Mechanisms

Mechanisms

What is a Mechanism?In a machine - one part causing another to

moveUsed to transfer or change speed, torque,

force, type of motion and / or direction of motion.

Mechanisms - Change Direction

• Meshed gears in a gear train always turn in opposite directions

Mechanisms - Change Movement

Rotary

LinearReciprocating

Oscillating

Mechanisms - Change Speed• Gear ratios compare the output (or driven gear)

to the input (or drive gear)• Output : Input

• Gear Ratios can be determined using number (n) of teeth on the gear or diameter (d) of the gear

• If the output gear is larger than the input gear the speed will decrease

• If the output gear is smaller than the input gear the speed will increase

Mechanisms – Change Force or Torque

A force is a push or pull in a straight line.

Torque is a push or pull in a circular direction or twisting motion

Simple Gear TrainInput and Output Shafts

parallel (A & B)A – Ratio 1:1 [Output to Input]• Speed is constant• Torque is constant

B – Ratio 3:5 [Output to Input]36 teeth : 60 teeth

• Speed is increased• Torque is decreasedFlow of power - reversibleMotion - rotational to rotationalDirection – opposite

A.

B.

Driven / OutputDrive / Input

Driven / outputDrive / Input

Where Do You Find a Simple Gear Train?

Two meshed gears will rotate in opposite directions

Watch gears

Found in:– Watch– Sewing Machine– Motor

Simple Gear Train with IdlerInput and Output Shafts

parallel Ratio 1:1 [Output to Input]• Speed is constant• Torque is constant

Flow of power - reversibleMotion - rotational to rotational to rotationalDirection – same

Driven / OutputDrive / InputIdler

Where Do You Find a Simple Gear Train with Idler?

Two meshed gears will rotate in opposite directions.

An Idler Gear allows the drive and driven gears to rotate in the same direction.

7. Found in - Paper Transport Rollers / Car Transmission

Bevel GearInput and Output Shafts

90 degrees Ratio 1:1 [Output to Input]• Speed is constant• Torque is constant

Flow of power - reversibleMotion - rotational to rotationalDirection – same

Where Can You Find a Bevel Gear?

• The bevel gear is used to change rotational motion at a 90˚ angle.

Found in:• Hand drill• Car Differential

Differential Gear

1. Gears used – Bevel2. Used in – rear end of rear wheel drive vehicles3. Purpose – Wheels spin at different speeds

when turninghttp://auto.howstuffworks.com/differential.htm

Worm and WheelInput and Output Shafts

90 Degrees Ratio 1:24 [Output to Input]• Speed is decreased• Torque is increased

Flow of power – not reversibleMotion - rotational to rotationalDirection – same &

reversible

Wheel

Worm

Where Do You Find a Worm and Wheel?

• A worm is used to reduce speed and increase torque.

Found in: • Tuning mechanism

on string instruments• Electric motors• Winch

LeadscrewSpeed is decreasedForce is increasedRevolutions 4.75 (per design)

Flow of power – not reversibleMotion - rotational to linearDirection – reversible

Where Do You Find a Lead Screw?

• Jack• Vice

• Changes rotary movement into linear movement

• Significantly increases force

• A person can put a little force into turning the handle to lift a heavy car

Rack and Pinion

Force increasedInput Movement

rotaryOutput Movement

linearWith a Larger Pinion Gear -

the rack will move a longer distance

Flow of power - reversibleMotion - rotational to linearDirection – same & Reversible

Pinion

Rack

Rack

Pinion

Where Do You Find a Rack and Pinion?

• Used to convert between rotary and linear motion.

• Provides gear reduction to make it easier to turn the wheels.

Used in steering systems of cars to convert rotary motion of steering wheel to the side to side motion in the wheels.

Universal Joint

Angular Range > 90˚ and < 270˚

Ratio 1:1• Speed is constant• Torque is constant

Flow of power - reversibleMotion - rotational to rotationalDirection – same

Where Can You Find a Universal Joint?

• Drive shaft of vehicles

• Power take-off

Universal joints are used to transmit rotary movement at an angle that is not 90°.

Chain DriveA - Shafts are parallelRatio 30:18 or 5:3 [Output to Input]

• Speed is increased• Torque is decreased B – Shafts are parallel

Ratio 18:30 or 3:5 [Output to Input]

• Speed is decreased• Torque is increasedFlow of power - reversibleMotion - rotational to rotational Direction – same

Driven / Output ADrive / Input

Drive / Input

Driven / Output B

Where Do You Find a Chain and Sprocket?

Advantage of Chain and Sprocket over spur gears:Transfer torque and speed over long distances

Found in: • Bicycle• Motorcycle

Belt Drive

Input and Output Shafts parallel

Ratio 1:1 [Output to Input]• Speed is constant• Torque is constant

Flow of power - reversibleMotion - rotational to rotational to rotationalDirection – open belt same

- crossed belt opposite

Drive

Driven

Where Do You Find a Pulley and Belt?

Found in:• Lawn mower• Car engine BELTS

Belts instead of chains:• Quieter /Less expensive• Less durable / slip

Crank and SliderSpeed / Force – N/A

Input Movement rotary

Output Movement reciprocating

Slider moves- diameter of the crank

Flow of power – not reversibleDirection – same & reversible

SliderCrank

Where Do You Find a Crank and Slider?

Found in:• Steam train• Internal combustion

engine

Cam and FollowerSpeed & Force N/AInput Movement rotaryOutput Movement reciprocatingFollower moves up and down 1 time for every revolution of the crankFlow of Power not reversibleDirection of Travel not reversible

CAM

FOLLOWER

Where Do You Find a Cam and Follower?

• As a cam rotates, the flat follower is raised and lowered, converting rotary motion to reciprocating (back and forth) motion.

• The cam pictured here would be reversible, as it is symmetrical.

Found in:Cam shaft