To study and analyse Pawl and Ratchet Mechanism and understand it's Functioning and application
Theory
A ratchet is a mechanical device that allows continuous linear or rotary motion in only one direction while preventing motion in the opposite direction. Ratchets are widely used in machinery and tools.
A Ratchet wheel provided with suitably shaped teeth, receiving an intermittent circular motion from an oscillating or reciprocating member.
When arm moves counterclockwise, driving pawl will force the wheel through a fractional part of a revolution dependent upon the motion of arm. When the arm moves back (clockwise), driving pawl will slide over the points of the teeth while the wheel remains at rest because of locking pawl , and will be ready to push the wheel on its forward (counterclockwise) motion as before.
PAWL AND RATCHET MECHANISM
The amount of backward motion possible varies with the pitch of the teeth. This motion could be reduced by using small teeth, and the expedient is sometimes used by placing several pawls side by side on the same axis, the pawls being of different lengths.
Application
In Shaper machine :
Pawl and Ratchet is used in automatic table feeding mechanism of shaper. This is done by rotating a ratchet wheel, mounted at the crossfeed screw . This enables a correspoing equal rotation of the crossfeed screw after each stroke
In Spanner :
A Ratchet incorporates a reversible ratcheting mechanism which allows the user to pivot the tool back and forth to turn it's socket instead of removing and repositioning a spanner to do so
Simulation Video
CAD Model
Other mechanism that gives intermittent motion
Geneva Mechanism, one of the most commonly used devices for producing intermittent rotary motion, Characterized by alternate periods of motion and rest with no reversal in direction. It is also used for Indexing