FLUIDICS HAS ARRIVED

Reproduced from Machinery Lloyd and Electrical Engineering (Vol. 37, No. 20 - 25th September 1965) with kind permission of the publishers - The Certificated Engineer Jan 1967

Into a world still somewhat uncertain about such terms as cryogenics, ergonomics and, above all, electronics, has been born a new science to which has been given the unlovely name 'fluidics.' However, its proponents promise that it will be understood more readily than electronics by ordinary engineers. If this is so, fluidics will be welcomed-despite its name.

Perhaps, it is this incomprehensibility of electronics that has produced so much interest among 'ordinary engineers' during the past four or five years in the possibility of developing fluid logic systems and even pneumatic computers. Added to this there is the advantage of being able to eliminate electricity from certain hazardous areas or of being able to use only one source of power for detecting, sensing, and other control purposes as well as operations. This last consideration is important, not only because a mixed system involves means of converting from one power ward in fluidic control systems as did the transistor in electronics. The turbulence amplifier forms one part of a fluid logic system called Maxalog.

The fundamental idea is that a fluid stream in the laminar state can be transformed into the turbulent state very easily and the transformation can be made to produce much larger effects than the disturbance causing it. The turbulence amplifier (Fig. 1) is essentially a metal tube about the size of a cigarette. A laminar stream, normally of air, at about 10 in wg enters through a tube 1/32 in d. This laminar stream is projected across a gap of about 1 in to another (output) tube, coaxial with the first and of about the same size. So, long as the stream remains laminar the output tube collects a large part of it and the pressure in it is about half that in the supply tube.

If the stream is made turbulent the pressure in the output tube is greatly reduced-almost to zero and the stream can be made turbulent by a very small medium to the other and back again, but also because it requires two distinct kinds of installation and maintenance labour.

Fig. 1 A turbulence amplifier showing the inlet tube at the right with the four control jets above it.

There has been one great problem. A valve or switch was required, small but of formidable reliability and ability to use a small force to control a much larger force. Obviously, the use of an aerodynamic or hydrodynamic effect would permit moving parts to be eliminated. Maxam Power Ltd., Camborne, Cornwall, investigating this problem, realised that several possibilities existed. One obvious physical effect is the deflection of a jet by the impingement of another much smaller jet. Less obvious are the Coanda effect and the transition from laminar to turbulent flow. This last phenomenon is the one used by Maxam Power Ltd. in its new device, the turbulence amplifier, which it claims represents as big a step for airflow impinging on it from one of the four control jets mounted in the wall of the device.

 Fig.2 Three turbulence amplifiers provide the logic state AND.

When the control jet flow stops, laminar flow is re-established and the output signal restarts. Alternatively, the disturbance can be initiated by mechanical or electrical means or by noise or vibration, although normally the turbulence amplifier is insensitive to these.

Switching speed is high enough for the control of most mechanical and chemical processes. Switch off time is about 2 milliseconds and complete cycle time about 7 milliseconds. Power consumption is about 3 ft 3/h of air at 10 in wg pressure.

Apart from its ability to work safely in explosive atmospheres, the device is unaffected by other environmental conditions, by nuclear or mag-netic radiation, and its operation cannot be jammed or otherwise upset by electrical means.

As turbulence amplifier output pressures are of the order of 4 in wg and flows of 1 ft 3/h, it is necessary at some stage in most applications to provide one or further stages of amplification so that normal pneumatic valves and cylinders may be operated. This could be provided, for example, by a pneumatic step-up relay giving a pressure amplification of over 100 to 1 and a power amplification of 100 000 to 1.

The device on its own provides a simple NOR function. An output is present so long as there is no input signal at each of the four inputs. Also, on its own it provides a NOT function as a signal at any one input will prevent the output signal.

 Fig.3 Logic state NAND provided by five turbulence amplifiers.

Fig.4 A memory or FLIP-FLOP.

The OR function is obtained simply by connecting a NOT function immediately following a NOR unit. Figs. 2, 3 and 4 show the connections for the AND, NAND and FLIP-FLOP functions.

These simple combinations of turbulence amplifiers, which are linked to perform various logic functions, can, in turn, be interconnected into a complete control logic system. The circuits will be analogous to those using semi-conductor triodes to give digital control over a sequence of operations, with automatic feedback control if required.

Fig.5 The interruptible jet-a form of open turbulence amplifier.

Input signals can be obtained from a variety of sources but the most important methods are the interruptible jet (Fig. 5), the air stream detector (Fig. 6), and the build-up of pressure (Fig. 7). The first of these is a form of open turbulence amplifier which can detect objects physically interrupting the laminar stream. As shown, the interruptible jet is normally holding the turbulence amplifier 'off' until interrupted.

Fig.6 Airstream detector with one large control jet.

Fig.7 A sensing head in which the proximity of component A builds up pressure to the turbulence amplifier.

The airstream detector (Fig. 6) is somewhat like a turbulence amplifier but has one large input. It is very sensitive and will 'turn off' when a very low-pressure air stream is directed at the input. Thus, it is normally 'off' and the turbulence amplifier 'on' until the air stream is interrupted. This equipment provides a means of detecting objects in the same way as a photo-cell. An indication of its sensitivity is that a domestic fan will operate an airstream detector at a range of about 10 ft.

When component A in Fig. 7 closes the gap between itself and the sensing head, pressure build-up will cause the turbulence amplifier to be switched 'off.' The sensitivity can be controlled by the restrictor, so that this system can be used as a basis for the automatic gauging of components. This sensing head may be used as a no-moving- part pushbutton or adapted to be a limit switch, requiring practically no effort to operate, and could have pre-travel and over-travel as required.

At present turbulence, amplifiers are not being marketed as separate items but as parts of complete systems engineered by Maximum Power Ltd.