jueves, 8 de diciembre de 2016

MECHANISMS THAT CONTROL MOTION

DIRECTION CONTROL: ratchets
A rachet is a mechanism that controls the direction of motion. It allows motion in one direction, but not in the other.


SPEED REDUCTION: brakes
Brakes use friction to reduce speed and they are activated by levers that transmit force to an output receptor, which put pressure on the wheel. This produces friction, and slow down the wheel.

There are various types of brakes according to where the friction is produced:

Resultado de imagen de disc brake
Disc brake
Imagen relacionada
Band brake
Resultado de imagen de drum brake
Drum brake
Disc brakes: A disc is connected to an axle. Brake pads apply pressure to the disc.
Band brakes: A drum is connected to an axle. A flexible band applies pressure to the outside of the drum.
Drum brakes: A drum is connected to the axle. A pair of brake shoes apply pressure to the inside of the drum.


domingo, 27 de noviembre de 2016

  ⇒TRANSFORMATION OF MOTION⇐


ROTARY-LINEAR TRANSFORMATION

WHEEL
Wheels reduce contact with the ground and decrease friction. If there isn't enough friction, they can slide out of control. We need less force to move vehicles with larger wheels and they move more quickly.
Resultado de imagen de wheels gif
RACK AND PINION
This mechanism has two parts: the rack is a bar with many theeth and the pinion is a gear with theeth that interlock with the rack. It transforms rotary motion into linear motion.

Resultado de imagen de rack and pinion gif

NUT AND BOLT
This mechanism transforms rotary motion into linear motion. It has two parts: a bolt with a spiral groove and a nut that turns around it.

Resultado de imagen de nut and bolt gif



WINCH AND CRANK
It is a cylinder that rotates around a horizontal axis. We turn the crank to rotate the winch. The crank increases the force and the winch transforms rotary motion into linear motion. This mechanism has the Law of the Lever.

Resultado de imagen de winch and crank handle

RECIPROCATING ROTARY-LINEAR TRANSFORMATION

CRANKSHAFT
We can conect multiple rods to one shaft. The rods are connected to cranks, and the cranks are connected to the crankshaft. It can synchronise the movements of various parts.

Resultado de imagen de crankshaft gif
CAM
A cam is a irregulary device that rotates on a shaft. When the cam rotates, it pushes a special bar called follower. This follower can move other parts or it can turn a switch on and off.
When we put multiple cams on a shaft, it's called a camshaft. We can use it to synchronise the movements of various parts.

Resultado de imagen de camshaft

ROTARY TRANSMISSION



Rotary transmission systems put two rotating elements into contact. These mechanisms have two purposes:
⇒Transferring rotary force to an input location to another location.
⇒Changing the rotary speed by using rotating elements of different sizes.
There are various mechanisms:
    
Pulleys with belts
Friction wheels


Interlocking gears
Sprockets with chains
 


Here, the most reliable mechanism is the interlocking gears, because they don't slip easily.

CHANGES IN SPEED
We can increase, decrease and make constant the speed with these systems:
2009_q1.png Resultado de imagen de pulley with belt 
Decreasing and  Increasing speed system
Resultado de imagen de pulley with belt
Cosntant speed system

SPEED RATIOS
The relationship between the speeds of the two wheels is inversely proportional to their sizes. 
                                      
                         N2/N1=D1/D2

The relationship is called the ratio of transmission, where N is the speed of relation and D is the diameter of the wheel. 

BELT DRIVES AND GEAR TRAINS  


Resultado de imagen de belt drives compound


-Wheel 1 turns wheel 2, wich moves faster because it is smaller. If wheel 1 makes 1 rotation, wheel 2 makes 1.5 rotations.
-Wheel 2 and wheel 3 are connected to the same axis, so they turn together.
-Wheel 3 turns wheel 4, wich moves faster because it is smaller. If wheel 3 makes 1.5 rotations, wheel 4 makes 3 rotations (1.5x2=3)

                      N4/N1=D1XD3/D2XD4


CHANGES IN DIRECTION AND ROTATIONS

We can change the direction of the rotation by using belts in different possicions or different axis.
Resultado de imagen de gears gif
Parallel axes

Resultado de imagen de perpendicular gears gif
Perpendicular axes
Different posicion of the belts
Resultado de imagen de perpendicular gears gif
Crossed axes

 








WORM DRIVE
A worm drive reduces the speed of rotary system very well. It has two parts: a worm shaft and a worm gear. The shaft has more than one groove. Each groove interlocks with one of the worm gear. This mechanism is not reversible.

Resultado de imagen de worm gear gif

viernes, 25 de noviembre de 2016

LINEAR TRANSMISSION OF MOTION

Levers
A lever is a rigid bar that truns around  point called fulcrum. Various forces may act on the lever at the same time. When the forces acting on opposite ends of a lever are equal, we say the lever is in equilibrium. We can express this mathematically as the Law of the Lever:
                                       F x d = R  x r                            

CLASSES OF LEVERSResultado de imagen de classes of levers

A HAND CRANK
It has two parts, one is connected to a rotating shaft and the other forms a handle. We can use a hand crank to apply force at a distance from the axis of the shaft. It has the Law of the Lever.
Resultado de imagen de molinillo de cafe
Class 2 lever


PULLEYS AND COMPOUND OF PULLEYS SYSTEMS
In a system of pulleys, equilibrium between the forces depends on the path that the rope follows.

PULLEYS
A pulley is a wheel that rotates around an axis and has a groove. We use this mechanism to apply less force. There are two basic pulleys:
Fixed pulley (F=R)
Movable pulley (F=R/2)
                                                     








COMPOUND PULLEY SYSTEMS
This is a special combination of fixed and movable pulleys.The more pulleys we have, the mechanism is more complex, but  it is easier to lift the load.
    
  Vertical and Exponential systems
Resultado de imagen de horizontal pulley system
Horizontal System




domingo, 20 de noviembre de 2016

CLASSIFICATIONS OF MECHANISMS 

Resultado de imagen de gear gif
Rotary transmission
Transmision of motion
* Linear transmissionpuley
* Rotary transmisiongears


Resultado de imagen de pulley gif
Linear transmission

Transformation of motion
* Rotary-linear⇒ rack and pinion
* Reciprocating rotary-linear⇒ crankshaft
Resultado de imagen de rack and pinion animation
Rotary-linear
Resultado de imagen de crankshaft
Reciprocating rotary-linear

                                           



                     


Motion control
* Direction control⇒ ratchet
* Speed reduction⇒ brake
Resultado de imagen de brake gif
Speed reduction

Imagen relacionada
Direction control










Energy accumulation
* Absorption/Dissipation⇒ spring


Resultado de imagen de spring mechanism gif

Connection
*Linkage⇒ clutch
*Support⇒plain bearning
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Linkage (clutch)

Resultado de imagen de clutch gif
Support (plain bearning)

CONSERVATION OF ENERGY AND WORK IN MECHANISMS

Mechanisms can´t create energy on their own. All mechanisms produce the same amount of work that is done to them, including energy that is lost to friction and heat.
If a mechanism increases force, it must decrease motion, in this way, energy and motion are conversed.

 MECHANISMS




WHAT IS A MECHANISM?
mechanism is a device designed to transform input forces and movement into an output force and motion.

Imagen relacionada

Mechanisms transmit and transform force and motion from an input source, to an output receptor.In the case of a bicycle the input source is our legs.
                               Resultado de imagen de gif bicicleta
                               

THE PARTS OF A MECHANISM

                      Input of force and motion
                                      ⇩
                               Mechanism
                                      ⇩
                      Output force and motion

domingo, 6 de noviembre de 2016

BLOGS
Blogs are a special type of web page. Many blogs are opinion generator about a variety of topics. Other blogs are used as 'online diaries' for people.

Bloggers publish entries in chronological order, with newer posts appearing at the top of the list. People can write a comment with their opinion as well.

Resultado de imagen de tumblr and blogger
Tumblr, Wordpress and Blogger are some of
the most popular weblogs.

WIKIS
A wiki is a collection of web pages that visitors can edit, modify or expand.
 Adding new content to a wiki page is easy:

Resultado de imagen de pbworks
Other example of wiki
1.-Click in the Edit button.
2.-Write a new contribution.
3.-Click in the Save button.

Resultado de imagen de wikispaces
An example of wiki







WIKIPEDIA

Wikipedia is a universal encyclopedia with no restrictions on use, modification or redistribution. Anyone can contribute their knowledge to this project.
Resultado de imagen de wikipedia