Research On Reconfigurable Strategy Of Modular Self-Reconfigurable Robot Based On Crystal's Crystallization Theory

A modular self-reconfigurable robot (MSR) is a complex distributed system which is composed of multiple modular robotic units. These units can be rearranged to form different structures for adapting to specific tasks. This kind of robot has many merits, such as extensibility, variety of robot's configuration, and adaptation to the environment and tasks. MSR is especially suitable for the situations of unknown environment and changing tasks. MSR is composed of many modules, which can be combined in many different ways. Hence, it provides an ideal platform for checking self-reconfiguring planning strategy and artificial intelligence (AI) searching algorithm. Therefore, the research on the MSR system has the important theoretical and practical significance to enhance the research level and extend the application backgrounds. Meanwhile, some new problems about the robot structure design, self-reconfiguring theory and motion planning come with the proposed MSR.MSR body is the foundation for studying all the related contents in MSR research. Its structural characteristics directly affect the robot's motion mode and the establishment of the self-reconfiguring theoretical model. After analysis on structural properties of essential unit cell and the functions needed for MSR, a novel cubic crystal cell module with one degree of freedom (DOF) is developed, which is composed of double L-like components. Double L-like components of a cubic crystal cell module are linked by a server motor. Modules are divided into active and passive categories. Active modules and passive modules can be connected by a planar self-locking connecting mechanism. Such mechanism consists of rotating hooks, hole and direct-current deceleration micro-motor. In order to get the whole structure of the robot configuration visually and clearly, the robot configuration is described by topological theory. When a computer deals with the robot configuration information, the spatial position of a module is described by an array which contains ten elements. Connections and connection azimuths between two arbitrary connecting modules are recorded in the configuration by a topology connection table and a node connection table, in which the spatial position of the robot and the connection relationship between the modules are expressed exactly.Self-reconfiguring theory is an important research domain in the study of self-reconfigurable robot, and is a key factor which has influence on whether MSR can be applied in practice or not. In order to describe self-reconfiguring process according to crystal's crystallization theory, after analysis on the similarities between crystal crystallization process and the self-reconfigurable process, this paper analyzed self-reconfiguring process of self-reconfigurable robots simulating crystal's crystallization. Firstly, the growth center, the center for changing module's azimuth and the module placement center are set up. Secondly, the growth process of goal configuration is determined by layer growth theory of crystal crystallization. Finally, the moving process and changing azimuth of the module are realized by single module that is assisted by meta-module. At the same time, the self-reconfiguring process model based on crystal's crystallization oriented to cubic cell robot system is established. The model complies with general execution steps of self-reconfiguring process simulating crystal's crystallization. Besides, the growth direction, the priority of positions to grow, the shape of meta-module, the method of transferring goal module, the method of placing goal module and the method of changing azimuth of goal module are planned in detail. The designed meta-module is called windmill-like crystal cell group (WLCCG). It has the abilities of moving, self-reconfiguring, changing azimuth of the other modules and carrying other modules. These abilities are helpful for the module to realize free motion. The motion is similar to the molecular motion.When the problem about how to realize transition between two different states are handled, the methods usually adopted are as follows: Firstly, find some common points between two states. Secondly, seek some concrete schemes of solving problem. Thus some problems can be simplified by this method and it is most important that the efficiency of problem solving can be improved. Aiming to the case that the numbers of modules in the initial and goal configuration are relatively few, self-reconfigurable planning strategy based on seed crystal and layer growth theory is proposed using the philosophies of the methods introduced above. Firstly, the most common topology between initial and goal configuration is searched out by intelligent searching algorithm and is used as growth seed crystal of goal configuration. Secondly, the goal configuration is constructed based on the common topology. In the process of constructing goal configuration, the growth sequence of modules is determined by layer growth theory of crystal's crystallization, and the tasks of transmitting and changing azimuth of the goal module is implemented by WLCCG.Motion is a basic ability of robot, most MSRs'unit modules do not have this ability. Only when many modules are connected together, self-reconfigurable robot has the ability of moving. In the process of planning the sequence of module connecting, disconnecting and rotating, it was found that the robot configuration made of four WLCCGs can realize reconfigurable moving function. If there are no obstacles on a moving plane, the algorithm based on the gradient of the potential field is used in planning the moving path of robot composed of WLCCGs. If there are obstacles on a moving plane, the algorithm of heuristics rapidly-exploring random tree is chosen. The actions of robot are realized by fixed motion sequence database.Finally, the basic functions of WLCCG were verified by cubic crystal cell self-reconfigurable robot system. The experiments results show that the WLCCG can realize the functions of moving, self-reconfiguring, changing azimuth of the other modules and carrying the other modules. The effectiveness of the self-reconfiguring process model based on crystal's crystallization oriented to cubic cell robot system is verified by a simulation experiment. The goal configurations are composed of four MLMMs or H-like configuration. The results show that the theory presented in the chapter above is feasible and effective.