High frequency vibration test fixture with hydraulic servo valve and piston actuator

A high frequency linear hydraulic servo valve-actuated vibrating test assembly for producing alternating hydraulic fluid flow control outputs the servo valve-actuated test assembly comprising:

• an energy input source comprising a transducer to receive an alternating input signal of a selected frequency and convert the input signal to linear mechanical vibrational motion;
• a servo valve having a pair of fluid flow control output ports and in which an output flow of hydraulic fluid is produced from the control output ports of the servo valve;
• the servo valve including a movable hydraulic pilot valve spool that receives the vibrational motion from the transducer to apply linear reciprocating motion to the pilot valve spool along an axis;
• a movable hydraulic slave valve spool surrounding and concentric with the pilot valve spool;
• a fixed pilot valve sleeve surrounding and concentric with the pilot valve spool, the pilot valve sleeve located between the pilot valve spool and the slave valve spool, to direct alternating fluid flow to the slave valve spool as a result of the linear motion of the pilot valve spool to thereby induce linear motion of the slave valve spool;
• and a fixed slave valve sleeve surrounding and concentric with the slave valve spool to receive alternating fluid flow from the movable slave valve spool to direct the output flow of hydraulic fluid to the fluid flow control output ports of the servo valve, the slave valve spool and the slave valve sleeve providing a power amplification stage for the servo valve output flow that minimizes the volume of trapped hydraulic fluid passing from the pilot valve spool and the pilot valve sleeve to the output ports of the servo valve;
• the servo valve-actuated test assembly further comprising a vibration test fixture having a fixture base for carrying a unit under test, and a hydraulic vibration actuator affixed to the fixture base and comprising a pair of opposed cylinders, each cylinder having a separate piston that reciprocates along a linear axis in a corresponding bore within the cylinder, each piston having a corresponding piston rod, the piston rods extending in opposite directions from the actuator, each piston having an end face opposite from the piston's corresponding piston rod, said end face exposed to trapped hydraulic fluid contained within a volume in the bore adjacent the end face of each piston, each cylinder having a separate inlet port to the trapped volume of fluid adjacent the piston, and in which the hydraulic servo valve output flow from the control output ports of the servo valve are connected to the inlet ports of the pistons for supplying hydraulic fluid to the trapped volumes within the piston cylinders for reciprocating the piston rods to induce a linear vibrating motion to the fixture base.