Lecture - 15 (Mechanical advantage, mechanism efficiency, toggle mechanism)

Mechanical advantage 

It is defined as the ratio of the force produced by a machine to the force applied to it, used in assessing the performance of machine. 

The combination of pulley system is shown in the below figure- 

Here for lifting download F force is required but the effort given to the system is 8 times less, which is the good example of mechanical advantage. For the above system mechanical advantage is 8

Mechanical advantage = load / effort 

• Mechanical advantage for linear motion is - 
  
• Mechanical advantage for angular motion is - 
  

Efficiency of system or mechanism

Efficiency of the system is defined as the ratio of output power to the input power.

PROBLEM- Find out mechanical advantage of the given mechanism having 100% efficiency.

Solution - In the sense of angular velocity

It means that above mechanism is toogle mechanism. 

Toggle mechanism 

Those mechanism whose mechanical advantage is so high that it approaches to infinity is called toggle mechanism. Due to high mechanical advantage, the force at output we get is excessively very high. Example of toggle mechanism is shown below

Toggle position is defined as the moment at which mechanism is at its extreme position where output force is very high and mechanical advantage tends to infinity.

Above mechanism at extreme position where mechanical advantage tends to infinity is shown below- 

Toggle position in four bar mechanism 

Toggle position of Rocker in four bar mechanism is when extreme position of output link is achieved, at 'β' = 0 degrees and 'β' = 180 degrees. 'β' is the angle between link 2 and link 3.

• LEFT EXTREME POSITION OF OUTPUT LINK ( when β = 0 degrees )

• RIGHT EXTREME POSITION OF OUTPUT LINK (when β = 180 degrees) -

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