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 MovementRotary

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.

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

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

Image ResourcesMicrosoft, Inc. (2008). Clip Art. Retrieved November

25, 2008, from http://office.microsoft.com/en-us/clipart/default.aspx