- Slides: 24
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 Oscillating Linear Reciprocating
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 Universal joints are used to transmit rotary movement at an angle that is not 90°. www. rqriley. com/imagespln/pattersn_ujoint. jpg
Bevel Gear • 90˚ Angle • Speed and Torque constant • Gear Ratio 1: 1 • Flow of Power reversible
Where Can You Find a Bevel Gear? • Hand drill • Car differential • Shaft-driven bicycle • 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.
Simple Gear Train with Idler IDLER GEAR • 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
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? • Tuning mechanism on string instruments • Electric motors • A worm is used to • Winch reduce speed and increase torque. • The motion is not reversible; a gear cannot drive a worm.
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 in steering systems • Used to convert between rotary of cars to convert rotary and linear motion of steering wheel motion. to the side to side motion • Provides gear in the wheels. reduction to • Rack and pinion make it easier to steering Pinion turn the wheels. Rack
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 FOLLOWER CAM • 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
Where Do You Find a Cam and Follower? • Cam shaft • As a cam rotates, the flat follower is raised and lowered, converting rotary motion to reciprocating (back and forth) motion.
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