Shigeru Kokaji

National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan

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Publications (57)18.04 Total impact

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    ABSTRACT: A new prototype of a self-reconfigurable modular robot, M-TRAN III, has been developed, with an improved fast and rigid connection mechanism. Using a distributed controller, various control modes are possible: single-master, globally synchronous control or parallel asynchronous control. Self-reconfiguration experiments using up to 24 modules were undertaken by centralized or decentralized control. Experiments using decentralized control examined a modular structure moved in a given direction as a flow produced by local self-reconfigurations. In all experiments, system homogeneity and scalability were maintained: modules used identical software except for their ID numbers. Identical self-reconfiguration was realized when different modules were used in initial configurations.
    The International Journal of Robotics Research 01/2008; 27:373-386. · 2.86 Impact Factor
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    ABSTRACT: Metamorphosis by a self-reconfigurable modular robot is presented in this report. We have developed a new prototype, “M-TRAN III”, which is improved in its high speed and rigid connection mechanism. Using its integrated design of a multi-CPU controller with various programming tools, experiments of self-reconfiguration were successfully carried out through single master synchronous control. Based on the obtained results, decentralized and locally synchronous control was accomplished, which controlled self-reconfiguration of up to 20 modules using the same program.
    06/2007: pages 115-124;
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    ABSTRACT: M-TRAN is a self-reconfigurable modular robot: each module has an independent battery, two-degree-of-freedom motion, six-surface-connection capability, and intelligence with inter-module communication. The M-TRAN system can perform flexible and adaptive locomotion in various configurations using coordination control based on a central pattern generator (CPG). Various structures of several modules can perform metamorphosis, such as that between a four-legged robot and a snake-like one. In addition to these self-reconfigurations with synchronous control, M-TRAN structures having regularity can move using parallel distributed control and message exchange via the network bus. Self-reconfiguration using infrared local communication has been attempted to improve the system's scalability.
    Proceedings of the 1st International Conference on Robot Communication and Coordination, ROBOCOMM 2007, Athens, Greece, October 15-17, 2007; 01/2007
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    ABSTRACT: A behavior planning method is presented for reconfigurable modular robots with coherent structure using a randomized planning. Coherent structure is introduced to cope with difficulty in planning of many degrees of freedom, in terms of control system and robot configuration. This is realized by a phase synchronization mechanism together with symmetric robot configuration, which enables the robot to generate various coherent dynamic motions. The parameters of control systems are explored using a randomized planning method called rapidly exploring random trees (RRTs). The RRT planner has an advantage of simple implementation as well as possibility of integrating differential constraints. The dynamic robot motion is thus planned and preliminary simulation results are shown to demonstrate the proposed planning scheme can generate appropriate behaviors according to environments.
    12/2006: pages 149-158;
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    ABSTRACT: The M-TRAN is a modular robot capable of both three-dimensional self-reconfiguration and whole body locomotion. Introducing regularity in allowed structures reduced difficulties of its reconfiguration problems. Several locomotion patterns in various structures were designed systematically using a CPG controller model and GA optimization. Then they were verified by experimentation. Results showed a feasible scenario of operation with multiple M-TRAN modules, which is presented herein, including metamorphosis of a regular structure, generation of walkers from the structure, walker locomotion, and reassembling of walkers to the structure.
    Robotics and Autonomous Systems. 01/2006; 54:142-149.
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    ABSTRACT: Geometric self-reconfiguration sequences and a distributed control method are developed for the modular robot M-TRAN. Large scale self-reconfiguration contains several clusters of modules moving in parallel. A decentralized and asynchronous control is suitable for such a task. A multi thread type simulation program was developed to design and verify such self-reconfiguration sequences. A distributed controller system was developed for the new M-TRAN hardware, which can realize decentralized and asynchronous control of modules. Its basic functions were verified by experiments.
    Mechatronics and Automation, 2005 IEEE International Conference; 01/2005
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    ABSTRACT: This paper presents a design method and experiments for whole-body locomotion by a modular robot. There are two types of locomotion for modular robots: a repeating self-reconfiguration and whole-body motion such as walking or crawling. For whole-body locomotion, designing a control method is more difficult than for ordinary robots because a modular robotic system can form various configurations, each of which has many degrees of free-dom. This study proposes a unified framework for automatically designing an efficient locomotion controller suitable for any mod-ule configuration. The method utilizes neural oscillators (central pattern generators, CPGs), each of which works as a distributed joint controller of each module, and a genetic algorithm to optimize the CPG network. We verified the method by software simulations and hardware experiments, in which our modular robotic system, named M-TRAN II, performed stable and effective locomotion in various configurations.
    IEEE/ASME Transactions on Mechatronics 01/2005; 10. · 3.14 Impact Factor
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    ABSTRACT: A method for behavior planning is presented for a modular robot that applies a randomized planner to coherent structure of the robot. To cope with difficulty in planning of many degrees of freedom (DOFs) of a modular robot, coherent structure is introduced in terms of control system and robot configuration. As the control system, a simple phase synchronization mechanism is introduced that can control the robot with many DOFs with reduced number of parameters. Together with symmetrical configuration, this control system generates various dynamic motions. In order to plan the behaviors of the modular robot determined by the parameters of the control system, we adopt a randomized planner called rapidly exploring random trees (RRTs). This can benefit from a number of advantages of RRT planner, including simple implementation, uniform search, and applicability to a dynamic system with differential constraints. By exploring parameter space of the coherent control system, behaviors including dynamic motions can be planned. We have applied the proposed planner to M-TRAN modular robot to demonstrate the effectiveness of the proposed method through preliminary simulation results.
    Intelligent Robots and Systems, 2004. (IROS 2004). Proceedings. 2004 IEEE/RSJ International Conference on; 11/2004
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    ABSTRACT: The M-TRAN is a modular robot capable of both three dimensional self-reconfiguration and whole body locomotion. The difficulties of its self-reconfiguration problem were reduced by introducing regularity in allowed structures. Several locomotion patterns in various structures were designed systematically and verified by experiments. Based on those results, a feasible scenario of operation with multiple M-TRAN modules is presented, including metamorphosis of a deformable multi-module structure, generation of walkers from the structure, walker locomotion and reassembling of walkers to the structure.
    01/2004;
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    ABSTRACT: A modular robot has a distributed mechanical composition which can make various configurations and also make locomotion in a wide variety of configurations. Modular robots are thought to be useful in extreme or unknown environments by adaptively changing their shape and locomotion patterns. As for locomotion, two types can be used; one is whole-body fixed-configuration locomotion and the other is locomotion by self-reconfiguration. In this paper we deal with the former type of locomotion which is realized by coordinated joint actuation. So far, proposed control methods for whole-body locomotion by modular robots have been based on predefined locomotion sequences. However, locomotion based on predefined sequences cannot adapt to changing terrain conditions such as uphill, downhill, slippery and sticky grounds. To solve such problems, we propose a distributed control mechanism using a CPG controller which enables adaptive locomotion by modular robots. Besides the real-time CPG control we introduce a decentralized control mechanism for detecting the situation that the robot is stuck and initiating transformation to another shape for recovering the situation. The results of various hardware experiments by 4-legged structure prove the feasibility of the method for adaptive locomotion and transformation by our M-TRAN II modules.
    Intelligent Robots and Systems, 2004. (IROS 2004). Proceedings. 2004 IEEE/RSJ International Conference on; 01/2004
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    ABSTRACT: We have been developing a self-reconfigurable modular robotic system (M-TRAN) which can make various 3-D configurations and motions. In the second prototype (M-TRAN II), various improvements are integrated in order to realize complicated reconfigurations and versatile whole body motions. Those are a reliable connection/detachment mechanism, on-board multi-computers, high speed inter-module communication system, low power consumption, precise motor control, etc. Programing environments are also integrated to design self-reconfiguration processes, to verify motions in dynamics simulation, and to realize distributed control on the hardware. Hardware design, developed software and experiments are presented in this paper.
    Intelligent Robots and Systems, 2003. (IROS 2003). Proceedings. 2003 IEEE/RSJ International Conference on; 11/2003
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    ABSTRACT: In this paper we present the development of hardware and software of self-reconfigurable modular robots in National Institute of Advanced Industrial Science and Technology (AIST), Japan. Thanks to their flexibility, versatility and fault-tolerance, self-reconfigurable modular robots are expected to be used in various application fields, such as space, rescue or micro-sized world. Our research group has been pioneering this new field and developed several hardware prototypes and corresponding software that exploit the robots' potential. We have been successfully demonstrated the feasibility of the self-reconfigurable modular robots based on experiments from different aspects. Starting from two-dimensional (2D) self-assembling and self-repairing machine fractum, we review hardware development in diverse directions, like to micro-world, three-dimensional (3D) structures and motions; as well as the progress of control software, including distributed control and recent evolutionary motion inquisition.
    Robotics, Intelligent Systems and Signal Processing, 2003. Proceedings. 2003 IEEE International Conference on; 11/2003
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    ABSTRACT: Locomotion, one of the most basic robotic functions, has been widely studied for several types of robots. As for self-reconfigurable modular robots, there are two types of locomotion; one type is realized as a series of self-reconfiguration and the other is realized as a whole body motion such as walking and crawling. Even for the latter type of locomotion, designing control method is more difficult than ordinary robots. This is because the module configuration includes many degrees of freedom and there are a wide variety of possible configurations. We propose an offline method to generate a locomotion pattern automatically for a modular robot in an arbitrary module configuration, which utilizes a neural oscillator as a controller of the joint motor and evolutionary computation method for optimization of the neural oscillator network, which determines the performance of locomotion. We confirm the validity of the method by software simulation and hardware experiments.
    Robotics and Automation, 2003. Proceedings. ICRA '03. IEEE International Conference on; 10/2003
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    ABSTRACT: In this paper we present a couple of evolutionary motion generation methods using genetic algorithms (GA) for self-reconfigurable modular robot M-TRAN and demonstrate their effectiveness through hardware experiments. Using these methods, feasible solutions with sufficient performance can be derived for a motion generation problem with high complexity coming from huge configuration and motion possibilities of the robot. The first method called ERSS (Evolutionary Reconfiguration Sequence Synthesis) applies GA (Genetic Algorithm) to evolution of motion sequence including configuration changes though natural genetic representation. The effectiveness of the generated full-body dynamic motions are verified through hardware experiments. The second method called ALPG (Automatic Locomotion Pattern Generation) Method seeks locomotion pattern using a neural oscillator as a CPG (Central Pattern Generator) model and GA to optimize the parameters for locomotion. A number of efficient locomotion patterns has been derived, which are also experimentally verified.
    Computational Intelligence in Robotics and Automation, 2003. Proceedings. 2003 IEEE International Symposium on; 08/2003
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    ABSTRACT: We have developed a modular robotic system (M-TRAN), which can change its configuration by itself. By using many DOFs of mechanism and self-reconfiguration capability, it can realize several types of motion, and can make various configurations. We have made two models of the system (M-TRAN I & II). In M-TRAN II, various improvements are integrated such as onboard multi-computers, reliable inter-module communication system, low power consumption, precise motor control, etc. Its hardware design, basic experiments and examples of motion are presented in this paper.
    Control, Automation, Robotics and Vision, 2002. ICARCV 2002. 7th International Conference on; 01/2003
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    ABSTRACT: An evolutionary motion synthesis method using genetic algorithm (GA) is presented for self-reconfigurable modular robot M-TRAN designed to realize various robotic motions and three-dimensional structures. The proposed method is characterized by its capacity to derive feasible solutions for complex synthesis problem of M-TRAN through natural genetic representation. For this purpose, the behavior of the robot is described using a motion sequence including both the dynamic motions and configuration changes of the robot. It is a series of segments each of which can specify simultaneous motor actuations and self-reconfiguration by connection/disconnection, starting from a given initial configuration. This simple description can be straightforwardly en-coded into genetic representation to which genetic operations can be applied in a natural manner. We adopt traveling distance achieved by the evolved motion as the fitness function of GA. To verify the effectiveness of the proposed method, we have conducted simulations of evolutionary motion synthesis for certain initial configurations. Consequently, we confirm various adaptive motions are acquired according to different initial configurations and fitness functions. We also verify the physical feasibility of the evolved motions through experiments using hardware module M-TRAN II.
    Journal of Robotics and Mechatronics. 01/2003;
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    ABSTRACT: We have studied modular self-reconfigurable robots that are capable of changing their overall shape and functionality by automatic recombination of homogenous robotic modules. Our latest model, called Modular Transformer (M-TRAN), is able to metamorphose into various 3-D configurations and gen- erate robotic motions that are suitable to its configuration. This paper presents a review of hardware design of the module, some developed software for self- reconfiguration and motion generation, and some experimental results.
    Ad-Hoc, Mobile, and Wireless Networks, Second International Conference, ADHOC-NOW 2003 Montreal, Canada, October 8-10, 2003, Proceedings; 01/2003
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    ABSTRACT: Self-reconfigurable robotic systems composed of multiple modules have been investigated intensively with respect to their versatility, flexibility, and fault-tolerance. Although some microscale self-assembly systems have been reported, they are passively assembled to predetermined shape by surface tension in an irreversible manner and cannot form arbitrary shapes. To develop a modular microrobot that can actively reconfigure itself, we adopt an actuating mechanism driven by a shape memory alloy (SMA). One of the advantages of an SMA actuator is that it keeps a higher power-weight ratio on microscales than electromagnetic motors.
    IEEE Robotics &amp amp amp Automation Magazine 01/2003; · 2.48 Impact Factor
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    ABSTRACT: In this paper, a novel robotic system called modular transformer (M-TRAN) is proposed. M-TRAN is a distributed, self-reconfigurable system composed of homogeneous robotic modules. The system can change its configuration by changing each module's position and connection. Each module is equipped with an onboard microprocessor, actuators, intermodule communication/power transmission devices and intermodule connection mechanisms. The special design of M-TRAN module realizes both reliable and quick self-reconfiguration and versatile robotic motion. For instance, M-TRAN is able to metamorphose into robotic configurations such as a legged machine and hereby generate coordinated walking motion without any human intervention. An actual system with ten modules was built and basic operations of self-reconfiguration and motion generation were examined through experiments. A series of software programs has also been developed to drive M-TRAN hardware, including a simulator of M-TRAN kinematics, a user interface to design appropriate configurations and motion sequences for given tasks, and an automatic motion planner for a regular cluster of M-TRAN modules. These software programs are integrated into the M-TRAN system supervised by a host computer. Several demonstrations have proven its capability as a self-reconfigurable robot.
    IEEE/ASME Transactions on Mechatronics 01/2003; · 3.14 Impact Factor