Željko Šitum

Robust H∞ position control synthesis of an electro-hydraulic servo system

This paper focuses on the use of the techniques based on linear matrix inequalities for robust H(infinity) position control synthesis of an electro-hydraulic servo system. A nonlinear dynamic model of the hydraulic cylindrical actuator with a proportional valve has been developed. For the purpose of the feedback control an uncertain linearized mathematical model of the system has been derived. The structured (parametric) perturbations in the electro-hydraulic coefficients are taken into account. H(infinity) controller extended with an integral action is proposed. To estimate internal states of the electro-hydraulic servo system an observer is designed. Developed control algorithms have been tested experimentally in the laboratory model of an electro-hydraulic servo system.

Control of a pneumatic drive using electronic pressure valves

The primary task of the electronic pressure (E/P) valves is to control the pressure continuously in different industrial automation processes. Their use in pneumatic drives allows regulating pressures in both cylinder chambers and so it is possible to achieve a direct force controlled actuator. Additionally to the force control, position control of the pneumatic actuator using E/P valves has been presented. A dynamic model for control purposes of the process has been derived, followed by the PID controller tuned according to damping optimum criteria. The control algorithms have been experimentally verified on an industrial cylindrical rod-less actuator controlled by two E/P valves. The control performances are comparable with the set-up with proportional directional control valves (servo-valves). Based on the experimental results, it can be concluded that these valves have potential for successful implementation in industry for position and force control applications.

Pneumatic Inverted Wedge

Abstract The paper describes the inverted wedge actuated by the pneumatic cylinder. It can be considered as a two degrees-of-freedom planar robot, which is controlled by a single control input (movement of the slider) in order to keep the frame of the wedge in balance. Only one measured variable (angle of the frame) was anticipated, hence an observer was necessary to control this model using state controller. The nonminimum-phase characteristic and pneumatics make control of described system even more challenging. Thus, this model offers great possibilities as an experimental device in control education.

A pneumatically actuated ball and beam system

A ball and beam balancing mechanism actuated by a pneumatic rotary drive is presented in this paper. A laboratory model of the pneumatically actuated ball and beam system has been developed within student projects during courses related to mechatronics and automatic control. A mathematical model of the nonlinear system is developed using Lagranges equations. The model is linearized at the equilibrium point, and the linear model has been implemented for the design of control algorithms. The cascade proportional derivative (PD) controller and the optimal linear quadratic regulator have been applied and experimentally verified. The utilization of a pneumatic actuator introduces additional dynamic terms and nonlinear effects, and that makes the balancing mechanism even more difficult to control. The methods discussed in this paper have good potential application to other control techniques and offer great possibilities for giving students a better understanding of the theoretical and practical aspects of nonlinear system control.

A BPTT‐like Min‐Max Optimal Control Algorithm for Nonlinear Systems

This paper presents a conjugate gradient‐based algorithm for feedback min‐max optimal control of nonlinear systems. The algorithm has a backward‐in‐time recurrent structure similar to the back propagation through time (BPTT) algorithm. The control law is given as the output of the one‐layer neural network. Main contribution of the paper includes the integration of BPTT techniques, conjugate gradient methods, Adams method for solving ODEs and automatic differentiation (AD), to provide an effective, novel algorithm for solving numerically optimally min‐max control problems. The proposed algorithm is applied to the rotational/translational actuator (RTAC) nonlinear benchmark problem with control and state vector constraints.

A Newton-Like Algorithm for L2-Gain Optimal Control of an Electro-Hydraulic Servo-System

This paper is concerned with L2-gain optimal control approach for rotary electro-hydraulic servo-system. The electro-hydraulic dynamics with respect to hydraulic motor velocity, with input voltage to the servo valve as control input and load torque as disturbance input, is formulated. The mathematical model results in input-affine nonlinear system. A numerical algorithm based on Newton method to solve a finite-horizon minimax problem for L2-gain minimisation of electro-hydraulic system is presented. The feedback control and disturbance variables are formulated as linear combination of approximation functions. The proposed algorithm, which has recursive matrix structure, directly finds approximations of the feedback control and the “worst case” disturbance variables. Developed controller has been tested experimentally in the laboratory model of an electro-hydraulic servo system.