JP4288973B2 - Droplet ejection apparatus and droplet ejection method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a droplet discharge apparatus and a droplet discharge method. More specifically, the present invention discharges droplets to record characters or images on a recording medium, and forms a fine pattern or a thin film on a substrate. The present invention relates to a droplet discharge device and a droplet discharge method.
[0002]
[Prior art]
In general, in a droplet discharge device such as an ink jet recording device, there is a limit to the uniformity of droplet discharge and the accuracy of the head drive mechanism and the paper transport mechanism, and there is variation in the dot landing state on the recording paper surface. It will occur. As shown in FIG. 9, when an image is formed by ejecting ink droplets from the nozzles N1 to Nn while moving the inkjet head 102 in the main scanning direction, a deviation occurs in the landing position of the ink ejected from the nozzle N2. In this case, there is an inconvenience that streaky unevenness 104, 106 called banding is formed by the landing row L0 formed by the nozzle N2.
[0003]
Therefore, in order to reduce this banding, Patent Document 1 discloses a technique for reducing the banding by shaking the head to give fluctuation to the ink landing position.
[0004]
However, in the technique described in Patent Document 1, the head must be physically moved, and there is a problem of cost increase due to the addition of a drive mechanism and a control mechanism.
[0005]
[Patent Document 1]
JP-A-11-227183 [0006]
[Problems to be solved by the invention]
An object of the present invention is to provide a droplet discharge device and a droplet discharge method that can reduce banding by a simple method in consideration of the above facts.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, a droplet discharge device according to the present invention includes a droplet discharge unit capable of discharging a droplet toward a recording medium, and the droplets used for expressing the same gradation value. A plurality of drive signal generation circuits that generate drive signals having different waveforms, which have different landing states on the recording medium, and the plurality of drive signal generation circuits corresponding to image data having the same gradation value. A drive signal selection circuit that selects a different drive signal from the plurality of drive signals, and each of the drive signals output from the plurality of drive signal generation circuits has a different droplet velocity. At least one of the following: one that makes the discharge timing of the droplets different, one that divides the droplets into two, and one that makes the discharge direction of the droplets unstable. By the drive signal selection circuit It is characterized in that the driven receiving-option drive signal to eject droplets toward a recording medium.
[0008]
The droplet discharge method of the present invention is a droplet discharge method for discharging a droplet from a droplet discharge means toward a recording medium based on a drive signal, and is used for expressing the same gradation value. Drive signals having different waveforms, each of which has a different landing state on the recording medium, and each of the plurality of drive signals has different droplet speeds of the droplets, It is at least one of those that make the discharge timing different, those that divide the droplet into two, and those that make the discharge direction of the droplet unstable,
Corresponding to image data of the same gradation value, a different drive signal is selected from a plurality of generated drive signals, and droplets are ejected toward a recording medium based on the selected drive signal It is.
[0009]
In the droplet discharge device and the droplet discharge method, a plurality of drive signals having different waveforms are generated. Each drive signal varies the landing state of the droplets used for expressing the same gradation value when the droplets land on the recording medium.
[0010]
The gradation value here corresponds to the light and shade gradation expressed in one pixel. For example, when ink droplets of three sizes of large size, medium size, and small size are ejected from the inkjet head, droplets classified into the same size have the same gradation value. Normally, droplets expressing the same gradation value have substantially the same droplet amount, but it is not always necessary to have the same droplet amount for all droplets, and the average value is within a predetermined range. There is no problem with the density and color on the paper. The landing state refers to an apparent state when a droplet has landed on a recording medium. For example, if the position and shape of the droplet are different, the landing state is different.
[0011]
Usually, the same drive signal is used for image data having the same gradation value. Therefore, the landing state of the droplets ejected from the droplet ejecting means is also the same and the same deviation occurs, so that the banding becomes conspicuous as shown in FIG.
[0012]
Therefore, in the present invention, a plurality of drive signals having different waveforms as described above are generated as drive signals corresponding to droplets having the same gradation value, and the plurality of drive signals corresponding to image data having the same gradation value are generated. Different drive signals are selected from the drive signals. Therefore, even droplets having the same gradation value are landed on the recording medium in different states, so that banding caused by the same shift can be reduced.
[0013]
In the droplet discharge device of the present invention, each of the drive signals output from the plurality of drive signal generation circuits varies the droplet droplet velocity, the droplet ejection timing varies, It is at least one of the one that divides the droplet into two and the one that makes the discharge direction of the droplet unstable .
[0014]
Also, in the droplet discharge method of the present invention, each of the plurality of drive signals is one in which the droplet speed of the droplet is different, one in which the droplet discharge timing is different, and one in which the droplet is divided into two and those that destabilize the discharge direction of the droplets, characterized by at least 1 Tsudea Rukoto of.
[0015]
In this way, each of the drive signals varies at least one of the droplet velocity, the ejection timing of the previous droplet, the droplet amount, and the shape of the droplet. The landing state of the droplets ejected from the ejection means can be varied.
[0016]
According to a third aspect of the present invention, in the droplet discharge device, the drive signal selection circuit selects a different drive signal from the plurality of drive signals at a predetermined period. The droplet discharge method of the present invention can also be characterized in that, as described in claim 7, different drive signals are selected from the plurality of drive signals at a predetermined cycle.
[0017]
In this way, different landing states can be generated at a predetermined cycle, and banding can be reduced.
[0018]
The droplet discharge device of the present invention may be characterized in that, as described in claim 4, the drive signal selection circuit randomly selects a different drive signal from the plurality of drive signals. The droplet discharge method according to the present invention may be characterized in that a different drive signal is selected from the plurality of drive signals at a predetermined period.
[0019]
By doing so, different landing states can be generated at random, and banding can be reduced.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following, specific numerical values may be given for convenience of explanation, but the present invention is not limited to this.
[0021]
FIG. 1 shows a droplet discharge section 20A of a droplet discharge head 20 according to the first embodiment of the present invention. FIG. 2 shows a droplet discharge apparatus including the droplet discharge head 20. 10 is shown. The droplet discharge head 20 of the present embodiment is a so-called inkjet recording head, and the droplet discharge device 10 provided with the droplet discharge head 20 is an inkjet recording device. The droplet discharge device 10 discharges droplets (ink droplets) of colored ink from the nozzles 24 of the droplet discharge head 20 (see FIG. 1) onto a recording sheet P that is a recording medium. Used to record images.
[0022]
As shown in FIG. 2, the droplet discharge device 10 includes a carriage 14 on which the droplet discharge head 20 is mounted, and moves the carriage 14 in a predetermined main scanning direction along the recording surface of the recording paper P (main scanning). ) And a sub-scanning mechanism 18 for transporting (sub-scanning) the recording paper P in a predetermined sub-scanning direction that intersects (preferably orthogonally) the main scanning direction. In the drawings, the main scanning direction is indicated by an arrow M, and the sub-scanning direction is indicated by an arrow S.
[0023]
The droplet discharge head 20 is mounted on the carriage 14 such that the nozzle surface 24S (see FIG. 1) on which the nozzles 24 are formed faces the recording paper P, and is moved in the main scanning direction by the main scanning mechanism 16. On the other hand, by discharging droplets onto the recording paper P, an image is recorded on a certain band area BE. When one movement in the main scanning direction is completed, the recording paper P is conveyed in the sub scanning direction by the sub scanning mechanism 18, and the next band area is recorded while moving the carriage 14 in the main scanning direction again. By repeating such an operation a plurality of times, image recording can be performed over the entire surface of the recording paper P.
[0024]
As can be seen from FIG. 1, the nozzle plate 30 is formed by aligning and stacking a total of five plates: a nozzle hole plate 32, a common flow path plate 34, a supply path plate 36, a pressure generation chamber plate 38, and a vibration plate 40. And it is formed by joining by joining means, such as an adhesive agent. In the nozzle plate 24, a common flow path 42, an ink supply path 44, a pressure generation chamber 46, an ink discharge path 48, a communication path 50, and an ink discharge port 51 are configured by these plates. A piezoelectric actuator 52 is provided for each of the pressure generation chambers 46. A drive voltage corresponding to image information is applied to the piezoelectric actuator 52 in a state where ink supplied from an ink supply hole (not shown) is stored in the pressure generation chamber 46 via the common flow path 142 and the ink supply path 44. Then, the diaphragm 40 of the piezoelectric actuator 52 is bent and deformed, and the pressure generating chamber 46 is expanded or compressed. Accordingly, when a volume change occurs in the pressure generation chamber 46, a pressure wave is generated in the pressure generation chamber 46. By the action of the pressure wave, the ink in the nozzle 24 (the ink discharge path 48, the communication path 50, and the ink discharge port 51) moves, and a liquid droplet (ink droplet) is formed by being discharged from the ink discharge port 51 to the outside. The
[0025]
FIG. 3 shows a schematic block diagram of the control system of the present embodiment. The droplet discharge device 10 includes a control unit 60 that performs system control of the droplet discharge device 10. The control unit 60 includes an interface 62, a CPU 64, a ROM 66, and a RAM 68, which are connected to each other via a bus B. The interface 62 exchanges various signals with an external device such as a personal computer. The CPU 64 can execute a predetermined process. The ROM 66 stores various programs for operating the inkjet recording apparatus 10 and various data.
[0026]
Further, as shown in FIG. 3, the control unit 60 includes an image data transmission circuit 70 and five drive signal generation circuits 72A, 72B, 72C, 72D, 72E, which are also connected to the bus B. The image data transmission circuit 70 transmits the image data on which the predetermined process has been performed to an image data reception circuit 80 described later in the droplet discharge head 20.
[0027]
An image data receiving circuit 80 is provided in the droplet discharge head 20, and a piezoelectric actuator 52 is provided for each nozzle 24 (hereinafter, as a code for identifying the N nozzles 24 in the sub-scanning direction). Nozzles 24-1, 24-2,..., 24n are used in order from the upstream side). A drive signal selection circuit 82 is provided corresponding to the piezoelectric actuator 52. The image data receiving circuit 80 receives image data from the image data transmitting circuit 70. Each drive signal selection circuit 82 is supplied with image data from the image data receiving circuit 80 and five drive signals 74A, 74B, 74C, 74D, and 74E. The drive signal selection circuit 82 selects any one of the five drive signals 74 </ b> A to 74 </ b> E and transmits the voltage of the selected drive signal to the piezoelectric actuator 52. As a method of selecting one drive signal from the five drive signals 74A to 74E, the drive signal may be sequentially selected at a constant cycle or may be selected randomly. In this embodiment, drive signal 74A → drive signal 74B → drive signal 74A → drive signal 74C → drive signal 74A → drive signal 74D → drive signal 74A → drive signal 74E are sequentially selected as one cycle. It is preferable that the adjacent nozzles 24 are set so that the phases of the cycles are different from each other.
[0028]
As shown in FIGS. 4 to 7, the drive signal generation circuits 72A, 72B, 72C, 72D, and 72E are different from each other in the drive signal 74A, the drive signal 74B (see FIG. 4), the drive signal 74C (see FIG. 5), and the drive. A signal 74D (see FIG. 6) and a drive signal 74E (see FIG. 7) are generated. The voltage waveforms of these drive signals 74A, 74B, 74C, 74D, and 74E are a voltage drop process 76A for once dropping the voltage from a predetermined bias voltage 76G, and a low voltage maintenance for maintaining the lowered voltage (low voltage). A process 76B, a voltage raising process 76C for raising the voltage from the low voltage, a high voltage maintaining process 76D for maintaining the raised voltage (high voltage), and a voltage restoration process 76E for returning the high voltage to the bias voltage are configured. Yes. When any one of the drive signals 74A, 74B, 74C, 74D, and 74E is applied to the piezoelectric actuator 52, in the voltage drop process 76A and the low voltage maintenance process 76B, the vibration is generated so that the volume of the pressure generating chamber 46 is once increased. The plate 40 is deformed. In the voltage increasing process 76C and the high voltage maintaining process 76D, the diaphragm 40 is deformed so that the volume of the pressure generating chamber 46 is reduced. As a result, an acoustic wave is generated in the pressure generation chamber 46 and a droplet is ejected from the nozzle 24. In FIGS. 4 to 7, the bias voltage 76G is changed for each drive signal in order to clarify the difference in the waveforms of the drive signals 74A to 74E. The voltage is constant.
[0029]
Here, as can be seen from FIG. 4 to FIG. 7, in this embodiment, the waveform of the voltage is different for each of the five drive signals. Due to the difference in waveform, the landing state of the ejected droplets on the recording paper P changes. Here, on the basis of the drive signal 74A, each drive signal and the characteristics of the droplets ejected when the drive signal is applied will be described. Hereinafter, droplets ejected by applying the drive signals 74A, 74B, 74C, 74D, and 74E are referred to as droplets 78A, 78B, 78C, 78D, and 78E, respectively.
[0030]
As shown in FIG. 4, in the drive signal 74B, the slope (voltage increase rate) in the voltage increase process 76C is set to be larger than that of the drive signal 74A. In general, the steeper the slope in the voltage increasing process 76C, the faster the droplet velocity of the ejected droplets. Accordingly, the droplet speed of the droplet 78B ejected by applying the drive signal 74B is higher than that of the droplet 78A ejected by applying the drive signal 74A. Accordingly, the droplet 78B is landed at a position different from the landing position of the droplet 78A.
[0031]
As shown in FIG. 5, in the drive signal 74C, the length (time) of the high voltage maintaining process 76D is set to be longer than that of the drive signal 74A. In general, the longer the high voltage maintenance process 76D, the greater the amount of droplets ejected. Therefore, the droplet amount of the droplet 78C ejected by applying the drive signal 74C is larger than that of the droplet 78A ejected by applying the drive signal 74A. Accordingly, the droplet 78C constitutes a landing area larger than the landing area of the droplet 78A.
[0032]
As shown in FIG. 6, in the drive signal 74D, the voltage is dropped to a level lower than that of the drive signal 74A in the voltage drop process 76A, thereby increasing the potential difference in the voltage rise process 76C. In general, when the potential difference in the voltage increasing process 76C increases, the droplet is divided into two as shown in FIG. Accordingly, the droplet 78D ejected by the application of the drive signal 74D has a different shape from the droplet 78A ejected by the application of the drive signal 74A, and has a different landing shape.
[0033]
As shown in FIG. 7, in the drive signal 74E, the bias voltage 76G is in an unstable state. In general, when the bias voltage 76G is in an unstable state, the direction of the ejected liquid droplet is also unstable, and the ink is not ejected in a certain direction. Therefore, the droplet 78E ejected by the application of the drive signal 74E has a different landing position from the droplet 78A ejected by the application of the drive signal 74A.
[0034]
The sizes of the droplets 78A to 78E ejected by the drive signals 74A to 74E are used corresponding to the same gradation value, for example, the gradation value expressed by a small size droplet. is there. However, the droplet amounts of the droplets 78A to 78E do not have to be the same, and may be a droplet amount within a certain range.
[0035]
Next, the operation of this embodiment will be described.
[0036]
The image data that has been subjected to the predetermined processing by the CPU 24 is output to the image data transmission circuit 70, and further output to the image data reception circuit 80. Then, the image data receiving circuit 80 allocates image data corresponding to each nozzle 24, and transmits the allocated image data to the corresponding drive signal selection circuit 82. In the drive signal selection circuit 82, the drive signals 74A to 74E are sequentially selected in the above-described order, and the selected drive signal is applied to the predetermined timing piezoelectric actuator 52 based on the image data transmitted from the image data receiving circuit 80. To do. As a result, any one of the droplets 78A to 78E is ejected, and an image is formed on the recording paper P.
[0037]
Here, an image formed in this embodiment will be described by taking an image formed by ejecting droplets of the same gradation for all pixels as an example. FIG. 8A shows an image formed by only the droplet 78A ejected by applying the drive signal 74A. In this case, the liquid droplets ejected from the nozzles 24-1, 24-3, 24-4, and 24-n are landed at predetermined pixel positions without deviation, but the liquid droplets ejected from the nozzle 24-2. Are landed with the same amount of deviation on the image side formed by the nozzle 24-1. For this reason, the density of the line L1 indicated by the alternate long and short dash line in the drawing becomes high, and the density of the line L2 becomes low, and banding is clearly confirmed.
[0038]
On the other hand, FIG. 8B shows an image formed by droplets ejected by applying the selected drive signal by selecting the drive signals 74A to 74E in the above order by the drive signal selection circuit 82. FIG. The liquid droplets ejected from the nozzle 24-2 are landed with the same amount of deviation on the image side formed by the nozzle 24-1, but since the liquid droplets 78A to 78E are mixed, The landing state is different. As a result, in FIG. 8B, compared to the lines L1 and L2 in FIG. 8A, the horizontal stripes are less visible and banding is reduced.
[0039]
In this embodiment, the example in which the drive signals 74A to 74B having five different waveforms are selected in a predetermined cycle has been described. However, one drive signal may be selected at random based on a random number table. Further, the drive signals having different waveforms are not necessarily five types, and may be two, three, four, or six or more types. As another effective method of changing the landing position of the droplet, a method of shifting the timing of discharging the droplet can be considered. Even if a plurality of drive signals with different waveforms that change only the droplet velocity of the discharged droplets are provided, or a plurality of drive signals with different waveforms that change only the droplet amount of the discharged droplets are provided, they are discharged. A plurality of drive signals having different waveforms that change only the timing of the droplets to be generated may be provided.
[0040]
Further, the waveform for changing the drop amount is not limited to the present embodiment. For example, the drive signal 74C that slightly changes the drop amount increases the drop amount by extending the high voltage process 76D as shown in FIG. 5 compared to the other drive signals, but the voltage of the high voltage process 76D is increased. The droplet amount can be increased by making the value of itself higher than the other drive signals (increase the potential difference from the bias voltage 76G).
[0041]
As mentioned above, although embodiment of this invention was described, these embodiment showed embodiment suitable for this invention, and this invention is not limited to these. That is, various modifications, improvements, corrections, simplifications, and the like may be added to the above-described embodiment without departing from the gist of the present invention.
[0042]
In the above embodiment, the liquid droplet ejection head and the liquid droplet ejection apparatus according to the present invention have been described using a piezoelectric actuator as the pressure generating unit. In addition to this, electromechanical conversion using electrostatic force or magnetic force is used. Other pressure generating means such as an element or an electrothermal conversion element for generating pressure by utilizing a boiling phenomenon may be used. Also, as the piezoelectric actuator, in addition to the single plate type piezoelectric actuator used in the present embodiment, another type of actuator such as a longitudinal vibration type stacked piezoelectric actuator may be used.
[0043]
Further, in the above description, the flow path is formed by stacking a plurality of plates as the nozzle plate 24, but the configuration and material of the plate are not limited to the above embodiment. For example, the flow path may be integrally formed using a material such as ceramics, glass, resin, or silicon.
[0044]
In the above embodiment, an inkjet recording head and an inkjet recording apparatus that record characters, images, and the like by discharging colored ink droplets (ink droplets) onto the recording paper P have been described as examples. The droplet discharge head and the droplet discharge device are not limited to those used for such ink jet recording, that is, for recording characters and images on recording paper. Further, the recording medium is not limited to paper, and the liquid to be ejected is not limited to colored ink. The “recording medium” only needs to be a target for ejecting droplets by the droplet ejection head. Similarly, an “image” or “recording image” can be obtained by attaching droplets to the recording medium. Any dot pattern on the resulting recording medium is included. Accordingly, the “recording medium” includes recording sheets, OHP sheets, and the like, but also includes, for example, a substrate and a glass plate. The “image” or “recorded image” includes not only general images (characters, pictures, photographs, etc.) but also wiring patterns on the substrate, three-dimensional objects, organic thin films, and the like. For example, production of a color filter for display performed by discharging colored ink on a polymer film or glass, formation of bumps for component mounting performed by discharging molten solder onto the substrate, and organic EL solution on the substrate For general liquid droplet ejecting devices intended for various industrial applications, such as the formation of EL display panels that are ejected onto the substrate and the formation of bumps for electrical mounting that are performed by ejecting molten solder onto the substrate. It is also possible to apply the droplet discharge head and the droplet discharge device of the invention.
[0045]
In the above description, the droplet discharge device is configured to perform droplet discharge while moving the droplet discharge head by the carriage. However, a line type droplet discharge head in which the ink discharge ports 51 are arranged over the entire width of the recording medium is used. It is also possible to apply the present invention to other apparatus forms such as using this line type head and performing recording while conveying only the recording medium (in this case, only main scanning).
[0046]
【The invention's effect】
Since the present invention has the above-described configuration, even droplets of the same size ejected by the same droplet ejecting means are landed on the recording medium in different states, so that banding caused by the same misalignment can be reduced. Can do.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view partially showing a droplet discharge head of an embodiment.
FIG. 2 is a perspective view showing a droplet discharge device of the present embodiment.
FIG. 3 is a block diagram illustrating an internal configuration of a control unit and a droplet discharge head of the droplet discharge device according to the present embodiment.
FIG. 4 is a diagram showing a waveform of a basic drive signal used in the present embodiment and a waveform of a drive signal corresponding to a droplet corresponding to the basic drive signal and a droplet having a different droplet velocity.
FIG. 5 is a diagram illustrating a waveform of a basic drive signal used in the present embodiment and a waveform of a drive signal corresponding to a droplet corresponding to the basic drive signal and a droplet having a different droplet amount.
FIG. 6 is a diagram showing a waveform of a basic drive signal used in the present embodiment and a waveform of a drive signal for discharging a droplet divided into two.
FIG. 7 is a diagram illustrating a waveform of a basic drive signal used in the present embodiment and a waveform of a drive signal corresponding to a droplet corresponding to the basic drive signal and a droplet having a different ejection direction.
8A is a diagram illustrating an image formed using only one type of drive signal, and FIG. 8B is a diagram illustrating an image formed using five types of drive signals. It is.
FIG. 9 is a diagram showing banding formed in a conventional droplet discharge device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Droplet discharge device 20 Droplet discharge head (Droplet discharge means)
24 nozzle (droplet discharge means)
72A Drive signal generation circuit 72B Drive signal generation circuit 72C Drive signal generation circuit 72D Drive signal generation circuit 72E Drive signal generation circuit 74A Drive signal 74B Drive signal 74C Drive signal 74D Drive signal 74E Drive signal 82 Drive signal P Drive sheet P Recording paper (recording medium)

Claims (6)

Droplet discharge means capable of discharging droplets toward a recording medium;
A plurality of drive signal generation circuits for generating drive signals of different waveforms, which vary the landing state of the droplets used to express the same gradation value on the recording medium;
A drive signal selection circuit that selects different drive signals from a plurality of drive signals generated by the plurality of drive signal generation circuits in correspondence with image data of the same gradation value;
Have
Each of the drive signals output from the plurality of drive signal generation circuits has a different droplet speed, a different droplet discharge timing, a two-divided droplet, and At least one of making the discharge direction of the droplet unstable,
The droplet discharge device, wherein the droplet discharge unit is driven in response to a drive signal selected by the drive signal selection circuit and discharges droplets toward a recording medium.   The liquid droplet ejection apparatus according to claim 1, wherein the drive signal selection circuit selects different drive signals from the plurality of drive signals at a predetermined period.   3. The droplet discharge apparatus according to claim 1, wherein the drive signal selection circuit randomly selects a different drive signal from the plurality of drive signals. 4. A droplet discharge method for discharging a droplet from a droplet discharge means toward a recording medium based on a drive signal,
Generating drive signals having different waveforms, differently landing states of the droplets used to express the same gradation value on the recording medium,
Each of the plurality of driving signals has a different droplet velocity, a different droplet discharge timing, a two-divided droplet, and an unstable droplet discharge direction. At least one of
Corresponding to the image data of the same gradation value, a different drive signal is selected from a plurality of generated drive signals,
A droplet discharge method for discharging droplets toward a recording medium based on a selected drive signal.   5. The droplet discharge method according to claim 4, wherein different drive signals are selected from the plurality of drive signals at a predetermined cycle.   6. The droplet discharge method according to claim 4, wherein different drive signals are randomly selected from the plurality of drive signals.

Images