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MECHANISMS (ROTARY MOTION MECHANISMS (Friction drives, Pulleys with belt,…
MECHANISMS
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The motion produced by a motor is transformed and converted by those mechanisms to receiving elements, so they can do the job for which they were constructed.
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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The ration between the rotation velocities 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
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- F is the force of 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.
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A fixed pulledy is a wheel that has a groove around it into which a rope, chain or belt fits. It rotates around an axle that is fixed to an immobile surface.
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A fixed pulley is a balanced when the effort F is equal to the resistance of the load, R:
F=R
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This is a system of fixed and moveable pulleys, often called block and tackle. If we use more pulleys, the system becomes more complex, but less effort is needed to move the load. On the left you can see two different types of block and tacle pulleys (n= the number of movable pulleys)
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These 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.
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The ration 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·D1=N2·D2 --> D1/D2=N2/N1
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They consist of two 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 rotation of one axle is transmitted to the other through the connected pulleys.
The two pulleys, and the two axles, rotate in the same direction.
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The relation between the rotation velocities of the wheels depends on the number of teeth on each gear:
N1·Z1=N2·Z2-->Z1/Z2=N2/N1
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- Transport people from A to B.
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- Entertain children in the park.
- Lifting and carrying objects.
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Friction drives are made up of two 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 two wheels, each one rotates in the opposite direction to the one next to it.
- N1 and N2 are the velocities of the primary drive wheel and the output wheel.
- D1 and D2 are the corresponding diameters.
They are expressed in units of length: usually millimitres.
The ratio D1/D2 is called gear ratio.
Cogwheels are sets of wheels that have teeth called cogs.
The cogs fit into the spaces between the cogs of another wheel, so that one wheel moves the other.
They transmit a rotary motion between the two connected axles, which can be parallel, perpendicular or oblique. Gears can be cylindrical or conical. All the teeth must be the same shape and size. The two wheels and the two axles rotate in opposite directions.
- 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.
This is a screw that moves a helical cogwheel that is set perpendicular to the screw.
Each time the screw rotates, the gear moves forward as many teeth os there are grooves in the screw, usually a small number: 1, 2 or 3.
This is used to reduce velocity as well as functioning as a brake system.
- Nwheel and Nscrew are the velocities of the wheel and of the screw.
- Zgrooces is the number of grooves of the screw and Zwheel
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 chain transmits the rotary motion of axle 1 to axle 2 by means of gears 1 and 2, and the two gears rotate in the same direction.
This system transmits greater forces without losing velocity of the drive wheel (1) and the driven wheel (2), use the same formula as for gear mechanisms.
- N1 and N2 are the velocities of the corresponding wheels.
- Z1 and Z2 are the number of teeth.
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