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Industrial Ergonomics ELSEVIER
International Journal of Industrial Ergonomics 15 (1995) 25-37
A Kansei Engineering approach to a driver/vehicle system Akinori Horiguchi, Takamasa Suetomi Mazda R&D Research Center Yokohama, 2-5, Moriya-cho, Kanagawa-ku, Yokohama, Kanagawa Prefecture, 221, Japan
Abstract
In every process of car development, Kansei Engineering has turned out to be a good tool for adapting car products to the tastes or lifestyles of customers. Kansei Engineering approaches to car development have already been applied in some areas, for example, tuning the exhaust sound of a sports car. A Kansei Engineering approach to a driver/vehicle system is a difficult research area because it involves handling a full-range of human feelings or emotions and evaluating many car product parameters. To assist such an approach, an advanced driving simulator which has a large amplitude motion system has been developed at Mazda Technical Research Center (Yokohama). In this initial stage, a study on the human perception mechanism for vehicle yaw motion has been conducted as a basic study of human senses. This paper describes the concepts of the Kansei Engineering approach to a driver/vehicle system using a driving simulator, and the results of an application study on human perception. Relevance to industry
If the relationship between full range human feelings or emotions and the physical parameters of vehicle motion were clarified, car designs based on the characteristics of human senses or feelings would be easier and the car development process would be greatly changed to fit car products to human Kansei.
Keywords: Kansei Engineering; Driver-vehicle system; Driving simulator; Human perception
I. Introduction
T h e value o f an automobile changes with the times. In the early days of its history, the a u t o m o bile was simply a valuable m e a n s of transportation. T h e n it was given additional value as a comfortable vehicle for transporting people. But now that the car has b e c o m e indispensable for daily life, people are no longer satisfied with the c o m f o r t it can provide. T h e y want to use it for a n o t h e r purpose, which may be described as a place to stage their individuality. In o t h e r words,
consumers are not buying cars just because of their inherent utility but also because of their subjective values. T h e y are m o v e d to buy a car, because "it fits t h e m well", "it has a g o o d styling", or "it just feels right". To stay abreast of these changes, the automobile m a n u f a c t u r e r has to c h a n g e the way it develops automobiles. W e at Mazda, having defined Kansei Engineering as a technology to transfer h u m a n perceptions, feelings and mental images into a tangible product, are trying to develop cars focusing on the sensory aspects of individual people ( Y a m a m o t o , 1986).
0169-8141/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0 1 6 9 - 8 1 4 1 ( 9 4 ) 0 0 0 5 4 - 7
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A. Horiguchi, T. Suetomi / International Journal of lndustrial Ergonomics 15 (1995) 25-37
Also, Kansei Engineering deals with a wide spectrum of disciplines, ranging from human factors engineering to psychology. The process of bringing an automobile to the market can be divided roughly into two stages: development of the product itself and marketing the assembled product. Both stages need what we call a Kansei Engineering approach. But in most cases this approach, based as it is on human response, has been used in the area of product development; for example, developing a styling (lnoue et al., 1989) or realizing a fitting for exhaust sounds (Okamoto et al., 1991). Experiments are also being done on how to reflect human sensations into the product by analyzing the driver's reactions to stimuli given to him when driving. The closed loop in which a driver is driving a car is referred to as a "driver/vehicle system" and this is the subject of the Kansei Engineering approach applied here. The focus of the approach covers a full range of feelings from highorder emotions the driver feels when the car is accelerating or being steered to low-order physiological phenomena like tiredness or carsickness. The latter phenomena are more properly handled from an ergonomics perspective rather than the Kansei Engineering approach, though we would not deny their importance. With the aim of developing a tool to support automobile development based on the d r i v e r / vehicle system study, Mazda has developed a driving simulator (Suetomi et al., 1989). In this paper we report on some experiments with the driver/vehicle system carried out at Mazda Yokohama Research Center using the driving simulator.
2. Kansei Engineering approach using a driving simulator 2.1. Kansei Engineering for the driver/vehicle system One of the objectives of Kansei Engineering in the evaluation of a driver/vehicle system is to
clarify a relationship between the driver's physiological responses and emotions to physical vehicle behavior. For this purpose it is useful to know what kind of stimuli the driver receives from the vehicle, in what driving conditions he feels them and how he feels them. However, such an evaluation is not an easy task because the driver usually gets complicated sensations as a result of interactions between the driver's steering operation and so on, and the corresponding vehicle behavior. This is one of the reasons why it is difficult to make a car focusing on human sensations. There are, in short, two factors which make the situation complicated. First, every driver makes his own emotional judgment based on his perception of the vehicle behavior, which again varies according to the way he controls the vehicle. On top of that, environments and conditions are always different and what one driver perceives is not always the same as what another driver does. Second, the physical features of the vehicle cause various sensations in the driver, but the driver does not perceive them separately but as a combined whole. When turning a corner, for example, the driver senses and evaluates the lateral acceleration, yawing and rolling at the same time. Some problems can arise when Kansei Engineering is applied to a real car. Suppose that to make experiments on the driver's rating of the vehicle's cornering behavior, we make tests with changing speeds on various curves. The Kansei test needs several drivers, including those with average ability. It is dangerous, however, to use non-specialists with different driving skills for such a test, because we cannot predict how these drivers will react in a real car. And in the case of the real car test, it is necessary to limit the number of variable vehicle characteristics. However, it is never possible to alter only one special characteristic. If a vehicle characteristic about yaw motion, for instance, is changed by tuning suspensions, it inevitably results in changes to other characteristics (in this case the roll of the vehicle). For these reasons the driving simulator can be regarded as being a good tool for carrying out Kansei Engineering experiments. The next sec-
A. Horiguchi, T. Suetomi / International Journal of lndustrial Ergonomics 15 (1995) 25-37
Visual System
il Real TIme s°ltware II I [ t ~ i ~l Motion System I~Or I I ' I Vehicle Dynamics ~.j I Experimental I L Sound System I [-..,t--------~[ Conditions I etc .... ['-"1 Control Load Driving Scenario i , ; System Vehicle Characteristics
I_,
Fig. 1. General configuration of a driving simulator.
1
tion describes the features and merits of a driving simulator, as well as problems still to be solved.
2.2. Merits of the driving simulator Fig. 1 shows the general configuration of a driving simulator. The major components are a visual system which generates a road image, a motion system to give the feelings of motion, a sound system to make engine and wind noises, a steering wheel and other control elements and a computer which controls the whole driving simulator. A driver on board the driving simulator feels as if he were driving a real car on a real road. However, even at the scene of an accident, he is always safe from injury. Vehicle features and road conditions are calculated on a computer and can be changed arbitrarily by the experimenter. The merits of the driving simulator can be summarized as follows: (1) Safety - drivers are free from injury even at the scene of an accident. (2) Flexibility - vehicle features and road conditions can be rapidly and arbitrarily set by the experimenter. (3) Reproducibility - tests can be repeated under the same conditions many times. (4) Expansibility - not-yet-built future vehicle systems can be tested. (5) Observability - driver's physiological and psychological conditions and behaviors are easy to measure.
2.3. Problems with the driving simulator Even the best driving simulator cannot simulate the driving of a real vehicle completely. We
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discuss here some problems with the simulator that remain to be solved. First, space limitations are put on the driver; the driver's vision and the stroke of motions the driver can perform are restricted. The first limitations in visibility are of particular importance. Three-dimensional data representing roads and environments must be converted into two-dimensional data before they are projected on the screen, and this conversion makes the depth of the scene look different from that of the real scenery. For example, when the driver focuses his eyes on the projected scene, the focal distance is very different from that when he looks at the real scene. Contrary to flight simulators, which use an infinite focal distance technique, the driving simulator must cover a wide range of focal distances like a real traffic scene. The second limitation of the system lies in the difficulty of reproducing the acceleration the driver feels when driving on a real road. It is hardly possible to simulate the m o v e m e n t of a free moving vehicle within a limited area of space. We must use a technique which makes the driver perceive the acceleration. One example of such an illusion is to incline the simulator cabin. This makes the driver feel as if he were exposed to acceleration. In this technique a gravity component plays a role, as rotation and lateral movement are combined to simulate acceleration. The ratio of rotation to lateral movement is crucial; excess rotation causes the driver to feel the roll, not the acceleration. The next problem is of a technical character and relates to the response delay of the motion system and graphic generator. The driver gets "simulator sickness" when the simulator reacts after a delay to the driver's steering action. The computer-generated image lacks accuracy (reality). An unrealistic display does not give the driver the feeling of real driving and influences the test results unfavorably. The above problems, which relate to the method for controlling actuators or the computer technology, can be expected to be solved in the course of technical progress. Another problem is determining to what extent the simulator should simulate driving sensations. For each simulator we have to decide what
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A. Horiguchi, T. Suetomi / International Journal o f lndustrial Ergonomics 15 (1995) 25-37
acceleration is to be generated or how wide the vision angle should be. However, if we try to solve all these problems at once, we would have to build a large-scale system and the cost would be far beyond the acceptable level. Wide vision angle, for example, requires a large moving base, reducing the motion performance of the system. We must always handle these technical issues with full attention to the overall balance of cost and achievable performance. To find compromises for these problems we are trying to develop a driving simulator as described in the following.
3. Driving simulator
3.1. Concept of Mazda driving simulator In order to apply a driving simulator to the evaluation of a driver/vehicle system, which is one of the main fields of the Kansei Engineering approach, the most important thing is to be able to feel the vehicle motion as exactly as possible. In actual driving, a driver acquires much information via his eyes, ears, vestibular sensors, tactile sensors, and so on, from vehicle and road environments. Although most of that information is acquired through his eyes, the driver drives not only with visual cues, but also with motion and auditory cues and control feelings. Motion cues are also very important in a driving simulator not only to increase realism, but also to prevent a driver from getting so-called "simulator sickness" owing to v i s u a l / m o t i o n cue conflicts. Further, in certain critical conditions or emergencies, it is impossible for a driver to control a vehicle if he depends on only visual cues, because the speed of reactions to changes in lateral acceleration or yaw rate is crucial to the driver in sensing vehicle motion. From this perspective, on one side of designing the driving simulator there are the number of degrees-of-freedom and the scale of motion system. In driving, the driver feels yaw, roll and lateral acceleration due to his steering actions, pitch and longitudinal acceleration due to his
Mini-Super-Computer
SouniSignals ~--Real -TiS~nthesizer meVehicle II II II Sound CruisingSound
h MotionSystem
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~Control Signals
Fig. 2. Overall system configuration.
braking and acceleration, and vertical acceleration due to road roughness and vehicle roll and pitch. The more degrees-of-freedom a motion system has, the larger the scale of motion the system should be. So, in the case of a larger scale motion system, high-response motion cannot be realized. The other side of the design includes delay and accuracy. Delay and accuracy of motion cues as well as visual cues are very important because the driver uses them to estimate simulated vehicle responses including simulator delay. That is to say, the time delay must be short compared to a real vehicle lag, which is from 100 to 150 milliseconds to research driver/vehicle dynamic response accurately.
3.2. Driving simulator cot,figuration Fig. 2 shows the overall configuration of the Mazda driving simulator. It is an advanced driving simulator which consists of a mini-super-computer, a large scale motion system, a high speed visual system, a sound system and a movable cabin. The computer calculates vehicle motion and controls the whole system. The four degreesof-freedom motion system moves the cabin to simulate motion sensations. The visual system generates a road image onto a screen in front of the driver. The sound system generates a cruising sound. Driver control signals, such as steering, accelerating and braking, are input into the computer to calculate vehicle dynamics in real time.
A. Horiguchi, T. Suetomi / International Journal of Industrial Ergonomics 15 (1995) 25-37
The road image generator makes a visual scene according to the calculated driver's position. The generated image is projected on an 80-inch screen placed in front of the driver from a projector in the movable cabin. Calculation results are also sent to the motion system, to the cruising sound generator named Real-time Vehicle Sound Synthesizer, to the control feel system, and to the dashboard instruments. The motion system controls the movable cabin's four degrees-of-freedom roll, pitch, yaw, and translational motion - to simulate lateral and longitudinal accelerations, roll, pitch and yaw. The real-time vehicle sound synthesizer makes exhaust sounds that correspond to engine rotation and throttle, wind and road noise, and tire squealing sounds. To simulate control feel, an electric motor connected to the steering wheel generates steering reaction forces. One driver can be seated in the movable cabin. The cabin is equipped with a seat, dashboard, pedals, and a steering wheel, all having production car specifications. -
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3.3. Motion system
Fig. 3 shows the mechanism of the motion system. The motion system consists of a rotational mechanism that controls the three axes of roll, pitch, and yaw of the movable cabin and a translational mechanism that controls the horizontal motion of the cabin. The three rotational axes pass through the area of the driver's head, where the driver's vestibular sensors are located. In general, because of the motion limitations of driving simulators, the following techniques are used to simulate realistic motion sensation. (1) Simulate horizontal acceleration using a component of the gravitational acceleration vector, realized by tilting the cabin. (2) Reproduce only the high-frequency component of motion (This technique is called "washout".) (3) Reduce motion cues. In simulating lateral acceleration, the highfrequency component is produced by actual lateral motion and the low-frequency component is
PITCH
ROLL
YA~ Fig. 3. Configurationof motionsystem.
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A. Horiguchi, T. Suetomi /International Journal of Industrial Ergonomics 15 (1995) 25-37
Table 1 Moving range of Mazda driving simulator Coordinate
Range
Roll Pitch Yaw Lateral
+ / - 40 degrees +/40 degrees + / - 160 degrees + / - 3.6 meters
ters can generate acceleration of 0.8 G, using linear motors. 3.4. Visual system
produced as a component of gravitational acceleration by tilting the roll of the cabin. As we need large amplitude of both lateral and yaw motions to study drvier's steering behaviors, we adopted a gimbal and rail type four degrees-of-freedom motion system. Table 1 shows the moving range of this motion system. The motion system is capable of simulating lateral acceleration by combining lateral motion and roll, longitudinal acceleration through pitch only, and yaw rate up to spinning. Simulation of 0.64 G acceleration can be attained using gravitational components by inclining roll or pitch to a maximum angle of 40 degrees. Roll and pitch are smoothly controlled without backlash by 2 electric servo motors for each motion, and yaw by 4 motors. Lateral motion with a stroke of 7.2 me-
The visual system generates a road image onto an 80-inch screen placed 1.2 m in front of the driver. The visual angle from the driver is 68 degrees horizontally and 20 degrees up and 14 degrees down from the horizon. A full color (16.78 million colors) textured road and environment image is generated every 20 milliseconds by a special road image generator. An example of road images is shown in Fig. 4. To produce driving conditions, the road image generator has many functions. Road curvature can be specified both horizontally and vertically. The system can control traffic such as leading cars, oncoming cars and obstacles. It can change the road surface to dry asphalt, wheel tracks, snow and so on. The number of lanes and the pattern and the color of lane marks can be specified freely. As background, sky and distant mountains round according to vehicle direction. As
Fig. 4. Road image.
A. Horiguchi, T. Suetomi / International Journal of lndustrial Ergonomics 15 (1995) 25-37
foreground, a bonnet hood and text display are generated statically. A fog effect is also available to change the visible distance. Roll and pitch of the car body are also expressed by road image inclination and vertical motion. As mentioned above, the time lag must be reduced when compared to real vehicle response time and human response time, because the driver estimates additional lag time, not the simulated vehicle response time. Generally in computer graphic systems, a 3-dimensional perspective image is generated to transfer visible objects in a 3-dimensional geometric database to a perspective representation as seen from the driver position and to render the transferred 2-dimensional image. The more complex the scene is, the more calculation time is spent to draw the image. Many systems using parallel pipeline techniques need at least about three frame cycles, which require over 50 milliseconds. Adopting non-pipeline architecture, the transport delay df our system is 25 milliseconds. 3.5. Sound system Cruising sound is important for a driver to control vehicle speed. In the sound system generator, car sounds such as those from the engine, road, wind and tires are recorded during real driving, and are stored in a digital sampler. The generator receives signals indicating the engine rotational speed, throttle opening level, speed and tire slipping conditions from the host computer and reproduces the corresponding stored sounds. It is easy to change an engine sound of a simulation vehicle to that of another car by exchanging sampler data. Five speakers generate cruising sounds; two pillow speakers are attached to the head rest of the driver's seat, two are in the dashboard, and one (a 30 cm woofer) is under the back of the seat. 3.6. Vehicle dynamic model A vehicle dynamic model is calculated to generate visual, motion, auditory and other cues according to the driver's steering, accelerating and
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braking actions. The vehicle model must therefore be simple enough to be calculated in real time. In this system the vehicle dynamic model has a total of 12 degrees of freedom: 5 for longitudinal, lateral, roll, pitch, and yaw for the body, 2 for front and rear wheel steering, 4 for 4-wheel rotations, and 1 for engine rotation. To simulate some types of vehicle characteristics, many vehicle model parameters are specified. For characteristics of suspension springs and dampers, non-linear characteristic values are input for interpolation computation. Wheel alignment changes, such as roll or compliance steer according to longitudinal and lateral forces, are also included. As non-linearity from load, slip angle, and slip ratio is taken into account for tire characteristics, braking and driving behavior can also be simulated. The rigidity, viscosity, friction, and inertial force of the steering column are taken into account for steering dynamics. The power plant consists of an engine, a torque converter (or clutch) and gears. Engine output torque, corresponding to engine rotational speed and throttle opening level, are input for interpolation computation. For an automatic transmission, the gear is shifted automatically according to vehicle speed and throttle. These models are calculated every 5 milliseconds.
4. Kansei Engineering researches using a driving simulator 4.1. Experimental methods using a driving simulator Fig. 5 shows the flow of a Kansei Engineering experiment using a driving simulator. First the purpose of the experiment is to be made clear; we decide, for example, which human sensation shall be the object of the experiment. Then a driving scenario is considered. In the next preparatory stage a program for executing the experiment is drawn up. The conditions for the experiment will be checked for their validity through a preliminary test. Subjects are recruited and then the main experiment starts. After the
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A. Horiguchi, T. Suetomi / International Journal of lndustrial Ergonomics 15 (1995) 25-37
main test has been finished, the results are analyzed and conclusions drawn. The most important thing when carrying out experiments with the help of a driving simulator is to draw up a good test plan which ensures the desired results for a specified purpose. The subject of our test is not a machine, but human beings, who show seemingly endless variety. Humans are sensible about the order of applying loads or stimuli. The combination of conditions and the order of applications should be decided from the viewpoint of human factors engineering. For example, when we want to know how stable the driver feels in a crosswind on the highway, we must determine in advance of the test how the driver reacts to a strong gust of wind and to a weak crosswind. For this purpose our test program must include a compensation process for the different reactions to various crosswinds by the driver. Further, we have to investigate in a preliminary test whether the fixed test conditions will lead to differentiated results or whether the test results can be reproduced. Fig. 6 shows the results of a driver exposed to crosswinds on a highway. G o o d reproducibility can be seen in this case, but this reproducibility can deteriorate if the intervals between the crosswinds are too short. The main experiment is carried out according to a plan which has been worked out as described above. The next step is to analyze the experimental results. It is essential to choose a suitable method of analysis based on the human factors which are to be investigated (or measured). To Test Schedule
Plan Drive Scene Vehicle
Analysis Subject
i
'reparation
Experiment
Analysis
ro~lrammi.n~ Process Visual Scene Motion Control Vehicle Model Data Storage
Objective Eva~uation Driver's Maneuvers Vehicle Motion
Visualization
Pre-test
Subjective Evaluation
Recruiting Subjects
Physiological Evaluation
Statistics Physiology
Fig. 5. Test schedule for experiments using a driving simulator.
Steering Wheel Angle (deg)
Lateral Acceleration
10 0 -10 -20 -30 -40 2 1 0 -1
(m/s 2)
Yaw Rate
(deg/s)
15
0
4 6 Time (s)
8
10
Fig. 6. Driver's response against a crosswind.
examine the correlation between the vehicle characteristics and human sensations, for example, analysis methods such as factor analysis, scale construction method, regression analysis, multi regression analysis ~nd so on must be used. To clarify the driver's driving mechanism, a system identification method would become necessary. To handle even higher-order sensations, statistical methods such as paired comparisons method, analysis of variance, and other methods must be used. Additionally, psychological evaluation methods are needed.
4.2. Application study using the driving simulator We studied the human perception mechanism with regard to yaw direction of vehicle motion as an application study for our driving simulator. Such human perception of vehicle yaw motion is one of the basic factors of driving sensations. In this section, we would like to discuss the results of this study. Fig. 7 illustrates a driver model based on the proposed human perception mechanism of yaw motion. In this model, the two types of information from the vehicle and environment are the yaw rate of vehicle motion and the sight point angle (see Fig. 8), as defined by Reid et al. (Reid et al., 1982). The perception mechanism of this model consists of visual and vestibular sensors. When yaw rate change is perceived through the respective
A. Horiguchi, T. Suetomi / International Journal of lndustrial Ergonomics 15 (1995) 25-37
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Sight Point
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Fig. 9. Definition of sight point angle.
Fig. 7. Driver model based on perception mechanism.
sensors, yaw rate and sight point angle are set through the decision block into the control block with appropriate time delays. The main parameters of this driver model are sensory thresholds and reaction time delays of the vestibular and visual sensors. In order to identify these parameters, the perception model is expressed mathematically as follows. The yaw rate of a vehicle is supposed to increase with a constant yaw angular acceleration after a constant speed cornering for a certain period (see Fig. 9). Since this increase of yaw rate exceeds the human driver's sensory threshold Ar, the human driver experiences a time delay T, for the reaction upon the change of yaw rate. Letting the time when a driver takes a reaction equal t', we have Ar
t'=--+T.
(1)
The time from the point of yaw rate change to the human driver's reaction is defined as the total reaction time. Expressing the yaw rate at the time t' as r', the relationship between t' and r' is hyperbolical, as shown in the following equation and Fig. 10. ( r' - rt, - a r ) ( t' - T~) = A r .
T.
(2)
For the sight point angle, supposing that yaw acceleration / is constant, the yaw angle ~b is qJ=frdt=
(3)
7rt L. 2 + r o t
Assuming that there is no lateral deviation, the increase of the sight point angle is equal to the first term on the right hand side of the above equation. Similarly, since the increase of the driver's sight point angle reaches his sensory threshold at A~O, a time delay Tr will occur for the reaction upon the change of yaw motion. The relationship of total reaction time t' and the yaw rate r' is therefore expressed in the following equation. (r' - ro)(t' - T~) 2 = 2a~,.
t'
(4)
Yaw rate changes after a constant speed cornering. Yaw rate in a constant speed cornering is 0.174 r a d / s (10.0 d e g / s ) and changes under a constant yaw angular acceleration. In order to identify sensory thresholds and reaction time de-
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Fig. 10. Relationship between yaw rate and reaction time according to the perception model.
A. Horiguchi, T. Suetomi / International Journal of lndustrial Ergonomics 15 (1995) 25-37
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Table 2 Experimental conditions
Condition Condition Condition Condition
1 2 3 4
Motion cue Yaw motion
Visual cue Road
Landscape
© © x x
© x © x
x x x O
lays of visual and vestibular sensations independently, stimuli such as visual and motion cues are combined under four conditions as shown in Table 2. All these conditions are provided by the driving simulator. Two kinds of visual images were p r e p a r e d for this experiment. One was a road image, and the other was a landscape image that consists simply of distant mountains. It is impossible for a human driver to perceive a sight point angle with only the landscape image. (1) Road image (see Fig. 11). Left and right corners were represented by turns. T h e r e were straight courses between them. The curvature of the corners was 140 m. (2) Landscape image (see Fig. 12). Mountains make up a distant view. When only the motion cues were generated, the visual images were displayed only at straight courses. The image generated by the visual system is projected on a screen. The driving simulator produces only yaw motion as a motion cue to subjects. The center of yaw rotation is set up to be located near the head of the subject. The subject did not handle the steering wheel, but was instructed to push a switch button in his hand as quickly as possible when he perceived a
Fig. 12. Landscape image condition.
change of yaw rate. There were three groups of subjects:
Group 1 9 male drivers aged from 24 to 34 years old.
Group 2 4 male drivers aged from 50 to 60 years old.
Group 3 5 unexperienced female drivers aged from 20 to 30 years old.
4.3. Experimental results and considerations Sensory threshold Ar and reaction time delay Tr of yaw rate can be identified from Eq. (2) using total reaction time data for the period from a changing point of yaw rate to the pushing of the switch button by a subject. Fig. 13 shows the response of group 1 when only motion cues were indicated. In this figure, o
60.0
,•
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Subject : Male Drivers (20-35 years old) Condition : Motion Cue ~ : Experimental ResuRs .~ : Estimated Line
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Response Time (s) Fig. 11. Road image condition.
Fig. 13. Verification of perception model for motion cue.
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A. Horiguchi, T. Suetomi / lnternational Journal of lndustrial Ergonomics 15 (1995) 25-37 60.0 50.0 40.0
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Response Time (s) Fig. 14. Verification of perception model for visual cue. represent the m e a n of total reaction time, and the thin lines express the standard deviation. As shown in this figure, experimental results correlate well with the perception model which includes the sensory threshold and the reaction time for yaw rate change. We could verify the perception model by observing the same results in the data of other groups. In addition, the reaction time delay Ty and the sensory threshold of sight point angle can be determined with Eq. (4) by using the data obtained in experiments under a road image condition with only visual cues. Fig. 14 shows the results of the verification in such a case. The experimental results of all groups are shown in Fig. 15. In these graphs, the averages of the total reaction times under the same yaw angular accelerations are plotted for each stimulus condition. The averages of the total reaction times under the same yaw angular accelerations for different
35
conditions were compared in order to determine the differences between visual and vestibular sensors. The results of group 1 showed that when the value of yaw angular acceleration was large, the total reaction times measured under the experimental condition using only motion cues were about 0.2 seconds less than when only visual cues were used (see Fig. 15c). With smaller yaw angular accelerations near 9.0-6.5 d e g / s 2, the total reaction times measured under the condition of only having visual cues were shorter than when there were only motion cues. And the total reaction times measured under the experimental condition of both visual and motion cues were close to the shorter reaction times with only visual cues or only motion cues at a 95% level of confidence in overall yaw acceleration range. The results of other groups show the same tendency. However, there were differences among individual subjects for the turning points where the line of motion cue condition and the visual cue condition converged. The range of the turning points was observed in a region of yaw angular accelerations smaller than 25.0 d e g / s 2. We compared the response times of three groups, and Fig. 16 shows the results when both visual (road image) and motion cues were given to the subjects. Comparing the results of group 1 and group 2, the response times of group 2 (elder drivers) were longer than group 1 over the whole Condition : Motion & Visual Cues
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Response Time (s) Fig. 16. Comparison of perception mechanism among three groups when both visual and motion cues are indicated.
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A. Horiguchi, T. Suetomi / International Journal of Industrial Ergonomics 15 (1995) 25-37
range. When the yaw acceleration is about 3 d e g / s 2, the difference in response time between group 1 and group 2 was about 1 second. We could therefore reconfirm that response time is longer according to the age of the driver, and we observed that the perception ability of older drivers tends to weaken, as their perception thresholds were larger than those of younger subjects.
simulator (Richter, 1984). In the experiment they changed vehicle response characteristics which are regarded as being closely correlated to the ease of driving, such as time constant and overshoot of yaw response or those of body slip angle. From the test results, the TB factor which consists of yaw response delay and a steady state in body slip angle was proved to have a strong relation with ease of driving. Fig. 17 shows this index in relation to the ease of driving. H a h n and K~iding have evaluated the ease of various driving configurations, including 4-wheel drive using the Daimler-Benz driving simulator (Hahn et al., 1988). They make the driver on board the simulator experience various types of driving systems and measure the driver's work performance and physiological responses. T6rnros et al. (1988) have studied the influence of drugs on the driver using the VTI driving
4. 4. Other studies using driuing simulators
Driving simulators are being used worldwide as a tool in automobile development. One such study was to examine the correlation between vehicle features and human feelings. Richter conducted an experiment to establish a correlation between vehicle response characteristics and ease of driving felt by a driver using the VW driving
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36
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Fig. 17. Definition of verhicle characteristic TB and relationship between subjectivejudgment and vehicle characteristic TB.
z. 2
A. Horiguchi, T. Suetomi / International Journal of Industrial Ergonomics 15 (1995) 25-37 Reaction Seconds
time
101rotiz°la Nitrazepam
Placebo 0.90
I0
150 m i n u t e s
Fig. 18. Brake reaction times in the driving simulator: Brotizolam study, acute phase.
simulator. They prescribed alcohol or sleeping tablets and measured the response time of drivers when applying brakes. The results shown in Fig. 18 reveal that the intake of drugs retards reactions. Other studies have been done for automobile telephones, car interiors and road traffic signals. 5. Conclusions
In this paper we discussed the use of a driving simulator as a tool for the Kansei Engineering approach to automobile development. Furthermore, we described the merits and problems of a driving simulator, taking the Mazda driving simulator as an example. The driving simulator cannot simulate all the driver's feelings. When the simulator is used for the Kansei Engineering approach, it is essential to make ad hoc study programs specially tailored to the certain feeling under examination. In developing a driving simulator, technical tradeoffs between a wide visibility angle and a high rapidity of movement as well as a balance between cost and performance should be considered. In order to study the driver's sensations of and reactions to the vehicle's dynamic characteristics,
37
a driving simulator with high motion performance is required. Mazda has therefore developed a driving simulator with a large amplitude motion system. Using this simulator we developed a new technique to simulate vehicle movements more realistically. Our final aim is to study high-order sensations using this simulator. As one of the fundamental steps to this goal we are now studying how a driver perceives vehicle motion and how he controis a vehicle. Our study revealed only a fragment of the driver's perception related to vehicle yaw motion. We hope, however, that by conducting a series of such experiments we can accumulate knowledge and gradually grasp the driver's higher-order senses. To achieve this, objective simulating techniques must be further improved by enhancing the reality of the simulated world. It would finally be of great importance to establish an organization which enables us to turn the results of Kansei Engineering studies into car products.
References Hahn, S. and K~iding, W., 1988. The Daimler-Benz driving simulator-presentation of selected experiments. SAE paper, No. 880058. Inoue, H., Furugouri, S., Suetomi, T. and Hata, S., 1989. Sensory evaluation technique for computer aided styling. Mazda Technical Review, 7:141-147 (in Japanese with English summary). Okamoto, Y., Furugouri, S., Hirahata,N., Abe, T. and Hata, S., 1991. Evaluation of vehicle sounds through synthesized sounds that respond to driving operation. JSAE Review, 12(4): 52-57. Reid, L.D., Graf, W.O. and Billing, A.M., 1982. The fitting of linear models to driver response records. SAE paper, No. 820304. Richter, B., 1984. Driving simulator studies: The influence of vehicle parameters on safety in critical situations. SAE paper, No. 741105. Suetomi, T,, Horiguchi, A., Okamoto, Y. and Hata, S., 1991. The driving simulator with large amplitude motion system. SAE paper, No. 910113. T6rnrons, J., Jansson,H., Laurell, H., Lindstr6m, M., Mor~n, B., Nordmark, S. and Palmkvist, G., 1988. The VTI driving simulator-driver performance applications. Workshop simulation in traffic systems - Human aspects, VTI s~irtryck 122. Yamamoto, K., 1986. A better relationship between people and car. Keynote Speech of 21st FISITA Congress.
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Industrial Ergonomics ELSEVIER
International Journal of Industrial Ergonomics 15 (1995) 25-37
A Kansei Engineering approach to a driver/vehicle system Akinori Horiguchi, Takamasa Suetomi Mazda R&D Research Center Yokohama, 2-5, Moriya-cho, Kanagawa-ku, Yokohama, Kanagawa Prefecture, 221, Japan
Abstract
In every process of car development, Kansei Engineering has turned out to be a good tool for adapting car products to the tastes or lifestyles of customers. Kansei Engineering approaches to car development have already been applied in some areas, for example, tuning the exhaust sound of a sports car. A Kansei Engineering approach to a driver/vehicle system is a difficult research area because it involves handling a full-range of human feelings or emotions and evaluating many car product parameters. To assist such an approach, an advanced driving simulator which has a large amplitude motion system has been developed at Mazda Technical Research Center (Yokohama). In this initial stage, a study on the human perception mechanism for vehicle yaw motion has been conducted as a basic study of human senses. This paper describes the concepts of the Kansei Engineering approach to a driver/vehicle system using a driving simulator, and the results of an application study on human perception. Relevance to industry
If the relationship between full range human feelings or emotions and the physical parameters of vehicle motion were clarified, car designs based on the characteristics of human senses or feelings would be easier and the car development process would be greatly changed to fit car products to human Kansei.
Keywords: Kansei Engineering; Driver-vehicle system; Driving simulator; Human perception
I. Introduction
T h e value o f an automobile changes with the times. In the early days of its history, the a u t o m o bile was simply a valuable m e a n s of transportation. T h e n it was given additional value as a comfortable vehicle for transporting people. But now that the car has b e c o m e indispensable for daily life, people are no longer satisfied with the c o m f o r t it can provide. T h e y want to use it for a n o t h e r purpose, which may be described as a place to stage their individuality. In o t h e r words,
consumers are not buying cars just because of their inherent utility but also because of their subjective values. T h e y are m o v e d to buy a car, because "it fits t h e m well", "it has a g o o d styling", or "it just feels right". To stay abreast of these changes, the automobile m a n u f a c t u r e r has to c h a n g e the way it develops automobiles. W e at Mazda, having defined Kansei Engineering as a technology to transfer h u m a n perceptions, feelings and mental images into a tangible product, are trying to develop cars focusing on the sensory aspects of individual people ( Y a m a m o t o , 1986).
0169-8141/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0 1 6 9 - 8 1 4 1 ( 9 4 ) 0 0 0 5 4 - 7
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A. Horiguchi, T. Suetomi / International Journal of lndustrial Ergonomics 15 (1995) 25-37
Also, Kansei Engineering deals with a wide spectrum of disciplines, ranging from human factors engineering to psychology. The process of bringing an automobile to the market can be divided roughly into two stages: development of the product itself and marketing the assembled product. Both stages need what we call a Kansei Engineering approach. But in most cases this approach, based as it is on human response, has been used in the area of product development; for example, developing a styling (lnoue et al., 1989) or realizing a fitting for exhaust sounds (Okamoto et al., 1991). Experiments are also being done on how to reflect human sensations into the product by analyzing the driver's reactions to stimuli given to him when driving. The closed loop in which a driver is driving a car is referred to as a "driver/vehicle system" and this is the subject of the Kansei Engineering approach applied here. The focus of the approach covers a full range of feelings from highorder emotions the driver feels when the car is accelerating or being steered to low-order physiological phenomena like tiredness or carsickness. The latter phenomena are more properly handled from an ergonomics perspective rather than the Kansei Engineering approach, though we would not deny their importance. With the aim of developing a tool to support automobile development based on the d r i v e r / vehicle system study, Mazda has developed a driving simulator (Suetomi et al., 1989). In this paper we report on some experiments with the driver/vehicle system carried out at Mazda Yokohama Research Center using the driving simulator.
2. Kansei Engineering approach using a driving simulator 2.1. Kansei Engineering for the driver/vehicle system One of the objectives of Kansei Engineering in the evaluation of a driver/vehicle system is to
clarify a relationship between the driver's physiological responses and emotions to physical vehicle behavior. For this purpose it is useful to know what kind of stimuli the driver receives from the vehicle, in what driving conditions he feels them and how he feels them. However, such an evaluation is not an easy task because the driver usually gets complicated sensations as a result of interactions between the driver's steering operation and so on, and the corresponding vehicle behavior. This is one of the reasons why it is difficult to make a car focusing on human sensations. There are, in short, two factors which make the situation complicated. First, every driver makes his own emotional judgment based on his perception of the vehicle behavior, which again varies according to the way he controls the vehicle. On top of that, environments and conditions are always different and what one driver perceives is not always the same as what another driver does. Second, the physical features of the vehicle cause various sensations in the driver, but the driver does not perceive them separately but as a combined whole. When turning a corner, for example, the driver senses and evaluates the lateral acceleration, yawing and rolling at the same time. Some problems can arise when Kansei Engineering is applied to a real car. Suppose that to make experiments on the driver's rating of the vehicle's cornering behavior, we make tests with changing speeds on various curves. The Kansei test needs several drivers, including those with average ability. It is dangerous, however, to use non-specialists with different driving skills for such a test, because we cannot predict how these drivers will react in a real car. And in the case of the real car test, it is necessary to limit the number of variable vehicle characteristics. However, it is never possible to alter only one special characteristic. If a vehicle characteristic about yaw motion, for instance, is changed by tuning suspensions, it inevitably results in changes to other characteristics (in this case the roll of the vehicle). For these reasons the driving simulator can be regarded as being a good tool for carrying out Kansei Engineering experiments. The next sec-
A. Horiguchi, T. Suetomi / International Journal of lndustrial Ergonomics 15 (1995) 25-37
Visual System
il Real TIme s°ltware II I [ t ~ i ~l Motion System I~Or I I ' I Vehicle Dynamics ~.j I Experimental I L Sound System I [-..,t--------~[ Conditions I etc .... ['-"1 Control Load Driving Scenario i , ; System Vehicle Characteristics
I_,
Fig. 1. General configuration of a driving simulator.
1
tion describes the features and merits of a driving simulator, as well as problems still to be solved.
2.2. Merits of the driving simulator Fig. 1 shows the general configuration of a driving simulator. The major components are a visual system which generates a road image, a motion system to give the feelings of motion, a sound system to make engine and wind noises, a steering wheel and other control elements and a computer which controls the whole driving simulator. A driver on board the driving simulator feels as if he were driving a real car on a real road. However, even at the scene of an accident, he is always safe from injury. Vehicle features and road conditions are calculated on a computer and can be changed arbitrarily by the experimenter. The merits of the driving simulator can be summarized as follows: (1) Safety - drivers are free from injury even at the scene of an accident. (2) Flexibility - vehicle features and road conditions can be rapidly and arbitrarily set by the experimenter. (3) Reproducibility - tests can be repeated under the same conditions many times. (4) Expansibility - not-yet-built future vehicle systems can be tested. (5) Observability - driver's physiological and psychological conditions and behaviors are easy to measure.
2.3. Problems with the driving simulator Even the best driving simulator cannot simulate the driving of a real vehicle completely. We
27
discuss here some problems with the simulator that remain to be solved. First, space limitations are put on the driver; the driver's vision and the stroke of motions the driver can perform are restricted. The first limitations in visibility are of particular importance. Three-dimensional data representing roads and environments must be converted into two-dimensional data before they are projected on the screen, and this conversion makes the depth of the scene look different from that of the real scenery. For example, when the driver focuses his eyes on the projected scene, the focal distance is very different from that when he looks at the real scene. Contrary to flight simulators, which use an infinite focal distance technique, the driving simulator must cover a wide range of focal distances like a real traffic scene. The second limitation of the system lies in the difficulty of reproducing the acceleration the driver feels when driving on a real road. It is hardly possible to simulate the m o v e m e n t of a free moving vehicle within a limited area of space. We must use a technique which makes the driver perceive the acceleration. One example of such an illusion is to incline the simulator cabin. This makes the driver feel as if he were exposed to acceleration. In this technique a gravity component plays a role, as rotation and lateral movement are combined to simulate acceleration. The ratio of rotation to lateral movement is crucial; excess rotation causes the driver to feel the roll, not the acceleration. The next problem is of a technical character and relates to the response delay of the motion system and graphic generator. The driver gets "simulator sickness" when the simulator reacts after a delay to the driver's steering action. The computer-generated image lacks accuracy (reality). An unrealistic display does not give the driver the feeling of real driving and influences the test results unfavorably. The above problems, which relate to the method for controlling actuators or the computer technology, can be expected to be solved in the course of technical progress. Another problem is determining to what extent the simulator should simulate driving sensations. For each simulator we have to decide what
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A. Horiguchi, T. Suetomi / International Journal o f lndustrial Ergonomics 15 (1995) 25-37
acceleration is to be generated or how wide the vision angle should be. However, if we try to solve all these problems at once, we would have to build a large-scale system and the cost would be far beyond the acceptable level. Wide vision angle, for example, requires a large moving base, reducing the motion performance of the system. We must always handle these technical issues with full attention to the overall balance of cost and achievable performance. To find compromises for these problems we are trying to develop a driving simulator as described in the following.
3. Driving simulator
3.1. Concept of Mazda driving simulator In order to apply a driving simulator to the evaluation of a driver/vehicle system, which is one of the main fields of the Kansei Engineering approach, the most important thing is to be able to feel the vehicle motion as exactly as possible. In actual driving, a driver acquires much information via his eyes, ears, vestibular sensors, tactile sensors, and so on, from vehicle and road environments. Although most of that information is acquired through his eyes, the driver drives not only with visual cues, but also with motion and auditory cues and control feelings. Motion cues are also very important in a driving simulator not only to increase realism, but also to prevent a driver from getting so-called "simulator sickness" owing to v i s u a l / m o t i o n cue conflicts. Further, in certain critical conditions or emergencies, it is impossible for a driver to control a vehicle if he depends on only visual cues, because the speed of reactions to changes in lateral acceleration or yaw rate is crucial to the driver in sensing vehicle motion. From this perspective, on one side of designing the driving simulator there are the number of degrees-of-freedom and the scale of motion system. In driving, the driver feels yaw, roll and lateral acceleration due to his steering actions, pitch and longitudinal acceleration due to his
Mini-Super-Computer
SouniSignals ~--Real -TiS~nthesizer meVehicle II II II Sound CruisingSound
h MotionSystem
JI
II
~Control Signals
Fig. 2. Overall system configuration.
braking and acceleration, and vertical acceleration due to road roughness and vehicle roll and pitch. The more degrees-of-freedom a motion system has, the larger the scale of motion the system should be. So, in the case of a larger scale motion system, high-response motion cannot be realized. The other side of the design includes delay and accuracy. Delay and accuracy of motion cues as well as visual cues are very important because the driver uses them to estimate simulated vehicle responses including simulator delay. That is to say, the time delay must be short compared to a real vehicle lag, which is from 100 to 150 milliseconds to research driver/vehicle dynamic response accurately.
3.2. Driving simulator cot,figuration Fig. 2 shows the overall configuration of the Mazda driving simulator. It is an advanced driving simulator which consists of a mini-super-computer, a large scale motion system, a high speed visual system, a sound system and a movable cabin. The computer calculates vehicle motion and controls the whole system. The four degreesof-freedom motion system moves the cabin to simulate motion sensations. The visual system generates a road image onto a screen in front of the driver. The sound system generates a cruising sound. Driver control signals, such as steering, accelerating and braking, are input into the computer to calculate vehicle dynamics in real time.
A. Horiguchi, T. Suetomi / International Journal of Industrial Ergonomics 15 (1995) 25-37
The road image generator makes a visual scene according to the calculated driver's position. The generated image is projected on an 80-inch screen placed in front of the driver from a projector in the movable cabin. Calculation results are also sent to the motion system, to the cruising sound generator named Real-time Vehicle Sound Synthesizer, to the control feel system, and to the dashboard instruments. The motion system controls the movable cabin's four degrees-of-freedom roll, pitch, yaw, and translational motion - to simulate lateral and longitudinal accelerations, roll, pitch and yaw. The real-time vehicle sound synthesizer makes exhaust sounds that correspond to engine rotation and throttle, wind and road noise, and tire squealing sounds. To simulate control feel, an electric motor connected to the steering wheel generates steering reaction forces. One driver can be seated in the movable cabin. The cabin is equipped with a seat, dashboard, pedals, and a steering wheel, all having production car specifications. -
29
3.3. Motion system
Fig. 3 shows the mechanism of the motion system. The motion system consists of a rotational mechanism that controls the three axes of roll, pitch, and yaw of the movable cabin and a translational mechanism that controls the horizontal motion of the cabin. The three rotational axes pass through the area of the driver's head, where the driver's vestibular sensors are located. In general, because of the motion limitations of driving simulators, the following techniques are used to simulate realistic motion sensation. (1) Simulate horizontal acceleration using a component of the gravitational acceleration vector, realized by tilting the cabin. (2) Reproduce only the high-frequency component of motion (This technique is called "washout".) (3) Reduce motion cues. In simulating lateral acceleration, the highfrequency component is produced by actual lateral motion and the low-frequency component is
PITCH
ROLL
YA~ Fig. 3. Configurationof motionsystem.
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A. Horiguchi, T. Suetomi /International Journal of Industrial Ergonomics 15 (1995) 25-37
Table 1 Moving range of Mazda driving simulator Coordinate
Range
Roll Pitch Yaw Lateral
+ / - 40 degrees +/40 degrees + / - 160 degrees + / - 3.6 meters
ters can generate acceleration of 0.8 G, using linear motors. 3.4. Visual system
produced as a component of gravitational acceleration by tilting the roll of the cabin. As we need large amplitude of both lateral and yaw motions to study drvier's steering behaviors, we adopted a gimbal and rail type four degrees-of-freedom motion system. Table 1 shows the moving range of this motion system. The motion system is capable of simulating lateral acceleration by combining lateral motion and roll, longitudinal acceleration through pitch only, and yaw rate up to spinning. Simulation of 0.64 G acceleration can be attained using gravitational components by inclining roll or pitch to a maximum angle of 40 degrees. Roll and pitch are smoothly controlled without backlash by 2 electric servo motors for each motion, and yaw by 4 motors. Lateral motion with a stroke of 7.2 me-
The visual system generates a road image onto an 80-inch screen placed 1.2 m in front of the driver. The visual angle from the driver is 68 degrees horizontally and 20 degrees up and 14 degrees down from the horizon. A full color (16.78 million colors) textured road and environment image is generated every 20 milliseconds by a special road image generator. An example of road images is shown in Fig. 4. To produce driving conditions, the road image generator has many functions. Road curvature can be specified both horizontally and vertically. The system can control traffic such as leading cars, oncoming cars and obstacles. It can change the road surface to dry asphalt, wheel tracks, snow and so on. The number of lanes and the pattern and the color of lane marks can be specified freely. As background, sky and distant mountains round according to vehicle direction. As
Fig. 4. Road image.
A. Horiguchi, T. Suetomi / International Journal of lndustrial Ergonomics 15 (1995) 25-37
foreground, a bonnet hood and text display are generated statically. A fog effect is also available to change the visible distance. Roll and pitch of the car body are also expressed by road image inclination and vertical motion. As mentioned above, the time lag must be reduced when compared to real vehicle response time and human response time, because the driver estimates additional lag time, not the simulated vehicle response time. Generally in computer graphic systems, a 3-dimensional perspective image is generated to transfer visible objects in a 3-dimensional geometric database to a perspective representation as seen from the driver position and to render the transferred 2-dimensional image. The more complex the scene is, the more calculation time is spent to draw the image. Many systems using parallel pipeline techniques need at least about three frame cycles, which require over 50 milliseconds. Adopting non-pipeline architecture, the transport delay df our system is 25 milliseconds. 3.5. Sound system Cruising sound is important for a driver to control vehicle speed. In the sound system generator, car sounds such as those from the engine, road, wind and tires are recorded during real driving, and are stored in a digital sampler. The generator receives signals indicating the engine rotational speed, throttle opening level, speed and tire slipping conditions from the host computer and reproduces the corresponding stored sounds. It is easy to change an engine sound of a simulation vehicle to that of another car by exchanging sampler data. Five speakers generate cruising sounds; two pillow speakers are attached to the head rest of the driver's seat, two are in the dashboard, and one (a 30 cm woofer) is under the back of the seat. 3.6. Vehicle dynamic model A vehicle dynamic model is calculated to generate visual, motion, auditory and other cues according to the driver's steering, accelerating and
31
braking actions. The vehicle model must therefore be simple enough to be calculated in real time. In this system the vehicle dynamic model has a total of 12 degrees of freedom: 5 for longitudinal, lateral, roll, pitch, and yaw for the body, 2 for front and rear wheel steering, 4 for 4-wheel rotations, and 1 for engine rotation. To simulate some types of vehicle characteristics, many vehicle model parameters are specified. For characteristics of suspension springs and dampers, non-linear characteristic values are input for interpolation computation. Wheel alignment changes, such as roll or compliance steer according to longitudinal and lateral forces, are also included. As non-linearity from load, slip angle, and slip ratio is taken into account for tire characteristics, braking and driving behavior can also be simulated. The rigidity, viscosity, friction, and inertial force of the steering column are taken into account for steering dynamics. The power plant consists of an engine, a torque converter (or clutch) and gears. Engine output torque, corresponding to engine rotational speed and throttle opening level, are input for interpolation computation. For an automatic transmission, the gear is shifted automatically according to vehicle speed and throttle. These models are calculated every 5 milliseconds.
4. Kansei Engineering researches using a driving simulator 4.1. Experimental methods using a driving simulator Fig. 5 shows the flow of a Kansei Engineering experiment using a driving simulator. First the purpose of the experiment is to be made clear; we decide, for example, which human sensation shall be the object of the experiment. Then a driving scenario is considered. In the next preparatory stage a program for executing the experiment is drawn up. The conditions for the experiment will be checked for their validity through a preliminary test. Subjects are recruited and then the main experiment starts. After the
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A. Horiguchi, T. Suetomi / International Journal of lndustrial Ergonomics 15 (1995) 25-37
main test has been finished, the results are analyzed and conclusions drawn. The most important thing when carrying out experiments with the help of a driving simulator is to draw up a good test plan which ensures the desired results for a specified purpose. The subject of our test is not a machine, but human beings, who show seemingly endless variety. Humans are sensible about the order of applying loads or stimuli. The combination of conditions and the order of applications should be decided from the viewpoint of human factors engineering. For example, when we want to know how stable the driver feels in a crosswind on the highway, we must determine in advance of the test how the driver reacts to a strong gust of wind and to a weak crosswind. For this purpose our test program must include a compensation process for the different reactions to various crosswinds by the driver. Further, we have to investigate in a preliminary test whether the fixed test conditions will lead to differentiated results or whether the test results can be reproduced. Fig. 6 shows the results of a driver exposed to crosswinds on a highway. G o o d reproducibility can be seen in this case, but this reproducibility can deteriorate if the intervals between the crosswinds are too short. The main experiment is carried out according to a plan which has been worked out as described above. The next step is to analyze the experimental results. It is essential to choose a suitable method of analysis based on the human factors which are to be investigated (or measured). To Test Schedule
Plan Drive Scene Vehicle
Analysis Subject
i
'reparation
Experiment
Analysis
ro~lrammi.n~ Process Visual Scene Motion Control Vehicle Model Data Storage
Objective Eva~uation Driver's Maneuvers Vehicle Motion
Visualization
Pre-test
Subjective Evaluation
Recruiting Subjects
Physiological Evaluation
Statistics Physiology
Fig. 5. Test schedule for experiments using a driving simulator.
Steering Wheel Angle (deg)
Lateral Acceleration
10 0 -10 -20 -30 -40 2 1 0 -1
(m/s 2)
Yaw Rate
(deg/s)
15
0
4 6 Time (s)
8
10
Fig. 6. Driver's response against a crosswind.
examine the correlation between the vehicle characteristics and human sensations, for example, analysis methods such as factor analysis, scale construction method, regression analysis, multi regression analysis ~nd so on must be used. To clarify the driver's driving mechanism, a system identification method would become necessary. To handle even higher-order sensations, statistical methods such as paired comparisons method, analysis of variance, and other methods must be used. Additionally, psychological evaluation methods are needed.
4.2. Application study using the driving simulator We studied the human perception mechanism with regard to yaw direction of vehicle motion as an application study for our driving simulator. Such human perception of vehicle yaw motion is one of the basic factors of driving sensations. In this section, we would like to discuss the results of this study. Fig. 7 illustrates a driver model based on the proposed human perception mechanism of yaw motion. In this model, the two types of information from the vehicle and environment are the yaw rate of vehicle motion and the sight point angle (see Fig. 8), as defined by Reid et al. (Reid et al., 1982). The perception mechanism of this model consists of visual and vestibular sensors. When yaw rate change is perceived through the respective
A. Horiguchi, T. Suetomi / International Journal of lndustrial Ergonomics 15 (1995) 25-37
-Driver ~Perceptlon - ~
~ehicle] I
~Vullbular
X
I
•
(.-Declslon ~
33
Sight Point
:ontrol
Senior
Vkmal Seneor
819ht Polrd
Fig. 9. Definition of sight point angle.
Fig. 7. Driver model based on perception mechanism.
sensors, yaw rate and sight point angle are set through the decision block into the control block with appropriate time delays. The main parameters of this driver model are sensory thresholds and reaction time delays of the vestibular and visual sensors. In order to identify these parameters, the perception model is expressed mathematically as follows. The yaw rate of a vehicle is supposed to increase with a constant yaw angular acceleration after a constant speed cornering for a certain period (see Fig. 9). Since this increase of yaw rate exceeds the human driver's sensory threshold Ar, the human driver experiences a time delay T, for the reaction upon the change of yaw rate. Letting the time when a driver takes a reaction equal t', we have Ar
t'=--+T.
(1)
The time from the point of yaw rate change to the human driver's reaction is defined as the total reaction time. Expressing the yaw rate at the time t' as r', the relationship between t' and r' is hyperbolical, as shown in the following equation and Fig. 10. ( r' - rt, - a r ) ( t' - T~) = A r .
T.
(2)
For the sight point angle, supposing that yaw acceleration / is constant, the yaw angle ~b is qJ=frdt=
(3)
7rt L. 2 + r o t
Assuming that there is no lateral deviation, the increase of the sight point angle is equal to the first term on the right hand side of the above equation. Similarly, since the increase of the driver's sight point angle reaches his sensory threshold at A~O, a time delay Tr will occur for the reaction upon the change of yaw motion. The relationship of total reaction time t' and the yaw rate r' is therefore expressed in the following equation. (r' - ro)(t' - T~) 2 = 2a~,.
t'
(4)
Yaw rate changes after a constant speed cornering. Yaw rate in a constant speed cornering is 0.174 r a d / s (10.0 d e g / s ) and changes under a constant yaw angular acceleration. In order to identify sensory thresholds and reaction time de-
4
IF I/ J~ /~:~,
'~"
~ ~ &r Tr
Change Direction Response Curve : Threshold : Reaction Time
Tr: Reaction • Time Jf ~
O
n-
~ J e s p o n s e Time
/
~ A r : Threshold
>-
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,
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i ~ . .
' --,
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/
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~
~
,
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Fig. 8. Response of perception model.
Fig. 10. Relationship between yaw rate and reaction time according to the perception model.
A. Horiguchi, T. Suetomi / International Journal of lndustrial Ergonomics 15 (1995) 25-37
34
Table 2 Experimental conditions
Condition Condition Condition Condition
1 2 3 4
Motion cue Yaw motion
Visual cue Road
Landscape
© © x x
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lays of visual and vestibular sensations independently, stimuli such as visual and motion cues are combined under four conditions as shown in Table 2. All these conditions are provided by the driving simulator. Two kinds of visual images were p r e p a r e d for this experiment. One was a road image, and the other was a landscape image that consists simply of distant mountains. It is impossible for a human driver to perceive a sight point angle with only the landscape image. (1) Road image (see Fig. 11). Left and right corners were represented by turns. T h e r e were straight courses between them. The curvature of the corners was 140 m. (2) Landscape image (see Fig. 12). Mountains make up a distant view. When only the motion cues were generated, the visual images were displayed only at straight courses. The image generated by the visual system is projected on a screen. The driving simulator produces only yaw motion as a motion cue to subjects. The center of yaw rotation is set up to be located near the head of the subject. The subject did not handle the steering wheel, but was instructed to push a switch button in his hand as quickly as possible when he perceived a
Fig. 12. Landscape image condition.
change of yaw rate. There were three groups of subjects:
Group 1 9 male drivers aged from 24 to 34 years old.
Group 2 4 male drivers aged from 50 to 60 years old.
Group 3 5 unexperienced female drivers aged from 20 to 30 years old.
4.3. Experimental results and considerations Sensory threshold Ar and reaction time delay Tr of yaw rate can be identified from Eq. (2) using total reaction time data for the period from a changing point of yaw rate to the pushing of the switch button by a subject. Fig. 13 shows the response of group 1 when only motion cues were indicated. In this figure, o
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Fig. 13. Verification of perception model for motion cue.
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A. Horiguchi, T. Suetomi / lnternational Journal of lndustrial Ergonomics 15 (1995) 25-37 60.0 50.0 40.0
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Response Time (s) Fig. 14. Verification of perception model for visual cue. represent the m e a n of total reaction time, and the thin lines express the standard deviation. As shown in this figure, experimental results correlate well with the perception model which includes the sensory threshold and the reaction time for yaw rate change. We could verify the perception model by observing the same results in the data of other groups. In addition, the reaction time delay Ty and the sensory threshold of sight point angle can be determined with Eq. (4) by using the data obtained in experiments under a road image condition with only visual cues. Fig. 14 shows the results of the verification in such a case. The experimental results of all groups are shown in Fig. 15. In these graphs, the averages of the total reaction times under the same yaw angular accelerations are plotted for each stimulus condition. The averages of the total reaction times under the same yaw angular accelerations for different
35
conditions were compared in order to determine the differences between visual and vestibular sensors. The results of group 1 showed that when the value of yaw angular acceleration was large, the total reaction times measured under the experimental condition using only motion cues were about 0.2 seconds less than when only visual cues were used (see Fig. 15c). With smaller yaw angular accelerations near 9.0-6.5 d e g / s 2, the total reaction times measured under the condition of only having visual cues were shorter than when there were only motion cues. And the total reaction times measured under the experimental condition of both visual and motion cues were close to the shorter reaction times with only visual cues or only motion cues at a 95% level of confidence in overall yaw acceleration range. The results of other groups show the same tendency. However, there were differences among individual subjects for the turning points where the line of motion cue condition and the visual cue condition converged. The range of the turning points was observed in a region of yaw angular accelerations smaller than 25.0 d e g / s 2. We compared the response times of three groups, and Fig. 16 shows the results when both visual (road image) and motion cues were given to the subjects. Comparing the results of group 1 and group 2, the response times of group 2 (elder drivers) were longer than group 1 over the whole Condition : Motion & Visual Cues
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A. Horiguchi, T. Suetomi / International Journal of Industrial Ergonomics 15 (1995) 25-37
range. When the yaw acceleration is about 3 d e g / s 2, the difference in response time between group 1 and group 2 was about 1 second. We could therefore reconfirm that response time is longer according to the age of the driver, and we observed that the perception ability of older drivers tends to weaken, as their perception thresholds were larger than those of younger subjects.
simulator (Richter, 1984). In the experiment they changed vehicle response characteristics which are regarded as being closely correlated to the ease of driving, such as time constant and overshoot of yaw response or those of body slip angle. From the test results, the TB factor which consists of yaw response delay and a steady state in body slip angle was proved to have a strong relation with ease of driving. Fig. 17 shows this index in relation to the ease of driving. H a h n and K~iding have evaluated the ease of various driving configurations, including 4-wheel drive using the Daimler-Benz driving simulator (Hahn et al., 1988). They make the driver on board the simulator experience various types of driving systems and measure the driver's work performance and physiological responses. T6rnros et al. (1988) have studied the influence of drugs on the driver using the VTI driving
4. 4. Other studies using driuing simulators
Driving simulators are being used worldwide as a tool in automobile development. One such study was to examine the correlation between vehicle features and human feelings. Richter conducted an experiment to establish a correlation between vehicle response characteristics and ease of driving felt by a driver using the VW driving
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A. Horiguchi, T. Suetomi / International Journal of Industrial Ergonomics 15 (1995) 25-37 Reaction Seconds
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Fig. 18. Brake reaction times in the driving simulator: Brotizolam study, acute phase.
simulator. They prescribed alcohol or sleeping tablets and measured the response time of drivers when applying brakes. The results shown in Fig. 18 reveal that the intake of drugs retards reactions. Other studies have been done for automobile telephones, car interiors and road traffic signals. 5. Conclusions
In this paper we discussed the use of a driving simulator as a tool for the Kansei Engineering approach to automobile development. Furthermore, we described the merits and problems of a driving simulator, taking the Mazda driving simulator as an example. The driving simulator cannot simulate all the driver's feelings. When the simulator is used for the Kansei Engineering approach, it is essential to make ad hoc study programs specially tailored to the certain feeling under examination. In developing a driving simulator, technical tradeoffs between a wide visibility angle and a high rapidity of movement as well as a balance between cost and performance should be considered. In order to study the driver's sensations of and reactions to the vehicle's dynamic characteristics,
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a driving simulator with high motion performance is required. Mazda has therefore developed a driving simulator with a large amplitude motion system. Using this simulator we developed a new technique to simulate vehicle movements more realistically. Our final aim is to study high-order sensations using this simulator. As one of the fundamental steps to this goal we are now studying how a driver perceives vehicle motion and how he controis a vehicle. Our study revealed only a fragment of the driver's perception related to vehicle yaw motion. We hope, however, that by conducting a series of such experiments we can accumulate knowledge and gradually grasp the driver's higher-order senses. To achieve this, objective simulating techniques must be further improved by enhancing the reality of the simulated world. It would finally be of great importance to establish an organization which enables us to turn the results of Kansei Engineering studies into car products.
References Hahn, S. and K~iding, W., 1988. The Daimler-Benz driving simulator-presentation of selected experiments. SAE paper, No. 880058. Inoue, H., Furugouri, S., Suetomi, T. and Hata, S., 1989. Sensory evaluation technique for computer aided styling. Mazda Technical Review, 7:141-147 (in Japanese with English summary). Okamoto, Y., Furugouri, S., Hirahata,N., Abe, T. and Hata, S., 1991. Evaluation of vehicle sounds through synthesized sounds that respond to driving operation. JSAE Review, 12(4): 52-57. Reid, L.D., Graf, W.O. and Billing, A.M., 1982. The fitting of linear models to driver response records. SAE paper, No. 820304. Richter, B., 1984. Driving simulator studies: The influence of vehicle parameters on safety in critical situations. SAE paper, No. 741105. Suetomi, T,, Horiguchi, A., Okamoto, Y. and Hata, S., 1991. The driving simulator with large amplitude motion system. SAE paper, No. 910113. T6rnrons, J., Jansson,H., Laurell, H., Lindstr6m, M., Mor~n, B., Nordmark, S. and Palmkvist, G., 1988. The VTI driving simulator-driver performance applications. Workshop simulation in traffic systems - Human aspects, VTI s~irtryck 122. Yamamoto, K., 1986. A better relationship between people and car. Keynote Speech of 21st FISITA Congress.