Robust exact differentiation via sliding mode technique

The authors give some initial results on the adaptive control of minimum-phase nonlinear systems which are exactly input-output linearizable by state feedback. Parameter adaptation is used as a technique to make robust the exact cancellation of nonlinear terms, which is called for in the linearization technique. The application of the adaptive technique to control of robot manipulators is discussed. Only the continuous-time case is considered; extensions to the discrete-time and sampled-data cases are not obvious. >

Adaptive control of linearizable systems

This paper provides a survey of modern nonlinear filtering methods for attitude estimation. Early applications relied mostly on the extended Kalman filter for attitude estimation. Since these applications, several new approaches have been developed that have proven to be superior to the extended Kalman filter. Several of these approaches maintain the basic structure of the extended Kalman filter, but employ various modifications in order to provide better convergence or improve other performance characteristics. Examples of such approaches include: filter QUEST, extended QUEST and the backwards-smoothing extended Kalman filter. Filters that propagate and update a discrete set of sigma points rather than using linearized equations for the mean and covariance are also reviewed. A twostep approach is discussed with a first-step state that linearizes the measurement model and an iterative second step to recover the desired attitude states. These approaches are all based on the Gaussian assumption that the probability density function is adequately specified by its mean and covariance. Other approaches that do not require this assumption are reviewed, Associate Professor, Department of Mechanical & Aerospace Engineering. Email: johnc@eng.buffalo.edu. Associate Fellow AIAA. Aerospace Engineer, Guidance, Navigation and Control Systems Engineering Branch. Email: Landis.Markley@nasa.gov. Fellow AIAA. Postdoctoral Research Fellow, Department of Mechanical & Aerospace Engineering. Email: cheng3@eng.buffalo.edu. Member AIAA.

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Survey of nonlinear attitude estimation methods

We present an adaptive version of the computed torque method for the control of manipulators with rigid links. The algorithun estimates parameters on-line which appear in the non-linear dynamic model of the manipulator, such as load and link mass parameters and friction parameters, and uses the latest estimates in the computed torque servo. We present what we believe is the first golbally convergent, rigorous proof of the stability of such a scheme in its non-linear setting, as well as its asymptotic properties and conditions for parameter convergence. We illustrate the theory with some simulation results.

Adaptive control of mechanical manipulators

This paper describes a general passivity-based framework for the control of flexible joint robots. Recent results on torque, position, as well as impedance control of flexible joint robots are summarized, and the relations between the individual contributions are highlighted. It is shown that an inner torque feedback loop can be incorporated into a passivity-based analysis by interpreting torque feedback in terms of shaping of the motor inertia. This result, which implicitly was already included in earlier work on torque and position control, can also be used for the design of impedance controllers. For impedance control, furthermore, potential energy shaping is of special interest. It is shown how, based only on the motor angles, a potential function can be designed which simultaneously incorporates gravity compensation and a desired Cartesian stiffness relation for the link angles. All the presented controllers were experimentally evaluated on DLR lightweight robots and their performance and robustness shown with respect to uncertain model parameters. Experimental results with position controllers as well as an impact experiment are presented briefly, and an overview of several applications is given in which the controllers have been applied.

http://journals.sagepub.com/doi/pdf/10.1177/0278364907073776

A Unified Passivity-based Control Framework for Position, Torque and Impedance Control of Flexible Joint Robots

An observer for reconstructing the joint velocities of rigid-joint robots is proposed. The approach consists of exploiting the structural properties of the robot dynamics. The associated error dynamics are shown to be asymptotically stable. The observer furnishes the state estimate directly in the physical coordinates, so that no transformation is needed. The stability of some state feedback controllers having the proposed observer inserted in the feedback loop is proved. The structure of the observer and its convergence are shown. The stability of the whole system is analyzed when the observer is used in connection with a point-to-point controller and a trajectory controller. >

Robot control by using only joint position measurements

Paper: Model reference adaptive control algorithms for industrial robots

High-gain observers in the state and estimation of robots having elastic joints

Robot manipulators in which the joints exhibit a certain amount of elasticity are discussed. The model of such robots is highly nonlinear, and available techniques to build nonlinear observers generally do not apply. A procedure to construct approximate nonlinear observers is proposed that uses a recent approach to deriving observers based on geometric nonlinear control theory together with an approximation technique. The conditions under which an exact observer exists are derived. Some examples are given for which simulation tests assure a good performance even when the observer is connected to a control system. >

A nonlinear observer for elastic robots

A dynamic output feedback controller for flexible joint robots is presented which guarantees asymptotic tracking of a desired trajectory, starting from arbitrary initial conditions. The controller needs only the measurements of the positions of the links and the knowledge of an upper bound on the initial tracking error. >

Salvatore Nicosia

Papers

Robot control by using only joint position measurements

Paper: Model reference adaptive control algorithms for industrial robots

High-gain observers in the state and estimation of robots having elastic joints

A nonlinear observer for elastic robots

A tracking controller for flexible joint robots using only link position feedback