In engineering testing, a requirement frequently arises for subjecting components or assemblies to vibrations, in order to observe whether they possess undesirable resonances in their component parts, or whether they are sufficiently robust to operate under environmental conditions of severe vibration. Accelerometers also must be subjected to vibrations of known characteristics for calibration purposes.
While these duties could conceivably be performed by a timed spring-mass system executing sinusoidal vibrations, it has become usual over the past few years to subject components to vibrations which more closely simulate the vibrations they can expect to encounter in operation, namely random vibrations and stochastic or semi-random vibrations, because of non-linear effects.
A device to execute stochastic motion of a controlled nature must have a closed loop feedback control system associated with it, enabling it to accept electrical signals from signal generators and to produce an output which is either a displacement or an acceleration, proportional to the value of the input. This thesis describes the design and construction of such a device using, initially, displacement feedback. Under test, the machine has functioned satisfactorily at frequencies up to 150 Hz, at amplitudes up to 0.025 inches corresponding to an acceleration of 58g. Designed with as much flexibility as possible in the values of the physical parameters of the system, the machine also promises to be a useful test case for research into adaptive control systems using parameter perturbation techniques.