Torsional resonant system

Claim 1

A hydraulic resonant test device for testing specimens in torsion comprising a support means to mount said specimen, flywheel means acting in combination with said specimen mounted for rotation therewith adjacent at least one end thereof, a rotary hydraulic actuator having internal chambers divided by an active pressure responsive element, connected to drive said specimen, fluid pressure means, servovalve means coupled to said rotary hydraulic actuator to provide fluid pressure to said chambers of said hydraulic actuator to supply force to rotate said specimen in either direction of rotation about a longitudinal axis of said specimen, differential pressure means for sensing the pressure difference in said chambers in said rotary actuator, and delivering a signal proportional thereto, torque cell means for sensing the torque in said specimen and delivering a signal proportional to torque, means for comparing the output signals of said differential pressure sensor and said torque cell means to supply a control signal which is a function of the difference in phase between said differential pressure signal and said torque cell signal, controller means, means coupling said torque cell means to said controller means, means coupling said comparing means to said controller means, said controller means being responsive to said control and torque signals to produce a cyclic command signal for driving said servovalve means and said rotary actuator at a phase and frequency to maintain resonance and to minimize the power input to said hydraulic actuator means while maintaining a desired torque in said specimen.