ELEVATOR SAFETY: GIVE THE MINER A BRAKE ABSTRACT Over a five-year period, there were at least 18 documented cases of ascending elevators striking the overhead. In some cases, theaccidents 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 withsafeties that grip 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 authoritieshave already revised their regulations to require ascending caroverspeed protection. This paper will discuss basic elevator design, hazards, regulations, and emergency braking systems designed toprovide ascending car overspeed protection. In addition, a case-studyreport on a pneumatic rope brake system installed and tested on a mineelevator will be discussed. I NTRODUCT I ON Elevators incorporate several safety features to prevent the carfrom crashing into the bottom of the shaft. Safeties installed on thecar can prevent this type of accident from occurring when the machine brake fails or the wire ropes suspending the car break. However, 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. 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 retarding 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 overspeed and strike the headframe. The high-speed elevator crashes into the overhead structure caused extensive mechanical damage 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 elevator, the ear is raised and loered by six toeight motor–driven wire ropes that are attached to the top of the car at one end, travel around a pair of sheaves, and are again attachedto a counterweight at the other end. The counterweight adds accelerating force when the elevator car is ascending and provides 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 underside 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 andcounterweight from swaying
or twisting during their travel. Rollersare attached to the car and the counterweight to provide smooth travel along 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. Motor-generator (M-G) sets typically pro-vide to dc power for the drive motor. Newer systems use a static 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 shaftway. As the car approaches its destination, a switch near the landing signals the controls to stop the car at floor level. Additional shaftway limit switches are installed to monitor overtravel 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 the 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 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 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 acceptable 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 suspension 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.
Later on, it was realized that passengers may be injured when the car overspeeds in the down direction with suspension ropes intact, as shown in figure 3. To prevent this hazard, an o-verspeed governor with gradually applied safeties was developed. It detected the over peeling condition and activated the safeties.
Furthermore, it was noticed that frequent application of safeties caused mechanical stress on the elevator structure and safety system.Therefore, a governor overspeed switch was installed that would try to stop the car by machine brake before the safeties activated. The switch was a useful idea because it could also initiate stopping in the case of overspeeding in the up direction as well. The problem started in the 1920's when the American Elevator Safety Code was developed. The writers most likely looked at the technology that was available at that time and subsequently required it on all elevators covered by the Code. The writers were so concentrated on describing the design of the required devices that they forgot to acknowledge the hazards that the devices are guarding against and the elevator components that may fail and cause the hazards. They did not consider the fact that for 90% of the elevator trips, the elevator is partially loaded (i. e. less than 45% of rated load) [5]. Therefore, if a brake failure occurs, the elevator will overspeed and crash in the up direction as shown in figure 4
.
Fig.4 Car overspeed UP
Until recently, elevator safety systems have not differed significantly from the early 1900' s designs. The problem arises because rulernaking committees and regulatory authorities are reluctant to require new safeguards when the technology has not been fully developed. Conversely, the elevator manufacturing industry cannot justify the product development expense for a new safety device with little marketability. This problem will be addressed in the following sections RULES AND REGULATIONS Several rulemaking committees and government safety authorities have addressed the deficiencies in the existing elevator regulations and have proposed revisions to the elevator safety codes. The report from the American Society of Mechanical Engineers - A17 Mechanical Design Committee on \"Cars ascending into the building overhead, \"-dated September 1987, contained the types of failures that could result in elevators accelerating into overhead structure and an analysis of the possible solutions. In addition, a proposal to the A17. 1 Committee for a new code Rule 205. 6 was introduced as follows: Rule 205. 6 (\"Prevention of overspeeding car from striking the overhead structure') : All traction elevators shall be provided with a means to prevent an ascending car from striking the overhead structure. This rneans shall conform to the following requirements:
1.Prior to the time when the counterweight strikes its buffer, it shall reduce the speed of the car to the speed for which the counterweight buffer is designed. 2.It shall not develop an average retardation of the car in excess of 32.2 ft /s2 (9.81 m/s2) during the stopping phase. 3.1t shall be a mechanical means independent of the driving machine brake. 4.1t shall prevent overspeeding of the elevator system through the control of one or more of the following a.counterweight b.car c.suspension or compensating rope system. This proposed rule is currently under committee review, and consideration has been given to requiring protection to prevent the car from leaving the landing with the doors opened or unlocked. Pennsylvania Bureau of Deep Mine Safety An ascending elevator car accident occurred at a western Pennsylvania coal mine on February 4, 1987 and caused extensive structural damage and disabled the elevator for two months. Following this accident, the Pennsylvania. Bureau of Deep Mine Safety established an advisory committee to determine these devices that are available to provide ascending car overspeed protection for new and existing mine elevator installations. The following four protective methods were determined to be feasible based on engineering principles or extensive mine testing. 1.Weight balancing (counterweight equals the empty car weight) 2.Counterweight safeties 3.Dynamic braking 4.Rope brake The Pennsylvania Bureau of Deep Mine Safety has approved these four methods and has made ascending car overspeed protection mandatory on all existing counterweighted mine elevators. Dynamic Braking A second solution used in the United States mining industry is the application of passive dynamic braking to the elevator drive motor [6]. As mentioned earlier, most elevators use direct current drive motors that can perform as generators when lowering an overhauling load. Dynamic braking simply connects a resistive load across the motor armature to dissipate the electrical energy generated by the falling counterweight. The dynamic braking control can he designed to function when the main power is interrupted. Dynamic braking does not stop the elevator but limits the runaway speed in either direction; therefore, the buffers can safely stop the conveyance. Rope Brake A pneumatic rope brake that grips the suspension ropes and stops the elevator during emergency conditions has been developed by Bode Aufzugel [7]. This rope brake has been
used in the Netherlands since August 12, 1957. Case Study: Rope Brake Testing and Evaluatio The first pneumatic rope brake was installed in the United States at a western Pennsylvania coal mine on September 8, 1989. The largest capacity Bode rope brake (model 580) was installed on this coal mine melevator. This rope brake installation was tested extensively by Mine Safety and Health Administration engineers from the Pittsburgh Safety and Health Technology Center. A summary of the findings will be presented in this study. Function The rope brake is a safety device to guard against overspeed in the upward and downward directions and to provide protection for uncontrolled elevator car movements The rope brake is activated when the normal running speed is exceeded by 15%as a result of a mechanical drive, motor control system, or machine brake failure. The rope brake does not guard against free fall as a result of a break in the suspension ropes. Standstill of the elevator car is also monitored by the rope brake system. If the elevator car moves more than 2 to 8 inches in either direction when the doors are open or not locked, the rope brake is activated and the control circuit interrupted. The rope brake control must be manually reset to restore normal operation. The rope brake also provides jammed conveyance protection for elevators and friction driven hoists. If the elevator car does not move when the drive sheave is turning, the rope brake will set, and the elevator control circuit will be interrupted. The rope brake control contains self-monitoring features. The rope brake is activated if a signal is not received from the pulse tachometer when the drive is running The rope brake requires electrical power and air pressure to function properly. The rope brake sets if the control power is interrupted. When the power is restored, the rope brake will automatically release. Typically, elevator braking systems are spring applied and electrically release. Therefore, no external energy source is needed to set the brake. The rope brake requires stored pressurized air to set the brake and stop the elevator. Therefore, monitoring of the air pressure is essential. If the working air pressure falls below a preset minimum, the motor armature current is interrupted, and the machine brake is set. When the air pressure is restored, the fault string is reset. Pneumatic Design The rope brake system is shown in figure 5. Starting from the air compressor tank, the pressurized air passes through a water separator and manual shut off valve to a check valve. The check valve was required to ensure the rope brake remains set even if an air leak develops in the compressed air supply. A pressure switch monitors for low air pressure at this point and will set the machine brake as mentioned earlier. The air supply is split after the check valve and goes to two independent magnetic two-way valves. The air supply is shut off (port A), while the magnetic valve coil is energized. When the magnetic valve coil is
deenergized, the air supply is directed to the B port, which is open to the rope brake cylinder. The air pushes the piston inside the rope brake cylinder and forces a movable brake pad toward a stationary brake pad. The suspension ropes are clamped between the two brake pads. The rope brake is released by energizing the magnetic valve, which vents the pressurized rope brake cylinder to the atmosphere through a blowout silencer on port S. The force exerted on the suspension ropes equals the air pressure multiplied by the surface area of the piston. The rope brake model number 580 designates the diamoter of the brake cylinder in millimeters. This translates into 409. :36 in of surface area.. The working air pressure varies from 90 to 120 lbf/in2. The corresponding range of force applied to the suspension ropes is 36, 842 to 49, 123 lb. The force experienced by the ropes as they pass over the drive sheave under fully loaded conditions is about 34, 775 lb. Therefore, the ropes experience a 6 to 41% greater force during emergency conditions than normally encountered during full load operation. Mechanical Modifications Prior to testing, several mechanical modifications were required to protect the rope brake system from environmental and mechanical damage. The modifications also reduced the possibility and the undesirable effect of an air leak in the pneumatic system. The following modifications were included in the rope brake design: 1.The 200 lbf/in2 rated plastic air hose was replaced with 2, 000 lbflin2 rated metal braided hose with integral couplings. 2.The air hose compression fittings were replaced by stainless steel threaded connectors. 3.All the electrical components were installed in protective
enclosures, and the wiring was installed in conduit. 4. A check valve was installed in the compressed air supply line to hold the rope in the applied position once it was set even if air pressure was lost in the air compressor tank. 5. The added check valve required an additional pressure switch to monitor the supply air pressure. The original pressure switch would not detect a. pressure loss in the air compressor tank when the check valve was installed. The contacts of the two pressure switches were installed in series. Mechanical Testing Tests were conducted to determine if the rope brake would operate reliably in the mining environment to provide ascending car overspeed protection. First, accelerated mechanical testing was performed to determine if the braking system could withstand repeated operation without experiencing significant wear or failure. These tests were performed while the suspension ropes were stationary. This testing was conducted at both the mine site installation and in the laboratory. Mine site testing was conducted every 4 hr. Mechanical counters were installed on both the machine brake and the rope brake to record the total number of operations for each brake. Every 4 hr, the number of times the machine brake had set during the previous 4 hr period was noted, and then, the rope brake was operated an equal number of times. The mechanical testing concluded after 30 days of around the clock testing. The total number of rope brake operations was 3430. The temperature range varied from 25 to 83. One of the rope brake components subjected to wear was the piston ring gasket. This gasket provides the air seal between the moving piston, which presses against the traveling brake pad, and the stationary cylinder. An overload test was conducted to determine the integrity of this seal. For the test, 8750 lb (125% of rated load) was loaded onto the car at the bottom of the shaft. Then, the rope brake was set, and the machine brake was disengaged. The air pressure was released from the air compressor tank, and the air pressure inside the rope brake cylinder was monitored. The load was successfully held stationary for 1 hr. The initial air pressure was 114 lbflin2, and after 1 hr, the pressure was 102 lbflin2. The pressured reduction may be attributed to an air leak through the check valve or past the piston ring gasket as a result of wear. Laboratory mechanical tests were also performed on the rope brake in the Mine Electrical Systems Division laboratories located at. The Pittsburgh Safety and Health Technology Center. The testing was performed on the smaller Bode rope brake model 200. The rope brake system was positioned outside the laboratory building under an awning that allowed the brake system to be exposed to the outside air temperature and humidity but was protected from direct contact with the rain and snow. The rope brake was activated remotely by computer control. The computer was programmed to apply and then release the rope brake every
38 s and log the number of operations. The outside air temperature, relative humidity, and barometric pressure were also continuously recorded. After 2 mo of testing and 146, 836 operations, the rope brake was disassembled and inspected for wear. The pneumatic. piston ring gasket exhibited minimal wear. Superficial rust was evident where the compressed air entered the rope brake and displaced the lubricant. Over the 70 days of testing, the temperature ranged from 5 to 82, and the relative humidity varied from 25 to 100%. At times, thick accumulations of frost build up on the air line between the magnetic valve and the rope brake cylinder. Therefore, the formation of ice inside the compressed air lines was possible; however, no adverse affects were observed. Rope Brake Control Failure Analysis In addition to the previously discussed mechanical analysis, testing and evaluation of the rope brake electrical control system was conducted. Brake control system studies were performed at the mine site and in the laboratory. The safety evaluation was conducted to ensure that a single undetected failure would not defeat the protection provided by the rope brake. Component failure should be detected by the brake control system and cause the elevator to stop safely and remain at rest until the failure is corrected. If automatic detection was not feasible, the periodic inspection and maintenance procedures were required to specify detailed testing of the possible failed component.
The rope brake control system, which is shown in figure 6, monitors the following four inputs: NI contactor, speed relay, pressure switch, and the rope pulse tachometer. Based on this input information, the brake logic decides to set the machine brake or both the machine brake and the rope brake. A test board was designed and built to simulate the brake control inputs with toggle switches and to provide relay coil loads for the brake logic output. A separate power source supplied 24 Vdo to the simulator board and brake control box. Evaluation of this simulation board provided the following information on the function of each input.
中文翻译 电梯安全 摘要
在五年期间，至少有18起上升电梯撞毁高架建筑物的案例。在某些情况下，造成重伤或死亡事故。这些事故发生在电梯对重装置因电气、机械、结构的不合格。电梯轿厢通过紧夹导轨得到适当的保护，阻止轿厢坠落；不过， 这种装置不提供方向向上的保护。 适用于电梯安全的法规己经针对这些事故进行审查。一些主管单位己修 订的条例规定上升轿厢的超速保护。这份文件将讨论基本电梯设计、灾害、 法规和制度，以提供紧急制动系统给向上轿厢的超速保护。此外，个案研究报 告的气压绳索制动系统的安装和测试煤矿电梯将会被讨论。
绪论 电梯安装了几个安全保险装置，以防止轿厢坠入井道底部。当机械制动 失败或悬挂轿厢的绳线断裂时,安装在轿厢上的保险装置可以防止这类事故 的发生。然而，固有的保险装置的设计在向上方向上是不起作用的。
向上的方向上，当出现紧急情况时，机械制动必须制止轿厢运行。在正 常运转情况下，机械制动系统只能作为停车的闸来控制轿厢保持静止。然而， 紧急状况发生时，现代电梯控制系统设计单靠机械制动来制止轿厢的运行。
在美国采矿业，事故历史已经证明这不是最好的控制策略。当机械刹车失效，当驱动发电机的减速效力失败时，事故就发生了。这使得对重装置坠 入井道的底端，造成轿厢超速运行并且击毁井架。高速电梯坠入高架建筑物 造成严重的机械破坏，和潜在的致命性的伤害。
电梯设计
了解电梯运行基本要求，以评估目前的安全威胁，并确定事故预防的有效方法。图1显示了一个完整的矿井电梯示意图。
图1 矿井电梯
在典型的电梯中，轿厢的升降是由六到八条由电机驱动的钢索牵引的。 这些钢索的一端附在轿厢顶部，围绕一对滑轮运转，而另一端则附在对重装 置上。
当轿厢上升时，对重装置提供用以加速的动力，而当轿厢下降时，对重 装置则提供延缓作用，以减少所需的电机马力。对重是对金属重量的一种采 集，它的量等于包含45%的额定负载的轿厢的重量。一组链通过偏置悬吊锁 的重量，从对轿厢的底部到轿厢的下侧构成环状以帮助维持轿厢的平衡。
当轿厢和对重装置运行时，井道的导轨用以防止它们摆动。附在轿厢和对重装置上的滚轮则是保证它们沿导轨平稳运行的。
轿厢升降的牵引力来自于钢索对滑轮的摩擦力，而主滑轮是由电机驱动的。
大多数电梯是使用直流电机的，因为它的转速可以被精确地控制己满足 轿厢的平稳的加速或减速的要求。电动发电机装置为驱动电机提供直流电 力。较新型的系统都使用静态驱动控制，通过表示轿厢在井道中的位置的反 馈信号，电梯控制可以改变电机的转速。当轿厢接近目的地楼层时，靠近层 站的幵关就会发出控制信号使轿厢停在相应层上。
首先就是高强度钢索本身，每根直径为0.625英寸的钢索可以负担 32000磅的重量，或者一部乘载20名乘客的矿井电梯的重量的两倍。为了 安全和减小磨损，每个轿厢都配有6到8条电缆。此外，精到的底部还装有 缓冲器，以防电梯故障时造成乘客的损伤。
正如先前讨论的，现代电梯有许多速度控制方法。当它们出现故障时， 这些控制可以切断与电动机的联系并使电梯刹住。最后，电梯本身也备有安 全钳，如果轿厢速率超过额定速率15^到25^，安全钳便会夹紧导轨使轿厢 停住。这个发明使得电梯这一运送工具被普遍地应用于社会。
安全威胁
一次电梯发展的过程中的预言可以解释今天电梯的安全规则。当现代电 梯刚幵始发展时，人们就意识到尽管在悬吊绳索中设有安全钳，但建筑物的 质量和定期的检验无法保证。因此，电梯轿厢需要装备一种可以在悬索失效 时仍能安全地停止轿厢的装置。1853年，一位名叫伊利沙奥蒂斯的纽约机 械师，设计并示范了一种能够及时停止轿厢下落的装置。这种危险如图2 所示。
图2 悬吊故障 稍后，人们意识到即使悬索完整无缺，当轿厢下降时，乘客也可能会受伤，如图3所示。为了防止这种危害一种带有逐步式安全钳的限速器被设计出来。它可以检测到超速情况并激活安全措施。
图3 轿厢超速下降
此外，还注意到安全前的频繁使用会引起电梯结构和安全系统的机械压 力。因此，安装了一种限速器超速开关，它可以在安全钳使用前通过机械制 动停止轿厢。这种开关非常有用，因为在轿厢超速上升时它也可以发挥作用。
问题出现于二十世纪二十年代，当时美国电梯安全代码己经发展起来。 作者很可能出于对当时可行的技术和后来的需要，因此将所有电梯都设置了 这种代码保护。
作者们如此将注意集中在所需设备的设计描述上以至于忽略了这些设 备所预防的危险以及电梯的部件有可能发生故障从而导致危险。他们没有考 虑到这个90^的电梯在不满载时(例如负载小于额定值的45^时〉的运行中都 会发生的事实。因此，如果制动故障发生，电梯将
会超速上升，如图4所示。
图4 轿厢超速上升
直到最近，自1900年初设计的电梯安全系统还没有很大差别。这个问题 的产生是因为在安全体系技术没有被完全改进的情况下，规则委员和权威人 士难以去要求新的安全措施。反过来说，电梯制造产业投入到没有市场的新 安全设备的发展费用很少。这个问题将在以下各节讨论。
法规
安全规则委员会和一些政府机关的安全权威指出了现行电梯规则的缺 陷，并提议对电梯安全规则进行修订。
该报告来自美国机械工程师学会-八17机械设计委员会关于\"轿厢向上 冲进建筑物的顶端，\"该报告包括了各种可能导致电梯加速进入架空结构的
故障，分析可能的解决办法。此外，提案委员会对新417. 1规则205，6法介 绍如下：
205． 6规则(\"预防超速轿厢撞击高架建筑物“）：曳引电梯应提供一种方 法来防止上升轿厢撞击高架建筑物。这意味着应符合下列条件：
1.在对重装置撞击缓冲器之前，轿厢的速度将会被降低，目的是平衡缓
2.轿厢在停止运行的过程中不得超过220ft/2s(9.18M/S2)的平均延 迟时间。
3.它应是独立的驱动机械制动器。
4它应通过控制下列一个或多个事项来防止电梯系统的超速运行： a.对重装置 b.轿厢
c．悬吊或补偿绳装置。
这个委员会目前拟议规则期间，曾经考虑到轿厢离开地面时需要防止门 开启或上锁。
宾夕法尼亚深矿安全局
在1987年2月4号，宾夕法尼亚州西部的煤矿井发生了一起上升电梯 轿厢事故，造成很多建筑物毁坏和电梯升降机两个月无法运行。在这次事故 中，美国宾夕法尼亚深矿安全局成立一个咨询委员会，以确定这些装置,能否 为向上超速运行的轿厢及现有矿井电梯提供保护措施。
下面四种保护方法基于工程原理或广泛的矿井测试，被证明是可行的。
1）平衡重(重量等于空轿厢的重量） 2)平衡物保险装置 3）动态制动 4）制动绳索。
宾夕法尼亚州的深矿安全局已经批准了这四种方法，并且在所有现存对
重装置的煤矿电梯中，强制用来保护向上超速的轿厢。 动态制动
美国釆矿工业釆用的第二个解决方案是应用于电梯驱动电机的被动动 态制动措施。如前文中所述，大部分电梯使用的是当降低大修负
载时可以作 为发电机使用的直流驱动电机。动态制动可以很方便地将阻性负载与电机电 枢连接起来，以抵消由下降对重产生的电能。
绳索制动
一种出现突发情况时可以夹紧悬索、停止电梯的气动绳索制动由波得奥 福泽格发明出来。这种绳索制动自1957年8月12日在荷兰被投入使用。
案例研究：绳索制动测试和评估
气动绳索制动装置第一次在美国安装是1989年9月8日在宾夕法尼亚 州煤矿。最大容量的波得式绳索制动装置〈580型)就是安装在这座煤矿的电 梯上的。这台绳索制动装置的安装是经来自匹斯堡安全委员会和技术安全中 心的矿场安全工程师和安监工程师广泛检测过的。有关这一发现的摘要将在 本文中加以介绍。
功能
绳索制动是一种保险装置，以防止向上或向下的方向的超速行驶并为失 控电梯轿厢的运行提供保护。
当超过正常运行速度的15卩。，机械驱动、发动机控制系统，或机械制动 失灵时，绳索制动系统被激活。绳索制动系统不能防护由于悬吊绳索断裂而 导致轿厢向由下落。
电梯轿厢的停止也受绳索制动系统的监测。如果电梯轿厢移动多于2至 8英寸的任一方向时，同时门是打开的或没有上锁，这时绳索制动被启动同 时控制电路被中断。绳索制动控制系统必须人工重新恢复正常运转。
刹车绳控制包含自我监测的特点。当发动机运行过程中，如果没有接收到来自脉冲转速计的信号，那么刹车绳索将被激活。
刹车绳需要电能和空气压力来适当运行。如果控制动力被阻断，刹车绳 幵始工作。当动力恢复后，刹车绳将自动放弃。
通常，电梯制动系统采用触发和电力释放式。因此，任何外来的能源都 不能起动制动器。储存加压空气制动的绳子能启动制动器并让电梯停止。因 此，监测空气压力是非常重要的。如果工作气压低于设定的最小值，发电机 电流被中断，此时机械制动被激活。当空气压力被恢复，故障又重新生成。
气动设计
图5显示绳索制动系统。从空气压缩机幵始，空气压缩通过一个液体分 离器和人工关闭阀门进行检查。检查阀必须保证制动绳索即使是在空气泄漏 时也可以正常工作。低气压监测幵关，如前所述将启动机械制动。供应空气 被阀检查后，分为两个独立的磁性双向阀。关掉空
气供应(A口〉，同时打开电 磁阀线圈。当电磁阀线圈被加强时，空气供应被引到B口，这是开放的绳索制 动汽缸。空气推动活塞进入绳索制动缸，强迫一个活动的制动垫逼近固定的 制动垫。在两个制动垫之间，悬浮绳索被夹紧。绳索制动被磁性阀释放，排 气制动缸的压力,通过安装在每个口的爆炸消音器释放。
图5 绳索制动系统
对悬浮绳索施加压力，等于通过活塞的面积增加了空气压力。580指定 型号的制动绳模型的直径为毫米的制动缸。因工作气压在90至1201cf/ in2 之间变化。相应的悬浮绳压力是36842至49123磅。因为他们运用滑车轮 驱动下满载条件是34775磅。因此，在超负荷运转下，绳索承受比正常情况 下多6%至41%的压力。
机械调整
测试之前，还需要进行机械修正来防止环境和机械对绳索制动系统的破 坏。修正同时也降低了气动系统漏气的不良影响。以下修正包括在绳索制 动设计中：
1. 2001bf/in2中空塑料软管被200011bf/in2金属管连轴替换。 2.中空软管压缩设备被不锈钢螺纹连接器替换。
3.所有电气部件都安装在防护罩内，配线安装在管道里。 4.校验阀安装在压缩空气供给线路上，即使空气压缩罐的气压下降也可 以防止绳索位置发生移动。
5.附加的校验阀需要额外的压力开关阀监测气压的供应。在校验阀被安 装情况下，原始的压力幵关将检测空气压力罐的压力损失。接触压力开关安装在两个系列。
机械测试
测试以决定，在矿井环境中，绳索制动能否给轿厢超速上升提供可靠的 保护措施。
第一，加速的机械测试，以确定是否制动系统的运作，可以承受多次的磨 损与故障。这些测试是在悬浮绳索固定的情况下进行的。这两个测试是在实 验室和矿区进行的。
矿区每4小时进行测试，。机械计数器安装在机械制动和绳索制动上来 记录每个制动运转的总数。每4小时，机械制动总数被设定，然后，绳索制动 操作次数与之相等。
30天每天24小时后，机械测试结束。绳索制动运转总数为3430次。 温度波动范围从25度到83度。
部分绳索制动受制于活塞垫圈的磨损。垫圈在运动的活塞之间密封空气， 压紧运行的制动垫和固定的气缸。一个超负荷测试来评估密封的完整性。
作为测试，8750让装在轿厢的底端轴上。然后，绳索制动被启动，机械 制动被停止。释放空气压缩机的空气压力，监测绳索制动气缸里的气压。负 荷被顺利固定一个小时。初始气压为11416bf/in2，一小时后，压力为 10211bf/in2。压力降低的原因可能是校验阀漏气或活塞环行垫圈磨损。
匹兹堡安全与健康技术中心机械测试实验室还进行了矿井有关绳索制 动电气系统的实验。测试是针对较小的忍耐绳索制动模型。绳索制动系统安 置在实验室外面的帐篷下，让制动系统暴露在外界温度和湿度下，但不直接 接触雨雪。制动绳索被电脑远程控制。应用电脑程序，每38秒释放一次制动 绳索，同时记录运转次数。外面的空气温度、相对湿度、气压也需要连续记录。
二个月运转了 146836次后，制动绳索因磨损而断幵。气动活塞环型垫圈 磨损的最小。在压缩空气进入制动绳索并转移了润滑剂的地方，表面锈迹是 很明显的。
超过70天的测试，温度范围从5度至82度，相对湿度范围为25%至 100%。有时，厚厚的霜附着在磁性阀线和绳索制动缸之间的真空线路上。因此，结冰在压缩真空线路上是可能的；然而，没有观察到不利影响。
绳索制动控制失败的分析
除了前面所述机械分析、测试和绳索制动电气控制系统的评估被操作 外。制动控制系统的研究工作，在实验室和矿区里进行。进行安全评估，以确 保没有隐藏的故障让绳索制动保护失败。
部分故障应该能被制动控制系统监测到，从而让电梯安全的停止下来并 保持静止状态，直到故障被修复。如果自动检测并不可行，还需要定期检查和维护程序详细说明测试失败了的可能成分。
绳索制动控制系统，监测下列四个输入：M电流接触器，传达速度、压力幵关、绳索脉冲转速计。在此基础上输入信息，制动逻辑就决 定是幵启机械制动还是机械制动和绳索制动一起开启。测试板设计和制造模 拟制动控制按钮开关输入，并为制动逻辑输出提供中继线圈。独立电源为模拟板和制动控制盒提供24伏电压。
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