Marco Ajovalasit

Human subjective response to steering wheel vibration caused by diesel engine idle

Abstract This study investigated the human subjective response to steering wheel vibration of the type caused by a four-cylinder diesel engine idle in passenger cars. Vibrotactile perception was assessed using sinusoidal amplitude-modulated vibratory stimuli of constant energy level (r.m.s. acceleration, 0.41 m/s2) having a carrier frequency of 26 Hz (i.e. engine firing frequency) and modulation frequency of 6.5 Hz (half-order engine harmonic). Evaluations of seven levels of modulation depth parameter m(0.0, 0.1, 0.2, 0.4, 0.6, 0.8, and 1.0) were performed in order to define the growth function of human perceived disturbance as a function of amplitude modulation depth. Two semantic descriptors were used (unpleasantness and roughness) and two test methods (the Thurstone paired-comparison method and the Borg CR-10 direct evaluation scale) for a total of four tests. Each test was performed using an independent group of 25 individuals. The results suggest that there is a critical value of modulation depth m = 0.2 below which human subjects do not perceive differences in amplitude modulation and above which the stimulus-response relationship increases monotonically with a power function. The Stevens power exponents suggest that the perceived unpleasantness is non-linearly dependent on modulation depth m with an exponent greater than 1 and that the perceived roughness is dependent with an exponent close to unity.

Effect of automobile operating condition on the subjective equivalence of steering wheel vibration and sound

The research described here was performed to define curves of subjective equivalence between steering wheel rotational vibration and sound using stimuli from different automobile operating conditions. The steering wheel acceleration stimuli were summarised in terms of the unweighted and Wh weighted r.m.s. values, while the sound stimuli were summarised in terms of the unweighted SPL in decibels, the A-weighted SPL in decibels, the Stevens Mark VI loudness in sones, the Stevens Mark VII loudness in sones and the Zwicker loudness in sones. The results suggest that both the statistical properties of the stimuli, and the choice of metric, effect the shape of the equivalence curve.

Facilitating the driver detection of road surface type by selective manipulation of the steering-wheel acceleration signal

Abstract Previous research has investigated the possibility of facilitating the driver detection of road surface type by means of selective manipulation of the steering-wheel acceleration signal. In previous studies a selective increase in acceleration amplitude has been found to facilitate road-surface-type detection, as has selective manipulation of the individual transient events which are present in the signal. The previous research results have been collected into a first guideline for the optimization of the steering-wheel acceleration signal, and the guideline has been tested in the current study. The test stimuli used in the current study were ten steering-wheel acceleration—time histories which were selected from an extensive database of road test measurements performed by the research group. The time histories, which were all from midsized European automobiles and European roads, were selected such that the widest possible operating envelope could be achieved in terms of the r.m.s. value of the steering acceleration, the kurtosis, the power spectral density function, and the number of transient events present in the signal. The time histories were manipulated by means of the mildly non-stationary mission synthesis algorithm in order to increase, by a factor of 2, both the number and the size of the transient events contained within the frequency interval from 20 Hz to 60 Hz. The ensemble, composed of both the unmanipulated and the manipulated time histories, was used to perform a laboratory-based detection task with 15 participants, who were presented the individual stimuli in random order. The participants were asked to state, by answering ‘yes’ or ‘no’, whether each stimulus was considered to be from the road surface that was displayed in front of them by means of a large photograph on a board. The results suggest that the selectively manipulated steering-wheel acceleration stimuli produced improved detection for eight of the ten road surface types which were tested, with a maximum improvement of 14 per cent in the case of the broken road surface. The selective manipulation did lead, however, to some degradation in detection for the motorway road stimulus and for the noise road stimulus, thus suggesting that the current guideline is not universally optimal for all road surfaces.

Embedding Smart Materials into Products to Motivate the User: Flexers, a Smarter Approach to Finger Splinting

Embedded intelligence is radically changing the way designers conceptualize and develop technological artifacts. The use of smart materials to design products are uncovering new ways to interact with users so as to engage, entertain and inform them, coding new languages of communication. This study investigates how Smart Materials could support the monitoring of the user’s health condition in rehabilitation situations through an embedded input/output system, and how the occurring feedback could be perceived as unobtrusive, easy to understand and motivating. In this study, Flexers, an interactive finger splint is presented which includes adaptive and sensitive materials as a vehicle to achieve an intuitive interaction that promisingly shapes the occurring product experience with renewed engagement of the user. The results suggest that the use of smart materials combined with light based feedback could be used as a motivating tool for engaging the user in the rehabilitation activity.

Human emotional response to steering wheel vibration in automobiles

This study investigates what form of correlation may exist between measures of the valence and the arousal dimensions of the human emotional response to steering wheel vibration and the vibration intensity metrics obtained by means of the unweighted and the frequency weighted root mean square (rms). A laboratory experiment was performed with 30 participants who were presented 17 acceleration time histories in random order and asked to rate their emotional feelings of valence and arousal using a self-assessment manikin (SAM) scale. The results suggest a highly linear correlation between the unweighted, Wh weighted and Ws weighted vibration intensity metrics and the arousal measures of the human emotional response. The results also suggest that while vibration intensity plays a significant role in eliciting emotional feelings, there are other factors which influence the human emotional response to steering wheel vibration such as the presence of high peaks or high frequency band amplitudes.

Special Issue on Human Perception of Sound and Vibration in Automobiles

With the advent of the industrial revolution humans have been thrust into ever more frequent contact with machines and environments that radiate significant amounts of vibrational and/or acoustical energy. The frequency and amplitude characteristics of the radiated energy have often differed greatly from those of the natural habitats in which we evolved, and thus to those for which we are best adapted. From the time of the early industrial revolution much effort has thus been invested in studying the effects of these new stimuli on humans. With the railways was born a new type of applied research, which investigated the physical effects upon the human body of whole-body vibration, hand–arm vibration, and sound. Anecdotal evidence of the physically damaging effects of these stimuli on machine operators and passengers were the motivation behind a variety of studies which can be considered to have had as their objective what we might today call ‘health and safety’. Early studies of vibration and sound often focussed on disturbance, damage, and health. The objective was usually to understand how to control, reduce, and isolate the vibration and sound. With the birth of the motor vehicle the focus became instead the psychological construct that we today call ‘comfort’. While a few 19th century railway studies addressed human comfort, much of the academic and industrial research output of the 20th century directly addressed the concept of comfort in all its multiple forms. This vast research effort included applications of vibration or sound from a single direction, from multiple directions, and with various intermediate bodies, which coupled the emission source to the human test subject. The vast research effort also carefully defined the ‘comfort’ construct itself by subdividing it into component parts, and by testing its robustness under variations of the physical, perceptual, and cognitive characteristics of the human test subjects. The results of the enormous 20th century programme of research are clearly visible today in the high levels of vibrational and acoustical comfort that characterize the modern motor vehicle. The modern automobile, in all its shapes and forms, is a machine that has transcended its humble beginnings to become the defacto embodiment of safety and comfort, an environment which is routinely inhabited by drivers and passengers for hour-upon-hour without any but the most minimal signs of discomfort or fatigue. The modern motor vehicle is indeed comfortable. The early years of our new millennia are characterized instead by a number of new goals. With both ‘health and safety’ and ‘comfort’ having been largely achieved in today’s motor vehicles, attention is now also being turned to issues such as ‘situation awareness’, ‘quality’, ‘experience’, and ‘emotion’. The same automotive vibration and sound stimuli which were once dissected and analysed from the point of view of their impact on health or comfort are now being looked at in a very different light, that of their potential for transmitting information and for engaging emotion. Where a stimulus was once an unwanted artefact of motor vehicle physics, it is today a defining characteristic and a part of motor vehicle heritage that must be shaped and moulded by designers who understand human perception, cognition, and emotion. Vibration and sound are no longer considered distractions or dangers, but are instead an integral part of the driving experience, and an opportunity for articulating product identity and brand. Where the i