WEEK 5 Dynamics of Machinery References Theory of

WEEK 5 Dynamics of Machinery • References • Theory of Machines and Mechanisms, J. J. Uicker, G. R. Pennock ve J. E. Shigley, 2003 Prof. Dr. Hasan ÖZTÜRK 1

Prof. Dr. Hasan ÖZTÜRK CAMS A cam is a rotating machine element which gives reciprocating or oscillating motion to another element known as follower. The cam and the follower have a line contact and constitute a higher pair. The cams are usually rotated at uniform speed by a shaft, but the follower motion is predetermined and will be according to the shape of the cam. The cam and follower is one of the simplest as well as one of the most important mechanisms found in modern machinery today. The cams are widely used for operating the inlet and exhaust valves of internal combustion engines, automatic attachment of machineries, paper cutting machines, spinning and weaving textile machineries, feed mechanism of automatic lathes etc. retaining spring 2

ANALYSIS OF AN ECCENTRIC CAM (a) Eccentric plate cam and flat-face follower; (b) free-body diagram of the follower; (c) free-body diagram of the cam. An eccentric is the name given to a circular plate cam with the cam-shaft mounted off center. The distance e between the renter of the disk and the center of the shaft is called the eccentricity. Prof. Dr. Hasan ÖZTÜRK 3

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P: preload F 23 is the critical condition. It must always have positive value. When F 23=0, the contact is lost and hence cam and follower are no longer touching each other. It means that follower is no more following the profile of the cam. It is free and floating in the air. Prof. Dr. Hasan ÖZTÜRK 5

which can be written, through a trigonometric identity, as: Prof. Dr. Hasan ÖZTÜRK 6

Plot of displacement, velocity, acceleration, and contact force for an eccentric cam system; Jump (float) may occur (F 23=0) 7 Prof. Dr. Hasan ÖZTÜRK

Graph of Torque Components and Total Cam-Shaft Torque Prof. Dr. Hasan ÖZTÜRK 8

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Displacement diagram and derivatives for full-rise parabolic motion. Prof. Dr. Hasan ÖZTÜRK 11

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Displacement diagram and derivatives for full-rise parabolic motion. Prof. Dr. Hasan ÖZTÜRK 13

Harmonic Motion: Parabolic Motion: Prof. Dr. Hasan ÖZTÜRK 14

EXAMPLE: Parabolic Motion Prof. Dr. Hasan ÖZTÜRK 15

The cam-contact force can be written as: Note that jump will first occur at = t=600 because this is the first position where F approaches zero. Prof. Dr. Hasan ÖZTÜRK 16

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