Sensors and Actuators A: Physical

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1 Sensors and Actuators A 155 (2009) Contents lists available at ScienceDirect Sensors and Actuators A: Physical journal homepage: Flow control valve for pneumatic actuators using particle excitation by PZT vibrator Daisuke Hirooka, Koichi Suzumori, Takefumi Kanda Graduate School of Natural Science and Technology, Okayama University, Tsushima-naka, Okayama , Japan article info abstract Article history: Received 24 December 2008 Received in revised form 23 June 2009 Accepted 13 July 2009 Available online 21 July 2009 Keywords: Variable orifice PZT Pneumatic actuator Pneumatic valve This paper reports a new flow control valve for pneumatic actuators that has a lightweight and simple structure and uses particle excitation by PZT vibrator. The flow control valve in this report consists of an orifice plate which has plural orifices, PZT vibrator which is adhered on the orifice plate and iron particles. The valve is normally closed, because air flow carries the particles on to the orifice and particles seal the air flow. Because the orifice plate excitation by the PZT vibrator works to make the particles away from the orifice plate, the air flows through the orifices. It is driven at resonance mode and can be used as a variable speed controller for pneumatic actuators. The new flow control valve avoids the stopping shock of pneumatic actuators at the stroke ends while retaining the advantages of pneumatic actuators Elsevier B.V. All rights reserved. 1. Introduction Pneumatic actuators such as pneumatic cylinders are widely used in the automation industry because they are simple, lightweight, cheap, and suitable for achieving high speed linear motions. In general, pneumatic actuators need speed controllers to avoid the stopping shock at the stroke ends. But conventional speed controllers cannot smoothly control the airflow rate and cannot drive pneumatic actuators at high speed without shock at the stroke ends. They also greatly increase the system s size and the weight. Several new actuating methods and new valves have been developed to solve these faults [1 4]. Uehara and Hirai developed an unconstrained vibrational pneumatic valve using metal ball popet [1], Akagi et al. developed a flow control valve using a vibration motor [2], Yun et al. developed a pneumatic valve with bimorph type PZT actuator [3], Liu et al. developed a pneumatic actuator control system using PZT impact force [4]. But they still have some problems on size, weight, flow capacity and controllability for practical uses. This study develops a new flow control valve driven by PZT. The new flow control valve, which solves all these problems while retaining the advantages of pneumatic actuators, consists of an orifice plate that is 19 mm in diameter and 0.8 mm thick, a PZT vibrator that is adhered to the orifice plate, and iron particles. Experimental results show that this flow control valve works successfully at pressure up to 0.70 MPa and can Corresponding author. Fax: address: hirooka@act.sys.okayama-u.ac.jp (D. Hirooka). manage the flow rate by controlling the amplitude of particle excitation. 2. Working principle The principle of the new flow control valve is shown in Fig. 1. The flow control valve, which is arranged at the outlet port of a pneumatic actuator, consists of an orifice plate with 10 to 20 orifices of 0.5 mm diameter, a PZT vibrator adhered to the orifice plate, and iron particles. Fig. 1(a) shows the non-driving state of the PZT actuator. The airflow from the outlet port of the pneumatic actuators carries the particles to the orifices and seals the airflow. Fig. 1(b) shows the driving state of the PZT actuator. In this state, the orifice plate excitation by the PZT vibrator moves the particles away from the orifice plate. As a result, space is generated between the particles and the orifices, and air flows through the orifices. The excitation intensity controls the flow rate from the pneumatic actuator. 3. Basic analysis of particle motion The flow control valve is designed through calculation and analysis. Its drive condition is decided by acceleration in the orifice part. The condition for making the particles away the plate is derived as follows from the dynamic balance of forces acting on the particle: a> r2 P ± mg (1) m where a represents the acceleration at the orifice, P is the airflow pressure from the outlet port of the pneumatic actuators, r is the /$ see front matter 2009 Elsevier B.V. All rights reserved. doi: /j.sna

2 286 D. Hirooka et al. / Sensors and Actuators A 155 (2009) Fig. 2. Schematic of orifice plate. Fig. 1. Working principle of new flow control valve. radius of the orifice, m is the particle mass, and g is the acceleration due to gravity. In this equation, ± depends on the installation direction of the flow control valve. In this research, we used three kinds of particles: 0.6, 0.7, and 0.8 mm in diameter. When the parameters of r and P are determined to be 0.25 mm and 0.70 MPa, the parameter of a is obtained from expression (1). Table 1 shows that particle mass m and acceleration a are obtained by the calculation. r 2 P is generally much larger than mg for the pressure higher than 0.40 MPa; r 2 P = 0.84 N, mg = N for typical values of r = 0.25 mm, P = 0.40 MPa, and m = g, for example. Thus, the influence of gravity is small. Actually, the developed valve works very well in any orientation as described later in the section on experimental results. 4. FEM analysis The orifice plate is designed using the finite element method (FEM). Fig. 2 displays its schematic view. The orifice plate is 19 mm in diameter and 0.8 mm thick. The orifice aperture diameter is 0.5 mm, and 19 orifices were circularly arranged on the orifice plate made of stainless steel with high-carbon high-chromium steel particles. The PZT actuator, which is ring-shaped with an outer diameter of 19 mm and an internal diameter of 10.2 mm, is 0.5 mm thick. The PZT is located on the back surface of the orifice plate (Fig. 3). In general, a fixed mounting structure rim is suitable for such vibrators to generate large displacement at the plate s center [5]. Fig. 3 shows the analytical results of the flow control valve deformation mode calculated by FEM. The flange part vibrates and excites the orifice plate on which the orifices are fabricated. In this research, we used flexural oscillation as a driving mode (Fig. 3) because the orifice plate acceleration grows in the vicinity of the center. As a result, a difference can be generated in the acceleration by considering where orifice was setup. The orifice plate is combined with the acrylic case during a flowing quantity evaluation experiment. The acrylic case, which is cylinder-shaped and 22 mm high, has a 30 mm diameter. As shown in Fig. 4, the dimensions of the flow control valve, those of the case, and their material properties gave a suitable vibration mode. The values on color bars in Figs. 3 and 4 mean the displacement values in the unit of meter. Fig. 5 shows the analytical results by FEM for acceleration in the orifice part. The analyses were made with an alternating voltage of 100 V p-p and a frequency from 27 to 29 khz. Orifice 1 is the center orifice, and orifice 4 is the outside orifice, as shown in Fig. 6(b). The interval of each orifice is 0.9 mm in the circular direction. Fig. 5 shows that the analytical results demonstrate sufficient acceleration to satisfy the driving condition. A prototype orifice plate was made based on this analysis. Fig. 6(a) shows its prototype and Fig. 6(b) shows its close-up. The orifices are arranged radially with a 0.9 mm interval in the radial direction and 60 angular interval. In general, the orifices Table 1 Orifice acceleration necessary for particle excitation a. Particle diameter 0.6 (mm) 0.7 (mm) 0.8 (mm) m (kg) a (m/s 2 ) Fig. 3. FEM analytical result of orifice plate deformation mode.

3 D. Hirooka et al. / Sensors and Actuators A 155 (2009) Fig. 7. Relationship between admittance of orifice plate and frequency. Fig. 4. Analytical result of deformation mode of orifice plate and acryl case. are arranged radially to reduce swirl passing through the orifice plate [6]. The mass of the orifice plate is only 6 g, which is very lightweight. Fig. 6(c) shows the orifice plate combined with an acrylic case. Air is applied to the upper part of the acrylic case. 5. Experiment of flowing quantity evaluation The performance of the orifice plate s prototype was experimentally evaluated by investigating the relationship between its admittance and the driving frequency. The experimental result is shown in Fig. 7. The resonant frequency was khz; this is the frequency at which the valve evaluation experiments were made. Fig. 5. FEM analytical results by acceleration in orifice. Fig. 8. Experimental setup for flow quantity evaluation of characteristics system. Fig. 6. Prototype of orifice plate and acryl case. Fig. 9. Experimental results of 0.8 mm diameter particles.

4 288 D. Hirooka et al. / Sensors and Actuators A 155 (2009) Fig. 10. Experimental results of 0.7 mm diameter particles. Fig. 8 shows the experimental system for the flowing quantity evaluation. A function generator, a voltage amplifier, an airflow meter, an air pressure gauge, and a compressor were used. With this setup, the relation between the applied voltage and the flow rate change were measured for pneumatic pressure of 0.40 to 0.70 MPa in 0.10 MPa steps. The experiments were made for particle diameters of 0.8, 0.7, and 0.6 mm. Fig. 9 shows that the flow rate can be controlled continuously by changing the applied voltage. This flow control valve achieves a maximum flow rate of L/min under conditions of 56.2 V p-p and 0.70 MPa. By comparing Figs. 9 and 10, we found that the 0.7 mm particles need higher voltage than the 0.8 mm particles to start the Fig. 12. Experimental results of 0.6 mm diameter particles. Table 2 Comparison with the previous flow control valve. This valve SMC VEF2121 CKD 2AF-2 Effective sectional area (mm 2 ) Volume (mm 3 ) Mass (g) Dissipation power (W) airflow because greater acceleration is necessary for lighter particles to generate sufficient inertial force to move the particles away from the orifice plate. The ratio of the flow rate/applied voltage is larger in Fig. 10 than in Fig. 9; rapid increase of the flow rate is found with pressure of 0.70 MPa. These phenomena are caused by the influence of the airflow, which acts much more on smaller particles. During voltage increases, the particle located in the center of the plate is moved first and causes airflow thorough the center orifice, as shown in Fig. 11. When the other particles are heavy enough to avoid being excited by the airflow, they retain orifices to seal the airflow, as shown in Fig. 11(a). But when the particles are light, they are easily blown up by the airflow, which is caused by the first excited particle, as shown in Fig. 11(b), resulting in rapid increase of the airflow rate. This tendency is found more clearly in Fig. 12, where rapid changes of the airflow are found around the applied voltage 57.0 V p-p and 0.60 MPa. Because the valve resembles an on/off valve at 0.70 MPa, the relation between the applied voltage and the flow rate change were not measured. Fig. 11. Relation of airflow and particle mass. Fig. 13. Comparison of effective sectional area/volume of valves.

5 D. Hirooka et al. / Sensors and Actuators A 155 (2009) The response time of the valve depends on various factors. Roughly speaking, it is less than 0.1 s for opening and s for closing. In addition, the size and the characteristics of the new valve were evaluated. Comparison with typical commercial models of small flow control valves is shown in Table 2. Fig. 13 compares the ration of the effective sectional area/volume of the new flow control valve with commercial proportional control valves. We conclude that the new valve is small and efficient because the effective sectional area/volume is large. 6. Conclusion In this paper we proposed a new type of flow control valve for pneumatic actuators that is lightweight and has a simple structure and uses particle excitation by a PZT vibrator. It is driven at resonance mode and can be used as a variable speed controller for pneumatic actuators. The flow control valve consists of an orifice plate, a PZT vibrator adhered to the orifice plate, and iron particles. The orifice plate is designed based on FEM analysis. Its frequency response was measured, and its flowing characteristics were evaluated. The experiment results show that this flow control valve works successfully at pressure up to 0.70 MPa and has a maximum flow rate of L/min. Additionally, it can manage the flow rate by controlling the amplitude of particle excitation. Furthermore, adjustment of the precise flowing quantity was confirmed to be closely related to particle mass. Comparing the effective sectional area/volume with commercial proportional control valves, the new flow control valve is small and efficient. Acknowledgement This research was aided by the Koganei Corporation, who supported the fabrication of this valve s prototype. References [1] S. Uehara, S. Hirai, Unconstrained vibrational pneumatic valves for miniaturized proportional control devices, in: Proceedings of 9th International Conference on Mechatronics Technology, (ICMT2005), [2] T. Akagi, S. Dohta, S. Katayama, Development of small-sized flexible control valve using vibration motor, in: Proceedings of 7th JFPS International Symposium on Fluid Power, TOYAMA, 2008, P2-25. [3] S. Yun, K. Lee, H. Kimb, H. Sob, Development of the pneumatic valve with bimorph type PZT actuator, Materials Chemistry and Physics 97 (2006) 1 4. [4] Y.-T. Liu, C.-C. Jiang, Pneumatic actuating device with nanopositioning ability utilizing PZT impact force coupled with differential pressure, Precision Engineering 31 (3) (2007) [5] K.H. Lam, H.L.W. Chan, H.S. Luo, Q.R. Yin, Z.W. YIN, Piezoelectrically actuated ejector using PMN PT single crystal, Sensors and Actuators A 121 (2005) [6] G.L. Morrison, K.R. Hall, J.C. Holste, M. Macek, L. Ihfe, R.E. DeOtte Jr., Comparison of orifice and slotted plate flow meters, Flow Measurement and Instrumentation 5 (2) (1994) Biographies Daisuke Hirooka was born in Kobe, Japan, on August 24, He received the B. Eng. in Systems Engineering form Okayama University, Japan in Since 2007, he has been a graduate student at graduate school of Okayama University. His current research interest is in the mechatronics. Koichi Suzumori was born in He received the Doctor degree from Yokohama National University in He had worked for Toshiba R&D Center from 1984 to 2001, and worked also for Micromachine Center, Tokyo from 1999 to He has been a professor at Okayama University, Japan since He is a member of the Japan Society of Mechanical Engineers, the Robotics Society of Japan, IEEE and the Institute of Electrical Engineers of Japan. Takefumi Kanda was born in Fukuoka, Japan, on June 18, He received the B. Eng., the M. Eng. and the Dr. Eng. degrees in precision machinery engineering from The University of Tokyo, Japan in 1997, 1999 and 2002, respectively. From 2002, he was a research associate at the Graduate School of National Science and Technology, Okayama University, Japan. Since 2003, he has been a lecturer at Okayama University. His research interests are micro sensors, micro actuators, micro systems and piezoelectric film. He is a member of the Japan Society for Precision Engineering, the Institute of Electrical Engineers of Japan, IEEE, the Japan Society of Mechanical Engineers and the Robotics Society of Japan.

6 ID Title Pages Flow control valve for pneumatic actuators using particle excitation by PZT vibrator 5