal flight direction Dn. This allows for highly accurate detection of ejection defects based on the flight speed and the amount of deflection. In this case, the flight speed is calculated when the distance between the ejection surface NM of the ejection head 10 and the electrode 11 is a first distance L1, and the amount of deflection is calculated when the distance between the ejection surface NM and the electrode 11 is a second distance L2, which is greater than the first distance L1. In this regard, when the distance between the ejection surface NM and the electrode 11 is relatively short, the effect of air resistance is small, making it easy to detect the flight speed with high accuracy. Furthermore, when the distance between the ejection surface NM and the electrode 11 is relatively long, the degree of deflection of the ink droplet Id due to air resistance is more pronounced, making this method suitable for detecting the amount of deflection. This allows for highly accurate detection of the amount of deflection.

[0079] Furthermore, in this embodiment, when changing the distance between the discharge surface NM of the discharge head 10 and the electrode 11, the discharge head 10 can be raised and lowered by the head lifting device 55. In this case, the distance between the discharge surface NM of the discharge head 10 and the electrode 11 can be easily changed. In particular, when a serial head is used as the discharge head 10, the serial head is scanned in the movement direction (main scanning direction) Ds, and the discharge head 10 becomes a moving component. Therefore, if the discharge head 10, which is a moving component, is further raised and lowered and the electrode 11 is used as a fixed component, it becomes easier to achieve positional accuracy of the discharge head 10 relative to the electrode 11, since one of them is fixed.

[0080] Furthermore, in this embodiment, when changing the distance between the discharge surface NM of the discharge head 10 and the electrode 11, the electrode 11 can be raised and lowered by the electrode lifting device 56. In this case, the distance between the discharge surface NM of the discharge head 10 and the electrode 11 can be easily changed. In particular, when a line head is used as the discharge head 10, the line head is fixed, so it is more suitable to raise and lower the electrode 11. Furthermore, since the electrode 11 is lighter than the discharge head 10, moving the lightweight electrode 11 provides greater braking when moved, shortening the time to stop and making it easier to achieve positional accuracy of the electrode 11 relative to the discharge head 10. Furthermore, a relatively small motor can be used for the electrode lifting device 56, allowing the device to be made smaller. Furthermore, moving the lightweight electrode 11 shortens the movement time.

[0081] Furthermore, in this embodiment, the control device 20 calculates the amount of deflected ejection when the difference between the calculated flight speed of the ink droplet Id and the normal speed is equal to or greater than a threshold. In this case, when the occurrence of a discharge defect can be determined based on the flight speed of the ink droplet Id alone, it is possible to avoid unnecessary calculation of the amount of deflected ejection. This makes it possible to shorten the time required to determine the occurrence of a discharge defect compared to when the amount of deflected ejection is calculated for all nozzles 121.

[0082] Furthermore, in this embodiment, the control device 20 may calculate the flight speed if the calculated amount of deflection is equal to or greater than a threshold value. In this case, if the occurrence of a discharge defect can be determined based solely on the amount of deflection of the ink droplet Id, unnecessary calculation of the flight speed can be avoided. This reduces the time required to determine the occurrence of a discharge defect compared to when the flight speed is calculated for all nozzles 121.

[0083] In addition, in this embodiment, the distance between the ejection surface NM and the electrode 11 can be easily changed by moving the ejection head 10 in the movement direction Ds while the upper surface of the electrode 11 is inclined with respect to the ejection surface NM using the drive device 58.

[0084] Furthermore, in this embodiment, the electrode 11 includes a conductive portion 11a and a non-conductive portion 11b adjacent to the conductive portion 11a. In this case, when an ink droplet Id ejected from a nozzle hole 121a of the ejection surface NM is between the ejection surface NM and the non-conductive portion 11b of the electrode 11, no potential difference occurs between the ejection head 10 and the electrode 11. By setting the boundary point 11c between the non-conductive portion 11b and the conductive portion 11a, where no potential difference occurs, as the origin of the relative movement of the electrode 11 with respect to the ejection surface NM, it is possible to prevent the distance between the ejection surface NM and the electrode 11 from changing due to positional deviation in the relative movement between the ejection head 10 and the electrode 11. This improves the accuracy of calculating the distance between the ejection surface NM and the electrode 11.

[0085] Furthermore, in this embodiment, by detecting the boundary point 11c, which is the origin, and then calculating the flight speed of the ink droplet Id and the amount of ejection deflection, it is possible to eliminate the influence of relative positional misalignment between the ejection head 10 and the electrode 11, thereby obtaining highly reliable calculation results.

[0086] In this embodiment, the electrode 11 has an uneven portion 11d formed on the upper surface thereof on the ejection surface NM side, which prevents the ink droplets Id that land on the inclined electrode 11 from dripping.

[0087] Furthermore, in this embodiment, there is no need to provide a new space for the electrode 11 because the electrode 11 is formed in the cap 51. This allows the droplet discharge device 1a to be made smaller.

[0088] Furthermore, in this embodiment, when calculating the flight speed of the ink droplets Id, the control device 20 ejects ink droplets Id with a relatively large volume. In this case, since large-volume ink droplets Id have less air resistance than small-volume ink droplets Id, the flight speed is relatively maintained even at positions far from the ejection head 10, and the difference between the flight speed of ink droplets Id associated with normal ejection and the flight speed of ink droplets Id associated with ejection defects becomes more likely to occur. Furthermore, the charge amount of the ink droplets Id increases in proportion to their volume, and the amount of charge flowing between the two electrodes as the ink droplets Id move increases, making it easier to detect ejection defects.

[0089] Furthermore, in this embodiment, when the tilting device 57 is used to tilt the ejection head 10, the electrodes 11 can be arranged horizontally. Therefore, it is possible to prevent the ink droplets Id that land on the horizontally arranged electrodes 11 from dripping.

[0090] Furthermore, the control device 20 may calculate the flight speed and the amount of deflection when the ejection head 10 ejects ink droplets Id while moving the ejection head 10 back and forth in the movement direction Ds with the electrode 11 tilted relative to the ejection surface NM by the tilting device 57 or the driving device 58. In this case, simply by scanning the ejection head 10 back and forth in the movement direction Ds, the distance between the ejection surface NM and the electrode 11 when calculating the flight speed and the amount of deflection for one nozzle 121 can be set to the above-mentioned first distance L1 and second distance L2. This saves the time required to change the distance between the ejection surface NM and the electrode 11 for each nozzle 121, thereby shortening the detection time.

[0091] (Variation) The present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the gist of the present invention.

[0092] In the above embodiment, either the ejection head 10 or the electrode 11 is tilted, but this is not limiting, and both the ejection head 10 and the electrode 11 may be tilted. In this case, both the ejection head 10 and the electrode 11 are tilted so that the distance between one end of the ejection head 10 in the movement direction Ds and one end of the electrode 11 in the movement direction Ds is different from the distance between the other end of the ejection head 10 in the movement direction Ds and the other end of the electrode 11 in the movement direction Ds.

[0093] In the above embodiment, the electrode 11 is formed on the cap 51 , but this is not limitative, and the electrode 11 may be disposed separately from the cap 51 .

[0094] In the above embodiment, the uneven portion 11d is formed on the entire upper surface of the electrode 11 on the ejection surface NM side in order to prevent the ink droplets Id from dripping, but this is not limiting. A wall portion or the like may be formed to surround the edge of the upper surface of the electrode 11.

[0095] In addition, in the above embodiment, the head lifting device 55, the electrode lifting device 56, the tilting device 57, and the driving device 58 are described, but to change the distance between the ejection surface NM of the ejection head 10 and the electrode 11, it is sufficient to provide at least one of the head lifting device 55, the electrode lifting device 56, the tilting device 57, and the driving device 58.

[0096] 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]

[0097] 1a Droplet discharge device 10 Discharge head 11 electrodes 11a Conductive part 11b Non-conductive part 11c Boundary point 11d Uneven part 20 Control device 37 Voltage Source 38 Current detection unit 51 Cap 55 Head lifting device 56 Electrode lifting device 57 Tilt device 58 Drive Unit 121a Nozzle hole Dn Normal flight direction ID ink drops L1 1st distance L2 2nd distance NM discharge surface Rm distance W Printing medium

Claims

1. a metallic ejection head having an ejection surface on which nozzle holes for ejecting droplets onto a print medium are formed; an electrode that moves relatively to the ejection surface; 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 potential difference is generated by the voltage source between the discharge head and the electrode, which are separated by a first distance, and when the discharge head discharges a droplet, the flight speed of the droplet is calculated based on the time during which the current flows and the first distance; and A droplet ejection device that changes the relative distance between the ejection surface and the electrode so that the distance between the ejection surface and the electrode becomes a second distance that is greater than the first distance, and calculates the amount of ejection deflection of the droplet relative to its normal flight direction based on the time from when the droplet is ejected until when it hits the electrode.

2. The droplet ejection device according to claim 1 , further comprising a head lifting device that lifts and lowers the ejection head.

3. The droplet ejection device according to claim 1 , further comprising an electrode lifting device that lifts and lowers the electrode.

4. The droplet ejection device according to claim 1 , wherein the control device calculates the amount of ejection deflection when, as a result of calculating the flight speed, a difference between the calculated flight speed and a normal speed is equal to or greater than a threshold value.

5. The droplet ejection device according to claim 1 , wherein the control device calculates the flight speed when the calculated amount of ejection deflection is equal to or greater than a threshold value.

6. The droplet ejection device according to claim 1 , wherein the surface of the electrode facing the ejection surface is inclined with respect to the ejection surface.

7. The droplet ejection device according to claim 1 , wherein the electrode includes a conductive portion and a non-conductive portion adjacent to the conductive portion.

8. The droplet ejection device according to claim 7, wherein the control device detects a boundary point between the conductive portion and the non-conductive portion as an origin of relative movement of the electrode with respect to the ejection surface before calculating the flight speed and the amount of ejection deflection.

9. The droplet ejection device according to claim 1 , wherein the surface of the electrode on the ejection surface side is formed unevenly.

10. the electrodes are formed on a cap that covers the ejection surface of the ejection head when printing on the print medium is not being performed, The droplet ejection device according to claim 1 , further comprising a drive device that moves the cap so that the cap is parallel to the ejection surface when covering the ejection surface.

11. The droplet ejection device according to claim 1 , wherein the control device is capable of changing the volume of droplets ejected from the nozzles, and ejects droplets with a relatively large volume when calculating the flight velocity.

12. The electrodes are arranged horizontally, The droplet ejection device according to claim 1 , further comprising a tilting device that tilts the ejection head so that the ejection surface is inclined relative to the electrode.

13. a carriage that moves the ejection head in a movement direction; a drive device that tilts the electrode relative to the ejection surface, 2. The droplet ejection device according to claim 1, wherein the control device calculates the flight speed and the amount of ejection deflection when the ejection head is caused to eject the droplets while the drive device moves the ejection head back and forth in the movement direction with the electrode tilted relative to the ejection surface.

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