Optimal controllers for finite wordlength implementation

When a controller is implemented in a digital computer, with A/D and D/A conversion, the numerical errors of the computation can drastically affect the performance of the control system. There exists realizations of a given controller transfer function yielding arbitrarily large effects from computational errors. Since, in general, there is no upper bound, it is important to have a systematic way of reducing these effects. Optimum controller designs are developed which take account of the digital round-off errors in the controller implementation and in the A/D and D/A converters. These results provide a natural extension to the Linear Quadratic Gaussian (LQG) theory since they reduce to the standard LQG controller when infinite precision computation is used. But for finite precision the separation principle does not hold

Sensor/Actuator Selection for the Constrained Variance Control Problem

The problem of designing a linear controller for systems subject to inequality variance constraints is considered. A quadratic penalty function approach is used to yield a linear controller. Both the weights in the quadratic penalty function and the locations of sensors and actuators are selected by successive approximations to obtain an optimal design which satisfies the input/output variance constraints. The method is applied to NASA's 64 meter Hoop-Column Space Antenna for satellite communications. In addition the solution for the control law, the main feature of these results is the systematic determination of actuator design requirements which allow the given input/output performance constraints to be satisfied

Closed-form solutions for linear regulator design of mechanical systems including optimal weighting matrix selection

Vibration in modern structural and mechanical systems can be reduced in amplitude by increasing stiffness, redistributing stiffness and mass, and/or adding damping if design techniques are available to do so. Linear Quadratic Regulator (LQR) theory in modern multivariable control design, attacks the general dissipative elastic system design problem in a global formulation. The optimal design, however, allows electronic connections and phase relations which are not physically practical or possible in passive structural-mechanical devices. The restriction of LQR solutions (to the Algebraic Riccati Equation) to design spaces which can be implemented as passive structural members and/or dampers is addressed. A general closed-form solution to the optimal free-decay control problem is presented which is tailored for structural-mechanical system. The solution includes, as subsets, special cases such as the Rayleigh Dissipation Function and total energy. Weighting matrix selection is a constrained choice among several parameters to obtain desired physical relationships. The closed-form solution is also applicable to active control design for systems where perfect, collocated actuator-sensor pairs exist

Control by model error estimation

Modern control theory relies upon the fidelity of the mathematical model of the system. Truncated modes, external disturbances, and parameter errors in linear system models are corrected by augmenting to the original system of equations an 'error system' which is designed to approximate the effects of such model errors. A Chebyshev error system is developed for application to the Large Space Telescope (LST)

Increasing Children’s Working Memory Capacity: Preliminary Evaluation of a Card-Based Programme

Working memory (WM) is recognised as universally foundational to children’s learning. While computerised training programmes can increase working memory capacity, their application in school contexts may be limited by resources and pedagogy, which may restrict use to pupils with the greatest difficulty. This research presents findings from a preliminary evaluation into the effectiveness of a novel, six-week, whole-class working memory programme, which involved pairs of children undertaking daily card-based activities within a single mainstream primary school classroom, involving 24 eight- and nine-year-old children. Post and follow-up measures demonstrated significant gains in children’s working memory and verbal short-term memory, with large effect sizes. While promising, these results should be interpreted with caution due to the sample size and age of participants. Before it can be concluded that this working memory training programme holds potential to increase children’s capacity to learn and achieve, further research needs to establish its usefulness for children with the most prominent WM difficulties, justify its application for children without WM difficulties and eliminate the possibility that gains could have occurred as a result of task-specific learning

Linearized dynamical model for the NASA/IEEE SCOLE configuration

The linearized equation of motion for the NASA/IEEE SCOLE configuration are developed. The derivation is based on the method of Lagrange and the equations are assembled into matrix second order form

Testing and evaluation of Dacron parachute elements after exposure to ethylene oxide and simulated package loading and heat cycle

Testing Dacron parachute components and assemblies by exposure to ethylene oxide sterilization, simulated package loading, and heat cycl