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SPACING CONTROL FOR AUTOMATED VEHICLES USING DISCRETE MAGNETIC MARKERS C. Chen and R. Rajamani Abstract This paper describes the design and experimental implementation of longitudinal spacing control for automated vehicles using measurements from discrete magnetic markers embedded in the highway. Such discrete markers have previously been used as the primary sensing elements for lateral control by several research teams. Their use for longitudinal control therefore comes at no additional cost. A magnetic observer is designed to obtain a smooth and accurate estimate of inter-car spacing from the discrete markers. The magnetic observer keeps count of the number of magnets passed by the car and utilizes velocity and marker information obtained over wireless radio from the preceding car. Experimental results on using the magnetic markers to follow a lead vehicle as it performs several acceleration-deceleration maneuvers over a 8 mile highway are described. The use of the magnetic observer as a redundant estimator to diagnose malfunctions in a radar and to replace the radar in the even of a fault are also presented. |
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D. Swaroop and R. Rajamani Abstract This paper investigates the broadband control of structure-borne acoustic noise inside a rectangular enclosure. An analytical model of the structural-acoustic vibrations in the enclosure developed by a modal approach is presented. It is well known that the number of acoustic modes increase cubically with the broadband frequency range while the number of structural modes only increase linearly. A study of the model further indicates that typically only a few of the structural modes are responsible for most of the acoustic energy disturbance. A control strategy that utilizes a small number of cross-coupled accelerometers and point force actuators is suggested to control the important structural modes. The developed control strategy is completely independent of the structural-acoustic plant model and is therefore a viable approach towards ensuring successful practical implementation. We show analytically that this control strategy is guaranteed to be stable and will lead to broadband sound attenuation. |
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R. Rajamani, J.K. Hedrick and A. Howell Abstract A complete system for fault diagnostics of the longitudinal controllers in a platoon of automated vehicles is developed. The diagnostic system is designed to provide automated monitoring and fault identification of all the sensors and actuators used in the longitudinal control system, including radar sensors and inter-vehicle communication. The system uses several reduced-order nonlinear observers constructed from a longitudinal dynamic model of the vehicle. Multiple estimates of signals are obtained by designing each observer to utilize a different sensor measurement. Different combinations of all the available sensor signals and the observer estimates are then processed to construct a bank of 10 different residues. We show analytically that a fault in any of the sensors or actuators creates a unique subset of these residues to grow so as to enable exact identification of the faulty component.
Simulation results are presented to demonstrate the working of the fault diagnostic
system in the presence of various faults.
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S. Gopalasamy, C. Osorio, R. Rajamani and J.K. Hedrick Abstract |
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R. Rajamani, S.B. Choi, J.K. Hedrick, B. Law, R. Prohaska and P. Kretz Abstract This paper presents the design and experimental implementation of a longitudinal control system for the operation of automated vehicles in platoons. The control system on each vehicle is designed to have a hierarchical structure consisting of an upper level controller and a lower level controller. The upper controller determines the desired acceleration for each vehicle in the platoon so as to maintain constant accurate spacing between vehicles and ensure string stability in the platoon. The lower controller determines the throttle and/or brake commands required to track the desired acceleration. The design of the lower level controller for low speed operation is made difficult by the fact that the torque converter remains unlocked and the engine speed is not directly proportional to vehicle speed. In addition, the drive torque drops to zero for a brief time interval during each gear shift. Solutions to overcome these low speed problems are described. The design of safe intra-platoon maneuvers so as to allow any car in the platoon to exit by making a lane change are presented. Design of the co-ordination between vehicles for these maneuvers is described. The paper presents extensive experimental results from the public NAHSC demonstration of automated highways conducted in August 1997 at San Diego, California. The demonstration included an eight-car platoon operating continuously over several weeks with passenger rides being given to visitors. The maneuvers demonstrated included starting the automated vehicles from complete rest, accelerating to cruising speed, allowing any vehicle to exit from the platoon, allowing new vehicles to join the platoon and bringing the platoon to a complete stop at the end of the highway. |
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FOR LONGITUDINAL CONTROL OF AUTOMATED VEHICLES R. Rajamani, B. Law, S.B. Choi and J.K. Hedrick Abstract The practical implementation of a completely automated highway system requires an ability to safely handle a malfunction at any time in any of the software or hardware in the system. In the case of automated cars operating as a platoon, a reliable fault handling system becomes absolutely critical due to the small longitudinal spacing between the cars. This paper develops a fault management system with strategies to handle faults in any of the sensors or actuators in the cars. A fault in any one sensor is handled by continuing automated operation under a degraded mode. In the case of multiple faults or actuator faults, the faulty car is either brought to a stop or its driver is alerted after the car has been isolated. The paper also presents experimental results from the public NAHSC demonstration of automated highways conducted in August 1997 at San Diego, California. The demonstration included an eight-car platoon operating continuously over several weeks with passenger rides being given to visitors. The fault management system was able to safely handle faults and continue automated operation when component malfunctions occurred several times during the demonstration. |
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H.S. Tan, R. Rajamani and W.B. Zhang Abstract The National Automated Highway Systems Consortium (NAHSC), in partnership with the Department of Transportation, demonstrated several potential AHS technologies on I-15 in San Diego in August 1997. One of the key elements in the demonstration event was a platoon system that contained a group of fully automated automobiles travelling at close spacing. The platoon system demonstrated a number of AHS features such as lane keeping, lane changing, longitudinal space and speed regulation using proved enabling technologies. This paper describes the platoon concept, the configuration of the demonstration system, the demonstration scenarios and reports the development of the platoon demonstration system and the data collected during the demonstration. |
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R. Rajamani and Y.M. Cho Abstract This paper presents an observer design methodology for a class of nonlinear systems in which the nonlinearity is assumed to be Lipschitz. The stability of the observer is shown to be related to finding solutions to a Riccati inequality. Via a co-ordinate transformation, the Riccati inequality is reformulated as a Linear Matrix Inequality amenable to convex optimization.The result is a sytematic algorithm that finds a stable observer whenever the Riccati inequality has a feasible solution. Other attractions of the method lie in the fact that the value of the maximum allowable Lipschitz constant for stability can be calculated and that the desired convergence rate can be incorporated into the design procedure. |
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Y.M. Cho and R. Rajamani Abstract This paper addresses the issue of state estimation from limited sensor measurements in the presence of parameter uncertainty. An adaptive nonlinear observer is suggested for Lipschitz nonlinear systems and the stability of this observer is shown to be related to finding solutions to a quadratic inequality involving two variables. A coordinate transformation is used to reformulate this inequality as a linear matrix inequality. A systematic algorithm is presented which checks for feasibility of a solution to the quadratic inequality and yields an observer whenever the solution is feasible. The state estimates then are guaranteed to converge to zero asymptotically. The convergence of the parameters, however, is determined by a persistence-of-excitation type constraint. |
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R. Rajamani and J.K. Hedrick Abstract This paper makes an objective analysis of the performance obtained when using a hydraulic actuator as a variable force element in the active suspension system of an automobile. A nonlinear control method is used in an attempt to provide classical "sky-hook" damping. Experimental and simulation results obtained with the use of a standard hydraulic actuator are presented. The use of the actuator results in significant overall improvement in ride quality with an acceleration reduction of as much as 50 % compared to an ordinary passive shock ansorber at the sprung mass natural frequency. The suspension deflection performance is also improved but the tire deflection performance is somewhat worse than the passive at frequencies close to the unsprung mass natural frequency. This is because the active controller fails to track the "sky-hook" damping force accurately at high frequencies. The cause of this failure is investigated. A theoretical analysis of the actuator dynamics are made and changes in actuator parameters for this specefic application are suggested. |
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R. Rajamani and J.K. Hedrick Abstract An adaptive observer for a class of nonlinear systems is developed. Conditions for convergence of state estimates and parameters are presented. The developed theory is used for observed-based parameter identification in the active suspension system of an automobile. The observer uses measurements from two accelerometers and a low-voltage differential transducer (LVDT). It adapts on dry friction, which is usually present in significant magnitudes in hydraulic actuators of active suspensions. Experimental results on a half-car suspension test rig are presented. |
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S. Leonhardt, J. Busshardt, R. Rajamani, J.K. Hedrick and R. Isermann Abstract A method for identification of adjustable shock absorbers is presented which combines a modern QR-recursive least squares (RLS) parameter estimation algorithm (DSFI) with an artificial neural network (ANN) for classification purposes. The parameter estimation algorithm is based on a discrete-time linear model. No state variable filter (SVF) as for continuous time identification problems is required. For the ANN, a multilayer feedforward perceptron trained by backpropagation is used. The method is tested by simulation and with data drawn from shock absorber test stands. |
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R. Rajamani and J.K. Hedrick Abstract |
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