JP6935735B2 - Liquid discharge device - Google Patents

Description

The present invention relates to a liquid discharge device that discharges a liquid from a nozzle.

In the recording head described in Patent Document 1, when the piezoelectric element is driven, the ink in the pressure generating chamber is ejected from the nozzle, and at the same time, a part of the ink is returned to the reservoir through the circulation passage. That is, the ink can circulate between the reservoir and the pressure generating chamber.

Japanese Unexamined Patent Publication No. 2012-71485

Therefore, for example, when the ink is settled, the settling can be eliminated by circulating the ink. Further, when the piezoelectric element is driven to such an extent that the ink is not ejected, the meniscus of the ink vibrates at the nozzle. Therefore, when the thickening of the ink occurs, the thickening can be eliminated by this vibration.

However, in the recording head of Patent Document 1, when the piezoelectric element is driven, ink circulation and meniscus vibration occur at the same time. Therefore, for example, when the ink is circulated to eliminate the sedimentation of the ink, the meniscus of the ink formed in the nozzle continues to vibrate. At this time, the elimination of sedimentation often takes more time than the elimination of thickening. With the meniscus in between, the thickened ink is diluted with fresh ink on the ink side, while the volatile components of the ink are released from the meniscus on the atmospheric side. As a result, the thickening of the ink progresses in the entire recording head, and the ejection characteristics may change.

An object of the present invention is to provide a liquid discharge device capable of independently circulating a liquid and vibrating a meniscus formed in a nozzle.

The liquid discharge device according to the first invention includes a plurality of individual flow paths and a common flow path to which the plurality of individual flow paths are connected, and each individual flow path includes a nozzle, a pressure chamber, and the above. A descender flow path connecting the nozzle and the pressure chamber, a throttle flow path connecting the pressure chamber and the common flow path, and a circulation flow path connecting the descender flow path and the common flow path. The control device is formed on the nozzle, further comprising an actuator for applying pressure to the liquid in the pressure chamber, a drive device for driving the actuator, and a control device for controlling the drive device. When vibrating the liquid meniscus, the drive device is driven by the first resonance frequency at which the pressure chamber to which the actuator is added in the individual flow path resonates, and the pressure chamber and the circulation flow are driven. When the liquid is circulated through the path, the drive device drives the actuator at a second resonance frequency at which the descender flow path resonates among the individual flow paths.

In the present invention, by selectively driving the actuator at either the first resonance frequency or the second resonance frequency, the vibration of the meniscus of the liquid formed in the nozzle and the circulation of the liquid are independently performed. Can be done. By properly using the resonance frequency, two effects of eliminating thickening in the vicinity of the nozzle and eliminating sedimentation in the flow path can be obtained in an effective state.

The liquid discharge device according to the second invention is the liquid discharge device according to the first invention, and the total of the compliance of the pressure chamber and the compliance of the actuator is the compliance of the throttle flow path and the descender flow. It is larger than the compliance of the road and smaller than the compliance of the liquid meniscus in the nozzle, and the first resonance frequency is a resonance frequency corresponding to the sum of the compliance of the pressure chamber and the compliance of the actuator.

If the sum of the compliance of the pressure chamber and the compliance of the piezoelectric actuator is larger than the compliance of the throttle flow path and the compliance of the descender flow path and smaller than the compliance of the liquid meniscus in the nozzle, the first resonance frequency is set. The resonance frequency can be set according to the sum of the compliance of the pressure chamber and the compliance of the piezoelectric actuator.

In the liquid discharge device according to the third invention, in the liquid discharge device according to the first or second invention, the compliance of the descender flow path is larger than the compliance of the circulation flow path, and the second resonance frequency is high. , The frequency corresponds to the compliance of the descender flow path.

When the compliance of the descender flow path is larger than the compliance of the circulation flow path, the second resonance frequency can be set to the resonance frequency corresponding to the compliance of the descender flow path.

In the liquid discharge device according to the fourth invention, in the liquid discharge device according to any one of the first to third inventions, the compliance of the descender flow path is based on the sum of the compliance of the pressure chamber and the compliance of the actuator. The second resonance frequency is higher than the first resonance frequency.

In general, the lower the compliance, the higher the resonance frequency. In the present invention, since the compliance of the descender flow path is smaller than the sum of the compliance of the pressure chamber and the compliance of the actuator, the second resonance frequency can be set to be higher than the first resonance frequency. Further, driving at the second resonance frequency, which has a high frequency, can speed up the flow of the liquid when circulating the liquid, and can efficiently eliminate the sedimentation of the liquid (when the second resonance frequency is low, the liquid can be driven. The flow of the liquid during circulation is slowed down, and the liquid settling may not be eliminated).

The liquid discharge device according to the fifth invention is the liquid discharge device according to any one of the first to fourth inventions, wherein the control device drives the liquid meniscus formed in the nozzle when it vibrates. The device drives the actuator at the second resonance frequency and then at the first resonance frequency.

When the actuator is driven at the second resonance frequency, the liquid circulates, but even if this drive is stopped, the circulation continues for a while. Therefore, in the present invention, the actuator is driven at the second resonance frequency and then at the first resonance frequency. In the nozzle, the thickened liquid is agitated by the vibration of the meniscus. Since the circulation continues even after the drive is stopped, the agitated liquid is diffused by the flow of the liquid due to the circulation. As a result, the liquid in the nozzle can quickly eliminate the thickening.

The liquid discharge device according to the sixth invention is the liquid discharge device according to the fifth invention. The actuator is driven at the first resonance frequency while the circulation continues after being driven at the resonance frequency.

In the present invention, the liquid agitated by the vibration of the meniscus is generated by driving the actuator at the first resonance frequency and vibrating the meniscus while the circulation after driving the actuator at the second resonance frequency continues. , Can be diffused on the flow of liquid by circulation.

The liquid discharge device according to the seventh invention is the liquid discharge device according to the fifth or sixth invention. The driving of the actuator at the second resonance frequency and the driving of the actuator at the first resonance frequency are alternately and repeatedly performed.

In the present invention, when the meniscus of the liquid formed in the nozzle is vibrated, the liquid in the nozzle thickens by repeating the driving at the first resonance frequency following the driving of the actuator at the second resonance frequency. It can be resolved quickly.

The liquid discharge device according to the eighth invention is the liquid discharge device according to any one of the first to seventh inventions. When the control device vibrates the liquid meniscus formed in the nozzle, the drive device is described. When the actuator is driven at the first resonance frequency using a rectangular wave and the liquid in the pressure chamber is circulated through the circulation flow path, the driving device uses a trapezoidal wave to drive the second resonance frequency. Drives the actuator.

When vibrating the liquid meniscus formed in the nozzle, the actuator is driven at the first resonance frequency using a square wave. When the liquid is circulated, the trapezoidal wave is used to drive the actuator at the second resonance frequency. Since the trapezoidal wave of the second resonance frequency has a smaller frequency component of the sine wave other than the second resonance frequency as compared with the square wave of the second resonance frequency, the meniscus of the liquid formed in the nozzle during the circulation of the liquid is removed. It is possible to prevent unnecessary vibration.

The liquid discharge device according to the ninth invention is the liquid discharge device according to any one of the first to eighth inventions, and the circulation flow path has a larger inertia than the nozzle.

In the present invention, since the inertia of the circulation flow path is larger than the inertia of the nozzle, the pressure generated in the pressure chamber can be efficiently transmitted to the nozzle when the actuator is driven to discharge the liquid from the nozzle. ..

The liquid discharge device according to the tenth invention is the liquid discharge device according to any one of the first to ninth inventions. A damping coefficient is small.

When continuously discharging the liquid from the nozzle, in order to stabilize the discharge characteristics, after discharging the liquid, the vibration of the meniscus of the liquid formed in the nozzle should be sufficiently attenuated before the next liquid is discharged. Is preferable. In the present invention, since the damping coefficient of the nozzle is large, the vibration of the meniscus is rapidly damped when the liquid is discharged from the nozzle. As a result, the time interval for discharging the liquid from the nozzle can be shortened. Further, since the attenuation coefficient of the circulation flow path is small, the pressure of the liquid in the circulation flow path is not easily attenuated when the liquid is circulated, and the circulation of the liquid can be efficiently maintained.

In the present invention, the vibration of the liquid meniscus formed in the nozzle and the circulation of the liquid can be performed independently.

It is a schematic block diagram of the printer which concerns on embodiment of this invention. It is a top view of the inkjet head of FIG. (A) is an enlarged view of the area surrounded by the alternate long and short dash line shown in FIG. 2, (b) is a sectional view taken along line BB of (a), and (c) is an enlarged view of the nozzle portion of (b). It is a figure. Is a block diagram showing an electrical configuration of the printer of the first embodiment. It is an equivalent circuit of an individual flow path and a piezoelectric actuator. It is a figure which shows the relationship between the drive frequency of a piezoelectric actuator, the meniscus of a nozzle, and the gain in a circulation flow path calculated by using an equivalent circuit. (A) is a diagram showing a drive signal applied to individual electrodes when ink is ejected from a nozzle, and (b) is a signal indicating a drive signal applied to individual electrodes when the meniscus is vibrated, and (c). ) Is a diagram showing a drive signal applied to individual electrodes when the ink is circulated. In the first modification, it is a flowchart which shows the flow of the process for eliminating the thickening of the ink in a nozzle. In the second modification, it is a flowchart which shows the flow of the process for eliminating the thickening of the ink in a nozzle.

Hereinafter, preferred embodiments of the present invention will be described.

As shown in FIG. 1, the printer 1 (“liquid ejection device” of the present invention) according to the present embodiment includes a carriage 2, an inkjet head 3, a platen 4, and transfer rollers 5 and 6. ..

The carriage 2 is supported by two guide rails 7 and 8 extending in the scanning direction. The carriage 2 is connected to the carriage motor 56 (see FIG. 4) via a gear or the like (not shown). When the carriage motor 56 is driven, the carriage 2 moves in the scanning direction along the guide rails 7 and 8. In the following, as shown in FIG. 1, the right side and the left side in the scanning direction will be defined and described.

The inkjet head 3 is mounted on the carriage 2 and moves in the scanning direction together with the carriage 2. The inkjet head 3 is a so-called serial head. The lower surface of the inkjet head 3 is a discharge surface 3a, and a plurality of nozzles 15 are formed. The plurality of nozzles 15 form a nozzle row 9 by arranging them in a transport direction orthogonal to the scanning direction. On the discharge surface 3a, four nozzle rows 9 are arranged along the scanning direction. Each nozzle row 9 corresponds to black, yellow, cyan, and magenta pigment inks from the rightmost to the left in the scanning direction.

The platen 4 faces the ejection surface 3a and supports the entire recording paper P in the scanning direction from below. The transport rollers 5 and 6 are both roller pairs, and the inkjet head 3 and the platen 4 are arranged so as to be sandwiched in the transport direction. The transfer rollers 5 and 6 are connected to the transfer motor 57 (see FIG. 4) via a gear or the like (not shown). When the transfer motor 57 is driven, the transfer rollers 5 and 6 rotate to transfer the recording paper P in the transfer direction.

<Inkjet head>
Next, the inkjet head 3 will be described. As shown in FIGS. 3A and 3B, the inkjet head 3 applies pressure to the flow path unit 21 in which the ink flow path including the nozzle 15, the pressure chamber 10, and the like is formed, and the ink in the pressure chamber 10. It is provided with a piezoelectric actuator 22 to be applied. Note that FIG. 3A is an enlarged view of the region surrounded by the alternate long and short dash line shown in FIG.

The flow path unit 21 is a laminated body of six plates 31 to 36. Inside, a plurality of individual flow paths 20 and four manifold flow paths 11 are formed.

The plurality of individual flow paths 20 are arranged in the transport direction to form the individual flow path rows 19. Here, four individual flow path rows 19 are arranged along the scanning direction. Each individual flow path 20 has a nozzle 15, a pressure chamber 10, a throttle flow path 12, a descender flow path 14, and a circulation flow path 16.

The nozzle 15 is formed through the plate 36. The lower surface of the plate 36 is the ejection surface 3a of the inkjet head 3 with all the nozzles open. The pressure chamber 10 is formed through the plate 31. The pressure chamber 10 has a substantially rectangular planar shape with the scanning direction as the longitudinal direction, and overlaps the nozzle 15 in the vertical direction at the right end portion in the scanning direction.

The throttle flow path 12 is formed so as to straddle the two plates 32 and 33. In the scanning direction, the throttle flow path 12 extends along the upper surface of the plate 33 and one end is connected to the left end of the pressure chamber 10. The other end is connected to the manifold flow path 11 (described later). The descender flow path 14 is formed through the plates 32 to 35. The descender flow path 14 connects the right end of the pressure chamber 10 in the scanning direction to the nozzle 15 in the vertical direction. The circulation flow path 16 is formed in the plate 35 and extends in the scanning direction along the lower surface thereof. The circulation flow path 16 connects the lower end of the descender flow path 14 to the manifold flow path 11 (described later).

The four manifold flow paths 11 are formed so as to penetrate the two plates 34 and 35. One manifold flow path 11 corresponds to one individual flow path row 19. Each extends along the individual flow path row 19 and is aligned in the scanning direction. In the scanning direction, each manifold flow path 11 is located on the left side of the corresponding nozzle 15 and circulation flow path 16 and overlaps the left half of the pressure chamber 10 and the throttle flow path 12. At this time, the left end of the manifold flow path 11 is connected to the left end of the corresponding throttle flow path 12, and the right end is connected to the left end of the circulation flow path 16. Further, in each manifold flow path 11, the upstream end portion in the transport direction extends vertically through the four plates 31 to 35. The opening at the upper end is the ink supply port 11a.

An ink cartridge (not shown) is connected to the ink supply port 11a via an external pipe (for example, a tube). As a result, the ink stored in the ink cartridge is supplied to the manifold flow path 11 from the ink supply port 11a. The four ink supply ports 11a are arranged in the scanning direction to form one supply port row.

As shown in FIG. 3, the piezoelectric actuator 22 has two piezoelectric layers 41 and 42, one common electrode 43, and a plurality of individual electrodes 44. The piezoelectric layers 41 and 42 are piezoelectric materials whose main component is lead zirconate titanate. The piezoelectric layer 41 is fixed to the upper surface of the flow path unit 21 (plate 31) and seals the opening of the pressure chamber 10. That is, the piezoelectric layer 41 constitutes the side walls of the plurality of pressure chambers 10.

The common electrode 43 is sandwiched between two piezoelectric layers 41 and 42. The individual electrodes 44 are formed on the upper surface of the piezoelectric layer 42 and are arranged in a 1: 1 positional relationship with the pressure chamber 10.

The control device 50 controls the driver IC 58 (“driving device” of the present invention, see FIG. 4) based on the print command. In the standby state before the start of printing, both electrodes 43 and 44 have a ground potential.

When ejecting ink, a drive signal is applied from the driver IC 58 between the electrodes 43 and 44. At this time, the individual electrode 44 selectively takes one of the ground potential GND and the drive potential Va. The common electrode 43 is always at the ground potential GND. The piezoelectric layer 42 between the electrodes 43 and 44 is a polarized active portion, and shrinks in the plane direction when an electric field is applied in the thickness direction (polarization direction). The piezoelectric layer 41 does not spontaneously displace.

Therefore, when the individual electrode 44 takes the driving potential Va (when an electric field is applied), the unit actuator (the portion of the piezoelectric layers 41 and 42 including the electrode that overlaps with the pressure chamber 10) is deformed convexly toward the pressure chamber 10. do. The volume of the pressure chamber 10 is rapidly reduced, and the ink inside is pressurized. This pressure wave reaches the nozzle 15 with vibrations in various parts of the flow path. Ink will be ejected from the nozzle 15. Subsequently, the individual electrode 44 takes a ground potential. As a result, the unit actuator returns to the state before deformation. Based on the image data, this convex deformation and its recovery are repeated, and printing is performed.

<Control device>
Next, the control device 50 that controls the printer 1 will be described. As shown in FIG. 4, the control device 50 is composed of a CPU (Central Processing Unit) 51, a ROM (Read Only Memory) 52, a RAM (Random Access Memory) 53, a flash memory 54, an ASIC (Application Specified Integrated Circuit) 55, and the like. Therefore, the operation of the carriage motor 56, the transfer motor 57, the driver IC 58, etc. is controlled.

Although only one CPU 51 is shown in FIG. 4, the control device 50 has one CPU 51, and this one CPU 51 may collectively perform processing, or has a plurality of CPU 51s. However, the plurality of CPUs 51 may share the processing. Further, although only one ASIC 55 is shown in FIG. 4, the control device 50 has one ASIC 55, and the one ASIC 55 may collectively perform processing, or may have a plurality of ASIC 55s. However, these plurality of ASIC 55s may share the processing.

<Equivalent circuit of individual flow path and piezoelectric actuator>
Next, the individual flow path 20 and the piezoelectric actuator 22 will be described. These can be represented by the equivalent circuit 60, as shown in FIG. In the equivalent circuit 60, R _APA , R _DES , R _NOZ, and R _CIR are the flow path resistances of the throttle flow path 12, the descender flow path 14, the nozzle 15, and the circulation flow path 16, respectively. L _APA , L _DES , L _NOZ, and L _CIR are inertia of the throttle flow path 12, the descender flow path 14, the nozzle 15, and the circulation flow path 16, respectively. C _APA , C _CAV , C _PZT , C _DES , C _CIR and C _NOZ are applied to the throttle flow path 12, the pressure chamber 10, the piezoelectric actuator 22, the descender flow path 14, the circulation flow path 16, and the nozzle 15, respectively. Compliance with the formed ink meniscus M (see FIG. 3C).

The flow path resistance of the pressure chamber 10 is negligibly small as compared with _{R APA} , R _DES , R _NOZ and R _CIR. The inertia of the pressure chamber 10 and the piezoelectric actuator 22 is also negligibly small compared to _{L APA} , L _DES , L _NOZ and L _CIR. Therefore, in FIG. 5, these illustrations are omitted.

Also, with respect to inertia, L _DES is greater than _{L NOZ.} Regarding compliance, the total [C _CAV + C _PZT ] of _{C CAV} and C _PZT is larger than _{CA PA} and C _{DE S.} Also, [C _CAV + C _PZT ] is smaller than _{C NOZ.} In addition, C _APA and C _CIR are sufficiently small compared to _{C CAV} , C _PZT and C _DES. Regarding the damping coefficient R / L, the damping coefficient R _CIR / L _CIR of the circulation flow path 16 is smaller than the damping coefficient R _NOZ / L _{NOZ of the nozzle 15.} The damping coefficient R / L represents the ease with which the applied vibration is damped in the specific flow path portion.

Here, using the equivalent circuit 60, the gains in the meniscus M of the nozzle 15 and the circulation flow path 16 were obtained. The drive frequency of the piezoelectric actuator 22 was changed in the range of 10 kHz to 1 MHz. FIG. 6 shows an example of the calculation result. In this example, for the meniscus M, its frequency profile shows the highest gain near 100 kHz. The circulation flow path 16 shows the highest gain near 750 kHz. The high gain frequency corresponds to the primary resonance frequency of the pressure chamber 10 and the piezoelectric actuator 22 (“first resonance frequency” of the present invention), and the latter corresponds to the primary resonance frequency of the circulation flow path 16 (the present invention). Corresponds to the "second resonance frequency").

The present embodiment is characterized in that the piezoelectric actuator 22 is driven at a specific frequency when the ink is ejected. The control device 50 controls the driver IC 58 and applies a drive signal to the individual electrodes 44 as shown in FIG. 7A. The drive signal is composed of a plurality of voltage pulses, the frequency of which is the first resonance frequency F1. The voltage pulse is a rectangular pulse in which the potential switches between the ground potential GND and the potential Va (≠ 0).

The first resonance frequency F1 is a frequency at which the pressure chamber 10 and the piezoelectric actuator 22 resonate. Here, the first resonance frequency F1 is a resonance frequency corresponding to _{[C CAV} + C _PZT]. [C _CAV + C _PZT ] has a _{large difference from CAPA} and C _DES, and when driven at this frequency, the pressure chamber 10 and the piezoelectric actuator 22 vibrate efficiently. At the same time, ink can be efficiently ejected from the nozzle 15.

<Vibration of meniscus>
On the other hand, if the state in which the ink is not ejected continues, the ink thickens in the nozzle 15. Ink thickening causes fluctuations in ejection characteristics. Therefore, the meniscus M is vibrated to stir the ink in the vicinity of the nozzle 15.

The piezoelectric actuator 22 is also driven at the first resonance frequency F1 when the meniscus M is vibrated. The control device 50 controls the driver IC 58 and applies a drive signal to the individual electrodes 44 as shown in FIG. 7 (b). The rectangular voltage pulse constitutes the drive signal, and its potential switches between the ground potential GND and the potential Vb (<Va). As a result, the meniscus M vibrates without ejecting ink. The ink in the vicinity of the nozzle 15 is agitated, and the thickening is eliminated.

<Ink circulation>
Further, if left for a long period of time, the pigment particles in the ink will settle. Sedimentation of ink components may even lead to non-ejection. On the other hand, in the present embodiment, ink is circulated between the individual flow path 20 and the manifold flow path 11.

When the ink is circulated, the piezoelectric actuator 22 is driven at the second resonance frequency F2. The control device 50 controls the driver IC 58 and applies a drive signal to the individual electrodes 44 as shown in FIG. 7 (c). The trapezoidal voltage pulse constitutes the drive signal, and its potential switches between the ground potential GND and the potential Vc. As a result, the ink in the manifold flow path 11 flows from the throttle flow path 12 into the pressure chamber 10 and the descender flow path 14. The ink that has reached the descender flow path 14 returns to the manifold flow path 11 via the circulation flow path 16. This circulation of the ink eliminates the sedimentation of the pigment particles.

In general, the lower the compliance, the higher the corresponding resonant frequency. In this embodiment, C _DES is smaller than [C _CAV + C _PZT]. Correspondingly, the second resonance frequency F2 corresponding to C _DES has a higher resonance frequency than the first resonance frequency F1 corresponding to _{[C CAV} + C _PZT]. Specifically, the first resonance frequency F1 is about 100 kHz, and the second resonance frequency F2 is about 750 kHz.

Here, when the piezoelectric actuator 22 is driven at a certain frequency, if the frequency is the first resonance frequency F1, the energy input from the outside is effectively used for the vibration of the pressure chamber 10 and the piezoelectric actuator 22. When the frequency is the second resonance frequency F2, the input energy is effectively used for the vibration of the descender flow path 14. For frequencies other than this, the input energy is dispersed in the vibrations of the various flow path portions.

Usually, the time required to eliminate the sedimentation of the pigment particles is longer than the time required to eliminate the thickening of the ink. When sedimentation elimination (ink circulation) is performed at a frequency other than the second resonance frequency F2, the meniscus M is exposed to vibration for an unnecessarily long time. On the contrary, the ink jet head 3 as a whole may promote the thickening of the ink.

On the other hand, in the present embodiment, the piezoelectric actuator 22 is driven at the second resonance frequency F2. While the descender flow path 14 resonates, the ink can be circulated while the vibration of the meniscus M is suppressed as much as possible.

Further, by properly using the drive frequency, the thickening in the vicinity of the nozzle 15 and the sedimentation in the ink flow path can be eliminated in an effective state.

It should be noted that the settlement elimination is affected by the flow velocity of the ink. The higher the drive frequency, the faster the flow velocity during circulation and the shorter the elimination time. If the flow velocity is slow, there is concern that the sedimentation cannot be eliminated. On the other hand, in the present embodiment, the higher second resonance frequency F2 (> F1) is the driving frequency for ink circulation, and the settling can be efficiently eliminated.

Further, when the ink is circulated, a trapezoidal wave is used as a drive signal. The drive signal contains few frequency components of sine waves other than the second resonance frequency F2. Therefore, when the ink is circulated, the input energy is effectively used for the vibration of the descender flow path 14.

Further, in general, the larger the inertia, the more difficult it is for the liquid in the flow path to be displaced (the position is easily maintained). In this embodiment, L _CIR is larger than _{L NOZ.} As a result, when the piezoelectric actuator 22 is driven to vibrate the meniscus M, the pressure generated in the pressure chamber 10 is efficiently transmitted to the nozzle 15. The circulation flow path 16 also communicates with the descender flow path 14, but due to _{the relationship of L CIR} > L _NOZ , this pressure is difficult to be transmitted to the circulation flow path 16. In particular, if it is driven at the first resonance frequency F1, this tendency is promoted because the input energy is easily used for the vibration of the pressure chamber 10 and the piezoelectric actuator 22.

Further, when the ink is continuously ejected from the nozzle 15, it is preferable that the residual vibration of the meniscus M is sufficiently attenuated immediately before the ink is ejected from the viewpoint of stable ink ejection. In the present embodiment, the attenuation coefficient R _NOZ / L _NOZ of the nozzle 15 is large. The residual vibration of the meniscus M is rapidly damped. As a result, the ink ejection interval can be shortened.

On the other hand, in the present embodiment, the attenuation coefficient R _CIR / L _CIR of the circulation flow path 16 is small. When the ink is circulated, the force that displaces the ink is not easily attenuated, and the ink circulation can be efficiently maintained.

Although the preferred embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and various modifications can be made as long as it is described in the claims.

In the above-described embodiment, when the thickening of the ink is eliminated, the piezoelectric actuator 22 is simply driven at the first resonance frequency F1, but the present invention is not limited to this.

For example, in the first modification, the operation procedure shown in FIG. 8 is followed in order to eliminate the thickening of the ink. First, the control device 50 drives the piezoelectric actuator 22 at the second resonance frequency F2. As a result, the ink circulates (S101). Subsequently, the piezoelectric actuator 22 is driven at the first resonance frequency F1 for a predetermined time T. As a result, the meniscus M vibrates (S102).

Here, even if the driving of S101 is stopped, the ink circulation continues for a while. Therefore, if the ink is circulated before the meniscus vibration, the ink agitated by the vibration of the meniscus M can be put on the remaining ink flow and diffused. As a result, the thickened ink is quickly replaced with fresh ink in the vicinity of the nozzle 15.

Further, in the first modification, the driving may be performed at the first resonance frequency F1 for a predetermined time T in which the ink circulation continues. This causes the meniscus M to vibrate while the ink circulation remains. Therefore, the agitated thickening ink can be put on the remaining ink flow and diffused while effectively using the input energy for the meniscus vibration.

In the second modification, the circulation of the ink and the vibration of the meniscus M are alternately repeated Na times. As shown in FIG. 9, the control device 50 first resets the number of times N to 0 (S201). Subsequently, the ink is circulated in the same manner as in S101 of the first modification (S202). At this time, the piezoelectric actuator 22 is driven at the second resonance frequency F2. After the ink circulation continues for T1 for a predetermined time, the control device 50 switches the operation to the vibration of the meniscus M as in S102 of the first modification (S203). The drive of the piezoelectric actuator 22 is performed at the first resonance frequency F1 and is continued for a predetermined time T2. When continuing for the predetermined time T2, the control device 50 increases the number of times N by 1 (updates to [N + 1]) (S204), returns to S202 when the number of times N is less than Na (S205: NO), and returns to the number of times N. When Na reaches (S205: YES), the process ends.

In the second modification, the circulation of the ink and the subsequent vibration of the meniscus are repeated a plurality of times, so that the ink settling and thickening can be surely eliminated.

Further, in the modified examples 1 and 2, the ink was circulated before the meniscus vibration. At this time, the meniscus vibration is started while the ink flow remains. The meniscus vibration may be stopped during the residual ink flow or after the flow is interrupted. If the meniscus vibration is started immediately after the ink circulation is stopped, the ink can be quickly replaced by the remaining ink flow.

Further, in the above-described embodiment, the piezoelectric actuator 22 is driven by the drive signal of the trapezoidal wave when the ink is circulated, but the present invention is not limited to this. For example, a square wave may be used as the drive signal.

Further, in the above-described embodiment, the second resonance frequency F2 is set higher than the first resonance frequency F1 corresponding to _{the C DES} smaller than [C _CAV + C _{PZT], but the present invention is not limited to this.} If the first resonance frequency F1 is the frequency that resonates the pressure chamber 10 and the piezoelectric actuator 22, and the second resonance frequency F2 is the frequency that resonates the descender flow path 14, the second resonance frequency F2 is from the first resonance frequency F1. May be low.

Further, in the above-described embodiment, the second resonance frequency F2 is set _{to a frequency corresponding to C DES corresponding to the fact that C DES} is _{larger than C CIR} , but the frequency is not limited to this. The second resonance frequency F2 may be a frequency set regardless of _{C DES as} long as it is a frequency that resonates the descender flow path 14.

In the embodiment described above, [C _CAV + C _PZT] is, C _APA, C _DES, corresponding to larger than C _NOZ, the first resonance frequency F1, the [C _CAV + C _PZT] The frequency was adjusted according to the frequency, but the frequency is not limited to this. The first resonance frequency F1 may be a frequency set regardless of _{[C CAV} + C _PZT ] as long as it is a frequency that resonates the pressure chamber 10 and the piezoelectric actuator 22.

Further, in the above-described embodiment, the inkjet head 3 causes the volume of the pressure chamber 10 to be changed by the piezoelectric actuator 22 to apply pressure to the ink, but the present invention is not limited to this. For example, an actuator other than the piezoelectric method may be used, such as an actuator that expands air bubbles in the pressure chamber by heating to apply pressure, an actuator that causes a volume change of the pressure chamber 10 by electrostatic force to apply pressure, and the like.

Further, in the above-described embodiment, the inkjet head 3 ejects four colors of pigment ink, but the present invention is not limited to this. For example, the inkjet head 3 may eject black pigment ink and color dye ink, and only a part of the ink ejected by the inkjet head 3 may be pigment ink.

Further, in the above, an example in which the present invention is applied to a printer provided with a so-called serial head has been described, but the present invention is not limited thereto. It is also possible to apply the present invention to a printer provided with a so-called line head extending over the entire length of the recording paper P in the scanning direction.

Further, in the above, an example in which the present invention is applied to a printer that ejects ink from a nozzle to perform printing has been described, but the present invention is not limited thereto. For example, the present invention can be applied to a liquid ejection device that ejects a liquid other than ink, such as a material for a wiring pattern of a wiring board.

1 Printer 10 Pressure chamber 12 Aperture flow path 14 Descender flow path 15 Nozzle 16 Circulation flow path 11 Manifold flow path 20 Individual flow path 22 Piezoelectric actuator 58 Driver IC
50 Control device

Claims (10)

With multiple individual channels
A common flow path to which the plurality of individual flow paths are connected is provided.
Each individual flow path
A nozzle, a pressure chamber, a descender flow path connecting the nozzle and the pressure chamber, a throttle flow path connecting the pressure chamber and the common flow path, and the descender flow path and the common flow path. Has a circulation flow path to connect,
An actuator that applies pressure to the liquid in the pressure chamber and
The drive device that drives the actuator and
A control device for controlling the drive device is further provided.
The control device is
When vibrating the liquid meniscus formed in the nozzle, the drive device is driven by the actuator at the first resonance frequency at which the pressure chamber to which the actuator is added in the individual flow path resonates.
When the liquid is circulated through the pressure chamber and the circulation flow path, the liquid is characterized in that the drive device drives the actuator at a second resonance frequency at which the descender flow path resonates among the individual flow paths. Discharge device. The sum of the compliance of the pressure chamber and the compliance of the actuator is larger than the compliance of the throttle flow path and the compliance of the descender flow path, and smaller than the compliance of the liquid meniscus in the nozzle.
The liquid discharge device according to claim 1, wherein the first resonance frequency is a resonance frequency corresponding to the sum of the compliance of the pressure chamber and the compliance of the actuator. The compliance of the descender flow path is larger than the compliance of the circulation flow path.
The liquid discharge device according to claim 1 or 2, wherein the second resonance frequency is a frequency corresponding to the compliance of the descender flow path. The compliance of the descender flow path is smaller than the sum of the compliance of the pressure chamber and the compliance of the actuator.
The liquid discharge device according to any one of claims 1 to 3, wherein the second resonance frequency is higher than the first resonance frequency. The control device is
Claims 1 to 1, wherein when the liquid meniscus formed in the nozzle is vibrated, the drive device drives the actuator at the second resonance frequency and then at the first resonance frequency. 4. The liquid discharge device according to any one of 4. The control device is
When the liquid meniscus formed in the nozzle is vibrated, the actuator is driven at the first resonance frequency while the circulation after the driving device is driven at the second resonance frequency is maintained. The liquid discharge device according to claim 5. The control device is
When the liquid meniscus formed in the nozzle is vibrated, the driving device is made to alternately and repeatedly drive the actuator at the second resonance frequency and the actuator at the first resonance frequency. The liquid discharge device according to claim 5 or 6, characterized in that. The control device is
When vibrating the liquid meniscus formed in the nozzle, the drive device is driven by the actuator at the first resonance frequency using a square wave.
Any of claims 1 to 7, wherein when the liquid in the pressure chamber is circulated through the circulation flow path, the drive device drives the actuator at the second resonance frequency using a trapezoidal wave. The liquid discharge device according to. The liquid discharge device according to any one of claims 1 to 8, wherein the circulation flow path has a larger inertia than the nozzle. The liquid discharge device according to any one of claims 1 to 9, wherein the circulation flow path has a smaller attenuation coefficient, which is a value obtained by dividing the flow path resistance by inertia, than the nozzle.

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