Droplet discharge device

Abstract

To provide a droplet discharge device that can detect discharge abnormality before discharge failure occurs.SOLUTION: A droplet discharge device includes: a discharge head for discharging droplets on a medium to be printed; a light source which irradiates a flying droplet after being discharged from the discharge head until it impacts on the medium to be printed, with light; a detection device which is movable in an optical axis direction of light in order to detect refracted light that is light emitted from the light source and having passed through a flying droplet; and a control device. The control device causes the light source to radiate light, and causes the detection device to scan in the optical axis direction, in a state that droplets are continuously discharged by the discharge head, in order to calculate a volume of a droplet on the basis of an amount of refracted light detected by the detection device when the detection device is caused to scan.SELECTED DRAWING: Figure 5

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] Conventionally, there are technologies for detecting defective nozzles that do not eject ink. For example, Patent Document 1 discloses a technology for detecting defective nozzles using a laser. In the technology of Patent Document 1, an ejection pattern for ejecting droplets from desired nozzles is first selected, and droplets ejected based on this ejection pattern are detected by a detection mechanism. The defective nozzle is then identified based on a first output signal that is expected to be output by the detection mechanism and a second output signal that is actually output by the detection mechanism. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-275801 Summary of the Invention [Problem to be solved by the invention]

[0004] However, before a nozzle fails to eject properly, the piezoelectric element may deteriorate over time, causing the volume of ink droplets to change. This can reduce the ejection accuracy of each nozzle, potentially making it impossible to achieve the desired image quality.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a droplet ejection device that can detect ejection abnormalities before they lead to ejection failures. [Means for solving the problem]

[0006] The droplet ejection device of the present invention comprises an ejection head that ejects droplets onto a printing medium; a light source that irradiates light onto the droplets in flight after they are ejected from the ejection head and before they land on the printing medium; a detection device that is configured to be movable in the optical axis direction of the light and that detects refracted light, which is light that has passed through the droplets in flight after being emitted from the light source; and a control device, wherein the control device causes the light source to irradiate the light while the droplets are continuously ejected by the ejection head, and scans the detection device in the optical axis direction, and calculates the volume of the droplets based on the amount of refracted light detected by the detection device when the detection device is scanned.

[0007] According to the present invention, by calculating the droplet volume, it is possible to determine whether the piezoelectric element has deteriorated before the nozzle experiences ejection failure. This allows correction to be performed to adjust the ink droplet volume based on the determination result. This prevents a decrease in the ejection accuracy of each nozzle, thereby making it possible to obtain the desired image quality. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a droplet ejection device that can detect ejection abnormalities before they lead to ejection failures. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a plan view showing a schematic configuration of a droplet ejection device. [Figure 2] 2 is a cross-sectional view showing the configuration of a discharge head in the droplet discharge device of FIG. 1. FIG. [Figure 3] FIG. 2 is a block diagram showing the configuration of the droplet ejection device of FIG. [Figure 4] 10A and 10B are diagrams illustrating how ink droplets ejected from an ejection head and flying are irradiated with laser light. [Figure 5] FIG. 5 is an enlarged view of the area indicated by the dotted line in FIG. [Figure 6] FIG. 2 is a plan view showing the arrangement of a light source and a detection device. [Figure 7] 10A to 10C are diagrams showing ejection pulses in an ejection waveform before correction and ejection pulses in an ejection waveform after correction. [Figure 8] 10 is a flowchart showing a process after calculating the volume of an ink droplet. 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] (First embodiment) 1, a droplet ejection device 10 of this embodiment ejects ink droplets as an example of droplets, and includes a storage tank 12, a carriage 16, an ejection head 20, a pair of transport rollers 15, a pair of guide rails 17, and a sub-tank 18. In the droplet ejection device 10, a print medium W is placed on a platen (not shown).

[0012] An ejection head 20 is mounted on the carriage 16. The carriage 16 is supported by a pair of guide rails 17 that extend in a main scanning direction perpendicular to the transport direction of the print medium W, and moves back and forth in the main scanning direction along the guide rails 17. This causes the ejection head 20 to move back and forth in the main scanning direction. In addition, the carriage 16 is mounted with, for example, four sub-tanks 18. Each sub-tank 18 is connected to a corresponding storage tank 12 via a tube.

[0013] The pair of transport rollers 15 are arranged parallel to each other along the main scanning direction. The transport rollers 15 rotate when a transport motor (not shown) is driven, thereby transporting the print medium W on the platen in the transport direction.

[0014] Ink is stored in the storage tanks 12. The storage tanks 12 are connected to the ejection heads 20 via ink flow paths to supply ink to the ejection heads 20. A storage tank 12 is provided for each type of ink. For example, four storage tanks 12 are provided, each storing black, yellow, cyan, and magenta ink.

[0015] The ejection head 20 moves in a main scanning direction perpendicular to the transport direction. As shown in FIG. 2, the ejection head 20 has a plurality of nozzles 21 that eject ink. The ejection head 20 has a laminate of a flow path forming body and a volume changing unit. A liquid flow path is formed inside the flow path forming body, and a plurality of nozzle holes 21a are opened in the nozzle surface 40a, which is the lower surface of the flow path forming body. The volume changing unit is driven to change the volume of the liquid flow path. At this time, the meniscus vibrates in the nozzle holes 21a, and ink droplets are ejected.

[0016] 2, the flow path forming body of the ejection head 20 is a laminate of multiple plates, and the volume changing section includes a vibration plate 55 and an actuator (piezoelectric element) 60. An insulating film 56 is connected to the top of the vibration plate 55, and a common electrode 61 (described later) is connected to the top of the insulating film 56.

[0017] The multiple plates are stacked including, in order from the bottom, a nozzle plate 46, a spacer plate 47, a first flow path plate 48, a second flow path plate 49, a third flow path plate 50, a fourth flow path plate 51, a fifth flow path plate 52, a sixth flow path plate 53, and a seventh flow path plate 54. The first flow path plate 48, the second flow path plate 49, the third flow path plate 50, the fourth flow path plate 51, and the fifth flow path plate 52 configure the manifold plate 44.

[0018] 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 21, a plurality of individual flow paths 64, and a manifold 22 as liquid flow paths.

[0019] The nozzles 21 are formed to penetrate the nozzle plate 46 in the stacking direction. A plurality of nozzle holes 21a, which are the tips of the nozzles 21, are aligned in an arrangement direction on the nozzle surface 40a of the nozzle plate 46 to form a nozzle row. The arrangement direction is perpendicular to the stacking direction.

[0020] The manifold 22 supplies ink to pressure chambers 28 (described later) to which ink ejection pressure is applied. The manifold 22 extends in the arrangement direction and is connected to one end of each of the individual flow paths 64. In other words, the manifold 22 functions as a common flow path for the ink. The manifold 22 is formed by through-holes that penetrate the first flow path plate 48 to the fourth flow path plate 51 in the stacking direction and recesses that are recessed from the lower surface of the fifth flow path plate 52, which are overlapped in the stacking direction.

[0021] The nozzle plate 46 is disposed below the spacer plate 47. The spacer plate 47 has a recess 45 formed by, for example, half-etching the surface on the nozzle plate 46 side in the thickness direction of the spacer plate 47, whereby a thin portion constituting the damper portion 47a and a damper space 47b are formed. With this configuration, the damper space 47b is formed as a buffer space between the manifold 22 and the nozzle plate 46.

[0022] A supply port 22a communicates with the manifold 22. The supply port 22a is formed, for example, in a cylindrical shape and is provided at one end in the arrangement direction (longitudinal direction of the manifold 22). The manifold 22 and the supply port 22a are connected by unillustrated flow paths that penetrate the upper portion of the fifth flow path plate 52, the sixth flow path plate 53, and the seventh flow path plate 54, respectively.

[0023] The multiple individual flow paths 64 are each connected to the manifold 22. The upstream ends of the individual flow paths 64 are connected to the manifold 22, and the downstream ends are connected to the base ends of the nozzles 21. Each individual flow path 64 is made up of a first communication hole 25, a supply throttle path 26 which is an individual throttle path, a second communication hole 27, a pressure chamber 28, and a descender 29, and these components are arranged in this order.

[0024] The first communication hole 25 has a lower end connected to the upper end of the manifold 22, extends upward in the stacking direction from the manifold 22, and penetrates an upper portion of the fifth flow path plate 52 in the stacking direction.

[0025] The upstream end of supply throttle path 26 is connected to the upper end of first communication hole 25. Supply throttle path 26 is formed by half etching, for example, and is configured as a groove recessed from the lower surface of sixth flow path plate 53. Furthermore, second communication hole 27 has its upstream end connected to the downstream end of supply throttle path 26, extends upward in the stacking direction from supply throttle path 26, and is formed to penetrate sixth flow path plate 53 in the stacking direction.

[0026] The upstream end of the pressure chamber 28 is connected to the downstream end of the second communication hole 27. The pressure chamber 28 is formed to penetrate the seventh flow path plate 54 in the stacking direction.

[0027] The descender 29 is formed to penetrate the spacer plate 47, the first flow path plate 48, the second flow path plate 49, the third flow path plate 50, the fourth flow path plate 51, the fifth flow path plate 52, and the sixth flow path plate 53 in the stacking direction, and is disposed to the left of the manifold 22 in the width direction in FIG. 2. The descender 29 has an upstream end connected to the downstream end of the pressure chamber 28, and a downstream end connected to the base end of the nozzle 21. The nozzle 21 overlaps the descender 29 in the stacking direction, for example, and is disposed in the center of the descender 29 in the direction (width direction) perpendicular to the stacking direction.

[0028] The vibration plate 55 is laminated on the seventh flow path plate 54 and covers the upper openings of the pressure chambers 28.

[0029] The actuator 60 includes a common electrode 61, a piezoelectric layer 62, and an individual electrode 63, which are arranged in this order. The common electrode 61 covers the entire surface of the vibration plate 55 via an insulating film 56. The piezoelectric layer 62 covers the entire surface of the common electrode 61. The individual electrode 63 is provided for each pressure chamber 28 and is arranged on the piezoelectric layer 62. One individual electrode 63, the common electrode 61, and the portion of the piezoelectric layer 62 sandwiched between the two electrodes constitute one actuator 60.

[0030] The individual electrodes 63 are electrically connected to a driver IC. This driver IC receives control signals from a control device 71 (described later) and generates drive signals to apply to the individual electrodes 63. In contrast, the common electrode 61 is always maintained at ground potential. In this configuration, the active portion of the piezoelectric layer 62 expands and contracts in the planar direction together with the two electrodes 61, 63 in response to the drive signals. In response, the vibration plate 55 deforms in cooperation with the drive signals, and the volume of the pressure chamber 28 changes in a direction that increases or decreases. As a result, an ejection pressure is applied to the pressure chamber 28, causing ink droplets to be ejected from the nozzle 21.

[0031] In the ejection head 20 described above, the supply port 22a is connected to the subtank 18 via a pipe. When a pressure pump provided in the pipe is driven, ink passes from the subtank 18 through the pipe and flows into the manifold 22 via the supply port 22a. The ink then flows from the manifold 22 into the supply throttle passage 26 via the first communication hole 25, and from the supply throttle passage 26 into the pressure chamber 28 via the second communication hole 27. The ink then flows through the descender 29 and into the nozzle 21. When an ejection pressure is applied to the pressure chamber 28 by the actuator 60, an ink droplet is ejected from the nozzle hole 21a.

[0032] Fig. 3 is a block diagram showing the configuration of the droplet ejection device 10 of Fig. 1. Fig. 4 is a diagram showing how a laser beam Li is irradiated onto an ink droplet Id in flight after being ejected from the ejection head 20, and Fig. 5 is an enlarged view of an area Ep in Fig. 4. Fig. 6 is a plan view showing the arrangement of a light source 80 and a detection device 81.

[0033] As shown in FIG. 3, in addition to the above components, the droplet ejection device 10 includes a control device 71 consisting of a CPU or the like, a RAM 72, a ROM 73, a head driver IC 74, a waveform generating circuit 76, a light source 80, a detection device 81, motor driver ICs 30 and 32, a conveying motor 31, and a carriage motor 33.

[0034] The light source 80 irradiates light onto the ink droplets Id in flight after they are ejected from the ejection head 20 and before they land on the print medium W. In this embodiment, the light source 80 is, for example, a semiconductor laser, and irradiates the ink droplets Id in flight with laser light Li. When the laser light Li is irradiated onto the ink droplets Id, the ink droplets Id act like a spherical lens, causing the laser light Li to be refracted.

[0035] The detection device 81 is configured to be movable in the optical axis direction Dl of the laser light Li. The detection device 81 detects refracted light Lk after the laser light Li emitted from the light source 80 passes through an ink droplet Id in flight. In this embodiment, the detection device 81 is, for example, a photodiode.

[0036] The control device 71 receives the detection results from the detection device 81. The control device 71 causes the light source 80 to irradiate laser light Li while the ejection head 20 is continuously ejecting ink droplets Id. At this time, the control device 71 causes the detection device 81 to scan in the optical axis direction Dl. The control device 71 then calculates the volume of the ink droplet Id based on the amount of refracted light Lk detected by the detection device 81 when the detection device 81 is scanned. The method by which the control device 71 calculates the volume of the ink droplet Id will be described in detail later. The waveform generation circuit 76 generates an ejection waveform of a signal that drives the actuator 60.

[0037] The RAM 72 stores information on the ejection data and the refractive index of the ink droplets Id, etc. The ROM 73 stores a droplet ejection program and a control program for performing various data processing.

[0038] The head driver IC 74 receives instructions from the control device 71 to cause the ejection head 20 to continuously eject ink droplets Id. The motor driver IC 30 receives instructions from the control device 71 to control the drive of the transport motor 31. The transport motor 31 operates the transport rollers 15 to transport the print medium W in the transport direction. In addition, the motor driver IC 32 receives instructions from the control device 71 to control the drive of the carriage motor 33. The carriage motor 33 operates the carriage 16 to move the ejection head 20 in the main scanning direction.

[0039] Next, the method for calculating the volume of the ink droplet Id by the control device 71 will be described with reference to the drawings.

[0040] As shown in Fig. 4, the light source 80 is arranged on one side of the position of the ejection head 20 in the optical axis direction Dl of the laser light Li emitted from the light source 80. The light source 80 is arranged inside a box-shaped light source housing section 82. The light source housing section 82 has a slit 82a on the side in the emission direction of the laser light Li emitted from the light source 80. A lens 83 is arranged inside the light source housing section 82 so as to cover the slit 82a from the inside of the light source housing section 82. In this configuration, the laser light Li emitted from the light source 80 passes through the lens 83, and is then ejected from the ejection head 20 and irradiated onto an ink droplet Id in flight.

[0041] As shown in FIG. 5, the detection device 81 is disposed on the other side of the optical axis direction Dl of the laser light Li relative to the position of the discharge head 20. The detection device 81 is disposed a predetermined distance away from the light source 80 in the optical axis direction Dl. The initial position of the detection device 81 in the optical axis direction Dl is stored in advance in the RAM 72 or the like. The detection device 81 is configured to be able to scan along the optical axis direction Dl of the laser light Li. The detection device 81 also has a slit 85 through which the refracted light Lk enters. The detection device 81 detects the refracted light Lk that enters through the slit 85.

[0042] The light source 80 and detection device 81 described above are arranged relative to the ejection head 20 as follows. As shown in Fig. 6, the ejection head 20 has a plurality of nozzle rows NL arranged side by side in the main scanning direction. The plurality of nozzle rows NL includes, for example, a nozzle row NL that ejects yellow ink droplets Id, a nozzle row NL that ejects magenta ink droplets Id, a nozzle row NL that ejects cyan ink droplets Id, and a nozzle row NL that ejects black ink droplets Id. A light source 80 and a detection device 81 are provided for each nozzle row NL.

[0043] As described above, the control device 71 causes the detection device 81 to scan in the optical axis direction Dl when the light source 80 irradiates the ink droplets Id with laser light Li while the ejection head 20 is continuously ejecting the ink droplets Id. At this time, the control device 71 calculates the volume of the ink droplets Id based on the amount of refracted light Lk detected by the detection device 81 when the detection device 81 is scanned. This will be explained in detail below.

[0044] The control device 71 receives the specification information of the light source 80 and the detection device 81 and the maximum light intensity position Z PDmax 5, the control device 71 causes the detection device 81 to scan the light source 80, and detects the position Z where the signal value detected by the detection device 81 is maximum (hereinafter referred to as the maximum light amount position). PDmax In this case, the control device 71 acquires the maximum light intensity position Z based on the initial position of the detection device 81 and the distance the detection device 81 has been moved. PDmax Get.

[0045] Next, the control device 71 determines the focal position Z of the refracted light Lk. f In this case, considering that the laser light Li is a beam whose intensity distribution in the plane perpendicular to the optical axis direction Dl is close to a Gaussian distribution, the focal position Z is calculated based on the beam radius ω of the Gaussian beam expressed by the following formula 1. f In the following formula 1, ω(z) is the laser beam radius at an arbitrary coordinate z in the optical axis direction Dl, and is equal to the slit diameter d of the slit 85. ω0 is the focal position Z fis the laser radius at the focal position Z f From maximum light intensity position Z PDmax In Figure 5, the distance is Z g Also, M 2 is a factor that represents the quality of the laser beam.

[0046]

number

[0047] From the above formula 1, the control device 71 calculates the focal position Z f = Maximum light intensity position Z PDmax -Distance Z g Therefore, the focal position Z f Calculate.

[0048] Here, the focal length f can be calculated by the following formula 2. In the formula 2, n is the refractive index of the ink droplet Id, and r is the radius of the ink droplet Id. The refractive index n is stored in advance in the RAM 72. The control device 71 calculates the radius r of the ink droplet Id using the formula 2. In this case, the control device 71 first calculates the radius r of the ink droplet Id based on the focal position Z calculated above. f and coordinate Z x That is, the control device 71 calculates the focal length f by f -coordinate Z x The focal length f is calculated by Z x is the coordinate in the optical axis direction Dl of the x-th nozzle 21 in the nozzle row NL (FIG. 6) that ejects the ink droplet Id irradiated with the laser beam Li, and the control device 71 has previously set Z x The control device 71 calculates the radius r of the flying ink droplet Id using the following formula 2 based on the calculated focal length f and refractive index n.

[0049]

number

[0050] Next, the control device 71 calculates V=(4 / 3)×π×r using the calculated radius r of the ink droplet Id. 3 The control device 71 calculates the volume V of the ink droplet Id from the calculation formula. The control device 71 compares the calculated volume V of the ink droplet Id with the volume of the ink droplet Id based on the ejection waveform (i.e., the volume of the ink droplet Id to be ejected) and determines whether or not there is an ejection abnormality. If there is an ejection abnormality, the control device 71 executes correction processing, etc., as described below, and if there is no ejection abnormality, the control device 71 causes the ejection head 20 to perform normal printing without executing correction processing, etc.

[0051] 7A to 7C are diagrams showing the ejection pulses in the ejection waveform before correction and the ejection pulses in the ejection waveform after correction.

[0052] The control device 71 determines whether or not there is an ejection abnormality based on the calculated volume of the ink droplet Id, and if there is an ejection abnormality, executes a correction process to change the ejection waveform.

[0053] As shown in FIG. 7(a), the ejection pulses P1, P2, and P3 before the correction process have the same voltage but different pulse widths. When an ejection abnormality is detected, an ejection waveform is generated with a different pulse number and pulse width, as shown in FIG. 7(a). Specifically, ejection pulses P4, P5, and P6 are added to the ejection waveform while leaving the ejection pulses P1, P2, and P3. The voltages of these ejection pulses P4, P5, and P6 are the same as those of the ejection pulses P1, P2, and P3. The pulse widths of the ejection pulses P4, P5, and P6 may be the same as the pulse width of any of the ejection pulses P1, P2, and P3, or may be different from the pulse width of any of the ejection pulses P1, P2, and P3.

[0054] Alternatively, the ejection pulses P1, P2, and P3 before the correction process may be changed to ejection pulses P1a, P2a, and P3a shown in Fig. 7(b) by the correction process. The voltage of the ejection pulse P1a is higher than the voltage of the ejection pulse P1, the voltage of the ejection pulse P2a is higher than the voltage of the ejection pulse P2, and the voltage of the ejection pulse P3a is higher than the voltage of the ejection pulse P3. The voltages of the ejection pulses P1a, P2a, and P3a increase in the order of ejection pulse P1a, ejection pulse P3a, and ejection pulse P2a.

[0055] Alternatively, the ejection pulses P1, P2, and P3 before the correction process may be changed to ejection pulses P1a, P2a, and P3a shown in Figure 7(c) by the correction process, and ejection pulses P4a, P5a, and P6a may be added. The ejection pulse P4a has the same pulse width as the ejection pulse P4 in Figure 7(a), but has a lower voltage. The ejection pulse P5a has the same pulse width as the ejection pulse P5 in Figure 7(a), but has a higher voltage. The ejection pulse P6a has the same pulse width as the ejection pulse P6 in Figure 7(a), but has a higher voltage.

[0056] Fig. 8 is a flowchart showing the processing performed after the volume of the ink droplet Id is calculated by the control device 71. As shown in Fig. 8, the control device 71 calculates the volume V of the ink droplet Id using the method described above (step S1).

[0057] Next, the control device 71 compares the calculated volume V of the ink droplet Id with the volume of the ink droplet Id based on the ejection waveform to determine whether or not an ejection abnormality exists (step S2). If an ejection abnormality exists (YES in step S2), the control device 71 determines whether or not a correction process is possible (step S3). In this case, the control device 71 determines whether or not the ejection abnormality can be improved by the above-mentioned correction process based on a comparison of the calculated volume of the ink droplet Id with a threshold value or a comparison of the number of nozzles in which an ejection abnormality is found with a threshold value. For example, if the calculated volume of the ink droplet Id is too small compared to the threshold value or if the number of nozzles in which an ejection abnormality is found is too large compared to the threshold value, the control device 71 determines that the ejection abnormality cannot be improved.

[0058] If the correction process is possible (YES in step S3), the control device 71 executes the above-mentioned correction process (step S4). On the other hand, if the correction process is not possible (NO in step S3), the control device 71 displays a message urging the user to replace the ejection head 20 (step S6). In this case, the control device 71 may light or blink a lamp or the like that may be provided in the droplet ejection device 10, or may display a message on a touch panel display or the like of a printer in which the droplet ejection device 10 is provided.

[0059] On the other hand, if there is no ejection abnormality (NO in step S2), the control device 71 causes the ejection head 20 to perform normal printing without performing correction processing or the like (step S5).

[0060] As described above, according to the droplet ejection device 10 of this embodiment, the detection device 81 is moved to detect the focal position Z f By calculating the volume of the ink droplet Id, it is possible to determine whether the actuator 60, which is a piezoelectric element, has deteriorated before the nozzle 21 experiences ejection defects. This makes it possible to execute a correction process to adjust the volume of the ink droplet Id based on the results of this determination. This prevents a decrease in the ejection accuracy of each nozzle 21, thereby making it possible to obtain the desired image quality.

[0061] In this embodiment, the radius r of the ink droplet Id obtained from the calculation formula f={n / [2×(n−1)]}×r is used to calculate V=(4 / 3)×π×r 3 The volume of the ink droplet Id is calculated using the following formula: This makes it possible to accurately calculate the volume of the ink droplet Id, and therefore to accurately determine whether the nozzle 21 is experiencing an ejection abnormality.

[0062] Furthermore, in this embodiment, the ejection waveform is changed according to the calculated volume of the ink droplet Id, thereby making it possible to make the nozzle 21 in which the ejection abnormality occurs eject an ink droplet Id having the desired volume after the correction process.

[0063] Furthermore, in this embodiment, by providing a light source 80 and a detection device 81 for each nozzle row NL, it is possible to sequentially calculate the droplet volume for each of the multiple nozzles 21 in each nozzle row NL, thereby increasing the processing speed when calculating the droplet volume.

[0064] (Second embodiment) In the first embodiment, the radius r of the ink droplet Id is calculated from Equation 2 above based on the calculated focal length f and the refractive index n pre-stored in RAM 72. In contrast, in the second embodiment, the control device 71 obtains the radius r of the ink droplet Id from the ejection waveform. Then, using the focal length f calculated in the same way as in the first embodiment and the obtained radius r of the ink droplet Id, the control device 71 calculates the refractive index of the ink droplet Id related to the ink currently being used from Equation 2 above. The control device 71 determines whether the calculated refractive index is the same as the refractive index n pre-stored. If there is no such identity, it can be determined that the ink currently being used is not genuine.

[0065] According to this embodiment, the refractive index of the ink droplet Id can be accurately calculated from the focal length f of the refracted light Lk and the radius r of the ink droplet Id using Equation 2. This improves the accuracy of determining the authenticity of ink currently in use.

[0066] (Variation) The present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit of the present invention. For example, the following modifications are possible.

[0067] In the above embodiment, in the correction process of the ejection waveform performed when an ejection abnormality is detected, the number of pulses of the ejection pulse before correction is increased or decreased, and the pulse width of one of the multiple ejection pulses after the increase or decrease is changed. Alternatively, only the voltage of the ejection pulse before correction is changed. Alternatively, the number of pulses of the ejection pulse before correction is increased or decreased, and the pulse width and voltage of one of the multiple ejection pulses after the increase or decrease are changed. However, this is not limited to this. The content of the above correction process is merely an example, and the combination of the number of ejection pulses, voltage, and pulse width to be changed before and after the correction process can be set as appropriate.

[0068] In the above embodiment, the light source 80 and the detection device 81 are provided for each of the nozzle rows NL that eject yellow ink droplets Id, the nozzle rows NL that eject magenta ink droplets Id, the nozzle rows NL that eject cyan ink droplets Id, and the nozzle rows NL that eject black ink droplets Id. However, this is not limited to this. For an ejection head provided with a nozzle row NL that ejects white ink droplets Id and a nozzle row NL that ejects clear ink droplets Id, the light source 80 and the detection device 81 may be provided for each of these nozzle rows NL. [Explanation of symbols]

[0069] 10 Droplet discharge device 20 Discharge head 21 nozzles 60 Actuator 71 Control device 72 RAM 73 ROM 80 light source 81 Detection Device Dl Optical axis direction ID ink drops Li laser light Lk refracted light NL nozzle row W Printing medium

Claims

1. a discharge head that discharges droplets onto a print medium; a light source that irradiates light onto the droplets in flight from the time they are ejected from the ejection head until they land on the print medium; a detection device configured to be movable in the direction of the optical axis of the light, and detecting refracted light, which is light emitted from the light source and then passes through the droplet in flight; a control device; The control device While the droplets are continuously discharged from the discharge head, the light source is irradiated with the light, and the detection device is scanned in the optical axis direction; The droplet ejection device calculates the volume of the droplet based on the amount of refracted light detected by the detection device when the detection device is scanned.

2. Further, a storage unit is provided that stores information about the refractive index of the droplets in advance, The control device a maximum light intensity position, which is a position of the detection device where the amount of refracted light is maximum when the detection device is scanned in the optical axis direction; calculating a focal length of the refracted light based on the specification information of the light source and the detection device and the maximum light intensity position; The droplet ejection device according to claim 1 , wherein the volume of the droplet is calculated based on the focal length and the refractive index stored in the storage unit.

3. The control device When the focal length is f and the refractive index is n, the radius r of the droplet obtained from the relational expression f = {n / [2 × (n-1)]} × r and the volume of the droplet are V, V = (4 / 3) × π × r ３ The droplet ejection device according to claim 2 , wherein the volume of the droplet is calculated by the following calculation formula:

4. Further, a storage unit is provided that stores information about the refractive index of the droplets in advance, The control device a maximum light intensity position, which is a position of the detection device where the amount of refracted light is maximum when the detection device is scanned in the optical axis direction; calculating a focal length of the refracted light based on the specification information of the light source and the detection device and the maximum light intensity position; obtaining the radius of the droplet; Calculating the refractive index of the droplet based on the radius of the droplet and the focal length; The droplet ejection device according to claim 1 , further comprising: determining whether the calculated refractive index is equal to the refractive index stored in the storage unit.

5. The droplet ejection device according to claim 4, wherein the control device calculates the refractive index based on the relational expression f = {n / [2 x (n-1)]} x r, where f is the focal length, n is the refractive index, and r is the radius of the droplet.

6. The droplet ejection device according to claim 1 , wherein the control device changes the ejection waveform in accordance with the calculated volume of the droplet.

7. the ejection head has a plurality of nozzle rows arranged side by side in a main scanning direction, The droplet ejection device according to claim 1 , wherein the light source and the detection device are provided for each of the nozzle rows.

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