| 1. |
- Falcone, Paolo, 1977, et al.
(författare)
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A Hierarchical Model Predictive Control Framework for Autonomous Ground Vehicles
- 2008
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Ingår i: American Control Conference. - 0743-1619. - 9781424420797 ; , s. 3719 - 3724
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Konferensbidrag (refereegranskat)abstract
- A hierarchical framework based on Model Predictive Control (MPC) for autonomous vehicles is presented. We formulate a predictive control problem in order to best follow a given path by controlling the front steering angle while fulfilling various physical and design constraints.We start from the low-level active steering-controller presented in [3], [9] and integrate it with a high level trajectory planner. At both levels MPC design is used. At the high-level, a trajectory is computed on-line, in a receding horizon fashion, based on a simplified point-mass vehicle model. At the low-level a MPC controller computes the vehicle inputs in order to best follow the desired trajectory based on detailed nonlinear vehicle model.This article presents the approach, the method for implementing it, and successful preliminary simulative results on slippery roads at high entry speed.
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| 2. |
- Mirkin, Boris, et al.
(författare)
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Adaptive Output-Feedback Control of MIMO Plants with Unknown, Time-Varying State Delay
- 2008
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Ingår i: American Control Conference. - 0743-1619. - 9781424420797 ; , s. 4761 - 4766
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Konferensbidrag (refereegranskat)abstract
- In this paper, we develop a simple model reference adaptive control (MRAC) scheme for a class of multi-inputmulti-output (MIMO) linear dynamic systems with unknown time-varying state delay which is also robust with respect to an external disturbance with unknown bound. A suitable Lyapunov-Krasovskii type functional with “virtual” gain is introduced to design the adaptation algorithms and to prove stability.
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| 3. |
- Dahl, Ola, et al.
(författare)
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Nonlinear and Adaptive Observers for Perspective Dynamic Systems
- 2007
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Ingår i: Proceedings American Control Conference. - : IEEE. - 0743-1619. - 9781424409884 ; , s. 2230-2235
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Konferensbidrag (refereegranskat)abstract
- Estimation of 3D structure and motion from 2D images in computer vision systems can be performed using a dynamic system, often referred to as a perspective dynamic system. This paper presents a novel parametrization of the nonlinear perspective dynamic system, from which different estimators for rigid body structure as well as motion can be derived in a straightforward manner. The parametrization allows a structure estimator to be formulated as a nonlinear observer which estimates 3D position, assuming knowledge of angular and linear velocities. The observer performance is demonstrated using simulation examples, where it is also shown how a time scaling parameter can be used to tune the transient response. The parametrization also allows a motion estimator to be formulated as an adaptive observer, estimating angular velocity and 3D position assuming knowledge of the linear velocity. This is demonstrated by deriving an estimator and illustrating its performance in a simulation example. The presented investigations and simulations indicate that the parametrization has a potential for future development of estimators for structure as well as motion in perspective dynamic systems, and for the investigation of similarities and differences in comparison to discrete, projective geometry based, methods.
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| 4. |
- Gattami, Ather, et al.
(författare)
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Minimax Team Decision Problems
- 2007
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Ingår i: ; , s. 4333-4338, s. 766-771
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Konferensbidrag (refereegranskat)abstract
- We consider the problem of distributed decision making in a quadratic game between a "team" of players and nature. Each player has limited information that could be different from the other players in the team. We show that if there is a solution to the minimax team problem, then the linear policies are optimal, and we show how to find the linear optimal solution by solving a linear matrix inequality. The result is used to solve the distributed H infinity control problem. It shows that the information structure restricted to exchange information with neighbours only, is enough to obtain a linear optimal feedback law.
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| 5. |
- Linderoth, Magnus, et al.
(författare)
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Nonlinear lateral control strategy for nonholonomic vehicles
- 2008
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Ingår i: American Control Conference. - 0743-1619. - 9781424420780 ; , s. 3219-3224
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Konferensbidrag (refereegranskat)abstract
- This paper proposes an intuitive nonlinear lateral control strategy for trajectory tracking in autonomous nonholonomic vehicles. The controller has been implemented and verified in Alice, Team Caltech's contribution to the 2007 DARPA Urban Challenge competition for autonomous motorcars. A kinematic model is derived. The control law is described and analyzed. Results from simulations and field tests are given and evaluated. Finally, the key features of the proposed controller are reviewed, followed by a discussion of some limitations of the proposed strategy.
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| 6. |
- Nilsson, Magnus, 1978, et al.
(författare)
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Nonlinear Adaptive Feedforward in a Two-Degrees-of-Freedom Controller
- 2007
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Ingår i: American Control Conference. - 0743-1619. - 1424409888 ; , s. 3979-3984
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Konferensbidrag (refereegranskat)abstract
- An adaptive feedforward steady-state gain in a two-degrees-of-freedom controller for a nonlinear SISO plant is investigated. The examination of a less complicated structure gives hints to how an update law may be constructed in the nonlinear case. Stability is shown in the simpler case for an update law based on an estimation error using projection, and simulations show that Altering may lead to improved performance. By using an adaptive feedforward function inspired by gain-scheduling techniques, a simulation example for the nonlinear structure is also shown. The conclusions are that the scheme has potential but that more research is needed for the nonlinear setup.
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| 7. |
- Nilsson, Oskar, et al.
(författare)
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A novel nonlinear model reduction method applied to automotive controller software
- 2009
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Ingår i: 2009 American Control Conference, Vols 1-9. - 0743-1619. ; , s. 4587-4592
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Konferensbidrag (refereegranskat)abstract
- The automotive industry is experiencing tightening emission legislations together with high demands on performance and driveability. As a counteraction, controller software tends to become more and more complex. Intricate controller software has several downsides, the large number of controller parameters yields an exhaustive calibration task, often performed through costly experiments. In addition, to guarantee reliability, validation and verification analysis is performed on the controller in combination with the engine. This task would also greatly benefit from a less complex controller structure. Here a novel model reduction method of nonlinear discrete-time systems is introduced and applied to an engine controller used in current production cars. The result is a nonlinear piece-wise affine system with improved simulation speed.
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| 8. |
- Purvis, K.B., et al.
(författare)
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Estimating radar positions using unmanned air vehicle teams engaged in cooperative deception
- 2005
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Ingår i: American Control Conference, 2005. Proceedings of the 2005. - 0743-1619. ; 5, s. 3512-3517
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Konferensbidrag (refereegranskat)abstract
- Standard TDOA (time-difference of arrival) estimation techniques are modified and applied to locate networked enemy radars using a cooperative team of unmanned electronic combat air vehicles (ECAVs). The team is engaged in deceiving the radars, which limits where the ECAVs can fly and requires accurate radar positions to be known. Two TDOA measurements of radar pulses taken by two ECAV pairs are used to estimate the position of the middle radar. A nonlinear system model for estimation is formulated and used to perform simulations with "noisy" TDOAs; a linearized time-varying model for straight nominal ECAV trajectories is derived from the nonlinear model. The choice of optimal ECAV trajectories and an observer to minimize the variance of the middle radar position - using the linearized model is addressed. Application of a time-varying Kalman filter to the linearized system shows drastic improvement in reducing the variance of position estimates when compared to the original nonlinear system via simulations.
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| 9. |
- Rantzer, Anders
(författare)
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Linear quadratic team theory revisited
- 2006
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Ingår i: Proceedings of the American Control Conference. - 0743-1619. ; 2006, s. 1637-1641
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Konferensbidrag (refereegranskat)abstract
- A linear quadratic stochastic control problem is considered. The problem involves several different controllers acting as a team, but with access to different measurements. Under appropriate assumptions on communication delays between the controllers, a quadratic control objective can be optimized using finite-dimensional convex optimization. Versions of this problem has been discussed in economic literature, as well as in statistical decision theory. Some instances were solved in the 1960-70's, but significant progress on convexity properties and the role of communication delays has recently been made. In this paper a stochastic criterion is optimized subject to communication delays. Control of vehicle formations is considered as an example.
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| 10. |
- Schofield, Brad
(författare)
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On active set algorithms for solving bound-constrained least squares control allocation problems
- 2008
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Ingår i: American Control Conference, 2008, vols 1-12. - 0743-1619. - 9781424420780 ; , s. 2597-2602
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Konferensbidrag (refereegranskat)abstract
- Control allocation problems, in which optimal actuator values are assigned based on desired control actions and actuator constraints, are typically formulated as constrained optimization problems. Initially, only approximate solutions to the problems were deemed tractable for real-time applications. Recently however, active set algorithms have been identified as a means for solving control allocation problems in real-time applications. In this paper a modified active set algorithm for the solution of bound-constrained least-squares problems is presented, which has numerous advantages particularly for time-varying control allocation problems. A vehicle dynamics control system for rollover mitigation is used as an example.
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| 11. |
- Schofield, Brad, et al.
(författare)
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Optimal control allocation in vehicle dynamics control for rollover mitigation
- 2008
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Ingår i: American Control Conference, 2007, vols 1-13. - 0743-1619. - 9781424420780 ; , s. 3231-3236
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Konferensbidrag (refereegranskat)abstract
- Vehicle dynamics control systems, previously only intended for yaw stabilization, are now being extended to incorporate rollover mitigation via braking. Current systems typically use a heuristic approach to control allocation, often utilizing only a subset of the available actuators. In this article a computationally-efficient, optimization-based control allocation strategy is used to map controller commands to braking forces on all four wheels, taking into account actuator constraints. Simulations show that the strategy is capable of preventing vehicle rollover for various standard test manoeuvres.
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| 12. |
- Slätteke, Ola, et al.
(författare)
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Modeling of a Steam Heated Rotating Cylinder—A Grey-Box Approach
- 2005
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Ingår i: Proceedings / American Control Conference. - 0743-1619. - 0780390989 ; 2, s. 1449-1454
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Konferensbidrag (refereegranskat)abstract
- Drying is an important process in paper manufacturing, where steam heated cylinders are used to dry paper. Control of the moisture content is accomplished by adjusting the steam pressure in the cylinders. In previous work it has been shown that the dynamics from steam flow to steam pressure in the cylinder can be described by a linear second order black box model. This paper presents a first principles model which has a structure similar to the black box model.
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| 13. |
- Tisdale, John, et al.
(författare)
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A Multiple UAV System for Vision-Based Search and Localization
- 2008
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Ingår i: Proceedings of the '08 American Control Conference. - Linköping : IEEE. - 9781424420797 - 9781424420780 ; , s. 1985-1990
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Konferensbidrag (refereegranskat)abstract
- The contribution of this paper is an experimentally verified real-time algorithm for combined probabilistic search and track using multiple unmanned aerial vehicles (UAVs). Distributed data fusion provides a framework for multiple sensors to search for a target and accurately estimate its position. Vision based sensing is employed, using fixed downward-looking cameras. These sensors are modeled to include vehicle state uncertainty and produce an estimate update regardless of whether the target is detected in the frame or not. This allows for a single framework for searching or tracking, and requires non-linear representations of the target position probability density function (PDF) and the sensor model. While a grid-based system for Bayesian estimation was used for the flight demonstrations, the use of a particle filter solution has also been examined.Multi-aircraft flight experiments demonstrate vision-based localization of a stationary target with estimated error covariance on the order of meters. This capability for real-time distributed estimation will be a necessary component for future research in information-theoretic control.
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| 14. |
- Ugander, Johan, et al.
(författare)
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Analysis of a digital clock for molecular computing
- 2007
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Ingår i: American Control Conference, 2007, vols 1-13. - 0743-1619. - 1424409888 ; , s. 2678-2682
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Konferensbidrag (refereegranskat)abstract
- The control of synthetic genetic regulatory networks is an emerging engineering challenge. In this study, we propose a new synthetic genetic network that behaves as a digital clock, producing square waveform oscillations. We analyze two models of the network: a deterministic model based on Michaelis-Menten kinetics, as well as a stochastic model based on the Gillespie algorithm. Both models predict regions of oscillatory behavior; the deterministic model provides insight into the conditions required to produce the oscillating clock-like behavior, while the stochastic model is truer to natural dynamics. Intracellular stochasticity is seen to contribute phase noise to the oscillator, and we propose improvements for the network and discuss the conceptual foundations of these improvements.
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