Yohei Ota, Shin-Ichiro Nishida, Masashi Miura , Kazunori Sakurama

(4-101, Koyama-Cho South, Tottori 680-8552, Japan)

A study on path planning method for exploration robot taking account of communication transmissibility

Yohei Ota, Shin-Ichiro Nishida, Masashi Miura , Kazunori Sakurama

(4-101, Koyama-Cho South, Tottori 680-8552, Japan)

Abstract:Rovers, such as MER and MSL, are sent to Mars and the geology search for the surface is performed by JPL/NASA. MER and MSL are large-sized Rovers and have the communication system which can perform direct communication with ground stations on the earth. Rover needs to consist of Mars sample return missions currently assumed by this research very lightweight. In this case, the direct communication with the earth of the small rover is difficult. Therefore, communication of rover cannot but serve as a communication system through a lander. Moreover, since it is the opportunity of precious sample extraction, it is necessary to extract the topsoil of various places, and the sample of rock efficiently. Then, it is inquiring about the exploration system using two or more lightweight rovers. This study is about a method of a path planning for a robot(rover)exploration to somehow the robot can get to the target place, facing fewer problems and also about a way of transmission for do not have a loss of communication due to obstacles. We assume a robot has a transmission device and ensure the communication transmissibility by putting it in the prescribed place on the path. In the path planning, candidate paths including the transmission device position by RRT are generated and path optimization is carried out by evaluation function. In the simulation, the path taking account of communication transmissibility is planned with using transmission device. The proposed path planning method is confirmed by simulation.

Key words:means of communication;path planning; robotic exploration

The exploration using the robot(rover)is very effective for detailed research in planetary surface. This method has been studied due to several issues, like the binding and damaging the wheel of the robot due to the harsh relief and the slippage of the wheels. And possibly the rover avoids some obstacles because it has no way to pass over, and when it reaches that point, it is possible that the loss of signal occurs. So it was proposed the method of path planning, which uses a transmission device to transmit radio waves.

1Preconditions

Fig.1 shows block diagram of rover remote control system. For planetary exploration there are some pre-established conditions that are stated below.

(1)The main target for exploring is the planet Mars;

(2)Exact Digital Elevation Model(DEM)can be obtained in the terrain of Mars surface;

(3)One rover is used. It runs from the lander to the target position(exploration area)avoiding areas of over 20(°)of inclination and the upper limit of the steering angle is 30 (°);

(4)Communication transmissibility has been obtained between the two communication devices of the rover, lander and transmission device in the case there is no obstacle on a straight line connecting between the two communication devices;

(5)Transmission device relays radio waves between two communication devices. A rover has only one transmission device and put it in the prescribed place on the path.

Fig.1　Block diagram of rover remote control system

2Path planning algorithm

To generate a path to the target position: exploration area from the initial position: the position of the lander landed on Mars in the path planning. In this study, a path P is represented by column of coordinates. And a path is treated as a matrix of nodesnj=[xjyjzj]Tasthefollowingequation(1).Here, c=[xcyczc]Trepresents the transmission device position in the pathP.

P=[n1…njnj+1…nm│c](2≤m)

(1)

GiventhebodycoordinatesasshowninFig.2betweentwonodesnjandnj+1inthepathP.Wedefinethetiltangle,steeringangle,pathlengthbetweentwonodesnjandnj+1asshowninFig.2.

Fig.2　Body axis between njand nj+1

Theprocessofpathplanningisshownbelow.

(1)TogeneratecandidatepathsincludingthetransmissiondevicepositionbyRRT(Rapidlyexploringrandomtree)method.Fig.3showsallpossiblepathsofthepathgenerator.

Fig.3　Process of path generation

(2)TosetassessmentsisnecessarytotakeintocommunicationfourfunctionsEqs.(2)～(5).Equation(2), t(P)isevaluationfunctionabouttiltangle.Equation(3), y(P)isevaluationfunctionaboutsteeringangle.Equation(4), l(P)isevaluationfunctionaboutpathlength.Equation(5), c(P)isevaluationfunctionaboutdistancebetweentheinitialpositionandthetransmissiondeviceposition,andbetweenthetransmissiondevicepositionandthetargetposition.

(2)

(3)

(4)

(5)

(3)Toselectoneofthecandidatepathsminimizingsumoftheevaluationfunctionasrover’spath.Thesumoftheevaluationfunctionistheequation(6)asfollowing.Thisisthesumwhichcarriedoutweighting(degreeofimportance)ofeachequation(2)～(5).

f(P)=ntt(P)+nyy(P)+nll(P)+ncc(P)

(6)

3Results

Fig.4showstheresultsofpathplanningsimulationusingMatlabbasedonthealgorithmmentionedbefore.Itisinasituationwheretherovercan’tensureoutlookbetweentheinitialpositionandthetargetpositionbythereliefoftheterraininthemiddle.Theareaof20 (°)ofinclinationisshowninFig.4bylightblue.TwopathsP1andP2areresultsofpathplanningshowninFig.4byblueandredline.ThepathP1givenweightonntintheequation(6)showninFig.4byblue,thepathP2givenweightonncintheequation(6)

showninFig.4by

red.Fig.4showsbothpathsP1,P2ensureoutlookbetweentheinitialpositionandthetransmissiondevicepositionandbetweenthetransmissiondevicepositionandthetargetposition.

Fig.4　Simulation result

Theresultshowsthatthepathtakingaccountofcommunicationtransmissibilityisplannedwithusingtransmissiondevice.Theresultalsoshowsflexiblepathplanningconsideringrover’seachconsiderationmattersispossiblebecausethepathandthetransmissiondevicepositionischangedbychangingthe

weight(degreeofimportance)ofrover’seachconsiderationmatters.

4Conclusions

Weproposeapathplanningmethodforexplora-tionrobottakingaccountofcommunicationtransmissibilityassumedusingatransmissiondeviceinthisstudy.Theproposedpathplanningmethodwasconfirmedbycomputersimulation.Inthefuture,weconsiderthepathplanningmethodinthecaseusingmulti-roversandmoretransmissiondevices.

References:

[1]Grotzinger J P, Crisp J, Vasavada A R,etal. Mars Science Laboratory Mission and Science Investigation . Space Sci Rev, 2012, 170: 5-56.

[2]Nishida S I, Wakabayashi S. Operation control system of lunar rover (in Japanese) //Proceedings of the 55th Space Sciences and Technology Conference. Matsuyama, Japan: The Japan Society for Aeronautical and Space Sciences, 2011: 1-4.

[3]LaValle S, Kuffner J. Randomized kinodynamic planning //1999 IEEE International Conference on Robotics and Automation. Detroit, Michigan, USA: IEEE Service Center, 1999: 473-479.

[4]Ota Y. A Study on path planning method for exploration robot taking account of communication transmissibility (in Japanese) . Tottori, Japan: Tottori University, 2014.

中圖分類號(hào)：TN 911

文獻(xiàn)標(biāo)識(shí)碼：A

文章編號(hào)：1671-6620(2015)03-0236-03

doi:10.14186/j.cnki.1671-6620.2015.03.016