Knife edge follower:
Draw profile of a cam operating a knife edge follower for the given data :
Maximum lift of the follower = 4.5 cm
Angle for rise of follower having SHM = 150o
Angle for dwell period after rise = 60o
Angle for return of the follower having uniform velocity = 100o
Least radius of the cam = 3 cm
The cam rotates at a regular velocity of 120 rpm.
Find out the maximum velocity & acceleration of the follower throughout rise and return.
Solution
The maximum lift (L) = 4.5 cm ,Speed of the cam = 120 rpm, Angle for rise (θo) = 150o Angle for return (θr) = 100o
Let suitable scale.
Draw cam profile as:
(a) Draw a circle having minimum radius of the cam to scale that was chosen for displacement diagram.
(b) Denote the sense of rotation of the cam. In the current example, it is not provided and it can be supposed say clockwise sense. Situate initial position of the follower. As eccentricity is not given, the follower axis might be supposed to pass through the centre of the cam.
(c) For drawing cam profile cam is supposed stationary & follower is taken around the cam in a sense opposite to the sense of rotation of the cam. Beginning from zero, plot for angle for rise θo. Next mark for dwell period that is 60o and then mark for return, that means. θr.
(d) Draw semi-circle & divide into similar number of equal parts as it is completed in displacement diagram and in this case it is 6 equal portions. Draw radial lines.
(e) On the extended radial lines, transfer the equivalent displacement for the follower from displacement diagram above the base circle, that means 1 - 1′, 2 - 2′, etc.
(f) Draw an arc of radius 7.5 cm for the dwell period having cam centre like the centre and join the points entire 0′ prime, 2 ′ . . . 12′ by a smooth curve. this is the needed cam profile.
Angular speed of the cam =
Maximum velocity during rise =
Maximum acceleration throughout rise =
= 511.9 cm/s or 5.119 m/s2
Maximum velocity during return =
Acceleration = ∞.