EXPERIMENT No. 5

                                                     EXPERIMENT No. 5

7.0    1. Stepwise procedure for drawing displacement diagram-

1. By taking proper scale mark out stroke, dwell, return stroke and dwell as per the data  

given in problem.

2. Mark lift of follower on vertical line.

3. make divisions as per the motion of follower. like Uniform velocity, SHM, and uniform

acceleration and retardation.

4. Make same no. of equal divisions( as that of vertical lift of follower.) of the out stroke

and return stroke.

5. By considering motion of the follower connect the points to form a straight line or a

curve, as the case may be.

            2.  Stepwise procedure for drawing cam profile.

1. 1.With proper scale draw the displacement diagram with outstroke, dwell, return stroke and lift  of the follower, considering motion of the follower.

2. Draw the axis considering axis of the follower and axis of cam shaft. See whether there is a offset.

3. Draw base circle, mark trace point A with A as center.

4. Mark AOS out stroke , SOT dwell and TOP return stroke with the given angles.

5. Divide the angular displacements during out stroke and return stroke in the same no. of equal parts as in displacement diagram.

6. Join points 1,2,3 etc. and 1’,2’,3’ etc. with ‘O’ .and produce beyond the base circle.

7. Set off 1B, 2C, 3D etc. and  0’H,  1’J   etc. from the displacement diagram.

             8. Join points A,B,C……M,N,P with a smooth curve  

9.0 Student Related Activity:

We know about the valves that let the air/fuel mixture into the engine and the exhaust out of the engine. The camshaft uses lobes (called cams) that push against the valves to open them as the camshaft rotates; springs on the valves return them to their closed position. This is a critical job, and can have a great impact on an engine's performance at different speeds. On the next page of this article you can see the animation we built to really show you the difference between a performance camshaft and a standard one.

10.0 Qustions for confirmation of learning:-

1.  A cam is a mechanical member which is used to transmit a rotary motion into reciprocating or oscillatory motion of another mechanical member called as follower.

2. It is the smallest circle that can be drawn to the cam profile from the center of rotation of cam.

3. Dwell period is the period when there is no movement of follower is taking place.

4. Offset circle is the circle drawn by taking a radius equal to the distance of the follower axis  which is some distance away  from the cam axis.

5. It is the point on the follower which is used to generate the pitch curve. Trace point represents the point on the knife edge in case of knife edged follower and the center of the roller in case of roller follower.

11.0 Conclusion/ Result:

            1. Pitch circle.   2. Higher pair.    3. remains stationary.      4. perpendicular. 5. away

Application in operating inlet and exhaust valves of I.C. engines, automatic attachments  

 of Machineries, Paper cutting machines, spinning and weaving textile machines feed mechanism of automatic lathes etc. Another device such as gear train can be used with special attachments instead of a combination of cam and follower to give a certain motion for a particular time repeatedly.

12.0 Questions:

1. Follower motion is predetermined and will be according to the shape of the cam. When cam rotates follower reciprocates or oscillates to give the desired motion. It follows cam.

2. As cam and follower have line contact between them when relative motion  takes place, so it is higher pair. Relative motion between cam and follower is partly turning and partly sliding.

3.                     Radial cam                                                     Cylindrical cam

 a) the follower reciprocates or oscillates                a)  the follower reciprocates or oscillates in a direction perpendicular to the cam axis                  in a direction parallel to     the cam axis     

b) follower is mounted over the periphery of          b)  the follower rides in a grove at it’s

           cam profile.                                                                 cylindrical surface.

4. i)  Radial follower with radial cam                       ii) Offset follower with radial cam.                                                      

                                                    

     

 iii) Cylindrical cam and follower.     

 

6. Pressure angle is included angle at any point on the pitch curve between line of motion of the 

follower and the normal to that point on the cam profile. If pressure angle is too large, reciprocating follower will jam in it’s bearing.

8. Wear resistant and heat resistant are the properties which cam should posses for reliability and durability.

9. i) Reliable and durable mechanism           ii)  Repair and malignance is easy.   iii)  Replacement takes less time compared to other motion transmitting devices.