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Development of Cooperative Mini Robots

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Development of Cooperative Mini Robots
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   21 CHAPTER 4   Development of Cooperative Mini Robots   Amir A. Shafie 1.a , Siti E.M.Z 2 and Shazeela A. 3 , 1,2,3 Department of Mechatronics, Kulliyah of Engineering,International Islamic University Malaysia (IIUM), 50728Kuala Lumpur a aashafie@iium.edu.my 4.1 Introduction Many teams of intelligent robots have been developed at different labs for mainly for researchissues in specific areas of collaborative and cooperative work. The teams of intelligent robots canalso be classified according to the robotic system either homogeneous or non-homogeneous.   Cooperative actions can be defined as to associate with another for mutual, often economic benefit.It also can be defined as joint collaborative behaviour that is directed toward some goal in whichthere is a common interest or reward, the form of interaction usually based on communication.   Cooperative behaviors enable a team of mobile robots to accomplish missions that cannot beachieved with individual mobile robot. Since each of robots is only responsible for partialfulfillment of the task, the robots can be less complex. Multiple robots can be used for numeroustasks such as foraging and coverage, box pushing and object transportation, exploration andflocking, multi-target observation as well as entertainment purposes such robotic soccer orcoordinated dancing robot.In this paper, a description of the design and structure of a pair of mini robot to be used incooperative work is presented. The immediate aim of the development is to design and develop apair of mini robot which has the ability of moving and balancing the long beam at the same time.Each of the robots can be programmed to be a leader or follower, whereby the leader will beinstruction to other robots whilst the follower will receive instructions from the leader robot. Therobots as presented here are homogeneous multi-robot system as both of the robots are similar witheach other (sensor, microcontroller and mechanical components). Implicit communication wherethe robots communicate through physical interaction is implemented. 4.2 Literature Review Farinelli et al. [1] classified the works on multi-robot system (MRS) as two group of dimensions;Coordination dimensions and System dimension. Coordination dimension is divided into four level;Cooperation, Knowledge, Coordination and Organization.   The first level, Cooperation level is focused on the ability of the system to cooperate in order toaccomplish a specific task. The second level, Knowledge level is concerned with the knowledge theteach robot in the team has about its team mates. In this level, there is aware and unaware robotwhich the former robot has knowledge of their team mates while the latter robot is in the other wayround. The Coordination level is concerned with the mechanism used for cooperation. The finallevel, Organization level introduces the distinction in the form of coordination, distinguishingcentralized approach from distributed ones.     22 System dimension meanwhile concentrate on the intra-robot communication, team composition,system architecture and team size. In this dimension the team of robots is considered as one singleentity as opposed to different entity in the Coordination dimension.   Burgard et al [2] presented an algorithm that considers the utility of unexplored areas and the costfor reaching these areas. The aim of the exploration process is to cover the whole environment in aminimum amount of time. Cao et. Al. [3] described in their paper the five research axes which arethe main points in order to achieve cooperative behaviour. Firstly, the group architectureencompasses such concepts as robot heterogeneity, homogeneity, the ability to recognize otherrobot and communication structure. Next, a mechanism is needed in order to resolve resourceconflict.   Hougen et al.[4] present their design philosophy for robotic teams involved in distributedexploratory mission such as military reconnaissance, scientific exploration, security patrols,surveying as well as survivor detection and location. They have designed and built a team of robots,‘scouts’ which is suitable for a range of distributed exploratory missions..   Jung et. al. [5] develops and designs a multi-robot cooperative cleaning which are heterogeneousmulti-robot systems. There are two autonomous mobile robots named Flo and John, which havedifferent tools and sensors that neither can accomplish the task alone. Rybski et. al. [6] discussedabout the foraging experiments using real robot – Minnesota Distributed Autonomous RoboticTeam (MinDART). The main objective of the experiment is to explore the effects of differentsimple communication strategies on performance of robot teams. There are three sub taskscomprising the search and retrieval task, which are find a target, grab a target and return a target tohome base.   Rybski et al. [7] describes on their paper about the scouts and their performance in the UrbanSearch and Rescue (USAR) course. The scouts robot had to enter the enter the course which haddebris on the floor, passages that were partially blocked and difficult to traverse and a second levelthat could be reached by a ramp a staircase. Scouts are designed to be hand-deployed, thrown orlaunched into the operating area.   This literature review summarised some recent approaches in completing tasks given with the use of a team of robot. The design of the robots reported here will take some cues from the researchsummarized in this section.   4.3 Methodology The objectives of the robot design are to create a robot (either leader or follower) that is efficientand cost effective [8]. Efficiency here can be defined as ease of assembly, communication andability to work cooperatively. The cost of the robot is described by the cost of material andprocesses.   Fig. 1 Project objective tree     23 4.4 Methodology The functional composition describes the function of the overall design as well as the function of each sub-component. It shows the connection of each of the sub-component of the mini-robotincluding sensors, microcontroller and the mechanical actuators. This is how the flow of equipmentto be laid out on the hardware side.   Fig.2 Functional composition   4.5 Conceptual Design   Fig. 3 Side view of the conceptual design of mini robot   The robot will be moved using two wheeled connected to a single motor. A caster is added forsupport at the front of the robot. IR sensor will be used for detecting obstacles. The position of thebalanced beam will be indicated by two pairs of photoelectric sensors (R1, R2). The robot willmoveforward cooperatively until the R1 and R2 indicate the beam is balanced.   4.6 Application Design In order to simplify the design of the application of the mini robot the objective of the movementisdivided into tasks and subtasks. As each of the mini robot will have a different role the tasks andsubtasks can also be viewed according to the robot requirement.   The task of the leader robot is to initiate the movement so that the follower robot can mimic withthe objective of moving the beam forward. The leader robot will initiate the forward move until thephotoelectric sensor signal activates to imply that the beam is in unbalanced condition. At this stagethe leader robot will stop and the follower robot will move forward.   Sensor   Communication   M o t   or  Wh  e  e l   On M o v e m e n t   Wh  e   e l     24 The loop will continue until the leader robot sensed an obstacle in front of it, where by at thispointthe robot will stop moving. The logical structure of the system is represented in the form of truthtable presented in Table 1.   Table 1: Truth Table   Translating the truth table into program flowchart shows the implementation of the logic system.Fig. 4 Mini robot application flowchart   4.7 Analysis of Results   Analysis of the system in term of its cooperative behaviour will depend mainly on thecommunication ability of the system. In this case the implemented communication is via reflectivecommunication where the robot will react to its partner. Reflective communication implementationdoes not require large vocabulary.   On the other hand the scalability of the system is restricted due to the close cooperation between theleader robot and follower robot. This effectively do not allow additional robot to be inserted due tothe ‘close’ system implemented here.   Photoelectricsensor   InfraredProximitysensor   Infraredsensor(transmitter)   Motor   R1   R2   Output   1   1   1   1   1   0   1   1   1   0   1   1   2   1   0   0   1   1   1   2   1   1   0   1   0     25 The localization of the system is also restricted due to the communication vocabulary that onlyconsists of the condition of the beam. Relating to this limited degree of intelligence the localizationof the system is adequate only for this specific task.   The system performance in environmental factors is not analysed as the simplistic search andcommunication strategies implemented here do not support the environmental disturbances. Basedon the literature review it is expected that the localization will greatly assist the robot in the non-uniformly distributed environment.   4.8 Summary In this chapter we have presented a cooperative mini-robots with design requirements formulatedthrough Coordination Dimensions (team coordination) and System dimension (teamorganization).Thus the prototype formulated is thoroughly suited for the application domains.Communication experiments were designed to test the robot's abilities to lead each other to a singleclump of targets. One hypothesis was that once one robot located the group of targets, it would leadthe others to that group and thus the overall time to pick up the targets would decrease. Robots thatcommunicated typically had reduced variance in the time to complete the task as well sin the timeto retrieve a new target after dropping one.   However, the analysis of the recent works in the literature shows that for more complex tasks (e.g.Soccer, Rescue missions, etc.), where the unpredictable, uncertain and sometimes competingenvironment requires both a very effective performance and high robustness, more complexcoordination capabilities are required.Summarizing, this paper addressed in the present work may covers a broad range of approacheswith many form of coordination that can vary significantly depending on the task to be performed.The complexity of the tasks in which robots are involved (e.g. building patrolling, large-scaleassembly, rescue operations) entails increasingly complex capabilities both in software and inhardware.In the recent efforts on large scale systems, heterogeneity is often chosen over homogeneity in orderto exploit different robot capabilities and reduce the cost of the overall system [9]. However in thiswork homogeneous solution also can complete the most complex tasks selected here which iscooperative localization. 4.9 References [1] Dj.M. Maric, P.F. Meier and S.K. Estreicher: Mater. Sci. Forum Vol. 83-87 (1992), p. 119[2] M.A. Green:  High Efficiency Silicon Solar Cells (Trans Tech Publications, Switzerland 1987).[3] Y. Mishing, in:  Diffusion Processes in Advanced Technological Materials , edtied by D. GuptaNoyes Publications/William Andrew Publising, Norwich, NY (2004), in press.[4] G. Henkelman, G.Johannesson and H. Jónsson, in: Theoretical Methods in Condencsed PhaseChemistry, edited by S.D. Schwartz, volume 5 of Progress in Theoretical Chemistry andPhysics, chapter, 10, Kluwer Academic Publishers (2000).[5] R.J. Ong, J.T. Dawley and P.G. Clem: submitted to Journal of Materials Research (2003)[6] P.G. Clem, M. Rodriguez, J.A. Voigt and C.S. Ashley, U.S. Patent 6,231,666. (2001)[7] Information on http://www.weld.labs.gov.cn
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