Design And Fabrication Of Quick Return Method Using Geneva Mechanism.docx

DESIGN AND FABRICATION OF QUICK RETURN METHOD USING GENEVA MECHANISM A PROJECT REPORT

Submitted by MOHANPRASANTH S

(Reg No: 422516114038)

NEDUMARAN A

(Reg No: 422516114042)

PRAVEEN KUMAAR V

(Reg No: 422516114043)

In partial fulfilment for the award of the degree Of

BACHELOR OF ENGINEERING IN MECHANICAL ENGINEERING

UNIVERSITY COLLEGE OF ENGINEERING VILLUPURAM (A Constituent College of Anna University Chennai) Kakuppam, Villupuram-605 103 APRIL 2019

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ANNA UNIVERSITY, CHENNAI 600 025 BONAFIDE CERTIFICATE Certified that this project report “DESIGN AND FABRICATION OF QUICK RETURN METHOD USING GENEVA MECHANISM “is the bonafide work of MOHANPRASANTH . S (422516114038), NEDUMARAN. A (422516114042), PRAVEEN KUMAAR. V (422516114043), who carried out the project work under my supervision

Dr.V.GNANAMOORTHI, M.E, Ph.D.

Mr. S.V.SASIKARAN, M.TECH

HEAD OF THE DEPARTMENT,

TEACHING FELLOW,

Dept. of Mechanical Engineering,

Dept. of Mechanical Engineering,

UCEV, Kakuppam,

UCEV, Kakuppam,

Villupuram - 605103.

Villupuram - 605103.

Submitted for the University project viva voce examination held on……………

INTERNAL EXAMINER

EXTERNAL EXAMINER 2

ACKNOWLEDGEMENT

We thank ALMIGHTY GOD for giving us his blessings, dedication and the motivation to fulfil our goals in completing the project.

It’s our pleasure in expressing our immense gratitude and heartfelt thanks to our honourable DEAN Dr. R. Senthil M.E., Ph.D.,

We express our heartfelt thanks to our respected Head of the Mechanical Department, Dr.V.Gnanamoorthi M.E., Ph.D., Who has contributed his fruitful ideas and valuable suggestions in doing this project.

We are profoundly grateful to our project guide, teaching fellow Mr. S.V.SASIKARAN M.TECH, guided us with his tremendous effort towards the completion of the project.

We extend our gratitude to all the faculty members and technical assistance of the Mechanical lab for their help in implementing our project

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ABSTRACT The geneva mechanism or maltese mechanism is a gear mechanism that translates continuous rotary motion into reciprocating motion .In this project we use geneva mechanism to achieve quick return method instead of using crank and slotted lever mechanism & whitworth quick return mechanism. In geneva mechanism we use gears to achieve the quick return method. In this project there will be sun gear, planet gear, and orbital gear. The sun and orbital gear have equal number of tooth and those gears having teeth at certain degrees present opposite to each other. The planet gear is present between the orbital gear and sun gear which is full toothed gear. The orbital gear and sun gear is attached in a single round plate and it fixed in same axis. The input is given through it. The output is taken from the planet gear which is attached to the rack and pinion gear. When it start to rotate due to change in module and direction of teeth present in both orbital gear and sun gear we get the output as reciprocating motion with variation of speed. The forward stroke is slower when compared to the return stroke.

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TABLE OF CONTENTS

CHAPTER NO

1.

TITLE

PAGE NO

ABSTRACT

4

INTRODUCTION

7

2.

CONCEPT

8

2.1 GEAR CONCEPT

8

2.2 GENEVA CONCEPT

9

3.

CONSTRUCTION

10

4.

WORKING

11

4.1 EXISTING MODEL

11

4.2 PROPOSED MODEL

20

5.

ORBITAL GEAR

22

6.

SUN GEAR

23

7.

PLANET GEAR

23

8.

RACK AND PINION

24

9.

APPLICATION

27

10.

ADVANTAGES

28

11.

DISADVANTAGES

28

12

COST ESTIMATION

29

13

CONCLUSION

30

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LIST OF FIGURES 1. 2. 3. 4. 5. 6.

ORBITAL GEAR SUN GEAR PLANET GEAR GENEVA SETUP CRANK AND SLOTTED LEVER WITHWORTH QUICK RETURN

LIST OF TABLES

1. COST ESTIMATION 2. DIMENSIONS OF GEAR

COMPONENTS USED 1. ORBITAL GEAR 2. SUN GEAR 3. PLANET GEAR 4. RACK AND PINION 5. SHAFT 6. BEARINGS 7. HANDLE 6

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 the return stroke, it is a quick return mechanism. It yields the significant improvement in machine 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 return stroke with non intensive loading. Several quick return mechanisms can be found in nowadays, including the offset crank- slider mechanism, the crank shaper mechanism, the double crank mechanism and the whitworth mechanism. All the above mechanisms are inexpensive but bulky and difficult to balance. In situations, if compact space is essential to the design, than the linkage is not a good choice. Therefore we find al0074ernate way for this quick return mechanism. This work aims to present a new design for the quick return mechanism, and verify its feasibility by conducting simulation and experimental studies by using gears. In our mechanism we use gears instead of using linkages. These gears convert the continuous rotary motion into reciprocating motion with the help of rack and pinion at different speed ratio. The orbital gear and sun gear is present. The planet gear is slides between those two gears. Both the orbital gear and sun gear have equal number of teeth at certain angles opposite to each other. The planet rotates in between them and gives the reciprocating motion at different speed ratio.

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CONCEPTS GEAR CONCEPT: A gear or cogwheel is a rotating machine part having cut teeth, or in the case of a cogwheel, inserted teeth (called cogs), which mesh with the another toothed part to transmit torque. Geared device can change the speed, torque, and direction of power source. Gears almost always produce a change in torque, creating a mechanical advantage through their gear ratio, and thus considered a simple machine. An advantage of gear is that the teeth of a gear prevent slippage. When two gear mesh, if one gear is bigger than the other, a mechanical advantage is produced, with the rotational speed, and the torques, of the two gears differing in proportion to their diameters.

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GENEVA CONCEPT: The geneva mechanism or maltese mechanism is a gear mechanism that translates continuous rotary motion into reciprocating motion. The sun and orbital gear have equal number of tooth and those gears having teeth at certain degrees present opposite to each other. The planet gear is present between the orbital gear and sun gear which is full toothed gear. These planet gear gives the output as reciprocating motion through rack and pinion.

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CONSTRUCTION The construction of geneva mechanism is quit easy when compared to the other quick return mechanism like crank and slotted lever mechanism & whitworth quick return mechanism. There is orbital gear, sun gear, planet gear and finally rack and pinion to get the output. The orbital gear and sun gear are attached at the

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same shaft with equal number of teeth is present, but those gears are present at the certain angles and opposite to each other. The planet gear is full toothed which rotates in between those orbital and sun gears. The input is given through the other side of shaft with the help of handle. When handle starts rotates in clockwise direction the planet gear meshes with that sun gear and starts rotate through anticlockwise direction for certain angles then it meshes with the orbital gear and starts rotate in clockwise direction due to variation module the planet gear rotates at different speed ratio. The ouput is taken from planet gear with the help of rack and pinion. The pinion is attached to the planet gear through the shaft. The sun and orbital gear is constrained at the same place with the help of a round plate. Bearings are present to rotate the shaft freely. Totally four bearings are present, two bearings are present at either side of the input shaft and other two bearings are present at the output shaft to reduce friction and the shaft moves freely.

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CONSTRUCTION OF GENEVA MECHANISM

WORKING OF QUICK RETURN METHOD: EXISTING MODEL

1. CRANK AND SLOTTED LEVER MECHANISM: This mechanism is mostly used in shaping machines, slotting machines and in rotary internal combustion engines. In this mechanism, the link AC (i.e. link 3) forming the turning pair is fixed, as shown in fig. The link 3 corresponds to the connecting rod of a reciprocating steam engine. The driving crank CB revolves with uniform angular speed about the fixed 12

centre C. A sliding block attached to the crank pin at B slides along the slotted bar AP and thus causes AP to oscillate about the pivoted point A. A short link PR transmits the motion from AP to the ram which carries the tool and reciprocates along the line of stroke R1R2. The line of stroke of the ram (i.e. R1R2) is perpendicular to AC produced.

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2. THE

WITHWORTH

QUICK

RETURN

MECHANISM: The withworth quick return mechanism is used to increase the speed of a useless stoke in quick return mechanism. This is basically converting a rotary motion into reciprocating motion. In reciprocating motion, the forward stroke is the useful stroke where work is done. It is one of the inversion of the slider-crank shown in fig. (a)

obtained

by

fixing

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of

the

link

2.

When the link 2 is fixed, the link 3 along with slider at its end B becomes a crank. This makers the link 1 to rotate about O along with the slider which also reciprocates on it [fig. (b)] Slider 4 rotates in circle about A and slider on link 1. C is a point on link 1 extended backwards where the link 5 is pivoted. The other end of the link 5 is pivoted to the tool. The axis of the motion of slider 6 (tool)passes through o and is perpendicular to OA, the fixed link . the crank 3 rotates in counter clockwise direction. Intially, let the slider 4 be at B so that C. cutting tool 6 will be at extreme left position. With the movement of crank, the slider traverses the path B whereas the point C move through C. cutting tool 6 will have forward of the slider 6 is proportional to the obtuse angleB”AB at A. Similarly, the slider 4 completes the rest of the circle through the part B and passes through CC. there is backward stroke of the tool 6. The time taken in this is proportional to the acute angle B AB at A.

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3. DOUBLE SLIDER CRANK CHAIN MECHANISM A four bar chain having two turning and two sliding pairs such that two pairs of the same kind are adjacent is known as double slider crank chain.

Inversions of Double slider Crank chain: It consists of two sliding pairs and two turning pairs. They are three important inversions of double slider crank chain. 1) Elliptical trammel. 2) Scotch yoke mechanism. 3) Oldham‘s Coupling.

1. Elliptical Trammel: This is an instrument for drawing ellipses. Here the slotted link is fixed. The sliding block P and Q in vertical and horizontal slots respectively. The end R generates an ellipse with the displacement of sliders P and Q.

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The co-ordinates of the point R are x and y. From the fig. cos θ = x. PR and Sin θ = y. QR Squaring and adding (i) and (ii) we get x2 + y2 = cos2 θ + sin2 θ (PR) 2 (QR) 2

x2

+ y2 = 1 (PR) 2

(QR) 2

The equation is that of an ellipse, Hence the instrument traces an ellipse. Path traced by mid-point of PQ is a circle. In this case, PR = PQ and so x 2 +y 2 =1 (PR) 2 (QR) 2 It is an equation of circle with PR = QR = radius of a circle. 2. Scotch yoke mechanism: This mechanism, the slider P is fixed. When PQ rotates above P, the slider Q reciprocates in the vertical slot. The mechanism is used to convert rotary to reciprocating mechanism.

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2. Oldham’s coupling: The third inversion of obtained by fixing the link connecting the 2 blocks P & Q. If one block is turning through an angle, the frame and the other block will also turn through the same angle. It is shown in the figure below.

An application of the third inversion of the double slider crank mechanism is Oldham‘s coupling shown in the figure. This coupling is used for connecting two parallel shafts when the distance between the shafts is small. The two shafts to be connected have flanges at their ends, secured by forging. Slots are cut in the flanges. These flanges form 1 and 3. An intermediate disc having tongues at right angles and opposite sides is fitted in between the flanges. The intermediate piece forms the link 4 which slides or reciprocates in flanges 1 & 3. The link two is fixed as shown. When flange 1 turns, the intermediate disc 4 must turn through the same 19

angle and whatever angle 4 turns, the flange 3 must turn through the same angle. Hence 1, 4 & 3 must have the same angular velocity at every instant. If the distance between the axis of the shaft is x, it will be the diameter if the circle traced by the centre of the intermediate piece. The maximum sliding speed of each tongue along its slot is given by v=xω where, ω = angular velocity of each shaft in rad/sec v = linear velocity in m/sec

3. Scotch yoke mechanism: This mechanism, the slider P is fixed. When PQ rotates above P, the slider Q reciprocates in the vertical slot. The mechanism is used to convert rotary to reciprocating mechanism.

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4. Mechanical Advantage, Transmission angle: The mechanical advantage (MA) is defined as the ratio of output torque to the input torque. (or) ratio of load to output. Transmission angle. The extreme values of the transmission angle occur when the crank lies along the line of frame.

PROPOSED MODEL GENEVA MECHANISM: The

geneva

mechanism

or

maltese

mechanism is a gear mechanism that translates continuous rotary motion into reciprocating motion. There is orbital gear, sun gear, planet gear and finally rack and pinion to get the output. The orbital gear and sun gear are attached at the same shaft with equal number of teeth is present, but those gears are present at the certain angles and opposite to each other. The planet gear is full toothed which rotates in between those orbital and sun gears. The input is given through the other side of shaft with the help of handle. When handle starts rotates in clockwise direction the planet gear meshes with that sun gear and starts rotate through anticlockwise direction for certain angles then it meshes with the orbital gear and starts rotate in clockwise direction due to variation module the planet gear rotates at different speed ratio.

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The orbital gear has number of teeth which present only at 230 degrees and the same number of teeth present in sun gear at 110 degrees which is opposite to the orbital gear. The remaining 20 degree gap is provided for the planet gear to reduce the speed of gear in one direction and changes into another direction with different velocity. The output is taken from the from the planet gear with help of rack and pinion attached to through the shaft. These shaft is supported by bearings to reduce the friction and moves freely. When it start to rotate due to change in module and direction of teeth present in both orbital gear and sun gear we get the output as reciprocating motion with variation of speed. The forward stroke is slower when compared to the return stroke.

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COMPONENTS

DIMENSIONS

ORBITAL GEAR

300mm

SUN GEAR

45mm

PLANET GEAR

15mm

PINION

40mm

RACK

75mm

ORBITAL GEAR: This is the outer internal gear which is used to rotate the planet gear in clockwise direction due to this action we get output return stroke with lesser time period. The number of teeth present in the orbital gear is 28 at 230 degrees. The dimension of outer gear is 30cm.

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SUN GEAR: The sun gear is the gear present at the centre of the system which is also has same number of gears present in orbital gear at 110 degrees. The size of the sun gears is 45mm. Both the sun gear and orbital gear fixed in the same shaft.

PLANET GEAR: This is the gear which is rotates between the sun gear and orbital gear. The dimension of the sun gears is 15mm. this gear rotates both the direction when orbital and sun gear rotates in same direction. This is due to the teeth present in the orbital gear and sun gear. The planet gear is the full toothed gear present at 360 degrees.

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RACK AND PINION GEAR: Rack and pinion gear is used to convert the rotary motion into linear motion. The length of rack is 75mm and the diameter of pinion is 40mm. In this mechanism the output from the planet gear is converted in to linear reciprocating motion by means of rack and pinion.

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SIDE VIEW OF QUICK RETURN METHOD USING GENEVA MECHANISM

APPLICATIONS: 

This mechanism is used in the shaper machine where there is forward stroke is slower than the return stroke.



It is also used in planar machines, vertical drilling machine, power-driven saws, mechanical actuators and revolver mechanism.

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ADVANTAGES:  By using gears, large velocity ratio can be obtained with minimum space.  Gears can be mechanically strong, so higher loads can be lifted  Gears requires only less lubrication, hence less maintenance is required.  They have long life, so the gear system is very compact.  Using gear systems, we can transmit motion between non intersecting shafts.

DISADVANTAGES:  They are not suitable for large velocities.  They have no flexibility.  Gear operation is noisy.  Due to the engagement of toothed wheel of gears, some part may be permanently damaged in case of excessive loading.

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COST ESTIMATION:

S.NO 1

MATERIALS QUANTITY COST Wood

7Sq.ft

500

2

Belt

3

300

3

bearings

4

400

4

Shaft

2

250

5

anabond

1

50

6

Nail

500g

100

7

fevicol

1

75

8

Wood

cutting 1(3days)

2250

machine(rent) 9

handle

1

75

10

Emery sheet

5

50

TOTAL : 4050

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CONCLUSION: Therefore from this project we conclude that the usage of geneva mechanism will be alternative for other quick return mechanisms with more efficient in some of the application. Due to compact size of this mechanism, it will be useful for less space requirement areas and useful in low velocity areas.

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