Homework SourseConsider a four bar linkage system with crank length 115 cm
Solution
The question is conceptually not correct , since in the question it has been mentioned that crank link i.e input link is 115 cm, coupler is 225 cm and crank output link is 345 cm.
Now the only link left is the fixed link which for the case (i) can be
I) for crank rocker the smallest link has to be adjacent to the fixed. Therfore smallest will be 115 cm since input is adjacent to fixed. there fore we have 2 possibilities as per grashoff\'s rule which state sum of smallest and largest has to be lesser or equal to other two links.
Case a) considering largest to be output link i.e 345 cm we have
115 + 345 = 225 + x => x= 235 cm ( fixed)
Case b) Fixed can be the largest link => 115 + X = 345 + 225 => x= 455 cm
II) Drag link or double crank : The shortest link has to be fixed one which is the fourth link missing as per question.
so we can say X+ 345 = 225 +115 but it gives X= -5 cm which is not possible
III) Double rocker : Concept says coupler is the smallest link but as per question coupler defined as 225 cm is not.
So, in the question by defining the names of the links you are defining that only fixed link has to be found out in each case as per my understanding.
Now Second alternative is that you provide that 3 links have length as 115, 225,345 cm ....What will be the fourth link and define the position of these pairs for the inversions listed below ?
Now you can find in this way a) fouth link smallest so X+345= 225 +115 so not possible
b) fourth link largest X+115 = 345 +225 So X= 455 cm which is possible
c) Not smallest or largest 115 +345 =225 +X so X= 235 cm which is possible
Now based on sub partsyou can decide the smallest has to be adjacent to fix for crank rocker, for double crank smallest is to be fixed and for double rocker smallest has to be coupler.
