The minimum-time manipulator control problem is solved for the case when the path is specified and the actuator torque limitations are known. The optimal open-loop torques are found, and a method is given for implementing these torques with a conventional linear feedback control system. The algorithm allows bounds on the torques that may be arbitrary functions of the joint angles and angular velocities. This method is valid for any path and orientation of the end- effector that is specified. The algorithm can be used for any manipulator that has rigid links, known dynamic equations of motion, and joint angles that can be determined at a given position on the path.

Dielectric elastomer actuators (DEAs) show promise for robotic and mechatronic applications. However, to date, these actuators have experienced high rates of failure that have prevented their practical application. Here, large scale modes of failure of DEAs and their performance limits are studied. The objective is to provide design guidelines and bound the performance of DEAs that avoid failure. An idealized DEA is modeled and its failure is predicted as a function of film prestretch used during actuator fabrication, actuation voltage, and stretch rate. Three failure modes are considered: pull-in, dielectric strength, and material strength. Each failure mode is shown to dominate for different combinations of pre-stretch and stretch rate. High stretch rates lead to dielectric strength failure while low stretch rates lead to pull-in failure. Material strength failure is less important for most cases. Model predictions are validated experimentally using practical DEAs operating under load. This study suggests that DEAs cannot be operated reliably under load for long periods of time or low stretch rates due to pull-in failure limitations. To be reliable, DEAs must be used for short periods of time with high stretch rates.

The dynamics of space robotic systems can be quite complex and hence their control can be difficult. In this paper some important dynamics and control problems, unique to space robotic systems are discussed. Particular attention is paid to freeflying and free-floating space robots that might be used for such tasks as space station repair and construction. Recent advances made by the research community in solving these problems are briefly reviewed. Three examples of promising methods for planning and controlling the motion of space robotic systems are presented. It is suggested that a thorough understanding of the fundamental dynamics of these systems, will result in effective solutions to their control problems.

Abstract-Future planetary exploration missions will require wheeled mobile robots ("rovers") to traverse very rough terrain with limited human supervision. Wheel-terrain interaction plays a critical role in rough-terrain mobility. In this paper, an online estimation method that identifies key terrain parameters using on-board robot sensors is presented. These parameters can be used for traversability prediction or in a traction control algorithm to improve robot mobility and to plan safe action plans for autonomous systems. Terrain parameters are also valuable indicators of planetary surface soil composition. The algorithm relies on a simplified form of classical terramechanics equations and uses a linear-least squares method to compute terrain parameters in real time. Simulation and experimental results show that the terrain estimation algorithm can accurately and efficiently identify key terrain parameters for various soil types.Index Terms-Mobile robots, planetary rovers, rough terrain, wheel-terrain interaction.

A mathematical model of an elastic mechanical joint with clearances has been formulated and the dynamical equations of motion derived (Part I). The model, which we have called an Impact Pair, is basic to the determination of the dynamical response of mechanical and electromechanical systems with clearances, including determination of dynamic force amplification, frequency response, time-displacement characteristics, and other dynamic characteristics. Whenever possible, the results for the impact pair under various operating conditions are illustrated by graphs, which may also offer some insight into the behavior of clearance-coupled systems.