CAMs and Gears Flashcards
What is a CAM?
It changes the input motion which is usually rotary to a reciprocating motion of the follower
What are the parts of a cam mechanism?
CAM - attached to a crankshaft which rotates
Follower - attaches to the cam and follows the shape going up and down
What are most common shapes of CAMs?
Circular/ eccentric
Pear
Snail/ drop
Heart shaped/ constant velocity
Square
Explain how circular/ eccentric CAMs work:
Uses an off-centre pivot and causes the follower to move up and down (rises and falls by a large amount)
Circular/ eccentric CAMs use:
Pistons on steam engines
Explain how pear CAMs work:
Follower remains stationary for half a turn and then rises and falls gently
Pear CAMs use:
Carousel horses
Explain how Snail/ drop CAMs work:
Follower remains stationary for half a turn and the gently rises before suddenly falling (can only rotate in one direction)
Snail/ drop CAMs use:
Used in production to make holes at regular intervals
Explain how Heart shaped/ constant velocity CAMs work:
Follower rises and falls continuously with uniform velocity (no stationary period)
Heart-shaped or constant velocity CAMs use:
Sewing machines to wind the bobbin
What do gears do?
Transfer rotary motion, they are linked in gear trains and the simplest form being a 2 gear wheel
Explain spur gears:
Input and output are in opposite directions, if one gear was larger than the other the rotational speed would change
Explain idler gear:
If the gears were required to turn in the same direction an idler gear would be used between the input and output
Explain compound gears:
A number of gears connected together, can significantly increase or decrease the number of possible rotational speed
How to calculate gear ratio?
Gear ratio = number of teeth on driven gear / number of teeth on driver gear
Driven : driver
Explain bevel and mitre:
Shafts can be at 90 degrees, different sizes of gears can change the speeds
Explain worm gear:
Transmits force and motion through 90 degrees, reduction on rotational speed is possible, used in food mixers
Explain rack and pinion:
Changes rotary motion to linear, used in pillar drills and steering mechanisms in cars
