Update 2

• Why Modernize?
• Elevators as Policemen
• Door Operators
• Buffer Bumph

The purpose of an elevator modernization is to allow the building to compete with other new buildings and existing buildings that have already been modernized. Once a wave of modernizations or extensive new building starts in the core of the city it is difficult for any building owner to resist the trend to modernize. If he does not follow the trend, his building is left with a second-rate image.

For a period of some 25 years from 1955 to 1980 elevator technology remained relatively unchanged without any significant innovation. During that period there was little reason for modernization since the new equipment was very much like the older equipment. However, over the last fifteen years there have been major changes in the controls of traction elevators. The changes are due to the implementation of solid state power units (SCR and VVVF drives), closed loop feedback speed controls and microprocessor logic. All these changes are aimed at improving reliability and performance as well as reducing ongoing adjustment requirements. In addition to this there has been increasing emphasis on ride quality and noise levels. As a result of these developments there is a perceptible difference between an elevator installed today as compared to one installed 20 years ago. The differences are obvious enough that the building tenant becomes aware that the space being rented is no longer first class space. This has a direct impact on rental and vacancy rates.

Sometimes it is suggested that the existing equipment be modernized since it is "getting old" and therefore impossible to maintain. This thinking has no basis in reality. Elevator equipment for office buildings has been designed to run indefinitely. With proper maintenance - which most building owners have been paying for - there is no reason why it should deteriorate. It is true that new elevators require less maintenance than earlier designs but this just means that it is easier and more profitable for elevator companies to maintain newer equipment rather than older equipment.

The problem of maintaining older equipment is compounded by the practices in the elevator industry. New equipment development and installation tends to be the training ground for new mechanics and adjustors. Adjustment of the older relay systems is generally left to the older adjustors. Due to the seniority provisions of many elevator union agreements the average age in a union local is often over fifty years. Some companies are already finding it difficult to find enough adjustors to meet their maintenance obligations on older equipment.

The upshot is that in the near future there will not be enough personnel capable of keeping the older systems running reliably at their potential.

All of these factors tend to force building owners to examine the question of modernization. It becomes not a matter of whether to modernize but when to modernize bearing in mind the length of time the modernization program will take. For example, it would take almost two years to completely modernize a group of four elevators from the time the "go" decision is made.

It has been recently reported that the Singapore housing authorities are installing urine detectors in elevator car cabs. These are to be used in the various subsidized low rental housing developments.

The detector when it senses urine in the cab, presumably because someone has decided not to wait, causes the elevator to shut down with the doors closed. The passenger is then trapped until the police arrive.

Whatever the moral and practical merits of this device, it perhaps reflects a growing trend to replace the "men in blue" with machines and electronics. Obviously, an elevator cab is ideal for this purpose since it is, in effect, a ready-made prison cell. The mind boggles at the possibilities: we could have people press their hands on a palm print sensor in the cab as a prerequisite to activating a push button. If the prints were those of a wanted villain then the elevator could be stopped and the miscreant trapped to await the ministrations of the forces of law and order.

Nor do we need to stop there. We could construct high rise schools with elevators that would allow pupils to access the upper floors only if they could answer skill-testing questions posed by the elevator. Those that could not answer the questions would have to walk up. There is, as always, a down side to this. The students who were always using the stairs would become physically fitter than those who did not - which would mean that the current split in our scholastic population between nerds and jocks would widen.

In the early days of elevators, doors were manually operated. Even today there are some residence elevators or handicap lifts which have manually operated doors.

However, with the advent of the automatic elevator it was obviously desirable that the doors be motorized.

The door operator consists of an electric motor generally with some type of speed reduction system (either gears or belts), mechanical linkages to the car doors and a motor speed control system.

It was apparent to the elevator designers that a door operator for each entrance was an expensive proposition and for that reason the "master door operator" was developed.

The master door operator uses one door operator on the car to open and close the car doors. The car doors in turn are mechanically linked to the hall doors so that when the elevator is stopped at a particular landing the hall doors for that landing open and close in synchronism with the car doors.

Although a bit difficult to describe, the concept is simple. A typical design uses a "skate" or "vane" mounted on the car cab door. This is a piece of steel about 12 mm thick (1/2"). On the hoistway door two rollers are mounted, located so that the car door vane runs between them as the elevator goes up and down the hoistway. The typical clearance between each roller and the car door vane is 6 mm (1/4"). When the elevator stops at a floor and the car door opens, the car door vane pushes against one of the rollers, tripping the hoistway door lock open and moving the hoistway door together with the car door.

Other designs (e.g. GAL) use "clutches" mounted on the car cab doors arranged to engage rollers on the hoistway doors.

As can be seen, there are some rather small clearances given that the elevator is running past the doors at speeds up to 9 meters per second (1800 fpm). If something goes wrong with the guiding devices that restrict the lateral movement of the car cab the vane will sometimes touch the hoistway door rollers when running past the doors at full speed. This can cause the hoistway door lock to open, interrupting the safety circuit, and the elevator will lose power for an instant. If you are riding the car you might notice a sharp blip in the car motion and perhaps you may hear the noise of the vane clipping the roller.

Common faults are: a door failing to close; a door recycling; a door hitting people as they go through the entrance; the electrical contact used to indicate the door is closed, failing to complete the electrical safety circuit even though the door appears to be closed.

Generally the door fails to close because the door detector (the device that monitors the opening to ensure that the doors do not close when something or someone is in the entrance) fails. This can commonly occur with dust on the detector surface (which prevents the infra-red light from getting through). If there is any construction work going on in the building then a more frequent cleaning of the detectors is required. Although the maintenance mechanic may do this, it is a good idea for the building staff to clean the detectors when cleaning the car cabs. They should receive instructions on this from the elevator maintenance contractor.

Doors often recycle because the lock does not make up and a control circuit designed just for that purpose tells the doors to "try again" by opening and closing. Sometimes, as well, the detectors "false fire" when the doors are almost closed. Both of these are maintenance problems which should occur only rarely if proper routine maintenance is being performed. Doors hitting people can result from a faulty door detector device or from incorrect door operator speed settings. This is a serious fault since it may result in injury and litigation. For this reason immediate action is required; it is a good idea to shut the elevator down until the fault is corrected.

Electrical contacts on the door locks failing to make up can be frustrating for everyone. Frequently this is an intermittent fault and as a result somewhat difficult to pinpoint. However, good routine maintenance on the hoistway doors will minimize this type of failure to the point that it virtually never happens.

Close to half of the trouble calls on elevators are related to the door operators and door equipment. Concentrating on first class maintenance in this area will pay dividends in passenger satisfaction.

The buffer is a device that provides a "soft landing" or a "buffer" if the car travels past the terminal landing. The buffers are installed in the elevator pit under the cab and under the counterweight. Elevators with speeds under 1 meter per second (200 feet per minute) use simple spring buffers; elevators traveling at higher speeds use oil buffers.

The use of buffers on elevators quite likely evolved from their use on trains. In the early elevators with simple control systems and manual attendants operating the elevators it was not unusual to slide past the terminal landing occasionally just as with trains it was not unusual to have some bumps when shunting box cars.

There are a couple of problems with buffers.

Spring buffers do not improve safety much. If the elevator hits a spring buffer at 1 meter per second the spring compresses and then bounces back. A passenger in the car would get a bit of a jolt. The oil buffer is better since it provides a regulated rate of deceleration. But there is a significant difference between the deceleration with a full load in the car and with just one or two people in the cab. Since the buffer has to be designed for the full load condition, the near empty car condition can result in some fairly severe stops. Nor is the deceleration always uniform; there will be peaks that exceed the average. To alleviate this problem the buffer can have a longer stroke but there are penalties to be paid in increased pit depths and overheads.

One answer is to provide speed slowdown switches to restrict the speed of the elevator as it approaches the terminal floor. This is a typical "Catch 22" situation: the buffer is there to provide a reasonable emergency stop in the event that the speed control system fails but the electrical control system must function to bring the elevator to a safe speed prior to striking the buffer. If we are going to rely on the speed control system to do this, why not rely on it to bring the elevator to a safe stop without using a buffer?

The industry appears to be moving, as in aircraft, to a 'fly-by-wire' approach. More reliance will be placed on the speed control systems with fewer mechanical backups such as buffers. With the improvements in the technology of elevator speed control systems and their increasingly high level of reliability, the buffer may become an anachronism on the elevator of the future.