Design of discrete time adaptive PID control systems with parallel feedforward compensator

This paper deals with the design of an adaptive PID control system with a parallel feedforward compensator (PFC) for discrete-time SISO systems and its application to water level control of a 3-tank system. The proposed method utilizes the characteristics of almost strict positive realness (ASPR) of the controlled plant. A conventional design scheme of a PFC which realizes an ASPR augmented controlled plant is also proposed. Further it is shown that the introduction of an internal model improves the control performance of the control system with the PFC. The effectiveness of the proposed method is confirmed through water level control experiments on a three-tank SISO system.     

ROBUST ADAPTIVE CONTROL FOR STRICT‐FEEDBACK NONLINEAR SYSTEMS

In this paper, we propose a robust adaptive tracking control based on the backstepping strategy for strict‐feedback nonlinear systems with nonparametric uncertain nonlinearities. It is shown that one can design a stable adaptive control system provided that the uncertain nonlinearities can be decomposed by unknown bounded nonlinear functions and known nonlinear functions. The proposed method can deal with uncertain nonlinearities that appear at the control input term too. It is also shown that suitable choice of design parameters guarantees the convergence of tracking error to any desired bound.     

Role of internal and external fixation in ankle fusion

Between August 1980 and September 1993, 35 tibiotalar arthrodeses in 34 patients with primary and secondary osteoarthritis of the ankle were performed. Two different surgical techniques were employed. Internal screw fixation according to Wagner and Pock [20] and an external fixation method according to the resection compression arthrodesis by Charnley and Muller [14]. Twenty patients with 21 fusions could be investigated retrospectively. For evaluation we used self-assessment, clinical examination and radiographic analysis in combination with the score described by McGuire et al. [12]. In 80% the results were good and satisfactory with a median improvement of 23 score points on a scale of 100% 95 points, respectively. The most important advantages were pain relief and increase of walking distance. The fusion rate was 95%. We found osteoarthritis in the neighbouring joints did not have any influence on the surgical result. With respect to the two surgical techniques, the internal screw fixation method achieved fusion earlier with fewer complications and better improvement according to the McGuire score. Tibiotalar fusion is a safe therapy with reproducible good results involving pain relief, full weight-bearing and increase of walking distance.     

Adaptive observer for systems with pure time delay

This note is concerned with the application of adaptive techniques for simultaneous parameter identification and state estimation to the design of an adaptive observer for systems having unknown pure time delay and parameters.     

Changes in the mechanical properties, biochemical contents and wall structure of the human coronary arteries with age and sex

An experimental study of the mechanical properties, biochemical composition and structure was carried out on the proximal and distal parts of the right and the anterior descending branch of left human coronary arteries. The vessels were removed during an autopsy of 121 males and 84 females being 1 day to 80 years old. The material was divided into six age groups. Branchless segments of vessels 15-20 mm long were cut from proximal and distal parts. The mechanical properties of the coronary arteries were determined by passing fluid at pressures ranging from 0 to 240 mmHg. It was found that the part of the wall of the coronary artery adjacent to the myocardium is thicker in all cases than the other part of the arterial wall. With increasing age the mean thickness of the wall of both coronary arteries increases but the wall-thickening process is non-uniform in nature in both the proximal and distal parts and in the individual layers. The changes in the stretch ratio and tangential modulus in circumferential direction with age and sex were investigated. The greatest changes in the wall thickness and in the mechanical parameters were found for the left coronary artery wall in men over 40 years of age and for the right coronary artery wall in women over 50 years of age. The results of biochemical and densitometric investigations were compared.     

Robust parallel compensator design for output feedback stabilization of plants with structured uncertainty

This paper deals with a design problem of robust parallel compensator which guarantees the existence of a constant gain output feedback controller for plants with structured uncertainty. First, robust design conditions of such a compensator are derived by using Kharitonov’s Theorem. Then, based on conditions provided, the parallel compensator is designed by utilizing the maximal range of interval perturbations of the plant. A numerical example is given to demonstrate the validity of the results.     

Simple adaptive control of processes with time-delay

This paper is concerned with the development of tuning guidelines and robustness evaluation tools for a simple adaptive control (SAC) scheme. The adaptive technique requires knowledge of only the relative degree of the plant and an upperbound of the process gain. This is an explicit or direct adaptive scheme. The SAC method is evaluated by simulated applications to two processes. The application of SAC to a process with time-delay is also considered in this paper. This issue has both theoretical, because of the strictly positive real (SPR) requirements, as well as practical appeal. Simulation results show the practicality and usefulness of the proposed algorithm.     

Adaptive output feedback control of general MIMO systems using multirate sampling and its application to a cart–crane system

In adaptive output feedback control based on almost strictly positive real conditions, a technical difficulty arises when the multi-input multi-output (MIMO) system under consideration is non-square, and in particular, has less inputs than outputs. To overcome this, we propose the idea of multirate sampled-data control—by carefully choosing faster input sampling rates, we obtain a lifted discrete-time system, which has the same number of inputs and outputs and does not give rise to the causality constraint. The adaptive control strategy is then applied to the lifted system, resulting in a multirate adaptive output feedback controller which is implementable digitally and provides closed-loop stability under certain conditions. The results reported here are validated on an experimental cart–crane system.