Quick Return

UNIVERSITY OF MAURITIUS FACULTY OF ENGINEERING MECHANICAL AND PRODUCTION ENGINEERING DEPARTMENT E443 – Beng(Hons.) Mechanical Engineering (Minor: Energy Systems)

MECH 2012Y Mechanics of Materials II Quick Return Mechanism GROUP 9 1. BADULLA Muhammad Twaaha

(1311150)

-Date of Experiment: - Date Submitted:

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TABLE OF CONTENTS

1. INTRODUCTION 2. OBJECTIVES

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3. APPARATUS USED

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4. PROCEDURES 4 5. THEORY 4 6. RESULTS 5 7. OBSERVATION 6 8. CONCLUSION 8 9. REFERENCES 8

Whitworth’s Quick Return Mechanism 2

1. INTRODUCTION The implementation of a Whitworth Quick Return Mechanism can be useful for applications requiring slow initial force and a quick reset operation. The Whitworth quick return mechanism converts rotary motion into reciprocating motion, but unlike the crank and slider, the forward reciprocating motion is slower rate than the return stroke. 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.

2. OBJECTIVES The objective of this experiment is to investigate the performance of a Whitworth’s Quick Return Motion and to verify that the motion does have a quick return stroke and a slow cutting or forward stroke.

3. APPARATUS USED Protractor 1&2(0° - 360 °)

Leve r

Cran Verni er Scale

Figure 1: Whitworth’s quick return mechanism apparatus

4. PROCEDURES 3

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Starting with the crank in the horizontal direction, it was rotated through an angle of 45 ° clockwise.

2. 3. 4. 5.

The displacement of the slider was measured via use of the Vernier scale. The relative positions of the crank and the connecting rod are drawn. The experiment was repeated for increments of 45° till 360°. Packing blocks of the following dimensions 6.40 and 12.70 mm respectively were then used to raise of the height of the slider and steps 1-4 were repeated.

6. THEORY

Figure 2: Whitworth’s quick return mechanism Link 1 on the top diagram is extended to point A. Attached to point A is another link with a pivot. The other end of link terminates in a slider. The link POA rotates about O. The mechanism is driven by crank PC which rotates about C with constant velocity. The slider at P slides along POA as the crank is turned. Its path is shown by the dashed circle, centered on C and through P. Clearly when P is at P1 the slider S is at the outer extremity of its travel. When P is at P2 the slider is at the inner extremity of its travel. Now as PC rotates with constant velocity the time taken to go from P1 to P2 is less than that taken to go from P2 to P1. However, during both those time intervals the slider S is moving the same distance. Therefore, the speed of S is different during the different parts of the cycle. During the shorter time interval P1 to P2 the slider has the greater speed and during the interval P1 to P2 it has the slower speed. Thus P1 to P2 is the quick return and P2 to P1 the slower cutting stroke. Thus the overall performance of this mechanism is to provide a high power forward cutting stroke with a low power and higher quick return in preparation for the next cut.

6. RESULTS 4

Table 1: Raw data without Protractor 1(Crank angle)/° 45 90 135 180 225 270 315 360

packing blocks Protractor 2/° 41 77 112 149 191.5 246.5 309 0

Lever/cm 2.64 7.70 12.28 15.16 15.86 12.54 3.92 0

Table 2: Raw data with packing block 6.4mm Protractor 1(Crank Protractor 2/° angle)/° 45 41 90 77 135 112 180 149 225 191.5 270 246 315 309 360 0 Table 3: Raw date with packing block 12.7mm Protractor 1(Crank Protractor 2/° angle)/° 45 41 90 77 135 112 180 149 225 191.5 270 246 315 309 360 0

7.OBSERVATIONS

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Lever/cm 2.48 7.44 12.06 15.04 15.9 12.82 4.14 0

Lever/cm 2.32 7.18 11.80 14.90 15.96 13.08 4.38 0

EXP I: Stroke 18 16 14 12 10

Stroke/cm

8 6 4 2 0

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50

100

150

200

250

300

350

400

Crank rotation/°

Graph 1

EXP II(6.4mm): Stroke 18 16 14 12 10

Stroke/cm

8 6 4 2 0

0

50

100

150

200

250

Crank rotation/°

Graph 2

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300

350

400

EXP III(12.70mm): Stroke 18 16 14 12 10

Stroke/cm

8 6 4 2 0

0

50

100

150

200

250

Crank rotation/°

Graph 3

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300

350

400

8. CONCLUSION It can be observed from the 3 graphs above that the mechanism has a slow forward stroke and a quick return stroke thus proving the Whitworth’s quick return mechanism.

10.REFERENCES Kinematic Inversions of Four Bar Chain, Slider Crank and Double Slider Crank Mechanism Engineering Tutorials. 2016. [ONLINE] Available at: http://engineering.myindialist.com/2013/kinematic-inversions-of-four-bar-chainslider-crank-and-double-slider-crank-mechanism/#.VxiI-DB94bw. [Accessed 21 April 2016]. Add to My References

MEMB321. 2016. [ONLINE] Available at: http://webcabinet.tripod.com/Assignment/whit2.htm. [Accessed 21 April 2016].

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