FLUIDICS

the technology of using the flow characteristics of liquid or gas to operate a control system (q.v.). One of the newest of the control technologies, fluidics has in recent years come to compete with mechanical and electrical systems. Although fluidic principles are fairly old, it was not until about 1960 that researchers attempted to use fluidics commercially. The demand for reliable controls in space research stimulated progress. In the 1930s Henri Coanda, a Romanian scientist, described what is now known as the Coanda effect, a major contribution to fluidic technology. He observed that as a free jet emerges from a jet nozzle the stream will tend to follow a nearby curved or inclined surface. It also attaches itself to and flows along this surface if the curvature or angle of inclination is not too sharp. Coanda explained this tendency as being caused by the jet stream's entraining (picking up) nearby fluid molecules. When the supply of these molecules is limited by an adjacent surface, a partial vacuum develops between the jet and the surface. If the pressure on the other side of the jet remains constant, the partial vacuum, which is a lower pressure region, will force the jet to bend and attach itself to the wall. Because fluidics is not as rapid as electronics, it is unlikely to compete in fields with ultrahigh-speed requirements. On the other hand, in many applications fluidics is advantageous. It is now possible to detect, interlock, and power complex operations by using air throughout a system. Controls can be installed by a competent fitter who might not be capable of dealing with electronic or electrical systems. The elimination of electrical contacts prevents a possible fire hazard. Pneumatic circuits require controls with simple interlocking, performed by air-piloted and mechanically operated control valves. Because it employs the same medium, fluidics is useful for sensitive detection and complex control as part of a pneumatic system. Combining hydraulics and fluidics is more complicated, however, because the same medium is not used. Yet since both systems require plumbing expertise, labour problems can be reduced. Power-output devices handling hydraulic pressures that respond to fluidic signals are available commercially. Fluidics has been applied to industrial problems on a wide scale, with no particular industry emerging as an obvious choice. Fluidics can operate in hazardous environments and sense objects by methods not available previously. Some typical applications include a weighing system that selects 10 different weights of raw material before machining; air-jet detection of delicate material (the roof lining of an automobile) that would be damaged by mechanical methods; and sonic detectors operating in the highly inflammable, contaminated area of a paint-spray booth. These detectors sense sound waves without disturbing the freshly painted surface.