1、 中文 5060字 ， 3400单词 出处： Barkland T D. Elevator safety: give the miner a brakeC/ Industry Applications Society Annual Meeting, 1990., Conference Record of the 1990 IEEE. 1990:1421-1429 vol.2. ELEVATOR SAFETY: GIVE THE MINER A BRAKE TD Barkland ABSTRACT Over a five-year period, there were at least 18 d
2、ocumented cases of ascending elevators striking the overhead. In some cases, the accidents resulted in serious injuries or fatalities. These accidents occurred on counter weighted elevators as a result of electrical, mechanical, and structural failures. Elevator cars are fitted with safeties that gr
3、ip the guide rails and stop a falling car； however, these devices do not provide protection in the upward direction. Rules and regulations applying to elevator safety have come under review in response to these accidents. Some governing authorities have already revised their regulations to require a
4、scending carover speed protection. This paper will discuss basic elevator design, hazards, regulations, and emergency braking systems designed top rovide ascending car over speed protection. In addition, a case-study report on a pneumatic rope brake system installed and tested on a mine elevator wil
5、l be discussed. I NTRODUCT I ON Elevators incorporate several safety features to prevent the car from crashing into the bottom of the shaft. Safeties installed on the car can prevent this type of accident from occurring when the machine brake fails or the wire ropes suspending the car break. However
6、, the inherent design of the safeties render them inoperative in the ascending direction. In the upward direction, the machine brake is required to stop the cage Irvhen an emergency condition occurs. Under normal operation, the machine brake serves only as a parking braked to hold the cage at rest.
7、However, when an emergency condition is detected, modern elevator control system designs rely solely on the machine brake to stop the car. In the United States mining industry, the accident history has proven that this is not the best control strategy 2, 3. These accidents occurred when the retardin
8、g effort of the drive motor was defeated when the mechanical brakes were inoperative. This allowed the counterweight to fall to the bottom of the shaft, causing the car to over speed and strike the head frame. The high-speed elevator crashes into the overhead structure caused extensive mechanical da
9、mage and potentially fatal injuries. ELEVATOR DES I GN A basic understanding of elevator operation is required in order to assess the safety hazards present and determine the accident prevent methods available. Figure 1 shows a complete view of a mine elevator. Fig.1 Mico Elevator In a typical eleva
10、tor, the ear is raised and loered by six to eight motordriven wire ropes that are attached to the top of the car at one end, travel around a pair of sheaves, and are again attached to a counterweight at the other end. The counterweight adds accelerating force when the elevator car is ascending and p
11、rovides a retarding effort when the car is descending so that less motor horsepower is required. The counterweight is a collection of metal weights that is equal to the weight of the car containing about 45% of its rated load. A set of chains are looped from the bottom of the counterweight to the un
12、derside of the car to help maintain balance by offsetting the weight of the suspension ropes Guide rails that run the length of the shaft keep the car and counterweight from swaying or twisting during their travel. Roll ersare attached to the car and the counterweight to provide smooth travel along
13、the guide rails. The traction to raise and lower the car comes from the friction of the wire ropes against the grooved sheaves. The main sheave is driven by an electric motor. SUSPENSION riCPCS Motor-generator (M-G) sets typically pro-vide to dc power for the drive motor. Newer systems use a static
14、drive control. The elevator controls vary the motor s speed based on a set of feedback signals that indicate the car s position in the shaft way. As the car approaches its destination, a switch near the landing signals the controls to stop the car at floor level. Additional shaft way limit switches
15、are installed to monitor over travel conditions. The worst fear of litany passengers is that the elevator will go out of control and fall through space until it smashes into the bottom of the shaft. There are several safety features in modern elevators to prevent this from occurring. The first is th
16、e high-strength wire ropes themselves. Each 0. 625-in-diameter extra-high-strength wire rope can support 32, 000 lb, or about twice the average weight of a mine elevator filled with 20 passengers. For safety s sake and to reduce wear, each car has six to eight of these cables. In addition, elevators
17、 have buffers installed at the shaft bottom that can stop the car without killing its passengers if they are struck at the normal speed of the elevator As previously discussed, modern elevators have several speed control features. If they do not work, the controls will disconnect the motor and apply
18、 the machine brake. Finally, the elevator itself is equipped with safeties mounted underneath the car. If the car surpasses the rated speed by 15 to 25%, the governor will trip, and the safeties will grip the guide rails and stop the car. This was the invention that made elevator transportation acce
19、ptable for the general public. SAFETY HAZARDS A historical perspective of elevator development can account for today s problems with elevator safety rules and regulations 4. In the beginning of modern elevator history, it was realized that although there were several factors of safety in the suspens
20、ion rope design, the quality of construction and periodic inspection could not be assured. Therefore, the elevator car was equipped with reliable stand by safeties that would stop the car safely if the suspension ropes failed. In 1853, Elisha. Otis, a New York mechanic, designed and demonstrated an instantaneous safety capable of safely stopping a free falling car. This addressed the hazard shown in figure 2.
