Droplet ejection device

Abstract

To provide a droplet dispensing device that reduces the likelihood of misidentification of dispensing failures. [Solution] The droplet ejection device comprises an ejection head having a plurality of nozzles for ejecting droplets onto a printing medium, a light source having an emission surface for emitting light toward a flight space in which the droplets ejected from the nozzles fly, a light receiving unit having a light receiving surface for detecting the amount of light received after the light emitted from the light source has passed through the flight space, and a control device. When the control device ejects droplets from the ejection head and emits light from the light source, it performs nozzle ejection failure detection processing based on the amount of light received detected by the light receiving unit, and the light receiving surface is positioned at a relative inclination in a predetermined inclination direction with respect to a state facing the emission surface.

Description

Technical Field

[0001] The present disclosure relates to a droplet ejection device that ejects droplets such as ink droplets.

Background Art

[0002] Conventionally, a liquid ejection failure detection device including a discharge head having a nozzle, a light emitting element, and a light receiving element has been known (Patent Document 1). In this liquid ejection failure detection device, the light receiving element is arranged directly opposite to the light emitting element.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the light emitted from the light emitting element may be reflected by the light receiving element, and the reflected light may enter the light emitting element. Therefore, the oscillation mode of the light source may change discretely (that is, the wavelength may change discretely) due to the reflected light entering the light source. For this reason, there has been a problem that the voltage output by the light receiving element having wavelength dependence changes due to the above wavelength, resulting in noise.

[0005] Therefore, an object of the present disclosure is to provide a droplet ejection device in which false determination of ejection failure is less likely to occur.

Means for Solving the Problems

[0006] The droplet ejection device of this disclosure comprises an ejection head having a plurality of nozzles for ejecting droplets onto a printing medium, a light source having an emission surface for emitting light toward a flight space through which the droplets ejected from the nozzles fly, a light receiving unit having a light receiving surface for detecting the amount of light received after the light emitted from the light source has passed through the flight space, and a control device, wherein the control device performs nozzle ejection failure detection processing based on the amount of light received detected by the light receiving unit when the droplets are ejected from the ejection head and the light is emitted from the light source, and the light receiving surface is positioned at an angle relative to a predetermined inclination direction with respect to a state facing the emission surface.

[0007] According to this disclosure, reflected light, which is formed when light emitted from a light source is reflected by a light-receiving surface, is suppressed from being incident on the light source. As a result, by suppressing the incident of reflected light on the light source, discrete changes in the oscillation mode of the light source (i.e., discrete changes in wavelength) can be suppressed. Therefore, the voltage output by the light-receiving unit, which has wavelength dependence, is suppressed from containing noise due to the above-mentioned change in wavelength. Thus, nozzle ejection failure detection processing can be performed based on the noise-suppressed voltage output by the light-receiving unit. Consequently, misjudgments of ejection failures become less likely. [Effects of the Invention]

[0008] According to this disclosure, it is possible to provide a droplet dispensing device that is less prone to misjudgment of dispensing defects. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a plan view showing a droplet dispensing device according to one embodiment of the present disclosure. [Figure 2] Figure 2 is a cross-sectional view showing the configuration of the discharge head in Figure 1. [Figure 3] Figure 3 is a block diagram showing the components of a printing apparatus equipped with the droplet ejection device shown in Figure 1. [Figure 4]Figure 4 shows a configuration in which a laser beam is irradiated onto ink droplets ejected from the ejection head while they are in flight. [Figure 5] Figure 5 shows a configuration in which the light-receiving surface of the first detection element is positioned at an angle with respect to the light-emitting surface of the light source. [Figure 6] Figure 6A shows an example of the effective light-receiving surface of the light-receiving surface as seen from the output surface side when the light-receiving surface is positioned without tilting it in the second direction, and Figure 6B shows an example of the effective light-receiving surface of the light-receiving surface as seen from the output surface side when the light-receiving surface is positioned tilted at a predetermined angle in the second direction. [Figure 7] Figure 7A is a graph showing the relationship between the effective light-receiving area on the light-receiving surface and the inclination angle of the light-receiving surface, and Figure 7B is a graph showing the relationship between the amount of reflected light deviation and the inclination angle of the light-receiving surface. [Figure 8] Figure 8 is a graph showing an example of the relationship between wavelength and time of laser light, which is the output light emitted by a light source. [Figure 9] Figure 9A is a graph showing an example of the relationship between the output signal from the second detection element and time, and Figure 9B is a graph showing an example of the relationship between the output signal from the first detection element and time. [Figure 10] Figure 10 shows a correction table in which the correction amount in the correction process is stored for each state. [Figure 11] Figure 11 is a flowchart showing an example of a process that includes grouping. [Figure 12] Figure 12 is a block diagram showing the configuration of the signal amplification section. [Figure 13] Figure 13 is a flowchart showing an example of the ink droplet ejection process. [Modes for carrying out the invention]

[0010] Hereinafter, a droplet dispensing device according to an embodiment of this disclosure will be described with reference to the drawings. The droplet dispensing device described below is merely one embodiment of this disclosure. Therefore, this disclosure is not limited to the following embodiments, and additions, deletions, and modifications are permitted without departing from the spirit of this disclosure.

[0011] Figure 1 is a perspective view showing a droplet ejection device 100 according to one embodiment of the present disclosure. Figure 2 is a cross-sectional view showing the configuration of the ejection head 10 of Figure 1. Figure 3 is a block diagram showing the components of a printing apparatus 1 equipped with the droplet ejection device 100 of Figure 1. In Figures 1 and 2, mutually orthogonal directions are denoted as the first direction Ds, the second direction Df, and the third direction Dz. In this embodiment, for example, the first direction Ds is the direction of movement of the carriage 3 described later, the second direction Df is the direction of transport of the printing medium W described later, and the third direction Dz is the vertical direction. In the following description, Ds will be referred to as the direction of movement, Df as the transport direction, and Dz as the vertical direction.

[0012] As shown in Figures 1 and 3, the droplet ejection device 100 includes, for example, two ejection heads 10 (10A, 10B), two ultraviolet irradiation devices 40 (40A, 40B), a carriage 3 on which the ejection heads 10 and ultraviolet irradiation devices 40 are mounted, a storage tank 62, a pair of guide rails 63, and a controller unit 19 including a control device 20. In this embodiment, an inkjet head that ejects ultraviolet-curable ink droplets is exemplified as the ejection head 10. In this embodiment, the ink droplet corresponds to a liquid droplet.

[0013] The carriage 3 is supported by a pair of guide rails 63 that extend in the direction of movement Ds, and reciprocates along the guide rails 63 in the direction of movement Ds. As a result, the two discharge heads 10 (10A, 10B) and the two ultraviolet irradiation devices 40 (40A, 40B) reciprocate in the direction of movement Ds. The discharge heads 10 are also connected to the storage tank 62 via tubes 62a.

[0014] In this embodiment, the ejection head 10A ejects ink droplets of each color of cyan (C), magenta (M), yellow (Y), and black (K), which are collectively referred to as color ink, for example. By ejecting the ink droplets of the above four colors onto the printing medium W supported on a platen (not shown), a color image is printed on the printing medium W. On the other hand, the ejection head 10B ejects, for example, white (W) ink droplets and clear (Cr) ink droplets. When printing a color image on, for example, a fabric as the printing medium W, in order to reduce the influence on the color and material of the fabric, white ink droplets are first ejected as undercoat ink, and color ink droplets are ejected onto the white ink droplets. Further, clear ink droplets are ejected when imparting gloss or protecting the printed portion.

[0015] Ink is stored in the storage tank 62. The storage tank 62 is provided for each type of ink. For example, six storage tanks 62 are provided, and black, yellow, cyan, magenta, white, and clear ink are stored respectively.

[0016] The droplet ejection device 100 further includes a purge unit 50 and a receiving unit 54. The receiving unit 54 is disposed at one end side in the moving direction Ds of the pair of guide rails 63 so as to overlap the moving region of the carriage 3. The purge unit 50 is disposed at the other end side in the moving direction Ds of the pair of guide rails 63 so as to overlap the moving region of the carriage 3.

[0017] The purging unit 50 includes a cap 51, a suction pump 52, and a lifting mechanism (not shown) that raises and lowers the cap 51 between a suction position and a standby position. The suction pump 52 is connected to the cap 51. In the standby position, the nozzle surface NM in Figure 2 is separated from the cap 51. On the other hand, in the suction position, the nozzle surface NM is covered by the cap 51, forming a sealed space. When the suction pump 52 is driven while the cap 51 is in the suction position, the sealed space is sucked open, and a purging process is performed in which ink is discharged from the nozzle hole 121a in Figure 2. The receiving unit 54 receives ink droplets discharged from the discharge head 10 by the flushing process. The ink discharged by the purging process and the ink discharged by the flushing process are treated as waste liquid.

[0018] As shown in Figure 2, the discharge head 10 has a plurality of nozzles 121 that discharge ink droplets using ink from the storage tank 62. The discharge head 10 has a laminated structure consisting of a flow channel forming body and a volume changing section. An ink flow channel is formed inside the flow channel forming body, and a plurality of nozzle holes 121a open on its lower surface, the nozzle surface NM. The volume changing section is driven to change the volume of the ink flow channel. At this time, the meniscus vibrates in the nozzle holes 121a, causing ink to be discharged.

[0019] The flow channel forming body of the discharge head 10 is a laminate of multiple plates, and the volume changing section includes a diaphragm 155 and an actuator (piezoelectric element) 160. A common electrode 161 is connected to the diaphragm 155.

[0020] Multiple plates are stacked, from bottom to top, including a nozzle plate 146, a spacer plate 147, a first channel plate 148, a second channel plate 149, a third channel plate 150, a fourth channel plate 151, a fifth channel plate 152, a sixth channel plate 153, and a seventh channel plate 154.

[0021] Each plate has holes and grooves of various sizes formed in it. Inside the flow channel forming body formed by stacking the plates, the holes and grooves are combined to form multiple nozzles 121, multiple individual flow channels 164, and a manifold 122 as ink flow channels.

[0022] The nozzle 121 is formed by penetrating the nozzle plate 146 in the stacking direction. On the nozzle surface NM of the nozzle plate 146, multiple nozzle holes 121a, which are the tips of the nozzles 121, are arranged in the transport direction Df to form a nozzle row.

[0023] The manifold 122 supplies ink to the pressure chamber 128 to which discharge pressure is applied. The manifold 122 extends in the transport direction Df and is connected to one end of each of the multiple individual flow channels 164. In other words, the manifold 122 functions as a common flow channel for the ink. The manifold 122 is formed by through holes that penetrate the first flow channel plates 148 to the fourth flow channel plates 151 in the stacking direction, and recesses that are recessed from the lower surface of the fifth flow channel plate 152, overlapping in the stacking direction.

[0024] The nozzle plate 146 is positioned below the spacer plate 147. The spacer plate 147 is made of, for example, stainless steel. The spacer plate 147 has a recess 145 formed by, for example, half-etching, which causes a recess in the thickness direction of the spacer plate 147 from the surface facing the nozzle plate 146, thereby forming a thin-walled portion that forms a damper portion 147a and a damper space 147b. This creates a damper space 147b as a buffer space between the manifold 122 and the nozzle plate 146.

[0025] A supply port 122a is connected to the manifold 122. The supply port 122a is formed, for example, in a cylindrical shape and is provided at one end in the conveying direction Df. The manifold 122 and the supply port 122a are connected by a flow path not shown in the figure.

[0026] 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 consists of a first communication hole 125, an individual throttling passage which is a supply throttling passage 126, a second communication hole 127, a pressure chamber 128, and a descender 129, and these components are arranged in this order in the direction of ink supply.

[0027] The first communication hole 125 has its lower end connected to the upper end of the manifold 122, extends upward from the manifold 122 in the stacking direction, and penetrates the upper portion of the fifth flow path plate 152 in the stacking direction.

[0028] The upstream end of the supply throttling passage 126 is connected to the upper end of the first communication hole 125. The supply throttling passage 126 is formed, for example, by half-etching and consists of a groove recessed from the lower surface of the sixth flow channel plate 153. The second communication hole 127 has its upstream end connected to the downstream end of the supply throttling passage 126, extends upward from the supply throttling passage 126 in the stacking direction, and is formed by penetrating the sixth flow channel plate 153 in the stacking direction.

[0029] The pressure chamber 128 has its upstream end connected to the downstream end of the second communication hole 127. The pressure chamber 128 is formed by penetrating the seventh flow channel plate 154 in the stacking direction.

[0030] 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 upstream end of the descender 129 is connected to the downstream end of the pressure chamber 128, and the downstream end is connected to the base end of the nozzle 121. The nozzle 121 overlaps the descender 129 in the stacking direction, for example, and is positioned in the center of the descender 129 in the width direction.

[0031] The diaphragm 155 is laminated on the seventh flow path plate 154 and covers the upper end opening of the pressure chamber 128.

[0032] The actuator 160 includes a common electrode 161, a piezoelectric layer 162, and individual electrodes 163, arranged in this order. The common electrode 161 covers the entire surface of the diaphragm 155. The piezoelectric layer 162 covers the entire surface of the common electrode 161. Individual electrodes 163 are provided for each pressure chamber 128 and are arranged on the piezoelectric layer 162. One actuator 160 is composed of one individual electrode 163, the common electrode 161, and the portion of the piezoelectric layer 162 sandwiched between the two electrodes.

[0033] The individual electrodes 163 are electrically connected to the head driver IC 32 (Figure 3). The head driver IC 32 receives a control signal from the control device 20, generates a drive signal (voltage signal), and applies it to the individual electrodes 163. In contrast, the common electrode 161 is always kept 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. Accordingly, the diaphragm 155 deforms in cooperation, changing the volume of the pressure chamber 128 in a direction that increases or decreases it. As a result, the discharge pressure that causes ink droplets to be ejected from the nozzle 121 is applied to the pressure chamber 128.

[0034] 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 throttling passage 126 via the first communication hole 125, and from the supply throttling 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. At this point, when ejection pressure is applied to the pressure chamber 128 by the actuator 160, ink droplets are ejected from the nozzle hole 121a.

[0035] The printing device 1 is, for example, an inkjet printer capable of printing on a three-dimensional object, the printing medium W. The printing device 1 may also be an inkjet printer capable of printing only on paper. As shown in Figure 3, the printing device 1 includes an operation key 4, a display unit 5, and a reading device 26. The droplet ejection device 100 includes motor driver ICs 30, 31, a head driver IC 32, a transport motor 33, a carriage motor 34, an irradiation device driver IC 35, a purge driver IC 36, a light source driver IC 37, a detection driver IC 38, and a rotation driver 55. The droplet ejection device 100 also includes a rotation device 57 (Figure 5) having a rotation motor 56, a light source 65, a first detection element 67 for detecting laser light emitted from the light source 65, and a second detection element 69 provided within the light source 65 for detecting laser light emitted from the light source 65. In this embodiment, the first detection element 67 corresponds to the light receiving unit.

[0036] The controller unit 19 includes, for example, a control device 20 composed of a CPU, a storage device (ROM 21, RAM 22, EEPROM 23, HDD 24), and an ASIC 25. The control device 20 is connected to each of the above-mentioned storage units and controls each of the driver ICs 30~32, 35~38, 55 and the display unit 5.

[0037] The control device 20 performs various functions by executing a predetermined droplet ejection program stored in the ROM 21. The control device 20 may be implemented as a single processor in the controller unit 19, or as multiple processors working together. The droplet ejection program is read by the reader 26 from a recording medium KB such as a computer-readable magneto-optical disk or USB flash memory and stored in the ROM 21. The RAM 22 stores image data received from an external source and calculation results of the control device 20. The EEPROM 23 stores various initial setting information entered by the user. The HDD 24 stores various information.

[0038] The ASIC25 is connected to motor driver ICs 30 and 31, head driver IC 32, irradiation device driver IC 35, purge driver IC 36, light source driver IC 37, detection driver IC 38, and rotation driver IC 55. When the control device 20 receives a print job from the user, it outputs an image recording command to the ASIC25 based on the droplet ejection program. The ASIC25 controls each driver IC 30-32, 35-38, and 55 based on the image recording command. The control device 20 moves the platen in the transport direction Df by driving the transport motor 33 with the motor driver IC 30. As a result, the printing medium W supported by the platen is transported in the transport direction Df. The control device 20 moves the carriage 3 in the movement direction Ds by driving the carriage motor 34 with the motor driver IC 31. As a result, the ejection head 10 moves in the movement direction Ds.

[0039] The control device 20 converts image data acquired from an external device into ejection data for ejecting ink droplets onto the printing medium W. Based on the converted ejection data, the control device 20 ejects ink droplets from the ejection head 10 using the head driver IC 32. The control device 20 also irradiates ultraviolet light from the light-emitting diode chip of the ultraviolet irradiation device 40 using the irradiation device driver IC 35. The control device 20 drives the purge unit 50 using the purge driver IC 36. The control device 20 controls the laser light emission operation of the light source 65 using the light source driver IC 37. The control device 20 controls the detection operation of the first detection element 67 and the second detection element 69 using the detection driver IC 38 and receives signals output from the first detection element 67 and the second detection element 69. The control device 20 also tilts the first detection element 67 by driving the rotation motor 56 of the rotation device 57 using the rotation driver IC 55. The process of tilting the first detection element 67 will be described in detail later.

[0040] Figure 4 shows a configuration in which a laser beam Lz is irradiated onto an ink droplet being ejected from the ejection head 10 while it is in flight.

[0041] The light source 65 is, for example, a laser diode. As shown in Figure 4, the light source 65 emits laser light Lz in a specific wavelength range. Specifically, the light source 65 irradiates the laser light Lz towards the flight space Sh in which the ink droplets ejected from the ejection head 10 fly. In this embodiment, the laser light Lz corresponds to light.

[0042] The light source 65 is positioned on one side of the position of the discharge head 10 with reference to the optical axis DL of the optical axis La of the laser light Lz emitted from the light source 65. Examples of the light source 65 include light-emitting diodes (LEDs) and semiconductor lasers (LDs). The light source 65 is housed in a box-shaped light source housing 65a. The light source housing 65a has a slit 65b on the side facing the direction of emission of the laser light Lz emitted from the light source 65. The slit 65b allows the laser light Lz emitted from the light source 65 to pass to the outside. A lens 65c is positioned inside the light source housing 65a so as to cover the slit 65b from the inside of the light source housing 65a. One or more lenses may be provided in addition to lens 65c. The light source housing 65a is supported by a frame 71 that extends in the optical axis DL of the laser light Lz.

[0043] On the other hand, the first detection element 67 is positioned on the other side of the optical axis direction DL, with reference to the position of the discharge head 10. The first detection element 67 generates a current based on the received laser light Lz and outputs the current signal to a current-voltage conversion circuit (not shown). The current-voltage conversion circuit converts the current signal from the first detection element 67 into a voltage signal and outputs the voltage signal to an amplification circuit. The amplification circuit amplifies the voltage signal from the current-voltage conversion circuit and outputs it to the control device 20. The first detection element 67 is supported by the frame 71, similar to the light source housing 65a.

[0044] In the above configuration, the laser beam Lz emitted from the light source 65 passes through the lens 65c and is then ejected from the ejection head 10, irradiating the flying ink droplet in the flight space Sh. The first detection element 67 detects the amount of light received after the laser beam Lz emitted from the light source 65 has passed through the flight space Sh, and outputs a signal corresponding to the detected amount of light received to the control device 20. The control device 20 receives the signal output from the first detection element 67. Based on the received signal corresponding to the amount of light received, the control device 20 performs nozzle ejection failure detection processing. In the ejection failure detection processing, ejection failures such as abnormal ink droplet speed, abnormal ink droplet volume, and ink droplet distortion are detected. Distortion means that the ink droplet flies in a direction different from the normal flight direction.

[0045] Figure 5 shows a configuration in which the light-receiving surface 68 of the first detection element 67 is positioned at an angle with respect to the emission surface 66 of the light source 65. Figure 6A shows an example of the effective light-receiving surface S1 of the light-receiving surface 68 as seen from the emission surface 66 side when the light-receiving surface 68 is positioned without being tilted in the second direction D2, and Figure 6B shows an example of the effective light-receiving surface S2 of the light-receiving surface 68 as seen from the emission surface 66 side when the light-receiving surface 68 is positioned at a predetermined angle in the second direction D2.

[0046] As shown in Figure 5, the light source 65 has an emission surface 66 that emits laser light Lz. The first detection element 67 has a light-receiving surface 68 that detects the amount of light received related to the laser light Lz emitted by the light source 65.

[0047] The light-receiving surface 68 is positioned at an angle relative to a predetermined inclination direction Dt with respect to a state where it is directly facing the output surface 66. By positioning the light-receiving surface 68 at an angle in this manner, it is possible to suppress the reflected light reflected by the light-receiving surface 68 from being incident on the light source 65. The inclination direction Dt is opposite to the direction of the ejection head 10, with respect to a first direction D1 which is parallel to the ejection direction of the ink droplet. Therefore, the light-receiving surface 68 is inclined in the opposite direction to the nozzle surface NM of the ejection head 10, with respect to a virtual line Lv connecting the output surface 66 and the light-receiving surface 68.

[0048] The light-receiving surface 68 is arranged to be inclined with respect to the emission surface 66 in a direction orthogonal to both the first direction D1, the first direction D1 and the direction along the virtual line Lv, that is, in a second direction D2, and also in any one of the first direction D1 and the second direction D2. In the aspect where the light-receiving surface 68 is arranged to be inclined with respect to the emission surface 66 in the first direction D1 and the second direction D2, the light-receiving surface 68 is two-dimensionally inclined. Note that FIG. 5 shows an example in which the light-receiving surface 68 is arranged to be inclined with respect to the emission surface 66 in the first direction D1.

[0049] In the present embodiment, only the light-receiving surface 68 may be arranged to be inclined with respect to the emission surface 66, or only the emission surface 66 may be arranged to be inclined with respect to the light-receiving surface 68. Alternatively, both the emission surface 66 and the light-receiving surface 68 may be inclined. In the example of FIG. 5, only the light-receiving surface 68 is arranged to be inclined in a predetermined inclination direction with respect to the state of facing the emission surface 66 directly. The first detection element 67 may be arranged in a state where the light-receiving surface 68 is inclined by an operator before the start of execution of the discharge defect detection process, or the light-receiving surface 68 may be inclined by rotating the first detection element 67 by a rotation device 57 as described later.

[0050] In FIG. 5, when the angle (inclination angle) formed by the above virtual line Lv and the inclination direction Dt in which the light-receiving surface 68 faces is θ, the half value of the opening dimension in the inclination direction Dt of the slit 65b is a, and the distance between the slit 65b and the light-receiving surface 68 (that is, the distance between the slit 65b and the point on the light-receiving surface 68 where the virtual line Lv intersects) is L, then a < L × tan θ holds.

[0051] Here, as an example for explanation, consider the case where the light-receiving surface 68 is tilted in a second direction D2, which is perpendicular to both the first direction D1 and the direction along the virtual line Lv. As shown in Figure 6A, when the light-receiving surface 68 is not tilted in the second direction D2, the effective light-receiving surface S1 of the light-receiving surface 68 as seen from the output surface 66 side is relatively large. The effective light-receiving surface is the surface of the light-receiving surface 68 that can receive the laser light Lz, that is, the surface that can detect the laser light Lz. In contrast, as shown in Figure 6B, when the light-receiving surface 68 is tilted at a predetermined angle in the second direction D2, the effective light-receiving surface S2 of the light-receiving surface 68 as seen from the output surface 66 side becomes smaller than the effective light-receiving surface S1 mentioned above. This point is also true in the case where the light-receiving surface 68 is tilted with respect to the first direction D1 (the case shown in Figure 5 above). Therefore, it is important to suppress the reduction of the effective light-receiving surface by tilting the light-receiving surface 68 too much, while also preventing the reflected light reflected from the light-receiving surface 68 from being incident on the light source 65. Specific examples will be explained below.

[0052] Figure 7A is a graph showing the relationship between the effective light-receiving area of ​​the light-receiving surface 68 and the angle θ of the light-receiving surface 68, and Figure 7B is a graph showing the relationship between the amount of reflected light deviation from the light-receiving surface 68 and the angle θ of the light-receiving surface 68. Note that the angle θ in Figures 7A and 7B represents the inclination angle of the light-receiving surface 68 when the light-receiving surface 68 is tilted as shown in Figure 5 above.

[0053] As shown in Figure 7A, it can be seen that the effective light-receiving area decreases as the angle θ increases. Also, as shown in Figure 7B, it can be seen that the amount of reflected light deviation increases as the angle θ increases. The amount of reflected light deviation is the distance between the position where the reflected light reflected from the light-receiving surface 68 irradiates the wall of the light source housing 65a and the upper or lower end of the slit 65b of the light source housing 65a. As described above, from a technical standpoint, it is desirable to tilt the light-receiving surface 68 such that the effective light-receiving area on the light-receiving surface 68 is 90% or more of the area when the emission surface 66 and the light-receiving surface 68 are directly facing each other. For example, when the distance L between the slit 65b and the light-receiving surface 68 is 100 mm, it is preferable that the angle θ is approximately 30°.

[0054] Next, the calibration process for determining the inclination of the light-receiving surface 68 with respect to the emission surface 66 will be described. The calibration process is a process for determining the relative inclination of the light-receiving surface 68 with respect to the emission surface 66. In the calibration process, the light-receiving surface 68 is tilted by rotating the first detection element 67 by the rotating device 57.

[0055] Calibration processing is performed, for example, during manufacturing and assembly, and after shipment. Calibration processing is performed when the amount of noise included in the output value of the first detection element 67 is large, or when the amount of light received by the first detection element 67 is small. Specifically, the control device 20 performs calibration processing when the amount of noise included in the output value of the first detection element 67 (i.e., the amount of noise caused by reflected light) is greater than or equal to a first threshold when the laser light Lz is emitted from the light source 65, or when the amount of light received by the first detection element 67 is less than or equal to a second threshold when the laser light Lz is emitted from the light source 65.

[0056] In the calibration process, the control device 20 performs tilt modification, initial value acquisition, and tilt determination. In the tilt modification process, the control device 20 changes the relative tilt of the light-receiving surface 68 with respect to the light-emitting surface 66. In this case, the control device 20 rotates the first detection element 67 using the rotation device 57 so that the angle θ changes by a predetermined range. In the example of Figure 5, the rotation device 57 may rotate the first detection element 67 counterclockwise. As a result, the light-receiving surface 68 is rotated and tilted counterclockwise.

[0057] In the initial value acquisition process, the control device 20 uses the angle θ, which is the tilt at which the noise amount is maximum when the tilt change process is executed, as the initial value. In this case, the control device 20 acquires the noise amount included in the output value of the first detection element 67 each time the angle θ is changed during the tilt change process. The control device 20 then extracts the noise amount with the maximum value from among the acquired noise amounts and stores the angle θ corresponding to the extracted maximum noise amount as the initial value in the memory. Typically, the noise amount is at its maximum value when the light-receiving surface 68 is positioned almost directly opposite the light-emitting surface 66.

[0058] In the tilt determination process, the control device 20 determines the tilt when the amount of noise falls below the third threshold after executing the tilt change process based on the initial value. In this case, the control device 20 rotates the first detection element 67 using the rotation device 57 so that the angle θ changes by a predetermined range. The control device 20 then acquires the amount of noise included in the output value of the first detection element 67 each time the angle θ is changed during the tilt determination process. When the amount of noise falls below the third threshold, the control device 20 determines the angle θ corresponding to that noise amount as the angle θ at the time of execution of the ejection defect detection process. As a result, the ejection defect detection process is executed with the tilt angle of the light-receiving surface 68 set to the determined angle θ.

[0059] Next, we will explain the correction process for the detection signal of the first detection element 67, which takes into account the variation in the wavelength of the output light from the light source 65.

[0060] Figure 8 is a graph showing an example of the relationship between the wavelength of the laser light Lz, which is the output light emitted by the light source 65, and time. Figure 9A is a graph showing an example of the relationship between the output signal from the second detection element 69 and time, and Figure 9B is a graph showing an example of the relationship between the output signal from the first detection element 67 and time.

[0061] When a laser diode or the like is used as the light source 65, the wavelength of the output light from the light source 65 may fluctuate due to the instability of the temperature of the light source 65 immediately after startup and the incidence of ambient light on the light source 65. Specifically, as shown in Figure 8, the output light from the light source 65 may hop over time. Therefore, as shown in Figure 9A, the voltage value of the output signal of the second detection element 69, which has wavelength dependence in its sensitivity, also hops downwards. Subsequently, as shown in Figure 9A, the control device 20 controls the emission operation of the output light from the light source 65 so that the output light from the light source 65 remains constant. The above sensitivity is based on the product of the illuminance at the position of the ink droplet due to the output light from the light source 65 and the illuminance gradient in the optical axis direction of the output light. Here, let the sensitivity of the first detection element 67, which has wavelength dependence in its sensitivity similar to the second detection element 69, be A'', and let the sensitivity of the second detection element 69 be A'. In this case, if sensitivity A' > sensitivity A'', the voltage value of the output signal of the first detection element 67 rises significantly after the hop, as shown in Figure 9B. On the other hand, when sensitivity A' < sensitivity A'', the voltage value of the output signal of the first detection element 67 rises slightly after the hop, as shown in Figure 9B. In this way, the voltage value of the output signal of the first detection element 67 fluctuates due to variations in the wavelength of the output light from the light source 65.

[0062] Therefore, in order to avoid a decrease in the discrimination accuracy in the discharge failure detection process when the wavelength of the output light from the light source 65 fluctuates, the following correction process is performed. Figure 10 shows a correction table Tc in which the correction amount in the correction process is stored for each state. The correction table Tc is stored in a memory device.

[0063] In this embodiment, the control device 20 performs reception processing and correction processing. In the reception processing, the control device 20 receives a detection signal and a state determination signal from the first detection element 67, which are signals output from the first detection element 67 when the light source 65 emits laser light Lz and ink droplets are ejected from the ejection head 10. The state determination signal is a signal that precedes or follows the detection signal and is output from the first detection element 67 when ink droplets are not ejected from the ejection head 10. The control device 20 may perform the reception processing after a predetermined time has elapsed since the start of emission of laser light Lz from the light source 65.

[0064] As shown in Figure 10, the correction table Tc stores a correction amount (a correction amount to be applied to the detection signal) for each reference voltage, which is a state determination signal, and the sensitivity of the first detection element 67. That is, each correction amount is stored in association with the state determination signal and the sensitivity of the first detection element 67. The reference voltage in Figure 10 may be a single value, or it may have a range that includes an upper and lower limit. In the correction process, the control device 20 performs a correction by multiplying the detection signal by the correction amount according to the state determination signal and the sensitivity. Although three reference voltages are shown in Figure 10 for the sake of explanation, the number of reference voltages stored in the correction table Tc can be changed as appropriate.

[0065] Instead of the above correction process, the control device 20 may perform the following process. Figure 11 is a flowchart showing an example of a process that includes grouping.

[0066] In this embodiment, the control device 20 performs multiple discharge processing, multiple reception processing, grouping processing, group selection processing, and output value acquisition processing. Note that in Figure 11, the multiple discharge processing and multiple reception processing are combined into the processing of step S1.

[0067] In the multiple ejection process, as shown in Figure 11, the control device 20 emits laser light Lz from the light source 65 and ejects multiple ink droplets from a single nozzle 121 (step S1). Then, in the multiple reception process, the control device 20 receives the detection signal and the reference voltage, which is a state determination signal, from the first detection element 67, corresponding to each ejection by the single nozzle 121 in the multiple ejection process (step S1).

[0068] Next, in the grouping process, the control device 20 divides the detection signals corresponding to the reference voltage into multiple groups based on a comparison between the voltage value (e.g., peak value) of the reference voltage and a threshold. Specifically, in the example in Figure 11, the control device 20 determines whether the reference voltage is within the range of V1±v1 (step S2). If the reference voltage is not within the range of V1±v1 (No in step S2), the control device 20 assigns the detection signal corresponding to the reference voltage to, for example, group 1 (step S3). On the other hand, if the reference voltage is within the range of V1±v1 (Yes in step S2), the control device 20 determines whether the reference voltage is within the range of V2±v2 (step S4). If the reference voltage is not within the range of V2±v2 (No in step S4), the control device 20 assigns the detection signal corresponding to the reference voltage to, for example, group 3 (step S5). On the other hand, if the reference voltage is within the range of V2±v2 (Yes in step S4), the control device 20 assigns the detection signal corresponding to the reference voltage to, for example, group 2 (step S6). Note that in the example in Figure 11, three groups were used for explanatory purposes, but the number of groups can be changed as appropriate.

[0069] The control device 20 then determines whether or not grouping has been completed for all detection signals (step S7). If grouping has not been completed for all detection signals (No in step S7), the control device 20 returns to the process in step S2 described above and repeats the subsequent processes. On the other hand, if grouping has been completed for all detection signals (Yes in step S7), the control device 20 executes the group selection process.

[0070] In the group selection process, the control device 20 selects one group from a plurality of groups based on predetermined conditions (step S8). Specifically, the control device 20 selects the group with the largest number of detection signals from among the plurality of groups, based on the predetermined conditions.

[0071] Next, in the output value acquisition process, the control device 20 takes the average of, for example, the peak values ​​of each detection signal belonging to the selected group as the output value of the detection signal corresponding to one nozzle 121 in the discharge defect detection process (step S9). This process also helps to suppress a decrease in the discrimination accuracy in the discharge defect detection process when the wavelength of the output light from the light source 65 fluctuates.

[0072] Alternatively, instead of performing the above correction process, the following configuration may be adopted. Figure 12 is a block diagram showing the configuration of the signal amplification unit 200.

[0073] As shown in Figure 12, the droplet dispensing device 100 includes a signal amplification unit 200. The signal amplification unit 200 includes a current-voltage conversion unit 201, a switching unit 202, a first amplification unit 203, a second amplification unit 204, and a third amplification unit 205. The current-voltage conversion unit 201 converts the detection signal from the first detection element 67 from a current value to a voltage value. The first amplification unit 203, the second amplification unit 204, and the third amplification unit 205 amplify the output signal from the current-voltage conversion unit 201 at predetermined amplification ratios. Note that the amplification ratios in each amplification unit are different.

[0074] In this embodiment, the control device 20 receives the detection signal and state determination signal described above from the first detection element 67. Based on the state determination signal, the switching unit 202 switches the amplifier unit to be connected to the current-voltage conversion unit 201 from among the first amplifier unit 203, second amplifier unit 204, and third amplifier unit 205. The switched amplifier unit from among the amplifier unit 203, second amplifier unit 204, and third amplifier unit 205 amplifies the output signal from the current-voltage conversion unit 201 by a predetermined amplification factor. The output signal amplified by the predetermined amplification factor is used in the ejection failure detection process. Even with the above processing, a decrease in the discrimination accuracy in the ejection failure detection process can be suppressed when the wavelength of the output light from the light source 65 fluctuates.

[0075] Alternatively, instead of performing the above correction process, the control device 20 may perform the following process. Figure 13 is a flowchart showing an example of an ink droplet ejection process.

[0076] In this embodiment, the control device 20 ejects a first-size ink droplet (e.g., an extra-large droplet) from the nozzle 121 before a predetermined time has elapsed during the ejection failure detection process, and ejects a second-size ink droplet (e.g., a medium droplet) smaller than the first size from the nozzle 121 after the predetermined time has elapsed. Specifically, as shown in Figure 13, the control device 20 determines whether the fluctuation of the reference voltage over the past t seconds is within a predetermined Δv (step S21). If the fluctuation of the reference voltage is not within the predetermined Δv (No in step S21), the control device 20 ejects a first-size ink droplet from the nozzle 121 (step S22). On the other hand, if the fluctuation of the reference voltage is within the predetermined Δv (Yes in step S21), the control device 20 ejects a second-size ink droplet smaller than the first size from the nozzle 121 (step S23). In this way, the detection signal becomes larger because a first-size ink droplet is ejected before the predetermined time has elapsed. This makes it possible to suppress a decrease in the discrimination accuracy in the ejection failure detection process when the wavelength of the output light from the light source 65 fluctuates.

[0077] As described above, in the droplet ejection device 100 of the present embodiment, the light receiving surface 68 is disposed so as to be inclined in a predetermined inclination direction Dt with respect to the state where the light receiving surface 68 faces the emission surface 66. Thereby, it is possible to suppress the reflected light obtained by reflecting the laser light Lz emitted from the light source 65 by the light receiving surface 68 from entering the light source 65. As a result, it is possible to suppress the oscillation mode of the light source 65 from discretely changing (that is, the wavelength from discretely changing) due to the reflected light entering the light source 65. Therefore, it is possible to suppress the voltage output by the first detection element 67 having wavelength dependency from including noise due to the change in the wavelength. Thus, it is possible to perform ejection failure detection processing of the nozzle 121 based on the voltage from which noise has been suppressed and output by the first detection element 67. Therefore, it is difficult for an erroneous determination of ejection failure to occur.

[0078] Further, in the present embodiment, the inclination direction Dt is the direction opposite to the ejection head 10 with respect to the first direction D1 parallel to the ejection direction of the ink droplets. Therefore, the light receiving surface 68 is inclined in the direction opposite to the nozzle surface NM of the ejection head 10 with respect to the virtual line Lv connecting the emission surface 66 and the light receiving surface 68. Thereby, it is difficult for the reflected light reflected by the light receiving surface 68 to be reflected by the nozzle surface NM of the ejection head 10 and enter the light source 65.

[0079] Further, in the present embodiment, by disposing the light receiving surface 68 to be inclined with respect to the emission surface 66 so that a < L × tan θ holds, it is difficult for the reflected light from the light receiving surface 68 to enter the light source 65 through the slit 65b of the light source housing portion 65a.

[0080] Further, in the present embodiment, the light receiving surface 68 is inclined so that the effective light receiving area on the light receiving surface 68 is 90% or more of the state where the emission surface 66 and the light receiving surface 68 face each other. Thereby, it is possible to avoid the difficulty of performing ejection detection with high accuracy due to the effective light receiving area of the light receiving surface 68 being less than 90% of the state where the emission surface 66 and the light receiving surface 68 face each other.

[0081] Furthermore, if the light source 65 and the first detection element 67 are used over time, the relative tilt of the first detection element 67 with respect to the light source 65 may change due to vibration or other factors. In this embodiment, the calibration process described above can determine a tilt that can suppress the amount of noise included in the output value of the first detection element 67.

[0082] Furthermore, in this embodiment, when the control device 20 performs a tilt modification process based on the initial value during the tilt determination process, it determines the tilt of the light-receiving surface 68 when the amount of noise falls below the third threshold. This makes it easy to determine a tilt that suppresses the amount of noise included in the output value of the first detection element 67.

[0083] Furthermore, when using a light source 65 such as a laser diode, the wavelength of the output light from the light source 65 may fluctuate due to the instability of the temperature of the light source 65 immediately after startup. In this embodiment, even if the wavelength of the output light fluctuates, the detection signal is corrected using an appropriate correction amount according to the state determination signal, making it less likely for false judgments to occur in the discharge detection process. In addition, the warm-up process performed to stabilize the temperature of the light source 65 before the discharge detection process to resolve the temperature instability is eliminated. As a result, energy savings can be achieved and the discharge detection process can be performed quickly.

[0084] Furthermore, in this embodiment, since the correction amount stored in the memory device can be used, the process of calculating the correction amount is unnecessary. This suppresses the need to increase the specifications of the control device 20, thereby reducing the cost of the droplet dispensing device 100.

[0085] Furthermore, in this embodiment, the control device 20 may perform the reception processing after a predetermined time has elapsed since the start of emission of laser light Lz from the light source 65. This suppresses temperature instability of the light source 65 and makes it less likely for the wavelength of the output light from the light source 65 to fluctuate. As a result, a detection signal and a state determination signal with suppressed noise can be obtained.

[0086] Furthermore, in this embodiment, the control device 20 may perform the above-described multiple ejection processing, multiple reception processing, grouping processing, group selection processing, and output value acquisition processing. This makes it possible to perform ejection failure detection processing early without having to wait for a predetermined time to elapse from the start of laser light Lz emission from the light source 65 in order to stabilize the temperature of the light source 65.

[0087] Furthermore, in this embodiment, the first amplification unit 203, the second amplification unit 204, and the third amplification unit 205 may each amplify the output signal from the current-voltage conversion unit 201 at a predetermined amplification factor. This makes it less likely for misjudgments to occur even if the voltage output by the first detection element 67 changes due to the wavelength dependence of the first detection element 67 as described above, by performing discharge failure detection processing based on the amplified detection signal.

[0088] Furthermore, in the ejection failure detection process of this embodiment, in the example before a predetermined time has elapsed, before the temperature of the light source 65 stabilizes, the amplitude and signal width of the detection signal can be increased by ejecting a first-size ink droplet. Therefore, even if the voltage output by the first detection element 67 changes due to the wavelength dependence of the first detection element 67 as described above, misjudgment becomes less likely by performing the ejection failure detection process based on the detection signal with increased amplitude and signal width. On the other hand, in the example after a predetermined time has elapsed, after the temperature of the light source 65 stabilizes, a second-size ink droplet, smaller than the first size, is ejected. Therefore, cost increases related to the amount of ink droplet ejected can be suppressed.

[0089] In the above embodiment, the light-receiving surface 68 is tilted relative to the emission surface 66 by the rotating device 57 during the calibration process, but the invention is not limited to this. The light-receiving surface 68 only needs to be tilted relative to the emission surface 66, and a configuration in which any one of the light source 65, the first detection element 67, or the light source 65 and the first detection element 67 is rotated may also be adopted.

[0090] Furthermore, in the above embodiment, the control device 20 performs the correction process using the correction amount stored in the correction table Tc, but it is not limited to this. The control device 20 may also perform the correction process using a predetermined calculation formula.

[0091] Furthermore, in the above embodiment, the platen supporting the printing medium W is moved in the transport direction Df to transport the printing medium W, but the system is not limited to this. A system in which the printing medium W is transported in the transport direction Df by transport rollers may also be adopted.

[0092] Furthermore, in the above embodiment, an inkjet head that ejects UV-curable ink droplets was exemplified as the ejection head 10, but the form of the ejection head 10 is not limited to this. An ejection head that ejects ordinary ink droplets instead of UV-curable ink droplets may also be used. If the ejection head is configured to eject ordinary ink droplets, the UV irradiation device 40 is not required. [Explanation of symbols]

[0093] 10 Discharge heads 20 Control device 57 Rotating device 65 Light source 65a Light source storage section 65b Slit 66 Ejection surface 67 First detection elements 68 Photosensitive surface 100 Droplet discharge device 121 Nozzles 203 First Amplifier 204 Second Amplifier Section 205 Third Amplifier Section D1 1st direction D2 2nd direction Lz laser light Sh flight space W Printing medium

Claims

1. A dispensing head having multiple nozzles for dispensing droplets onto the printing medium, A light source having an emission surface that emits light toward the flight space in which the droplet ejected from the nozzle flies, A light-receiving unit having a light-receiving surface that detects the amount of light received after the light emitted from the light source has passed through the flight space, A control device is provided, When the control device discharges the droplet from the discharge head and emits the light from the light source, it performs a nozzle discharge failure detection process based on the amount of light detected by the light receiving unit. A droplet dispensing device wherein the light-receiving surface is positioned at a relative inclination in a predetermined inclination direction with respect to a state where it is directly facing the emission surface.

2. The droplet dispensing device according to claim 1, wherein the inclination direction is opposite to the dispensing head, with reference to a first direction parallel to the droplet dispensing direction.

3. The light source housing section further comprises a light source housing the light source and a slit that allows the light emitted from the light source to pass to the outside, The droplet ejection device according to claim 1, wherein the angle between the imaginary line connecting the emission surface and the light-receiving surface and the direction in which the light-receiving surface faces is θ, half of the opening dimension of the slit in the inclined direction is a, and the distance between the slit and the light-receiving surface is L, such that a < L × tanθ holds true.

4. The droplet dispensing device according to claim 1, wherein the light-receiving surface is positioned at an angle to the discharge surface such that the effective light-receiving area on the light-receiving surface is 90% or more of the area when the discharge surface and the light-receiving surface are facing each other, in one of the following directions: a first direction parallel to the droplet dispensing direction, and a second direction that intersects both the direction along the imaginary line connecting the discharge surface and the light-receiving surface and the first direction.

5. The system further comprises a rotating device for rotating the light source, the light receiving unit, and any one of the light source and the light receiving unit, such that the light receiving surface is tilted relative to the light emitting surface. The control device is The droplet dispensing device according to claim 1, wherein a calibration process is performed to determine the relative inclination of the light-receiving surface with respect to the emission surface when the amount of noise included in the output value of the light-receiving unit is equal to or greater than a first threshold when the light is emitted from the light source, or when the amount of light received by the light-receiving unit is equal to or less than a second threshold when the light is emitted from the light source.

6. The control device is The calibration process includes a tilt modification process that changes the relative tilt of the light-receiving surface with respect to the light-emitting surface, An initial value acquisition process that sets the initial value to the slope at which the noise amount is maximum when the aforementioned slope modification process is executed, A droplet dispensing device according to claim 5, which performs a slope determination process to determine the slope when the amount of noise becomes less than or equal to a third threshold when the slope change process is performed based on the initial value.

7. The control device is A receiving process that receives a detection signal, which is a signal output from the light receiving unit when the droplet is ejected from the ejection head, and a state determination signal, which is a signal before and after the detection signal and is output from the light receiving unit when the droplet is not ejected from the ejection head, from the light receiving unit. A droplet dispensing device according to claim 1, which performs a correction process in which a correction is applied to the detection signal using a predetermined correction amount in accordance with the state determination signal.

8. The droplet dispensing device according to claim 7, further comprising a storage device for storing a correction amount in correspondence with the state determination signal.

9. The droplet dispensing apparatus according to claim 7, wherein the control device performs the receiving process after a predetermined time has elapsed from the start of emission of the light from the light source.

10. The control device is A multiple discharge process in which the liquid droplet is discharged multiple times from one nozzle, Multiple receiving processes receive from the light receiving unit, corresponding to each discharge by the single nozzle in the multiple discharge process, a detection signal which is a signal output from the light receiving unit when the droplet is discharged from the discharge head, and a state determination signal which is a signal before and after the detection signal and is output from the light receiving unit when the droplet is not discharged from the discharge head. A grouping process that divides the detection signals corresponding to the state determination signal into multiple groups based on a comparison between the voltage value of the state determination signal and a threshold, A group selection process that selects one group from the aforementioned multiple groups based on predetermined conditions, A droplet dispensing device according to claim 1, comprising: performing an output value acquisition process in which the average value of the peak values ​​of each of the detection signals belonging to the selected group is set as the output value of the detection signal corresponding to one nozzle in the dispensing failure detection process.

11. It also includes an amplification section, The control device performs a receiving process to receive from the light receiving unit a detection signal, which is a signal output from the light receiving unit when the droplet is discharged from the discharge head, and a state determination signal, which is a signal before and after the detection signal and is output from the light receiving unit when the droplet is not discharged from the discharge head. The droplet dispensing device according to claim 1, wherein the amplification unit amplifies the detection signal by an amplification factor determined based on the state determination signal.

12. The droplet dispensing device according to claim 1, wherein the control device, in the dispensing failure detection process, dispenses a droplet of a first size from the nozzle before a predetermined time has elapsed, and dispenses a droplet of a second size smaller than the first size from the nozzle after the predetermined time has elapsed.

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