Showing papers on "Vehicle dynamics published in 1991"

Dynamic motion planning of autonomous vehicles

Abstract: A method for planning the motions of autonomous vehicles moving on general terrains is presented that obtains the geometric path and vehicle speeds that minimize motion time considering vehicle dynamics, terrain topography, obstacles, and surface mobility. The terrain is represented by a smooth cubic B patch, and the geometric path consists of a B spline curve mapped to the surface. The time-optimal motions are computed by first obtaining the best obstacle-free path from all paths represented by a uniform grid. This path is further optimized using a local optimization procedure, using the optimal motion time along the path as the cost function and the control points of a B spline as the optimizing parameters. Examples are presented that demonstrate the method for a simple dynamic model of a vehicle moving on mountainous terrain. >

Path planning for space manipulators to minimize spacecraft attitude disturbances

Abstract: A technique, called the enhanced disturbance map, for planning space manipulator motions that will result in relatively low spacecraft disturbance is presented. Although a spacecraft's attitude control reaction jet can compensate for the dynamic disturbances imposed on the spacecraft by the manipulator's motions, reaction jet fuel is a limited resource. Excessive disturbances would limit the life of a system. The enhanced disturbance map can aid in understanding this complex problem and in the development of algorithms to reduce disturbances, including ones that use manipulator redundancy to eliminate the disturbances. >

Large motion control of mobile manipulators including vehicle suspension characteristics

Abstract: Conventional fixed-base controllers are shown not to perform well on mobile manipulators due to the dynamic interactions between a manipulator and its vehicle. An extended Jacobian transpose control algorithm is developed to improve the performance of such manipulator systems. It is shown to perform well in the presence of modeling errors and the practical limitations imposed by the sensory information available for control in highly unstructured field environments. >

Longitudinal Control of a Platoon of Vehicles with no Communication of Lead Vehicle Information

Abstract: Evaluates the performance of longitudinal control laws with no communication of lead vehicle information. After using exact linearization methods, the authors propose a linear control law for each vehicle which uses only the information from the preceding vehicle in the platoon.

Differential-algebraic Equations in Vehicle System Dynamics

Abstract: The multibody system approach provides an efficient tool for the analysis of mechanical systems arising in vehicle dynamics. The computer-aided formalisms generate the equations of motion as a system of differential-algebraic equations (DAEs). A short review of their solution theory and of the implications for the numerical integration is presented. The available integr. methods are describ. and a method for the computation of consistent initial values is introduced. The investigation of a wheelset moving on a rail track demonstrates the advantages of the DAE-formulation in railway vehicle dynamics. Thus an alternative to the usual state space form approach is provided for this class of problems. The computation of static equilibrium solutions of the wheelset yields consistent initial values and allows an analysis of wheel and rail design. Finally, a numerical integration determines the limit cycle behaviour of the wheelset in accordance with measurement on a hardware model.

Design and Modeling Issues for Integrated Airframe/Propulsion Control of Hypersonic Flight Vehicles

Abstract: TraditionaLly the systems integration process in aerospace controls is to make individually desig subsystems work together, that is, to ensure functional compatibility and minimize adverse interactions. With large hypersonic vehicles the aerodynamic, propulsion, structural, and controls features are intrinsically highly interactive dynamically over a wide range of frequencies. Consequently, systems integration activities must be enormously expanded in scope and degree to assure a successful result. In essence the new goal of dynamic systems integration is to carry out concurrent multidisciplinary design of the highly interactive systems to maximize overall aircraft performance in its broadest terms. Cooperative consolidation and interaction of functions and subsystems to achieve performance levels and design synergism greater than would be possible with independent, individual subsystem designs are the natural consequences desired.

Vehicle Traction Control: Variable-Structure Control Approach

Abstract: A longitudinal one-wheel vehicle model is described for both anti-lock braking and anti-span acceleration. Based on this vehicle model sufficient conditions for applying sliding-mode control to a vehicle traction are derived via Lyapunov Stability Theory. With the understanding of these sufficient conditions, control laws are designed to control vehicle traction. Both the sufficient conditions and the control laws are verified using computer simulations.

Active toe adjustment apparatus

Abstract: The advantage of the theoretically correct Ackerman steering of land vehicles is well documented in the literature. Steering forces, vehicle handling, and tire wear are greatly improved by having correct toe angles of all steerable wheels. Adjustements in the suspension system and steering apparatus at the factory only provide first-order corrections to toe angles. A process for actively adjusting toe angles during operation of the vehicle is disclosed in this invention. Vehicle dynamics measuring devices to sense vehicle motion or position steering devices to measure toe angles are used in this process. Secondary toe angle corrections can be actively provided to account for inherent toe angle changes during maneuvers of the vehicle. An aftermarket apparatus for actively adjusting the toe angle is an embodiment of this invention. One such device includes a mechanical screw actuator apparatus, a microstepping motor with optical encoder, computer with control strategy chip and a toe angle sensing device or an onboard dynamics computer. This apparatus can be used on all land vehicles and is especially useful for modifying existing truck and bus steering systems.

Lagrangian formulation of underwater vehicles' dynamics

Abstract: Key properties of the equations of motion for underwater vehicles are derived both theoretically and experimentally. The equations of motion for underwater vehicles are derived in a Lagrangian framework. The Lagrangian approach has several distinctive advantages compared to the Newtonian approach. This is especially true in the context of underwater vehicles. The derivation of the hydrodynamic added inertia and the vehicle's rigid body equations of motion can be done in a common framework. The added inertia is given a clear and physical interpretation when the vehicle-ambient water system is considered from an energy point of view instead of a force-moment approach. >

Modeling methods for underwater robotic vehicle dynamics

Abstract: Models of the open-loop dynamics for prototype Remotely Operated Underwater Vehicles (ROVs) and Autonomous Underwater Vehicles (AUVs) are required for performance prediction and autopilot design. This article describes techniques which can be used to derive these models. The methods may be conveniently grouped into predictive techniques i.e., those which require only vehicle design data and which predict dynamics before the prototype is built and testing techniques i.e., methods which measure open-loop dynamics from the trials performance of a prototype ROV. The relative benefits and drawbacks of the various methods are examined.

Linearized Flexible Multibody Dynamics Including Geometric Stiffening Effects

Abstract: In multibody system simulation for vehicle dynamics applications, it is often sufficient to consider a set of system equations in which the kinematics are linearized. On the other hand, care must be taken to model the flexibility of the system bodies correctly and to be able to introduce the highly nonlinear force laws appearing in multibody vehicle models into the simulation. A formalism meeting these objectives is presented here. Special care has been taken to incorporate geometric stiffening terms that result from nominal loads on the system. This formalism is the core of the vehicle dynamic simulation code MEDYNA.

Control of an underwater vehicle using H/sub infinity / synthesis

Abstract: The authors present the results of a design exercise in which recent developments in H/sub infinity / synthesis theory were applied to the design of a controller for an autonomous underwater vehicle (AUV). The problem statement requires the design of a position and attitude control system for the vehicle to achieve precise trajectory following. The major steps in the synthesis procedure were as follows. A detailed nonlinear dynamic model of the AUV was derived, and an operating point for nominal design was selected. After linearization around the nominal operating point, a multivariable controller was designed using standard techniques of H/sub infinity / theory. The performance of the controller was evaluated in simulations with a full nonlinear model of the vehicle. >

Steering and Stability of the Bogie: Vehicle Dynamics and Suspension Design:

Abstract: Recent progress in the development of railway vehicle bogies and other forms of running gear is reviewed, with particular reference to the conflict between stability and curving. It is shown how th...

Control of vehicle with power wheeled steering using feedforward dynamics compensation

Abstract: The design of an efficient vehicle control method for an autonomous vehicle using the power wheeled steering (PWS) method by two driving wheels is described First, the vehicle dynamics using the PWS method is analysed Next, an efficient controller for the PWS method is proposed This controller includes a feedforward compensator which has the inverse dynamics of the vehicle and controls both sides of the wheel angular velocities Additionally, in order to confirm the effectiveness of the proposed control method, numerical simulation and experimental results are shown >

Physical modeling as a help for planning the motions of a land vehicle

Abstract: Deals with the problem of planning the motions of a complex land vehicle moving in a natural environment. The contribution presented is a motion generator which predicts the dynamic behaviour of the vehicle when executing a given nominal motion plan. This plan is expressed in terms of a channel to follow and of a set of intermediate subgoals to reach. Solving this motion generation problem requires to explicitly reason about the geometric and the physical aspects of the movements that the vehicle has to execute. In the authors' approach, this is done using two basic constructions derived from the concept of physical model: the 'generalized obstacles' are used for physically guiding the movements of the vehicle using an explicit model of the vehicle/terrain interactions, and the 'physical targets' are used to map the strategic information onto the physical representation of the world. >

Reactive motion planning in a dynamic world

Abstract: Deals with the problem of planning and controlling the motion of a car like vehicle moving in a dynamic and roadway like environment. A motion controller is presented which executes in a reactive way a given nominal motion plan. Such a plan is made up of a smooth trajectory C and of time constraints of the type 'reach location l at time t/sub l/'. Data concerning the actual environment of the vehicle considered are assumed to be obtained through perception. In order to get the required reactivity, the authors have developed a motion controller with two main components: the pilot which analyses the current situation and adapts the nominal plan accordingly, and the executor which generates the required motion commands. The pilot operates at a symbolic level using a set of behavioural rules. The executor makes use of a potential field approach to generate the motion commands. >

Detection and Isolation of Plant Failures in Dynamic Systems

Abstract: This paper presents a method of distinguishign between actuator failures and changes in the system dynamics. The method is based upon exploitation of the system input. In particular, a class of control laws are derived that when used with conventional estimators/observers, enable isolation of actuator calibration changes from shifts in the plant dynamics. It is assumed that any calibration change or shift in the plant dynamics is detected by some form of detection scheme (e.g., a Beard-Jones Detection Filter). This paper demonstrates the subsequent procedure for distinguishing between these two events. Theorems are presented for the existence and characterization of these special inputs, referred to as designed inputs. Other issues, such as operator freedom and robustness to system noise and errors, are analyzed and discussed. To illustrate this method, an example is presented involving failures in an automobile having 4-wheel electronically controlled steering. For this example, a designed input is constructed to isolate rear wheel actuator failures from changes in the tire cornering force parameter.

A goal seeking and obstacle avoiding algorithm for autonomous mobile robots

Abstract: The authors present an algorithm designed to provide a robot-vehicle with sufficient 'intelligence' to be able to optimize its behavior in the light of information while carrying out the task of moving from any position and orientation to any other position and orientation. The kinematic and dynamic constraints of a nonholonomic vehicle are included explicitly. It is thus possible to finesse issues concerned with producing planned paths that cannot be achieved in practice by a real vehicle. Some of the maneuvers that this algorithm can support are shown. The algorithm has been designed to allow the inclusion of unmapped obstacles and thus has the potential of being extended to situations where there are multiple moving vehicles. >

Dynamic Vehicle Control (Problem)

Abstract: The problem presented in this paper is the design of a system to control a flexible space launch vehicle which travels from liftoff at the Earth's surface through the atmosphere to low Earth orbit. The model given in the paper is one that has been used for many years in the aerospace industry to evaluate controller design and performance. The model is linear with variable parameters and is subject to a completely unknown and unmeasurable disturbance. In addition to stating the problem, brief details are provided of a design concept that has proved to work well, within the bounds of classical control theory.

A Brake Control Algorithm for Emergency Stops (Which may Involve Steering) of Tow-Vehicle/Trailer Combinations

Abstract: This paper presents a control algorithm for controlling the brakes of a tow-vehicle/trailer combination during emergency braking. The control algorithm determines wheel slip levels for the wheels of the tow-vehicle and trailer. These wheel slip levels are chosen to provide the maximum braking force while preserving the stability of the tow-vehicle and trailer and providing the necessary directional control. The algorithm is able to compensate for uneven traction among the wheels and to increase the cornering capability of the tires when the driver attempts to steer. This paper outlines the structure of the control algorithm and presents simulation results to show its effectiveness. The simulation results study a situation where the driver of a mid-size passenger car towing a utility trailer attempts to avoid an obstacle while braking on a surface with checkered traction properties.

Stochastic optimal control of vehicle suspension with preview on an irregular surface

Abstract: An active suspension system with preview under stochastic optimal control of a vehicle travelling on an irregular surface is discussed. The vehicle is modelled as a mass-damper-spring system with two degrees of freedom and the dynamic behaviour of the irregular surface is described by a first-order system subject to a gaussian white random input. The acceleration of the vehicle and the irregular quantity of the surface ahead of the vehicle are in a noisy environment measured using sensors mounted on the vehicle. The state variables of the vehicle dynamics and the dynamic behaviour of the irregular surface are estimated using the Kalman filter. The stochastic optimal control is determined by minimizing the given performance index, and is composed of the weighted linear combination of the estimated state variables of the vehicle dynamics and the dynamic behaviour of the irregular surface. A numerical example shows the effectiveness of the proposed active suspension system with preview.

Laboratory Tire Wear Simulation Derived from Computer Modeling of Suspension Dynamics

Abstract: A method for determining the effect of suspension dynamics on tire wear has been developed. Typical city cycle maneuvers are defined by instrumented vehicle testing and data in the form of forward velocities and steer angles are used as an input to an ADAMS computer model of the vehicle. A simulation of the maneuvers generates a tire's operating environment in the form of normal load, slip, and camber variations, which contain all the subtle effects of the vehicle's suspension, steering, and handling characteristics. A cyclic repetition of the tire's operating environment is constructed and used to control an MTS Flat‐Trac machine. In this way, accelerated tire wear can be generated in the laboratory which is directly related to the design features of the vehicle's suspension and steering systems.