An improved rotary servovalve
system employs a rotary magnetic solenoid having an armature that includes at least one permanent
magnet. The armature is rotatable relative to a
stator formed as an
electromagnet which is energizable to create alternative electromagnetic fields having opposite polarities from each other. When deenergized, the
stator allows the armature to return to a neutral, null position from positions of extreme rotation in opposite angular directions due to the magnetic force of the permanent
magnet of the armature. The armature is coupled to carry a movable valve element in
angular rotation therewith, so that flow through the servovalve of the
system can occur in alternative directions. Also, the valve element is biased toward a position in which all of the valve ports are closed when power is removed from the rotary solenoid. The
control circuit employed in the rotary servovalve
system expands the bandwidth of response of the
solenoid actuator by compensating for frequency variations in the input command
signal and in the feedback
signal. This compensation is achieved utilizing a combined proportional, integral, and
differential amplification circuit. Also, imbalance of fluid forces within the servovalve mechanism can be avoided by utilizing a pair of inlet orifices, a pair of outlet orifices, a pair of first
fluid control orifices, and a pair of second
fluid control orifices. The orifices within each pair are located on opposite sides of the valve housing from each other.