Position Control of an Electro-Hydraulic Servo-Valve : IDENTIFICATION, MODELLING, CONTROLAND IMPLEMENTATION

Abstract:

Hydraulic drives, systems that use pressurized fluids as transmis-sion medium, have a wide range of applications are widespread in to-day’s industry. Like many other systems, hydraulic drives can get dra-matically improved performance by an appropriately designed feedback controller. Without any automatic control, these systems are often very difficult for a user to operate.

Olsberg is a Swedish company specialized in hydraulic drives, pre-dominantly for cranes and other heavy machinery. Their product offer-ing includes completely mounted systems, where Olsbergs’ own electro-hydraulic valves are central to providing a pleasant handling for the human operator.

The hydraulic valves distribute oil from a hydraulic pump to other hydraulic mechanisms that customers wish to control. To regulate the oil flow through every channel in the valves, Olsbergs have designed an electrically driven position controller that actuates the valve openings. The control of this valve is the main focus of this thesis.

Although Olsbergs are satisfied with their products, and their cus-tomers are happy with their solution, they continuously look for im-provements. To this end, this thesis presents an analysis of the com-plete system and suggests, implements and evaluates a new controller.

Due to system limitations, the possibilities for automatic control are restricted, and a traditional proportional-integral-derivative (PID) controller was found to be the most appropriate control law. The basic control law was modified to support multi-rate reference handling and decrease the sensitivity to noise and disturbances. Testing in both the laboratory and in the field demonstrated that this quite simple solution gave a satisfactory result on today’s systems.