Abstract: Safety apparatus for an electrohydraulic servovalve. The safety apparatus includes a digital programmable switch (14) which is programmed to make switching decisions on the basis of whether or not the electrohydraulic servovalve is subjected to an external error and whether or not the electrohydraulic servovalve is free from internal error. Logic inputs that supply this information are provided to the programmable switch (14) by a logic device (16). On the basis of the logic inputs, the programmable switch (14) is programmed to interconnect, in a sequential manner, the analog electrohydraulic servovalve to one of four different analog drive systems. One of the drive systems is employed for the case whether there is no external or internal error, so that the electrohydraulic servovalve is in a normal mode of operation. Two of the drive systems are employed to quickly and safely de-energize the electrohydraulic servovalve upon the occurrence of an external error.

Abstract: Electronic compensation apparatus for modifying an input control signal, to produce a drive signal for a torque motor of an electrohydraulic servovalve. The torque motor has a frequency variable response characteristic. The apparatus includes means to determine a first voltage magnitude across the armature of the torque motor when it is not moving; means to determine a second voltage magnitude across the armature of the torque motor when it is moving; and means to determine a difference voltage of the first and second voltages. The difference voltage measures the dynamic motion of the armature and provides a feedback control signal. The apparatus further includes compensation means responsive to the feedback control signal for compensating the electrohydraulic servovalve so as to avoid resonance, and feedback means connected to the compensation means for providing a modified control signal.

Abstract: Electronic compensation apparatus for a drive system associated with a torque motor of an electrohydraulic servovalve. The apparatus includes means to define an open loop transfer function characteristic of the drive system, wherein the transfer function corresponds to a notch filter. Further included are means to provide the open loop characteristic with a closure rate of approximately no more than 6 db/octave with respect to a function 1/.beta.=1-G.sub.cl (s), where G.sub.cl (s) corresponds to a closed loop transfer function of the drive system. In particular, the notch filter may be realized in a drive system that includes a series resistive-capacitive circuit connected in parallel with the torque motor. The 6 db/octave closure rate is provided by a variation of the impedance of the series resistive-capacitive circuit.

Abstract: Method and apparatus for driving the motion system of a flight trainer to simulate aircraft buffeting which method and apparatus avoids the resonant frequency of the motion systems hydraulic actuators by using a "Linear Tracking Band-Stop Filter". Band-stop filter circuitry is combined with linear tracking band pass filter circuitry to provide the linear tracking band-stop filter. This circuit receives command signals intended for the servoamplifier used to drive a hydraulic actuator. The band-stop filter eliminates or substantially attenuates those frequencies contained in the command signal which would cause resonance of the hydraulic actuator. It has been discovered that the resonance frequency of the hydraulic actuator varies as a function of the extension of the actuator, and therefore in this invention the center frequency of the band-stop filter tracks the resonant frequency of the actuator such that a much smaller band of frequencies is eliminated.