1. 广东工程职业技术学院 Elevator Mechanical 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  The annoying thing about elevators (if you're trying to understand them) is that their working parts are usually covered up! From the viewpoint of someone travelling from the lobby to the 18th floor, an elevator is simply a metal box with doors that close on one floor and then open again on another. For those of us who are more curious, the key parts of an elevator are ：

4. 广东工程职业技术学院  One or more cars (metal boxes) that rise up and down.  Counterweights that balance( 平衡 ) the cars.  An electric motor （电机） that hoists the cars up and down, including a braking system.  A system of strong metal cables and pulleys （滑轮） running between the cars and the motors.  Various safety systems （安全系统） to protect the passengers if a cable breaks.

5. 广东工程职业技术学院  An electronic control system （电气控制系统） that directs the cars to the correct floors using a so-called "elevator algorithm" （电梯算法） (a sophisticated kind of mathematical logic) to ensure large numbers of people are moved up and down in the quickest, most efficient way (particularly important in huge, busy skyscrapers at rush hour). Intelligent systems （智能系统） are programmed to carry much more people upward than downward at the beginning of the day and the reverse at the end of the day.

6. 广东工程职业技术学院 ■ The counterweight In practice, elevators work in a slightly different way from simple hoists. 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, which helps us in four ways:

7. 广东工程职业技术学院  The counterweight makes it easier for the motor to raise and lower the car—just as sitting on a see-saw makes it much easier to lift someone's weight compared to lifting them in your arms. Thanks to the 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.

8. 广东工程职业技术学院 ● The counterweight reduces the amount of energy the motor needs to use. This is intuitively obvious to anyone who's ever sat on a see-saw ： assuming the see-saw is properly balanced, you can bob up and down any number of times without ever really getting tired—quite different from lifting someone in your arms, which tires you very quickly. This point also follows from the first one ： If the motor is using less force to move the car the same distance, it's doing less work against the force of gravity.

9. 广东工程职业技术学院  The counterweight reduces the amount of braking the elevator needs to use. 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. The counterweight makes it much easier to control the elevator car.  In a different design, known as a duplex counterweightless elevator, （双轿 箱无对重电梯） two cars are connected to opposite ends of the same cable and effectively balance each other, doing away with （废除，取消） the need for a counterweight.

10. 广东工程职业技术学院 Traction Drive/Roping System  A roping system is used to attach the motor/gear reducer, the elevator car and the counterweight. There are many different kinds of arrangements that can be used. In one possible arrangement, both ends of the elevator rope are anchored to the overhead beam. Both the elevator car and the counterweight are attached to free moving pulleys. The traction drive is attached to a stationary pulley.

11. 广东工程职业技术学院  The traction drive is the method of converting the input mechanical power (in this case the turning of a shaft) into useable mechanical power in the system (the vertical movement of the elevator). The friction between the ropes and the sheave grooves, which are cut on the pulley, initiates the traction force between the traction drive and the rope.  When the traction drive is rotated power is transferred from the traction drive to the elevator car and counter weight. Power is only needed to move the unbalanced load between the elevator and the counterweight.

12. 广东工程职业技术学院 Gears （传动装置）  An elevator's function is to convert the initial electrical power, which runs the motor, into mechanical power, which can be used by the system. The elevator is composed of a motor and, most commonly, a worm gear reducer system （涡轮减速系统）. A worm gear system （涡轮传动系统） is made up of a worm gear, typically called the worm, and a larger round gear, typically called the worm gear. These two gears which have rotational axes perpendicular to each other, not only decrease the rotational speed of the traction pulley (1), but also change the plane of rotation. By decreasing the rotation speed, with the use of a gear reducer, we are also increasing the output torque, therefore, having the ability to lift larger objects for a given pulley diameter. A worm gear is chosen over other types of gearing possibilities because of its compactness and its ability to withstand higher shock loads. It is also easily attached to the motor shaft, sometimes through use of a coupling. The gear reduction ratios typically vary between 12:1 and 30:1.

13. 广东工程职业技术学院  The motor component of the elevator machine can be either a DC motor or an AC motor. A DC motor had a good starting torque and ease of speed control. An AC motor is more regularly used because of its ruggedness and simplicity. A motor is chosen depending on design intent for the elevator. Power required to start the car in motion is equal to the power to overcome static, or stationary friction, and to accelerate the mass from rest to full speed. Considerations that must be included in the choice of an acceptable motor are good speed regulation and good starting torque. In addition, heating of various electrical components in continuous service should not be excessive.

14. 广东工程职业技术学院 Brakes （制动器）  The most common elevator brake is made up of a compressive spring assembly, brake shoes with linings, and a solenoid assembly. When the solenoid is not energized, the spring forces the brake shoes to grip the brake drum and induce a braking torque. The magnet can exert a horizontal force for the break release. This can be done directly on one of the operating arms or through a linkage system. In either case, the result is the same. The break is pulled away from the shaft and the velocity of the elevator is resumed.  In order to improve the stopping ability, a material with a high coefficient of friction is used within the breaks, such as zinc bonded asbestos. A material with too high a coefficient of friction can result in a jerky motion of the car. This material must be chosen carefully.  Typically the efficiency of the geared machine is 60 percent for the motor and gear box assembly. This efficiency was estimated for a load of 2500lb, which matches a regularly sized residential elevator, being driven at 1.75 m/s.

15. 广东工程职业技术学院  Elevator brake is an important safety device; it's safe, reliable and safe operation of the lift to ensure one of the factors. The role of the brake can be summarized in the following two: (1) enable the elevator to run automatically when the car cut off the power supply system stop. (2) The elevator stops running, the brakes should be able to guarantee 125% of rated load in the circumstances, so maintain a stationary car, the location change.

16. 广东工程职业技术学院  China's new "elevator manufacturing and installation of the safety norms" GB7588-2003 has been promulgated, including the biggest change on the braking system is to GB7588- 1995 section 12.4.2.1 in the article "Note: This category can also be suspended." This sentence deleted. Then, after 2004 the production of elevators, its braking system （制动系 统） must meet the requirements of 12.4.2.1: When the car containing 125% of rated load and rated speed down the run, the operating brakes should enable the tractor to stop running. In this case, the car's deceleration should not exceed the safety gear or car movements generated by the impact speed buffer. All involved in the brake wheel or brake disc braking force applied mechanical components should be divided into two groups to install. If a component does not work, there should still be sufficient braking force to contain the rated load at rated speed slowing down the car down. Electromagnetic coil core is regarded as mechanical parts, while the coil is not.

17. 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.

18. 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.

19. 广东工程职业技术学院 2013-5