Feedback control of unsupported standing in paraplegia. Part I: optimal control approach

This is the first of a pair of papers which describe an investigation into the feasibility of providing artificial balance to paraplegics using electrical stimulation of the paralyzed muscles. By bracing the body above the shanks, only stimulation of the plantarflexors is necessary. This arrangement prevents any influence from the intact neuromuscular system above the spinal cord lesion. Here, the authors extend the design of the controllers to a nested-loop LQG (linear quadratic Gaussian) stimulation controller which has ankle moment feedback (inner loops) and inverted pendulum angle feedback (outer loop). Each control loop is tuned by two parameters, the control weighting and an observer rise-time, which together determine the behavior. The nested structure was chosen because it is robust, despite changes in the muscle properties (fatigue) and interference from spasticity

The Optimal Projection Equations for Fixed-Order Sampled-Data Dynamic Compensation with Computation Delay

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/57876/1/FixedOrderSampledData.pd

Jitterbug - Reference Manual

The manual describes the use of Jitterbug, a Matlab toolbox for analysis of real-time control performance. The tool facilitates the computation of a quadratic performance index for a linear control system under various timing conditions

Networked Control System Design and Parameter Estimation

Networked control systems (NCSs) are a kind of distributed control systems in which the data between control components are exchanged via communication networks. Because of the attractive advantages of NCSs such as reduced system wiring, low weight, and ease of system diagnosis and maintenance, the research on NCSs has received much attention in recent years. The first part (Chapter 2 - Chapter 4) of the thesis is devoted to designing new controllers for NCSs by incorporating the network-induced delays. The thesis also conducts research on filtering of multirate systems and identification of Hammerstein systems in the second part (Chapter 5 - Chapter 6). Network-induced delays exist in both sensor-to-controller (S-C) and controller-to-actuator (C-A) links. A novel two-mode-dependent control scheme is proposed, in which the to-be-designed controller depends on both S-C and C-A delays. The resulting closed-loop system is a special jump linear system. Then, the conditions for stochastic stability are obtained in terms of a set of linear matrix inequalities (LMIs) with nonconvex constraints, which can be efficiently solved by a sequential LMI optimization algorithm. Further, the control synthesis problem for the NCSs is considered. The definitions of H₂ and H∞ norms for the special system are first proposed. Also, the plant uncertainties are considered in the design. Finally, the robust mixed H₂/H∞ control problem is solved under the framework of LMIs. To compensate for both S-C and C-A delays modeled by Markov chains, the generalized predictive control method is modified to choose certain predicted future control signal as the current control effort on the actuator node, whenever the control signal is delayed. Further, stability criteria in terms of LMIs are provided to check the system stability. The proposed method is also tested on an experimental hydraulic position control system. Multirate systems exist in many practical applications where different sampling rates co-exist in the same system. The l₂-l∞ filtering problem for multirate systems is considered in the thesis. By using the lifting technique, the system is first transformed to a linear time-invariant one, and then the filter design is formulated as an optimization problem which can be solved by using LMI techniques. Hammerstein model consists of a static nonlinear block followed in series by a linear dynamic system, which can find many applications in different areas. New switching sequences to handle the two-segment nonlinearities are proposed in this thesis. This leads to less parameters to be estimated and thus reduces the computational cost. Further, a stochastic gradient algorithm based on the idea of replacing the unmeasurable terms with their estimates is developed to identify the Hammerstein model with two-segment nonlinearities. Finally, several open problems are listed as the future research directions

The analysis and design of multirate sampled-data feedback systems via a polynomial approach

This thesis describes the modelling, analysis and design of multirate sampled-data feed-back via the polynomial equations approach. The key theoretical contribution constitutes the embedding of the principles underpinning and algebra related to the switch and frequency decomposition procedures within a modern control framework, thereby warranting the use of available computer-aided control systems design software. A salient feature of the proposed approach consequently entails the designation of system models that possess dual time- and frequency-domain interpretations. Expositionally, the thesis initially addresses scalar systems excited by deterministic inputs, prior to introducing stochastic signals and culminates in an analysis of multivariable configurations. In all instances, overall system representations are formulated by amalgamating models of individual sub-systems. The polynomial system descriptions are shown subsequently to be compatible with the Linear Quadratic Gaussian and Generalised Predictive Control feedback system synthesis methods provide causality issues are dealt with appropriately. From a practical perspective, the polynomial equations approach proffers an alternative methodology to the state-variable techniques customarily utilised in this context and affords the insights and intuitive appeal associated with the use of transfer function models. Numerical examples are provided throughout the thesis to illustrate theoretical developments

Perturbation and stability theory for Markov control problems

A unified approach to the asymptotic analysis of a Markov decision process disturbed by an ε-additive perturbation is proposed. Irrespective of whether the perturbation is regular or singular, the underlying control problem that needs to be understood is the limit Markov control problem. The properties of this problem are the subject of this study

The generation of dual wavelength pulse fiber laser using fiber bragg grating

A stable simple generation of dual wavelength pulse fiber laser on experimental method is proposed and demonstrated by using Figure eight circuit diagram. The generation of dual wavelength pulse fiber laser was proposed using fiber Bragg gratings (FBGs) with two different central wavelengths which are 1550 nm and 1560 nm. At 600 mA (27.78 dBm) of laser diode, the stability of dual wavelength pulse fiber laser appears on 1550 nm and 1560 nm with the respective peak powers of -54.03 dBm and -58.00 dBm. The wavelength spacing of the spectrum is about 10 nm while the signal noise to ratio (SNR) for both peaks are about 8.23 dBm and 9.67 dBm. In addition, the repetition rate is 2.878 MHz with corresponding pulse spacing of about 0.5 μs, is recorded

Aircraft adaptive learning control

The optimal control theory of stochastic linear systems is discussed in terms of the advantages of distributed-control systems, and the control of randomly-sampled systems. An optimal solution to longitudinal control is derived and applied to the F-8 DFBW aircraft. A randomly-sampled linear process model with additive process and noise is developed