INVESTIGATION OF THE MEMBRANES PERMEABILITY OF THE FLOW CONTROL DEVICE BASED ON PIEZO ACTUATOR

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1 8th International DAAAM Baltic Conference "INDUSTRIAL ENGINEERING April 2012, Tallinn, Estonia INVESTIGATION OF THE MEMBRANES PERMEABILITY OF THE FLOW CONTROL DEVICE BASED ON PIEZO ACTUATOR Rimašauskas, M.; Rimašauskienė, R. Abstract: Piezoelectric actuators are simple design, small size, and relatively low cost elements, suitable for precision positioning systems. Therefore, actuators of such type were chosen for the design of the flow control device. Flow control membrane of the device consists of two plates with micro pores or notches. One of the plates, depending on the type of the actuator, may carry out a rotary motion. While mowing, membrane plates with notches or formed micro pores create a Moiré pattern between them, which depends on the flow throughput parameters. Adjusting piezoelectric actuator s position and the Moiré effect resulted between the membranes, it was created a quick, accurate, and relatively inexpensive flow control device. The created flow control device with piezoelectric actuators and Moiré geometric effect is used in gas, liquid, and light flow control systems, and is characterized by its throughput and precision. Such devices are simple and are suitable particularly for precise dosing of flows. The design of the flow control device is patented protected. Key words: flow control, piezo actuator. 1. INTRODUCTION The piezoelectric and moiré effects were noticed in the end of the 19 th century. Over the time, manufacturing technologies of piezoelectric elements advanced and new areas of moiré effect implementation were discovered; they were increasingly introduced in various fields [1, 2]. Literature analysis revealed, that piezoelectric actuators have been used in flow control devices of various structures for a long time [3, 4], but the information about the use of moiré effect in equipment of such type is limited. Moiré effect is an interference pattern created, for example, between two grids that overlay on each other at a certain angle, or have slightly different mesh sizes. It is an interaction of two rasters. Exposed to the light, the unit transmits or reflects it in this time forming bright and dark areas moiré pattern [5]. Natural and technological Moiré patterns are observed in various environments [6, 7]. They can be made of light, sound, or other types of waves. The category of flow control and transmission devices covers a range of products designed for facilitating flow management: carrying measurements, fixing parameters of a stream flowing through pipes or hoses, etc.. They can be used for light, gas, liquid, or semi-solid materials. Flow control and transmission devices can be divided into the following groups: valves, valve acting as flow positioning systems, dispensers, and others. This article analyses high-speed flow control systems based on piezoelectric actuators and moiré interference principles. Moiré effect is created in a flow control membrane between two plates with micro pores or notches. It needs to rotate at a certain angle or to move only one of the plates and moiré pattern changes. In such a way the flow closes, opens, or obtains intermediary positions. 92

2 Destination of a piezoelectric actuator in a flow control device is to convert electric power to mechanical energy (by movement or turning). Its operational characteristics (speed and accuracy) influence rotation or movement of membrane plates. As it is known, characteristics of piezoelectric actuators are suitable of the use in micro flow control devices, since they enable getting high speed and resolution, and offer great variety of sizes and relatively low price [8-10]. 2. SELECTION OF THE PIEZO ACTUATORS To generate a rotary movement in a membrane of a flow control device many types of the piezoelectric actuators can be used. However, most technological constructions are made using ring or cylindrical piezoceramic elements. Actuators of such shapes produce the lowest number of units, thus generating maximum speed of the flow control and obtaining nanometer scale resolution at the lowest cost of the device. The excitation of one of the electrode sectors of cylinder or ring-shaped actuator generates a linear motion. Dividing electrodes to a larger number of segments and using multiphase excitation allows awakening of traveling wave and getting rotating movement of the ring in contact the output link. Traveling wave motors work on a basis of frictional interaction of flexural or surface acoustic waves of piezoceramic input link with a driven element, since propagating waves produce elliptical trajectories of input link s surface points [11, 12]. When closed piezoelectric ring is driven at one point at a frequency corresponding to the resonance of this ring, it excitates a standing wave only, since vibrations propagate in both directions, symmetrically to the vibration source, and interfere with each other. When two vibration sources are installed on the ring, traveling waves can be obtained by superimposing these waves. Using this superposition principle, we can generate a traveling wave with a shape corresponding to the standing wave s shape. The n-th mode of an elastic ring is expressed as: while propagating wave is expressed as: (1) (2) Using a trigonometric relation, equation (2) can be transformed to: u p (φ,t) = A cos(kφ)cos(ωt)+ +A cos ( k ) cos( t ) (3) 2 2 In this way, a traveling wave can be generated by superimposing two standing waves, whose phases differ by 90 degrees from each other. Generally, the phase difference can be chosen arbitrarily (except 0, π and π). As a flow control device having a single degree of freedom (which can perform a rotating motion) cylindrical piezoelectric actuator was selected and investigated experimentally. It is easy to choose actuators suitable for different constructions, since the variety of them is sufficiently large. Monolithic piezoceramic cylinder has unique characteristics; they can work in a super high vacuum (130 npa and fewer); depolarization temperature occurs at 500 V voltage in the first working cycle. Depending on the location of electrodes on a piezoceramic cylinder, it can create radial, longitudinal, bending, and travelling wave type vibrations in the output link. Inner and outer surfaces of the monolithic piezoceramic cylinder are coated with a layer of silver. In case, when voltage is connected to inner and outer elements of a piezoelectric actuator with thin walls, it works in radial or longitudinal vibration mode. Cylindrical piezoelectric actuator s inner and outer surfaces are covered with silver 93

3 and divided into three segments, two of 90 and one 180. Inner and outer opposing electrodes (180 ) are connected to each other; other two electrodes (90 ) are connected to the opposite two; and the condenser is connected between them (Fig. 1). Thus, combining piezoelectric cylindrical electrodes formed asymmetrical output unit with travelling wave type oscillations. Fig. 1. Connection scheme Moving the second phase of the harmonics 180 or the first 90 to each other can generate a reverse actuator output. Traveling wave oscillations are obtained connecting respective electrodes to a multiphase signal generator. If one of the active components of the connector is a hollow of cylindrical shape, then traveling wave is expressed as follows: (4) where ζ - relative amplitude of vibrations; n 1 - wave number, and φ - angular coordinate of available cross-section. In this case, tangential ε t and radial e r - points on the neutral surface of sphere displacements - are related in such a way: (5) where angular speed of the wave (when ); it is equal to the angular harmonic signal. Angular speed of the rotor ω depends on mechanical attachment between the components and external value of the moment, but, in any case, it is less than the effect of frictional interaction between components. 3. ANALYSIS OF THE DYNAMIC CHARACTERISTICS OF A CYLINDRICAL PIEZO ACTUATOR Experiments aimed to find out resonant frequency that would enable achieving the largest output link s shift of piezoelectric actuator (cylinder). In order to determine these parameters experiments on the experimental stand were carried out. The experimental stand consists of a programmable signal generator, high voltage amplifier, laser doppler vibrometer PolytecTM, analog capture card, and a computer with installed scanning vibrometer software PSV8.8. Data were collected and processed by specific program in PSV 8.8 graphical environment that allows obtaining the amplitude frequency characteristics of experimental output link. Displacement, pm Frequency, khz Fig. 2. Displacement s dependence on frequency (voltage ±100 V) With a help of laser vibrometer PolytecTM and computer with specially made PSV 8.8 program, shift s dependence on frequency was found. Measuring the displacement of piezoelectric actuator s output link, the excitation voltage was kept at ±100 V, and frequency was khz. Figure 2 shows that the greatest displacement is achieved at resonant frequencies (52.52 khz and khz). The experiment confirmed that the output link of piezoelectric cylinder moves in trajectory of ellipses. Figure 3 shows movement trajectories of the output link. 94

4 f=93.86 khz for periods of package. The transition process ended after 12ms from the end of the excitation package. After the recalculation of the displacement, in turn, the resolution of 0026', and the in the second case of 0029', was obtained. Fig.3. Movement trajectories The same experimental stand was used for investigation of the resolution of flow control device with piezoelectric actuators (cylinder shape). Displacements of reference point were measured in the following way: a steel ring with a tightly fixed plate with micro pores was fitted on the output link of a piezoelectric cylinder. The same unit was fixed on the steel ring as the starting point. Data was collected and processed by specifically designed program in PSV 8.8 graphical environment, which enables detecting experimental characteristics of reading point s amplitude. After the experiment, the shifts of the reading point were converted into angular degrees of shifting. The package containing the same number of periods of harmonic signal (U RMS =60 V, f=52.52 khz or f=93.86 khz) was used in investigation of the resolution of a flow control device. Shift s dependence on harmonic number of signal cycles in the package is presented in Fig. 4. Turning angle, min f=52.52 khz f=93.86 khz Nuber of the periods in the package Fig. 4. The dependence of turning angle on the number of periods in the package. The rotor starts to rotate after forming two harmonic signals whose amplitude U RMS =60 V and frequency f=52.52 khz or Notwithstanding that actuators of such type (generated traveling radial oscillations) are studied very widely, still it is difficult to determine nodal points of its mounting on the surface. Therefore, this problem was solved using an experimental method of holography. With a help of holographic imaging method the maximum vibration amplitude of actuators output links points was determined.. a) frequency voltage 0 V c) frequency voltage 50 V b) frequency voltage 12 V d) frequency voltage 60 V Fig. 5. Holograms of piezoceramic actuator (cylinder form) This investigation is needed for construction of flow control device in order to know where to place a steel ring (rotating motion) ensuring minimum friction between links. After the holography of piezoelectric actuators (cylinder form) at working resonance frequency 52.52kHz and khz, the location of interference bands and holograms at resonant frequency of khz (Fig. 5) were obtained. At the same 95

5 time, it was detected that the output piezoelectric actuators link is not deformed when the voltage is 0 V (Fig. 5 a). Increasing excitation voltage to 12 V (Fig. 5 b), two symmetric interference bands appear; the circle repeats to (Fig. 5 c) and so on. The experiment showed that places of shock and abrasion resistant material of supporting elements, where four interfering bands of the output link were obtained, needed to be glued and strengthened with a steel ring in order to obtain lower friction between the output link and the surface of the steel ring so that the ring will not use the entire surface and spin faster and more efficiently. 5. RESULTS OF THE SIMULATION Further simulations were carried out using ANSYS CFX software. First of all the boundary conditions were set. Two identical construction plates were used for the simulation. Water inlet was kept at constant speed m / s, while the outlet was set like a static pressure of 0 Pa. Simulation was carried out without changing boundary conditions, just turning one plate by 0.5 degree. Figure 6 presents the results of the simulation. 4. MEMBRANE CONSTRUCTION In flow control devices of such type, membranes can be made of the plates with different structures, depending on what flow rates and management options are expected. In this article were presented two structures of the membranes: 1. The membrane is made of plates with the same number of notches. In order to obtain maximum throughput and full closure it is necessary to choose an appropriate ratio between closed and open areas of the plate. Simulations performed showed that the best flow control option is obtained when this ratio is equal to The membrane is made of plates with different number of notches. The most important variable is the number of notches. In case where the number of notches differs by one notch, only one interference fringe emerges and the flow runs through one side of a membrane leaving the other side completely closed on that time. The greatest influence is caused by the ratio of closed and open areas angles β 1 /β 2. This parameter was set to 0.3. Only this ratio gives maximum permeability on one side of the membrane and minimum permeability on the other side. Fig. 6. The dependence between the flow and the turn angle of the plate It can be seen that when the valve is fully open the flow rate reaches 0.03 l/s. Rotating one of the plate till 3 degrees the flow rate was decreasing and from 3 till 6 degrees the valve was closed. Increasing the angle of rotation til 9º the membrane was opened. And in this point it was completely open and the maximum flow rate was obtained. Further turning repeated opening-closing cycle of the plate. Analogical simulations were performed with different types of the plates. Boundary conditions remained the same as in the first case. Simulations with plates of different structure showed that maximum flow rate was l/s and turning angle did not interfere with it. Although the flow was stable, changing the turning angle altered the place of flow s passage through the membrane. This operation principle might be used for flow control in certain flow control devices. 96

6 6. CONCLUSIONS 1. After the analysis of industrial piezoelectric actuators it was decided that cylindrical actuator is the best choice for the construction of technological flow control devices. The electrode configuration was selected in order to obtain the travelling wave oscillations in the output link of the cylindrical actuator. 2. The experimental analysis disclosed working characteristics of cylindrical piezoelectrical actuator: resonance frequencies (52.52 khz and khz) and output link movements of the piezoelectrical actuator. 3. The relationship between plate rotation angle and flow rates was found. When plates are of the same construction, maximum flow rate is 0.03 l / s; when the construction rate is different, the flow rate is l / s. 7. REFERENCES 1. Lee, K.S. Measurement of stress in aluminum film coated on a flexible substrate by the shadow moiré method. Applied Optics, 2008, 47, Liou, N.S. Specimen gratings made from body art paper for in-plane moiré strain analysis. Polymer Testing, 2005, 24, Bullough, W.A., Ellam, D.J., Wong, A.P., Tozer. R.C. Computational fluid dynamics in the flow of ERF/MRF in cotrol devices and of oil through piezohydraulic valves. Computers & Structures, , Suh, H.K., Park, S.W., Lee. C.S. Effect of piezo-driven injection system on the macroscopic and microscopic atomization characteristics of diesel fuel spray. Fuel, 2007, 86, Li, X.L., Kang, Y.L., Qiu, W., Qin, Q.H., Xiao. X. A study on the digital moire technique with circular and radial gratings. Optics and Lasers in Engineering, 2007, 45, Yin, L.W., Li, M.S., Sunm, D.S., Zou, Z.D., Liu, Y.X., Hao, Z.Y. Features of moire patterns in HPHT-grown diamond single crystals. Materials Letters, 2002, 52, Lee, J.Y., Wang, Y.H., Lai, L.J., Lin, Y.J., Chang, Y.H. Development of an autofocus system based on the moire method. Measurement, 2011, 44, May, F., Dual. J. Focusing of pulses in axially symmetric elastic tubes with fluid filling and piezo actuator by a finite difference simulation and a method of time reversal. Wave Motion, 2006, 43, Merry, R., Molengraft, R., Steinbuch, M. Modeling of a walking piezo actuator. Sensors and Actuators A: Physical, 2010, 162, Juhas, L., Vujanić, A., Adamović, N., Nagy, L., Borovac. B. A platform for micropositioning based on piezo legs. Mechatronics, 2001, 11, Ragulskis, K., Bansevicius, R., Barauskas, R., Kulvietis, G. Vibromotors for Precision Microrobots. Hemisphere Publishing, USA, Kuribayashi, M., Ueda, S., Mori. E. Excitation Conditions of Flexural Traveling Waves for a Reversible Ultrasonic Linear Motor. J. Acoust. Soc. Am, 1985, 77, ADDITIONAL DATA ABOUT AUTHORS Rimašauskas Marius, Dr. Lecturer. Kaunas University of Technology Kęstučio 27, LT Kaunas, Lithuania Phone: marius.rimasauskas@ktu.lt Rimašauskienė Rūta, Dr. Researcher. The Szewalski Institute of Fluid-Flow Machinery, Polish Academy of Sciences Fiszera 14, Gdansk, Poland Phone: rrimas@imp.gda.pl 97