Showing papers by "Robert F. Stengel published in 1987"

An Architecture for Real-Time Rule-Based Control

Abstract: A method for control employing rule-based search is reviewed, and a Rule-Based Controller achieving economical real-time performance is described. Code optimization, in the form of LISP-to-Pascal knowledge base translation, provides real-time search execution speed and a processing environment enabling highly integrated symbolic and numeric computation. With a multiprocessor software architecture specifying rule-based protocol for control task communication, and a hardware architecture providing concurrent implementation within a multi-microprocessor system, the controller realizes a set of cooperating real-time expert systems. Based on experience gained through the design and implementation of a Rule-Based Flight Control System, the proposed approach appears applicable to a large class of complex control problems.

Failure Model Determination in a Knowledge-Based Control System

Abstract: A technique for determining the most probable failure state of a restructurable control system is presented. The approach is to build a knowledge base that contains and makes use of inference mechanisms to deduce the most likely failures given the symptoms. The analysis is first carried out in a local sense, where only probabilistic information and causality are used to generate failure models, then in a global sense, where the models are grouped and heuristics are used to prune the number of candidate models. Procedures are illustrated using failure patterns of a generic database as well as a fault scenario for a hypothetical helicopter flight control system. It is concluded that the methods are potentially capable of handling generic failures and thus are useful in truly restructable control systems.

Cooperative rule-based systems for aircraft control

Abstract: This paper examines the application of artificial intelligence theory in the flight domain of a military aircraft. Nine rule-based systems were implemented to demonstrate complex system cooperation in combat aircraft operations. The organization of tasks within each rule-based system is described, and details of knowledge-base development and implementation are given. An interactive simulation testbed was developed to provide a realistic view of intersystem cooperation and pilot-system interaction. Single-processor emulations demonstrate cooperation of parallel rule-based systems. Software tools developed to aid in fast prototyping of rule-based systems are described. Search effort metrics were used to quantify and compare light- and heavy-workload phases of a combat mission.

Nonlinear Inverse Dynamics Control Laws - A Sampled Data Approach

Abstract: A sampled-data approach for the implementation of Nonlinear Inverse Dynamics (NID) control laws in real time is presented. The control laws developed place the same number of poles as their continuous-time counterparts, take into account the system dynamics in between the sample points, and embed the computational delays associated with the inverse calculations directly into their design.

Restructurable control using proportional-integral implicit model following

Abstract: Studies of a proportional-integral implicit modelfollowing control law are presented. The research focuses on the ability of the control law to recover the performance of a failed system to its pre-failure level. Properties of the implicit model-following strategy are examined, and conditions for control reconfiguration are stated. The control law is applied to the lateral-directional model of a fighter aircraft, and control restructuring is shown for changes in control and system matrices. It is concluded that the implicit-model following scheme is a good candidate for control reconfiguration.

Unresolved issues in wind shear encounters

Abstract: Much remains to be learned about the hazards of low altitude wind shear to aviation. New research should be conducted on the nature of the atmospheric environment, on aircraft performance, and on guidance and control aids. In conducting this research, it is important to distinguish between near-term and far-term objectives, between basic and applied research, and between uses of results for aircraft design or for real-time implementation. Advances in on-board electronics can be applied to assuring that aircraft of all classes have near optimal protection against wind shear hazards.

Closed-loop digital control of an impact printer hammer.

Abstract: This paper explores closed-loop digital control of a high-speed impact printer hammer in the presence of sensor measurement noise and disturbances. Conventional control of high-speed impact printers is accomplished without feedback; hence disturbances, such as mechanical and magnetic interaction between hammers and hammer settle-out period, force long delays between hammer firings to assure proper time and velocity of impact. By computer simulation, we show the feasibility of using the solenoid actuator to control both time and velocity of impact