Patent Application
20120026262
The present application claims priority from Japanese Patent Application No. 2010-154949, which was filed on Jul. 7, 2010, the disclosure of which is herein incorporated by reference in its entirety.
The present invention relates to a liquid ejection head having ejection ports ejecting a liquid, and a recording apparatus having the liquid ejection head.
A recording head disclosed in Patent Document 1 has an ink flow channel. The ink flow channel includes a flow channel which supplies ink to ejection ports ejecting ink and a flow channel which discharges ink from the flow channel outside the recording head. In the related art, a technique is known in which a filter is provided in a flow channel of the head to filter a liquid, such as ink. When the above-described filter is provided in the flow channel of the head, the head is configured as described in Patent Document 2 so as to remove bubbles remaining in the filter. A liquid flows from the supply side of the flow channel provided in the head to the discharge side, such that bubbles remaining in the filter are removed.
In order to adjust the flow rate of the liquid flowing toward the ejection ports, a sub flow channel is provided separately from a main flow channel, in which the liquid is directed from the supply side of the flow channel to the discharge side, such that the liquid bypasses the supply side and the discharge side of the main flow channel. This is because, if the flow rate of the liquid toward the ejection ports is high, a meniscus formed in the ejection ports may be broken, and the liquid may be unnecessarily ejected from the ejection ports.
In this configuration, if the viscosity of the liquid decreases due to variations in the environmental conditions outside the head, or the like, a high flow rate is required to sweep out bubbles in the main flow channel. Meanwhile, if the flow rate of the liquid which is supplied to the head increases, the flow rate of the liquid in the main flow channel increases, and the flow rate in the sub flow channel also increases. For this reason, the flow rate in the main flow channel insufficiently increases, such that the ability to sweep out bubbles from the filter may be insufficiently exhibited.
An object of the invention is to provide a liquid ejection head which easily secures the ability to sweep out bubbles from a filter in accordance with variations in the environmental conditions, and a recording apparatus having the liquid ejection head.
According to an aspect of the invention, there is provided a liquid ejection head comprising: an ejection port for ejecting a liquid; a supply section and a discharge section for the liquid; a main flow channel which connects the supply section and the discharge section; a supply flow channel which branches off from the main flow channel and supplies the liquid to the ejection port; a filter which is disposed in the vicinity of a branch position in which the supply flow channel is branched from the main flow channel; and a sub flow channel, one end of which is connected to a first connection position closer to the supply section rather than the branch position in the main flow channel, and the other end of which is connected to a second connection position closer to the discharge section rather than the branch position in the main flow channel, wherein the main flow channel and the sub flow channel are formed such that, in supplying the liquid from the supply section to the main flow channel at a predetermined flow rate, the higher the predetermined flow rate is, the more the ratio of a flow rate in the main flow channel from the first connection position to the second connection position to a flow rate in the sub flow channel increases.
According to another aspect of the invention, there is provided a recording apparatus comprising: the liquid ejection head described above; a liquid supply unit which supplies a liquid from the supply section to the main flow channel; a return flow channel which returns the liquid from the discharge section to the liquid supply unit; and a valve which switches a state where the liquid flows through the return flow channel and a state where the liquid does not flow through the return flow channel.
With the liquid ejection head and the recording apparatus according to the aspects of the invention, the main flow channel and the sub flow channel are formed such that, when the flow rate of the liquid which is supplied from the supply section to the head increases, the ratio of the flow rate in the main flow channel to the flow rate in the sub flow channel increases. For this reason, if the flow rate of the liquid which is supplied from the supply section to the head increases, the liquid easily flows into the main flow channel rather than the sub flow channel. Therefore, when the flow rate of the entire liquid which is supplied to the head increases because the viscosity of the liquid decreases, or the like, it is easy to secure the ability to sweep out bubbles remaining in the filters.
Illustrative aspects of the invention will be described in detail with reference to the following figures wherein:
Hereinafter, a preferred embodiment of the invention will be described with reference to the drawings.
First, the overall configuration of an ink jet printer according to an embodiment of the invention will be described with reference to
The printer 500 has a rectangular parallelepiped housing 501a. A sheet discharge section 531 is provided above the top panel of the housing 501a. The internal space of the housing 501a can be divided into spaces A, B, and C in order from above. In the space A, conveying of a sheet P and image formation on the sheet P are performed. In the space B, an operation relating to sheet feed is carried out. In the space C, main tanks 58 as an ink supply source are accommodated.
In the space A are provided four heads 1, ink supply units 50 which supply ink to the heads 1, a conveying unit 521 which conveys the sheet P, guide portions which guide the sheet P, and the like. At the upper part of the space A, a controller 501 (supply control means) is arranged to control the operations of the respective sections of the printer 500 to manage the overall operation of the printer 500.
Each head 1 substantially has a rectangular parallelepiped shape which is elongated in the main scanning direction. The four heads 1 are arranged in parallel at a predetermined pitch in the sub scanning direction and supported by the housing 501a through a head frame 503. Ink droplets of magenta, cyan, yellow, and black are respectively ejected from the lower surfaces 4a (ejection surfaces) of the four heads 1 onto the sheet P. The ink supply units 50 supply ink from the main tanks 58 to the heads 1. A temperature sensor 1a is fixed to each of the heads 1, and the detection result of the temperature sensor 1a is sent to the controller 501. The specific configuration of the heads 1 and the ink supply units 50 will be described below in detail.
The conveying unit 521 has two belt rollers 506 and 507, an endless conveying belt 508 which is wound around both rollers 506 and 507, a nip roller 504 and a separating plate 505 which are arranged outward of the conveying belt 508, a platen 519 which is arranged inward of the conveying belt 508, and the like. The belt roller 507 is a driving roller and rotates with driving of a conveying motor (not shown) in the clockwise direction of
The guide portions are arranged on both sides of the conveying unit 521 so as to sandwich the conveying unit 521 therebetween. The upstream-side guide portion has two guides 527a and 527b, and a pair of feed rollers 526. This guide portion connects a sheet feed unit 501b (described below) and the conveying unit 521. The downstream-side guide portion has two guides 529a and 529b, and two pairs of feed rollers 582. This guide portion connects the conveying unit 521 and the sheet discharge section 531.
In the space B, the sheet feed unit 501b is arranged. The sheet feed unit 501b has a sheet feed tray 523 and a sheet feed roller 525, and the sheet feed tray 523 is provided detachably with respect to the housing 501a. The sheet feed tray 523 is a box which is opened upward and stores a plurality of sheets P. The sheet feed roller 525 sends the uppermost sheet P in the sheet feed tray 523 under the control of the controller 501 and feeds the sheet to the upstream-side guide portion.
As described above, in the spaces A and B, a sheet conveying path is formed from the sheet feed unit 501b to the sheet discharge section 531 through the conveying unit 521. The controller 501 sends the sheet P from the sheet feed roller 523 on the basis of a recording command. The sheet P is sent to the conveying unit 521 through the upstream-side guide portion. When the sheet P passes through directly below the ejection surfaces 4a of the heads 1 in the sub scanning direction, ink droplets are sequentially ejected from the heads 1, and a desired color image is formed on the sheet P. Thereafter, the sheet P is separated from the outer circumferential surface 508a by the separating plate 505 and discharged to the upper sheet discharge section 531 through the downstream-side guide portion.
The sub scanning direction is the direction parallel to the conveying direction of the sheet P by the conveying unit 521, and the main scanning direction is the direction perpendicular to the sub scanning direction along the horizontal plane.
In the space C, a tank unit 501c is provided detachably with respect to the housing 501a. The tank unit 501c has a tray 535 and four main tanks 58. The four main tanks 58 correspond to the four heads 1 one-to-one, and are arranged in parallel in the sub scanning direction in the tray 535.
Hereinafter, the heads 1 will be described with reference to
The filter unit 2 has a unit main body 20 made of a resin material, and performs filtering of ink and adjustment of flow channel resistance. As shown in
As shown in
The upper filter chamber 24a communicates with the joint 2a through a communicating flow channel 21 (discharge flow channel) formed in the unit main body 20. At one end of the upper filter chamber 24a near the joint 2a in the main scanning direction, a communicating hole 21a which is a communicating portion with the communicating flow channel 21 is formed. The communicating hole 21a passes through the unit main body 20 vertically. The communicating flow channel 21 is a concave portion (see
The low filter chamber 24b is a concave portion (see
As shown in
The linear flow channel 26 is constituted by a concave portion which is opened in the upper surface of the unit main body 20 (
The linear flow channel 26 communicates with an end portion of the lower filter chamber 24b on the linear flow channel 26 side through a communicating flow channel 23 in an end portion on the lower filter chamber 24b (see
The end portion of the linear flow channel 26 on the joint 2c communicates with the joint 2c through a communicating flow channel 29 (see
As shown in
Through holes 31a and 31b are formed in both end portions of the flat plate member 31 in the main scanning direction. All the through holes 31a and 31b are arranged at the center of the flat plate member 31 in the sub scanning direction. In the flat plate member 32, through holes 32a and 32b are formed at the positions facing the through holes 31a and 31b. A reservoir 32c is formed in the main scanning direction between the through hole 32a and the through hole 32b. The reservoir 32c forms a storage space which stores ink in the reservoir unit 3. The reservoir 32c is formed such that a portion other than end portions 32x and 32y substantially has a certain width over the entire width of the flat plate member 32 with respect to the sub scanning direction. As shown in
In the flat plate member 33, as shown in
The flat plate members 34x and 34y face near the edge of the flat plate member 33. In the flat plate member 34x, dropping flow channels 34a are formed to face the dropping flow channels 33a and 33b. The flat plate members 34x and 34y are arranged at the positions away from the actuator units 5 (described below) in plan view. The flat plate members 34x and 34y also serve a spacer which forms the installation space of the actuator unit 5 and the flexible printed boards 6 between the reservoir unit 3 and the flow channel unit 4.
As shown in
The region corresponding to the actuator units 5 in the lower surface 4a (see
With the above-described configuration, in this embodiment, as schematically shown in
In this way, the sub flow channel S branches off the main flow channel M at the connection position J1 on the joint 2b side with respect to the branch positions of the supply flow channels Y from the main flow channel M, and is joined again with the main flow channel M at the connection position J2 on the joint 2c. That is, the sub flow channel S serves as a bypass flow channel which bypasses a partial flow channel from the connection position J1 to the connection position J2 in the main flow channel M.
Next, the ink supply unit 50 (liquid supply means) which supply ink to the heads 1 will be described with reference to
In the elastic tubes 51, 53, and 57, opening/closing valves 61, 62, and 63 are provided to switch an open state where ink flows through the tubes and a closed state where ink does not flow through the tubes. When the opening/closing valve 61 or 62 is in the open state, a circulation path is formed such that ink flows into the filter unit 2 through the sub tank 54 and the pump 56, and ink flows out of the filter unit 2 to the sub tank 54 through the opening/closing valve 61 or 62 in the open state. With this pump driving, ink in which a foreign substance, such as bubbles or dust, is mixed can be discharged from the filter unit 2 to the sub tank 54. When the pump 56 operates in a state where the opening/closing valve 63 is in the open state, ink is supplied from the main tank 58 to the sub tank 54. The states of the opening/closing valves 61 to 63 are switched under the control of the controller 501.
Next, the flow of ink at the time of recording and purging in the ink jet head 1 will be described with reference to
Purging is processing for forcibly discharging ink outside the head 1 to remove a foreign substance, such as bubbles, in the head 1. The purging processing of this embodiment includes (1) circulative purging in which ink is circulated on the upstream side from the filter 2f, (2) inter-filter purging in which ink is circulated so as to pass through a flow channel between the filters 2f and 72, and (3) nozzle purging in which ink is discharged from the ejection ports 4y.
At the time of (1) circulative purging, the controller 501 puts the opening/closing valve 61 in the open state, puts the opening/closing valves 62 and 63 in the closed state, and operates the pump 56. Thus, ink in the sub tank 54 flows from the joint 2b into the upper filter chamber 24a. In the upper filter chamber 24a, ink flows into the communicating flow channel 21 along the upper surface of the filter 2f. Accordingly, a foreign substance, such as bubbles, remaining in the upstream-side surface of the filter 2f is removed, and clogging of the filter 2f is avoided. Ink directed toward the communicating flow channel 21 is discharged from the joint 2a to the outside and returns to the sub tank 54 through the elastic tube 51. That is, the joint 2a also serves as a discharge section (another discharge section in the invention) which discharges ink from the filter unit 2 to the outside at the time of circulative purging. The flow channel resistance of the flow channel which returns from the upper filter chamber 24a to the sub tank 54 through the joint 2a is smaller than the flow channel resistance of the flow channel which is directed from the upper filter chamber 24a to the ejection ports 4y beyond the filter 2f. For this reason, during circulative purging, even when the joint 2b communicates with the ejection ports 4y, there is little possibility that ink will leak from the ejection ports 4y.
At the time of (2) inter-filter purging, the controller 501 puts the opening/closing valve 62 in the open state, puts the opening/closing valves 61 and 63 in the closed state, and operates the pump 56. Thus, ink in the sub tank 54 flows from the joint 2b into the upper filter chamber 24a. In turn, ink is directed toward the joint 2c through the reservoir 32c along the main flow channel M, and is also directed toward the joint 2c along the sub flow channel S which branches off the main flow channel M. Ink discharged from the joint 2c returns to the sub tank 54 through the elastic tube 53. Thus, a foreign substance, such as bubbles, in the flow channel between the filter 2f and the filter 72 is discharged outside the head 1.
The flow channel resistance of the flow channel which returns to the sub tank 54 through the joint 2c along the main flow channel M and the sub flow channel S with the connection position J1 of the linear flow channel 26 and the dropping flow channel 27 as a starting point is smaller than the flow channel resistance of the flow channel which is directed toward the ejection ports 4y along the main flow channel M and the supply flow channels Y with the connection point J1 as a starting point. For this reason, during inter-filter purging, even when the joint 2b communicates with the ejection ports 4y, there is little possibility that ink will leak from the ejection ports 4y.
In particular, in this embodiment, in the flow channel from the lower filter chamber 24b to the joint 2c, the flow channel along the main flow channel M and the sub flow channel S which bypasses the main flow channel M are provided. This contributes to decrease the flow channel resistance of the flow channel from the lower filter chamber 24b to the joint 2c. Meanwhile, if ink excessively easily flows into the sub flow channel S, it is not possible to secure the flow rate in the main flow channel M, thereby making it impossible to sufficiently remove a foreign substance in the main flow channel M. For this reason, the sub flow channel S is configured to have the flow channel resistance such that, even when the flow channel resistance of the whole of the main flow channel M and the sub flow channel S is lowered, the flow rate in the main flow channel M can be sufficiently secured. For example, the flow channel resistance of the sub flow channel S is adjusted so as to substantially become equal to the flow channel resistance from the connection position J1 to the connection position J2 in the main flow channel M.
At the time of (3) nozzle purging, the controller 501 puts all the opening/closing valves 61 to 63 in the closed state, and operates the pump 56. Thus, ink in the sub tank 54 flows from the joint 2b into the upper filter chamber 24a. In turn, similarly to the flow of ink at the time of recording, ink reaches the ejection ports 4y and is ejected from the ejection ports 4y. Therefore, an increase in the viscosity of ink near the ejection ports 4y in the flow channel unit 4 or clogging of the ejection ports 4y is avoided.
If the temperature of ink changes due to variations in the external environment, the viscosity of ink also varies. If the ink temperature rises and the viscosity of ink decreases, pressure loss due to the viscous property of ink in the main flow channel M or the sub flow channel S is reduced. For this reason, the possibility that ink will leak from the ejection ports 4y during circulative purging or inter-filter purging is reduced. On the other hand, if viscosity decreases, the resistance against a foreign substance, such as bubbles, decreases, and the ability to sweep out a foreign substance in the ink flow channel is lowered. Accordingly, when removing a foreign substance through purging, it is necessary to change the flow rate of ink in accordance with the external environment so as to adjust the ability to discharge a foreign substance. For example, if it is determined that the temperature of the head 1 rises on the basis of the detection result of the temperature sensor 1a, the controller 501 of this embodiment increases the applied pressure to ink in the pump 56 and increases the flow rate of ink which is supplied to the head 1. A temperature sensor may be configured to directly detect the temperature of ink in the head 1.
However, as in this embodiment, if the sub flow channel S which bypasses the main flow channel M is formed, even when the flow rate of all the ink increases, the flow rate necessary for discharging a foreign substance in the main flow channel M may not be secured because the flow rate of ink flowing in the sub flow channel S as well as the main flow channel M increases.
Accordingly, the sub flow channel S of this embodiment is configured such that, as the flow rate of all the ink flowing in the main flow channel M and the sub flow channel S increases, the ratio of the flow rate of the sub flow channel S to the flow rate of the partial flow channel from the connection position J1 to the connection position J2 in the main flow channel M decreases. At this time, the amount of distribution of ink to the partial flow channel increases.
Specifically, as shown in
ΔP1=ζ1*ρ*(u1−u2)2/2 (Expression 1-1)
If pressure loss due to a change in velocity when ink passing through the ink outflow portion 26y is ΔP1′, a loss coefficient is ζ1′, and the flow velocity before and after passing is u1′ and u2′, ΔP1′ is expressed as follows. Since the ink outflow portion 26y is a portion which rapidly contracts with respect to the sub scanning direction, ζ1′=1.
ΔP1′=ζ1′*ρ*(u1′−u2′)2/2 (Expression 1-2)
A plurality of expanded portions 26b having the above-described flow channel characteristic are formed in the sub flow channel S. Pressure loss includes pressure loss due to a change in velocity and pressure loss due to viscosity. Thus, the entire pressure loss ΔP1ALL in the sub flow channel S is expressed as follows. Σ means that pressure loss is summed for all the expanded portions 26b, and Δp1 represents pressure loss due to viscosity.
ΔP1ALL=Σ(ΔP1+ΔP1′)+Δp1 (Expression 1-3)
In the main flow channel M, the flow channel shape changes at both end portions 32x and 32y of the reservoir 32c, and this is one of the main factors for a change in velocity in the main flow channel M. In the end portion 32x, the cross-section perpendicular to the extension direction of the reservoir 32c is gradually expanded with respect to the inflow direction (main scanning direction) of ink flowing in the extension direction of the reservoir 32c. In the end portion 32y, the cross-section perpendicular to the extension direction of the reservoir 32c is gradually reduced with respect to the outflow direction (main scanning direction) of ink flowing in the extension direction of the reservoir 32c. If pressure loss due to a change in velocity when ink passes through the end portion 32x is ΔP2, a loss coefficient is ζ2, and the flow velocity before and after passing is v1 and v2, ΔP2 is expressed as follows. The end portion 32x is a portion (second change portion) which is gradually expanded with respect to the sub scanning direction, and in which the cross-sectional area continuously changes in the ink flow direction. For this reason, 0<ζ2<1.
ΔP2=ζ2*ρ*(v1−v2)2/2 (Expression 2-1)
If pressure loss due to a change in velocity when ink passes through the end portion 32y is ΔP2′, a loss coefficient is ζ2′, and the flow velocity before and after passing is v1′ and v2′, ΔP2′ is expressed as follows. The end portion 32y is a portion (second change portion) which is gradually reduced with respect to the sub scanning direction, and in which the cross-sectional area continuously changes in the ink flow direction. For this reason, 0<ζ2′<1.
ΔP2′=ζ2′*ρ*(v1′−v2′)2/2 (Expression 2-2)
Thus, the entire pressure loss ΔP2ALL in the reservoir 32c is expressed as follows. Δp2 represents pressure loss due to viscosity.
ΔP2ALL=ΔP2+ΔP2′+Δp2 (Expression 2-3)
As shown in (Expression 1-1), (Expression 1-2), (Expression 2-1), and (Expression 2-2), while pressure loss ΔP, ΔP1′, ΔP2, and ΔP2′ due to a change in velocity is proportional to the square of the change in velocity, pressure loss Δp1 and Δp2 due to viscosity depends on the first order of the flow velocity (for example, in the case of a laminar flow in a pipe line with a uniform cross-section, pressure loss Δp1 and Δp2 due to viscosity is proportional to the average flow velocity of ink which cuts across one cross-section of the pipe line). Thus, if the flow rate of ink increases and the flow velocity increases, in (Expression 1-3) and (Expression 2-3), the influence of pressure loss ΔP1, ΔP1′, ΔP2, and ΔP2′ due to a change in velocity relatively increases compared to pressure loss Δp1 and Δp2 due to viscosity. As described above, the loss coefficients ζ1 and ζ1′ are greater than the loss coefficients ζ2 and ζ2′. For this reason, pressure loss ΔP1 and ΔP1′ due to a change in velocity in the sub flow channel S undergoes a large degree of change when the flow rate of ink increases compared to pressure loss ΔP2 and ΔP2′ due to a change in velocity in the main flow channel M. That is, in the sub flow channel S, pressure loss when the flow rate of ink increases easily increases compared to the main flow channel M. For this reason, as the flow rate of all the ink increases, the ratio of the flow rate of the sub flow channel S to the flow rate of the main flow channel M decreases.
According to this embodiment described above, when increasing the flow rate of all the ink, the ratio of the flow rate of the main flow channel M to the flow rate of the sub flow channel S increases. For this reason, if the flow rate of ink flowing from the pump 56 into the head 1 increases, the ratio of ink branching into the main flow channel M to ink branching into the sub flow channel S increases. Accordingly, for example, when the ability to sweep out a foreign substance, which is reduced because the viscosity of ink decreases, is restored by increasing the flow rate of ink, the ratio of ink branching into the main flow channel M with an increase in the flow rate of ink increases, making it easy to secure the ability to sweep out a foreign substance.
When there is no flow channel resistance adjustment function of the sub flow channel S, it is also necessary to increase the flow rate of the sub flow rate S so as to increase the flow rate of the main flow channel M. For this reason, an excessive pressure is applied from the pump to ink. Accordingly, for example, at the time of inter-filter purging, ink leaks from the ejection ports 4y. However, in this embodiment, since the sub flow channel S has the flow channel resistance adjustment function, even when an excessive pressure is not applied from the pump to ink, it is possible to increase the flow rate of the main flow channel M. For this reason, a foreign substance is appropriately discharged, and no wasteful ink consumption occurs.
In increasing the flow rate of all the ink, a plurality of expanded portions 26b are provided in the sub flow channel S to form a flow channel such that the ratio of the flow rate of the main flow channel M to the flow rate of the sub flow channel S increases. The expanded portions 26b are portions in which pressure loss easily increases with a change in the cross-sectional area of the flow channel when the flow rate increases. Specifically, a configuration is made such that the loss coefficient ζ1 of each of the expanded portions 26b becomes greater than the loss coefficient ζ2 of each of the end portions 32x and 32y of the main flow channel M. For this reason, when the entire flow rate increases, the flow rate of the main flow channel M easily increases compared to the flow rate of the sub flow channel S.
Although the preferred embodiment of the invention has been described, the invention is not limited to the above-described embodiment, and various modifications may be made without departing from the scope described in the means for solving the problem.
For example,
The ink supply unit 50 may have a configuration other than the above-described embodiment insofar as ink can be introduced from the joint 2b and ink can be discharged from the joint 2a or 2c. For example, a configuration may be made such that ink discharged from the joint 2b or 2c directly flows into the joint 2a without passing through the sub tank 54.
Although in the above-described embodiment, the sub tank 54 and the head 1 constitute a circulative flow channel through the pump 56, at least one of the elastic tube 51 and the elastic tube 53 as the return flow channel from the head 1 to the sub tank 54 may be connected to a portion (for example, a waste liquid tank) other than the sub tank 54. At this time, while part of ink sent by the pump is discarded, the exhaust amount may be small due to the flow channel resistance adjustment function of the sub flow channel S.
Although in the above-described embodiment, the flow channel width in each of the main flow channel M and the sub flow channel S is linearly changed, the flow channel width may change in a different form. For example, the change portion of the flow channel width may change in a curve form.
The above-described embodiment is an example where the invention is applied to an ink jet head which ejects ink from nozzles, and the invention is not limited to the ink jet head. For example, the invention may be applied to a liquid ejection head which ejects conductive paste to form a minute wire pattern on a substrate, ejects an organic luminescent material to a substrate to form a high-definition display, or ejects optical resin to a substrate to form a minute electronic device, such as an optical waveguide.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-154949 | Jul 2010 | JP | national |
