MECHANISMS
Around us we can see many moving objects and mechanisms that produce that we can also call motion.
How do these objects move?The chain gear system of a bicycle, the gears of a clock or watch,the lever in a seesaw and the pulley in a well are some of the simpler mechanisms that can be found in many objects.
Uses:
Transporting people from A to B
lifting and carrying objects.
entertaining the children
telling the time
The most important element in all of them is the driving force that initiates the movement.
The driving force can be a spring, an electric motor or our own muscles.
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.
Classification of Mechanisms
Controlling and regulating motion
Joining elements
Transforming motion
Storing energy
Transmitting motion
Linear
rotary
Rotary to linear
rotary to recipocrating.
Linear motion mechanisms
Mechanisms that transmit motion and force in a straight line from one point to another.
Lever:A lever is a rigid bar that is support 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 others end of the bar.d is the distance from F to the fulcrum.r is the distance from R to the fulcrum.
Types of levers:These are classified on three types:Class 1,Class 2 and Class 3 based on their relative postion of the lever,the effort applied and the resistance.
Fixed pulley:A fixed pulley is a wheel that has a groove around it into which a rope,chain or belt fits.I.Uses:Well and gym equipent for example.
Movable pulley:A moveable pulley is a set of two pulleys,one is fixed while the other can move in a linear direction.
Compound pulley:This is a system of fixed and moveable pulleys,often called block and tackle.Uses:Lifts,good lifts and cranes.
Rotary motion mechanisms.
These mechanisms transmit motion and effort in a circular way,from input to the output.They include friction drives,pulley systems, gears and worm gears.
Friction drives:Friction drives are made up of two more wheels that are in contact.TUses:Often in industry to make metal sheets,rolls of paper or the other fine materials.
Pulleys with belt:They consist of two pulleys or wheels that are certain distance apartUses:Industrial machines,vehicle engines,washing machines and drills.
Gear mechanisms and cogwheels:Cogwheels are sets of wheels that have teeth called cogs..Uses:In industrial machenary,vehicles domestic appliances such as drills and food processors.
Worm gear:This is a screw that moves a helical cogwheel that is a set of perpendicular to the screw..Uses:Lap counters,gear reduction systems,musical turning keys and windscreen wipers.
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 streched over both wheels.Uses:Industrial mechanery,engines and motors,bicycles,motorbikes and three wheeled vehicles.
Gear train:This is a system of more than gears,connected togheter as a shown in the diagram.Uses:Machine tools,vehicles gearboxes and some electrical appliances.
Mechanisms that transform motion:There are two ways in which motion can be transfromed:From rotary into linear,from rotary into reciprocating.
From rotary into linear:Rack and pinion system:This uses a pinion that is small cogwheel mounted on a rack that is toothed belt or bar.
Winch and crank handle:A crank is a bar attached to an axle that is used to turn it.The longer the crank handle,the less effort is needed to lift the load.Uses:Roller blinds,coffe grinders,crushing machines and cranes.
Nut and bolt system.This consists of a bolt or threaded bar and a nut that has the same interior diameter as the diameter of the bolt.Uses:Presses.taps,car jacks,tops for bottles.
From rotary into reciprocating motion:Crank -link slider:This is composed of a crank and a rod called a connecting rod or link.Uses:Internal combustion engines,windscreen wipers and machine tools.
Crankshaft:This is a set of connection rods attached to a jointed axle.Each of the joints of the axle acts as a crank.Uses:Combustion engines and sewing machines.
Cam:This is basically a rotating obhject that pushes a follower as it moves.We can change the shape and the usable profiles.Uses:combustion engines,automatic systems...
Eccentric cam:This consists of a wheel with an offcentre rotation axle that doesnt coincide with the centre of its circumference.Uses:sewing machines,windscreen wipers.
Other mechanisms:Mechanisms for controlling and directing motion:The most typical mechanism of this type is the ratchet.Uses:watch-making,security cables and brakes.
Band brakes:metal band that puts preassure attached to the axle of the object.
Drum beakes:Include one or two brake shoes that come into contact with the drum.
disc brakes:Pads and a disc attached to the object
Mechanisms that store energy:Springs are devices that absorb energy.This energy can be relased later,little by little or all at once.Uses:Vehicle suspension systems.
Traction:The spring is streched,in a bed frame for example.
Torsion:The springs is twisted,in a clothes peg for example,
Compression:The springs is compressed,in a chair for example.
Connecting mechanisms:Clutches are mechanisms that allow axles or shafts to be connected or separated.
Movable connections:Are used to connect shafts that can move along the axles or at an angle to each other.There are two main types:Oldham joints and Cardan joints.
Fixed connections:Are used to make permanent connections between axles and shafts.
Supports:Bushings and bearings.
Bearings:Are made up of two concentric rings with balls or rollers between them.
Bushings:The axle or the shaft is inserted in a plain circular piece that is placed inside a housing to provide a bearing surface