Claudio Bonivento

A theory of generalized inverses applied to robotics

Robokcs research has made extensive use of techniques based on me Moore-Penrose inverse, or generalized inverse, of matri als. Recently it has been pointed out how noninvariant results may, in general, be obtained by applying these techniques to other areas of robotics, namely hybrid control and inverse ve locity kinematics. Unfortunately, the problems are not restricted to just these particular areas in robotics but are connected with misleading definitions of the metric properties of the six- dimensional wrench and twist vector spaces used in robotics. The current definitions lead to inconsistent results (i.e., results that are not invariant with respect to changes in the reference frame andlor changes in the dimensional units used to express the problem. As a matter of fact, given a linear system u = Ax, where the matrix A may be singular, the Moore-Penrose theory of generalized inverses may be properly and directly applied only when the vector space U of vector u and the vector space X of vector x are inner product spaces. Arbitrary assignment of Euclidean inner products to the space U and X when the vectors u and x have elements with different physical units can lead to inconsistent and noninvariant results. In this article the problem of inconsistent, noninvariant solutions X s to u = Ax in robotics is briefly reviewed and a general theory for com puting consistent, gauge-invariant solutions to nonhomogeneous systems of the form u = Ax is developed. In addition, the dual relationship between rigid-body kinematics and statics is de fined formally as a particular, linear algebraic system whose solution system is also a dual system. Examples illustrate the theory.

Implicit fault-tolerant control: application to induction motors

In this paper we propose an innovative way of dealing with the design of fault-tolerant control systems. We show how the nonlinear output regulation theory can be successfully adopted in order to design a regulator able to offset the effect of all possible faults which can occur and, in doing so, also to detect and isolate the occurred fault. The regulator is designed by embedding the (possible nonlinear) internal model of the fault. This idea is applied to the design of a fault-tolerant controller for induction motors in presence of both rotor and stator mechanical faults.

On the invariance of the hybrid position/force control

Recently, the noninvariance nature of the Raibert and Craig hybrid control scheme, based on the work of Mason and others, has been pointed out. In fact, on the basis of the screw theory, Lipkin and Duffy demonstrated that the selection of the position and force controlled degrees of freedom in the Raibert and Craig scheme, may give wrong results if a translation or change in unit length of the coordinate frame is performed. A general theoretical solution to this problem, called ‘kinestatic filtering’, has been given by Lipkin and Duffy. In this paper, the two approaches are summarized and discussed. First, the conditions in which the Mason filtering technique fails are determined and, second, the situations where the Lipkin and Duffy approach cannot be applied owing to degeneracy of the twist and wrench spaces, are reported. As a consequence of this analysis, a new invariant kinestatic filtering method is proposed. The method here presented is based on the original Mason approach and requires the definition of a task-dependent filter based on the knowledge of the position of the compliant frame. Examples are presented and discussed.

Fault-tolerant control of the ship propulsion system benchmark☆

The application of a new fault-tolerant control methodology to the benchmark proposed in Zamanabadi and Blanke (Control Engineering Practice 7(2) (1999)) is considered. The benchmark regards the model of a propulsion system for a marine vehicle developed by the Control Engineering Department of Aalborg University. After a brief description of the system, a fault analysis is carried out leading to a set of possible faults and remedial actions. Then the fault detection and identification method, and the reconfiguration algorithm are described. Simulations on the model illustrate the performance of the fault tolerant system for some selected fault scenarios.

WireMan: a portable wire manipulator for touch-rendering of bas-relief virtual surfaces

An haptic interface actuated by parallel wires is under development. Differently from other known wire-based haptic devices, the proposed system explicitly addresses the capability to be tailored on a human body in order to obtain a portable interface, that should be used for achieving haptic perception by visually impaired people. The device is based on a system of three concurrent wires connected to the operators finger, obtaining 3D mobility capabilities. The paper shows in particular how this device can be efficiently used in the exploration of bas-relief virtual surfaces in spite of its intrinsic manipulability limits. This capability has been fully confirmed by preliminary 2D tests, whose results are presented and discussed.

Balanced robust regulation of a magnetic levitation system

In this brief, we consider the problem of disturbance suppression for a magnetic levitation system in presence of physical uncertainties. The problem is cast as a nonlinear regulation problem in presence of input constraint and an internal model-based regulator is designed. A control law which does not rely upon complementarity or relaxed complementarity conditions is proposed and compared, from an energetic viewpoint, with complementary control strategies usually presented in literature. Simulation results are presented to confirm the effectiveness of the design.

Discrete variable-structure integral controllers

The subject of this paper is the analysis and the design of a class of robust discrete-time variable-structure controllers of integral type. We refer to the discontinuous integral control (DIC) technique, already developed by the authors for the time-continuous case, where a nonlinear integral action is used for estimating the external disturbance and keeping small the discontinuous term in the control law and the subsequent chattering effect. A discretised version of the DIC algorithm, which is properly modified in order to take into account the time-derivative information on the controlled variable, is introduced and discussed. The so-obtained discrete-time controller shows to be very effective in reducing the chattering when the system parameters are known. Moreover, to cope with a specific case of unknown parameters, a new adaptive control structure is proposed and analysed. The local asymptotic stability of the resulting closed-loop system is proved in the case of constant external disturbances. Finally, simulation results on the velocity control of a DC motor end the paper.

Advances in Control Theory and Applications

Modeling and Control of Autonomous Helicopters.- Efficient Quantization in the Average Consensus Problem.- Human-Robot Interaction Control Using Force and Vision.- A Dissipation Inequality for the Minimum Phase Property of Nonlinear Control Systems.- Input Disturbance Suppression for Port-Hamiltonian Systems: An Internal Model Approach.- A Systems Theory View of Petri Nets.- Wireless Sensing with Power Constraints.- The Important State Coordinates of a Nonlinear System.- On Decentralized and Distributed Control of Partially-Observed Discrete Event Systems.- A Unifying Approach to the Design of Nonlinear Output Regulators.- Controller Design Through Random Sampling: An Example.- Digital Control of High Performance Power Supplies for a Synchrotron Light Source.- Distributed PCHD-Systems, from the Lumped to the Distributed Parameter Case.- Observability and the Design of Fault Tolerant Estimation Using Structural Analysis.- Robust Hybrid Control Systems: An Overview of Some Recent Results.

Control System Design of a Dexterous Hand for Industrial Robots

Abstract The paper illustrates the goals and the present development state of a research programme aimed at the realization of a robot’s dexterous extremity device, suitable for carrying out grasping and manipulation operations on objects of different type and shape. Following a brief description of the device’s mechanical configuration, sensorial equipment and driving system, the main design issues and the solutions adopted up to now in the prototype, as regards the control strategies and the system architecture, are outlined. Experimental results related to the grasping performance of the device are also presented, together with the future development plans for the project.

A Detection-Estimation Multifilter Approach with Nuclear Application

Abstract This paper deals with the use of the optimal filtering for realizing a detector of system abnormal operating conditions. In particular, a pulsed extraction column, which is a very critical unit in the nuclear fuel reprocessing cycle, is considered and a system based on two different filters and a sequential innovation-detector is proposed. The obtained results show that it is possible to satisfy both column hold-up tracking and early detection of nuclear material diversion requirements.