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Kinematics of Machine Lab Experiments

To draw acam profile



Aim

To draw acam profile.

Theory

Types of Follower motion

The construction of cam profiles for different types of follower with different types ofmotions are discussed

Problem

A cam is to give the following motion to a knife-edged follower : 1. Outstroke during 60° of cam rotation ; 2. Dwell for the next 30° of cam rotation; 3. Return stroke during next 60° of cam rotation, and 4. Dwell for the remaining 210° of cam rotation. The stroke of the follower is 40 mm and the minimum radius of the cam is 50 mm. The follower moves with uniform velocity during both the outstroke and return strokes. Draw the profile of the cam when (a) the axis of the follower passes through the axis of the cam shaft, and (b) the axis of the follower is offset by 20 mm from the axis of the cam shaft.

Construction

construction

First of all, the displacement diagram, as shown in Fig. , is drawn as discussed in the following steps :

  1. Draw a horizontal line AX = 360° to some suitable scale. On this line, mark AS = 60° to represent outstroke of the follower, ST = 30° to represent dwell, TP = 60° to representreturn stroke and PX = 210° to represent dwell.
  2. Draw vertical line AY equal to the stroke of the follower (i.e. 40 mm) and complete the rectangle as shown.
  3. Divide the angular displacement during outstroke and return stroke into any equal number of even parts (say six) and draw vertical lines through each point.
  4. Since the follower moves with uniform velocity during outstroke and return stroke, therefore the displacement diagram consists of straight lines. Join AG and HP.
  5. The complete displacement diagram is shown by AGHPX.

The profile of the cam when the axis of the follower passes through the axis of the cam shaft, is drawn as discussed in the following steps:

diagram
  1. Draw a base circle with radius equal to the minimum radius of the cam (i.e. 50 mm) with O as centre.
  2. Since the axis of the follower passes through the axis of the cam shaft, therefore mar ktrace point A, as shown.
  3. From OA, mark angle AOS = 60° to represent outstroke, angle SOT = 30° to representd well and angle TOP = 60° to represent return stroke.
  4. Divide the angular displacements during outstroke and return stroke (i.e. angle AOS andangle TOP) into the same number of equal even parts as in displacement diagram.
  5. Join the points 1, 2, 3 ...etc. and 0ʹ ,1ʹ , 2ʹ , 3ʹ , .. etc. with centre O and produce beyond the base circle.
  6. Now set off 1B, 2C, 3D ... etc. and 0ʹ H,1ʹ J ... etc. from the displacement diagram.
  7. Join the points A, B, C,... M, N, P with a smooth curve. The curve AGHPA is the complete profile of the cam.

Profile of the cam when the axis of the follower is offset by 20 mm from the axis of the camshaft

The profile of the cam when the axis of the follower is offset from the axis of the cam shaft, is drawn as discussed in the following steps:

diagram-1
  1. Draw a base circle with radius equal to the minimum radius of the cam (i.e. 50 mm) with O as centre.
  2. Draw the axis of the follower at a distance of 20 mm from the axis of the cam, which intersects the base circle at A.
  3. Join AO and draw an offset circle of radius 20 mm with centre O.
  4. From OA, mark angle AOS = 60° to represent outstroke, angle SOT = 30° to represent dwell and angle TOP = 60° to represent return stroke.
  5. Divide the angular displacement during outstroke and return stroke (i.e. angle AOS and angle TOP) into the same number of equal even parts as in displacement diagram.
  6. Now from the points 1, 2, 3 ... etc. and 0 ,1 , 2 ,3 ʹ ʹ ʹ ʹ ... etc. on the base circle, draw tangents to the offset circle and produce these tangents beyond the base circle as shown in Fig.
  7. Now set off 1B, 2C, 3D ... etc. and 0ʹ H,1ʹ J ... etc. from the displacement diagram.
  8. Join the points A, B, C ...M, N, P with a smooth curve. The curve AGHPA is the complete profile of the cam.

Conclusion

Cam profiles under different conditions were drawn.