19 th INTERNATIONAL CONGRESS ON ACOUSTICS MADRID, 2-7 SEPTEMBER 2007 A NON-CONTACT SYSTEM FOR TRANSPORTING OBJECTS USING ULTRASONIC LEVITATION

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1 19 th INTERNATIONAL CONGRESS ON ACOUSTICS MADRID, -7 SEPTEMBER 007 A NON-CONTACT SYSTEM FOR TRANSPORTING OBJECTS USING ULTRASONIC LEVITATION PACS: 3.5.Uv Gudr, Tdeusz 1 ; Perkowski, Dniel ; Opielinski, Krzysztof J. 3 1,,3 Institute of Telecommunictions, Teleinformtics nd Acoustics, Wroclw University of Technology, Wybrzeze Wyspinskiego 7, Wroclw, Polnd; 1 tdeusz.gudr@pwr.wroc.pl; 3 krzysztof.opielinski@pwr.wroc.pl ABSTRACT The pper presents system of non-contct verticl trnsport using sonotrode focusing ultrsonic energy in the ir nd system of horizontl trnsport using levittion obtined thnks to the vibrtions of rectngulr plte fixed on one end nd vibrting in the stripe mode. Clcultion results for plte vibrtions using the SYSNOISE softwre were presented nd the plte sizes were optimized. Wht ws obtined s the result of the simultions crried out ws distribution of vibrtions close to the pure striped mode. The results obtined by mens of simultion were then experimentlly confirmed by mens of Chldni's figures nd by mesuring vibrtions using POLYTEC lser vibrometer. The conducted experiments bound up with the trnsport of objects in the shpe of pltes mde of different mterils proved it ws possible to control the movement of the levitting object bove the plte surfce using terrestril grvittion force, using strem of ir directed upon the levitting object, by mens of switching over the frequency of plte vibrtions nd by using n coustic reflector situted t certin ngle towrds the trnsported object surfce. The stbility of levittion trnsport depends on the rtio of the object surfce to the vibrting plte surfce. INTRODUCTION Ultrsonic levittion cn be used both for verticl nd horizontl non-contct trnsport of objects. There re two kinds of levittion: coustic levittion in stnding wve nodes [1] nd ner field coustic levittion (NFAL) []. Ultrsonic levittion in stnding wve nodes cn be observed both in liquid medi nd in gs medi. Ultrsonic levittion in the stnding wve field nd the ner field levittion hve their source in rdition pressure counterblncing grvittion. In spite of the common source ech of the mentioned kinds of levittion hs slightly different nture. ULTRASONIC LEVITATION IN STANDING WAVE NODES (NON-CONTACT VERTICAL TRANSPORT) To trnsport objects verticlly it is possible to use n xilly symmetricl plte excited to produce vibrtions in its xis of symmetry [3,]. The trnsfer of n object is ffected in leps between the nodes of the stnding wve pressure. This kind of trnsport requires flt reflector plced prllel to the surfce of the ultrsonic wve source. Becuse of the often insufficient vlue of the sound intensity necessry for trnsferring objects of hevier mss it is dvntgeous to use sonotrode with profile tht enbles focusing ultrsonic energy. Fig.1 shows the pressure distribution nd the distribution of the rdition force for the observtion of levittion in the stnding wve field.

2 Figure 1.-Distribution of pressure nd distribution of rdition force for ultrsonic levittion in stnding wve field In the stnding wve pressure nodes between the source nd the reflector objects with sizes smller thn the wvelength cn levitte. The distnce between the trnsducer generting the ultrsonic wve nd the reflector equls the totl multiple of the hlf-wvelength. Under the conditions of micro-grvittion levittion occurs precisely t points corresponding to coustic pressure nodes. Under the conditions of the Erth levitting objects find themselves slightly below the node where their position is stbilized by force whose source is believed to come from the symmetricl prt of rdition pressure [5]. One of the first equtions for the vlue of rdition pressure ffecting sphericl objects plced in gs in the stnding wve field ws formulted by R. Whymrk [1]: F 5 = πr ( k R) ρ v o ( Eq. 1) 6 where: R rdius of sphere, k wve number for the gs, ρ density of the gs, v o coustic prticle velocity. Fig. shows the results of n experiment confirming the possibility for trnsporting verticlly two sphericl objects with different msses. Chnging the vlue of the sound intensity generted by the rditing focusing plte wht cn be obtined is the plcement of objects with different msses t definite height. ) b) c) d) Figure.-Demonstrition of ultrsonic levittion used for verticl trnsport of two objects with different msses: ) two fomed polystyrene spheres in first stnding wve node b) two spheres trnsferred to second stnding wve node, c) spheres with different msses trnsferred to second nd third nodes, d) spheres with different msses plced in first nd third nodes

3 NEAR FIELD LEVITATION (NON-CONTACT HORIZONTAL TRANSPORT) To relize the non-contct horizontl object trnsport using levittion it is most dvntgeous to use rectngulr plte vibrting in the striped mode. A few solutions cn be distinguished in this cse, nd their common feture is using the ner field ultrsonic levittion [6,7]. In levittion using the stnding wve the use of reflector is necessry. In the ner field levittion there is no need for reflector the ultrsonic wve is reflected directly from the levitting object. The first elbortions on the NFAL cme in the 1990s. Hshimoto Y., Koine Y., Ueh S. in work [7] inform us bout noticing phenomenon llowing flt objects of considerble msses (even few kilos) to levitte over vibrting surfce of n ultrsonic wve source to the height of few dozens of micrometers. In spite of very short distnce between the vibrting surfce nd the levitting object it is possible to levitte objects much lrger nd much hevier from those tht could levitte in the stnding wve field. Assuming tht the ultrsonic wve source is rigid piston moving hrmoniously t the velocity v = v o cos(ω t) nd tht the bottom surfce of the levitting object cn be treted s rigid surfce, the force counterblncing the grvittion is the rdition pressure. Its vlue is expressed by n eqution formulted by Chu B. nd Apfel R. [8]: 1+ γ sin Π = 1+ k ( k h) h ρ ρ c ρ v + o ( Eq. ) where: γ specific het rtio, k wve number for wve propgted in the gs, h levittion height, ρ density of the gs, c sound velocity for the gs, v o vibrtion velocity mplitude. If h is smll enough to meet the condition k h << 1, then the eqution () cn be written s follows: 1+ γ Π = ρ c h o ( Eq. 3) where o - vibrtion mplitude. The correctness of this eqution ws confirmed empiriclly in experiments run by Hshimoto, Koike, Ueh nd others [,9]. In order to produce ultrsonic levittion of the ner filed it is possible to use sound source whose vibrtions re different from the vibrtions of the rigid piston, e.g. source in the shpe of rectngulr plte producing flexul vibrtions in the striped mode, fixed nd excited to vibrte t one end by mens of n ultrsonic trnsducer. An importnt fctor determining the NFAL using flexurl vibrtions is the size of the levitting object. It ws proved tht the levittion is stble if the object levitted hs size lrger thn 1.5 of the wvelength propgting in the plte []. Clculting the vlue of rdition pressure in the function of the distnce from the plte vibrting flexurl is more complicted thn in the cse of the vibrtions of the fixed rigid piston. Assuming tht the condition k h << 1 is fulfilled, the rdition pressure cn be expressed s follows [6]: 3

4 ρ c Π = ξ o h 1 sin α ( Eq. ) where: ξ o vibrtion mplitude of the plte, α = rccos(k/k ), k wve number for wve propgted in the vibrting plte. The clculted vlue of the rdition pressure is slightly higher thn the pressure occurring in relity, which cuses the objects to levitte slightly lower thn wht would result from compring the grvittion ffecting them. For the flexurl vibrting plte there is lso possibility for different pproch to clculting the rdition pressure in which the plte vibrtions re nlyzed s sum of flt wves. Such solution cn be found in work [9]. Fig.3 shows the bsic element of the reserch setup for exmining the non-contct trnsport of objects using the ner field ultrsonic levittion. Figure 3.-Bsic element of reserch setup for non-contct trnsport of mterils The most importnt element of the setup is n ppropritely designed vibrting plte fixed t one end to the vibrtion exciter tht is sndwich-type ultrsonic trnsducer with trnsformer of vibrtions velocity. The frequency of exciting the plte to vibrte equls the frequency of the striped mode of the plte vibrtions. Fig. shows the results of clcultions of flexurl vibrtions of rectngulr luminium plte by mens of the SYSNOISE softwre nd the results of mesurements of vibrtions distribution obtined by lser vibrometry nd by the Chldni figures observtion method. ) b) c) Figure.-Distribution of flexurl vibrtions of plte: ) obtined by simulting in SYSNOISE, b) obtined experimentlly mesured with lser vibrometer Polytec PSV 00, c) obtined experimentlly by mens of Chldni figures method

5 The levitting object in the form of pltes mnufctured of different mterils ws plced on the surfce of the luminum plte vibrting t f = khz. Fig.5 shows luminum plte levitting bove the vibrting plte surfce t the height of c 70 micrometers. ) b) Figure 5.-View of luminum plte levitting over surfce of plte vibrting flexurl: ) generl view, b) mesurement of levittion height The effect of pltes trnsport cn be obtined in different wys: by slight inclining of the plte vibrting flexurl nd using the grvittion force, involving strem of ir directed upon the levitting plte, by retuning the vibrtion frequency of the plte vibrting flexurl, nd by mens of reflector situted t certin ngle towrds the plte vibrting flexurl nd the trnsported object surfce. The ltter method is prticulrly interesting becuse of possibility for the esy controlling of the trnsport velocity of the object relized by chnging the reflector s ngle towrds the plte surfce. Fig.6 shows the distribution of forces with different ngles of the reflector s position towrds the vibrting plte. Chnging the vlue of the lph ngle, trnsport of the object in ny direction nd t ny velocity cn be obtined or the levitting object cn be held up (with the reflector plced prllel to the vibrting plte surfce). ) b) Figure 6.-Distribution of forces with different ngles of reflector s plcement towrds plte: ) trnsport direction to the right, b) trnsport direction to the left CONCLUSIONS The conducted experiments bound up with the lep verticl trnsfer of fomed polystyrene spheres (levittion in the stnding wve field) nd with the horizontl (continuous) trnsfer of pltes mde of different mterils (ner field levittion) point to the potentil possibilities of obtining the trnsport of different objects t desired height nd in the desired direction. The stbility of verticl trnsport depends on the precision of regulting the intensity of sound generted by circulr plte or by focusing sonotrode, wheres the stbility of the horizontl 5

6 trnsport depends of the rtio of the trnsported object s surfce to the vibrting plte s surfce. The result of the object s trnsfer with different velocities cn be obtined by using system of reflectors with regulted ngle of inclintion towrds the plte vibrting flexurl. The ner field levittion llows us to trnsport objects with sizes nd msses much lrger thn in the cse of using the stnding wve levittion. References: [1] R. R. Whymrk: Acoustic field positioning for continerless processing. Ultrsonics (November 1975) 5-61 [] Y. Hshimoto, Y. Koike, S. Ueh: Ner-field coustic levittion of plnr specimens using flexurl vibrtions. Proc. of 1995 World Congress on Ultrsonics, Berlin (1995) [3] T. Otsuk, K. Higuchi, K. Sey: Ultrsonic Levittion by Stepped Circulr Vibrting Plte. Proc. of 10 th Symposium on Ultrsonic, Tokyo, 1989, Jp. Journl of Applied Physics 9, supl. 9-1 (1990) [] E. Mtsuo, Y. Koike, K. Nkmur, S. Ueh, Y. Hshimoto: Holding chrcteristics of plnr objects suspended by ner field coustic levittion. Ultrsonics 38 (000) [5] V. Vndele, P. Lmbert, A. Delchmbre: Noncontct hndling in microssembly. Acoustic Levittion, Precision Engineering 9 (005) [6] Y. Koike, S. Ueh, Y. Hshimoto: A theoreticl study of ner-field coustic levittion of plnr objects. Proc. of 1995 World Congress on Ultrsonics, Berlin (1995) [7] Y. Hshimoto, Y. Koike, S. Ueh: Ner-field coustic levittion of plnr specimens using flexurl vibrtions. JASA 100, No. (1996) [8] B. Chu, R. E. Apfel: Acoustic rdition pressure produced by bem of sound. Journl of the Acousticl Society of Americ 7, No.6 (198) 1673 [9] S. Ueh, Y. Hshimoto, Y. Koike: Noncontct trnsporttion using ner field coustic levittion. Ultrsonics 38 (000) 6-3 6