Elevator Mechanism Service - Case Study Example

LIFT SERVICE The building under consideration is constructed over three stories and is designed as a part of commercial building. In commercial building passenger carrying capacity is kept maximum and other parameters are checked to ensure smooth and fault free functioning of the entire lift mechanism. Before analyzing the lift mechanism being used in the building, we will first focus on the type of power sources and motors available for lifting operation in such critical places. Elevator Hoisting Mechanism The building in which we are needed to implement the lift service is based on three stories but the lift design is double deck type. In this design a single lift mechanism is responsible to move passengers in two cabin cars to the desired height. While dealing with such systems, the only complication is to handle both the lift services with perfection. For doing this we need to have a perfect hoisting system for moving the lift up or down. There are three most commonly used hoisting mechanisms as listed below: 1. Traction system: Traction system is either geared or gearless depending upon the requirement. Geared traction systems make used of worm gears along with AC motor drives to move the lift u and down. Such systems make use of gear box which provides extra strength and seed to the lifting mechanism and is a good option for high speed requirements in multi-story buildings. Another type of traction hoisting system implements gearless systems which are having comparatively low speeds as compared to geared ones and need high torque motors to keep the system going. In such systems drive sheave is connected directly to the motors. In order to avoid elevator from falling, it is engaged with brake which is introduced between motor and its drive. 2. Hydraulic system: Elevators based on hydraulic system are used for lower buildings with equal to or less than 6 floors. These systems incorporate hydraulic cylinders which are difficult to manage with taller buildings in terms of precision as well as speed. These hydraulic hoisting systems require large space in basement in order to adjust the cylinders including hydraulic fluid and the rope hoisting system. Hydraulic hoisting systems are less complex as compared to traction ones but are useful for lower height and lesser traffic demands. On the contrary, these systems are less energy efficient as compared to other systems. Advancement in technology has resulted in miniaturized hydraulic hoisting systems with the development of machine room less lift services. 3. Climbing System: Climbing elevator system are those which are used towers or buildings where simple traction elevator systems cannot be introduced. These skyscrapers need some efficient lifting system with best precision and least energy demands. Therefore, climbing elevator systems are introduced which are self-ascending in nature and are having their own propulsion mechanism which reduces energy demands. The hoisting system we selected to be used in our lift service design is based on traction system. This system is efficient as well as less energy consuming and also we are able to design a lift service with average load more than 2000kg in this case. Another reason for selecting traction based elevators is that they only make use of a single machine room at the top of the hoisting system. No underground space is required for cylinders and rope hoisting. Here is a detailed diagram of the traction system being implemented in our lift service. Figure 1(a) Figure 1(b) Figure 1(a) gives the detailed diagram of the Lift service designed for our three story building with machine room located at the top of the lifting mechanism, whereas Figure 1(b) illustrates two different traction mechanisms. One is the primitive design based on lifting drum arrangement and the second one is the latest design arrangement based on traction drum arrangement. Detail of components shown in Figure 1(a) are listed below: 1. Engine room at the top of the building. 2. Power mechanism capable of operating lift, based on winch 3. Hoisting cables responsible for moving the lift to desired position. 4. Suspension system for the hoisting mechanism. 5. Catchers for the support of suspension system. 6. Cabin or car, dedicated to carry passengers. 7. Shifter 8. Shoe of the lift provides better support. 9. Shaft on which lift moves up and down and is responsible for smooth operation. 10. Guide rails which ensure vibration less motion of lift and provides support to the cabin. 11. Guide rails for counter weights, introduced to make the uphill movement easy. 12. Counterweight, help in keeping the lift in position when passengers are entering or leaving the cabin. 13. Buffer, to avoid hammering and noise when the cabin reaches ends. 14. Bottom pit is the empty space introduced to avoid accident and provides cushioning. 15. Tension pulley 16. Speed limiter cables 17. Speed limiters 18. Magnetic station Elevator Control Mechanism The designed elevator is having following properties: Guard rails are provided for standing. Load sensor allows the system to avoid overloading beyond the lift capacity. Air conditioning system is also introduced to facilitate the passengers by using duct system along supporting rails of lift outside the cabin. Control panel is provided to call various operations including the commands to go up and down and command to hold the lift until all passengers have boarded. Proper locking mechanism for the doors so that no one can interrupt the functioning of lift by entering the shaft mechanism. Alarm switch is also introduced in the lift system to inform the manager through an alarm that the passenger is in trouble. Security camera is introduced to ensure safety of the passengers within the lift cabin. Interior of the lift is designed to provide refreshing look to the passengers by making use of mirrored walls. Lift service will be equipped with proper fire extinguishing service and escape. Inspection switch is also introduced in order to check the elevator at regular intervals. Elevator is also equipped with a backup system which is capable of working automatically if lift service undergoes sudden power shutdown. This approach helps in providing escape to the people present in cabin. Energy consumption Our proposed elevator design is capable of carrying 20 people in one shift. If more than 20 people enter the car or weight within the car increases beyond 1400kg, the lift door does not close. This is done by making use of load cells in the cabin’s floor which continuously monitor the weight within the lift and on excess weight control signal generates warning on the LCD on the inner wall of lift cabin. After the people have rode on the lift cabin, lift needs power to operate. If the lift has to move upwards it needs excess energy to overcome gravity and to carry load of 20 persons. While moving downwards speed limiters are needed to control the speed and avoid any unpleasant situation. An elevator approximately requires energy of 2.5 kWH to in moving from one floor to another (one sided). If we want an elevator to move three floors up and then three floors down it requires cumulative energy of about 15kWH for one round trip. Counterweights Elevators work properly by the help of counterweights. Counterweights are the heavy weights approximately equal to the weight of the car and are supposed to cancel out the effect of car’s weight. This is really helpful in reducing the energy demands by the lift because in this case energy is only required to move the weight of passengers in the lift not the weight of car. The motor just needs to work in order to overcome frictional forces exerted on pulleys and passenger’s weight. In this way force exerted on cables is also reduced and they can run longer before they wear. Another benefit of loading counterweight is that less braking is needed. It means that with the addition of counterweights, weight of car is balanced and as a result, while braking, system does not needs to manage excess load of car, rather it only needs to apply braking force against the passengers’ weight. Other than conventional braking system, elevators are also equipped with the safety brakes which are required only when the elevators undergo emergency situation mainly due to rupture of cables carrying the car. In such situations safety brakes get activated and avoid the crashing of elevators. These safety brakes make use of ratchet system and provide necessary back up when needed. Elevators are also having various other security systems and are designed with a number of standard parameters in order to avoid unpleasant situations. Therefore, specially designed cables are used for hoisting traction mechanism are specially designed metallic cables with multiple strands twisted together to form a single cable. The detailed CAD drawing of lift mechanism being used in our three story building is shown below with all three views. While designing this elevator, standard dimensions were considered for center opening automatic door lifts. For 20 people lift, inside car dimensions are 2000×1500 and lift well is having dimensions of 2500×2000. Machine Room Layout Above is the CAD drawing of a typical control room/ machine room layout. Machine room is having all the controls of elevators including temperature, humidity and light facilities to be provided in the lift. The power unit consists of all necessary motor units required to deliver power for the successful operation of elevators. Also an air exchanger is provided with the rotating machinery in order to maintain the temperature of all rotating parts undergoing frictional forces. The control room is also equipped with a monitor showing the results of camera installed within the lift for security purposes. The machine/ control rooms are equipped with the service team for handling any unpleasant situation and electricity backup is also essential part of control room which is used to provide electricity to keep the lift moving if sudden electric shutdown occurs within the building. Quality of Service Quality of lift service extensively depends upon the requirement of the system. Normally a medium ranged economic lift service is suitable for not more than three floors. With these specifications lift provide excellent service with a proper balance in speed and productivity. Calculation of lift performance is based on a number of parameters which majorly include acceleration and deceleration of lift, speed of opening and closing the door, control strategy etc. all these parameters vary from manufacturer to manufacturer. Round Trip Time The round trip time is the total time consumed by the lift service to complete one cycle, ground floor to top floor and then back to ground floor. This include the total time lift takes from moving ground-top floor-ground, time taken by the passengers to enter and exit the lift car at each floor, and operating time to open and close the door. All these times when added together give the round trip time. Round trip time can vary from trip to trip. Door operating time and time to complete one trip remains same, the only thing that varies is the time required to transfer the passengers in and out of the lift. Mathematical expression of round trip time is given below: Where = time required by the lift cabin to move upward from ground floor to top floor = time required by the lift cabin to move from top floor to ground floor = time required by the system to operate closing and opening of the door = time required by the passengers to move in and out of the lift The probable number of stops a lift service has to face can be determined as follows: Where S: probable number of stops N: total number of floors above the ground floor P: probable number of passengers. Door operating time is given as: Where W: width of door in standard measurement Vd: operating speed of door Passenger transfer time is taken as 2 seconds per passenger: Where P: no of passengers moving in and out of lift Read More