Control of Machines with Friction by Brian Armstrong-Hélouvry (auth.)

By Brian Armstrong-Hélouvry (auth.)

It is my ambition in scripting this e-book to deliver tribology to the research of keep watch over of machines with friction. Tribology, from the greek for examine of rubbing, is the self-discipline that matters itself with friction, put on and lubrication. Tribology spans a superb diversity of disciplines, from floor physics to lubrication chemistry and engineering, and includes investigators in diversified specialities. The English language tribology literature now grows at a expense of a few seven hundred articles in step with 12 months. yet for all of this job, within the 3 years that i've been fascinated by the keep watch over of machines with friction, i've got yet as soon as met a fellow controls engineer who used to be conscious that the sphere existed, this together with many that have been fascinated about friction. during this vein i need to confess that, sooner than venture those investigations, I too was once unaware that an lively self-discipline of friction existed. The event sticks out as a mark of the specialization of our time. inside tribology, experimental and theoretical figuring out of friction in lubricated machines is definitely built. The controls engineer's curiosity is in dynamics, which isn't the significant curiosity of the tribologist. The tribologist is extra frequently desirous about put on, with recognize to which there was huge, immense growth - witness the various mechanisms which we purchase this present day which are lubricated as soon as basically, and that on the manufacturing facility. even though a secondary curiosity, frictional dynamics are observe forgotten via tribology.

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The principle limitations of EP additives are a weaker friction modification than is achieved by the lubricity agents, and chemical reaction with the surface, which is by its nature corrosive. With EP agents one in effect acquires greatly reduced mechanical wear at the price of slow corrosion [Wills 80; Fuller 84; Papay 88]. Anti-wear agents extend the service life of machine parts through a remarkable chemistry that can repair some forms of wear induced surface damage [Estler 80; Booser 84]. The issue of principle concern for the controls engineer is that the anti-wear agent can interfere with the friction modification of lubricity or EP additives.

A reunion is coming. Using refined numerical methods and more powerful computers, several authors discussed above probe the transient dynamics of fluid lubrication. Partial fluid lubrication is coming under investigation; and even transient partial fluid lubrication, the essence of stick-slip, is considered. Evidence suggests that in servo mechanisms friction can be highly repeatable. Repeatability, coupled with knowledge of the relevant model structure, will permit experimental identification of the friction model describing a particular mechanism.

Lubrication additives may be broken into three broad classes: • Lubricity Agents; • Extreme Pressure Agents; • Anti-Wear Agents. Long chain hydrocarbons with a polar group at one end are commonly used as lubricity agents. The polar group bonds to the metal and the long chain sticks away from the surface, creating, in effect, a mat of bristles [Merchant 46; Bowden and Tabor 73; Fuller 84]; the longer the chain (bristle) the lower the friction. These additives are sometimes called oiliness agents, anti-friction agents or friction modifiers.

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