7-IC Analysis - AME 352 INSTANT CENTERS Velocity Analysis...

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AME 352 INSTANT CENTERS P.E. Nikravesh 1 Velocity Analysis With Instant Centers In this lesson we use instant centers to perform velocity analysis for several mechanisms. It is always assumed that either the angular velocity of one link or the linear velocity of one point is given. A velocity analysis can provide magnitude and direction for other unknown angular and linear velocities. Four-bar Mechanism Assume the angular velocity of link 2 of this four-bar is given. We are asked to find: a) Velocity of point P on link 3 ; b) Angular velocity of link 4 . We solve the problem using the instant center method. We already know how to find the IC’s for a four-bar. (1) (2) (3) (4) P ± 2 P 1,2 I 2,3 I 3,4 I 1,4 I 1,3 I 2,4 I (1) (2) (3) (4) a) Selecting the right combination of IC’s makes velocity analysis with the instant center method a simple task. In this problem, the angular velocity of link 2 is known, and we are asked to find the velocity of point P on link 3 . We need to pick a third link, and that link is always the ground, link 1 . So, we pick the three centers between these three links: I 1,2 , I 2,3 , and I 1,3 . These centers are on a straight line. We can ignore other centers and links. Link 2 rotates about I 1,2 . The magnitude of the velocity of I is computed as V I = 2 R I I 1,2 and its direction is as shown. I is also a point on link 3, and link 3 rotates about I 1,3 . The angular velocity of link 3 is computed as 3 = V I / R I I 1,3 , CW.
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7-IC Analysis - AME 352 INSTANT CENTERS Velocity Analysis...

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