Emiliano Pereira

Integral Resonant Control for Vibration Damping and Precise Tip-Positioning of a Single-Link Flexible Manipulator

In this paper, we propose a control design method for single-link flexible manipulators. The proposed technique is based on the integral resonant control (IRC) scheme. The controller consists of two nested feedback loops. The inner loop controls the joint angle and makes the system robust to joint friction. The outer loop, which is based on the IRC technique, damps the vibration and makes the system robust to the unmodeled dynamics (spill-over) and resonance frequency variations due to changes in the payload. The objectives of this work are: 1) to demonstrate the advantages of IRC, which is a high-performance controller design methodology for flexible structures with collocated actuator-sensor pairs and 2) to illustrate its capability of achieving precise end-point (tip) positioning with effective vibration suppression when applied to a typical flexible manipulator. The theoretical formulation of the proposed control scheme, a detailed stability analysis and experimental results obtained on a flexible manipulator are presented.

Brief paper: Adaptive input shaping for manoeuvring flexible structures using an algebraic identification technique

Input shaping is an efficient feedforward control technique which has motivated a great number of contributions in recent years. Such a technique generates command signals with which manoeuvre flexible structures without exciting their vibration modes. This paper presents a novel adaptive input shaper based on an algebraic non-asymptotic identification. The main characteristic of the algebraic identification in comparison with other identification methods is the short time needed to obtain the system parameters without defining initial conditions. Thus, the proposed adaptive control can update the input shaper during each manoeuvre when large uncertainties are present. Simulations illustrate the performance of the proposed method.

Feedforward control of multimode single-link flexible manipulators based on an optimal mechanical design

Abstract This paper proposes a method to modify the dynamics of single-link flexible arms in order to allow the design of a control system which is more robust to changes in the payload value. This is achieved by attaching some small lumped masses at some points of the link. Therefore, connections between the dynamics and the feedforward control of single-link flexible manipulators are considered to simplify the control and make the system faster and more robust. The feedforward controller design is based on the so-called dynamic model inversion technique derived from a discretization of the system dynamic model. A comparative assessment between the discrete model inversion based on feedforward control and the command preshaping technique is presented. Numerical examples and experimental results thus changing the payload values are carried out.

Concurrent Design of Multimode Input Shapers and Link Dynamics for Flexible Manipulators

This paper proposes a concurrent design of a robust multimode input shaper and a modification of the link dynamics for flexible manipulators. The input shaper design takes advantage of this modification in reducing the time delay introduced while the residual vibration is kept under a prescribed level in the presence of significant parameter variations. An optimization procedure to tune the shaper coefficients concurrently, which are calculated simultaneously for all considered vibration modes, and the modification of the link dynamics, carried out by attaching small lumped masses along the link. Significant reductions in the time delay introduced by the proposed concurrent design are reported on an experimental single-link flexible manipulator.

A new design methodology for passivity-based control of single- link flexible manipulators

This work presents a new methodology for the design of passivity-based controls as applied to single-link flexible arms. The objective is the end-point position control with effective vibration suppression. The control scheme consists of two nested control loops (named inner and outer loop) and a linear strain feedback to decouple the motor and the link dynamics. The controller design is based on the passivity relationship existing between the integral of the torque measured at the base of the arm (coupling torque) and the motor angle. The inner loop controls the motor position and the outer loop keeps the stability of the overall system to large changes in the robot payload and cancels the residual vibration. The control scheme design is validated both in simulation as well as in experiments.

Approaches of Discrete Feedforward Control for Vibration Cancellation in Multimode Single-Link Flexible Manipulators

This paper presents a new approach to the feedforward control of flexible arms. The objective is the end-point position control and vibration suppression in a single-link flexible manipulator with several vibration modes. The feedfoward controller is designed based on the so-called dynamic model inversion technique derived from a discretization of its dynamic model. By modifying the system dynamics with a feedback of the torque at the base of the arm, this technique can be applied in a very simple way. The proposed method is general in the sense that it removes remaining oscillations in the steady state under any number of significant vibration modes. A numerical example of the application of the method on an experimental robot arm is carried out and finally, some preliminary experimental results are presented

Exploring vibration control strategies for a footbridge with time-varying modal parameters

This paper explores different vibration control strategies for the cancellation of human-induced vibration of a structure with time-varying modal parameters. The motivation of this study is an urban stress-ribbon footbridge (Pedro Gomez Bosque, Valladolid, Spain) that, after a whole-year monitoring, it has been obtained that the natural frequency of a vibration mode at approximately 1.8 Hz (within the normal range of walking) changes up to 20%, mainly due to temperature variations. Thus, this paper takes the annual modal parameter estimates (aprox. 14000 estimations) of this mode and designs three control strategies: a) a tuned mass damper (TMD) tuned to the aforementioned mode using its most-repeated modal properties, b) a semi-active TMD with an on-off control law for the TMD damping, and c) an active mass damper designed using the well-known velocity feedback control strategy with a saturation nonlinearity. Illustrative results have been reported from this preliminary study.