Design of noise and period-time robust high-order repetitive control, with application to optical storage

Repetitive control is useful if periodic disturbances or setpoints act on a control system. Perfect (asymptotic) disturbance rejection is achieved if the period time is exactly known. The improved disturbance rejection at the periodic frequency and its harmonics is achieved at the expense of a degraded system sensitivity at intermediate frequencies. A convex optimization problem is defined for the design of high-order repetitive controllers, where a trade-off can be made between robustness for changes in the period time and for reduction of the error spectrum in-between the harmonic frequencies. The high-order repetitive control algorithms are successfully applied in experiments with the tracking control of a CD-player system.     

Uncertainty propagation in puff-based dispersion models using polynomial chaos

Atmospheric dispersion is a complex nonlinear physical process with numerous uncertainties in model parameters, inputs, source parameters, initial and boundary conditions. Accurate propagation of these uncertainties through the dispersion models is crucial for a reliable prediction of the probability distribution of the states and assessment of risk. A simple three-dimensional Gaussian puff-based dispersion model is used as a test case to study the effect of uncertainties in the model parameters and initial conditions on the output concentration. A polynomial chaos based approach is used to numerically investigate the evolution of the model output uncertainties due to initial condition and parametric uncertainties. The polynomial chaos solution is found to be an accurate approximation to ground truth, established by Monte Carlo simulation, while offering an efficient computational approach for large nonlinear systems with a relatively small number of uncertainties.     

The effects of adverse condition warning system characteristics on driver performance: an investigation of alarm signal type and threshold level

This study addresses the issues concerning the design of adverse condition warning systems (ACWS). ACWS are designed to sense adverse road and weather conditions as well as system states that can negatively impact driving performance leading to skids or accidents, and alert drivers to these conditions. In this case, an ACWS was designed to sense when a car was likely to skid. A virtual-driving environment was used to test two levels of alarm sensitivity (low and high) and two types of auditory alarm signal (Binary ON/OFF and Graded) along with a no-alarm control group. Dependent measures reflected driver performance, response to the alarm signal and trust in the alerting system. Results indicated that participants had fewer skids in the low sensitivity and graded alarm signal condition compared to some other alerting system configurations. Participants in the graded alarm signal condition also had a greater degree of lateral control over the vehicle. Additionally, trust was found to be lower for the high vs. low sensitivity alarm condition, indicating a reduction in trust when the alerting system activated more often, perhaps because participants did not feel the system was accurately reflecting a dangerous condition. This simulator-based research emphasizes the fact that while ACWS may provide an advantage in terms of vehicle control, characteristics of both the alerting signal and system configuration should be considered.     

Effects of joint flexibility on the motion of a flexible-arm robot

Once flexibility is introduced into the arm of the robot severe problems in the accuracy and stability are likely to occur which make control a critical issue. These problems could amplify drastically once the joint flexibility is also added to the system. A more successful control algorithm can be developed if the nonhnear dynamics associated with the flexible joint-arm is properly accounted for

In this paper we study the behaviour of a three degree of freedom flexible joint-arm. Robot with quadratic and cubic nonlinearities. The symibolic manipulator language MAPLE is used to develop a simplified mathematical model of the system and to perform the analytical study. The two-variable expansion perturbation method is used to show the existence of various nonlinear resonances. If the system natural frequencies are defined as ω₁,ω₂ and ω_$inf;2 internal resonance occurs when omega;_{2$einf; = 2ω 1}ω₃/(ω² ₁ + ω² ₃)½. Moreover, once subjected to harmonic forcing with frequency Ω a nonlinear forced resonance occurs at Ω ≈ ω₂ the system undergoes a jump phenomenon

Numerical simulation concurs with the analytical results for small motions. However, at higher amplitudes of forcing, numerical studies indicate the existence of a chaotic solution in the resonance region. The route to chaos contains subharmonic bifurcations     

Equilibrium stability in decentralized design systems

The focus of this paper is on complex systems, and it presents a theoretical study of the design of complex engineering systems. More particularly, this paper studies the stability of equilibria in decentralized design environments. Indeed, the decentralization of decisions is often recommended in the design of complex systems, and the decomposition and coordination of decisions are a great challenge. The mechanisms behind this network of decentralized design decisions create difficult management and coordination issues. However, developing efficient design processes is paramount, especially with market pressures and customer expectations. Standard techniques to modelling and solving decentralized design problems typically fail to understand the underlying dynamics of the decentralized processes and therefore result in suboptimal solutions. This paper aims to model and understand the mechanisms and dynamics behind a decentralized set of decisions within a complex design process. Complex systems that are multidisciplinary and highly nonlinear in nature are the primary focus of this paper. Therefore, techniques such as response surface approximations and Game Theory are used to discuss and solve the issues related to multidisciplinary optimization. Nonlinear control theory is used in this paper as a new approach to study the stability of equilibrium points of the design space. Illustrations of the results are provided in the form of the study of the decentralized design of a pressure vessel.