8/3/2019 A7 Cam Design

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MEU304 Mechanics of Machinery

 Assignment 7 Cam Design x Submit on 18-10-

11

 Note: In the following problems use graphical solution unless mentioned otherwise 

1. A translating roller follower is offset to the right by 1 cm. The lift of the follower is 2 cm. The base circle

radius of the cam is 2.5 cm, and the roller radius is 0.8 cm. The cam rotates in the ccw direction. Lay out

the cam profile if (i) the rise is for 150o, the first 60o being at constant acceleration and the rest at

constant deceleration, (ii) dwell is for 30o, (ii) the return is for 120o of cam rotation with cycloidal

motion and (iv) the second dwell is for 60o.

2. An oscillating flat-face follower is to rise through an angle of 20o with modified uniform motion# in 180o.

This is followed by a dwell for 30o and return with SHM for 150o of cam rotation. Layout the cam

 profile. There are several variables to be assumed and they are to be stated clearly.

# A modified uniform motion is a parabolic motion except in the middle portion where uniform velocity motion is used

to connect the uniform acceleration portions at the two ends with the uniform velocity region.

 Exercise 7 

1. The follower rises through a distance L with cycloidal motion for  β θ ≤≤0 where θ is the cam rotation.

Determine the value of θ for which the acceleration of the follower is maximum. Find the velocity and

the jerk for θ=β /2. The cam rotates at constant speed ω.

2. Construct a cam profile for a disk cam with an offset translating flat-faced follower for generating the

following motion. Angle of rotation of the cam 0 to 90o: dwell, 90o to 150o : 3 cm rise with parabolic

motion, 150o to 270o: dwell, 270o to 360o: fall with simple harmonic motion. The offset is 2 cm and take

the base circle diameter as 5 cm.

3. Write a short note on cam manufacturing methods.

4. (Study this mechanism) Figure 1 shows an intermittent motion mechanism called Geneva mechanism.

The crank is the input that rotates at uniform speed. The slotted wheel gives an intermittent output. In the

fig. the pin of the crank is about to enter smoothly into a slot and the motion of wheel begins and the

wheel stops when the pin goes out of the slot. The crank is shaped in such a way that the wheel remains

locked until the pin enters the next slot. Analyze the mechanism in detail-  Ref.Shigley. Obtain

expressions for angular velocity and acceleration ratios (ω3/ω2 and α3/α2) of this drive. What is the

maximum acceleration and when does it occur? Plot he variation of angular displacement, velocity and

acceleration of the wheel wrt  the crank rotation for one complete rotation of the wheel. Mention an

application of this mechanism.

 Fig.1