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(MECHANISMS 2(MECHANISMS 2ndnd E.S.OE.S.O.).)TechnologyTechnology

Transmission of Transmission of circular movement.circular movement.

Jesús Prieto FuentesP.A.L.E. 2008

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►22nd nd year ESOyear ESO►Thematic Block VII: Thematic Block VII:

MechanismsMechanisms►Students: two years in the Students: two years in the

bilingual section, first year with bilingual section, first year with Technology.Technology.

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GoalsGoals

►To approach to the technical To approach to the technical vocabulary. vocabulary.

►To identify the main To identify the main mechanisms in usual things.mechanisms in usual things.

►To know the main applications To know the main applications of the different mechanisms.of the different mechanisms.

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Circular movement.Circular movement.► Circular or rotary movement is the most Circular or rotary movement is the most

usual in machines.usual in machines.► Generally this movement is produced by Generally this movement is produced by

any kind of engine.any kind of engine.► The rotary movement is transmitted The rotary movement is transmitted

between two shafts: between two shafts: ► In order to transmit this movement we In order to transmit this movement we

need different mechanisms. need different mechanisms.

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MECHANISMS

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Types of transmission of Types of transmission of the circular movement the circular movement

and mechanismsand mechanismsBetween parallel shafts Between parallel shafts Toothed wheels and chainsToothed wheels and chainsPulleys and beltPulleys and beltSpur gear system.Spur gear system.Between perpendicular shafts Between perpendicular shafts Bevel gearsBevel gearsSpur Gear-worm gearSpur Gear-worm gear

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ROTARY SPEED AND VELOCITY

RATIO

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Rotary speeds.Rotary speeds. The rotary speed depends on the diameter of the wheel and, in case of the gears, also on the number of teeth.

The rpm (revolutions per minute) of a large wheel will be less than a smaller one.

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Velocity ratio (i)Velocity ratio (i) The relationship between the speeds The relationship between the speeds

is inverse to the diameters´ one, that is inverse to the diameters´ one, that is known as is known as velocity ratiovelocity ratio..

If the driver wheel is larger than the If the driver wheel is larger than the driven one, then i>1 so the driven one, then i>1 so the transmission transmission multipliesmultiplies the speed. the speed. If the driver wheel is smaller than If the driver wheel is smaller than the driven one, then i<1 so the the driven one, then i<1 so the transmission transmission reducesreduces the speed. the speed.

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ExampleExampleIn this case; the diameter of the driven wheel (400mm.) is twice the diameter of the driver wheel (200mm.), so the speed must be the half.

Diameter of the driver wheel

Diameter of the driven wheel

200

400

1

2i = = =

Which is the velocity ratio?

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GlossaryGlossary►ShaftShaft►PulleyPulley►Gear / Spur gear / Bevel gearGear / Spur gear / Bevel gear►Worm gear / endless screwWorm gear / endless screw►Rotary speed / rpmRotary speed / rpm►Velocity ratioVelocity ratio

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ACTIVITIES

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Activity 1 (Test)Activity 1 (Test)1. Which of the following assemblies transmit the rotary movement between parallel shafts in the same direction?

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Activity 2Activity 2

2. Driven pulley

Diameter = 300mm.

1. Driver pulley

Diameter = 100mm.

Speed: 1500 r.p.m.

CALCULATE:

Speed of the driven pulley:Velocity ratio:

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Questions are Questions are welcome.welcome.

PlenaryInvestigate at home and try to discover this mechanisms in some machine that you use.

Do you want to comment something about this subject?

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Thank you very Thank you very much for your much for your

attention!attention!

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Toothed wheels and chainsToothed wheels and chains

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Pulleys and beltPulleys and belt

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Spur gear system.Spur gear system.

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Bevel gearsBevel gears

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Spur Gear-worm gearSpur Gear-worm gear

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Circular movement.Circular movement.

►Circular or rotary movement is the Circular or rotary movement is the most usual in machines.most usual in machines.

►Generally this movement is produced Generally this movement is produced by any kind of engine.by any kind of engine.

►The rotary movement is transmitted The rotary movement is transmitted between two shafts: between two shafts:

► In order to transmit this movement we In order to transmit this movement we need different mechanisms. need different mechanisms.

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Velocity ratio (i)Velocity ratio (i) The relationship between the speeds The relationship between the speeds

is inverse to the diameters´ one, that is inverse to the diameters´ one, that is called is called velocity ratiovelocity ratio..

If the driver wheel is larger than the If the driver wheel is larger than the driven one, then i>1 so the driven one, then i>1 so the transmission transmission multipliesmultiplies the speed. the speed. If the driver wheel is smaller than If the driver wheel is smaller than the driven one, then i<1 so the the driven one, then i<1 so the transmission transmission reducesreduces the speed. the speed.

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Activity 1 (Test)Activity 1 (Test)1.1. Which of the following assemblies transmit Which of the following assemblies transmit

the rotary movement between parallel the rotary movement between parallel shafts in the same direction?shafts in the same direction?

3. In the following arrangements. Which one multiplies the speed?

2. One of the following gear systems transmit the movement between parallel shafts. Which one?