Basic mechanisms

Mechanisms

What is a Mechanism?A mechanism is the part of a machine which contains two or more pieces arranged so that the motion of one compels the motion of the others.

Generally used to:

– Change the direction of movement

– Change the type of movement

– Change the speed of movement

– Change the amount of torque or force available to do work

Mechanism Movement

Rotary

LinearReciprocating

Oscillating

Universal Joint

• Angular Range

> 90˚ and < 270˚

• Speed and Torque

constant

• Ratio 1:1

• Flow of Power

reversible

• Input & Output Shafts

same direction

Where Can You Find a

Universal Joint?

• Drive shaft of

vehicles

• Power take-off

www.rqriley.com/imagespln/pattersn_ujoint.jpg

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

Bevel Gear

• 90˚ Angle

• Speed and Torque

constant

• Gear Ratio 1:1

• Flow of Power

reversible

Where Can You Find a

Bevel Gear?

• The bevel gear is

used to change

rotational motion at a

90˚ angle.

• Using gears with

differing numbers of

teeth will change the

speed and torque.

• Hand drill

• Car differential

• Shaft-driven bicycle

Simple Gear Train with Idler• Input and Output Shafts

parallel

• Speed is decreased

• Torque is increased

• Ratio 4:1

• Flow of Power

reversible

• Input and Output Gears same direction

• Without Idler Gear different direction

IDLER GEAR

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.

Paper Transport Rollers

Worm and Wheel

• 90˚ Angle

• Speed is decreased

• Torque is increased

• Gear Ratio 20:1

• Flow of Power

NOT reversible

• Direction of Travel

reversible

Where Do You Find a

Worm and Wheel?

• A worm is used to

reduce speed and

increase torque.

• The motion is not

reversible; a gear

cannot drive a worm.

• Tuning mechanism on

string instruments

• Electric motors

• Winch

Crown and Pinion

• 90˚ Angle

• Speed is decreased

• Torque is increased

• Gear Ratio 3.2:1

• Flow of Power

reversible

• Direction of Travel

reversible

Where Do You Find

a Crown and Pinion?

• Watches

• Carousel

• DVD player

How many crown and pinion gears do you see in this pendulum clock?

Rack and Pinion

• Input Movement

rotary

• Output Movement

linear

• Distance is

2 in.

• With a Larger Pinion Gear -

the rack will move a longer distance

• Flow of Power

reversible

• Direction of Travel

reversible

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.

• Rack and pinion

steering

Rack

Pinion

Lead Screw

• Input Movement

rotary

• Output Movement

linear

• 6 Revolutions = 1 in.

• Flow of Power

NOT reversible

• Force is Increased

• Direction of Travel

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

move a heavy car.

Pulley and Belt

• Input and Output Shaft parallel

• Speed is increased

• Torque is decreased

• Ratio 1:2.5

• Flow of Power is reversible

• Open Belt wheels turn in same direction

• Crossed Belt wheels turn in opposite direction

Where Do You Find a

Pulley and Belt?

• Lawn mower

• Car engine

BELTS

Cam and Follower

• Input Movement

rotary

• Output Movement

reciprocating

• Follower moves up and

down 1 time for every

revolution of the crank

• Flow of Power

Not reversible

• Direction of Travel

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.

• Cam shaft

Crank and Slider• Input Movement

rotary

• Output Movement reciprocating

• Slider Moves

1 in. - diameter of crank

• Increased Crank increased distance slider moves

• Flow of Power not reversible

Where Do You Find a

Crank and Slider?

• Steam train

• Internal combustion

engine

Image Resources

Microsoft, Inc. (2008). Clip Art. Retrieved November 25, 2008, from

http://office.microsoft.com/en-us/clipart/default.aspx