Force based impedance control of electro-hydrostatic actuator

As a kind of compliance control method, impedance control can realize force and position coordination control. So it has obvious advantages in the applications that the actuating systems are required to interact with the environments. Because of high energy efficiency and compact structure, electro-hydrostatic actuator (EHA) with force based impedance control has an extensive prospect. The force controller of EHA is the foundation of the impedance control. Due to the uncertain external load characteristics in impedance control and the time-invariant parameters of EHA, the quantitative feedback theory (QFT) was employed to design the force controller. The mathematical model of EHA was analyzed first. Then the uncertainty range of the controlled plant was combined with the performance specifications of the system to quantitatively plot the boundaries on the Nichols chart. The open-loop frequency characteristic curve of the nominal element was adjusted to satisfy the limitations of boundaries and the force controller was completed simultaneously. The force control and static/dynamic impedance control experiments under various load characteristics were conducted to examine the efficacy of the system. The experimental results demonstrate that the force controller designed by QFT method has sufficient robustness and the impedance control of EHA is achieved successfully.