Mechanical Control Systems Flashcards
What are the four types of motion?
Reciprocating ↔️ (jack hammer, yo-yo)
Linear ➡️ (toaster, firework)
Oscillating ↪️ (swing, pondulem, windscreen wipers)
Rotary ➰🔄 (wheel)
What is mechanical control made of? (eg. Key)
Input (turn key)
Process (motion transmitted by levers)
Output (snib withdrawn)
What is the input? (Mechanical control)
a force/Change of condition that will influence the output
What is the process? (Mechanical control)
Transfers or converts information provided by the input
What is the output? (Mechanical control)
Performs the desired task of the mechanism
A predictable end result produced by the input.
A mechanism…
4 points
Has an input, process and output
can change the direction of the force
Can change the size of the force
Can change the place where the force acts
Safety rules when using mechanical systems?
6
- keep fingers clear of all moving parts
- never attempt to remove an obstruction from a mechanical system in motion
- keep moving parts clean to avoid obstruction or sticking
- never try to slow moving parts with your hands
- ensure machine guards are in place before using machinery
- dress appropriately, wearing eye protection and avoid clothing that could get stuck.
What are levers used for?
To lift heavy weights with the least amount of effort possible
What is a class one lever?
Load⬇️- falcrum - effort⬇️
Trolly, to carry large package cases, the falcrum is the wheel
What is a class two lever?
Falcrum - Load ⬇️- effort⬆️
Wheel barrow, to lift tools and garden waste, load is in the centre of the barrow
What is a class 3 lever?
Load⬇️ - effort⬆️ - fulcrum
Fishing rod, fisherman catches fish which becomes the load at the end of the lever.
What does a cam do?
Changes the input motion, which is usually a rotary motion, to a reciprocating motion of the follower
What are the parts of a CAM?
The follower and the CAM profile.
Define one cycle
cams
One full rotation of cam
Define dwell
Cams
The part of the cycle where the cam stays at the same height
Define rise
Cams
The part of the cam that causes the follower to rise
Define fall
Cams
The part of the cam that causes the follower to fall
What are the 3 types of follower
Cams
•Flat follower
- used in cars to open/close valves
- used when a small force is required
- used when you don’t need a detailed profile
•Knife follower
- used when you have a detailed cam profile
- the point will become rounder with wear and tear
- bigger push will be achieved
•Roller follower
- reduced wear and tear
- used in aircraft engines
What are the four different types of cam profiles?
•Pear
- usually used on the shafts of cars
- follower remains motionless for half the cycle of the cam and during the second half it rises and falls
- RECIPROCATING motion
•Eccentric
- circular cams produce smooth motion
- used in steam engines
•Snail
-gradual rise and sudden drop
•Heart
-allow the follower to rise and fall with ‘uniform’ vilocity
Describe belts
- they are quiet in operation
- require no lubrication and are relatively cheap to produce
- disadvantages are that they can slip and can only be used if slip will not harm the operation system
What are the 3 types of belts?
•Round belts
- used for light machines that require small force or only turn 90°
- used for CD players, light duty milling machines, vacuum cleaners, drills and power tools
•Toothed belts
- belts with teeth cut into the inside of them
- used in situations where slippage needs to be avoided for safety reasons
- used for applications of constant speeds and timing
- quietest option
- used for car timing belts and car fan belts.
•V-belts
-larger are of belt is in contact with the pully
This gives greater force before the belt starts to slip because of the increased friction (eg. Pillar drills)
-the shaft speed can be controlled
-used for pillar drills
Name the 5 types of gears
Spur gears Bevel gears Worm and wheel Rack and pinion Sprocket and chains
Explain spur gears
- used to transmit rotary motion in the driver wheel to rotary motion in the driver pinion
- mounted on parallel shafts
- wind up alarm clock
- washing machines
- salad spinner
Explain bevel gears
- useful when the direction of a shaft’s rotation needs to be changed
- transmits motions at 90°
- teeth are cut on a cone instead of a dusk or wheel
- hand drills
- Hand whisks
- shaft driven major cycles
