889

Human Sensibility Ergonomics Approach to Vehicle Simulator

Based on Dynamics∗

Kwon SON∗∗, Kyung-Hyun CHOI∗∗∗ and Ji-Sup YOON∗∗∗∗

Simulators have been used to evaluate drivers’ reactions to various transportation prod-ucts. Most research, however, has concentrated on their technical performance. This paperconsiders driver’s motion perception on a vehicle simulator through the analysis of humansensibility ergonomics. A sensibility ergonomic method is proposed in order to improve thereliability of vehicle simulators. A simulator in a passenger vehicle consists of three mainmodules such as vehicle dynamics, virtual environment, and motion representation modules.To evaluate drivers’ feedback, human perceptions are categorized into a set verbal expres-sions collected and investigated to find the most appropriate ones for translation and angularaccelerations of the simulator. The cut-off frequency of the washout filter in the representa-tion module is selected as one sensibility factor. Sensibility experiments were carried out tofind a correlation between the expressions and the cut-off frequency of the filter. This studysuggests a methodology to obtain an ergonomic database that can be applied to the sensibilityevaluation of dynamic simulators.

Key Words: Vehicle Simulator, Human Sensibility Ergonomics, Motion Perception, VehicleDynamic Model, Virtual Environment

1. Introduction

A vehicle simulator is a kind of virtual reality deviceto make a driver feel that he/she is driving a car in a real-life situation by transmitting the ride comfort to the driverthrough motion, visualization, and sound queue. Demandfor a vehicle simulator is increasing owing to its usefulnessin the sense that it can reproduce dangerous and urgentsituations safely, while developing a new concept vehicle.

The driving simulator developed in the University ofIowa contributes to strengthening the competitiveness ofthe automobile industry in the U.S.A. Also, it is wellknown as a large scale simulator which can be employedeffectively for traffic accident research(1). The Japaneseautomobile company, Mazda, has manufactured and used

∗ Received 27th August, 2003 (No. No.03-5106)∗∗ School of Mechanical Engineering, Pusan National Uni-

versity, San 30, Jangjeon-Dong, Gumjeong-Gu, Pusan609–735, Korea. E-mail: kson@pusan.ac.kr

∗∗∗ School of Mechanical Engineering, Cheju National Uni-versity, #1 Ara-Dong, Jeju-Shi, Jeju-Do 690–756, Korea.E-mail: khchoi@cheju.ac.kr

∗∗∗∗ Korea Atomic Energy Research Institute, P.O.Box 105,Yudong, Daejon, 305–600, Korea.E-mail: jsyoon@kaeri.re.kr

a simulator employing a parallel computer(2). Korean au-tomobile companies have also developed diverse simula-tors and employed them in different driving conditions andvehicle designs. It is confirmed, however, that the subjectriding in a high-tech simulator must notice a decline in themotion perception, so the attempts to investigate and im-prove these problems have been tried out(3). Since there isa limitation to developing simulator technology, it is nec-essary to study the advanced simulator development tech-nology enough to satisfy driver’s ergonomic sensibility de-sires.

This research will attempt to pursue the human sensi-bility ergonomics approach to the driver’s motion percep-tion employing a vehicle simulator. To do this, the tradi-tional human sensibility ergonomics method is modifiedto extract sensibility vocabulary for the human sensibilityergonomics method and motion perception. Also, cut-offfrequency is determined as an ergonomic sensibility factorin the washout algorithm of a simulator and its effect onmotion perception is addressed in this paper.

2. Vehicle Simulator

2. 1 Vehicle simulator structureA simulator is a device capable of reproducing a

virtual reality environment and motion perception using

JSME International Journal Series C, Vol. 47, No. 3, 2004

890

Fig. 1 Vehicle simulator structure

computer graphics. Especially, a driving simulator of a ve-hicle consists of a control force loading module, a motionanalysis module, an audiovisual reproduction module, anda motion reproduction module. All these modules are in-tegrated by the communication system. The control force-loading module detects the driver’s operation and repro-duces an appropriate reaction force to the operation. Themotion analysis module analyzes the vehicle behavior andgenerates the driving situations. The audiovisual repro-duction module takes charge of the driving environmentand sound information. Also, the motion reproductionmodule makes the driver experience a real driving situa-tion by reproducing the vehicle behavior through the mo-tion generator. Figure 1 shows the structure of a developedvehicle simulator.

2. 2 Dynamic analysis of driving deviceThe dynamic analysis of a driving device is an essen-

tial element for reproducing the vehicle behavior throughthe motion generator of a simulator and for developing thegraphic module. As shown in Fig. 2, this paper carried outthe dynamic analysis of a vehicle chassis model over thevehicles equipped with a McPherson suspension system inorder to develop a dynamic vehicle simulation model. Thevehicle model has a chassis mass of 1 429 kg and consistsof 24 bodies. There are 8 universal joints, 6 revolutionjoints, 14 spherical joints and 5 translation joints amongthe bodies. The vehicle model is structured to have 15 de-grees of freedom, which include four-wheel revolutions, 8pitches, translation and rotational motions of the car bodyand movement to allow for vehicle steering. ADAMS isused for dynamic analysis of a vehicle. The coordinatorsystem is determined with x, (the vehicle driving direc-tion), y (left of a vehicle), and z (a line perpendicular to xand y plane).

The dynamic simulation of a vehicle is carried out un-der the driving conditions of acceleration and decelerationintervals, lane changes, and bump pass in order to obtain

Fig. 2 Vehicle dynamic model

Fig. 3 Analysis results using ADAMS

acceleration and rotation perception through the simula-tor operation. It starts at a standstill position and drivesthrough the acceleration interval and changes lanes keep-ing a fixed speed (about 35 km/h). Then it passes a bumpshaped semi-sine curve with 2 m of width and 0.1 m ofheight at a fixed speed (about 18 km/h). Figure 3 showsthe driving condition of a lane change. The dark dottedline shows the velocity of a vehicle in terms of its drivingdirection and the light dotted line represents the displace-ment of y-direction. Figure 4 (a) shows the driving situa-tion on passing a bump and (b) is the simulation result ofacceleration in the z-direction.

2. 3 Virtual driving environmentAmong simulator components, visual elements are

essential for enhancing the driver’s motion perception. Todevelop a graphic simulator, dVISE is used as the tool forproducing virtual reality(4). Also, to develop the virtualdriving environment with a high degree of reality, tex-ture images are extracted from the real world and mappedinto the modeled environment through CAD. Besides, thegraphic simulator contains the 4-lane straight roads with

Series C, Vol. 47, No. 3, 2004 JSME International Journal

891

(a) Passing bump

(b) Chassis vertical acceleration corresponding time

Fig. 4 Analysis results of bump passing

Fig. 5 Virtual driving environment

buildings on the sides as near view components in order toincrease motion perception in the virtual driving environ-ment.

Driving on the graphic module is operated based onthe data gained from the dynamic analysis module. Fig-ure 5 shows the virtual driving environment offering visualinformation at constant 20 frames/sec. The developed vir-tual driving environment is connected directly to the beamprojector through a PC monitor and then is displayed onthe screen in front of the simulator. Attempting the coinci-dence of the motion reproducing device and the virtual en-vironment reduces the driver’s simulator sickness, whichis analogous to motion sickness.

Fig. 6 Washout algorithm structure

2. 4 Motion reproductionThe motion reproduction is responsible for directly

delivering the motion perception to the driver on the sim-ulator. The important thing is that the driver experiencesmotion perception through a simulator in order to have thedriver experience the dynamic features and the changes indriving conditions as real as real-world driving situations.Therefore, the most important part of a simulator is how toreproduce motion with the high reality motion reproduc-tion module.

In general, there is no restriction on the range of vehi-cle motions, but the motion system simulating motion hasits limit in terms of the kinematics motion range and dy-namic characteristics. So it is difficult to generate perfectmotion reproduction. Therefore, a washout algorithm isrequired, which can restrict motion range within the phys-ical limitation of the motion system and maintain the re-sults accompanied by command queues from a driver. Thecommand queue simulated in the motion platform inputslinear acceleration and angular velocity of the driver’s seatwhich are gained from the results of dynamic analysis aswashout algorithm input in order for the driver to expe-rience the driving scenarios sensitively. The washout al-gorithm consists of a high frequency filter and a low fre-quency filter. The high frequency filter can eliminate lowfrequency elements of the motion queue, which causesthe deviated motion from the restricted range of the mo-tion platform. Then, it returns the motion platform to thestarting point. The low frequency filter plays the role oftilt coordination reproducing constant bursts of accelera-tion. The low frequency signal found amid the commandqueue elements is not able to reproduce the motion due tothe kinematics limitations, so the responses in the rangedrivers become aware of can be reproduced through thehigh frequency passing filter. Figure 6 illustrates the struc-ture of the conventional washout algorithm.

3. Human Sensibility Evaluation

3. 1 Human sensibility ergonomics approachThis paper explores the human sensibility ergonomics

approach fit for the dynamic system based on a lot of ex-isting human sensibility research for the evaluation of asimulator. The most representative approach among theexisting human sensibility ergonomic approaches includes

JSME International Journal Series C, Vol. 47, No. 3, 2004

892

Fig. 7 Sensibility ergonomics method

functional expansion, a human sensibility ergonomics sys-tem, human sensibility ergonomics modeling, hybrid hu-man sensibility ergonomics, virtual reality engineering,and remote user sensibility evaluation(5). Among these,human sensibility ergonomics techniques suitable for asimulator have been studied in this paper by applying mul-tivariate analysis techniques, functional expansion tech-niques, and virtual reality human sensibility ergonomics,etc. The human sensibility ergonomics approach evalu-ates the driver’s sensibility not by quantitative methodslike vital signals but by the qualitative way in which vo-cabulary is used. Figure 7 shows a series of processesof the integrated human sensibility ergonomics technique.According to the human sensibility ergonomics techniqueprocess, sensibility expressions are considered as ways ofexpressing the driver’s perception in the simulator. So sen-sibility expressions about motion perception can be ex-tracted. After analyzing a simulator, the dominant fac-tors appealing to the driver’s sensibility are selected fromamong the considered factors. To ascertain the relationsbetween the sensibility expressions and the sensibility fac-tors, the sensibility experiments are carried out and ana-lyzed by using a vehicle simulator. Through a series ofsuch processes, human sensibility ergonomics techniquessuitable for evaluating a vehicle simulator have been de-veloped.

3. 2 Sensibility expressions extractionThe motion perception of a simulator is taken as the

object sensibility in human sensibility ergonomics tech-nique and the motion perception is divided into accelera-tion and rotational feeling. Sensibility expressions apply-ing to these perceptions are extracted. The motion percep-tion as the object of sensibility is defined as the percep-tion that a human being feels when the fixed coordinate

Table 1 Selected vocabulary

system carries out a revolution or translation movement.In that case, human body is considered as rigid opposedto experiencing contraction of skeletal muscles control-ling the body. Accordingly, motion perception is dividedinto revolution and translation factors, and these factorsare matched to revolution and to acceleration perception.

A driver’s sensibility to the defined motion perceptionis detected through sensibility expressions. Also, the rota-tion perception and acceleration perception are examinedconcretely. At first, sensibility expressions are collectedfrom a dictionary and then added from questionnaires dueto the ambiguity of expressions found in the dictionary anda lack of applicable expressions for the dynamic system.Table 1 list the finally selected expressions for rotation andacceleration perception.

3. 3 Sensibility factors and category determinationThe motion reproduction module is in charge of trans-

ferring motion perception by operating the platform. Themost important thing is that the filtering algorithm of thevehicle dynamic analysis results in the platform motionqueue. Also, there are factors related to lots of motion per-ceptions such as cut-off frequency and scale coefficient inthe conventional washout algorithm for generating a Stew-art platform signal. The cut-off frequency has a major in-fluence on the queue offered to the driver and the motionrange in the motion system. So the cut-off frequency ischosen as a sensibility factor among the possible detectedfactors in the motion reproduction module.

It is believed that motion perception is closely relatedto the various kinds of body protective reflexes that have atendency to keep one’s balance no matter where the bodyis located in order to categorize the cut-off frequency as asensibility factor. A body protective reflex is closely re-lated to the vestibular organ of the inner ear among thehuman sense organs.

To categorize the cut-off frequency selected as a sen-sibility factor, the human senses are modeled mathemat-ically. The motion sense organ is the vestibular organlocated in the inner ear. The semicircular canal of thevestibular organ takes the role of sensing rotational motionand otolith organ senses linear movement and position ofthe cranial bone. After modeling these two organs mathe-

Series C, Vol. 47, No. 3, 2004 JSME International Journal

893

matically, the transfer function is calculated as follows:(6)

Gwidth(s)=k(1+τAs)

(1+τLs)(1+τS s)(1)

Gsense(s)=−(1+γ/β)sλ2

1/8

(s+T−11 )(s+T−1

2 )(2)

where, k = 0.17, τA = 13.2, τL = 5.33, τs = 0.66, T1 =

7.6 µHz, T2 =41 Hz, β=1.4π, γ=0.42π, λ1=2.405Considering the characteristics of sense organs, the

categories for the sensibility experiment are divided intothree to identify the features of low, mid- and high fre-quencies. According to the transfer functions (1) and(2), the transferring area of otolith organs ranges from0.001–5 Hz, and that of the semicircular canal ranges from0.001–10 Hz. When considering the common area ofotolith organs and the semicircular canal, the sensibilitycategory is determined as a low-frequency area, 0.001 Hz,and the high-frequency area, 5 Hz, and the middle area,0.16 Hz.

3. 4 Sensibility experimentThe sensibility experiment of a vehicle simulator has

been conducted by employing the integrated human sensi-bility ergonomics method. A total of 21 people who are intheir late 20 s and have over 6 months’ driving experiencesare selected in order to differentiate the vehicle simulatorfrom the real vehicle. The sample size of the participantsis determined in order to minimize the range of estimatederror within a 20% of 95% significance probability. Thedriving situation obtained from the vehicle simulator isdisplayed to the subjects through a beam projector. Themotion platform displaying 6 degrees of freedom gener-ates appropriate motion corresponding to the driving sit-uation, and provides subjects with the correct degree ofmotion perception. The subjects in the driving simulatorexperience various driving situations and are questionedabout the relationships between the sensibility factors andthe sensibility vocabulary on the questionnaire. This ex-perimental environment is offered after enough scrutinyabout security so that the subject can exclude the restless-ness.

In this research, evaluations concerning the accelera-tion and rotation perception are implemented. The exper-iment is carried out three times, by constructing a drivingsituation according to the three categories decided one ofselected a cut-off frequency as a sensibility factor. Exper-iments I, II, and III show the cases for cut-off frequencys0.001 Hz, 0.016 Hz, and 5 Hz, respectively. As shown inFig. 8, the subjects experienced various driving situationson one way and two-lane roads for 45 seconds at a speedof 40 km/s. To summarize the scenario of the experiment,accelerate up to 35 km/h from the start position and main-tain that speed, then change lanes after 10 seconds. Thesimulator decelerates after 20 seconds and passes a bumpwith a width of 2 m and a height of 0.1 m at a speed of

Fig. 8 Driving road for experiment

18 km/h.The contents on the questionnaire are divided into

four major categories. The first category consists of thepurpose of the experiment and an explanation concerningsecurity. And the second category consists of the personalaffairs of the subjects such as age, sex, and driving expe-rience. The third category concerns the literal meaning ofthe vocabulary and examples of vocabulary in sentences inorder to eliminate the ambiguity of vocabulary used in thequestionnaire. The last part consists of questions regard-ing sensibility vocabulary on a value scale of 5, respec-tively so as to evaluate the sensibility degrees from eachexperiment.

The questions are based on a value scale of 5, forexample, the values 5 and 1 indicate “strong agree” and“never agree”, respectively. Figure 9 (a) shows that thesubject sits in the driving simulator and (b) shows that thedriving simulator is being operated.

3. 5 Experiment resultsTable 2 represents the results of variance analysis by

SAS. Here, the degree of freedom means the numberof cases that can have any values freely maintaining theaverage. For example, the degree of freedom 2 on Ta-ble 2 means that the subjects are experimented on threetimes and they can respond freely two times, but a com-pulsory response only once to achieve a zero summationof deviation. The summation of the deviation square indi-cates the item for investigating the effects of the possibledifferences between the groups or the experiments, eventhough the personal deviation is zero. Items F- value andPr>F are responsible for verification of hypothesis definedthrough comparison of variances within groups. In fact,item Pr>F-value rather than the item F value illustratesthe acceptance or rejection of the hypothesis concerningthe significance level. That is, the acceptance or rejectionof the hypothesis can be decided by item Pr>F, in case ofthe hypothesis that there’s no difference in sensibility vo-cabulary according to the cut-off frequency categories at

JSME International Journal Series C, Vol. 47, No. 3, 2004

894

(a) (b)

Fig. 9 Experiment scene

Table 2 ANOVA result

Table 3 Scheffe result

a defined significance level. In cases concerning the 95%significance level, the sensibility vocabulary marked by *shows a value under 0.05 of the item Pr>F, which has asubtle difference according to the categories of the sen-sibility factors. The vocabulary are as follows: tipping,learning, staggering, running forward, being pulled, beingretarded, getting faster, speeding up, being caught, drivingon, rushing forward, and being dynamic.

The experiment results are analyzed by employingScheffe, which divides groups after analyzing differencescaused by the factors. Table 3 shows a part of the Schefferesult about the experiment. Groups 1, 2, and 3 refer to

experiment I, experiment II, and experiment III, respec-tively. While Groups 1 and 2 are classified as Scheffe A,Group 3 belongs to Scheffe B. Based on the analysis, sen-sibility vocabulary show no differences in the cases of ex-periments I and II, but do show differences in experimentIII among the three cut-off frequency categories. Accord-ingly, the changes at low frequency cannot have just a sub-tle affect on motion perception, but the changes betweenhigh frequency and low frequency can have an influenceon the driver’s perception.

4. Conclusion

This paper focused on the human sensibility er-gonomics approach to the motion perception by using avehicle simulator. The major components of a simulator,such as movement analysis, visual representation, and mo-tion reproduction were investigated and developed. Then,applicable human sensibility ergonomics techniques to thedynamic system were developed by modifying existingtechniques. The developed approach was able to ana-lyze and evaluate the acceleration and rotation perceptionsamong the various motion perceptions.

The cut-off frequency is chosen as a sensibility factoramong the possible detected factors in the motion repro-duction module. Based on the common area of otolith or-gans and semicircular canal, the sensibility category wasdetermined as the low-cut-off frequency, 0.001 Hz, and thehigh-cut-off frequency, 5 Hz, and the middle one, 0.16 Hz.The sensibility experiment of a vehicle simulator was con-ducted to figure out differences among the various kindsof sensibility vocabulary. As the results obtained from theexperiment were analyzed employing statistical analysislike variance analysis, 12 items of sensibility vocabularywere determined, which were closely related to cut-off fre-quency, and analyzed for differences according to the cat-egory they belong to.

An ergonomic evaluation database is required forsimulators by applying the sensibility ergonomic ap-proaches presented in this study. A special system forsensibility evaluation can be constructed for airplanes and

Series C, Vol. 47, No. 3, 2004 JSME International Journal

895

ships as well as passenger vehicles.

References

( 1 ) Cremer, J., Kearney, J. and Papelis, Y., Driving Simula-tion: Challenges for VR Technology, IEEE ComputerGraphics and Applications, (1996), pp.16–20.

( 2 ) Suetomi, T., Horiguchi, A., Okamoto, Y. and Hata, S.,The Driving Simulator with Large Amplitude MotionSystem, SAE 910113, (1991).

( 3 ) Distler, H.K., Gegenfurtner, K.R., van Veen, H.A. and

Hawken, M.J., Velocity Constancy in Virtual RealityEnvironments, Investigative Ophthalmology & VisualScience, Vol.38 (1997), pp.76–81.

( 4 ) Division Ltd. UK, dV/Reality for UNIX WorkstationsUser Guide, (1997).

( 5 ) Japanese Society of Kansei Engineering,http://wwwsoc.nii.ac.jp/jske

( 6 ) Skalak, R. and Chien, S., Handbook of Bioengineering,(1987), p.31.7, McGraw-Hill, New York.

JSME International Journal Series C, Vol. 47, No. 3, 2004