OBSTACLE DETECTION USING RING BEAM SYSTEM

Transcription

1 OBSTACLE DETECTION USING RING BEAM SYSTEM M. Hiaki, K. Takamasu and S. Ozono Depatment of Peision Engineeing, The Univesity of Tokyo Hongo, Bunkyo-ku, Tokyo, Japan Abstat: In this pape, we popose a novel obstale detetion system using Ring Beam System (RBS) fo mobile obots. This system onsists of RBS with a one mio, a spheial mio and a CCD amea. The piniple of this system is same as tiangulation. The advantages ae having no moving pats and deteting all obstales aound the obot simultaneously. Fistly, we alulate a elationship between the position of bight point on pitue fom CCD amea and the distane to obstales. Next, we show developed expeimental devie and esults of obstale detetion. Keywods: Obstale detetion, Tiangulation, Mobile obots 1 INTRODUCTION Thee ae many eseahes about omni-dietional mobile obots, espeially fo indoo use. So, it is neessay fo autonomous mobile obots to detet obstales aound it. The obstale detetion systems ae vaious, fo example, image poessing using CCD amea [1], ultasoni wave system, and so on. A tiangulation using lase slit and CCD amea is used fo obstale detetion beause thee-dimensional shapes of objets an be measued easily [2]. In this eseah, using Ring Beam System (RBS) [3] that an pojet lase slit to all dietion, we develop the novel obstale detetion system that has no moving pats. 2 CALCULATING DISTANCE USING GEOMETRIC MODEL Figue 1 shows the geometi model of ou expeimental devie. The ente of spheial mio whose adius is is egaded as an oigin and oodinates ae deided as the figue. Moeove, it is assumed that the CCD amea and the RBS ae distane l and d away fom the oigin, espetively. Hee, a distane x to the obstales is alulated by following equations: φ = sin 1 α = os 1 l sinθ osθ sinθ 1 [ 2os( θ + φ ) osφ osθ ] l 2 sinθ x = sinφ + ( d osφ) tanα (3) (1) (2) Figue 1. Geometi model of obstale detetion system.

2 Figue 2. Expeimental devie. Figue 3. Example of obtained pitue. Figue 4. Pitue of inside of a box in ase of applying lase slit by RBS Figue 5. Deteting esult of bight line. 3 EXPERIMENT (1) The expeimental devie onsists of a spheial mio, a CCD amea and a RBS with a one mio. Developed expeimental devie is shown in figue 2 and an example of obtained pitue using this obstale detetion system is shown in figue 3. This pitue is obtained while this expeimental system is put on a desk in ou laboatoy.

3 Figue 6. Measuing esult of inside of box. Figue 7. New geometial model with geometial eos. In this expeiment, we measue inside of a box with sides 300mm long as an obstale. Fistly, we obtain two pitues by the CCD amea and a pitue boad in PC: one is a pitue in ase of applying lase slit by RBS (figue 4) and anothe is in ase of no lase beam. Seondly, we alulate diffeenes of these two pitues to detet the bight line on obstales. Figue 5 shows the deteting esult of bight line. Finally, we alulate anglesθ fo eah bight point in figue 5 and alulate the distane x to obstales using equations (1) (3). Figue 6 shows measuing esult of inside of the box. In this figue, solid lines give the position of the eal obstales and small iles give the position of deteted obstales. This esult shows the possibility of deteting obstales using ou system. 4 CONSIDERATION OF GEOMETRICAL ERRORS In the expeiment, a maximum measuing eo is 15.4 mm. We think that fatos of this eo ae eos of ente axis of eah devie and paameti eos, fo example, the length between the CCD amea and the spheial mio. Theefoe, we build a new geometial model with geometial eos in figue 7. Same as figue.2, the ente of spheial mio whose adius is is egaded as an oigin and oodinates ae deided as the figue. Moeove, it is assumed that the CCD amea and the RBS ae distane l and d away fom the oigin, espetively. As geometial eos, we intodue a position eo of CCD amea e, an oientation eo of CCD amea ψ and an oientation eo of RBS ψ. The position eos and the oientation eos ae 3 degees of feedom. Howeve, it seems that the position eos along z-axis ae inluded position l and d. Position eos x and y of RBS an be ignoed beause the slit ay fom RBS extends hoizontally. Hee, we disuss about influene that

4 eo fatos give to esults of measuement, so we use easie 2 DOF model. A elationship between a distane x to the obstales and θ is alulated by following equations: 2 1 l sin( θ ψ ) + e os( θ ψ ) l sin( θ ψ ) + e os( θ ψ ) φ = sin os sin( θ ψ ) 1 (4) α = os 1 [ 2os( θ ψ + φ)osφ os( θ ψ )] sinφ + ( d osφ) tanα x = (6) 1+ sinψ tanα 5 ANALYSIS OF ERRORS We disuss about the influene that eah geometial paamete gives to the esults of measuement. Using equations (4) - (6), diffeentials between distane x and geometial paametes ae as follows: = 2.23, = 1.46, = 14.8, = 8.87, when x = 150. l d e Hee, eah value of diffeential epesents an eo of deteting distane fo a small vaiation of the geometial paamete. We an find out that an influene of position eo of CCD amea e is biggest. About oientation eos, following equations shows diffeentials. = 2270, = 219, when x = 150. ψ ψ These diffeentials annot be ompaed with above position eos shown by equation (7), beause a unit of equation (7) is diffeent fom a unit of equation (8). Howeve, we an ealize that an influene of oientation eo of CCD amea ψ is bigge than an influene of oientation eo of RBS ψ. 6 PARAMETER IDENTIFICATION AND EXPERIMENT (2) We identify the paamete e that is the position eo of CCD amea. In fat, it is neessay to onside an eo in x-axis e and in y-axis x e fo position eos of CCD amea. Howeve, the y measuement esult of inside of box in figue 5 is almost symmety with espet to y-axis. Theefoe, we identified only the paamete e. Figue 8 shows a esult of measuing expeiment afte the y identifiation of the paamete. Using modified geometial model, we aied out an expeiment of deteting obstales. We seleted passageway in font of ou laboatoy fo the measuing envionment, beause poposed sensing system was loaded on mobile obot fo indoo use. The measuing envionment is shown by figue 9. In this figue, the lase slit fom RBS an be seen on a wall and a doo. (5) (7) (8) y mm x mm Figue 8. Measuing esult of inside of box afte paamete identifiation.

5 1000 y mm Figue 9. Measued Envionment x mm Figue 10. Result of deteting obstales Figue 10 shows a esult of an expeiment of deteting obstales. The developed measuing system is put at a position (0,0). The fou deteted points aound it ae esults of deteting the fou poles inluded in the measuing system. The points on the ight side of the oigin ae esults of deteting a box that is fixed in ode to put a ompute. This esult of expeiment shows the possibility of deteting obstales unde the eal envionment using ou developed system. 7 CONCLUSIONS We poposed a novel obstale detetion system using RBS (Ring Beam System), a spheial mio and CCD amea fo indoo use mobile obots. We showed the alulating method of distane to obstales and aied out the expeiment of deteting obstales. The esult of expeiment shows the possibility of deteting obstales using ou system, howeve, thee ae some eos fom paameti eos o geometial eos. Theefoe, we build anothe geometial model inlude geometial eos and identified paametes based on the esult of expeiment. Afte the identifiation of unknown paametes, we aied out the othe expeiment of deteting obstales and the esult of expeiment shows the possibility of deteting obstales aound this system simultaneously unde the eal envionment. REFERENCES [1] Y. Yagi, Real-time Omnidietional Image Sensos, Jounal of the Robotis Soiety of Japan 13 (3) (1995) (Japanese). [2] S. Kato and S. Tsugawa, Obstale Region Detetion Senso by Extended Slit-Ray Pojetion: Detetion Tehnique and Ahitetue fo a High-Speed Poessing Realization, Poeedings of the 5th Symposium on Robot Sensos (1996) 109 (Japanese). [3] Y. Kawaguhi, J. Mizuno and K. Ito, Piniple of Ring Beam System (R.B.S.) and Its Appliations, O plus E 210 (1997) (Japanese). AUTHORS: Reseah Assoiate D. Masahiko HIRAKI, Assoiate Pof. D. Kiyoshi TAKAMASU, Pof. D. Shigeo OZONO, Depatment of Peision Engineeing, Shool of Engineeing, The Univesity of Tokyo, Hongo, Bunkyo-ku, Tokyo, Japan, Phone Int , Fax Int , hiaki@ozono.pe.u-tokyo.a.jp