Mechanisms Flashcards
What do mechanical devices do?
They change an input force and movement into a desired output force and movement they can change the magnitude and direction of force
What can mechanisms be used for?
To make a force, bigger or smaller
What can mechanical devices be used for?
To produce different types of movement
What is linear movement?
Movement in a straight line in One Direction
What is reciprocating movement?
Movement in a straight line in two directions
What is rotary movement?
Rotational movement on or around an axis
What is oscillating movement?
The movement back and forth along a curved path
Name is six simple mechanisms
Inclined plane
Wedge
Screw
A lever
Wheel and axle.
Pulley
What is mechanical advantage?
A measure of the force amplification achieved by using a mechanism
What does MA stand for?
Mechanical advantage
What does mechanical advantage measure?
The ratio of the input force (effort) to the output force (load)
How do you calculate mechanical advantage?
Load divided by effort
What are gears? And what are they used for?
They are toothed wheels attached to shafts. They are used to transmit power and rotational motion around mechanical systems.
What do gear trains consist of?
Two or more interlocking gears that transmit torque and rotary motion
What is torque?
Determine force that causes rotation
What do the teeth of the gears do in a gear train?
- The teeth of the gears interlock
What is the output gear in a geartrain called?
The driver gear
What is the output gear in the geartrain called?
The driven gear
What happens if the driver gear rotates clockwise?
The driven gear rotate anticlockwise
How can the direction of rotation of the driven gear be changed?
By adding an idler gear
How does the idler gear change the direction of rotation?
It changes the direction of rotation, so that both the driver gear and the driven gear I’m moving in the same direction
Why does the size of the idler gear not matter?
It transfers, the movement without altering the speed of the gears
How do you make a faster output speed?
The input gear must be larger than the output gear
How do you create a slower output speed?
The input gear must be smaller than the output gear
How do you calculate. The number of teeth of a small gear in gear ratios?
by dividing the number of teeth on the last year by the number of teeth on the smaller gear
How do you calculate the large gear in gear ratios
The last year always equals one
What are cam mechanisms used for?
They used to convert rotary motion into reciprocal motion
What do you mechanisms consist of?
mechanisms consist of a cam and a follower
What is a cam?
Especially shaped piece of material attached to a rotating shaft
How does a cam and a follower create a reciprocating motion?
A rod known as a follower rests on the cam and rises and falls as the cam rotates
What depends on the shape of the cam
Whether the follower will either rise, fall or dwell ( Remain stationary)
Does a cam mechanism often also include
1.A slide to prevent the follower from slipping.
2.A crack (handle) to manually rotate the camshaft.
3. A wheel follower to reduce friction between the cam and the follower
List of four common cams
1.eccentric ( Circular)
2.pear-shaped,
3.snail
4.heart-shaped ( Constant velocity)
How do eccentric cams work?
The pivot ( Rotating shaft )is positioned off centre, causing the follower to steadily rise and fall
How does a snail cam work?
The follower gradually rises, and then suddenly drops. It can only rotate in One Direction.
How does a pear-shaped cam work?
The follower dwells for half a turn
It then rises as the point approaches for a quarter of a term before falling for the last quarter rotation.
How does a heart shaped cam work?
The follower rises, and falls, with no dwell period is said to have constant velocity
What is a simple fixed pulley Mechanism made from
It is made up of a rimmed wheel and a cable which sits inside of the rimmed wheel
What are the positives of a simple fixed pulley mechanism?
It provides no mechanical advantage, but it can make items easier to lift by changing the direction of force
What can reduce the magnitude of force required to lift a load?
Using two or more police together in a block and tackle system
Give an example of a block and tackle system
half the required input force to lift the load
What happens in a belt and pulley system?
Two or more pulley are connected by about to transfer rotary, motion, and force from the driver pulley to the driven pulley
Give an example of when a belt and pulley system is used
They’re used in car engines and washing machines
As the belts need to remain taught in a belt and police system, what are they made out of?
They are often made of rubber to reduce the thing
What does crossing the belts and a belt and pulley system do?
It changes the direction of the output movement
In a belt and pulley system, what happens when the driver pulley is larger than the driven pulley?
The driven pulley will rotate faster, but the torque will be less
In a belt and Pulley system, what happens when the driver pulley is smaller than the driven pulley?
The driven Polly will rotate slower, but the torque will be greater
How can the velocity ratio between two pulleys be calculated?
Diameter of driven, pulley, divided by diameter of driver pulley
What is a lever?
A mechanical device used to transmit and transform the effects of forces
What is transmitted through the lever to move the load?
Motion and input force (effort)
What are the three parts to a lever?
Effort, fulcrum/pivot,load
What is the effort in A lever?
The input force exerted on the lever
What is the fulcrum/ pivot in the lever?
The point around which the lever acts
What is the load in a lever?
The force of the object that needs to be moved
What are the three classes of levers?
First order
second order
third order
How does the first order lever work?
The fulcrum is position between the Loader and the effort.
How can the input effort required to lift the load be reduced in a first order lever?
by moving the fulcrum closer to the load.
3 examples of a first order lever….
Scissors
Seesaw
Crowbar
How does a second order lever work??
The load is positioned between the fulcrum and the effort
How can the input effort required to lift the load be reduced?
By moving the load closer to the Fulcrum
3 examples of a second order lever….
Bottle opener
Wheelbarrow
Nutcracker
What Happens in a third order lever?
The effort this position between the Fulcrum and a load
What do third order leavers not have compared to 1st and second order leavers
Mechanical advantage as the effort is closer to the fulcrum than the load. As a result, the input effort is greater than the output force.
3 examples of a third order lever
Tweezers
Human arm
Fishing rod
Name, the 3 types of linkages
Push and pull linkages
Bell crank linkages.
Changing magnitude of force
What can be joined together to make linkages?
Leavers
What do linkages change?
1.And input motion
2.force into an output motion
3.force
What dopush/pull linkages make?
Creates an identical parallel motion at the output
What kind of a push/pull linkage also be called
A parallel motion
What do bell crank linkages do?
Change the direction of motion through 90°
What happens in a reverse linkage? ( changing magnitude and force)
The fixed point (pivot)is an equal distance from the input and output leavers so the output force is equal to the input force
In a reverse linkage, what must be done to make the output force greater than the input force
You must move the fixed (pivot) point closer to the output
