[2]Three-Dimensional Gait Analysis System With Mobile Force Plates And

8/12/2019 [2]Three-Dimensional Gait Analysis System With Mobile Force Plates And

1/4

Three-dimensional Gait Analysis System with Mobile Force Plates and

Motion Sensors

Tao Liu1, Yoshio Inoue

1, Kyoko Shibata

1, and Kouzou Shiojima

2

1

Department of Intelligent Mechanical Systems Engineering, Kochi University of Technology, 185 Miyanokuchi,Tosayamada-Cho, Kami-City, Kochi 782-8502, Japan

(Tel : +81-887-57-2177; E-mail: [email protected])2TEC GIHAN Co., LTD, 1-22, Nishinohata, Okubo-Cho, Uji-City, Kyoto, 611-0033, Japan

(Tel : +81-774-48-2334; E-mail: [email protected])

Abstract To overcome limitations of a traditional gaitanalysis laboratory, in which stationary force plates andcamera system can not measure more than one stride, inthis paper, we propose a three-dimensional gait analysissystem (M3D) composed of mobile force plates andmotion sensors. Coordinate transformation from local

coordinate system of M3D to global coordinate system isimplemented by using measurements of the mobile forceplate. A stick-chain model was built to visually analyzethree-dimensional human gait and joint trajectories, and

triaxial joint moments during gait can be calculated.

Keywords Coordinate transformation, Force plate, Gaitanalysis, Joint moments, Wearable sensor.

1. Introduction

In order to implement three-dimensional (3D) gaitanalysis, a complete human kinematic analysis usinginertial sensors is not enough, and a mobile force plate

system to measure ground reaction force (GRF) duringsuccessive gaits is necessary for inverse human dynamics

analysis. By mounting multi-axial force sensors beneath aspecial shoe, some instrumented shoes have beendeveloped for ambulatory measurements of triaxial GRFin a variety of non-laboratory environments [1-3]. Toanalyze dynamics gait and joint loads, 3D inertial sensormodules have been integrated into wearable force plates.An integrated sensor system including six degrees offreedom force and moment sensors and miniature inertialsensors of Xsens Motion Technologies has been proposedto estimate joint moments and powers of the ankle [4]. In

our past research, a thin and light force plate based ontriaxial sensors and inertial sensors was also proposed to

analyze continuous gaits by measuring triaxial GRF andfoot orientations [5]. Moreover, we are presentlyconcentrating on the development of some wearablesensors to measure human segment orientations duringgait [6]. If 3D orientations of all the leg segments areintegrated with the measured triaxial GRF, an inversedynamic method can be used to implement joint dynamicsanalysis of lower limb.

In this paper, a complete 3D gait analysis based on awireless sensor system is proposed. The sensor system

named as M3D was developed by integrating a mobileforce plate, 3D motion analysis units based on MEMS

sensors and a wireless data logger. A stick-chain modelwas built to visually analyze 3D human gait and jointtrajectories.

2. Methods and Materials

2.1 Sensor SystemAs shown in Fig. 1, a small motion sensor unit (weight:

20g, size: 355015mm3) was designed using a triaxial

accelerometer, three uniaxial gyroscopes and a triaxialmagnetic sensor and micro-computer system, which wereprovided by Tec Gihan Co. Japan. The sensor unit cancommunicate with a data transfer or personal computer bya RS-485 serial communication port. The inertial andmagnetic sensors specification parameters are given inTable 1. Nine channels sensor signals (triaxialaccelerations, triaxial angular rates, and triaxial magneticintensities) are provided after a 16-bit A/D conversion.

Fig. 1 Wearable motion sensor unit.

Table 1. MAIN SPECIFICATIONS OF INERTIAL AND

MAGNETIC SENSORS

Accelerometer Gyroscope Magnetic sensor

Capacity 8g 1200/s 70T

Nonlinearity 0.5% 1% 0.1%

Response 2kHz 140Hz 10kHz

- 107 -


2/4

A Kalman-based fusion algorithm has been applied to

process signals of the triaxial accelerometer and triaxial

magnetic sensor by incorporating excellent dynamics of

gyroscope and stable drift-free performance of the

accelerometer and magnetic sensors. 3D orientations of

the sensor units when mounted on human body segments

can be calculated using the filtered signals. In order toremove the effects from motion accelerations and

measurement errors on accelerometer measuring the

gravity acceleration, we design an EKF algorithm using (1)

and (2), and the state variables and measurement vector

are given. Since the estimated variables are derived from

the hybrid of accelerometer and gyroscope, it incorporates

excellent dynamics of the gyroscope measurement and

stable drift-free performance of gravity acceleration using

the accelerometer.

)1(

)1(

)1(

1)1()1(

)1(1)1(

)1()1(1

)(

)(

)(

kA

kA

kA

kTkT

kTkT

kTkT

kA

kA

kA

Zg

Yg

Xg

XY

XZ

YZ

Zg

Yg

Xg

(1)

)(

)(

)(

)(

)(

)(

kA

kA

kA

kZ

kZ

kZ

Zg

Yg

Xg

Z

Y

X (2)

k=1, 2, 3

where [A] is the state vector and [Z] denotes the

measurement acceleration vector directly equal to the

accelerometer measurement vector; [] is a 3D angularvelocity vector obtained from the gyroscope

measurements.After the Kalman filter processing, we can calculate the

pitch angle (Cx: x-axial angular displacement) and rollangle (Cy: y-axial angular displacement) using the 3Dacceleration measurements.

22 ))(())((/)(tan()( kAkAkAakCx XgZ

g

Y

g (3)

Undefined

kAkAifkAkAa

kAkAifkAkAa

kAkAifkAkAa

kCy

xg

zg

zg

Xg

xg

zg

zg

Xg

xg

zg

zg

Xg

)0)((&)0)(())(/)(tan(

)0)((&)0)(())(/)(tan(

)0)((&)0)(())(/)(tan(

)(

(4)

We can adopt the same model as (1) and (2) to processthe 3D magnetic sensor measurements, and calculate the

heading angle (Cz: z-axial angular displacement) using (5)and (6).

)(

)(

)(

))(cos(0))(sin(

010

))(sin(0))(cos(

))(cos())(sin(0

))(sin())(cos(0

001

)(

)(

)(

kM

kM

kM

kCykCy

kCykCy

kCxkCx

kCxkCx

kM

kM

kM

Zg

Yg

Xg

Z

Y

X (5)

)0)((&)0)(())(/)(tan(

)0)((&)0)(())(/)(tan(

)0)((&)0)((2/

)0)((&)0)((2/

))0)(())(/)(tan(

)(

kMkMifkMkMa

kMkMifkMkMa

kMkMif

kMkMif

kMifkMkMa

kCz

YXYX

YXYX

YX

YX

YYX

(6)

Small triaxial force sensors (USL06-H5-500N)provided by Tec Gihan Co. Japan can only detect the

three-directional force induced on a small circular plate (6 mm), so it is difficult to apply directly to themeasurement of the GRF distributed under feet. As shownin the right photos of Fig. 2, a mobile force plate (weight:

110g, size: 82889mm3

) to measure triaxial force andtriaxial moment was developed using the three smalltriaxial force sensors, in which two aluminum plates wereused as top and bottom plates to accurately fix the threesensors and signal processing circuits. A detaileddescription of the method to extract the triaxial GRF canbe found in our previous publications [5]. In this research,range of force measurement of the developed force plate in

instrumented shoes for the vertical direction and twohorizontal directions is 1000N and 500N, respectively.

The maximum torque measured by the force plate is 30Nmfor all directions.

In order to implement ambulatory GRF measurementswhen the force plates move with feet, a 3D motion sensorunit based on MEMS sensors to measure 3D orientationsof the mobile force plate was added inside the force plate.The motion sensor unit can measure triaxial accelerations,

angular velocities and magnetic vector, and data from themotion sensors can be combined with force sensors data

for a dynamic GRF measurement. As shown in Fig. 3,coordinate transformation from local coordinate system ofM3D-FP (FP) to global coordinate system (G) isimplemented by using the measurements of the force plate

system

Fig.3 Coordinate transformation from local coordinatesystem of M3D-FP (FP) to global coordinate system (G)

Triaxial force sensors

Mobile force lates

Instrumented shoes

Fig. 2 Prototype of an instrumented shoes system with two

mobile force plates mounted under the heel and forefoot.

- 108 -


3/4

2.2 Human Dynamics Analysis

Lower limbs kinematic and kinetic analysis wasimplemented based on measurements of 3D segmentorientations and GRF using the developed sensor system.Firstly, 3D joints coordinates were calculated by

combining 3D orientation estimations of the motion sensorunits and gait phase detection of the force plate system.Secondly, GRF measurements on the feet and 3D jointscoordinates of lower limbs were used to estimate jointmoments.

An inverse dynamics method was adopted to calculate

joint moments in lower limbs. As shown in Fig. 4, after allthe vectors including joint position vector, GRF vector,

moment vector and gravity vector are expressed in thesame coordinate system, being the global coordinatesystem, we could obtain the mass center positions

Right

FootO ,Right

ShankO ,Right

ThighO by vector calculations on the related jointpositions and segment orientations. The mass of lower

limb segments ( Footm , Shankm , Thighm

) were estimated using astatics method based on the height and weight information[7].

Fig. 4 Stick-chain model defined for the lower limb kineticanalysis. The coordinate system indicates the globalcoordinate.

3. Experiments3.1 Human Motion and Force Measurements Using

M3D

As shown in Fig. 5, we used the 3D motion sensor unitsto measure orientations of the shank and the thigh of two

legs, and the instrumented shoes were worn by subjects tomeasure GRF, and foot segments orientations.

Fig. 5 Measurement system (M3D) for 3D gait analysis

The 3D orientations data of lower limbs segments fromone subject during a representative walking trial is shownin Fig. 6. 3D lower limb gait posture was calculated withthe segment orientations, detections of gait phase cycle,and lengths of the leg segments. As shown in Fig. 7, astick-chain model is used to visually analyze the lower

limb postures, and a group of representative results in levelnormal walking.

Fig. 6 Triaxial orientation angles of two legs segments(the thighs). The dot lines indicate the orientation angles ofthe left leg, and the solid lines are the triaxial orientationangles of the right leg.

Real-time communication by wireless modules

Motion sensor units

Data logger

Note PC with

Wireless LAN

Force plates

X

Y

Z

X Y

Z

Hip

Knee

Ankle

Z

YX

1

2

3

4

5

7

89

10

11

12

13

14

1516

17

- 109 -


4/4

Fig. 7 Visualized lower limb postures by a stick-chainmode in a level normal walking trial

3.2 Joint Moments

3D lower limb gait posture was calculated with thesegment orientations, detections of gait phase cycle, andlengths of the leg segments. As shown in Fig. 8 and Fig. 9,a stick-chain model is used to visually analyze the lowerlimb postures, and a group of representative results of jointmoments in stair climbing trials are given.

Fig.8 Stick-link results of stair climbing

Fig.9 Joint moments during stair climbing

4. Conclusions

As an alternative tool of the traditional gait analysissystem based on high-speed cameras and stationary forceplates, a wireless sensor system was developed to obtain

3D motion and force data on successive gait in variouswalking environments. A stick-chain model based the

sensor system is proposed to implement human lower limbkinematic and kinetic analysis. The visualized bodysegment orientation and 3D joint moment data should behelpful to medical doctors in monitoring and evaluatingpatient recovery status.

References

[1] G. S. Faber, I., Kingma, M. H. Schepers, P. H. Veltink,J. H. van Dien, Determination of joint moments withinstrumented force shoes in a variety of tasks,Journalof Biomechanics,43, 28482854, 2010.

[2] H. M. Schepers, H. F. J. M. Koopman, P.H. Veltink,Ambulatory assessment of ankle and foot dynamics,IEEE Transactions on Biomedical Engineering, 54,

895-902, 2007.[3] T. Liu, Y. Inoue, K. Shibata, Wearable force sensor

with parallel structure for measurement ofground-reaction force, Measurement, 40, 644-653,2007.

[4] C. Liedtke, S.A.W. Fokkenrood, J.T. Menger, H. vander Kooij, P.H. Veltink, Evaluation of instrumentedshoes for ambulatory assessment of ground reactionforces, Gait and Posture, 26(1), pp. 39-47, 2007.

[5] T. Liu, Y. Inoue, K. Shibata, A wearable force plate

system for the continuous measurement of triaxialground reaction force in biomechanical applications,Measurement Science and Technology, 20(8), no.085804, 2010.

[6] T. Liu, Y. Inoue, K. Shibata, Development of aWearable Sensor System for Quantitative GaitAnalysis, Measurement,42(7), 978-988, 2009.

[7] V. Zatsiorsky, V.N. Seluyanov, The mass and inertiacharacteristics of the main segments of the humanbody, in Biomechanics V-IIIB, Human KineticsPublishers, Chamapaign, IL, pp. 1152-1159, 1983.

- 110 -

Documents

[2]Three-Dimensional Gait Analysis System With Mobile Force Plates And