On position/force tracking control problem of cooperative robot manipulators using adaptive fuzzy backstepping approach

In this paper, the position and force tracking control problem of cooperative robot manipulator system handling a common rigid object with unknown dynamical models and unknown external disturbances is investigated. The universal approximation properties of fuzzy logic systems are employed to estimate the unknown system dynamics. On the other hand, by defining new state variables based on the integral and differential of position and orientation errors of the grasped object, the error system of coordinated robot manipulators is constructed. Subsequently by defining the appropriate change of coordinates and using the backstepping design strategy, an adaptive fuzzy backstepping position tracking control scheme is proposed for multi-robot manipulator systems. By utilizing the properties of internal forces, extra terms are also added to the control signals to consider the force tracking problem. Moreover, it is shown that the proposed adaptive fuzzy backstepping position/force control approach ensures all the signals of the closed loop system uniformly ultimately bounded and tracking errors of both positions and forces can converge to small desired values by proper selection of the design parameters. Finally, the theoretic achievements are tested on the two three-link planar robot manipulators cooperatively handling a common object to illustrate the effectiveness of the proposed approach.

A Practical Approach to Near Time-Optimal Inspection-Task-Sequence Planning for Two Cooperative Industrial Robot Arms

A near time-optimal inspection-task-sequence planning for two co operative industrial robots is outlined. The objective of the task- sequence planning is not only to find a series of near time-optimal final configurations for two arms where the inspection operations are undertaken for segment motions, but also to find a near time-optimal task sequence of inspection points.

A time-efficient, continuous joint-acceleration profile is proposed for a class of general industrial robots, and simplified by suitably choosing the time intervals of the profile for each segment motion between any two points to be inspected. The optimization problem to find near time-optimal final configurations is solved using the non linear optimization method of sequential quadratic programming (SQP). The computation overhead arising with this approach is suc cessfully dealt with. The task-sequence planning is formulated as a variation of the travelling salesman problem, and simulated anneal ing is used to find a near time-optimal route. The near time-optimal task-sequence planning and time-efficient trajectory planning are effectively integrated with the related computational problems ad dressed and solved.

The proposed method is applied to an environment containing two RTX SCARA-type industrial robots with six joints. Computations have been carried out for moving points in a route, as compared with the same fixed points in a route where only one arm moves. The conclusion is that it is much more efficient if two robot arms work in a cooperative mode. A speed increase by a factor of close to 3 has been achieved through effective use of joint capabilities in the cooperative system. Experiments have also been conducted on the RTX system, yielding satisfactory results that are consistent with those obtained by simulation.

Control of Mechanical Systems With Rolling Constraints

There are many examples of mechanical systems that require rolling contacts between two or more rigid bodies. Rolling contacts engender nonholonomic constraints in an otherwise holonomic system. In this article, we develop a unified ap proach to the control of mechanical systems subject to both holonomic and nonholonomic constraints. We first present a state space realization of a constrained system. We then dis cuss the input-output linearization and zero dynamics of the system. This approach is applied to the dynamic control of mo bile robots. Two types of control algorithms for mobile robots are investigated: trajectory tracking and path following. In each case, a smooth nonlinear feedback is obtained to achieve asymptotic input-output stability and Lagrange stability of the overall system. Simulation results are presented to demonstrate the effectiveness of the control algorithms and to compare the performance of trajectory-tracking and path-following algo rithms.

A general dynamic force distribution algorithm for multifingered grasping

A general dynamic force distribution (DFD) algorithm for multifingered grasping is presented. Based on the convexity and cone property of contact constraints, the optimal internal force is defined. Determination of the contact force is divided into two phases: (1) determine the direction of the optimal internal force during grasp planning and (2) determine the manipulation force and compensation factor during task manipulation. The total computation cost consists of off-line numerical iterations and on-line analytical computations. Only the latter is related to the real-time control. The algorithm can directly deal with the nonlinear and/or coupled constraints and well overcome the temporal discontinuity.

Dynamic redundancy resolution in a nonholonomic wheeled mobile manipulator

Wheeled Mobile Manipulators (WMM) possess many advantages over fixed-base counterparts in terms of improved workspace, mobility and robustness. However, the combination of the nonholonomic constraints with the inherent redundancy limits effective exploitation of end-effector payload manipulation capabilities. The dynamic-level redundancy-resolution scheme presented in this paper decomposes the system dynamics into decoupled task-space (end-effector motions/forces) and a dynamically consistent null-space (internal motions/forces) component. This simplifies the subsequent development of a prioritized task-space control (of end-effector interactions) and a decoupled but secondary null-space control (of internal motions) in a hierarchical WMM controller. Various aspects of the ensuing novel capabilities are illustrated using a series of simulation results.