TETROBOT is a modular system for the design, implementation, and control of a class of highly redundant parallel robotic mechanisms. This paper describes new experimental results based on evaluation of prototype configurations with up to 18 nodes, 48 links and 15 actuators. TETROBOT is an actuated robotic structure which may be reassembled into many different configurations while still being controlled by the same hardware and software architecture. Implementations of a double octahedral platform, a tetrahedral arm and a six-legged walker, constructed from the same set of parts, are described. The TETROBOT system addresses the needs of application domains, such as space, undersea, mining, and construction, where adaptation to unstructured and changing environments and custom design for rapid implementation are required.

A modular system for the design, implementation, and control of a class of highly redundant parallel robotic mechanisms is described. The Tetrobot system features a novel concentric multilink spherical (CMS) joint which allows an arbitrary number of links to share a common center of rotation. The CMS joint facilitates the construction of a wide variety of variable geometry truss mechanisms using an integrated control and computational framework. A distributed control algorithm is based on an iterative virtual force based solution which propagates the goal positions of target nodes to determine systematic adjustments of actuators. Capabilities of the Tetrobot system have been demonstrated by the construction of several configurations of up to 18 nodes, 48 links, and 15 actuators. Implementations of a double Stewart platform and a six-legged walker, constructed from the same set of parts, are described in this paper.

A new spherical joint mechanism which is well suited to parallel robotics is presented. The concentric multilink spherical (CMS) joint allows two or more struts to be connected together such that they rotate about a single point. This joint can replace the traditional ball or universal (Hooke) joints in Stewart platforms, variable geometry truss manipulators, and other parallel robots. The TETRA2 robot consists of five nodes and six actuated struts. It provides a range of motion of 1m/spl times/0.5m/spl times/0.5m and has lifted a payload of 10 kg at full lateral extension. Simulation of a 48 struct walking robot illustrates the use of CMS joints to design more complex structures. The simulation also demonstrates new algorithms for parallel robot control.>

An object representation scheme which allows fast Euclidean distance calculation is presented. The object model extends the polytope model by representing objects as the convex hull of a finite set of spheres. Objects with rounded surfaces can be represented with far fewer vertices than would be required with the polytope model. An algorithm for calculating distances between objects is developed which is linear in the total number of spheres specifying the two objects. To determine the efficiency of the distance computation algorithms, a program was written and tested using randomly generated objects with varying numbers of vertices.>