The problem of finding the smallest DNA tile set that self-assembles into a desired pattern or shape is a research focus that has been investigated by many researchers. In this paper, we take a polyomino, which is a non-square element composed of several connected square units, as an element of assembly and consider the design problem of the minimal set of polyominoes that self-assembles into a desired shape. We developed a self-assembly simulator of polyominoes based on the agent-based Monte Carlo method, in which the potential energy among the polyominoes is evaluated and the simulation state is updated toward the direction to decrease the total potential. Aggregated polyominoes are represented as an agent, which can move, merge, and split during the simulation. In order to search the minimal set of polyominoes, two-step evaluation strategy is adopted, because of enormous search space including many parameters such as the shape, the size, and the glue types attached to the polyominoes. The feasibility of the proposed method is shown through three examples with different size and complexity.

The ability to walk is particularly important to maintain a person's quality of life (QOL). In today's aged society, ways to support the impaired gait of elderly people with a decline in physical function is in great demand. This paper proposes wearable projector-based gait assistance as a novel application of mobile projectors. The technical challenge is to compensate the projected image with the intended position and size during walking. To verify the concept, we developed a self-gait training assistance system that displays stride length information on the floor while the user is walking. We conducted a study with ten healthy older adults (ages: 76-91). The results show the effectiveness of visual clues in controlling stride length and elderly people's acceptance of the wearable projector device.

Studies on supporting user task with a wearable projector are attracting attention in recent years. However, previous work did not consider the utilization in moving state because an image swing is caused by a body sway. Such instability of projected images does not only affect the viewability, but also makes it difficult to present spatial information. In this paper, we propose a projection stabilization method for wearable projector applications.

In this paper, we propose a concept of real-time walking support system for the elderly who need preventive care. The system presents visual information on the floor by a wearable projector. Moreover, we describe a method to reduce swing of projected images during walking. Such unstability of projected images does not only affect the view ability, but also makes it difficult to present spatial information, such as footstep. An implementation of a stabilizing functionality is presented. The result of a quantitative experiment showed that an error in the projected position was reduced by 48.7%. Additionally, the result of a qualitative evaluation supported the effect of stabilization.

This article shows how self-description can be realized for construction and computation in a single framework of a variant of graph-rewriting systems called graph-rewriting automata. Graph-rewriting automata define symbol dynamics on graphs, in contrast to cellular automata on lattice space. Structural change is possible along with state transition. Self-replication based on a self-description is shown as an example of self-description for construction. This process is performed using a construction arm, which is realized as a subgraph, that executes a program described in the graph structure. In addition, a metanode structure is introduced to embed rule sets in the graph structure as self-description for computation. These are regarded as universal graph-rewriting automata that can serve as a model of systems that maintain themselves through replication and modification.

This paper proposes a new method of locomotion control, named "stiffness distribution control (SDC)", to realize various locomotion of a closed link robot with mechanical softness. SDC directly defines the reference stiffness coefficient at each hinge by SDC string which represents the distribution of the stiffness. This simple method does not need costly calculation at all and thus is suitable for controlling closed link robots. We build "BIYOn" as the prototype of closed link robots, the variable stiffness hinge (VSH) of which is newly designed. SDC is experimented on BIYOn and then it's found that SDC is effective in a controlling locomotion in practice. We also develop a systematic optimization method of stiffness distribution composed of two-stage approach and succeed in optimization to obtain a fast and smooth rolling motion and a sudden stopping motion

We have been developing a self-reconfigurable robot M-TRAN. In this paper, we focus on the docking of M-TRAN modules. In order to dock modules in separate configurations, we use a camera module, which is compatible to the M-TRAN system. Proposed docking is a combination of a simple visual feedback procedure and a special docking configuration to absorb positional errors. We verified reliability of the docking method by experiments

Automated construction is in high demand in many applications in the extreme environments. Fully automatic construction system is desired but difficult to realize for many reasons. We have proposed a novel concept of full-automated construction called automatic modular assembly system (AMAS), which drastically reduces the difficulty of automated construction task. In this paper, we focus on distributed control method of the assembler robots. We assume large number of modules and robots; therefore we need to organize the motion paths of these robots to avoid collision among them. Moreover, the area on which the assembler robots can move dynamically expands during the construction process. In order to optimize the complex coordinated motion among the assembler robots, we introduce a distributed algorithm based on a gradient field. The structure modules generate the gradient field by using neighbor-to-neighbor communication, and the robots are led by the field. Incorporating some additional rules for the field and robots, we can make a kind of self-organized flow on the system, and it enables collision-free and time-effective assembly. Some results of simulations give quantitative evaluation of the algorithm

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.

The main difficulty of construction automation is the variety of materials. To cope with this problem, we propose a concept of automated assembly system for a modular structure. This system uses passive building blocks called "structure modules" and an assembler robot that is specialized to handle them. This "modular" concept drastically simplifies structural construction and allows automation. This paper describes the hardware design of the structure module and the assembler robots. Especially, the connection mechanism, the essential element of the system, is explained in detail. We built a prototype model based on the design to evaluate its automatic construction capability. Some experimental results illustrate the feasibility of the proposed method.

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.

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.

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.

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.

We propose a novel method of self-organizing formation. It is assumed that elements are not connected to each other and they can move in continuous space. The objective is to arrange elements in a certain spatial pattern like a crystal, and to make the outline of the group in the desired shape. For this purpose, we propose a method by using virtual springs among the elements. In this algorithm, an element generates virtual springs between the neighbor element based on information of how many other elements exist in the neighborhood with a certain radius. Although the elements interact locally, only by virtual springs, and they do not have global information at all, they form a shape much larger than the sensory radius. By a simulation study, we confirmed convergence to a target shape from a random state in very high probability. This kind of algorithm gives a new principle of self-organizing formation, and its simplicity will be useful for the design of self-assembling nano machines in future.

We have proposed a self-reconfigurable robotic module, which has a very simple structure. The system is capable of not only building a static structure, but also generating a dynamic robotic motion. We have also developed a simulator for the motion planning. In this paper, we present details of the mechanical and electrical designs of the developed module and its control system architecture. Experiments using ten modules demonstrate the robotic configuration change, crawling locomotion and three types of quadruped locomotion.

This paper addresses motion planning of a homogeneous modular robotic system. The modules have self-reconfiguration capability so that a group of the modules can construct a robotic structure. Motion planning for self-reconfiguration is a kind of computationally difficult problem because of many combinatorial possibilities of modular configuration and the restricted degrees of freedom of the module; only two rotation axes per module. We will show a motion planning method for a class of multimodule structures. It is based on global planning and local motion scheme selection that is effective to solve the complicated planning problem.

In this paper we describe the hardware design of a novel self-reconfigurable robotic system. We have classified previous studies on self-reconfigurable robotic systems into "lattice type" composed of spatially symmetric modules and "string type" like snake robots. The proposed system has both the advantages of simple operation of self-reconfiguration of the former and motion generation ability of the latter. Its simple structure and reliable operation allows us to construct large 3D self-reconfigurable structure which functions as a robotic system such as a legged walking machine. We have examined its basic mechanical functions and verified its reliable operation of self-reconfiguration.

Presents a miniaturized self-reconfigurable modular robotics system using shape memory alloy (SMA). The system is designed so that various shapes can be actively formed by a group of identical mechanical units. The unit realizes rotational motion by using an actuator mechanism composed of two SMA torsion coil springs which generate sufficient motion range and torque for reconfiguration. The fundamental functions of the system are tested by experiments. Applicability of the developed unit model to a 3-D self-reconfigurable system is also discussed.

We propose a self-assembly and self-repair method for a homogeneous distributed mechanical system. We focus on a category of distributed systems composed of numbers of identical units which can dynamically change connections among themselves. Each unit has an onboard microprocessor, and local communication between neighboring units is possible. We discuss a distributed method for a group of such units to metamorphose from an arbitrary configuration into a desired configuration through cooperation by the units. This process, called self-assembly, is realized by identical software on each unit with local inter-unit communication. An extension of self-assembly, self-repair, is also examined. In this process, an occasional cut-off of an arbitrary part of the system is assumed. When some part of the system detects damage, the whole system degenerates and reconstructs itself. Computer simulations show the feasibility of self-assembly and self-repair.

A three-dimensional, self-reconfigurable structure is proposed. The structure is a fully distributed system composed of many identical 3-D units. Each unit has functions of changing local connection, information processing, and communication among neighborhood units. Groups of units cooperate to change their connection so that the shape of the whole solid structure transforms into an arbitrary shape. Also, the structure can repair itself by rejecting faulty units, replacing them with spare units. This kind of self-maintainability is essential to structure's longevity in hazardous or remote environments such as space or deep sea where human operators cannot approach. We have designed and built a prototype unit to examine the feasibility of the 3-D self-reconfigurable concept. The design of the unit, method of reconfiguration, hardware implementation, and results of preliminary experiments are shown. In the last part of the paper, distributed software for self-reconfiguration is discussed.

A three-dimensional self-reconfigurable structure made of identical units is proposed. Each unit has six arms on the surface of its base cube which can connect to neighboring units mechanically. By the connection, cubic lattice structure is formed. A unit can carry its neighbor unit from one node of the lattice to another by rotating its arm by 90 degrees. Repeating this movement, the structure can reconfigure itself to realize various 3D structures. General process of reconfiguration were proposed for this system. Four units were made and basic motions of self-reconfiguration were verified.

A distributed reconfiguration method is proposed for a 3D reconfigurable machine, composed of many identical mechanical units. The method aims to enable the machine to transform itself into desired structure from an arbitrary initial configuration. The proposed method is implemented in such a way that each unit has identical software, so that any unit can play any role in the system. It is also featured by a stochastic relaxation process, which allows the system to converge to a given target structure by searching for a proper unit motion over many degrees of freedom. Furthermore, the method is extended for the structure to reconfigure itself dynamically according to the environment. The effectiveness of the method is confirmed by computer simulations.

A distributed formation control method is proposed for a modular mechanical system. We have developed a totally decentralized system composed of many homogeneous mechanical units which are designed to change their connective configuration using only local information. The control method proposed in this paper enables the systems to re-organize themselves so that various configurations can be formed in a robust way. Computer simulations and experiments are carried out to show its effectiveness.

The design of a machine which is composed of homogeneous mechanical units is described. We show the design of both hardware and control software of the unit. Each unit can connect with other units and change the connection by itself. In spite of its simple mechanism, a set of these units realizes various mechanical functions. We developed the control software of the unit which realizes "self-assembly," one of the basic functions of this machine. A set of these units can form a given shape of the whole system by themselves. The units exchange information about local geometric relation by communication, and cooperate to form the whole shape through a diffusion-like process. There is no upper level controller to supervise these units, and the software of each unit is completely the same. Three actual units have been built to test the basic movements, and the function of self-assembly has been verified by computer simulation.>