  This paper describes the full- and reduced-order models of an actuated
hydraulic cylinder suitable for system dynamics analysis and motion control
design. The full-order model incorporates the valve spool dynamics with
combined dead-zone and saturation nonlinearities - inherent for the orifice
flow. It includes the continuity equations of hydraulic circuits coupled with
the dynamics of mechanical part of cylinder drive. The resulted model is the
fifth-order and nonlinear in states. The reduced model neglects the fast valve
spool dynamics, simplifies both the orifice and continuity equations through an
aggregation, and considers the cylinder rod velocity as output of interest. The
reduced model is second-order that facilitates studying the system behavior and
allows for direct phase plane analysis. Dynamics properties are addressed in
details, for both models, with focus on the frequency response, system damping,
and state trajectories related to the load pressure and relative velocity.
