micromachines
Article
A Resonant Piezoelectric Diaphragm Pump
Transferring Gas with Compact Structure
Jiantao Wang, Yong Liu, Yanhu Shen *, Song Chen and Zhigang Yang
School of Mechanical Science and Engineering, College of Biological and Agricultural Engineering,
Jilin University, Changchun 130025, China; [email protected] (J.W.); [email protected] (Y.L.);
[email protected] (S.C.); [email protected] (Z.Y.)
* Correspondence: [email protected]; Tel.: +86-519-8158-4393; Fax: +86-519-8158-4395
Academic Editor: Nam-Trung Nguyen
Received: 11 October 2016; Accepted: 24 November 2016; Published: 1 December 2016
Abstract: In order to improve the output capacity of a piezoelectric pump when transferring gas,
this paper presents a compact resonant piezoelectric diaphragm pump (hereinafter referred to as the
piezoelectric diaphragm pump), which is driven by a rectangular piezoelectric vibrator. The compact
structure can effectively release the vibrating constraints of the vibrator, and enlarge its center output
displacement, so as to increase the volume change rate of the pump chamber. Based on the structure
and the working principle of this piezoelectric diaphragm pump, a dynamic model for the diaphragm
system is established in this paper, and an analysis on factors affecting the resonant frequency of
the system is then conducted. We tested on the prototype under the driving voltage of 260 Vpp.
The results show that the diaphragm system reaches resonance under the driving frequency of 265 Hz,
which is very close to the fundamental frequency of check valve. Compared with the rectangular
piezoelectric vibrator’s amplitude, the diaphragm’s amplitude is double amplified. At this time,
the piezoelectric diaphragm pump achieves the maximum gas flow rate as 186.8 mL/min and the
maximum output pressure as 56.7 kPa.
Keywords: rectangular piezoelectric vibrator; resonance; piezoelectric diaphragm pump;
piezoelectric gas pump; diaphragm system
1. Introduction
Decades of development has given the piezoelectric diaphragm pump an extensive application
and a favorable prospect. The media it can transfer include micro-compressible liquid with low
viscosity, high viscosity liquid, particle flow, and compressible gas [1–3]. Commonly, the diaphragm
of a piezoelectric diaphragm pump is the piezoelectric vibrator itself. However, it has a low transfer
capacity when conveying compressible gas, constrained by the small deformation of this kind of
vibrator [4]. To solve this problem, researchers separated the pump’s diaphragm and the piezoelectric
vibrator and amplified the vibrator’s deformation (by using the principle of resonance) to drive the
diaphragm, so that the transfer capacity of the piezoelectric diaphragm pump can be improved [5].
The document regarding the resonant piezoelectric pump is first seen in June-Ho Park’s
study [6–8]. The pump is constituted by the piezoelectric stack, added mass, bellows, and check valve.
With water as the transfer medium, the maximum output flow rate is 4.8 mL/min, and the maximum
pumping pressure is 0.32 MPa, but the output capacity of gas is unknown. In 2007, the Lyndon Johnson
Space Center in Texas successfully developed a resonant piezoelectric diaphragm pump, of which the
diaphragm movement in the pump chamber was driven by a piezoelectric stack [9]. In a resonance
state, the displacement of the piezoelectric stack is amplified 50 times, greatly improving the flow rate of
the piezoelectric diaphragm pump. However, as the piezoelectric stack have complex manufacturing
process and high cost, this resonant piezoelectric diaphragm pump was failed in large-scale applications.
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stack
have 2016,
complex
pump was failed in large-scale applications.
For the precise conveying of fuel cells, in 2014, the University of Science and Technology of China
For the precise conveying of fuel cells, in 2014, the University of Science and Technology
presented a resonant piezoelectric diaphragm pump, which has compressible spaces at the inlet and
of China presented a resonant piezoelectric diaphragm pump, which has compressible spaces
outlet of the pump chamber [10,11]. The external dimensions of the pump are 100 mm × 20 mm × 15
at the inlet and outlet of the pump chamber [10,11]. The external dimensions of the pump are
mm. It is driven by the vibrating inertia of the piezoelectric vibrator. When the drive voltage is 400 V
100 mm × 20 mm × 15 mm. It is driven by the vibrating inertia of the piezoelectric vibrator. When
and the driving frequency is 490 Hz, the maximum liquid flow rate is 105 mL/min, and the maximum
the drive voltage is 400 V and the driving frequency is 490 Hz, the maximum liquid flow rate is
pumping pressure is 23 kPa.
105 mL/min, and the maximum pumping pressure is 23 kPa.
The number of the studies on gas piezoelectric diaphragm pump is not large. In 2013, Jilin
The number of the studies on gas piezoelectric diaphragm pump is not large. In 2013, Jilin
University in China successfully developed a new type of resonant gas piezoelectric diaphragm
University in China successfully developed a new type of resonant gas piezoelectric diaphragm
pump, which adopts a low-cost annular piezoelectric bimorph as the driving source, constructing
pump, which adopts a low-cost annular piezoelectric bimorph as the driving source, constructing
the resonance system [12]. It enlarged the displacement of the piezoelectric vibrator 4.2 times, with a
the resonance system [12]. It enlarged the displacement of the piezoelectric vibrator 4.2 times, with a
gas flow rate reaching 1685 mL/min. However, this diaphragm pump has such disadvantages as a
gas flow rate reaching 1685 mL/min. However, this diaphragm pump has such disadvantages as a
complicated structure, a large volume, and significant working noise.
complicated structure, a large volume, and significant working noise.
In order to improve the gas output capacity and achieve a compact structure, a resonant
In order to improve the gas output capacity and achieve a compact structure, a resonant
piezoelectric diaphragm pump that is driven by a rectangular bimorph is presented in this paper.
piezoelectric diaphragm pump that is driven by a rectangular bimorph is presented in this paper.
The two fixed ends of the rectangular piezoelectric vibrator can improve the stability of the
The two fixed ends of the rectangular piezoelectric vibrator can improve the stability of the diaphragm
diaphragm vibration and reduce the impact that the installation method has on the pump’s output
vibration and reduce the impact that the installation method has on the pump’s output performance.
performance. The vibrator and the diaphragm are connected by an elastic mass. By changing its
The vibrator and the diaphragm are connected by an elastic mass. By changing its mass and stiffness,
mass and stiffness, the resonant frequency of the system can be adjusted conveniently. Moreover,
the resonant frequency of the system can be adjusted conveniently. Moreover, the relatively open
the relatively open structure facilitates the heat radiating of the piezoelectric vibrator.
structure facilitates the heat radiating of the piezoelectric vibrator.
In this paper, we conduct a dynamic analysis on the diaphragm system of the piezoelectric
In this paper, we conduct a dynamic analysis on the diaphragm system of the piezoelectric
diaphragm gas pump and identify the factors that affect the diaphragm amplitude. We designed and
diaphragm gas pump and identify the factors that affect the diaphragm amplitude. We designed
produced a prototype of resonant piezoelectric diaphragm gas pump, and we then tested and
and produced a prototype of resonant piezoelectric diaphragm gas pump, and we then tested and
analyzed its gas output performance. By adjusting the parameters of the diaphragm vibration
analyzed its gas output performance. By adjusting the parameters of the diaphragm vibration system,
system, the performance of the pump has been optimized to the maximum.
the performance of the pump has been optimized to the maximum.
2.
2. Structure
Structure and
and Working
Working Principle
Principle
2.1. Structure
Structure
The
developed
in in
this
study
is
The structure
structure of
of the
the compact
compactresonant
resonantpiezoelectric
piezoelectricdiaphragm
diaphragmpump
pump
developed
this
study
shown
in in
Figure
1. 1.
It consists
of of
a pump
body,
a arectangular
piezoelectric
vibrator,
elastic
mass,
a
is shown
Figure
It consists
a pump
body,
rectangular
piezoelectric
vibrator,
elastic
mass,
diaphragm,
anan
inlet
check
valve,
an an
outlet
check
valve,
andand
a restraining
washer.
Specifically,
the
a diaphragm,
inlet
check
valve,
outlet
check
valve,
a restraining
washer.
Specifically,
rectangular
piezoelectric
vibrator,
the the
driving
element,
is is
a arectangular
the rectangular
piezoelectric
vibrator,
driving
element,
rectangularmetal
metalsubstrate
substrate with
with a
rectangular
elastic
mass
does
notnot
only
transmit
thethe
vibration
for
rectangular bimorph
bimorphadhered
adheredtotoboth
bothitsitssides.
sides.The
The
elastic
mass
does
only
transmit
vibration
the
system,
but but
alsoalso
adjusts
the system’s
resonance
frequency
by changing
its stiffness
and mass.
The
for the
system,
adjusts
the system’s
resonance
frequency
by changing
its stiffness
and mass.
check
valve,
which
employs
a cantilever
structure,
is is
processed
bybyUV
The check
valve,
which
employs
a cantilever
structure,
processed
UVlaser
lasercutting,
cutting, with
with PET
(polyethylene terephthalate) as the material. The
The diaphragm
diaphragm is
is made
made from
from a circular beryllium bronze
sheet,
sheet, of
of which
which the
thecircumferential
circumferentialedge
edgeisisbonded
bondedand
andsealed
sealedtotothe
thepump
pumpchamber
chambervia
viaepoxy.
epoxy.
Figure
Figure 1.
1. Structure
Structure of
of the
the piezoelectric
piezoelectric diaphragm
diaphragm gas
gas pump.
pump.
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2.2. Working Principle
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When the
AC (alternating current) voltage is applied to the rectangular piezoelectric vibrator, it
2.2. Working
Principle
will have
a periodically
2.2. Working
Principle reciprocating vibration, but the amplitude is small. When the excitation
Whenreaches
the AC the
(alternating
voltage
applied
the rectangular
piezoelectric
vibrator,
frequency
resonant current)
frequency
of the is
system,
thetodiaphragm
system,
which includes
the
When
the AC (alternating
current)vibration,
voltage is applied
to
the rectangular
piezoelectric
vibrator,
it
it
will
have
a
periodically
reciprocating
but
the
amplitude
is
small.
When
the
excitation
rectangular
vibrator,
elastic
mass
and
the
diaphragm,
will
achieve
resonance.
Consequently,
the
will have
a periodically
reciprocating
but the amplitude
is small.
When
the excitation
frequency
reaches
the resonant
frequencyvibration,
of
the system,
diaphragm
system,
which
includes
the
amplitude
of thereaches
rectangular
piezoelectric
vibrator
will bethe
amplified.
The
diaphragm
vibrating
leads
frequency
the resonant
frequency
of the system,
the
diaphragm
system,
which includes
the
rectangular
vibrator,
elastic
mass
and
the
diaphragm,
will
achieve
resonance.
Consequently,
the
to periodic
changes
of theelastic
pumpmass
chamber
volume.
Underwill
theachieve
coordination
of the
two check valves,
rectangular
vibrator,
and the
diaphragm,
resonance.
Consequently,
the
amplitude
of
the
rectangular
piezoelectric
vibrator
will
be
amplified.
The
diaphragm
vibrating
leads
the process
of of
the
suction
and discharge
formed.
The constant
suction
and discharge
amplitude
thefluid
rectangular
piezoelectric
vibratoriswill
be amplified.
The diaphragm
vibrating
leads
to
periodic
changes
of the
chamber
volume.
Under
coordination
ofofthe
to periodic
changes
ofpump
the one-way
pump
chamber
volume.
Under
the
coordination
thetwo
twocheck
check valves,
valves, the
eventually
achieve
the
fluid’s
flow,
as shown
inthe
Figure
2.
process
of
the
fluid
suction
and
discharge
is
formed.
The
constant
suction
and
discharge
eventually
the process of the fluid suction and discharge is formed. The constant suction and discharge
achieve
the fluid’s
one-way
flow, one-way
as shown
in Figure
2. in Figure 2.
eventually
achieve
the fluid’s
flow,
as shown
(a)
(b)
(a)
(b)
Figure 2. Working principle of piezoelectric diaphragm pump. (a) Suction process; (b) Discharge process.
Figure 2. Working principle of piezoelectric diaphragm pump. (a) Suction process; (b) Discharge process.
Figure 2. Working principle of piezoelectric diaphragm pump. (a) Suction process; (b) Discharge process.
3. Dynamic
Model
3. Dynamic
Model
3. Dynamic Model
The interaction
among
gas,gas,
thethe
diaphragm,
valvesisiscomplicated.
complicated.
Therefore,
The interaction
among
diaphragm,and
and the
the check
check valves
Therefore,
in in
The
interaction
among
gas,
the
diaphragm,
and
the
check
valves
is
complicated.
Therefore,
order
to
simplify
the
analysis
objects,
the
diaphragm
system
composed
by
the
rectangular
order to simplify the analysis objects, the diaphragm system composed by the rectangular
piezoelectric
vibrator,
the
elastic
mass,
and
thediaphragm
diaphragm
is considered
asas
anan
independent
in
order
to simplify
the
analysis
objects,
the
diaphragm
system composed
by the vibration
rectangular
piezoelectric
vibrator,
the elastic
mass,
and
the
is
considered
independent
vibration
system.
Among
them,
the
vibrator
is
considered
as
a
massless
ideal
spring
that
provides
vibrating
piezoelectric
vibrator,
mass,
and the diaphragm
is considered
as anthat
independent
vibration
system. Among
them,the
theelastic
vibrator
is considered
as a massless
ideal spring
provides
vibrating
excitation,
and
thethe
elastic
mass is
and
the diaphragm
are regarded
asspring
the perfect
andvibrating
mass
system.
Among
them,
vibrator
considered
as a are
massless
ideal
that elastic
provides
excitation,
and the
elastic
mass and
the diaphragm
regarded
as the perfect
elastic and
mass
components, ignoring their vibration damping. The interaction of gas, the flow passage, and the
excitation,
and
the elastic
and the
diaphragm
regarded
thethe
perfect
and
mass
components,
ignoring
theirmass
vibration
damping.
The are
interaction
of as
gas,
flow elastic
passage,
and
the
check valve is equivalent to damping c. The dynamic model of the piezoelectric diaphragm gas
components,
their vibration
damping.
The
interaction
of of
gas,
thepiezoelectric
flow passage,
and the check
check pump
valve isignoring
is shown
equivalent
to
damping
c.
The
dynamic
model
the
diaphragm
gas
in Figure 3. Wherein m is the equivalent mass of the elastic mass and the
valve
damping
c. The dynamic
of the piezoelectric
diaphragm
gas pump
is
m is model
pumpisisequivalent
shown intoFigure
3. Wherein
the equivalent
mass of the
elastic mass
and the
diaphragm, k1 is the equivalent stiffness of the rectangular piezoelectric vibrator, k2 is the
shown
in
Figure
3.
Wherein
m
is
the
equivalent
mass
of
the
elastic
mass
and
the
diaphragm,
k
is
the
1
diaphragm, k1 is the equivalent stiffness of the rectangular piezoelectric vibrator, k2 is the
stiffness
of the elastic
and k3piezoelectric
is the stiffness
of the diaphragm.
equivalent
stiffness
of the mass,
rectangular
vibrator,
k2 is the stiffness of the elastic mass, and
k
stiffness
of
the
elastic
mass,
and
is
the
stiffness
of
the
diaphragm.
k3 is the stiffness of the diaphragm.3
k1
F0 k1
F0
y0 =A cos ωt
k2
k2
y0 =A cos ωt
m
c m
c
y
k3
y
k3
Figure 3. Dynamic model of piezoelectric diaphragm pump.
3. Dynamic model of piezoelectric diaphragm
diaphragm pump.
pump.
Figure 3.
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Assuming the driving frequency of the piezoelectric vibrator is ω, the vibration amplitude is A,
then the vibration displacement of the rectangular piezoelectric vibrator is y0 = Acosωt. Assuming
the displacement of the diaphragm is y, the motion differential equation of the system is
(
..
.
m y + c y + k 2 ( y − y0 ) + k 3 y = 0
.
F0 + k2 (y − y0 ) − k1 y0 = 0
(1)
Obtained by Equation (1),
..
.
my + cy +
k1 k2 + k1 k3 + k2 k3
k2 F0
y=
.
k1 + k2
k1 + k2
(2)
Obtained by Equation (2),
..
y+
c .
k k2 + k1 k3 + k2 k3
k2 F0
y+ 1
y=
.
m
m (k1 + k2 )
m (k1 + k2 )
According to Equation (3), the natural frequency of the system is ωn =
damping ratio is ζ =
c
2mωn ;
(3)
q
k1 k2 +k1 k3 +k2 k3
,
m(k1 +k2 )
and the
therefore, we obtain Equation (4),
..
.
y + 2ζωn y + ωn2 y =
k1 k2
Aωn2 cosωt.
k1 k2 + k1 k3 + k2 k3
(4)
To calculate and obtain the steady-state response of the system, we use the following Equation (5):
y=
k1 k2
•
k1 k2 + k1 k3 + k2 k3
Acosωt
2 2 2 .
ω
ω
+ 2ζ ωn
1 − ωn
(5)
The amplitude amplification coefficient of vibration system is
| H (ω )| =
Y
=
A
k k
s1 2
.
2 2 2
1 − ωωn
+ 2ζ ωωn
(k1 k2 + k1 k3 + k2 k3 )
(6)
When the driving frequency ω = ωn , the system reaches a resonance state; at this time, based on
Equation (6), the amplitude amplification coefficient of the vibration system reaches the maximum, as
shown by Equation (7):
k1 k2
.
(7)
| H (ω )| =
2ζ (k1 k2 + k1 k3 + k2 k3 )
When the driving frequency is equal to the resonant frequency of the piezoelectric diaphragm
gas pump, the volume change rate of the pump chamber can be increased, so as to improve the
capacity of conveying gas. Accordingly, when the external driving frequency is a given value, it is very
significant that the resonance frequency of the diaphragm system can be adjusted to approach the
value. According to Equation (3), we can change the resonant frequency of the system effectively by
changing the mass and stiffness of the elastic mass.
4. Performance Testing and Structure Optimization
When the piezoelectric pump is driven by the piezoelectric vibrator directly, its optimal working
frequency is mainly determined by the resonant frequency of the check valve, regardless of conveying
gas or liquid [13]. In addition, when the equivalent stiffness of the check valve is small, the fundamental
frequency is low. At this time, the opening degree of the check valve is large, resulting in a small flow
resistance, which entails the enhancement of the output performance of the pump. Based on the above
4. Performance Testing and Structure Optimization
When the piezoelectric pump is driven by the piezoelectric vibrator directly, its optimal
working frequency is mainly determined by the resonant frequency of the check valve, regardless of
conveying gas or liquid [13]. In addition, when the equivalent stiffness of the check valve is small,
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the
fundamental
is low. At this time, the opening degree of the check valve is large,
resulting in a small flow resistance, which entails the enhancement of the output performance of the
pump. Based on the above principle, we employed a PET film, whose elastic modulus is small, as the
principle, we employed a PET film, whose elastic modulus is small, as the material of the check valve
material of the check valve in this study.
in this study.
In the testing stage, we measured the fundamental frequency of the given check valve at first.
In the testing stage, we measured the fundamental frequency of the given check valve at first.
Based on the analyzing results of the dynamic model in Section 3, we changed the mass of the elastic
Based on the analyzing results of the dynamic model in Section 3, we changed the mass of the elastic
mass block to make the resonant frequency of the diaphragm system as close to the fundamental
mass block to make the resonant frequency of the diaphragm system as close to the fundamental
frequency of the check valve as possible, so as to optimize the output performance of the
frequency of the check valve as possible, so as to optimize the output performance of the piezoelectric
piezoelectric diaphragm pump.
diaphragm pump.
4.1.
4.1. Prototype
Prototype Parameters
Parameters
Figure
Figure 44 shows
shows aa prototype
prototype photo
photo of
of the
the piezoelectric
piezoelectric diaphragm
diaphragmpump
pumppresented
presentedin
inthis
thispaper.
paper.
Its
dimensions are
are 52
52mm
mm×
× 52
Its external
external dimensions
52 mm
mm ××36
36mm.
mm.The
Thepiezoelectric
piezoelectricbimorph
bimorph is
is square
square with
with aa side
side
length
of
20
mm;
the
metal
substrate
of
the
vibrator
is
52
mm
×
21
mm
×
0.5
mm.
The
diaphragm
length of 20 mm; the metal substrate of the vibrator is 52 mm × 21 mm × 0.5 mm. The diaphragm is
is
made
of beryllium
berylliumbronze,
bronze,with
witha diameter
a diameter
of mm
21 mm
a thickness
0.2 The
mm.mass
The of
mass
of the
made of
of 21
andand
a thickness
of 0.2ofmm.
the elastic
elastic
massisblock
10 g,
the equivalent
stiffness
is 346 N/mm.
The check
is made
of PET,
mass block
10 g,isand
theand
equivalent
stiffness
is 346 N/mm.
The check
valvevalve
is made
of PET,
with
with
a
thickness
of
0.03
mm.
The
pump
body
is
made
from
PMMA
(polymethyl
methacrylate),
a
a thickness of 0.03 mm. The pump body is made from PMMA (polymethyl methacrylate), a highly
highly
transparent
material,
so
that
we
can
observe
the
check
valve’s
working
state
inside
the
pump
transparent material, so that we can observe the check valve’s working state inside the pump chamber
chamber
during
the diameter
test. The diameter
of the
pump
and the
outletischannel
during the
test. The
of the pump
inlet
and inlet
the outlet
channel
2.5 mm.is 2.5 mm.
Dynamic model of piezoelectric diaphragm pump.
Figure 4. Dynamic
The
mainequipment
equipment
used
during
the consists
test consists
of a numeric
piezoelectric
The main
used
during
the test
of a numeric
piezoelectric
frequencyfrequency
controller,
controller,
a
precision
impedance
analyzer,
a
laser
micrometer,
and
a
digital
pressure
gauge.
During
a precision impedance analyzer, a laser micrometer, and a digital pressure gauge. During the test,
the
the
test,
the
inlet
pipe
communicated
with
the
atmosphere.
We
used
the
drainage
method
to
inlet pipe communicated with the atmosphere. We used the drainage method to measure the flow rate
measure
the flow diaphragm
rate of the
piezoelectric
diaphragm
The performance
test
the
of the piezoelectric
pump.
The performance
test ofpump.
the piezoelectric
diaphragm
gasof
pump
piezoelectric
diaphragm
gas
pump
is
shown
in
Figure
5,
when
the
driving
signal
is
a
sine
wave
with
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is shown
in Figure
when the driving signal is a sine wave with 260 Vpp.
260 Vpp.
Figure
5. Performancetest
testof
of the
the piezoelectric
gasgas
pump.
Figure
5. Performance
piezoelectricdiaphragm
diaphragm
pump.
4.2. Prototype’s Optimum Working Frequency Test
We applied an initial vibration excitation to the check valve installed in the prototype and used
the laser micrometer to test the vibration curve of the check valve, achieving the fundamental
frequency of 292 Hz for the check valve.
The driving signal of the rectangular piezoelectric vibrator is a sine wave. When the driving
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Figure 5. Performance test of the piezoelectric diaphragm gas pump.
4.2. Prototype’s Optimum Working Frequency Test
4.2. Prototype’s Optimum Working Frequency Test
We applied an initial vibration excitation to the check valve installed in the prototype and used the
We applied
an the
initial
vibration
excitation
the check
valve
installedthe
in fundamental
the prototype and
used of
laser micrometer
to test
vibration
curve
of thetocheck
valve,
achieving
frequency
the laser micrometer to test the vibration curve of the check valve, achieving the fundamental
292 Hz for the check valve.
frequency of 292 Hz for the check valve.
The driving signal of the rectangular piezoelectric vibrator is a sine wave. When the driving
The driving signal of the rectangular piezoelectric vibrator is a sine wave. When the driving
voltage
was maintained
260260
Vpp,
wewe
changed
constantly
and
obtained
the flow
voltage
was maintained
Vpp,
changedthe
thedrive
drive frequency
frequency constantly
and
obtained
the flow
rate–driving
frequency
curve,
shown
ininFigure
the figure,
figure,ititisisevident
evident
that,
when
drive
rate–driving
frequency
curve,
shown
Figure6.6.From
From the
that,
when
the the
drive
frequency
was
286
Hz,
the
output
flow
rate
of
the
piezoelectric
diaphragm
gas
pump
reached
frequency was 286 Hz, the output flow rate of the piezoelectric diaphragm gas pump reached the the
maximum
of 124.6
mL/min.
Therefore,
wewe
can
conclude
frequencyofofthe
theprototype
prototype is
maximum
of 124.6
mL/min.
Therefore,
can
concludethat
thatthe
the optimal
optimal frequency
is 286
Hz, is
which
is nearly
the fundamental
frequency
thecheck
checkvalve.
valve.
286 Hz,
which
nearly
equalequal
to thetofundamental
frequency
ofof
the
Figure
Flowrate—driving
rate—driving frequency
frequency curve.
Figure
6. 6.
Flow
curve.
4.3. Performance Optimization
4.3. Performance Optimization
Based on the analysis and calculation on the dynamic model of the diaphragm system, we
Based
on the
andofcalculation
on the pump
dynamic
model to
of the
we100
adjusted
adjusted
the analysis
elastic mass
the piezoelectric
prototype
10 g,diaphragm
30 g, 60 g, system,
80 g, and
g,
the elastic
mass
of
the
piezoelectric
pump
prototype
to
10
g,
30
g,
60
g,
80
g,
and
100
g,
respectively,
respectively, and tested the resonant frequency of the diaphragm system using the precision
and tested
the resonant
the diaphragm
impedance
analyzer.frequency
Results areof
shown
in Table 1. system using the precision impedance analyzer.
Results are shown in Table 1.
Table 1. Resonant frequency of the diaphragm system.
Elastic Mass (g)
10
30
60
80
100
Resonant Frequency (Hz)
741
427
302
269
117
Only when the mass of the elastic mass block is 80 g, the resonant frequency of the system is close
to the fundamental frequency of the check valve. Based on this, we tested the output performance
of this prototype. The diaphragm amplitude–frequency characteristic of the prototype is shown in
Figure 7 for a drive voltage of 260 Vpp. The curve indicates that, when the driving frequency was
265 Hz, we achieved the maximum amplitude of 62.5 µm for the diaphragm, and the maximum
amplitude of the rectangular piezoelectric vibrator was 30 µm. It can be seen when the system is
resonant, the displacement of the rectangular piezoelectric vibrator is amplified twice.
Only when the mass of the elastic mass block is 80 g, the resonant frequency of the system is
when the mass
of the elastic
mass
block
is 80 Based
g, the resonant
theoutput
system is
close to Only
the fundamental
frequency
of the
check
valve.
on this, frequency
we tested ofthe
close
to
the
fundamental
frequency
of
the
check
valve.
Based
on
this,
we
tested
the
output
performance of this prototype. The diaphragm amplitude–frequency characteristic of the prototype
performance
of
this
prototype.
The
diaphragm
amplitude–frequency
characteristic
of
the
prototype
is shown in Figure 7 for a drive voltage of 260 Vpp. The curve indicates that, when the driving
is shown
Figure
7 for
a drivethe
voltage
of 260
Vpp. The
indicates
that, when the
frequency
wasin265
Hz, we
achieved
maximum
amplitude
of curve
62.5 μm
for the diaphragm,
anddriving
the
frequency
was
265
Hz,
we
achieved
the
maximum
amplitude
of
62.5
μm
for
the
diaphragm,
maximum
amplitude
of the rectangular piezoelectric vibrator was 30 μm. It can be seen whenand
the the
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maximum
amplitude
of the rectangular
piezoelectric
vibrator was
30 μm.
can be seen
when the
system
is resonant,
the displacement
of the rectangular
piezoelectric
vibrator
is It
amplified
twice.
system is resonant, the displacement of the rectangular piezoelectric vibrator is amplified twice.
Figure7.7.Diaphragm
Diaphragm amplitude—frequency
curve.
Figure
amplitude—frequency
curve.
Figure 7. Diaphragm amplitude—frequency curve.
Test results of the gas flow rate and the gas output pressure of the piezoelectric diaphragm
Test results
the gas
flowgas
rate
andrate
the gasthe
output output
pressure
of the of
piezoelectric
diaphragm
pump
Test of
results
the
flow
pressure
the
piezoelectric
diaphragm
pump prototype
are of
illustrated
in
Figures and
8 and 9, gas
respectively,
for a drive
voltage
of 260 Vpp.
The
Figures
8 and
respectively,
for is
avoltage
drive
voltage
of Vpp.
260 Vpp.
prototype
are prototype
illustrated
inillustrated
Figures
8inand
9,
respectively,
for
a drive
ofthe
260
TheThe
two
twopump
graphs
show anare
identical
tendency.
When
the9,drive
frequency
265 Hz,
piezoelectric
two
graphs
show
an
identical
tendency.
When
the
drive
frequency
is
265
Hz,
the
piezoelectric
graphs
show
an
identical
tendency.
When
the
drive
frequency
is
265
Hz,
the
piezoelectric
diaphragm
diaphragm gas pump achieves the maximum gas flow rate as 186.8 mL/min and the maximum
diaphragm
pump
maximum
gas flow
rate as
186.8
andoutput
the maximum
gas pump
achieves
the56.7
maximum
gasthe
flow
rate as 186.8
mL/min
and
themL/min
maximum
pressure
output
pressuregas
as
kPa.achieves
output
pressure
as
56.7
kPa.
as 56.7 kPa.
Figure 8. Flow rate—driving frequency curve.
Micromachines 2016, 7, 219
8. Flow
rate—driving
frequency
curve.
FigureFigure
8. Flow
rate—driving
frequency
curve.
8 of 9
Figure9.9.Output
Output pressure—driving
pressure—driving frequency
Figure
frequencycurve.
curve.
5. Conclusions
This paper presents a resonant piezoelectric diaphragm gas pump driven by a rectangular
piezoelectric vibrator. It constructs a vibration system with two degrees of freedom. Under the given
structure, tests on the pump demonstrate that, when the elastic mass is 80 g, the equivalent stiffness
is 346 N/mm. The impedance analyzer shows the resonant frequency of the diaphragm system is 269
Hz, which is close to the fundamental frequency of the check valve. After the performance testing,
we know the optimum working frequency of the pump is 265 Hz. At this time, the vibrating
Micromachines 2016, 7, 219
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5. Conclusions
This paper presents a resonant piezoelectric diaphragm gas pump driven by a rectangular
piezoelectric vibrator. It constructs a vibration system with two degrees of freedom. Under the
given structure, tests on the pump demonstrate that, when the elastic mass is 80 g, the equivalent
stiffness is 346 N/mm. The impedance analyzer shows the resonant frequency of the diaphragm
system is 269 Hz, which is close to the fundamental frequency of the check valve. After the performance
testing, we know the optimum working frequency of the pump is 265 Hz. At this time, the vibrating
displacement of the piezoelectric vibrator is double amplified; the pump achieves the maximum gas
flow rate as 186.8 mL/min and the maximum output pressure as 56.7 kPa.
It should be noted that this conclusion has some limitations. In general cases, when the
fundamental frequency of the check valve is low, its opening degree is large, so the small flow
resistance helps to improve the output performance of the piezoelectric pump in a single work cycle.
This experiment demonstrates, if we adjust the resonant frequency of the diaphragm system to make
it close to the fundamental frequency of the check valve, we can further improve the gas output
performance of the pump effectively. However, the above method has a marked effect on the gas
output pressure, but not necessarily leads to the maximum flow rate. The output flow rate of the pump
is determined by both the external driving voltage and the flow rate of a single work cycle. Their
complicated relationship is not fully discussed in this paper, which could provide other researchers
with implications for further research.
Acknowledgments: This study is supported by the National Natural Science Foundation of China (Grant
No. 51406065 & No. 51375207).
Author Contributions: Yong Liu is responsible for the overall planning, task assigning, and modification of the
paper. Jiantao Wang is responsible for conducting the experiment, collecting data, analyzing experiment results,
and composing the draft paper. Song Chen is responsible for experiment preparation and prototype assembly.
Yanhu Shen is responsible for literature review and the deduction of the formula. Zhigang Yang is responsible for
instruction of the theory and the experiment methodology.
Conflicts of Interest: The authors declare no conflict of interest.
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