Snakes and Strings: New Robotic Components for 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 Complex to promote research and development of key technologies for realization of practical search-and-rescue robots, anticipating for future large-scale earthquakes and other catastrophic disasters. This paper proposes a new paradigm called “snakes and strings”, for developing practical mobile robot systems that may be useful in such situations. “Snakes” stands for snake-like robots, which can skillfully move among the debris of the collapsed buildings. “Strings”, on the other hand, means robotic systems using strings or tethers, such as proposed in the “hyper-tether” research [9]. Theters can continuously supply energy, accomplish reliable communication link, and also exhibit high traction force. This paper will present many new mechanical implementations of snake-like robots developed in our lab., and also explain in detail the new paradigm.

1

Introduction

The world has been suffering from many natural and man caused catastrophic disasters during the last decades, such as large-scale earthquakes and terrorist attacks. In such events, collapsing of houses and buildings in large areas is almost inevitable. Hence, searching for victims and subsequent rescue operations from the rubble of collapsed buildings are major problems that must be faced and planned well ahead from the actual disasters. However, these operations are very dangerous for human workers and even for trained dogs. Furthermore, the places where most of the victims are trapped, are in most cases inaccessible using traditional methods and existing technologies. These are only few, but important reasons, which may motivate researchers to direct efforts for the research and development of practical and useful search-and-rescue robot systems. This research proposes a new paradigm for developing practical robotic systems, which aims to be useful for search and rescue operations in situations such as described above. This paper is organized as follow: Section 2 explains a general scenario of a rescue operation, and analyses the characteristics needed for a useful rescue-robot. Section 3 presents many types of snake-like robots developed by the authors. Section 4 explain in detail the hyper-tether concept, and show some applications that are important for rescue operations. Finally, Section 5 presents the conclusions.

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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 especial research and development project to establish new scientific and technological foundations for disaster measures. This project aims to largely reduce the infrastructure damages and human casualties in the event of large-scale earthquakes that will occasionally happen in the future. Many research subprograms form this project, so a detailed explanation is out of scope of this paper. Nonetheless, the following list depict a part of this project, i.e., Program 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 related topics 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 technologies to build mobile robots with high degree of mobility. Useful mobile robots should be able to move on uneven terrain, inside the rubble of collapsed buildings, through the remains of underground shopping centers, and also around the entire stricken areas. Mobility is an essential characteristic for search-and-rescue robots, which primary task is gathering of information about conditions of the victims and also the surrounding structures where they are trapped. Needless to say, information is crucial to plan an optimal rescue strategy, which can be undertaken by trained human rescue teams. Information gathering robots should be small enough to be able to thread through the narrow spaces under the collapsed buildings. Moreover, searching

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is not made only in descent paths, so a robot should also be able to perform ascend motions on stairs and piles inside the rubble. In extreme cases, it would be nice if a robot could even climb up vertical piles, and move through the air. Most traditional types of robots cannot meet these requirements: (a) walking robots; (b) wheeled robots; (c) crawler-type robots. In contrast, snake-like robots seems to be a very promising class of mobile robot, which can fulfill most 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 function as “legs” when moving; as “arms” when traversing branches; and as “fingers” when grasping objects. However it is their long, slender and smooth articulated body shape that make them especially suited to enter and move inside small cracks and crevices, such as encountered in the disaster sites. The same performance can be expected from mechanical snakes that inherit these physical characteristics. Mechanical snakes are complex to design because there are many degrees of freedom (DOF) involved, and also for the complexity on motion planning. After the pioneer study on mechanical snakes by one of the authors [1], many other researchers have been considering various other alternative types of mechanisms for snake robots, and even practical applications on search-andrescue operations [2]. Nevertheless, the authors also have been developing many new types of snake-like robots with unique characteristics. The mechanical details and advantages of each of them, including an amphibious type, 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 robots should operate continuously for hours, if not days, and one cannot tolerate a robot returning to the surface just for recharging or change of batteries. And to 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/or for data communication are usually regarded as systems still “under development”. In general, the term “untethered” system is used as synonym to autonomous and/or self-contained systems that have all controllers and energy supply on-board. There is no doubt that untethered autonomous systems are important when considering robots to freely move in general environments. However, with the application of the “hyper-tether” concept [9] to searchand-rescue mobile robots, many positive contributions can be expected. Hypertether research proposes the use of high-strength tether with built-in electrical

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conductors, which can be reeled-in and out by a winch or reel. It is important to 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 with the robot movement, and the friction between the tether and the surrounding environment is kept to a minimum. The followings advantages are also relevant. • The on-board battery can be of small capacity, because it will be continuously charged through the tethers. This will contribute to decrease the total weight of the system. • Highly reliable cable communication link can be established at no extra cost. Wireless communication technology is very commonly used these days, so an ordinary search-and-rescue robot system, not equipped with hyper-tether, will possibly use a wireless communication link to send sensory data and camera’s image to the external team. However, these robots will interfere not only with each other, but also will pollute the wireless communication spectrum, which otherwise could be in use by the victims in a desperate attempt to reach the rescue teams. Nonetheless, a search-and-rescue robot should carry receivers to probe and monitor for Cellular Phone, Wireless LAN, Bluetooth, and other sources of wireless signals. • The tether can be used to drag the robot out from the rubble, in case of malfunction. More details of hyper-tether applications for rescue tasks will be discussed in Section 4.

3

Snake-like Robots Development at Hirose Lab.

This Section will introduce some types of snake-like robots that have been developed at our lab., recently. By the way, no strict distinction has been made in the literature so far, between snake-robots and snake-like robots. In this paper, snake-like robots will refer not only to mechanisms that imitate real snakes, but it will also extend the definition to the class of mobile robot that 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 cord mechanism (ACM-III, 1972). It was in fact a 2-dimensional mechanism that generated propulsion force using the same creeping propulsion movement principle that governs the motion of real snakes. In 1995, a self-contained version of this snake robot was build, and named ACM-R1. The ACM series was 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

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latest models are all self-contained and semi-autonomous. They are equipped with on-board batteries, motor drivers, and also computers that calculate and generate the desired motions in real-time. ACM-R3 does not only feature 3-D motion, but it also extends the capabilities 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 to bend its articulation, and two passive wheels that are free to rotate and placed at 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 creeping movement, the wheels positioned horizontally do not contribute to propel the robot, but ACM-R3 can take advantage of both horizontal and vertical 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 can move both on the ground and in the water. However, unlike the traditional ACM series, its creation was based on the study of motion of a corkscrew shaped microorganism called “Spirochete”. Although the great difference in size, spirochetes measure about 8 to 10 [µm] in length and HELIOS-I shown in Fig.2 measures 1.7 [m], the mechanical model HELIOS-I has successfully reproduced the unique spiral propulsion motion of these microorganisms. The explanation about the theory that govern its motion, as well as mechanism details can be found in [4]. This research is still in an initial phase, but the experimental results from the first prototype gives light for the development of a totally new class of

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amphibious snakes. Amphibious robots may be extremely useful in searchand-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 parts and degrees of freedoms a robot has, less are the possibilities of mechanical failures. In order to optimize the snake-like robot mechanical design, a crawler-type articulated body mobile robot Souryu-I [5] shown in Fig.3 was created. Although it was intentionally conceived with a limited number of degrees of freedoms, it still presents good mobility characteristics peculiar to snake-robots. This robot is composed of front, center and rear bodies, which are connected by special 2 dimensional joint mechanisms that change the front and rear bodies’ postures symmetrically around the center body’s pitch and yaw axes. Moreover, all the 6 crawler segments are actuated by a single electric motor, thus totaling only 3 DOF for the entire robot. This robot includes a CCD camera and a microphone in the foremost part, and is suitable for finding 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 advantageous characteristic of using the fire hose’s hydraulic energy as source of energy for its actuation. Fire trucks supplies water at a high pressure through the fires hoses, so that a robot properly actuated by this hydraulic energy could powerfully thrust its way through the debris inside a fire scene. In order to evaluate the mobility performance and to develop control algorithms for this type of robot, a first prototype equipped with DC motors was built. But

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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 a practical 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 possible to a disaster scene, so that they can work independently and in parallel to finish the rescue operations in a minimum time. However, some tasks

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such as removing heavy objects or overcoming high obstacles are difficult if not impossible to be performed by a single robot alone. In such cases, the cooperation among the robots can be an effective solution. Fig.5 shows GUNRYU [7], a group robot that can work independently or in cooperation with each other. Each robot unit is equipped with manipulators that can be used for independent or cooperative working tasks, but also function as a connection means for connecting/disconnecting to/from the other robots in the group. Experiments demonstrate that much higher terrain adaptability and traveling performance are achieved for a group of mobile robots connected in series, than compared to the performance of a single 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 be programmed to execute autonomous missions on disaster sites, without any help of tethers. However, as explained in Section 2.4, there are many advantages when a robot is correctly connected by tethers, i.e., using the hypertether concept. Hence, new mechanisms are been sough, which will carry on-board reels or winches. These mechanisms will be presented in future works. Nonetheless, hyper-tether is a much broad concept that can be used in many other practical applications. It can also be extremely useful for robotic systems for rescue operations. In this Section, the hyper-tether concept will be explained in more detail. 4.1

The Basic Concept of Hyper-Tether

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

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ered, include but are not limited to: power transmission, data communication, 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 locomotion on 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

tip interface base interface

working-tool

tether mobile platform

(c) Far-reach tethered working tool

(d) Grass-cutting, remote-sensing

Fig. 6. Examples of Hyper-Tether Applications

Hyper-tether basic hardware: Many tethered robotic applications can be accomplished by using the hyper-tether basic hardware, which consists of 3 parts: 1) tip interface; 2) tether; 3) base interface. These parts are implemented with one or more of the following characteristics and functions: 1. Tip interface: simple mechanical and electrical connection with the other part (other robot or device); tether thrusting device; anchoring capability on rocks and/or trees.

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2. Tether: small outer diameter; light weight; high strength; good flexibility; abrasion resistant; high power transmission with good efficiency (low wire resistance); high data communication bandwidth; bidirectional transmission 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 mobile platform; power line and data communication connection with the mobile platform; tether launching/throwing device. For rescue applications, the following related applications: “on-site energy generation by engine-driven mobile robots”; “far-reach tethered working tool”; and “locomotion using launching and anchoring of tethers”, can be of importance. 4.2

On-site Energy Generation by Engine-Driven Mobile Robots

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

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

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

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driven by a gasoline-engine. This mobile platform can serve as a mobile electricity generator, and also as a working platform for many applications. The original 4-wheel buggy itself presents high terrain adaptability and reliable mechanical structure. These characteristics are maintained in the modified buggy robot, where the steering, throttle and brakes are actuated by electrical motors, and an extra alternator with 400[VA] power capacity was added 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 a human 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 and will be presented soon. 4.3

Far-reach Tethered Working-Tool

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

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

mobile platform 2 an electric actuated mobile robot (e.g., a crawler or walking robot). The batteries can be charged by the tethers - high strength - electrical power transmission

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

tip interfaces mechanical and electrical mobile platform 1 electricity generation capability. (e.g., a combustion engine

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

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

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which each-other to control the position/orientation of a common workingtool, as shown in Fig.6(c). This approach called “far-reach tethered working tool” can take advantage of most characteristics of cable suspended manipulators, and at the same time extends the systems’s workspace to an almost unlimited area, reachable by the mobile platforms. Even a minimized system that uses only 2 mobile platforms, as shown in Fig.8 can be extremely useful in practical situations. The use of mobile platforms with electric generators such as “Gryphon-I”, makes this system ideal for long and continuous operations. 4.4

Novel Type of Locomotion Using Launching and Anchoring of Tethers

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

(2) anchor

(3) winch up (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 Areas for Mobile Robots

Snakes and Strings for Rescue Operations

(a) Example of hyper-tether tip interface: passive anchoring device

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(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 this experiment, a passive anchoring device called “flying gripper” was used. This gripper, shown in Fig.10(a), was designed to automatically close when hitting a target, in this case the trunk of a tree, and to mechanically release the gripper 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 of autonomous robots in a variety of environments (Fig.10(b)). New models of flying grippers, passive ones and also active ones, which use the electrical energy available at the tip of the tether, are under development.

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Conclusions

This paper introduced a new paradigm called “snakes and strings” for rescue operations. It consists of two parts: (1) snake-like robot technology for developing information gathering mobile robots, which can thread through the narrow spaces under the collapsed buildings, and (2) the hyper-tether concept, which can be advantageously applied to assist the snake-like robots, and also to build mobile robot systems that can move and work around the disaster sites. All presented robots are actual mechanical models, and some of them have already been tested in simulated disaster sites and are ready for practical use. Nonetheless, the authors and their research group are continuously working on the improvement and development of new mechanisms and control algorithms in order to create even more reliable and efficient rescue robots and equipments. Detailed explanation and new advancement reports concerning

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

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