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Snakes and Strings: New Robotic Componentsfor Rescue Operations

Shigeo Hirose and Edwardo F. Fukushima

Tokyo Institute of Technology, 2-12-1 Ookayama Meguro-ku, JAPAN

Abstract. The Japanese government is establishing an International Rescue Com-plex to promote research and development of key technologies for realization of prac-tical search-and-rescue robots, anticipating for future large-scale earthquakes andother catastrophic disasters. This paper proposes a new paradigm called “snakesand strings”, for developing practical mobile robot systems that may be useful insuch situations. “Snakes” stands for snake-like robots, which can skillfully moveamong the debris of the collapsed buildings. “Strings”, on the other hand, meansrobotic systems using strings or tethers, such as proposed in the “hyper-tether”research [9]. Theters can continuously supply energy, accomplish reliable communi-cation link, and also exhibit high traction force. This paper will present many newmechanical implementations of snake-like robots developed in our lab., and alsoexplain in detail the new paradigm.

1 Introduction

The world has been suffering from many natural and man caused catas-trophic disasters during the last decades, such as large-scale earthquakes andterrorist attacks. In such events, collapsing of houses and buildings in largeareas is almost inevitable. Hence, searching for victims and subsequent rescueoperations from the rubble of collapsed buildings are major problems thatmust be faced and planned well ahead from the actual disasters. However,these operations are very dangerous for human workers and even for traineddogs. Furthermore, the places where most of the victims are trapped, are inmost cases inaccessible using traditional methods and existing technologies.These are only few, but important reasons, which may motivate researchersto direct efforts for the research and development of practical and usefulsearch-and-rescue robot systems.

This research proposes a new paradigm for developing practical roboticsystems, which aims to be useful for search and rescue operations in situationssuch as described above.

This paper is organized as follow: Section 2 explains a general scenarioof a rescue operation, and analyses the characteristics needed for a usefulrescue-robot. Section 3 presents many types of snake-like robots developedby the authors. Section 4 explain in detail the hyper-tether concept, and showsome applications that are important for rescue operations. Finally, Section5 presents the conclusions.

2 S. Hirose and E. F. Fukushima

2 Mobile Robots To Operate In Disaster Scenes

2.1 The MEXT Project on Disaster Measures

The Ministry of Education, Culture, Sports, Science and Technology of Japan(MEXT, http://www.mext.go.jp) has just introduced recently, an especialresearch and development project to establish new scientific and technolog-ical foundations for disaster measures. This project aims to largely reducethe infrastructure damages and human casualties in the event of large-scaleearthquakes that will occasionally happen in the future. Many research sub-programs form this project, so a detailed explanation is out of scope of thispaper. Nonetheless, the following list depict a part of this project, i.e., Pro-gram III, which is mainly related to robotics technology.

• 4. Information Gathering Robot– 4.1 Mobile Robot Technology– 4.2 Information Mapping

• 5. Intelligent Sensor and Portable Terminal– 5.1 Information Gathering Technology– 5.2 Technology for Integration of Disperse Information

• 6. Human Interface– 6.1 Remote Operation Technology– 6.2 Information Displaying Technology

• 7. Total System– 7.1 Study on System Integration– 7.2 Study on System Assessment and Standardization– 7.3 Study on Human Society Behavior when Incorporating Robots

and Distributed Sensors in the Human Society

This paper in particular, will mainly focus on the research program 4.1, i.e.,information gathering mobile robot technology. Nonetheless, all other relatedtopics are also important, and are been considered in our research efforts.

2.2 Information Gathering Mobile Robots

The main goal underlined in program 4.1, is research and development of tech-nologies to build mobile robots with high degree of mobility. Useful mobilerobots should be able to move on uneven terrain, inside the rubble of col-lapsed buildings, through the remains of underground shopping centers, andalso around the entire stricken areas. Mobility is an essential characteristicfor search-and-rescue robots, which primary task is gathering of informationabout conditions of the victims and also the surrounding structures wherethey are trapped. Needless to say, information is crucial to plan an optimalrescue strategy, which can be undertaken by trained human rescue teams.

Information gathering robots should be small enough to be able to threadthrough the narrow spaces under the collapsed buildings. Moreover, searching

Snakes and Strings for Rescue Operations 3

is not made only in descent paths, so a robot should also be able to performascend motions on stairs and piles inside the rubble. In extreme cases, itwould be nice if a robot could even climb up vertical piles, and move throughthe air.

Most traditional types of robots cannot meet these requirements: (a) walk-ing robots; (b) wheeled robots; (c) crawler-type robots. In contrast, snake-likerobots seems to be a very promising class of mobile robot, which can fulfillmost of the requirements needed for practical search-and-rescue robots.

2.3 Snake-like Robots

Real snakes possess many advanced motion capabilities: their body can func-tion as “legs” when moving; as “arms” when traversing branches; and as“fingers” when grasping objects. However it is their long, slender and smootharticulated body shape that make them especially suited to enter and moveinside small cracks and crevices, such as encountered in the disaster sites.The same performance can be expected from mechanical snakes that inheritthese physical characteristics.

Mechanical snakes are complex to design because there are many degreesof freedom (DOF) involved, and also for the complexity on motion planning.After the pioneer study on mechanical snakes by one of the authors [1], manyother researchers have been considering various other alternative types ofmechanisms for snake robots, and even practical applications on search-and-rescue operations [2]. Nevertheless, the authors also have been developingmany new types of snake-like robots with unique characteristics. The me-chanical details and advantages of each of them, including an amphibioustype, will be explained in Section 3.

However, despite the good performance achieved by our mobile robots,a major concern still remains: the energy source. Search-and-rescue robotsshould operate continuously for hours, if not days, and one cannot tolerate arobot returning to the surface just for recharging or change of batteries. Andto be realistic, one cannot expect that the robot will ever succeed to return.The use of tethers can be a good solution, as discussed next.

2.4 Strings and Tethers

Mobile robots using tethers (“strings”) for supplying electrical energy and/orfor data communication are usually regarded as systems still “under develop-ment”. In general, the term “untethered” system is used as synonym to au-tonomous and/or self-contained systems that have all controllers and energysupply on-board. There is no doubt that untethered autonomous systems areimportant when considering robots to freely move in general environments.

However, with the application of the “hyper-tether” concept [9] to search-and-rescue mobile robots, many positive contributions can be expected. Hyper-tether research proposes the use of high-strength tether with built-in electrical


conductors, which can be reeled-in and out by a winch or reel. It is importantto note, that the winch/reel is carried on-board by the mobile robot itself.In this scheme, the tether can be reeled-in or out in synchronization withthe robot movement, and the friction between the tether and the surround-ing environment is kept to a minimum. The followings advantages are alsorelevant.

• The on-board battery can be of small capacity, because it will be contin-uously charged through the tethers. This will contribute to decrease thetotal weight of the system.

• Highly reliable cable communication link can be established at no extracost. Wireless communication technology is very commonly used thesedays, so an ordinary search-and-rescue robot system, not equipped withhyper-tether, will possibly use a wireless communication link to sendsensory data and camera’s image to the external team. However, theserobots will interfere not only with each other, but also will pollute thewireless communication spectrum, which otherwise could be in use by thevictims in a desperate attempt to reach the rescue teams. Nonetheless, asearch-and-rescue robot should carry receivers to probe and monitor forCellular Phone, Wireless LAN, Bluetooth, and other sources of wirelesssignals.

• The tether can be used to drag the robot out from the rubble, in case ofmalfunction.

More details of hyper-tether applications for rescue tasks will be discussed inSection 4.

3 Snake-like Robots Development at Hirose Lab.

This Section will introduce some types of snake-like robots that have beendeveloped at our lab., recently. By the way, no strict distinction has beenmade in the literature so far, between snake-robots and snake-like robots. Inthis paper, snake-like robots will refer not only to mechanisms that imitatereal snakes, but it will also extend the definition to the class of mobile robotthat are composed of many articulated body segments linked in series.

3.1 Active Cord Mechanism - ACM-R3 -

The first successful mechanical snake developed by Hirose was the active cordmechanism (ACM-III, 1972). It was in fact a 2-dimensional mechanism thatgenerated propulsion force using the same creeping propulsion movementprinciple that governs the motion of real snakes. In 1995, a self-containedversion of this snake robot was build, and named ACM-R1. The ACM serieswas followed by a model capable of 3-dimensional (3-D) motion, ACM-R2.This is now replaced by the latest model ACM-R3 [3], shown in Fig.1. These


latest models are all self-contained and semi-autonomous. They are equippedwith on-board batteries, motor drivers, and also computers that calculateand generate the desired motions in real-time.

ACM-R3 does not only feature 3-D motion, but it also extends the capa-bilities of real snakes. ACM-R3 is composed of 20 segments linked in series.Each unit-segment has only one active degree of freedom, say the DOF tobend its articulation, and two passive wheels that are free to rotate and placedat both sides of the segment. These unit-segments are connected in series,rotated 90 degrees each other, as shown in Fig.1(a). In a normal creepingmovement, the wheels positioned horizontally do not contribute to propelthe robot, but ACM-R3 can take advantage of both horizontal and verti-cal wheels when performing new artificial gates, such as shown in Fig.1(b).Moreover, these wheels protect internal electrical circuits and mechanisms,making it robust for search-and-rescue operations.

(a) Lift-up motion of the front part (b) Motion using both horizontal and

vertical wheels

Fig. 1. Active Cord Mechanism “ACM-R3” [3]

3.2 Amphibious Snake-like Robot “HELIX-I”

HELIX-I shown in Fig.2, is an hermetic 3D active cord mechanism that canmove both on the ground and in the water. However, unlike the traditionalACM series, its creation was based on the study of motion of a corkscrewshaped microorganism called “Spirochete”. Although the great difference insize, spirochetes measure about 8 to 10 [µm] in length and HELIOS-I shownin Fig.2 measures 1.7 [m], the mechanical model HELIOS-I has successfullyreproduced the unique spiral propulsion motion of these microorganisms. Theexplanation about the theory that govern its motion, as well as mechanismdetails can be found in [4].

This research is still in an initial phase, but the experimental results fromthe first prototype gives light for the development of a totally new class of


amphibious snakes. Amphibious robots may be extremely useful in search-and-rescue operations around the bay area.

(a) Moving on the ground (b) Swimming in the water

Fig. 2. Amphibious Snake-like Robot “HELIX-I”

3.3 Connected Crawler Vehicle - SOURYU -

In a general mechanical engineering point-of-view, the less mechanical partsand degrees of freedoms a robot has, less are the possibilities of mechani-cal failures. In order to optimize the snake-like robot mechanical design, acrawler-type articulated body mobile robot Souryu-I [5] shown in Fig.3 wascreated. Although it was intentionally conceived with a limited number ofdegrees of freedoms, it still presents good mobility characteristics peculiar tosnake-robots.

This robot is composed of front, center and rear bodies, which are con-nected by special 2 dimensional joint mechanisms that change the front andrear bodies’ postures symmetrically around the center body’s pitch and yawaxes. Moreover, all the 6 crawler segments are actuated by a single electricmotor, thus totaling only 3 DOF for the entire robot. This robot includesa CCD camera and a microphone in the foremost part, and is suitable forfinding victims buried under the rubble of a disaster scene.

3.4 Articulated Multi-Wheeled Robot - GENBU -

Fig.4 shows Genbu [6], a fire-fighting robot. This robot has a unique and ad-vantageous characteristic of using the fire hose’s hydraulic energy as source ofenergy for its actuation. Fire trucks supplies water at a high pressure throughthe fires hoses, so that a robot properly actuated by this hydraulic energycould powerfully thrust its way through the debris inside a fire scene. In orderto evaluate the mobility performance and to develop control algorithms forthis type of robot, a first prototype equipped with DC motors was built. But


Fig. 3. Connected Crawler Vehicle for Inspection of Disaster Scenes “Souryu I” [5]

a new type of high torque hydraulic motor is under development to equip apractical fire-fighting robot Genbu.

Fig. 4. Articulated Multi-Wheeled Fire-Fighting Mobile Robot “Genbu” [6]

3.5 Robots to Work in Group

Needless to say, it is advantageous to deploy as many robots as possibleto a disaster scene, so that they can work independently and in parallelto finish the rescue operations in a minimum time. However, some tasks


such as removing heavy objects or overcoming high obstacles are difficult ifnot impossible to be performed by a single robot alone. In such cases, thecooperation among the robots can be an effective solution.

Fig.5 shows GUNRYU [7], a group robot that can work independentlyor in cooperation with each other. Each robot unit is equipped with manip-ulators that can be used for independent or cooperative working tasks, butalso function as a connection means for connecting/disconnecting to/fromthe other robots in the group. Experiments demonstrate that much higherterrain adaptability and traveling performance are achieved for a group ofmobile robots connected in series, than compared to the performance of asingle mobile robot.

Fig. 5. Cooperative Robot Composed of Autonomous Segments “Gunryu”

4 Hyper-Tether

All robots introduced in the previous Section are self-contained and can beprogrammed to execute autonomous missions on disaster sites, without anyhelp of tethers. However, as explained in Section 2.4, there are many advan-tages when a robot is correctly connected by tethers, i.e., using the hyper-tether concept. Hence, new mechanisms are been sough, which will carryon-board reels or winches. These mechanisms will be presented in futureworks.

Nonetheless, hyper-tether is a much broad concept that can be used inmany other practical applications. It can also be extremely useful for roboticsystems for rescue operations. In this Section, the hyper-tether concept willbe explained in more detail.

4.1 The Basic Concept of Hyper-Tether

Hyper-tether research aims to systematically study optimal use of tetheredconnections for robotic systems [8]-[9]. Some functionalities that are consid-


ered, include but are not limited to: power transmission, data communica-tion, active control of the tether’s tension and/or length, tether launching,anchoring, and follow-the-leader type trajectory command generation.

Many applications can be accomplished using the hyper-tether concept.For instance: 1) cooperative material transportation; 2) stable locomotionon steep slopes; 3) locomotion of micro-rovers in micro-gravity environment;4) far-reach tethered working-tool; and many others, as already discussed in[8][9]. Fig.6 illustrates some of these applications.

(a) Cooperation work: support for other

heavy machines

(b) Spraying of agricultural

chemicals

(c) Far-reach tethered working tool (d) Grass-cutting, remote-sensing

tether

tip interface base interface

working-tool

mobile platform

Fig. 6. Examples of Hyper-Tether Applications

Hyper-tether basic hardware: Many tethered robotic applications can be ac-complished by using the hyper-tether basic hardware, which consists of 3parts: 1) tip interface; 2) tether; 3) base interface. These parts are imple-mented with one or more of the following characteristics and functions:

1. Tip interface: simple mechanical and electrical connection with theother part (other robot or device); tether thrusting device; anchoringcapability on rocks and/or trees.


2. Tether: small outer diameter; light weight; high strength; good flexi-bility; abrasion resistant; high power transmission with good efficiency(low wire resistance); high data communication bandwidth; bidirectionaltransmission of power and data; power-line communication.

3. Base interface: fast reel in/out; high-torque reel in/out; tether’s length,tension and orientation sensors; mechanical connection with the mobileplatform; power line and data communication connection with the mobileplatform; tether launching/throwing device.

For rescue applications, the following related applications: “on-site en-ergy generation by engine-driven mobile robots”; “far-reach tethered workingtool”; and “locomotion using launching and anchoring of tethers”, can be ofimportance.

4.2 On-site Energy Generation by Engine-Driven Mobile Robots

Electrical energy source is essential for most tools and robots. However, onecan not expect that electricity is available from existing electrical infras-tructures, soon after a large-scale disaster. Thus, energy generators mustbe urgently deployed to the disaster sites, so that tools and robots can beused continuously without delays. Although many types of generators can bethought, including the ones based on fuel-cells, most of them are too heavyto be carried by human workers.

Fig. 7. Autonomous Buggy Robot “Gryphon-I” Features High Terrain Adaptabil-ity, Energy Generation Capability, and Hyper-Tether Basic Hardware

An alternative solution sough in this research, proposes the use of engine-driven mobile robots equipped with hyper-tether basic hardware. The firstprototype, Gryphon-I shown in Fig.7, is based on a commercial 4-wheel buggy


driven by a gasoline-engine. This mobile platform can serve as a mobile elec-tricity generator, and also as a working platform for many applications.

The original 4-wheel buggy itself presents high terrain adaptability andreliable mechanical structure. These characteristics are maintained in themodified buggy robot, where the steering, throttle and brakes are actuatedby electrical motors, and an extra alternator with 400[VA] power capacity wasadded to generate and distribute electrical energy to other robots and/or tools[14]. This mobile robot can be remote controlled, but it is also possible for ahuman pilot to ride Gryphon-I and control the buggy in the traditional way.This “ride-by-wire” approach is already accomplished in the actual robot andwill be presented soon.

4.3 Far-reach Tethered Working-Tool

Many types of wire/cable-driven parallel manipulators have been proposedin the literature [10]-[13]. Cable suspended manipulators present advancedcharacteristics such as: large workspace; good reconfigurability/adaptabilityand fast and simple installation; low weight; good energy efficiency. The useof such systems for rescue operations is also under investigation [13].

mechanical and electrical

electricity generation capability. (e.g., a combustion engine

an electric actuated mobile robot (e.g., a crawler or walking robot). The batteries can be charged by the

mobile platform 2

- grass-cutter- landmine detector- manipulator- changeable tools

working-tool

tip interfaces

- high strength- electrical power transmission

tethers

- mechanical and electrical connection to the mobile platform. - winch mechanism- CPU unit

base interface

mobile platform 1

Fig. 8. Example of Hyper-Tether System Used for Grass-cutting and LandmineDetection and Removal

This research proposes a new tethered manipulator approach where mo-bile robots equipped with hyper-tether basic hardware, work in coordination


which each-other to control the position/orientation of a common working-tool, as shown in Fig.6(c). This approach called “far-reach tethered workingtool” can take advantage of most characteristics of cable suspended manip-ulators, and at the same time extends the systems’s workspace to an almostunlimited area, reachable by the mobile platforms. Even a minimized sys-tem that uses only 2 mobile platforms, as shown in Fig.8 can be extremelyuseful in practical situations. The use of mobile platforms with electric gen-erators such as “Gryphon-I”, makes this system ideal for long and continuousoperations.

4.4 Novel Type of Locomotion Using Launching and Anchoringof Tethers

The hyper-tether winch can be equipped with a launching device to throw thetether tip to distant places such as cliffs, other bank of a river, an island orboat, or even on upper stairs of a building, which are difficult to reach in otherways during an emergency in disaster sites. An anchoring tool connected tothe tether tip could then automatically anchor itself to a firm place such asrocks or trees. This tether link itself works as a rescue rope, but it also helpthe mobile robot to move towards the anchored point and continue the rescueoperation.

(3) winch up

(2) anchor

(1) launch

(a) A crawler type robot equipped

with launching device ...

(b) can go up the step with the

help of hyper-tether winch

Fig. 9. Hyper-tether Launching and Anchoring Functions Expand Reachable Areasfor Mobile Robots


(a) Example of hyper-tether tip

interface: passive anchoring

device (b) Example using Gryphon-I

Fig. 10. Anchoring Device Prototype and Anchoring Example Using Gryphon-I

An example of obstacle overcoming experiment is shown in Fig.9. In thisexperiment, a passive anchoring device called “flying gripper” was used. Thisgripper, shown in Fig.10(a), was designed to automatically close when hittinga target, in this case the trunk of a tree, and to mechanically release the grip-per after pulling the tether in a pre-defined sequence. In the first prototype,the releasing sequence consists of pulling and loosening the tether 3 times.

Launching and anchoring tethers can help locomotion of many types ofautonomous robots in a variety of environments (Fig.10(b)). New models offlying grippers, passive ones and also active ones, which use the electricalenergy available at the tip of the tether, are under development.

5 Conclusions

This paper introduced a new paradigm called “snakes and strings” for res-cue operations. It consists of two parts: (1) snake-like robot technology fordeveloping information gathering mobile robots, which can thread throughthe narrow spaces under the collapsed buildings, and (2) the hyper-tetherconcept, which can be advantageously applied to assist the snake-like robots,and also to build mobile robot systems that can move and work around thedisaster sites.

All presented robots are actual mechanical models, and some of them havealready been tested in simulated disaster sites and are ready for practical use.Nonetheless, the authors and their research group are continuously workingon the improvement and development of new mechanisms and control algo-rithms in order to create even more reliable and efficient rescue robots andequipments. Detailed explanation and new advancement reports concerning


this research area and related technologies can be found in the author’s webpage (http://www-robot.mes.titech.ac.jp).

References

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