mechanisms

mechanisms

1. transformation of motion

   • rotary-linear transformation
     • wheel
       • reduce contact with the ground
       • decrease friction
       • moves forward a distance that is equals to its circunference.
       • less force to move vehicles with larger wheels
         • they move quickly
     • rack & pinion
       • 2 parts
         • rack
           • bar with many teeths
             • are interlock
         • pinion
           • gear with teehts
       • sliding doors
       • conveyor belts
     • nut & bolt
       • 2 parts
         • bolt
           • spiral groove
         • nut
           • turns around it
       • move forward
       • lift loads
         • reducing system
       • hold things together
     • winch & crank
       • cylinder that rotates around a horizontal axis
       • increases the force
         • the crank
       • transform rotary to linear
         • the winch
       • like Law of the Lever
         • F x d = R x r
       • lift or pull heavy loads
   • reciprocating rotary-linear transformation
     • crank & rod
       • piston
         • moves foward and backward
       • rod
         • turns the first wheel
         • second wheel
           • turns because it is connected to the first wheel by another rod
       • windscreen wisper
     • crankshaft
       • multiple rods to one shaft
         • rods are connected to cranks, and cranks are connected to the crankshaft
       • syncronise the movements of various parts
       • combustion motors that use pistons
     • cam
       • irregular shaped device that rotates on a shaft
       • follower
         • move other parts or turns a switch & off
       • camshaft
         • multiple cams on one shaft. 
         •  It is use to syncronise the movements of various parts.
         • toys
       • eccentric cams
         • circular cams with an axis of rotation that is off-centre.
         • because they rotate in an irregular or eccentric way
         • sewing machines

2. that control motion

   • speed reduction
     • brakes
       • use friction to reduce speed they are activated by some type of lever.
       • disc brakes
         • a disc connected to an axle
         • brake apply pressure to the disc
       • band brakes
         • a drum connected to an axle.
         • a flexible band applies pressure to the outside of the drum 
         • these brakes were used in carriages and they depended on the strength of the driver
       • drum brakes
         • a drum is connected to the axle.
         • a pair of brake shoes apply pressure to the inside of the drum
   • direction control
     • rachets
       • mechanism that controls the direction of motion. 
       • it allows motion in one direction.
         • but not in the other.
       • rachets in watches

3. energy accumulation

   • accumulation
     • springs
       • flexible devices that absorb energy when we apply force to them. we can release the energy in acontrolled way
       • compression
         • sofas
       • traction
         • metallic bed frames
       • torsion
         • clothes pins
   • dissipation
     • suspension systems
       • they are use to absorb and dissipate motion
       • shock absorbers
         • spiral steel springs
       • leaf springs
         • long, curved pieces of steel of differents lengths placed on top of each other and joined in the middle

4. couplings and clutches

   • they are use to transmit rotation from one axis to another
   • rigid couplings
     • form a permanent connection between two shafts. these shafts may have different diameters, but they must be perfectly aligned.
   • clutches
     • form a rigid connection which isn't permanent.
     • this systemm also permits various combinations that chgange the gear ratio between the engine and the wheels.
   • flexible couplings
     • they are also useful

5. bearings

   • plain
     • formed by two rings
     • one of the ring is connected to the rotating shaft 
     • the other is connected to the support.
     • plain bearings are made of smooth materials, but they need lubrication to reduce friction
     • plain bearings are quiet, but they produce a lot of heat at the high speeds
   • antifriction
     • they are used in many machines
     • they reduce the amount of surface contact between the shaft and other parts.
     • the inner ring
       • is in contact with the rotating shaft
     • the outer ring
       • is connected to the rest of the mechanism
     • the rolling elements
       • are cylindrical rollers or round balls ( ball bearings).
     • the retainer
       • keeps the rolling elements in position.

6. freewheel

   • transmits motion in one direction, and turns freely in the opposite direction.
   • mechanism on our bycicles