Rafael Kelly

Bio: Rafael Kelly is an academic researcher from Ensenada Center for Scientific Research and Higher Education. The author has contributed to research in topics: Control theory & Robot control. The author has an hindex of 38, co-authored 142 publications receiving 5083 citations. Previous affiliations of Rafael Kelly include University of California, Santa Barbara.

Control of Robot Manipulators in Joint Space

Abstract: Part I: Preliminaries.- Introduction to Part I.- What Does 'Control of Robots' Involve?.- Mathematical Preliminaries.- Robot Dynamics.- Properties of the Dynamic Model.- Case Study: The Pelican Prototype Robot.- Part II: Position Control.- Introduction to Part II.- Proportional Control plus Velocity Feedback and PD Control.- PD Control with Gravity Compensation.- PD Control with Desired Gravity Compensation.- PID Control.- Part III: Motion Control.- Introduction to Part III.- Computed-torque Control and Computed-torque+ Control.- PD+ Control and PD Control with Compensation.- Feedforward Control and PD Control plus Feedforward.- Part IV: Advanced Topics.- Introduction to Part IV.- P'D' Control with Gravity Compensation and P'D' Control with Desired Gravity Compensation.- Introduction to Adaptive Robot Control.- PD Control with Adaptive Desired Gravity Compensation.- PD Control with Adaptive Compensation.- Appendices.- A. Mathematical Support.- B. Support for Lyapunov Theory.- C. Proofs of some Properties of the Dynamic Model.- D. Dynamics of Direct-current Motors.

Robust asymptotically stable visual servoing of planar robots

Abstract: In this paper we address the visual servoing of planar robot manipulators under fixed-camera configuration. The control goal is to place the robot end-effector over a desired static target by using a vision system equipped with a fixed camera to 'see' the robot end-effector and target. We analyze an image-based controller, whose implementation requires the robot Jacobian, the gravitational torque vector, and the camera orientation. Further, the robot manipulator is not treated as an ideal positioning device but modeled by the Lagrangian dynamics. We formally prove that the overall closed-loop system composed by the full nonlinear robot dynamics and the controller is Lyapunov stable. Also, we demonstrate that the controller is capable to yield an asymptotically stable system which is robust against radial lens distortions and uncertainty in the camera orientation. Simulations on a two degrees of freedom arm are presented to illustrate the controller performance.

Global positioning of robot manipulators via PD control plus a class of nonlinear integral actions

Abstract: Deals with the position control of robot manipulators. Proposed is a simple class of robot regulators consisting of a linear proportional-derivative (PD) feedback plus an integral action of a nonlinear function of position errors. By using Lyapunov's direct method and LaSalle's invariance principle, the authors characterize a class of such nonlinear functions, and they provide explicit conditions on the regulator gains to ensure global asymptotic stability. These regulators offer an attractive alternative to global regulation compared with the well-known partially model-based PD control with gravity compensation and PD control with desired gravity compensation.

A semiglobally stable output feedback PI/sup 2/D regulator for robot manipulators

Abstract: Provides an answer to the long-standing question of designing asymptotically stable proportional plus integral regulators with only position feedback for robots with uncertain payload. It has previously been shown in Kelly (1993) and Ailon and Ortega (1993) that globally asymptotically stable set-point regulators for robot manipulators without velocity measurement can be obtained replacing the velocity feedback of a proportional plus derivative controller by a filtered position feedback. In these schemes, the only robot prior information required is the evaluation of the gravity forces at the reference (constant) position. This prior knowledge is used to shape the robot potential energy to have a unique minimum at the desired position. A mismatch in the estimation of the gravity forces leads to a position steady-state error. The authors' main contribution in this paper is to obviate the need of this prior information via the inclusion of two integral terms, around the position error and the filtered position, respectively. Semiglobal stability of the resulting control law is established. >

A tuning procedure for stable PID control of robot manipulators

Abstract: In this paper we propose some simple rules for PID tuning of robot manipulators. The procedure suggested requires the knowledge of the structure of the inertia matrix and the gravitational torque vector of the robot dynamics, but only upper bounds on the dynamics parameters are needed. This tuning procedure is extracted from the stability analysis by using a suitable Lyapunov function together with the LaSalle invariance principle. We show that with this guideline, the overall closed-loop system is asymptotically stable. This procedure is illustrated for a two degrees-of-freedom robot

Adaptive Control

Abstract: This book, written by two major figures in adaptive control, provides a wealth of material for researchers, practitioners, and students. While some researchers in adaptive control may note the absence of a particular topic, the book‘s scope represents a high-gain instrument. It can be used by designers of control systems to enhance their work through the information on many new theoretical developments, and can be used by mathematical control theory specialists to adapt their research to practical needs. The book is strongly recommended to anyone interested in adaptive control.

A Survey on Analysis and Design of Model-Based Fuzzy Control Systems

Abstract: Fuzzy logic control was originally introduced and developed as a model free control design approach. However, it unfortunately suffers from criticism of lacking of systematic stability analysis and controller design though it has a great success in industry applications. In the past ten years or so, prevailing research efforts on fuzzy logic control have been devoted to model-based fuzzy control systems that guarantee not only stability but also performance of closed-loop fuzzy control systems. This paper presents a survey on recent developments (or state of the art) of analysis and design of model based fuzzy control systems. Attention will be focused on stability analysis and controller design based on the so-called Takagi-Sugeno fuzzy models or fuzzy dynamic models. Perspectives of model based fuzzy control in future are also discussed

A decentralized approach to formation maneuvers

Abstract: This paper presents a behavior-based approach to formation maneuvers for groups of mobile robots. Complex formation maneuvers are decomposed into a sequence of maneuvers between formation patterns. The paper presents three formation control strategies. The first strategy uses relative position information configured in a bidirectional ring topology to maintain the formation. The second strategy injects interrobot damping via passivity techniques. The third strategy accounts for actuator saturation. Hardware results demonstrate the effectiveness of the proposed control strategies.

Putting energy back in control

Abstract: Energy is one of the fundamental concepts in science and engineering practice, where it is common to view dynamical systems as energy-transformation devices. This perspective is particularly useful in studying complex nonlinear systems by decomposing them into simpler subsystems that, upon interconnection, add up their energies to determine the full system's behavior. The action of a controller may also be understood in energy terms as another dynamical system. The control problem can then be recast as finding a dynamical system and an interconnection pattern such that the overall energy function takes the desired form. This energy-shaping approach is the essence of passivity-based control (PBC), a controller design technique that is very well known in mechanical systems. Our objectives in the article are threefold. First, to call attention to the fact that PBC does not rely on some particular structural properties of mechanical systems, but hinges on the more fundamental (and universal) property of energy balancing. Second, to identify the physical obstacles that hamper the use of standard PBC in applications other than mechanical systems. In particular, we show that standard PBC is stymied by the presence of unbounded energy dissipation, hence it is applicable only to systems that are stabilizable with passive controllers. Third, to revisit a PBC theory that has been developed to overcome the dissipation obstacle as well as to make the incorporation of process prior knowledge more systematic. These two important features allow us to design energy-based controllers for a wide range of physical systems.