U.S. patent application number 11/848989 was filed with the patent office on 2008-03-06 for tube pump and liquid ejection apparatus.
This patent application is currently assigned to SEIKO EPSON CORPORATION. Invention is credited to Shuhei Harada.
Application Number | 20080056918 11/848989 |
Document ID | / |
Family ID | 39151801 |
Filed Date | 2008-03-06 |
United States Patent
Application |
20080056918 |
Kind Code |
A1 |
Harada; Shuhei |
March 6, 2008 |
TUBE PUMP AND LIQUID EJECTION APPARATUS
Abstract
A tube pump including a housing, a tube, a rotor, and a pressing
member is disclosed. The tube has a section that is arranged in the
housing in such a manner as to annularly extend along an inner
circumferential surface. The rotor has a cam surface. The pressing
member has a main body that selectively presses the tube toward the
inner circumferential surface and a shaft that extends from the
main body and contacts the cam surface. During rotation of the
rotor, the pressing member moves, with the shaft contacting the cam
surface, along the inner circumferential surface while pressing the
tube. The shaft has a contact part that contacts the cam surface,
and is formed in such a manner that the frictional coefficient of
the shaft is lower than the frictional coefficient of the main body
at least in the contact part.
Inventors: |
Harada; Shuhei; (Chino-shi,
JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W., SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
SEIKO EPSON CORPORATION
Tokyo
JP
|
Family ID: |
39151801 |
Appl. No.: |
11/848989 |
Filed: |
August 31, 2007 |
Current U.S.
Class: |
417/412 |
Current CPC
Class: |
F04B 43/12 20130101;
B41J 2/1714 20130101; B41J 2/185 20130101 |
Class at
Publication: |
417/412 |
International
Class: |
F04B 45/00 20060101
F04B045/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 31, 2006 |
JP |
2006-236909 |
Aug 31, 2006 |
JP |
2006-236911 |
Claims
1. A tube pump comprising: a housing having an inner
circumferential surface; a tube having a section that is arranged
in the housing in such a manner as to annularly extend along the
inner circumferential surface; a rotor rotatably arranged in the
housing, the rotor having a cam surface; and a pressing member
arranged in the housing, the pressing member having a main body
that selectively presses the tube toward the inner circumferential
surface and a shaft that extends from the main body and contacts
the cam surface, wherein, during rotation of the rotor, the
pressing member moves, with the shaft contacting the cam surface,
along the inner circumferential surface while pressing the tube,
wherein the shaft has a contact part that contacts the cam surface,
and the shaft is formed in such a manner that the frictional
coefficient of the shaft is lower than the frictional coefficient
of the main body at least in the contact part.
2. The pump according to claim 1, wherein the shaft and the main
body are components formed separately from each other, and the main
body has an insertion hole into which the shaft is inserted.
3. The pump according to claim 2, wherein the pressing member
includes a retaining member for preventing the shaft from coming
off the insertion hole.
4. The pump according to claim 1, wherein the contact part is
formed of a metal or a synthetic resin having a low friction.
5. The pump according to claim 1, wherein the shaft is rotatable
relative to the main body.
6. A liquid ejection apparatus comprising: a liquid ejection head
having a nozzle-forming surface in which a nozzle for ejecting
liquid is formed; a cap capable of sealing the nozzle-forming
surface; and a suction device capable of applying suction to the
interior of the cap, wherein the suction device is formed by the
tube pump according to claim 1.
7. A tube pump comprising: a housing having an inner
circumferential surface; a tube having a section that is arranged
in the housing in such a manner as to annularly extend along the
inner circumferential surface; a rotor rotatably arranged in the
housing, the rotor having a cam surface; and a pressing member
arranged in the housing, the pressing member having a main body
that selectively presses the tube toward the inner circumferential
surface and a shaft that extends from the main body and contacts
the cam surface, wherein, during rotation of the rotor, the
pressing member moves, with the shaft contacting the cam surface,
along the inner circumferential surface while pressing the tube,
wherein the main body has an insertion hole into which the shaft is
inserted, the shaft contacting the inner surface of the insertion
hole and being rotatable relative to the main body, and wherein, at
a contacting portions of the shaft and the main body, the
frictional coefficient of one of the shaft is lower than the
frictional coefficient of the other.
8. A liquid ejection apparatus comprising: a liquid ejection head
having a nozzle-forming surface in which a nozzle for ejecting
liquid is formed; a cap capable of sealing the nozzle-forming
surface; and a suction device capable of applying suction to the
interior of the cap, wherein the suction device is formed by the
tube pump according to claim 7.
9. A tube pump comprising: a housing having an inner
circumferential surface; a tube having a section that is arranged
in the housing in such a manner as to annularly extend along the
inner circumferential surface; a rotor rotatably arranged in the
housing, the rotor having a cam surface that extends in a
circumferential direction of the rotor; and a pressing member
arranged in the housing, the pressing member selectively pressing
the tube toward the inner circumferential surface and being
slidable on the cam surface between an actuation position and a
non-actuation position, wherein, during rotation of the rotor, the
pressing member, if at the actuation position, moves along the
inner circumferential surface while pressing the tube, thereby
producing negative pressure in the tube, and, if at the
non-actuation position, moves along the inner circumferential
surface while pressing the tube in such a manner that no negative
pressure is produced, wherein the frictional coefficient of the cam
surface is partially different.
10. The pump according to claim 9, wherein the cam surface has a
contact part, the pressing member contacting the contact part when
at the actuation position, and wherein the frictional coefficient
of the contact part is lower than the frictional coefficient of the
remainder of the cam surface.
11. The pump according to claim 10, wherein the contact part is
formed of a material having a lower frictional coefficient than the
friction coefficient of the remainder of the cam surface.
12. The pump according to claim 10, wherein the contact part is
formed as a component separate from the pressing member and is made
of a material having a lower frictional coefficient than the
friction coefficient of the remainder of the cam surface.
13. The pump according to claim 10, wherein coating for reducing
frictional resistance is applied to the contact part.
14. A liquid ejection apparatus comprising: a liquid ejection head
having a nozzle-forming surface in which a nozzle for ejecting
liquid is formed; a cap capable of sealing the nozzle-forming
surface; and a suction device capable of applying suction to the
interior of the cap, wherein the suction device is formed by the
tube pump according to claim 9.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from prior Japanese Patent Application No. 2006-236909,
filed on Aug. 31, 2006 and No. 2006-236911, filed on Aug. 31, 2006,
the entire content of which is incorporated herein by
reference.
BACKGROUND
[0002] 1. Technical Field
[0003] The present invention relates to a liquid ejection apparatus
such as an inkjet printer and a tube pump used in a liquid ejection
apparatus.
[0004] 2. Related Art
[0005] Inkjet printers (hereinafter referred to as printers) are
widely known as liquid injection apparatuses for injecting liquid
from a nozzle formed in a recording head onto target. In a printer,
since nozzles have openings on a nozzle-forming surface of a
recording head (liquid ejection head), ink solvent evaporates from
the nozzles. As a result, the viscosity of the ink increases, which
may influence the ejection characteristics of the ink. Printers are
therefore provided with a maintenance mechanism that performs
maintenance of a recording head.
[0006] A maintenance mechanism includes a cap for sealing a
nozzle-forming surface of the recording head and a suction pump
located in a drain passage. The maintenance mechanism drives the
suction pump while sealing the nozzle-forming surface with the cap,
thereby producing negative pressure in the cap. Ink having an
increased viscosity is drawn out of the nozzles, and the ink
ejection is prevented from deteriorating. As such suction pumps,
tub pumps that are disclosed, for example, in Japanese Laid-Open
Patent Publication No. 2001-301195 and Japanese Laid-Open Patent
Publication No. 2002-349452 are used.
[0007] The above publications each disclose a tube pump having a
substantially cylindrical housing. The housing accommodates an
intermediate portion of a flexible tube in the longitudinal
direction, a rotor that rotates about the axis of the housing, and
a roller (pressing member). When the rotor rotates in one
direction, the roller moves along the inner circumferential surface
of the housing while pressing the tube.
[0008] The tube is accommodated in the housing in such a manner
that the intermediate portion in the longitudinal direction wound
one turn along the inner circumferential surface of the housing to
form a circle. Thus, in the housing, different sections of the tube
partially overlap. An elongated hole that extends along the
circumferential direction of the rotor is formed in a side of the
rotor. The inner wall of the elongated hole defines a cam surface.
The elongated hole extends in such a manner that the radial
distance from the axis of the rotor is gradually reduced from one
end in the circumferential direction to the other end. The roller
has a shaft that extends along the axis, which shaft is slidably
inserted in the elongated hole of the rotor. The roller is movable
relative to the rotor between one end of the elongated hole
(actuation position) and the other end (non-actuation position). As
the roller moves from the non-actuation position toward the
actuation position, the roller moves radially outward in the
rotor.
[0009] When the rotor rotates in an actuation direction, which is
one of the circumferential directions, the shaft of the roller
slides toward the actuation position (pressing position) in the
elongated hole. At the actuation position, the roller operates with
the inner circumferential surface of the housing. That is, the
roller moves along the inner circumferential surface of the
housing, while consecutively pressing part of the intermediate
portion of the tube. As the roller moves, portion of the tube that
have been released from the pressing of the roller sequentially
restore. Accordingly, the interior of a portion of the tube that is
upstream of the intermediate portion, which is accommodated in the
housing, is decompressed, so that negative pressure is produced in
the cap. This draws ink with an increased viscosity from the
nozzles.
[0010] When the tube pump is operating, the roller shaft moves
along the elongated hole, and rotates at the actuation position. In
these cases, frictional resistance is generated between the roller
shaft and the cam surface. Particularly, when tube pump is
performing suction, the roller shaft, at the actuation position,
rotates and slides on the cam surface while receiving a reactive
force from the pressed tube. Therefore, the frictional resistance
is particularly increased when the roller is at the actuation
position. Such frictional resistance is preferably minimized from
the perspective of reducing the friction of the cam surface,
reducing the torque required for operating the tube pump, and
improving the pump efficiency.
[0011] However, the tube pumps disclosed in the above publications
take no countermeasures to reduce the frictional resistance between
a roller shaft and a cam surface.
SUMMARY
[0012] Accordingly, it is an objective of the present invention to
provide a tube pump and a liquid ejection apparatus that reduce the
torque required for operation and improves the pump efficiency.
[0013] To achieve the foregoing objective and in accordance with a
first aspect of the present invention a tube pump having a housing,
a tube, a rotor, and a pressing member is provided. The housing has
an inner circumferential surface. The tube has a section that is
arranged in the housing in such a manner as to annularly extend
along the inner circumferential surface. The rotor is rotatably
arranged in the housing, and has a cam surface. The pressing member
is arranged in the housing. The pressing member has a main body
that selectively presses the tube toward the inner circumferential
surface and a shaft that extends from the main body and contacts
the cam surface. During rotation of the rotor, the pressing member
moves, with the shaft contacting the cam surface, along the inner
circumferential surface while pressing the tube. The shaft has a
contact part that contacts the cam surface. The shaft is formed in
such a manner that the frictional coefficient of the shaft is lower
than the frictional coefficient of the main body at least in the
contact part.
[0014] In accordance with a second aspect of the present invention,
a liquid ejection apparatus having a liquid ejection head, a cap,
and a suction device is provided. The liquid ejection head has a
nozzle-forming surface in which a nozzle for ejecting liquid is
formed. The cap is capable of sealing the nozzle-forming surface.
The suction device is capable of applying suction to the interior
of the cap. The suction device is formed by the tube pump according
to the first aspect of the present invention.
[0015] In accordance with a third aspect of the present invention,
a tube pump having a housing, a tube, a rotor, and a pressing
member is provided. The housing has an inner circumferential
surface. The tube has a section that is arranged in the housing in
such a manner as to annularly extend along the inner
circumferential surface. The rotor is rotatably arranged in the
housing, and has a cam surface. The pressing member is arranged in
the housing. The pressing member has a main body that selectively
presses the tube toward the inner circumferential surface and a
shaft that extends from the main body and contacts the cam surface.
During rotation of the rotor, the pressing member moves, with the
shaft contacting the cam surface, along the inner circumferential
surface while pressing the tube. The main body has an insertion
hole into which the shaft is inserted. The shaft contacts the inner
surface of the insertion hole and is rotatable relative to the main
body. At a contacting portions of the shaft and the main body, the
frictional coefficient of one of the shaft is lower than the
frictional coefficient of the other.
[0016] In accordance with a fourth aspect of the present invention,
a liquid ejection apparatus having a liquid ejection head, a cap,
and a suction device is provided. The liquid ejection head has a
nozzle-forming surface in which a nozzle for ejecting liquid is
formed. The cap is capable of sealing the nozzle-forming surface.
The suction device is capable of applying suction to the interior
of the cap. The suction device is formed by the tube pump according
to the third aspect of the present invention.
[0017] In accordance with a fifth aspect of the present invention,
a tube pump having a housing, a tube, a rotor, and a pressing
member is provided. The housing has an inner circumferential
surface. The tube has a section that is arranged in the housing in
such a manner as to annularly extend along the inner
circumferential surface. The rotor is rotatably arranged in the
housing. The rotor has a cam surface that extends in a
circumferential direction of the rotor. The pressing member is
arranged in the housing. The pressing member selectively presses
the tube toward the inner circumferential surface and is slidable
on the cam surface between an actuation position and a
non-actuation position. During rotation of the rotor, the pressing
member, if at the actuation position, moves along the inner
circumferential surface while pressing the tube, thereby producing
negative pressure in the tube, and, if at the non-actuation
position, moves along the inner circumferential surface while
pressing the tube in such a manner that no negative pressure is
produced. The frictional coefficient of the cam surface is
partially different.
[0018] In accordance with a sixth aspect of the present invention,
a liquid ejection apparatus having a liquid ejection head, a cap,
and a suction device is provided. The liquid ejection head has a
nozzle-forming surface in which a nozzle for ejecting liquid is
formed. The cap is capable of sealing the nozzle-forming surface.
The suction device is capable of applying suction to the interior
of the cap. The suction device is formed by the tube pump according
to the fifth aspect of the present invention
[0019] Other aspects and advantages of the present invention will
become apparent from the following description, taken in
conjunction with the accompanying drawings, illustrating by way of
example the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The invention, together with objects and advantages thereof,
may best be understood by reference to the following description of
the presently preferred embodiments together with the accompanying
drawings in which:
[0021] FIG. 1 is a perspective view illustrating an inkjet printer
according to one embodiment of the present invention;
[0022] FIG. 2 is a schematic cross-sectional view showing a part of
the printer of FIG. 1;
[0023] FIG. 3 is a perspective view illustrating the tube pump of
the printer shown in FIG. 1;
[0024] FIG. 4 is an exploded perspective view of the tube pump of
FIG. 3;
[0025] FIG. 5 is a cross-sectional view of the tube pump of FIG.
3;
[0026] FIG. 6 is an exploded perspective view illustrating the pump
wheel and the pressing member in the tube pump shown in FIG. 3;
and
[0027] FIG. 7 is a side view showing the pressing member of FIG.
6.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0028] One embodiment of the present invention will now be
described with reference to the drawings. Unless otherwise
specified, a front-and-back direction, an up-and-down direction,
and a left-and-right direction each agree with an arrow in all the
drawings.
[0029] As shown in FIG. 1, an inkjet printer 11, which functions as
a liquid ejection apparatus, has a frame 12, which is shaped like a
rectangular box. A platen 13 is located in a lower portion of the
frame 12. The platen 13 extends along the longitudinal direction,
or left-and-right direction, of the frame 12. A paper feeding motor
14 is located in a lower back portion of the frame 12. Based on the
driving force of the paper feeding motor 14, a paper feeding
mechanism (not shown) feeds sheets of recording paper P forward
from the rear side onto the platen 13.
[0030] A guide shaft 15 extends in the frame 12. The guide shaft 15
is located above the platen 13 and extends along the longitudinal
direction of the platen 13. A carriage 16 is supported by the guide
shaft 15, so that the carriage 16 reciprocates along the axial
direction of the guide shaft 15. That is, the guide shaft 15 is
passed through a support hole 16a that extends through the carriage
16 in the left-and-right direction. The guide shaft 15 supports the
carriage 16 such that the carriage 16 can reciprocate along the
longitudinal direction of the guide shaft 15.
[0031] A drive pulley 17a and a driven pulley 17b are rotatably
supported on a back wall of the frame 12 at positions corresponding
to opposite ends of the guide shaft 15. An output shaft of a
carriage motor 18 is connected to the drive pulley 17a. An endless
timing belt 17, which is coupled to the carriage 16, is wound
around the pulleys 17a, 17b. The carriage 16 is thus moved in the
left-and-right direction through the timing belt 17 while driven by
the carriage motor 18 and guided by the guide shaft 15.
[0032] A recording head 19, or a liquid ejection head, is formed on
a bottom surface of the carriage 16. Ink cartridges 20 are
detachably mounted on the carriage 16. The ink cartridges 20 supply
liquid, which is ink, to the recording head 19. The recording head
19 has piezoelectric elements 21 and nozzles 22 (see FIG. 2). When
the piezoelectric elements 21 are activated, ink that has been
supplied to the recording head 19 is injected onto the paper sheet
P on the platen 13. Printing is thus performed.
[0033] A home position area (non-printing area), which does not
correspond to the paper sheet P, is provided near the right end in
the frame 12. A maintenance mechanism 23 is located in the home
position area. The maintenance mechanism 23 performs maintenance
such as cleaning of the recording head 19 when printing is not
being performed.
[0034] Next, the maintenance mechanism 23 will be described.
[0035] As shown in FIG. 2, the maintenance mechanism 23 has cap 24
and a lift device 25. The cap 24 is shaped like a rectangular box
with a bottom. The lift device 25 lifts and lowers the cap 24. The
maintenance mechanism 23 moves the carriage 16 to the home position
area, and in this state, lifts the cap 24 with the lift device 25,
thereby sealing a nozzle-forming surface 19a (the nozzles 22) of
the recording head 19 with the cap 24. A projection 26 extends
downward from the bottom of the cap 24. A drain passage 26a for
draining ink extends through the projection 26 along the
up-and-down direction.
[0036] A first end (a proximal end or an upstream end) of a drain
tube 27 made of a flexible material is connected to the projection
26. A second end (a distal end or a downstream end) of the drain
tube 27 is inserted in a waste ink tank 28, which shaped like a
rectangular parallelepiped. A tube pump 29, serving as a suction
device, is located in an intermediate portion of the drain tube 27
between the cap 24 and the waste ink tank 28. The tube pump 29
draws air in the cap 24 from the cap 24 to the waste ink tank
28.
[0037] With the nozzle-forming surface 19a being sealed with the
cap 24, the tube pump 29 is activated so that viscous ink is drawn
out of the nozzles 22 together with bubbles. The ink and bubbles
are drained to the waste ink tank 28 through the cap 24 and the
drain tube 27. This process is referred to as cleaning. A waste ink
absorber 30 is accommodated in the waste ink tank 28. The waste ink
absorber 30 absorbs and retains ink drained into the waste ink tank
28.
[0038] The tube pump 29 will now be described.
[0039] As shown in FIGS. 3 and 4, the tube pump 29 has a
cylindrical housing 31 that is fixed in the frame 12 (see FIG. 1).
The housing 31 has a bottom wall, and a through hole 31a is formed
in the bottom wall to connect the inside and the outside of the
housing 31. A pump wheel 32 serving as a rotor is accommodated in
the housing 31. The pump wheel 32 is rotatable about an axis of the
housing 31. That is, the pump wheel 32 has a wheel shaft 33 that
extends along the axis A and is inserted in the through hole 31a.
The pump wheel 32 is rotatable about the wheel shaft 33 in the
housing 31.
[0040] An upstream opening (a first opening) 34 and a downstream
opening (a second opening) 35 are formed in the circumferential
wall. When viewed from above, the upstream opening 34 and the
downstream opening 35 extend along a tangential direction of an
inner circumferential surface 31b of the housing 31. The upstream
opening 34 and the downstream opening 35 are displaced from each
other in the direction of the axis A. An intermediate portion 36 of
the drain tube 27 in the longitudinal direction is accommodated in
the housing 31, so as to be routed to draw a circle along the inner
circumferential surface 31b of the housing 31. The drain tube 27
extends to the outside of the housing 31 through the upstream
opening 34 and the downstream opening 35.
[0041] In the housing 31, an upstream section 36a and a downstream
section 36b in the intermediate portion 36 are partially overlap in
the direction of the axis A. A section in which the upstream
section 36a and the downstream section 36b partially overlap is
defined as a tube overlapping section B. In the present embodiment,
the drain tube 27 is wound one turn in the housing 31 such that the
tube overlapping section B is minimized.
[0042] In the tube overlapping section B, the upstream section 36a
and the downstream section 36b each form a thin portion 37 that is
thinner than the remainder of the intermediate portion 36. The
thickness of each thin portion 37 is determined such that the
flexibility of the tube overlapping section B is close to the
flexibility of the remainder of the intermediate portion 36 in the
housing 31. That is, the thickness of each thin portion 37 is
determined such that the flexibility of the drain tube 27 is
constant over the entire circumferential direction in the housing
31.
[0043] As shown in FIG. 5, runout portions are provided on the
inner circumferential surface 31b of the housing 31 at positions
corresponding to the upstream section 36a and the downstream
section 36b. The runout portions can accommodate the upstream
section 36a and the downstream section 36b. Specifically, an
upstream recess 38 and a downstream recess 39 are formed in the
inner circumferential surface 31b of the housing 31. The upstream
recess 38 serves as an upstream runout portion that corresponds to
the upstream section 36a. The downstream recess 39 serves as a
downstream runout portion that corresponds to the downstream
section 36b. When viewed from above, the upstream recess 38 and the
downstream recess 39 are arranged to be adjacent to each other in
the circumferential direction of the inner circumferential surface
31b of the housing 31.
[0044] As shown in FIG. 6, the pump wheel 32 has a disk-shaped
large plate 40 and a small plate 41, which has a smaller diameter
than that of the large plate 40. The large plate 40 and the small
plate 41 are fixed to the wheel shaft 33 with the centers
penetrated by the wheel shaft 33. The large plate 40 and the small
plate 41 are spaced from each other at a predetermined distance
along the axial direction. A roller guiding slit 42 extends through
the large plate 40. The roller guiding slit 42 is arcuate and
bulges radially outward. The roller guiding slit 42 has a first end
and a second end. The roller guiding slit 42 extends in such a
manner that the first end is located outside of the second end with
respect to the radial direction of the large plate 40. That is, the
roller guiding slit 42 extends so as to gradually approach the axis
of the large plate 40 from the first end to the second end.
[0045] A roller guiding recess 43 is formed in a peripheral portion
of the small plate 41. The roller guiding recess 43 corresponds to
the roller guiding slit 42 of the large plate 40. Among the wall
surfaces of the large plate 40 that define the roller guiding slit
42, the inner surface functions as a cam surface C. Also, a wall
surface of the small plate 41 that defines the roller guiding
recess 43 functions as a cam surface C.
[0046] A pressing member 46 is supported by the large plate 40 and
the small plate 41 at the axial ends. The pressing member 46
includes a main body, which is a roller 44, and a shaft 45. A first
end of the shaft 45 is inserted through the roller guiding slit 42
to be slidable on the cam surface C. A second end of the shaft 45
is arranged in the roller guiding recess 43 to be slidable on the
cam surface C. That is, the roller 44 moves along the cam surfaces
C with the first and second ends of the shaft 45 sliding on the cam
surfaces C.
[0047] As shown in FIG. 7, the roller 44 and the shaft 45 are
separate components. That is, the roller 44 has an insertion hole
44a extending along the axis. The shaft 45, which is longer than
the roller 44 in the axial direction is fitted in the insertion
hole 44a. Thus, the ends of the shaft 45 project from both ends of
the roller 44. The shaft 45 is slidable on the inner surface of the
insertion hole 44a, so that the roller 44 and the shaft 45 are
rotatable relative to each other.
[0048] A material having a lower frictional coefficient than that
of the roller 44 is used for forming the shaft 45. Specifically, a
metal or a synthetic resin having a low friction is used. A
synthetic resin having a low friction includes resins of a sliding
grade, such as polyacetal (POM) and polystyrene (PS). In the
present embodiment, the material for forming the shaft 45,
polyacetal of a sliding grade is used. Accordingly, the frictional
coefficient of the shaft 45 is lower than that of the roller
44.
[0049] Retaining members, or retaining pins 47, for preventing the
shaft 45 from coming off are provided at both ends of the roller
44. The retaining pins 47 prevent the shaft 45 from coming off the
insertion hole 44a of the roller 44. The retaining pins 47 are
configured no to prevent relative rotation between the roller 44
and the shaft 45.
[0050] When a pump motor (not shown) is activated and the pump
wheel 32 is rotated in an actuation direction of the pump 29, that
is, in a direction causing tube the pump 29 to perform suction (a
direction indicated by an arrow in FIG. 5), the pressing member 46
is moved to the first end of the roller guiding slit 42. That is,
the pressing member 46 is located at a pressing position, which is
a radially outer position in the pump wheel 32, or an actuation
position. At the actuation position, the pressing member 46 moves
from a upstream side to a downstream side along the longitudinal
direction of the drain tube 27 as the roller 44 rotates, while
pressing and squeezing the intermediate portion 36 of the drain
tube 27.
[0051] As the pressing member 46 moves, a section of the drain tube
27 that is upstream of tube the pump 29 is decompressed. Air and
ink in the cap 24, which seals the nozzle-forming surface 19a, are
gradually drained to the waste ink tank 28 by the rotation of the
pump wheel 32 in the actuation direction, which produces negative
pressure in the cap 24.
[0052] In contrast, when the pump wheel 32 is rotated in a
direction opposite to the actuation direction (a direction opposite
to the direction of the arrow in FIG. 5), the pressing member 46 is
moved to the second end of the roller guiding slit 42. That is, the
pressing member 46 is located at a non-pressing position, which is
a radially inner position in the pump wheel 32, or a non-actuation
position. At the non-actuation position, the pressing member 46
contacts the intermediate portion 36 of the drain tube 27 with a
pressing force that is smaller compared to that in the case where
the pressing member 46 is at the actuation position, and does not
squeeze the drain tube 27. The decompressed state in the drain tube
27 is eliminated.
[0053] As shown in FIG. 6, when the pressing member 46 is moved to
the first end of the roller guiding slit 42 on the cam surface of
the pump wheel 32, the shaft 45 of the pressing member 46 contacts
contact parts N. The contact parts N are formed of a material
having a lower frictional coefficient than the remainder of the
pump wheel 32. In the present embodiment, polytetrafluoroethylene
(PTFE) is used as the low friction material.
[0054] The operation of the tube pump 29 will now be described.
[0055] When performing the cleaning of the recording head 19, the
nozzles 22 (the nozzle-forming surface 19a) of the recording head
19 are sealed by the cap 24. In this state, the pump motor (not
shown) is activated and the pump wheel 32 is rotated in the
actuation direction. Accordingly, the roller 44 is moved while
rotating about the shaft 45, while squeezing the intermediate
portion 36 of the drain tube 27 from the upstream side to the
downstream side. At this time, both ends of the shaft 45 slide and
rotate on the contact parts N on the cam surfaces C of the pump
wheel 32, while the intermediate portion of the shaft 45 slides and
rotate on the inner surface of the insertion hole 44a.
[0056] In the present embodiment, the contact parts N are formed of
polytetrafluoroethylene, which is a low friction material, and the
shaft 45 is formed of polyacetal of a sliding grade. Therefore, the
frictional resistance between the shaft 45 and the cam surfaces C
and the frictional resistance between the shaft 45 and the roller
44 are both reduced.
[0057] When the roller 44 presses the tube overlapping section B,
the upstream section 36a and the downstream section 36b of the
drain tube 27 in the tube overlapping section B are moved to the
upstream recess 38 and the downstream recess 39, respectively, so
as to escape the pressing by the roller 44 at different timing. In
addition, the thin portion 37 of the tube overlapping section B
causes the flexibility of the tube overlapping section B to be
close to the flexibility of the intermediate portion 36 except for
the tube overlapping section B. Therefore, the fluctuation of
torque when the intermediate portion 36 of the drain tube 27 is
pressed by the roller 44 is suppressed.
[0058] When the roller 44 is moved on the intermediate portion 36
of the drain tube 27, while squeezing the upstream side to the
downstream side of the intermediate portion 36, the interior of the
drain tube 27 that is upstream of the tube pump 29 is decompressed,
so that a negative pressure is produced in the cap 24. On the basis
of the negative pressure, air and ink in the nozzles 22 and the cap
24 are drawn and drained to the waste ink tank 28 through the drain
tube 27. Accordingly, the cleaning of the recording head 19 is
completed.
[0059] The present embodiment provides the following
advantages.
[0060] (1) In the pressing member 46, the shaft 45 is made of
polyacetal of a sliding grade having lower frictional coefficient
than that of the roller 44. Therefore, the frictional resistance
between the shaft 45 and the cam surfaces C is lowered. This
reduces the force required for rotating the pump wheel 32 when
actuating the pump. Thus, the pump torque is reduced. Accordingly,
the size of the pump motor (not shown) for driving the pump wheel
32 can be reduced, and the pump efficiency of the tube the pump 29
is improved. As a result, in the cleaning of the recording head 19,
the interior of the cap 24 is efficiently and reliably vacuumed by
the tube the pump 29.
[0061] (2) Since the shaft 45 and the roller 44 of the pressing
member 46 are components formed separately from each other, the
materials for the shaft 45 and the roller 44 are easily altered in
accordance with the configuration of the tube the pump 29.
[0062] (3) The pressing member 46 is structured such that the shaft
45 and the roller 44 are rotatable relative to each other. The
frictional resistance between the shaft 45 and the roller 44 is
lower than the frictional resistance between the shaft 45 and the
cam surfaces C, so that, during the activation of the pump, the
roller 44 is mainly rotated relative to the shaft 45. Since this
suppresses the friction between the shaft 45 and the cam surfaces
C, the wear of the shaft 45 and the cam surfaces C is
suppressed.
[0063] (4) The retaining pins 47 for preventing the shaft 45 from
coming off the insertion hole 44a of the roller 44 are attached to
the shaft 45 of the pressing member 46. Therefore, the positional
relation between the shaft 45 and the roller 44 is maintained.
[0064] (5) On the cam surfaces C of the pump wheel 32, the contact
sections N are formed of polytetrafluoroethylene, which has a lower
frictional coefficient than that of the remainder of the cam
surfaces C. Thus, when the pressing member 46 presses the
intermediate portion 36 of the drain tube 27, the sliding
resistance between the shaft 45 and the cam surface C is reduced.
Since this reduces the load during the actuation of tube the pump
29, the pump torque is reduced and the pump efficiency is
improved.
[0065] (6) The pressing of the tube overlapping section B by the
pressing member 46 corresponds to simultaneously pressing of two
sections of the drain tubes 27 by the pressing member 46. In this
respect, since the present embodiment provides the thin portion 37
in the tube overlapping section B, the tube overlapping section B
is easily flexed. Therefore, the load required for squeezing the
tube overlapping section B with the pressing member 46 is reduced
by a simple structure that only has the thin portion 37. Thus, the
pump torque is reduced and the pump efficiency is improved.
[0066] (7) The flexibility of the tube overlapping section B is
made close to the flexibility of portions other than the tube
overlapping section B. That is, the load required for squeezing the
tube overlapping section B with the pressing member 46 is made
close to the load required for squeezing sections of the
intermediate portion 36 other than the tube overlapping section B.
Thus, the load required for squeezing the intermediate portion 36
is equalized over the entire length of the intermediate portion 36
in the housing 31. Therefore, fluctuation of the pump torque is
suppressed. This allows the tube the pump 29 to operate in a stable
manner.
[0067] (8) The upstream recess 38 and the downstream recess 39 are
formed in the housing to correspond to the upstream section 36a and
the downstream section 36b, which form the tube overlapping section
B, respectively. When the tube overlapping section B is pressed by
the pressing member 46, the upstream section 36a and the downstream
section 36b moved to the corresponding recesses 38, 39,
respectively, so as to escape the pressing. Therefore, the load
required for squeezing the tube overlapping section B with the
pressing member 46 is effectively reduced. This reduces the pump
torque and improves the pump efficiency.
[0068] (9) Since the upstream recess 38 and the downstream recess
39 are arranged in the housing 31 to be adjacent to each other
along the circumferential direction of the inner circumferential
surface 31b of the housing 31, the intermediate portion 36 of the
drain tube 27 can be routed in the housing 31 to minimize the tube
overlapping section B. Therefore, when the pump is used, the load
for squeezing the intermediate portion 36 of the drain tube 27 with
the pressing member 46 is made equal to a load required for
squeezing a single drain tube 27 along the entire circumference of
the housing 31, while substantially eliminating the amount of leak.
Thus, the pump torque is reduced and the pump efficiency is
improved.
[0069] The present invention is not limited to the above described
embodiment, but may be embodied as follows, for example.
[0070] The upstream section 36a and the downstream section 36b of
the tube overlapping section B may be made of a material having a
lower rigidity than that of sections of the intermediate portion 36
other than the tube overlapping section B, thereby increasing the
flexibility of the tube overlapping section B. This reliably
reduces the load required for squeezing the tube overlapping
section B with the pressing member 46.
[0071] The frictional coefficient on the cam surfaces C of the pump
wheel 32 may be partially changed in accordance with the
configuration of the tube the pump 29. This allows the pressing
member 46 to press the drain tube 27 in a favorable manner, and to
smoothly move between the pressing position and the non-pressing
position. As a result, the pump torque is reduced and the pump
efficiency is improved.
[0072] The contact parts N in the cam surfaces C may be formed as
components separate from the large plate 40, and made of a low
friction material such as polytetrafluoroethylene and polyacetal or
polystyrene of a sliding grade. In this case, the low frictional
resistance members are molded products that are press fitted to the
large plate 40. Accordingly, the sliding resistance between the
shaft 45 and the contact parts N when the pressing member 46
presses the intermediate portion 36 of the drain tube 27 is
reliably reduced by a simple structure.
[0073] Low friction coating such as polytetrafluoroethylene or
grease for reducing frictional resistance may be applied to the
contact parts N of the cam surfaces C. Accordingly, the sliding
resistance between the shaft 45 and the contact parts N when the
pressing member 46 presses the intermediate portion 36 of the drain
tube 27 is easily and reliably reduced.
[0074] The contact parts N on the cam surfaces C may be subject to
surface treatment such as polishing, thereby reducing the
frictional coefficient of the contact parts N.
[0075] The retaining pins 47 may be replaced by seal rings
functioning as retaining members.
[0076] Without reducing the frictional resistance between the shaft
45 of the pressing member 46 and the cam surfaces C of the pump
wheel 32, the frictional coefficient of one of the sliding section
of the shaft 45 and the sliding section of the roller 44 may be set
lower than the frictional coefficient of the other. Since this
reduces the frictional resistance of the shaft 45 and the roller
44, only the roller 44 is rotated without causing the shaft 45 to
rotate when the pump wheel 32 is rotated during the activation of
the pump. Therefore, the load applied to the cam surfaces C from
the shaft 45 is reduced, which reduces the wear of the cam surfaces
C caused by the shaft 45. Further, the frictional resistance
between the shaft 45 and the roller 44. This reduces the force
required for rotating the pump wheel 32 when actuating the pump.
Thus, the pump torque is reduced and the pump efficiency is
improved.
[0077] The shaft 45 may be press fitted to the insertion hole 44a
of the roller 44 so that the roller 44 and the shaft 45 rotate
integrally.
[0078] The shaft 45 of the pressing member 46 may be made of a low
friction material such as polytetrafluoroethylene.
[0079] Only parts of the shaft 45 of the pressing member 46 that
slide on the cam surfaces C, that is, only both end portions of the
shaft 45 may be formed of a low friction material such as
polytetrafluoroethylene, metal, and polyacetal or polystyrene of a
sliding grade.
[0080] The roller 44 and the shaft 45 may be formed as an integral
body.
[0081] The upstream recess 38 and the downstream recess 39 do not
need to be arranged to be adjacent to each other in the
circumferential direction of the inner circumferential surface 31b
of the housing 31.
[0082] Either one of the upstream recess 38 and the downstream
recess 39 may be omitted.
[0083] Instead of the roller 44 and the shaft 45, the pressing
member 46 may include a sliding member that slides on the
intermediate portion 36 of the drain tube 27, while pressing the
intermediate portion 36.
[0084] In the illustrated embodiment, the liquid ejection
apparatus, which is equipped with the tube pump 29, is embodied as
the inkjet printer 11. However, for example, the present invention
may be embodied as a liquid ejection apparatus used for
manufacturing color filters for liquid crystal displays or pixels
of organic EL displays. Alternatively, the tube pump 29 may be
mounted on apparatus other than liquid ejection apparatuses.
* * * * *