page_title: Self-reconfiguring modular robot
section_title: A taxonomy of architectures
hierarchical_section_title: Self-reconfiguring modular robot / Structure and control / A taxonomy of architectures
caption_attribution_description: English: An assembly of several units of the Micro Unit system shown with the corresponding lattice and network of docking points
context_page_description: Modular self-reconfiguring robotic systems or self-reconfigurable modular robots are autonomous kinematic machines with variable morphology. Beyond conventional actuation, sensing and control typically found in fixed-morphology robots, self-reconfiguring robots are also able to deliberately change their own shape by rearranging the connectivity of their parts, in order to adapt to new circumstances, perform new tasks, or recover from damage.
  For example, a robot made of such components could assume a worm-like shape to move through a narrow pipe, reassemble into something with spider-like legs to cross uneven terrain, then form a third arbitrary object to move quickly over a fairly flat terrain; it can also be used for making "fixed" objects, such as walls, shelters, or buildings.
  In some cases this involves each module having 2 or more connectors for connecting several together. They can contain electronics, sensors, computer processors, memory and power supplies; they can also contain actuators that are used for manipulating their location in the environment and in relation with each other.
context_section_description: Modular self-reconfiguring robotic systems can be generally classified into several architectural groups by the geometric arrangement of their unit (lattice vs. chain). Several systems exhibit hybrid properties, and modular robots have also been classified into the two categories of Mobile Configuration Change (MCC) and Whole Body Locomotion (WBL).
  Lattice architecture have their units connecting their docking interfaces at points into virtual cells of some regular grid. This network of docking points can be compared to atoms in a crystal and the grid to the lattice of that crystal. Therefore, the kinematical features of lattice robots can be characterized by their corresponding crystallographic displacement groups (chiral space groups). Usually few units are sufficient to accomplish a reconfiguration step. Lattice architectures allows a simpler mechanical design and a simpler computational representation and reconfiguration planning that can be more easily scaled to complex systems.
  Chain architecture do not use a virtual network of docking points for their units. The units are able to reach any point in the space and are therefore more versatile, but a chain of many units may be necessary to reach a point making it usually more difficult to accomplish a reconfiguration step. Such systems are also more computationally difficult to represent and analyze.
  Hybrid architecture takes advantages of both previous architectures. Control and mechanism are designed for lattice reconfiguration but also allow to reach any point in the space.
  Modular robotic systems can also be classified according to the way by which units are reconfigured (moved) into place.
  Deterministic reconfiguration relies on units moving or being directly manipulated into their target location during reconfiguration. The exact location of each unit is known at all times. Reconfiguration times can be guaranteed, but sophisticated feedback control is necessary to assure precise manipulation. Macro-scale systems are usually deterministic.
  Stochastic reconfiguration relies on units moving around using statistical processes (like Brownian motion). The exact location of each unit only known when it is connected to the main structure, but it may take unknown paths to move between locations. Reconfiguration times can be guaranteed only statistically. Stochastic architectures are more favorable at micro scales.
  Modular robotic systems are also generally classified depending on the design of the modules.
  Homogeneous modular robot systems have many modules of the same design forming a structure suitable to perform the required task. An advantage over other systems is that they are simple to scale in size (and possibly function), by adding more units. A commonly described disadvantage is limits to functionality - these systems often require more modules to achieve a given function, than heterogeneous systems.
  Heterogeneous modular robot systems have different modules, each of which do specialized functions, forming a structure suitable to perform a task. An advantage is compactness, and the versatility to design and add units to perform any task. A commonly described disadvantage is an increase in complexity of design, manufacturing, and simulation methods.
  Other modular robotic systems exist which are not self-reconfigurable, and thus do not formally belong to this family of robots though they may have similar appearance. For example, self-assembling systems may be composed of multiple modules but cannot dynamically control their target shape. Similarly, tensegrity robotics may be composed of multiple interchangeable modules but cannot self-reconfigure. Self-reconfigurable robotic systems feature reconfigurability compared to their fixed-morphology counterparts and it can be defined as the extent/degree to which a self-reconfigurable robot or robotic systems can transform and evolve to another meaningful configuration with a certain degree of autonomy or human intervention. The reconfigurable system can also be classified according to the mechanism reconfigurablity.
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caption: Lattice architecture: 12 modules of the homogeneous lattice system Micro Unit assembled together shown with corresponding grid and docking points network
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