計測自動制御学会東北支部 第 309 回研究集会 (2017.6.23)
資料番号 309-5

慣性センサを用いた高速歩行時の歩行パラメータの測定
Estimation of gait parameter during high speed walking using
Inertial sensors○アミル

ムクリズ，久我拓史，佐川貢一，長井力○ Amir Mukhriz, Hirofumi Kuga, Koichi Sagawa, Chikara Nagai
弘前大学

Hirosaki University
キーワード : 認知症の予兆 (Prediction of dementia)，最速歩行 (Fastest gait)，慣性センサ (Inertialsensor)，歩行解析 (Gait analysis)，歩行パラメータ (Gait parameter)

連絡先 : 〒 036-8561 青森県弘前市文京町 3 弘前大学 理工学研究科 佐川研究室
Amir Mukhriz，Tel.: (080)3336-1370 E-mail: h17ds201@hirosaki-u.ac.jp

1.

Introduction2014 onwards and conducted 10 meter fastest

In recent years, relationship between motor
function and risk of dementia were noticed[1–5] .
Surveillance of walking condition is conducted
as an indication of finding dementia symptoms
and mild cognitive impairment[6] . The walking
performance is evaluated using gait parameterssuch as walking speed and stride length.
Hirosaki University has conducted a healthexamination called Iwaki Project for approximately 1000 citizens of Hirosaki city since 2005.
The aim of this project is to increase the healthlevel of residents in Iwaki district and extendthe average lifespan. 10 meter fastest walking
examination was originally conducted to investigate the sign of dementia. Researches on gait
analysis utilizing inertial sensor have been conducted in recent years[7–11] . Faculty of Scienceand Technology took part in the project fromwalking examination to predict the sign of dementia and other diseases.
Optical three-dimensional motion measurement device is generally used for measurementof gait parameters, but it is unsuitable for large
scale survey targeting multiple subjects. There
are also problems such as limited measurement
environment and preparation takes time. Meanwhile, Wearable Wireless Inertial Measurement
Unit (WIMU) has been widely used for thequantitative evaluation of walking because it
has been downsized and the measurement accuracy has been improved significantly. WIMU
consists of a triaxial acceleration sensor anda triaxial gyroscope, and by using data obtained from these two sensors, the time changeof the position and orientation of the WIMU isreconstructed into a three-dimensional space.

–1–

The authors have attempted to measure thegait parameters using the WIMU attached tothe toe and succeeded in the measurement ofgeneral walking speed of about 2.8 [m/s][12] .
However, when the walking speed goes as fast
about 4 [m/s], desirable analysis results could
not be obtained. This is because it is relatively easy to distinguish the gait cycle into
swing phase and stance phase in general walking, but it is diﬃcult to distinguish the gait

Fig. 1scale)

WIMU without case (100yen coin for

cycle in high speed walking and it may exceed
the measurement range of the sensor in somecases.
Conventional method uses inertial sensors
with high sensitivity only and with sampling
rate of 100 [Hz][13] . We found out that somesubjects walk fast enough to exceed the mea-Fig. 2

Outline of the WIMU systemsuring ranges of the older sensors and it is impossible to analyze their data properly. In thissensors could not measure these values because

study, to solve this problem, inertial sensor sys-

they are over the measurement ranges.

tem composed of low-sensitivity sensor in ad-

overcome this problem, we introduced sensor

dition to high-sensitivity sensor is introduced.

which has wide measuring range in addition

Sensor that operates at sampling rate 1 [kHz]to sensor which has small measuring range.

is also introduced. Furthermore, we propose

WIMU consists of two sensor boards; one mounts

integration interval determination method ofhigh-sensitivity acceleration sensor, high-sensitivity

the gait cycle that can be applied to fast walk-gyroscope, microprocessor unit, wireless com-ing. Using the proposed method, we perform

munication module, and microSD card slot andhigh speed walking experiment and examine

the other board mounts low-sensitivity accel-the measurement accuracy. Moreover, gait pa-

eration sensor and low-sensitivity gyroscope.

rameters such as stride length, toe’s height,

Both boards are connected vertically to a switch

and toe’s angle are estimated from the mea-

board which consists of two controller switches,

sured walking motion and then compared with

LEDs for information display, USB slot withcalculated results obtained from motion cap-charging function, and voltage regulator con-ture system.

nected to lithium ion battery (Fig. 1). Table 1To

shows the list of components used to build the2.

WIMU. It consists of two kinds of sensors with

Measurement systemdiﬀerent measurement ranges, sensor with small

During fast motion, large acceleration andmeasurement range is called ‘high-sensitivity

angular velocity occur. In this case, high-sensitivity sensor’ and sensor with wide measurement range–2–

Component nameMPU
RF module
Acceleration sensor
Gyro sensor
Acceleration sensor
Gyro sensor

Table 1 List of components
Pattern number
Manufacturer
dsPIC33FJ128GP802
XBee
MPU-6050Microchip Technology
MaxStream
InvenSense Inc.

ADXL375
LPY4150AL

Analog Devices Inc.
STMicroelectronics

Specification
28 pinS1, S2±16[g]±2000[dps]±200[g]±6000[dps]is called ‘low-sensitivity sensor’. Outline of thesensor system is shown in Fig. 2. Sampling frequency is set at 1 [kHz] to cope with extremely
fast movement.

3.

TheoryThe gait parameters derived in this study

Fig. 3 Gait parameters investigated consistof toe’s height, toe’s angle, and stride length

are stride length, toe’s height, and toe’s angle
shown in Fig. 3. A stride is an operation fromthe contact of the heel of one side of the footto the next contact of the heel on the sameside to the support surface and the distance isdefined as stride length. Applying double integration to vertical acceleration, toe’s heightis obtained. There are generally two maximal values and one minimal value in the toe’sheight in one stride[14] . When the toe apartFig. 4The stance phase starts with heelcontact (HC) and ends with heel oﬀ. Swingphase starts with toe oﬀ (TO) and ends withheel contactfrom the support surface, the first maximum
point is reached immediately, during the swing
phase. When the foot is swing forward, minimum point is reached and just before the footlands on the support surface, second maximum
point appears. In this study, during the swing
phase, the two maximum points of the toe’sheight are defined as P1 and P3 and the minimum point is defined as P2 as shown in Fig. 3.

A series of stride is called gait cycle and consists of stance phase and swing phase (Fig. 4).
The stance phase refers to the period from theheel contact to the toe oﬀ and the foot is incontact with the support surface in this period.
The swing phase refers to the time when thetoe aparts from the ground until the next heelcontact and the foot is away from the groundin this period.

The toe’s angle is amplitude of the angle ofthe toe direction from the floor and is definedby the diﬀerence between the maximum angle

Velocity is derived by integrating the acceleration data obtained from the sensor attachedto the toe and further integration derives tra-

θmax and the minimum angle θmin .

–3–jectory of the toe. In order to accurately estimate the moving distance, it is necessary to accurately distinguish the swing phase with thestance phase, and then to determine the integration interval. In this study, to determine
the integration interval, we focus on the angular velocity in the dorsi-plantar-flexion direction of the foot (Fig. 5). Fig. 6 shows the relationship between the angular velocity in thedorsi-plantar-flexion direction of the foot andthe movement of the foot. Point cn in the fig-Fig. 5 Dorsiflexion is when the toe goes upward and the heel goes downward. Plantarflexion is when the toe goes downward and theheel goes upward

ure is the minimum value of the angular velocity occurred when the foot is swing forward
during the swing phase. Maximum point anof the angular velocity occurs before point cn
when the toe aparts from the support surface,and maximum point bn of the angular velocity occurs after point cn when the heel landson the support surface. The integration interval is determined by including the maximum
values of point an and point bn .
The sensor system used in the conventional
method used only high-sensitivity sensor. However in case of fast walking, the acceleration

Fig. 6 The swing phase starts with toe oﬀ(TO) an and ends with heel contact (HC) bn .
In synthetic angular velocity waveform, maximal value is observed during TO and HC

and the angular velocity exceed the measurement range of the high-sensitivity sensor used[15, 16] .
In this case, the gait analysis accuracy decreases.
Therefore, in this study, we attempt to copewith fast walking by introducing low-sensitivity
sensor in addition to high-sensitivity sensor.
Value exceeding the measurement range of highsensitivity sensor is interpolated with the lowsensitivity sensor. Fig. 7 shows the procedureof interpolation of value exceeding measurement ranges. Acceleration threshold is set at±100 [m/s2 ] and angular velocity threshold isset at ±1000 [deg/s]. When the measured valueof high-sensitivity sensor exceeds the threshold, the value is interpolated using the mea-Fig. 7 When the measured value of the highsensitivity sensor exceeds the threshold, themeasurement value of the low sensitivity sensor is used–4–sured value of low-sensitivity sensor.

4.

Experiment

To evaluate the accuracy of the foot trajectory estimated using new sensor system and8
WIMU with reflective markers
the new integration interval determination method, Fig.
mounted on shoe
we asked 8 adult male participants aged 24.7
± 7.5 years old to walk along a walkway attheir fastest speed for 5 times. As shown in
Fig. 8, WIMU is fixed on the tiptoe with vinyltape, and acceleration and angular velocity information during gait are recorded. We simultaneously measured the position of the threemarkers attached to the WIMU using optical
3-dimensional Motion Capture System (MCS,Optitrack Prime 13, NaturalPoint Inc.) withsix cameras placed on a side way focusing on aFig. 9
MCS cameras are arranged on theright side of walking course

certain measurement volume as shown in Fig. 9.
Fig. 10 shows schematic diagram of the entire
experimental environment. The data of a stride,angle and trajectory of the right foot captured
by MCS is used for reference. Motion-captured
trajectory is considered as a reference foot trajectory and used for evaluation of estimation
accuracy of sensor system. From the referenceters such as toe’s height, toe’s angle, and stride

Fig. 10ment

length are calculated and compared.

represents the magnitude of synthetic angu-

and estimated foot trajectories, gait parame-

Schematic diagram of gait experi-

lar velocity.

The blue line is synthetic an-

gular velocity waveform sampled at 100 [Hz]5.

Results and discussion

5.1

Validity of sensor with sampling
rate of 1 [kHz]and the orange line is the synthetic angularvelocity waveform sampled at 1 [kHz]. There
are immeasurable data points in the waveform

Fig. 11 shows the waveforms of synthetic an-obtained by sensor with sampling rate of 100

gular velocity of sampling rate 100 [Hz] and[Hz]. Fig. 12 is the enlarged bottom right part

1 [kHz] plotted together. The horizontal axisof Fig. 11. The peak observable at 11 [s] inrepresents time in second and the vertical axis

Fig. 11 is the heel contact. After the momentof the heel contact, there is vibration observed–5–Fig. 11
Comparison of waveform betweensynthetic angular velocity measured with sampling rate 100 [Hz] and those measured withsampling rate 1 [kHz]Fig. 13

Fig. 14

Estimation error of angle amplitudeFig. 15

Estimation error of stride length

Fig. 12More data can be observed whensampling rate of sensor is set to 1 [kHz] compare to those set at 100 [Hz]in the 1 [kHz] sampling rate waveform but unclear in the 100 [Hz] sampling rate waveform.
Estimation results of gait parameters for sam-

Estimation error of toe’s height

estimate the gait parameters precisely, the utilization of sensor with sampling rate of 1 [kHz]is necessary.

pling frequency 100 [Hz] and 1 [kHz] are compared. Fig. 13 shows the comparison of toe’s

5.2

Comparison of gait parameters

height. Estimation error drops for P2 , and P3

There are a total of 40 samples (8 subjects ×

but increase for P1 when sampling rate 1 [kHz]5 trials). Within that, there are 12 toe’s heightis applied. Fig. 14 and Fig. 15 show the estima-

waveforms of WIMU or MCS which do nottion error for angle amplitude and stride length

have P1 and P2 . In this case, since the angle

respectively. Error became slightly smaller inamplitude and stride length calculated fromangle amplitude estimation. However for stride

these data are reliable, only the toe’s height

length, estimation precision significantly im-data is excluded from accuracy comparison.

proved. These results shows that in order toThus, there are 28 data of toe’s height, 40 data–6–

Table 2Parameters

Error in estimation of gait parameters
Average error
100 [Hz]
1 [kHz]Toe’s height
P1
P2
P3
Toe’s angle amplitude
Stride length0.22±17 [mm]-11.18±19 [mm]-18.77±29 [mm]-8.42±6 [deg]-24.15±103 [mm]6.23±17 [mm]7.10±8 [mm]13.72±15 [mm]-7.46±4 [deg]-10.64±32 [mm]of toe’s angle amplitude, and 40 data of stride

and examined the measurement accuracy. Us-length. Table 2 shows the estimation error ofing this new WIMU system, the accuracy ofeach parameters for sampling rate 100 [Hz] andfoot trajectory was evaluated by comparing the1 [kHz]. Estimation of toe’s height has low ac-gait parameters with data calculated from MCS.

curacy entirely. The method of choosing theThe results of high speed walking analysis wereintegral section plays important role in deter-

as follows. The estimation of toe’s angle am-mining the accuracy of estimation of toe’s height.

plitude and stride length is proved to be of highEach person has diﬀerent characteristic of gait

accuracy. However, the estimation of toe’s height

and finding a new algorithm which can copestill needs improvement. We also confirmed

more type of gait will be our task in the fu-that the method of interpolating values exceed-ture. Estimation of amplitude of toe’s angle

ing the measurement range of high-sensitivity

has considerably high accuracy with error ofsensor by introducing low-sensitivity sensor is-7.46 [deg]. The estimation accuracy of strideeﬀective for the analysis of fastest walking. Us-length shows the highest accuracy with error

ing WIMU with higher sampling rate improvesof -10.64 [mm].

the measurement of characteristics of high speedwalking.

6.

Conclusion

In this study, we developed new toe-mounted

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サポート学会大会, 第１６回日本生活支援工学会大会, 日本機械学会 福祉工学シンポジウム
2016 (LIFE2016), 2016/09/04-06, 東北大学 青葉山キャンパス, 日本, 2016