Leonardo Lanari

Tracking with disturbance attenuation for rigid robots

In this paper a tracking controller for rigid robots is presented solving a disturbance attenuation problem with global internal stability in the general case of unknown constant parameters. By using the well-known property of linearity in the parameters for the rigid robot dynamic equations, adaptive and H/sub /spl infin// control are combined successfully. Simulation results show a good behavior of the proposed tracking controller.

A family of asymptotically stable control laws for flexible robots based on a passivity approach

A general family of asymptotically stabilizing control laws is introduced for a class of nonlinear Hamiltonian systems. The inherent passivity property of this class of systems and the passivity theorem are used to show the closed-loop input/output stability which is then related to the internal state space stability through the stabilizability and detectability condition. Applications of these results include fully actuated robots, flexible-joint robots, and robots with link flexibility.<<ETX>>

Boundedness issues in planning of locomotion trajectories for biped robots

It is in general complex to consider the complete robot dynamics when planning trajectories for bipedal locomotion. We present an approach to trajectory planning, with the classical Linear Inverted Pendulum Model (LIPM), that takes explicit consideration of the unstable dynamics. We derive a relationship between initial state and the control input that ensures the overall system dynamics will converge to a stable steady state solution. This allows us to exploit the unstable dynamics to achieve system goals, while imposing constraints on certain degrees of freedom of the input and initial conditions. Based on this, we propose an approach to trajectory planning, and derive solutions for several typical applications. Experimental simulations using the REEM-C biped robot platform of Pal Robotics validate our approach.

Nonlinear Regulation of End-Effector Motion for a Flexible Robot Arm

In this paper we consider the problem of controlling via state-feedback the end-effector motion of a one-link flexible robot arm described by a nonlinear dynamic model. Due to the non-minimum phase nature of the system zero-dynamics, use of pure inversion-based techniques is unfeasible. In order to obtain stable tracking of desired tip trajectories, a nonlinear regulation approach is followed. Alternate general design procedures that exploit system invertibility are presented, leading to regulators of different complexity and realtime demand. Issues about the generation of output reference trajectories and the off-line computation of the associated steady-state trajectories are discussed, using the one-link flexible arm as a case study. Simulation results obtained for a spline trajectory and for a point-to-point motion show the achievable tracking accuracy and the wide applicability of the presented control technique.

Brief A new separation result for a class of quadratic-like systems with application to Euler-Lagrange models

A separation result for some kind of global stabilization via output feedback of a class of nonlinear systems, under the form of some stabilizability by state feedback on the one hand, and some unboundedness observability on the other hand is presented. They allow to design, for any domain of output initial condition, some dynamic output feedback controller achieving global stability. It is also highlighted how disturbance attenuation can further be achieved on the same basis. As an example, the proposed conditions are shown to be satisfied by the class of so-called Euler-Lagrange systems, for which a tracking output feedback control law is thus proposed.

ENERGY-BASED CONTROL OF THE BUTTERFLY ROBOT

Abstract We address the control problem for the Butterfly, an interesting example of 2-dof underactuated mechanical system. This robot consists of a butterfly-shaped rotational link on whose rim a ball rolls freely. The control objective is to stabilize the robot at a certain unstable equilibrium. To this end, exploiting the existence of heteroclinic trajectories, we extend a previously proposed energy-based technique. Simulation results show the effectiveness of the presented method.

On the Role of Passivity and Output Injection in the Output Feedback Stabilisation Problem: Application to Robot Control

Existing dynamic output feedback stabilisation techniques of non-linear systems are applicable mainly when the unmeasurable part of the state enters linearly. Our objective in this paper is to identify a class of systems, non-linear with respect to the unmeasured variables, which are globally asymptotically stabilisable via dynamic output feedback. To achieve this characterisation we explore two routes: systems passifiability, and the combination of state feedback plus output injection. While the first line of research is motivated by the recent developments in robot control, the second one is an attempt to extend the work of the first author to the non-linear dependence case. Our contributions are twofold: first, we present a series of general theorems that identify the class mentioned above. Second, we apply these theorems to derive in a systematic manner, and using a unified framework, some recent schemes on global set point control of rigid and elastic joint robots using only position measurements.

Manual guidance of humanoid robots without force sensors: Preliminary experiments with NAO

In this paper we propose a method to perform manual guidance with humanoid robots. Manual guidance is a general model of physical interaction: here we focus on guiding a humanoid by its hands. The proposed technique can be, however, used also for joint object transportation and other tasks implying human-humanoid physical interaction. Using a measure of the Instantaneous Capture Point, we develop an equilibrium-based interaction technique that does not require force/torque or vision sensors. It is, therefore, particularly suitable for low-cost humanoids and toys. The proposed method has been experimentally validated on the small humanoid NAO.

Inversion-based gait generation for humanoid robots

In this paper, we address the problem of gait generation for bipedal robots. We cast the determination of a Center of Mass (CoM) reference trajectory for a given Zero Moment Point (ZMP) desired behaviour as a stable inversion problem for non-minimum phase systems and obtain an analytical solution for any given ZMP trajectory. Our method exploits results from our previous research, in which we derived a family of bounded CoM trajectories associated to a given desired ZMP trajectory.

Hierarchical control implementation

The recently introduced concept of system abstraction appears to be a promising tool for control purposes in a hierarchical framework. While propagation of systems properties has been extensively studied, little investigation has been carried out on how a high-level control law is implemented on the low-level original system. In this paper we address this problem from a geometric point of view.