Geneva Wheel Presentation

8/18/2019 Geneva Wheel Presentation

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TO DESIGN & FABRICATE A SIX SLOT

GENEVAWHEEL MECHANISM

OBJECTIVE


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The Geneva mechanism is a timing device. It is

used in many counting instruments and in other

applications where an intermittent rotary motion is required.

Essentially, the Geneva mechanism consists of a rotating

disk with a pin and another rotating disk with slots (usually

six) into which the pin slides. The Geneva mechanism wasoriginally invented by a watch maker. The watch maker only

put a limited number of slots in one of the rotating disks so

that the system could only go through so many rotations.

This prevented the spring on the watch from being wound

too tight, thus giving the mechanism its other name, theGeneva Stop. The Geneva Stop was incorporated into

many of the first film projectors used in theaters.

INTRODUCTION


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The basic design criteria of a Geneva wheel is that the centerlines of the

slot and crank are mutually perpendicular at engagement and at

disengagement. The crank, which usually rotates at a uniform angular

velocity, carries a roller to engage with the slots. During one revolution

of the crank the Geneva wheel rotates a fractional part of the revolution,

the amount of which is dependent upon the number of slots. The circular segment attached to the crank effectively locks the wheel against

rotation when the roller is not in engagement and also positions the

wheel for correct engagement of the roller with the next slot.

DESIGN CRITERIA


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DESIGN WORK

The designing work was carried out using Auto CAD 2010software. The required dimensions of the driver and the

driven wheels were taken as per the design equations.

Auto CAD is the most widely used design software's which

helps in designing 2 as well as 3 dimensional models

using simplified alphabetical and numerical commands.

Both the driving and the driven wheels were drawn to the

required dimensions using the circle command. A slot was

cut on the Geneva wheel using the trim tool. It was then

edited using polyline command and the remaining slots

were constructed using the array tool. The crank pin and

the driving wheel were drawn to the required dimensions


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The Geneva Wheel Mechanism designed in thisproject has the following design specifications:

Number of Slots = 6

Radius of Crank = 60mm

Distance between centers of Geneva Wheel and

Crank = 84.8mmOuter radius of Geneva Wheel = 70mm

Slot width = 16mm

Length of Slot = 53.2mm

Crank pin diameter = 10mm

Shaft pin diameter = 10mmThickness of the base plate = 5mm

Diameter of roller pin = 16mm

DESIGN SPECIFICATIONS


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The Geneva Wheel Mechanism constructed by us was

manufactured with 6 slots, having 6

Parts overall.

Model consist of one Geneva wheel piece, a circular & a

semicircular locking

wheels, a Crank Pin and a Base plate.

The Geneva wheel was manufactured by turning a 2mmthick

MS Plate to the external dimensions.

Then the profile was punch marked on the plate.

The plate was then machined to required dimensions

including the cutting of slots.

FABRICATION PROCEDURE


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The locking wheel was also punch marked and machinedto the required dimensions.

The crank pin was made by plain turning the required

shape and the roller pin was fitted at the required

distance of 60mm from the crank center.

All the other components were turned to the requireddimensions.

The Base plate was then cut out of a 5mm thick MS

plate. The holes for carrying the shafts were then drilled

by using a 10mm drill taking care of the distance between

the centers.


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GENEVA WHEEL ANALYSIS

β = Л/2 – α [were α & β are the semi-indexing angle of the driven & α the driver wheelsrespectively]

For entry without shock: e = 1.414r [were r is the radius of the dist. btw the centre of the pinand centre of the crank & e the dist. Btw the centre of the crank and centre of the Geneva wheel

respectively]


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γ = Л*(N+2)/N [were γ is the angle of locking action]

γ = r/e = sinα = sin Л/N [were N is the no:

slots on the driven disc and ]

β = Л/2 – α = Л(N-2)/2N

tanΨ = λsinΦ/1- λcosΦ [were Φ is theangular position of the crank at ant time t &

Ψ the angular position of the driven disc]

ω = d Ψ/dt [were ω is the angular velocity of

the driving crank, assumed to be constant]

GENEVA WHEEL ASSEMBLY


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ADVANTAGES

Cheapest mode of producing intermittent motions .

Can be made out of simpler designs

If designed correctly , the pin enters and leaves the slot in a

direction tangential to the slot surfaces , so that impact

forces are minimized. Ratio of the dwell time to motion time can be modified by

staggering the driver pins or combining the geneva

mechanism with chain drivers with chain drivers or gear trains


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DISADVANTAGES

During the beginning and end of the indexing motion are marked by

sharp acceleration and deceleration. However, as the ratio between the

diameter of the follower and the diameter of the driver increases, the

peak acceleration and velocity of the indexing motion decrease. In other

words, the index motion gets gentler as the number of slots increases.

Another limitation of Geneva mechanisms is that they aren’t flexible.

Once the number of slots has been established, so too are the curves for

acceleration, velocity and displacement. The ratio of dwell time to motion

time is also set


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CONCLUSION

The 6 slot Geneva Mechanism is successfully designed and fabricated based

on the selected design parameters.

BIBLIOGRAPHY

Design data book PSG

Wikipedia

ehow.com

howstuffworks.com

Geneva Wheel Presentation

Documents

Transcript of Geneva Wheel Presentation