Regenerative Breaking G3

 

Mechanism With Higher Pair

 

Basic definitions-

Machines is a device which is used to accomplish work. Mechanism is the mechanical portion of a machine that has the function of transferring motion and forces to an output whit the help of a power source.

Mechanisms are collection of rigid members or links connected by joints. In other words, if several bodies are grouped in such a way that the motion of one cause constrained and  predictable motion to the others, it is known as mechanism.

Rigid and Resistant bodies-

If a body undergoes the action of forces and it does not suffer any distortion, it is said to be a rigid body.

Resistant bodies are those which are rigid for a cause. For example, in a case of hydraulic press, fluids can also act as resistant bodies when they are compressed.

Links-

A resistant body or group of resistant bodies connecting each other and preventing their relative motion is called as a link.

It can be also defined as a member or group of members in a mechanism which have relative motion when connecting to other members.

Links are classified in binary, ternary, and quaternary.

    

 

Kinematic Pair-

A joint of two links having relative motion between them is called a kinematic pair.

 

Degrees of freedom (DOF)-

It is defined as the number of independent relative motion a pair can have.

DOF=(6 – number of constraints)

Kutzbach Criteria-

In planer mechanisms (2-Dimensional), degrees of freedom is determined by the Kutzbach criteria.

DOF = 3( L-1)- 2J- H

Here,

         L is number of links.

         J is number of lower pairs.

        H is number of higher pairs.

 

Grubler’s Criteria-

When the number of higher pairs in Kutzbach criteria is 0, then the equation obtained is Grubler’s criteria.

DOF = 3( L-1)- 2J

Here,

         L is number of links.

         J is number of lower pairs.

 

Higher Pair Mechanisms-

A higher pair is a constraint which requires a line contact or point contact between the elemental surfaces.

For example, contact between a cam and follower is a higher pair referred as a cam joint.

In higher pairs, only one point or line form a joint between two links. The elements of higher pair must have a curve in its shape.

 

What do you need to know about higher pairs ?

1.     While in motion, when two elements have point or line contact then the pair is referred to as higher pair.

2.     In higher pairs, to form a joint between two links, only one point or line is responsible.

3.     The shape of the elements of a higher pair must have a curve in it.

4.     Some examples of higher pair mechanism are Belt, rope and chain drives, gears, the cam and follower ball and roller bearings, etc.

 

Cam and Follower Mechanism-

It is important to keep the surface contact between the cam profile and the follower at all times of rotation and any motion for proper functioning of the cam and follower. For this, spring force, gravitational force, or positive drive are used in the mechanism.

When one point or line form a joint between two links, it is called a higher pair. In a cam-follower system two such higher pair will be included. A higher pair mechanism is known as cam and follower.

A cam and follower mechanism includes a profiled shape which is mounted on a shaft that causes follower to move. To convert rotary to linear (reciprocating) motion, cams are used. As the cam rotates, the follower rises and fall in a process called as reciprocating motion.

The working principle of Cam and Follower depends on the mechanism of both Cam and Followers in combination.

Cams are either in rotary motion or reciprocating motion or oscillating motion. In cam follower mechanism, the driver member is called as cam and the driven member is the follower.

Importance of Cam and followers-

In the field of mechanical engineering, the cam follower mechanism plays an important role in achieving even distribution of forces in a single machine.

Attaching a cylindrical roller in a machine component voluntary movement can be achieved.

Varieties of linear motions can found by utilizing the mechanism. Apart from that, it can be used in a machine component despite of the shape and size of the nut.

Moreover, the mechanism is entirely adaptive i.e., it can use in a soda machine to  an aircraft application.

Flat followers are used to operate the valves of an engine whereas roller followers are used in oil and stationary engines.

Terminology used in cam and follower-

1.     Cam Profile:- Cam profile is outer surface of disc cam.

2.     Base Circle:- Base circle is the smallest circle, it is tangential to the cam profile.

3.     Trace Point:- It is a point on the follower, trace point motion tells the movement of the follower.

4.     Pitch Curve:- Pitch curve is the path formed by the trace point when the follower is rotated about a stationery cam.

5.     Pitch Point:- It is the point of maximum pressure angle.

6.     Prime Circle: This is a circle that is tangential to the pitch curve and concentric to the base circle.

7.     Pitch Circle: It is a circle drawn from the cam center which passes through the pitch point.

8.     Pressure Angle: It is the angle between the direction of the follower movement and the normal to the pitch curve.

Cam mechanism-

A cam is a rotating or sliding piece in the mechanical linkage which is often a part of a rotating wheel or the shaft that strikes the lever at one or multiple points on its circular path.

Cam, mechanical component, is always rotating circle or eclipse about the minor axis of the Follower.

Hence, it can be understood easily that Cam is a mechanical component that transmits reciprocating, oscillating, or linear motion to the follower. Cam’s shape is usually an oval. In an oval-shaped cam we can see the movements which will form the outer burge, which will be periodic to its locus.

Follower mechanism-

Follower is a mechanical component which is responsible for the push and pulls of the Cam. A follower helps to transfer motion to required machine part. The Follower rotates in a circular or oscillating arc.

A follower follows the motion of cam by direct contact.

For the main mechanism of the cam and follower, the mechanism of cam and the mechanism of the follower depends on each other.

Application of cam and follower-

• Widely used for operating inlet and exhaust valve of an internal combustion engine.
• Used in wall clocks.
• Used in the feed mechanism of the automatic Lathe Machine.
• Used in screw pieces of machinery.
• Used in gear cutting machinery.
• The main mechanism in hydraulic systems is cam follower.
• In that case, the mechanism is dependent on the fluid pressure.
• Cam and follower mechanism are used in different parts that are automated in motion.