Theory of Mechanisms & Machines

Course Project 

Title of the Project: QUICK RETURN MECHANISM

INTRODUCTION

A quick return mechanism is a mechanism that converts rotary motion into reciprocating motion at different rate for its two strokes. When the time required for the working stroke is greater than that of the return stroke, it is a quick return mechanism. It yields a significant improvement in machining productivity. Currently, it is widely used in machine tools, for instance, shaping machines, power-driven saws, and other applications requiring a working stroke with intensive loading, and a return stroke with non-intensive loading.

This mechanism is made of a driving crank and of a driven slider crank in the considered configuration the fixed pivot of the driven crank is located on the outside of the circle on which the end of the driving crank moves this leads to an alternated motion of the slider crank

The angular speed of the driven crank is variable .the duration of the motion for its part corresponding to the blue arc is shorter than the one related to the red arc .this is why this device is named as the quick return mechanism ,which was used in crank shaper with the slow part or the stroke being used for the working time of the tool and the quick part for the non productive time

THEORY

If we go for the classification of the mechanism then we have simple mechanism, Means the mechanism with four links whereas the mechanism with more than four links as known as “compound mechanism” as we know that mechanism is used that for transformation of the motion.

When the mechanism has to do specific task it will became a machine in that case every component should has to design to perform specific tasks according to the requirement there are various type of mechanism including, Double crank mechanism, Single slider crank mechanism, Crank shaper mechanism, but among all the mechanism the common thing is that all of them are linkage

HISTORY

Whitworth quick return mechanism was developed by the British manufacturer Sir Joseph Whitworth around 1840.He was a machine tool builder and he sensed that speed of cutting tool on the shaping machines in his factory were not quick enough. So he adopted an inversion of the slider crank mechanism and fixed the crank. In the resultant mechanism backward stroke was faster than the forward stroke hence this mechanism speeded up the return of the cutting tool to the beginning of the cutting stroke thus saving time.

Working of mechanism:

Working stroke- theta2 =α

Return stroke- theta1= β

Working > Return

Fig.1.2- working

.

2

Working stroke

1

Return stroke

advantages of quick return mechanism Whitworth quick return mechanism is a device where reciprocation

motion in forward stroke is slower then the return stroke Quick return mechanism A reciprocating motion, for operating the

tool of a shaping machine etc, in which the return is made more rapidly than the cutting stroke, so as to reduce the idling time.

disadvantages of quick return mechanism As we know that Quick-Return Mechanism consist of various components these

are used to transformation of motion and they have relative motion with each other due so some disadvantages will occur.

As we know that in all type of mechanisms in the common thing is that all of that are linkages and balancing of linkage is also big problem.

As there is faster motion in the piston it causes the heat which results in loss of energy via heat

And another type of disadvantage is friction in the slider and in piston More power is required to work the mechanism as the normal.

CONCLUSIONS

A quick return mechanism is an apparatus that converts circular motion (rotating motion following a circular path) into reciprocating motion (repetitive back-and-forth linear motion) in presses and shaping machines, which are utilized to shape stocks of metal into flat surfaces, throughout mechanical engineering.

REFERENCES

WWW.Wikipedia.COM TCSME.ORG Transactions of the Canadian Society for Mechanical Engineering, Vol.

33, No. 3, 2009 WWW.YOUTUBE.COM