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MECHANISMS :male-mechanic::skin-tone-2: - Coggle Diagram
MECHANISMS :male-mechanic::skin-tone-2:
MECHANISMS
transporting people from A to B
telling the time
entertaining children in the park
lifting and carrying objects
LINEAR MOTION MECHANISMS
LEVERS
A lever is a rigid bar that is supported by a fulcrum
F is the force or effort applied at one end of the bar.
R is the resistance or load which acts at the other end of the bar
d is the distance from F to the fulcrum
r is the distance from R to the fulcrum
F · d = R · r
TYPES OF LEVERS
Class 1
Class 2
Class 3
FIXED PULLEY
A fixed pulley is a wheel that has a groove around lt into which a rope,
cham or belt fits It rotates around an axle that is fixed to an immobile
F = R
MOVABLE PULLEY
A moveable pulley ts a set of two pulleys — one is fixed while the other
can move in a linear direction.
F = R/2
COMPOUND PULLEY
This is a system of fixed and moveable pulleys, often called block and
tackle.
Uses; lifts, goods lifts and cranes
ROTARY MOTION MECHANISMS
Friction drives
The ratio between the rotation velocity of the wheels or pulleys depends on the relative size of the wheels.
N1 · D1 = N2 · D2 => D1/D2 = N2/N1
N1 and N2 are the velocities of the primary drive wheel and the
output wheel
D1 and D2 are the corresponding diameters
Friction drives are made up of two or more wheels that are in contact
Pulleys with belt
They consist of two pulleys or wheels that are a certain distance apart.
Uses: industnal machines, vehicle engines, washing machines and dulls
Gear mechanisms and cogwheels
Cogwheels are sets of wheels that have teeth called cogs.
The ratio between the rotation veloaues of the wheels depends on the
number of teeth on each wheel. It's expressed by this equation:
N1 · Z1 = N2 ·Z2 => Z1/Z2 = N2/N1
N1 and N2 are the velocities of the corresponding wheels
Z1 and Z2 are the numbers of teeth.
Worm gear
This is a screw that moves a helical cogwheel that is set perpendicular
to the screw
A worm screw fulfils this equation:
Nwheel = Nscrew · Zgrooves / Zwheel
Gear mechanisms with a chain
These are two cogwheels with parallel axles that are a certain distance apart; they rotate simultaneously by means of a metal chain or a toothed belt stretched over both wheels.
The relation between the rotation veloaties of the wheels depends on the
number ofteeth on each gear:
N1 · Z1 = N2 · Z2 => Z1/Z2 =N2/N1
Gear train
This is a system of more than two gears, connected together as shown in
the diagram
The gear ratio between the drive wheel (I) and the dnven wheel (4) depends on the number of geared teeth m the system:
N4/N1 = Z1 · Z3 / Z2 ·Z4
Pulley trains with belts
t's a system of pulleys, or wheels, with a belt formed by more than two wheels.
The gear rauo between the dnve pulley (I) and the dnven pulley l4) depends on the relauve size of the pulleys in the system. It's expressed as a function of their diameters.
N4/N1 = D1 · D3 / D2 · D4
variation in velocity
Apart from transmitting force and motion, rotary transmission
mechanisms allow velocity to vary.
Constant system
velocity remains constant
Reducing system
velocity is reduced
Multiplying system
velooty is increased
MECHANISMS THAT TRANSFORM MOTION
From rotary into reciprocating motion
Cam
This is basically a rotating object that pushes a follower as it moves
Eccentric cam
This consists of a wheel with an off-centre rotation axle that doesn't coincide with the centre of its circumference
Crankshaft
This is a set of connecting rods attached to a jointed axle. Each of the
joints of the axle acts as a crank.
Crank-link-slider
This is composed of a crank and a rod called a connecting rod or link.
From rotary into linear
Nut and bolt system
This consists of a bolt or threaded bar and a nut that has the same
intenor diameter as the diameter of the bolt.
Uses: presses, taps, car jacks, screw tops for bottles
Rack and pinion system
This uses a pinion that is a small cogwheel, mounted on a rack that is a
toothed belt or bar
lhe ratio between the number of rotations of the pinion and the veloaty of
the movement of the rack is expressed by this equation:
L = P · Z · N
Winch and crank handle
A winch and crank handle system consists of a drum that rotates and a
A winch is balanced when it satisfies this equation:
F · d = R ·r => F = R · (R ·r / d)
OTHER MECHANISMS
Mechanisms for controlling and directing motion
The mechanisms used to reduce velocity are called brakes. There are
severaltypes
Mechanisms that store energy
Springs are devices that absorb energy This energy can be released
later, little by little or all at once.
Connecting mechanisms
Clutches are mechanisms that allow axles or shafts to be connected
or separated
Fixed connections are used to make permanent connections
between axles and shafts
Mo v able connections are used to connect shafts that can move
along the axle or at an angle to each other. There are two main types : Oldham iomts and Cardan joints
Supports: bushings and bearings
In bushings the axle or the shaft is inserted in a plain circular piece
that is placed inside a housing to provide a bearing surface.
Bearings are made up of two concentric rings with balls or rollers
between them.
