1. 广东工程职业技术学院 Elevator Control System 主讲：肖青 广东工程职业技术学院

2. Objectives  Organize the students to have a discussion about the elevator mechanical system  Basic introduction to the elevator mechanical system  Learn why the people need the help of elevators  Find out the basic difference between traditional transportation tools and elevators

3. 广东工程职业技术学院 Elevator Mechanical System  Elevators themselves are simple devices, and the basic lifting systems have not changed much in over 50 years. The control systems, however, have changed substantially to improve safety and speed of operation. Elevator control system is used to manipulate each control process by managing such commands as running direction, car call, landing call, load signal, landing indication, safety protection. The Elevator Control Electronics is a Micro- processor based card for communicating and controlling all the functions of an Elevator. It works on the principle of multiplexed scanning of input & output. It controls the drives for the door as also the elevator movement. It displays the position of the elevator both in the car as also in the halls.

4. 广东工程职业技术学院  Elevators in different applications have different load, speed and drive/control modes. Elevators in same application may also have different control mode. Whatever control mode is adopted, the objective is the same, to be specific, according to car call and landing call, elevator control system will execute automatic logic judgment to determine which elevator will receive signal, which direction elevator will run towards and complete programmed control objective through electrical automatic system based on command.

5. 广东工程职业技术学院 Types of elevator control system  Control system development chronicle indicates that there has appeared many control modes, such as relay control, PLC, single computer control, multiple-computer control. Prevailing in different era, these control modes are still employed in elevators now due to massive integrated circuit and computer technology development.

6. 广东工程职业技术学院 ■ Relay – Contact control system  Mainly used before 1980’, this control mode is simple in structure and easy to understand and master. However, it has almost been out of use because of having such advantages as wear-prone contact, poor contact, slow close-closing contact, big volume, time-demanding maintenance, high cost.  With semiconductor technology development and application in 1960’, relay contactor system with contact has been replaced by transistor and diode. This control mode does not have the disadvantages above mentioned, but it is designed based on “hardware” logic computation, to be specific, wiring is based on algorithm and requirement, and wiring of each control component must be made separately. Wiring must be modified if programmed control requirement (algorithm) is changed.

7. 广东工程职业技术学院 PLC control system  As abbreviation of programmable logic controller, PLC is a microprocessor- based electronic control system designed for automation processes in industrial environments featuring digital computation. It adopts programmable EPROM for the internal storage of user-orientated instructions for implementing specific functions such as logic, sequential control, timing, number counting, arithmetic computation, besides, it can input and output through digital or analogy modes. A PLC can be programmed to sense, activate, and control industrial equipment and, therefore, incorporates a number of I/O points, which allow electrical signals to be interfaced. Input devices and output devices of the process are connected to the PLC and the control program is entered into the PLC memory.

8. 广东工程职业技术学院 ● The mechanism of PLC control is as follows: input of PLC includes such command signals, as power key to home landing, car call, landing call, various safety switches, position signal, door opening and closing signals etc., while output of PLC includes contactor, relay, indicators of car/landings and communication unit. What we should do is to send the signals to PLC digital input terminals. The DC power which is provided to PLC can be used as power of indicator light. The PLC output can be directly used to control transducers achieve the motor forward and reverse, stop and speed control purposes.

9. 广东工程职业技术学院  The control cabinet is the control center, from which we can send out various control commands. The control cabinet often was installed in the machine room. The electric devices and signal systems, for example the contactors, relays, capacitances, resistors, rectifiers and transformers etc., are centralized in the control cabinet. The power of the control cabinet was imported from the chief power of the elevator room. This power was also introduced into control panel by soft cables and was linked with each control buttons. The power line which was derived from control cabinet was delivered to traction motor. Other control lines and signal lines were separately sent to each floor junction.switch, position signal, are input to PC, while other executing com

10. 广东工程职业技术学院  The software used for PLC programming is based on a special language known as the ladder diagram. The ladder diagram is an easy programming language since it is based on Boolean logic functions. This makes the task of modifying any system much easier and more cost- effective. The size of the PLC is one of the factors considered when it is selected to control a process. PLCs come in various sizes and different capabilities; the sizes range from small controllers with limited inputs and outputs used for controlling small processes, to very large ones with more inputs and outputs provided which are used to control much larger processes and operations. Choosing the appropriate PLC is based on analyzing the process to be controlled and accordingly identifying the number of inputs and outputs required.

11. 广东工程职业技术学院  Programming principle is determined by elevator control mode. Programming can either be made according to relay logic control circuit or individually in different phases according to elevator control functions after completely separating from relay control circuit. Based on the ready made control circuit, the former is simple and easy to master, while the latter involves less programs by integrating programs of small function.

12. 广东工程职业技术学院  The PLC continuously monitors the inputs and activates the outputs according to the control program. This PLC system is of modular type composed of specific hardware building blocks (modules), which plug directly into a proprietary bus: a central processor unit (CPU), a power supply unit, input-output modules I/O, and a program terminal. Such a modular approach has the advantage that the initial configuration can be expanded for other future applications such as multi-machine systems or computer linking. Used in elevator control system, PLC has such advantages as high reliability, stability, easy programming, user- friendliness, convenient maintenance & inspection.

13. 广东工程职业技术学院 Computer control system  Computer control system, in essence, will make control algorithm fixed by means of programming (software) in “program EPROM” rather than by “hardware” logic. For elevator controls that require different functions, only software in “program EPROM” needs changing without modifying or deducting “Hardware” wiring. Computer has developed from massive integrate circuit, featuring more functions, more flexible control and wider applications.

14. 广东工程职业技术学院  Many modern elevators are controlled by a computer. The computer's job is to process all of the relevant information about the elevator and turn the motor the correct amount to put the elevator car where it needs to be. In order to do this, the computer needs to know at least three things. Where people want to go? Where each floor is? Where the elevator car is?  Finding out where people want to go is very easy. The buttons in the elevator car and the buttons on each floor are all wired to the computer. When you press one of these buttons, the computer logs this request. There are lots of ways to figure out where the elevator car is. In one common system, a light sensor or magnetic sensor on the side of the car reads a series of holes on a long vertical tape in the shaft. By counting the holes speeding by, the computer knows exactly where the car is in the shaft. The computer varies the motor speed so that the car slows down gradually as it reaches each floor. This keeps the ride smooth for the passengers.

15. 广东工程职业技术学院  In a building with many floors, the computer needs to have some sort of strategy to keep the cars running as efficiently as possible. In older systems, the strategy is to avoid reversing the elevator's direction. That is, an elevator car will keep moving up as long as there are people on the floors above that want to go up. The car will only answer "down calls" after it has taken care of all the "up calls." But once it starts down, it won't pick up anybody who wants to go up until there are no more down calls on lower floors. This program does a pretty good job of getting everybody to their floor as fast as possible, but it is highly inflexible.

16. 广东工程职业技术学院  More advanced programs take passenger traffic patterns into account. They know which floors have the highest demand, at what time of day, and direct the elevator cars accordingly. In a multiple car system, the elevator will direct individual cars based on the location of other cars. In one cutting-edge system, the elevator lobby works like a train station. Instead of simply pressing up or down, people waiting for an elevator can enter a request for a specific floor. Based on the location and course of all the cars, the computer tells the passengers which car will get them to their destinations the fastest. Most systems also have a load sensor in the car floor. The load sensor tells the computer how full the car is. If the car is near capacity, the computer won't make any more pick-up stops until some people have gotten off. Load sensors are also a good safety feature. If the car is overloaded, the computer will not close the doors until some of the weight is removed.

17. 广东工程职业技术学院  Controlled by computer, individual elevator control system can be equipped with two or more computers. For instance, one computer is used for communication between machine room and car, while the other for various control of car.

18. 广东工程职业技术学院  In signal transmission and control, there are parallel and serial interface transmission modes. Characteristic of high speed, the former needs a large number of interfaces and transmission lines and does badly in anti- interference ability, while the latter is characteristic of economy in interface and cable amount, high reliability and strong anti-interference ability. To serially scan landing call and car call, main machine will give off serial scanning signals, and then scanners distributed in each landing will have an effect on serial signals and communicate with main machine, so as to register and display signals. In the order control of car, after collecting various controls protection and testing signals from car interior/exterior, well and machine room, computer will execute logic judgment and compute according to software program and determine operation order and mode.

19. 广东工程职业技术学院 Elevator control function  Many functions are involved from the time landing call is pressed to the time passengers get out of car, such as response to call, start-up, running, stop, door-open/close. In the design of elevator control system, some functions are standard, while some optional, which customers can select. Below is the introduction of typical control functions for collective selective elevator.

20. 广东工程职业技术学院 Response to car call and landing call  Car call and landing call are referred to as call signals. If car call and landing call are on the same direction as car running, car will respond according to order. If car is dwelling on a certain landing or decelerating towards a certain landing, car call of the landing will not be registered. If a car call is registered, car call indicator or LED will light up and display. Car call will be canceled at door zone. If landing call in on reverse direction to car running, the call will be reserved. If landing call from a certain landing on which car is dwelling is on the same direction as car running, door can re- open; if this landing call is on reverse direction with car running, it will be reserved. The prerequisites are: car arrives at a certain landing and reserves its running direction, or its running direction has been preset.

21. 广东工程职业技术学院  Landing call will be canceled under the following circumstances: If landing call is registered before deceleration point, landing call will be canceled on deceleration point. If landing call is registered after deceleration point, landing call will canceled in door zone. If up/down call buttons are pressed in the middle landing, the call on the same direction as car running will be canceled as soon as car arrives at the landing, while the call on the reverse direction will be reserved. In case of full load (LNS), full load indicator will light up. Landing call will be reserved rather being responded. After landing call is registered, landing call indicator or LED will light up.

22. 广东工程职业技术学院 Home landing parking  After responding to the last call, car will return to home landing if no calls are received in a period of time; After returning to home landing, car will remain waiting, with car door closed. In the course of returning to home landing, car will respond to call from following landing that is on the same direction as car running; car will not respond to call from preceding landing and park at the nearest landing, with door closed and will respond to the call by running in reverse direction.

23. 广东工程职业技术学院 Dwelling  When connecting with dwelling switch, elevator enters dwelling status, car returns to dwelling landing. When car arrives at dwelling landing, all calls are canceled rather than being registered. When car dwells at dwelling landing, all position indicators, car lights, fan will be closed, non-operation light will light up. During car inspection, dwelling function will not activate.

24. 广东工程职业技术学院 Manual emergency stop  Normally mounted on car top, machine room and pit, emergency switch is used by inspection staff. As non-automatic reset switch, it must be manually reset once opened so that elevator can restore normal state. Inspection staff can press this switch under inspection status, making elevator stop and ensuring personal safety. In the course of running, car will stop immediately and cancel all call signals if emergency switch is opened. During emergency stop, car will not register any calls and door be closed.

25. 广东工程职业技术学院  Failure and emergency stop  To ensure safe operation and protect passengers against personal injury, elevator is equipped with a series of safety devices, such as over speed governor, safety gear, buffer, limit switch, safety window, rope rupture protection, motor overheat protection. Should any failure occur, elevator emergency stop will be caused by the activation of any safety device and switch or break of contact in safety circuit. When failure or emergency occurs on elevator, passengers can inform attendants of the situation by pressing alarm button or other device for rescue.

26. 广东工程职业技术学院  Re-leveling  Car will re-level if elevator is in door zone with leveling error of rate ±15mm and receives re-leveling signal from control system. If car is above and below leveling position by 15mm, it will relevel by moving downwards and upwards.

27. 广东工程职业技术学院  Door open / close  After leveling, door will automatically open. Door will automatically close after a specific period of time delay that can be adjusted. Control panel is equipped with door open/close buttons. Manually press these buttons to close or open door. When a car that will continue toward preset direction is on a landing, door will open if landing call button is pressed that is on the same direction as car running. If car is on a certain landing waiting, landing call button can be pressed to open door. In the course of closing, door will re-open if safety edge (door vane) or light curtain (ray protection) touches obstruction. During door closing, door open button can be pressed to re-open door. In case of car overload, overload indicator will light up and buzzer will sound; elevator will not close door or door will re- open in the course of closing until overload is eliminated.

28. 广东工程职业技术学院 Conclusion  Get an overview of the history of elevator development  Learn the need of the people  Discuss the measures we should take to prevent this kind of accident from happening again.  Listen and practice a conversation about elevator accident.

29. 广东工程职业技术学院 Homework  Write a short composition about the elevator accident in Shenzhen. In this writing, you are required to introduce the details of this accident and then analyze the reasons. Finally give your opinion about how to prevent this kind of accident from happening again.

30. 广东工程职业技术学院 2013-5