WO2017099008A1 - Inkjet recording apparatus and air bubble removal method - Google Patents

Abstract

To provide an inkjet recording apparatus for easily and quickly removing an air bubble in an ink flow path, and an air bubble removal method. The inkjet recording apparatus is provided with: a recording head; a first discharge section (2115); a second discharge section (2116); a feeding unit; and a control unit. In the ink flow path of the recording head, there are disposed an ink flow inlet (2111d), a filter (2118) that filters the ink, a first flow outlet (2111e) to the first discharge section for ink on an upstream side of the filter, a second flow outlet (2111f) to the second discharge section for filtered ink on a downstream side, and a shared ink chamber (2111) having a connecting hole (2111c) to a nozzle for the downstream side ink. The control unit determines an ink feeding amount by the feeding unit so that a minimum flow rate of the ink on the upstream side and a minimum flow rate of the ink on the downstream side are simultaneously equal to or more than a predetermined reference rate.

Description

Ink jet recording apparatus and bubble removing method

The present invention relates to an ink jet recording apparatus and a bubble removing method.

Conventionally, there is an ink jet recording apparatus that performs image recording and formation of a three-dimensional structure by ejecting ink droplets and landing on a recording medium in a desired pattern. In this ink jet recording apparatus, a technique is used in which ink droplets are ejected from a nozzle at a desired amount and speed by pressurizing ink with an appropriate pressure change pattern.

At this time, if foreign matter such as dust or dust is mixed in the ink, the quality of the recorded image and the formed structure will be deteriorated. Therefore, in the inkjet head, before the ink supplied from the ink tank reaches the nozzles, for example, a filter for removing these foreign substances is provided in a common flow path or a common ink chamber immediately before the ink is distributed to each nozzle. It has been.

On the other hand, when bubbles are mixed in the ink, there is a problem that pressure is not properly applied to the ink due to the bubbles and ink ejection failure occurs. On the other hand, there is a technique for removing bubbles in the ink flow path by pressurizing and forcibly discharging or circulating the ink in the ink flow path. In Patent Document 1, a three-way valve is provided at a merging position of a circulation flow path for returning ink to an ink tank from an upstream side and a downstream side of a filter provided in an ink liquid filling unit in a recording head. A technique is disclosed in which such ink is controlled to flow to the ink tank and bubbles are removed as necessary. Further, in Patent Document 2, a first bubble removal path and a second bubble removal path via a filter are respectively provided above the first liquid chamber on the upstream side and the second liquid chamber on the downstream side of the filter in the recording head. There is disclosed a technique for sequentially discharging bubbles generated in each nozzle while adjusting the flow rate so as not to destroy the ink meniscus in the nozzle.

JP 2010-221589 A JP 2012-218398 A

However, with the conventional technology, only one of the upstream and downstream bubbles of the filter can be removed at a time, and the bubbles must be discharged sequentially by switching the flow rate and opening / closing of the valve. There is a problem that it takes time and effort.

An object of the present invention is to provide an ink jet recording apparatus capable of removing bubbles in an ink flow path more easily and quickly and a method for removing bubbles in ink.

In order to achieve the above object, the invention according to claim 1
A recording head having a nozzle for ejecting ink and an ink flow path for supplying ink to the nozzle;
A first discharge path and a second discharge path through which ink discharged from the recording head flows;
A liquid feeding unit that applies pressure to the ink and feeds the ink to the ink flow path;
A control unit that controls the amount of ink fed per unit time by the liquid feeding unit;
With
In the ink flow path, an inflow port through which ink supplied from outside flows in, a filter that filters the ink that flows in from the inflow port, and an upstream ink that does not pass through the filter flow out to the first discharge path. There is provided an ink chamber having a first outlet, a second outlet for allowing the downstream ink filtered by the filter to flow out to the second discharge path, and a nozzle communication port for sending the downstream ink to the nozzle. And
The control unit may determine the liquid feeding amount so that the minimum flow speed of the upstream ink and the minimum flow speed of the downstream ink are simultaneously equal to or higher than a predetermined reference speed.

According to a second aspect of the present invention, in the ink jet recording apparatus of the first aspect,
The ink feeding amount is such that the minimum flow velocity of the upstream ink and the minimum flow velocity of the downstream ink according to the type of the ink that changes within a predetermined assumption range and the viscosity of the ink are within the assumption range. It is characterized in that it is set to a value that is kept above the predetermined reference speed.

According to a third aspect of the present invention, in the ink jet recording apparatus according to the first aspect,
The control unit is characterized in that the ink feeding amount is changed according to at least one of the type of ink and the viscosity of the ink.

The invention according to claim 4 is the ink jet recording apparatus according to any one of claims 1 to 3,
The flow rate of the upstream ink is decreased as compared with the flow rate of the downstream ink corresponding to the liquid supply by the liquid supply unit, or the flow rate of the downstream ink is increased as compared with the flow rate of the upstream ink. Alternatively, a flow rate ratio adjusting unit that decreases the flow rate of the upstream ink and increases the flow rate of the downstream ink is provided.

According to a fifth aspect of the present invention, in the ink jet recording apparatus according to the fourth aspect,
The flow rate ratio adjustment unit is characterized in that a ratio between a minimum flow rate of the upstream ink and a minimum flow rate of the downstream ink is within a predetermined range.

The invention according to claim 6 is the ink jet recording apparatus according to claim 4 or 5,
The flow rate ratio adjusting unit includes a pressure loss unit that applies pressure loss to the upstream ink.

The invention according to claim 7 is the ink jet recording apparatus according to claim 6,
At least a part of the first discharge path is provided with a constricted portion in which the flow path cross-sectional area is locally smaller than the flow path cross-sectional area of the second discharge path.

The invention according to claim 8 is the ink jet recording apparatus according to claim 7,
The constriction portion is formed when the ink is supplied to the ink flow path by the liquid feeding portion under a predetermined condition within a predetermined assumption range related to the type of ink and the viscosity of the ink. The minimum flow velocity to the first outlet is provided to be equal to the minimum velocity of the downstream ink to the second outlet.

The invention according to claim 9 is the ink jet recording apparatus according to claim 7 or 8,
The channel cross-sectional area and the channel length of the narrowed portion are values corresponding to the pressure loss of the filter.

The invention according to claim 10 is the ink jet recording apparatus according to any one of claims 7 to 9,
The narrowed portion includes a narrowing member that is inserted into the first discharge path and reduces a cross-sectional area of the flow path of the first discharge path.

The invention according to claim 11 is the ink jet recording apparatus according to any one of claims 4 to 10,
The flow rate ratio adjustment unit includes a liquid absorption unit that sucks the downstream ink in the second discharge path.

The invention according to claim 12 is the ink jet recording apparatus according to any one of claims 1 to 11,
In the filter, an area of a channel cross section perpendicular to the upstream ink flow from the inlet to the first outlet is constant along the upstream ink flow, and the downstream side The flow path cross section perpendicular to the flow of the ink to the second outlet is provided so as to be constant along the downstream ink flow.

The invention according to claim 13 is the ink jet recording apparatus according to any one of claims 1 to 12,
The predetermined reference speed is 2.31 cm / sec.

The invention according to claim 14 is the ink jet recording apparatus according to any one of claims 1 to 13,
A storage unit that stores in advance the predetermined reference speed or a reference liquid supply amount corresponding to the reference speed;
The control unit is characterized in that when performing a bubble removal operation, the liquid supply amount per unit time is determined with reference to the reference speed or the reference liquid supply amount stored in the storage unit.

The invention as set forth in claim 15 is the ink jet recording apparatus according to any one of claims 1 to 14,
A waste liquid flow path through which ink discharged from the first discharge path and the second discharge path flows in common;
An on-off valve that determines whether ink flows in the waste liquid flow path;
It is characterized by having.

In addition, the invention according to claim 16
A recording head having a nozzle for ejecting ink; an ink flow path for supplying ink to the nozzle; a first discharge path and a second discharge path through which ink discharged from the recording head flows; And a liquid feeding section that feeds ink to the ink flow path, and an ink inlet into which ink supplied from the outside flows into the ink flow path, and ink that has flowed in from the fluid inlet A first outlet for allowing upstream ink that does not pass through the filter to flow to the first discharge path, and a second flow for allowing downstream ink filtered by the filter to flow to the second discharge path. A method for removing bubbles in an ink flow path of an ink jet recording apparatus provided with an ink chamber having an outlet and a nozzle communication port that sends the downstream ink to the nozzle,
The liquid feeding unit supplies, from the inflow port, a reference liquid supply amount per unit time at which the minimum flow speed of the upstream ink and the minimum flow speed of the downstream ink simultaneously exceed a predetermined reference speed. It is said.

According to the present invention, there is an effect that bubbles in the ink flow path can be removed more easily and quickly in the ink jet recording apparatus.

1 is a perspective view illustrating an overall configuration of an ink jet recording apparatus according to an embodiment of the present invention. FIG. 5 is a diagram for explaining the flow of ink in the ink jet recording apparatus. It is a front view of an inkjet head. It is a figure explaining the ink flow path in an inkjet head. It is a figure explaining the ink flow path in an inkjet head. It is a perspective view which shows the example of the constriction member provided in a discharge pipe. It is a block diagram which shows the function structure of an inkjet recording device. It is a flowchart which shows the control procedure of the bubble removal process performed with an inkjet recording device. It is a graph which shows the observation result of the bubble omission state in an upper ink chamber and a lower ink chamber. It is sectional drawing which shows the modification 1 of an inkjet head. It is sectional drawing which shows the modification 2 of an inkjet head. It is sectional drawing which shows the modification 3 of an inkjet head. It is sectional drawing which shows the modification 3 of an inkjet head. It is a front view which shows the modification 4 of an inkjet head.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a perspective view showing the overall configuration of the ink jet recording apparatus of the present embodiment.
The ink jet recording apparatus 100 is of a scan type that forms an image on a two-dimensional surface by a combination of transport movement of a recording medium and movement (scanning) of an ink jet head.
The ink jet recording apparatus 100 includes a transport unit 10, an image forming unit 20, an ink storage unit 30, and the like.

The transport unit 10 transports the recording medium in a predetermined transport direction (+ y direction). The transport unit 10 includes a drive roller 11 and a driven roller (not shown), a transport motor 13, a transport belt 14, and the like.

The transport belt 14 is an endless belt, and moves around with the rotation of the driving roller 11 and a driven roller (not shown). The recording medium is transported by placing the recording medium on the outer peripheral surface (conveying surface) of the conveyor belt 14 that moves around at a predetermined speed.

The driving roller 11 rotates around the central axis according to the rotation operation of the conveyance motor 13, thereby moving the conveyance belt 14 around.

The transport motor 13 rotates the drive roller 11 by being supplied with electric power based on the control of the control unit 40 (see FIG. 6) and being driven to rotate at a predetermined rotational speed.

The image forming unit 20 includes a carriage 22, a scanning unit 23, a maintenance unit 24, a support unit 25, and the like.

A plurality of inkjet heads 211 (see FIG. 2) arranged in a predetermined pattern such as a houndstooth pattern are attached to the carriage 22. In the inkjet head 211, the nozzle opening is disposed on a surface (nozzle surface) facing the transport surface, and ejects ink from the nozzle opening. The inkjet head 211 is provided for each color of ink to be ejected. The ink flow path configuration and the control operation in the image forming unit 20 will be described in detail later.

The carriage 22 holds the plurality of ink jet heads 211 and is reciprocated in the width direction (x direction) perpendicular to the transport direction (y direction) by the scanning unit 23, so that the ink jet head 211 faces the recording medium. The position changes.

The scanning unit 23 moves the carriage 22 in the width direction. The scanning unit 23 includes rails 231 and 232, a scanning motor 233 (see FIG. 6), and the like. The rails 231 and 232 are arranged to extend in the width direction (x direction) in parallel to each other, and hold the carriage 22 by supporting two arm portions provided on the carriage 22 respectively. The scanning motor 233 is driven to move the carriage 22 in the width direction along the rails 231 and 232. The scanning motor 233 is not particularly limited as long as the moving speed and the position of the carriage 22 are accurately determined. For example, a linear motor is used. In this case, the stator of the linear motor is provided on the carriage 22.

The maintenance unit 24 performs a maintenance operation of the inkjet head 211 during a period when the inkjet head 211 does not perform a recording operation on the recording medium. The maintenance unit 24 is provided in a retracted position within the range of movement of the carriage 22 by the scanning unit 23 and out of the conveyance surface of the conveyance unit 10 in the width direction. The maintenance unit 24 performs a maintenance operation in a state where the carriage 22 is moved by the scanning unit 23 and faces each inkjet head 211. The maintenance operation is appropriately determined according to the type of ink, etc., but is a flushing operation in which ink is ejected to the ink tray 241 (see FIG. 2) with a predetermined pressure, or the ink fixed on the nozzle surface of the inkjet head 211 is wiped. A wiping operation of wiping with a member is exemplified.

The ink tray 241 receives this ink and sends it to the waste liquid tank 33 (see FIG. 2) when the ink is ejected from the nozzle opening in association with the operation other than the image recording on the recording medium or when the ink leaks.

The support unit 25 is a frame and a plate for mounting and supporting the above-described components in the image forming unit 20. As the members of the support portion 25, strong members that do not cause displacement and vibration in the ink discharge operation from the inkjet head 211 and the movement of the carriage 22 by the scanning portion 23 are used, and are fixed to each other.

The ink storage unit 30 stores ink of each color used for image formation and supplies it to the inkjet head 211. The ink storage unit 30 is disposed in a dedicated rack or the like, and is connected to the image forming unit 20 via an ink flow path.

Next, a configuration related to the flow of ink from the ink storage unit 30 to the image forming unit 20 in the inkjet recording apparatus 100 of the present embodiment will be described.
FIG. 2 is a diagram for explaining the flow of ink in the inkjet recording apparatus 100 of the present embodiment.

The ink storage unit 30 includes a main tank 31, a filter 31a, a supply valve 31b, a supply pump 32, a waste liquid tank 33, and the like.

The ink in the main tank 31 is sent to the sub tank 212 through the filter 31a and the supply valve 31b by the operation of the supply pump 32. The filter 31a removes foreign matters and impurities in the ink. The supply valve 31 b determines whether ink can be supplied from the main tank 31 to the sub tank 212. The supply valve 31b may be manually switchable when ink is supplied to the main tank 31 or when the main tank 31 is replaced.

The ink supplied from the main tank 31 to the image forming unit 20 by the supply pump 32 includes a sub tank 212, a deaeration unit 213, a liquid supply pump 214 as a liquid supply unit, a three-way switching valve 214b, and a supply flow path 217. The ink discharged from each inkjet head 211 through each of the inkjet heads 211 passes through the waste liquid flow path 219 via the check valve 219a and is sent to the waste liquid tank 33.

The sub tank 212 is an ink tank having a smaller capacity than the main tank 31. The sub tank 212 is opened to air through an opening valve 212a, and maintains the ink at atmospheric pressure. The sub tank 212 is provided with a liquid level sensor 212b. The liquid level sensor 212b detects the amount of ink in the sub tank 212 and outputs it to the control unit 40 (see FIG. 6). The liquid level sensor 212b may simply detect whether the ink amount has fallen below a predetermined lower limit reference value and output a detection signal to the control unit 40.

The deaeration unit 213 removes air in the ink. The deaeration unit 213 includes a deaeration module 213a, a vacuum pump 213b, a pressure sensor 213c, and the like. The degassing module 213a has a structure in which the vacuum flow path reduced by vacuum suction by the vacuum pump 213b and the ink flow path are in contact with each other through the degassing film, and only the air in the ink permeates the degassing film. This removes air from the ink. The pressure sensor 213c is used for abnormality detection such as operation control of the vacuum pump 213b and breakage of the deaeration film.

The liquid feed pump 214 controls the ink degassed by the deaeration unit 213 in the state where the liquid feed valve 214a provided between the liquid feed pump 214 and the deaeration unit 213 is opened (see FIG. 6). The flow is set to the negative pressure forming unit 215 or the detour channel 216 at a flow rate set by (see). A conventionally known pump can be used as the liquid feed pump 214.
A passage for returning ink to the sub tank 212 via the relief valve 212c is branched from between the liquid feed pump 214 and the three-way switching valve 214b, and relief is provided when the ink pressure exceeds a specified value. The valve 212c is opened to release the pressure.

The three-way switching valve 214b switches the destination of the ink delivered by the liquid feed pump 214 to either the negative pressure forming unit 215 or the bypass channel 216 based on the control of the control unit 40. When the destination is switched to the bypass channel 216, the ink is sent directly to the supply channel 217 via the bypass channel 216.

The negative pressure forming unit 215 keeps the pressure of the ink supplied to the inkjet head 211 lower than the air pressure, thereby preventing the ink from leaking from the nozzles at times other than the timing of ejecting the ink, and the ink from the inkjet head 211. Ink corresponding to the amount of ink accompanying the ejection of the ink is supplied to the inkjet head 211 via the protective valve 215a. As the negative pressure forming unit 215, a configuration for generating and maintaining a negative pressure by a conventionally known method can be used. The negative pressure forming unit 215 may include a simple intermediate tank, and may have a similar function by gravity using a height difference from the inkjet head 211.

From the supply flow path 217, an inflow path connected to the inlet 2114 of each inkjet head 211 is branched through a plurality of operation valves 217a. The supply flow path 217 is connected to the waste liquid flow path 219 via the first waste liquid valve 218a on the most downstream side.

The waste liquid channel 219 is connected to an outlet 2117 of each inkjet head 211 via a plurality of check valves 219a. The waste liquid flow path 219 is connected to the waste liquid tank 33 via the second waste liquid valve 218 b (open / close valve), and sends the waste ink flowing in from the outlet 2117 and the supply flow path 217 to the waste liquid tank 33.

FIG. 3 is a front view of the inkjet head 211.
The plurality of inkjet heads 211 attached to the carriage 22 are each in the direction of the front view when viewed from the width direction (x direction).
In the ink jet head 211, an ink discharge unit 2110 is attached to the lower part of a casing B in which a circuit board of the head drive unit 26 (see FIG. 6) that performs an operation of discharging ink is stored.

The ink discharge unit 2110 supplies ink to a nozzle and discharges it as a droplet having an appropriate liquid amount from the opening of the nozzle. The nozzle opening is provided on a surface (nozzle surface) facing the transport surface of the inkjet head 211, and ink is configured to fly and land substantially perpendicularly to the recording medium (transport surface). A plurality of nozzle openings are arranged on the nozzle surface of each inkjet head 211 in a predetermined interval (pitch) in the transport direction. The arrangement pattern of the nozzle openings is not particularly limited, and may be a simple one-dimensional arrangement, or a staggered arrangement having a plurality of rows in the width direction. Nozzle openings provided in the inkjet head 211 adjacent to each other in the transport direction are arranged partially overlapping in the transport direction, so that even when a slight relative position shift occurs, It can be set as the structure which a space | interval does not open too much.
The ink ejection unit 2110 includes a common ink chamber 2111 and a head chip 2112. The ink supplied to the inkjet head 211 is distributed from the common ink chamber 2111 to the individual flow path 2112b (see FIG. 4A) in the head chip 2112. Ink flow paths to each nozzle are provided.

The common ink chamber 2111 is provided to extend in the transport direction (y direction), and is connected to an inlet 2114 into which ink supplied to the inkjet head 211 flows and protrudes upward (z direction). An outlet 2117 for flowing ink discharged from the inkjet head 211 to the waste liquid flow path 219 includes a first discharge section 2115 (first discharge path) and a second discharge section 2116 (second discharge) connected to the common ink chamber 2111. Road) and a connection portion 2117a.

Here, the head chip 2112 has an upper surface (surface opposite to the surface facing the transport surface) joined to the common ink chamber 2111 and a lower surface (surface facing the transport surface) serving as a nozzle surface.

FIGS. 4A and 4B are diagrams illustrating ink flow paths inside the common ink chamber 2111 and the head chip 2112. FIG.

The common ink chamber 2111 forms a manifold that distributes ink to the individual channels 2112b of the head chip 2112 via a plurality of communication ports 2111c (nozzle communication ports) provided on the bottom surface. The inside of the common ink chamber 2111 is divided into upper and lower portions by a filter 2118.

The upper ink chamber 2111a on the upper side of the filter 2118 has a rectangular parallelepiped shape, communicates with the tubular inlet 2114 through an inlet 2111d provided on the upper surface near one end in the major axis direction, and is provided on the upper surface near the other end. The first outlet 2111e communicates with the tubular first discharge portion 2115. The ink flowing into the upper ink chamber 2111a from the inlet 2114 passes through the filter 2118 and flows into the lower ink chamber 2111b below the filter 2118, and can be directly discharged from the first discharge portion 2115.

A constriction member 2115a (flow rate ratio adjustment unit, pressure loss unit, constriction unit) is inserted into the first discharge unit 2115. The constricting member 2115a increases the pressure loss of the ink flowing through the first discharge portion 2115. The increase amount of the pressure loss is preferably set to be approximately the same as the magnitude of the pressure loss that the ink flowing through the second discharge unit 2116 receives when passing through the filter 2118.

The lower ink chamber 2111b has a rectangular parallelepiped shape longer in the major axis direction than the upper ink chamber 2111a, and one end in the major axis direction is a wall surface common to the upper ink chamber 2111a. A second outlet 2111f is provided on the upper surface near the other end, and communicates with the tubular second discharge portion 2116. The ink that has flowed from the upper ink chamber 2111a into the lower ink chamber 2111b through the filter 2118 flows into the individual flow path 2112b of the head chip 2112 through the communication port 2111c and can be discharged from the second discharge portion 2116.

In addition, a buffer member 2119 (damper) is provided in the lower ink chamber 2111b so as to cover the upper side of the communication port 2111c, and is separated from the bottom surface (communication port 2111c). Is absorbed at least in part to reduce the propagation of the influence into the other individual flow path 2112b. As the buffer member 2119, a flexible film whose surface can be deformed according to a change in ink pressure is used, and it may be formed in a bag shape in which gas (air) is sealed.

The ink flow to the first outlet 2111e in the upper ink chamber 2111a and the ink flow to the second outlet 2111f in the lower ink chamber 2111b are in the direction along the major axis direction. Therefore, the area of the channel cross section perpendicular to the ink flow (channel cross-sectional area) is constant along the major axis direction. The ratio of these channel cross-sectional areas is determined by the position of the filter 2118. Further, here, the cross-sectional areas of these flow paths are sufficiently larger than the cross-sectional areas of the first discharge part 2115 (constriction member 2115a) and the second discharge part 2116, respectively. Therefore, the pressure loss related to the ink flow from the inlet 2111d to the connection portion 2117a mainly occurs in the constriction member 2115a and the second discharge portion 2116 in addition to the filter 2118.

The head chip 2112 has individual flow paths 2112b arranged corresponding to the communication ports 2111c of the common ink chamber 2111, respectively. In at least a part of the individual flow path 2112b, it is possible to apply pressure to the ink in a predetermined pattern. Here, at least a part of the wall surface (partition wall) of the individual flow path 2112b is provided so as to be deformable in accordance with the deformation of the piezoelectric element electrically connected to the head driving unit 26, and the individual surface facing the deformable wall surface. The portion of the flow path 2112b forms a pressure chamber that applies a pressure change to the ink. The structure and shape of the individual flow path 2112b can be designed as appropriate.

A nozzle plate 2112a is bonded to the lower surface of the head chip 2112, that is, the surface facing the transport surface. The nozzle plate 2112a is provided with nozzle holes respectively corresponding to the individual flow paths 2112b, and ink is ejected from the nozzle holes in accordance with the pressure pattern applied to the ink in the pressure chamber.

FIG. 5 is a perspective view showing an example of the constriction member 2115a provided in the first discharge part 2115. FIG.
The constriction member 2115a is a tube-shaped member having a hollow through portion Hh, and a connector or the like may be provided so that the outer periphery thereof is equal to the inner periphery of the tubular first discharge portion 2115. Here, connectors Hc1 and Hc2 are attached to the upper end and lower end of the tube Hp having a predetermined length, and are embedded in the first discharge portion 2115.
Here, a narrow groove Ht is provided on the outer surface of the connector Hc1 on the upper end side (downstream side), and when the constriction member 2115a is inserted and attached to the first discharge portion 2115, the connector Hc1 and Hc2 are connected to each other. The air remaining around the tube Hp can be discharged.

As described above, the ratio between the flow path cross-sectional area of the lower ink chamber 2111b and the flow path cross-sectional area of the upper ink chamber 2111a, the pressure loss due to the flow path of the constriction member 2115a, the pressure loss due to the filter 2118, and the second discharge The ratio of the pressure loss of the portion 2116 (substantially equal to the pressure loss due to the filter 2118, so that the length of the constriction member 2115a and the flow path diameter are easily determined according to the pressure loss due to the filter 2118) is determined to be approximately equal. As a result, the ink delivered from the liquid feed pump 214 at the set flow rate passes through the upper ink chamber 2111a and the lower ink chamber 2111b along the both surfaces of the filter 2118 at a substantially constant speed.
Note that the flow rate varies depending on the position in the cross section of the flow path due to the friction on the wall surface of the common ink chamber 2111 and the surface of the filter 2118, and the speed here is the flow path of the upper ink chamber 2111a and the lower ink chamber 2111b. Average flow velocity for the cross section. Alternatively, the setting target may be a speed at a position separated from the surface of the filter 2118 by a predetermined minute distance, for example, 0.5 mm. In this case, adjustments may be made based on actual measurement values or simulation results, and in the case of obtaining analytically appropriate design parameters, terms of smaller values may be omitted as appropriate.

In the ink jet recording apparatus 100, when the air bubbles remain in the common ink chamber 2111 and are mixed and caught on the filter 2118, the ink jet recording apparatus 100 applies pressure to the air bubbles by the flow of the ink to cause the air bubbles to be detached from the filter 2118. Then, the ink flows out of the common ink chamber 2111 from the first outlet 2111e and the second outlet 2111f. The ink flow velocity reference value (predetermined reference velocity) necessary for removing the bubbles depends on the frictional force according to the material of the filter 2118 and the fineness of the eyes. The filter 2118 It depends on the necessary conditions for the foreign material. Therefore, in the inkjet recording apparatus 100, the flow velocity reference value can be determined as a normal constant value.
Note that the flow velocity (nearest flow velocity) in the immediate vicinity of the filter 2118 (for example, a distance of 0.5 mm from the filter 2118) is important for the removal of bubbles. Therefore, the flow velocity reference value is determined so that the latest flow velocity becomes an appropriate value. Bubbles can be easily and reliably removed by simultaneously causing an ink flow above the flow velocity reference value in the upper ink chamber 2111a in contact with the upper surface of the filter 2118 and the lower ink chamber 2111b in contact with the lower surface.

A flow rate setting value (reference liquid supply amount) at which the flow rates of the upper ink chamber 2111a and the lower ink chamber 2111b are both equal to or higher than the flow velocity reference value is inspected and set in advance and stored in the storage unit 403 (see FIG. 6). . Here, depending on the type of flowing ink (reactive ink, dispersed ink, or ink color) and the viscosity of the ink that changes mainly depending on the ink temperature, the pressure loss and the ratio due to the filter 2118 and the constriction member 2115a. Can change. Therefore, the reference liquid supply amount is determined so that the flow rates of the upper ink chamber 2111a and the lower ink chamber 2111b are equal to or higher than the flow velocity reference value even if the pressure loss changes within the expected range of these changes and changes. . On the other hand, if the flow rate ratio between the upper ink chamber 2111a and the lower ink chamber 2111b is greatly deviated from 1: 1, the flow rate for obtaining a flow rate equal to or higher than the flow velocity reference value in both the upper ink chamber 2111a and the lower ink chamber 2111b. The set value increases and the amount of waste liquid increases. Therefore, the size of the constriction member 2115a can be determined so that the maximum value and the minimum value of the flow rate ratio within the assumed range of the change of the ink type and the ink viscosity are within a predetermined range including 1.
For example, in the case where the type is fixed for each inkjet head 211 such as the color of ink, the size (that is, the flow path cross-sectional area and the length) of the appropriate narrowing member 2115a separately for each inkjet head 211. And / or a reference liquid supply amount may be determined. As for the viscosity of the ink, a reference liquid supply amount may be determined for each ink temperature range.
In addition, it is desirable that this flow velocity reference value be higher than the minimum value obtained experimentally or by simulation, etc., in order to ensure that the bubbles are removed. The flow rate reference value may be further reduced to a level that does not cause the occurrence of air bubbles, for example, to a value at which bubbles are generally removed. Such setting may be changeable according to the required image quality to be set.

FIG. 6 is a block diagram showing a functional configuration of the inkjet recording apparatus 100 of the present embodiment.

As described above, the inkjet recording apparatus 100 includes the transport motor 13, the scanning motor 233, the supply valve 31b, the supply pump 32, the liquid level sensor 212b, the vacuum pump 213b, the pressure sensor 213c, and the liquid supply valve. 214a, a liquid feed pump 214, a three-way switching valve 214b, a protection valve 215a, a plurality of operation valves 217a, a first waste liquid valve 218a, a second waste liquid valve 218b, and the like. The ink jet recording apparatus 100 includes a control unit 40, a head driving unit 26, an operation display unit 16, a communication unit 17, a bus 18, and the like.

The control unit 40 controls the overall operation of the inkjet recording apparatus 100. The control unit 40 includes a CPU 401 (Central Processing Unit), a RAM 402 (Random Access 記憶 Memory), a storage unit 403, and the like.

The CPU 401 performs various arithmetic processes and controls the conveyance of the recording medium, the ejection of ink, the maintenance operation, and the like in the inkjet recording apparatus 100. This maintenance operation includes a bubble removal process for removing bubbles in the ink flow path.

The RAM 402 provides a working memory space to the CPU 401 and stores temporary data.
The storage unit 403 includes auxiliary storage means such as a nonvolatile memory or HDD, and stores a control program, initial setting data, setting data to be maintained, and the like. The control program includes a program related to the above-described bubble removal processing, and the initial setting data includes the shape of the inkjet head 211, the type of filter in the common ink chamber, the first discharge unit 2115, and the second discharge unit 2116. And a setting related to a reference liquid supply amount such as a predetermined ink flow rate according to the size and length of the constriction member 2115a and a liquid supply time at the ink flow rate. As described above, the setting related to the reference liquid feeding amount may be separately determined and stored for each ink type. The storage unit 403 includes a RAM that temporarily stores image data to be recorded.

The head drive unit 26 generates and outputs a drive voltage signal for causing the head chamber 2112 to deform the pressure chamber (piezoelectric element) for properly ejecting ink. The head drive unit 26 selects a voltage waveform pattern stored in advance based on a control signal from the control unit 40 and generates a drive voltage signal that is power-amplified, and also according to image data input from the storage unit 403. Whether to output a drive voltage signal to each piezoelectric element is switched.
The wiring related to the head driving unit 26 is wired together with the ink flow path in the inkjet head 211, and is partially formed separately.

The communication unit 17 is a communication interface that controls a communication operation with an external device. As the communication interface, for example, one or a plurality of communication interfaces such as a LAN board and a LAN card corresponding to various communication protocols are included. The communication unit 17 acquires image data to be recorded and setting data (job data) related to image recording from an external device based on the control of the control unit 40, and transmits status information and the like to the external device. I can do it.

The operation display unit 16 displays a status, an operation menu, and the like of the ink jet recording apparatus 100 according to a control signal from the control unit 40, and receives a user operation and outputs it to the control unit 40. The operation display unit 16 includes, for example, a liquid crystal display unit in which a touch sensor as an operation receiving unit is provided so as to overlap with a display screen as a display unit. The control unit 40 indicates the status and various menus for accepting commands by the touch sensor on the liquid crystal display unit, and displays the contents and position information of the displayed menu and the touch operation of the user detected by the touch sensor. A control operation is performed to cause each unit of the inkjet recording apparatus 100 to perform a corresponding process.

The bus 18 is a path for exchanging signals by electrically connecting the above components.

In addition to these configurations, the inkjet recording apparatus 100 includes a notification operation unit such as an LED lamp and / or a beep sound generation unit used for the notification operation, and a line for detecting a poor image quality of an image formed on the recording medium. A reading unit such as a sensor may be provided.

Next, the bubble removal operation in the inkjet recording apparatus 100 of the present embodiment will be described.

In the ink jet recording apparatus 100 of the present embodiment, when refilling ink once removed from the ink flow path at the time of initial ink introduction, maintenance operation, or change of ink type, bubbles are mixed in the ink flow path. In such a case, the ink is allowed to flow into the common ink chamber 2111 of the recording head at the above-described flow velocity reference value or at a slightly higher flow velocity (for example, 1.2 times the flow velocity reference value). The air bubbles caught inside the filter 2118 are removed with the flow of the ink.

As described above, in the three-way switching valve 214b, during normal recording operation, the ink is switched to be sent to the negative pressure forming unit 215, and the ink is transferred from the negative pressure forming unit 215 to the inkjet head 211 as needed according to the ejected ink. In contrast, during the bubble removal operation (maintenance operation), the ink is switched to be sent to the bypass flow path 216, and the liquid is fed by the liquid feed pump 214 at a predetermined flow rate. As a result, ink flows through the upper ink chamber 2111a and the lower ink chamber 2111b at a substantially constant speed and is discharged from the first discharge portion 2115 and the second discharge portion 2116.

FIG. 7 is a flowchart showing a control procedure by the control unit 40 of the bubble removal process executed in the inkjet recording apparatus 100.
This bubble removal process is a maintenance operation when it is manually activated by a user operation, when the inkjet recording apparatus 100 is turned on, when an abnormal image quality is detected during the image recording operation, or the like. Is called from the storage unit 403 by the CPU 401 and executed.

When the bubble removal process is started, the control unit 40 (CPU 401) moves the carriage 22, that is, the inkjet head 211, to the maintenance position, that is, the position where the nozzle surface faces the ink tray 241 (step S101). The control unit 40 closes the protection valve 215a and the first waste liquid valve 218a, opens the operation valve 217a and the second waste liquid valve 218b corresponding to (all in this case) the inkjet head 211 that is a target for removing bubbles, and The switching valve 214b is set on the bypass channel 216 side (step S102).

The control unit 40 acquires the setting related to the reference liquid supply amount corresponding to the flow velocity reference value necessary for removing bubbles from the storage unit 403 (step S103). The control unit 40 operates the liquid feeding pump 214 to send ink to each inkjet head 211 with the acquired reference liquid feeding amount (step S104). The control unit 40 counts the operation time of the liquid feed pump 214 and stops the operation of the liquid feed pump 214 after a preset liquid feed time has elapsed (step S105). Then, the control unit 40 closes the second waste liquid valve 218b (step S106). Other valves are opened and closed according to the subsequent operation. Then, the control unit 40 ends the bubble removal process.

[Example]
An ink jet head was prepared by providing a communication port on the lower surface of the common ink chamber, and joining a head chip provided with an individual flow path corresponding to the communication port.
A filter is provided horizontally in the center in the height direction of the common ink chamber, the flow path cross section of the rectangular parallelepiped upper ink chamber is 36 mm ^2, and the flow path cross section of the rectangular parallelepiped lower ink chamber is 28 mm ² . Cylindrical inflow passages and discharge passages having a diameter of 2.8 mm are provided at both ends of the upper surface of the upper ink chamber, and discharge passages of the same size are provided on the upper surface of the end portion opposite to the inflow passage in the lower ink chamber. It was. A narrowing member having a length of 14 mm having a cylindrical hollow structure with a diameter of 0.9 mm was further inserted into the discharge path provided in the upper ink chamber.

In this ink-jet head, a liquid feed pump was attached to the inflow path, and the state of air bubbles in the upper ink chamber and the lower ink chamber was visually observed while changing the flow rate.

FIG. 8 is a chart showing the observation results of how bubbles are removed in the upper ink chamber and the lower ink chamber.
Here, 25 ° C. Y color reaction ink having a specific gravity of 1.12 and a viscosity of 4.2 ± 0.3 cp (mPa · s) was allowed to flow.

In the upper ink chamber, when the flow rate was 1.25 cm / sec, bubbles did not escape (×), and even when the flow rate was 1.67 cm / sec, the bubbles were almost removed but not completely removed (Δ). On the other hand, when the flow rate was 2.31 cm / sec or more, the bubbles were completely removed (◯).
In the lower ink chamber, bubbles were generally removed at a flow rate of 1.61 cm / sec, but they were not completely removed (Δ), and when the flow rate was 2.14 cm / sec or more, the bubbles were completely removed (◯). .

Thus, a result was obtained that there was a correlation between the degree of bubble removal and the flow rate of ink flowing through each ink chamber.

Also, this Y-color reactive ink increases in viscosity to 5.5 cp when the temperature is lowered to 20 ° C., and decreases to 3.4 cp when the temperature is raised to 30 ° C. In this range, when a total of 150 ml / min of ink was flowed into the upper ink chamber and the lower ink chamber, the ratio of the flow velocity in the upper ink chamber to the flow velocity in the lower ink chamber increased the temperature (decrease in viscosity). It rose from 1.13 to 1.45.

Similarly, for Y-color dispersion ink having a viscosity of 12.6 cp at 20 ° C. and decreasing to 5.3 cp as the temperature is increased to 30 ° C., a total of 150 ml is added to the upper ink chamber and the lower ink chamber in this temperature range. When the ink at a flow rate of / min was flowed, the ratio of the flow rate in the upper ink chamber to the flow rate in the lower ink chamber increased from 0.74 to 0.95 as the temperature increased (decrease in viscosity).

As described above, the ink jet recording apparatus 100 according to the present embodiment includes the ink jet head 211 having the nozzle for ejecting ink, the ink flow path for supplying ink to the nozzle, and the ink discharged from the ink jet head 211. The first discharge unit 2115 and the second discharge unit 2116 that flow, the liquid supply pump 214 that applies pressure to the ink and supplies the ink to the ink flow path, and the ink supply per unit time by the liquid supply pump 214 A control unit 40 that controls the amount of the ink, and an ink inlet 2111d into which ink supplied from the outside flows, a filter 2118 that filters the ink that flows in from the inlet 2111d, and a filter 2118 are provided in the ink flow path. A first outlet 2111e for allowing the upstream ink that does not pass to flow out to the first discharge portion 2115, and a filter; A common ink chamber 2111 having a second outlet 2111f that allows the downstream ink filtered by 118 to flow out to the second discharge portion 2116 and a communication port 2111c that sends the downstream ink to the nozzle is provided. The flow rate of the upstream ink to the first outlet 2111e in the upper ink chamber 2111a and the flow rate of the downstream ink to the second outlet 2111f in the lower ink chamber 2111b are simultaneously greater than or equal to a predetermined reference speed (2.31 cm / sec). The ink feed reference amount is determined so that
As a result, liquid is fed from the liquid feed pump 214 at the liquid feed reference amount, so that bubbles in both the upper ink chamber 2111a and the lower ink chamber 2111b can be removed at a time. Accordingly, bubbles in the ink flow path can be removed more easily and quickly.
As described above, the velocity (flow velocity) referred to here is an average velocity with respect to the flow path cross section of the upper ink chamber 2111a and the lower ink chamber 2111b.

Further, the ink supply reference amount is the minimum flow rate of the upstream ink and the minimum flow rate of the downstream ink corresponding to the type of ink that changes within a predetermined assumed range and the viscosity of the ink (that is, the ink temperature). Is determined to be a value that is kept above the reference speed within the above-mentioned assumed range.
Therefore, even if the temperature fluctuates slightly during the operation of the inkjet head 211, bubbles in the ink flow path can be easily and quickly removed without greatly reducing the efficiency.

Further, the control unit 40 changes the amount of ink fed by the liquid feed pump 214 in accordance with at least one of the ink color, the type of reactive ink / dispersed ink, and the viscosity (temperature) of the ink. That is, the magnitude and ratio of the pressure loss due to the filter 2118 and the pressure loss due to the constriction member 2115a vary depending on the type and state of the flowing ink, and accordingly the flow rates of the upstream ink and the downstream ink are approximately equal. The bubbles can be efficiently removed without wasting a lot of ink. In particular, once the ink type is set, it is not necessary to perform a detection operation or a control operation for changing the liquid feeding amount during the use of the ink, so that bubbles can be removed easily and more efficiently. .

Further, since the narrowing member 2115a for reducing the flow rate of the upstream ink as compared with the flow rate of the downstream ink corresponding to the liquid feed by the liquid feed pump 214 is provided, the flow rate of the downstream ink exceeds the reference speed by a single liquid feed. Therefore, it is not necessary to flow a large amount of ink by extremely increasing the flow rate of the downstream ink.

Further, the size (the cross-sectional area and the length of the flow path) of the constricting member 2115a is appropriately determined, and the ratio between the minimum flow rate of the upstream ink and the minimum flow rate of the downstream ink is assumed within a predetermined range, particularly in advance. The upstream ink flow rate at a predetermined liquid feed rate (150 ml / min) by the liquid feed pump 214 with respect to the range of ink type and ink viscosity (temperature) (for example, 20 to 30 ° C. for the Y color ink described above) In addition, the flow rate of the ink on the downstream side and the flow rate of the downstream ink are both kept within the reference speed (0.74 to 1.49), and the upstream ink or the downstream ink, whichever has the higher flow rate, is more than necessary. It can be prevented from flowing. Thereby, since it is not necessary to use the liquid pump 214 having extremely high capacity for removing bubbles, it is possible to avoid an increase in cost and an increase in size. In addition, since the necessary ink flow rate can be suppressed, the amount of wasted ink can be reduced.

Further, since the channel cross-sectional area and the channel length of the constriction member 2115a are set according to the pressure loss of the filter 2118, the ink flow to the first outlet 2111e and the lower ink in the upper ink chamber 2111a can be easily and appropriately performed. The speed of the ink flow to the second outlet 2111f in the chamber 2111b can be determined with a good balance.

Further, the constriction part of the first discharge part 2115 is formed by inserting a constriction member 2115a for reducing the flow path cross-sectional area of the first discharge part 2115 into the first discharge part 2115, so that the first discharge of the original design is performed. Improvement can be easily made by adding parts while maintaining the portion 2115. In addition, the narrowed portion can be formed more easily than forming a pipe having a locally narrowed portion.

Further, the filter 2118 has an area of the flow path cross section perpendicular to the ink flow in the upper ink chamber 2111a from the inlet 2111d to the first outlet 2111e, so that the ink in the major axis direction of the upper ink chamber 2111a The flow of ink in the major axis direction of the lower ink chamber 2111b is constant along the flow, and the area of the flow path cross section perpendicular to the flow of the ink in the lower ink chamber 2111b to the second outlet 2111f is Therefore, the flow velocity can be kept substantially constant along the major axis, so that the relationship between the flow velocity and the flow rate can be easily determined, and the flow passage cross-sectional area is large. It is not necessary to set a large flow rate in accordance with. In particular, the pressure loss is not increased unnecessarily by the occurrence of stagnation and vortices according to the shape of the wall surface of each ink chamber.

By setting the flow velocity reference value to 2.31 cm / sec, air bubbles can be easily removed simultaneously in the upper ink chamber 2111a and the lower ink chamber 2111b in the common ink chamber 2111 of the ink jet head 211 that is normally used at present. I can do it.

In addition, a storage unit 403 that stores in advance a flow velocity reference value or a reference liquid supply amount corresponding to the flow velocity reference value is provided, and the control unit 40 stores the flow velocity reference value stored in the storage unit 403 when performing a bubble removal operation. Alternatively, the liquid feed amount per unit time by the liquid feed pump 214 is determined with reference to the reference liquid feed amount.
Accordingly, bubbles can be removed simultaneously in both the upper ink chamber 2111a and the lower ink chamber 2111b appropriately with easy control.

Also, a waste liquid channel 219 through which the ink discharged from the first discharge unit 2115 and the second discharge unit 2116 flows in common, and a second waste liquid valve 218 b that determines whether ink flows in the waste liquid channel 219 are provided.
In this way, by allowing bubbles to be removed simultaneously in the upper ink chamber 2111a and the lower ink chamber 2111b, the valve control relating to the ink waste liquid from the inkjet head 211 is integrated into one of the second waste liquid valves 218b. Therefore, the processing becomes easier than in the prior art, which requires switching between two or three-way valves, and the cost can be reduced.

Further, the bubble removal method in the ink flow path of the ink jet recording apparatus 100 of the present embodiment includes an ink jet head 211 having a nozzle for ejecting ink and an ink flow path for supplying ink to the nozzle, and the ink jet head 211. A first discharge unit 2115 and a second discharge unit 2116 through which ink discharged from the liquid flows, a liquid feed pump 214 that applies pressure to the ink to feed the ink to the ink flow path, and a unit by the liquid feed pump 214 A control unit 40 that controls the amount of ink fed per time, and an ink inlet 2111d into which ink supplied from the outside flows into the ink flow path, and a filter 2118 that filters ink that flows in from the inlet 2111d. And a first outlet that causes the upstream ink that does not pass through the filter 2118 to flow out to the first discharge portion 2115. A common ink chamber 2111 having 111e, a second outlet 2111f that allows the downstream ink filtered by the filter 2118 to flow to the second discharge portion 2116, and a communication port 2111c that sends the downstream ink to the nozzle, is provided. Ink of the inkjet recording apparatus 100 in which at least a part of the first discharge unit 2115 is provided with a constriction member 2115a having a narrowing portion whose flow passage cross-sectional area is locally smaller than the flow passage cross-sectional area of the second discharge portion 2116. This is a method for removing bubbles in a flow path, and a liquid feed pump 214 supplies a reference liquid supply amount per unit time at which the flow rates of upstream ink and downstream ink simultaneously exceed a predetermined flow rate reference value from an inlet 2111d. Supply.
By such an operation, bubbles in both the upper ink chamber 2111a and the lower ink chamber 2111b can be removed at a time. Accordingly, bubbles in the ink flow path can be removed more easily and quickly.

[Modification]
9A to 11 are diagrams showing modifications of the ink flow path of the ink jet head in the ink jet recording apparatus 100 of the present embodiment.
In the inkjet head 211a of Modification 1 shown in the cross-sectional view of FIG. 9A, a first discharge portion 2115b is provided instead of the first discharge portion 2115 and the constriction member 2115a provided therein. The other points are the same as those of the inkjet head 211, and the same components are denoted by the same reference numerals and the description thereof is omitted.

In the inkjet head 211a of the first modification, the first discharge portion 2115b has a constricted portion in which the flow path cross-sectional area is reduced in the middle. As described above, since the first discharge portion 2115b itself has the constriction portion, in this inkjet recording apparatus 100, it is not necessary to separately arrange and join the constriction member 2115a in the tube of the first discharge portion.

The inkjet head 211b of Modification 2 shown in the cross-sectional view of FIG. 9B differs from the inkjet head 211 of the above-described embodiment in the arrangement of the filter 2118, and accordingly, the first outlet 2111e in the upper ink chamber 2111a is connected to the inkjet head 211b. The same as the inkjet head 211 except that the flow path shape (flow path cross-sectional area) related to the flow of ink and the flow of ink to the second outlet 2111f in the lower ink chamber 2111b changes in the flow path, The same components are denoted by the same reference numerals and description thereof is omitted.

In the inkjet head 211b of Modification 2, the filter 2118 is provided obliquely upward in the direction (leftward in the drawing) from the inlet 2111d side to the first outlet 2111e and the second outlet 2111f. This makes it easier for air bubbles mixed in on the lower ink chamber 2111b side to flow to the second outlet 2111f according to buoyancy. On the other hand, since the flow path cross-sectional area of the lower ink chamber 2111b increases toward the second discharge portion 2116, the flow velocity decreases with respect to a constant flow rate of ink. Similarly, the flow path cross-sectional area of the upper ink chamber 2111a becomes narrower toward the first outlet 2111e, so that the flow velocity increases for a constant flow of ink.

In the inkjet head 211b, in order to appropriately remove the bubbles caught on the filter 2118, in the inkjet recording apparatus 100 including the inkjet head 211b, the upper ink chamber 2111a has the largest channel cross-sectional area and the lower ink chamber 2111b. The liquid feed amount by the liquid feed pump 214 is set so that the flow velocity (minimum flow velocity) at the position where the flow path cross-sectional area is the largest, that is, the position where the flow velocity is the slowest, simultaneously becomes equal to or higher than the reference flow velocity.

In the inkjet head 211c of the third modified example shown in the cross-sectional view of FIG. 10A, the first discharge portion 2115c is made longer than the second discharge portion 2116c and bent to the first discharge portion 2115c instead of using the narrowing member 2115a. Pressure loss is given by providing. Or any one of these may be sufficient. In particular, this assumption is made so that the ratio between the minimum ink flow velocity in the upper ink chamber 2111a and the minimum ink flow velocity in the lower ink chamber 2111b is within a predetermined range within the assumed range of ink type and viscosity. The inkjet head 211c is configured so that the ratio is 1: 1 at an optimal setting value related to a predetermined condition within a range, for example, an average viscosity value, a median value, and an ink ejection operation within an assumed temperature range of a specific ink. As a result, the flow rate for obtaining a flow rate higher than the reference flow rate in both the upper ink chamber 2111a and the lower ink chamber 2111b is not increased more than necessary.

Furthermore, a heater 2116q (flow rate ratio adjusting unit) is provided so as to cover the second discharge unit 2116c, and heats the ink flowing through the second discharge unit 2116c. In the case of using ink whose viscosity is lowered due to temperature rise, the pressure loss of the ink flowing through the second discharge portion 2116c can be further reduced by increasing the temperature of the ink flowing through the second discharge portion 2116c. Alternatively, a cooler may be provided so as to cover the first discharge part 2115c, thereby lowering the temperature of the ink flowing through the first discharge part 2115c to increase the viscosity and further increasing the pressure loss.

Further, instead of or in addition to applying pressure loss by the constriction member 2115a in the first discharge part 2115c, as shown in the cross-sectional view of FIG. 10B, pressure loss is applied by the constriction member 2111p in the upper ink chamber 2111a. There may be. The narrowing member 2111p is disposed so as not to prevent ink from flowing in from the inflow port 2111d or passing through the ink filter 2118. In addition, as described above, when the flow path cross-sectional area related to the flow of the upper ink chamber 2111a to the first outlet 2111e is sufficiently larger than the flow path cross-sectional area of the first discharge portion 2115c, sufficient pressure loss is caused. Is assumed to be sufficiently long in the direction perpendicular to the flow path cross section, or the flow path cross-sectional area is locally reduced in the vicinity of the first outlet 2111e.

In the inkjet head 211d of the fourth modified example shown in the front view of FIG. 11, ink is absorbed from the upper ink chamber 2111a and the lower ink chamber 2111b in the middle of the first discharge portion 2115 and the second discharge portion 2116, respectively. Suction pumps 2115d and 2116d (flow rate ratio adjustment unit, liquid absorption unit) are provided. In this case, by setting the liquid absorption amount of the suction pump 2116d provided in the second discharge part 2116 to be larger than that of the suction pump 2115d provided in the first discharge part 2115, the filter 2118 for ink flowing through the lower ink chamber 2111b. It can be configured to compensate for the pressure loss due to. Alternatively, the suction pump 2116d may be provided only in the second discharge unit 2116.
In this case, if the total liquid absorption amount is made too large compared to the liquid supply amount by the liquid supply pump 214, air further enters from the nozzles and bubbles are not removed, so that the liquid absorption amount is appropriately adjusted. Need to be defined.

As described above, in the inkjet head 211d of the fourth modification, the flow rate of the downstream ink is set to be lower than the flow rate of the upstream ink while the flow rate of the upstream side ink is not changed or decreased compared to the flow rate of the downstream ink. A suction pump 2116 d for raising is provided in the middle of the second discharge unit 2116. Accordingly, when the pressure loss due to the filter 2118 is compensated and the flow rate of the downstream ink is set to be equal to or higher than the reference speed according to the liquid feed by the liquid feed pump 214, the flow rate of the upstream ink is extremely increased to increase the ink flow rate. Do not increase.

The present invention is not limited to the above-described embodiment, and various modifications can be made.
For example, in the above embodiment, the filter 2118 divides the common ink chamber 2111 into upper and lower ink chambers 2111a and 2111b, but it may be divided in the left-right direction. Further, the rectangular parallelepiped common ink chamber 2111 has been described as an example. However, the common ink chamber 2111 may be curved in a range where the common ink chamber 2111 is not in contact with the filter 2118, or the inlet 2111d, the first outlet 2111e, and the first outlet. A part or all of the two outlets 2111f may be provided in addition to the upper surfaces of the upper ink chamber 2111a and the lower ink chamber 2111b.

In addition, the configuration of the ink flow path before and after the ink jet head 211 shown in the above embodiment is the supply of a predetermined ink flow rate for ink discharge related to normal image recording from the ink jet head 211 and for maintenance such as bubble removal. Any configuration that can supply ink that is sometimes required can be appropriately changed.

In the above embodiment, the individual flow path 2112b is expressed in a simple rectangular parallelepiped shape. However, the structure of the individual flow path 2112b depends on the manufacturing method of the head chip 2112, the shape of the pressure chamber, the method of applying pressure, and the like. May be appropriately bent or the channel cross-sectional area may be locally changed. Further, when there is no need according to such a structure, the buffer member 2119 is not necessarily provided.

Further, in the above embodiment, the ink that has flowed out of the first discharge unit 2115 and the second discharge unit 2116 through the waste liquid flow path 219 is sent to the waste liquid tank 33 as it is to be discarded, but is returned to the sub tank 212. It may be configured to be recycled.

In the above embodiment, the first discharge part 2115 and the second discharge part 2116 are joined at the connection part 2117a and then connected to the waste liquid flow path 219 via the outlet. However, they may be connected individually. . Even with such a connection, the bubble removal operation can be easily performed all at once, and the amount of waste ink is not increased unnecessarily.

In the above embodiment, the ink jet recording apparatus having a scan type ink jet head has been described as an example. However, the present invention is not limited thereto, and an ink jet recording apparatus having a line head may be used.
In addition, specific details such as configurations and settings shown in the above embodiments can be changed as appropriate without departing from the spirit of the present invention.

The present invention can be used for an ink jet recording apparatus and a bubble removing method.

DESCRIPTION OF SYMBOLS 10 Conveyance part 11 Drive roller 12 Driven roller 13 Conveyance motor 14 Conveyor belt 16 Operation display part 17 Communication part 18 Bus 20 Image formation part 22 Carriage 23 Scan part 231 Rail 233 Scan motor 24 Maintenance part 241 Ink tray 25 Support part 26 Head drive Unit 30 Ink storage unit 31 Main tank 31a Filter 31b Supply valve 32 Supply pump 33 Waste liquid tank 40 Control unit 401 CPU
402 RAM
403 Storage unit 100 Inkjet recording apparatus 211, 211a to 211d Inkjet head 2110 Ink ejection unit 2111 Common ink chamber 2111a Upper ink chamber 2111b Lower ink chamber 2111c Communication port 2111d Inlet port 2111e First outlet port 2111f Second outlet port 2111p Narrowing member 2112 Head chip 2112a Nozzle plate 2112b Individual flow path 2114 Inlet 2115 First discharge part 2115a Narrowing member 2115b, 2115c First discharge part 2115d Suction pump 2116, 2116c Second discharge part 2116d Suction pump 2116q Heater 2117 Outlet 2117a Connection part 2118 Filter 2119 Buffer Member 212 Sub tank 212 Opening valve 212b Liquid level sensor 212c Relief valve 213 Deaeration part 213a Deaeration module 213b Vacuum pump 213c Pressure sensor 214 Liquid supply pump 214a Liquid supply valve 214b Three-way switching valve 215 Negative pressure formation part 215a Protection valve 216 Bypass flow path 217 Supply flow Path 217a operation valve 218a first waste liquid valve 218b second waste liquid valve 219 waste liquid flow path 219a check valve B housing Hc1 connector Hh penetrating portion Hp tube Ht narrow groove

Claims (16)

1. A recording head having a nozzle for ejecting ink and an ink flow path for supplying ink to the nozzle;
   A first discharge path and a second discharge path through which ink discharged from the recording head flows;
   A liquid feeding unit that applies pressure to the ink and feeds the ink to the ink flow path;
   A control unit that controls the amount of ink fed per unit time by the liquid feeding unit;
   With
   In the ink flow path, an inflow port through which ink supplied from outside flows in, a filter that filters the ink that flows in from the inflow port, and an upstream ink that does not pass through the filter flow out to the first discharge path. There is provided an ink chamber having a first outlet, a second outlet for allowing the downstream ink filtered by the filter to flow out to the second discharge path, and a nozzle communication port for sending the downstream ink to the nozzle. And
   The ink jet recording apparatus, wherein the control unit determines the ink feeding amount so that the minimum flow speed of the upstream ink and the minimum flow speed of the downstream ink simultaneously become equal to or higher than a predetermined reference speed.
2. The ink feeding amount is such that the minimum flow velocity of the upstream ink and the minimum flow velocity of the downstream ink according to the type of the ink that changes within a predetermined assumption range and the viscosity of the ink are within the assumption range. 2. The ink jet recording apparatus according to claim 1, wherein the value is set to a value maintained at or above the predetermined reference speed.
3. 2. The ink jet recording apparatus according to claim 1, wherein the control unit changes the ink feeding amount according to at least one of the type of ink and the viscosity of the ink.
4. The flow rate of the upstream ink is decreased as compared with the flow rate of the downstream ink corresponding to the liquid supply by the liquid supply unit, or the flow rate of the downstream ink is increased as compared with the flow rate of the upstream ink. The inkjet recording apparatus according to any one of claims 1 to 3, further comprising a flow rate ratio adjusting unit that reduces the flow rate of the upstream ink and increases the flow rate of the downstream ink.
5. 5. The ink jet recording apparatus according to claim 4, wherein the flow rate ratio adjusting unit causes a ratio of a minimum flow rate of the upstream ink and a minimum flow rate of the downstream ink to fall within a predetermined range.
6. 6. The ink jet recording apparatus according to claim 4, wherein the flow rate ratio adjusting unit includes a pressure loss unit that applies pressure loss to the upstream ink.
7. 7. The constriction part in which the flow path cross-sectional area is locally smaller than the flow path cross-sectional area of the second discharge path is provided in at least a part of the first discharge path. Inkjet recording apparatus.
8. The constriction portion is formed when the ink is supplied to the ink flow path by the liquid feeding portion under a predetermined condition within a predetermined assumption range related to the type of ink and the viscosity of the ink. 8. The ink jet recording apparatus according to claim 7, wherein a minimum flow velocity to the first outlet and a minimum velocity of the downstream ink to the second outlet are equal.
9. 9. The ink jet recording apparatus according to claim 7, wherein a flow path cross-sectional area and a flow path length of the narrowed portion are values corresponding to a pressure loss of the filter.
10. The inkjet according to any one of claims 7 to 9, wherein the constriction portion includes a constriction member that is inserted into the first discharge passage and reduces a cross-sectional area of the first discharge passage. Recording device.
11. The inkjet recording apparatus according to any one of claims 4 to 10, wherein the flow rate ratio adjusting unit includes a liquid absorbing unit configured to suck the downstream ink in the second discharge path.
12. In the filter, an area of a channel cross section perpendicular to the upstream ink flow from the inlet to the first outlet is constant along the upstream ink flow, and the downstream side 12. The flow path cross section perpendicular to the flow of ink to the second outlet is provided so as to be constant along the flow of the downstream ink. The ink jet recording apparatus according to any one of the above.
13. 13. The ink jet recording apparatus according to claim 1, wherein the predetermined reference speed is 2.31 cm / sec.
14. A storage unit that stores in advance the predetermined reference speed or a reference liquid supply amount corresponding to the reference speed;
    The said control part determines the liquid feeding amount per said unit time with reference to the said reference speed or the said reference | standard liquid feeding amount memorize | stored in the said memory | storage part, when performing the bubble removal operation | movement. 14. The ink jet recording apparatus according to any one of 1 to 13.
15. A waste liquid flow path through which ink discharged from the first discharge path and the second discharge path flows in common;
    An on-off valve that determines whether ink flows in the waste liquid flow path;
    The inkjet recording apparatus according to any one of claims 1 to 14, further comprising:
16. A recording head having a nozzle for ejecting ink; an ink flow path for supplying ink to the nozzle; a first discharge path and a second discharge path through which ink discharged from the recording head flows; And a liquid feeding section that feeds ink to the ink flow path, and an ink inlet into which ink supplied from the outside flows into the ink flow path, and ink that has flowed in from the fluid inlet A first outlet for allowing upstream ink that does not pass through the filter to flow to the first discharge path, and a second flow for allowing downstream ink filtered by the filter to flow to the second discharge path. A method for removing bubbles in an ink flow path of an ink jet recording apparatus provided with an ink chamber having an outlet and a nozzle communication port that sends the downstream ink to the nozzle,
    The liquid feeding unit supplies, from the inflow port, a reference liquid supply amount per unit time at which the minimum flow speed of the upstream ink and the minimum flow speed of the downstream ink simultaneously exceed a predetermined reference speed. A method for removing bubbles.

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