Formal specification methods

Recently, the Plant Input Mapping (PIM) method was proposed as a digital-redesign (or an emulation) approach in digital control system design. This method guarantees stability of a redesigned digital control system for a wide range of sampling periods. In this paper the PIM method is applied to the design of a digital model-matching flight control system. In the model-matching control system design a plant must have no unstable zeros. However, unstable zeros appear for small sampling periods in a step invariance model of a continuous-time (CT) plant with the relative degree greater than two, even if the CT plant has no unstable zeros. Hence, in such a case, the direct-digital approach cannot be applied to the design of a digital model-matching control system. By contrast, the digital-redesign approach such as the Tustin's method or the PIM method is free from the problem. Simulation results for an unstable VTOL aircraft show that the proposed method gives better performance than the conventional design methods.

The availability of digital MSI and LSI has made digital flight control systems more cost effective than analog systems for all but the simplest systems. The organization of a digital flight control system is concerned not only with implementation of the control laws and associated logic but also with the management of the data used in these computations and the organization of the computation. The configuration taken by a digital flight control system is dominated by the integrity and data handling requirements. This paper considers the impact of these factors on the design and operation of digital flight control systems with particular emphasis on the use of fiber optics for transmission of data between lanes.

A digital flight control system (DFCS) for a highly maneuverable fighter aircraft is described and evaluated in this paper. The aircraft and DFCS exhibit uniform handling qualities over the entire velocity-angle of attack-roll rate regime encountered in air combat maneuvering (ACM). This is verified by the use of a nonlinear six-degree-of-freedom aircraft simulation and an ACM pilot model. Comparison of the tracking accuracy of the DFCS-aircraft to that of a conventionally controlled aircraft indicates that the DFCS provides better tracking and reduces the likelihood of control-induced departure.

It is demonstrated that reconfigurable digital multiple model-following flight control systems incorporating fast-sampling error-actuated digital PID (proportional plus integral plus derivative) controllers can be easily designed using directly measurable input/output data. Thus, for example, it is shown in the case of the F-16 aircraft that desired flying qualities with respect to both pitch-rate and angle-of-attack response characteristics can be simultaneously achieved in the absence of sensor failures. In addition, in the case of failure of the angle-of-attack sensor, it is shown that desired flying qualities with respect to pitch-rate response characteristics and satisfactory flying qualities with respect to angle-of-attack response characteristics can still be achieved by reconfiguring the digital controller. >

Using the waveforms from a digital electronic system, an offline analysis technique on pulse shape discrimination (PSD) has been developed to improve the neutron-gamma separation in a bar-shaped NE-213 scintillator that couples to a photomultiplier tube (PMT) at each end. The new improved method, called the “valued-assigned PSD” (VPSD), assigns a normalized fitting residual to every waveform as the PSD value. This procedure then facilitates the incorporation of longitudinal position dependence of the scintillator, which further enhances the PSD capability of the detector system. In this article, we use radiation emitted from an AmBe neutron source to demonstrate that the resulting neutron-gamma identification has been much improved when compared to the traditional technique that uses the geometric mean (GM) of light outputs from both PMTs. The new method has also been modified and applied to a recent experiment at the National Superconducting Cyclotron Laboratory (NSCL) that uses an analog electronic system.

The insertion of communication networks in closed-loop of digital control systems makes the system synthesis and analysis complex. In this paper, we consider the combination of classical reliability, risk and safety evaluation with typical control system through digital networked control systems. The main purpose is to study the influence of transmission delays and packet dropouts on the reliability of digital networked control systems by using a modified statistical method-Monte Carlo simulation. The behaviors of two types of fault are modelled by different statistical distribution. The control strategies we apply for digital control systems are Proportion Integration Differentiation control strategies, generated by Genetic Algorithm. In terms of a realistic system model, we evaluate and compare the influences on the reliability of digital networked control systems with different control strategies from quantitative aspect. Numerical examples are presented to illustrate the effectiveness and correctness of the approach.

In the face of shrinking defense budgets, survival of the United States rotorcraft industry is becoming increasingly dependent on increased sales in a highly competitive civil helicopter market. As a result, only the most competitive rotorcraft manufacturers are likely to survive. A key ingredient in improving our competitive position is the ability to produce more versatile, high performance, high quality, and low cost of ownership helicopters. Fiber optic technology offers a path of achieving these objectives. Also, adopting common components and architectures for different helicopter models (while maintaining each models' uniqueness) will further decrease design and production costs. Funds saved (or generated) by exploiting this commonality can be applied to R&D used to further improve the product. In this paper, we define a fiber optics based avionics architecture which provides the pilot a fly-by-light / digital flight control system which can be implemented in both civilian and military helicopters. We then discuss the advantages of such an architecture.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

This thesis outlines the effort in developing an integrated simulation framework for assessing the stability and control characteristics of an Unmanned Aerial Vehicle (UAV). The objectives are to understand flight instabilities experienced by the UAV and to propose solutions for the flight stability and control problems via an integrated modeling framework. The basic core of the framework involves the incorporation and integration of the UAV aerodynamic characteristics, flight stability derivatives and digital flight control system, into a six degree-of-freedom flight simulation model, the outputs of which are visualized graphically. To support the development of the simulation model, a comprehensive aerodynamic database for the UAV is required. Empirical aerodynamic estimation software such as USAF Digital Datcom and computational flow simulation software suites such as FLUENT and Solidworks Flo Works have been used to estimate the aerodynamic force and moments as well as stability and control derivatives of the UAV. By combining these estimates with wind tunnel data, a comprehensive aerodynamic characteristics model is constructed for augmenting the flight dynamics model of the UAV. Initially, a de-coupled longitudinal and lateral stability analysis based on the small disturbance theory has been developed to understand the stability modes of the UAV. A coupled longitudinal and lateral stability analysis was then developed to study the effects of the aerodynamic coupling caused by the single propulsion system to the stability and control characteristics. The model is created within the programmable software environments of d at lab^, ~imulink' and Aerospace s lock set@ which are used to construct the six-degree-of-freedom model for the dynamical motion of the UAV. The inputs to the model include the aerodynamic information based on the aerodynamic characteristics, stability derivatives, engine characteristics, flight variables and atmospheric disturbances. The outputs from this model are the responses of the flight variables depicting lateral, longitudinal and directional stability characteristics of the flight vehicle. Virtual Reality based systems such as the Flight Gear software has been used as a graphical interface for displaying the UAV trajectory, the orientation of the vehicle and the stability and control characteristics of the UAV based on the outputs from the model.

Over the past forty years, the number of fighter aircraft controlled flight into terrain (CFIT) accidents per flight hour has not improved despite the addition of multiple manual warning systems. The Air Force Research Laboratory (AFRL) has undertaken a program to develop an automatic system that will take over when the pilot can no longer recover the aircraft, perform an automatic recovery and quickly return control to the pilot. It is called the Automatic Ground Collision Avoidance System or Auto GCAS. This system has been successfully demonstrated on a Block 50 F-16 with a digital flight control system as shown in Figure 1 and is transitioning to operational Block 40/50 F-16s. Until now the technology could not be applied to early model F-16s with analog flight control systems because of the lack of a high authority autopilot needed for the automatic recovery and the absence of a way for the flight control system to ascertain system integrity to insure safe operation. AFRL is now focused on finding a technical solution that will allow the implementation of Auto GCAS on aircraft with analog flight control systems. The effort is called Analog Auto GCAS. The Analog Auto GCAS project has developed an innovative method of adding redundant digital processor modules to the existing analog flight control computers of pre-block 40 F-16's. This will not only allow Auto GCAS to be added to F-16s with analog flight control computer but demonstrates a technical path forward for incorporating Auto GCAS onto other older aircraft with analog flight control computers. This paper provides a description of Auto GCAS, discusses the changes needed to implement Auto GCAS on an analog aircraft, and covers the results to date as well as the future path forward for implementing Auto GCAS on the pre-block 40 F-16 fleet.

The solution for the non-determinism of real-time expert systems is found in the state-based approach. Timing verification can be performed off-line before the expert system is taken in use. This approach has been verified on a digital (fly-by-wire) flight control system of a jet aircraft.

Dynamical model of electrocardiogram and cardiovascular system are important in medicine because they can be used as approximation of the real patient. A synthetic electrocardiogram and cardiovascular signals can be generated with different sampling frequencies and different noise levels in order to establish the performance of used technique. The model implementation is based on digital and analog electronic systems which enable simple modifications.

Dynamical model of electrocardiogram, cardiovascular and seismocardiographic system are important in medicine because they can be used as an approximation of the real patient. Synthetic cardio-signals can be generated with different shapes, different sampling frequencies, and different noise levels to establish the performance of the used technique. In this paper, the cardio-signals were modeled, and system for signals generation, based on digital and analog electronic systems was constructed. The simulation results and also examples of cardiographic signals generated by the electronic system are presented.

Selected experiences of the author and other engineers that have affected the progress in reliability are presented. The experiences are primarily taken from the development, production, and field usage of analog and digital electronic systems. The experiences are associated with the following factors that have contributed to reliability progress: the design process, the development and application of piece parts, part, unit, and system testing, contracting for reliability, and the attitude of top management. >

<p>A DC-DC converter is used to convert from one DC voltage level to another DC voltage level. The output voltage may be increased or decreased when compare to the input voltage based on the circuit topology. DC – DC converters are mainly used as a regulated and isolated power supplies in many applications. Regulated dc power supplies are needed for most analog and digital electronic systems. Most power supplies are designed to meet some or all of the following requirements:</p> <p><strong>Regulated output: </strong>The output voltage must be kept constant with respect to the change in output loading.</p> <p><strong>Isolation: </strong>The output may be required to be electrically isolated from the input.</p> <p>In addition to these requirements, common goals are to reduce power supply size and weight and improve their efficiency. A few applications of DC-DC converters are where 5V DC on a personal computer motherboard must be stepped down to 3V, 2V or less for one of the latest CPU chips; where 1.5V from a single cell must be stepped up to 5V or more, to operate electronic circuitry. The main focus in this paper is to generate dc voltage from a one level to other level with minimum loss. The need for such converters has risen due to the fact that transformers are unable to function on dc.</p>

In airline service the reliability of a system is more than the confirmed failures for the system; it is the total removal experience of the system. Thus, the reliability of a system lies not only in the piece part failure rates, but also in the capability to verify and isolate failures. The application of digital technology brings several significant reliability improvements to automatic flight control systems (AFCS) when compared to contemporary analog systems. These advantages are demonstrated by the experience of the digital air data computer (DADC) of the DC-10 and the digital AFCS of the JA-37 Viggen. Experience with this equipment is reviewed, and the results are interpreted in terms of projections for airline DAFCS reliability. The digital system built-in test implemented by a stored program and the central processor gives a system integrity and dispatch reliability unequaled by analog systems. This high-integrity self-test reduces removal rates by giving line personnel a trustworthy tool and more complete automatic test processes for verifying maintenance actions. Digital circuit technology is directly suitable to largescale integrated circuits (LSIC) which reduce piece part counts and improve LRU reliability. Digital circuits are less subject to drift and the attendant difficulty to detect failures. These factors, coupled with the inherent high-integrity self-test, provide the basis for a significant improvement in reliability by the use of a digital automatic flight control system.