الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Electrohydraulic Servo Systems (EHSS) are used extensively in many industrial applications such as flight, ship engineering, machines of injection molding, robotics and steel, and aluminum factory’s equipment. They have the advantages of high power to weight ratio, linear movement, and fast response. However, controlling EHSS is a nonlinear process. To overcome the problem of nonlinearity of hydraulic control system used in this study, a sliding mode controller with error, SMCE, is proposed in such a way that the error signal modifies the ordinary switching mode control action. Pulse width modulation (PWM) technique is used to convert the control action into a digital signal capable of driving the solenoid of an electrohydraulic servo valve to control the oil flow entering the hydraulic cylinder so that piston position could be controlled. A dynamic model of an electrohydraulic control system is simulated using MATLAB/Simulink software where the control parameters are optimized for experimental testing of PID and sliding mode controllers. The two controllers are then fine-tuned experimentally, and their performance is compared under square and sinusoidal reference inputs. The experiments showed that the proposed SMCE gives less steady state error, less overshoot and less settling time compared to both PID and the ordinary switching sliding mode controllers. In the case of sinusoidal input, although the SMCE was found to bound the error to 4.5 % of total piston stroke at a frequency of 0.1 Hz, the steady-state error continued to increase with an increase in signal frequency. Because it could be, due that, the uncertain damping forces becomes relevant as the cylinder velocity increases with the switching frequency. This motivates future research to investigate modifying the SCME to account for this issue.