Levent Güvenç

Robust two degree-of-freedom vehicle steering controller design

Robust steering control based on a specific two degree-of-freedom control structure is used here for improving the yaw dynamics of a passenger car. The usage of an auxiliary-steering actuation system for imparting the corrective action of the steering controller is assumed. The design study is based on six operating conditions for vehicle speed and the coefficient of friction between the tires and the road representing the boundary of the operating domain of the vehicle. The design is carried out by finding the region in controller parameter plane where Hurwitz stability and a mixed-sensitivity frequency-domain constraint are simultaneously satisfied. A velocity-based gain scheduling type implementation is used. Moreover, the steering controller has a fading effect that leaves the low-frequency driving task to the driver, intervening only when necessary. The effectiveness of the final design is demonstrated with linear simulations and nonlinear simulations using a highly realistic model of an actual car.

Robust Yaw Stability Controller Design and Hardware-in-the-Loop Testing for a Road Vehicle

Unsymmetrical loading on a car like mu-split braking, side wind forces, or unilateral loss of tire pressure results in unexpected yaw disturbances that require yaw stabilization either by the driver or by an automatic driver-assist system. The use of two-degrees-of-freedom control architecture known as the model regulator is investigated here as a robust steering controller for such yaw stabilization tasks in a driver-assist system. The yaw stability-enhancing steering controller is designed in the parameter space to satisfy a frequency-domain mixed sensitivity constraint. To evaluate the resulting controller design, a real-time hardware-in-the-loop simulator is developed. Steering tests with and without the controller in this hardware-in-the-loop setup allow the driver to see the effect of the proposed controller to improve vehicle-handling quality. The hardware-in-the-loop simulation setup can also be used for real-time driver-in-the-loop simulation of other vehicle control systems.

Coordination of steering and individual wheel braking actuated vehicle yaw stability control

Active safety of road transport requires, among other things, the improvement of road vehicle yaw stability by active control. One approach for yaw dynamics improvement is to use differential braking, thereby creating the moment that is necessary to counteract the undesired yaw motion. An alternative approach is to command additional steering angles to create the counteracting moment. The maximum benefit, of course, can be gained through coordinated and combined use of both methods of corrective yaw motion generation in a control strategy. This problem has been approached by using a revised model regulator here as the main controller that utilizes coordinated steering and individual wheel braking actuation, with the aim of achieving better vehicle yaw stability control. Independent use of the individual means of actuation are treated first. Possible strategies for combined and coordinated use of steering and individual wheel braking action in a vehicle yaw dynamics controller are then presented. Simulation results on a nonlinear two track vehicle model are used to illustrate the effectiveness of the coordinated approach.

Heavy duty vehicle rollover detection and active roll control

This paper presents the results of a comprehensive study on heavy-duty vehicle (HDV) roll stability improvement technology. The proposed rollover threat warning system uses the real-time dynamic model-based time-to-rollover (TTR) metric as a basis for online rollover detections. Its feasibility for implementation in a HDV rollover threat detection system is demonstrated through vehicle dynamic simulation studies. The research on the development of a rollover threat detection system is further enhanced in combination with an active roll control system using active suspension mechanism to improve heavy-duty trucks’ roll stability both in the static cornering and in emergency maneuvers. It has been demonstrated that the roll stability of typical heavy-duty trucks has been largely improved by the proposed active safety monitoring and control system.

Robust two degree-of-freedom add-on controller design for automatic steering

A robust 2-DOF add-on controller design based on the disturbance observer is presented in this paper for improved performance in vehicle automatic steering. The application example is the benchmark problem on automatic steering of a city bus with large variations in mass and speed and for which the reference maneuvers and specifications are available in the literature. The analytical formulation of the compensator is presented, followed by evaluation and demonstration of the enhanced model regulation and disturbance rejection properties achieved by its use. Improved steering dynamics can be achieved using yaw rate feedback without the need for a yaw rate sensor. Noting that the steering angle rate actuator saturation forms a major limitation of performance, especially in the presence of the integrating actuator used in the city bus example, the performance enhancement due to the disturbance observer-based add-on compensator is investigated in the presence of actuator saturation. Finally, a disturbance feedforward-based add-on compensator is also presented for well-defined reference trajectories like the entering a bus stop bay maneuver, enabling preview.

An overview of robot-assisted die and mold polishing with emphasis on process modeling

Abstract A significant portion of the total manufacturing time for a die or mold is spent on polishing operations following primary machining and grinding of scallops left by primary machining. Hence, there is considerable incentive for automation of die or mold polishing operations. An overview of robot-assisted die and mold polishing is presented here in the framework of a conceptual automation structure consisting of process, control, surface measurement, and planning phases. The emphasis in this paper is on the process phase, with reciprocating stones as the polishing tools because they result in uniform surface finish. A tool-work-piece interaction model is developed for robot-assisted polishing using hard reciprocating tools by modifying a model that has been used successfully in precision grinding. This model is simplified by using experimentally determined numerical values characteristic of these polishing processes. The averaging effect of the finite contact time between the tool and the workpiece is explained, and its significance is demonstrated experimentally. The control, surface measurement, and pass planning phases of robot-assisted die and mold polishing are also described, along with a discussion of associated problems.

Laser Scanners for Driver-Assistance Systems in Intelligent Vehicles [Applications of Control]

Laser scanners find potential application in the automotive field for driver assistance and autonomous operation. Laser scanners that are commercially available are expensive compared to the cost of other commercial automotive sensors, limiting their implementation in cars at this time. The development in laser scanner technology and the anticipated reduced prices that will be available after mass production are expected to result in a growing market share in the near future.

Tire Pressure Monitoring [Applications of Control]

Proper tire inflation pressure improves fuel economy, reduces braking distance, improves handling, and increases tire life, while underinflation creates overheating and can lead to accidents. Approximately 3/4 of all automobiles operate with at least one underinflated tire. Beginning with 2006 models, all passenger cars and trucks in the United States are required to have tire-pressure monitoring systems (TPMSs). A TPMS is a driver-assist system that warns the driver when the tire pressure is below or above the prescribed limits. TPMSs are classified into two categories, namely, direct and indirect. In direct TPMSs, the pressure drop is calculated based on actual pressure measurements through sensors. In contrast, measurements such as wheel speed are used in indirect TPMSs.

Vision based lane keeping assistance control triggered by a driver inattention monitor

Inattentive and impaired drivers are a major cause of road accidents. Especially when impaired by drugs, fatigue or physical handicaps, the skill levels, driving habits, capabilities and decisions of a human driver are adversely affected. In such cases, the ability of a driver to safely operate a vehicle may be augmented considerably by well tuned and driver adaptive warning and assistance systems. Data from 105 drivers were collected in the Drive Safe project on an approximately 30 km route containing both city and highway traffic. The data was used to develop methods for determining inattentive/impaired drivers. This paper is on a lane keeping driver assistant system that is activated once such an inattentive/impaired driver who cannot perform a good task of lane keeping by himself is determined. Robust, parameter space based and velocity scheduled control design techniques carried out in the COMES toolbox are used for designing the lane keeping controller. A camera based image processing algorithm for lane detection and tracking is used. The image processing algorithm and the lane keeping assistant control system are evaluated first using offline simulations and then using more realistic, real time hardware-in-the-loop simulations. While a relatively simple linear model is used for lane keeping controller design, evaluation of the designed controller also uses the high fidelity, high order, realistic and nonlinear vehicle model in Carmaker HiL. A PC is used for processing video frames coming from an in-vehicle camera pointed towards the road ahead. Lane detection and tracking computations including fitting of composite Bezier curves to curved lanes are carried out in this PC. A dSpace microautobox is available for obtaining the lane data from the PC and the Carmaker vehicle data from the dSpace compact simulator used and calculating the required steering actions and sending them to the Carmaker vehicle model. Offline and real time simulation results demonstrate the effectiveness of the proposed lane keeping assistant in automatically following lanes.

State feedback control for adjusting the dynamic behavior of a piezoactuated bimorph atomic force microscopy probe

We adjust the transient dynamics of a piezoactuated bimorph atomic force microscopy (AFM) probe using a state feedback controller. This approach enables us to adjust the quality factor and the resonance frequency of the probe simultaneously. First, we first investigate the effect of feedback gains on dynamic response of the probe and then show that the time constant of the probe can be reduced by reducing its quality factor and/or increasing its resonance frequency to reduce the scan error in tapping mode AFM.