P1-33 Proceedings of the 7th JFPS International Symposium on Fluid Power, TOYM 28 September 1-18, 28 STUDY ON SOUND OPERTED VLVE FOR WERBLE PNEUMTIC SYSTEM to KITGW, Shuyi JING, Canghai LIU and Hideyuki TSUKGOSHI * Department of Mechanical and Control Engineering Tokyo Institute of Technology 2-12-1 Ookayama, Meguro-ku, Tokyo 12-8 Japan (E-mail: kitagawa.a.aa@m.titech.ac.jp) BSTRCT sound operated directional control (Valve) is proposed which opens and closes in response to the sound of a specific frequency propagated inside the gas supply tube and therefore needs no electric wiring to convey the control signals. By using multi-frequency sound, several s can be controlled simultaneously and resultantly the pneumatic multi-degree wearable system can be constructed compactly. Firstly, the sound-gas pressure converter is proposed and improved so that self-excited vibration can be suppressed. Secondly, the basic characteristic of the sound-gas pressure converter is investigated to show that the back pressure is different depending on whether the sound of specific frequency is added or not. Furthermore, a pilot is developed. Because the pilot pressure change of the pilot developed is only 2kPa, a main is proposed and developed. Finally, a pneumatic multi-degree-of-freedom wearable power-assist system is constructed by using a Dry Ice Power Cell as the portable gas supply, wearable s developed in the previous study, and two sound operated directional control s developed. Experimental results show that the sound operated directional control is feasible and practical in the pneumatic multi-degree-of-freedom wearable system. KEY WORDS, wearable, sound-operated,, resonance NOMENCLTURE : Back pressure of nozzle : Change of back pressure of nozzle p s : Supply pressure x : Space between nozzle and head [mm] y : Displacement of center of head from center of nozzle [mm] z : Wave length of sound [mm] INTRODUCTION power assist multi-degree-of-freedom wearable system has been developed by many researchers. But in most of the traditional pneumatic systems, their focuses are concentrated on the development of s [1] [2]. Few of them are argued about wearable power supply sources or s. Therefore, there exist the problems when the pneumatic systems are used for wearable power assist. For example, the tubes and electrical cords connected between the s and s are troublesome. In Copyright 28 by JFPS, ISBN 4-9317-7-X
this paper, a novel called Sound Operated Directional Control Valve (Valve) is developed. The Valve opens and closes in response to the sound of a specified frequency propagated inside the gas supply tube and therefore needs no electric wiring to convey the control signal for the. By using multi-frequency sound, several s can be controlled simultaneously. Using the previously developed Dry-ice Power Cell [3] as power supply, the Valve is expected to be used in pneumatic power assist wearable system. In this paper, firstly, the sound-gas pressure converter is proposed and improved so that self-excited vibration can be suppressed. Secondly, the basic characteristic of the sound-gas pressure converter is investigated to verify that the back pressure is different depending on whether the sound of specific frequency is added or not. Furthermore, a pilot of the sound operated directional control is developed. Because the pilot pressure change of the pilot developed is only 2kPa, a main is proposed and developed. Finally, a pneumatic multi-degree-of-freedom wearable system is constructed by using Dry Ice Power Cell as the portable gas supply, wearable s developed in the previous study, and two Valves developed. Experimental results verify that the sound operated directional control s are feasible and practical in pneumatic multi-degree-of-freedom wearable power assist system. SOUND-GS PRESSURE CONVERTER The Valve opens and closes in response to the specified frequency sound propagated inside the gas supply tube. If several Valves are set along the supply tube as shown in figure 1, several s can be controlled with the s simultaneously by adding sound of each s resonance frequency into the supply tube. Valve (92Hz) Valve (9Hz) Valve (98Hz) Figure 1 Schematic of multi Valves system s the kernel-element of the Valve, the Sound-Gas Pressure Converter is developed to convert the sound into change of pressure. For convenience, the Sound-Gas Pressure Converter is called S-P Converter. The S-P Converter consists of a nozzle and a vibration element, as shown in figure 2. nd the vibration element consists of a mass called head and leaf spring, as shown in figure 3. The head is adjusted to be as close to the nozzle as possible without touching the nozzle. Resultantly, the leakage from the nozzle is small when the head stands still. If the head of the vibration element responses to the specified frequency sound in the supply tube and resonates near the nozzle in the arrow direction shown in figure 2, the effective area of flow path out from the nozzle to the atmosphere becomes larger and then the flow rate out from the nozzle becomes larger. s a result, the back pressure in figure 2 falls down. In one word, if sound is added to the S-P Converter, the head resonates and the back pressure changes (become smaller). In this paper, the change of the back pressure is used to make the Valve open and close. p s Nozzle z Head x Variable restriction Leaf spring Sound-Gas Pressure Converter y Sound Figure 2 Concept of S-P Converter Leaf spring Head Fixed base Figure 3 Vibration element The developed S-P Converter has a resonance frequency of 98Hz. The diameter of the nozzle is.mm, the same with width of the head. The length of the leaf spring is 2mm. The mass of the head is.29g. Because the mass is set at the end of the leaf spring, the base mode resonance vibration has larger amplitude and the influence of the higher mode can be neglected. In order to investigate the vibration characteristics of the vibration element, sound of a specified frequency is added near the vibration element at the atmosphere. s shown in figure, when the frequency of the sound is equal to the resonance frequency of 98Hz, the amplitude of the head reaches the maximum of 1.mm. If the frequency is set apart from 98Hz with over 1Hz, the amplitude becomes half of the maximum. By using this characteristic, several S-P Converters with different resonance frequency can be controlled simultaneously. SELF-EXCITED VIBRTION In order to investigate the characteristics of the S-P Converter when supply pressure is added, experiments using circuit shown in figure 2 are conducted. The Copyright 28 by JFPS, ISBN 4-9317-7-X
phenomenon of self-excited vibration arises when the supply pressure is added without any sound. When the supply pressure is raised up to 1~2kPa, self-excited vibration starts even though the sound is not added. Once the self-excited vibration starts, it will not stop until the supply pressure is lowered down to about kpa. If measures are not taken to solve the self-excited vibration problem, development of Valve is impossible. Two methods are found to prevent the self-excited vibration through trial and error. The first one is introducing the overlap to the head in y direction (i.e. vibration direction) which means that the width of the head is larger than the diameter of the nozzle. The second one is introducing the underlap to the head in z direction (i.e. vertical to vibration direction) which means that the nozzle protrudes from the end of the head. The S-P Converter initially developed is adjusted to be zerolap in y direction which means that the diameter of the nozzle is the same with width of the head in order to obtain a larger effective area change of the nozzle when the head resonates. Because of the self-excited vibration, an overlap in y direction and an underlap in z direction are necessary. In y direction, if width of the head is set with 1.2mm which is larger than the diameter of nozzle.mm, in other words, if overlap of.3mm is set on both side of the head as shown in figure 4(b), the self-excited vibration does not arise even though the back pressure is raised up to 1kPa in the experiments. It should be mentioned that the overlap should be adjusted to be the minimum. If the overlap is too large, the change of the effective area of the nozzle will become too small. However, the overlap in y direction is not enough. If the sound or disturbance is added, the self-excited vibration will continue unless the back pressure is lowered down to kpa even if the overlap is adjusted to very large. s regards to z direction, the relative position of the nozzle to the head can be adjusted so that the relationship between the nozzle and the head can be change from overlap to zerolap and underlap as shown in figure. Overlap Zerolap Nozzle Overlap Head Leaf spring (a) y-zerolap (b) y-overlap Zerolap (c) z-overlap (d) z-zerolap (e) z-underlap Figure 4 Suppression methods of self-excited vibration Underlap (a) Overlap(z<) (b) Zerolap (z=) (c) Underlap (z>) Figure Photos of relative position of head and nozzle In case of overlap in z direction as initially adjusted to suppress the leakage, the back pressure falls when the 98Hz sound is added. But the vibration turns into the self-excited vibration even if the sound is stopped. It is interesting that if the nozzle is raised up and reaches the position of underlap, the self-excited vibration stops and again the back pressure jumps up. Under the condition of underlap, the head responses to the 98Hz sound to resonate and stops without any self-excited vibration when the sound is stopped. In one word, the back pressure is controllable by the 98Hz sound. 4 3 2 1 B (Self-excited vibration) Unstable D C Stable No vibration Self-excited vibration x=.mm -.2 -.1..1.2.3.4..6 z [mm] Figure 6 -z characteristic curve 3 2 2 1 1 ir supply pressure:4kpa ir supply pressure:2kpa ir supply pressure:1kpa ir supply pressure: kpa 1 1 2 2 3 3 Figure 7 of S-P Converter In order to investigate the best underlap of z direction, experiment is conducted. The vibration of the head is investigated when disturbance (i.e. touching the head ) is added or not. The supply pressure is set as 4kPa and the sound is not added. The result is shown in figure 6. The solid line is the result when no disturbance is added. The position of the nozzle is adjusted from overlap to zerolap and underlap. The back pressure falls down from the position of zerolap. The Copyright 28 by JFPS, ISBN 4-9317-7-X
fall of pressure is due to the increment of the effective area and not due to vibration. On the other hand, the dashline is the result when disturbance is added at the point. Because at the point the position of nozzle is overlap, the disturbance triggers the self-excited vibration of the head to start immediately and the back pressure to fall down to B point. If the nozzle is raised continuously, from point C the back pressure jumps up again to reach D where z is.3mm (i.e. underlap) and the back pressure is the biggest and the self-excited vibration stops. fter point D, the dash line follows the solid line. From the result, it is clear that the position of the nozzle z must be bigger than.3mm to ensure that the nozzle is in underlap to suppress the self-excited vibration. On the other hand, it is desired that the underlap of z is set to be as smaller as possible so that change of effective area of nozzle and the back pressure is big. Therefore, z should be adjusted to be as near D point as possible. Using the S-P Converter as shown in figure 2 with the interval x between nozzle and head adjusted to.mm, overlap on both side of the head in y direction adjusted to.3mm and overlap in z direction adjusted to.mm, experiments are conducted. The supply pressure is arranged with 4 conditions and under each condition the back pressure is investigated. In the preparation, the back pressure is tuned using the adjustable orifice shown in Figure 2 without any sound. The change of back pressure before and after the sound of 98Hz is added is shown in figure 7. From the results, it is clear that when the supply pressure is set as 4kPa, the back pressure changes from 3kPa when the head does not resonate to 12kPa when the head resonates. Therefore, it is concluded that the maximum change of back pressure is about 2 kpa in the developed S-P Converter. bsolutely speaking, the change of 2kPa is small, but it is big enough to drive a pilot to control an. PILOT VLVE ND EXPERIMENTS The developed pilot is shown in figure 8. In figure 2, the sound is added to the S-P Converter directly in the air with the sound source placed very close to the head. But in the proposed Valve, it is required that the sound is conveyed by the supply tube. That means the head in figure 2 must be inserted inside the supply tube. It is clear that the S-P Converter in figure 2 can not be applied directly to a Valve. This problem is solved by introducing another vibration head. s shown in figure 8(a), the leaf spring stretches to both side of the fixing part with two heads attached at the end to compose two vibration elements. One is called resonance vibration element and the other is called flapped vibration element. Their heads are called resonance head and flapper head. The flapper vibration element is at atmosphere while the resonance vibration element is inserted in the supply tube filled with the sound. The resonance vibration element is adjusted with the vibration direction being along with the sound propagation direction to realize a large resonance vibration amplitude. The resonance vibration of the resonance vibration element is propagated through the leaf spring to the flapper vibration element. The resonance frequencies of the resonance vibration element and flapper vibration element are adjusted to be the same. From figure 8(b), the developed pilot has two parts. The upper part is consisted of flapper vibration element and nozzle, while the lower part is consisted of the resonance vibration element which is inserted into the supply tube with joint. Pilot Flapper head Fixed base Elasticity adhesive Resonance head Fixed base (a) Concept Flapper head Nozzle Body Fixed base Linker Leaf spring Resonance head 23 Flapper Vibration object Leaf spring Resonance Vibration object Main Tube (b) Schematic diagram Figure 8 Pilot Experiments are conducted to investigate the developed pilot using the circuit shown in figure 9. The supply pressure is arranged with 4 conditions and under each condition the back pressure is investigated. Dry-ice Power Cell is used as the power supply. From the results of figure 1, it is clear that when the supply pressure is set as 42kPa, the back pressure has a change of 2 kpa in the developed S-P Converter and is about the same as the results shown in figure 7. By selecting a large area, back pressure change of 2kPa in the pilot is able to drive a main. Copyright 28 by JFPS, ISBN 4-9317-7-X
/D D/ conv. Computer p s Pressure sensor Pilot Tube Figure 9 Pilot experimental circuit 3 2 2 1 1 Gas supply pressure:42kpa Gas supply pressure:2kpa Gas supply pressure:1kpa Gas supply pressure: kpa 1 1 2 2 3 3 Figure 1 change after pilot opens L s [db] 12 6 2 1 1..2.4.6.8 1. Time [s] (a) Response of pilot turning ON pressure change. For convenience, a three port main is developed in this paper instead of a two port main. The schematic of main is shown in figure 12 and cross-sectional view is shown in figure 13. The diaphragm is fixed to the poppet so that the pilot pressure can drive the poppet directly. The spring force of the diaphragm is very small and can be neglected. The forces acts on the main can be described as the force of pilot pressure, spring force and force of supply pressure. When the pilot is OFF, the pilot pressure jumps up to its maximum and the sum of the spring force and the force of pilot pressure becomes bigger than the force of supply pressure. Resultantly, supply pressure port P is closed and port is opened to the air through port R. When the pilot is ON, the pilot pressure falls down to its minimum and the force of supply pressure becomes bigger than the sum of the spring force and the force of pilot pressure. Resultantly, supply pressure port P is opened to port and port R is closed. The main can be controlled by the pilot pressure without any influence of supply pressure. The room above the diaphragm is the pilot room while the room below the diaphragm is open to the air. The stroke of the main poppet is about.mm. When the O ring attached to the main poppet is pushed down to the seat, port is connected to port R. When the O ring is pushed up to the seat, port is connected to port P. L s (db) 12 6 2 1 1..2.4.6.8 1. Time [s] (b) Response of pilot turning OFF Figure 11 Step response of pilot The step response of the pilot is investigated. From figure 11(a), the time lag of the back pressure is about 2ms, which means the interval from the time sound is added to the time when the back pressure rises to % of its maximum value. On the other hand, from figure 11(b), the time lag of the back pressure is 22ms, which means the interval from the time sound is stopped to the time when the back pressure falls to % of its maximum value. Two time lags are almost the same. (a) OFF (b) ON Figure 12 Schematic diagram of the main Spring Diaphragm R Poppet R P R O ring Seat MIN VLVE The pilot pressure is about 2kPa and very small compared with supply pressure. main is developed which can be driven by the 2kPa pilot P P Seat Figure 13 Cross-sectional view of the main Copyright 28 by JFPS, ISBN 4-9317-7-X
SODC VLVE The SODC is shown in figure 14 and is composed of the developed pilot and main. The goal of this study is to construct a pneumatic multi-degree wearable system. In this study, two SODC s are developed. The picture of two SDOC s with resonance frequency of 96Hz and 98Hz are shown in figure 1. Using Dry Ice Power Cell as power supply, wearable s developed in previous study and two SODC s, a novel pneumatic multi-degree wearable system is realized. s shown in figure 16, there is no cord connected to the s. The s used are Tail-Wrist and [2]. Pilot Flapper head Fixed base Resonance head P Tube Figure 14 Valve Pilot 1 Main 1 Valve1(96Hz) R Pilot 2 Main 2 Valve2(98Hz) Main Fig.1 Photo of assembled Valves Dry-ice power cell Supply line Tail-wrist Valve2 (96Hz) Valve1 (98Hz) Fig.16 Wearable system driven by Valves with Dry-ice Power cell Tail-wrist Initial-shape Sound frequency[hz] 1 98 96 94 92 9 2 4 6 8 1 Time [s] Pressurized Pressurized Tail-wrist Initial-shape Fig.17 Photos of two wearable s driven by SODC s In figure 17, the SODC with 96 Hz resonance frequency opens from 4s-6s, while the SODC with 98 Hz resonance frequency opens from 2s-8s. The two SODC s can be controlled by sound simultaneously to drive two s. CONCLUSIONS In this paper, a sound operated directional control (Valve) is proposed which opens and closes in response to the sound of a specific frequency propagated inside the gas supply tube and therefore needs no electric wiring to convey the control signals. By using multi-frequency sound, several s can be controlled simultaneously and resultantly the pneumatic multi-degree wearable system can be constructed compactly. Experimental results verify that the sound operated directional control s are feasible and practical in pneumatic multi-degree-of-freedom wearable power assist system. REFERENCES 1. Yamamoto, K., Ishii, M., Hyodo, K., Yoshimitsu, T. and Matsuo, T. : Development of Power ssisting Suit for ssisting Nurse Labor (Miniaturization of supply system to realize wearable suit), JSME International Journal, Series C, 46-3, pp.923-93 (23). 2. Tsukagoshi, H., Kase, S., Kitagawa,., : Development of active installation band with adaption to the human body, JSME Dynamics & Design Conference 27, pp.289 (27). 3. Kitagawa,., Wu, H., Tsukagoshi, H., Park, S.H., Development of a portable pneumatic power source using phase transition at the triple point, Transactions of the Japan Fluid Power System Society, 36-6, pp.18-164(2). Copyright 28 by JFPS, ISBN 4-9317-7-X