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PY 2: GATE ME 2020 Official Paper: Shift 2

Option 3 : 3

CT 1: Indian History

20365

10 Questions
10 Marks
6 Mins

**Explanation:**

The following points are important about the inversion of a kinematic chain:

- The inversions of a kinematic chain are obtained by fixing different links one at a time.
- For a kinematic chain consisting of 4 links, the maximum possible kinematic inversions are four.
- The
**qualitatively distinct inversions mean**that all the inversions should be**able to convert the input into a distinct output**.

A 4 revolute pair chain is called the Grashof chain if the following condition is satisfied:

**l + s < p + q (Class-I four-bar linkage)**

i.e. the sum of the shortest and longest link should not be greater than the other two.

If a Grashof chain with 4 revolute pairs is considered then the following **three distinct** inversions are possible.

**Double crank:**

A double-crank results when the shortest link is fixed.

In this mechanism both the driving and the driven links make a complete rotation.

**Double rocker:**

A double rocker results when the shortest link is made coupler.

In this mechanism, both the driving and the follower links make only oscillations and none of them makes a complete rotation.

**Crank-rocker:**

If the link adjacent to the shortest link is fixed then it results in a crank-rocker.

In this mechanism, the driving link makes complete rotation and the driven link makes only oscillation.

**Class-II four-bar linkage**:

When the sum of the lengths of the largest and the shortest links is more than the sum of the lengths of the other two links, the linkage is known as **class-II, four-bar linkage** i.e. **l + s > p + q.**

In such links, fixing of any of the links always results in a **rocker-rocker or double rocker mechanisms**.

In other words, the mechanism and its inversions give the same type of motion i.e. (**not distinct**).