An efficient search algorithm for finding optimal deadlock-free schedules in FMS modeled by S/sup 4/R nets is presented. The algorithm is based on the branch and bound principle, the depth first search and truncation techniques based on the structure theory of Petri nets. It is applied to the timed S/sup 4/R net extended with priority rules. The efficiency of the proposed approach is illustrated using an example from the literature.

This paper describes the path planning module of a computer-aided tactile inspection planning (CATIP) system. The path planner is based on Dijkistra's shortest path algorithm combined with collision detection routines. The working space is dicretized into a regular grid of nodes. The workpiece, the objects in the environment and the probe are automatically approximated by a set of cartesian boxes generated from their octree representation. Optimization and robustness are the main issues considered in this work, and the use of heuristics is completely avoided. The results are demonstrated using an example.

An approach for evaluating the global accessibility for 5-axis machining of sculptured surfaces is presented. The objective is to develop an algorithm which can determine all the feasible orientations along which the tool can reach a specified point without colliding with the workpiece. It is based on the projection of features, which define the unfeasible domains, on a unit sphere centered at the target point. The local curvature of the surface, the shape and the size of the tool and other obstacles (i.e. clamps and fixtures) are taken into consideration. The method also has potential applications in fields such as workpiece set-up, inspection planning and robotics manipulation.

The effect of routing flexibility on the performance of the manufacturing system is studied. A deadlock-free scheduling algorithm, developed for S/sup 4/R nets is used for experimentation. The issues addressed in the paper include extending the S/sup 4/R nets with additional places to take into account machine breakdowns, and the derivation of the set of uncontrolled minimal siphons of the extended net from the set of the original net. Finally, an experimental study is conducted for performance evaluation.

This paper presents a general method for the accessibility analysis of points in 3D space by straight lines such as light rays, measurement probes and welding rods. This method can be applied to any type of solid or surface and is not limited by continuity or derivability constraints and may be implemented on any commercial solid modeler with an exact representation of spheres. It is based on the intersection of concentric spherical shells (ICSS) centred at the analyzed point. The exact accessibility cones can be generated easily as a limit case of the ICSS. This method has been used for the accessibility analysis of measurement points by coordinates measuring machines and has potential applications in fields such as machining and robotics.

This paper presents a novel application of dual kriging for the automatic inference of analytical equations of geometric entities. It is based on the combination of interpolation profiles representing generally classical shapes. These profiles are deduced from designer intuition of the shape of the curve, surface or solid. Dual kriging was successfully used for curve/surface modeling. It is a general method which incorporates several interpolation techniques such as piecewise interpolation, cubic splines, Bezier and NURBS curves/surfaces and solids in a single formulation. Elementary shapes such as conics, cylinders are represented exactly. Detailed examples of curve, surface and solid equations inference are presented.

Presents a novel direct adaptive neurocontrol scheme for flexible joint robots with structural uncertainty and arbitrary nonlinear joint flexibility. The localized polynomial networks are used to represent unknown system dynamics. It is proved that all the signals in the closed-loop direct adaptive neurocontrol systems can be made uniformly bounded and the output tracking errors can be guaranteed to converge globally to a specified neighborhood of zero. Therefore, global stability of the neurocontrol systems is guaranteed. The learning process is fast convergent and needs less computation, due to the usage of the localized polynomial networks. Compared with conventional schemes, this direct adaptive neurocontrol scheme allows robotic dynamics to have more general structure and is more robust to robotic system modeling errors. No link acceleration and jerk measurements are needed, and the control actions are chatter-free.>

The authors describe a real-time approach to solve the trajectory planning problem using the latest feedback of robot joint locations from robot controllers. The approach incorporates an efficient collision avoidance strategy to allow decisions to be made during execution by means of cylindrical robot link approximation. The developed algorithm has been verified with a dual-robot planning and control system for the mechanical assembly of a dish-washer power unit. The system consists of an ADEPTI and a PUMA 560 industrial robot running under the control of a Sun-4 Sparc 2 workstation at the high control level. A coarse motion planner is available to prevent the arm from colliding with stationary objects. In this dual-arm system, a task level multi-agent plan is generated to specify the logical sequence of assembly. From the execution results, it was found that even when the robot speed was varied from 25% to 80% of its full capacity, a collision-free path was found for each robot.>

An application of self-organizing neural-network maps is presented for real-time execution monitoring and diagnosing of robotic assembly. The self-organizing maps not only have the ability to spontaneously react to changes in dynamic assembly processes, but also to offer simplicity and feasibility for organizing diverse assembly interactions between tools, parts, robot, and sensory data. A number of different types of multidimensional maps are described for various combinations of assembly interactions.>

Nonlinear feedback control for force-controlled robots with constrained end-effector motion is considered. A general method is presented that assures an exact feedback linearization for both rigid and flexible-joint robots, as the joint flexibility can cause instability of robot control. The feedback control linearizes and decouples the original nonlinear system into a number of decoupled linear subsystems. The effect of stiction on the end-effector contact with the environment is inherently incorporated in the formulation, using the same constrained system formalism. A version of the controller with improved robustness characteristics, based on the robust servomechanism theory, is proposed. The derivation of the control algorithm for a two-link planar robot interacting with a rough plane surface is presented as an example. Numerical simulation results confirm the effectiveness of the method. The issues associated with real-time robot control, such as the choice of sampling frequency and the influence of modeling errors, are discussed.>

A nonlinear decoupling and linearizing feedback control for force-controlled robots with constrained end-effector motion is considered. A general method is presented which assures an exact feedback linearization for both rigid and flexible joint robots, as the joint flexibility can cause instability of robot control. The application of the developed control laws produces a set of decoupled linear subsystems, corresponding to the position/velocity constraint space and contact force constraint space. The implementation of this method is demonstrated for the case of a two-link robot with the end-effector constrained to move along a rough plane.>

A method for interpreting the measured contact forces during compliant robot motions using kinematic screws is presented. Domain-specific rules combined with partial a priori knowledge of mating parts geometry and interpreted force signals are used to reason and make inferences about the initial contact configuration. The likely contact surfaces are predicted and point(s) or line(s) of contact are fully defined. These surfaces are idealized and represented by quadratic equations or polyhedral surfaces. The geometric properties of surfaces at the contact location are used to select the contact configuration when multiple solutions exist. The developed methodology has been validated experimentally using a 6R manipulator, six-axis force sensor, and host computer.>