four-bar chain (or quadratic cycle chain)

FOUR-BAR CHAIN (OR QUADRATIC CYCLE CHAIN)

• A four-bar chain is the most fundamental and the simplest kinematic chain. It consists of four links and four turning pairs, as shown in Fig.1.26.

• Since the four-bar chain looks like a cycle frame, it is also known as quadric cycle chain.

• Four links of a four-bar chain are:

1. Frame: The fixed link is known as frame (link AD in Fig.1.26)

2. Crank (or driver): A link that makes complete revolutions is called as crank (link AB in Fig. 1.26).

3. Coupler (or connecting rod): The link opposite to the fixed link is known as coupler (link BC in Fig.1.26). In other words, the coupler is the link which is not connected to the frame.

4. Lever (or rocker or follower): The link which makes oscillation (ie., a partial rotation) is known as lever (link CD in Fig.1.26).

• In most practical applications, the electric motors are used to drive the mechanisms. In such case, one of the link must be a crank to receive power from motor.

• For four-barin, Grashof's law is used to test whether any of the links in the chain can be a crank.