Machines, Mechanisms, and Components

• Technical development began through using primitive tools to perform tasks easier than by hand.
• Humans have developed machines to control their environment for self-benefit.
• Machines function by converting, transferring, or modifying the speed of movements to simplify life.

Machines and Mechanisms

• Since prehistoric times, auxiliary elements have been needed to perform tasks.
• Initially, sticks and stones were used, evolving into machines.
• A machine consists of parts working together to use energy for work and benefit.
• Machines have three key components

Machine Components

• Motor: it is an element responsible to supply the initial energy to the machine.
• Receptor: it recieves the force generated in them achine.
• Transmitter: it is an element responsible to transmit and transform the movement from the motor to the receptor.
• Most machines use motors that generate circular motion, but this isn't always ideal.
• Mechanisms are used to transmit this circular motion and transform them into linear motion.

Mechanisms

• Mechanisms are devices designed to transmit or transform motion.

Types of Mechanisms

Motion Transmission Mechanisms

• These mechanisms recieve energy and simply transfer it to the receptor.
• An example is the gears of a clock, which transmit circular motion to move the hands.
• These classified as linear or circular

Linear Transmission Mechanisms

• Are simple machines like levers and pulleys.

Circular Transmission Mechanisms

• Include friction wheels, pulley systems, gears, and worm-gear systems.

Motion Transformation Mechanisms

• These mechanisms Receive motion and transform it to suit the components of the receptor.
• These are the group of mechanisms of the screw and nut system, the pinion and rack, the connecting rod and crank, and the cams

Levers

• Levers are rigid bars that pivot on a support point called a fulcrum.

• They lift weights by applying force and have components of; effort/power, resistance/load arm

• Effort is the applied force, while resistance is the weight or force to be overcome.

• The law of the lever states: P·bp=R·br where:

  • P is the applied power.
  • bp is the distance to the support point.
  • R is the resistance
  • br is the distance of resistance

Lever Classification

• The classification is based on the locations of force, fulcrum, and resistance:

First-Class Levers

• Fulcrum between load.
• Examples are seesaws or scissors.

Second-Class Levers

• Load between fulcrum
• e.g., wheelbarrows.

Third-Class Levers

• Effort between fulcrum and load
• e.g., tweezers.

Pulleys

• Pulleys are wheels with a grooved rim, used to lift heavy loads using a groove.

Pulleys fixed

• the axis of rotation is subject to a support,
• They don't reduce effort but offer comfort and allow the force to pull downwards.
• F = R the equation can be found by adding the force on the axis that supports it to the force being made.

Mobile Pulleys

• Move vertically with rope traction, often combined with fixed pulleys to reduce effort for lifting.
• For each mobile pulley the effort needed to lift decreases by half.

Friction Wheels

• Two wheels placed side by side transmit motion through friction with conductor and driven wheels.
• Conductors are labelled with odd numbers, and driven wheels with even numbers.
• The equation is: ω1d1 = ω2d2 where ω1 = speed of wheel 1

Wheel Revolution Speed

• Wheel revolution speed is measured in RPM (revolutions per minute).
• The transmission ratio i = ω2 i= d2/d1
• The same proportion is upheld if we are finding the radius.

Friction Wheel Applications

• Friction wheels application is used in record players and electronic equipment.
• Wheels never skid and drive in opposite directions, and transmission relies on friction.

Pulley and Belt Systems

• Two pulleys connected by a belt that runs in the canals of both wheels.
• Both rotate in the same direction.

Belt and pulley characteristics

• Allows movement transmission between distant axes:
  • It´s quiet
  • It´s cheap. Used in washing machine machines

Gears

• Gears contain two toothed wheels, a larger crown and smaller pinion.
• Transmission ratio depends on the number of teeth of each wheel so i=number of teeth of driving wheel/ number of teeth on driven wheel

Gears characteristics

• allows great transmission
• wheels run tooth to tooth
• movement transmission is very accurate
• produces high friction
• is expensive and difficult to manufacture
• Used in car gear boxes .watches and toys

Belt and chain devices

• Two toothed wheels linked by chain to the grooves of both ,located ata certain distance For perfect performance it should be greased frequently

Belt and chain device characteristics

• allows to transmit great power because the wheels interlock the teethe and the chair dont allow slipping
• They dont run very smoothly
• They require frequent maintenance
• Used in bicycles motorcycles and elevators.

Worm system

• The screw has only one groove cut to its shape . When the screw gives an entire rotation it just advances the screw.
• The screw must rotate as many teeth as the cone teeth must connect.
• Z for a system containing a screw equals 1 at the transmission.

Worm system characteristics

• It,s an excellent speed reducer
• Its silent and covers little space
• Movement is not reversible and the mechanism locks in places, it is very secure.
• Used in musical instrument strings, car wipers and elevators.

Chain of mechanisms

• When various mechanisms are associated on top of one another so each one impulse the other mechanisms previously.

Principal Characteristics

• May allow speed increase and speed reducer
• Consecutive gears rotate into uposit directions, but many connected items reduce friction.

Applications for chain systems:

• Mechanic clocks
• Car gears, machines or wind mills.

Movement transformation mechanisms

• Mechanisms that doesn´t just simply transmit movement
• Some transforms movement through lineat motions
• Screw wheel can be used to convert

Screw Wheel Device

• The linear motions and motions can reversible
• Used in bench presses, cars, and lids.

Drive wheel and Crank device

• Consisting of three items, the drive wheel, crank, the piston
• Its used to have alternating and linear movements:
  • Can reverse to allow motor to spin the shaft
  • Used in sewing machines, steam engines, and vehicles

A cam and follower system

• Non reversible mechanism
• Cam and follower transforms a rotation into linear or vertical motion. Consisting of one rotating piece, the cam and a follower, moving parallel to the spindle.
• Used in cutting machines or loundry products.

Gear and rack device

• Reversible mechanism so the gear can alter linear movement of the rack. Rack its a type of metal with teethe to fit perfectly to a wheel,
• Used in elevators or doors.