Force/position control strategies provide an effective framework to deal with tasks involving interaction with the environment. In this paper the parallel approach to force/position control of robotic manipulators is presented. It shows a complete use of the available sensor measurements by operating the control action in a full-dimensional space without using selection matrices. Conflicting situations between the position and force tasks are managed using a priority strategy: the force control loop is designed to prevail over the position control loop. This choice ensures limited deviations from the prescribed force trajectory in every situation, guaranteeing automatic recovery from unplanned collisions. A dynamic force/position parallel control law is presented and its performance in presence of an elastic environment is analyzed; simplification of the dynamic control law is also discussed leading to a PID-type parallel controller. Two case studies are worked out that show the effectiveness of the approach in application to an industrial robot.>

The manipulability ellipsoids are used in robotics as a measure of manipulators' performances achievable during task execution. The definition of these geometrical entities is based on the Jacobian of the manipulator, and the physical meaning given to the ellipsoids is related to the capability of the mechanism to apply forces with the end effector or to move the tool in some directions of the task-space. P. Chiacchio et al. (ibid., vol.7, p.678-685, 1991) have extended this concept to the case of cooperating manipulators. Nevertheless, some questions are still open, both with respect to the basic definition and use of manipulability ellipsoids. The commenter shows by simple examples that the use of manipulability ellipsoids for multiarm systems gives misleading results, and he disagrees with the above authors' definition of ellipsoids. The authors defend their work.>

New definitions of force and velocity manipulability ellipsoids for multiple-arm systems are given. A suitable kinetostatic formulation for multiple cooperating arms is adopted that allows a global task space description of external and internal forces as well as absolute and relative velocities at the object level. The concept of a force manipulability ellipsoid for a single arm is formally extended to the multi-arm case by regarding the whole system as a mechanical transformer from the extended joint space to the global task space. Kinetostatic duality properties are then exploited to derive velocity manipulability ellipsoids for the multiple-arm system. The proposed method is compared with other approaches using numerical examples.>

A novel algorithmic approach to the reachable workspace determination is presented. The reachable workspace is that volume of space which the end effector can reach. The present work is restricted to special geometries which have a 2R or a 3R planar pair, but the resulting algorithm appears to be applicable to any manipulator geometry. Computation results are presented for a 2R and a 3R redundant planar pair.>

Based on a recently proposed algorithmic solution technique, the inverse kinematic problem for redundant manipulators is solved. The kinematics of the manipulator is appropriately augmented to include mentioned constraints; the result is an efficient, fast, closed-loop algorithm which only makes use of the direct kinematics of the manipulator. Simulation results illustrate the tracking performance for a given trajectory in the Cartesian space, while guaranteeing a collision-free trajectory and/or not violating a mechanical joint limit.>

Redundancy represents one key towards design and synthesis of more versatile manipulators. Obstacle avoidance and limited joint range constitute two kinds of constraints which can be potentially met by a kinematically redundant manipulator. The natural scenario is the inverse kinematic problem which is certainly a crucial point for robotic manipulator analysis and control. Based on a recently proposed dynamic solution technique, the inverse kinematic problem for redundant manipulators is solved in this paper. The kinematics of the manipulator is appropriately augmented in order to include the above mentioned constraints; the result is an efficient, fast dynamic algorithm which only makes use of the direct kinematics of the manipulator. Extensive simulation results illustrate the tracking performance for a given trajectory in the Cartesian space, while guaranteeing a collision-free trajectory and/or not violating a mechanical jointiimit.

One of the most important features of an advanced control system for articulated robots is the capability of transforming the work space coordinates, which naturally characterize any robot task, into the joint coordinates, on which control actions are developed (Inverse Kinematic Problem). While simple kinematical structures allow for closed form solutions, there is a class of robots for which this is not true. If the three axes of revolution at the end effector intersect two-by-two an exact solution seems not to exist. The goal of the paper is to establish a fairly different solution algorithm, as compared to the trigonometric approach, which yields solutions in the above case. The algorithm is shown to be convergent along any trajectory. It proves very fast since it is based only on direct kinematics. Numerical examples are finally developed.

One of the most important features of an advanced control system for articulated robots is the capability of transforming the work space coordinates, which naturally characterize any robot task, into the corresponding joint coordinates, on which control actions are developed. For each task, the coordinate transformation problem consists in calculating one trajectory in the joint space which corresponds to the end effector trajectory, usually given in the Cartesian space. While simple kinematical structures allow for closed-form solutions, there is a class of robots for which this is not true. Typical articulated robot structures have three revolute joints at the end effector; the geometric parameters of these joints actually determine the spatial configuration of the last axes of motion. The large majority of today's nonredundant structures have three intersecting axes at the end effector, and closed form solutions do exist in this case. If the axes intersect two-by-two, as in some rather common arm design, an exact solution seems not to exist. A quite different solution algorithm is established, as compared to the trigonometric approach widely adopted so far, which yields solutions in case of two-by-two intersecting axes. The convergence of the algorithm along any trajectory is proved. Effectiveness of the proposed technique can be argued by the fact that it only makes use of direct kinematics, thus resulting in a contained computational burden. A robot prototype of the kind described above is taken as a reference in order to discuss digital implementation and develop numerical examples.