| 1. |
- Aguilar, Luis T., et al.
(författare)
-
Generating oscillations in inertia wheel pendulum via two-relay controller
- 2012
-
Ingår i: International Journal of Robust and Nonlinear Control. - Malden : Wiley-Blackwell. - 1049-8923 .- 1099-1239. ; 22:3, s. 318-330
-
Tidskriftsartikel (refereegranskat)abstract
- The problem of generating oscillations of the inertia wheel pendulum is considered. We combine exact feedback linearization with two-relay controller, tuned using frequency-domain tools, such as computing the locus of a perturbed relay system. Explicit expressions for the parameters of the controller in terms of the desired frequency and amplitude are derived. Sufficient conditions for orbital asymptotic stability of the closed-loop system are obtained with the help of the Poincare map. Performance is validated via experiments. The approach can be easily applied for a minimum phase system, provided the behavior of the states of the zero dynamics is of no concern. Copyright (C) 2011 John Wiley & Sons, Ltd.
|
|
| 2. |
- Pchelkin, Stepan S., et al.
(författare)
-
Algorithms for finding gaits of locomotive mechanisms : case studies for Gorilla robot brachiation
- 2016
-
Ingår i: Autonomous Robots. - : Springer Science and Business Media LLC. - 0929-5593 .- 1573-7527. ; 40:5, s. 849-865
-
Tidskriftsartikel (refereegranskat)abstract
- We consider a model of a 24-degree-of-freedom monkey robot that is supposed to perform a brachiation locomotion, i.e. to swing from one row of a horizontal ladder to the next one using the arms. The robot hand is constructed as a planar hook so that the contact point, about which the robot swings, is a passive hinge. We identify the 10 most relevant degrees of freedom for this underactuated mechanical system and formulate a tractable search procedure consisting on the following steps: (a) to introduce a parametrized family of coordination patterns to be enforced on the dynamics with respect to a path coordinate; (b) to formulate geometric equality constraints that are necessary to achieve a periodic locomotion; (c) to generate trajectories from integrable reduced dynamics associated with the passive hinge; (d) to evaluate the energetic cost of transport. Moreover, we observe that a linear approximation of the reduced dynamics can be used for trajectory generation, which allows us to incorporate computation of an approximate gradient of the cost function into the search algorithm significantly improving the computational efficiency.
|
|
| 3. |
- Pchelkin, Stepan S., et al.
(författare)
-
On Orbital Stabilization for Industrial Manipulators : Case Study in Evaluating Performances of Modified PD plus and Inverse Dynamics Controllers
- 2017
-
Ingår i: IEEE Transactions on Control Systems Technology. - 1063-6536 .- 1558-0865. ; 25:1, s. 101-117
-
Tidskriftsartikel (refereegranskat)abstract
- Orbital stabilization is one of the available alternatives to the classical asymptotic stabilization, known as the reference tracking control, which is typically considered and implemented for controlling motions of industrial robot manipulators. Since asymptotic orbital stability means convergence of solutions of a closed-loop system to an orbit of a reference trajectory, instead of tracking it as a function of time, new feedback designs can potentially improve performance with respect to several key criteria for industrial manipulators such as absolute path accuracy for tool's motions and robustness to uncertainties in the model. The main outcomes of this paper are a new class of controllers that achieve asymptotic orbital stabilization of motions and a novel analytical method for analysis and redesign of system's dynamics using an excessive set of easy-to-compute transverse coordinates. The contributions have been validated in a series of experimental studies performed on a standard industrial robot ABB IRB 140 with the IRC5-system extended with an open control interface. The outcomes of the tests show that the proposed redesign allows achieving significantly reduced deviations of the actual trajectories from the desired ones at different ranges of speeds and for several different paths, often outperforming the state-of-the-art commercial implementations. A comprehensive discussion of one of such experiments is given.
|
|
| 4. |
- Sætre, Christian Fredrik, et al.
(författare)
-
Robust orbital stabilization : A Floquet theory-based approach
- 2021
-
Ingår i: International Journal of Robust and Nonlinear Control. - : John Wiley & Sons. - 1049-8923 .- 1099-1239. ; 31:16, s. 8075-8108
-
Tidskriftsartikel (refereegranskat)abstract
- The design of robust orbitally stabilizing feedback is considered. From a known orbitally stabilizing controller for a nominal, disturbance-free system, a robustifying feedback extension is designed utilizing the sliding-mode control (SMC) methodology. The main contribution of the article is to provide a constructive procedure for designing the time-invariant switching function used in the SMC synthesis. More specifically, its zero-level set (the sliding manifold) is designed using a real Floquet–Lyapunov transformation to locally correspond to an invariant subspace of the Monodromy matrix of a transverse linearization. This ensures asymptotic stability of the periodic orbit when the system is confined to the sliding manifold, despite any system uncertainties and external disturbances satisfying a matching condition. The challenging task of oscillation control of the underactuated cart–pendulum system subject to both matched- and unmatched disturbances/uncertainties demonstrates the efficacy of the proposed scheme.
|
|
| 5. |
- Andersson, Alina, et al.
(författare)
-
Analytic Parameterization of Stabilizing Controllers for the Surge Subsystem of the Moore-Greitzer Compressor Model
- 2013
-
Ingår i: Proc. 2013 American Control Conference (ACC2013). - 0743-1619. - 9781479901777 ; , s. 5257-5262
-
Konferensbidrag (refereegranskat)abstract
- This paper is based on a new procedure for dynamic output feedback design for systems with nonlinearities satisfying quadratic constraints. The new procedure is motivated by the challenges of output feedback control design for the 3-state Moore-Greitzer compressor model. First, we use conditions for stability of a transformed system and the associated matching conditions to find the data of the stabilizing controllers for the surge subsystem. Second, using the set of stabilizing controllers satisfying the given constraints for the closed-loop system with the dynamic output feedback controller we made optimization over the parameter set. We present the data of the stabilizing controllers and the new constraints for the corresponding parameters. The contributions in this paper are simplified conditions for the synthesis and optimization over the control parameter set.
|
|
| 6. |
- Andersson, Alina, et al.
(författare)
-
Sufficient Conditions for Dynamic Stabilization of 3-State Moore-Greitzer Compressor Model
- 2015
-
Ingår i: 2015 IEEE 54th Annual Conference on Decision and Control (CDC). - 9781479978861 - 9781479978847 ; , s. 4394-4399
-
Konferensbidrag (refereegranskat)abstract
- We consider the classical 3-state Moore-Greitzer model, which is commonly used for approximating dynamics of deviations of flow and pressure variables in an axial compressor from their nominal steady-state values. The linearization of the nonlinear system is not controllable and, therefore, even local asymptotic stability cannot be achieved using methods of linear control theory. We propose a family of parametrized partialstate feedback control laws and derive sufficient conditions to guarantee global asymptotic stability of the closed-loop system. The stability analysis uses the integral quadratic constraints technique for the case of non-strict frequency condition and novel arguments for characterization of omega-limit sets.
|
|
| 7. |
- Burdakov, S. F., et al.
(författare)
-
Robust control of nonlinear mechanical systems using linear feedback
- 1999
-
Ingår i: Automation and remote control. - NEW YORK, NY, USA. - 0005-1179 .- 1608-3032. ; 60:11, s. 1577-1586
-
Tidskriftsartikel (refereegranskat)abstract
- A linear law of control of a mechanical system through drives nonrigidly connected to the system is suggested. The law involves measurement of the positions of links and angular velocities of drives and features a nonminimal-phase character of the transfer function. Stability conditions that remain valid with an increase in the gain are set zip. Results of the numerical modeling in solving problems of positioning anal tracking for robots (manipulators) are described.
|
|
| 8. |
- Burkov, Ilya V., et al.
(författare)
-
Stabilization of an Elastic Robot by a Two-Component Plane Controller
- 1996
-
Ingår i: Journal of Computer and Systems Sciences International. - 1064-2307. ; 53:1, s. 151-157
-
Tidskriftsartikel (refereegranskat)abstract
- Two models of an elastic controller are studied. A control rule with feedback for members and rotor velocities is proposed. The global stability of the equilibrium of a controlled system is proved within the frame-work of a simplified model. Numerical experiments demonstrate that the stability area includes all reasonable initial data, even taking into account discarded small factors.
|
|
| 9. |
- Burkov, I.V., et al.
(författare)
-
Stabilization of the position of a Lagrangian system with elastic elements and bounded control, with and without measurement of velocities
- 1997
-
Ingår i: PMM. - : Elsevier. - 0021-8928 .- 1873-4855. ; 61:3, s. 433-441
-
Tidskriftsartikel (refereegranskat)abstract
- It is required to position a Lagrangian system whose free and controllable degrees of freedom are elastically linked. The equations of motion of such systems describe, in particular, the dynamics of a robot manipulator with elastic joints. The proposed control laws enable restrictions on the value of the control impulse to be taken into account. Zn particular, attention is given to the situation in which the velocities are not accessible to measurement. The analysis of the proposed control laws is based on Lyapunov’s direct method or, more specifically, on the Barbashin-Krasovskii theorem on asymptotic stability in the large. The proof uses an original method to verify that an auxiliary non-linear function, analogous to the total mechanical energy of a system, closed by a control law, is positive-definite. (C) 1997 Elsevier Science Ltd. All rights reserved.
|
|
| 10. |
- Castillo, Ismael, et al.
(författare)
-
Barrier sliding mode control and on-line trajectory generation for the automation of a mobile hydraulic crane
- 2018
-
Ingår i: 15th International Workshop on Variable Structure Systems (VSS). - : IEEE. - 9781538664391 ; , s. 162-167
-
Konferensbidrag (refereegranskat)abstract
- In this paper we propose an implementation scheme of independent joint control for a four-degree-of-freedom heavy-duty hydraulic actuated crane. First, on-line generation of feasible trajectories, following a driver's lead and satisfying the actuator constrains for the redundant kinematic chain, is performed. Second, an implementation of two new Sliding Mode algorithms with variable barrier function gains, which allow robust tracking of the generated trajectory with alleviation of high frequency oscillations, is presented. Experimental results are presented to show the effectiveness of the proposed semi-automation scheme, exploiting the forestry application motivated low accuracy requirement.
|
|
| 11. |
- Castillo, Ismael, et al.
(författare)
-
Describing-function-based analysis to tune parameters of chattering reducing approximations of Sliding Mode controllers
- 2020
-
Ingår i: Control Engineering Practice. - : Elsevier. - 0967-0661 .- 1873-6939. ; 95
-
Tidskriftsartikel (refereegranskat)abstract
- Sliding Mode Control (SMC) is a powerful feedback control design technique leading to insensitivity to certain types of disturbances under ideal conditions. Among these conditions, there are discontinuity in the generated control signal and absence of unmodeled dynamics. In many cases, the former maybe not implementable while the latter is often not holdable. Such non-ideal conditions typically excite high-frequency oscillations, known as chattering, not only in the input to the plant but also in the output, leading to a degradation of performance and losing the attractive insensitivity property. One of well-known and widely used approaches to achieve chattering reduction, caused by delays, parasitic dynamics, unmatched perturbations, etc., is implicitly or explicitly approximating the discontinuity. Theoretically, removing the discontinuities in the input to the plant, as well as in the internal controller dynamics, leads to loosing the insensitivity property under ideal conditions, but may insure better performance under more realistic conditions. This paper presents a Describing Function analysis in frequency domain of some SMC algorithms under presence of unmodeled (parasitic) dynamics, in the case when the discontinuous sign function is replaced or approximated by a saturation function. We are to concentrate here on a systematic procedure to tune parameters of the approximation.
|
|
| 12. |
- Freidovich, Leonid B., Docent, 1973-, et al.
(författare)
-
Analysis of limit-cycle walking for a compass-like biped robot
- 2010
-
Ingår i: 8th IFAC Symposium on Nonlinear Control Systems. - : Elsevier. - 9783902661807 ; , s. 1181-1186
-
Konferensbidrag (refereegranskat)abstract
- We consider an impulsive mechanical system modeling dynamics of a planar two-link walker commonly known as a compass-gait biped. It is assumed that there is actuation in the hip but that the desired periodic trajectory describes an unstable passive walking gait. We recall and apply a recently developed technique for design of orbitally stabilizing feedback controllers. After that, we illustrate how to assess various properties of the closed-loop system. In particular, sensitivity to perturbations of the slope of the walking surface is analyzed and an estimate for possible deviations from the nominal trajectory is computed analytically.
|
|
| 13. |
- Freidovich, Leonid B, et al.
(författare)
-
Experimental implementation of stable oscillations of the Furuta pendulum around the upward equilibrium
- 2007
-
Ingår i: IEEE/RSJ International conference on intelligent robots and systems, 2007. IROS 2007. - Piscataway, N.J : IEEE Operations Center. - 9781424409129 ; , s. 171-176
-
Konferensbidrag (refereegranskat)abstract
- Recently, a new technique for generating periodic motions in mechanical systems which have less actuators than degrees of freedom has been proposed. A motivating example for studying such motions is a dynamically stabilized walking robot, where the target trajectory is periodic, and one of the joints - the ankle joint - is unactuated, or weakly actuated. In this paper, the technique is implemented on the Furuta pendulum, an experimental testbed that is simpler than a walking robot but retains many of the key challenges - it is underactuated, open-loop unstable, and practical problems such as friction and velocity estimation must be overcome. We present a detailed description of the practical implementation of the controller. The experiments show that the technique is sufficiently robust to be useful in practice.
|
|
| 14. |
- Freidovich, Leonid B., Docent, 1973-, et al.
(författare)
-
On generating pre-defined periodic motions in underactuated mechanical systems : The cart-pendulum example
- 2011
-
Ingår i: 18th IFAC World Congress. - : Elsevier. - 9783902661937 ; , s. 4588-4593
-
Konferensbidrag (refereegranskat)abstract
- We study the problem of generating oscillations in underactuated mechanical systems with a chosen time-evolution of some of the generalized coordinates. We consider a classical planar pendulum on a cart example and find conditions of existence of a solution. These conditions are expressed in terms of functions defining synchronization between the actuated and underactuated variables known as virtual holonomic constraints. Explicit expressions for these functions are computed for the cart-pendulum system where the pendulum angle is set to follow a trajectory like a pure sinusoidal waveform around the upright equilibrium. Once the valid virtual constraint has been found with the proposed method, the earlier developed techniques can be applied in order to design an orbitally stabilizing feedback control law. © 2011 IFAC.
|
|
| 15. |
|
|
| 16. |
- Freidovich, Leonid B, et al.
(författare)
-
Performance recovery of feedback-linearization-based designs
- 2008
-
Ingår i: IEEE Transactions on Automatic Control. - 0018-9286 .- 1558-2523. ; 53:10, s. 2324-2334
-
Tidskriftsartikel (refereegranskat)abstract
- We consider a tracking problem for a partially feedback linearizable nonlinear system with stable zero dynamics. The system is uncertain and only the output is measured. We use an extended high-gain observer of dimension n+1, where n is the relative degree. The observer estimates n derivatives of the tracking error, of which the first (n-1) derivatives are states of the plant in the normal form and the $n$th derivative estimates the perturbation due to model uncertainty and disturbance. The controller cancels the perturbation estimate and implements a feedback control law, designed for the nominal linear model that would have been obtained by feedback linearization had all the nonlinearities been known and the signals been available. We prove that the closed-loop system under the observer-based controller recovers the performance of the nominal linear model as the observer gain becomes sufficiently high. Moreover, we prove that the controller has an integral action property in that it ensures regulation of the tracking error to zero in the presence of constant nonvanishing perturbation.
|
|
| 17. |
- Freidovich, Leonid B., et al.
(författare)
-
Robust feedback linearization using extended high-gain observers
- 2006
-
Ingår i: 45th IEEE Conference onDecision and Control. - New York : IEEE. - 1424401712 ; , s. 983-988
-
Konferensbidrag (refereegranskat)abstract
- We consider a partially feedback linearizable system with stable zero dynamics. The system is uncertain and only the output is measured. Consequently, exact feedback linearization is not applicable. We propose to design an extended high-gain observer to recover unmeasured derivatives of the output and an extra one, which contains information about the uncertainty. The observer can be stabilized via feedback linearization followed by a linear control design, such as pole placement or LQR. After a short peaking period, a partial state vector, which includes the output and its derivatives, will be in a small neighborhood of the state of the observer; therefore, the performance achievable under exact feedback linearization will be recovered.
|
|
| 18. |
- Freidovich, Leonid B., 1973-, et al.
(författare)
-
Shaping stable periodic motions of inertia wheel pendulum : theory and experiment
- 2009
-
Ingår i: Asian Journal of Control. - : Wiley. - 1561-8625 .- 1934-6093. ; 11:5, s. 549-556
-
Tidskriftsartikel (refereegranskat)abstract
- We consider an underactuated two-link robot called the inertia wheel pendulum. The system consists of a free planar rotational pendulum and a symmetric disk attached to its end, which is directly controlled by a DC-motor. The goal is to create stable oscillations of the pendulum, which is not directly actuated. We exploit a recently proposed feedback-control design strategy based on motion planning via virtual holonomic constraints. This strategy is shown to be useful for design of regulators for achieving orbitally exponentially stable oscillatory motions. The main contribution is a step-by-step procedure on how to achieve oscillations with pre-specified amplitude from a given range and an arbitrary independently chosen period. The theoretical results are verified via experiments with a real hardware setup.
|
|
| 19. |
- Freidovich, Leonid B, et al.
(författare)
-
Transverse linearization for mechanical systems with passive links, impulse effects, and friction forces
- 2009
-
Ingår i: Proceedings of the 48th IEEE conference on decision and control, 2009, held jointly with the 2009 28th Chinese control conference (CDC/CCC 2009). - : IEEE conference proceedings. - 9781424438723 - 9781424438716 ; , s. 6490-6495
-
Konferensbidrag (refereegranskat)abstract
- We consider a class of mechanical systems with an arbitrary number of passive (non-actuated) degrees of freedom. In addition to control forces, we take into account viscous and Coulomb friction forces and impacts with the environment modeled as impulsive updates of the states. We assume that a motion planning task is solved and a feasible forced periodic motion is described in terms of piece-wise smooth virtual holonomic constraints. The main contribution is an analytical method for computing coefficients of an impulsive linear control system, solutions of which approximate dynamics transversal to the preplanned trajectory. This linear system is shown to be useful for stability analysis and for design of feedback controllers orbitally stabilizing forced periodic motions in the hybrid mechanical system. As an illustration, we apply the obtained theoretical results providing a rigorous proof of orbital exponential stability of the periodic tumbling motion for a model of a descending strip of paper in a still air.
|
|
| 20. |
- Freidovich, Leonid B., Docent, 1973-, et al.
(författare)
-
Transverse linearization for underactuated nonholonomic mechanical systems with application to orbital stabilization
- 2012. - 1
-
Ingår i: Distributed decision making and control. - London : Springer. - 9781447122647 - 9781447122654 ; , s. 245-258
-
Bokkapitel (refereegranskat)abstract
- We consider a class of mechanical systems with an arbitrary number of passive (nonactuated) degrees of freedom, which are subject to a set of nonholonomic constraints. We assume that the challenging problem of motion planning is solved giving rise to a feasible desired periodic trajectory. Our goal is either to analyze orbital stability of this trajectory with a given time-independent feedback control law or to design a stabilizing controller. We extend our previous work done for mechanical systems without nonholonomic constraints. The main contribution is an analytical method for computing coefficients of a linear reduced-order control system, solutions of which approximate dynamics that is transversal to the preplanned trajectory. This linear system is shown to be useful for stability analysis and for design of feedback controllers orbitally, exponentially stabilizing forced periodic motions in nonholonomic mechanical systems.We illustrate our approach on a standard benchmark example.
|
|
| 21. |
- Gusev, Sergei V., et al.
(författare)
-
LMI approach for solving periodic matrix Riccati equation
- 2007
-
Ingår i: 3<sup>rd</sup> IFAC workshop on Periodic Control Systems (PSYCO). - : Elsevier. - 9783902661302 ; , s. 254-256
-
Konferensbidrag (refereegranskat)abstract
- The paper presents a new method for numerical solution of matrix Riccati equation with periodic coefficients. The method is based on approximation of stabilizing solution of the Riccati equation by trigonometric polynomials.
|
|
| 22. |
- Gusev, Sergei V., et al.
(författare)
-
SDP-based approximation of stabilising solutions for periodic matrix Riccati differential equations
- 2016
-
Ingår i: International Journal of Control. - : Informa UK Limited. - 0020-7179 .- 1366-5820. ; 89:7, s. 1396-1405
-
Tidskriftsartikel (refereegranskat)abstract
- Numerically finding stabilising feedback control laws for linear systems of periodic differential equations is a nontrivial task with no known reliable solutions. The most successful method requires solving matrix differential Riccati equations with periodic coefficients. All previously proposed techniques for solving such equations involve numerical integration of unstable differential equations and consequently fail whenever the period is too large or the coefficients vary too much. Here, a new method for numerical computation of stabilising solutions for matrix differential Riccati equations with periodic coefficients is proposed. Our approach does not involve numerical solution of any differential equations. The approximation for a stabilising solution is found in the form of a trigonometric polynomial, matrix coefficients of which are found solving a specially constructed finite-dimensional semidefinite programming (SDP) problem. This problem is obtained using maximality property of the stabilising solution of the Riccati equation for the associated Riccati inequality and sampling technique. Our previously published numerical comparisons with other methods shows that for a class of problems only this technique provides a working solution. Asymptotic convergence of the computed approximations to the stabilising solution is proved below under the assumption that certain combinations of the key parameters are sufficiently large. Although the rate of convergence is not analysed, it appeared to be exponential in our numerical studies.
|
|
| 23. |
- La Hera, Pedro M., 1981-, et al.
(författare)
-
Gait synthesis for a three-link planar biped walker with one actuator
- 2010
-
Ingår i: IEEE International Conference on Robotics and Automation (ICRA), 2010. - 9781424450381 ; , s. 1715-1720
-
Konferensbidrag (refereegranskat)abstract
- We consider a 3-link planar walker with two legs and an upper body. An actuator is introduced between the legs, and the torso is kept upright by torsional springs. The model is a 3-DOF impulsive mechanical system, and the aim is to induce stable limit-cycle walking in level ground. To solve the problem, the ideas of the virtual holonomic constraints approach are explored, used and extended. The contribution is a novel systematic motion planning procedure for solving the problem of gait synthesis, which is challenging for non-feedback linearizable mechanical systems with two or more passive degrees of freedom. For a preplanned gait we compute an impulsive linear system that approximates dynamics transversal to the periodic solution. This linear system is used for the design of a stabilizing feedback controller. Results of numerical simulations are presented to illustrate the performance of the closed loop system.
|
|
| 24. |
- La Hera, Pedro M., 1981-, et al.
(författare)
-
Orbital stabilization of a pre-planned periodic motion to swing up the Furuta pendulum : theory and experiments
- 2009
-
Ingår i: ICRA. ; , s. 3562-3567
-
Konferensbidrag (refereegranskat)abstract
- The problem of swinging up inverted pendulums has often been solved by stabilization of a particular class of homoclinic structures present in the dynamics of the standard pendulum. In this article new arguments are suggested to show how different homoclinic curves can be preplanned for dynamics of the passive-link of the robot. This is done by reparameterizing the motion according to geometrical relations among the generalized coordinates. It is also shown that under certain conditions there exist periodic solutions surrounding such homoclinic orbits. These trajectories admit designing feedback controllers to ensure exponential orbital stabilization. The method is illustrated by simulations and supported by experimental studies.
|
|
| 25. |
- La Hera, Pedro, 1981-, et al.
(författare)
-
Stable walking gaits for a three-link planar biped robot with one actuator
- 2013
-
Ingår i: IEEE Transactions on robotics. - 1552-3098 .- 1941-0468. ; 29:3, s. 589-601
-
Tidskriftsartikel (refereegranskat)abstract
- We consider a benchmark example of a three-link planar biped walker with torso, which is actuated in between the legs. The torso is thought to be kept upright by two identical torsional springs. The mathematical model reflects a three-degree-of-freedom mechanical system with impulse effects, which describe the impacts of the swing leg with the ground, and the aim is to induce stable limit-cycle walking on level ground. The main contribution is a novel systematic trajectory planning procedure for solving the problem of gait synthesis. The key idea is to find a system of ordinary differential equations for the functions describing a synchronization pattern for the time evolution of the generalized coordinates along a periodic motion. These functions, which are known as virtual holonomic constraints, are also used to compute an impulsive linear system that approximates the time evolution of the subset of coordinates that are transverse to the orbit of the continuous part of the periodic solution. This auxiliary system, which is known as transverse linearization, is used to design a nonlinear exponentially orbitally stabilizing feedback controller. The performance of the closed-loop system and its robustness with respect to various perturbations and uncertainties are illustrated via numerical simulations.
|
|
| 26. |
- Luan, Siyu, et al.
(författare)
-
Out-of-Distribution Detection for Deep Neural Networks with Isolation Forest and Local Outlier Factor
- 2021
-
Ingår i: IEEE Access. - : Institute of Electrical and Electronics Engineers (IEEE). - 2169-3536. ; 9, s. 132980-132989
-
Tidskriftsartikel (refereegranskat)abstract
- Deep Neural Networks (DNNs) are extensively deployed in today's safety-critical autonomous systems thanks to their excellent performance. However, they are known to make mistakes unpredictably, e.g., a DNN may misclassify an object if it is used for perception, or issue unsafe control commands if it is used for planning and control. One common cause for such unpredictable mistakes is Out-of-Distribution (OOD) input samples, i.e., samples that fall outside of the distribution of the training dataset. We present a framework for OOD detection based on outlier detection in one or more hidden layers of a DNN with a runtime monitor based on either Isolation Forest (IF) or Local Outlier Factor (LOF). Performance evaluation indicates that LOF is a promising method in terms of both the Machine Learning metrics of precision, recall, F1 score and accuracy, as well as computational efficiency during testing.
|
|
| 27. |
- Luan, Siyu, et al.
(författare)
-
Timing performance benchmarking of out-of-distribution detection algorithms
- 2023
-
Ingår i: Journal of Signal Processing Systems. - : Springer-Verlag New York. - 1939-8018 .- 1939-8115. ; 95:12, s. 1355-1370
-
Tidskriftsartikel (refereegranskat)abstract
- In an open world with a long-tail distribution of input samples, Deep Neural Networks (DNNs) may make unpredictable mistakes for Out-of-Distribution (OOD) inputs at test time, despite high levels of accuracy obtained during model training. OOD detection can be an effective runtime assurance mechanism for safe deployment of machine learning algorithms in safety–critical applications such as medical imaging and autonomous driving. A large number of OOD detection algorithms have been proposed in recent years, with a wide range of performance metrics in terms of accuracy and execution time. For real-time safety–critical applications, e.g., autonomous driving, timing performance is of great importance in addition to accuracy. We perform a comprehensive and systematic benchmark study of multiple OOD detection algorithms in terms of both accuracy and execution time on different hardware platforms, including a powerful workstation and a resource-constrained embedded device, equipped with both CPU and GPU. We also profile and analyze the internal details of each algorithm to identify the performance bottlenecks and potential for GPU acceleration. This paper aims to provide a useful reference for the practical deployment of OOD detection algorithms for real-time safety–critical applications.
|
|
| 28. |
- Luan, Siyu, 1992-
(författare)
-
Towards safe and efficient application of deep neural networks in resource-constrained real-time embedded systems
- 2023
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- We consider real-time safety-critical systems that feature closed-loop interactions between the embedded computing system and the physical environment with a sense-compute-actuate feedback loop. Deep Learning (DL) with Deep Neural Networks (DNNs) has achieved success in many application domains, but there are still significant challenges in its application in real-time safety-critical systems that require high levels of safety certification under significant hardware resource constraints. This thesis considers the following overarching research goal: How to achieve safe and efficient application of DNNs in resource-constrained Real-Time Embedded (RTE) systems in the context of safety-critical application domains such as Autonomous Driving? Towards reaching that goal, this thesis presents a set of algorithms and techniques that aim to address three Research Questions (RQs): RQ1: How to achieve accurate and efficient Out-of-Distribution (OOD) detection for DNNs in RTE systems? RQ2: How to predict the performance of DNNs under continuous distribution shifts? RQ3: How to achieve efficient inference of Deep Reinforcement Learning (DRL) agents in RTE systems?For RQ1, we present a framework for OOD detection based on outlier detection in one or more hidden layers of a DNN with either Isolation Forest (IF) or Local Outlier Factor (LOF). We also perform a comprehensive and systematic benchmark study of multiple well-known OOD detection algorithms in terms of both accuracy and execution time on different hardware platforms, in order to provide a useful reference for the practical deployment of OOD detection algorithms in RTE systems. For RQ2, we present a framework for predicting the performance of DNNs for end-to-end Autonomous Driving under continuous distribution shifts with two approaches: using an Autoencoder that attempts to reconstruct the input image; and applying Anomaly Detection algorithms to the hidden layer(s) of the DNN. For RQ3, we present a framework for model compression of the policy network of a DRL agent for deployment in RTE systems by leveraging the relevance scores computed by Layer-wise Relevance Propagation (LRP) to rank and prune the convolutional filters, combined with fine-tuning using policy distillation.The algorithms and techniques developed in this thesis have been evaluated on standard datasets and benchmarks. To summarize our findings, we have developed novel OOD detection algorithms with high accuracy and efficiency; identified OOD detection algorithms with relatively high accuracy and low execution times through benchmarking; developed a framework for DNN performance prediction under continuous distribution shifts, and identified most effective Anomaly Detection algorithms for use in the framework; developed a framework for model compression of DRL agents that is effective in reducing model size and inference time for deployment in RTE systems. The research results are expected to assist system designers in the task of safe and efficient application of DNNs in resource-constrained RTE systems.
|
|
| 29. |
- Mettin, Uwe, et al.
(författare)
-
Generating human-like motions for an underactuated three-link robot based on the virtual constraints approach
- 2007
-
Ingår i: Proceedings of the 46th IEEE conference on decision and control. - 9781424414970 ; , s. 5138-5143
-
Konferensbidrag (refereegranskat)abstract
- In the field of robotics there is a great interest in developing strategies and algorithms to reproduce human-like behavior. In this paper, we consider motion planning and generation for humanoid robots based on the concept of virtual holonomic constraints. For this purpose, recorded kinematic data from a particular human motion are analyzed in order to extract geometric relations among various joint angles defining the instantaneous postures. The analysis of a simplified human body representation leads to dynamics of a corresponding underactuated mechanical system with parameters based on anthropometric data of an average person. The motion planning is realized by considering solutions of reduced system dynamics assuming the virtual holonomic constraints are kept invariant The relevance of such a mathematical model in accordance to the real human motion under study is shown. An appropriate controller design procedure is presented together with simulation results of a feedback-controlled robot.
|
|
| 30. |
- Mettin, Uwe, 1979-, et al.
(författare)
-
Optimal ball pitching with an underactuated model of a human arm
- 2010
-
Konferensbidrag (refereegranskat)abstract
- A new approach for solving an optimal motion planning problem for a simplified 2-degrees-of-freedom model of a human arm is proposed. The motion of interest resembles ball pitching. The model of a planar two-link robot is used with actuation only at the shoulder joint and a passive spring at the elbow joint representing the stiffness of the arm. The goal is formulated as finding a trajectory and the associated torque of the active joint that maximizes the velocity of the end effector in horizontal direction at the moment of crossing a vertical ball-release line. The basic idea is to search for an optimal motion parametrized by the horizontal displacement of the end-effector from the start point to the release point. The suggested procedure leads to analytical expressions for the coefficients of a nonlinear differential equation that governs the geometric relation between the links along an optimal motion. The motion planning task is reformulated to a finite-dimensional search for the corresponding initial conditions.
|
|
| 31. |
- Mettin, Uwe, 1979-, et al.
(författare)
-
Parallel elastic actuators as a control tool for preplanned trajectories of underactuated mechanical systems
- 2009
-
Ingår i: The international journal of robotics research. - : Sage journals online. - 0278-3649 .- 1741-3176. ; 29:9, s. 1186-1198
-
Tidskriftsartikel (refereegranskat)abstract
- A lack of sufficient actuation power as well as the presence of passive degrees of freedom are often serious constraints for feasible motions of a robot. Installing passive elastic mechanisms in parallel with the original actuators is one of a few alternatives that allows for large modifications of the range of external forces or torques that can be applied to the mechanical system. If some motions are planned that require a nominal control input above the actuator limitations, then we can search for auxiliary spring-like mechanisms complementing the control scheme in order to overcome the constraints. The intuitive idea of parallel elastic actuation is that spring-like elements generate most of the nominal torque required along a desired trajectory, so the control efforts of the original actuators can be mainly spent in stabilizing the motion. Such attractive arguments are, however, challenging for robots with non-feedback linearizable non-minimum phase dynamics that have one or several passive degrees of freedom. We suggest an approach to resolve the apparent difficulties and illustrate the method with an example of an underactuated planar double pendulum. The results are tested both in simulations and through experimental studies.
|
|
| 32. |
- Meza-Sánchez, Iliana M., et al.
(författare)
-
Nonlinear output feedback H∞-tracking control of a 3-DOF underactuated helicopter
- 2011
-
Ingår i: 18th IFAC World Congress. - : Elsevier. - 9783902661937 ; , s. 11145-11150
-
Konferensbidrag (refereegranskat)abstract
- Nonlinear H∞-control synthesis is developed to solve the tracking control problem to induce periodic behavior in a 3-DOF underactuated helicopter prototype. Due to the nature of the approach, the proposed controller yields the desired robustness properties against unknown bounded external disturbances. Stabilizability and detectability properties of the control system are ensured by the existence of proper solutions of the corresponding differential Riccati equations. Virtual constraints approach for motion planning is considered prior the controller design in order to achieve the control goal. Performance issues of the proposed controller are illustrated via numerical simulations.
|
|
| 33. |
-
Proceedings of the 16th Student Conference in Interaction Technology and Design and the 5th Student Conference in Electronics and Mechatronics
- 2019
-
Proceedings (redaktörskap) (refereegranskat)abstract
- The joint Student Conference in Interaction Technology and Design and Student Conference in Electronics and Mechatronics is the annual grand finale of the courses Current Topic in Interaction Technology and Design and Student Conference in Electronics and Mechatronics at the Department of Applied Physics and Electronics, Umeå University. The idea and objective of the two courses are to give the students a forum where they can actively participate in scientific research and development through their own ideas and interests. The course introduces students to independently researching an interesting topic, using a foreign language orally and in writing, writing a scientific article, peer-review and presenting their work at a conference. The conference format was chosen to provide a realistic environment for the presentation of the results. The work has been reviewed both by other participant on the course and members of the department. If the reviews are favorable, the paper is accepted as a full paper at the conference and included in the proceedings. Research that has an interesting topic and potential for future publication is presented as work-in-progress at the conference and the abstract is included in the conference proceedings. This year 10 full papers and 2 work-in-progress papers were accepted at the conference and all included in this proceedings as full papers and extended abstracts, respectively.
|
|
| 34. |
-
Proceedings of the 18th Student Conference in Interaction Technology and Design and the 6th Student Conference in Electronics and Mechatronics
- 2020
-
Proceedings (redaktörskap) (övrigt vetenskapligt/konstnärligt)abstract
- The joint Student Conference in Interaction Technology and Design and Student Conference in Electronics and Mechatronics is the annual grand finale of the courses Current Topic in Interaction Technology and Design and Student Conference in Electronics and Mechatronics at the Department of Applied Physics and Electronics, Umeå University. The idea and objective of the two courses are to give the students a forum, where they can actively participate in scientific research and development through their own ideas and interests. The course introduces students to independently finding and researching a topic of interest for them, using a foreign language orally and in writing, writing a scientific article, peer-reviewing and presenting their work at a conference. The conference format was chosen to provide a realistic environment for the presentation of the results. The work has been reviewed both by other participant on the course and members of the department. If the reviews are favorable, the paper is accepted as a full paper at the conference and included in the proceedings.
|
|
| 35. |
-
Proceedings of the 19th Student Conference in Interaction Technology and Design
- 2020
-
Proceedings (redaktörskap) (övrigt vetenskapligt/konstnärligt)abstract
- The Student Conference in Interaction Technology and Design is the annual grand finale of the course Current Topic in Interaction Technology and Design at the Department of Applied Physics and Electronics, Umeå University. The idea and objective of the course are to give the students a forum, where they can actively participate in scientific research and development through their own ideas and interests. The course introduces students to independently finding and researching a topic of interest for them, writing a scientific article, peer-reviewing, and presenting their work at a conference. The course is conducted in English both in writing and orally, and it is a foreign language for most of the students. The conference format is chosen to provide a realistic environment for the presentation of the results. The work of each student has been reviewed both by other participants on the course and members of the department. If the reviews are favorable, the paper is accepted as a full paper at the conference and included in the proceedings.
|
|
| 36. |
-
Proceedings of the 21st Student Conference in Interaction Technology and Design
- 2021
-
Proceedings (redaktörskap) (refereegranskat)abstract
- The Student Conference in Interaction Technology and Design is the annual grand finale of the course Current Topic in Interaction Technology and Design at the Department of Applied Physics and Electronics, Umeå University, Sweden. The main objective of the course is to give the participants a forum, where they can actively discuss scientific research and development through the implementation of their own ideas and interests. The course introduces students to independently finding and researching a topic of interest for them, finding related sources of information and related research publications, writing a scientific article, peer-reviewing, and presenting their work at a conference. The course is conducted in English which is a foreign language for most of the students. The final examination format is chosen as a conference to provide a realistic environment for the presentation of the results. The work of each student has been reviewed by other participants on the course and members of the department acting not only as teachers and consultants but also as program committee members. If the reviews are favorable, the paper is accepted as a full paper at the conference and included in the proceedings.
|
|
| 37. |
- Rosales, Antonio, et al.
(författare)
-
Describing function-based analysis and design of approximated sliding-mode controllers with reduced chattering
- 2023
-
Ingår i: Sliding-mode control and variable-structure systems. - : Springer Science+Business Media B.V.. - 9783031370885 - 9783031370892 ; , s. 357-381
-
Bokkapitel (refereegranskat)abstract
- Sliding-mode control (SMC) is a powerful robust control design technique that, when appropriately implemented, ensures insensitivity to the so-called matched bounded disturbances and finite-time convergence. However, the insensitivity requires an ideal implementation of discontinuous signals, often based on the sign function that, in practice, results in the presence of parasitic oscillations called chattering. Chattering is unavoidable in systems with SMC, including continuous and higher-order SMC (HOSM) approaches. One of the simplest and commonly used solutions to alleviate chattering is the approximation of the SMC by substituting the sign function with its approximation by a sigmoid function or a saturation function, although this obviously transforms the insensitivity property into a reduction of the influence of the disturbances. In fact, the accuracy of approximating discontinuity creates a trade-off between the reduction of the influence of the disturbances and the amount of chattering. Hence, the following question appears: Is it possible to systematically design a SMC-approximation avoiding a blind search requiring a huge number of numerical and/or hardware experiments? This chapter presents a method to design the boundary-layer parameter of the saturation function. The design is based on the describing function (DF) and harmonic balance (HB) techniques for estimating the parameters of chattering, i.e., frequency and amplitude of the parasitic oscillations.
|
|
| 38. |
- Rosales, Antonio, et al.
(författare)
-
Estimation of time-varying parameters defining contact of a planar manipulator with a surface
- 2022
-
Ingår i: CDC 2022. - : Institute of Electrical and Electronics Engineers (IEEE). - 9781665467612 ; , s. 1392-1397
-
Konferensbidrag (refereegranskat)abstract
- The knowledge of parameters, defining interaction of a robotic manipulator with environment, is crucial when robots execute contact-tasks involving tracking of trajectories while desired forces are applied on the environment. For contact tasks on planar surfaces, the inclination and stiffness of the surface are key parameters since the first one defines the direction of the desired force and trajectory, which are typically defined relative to a frame attached to the environment, and the second one is required to compute the control signal. There exist methods for estimation of inclination and stiffness, whenever they are constant. The estimation of time-varying stiffness and inclination is less studied. In this paper, we propose a method to estimate on-line the stiffness and inclination of the planar surface, when they are varying during the task execution. The method is based on adaptive observers that ensure asymptotic or finite-time convergence of the estimates to the real values of the parameters.
|
|
| 39. |
- Shiriaev, Anton, et al.
(författare)
-
A remark on controlled Lagrangian approach for completely integrable mechanical systems
- 2012
-
Ingår i: 4th IFAC Workshop on Lagrangian and Hamiltonian Methods for Non Linear Control. - : Elsevier. - 9783902823083 ; , s. 54-59
-
Konferensbidrag (refereegranskat)abstract
- Using an example of cart-pendulum system we give some new insights into the methods of Controlled Lagrangians that can be used for planning forced trajectories and their orbital stabilization. The issue of integrability as a result of preservation and creation of conserved quantities is emphasized and discussed in detail.
|
|
| 40. |
- Shiriaev, Anton, et al.
(författare)
-
Can we make a robot ballerina perform a pirouette? : orbital stabilization of periodic motions of underactuated mechanical systems.
- 2008
-
Ingår i: Annual Reviews in Control. - : Elsevier BV. - 1367-5788 .- 1872-9088. ; 32:2, s. 200-211
-
Tidskriftsartikel (refereegranskat)abstract
- This paper provides an introduction to several problems and techniques related to controlling periodic motions of dynamical systems. In particular, we consider planning periodic motions and designing feedback controllers for orbital stabilization. We review classical and recent design methods based on the Poincaré first-return map and the transverse linearization. We begin with general nonlinear systems and then specialize to a class of underactuated mechanical systems for which a particularly rich structure allows many of the problems to be solved analytically.
|
|
| 41. |
- Shiriaev, Anton S., et al.
(författare)
-
Controlled invariants and trajectory planning for underactuated mechanical systems
- 2014
-
Ingår i: IEEE Transactions on Automatic Control. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9286 .- 1558-2523. ; 59:9, s. 2555-2561
-
Tidskriftsartikel (refereegranskat)abstract
- We study the problem of motion planning for underactuated mechanical systems. The idea is to reduce complexity by imposing via feedback a sufficient number of invariants and then to compute a projection of the dynamics onto an induced invariant sub-manifold of the closed-loop system. The inspiration comes from two quite distant methods, namely the method of virtual holonomic constraints, originally invented for planning and orbital stabilization of gaits of walking machines, and the method of controlled Lagrangians, primarily invented as a nonlinear technique for stabilization of (relative) equilibria of controlled mechanical systems. Both of these techniques enforce the presence of particular invariants that can be described as level sets of conserved quantities induced in the closed-loop system. We link this structural feature of both methods to a procedure to transform a Lagrangian system with control inputs via a feedback action into a control-free Lagrangian system with a sufficient number of first integrals for the full state space or an invariant sub-manifold. In both cases, this transformation allows efficient (analytical) description of a new class of trajectories of forced mechanical systems appropriate for further orbital stabilization. For illustration purposes, we approach the challenging problem for a controlled mechanical system with two passive degrees of freedom: planning periodic (or bounded) forced upperhemisphere trajectories of the spherical pendulum on a puck. Another example of the technique is separately reported in [21].
|
|
| 42. |
- Shiriaev, Anton S., et al.
(författare)
-
Controlled Invariants and Trajectory Planning for Underactuated Mechanical Systems
- 2013
-
Ingår i: 2013 IEEE 52nd Annual Conference on Decision and Control (CDC). - : IEEE. - 9781467357173 ; , s. 1628-1633
-
Konferensbidrag (refereegranskat)abstract
- We study the problem of motion planning for underactuated mechanical systems. The idea is to reduce complexity by imposing via feedback a sufficient number of invariants and then compute a projection of the dynamics onto an induced invariant sub-manifold of the closed-loop system. The inspiration comes from two quite distant methods, namely the method of virtual holonomic constraints, originally invented for planning and orbital stabilization of gaits of walking machines, and the method of controlled Lagrangians, primarily invented as a nonlinear technique for stabilization of (relative) equilibria of controlled mechanical systems. Both of these techniques enforce the presence of particular invariants that can be described as level sets of conserved quantities induced in the closed-loop system. We link this structural feature of both methods to a procedure to transform a Lagrangian system via a feedback action into a new dynamical system with a sufficient number of first integrals for the full state space or an invariant sub-manifold. In both cases, this transformation allows efficient (analytical) description of a new class of trajectories of forced mechanical systems appropriate for further orbital stabilization. The contribution is illustrated with a spherical pendulum example that is discussed in detail.
|
|
| 43. |
- Shiriaev, Anton S., et al.
(författare)
-
Criteria for Global Stability of Coupled Systems with Application to Robust Output Feedback Design for Active Surge Control
- 2009
-
Ingår i: Proc. 2009 IEEE Multi-conference on Systems and Control (MSC 2009). ; , s. 1021-1026
-
Konferensbidrag (refereegranskat)abstract
- The well-known and commonly accepted finite dimensional model qualitatively describing surge instabilities in centrifugal (and axial) compressors is considered. The problem of global output feedback stabilization for it is solved. The solution relies on two new criteria for global stability proposed for a class of nonlinear systems exploiting quadratic constraints for infinite sector nonlinearities. Two families of robust output feedback controllers are proposed. Controllers from the first family ensure global exponential stabilization. The ones from the second family provide integral action but only ensure local exponential and global asymptotic stability. Performance is verified by simulations.
|
|
| 44. |
- Shiriaev, Anton S., et al.
(författare)
-
IQC Arguments for Analysis of the 3-State Moore-Greitzer Compressor System
- 2015
-
Ingår i: IFAC-PapersOnLine. - : Elsevier BV. - 2405-8963. ; 28:11, s. 252-257
-
Tidskriftsartikel (refereegranskat)abstract
- The Integral Quadratic Constraint (IQC) framework developed by Professor Yakubovich and his co-workers, see Yakubovich et.al. (2004), is one of few available constructive tools for establishing robust stability of nonlinear systems. An explicit format of stability conditions, procedures for computing a Lyapunov function and developed libraries IQCs for common nonlinearities in dynamics, all together have made the approach unique and at the same time so to say automatic for recovering stability conditions for many applications: in the process of analyzing a dynamical system, an engineer is just required to search for a sufficiently rich set IQCs describing nonlinearities in the dynamics so that such nonlinearities can be substituted in analysis by quadratic constraints, which they satisfy. The power of the methodology becomes also its weak part in an analysis of concrete systems. Searching IQCs is the difficult task in new examples, where a lack of a rich set of IQCs for concrete nonlinearities makes the method inconclusive or too rough to detect (in)-stability. The paper is aimed at a discussion of such an example of a nonlinear dynamical system (the classical 3-state Moore-Greitzer compressor model) augmented with the dynamical feedback controller, whose parameters should be adjusted to meet a stability condition. The closed-loop system has several nonlinearities and searching the corresponding IQCs to meet the stability conditions for this example is rather involved. To overcome the problem, we have previously described by different methods a set of parameters for which any solution of the closed loop system, if bounded, will converge to the origin and that the origin is locally asymptotically stable. However, the proof is incomplete without showing a boundedness of all solutions. To solve the task we have re-used some of the IQC framework ideas, where the method has been utilized and the corresponding IQCs have been found only for unbounded trajectories, if they would be present in closed loop system. The arguments have allowed completing the proof of stability and illustrating deliberate use of the IQC framework aimed at analysis of behavior specific trajectories.
|
|
| 45. |
- Shiriaev, Anton S., et al.
(författare)
-
Transverse linearization for mechanical systems with several passive degrees of freedom with applications to orbital stabilization
- 2009
-
Ingår i: American Control Conference, 2009. ACC '09. - 9781424445233 ; , s. 3039-3044
-
Konferensbidrag (refereegranskat)abstract
- A class of mechanical systems with many unactuated degrees of freedom is studied. An analytical method for computing coefficients of a linear controlled system, solutions of which approximate dynamics of transverse part of coordinates of an underactuated mechanical system along a feasible motion, is proposed. The procedure is constructive and is based on a particular choice of coordinates in a vicinity of the motion. It allows explicit introduction of the so-called moving Poincare section associated with a finite-time or periodic motion. It is shown that the coordinates admit analytical linearization of transverse part of the system dynamics prior to any controller design. If the motion is periodic, then these coordinates are used for developing feedback controllers. Necessary and sufficient conditions for exponential orbital stabilization of a cycle for underactuated mechanical systems are derived. Two illustrative examples are elaborated in details.
|
|
| 46. |
- Surov, Maksim, et al.
(författare)
-
Constructing Transverse Coordinates for Orbital Stabilization of Periodic Trajectories
- 2020
-
Ingår i: 2020 American Control Conference (ACC). - : IEEE. - 9781538682661 - 9781538682678 ; , s. 836-841
-
Konferensbidrag (refereegranskat)abstract
- An approach for introduction of transverse coordinates in a vicinity of a periodic trajectory is presented. The approach allows finding by numerical integration periodic normalized mutually-orthogonal vector-functions that form a continuously differentiable basis on moving Poincare sections for a given periodic solution of a nonlinear dynamical system. The found moving frame is used to define new local (transverse) coordinates for an associated affine nonlinear control system in a neighborhood of the trajectory, and to proceed with orbital stability analysis and/or synthesis of a stabilizing feedback control law. As a demonstrating example of the approach, the problem of orbital stabilization of a trajectory of a multibody car system is considered. The results of computer simulations of the system are presented.
|
|
| 47. |
- Vázquez, Carlos, et al.
(författare)
-
Input nonlinearity compensation and chattering reduction in a mobile hydraulic forestry crane
- 2016
-
Ingår i: Elektrotechnik und Informationstechnik. - : Springer. - 0932-383X. ; 133:6, s. 248-252
-
Tidskriftsartikel (refereegranskat)abstract
- We present a sliding-mode-based control design for a telescopic link of a mobile-hydraulic forestry crane under bounded modeling uncertainties and external disturbances. Mobile hydraulic systems are typically subject to strong perturbation conditions and the design of resilient control solutions is an important challenge. Furthermore, nonlinear phenomena primarily, characterized by easily excited oscillations, an input nonlinearity, and friction, are dominating the dynamics. The proposed control scheme takes advantage of an input-nonlinearity compensation in order to overcome these problems and includes the formulation of a sliding-mode-control-based design. Two strategies for chattering attenuation are examined aimed at improving the controller performance. Experimental results performed over an industrial setup, including a comparison with a PID controller, confirm the efficacy of the proposed methodology.
|
|
| 48. |
- Verdés, Ramón I., et al.
(författare)
-
Accurate Position Regulation of an Electro-Hydraulic Actuator via Uncertainty Compensation-Based Controller
- 2021
-
Ingår i: Emerging Trends in Sliding Mode Control. - Singapore : Springer. - 9789811586125 - 9789811586132 ; , s. 279-303
-
Bokkapitel (refereegranskat)abstract
- Electro-hydraulic actuators are complex systems with uncertainties in their parameters and disregarded dynamics due to its complexity. This paper presents a disturbance observer-based controller method for the accurate position regulation of an electro-hydraulic actuator. To this aim, a super-twisting algorithm-based observer identifies the plant uncertainties and neglected dynamics, theoretically, in finite-time. Thus, a compensation based controller is designed to counteract the uncertainty and neglected dynamics effects through feedback, improving the position regulation accuracy. The closed-loop analysis is carried out using Lyapunov theory. The feasibility of the controller is validated through high-fidelity simulations and experiments in a forestry crane.
|
|
| 49. |
- Wang, Zeguo, et al.
(författare)
-
Almost periodic motion planning and control for double rotary pendulum with experimental validation
- 2020
-
Ingår i: Asian Journal of Control. - : John Wiley & Sons. - 1561-8625 .- 1934-6093. ; 22:6, s. 2434-2443
-
Tidskriftsartikel (refereegranskat)abstract
- The aim is to develop a systematic procedure for planning feasible motions for a double rotary pendulum. This pendulum has one directly actuated horizontal link and two passive links, moving in a rotating vertical plane. We plan a nontrivial oscillatory motion for the passive links that is consistent with the horizontal link rotating at a given average speed and also design a stabilizing controller to approximately induce such a motion. For the motion planning, a numerical optimization procedure is proposed in the form of a sequence of three simpler problems to systematically derive initial guesses for the final optimization search. For the controller design, firstly the system is linearized along a nominal trajectory, and then a parametrized family of candidate stabilizing controllers is designed. For each set of parameters, a necessary and sufficient stability condition can be checked for the derived linear time varying periodic system. Therefore, a numerical optimization procedure is used to find the controller gain for the linear system based on the stability condition. The performance of the closed-loop system is illustrated via numerical simulations and verified via experiments with an educational platform produced by PendCon, demonstrating achieving oscillations with required characteristics. However, the formal proofs for convergence and even for existence of almost periodic solutions are left for future studies.
|
|
| 50. |
- Wang, Zeguo, et al.
(författare)
-
Periodic Motion Planning and Control for Double Rotary Pendulum via Virtual Holonomic Constraints
- 2019
-
Ingår i: IEEE/CAA Journal of Automatica Sinica. - : Institute of Electrical and Electronics Engineers (IEEE). - 2329-9266 .- 2329-9274. ; 6:1, s. 291-298
-
Tidskriftsartikel (refereegranskat)abstract
- Periodic motion planning for an under-actuated system is rather difficult due to differential dynamic constraints imposed by passive dynamics, and it becomes more difficult for a system with higher underactuation degree, that is with a higher difference between the number of degrees of freedom and the number of independent control inputs. However, from another point of view, these constraints also mean some relation between state variables and could be used in the motion planning. We consider a double rotary pendulum, which has an underactuation degree 2. A novel periodic motion planning is presented based on an optimization search. A necessary condition for existence of the whole periodic trajectory is given because of the higher underactuation degree of the system. Moreover this condition is given to make virtual holonomic constraint (VHC) based control design feasible. Therefore, an initial guess for the optimization of planning a feasible periodic motion is based on this necessary condition. Then, VHCs are used for the system transformation and transverse linearization is used to design a static state feedback controller with periodic matrix function gain. The controller gain is found through another optimization procedure. The effectiveness of initial guess and performance of the closed-loop system are illustrated through numerical simulations.
|
|
