chap3 - Automation Engineering Services(ENG3618 Chapter 3...

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Automation & Engineering Services (ENG3618) Chapter 3 Page 1 Chapter 3 Drives and Actuators Overview of electrical, pneumatic and hydraulic actuators All mechanical systems involve motion or action of some sort. Even an electric motor, which is of electrical engineering discipline, requires many mechanical parts, such as the shaft, bearings, seals, housing, bolts and nuts etc. The modern control systems have microprocessors which are very powerful and intelligent; however, any decision from the microcontroller can go nowhere without the help of actuators. We need actuators to perform any functions. The actuators produce motions both linearly and rotationally. These can be electrical, mechanical, hydraulic or pneumatic. Types of Actuators There are basically the linear and rotational actuators. The actuators belonging to the linear type are: • Pneumatic rams: rod types • Pneumatic rams: rod less type • Pneumatic diaphragms • Pneumatic bellows • Hydraulic cylinders • Solenoids • Other less common forms of electric actuators Examples of the rotational type are: • Pneumatic motors: continuous rotation • Pneumatic motors: limited rotation • Hydraulic motors: continuous rotation • Gear motors • Vane motors • Axial piston motors • Radial piston motors • Hydraulic motors limited rotation • DC motors • DC servomotors • Induction motors • Stepper motors • Variable reluctance stepper motors • Permanent magnet stepper motors • Hybrid stepper motors • Synchronous motors Motion from the driver must be converted or transmitted to other parts. Examples of motion converters are: • Fixed ratio motion converters
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Automation & Engineering Services (ENG3618) Chapter 3 Page 2 • Parallel shaft gears • Epicyclic gears • Harmonic drives • Worm & bevel gears • V belt drives • Toothed belt drives • Chains & sprockets • Friction wire wrap drives • Rack & pinion • Screw nut systems • Motion converters with invariant motion profile • Cams • Indexing mechanism • Linkages • Variators (continuously variable transmissions) • Conical pulley/disc systems • Ball/disc friction drive system • Remotely controlled couplings Electro-hydro-mechanical Actuators These actuators have been very popular in many industries. In particular, hydraulic actuators are often used in heavy industries where a lot of force and power are needed. Hydraulic relays are widely used in power and heavy industries too. Pneumatic Actuators Recently pneumatic actuators are getting more popular in robotic field because they are cheaper and environmentally friendlier. Also, the motion can be made much faster. The only drawback is the difficulty in controlling motions. This is partly due to air being compressible thus making the motion less decisive. A compensation scheme is required to cancel out this ill effect.
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