Nonlinear Robust Position Tracking Control of Electro-Hydraulic Systems Without Velocity Measurements

Dynamical equations representing an electrohydraulic system (EHS) is composed of hydraulic, mechanical, and electrical subsystems. As a consequence, monitoring and/or controlling an EHS system requires the measurement of multiple state variables, which in turn mandates the use of additional sensory equipment. In particular, in systems where multiple hydraulic actuators are required, such as robotic arms or excavators, each additional sensor would increase the overall manufacturing and maintenance cost. In this study, we propose a robust observer/controller formulation to eliminate the need of velocity measurements in EHSs. The proposed formulation solely rely on nominal model information. The stability of the closed-loop system is ensured via novel Lyapunov-based arguments and the global uniform ultimate boundedness of the position tracking error and the velocity observation error are established. The effectiveness of the method is evaluated through simulation studies.