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Sunday, April 26, 2020

CAM & FOLLOWER:- (Part-4) (Radial Cam With Roller Follower)

CAM & FOLLOWER:- (Part-4) (Radial Cam With Roller Follower Tutorial) :-

⇒Construction of CAM Profile for Radial CAM / Offset CAM with Roller Follower:-

In order to draw the cam profile for a radial cam, first of all the displacement diagram for the given motion of the follower is drawn. Then by constructing the follower in its proper position at each angular position, the profile of the working surface of the cam is drawn.

In constructing the cam profile, the principle of kinematic inversion is used, i.e. the cam is imagined to be stationary and the follower is allowed to rotate in the opposite direction to the cam rotation. 

The construction of cam profiles for different types of follower with different types of motions are discussed in the following examples.

Q. . A cam, with a minimum radius of 25 mm, rotating clockwise at a uniform speed is to be designed to give a roller follower, at the end of a valve rod, motion described below :
1. To raise the valve through 50 mm during 120° rotation of the cam ;
2. To keep the valve fully raised through next 30°;
3. To lower the valve during next 60°; and
4. To keep the valve closed during rest of the revolution i.e. 150° ; The diameter of the roller is 20 mm and the diameter of the cam shaft is 25 mm. Draw the profile of the cam when ,the line of stroke of the valve rod passes through the axis of the cam shaft

Sol. 
Construction

(a) Profile of the cam when the line of stroke of the follower passes through the axis of the cam shaft :-
The profile of the cam when the line of stroke of the follower passes through the axis of the cam shaft, as shown in Fig. 3.3.

STEPS:-
1. Draw a base circle with center O and radius equal to the minimum radius of the cam.

Fig 3.1

2. Draw a prime circle with centre O and radius, 
     OA = Min. radius of cam + 1/2 Dia. of roller = 25+(1/2)x 20=35 mm 
3. Draw angle AOS = 120° to represent raising or out stroke of the valve, angle SOT = 30° to                   represent dwell and angle TOP = 60° to represent lowering or return stroke of the valve. 
4. Divide the angular displacements of the cam during raising and lowering of the valve (i.e. angle           AOS and TOP ) into the same number of equal even parts as in displacement diagram.
5. Join the points 1, 2, 3, etc. with the centre O and produce the lines beyond prime circle as shown        in Fig. 3.2. 
6. Set off 1B, 2C, 3D etc. equal to the displacements from displacement diagram. 
7. Join the points A, B, C ... N, P, A. The curve drawn through these points is known as pitch curve.
8. From the points A, B, C ... N, P, draw circles of radius equal to the radius of the roller. 
9. Join the bottoms of the circles with a smooth curve as shown in Fig. 3.2. This is the required                profile of the cam. 

Fig 3.2


(b) Profile of the cam when the line of stroke is offset 15 mm from the axis of the cam shaft :-

STEPS:-
1. Draw a base circle with centre O and radius equal to 25 mm. 
2. Draw a prime circle with centre O and radius OA = 35 mm. 
3. Draw an off-set circle with centre O and radius equal to 15 mm. 
4. Join OA. From OA draw the angular displacements of cam i.e. draw angle AOS = 120°, angle SOT = 30° and angle TOP = 60°. 
5. Divide the angular displacements of the cam during raising and lowering of the valve into the same number of equal even parts (i.e. six parts ) as in displacement diagram. 
6. From points 1, 2, 3 .... etc. and 0′,1′,3′ , ...etc. on the prime circle, draw tangents to the offset circle. 7. Set off 1B, 2C, 3D... etc. equal to displacements as measured from displacement diagram. 
8. By joining the points A, B, C ... M, N, P, with a smooth curve, we get a pitch curve. 
9. Now A, B, C...etc. as centre, draw circles with radius equal to the radius of roller. 
10. Join the bottoms of the circles with a smooth curve as shown in Fig. 3.3. This is the required profile of the cam. 
Fig 3.3

Credit (Resources) :- Theory of Machine by khurmi & Gupta 

To Download the book Click Here.

Click Here to see the CAM & Follower (part-1)

Click Here to see the CAM & Follower (part-2)

Click Here to see the CAM & Follower (part-3)

Stay tuned with us.

ⒸMukesh Ch. Joshi
@ joshimukesh410820@gmail.com

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