Magnetic drives, actuators

One important application of pneumatic transmission is in the operation of diaphragm actuators. These are the elements generally employed to drive the spindles of control valves (Section 7.22.3) and, if hard-wired transmission systems are employed, require devices which convert electric current into air pressure or air flowrate, i.e. electropneumatic (E/P) converters. The basic construction of a typical E/P converter is illustrated in Fig. 6.77. A coil is suspended in a magnetic field in such a way that when a current is passed through the coil it rotates. This rotation is sensed by a flapper/nozzle system (Section 7.22.1). The nozzle is supplied with air via a restrictor and its back pressure actuates a pneumatic relay. The output from the latter is applied to the feedback bellows and also acts as output from the E/P converter. Electropneumatic valve positioners employ the same principle of operation. 

The specific power of rare earth permanent magnet motors can exceed 1 kW/kg. The combination of reliable, low-cost, solid-state controllers and brushless permanent magnet motors will find applications in (i) computer accessories like disk drives, printers, x-y plotters, (ii) consumer goods like hand tools, fans, and air-conditioners, (iii) robotics, traction motors, steel mills, lift motors, and (iv) aerospace flight control actuators. 

Column heads of semi-technical plants are made up of separate condenser and reflux units. The valves are operated mechanically and, more commonly, electro-magnetically. Their operation is similar to that in laboratory column heads (Figs. 306, 247). The valves are controlled automatically by means of electromagnets, electromotors or pneumatic drives (Fig. 248). For the automatic division of liquid, however, the swinging funnel is chiefly used (Fig. 142) which is actuated by an electromagnet placed outside the column wall. With the magnet switched on the distillate is taken off laterally. 

Fig. 10 Utilization of magnetic hyperthennia to drive shape actuation. The stored, corkscrew shape is released to the global minimum, flat shape by the application of an alternating magnetic field. Reprinted from Mohr et al. [122], Copyright 2006, with permission from the National...

XIV-4] KOBAYASHI, Y., et al., A study of magnetic impact type micro-stepping actuator to drive large payload reflector for 4S reactor, IMECE2004-59372, 2004 ASME International Mechanical Engineering Congress and RD D Expo (Anaheim CA, USA, Nov. 13-19, 2004). 

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