JP5504599B2 - Droplet discharge head and image forming apparatus - Google Patents

Description

  The present invention relates to a droplet discharge head that discharges droplets and an image forming apparatus including the droplet discharge head.

  In Patent Document 1, a driving waveform is applied to a driving element to contract a pressure chamber and eject a droplet from a nozzle, and a meniscus caused by a reaction of the first contracting process. There is described a droplet discharge head comprising a second contraction step for contracting a pressure chamber to reduce retraction.

In this droplet discharge head, droplets are discharged by setting the time difference between the start time of the first contraction step and the start time of the second contraction step to ¼ to ¾ of the natural vibration period of the ejector. After that, the residual vibration of the meniscus is suppressed.
JP 2000-94671 A

  An object of the present invention is to suppress unintended ejection such as satellites and mists when ejecting liquid droplets from a nozzle.

A droplet discharge head according to claim 1 of the present invention includes a nozzle that discharges a droplet, a pressure chamber that communicates with the nozzle via a communication path, and a drive element that applies pressure to the liquid in the pressure chamber. A first negative direction variation step of drawing a meniscus from the nozzle to the pressure chamber side, and a first negative direction variation, comprising: an ejector having a control unit that applies a drive waveform based on image information to the drive element; The meniscus drawn in the process is pushed out to the side opposite to the pressure chamber side and discharged from the nozzle by the first positive direction changing step for discharging the tip of the liquid column from the nozzle and the first positive direction changing step. The second negative direction fluctuation step of drawing the rear end portion of the liquid column to the pressure chamber side, and the rear end portion of the liquid column drawn into the opposite side of the pressure chamber side by the second negative direction fluctuation step. 2nd positive direction to push out To perform a process comprising a dynamic process, wherein the control unit, the driving waveform applied to the driving element, a first voltage changing process for expanding the pressure chamber is lowered voltage, the first voltage A first voltage maintaining process for maintaining a voltage dropped in the changing process; a second voltage changing process for increasing the voltage maintained in the first voltage maintaining process to contract the pressure chamber; and the second voltage changing process. A second voltage maintaining process for maintaining the voltage increased in step (b), and a third voltage changing process for contracting the pressure chamber by further increasing the voltage maintained in the second voltage maintaining process. The interval between the start of the voltage change process and the start of the third voltage change process is 0.6 to 0.8 times the natural vibration period of the ejector.

According to a second aspect of the present invention, a liquid droplet ejection head includes: a nozzle that ejects liquid droplets; a pressure chamber that communicates with the nozzle through a communication path; and a drive element that applies pressure to the liquid in the pressure chamber. A first negative direction variation step of drawing a meniscus from the nozzle to the pressure chamber side, and a first negative direction variation, comprising: an ejector having a control unit that applies a drive waveform to the drive element based on image information; The meniscus drawn in the process is pushed out to the side opposite to the pressure chamber side and discharged from the nozzle by the first positive direction changing step for discharging the tip of the liquid column from the nozzle and the first positive direction changing step. The second negative direction fluctuation step of drawing the rear end portion of the liquid column to the pressure chamber side, and the rear end portion of the liquid column drawn into the opposite side of the pressure chamber side by the second negative direction fluctuation step. 2nd positive direction to push out A driving waveform applied to the driving element by the control unit to reduce the voltage to expand the pressure chamber, and the first voltage changing process for expanding the pressure chamber. A first voltage maintaining process for maintaining a voltage dropped in the voltage changing process of the second voltage changing process, and a second voltage changing process for further expanding the pressure chamber by further dropping the voltage maintained in the first voltage maintaining process. A second voltage maintaining process for maintaining the voltage dropped in the second voltage changing process, and a third voltage change for contracting the pressure chamber by increasing the voltage maintained in the second voltage maintaining process. comprises a process, and the third fourth voltage change process voltage changing process raises the voltage was increased by returning to the beginning of the voltage of the first voltage changing process, wherein the first voltage The beginning of the process and the interval at the start of the second voltage changing process and 0.9 to 1.1 times the natural vibration period of the ejector, characterized in that.

An image forming apparatus according to a third aspect of the present invention is a droplet discharge head according to claim 1 or 2, wherein a droplet is discharged onto a conveyance unit that conveys a recording medium and the recording medium that is conveyed by the conveyance unit. And.

According to the first aspect of the present invention, as compared with a case not having this configuration, the speed of the rear end of the liquid column discharging from the nozzle becomes faster than the speed of the tip, the rear end of the liquid column The unintentional discharge such as satellite and mist can be suppressed by combining the part and the tip part.

According to the configuration of claim 1 of the present invention, by increasing the voltage dropped in the first voltage change process in two stages of the second voltage change process and the third voltage change process and compressing the pressure chamber in two stages, Compared to the case without this configuration, the speed of the rear end of the liquid column ejected from the nozzle can be made faster than the speed of the front end.

According to the configuration of claim 1 of the present invention, the interval between the start of the second voltage change process and the start of the third voltage change process is 0.6 to 0.8 times the natural vibration period of the ejector. Thus, as compared with the case where this configuration is not provided, the speed of the rear end of the liquid column discharged from the nozzle can be reliably made higher than the speed of the front end.

According to the configuration of claim 2 of the present invention, this configuration is achieved by lowering the voltage in two stages and expanding the pressure chamber in two stages by the first voltage change process and the second voltage change process. Compared with the case where it does not, the speed | rate of the rear-end part of the liquid column discharged from a nozzle can be made faster than the speed | rate of a front-end | tip part.

According to the second aspect of the present invention, furthermore, 0.9 times the natural vibration period of the ejector the interval between the beginning of the start and the second voltage changing process of the first voltage changing process to 1. By setting it to 1 time, the speed of the trailing edge of the droplet discharged from the nozzle can be reliably made higher than the speed of the leading edge compared to the case without this configuration.

According to the configuration of the third aspect of the present invention, unintentional discharge such as satellites and mist is suppressed as compared with the case without this configuration, and an intended image can be formed on the recording medium.

  An example of an image forming apparatus employing the liquid droplet ejection head according to the first embodiment of the present invention will be described with reference to FIGS.

(overall structure)
FIG. 9 schematically shows a configuration of an FWA (Full Width Array) type ink jet printer (hereinafter simply referred to as “printer”) 10 which is an image forming apparatus according to the present embodiment.

  The printer 10 is provided with a conveyance belt 12, which is wound around a plurality of rollers 14 and circulates in a direction indicated by an arrow A in the drawing. A part of the plurality of rollers 14 is a driving roller that rotates by receiving a driving force of a driving means (not shown), and the other rollers are rotated by the rotation of the driving roller.

  Further, the printer 10 is provided with a paper tray 20, and sheet members P for recording images are stacked and accommodated in the paper tray 20. The sheet members P accommodated in the paper tray 20 are taken out one by one from the uppermost layer by a pickup mechanism (not shown), guided along the paper feed conveyance path 22 by the conveyance roll 11, and at a predetermined position on the conveyance belt 12. Sent out. The transport belt 12 has a function of holding the sheet member P in close contact. As a result, the sheet member P fed from the paper feed conveyance path 22 is conveyed in the direction of the arrow A while being held in close contact.

  Further, a head array 37 is disposed along the conveyance path of the sheet member P on the downstream side in the conveyance direction at a predetermined position where the sheet member P is fed onto the conveyance belt 12. The head array 37 includes, for example, cyan (C) color ink discharge, magenta (M) color ink discharge, yellow (Y) color ink discharge, black ( K) The recording heads 36 are provided as four liquid droplet ejection heads for color ejection, and the conveyed sheet member P is sequentially opposed to each recording head 36.

  Then, based on the control of a recording head controller 90 (see FIG. 9) as a control unit, ink droplets (droplets) of each color are provided in the ink head unit 60 (see FIG. 8) of each recording head 36 (see FIG. 8). (See FIG. 7). As a result, ink droplets are ejected from the recording heads 36 that are sequentially opposed to the sheet member P that is in close contact with the conveying belt 12 to record a full-color image.

  Further, a scraper 26 is provided on the conveyance path of the sheet member P by the conveyance belt 12 and on the downstream side of the head array 37 so as to correspond to the arrangement position of the roller 14 provided at a position where the conveyance path is bent. The sheet member P that has been provided is separated from the conveying belt 12 and is sent out to the paper discharge tray 30 via the discharge path 28.

  Next, the recording head 36 will be described.

  As shown in FIG. 8, the recording head 36 is a long head that is wider than the maximum width of the sheet member P. Further, the recording head 36 includes an ink head unit 60 as a plurality of rectangular droplet discharge head units, and each ink head unit 60 is provided upstream and downstream of the sheet member P to be conveyed. Two rows are arranged in a staggered pattern with a half-pitch shift.

  Further, the ink head unit 60 is formed with a rectangular ejector region (arrangement part of the ejector group) 43 in which a plurality of ejectors are arranged. In the ejector region 43, a plurality of common flow paths 41 for supplying ink from ink cartridges (not shown) are provided. The common channel 41 communicates with a plurality of nozzles 40 (see FIG. 7).

  As shown in FIG. 7, the ejector 34 provided in the ink head unit 60 includes a nozzle 40 that ejects ink, a pressure chamber 46 that communicates with the nozzle 40, and ink from an ink cartridge (not shown) to the pressure chamber 46. And a common flow path 41 for supplying the liquid.

  A nozzle communication path 64 is provided in the pressure chamber 46, and the nozzle 40 and the pressure chamber 46 are communicated with each other by the nozzle communication path 64. Further, the pressure chamber 46 and the common flow path 41 are communicated with each other by the communication path 70 and the ink supply path 44.

  These are formed by stacking plates, and are common to the nozzle plate 62 in which the nozzles 40 are formed, the ink pool plate 66 and the ink pool plate 68 in which the nozzle communication path 64 and the common flow path 41 are formed. The through plate 72 in which the communication path 70 and the nozzle communication path 64 of the flow path 41 are formed, the ink supply path plate 74 in which the ink supply path 44 is formed, and the pressure chamber plate 76 in which the pressure chamber 46 is formed. The flow path plate unit 78 is formed by being laminated in order.

  The ceiling of the pressure chamber 46 is constituted by a diaphragm 47, and a drive element 42 is attached to the diaphragm 47. Further, a substrate 45 is provided above the drive element 42 and is joined to the drive element 42 via a solder bump 39.

  With this configuration, the driving element 42 to which the driving waveform determined by the recording head controller 90 is applied changes the pressing force on the vibration plate 47 to contract or expand the volume in the pressure chamber 46. That is, the ink (liquid) stored in the pressure chamber 46 due to the change in the volume in the pressure chamber 46 passes through the nozzle communication path 64 and is ejected from the nozzle 40 as an ink droplet.

(Main part)
Next, a driving waveform applied to the driving element 42 by the recording head controller 90 will be described.

  As shown in FIG. 1A, the drive waveform applied to the drive element 42 is an analog waveform, and the process of lowering the voltage to expand the pressure chamber 46 (first voltage change process) and the reduced voltage For maintaining the voltage (first voltage maintaining process), a process for increasing the dropped voltage to contract the pressure chamber 46 (second voltage changing process), and a process for maintaining the voltage increased in the second voltage changing process (Second voltage maintaining process) and a process (third voltage changing process) of further contracting the pressure chamber 46 by further increasing the voltage increased in the second voltage changing process.

  That is, the process of contracting the pressure chamber 46 to push out the droplet from the nozzle 40 is provided twice. This is a so-called two-stage push.

  FIG. 1B shows the relationship between the ink flow velocity of ink ejected from the nozzle 40 in the vicinity of the nozzle 40 and time when the drive waveform of FIG. 1A is applied to the drive element 42. . The vertical axis of the grab in FIG. 1B shows the ink flow velocity of the ink ejected from the nozzle 40 in the vicinity of the nozzle 40, the plus direction is the speed in the direction of ejecting ink from the nozzle 40, and the minus direction is the ink. The speed in the direction of drawing into the nozzle 40. The horizontal axis of the grab indicates time.

  As can be seen from this figure, the step of changing the flow rate of the ink ejected from the nozzle 40 is a first negative direction fluctuation step (FIG. 2 (FIG. 2)) that draws the meniscus 32 (see FIG. 2) from the nozzle 40 to the pressure chamber 46 side. B)), and the meniscus 32 drawn in the first negative direction changing step is pushed out to the side opposite to the pressure chamber 46 side, and the tip portion of the liquid column is discharged from the nozzle 40 (FIG. 2). (See (C)), a second negative direction fluctuation step (see FIG. 2D) for drawing the rear end of the liquid column discharged from the nozzle 40 in the first positive direction fluctuation step into the pressure chamber 46 side, 2 includes a second positive direction changing step (see FIG. 2E) for pushing the rear end portion of the drawn liquid column to the side opposite to the pressure chamber 46 side by the negative direction changing step.

  Before the recording head controller 90 applies a driving waveform to the driving element 42, as shown in FIG. 2A, the meniscus 32 of the nozzle 40 balances the capillary force and the ink back pressure (negative pressure). In the state, it is held at the end of the nozzle 40. On the other hand, after the second positive direction changing step, as shown in FIG. 2 (F), the rear end portion of the liquid column accelerated by the second positive direction changing step is cut from the ink inside the nozzle 40 to form a columnar shape. Ink droplets (droplets) are ejected toward the sheet member P. That is, the ink droplets are ejected by so-called striking in which the meniscus 32 is once pulled into the nozzle 40 to eject the ink droplets.

  In the first embodiment, as shown in FIG. 1B, the head controller 90 applies a predetermined driving waveform to the driving element 42, so that the first positive direction changing step and the second positive direction are performed. The interval (B shown in the figure) of the fluctuation process is set to 0.8 to 0.9 times the natural vibration period (Tc) of the ejector 34, and further, the ink flow rate and the second positive flow in the first positive direction fluctuation process. The flow rate ratio (C2 / C1 shown in the figure) of the flow rate of ink in the direction changing step is set to 0.25 to 0.55.

(Function)
Thus, the interval (B shown in the figure) between the first positive direction variation step and the second positive direction variation step is 0.8 to 0.9 times the natural vibration period (Tc) of the ejector 34, and By setting the flow rate ratio (C2 / C1 shown in the figure) of the ink flow rate in the first positive direction changing step and the ink flow rate in the second positive direction changing step to 0.25 to 0.55, the nozzle 40 The speed of the satellite droplets of the columnar ink droplets ejected from the ink (the trailing edge velocity of the ink droplets) becomes faster than the velocity of the main droplets (the leading edge velocity of the ink droplets), and the satellite droplets catch up with the main droplets and fly. To do.

  Here, the inventor of the present application sets an interval (D shown in FIG. 1A) between the start of the second voltage change process and the start of the third voltage change process of the drive waveform applied to the drive element 42. The ink droplets ejected from the nozzle 40 were actually evaluated by shaking to some level.

  Specifically, the ink droplets ejected from the nozzle 40 are ejected from the nozzle 40 in a columnar shape. The columnar ink droplet includes a relatively large main droplet located at the front end portion and a satellite droplet formed along with the main droplet and located at the rear end portion. It was evaluated whether or not the main droplet and the satellite droplet were combined, and whether or not the unnecessary droplet was ejected from the nozzle 40 after ejecting the ink droplet (main droplet and satellite droplet).

  In the evaluation method, the shape of the ink droplet ejected from the nozzle 40 is confirmed from the side every time, and the satellite droplet catches up with the main droplet at a position 700 μm away from the nozzle surface and flies together (integrates) and flies. It was evaluated whether or not. Furthermore, it was evaluated whether or not unnecessary ink droplets (unnecessary droplets) were ejected from the nozzle 40 after ejecting ink droplets (main droplets and satellite droplets).

  In general, in the case of an image forming apparatus, the sheet member P as a recording medium is generally located at a position 1 mm to 1.5 mm away from the nozzle 40. The purpose of this evaluation is to confirm whether or not the main droplet and the satellite droplet are combined before reaching the sheet member P. As an example, the evaluation was performed at a position 700 μm away from the nozzle surface. It is sufficient that the main droplet and the satellite droplet are united until P is reached, and it is not limited to 700 μm.

  As shown in FIGS. 4 (A), (B), (C), FIGS. 5 (A), (B), and (C), and FIGS. 6 (A), (B), and (C), The interval (D shown in the figure) at the start of the third voltage change process is 0.2 Tc (Tc: natural vibration period of the ejector 34), 0.3 Tc, 0.4 Tc, 0.5 Tc, 0.6 Tc, 0 The evaluation was performed by shifting to 9 levels of 0.7 Tc, 0.8 Tc, 0.9 Tc, and 1.0 Tc. Furthermore, the ink flow velocity in the vicinity of the nozzle 40 corresponding to each drive waveform was confirmed.

  The interval (B shown in the figure) between the first positive direction changing step and the second positive direction changing step according to the interval (D shown in the figure) at the start of the second voltage changing process and the start of the third voltage changing process (D shown in the figure). The ink flow rate ratio in the first positive direction changing step and the ink flow rate ratio (C2 / C1 shown in the drawing) in the second positive direction changing step were confirmed, and ink droplets were further evaluated.

  As shown in the evaluation result of FIG. 3, when the interval (D) between the start of the second voltage change process and the start of the third voltage change process is 0.6 Tc to 1.0 Tc, the first positive direction The interval (B) between the changing step and the second positive direction changing step is 0.8 Tc to 1.01 Tc, and further, the ink flow rate in the first positive direction changing step and the ink flow rate in the second positive direction changing step. The flow rate ratio (C2 / C1) is 0.28 to 0.7, and the main droplet and the satellite droplet are combined.

  Further, when the interval (D) between the start of the second voltage change process and the start of the third voltage change process is 0.2 Tc to 0.8 Tc, the first positive direction change step and the second positive direction change step The interval (B) is 0.8 Tc to 1.10 Tc, and the flow rate ratio (C2 / C1) of the ink flow rate in the first positive direction changing step and the ink flow rate in the second positive direction changing step is C2 / C1. 0.08 to 0.53, and unnecessary droplets are not discharged.

  That is, if the interval (D) between the start of the second voltage change process and the start of the third voltage change process is 0.6 Tc to 0.8 Tc, the first positive direction change step and the second positive direction change step The interval (B) is 0.8 Tc to 0.9 Tc, and the flow rate ratio (C2 / C1) of the ink flow rate in the first positive direction changing step and the ink flow rate in the second positive direction changing step is: 0.28 to 0.53, the main droplet and the satellite droplet are combined, and unnecessary droplets are not discharged.

  Then, as described above, in the first embodiment, the head controller 90 applies the determined drive waveform to the drive element 42, thereby setting the interval between the first positive direction variation process and the second positive direction variation process to the ejector 34. The natural vibration period (Tc) is 0.8 to 0.9 times, and the flow rate ratio of the ink flow rate in the first positive direction changing step and the ink flow rate in the second positive direction changing step (in the figure) C2 / C1) is set to 0.25 to 0.55. From the above evaluation results, it can be seen that in the first embodiment, the main droplet and the satellite droplet are combined, and further, unnecessary droplets are not discharged.

  Although the present invention has been described in detail with respect to specific embodiments, the present invention is not limited to such embodiments, and various other embodiments are possible within the scope of the present invention. It is clear to the contractor. For example, in the above-described embodiment, the liquid droplets ejected from the recording head 36 are described as being limited to ink droplets, but are not limited to ink droplets. For example, liquids intended for various industrial applications such as the formation of bumps for component mounting by discharging molten solder onto the substrate, and the formation of EL display panels by discharging organic EL solution onto the substrate The present invention can be applied to a droplet discharge head.

  In the above-described embodiment, the image forming apparatus that ejects ink droplets in a state where the recording head 36 is fixed using the long recording head 36 has been described as an example. However, the recording head has a width of the sheet member P. An image forming apparatus that scans in the direction and ejects ink droplets while scanning may be used.

  Next, an example of an image forming apparatus that employs a droplet discharge head according to a second embodiment of the present invention will be described with reference to FIGS.

  In addition, about the same member as 1st Embodiment, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

  In the present embodiment, unlike the first embodiment, the drive wave applied to the drive element 42 by the recording head controller 90 is provided with a process of expanding the pressure chamber 46 twice.

  As shown in FIG. 10A, the drive waveform applied to the drive element 42 is an analog waveform, and the process of lowering the voltage to expand the pressure chamber 46 (first voltage change process) and the drive waveform 42 dropped. A process for maintaining the voltage (first voltage maintaining process), a process for further reducing the voltage to expand the pressure chamber 46 (second voltage changing process), and a process for maintaining the lowered voltage (second voltage) Maintenance process), a process of raising the voltage to contract the pressure chamber 46 (third voltage change process), and a process of raising the voltage and returning to the initial voltage (fourth voltage change process). .

  That is, the process of expanding the pressure chamber 46 and drawing a droplet from the nozzle 40 is provided twice. This is a so-called two-stage drawing.

  Further, in the second embodiment, as shown in FIG. 10B, the head controller 90 applies a predetermined driving waveform to the driving element 42, so that the first positive direction changing step and the second positive direction are performed. The interval (F shown in the figure) of the fluctuation process is set to 0.8 to 0.9 times the natural vibration period (Tc) of the ejector 34, and the ink flow rate and the second positive flow in the first positive direction fluctuation process. The flow rate ratio (G2 / G1 shown in the figure) of the flow rate of ink in the direction changing step is set to 0.25 to 0.55.

  Here, the inventor of the present application refers to an interval between the start of the first voltage change process of the drive waveform applied to the drive element 42 and the start of the second voltage change process (H shown in FIG. 10A). The ink droplets ejected from the nozzle 40 were actually evaluated.

  Specifically, the ink droplets ejected from the nozzle 40 are ejected from the nozzle 40 in a columnar shape. The columnar ink droplet includes a relatively large main droplet located at the front end portion and a satellite droplet formed along with the main droplet and located at the rear end portion. It was evaluated whether or not the main droplet and the satellite droplet were combined, and whether or not the unnecessary droplet was ejected from the nozzle 40 after ejecting the ink droplet (main droplet and satellite droplet).

  The evaluation method is the same as in the first embodiment.

  As shown in FIGS. 12 (A), (B), (C), FIGS. 13 (A), (B), and (C), and FIGS. 14 (A), (B), and (C), at the start of the first voltage change process And the interval at the start of the second voltage change process (H shown in the figure) is 0.5 Tc (Tc: natural vibration period of the ejector 34), 0.6 Tc, 0.7 Tc, 0.8 Tc, 0.9 Tc , 1.0 Tc, 1.1 Tc, 1.2 Tc, and 1.3 Tc, and evaluated at 9 levels. Furthermore, the ink flow velocity in the vicinity of the nozzle 40 corresponding to each drive waveform was confirmed.

  The interval between the first positive direction variation step and the second positive direction variation step (shown in the drawing) is separated according to the interval (H shown in the drawing) at the start of the first voltage changing process and the second voltage changing process. F), and the flow rate ratio (G2 / G1 shown in the figure) of the ink flow rate in the first positive direction variation step and the ink flow rate in the second positive direction variation step was confirmed, and the ink droplets were further evaluated. .

  As shown in the evaluation results of FIG. 11, when the interval (H) between the start of the first voltage change process and the start of the second voltage change process is 0.9 Tc to 1.3 Tc, the first positive change process is performed. The interval (F) between the direction changing step and the second positive direction changing step is 0.75 Tc to 1.00 Tc, and further, the ink flow rate in the first positive direction changing step and the ink flow rate in the second positive direction changing step. The flow rate ratio (G2 / G1) is 0.25 to 0.94, and the main droplet and the satellite droplet are combined.

  Further, when the interval (H) between the start of the first voltage change process and the start of the second voltage change process is 0.5 Tc to 1.1 Tc, the first positive direction variation step and the second positive direction The interval (F) of the variation process is 0.40 Tc to 1.25 Tc, and the flow rate ratio (G2 / G1) of the ink flow rate in the first positive direction variation step and the ink flow rate in the second positive direction variation step. ) Is 0.19 to 0.55, and no unnecessary droplets are discharged.

  That is, when the interval (H) between the start of the first voltage change process and the start of the second voltage change process is 0.9 Tc to 1.1 Tc, the first positive direction change step and the second positive direction change The step interval (F) is 0.75 Tc to 0.85 Tc, and the flow rate ratio (G2 / G1) of the ink flow rate in the first positive direction changing step and the ink flow rate in the second positive direction changing step is 0.25 to 0.55, the main droplet and the satellite droplet are combined, and unnecessary droplets are not discharged.

  Next, an example of an image forming apparatus that employs a droplet discharge head according to a third embodiment of the present invention will be described with reference to FIGS.

  In addition, about the same member as 1st Embodiment, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

  In the present embodiment, unlike the first embodiment, the drive wave applied to the drive element 42 by the recording head controller 90 is provided with a process of expanding the pressure chamber 46 twice.

  As shown in FIG. 15A, the drive waveform applied to the drive element 42 includes a process of lowering the voltage to expand the pressure chamber 46 (first voltage transition process) and a process of holding the lowered voltage (first process). 1 voltage holding process), a process of raising the voltage dropped in the first voltage transition process and returning it to the initial voltage (second voltage transition process), a process of holding the dropped voltage (second voltage holding process), and again The process of lowering the voltage to expand the pressure chamber 46 (third voltage transition process), the process of holding the dropped voltage (third voltage holding process), and the voltage dropped by the third voltage transition process to increase the initial And a process for returning the voltage (fourth voltage transition process).

  That is, the process of expanding the pressure chamber 46 and drawing a droplet from the nozzle 40 is provided twice.

  In the third embodiment, as shown in FIG. 15B, the head controller 90 applies the determined drive waveform to the drive element 42, so that the first positive direction variation process and the second positive direction are performed. The variation process interval (K shown in the figure) is set to 0.45 to 0.95 times the natural vibration period (Tc) of the ejector 34, and further, the ink flow rate and the second positive flow rate in the first positive direction variation process. The flow rate ratio (L2 / L1 shown in the figure) of the flow rate of ink in the direction changing step is set to 0.1 to 0.7.

  Here, the inventor of the present application defines an interval (T1 shown in FIG. 15A) at the start of the first voltage transition process and the second voltage transition process of the drive waveform applied to the drive element 42, Interval between the start of the second voltage transition process and the start of the third voltage transition process (T2 shown in FIG. 15A), the interval between the start of the third voltage transition process and the start of the fourth voltage transition process ( The ink droplets ejected from the nozzle 40 were actually evaluated by shaking T3) shown in FIG.

  Specifically, the ink droplets ejected from the nozzle 40 are ejected from the nozzle 40 in a columnar shape. The columnar ink droplet includes a relatively large main droplet located at the front end portion and a satellite droplet formed along with the main droplet and located at the rear end portion. It was evaluated whether or not the main droplet and the satellite droplet were combined, and whether or not an unnecessary droplet was ejected from the nozzle 40 after ejecting the ink droplet (main droplet and satellite droplet).

  In the evaluation method, the shape of the ink droplets ejected from the nozzle 40 is confirmed from the side at every hour, and the satellite droplets catch up with the main droplet at positions 500 μm and 700 μm away from the nozzle surface and merge (integrate). We evaluated whether or not to fly. Furthermore, it was evaluated whether or not unnecessary ink droplets (unnecessary droplets) were ejected from the nozzle 40 after ejecting ink droplets (main droplets and satellite droplets).

  In general, in the case of an image forming apparatus, the sheet member P as a recording medium is generally located at a position 1 mm to 1.5 mm away from the nozzle 40. The purpose of this evaluation is to confirm whether or not the main droplet and the satellite droplet merge before reaching the sheet member P. As an example, the evaluation was performed at positions 500 μm and 700 μm away from the nozzle surface. It is sufficient that the main droplet and the satellite droplet are united and the unnecessary droplet is not discharged from the nozzle 40 until reaching the sheet member P, and is not limited to 500 μm and 700 μm.

  As shown in FIG. 16, by changing the above-described T1, T2, and T3, the interval (K) between the first positive direction changing step and the second positive direction changing step, and the ink in the first positive direction changing step. The union of main droplets and satellite droplets and the ejection of unnecessary droplets were evaluated by shaking the flow velocity and the flow velocity ratio (L2 / L1) of the ink flow velocity in the second positive direction fluctuation step.

  In the third embodiment, T1 is in the range of 0.25 Tc to 0.8 Tc, T2 is in the range of 0.2 Tc to 0.75 Tc, and T3 is in the range of 0.1 Tc to 0.2 Tc. Evaluation was carried out by changing.

  The horizontal axis in FIG. 16 indicates the interval (K) between the first positive direction variation process and the second positive direction variation process, and the vertical axis in FIG. 16 indicates the ink flow rate and the second positive direction variation in the first positive direction variation process. The flow rate ratio (L2 / L1) of the ink flow rate in the process is shown.

  In addition, “x” is evaluated at a position 700 μm away from the nozzle surface, and indicates that the main droplet and the satellite droplet are not merged or unnecessary droplets are ejected. ○ indicates evaluation at a position 700 μm away from the nozzle surface, and indicates that the main droplet and the satellite droplet are combined, and further no unnecessary droplet was discharged (satellite free discharge). ◎ is evaluated at a position 500 μm away from the nozzle surface, and indicates that the main droplet and the satellite droplet merged, and further no unnecessary droplet was discharged (satellite free discharge).

  As shown in FIG. 17, the interval (K) between the first positive direction fluctuation process and the second positive direction fluctuation process is 0.45 to 0.95 times the natural vibration period of the ejector, and the first positive direction fluctuation In the range (range D shown in FIG. 17) in which the flow rate ratio (L2 / L1) between the ink flow rate in the process and the ink flow rate in the second positive direction changing step is 0.1 to 0.7, the evaluation is good. It can be seen that unintentional discharge such as satellites and mist can be suppressed.

  Further, the interval (K) between the first positive direction changing step and the second positive direction changing step is 0.6 to 0.9 times the natural vibration period of the ejector, and the ink flow rate in the first positive direction changing step is In the range where the flow rate ratio (L2 / L1) of the ink flow rate in the second positive direction variation step is 0.1 to 0.6 (range Q shown in FIG. 17), the evaluation is not x, It can be seen that unintentional discharge such as satellites and mist can be effectively suppressed.

  Further, the interval (K) between the first positive direction changing step and the second positive direction changing step is 0.7 times to 0.9 times the natural vibration period of the ejector, and the ink flow rate in the first positive direction changing step. In the range where the flow rate ratio (L2 / L1) of the ink flow rate in the second positive direction variation step is in the range of 0.15 to 0.55 (range R shown in FIG. 17), all the evaluations are ◎, and the satellite and mist It can be seen that unintentional discharge can be reliably suppressed.

(A) and (B) are diagrams showing a driving waveform applied to a droplet discharge head employed in the image forming apparatus according to the first embodiment of the present invention and an ink flow velocity in the vicinity of the nozzle. (A) (B) (C) (D) (E) (F) Meniscus until ink droplets are ejected from the nozzles of the droplet ejection head employed in the image forming apparatus according to the first embodiment of the present invention. It is sectional drawing which showed the change of the shape. 6 is a drawing showing evaluation results when evaluating a droplet discharge head employed in the image forming apparatus according to the first embodiment of the present invention and a droplet discharge head as a comparative example; (A), (B), and (C) a driving waveform and a vicinity of the nozzle when the droplet discharge head employed in the image forming apparatus according to the first embodiment of the present invention and the droplet discharge head as a comparative example are evaluated. It is drawing which showed the ink flow velocity. (A), (B), and (C) a driving waveform and a vicinity of the nozzle when the droplet discharge head employed in the image forming apparatus according to the first embodiment of the present invention and the droplet discharge head as a comparative example are evaluated. It is drawing which showed the ink flow velocity. (A), (B), and (C) a driving waveform and a vicinity of the nozzle when the droplet discharge head employed in the image forming apparatus according to the first embodiment of the present invention and the droplet discharge head as a comparative example are evaluated. It is drawing which showed the ink flow velocity. 1 is a cross-sectional view of a liquid droplet ejection head employed in an image forming apparatus according to a first embodiment of the present invention. 1 is a plan view of a droplet discharge head employed in an image forming apparatus according to a first embodiment of the present invention. 1 is a schematic diagram illustrating an image forming apparatus according to a first embodiment of the present invention. (A) (B) It is drawing which showed the drive waveform applied to the droplet discharge head employ | adopted as the image forming apparatus which concerns on 2nd Embodiment of this invention, and the ink flow velocity near a nozzle. 6 is a drawing showing evaluation results when evaluating a droplet discharge head employed in an image forming apparatus according to a second embodiment of the present invention and a droplet discharge head as a comparative example. (A), (B), and (C) a drive waveform and a vicinity of the nozzle when the droplet discharge head employed in the image forming apparatus according to the second embodiment of the present invention and the droplet discharge head as a comparative example are evaluated. It is drawing which showed the ink flow velocity. (A), (B), and (C) a drive waveform and a vicinity of the nozzle when the droplet discharge head employed in the image forming apparatus according to the second embodiment of the present invention and the droplet discharge head as a comparative example are evaluated. It is drawing which showed the ink flow velocity. (A), (B), and (C) a drive waveform and a vicinity of the nozzle when the droplet discharge head employed in the image forming apparatus according to the second embodiment of the present invention and the droplet discharge head as a comparative example are evaluated. It is drawing which showed the ink flow velocity. (A) (B) It is drawing which showed the drive waveform applied to the droplet discharge head employ | adopted as the image forming apparatus which concerns on 3rd Embodiment of this invention, and the ink flow velocity near a nozzle. It is drawing which showed the evaluation result when evaluating the droplet discharge head employ | adopted as the image forming apparatus which concerns on 3rd Embodiment of this invention, and the droplet discharge head as a comparative example. It is drawing which showed the evaluation result when evaluating the droplet discharge head employ | adopted as the image forming apparatus which concerns on 3rd Embodiment of this invention, and the droplet discharge head as a comparative example.

Explanation of symbols

10 Printer (image forming device)
11 Transport roll (transport means)
12 Conveying belt (conveying means)
32 Meniscus 34 Ejector 36 Recording head (droplet ejection head)
40 Nozzle 42 Drive element 46 Pressure chamber 64 Nozzle communication path (communication path)
90 Recording head controller (control unit)

Claims (3)

An ejector comprising: a nozzle that discharges droplets; a pressure chamber that communicates with the nozzle via a communication path; and a drive element that applies pressure to the liquid in the pressure chamber;
A control unit for applying a drive waveform to the drive element based on image information;
With
A first negative direction fluctuation step of drawing a meniscus from the nozzle to the pressure chamber side, and pushing out the meniscus drawn in the first negative direction fluctuation step to the side opposite to the pressure chamber side, and the tip of the liquid column is A first positive direction changing step of discharging from the nozzle, a second negative direction changing step of drawing the rear end portion of the liquid column discharged from the nozzle in the first positive direction changing step to the pressure chamber side, and the second In order to execute a step including a second positive direction changing step of pushing out a rear end portion of the drawn liquid column to a side opposite to the pressure chamber side by a negative direction changing step, the control unit performs the driving The drive waveform applied to the element is
A first voltage change process for expanding the pressure chamber by dropping a voltage;
A first voltage maintaining process for maintaining a voltage dropped in the first voltage change process;
A second voltage change process in which the voltage maintained in the first voltage maintenance process is increased to contract the pressure chamber;
A second voltage maintaining process for maintaining the increased voltage in the second voltage changing process;
A third voltage changing process for further increasing the voltage maintained in the second voltage maintaining process to contract the pressure chamber;
Have
The interval between the start of the second voltage change process and the start of the third voltage change process is 0.6 to 0.8 times the natural vibration period of the ejector.
Droplet discharge head. An ejector comprising: a nozzle that discharges droplets; a pressure chamber that communicates with the nozzle via a communication path; and a drive element that applies pressure to the liquid in the pressure chamber;
A control unit for applying a drive waveform to the drive element based on image information;
With
A first negative direction fluctuation step of drawing a meniscus from the nozzle to the pressure chamber side, and pushing out the meniscus drawn in the first negative direction fluctuation step to the side opposite to the pressure chamber side, and the tip of the liquid column is A first positive direction changing step of discharging from the nozzle, a second negative direction changing step of drawing the rear end portion of the liquid column discharged from the nozzle in the first positive direction changing step to the pressure chamber side, and the second In order to execute a step including a second positive direction changing step of pushing out a rear end portion of the drawn liquid column to a side opposite to the pressure chamber side by a negative direction changing step, the control unit performs the driving The drive waveform applied to the element is
A first voltage change process for expanding the pressure chamber by lowering the voltage;
A first voltage maintaining process for maintaining a voltage dropped in the first voltage change process;
A second voltage change process for further expanding the pressure chamber by further lowering the voltage maintained in the first voltage maintenance process;
A second voltage maintaining process for maintaining the voltage dropped in the second voltage change process;
A third voltage changing process for increasing the voltage maintained in the second voltage maintaining process to contract the pressure chamber;
A fourth voltage change process for raising the voltage raised in the third voltage change process and returning it to the voltage at the start of the first voltage change process;
Have
The interval between the start of the first voltage change process and the start of the second voltage change process is 0.9 to 1.1 times the natural vibration period of the ejector.
Droplet discharge head. Conveying means for conveying the recording medium;
The droplet discharge head according to claim 1 or 2, wherein droplets are discharged onto a recording medium conveyed by the conveyance unit;
An image forming apparatus comprising:

Images