Electrostatic Spray Painting - Lnx01lnx01.ee.polyu.edu.hk/~eewlchan/EE1D01/EE1D01_2a.pdf · Electrostatic Spray Painting During car production, the unpainted car body and ... Apermanent

EE1D01 Electrical Science for Everyone

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Negative car

Positive spray gun

� Static electricity can be used in spraying liquids e.g. spraying pesticides, spray painting

� The car gains electrons

� The gun looses electrons so the paint looses electrons

� The paint spreads out as each positive drop repels

� No paint is wasted as the negative car attracts the positive paint

Electrostatic Spray Painting


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Electrostatic Spray Painting

� During car production, the unpainted car body and the paint are given opposite electric charges.

� Unlike charges attract, so:

� The paint sticks to every corner of the car body

� The paint covers the car body evenly.


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Principle: Electrodes at high voltage create a corona effect (ionized atmosphere) surrounding them. This charges the passing particles. Once charged, particles are subject to a transverse electrostatic force that pulls them toward the collecting plates.Plates are periodically rapped (vibrated) to make the collectedparticles fall down into a receiver basket.

Electrostatic Precipitators


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Static Electricity in a Photocopier

� (1) & (3) drum inside is charged. Light reflects an image of document on drum. Dark areas (writing and images on the original) retains a positive charge.

� (4 & 5) Charged parts of the drum attracts the negatively-charged toner ink (black powdered particles).

� (6) Toner ink transferred from drum to positively-charged paper, producing a copy of original.


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The Xerographic Process


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In an average American home, a total of approx. 125 motors accountsfor 43% of the electricity consumption.

Applications of Electric Motors


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Basic Principles DC Motor

Current in

Current out

φa

φf

By keeping flux constant, torque can be controlled by controlling armature current

Te = k If Ia

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DC Motor - Construction


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Carbon brushes


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AC Induction Motor


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Three Phase Rotating Fields


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Rotating Field


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Operation Principle� The rotating flux induces a voltage in the short-

circuited bars of the rotor. This voltage drives current through the bars.

� The induced voltage is proportional with the difference of motor and synchronous speed. Consequently the motor speed is less than the synchronous speed.

� The interaction of the rotating flux and the rotor current generates a force that drives the motor.

� The force is proportional with the flux density and the rotor bar current

Induction Motors


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Squirrel cage rotor. � This rotor has a laminated iron core with slots, and

is mounted on a shaft. � Aluminum bars are molded in the slots and the

bars are short circuited with two end rings. � The bars are slanted on a small rotor to reduce

audible noise. � Fins are placed on the ring that shorts the bars.

These fins work as a fan and improve cooling.

Induction Motors


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Induction Motors (5)


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� Difference between angular velocity of rotor and angular velocity of the rotating field causes squirrel cage bars to cut the field magnetic field inducing current into squirrel cage bars.

� This current in turn magnetizes the rotor

Rotor of Induction Motor


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s

rssϖ

ϖϖ −=

Slip of Induction Motor

Slip


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Torque Speed Curve


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� New Designs for Compact Gearless Machines

� Torque Strength from Permanent Magnets

� 90–95% Efficient

� Compatible with Inverters to Control Speed

� Requires Synchronous Flux Vector / Angle Control to Regulate / Modulate Torque

� Supply Limited to Specialty Machine Builders

� Not Suitable for High Speed Geared Designs

� Can Act Like a Generator

AC Permanent Magnet Motors


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Three phase AC current

Phase 1

Coil 1

Phase 2

Coil 2

Phase3

Coil 3

Three phase AC current

Phase 1

Coil 1

Phase 2

Coil 2

Phase3

Coil 3

AC Permanent Magnet Motor


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KONE EcoDisc®


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� Since early 2011, prices of NdFeB PMs have been increasing considerably, due to China’s limited quotas and raised taxes on rare-earths exports.

� Increasing price of rare-earth magnets poses a possibility of magnet manufacturing in other countries, including Brazil.

� Prices of Rare-earth magnets are not stabilized yet.

� Search for efficient but non-rare-earth motor technologies

Rare-earth PM challenge

Neodymium Samarium


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The Electrical Elevator/Lift

A permanent lifting equipment

serving two or more landing

levels, including a car for

transportation of passengers,

goods, running al least partially

between rigid guide rails.


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� 236 BC – First Passenger Lift, Archimedes

� 1853 – Safe Elevator Demo, Elisha Otis

� 1857 – First Safe Elevator Installation, Cooper Union, NYC

� 1861 – Otis Elevator Patent

Brief History of Lift


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� 1873 – First Modern DC Motor

� 1874 – J. W. Meaker Door Opener Patent

� 1880 – First Electric Motor Controlled Elevator Siemens / Sprague

� 1882-1889 – Tesla AC Induction Motor 3-Phase Squirrel Cage Design

� 1889 – Otis Elevator uses DC Motor



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Otis DC

Elevator Motor

1889



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� 1891 – Ward Leonard Variable Speed Control� AC induction motor turning DC generator

� Rheostat to control the generated voltage

� DC Voltage Controls DC Motor Speed

� 1900-1970’s – Ward-Leonard M-G Sets and DC Motors used for Variable Speed Elevators

� AC Motors used 1 and 2 Speed Starters



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Otis No. 1 Geared DC Machine (1915)


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Otis Gearless DC Machine (1919)


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M-G Set Controls (Otis Elevator, 1920’s)


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Otis Type 84

Broadway,NYC

1930’s


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� 1975-Present

� Thyristor (SCR) DC drives

� All analog components in the 70’s

� Replaces aging M-G Sets

� 1980’s – Microprocessors Improve

� Car Dispatch and Motor Drive Controllers



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Elevator Control System

� Elevator Control System is the system responsible for coordinating all aspects of elevator service such as travel, speed, and accelerating, decelerating, door opening speed and delay, leveling and hall lantern signals.

� It accepts inputs like (button signals) and produces outputs like (elevator cars moving, doors opening, etc.).


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Aims of the control system

� To bring the lift car to the correct floor.

� To minimize travel time.

� To maximize passenger comfort by providing a smooth ride.

� To accelerate, decelerate and travel within safe speed limits.


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32-bit microprocessor

relay logic solid state


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� Late 1980’s –� Variable Frequency Inverters AC Induction Motors,

Geared applications only

� Early 1990’s –� More AC inverters and motors begin to displace small

DC, 3-15 HP

� Mid-1990’s –� Vector Control AC Inverters 10-40 HP almost as good as

SCR-DC.

� KONE Introduces PM EcoDisc AC Machine



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– Custom Gearless AC Induction Machines

– First Fully Regenerative AC Elevator Drives

– Much Discussion on PM-AC and Machine Room-Less (MRL)

– SCR-DC still used for medium and large building

• Late 1990’s –



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– More PM-AC Motor manufacturers. PM Gearless begins to replace AC Geared

– EU focus on efficiency and harmonics/EMC

– Lower cost IGBT inverter components

– North America begins to focus on energy reduction

– New construction leaning toward AC

– SCR-DC still used

•2000-Present –

Brief History

Machine room -

- Counter weights

- Guide rails

- Motor with sheave

- Speed governor

Hoistway doors -

- Controller

Basic Components of Traction Elevators

Car -

Operating Modes


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Lift Car

Typical

Speed

Profile

Acc/Dec

normally

limited to

1-1.5 m/s2

Jerk

normally

limited to

1 m/s3

Speed Profile

Mo

tor

Po

wer

[kW

]

Motor power

velocity

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70

60

40

20

0

20

40

60

Time [s]

DC-motor, SCR drive 80m / 3.6m/s / 1600kg

DC Lift Drive Power Regeneration


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Lift System Configuration


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Elevator Machine and Drive System

� Driving machine is the power unit of the elevator, and usually located at the elevator machine room.

� The Driving machine used to refer to the collection of components that raise or lower the elevator.

� These include the drive motor, brake, speed reduction unit, sheaves and encoders.


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Hoistway

� Hoistway is the space enclosed by fireproof walls and elevator doors for the travel of one or more elevators, dumbwaiters or material lifts. It includes the pit and terminates at the underside of the overhead machinery space floor or grating or at the underside of the roof where the hoistway does not penetrate the roof. (Hoistway is sometimes called "hatchway" or "hatch".)


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Hoistway


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Landing (Hoistway) Doors

� The door that is seen from each floor of a building is referred to as the outer or hoistway door.

� This hoistway door is a part of the building (each landing).

� It is important to realize that the car door does all the work; the hoistway door is a dependent. These doors can be opened or closed by electric motors, or manually for emergency incidents.


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Landing Door


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� Suspension Ropes are Suspension means for car and counterweight, which are represented by steel wire ropes.

� They are used on traction type elevators, usually attached to the crosshead and extending up into the machine room looping over the sheave on the motor and then down to the counter weights.

Hoisting Cables (or ropes)


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Sheave



52traditional rope new flat belt



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Elevator Car

� Elevator Car is the vehicle that travels between the different elevator stops carrying passengers.

� It is usually a heavy steel frame surrounding a cage of metal and wood panels.


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Cross head

Elevator Car


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Roller guides on

Cross head

Guide Rails


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Counter weight

Counterweight

Counterweight is a tracked weight that is suspended from cables and moves within itsown set of guide rails along the hoistway walls.

The elevator car is balanced by a heavy counterweight that weighs roughly the same amount as the car when it's loaded half-full.


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Brake

� Traction machines are provided with a mechanical brake, designed to stop and safely hold an elevator.

� A centrifugal force governor is provided on most elevators to guard against over speeding (when a car travels in excess of 20% of top speed, the governor will activate a safety stop device).

� Safeties are installed at the bottom of an elevator car and occasionally on counterweights to provide positive emergency stopping when activated by the governor.


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Brake


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Governor rope

Governor and Safety Clamp


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� Safety gear is a mechanical device for stopping the car (or counterweight) by gripping the guide rails in the event of car speed attaining a pre-determined value in a downward direction of travel, irrespective what the reason for the increase in speed may be.

Progressive Safety Gear


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Buffers in the pit

� A Buffer is a device designed to stop a descending car or counterweight beyond its normal limit and to soften the force with which the elevator runs into the pit during an emergency. They may be of polyurethane or oil type in respect of the rated speed.


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Buffers


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Safety system

� Safety system components:� 1- Device for locking landing doors

(Hoistway Door Interlock).� 2- Progressive safety gear.� 3- Overspeed governor.� 4- Buffers.� 5- Final Limit switches.� 6- Other safety devices and switches.


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Car Positioning

Every Floor Top of Car


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Car Positioning


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Geared Traction Elevator

� Geared traction machines are driven by AC or DC electric motors, they use gears to control mechanical movement of elevator cars by “rolling” steel hoist ropes over a drive sheave which is attached to a gearbox driven by a high speed motor.

� These machines are generally the best option for basement or overhead traction use for speeds up to 2.5 m/s.

� In order to allow accurate speed control of the motor, to allow accurate leveling and for passenger comfort, a DC hoist motor was the preferred solution in high-traffic elevator installations for many decades.


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Gearless Traction Drive

� Gearless traction machines are low speed (low RPM), high torque electric motors powered either by AC or DC. In this case, the drive sheave is directly attached to the end of the motor.

� Gearless traction elevators can reach speeds of up to 10 m/s, or even higher.

� A brake is mounted between the motor and drive sheave (or gearbox) to hold the elevator stationary at a floor. This brake is usually an external drum type and is actuated by spring force and held open electrical.

� a power failure will cause the brake to engage and prevent the elevator from falling.


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Geared and Gearless Drives


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ThyssenKrupp Elevator: TWIN� Two independent cars in one shaft

� Save the building space, reduce waiting time and increase the capacity.

� Buildings floors can exceed 100.

Landing floor selection system

Counterweight TWIN panorama elevator

1350kg, 2.5m/s, 60m


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Hydraulic Elevators

� Conventional hydraulic elevators: They use an underground cylinder, are quite common for low level buildings with 2-5 floors (sometimes but seldom up to 6-8 floors), and have speeds of up to 200 feet/minute (1 meter/second).

� Holeless hydraulic elevators were developed in the 1970s, and use a pair of above ground cylinders, which makes it practical for environmentally or cost sensitive buildings with 2, 3, or 4 floors.

� Roped hydraulic elevators use both above ground cylinders and a rope system, which combines the reliability of inground hydraulic with the versatility of holeless hydraulic, even though they can serve up to 8-10 floors.

� The low mechanical complexity of hydraulic elevators in comparison to traction elevators makes them ideal for low rise, low traffic installations. The main disadvantage is their lower efficiency – with no counterbalancing, they require more power to operate.

� The design of a hydraulic elevator is shown in the next slide.


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Hydraulic Lifts

Piston and cylinder

Hydraulic oil reservoir

Pump and piping

Control system


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Hydraulic Pump


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Guide railGuide rail

Guide Rails


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Elevator Technologies Summary


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Escalators

� Jesse Reno, a graduate of Lehigh University, produced the first working escalator (he actually called it the "inclined elevator") and installed it alongside the Old Iron Pier at Coney Island, New York in 1896.

� Piat installed its "stepless" escalator in Harrods Knightsbridge store on Wednesday, November 16, 1898 Customers were given Brandy to recover from the experience!


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� A single 1m wide escalator can move up to 4500 passengers in an hour

� Can be used in stacks to cover up to 4 floors

� Suitable for able bodied adults

� Not unsupervised children, persons with disabilities or elderly persons.

Escalators


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Each step in the escalator hastwo sets of wheels, which rollalong two separate tracks. Theupper set (the wheels near thetop of the step) are connected tothe rotating chains, and so arepulled by the drive gear at thetop of the escalator. The other setof wheels simply glides along itstrack, following behind the firstset.

Step


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Step Chain Drive

The Step Chains are endless links connected with link pins to make a complete loop and are attached to an axle on each side of the steps forming a loop which runs for the length of the truss from the upper Main Drive Axle to the lower Tension.


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Step Chain Drive


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The Handrail provides a convenient handhold for passengers.

The Handrail is constructed of fourdistinct sections. At the center ofthe handrail is a "slider“. The nextlayer, known as the “tensionmember” consists of either steelcable or flat steel tape. On top ofthe tension member are the innerconstruction components. Finally,the outer layer, which is a blend ofsynthetic polymers and rubber.

Handrail


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Basic components

of an escalator


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Moving Walks

Available as flat walkways to reduce walking timesOr inclined at up to 12 degrees (10 degrees is best)Can transport up to 3600 passengers per hourOr 900 shopping trolleys with passengers

Not suitable for unsupervised children, the elderly and disabled


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Moving Walks


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Other Escalators

Electrostatic Spray Painting - Lnx01lnx01.ee.polyu.edu.hk/~eewlchan/EE1D01/EE1D01_2a.pdf · Electrostatic Spray Painting During car production, the unpainted car body and ... Apermanent

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