The consensus problem for multi-agent systems with input and communication delays is studied based on the frequency-domain analysis. Two decentralized consensus conditions are obtained, one of which is given for the systems based on undirected graphs with diverse input delays and the other is for the systems based on directed graphs with diverse communication delays and input delays. For the systems with both communication delays and input delays, the consensus condition is dependent on input delays but independent of communication delays.

Consensus of Multi-Agent Systems With Diverse Input and Communication Delays

Adaptive position/force control for robot manipulators in contact with a rigid surface with uncertain parameters

Force position control for a robot finger with a soft tip and kinematic uncertainties

We consider the position and force regulation problem for a soft tip robot finger in contact with a rigid surface under kinematic and dynamic parametric uncertainties. The reproducing force is assumed to be related to the displacement through a nonlinear function whose characteristics are unknown, but both the actual displacement and force can be directly measured. Kinematic uncertainties concern the rigid surface orientation and the contact point location. Kinematic parameters involved in the contact point location concern the length from the last joint to the contact point and the rest of the link lengths in the general case. An adaptive controller with a composite update parameter law is proposed, and the asymptotic stability of the force and estimated position errors under dynamic and kinematic uncertainties is shown for the planar case. Simulation results for a three-degrees-of-freedom planar robotic finger are presented. © 2002 Wiley Periodicals, Inc.

A position/force control for a robot finger with soft tip and uncertain kinematics

This work proposes an adaptive control law for the force position regulation problem under surface kinematic uncertainties. A compliant contact with friction is considered. The control law achieves exact regulation of force and position along the surface tangent by identifying the surface slope. The asymptotic stability of the closed loop system equilibrium point is proved in a local sense and is demonstrated by a simulation example

An adaptive law for slope identification and force position regulation using motion variables

In this paper, the global stability problem for constrained robot motions in the presence of constraint uncertainties is investigated. We focus on the uncertainties in the constraint functions and their effects on the global stability. PD type controllers are used and conditions for global stability are developed using Lyapunov's direct approach. In the presence of the constraint uncertainties under investigation, the desired position and constraint force can be guaranteed with global asymptotic convergence. The developed conditions for feedback gain selections clearly show the effects of the constraint uncertainties. For the case when the velocity measurements are not available, conditions for global stability regulation are also established and the robot controller uses only the measurements of the position angles. Finally, we consider the case where the robot joints are flexible and global stability conditions are given.

Y. K. Ho

Papers

Global stabilization for constrained robot motions with constraint uncertainties