Research on a Sea Snake Robot

Transcription

1 ICCA005 June -5, KINTEX, Gyeonggi-Do, Korea Research on a ea nake Robot Hiroshi hiozaki*, Etsuro himizu* and Masanori Ito * *Tokyo Univ. of Marine ci. & Tech. (Te : ; E-mai: hshioza@e.kaiyodai.ac.jp) Abstract: ince a snake achieves various movements just by a sender body, the mechanism of it is very amazing Many researches have been focusing on a snake ike robot and have done for it on the ground. However the meander motion of the snake not ony can be done by ground creatures, but aso can be done by a water creature such as a sea snake or an ee. Therefore, the purpose of our research is to deveop an autonomous underwater robot ike the sea snake. As an approach to this goa, we deveop an experimenta sea snake-ike-robot for examining basic characteristics, incuding propusion, a turning and other performance. Our deveoped robot is composed of the head and 4 bodies. Each body equips one servomotor, which is operated with puse signa. In the head unit, - chip-microcomputer, which generates the servomotor contro signa for reaizing a snake motion and the battery, is equipped. Our robot is covered with a rubber fim for the waterproof. Using our deveoped robot, characteristics of the snake-ike-robot moved in water are examined.. Keywords: snake-ike-robot, biomimetics, experimenta verification, robotic ocomotion. INTRODUCTION A machine made by human hasn t yet achieve high functiona movements, which can be easiy done by a iving creature, unti now. Therefore, understanding the principe of the movement of a iving creature and using it technoogicay are very usefu for deveoping a new kind robot. In this paper, we focus on a iving creature with sender body ike a snake. A snake can generate an extraordinary variety of motions. For exampe, changing the sender body shape to adjust to rugged surface when it creep on the ground, changing the sender body shape ike a bridge when it gets over the gap, changing the body shape to wrap around a object when it try to grip the object, and so on. Namey, since the snake achieves various movements just by a sender body, the mechanism of the snake is very amazing. However, most researches about a snake ike robot have focused on the movement of the ground [],[],[3]. But, the meander motion of the snake not ony can be done by the ground creature, but aso can be done by a water creature such as a sea snake or an ee. ince the direction of the wave changes rapidy when the wave is sent to the sender body and it advances, go ahead and go astern are easiy switched. In other words, the dynamic positioning or the position keeping is very easy work for these creatures. If we can construct the snake ike robot, it is possibe to create an autonomous underwater robot, which can act in narrow waters. A detaied position contro is needed if the snake ike robot is used in such a pace. Athough the sea snake-ike-robot has possibiity to become an exceent underwater robot, it wi be a compicated research compared with the research about the ground snake-ike-robot. Therefore, the purpose of our research is to deveop an autonomous underwater robot ike the sea snake. As an approach to this goa, we deveop an experimenta sea snake-ike-robot for examining basic characteristics, incuding propusion, a turning and other performance. Our deveoped robot is composed of the head and 4 bodies. Each body equips one servomotor, which is operated with puse signa. In the head unit, -chipmicrocomputer which generates the servomotor contro signa for a snake motion and the battery is equipped. By those four servomotors and -chip-microcomputer, our deveoped robot can simuate many moving patterns. Our robot is covered with a rubber fim for the waterproof. Using our deveoped robot, characteristics of the snake-ike-robot moved in water are examined.. PRINCIPLE OF PROPULION Fig. Anaysis of swim by sender body theory In the propusion with sender body ike the sea snake, there is an anaysis method appying "sender body theory" beow [6][7]. Fig. shows the coordinate system where the starting point is fixed to the head of the sea snake of ength. The sea snake is osciating in the direction of y as a symmetry pane in xz-pane and the moving constant speed V. When y direction dispacement in arbitrary section (x) aong the body axis x is defined as h(x,t), y direction veocity of the surrounding fuid caused by the motion is, as the sum of a non-stationary eement and the convection eement, as foows: v( x, t) = h + V h x () If the virtua mass per unit ength in the section is defined as m a (x), y direction momentum and the kinetic energy in the section become m a vdx and (/)m a v dx respectivey. Therefore, since it is equa to the substance change in y direction momentum, the force necessary for the motion of this section is shown as foows: F = + V x m () ( ) vdx a If F is mutipied by the dispacement veocity h in the section, and it is integrated from 0 to, the power P(t) that the sea snake gives to a surrounding fuid is as foows with Eq. () :

2 ICCA005 h h P = F = + V mavdx 0 0 x h v = + V mav dx mavdx 0 x 0 h h = mavdx mav dx + V mav 0 t 0 t 0 By integrating the above equation at time, the mean vaue of the necessary power is as foows: T P = P( t) dt (4) T 0 If this is executed, it is considered that the mean vaue the first term of the ast equation in Eq.(3) obviousy becomes 0. In addition, thinking about the distribution of the section in the direction of the axis of the sea snake that Figure shows, it can be considered as foows: ma (0) = 0 (5) ma ( ) 0 Therefore, the ast paragraph remains ony the vaue in, and becomes as foows, too: h P = V ma v (6) Because the power of the above equation divides into the kinetic energy invaidy discharged in the sipstream and the effective power th at the sea snake is made to advance, P = TV + { m a V v } x = (7) As a resut, the average thrust and the propusion efficiency of the sea snake are cacuated respectivey as foows: h h T = ma V (8) x v η = = (9) v( h ) Next, as a motion of the body axis, it thinks about the progressive wave motion as foows: (0) h = f ( x) g( t x / c) Where f(x) is the ampitude distribution aong the body axis of the progressive wave, and c is the sound wave veocity of the wave. If Eq.(0) is substituted for Eqs.(8),(9), V T = ma f g V f g () c (3) June -5, KINTEX, Gyeonggi-Do, Korea If f ( ) = 0 is substituted for expression () and (), as foows: V T = m a f g. (3) c V η = +. (4) c In this case, A and B as a function of c are shown in Fig.. Fig. Thrust and Efficiency as a function of V/c 3. DEVELOPMENT OF EA NAKE ROBOT 3. Mode of sea snake robot Mode of snake robot is structured by the seria ink system, and each ink connects with active joints. This corresponds to the muscuoskeeta system that the body of snake consists of the spine bone and the rivary musce group that accompanies it. Thinking about the two-dimensiona motion on the pane as the most basic one, the winding ange for the meander motion around a vertica axis from the siding surface. To add a friction characteristic necessary for the propusion of snake robot, it is equipped with the passive whee that rotates freey in the direction of roing as shown in Fig.3. V V = f g V f g η + / f g c c () As a resut of the above equations, it shoud be V/c< that the sea snake promotes efficienty. That is, the wave veocity c is aways arger than the forward veocity V, and the incination of the ampitude of the osciation of the body axis in the point of the tai ony has to become f ( ) = 0. Fig.3 Mode of snake robot on and[] On the other hand, if we consider the mode of sea snake, it ony has to connect the joint that basicay does the winding movement as we as the mode of the snake on and with the seria. However, the sea snake is moved in the fuid by pushing the fuid in the vertica direction to the body axis, the

3 ICCA005 mode ike a ribbon of which surface area is sma in the direction of the body axis and arge in the vertica direction to the body axis is considered as shown by Figure 4. However it is impossibe to do the fat on the structure of unit The mode by whom the resistance in the vertica direction is increased to the body axis is regarded by attaching the fin in the unit. Fig.4 Mode of sea snake robot[8] 3. tructure of sea snake robot Figs. 5,6 shows the structure of the robot. This robot divides into the head equipping with the microcomputer and the battery and the body parts. The body parts are the same structura modues equipping with the servomotor and are connected with the vertica joints. To operate in water, the watertight structure has been achieved by covering the main body with the fim made of a rubber. In order to stabiize posture, the fin is attached of the head part. The fin to increase the resistance is attached to the each body in the vertica direction of to increase the resistance. Moreover, this robot is aso possibe the meander movement on the ground by attaching of the passive whee. Tabe. shows the specification of the sea snake robot. Fin June -5, KINTEX, Gyeonggi-Do, Korea Tabe. The specification of sea snake robot Mode Landscape Under-Water Length 440mm 473mm Weight 430g 790g Joint 4 Actuator Torque 0.4Nm(4.kgfcm) peed 0.9sec/60degrees CPU H8/3048F Battery Lithium-Poymer Battery 7.4V/000mAh 3.3 Waterproof The sea snake robot sends the wave to the body and goes ahead, and thrust is generated ony with the meander motion of the body. The waterproof sea is necessary for the rotation part to have to put out the rod that rotates infinitey from the hu outside in the ship etc. and to rotate the screw. However, such a sea mechanism is unnecessary for the swimming mechanism that can be ony generated by the meander motion as the sea snake robot. Therefore, it is enough to sea up the entire body. However, in order to generate the wave by using the entire body for the sea snake robot, the body is aways transformed. Therefore, it is necessary to cover the joint part with a fexibe materia that doesn't disturb the movement of the actuator. Then, the head was encosed in the waterproof container that was abe to remove the id, and the body in the joint part was covered with the bathing suit made of rubber in this sea snake robot. And, both are firmy stuck together with the waterproof tape and have been seaed up. The rubber was the atex rubber of the iquid used by a specia make-up etc. tabiizer Fig.6 Detais of each part Fig.5 tructure of sea snake robot 3.4 ystem configuration of robot The servomotor used as the actuator can contro the ange in every 0ms with giving the puse signa of the width of 0.5ms-.4ms. This robot used the singe-chip microcomputer named H8 with the timer function to generate this puse signa accuratey. H8 can do the program deveopment by using PC. C anguage was used for the program. Because the pin number, 4, 6, and 8 of the channes of H8 are the output ports of the PWM signa using a buit-in timer, H8 and the servomotor are directy connected of the contro ine of four servomotors. ince the PWM signa that contros the servomotor is generated by a programs buit into CPU, an externa circuit is unnecessary. Moreover, the power suppy system divides one ithium Poymer battery system of 7.4V- 000mAh into two systems of 6V in CPU and 5V in servomotors in. The power suppy stabiized respectivey by

4 ICCA005 using two three termina reguators for the distribution of the power suppy is suppied. June -5, KINTEX, Gyeonggi-Do, Korea 4. EXPERIMENT 4. Propusive performance experiment 4.. Experiment of frequency - veocity ince the puse width when the servomotor was driven was output by constant transfer rate, the frequency was changed by changing the data density for one waveength output to the servomotor. And, the reation between the frequency and the moving veocity was examined. As experimenta conditions: 3.5 Contro method The meander movement of the snake has been achieved by giving the osciation of the sine wave to each joint, and transmitting it backward appying a constant phase difference. Therefore, the contro instruction ike Eqs. (5)-(8) is given to each servo motor in this robot and the meander movement is generated Phase difference: θ =30deg 3 4 = A sin(πf = A sin(πf θ = A sin(πf θ 3 = A sin(πf 3θ 4 (5) (6) (7) (8) where A is ampitude A max =90degf is frequency θ is phase difference B is bias ange of deviation. The propusive veocity can be controed by changing each parameter of ampitude A, frequency f, and the phase differenceθ. Moreover, the traveing direction is controed with bias B. The traveing direction is changed by moving a center vaue of the osciation by putting the bias on the sine wave instruction that generates the meander movement as shown in Figure 6. When the bias is 0, the winding standard of the entire body is straight. However, the winding standard becomes by the bias being added ike the circuar arc, and the direction of propusion changes into the direction where added the bias ony at time to have added the bias. In a word, because it is possibe that the direction contro of the meander movement that seems to be difficut seemingy is divided into the sine wave instruction as the propeer and the bias vaue as the vertica rudder, and think about it, it is thought that the anaysis of turning characteristics and the contro of the turn ange are comparativey easy. Ampitude: A =30deg, A =35deg, A 3 =40deg, A 4 =45deg The time took to advance in the distance of.65 meters was m easured. Tabe. Experiment data of frequency veocity Frequency f(hz) No. No. No.3 Average Veocity V(cm/s) V f Fig.8 Graph of frequency veocity Fig.8 shows the resut of experiment. From the experimenta resut, we found that the frequency and the veocity are proportiona under the frequency being equa to Hz. However, there is a sudden dip when the frequency exceeds Hz. The re ason is that the robot went under the water. Afterwards, ther e is proportiona increase again and steady when the freq uency exceeds.4hz. The reason is that the servo speed doesn't catch up with change of the ange. Moreover, the frequency is controed by changing the data density of the sine wave instruction. Therefore, when the frequency is increased, it is necessary to generate the sine wave with a itte number of data. Consequenty, the error margin with a true sine wave grows, and the veocity doesn't increase either. Fig.7 Contro of traveing direction[] 4.. Experiment of phase difference - veocity As experimenta conditions: Frequency: f=0.93hz Ampitude: A =30deg, A =35deg, A 3 =40deg, A 4 =45deg The time took to advance in the distance of.65 meters was measured.

5 ICCA005 Tabe.3 experimenta data of phase difference - veocity Phase difference No. No. No.3 Average Veocity (cm/s) θ(deg) V θ Fig.9 Graph of phase difference - veocity From the experiment resut, it was found that the maximum speed coud be obtained when the phase difference was amost 45deg. Because the entire body became a phase difference ike one wing when it was too sma, it became inefficient. Moreover, the wave speed sowed more than the forward speed of the robot when the phase difference was too great, and it didn't advance. V(cm /s )/D (cm ) June -5, KINTEX, Gyeonggi-Do, Korea Bias deg Fig.0 The graph of turn-performance From the experiment resut, it was found that the turn diameter was in inverse proportion to the bias and had surey become sma. However, it had been understood that the turn speed didn't change too much even if the vaue of the bias changes. As a resut, it is found that the bias contributes ony to the contro of the traveing direction. Figure shows the appearance of the turn experiment.. t= t= t=3 4. Turn performance experiment As experiment conditions: Frequency: f = 0.93Hz Phase difference:θ = 45deg Ampitude: A = 30deg, A = 35deg, A 3 40deg, A 4 = 45deg Tabe.4 experiment data of turn performance t=4 t=5 t=6 Bias (deg) Turn-time(s)/Turn-diameter (cm) No. No. No.3 Average Turn-veocity (cm/s) t=7 t=8 t=9 Fig. Appearance of turn experiment (bias = 0deg 5 CONCLUION In this research, the snake robot that has been studied as a ground robot was appied as an underwater robot. As the first approach to this purpose, a propusive principe of sea snake was studied, and the experimenta sea snake robot was deveoped on the basis of it. And, a basic characteristic of its meander swimming was verified, and foowing resuts were obtained. () The frequency of each joint motion and the veocity were amost proportiona. () Maximum speed was obtained when the phase

6 ICCA005 difference was 45deg. (3) Consequenty, it was found that the sea snake robot became the maximum speed when the frequency was.4hz and phase difference was 45deg. (4) The traveing direction was changed by moving the center vaue of the osciation by adding the bias to the sine wave instruction that generated the meander movement. As a resut of the turning experiment, it was found that the turning radius coud be controed. Moreover, it had been understood that the turn speed was not infuenced too much by the bias. This showed no interference mutuay by a basic sine wave and the bias From these resuts, a basic characteristic necessary to use the snake ike robot in water coud be examined. Next, sensors are mounted into the robot, and the robot that moves autonomous is made. The gyro sensor is mounted to put the camera on the head of the robot and posture is controed. Moreover, the sea snake robot that can move three dimensions is made from the combination of joints that rotate by mutuay perpendicuar panes. June -5, KINTEX, Gyeonggi-Do, Korea REFERENCE [] F. Matsuno, nake-ike Robot uper-bioogica ro bots and imitative bioogica robots, The Robotics ociety of Japan, Vo. 0, No. 3, pp. 6-64, 00. [] G. Endo, K Togawa and Hirose, tudy on sef-c ontained and terrain adaptive active cord mechanis m, The Robotics ociety of Japan, Vo.8, No.3, pp , 000. [3]. Hirose, E. F. Fukushima and. Tsukagoshi, An Optima teering Contro for the Articuated Body Mobie Robot, The Robotics ociety of Japan, Vo. No.5, pp , 994. [4] T. Takayama and Hirose tudy on 3D active co rd mechanism with heica rotationa motion, The Robotics ociety of Japan, Vo., No.5, pp , 004. [5] K.A. McIsaac and J.P. Ostrowski Experimenta of Verification of Open-oop Contro for an Underwater Ee-ike Robot The Internationa Journa of Robotics Research,Vo., No.0-, pp , 00. [6] Lighthi, J., J. Fuid Mech., 9(960), 305~37. [7],, (987-7),, 758. [8] K. Hirata, Deveopment of Experimenta Fish Robot, ixth Internationa ymposium On Marine Engineering, p.7-74, Oct. 000.