Navigation of mobile robot in the configuration space requires the robot pose measurement for control algorithms implementation. Calibrated fixed cameras may be utilized to such measurements. A promising approach where calibration can be avoided is navigation in the image space. This leads to the concept of direct image based control where absolute measurement of the robot pose in the configuration space is obviated; only information extracted from visual information — and partial camera calibration— is utilized for guidance of the robot. This paper adopt this concept and the application of the velocity field control philosophy to visual guidance of wheeled mobile robots. The main feature of this approach is that the robot task is encoded by means of a specified velocity field in image space.

This paper addresses the set-point control of robot manipulators with friction where avoiding saturation of the actuators is a major issue. The original contribution is a novel direct fuzzy control system dealing with both practical constraints in mechanical manipulators: saturation and friction. The control system is made by taking advantage of input-output properties of the so-called sectorial fuzzy controllers. When friction is considered, we prove, via Lyapunov theory, that the steady state position errors owing to static friction are inside of a global attractor, which can be arbitrarily reduced. In case of absence of friction, the closed-loop system becomes globally asymptotic stable. In both cases, the important theoretical and practical feature of maintaining the control actions always within prescribed limits according to the actuator torque capabilities is guaranteed. Experimental evaluation of the proposed direct fuzzy control system on a nonlinear direct-drive robot arm is presented to validate its effectiveness.

Most robust control schemes for rigid robots assume velocities measurements to be available. Although it is possible to measure velocities by using tachometers, this increases costs, and the signals delivered may be contaminated with noise. Since the use of encoders allows reading joint position pretty accurately, sometimes it is desirable to estimate joint velocities through an observer. This paper presents a robust control scheme designed in conjunction with a linear observer. Uniform ultimate boundedness for the tracking and observation errors are guaranteed. Experiments are included to support the theoretical results and to show that the performance of the new control-observer law is better, in comparison with well-known algorithms reported in the literature.

This paper shows that fuzzy control systems satisfying sectorial properties are effective for motion tracking control of robot manipulators. We propose a controller whose structure is composed by a sectorial fuzzy controller plus a full nonlinear robot dynamics compensation, in such a way that this structure leads to a very simple closed-loop system represented by an autonomous nonlinear differential equation. We demonstrate via Lyapunov theory, that the closed-loop system is globally asymptotically stable. Experimental results show the feasibility of the proposed controller.

It is known in the practice of closed-loop identification of mechanical systems that, since the Langrangian dynamic model is linear in the constant physical parameters, a sufficient condition for parameter convergence is that the robot be made to follow reference trajectories which render the regressor matrix, persistently exciting. Slotine and Li established this many years ago for a particular adaptive controller. This result is based on adaptive linear systems theory and relies on the condition that the applied control law makes the robot asymptotically track the imposed rich reference trajectories. This paper revisits this problem and establishes a proof that this condition is not only sufficient but also necessary to establish the stronger property of uniform global asymptotic stability of the overall closed-loop system.

This paper concerns the velocity field control in operational space of robot manipulators. Velocity field control is a recent control formulation in robotics. A velocity field defines the desired robot velocity in the operational space as a function of its current position, thus the robot performs the desired motions. In this paper, a controller is proposed for operational space velocity field control. The proposed controller is based on a hierarchical structure that result of using the kinematic control concept and a joint velocity controller. Experimental results on a two degrees-of-freedom direct-drive robot arm illustrate the viability of the proposed scheme.

This paper presents an experimental evaluation of four regulators in task space using unit quaternions to represent the end-effector orientation. We address the problem of regulation, that is, when the desired pose is constant. We present experimental results of the following control schemes: the resolved acceleration control, damped resolved acceleration control, hybrid damped resolved acceleration control, and transpose Jacobian-based control. All the controllers are tested on a three degrees-of-freedom spherical wrist.

The velocity control of a direct-drive robot arm with high friction is considered in this paper. The friction at the robot joints is assumed to be captured by the Dahl model (1976), which has a bristle deflection interpretation. A joint velocity controller with friction compensation based on the Dahl model is introduced. Experiments show the superiority of the proposed scheme with respect to the velocity controller when friction is compensated using the classical viscous plus Coulomb model of friction.

Resolved acceleration control is a method for motion control of robot manipulators in task space where a desired end-effector pose trajectory is specified. We consider the orientation part of the pose given by the Euler parameters or unit quaternion. The main contribution is a novel proof of asymptotic stability based in the use of a strict Lyapunov function. This is a one stage procedure which improves previously reported analysis where two-stage mechanisms are in general invoked: first demonstrating stability and then convergence.

This paper deals with applications of fuzzy logic systems to motion control of robot manipulators. In the proposed application, the fuzzy logic system plays the role of a tuner of the robot controller gains. This idea is evoked for the gains of the so-called PD+ control scheme and we demonstrate, by taking into account the full nonlinear and multivariable nature of the robot dynamics, that the overall closed loop system is globally asymptotically stable. Experimental results on a two degrees of freedom direct-drive arm show the usefulness of the proposed control approach.

Computed-torque control is a well-known motion control strategy for manipulators which ensures global asymptotic stability for fixed symmetric positive definite (proportional and derivative) gain matrices. In this paper, we show that global asymptotic stability also holds for a class of gain matrices depending on the manipulator state. This feature increases the potential of the computed-torque control scheme to handle practical constraint in actual robots such as presence of friction in the joints and actuators with limited torque capabilities. We illustrate this potential by means of a fuzzy self-tuning algorithm to select the proportional and derivative gains according to the actual tracking position error. Experiments on a two degrees of freedom robot arm show the usefulness of the proposed approach.

Reports the results of an experimental study conducted on a direct-drive motor to evaluate the predicted behavior of selected friction models. We focus the study on the velocity response when torque ramp inputs are employed. Among the considered friction models, the dynamic friction model, the so-called LuGre model, captures very well the experimental behavior. As a consequence of the study, we derive a simple procedure to determine the viscous and Coulomb friction from experimental velocity responses.

This paper addresses the visual servoing of robot manipulators in fixed-camera configuration for considering a moving target. We propose a control scheme consisting of two loops: an inner loop which is a joint velocity controller; and an outer loop which is an image-based feedback loop. We present the stability analysis and the experimental evaluation on a two degrees of freedom direct-drive planar robot arm.

One of the simplest and naturally appealing adaptive tracking controllers for robot manipulators is the so-called adaptive PD controller with computed feedforward. Since its introduction, in the middle of eighties, to the best of author knowledge, only local convergence analyses have been presented. In this paper, based on some properties of the robot dynamics, which deal with continuously differentiable increasing saturating functions, we present the global convergence analysis of this adaptive tracking controller.

The position control of robot manipulators in generic task space is addressed in this paper. The main ingredient in the formulation is the use of the task function concept which includes as particular cases the task specifications in joint and Cartesian spaces. The main theoretical contribution is a novel stability analysis of a wide class of robot regulators based in energy shaping plus damping injection. We also provide sufficient conditions to design effective regulators. This approach is illustrated via experimental tests on a direct drive arm where specifications are given in Cartesian and image-based task spaces, respectively.

Computed-torque control is a well known motion control strategy for manipulators which ensures global asymptotic stability for fixed symmetric positive definite (proportional and derivative) gain matrices. We show that the global asymptotic stability attribute also holds for a class of gain matrices depending on the manipulators state. This feature increases the potential of the computed-torque scheme to handle practical constraints in actual robots such as presence of friction in the joints and actuators with limited torque capabilities. We illustrate this potential by means of a fuzzy self-tuning algorithm to select the proportional and derivative gains according to the actual tracking position error. Experiments on a two degrees of freedom robot arm shown the usefulness of the proposed approach.

Addresses the visual servoing of robot manipulators in fixed-camera configuration. We present the experimental evaluation of three direct visual servo controllers on a planar two degrees of freedom direct-drive robot arm. These visual servo controllers belong to the family of transpose Jacobian-based control schemes yielding local asymptotic stability.

In this paper we propose a class of nonlinear PID global regulators for manipulators which do not include their dynamics in the central law. The structure of this class of global regulators is based on a linear PD feedback, plus an integral action driven by a nonlinear function of the joint position error, and the addition of the gradient of a C/sup 1/ artificial potential function satisfying some typical features required by the energy shaping methodology. By using Lyapunov's direct method and LaSalle's invariance principle we provide simple explicit conditions on the regulators gains to ensure global asymptotic stability.

This paper is focused on estimating the dynamic parameters of robot manipulators. A new hybrid identification scheme based on the supplied energy regression model is proposed. Experimental results on a two degrees of freedom direct-drive robot are presented.

In this paper we present in a simple and unified framework, the asymptotic stability analysis for energy shaping plus damping injection based set-point controllers for rigid and elastic joint robot manipulators by involving passivity theorems. Such an analysis is made for both cases: when position and velocity measurements are available for feedback purposes, and when only position measurements are available. To this end we use a particular case of a theorem introduced by Byrnes et al. (1991) and we present an adaptation, for asymptotic stability purposes, of a passivity theorem given by Canudas de Wit et al. (1996) and Khalil (1996).

We present a new controller to solve the visual servo control problem for planar robots in the fixed-camera configuration. For a static target we characterize the global closed loop attractor using the full robot dynamics, and prove local asymptotic stability of the end-effector tracking error. Neither the inverse kinematics nor the inverse Jacobian are used in the controller. Experimental results on a 2-DOF direct drive manipulator are presented.

In this paper, we propose a simple controller: the saturated P-saturated D controller with gravity compensation to solve the global regulation problem under actuator torque constraints. The performance of the proposed controller is illustrated via simulations on a two degree-of-freedom robot.

In this paper we address the visual servoing of planar robot manipulators under fixed-camera configuration. The control goal is to place the robot end-effector over a desired static target by using a vision system equipped with a fixed camera to 'see' the robot end-effector and target. We analyze an image-based controller, whose implementation requires the robot Jacobian, the gravitational torque vector, and the camera orientation. Further, the robot manipulator is not treated as an ideal positioning device but modeled by the Lagrangian dynamics. We formally prove that the overall closed-loop system composed by the full nonlinear robot dynamics and the controller is Lyapunov stable. Also, we demonstrate that the controller is capable to yield an asymptotically stable system which is robust against radial lens distortions and uncertainty in the camera orientation. Simulations on a two degrees of freedom arm are presented to illustrate the controller performance.

Proposes a systematic methodology, based on the energy shaping framework, to find strict Lyapunov functions for a class of global regulators for robot manipulators. The class of controller is described by control laws composed by a gradient of an artificial potential energy plus a linear velocity feedback. The authors provide explicit sufficient conditions on the artificial potential energy which allows them to obtain in a straightforward manner a strict Lyapunov function. Based on this technique the authors establish strict Lyapunov functions for well known regulators and propose a new one.

In this paper we characterize a class of passivity-based regulators for robot manipulators which, without assuming velocity measurement, aims at modifying the total energy of the closed loop and adding the required dissipation. The class is parametrized in terms of the desired closed loop total energy function, specified by the designer. We show that several apparently unrelated stabilizing output feedback regulators recently reported in the literature, are in fact particular cases of this class. Our results aim at providing a unified framework to compare different stabilizing schemes via analysis of their energy dissipation properties.>

In the present paper, we propose an explicit design procedure for selecting the proportional and derivative gains of the PD control with computed feedforward of robot manipulators. The proposed procedure, which is easily obtained from the robot dynamics and desired trajectory, assures that the closed-loop system has an unique equilibrium point. In addition, this equilibrium turns out to be (locally) exponentially stable. Simulation tests are included, with reference to a robot having two degrees of freedom.>

An alternative analysis that does not invoke the LaSalle invariance principle of the PD proportional-differential controller with gravity compensation for robots, presented in the above-titled paper by P. Tomei (ibid., vol.7, no.4, p.565-70, Aug. 1991) is established. The result is used to develop straightforwardly a new PD controller with adaptive gravity compensation, and conditions to ensure closed-loop stability and global zero position error convergence are given.>

Impedance control specifications for robot manipulators are given in terms of a desired motion trajectory and a desired dynamic relationship between position errors and interaction forces. An adaptive implementation is proposed as an alternative to reduce the design sensitivity due to model-manipulator parameter mismatch. Two adaptive controllers that globally achieve the impedance objective for the general nonlinear dynamic model are presented. The controller structures consist of a nonlinear feedback of positions, velocities, and end-effector applied forces. Computer simulations were carried out to demonstrate stability and performance control.>

The stability of adaptive controllers for robot manipulators using an input-output approach is studied. A recently proposed adaptive controller is analyzed in this functional analytic framework. Global stability results are presented. The input-output approach provides a framework for control and adaptation laws design.>