JP2013184362A - Apparatus of discharging liquid, and method of switching liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reliably switch liquids, and to reduce the discharge amount of the liquid by switching.SOLUTION: An apparatus of discharging liquid includes: a nozzle for discharging liquid; a liquid supply path for supplying the liquid to the nozzle; an inspection unit that inspects a discharging state of the liquid by making the liquid discharged from the nozzle the first potential by the first electrode, and discharging the liquid toward the second electrode of the second potential different from the first potential, and inspects the discharging state of the liquid from the nozzle based on the change in capacitance between the first electrode and the second electrode; a switching unit that switches the liquid supplied to the nozzle through the liquid supply path into either a first liquid or a second liquid different in viscosity from the first liquid; and a control unit that causes the first liquid to be discharged from the nozzle to replace the first liquid in the liquid supply path with the second liquid when the switching unit switches from the first liquid to the second liquid, and determines the timing of the switching completion from the first liquid to the second liquid based on the change in the capacitance detected by the inspection unit.

Description

  The present invention relates to a liquid ejection apparatus and a liquid switching method.

As a liquid ejecting apparatus, an ink jet printer that forms an image on a medium by ejecting ink, which is a kind of liquid, from a nozzle of a head is known.
As such an ink jet printer, there has been proposed an ink jet printer in which two types of ink are switched and supplied to one nozzle (nozzle row) via a common ink supply path (see, for example, Patent Document 1).

JP 2010-105286 A

In the printer described above, when ink is switched, it is necessary to reliably replace the ink by ejecting ink from the nozzle so that the ink does not remain in the ink supply path. For this reason, it is necessary to discharge (discharge) a large amount of ink from the nozzles in consideration of variations and the like, and there is a problem that the amount of ink discharged (discarded) when switching ink is increased.
It is an object of the present invention to reliably change the liquid and reduce the liquid discharge amount by switching.

A main invention for achieving the above object includes a nozzle that discharges a liquid, a liquid supply path that supplies the liquid to the nozzle, and the liquid discharged from the nozzle is set to a first potential by a first electrode. An inspection unit that inspects a discharge state of the liquid by discharging toward a second electrode having a second potential different from the first potential, and changes in capacitance between the first electrode and the second electrode The first liquid or the first liquid is the viscosity of the liquid supplied to the nozzle via the liquid supply path, the inspection unit for inspecting the discharge state of the liquid from the nozzle A switching unit that switches to any one of the different second liquids, and when the switching unit switches from the first liquid to the second liquid, the first liquid in the liquid supply path is changed to the second liquid. From the nozzle to replace the A control unit that discharges one liquid, and determines a timing of completion of switching from the first liquid to the second liquid based on a change in the capacitance detected by the inspection unit; A liquid ejection apparatus including the liquid ejection device.
Other features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

FIG. 1A is a block diagram illustrating a printing system having a printer 1 and a computer CP, and FIG. 1B is a perspective view of the printer 1. 2A is a cross-sectional view of the head 31, and FIG. 2B is a diagram illustrating an arrangement of nozzles (Nz) provided on the nozzle plate 33b. 3A to 3C are diagrams showing the positional relationship between the head 31 and the cap mechanism 60 during the recovery operation. It is the figure which looked at the cap 61 from upper direction. FIG. 5A is a diagram illustrating the missing dot detection unit 50, and FIG. 5B is a block diagram illustrating the detection control unit 57 of the missing dot detection unit 50. FIG. 6A is a diagram illustrating an example of the drive signal COM used at the time of ejection inspection, and FIG. 6B illustrates the voltage signal SG output from the amplifier 55 when ink is ejected from the nozzle by the drive signal COM of FIG. 6A. FIG. 6C is a diagram illustrating a voltage signal SG which is a discharge inspection result of a plurality of nozzles. It is a figure which shows the drive waveform W which generate | occur | produces with the drive signal COM for a test | inspection. 8A to 8C are explanatory diagrams of the relationship between the ink viscosity and the length of the ink column. FIG. 9A is a schematic explanatory diagram of an ink supply path to the head 31 in the present embodiment. FIG. 9B is a schematic explanatory diagram of a portion corresponding to the white ink nozzle row W. It is a flowchart which shows the operation | movement of the switching process of the ink in this embodiment. It is explanatory drawing of the change of the ink viscosity at the time of ink switching.

  At least the following matters will become clear from the description of the present specification and the accompanying drawings.

A nozzle that discharges liquid, a liquid supply path that supplies the liquid to the nozzle, and the liquid discharged from the nozzle is set to a first potential by a first electrode, and a second potential that is different from the first potential. An inspection unit that inspects the discharge state of the liquid by discharging toward two electrodes, and based on a change in capacitance between the first electrode and the second electrode, the liquid from the nozzle An inspection unit for inspecting the discharge state, and switching for switching the liquid supplied to the nozzle via the liquid supply path to either the first liquid or the second liquid having a viscosity different from that of the first liquid. And when the switching unit performs switching from the first liquid to the second liquid, the first liquid in the liquid supply path is replaced with the second liquid from the first liquid. Control unit for discharging liquid, A liquid ejecting apparatus comprising: a control unit that determines a timing of completion of switching from the first liquid to the second liquid based on a change in the capacitance detected by an inspection unit. It becomes.
According to such a liquid ejecting apparatus, the replacement completion timing can be determined with high accuracy, so that the liquid can be reliably replaced and the amount of liquid discharged by switching can be reduced.

In this liquid ejection apparatus, the control unit estimates the viscosity based on the change in the capacitance, and determines the timing for completing the switching from the first liquid to the second liquid based on the estimation result. It is desirable to do.
According to such a liquid ejecting apparatus, it is possible to detect the timing of completion of liquid switching with high accuracy from the viscosity estimation result.

  In this liquid ejection apparatus, a first liquid supply pipe that supplies the first liquid from the first liquid tank in which the first liquid is stored to the liquid supply path, and a second in which the second liquid is stored. A second liquid supply pipe that supplies the second liquid to the liquid supply path from a liquid tank, and the switching unit connects either the first liquid supply pipe or the second liquid supply pipe to the liquid. It is desirable to switch the liquid supplied to the nozzle by communicating with the supply path.

  According to such a liquid ejecting apparatus, the first liquid and the second liquid can be switched and supplied to one nozzle (nozzle row).

  Further, it is a liquid switching method by a liquid ejection device including a nozzle that ejects liquid and a liquid supply path that supplies the liquid to the nozzle, and the liquid that is supplied to the nozzle via the previous liquid supply path. Switching from the first liquid to the second liquid, discharging the first liquid from the nozzle to replace the first liquid in the liquid supply path with the second liquid, and discharging from the nozzle The change in capacitance between the first electrode and the second electrode when the liquid is made a first potential by the first electrode and discharged toward the second electrode having a second potential different from the first potential. And a liquid switching method characterized by comprising: detecting and determining a timing of completion of switching from the first liquid to the second liquid based on the change in capacitance. .

  In the following embodiments, an ink jet printer (hereinafter also referred to as a printer 1) will be described as an example of the liquid ejection device.

=== About printer configuration ===
FIG. 1A is a block diagram illustrating a printing system having a printer 1 and a computer CP, and FIG. 1B is a perspective view of the printer 1. The printer 1 ejects ink, which is a kind of liquid, toward a medium such as paper, cloth, or film. The computer CP is communicably connected to the printer 1. In order to cause the printer 1 to print an image, the computer CP transmits print data corresponding to the image to the printer 1. The printer 1 includes a paper transport mechanism 10, a carriage movement mechanism 20, a head unit 30, a drive signal generation circuit 40, a dot dropout detection unit 50, a cap mechanism 60, a detector group 70, and a controller 80.

  The paper transport mechanism 10 transports a medium (paper) in the transport direction. The carriage moving mechanism 20 moves the carriage 21 to which the head unit 30 is attached in the moving direction (direction intersecting the transport direction).

  The head unit 30 includes a head 31 and a head controller HC. The head 31 ejects ink toward the paper. The head controller HC controls the head 31 based on a head control signal from the controller 80 of the printer 1.

  FIG. 2A is a cross-sectional view of the head 31. The head 31 includes a case 32, a flow path unit 33, and a piezo element unit 34. The case 32 is a member for housing and fixing the piezoelectric element PZT and the like, and is made of, for example, a non-conductive resin material such as an epoxy resin.

  The flow path unit 33 includes a flow path forming substrate 33a, a nozzle plate 33b, and a vibration plate 33c. The nozzle plate 33b is bonded to one surface of the flow path forming substrate 33a, and the vibration plate 33c is bonded to the other surface. The flow path forming substrate 33 a is formed with a pressure chamber 331, an ink supply port 332, and voids and grooves that become the common ink chamber 333. The flow path forming substrate 33a is made of, for example, a silicon substrate. Ink is supplied to the common ink chamber 333 from an ink cartridge (ink tank) (not shown) through an ink supply pipe 36.

  The nozzle plate 33b is provided with a nozzle group including a plurality of nozzles Nz. The nozzle plate 33b is made of a conductive plate-like member, for example, a thin metal plate. The nozzle plate 33b is connected to the ground line and has a ground potential. A diaphragm portion 334 is provided in a portion corresponding to each pressure chamber 331 in the diaphragm 33c. The diaphragm portion 334 is deformed by the piezo element PZT and changes the volume of the pressure chamber 331. In addition, the piezoelectric element PZT and the nozzle plate 33b are electrically insulated by interposing the vibration plate 33c, the adhesive layer, and the like.

  The piezo element unit 34 includes a piezo element group 341 and a fixed plate 342. The piezo element group 341 has a comb shape. Each of the comb teeth is a piezo element PZT. The front end surface of each piezo element PZT is bonded to an island portion 335 included in the corresponding diaphragm portion 334. The fixing plate 342 supports the piezo element group 341 and serves as a mounting portion for the case 32. The piezo element PZT is a kind of electromechanical conversion element. When a drive signal COM is applied, the piezo element PZT expands and contracts in the longitudinal direction and gives a pressure change to the liquid in the pressure chamber 331. The ink in the pressure chamber 331 undergoes a pressure change due to a change in the volume of the pressure chamber 331. By utilizing this pressure change, ink droplets can be ejected from the nozzle Nz.

  FIG. 2B is a diagram illustrating an arrangement of nozzles (Nz) provided on the nozzle plate 33b. The nozzle plate is provided with a plurality of nozzle rows in which 180 nozzles (# 1 to # 180) are arranged at intervals of 180 dpi along the paper transport direction. Each nozzle row discharges ink of a different color, and this nozzle plate 33b is provided with five nozzle rows. Specifically, a black ink nozzle row K, a cyan ink nozzle row C, a magenta ink nozzle row M, a yellow ink nozzle row Y, and a white ink nozzle row W.

  In the present embodiment, the white ink ejected from the white ink nozzle row W is an ink for printing the background color (white) of a color image, for example, when printing on a transparent medium. Thus, by making the background white, it becomes easier to see the color image. The white ink contains a white pigment (corresponding to a sedimenting substance) as a color material. Examples of the white pigment include metal oxide, barium sulfate, calcium carbonate, and the like. Examples of the metal oxide include titanium dioxide, zinc oxide, silica, alumina, magnesium oxide and the like. Among these, titanium dioxide is preferable from the viewpoint of excellent whiteness. White ink tends to thicken and solidify when left for a long time. In addition, the pigment tends to settle if left for a long time.

  In this embodiment, clear ink is also ejected from the white ink nozzle row W. That is, the white ink nozzle row W is used in common for white ink and clear ink. The clear ink is a colorless and transparent ink, and is used for coating the image surface, preventing clogging of the nozzle, and the like. Clear ink does not have any solid components, and accordingly, moisturizing components (such as glycerin) are increased and the water content is increased, so that it is difficult to thicken and solidify. Moreover, it is hard to settle even if left for a long time. In this embodiment, clear ink is used for preventing clogging, but it may be used for cleaning nozzles and the like.

  The drive signal generation circuit 40 generates a drive signal COM. When the drive signal COM is applied to the piezo element PZT, the piezo element PZT expands and contracts, and the volume of the pressure chamber 331 corresponding to each nozzle Nz changes. The drive signal COM is applied to the head 31 at the time of printing, at the time of dot missing inspection (described later), at the time of flushing that is a recovery operation of the nozzle Nz that is missing dots.

  The missing dot detection unit 50 (corresponding to an inspection unit) inspects the ejection state of ink from each nozzle Nz. The cap mechanism 60 performs a suction operation for sucking ink from each nozzle Nz in order to suppress the evaporation of the ink solvent from the nozzle Nz or to restore the discharge capability of the nozzle Nz. The detector group 70 includes a plurality of detectors that monitor the status of the printer 1. Detection results by these detectors are output to the controller 80.

  A controller 80 (corresponding to a control unit) performs overall control in the printer 1. The controller 80 includes an interface unit 80a, a CPU 80b, and a memory 80c. The interface unit 80a exchanges data with the computer CP. The memory 80c secures an area for storing a computer program, a work area, and the like. In accordance with the computer program stored in the memory 80c, the CPU 80b controls each control target unit (the paper transport mechanism 10, the carriage movement mechanism 20, the head unit 30, the drive signal generation circuit 40, the missing dot detection unit 50, the cap mechanism 60, and the detection. The instrument group 70) is controlled.

  In such a printer 1, the controller 80 intermittently ejects ink from the head 31 while moving the carriage 21 in the moving direction, and forms dots on the paper, and transports the paper in the transport direction. And the carrying process to be executed repeatedly. As a result, dots are formed at positions different from the positions of the dots formed by the previous dot formation process, and a two-dimensional image is printed on the medium.

=== Discharge inspection (outline) and recovery operation ===
If ink (liquid) is not ejected from the nozzle for a long time or if foreign matters such as paper dust adhere to the nozzle, the nozzle may be clogged. When the nozzle is clogged, ink is not ejected when ink is to be ejected from the nozzle, and a phenomenon that dots are not formed (dot missing) occurs where dots are to be formed. When “dot missing” occurs, the image quality deteriorates. Therefore, in the present embodiment, when the dot missing nozzle is detected as a result of the “ejection inspection” performed by the dot missing detection unit 50, the “recovery operation” is performed, so that the ink is normally discharged from the dot missing nozzle. To be discharged.

  The dot dropout inspection is preferably performed immediately after the printer 1 is turned on or when the printer 1 receives print data from the computer CP and starts printing. Further, dot missing inspection may be performed every predetermined time during long-time printing. Hereinafter, after describing the recovery operation of the missing dot nozzle, the discharge inspection (outline) will be described.

<Recovery action>
3A to 3C are diagrams showing the positional relationship between the head 31 and the cap mechanism 60 during the recovery operation. First, the cap mechanism 60 will be described. The cap mechanism 60 includes a cap 61 and a slider member 62 that supports the cap 61 and is movable in a slanting vertical direction. The cap 61 has a rectangular bottom portion (not shown) and a side wall portion 611 standing from the periphery of the bottom portion, and has a thin box shape with an upper surface facing the nozzle plate 33b being opened. In a space surrounded by the bottom portion and the side wall portion 611, a sheet-like moisture retaining member made of a porous member such as felt or sponge is disposed.

  As shown in FIG. 3A, when the carriage 21 is out of the home position (right side in the movement direction, specifically, the position shown in FIG. 3C described later), the cap 61 is the surface of the nozzle plate 33b (hereinafter also referred to as a nozzle surface). ) Is located at a position sufficiently lower than. 3B, when the carriage 21 moves to the home position side (right side in the figure), the carriage 21 comes into contact with the contact portion 63 provided on the slider member 62, and the contact portion 63 together with the carriage 21 Move to the home position. When the contact portion 63 moves to the home position side, the slider member 62 rises along the guide slot 64, and the cap 61 also rises accordingly. Finally, as shown in FIG. 3C, when the carriage 21 is positioned at the home position, the side wall 611 (porous member) of the cap 61 and the nozzle plate 33b are brought into close contact with each other. For this reason, the evaporation of the ink solvent from the nozzles can be suppressed by positioning the carriage 21 at the home position when the power is turned off or during a long pause.

  Next, the recovery operation will be described. One of the recovery operations for the missing dot nozzle is a “flushing operation”. As shown in FIG. 3B, the flushing operation is performed by forcibly and continuously ejecting ink droplets from each nozzle with a slight gap between the nozzle surface and the opening edge of the cap 61. This is an action to eliminate clogging.

  A waste liquid tube 65 is connected to the space between the bottom surface of the cap 61 and the side wall portion 611, and a suction pump (not shown) is connected to the middle of the waste liquid tube 65. As another recovery operation, “pump suction” is performed with the opening edge of the cap 61 in contact with the nozzle surface as shown in FIG. 3C. When the suction pump is operated in a state where the side wall portion 611 of the cap 61 and the nozzle surface are in close contact with each other, the space of the cap 61 can be set to a negative pressure. Thereby, the ink in the head 31 can be sucked together with the thickened ink and paper dust, and the dot missing nozzle can be recovered.

  In addition, by maintaining the cap mechanism 60 at the position shown in FIG. 3B and moving the carriage 21 in the moving direction, the ink droplets adhered to the nozzle surface by the wiper 66 protruding above the side wall portion 611 of the cap 61. And remove foreign matter. As a result, the ink can be normally ejected from the nozzle clogged with the foreign matter.

<About the missing dot detection unit 50>
4 is a diagram of the cap 61 as viewed from above, FIG. 5A is a diagram illustrating the dot dropout detection unit 50, and FIG. 5B is a block diagram illustrating the detection control unit 57 of the dot dropout detection unit 50. It is. The missing dot detection unit 50 actually discharges ink from each nozzle and detects the ink discharge state, such as whether or not the ink has been normally discharged. First, the configuration of the missing dot detection unit 50 will be described. As shown in FIG. 5A, the missing dot detection unit 50 includes a high voltage power supply unit 51, a first limiting resistor 52, a second limiting resistor 53, a detection capacitor 54, an amplifier 55, a smoothing capacitor 56, and a detection control unit 57. Have.

  When detecting missing dots, as shown in FIGS. 3B and 5A, the nozzle surface and the cap 61 face each other with a predetermined distance d. In the space surrounded by the side wall 611 of the cap 61, as shown in FIG. 4, a moisturizing member 612 and a wire-like detection electrode 613 are arranged. The detection electrode 613 has a high potential of about 600 V to 1 kV during the dot missing detection operation. The detection electrode 613 illustrated in FIG. 4 includes a frame portion provided in a double rectangular shape, a diagonal line portion that connects the diagonal portions of the frame portion, and a cross portion that connects the midpoints on each side of the frame portion. Have. With this structure, it is uniformly charged over a wide range. In addition, when the ink solvent of the present embodiment is a liquid having conductivity (for example, water) and the detection electrode 613 is set to a high potential while the moisturizing member 612 is wet, the surface of the moisturizing member 612 also has the same potential. Also in this respect, the area where ink is ejected from the nozzle is uniformly charged over a wide range.

  The high-voltage power supply unit 51 is a type of power supply that makes the detection electrode 613 in the cap 61 have a predetermined potential. The high-voltage power supply unit 51 of this embodiment is configured by a DC power supply of about 600 V to 1 kV, and the operation is controlled by a control signal from the detection control unit 57.

  The first limiting resistor 52 and the second limiting resistor 53 are disposed between the output terminal of the high-voltage power supply unit 51 and the detection electrode 613, and limit the current flowing between the high-voltage power supply unit 51 and the detection electrode 613. . In the present embodiment, the first limiting resistor 52 and the second limiting resistor 53 have the same resistance value (for example, 1.6 MΩ), and the first limiting resistor 52 and the second limiting resistor 53 are connected in series. As shown in the figure, one end of the first limiting resistor 52 is connected to the output terminal of the high voltage power supply unit 51, the other end is connected to one end of the second limiting resistor 53, and the other end of the second limiting resistor 53 is connected to the detection electrode. Connect to 613.

  The detection capacitor 54 is an element for extracting a potential change component of the detection electrode 613, and one end is connected to the detection electrode 613 and the other end is connected to the amplifier 55. By interposing the detection capacitor 54 at this location, the bias component (DC component) of the detection electrode 613 can be removed, and the signal can be handled easily. In the present embodiment, the capacitance of the detection capacitor 54 is 4700 pF.

  The amplifier 55 amplifies and outputs a signal (potential change) appearing at the other end of the detection capacitor 54. The amplifier 55 of this embodiment is configured with a gain of 4000 times. As a result, the potential change component can be acquired as a voltage signal having a change width of about 2 to 3V. The set of the detection capacitor 54 and the amplifier 55 corresponds to a kind of detection unit, and detects an electrical change generated in the detection electrode 613 caused by ejection of an ink droplet.

  The smoothing capacitor 56 suppresses a rapid change in potential. The smoothing capacitor 56 of this embodiment has one end connected to a signal line connecting the first limiting resistor 52 and the second limiting resistor 53, and the other end connected to the ground. In this embodiment, the capacity of the smoothing capacitor 56 is 0.1 μF.

  The detection control unit 57 is a part that controls the missing dot detection unit 50. As shown in FIG. 5B, the detection control unit 57 includes a register group 57a, an AD conversion unit 57b, a voltage comparison unit 57c, and a control signal output unit 57d. The register group 57a includes a plurality of registers. Each register stores a determination result for each nozzle Nz, a voltage threshold for determination, and the like. The AD converter 57b converts the amplified voltage signal (analog value) output from the amplifier 55 into a digital value. The voltage comparison unit 57c compares the magnitude of the amplitude value based on the amplified voltage signal with a voltage threshold value. The control signal output unit 57d outputs a control signal for controlling the operation of the high voltage power supply unit 51.

<Outline of discharge inspection>
In the printer 1, the nozzle plate 33 b (corresponding to the first electrode) is connected to the ground so as to have a ground potential (corresponding to the first potential), and the detection electrode 613 (corresponding to the second electrode) disposed on the cap 61 is used. A high potential (corresponding to the second potential) of about 600 V to 1 kV is set. The ink droplet ejected from the nozzle becomes the ground potential by the nozzle plate having the ground potential. The nozzle plate 33b and the detection electrode 613 are opposed to each other with a predetermined distance d (see FIG. 5A), and ink droplets are ejected from the detection target nozzle. Then, the detection control unit 57 acquires the electrical change generated on the detection electrode 613 side due to the ejection of the ink droplets as the voltage signal SG via the detection capacitor 54 and the amplifier 55. Based on the amplitude value (potential change) in the voltage signal SG, the detection control unit 57 determines the ink ejection state such as whether or not the ink droplets are ejected normally from the detection target nozzle.

  The principle of detection is as follows. By disposing the nozzle plate 33b and the detection electrode 613 at a predetermined interval d, these members behave like a condenser. That is, as shown in FIG. 5A, the nozzle plate 33b is connected to the ground, and the ink extending in a columnar shape from the nozzle Nz (hereinafter also referred to as an ink column) also becomes the ground potential by coming into contact with the nozzle plate 33b. This elongation of the ink (the length of the ink column) changes the capacitance of the capacitor. That is, when ink is ejected from the nozzle, the ground potential ink and the detection electrode 613 form a capacitor, and the capacitance changes.

  When the electrostatic capacity is reduced, the amount of charge that can be stored between the nozzle plate 33b and the detection electrode 613 is reduced. For this reason, surplus charges move from the detection electrode 613 to the high-voltage power supply unit 51 side through the limiting resistors 52 and 53. That is, a current flows toward the high voltage power supply unit 51. On the other hand, when the capacitance increases or the decreased capacitance returns, the charge moves from the high-voltage power supply unit 51 to the detection electrode 613 side through the limiting resistors 52 and 53. That is, a current flows toward the detection electrode 613. When such a current (also referred to as a discharge inspection current If for convenience) flows, the potential of the detection electrode 613 changes. The change in the potential of the detection electrode 613 also appears as a change in the potential of the other conductor (the conductor on the amplifier 55 side) in the detection capacitor 54. Therefore, the discharge state of the ink droplet can be determined by monitoring the potential change of the other conductor.

  FIG. 6A is a diagram illustrating an example of the drive signal COM used at the time of ejection inspection, and FIG. 6B illustrates the voltage signal SG output from the amplifier 55 when ink is ejected from the nozzle by the drive signal COM of FIG. 6A. FIG. 6C is a diagram illustrating a voltage signal SG which is a discharge inspection result of a plurality of nozzles (here, ten nozzles # 1 to # 10). The drive signal COM has a plurality of drive waveforms W (for example, 24) for ejecting ink from the nozzles in the first half period TA of the repetition period T, and a constant potential is maintained at an intermediate potential in the second half period TB. The drive signal generation circuit 40 repeatedly generates a plurality of drive waveforms W (24 drive waveforms) every repetition period T. This repetition period T corresponds to the time required for inspection of one nozzle.

  First, a drive signal COM is applied to a piezo element PZT corresponding to a certain nozzle to be inspected over a repetition period T. Then, ink droplets are continuously ejected from the nozzles targeted for ejection inspection in the first half period TA (for example, 24 shots are hit). As a result, the potential of the detection electrode 613 changes, and the amplifier 55 outputs the potential change to the detection control unit 57 as a voltage signal SG (sine curve) shown in FIG. 6B. Since the amplitude of the voltage signal SG due to the ink droplet for one shot is small, the voltage signal SG having an amplitude sufficient for inspection can be obtained by continuously ejecting the ink droplet from the nozzle.

  The detection control unit 57 calculates the maximum amplitude Vmax (difference between the maximum voltage VH and the minimum voltage VL) from the voltage signal SG in the inspection period (T) of the nozzle to be inspected, and compares the maximum amplitude Vmax with a predetermined threshold value TH. To do. When ink is ejected from the nozzle to be inspected according to the drive signal COM, the potential of the detection electrode 613 changes, and the maximum amplitude Vmax of the voltage signal SG becomes larger than the threshold value TH. On the other hand, if ink is not ejected from the nozzle to be inspected or the amount of ejected ink is small due to clogging or the like, the potential of the detection electrode 613 does not change or the potential change is small. The maximum amplitude Vmax of the signal SG is equal to or less than the threshold value TH.

  After the drive signal COM is applied to the piezo element PZT corresponding to a certain nozzle, the drive signal COM is repeatedly applied to the piezo element PZT corresponding to the next inspection target nozzle over the period T, so that For each nozzle, the drive signal COM is applied to the piezo element PZT corresponding to the nozzle over a repetition period T. As a result, as shown in FIG. 6C, the detection control unit 57 can acquire the voltage signal SG in which the potential change of the sine curve occurs for each repetition period T.

  For example, in the result of FIG. 6C, since the maximum amplitude Vmax of the voltage signal SG corresponding to the inspection period of the nozzle # 5 is smaller than the threshold value TH, the detection control unit 57 determines that the nozzle # 5 is a missing dot nozzle. Since the maximum amplitude Vmax of the voltage signal SG corresponding to each inspection period of the other nozzles (# 1 to # 4 and # 6 to # 10) is equal to or greater than the threshold value TH, the detection control unit 57 determines that the other nozzles are normal nozzles. It is judged that. When the dot missing nozzle is detected by the dot missing detection unit 50 in this way, the controller 80 of the printer 1 performs a recovery operation on the head 31. As a result, a high-quality image with no missing dots can be printed.

=== Relationship Between Ink Viscosity and Ink Column Length ===
FIG. 7 is a diagram showing a drive waveform W generated by the test drive signal COM (FIG. 6A), and FIGS. 8A to 8C are diagrams showing differences in ink column length depending on ink viscosity. 8A to 8C show a state in which ink protrudes in a columnar shape from the nozzle surface of the head 31 (the lower surface of the nozzle plate 33b), and the hatched portion in the drawing corresponds to the ink. Further, in FIGS. 8A, 8B, and 8C, the viscosity of the ink decreases in this order.

  First, the drive waveform W generated by the test drive signal COM will be described in detail. The drive waveform W includes a first expansion element P1 in which the potential increases from the intermediate potential Vc to the maximum potential Vh, a first hold element P2 that holds the maximum potential Vh, and a contraction in which the potential decreases from the maximum potential Vh to the minimum potential Vl. It has an element P3, a second hold element P4 that holds the lowest potential Vl, and a second expansion element P5 whose potential rises from the lowest potential Vl to the intermediate potential Vc.

  In a state where the intermediate potential Vc is applied to the piezo element PZT (see FIG. 2A), the piezo element PZT does not expand and contract. The volume of the pressure chamber 331 (see FIG. 2A) when the intermediate potential Vc is applied to the piezo element PZT is set as a reference volume. Thereafter, when the first expansion element P1 having the drive waveform W is applied to the piezo element PZT, the piezo element PZT contracts in the longitudinal direction, and the volume of the pressure chamber 331 expands. When the first hold element P2 is applied to the piezo element PZT, the contracted state of the piezo element PZT is maintained, and accordingly, the expanded state of the pressure chamber 331 is also maintained. Next, when the contraction element P3 is applied to the piezo element PZT, the piezo element PZT expands at a stretch from the contracted state, and the volume of the pressure chamber 331 contracts at a stretch. Due to the contraction of the pressure chamber 331, the ink pressure in the pressure chamber 331 increases rapidly, the ink column protrudes from the nozzle, and the ink droplets fly in the ejection direction. Thereafter, the second hold element P4 is applied to the piezo element PZT, and the expanded state of the piezo element PZT and the expanded state of the pressure chamber 331 are maintained. Finally, when the second expansion element P5 is applied to the piezo element PZT, the volume of the pressure chamber 331 returns to the reference volume.

  When the pressure chamber 331 contracts due to the contraction element P3 of the drive waveform W, as shown in FIGS. 8A to 8C, the ink protrudes from the nozzle in a columnar shape. Thereafter, the tip portion of the ink column is separated from the ink column and flies in the ejection direction. The tip portion of the ink column is referred to as “main droplet”, and the distance between the point where the tip portion (main droplet) is divided and the nozzle surface (lower surface of the nozzle plate 33b) is referred to as “tailing amount”. When printing, the main droplets separated from the ink pillars land on the medium to form dots. On the other hand, the remaining ink column after the tip portion (main droplet) is divided forms a minute ink droplet (satellite) or returns to the pressure chamber 331.

8A to 8C, the drive waveform W (contraction element P3) applied to the piezo element PZT is the same, but the type (viscosity) of the ink used is different. As shown in FIGS. 8A to 8C, the length of the ink column when the contraction element P3 is applied to the piezo element PZT varies depending on the viscosity of the ink. For example, when the relationship between the lengths l ₁ , l ₂ , and l ₃ of the ink column is l ₁ > l ₂ > l ₃ as shown in the figure, the viscosity of the ink in FIG. Is the lowest. Further, when the lengths of the ink pillars are different in this way, the magnitude of the electrostatic capacity when the dot missing detection unit 50 described above performs the ejection inspection changes.

=== About the ink flow path ===
Next, the ink flow path to the head 31 in this embodiment will be described.
FIG. 9A is a schematic explanatory diagram of an ink flow path to the head 31 in the present embodiment. FIG. 9B is a schematic explanatory diagram of a portion corresponding to the white ink nozzle row W.

  As shown in FIG. 9A, a corresponding color ink cartridge is detachably connected to each nozzle row of the head 31, and by mounting the color ink cartridge corresponding to the mounting portion of the carriage 21, Ink in the ink cartridge is supplied to the head 41.

  As described above, in this embodiment, white ink and clear ink are prepared in addition to black ink, cyan ink, magenta ink, and yellow ink. Therefore, in this embodiment, the ink cartridge Tw for white ink, the ink cartridge Tcl for clear ink, the ink cartridge Tm for magenta ink, the ink cartridge Ty for yellow ink, and the ink cartridge Tk for black ink are used as the ink cartridge. Is coupled to the head 31.

  As is clear from FIG. 9A, for each of cyan, magenta, yellow, and black, only one ink cartridge (that is, ink cartridge Tc, ink cartridge Tm, ink cartridge Ty, ink cartridge Tk) is provided for each ink supply pipe 36. Are connected to a common ink chamber 333 for each color of the head 31.

  On the other hand, for the white ink nozzle row W, as shown in FIGS. 9A and 9B, the two ink cartridges, the ink cartridge Tw for white ink and the ink cartridge Tcl for clear ink, To the common ink chamber 333 for white ink. In the following description, the flow path downstream of the switching valve 90 in the ink supply direction (that is, the portion where the white ink and the clear ink flow in common) is referred to as an ink supply path 360 (corresponding to a liquid supply path). The ink flow path from the ink cartridge Tw to the switching valve 90 is called an ink supply path 361 (corresponding to the first liquid supply pipe), and the ink flow path from the ink cartridge Tcl to the switching valve 90 is the ink supply path 362. (Corresponding to the second liquid supply pipe).

  As described above, on the upstream side (the ink cartridge side) of the switching valve 90, there are two channels: a flow path from the ink cartridge Tw via the ink supply path 361 and a flow path from the ink cartridge Tcl to the ink supply path 362. There is a channel. On the other hand, the downstream side of the switching valve 90 (the head 31 side) has only one flow path for discharging ink from the nozzles via the ink supply path 360. That is, the switching valve 90 has a function of switching the ink supplied to the head 31 white nozzle row W to either the ink cartridge Tw side (white ink) or the ink cartridge Tcl side (clear ink). For example, when the ink supply path 360 and the ink supply path 361 communicate with each other through the switching valve 90, white ink is supplied to the ink supply path 360 (the common ink chamber 333, etc.). Further, when the ink supply path 360 and the ink supply path 362 communicate with each other by the switching valve 90, the clear ink is supplied to the ink supply path 360 (such as the common ink chamber 333). The switching of the switching valve 90 is controlled by the controller 80.

=== About Ink Switching Process ===
Here, the purpose of selecting either white ink or clear ink and supplying it to the white ink nozzle row W will be described.
The purpose is to prevent clogging in the white nozzle row W of the head 31. That is, when comparing the white ink and the clear ink, as described above, the white ink is more likely to cause the clogging, and the white ink is longer in a state where the white ink is filled in the flow path. If left unattended, the thickening of the white ink is promoted, and there is a high possibility that clogging will occur in the head 41 (particularly, the nozzle Nz). Therefore, in view of this, when the ink is left for a long time, the white ink is switched to the clear ink which is not likely to be clogged instead of the white ink.

<Switching from white ink to clear ink>
Next, an example of the switching timing from white ink to clear ink will be described. In the present embodiment, when the printer 1 is powered off, the white ink flow path is filled with clear ink. Therefore, when the power is turned off, the controller 80 executes switching from white ink to clear ink.

  When switching from white ink to clear ink, first, the controller 80 controls the head unit 30 to switch the switching valve 90 described above. That is, the controller 80 shifts from the state where the ink supply path 360 and the ink supply path 361 are communicated to the state where the ink supply path 360 and the ink supply path 362 are communicated by switching the switching valve 90.

  Next, the controller 80 controls the cap mechanism 60 to perform ink suction. Thus, the white ink filled in the ink supply path 360 is discharged through the waste liquid tube 65, and the clear ink is supplied from the ink cartridge Tcl to the ink supply path 360 so that the white ink is replaced. . That is, the ink in the ink supply path 360 is replaced with the clear ink from the white ink.

  Ink may be discharged by performing flushing or the like using a drive signal instead of ink suction. Also in this case, the white ink in the ink supply path 360 is replaced with the clear ink.

<Switching from clear ink to white ink>
Next, an example of switching timing from clear ink to white ink will be described. In the present embodiment, when the power of the printer 1 is turned on, the flow path downstream of the switching valve 90 in the ink supply direction (such as the ink supply path 360) is filled with white ink. Therefore, when the power is turned on, the controller 80 executes switching from clear ink to white ink. However, the present invention is not limited to this. For example, when the printer is in a standby state even after the power is turned on, or when executing a printing mode that does not use white ink, switching from clear ink to white ink is performed. Instead, the clear ink may be switched to the white ink only when the print mode using the white ink is executed.

  The operation when switching from clear ink to white ink is the same as the operation when switching from white ink to clear ink, and the description thereof will be omitted.

  The ink switching timing is not limited to the case described above. For example, when there is a missing dot in the discharge inspection of the white ink nozzle row W, the nozzles of the white ink nozzle row W are washed by switching from white ink to clear ink and discharging (discharge or suck) ink. May be. Then, after the cleaning is completed, the clear ink may be switched to the white ink.

=== Issues when switching ink ===
For example, after switching from clear ink to white ink, even if suction or flushing is performed, the clear ink may remain in a flow path such as the ink supply path 360. The white ink ejected from each white nozzle Nz (white nozzle row W) may be light. For this reason, conventionally, a large amount of ink to be discharged is set in consideration of a margin such as an error so that residual ink does not occur when the ink is switched. That is, there is a problem in that the amount of ink discarded without being used for printing increases due to ink switching.

  Therefore, in this embodiment, the ink is reliably switched and the amount of ink discharged at the time of switching is reduced. Specifically, the viscosity of the ink is estimated from the detection result of the missing dot detection unit 50, and it is determined whether or not the ink switching has been completed based on the viscosity of the ink.

=== About Ink Switching Process ===
FIG. 10 is a flowchart showing the operation of the ink switching process in the present embodiment.
In the present embodiment, a case of switching from clear ink (low viscosity ink) to white ink (high viscosity ink) will be described, but similar processing may be performed when switching from white ink to clear ink. Moreover, (the N ₁₎ the value of the viscosity of the clear ink, and the value of viscosity of the white ink (and N _2), it is assumed that stored in advance in, for example, a memory 80c.

  First, as an initial state, in order to prevent clogging, the switching valve 90 communicates with the ink supply path 362 and the ink supply path 360 (that is, a state where clear ink is supplied downstream of the switching valve in the ink supply direction). ), The printer 1 is turned off.

  When the printer 1 is powered on (S101), the controller 80 switches the switching valve 90 from the ink cartridge Tcl side to the ink cartridge Tw side (S102). As a result, the ink supply path 361 from the ink cartridge Tw and the ink supply path 360 are in communication with each other. Then, the controller 80 discharges ink (here, clear ink) from each nozzle of the white ink nozzle row W in order to replace the clear ink in the ink supply path 360 with white ink (S103). In this embodiment, the drive signal COM is applied to the piezo element PZT and ink is ejected from the nozzle. However, the present invention is not limited to this, and the ink (clear ink) in the ink supply path 360 is ejected from the nozzle. If you can. For example, suction may be performed.

The controller 80 detects the change in capacitance between the nozzle plate 33b and the detection electrode 613 by controlling the missing dot detection unit 50 (S104), and determines the ink viscosity based on the change in capacitance. Estimate (S105). Estimate as to discharge the ink (viscosity) rises from the viscosity N ₁ of the clear ink. The controller 80 determines whether or not the estimated viscosity is that of white ink (N _{2 in} this case) (S106). If it is determined that the estimated viscosity is not the white ink viscosity N ₂ (NO in S106), the process returns to step S103 for ejecting ink. On the other hand, if the estimated viscosity is determined that the viscosity of _{N 2} white ink (YES in S106), immediately discharge the ink (ejection) stopped (S107), and terminates the switching process of the ink.

  FIG. 11 is an explanatory diagram of a change in ink viscosity at the time of ink switching. The horizontal axis in the figure is time, and ink is ejected at regular intervals. In addition, the vertical axis in the figure is the ink viscosity. Here, a change in viscosity when switching from a low viscosity ink (for example, clear ink) to a high viscosity ink (for example, white ink) is shown.

Initially, only the clear ink is discharged from the nozzle, so the viscosity is low as shown in the figure (N ₁ ). However, by continuing to discharge ink from the nozzle, the clear ink in the ink supply path 360 is replaced with white ink. Go. For this reason, as shown in the figure, the viscosity of the ink increases from N ₁ as time passes (every time ink is ejected). Eventually, the increase in the viscosity of the ink becomes gradual and then becomes substantially constant (N ₂ ). Thus, when the viscosity of the ink becomes constant, the clear ink in the ink supply path 360 is completely replaced with the white ink. Therefore, when it is detected that the ink viscosity has reached N2, the ink in the ink supply path 360 can be completely replaced by discharging ink from the nozzles, and wasteful ink can be discharged. You don't have to.

In the above-described embodiment, the low viscosity ink (clear ink) is switched to the high viscosity ink (white ink), but the high viscosity ink (white ink) is switched to the low viscosity ink (clear ink). The same processing may be performed for. In addition, when switching from a high viscosity ink to a low viscosity ink, the relationship is reversed (that is, the viscosity decreases as the ink is discharged). Therefore, the ink discharge may be terminated when the viscosity decreases from N ₂ to N ₁ .

  As described above, the printer 1 according to the present embodiment includes the head 31 (nozzles) that ejects ink, the ink supply path 360 that supplies ink to the nozzles, and the ink ejected from the nozzles of the head 31 using the nozzle plate 33b. Is provided with a dot dropout detecting unit 50 that inspects the ink discharge state by discharging toward the high-voltage detection electrode 613 with the ground potential. Further, the controller 80 of the printer 1 switches the ink supplied to the nozzles via the ink supply path 360 to white ink or clear ink by controlling the switching valve 90. When the ink is switched, the controller 80 discharges the ink from the nozzle in order to replace the ink in the ink supply path 360. Then, the controller 80 estimates the viscosity of the ink discharged from the nozzle based on the change in the electrostatic capacitance detected by the dot dropout detecting unit 50, and completes the ink discharge based on the estimated viscosity (in other words, Ink switching completion) is determined.

  This makes it possible to reliably replace the ink in the ink supply path 360 by switching the ink, and to reduce the amount of ink discharged (the amount of ink discharged without being used for printing) due to the switching. be able to.

=== Other Embodiments ===
Although a printer or the like as one embodiment has been described, the above embodiment is for facilitating the understanding of the present invention, and is not intended to limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and it is needless to say that the present invention includes equivalents thereof. In particular, the embodiments described below are also included in the present invention.

<About the printer>
In the above-described embodiment, the printer has been described as an example of the liquid ejection apparatus, but the present invention is not limited to this. For example, color filter manufacturing apparatus, dyeing apparatus, fine processing apparatus, semiconductor manufacturing apparatus, surface processing apparatus, three-dimensional modeling machine, liquid vaporizer, organic EL manufacturing apparatus (particularly polymer EL manufacturing apparatus), display manufacturing apparatus, film formation The same technology as that of the present embodiment may be applied to various liquid ejection devices to which inkjet technology such as a device and a DNA chip manufacturing device is applied.

  In the above-described embodiment, the image forming operation for ejecting ink droplets while the head 31 moves in the movement direction and the conveyance operation for relatively moving the head 31 and the medium in the conveyance direction intersecting the movement direction are alternately performed. The printer 1 (so-called serial printer) is taken as an example, but the present invention is not limited to this. For example, even in a printer (so-called line printer) that forms an image by arranging heads (nozzles) in the paper width direction intersecting the medium conveyance direction and ejecting ink droplets toward the medium conveyed under the head. Good.

<Discharge method>
In the above-described embodiment, ink is ejected using a piezoelectric element (piezo element). However, the method for discharging the liquid is not limited to this. For example, other methods such as a method of generating bubbles in the nozzle by heat may be used.

<About ink>
In the above-described embodiment, since the embodiment is a printer, ink is used as the liquid. However, the liquid ejected from the nozzle is not limited to such ink. For example, liquids (including water) including metal materials, organic materials (especially polymer materials), magnetic materials, conductive materials, wiring materials, film-forming materials, electronic inks, processing liquids, gene solutions, etc. are ejected from nozzles. May be.

  In the above-described embodiment, the ink supplied to the nozzles of one nozzle row (white ink nozzle row W) is switched between white ink and clear ink. However, the present invention is not limited to this. For example, other color inks (nozzle rows) may be used. Also in this case, by determining the completion of the switching based on the viscosity, the switching can be performed reliably and the ink discharge amount can be reduced.

<About the missing dot detection unit 50>
In the above-described embodiment, an abnormality of the detection electrode 613 is detected based on a change in the electrical state caused by the discharge inspection current If without providing a voltage dividing circuit in the dot dropout detection unit 50. However, the present invention is not limited to this, and the power supply voltage may be divided by a voltage dividing circuit, and an abnormality of the detection electrode 613 may be detected based on the detected voltage.

  In the above-described embodiment, the detection electrode 613 is set to a higher potential than the nozzle surface, and the change in the potential of the detection electrode 613 caused by the ejection of the ink droplet is extracted by the detection capacitor 54. However, the present invention is not limited to this. For example, a high voltage power supply unit is connected to the nozzle plate 33b to make it high potential, the detection electrode 613 is made to ground and made to ground potential, and a missing dot nozzle is detected by a potential change of the nozzle plate 33b due to ink ejection, or The missing dot nozzle may be detected by a potential change of the detection electrode 613. Further, in the high potential detection electrode 613 and the ground potential nozzle plate 33b, a missing dot nozzle may be detected by a potential change of the nozzle plate 33b due to ink ejection.

  In the above-described embodiment, the ink ejected from the nozzle is set to the ground potential by setting the nozzle plate to the first potential (ground potential). However, the present invention is not limited to this. If the ink ejected from the nozzle is configured to have the first potential (ground potential), the nozzle plate may not be used as an electrode. For example, a conductive member that is provided on a wall surface such as an ink flow path or a pressure chamber 331 and is electrically connected to ink in the nozzle may be provided, and this conductive member may be set to the ground potential. Further, the ink is not limited to the ground potential, and any potential difference necessary for detection may be required between the detection electrode 613 and the ink.

1 printer, 10 paper transport mechanism,
20 carriage movement mechanism, 21 carriage,
30 head units, 31 heads, 32 cases, 33 flow path units,
33a flow path forming substrate, 33b nozzle plate, 33c diaphragm,
331 pressure chamber, 332 ink supply port, 333 common ink chamber,
334 Diaphragm part, 335 island part, 34 piezo element unit,
341 Piezoelectric element group, 342 fixing plate, 36 ink supply pipe 360, 361, 362 ink supply path, 40 drive signal generation circuit,
50 missing dot detector, 51 high voltage power supply unit, 52 first limiting resistor,
53 second limiting resistor, 54 detecting capacitor, 55 amplifier,
56 smoothing capacitor, 57 detection control unit, 57a register group,
57b AD conversion unit, 57c voltage comparison unit, 57d control signal output unit,
60 cap mechanism, 61 cap, 611 side wall, 612 moisturizing member,
613 electrode for detection, 62 slider member, 63 contact part, 64 long hole,
65 waste tube, 66 wiper,
70 detector groups, 71 temperature sensors,
80 controller, 80a interface part,
80b CPU, 80c memory,
90 switching valve,
CP computer, HC head controller, PZT piezo element

Claims (4)

A nozzle for discharging liquid;
A liquid supply path for supplying the liquid to the nozzle;
An inspection unit that inspects the discharge state of the liquid by setting the liquid discharged from the nozzle to a first potential by a first electrode and discharging the liquid toward a second electrode having a second potential different from the first potential. And an inspection unit for inspecting a discharge state of the liquid from the nozzle based on a change in capacitance between the first electrode and the second electrode;
A switching unit that switches the liquid supplied to the nozzle via the liquid supply path to either a first liquid or a second liquid having a viscosity different from that of the first liquid;
When the switching unit performs switching from the first liquid to the second liquid, the first liquid is discharged from the nozzle to replace the first liquid in the liquid supply path with the second liquid. A control unit that determines a timing of completion of switching from the first liquid to the second liquid based on a change in the capacitance detected by the inspection unit;
A liquid ejection apparatus comprising: The liquid ejection device according to claim 1,
The controller estimates the viscosity based on the change in the capacitance, and determines the completion timing of switching from the first liquid to the second liquid based on the estimation result. apparatus. The liquid ejection device according to claim 1 or 2, wherein
A first liquid supply pipe for supplying the first liquid from a first liquid tank in which the first liquid is stored to the liquid supply path;
A second liquid supply pipe for supplying the second liquid to the liquid supply path from a second liquid tank in which the second liquid is stored;
Have
The switching unit performs switching of the liquid supplied to the nozzle by communicating either the first liquid supply pipe or the second liquid supply pipe with the liquid supply path. apparatus. A liquid switching method by a liquid ejection device comprising a nozzle for ejecting liquid and a liquid supply path for supplying the liquid to the nozzle,
Switching the liquid supplied to the nozzle via the previous liquid supply path from the first liquid to the second liquid;
Draining the first liquid from the nozzle to replace the first liquid in the liquid supply path with the second liquid;
The liquid discharged from the nozzle is set to a first potential by the first electrode and discharged between the first electrode and the second electrode when discharged toward the second electrode having a second potential different from the first potential. Detecting changes in capacitance,
Determining a timing of completion of switching from the first liquid to the second liquid based on the change in capacitance;
A liquid switching method characterized by comprising:

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