Publications

A direct visual-servoing algorithm for control of a space-based two-arm manipulator is proposed in this paper. The algorithm can be utilized in a two-arm manipulators configuration, where one of the arms performs the manipulation and the second arm is dedicated to the observation of the target zone of manipulation. The algorithm utilizes both visual features extracted from onboard cameras and force and torque measured at the manipulator's end-effector to control the movements of the manipulator during on-orbit servicing operations. The algorithm takes into account the relative dynamics of the bodies involved, it relies on images taken independently from de-localized cameras, e.g. at the end-effector of a second manipulator, and it integrates an impedance control for the compensation of eventual contact reactions when the end effector touches and operates the target body. The analytical derivations demonstrate the stability of the algorithm and incorporate an impedance compliance strategy into an optimal framework formulation. Simulations results in two different scenarios have been presented to show the adequate behavior of the presented approach in on-orbit-servicing operations.

Purpose The purpose of this paper has been to present new solutions to the nonlinear control problem of the degrees of freedom (6-DOF) attitude dynamics of reentry space vehicles. Among eligible control methods for the spacecraft’s attitude dynamics one can distinguish some sliding-mode control schemes. Besides there are several backstepping control approaches. In addition, one can find results on model predictive control concepts and optimal control-type concepts. Furthermore, one can distinguish methods which perform disturbance estimation and disturbance compensation thus improving the robustness of the reentry space vehicles’ control loop. Besides, this control problem is often treated with use of methods which rely on state-space model transformations and on changes of state variables. The aim of the present paper has been to achieve control and stabilization for the attitude dynamics of reentry space vehicles without forth and back state-space model transformations, changes of state variables (diffeomorphisms), and without the associated singularity issues. To this end, two new nonlinear control methods have been proposed: (i) nonlinear optimal control and (ii) flatness-based control in successive loops. Design/methodology/approach In this paper, the control problem for the multivariable and nonlinear 6-DOF dynamics of the attitude of autonomous reentry space vehicles is solved with the use of (i) a nonlinear optimal control method and (ii) a flatness-based control approach which is implemented in successive loops. To apply method (i) that is nonlinear optimal control, the dynamic model of the reentry space vehicle undergoes approximate linearization at each sampling instant with the use of first-order Taylor series expansion and through the computation of the associated Jacobian matrix. The linearization point is defined by the present value of the system’s state vector and by the last sampled value of the control inputs vector. To compute the feedback gains of the optimal controller an algebraic Riccati equation is repetitively solved at each time-step of the control algorithm. The global stability properties of the nonlinear optimal control method are proven through Lyapunov analysis. To implement control method (ii), that is flatness-based control in successive loops, the state-space model of the 6-DOF attitude dynamics of the autonomous reentry space vehicles is separated into two subsystems, which are connected between them in cascading loops. Each one of these subsystems can be viewed independently as a differentially flat system and control about it can be performed with inversion of its dynamics as in the case of input-output linearized flat systems. The state variables of the second subsystem become virtual control inputs for the first subsystem. In turn, exogenous control inputs are applied to the second subsystem. The whole control method is implemented in two successive loops and its global stability properties are also proven through Lyapunov stability analysis. The proposed method achieves stabilization of the attitude dynamics of the space vehicle without the need of diffeomorphisms and complicated state-space model transformations. Findings In the first control method that the article proposes, the dynamic model of the attitude of the reentry space vehicle undergoes approximate linearization around a temporary operating point which is updated at each sampling period. For the approximately linearized state-space description of the system, an H-infinity feedback controller is designed. To select the controller’s gains, an algebraic Riccati equation is repetitively solved at each time-step of the control method. The global stability properties of the control scheme are proven through Lyapunov analysis. In the second control method of the paper, the dynamic model of the reentry space vehicle is decomposed into a series of subsystems which are connected in chained form. It is proven that these subsystems if viewed independently, are differentially flat. In the chained subsystems, the state vector of the subsequent subsystem becomes virtual control input to the preceding subsystem. From the last subsystem, the real control inputs vector is found. The global stability properties of the flatness-based control method are also proven through Lyapunov analysis. Research limitations/implications There are no research limitations about the proposed control methods for the attitude dynamics of reentry space vehicles. On the contrary, a benefit from using either the nonlinear optimal control approach or the flatness-based control in successive loops for the attitude dynamics of the reentry space vehicle is that a solution of the control and stabilization problem for this nonlinear system can be reached without state-space model transformations and complicated changes of state variables. Practical implications A significant part of the research on nonlinear control for aerospace systems has been on the application of state-space model transformations which allow for writing these systems’ dynamics into an equivalent representation where the solution of the control and state estimation problems can be significantly simplified. In this regard, Lie algebra-based control methods and flatness-based control with transformation into canonical forms pursue the application of diffeomorphisms which allow for writing the initial nonlinear state-space model into an equivalent input-output linearized state-space form. These transformations often precede also the application of sliding-mode control, because it is only for systems in the input-output linearized form that one can follow a systematic procedure for selecting sliding surfaces. The nonlinear optimal and the flatness-based control method in successive loops, which are proposed in this paper, achieve solution for the control and stabilization problem of the attitude dynamics of reentry space vehicles without needing to apply any transformations for these spacecrafts’ state-space model and without imposing any changes of state variables. Social implications Control for autonomous reentry space vehicles has been a nontrivial research topic in the area of aerospace science and technology. Obviously, there is significant benefit from solving the attitude control problem for reentry space vehicles These aerospace systems become more reliable and the success of the associated missions is ensured. Space exploration and exploitation with the use of reentry space vehicles is carried out for civilian or defense purposes and affects the quality of living, prosperity, peace and international cooperation at a worldwide scale. Originality/value The results of this study are genuine and novel. The first method that the paper proposes for the 6-DOF attitude dynamics of reentry space vehicles is a nonlinear optimal (H-infinity) control scheme. The second method that the paper proposes for the attitude dynamics of reentry space vehicles is flatness-based control implemented in successive loops. The proposed methods achieve stabilization of the attitude dynamics of the space vehicle without the need of diffeomorphisms and complicated state-space model transformations.

En el presente articulo se describe la investigacion docente desarrollada con el objetivo de llevar a cabo el seguimiento y aplicacion, del sistema interno de garantia de calidad de la Escuela Politecnica Superior de la Universidad de Alicante, al Master Universitario en Automatica y Robotica. Esta investigacion es fruto de una red docente en la que han participado todos los profesores con docencia en el Master, y en la que han trabajado coordinadamente con el objetivo de recoger los principales indicadores de calidad del Master atendiendo a distintos criterios. Estos indicadores han servido, por un lado, para comprobar la existencia o no de deficiencias en la implantacion e imparticion del Titulo. Por otro lado, estos indicadores han servido como base para la elaboracion de la documentacion requerida para la reacreditacion del Master ante la ANECA. En este articulo se describe la coordinacion llevada a cabo, las principales consideraciones a tener en cuenta para la implantacion del sistema de garantia de calidad, asi como las conclusiones extraidas de la red.

This paper presents a non-destructive disassembly method. It tries to make up for limitations of other methods based on contact surfaces. It uses a contact surfaces graph and shows an algorithm to obtain the movement sequence needed for the disassembly of two objects, using a composition of transfer movement. It performs a second filter to obtain the exact disassembly direction from the group of directions obtained from the contact surfaces. The filter employs a mobile robotic heuristic to feedback the contact surface graph throughout the disassembly process. The heuristic generates an environment map to infer the region where the probability of collision with the other objects is lower. To achieve the disassembly the paper presents a method for modeling the elements implied in the disassembly process. This virtual model of the environment allows us to quickly process the elements and the simulation of the movements for disassembly. This model can be used to either schedule the disassembly process or to test, during the design stage, whether the products can be easily disassembled.

Summary The article proposes a nonlinear optimal control method for the model of the wheeled inverted pendulum (WIP). This is a difficult control and robotics problem due to the system’s strong nonlinearities and due to its underactuation. First, the dynamic model of the WIP undergoes approximate linearization around a temporary operating point which is recomputed at each time step of the control method. The linearization procedure makes use of Taylor series expansion and of the computation of the associated Jacobian matrices. For the linearized model of the wheeled pendulum, an optimal ( H -infinity) feedback controller is developed. The controller’s gain is computed through the repetitive solution of an algebraic Riccati equation at each iteration of the control algorithm. The global asymptotic stability properties of the control method are proven through Lyapunov analysis. Finally, by using the H -infinity Kalman Filter as a robust state estimator, the implementation of a state estimation-based control scheme becomes also possible.

Este trabajo ha sido parcialmente financiado por el proyecto GV05/007 “Diseno y experimentacion de estrategias de control visual-fuerza para sistemas flexibles de manipulacion”.

Abstract The control problem of the rotary double inverted pendulum (double Furuta pendulum) is nontrivial because of underactuation and strong nonlinearities in the associated state‐space model. The system has three degrees of freedom (one actuated and two unactuated joints) while receiving only one control input. In this article, a novel nonlinear optimal (H‐infinity) control approach is developed for the dynamic model of the rotary double inverted pendulum. First, the dynamic model of the double pendulum undergoes approximate linearization with the use of first‐order Taylor series expansion and through the computation of the associated Jacobian matrices. The linearization process takes place at each sampling instance around a temporary operating point which is defined by the present value of the system's state vector and by the last sampled value of the control inputs vector. At a next stage a stabilizing H‐infinity feedback controller is designed. To compute the controller's feedback gains an algebraic Riccati equation has to be solved at each time‐step of the control algorithm. The global stability properties of the control scheme are proven through Lyapunov analysis. To implement state estimation‐based control without the need to measure the entire state vector of the rotary double‐pendulum the H‐infinity Kalman filter is used as a robust state observer. The nonlinear optimal control method achieves fast and accurate tracking of setpoints by all state variables of the rotary double inverted pendulum under moderate variations of the control input.

This paper presents a novel control approach to dynamic visual servo control multi-fingered robotic hands for the manipulation performance of an object. The control approach allows the path tracking of the object motion by means of visual information and takes into account both the dynamics model of the robot hand and the grasping force of the fingertips. In addition, an optimal approach is employed to obtain the desired behaviour in the joint space based on an indicated cost function which determines how the control effort is distributed over the robot fingers' joints. Finally, authors show experimental verifications on a robotic manipulation system for some of the visual servo controllers derived from the control approach.

This paper describes a dynamic image-based control system to guide two coupled robots. The first robot is a Mitsubishi PA-10 robotic manipulator which has a second mini-robot with 3 degrees of freedom (DOF) attached at its end-effector. The vision system used for the guidance of both robots is composed of a camera at the end-effector of the mini-robot. The paper presents a new method to perform the mini-robot guidance using dynamic control to track a previous generated image trajectory. The mini-robot performs the tracking in a workspace in cooperation with a human operator. Therefore, the proposed visual control is combined with virtual visual servoing to perform a safety behavior.