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ABSTRACT
The utilization of autonomous intelligent roots in search and rescue (SAR) is a new and challenging field of Robotics dealing with the task in extremely hazardous and complex disaster environments. Autonomy, high mobility, robustness and modularity is critical design issues of rescue robotics requiring dexterous devices equipped with the ability to learn from prior experience, adaptable to variable types of usage with a wide enough functionality under different sensing modules and compliant to environmental and victim conditions. Intelligent, biologically inspired mobile robots and in particular serpentine mechanisms have turned out to Widely used robot effective, immediate and reliable responses to many SAR operations. This article puts a special emphasis on the challenges serpentine search robot hardware, Sensor-based path planning and control design.
INTRODUCTION
The utilization of autonomous intelligent robots in the search and rescue (SAR) is a new and challenging field of robotics, dealing with tasks in extremely hazardous and complex disaster environments. High mobility, robustness etc are design issues of rescue robots equipped with various devices such as devices having ability to learn from previous rescue, devices adaptable to variable types of working conditions. Looking to the future, intelligent biologically inspired mobile robots, i.e. serpentine mechanisms are widely used robots in the field of SAR operations.
Recent natural disasters and man-made catastrophes have focused attention on the area of emergency management arid rescue. These experiences have shown that most governmentâ„¢s preparedness and emergency responses are generally inadequate in dealing with disasters. Considering the large number of people who have died due to reactive, spontaneous, and unprofessional rescue efforts resulting from a lack of adequate equipment or lack of immediate response, researchers have naturally been developing mechatronic rescue tools and strategic planning techniques for planned rescue operations. Research and development activities have resulted in the emergence of the field of rescue robotics, which can be defined as the utilization of robotics technology for human assistance. This article puts a special emphasis on the challenges of serpentine search robot hardware, sensor based path planning and control design.
RESCUE ROBOTS
¢ Recent natural disasters and man-made catastrophes have focused attention on the area of emergency management and rescue. These experiences have shown that most government™s emergency responses are generally inadequate in dealing with disasters.
¢ Considering the large number of people died due to reactive, spontaneous and unprofessional rescue efforts research have naturally been developing mechatronic tools and planning techniques for research operation.
¢ This factor lead to the development of rescue robots for human assistances in any phase of rescue operations which may vary from country to country(different type of disaster, different regional policies).
¢ The main aspects of rescue robots are detection and identification of living bodies with the help of most modern mechatronic tools.
FUNCTIONS OF RESCUE ROBOTS
1. Detection and identification of livings bodies using modern tools. Sensors are used to detect the bodies.
2. Clearing of debris in accessing the victim.
3. Physical, emotional and medical stabilization of the survivor by bringing to him or her automatically administered first aid.
4. Fortification of the living body for preventing further damage.
5. Transportation of the victim with necessary first aid.
A BRIDGE MODE SNAKE ROBOT
MAJOR RESCUE PROBLEMS
¢ Nondexterous tools are generally cumbersome and destructive . So the operation of tool is very complicated and requires great attention.
¢ Debris-clearing machines are heavy construction devices. So when they function on the rubble, trigger the rubble.
¢ Tool operation is generally very slow . It takes so much time which might result in the death of victim.
¢ Although a few detectors are available , the search for survivors is mainly based on sniffing dogs and human voices, where calling and listening requires silences and focused attention that is very difficult.
¢ The supply of first aid can only be done at close distances.
¢ The retrieval of bodies generates extra injuries since professional stabilization of the victim is seldom obtained.
Aiming at enhancing the quality of rescue and life after rescue, the field of rescue robotics is seeking dexterous devices that are equipped with learning ability, adaptable to various types of usage with a wide enough functionality under multiple sensors, and compliant to the conditions of the environment and that of the person being rescued.
DESIGN OF THE SNAKE ROBOT
Snake robots are a new type of robots, known also as serpentine robots. As the name suggests, these robots possess multiple actuated joints thus multiple degrees of freedom. This gives them superior ability to flex, reach, and approach a huge volume in its workspace with infinite number of configurations. This redundance in configurations gives them the technical name: hyper redundant robots. Here we develop new snake robot designs. Ideally, the future snake design will consist of three degree of freedom stages --- roll, pitch, and extension. Sometimes stages are called bays.
For the applications that we are interested in, the main challenge in designing these robots deals with putting actuated joints in a tight volume where we minize the length of the stages and their cross sectional areas. For the next design iteration, we will omit the extension degree of freedom in favor of having a shorter bay length. Therefore, the main concept of our design, as well as many others, is to stack two degree-of-freedom joints on top of each other, forming a serpentine robot. There are three main schools of designs for these kinds of robots: actuated universal joint, angular swivel joints and angular bevel joint.
The simplest design that first comes to mind is stacking simple revolute joints as close as possible to each other and this led to the actuated universal joint design. However these kinds of designs are bulky and not appropriate of lots of serpentine robos applications. Another kind of bulky two DOF joints are pneumatic snakes.
The second design that evolved was the angular swivel joints, which is present in the JPL Serpentine Robot. These are much more compact two DOF joints. The design is simple: starting with a sphere, then slicing the sphere into two parts such that the slice plane is transverse to the south-north pole axis of the sphere. Now rotate one half sphere with respect to the other and notice the motion of the poles. Putting the snake bays orthognal to the sphere at the poles and coordinating the motors that rotate those hemispheres leads to a two DOF joint.
This is the most compact joint design till now. However research is going on to develop a new compact two DOF joint. Work on optimizing the size, strength, reachability and flexibility of these joint. So far three types are of joints are designed. The first prototype was designed and built using of the shelf components and using simple manufacturing machinary.
WORKING OF THE SNAKE ROBOT TO THE RESCUE
Ultra sonic sensors and thermal camera are located on its head the main function of the ultra sonic sensors is detect and identification of the living body six to seven segments are joined together by TWO DEGREE OF FREEDOM then all modes are controlled over here they are as follows:
1. Twisting modeIn this mode the robot mechanism folds certain joints to generate a twisting motion within its body, resulting in side wise movement.
2. Wheeled-locomotion modeThis is one of the common wheeled-locomotion modes where passive wheels are attached on the units, resulting in low friction along the tangential direction of the robot body line and increasing the friction in the direction perpendicular to that.
3. Bridge modeIn this mode the robot configures itself to stand on its two legs in a bridge-like shape. The basic movement consists of left-right swaying of the center of gravity (bipedal locomotion). Motions such as somersaulting may be other possibilities.
4. Ring modeThe two ends of the robots are brought together by its own actuation to form a circular shape. The drive to make uneven circular shape is achieved by proper deformation and shifting of the center of gravity.
5. Inching modeThe robots generates a vertical wave shape using its units from the rear end and propagates the wave along its body, resulting in the net advancement in its position.
Stepper motor is located below, it take the snake from line mode to the bridge mode then ultra sonic sends the signals and it detects the human voice or the body heat and goes to the final goal (i.e. where the victim is there) after moving the debris. Then the victim is taken out and the first aid is given to the victim with the human help. It will be occupied with the rescue equipments. Diagram of the snake robot to the rescue is shown below:
DIAGRAM OF A SNAKE ROBOT
REQUIRMENTS OF ROBOCUP RESCUE
Basic Real Disaster:
Disaster information collector- Real world interface- Action command transmission
1) Seismometer 1) Traffic signals
2) Tsunami meters 2) Evacuation Signals
3) Video cameras 3) Electricity controls
4) Mobile Telecommunications 4) Rescue Robots
Design of rescue robots mainly aims at the flexibility of design rescue usage in disaster areas of varying property. Any two disaster do no have damage alike and no to regions are likely to exhibit similar damage. Thus rescue robots should be adaptable, robust and predictive in control when facing different and changing needs. They should be intelligent enough in order to handle all disturbances generated from different source.
The rescue robot needs virtual experiences and training. It should take optimal action in disaster. It should be equipped with parties of rescue, fire fighters and back supports.
Rescue robots should be equipped with a multitude of sensors of different types. Sensors are the weakest component of the rescue system. They should be robust enough in data collection and enough intelligence to minimize errors. Multiple inexpensive and accurate sensors should be used so that the robotic structure can be manufactured cheaply and used in rescue operations.
SENSOR BASED ON LINE PATH PLANING
This sections presents multisensor- based online path planning of a serpentine robot in the unstructured, changing environment of earthquake rubble during the search of living bodies. The robot presented in this section is composed of six identical segments joined together through a two-way, two degrees of freedom (DOF). The robot configuration of this section results in 12 controllable degrees of freedom. Ultrasound sensors used for detecting the obstacles and a thermal camera are located in the first segment (head). The camera is dust free, anti-shock casting and operates intermittently when needed. Twelve infrared (IR) sensors e=are located on the left and right of the joints of the robot along its body.
LOCAL MAP BUILDING
THE MODIFIED DISTANCE TRANSFORM
The modified distance transform (MDT) is the original distance transform method modified for snake robot such that the goal cell is turned in to a valley of zero values within which the serpentine robot can nest. Other modifications are also made to render the method on line
¢ Distance transform is first computed for the line of sight directed towards the intermediate goal, without taking into account sensorial data about obstacles and free space. This is the goal-oriented planning.
¢ The obstacle cells are superimposed on the cellular workspace. This modification to the original distance transform integrates IR data that represent the obstacles are assigned high values.
This modification of partitioning the distance transform (DT) application into goal oriented and range-data oriented speeds up the planning considerably, rendering it online. It is also observed that DT performed for an intermediate goal at an angular displacement from the line of sight different than zero angle displacement first. Then, the resultant workspace matrix is rotated by the required goal angle. Since the matrix resolution is finite (in our case 100*100), some cells remain unassigned. Therefore, we pass the matrix through a median filter that removes glitches in local map caused by un assigned cells.
MDT-BASED EXPLORAITY PATH PLANNING METHODOLOGY
The major aim of the serpentine search robot is to find and identify living beings under rubble and lock onto their signals until they are reached. Therefore, local map building is an essential component of our path planning approach. Since the objects in the rubble environment are expected to change position and orientation, the local map is used to find the next desired position of the robot on its way to a goal, the living being, placed in an initially unknown but detected location.
The ultrasound sensor scans to determine obstacles and free space and develops a local map. Thus, sensory data constructs a local map within this sensor range. After the local map is obtained, the next possible intermediate goals are found by considering points that are at the middle of the arcs representing free space. The intermediate goal is selected from the candidate next states by considering the directions of the candidate states relative to the robotâ„¢s head. In real applications, the direction that gives the highest signal energy (thermal, sound) received from the goal (living being) is selected as an intermediate goal. The intermittent function of the camera is also used for choosing the most appropriate intermediate goal. However, in the simulation here, we represent, for illustrative purposes, the magnitude of the signals coming from the main goal as inversely proportional to the distance between sensor and goal. Thus, this distance becomes minimum when the robot sensor faces the goal that is an emulation of the maximum signal energy coming from the goal. After the intermediate goal is found, the MDT method is applied, and the robot moves to this intermediate goal by using the serpentine gaits that are selected from those with minimum cost in the output of MDT. The cost function F(s) of the possible next gait state s is formulated as
Where wi is the weight of the ith control point, and C(xi ,yi) is the cost value obtained from the MDT for the ith control point located at xi and yi. Six discrete control points are taken into consideration and are used for calculating a cost function for a gait. These control points are used to find the candidate cells where each of the robot segments could possibly move after deciding upon a gait. So, each of these cell values are multiplied with a weight value representing the possibility in candidacy of each cell and added to the cost function. Weights of control points i depend on the ranking of the importance of contribution of each segment i to the snake displacement. This importance is a degree of constraint put on that segment during serpentine locomotion. A gait is selected such that it has minimum cost, which is a way of demonstrating that this gait is the one that requires the least body energy in its realization in the corresponding local map. Thus, we assign weights for each control point such that the front section has the maximum value and the end section has the minimum value. When the snake has to backtrack on its path, the weights are reversed: the tail portion having maximum value and the front a minimum value. After reaching the intermediate goal, the robot makes a new scan and determines a next intermediate goal in this new local map. This process is repeated until the robot reaches the closest neighborhood of the main goal. Fig.3 represents a sample of (snake + environment) interactions tracked by a simulation program, while Fig.4 shows the local map built by sensory data obtained for this (snake + closest-environment) interaction. In Fig.3, the fishbone structure on the robot shows the line of sight of the IR sensor pairs located on each side of the snake robot, while the front radial line is the line of sight of the ultrasound sensor. The small squares in the middle of the arc are the candidates for the intermediate goal. The suitable goal is selected according to its direction relative to the main goal. As stated previously, the one that is closer to the main goal is selected as the next intermediate goal.
The cubic obstacle head-front from the snake robot in Fig.3 is clearly seen in the local map of Fig.4. In this figure, the different gray levels represent the cost values obtained from MDT, where darker regions represent minimum values and brighter regions represent the higher cost values. Since the dimension of a local map is much smaller than that of a global map, the errors related to location and orientation of the robot are minimized when compared to finding the location with a global map. When the intermediate goal is reached, the current local map is not needed anymore, a new local map is constructed, and a new intermediate goal is selected.
DIFFERENT TYPES OF MOVEMENT
The locomotion of the snake-like robot is achieved by adapting the natural snake motions to the multisegment robot configuration [4]. For the current implementation, the robot has four possible gaits that result in four possible next states.
¢ Move forward with rectilinear motion or lateral undulation (two separate gaits):In rectilinear motion, the segments displace themselves as waves on the vertical axis. In lateral undulation, the snake segments follow lines of propagating waves in the horizontal 2-D plane.
¢ Move right/left with flapping motion (flap right/left): In flapping, two body parts of the robot undergo a rowing motion in the horizontal plane with respect to its center joint and then pull that center. This results in parallel offset displacement.
¢ Change of direction right/left with respect to the pivot located near the middle of the robot: The robot undergoes a rotation in the horizontal plane to the right or left with respect to the joint at or nearest to the middle of the snake.
SPECIFICATION OF PROTOTYPE
Most of the basic components of the unit are made of super “ duralumin alloy to get a lightweight structure. The nominal size of the fabricated units is 83*82*67 mm with a weight o 300g. The units have a one degree of freedom. The motors are equipped with stepper motors to drive joints, making it possible to have motion. The torque generated by the actuator is amplified to 34 times and thus maximum available torque is 20kgf/cm and maximum angular speed of 50degrees per second. When are connected in series, this specification allows each joint to lift five similar joints. The present design allows a maximum +/- 60degrees range of angular movement.
Actuator àStepping motor
Material àAluminum Alloy
Dimension à82*82*67 cubic mm
Weight à300g
Max: Torque à20kgf/cm
Max: angle velocity à50degrees per sec:
DEVELOPMENT OF PROTOTYPE MECHANISM
As stated earlier, rescue applications in disaster scenarios require robotic mechanisms to be hyper- redundant mechanisms that allow the mechanisms to effectively adapt to uncertain circumstances and carry out required activates with necessary flexibility. The basic units are concatenate in series to create a simple yet flexible hyper-redundant robotic prototype- some of which are shared in this article.
The specification of the basic components of the units is made of super-duralumin alloy get a light weight structure. The nominal size of the fabrication units.
¢ Twisting mode: In this mode, the robot mechanism folds certain joints to generate a twisting motion within its body, resulting in a side-wise movement.
¢ Wheeled-locomotion mode: This is one of the common wheeled-locomotion modes where passive wheels (without direct drive) are attached on the units, resulting in low friction along the tangential direction of the robot body line and increasing the friction in the direction perpendicular to that [5].
¢ Bridge mode: In this mode the robot configures itself to stand on its two end units in a bridge-like shape. This mode has the possibility of implementing two-legged walking-type locomotion. The basic movement consists of left-right swaying of the center of gravity in synchronism by lifting and forwarding one of the supports like, bipeclal locomotion. Motions such as somersaulting may be other possibilities.
¢ Ring mode: The two ends of the robot body are brought together by its own actuation to form a circular shape. The drive to make the uneven circular shape rotate is expected to be achieved by proper deformation and shifting of the center of gravity as necessary.
¢ Inching mode: This is one of the common undulatory movements of serpentine mechanisms. The robot generates a vertical wave shape using its units from the rear end and propagates the wave along its body, resulting in a net advancement in its position.
The following sections will consider the twisting mode and the wheeled locomotion mode and will present some of the preliminary results.
Twisting Mode of Locomotion
In the twisting mode, two of the joints of the robot body are bent in a way that the rest of the body experiences a twisting force, resulting in a side-wise shift after each twist. Since, in this case, no other parts of the robots are moved, the robot can effectively be considered as a three link robot. Since, in this mode, the number of actuated joints is very small, this is a very fault-tolerant mode of movement. Even in the case of the failure of a number of joints, this mode may be applicable. In Fig.8, the method of generation of the twisting motion is shown.
In the present work, two joints are assembled with a 900 shift and actuated to realize the desired motion. As shown in Fig.8, the adjacent unit axles (with 90° offset) are referred as j1 and j2,. Let zi be the rotational axis of the ith joint ji. Let us refer the three effective links as L1, L2 and L3. Let the initial condition (state 1) be that L1 is displaced by a relative angle of , with respect to L2 (by the joint j1) and the relative angle between L1 and L3 is kept to 0 0 (by the joint j2) It is assumed that all other links are fixed in a straight-line alignment, i.e., the relative angular displacement between the adjacent links is 0 0.
From this initial state, the joint j1 is driven in the counter clockwise (positive) direction and joint j2 in clockwise (negative) direction at the same time (state 2). When the relative angle at j1 becomes 0°, and the relative angle at j2 becomes d the robot body turns to one side by 90° (state 3), as shown in Fig. 8.
An example of twisting locomotion using the developed
Prototype is shown in Fig.9. In that assemblage, each consecutive unit is offset by 90°, and ten such units are connected together. The fifth and sixth units from one end are used for the actuation drive. If the active units are driven by two 90° phase-shifted sine waves, the robot body will generate a smooth and continuous side-turning locomotion. In Fig.9, three consecutive 90°, turning-action sequences are shown.
Wheeled Locomotion Mode
To realize smooth, undulatory serpentine movement, it has been shown [5] that there must be a large difference between the friction along the tangential direction and the perpendicular direction at any point of the robot body. In the present work, as shown in Fig.10 (schematic) and Fig.11 (prototype), drive-less, passive wheels are attached to the units. This makes it possible to achieve that necessary condition of undulatory motion.
If a sinusoidal drive is applied to the joints with proper positional phase difference, the mechanism will move forward following a serpentine curve [5]. In this mode, it is possible to get faster locomotion on a relatively flat surface. On the other hand, on uneven or irregular surfaces, this mode of locomotion is not likely to be an effective option. Also, in the case of surfaces with very low friction (e.g., over ice), efficiency is likely to be low. The top-view of the prototype motion in this mode is shown in Fig.12.
The frames in Fig.13 are taken at an interval of 4 s, and the distance scale is marked with 50-cm separation. In the prototype, ten units are connected with 90° offset of the joint axis. Thus, five of the units are actually in contact with the floor. In the experiment shown, actuation was given to those five units only, and the other joints are kept fixed. Those fixed joints may also be driven if movement in the third dimension is desired. In the experiment, the actuations are designed to generate a sinusoidal angular displacement of joint axes with a frequency of 0.12 Hz. The amplitude of angular oscillation of the active joints was selected to be 24°. The sinusoidal drives between the consecutive active joints are time shifted by an amount of 1.75 s. The resulting net forward motion of the robot was 4.0 cm/s.
DIFFERENT MODES OF SNAKE ROBOT
A GA-BASED PLANNING OF SHAPE TRANSITION
To transform the shape of the hyper-redundant robotic mechanism from one shape to another without losing structural stability, proper planning methodology is essential. In this section, one of the possible methods of shape transformation planning, using a genetic algorithm (GA) is considered. The desired result is to make the mechanism stand on its two ends in a vertical position.
The transformation from the initial to final configuration is divided in k intermediate configurations. The genetic search algorithm is used to find the optimal set of those k configuration sequence through which the robot shape is to be transformed. Each configuration describes the sequence of relative joint angles of the body. The whole structure is encoded as shown in the following expression:
Where 0i represents the ith relative joint in the jth configuration sequence.
To find the optimal sequence of joint angles, several performance indices are considered, and a weighted combination of them is used as the overall fitness function for the genetic search. The performance indices, considered in the present example are stability margin of the structure, smoothness of angular transformations between successive shapes, and smoothness in positional change of the center of gravity from one shape to the next. The detail definitions of the indices and other issues of GA search parameters are considered elsewhere.
CONCLUSION
Recent natural disasters and man-made catastrophes have focused attention on the area of emerge ncy management rescue .These experiences have shown that most governmentâ„¢s preparedness and emergency responses are generally inadequate in dealing with disasters. Considering the large number of people who have died due to reactive, spontaneous, and unprofessional rescue efforts resulting from a lack of adequate equipment or lack of immediate response, researchers have naturally been developing mechatronic rescue tools and strategic planning techniques for planned rescue operations.Aiming at the enhancing the quality of rescue and life after rescue, the field of rescue robotics is seeking dexterous devices that are equipped with learning ability , adaptable to various types of situations.
Considering various natural disasters and man-made catastrophes need for rescue robots is focused.
Research and development activities have resulted in the emergence of the field of rescue robotics, which can be defined as the utilization of robotics technology for human assistance in any phase of rescue operations, which are multifaceted. Research and development are going on for further modification of rescue robots.
REFERENCES
1. Snake Robots to the Rescue: by Aydan M.Erkmen, Ranjaith Chatterjee and Tetsushi Kamegawa.IEEE-ROBOTICS AND AUTOMATION.SEPTEMBER 2002
2. Working with Robots in disasters: by Tomoichi takahashi and Satoshi Tadokoro.IEEE-ROBOTICS AND AUTOMATION DECEMBER 2002
3. Be Prepared: by Louise K.Comfort.IEEE-ROBOTICS AND AUTOMATION.SEPTEMBER 2002
4. www.snakerobots.com
CONTENTS
1. INTRODUCTION 1
2. RESCUE ROBOTS 3
3. FUNCTIONS OF RESCUE ROBOTS 4
4. MAJOR RESCUE PROLEM 5
5. DESIGN OF THE SNAKE ROBOT 6
6. WORKING OF THE SNAKE ROBOR TO THE RESCUE 8
7. REQUIREMENTS OF THE RBOCOP RESCUE 10
8. SENSOR BASED ON LINE PATH PLANNING 11
9. MDT-BASED EXPLORAITY PATH PLANNING 12
METHODOLOGY
10. DIFFERENT TYPES OF MOVEMENT 14
11. SPECIFICATION OF PROTOTYPE 15
12. A GA-BASED PLANNING OF SHAPE TRANSITION 19
13. CONCLUSION 20
14. REFRENCES 21
ABSTRACT
The utilization of autonomous intelligent roots in search and rescue (SAR) is a new and challenging field of Robotics dealing with the task in extremely hazardous and complex disaster environments. Autonomy, high mobility, robustness and modularity is critical design issues of rescue robotics requiring dexterous devices equipped with the ability to learn from prior experience, adaptable to variable types of usage with a wide enough functionality under different sensing modules and compliant to environmental and victim conditions. Intelligent, biologically inspired mobile robots and in particular serpentine mechanisms have turned out to Widely used robot effective, immediate and reliable responses to many SAR operations. This article puts a special emphasis on the challenges serpentine search robot hardware, Sensor-based path planning and control design.