Experimental Verfication of Fall Simulation and Wearable Protect

Airbag

Youngho Lee, Beomguen Jo, Jeoungwoo Lee, Jaemin Kim, Soonmoon Jung, Taekyung Lee

and Junghwa Hong

Department of Control and Instrument Engineering, Korea University, Seoul, Republic of Korea

Keywords: Fall Injury, Protective Device, Fall Simulation, Reducing Injury, Elderly Fall.

Abstract: Falling of the elderly becomes an important issue in the aging society. Falls could cause fractures which is

significant cause of morbidity and mortality. As a result, active protecting devices are being developed to

protect fallers’ body from severe injuries. In this study, as boundary condition and injury parameter are figured

out by experiments and simulation of falls situation, the wearable airbag for protecting from falls is designed

and make prototype of airbag. After that, compare contact force between fall simulation and experiments with

prototype airbag. It will be possible to establish the reliability of the development of the fall prevention system

for the elderly and to be the basis for the future development.

1 INTRODUCTION

Most people experiment fall accident by losing a

balance. Especially, more than 30% of the elderly

over the age of 65 years have experiences at least one

fall per year, which significantly deteriorates quality

of life. Based on movements, the elderly falls during

the level walking (43 %), going in-and-out of a

bathroom (30 %), during sitting down and standing

up from a seat (13 %), and in ascending and

descending stairs (15 %), which are the activities of

daily living (ADL) (W. L. Watson et al., 2011).

Particularly, it was found that a slip was a main cause

of falling injury. For the elderly, it was reported that

more than 66 % of the slip fallers have the hip injuries

in pelvis (Ambrose et al., 2013). However, it is still

unknown why the slip fallers in the old age have the

high injury value at the pelvic region. Many of these

falls may be avoided if fall risk assessment and

prevention tools where available as an integral part of

ADL. However, the fall risk assessment is still not

completed at this moment. Currently, active

protecting devices for fallers are developing to protect

fallers’ body from severe injuries as an alternative or

for a practical purpose. Developed equipment is

divided into passive and active type to protect the

body from falling. Research on active equipment is

divided into research on fall detection algorithms and

research on wearable airbags. In the case of wearable

airbags, there are studies to confirm the performance

of the airbag using a dummy. However, most studies

have designed the airbag only as a shock absorber

between the ground and the human body without

going through ergonomic design. In this study, the

wearable protect airbag is designed and is confirmed

through simulation of fall injury situation, and also,

compare with the fall experiments by using an

accelerometer and a gyro-sensor for an active

protecting device from the falling injuries.

2 MATERIALS AND METHODS

2.1 Design of Wearable Protect Airbag

and Simulation of Falls

2.1.1 Design of the Wearable Protect Airbag

For falls simulations, human models, environments

and algorithms must be applied to simulations.

Pedestrian facet model (mathematical dynamic

model) provided by the MADYMO program (Release

7.6, TASS international, Netherlands). Wearable

protective equipment has high protection

performance when it is made of hard material, but

users prefer the soft material because they don’t want

to wear it (Honkanen et al., 2006). Also, since there

is a difference in the protection performance

according to the wearing method of the wearer or the

Lee, Y., Jo, B., Lee, J., Kim, J., Jung, S., Lee, T. and Hong, J.

Experimental Veriﬁcation of Fall Simulation and Wearable Protect Airbag.

DOI: 10.5220/0006785202150218

In Proceedings of the 4th International Conference on Information and Communication Technologies for Ageing Well and e-Health (ICT4AWE 2018), pages 215-218

ISBN: 978-989-758-299-8

215

fall method, it is possible to fix the body to the

maximum to overcome it (Forsen et al., 2004). The

shape of the wearable airbag is designed to cover

body and to protect pelvic by considering the average

body size of the elderly over 65 years old.

(a)

(b)

Figure 1: (a) Designed wearable protect airbag and (b)

Human model with wearing airbag.

2.1.2 Simulation of Falls Situation and

Reduce the Fall Injury by Airbag

The falling simulation of the human model is

designed on a condition of concrete properties

(Density:



, Elastic modulus:  





, Poisson’s ratio:  ). and the angle of 70°

between the lower limb and the ground is set, where

the elderly person cannot maintain and regain the

balance (Hsiao, 2008) (Figure 2). Thereafter, gravity

is applied to allow the human body to fall back on the

ground.

To determine how much the human body model

was injured by the falls, Impact force and acceleration

is measured in simulation. Acceleration is important

parameter to calculate injury, such as HIC (Head

Injury Criterion), CTI (Combined Thoracic index)

and etc. At the beginning of the simulation, the human

body model is tilted toward the ground by gravity. As

the angle of the joint cannot be maintained due to the

characteristics of the human body model, the joint

collapses due to the gravity, and the human body

model impacts to the ground in the order of the hips,

thorax and head.

(a)

(b)

Figure 2: Initial position of human model in falling

simulation (a) without wearable airbag (b) with wearable

airbag.

2.2 Fall Experiments

2.2.1 Falling Experiments Toward

Backward

21 male subjects participated in the experiment for

falling data. The 3D accelerometer (L3G4200D, ±

2000 Deg/sec, 70 mdps/digit), and compass

(HMC5883L, ± 8 Gauss, 5 milli-gauss) put on the

sacrum, Thoracic and neck of the subjects for the

falling experiments. The data from the sensors were

wirelessly transmitted by using RF (nRF2401+,

2.4GHz). Fig. 3 (a) shows the experimental setups

and an example of the falling experiments, which was

using a slider to induce a backward falling. The

falling postures were determined based on the

resultant pelvic acceleration and angular velocity, and

pelvic tilt and obliquity angles. Based on the resultant

acceleration as depicted in Fig. 3 (b), a falling event

could be classified as the Fall 1; the period from the

start of fall to the lowest peak, and the Fall 2 + Impact

period; the period from the lowest peak to the highest

peak. Using the measured results, the falling posture

of the people was analyzed.

(a)

(b)

Figure 3: (a) Falling experiments and (b) Definitions of fall.

2.2.2 Falling Experiments by using Dummy

Model

60kg-dummy is used in the experiment for falling

data. Prototype of wearable pelvic airbag (Figure 4

(a)) is designed by simulation. Wearable protect

airbag is manufactured in the form of a belt and can

accommodate the airbag. And sensor module (3D

accelerometer, gyro-sensor and compass sensor) is

used to measure and calculate z-axis acceleration,

sum acceleration, angular velocity, tilt angle,

obliquity angle, resultant angle. These values is used

in double threshold algorithm to determine fall event.

If fall event is found, the inside airbag (thermoplastic

poly urethane) is unfolded by the gas. Force plate

(OR6-7 force platform, ADVANCED

MECHANICAL TECHNOLOGY INC, USA) is used

to measure contact force between dummy and

ground. Dummy is set on 100cm-height from ground.

ICT4AWE 2018 - 4th International Conference on Information and Communication Technologies for Ageing Well and e-Health

216

As the angle of the joint cannot be maintained due to

the characteristics of the human body model, the joint

collapses due to the gravity, and the human body

model impacts to the ground in the order of the hips

(Figure 4 (b)).

(a)

(b)

Figure 4: (a) Prototype of wearable pelvic airbag and

(b)Falling experiments by using dummy.

3 RESULTS AND DISCUSSION

After analysing the data collected from movements in

fall situation, the summation of acceleration at the

neck, thoracic, pelvic could detect almost all

movements of the fall. For perfect protection of the

falling person’s body, the detection should be

accomplished within the period from the start of the

fall to the lowest peak. And highest peak value can

calculate maximum impact force which indicates

numerically that the injury occurred to the human

body. First, compare the acceleration of each position

(neck, thoracic, pelvic) (Figure 1(a)). All of position

show similar tendency and lowest peak, but they have

different level of highest peak value. The reason for

this result is that the sequence of the impact of the

human body model with the ground changes in order

of hip, head and thoracic.

(a)

(b)

Figure 5: (a) Sum of acceleration on neck, thoracic and

pelvic and (b) Comparison between simulation and

experiments of acceleration.

Figure 5(b) show comparison between simulation

and experiments. As a result, the simulation is set

similarly with experiments. Based on the results of

the simulation, the wearable pelvic airbag was

developed.

The graph of Figure 6(a) shows the impact force

applied to the hips of the human model at the time of

the falls in case 1 (before wearing airbag) and case 2

(after wearing airbag) in simulation.

In case 1, maximum impact force is 4694N, and

in case 2, maximum impact force is 2240N,

respectively. Case 1 (4694N) exceed the reference hip

fracture point of the elderly people (3100N) and case

2 (2240N) not exceed (Kennedy, 1987).

(a)

(b)

Figure 6: Impact force of before and after wearing pelvic

airbag (a) simulation and (b) dummy experiments.

The graph of Figure 6(b) shows the impact force

applied to the hips of the dummy at the time of the

falls in case 1 (before wearing airbag) and case 2

(after wearing airbag) in simulation.

In case 1, maximum impact force is 5733N, and

in case 2, maximum impact force is 2911N,

respectively.

4 CONCLUSIONS

In this study, the simulation of the fall and wearable

airbag is verified by fall experiments. All condition of

simulation is set similarly with real fall situation. It

can be simulation method that can be used as a basis

of safety research for the elderly.

Based on simulation and experiment results, the

effectiveness of the airbag is proved by showing the

injury value in the simulation and prototype. This

airbag is expected to prevent fractures and reduce cost

of treatment. In addition, through this study, it is

possible to develop wearable airbags in other parts to

prevent injuries caused by falls.

ACKNOWLEDGEMENTS

This work was supported by the Korea Health

Technology R&D Project (HI15C1025) funded by

the Korean Ministry of Health & Welfare.

Experimental Veriﬁcation of Fall Simulation and Wearable Protect Airbag

217

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