The Self-Reconfiguring Crystal Robot

Self-reconfiguring robots change their shape without human intervention, and are typically designed with the goal of making arbitrary shapes. A general way to achieve this is to build a robot composed of many individual modules: if the modules can attach together into a structure, and if individual units can relocate within and about the structure, then self-reconfiguration is possible.

Since the early 1990s, several research groups have proposed a variety of ways to implement the modules. One concept our group has explored is a system composed of cubes (or squares in 2D) with expanding and contracting faces. We call this the crystalline robot concept because motion in this system in some ways resembles models of plastic deformation in solid materials with crystalline atomic structure. Continuing with this analogy, we call the modules in a crystalline robot atoms.

We first developed and popularized the basic concept of crystalline robots in the late 1990s. As is often the case, we found that we were not the absolute first to consider the idea: a Japanese research group had previously described lattice modules with expanding faces in a patent document, but it appears this was their only publication on the subject.

Several other research groups have also contributed new developments. Suh, Yim, and their collaborators at Xerox Parc developed a 3D module implementation and new reconfiguration algorithms. Aloupis and collaborators from 8 other institutions recently published a planning algorithm for arbitrary reconfiguration in systems made of 2x2x2 meta-modules which requires only a linear number of parallel expansions and contractions (previous algorithms were quadratic). While much of the work in reconfiguration planning for crystalline robots has considered only kinematics, Reif and Slee at Duke University have recently developed a model with relevant energetic constraints and reconfiguration planning algorithms which are proven optimal in that model.