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

Vocabulary Torque-A twisting force. Energy-The ability to do work. Work-The application of force that moves an object a certain distance Gear ratio-The ratio of the speed of the driving member of a gear train to that of the driven member.

Continued Vocabulary Input-Something put into a system, such as resources, in order to achieve a result. Output-The results of the operation of any system.

Mechanism Movement Rotary Linear Reciprocating Oscillating

Linear motion Movement in a straight line.

Oscillate A swing back and forth at a regular rate.

Reciprocating A back and forth movement.

Rotary motion Circular movement.

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°.

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 steeringRack 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