Liquid ejection device

A liquid ejection device includes a liquid ejection head, a supply tank connected to the liquid ejection head via a first flow path, a recovery tank connected to the liquid ejection head via a second flow path, a circulation pump arranged in a third flow path, a pressure pump arranged in a fourth flow path configured to connect the recovery tank and the liquid ejection head to each other, and a control portion configured to switch between liquid ejection operation in which liquid is ejected from the liquid ejection head while the liquid is circulated along the first to third flow paths and pressurizing recovery operation in which the liquid pressurized by the pressure pump is supplied to the liquid ejection head via the fourth flow path.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a liquid ejection device having mounted thereon a liquid ejection head configured to eject liquid.

Description of the Related Art

A liquid ejection device configured to record an image on a recording medium through ejection of liquid such as ink generally has mounted thereon a liquid ejection head configured to eject liquid. As a mechanism configured to eject liquid from the liquid ejection head, in many cases, there is used a mechanism configured to generate a pressure in a pressure chamber storing the liquid, to thereby eject, using the pressure, the liquid in the pressure chamber through an ejection orifice formed at one end of the pressure chamber. As methods of generating the pressure, there are given by, for example, reducing the capacity of the pressure chamber using a piezoelectric element, and by bubbling the liquid using a heating element to generate the pressure.

It is known that, in a liquid ejection head, presence of an air bubble in the pressure chamber considerably lowers droplet ejection performance. An air bubble is present in the pressure chamber due to various factors. For example, an air bubble is formed due to cavitation caused by pressure change in ejection or is brought into the pressure chamber from a supply flow path of the liquid. In order to remove such an air bubble from the pressure chamber, some methods are hitherto proposed.

For example, in Japanese Patent Application Laid-Open No. 2012-187862, there is disclosed a liquid ejection device in which a liquid circulating path including an upper tank, a liquid ejection head, a lower tank, and a circulation pump is formed. The upper tank is located above the liquid ejection head in a gravitational direction and can supply liquid to the liquid ejection head using a pressure head difference. The lower tank is located below the liquid ejection head in the gravitational direction and can recover the liquid from the liquid ejection head using a pressure head difference. The circulation pump is configured to return the liquid in the lower tank to the upper tank. With this configuration, the liquid ejection device disclosed in Japanese Patent Application Laid-Open No. 2012-187862 can record an image through ejection of the liquid from the liquid ejection head while the liquid is circulated along the circulating path described above. Through circulation of the liquid through the pressure chamber of the liquid ejection head in this way, not only an air bubble remaining in the pressure chamber can be removed together with the liquid but also thickening of the liquid in an ejection orifice can be suppressed.

Further, in the liquid ejection device disclosed in Japanese Patent Application Laid-Open No. 2012-187862, through driving of the circulation pump under a state in which an air release valve of the upper tank is closed to shut off a flow path between the liquid ejection head and the lower tank, pressurized liquid can be supplied to the liquid ejection head and can be discharged through the ejection orifice. Such pressurizing recovery operation enables droplet ejection performance to be satisfactorily maintained even in a liquid ejection head having a larger number of ejection orifices for attaining higher speed recording.

The liquid ejection device disclosed in Japanese Patent Application Laid-Open No. 2012-187862 is configured to pressurize the liquid via air in the upper tank in the pressurizing recovery operation described above. Therefore, at the end of the pressurizing recovery operation, compressed air in the upper tank expands until the pressure becomes equal to atmospheric pressure, and the expanded air causes the liquid to be kept discharged through the ejection orifices wastefully. Meanwhile, when, in order to suppress this problem, the air release valve of the upper tank is opened, the pressure of the compressed air abruptly becomes atmospheric pressure. The abrupt pressure reduction causes the ejection orifices to take in air, and as a result, the droplet ejection performance is lowered.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a liquid ejection device that can satisfactorily maintain droplet ejection performance while reducing unnecessary liquid consumption.

In order to attain the object described above, according to one embodiment of the present invention, there is provided a liquid ejection device, including: a liquid ejection head including: a supply port configured to supply liquid to a pressure chamber, the pressure chamber communicating with an ejection orifice for ejecting the liquid; and a recovery port configured to recover the liquid supplied to the pressure chamber; a first flow path connected to the supply port of the liquid ejection head; a supply tank configured to store the liquid supplied to the liquid ejection head, the supply tank being connected to the supply port of the liquid ejection head via the first flow path; a second flow path connected to the recovery port of the liquid ejection head; a recovery tank configured to store the liquid recovered from the liquid ejection head, the recovery tank being connected to the recovery port of the liquid ejection head via the second flow path, and a liquid level of the recovery tank being below an ejection orifice surface in which the ejection orifice of the liquid ejection head opens in a gravitational direction and being below a liquid level of the supply tank in the gravitational direction; a third flow path configured to connect the supply tank and the recovery tank to each other; a circulation pump configured to return the liquid in the recovery tank to the supply tank, the circulation pump being arranged in the third flow path; a fourth flow path configured to connect one of the supply tank and the recovery tank to the liquid ejection head; a pressure pump configured to pressurize the liquid in the one of the supply tank and the recovery tank and supply the liquid to the liquid ejection head, the pressure pump being arranged in the fourth flow path; and a control portion configured to switch between liquid ejection operation in which the liquid is ejected from the liquid ejection head while the liquid is circulated along the first flow path to the third flow path and pressurizing recovery operation in which the liquid pressurized by the pressure pump is supplied to the liquid ejection head via the fourth flow path.

In the liquid ejection device, the pressurized liquid is supplied to the liquid ejection head by the pressure pump only via the fourth flow path without passing through a tank containing air or the like. Therefore, unnecessary liquid consumption accompanying return to atmospheric pressure after the pressurizing recovery operation can be reduced to the minimum.

DESCRIPTION OF THE EMBODIMENTS

Now, embodiments of the present invention are described with reference to the attached drawings.

First Embodiment

First, the structure of a liquid ejection head according to a first embodiment of the present invention is described with reference toFIG. 1toFIG. 4.

FIG. 1is a sectional view of a liquid ejecting portion of the liquid ejection head according to this embodiment.FIG. 2is an exploded perspective view of the liquid ejecting portion of the liquid ejection head according to this embodiment.

A liquid ejecting portion100includes a plurality of ejection orifices101for ejecting liquid therethrough and a plurality of pressure chambers102configured to store the liquid and communicating with the plurality of ejection orifices101, respectively. A supply path103and a supply opening104configured to supply the liquid to each of the pressure chambers102and a recovery path105and a recovery opening106configured to recover the liquid from the pressure chamber102communicate with the pressure chamber102. Therefore, a flow path is formed in the liquid ejecting portion100for the liquid to flow into the pressure chamber102from the supply opening104via the supply path103, and to flow out of the recovery opening106from the pressure chamber102via the recovery path105.

The ejection orifices101are formed in an ejection orifice forming member107. A surface of the ejection orifice forming member107opposite to the pressure chambers102, that is, a surface of the ejection orifice forming member107on a liquid ejection side is water-repellent. Further, the pressure chambers102, the supply paths103, and the recovery paths105are formed in a pressure chamber forming member108.

The liquid ejecting portion100further includes a diaphragm109formed on the pressure chamber forming member108and forming an upper surface of the pressure chambers102and a plurality of piezoelectric elements111formed on the diaphragm109via a common electrode110so as to correspond to the pressure chambers102, respectively. In addition to the common electrode110, individual electrodes112for applying electric signals to the piezoelectric elements111are electrically connected to the piezoelectric elements111, respectively. A protective film113for insulating and protecting the diaphragm109, the common electrode110, the piezoelectric elements111, and the individual electrodes112is formed thereon.

The individual electrode112is formed for each of the piezoelectric elements111and is electrically connected to a bump116via lead out wiring114and a bump pad115. The common electrode110is also electrically connected to another bump (not shown). The bump116is formed of, for example, Au, and is electrically connected to a control circuit (not shown) formed outside the liquid ejection head via electric wiring117on a wiring board120. Through use of the bump116, electric connection between the electric wiring117and the piezoelectric element111can easily be made. A protective film118for insulating and protecting the electric wiring117is formed on the wiring board120.

When an electric signal is applied from the control circuit to the piezoelectric element111, the piezoelectric element111deforms the diaphragm109. With this, the pressure chamber102contracts and expands to apply pressure to the liquid in the pressure chamber102, thereby enabling ejection of the liquid through the ejection orifice101. The supply path103and the recovery path105for the liquid have capacity generating inertia larger than that of the ejection orifice101so that the pressure generated in the pressure chamber102goes toward the ejection orifice101.

A photosensitive resin119is formed on the protective film113, and the wiring board120described above is joined to the photosensitive resin119. As the photosensitive resin119, for example, a photosensitive dry film such as DF470 (manufactured by Hitachi Chemical Co., Ltd.) can be used. It is enough that the photosensitive resin119is a resin material that can be photopatterned, and thus the photosensitive resin119may be alternatively a photosensitive liquid resist.

The supply openings104and the recovery openings106are formed so as to penetrate the wiring board120, the protective film118, the photosensitive resin119, the protective film113, and the diaphragm109to communicate with the supply paths103and the recovery paths105, respectively, in the pressure chamber forming member108. A structure121for reducing the cross sectional areas of the supply path103and the recovery path105to narrow the flow path is arranged in the pressure chamber forming member108. The structure121is formed so as to be in contact with the diaphragm109, and also has the function of suppressing deformation of the diaphragm109due to swelling of the photosensitive resin119in contact with the liquid to change the cross sectional area of the supply path103and to damage the diaphragm109.

FIG. 3is an exploded perspective view of a manifold portion of the liquid ejection head according to this embodiment.

A manifold portion150of a liquid ejection head201includes a port layer158, a transport flow path layer157, and a common flow path layer156. A supply port154and a recovery port155are formed in the port layer158. A supply transport flow path152and a recovery transport flow path153are formed in the transport flow path layer157. Common supply flow paths122and common recovery flow paths123are formed in the common flow path layer156.

The supply port154communicates with a liquid supply flow path (not shown) to be described below that is formed outside the liquid ejection head201and with the supply transport flow path152. The supply transport flow path152communicates with the common supply flow paths122. The common supply flow paths122communicate with the plurality of supply openings104. Further, the recovery port155communicates with a liquid recovery flow path (not shown) to be described below that is formed outside the liquid ejection head201and with the recovery transport flow path153. The recovery transport flow path153communicates with the common recovery flow paths123. The common recovery flow paths123communicate with the plurality of recovery openings106.

The arrows inFIG. 3indicate flows of the liquid in the manifold portion150and the liquid ejecting portion100. Specifically, the liquid supplied from the liquid supply flow path flows into the common supply flow paths122from the supply port154via the supply transport flow path152, and flows into the respective pressure chambers102via the supply openings104. The liquid passing through the pressure chambers102flows into the common recovery flow paths123via the recovery openings106, and is recovered to the liquid recovery flow path via the recovery transport flow path153and the recovery port155.

FIG. 4is a transparent plan view of the liquid ejecting portion and the manifold portion according to this embodiment.

Horizontal intervals between adjacent ejection orifices101in each of ejection orifice lines are, for example, 21.17 μm (corresponding to 1,200 dpi). With this, an image of 1,200 dpi can be formed through ejection of liquid simultaneous with relative up-and-down movement of the liquid ejection head with respect to a recording medium in a plane ofFIG. 4.

The pressure chambers102adjacent to each other in a transverse direction are formed so that the supply openings104or the recovery openings106are adjacent to each other. One common supply flow path122is formed for two supply opening columns, and one common recovery flow path123is formed for two recovery opening columns. With this, the area efficiency of the liquid ejection head can be improved.

Next, the structure of the liquid ejection device according to this embodiment is described with reference toFIG. 5.FIG. 5is a schematic view for illustrating the flow path structure of the liquid ejection device according to this embodiment.

A liquid ejection device200includes the liquid ejection head201, a main tank202, a supply tank203, a recovery tank205, a cap218, and a control portion220.

The liquid ejection head201includes the liquid ejecting portion and the manifold portion described above, and is connected to a liquid supply flow path215and a liquid recovery flow path217via the supply port154and the recovery port155, respectively, in the manifold portion. The cap218is arranged below the liquid ejection head201and is formed so as to be movable between a position at which the cap218abuts against a surface of the liquid ejection head201in which the ejection orifices are opened, that is, an ejection orifice surface201a, so as to cover the ejection orifices of the liquid ejection head201, and a position at which the cap218is apart from the ejection orifice surface201a. A cap sealing valve219for opening/closing a space formed between the cap218and the ejection orifice surface201awhen the cap218abuts against the ejection orifice surface201ain the liquid ejection head201is mounted to the cap218. Through opening/closing of the cap sealing valve219, discharge of waste fluid and sealing of the ejection orifices can be switched.

One end of the liquid supply flow path215is connected to the supply port154in the liquid ejection head201and another end thereof is connected to a supply switching valve212. The supply switching valve212is connected to one end of a supply connection flow path209and another end of the supply connection flow path209is connected to the supply tank203. The supply tank203is connected to the main tank202via a refill flow path208. The refill flow path208includes a refill pump207configured to refill the supply tank203with the liquid from the main tank202. A liquid level sensor204configured to detect a liquid level in the supply tank203is mounted to the supply tank203.

One end of the liquid recovery flow path217is connected to the recovery port155in the liquid ejection head201and another end thereof is connected to the recovery tank205. The recovery tank205is connected to one end of a circulation flow path216, and another end of the circulation flow path216is connected to a circulation switching valve213. The circulation switching valve213is connected to one end of a return flow path210, and another end of the return flow path210is connected to the supply tank203. The circulation switching valve213is also connected to one end of a pressurized flow path211, and another end of the pressurized flow path211is connected to the supply switching valve212. The circulation flow path216includes a circulation pump214. A liquid level sensor206configured to detect a liquid level in the recovery tank205is mounted to the recovery tank205.

The supply tank203is arranged so that a liquid level203ain the supply tank203is above a liquid level205ain the recovery tank205in a gravitational direction. The recovery tank205is arranged so that the liquid level205ais below the ejection orifice surface201aof the liquid ejection head201in the gravitational direction.

The control portion220controls driving of the refill pump207and the circulation pump214based on output signals from the liquid level sensors204and206, respectively. Further, the control portion220controls the supply switching valve212, the circulation switching valve213, the cap218, and the cap sealing valve219to switch operation of the liquid ejection head201. Specific control operation by the control portion220is to be described below.

Here, operation of the liquid ejection device according to this embodiment is described with reference toFIG. 6toFIG. 8.FIG. 6,FIG. 7, andFIG. 8are schematic views for illustrating the flow path structure of the liquid ejection device according to this embodiment in liquid ejection operation, pressurizing recovery operation, and power off operation, respectively.

In the liquid ejection operation, as illustrated inFIG. 6, the control portion220controls the supply switching valve212to connect the supply connection flow path209and the liquid supply flow path215to each other, and controls the circulation switching valve213to connect the circulation flow path216and the return flow path210to each other. With this, the supply connection flow path209and the liquid supply flow path215function as a first flow path configured to connect the supply tank203and the liquid ejection head201to each other, and the liquid recovery flow path217functions as a second flow path configured to connect the liquid ejection head201and the recovery tank205to each other. Further, the circulation flow path216and the return flow path210function as a third flow path configured to connect the recovery tank205and the supply tank203to each other. Therefore, in the liquid ejection operation, a circulating path is formed that includes the supply tank203, the first flow path209and215, the liquid ejection head201, the second flow path217, the recovery tank205, and the third flow path216and210.

The liquid fills the entire circulating path. Due to a pressure head difference between the supply tank203and the recovery tank205, the liquid can flow in a direction of the arrows inFIG. 6from the supply tank203to the recovery tank205. When the liquid level sensor206detects that the liquid level205ain the recovery tank205is above a predetermined level, the control portion220drives the circulation pump214to return the liquid in the recovery tank205to the supply tank203. With this, the liquid level in the recovery tank205is controlled to be the predetermined level or lower. In this way, in the liquid ejection operation, the liquid can be ejected from the liquid ejection head201while the liquid is circulated along the circulating path described above.

As described above, the recovery tank205is arranged so that the liquid level205ais below the ejection orifice surface201aof the liquid ejection head201in the gravitational direction. More specifically, the liquid level205ain the recovery tank205is located below the ejection orifice surface201aof the liquid ejection head201in the gravitational direction so that the pressure in the ejection orifices in the liquid ejection head201may be an appropriate negative pressure. With this, the liquid ejection head201according to this embodiment can keep a state in which liquid menisci are formed in the ejection orifices while the liquid is circulated along the circulating path described above, thereby being capable of normally ejecting the liquid.

Meanwhile, in the pressure chamber in the liquid ejection head201, the liquid flows from the supply opening toward the recovery opening in the vicinity of the ejection orifice because the liquid is circulated. With this, an air bubble formed due to pressure fluctuations when the liquid is ejected can be discharged to the recovery opening without remaining in the vicinity of the ejection orifice, and further, thickening of the liquid in the ejection orifice can be suppressed.

As the liquid is consumed through ejection, the liquid in the supply tank203gradually reduces. In such a case, the supply tank203can be refilled with the liquid from the main tank202. Specifically, when the liquid level sensor204detects that the liquid level203ain the supply tank203is below a predetermined level, the control portion220can drive the refill pump207to refill the supply tank203with the liquid from the main tank202via the refill flow path208. With this, the liquid level203ain the supply tank203can be held at the predetermined level or higher.

In the pressurizing recovery operation, as illustrated inFIG. 7, the control portion220controls the supply switching valve212to connect the pressurized flow path211and the liquid supply flow path215to each other, and controls the circulation switching valve213to connect the circulation flow path216and the pressurized flow path211to each other. With this, the circulation flow path216, the pressurized flow path211, and the liquid supply flow path215function as a fourth flow path configured to connect the recovery tank205and the liquid ejection head201to each other. Therefore, in the pressurizing recovery operation, there is formed a circulating path including the recovery tank205, the fourth flow path216,211, and215, the liquid ejection head201, and the second flow path217, that is, a circulating path that does not include the supply tank203.

In this state, the control portion220first drives the circulation pump214and performs forced circulation as indicated by the arrows inFIG. 7. Therefore, the circulation pump214functions as a pressure pump configured to pressurize the liquid in the recovery tank205and supply the liquid to the liquid ejection head201via the fourth flow path216,211, and215. In this way, the pressurized liquid is supplied to the liquid ejection head201, and as a result, an air bubble remaining in the flow paths and in the pressure chamber can be discharged to the recovery tank205. At this time, in the recovery tank205, an opening (outlet) of the liquid recovery flow path217is located above an opening (inlet) of the circulation flow path216in the gravitational direction to prevent an air bubble discharged from the liquid ejection head201from being recirculated via the circulation flow path216. Further, according to this embodiment, the liquid is pressurized by the circulation pump (pressure pump)214without air therebetween, and thus efficient pressurization can be performed.

Incidentally, in the liquid ejection head201having the structure illustrated inFIG. 1, the recovery path has a large flow path resistance, and thus, in order to remove an air bubble remaining in the recovery path, the circulated liquid is required to have a large flow rate and a large pressure difference. However, when the ejection orifices are in an uncovered state, such a large flow rate and such a large pressure difference results in jetting of the liquid through the ejection orifices, which disables pressurizing recovery of the recovery path and wastes a large amount of the liquid.

Therefore, the control portion220then brings the cap218into abutment against the ejection orifice surface201aof the liquid ejection head201and controls the cap sealing valve219to hermetically seal a space formed by the cap218and the ejection orifice surface201a. With this, even when the liquid flows with a large pressure difference, the pressure in the cap218is balanced with the pressure in the pressure chambers in the liquid ejection head201, and thus the liquid flows toward the recovery openings instead of being jetted through the ejection orifices. As a result, an air bubble remaining in the recovery path can be removed without fail, and the consumption of the liquid can be reduced.

Through both pressurization and supply of the liquid by the circulation pump (pressure pump)214and formation of the hermetically sealed space by the cap218, a substantially similar effect of recovery can be obtained regardless of the order of performing the two operations. Therefore, the order may be opposite to that described above, i.e., the circulation pump214may pressurize and supply the liquid after the cap218forms the hermetically sealed space, or the two operations may be performed at the same time. When the liquid is pressurized and supplied first, not only the thickened liquid or air in the ejection orifices can be discharged but also additional air, which is forced into the ejection orifices when the hermetically sealed space is formed, can be prevented from mixing into the liquid. When the hermetically sealed space is formed first, the amount of the liquid wasted by being jetted through the ejection orifices can be further reduced.

After that, the control portion220drives the circulation pump (pressure pump)214for a predetermined time period to sufficiently remove an air bubble in the liquid supply flow path215and the liquid recovery flow path217. Then, the control portion220opens the cap sealing valve219to unseal the space in the cap218. This is for the purpose of, simultaneously with depressurization of the space in the cap218, discharging an air bubble and the thickened liquid in the ejection orifices in the liquid ejection head201through the ejection orifices.

Then, the control portion220stops the circulation pump214, depressurizes the liquid in the liquid supply flow path215and the liquid ejection head201, and moves the cap218away from the ejection orifice surface201aof the liquid ejection head201. Then, the control portion220moves a wiping member (not shown) to a position opposed to the ejection orifice surface201aand causes the wiping member to wipe and remove the liquid remaining on the ejection orifice surface201a. After that, the control portion220controls the supply switching valve212to connect the supply connection flow path209and the liquid supply flow path215to each other, thereby resuming the circulation of the liquid due to the pressure head difference described above. Then, the control portion220controls the circulation switching valve213to connect the circulation flow path216and the return flow path210to each other. Finally, the control portion220resumes control of driving of the circulation pump214using the liquid level sensor206of the recovery tank205and control of driving of the refill pump207using the liquid level sensor204of the supply tank203, to thereby resume the circulation of the liquid when the liquid is ejected illustrated inFIG. 6.

According to this embodiment, through such pressurizing recovery operation, an air bubble in the flow path that cannot be removed through circulation of the liquid when the liquid is ejected as described above can be discharged. Further, the liquid pressurized by the circulation pump (pressure pump)214is supplied to the liquid ejection head201only via the fourth flow path (the circulation flow path216, the pressurized flow path211, and the liquid supply flow path215) without passing through a tank containing air or the like. Therefore, return to atmospheric pressure after the pressurizing recovery operation can be made promptly, and as a result, unnecessary consumption of the liquid can be reduced. Further, formation of the hermetically sealed space by the cap218between the cap218and the ejection orifice surface201aof the liquid ejection head201can suppress jetting of the liquid through the ejection orifices to reduce the consumption of the liquid.

In the illustrated embodiment, the cap218is configured to form the hermetically sealed space in a state of being away from the ejection orifices, but when a member that does not damage the ejection orifice surface201ais used, the cap218may include a member that is brought into close contact with the ejection orifices for hermetic sealing and a liquid sump.

In the power off operation, the control portion220controls the supply switching valve212to connect the pressurized flow path211and the liquid supply flow path215to each other, and controls the circulation switching valve213to connect the circulation flow path216and the return flow path210to each other. With this, a circulating path of the liquid is not formed as illustrated inFIG. 8, and thus the liquid no longer flows. As a result, such a state can be prevented from being established that the liquid is not present in the liquid ejection head201. Further, on the recovery tank205side, the negative pressure is kept due to the pressure head difference with the ejection orifice surface201aof the liquid ejection head201, and thus the state in which appropriate menisci are formed in the ejection orifices can be kept.

Second Embodiment

FIG. 9is a schematic view for illustrating the flow path structure of a liquid ejection device according to a second embodiment of the present invention. This embodiment is different from the first embodiment in that a pressure pump301configured to pressurize and supply the liquid to the liquid ejection head201for the pressurizing recovery operation is arranged separately from the circulation pump214. Specifically, in this embodiment, instead of the supply switching valve212according to the first embodiment, a liquid supply valve302configured to connect the supply connection flow path209and the liquid supply flow path215to each other is arranged. The pressurized flow path211is connected to the supply connection flow path209and the liquid supply flow path215so as to bypass the liquid supply valve302, and the pressure pump301is arranged in the pressurized flow path211. Therefore, according to this embodiment, the pressurized flow path211connects the supply tank203and the liquid ejection head201to each other, and functions as a fourth flow path configured to supply the liquid pressurized by the pressure pump301to the liquid ejection head201. Further, the one end of the circulation flow path216is connected to the recovery tank205, and the another end thereof is connected to the supply tank203. Specifically, according to this embodiment, the circulation flow path216functions as a third flow path configured to connect the recovery tank205and the supply tank203to each other. Therefore, the circulation switching valve213and the return flow path210according to the first embodiment are not arranged.

In a liquid ejection device300according to this embodiment, in the liquid ejection operation, the control portion220opens the liquid supply valve302to connect the supply connection flow path209and the liquid supply flow path215to each other. In this way, the liquid is circulated due to a pressure head difference similarly to the first embodiment. Meanwhile, in the pressurizing recovery operation, the control portion220closes the liquid supply valve302to shut off the connection between the supply connection flow path209and the liquid supply flow path215, and stops the supply of the liquid from the supply tank203to the liquid ejection head201. Then, the control portion220drives the pressure pump301to pressurize the liquid in the supply tank203and supply the liquid to the liquid ejection head201. In this manner, the pressurizing recovery operation similar to that of the first embodiment is performed.

With this structure, there can be performed high-flow control for supplying the pressurized liquid to the liquid ejection head201and low-flow control for adjusting the liquid level in the recovery tank205by separate pumps, which are performed by a single pump according to the first embodiment. Therefore, the respective types of flow control can be performed with ease. Further, in the pressurizing recovery operation, the liquid is conveyed from the recovery tank205to the supply tank203, and thus liquid shortage in the supply tank203and a liquid overflow from the recovery tank205can be suppressed to enable the pressurizing recovery operation for a long time.

Instead of connecting a downstream side of the pressurized flow path211to the liquid supply flow path215, two supply ports may be formed in the liquid ejection head201, and one of the supply ports may be connected to the liquid supply flow path215and another of the supply ports may be connected to the pressurized flow path211. Further, an upstream side of the pressurized flow path211may be directly connected to the supply tank203.

Third Embodiment

FIG. 10is a schematic view for illustrating the flow path structure of a liquid ejection device according to a third embodiment of the present invention.

The pressurizing recovery operation for the liquid ejection head201is expected to have an equivalent effect regardless of whether the operation is conducted from the supply-side flow path or the operation is conducted from the recovery-side flow path. Accordingly, this embodiment is different from the first embodiment in that, in the pressurizing recovery operation, the pressurized liquid is supplied to the liquid ejection head201from the recovery-side flow path. Specifically, instead of the supply switching valve212according to the first embodiment, a liquid supply valve401configured to connect the supply connection flow path209and the liquid supply flow path215is arranged, and the pressurized flow path211is directly connected to the recovery port in the liquid ejection head201. Along with this, according to this embodiment, the liquid recovery flow path217is connected to the pressurized flow path211via a liquid recovery valve402.

In a liquid ejection device400according to this embodiment, in the liquid ejection operation, the control portion220opens the liquid supply valve401to connect the supply connection flow path209and the liquid supply flow path215to each other. Then, the control portion220opens the liquid recovery valve402to connect the recovery port in the liquid ejection head201and the liquid recovery flow path217to each other, and controls the circulation switching valve213to connect the circulation flow path216and the return flow path210to each other. In this way, the liquid is circulated due to a pressure head difference similarly to the first embodiment. Meanwhile, in the pressurizing recovery operation, the control portion220closes the liquid recovery valve402to shut off the connection between the recovery port in the liquid ejection head201and the liquid recovery flow path217, and controls the circulation switching valve213to connect the circulation flow path216and the pressurized flow path211to each other. Therefore, in this case, the circulation flow path216and the pressurized flow path211function as a fourth flow path configured to connect the recovery tank205and the liquid ejection head201to each other. Through driving of the circulation pump214, forced circulation in a direction opposite to that according to the first embodiment, that is, from the recovery-side flow path to the supply-side flow path in the liquid ejection head201, is performed.

Incidentally, in the liquid ejection head201having the structure illustrated inFIG. 1, when the liquid is circulated through the pressure chamber, it is desired that the supply path and the recovery path have a flow path resistance larger than that of the ejection orifices. Further, for the purpose of supplying the liquid sufficiently, it is desired that the recovery path have a flow path resistance larger than that of the supply path. In such a liquid ejection head201, it is more difficult to remove an air bubble in the recovery path than in the supply path. According to the structure of this embodiment, the pressurizing recovery operation can be performed from the recovery-side flow path, and as a result, the recovery path can be recovered without fail.

Instead of connecting an upstream side of the liquid recovery flow path217to the pressurized flow path211, two recovery ports may be formed in the liquid ejection head201, and one of the recovery ports may be connected to the pressurized flow path211and another of the recovery ports may be connected to the liquid recovery flow path217.

As described above, according to the present invention, droplet ejection performance can be satisfactorily maintained while unnecessary liquid consumption is reduced.

This application claims the benefit of Japanese Patent Application No. 2015-208144, filed Oct. 22, 2015, which is hereby incorporated by reference herein in its entirety.