MECHANISMS
1. MECHANISMS
2.LINEAR MOTION MECHANISMS
3. ROTARY MOTION MECHANISMS
5. OTHER MECHANISMS
4. MECHANISMS THAT TRANSFORM MOTION
Aeround us we can see many moving objects and mechamisms that produce movement that we can aslo call motion
The most important element in all of them is teh driving force.
How do these objects move?
The chain gear of a bicycle or the gears of a clock are some of the simpler mechanisms that can be found in many objects.
They have diverse uses
Telling the time
entretening childrens in the park
Trasporting people from A to B
CAN BE
electric motor
muscles
sparing
Mechanisms are devices that transmit and convert forces and motion from a diving force or input element to an output element
DIVING FORCE
MECANISM
OUTPUT ELEMENT
Mechanisms that transmit motion and force in a straight line frome one point to onother.
Exemples incluide levers and fixed, mobile
compund pulleys.
2.1. LEVERS
A lever is a rigid bar that is suported by a fulcrum.
✅ R is the resistence or load wich acts at the otherend of the bar
✅d is the distance from F to the fulcrum
✅ r is the distance from R to the fulcrum.
✅ F is the force or effort applied at on end of the bar
The following equation indicates a balanced lever: F x d= R x r
TYPES OF LEVERS
CLASS 1
CLASS 2
CLASS 3
the effort is in the middle between the fulcrum and the load.
the load is in the middle between the fulcrum and the effort.
the fulcrum is in the middle of the effort and the load.
2.2 FIXED PULLEY
A fixed pully is a wheel that has a grove around it into which a rope chain or belt fits
A foxed pulley is balanced when the effort F is equal to the resistemce of the load, R: F=R
USES: wells and gym equipamnet
2.3. MOVABLE PULLEY
A movable pulley is a set of two pulleys
A movable pulley is balanced when is satisfies this equation: F=R/2
2.4.COMPOUND PULLEY
This is a system of fixed and movable pulley, often called block and tackle.
USES: Lifts, goods lifts and cranes
These mechanisms transmit motion and effort in a circular way, frome the input to the output.
3.1.FRICTION DRIVES
Friction drives are made up of two or more wheels that are in contact. The frist wheel is called the primary drive wheel. when it moves, it turns or drive the seconde or output wheel, causing to move as well.
The radio between the rotation velocityof the weels or pulleys depends on the relative size of the wheels. It is expressed by following eqation:
N1·D1=N2·D2 ➡ D1/D2=N2/N1
✴ N1 and N2 are the velocites of the primary drive wheeland the **output wheel.
✴D! and D2 are the coresponding diameters
USES: often in industry to make metal sheets...
3.2.PULLEYS WITH BELT
They consist of two pulleys or wheels that are a ceratindistance aparat.
USES: INDUSTRIAL MACHEINES...
3.5. GEAR MECHANISMS WITH A CHAIN
These are two cogwheeles with parallel axles that are a ceratin distance apart, they route simultaneously by means of a metal chain or a toothed belt sterched over both wheels.
The relation between the rotation velocities of the wheels depends on the number of teeth on each gear.
N1·Z1=N2·Z1 ➡Z1/Z2=N2/N1
USES: Industrial machinery, engines and motors
3.6. GEAR TRAIN
This are a system of more than two gears, connected together as shoun in the diagram
The gear ratio between the drive wheel (1) and the driven wheel (4) depends on the number of gered teeth in the system:
N4/N1=Z1·Z3/Z2·Z4
USES: Machine tools, robotics...
3.7. PULLEY TRAINS WITH BELTS
This are a system of pulley or wheels, with a belt formed by mopre than two wheels.
The gear ratio between the drive pulley (1) and the pulley (4) depends on the relative size of the pulleys in the system. It´s exprressed as a function of thier diameters.
N4/N1=D1·D3/D2·D4
USES: machine tools and drills
VARIATION IN VELOCITY
Apart from transmitting force and motion, rotary transmission mechanisms allow velocity to vary.
CONSTANR SYSTEM
REDUCING SYSTEM
MULTIPLYING SYSTEM
There are two ways in which can be transformed:
▶From rotary into linear
▶From rotary into reciprocating
4.1. FORM ROTARY INTO LINEAR
RACK AND PINION SYSTEM
This uses apinion that is a small cogwheel, mounted on a rack that is a toothed belt or bar.
The ratio between the number of rotations of the pinion and the velocity of the movement of the rack is expressed by this eqation:
L=P·Z·N
USES:bench drills, corkscrews
NUT AND BOLT SYSTEM
This consist of a bolt or threadedbar and a nut that has the same interior diameter as the diameter of the bolt
USES: presses, taps...
WINCH AND CRANK HANDLE
A crank is a bar attached toan axle that is used to turn it. A winch and crank handle system consist of a drum rhat rotates and a crank handle that allows to pull oe lift objects.
USES: roller blinds, coffe grinders...
4.2. FROM ROTARY INTO RECIPROCATING MOTION
CRANK-LINK-SLIDER
this is composed of a crank and a rod called conneting rod or link
This device was very important in the development of steam engines
USES: internal combustion engines, machine tools...
CRANKSHAFT
This is a set of conneting rods attached to a jointed axle
USES: combustion engines and sewing machimes
CAM
This is basically a rotating objetc that pushes a follower as it moves.
USES: combustion engines , automatic system...
A set of cams fixed om the same axle is called camshaft
ECCENTRIC CAM
This consist of a wheel with an offcentre rotation axle that dose not coincide with the centre of its circumference,
USES: sewing machines, windscreen wipers
5.1. MECHANISMS FOR CONTROLLING AND DIRECTING MOTION
The most typicalmechansm of this type is the ratchet
USES: watch-making, securitycables and brakes
there are many types of brakes
DISC BRAKES
BAND BRAKES
DRUM BRAKES
5.2. MECHANISMS THAT STORE ENERGY
Springs are devices that absorb energy. this energy can be released later. litle by litele or
all at once
Springs work in different ways:
BY TRACTION
BY TORSION
BY COMPRESSION
5.3.CONNECTING MECHANISMS
Movable connections are used to connect shafts that can move along the axle or at an angle to each other.
Clutches are mechanisms tahat allow axles or shafts to be connected or separeted.
Fixed connections are used to makeperment connections between axle and shafts
5.4. Supports: bushings and bearings
In bushings the axle or the shafts is inserted in a plain cilcular pice that is placed inside a housing to provide a bearing surface.
Bearnings are made up of two concentric rings with balls or rollers between them.
This mechanisms support shafts and tramission axle.