Elevator Safety Components

Abstract

Safety is vital for all occupants of a building, whether it is a residential building or a commercial building, or a combination of both. Although all users know that their lives depend only on these vertical machines, they know nothing about the safety gears used in elevators, which cause them to feel stress during their travel. After many years, this stress may even cause cardiovascular diseases and high blood pressure. Therefore, a setup that is invented and used for making the lives of people easier may cause immediate death when it is not safe and, when it is not comfortable, may invite death after many years. The only way to prevent this is to know the vital role of the comfort and the safety gears of the elevators and to manufacture safety gears with the awareness of this responsibility. In this article, we examine the structure, types and standards of safety gears designed on the principle, “never run a machine you cannot stop.” 

Introduction

While the world population increases day by day, the surface of the world and the available living spaces narrow due to various global effects. Therefore, in order to create living spaces for the increasing population, buildings, like residences, hospital and shopping malls, are constructed as high-rise. Living spaces are created in these high-rise buildings, and transportation within these living spaces is provided by elevators. Climbing up the stairs, which was once a kind of exercise, in the buildings that the people moved into when they were young create an obstacle when they get older. Therefore, as the residents have established emotional bonds with their houses but cannot use the stairs, instead of moving to another house try to find a way to install elevators to their old buildings. Elevators are not only used for carrying passengers, but also for loads and even in construction works and carrying meals. The person who uses an elevator is called the passenger, the time between pushing the call button and landing on the car is called waiting time, and the time between getting onto the car and reaching the target floor is called travel time.

Although travel time is quite short, waiting for the elevator at the landing and traveling in the cabin is boring for many people. There is also a considerable number of people who have phobia about being confined in elevator. The reason why the waiting and the travel time in the cabin is so boring compared to the trips made by other vehicles is actually the security concern that lingers in the memory of the users, even if they do not know why.

For elevators, quality safety gears should be manufactured compatible to the other units and equipment, and the equipment should be installed, maintained and repaired by personnel who have a vocational competence certificate.  

Elevator Safety Systems

TS EN 81-20 defines persons to be safeguarded as,

• a) Users;
• b) maintenance and inspection personnel; and,
• c) persons outside the lift well, the machine room and the pulley room, if any.

The safe standard defines objects to be safeguarded as;

• a) Loads in car,
• b) Components of the lift installation,
• c) Building in which the lift is installed.

It is clear that the standard is prepared in order to create a unique safety system addressing any undesired situation considering the loads, components and at the site. In order to examine elevator safety systems, we need to see the list that contains the possible risks in the same standard. Possible accidents at elevators may be listed as, a) Shearing; b) Crashing; c) Falling; d) Overspeed; e) Fall of the lift;  f) Impact; g) Trapping; h) Fire; i) Electric shock; j) Failure of material; and, k) Wear and corrosion. Safety gears consist of equipment used for preventing the any of the kind of accident listed above. The new European Standards starting with the EN marking are the standards that not only give product definitions, but also consider product safety. Therefore, meeting the safety requirements mentioned in the EN Standards indicates that the relevant product is safe. The safety requirements for elevators require compliance to all of the specifications in TS EN 81-20. It is necessary to maintain the safety level mentioned in the standard. Essential Health and Safety Requirements mentioned in Annex 1 of the 2014/33/EU Lift Directive are the basic principles required for a lift to be considered safe and for getting the approval for manufacturing. For the companies that do not have comprehensive research and design teams, the simplest way to reach the referent safety level is to implement the requirements of the standard. Some of the safety elements used in elevators are:

1. Stopping Devices and Safety Contacts

While the safety components used in elevators comprise landing door locks, cabin safety gear block, overspeed governor, buffers, counterweight safety gear to prevent upward acceleration, motor brake in gearless motors and protection means for involuntary cabin movement. These components are used:

• a) Below the pit
• b) Below or over the cabin

In these places, it is obligatory to put stopping devices suitable for the switch described above.

Additionally, apart from the safety components that are required for being certified in the directive, different parts that are required in the standard are also used for safety. For example,  in order to avoid trapping and crushing at the cabin entrances, sill contacts, trapping contacts or photocells are used.

• a) Photocell or sill contacts for the elevators without door
• b) In all new elevators, car entrances shall be provided with doors. In closed elevators, in order to avoid accidents, trapping contacts and lighting fixtures are placed.

Such accidents may occur at the doors opening to the well, emergency trap doors, emergency doors and pit bottom doors. Although there are stopping devices in these openings, they also have door contacts.  When any of the contacts are opened, the contact is activated and the movement of the elevator is stopped without delay.  Stopping devices and jamming safety contacts must be kept under constant control to ensure operational safety. Safety contacts are the ones specified in the standard. Not every switch can be used as a safety contact. All safety contacts and switches should have the below-mentioned features, and contacts that are closed normally should be actuated by mechanical stress. Pressed contacts or switches cannot be used as a safety contact. The operation of a safety contact shall be by positive separation of the circuit-breaking devices. This separation shall occur even if the contacts have welded together. The safety contacts shall be provided for a rated insulation voltage of 250 V if the enclosure provides a degree of protection of at least IP 4X, or 500 V if the degree of protection of the enclosure is less than IP 4X. In the case of multiple breaks, the distance after separation between the contacts shall be at least 4 mm. Abrasion of conductive material should not lead to short-circuiting of contacts.

2. Door Locks

Plug-socket and lock contacts, which control the locking of the doors electrically and mechanically, prevent the elevator from moving before the doors are closed. The elevator landing lock is one of the main elements that disconnect the thing inside the cabin with the pit and the things outside the pit with the downhole during the movement of the elevator. Below you may see a double safety locking device and plug-socket connection.

3. Overload contacts

As mentioned above, the cabin tries to stop with a force above the friction calculations made in overload, and this causes the cabin to slide. To prevent this, there are contacts on the top or bottom of the cabin or on the suspension ropes that prevent the cabin from moving when the cabin is loaded above the rated load. While these contacts are not safety devices, they should be used as defined by the standard. The function of this contact is to prevent lift movement until the car load falls to the rated load and the possible danger is prevented. In addition to overload contacts, full-load contacts are also used in elevators. The function of these contacts is to prevent the response to external controls while the elevator is loaded with the rated load and to eliminate unnecessary stops. The lift shall be fitted with a device to prevent normal starting, including re-leveling, in the event of overload in the car. The overload is considered to occur when the rated load is exceeded by 10%, with a minimum of 75 kg. In the event of overload:

• a) Users shall be informed by an audible and/or a visible signal in the car;
• b) Automatic power-operated doors shall be brought into the fully open position;
• c) Manually operated doors shall remain unlocked.

4. Buffers

Buffers are classified as linear and nonlinear, with buffered return movement and energy dissipation-type buffers. These buffers are sometimes used as a mechanism that prevents falling and sometimes as safety gears connected to the lifts of the hydraulic power circuits. In Figure 1 we see a hydraulic buffer manufactured, tested and approved by Aspar Asansör, in accordance with the EN 81:20/50 standard.

If the elevator continues on its way outside the travel distance limits as a result of the above-mentioned situations or a malfunction in the drive system, the car or counterweight will hit the bottom of the pit. When the pit is built, the gap above it is planned to prevent the the car or the counterweight from hitting the top of the pit. Therefore, buffers are placed at the bottom of the pit. A buffer is a stopping element that receives the force of the cabin or the counterweight by bending, which can change its shape. Buffers are classified based on the elevator speed and load. Energy accumulation-type buffers can be used when the rated speed of the elevator does not exceed 1 m/s. A spring stop is a buffer that meets the kinetic energy of the cabin, loaded car or the counterweight with a spring setup. The stroke of this type of buffers shall not be less than 65 mm. For buffers, stroke distances are calculated based on the rated speed as 0,135 v². Buffers are designed to cover the stroke under a static load of between 2.5 times and 4 times the sum of the mass of the car and its rated load (or the mass of the counterweight). Energy-dissipation buffers are hydraulic buffers in general, and they are used in elevators that travel over 1,6 m/s. They can be used in all speed groups. The hydraulic buffer is a hydraulic piston buffer that absorbs the kinetic energy of the loaded cabin or counterweight and is automatically restored after impact when the cabin is lifted off the buffer. Hydraulic buffers that do not have self-setup have a setup device. Buffer definitions and requirements given in international standards are summarized below:

1. Buffers placed at the lowest part of the car and the counterweight: These buffers should be placed at the lowest point of the travel of the car and counterweight. Here, under the projection of the cabin, the surfaces on which the buffer or buffers affect should be determined with a proper obstacle not less than 0.3 m in height. In drum and chain elevators, the buffer should be placed on the cabin to act on the upper limit of the travel range.

2. Energy accumulation-type buffers, with linear and nonlinear characteristics: These types of buffers shall only be used if the rated speed of the lift does not exceed 1 m/s. Energy dissipation-type buffers can be used whatever the rated speed of the lift.

3. Buffers: Buffers shall be designed to cover the stroke under a static load of between 2.5 times and 4 times the sum of the mass of the car (or the counterweight) and its rated load.

4. Fully Compressed Buffer: The term “fully compressed” means a compression of 90% of the installed buffer height.

5. Hydraulic Buffers: Normal operation of elevators with hydraulic buffers should depend on the return of the buffer to its normal position. It should be checked with an electrical safety gear. When hydraulic buffers are used, the hydraulic level should be easily controlled.

5. Electromagnetic Brake Lever and Operation

The safety gear mentioned in the traction section works when it is supplied with power. As it locks the elevator in case of power cutoff, one of the safety gears maintains security by retarding the elevator in case of disconnection. A manual brake-release lever placed on the brake is used to rescue those who are stuck in the elevator in case of any failure. With the help of this lever, the brake is opened, the motor is winded with the wheel on the motor and the cabin is brought to the floor. When this lever is released, it must return to its original position, or a switch should prevent lift movement while the arm is raised. The brake opening device can be actuated electrically in cases when there is no access to the motor. The wheel, which is another part of the emergency operation, allows the manual operation of the motor. If it is not connected to the motor, the wheel should be located in an easily accessible place in the machine room. (Necessary precautions should be taken to determine the location of the car during manual emergency operation through putting landing marks on the ropes or with a lamp.) Additionally, passengers isolated in the car may call for outside assistance through an emergency alarm device. An intercom system shall be installed between inside the car and the machine room if the lift travel exceeds 30 m. When the elevator safety system is locked, the landing doors can be opened with the emergency unlocking key. When the distance between consecutive landing doorsills exceeds 11 m, intermediate emergency doors shall be provided and emergency trap doors will provide access to the cabin. Emergency doors and emergency trap doors are obligatory when the cabin passes through floors without landing doors or when the height between the floors is greater than the cabin entrances. The specifications of the emergency doors and emergency trap doors are given under the title Landing Doors and Car Doors.

6. Governor and Mechanical Brake

When the elevator reaches a speed that is more than the 115% of its rated speed, a mechanical system that clamps the car to the rails is activated to stop it. This system, which is called a mechanical brake, or safety gear, consists of two main parts: the governor, which activates the system, and the safety gear, which stops the car when the system is activated.

6.1.  Governor

A governor is a system that makes an assessment of the speed through mechanical means. Although there are various types of governors, their common characteristics are operating based on centrifugal feature, locking when it reaches a certain speed and stopping the governor rope. The governor functions completely mechanically. Using a governor electrically in the downward direction is not accepted. In order to actuate the cabin safety gear, the overspeed governor should be activated after the cabin reaches a speed equal to 115% of the rated speed. The maximum distance between tripping points on the governor should not exceed 250 mm related to the movement of the governor rope. At speeds above the rated speed and in cases where the rope loosens, the governor contact should cut the circuit. The locking direction of the governor should be in the descending direction. If there is passenger traffic below the pit, then there should also be a governor and mechanical brake on the counterweight. The ratio between the diameter of the sheave and the rope should be 30. The overspeed governor is tensioned by a tensioning pulley, which should be tensioned with a very flexible rope. The governor rope should be easily detachable from the safety gear, and tested when needed. An overspeed governor or other means should stop the elevator motor through an electric safety device before the cabin reaches the speed to actuate the governor. Governor rope contacts on the governor should stop the elevator in case or breakage or excessive rope stretch. In Figure 2, we see the details of a governor installation.

In Figure 2, there are the pictures of governors manufactured by Aspar Asansör in ac cordance with EN 81/20 Standards:

•  a)235/315 mm
• b)120 mm

6.2 Mechanical Brake (Parachute System)

The mechanical brake is actuated with the tensioning of the governor rope and locks the cabin.  Mechanical safety gears installed on the car frame operate based on the principle of compressing the rails. They can be installed under or over the car frame, but installation under the car frame is preferred. If it is under the cabin, the braking force is generated in the parachute system and connecting bolts, but it does not generate force in the suspension beams and carrier beams. This is a safer placement. However, it can be placed on the cabin due to difficulties in maintenance and installation. Cabin frame and safety gear connection is provided by bolt coupling with sufficient endurance. When the braking occurs, on the rails a damping force and acceleration above 1.5 m/s2 is generated in high speed. Therefore, different safety gears are used based on the car speed. Car safety gear may be of the instantaneous type if the rated speed of the lift does not exceed 0.63 m/s. The safety gear should be of the progressive type if the rated speed exceeds 1 m/s. The maximum acceleration that occurs when the safety gear is actuated should not exceed 1g. Safety gears should not be tripped by devices that operate electrically, hydraulically or pneumatically. When the car safety gear is engaged, an electric safety device mounted on the car initiates the stopping of the machine before or at the moment of safety gear operation. This contact, which is called safety contact or parachute contact, ensures that the motor circuit is cut and the electromagnetic circuit is activated when the mechanical brake is locked. Before the actuation of the safety system, actuation of the safety contact has vital importance.

Similarly, there is a means of detecting uncontrolled acceleration of the ascending car. In new elevators, it is obligatory to provide safety against acceleration in both directions. Below, various safety gears are shown.

Another important point about the safety gear connection is the governor connection and provision of sufficient tension of the rope. The governor rope and safety gear arm should be made should be in such a way that they will not loosen. Except for custom systems, two clamps should be used in this connection. In order to actuate the safety gear, the governor rope should be tightened. In case the governor rope loosens or comes off, necessary safety precautions should be taken to prevent the functioning of the elevator through a contact that will be actuated with a swivel arm. For the governor tension weight to fulfill its tensioning function, there should be an obstacle to prevent tensioning when the arm goes down, and a swivel arm to allow its descending. Additionally, this swivel arm should fix the guiding part of the swivel and should allow vertical movements of the weight when the braking drags. When a bidirectional safety gear is used, the weight of the governor should be calculated to overcome the spring force that will provide the upward braking. In Figure 3, we see a safety gear block.

In Figure 5, we see a progressive safety gear block manufactured by Aspar Asansör pursuant to EN 81/20 Standards.

In addition to a downward safety gear, TS EN 81/1 requires the use of a safety gear operating in upward direction that prevents the overspeed of the cabin. The means should detect uncontrolled movement of the ascending car at a minimum of 115 % of the rated speed, and cause the car to stop, or at least reduce its speed to that for which the counterweight buffer is designed. The means that protects an ascending cabin against overspeed should act at the car, to the counterweight or on the rope system (suspension or compensating) or on the traction sheave (on the sheave directly or on the same shaft in the immediate vicinity of the sheave).

When this system works, a proper electrical safety gear should be activated and cut off the supply of the motor and brake circuit. If power is needed for this system, it should be designed in such a way that it can operate in case of power failure. Safety gears that operate in both directions are safety components and should carry the CE marking. In Drawing 3, we see a common governor-safety gear connection.

A safety gear can be installed on the counterweight for maintaining counter-direction safety. The safety gear of the counterweight or balancing weight shall be of the progressive type if the rated speed exceeds 1 m/s. In other cases, instantaneous safety gear can be used. The safety gear of the car, counterweight or balancing weight shall each be tripped by its own overspeed governor.

Apart from these, it is possible to maintain safety with uncontrolled movement of the ascending car through the use of rope locks and by maintaining safety on the sheave with accumulator-fed systems, which operate like magnetic brakes. Although they are expensive, rope locks are recommended for preventing slipping of the ropes or blockage of the cabin, especially in high-speed elevators. Uncontrolled slipping of the ropes is one of the risks that should be prevented. The requirements about the descending and ascending safety gears in the standard are summarized below:

6.2.1 Descending safety gear

1. In the car, there should be a safety gear that is only capable of operating in the downward direction at the rated speed at which the overspeed governor is activated, and capable of stopping a car by gripping the guide rails, and of holding the car, even if the suspension devices break. Preferably, the safety gear should be placed under the car. 
2. The safety gear shall be capable of operating in the downward direction and capable of stopping a car carrying the rated load, or a counterweight or balancing weight at the tripping speed of the overspeed governor (or if the suspension devices break) by gripping the guide rails, and of holding the car, counterweight or balancing weight.
3. The safety gear of the car shall be of the progressive type if the rated speed exceeds 1 m/s:
   • Instantaneous safety gear may be used if the rated speed of the lift does not exceed 0.63 m/s. If there are more than one safety gears in a car, they shall be of the progressive type.
   • The safety gear of the counterweight or balancing weight shall be of the progressive type if the rated speed exceeds 1 m/s; otherwise, the safety gear may be of the instantaneous type. In other cases, instantaneous safety gear can be used.
4. A proper electric safety device mounted on the car shall initiate the stopping of the machine before or at the moment of safety gear operation.

6.2.2. Ascending car overspeed protection means

1. Ascending-car overspeed protection means, comprising speed monitoring and speed-reducing elements, detects uncontrolled movement of the ascending car at a minimum 115% of the rated speed and causes the car to stop, or at least reduce its speed to that for which the counterweight buffer is designed.
2. Ascending-car overspeed protection means should be capable of performing without assistance from any lift component that, during normal operation, controls the speed or retardation, or stops the car, unless there is built-in redundancy. A mechanical linkage to the car, whether or not such linkage is used for any other purpose, may be used to assist in this performance.
3. It should be effective on the counterweight or rope system (suspension or balancing rope) or d) traction sheave (on the traction sheave or near sheave). Motor brake can be used in gearless machines.
4. When the ascending-car overspeed protection means operates, it should activate an appropriate electrical safety gear.

Acknowledgement

I would like to thank Aspar Asansör and AKSÖZ Makine for providing a reference with the pictures, and also Ayşen Baysal for contributions about the references and pictures during the preparation of this article.