university of jordan electrical engineering department electric drive electrical elevators...

University of Jordan University of Jordan Electrical Engineering DepartmentElectrical Engineering Department

Electric Drive Electric Drive

The Electrical Elevator

a permanent lifting equipmentserving two or more landinglevels, including a car fortransportation of passengers, goods, running al least partiallybetween rigid guide rails.

Basic Components:

• Elevator Car.• Hoistway.• Machine/drive system.• Safety system.• Control system.

1. 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.

1.1 Standard car size:

• To prevent overloading of the car by persons, the available area of the car shall be limited and related to the rated load of the elevator.

The following table shows the standard car sizes related to the elevator rated loads.

• # of passengers = rated load /75

Where:75 represents the average weightof a person in Kg.

• The value obtained for thenumber of passengers shall berounded to the nearest wholenumber.

• Car Width (CW): The horizontal dimensions between the inner surfaces of the car walls measured parallel to the front entrance and at 1m above the car floor.

Car Height (CH): The inside vertical distance between the entrance threshold and the constructional roof of the car. Light fittings and false ceilings are accommodated within this dimension.

Car Depth (CD): The horizontal dimensions between the inner surfaces of the car walls measured at right angles to the car width and at 1m above the car floor.

1.2 Elevator Car Components:

• Car Sling, a metal framework connected to the means of suspension.

• The elevator cabin.• Mechanical accessories which are: Car door and door operator. Guide shoes. Door Protective Device.

2. 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".)

• A simple definition forthe hoistway is the shaftthat encompasses theelevator car.

• Note: Generally the Hoistway serving all floors of the building but in high-rise buildings hoistways may be banked with specific hoistways serving only the lower floors and others serving only middle or upper floors while traveling in a blind hoistway until reaching the floors that it serves. A blind hoistway has no doors on the floors that it does not serve.

2.1 Hoistway components:

• Guide rails for both the car & counterweight.• Counterweight.• Suspension (Hoisting) Ropes (Cables).• Landing (Hoistway) doors.• Buffers in the pit.

2.1.1 Guide Rails

2.1.2 Counterweight

• Counterweight is atracked weight that issuspended from cablesand 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.

• When the elevator goes up, the counterweight goes down and vice-versa .

Benefits of counterweight

• Balancing the mass of the complete car and a portion of rated load, and it will be equal to the dead weight of the car plus about 40% of the rated load.

• Reducing the necessary consumed power for moving the elevator.

• By using counterweight, the motor needs to use much less force to move the car either up or down. Assuming the car and its contents weigh more than the counterweight, all the motor has to lift is the difference in weight between the two and supply a bit of extra force to overcome friction in the pulleys and so on.

• Since less force is involved, there's less strain on the cables which makes the elevator a little bit safer.

• If the motor is using less force to move the car the same distance, it's doing less work against the force of gravity so the counterweight reduces the amount of energy the motor needs to use.

• The counterweight reduces the amount of braking the elevator needs to use so it makes it much easier to control the elevator car.

• Imagine if there were no counterweight: a heavily loaded elevator car would be really hard to pull upwards but, on the return journey, would tend to race to the ground all by itself if there weren't some sort of sturdy brake to stop it.

• In a different design, known as a duplex counterweight-less elevator, two cars are connected to opposite ends of the same cable and effectively balance each other, doing away with the need for a counterweight.

Counterweight components:

2.1.3 Suspension (Hoisting) Ropes (Cables)

• 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.

• The term Roping system can be defined as the arrangement of cables supporting the elevator and which has many types or arrangements as follows:

• Single wrap: rope passes over sheave once and connected to counterweight.

• Double wrap: rope wound over sheave twice in high speed elevators for additional traction.

• 1:1 roping: when rope connected to counterweight where cable travels as far as car in opposite direction.

• 2:1 roping: rope wraps sheave on counterweight and connects to top of the shaft, rope moves twice as far as cab.

2.1.4 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.

• Safety devices are located at each landing to prevent inadvertent hoistway door openings and to prevent an elevator car from moving unless a door is in a locked position.

• The difference between the car doors and the

hoistway doors is that the elevator car door travels through the hoistway with the car but the hoistway doors are fixed doors in each landing floor.

2.1.5 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.

• There are two principal types of buffers in existence:

• Energy accumulation: accumulate the kinetic energy of the car or counterweight.

• Energy dissipation: dissipate the kinetic energy of the car or counterweight.

The main types of elevator buffers

• A Spring Buffer is one type of buffer most commonly found on hydraulic elevators or used for elevators with speeds less than 200 feet per minute. These devices are used to cushion the elevator and are most always located in the elevator pit.

• An Oil Buffer is another type of buffer more commonly found on traction elevators with speeds higher than 200 feet per minute.

• This type of buffer uses a combination of oil and springs to cushion a descending car or counterweight and are most commonly located in the elevator pit, because of their location in the pit buffers have a tendency to be exposed to water and flooding.

• They require routine cleaning and painting to assure they maintain their proper performance specifications. Oil buffers also need there oil checked and changed if exposed to flooding

3. 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.

3.1 Types of Driving Machines:

• 1- Gearless Machine• 2- Geared Machine• 3- Drum Machine

• Look at the figures:

• Gearless Machine

• Geared Machine

• Drum Machine

3.1.1 Gearless Machine

• It used in high rise applications whereby the drive motor and drive sheave are connected in line on a common shaft, without any mechanical speed reduction unit located between the drive motor and drive sheave.

• Their sizes and shapes vary with load, speed and manufacture but the underlying principles and components are the same.

• Generally, Gearless machines are used for high speed lifts between (2.5 m/s) to (10 m/s) and they can be also used for lower speeds for special applications.

Gearless Machines Components:

• Electrical Motor.• Traction Sheave or drum.• Direct current armature in case of DC motor.• Rotor in case of AC motor.• Brake.• Machine Bedplate.• Supporting bearings.• Deflector or double warp sheave.

3.1.2 Geared Machine

• It used in low and mid rise applications. This design utilizes a mechanical speed reduction gear set to reduce the rpm of the drive motor (input speed) to suit the required speed of the drive sheave and elevator (output speed).

• Their sizes and shapes vary with load, speed and manufacture but the underlying principles and components are the same.

• Generally, geared machines are used for speeds between (0.1 m/s) and (2.5 m/s) and are suitable for loads from (5 Kg) up to (50,000 Kg) and above.

Geared Machines Components

• Drive motor.• Brake.• Speed reduction unit or gearbox.• Drive sheave.• Bedplate.• Deflector sheave (if mounted as integral part

of the bedplate assembly).

Types of geared machine drive according to location of installation:

• 1-Overhead traction: The drive machine located directly over top its hoistway or shaft.

• 2-Basement traction: The drive machine located at a basement.

• 3-Offset traction: The drive machine located at the side of the hoistway.

• Note: Basement and offset applications require

additional deflector sheaves to properly lead suspension ropes off the drive sheave and to the car top or counterweight.

3.1.3 Drum Machine

• It widely used in older passenger and freight elevator applications, though now rarely seen except for dumbwaiters.

• A drum design has one end of the suspension rope affixed to the inside of the winding drum’s drive sheave, and then allows to rope to reel in or off the outer surface of its sheave, depending upon the car direction of travel.

3.2 Main Components of machine drive system

• 1- Electrical Motor• 2- Traction (Drive) Sheave• 3- Secondary Sheave• 4- Deflector Sheave• 5- Brake• 6- Speed reduction unit or gearbox• 7- Machine Bedplate

3.2.1 Electrical Motor

• Electrical Motor is used to raise and lower the elevator cab, the direction of motor rotation and speed (rpm) are directed and supervised by devices located within the elevator controller.

• The motor component of the elevator machine can be either a DC motor or an AC motor .

A) DC Motor:

• DC motors use carbon brushes to control or regulate the operational speed of its motor.

• It is an important maintenance task to regularly inspect, repair and replace these brushes.

• Failure to do so in a timely fashion can result in equipment mis-operation and lead to significant motor damage.

Advantages of using DC motors:

•Has a good starting torque. •Ease of speed control using a DC generator with a variable output or static converters.

B) AC Motor

Advantages of using AC motors:

•More regularly used because of its ruggedness and simplicity. •More ride quality.

Types of Electrical Traction Drive Systems

A- Geared traction control, which includes: •Single speed AC motor.•Two speed AC motor.•Variable voltage AC motor (VVAC).•Variable voltage, variable frequency AC motor (VVVFAC).•Variable voltage DC motor(VVDC).

B- Gearless traction drives, which include:

•Variable voltage DC motor (VVDC). •Variable voltage, variable frequency AC motor(VVVFAC).

3.2.2 Traction (Drive) Sheave• The powered pulley connected to either the elevator

drive motor’s output shaft (gearless) or to the output side of the mechanical speed reduction unit (geared).

• The circumference of the sheave has a series of “U” or “V” shaped grooves cut into it , in which sit the elevator suspension or hoist ropes.

• The friction loads created as the suspension ropes pass over the grooved surface of the sheave causes motion to be transmitted from the drive motor to the elevator cab or counterweight.

3.2.3 Secondary Sheave

• Pulley that is normally used on gearless elevators and is located directly beneath the machine or drive sheave.

• It has a grooved surface over which pass the suspension or hoist ropes.

3.2.4 Deflector Sheave

• Pulley used to offset or direct the vertical drop or location of the steel hoist ropes running between the elevator car and its counterweight.

• Where the horizontal distance between the hitch point for the car and the counterweight is larger than the diameter of the drive sheave, one or more deflector sheaves are used to guide the hoist ropes.

• These devices are grooved sheaves that lead elevator suspension ropes off the drive sheave down to the car top and counterweight.

• The number and size of deflector sheaves will be a function of the elevator’s size, machine placement and roping arrangement.

Drive Sheave without Deflector Sheave

Drive Sheave with Deflector Sheave

3.2.5 Brake• Traction and drum 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.

• During typical operation, thisbrake is electrically lifted or“picked” against adjustabletensioned springs.

• In the event electrical power isremoved from the brake, these springs ensure it immediately drops back against its drum or disk, bringing the car to a safe stop.

• While applied, the brake will securely hold in place the elevator and its counterweight.

• Some older elevators have a control design whereby the brake is used to decelerate the car from full speed to a stop.

• Modern elevator controls use electrical circuitry to slow and stop the car under normal operation.

• Once the car has stopped, the brake is released to hold the car in position.

• However, in the event an elevator’s safety circuit is actuated, the brake is immediately applied to stop and hold the car and its counterweight, regardless of the type of control.

Brake Components and Configurations:

• The most common form of elevator brake consists of a machined drum onto which two curved shoes or pads drop onto the surface of the drum.

• The brake drum or disk is directly coupled to the elevator drive shaft. On some machines, the brake is an external element whereby the brake arms and their shoes are located outside and above the rotating drum surface as shown:

• There is one type of gearless machine that has its two brake arms applying force against an inside or interior rim on the drive sheave as shown:

3.2.6 Speed reduction unit or gearbox

• The most common type of speed reduction unit consists of a hardened steel worm shaft, mated with a bronze ring or crown gear (worm-gear set).

• The mating surfaces of these two elements are contained within an oil bath for lubrication.

• Regular access to the machine to check the level of oil, as well as the condition of the oil and the ring gear is an important aspect of ongoing equipment maintenance.

3.2.7 Machine Bedplate

• The gear box, motor and brake may be assembled on a common bedplate. This fabricated steel structure serves to keep all parts in accurate alignment and allows one-piece shipment.

• Some machines have the motor and brake as an integral part of the gear case, removing the need for a separate bedplate.

4. 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.

4.1 Device for locking landing doors (Hoistway Door Interlock).

Device for locking landing doors Hoistway Door Interlock

• It shall not be possible in normal operation to open the landing door (or any of the panels in the case of a multi-panel door) unless the car has stopped, or is on the point of stopping, in the unlocking zone of the door.

• The unlocking zone shall not extend more than 0.2 meter above and below the landing level.

• The hoistway door locking mechanism provides a means to mechanically lock each hoistway door and the elevator cannot leave a landing unless the doors are fully closed and secured.

• They are also interconnected electrically to prevent operation of the elevator if any of the elevator’s hoistway doors are open. Should the doors be forced open, the interlock circuit will be broken, causing the elevator to immediately stop.

• Each landing door shall be provided with a locking device satisfying the previous conditions. This device shall be protected against deliberate misuse.

• Landing doors shall be capable of being unlocked from the

outside with the aid of key , which fit the unlocking triangle (Hoistway Emergency Door Keys).

• Hoistway Emergency Door Keys permit the unlocking of the hoistway door interlock.

4.2 Progressive safety gear

• 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 retardation is affected by a breaking action on the guide rails and for which special provisions are made so as to limit the forces on the car, counterweight o balancing weight to a permissible value.

• Pair of safety gears is mounted in the lower part of car sling and operated simultaneously by a linkage mechanism that actuated by overspeed governor.

Safety Mechanism

• The progressive safetygear and the braking device are activated bymeans of a linkage with a shearing mechanism asshown beside.

Operation of Safety Mechanism

•Dependent on the direction the safety lever is pulled upwards or downwards; the movement of the lever is transmitted to the shearing mechanism by means of a rocker.

•The grip wedges of progressive safety gear or braking device which are linked with the safety-gear levers are released from their rest position between rail and jaw body which is maintained by a spring assembly.

•The safety-gear lever assembly which is arranged in the form of a shearing mechanism ensures that the progressive safety gears and/or braking device are activated simultaneously and in pairs.

Reset

• The progressive safety gear and the braking device are reset by moving the car opposite to direction of safety gear operation.

• (Move car in electric recall mode, or if necessary, by releasing the car from the engaged position).

Safety switch• Safety switch is mounted on the bottom transom

on the side of the safety-gear.

• The switch is operated by the movement of the safety-gear lever up or down according to actuation direction if the car travels at over speed.

• The switch interrupts the safety circuit causing machine drive power off.

4.3 Over Speed Governor

• Over speed governor function is to actuate the safety gear if the car speed exceeds 115% of its rated value.

• Usually a cable is attached to the safeties on the underside of the car, called the governor rope. This rope runs down through a pulley at the bottom of the shaft and back up to the machine room and around the governor sheave.

• When over-speeding is detected, the governor grips the cable which applies the safeties that wedge against the guide rails and stops the car.

• The over speed governor works on the floating principle with a cam curve and roller guided rocker.

• It is situated either in the machine room or in the head room.

• Over speed governor is provided by a factory adjusted switch activated when the tripped speed is reached to disconnect the machine drive starting with governor pulley blocking.

4.4 Buffers

• 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.

• There are two principal types of buffers in existence: A- Energy accumulation: accumulate the kinetic energy of the car or counterweight.

B- Energy dissipation: dissipate the kinetic energy of the car or counterweight.

• Polyurethane buffers which are energy accumulation type with non-linear characteristics are used for lifts that have rated speed not more than 1 m/sec.

• The main types of elevator buffers are:

• look at slides (30,31,32) to get more details.

4.5 Final Limit Switches

• Final limit switches shall be set to function as close as possible to the terminal floors (the highest or lowest landing of lifts), without risk of accident.

• Final limit switches shall operate before the car comes into contact with the buffers. The action of the final limit switches shall be maintained whilst the buffers are compressed.

• After the operation of final limit switches, the return to service of the lift cannot occur automatically.

4.6 Other Safety Devices and Switches

• A- Overload Device.

• B- Door Protective Device such as: (photo-electric and infrared sensors, safety edges).

• C- Emergency Stop Switch.

• D- Emergency Alarm Switch.

• E- Anti-Egress Lock Device.

5. 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.).

5.1 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.

5.2 Types of elevator control systems

• 1- Single Automatic operation:• First automated system w/o single call button

on each floor and single button for each floor inside car.

• Called if no one is using it.• Passenger has exclusive use of the car until rip

is complete.

• 2- Selective collective operation:• Most common, remembers and answers calls in

one direction then reverses. When trip complete, programmed to return to a home landing.

• 3- Group automatic operation: • For large buildings with many elevators which are

controlled with programmable microprocessors to respond.

5.3 Elevator control system components

• 1. Inputs (sensors, buttons, system controls).

• 2. Outputs (actuators, bells, displays).

• 3. Controllers such as:a. (Relay based controller “electromechanical

switching”)b. (Solid-state logic technology,c. PLC controller “computer based technology”).

5.3.1.A Sensors

• A.1 Magnetic and/or photo electric: • These pick up signals regarding the location of the car. This

sensor is usually placed on the car itself and reads the position by counting the number of holes in the guide rail as they pass by in the photo-electric sensor or in the case of the magnetic sensor, the number of magnetic pulses.

• A.2 Infrared:• This is used to detect people entering or leaving the elevator.

• A.3 Weight sensor (Over Load Device):• This is placed on the car to warn the control

system if the design load is exceeded.

• A.4 PVT (primary velocity transducer): • Velocity of the drive sheave is sensed with this

encoder

5.3.1.B Buttons

5.3.1.C System Controls

• They are used to turn the elevator system on and off.

• They are only accessible from an elevator control room.

• They would typically be used quite infrequently.

5.3.2.A Actuators• 5.3.2.A.1 Door Opening Device:• It opens the inner door of the elevator cab and the outer

door of the elevator shaft simultaneously at each floor.

• 5.3.2.A.2 Electric Motor:• The controller interacts with the elevator engine by sending

it a signal that specifies at which speed and in what direction the engine should be going in.

• A stop signal is constructed by setting the speed parameter of the signal to zero.

• 5.3.2.A.3 Brake:• Brakes in elevator system are electromagnetic and

mechanical.

• The electromagnetic brakes activate automatically if there is sudden loss of power or when the car is stationary.

• The mechanical brakes at the sheave itself also stop the car from moving when the car is inactive.

5.3.2.B Bells• 5.3.2.B.1 Emergency Bell:• It is used to alert people outside of the elevator system

when someone is trapped inside the elevator cab.

• 5.3.2.B.2 Load Bell:• It is used to alert the passengers inside the cab that

there is too much weight in it.

• The controller interacts with the emergency bell and the load bell by sending each one of them a signal to ring.

5.3.2.C Displays

5.3.3 Controller

• It is a device which manages the visual monitoring, interactive command control and traffic analysis system to ensure the elevators are functioning efficiently.

What is the function of the elevator controller?

• It controls the speed of elevator engines.

• Processes elevator summons and floor requests from passengers.

• Controls the operation of the elevator doors of a cab through communication with door opening devices.

5.3.3.1 Relay Based Controller (Electromechanical Switching)

• A simple elevator with few stops and manual door operation can be served well by a relay controller.

5.3.3.2 Solid State Logic Technology

• It includes both discreet transistors circuits and integrated circuit boards.

• It gives improved reliability, lower power consumption and easy fault diagnosis than electromagnetic relay technology.

5.3.3.3 PLC Controller (Computer Based Technology)

• Elevator concepts utilizes a special type of industrial computer called a (PLC) or a Programmable Logic Controller to control the logic of more complex jobs.

• They are very dependable, compact and simple to troubleshoot.

5.4 Elevator Control System Sequence Diagrams

• The elevator control system may be viewed either from:

• The point of view of an individual user. or as:• A system being acted on by many users.

5.4.1 The Point of View of an Individual User

5.4.2 A System Being Acted On By Many Users

Thank you