Control Techniques for Electrohydraulic Actuators in Aerospace, Civil and Robotics Engineering

Dear Colleagues

After World War II, the use of electrohydraulic actuators (EHAs) spread significantly and they became the right choice for a variety of areas, including civil engineering, machine tools, mobile equipment and robots, radar antenna, land vehicles, naval and aerospace systems, and missile launchers. EHS is in fact a position tracking system, but EHA as a stabilizing system can be viewed as a special case of the tracking system. An eloquent example of practical interest for EHA as a stabilizing system is the well-known problem of altitude-hold autopilot synthesis, involving an EHA, where the target is the maintenance of the desired altitude of the aircraft, thus allowing the pilot to perform other more important tasks.

Therefore, the study of stabilization and tracking problems for EHAs remains attractive and important. EHAs do not only allow the generation of large forces but, thanks to modern control technology and sensors, are also capable of assuming important control tasks, such as highly precise positioning of heavy loads.

The mathematical model of servovalve-controlled EHA is a strongly nonlinear one and reveals a switching nonlinearity due to constructive directional changes in the spool valve ports opening. This physical aspect gives the mathematical model the statute of a system with structural, autonomous switching. EHA is itself an actuator with feedback, but it can be viewed broadly as a system with feedback of the real world, and the delay on control will be regarded as a delay of the control signal in the block of the electrohydraulic servovalve. If we also consider the delay in the elaboration of the control law, the mathematical model of EHA becomes even more challenging.

Noting the competition with other types of actuators—electromechanical actuators, hydrostatic actuators, piezo actuators (see the so-called “green aircraft”)—we believe that the EHAs will for many years still be the right choice in many application domains.

This Special Issue is devoted to coverage of various advanced approaches in control techniques of EHAs, including for electrohydrostatic actuators: LQG, backstepping, sliding mode, and geometric control; adaptive control synthesis; intelligent control synthesis: neural, and fuzzy control; systems with delay; switching systems; Liapunov stability; and critical stability.

Dr. Ioan Ursu
Guest Editor

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