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Elevator Design Safety Factors
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(Mechanical)
(OP)
19 Feb 03 08:08I’m currently designing and building a powered elevator / lift for my cottage. In recent years, the 130-stair climb up from the lake is getting challenging for my ageing parents. The lift will consist of a track at about a 32 deg. angle with a winch at the top to pull a car up and down. The car will have an emergency braking system that will automatically trip it if the cable tension drops below the weight of the empty car. The winch will be a simple cable and drum assembly mounted on self-aligning pillow blocks. The motor / gearbox will hang off the drum shaft with a torque arm to hold it in place. It will be powered by a PLC controlled 3 ph, 220 Vac, variable frequency drive with dynamic braking. Much of the design is being done on solid modelling s/w and FEA will be done on key elements. …OK I admit that designing stuff is also my hobby. This is actually my summer project at the cottage this year.
I’m not actually required to build it to elevator code, since it is a cottage / private application, however I plan to use common elevator design practices for guidance. Unfortunately I don’t have a copy of the relevant code for the area and would rather not buy one if I don’t have to. Does anyone have the commonly used safety factors for the following?
1. The gearbox on the winch drum. Is the SF on the working load, the maximum load (200% for the type I’m looking at) or on the ultimate load (I would need to contact the mfgr for the ultimate load or the internal SF’s)
2. The pillow block bearings on the winch drum
3. I believe the SF for the cable should be 10:1 for the working load limit. My cable load is only about 1000 lbf. I may even go for a 15:1 SF for the cable, since cable is relatively cheep.
4. I’ve seen values of 1/920th of span for the allowable track deflection. Does that make sense?
Thank you in advance for the help.
Rob
(Mechanical)
20 Feb 03 04:32Hi Perrins,
1. For a portable ski tow SF for cable is 4 - 4.5
2. SF for transmission - >1.5* Mdyn.max
3. SF for drum axe, pillow block bearings, fasteners and others >2.5*Max.dynamic Load
4.???
Success,
G.
(Mechanical)
20 Feb 03 15:22Rob,
I'm not familiar with specific industry standards for the design of powered man lifts, but if I were building one for personal use here is the approach I would take:
1) Determine the normal operating load - posted capacity, plus weight of the cart and cable.
2) Calculate the design load in the cable by dividing by sine 32 degrees and multiplying by a factor of safety to account for rolling resistance, intentional or unintentional overloading, miscelaneous friction, etc. A F.S. between 3 and 5 would probably be adequate.
3) Size your gearbox, bearings and motor to handle the design load based on the manufacturers recomendations. I doubt you will have much sucess in finding out the ultimate structural design safety factors for these items.
4) Once the motor , gearbox and drum size have been selected, calculate the tension in the cable produced by the stall torque of the motor. Size the cable, keyways, shafts, torque arm, and cart structure to withstand this load. Be sure to apply another safety factor , perhaps 2:1 on yield strength and 3:1 on ultimate strength.
5) Perform a proof test at `200% or more of posted capacity before loading your parents in the cart.
Regards,
Andy
(Aerospace)
20 Feb 03 19:56not at expert, but am certainly paranoid...I'd look into a track or roller system that does not allow the cars to jump track, ever, short of having an earthquake. The braking system would only work if the car stayed on the track.
TTFN
(Mechanical)
(OP)
21 Feb 03 08:41Alterson, thx.
as per item 1, done
Item 2, done
Item 3 Agreed, I would rather base the SF on the working or allowable loading of the components. I know that for elevator applications the SF tends to be considerably higher, since it is for people. I plan to use a SF of 10 to 15 for the cable, since it is cheap and at a higher risk of wear.
Item 4, good point. I haven’t finished sizing the motor. It will be either a 7.5 Hp or 10 Hp, depending on how fast I run the lift. This is partly cost driven.
Item 5, yes. I plan to test it by filling 40 Gal drums with water. The car will have a GVW of 2000 lbs. and the car will car about 1000 lbs. or four people.
Irstuff, thx
That has been accounted for. Some of the design is based on a roller coaster concept, so the car can’t actually come off the track
I’m also working through a failure mode analysis to outline the risks / mitigation.
(Mechanical)
3 Mar 03 14:15Check out ANSI A10.4 and A10.8. In suspended scaffolding design the factor of safety is based on the hoist's rated capacity, not the design load. The hoist's rated capacity must be less than 1/3 of the stall load or cut-off load of the hoist. On a multi-layer drum hoist the load the hoist can apply to the wire rope for a given motor torque will increase as the number of layer of rope decreases. With the cutoff set at 3:1, a factor of safety of 4:1 will provide a margin of one. The rope safety factor is anywhere from 6 to 1 to 10 to 1 dependent on application.
(Mechanical)
5 Mar 03 03:26I'd consider the fail-safe braking system used on elevators if I were you.... also run the cable within the under side of the track where possible, wire cables can be lethal when they snap.
Speedy
"Tell a man there are 300 billion stars in the universe and he'll believe you. Tell him a bench has wet paint on it and he'll have to touch to be sure."
(Automotive)
5 Mar 03 05:33
If your winch drum is multi-layer, there is a change in velocity ratio as johnhanging says. You should also consider that wire rope can jump as it its tension forces it into gaps in the second and subsequent layers. This isn't particularly dangerous (although it's not good for the rope) but it's pretty alarming for your pasengers when being hauled up a long slope and the car lurches back an inch or two. Might even trip your emergency braking system.
You can get round this by using a capstan winch for hauling, and having a secondary powered drum for the (low tension) take up drum. Or you can lay the rope precisely using a reverser screw to feed the wire onto the drum one layer at a time with no gaps between the rope.
Have you thought of having a counterbalance weight travelling in opposite direction to the car? This means more track (between the rails of the existing track?) but the rope handling problem is easier. Also less power and more safety.
Who makes the system stop and go? Passengers? If so, how do you control your motor? Please, not radio control for safety critical stuff. Some kid may be playing with his RC boat in the lake .......
Finally, hauling up slopes is sometimes easier than controlled descent. Are you controlling speed using dynamic braking only? If so, what happens to the energy you're creating? Gotta go somewhere!
Best of luck with the project - sounds fun
Regards - John
(Mechanical)
(OP)
5 Mar 03 08:16Johnhanging, thx, I'll take a look
Speedy, thx,
Yes the elevator will have two independent clamping systems, which will clamp the track, similar to a table saw kickback. The weight of the cart will clamp it tighter. The clamps will engage if the cable tension drops below about 800 lbs. I may add a shock absorbing system to it but I'm still thinking about the added complexity. I also plan to drop test the brake system.
Good Quote, but I prefer, "If necessity is the mother of invention, you can be assured that laziness is the father" Rob Perrins '92
harrisj, thx,
1 & 2. The winch drum will be a single wrap with a machined grove. The drum will be machined from a 12" pipe so it will be less than 20" wide for the 140 ft cart travel. The angle of misalignment will be very small, so I won't need to guide the cable onto the machined drum groove. This is a very simple system.
3. Yes I liked the idea and the related benefits, but a counter balance system seemed to be a little too complicated. As it is I'm laying 2000+ lbs. of steel down a mountainside for the track. I've already poured 15,000 lbs of concrete, buy hand, for the counter weight and footings.
4. The Up, Down, Stop & E-stop are located at the top, the bottom and on the cart. The E-stop will be hard wired through a relay and the others will be wired up to a PLC for the logic. The wiring to the cart will be done with a coiled cable riding on a 3/16" wire rope.
5. I'm still sourcing a surplus or used Variable Frequency Drive with dynamic braking for the downward deceleration). The VFD will ramp the speed down with the dynamic braking. They usually have resisters (heaters) to dissipate the deceleration energy.
(Automotive)
6 Mar 03 08:11
Sounds like you're way ahead of me.
On the last topic, the issue is not deceleration, it's the change in potential energy from top to bottom. I work out (very roughly) that if your car takes 100 seconds for the descent, you're dissipating 3.5 kW of potential energy. That's quite a resistor you need.
Of course, to haul up at the same speed, you'll need the same, plus losses (say 5 kW) produced by the motor. But I'm sure you've done all that stuff.
Wire the motor into a water heater and your passengers will have about 2 hot cups of coffee each when they reach the lakeside!
John
(Mechanical)
(OP)
6 Mar 03 21:50John,
You're in the right ballpark, but I'm not quite as patient, ...the travel time is only 50 seconds. I plan on using a 7.5 Hp motor. The conservation of energy approach is certainly valid (although, I can't say I thought of working it out that way), but the majority of that energy shouldn't make it back to the motor and VFD, on the descent. I plan to use a worm drive gearbox. As a general rule of thumb, if the gear ratio is >40:1 the winch won’t be able to back drive the worm gear. I plan to use a 3600 rpm motor to bump my gear ratio up to about 80:1. The heat generated should be mostly in the gearbox, between the worm and gear. This is a common application for a worm drive. The motor should be mostly idling on the descent.
rob
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Once you decide to buy a home elevator, you can choose from several options for styles, locations and features. Making the right selections for your lifestyle and home will give you the best return on your investment while giving your living space a safe, secure means of transportation between floors.
The steps to choosing a home elevator include examining your home, lifestyle and needs. You must make several decisions about features and operations. Fortunately, you are not alone in this process. When you go to a dealer for a home elevator, you can learn about how various technical components work and make a better choice on which of these suits your home and available space.
Where you install the elevator in your home will be a critical choice. You need it to be convenient for use while allowing for space to hide the drive equipment. If possible, try to install the device near the stairs in your home to allow for two people going to another floor to meet near each other, even if one takes the elevator and the other takes the stairs.
Areas near the stairs often are ideal for installing home elevators, anyway, thanks to the reinforced structure around the stairs and additional free space available. You may need an adjacent room next to the elevator to house the lifting equipment, depending on the model you select.
Where you enter and exit the elevator are also important factors when thinking about the site. Because you can choose where you locate the gates, you can pick a place where you enter and exit the elevator from opposite sides or even at 90-degree angles.
Good locations for elevators in the home include from the garage to the living area, from the living area to an upper hall near a bedroom or inside lower level halls to upper levels. The layout of your home and where you most often travel through it will help you find a location that provides the most convenient means of moving between floors.
Once you know where you will install the elevator, your work continues with customizing the cab and operating system. Not all brands offer you the same choices for tailoring the design to your tastes.
With five different cab styles, Inclinator elevators give you multiple interior options to match your home’s décor and your personal preferences. You won’t get these same options from other companies. Talk to your local Inclinator dealer about your cab style choices.
The 100 cab comes standard on Inclinator elevators. These cabs can be up to 15 square feet or larger depending on local building codes. The plain white walls of this cab give you the chance to paint or adorn them as desired. A commercial-grade laminate floor with a neutral-colored wood grain finish ensures a good grip for wheelchair wheels and a flat surface. A white ceiling helps this cab model to feel brighter by aiding light reflection from the fixtures you choose for the top of the space.
If you would like to upgrade the interior of the cab to a luxurious hardwood interior on the walls and ceiling, choose the 200 cab model. You will still enjoy the simple coloring of the same laminate flooring used in the 100 model, but the walls and ceilings have real wood. We have many kinds of wood available for the wall finish options. You will choose the wood type during the customization step for the cab.
Just like the 200 cab, the 300 model includes hardwood walls and ceiling. The difference between the two is the addition of decorative molding on the 300. Inside the 300 cab, you will find picture frame molding in the bottom half, chair railing around the middle, baseboard on the bottom and crown molding at the top. These trim additions enhance the appearance of the wood walls with texture.
With the 400 cab, you have various panel options to have in the wood walls and ceiling. Unlike the 100 and 200 cars, which use standard commercial laminate flooring, the cabs with model numbers 300, 400 and 500 give you the option to choose an unfinished base that allows you to use the same floor covering in your home at the bottom of the elevator. You can also replace some of the wall panels with acrylic, allowing you to see out of the elevator.
The most luxurious model, the 500 cab, features a modern aesthetic with its aluminum frame and acrylic ceiling. You have options for the frame color, including white, black and silver. Clear panels on all sides allow for the greatest amount of visibility from inside this elevator cab.
While the cab options give you customization for the interior, all offer similar standard safety features — handrails, ceiling lights, gates compliant with 2016 ASME code, interlocks to prevent access to the well while the elevator moves and emergency battery backup to lower the elevator to the lowest level in power outages. You also have the option to include a phone in the cab or automatic door opening.
You can customize several features in the interior of the cab — handrail, flooring, ceiling, walls, light fixtures and control panels. Adapting these to your preferences will improve how well the cab fits into your home’s style.
First, choose whether you want the standard or a custom handrail. The basic design is a flat wooden handle. We include a bar inside the elevator for safety, but you can choose a more appealing design if the flat wood does not appeal to you. Other options include rounded handrails made of metal. You have three choices for finishes — stainless, bronze and brass. Texturing ensures each of these is easy to grip.
Next, choose the flooring. Our standard floor is laminate with a faux wood finish. You can choose the wood the floor resembles. Options include walnut, cherry, oak and maple. For some cab models, you can also get unfinished oak wood or choose to leave the floor unfinished to have your home’s flooring extend into the elevator.
The ceiling options depend on the type of cab you pick. For the 100 cab, the ceiling has a white color that comes standard. Other cabs, 200, 300 and 400, provide you the option of choosing to leave the top white or have it match the finish of the walls. The 500 can have a clear dome of acrylic on the ceiling for improved lighting and view.
The wall finishes also depend on your cab selection. Models 200, 300 and 400 give you a choice of various woods for the walls inside the cab:
If you have a 400 model, you must also find the configuration of the panels you prefer. Choose between raised or recessed panels. Also, for the walls, you have two main options — one panel over a second or a pair over two others of the same width. Both choices have crown molding. For the ceiling, you can select one, two or four panels.
In addition to the style of the cab’s interior, you can also choose the colors of the lights and panel, which are among the electrical component decisions you will need to make.
While you have a pair of LED lights as standard inside the elevator, you may have as many as four lights. The finishes for the lights include white in the center and on the circular frame or white in the middle with a bronze exterior.
You can select electrical panel styles that include color and whether you want a flush or raised panel. The color options are brushed brass, stainless and oil-rubbed bronze. You have these same choices for the hall stations.
If desired, you can incorporate an automatic gate or door opener into the elevator. For those who experience difficulty opening the gate on their own, automated operation will make using the elevator more accessible. The automatic door feature also benefits those who prefer the added convenience of not needing to have a free hand when getting into or off the elevator after opening the gate.
Another electrical option you have is a telephone incorporated into the wall of the elevator. You would use this to call in an emergency while inside. It does require an analog phone line to function.
You get the choice of accordion or scissor gates for the elevator and manual or automatic operation.
The accordion gates have panels that completely cover the interior of the elevator. You can choose clear or bronze acrylic panels if you prefer to see through the door. Other panel options are vinyl or hardwood in a variety of colors and designs. You may also select the finish of the aluminum frame — silver, gold or bronze. This gate style is the only one that has automation as an option.
Scissor gates have a classic appearance and open manually. You may choose silver aluminum or oil-rubbed bronze for the finish of these openings. The design of these gates showcases the distinctive scissor-looking hinges that allow the gate to fold to one side.
If you select an accordion gate, you may also choose to install an automatic gate operator. We also will install automatic door openers for the doors that cover the entrances to the elevator shaft at each level. These move the gate or door open automatically when needed, making the elevator easier to use and more convenient.
The drive system is one of the most technical choices you will need to make for your home elevator. Your local Inclinator dealer can help you decide which is best for your home. You want to make certain you have enough space to operate the drive system. Carefully measure the available space to be sure you have the correct measurements to reference when making your choice.
Also, determine the maximum amount of travel distance you need. While all three drive systems can accommodate six separate landings, the machine-roomless (MRL) cable drum system has a travel distance of 40 feet, while cable drum and hydraulic systems can move 50 feet up.
The machine-roomless cable drum system has the mechanism installed at the top of the shaft. You do not need a separate room for the drive system. If you have more height available, you may prefer this option. It also has the smallest required distance between floors, so you can install this to reach half-floors or loft areas of your split-level home.
If you don’t have as much space for the elevator shaft but do have a separate room for the lift equipment, consider hydraulic or cable drum elevators. Inclinator’s hydraulic home elevator requires less fluid for the system than other brands do. The cable drum system offers the versatility for a smaller 500-pound capacity elevator with 12 square feet of cab space. This smaller space requires 6 inches of pit depth compared to 10 inches for 1,000-pound capacity elevators.
Regardless of the drive system you choose, you will get a microprocessor that reliably tells you if anything is wrong with the system as well as what is wrong. Additionally, these three drive mechanisms offer redundant safety features to keep the operation going even in an emergency. Emergency lighting and a separate battery to lower the elevator to the ground slowly both activate in a power loss. The hoisting mechanism uses a robust monorail system that lifts the supporting base under the lift.
Inclinator elevators offer these safety features to keep anyone who uses the elevator protected in emergencies that cause power outages.
Once you’ve made your choices, contact an authorized Inclinator dealer. You can readily find one near you with our dealer locator. When you find a dealer near you, you will also find people who can help you make the best choices for your home elevator and get it in your home for greater mobility.
If you aren’t sure whether a home elevator is for you, you probably still have some questions. Getting answers to these will help you make an informed decision. Researching information about home elevators puts you in an excellent position to also make quality choices when customizing your device. Here are some common concerns people have about home elevator systems.
The average cost for home elevator installation in the United States is $40,000. This amount depends heavily on where you live, local installation costs, taxes, type of drive system, size of the elevator, extra work for retrofitting and custom options.
While the costs may increase as you choose more custom options, this home elevator will likely be the only one you want for your home. It could also increase your home’s value, giving you a return on what you spend to install the elevator. Make the most of your investment by selecting choices that make it as comfortable and useful as possible.
Not all home elevators adhere to safety standards outlined in the ASME A17.1-2016 code. This code remains voluntary in many parts of the country, but the guidelines ensure the safe construction of home elevators. At Inclinator, we regularly review our safety features and design to ensure we stay in compliance with these standards for the security of anyone who uses our products.
Home elevators have many safety features inside to protect the rider. Inclinator installs emergency features such as lighting and battery-powered lowering. To prevent doors at landings from opening if the elevator is on another floor, we install interlocks on the doors, which block access to the empty well to protect others in the home while someone uses the elevator.
Our elevators have a switch inside that prevents the system from moving if you have the gate open. This action reduces the chances of someone getting caught by a moving cab. Additionally, if the power shuts off, the elevator does not stop between floors. A backup battery lowers it to the ground and emergency lights come on.
For those who stand while riding the elevator, we install a handrail in all our cabs. This railing helps to keep the rider steady throughout the ride.
Always ask about the safety features of an elevator before deciding on a brand for your home because not all manufacturers offer the same safety options for their products.
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The amount of space you need for your home elevator depends on the drive system. For example, cable drum systems require space in the shaft as well as another room for the equipment. The same is true of hydraulic elevators. MRL elevators do not need a separate room, but they require extra space at the top of the shaft.
Our cabs have a standard 15 square foot size, but you can also opt for a smaller 12 square foot cab if you choose a cable drum system. Because elevators will need space for the pit, cab and machinery, talk to a dealer for information about specifics for the model and drive system you want.
The number of floors a home elevator can reach depends significantly on the brand. Inclinator models can access six levels, but not all brands can. If you have a tall home, ask about the total travel distance the elevator can reach.
With a population that continues to grow older, the United States is the perfect place to build a home elevator as an investment. If you plan to sell your home in the future, having a home elevator adds to its value, especially since homebuyers may have aging family members, want to grow old in the home or have a personal need for extra accessibility.
While stair lifts generally do nothing for your home’s value, a home elevator can increase your home’s resale value by 10%, making this decision a valuable investment in your future.
You can continue to live in your home, regardless of your mobility level, by adding accessibility features, such as an elevator. A home elevator is safe and reliable and can raise your home’s value while improving your ability to move throughout the house. Now you know how to choose a home elevator, you need to find out where to get one.
Whether you know exactly what you want or need some help choosing, an Inclinator dealer can help you get the elevator that will fit your home and needs. Find your nearest Inclinator dealer to start the process of getting an elevator in your home.
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