DESIGN OF A MOTION CONTROL FOR A HYDRAULIC ROTARY ACTUATOR USING A VARIABLE DISPLACEMENT PUMP.

A new motion control system for a hydraulic rotary actuator was designed in this work. The hydraulic fluid that goes to the actuator was used in a variable displacement pump to control the actuator movement. A mathematical model was conducted and the stability and performance of the open loop system were studied. Routh-Hurwitz stability criterion was implemented to assess the system stability which showed that the system is stable as long as realistic parameters are chosen for the design. Since the open loop system showed poor performance, PID and H-infinity controllers were considered to improve the system overall performance. Multiplicative uncertainty was considered in the H-infinity design process to ensure that the system responds well when uncertainties in the system parameters exist within a specified range. The leakage and friction coefficients are the parameters that were considered uncertain due to their expected change with time. The uncertainty was considered in the viscous friction and the leakage coefficients within a range of ±3%. The results showed that the open system has about 20% percent overshoot, 10% steady state error for a unit step input signal and a poor disturbance rejection. The system with both H-infinity and PID controller has no steady state error and a low settling time which is about 7 time constants (6.3 ms). The H-infinity controller provides the least percent overshoot in response to the unit step input signal, 4% compared to 10% for the PID controller. In addition, the H-infinity controller provides faster response and better disturbance rejection characteristics. Finally, only the H-infinity controller meets the robustness requirements. [ABSTRACT FROM AUTHOR]