Chapter 2

The Grashof Condition - As Simple As It Gets

The Grashof condition is the condition that must be proven to be true so that one link on a system is able to make a full revolution. This condition is listed as the following: 

S + L < P + Q

This equation written out is 

Shortest Link + Longest Link < Remaining Link 1 + Remaining Link 2

The answer to the equation after plugging in all of the values from your own links will then determine whether or not the linkage is considered to be Grashof. This relationship is one that can make a potentially impossible linkage become much more manageable or at least let you know you need to redo something before moving on. The values on both sides of the equation will help you to understand the motion that will occur. 

Classes

The values you get on each side of the equation will then allow you to determine what type of class it will be. These classes are to help you determine what inversion of the fourbar linkage it will be. There are three different classes. 

    Class 1

    Class 1 is the class that will give a Grashof linkage. The equation is the main governing equation: 

S + L < P + Q

    In this class there is at least one link that will complete a revolution. 

    Class 2

    Class 2 is all non-Grashof. This inversion gives linkages that are triple rockers. The values you get satisfy this equation: 

S + L > P + Q

    This is a type of linkage in which none of the links can make a full revolution. 

    Class 3

    Class 3 is the class that is a special-case Grashof. The equation explain this is:

S + L = P + Q

    This is the type of linkage that has two change points per revolution. 

I found this topic to be interesting in the way that it is able to tell you the type of movement that you will get just by using the equation and understanding the meaning behind it.