BULETINUL INSTITUTULUI POLITEHNIC DIN IAŞI

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36 Radu Ibănescu and Cătălin Ungureanu Φ d F B h C A l R M m e O ϕ (t) G a Fig. 1 – Eccentric cam. h i diagram is obtained showing the dependence of the cam follower length with respect to the moment acting on the cam, so that the cam follower does not stick. The required length of the cam follower guide can be chosen from this diagram. 2. The Eccentric Cam Mechanism The eccentric cam mechanism consists of a disk of radius R actuated by a couple M m (Fig. 1). The disk can rotate about the fix point O located at the distance e from the centre of the circle. The cam follower is vertical and it has a horizontal bar at each of its ends. The bar at the bottom end lies on the cam. The bar at the top end is actuated by a spring having the spring stiffness k e and by a constant force F collinear to the spring. The disk weight is G and the weight of the cam follower is assumed to be very small and hence negligible. The friction coefficient between the cam follower and the disk and the cam follower and its guide is μ. The friction coefficient in the joint at O is μ 1 . All the dimensions are known and can be seen in Fig. 1. The problem is to determine the minimum value of the driving couple M m to maintain the mechanism in equilibrium at limit state. The disk and the cam follower are
Bul. Inst. Polit. Iaşi, t. LVIII (LXII), f. 3, 2012 37 drawn separately with all the forces (free body diagrams) in order to solve this problem. 3. The Equations of Equilibrium The cam follower is represented in Fig. 2. It is assumed that there is a small clearance between the cam follower and its guide. For this reason, the contact between the cam follower and its guide is at the points A and B, as it can be seen in Fig. 2. y Φ d F r + r F e B N r B h l 1 N r C N r A A F r fA F r fB F r fC C q O x Fig. 2 – The cam follower of the mechanism. The three equilibrium equations of the cam follower are: − FfC + NA − NB = 0 , (1) N − F − F − F − F = 0 , (2) C fA fB − N q − N l + N l + h) − ( F + F )( d + Φ) − F Φ 0 . (3) C The length l 1 is The length q is A 1 B ( 1 e fB = e l1 = l−R− esin φ . (4)
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