Design of Stairway Chair
by: Guest
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Word Count: 2276
Table of contents
Acknowledgement ............................................................................................ iv
List of Figures .................................................................................................... v
List of Tables ...................................................................................................... vi
Nomenclature ................................................................................................... vii
Chapter 1. Introduction
1.1
General objectives ...................................................................... 1
1.2
Literature review ........................................................................ 3
1.3
Scope and layout ........................................................................ 4
Chapter 2. Formulation
2.1
Introduction ............................................................................... 5
2.2
Applications of this chair..............................................................
6
2.3
Measurement ............................................................................ 8
2.4
Formulations & Calculations ........................................................ 9
2.5
Final results.................................................................................
19
2.6
Tables and Figures.......................................................................
20
Chapter 3. Conclusion
3.1
Concluding
remarks.....................................................................
29
References ........................................................................................................ 31
Appendix ........................................................................................................... 32
List of Figures
Fig. 1 Comparison between bending fatigue resistance
for wire rope constructions. [1].................... 20
Fig. 2 Various common wire rope configurations. [2] ........................................................................... 21
Fig. 3 Typical wire
rope system configuration. [2] ............................................................................... 21
Fig. 4 Fatigue lives for several wire rope construction. [2] .................................................................. 22
Fig. 5
The Rail Fastener .......................................................................................................................... 27
Fig. 6
The Wheel Holder of the Chair......................................................................................................
28
Fig. 7
The Chair Wheel.............................................................................................................................
28
Figs. 8,9
ACORN Stairlifts. [4] .................................................................................................. 32,33
Fig. 10
Acorn Stairlift with Dimensions. [4] ......................................................................................... 33
List of Tables
Table 1. Symptoms and Causes of Wire Rope Failures. [1] ................................................................ 22
Table 2. Experience-Based Wear-Related Allowable
Maximum Bearing Pressure. [1]......................
23
Table 3.
Material and
Construction Data. [2] ...................................................................................... 24
Table 4. Wire-Rope Data. [3] ............................................................................................................... 24
Nomenclature
|
Sign |
Representation |
|
p |
Unit
Radial Pressure |
|
|
Approximate
Metallic Cross Section of a Fiber Core |
|
|
Modulus of
Elasticity |
|
|
Wire
Diameter |
|
|
Diameter
of Sheave or Drum |
|
|
Nominal
Rope Diameter |
|
|
Bending
Stress |
|
|
Static
Direct Tensile Stress |
|
|
Static
Ultimate Strength |
|
|
Design
Stress for Static Loading |
|
|
Design
Life |
|
|
Fatigue
Strength Parameter |
Chapter 1. Introduction
1.1 General Objectives
|
N |
owadays, almost every building and house has
at least one stairway. Getting up and down the stairs has grown into a habit
for today’s people. Some of them have no problem with this habit, but there are
many people in the world, which cannot climb the stairs easily. Old or disabled
people for example, are afraid of facing stairways. What can we do for them?
They must not climb the stairs! On the other hand, if they want to, how can
those people, who are walking hardly or sitting on wheelchairs, climb the
stairs? In spite of the fact that today, everywhere even vehicles such as
busses have stairs. One remedy to this problem is to make an incline as well as
stairways in the city. However, inclines are useful for small heights, or need
a small slope in order to climb it easily. The other way, which we have studied
and chosen, is to make a chair that can get up and down the stairs without any
force used and only by the user call. At least they can use it in their houses,
where they spend much of their life.
There are many stair-climbing
wheelchairs all over the world. They have different features and equipment
combined with special styles, functionalities and drive systems. Each of them
is designed for a specific condition and has its own strengths and weaknesses.
These chairs can be driven by
several systems, an electric motor connected with rack and pinion, belt, cable
or chain or by the force of hydraulic or pneumatic. However, they are used for
one important purpose: To take people up and down the stairs.
In Iran, considering the large
amount of self-sacrifices (people who has missed parts of their bodies in war),
and old people too, it seems necessary to pay attention to their problems such
as one which has mentioned before.
The chair that we want to design
has some special features: low price, long life, high safety and convenience.
If we can design it, we have solved a big problem for those people.
1.2 Literature Review
With special thanks to
“ACORN” Stairlift Manufacturer, on their professional website on: http://www.acorn.com,
and all who has studied and performed designs about this stairlift.
Now, we are
willing to study, analyze and design significant parts of this stairlift to
find out whether it is stable, economic, and safe to be used by people in their
houses.
1.3 Scope and Layout
|
T |
his stairway wheelchair is designed for
indoor uses and has specific applications. It utilizes a 1/3 HP 120 V AC motor
as the main force-generator unit. The output shaft of the motor is connected
with a drum and its end leans on a deep-groove ball bearing. The power
transmition of this set is via a wire rope (cable). The motor, drum and wire
rope around it are situated in a box, and the box is situated upstairs hidden
in the ground in order to be protected. One end of the wire rope is attached
firmly to the hoist frame and the other end is fixed on the drum so that not to
slide on it. The motor-driven drum causes the chair getting up and down the
stairs by pulling or loosing the wire rope. An aluminum rail including two
grooves, which are in contact with four small plastic wheels and guide the
chair in a straight track, provides the path of the chair. At the bottom of the
chair, there is a case contains a drum like what has mentioned earlier, brake
plates and linkage. One side of the wire rope is on the motor-driven drum and
the other side passes around the chair drum, which is idler and rests on
deep-groove ball bearings on each side. There is a brake lever installed on the
chair armrest that can be pulled in order to stop the chair. In addition,
control buttons are located in a pad for controlling the chair motion. The
height of the chair is adjustable and the armrests, footrest and seat can be
folded. The chair is equipped with a seat belt for more safety and can be
turned to any direction easily.
This special design will satisfy
our goals for safety, convenience and is economical and for straight stairways,
it is an ideal design.
Chapter 2. Formulation
2.1 Introduction
Now, we will describe important
and vital parts of the chair and its power system in order to find out how much
they are under pressure. Then by choosing appropriate materials and shapes, we
will complete the design procedure. Looking at the whole system, it is obvious
that significant elements are wire rope, drums, chair wheels and the rail. The
design procedure is as follows:
First by conceiving an
approximate value for the weight of the user, having the power of the motor,
and considering an average distance for the stairs, we’ll gain access to the
final design factors for selecting appropriate dimensions, materials and shapes
for best operation. The chair shape and dimensions are selected by studying the
human ergonomics and comfort. All materials and dimensions are chosen so that
the best performance obtains with the lowest possible price. Let us take a
closer look at the chair and start with calculations.
2.2 Applications of this Chair
This
stairway wheelchair is designed for indoor uses and stairways up to 10 meters
long. Note that it could be used for longer stairways by a little change in the
transmition system. Because for long distances, the wire rope will start
vibrating and this vibration causes premature fatigue and wear as well as
unwished noise.
On the face of it, curved rail stairlifts
provide an appropriate solution for staircases that are anything but a straight
run. However, you should consider all options when choosing a stair lift
solution for your home. Curved Stair Lifts are very complex pieces of
equipment. They are usually very expensive when compared to straight stair
lifts. A Curved Stair Lift is custom-built for particular staircase. As a
result, it is difficult, if not impossible to relocate it. Therefore, there is
little if any residual value when you no longer need it. Curved stairlifts
should only be used when there is no other viable option. Straight stairlifts,
by comparison have much less mechanical complexity. The preparation for and the
installation of straight stairlifts is less complex. Curved rail lifts require
a highly detailed on-site survey prior to order. Often, straight stairlifts are
self-installed. Seldom is this the case with curved stairlifts.
If your staircase has a sub-landing (a flat platform)
where it turns, you should consider the option of installing two straight stair
lifts, as an alternative to one curved unit. This assumes that the user is
capable of transferring from one stair lift to the other on the flat landing,
of course. We accept that this is not always possible, but are always on hand
to offer advice and guidance.
A double installation of two straight
stairlifts will provide the following benefits to you:
- An average cost saving
- A neater, more reliable
stair lift system
- A stairlift system that is
easy to remove or relocate.
- Two stair lifts that each
have a significant resale value
- Self-installation is easy
and cost effective
However, in most houses, there are simple
straight stairways, and so we have chosen this type.
2.3 Measurement
It really is very easy to measure
for stairlift. All we need is a good quality metal tape measure. If you want to
measure for your stairlift, please pay attention to the following tips:
Take a general overview of the stairway
layout and decide which side of the staircase, the stairlift will be mounted
on, when viewed from the bottom. The lift may be mounted on the banister side
if desired. No wall is necessary, as the stairlift mounts to the stair treads,
not a wall. Be aware that the stairlift rail will overhang the top landing by
approximately 6" and meet the floor at the foot of the stairs
approximately 14" beyond the nose of the first step.
Now that you have decided which side of the stairway,
the stairlift will be mounted, you should measure the staircase.
The most important measurement is what
determines the length that the rail is cut for the lift. To obtain this
measurement, stand at the top of the stairs, and extend the tap measure until
it is laying on all the stair treads and the tip of the tape measure is
touching the landing at the bottom of the steps. How many inches is it from the
bottom landing to the top of the upper landing?
Then, measure from the edge of the top step
to the edge of the first step. Next, measure the width of the staircase. If
there is a wall or a door at the bottom of the stairway, measure from the
bottom step to the wall.
2.4 Formulations & Calculation
About the Author
This article is by: SADEGH FARIVAR, Mechanical Engineer.
E-Mail: sf_farivar@yahoo.com
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