Elevator Doors continued…
Most of the elevator doors in operation today use either a GAL or a MAC operator. These types of operators transfer the circular motion of an AC electric motor into the linear motion needed to open and close the doors though the use of some cleverly designed control arms. Using links these control arms allow the door motion to reverse when they run into an obstacle or they have reached their open/close limit. This type of door system has been in use for at least fifty years and the technology is well known and proven. Recent developments in the industry have produced DC powered linear door operators with reversible motors that move the doors with a belt system. The old circular motion door operators used a system of belts too but that was with sets of pulleys to reduce the speed of the motor and increase the power. The linear systems utilize a long, toothed belt that pushes the door in each direction. The door actually travels along the belt path. This eliminates many of the mechanical components of the door system thereby simplifying it making door maintenance a snap and greatly reducing wear problems.
In the past the geometric configuration of the door components had a huge impact on how well the door worked. The arm connection point on the car door has to be almost exact for the system to work properly. Locate it in the wrong place and the door would always be a real load for the motor causing burned up motors, stalling doors, and other problems. It could also be in a spot that would make some doors too easy to close making them prone to slamming and hard to adjust. For the first problem companies would just replace a standard operator with a heavy duty one creating the second problem which they consider easier to deal with. Heavy duty operators were invented for tall doors. The taller the door the more difficult it is to close. Not only is it heavier, if something gets stuck in the track the leverage factor kicks in and it becomes very difficult to close. Normal elevator doors are 8 feet high. Anything taller than that is more difficult to maintain and requires more attention. With old style door operators the technician had to adjust the system to be forceful enough to close the heaviest (some main lobby doors are more ornate and thus heavier) or most difficult hoistway door to close. That causes the others to slam. With the advent of new closed loop technology the motor draws just enough energy to allow it to close the door normally, changing at each floor. Many of the systems being manufactured today actually learn the different floor patterns and automatically add or decrease energy when opening or closing on certain floors.
Although most elevator technicians are more comfortable with the old style operators, the new linear operators are gaining wide acceptance. This is due to their simplicity really, there is almost zero maintenance to perform on them. They adjust themselves. Most have switches to control the opening and closing speeds. After an inspection of the belt for wear and lubrication of a very few of the parts the tech can be on to bigger and better things. I also expect them to reduce callbacks over time. One reason being is that if the door doesn’t close all of the way or not firmly enough, the safety switch contact may not be adequate causing either an open circuit or intermittent contact. This condition will shutdown the elevator creating a callback (and probably a bill) for you the customer. Linear operators are much more consistent. An added benefit is that engagement of the latch release mechanism and the clutch apparatus is direct. No space is left between the two apparatus to allow pass through. Eliminating the slack in the engagement enables the doors to open silently. How many times have you heard the elevator doors bang when they start to open? A final benefit is that the doors actually use less energy to operate. Although it’s a minute amount, over time it counts. Not available for all size doors yet, I expect that these will take over soon.
For modernization and upgrade processes there are many “drop in” closed loop replacements for conventional door operators today. These can reduce the cost of an upgrade or mod by a considerable amount by not having to rebuild the entire door closing mechanism. Allowing only the worn parts of the apparatus to be replaced and eliminating the time involved in relocation of components. Also because all different sizes and types of doors are not yet covered by replacement linear units.
Freight doors come in two types. Hand operated and motorized. The motorized doors operate very differently from the passenger elevator doors. Both hand and motorized utilize a system of counterweights for ease of opening. Rather than employing relating cables a system of chains is used. Like passenger elevators they have a car door (usually a gate) on the car and a set of hoistway doors at each landing. These are bi-parting doors, they open horizontally with the top panel going up into the hoistway and the lower panel descending down. The hoistway doors do not engage the car door. It opens (or is opened ) separately. In most cases the door operation is activated with a separate button. After the doors are closed you can place a floor call. The elevator will stay at a floor and not answer a hallway call until the doors are closed. Most are equipped with a bell for signaling that someone on an alternate floor needs the elevator and that the person at the current floor needs to close the doors to get the elevator to move. Most freight doors have a small window used for checking to see if the car is at the floor.
Freight doors require a lot more lubrication and maintenance than passenger doors. Lack of maintenance can make them very hard to open and close so constant attention is needed.
There are only a few freight door manufacturers around. Almost all of these doors are custom made. To get replacement parts the technician must get the manufacturers name and the serial number from the door panel. For older units this is sometimes difficult because plates have been removed or painted over. Original prints have been lost. In some cases if you can pinpoint the year of manufacture, the original job name (usually the name of the building) and the manufacturer. They can search their files and come up with the original prints for you and assemble a rebuild kit. In the case of hand operated doors they can also offer a kit to motorize the door. There are a few companies out there that do sell replacement parts only but you need the prints and original part numbers to order what’s necessary. Rebuilding freight doors is normally a pretty big job. The components weigh much more and each one is different. They are not as straightforward as passenger doors.
Time to close the book here today. I would like to ask you again if you have any questions, or comments. I have been thinking about possibly working on some software for you to be able to write your own maintenance plan and tailor it specifically to your equipment and conditions. Please let me know if this is something that you may be interested in. Also if there are any subjects that you would like me to tackle next please let me know. Otherwise I plan to write a bit about elevator controllers in the next posting. For questions or comments please don’t hesitate to contact me at elevatorernie@hotmail.com.
Thank you,
Ernie
Quote for the day “ If you die in an elevator, be sure to push the UP button.”
Sam Levinson
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