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MECHANISMS (Mechanisms are devices that transmit and convert forces and…
MECHANISMS
Mechanisms are devices that transmit and convert forces and motion from a driving force or input element to an output element.
They allow us to carry out certain tasks more easily and more efficiently.
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Mechanisms that transmit motion and force in a straight line from one point to another.
Examples include levers and fixed,mobile and compound pulleys.
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 and of the bar.
d is the distance from F to the fulcrum.
r is the distance from R to the fulcrum.
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Rotary motion mechanisms transmit motion and effort in a circular way, from the input to the output.
They include friction drives,pulley systems,gears and worm gears.
Friction drives are made up of 2 or more wheels that are in contact.
The first wheel is called the primary drive wheel.When it moves,it turns or drives the second or output wheel,causing it to move as well.
The output wheel rotates in the opposite direction of the primary wheel.If we use more than 2 wheels,each one rotates in the opposite direction to the one next to it.
The ratio between the rotation velocity of the wheels or pulleys depends on the relative size of the wheels.
It is expressed by the following equation:
N1 x D1 = N2 x 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.
The ratio D1/D2 is called the gear ratio.
Cogwheels are sets of wheels that have teeth called cogs.
They transmit a rotary motion between the 2 connected axles,which can be parallel,perpendicular or oblique.
Gears can be cyclindrical or conical.
The ratio between the rotation velocities of the wheels depends on the number of teeth on each wheel.It's expressed by this equation:
N1 x Z1 = N2 x Z2 -- Z1/Z2 = N2/N1
N1 and N2 are the velocities of the corresponding wheels.
Z1 and Z2 are the numbers of teeth.
The ratio Z1/Z2 is called the gear ratio.
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Pulley trains with belts
It´s a system of pulleys, or wheels, with a belt formed by more than 2 wheels.
1.The rotary motion of axle 1 is transmitted to axle 2 by the belt that connects them.
2.Pulleys 2 and 3 rotate at the same velocity.
3.The motion of pulley 3 is transmitted to pulley 4 by the belt that connects them.
4.All the wheels rotate in the same direction. 
The gear ratio between the drive pulley (1) and the driven pulley (4) depends on the relative size of the pulleys in the system.It's expressed as a function of their diameters.
N4/N1 = D1 x D3/D2 x D4
A fixed pulley is balanced when the effort F is equal to the resistance of the load,R
F=R
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Compound pulley is a system of fixed and moveable pulleys,often called block and tackle.
The pulleys with belt consist of 2 pulleys or wheels that are a certain distance apart.
Their axles are parallel and they rotate simultaneously due to the effect of the belt.
The 2 pulleys and the 2 axles rotate in the same direction.
The gear ratio between the drive wheel(1) and the driven wheel(4) depends on the number of geared teeth in the system:
N4/N1 = Z1 x Z3/Z2 x Z4