Loading and Driving System:

The FE and AA motions are implemented electro-mechanically by means of a dual motion mechanical crank, driven by a fixed speed a.c. gear-motor. With a 50 Hz excitation frequency, the resulting test frequency is 1.06 Hz. An optional inverter drive can be supplied to allow tests to be performed at lower test frequencies or with different supply frequencies.

Each test station is loaded by means of a low volume pneumatic actuator. The actuators are connected to a common manifold. Air pressure to the manifold is controlled by means of a pneumatic regulator with integral pressure servo loop. The regulator is manually set to give the required peak load, which is measured by the force transducer fitted to the master test station. The measured load signal is thus used for monitoring only. The system is very stable in operation and subsequent manual adjustments are rarely necessary.

The load profile control signal for the pressure servo loop of the regulator is generated electro-mechanically by means of a cam, fitted to the output shaft of the gear-motor, acting on an LVDT fitted with a roller follower. The signal-conditioned output of the LVDT provides the demand set-point for the pneumatic regulator. This eliminates the requirement for a real-time control system, thus reducing the requirement for complex tuning, calibration procedures and waveform signal generator. The load profile can be modified, if required, by altering the cam profile and the phasing adjusted by rotating the cam on the output shaft.