Path Planning with Risk Consideration by Hopping Mobility for Long Distance Traversability
本文運(yùn)用星球跳躍漫游者(hopping rover)的移動(dòng)特性(可以跳過而不是繞過障礙物)腾窝，提出了一種新的路徑規(guī)劃和導(dǎo)航方法笨篷，并且討論了因?yàn)樘S行為和測(cè)量誤差帶來的不確定性。
In this paper, a navigation method for a small size hopping rover with advantages on its mobility is discussed by considering with some uncertainties caused by jumping behavior and measurement error.
和通常的路徑規(guī)劃一樣，本文首先從環(huán)境數(shù)據(jù)中提取障礙物驳庭，構(gòu)建三角形(triangular polygons)的環(huán)境網(wǎng)格，然后使用 A star 算法來規(guī)劃安全的路徑。其中，算法著重考慮了和障礙物的碰撞風(fēng)險(xiǎn)旷档，復(fù)雜地形(roughness of terrain)和失敗的跳躍行為(failures of hopping action)。
By extracting obstacles from environmental data and constructing triangular polygons it is possible to form paths. the algorithm considers with safety of collision with obstacles, roughness of terrain and failures of hopping action, and then could generate safer path based on A* algorithm.
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INTRODUCTION
目前，月球等星球的表面探索主要是使用一個(gè)笨重的履帶機(jī)器人 (heavy wheel rovers)厂庇，但是履帶機(jī)器人開發(fā)周期長(zhǎng)渠啊，發(fā)射時(shí)極少，對(duì)安全的需求要求更多的資源來保障权旷，甚至進(jìn)入了惡性循環(huán)替蛉。
作者提出一種新的方法，使用多個(gè)輕量緊湊的探索機(jī)器智能體 (a light and compact exploration robot agent) 來共同工作拄氯，構(gòu)成一個(gè)大的智能體躲查。
One possibility is the introduction of a light and compact exploration robot agent, and it is possible that multiple types of agents work together in one system. Various roles (functions) can be played on various kinds of equipment, and all of them can constitute one exploration system.
一個(gè)創(chuàng)意：通過將同樣的功能分散到若干個(gè)智能體上，可以忽略一定程度的智能體功能失效坤邪，那么風(fēng)險(xiǎn)被分散到整個(gè)大系統(tǒng)上熙含，有可能獲得較高的效率。
By allocating the same function (equipment) to some or many of them, it is possible to ignore some percentage of the agent's loss rate, so that risk can be distributed to the system and the mission and there is a high possibility of obtaining higher efficiency.
雖然小機(jī)器人 (A small size rover) 因?yàn)榇笮?(size) 和重量 (weight) 有很多優(yōu)勢(shì)艇纺，但是其移動(dòng)性 (traversability) 和測(cè)量能力 (measurement) 卻受到局限。
However, its size causes problems on its traversability and measurement ability.
所以邮弹，可以引入跳躍行為 (hopping mobility) 來獲得更高的移動(dòng)性能 (higher traversability) 和更廣的測(cè)量范圍 (wider measurement range)黔衡。
We have introduced hopping mobility to obtain higher traversability and wider measurement range.
通過固定區(qū)域的地面機(jī)器人 (land-based agent) 和跳躍機(jī)器人互相配合，來構(gòu)成探測(cè)系統(tǒng) (exploration system)腌乡。
Introduction of two types of rovers is being
considered in the exploration system. One is a land-based agent and a stochastic existence region is given in the search region, contributing to the search of the ground surface. The other is hopping rover. the rover that makes path planning taking advantage of sensing from high places while moving the exploration area together with the ground moving rover plays an important role.
- 相比輪式機(jī)器人盟劫，在低重力環(huán)境下 (low gravitational environment)，可以通過跳躍的方式跳過障礙物与纽，從而抄近路 (adopt a short-cut path)侣签。
Especially under low gravitational environment such as other planet or satellite, it indicates higher performance, e.g.Thus, it can jump over a long distance upon terrains and obstacles, adopt a short-cut path without a detour of a wheeled type, and also measure an environment from higher position in the air of jumping trajectory.
ISSUE AND OBJECTIVES
- 為什么導(dǎo)航問題需要研究：現(xiàn)有的導(dǎo)航研究，沒有利用跳躍機(jī)器人的運(yùn)動(dòng)特性 (文章發(fā)表于2017)急迂，所以需要進(jìn)一步利用跳和遠(yuǎn)距離的優(yōu)勢(shì)來導(dǎo)航影所。
For a hopping rover, though a lot of jumping hardware designs have been studied, its software e.g. navigation algorithms have been discussed hardly. So, the navigation method hasn't been established by taking advantage of hopping mobility such as jumping over obstacles or a long distance yet.
本文利用跳躍機(jī)器人的運(yùn)動(dòng)特性，基于對(duì)移動(dòng)性和測(cè)量數(shù)據(jù)的風(fēng)險(xiǎn)考慮僚碎，提出一種導(dǎo)航方法(主要是如何規(guī)劃路徑)猴娩。
In this paper, a navigation method for a small size hopping rover with advantages on its mobility is discussed with some risk considerations on its mobility and measured data.
PATH PLANNING FOR HOPPING MOBILITY
Selection of Jumping Target Position
移動(dòng)機(jī)器人跳躍行為 (jumping motion) 的不確定性包括初始速度變化 (initial speed change)，跳躍距離 (jump distance)勺阐，跳躍方向 (jumping direction)卷中，落地后的束縛 (bound after landing) 以及跳躍失敗 (failure of leap)。
The uncertainty factor of hopping rover's jumping motion is the initial speed change, jump distance, jumping direction, bound after landing, failure of leap.
因?yàn)樘S行為的不確定性渊抽，所以需要選取目標(biāo)落地點(diǎn) (landing point)蟆豫。
如何環(huán)境建模
- 連接被識(shí)別到的障礙物，構(gòu)成不規(guī)則三角形的環(huán)境模型懒闷。
Each obstacle captured by sensing is connected and the observation area is divided into triangles
- 在觀測(cè)到的障礙物上使用狄洛尼三角剖分 (Delaunay triangulation)十减，可以獲得每三個(gè)點(diǎn)的外心(outside heart)栈幸，即可能的落地點(diǎn)。
By using Delaunay triangulation on the observed obstacles, we can set the landing point.
MC: 什么是Delaunay triangulation嫉称？ 完美三角剖分
> Delaunay三角剖分定義：平面上的點(diǎn)集P是一種三角剖分侦镇，使得P中沒有點(diǎn)嚴(yán)格處于剖分后中任意一個(gè)三角形**外接圓**的**內(nèi)部**(可以是圓上)。
外心安全設(shè)定：假設(shè)外心是落腳點(diǎn)织阅，那么它到三個(gè)端點(diǎn)的距離是一致的壳繁，只要有一定的距離保障，就可以確保安全荔棉。
Since the outer heart is equally distant from each vertex, it can be said that it is safe if a certain margin can be secured.
Safety distance is secured by creating a circumscribed circle (其實(shí)是 delaunay triangulation) so as not to include other obstacles in the circle
Candidate Path Network
- 通過連接外心闹炉，可以得到一個(gè)維諾圖 (Voronoi diagram)。
The Voronoi diagram is a method of dividing the region by joining the outer centers formed by Delaunay triangulation.
MC: 什么是 Voronoi diagram润樱？ Voronoi diagram
> 泰森多邊形是對(duì)空間平面的一種剖分渣触，其特點(diǎn)是多邊形內(nèi)的任何位置離該多邊形的樣點(diǎn)（如居民點(diǎn)）的距離最近，離相鄰多邊形內(nèi)樣點(diǎn)的距離遠(yuǎn)壹若，且每個(gè)多邊形內(nèi)含且僅包含一個(gè)樣點(diǎn)嗅钻。
維諾圖安全設(shè)定：維諾圖包含障礙物，那么可以生成安全的節(jié)點(diǎn) (safe nodes)店展。
It can be confirmed that there are no obstacles on the sides of the Voronoi diagram enclosing the obstacles and safe nodes can be generated.
Add Uncertainty
作者設(shè)定跳躍運(yùn)動(dòng)有一定的不確定度养篓，誤差通常是正態(tài)分布(不清楚是否有理論依據(jù))，取決于初始速度赂蕴，跳的角度柳弄，方向角。
The error is generally given in the form of a normal distribution, which rides on the initial speed, the jumping angle, and the direction angle, respectively.
基于上述假設(shè)概说，rover在未來的位置誤差會(huì)累加 (accumulated)碧注，可以使用一個(gè)誤差橢圓 (error ellipse) 來表示。
The position of the rover can be indicated as the existence probability, and generally takes a shape called an error ellipse.
MC: 通過橢圓來表示誤差和不確定性糖赔，算是一個(gè)新奇的做法萍丐，類似的文章有 Robust Trajectory Planning for a Multirotor against Disturbance based on Hamilton-Jacobi Reachability Analysis。
SIMULATION OF PATH PLANNING
作者在一個(gè)很理想的環(huán)境下仿真挂捻，認(rèn)為對(duì)于非質(zhì)點(diǎn)的碉纺、大塊的障礙物仍然可以規(guī)劃出路徑，但是沒有講清楚刻撒，如何實(shí)現(xiàn)骨田？假設(shè)障礙物很高，那么跳躍機(jī)器人是否就無法跳躍過去呢声怔？
Even if the obstacle is the size of the black part of the figure.
在虛擬的月球環(huán)境下仿真态贤，比簡(jiǎn)單的理論仿真，更具有說服力醋火。
Simulation was also carried out in the virtual lunar environment created based on the rock distribution collected by “Surveyor 7” of NASA.
當(dāng)在橢圓內(nèi)的障礙物到達(dá)一定比例后悠汽，進(jìn)行位置的自校正(self-position estimation)箱吕。
When the occupancy rate of the obstacle in the error ellipse exceeds the threshold value, the rover performs self-position estimation.
CONCLUSION
The results of this research
- In consideration of the uncertainty of the hopping rover, we were able to determine a safe landing point.
- By performing self-position estimation in the virtual lunar environment, it was possible to induce Rover while suppressing position error.
Works to do
- 路徑規(guī)劃限于2維，缺乏對(duì)障礙物和跳躍高度的考慮柿冲。
- 如何切分大的障礙物茬高，而不僅僅是把障礙物作為質(zhì)點(diǎn)考慮。
- 跳躍機(jī)器人的設(shè)計(jì)假抄，物理構(gòu)建怎栽，環(huán)境識(shí)別，以及規(guī)劃好路徑后宿饱，如何對(duì)跳躍行為進(jìn)行控制熏瞄，準(zhǔn)確抵達(dá)目標(biāo)點(diǎn)。
