Outlines a device under development at UMIST. The converter is based on the transition between laminar and turbulent flow. A smooth pneumatic beam is injected into a cylindrical cell through an emitting tube, and is adjusted so that the emitted flow remains laminar up to a collecting tube. With this arrangement, a pressure is built up in the collecting tube due to the entry of the laminar flow beam. The laminar flow may be disturbed by an acoustic signal at a specific frequency. When the acoustic signal is strong enough, the flow becomes turbulent in the cell, and as most of the flow is then exhausted from side vents before entering the collecting tube, the pressure in the collecting tube is sharply reduced. The optical command signal is modulated at the specific frequency. The energy from the light causes a photodiode to produce a current to drive a piezo disc, and the piezo disc generates the required acoustic signal to control the pressure level in the collecting tube. Both the static and the dynamic performance of the converter have been investigated. The output pneumatic signal can be fed directly to commercial pneumatic amplifiers without offsetting, and thence to standard pneumatic cylinders, etc. The fast response of the actuator to optical modulation frequency, rather than intensity, ensures that it has considerable immunity to intensity drift and stray inputs, and enables proportional control to be implemented by means of gate width modulation.
展开▼
