Showing papers by "Swaroop Darbha published in 2006"

Information flow and its relation to stability of the motion of vehicles in a rigid formation

Abstract: In this note, we consider the effect of information flow on the propagation of errors in spacing in a collection of vehicles trying to maintain a rigid formation during translational maneuvers. The motion of each vehicle is described using a linear time-invariant (LTI) system. We consider undirected and connected information flow graphs, and assume that each vehicle can communicate with a maximum of q vehicles, where q may vary with the size n of the collection. We consider translational maneuver of a reference vehicle, where its steady state velocity is different from its initial velocity. In the absence of any disturbing forces acting on the vehicles during the maneuver, it is desired that the collection be controlled in such a way that its motion asymptotically resembles that of a rigid body. In the presence of bounded disturbing forces acting on the vehicles, it is desired that the maximum deviation of the motion of the collection from that of a rigid body be bounded and be independent of the size of the collection. We consider a decentralized feedback control scheme, where the controller of each vehicle takes into account the aggregate errors in position and velocity from the vehicles with which it is in direct communication. We assume that all vehicles start at their respective desired positions and velocities. Since the displacement of every vehicle at the end of the maneuver of the reference vehicle must be the same, we show that the loop transfer function must have at least two poles at the origin. We then show that if the loop transfer function has three or more poles at the origin, then the motion of the collection is unstable, that is, its deviation from the rigid body motion is arbitrarily large, if the size of the formation is sufficiently large. If l is the number of poles of the transfer function relating the position of a vehicle with its control input, we show that if (q(n)/n)rarr0 as nrarrinfin, then there is a low frequency sinusoidal disturbance of at most unit amplitude acting on each vehicle such that the maximum errors in spacing response increase at least as Omega(((radicn/q(n))l+1)).A function p(n) is Omega(q(n)) if there exists a nonzero constant c>0 and a N* such that |p(n)|gesc|q(n)| for all n>N* . A consequence of the results presented in this note is that the maximum errors in spacing and velocity of any vehicle can be made insensitive to the size of the collection only if there is at least one vehicle in the collection that communicates with at least Omega(n) other vehicles in the collection

A Diagnostic System for Air Brakes in Commercial Vehicles

Abstract: The safe operation of vehicles on roads depends, among other things, on a properly functioning brake system. Air brake systems are widely used in commercial vehicles such as trucks, tractor-trailers, and buses. In these brake systems, compressed air is used as the energy transmitting medium to actuate the foundation brakes mounted on the axles. In this paper, a model-based diagnostic system for air brakes is presented. This diagnostic system is based on a nonlinear model for predicting the pressure transients in the brake chamber that correlates the brake chamber pressure to the treadle valve (brake application valve) plunger displacement and the pressure of the air supplied to the brake system. Leaks and "out-of-adjustment" of push rods are two prominent defects that affect the performance of the air brake system. Diagnostic schemes that will monitor the brake system for these defects will be presented and corroborated with experimental data obtained from the brake testing facility

Technical Notes and Correspondence Information Flow and Its Relation to Stability of the Motion of Vehicles in a Rigid Formation

Abstract: In this note, we consider the effect of information flow on the propagation of errors in spacing in a collection of vehicles trying to main- tain a rigid formation during translational maneuvers. The motion of each vehicle is described using a linear time-invariant (LTI) system. We consider undirected and connected information flow graphs, and assume that each vehicle can communicate with a maximum of vehicles, where may vary with the size of the collection. We consider translational maneuver of a reference vehicle, where its steady state velocity is different from its ini- tial velocity. In the absence of any disturbing forces acting on the vehicles during the maneuver, it is desired that the collection be controlled in such a way that its motion asymptotically resembles that of a rigid body. In the presence of bounded disturbing forces acting on the vehicles, it is desired that the maximum deviation of the motion of the collection from that of a rigid body be bounded and be independent of the size of the collection. We consider a decentralized feedback control scheme, where the controller of each vehicle takes into account the aggregate errors in position and velocity from the vehicles with which it is in direct communication. We assume that all vehicles start at their respective desired positions and velocities. Since the displacement of every vehicle at the end of the maneuver of the reference vehicle must be the same, we show that the loop transfer function must have at least two poles at the origin. We then show that if the loop transfer func- tion has three or more poles at the origin, then the motion of the collection is unstable, that is, its deviation from the rigid body motion is arbitrarily large, if the size of the formation is sufficiently large. If is the number of poles of the transfer function relating the position of a vehicle with its con- trol input, we show that if

An extremum seeking algorithm for determining the set point temperature for condensed water in a cooling tower

Abstract: Energy consumed by buildings accounts for approximately 20 % of the total energy consumption in the United States of America (USA). A significant number of commercial buildings in the USA are cooled using a bank of chillers which reject the thermal loads on the buildings to the atmosphere through cooling towers. About two-thirds of the total power consumption in such buildings is due to the power consumption of the compressors in the chillers and the fans in the cooling tower. The total steady state power consumed by the compressors and the fans seems to be a convex function of the chilled water temperature of the cooling tower at most operating thermal loads. In this paper, we propose an extremum seeking algorithm for determining the set point temperature for the tower given the load on a building.

Pressure control scheme for air brakes in commercial vehicles

Abstract: Air brake systems are widely used in commercial vehicles such as trucks, tractor-trailers and buses. In these brake systems, compressed air is used as the energy transmitting medium to actuate the foundation brakes mounted on the axles. Here, we present a control scheme for regulating the pressure of air in a brake chamber of these brake systems. This scheme is based on a non-linear model for predicting the pressure transients in the brake chamber that correlates the brake chamber pressure to the treadle valve (brake application valve) plunger displacement and the pressure of the air supplied to the brake system. The control scheme regulates the pressure in the brake chamber by modulating the displacement of the treadle valve plunger. We have implemented this control scheme on the brake testing facility at Texas A&M University and present results for a variety of test runs in which the controller tracks realistic desired pressure trajectories. (A)

Combinatorial Motion Planning of Multiple Vehicle Systems

Abstract: In this paper, we are concerned with the development of approximation algorithms for the combinatorial motion planning of a collection of m vehicles. Specifically, we consider the following multiple depot, generalized multiple traveling salesmen problem (GMTSP). We are given m vehicles that start at possibly different locations and n targets that must be visited. The problem is to choose at most p les m vehicles so that (1) each target is visited by exactly one of the chosen vehicles and (2) the cost of the tours of the chosen vehicles is a minimum among all possible choices and their corresponding tours of vehicles. The criteria for the cost of tours considered is the total distance (total cost of edges) traveled by the entire collection. This problem is a generalization of the symmetric traveling salesman problem (TSP) and is NP-hard. We show that there is a 2-approx algorithm for this problem. We also provide a branch and bound procedure for this problem

Optimal Sequential Inspection

Abstract: In this paper, we consider a problem of sequential resource allocation. Such a problem arises in a simplified intelligence, surveillance and reconnaissance (ISR) scenario where a micro air vehicle (MAV) is tasked with search and classification in an environment with false targets. The MAV visits the objects of interest in a specified sequence for classification. A human operator aids classification of objects based on the images sent to him from the MAV and the operator may request that the object be revisited if he requires further information. Such a request is made at most once by the operator for each object. The information gained by the operator when any object is revisited is the same. There is a random delay in communicating his findings to the MAV and the probability density function of the delay is assumed known. The MAV has a finite fuel reserve and upon receiving the feedback from the operator, it must decide whether to revisit the object or whether to continue to the next object in the sequence. In every revisit, fuel is expended from the reserve and equals twice the delay plus a fixed fuel cost. The objective is to maximize the number of revisits so as to maximize the information gained about the objects, which enables them to be classified as targets or false targets. Using stochastic dynamic programming, we show that there is a threshold delay for each object and it is optimal to revisit the object if the operator delay is smaller than the threshold and not to revisit otherwise

Developing a Diagnostic System for Air Brakes Used in Commercial Vehicles

Abstract: The safe operation of vehicles on roads depends amongst other things, on a properly functioning brake system. Air brake systems are widely used in commercial vehicles such as trucks, tractor-trailers and buses. In these brake systems, compressed air is used as the energy transmitting medium to actuate the foundation brakes mounted on the axles. In this report, a model-based diagnostic system for air brakes is presented. This diagnostic system is based on a nonlinear model for predicting the pressure transients in the brake chamber that correlates the brake chamber pressure to the treadle valve (brake application valve) plunger displacement and the pressure of the air supplied to the brake system. Leaks and “out-of-adjustment” of push rods are two prominent defects that affect the performance of the air brake system. Diagnostic schemes that will monitor the brake system for these two defects are presented. These schemes are corroborated with experimental data obtained from the brake testing facility constructed at Texas A&M University.