Electro-mechanical transducers convert mechanical displacements into electrical signals.
Electro-mechanical actuators convert electrical signals into mechanical displacements. The conversion may be direct or may include an amplifier between the signal and the displacement. (The word "transducer" is sometimes used for actuator as well as for transducer; in sonar, for example.)
A transducer and an actuator may be combined in a feedback control circuit.
A list of actuators is given first, as an overview, and then the individual types are described.
1.& 2. Motors are described in the tutorial Motors
3. Solenoids and electro-magnets. Current in a coil with a two piece iron core induces a magnetic field between the two portions of the core. The two portions attract each other.
4. Polarized electro-magnets. A magnetic field between two pieces of iron results from a combination of the magneto-motive forces of a coil and a permanent magnet. Typically the forces of two such fields act against each other and the MMFs add in one field and subtract in the other.
5. Voice coils. A coil lies in the air gap of a permanent magnet and a force is generated between current in the coil and the flux in the gap.
6. Electron beam deflection. In a cathode ray tube, where an electron beam passes through a controllable magnetic field, the trajectory of the beam is curved by the field.
7. Magneto-striction. In some materials, such as pure nickel, a magnetic field causes the material to shrink along the direction of the field.
8. Piezo-electric. Some insulators, such as quartz, change their shape when subject to an electric field.
9. Electro-thermal, linear expansion. All materials expand when heated.
10. Electro-thermal, differential expansion. Bimetal, heated electrically, bends.
11. Electro-thermal, steam. Electric heat boils water and the resulting steam, under pressure, does mechanical work.
12. Electro-thermal, electron beam. Electrical heat causes electrons to boil out of a solid and electrostatic force accellerates the electrons.
13. Electro-thermal, detonation. Most explosives are detonated by the heat from an electric current in a fine wire inside the explosive.
14. Electro-thermal, fusible link. Electric current melts the link and releases the energy in a spring.
15. Electric valves. Electromagnets, as in 3 and 4 above, are built into pneumatic and hydraulic valves to control fluid flow, either on/off or proportional.
16.Eddy current clutches and brakes. Conductive disks rotating in a magnetic field have currents induced in them which react with the magnetic field and produce torque.
17. Hysteresis clutches and brakes. Magnetic disks rotating in a magnetic field have reversing magnetic polarization which reacts with the magnetic field and produce torque.
18. Electro-magnetic particle clutches and brakes. An electromagnetic field causes magnetic particles to cluster and cling to magnetic discs. Friction between discs and paticles produces torque.
19. Electro-static particle clutches and brakes. This effect is the same as in 18 except that the particles are insulators and the field is electrostatic.
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