U.S. patent application number 13/610419 was filed with the patent office on 2013-03-14 for fluid feed pump, fluid circulation device, medical device and electronic device.
This patent application is currently assigned to SEIKO EPSON CORPORATION. The applicant listed for this patent is Akio Kobayashi, Takahiro Matsuzaki, Atsushi Oshima, Kazuaki Uchida. Invention is credited to Akio Kobayashi, Takahiro Matsuzaki, Atsushi Oshima, Kazuaki Uchida.
Application Number | 20130064698 13/610419 |
Document ID | / |
Family ID | 46829666 |
Filed Date | 2013-03-14 |
United States Patent
Application |
20130064698 |
Kind Code |
A1 |
Oshima; Atsushi ; et
al. |
March 14, 2013 |
FLUID FEED PUMP, FLUID CIRCULATION DEVICE, MEDICAL DEVICE AND
ELECTRONIC DEVICE
Abstract
A fluid feed pump is configured, such that a fluid is fed from
an outlet channel of the fluid feed pump through an outlet buffer
chamber to a fluid channel. The outlet buffer chamber is designed
to have a higher compliance than a compliance of a pump chamber.
The driving period of the fluid feed pump is set to a shorter
period than a time constant defined by the compliance of the pump
chamber and a flow resistance between an inlet of the outlet
channel and an outlet of the fluid channel. This enables the fluid
to be fed with high efficiency by taking advantage of the pressure
oscillation occurring between the pump chamber and the outlet
buffer chamber.
Inventors: |
Oshima; Atsushi;
(Shiojiri-shi, JP) ; Matsuzaki; Takahiro;
(Shiojiri-shi, JP) ; Uchida; Kazuaki;
(Matsumoto-shi, JP) ; Kobayashi; Akio;
(Shiojiri-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Oshima; Atsushi
Matsuzaki; Takahiro
Uchida; Kazuaki
Kobayashi; Akio |
Shiojiri-shi
Shiojiri-shi
Matsumoto-shi
Shiojiri-shi |
|
JP
JP
JP
JP |
|
|
Assignee: |
SEIKO EPSON CORPORATION
Tokyo
JP
|
Family ID: |
46829666 |
Appl. No.: |
13/610419 |
Filed: |
September 11, 2012 |
Current U.S.
Class: |
417/410.1 ;
417/540; 417/542 |
Current CPC
Class: |
F04B 43/046
20130101 |
Class at
Publication: |
417/410.1 ;
417/540; 417/542 |
International
Class: |
F04B 11/00 20060101
F04B011/00; F04B 17/03 20060101 F04B017/03 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 13, 2011 |
JP |
2011-199122 |
Sep 13, 2011 |
JP |
2011-199127 |
Nov 18, 2011 |
JP |
2011-252355 |
Mar 13, 2012 |
JP |
2012-55330 |
Claims
1. A fluid feed pump that feeds a fluid through a fluid channel,
comprising: a pump chamber having variable volume; an inlet channel
arranged to allow inflow of the fluid from the fluid channel to the
pump chamber; a check valve provided between the inlet channel and
the pump chamber; an outlet channel connected with the pump chamber
to feed the fluid out of the pump chamber; and an outlet buffer
chamber connected with the outlet channel to feed the fluid from
the outlet channel to the fluid channel, wherein the outlet buffer
chamber has a compliance higher than a compliance of the pump
chamber, and a time per cycle of changing the volume of the pump
chamber is shorter than a time constant defined by a product of the
compliance of the pump chamber and a flow resistance between an
inlet of the outlet channel and an outlet of the fluid channel.
2. The fluid feed pump according to claim 1, wherein the outlet
channel has a flow resistance lower than a flow resistance of the
fluid channel.
3. The fluid feed pump according to claim 1, wherein the compliance
of the outlet buffer chamber is at least 10 times as high as the
compliance of the pump chamber.
4. The fluid feed pump according to claim 1, further comprising: an
inlet buffer chamber provided between the inlet channel and the
check valve, wherein the fluid channel is connected with the inlet
channel, so that the fluid fed from the outlet channel to the fluid
channel is returned to the inlet buffer chamber.
5. The fluid feed pump according to claim 4, wherein the inlet
buffer chamber has a compliance that is at least five times as high
as the compliance of the outlet buffer chamber.
6. The fluid feed pump according to claim 1, further comprising: an
inlet buffer chamber provided between the inlet channel and the
check valve, wherein the inlet buffer chamber is a deformable
pack.
7. The fluid feed pump according to claim 1, further comprising: an
inlet buffer chamber provided between the inlet channel and the
check valve, wherein the inlet buffer chamber is a deformable pack
to be attachable to and detachable from the fluid feed pump.
8. The fluid feed pump according to claim 1, wherein the volume of
the pump chamber is changed by actuation of a piezoelectric
element.
9. A fluid circulation device, comprising the fluid feed pump
according to claim 1.
10. A medical device, comprising the fluid feed pump according to
claim 1.
11. An electronic device, comprising the fluid feed pump according
to claim 1.
12. A fluid feed pump, comprising: a pump chamber having volume
changeable by actuation of a piezoelectric element; an outlet
channel arranged to allow outflow of a fluid from the pump chamber
to a fluid channel; an inlet channel arranged to supply the fluid
to the pump chamber; and a check valve provided between the inlet
channel and the pump chamber, wherein the piezoelectric element is
actuated in a shorter period than a time constant when internal
pressure of the pump chamber increases and subsequently decreases,
the fluid feed pump further comprising: an outlet buffer chamber
provided between the outlet channel and the fluid channel and
configured to have a compliance that is higher than a compliance of
the pump chamber but is at most 100 times as high as the compliance
of the pump chamber.
13. The fluid feed pump according to claim 12, further comprising:
an inlet buffer chamber provided between the inlet channel and the
check valve, wherein the fluid channel is connected with the inlet
channel, so that the fluid fed from the outlet channel to the fluid
channel is returned to the inlet buffer chamber.
14. The fluid feed pump according to claim 12, further comprising:
an inlet buffer chamber provided between the inlet channel and the
check valve, wherein the inlet buffer chamber has a compliance that
is at least five times as high as the compliance of the outlet
buffer chamber.
15. The fluid feed pump according to claim 12, further comprising:
an inlet buffer chamber provided between the inlet channel and the
check valve, wherein the inlet buffer chamber is a deformable
pack.
16. The fluid feed pump according to claim 12, further comprising:
an inlet buffer chamber provided between the inlet channel and the
check valve, wherein the inlet buffer chamber is a deformable pack
to be attachable to and detachable from the fluid feed pump.
17. A fluid circulation device, comprising the fluid feed pump
according to claim 12.
18. A medical device, comprising the fluid feed pump according to
claim 12.
19. An electronic device, comprising the fluid feed pump according
to claim 12.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority to Japanese Patent
Applications No. 2011-199122 filed on Sep. 13, 2011; No.
2011-199127 filed on Sep. 13, 2011; No. 2011-252355 filed on Nov.
18, 2011; and No. 2012-55330 filed on Mar. 13, 2012, the
disclosures of which are hereby incorporated by reference in their
entireties.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a fluid feed pump operated
to pressure-feed a fluid, as well as a fluid circulation device, a
medical device and an electronic device.
[0004] 2. Description of Related Art
[0005] A fuel feed pump of one proposed structure repeats the
operation of increasing the volume of a pump chamber to suck in a
fluid and subsequently decreasing the volume of the pump chamber to
pressure-feed the fluid (e.g., JP 2011-103930A). This fluid feed
pump pressure-feeds the fluid in the pump chamber, every time the
volume of the pump chamber is increased and subsequently decreased.
The fluid feed amount per each operation is substantially equal to
the differential volume given by subtracting the minimum volume
from the maximum value of the pump chamber (excluded volume). The
fluid feed amount of the fluid feed pump is thus approximately
equal to the product of the number of cycles of increasing and
subsequently decreasing the volume of the pump chamber (frequency
of actuation) per unit time and the excluded volume. This means
that increasing the frequency of actuation per unit time
proportionally increases the fluid feed amount.
[0006] Operating the fluid feed pump in a certain operating range,
the energy efficiency decline has been pointed out.
SUMMARY
[0007] The reason that a fluid feed pump of this invention can
operate with high efficiency is described below with some figures.
FIG. 13 illustrates the general structure of a fluid feed pump. A
diaphragm forms part of a pump chamber and is deformed by expanding
a piezoelectric element placed in a casing. The fluid in the pump
chamber is then pressure-fed through an outlet channel. After the
pressure-feed of the fluid, removal of a driving voltage applied to
the piezoelectric element returns the expanded piezoelectric
element to the original length and thereby increases the volume of
the pump chamber. Accompanied with this volume increase, the fluid
in an inlet buffer chamber flows via a check valve into the pump
chamber. The inlet buffer chamber then receives supplement of the
fluid through an inlet channel.
[0008] FIGS. 14A and 14B illustrate changes in internal pressure of
the pump chamber by application of a driving signal to the
piezoelectric element. As illustrated in FIG. 14A, applying a
driving voltage to the piezoelectric element expands the
piezoelectric element and abruptly raises the internal pressure of
the pump chamber. This results in pressure-feeding the fluid in the
pump chamber through the outlet channel and thereby lowers the
internal pressure of the pump chamber. Removing the driving voltage
applied to the piezoelectric element contracts the piezoelectric
element and increases the volume of the pump chamber to further
lower the internal pressure of the pump chamber to negative
pressure. The fluid is then flowed into the pump chamber from the
inlet buffer chamber, so as to promptly recover the internal
pressure of the pump chamber.
[0009] Under the certain driving conditions of the fluid feed pump,
the time required to increase or decrease the internal pressure of
the pump chamber is significantly shorter than the period of
driving the fluid feed pump (i.e., time per cycle of changing the
volume of the pump chamber) and the time period between application
and removal of the driving voltage. It can thus be assumed that the
driving voltage is removed after the fluid pressurized in the pump
chamber is fully pressure-fed through the outlet cannel. Similarly
it can be assumed that the driving voltage is applied after the
fluid is fully supplemented from the inlet buffer chamber into the
pump chamber having the volume increased by removal of the driving
voltage. As a result, the fluid corresponding to the excluded
volume is pressure-fed, every time a driving signal pulse is
applied.
[0010] When a fluid channel connected with the outlet channel has
high flow resistance (as in the thin and long fluid channel) or
when a fluid of high viscosity is pressure-fed, it takes a
relatively long time to flow the fluid corresponding to the
excluded volume out of the pump chamber having the reduced volume.
This results in extending the time required for lowering the
internal pressure of the pump chamber.
[0011] In the graph of FIG. 14B, the dashed-dotted-line curve shows
the state that the internal pressure of the pump chamber decreases
when the fluid channel has high flow resistance or when the fluid
of high viscosity is pressure-fed. Compared with the ordinary case
shown by the broken-line curve (i.e., when the fluid channel has
low flow resistance and the pressure-fed fluid has low viscosity),
it takes a longer time to lower the internal pressure of the pump
chamber. This means that a longer time is required to pressure-feed
the fluid corresponding to the excluded volume. Removal of the
driving voltage before a sufficient decrease of the internal
pressure (i.e., before the fluid corresponding to the excluded
volume is fully fed out of the pump chamber) interrupts the fluid
feed and causes supplement of the fluid from the inlet buffer
chamber. This lowers the efficiency of fluid feed per cycle.
[0012] Even when the fluid channel does not have the high fluid
resistance and the pressure-fed fluid does not have the high
viscosity, the extremely short period of driving the fluid feed
pump (i.e., the time per cycle of changing the volume of the pump
chamber) (i.e., high driving frequency) may cause similar problem.
Even when the fluid channel does not have the high fluid resistance
and the pressure-fed fluid does not have the high viscosity, it is
impossible to fully flow the fluid corresponding to the excluded
volume out of the pump chamber at the instance of expanding the
piezoelectric element. It takes not long but still some time to
fully flow out the fluid corresponding to the excluded volume.
Driving the fluid feed pump in the shorter period than the time
required to fully flow out the fluid corresponding to the excluded
volume thus disadvantageously lowers the efficiency of fluid
feed.
[0013] Driving the fluid feed pump in the shorter period than the
time required to fully flow the fluid corresponding to the excluded
volume out of the pump chamber (i.e., the time required to
sufficiently reduces the internal pressure of the pump chamber)
lowers the efficiency of fluid feed, irrespective of the flow
resistance of the fluid channel and the viscosity of the
pressure-fed fluid. This decrease in efficiency of fluid feed
becomes non-negligibly large in the driving period of the fluid
feed pump shorter than a time constant .tau. when the internal
pressure of the pump chamber is reduced as shown in FIG. 14B. The
time constant .tau. herein is defined by the product of the
compliance of the pump chamber and the flow resistance between an
inlet of the outlet channel and an outlet of the fluid channel as
described later in detail.
[0014] FIG. 15 shows the relationship between the driving frequency
(reciprocal of the driving period) of the fluid feed pump and the
fluid feed amount. Under the ordinary driving conditions of the
fluid feed pump, the driving frequency is sufficiently lower than
1/.tau., so that the fluid feed amount increases in proportion to
the driving frequency. At the higher driving frequencies, however,
the fluid feed amount does not increase at a comparable rate to the
increase rate of the driving frequency as shown by the solid-line
curve in FIG. 15. At the driving frequency of higher than 1/.tau.,
there is a significant decrease in efficiency of fluid feed by the
fluid feed pump. The electrical energy applied to drive the
piezoelectric element is approximately proportional to the driving
frequency. Such a decrease in efficiency of fluid feed indicates an
increase in potential loss of the electrical energy applied to the
piezoelectric element.
[0015] The object of the invention is to provide a high-efficient
fluid feed pump that feeds a fluid with high efficiency even in a
shorter driving period than a time constant .tau. when the internal
pressure of a pump chamber decreases and that significantly
decreases a potential loss of electrical energy applied to a
piezoelectric element, as well as a fluid circulation device, a
medical device and an electronic device.
[0016] According to a first aspect, there is provided a fluid feed
pump that feeds a fluid through a fluid channel. The fluid feed
pump includes: a pump chamber having variable volume; an inlet
channel arranged to allow inflow of the fluid from the fluid
channel to the pump chamber; a check valve provided between the
inlet channel and the pump chamber; an outlet channel connected
with the pump chamber to feed the fluid out of the pump chamber;
and an outlet buffer chamber connected with the outlet channel to
feed the fluid from the outlet channel to the fluid channel. The
outlet buffer chamber has a compliance higher than a compliance of
the pump chamber. A time per cycle of changing the volume of the
pump chamber is shorter than a time constant defined by a product
of the compliance of the pump chamber and a flow resistance between
an inlet of the outlet channel and an outlet of the fluid
channel.
[0017] In the fluid feed pump of the first aspect, the volume of
the pump chamber is increased to suck the fluid out of the inlet
channel to the pump chamber via the check valve and is subsequently
decreased to feed the fluid from the outlet channel to the fluid
channel. The outlet buffer chamber having the higher compliance
than the compliance of the pump chamber is provided between the
outlet channel and the fluid channel. The time per cycle of
changing the volume of the pump chamber in the fluid feed pump is
shorter than the time constant .tau. defined by the product of the
compliance of the pump chamber and the flow resistance between the
inlet of the outlet channel and the outlet of the fluid
channel.
[0018] When the volume of the pump chamber decreases, the fluid
pressurized in the pump chamber moves through the outlet channel to
the outlet buffer chamber, so that the internal pressure of the
pump chamber immediately decreases (in a shorter time than the time
constant .tau.). The inertia of the fluid going through the outlet
channel causes the pump chamber to have negative internal pressure,
so that the fluid is immediately supplied to the pump chamber via
the check valve. This enables the fluid to be fed with high
efficiency even when the fluid feed pump is driven in the period
shorter than the time constant .tau.. The fluid flowing into the
outlet buffer chamber is supposed to flow toward the fluid channel,
but the flow resistance of the fluid channel interferes with the
smooth fluid flow. This increases the internal pressure of the
outlet buffer chamber, while the internal pressure of the pump
chamber decreases. This discourages the flow from the pump chamber
to the outlet buffer chamber. No check valve is provided between
the pump chamber and the outlet buffer chamber, so that there is
backflow from the outlet buffer chamber to the pump chamber. The
check valve is, on the other hand, provided between the pump
chamber and the inlet channel. The backflow of the fluid increases
the internal pressure of the pump chamber again. When the
increasing internal pressure of the pump chamber reaches or exceeds
the internal pressure of the outlet buffer chamber, the fluid stops
the backflow but starts flowing toward the outlet buffer chamber.
This causes the pump chamber to have negative pressure again and
enables further supply of the fluid from the inlet buffer chamber
to the pump chamber. The pressure oscillation occurring between the
pump chamber and the outlet buffer chamber via the outlet channel
results in increasing the amount of the fluid supplied to the pump
chamber. The fluid feed amount by each cycle of decreasing and
subsequently increasing the volume of the pump chamber is thus made
greater than the differential volume given by subtracting the
minimum volume from the maximum volume of the pump chamber
(excluded volume). Using the fluid feed pump that feeds the fluid
with high efficiency can significantly reduce the electrical energy
applied to the piezoelectric element, thus making a significant
contribution to energy saving.
[0019] According to one embodiment, there is provided the fluid
feed pump of the first aspect, wherein the outlet channel may have
a flow resistance lower than a flow resistance of the fluid
channel.
[0020] The fluid feed pump of this embodiment immediately lowers
the internal pressure of the pump chamber irrespective of the flow
resistance of the fluid channel, and additionally interferes with
attenuation of the pressure oscillation occurring between the pump
chamber and the outlet buffer chamber. This enables the pump
chamber to have the negative pressure many times and thereby
supplies the fluid to the pump chamber with high efficiency. This
configuration enables the fluid to be fed with high efficiency even
when the fluid feed pump is driven in the period shorter than the
time constant .tau..
[0021] According to another embodiment, there is provided the fluid
feed pump of the first aspect, wherein the compliance of the outlet
buffer chamber may be at least 10 times as high as the compliance
of the pump chamber.
[0022] When the compliance of the outlet buffer chamber is not
sufficiently higher than the compliance of the pump chamber, the
flow resistance of the fluid channel connected with the outlet
buffer chamber may affect the pressure-feed of the fluid from the
pump chamber to the outlet buffer chamber. In the fluid feed pump
of this embodiment, however, the compliance of the outlet buffer
chamber is at least 10 times as high as the compliance of the pump
chamber. This causes the flow resistance of the fluid channel
connected with the outlet buffer chamber to be substantially
negligible during the pressure-feed of the fluid from the pump
chamber. This configuration immediately lowers the internal
pressure of the pump chamber, thus enabling the fluid to be fed
with high efficiency.
[0023] According to another embodiment, there is provided the fluid
feed pump of the first aspect, which may further include an inlet
buffer chamber provided between the inlet channel and the check
valve, wherein the fluid channel may be connected with the inlet
channel, so that the fluid fed from the outlet channel to the fluid
channel is returned to the inlet buffer chamber.
[0024] In the fluid feed pump of this embodiment, the fluid fed to
the fluid channel is accumulated in the inlet buffer chamber and is
supplied to the pump chamber via the check valve. There is
accordingly no shortage of the fluid supplied via the check valve
to the pump chamber, even when the fluid fed from the pump chamber
is accumulated in the outlet buffer chamber and does not smoothly
flow out to the fluid channel. This configuration advantageously
avoids the decreased capacity of the fluid feed pump caused by
insufficient supply of the fluid to the pump chamber.
[0025] According to another embodiment, there is provided the fluid
feed pump of the first aspect, wherein the inlet buffer chamber may
have a compliance that is at least five times as high as the
compliance of the outlet buffer chamber.
[0026] It is experimentally confirmed that there is no shortage of
the fluid supplied to the pump chamber when the compliance of the
inlet buffer chamber is at least 5 times as high as the compliance
of the outlet buffer chamber. This configuration achieves the full
capacity of the fluid feed pump.
[0027] According to another embodiment, there is provided the fluid
feed pump of the first aspect, which may further include an inlet
buffer chamber provided between the inlet channel and the check
valve, wherein the inlet buffer chamber may be a deformable
pack.
[0028] This configuration readily achieves the inlet buffer chamber
of the required level of compliance.
[0029] According to another embodiment, there is provided the fluid
feed pump of the first aspect, which may further include an inlet
buffer chamber provided between the inlet channel and the check
valve, wherein the inlet buffer chamber may be a deformable pack to
be attachable to and detachable from the fluid feed pump.
[0030] The fluid feed pump of this embodiment enables easy
replacement of the deformed pack having the change in properties or
easy replacement to a pack of the optimum compliance according to
the application of the fluid feed pump.
[0031] According to another embodiment, there is provided the fluid
feed pump of the first aspect, wherein the volume of the pump
chamber may be changed by actuation of a piezoelectric element.
[0032] Using the piezoelectric element applies a large force to
abruptly reduce the volume of the pump chamber, so that large
pressure oscillation occurs between the pump chamber and the outlet
buffer chamber. The fluid is fed with high efficiency by taking
advantage of this pressure oscillation.
[0033] According to a second aspect, there is provided a fluid
circulation device using the fluid feed pump described above.
[0034] For example, the light source of a projector generates large
amount of heat and is thus required to be cooled down. An increase
in light intensity leads to an increase in generated heat and an
increase in required cooling capacity. The fluid feed pump of the
invention is small in size but has high fluid-feed capacity (high
cooling capacity). The fluid feed pump of the invention is thus
preferably applicable to a liquid circulation device that
circulates a fluid, such as coolant, to cool down. Applying the
fluid feed pump of the invention to the fluid circulation device
accordingly enables the configuration of a projector that is small
in size but has high light intensity.
[0035] According to a third aspect, there is provided a medical
device using the fluid feed pump described above.
[0036] The high-pressure spraying capacity is required, for
example, in a fluid injection device used to prepare microcapsules
containing medicinal substances or nutritional supplements and
surgical instruments like a surgical jet knife used to cut out or
remove body tissues by spraying a thin jet of a pressurized fluid,
such as water or normal saline solution, from a jet nozzle against
the body tissues. The fluid feed pump of the invention is small in
size but has high fluid-feed capacity. Using the fluid feed pump of
the invention accordingly enables the configuration of a medical
device that is small in size but has high spraying capacity. The
heat-generating part of the medical device may be cooled down by a
fluid circulation device including the fluid feed pump of the
invention. This enhances the reliability of the medical device. The
heat-generating part of the medical device may be, for example, a
piezoelectric actuator of the surgical jet knife.
[0037] According to a fourth aspect, there is provided an
electronic device using the fluid feed pump described above.
[0038] For example, circulating a fluid, e.g., coolant, efficiently
cools down the heat generated in an electronic device, such as a
projector. The fluid feed pump of the invention is small in size
but has high fluid-feed capacity. Using the fluid feed pump of the
invention accordingly enables the configuration of a compact
electronic device.
[0039] According to a fifth aspect, there is provided a fluid feed
pump, including: a pump chamber having volume changeable by
actuation of a piezoelectric element; an outlet channel arranged to
allow outflow of a fluid from the pump chamber to a fluid channel;
an inlet channel arranged to supply the fluid to the pump chamber;
and a check valve provided between the inlet channel and the pump
chamber. The piezoelectric element is actuated in a shorter period
than a time constant when internal pressure of the pump chamber
increases and subsequently decreases. The fluid feed pump further
includes an outlet buffer chamber provided between the outlet
channel and the fluid channel and configured to have a compliance
that is higher than a compliance of the pump chamber but is at most
100 times as high as the compliance of the pump chamber.
[0040] In the fluid feed pump of this aspect, the volume of the
pump chamber is increased to suck the fluid out of the inlet
channel to the pump chamber via the check valve and is subsequently
decreased to feed the fluid from the outlet channel to the fluid
channel. In the structure that the fluid channel is directly
connected with the outlet channel, due to the high flow resistance
of the fluid channel, the internal pressure of the pump chamber
increases with a decrease in volume of the pump chamber. The
subsequent direct flow of the fluid from the outlet channel to the
fluid channel lowers the internal pressure of the pump chamber. The
fluid feed pump is driven in the shorter period than the time
constant .tau. when the internal pressure of the pump chamber
decreases. The fluid feed pump of this aspect has the outlet buffer
chamber provided between the outlet channel and the fluid channel
and configured to have the compliance that is higher than the
compliance of the pump chamber but is at most 100 times as high as
the compliance of the pump chamber.
[0041] When the volume of the pump chamber decreases, the fluid
flows from the pump chamber to the outlet buffer chamber to
increase the internal pressure of the outlet buffer chamber. This
results in feeding the fluid from the outlet buffer chamber to the
fluid channel. The excessively high compliance of the outlet buffer
chamber extends the time until the expected fluid feed amount is
fulfilled after start of the operation of the fluid feed pump. As
described later in detail, the capacity of the fluid feed pump
increases with an increase in compliance of the outlet buffer
chamber relative to the compliance of the pump chamber, but reaches
the plateau when the compliance of the outlet buffer chamber
becomes about 100 times as high as the compliance of the pump
chamber. Setting the compliance of the outlet buffer chamber to be
higher than the compliance of the pump chamber but at most 100
times as high as the compliance of the pump chamber advantageously
shortens the time until the expected fluid feed amount is fulfilled
after start of the operation of the fluid feed pump.
[0042] According to one embodiment, there is provided the fluid
feed pump of the fifth aspect, which may further include an inlet
buffer chamber provided between the inlet channel and the check
valve, wherein the fluid channel may be connected with the inlet
channel, so that the fluid fed from the outlet channel to the fluid
channel is returned to the inlet buffer chamber.
[0043] In the fluid feed pump of this embodiment, the fluid fed to
the fluid channel is accumulated in the inlet buffer chamber and is
supplied to the pump chamber via the check valve. There is
accordingly no shortage of the fluid supplied via the check valve
to the pump chamber, even when the fluid fed from the pump chamber
is accumulated in the outlet buffer chamber and does not smoothly
flow out to the fluid channel. This configuration advantageously
avoids the decreased capacity of the fluid feed pump caused by
insufficient supply of the fluid to the pump chamber.
[0044] According to another embodiment, there is provided the fluid
feed pump of the fifth aspect, which may further include an inlet
buffer chamber provided between the inlet channel and the check
valve, wherein the inlet buffer chamber may have a compliance that
is at least five times as high as the compliance of the outlet
buffer chamber.
[0045] It is experimentally confirmed that there is no shortage of
the fluid supplied to the pump chamber when the compliance of the
inlet buffer chamber is at least 5 times as high as the compliance
of the outlet buffer chamber. This configuration achieves the full
capacity of the fluid feed pump.
[0046] According to another embodiment, there is provided the fluid
feed pump of the fifth aspect, which may further include an inlet
buffer chamber provided between the inlet channel and the check
valve, wherein the inlet buffer chamber may be a deformable
pack.
[0047] The fluid feed pump of this embodiment enables easy
replacement of the deformed pack having the change in properties or
easy replacement to a pack of the optimum compliance according to
the application of the fluid feed pump.
[0048] According to another embodiment, there is provided the fluid
feed pump of the fifth aspect, which may further include an inlet
buffer chamber provided between the inlet channel and the check
valve, wherein the inlet buffer chamber may be a deformable pack to
be attachable to and detachable from the fluid feed pump.
[0049] The fluid feed pump of this embodiment enables easy
replacement of the deformed pack having the change in properties or
easy replacement to a pack of the optimum compliance according to
the application of the fluid feed pump.
[0050] According to a sixth aspect, there is provided a fluid
circulation device using the fluid feed pump described above.
[0051] For example, the light source of a projector generates large
amount of heat and is thus required to be cooled down. An increase
in light intensity leads to an increase in generated heat and an
increase in required cooling capacity. The fluid feed pump of the
invention is small in size but has high fluid-feed capacity (high
cooling capacity). The fluid feed pump of the invention is thus
preferably applicable to a liquid circulation device that
circulates a fluid, such as coolant, to cool down. Applying the
fluid feed pump of the invention to the fluid circulation device
accordingly enables the configuration of a projector that is small
in size but has high light intensity.
[0052] According to a seventh aspect, there is provided a medical
device using the fluid feed pump described above.
[0053] The high-pressure spraying capacity is required, for
example, in a fluid injection device used to prepare microcapsules
containing medicinal substances or nutritional supplements and
surgical instruments like a surgical jet knife used to cut out or
remove body tissues by spraying a thin jet of a pressurized fluid,
such as water or normal saline solution, from a jet nozzle against
the body tissues. The fluid feed pump of the invention is small in
size but has high fluid-feed capacity. Using the fluid feed pump of
the invention accordingly enables the configuration of a medical
device that is small in size but has high spraying capacity. The
heat-generating part of the medical device may be cooled down by a
fluid circulation device including the fluid feed pump of the
invention. This enhances the reliability of the medical device. The
heat-generating part of the medical device may be, for example, a
piezoelectric actuator of the surgical jet knife.
[0054] According to an eighth aspect, there is provided an
electronic device using the fluid feed pump described above.
[0055] For example, circulating a fluid, e.g., coolant, efficiently
cools down the heat generated in an electronic device, such as a
projector. The fluid feed pump of the invention is small in size
but has high fluid-feed capacity. Using the fluid feed pump of the
invention accordingly enables the configuration of a compact
electronic device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0056] FIG. 1 illustrates the structure of a fluid feed pump
according to one embodiment of the invention;
[0057] FIGS. 2A to 2C show changes in internal pressure of a pump
chamber by application of a driving signal to a piezoelectric
element;
[0058] FIG. 3 illustrates different variations in fluid feed amount
in the presence and in the absence of an outlet buffer chamber;
[0059] FIG. 4 illustrates the effect of the volume of the outlet
buffer chamber on the volume of the pump chamber;
[0060] FIG. 5 illustrates time changes before stabilization of the
fluid feed amount after start of operation of the fluid feed
pump;
[0061] FIG. 6 illustrates the configuration of a circulation
channel using the fluid feed pump of the embodiment;
[0062] FIG. 7 illustrates the effect of the volume of an inlet
buffer chamber on the volume of the outlet buffer chamber;
[0063] FIG. 8 illustrates a fluid feed pump configured to increase
the compliance of the inlet buffer chamber according to one
modification;
[0064] FIGS. 9A to 9C illustrate circulation of a fluid through a
fluid channel by the operation of the fluid feed pump of the
modification;
[0065] FIGS. 10A to 10D illustrate the structure of a film pack
employed in the fluid feed pump of the modification;
[0066] FIGS. 11A and 11B illustrate an application of the fluid
feed pump to an electronic device;
[0067] FIG. 12 schematically illustrates the structure of a fluid
ejection system as an application of the fluid feed pump to a
medical device;
[0068] FIG. 13 illustrates the general structure of a fluid feed
pump;
[0069] FIGS. 14A and 14B illustrate changes in internal pressure of
a pump chamber by application of a driving signal to a
piezoelectric element; and
[0070] FIG. 15 shows the relationship between the driving frequency
of the fluid feed pump and the fluid feed amount.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0071] FIG. 1 illustrates the structure of a fluid feed pump 100
according to one embodiment. As illustrated, the fluid feed pump
100 of this embodiment differs from the fluid feed pump shown in
FIG. 13 by providing an outlet buffer chamber 118. More
specifically, in the fluid feed pump 100 of the embodiment, part of
a pump chamber 102 is formed from a diaphragm 104. A piezoelectric
element 106 is placed in a casing 108. An inlet buffer chamber 112
is provided via a check valve 110 above the pump chamber 102. A
fluid is supplied through an inlet channel 114 into the inlet
buffer chamber 112. The pump chamber 102 is connected with the
outlet buffer chamber 118 via an outlet channel 116, and a fluid
channel 122 is further connected with the outlet buffer chamber
118.
[0072] When a driving signal is applied to the piezoelectric
element 106 to extend the piezoelectric element 106, the diaphragm
104 is deformed to reduce the volume of the pump chamber 102. This
causes the fluid in the pump chamber 102 to flow through the outlet
channel 116 into the outlet buffer chamber 118 and then feeds the
fluid from the outlet buffer chamber 118 into the fluid channel
122.
[0073] FIGS. 2A to 2C show changes in internal pressure of the pump
chamber 102 by application of a driving signal to the piezoelectric
element 106 in the fluid feed pump 100 of the embodiment. FIG. 2A
shows a driving signal applied to the piezoelectric element 106.
FIGS. 2B and 2C show time changes in internal pressure with respect
to the outlet buffer chamber 118 of different volumes. As
illustrated in FIG. 2A, with an increase in voltage of the driving
signal (driving voltage), the piezoelectric element 106 is extended
to reduce the volume of the pump chamber 102, which abruptly
increases the internal pressure of the pump chamber 102. The outlet
buffer chamber 118 is provided between the outlet channel 116 and
the fluid channel 122, so that the fluid pressurized in the pump
chamber 102 moves to the outlet buffer chamber 118, so as to
immediately lower the internal pressure of the pump chamber 102.
This phenomenon is seen from the pump chamber 102. The fluid
channel 122 located beyond the outlet buffer chamber 118 hardly
affects the pump chamber 102, because of the presence of the outlet
buffer chamber 118. This configuration of connecting the fluid
channel 122 with the pump chamber 102 across the outlet channel 116
and the outlet buffer chamber 118 is thus substantially equivalent
to the configuration of simply connecting the outlet channel 116
with the pump chamber 102.
[0074] This phenomenon is explained more in detail below. When the
fluid flows at a flow rate Q through a circular channel, such as
the fluid channel 122 or the outlet channel 116, an internal
pressure difference .DELTA.P between two arbitrary points in the
circular channel is expressed by Equation (1) given below:
.DELTA.P=Q.times.R (1)
where R represents a flow resistance between the two arbitrary
points in the circular channel. When the fluid flow in the channel
is steady and laminar flow (Hagen-Poiseuille flow), the flow
resistance R is expressed by Equation (2) given below, wherein the
fluid of absolute viscosity .mu. flows through the circular channel
having the radius r and the length L between the two arbitrary
points:
R=8.times..mu..times.L/(.pi.r.sup.4) (2)
[0075] In the structure without the outlet buffer chamber 118
between the outlet channel 116 and the fluid channel 122 like the
fluid feed pump shown in FIG. 13, there is a variation in volume of
the pump chamber 102. The fluid flowing through the outlet channel
116 and the fluid channel 122 accordingly makes a non-stationary
flow, so that the flow resistance in the outlet channel 116 and in
the fluid channel 122 is increased to the level of about four times
as high as the flow resistance given by Equation (2).
[0076] When pressure is applied to inside the fluid chamber filled
with the fluid, such as the pump chamber 102 or the outlet buffer
chamber 118, there is volume expansion or fluid compression by
deformation of the fluid chamber. For example, in a simplest
application, a fluid chamber having the volume V and the bulk
modulus of elasticity K is filled with a fluid of compressibility
.kappa..sub.F (e.g., liquid), and a pressure P is applied to the
fluid in the fluid chamber. A variation .DELTA.V1 in volume by
deformation of the fluid chamber is expressed as the following
Equation (3).
.DELTA.V1=V/K.times.P (3)
[0077] A variation .DELTA.V2 in volume by compression of the fluid
is expressed as the following Equation (4).
.DELTA.V2=V.times..kappa..sub.F.times.P (4)
[0078] An apparent variation .DELTA.V in volume of the fluid
chamber by the pressure P is accordingly given as the following
Equation (5).
.DELTA.V=V.times.(1/K+.kappa..sub.F).times.P (5)
[0079] This product V.times.(1/K+.kappa..sub.F) is a value called
"compliance". Under the conditions that the fluid chamber is made
of a material of the same modulus of elasticity, that the fluid has
the same compressibility and that the same pressure P is applied,
Equation (5) indicates that the apparent variation .DELTA.V in
volume of the fluid chamber is proportional to the volume V of the
fluid chamber.
[0080] As described above, in the fluid feed pump without the
outlet buffer chamber 118 as shown in FIG. 13, the internal
pressure of the pump chamber 102 slowly decreases by a time
constant .tau. that is defined as the product of the flow
resistance in the outlet channel 116 and the fluid channel 122
(i.e., about four times as high as the flow resistance R given by
Equation (2) according to the experimental result) and the
compliance of the pump chamber 102. In the fluid feed pump 100 of
the invention with the outlet buffer chamber 118 having the higher
compliance than that of the pump chamber 102, however, the pump
chamber 102 is hardly affected by the flow resistance in the fluid
channel 122. The outflow of the fluid corresponding to volume
reduction of the pump chamber 102 is affected by only the flow
resistance and the inertance of the outlet channel 116. This
shortens the time required to complete the outflow of the fluid
corresponding to the volume reduction.
[0081] The fluid moving through the outlet channel 116 receives the
inertial force by the inertance of the outlet channel 116, so that
the internal pressure of the pump chamber 102 becomes negative. The
fluid can thus be supplied from the inlet buffer chamber 112 to the
pump chamber 102. The inertance of the outlet channel 116 is larger
than the inertance of a communicating path between the inlet buffer
chamber 112 and the pump chamber 102. The fluid moving through the
outlet channel 116 thus hardly goes back to the pump chamber 102,
and the fluid is supplied from the inlet buffer chamber 112 to the
pump chamber 102. This is attributed to the extremely small
inertance of the channel on the inlet side (i.e., passage with the
check valve 110) compared with the inertance of the channel on the
outlet side (i.e., outlet channel 116).
[0082] The inertance is a characteristic value of the channel and
indicates the flowability of the fluid flowing through the channel
under application of a pressure on one end of the channel. In a
simple example, it is assumed that a channel having the cross
sectional area S and the length L is filled with a fluid (e.g.,
liquid) having the density .rho. and that a pressure P is applied
on one end of the channel (more specifically, pressure difference P
between both ends). The force of pressure P.times.cross sectional
area S then acts on the fluid in the channel, so that the fluid in
the channel flows out. When the fluid flowing out has the
acceleration "a", since the mass of the fluid in the channel is
given by the density .rho..times.cross sectional area
S.times.length L, the equation of motion is transformed as the
following Equation (6).
P=.rho..times.L.times.a (6)
[0083] When the fluid flowing through the channel has the
volumetric flow rate Q and the flow velocity v, the following
equation is given:
Q=v.times.S,
so that
dQ/dt=a.times.S (7)
[0084] Substituting Equation (7) into Equation (6) gives the
following equation:
P=(.rho..times.L/S).times.(dQ/dt) (8)
[0085] This equation transforms the motion of equation with respect
to the fluid in the channel using the pressure P applied on one end
of the channel (more specifically, pressure difference between both
ends) and dQ/dt. Equation (8) indicates an increase in dQ/dt (i.e.,
a greater change in flow velocity) with a decrease in value
(.rho..times.L/S) under application of the same pressure P. This
value (.rho..times.L/S) is called inertance.
[0086] In the fluid feed pump 100 of FIG. 1 according to the
embodiment, the outlet channel 116 has the large inertance, because
of its small inner diameter and long channel length. The channel on
the inlet side of the pump chamber 102, on the other hand, has the
small inertance, because of the short channel length of the passage
with the check valve 110. When the pump chamber 102 has negative
pressure, the fluid on the outlet side having the large resultant
inertance is hardly sucked into the pump chamber 102, while the
fluid on the inlet side having the small resultant inertance is
sucked into the pump chamber 102. Because of the reasons described
above, reducing the volume of the pump chamber 102 causes the fluid
pressurized in the pump chamber 102 to move through the outlet
channel 116 to the outlet buffer chamber 118, so that the internal
pressure of the pump chamber 102 immediately decreases (within a
shorter time than the time constant .tau.). The internal pressure
of the pump chamber 102 becomes negative by the inertia of the
fluid flowing through the outlet channel 116, and the fluid is
immediately supplied to the pump chamber 102 via the check valve
110. The fluid can thus be fed into the pump chamber 102 with high
efficiency, even when the fluid feed pump 100 is driven in shorter
periods than the time constant .tau..
[0087] The fluid flowing into the outlet buffer chamber 118 hardly
flows out, due to the high flow resistance in the fluid channel
122. This results in increasing the internal pressure of the outlet
buffer chamber 118. The internal pressure of the pump chamber 102
decreases in this state, so that the inertial force of the fluid in
the outlet channel 116 gradually decreases. Since no check valve
110 is provided between the pump chamber 102 and the outlet buffer
chamber 118, there is a reverse flow from the outlet buffer chamber
118 into the pump chamber 102. Even when the fluid flows back to
the pump chamber 102, the check valve 110 prevents the fluid from
flowing into the inlet buffer chamber 112. This increases the
internal pressure of the pump chamber 102 again and causes the
back-flow fluid to flow toward the outlet buffer chamber 118. This
again causes the negative pressure in the pump chamber 102, so that
the fluid can further be supplied from the inlet buffer chamber 112
to the pump chamber 102. Repeating such oscillating motions opens
the check valve 110 a plurality of times (twice in the illustrated
example of FIGS. 2A to 2C) during one operation and enables the
fluid to be supplied to the pump chamber 102.
[0088] This phenomenon is typically regarded as propagation by the
pressure wave in the fluid propagating between the pump chamber 102
and the outlet buffer chamber 118. The fluid feed pump 100 of the
embodiment has the short distance between the pump chamber 102 and
the outlet buffer chamber 118 (about 10 cm at the longest,
irrespective of the size of the outlet buffer chamber). The
oscillation period by propagation of the pressure wave is expected
to be 0.2 msec at the longest when the sonic speed in the fluid is
about 1000 m/sec. The natural oscillation period of the oscillation
shown in FIG. 2B or FIG. 2C is, however, about 0.35 msec for the
outlet buffer chamber 118 of the smaller volume and about 0.4 msec
for the outlet buffer chamber 118 of the larger volume. These
values are not explainable by propagation of the pressure wave.
[0089] This phenomenon is explainable by taking into account the
compressibility of the fluid (in other words, by treating the fluid
as compressive fluid). When this phenomenon is regarded as natural
oscillation (resonance) defined by the compliance of the pump
chamber 102, the inertance of the outlet channel 116 and the
compliance of the outlet buffer chamber 118, the natural
oscillation period T is expressed by Equation (9) given below:
T=2.pi.(MC).sup.1/2 (9)
where M represents the inertance of the outlet channel 116 and C
represents the resultant compliance of the pump chamber 102 and the
outlet buffer chamber 118. When C.sub.1 represents the compliance
of the pump chamber 102 and C.sub.2 represents the compliance of
the outlet buffer chamber 118, the resultant compliance C is given
by Equation (10) below:
C=1/(1/C.sub.1+1/C.sub.2) (10)
[0090] Using the natural oscillation defined by Equation (9) can
reproduce the oscillations shown in FIGS. 2B and 2C and can explain
why the natural oscillation period T is increased with an increase
in volume of the outlet buffer chamber 118 (which results in
increasing the compliance of the outlet buffer chamber 118). From
Equations (9) and (10) given above, it is understood that the
volume of the pump chamber 102 affects the natural oscillation
period T.
[0091] FIG. 3 illustrates different variations in fluid feed amount
in the presence and in the absence of the outlet buffer chamber
118. More specifically, FIG. 3 shows the measurement results of the
fluid feed amount in the fluid feed pump without the outlet buffer
chamber 118 and in the fluid feed pump 100 of the embodiment with
the outlet buffer chamber 118. As shown in FIG. 3, providing the
outlet buffer chamber 118 significantly increases the fluid feed
amount. Additionally, the fluid feed amount increases with an
increase in volume of the outlet buffer chamber 118. This is due to
the reasons given below.
[0092] The fluid in the inlet buffer chamber 112 flows into the
pump chamber 102 during the time period when the pump chamber 102
has negative pressure (negative pressure time period). The longer
negative pressure time period increases the flow rate of the fluid
flowing from the inlet buffer chamber 112 into the pump chamber 102
(this flow rate corresponds to the fluid feed amount). As shown in
FIGS. 2B and 2C, the oscillation of the internal pressure of the
pump chamber 102 is attenuated by the flow resistance in the outlet
channel 116, so that there is a limited number of times when the
internal pressure of the pump chamber 102 becomes negative. The
longer negative pressure time period each time increases the flow
rate into the pump chamber 102. The longer natural oscillation
period T is accordingly preferable. As clearly understood from
Equation (9), the higher resultant compliance C results in
increasing the natural oscillation period T. Increasing the volume
(compliance) of the pump chamber 102, however, decreases the ratio
of the volume reduction caused by decreasing the volume of the pump
chamber 102 to the volume of the pump chamber 102 and thereby
lowers the pressure of the pump chamber 102. The volume
(compliance) of the outlet buffer chamber 118 is accordingly
increased to increase the fluid feed amount.
[0093] FIG. 4 illustrates the effect of the volume of the outlet
buffer chamber 118 on the volume of the pump chamber 102. More
specifically, FIG. 4 shows a variation in fluid feed amount with a
variation in volume (compliance) of the outlet buffer chamber 118
relative to the volume (compliance) of the pump chamber 102. As
illustrated, setting the volume (compliance) of the outlet buffer
chamber 118 to 10 times or more the volume (compliance) of the pump
chamber 102 at least doubles the fluid feed amount. The fluid feed
amount reaches the plateau when the volume (compliance) of the
outlet buffer chamber 118 is 100 times or more the volume of the
pump chamber 102. During this time period of natural oscillation,
the internal pressure of the pump chamber 102 varies. The variation
in internal pressure of the pump chamber 102 decreases with an
increase in volume (compliance) of the outlet buffer chamber 118
relative to the volume (compliance) of the pump chamber 102.
Increasing the volume (compliance) of the outlet buffer chamber 118
relative to the volume (compliance) of the pump chamber 102
accordingly has the effect of reducing pulsation.
[0094] FIG. 5 illustrates measurement examples of time change
before stabilization of the fluid feed amount after start of
operation of the fluid feed pump 100 of the embodiment. The
solid-line curve of FIG. 5 shows a time change with respect to the
outlet buffer chamber 118 of the large volume (the volume of the
outlet buffer chamber 118 is 100 times as large as the volume of
the pump chamber 102). The broken-line curve of FIG. 5 shows a time
change with respect to the outlet buffer chamber 118 of the larger
volume (the volume of the outlet buffer chamber 118 is 200 times as
large as the volume of the pump chamber 102). Immediately after
start of operation of the fluid feed pump 100, the fluid feed
amount increases, accompanied with a gradual increase in internal
pressure of the outlet buffer chamber 118. An excessively large
volume (high compliance) of the outlet buffer chamber 118 slows the
increase in internal pressure of the outlet buffer chamber 118 and
extends the time before stabilization of the fluid feed amount. The
excessively large volume (high compliance) of the outlet buffer
chamber 118 is thus non-preferable. In the presence of a
circulation channel where the fluid flowing through the fluid
channel 122 is circulated to the inlet channel 114 as illustrated
in FIG. 6, an increase in amount of the fluid accumulated in the
outlet buffer chamber 118 causes deficiency of the fluid
circulating through the fluid channel 122 and causes the inlet
buffer chamber 112 to have negative pressure, which may result in
decreasing the fluid feed amount. Due to these reasons, the volume
(compliance) of the outlet buffer chamber 118 is preferably at
least about 100 times as large as (as high as) the volume
(compliance) of the pump chamber 102.
[0095] FIG. 6 illustrates the configuration of a circulation
channel using the fluid feed pump 100 of the embodiment. Connecting
the circulation channel with the fluid feed pump 100 is referred to
as fluid circulation device 100X.
[0096] FIG. 7 illustrates the effect of the volume of the inlet
buffer chamber 112 on the volume of the outlet buffer chamber 118.
More specifically, FIG. 7 shows a variation in fluid feed amount
with a variation in volume (compliance) of the inlet buffer chamber
112 relative to the volume (compliance) of the outlet buffer
chamber 118. Setting the volume (compliance) of the inlet buffer
chamber 112 to 5 times or more the volume (compliance) of the
outlet buffer chamber 118 stabilizes the fluid feed amount. This
may be because the inlet buffer chamber 112 having the sufficient
volume (compliance) does not have extreme negative pressure even
when the fluid fed from the pump chamber 102 is accumulated in the
outlet buffer chamber 118. The volume (compliance) of the inlet
buffer chamber 112 is thus preferably 5 times or more the volume
(compliance) of the outlet buffer chamber 118.
[0097] FIG. 8 illustrates a fluid feed pump 200 configured to
increase the compliance of the inlet buffer chamber 112 according
to one modification. In the illustrated example of FIG. 8, a
circulation channel is configured using the fluid feed pump 200 of
the modification.
[0098] As illustrated, the fluid feed pump 200 of the modification
is generally structured by integrating a piezoelectric element
casing 210 with a channel casing 240. The piezoelectric element
casing 210 has a through hole 210h of circular cross section, which
is formed in the approximate center of a joint surface with the
channel casing 240 to pass through the piezoelectric element casing
210. The bottom of the through hole 210h is securely closed by a
bottom plate 212. A laminated-type piezoelectric element 214 is
placed in the through hole 210h of this piezoelectric element
casing 210, and the bottom of the piezoelectric element 214 is
fastened to the bottom plate 212. A circular reinforcement plate
216 is attached to the upper end of the piezoelectric element 214,
and a circular diaphragm 218 made of e.g., metal thin plate, is
fixed to the upper surface of the reinforcement plate 216. The
outer diameter of the diaphragm 218 is larger than the inner
diameter of the through hole 210h. The thickness of the
reinforcement plate 216 is set, such that the diaphragm 218 fixed
to the reinforcement plate 216 comes into contact with the upper
surface of the piezoelectric element casing 210 (i.e., joint
surface with the channel casing 240).
[0099] The channel casing 240 has a circular recess 240c formed on
the joint surface with the piezoelectric element casing 210, and a
ring-shaped annular member 220 is set in this recess 240c. The
inner diameter of the annular member 220 is smaller than the outer
diameter of the diaphragm 218. When the channel casing 240 and the
piezoelectric element casing 210 are fixed to each other, e.g., by
screwing, the diaphragm 218 is located between the annular member
220 and the piezoelectric element casing 210. A pump chamber 230 is
accordingly defined by the recess 240c of the channel casing 240,
the inner circumferential face of the annular member 220 and the
diaphragm 218. Deformation of the diaphragm 218 by expanding or
contracting the piezoelectric element 214 changes the volume of the
pump chamber 230 as described later in detail.
[0100] The channel casing 240 also has a fluid chamber 246 arranged
to lead the fluid to the pump chamber 230, an outlet channel 242
arranged to lead the fluid in the pump chamber 230 to one end of a
fluid channel 300 connected with the side face of the channel
casing 240, and an inlet channel 244 arranged to lead the fluid
supplied from the other end of the fluid channel 300 connected with
the side face of the channel casing 240 to the fluid chamber 246.
Although being omitted from the illustration to avoid complexity,
as in the fluid feed pump 100 of the embodiment, in the fluid feed
pump 200 of the modification, the pump chamber 230 is connected
with an outlet buffer chamber via the outlet channel 242, and the
fluid channel 300 is connected with the outlet buffer chamber.
[0101] The fluid chamber 246 has one end open to the upper surface
of the channel casing 240 (i.e., opposite surface opposed to the
joint surface with the piezoelectric element casing 210) and the
other end open to the pump chamber 230 and is tapered (to have the
smaller cross sectional area) toward the pump chamber 230. The
inlet channel 244 is connected with the middle of the fluid chamber
246. A check valve 248 is provided on one end of the fluid chamber
246 on the side of the pump chamber 230 to allow the inflow of the
fluid from the fluid chamber 246 to the pump chamber 230 but to
prohibit the backflow of the fluid from the pump chamber 230 to the
fluid chamber 246. A connection member 262 of a film pack 260 made
of a flexible film having gas barrier property and heat resistance
is air-tightly fit in an end of the fluid chamber 246 open to the
upper surface of the channel casing 240. The film pack 260 of the
embodiment is attachable to and detachable from the channel casing
240. The structure of the film pack 260 will be described later in
detail with reference to another drawing.
[0102] The fluid channel 300 may be made of a pressure-resistant
silicone tube or resin tube. In the circulation channel of this
structure, the fluid is circulated through the fluid channel 300 by
actuation of the piezoelectric element 214 of the fluid feed pump
200 as described below.
[0103] FIGS. 9A to 9C illustrate circulation of the fluid through
the fluid channel 300 by the operation of the fluid feed pump 200.
FIG. 9A shows the state that the fluid feed pump 200 does not work
(i.e., the state before application of the driving voltage to the
piezoelectric element 214). In this state, the pump chamber 230 is
filled with the fluid.
[0104] When the driving voltage is applied to the piezoelectric
element 214 in the state that the pump chamber 230 is filled with
the fluid as shown in FIG. 9A, the increasing driving voltage
expands the piezoelectric element 214 as shown in FIG. 9B. This
results in pressing the diagraph 218 toward the pump chamber 230
via the reinforcement plate 216, so that the volume of the pump
chamber 230 is reduced and the fluid in the pump chamber 230 is
pressurized. In this state, the check valve 248 is in the closed
position to prevent the backflow of the fluid from the pump chamber
230 to the fluid chamber 246. The fluid corresponding to the volume
reduction of the pump chamber 230 is accordingly pressure-fed
through the outlet channel 242 and the outlet buffer chamber (not
shown) toward the fluid channel 300.
[0105] While the fluid is fed into the fluid channel 300, the fluid
in the fluid channel 300 is gradually pressed downstream. As
described above, in the circulation channel of the modification,
the fluid channel 300 and the fluid feed pump 200 form the closed
system. The fluid pressed out of the fluid channel 300 and returned
to the fluid feed pump 200 flows through the inlet channel 244 into
the film pack 260. The film pack 260 is made of a flexible film and
is attached not in the fully-tense state filled with the fluid but
in the state having some room for further expansion. The fluid
going back from the fluid channel 300 flows into the film pack 260
to expand the film pack 260. This structure prevents the pressure
increase in the film pack 260 or in the fluid chamber 246
connecting with the film pack 260.
[0106] When the piezoelectric element 214 is subsequently
contracted to its original length by the decreasing driving voltage
as shown in FIG. 9C, the volume of the pump chamber 230 is
increased and returned to the original volume. In this state, the
pump chamber 230 has the negative pressure, so that the check valve
248 is opened to suck the fluid from the fluid chamber 246 into the
pump chamber 230. The negative pressure in the pump chamber 230
also acts on the outlet channel 242. The flow resistance of the
outlet channel 242 is set to be lower than the flow resistances of
the fluid chamber 246 and the check valve 248. The fluid is thus
likely to flow from the fluid chamber 246 into the pump chamber
230, rather than from the outlet channel 242. The fluid chamber 246
is connected with the film pack 260, and a sufficient amount of
fluid is kept in the film pack 260. The fluid can thus be
continuously supplied to the pump chamber 230. The film pack 260 is
contracted, accompanied with supply of the fluid in the film pack
260 to the pump chamber 230. This effectively prevents the fluid
chamber 246 and the film pack 260 from having negative
pressure.
[0107] When the piezoelectric element 214 is expanded again by the
increasing driving voltage after filling the fluid into the pump
chamber 230 returned to the original volume, the fluid pressurized
in the pump chamber 230 is press-fed toward the fluid channel 300
as shown in FIG. 9B. The fluid feed pump 200 repeats this series of
operations to circulate the fluid through the fluid channel
300.
[0108] FIGS. 10A to 10D illustrate the structure of the film pack
260. FIG. 10A is an exploded perspective view of the film pack 260.
The film pack 260 includes a pair of flexible films 264 having gas
barrier property and heat resistance, a connection member 262
provided to have a connection hole 262a and used to detachably
attach the film pack 260 to the fluid chamber 246, and an opening
member 266 provided to have an openable and closeable opening. The
pair of films 264 are formed in a substantially rectangular shape.
The film pack 260 is assembled by air-tightly bonding the
peripheries of the pair of films 264 by, e.g., thermal compressing
bonding, in the state that the connection member 262 is placed
between the pair of films 264 on one end in the longitudinal
direction and the opening member 266 is placed between the pair of
films 264 on the other end.
[0109] FIG. 10B illustrates the film pack 260 formed by bonding the
pair of films 264. The hatched areas in FIG. 10B show the sealed
portions bonded by, e.g., thermal compression bonding. As
illustrated in FIG. 10B, the pair of films 264 are in contact with
each other, when the film pack 260 contains no fluid.
[0110] When the fluid flows through the connection hole 262a of the
connection member 262 into the film pack 260, the film pack 260 is
expanded to increase the volume and allow accumulation of the fluid
between the pair of films 264 as shown in FIG. 10C. When the fluid
in the film pack 260 flows out through the connection hole 262a of
the connection member 262, on the other hand, the film pack 260 is
contracted to decrease the volume. In this manner, the film pack
260 is deformable according to the amount of fluid contained in the
film pack 260.
[0111] FIG. 10D illustrates the structure of the film 264 used for
the film pack 260. The illustrated film 264 has multilayer
structure and includes a middle layer of aluminum foil between an
outer layer of polyethylene terephthalate (PET) having excellent
impact resistance and an inner layer of polypropylene (PP) having
excellent fluid resistance. The respective layers are bonded to one
another. Providing the middle layer of aluminum foil enhances the
strength and the gas barrier property of the film 264. The film
pack 260 of this structure has excellent heat resistance to allow
treatment at high temperature (e.g., up to 150.degree. C.) and has
flexibility to be readily deformable. This film pack 260 is light
in weight and is readily formable by thermal compression
bonding.
[0112] The structure of the film 264 used for the film pack 260 is,
however, not limited to the structure shown in FIG. 10D. For
example, the middle layer of aluminum foil may be replaced with
ethylene-vinyl alcohol copolymer (EVOH) or polyvinylidene chloride
(PVDC). According to another embodiment, the film 264 may be a
transparent film prepared by directly bonding an outer layer of
polyamide (nylon) to an inner layer of polypropylene (PP). This
application enables the user to visually check the inside of the
film pack 260 (e.g., fluid level and fluid flow).
[0113] The fluid feed pump 200 of the modification structured as
described above has the film pack 260 for the inlet buffer chamber
112 in the fluid feed pump 100 of the embodiment described above.
Using the material having the small modulus of elasticity (film
264) for the inlet buffer chamber 112 sufficiently increases the
compliance of the inlet buffer chamber 112. As explained
previously, the sufficiently high compliance of the inlet buffer
chamber 112 relative to the compliance of the outlet buffer chamber
118 enables the fluid to be fed stably at a high flow rate (FIG.
7). Using the film pack 260 for the inlet buffer chamber 112
achieves the full capacity of the fluid feed pump 200.
[0114] The foregoing describes the fluid feed pump 100 of the
embodiment and the fluid feed pump 200 of the modification. The
invention is, however, not limited to the above embodiment or
modification, but a multiplicity of variations and modifications
may be made to the embodiment without departing from the scope of
the invention. The invention is applicable to various electronic
devices, for example, a fluid circulation device configured to
circulate a fluid, such as coolant, and thereby cool down the heat
generated in an electronic device, such as a projector. The
invention is also applicable to a fluid injection device used to
prepare microcapsules containing, for example, medicinal substances
or nutritional supplements, surgical instruments like a surgical
jet knife used to cut off a target with a high-pressure jet of
fluid (e.g., water, normal saline solution, or medicinal solution)
ejected from the small-diameter tapered end of the fluid channel,
and other medical devices, such as chemical injection device. In
the fluid feed pump 100 of the embodiment, the outlet buffer
chamber 118 or the inlet buffer chamber 112 may not be necessarily
made of a very hard material, such as stainless steel but may be
made of any material having small modulus of elasticity. Using the
material having small modulus of elasticity provides the
sufficiently high compliance even in small volume and thereby gives
an extremely-compact fluid feed pump. The following describes
applications of the fluid feed pump of the embodiment (or the fluid
feed pump of the modification) to an electronic device and a
medical device.
[0115] FIGS. 11A and 11B illustrate an application of the fluid
feed pump of the embodiment (or the fluid feed pump of the
modification) to an electronic device. More specifically, in the
illustrated example of FIGS. 11A and 11B, the fluid feed pump 100
of the embodiment is applied to a projector 301 as an electronic
device. As illustrated in FIG. 11A, the projector 301 has an
optical system including a plurality of optical components, cooling
devices 330 serving to cool down the optical components, a power
unit (not shown), and a control unit (not shown), which are placed
inside an outer casing 320. The optical system includes light
sources 322 arranged to emit light fluxes, liquid crystal light
valves 324 arranged to perform light modulation according to image
information, a dichroic prism 326 and a projection lens 328.
[0116] The light sources 322 include three light sources 322R to
322B, i.e., R light source 322R emitting R (red) color light, G
light source 322G emitting G (green) color light and B light source
322B emitting B (blue) color light. Various solid-state
light-emitting elements, such as LED elements, laser diodes,
organic EL elements and silicon light-emitting elements, may be
used for the respective color light sources 322R to 322B. The light
flux is emitted from each of the color light sources 322R to 322B
to the corresponding liquid crystal light valve 324.
[0117] The liquid crystal light valve 324 is a transparent liquid
crystal panel and changes the array of liquid crystal molecules in
the liquid crystal cell to allow or prohibit transmission of light,
in response to a driving signal from the controller (not shown), so
as to form an optical image according to image information. The
operation of allowing or prohibiting transmission of light in the
liquid crystal cell herein is called "light modulation". As the
results of light modulation by the liquid crystal light valves 324,
an R optical image is formed by a liquid crystal light valve 324R
receiving the light flux from the light source 322R; a G optical
image is formed by a liquid crystal light valve 324G receiving the
light flux from the light source 322G; and a B optical image is
formed by a liquid crystal light valve 324B receiving the light
flux from the light source 322B. The optical images of the
respective colors thus obtained are transmitted to the dichroic
prism 326.
[0118] The dichroic prism 326 is an optical element of
substantially cubic shape provided by bonding four rectangular
prisms. A dielectric multilayer film is formed on each interface
between adjacent rectangular prisms. The dielectric multilayer film
having the controlled film thickness reflects the light flux of
only a specific wavelength, while transmitting the light fluxes of
the other wavelengths. By taking advantage of this characteristic,
the dichroic prism 326 reflects the color light fluxes emitted from
the liquid crystal light valves 324 toward the projection lens 328.
As the results of reflecting the color light fluxes from the
respective liquid crystal light valves 324R to 324B toward the
projection lens 328, optical images of the respective color light
fluxes are combined and are transmitted to the projection lens 218
as a composite color image. The projection lens 328 projects the
composite color image to be enlarged on a screen (not shown).
[0119] The light sources 322 generate heat simultaneously with
emitting light. Fluid circulation devices 331 of the closed system
are accordingly employed as the cooling devices 330 to cool down
the respective color light sources 322R to 322B. Although the
cooling devices 330 are used to cool down the light sources 322
according to this embodiment, the cooling devices 330 may be
employed to cool down other components (e.g., the liquid crystal
line valves 324 or the power unit).
[0120] FIG. 11B illustrates the structure of the cooling device
330. As described previously with reference to FIG. 11A, a
plurality of (i.e., three) cooling devices 330 are provided for the
respective color light sources 322R to 322B. All the cooling
devices 330 have the same structure. The following thus describes
one cooling device 330 used to cool down one light source 322.
[0121] As illustrated, the cooling device 330 includes the fluid
feed pump 100 and a fluid tube 332 as the components of the fluid
circulation device 331. A heat receiver 334 to cause the fluid to
absorb the heat from the light source 322 and a radiator 336 to
release the heat of the fluid are provided in the middle of the
fluid tube 332. On activation of the fluid feed pump 100, a fluid
as coolant (for example, water, aqueous ethylene glycol, aqueous
propylene glycol or silicone oil) is circulated through the fluid
tube 332, the heat receiver 334 and the radiator 336. The flow
direction of the coolant is shown by the broken-line arrows in FIG.
11B.
[0122] In the heat receiver 334, the fluid flows in contact with a
heat transfer member (not shown) made of a material having high
thermal conductivity, such as metal, and the heat transfer member
is located in contact with the heat-generating part of the light
source 322. The heat of the light source 322 is accordingly
transferred to the fluid via the heat transfer member, so that the
light source 322 is cooled down. The radiator 336 releases the heat
of the fluid flowing inside to the surrounding air by a plurality
of radiator fins provided on the surface. The fluid going through
the radiator 336 is accordingly cooled down and returned to the
fluid feed pump 100.
[0123] The cooling device 330 is also equipped with a cooling
acceleration unit to accelerate the heat release by the radiator
336. This cooling acceleration unit includes a cooling fan 340, a
fan motor 342 operated to rotate the cooling fan 340, a motor
controller 344 provided to control the operations of the fan motor
342, and a temperature sensor 346. The temperature sensor 346 is
located in the vicinity of the light source 322 to detect the
temperature of the light source 322 and output the detected
temperature to the motor controller 344. The motor controller 344
controls the operations of the fan motor 342, based on the detected
temperature. For example, in response to the high temperature
detected by the temperature sensor 346, the motor controller 344
increases the rotation speed of the fan motor 342 to accelerate the
heat release by the radiator 336. This lowers the temperature of
the fluid flowing out of the radiator 336 and supplies the fluid of
the lowered temperature to the heat receiver 334, thus lowering the
temperature of the light source 322.
[0124] FIG. 12 schematically illustrates the structure of a fluid
ejection system 400 as an application of the fluid feed pump of the
embodiment (or the fluid feed pump of the modification) to a
medical device. The fluid ejection system 400 includes a fluid
ejection device 420 and a fluid circulation device 450 used to cool
down the fluid ejection device 420. The fluid ejection device 420
is a surgical water jet cutter to spray the water jet stream
against the body tissues, such as skin, and separate or cut the
body tissues by its impact energy. More specifically, the fluid
ejection device 420 of the embodiment is a surgical pulsative water
jet cutter to intermittently spray the water jet stream.
[0125] The fluid ejection device 420 includes a pulsation generator
430 operated to spray the water jet stream, a fluid vessel 440
provided to hold water, a feed pump 442 provided to suck water out
of the fluid vessel 440 and feed the water to the pulsation
generator 430, a connection tube 444 arranged to connect the fluid
vessel 440 with the feed pump 442, and a connection tube 446
arranged to connect the feed pump 442 with the pulsation generator
430.
[0126] The pulsation generator 430 includes a fluid chamber 432
provided to temporarily hold water supplied through the connection
tube 446, a piezoelectric actuator 434 provided to pulsate the
water held in the fluid chamber 432, a fluid spray pipe 436
arranged to allow passage of the water pulsated by the
piezoelectric actuator 434, a lower casing 438 provided to place
the piezoelectric actuator 434 therein, and an upper casing 439
coupled with the lower casing 438 to define the fluid chamber
432.
[0127] The piezoelectric actuator 434 is a laminated-type
piezoelectric element and deforms the diaphragm by taking advantage
of the piezoelectric effect of the piezoelectric element to change
the volume of the fluid chamber 432. Reducing the volume of the
fluid chamber 432 causes the water held in the fluid chamber 432 to
go through the fluid spray pipe 436 and to be sprayed out in the
form of water jet stream.
[0128] The fluid circulation device 450 is used to cool down the
piezoelectric actuator 434 of the fluid ejection device 420 and
includes a fluid channel 490 formed as a circulation channel having
both ends connected with the fluid feed pump 100 and a controller
496 provided to control the fluid feed pump 100. According to this
embodiment, the fluid feed pump 100 and the fluid channel 490 form
the circulation channel of the closed system. The fluid in the
fluid circulation device 450 is accordingly circulated in the state
isolated from the outside air.
[0129] The fluid channel 490 is made from a pressure-resistant,
flexible tube. Available examples of the pressure-resistant,
flexible tube include medical tubes and general industrial tubes
made of, for example, fluororesins such as PTFE, polyimide resins,
thermoplastic resins such as PVC, and silicone rubber, although
these are only illustrative. According to this embodiment, a
silicone tube is employed for the fluid channel 490. The fluid
channel 490 is wound on the piezoelectric actuator 434. The heat
generated in the piezoelectric actuator 434 is accordingly
transferred to the fluid circulating in the fluid channel 490
(circulating fluid), so as to cool down the piezoelectric actuator
434. The hot circulating fluid is cooled down by the air during
circulation through the fluid channel 490. A radiator may
additionally be provided to accelerate cooling down the circulating
fluid. From the standpoint of heat exchange efficiency, the
circulating fluid according to this embodiment is a liquid. Water
is employed as the liquid in the fluid circulation device 450.
[0130] As described above, the fluid feed pump of the embodiment
(or the fluid feed pump of the modification) is applicable to
various equipment including fluid circulation devices, electronic
devices and medical devices.
[0131] In the embodiments of FIGS. 1 and 6, the check valve 110 is
employed to prevent the backflow of the fluid from the pump chamber
102 to the inlet buffer chamber 112. Alternatively, any other
suitable fluid resistance element may be employed, instead of the
check valve 110, to prevent the flow of the fluid from the pump
chamber 102 to the inlet buffer chamber 112. The fluid resistance
element may be, for example, an orifice. In another example, a
channel having the diameter tapered from the inlet buffer chamber
112 toward the pump chamber 102 may be provided as the fluid
resistance element. A serpentine channel may also be provided
between the inlet buffer chamber 112 and the pump chamber 102 as
the fluid resistance element. The serpentine channel is preferable
made by a row of short flow paths having the diameter gradually
tapered from the inlet buffer chamber 112 toward the pump chamber
102. Similarly, in the embodiment of FIG. 8, any of such other
fluid resistance elements may be employed, instead of the check
valve 248.
* * * * *