BASIC INVESTIGATIONS OF ELECTROHYDRAULIC SERVOVALVE WITH PIEZO-BENDER ELEMENT

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1 KOMISJA BUDOWY MASZYN PAN ODDZIAŁ W POZNANIU Vol. 25 nr 2 Archiwum Technologii Maszyn i Automatyzacji 2006 DARIUSZ SĘDZIAK * BASIC INVESTIGATIONS OF ELECTROHYDRAULIC SERVOVALVE WITH PIEZO-BENDER ELEMENT One of romising today idea is usage of iezoelements like iezo stack or iezo-benders as control elements for hydraulic and neumatic valves. In the aer basic research of electrohydraulic servovalve with iezo-bender was resented and investigated. The main design concet of control stage was shown. Results of investigations from first stage of research were resented and discussed. Key words: servovalves, iezo-benders, exerimental investigations 1. INTRODUCTION Electrohydraulic servo drives can be found in many industrial alications. They can be controlled by small ower electrical signals and roduce high recision movements with big forces or torque moments at outut. Hydraulic acting drives are controlled by valves with many tyes of actuators in control stages, including roortional electromagnets, torque motors and steing motors. 2. PIEZO CONTROL STAGES One of ossible solution is usage of iezo-benders as control elements for hydraulic or neumatic valves [1, 2, 3, 4]. It small dimensions assure reduction of movable mass and enables getting better of dynamic arameters. Usable deflections and blocking forces obtained from iezoelements can be sufficient to fit requirements for servovalve control stages [5, 6]. Cost of today roduced iezoelements (about EUR) seems to be also accetable for mass alications. Because bending of iezo-beam is relevant to alied voltage they can be used as a flaer late between two nozzles inside the control stage of servovalve. * Ph.D. Eng. Institute of Mechanical Technology, Poznan University of Technology.

2 186 D. Sędziak Bending of iezo flaer can control ressure difference behind nozzles which acts on front surface of valve sool (Fig. 1). Thus iezo-bender can relace in near future wide used today an electromechanical torque motor. Today on a market accessible iezo-benders allow building servovalves with electric or barometric feedback (Fig. 1a). Building of servovalves with mechanical feedback requires a joining some additional linear sring to end of iezo-bender (Fig. 1b). a) iezobeam b) iezobeam with sring A B A B electrical feedback barometrical feedback Fig. 1. Piezo bender as servovalve flaer late: a) for electrical or barometrical feedback, b) for mechanical feedback Rys. 1. Belka iezo jako rzesłona dyszy serwozaworu: a) ze srzężeniem elektrycznego lub barometrycznego, b) ze srzężeniem mechanicznego 3. DESCRIPTION OF SERVOVALVE For first basics investigation servovalve WP3-10 form PZL-Hydral was used. It structure is resented in Fig. 2 [7]. Control stage of this valve is suorted with a rotating ush-ull flaer late droved by torque motor. Rotation nature of flaer requires a usage of barometric feedback between flaer and sool osition. Voluminal ratio of moving elements in control stage reduces working frequency range of servovalve. Scheme of new control stage with iezo-bender is shown in Fig. 3. It consists of four basic elements: cover (1) with iezo-bender (2) and chassis (4) with 2 control nozzles (3). As a flaer late iezo-element tye PL from PI-Ceramics was used. Its geometric dimensions are mm, theoretical deflection ± 80 μm and blocking force about 2 N [6]. Deflection of used iezo-bender was controlled by low ower source of voltage about ± 30 V. Picture with build control stage, mounded on servovalve were shown in Fig. 4 and Fig. 5.

Basic investigations of electrohydraulic servovalve 187

2 4 Fig. 3. Scheme of control stage with iezo-bender Rys.

3 Basic investigations of electrohydraulic servovalve 187 Fig. 2. Structural scheme of servovalve WP3-10 [7] Rys. 2. Schemat ideowy serwozaworu WP3-10 [7] Fig. 3. Scheme of control stage with iezo-bender Rys. 3. Rysunek stonia sterującego z belką iezo Fig. 4. Picture with modified servovalve Rys. 4. Zdjęcie zmodyfikowanego serwozaworu

4 188 D. Sędziak 5. EXPERIMENTAL INVESTIGATIONS OF SERVOVALVE Comarison of ressure ste resonses of servovalve with modified control stage was shown in Fig. 5. Some differences of resonse shae between orts A and B can be observed. That can be caused by some differences between dimensions of nozzles and its regulations. a) 8 [Ma] _0 _A _B 0 0 0,02 0,04 0,06 0,08 t [s] 0,1 b) 20 [Ma] _0 _A _B 5 0 t [s] 0 0,02 0,04 0,06 0,08 0,1 Fig. 5. Pressure ste resonses of servovalve: a) = 6 MPa, b) = 20 MPa Rys. 5. Skokowe odowiedzi ciśnieniowe serwozaworu: a) = 6 MPa, b) = 20 MPa One of imortant nonlinearities observed on iezoelements is a hysteresis. Because of caacitance nature of iezoelements size of it hysteresis deends on conditions of enforced control signal. Exerimental investigations of hysteresis for iezo-bender used in a servovalve alication were shown in Fig. 6a.

5 Basic investigations of electrohydraulic servovalve 189 Flow characteristic of modified valve taken from resonse of electrohydraulic servo drive were shown in Fig. 6b. Research was made for suly ressure about 16 MPa. The cylinder with stroke 400 mm and diameters of iston 100 mm and iston road 60 mm was used as actuator. Frequency of sinusoidal control signal given on the inut of iezo-bender electronic control circuit was about 0.4 Hz. b) Q [l/min] 10 0 U [V] Fig. 6. Hysteresis of iezo-bender and flow characteristic of servovalve Rys. 6. Histereza iezoelementu i charakterystyki rzeływowej serwozaworu

6 190 D. Sędziak 5. CONCLUSIONS In the following aer results of first basics research under alying iezobender as a flaer late in control stage of servovalve are resented. First exerimental results shown that iezo-bender can be used with good success as control element for servovalves. Comarison of first results has shown good ressure ste resonses of valve. In future investigations more attention will be aid to reduce an hysteresis of valve by changing a control methods of iezo actuators. Acknowlegment. This study was suorted by Polish Ministry of Science and Education in the years as a grant no 4T07C REFERENCES [1] Bauer F., Reichert M., Hochdynamische Piezoventile, O+P, 2005, 6. [2] Hagemeister W., Piezoelektrisch vorgesteuertes 3/3-Wegeservoventil, Ö+P, 1999, 1. [3] Hantke P., Develoment of iezo-actuated ilot valve for water-hydraulic mining alications, Ö+P, 2003, 6. [4] Koehler E., Kunzmann J., Schnelle Pneumatikventile mit iezoelektrischen Aktoren, Ö+P, 1998, 1. [5] htt:// [6] htt:// [7] htt:// Praca włynęła do Redakcji Recenzent: rof. dr hab. inż. Edward Palczak BADANIA WSTĘPNE SERWOZAWORU ELEKTROHYDRAULICZNEGO Z PIEZOELEMENTEM BELKOWYM S t r e s z c z e n i e W ublikacji rzedstawiono koncecję stonia sterującego do serwozaworu elektrohydraulicznego, w którym rzysłonę dysz stanowi iezoelektryczny element belkowy. Przedstawiono konstrukcję zmodyfikowanego stonia sterującego do wybranego zaworu. Omówiono wstęne wyniki badań doświadczalnych serwozaworu z takim stoniem. Słowa kluczowe: iezoelementy serwozaworu, badania doświadczalne

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