Sofía Avila-Becerril

Consensus control of flexible joint robots with uncertain communication delays

Synchronization of networks composed by fully-actuated Lagrangian systems has received a lot of attention from the control theory community. Unfortunately, the case of networks composed by under-actuated systems of the same kind has not been deeply studied and the related literature is very reduced. The aim of this paper is to contribute towards the establishment of a control scheme for this class of networks by solving the particular case of a network composed by agents defined by Flexible-joint robots. The proposed schemes consider the presence of unknown delays in the communication channels. The usefulness of the controllers is validated through numerical simulations.

Consensus control of flexible-joint robots

Synchronisation of networks composed by fully actuated robot manipulators has received a lot of attention from the control theory community. Unfortunately, the case of under-actuated robots has not been deeply studied. The aim of this paper is to extend previous results reported by the authors addressing the particular (but of practical interest) case of networks composed by flexible-joint robots. The main feature of the contribution is to consider a change of coordinates, first introduced in Nuno, Ortega, Basanes and Hill, to solve the consensus problem assuming the existence of unknown delays in the communication channels. The extension is twofold, namely: the presentation of a control scheme that, in contrast to the one considered in Avila-Becerril and Espinosa-Perez, does not require knowledge of the initial conditions and the proof that the controller can also be implemented in Cartesian coordinates. The usefulness of the contribution is illustrated through numerical simulations.

Global position-feedback tracking control of flexible-joint robots

We solve the open problem of global tracking control of 2nd-degree under-actuated lossless (without friction) Lagrangian systems via position measurements only. For flexible-joint robots, we design a dynamic controller which is based on measurements of link and joint positions only. Then, approximate differentiation is used for link velocities and a simple Luenberger observer for rotor velocities. The main results constitute a significant extension of recent work on observerless output-feedback control of Lagrangian systems. Strictly speaking, we establish uniform global asymptotic stability for the closed loop system.

Output-feedback global tracking control of robot manipulators with flexible joints

We present a controller for flexible-joint robots without link velocity measurement. Our main result consists in a simple controller of the type proportional-derivative plus feedforward and a series of cascaded filters; the control design is reminiscent of classical backstepping control. To avoid the assumption that link velocities, accelerations and jerks are measured, we use approximate differentiation. The originality of our work lays in establishing uniform global asymptotic stability for the closed-loop system.

Consensus control of flexible joint robots

Synchronization of networks composed by fully-actuated robot manipulators has received a lot of attention from the control theory community. Unfortunately, the case of under-actuated robots has not been deeply studied. The aim of this paper is to extend previous results reported by the authors [2] addressing the particular (but of practical interest) case of networks composed by flexible-joint robots. The main feature of the contribution is to consider a change of coordinates, first introduced in [1], to solve the consensus problem assuming the existence of unknown delays in the communication channels. The extensions consist in: the presentation of a control scheme that, in contrast to the one considered in [2], does not require knowledge of the initial conditions; the proof that the controller can also be implemented in Cartesian coordinates; and the statement of the stability properties adopting a Cascaded systems perspective. The usefulness of the contribution is illustrated through numerical simulations.

A Separation Principle for Underactuated Lossless Lagrangian Systems

We study under-actuated Lagrangian systems without dissipative forces, augmented by a chain of integrators. For such systems, we solve the open problem of global tracking control via position measurements only; strictly speaking, we establish uniform global asymptotic stability for the closed loop system. As a corollary, we obtain an original statement for flexible-joint robots, which closes a long-standing open problem of output feedback nonlinear control.

Dynamic Characterization of Typical Electrical Circuits via Structural Properties

The characterization of a class of electrical circuits is carried out in terms of both stability properties and steady-state behavior. The main contribution is the interpretation of the electrical topology (how the elements that conform the circuits are interconnected) in terms of mathematical properties derived from the structure of their models. In this sense, at what extent the topology by itself defines the dynamic behavior of the systems is explained. The study is based on the graph theory allowing capturing, departing from the well-known Kirchhoff laws, the topology of the circuits into several matrices with specific structure. The algebraic analysis of these matrices permits identifying conditions that determine whether the system is stable in the sense of Lyapunov and the kind of steady-state behavior that it exhibits. The approach is mainly focused on typical topologies widely used in practice, namely, radial, ring, and mesh networks.

A simple PI 2 D output feedback controller for the Permanent Magnet Synchronous Motor

In this paper it is presented a PI control scheme with guaranteed stability properties for the Permanent Magnet Synchronous Motor (PMSM). The proposed controller solves the speed tracking control problem and is of the output feedback type, since it is assumed that only stator currents and the rotor position are available for measurement, i.e. it is avoided the use of (noisy) speed sensors. The algorithm is equipped with an adaptation mechanism that compensates a (constant) unknown load torque. From a theoretical perspective its more valuable characteristic lies in the fact that Uniform Global Exponential Stability (UGES) of the desired operation regime is achieved. The usefulness of the proposed scheme is evaluated in a numerical setting.