JP6699211B2 - Printing device and ejection method - Google Patents

Description

  The present invention relates to a printing device and a discharging method.

  2. Description of the Related Art Conventionally, there is known an inkjet type printing apparatus that prints an image or the like on a print medium by discharging ink or the like into droplets from a discharge head having a nozzle toward a print medium. In such a printing apparatus, a technique has been proposed in which a plurality of droplets ejected from nozzles are combined and landed at a predetermined position in order to change the size of dots formed on a printing medium. For example, Patent Document 1 discloses a droplet discharge device (printing apparatus) including a droplet discharge unit capable of continuously discharging a plurality of droplets and combining the plurality of droplets to land the droplets.

JP, 2011-42144, A

  However, since the plurality of droplets ejected from the nozzles are combined in the vicinity of the print medium in the printing apparatus described in Patent Document 1, each of the droplets is alone before the droplets are combined. The flight time for the flight was getting longer. As a result, there is a problem in that a row (tailing) of fine satellites generated from each droplet becomes long and the amount of mist remaining between the ejection head and the print medium increases. Then, the mist may adhere to the ejection head to cause ejection failure such as missing nozzles in which droplets are not ejected or displacement of landing position of droplets, or may adhere to the print medium and contaminate the print medium. ..

  The present invention has been made to solve at least a part of the problems described above, and can be realized as the following modes or application examples.

  Application Example 1 In a printing apparatus according to this application example, an ejection head that ejects a plurality of droplets from a nozzle to a predetermined position on a print medium, and a distance from the nozzle to the print medium that is 1 And a control unit for outputting to the ejection head a drive waveform capable of being combined at a distance of /2 or less.

  According to this application example, the control unit of the printing apparatus outputs, to the ejection head, a drive waveform that combines a plurality of droplets at a distance that is ½ or less of the distance from the nozzle to the print medium. As a result, the plurality of droplets ejected from the nozzles are combined at a distance that is ½ or less of the distance from the nozzles to the print medium, so that the droplets ejected first fly with tailing. The distance can be shortened and the amount of mist generated from a plurality of droplets can be reduced. Since the mist staying between the ejection head and the print medium is reduced, ejection failure of droplets caused by the mist adhering to the ejection head is reduced. Further, it is possible to prevent the print medium from being contaminated with mist. As a result, the quality of the image printed on the print medium can be improved. Therefore, it is possible to provide a printing apparatus with improved print quality.

  Application Example 2 In the printing apparatus according to the above application example, the drive waveform is such that the drive voltage for ejecting the subsequent droplet is 95% or more and 130% or less of the drive voltage for the droplet ejected first. Is preferred.

  According to this application example, the subsequent droplet is ejected at a drive voltage that is 95% or more of the drive voltage of the droplet that is ejected first. If the driving voltage is 95% or more, the subsequent droplets can be combined with the droplets ejected earlier by the so-called slipstream in which the air resistance in the rear is reduced by the object moving in the front. Further, if the driving voltage for ejecting the droplets is increased more than necessary, the amount of mist generated when the droplets are ejected increases, so that the subsequent droplets are 130% or less of the previously ejected droplets. It is preferable to discharge with the driving voltage of.

  Application Example 3 In the printing apparatus according to the application example described above, it is preferable that the drive waveform is such that the drive voltage for ejecting the first droplet is 70% or more of the maximum drive voltage.

  According to this application example, when the driving voltage for ejecting the droplets is reduced, the droplets are more likely to be affected by the mist adhering to the nozzles, the viscosity increase of the ink, and the like. It is preferable to eject at a drive voltage of 70% or more of the maximum drive voltage in the drive waveform to be ejected.

  Application Example 4 In the ejection method according to this application example, an ejection head that ejects a plurality of droplets from a nozzle to a predetermined position on a print medium, and a distance of 1 from the nozzle to the print medium are used. And a control unit that outputs a drive waveform that can be combined at a distance equal to or less than /2 to the ejection head. The following droplets are ejected at a drive voltage of 95% to 130% of the drive voltage.

  According to this application example, the ejection method of ejecting a plurality of droplets at a predetermined position of the print medium is performed by using the following liquid at a drive voltage of 95% or more and 130% or less with respect to the drive voltage of the droplet to be ejected first. Eject drops. As a result, it is possible to combine a plurality of droplets ejected from the nozzle at a distance of ½ or less of the distance from the nozzle to the print medium, so that the droplet ejected earlier flies with trailing. The flight distance of the droplets can be shortened, and the amount of mist generated from the plurality of droplets can be reduced. Since the mist staying between the ejection head and the print medium is reduced, ejection failure of droplets caused by the mist adhering to the ejection head is reduced. Further, it is possible to prevent the print medium from being contaminated with mist. As a result, the quality of the image printed on the print medium can be improved. Therefore, it is possible to provide the ejection method with improved print quality.

FIG. 1 is a schematic diagram showing a schematic overall configuration of a printing apparatus according to an embodiment. FIG. 3 is an electrical block diagram showing an electrical configuration of the printing apparatus. Sectional drawing which shows the structure of a discharge head. The figure which shows the drive waveform at the time of making a liquid droplet discharge twice continuously. FIG. 3 is a side view when a droplet is discharged from a nozzle. FIG. 3 is a side view when a droplet is discharged from a nozzle. The relationship between the coalescence position of droplets and the stain on the print medium. 6 is a graph showing the relationship between the drive voltage and the speed of ejected droplets. The graph which shows the speed change of the discharged droplet. The figure which shows the drive waveform at the time of discharging a liquid droplet 4 times continuously. The figure which shows an example of the drive waveform table which discharges a droplet.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each of the following drawings, the scale of each layer and each member is different from the actual scale in order to make each layer and each member recognizable.
Further, in FIG. 1, for convenience of description, an X-axis, a Y-axis, and a Z-axis are illustrated as three axes orthogonal to each other, and the tip end side of the arrow indicating the axial direction is the “+ side” and the base end side is the same. "-Side". Further, hereinafter, a direction parallel to the X axis is referred to as “X axis direction”, a direction parallel to the Y axis is referred to as “Y axis direction”, and a direction parallel to the Z axis is referred to as “Z axis direction”.

(Embodiment)
<Schematic configuration of printing device>
FIG. 1 is a schematic diagram showing a schematic overall configuration of a printing apparatus according to an embodiment. First, a schematic configuration of the printing apparatus 100 according to the present embodiment will be described with reference to FIG. In the present embodiment, an inkjet type printing apparatus 100 that prints on the print medium 95 by forming an image on the print medium 95 will be described as an example.

  As shown in FIG. 1, the printing apparatus 100 includes a medium supply unit 10, a medium conveyance unit 20, a medium collection unit 30, a printing unit 40, a drying unit 27, a cleaning unit 50, a medium contact unit 60, and the like. And, it has a control section 1 for controlling each of these sections. Each unit of the printing apparatus 100 is attached to the frame unit 90.

  The medium supply unit 10 supplies the print medium 95 for forming an image to the printing unit 40 side. As the print medium 95, for example, cloth such as cotton, wool, chemical fiber, and mixed spinning is used. The medium supply section 10 has a supply shaft section 11 and a bearing section 12. The supply shaft portion 11 is formed in a cylindrical shape or a cylindrical shape, and is rotatably provided in the circumferential direction. A strip-shaped print medium 95 is wound around the supply shaft portion 11 in a roll shape. The supply shaft portion 11 is detachably attached to the bearing portion 12. As a result, the print medium 95 wound in advance on the supply shaft portion 11 can be attached to the bearing portion 12 together with the supply shaft portion 11.

  The bearing portion 12 rotatably supports both ends of the supply shaft portion 11 in the axial direction. The medium supply unit 10 has a rotation drive unit (not shown) that rotationally drives the supply shaft unit 11. The rotation drive unit rotates the supply shaft unit 11 in the direction in which the print medium 95 is sent out. The operation of the rotation drive unit is controlled by the control unit 1.

  The medium transport unit 20 transports the print medium 95 from the medium supply unit 10 to the medium collection unit 30. The medium carrying unit 20 includes a carrying roller 21, a carrying roller 22, an endless belt 23, a belt rotating roller 24, a belt driving roller 25, a carrying roller 26, and a carrying roller 28. The transport rollers 21 and 22 relay the print medium 95 from the medium supply unit 10 to the endless belt 23.

  The endless belt 23, the belt rotation roller 24, and the belt drive roller 25 are medium transporting units that transport the print medium 95 in the transporting direction (+X axis direction) in the printing unit 40. Specifically, the endless belt 23 is formed in an endless shape by connecting both ends of a belt-shaped belt, and is hung on the belt rotating roller 24 and the belt driving roller 25. The endless belt 23 is held in a state in which a predetermined tension is applied so that a portion between the belt rotating roller 24 and the belt driving roller 25 is parallel to the floor surface 99. An adhesive layer 29 that adheres the print medium 95 is provided on the surface (support surface) 23 a of the endless belt 23. The endless belt 23 supports (holds) the print medium 95 supplied from the transport roller 22 and adhered to the adhesive layer 29 at the medium adhering portion 60 described later. Accordingly, a stretchable cloth or the like can be handled as the print medium 95.

  The belt rotating roller 24 and the belt driving roller 25 support the inner peripheral surface 23b of the endless belt 23. It should be noted that a configuration may be adopted in which a support portion that supports the endless belt 23 is provided between the belt rotation roller 24 and the belt drive roller 25.

  The belt drive roller 25 has a motor (not shown) that rotationally drives the belt drive roller 25. When the belt driving roller 25 is rotationally driven, the endless belt 23 rotates with the rotation of the belt driving roller 25, and the rotation of the endless belt 23 causes the belt rotating roller 24 to rotate. By the rotation of the endless belt 23, the print medium 95 supported by the endless belt 23 is conveyed in a predetermined conveying direction (+X axis direction), and an image is formed on the print medium 95 by the printing unit 40 described later. In the present embodiment, the print medium 95 is supported on the side (+Z-axis side) where the surface 23a of the endless belt 23 faces the printing unit 40, and the print medium 95 together with the endless belt 23 moves from the belt rotation roller 24 side to the belt drive roller 25. Be transported to the side. On the side where the surface 23a of the endless belt 23 faces the cleaning unit 50 (−Z axis side), only the endless belt 23 moves from the belt driving roller 25 side to the belt rotating roller 24 side.

  The transport roller 26 separates the print medium 95 on which the image is formed from the adhesive layer 29 of the endless belt 23. The transport rollers 26 and 28 relay the print medium 95 from the endless belt 23 to the medium collecting unit 30.

  The medium collecting unit 30 collects the print medium 95 conveyed by the medium conveying unit 20. The medium recovery unit 30 has a winding shaft portion 31 and a bearing portion 32. The winding shaft portion 31 is formed in a cylindrical shape or a column shape, and is rotatably provided in the circumferential direction. A strip-shaped print medium 95 is wound around the winding shaft portion 31 in a roll shape. The winding shaft portion 31 is detachably attached to the bearing portion 32. As a result, the print medium 95 wound on the winding shaft portion 31 can be removed together with the winding shaft portion 31.

  The bearing portion 32 rotatably supports both ends of the winding shaft portion 31 in the axial direction. The medium recovery unit 30 has a rotation drive unit (not shown) that rotationally drives the winding shaft unit 31. The rotation driving unit rotates the winding shaft unit 31 in the direction in which the print medium 95 is wound. The operation of the rotation drive unit is controlled by the control unit 1.

  The drying unit 27 is for drying the liquid (droplets) ejected onto the print medium 95, and is provided between the transport roller 26 and the transport roller 28. The drying unit 27 includes, for example, an IR heater, and the liquid discharged onto the print medium 95 can be dried in a short time by driving the IR heater. Accordingly, the strip-shaped print medium 95 on which an image or the like is formed can be wound around the winding shaft portion 31.

  The medium contact portion 60 is for contacting the print medium 95 with the endless belt 23. The medium contact portion 60 is provided on the upstream side (−X axis side) of the printing portion 40 in the transport direction of the print medium 95. The medium contact portion 60 has a pressure roller 61, a pressure roller drive portion 62, and a roller support portion 63. The pressing roller 61 is formed in a cylindrical shape or a cylindrical shape, and is provided so as to be rotatable in the circumferential direction. The pressing roller 61 is arranged so that its axial direction intersects with the transport direction so as to rotate in the direction along the transport direction. The roller support portion 63 is provided on the inner peripheral surface 23b side of the endless belt 23 facing the pressing roller 61 with the endless belt 23 interposed therebetween.

  The pressing roller driving unit 62 presses the pressing roller 61 downward in the vertical direction (−Z axis side) while pressing in the transport direction (+X axis direction) and in the direction opposite to the transport direction (−X axis direction). The roller 61 is moved. The print medium 95 conveyed from the conveyance roller 22 and superposed on the endless belt 23 is pressed against the endless belt 23 between the pressing roller 61 and the roller support portion 63. Accordingly, the print medium 95 can be surely adhered to the adhesive layer 29 provided on the surface 23a of the endless belt 23, and the print medium 95 can be prevented from floating on the endless belt 23.

  The cleaning unit 50 is for cleaning the surface 23 a of the endless belt 23. The cleaning unit 50 has a cleaning section 51, a pressing section 52, and a moving section 53. The moving unit 53 integrally moves the cleaning unit 50 along the floor surface 99 and fixes it at a predetermined position. The cleaning unit 50 is arranged between the belt rotating roller 24 and the belt driving roller 25 in the X-axis direction.

  The pressing part 52 is, for example, an elevating device composed of an air cylinder 56 and a ball bush 57, and the cleaning part 51 provided on the upper part thereof is brought into contact with the surface 23 a of the endless belt 23. The cleaning unit 51 cleans the surface (supporting surface) 23a of the endless belt 23, which is hung under a predetermined tension between the belt rotating roller 24 and the belt driving roller 25, from below (-Z axis direction). To do.

  The cleaning unit 51 has a cleaning tank 54, a cleaning roller 58, and a blade 55. The cleaning tank 54 is a tank for storing a cleaning liquid used for cleaning the ink and foreign matter attached to the surface 23 a of the endless belt 23, and the cleaning roller 58 and the blade 55 are provided inside the cleaning tank 54. As the cleaning liquid, for example, water or a water-soluble solvent (alcohol aqueous solution, etc.) can be used, and a surfactant or a defoaming agent may be added as necessary.

  When the cleaning roller 58 rotates, the cleaning liquid is supplied to the surface 23a of the endless belt 23, and the cleaning roller 58 and the endless belt 23 slide. As a result, the ink adhering to the endless belt 23, the fibers of the cloth as the print medium 95, and the like are removed by the cleaning roller 58.

  The blade 55 can be formed of, for example, a flexible material such as silicon rubber. The blade 55 is provided downstream of the cleaning roller 58 in the transport direction of the endless belt 23. The cleaning liquid remaining on the surface 23 a of the endless belt 23 is removed by the sliding movement of the endless belt 23 and the blade 55.

  The printing unit 40 includes an inkjet type ejection head 42 that ejects ink as droplets toward the printing medium 95, a carriage moving unit 41 that moves a carriage 43 on which the ejection head 42 is mounted, and the like. The printing unit 40 is arranged above (+Z axis side) with respect to the arrangement position of the endless belt 23. The ejection head 42 is provided with a nozzle plate 44 in which a plurality of nozzle rows 45 are formed. For example, four nozzle rows 45 are formed on the nozzle plate 44, and ink of different colors (for example, cyan: C, magenta: M, yellow: Y, black: K) is ejected for each nozzle row 45. It has become. The nozzle plate 44 faces the print medium 95 conveyed by the endless belt 23.

  The carriage moving unit 41 moves the ejection head 42 in a direction intersecting the transport direction of the print medium 95 (width direction of the print medium 95 (Y-axis direction)). The carriage 43 is supported by guide rails (not shown) arranged along the Y-axis direction, and is configured to be reciprocally movable in the ±Y-axis directions by the carriage moving unit 41. As the mechanism of the carriage moving unit 41, for example, a mechanism combining a ball screw and a ball nut, a linear guide mechanism, or the like can be adopted.

  Further, the carriage moving unit 41 is provided with a motor (not shown) as a power source for moving the carriage 43 along the Y-axis direction. When the motor is driven under the control of the control unit 1, the ejection head 42 reciprocates along with the carriage 43 along the Y-axis direction. In the present embodiment, as the ejection head 42, a serial head type that is mounted on a movable carriage and ejects ink while moving in the width direction (±Y axis direction) of the print medium 95 is exemplified. It may be a line head type that extends in the width direction (Y-axis direction) and is fixedly arranged.

<Electrical configuration>
FIG. 2 is an electrical block diagram showing the electrical configuration of the printing apparatus. Next, the electrical configuration of the printing apparatus 100 will be described with reference to FIG.

  The printing apparatus 100 includes a control unit 1. The control unit 1 is a control unit for controlling the printing apparatus 100. The control unit 1 includes an external interface (external I/F) 2, storage elements such as a RAM (Random Access Memory) 4 and a ROM (Read Only Memory) 5, a CPU (CENTRAL PROCESSING UNIT) 3, and a drive signal generation circuit. 7, an oscillation circuit 8, and an internal interface (internal I/F) 6.

The external I/F 2 is for transmitting and receiving data between an external device (not shown) such as a computer that handles images and the printing device 100. The RAM 4 stores various data and the like, and the ROM 5 stores a control routine for processing various data.
The CPU 3 controls each unit of the printing apparatus 100 according to an operation program stored in the ROM 5. Further, the CPU 3 converts print data input from an external device via the external I/F 2 into ejection data used for ejecting droplets (ink) in the ejection head 42.

  The drive signal generation circuit 7 is a circuit that generates a drive signal COM having a waveform shape determined by the CPU 3. The oscillator circuit 8 is a timing device for generating the control signal CK of the printing apparatus 100. The internal I/F 6 outputs the ejection data obtained by expanding (data conversion) the print data for each dot, the drive signal COM, and the like to the carriage moving unit 41, the belt drive roller 25, and the ejection head 42. Is.

  Further, the ejection head 42 has a shift register (SR) 91 to which print data SI is set, a latch circuit 92 that latches the print data SI set to the shift register 91 based on a latch signal (LAT), and a voltage amplifier. A level shifter 93 that functions as the piezoelectric vibrator 72, and a switch circuit 94 that controls the supply of the drive signal COM to the piezoelectric vibrator 72 are provided.

FIG. 3 is a cross-sectional view showing the structure of the ejection head. Next, the structure of the ejection head 42 will be described.
As shown in FIG. 3, the ejection head 42 includes a vibrator unit 70 in which a plurality of piezoelectric vibrators 72, a fixing plate 73, a flexible cable 74, and the like are unitized, and a case 71 in which the vibrator unit 70 can be stored. And a flow path unit 80 joined to the front end surface of the case 71.

  The case 71 is a block-shaped member made of synthetic resin in which a storage empty portion 75 having an open front end and a rear end is formed, and the vibrator unit 70 is stored and fixed in the storage empty portion 75.

The piezoelectric vibrator 72 is formed in a comb shape that is elongated in the vertical direction. The piezoelectric vibrator 72 is a laminated piezoelectric vibrator configured by alternately stacking piezoelectric bodies and internal electrodes, and is a longitudinal vibration mode piezoelectric vibrator that can expand and contract in a vertical direction orthogonal to the stacking direction. Is. The tip surface of each piezoelectric vibrator 72 is joined to the island portion 76 of the flow path unit 80.
The piezoelectric vibrator 72 behaves like a capacitor. That is, when the supply of the signal is stopped, the potential of the piezoelectric vibrator 72 is held at the potential immediately before the stop.

  In the flow path unit 80, the nozzle plate 44 is arranged on one surface side of the flow path forming substrate 83 with the flow path forming substrate 83 interposed therebetween, and the elastic plate 84 is the other surface opposite to the nozzle plate 44. It is configured by arranging on the side and laminating.

  The nozzle plate 44 is formed of a thin metal plate material (for example, a stainless plate) in which a plurality of (for example, 180) nozzles 46 are opened along the sub-scanning direction (X-axis direction). The flow path forming substrate 83 is a plate-shaped member in which a series of ink flow paths including a common ink chamber 86, an ink supply port 87, a pressure chamber 88, and a nozzle communication port 89 is formed. In this embodiment, the flow path forming substrate 83 is manufactured by etching a silicon wafer. The elastic plate 84 is a composite plate material having a double structure in which a resin film 81 is laminated on a stainless steel support plate 82, and the support plate 82 in a portion corresponding to the pressure chamber 88 is annularly removed to remove the island portion 76. Is forming.

  In the ejection head 42, a series of ink flow paths from the common ink chamber 86 to the nozzles 46 through the pressure chambers 88 are formed for each nozzle 46. Then, the piezoelectric vibrator 72 is deformed by charging or discharging the piezoelectric vibrator 72. That is, the piezoelectric vibrator 72 in the longitudinal vibration mode contracts in the vibrator longitudinal direction by charging and expands in the vibrator longitudinal direction by discharging. Therefore, when the potential is raised by charging, the island portion 76 is pulled toward the piezoelectric vibrator 72 side, the resin film 81 around the island portion 76 is deformed, and the pressure chamber 88 expands. Further, when the potential is lowered by the discharge, the pressure chamber 88 contracts.

  In this way, since the volume of the pressure chamber 88 can be controlled according to the potential, it is possible to cause a pressure fluctuation in the ink in the pressure chamber 88 and to eject an ink droplet from the nozzle 46. For example, the pressure chamber 88 having a steady volume (reference volume) is once expanded and then rapidly contracted, whereby the ink can be ejected into the liquid droplets.

  In addition, in this embodiment, the configuration using the longitudinal vibration type piezoelectric vibrator 72 is illustrated, but the present invention is not limited to this. For example, a flexural deformation type piezoelectric vibrator in which a lower electrode, a piezoelectric layer, and an upper electrode are laminated and formed may be used. Further, as a means for expanding and contracting the pressure chamber 88, a discharge head may be used which has a configuration in which a heating element is used to generate bubbles in the nozzle and the bubbles cause ink to be discharged.

FIG. 4 is a diagram showing a drive waveform in the case where a droplet is ejected twice continuously.
5 and 6 are side views when droplets are ejected from the nozzle. Next, the droplets discharged from the nozzle will be described with reference to FIGS. 4 to 6.
The printing apparatus 100 of the present embodiment outputs a plurality of liquids from the nozzle 46 to a predetermined position (predetermined pixel) of the print medium 95 based on the drive waveform output from the control unit 1 and applied to the piezoelectric vibrator 72 of the ejection head 42. A drop 47 is ejected. When the control unit 1 generates the drive waveform shown in FIG. 4 and applies the drive waveform to the piezoelectric vibrator 72, the piezoelectric vibrator 72 expands and contracts according to the displacement of the drive voltage Va, and a droplet 47a is ejected from the nozzle 46. Then, after a lapse of time t (hereinafter, also referred to as ejection interval t), the piezoelectric vibrator 72 ejects the droplet 47b from the nozzle 46 according to the displacement of the drive voltage Vb. FIG. 5 shows a state in which two droplets 47a and 47b have been ejected.

  In addition, the control unit 1 can drive the plurality of droplets 47 at a distance L3 that is ½ or less of a distance WG (hereinafter, referred to as “gap WG”) between the nozzle 46 and the print medium 95. Since the waveform is output, the droplet 47a ejected earlier (hereinafter, also referred to as the preceding droplet 47a) and the droplet 47b ejected later (hereinafter, also referred to as the succeeding droplet 47b) up to the distance L3. The droplets 48 that have caught up and coalesced land on a predetermined pixel. FIG. 6 shows a state of the droplet 48 in which the droplets 47a and 47b are combined.

  It is known that when the droplets 47 are ejected from the nozzle 46, the droplets 47 fly with tailing, and the liquid having a small mass separated from the droplets 47 stays as a mist. In the printing apparatus 100 that prints on the printing medium 95 such as a cloth, it is necessary to widen the gap WG to, for example, 2 mm or more to perform printing. Mist is generated from the liquid droplets 47, and the amount of mist remaining between the ejection head 42 and the print medium 95 increases. Then, the mist adheres to the nozzle plate 44 of the ejection head 42 to cause ejection failure of the droplet 47, or adheres to the print medium 95 to contaminate the print medium 95, resulting in print quality such as a printed image. Was falling.

FIG. 7 is a table showing the relationship between the coalescence position of droplets and the stain on the print medium.
The inventors of the present application have investigated the distance L3 at which the droplets 47 ejected from the nozzle 46 are united and the state (dirt) in which the print medium 95 is contaminated by mist, and as a result, as shown in FIG. It has been found that the contamination of the print medium 95 by the mist is significantly improved by setting the distance L3 until the droplets 47 of the above are combined to 1/2 or less of the gap WG. It was also confirmed that the amount of mist adhering to the nozzle plate 44 was reduced.

FIG. 8 is a graph showing the relationship between the drive voltage and the speed of the ejected droplets. The horizontal axis of FIG. 8 represents a standardized voltage in which the voltage applied to the piezoelectric vibrator 72 when the droplet 47 is ejected is standardized with a predetermined voltage. The vertical axis in FIG. 8 represents the velocity of the droplet 47 discharged from the nozzle 46.
FIG. 9 is a graph showing changes in the velocity of ejected droplets. The horizontal axis of FIG. 9 indicates the distance from the nozzle 46 (nozzle plate 44). The vertical axis of FIG. 9 represents the velocity of the droplet 47 discharged from the nozzle 46. 8 and 9, the velocity of the droplet 47a ejected first is shown by a solid line, and the velocity of the droplet 47b ejected afterwards is shown by a one-dot chain line.

  The printing apparatus 100 and the discharging method thereof according to the present embodiment are based on the driving waveform output from the control unit 1, and the driving voltage of 95% or more and 130% or less with respect to the driving voltage of the droplet 47a to be ejected first. The subsequent droplet 47b is ejected. As shown in FIG. 8, when the droplets are continuously ejected at the same drive voltage, the speed of the later ejected droplet (subsequent droplet) 47b is the same as that of the earlier ejected droplet (preceding droplet). Drop) 47a. The moving object receives air resistance on the front side in the traveling direction, but the state where the atmospheric pressure is lowered behind the object (slip stream). The air resistance of the succeeding droplet 47b received by the slip stream of the preceding droplet 47a over the entire surface in the traveling direction is reduced, and the succeeding droplet 47b can move at a speed faster than that of the preceding droplet 47a. In other words, the succeeding droplet 47b can catch up with and merge with the preceding droplet 47a even if the succeeding droplet 47b is ejected at a driving voltage lower than that of the preceding droplet 47a. For example, the speed of the subsequent droplet 47b ejected with the drive voltage of the standardization voltage 0.95 is substantially the same as the velocity of the preceding droplet 47a ejected with the drive voltage of the standardization voltage 1.0, The subsequent droplet 47b ejected at the drive voltage of 0.95 to 1.0 is faster than the velocity of the droplet 47a.

  FIG. 9 shows the velocities of the droplets 47a and 47b at the point L1 at the distance L1 (see FIG. 5) from the nozzle 46 and at the point L2 at the distance L2 (see FIG. 5) from the nozzle 46. The speeds of both the preceding droplet 47a and the succeeding droplet 47b decrease in proportion to the moving distance. However, the trailing droplet 47b has a lower speed reduction rate than the leading droplet 47a due to the slipstream of the leading droplet 47a, and thus the driving voltage of the trailing droplet 47b is lower than the driving voltage of the leading droplet 47a. It is also possible to catch up with the preceding droplet 47a and merge. For example, with respect to the preceding droplet 47a and the succeeding droplet 47b, which are ejected at substantially the same velocity, the velocity of the succeeding droplet 47b is approximately 0.5 m/s faster than the preceding droplet 47a at the point L2.

  For example, the gap WG is 2 mm or more, the ejection interval (time t) is 17 μs, the average velocity of the preceding droplet 47a is 5 m/s, and the average velocity difference between the preceding droplet 47a and the subsequent droplet 47b is 0.5 m/s. When s is set, the droplets 47a and 47b become a droplet 48 that coalesces at a distance L3=1 mm or less. Therefore, by ejecting the succeeding droplet 47b with a driving voltage of 95% or more of the driving voltage of the droplet (preceding droplet 47a) ejected in advance, the droplets 47a and 47b become 1/of the gap WG. They are united at a distance L3 of 2 or less. If the drive voltage for ejecting the droplet 47 is increased more than necessary, the amount of mist generated when the droplet 47 is ejected increases, so that the subsequent droplet 47b is driven by 130% or less of the preceding droplet 47a. It is preferable to discharge with a voltage. Further, since the droplets 48 coalesced at the distance L3 that is ½ or less of the gap WG suppress the reduction in flight speed due to the increase in mass, the positional accuracy of landing the droplets is improved.

FIG. 10 is a diagram showing drive waveforms in the case where droplets are ejected four times in succession. FIG. 11 is a diagram showing an example of a drive waveform table for ejecting droplets.
Next, a drive waveform in the case of ejecting droplets four times in succession will be illustrated.
When the control unit 1 generates the drive waveform shown in FIG. 10 and applies it to the piezoelectric vibrator 72, the piezoelectric vibrator 72 expands and contracts according to the displacement of the drive voltage V1, and the first droplet is ejected from the nozzle 46. .. Then, after the time t1, the second droplet is ejected according to the displacement of the drive voltage V2, further after the time t2, the third droplet is ejected according to the displacement of the drive voltage V3, and further after the time t3, the displacement of the drive voltage V4. The fourth droplet is discharged in accordance with the above. The first to fourth droplets are united within a distance of ½ of the gap WG and land on a predetermined pixel. The maximum drive voltage output to eject the first to fourth droplets is referred to as the maximum drive voltage VH. In the example of FIG. 10, the drive voltage V4 for ejecting the fourth droplet is the maximum drive voltage VH for one cycle of the drive waveform. Further, one cycle of the waveform is set to about 80 μs, and the discharge intervals (time t1, t2, t3) of the first to fourth droplets are set to 20 μs or less.

  In the printing apparatus 100 of the present embodiment, a drive waveform table for ejecting liquid droplets according to the type of ink and the ambient temperature condition is stored in the RAM 4, and based on the ink type and ambient temperature input during printing. The drive waveform is generated by referring to the drive waveform table. In the drive waveform table shown in FIG. 11, the drive voltages V1 to V4 when four droplets are ejected and landed on a predetermined pixel are shown as a ratio to the maximum drive voltage HV (see the column of “Ratio to VH”). ing. In addition, in FIG. 11, the voltage ratio of the succeeding droplet to the preceding droplet is shown for reference (see the column of “voltage ratio with respect to preceding droplet”).

  The first droplet is ejected at a drive voltage V1 that is 70% or more of the maximum drive voltage VH based on the drive waveform output from the control unit 1. As shown in “Ratio to VH” in FIG. 11, the drive voltage V1 for ejecting the first droplet is set to 70% or more of the maximum drive voltage VH. This is because if the driving voltage for ejecting the first droplet is too low in order to combine the droplets with the subsequent droplets too quickly, the droplets will be easily affected by the mist adhering to the vicinity of the nozzle 46, the thickened ink, and the like. This is because the discharge of is unstable. In the printing apparatus 100 of the present embodiment, the drive voltage V1 for ejecting the first droplet is set to 70% or more of the maximum drive voltage VH under all the combination conditions of the ink type and the ambient temperature, so that the intermittent capability is obtained. Is ensured, and it is possible to reduce defective ejection due to thickening.

  Further, as shown in “voltage ratio to preceding droplet” in FIG. 11, the drive voltages V2 to V4 for ejecting the second to fourth droplets (subsequent droplets) are the first to the third droplets ejected immediately before. It is set to 95% or more and 130% or less (120% or less in the example of FIG. 11) with respect to the drive voltages V1 to V3 of the droplets (preceding droplets). Further, since the third and fourth droplets are greatly affected by the slipstream received from the preceding droplets described above, the first to fourth droplets are united at a distance L3 that is ½ or less of the gap WG and predetermined. Can be landed on the pixel. Since each droplet has a shorter flight distance, the amount of mist generated from each droplet is reduced, and the amount of mist remaining between the ejection head 42 and the print medium 95 is also reduced. As a result, it is possible to reduce ejection defects caused by the mist adhering to the nozzle plate 44 of the ejection head 42, and to stabilize the ejection of droplets. Further, the amount of mist floating in the area relatively close to the print medium 95 is reduced, and the contamination of the print medium 95 by the mist is significantly improved. As a result, the print quality of the image printed on the print medium 95 is improved.

Although the drive waveform table for ejecting four droplets is illustrated in FIG. 11, the printing apparatus 100 of the present embodiment has a drive waveform table for ejecting one to four droplets.
Further, in the present embodiment, the ink jet type printing apparatus 100 for printing is exemplified, but the present invention can be applied to all ink jet type printing apparatuses.

As described above, according to the printing apparatus 100 according to this embodiment, the following effects can be obtained.
The printing apparatus 100 includes the control unit 1 that outputs a drive waveform that can combine the plurality of droplets 47 at a distance L3 that is ½ or less of the distance (gap WG) from the nozzle 46 to the print medium 95. There is. By merging the plurality of droplets 47 at a distance L3 that is ½ or less of the gap WG, the distance that the plurality of droplets 47 independently fly is shortened, and the amount of mist generated from each droplet 47 is reduced. However, the amount of mist remaining between the ejection head 42 and the print medium 95 also decreases. As a result, it is possible to reduce ejection defects caused by the mist adhering to the nozzle plate 44 of the ejection head 42, and to stabilize the ejection of droplets. Further, the mist floating in the area relatively close to the print medium 95 is reduced. As a result, the print medium 95 is prevented from being contaminated with mist, so that the quality of an image or the like printed on the print medium 95 is improved. Further, the droplet 48 combined at a distance L3 that is 1/2 or less of the gap WG suppresses a decrease in flight speed due to an increase in mass, and thus the positional accuracy of landing the droplet is improved. Therefore, the printing apparatus 100 with improved print quality can be provided.

The subsequent droplet 47b is ejected at a driving voltage of 95% or more of the driving voltage of the preceding droplet 47a. As a result, the succeeding droplet 47b can catch up with the preceding droplet 47a and be merged at a distance L3 that is ½ or less of the gap WG. Further, since the subsequent droplet 47b is ejected at a driving voltage which is 130% or less of that of the preceding droplet 47a, the amount of mist generated when the droplet is ejected from the nozzle 46 can be reduced.
Since the preceding droplet (first droplet) that is ejected first is ejected at a drive voltage of 70% or more of the maximum drive voltage VH, it is affected by mist adhering to the vicinity of the nozzle 46 or thickened ink. It is reduced, and the discharge of droplets can be stabilized.

  In the printing apparatus 100, the ejection method for ejecting the plurality of droplets 47 to the predetermined position of the printing medium 95 is to eject the succeeding droplet 47b at a driving voltage of 95% or more and 130% or less of the driving voltage of the preceding droplet 47a. Let As a result, the plurality of droplets 47 ejected from the nozzle 46 can be combined at a distance L3 that is ½ or less of the distance from the nozzle 46 to the print medium 95, so that the plurality of droplets 47 fly independently. The amount of mist generated from each droplet 47 is reduced, and the amount of mist remaining between the ejection head 42 and the print medium 95 is also reduced. As a result, it is possible to reduce ejection defects caused by the mist adhering to the nozzle plate 44 of the ejection head 42, and to stabilize the ejection of droplets. Further, the mist floating in the area relatively close to the print medium 95 is reduced. As a result, the print medium 95 is prevented from being contaminated with mist, so that the quality of an image or the like printed on the print medium 95 is improved. Further, the droplet 48 combined at a distance L3 that is ½ or less of the gap WG suppresses a decrease in flight speed due to an increase in mass, so that the positional accuracy of landing the droplet is improved. Therefore, it is possible to provide the ejection method with improved print quality.

  DESCRIPTION OF SYMBOLS 1... Control part, 2... External I/F, 3... CPU, 4... RAM, 5... ROM, 6... Internal I/F, 7... Drive signal generation circuit, 8... Oscillation circuit, 10... Medium supply part, 20 ... Medium transporting section, 30... Medium collecting section, 40... Printing section, 42... Ejecting head, 43... Carriage, 44... Nozzle plate, 46... Nozzle, 47, 47a, 47b, 48... Droplet, 50... Cleaning unit, 60... Medium contact part, 70... Oscillator unit, 72... Piezoelectric oscillator, 91... Shift register, 92... Latch circuit, 93... Level shifter, 94... Switch circuit, 95... Printing medium, 100... Printing device.

Claims (2)

A discharge head for discharging a plurality of droplets from a nozzle to a predetermined position on a print medium,
A controller that outputs to the ejection head a drive waveform capable of combining the plurality of droplets at a distance that is ½ or less of the distance from the nozzle to the print medium;
Equipped with
The control unit has a storage element that stores a drive waveform table for ejecting the droplets according to the type of ink and ambient temperature conditions, and is based on the ink type and the ambient temperature input during printing. Then, the drive waveform is generated by referring to the drive waveform table,
The storage element has, as the drive waveform table, a plurality of drive waveform tables including a first drive waveform table used to generate a drive waveform including a plurality of drive voltages having different voltages in one waveform period. And
All of the driving waveforms generated by referring to the first driving waveform table are 95% or more and 130% or less with respect to the driving voltage of the droplet ejected earlier by the driving voltage ejecting the subsequent droplet. And a drive voltage for ejecting the first droplet is 70% or more of the maximum drive voltage . A discharge head for discharging a plurality of droplets from a nozzle to a predetermined position on a print medium,
A controller that outputs to the ejection head a drive waveform capable of combining the plurality of droplets at a distance that is ½ or less of the distance from the nozzle to the print medium;
Equipped with
The control unit includes a storage element that stores a drive waveform table for ejecting the droplets according to the type of ink and ambient temperature conditions, and is based on the ink type and the ambient temperature input during printing. To generate the drive waveform by referring to the drive waveform table, and to generate a drive waveform including a plurality of drive voltages having different voltages in one cycle of the waveform in the storage element as the drive waveform table. A method for ejecting a printing apparatus having a plurality of drive waveform tables including a first drive waveform table used, comprising :
Based on the driving waveform generated by referring to the first drive waveform table, prior to as well as discharging a subsequent droplet drive voltage of 130% less 95% with respect to the driving voltage of the liquid droplet ejecting And a driving voltage for discharging the first liquid droplets of 70% or more of the maximum driving voltage .

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