Research Output
Articles
Publication Date: 2025
European Journal of Control (09473580)85
This research addresses the challenge of effective human-robot interaction in master-slave robotic systems, particularly for applications like manufacturing and healthcare. A method is proposed for transferring desired impedance from a human operator to a slave robot. A three-term model estimates the interactive force/torque between the human hand and the master robot, with adaptive rules for updating stiffness and damping coefficients in real-time to provide accurate and responsive haptic feedback. These updated coefficients dynamically adjust the reference impedance model used to control the slave robot. This architecture, incorporating robust control techniques and estimators, ensures stability and transparency, enabling the master-side user to perceive conditions faced by the slave robot (e.g., obstacles). The slave robot responds according to the user's desired impedance, providing a seamless and intuitive interaction. Input-to-state stability analysis demonstrates robustness to disturbances and uncertainties. The proposed approach in this paper allows replicating the user impedance of the master robot to the slave robot, with the input-to-state stability of the entire closed-loop system analyzed in the presence of the proposed three-term model. The comparison of the root mean square (RMS) error measure for the tracking position and the tracking force/torque when the slave robot encounters an obstacle shows the favorable performance of the proposed approach compared to the impedance reference model approaches with fixed stiffness and damping coefficients and traditional position control approaches. Numerical simulations and experimental implementation validate the efficiency and accuracy of the proposed approach. © 2025
Publication Date: 2025
International Journal of Dynamics and Control (2195268X)13(6)
This article proposes a novel method for rectifying solutions resulting from path planning algorithms like jump point search algorithm (JPS) in a cluttered environment, with the purpose to readjust waypoints occurring at the proximity of obstacles. In order to provide an area free of obstacles for generating a trajectory inside it, a safe flight corridor (SFC) is formed which imposes a set of linear inequality constraints on the trajectory planning. The first step for generating SFC is to form “inflatable” ellipsoids around the path segments created by the path planning algorithm. Indeed, in the stage of forming flight corridors, narrow ellipsoids are prone to be created at points of the path too close to the obstacles that will result in impractical corridors. As a solution, a virtual force field is applied that influences the points of the path, modifying its shape while staying close to optimal path. The results are presented for different obstacle shapes and compared with another path modification method. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2025.
Publication Date: 2025
Journal of Aerospace Engineering (08931321)38(4)
The nonlinear model predictive control (NMPC) of an underactuated spacecraft equipped with reaction wheels on special orthogonal (Lie) group SO(3) is discussed regarding numerical efficiency. Due to off-centricity in its structure, the spacecraft is subjected to an inner disturbance torque. The system has to deal with disturbance torques while one of its reaction wheels is out of order and, thus, is considered underactuated. Failure may occur from the beginning or in the middle of the assigned maneuver. Our goal is to design an appropriate control method that is able to compensate for the underactuation, especially when the system is subject to disturbance torques. This can be dealt with by using NMPC due to its capability of considering dynamic constraints. The NMPC is designed based on the discrete form of the equations of motion of the spacecraft, which are established using Lie group variational integrators permitting us to take advantage of Lie group properties such as being symplectic and momentum preserving while keeping the geometric structure of the system. In addition, the issue of underactuation is addressed in the MPC design by imposing a zero-torque constraint on the failed reaction wheel. For the sake of calculation reduction for enhancing the practical performance of the algorithm, the NMPC-related two-point boundary value problem is solved using an iterative Newton-like procedure. The calculation trick is based on ignoring nonessential nonlinear constraint-related parts of the sensitivity derivative equations in the repetitive process of estimating the initial conditions for the Lagrange multipliers. The proposed method is applied to the model of a spacecraft attitude control simulator through simulations. The obtained results confirm that the control system is able to bring the underactuated spacecraft to the desired position in absence of any disturbance. However, the disturbance rejection performance depends on whether the disturbance lies in the actuation span space and also on the time when the fault occurs. © 2025 American Society of Civil Engineers.
Publication Date: 2025
Optimal Control Applications and Methods (10991514)46(2)pp. 602-614
The present work revolves around employing the benefits of neighboring extremal approach in the nonlinear model predictive control of mechanical systems evolving on SE(3). In the NMPC process, necessary conditions of optimality are extracted based on some discrete-time version of the equations of motion referred as LGVI and the obtained TPBVP equations are solved using simplified sensitivity derivatives by means of an indirect shooting method. Taking into consideration that the repetitive optimization process of the NMPC is time consuming, making its implementation challenging, a method of neighboring extremal is proposed here for recalculating the responses of the systems in scenarios that face some unexpected changes in their parameters or are encountering some last-minute re-planning schemes. Based on the existing responses of the system to the first set of initial conditions, the reaction of the system to the altered set of initial conditions can be reconstructed without the need to solve the whole optimization process from scratch by utilizing the features of the NE method. A spacecraft model evolving on SE(3) with actuation constraints confirms the efficiency of the whole process in term of accuracy versus computation burden. Forasmuch as actuator failure is a probable yet important event in aerial/spatial missions, the performance of the control system in dealing with such situations is examined. The algorithm robustness and its capability to compensate the effects of the actuator loss is checked. © 2024 John Wiley & Sons Ltd.
