We introduce a method of planning fault tolerant trajectories based on the least constraint (LC) framework. Fault tolerance is achieved in two ways: exploiting properties of LC itself, and using a performance measure which assess the fault tolerant potential of a given configuration. LC encourages designs which are based solely on salient constraints of the task, allowing the inherent redundancy of the robot to be used to maintain a safe configuration. We compute the effects of faults on the topology of the configuration space and construct optimal recovery motions for a set of faults. We describe an efficient algorithm for computing the optimal recovery motions for a large number of faults over the entire configuration space simultaneously. A performance measure, called longevity, quantifies the ability of the recovery motions to complete the task. From the performance measure fault tolerant paths are constructed. We look at the simple task of positioning the end effector of a Puma 560 at a given point in the workspace.

Robotic tasks usually require some collision free motions, and there has been considerable work in methods for collision avoidance. However, noise in the sensor data, movement of the obstacles, and incomplete or inaccurate model of the surroundings all may lead to unexpected collisions. Detecting such collisions is necessary before recovery and/or replanning may take place. A means of detecting a collision, as well as the position of the collision on the manipulator has been developed. The detection scheme combines information from observed disturbance torques to detect collision and infer the location of contact with the environment. Knowledge of contact position allows for a more intelligent and less error-prone recovery scheme. A simulation using a three DOF manipulator shows that the collision identification and localization scheme is feasible and robust with respect to noise.

Describes class of spherically symmetric, high degree of freedom robots called "platonic beasts". A robot in this family is kinematically equivalent to a symmetric polyhedron, such as one of the platonic solids, with identical multi-purpose limbs attached to its vertices. The symmetry and regularity of the design have several advantages including robustness to toppling, novel gaits such as the rolling gait, and fault tolerance. The authors describe the design, simulation, and construction of a prototype platonic beast robot that the authors have built in their lab. The robot has four limbs, each with three degrees of freedom, and is controlled by a network of four embedded 32-bit microcontrollers. The authors also discuss the general features of these robots, including locomotion using the rolling gait and the implications of its novel features.>