Elevators Functions & Mechanism

ElevatorsFunctions & Mechanisms

Talha Rehmani

OutlineDefinitionMajor Elevator DesignsHydraulic Elevator SystemRoped Elevator SystemMRL

DefinitionCompartment attached to a rope

Modern Passenger & Freight Elevators are more complexMechanical SystemsControl MechanismSafety Devices

Tie a rope to box3Major Elevator DesignsThree Major designs are:

Hydraulic ElevatorTraction (Roped) ElevatorsMachine room lessHydraulic Elevator SystemLift car using a Hydraulic ramThe system has three main parts:

Tank (fluid reservoir)Rotary Pump (powered by Electric Motor)Valve (Between Cylinder & Tank)Direct acting plunger or ropedRam: a fluid driven piston mounted inside a cylinder5Hydraulic Elevator System: Operations

100-150fpm (200 max)Pump forces fluid from the tank into a pipe leading to the cylinderWhen the valve is Closed: Fluid has no where to go except cylinderOpen: Fluid takes the path of least resistance and goes back into the tankFluid collects in cylinder lift the car

6Hydraulic Elevator System: OperationsCar Approached Floor:Control System (CS) sends signal to Electric Motor (EM) To gradually shut the pumpPump off: No more fluid to cylinderThe fluid already in the cylinder can not escape as Valve is still closedPiston rests on fluid and stays where it isTo Lower Car:CS sends signal to ValveFluid can flow to tankWeight of car & cargo pushes down on piston: car descendsTo stop car at any floor, CS closes the valveValve is electrically operated by solenoid switch7Hydraulic Elevator System: Pros & ConsProsEasily multiply the relatively weak force of the pump to generate stronger force needed to lift the car

ConsSize of EquipmentDig Deeper: 10 story building, dig at least 9 stories deepFairly inefficient: Takes lots of energy and do not reserve it, so one have to regenerate energy on every turnHigher Floors > Longer Piston > Longer CylinderEntire Cylinder Structure must be buried in below the bottom elevator stopEnergy of position (PE) only works to push the fluid back to tank8Rope Elevator SystemCar is raised and lowered by Cable System

Main System ComponentsControl SystemElectric MotorSheaveTraction steel ropesCounterweightGuide RailsCushion back

Rope Elevator System: Operations

10Rope Elevator System: OperationsTraction steel ropes are attached to car and looped around sheaveThe other end of rope is connected to a counterweightWhy CW?To conserve energy: PE levels shiftTo act as a see-saw

Sheave is connected to electric motor and it raises/descends the elevator according to the motion of motorGearless Elevators: Motor rotates the sheave directlyGeared Elevators: Motor turns a gear train to rotate the sheaveCar and CW rides on guide rails along the sides of elevator shaft. No swaying back and forth

Rotate sheave, the ropes move tooCW weighs the same amount as the car filled to 40 percent capacity. Means, when car is full (the average amount) the CW& car are perfectly balancedSee-SAW: so that the motor require little energy to tip the car one way or other. Motor has to overcome friction. Machine Room is constituted of sheave, the motor and the control system and house above the elevator shaft

11Rope Elevator System: Gearless

1903, Speed 500FPM OR MORE(2.54 m/s)LARGE AC MOTOR (DC MOTOR) FOR HIH SPEED AND HIGH RISEwoven steel cables called hoisting ropessmoothertwice lifetime than gearedMalaysia Petronas Towers

12Rope Elevator System: Geared

350-500 feet/minute (1.7 to 2.5 m/s)AC Motorcarry loads up to 30,000 lbs (13,600 kgs)Slower than gearlessless powerful motor is required to turn sheave

13Rope Elevator System: Pros & ConsProsVersatileEfficientMore safety systemsConsMachine rooms must be air conditionedEnergy cost

Rope Elevator System: ComparisonRise Limitations 300 feet (G)Unlimited (GL)Cost 150,000 200,000 (G)200,000 + (GL)Speeds350-500 fpm (G)500 1800+ (GL)

Safety SystemsHollywood?Line of DefensesRope SystemSeveral length of steel material is used in each ropeMultiple ropes (between 4 & 8)Powerful enough to deal with the weight of car and counterweightSafetiesBuilt in braking systems that can grab railIt is activated by a governor if elevator moves too fastPlummeting in to ground, hoist ropes snapping into two16Safeties: Governor SystemGovernor rope looped around a governor sheaveConnected to the car and another weighted sheave at the bottom of the shaftAs car speed up so does the governorSafeties: Governor Sheave MechanismOutfitted with two hooked flyweights that pivot on pinFlyweights can move freely back and forth & kept in position by high tension springAs car speed up .. Rotary movement of governor .. Centrifugal forces moves the flyweight outwards (to the outer edges of governor) against the springFlyweight hooked ends catch hold of ratchets mounted to stationary cylinder sheaveFlyweights = weighted metal arms

18Safeties: Governor Sheave Mechanism

Animation19Safeties: Governor Sheave Break MechanismAnimationElevator falls governor is activatedGovernor lock and activate pull rodPull rod engages safety braked and wedge holds on to the rail guide

20Safeties: More BackupsElectromagnetic brakes (open position): Engages when car stopsAutomatic breaking system: Stop the car if it moves too far, located the top and bottomShock Absorber System: piston mounted in oil filled cylinder and acts as a giant cushionLoad sensors

Making Rounds?Computer controlButtons in car and floorVertical holes along the shaft (magnetic or light)

Building with many floorAvoid reversing the elevator directionPassenger traffic in specific timesComputer directs to the fastest elevator to desired floorCompass (OTIS Vs. Schindler)22Automatic Doors

Door on car (indoor) and door opening into the elevator shaft (outdoor)Doors are operated by electric motor (controlled by computer)Long metal arm guide doors on railsMotion Sensors

23Machine Room Less

2-30 stories high buildings (300 feet high)200-500fpmSmaller sheave than roped elevators, allows the machines to be mounted in hoist way itselfFlat poly-urethane cable (0.1 inch or 3mm thick) is used that replaces heavy steel woven cablesLow energy costs: 60% less than geared. Up to 2-3% of total building electric load50% faster installationsMovie: http://www.otisworldwide.com/k5-gen2.html

24ReferenceHow stuff works?Otis Elevators Mechanisms

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