| 1. |
- Bechlioulis, Charalampos P., et al.
(författare)
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Robust Image-Based Visual Servoing With Prescribed Performance Under Field of View Constraints
- 2019
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Ingår i: IEEE Transactions on robotics. - : Institute of Electrical and Electronics Engineers (IEEE). - 1552-3098 .- 1941-0468. ; 35:4, s. 1063-1070
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we propose a visual servoing scheme that imposes predefined performance specifications on the image feature coordinate errors and satisfies the visibility constraints that inherently arise owing to the camera's limited field of view, despite the inevitable calibration and depth measurement errors. Its efficiency is demonstrated via comparative experimental and simulation studies.
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| 2. |
- Guo, Meng, et al.
(författare)
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Hybrid Control of Multiagent Systems With Contingent Temporal Tasks and Prescribed Formation Constraints
- 2017
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Ingår i: IEEE Transactions on Control of Network Systems. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2325-5870. ; 4:4, s. 781-792
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we present a distributed hybrid control strategy for multiagent systems with contingent temporal tasks and prescribed formation constraints. Each agent is assigned a local task given as a linear temporal logic formula. In addition, two commonly seen kinds of cooperative robotic tasks, namely, service and formation, are requested and exchanged among the agents in real time. The service request is a short-term task provided by one agent to another. On the other hand, the formation request is a relative deployment requirement with predefined transient response imposed by an associated performance function. The proposed hybrid control strategy consists of four major components: 1) the contingent requests handlingmodule; 2) the real-time events monitoring module; 3) the local discrete plan synthesis module; and 4) the continuous control switching module, and it is shown that all local tasks and contingent service/formation requests are fulfilled. Finally, a simulated paradigm demonstrates the proposed control strategy.
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| 3. |
- Heshmati-Alamdari, Shahab, et al.
(författare)
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A robust interaction control approach for underwater vehicle manipulator systems
- 2018
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Ingår i: Annual Reviews in Control. - : Elsevier. - 1367-5788 .- 1872-9088. ; 46, s. 315-325
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Forskningsöversikt (refereegranskat)abstract
- In underwater robotic interaction tasks (e.g., sampling of sea organisms, underwater welding, panel handling, etc) various issues regarding the uncertainties and complexity of the robot dynamic model, the external disturbances (e.g., sea currents), the steady state performance as well as the overshooting/undershooting of the interaction force error, should be addressed during the control design. Motivated by the aforementioned considerations, this paper presents a force/position tracking control protocol for an Underwater Vehicle Manipulator System (UVMS) in compliant contact with a planar surface, without incorporating any knowledge of the UVMS dynamic model, the exogenous disturbances or the contact stiffness model. Moreover, the proposed control framework guarantees: (i) certain predefined minimum speed of response, maximum steady state error as well as overshoot/undershoot concerning the force/position tracking errors, (ii) contact maintenance and (iii) bounded closed loop signals. Additionally, the achieved transient and steady state performance is solely determined by certain designer-specified performance functions/parameters and is fully decoupled from the control gain selection and the initial conditions. Finally, both simulation and experimental studies clarify the proposed method and verify its efficiency.
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| 4. |
- Heshmati Alamdari, Shahabodin, et al.
(författare)
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Cooperative Impedance Control for Multiple Underwater Vehicle Manipulator Systems Under Lean Communication
- 2021
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Ingår i: IEEE Journal of Oceanic Engineering. - : Institute of Electrical and Electronics Engineers (IEEE). - 0364-9059 .- 1558-1691. ; 46:2, s. 447-465
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Tidskriftsartikel (refereegranskat)abstract
- This article addresses the problem of cooperative object transportation for multiple underwater vehicle manipulator systems (UVMSs) in a constrained workspace with static obstacles, where the coordination relies solely on implicit communication arising from the physical interaction of the robots with the commonly grasped object. In this article, we propose a novel distributed leader-follower architecture, where the leading UVMS, which has knowledge of the object's desired trajectory, tries to achieve the desired tracking behavior via an impedance control law, navigating in this way, the overall formation toward the goal configuration while avoiding collisions with the obstacles. On the other hand, the following UVMSs estimate locally the object's desired trajectory via a novel prescribed performance estimation law and implement a similar impedance control law that achieves tracking of the desired trajectory despite the uncertainty and external disturbance in the object and the UVMS dynamics, respectively. The feedback relies on each UVMS's force/torque measurements and no explicit data is exchanged online among the robots, thus reducing the required communication bandwidth and increasing robustness. Moreover, the control scheme adopts load sharing among the UVMSs according to their specific payload capabilities. Finally, various simulation studies clarify the proposed method and verify its efficiency.
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| 5. |
- Mehdifar, Farhad, 1992-, et al.
(författare)
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2-D Directed Formation Control Based on Bipolar Coordinates
- 2022
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Ingår i: IEEE Transactions on Automatic Control. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9286 .- 1558-2523. ; 68:7, s. 4175-4190
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Tidskriftsartikel (refereegranskat)abstract
- This work proposes a novel 2-D formation control scheme for acyclic triangulated directed graphs (a class of minimally acyclic persistent graphs) based on bipolar coordinates with (almost) global convergence to the desired shape. Prescribed performance control is employed to devise a decentralized control law that avoids singularities and introduces robustness against external disturbances while ensuring predefined transient and steady-state performance for the closed-loop system. Furthermore, it is shown that the proposed formation control scheme can handle formation maneuvering, scaling, and orientation specifications simultaneously. Additionally, the proposed control law is implementable in agents’ arbitrarily oriented local coordinate frames using only low-cost onboard vision sensors, which are favorable for practical applications. Finally, a formation maneuvering simulation study verifies the proposed approach.
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| 6. |
- Mehdifar, Farhad, 1992-, et al.
(författare)
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Control of Nonlinear Systems Under Multiple Time-Varying Output Constraints : A Single Funnel Approach
- 2023
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- This paper proposes a novel control framework for handling (potentially coupled) multiple time-varying output constraints for uncertain nonlinear systems. First, it is shown that the satisfaction of multiple output constraints boils down to ensuring the positiveness of a scalar variable (the signed distance from the time-varying output-constrained set’s boundary). Next, a single funnel constraint is designed properly, whose satisfaction ensures convergence to and invariance of the time-varying output-constrained set. Then a robust and low-complexity funnel-based feedback controller is designed employing the prescribed performance control method. Finally, a simulation example clarifies and verifies the proposed approach
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| 7. |
- Mehdifar, Farhad, 1992-, et al.
(författare)
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Control of Nonlinear Systems Under Multiple Time-Varying Output Constraints: A Single Funnel Approach
- 2023
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Ingår i: 2023 62nd IEEE Conference on Decision and Control, CDC 2023. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 6743-6748
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Konferensbidrag (refereegranskat)abstract
- This paper proposes a novel control framework for handling (potentially coupled) multiple time-varying output constraints for uncertain nonlinear systems. First, it is shown that the satisfaction of multiple output constraints boils down to ensuring the positiveness of a scalar variable (the signed distance from the time-varying output-constrained set's boundary). Next, a single funnel constraint is designed properly, whose satisfaction ensures convergence to and invariance of the time-varying output-constrained set. Then a robust and low-complexity funnel-based feedback controller is designed em-ploying the prescribed performance control method. Finally, a simulation example clarifies and verifies the proposed approach.
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| 8. |
- Mehdifar, Farhad, 1992-
(författare)
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Funnel-Based Control for Coupled Spatiotemporal Specifications
- 2024
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the past decade, the integration of spatiotemporal constraints into control systems has emerged as a crucial necessity, driven by the demand for enhanced performance, guaranteed safety, and the execution of complex tasks. Spatiotemporal constraints involve criteria that are dependent on both space and time, which can be represented by time-varying constraints in nonlinear control systems. Funnel-based control methods provide computationally tractable and robust feedback control laws to enforce time-varying constraints in uncertain nonlinear systems. This thesis begins by exploring the application of funnel-based control designs to address performance specifications in coordinate-free formation control of multi-agent systems. Moreover, we develop new robust feedback control schemes dealing with coupled spatiotemporal constraints in uncertain nonlinear systems that cannot be directly addressed by conventional funnel-based control methods.In the first part of the thesis, we present a novel coordinate-free formation control scheme for directed leader-follower multi-agent systems, exhibiting almost global convergence to the desired shape. The synthesis of fully decentralized robust controllers for agents is achieved through the application of the Prescribed Performance Control (PPC) method. This method imposes spatiotemporal funnel constraints on each agent's formation errors, ensuring a predefined transient and steady-state performance while maintaining robustness to system uncertainties. The core idea in this work is the utilization of bipolar coordinates to achieve orthogonal (decoupled) formation errors for each follower agent. This approach not only ensures the global convergence to the desired shape but also facilitates the effective application of the PPC method.In the second part of the thesis, first, we introduce a novel approach that extends funnel-based control schemes to deal with a specific class of time-varying hard and soft constraints. In this work, we employ an online Constraint Consistent Funnel (CCF) planning scheme to tackle couplings between hard and soft constraints. By satisfying these CCF constraints, we ensure adherence to hard (safety) constraints, while soft (performance) constraints are met only when they do not conflict with the hard constraints. Subsequently, we directly employ the PPC design method to craft a robust, low-complexity control law, ensuring that the system's outputs consistently stay within the online planned CCF constraints. In subsequent work, we tackle the challenge of satisfying a generalized class of potentially coupled time-varying output constraints. We show that addressing multiple constraints effectively boils down to formulating a single consolidating constraint. Ensuring the fulfillment of this consolidating constraint guarantees both convergence to and invariance of the time-varying output-constrained set within a user-defined finite time. Building on the PPC design method, we introduce a novel, robust low-complexity feedback control framework to handle this issue in uncertain high-order MIMO nonlinear control systems. Additionally, we present a mechanism for online modification of the consolidating constraint to secure a least-violating solution when constraint infeasibilities occur for an unknown time interval.
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| 9. |
- Mehdifar, Farhad, 1992-, et al.
(författare)
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Funnel control under hard and soft output constraints
- 2022
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Ingår i: Proceedings IEEE 61st Conference on Decision and Control (CDC). - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 4473-4478
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Konferensbidrag (refereegranskat)abstract
- This paper proposes a funnel control method under time-varying hard and soft output constraints. First, an online funnel planning scheme is designed that generates a constraint consistent funnel, which always respects hard (safety) constraints, and soft (performance) constraints are met only when they are not conflicting with the hard constraints. Next, the prescribed performance control method is employed for designing a robust low-complexity funnel-based controller for uncertain nonlinear Euler-Lagrangian systems such that the outputs always remain within the planned constraint consistent funnels. Finally, the results are verified with a simulation example of a mobile robot tracking a moving object while staying in a box-constrained safe space.
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| 10. |
- Sygkounas, Alkis, et al.
(författare)
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Multi-agent Exploration with Reinforcement Learning
- 2022
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Ingår i: 2022 30th Mediterranean Conference on Control and Automation (MED). - : IEEE. ; , s. 630-635
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Konferensbidrag (refereegranskat)abstract
- Modern robots are used in many exploration, search and rescue applications nowadays. They are essentially coordinated by human operators and collaborate with inspection or rescue teams. Over time, robots (agents) have become more sophisticated with more autonomy, operating in complex environments. Therefore, the purpose of this paper is to present an approach for autonomous multi-agent coordination for exploring and covering unknown environments. The method we suggest combines reinforcement learning with multiple neural networks (Deep Learning) to plan the path for each agent separately and achieve collaborative behavior amongst them. Specifically, we have applied two recent techniques, namely the target neural network and the prioritized experience replay, which have been proven to stabilize and accelerate the training process. Agents should also avoid obstacles (walls, objects, etc.) throughout the exploration without prior information/knowledge about the environment; thus we use only local information available at any time instant to make the decision of each agent. Furthermore, two neural networks are used for generating actions, accompanied by an extra neural network with a switching logic that chooses one of them. The exploration of the unknown environment is conducted in a two-dimensional model (2D) using multiple agents for various maps, ranging from small to large size. Finally, the efficiency of the exploration is investigated for a different number of agents and various types of neural networks.
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