2019 IEEE 1st Global Conference on Life Sciences and Technologies (LifeTech 2019)

Development of a non-actuated wearable device toprevent knee buckling
Shusuke NAITO

Yasuhiro AKIYAMA

Koichiro OHASHI

dept. Mechanical Systems Engineering
Nagoya University
Nagoya, Japan

dept. Mechanical Systems Engineering
Nagoya University
Nagoya, Japan

dept. Mechanical Systems Engineering
Nagoya University
Nagoya, Japan

Yoji YAMADA

Shogo OKAMOTO

dept. Mechanical Systems Engineering
Nagoya University
Nagoya, Japan

dept. Mechanical Systems Engineering
Nagoya University
Nagoya, Japan

Abstract—Wearable devices are required not only for assisting
the gait motion of the elderly but also for improving the gaitstability. Thus, a non-actuated wearable device was developedin this study. The device intended to prevent knee buckling by
supporting knee using string placed along with body surface. In
order to arrange the force pattern, a string length adjustment
mechanism was developed. The experimental result suggested
that this wearable device could successfully generate knee extension torque which mitigated knee buckling.
Index Terms—wearable device, knee buckling, gait assist

I. I NTRODUCTION
Decrease of walking ability of the elderly owing to aging
increases the risk of fall. Recently, many wearable devices
intended to improve the walking ability of the elderly [1]because fall sometimes compelled the elderly to be a nursing
care [2]. Thus, we previously developed a wearable device
which could generate and arrange the pattern of assistive
torque without actuator using strings placed along with bodysurface [3]. Now, assist devices can be classified into following
two types, the actuator type and the supporter type. Whereas
the actuator type can generate the large torque and adjustthe assist pattern, it tends to become heavy and it’s attach
process becomes complex. On the other hand, the supporter
type is very light and easy to attach. However, the assist of
it is constant or passive in addition to small assist force. Our
device aims to resolve drawbacks of them. The features ofthem are shown in the TABLE 1. In this study, knee buckling,which was a factor of fall of the elderly, was focused. The
knee buckling, which is sometimes caused by insufficientknee extension torque, causes gait instability especially whenloading weight on knee during support phase. To prevent kneebuckling, a device, which exerted the knee extension torqueonly during stance phase, was developed.

978-1-7281-0543-7/18/$31.00 ©2019 IEEE

II. D EVELOPMENT OF THE WEARABLE DEVICE
Overview of the developed device is shown in Fig. 1.
This device consists of strings and string guides fixed on thebody surface. Tension force of string applies torque to knee
joint through string guides. When a wearer steps on the footswitch during stance phase, the length of string is fixed. Thestring generates knee extension torque, which prevents kneebuckling, when the knee begins to flex through the increaseof string tension. On the other hand, during swing phase, thefoot switch doesn’t fix the string length. Thus, the string length
becomes longer owing to the extension of spring and doesn’t
prevent knee flexion.
By arranging the position of string guide, path of strings
can be tuned. Because the pattern of assistive torque wasdetermined by the layout of string path, a simulator, which
estimated the pattern of assistive torque and optimize theposition of string guide, was developed. The optimization wasbased on sequential quadratic programing and evaluation index
was designed to maximize the knee extension torque during
support phase.
III. E XPERIMENTAL CONDITION
Experiments were performed with the permission of the institutional review board of the Nagoya University. Two healthy
young males participated in the experiment. The following
experiments were conducted in order to verify the effect ofthe developed device.

247

TABLE IT YPE OF WALKING ASSIST DEVICETypeAssist power
Assist pattern
WeightRemoval performance

Actuator◎
Variable××

Supporter×
Constant◎◎

Our device○Variable○○Fig. 1. Overview of the device

Fig. 2. Knee extension torque

A. Knee buckling prevention effect verification experiment
An experiment was conducted in order to estimate the knee
extension torque to the knee buckling in the angles of the knee
joint (5, 15, and 25◦ ). At first, 5 N tension was applied to thestring in an upright position. Then, the subject bended by thedesignated angle and the sting tension was measured by thestrain gage five times at each angle.
B. Walking experiment
The developed device controls the string length using thefoot switch and spring. Thus, an experiment was designed
to verify the influence of spring coefficient on knee joint byusing different springs (0.36, 0.49, 0.57 N/mm). To prevent
strings to slack, small tension was applied to the string inthe upright position. The subject walked on the treadmill forthree minutes with self-selected speed. Angle of each joint
was measured by a motion capture system (MAC 3D Systems,Motion Analysis).
IV. E XPERIMENT RESULT
A. Knee buckling prevention effect verification experiment
The knee extension torque is shown in Fig. 2. It was clearthat the knee extension torque increased as the knee flexed.
The knee extension torque of 25◦ became approximately
quarter as volume as the maximum knee extension torqueof normal adults during support phase [4]. These results
suggested that the device exerted knee extension torque which
probably prevented knee buckling.

Fig. 3. Angle of the knee joint

V. C ONCLUSION
A non-actuated gait assist device, which intended to preventknee buckling, was developed and tested in this study. The
result of knee buckling prevention experiment suggested thatthe device successfully exerted knee extension torque, which
probably prevented knee buckling, during stance phase. Furthermore, the walking experiment suggested that the string did
not slack during walking, which was necessary to apply knee
extension torque during stance phase, using the foot switch andB. Walking experiment
The pattern of knee angle is shown in Fig. 3 and the string
tension is shown in Fig. 4. According to Fig. 3, compared tono spring, weak springs increased knee angle during swing
phase. However, it should be noted that knee angle undersuch conditions became smaller than that of normal walking,which was the gait motion without using the assist device.
This was because the spring applied extension torque to knee
joint during swing phase. In addition, Fig. 4 suggested thatthe string did not slack during the walking because the tensionof each spring does not go below the pre-tension. Thus, theresult suggested that the spring with a small spring constant
was sufficient to keep string length.

248

Fig. 4. String tension

spring although the device slightly affected the angle patternduring swing phase.
R EFERENCES[1] S. K. Banala, S. H. Kim, S. K. Agrawal, and J. P. Scholz, “Robot assisted
gait training with active leg exoskeleton(alex),” IEEE Transactions onneural systems and rehabilitation engineering, vol. 17, pp. 2-8, 2009.
[2] M. C. Nevitt, I. Tolstykh, N. Shakoor, Uyen-Sa D. T. Nguyen, N. A.
Segal, C. Lewis, D. T. Felson, and the Multicenter Osteoarthritis StudyInvestigators, “Symptoms of knee instability are risk factors for recurrent
falls,” Arthritis Care & Research, vol. 68, pp. 1089-1097, 2016.
[3] K. Ohashi, Y. Akiyama, S. Okamoto, Y. Yamada, “Development of astring driven walking assist device actuated by upper body,” Proceedingsof International Conference on Systems, Man, and Cybernetics, pp.
1411-1416, 2017.
[4] D. C. Kerrigan, M. K. Todd, L. Della, “Gender differences in joint
biomechanics during walking: normative study in young adults.” American Journal of Physical Medicine & Rehabilitation, vol. 77, pp. 2-7,
1998

249