| 1. |
- Freidovich, Leonid, 1973-, et al.
(författare)
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Comparison of logic-based switching control designs for a nonlinear system
- 2004
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Ingår i: PROCEEDINGS OF THE 2004 AMERICAN CONTROL CONFERENCE, VOLS 1-6. - 0780383354 ; , s. 1221-1222
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Konferensbidrag (refereegranskat)abstract
- We consider an example of a second order nonlinear system with large parametric uncertainties. The two parameters of the system are assumed to belong to a finite set. The goal is to guarantee (practical) convergence of the system output to a given constant reference signal. Feedback linearization-based candidate controllers with pole placement are designed for each possible set of parameters. After that, we consider the design of a high-level logic-based supervisor to organize switching between these candidate controllers. Three different approaches are used and compared.
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| 2. |
- Freidovich, Leonid, 1973-
(författare)
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Constrained joint PD plus controller for flexible link robots
- 2000
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Konferensbidrag (refereegranskat)abstract
- A class of globally asymptotically stable regulators for a finite-dimensional model of robot arm with flexible links under gravity is presented. The control law is formed as the sum of static compensation of gravity at the desired position and constrained state feedback. Only some of generalized coordinates (joint positions and velocities) are assumed available for measurement and saturation in amplifier characteristic curves is taken into account. Copyright (C) 2000 IFAC.
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| 3. |
- Freidovich, Leonid, 1973-, et al.
(författare)
-
Logic-based switching for the control of a class of nonlinear systems
- 2003
-
Konferensbidrag (refereegranskat)abstract
- We consider a nonlinear single-input-single-output minimum phase system with large parametric uncertainty. The system can be represented globally in the normal form and our goal is to find an output dynamic feedback control law to ensure that the output (practically) asymptotically tracks a bounded smooth reference signal. Earlier work used high-gain observers with saturation to derive adaptive as well as robust control laws for this problem. The adaptive control law requires the nonlinear functions to be linearly parameterized in the unknown parameters and could have unsatisfactory transient performance for a large parameter set. The robust control law is based on a worst-case design and could be overly conservative for a large parameter set. In this paper we propose a new approach based on partitioning the set of uncertain parameters into smaller subsets. Robust control laws are designed for each subset and logic based switching is used to choose the appropriate control law. The switching rule uses an estimate of the derivative of a Lyapunov function, which is estimated using a high-gain observer.
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| 4. |
- Freidovich, Leonid, 1973-, et al.
(författare)
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Universal integral controllers for robotic manipulators
- 2002
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Ingår i: Nonlinear control systems 2001. - Oxford : Pergamon Press. - 0080435602 - 9780080435602 ; , s. 351-356
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Konferensbidrag (refereegranskat)abstract
- As a standard model for a rigid multilink robotic manipulator, we consider a MIMO nonlinear system of uniform vector relative degree {2,...,2}, which has a globally defined normal form with no zero dynamics. We consider a trajectory-following problem for a class of smooth bounded time-varying vector reference signals. We design an output feedback integral controller that ensures ultimately bounded tracking error which could be made as small as required. In addition, if the reference signal has a constant limit, the output approaches this limit. The controller is robust with respect to parameter uncertainties, decentralized, saturated, and simple to implement. Locally, it is a PID regulator with derivatives estimated via a linear high-gain observer. Regional (and semiglobal) practical (and asymptotic) stability is shown with the help of a vector Lyapunov function and a technique, typical for "continuous" sliding mode control. Copyright (C) 2001 IFAC.
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