Candidate: Pedro Ivo Inácio Pereira
Program: UFSC / POSMEC
Date: September, 2006
Advisor: Raul Guenther
Co-advisor: Victor Juliano De Negri
Abstract: This work deals with the project and experimental implementation of position controllers in a hydraulic actuator, composed by an asymmetrical proportional directional valve and a double action differential cylinder. The hydraulics actuators are quite used in the construction industry, agricultural equipments, material handling, mining equipments, siderurgy, aviation, navy, manufacture process and leisure due, between others advantages, a high relation force/dimension and installation flexibility. However, these actuators have dynamics characteristics and nonlinearities that prejudice their closed loop control in applications that demand high performance. In this work is done an analysis about the influence of the proportional directional valve dynamic in the system behavior and in the project and performance of the classic controllers (P, PI, lead and lag compensators and state controller), proportional controller with forward loop and fixed cascade controller (CC) with and without leakage compensation. For that, it was done linear and nonlinear models of third and fifth order for the hydraulic actuator. The third order model doesn’t consider the valve dynamic, while the fifth order model does. It is proposed a nonlinear model to represent the internal leakage in the proportional directional valve and a control law in the cascade controller to compensate this leakage. The influence of external disturbances (weight force and spring force) in the position control of the hydraulic actuator is analyzed using a bench test where is possible apply external force and variable loads, simulating real situations lived by these components in industrial field. The dead-zone is identified and compensated by the analysis of the pressures dynamic in the actuation system. Experimental results show the main characteristics of the controllers, allowing establish a relation cost/benefit, once the number of sensors and the computational cost vary according to the kind of controller.
INÁCIO PEREIRA, P. I. Análise Teórico-Experimental de Controladores para Sistemas Hidráulicos. 2006. Dissertação (Mestrado em Engenharia Mecânica). Universidade Federal de Santa Catarina, Florianópolis.