Design of Wearable Airbag with Injury Reducing System

Beomgeun Jo, Youngho Lee, Jaemin Kim, Soonmoon Jung, Dongwook Yang, Jeongwoo Lee

and Junghwa Hong

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

Keywords: Wearable Airbag, Protective Device, Fall Prevention, Fall Simulation, Elderly Fall.

Abstract: Injuries caused by falls has become significant social problem in 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 body from severe injuries. In this study, simulation test method of falls situation is

established and the wearable airbag system for protecting from falls is designed through simulation.

Ergonomic design is considered in this wearable airbag system to reduce injury level effectively. 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

Falls are an accident that occurs when a person’s

balance is lost and the balance cannot be maintained

again. This falls occur in all age groups, but especially

in elder people. The fall of an elderly person causes a

fear of falling and reduces the amount of activity, and

acts as a major threat to the independent living and

quality of life of the elderly (Vellas et al., 1997). In

the injury statistics due to fall, about 68% of injuries

caused by falls were fractures, and about 47.1% of

injuries occurred in pelvic and thighs (Watson and

Mitchell, 2011). 90% of hip fractures in elderly

peoples are caused by falls, and 20% of elderly

patients hospitalized for hip fracture due to falls die

during treatment (Courtney et al., 1995). These

problems cause serious problems in the world, which

is turning into an aging society. To prevent injury by

falls in the elderly, it is necessary to have a device that

can relieve the fall impact. Developed equipment is

divided into passive and active type to protect the

body from falling of elderly person. In the case of

passive type, there is a fixed type of protective

material such as pad or form, and it shows about 2.5%

~ 50% protection performance in case of impact

energy equivalent to fall (Laing et al., 2011; Nabhani

and Bamford, 2002; Holzer et al., 2009). However,

this makes it less comfortable for the user and makes

the elderly person avoid wearing it (Honkanen et al.,

2006). Research on active equipment is divided into

research on fall detection algorithms and research on

wearable air bags. In the case of wearable airbags,

there are studies to confirm the performance of the

airbag using a dummy (Fukaya and Uchida, 2008).

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 addition, verification is not done through

simulation, so the expected performance before

device development can not be grasped.

Therefore, in this sutdy, the ergonomic wearable

airbag is designed and the effectiveness of the

wearable airbag is confirmed thorugh simulation of

reducing the fall injury.

2 MATERIALS AND METHODS

2.1 Design of the Ergonomic Wearable

Airbag System

For falls simulations, human models, environments

(boundary conditions) and algorithms must be

applied to simulations. First, in case of human

models, 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 do not want

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

188

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

Design of Wearable Airbag with Injury Reducing System.

DOI: 10.5220/0006365401880191

In Proceedings of the 3rd International Conference on Information and Communication Technologies for Ageing Well and e-Health (ICT4AWE 2017), pages 188-191

ISBN: 978-989-758-251-6

is a difference in the protection performance

according to the wearing method of the wearer or the

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 all

parts except the face part by considering the average

body size of the elderly over 65 years old, and parts

of the hips are designed as a skirt type to wrap around

the side and back direction.

Figure 1: Human model wearing airbag(front(a) back(b)

side(c)).

The human model in Figure 1 wear the

ergonomically designed airbag. The wearable airbag

system use acceleration sensor, gyro sensor and

compass sensor to input each sensor data to the CPU.

Then, CPU uses the input sensor data to convert them

to values such as angles, angular velocity and

acceleration. The converted values are substituted

into the threshold value determination algorithm to

determine whether the wearer’s state is falling or not.

When it is judged that the falls has not occurred, the

continuous voltage is transmitted to the sensor unit so

that the current state of the wearer can get feedback.

In case of a fall, the CPU sends a signal to the inflator

so that the airbag can be deployed.

The airbag is deployed in the order of the hips,

thorax and head, which are the order of contact

between the human body and the ground at the time

of falling. When the airbag touches the ground, the

vent hole is actuated at the moment and discharge the

gas inside the airbag into the outside.

Figure 2 shows the wearable airbag system as a

block diagram. The sensor block consists of gyro,

acceleration and geomagnetic sensor to measure the

current state of the wearer. The measured data is

transmitted to the CPU to calculate the angle, angular

velocity, and angular acceleration. The thresholding

algorithm input to the CPU has a threshold value for

each computed element. Further, when the condition

is satisfied, it is judged that a fall occurs. If the CPU

judges that a fall has occurred, the CPU sends a signal

to the driver block. When the CPU judges that the fall

has not occurred, the CPU sends a signal to the sensor

block. If a signal is received from the driver block, the

inflator is activated because a fall has occurred. The

airbag is deployed by the action of the inflator and

protects the wearer from collision with the ground.

After collision with the ground, the Venthole works

to release the air inside the airbag, reducing the

impact of collision between the wearer and the

ground. If the sensor block receives a signal, it will

not fall and will continue to measure the current state

of the wearer.

Figure 2: Block diagram of wearable airbag system.

2.2 Simulation of falls situation and

reducing the fall injury

Figure 3: Initial state of human model falling simulation.

The falling simulation of the human model is made

on a ground condition of concrete properties

(Density: 2300  



⁄

, Elastic modulus:

17E+9



⁄

, Poisson’s ratio : 0.15) 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 3). 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, HIC (Head Injury Criterion),

CTI (Combined Thoracic index), Impact force

Design of Wearable Airbag with Injury Reducing System

189

(between the hips and the ground) is measured in

simulation. 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.

This simulation compared case 1 (before wearing

airbag) and case 2 (after wearing airbag), and

determine the effectiveness of the designed wearable

airbag.

3 RESULTS AND DISCUSSION

Figure 4: The collision between the human body model and

the ground with airbags on the simulation.(Case 2-A(a),

Case 2-B(b), Case 2-C(c)).

Simulation results for four cases were measured.

Figure 4 shows the moments when the human model

with the airbag collided with the ground in case 2

simulations. (a) only wears a pelvic airbag and the

head and head collide after a pelvic impact. Case 1, in

which no airbag is worn, collides with the ground in

the same order as in (a). The collision simulation of

case 2-B, like (a), causes the head to collide with the

ground after collision between pelvic and ground.

Simulation (c) is the last time the head collides with

the ground on the volume of the chest airbag after a

primary collision between the pelvic and the ground.

Figure 5: Impact force of before and after wearing pelvic

airbag.

The graph of Figure 5 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 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).

Table 1: Head and spine injuries of before and after wearing

airbag.

HIC CTI

No Airbag(case 1) 1657 0.2163

Pelvic(case2-A) 4412.2 0.2015

Pelvic+Head(case2-B) 498.06 0.1517

Pelvic+Spine+Head(case2-C) 165.37 0.191

The injuries of the head and thoracic are shown in

Table 1. In case 1, the HIC value is 1657, which is

above the reference value of the concussion (1000).

This can cause more injuries depending on the

situation. And the CTI value not exceed the standard

value of fatal thoracic injury (1.0) but numerically

indicates that the injury occurred to the human body.

Case 2 is subdivided to wearing only pelvic airbag

(Case 2-A), wearing pelvic and head airbag (Case 2-

B), and wearing pelvic, thoracic and head airbag

(Case 2-C). And HIC and CTI were measured for

each case. HIC had a value of 4412.2 in case 2-A,

which was 2755 higher than that of case 1. This is

classified as a very serious injury. 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, in the process of protecting the

human body model. As a result, the head is more

impacted than the situation without airbags, and the

injury level has increased. However, when the head

airbag was worn (Case 2-B), the injury rate was

reduced to 498.06, which was about 89% reduction in

injury rate when wearing only the hip airbag (Case 2-

A). In case 2-C (wearing the entire airbag), it was

found that 90% of the injury rate were reduced than

case 1. If do not wear a thoracic airbag, head will

collide with the ground earlier than thoracic.

However, in case of wearing a thoracic airbag, the

volume of the airbag causes the chest to collide with

the ground earlier than head, and thoracic injury level

increase but head injury level decrease. To conclude,

when entire airbags were worn, the human body

model was found to be able to prevent fatal injuries

by reducing injury levels than without airbags.

Based on the results of the simulation, the

wearable pelvic airbag system was developed (Figure

5).

ICT4AWE 2017 - 3rd International Conference on Information and Communication Technologies for Ageing Well and e-Health

190

The main purpose of previous studies was to

determine falls. However, it did not address the injury

reduction by airbags. this study showed numerical

reduction of injuries caused by fall, which showed

that it is applicable to real human fall situation.

Figure 6: Pelvic airbag(before inflate(a) after inflate(b)).

This hip airbag system is manufactured in the

form of a belt as shown Figure 5-a, 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.

4 CONCLUSIONS

In this study, the ergonomic wearable airbag system

is designed and the effectiveness of the airbag is

proved by showing the injury value in the simulation.

And also, a simulation method that can be used as a

basis of safety research for the elderly. Based on

simulation results, the actual wearable airbag system

was developed. This airbag system 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.

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