EP3925779A1

EP3925779A1 - Liquid discharge apparatus

Info

Publication number: EP3925779A1
Application number: EP21178692.6A
Authority: EP
Inventors: Hiroshi Sawase
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 2020-06-19
Filing date: 2021-06-10
Publication date: 2021-12-22
Anticipated expiration: 2041-06-10
Also published as: JP2022001408A; EP3925779B1

Abstract

A liquid discharge apparatus includes a liquid discharge head (100) configured to discharge a liquid, a first tank (111) connected to the liquid discharge head (100) through a head connection channel (114), a second tank (112) connected to the first tank (111), a first switch valve (131) configured to open and close the head connection channel (114), a liquid feeder (125) configured to feed the liquid from the second tank (112) to the first tank (111), a reverse feeder (126) configured to reversely feed the liquid from the first tank (111) to the second tank (112), and a controller (400) configured to close the first switch valve (131) and drive the liquid feeder (125), to perform a forward feeding operation, and close the first switch valve (131) and drive the reverse feeder (126), to perform a reverse feeding operation.

Description

BACKGROUND

Technical Field

Aspects of the present disclosure relate to a liquid discharge apparatus.

Related Art

When a liquid containing a sedimentation component such as white ink is used as a liquid to be discharged from a liquid discharge head, a sedimentation component in the liquid sediments with increase in unused time of a liquid discharge apparatus. Hereinafter, the "liquid discharge head" is simply referred to as a "head".
Conventionally, as a liquid feeder to feed a liquid from an ink cartridge to a head tank, a reversible pump capable of feed liquid in either forward or reverse rotation has been used. When a non-operating time of the reversible pump becomes equal to or larger than a predetermined time, a set amount of liquid is fed back from the head tank to the ink cartridge at once. The reversible pump feeds the set amount of liquid from the ink cartridge to the head tank at once to stir the liquid in the head tank.
A configuration described in Japanese Patent No. 5811322 has a problem that takes time to recover the liquid discharge head if a nozzle meniscus of the liquid discharge head is affected by a forward feeding or a reverse feeding of the liquid.

SUMMARY

An object of the present invention is to provide a liquid discharge apparatus that can reduce the influence of a liquid feed on the nozzle meniscus of the liquid discharge head.
In an aspect of this disclosure, A liquid discharge apparatus includes a liquid discharge head configured to discharge a liquid, a first tank connected to the liquid discharge head through a head connection channel, a second tank connected to the first tank, a first switch valve configured to open and close the head connection channel, a liquid feeder configured to feed the liquid from the second tank to the first tank, a reverse feeder configured to reversely feed the liquid from the first tank to the second tank, and a controller configured to close the first switch valve and drive the liquid feeder, to perform a forward feeding operation, and close the first switch valve and drive the reverse feeder, to perform a reverse feeding operation.
The liquid discharge apparatus according to the present disclosure can reduce an influence of liquid feed on the nozzle meniscus of the liquid discharge head.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional side view of a printer as a liquid discharge apparatus according to a first embodiment of the present disclosure;
FIG. 2 is a schematic plan view of a discharge unit of the printer;
FIG. 3 is a circuit diagram illustrating a liquid supply system of a printing unit of the printer according to the first embodiment of the present disclosure;
FIGS. 4A and 4B are schematic front views of an example of a first tank;
FIG. 5 is a flowchart of a control of a stirring operation performed by a stir controller according to the first embodiment;
FIG. 6 is a circuit diagram of the printing unit illustrating a forward feeding operation using a first channel in the stirring operation;
FIG. 7 is a circuit diagram of the printing unit illustrating a reverse feeding operation using a second channel in the stirring operation;
FIG. 8 is a circuit diagram of the printing unit illustrating a state after completion of the stirring operation;
FIG. 9 is a graph illustrating an example of pressure fluctuation on a downstream of a liquid feed pump in a liquid feed direction (forward direction) to illustrate an effect and an operation of closing a first switch valve and a second switch valve when the forward feeding operation is performed;
FIG. 10 is a circuit diagram illustrating a liquid supply system of the printing unit of the printer according to a second embodiment of the present disclosure;
FIGS. 11A and 11B are schematic front views of the first tank according to the second embodiment;
FIG. 12 is a graph illustrating a relation between a change in a remaining amount of liquid in the first tank (supply-discharge amount) and a displacement amount of a sensor feeler;
FIG. 13 is a circuit diagram of the printing unit illustrating the forward feeding operation using the first channel in the stirring operation in the second embodiment;
FIG. 14 is a circuit diagram of the printing unit illustrating the reverse feeding operation using the second channel in the stirring operation in the second embodiment;
FIG. 15 is a circuit diagram of the printing unit illustrating a state after completion of the stirring operation in the second embodiment;
FIG. 16 is a graph illustrating a relation between a supply (forward feeding)-discharge (reverse feeding) amount of the liquid in the first tank, an inner pressure of the first tank, and a displacement amount of the sensor feeler;
FIG. 17 is a circuit diagram illustrating a liquid supply system of the printing unit of the printer according to a third embodiment of the present disclosure;
FIG. 18 is a circuit diagram of the printing unit illustrating the forward feeding operation in the stirring operation according to the third embodiment;
FIG. 19 is a circuit diagram of the printing unit illustrating the reverse feeding operation in the stirring operation according to the third embodiment; and
FIG. 20 is a circuit diagram of the printing unit illustrating a state after completion of the stirring operation according to the third embodiment.

DETAILED DESCRIPTION

Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, embodiments of the present disclosure are described below.
A printer 1 as a liquid discharge apparatus according to a first embodiment of the present disclosure is described with reference to FIGS. 1 and 2.
FIG. 1 is a schematic side view of the printer 1 according to the first embodiment.
FIG. 2 is a schematic plan view of a discharge unit of the printer 1.
A printer 1 according to the first embodiment includes a loading unit 10 to load a sheet P into the printer 1, a pretreatment unit 20, a printing unit 30, a drying unit 40, and an ejection unit 50. In the printer 1, the pretreatment unit 20 applies, as required, pretreatment liquid onto the sheet P fed (supplied) from the loading unit 10, the printing unit 30 applies liquid to the sheet P to perform required printing, the drying unit 40 dries the liquid adhering to the sheet P, and the sheet P is ejected to the ejection unit 50.
The loading unit 10 includes loading trays 11 (a lower loading tray 11A and an upper loading tray 11B) to accommodate a plurality of sheets P and feeding devices 12 (a feeding device 12A and a feeding device 12B) to separate and feed the sheets P one by one from the loading trays 11. The loading unit 10 supplies the sheets P to the pretreatment unit 20.
The pretreatment unit 20 includes, e.g., a coater 21 as a treatment-liquid application unit that coats a printing surface of the sheet P with a treatment liquid having an action and an effect of aggregation of ink particles to prevent bleed-through.
The printing unit 30 includes a drum 31 and a liquid discharge device 32. The drum 31 is a bearer (rotating member) that bears the sheet P on a circumferential surface of the drum 31 and rotates. The liquid discharge device 32 discharges liquid toward the sheet P borne on the drum 31.
The printing unit 30 further includes transfer cylinders 34 and 35. The transfer cylinder 34 receives the sheet P from the pretreatment unit 20 and forwards the sheet P to the drum 31. The transfer cylinder 35 receives the sheet P conveyed by the drum 31 and forwards the sheet P to the drying unit 40.
The transfer cylinder 34 includes a sheet gripper to grip a leading end of the sheet P conveyed from the pretreatment unit 20 to the printing unit 30. The sheet P thus gripped by the transfer cylinder 34 is conveyed as the transfer cylinder 34 rotates. The transfer cylinder 34 forwards the sheet P to the drum 31 at a position opposite (facing) the drum 31.
Similarly, the drum 31 includes a sheet gripper on a surface of the drum 31, and the leading end of the sheet P is gripped by the sheet gripper of the drum 31. The drum 31 includes a plurality of suction holes dispersed on a surface of the drum 31, and a suction unit generates suction airflows directed from desired suction holes of the drum 31 to an interior of the drum 31.
The sheet gripper of the drum 31 grips the leading end of the sheet P forwarded from the transfer cylinder 34 to the drum 31, and the sheet P is attracted to and borne on the drum 31 by the suction airflows by the suction device. As the drum 31 rotates, the sheet P is conveyed.
The liquid discharge device 32 includes discharge units 33 (33A to 33E) to discharge liquids of each color. The discharge unit 33 serves as a discharge unit. For example, the discharge unit 33A discharges a liquid of cyan (C), the discharge unit 33B discharges a liquid of magenta (M), the discharge unit 33C discharges a liquid of yellow (Y), the discharge unit 33D discharges a liquid of black (K), the discharge unit 33E discharges a liquid of white (W). Further, the discharge unit 33 may discharge a special liquid, that is, a liquid of spot color such as gold, silver, and the like.
The discharge unit 33 is a full line head and includes a plurality of heads 100 arranged in a staggered manner on a base 331 as illustrated in FIG. 2, for example. Each of the head 100 includes a plurality of nozzle arrays and a plurality of nozzles 104 arranged in each of the plurality of nozzle arrays. As described above, the "liquid discharge head" is simply referred to as the "head".
The printing unit 30 controls a discharge operation of each discharge unit 33 of the liquid discharge device 32 by a drive signal corresponding to print data. When the sheet P borne on the drum 31 passes through a region facing the liquid discharge device 32, the liquids of respective colors are discharged from the discharge units 33 toward the sheet P, and an image corresponding to the print data is printed on the sheet P.
The drying unit 40 dries the liquid adhered onto the sheet P by the printing unit 30. Thus, a liquid component such as moisture in the liquid evaporates, and the colorant contained in the liquid is fixed on the sheet P. Additionally, curling of the sheet P is restrained.
The reversing mechanism 60 reverses, in switchback manner, the sheet P that has passed through the drying unit 40 in double-sided printing. The reversed sheet P is fed back to an upstream side of the transfer cylinder 34 through a conveyance passage 61 of the printing unit 30.
The ejection unit 50 includes an ejection tray 51 on which a plurality of sheets P is stacked. The plurality of sheets P conveyed from the drying unit 40 through the reverse mechanism 60 is sequentially stacked and held on the ejection tray 51.
Although the printer 1 to perform printing on cut sheets P is described as the liquid discharge apparatus, aspects of the present embodiments are applicable to a printer or the like to perform printing on a continuous medium, such as continuous paper, or a web.
Next, the printing unit 30 of the printer 1 according to the first embodiment of the present disclosure is described with reference to FIG. 3.
FIG. 3 is a circuit diagram illustrating a liquid supply system of the printing unit 30 of the printer 1 according to the first embodiment of the present disclosure.
As described above, the discharge unit 33 includes the plurality of heads 100 arranged side by side. The printing unit 30 in the first embodiment includes a manifold 110 to supply a liquid to the plurality of heads 100. The head 100 includes a head part 100a to discharge the liquid and a tank part 100b to supply the liquid to the head part 100a. However, the head 100 is not limited to the embodiment as described above.
The printing unit 30 includes a first tank 111 and a second tank 112. The first tank 111 is connected to the head 100 via the manifold 110. The second tank 112 is connected to the first tank 111.
The printing unit 30 further includes a first channel 121, a second channel 122, and a switch 124. The first channel 121 connects the second tank 112 and the first tank 111. The second channel 122 also connects the first tank 111 and the second tank 112 in a path partially different from the first channel 121. The switch 124 includes a three-way switching valve (three-way valve) to switch the first channel 121 and the second channel 122.
The switch 124 includes a port "a" connected to the first tank 111 through a common channel 123. The switch 124 includes a port "b" connected to the second tank 112 through an individual first channel 121a. The switch 124 includes a port "c" connected to the second tank 112 through an individual second channel 122a.
Thus, the printing unit 30 in the first embodiment includes the first channel 121 that includes the common channel 123 and the individual first channel 121a. Further, the printing unit 30 in the first embodiment includes the second channel 122 that includes the common channel 123 and the individual second channel 122a.
In this way, the first channel 121 includes the individual first channel 121a and the common channel 123. The switch 124 functions as a boundary between the individual first channel 121a and the common channel 123.
The second channel 122 includes the individual second channel 122a and the common channel 123. The switch 124 functions as a boundary between the individual second channel 122a and the common channel 123. Thus, a part of the first channel 121 (common channel 123) can also serve as a part of the second channel 122. Thus, a size of a device (printing unit 30) can be reduced at low cost.
Thus, the second channel 122 includes the common channel 123 and the individual second channel 122a separated from the individual first channel 121a. The individual second channel 122a connects the switch 124 and the second tank 112.
The printing unit 30 includes an irreversible (one-way type) liquid feed pump 125 in the individual first channel 121a of the first channel 121. The liquid feed pump 125 serves as a liquid feeder to feed liquid from the second tank 112 to the first tank 111 through the first channel 121.
The second tank 112 is a closed tank. The printing unit 30 includes an air discharge pump 126 as a depressurize device. The air discharge pump 126 serves as a reverse feeder to depressurize an interior of the second tank 112 to reversely feed a liquid from the first tank 111 to the second tank 112 through the second channel 122. The second tank 112 includes an air release valve 127 that opens an interior of the second tank 112 to atmosphere.
The printing unit 30 includes a main tank 113 that is a third tank to store a liquid to be supplied to the second tank 112.
The printing unit 30 includes a first switch valve 131 in a head connection channel 114 (liquid channel) to open and close the head connection channel 114. The head connection channel 114 is a head connection channel to connect the first tank 111 and the head 100 (manifold 110). The printing unit 30 includes a second switch valve 132 in a tank connection channel 115 to open and close the tank connection channel 115. The tank connection channel 115 is a tank connection channel to connect the second tank 112 and the main tank 113. The main tank 113 serves as the third tank.
The "tank" may be molded of metal, resin, or the like and has an invariant shape, or may be flexible and have a variable shape. Further, the "tank" may have a part having an invariant shape and the remaining part having a variable shape. The "tank" may be a dedicated part or may form a single body together with a head unit or the like.
A stir controller 400 is a control device to perform a switching control of the switch 124, an opening and closing control of the first switch valve 131 and the second switch valve 132, and a drive control of the liquid feed pump 125 and the air discharge pump 126, and the like. The stir controller 400 may be simply referred to as a "controller".
Then, the stir controller 400 controls the liquid feed pump 125 and the air discharge pump 126 to perform a reverse feeding operation to feed the liquid from the first tank 111 to the second tank 112 and a forward feeding operation to feed the liquid from the second tank 112 to the first tank 111 to stir the liquid in the first tank 111.
Next, an example of the first tank is described with reference to FIG. 4. FIGS. 4A and 4B are schematic front views of the first tank 111.
FIG. 4A is an outer front view of the first tank 111.
FIG. 4B is an inner front view of the first tank 111.
The first tank 111 includes a tank case 201 and a film 202. The film 202 is elastic or flexible. The film 202 is welded to an opening of the tank case 201 to seal the tank case 201 to form an accommodation part 203 that accommodates a liquid inside the tank case 201. Then, the first tank 111 includes the spring 204 to generate a negative pressure in the accommodation part 203.
Next, a stir operation in the first embodiment is described with reference to FIGS. 5 to 8.
FIG. 5 is a flowchart of a control of the stirring operation performed by the stir controller 400.
FIG. 6 is a circuit diagram of the printing unit 30 illustrating the forward feeding operation using the first channel 121 in the stirring operation.
FIG. 7 is a circuit diagram of the printing unit 30 illustrating the reverse feeding operation using the second channel 122 in the stirring operation.
FIG. 8 is a circuit diagram of the printing unit 30 illustrating a state after completion of the stirring operation.
With reference to FIG. 5, when the stirring operation is started, the stir controller 400 closes the first switch valve 131 (step S1). Hereinafter, the step S1 is simply referred to as "SI". Next, the stir controller 400 closes the second switch valve 132 (S2).
Then, the stir controller 400 performs a forward feeding operation (forward feeding) to feed the liquid 300 from the second tank 112 to the first tank 111 (S3). Next, the stir controller 400 performs a reverse feeding operation (reverse feeding) to reversely feed the liquid 300 from the first tank 111 to the second tank 112 (S4).
Then, the stir controller 400 determines whether the forward feeding operation and the reverse feeding operation are performed a predetermined number of times (S5). The stir controller 400 returns the stirring operation to S3 until the forward feeding operation and the reverse feeding operation have been performed for a predetermined number of times (S5, NO).
When the forward feeding operation and the reverse feeding operation are performed the predetermined number of times (S5, YES), the stir controller 400 opens the first switch valve 131 (S6), opens the second switch valve 132 (S7), and ends the stirring operation.
As described above, the stir controller 400 of the printing unit 30 in the first embodiment performs the forward feeding operation and the reverse feeding operation while closing the first switch valve 131 and the second switch valve 132.
A control of the stir controller 400 to control the forward feeding operation and the reverse feeding operation in this stirring operation is specifically described below.
As illustrated in FIG. 3, it is assumed that a sedimented liquid 301 due to sedimentation of the liquid 300 is accumulated at a bottom of the first tank 111, and similarly, a sedimented liquid 301 due to sedimentation of the liquid 300 is accumulated at a bottom of the second tank 112 before the stirring operation is performed.
The stir controller 400 closes the first switch valve 131 and the second switch valve 132 when the stirring operation is started.
Then, the stir controller 400 opens the ports "a-b" of the switch 124 and closes the ports "a-c" to connect the first tank 111 and the second tank 112 through the first channel 121. Specifically, the stir controller 400 opens a path (a-b) between the ports "a" and "b" in the switch 124 and closes a path (a-c) between the ports "a" and "c" in the switch 124 to connect the first tank 111 and the second tank 112 through the first channel 121.
Then, the stir controller 400 rotationally drives the liquid feed pump 125 to feed the liquid 300 from the second tank 112 to the first tank 111 through the first channel 121 as indicated by arrow in broken line in FIG. 6.
Then, the stir controller 400 opens the ports "a-c" of the switch 124 and closes the ports "a-b" to connect the first tank 111 and the second tank 112 through the second channel 122 after performing the forward feeding operation through the first channel 121. Specifically, the stir controller 400 opens the path (a-c) between the ports "a" and "c" in the switch 124 and closes the path (a-b) between the ports "a" and "b" in the switch to connect the first tank 111 and the second tank 112 through the second channel 122 after performing the forward feeding operation through the first channel 121.
Thus, the switch 124 is configured to switch between the first channel 121 and the second channel 122 depending on whether the stir controller 400 performs the forward feeding operation or the reverse feeding operation.
Then, stir controller 400 closes the air release valve 127 and rotationally drives the air discharge pump 126 to depressurize an interior of the second tank 112. Next, the stir controller 400 performs the reverse feeding operation (reverse feeding) to reversely feed the liquid 300 from the first tank 111 to the second tank 112 through the second channel 122 as indicated by arrow in a dash-single-dot line in FIG. 7.
The stir controller 400 repeats such the forward feeding operation to feed the liquid from the second tank 112 to the first tank 111 and the reverse feeding operation to reversely feed the liquid from the first tank 111 to the second tank 112 a predetermined number of times to stir each of the liquid 300 in the first tank 111 and the liquid 300 in the second tank 112.
Thus, as illustrated in FIG. 8, the stir controller 400 disperses the sedimented liquid 301 in the first tank 111 and the sedimented liquid 301 in the second tank 112 so that the sedimented liquid 301 in the first tank 111 and the second tank 112 decreases or disappears.
Then, the stir controller 400 opens the first switch valve 131 and the second switch valve 132 when the stirring operation is completed.
Next, an operational effect of closing the first switch valve 131 and the second switch valve 132 when the stir controller 400 preforms the forward feeding operation is described with reference to FIG. 9.
FIG. 9 is a graph illustrating an example of pressure fluctuation on a downstream of the liquid feed pump 125 in a liquid feed direction (forward direction) when the liquid feed pump 125 is driven. The liquid feed direction (forward direction) is indicated by the dashed arrow in FIG. 6.

As described above, the stir controller 400 closes the first switch valve 131 to close the head connection channel 114 between the head 100 (manifold 110) and the first tank 111 when performing the forward feeding operation.
Thus, the stir controller 400 can prevent a pulsation of the liquid feed pump 125 used as the liquid feeder to be transmitted to the head 100.
That is, when the stir controller 400 drives the liquid feed pump 125 to feed the liquid from the second tank 112 to the first tank 111, a pressure changes due to a flow of the liquid in the first channel 121.
For example, FIG. 9 is an example of a result of measurement of a pressure on a downstream of the liquid feed pump 125 with respect to the liquid feed direction (forward direction) when the stir controller 400 drives the liquid feed pump 125 at a relatively high voltage.
In FIG. 9, a pressure of "0 kPa" means atmospheric pressure, and a vertical axis represents a differential pressure with respect to atmospheric pressure. From a measurement result of FIG. 9, it can be seen that a large pressure is mainly generated on a positive pressure side each time the liquid is fed. Further, a pressure of about half of the positive pressure is also generated on a negative pressure side.
A range in which a shape of a nozzle meniscus of the head 100 can be maintained normally is generally from - 4 kPa to + 3 kPa. When a large pressure fluctuation as illustrated in FIG. 9 is transmitted to the head 100, the head 100 cannot maintain a shape of the meniscus formed in the nozzle 104 (nozzle meniscus) of the head 100.
If the printing unit 30 cannot maintain a shape of the nozzle meniscus in the head 100, the liquid in the nozzle 104 may overflow from the nozzle 104 by influence of excessive positive pressure, and air bubbles may enter into the nozzle 104 by influence of excessive negative pressure.
The liquid overflow from the nozzles 104 leads to contamination of an interior of the printing unit 30, and an entrance of the air bubbles in the nozzles 104 leads to poor discharge (or non-discharge) of the head 100.
Normally, the pressure fluctuation can be absorbed by the first tank 111 when the liquid is replenished to the head 100 during a printing operation. For example, the first tank 111 includes a spring 204 to generate a negative pressure in the tank case 201 as described above. The first tank 111 uses a part of the tank case 201 as a deformable wall as the film 202 (see FIGS. 4A and 4B) to form a pressure damper. Thus, the pulsation generated by the liquid feed pump 125 is reduced by the displacement of the spring 204 and the deformable wall of the film 202. Thus, the first tank 111 can reduce the influence of the pulsation on the nozzle meniscus of the head 100.
Further, when the liquid is supplied to the head 100 during the printing operation, the liquid feed pump 125 is driven at a relatively low voltage so as to reduce the pulsation as illustrated in FIG. 9.
On the other hand, the stir controller 400 feeds the liquid between the first tank 111 and the second tank 112 when the stir controller 400 performs a stirring operation of the liquid in the first tank 111 and the second tank 112. Thus, the stir controller 400 stops the printing operation to perform the stirring operation that decreases productivity of the printing operation.
Therefore, the stir controller 400 has to finish the stirring operation in a short time. In this case, the stir controller 400 can increase the driving voltage of the liquid feed pump 125 used as the liquid feeder to increase a liquid feeding speed of the liquid feed pump 125. Therefore, when the stir controller 400 performs the stirring operation, the stir controller 400 increases the driving voltage of the liquid feed pump 125 as compared with a driving voltage during a normal printing operation to increase the liquid feeding speed to shorten a working time of the stirring operation.
However, when the stir controller 400 increases the driving voltage of the liquid feed pump 125, a problem of an increase in the pulsation occurs as illustrated in FIG. 9.
Therefore, the printing unit 30 in the first embodiment includes the first switch valve 131 in the head connection channel 114 that is the connection channel between the first tank 111 and the head 100 (manifold 110). Then, the stir controller 400 drives the liquid feed pump 125 to feed the liquid from the second tank 112 to the first tank 111 while closing the first switch valve 131.
As a result, the printing unit 30 can block a transmission of a liquid flow to the head 100 during the stirring operation to reduce the influence of the liquid flow on the nozzle meniscus of the head 100.

As described above, the stir controller 400 closes the second switch valve 132 to close the tank connection channel 115 between the main tank 113 (third tank) and the second tank 112 when the stir controller 400 performs the reverse feeding operation.
As a result, the printing unit 30 can prevent the second tank 112 from being replenished with new liquid from the main tank 113 during feeding the liquid from the second tank 112 to the first tank 111.
That is, when the liquid is fed from the second tank 112 to the first tank 111, a pressure inside the second tank 112 becomes slightly negative, and the liquid may be replenished from the main tank 113 to the second tank 112. Further, when the main tank 113 is installed at a position higher than the second tank 112 due to layout of an apparatus (printing unit 30), the liquid may be replenished from the main tank 113 to the second tank 112 by a head difference.
Here, the stir controller 400 in the first embodiment performs the forward feeding operation and the reverse feeding operation a plurality of times (predetermined number of times) as described in the control of the stirring operation described above. In this case, if the tank connection channel 115 is open, new liquid is replenished from the main tank 113 to the second tank 112 each time the liquid is fed from the second tank 112 to the first tank 111.
Since the liquid is replenished from the main tank 113 to the second tank 112, the liquid is excessively supplied from the main tank 113 to a downstream of the second switch valve 132 unless the liquid is consumed by the head 100 or the like.
In the above case, if there is no first switch valve 131 or the first switch valve 131 is in an open state, the liquid may be leaked from the nozzle 104 of the head 100 to contaminate the interior of the apparatus (printing unit 30) due to an influence of a positive pressure in the head 100 by an excessive replenishment of the liquid.
Conversely, even if the first switch valve 131 is controlled to be closed, a pressure in the first tank 111 increases by the excessive replenishment of the liquid from the main tank 113 to the first tank 111 through the second tank 112. In the above case, a welded portion between the tank case 201 and the film 202 of the first tank 111 may be peeled off buy the increased pressure in the first tank 111, and the liquid may be leaked out from the first tank 111 to contaminate an interior of the apparatus (printing unit 30).
Therefore, the stir controller 400 in the first embodiment performs the forward feeding operation from the second tank 112 to the first tank 111 while closing the second switch valve 132 in the tank connection channel 115 to prevent the liquid from excessively supplied from the main tank 113 to the second tank 112.
The stir controller 400 closes the air release valve 127 when the stir controller 400 performs the forward feeding operation. Thus, the stir controller 400 prevent air from being replenished from the atmosphere to the second tank 112. If the air release valve 127 is not closed, a volume of air in the second tank 112 increases by the replenishment of air from the atmosphere.
Thus, when the stir controller 400 performs a next reverse feeding operation, a time taken for accumulating the pressure that acts on the liquid to be reversely fed from the first tank 111 increases if the air release valve 127 is open. In other words, the stir controller 400 closes the air release valve 127 to reduce a time taken for discharge an air from the second tank 112 by the air discharge pump 126.

As described above, the stir controller 400 closes the first switch valve 131 to close the head connection channel 114 between the head 100 (manifold 110) and the first tank 111 when the stir controller 400 performs the reverse feeding operation.
When the stir controller 400 performs the reverse feeding operation, the stir controller 400 switches the switch 124 to open the second channel 122, closes the air release valve 127 and the second switch valve 132, and drives the air discharge pump 126 as the discharger. The air discharge pump 126 as the discharger forms a part of a reverse feeder.
At the time of driving the air discharge pump 126, if a large amount of reverse liquid is set and operated in one reverse feeding operation, the nozzle meniscus of the head 100 changes significantly to the negative pressure side. Thus, air bubbles may enter into the nozzles 104 of the head 100 from the nozzle 104 and mix with the liquid in the nozzles 104 of the head 100.
Therefore, the stir controller 400 performs the reverse feeding operation while closing the first switch valve 131 to prevent the head 100 from suctioning air bubbles from the nozzle 104. Particularly, the larger an amount of liquid fed by the reverse feeding operation, the higher an effect of the stirring operation.
Hereinafter, the "effect of the stirring operation" is simply referred to as "stirring effect".
Thus, it is more effective to close the first switch valve 131 during the reverse feeding operation.
Further, although not as much as the forward feeding operation as described above, a negative pressure generated by driving the air discharge pump 126 during the reverse feeding operation may also affect an upstream side (head side) of the second channel 122. Thus, the stir controller 400 preferably closes the first switch valve 131 to maintain the nozzle meniscus in the nozzle 104 of the head 100.

As described above, the stir controller 400 closes the second switch valve 132 to close the tank connection channel 115 between the main tank 113 (third tank) and the second tank 112 when the stir controller 400 performs the reverse feeding operation.
The stir controller 400 prevents the liquid from being replenished from the main tank 113 (third tank) to the second tank 112 when the stir controller 400 performs the reverse feeding operation.
Further, when the main tank 113 is installed at a position higher than the second tank 112 due to layout of an apparatus (printing unit 30), the liquid may be replenished from the main tank 113 to the second tank 112 by a head difference.
If the tank connection channel 115 is open (the second switch valve 132 is open) during the reverse feeding operation, the liquid is replenished from the main tank 113 to the second tank 112.
Thus, a liquid amount returning from the first tank 111 to the second tank 112 decreases. Therefore, the stirring effect between the first tank 111 and the second tank 112 may not be sufficiently exhibited.
The stir controller 400 closes the air release valve 127 when the stir controller 400 performs the forward feeding operation. The stir controller 400 prevents air from being replenished from the atmosphere to the second tank 112 during the stir controller 400 performs the reverse feeding operation.
If the air release valve 127 is not closed, an amount of air discharged by the air discharge pump 126 is replenished with outside air from atmosphere. Thus, a liquid amount returning from the first tank 111 to the second tank 112 decreases. Therefore, the stirring effect between the first tank 111 and the second tank 112 may not be sufficiently exhibited.
Here, the stirring operation is performed, for example, at a timing immediately before a power is turned on or the printing operation is started after the printer 1 has not been used continuously. Thus, the printing unit 30 can reduce sedimentation of the liquid and prevent printing of a defective output. Particularly, the longer an unused waiting time such as a non-printing time or a non-discharge operation continuation time, the more the sedimentation occurs. Thus, the stirring operation according to the first embodiment is effective to prevent sedimentation in the first tank 111 and the second tank 112.
Further, the stir controller 400 in the first embodiment drives the liquid feed pump 125 and the air discharge pump 126 to perform the forward feeding operation and the reverse feeding operation for a previously set predetermined time, for example. A drive time of the liquid feed pump 125 and a drive time of the air discharge pump 126 respectively correspond to an amount of liquid fed by the forward feeding operation (forward feed amount) and an amount of liquid fed by the reverse feeding operation (reverse feed amount).
Thus, the stir controller 400 can control the driving time of the liquid feed pump 125 and the air discharge pump 126 to control the liquid amount supplied to the first tank 111 (supply amount) and the liquid amount discharged from the first tank 111 (discharge amount).
In the above case, a liquid viscosity changes according to a temperature change. Thus, the stir controller 400 can determine an operation time of the forward feeding operation and the reverse feeding operation based on a predetermined temperature-time table.
Further, the number of times of the stirring operation including one forward feeding operation and one reverse feeding operation is preferably set to a plurality of times. That is, the forward feed amount and the reverse feed amount are limited to be within a range of a liquid amount that can be stored in the first tank 111 and the second tank 112. Therefore, the stir controller 400 alternately generates a flow in the first tank 111 and the second tank 112 and repeats the above generation of the flow a plurality of times to further enhance the stirring effect to disperse the sedimented liquid 301 in the first tank 111 and the second tank 112.
The stir controller 400 in the first embodiment controls a forward feeding time of the forward feeding operation and a reverse feeding time of the reverse feeding operation (driving time of the liquid feed pump 125 and the air discharge pump 126) to control the range of the liquid amount that can be stored in the first tank 111 and the second tank 112.
The stir controller 400 can change the number of times of the stirring operation according to the waiting time of the apparatus (printing unit 30). For example, when the waiting time is short, an amount of sedimentation is small so that the sedimentation can be dispersed by the stirring operation for a short time. Thus, the stir controller 400 performs the stirring operation a relatively small number of times. On the other hand, if the waiting time is long, the amount of sedimentation is large. Thus, the stir controller 400 performs the stirring operation a relatively large number of times to reliably stir the liquid in the first tank 111 and the second tank 112 over time.
An operation end time when the liquid feed pump 125 is driven is overwritten and stored every time, and a difference between the operation end time and a current time is calculated as the waiting time of the apparatus (printing unit 30). The difference is defined as the non-printing time (non-discharge operation continuation time) in which the printing unit 30 does not perform the printing operation. When a power is turned on or it becomes a timing before a print start in a state in which the non-printing time exceeds a preset predetermined timing, the stir controller 400 performs the stirring operation a predetermined number of times.
The printing unit 30 in the first embodiment uses an irreversible pump as the liquid feed pump 125 to feed the liquid from the second tank 112 to the first tank 111 through the first channel 121. The irreversible pump is a pump that can feed liquid in only one direction, and generally corresponds to a piston pump or a diaphragm pump.
The diaphragm pump includes a check valves at an inlet (suction side) and an outlet (discharge side) of the diaphragm pump. The diaphragm pump alternately repeats a suction operation and a discharge operation to feed the liquid. A liquid feed direction of the diaphragm pump is limited to one direction due to an action of the check valve. However, the diaphragm pump is known as a pump with a relatively long life without mechanical wear.
The printing unit 30 according to the first embodiment can perform forward feeding operation and the reverse feeding operation between the first tank 111 and the second tank 112 while feeding the liquid from the second tank 112 to the first tank 111 to stir the liquid in the first tank 111 and the second tank 112. Thus, the printing unit 30 can stably discharge the liquid for a long period of time.
Thus, the stir controller 400 is configured to control the liquid feed pump 125, the first switch valve 131, and the second switch valve 132 to repeatedly perform the forward feeding operation and the reverse feeding operation while closing the first switch valve 131 and the second switch valve 132 to stir the liquid in the first tank 111 and the second tank 112.
The printing unit 30 according to a second embodiment of the present disclosure is described with reference to FIG. 10.
FIG. 10 is a circuit diagram illustrating a liquid supply system of the printing unit 30 of the printer 1 according to the second embodiment of the present disclosure.
The printing unit 30 in the second embodiment includes a similar configuration with the first embodiment (see FIG. 8) except that the printing unit 30 includes a liquid amount detector 210 to detect a liquid amount of the first tank 111.
The liquid amount detector 210 includes a sensor feeler 205, an upper limit sensor 211, and a lower limit sensor 212. The sensor feeler 205 is displaced according to the liquid amount in the first tank 111. The upper limit sensor 211 is an upper limit detector. The lower limit sensor 212 is a lower limit detector.
The upper limit sensor 211 detects the sensor feeler 205 when the liquid amount reaches a preset upper limit value. The lower limit sensor 212 detects the sensor feeler 205 when the liquid amount reaches a preset lower limit value. The upper limit value and the lower limit value are limit values used when the stir controller 400 controls the forward feed amount and the reverse feed amount during the stirring operation.
The stir controller 400 inputs detection results of the upper limit sensor 211 and the lower limit sensor 212, and drives and controls the switch 124, the liquid feed pump 125, and the air discharge pump 126. The stir controller 400 performs the reverse feeding operation to feed the liquid from the first tank 111 to the second tank 112 and the forward feeding operation to feed the liquid from the second tank 112 to the first tank 111 to control the stirring operation that stirs the liquid in the first tank 111.
Next, a configuration related to the liquid amount detection of the first tank 111 is described with reference to FIGS. 11A and 11B, and FIG. 12.
FIGS. 11A and 11B are schematic front views of the first tank 111.
FIG. 12 is a graph illustrating a relation between a change in a remaining amount of liquid in the first tank 111 (supply-discharge amount) and a displacement amount of a sensor feeler 205.
The first tank 111 is sealed by welding an elastic member or a flexible film 202 to the opening of the tank case 201 as similarly described in the first embodiment to form the accommodation part 203 to store the liquid 300 in the tank case 201. Then, the first tank 111 includes the spring 204 to generate a negative pressure in the accommodation part 203.
Further, the first tank 111 in the second embodiment includes a mylar 207 on the film 202 and a pin 208 displaced according to a displacement of the film 202.
Further, one end of the sensor feeler 205 is rotatably supported by a bearing 206 on the tank case 201 and is brought into contact with the pin 208 by its own weight of the sensor feeler 205. Thus, another end of the sensor feeler 205 is displaced in a vertical direction according to the displacement of the film 202. The displacement of the film 202 corresponds to a displacement in an outer direction and an inner direction of the film 202.
Therefore, the tank case 201 includes a sensor holder and the like to hold the upper limit sensor 211 and the lower limit sensor 212 configured by a photo sensor or the like. The sensor holder is disposed at another end (right end in FIGS. 11A and 11B) of the sensor feeler 205 so that the upper limit sensor 211 and the lower limit sensor 212 can detect said another end of the sensor feeler 205.
The first tank 111 thus configured includes the sensor feeler 205 moves inward (downward in FIGS. 11A and 11B) and outward (upward in FIGS. 11A and 11B) of the tank case 201 according to the supply-discharge amount of the liquid supplied to and discharged from the first tank 111. Thus, a displacement position of the sensor feeler 205 is detected by using the upper limit sensor 211 and the lower limit sensor 212.
That is, when the liquid in the first tank 111 is discharged to the second tank 112, the film 202 is deformed inside the tank case 201 (see FIG. 12(c)). Therefore, as illustrated in FIG. 12(a), a certain point outside the sensor feeler 205 of the first tank 111 is set to zero, and the liquid in the first tank 111 is discharged to the second tank 112. Then, as illustrated in FIG. 12(c), the displacement amount of the sensor feeler 205 increases so that the sensor feeler 205 moves inward (downward in FIG. 12(c)) of the tank case 201 with discharge of the liquid 300 from the first tank 111 to the second tank 112.
Conversely, when the liquid is supplied from the second tank 112 to the first tank 111, the film 202 deforms to protrude outside the tank case 201. Therefore, as illustrated in FIG. 12(a), a certain point outside the sensor feeler 205 of the first tank 111 is set to zero, and the liquid is supplied to the first tank 111 from the second tank 112. Then, as illustrated in FIG. 12(b), the displacement amount of the sensor feeler 205 decreases so that the sensor feeler 205 moves outward (upward in FIG. 12(b)) of the tank case 201 with supply of the liquid 300 from the second tank 112 to the first tank 111.
Therefore, the stir controller 400 in the second embodiment controls the liquid amount of the forward feeding operation and the reverse feeding operation to the first tank 111 according to the detection results of the upper limit sensor 211 and the lower limit sensor 212 to detect the sensor feeler 205.
Next, the printing unit 30 according to a second embodiment of the present disclosure is described with reference to FIGS. 13 to 15. FIG. 13 is a circuit diagram of the printing unit 30 illustrating the forward feeding operation using the first channel 121 in the stirring operation. FIG. 14 is a circuit diagram of the printing unit 30 illustrating the reverse feeding operation using the second channel 122 in the stirring operation. FIG. 15 is a circuit diagram of the printing unit 30 illustrating a state after completion of the stirring operation.
The stir controller 400 closes the first switch valve 131 and the second switch valve 132 when the stir controller 400 starts the stirring operation as in the above described first embodiment. Then, the stir controller 400 performs the forward feeding operation to feed the liquid 300 from the second tank 112 to the first tank 111 and the reverse feeding operation to reversely feed the liquid 300 from the first tank 111 to the second tank 112.
Then, the stir controller 400 performs the forward feeding operation and the reverse feeding operation a predetermined number of times. After the stir controller 400 performs the forward feeding operation and the reverse feeding operation a predetermined number of times, the stir controller 400 opens the first switch valve 131 and the second switch valve 132.
A control of the stir controller 400 to control the forward feeding operation and the reverse feeding operation in this stirring operation is specifically described below.
As illustrated in FIG. 10, it is assumed that the sedimented liquid 301 due to sedimentation of the liquid 300 is accumulated at the bottom of the first tank 111, and similarly, the sedimented liquid 301 due to sedimentation of the liquid 300 is accumulated at the bottom of the second tank 112 before the stirring operation is performed.
The stir controller 400 closes the first switch valve 131 and the second switch valve 132 when the stirring operation is started.
Then, the stir controller 400 opens the ports "a-b" of the switch 124 and closes the ports "a-c" to connect the first tank 111 and the second tank 112 through the first channel 121.
Then, the stir controller 400 rotationally drives the liquid feed pump 125 to feed the liquid 300 from the second tank 112 to the first tank 111 through the first channel 121 as indicated by arrow in broken line in FIG. 13.
Therefore, the stir controller 400 performs the forward feeding operation until the upper limit sensor 211 detects the sensor feeler 205 displaced to the upper limit position to control the liquid feed amount.
Then, the stir controller 400 opens the ports "a-c" of the switch 124 and closes the ports "a-b" to connect the first tank 111 and the second tank 112 through the second channel 122 after performing the forward feeding operation through the first channel 121.
Then, stir controller 400 closes the air release valve 127 and rotationally drives the air discharge pump 126 to depressurize an interior of the second tank 112. Thus, the stir controller 400 performs the reverse feeding operation to reversely feed the liquid 300 from the first tank 111 to the second tank 112 through the second channel 122 as indicated by arrow in a dash-single-dot line in FIG. 14.
At the time of the reverse feeding operation, the stirring controller 400 performs the reverse feeding operation until the lower limit sensor 212 detects that the sensor feeler 205 displaces to a lower limit position to control the liquid amount of reverse feeding operation
The stir controller 400 repeats such the forward feeding operation to feed the liquid from the second tank 112 to the first tank 111 and the reverse feeding operation to reversely feed the liquid from the first tank 111 to the second tank 112 a predetermined number of times to stir each of the liquid 300 in the first tank 111 and the liquid 300 in the second tank 112.
Thus, as illustrated in FIG. 15, the stir controller 400 disperses the sedimented liquid 301 in the first tank 111 and the sedimented liquid 301 in the second tank 112 so that the sedimented liquid 301 in the first tank 111 and the second tank 112 decreases or disappears.
Then, the stir controller 400 opens the first switch valve 131 and the second switch valve 132 when the stirring operation is completed.
The printing unit 30 according to the second embodiment can perform the forward feeding operation and the reverse feeding operation according to characteristics of the first tank 111 as described in FIG. 12. Thus, even if temperature changes and the viscosity of the liquid to be fed changes, an absolute position (the upper limit position of the upper limit sensor 211 and the lower limit position of the lower limit sensor 212) does not change. Thus, the stir controller 400 can accurately control the liquid amount in the first tank 111.
Particularly, an influence of the liquid flow generated by the stirring operation on the nozzle meniscus formed in a large number of heads 100 increases in the line-type head including an array of the large number of heads 100.
That is, if the liquid is reversely fed (discharged) from the first tank 111 too much, air bubbles may enter into the nozzles 104 of the head 100. Further, if the liquid is fed (supplied) to the first tank 111 too much, the liquid may be leaked from the nozzles 104 of the head 100. Above-described entrance of the air bubbles into the nozzles 104 and leaking of the liquid from nozzles 104 significantly reduce image quality of printing.
Further, if a problem occurs in the nozzle meniscus, it takes time to recover the nozzles 104 since the line-type head includes many nozzles 104. Therefore, the printing unit 30 preferably has a configuration that prevents the problems in the nozzle meniscus such as the entrance of air bubbles into the nozzles 104 or the leaking of the liquid from the nozzles 104.
Therefore, the stir controller 400 controls a liquid supply (forward feeding) to the first tank 111 and a liquid discharge (reverse feeding) from the first tank 111 by the upper limit sensor 211 and the lower limit sensor 212. Thus, the printing unit 30 can reduce the influence of the stirring operation on the nozzle meniscus.
Next, an above-described point is described with reference to FIG. 16. FIG. 16 is a graph illustrating a relation between the supply-discharge amount of the liquid in the first tank 111, an inner pressure of the first tank 111, and the displacement amount of the sensor feeler 205. The supply-discharge amount of the liquid in the first tank 111 represents the liquid amount supplied to the first tank 111 (forward feeding operation) and the liquid amount discharged from the first tank 111 (reverse feeding operation).
The stir controller 400 can control the supply amount of the liquid fed to the first tank 111 and the discharge amount of the liquid reversely fed (discharged) from the first tank 111 according to the detection result of the upper limit sensor 211 and the lower limit sensor 212 so that the stir controller 400 can control pressures corresponding to the supply amount and the discharge amount.
The first tank 111 generates a negative pressure by a restoring force of the spring 204. Thus, the lower the remaining amount of liquid in the first tank 111, the lower the pressure in the first tank 111 (the higher the negative pressure in the first tank 111). Therefore, as illustrated in FIG. 16, the pressure inside the first tank 111 changes according to a change in remaining amount of liquid in the first tank 111 by the forward feeding operation and the reverse feeding operation performed on the first tank 111.
For example, as illustrated in FIG. 16, the inner pressure in the first tank 111 corresponding to a displacement amount "a" becomes Ph. The displacement amount "a" is a liquid amount in the first tank 111 when the upper limit sensor 211 and the lower limit sensor 212 detect that the sensor feeler 205 is at the upper limit position (preset upper limit value).
Further, as illustrated in FIG. 16, the inner pressure in the first tank 111 corresponding to a displacement amount "b" becomes P1. The displacement amount "b" is a liquid amount in the first tank 111 when the upper limit sensor 211 and the lower limit sensor 212 detect that the sensor feeler 205 is at the lower limit position (preset lower limit value).
Therefore, the stir controller 400 controls the forward feeding operation and the reverse feeding operation so that the remaining amount of liquid in the first tank 111 changes within a range detected by the upper limit sensor 211 and the lower limit sensor 212, for example.
Thus, the stir controller 400 can control the inner pressure in the first tank 111 within a pressure range (between the pressure Ph and PI) corresponding to the remaining amount of liquid in the first tank 111 detected by the upper limit sensor 211 and the lower limit sensor 212.
Thus, the "preset upper limit value" detected by the upper limit sensor 211 is corresponds to the displace amount "a" and the inner pressure Ph in FIG. 16. Further the "preset lower limit value" detected by the lower limit sensor 212 corresponds to the displace amount "b" and the inner pressure PI in FIG. 16.
Thus, the stir controller 400 controls the inner pressure in the first tank 111 within a predetermined pressure range so that the stir controller 400 can always keep the nozzle meniscus normally. Thus, the stir controller 400 can prevent an entrance of air bubbles into the nozzles 104 by the excessive reverse feeding operation and leaking of the liquid from the nozzles 104 by the excessive forward feeding operation. Thus, the printing unit 30 can prevent deterioration of image formed by the printing operation.
Next, the printing unit 30 according to a third embodiment of the present disclosure is described with reference to FIG. 17.
FIG. 17 is a circuit diagram illustrating a liquid supply system of the printing unit 30 of the printer 1 according to the third embodiment of the present disclosure.
The printing unit 30 in the third embodiment includes a liquid channel 120 that is a connection channel that commonly uses the second tank 112 and the first tank 111 for the forward feeding operation and the reverse feeding operation.
The printing unit 30 in the third embodiment includes the liquid feed pump 125 that is a reversible pump configured by a tube pump or the like in the liquid channel 120. Thus, the liquid feed pump 125 (the liquid feeder) also functions as the air discharge pump 126 (reverse feeder) in the third embodiment as illustrated in FIG. 17.
The stir controller 400 switches forward and reverse directions of an applied drive voltage to switches a liquid feed direction of the liquid feed pump 125 in one of the forward and reverse directions. Thus, the liquid feed pump 125 can feed the liquid 300 in both directions including a forward direction to feed the liquid 300 from the second tank 112 to the first tank 111 and a reverse direction to feed the liquid 300 from the first tank 111 to the second tank 112.
Further, the stir controller 400 controls to drive the liquid feed pump 125 and controls to open and close the first switch valve 131 and the second switch valve 132 as in the first embodiment. The stir controller 400 controls to drive the liquid feed pump 125 to switch the liquid feed direction between the forward direction (for forward feeding operation) and the reverse direction (for reverse feeding operation).
Further, the stir controller 400 uses each detection result of the upper limit sensor 211 and the lower limit sensor 212 of the liquid amount detector 210 to control the forward feed amount and the reverse feed amount to the first tank 111 as in the second embodiment.
A control of the stir controller 400 to control the stirring operation (forward feeding operation and reverse feeding operation) in the third embodiment is specifically described below with reference to FIGS. 18 to 20.
FIG. 18 is a circuit diagram of the printing unit 30 illustrating the forward feeding operation using the first channel 121 in the stirring operation.
FIG. 19 is a circuit diagram of the printing unit 30 illustrating the reverse feeding operation using the second channel 122 in the stirring operation.
FIG. 20 is a circuit diagram of the printing unit 30 illustrating a state after completion of the stirring operation.
Here, as illustrated in FIG. 17, it is assumed that the sedimented liquid 301 due to sedimentation of the liquid 300 is accumulated at a bottom of the first tank 111, and similarly, the sedimented liquid 301 due to sedimentation of the liquid 300 is also accumulated at a bottom of the second tank 112 before the stirring operation is performed.
Therefore, when the stirring operation is started, the stir controller 400 executes a control related to the stirring operation described in the first embodiment, and first closes the first switch valve 131 and the second switch valve 132.
Then, the stir controller 400 drives the liquid feed pump 125 in a normal rotational direction (forward direction). Thus, the stir controller 400 performs the forward feeding operation to feed the liquid 300 from the second tank 112 to the first tank 111 through the liquid channel 120 as indicated by arrow in a broken line in FIG. 18.
Therefore, the stir controller 400 performs the forward feeding operation until the upper limit sensor 211 detects the sensor feeler 205 displaced to the upper limit position to control the liquid feed amount.
Next, after feeding a predetermined amount of liquid to the first tank 111 from the second tank 112, the stir controller 400 reversely drives the liquid feed pump 125. Thus, the stir controller 400 performs the reverse feeding operation to reversely feed the liquid 300 from the first tank 111 to the second tank 112 through the liquid channel 120 as indicated by arrow in a dash-single-dot line in FIG. 19.
At this time, the stir controller 400 preforms the reverse feeding operation until the lower limit sensor 212 detects that the sensor feeler 205 displaces to the lower limit position to control the liquid amount of the reverse feeding operation (reverse feed amount).
The stir controller 400 repeats such the forward feeding operation to feed the liquid from the second tank 112 to the first tank 111 and the reverse feeding operation to reversely feed the liquid from the first tank 111 to the second tank 112 a predetermined number of times to stir each of the liquid 300 in the first tank 111 and the liquid 300 in the second tank 112.
Thus, as illustrated in FIG. 20, the stir controller 400 disperses the sedimented liquid 301 in the first tank 111 and the sedimented liquid 301 in the second tank 112 so that the sedimented liquid 301 in the first tank 111 and the second tank 112 decreases or disappears.
Then, the stir controller 400 opens the first switch valve 131 and the second switch valve 132 when the stirring operation is completed.
As described above, the printing unit 30 uses a reversible liquid feeder as the liquid feed pump 125 to simplify a configuration of the printing unit 30.
An operation of the first switch valve 131 and the second switch valve 132 during the forward feeding operation and the reverse feeding operation are similar to the operation of the first switch valve 131 and the second switch valve 132 in the first embodiment. Thus, an operation and effect of the operation of the first switch valve 131 and the second switch valve 132 is briefly described below.

As described above, the stir controller 400 closes the first switch valve 131 to close the head connection channel 114 between the head 100 (manifold 110) and the first tank 111 when performing the forward feeding operation.
Thus, the stir controller 400 can prevent a pulsation of the liquid feed pump 125 used as the liquid feeder to be transmitted to the head 100. Thus, the printing unit 30 can reduce the influence of the stirring operation on the nozzle meniscus in the head 100.

As described above, the stir controller 400 closes the second switch valve 132 to close the tank connection channel 115 between the main tank 113 (third tank) and the second tank 112 when the stir controller 400 performs the reverse feeding operation.
Thus, the printing unit 30 can prevent new liquid from being replenished from the main tank 113 to the second tank 112 during the forward feeding operation of the liquid from the second tank 112 to the first tank 111. Thus, the printing unit 30 can prevent the liquid to be excessively supplied from the main tank 113 to the downstream of the second switch valve 132.

As described above, the stir controller 400 closes the first switch valve 131 to close the head connection channel 114 between the head 100 (manifold 110) and the first tank 111 when the stir controller 400 performs the reverse feeding operation.
As a result, the printing unit 30 can reduce suction of air bubbles from the nozzle 104 of the head 100. Further, the stir controller 400 preferably closes the first switch valve 131 to maintain the nozzle meniscus in the head 100 since the printing unit 30 in the third embodiment uses the reversible liquid feeder as the liquid feed pump 125.

As described above, the stir controller 400 closes the second switch valve 132 to close the tank connection channel 115 between the main tank 113 (third tank) and the second tank 112 when the stir controller 400 performs the reverse feeding operation.
The stir controller 400 prevents the liquid from being replenished from the main tank 113 (third tank) to the second tank 112 when the stir controller 400 performs the reverse feeding operation.
Further, the timing of the stirring operation, the number of times of the stirring operation (one forward feeding operation and one reverse feeding operation), a measurement of the waiting time, and the like are the same as the above elements described in the first embodiment.
Further, "liquid" discharged from the head is not particularly limited as long as the liquid has a viscosity and surface tension of degrees dischargeable from the head. Preferably, the viscosity of the liquid is not greater than 30 mPa· s under ordinary temperature and ordinary pressure or by heating or cooling.
Examples of the liquid include a solution, a suspension, or an emulsion that contains, for example, a solvent, such as water or an organic solvent, a colorant, such as dye or pigment, a functional material, such as a polymerizable compound, a resin, or a surfactant, a biocompatible material, such as DNA, amino acid, protein, or calcium, or an edible material, such as a natural colorant.
Such a solution, a suspension, or an emulsion can be used for, e.g., inkjet ink, surface treatment solution, a liquid for forming components of electronic element or light-emitting element or a resist pattern of electronic circuit, or a material solution for three-dimensional fabrication.
Examples of an energy source in the head to generate energy to discharge liquid from the head include a piezoelectric actuator (a laminated piezoelectric element or a thin-film piezoelectric element), a thermal actuator that employs a thermoelectric conversion element, such as a heating resistor, and an electrostatic actuator including a diaphragm and opposed electrodes.
The term "liquid discharge apparatus" used herein also represents an apparatus including the head to discharge liquid by driving the head. The liquid discharge apparatus may be, for example, an apparatus capable of discharging liquid to a material to which liquid can adhere or an apparatus to discharge liquid toward gas or into liquid.
The "liquid discharge apparatus" may include devices to feed, convey, and eject the material on which liquid can adhere.
The liquid discharge apparatus may further include a pretreatment apparatus to coat a treatment liquid onto the material, and a post-treatment apparatus to coat a treatment liquid onto the material, onto which the liquid has been discharged.
The "liquid discharge apparatus" may be, for example, an image forming apparatus to form an image on a sheet by discharging ink, or a three-dimensional fabrication apparatus to discharge a fabrication liquid to a powder layer in which powder material is formed in layers to form a three-dimensional fabrication object.
The liquid discharge apparatus is not limited to an apparatus to discharge liquid to visualize meaningful images, such as letters or figures.
For example, the liquid discharge apparatus may be an apparatus to form arbitrary images, such as arbitrary patterns, or fabricate three-dimensional images.
The above-described term "material onto which liquid can adhere" represents a material onto which liquid at least temporarily adheres, a material onto which liquid adheres and fixes, or a material onto which liquid adheres to permeate.
Examples of the "material onto which liquid can adhere" include recording media such as a paper sheet, recording paper, and a recording sheet of paper, film, and cloth, electronic components such as an electronic substrate and a piezoelectric element, and media such as a powder layer, an organ model, and a testing cell.
The "material onto which liquid can adhere" includes any material on which liquid adheres unless particularly limited.
Examples of the "material onto which liquid can adhere" include any materials on which liquid can adhere even temporarily, such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, and ceramic.
The "liquid discharge apparatus" may be an apparatus to relatively move the head and a material onto which liquid can adhere.
However, the liquid discharge apparatus is not limited to such an apparatus.
For example, the liquid discharge apparatus may be a serial head apparatus that moves the head or a line head apparatus that does not move the head.
Examples of the "liquid discharge apparatus" further include a treatment liquid coating apparatus to discharge a treatment liquid to a sheet to coat the treatment liquid on a sheet surface to reform the sheet surface, and an injection granulation apparatus in which a composition liquid including raw materials dispersed in a solution is injected through nozzles to granulate fine particles of the raw materials.
The terms "image formation", "recording", "printing", "image printing", and "fabricating" used in the present embodiments may be used synonymously with each other.

Claims

A liquid discharge apparatus comprising:
a liquid discharge head (100) configured to discharge a liquid;

a first tank (111) connected to the liquid discharge head (100) through a head connection channel (114);

a second tank (112) connected to the first tank (111);

a first switch valve (131) configured to open and close the head connection channel (114);

a liquid feeder (125) configured to feed the liquid from the second tank (112) to the first tank (111);

a reverse feeder (126) configured to reversely feed the liquid from the first tank (111) to the second tank (112); and

a controller (400) configured to:
close the first switch valve (131) and drive the liquid feeder (125), to perform a forward feeding operation; and

close the first switch valve (131) and drive the reverse feeder (126), to perform a reverse feeding operation.
The liquid discharge apparatus according to claim 1, further comprising:
a third tank (113) connected to a second tank (112) through a tank connection channel (115); and

a second switch valve (132) configured to open and close the tank connection channel (115),

wherein the controller (400) is configured to:
close the second switch valve (132) and drive the liquid feeder (125), to perform the forward feeding operation; and

close the second switch valve (132) and drive the reverse feeder (126), to perform the reverse feeding operation.
The liquid discharge apparatus according to claim 1 or 2,
wherein the liquid feeder (125) is configured to function as the reverse feeder (126).
The liquid discharge apparatus according to claim 1 or 2, further comprising:
a first channel (121) connecting the second tank (112) and the first tank (111);

a second channel (122) connecting the first tank (111) and the second tank (112); and

a switch (124) configured to switch between the first channel (121) and the second channel (122),

wherein the liquid feeder (125) in the first channel (121) is configured to feed the liquid in one direction from the second tank (112) to the first tank (111),

the reverse feeder (126) is connected to the second tank (112) and is configured to depressurize the second tank (112) to reversely feed the liquid from the first tank (111) to the second tank (112), and

the controller (400) is configured to:
control the switch to switch to the first channel and drive the liquid feeder (125) to perform the forward feeding operation; and

control the switch to switch to the second channel and drive the reverse feeder (126) to perform the reverse feeding operation.
The liquid discharge apparatus according to claim 4,
wherein the first channel (121) comprises:
a common channel (123) connecting the first tank (111) and the switch (124); and

an individual first channel (121a) connecting the switch (124) and the second tank (112) via the liquid feeder (125), and

the second channel (122) comprises:
the common channel (123); and

an individual second channel (122a) separated from the individual first channel (121a) and connecting the switch (124) and the second tank (112).
The liquid discharge apparatus according to claim 5,
wherein the switch (124) is a three-way valve including:
a first port (a) connected to the common channel (123);

a second port (b) connected to the individual first channel (121a); and

a third port (c) connected to the individual second channel (122a), and

the controller (400) is configured to:
open a path (a-b) between the first port (a) and the second port (b) in the switch (124), close a path (a-c) between the third port (c) and the first port (a) in the switch (124), and drives the liquid feeder (125), to perform the forward feeding operation, and

the controller (400) is configured to:
open the path (a-c) between the third port (c) and the first port (a) in the switch (124), close the path (a-b) between the second port (b) and the first port (a) in the switch (124), and drives the reverse feeder (126), to perform the reverse feeding operation.
The liquid discharge apparatus according to claim 2,
wherein the controller (400) is configured to control the liquid feeder (125), the first switch valve (131), and the second switch valve (132) to repeatedly perform the forward feeding operation and the reverse feeding operation while closing the first switch valve (131) and the second switch valve (132) to stir the liquid in the first tank (111) and the second tank (112).
The liquid discharge apparatus according to claim 7, further comprising:
a sensor feeler (205) configured to displace according to a liquid amount in the first tank (111);

an upper limit sensor (211) configured to detect the sensor feeler (205) at an upper limit position at which the liquid amount in the first tank (111) reaches a preset upper limit value; and

a lower limit sensor (212) configured to detect the sensor feeler (205) at a lower limit position at which the liquid amount in the first tank (111) reaches a preset lower limit value,

wherein the controller (400) is configured to control a liquid amount fed by the forward feeding operation and the reverse feeding operation to be within a range detected by the upper limit sensor (211) and the lower limit sensor (212).