Droplet ejection head
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2026-01-27
- Publication Date
- 2026-08-13
Smart Images
Figure JP2026002604_13082026_PF_FP_ABST
Abstract
Description
Droplet ejection head
[0001] The present disclosure relates to a droplet ejection head including a flow path member having a plurality of individual flow paths and a common flow path.
[0002] As an example of a droplet ejection head, Patent Document 1 discloses an inkjet recording head including a flow path unit. In Patent Document 1, the flow path unit is provided with an ink flow path from a common ink chamber to a nozzle opening through an ink supply port and a pressure generating unit. Further, Patent Document 1 describes that ink droplets can be ejected at a high frequency by setting the inertance of the nozzle opening and the ink supply port to be larger than the inertance of the pressure generating unit.
[0003] International Publication No. 2003 / 084758
[0004] According to the technology of Patent Document 1, high-speed recording can be realized by ejecting ink droplets at a high frequency. However, in a droplet ejection head, in addition to high-speed recording, low-speed recording may be required depending on the process performed after recording. In low-speed recording, droplets are ejected at a frequency lower than the frequency during high-speed recording.
[0005] The inventor of the present application has found that the volume of droplets ejected changes according to the driving frequency, and further, the rate of change of the droplet volume with respect to the driving frequency differs depending on the configuration of the individual flow paths. When the above rate of change is large, the recording speed, that is, the driving frequency, can cause a large change in the density of the image recorded by the droplets, and the image quality may deteriorate.
[0006] An object of the present disclosure is to provide a droplet ejection head capable of suppressing a change in image density accompanying a change in recording speed.
[0007] The droplet dispensing head according to this disclosure comprises a flow channel member having a plurality of individual flow channels and a common flow channel communicating with the plurality of individual flow channels, wherein the flow channel member comprises a plurality of plates stacked on top of each other, and includes a plurality of plates having holes that constitute the plurality of individual flow channels and the common flow channel, and each of the plurality of individual flow channels includes a nozzle, a pressure chamber communicating with the nozzle, and a communication flow channel that connects the pressure chamber and the common flow channel, and is characterized in that its natural frequency is 130 kHz or higher, and the ratio of the inertance of the communication flow channel to the inertance of the entire individual flow channel is 59% or higher.
[0008] According to this disclosure, each individual channel has a natural frequency of 130 kHz or higher, and the ratio of the inertance of the connecting channel to the total inertance of the individual channels is 59% or higher. As a result, as will be clear from the analysis results described later, it is possible to suppress changes in image density due to changes in recording speed.
[0009] This is a plan view of a printer 100 including a head 1 according to one embodiment of the present disclosure. This is a block diagram showing the electrical configuration of the printer 100. This is a plan view of the head 1. This is an enlarged view of region IV in Figure 3. This is a cross-sectional view of the head 1 along the line V-V in Figure 3. This is a table showing the inertance and natural frequency of each element constituting the individual flow path 12B in analysis models A to E. This is a pie chart showing the ratio of the inertance of each element constituting the individual flow path 12B to the total inertance of the individual flow path 12B in analysis models A to E. This is a graph showing the relationship between the drive frequency and the volume of an ink droplet. This is a graph showing the relationship between the ratio of the inertance of the connecting flow path 12E to the total inertance of the individual flow path 12B and the rate of change of ink droplet volume with respect to the drive frequency.
[0010] The head 1 shown in Figure 1 is one embodiment of the droplet ejection head according to this disclosure. The head 1 is included in the printer 100.
[0011] The printer 100 comprises a housing 100A, a head unit 1X including four heads 1, a platen 3, a transport mechanism 4, and a control unit 5. The head unit 1X, platen 3, transport mechanism 4, and control unit 5 are located inside the housing 100A.
[0012] The length of the head unit 1X in the paper width direction is longer than the length of the head unit 1X in the transport direction. The head unit 1X is fixed to the housing 100A. The type of head unit 1X is a line type.
[0013] The paper width direction is the direction along the width of the paper 9 and is perpendicular to the vertical direction.
[0014] The four heads 1 are arranged in a staggered pattern in the paper width direction. The length of each head 1 in the paper width direction is longer than the length of each head 1 in the transport direction.
[0015] The platen 3 is located below the head unit 1X. The platen 3 is a plate aligned with a plane perpendicular to the vertical direction. The paper 9 is supported on the upper surface of the platen 3.
[0016] The conveying mechanism 4 includes a roller pair 41 having two rollers, a roller pair 42 having two rollers, and a conveying motor 43 as shown in Figure 2. In the conveying direction, the head unit 1X and the platen 3 are positioned between the roller pair 41 and the roller pair 42.
[0017] The transport direction is perpendicular to the vertical direction and the paper width direction.
[0018] When the transport motor 43 is driven by the control unit 5, the rollers of the roller pair 41 and 42 rotate. As the rollers of the roller pair 41 and 42 rotate, the paper 9 held between the rollers of the roller pair 41 and 42 is transported in the transport direction.
[0019] As shown in Figure 2, the control unit 5 includes a CPU 51, a ROM 52, and a RAM 53.
[0020] The CPU 51 executes various controls based on data input from either or both of the input unit and / or external device, according to the programs and data stored in the ROM 52 and RAM 53. The input unit is provided in the printer 100 and is located, for example, on the outside of the casing 100A. The external device is, for example, a personal computer (PC) and is connected to the printer 100 in a communication manner.
[0021] ROM 52 stores programs and data for the CPU 51 to perform various controls. RAM 53 temporarily stores data used by the CPU 51 when executing programs.
[0022] Next, the configuration of head 1 will be explained.
[0023] As shown in Figure 5, the head 1 includes a flow path member 12, an actuator member 13, and a sealing member 15.
[0024] The flow channel member 12 has six metal plates 11A to 11F. The plates 11A to 11F are stacked vertically on top of each other and bonded together. The plates 11A to 11F have holes that constitute a flow channel. The flow channel includes a common flow channel 12A and a plurality of individual flow channels 12B. The holes may include through holes that penetrate the plates 11A to 11F and recesses that do not penetrate the plates 11A to 11F. The holes may be formed by any method, including laser processing, punching, etching, etc.
[0025] As shown in Figure 3, the common channel 12A extends in the paper width direction. A supply port 121 is connected to one end of the common channel 12A in the paper width direction. A return port 122 is connected to the other end of the common channel 12A in the paper width direction. The supply port 121 and the return port 122 open to the upper surface of the channel member 12. The upper surface of the channel member 12 is the upper surface of the uppermost plate 11A among the six plates 11A to 11F. The supply port 121 and the return port 122 communicate with the ink tank via tubes. The common channel 12A communicates with the ink tank via the supply port 121 and the return port 122, and also communicates with a plurality of individual channels 12B.
[0026] As shown in Figure 3, the multiple individual flow paths 12B are arranged in a staggered pattern in the paper width direction. Each of the multiple individual flow paths 12B includes a nozzle 12N, a pressure chamber 12P, a communication flow path 12E, and a connecting flow path 12D.
[0027] The nozzles 12N are arranged in a staggered pattern in the paper width direction, forming two nozzle rows R1 and R2. Nozzle row R1 consists of multiple nozzles 12N aligned in the paper width direction. Nozzle row R2 consists of multiple nozzles 12N aligned in the paper width direction.
[0028] In each nozzle row R1, R2, multiple nozzles 12N are arranged at a pitch of 600 dpi in the paper width direction. The recording resolution in each nozzle row R1, R2 is 600 dpi. The recording resolution is the resolution of the image recorded by the ink droplets ejected from the nozzles 12N. In this embodiment, the volume of the ink droplets is 2 to 5 pl.
[0029] Between nozzle rows R1 and R2, the position of the nozzle 12N in the paper width direction is shifted by half a pitch. As a result, a recording resolution of 1200 dpi is achieved by the two nozzle rows R1 and R2. That is, the head 1 has a recording resolution of 1200 dpi × 1200 dpi in both the paper width direction and the transport direction.
[0030] Alternatively, in four nozzle rows having multiple nozzles 12N arranged at a pitch of 300 dpi in the paper width direction, a recording resolution of 1200 dpi × 1200 dpi may be achieved by shifting the positions of the nozzles 12N between rows in the paper width direction.
[0031] As shown in Figure 4, the pressure chamber 12P is arranged along a plane perpendicular to the vertical direction. The length of the pressure chamber 12P in the transport direction is longer than the length of the pressure chamber 12P in the paper width direction. The pressure chamber 12P has one end 12PX which is the downstream end in the transport direction and the other end 12PY which is the upstream end in the transport direction.
[0032] As shown in Figure 5, the pressure chamber 12P is composed of a hole formed in the plate 11A and opens to the upper surface of the flow channel member 12.
[0033] As shown in Figures 4 and 5, the communication channel 12E connects one end 12PX of the pressure chamber 12P to the common channel 12A. The communication channel 12E has a vertical hole 24, a vertical hole 25, and a horizontal hole 23.
[0034] As shown in Figure 5, the vertical hole 24 is formed in the plate 11B and extends downward from one end 12PX of the pressure chamber 12P. The vertical hole 25 is formed in the plate 11D and extends upward from the common flow path 12A. The horizontal hole 23 is formed in the plate 11C and extends in the conveying direction between the vertical holes 24 and 25.
[0035] As shown in Figures 4 and 5, the connecting channel 12D connects the other end 12PY of the pressure chamber 12P to the nozzle 12N. The connecting channel 12D has a vertical hole 26, a vertical hole 22, and a horizontal hole 21.
[0036] As shown in Figure 5, the vertical hole 26 is formed in plate 11B and extends downward from the other end 12PY of the pressure chamber 12P. The vertical hole 22 is formed in plates 11D and 11E and extends upward from nozzle 12N. The horizontal hole 21 is formed in plate 11C and extends in the conveying direction between the vertical holes 22 and 26.
[0037] As shown in Figure 5, the nozzle 12N is composed of a hole formed in the plate 11F and opens to the lower surface of the plate 11F. The lower surface of the plate 11F is the lower surface of the flow path member 12. The nozzle 12N opens downward, that is, in a direction intersecting the plane on which the pressure chamber 12P is located.
[0038] The vertical hole 22 and the nozzle 12N are cylindrical. The diameter of the vertical hole 22 is larger than the diameter of the nozzle 12N.
[0039] The ink in the ink tank is supplied to the common channel 12A via the supply port 121 by the pump 10 shown in Figure 2, which is driven by the control unit 5. The ink is then distributed from the common channel 12A to a plurality of individual channels 12B.
[0040] When the volume of the pressure chamber 12P decreases due to the operation of the piezoelectric element 13X, which will be described later, pressure is applied to the ink in the pressure chamber 12P. The pressurized ink is then ejected as ink droplets from the nozzle 12N through the connecting channel 12D.
[0041] Ink that is supplied to the common channel 12A via the supply port 121 but not distributed to the individual channels 12B returns to the ink tank via the return port 122.
[0042] As shown in FIG. 5, the sealing member 15 is disposed on the upper surface of the flow path member 12 so as to cover a plurality of pressure chambers 12P. The sealing member 15 is made of a material with low ink permeability such as stainless steel, for example. The sealing member 15 is disposed between the flow path member 12 and the actuator member 13.
[0043] As shown in FIG. 5, the actuator member 13 is fixed to the upper surface of the flow path member 12 so as to cover a plurality of pressure chambers 12P via the sealing member 15. The actuator member 13 includes piezoelectric layers 13A and 13B, a plurality of individual electrodes 13C, and a common electrode 13D. The individual electrodes 13C are provided for each pressure chamber 12P and are disposed so as to overlap with the one pressure chamber 12P in the vertical direction.
[0044] The actuator member 13 is a bulk piezo rather than a thin film piezo. A thin film piezo is a so-called micro electro mechanical systems (MEMS), which is an extremely small device in which a plurality of piezoelectric elements are integrated by sequentially forming thin films such as an electrode film and a piezoelectric film on a substrate, and has a thickness of about several μm. A bulk piezo is, for example, a stack of a plurality of piezoelectric sheets obtained by firing, and has a thickness of several tens of μm or more.
[0045] A portion of the actuator member 13 that overlaps with the pressure chamber 12P in the vertical direction functions as a piezoelectric element 13X. The piezoelectric element 13X can be deformed independently according to the potential applied to the individual electrode 13C.
[0046] The plurality of individual electrodes 13C and the common electrode 13D are electrically connected to the driver IC 14.
[0047] The driver IC 14 maintains the potential of the common electrode 13D at the ground potential while changing the potential of the individual electrode 13C. The common electrode 13D functions as a common electrode that is common to the plurality of piezoelectric elements 13X.
[0048] The driver IC 14 generates a drive signal based on a control signal from the control unit 5 and supplies the drive signal to the individual electrode 13C. The drive signal changes the potential of the individual electrode 13C between a predetermined drive potential and the ground potential.
[0049] In the present embodiment, from the viewpoint of increasing the driving frequency of the piezoelectric element 13X to support high-speed recording, the natural frequency of each individual flow path 12B is 130 kHz or more. More preferably, the natural frequency is 140 kHz or more.
[0050] The limit driving frequency of the piezoelectric element 13X is 40 to 80 kHz.
[0051] Further, in the present embodiment, from the viewpoint of suppressing the change in image density accompanying the change in recording speed, in each individual flow path 12B, the ratio of the inductance of the communication flow path 12E to the inductance of the entire individual flow path 12B is 59% or more. This limitation is based on the results of the analysis described below.
[0052] Hereinafter, the analysis performed by the inventor of the present application will be described.
[0053] The inventor of the present application focused on the fact that the configuration of the individual flow path 12B, particularly the ratio of the inductance of the communication flow path 12E to the inductance of the entire individual flow path 12B, affects the volume change rate of the ink droplets with respect to the driving frequency. Then, the inventor of the present application performed an analysis to obtain the above ratio such that the volume change rate of the ink droplets with respect to the driving frequency is small and the density of the image does not change significantly depending on the driving frequency. The analysis used LTspice (registered trademark), a circuit simulator provided by Analog Devices, Inc.
[0054] The inductance of the flow path is expressed as ρL / S [kg / m4] when the cross-sectional area of the flow path is S [m2], the length of the flow path is L [m], and the density of the ink in the flow path is ρ [kg / m3].
[0055] To adjust the inertance, it is conceivable to change the size of the flow path. The size includes length, width, and height. The individual flow path 12B has multiple flow path sections, consisting of a nozzle 12N, a pressure chamber 12P, a communication flow path 12E, and a connecting flow path 12D. Of these multiple flow path sections, the pressure chamber 12P is difficult to change in size because it needs to correspond to the design of the piezoelectric element 13X. On the other hand, the communication flow path 12E does not have the above-mentioned design constraints and is easy to change in size. From this viewpoint, the inventors of the present invention focused particularly on the communication flow path 12E among the multiple flow path sections that constitute the individual flow path 12B. The inventors of the present invention then verified, based on analysis, how the ratio of the inertance of the communication flow path 12E to the total inertance of the individual flow path 12B affects the ejected ink droplets.
[0056] The inventors of the present invention prepared analysis models A to E of a plurality of heads 1, each having a different configuration of individual flow channels 12B, and determined the volume of the ink droplets by ejecting ink droplets from the nozzle 12N in each analysis model. "Different configurations of individual flow channels 12B" means that the size of one or more of the elements constituting the individual flow channels 12B are different from each other. These elements include the nozzle 12N, the pressure chamber 12P, the communication flow channel 12E, and the connecting flow channel 12D.
[0057] The size of the elements constituting the individual flow paths 12B affects the inertance of those elements. In analysis models A to E, the sizes of the connecting flow paths 12E as elements differ from one another, so the inertance of the connecting flow paths 12E varies. Specifically, in analysis model A, the inertance of the connecting flow path 12E is 9.3 × 10⁷ [kg / m⁴]. In analysis model B, the inertance of the connecting flow path 12E is 1.7 × 10⁸ [kg / m⁴]. In analysis model C, the inertance of the connecting flow path 12E is 2.4 × 10⁸ [kg / m⁴]. In analysis model D, the inertance of the connecting flow path 12E is 3.1 × 10⁸ [kg / m⁴]. In analysis model E, the inertance of the connecting flow path 12E is 4.1 × 10⁸ [kg / m⁴].
[0058] In analysis models A to E, the ratio of the inertance of the connecting channel 12E to the total inertance of the individual channel 12B varies. Specifically, in analysis model A, the ratio is 40%. In analysis model B, the ratio is 51%. In analysis model C, the ratio is 59%. In analysis model D, the ratio is 65%. In analysis model E, the ratio is 81%.
[0059] Furthermore, the size of the elements constituting the individual flow path 12B affects the natural frequency. Therefore, the natural frequencies vary in analysis models A to E. Specifically, the natural frequency of analysis model A is 180 kHz. The natural frequency of analysis model B is 160 kHz. The natural frequency of analysis model C is 150 kHz. The natural frequency of analysis model D is 140 kHz. The natural frequency of analysis model E is 130 kHz.
[0060] Figure 6 shows the inertance and natural frequency of each element constituting the individual flow path 12B in analysis models A to E.
[0061] Figure 7 shows the ratio of the inertance of each element constituting the individual channel 12B to the total inertance of the individual channel 12B in analysis models A to E.
[0062] Figures 8 and 9 show the results of the analysis.
[0063] In Figure 8, the vertical axis represents the volume of the ink droplet, with the volume of the ink droplet ejected from nozzle 12N at a drive frequency of approximately 20 kHz being set to 100%. The horizontal axis represents the drive frequency. From Figure 8, it can be seen that in particular, analytical models A and B show a large increase in ink droplet volume with increasing drive frequency, and a large rate of change in ink droplet volume with respect to drive frequency. On the other hand, analytical models C, D, and E show a smaller increase in ink droplet volume with increasing drive frequency compared to analytical models A and B, and a smaller rate of change in ink droplet volume with respect to drive frequency.
[0064] In Figure 9, the vertical axis represents the rate of change in ink droplet volume with respect to the drive frequency, showing how much the volume of the ink droplet increases for every 1 kHz increase in the drive frequency. The horizontal axis represents the ratio of the inertance of the connecting channel 12E to the total inertance of the individual channels 12B. In analysis models C, D, and E, where the above rate of change in volume is judged to be relatively small based on the vertical axis of Figure 9 and Figure 8, the ratio of the inertance of the connecting channel 12E to the total inertance of the individual channels 12B is in the range of 59-81%.
[0065] When the ratio of the inertance of the connecting channel 12E to the total inertance of the individual channels 12B is less than 59%, the rate of change in ink droplet volume with respect to the drive frequency is large, as shown in analysis models A and B. In this case, the density of the image recorded by the ink droplets changes significantly depending on the recording speed, i.e., the drive frequency, and image quality tends to deteriorate.
[0066] When the ratio of the inertance of the connecting channel 12E to the total inertance of the individual channels 12B is 59% or more, the rate of change in ink droplet volume with respect to the drive frequency is small, as shown in analysis models C, D, and E. In this case, the density of the image recorded by the ink droplets does not change easily with respect to the recording speed, i.e., the drive frequency, and the image quality does not deteriorate easily.
[0067] As described above, according to this embodiment, each individual channel 12B has a natural frequency of 130 kHz or higher, and the ratio of the inertance of the connecting channel to the total inertance of the individual channels 12B is 59% or higher. As a result, as is clear from the analysis results above, it is possible to suppress changes in image density that occur with changes in recording speed.
[0068] The actuator member 13 is a bulk piezoelectric element. Compared to thin-film piezoelectric elements, bulk piezoelectric elements can be manufactured using a simpler process and at a lower cost. Therefore, the manufacturing of the head 1 can be simplified and the cost can be reduced.
[0069] The limiting drive frequency of the piezoelectric element 13X is 40 to 80 kHz. In this case, the drive frequency of the piezoelectric element 13X can be changed in the high-frequency band. Consequently, high-speed recording can be realized more effectively.
[0070] The ratio of the inertance of the connecting channel to the total inertance of the individual channels 12B is preferably 81% or less. If this ratio exceeds 81%, the under-refill phenomenon is likely to occur. The under-refill phenomenon refers to a phenomenon in which the amount of ink supplied from the common channel 12A to the individual channels 12B is insufficient. When this ratio is 81% or less, the under-refill phenomenon is less likely to occur.
[0071] The natural frequency of each individual flow path 12B is preferably 140 kHz or higher. In this case, ink droplets can be ejected at a higher drive frequency, enabling faster recording.
[0072] The recording resolution is 1200 dpi or higher, and the ink droplet volume is 2 to 5 pl. In this case, high image quality and good gradation expression can be achieved.
[0073] <Modification> Although preferred embodiments of the present disclosure have been described above, the present disclosure is not limited to the embodiments described above. The present disclosure is subject to various design modifications as described in the claims.
[0074] In the above-described embodiment, the electrodes constituting the piezoelectric element have a two-layer configuration including individual electrodes and a common electrode, but they may also have a three-layer configuration. For example, a three-layer configuration includes a driving electrode to which high potential and low potential are selectively applied, a high-potential electrode that is held at a high potential, and a low-potential electrode that is held at a low potential.
[0075] The droplet ejection head of this disclosure is not limited to being applied to line-type head units, but may also be applied to serial-type head units.
[0076] The target material for ejecting the droplets is not limited to paper. For example, the target material for ejecting the droplets may be cloth, a substrate, or plastic.
[0077] The droplets ejected from the nozzle are not limited to ink droplets. For example, the droplets may be droplets of a processing solution that causes components in the ink to agglomerate or precipitate.
[0078] This disclosure is not limited to printers, but is also applicable to facsimile machines, copiers, and multifunction devices.
[0079] This disclosure is also applicable to droplet dispensing devices used for purposes other than image recording. For example, this disclosure is applicable to droplet dispensing devices that dispense conductive liquid onto a substrate to form conductive patterns.
[0080] 1 Head (droplet dispensing head) 11A-11F Plate 12 Flow channel members 12A Common flow channel 12B Individual flow channel 12E Connecting flow channel 12N Nozzle 12P Pressure chamber 13 Actuator member 13X Piezoelectric element
Claims
1. A droplet dispensing head comprising a flow channel member having a plurality of individual flow channels and a common flow channel communicating with the plurality of individual flow channels, wherein the flow channel member is a plurality of stacked metal plates and includes a plurality of plates having holes that constitute the plurality of individual flow channels and the common flow channel, and each of the plurality of individual flow channels includes a nozzle, a pressure chamber communicating with the nozzle, and a communication flow channel connecting the pressure chamber and the common flow channel, wherein the natural frequency is 130 kHz or higher, and the ratio of the inertance of the communication flow channel to the inertance of the entire individual flow channel is 59% or higher.
2. The droplet dispensing head according to claim 1, further comprising an actuator member fixed to the flow channel member so as to cover the pressure chambers of the plurality of individual flow channels, the actuator member having a piezoelectric element that applies pressure to the liquid in the pressure chamber to discharge droplets from the nozzle, wherein the actuator member is a bulk piezoelectric element.
3. The droplet dispensing head according to claim 2, characterized in that the limiting driving frequency of the piezoelectric element is 40 to 80 kHz.
4. The droplet dispensing head according to claim 1, characterized in that the aforementioned ratio is 81% or less.
5. The droplet dispensing head according to claim 1, characterized in that the natural frequency is 140 kHz or higher.
6. A droplet ejection head according to any one of claims 1 to 5, characterized in that the recording resolution, which is the resolution of the image recorded by the droplets ejected from the nozzle, is 1200 dpi or more, and the volume of the droplets is 2 to 5 pl.