Eccentric

eccentric, in mechanics, device for changing rotary to back-and-forth motion. A disk is mounted off center on a shaft. One flat, open, circular end of a rod fits around the edge of the disk; the other end is usually attached to a block that slides in a slot. As the shaft rotates the block slides back and forth, carrying along whatever is attached to it, e.g., a valve. The distance between the center of the shaft and the center of the disk is the eccentricity. The so-called throw may mean either the eccentricity or the distance the block moves, which is twice the eccentricity. Cams and cranks perform the same function as the eccentric, which designers often prefer to the crank for short motions.

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eccentric

1. situated away from the centre or the axis

2. not having a common centre

3. a device for converting rotary motion to reciprocating motion

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eccentric [ek′sen·trik]

(science and technology)

Situated to one side with reference to a center.

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eccentric

eccentric head and shaft

Not having the same center or center line.

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Eccentric 

in astronomy, an auxiliary circle in the geocentric system of the world, introduced by Hipparchus to represent the annual revolution of the sun around the earth through motion along a circle with constant angular velocity. The nonuniformity of the sun’s motion along the ecliptic was attributed to the fact

Figure 1

that the sun moved (uniformly) along the circumference of an eccentric, whose center C did not coincide with the earth T (see Figure 1).

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Eccentric 

a circular disk whose axis of rotation does not coincide with its geometric center. In cam mechanisms, an eccentric, acting upon a rod that moves in a straight line, communicates to the rod a harmonic motion such that the displacement of the rod is proportional to the cosine (or sine) of the eccentric’s rotation angle. In linkage, an eccentric acts as a crank, that is, as a link that makes a complete revolution around its axis of rotation. Such an application of an eccentric is efficient when the crank (its throw equal to the eccentricity of an eccentric) must be very short. Eccentrics are also used in lathe attachments to clamp details that are being machined.