APPLICATION OF ALBER ' S PRINCIPLE TO DEVELOP A DEVICE SUPPORTING WHEELCHAIR IN STAIR CLIMBING

This paper presents developing Alber principle for machine supporting wheelchair in climbing stairs. The designed machine can support wheelchair and disabled people with total weight 80 kg climb up and down most of stairs and with speed 10-15 stairs per minute. Moving wheelchair and disabled people need assistant person who will hold handle and control the machine. The machine is designed with a simple structure, manufactured with low cost and simple controlling. Therefore the machine can be upgraded and manufactured in future.


INTRODUCTION
Our country experienced many wars, so quantity of disabled people have high rate in population.These disabled people do not have a lot of money to heal disease.Therefore, according to survey in 2005, number of disabled people of our country is up to 5.3 millions, this number account for 6.34% population in which the disabled people by movement account for more than 29.41%.[2] Helping these disabled people joined community activities now become necessary and significant.To do that, climbing stair of disabled people at home and public place should be especially considered.
Because of that desire, this machine was researched, designed, manufactured so that it can help disable people and their wheelchair climb most of stairs at home and public place in Viet Nam.

Introduction to Alber principle
According to figure 1, double chain sprocket 1.1 drive to two chain sprockets 1.2 and 1.3 by chain with the same transmission ratio, so two big wheels will revolve around center I 1 and I 2 with same angular velocity.
Two small chain sprockets 1.4 and 1.6 are fixed to I 1 I 2 I 3 frame, two small chain prockets 1.5 and 1.7 are connected with two safe wheel.
Because two chain sprockets 1.5 and 1.7 are driven two chain sprocket 1.4 and 1.6 by chains C and D, when big wheels revolve around center I 1 and I 2 the safe wheel fit will also move but those direction are constant with I 1 I 2 I 3 frame.Two big wheels are designed in order that they are not only able to revolve around center I 1 and I 2 but also they can revolve around their center.Therefore revolving around center I 1 and I 2 help machine can climb stair, and revolving around their center help machine ride on flat terrain.
The distance between two centers of two big wheels will change when machine climb stairs.The distances are designed as below.
The distances between revolving centers I 1 , I 2 and centers of big wheels are equal: The distance between two rovolving centers is 2a: I 1 I 2 = 2a.
Thank to above design, in one revolving circle around revolving ceters, the ceters of big wheels will be on a horizontal line in one time as figure 3.This means machine wheel can ride on flat terrain when the ceters of big wheels are on a horizontal line.Therefore four big wheels will stop at vertical plane of stair.

Experiment
Machine was tested with 500 steps with height of step is 16 cm and with average weight of disabled person is 65kg.

Result
Machine opertated stably.Machine opertated stably and safely for user.
Cost of manufacturing is low, controling way is simple.
However some of parts need to be changed by plastic materials.This mean machine will be lighter and power is used for machine is also lower.
From above result, we see that machine is potential to upgrade and manufacture.This is realy significant and helpful.

Figure 7 .
Figure 7. Machine is climbing down a stair 7.1: Four safe wheels; 7.2: Four connecting rods 1; 7.3: Four connecting rods 2 The revolving centers of two external big wheel are lower than revolving centers of two internal big wheels.So when machine climb down a stair the two internal big wheels will lift two external big wheels up to horizontal plane of next stair first.After being lifted the two external big wheels will lift two internal big wheels up to horizontal plane of next stair.At this time the machine has already climbing down a stair and centers of big wheels are on a horizontal line.And process of climbing down a different stair repeats.
Four safe wheels can safely stop machine at vertical planes of stair when machine climbing down stairs.Stair climbing speed of machine is proper with assistant person.Machine climbing smoothly,so disable person feel comfortable.Controling machine is rather simple but it also need person have to spend a short time to from being familiar.