SICE-ICASE International Joint Conference 2006Oct. 18-2 1, 2006 in Bexco, Busan, Korea

Pressure Regulator for Pneumatic Valve with a PZT Actuator

So-Nam Yun', Young-Bog Ham2, Jung-Ho Park3, Byung-Soon Ryu4 and Byung-Oh Choi5'Korea Institute of Machinery & Materials, Daejeon, Korea

(Tel: +82-42-868-7155; E-mail: ysn688gkimm.re.kr)2 Korea Institute of Machinery & Materials, Daejeon, Korea

(Tel: +82-42-868-7157; E-mail: hyb665gkimm.re.kr)3 Korea Institute of Machinery & Materials, Daejeon, Korea

(Tel: +82-42-868-7607; E-mail: jhparkgkimm.re.kr)4 Korea Institute of Machinery & Materials, Daejeon, Korea

(Tel: +82-42-868-7172; E-mail: bsryugkimm.re.kr)5 Korea Institute of Machinery & Materials, Daejeon, Korea

(Tel: +82-42-868-7170; E-mail: bochoigkimm.re.kr)

Abstract: The pressure regulator which is used for controlling the reducing pressure in the piezoelectrically drivenpneumatic valve has been studied. The pneumatic valve of this study object is 2-stage type and consists of apiezoelectric actuator, a controller, a poppet valve and a pressure regulator. Nominal flow of 50 1pm, maximumoperating pressure of 0.9MPa and frequency characteristic of 1OHz and over are required in this pneumatic valve, butthe pressure regulator is needed because piezoelectric actuator has no ability to control the pressure of 0.9MPa directly.In this study, bimorph type PZT actuator of 25.2 mm(L) x 7.2 mm(W) x 0.5 mm(H) with constant of -220 x 10-12 CN-1was proposed and investigated. Maximum operating force of 0.052 N and maximum displacement of 63 utm weregotten from the fabricated PZT actuator. From the analysis results, the orifice diameter of 0.6mm for a piezoelectricactuator was derived and then the pressure regulator which can be operated under 0.15 MPa easily was designed andmanufactured. Performance and effects of design parameters were simulated by the Simulink of Matlab software, and itwas confirmed that the performance characteristics of manufactured pressure regulator are superior in the common usepressure range of 0.5 MPa to 0.7 MPa. The results show that the proposed pressure regulator is suitable for thepneumatic valve with a PZT actuator.

Keywords: Pressure regulator, PZT actuator, Reducing pressure control, Solenoid actuator

NOMENCLATURE

Ap: Cross-sectional area of poppet [m2]

Ar Control part area of pressure regulator [m2]

Anrl Inlet area of pressure regulator [m2]

bp: Friction coefficient ofpoppet [N s/m]

br Friction coefficient ofpressure regulator [N * s/m]

Dr Control part diameter of pressure regulator [m]

Dr1 Inlet diameter of pressure regulator [m]

Gm: Mass flow of solenoid actuator [kg/s]

Gp Mass flow ofpoppet [m3]

Gr: Mass flow of pressure regulator [kg/s]k: Specific heat ratiokp: Spring constant ofpoppet [N/m]

kr : Spring constant of pressure regulator [N/m]

mp: Mass of poppet [kg]

mr Spool mass of pressure regulator [kg]

Pm Control pressure ofpoppet [Pa]

P, Output pressure ofpoppet [Pa]

Pr Control pressure of pressure regulator [Pa]

P: Supply pressure [Pa]Qm Control flow ofpoppet [m3/s]

Output flow ofpoppet [m3/s]

Qr Flow of pressure regulator [m3/s]R : Air constant

Sem : Effective area of solenoid actuator [m2]

Se: Effective area ofpoppet [m3]epSer : Effective area of pressure regulator [m2]T: Absolute temperature [ ° k]VO: Air volume ofpoppet [m3]

V : Air volume of pilot part [m3]

Vr: Air volume of pressure regulator [m3]

Vro : Control part initial volume ofpressure regulator [m3]Xpo Initial displacement ofpoppet spring [m]

Xr Displacement of pressure regulator [m]p: Air density [kg/m3]

1. INTRODUCTION

Piezoelectric actuators with many advantages such ashigh stiffness, fast frequency response, low energyconsumption have been used in many applications that

89-950038-5-5 98560/06/$10 C 2006 ICASE4121

control the fluid and require precise positioning controlin recent year. However, the bender type piezoelectricactuators like unimorph and bimorph have someproblems for control the pneumatic and hydraulic fluidbecause PZT actuator has not a constant operating forcein the control region independently on the strokeposition[1]. And this actuator is only used for very lowpressure and low frequency response system due to thelow output force compared to the solenoid actuator[3-6].These are why its use is restricted in industrial fieldapplication. For the purpose of solving theabovementioned problems, it is desirable that theactuator is fabricated to the multilayer for applied to thehigh pressure system[2], but this method also limits thedisplacement directly. In this study, bimorph type PZTactuator of 25.2 mm(L) x 7.2 mm(W) x 0.5 mm(H)with constant of -220x10-12 CN-1 was proposed andinvestigated[1]. Maximum operating force of 0.052 Nand maximum displacement of 63 utm were gotten fromthe fabricated actuator. From the analysis results, theorifice diameter of 0.6mm for a piezoelectric actuatorwas derived and then pressure regulator which can beoperated under 0.15MPa easily was designed andmanufactured. Performance and effects of designparameters were simulated by the Simulink of Matlabsoftware, and it was confirmed that the performancecharacteristics of manufactured pressure regulator issuperior in the pressure range of 0.5 MPa to 0.7 MPa.

2. THEORETICAL ANALYSIS

2.1 Pneumatic valve modeling

Fig. 1 shows the subject of this study, the pneumaticvalve. The pneumatic valve consists of thepressure-reducing part, pilot control part and poppetvalve part. The pressure regulator is for thepressure-reducing part and the bimorph-typepiezoelectric actuator is for the pilot control part. Thequantity of flow through the poppet valve, Qp is

determined by the pressure of the pressure-reducing part,Pr and the displacement of the poppet, xp driven by

the control pressure of the poppet, Pm from the pilotcontrol part. The purpose of the study is to evaluate thecharacteristics of a pressure regulator so that a solenoidactuator can be installed instead of a piezoelectricactuator in the pilot control part on the back of thepressure-reducing part[7]. The flow and kinetic equationof the pressure-reducing part can be expressed as Eq.(1)through Eq. (4).

0 . AO

Poppet Val

Poppet Valve Part

Fig. 1 Pneumatic valve model

Qr =Ser 2k 1

k-I p P!K

Gr =QrP

dPr _ 1

dt Vr

(1)

(2)

(3){GrRT-Pr dt }

F=P -Am p

d Xr dxr-M rt.+br +kr(xr+xr)rd!2 rdt(4)

Equation of continuity and equation of thedisplacement relation can be expressed as follows. Byinserting the solenoid actuator in the pilot control partfrom which characteristics can be verified in substitutefor a piezoelectric actuator, this study can facilitate toverify the characteristics of the pneumatic valve[8]. Asshown in Eq. (8) the displacement of the solenoidactuator, xm is expressed as the first order lagelement.

Qm = Sem

Gm =QmP

dPm I1dt Vp

(5)

(6)

{GmRT-Pm dV (7)

4122

AP

Xm =1-e (8)

The equation of continuity and equation of motion inthe poppet valve can be expressed as follows:

QP=Sep 2k j- 1- (9)

GP QpP (10)

dP" If dV (dtVJO

d2X dxF=m

P dt2+Pd -+kp(xp +xpo) (12)

Fig. 2 Simulink block for analysis

Fig. 2 shows the Simulink block to analyze thepiezoelectric pneumatic valve. Using Eq. (1) through Eq.(12), the control pressure of the pressure regulator, PrIthe control pressure of the poppet, Pm, and the output

pressure of the poppet, PO , can be solved in an

analytical strategy. In addition, it is constructed to easilyverify the characteristics of the piezoelectric pneumaticvalve in accordance with changes in design parameters.

2.2 Results of theoretical analysis

Fig. 3 shows the results of the theoretical analysisusing the Simulink block shown in Fig. 2, and thesupply pressure used for the analysis is 0.5MPa. (a) ofFig. 3 shows the pressure characteristics of thepressure-reducing part, which are very stable and fastacting. The point of 1 second shows the characteristicswhen the closed solenoid actuator is open, which

showed a little pitching but fast recovery. The settlingtime of the pilot pressure shown in (b) of Fig. 3 is lessthan 0. 18 second, which proves to be a system with very

fast response. (c) of Fig. 3 shows the output pressure ofthe poppet whose settling time is less than 0.4 second,which has been proven to obtain stable performancewithout over-shooting and vibration.

0.6 -

iu 0.4 -

n

cn

,) 0.2-

0.0 -

1.8 2.0 2.2 2.4

Time[s]

Fig. 3 Theoretical analysis results

3. EXPERIMENTAL RESULTS ANDDISCUSSION

3.1 Experimental setupFig. 4 shows the circuit for the experiment on the

pneumatic valve. To investigate the characteristics ofthe pressure regulator, pressure gauges were installed inthe front and back of the pressure regulator. They were

installed to generate pressure from the operation of theon-off solenoid valve.

Fig. 5 shows the test rig manufactured based on thestandard of the pneumatic circuit shown in Fig. 4. Fig. 6shows the control and data obtaining block configuredby the Simulink software, and data sampling was

conducted at a speed of 1 kHz.

Pressure Gauge 3[Pm]

On/off Solenoid valve

[PI IPressure Gauge 4

[P0]

Pressure Gauge 1

[P

PressureReducingValve

Air Source

Flowmeter Flow ControlValve

Fig. 4 Pneumatic circuit for experiment

4123

/ olenoicl operatinp sigal

-t- ------ - - - -- --

(b)

0, \---i 1,

.,ErT--E --tl.'. 71..-Ill-<E.IHX4 ,

zmy:D.. S- :ED,*

H-. EEHI..

Pwssure Sensor

for P meaurmeneta)

-Iu)a)

JreMum sensor

Jr PM measuremtenit

of experimental setup

Cloclk

Analog Input Total outl

DAQCard-6b62E simbut

|Total out

a)

-Iu)a)

Fig. 6 Data acquisition block using simulink

3.2 Experimental results and discussion

Fig. 7 shows the experimental characteristics of thepneumatic valve. a) of Fig. 7 displays the characteristicswhen the solenoid valve is on and off, and b) and c) ofFig. 7 display the characteristics when the solenoidvalve is on and off, respectively. The experiment was

conducted by inputting 24V DC voltage to the on-offsolenoid in the form of step. It was verified that the deadtime of the output pressure of the poppet is 60ms whenit is on and 83ms when it is off. It was also verified thatthe time constant is 150ms when it is on and 98ms whenit is off. The time constant of the control pressure of thepressure regulator was 45ms during both on and off, andthe pressure regular very stably controlled the pressure

without impact wave. Fig. 8 shows the results of theoutput pressure of the poppet. It was proven that boththeoretical and experimental results coincided well. Thereason for the more delayed response in comparisonwith the theoretical result is considered to be becausethe friction of the poppet and the flow coefficient were

not appropriately compensated.

---------- ------ - - -............. - - - - ----- - - --- - - - - - - - - - ------- - - - - - - - - - - - - - - l----- - - -- - - - - - ------

0.4-----L _4> L I_ _' L I_ _

-- -- ------ ----X--- - - ----f---- --------- - --f ------- -'--- -- --.--F'----- E --- -- --r -- -- -- t------- - --- f-------------- -f - - ----

0.3 -------_I- i-------- ia dq-

------L-----Pr--- -------- --- ---- ---,-- -------L ----X --------L-------4-------- -------- --------

062

O 3 ~~~~~~~~~~~~~~~~~~~~~~~-----r----S]Q;Q rT----------------------P>s0.2 Pr a Vt tso!!!!ttt

.1 2i~~-

0.0 \.. ...Pm ... --r ~--~

-------------, -------- t--------- t------ -t----------------------, --------t- -----t-------t---- -------

-01.-1.8 2.0 2.2 2.4 2.6 2.8 3.(

Time[s]

b) On characteristics

Time[s]

c) Off characteristics

Fig. 7 Pneumatic valve characteristics

a)

-Iu)a)

0670.

0.6~~ ~------ ---- - ------- I-----------I-- ----------I---'---------- ---

05- ------------- ------- --4---------- ------- ----------------L-------------------------4--------------------------->s

---------------r------- --------r-- -----r--------|-------.-F --- ----r---l----------------0.4 - --------L-I---------.-

L----------------- I__

03 - -- I '_ Oenqi.d Qopera.t[ng signa(24Vdc_--- _-------------- ---------t--- ----|----------- -------- -------- -------- t----- ----- t--- ---- t--- ---

0.2 Pr t P012 0.1 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~-!-------- -------______ --------

01-----L-------- -----------

--------'-----L----'---L---4----'----

0.0 PM

01 _ --t-----------

-0.1-1.8 2.0 2.2 2.4

Time[s]

2.6 2.8 3.0

a)

Fu1)a)

Time[s]

a) On-off characteristics

Fig. 8 Output pressure results ofpoppet

3.3 Proposed pneumatic valve

Fig. 9 shows the pneumatic valve manufactured byinserting the bimorph-type piezoelectric actuator withthe size of 25.2mm(L)x7.2mm(W)x0.5mm(H) and-220X 10-12 CN-' of the piezoelectric constant in the pilotcontrol part instead of the solenoid actuator explained inFig. 1. The piezoelectric actuator used in the pneumaticvalve has a maximum operating force of 0.052N, a

maximum displacement of 63,Mm, and square wave

frequency of 15Hz at -9dB gain. Fig. 10 shows thecharacteristics of the step response of the piezoelectricpneumatic valve. Its time constant is 74ms, which

4124

Srin ampifier

Va:lw j i

Fig. 5 Photo (

n-vot Outpu| aual Switch Analog Output

Na,ti-nr1 1-nt.-IersDAQCard-6062E to

Ground

0

proved to be a valve with fast response and goodstability.

ve PartP

Fig. 9 Manufactured pneumatic valve

24 -

22 -

20 -

18 -

16 -

14-

m 12-

a 10-QLC: 8 -

the solenoid valve for exhaust brake," Trans. ofKSAE, Vol. 12, No. 1, pp. 190 195, 2004.

[4] S. N. Yun, "Electro-Magnetic ProportionalSolenoid," Journal of the Japan Fluid PowerSystem Society, Vol. 35, No. 5, pp. 342-347, 2004.

[5] S. N. Yun, J. S. Ryu, Y. B. Ham and G. D. Kim,"Pressure control technique using proportionalsolenoid actuator," 9th Scandinavian InternationalConference on Fluid Power, pp. 1-5, 2005.

[6] Sonam Yun, Jae-Seop Ryu, Byung-Kyu Ahn,Mi-Ran Seo, Chang-Seop Koh, "Optimal Design ofElectro-Magnetic Proportional Solenoid usingGenetic Algorithm ", NCFP 105-7.6, pp.243-247,2005.

[7] SMC catalogue, CATKSJ1-82, pp. 1-8, 2004.[8] T. Kagawa, K. Kawashima, T. Fujita, Y. Tanaka

and K. Sakaki, "Measurement method for theeffective area using an isothermal chamber",hydraulics and pneumatics, Vol. 26, No. 1,pp.76-81, 1995.

Time[s]

Fig. 10 Step response characteristics ofmanufacturedpneumatic valve

4. CONCLUSIONS

In this study, as a basic research to provide the PZTmicro valve with a pressure regulator to a fluid control,a pressure regulator and a poppet type directionalcontrol valve were manufactured and experiments werecarried out. From the study, validity of this theoreticalstudy was established through the experiment.

The results of this study indicate that pressureregulator for PZT micro valve is needed for highpressure system application and multilayer PZT actuatoris also needed for compactness.

REFERENCES

[1] S. N. Yun, K. W. Lee, H. H. Kim and H. J. So,"Development of the Pneumatic valve withbimorph type piezoelectric actuator," MaterialsChemistry and Physics, Vol. 97, No. 1, pp. 1-4,2006.

[2] S. N. Yun, Y. B. Ham, C. Y. Kim and J. H. Park,"Hysteresis characteristics improvement of thePZT actuator for metal jet printing," 2nd IWPMA,pp. 56, 2005.

[3] S. N. Yun, Y. B. Ham, "Characteristics analysis of

4125