Driver seat comfort for level 3-4 autonomous vehicles.

BACKGROUND: Autonomous vehicles can be classified on a scale of automation from 0 to 5, where level 0 corresponds to vehicles that have no automation to level 5 where the vehicle is fully autonomous and it is not possible for the human occupant to take control. At level 2, the driver needs to retain attention as they are in control of at least some systems. Level 3-4 vehicles are capable of full control but the human occupant might be required to, or desire to, intervene in some circumstances. This means that there could be extended periods of time where the driver is relaxed, but other periods of time when they need to drive. OBJECTIVE: The seat must therefore be designed to be comfortable in at least two different types of use case. METHODS: This driving simulator study compares the comfort experienced in a seat from a production hybrid vehicle whilst being used in a manual driving mode and in autonomous mode for a range of postures. RESULTS: It highlights how discomfort is worse for cases where the posture is non-optimal for the task. It also investigates the design of head and neckrests to mitigate neck discomfort, and shows that a well-designed neckrest is beneficial for drivers in autonomous mode.

Improving long term driving comfort by taking breaks - How break activity affects effectiveness.

During long duration journeys, drivers are encouraged to take regular breaks. The benefits of breaks have been documented for safety; breaks may also be beneficial for comfort. The activity undertaken during a break may influence its effectiveness. Volunteers completed 3 journeys on a driving simulator. Each 130 min journey included a 10 min break after the first hour. During the break volunteers either stayed seated, left the simulator and sat in an adjacent room, or took a walk on a treadmill. The results show a reduction in driver discomfort during the break for all 3 conditions, but the effectiveness of the break was dependent on activity undertaken. Remaining seated in the vehicle provided some improvement in comfort, but more was experienced after leaving the simulator and sitting in an adjacent room. The most effective break occurred when the driver walked for 10 min on a treadmill. The benefits from taking a break continued until the end of the study (after a further hour of driving), such that comfort remained the best after taking a walk and worst for those who remained seated. It is concluded that taking a break and taking a walk is an effective method for relieving driving discomfort.

Effect of long term driving on driver discomfort and its relationship with seat fidgets and movements (SFMs).

Discomfort in vehicle seats is a multifactorial problem with large increases in discomfort occurring during extended duration driving. Due to the nature of driver discomfort, previous research has found it difficult to accurately quantify long term driver discomfort via the use of objective measures. This paper reports a laboratory study that investigates a novel objective measure of long term driver discomfort and its correlation with subjective discomfort ratings. Analysis of driver's seat fidgets and movements was conducted over the duration of a 140 min drive on a driving simulator in addition to collecting subjective ratings of discomfort. It is shown that as subjects' subjective discomfort increases, the frequency of subjects' seat fidgets and movements increases congruently. A large correlation is observed between the subjective and objective measures of driver discomfort and provides the opportunity for long term discomfort evaluations to be made via remote monitoring; removing the need for subjective assessment.

An approach to vehicle design: In-depth audit to understand the needs of older drivers.

The population of older people continues to increase around the world, and this trend is expected to continue; the population of older drivers is increasing accordingly. January 2012 figures from the DVLA in the UK stated that there were more than 15 million drivers aged over 60; more than 1 million drivers were aged over 80. There is a need for specific research tools to understand and capture how all users interact with features in the vehicle cabin e.g. controls and tasks, including the specific needs of the increasingly older driving population. This paper describes an in-depth audit that was conducted to understand how design of the vehicle cabin impacts on comfort, posture, usability, health and wellbeing in older drivers. The sample involved 47 drivers (38% female, 62% male). The age distribution was: 50-64 (n = 12), 65-79 (n = 20), and those 80 and over (n = 15). The methodology included tools to capture user experience in the vehicle cabin and functional performance tests relevant to specific driving tasks. It is shown that drivers' physical capabilities reduce with age and that there are associated difficulties in setting up an optimal driving position such that some controls cannot be operated as intended, and many adapt their driving cabins. The cabin set-up process consistently began with setting up the seat and finished with operation of the seat belt.

Driving a better driving experience: a questionnaire survey of older compared with younger drivers.

A questionnaire survey of drivers (n = 903) was conducted covering musculoskeletal symptoms, the vehicle seat, access to specific vehicle features, ingress/egress, driving performance and driving behaviours. Significantly, more discomfort was reported by older drivers (aged 65+) in the hips/thighs/buttocks and knees. Older drivers reported more difficulty parallel parking (p ≤ 0.01), driving on a foggy day (p ≤ 0.01), and turning their head and body to reverse (p ≤ 0.001). They also reported that their reactions were slower than they used to be (p ≤ 0.01). Dissatisfaction was found by all drivers with adjusting the headrest (height and distance), seat belt height and opening/closing the boot. There is a growing population of older people globally, and the number of older drivers is showing a parallel increase. Clearly, efforts are needed to ensure car design of the future is more inclusive of older drivers. Practitioner Summary: This paper describes a questionnaire survey of drivers on their driving experience - the vehicle seat, access to specific vehicle features, ingress/egress, driving performance and driving behaviours. Comparisons are made by age and gender. Issues with driving and vehicle design particularly for older drivers in the UK are identified.

Contribution of individual components of a job cycle on overall severity of whole-body vibration exposure: a study in Indian mines.

Drivers of earth-moving machines are exposed to whole-body vibration (WBV). In mining operations there can be a combination of relatively high magnitudes of vibration and long exposure times. Effective risk mitigation requires understanding of the main aspects of a task that pose a hazard to health. There are very few published studies of WBV exposure from India. This paper reports on a study that considered the contribution of the component phases of dumper operations, on the overall vibration exposure of the drivers. It shows that vibration magnitudes are relatively high, and that haulage tasks are the main contributor to the exposure. It is recommended that driver speed, haul road surfaces and vehicle maintenance/selection are optimized to ensure minimization of vibration. If this is not sufficient, operation times might need to be reduced in order to ensure that the health guidance caution zone from Standard No. ISO 2631-1:1997 is not exceeded.

Effects of vertical and side-alternating vibration training on fall risk factors and bone turnover in older people at risk of falls.

BACKGROUND: whole-body vibration training may improve neuromuscular function, falls risk and bone density, but previous studies have had conflicting findings. OBJECTIVE: this study aimed to evaluate the influence of vertical vibration (VV) and side-alternating vibration (SV) on musculoskeletal health in older people at risk of falls. DESIGN: single-blind, randomised, controlled trial comparing vibration training to sham vibration (Sham) in addition to usual care. PARTICIPANTS: participants were 61 older people (37 women and 24 men), aged 80.2 + 6.5 years, referred to an outpatient falls prevention service. METHODS: participants were randomly assigned to VV, SV or Sham in addition to the usual falls prevention programme. Participants were requested to attend three vibration sessions per week for 12 weeks, with sessions increasing to six, 1 min bouts of vibration. Falls risk factors and neuromuscular tests were assessed, and blood samples collected for determination of bone turnover, at baseline and following the intervention. RESULTS: chair stand time, timed-up-and-go time, fear of falling, NEADL index and postural sway with eyes open improved in the Sham group. There were significantly greater gains in leg power in the VV than in the Sham group and in bone formation in SV and VV compared with the Sham group. Conversely, body sway improved less in the VV than in the Sham group. Changes in falls risk factors did not differ between the groups. CONCLUSIONS: whole-body vibration increased leg power and bone formation, but it did not provide any additional benefits to balance or fall risk factors beyond a falls prevention programme in older people at risk of falls.

Predicting the health risks related to whole-body vibration and shock: a comparison of alternative assessment methods for high-acceleration events in vehicles.

In this paper, alternative assessment methods for whole-body vibration and shocks are compared by means of 70 vibration samples measured from 13 work vehicles, deliberately selected to represent periods containing shocks. Five methodologies (ISO 2631-1:1997, BS 6841:1987, ISO 2631-5:2004, DIN SPEC 45697:2012 and one specified by Gunston [2011], 'G-method') were applied to the vibration samples. In order to compare different evaluation metrics, limiting exposures were determined by calculating times to reach the upper limit thresholds given in the methods. Over 10-fold shorter times to exposure thresholds were obtained for the tri-axial VDV (BS 6841) than for the dominant r.m.s. (ISO 2631-1) when exposures were of high magnitude or contained substantial shocks. Under these exposure conditions, the sixth power approaches (ISO 2631-5, DIN SPEC, G-method) are more stringent than a fourth power VDV method. The r.m.s. method may lead to misleading outcomes especially if a lengthy measurement includes a small number of severe impacts. In conclusion, methodologies produce different evaluations of the vibration severity depending on the exposure characteristics, and the correct method must be selected. PRACTITIONER SUMMARY: Health risks related to whole-body vibration and high acceleration events may be predicted by means of several different methods. This study compares five such methods giving emphasis on their applicability in the presence of shocks. The results showed significant discrepancies between the risk assessments, especially for the most extreme exposures.

Design of digital filters for frequency weightings (A and C) required for risk assessments of workers exposed to noise.

Many workers are exposed to noise in their industrial environment. Excessive noise exposure can cause health problems and therefore it is important that the worker's noise exposure is assessed. This may require measurement by an equipment manufacturer or the employer. Human exposure to noise may be measured using microphones; however, weighting filters are required to correlate the physical noise sound pressure level measurements to the human's response to an auditory stimulus. IEC 61672-1 and ANSI S1.43 describe suitable weighting filters, but do not explain how to implement them for digitally recorded sound pressure level data. By using the bilinear transform, it is possible to transform the analogue equations given in the standards into digital filters. This paper describes the implementation of the weighting filters as digital IIR (Infinite Impulse Response) filters and provides all the necessary formulae to directly calculate the filter coefficients for any sampling frequency. Thus, the filters in the standards can be implemented in any numerical processing software (such as a spreadsheet or programming language running on a PC, mobile device or embedded system).

A survey of expert opinion on the effects of occupational exposures to trunk rotation and whole-body vibration.

We present a review of current expert opinion on the effects of combined exposures to trunk rotation and whole-body vibration (WBV), commonly experienced by operators of agricultural machinery. We evaluate the level of agreement between academic experts in the field of ergonomics, human response to WBV and agricultural operators, on the effects of exposure to WBV and trunk rotation. A total of 83 individuals responded to the paper-based questionnaire, which included questions on risk levels from individual and combined exposures, discomfort development, exposure duration limits and tasks within agriculture. The results showed that all groups considered exposure to WBV and trunk rotation as risk factors for the development of back pain. The experts were not in consensus regarding acceptable exposure durations, areas of discomfort experienced or recommendations for cab developments.

Subjective ratings of whole-body vibration for single- and multi-axis motion.

Real-world whole-body vibration exposures comprise motion in fore-aft, lateral, and vertical directions simultaneously. There can also be components of roll, pitch, and yaw. If evaluating vibration with respect to human response, most investigators will use methods defined in ISO 2631-1. This uses frequency weightings that were originally derived from laboratory studies of the subjective responses to vibration in one direction at a time. This paper describes experiments that were carried out using a 6 degree-of-freedom vibration simulator to validate the applicability of ISO 2631-1 in multi-axis environments. Fifteen subjects were exposed to 87 stimuli comprising single-axis, dual-axis, and tri-axial random vibration, to which they were required to produce subjective ratings. It is shown that in this study the root-sum-of-squares method of summation of subjective ratings in individual axes was an adequate technique for prediction of subjective rating of multi-axis vibration. Better agreement between objective and subjective measures of vibration was obtained for unweighted vibration than for frequency weighted signals. The best agreement for this study was achieved when axis multiplying factors were set at 2.2 and 2.4 for x- and y-axis vibration, respectively. Different values could be appropriate for other postures, seats, and vibration conditions and should be determined in future studies.

Relative contribution of translational and rotational vibration to discomfort.

Understanding how vibration affects discomfort is an important factor for improving work and travelling experience. Methods of evaluating health effects from whole-body vibration are closely linked to those for evaluating discomfort in ISO 2631-1. The standard includes a method to evaluate discomfort using twelve axes of vibration with a similar approach to that for evaluating health effects; thus using all twelve axes gives a possibility to evaluate both health and discomfort. The full 12-axis method has not been widely used in practice or validated in a multi-axis environment. The standard guidance is not explicit, thus different interpretations are possible especially when determining the method of comparing or combining vibration in different axes. Furthermore there are not enough studies conducted in multi-axis environments to suggest the optimal combination of axes. In this study ISO 2631-1 method was tested and optimised using a multi-axis test bench at Loughborough University, UK. Subjects were exposed to stimuli which represented vibration characteristics from field measurements. Each stimulus, lasting 15 s, was judged using a continuous judgement, cross-modal matching method. The seat translational and rotational and the backrest translational axes were used in the analyses. There was no vibration at the floor, in order to constrain the number of independent variables. Results showed that correlation for discomfort improved with more complex analysis procedures. However a good correlation was also achieved using just seat translational axes with optimised multiplying factors. The results showed that frequency weightings and r.m.s. averaging improved correlation between vibration and subjective ratings of discomfort. Multiplying factors specified in ISO 2631-1 degraded the correlation between objective and subjective measures of discomfort, therefore an improved set of factors were determined. The new factors showed improvement by placing more emphasis on seat fore-and-aft and lateral axes.

Effects of horizontal whole-body vibration and standing posture on activity interference.

Standing people are exposed to whole-body vibration in many environments. This paper investigates the effects of horizontal whole-body vibration and standing posture on task performance. Sixteen participants were exposed to random vibration (up to 4 Hz) whilst performing a timed pegboard task in two standing postures. Objective and subjective indicators of performance were used. Time taken to complete the task increased progressively with increases in vibration magnitude. The fore-and-aft posture generally showed greater performance decrements and postural interruptions (>1.0 ms(-2) root mean square) than the lateral. For both postures, performance was better during y-axis vibration than during x-axis vibration. Subjective ratings showed similar trends to time data. Impairments due to dual axis exposure were well predicted using root sum of squares calculations based on single axis components. These results indicate that best performance for those standing in moving environments will be achieved if individuals adopt a lateral posture with the most severe vibration in the y-axis. STATEMENT OF RELEVANCE: People have a need to work during transportation, either working for the transport provider or as a passenger. All modes of transport result in travellers being exposed to horizontal motion. This study demonstrates that task disturbance is affected by the orientation of the standing person to the vibration and, therefore, vehicle layouts can be optimised.

Earth moving machine whole-body vibration and the contribution of Sub-1Hz components to ISO 2631-1 metrics.

Exposure to whole-body vibration (WBV) is an occupational hazard for operators of industrial vehicles, such as earth-moving machines. Quantification of WBV exposure in terms of impact on health forms one aspect of the Standard ISO 2631-1 (1997). Regarding assessment of risk to health, ISO 2631-1 (1997) states that if WBV components below 1 Hz are not ;relevant nor important' then they can be excluded from the assessment. In this paper the influence of sub-1 Hz components in WBV acquired from a sample of 46 earth moving machines is evaluated in terms of their contribution to ISO 2631-1 WBV exposure dose metrics: frequency weighted r.m.s. and the vibration dose value (VDV). For the majority of machines, a high proportion of the horizontal (x- and y-axis) WBV r.m.s. and VDV values was generated by sub-1 Hz vibration components; there was a much lower proportion of the vertical (z-axis) vibration generated by such components.

Design of digital filters for frequency weightings required for risk assessments of workers exposed to vibration.

Many workers are exposed to vibration in their industrial environment. Vibration can be transmitted through a vehicle seat or a hand-held power tool. Excessive vibration exposure may cause health problems and therefore it is important that the worker's vibration exposure is assessed, which may require measurement by the equipment manufacturer or the employer. Human exposure to vibration may be measured using accelerometers; however, weighting filters are required to correlate the physical vibration measurements to the human's response to vibration. ISO 2631, BS 6841 and ISO 5349-1 describe suitable weighting filters, but do not explain how to implement them for digitally recorded acceleration data. ISO 8041 Annex C suggests a method but does not provide a solution. By using the bilinear transform, it is possible to transform the analogue equations given in the standards into digital filters. This paper describes the implementation of the weighting filters as digital IIR (Infinite Impulse Response) filters and provides all the necessary formulae to directly calculate the filter coefficients for any sampling frequency. Thus, the filters in the standards can be implemented in any numerical software.

The apparent mass of the seated human exposed to single-axis and multi-axis whole-body vibration.

Most workplaces where workers are exposed to whole-body vibration involves simultaneous motion in the fore-and-aft (x-), lateral (y-) and vertical (z-) directions. Previous studies reporting the biomechanical response of people exposed to vibration have almost always used single-axis vibration stimuli. This paper reports a study where apparent masses of 15 subjects were measured whilst exposed to single-axis and tri-axial whole-body vibration. Each subject was exposed to 28 vibration conditions comprising every combination of single-axis and tri-axial vibration with magnitudes of 0.4 and 0.8 ms(-2) r.m.s. in each direction, once with backrest contact and once without backrest contact. Results show that increasing the magnitude of vibration in directions orthogonal to that being measured affects the apparent mass, causing a reduction in the resonance frequency as the total magnitude of vibration increases. It is demonstrated that the apparent mass resonance frequency is a function of the total vibration magnitude in all axes rather than a function of the vibration magnitude in the direction being measured. It is also shown that, for individuals, the frequency of the peak in the apparent mass in one direction is not related to the frequency of the peak in another direction. It is concluded that more complex biomechanical models are required in order to simulate human response to multi-axis vibration.

Influence of carrying heavy loads on soldiers' posture, movements and gait.

Military personnel are required to carry heavy loads whilst marching; this load carriage represents a substantial component of training and combat. Studies in the literature mainly concentrate on physiological effects, with few biomechanical studies of military load carriage systems (LCS). This study examines changes in gait and posture caused by increasing load carriage in military LCS. The four conditions used during this study were control (including rifle, boots and helmet carriage, totalling 8 kg), webbing (weighing 8 kg), backpack (24 kg) and a light antitank weapon (LAW; 10 kg), resulting in an incremental increase in load carried from 8, 16, 40 to 50 kg. A total of 20 male soldiers were evaluated in the sagittal plane using a 3-D motion analysis system. Measurements of ankle, knee, femur, trunk and craniovertebral angles and spatiotemporal parameters were made during self-paced walking. Results showed spatiotemporal changes were unrelated to angular changes, perhaps a consequence of military training. Knee and femur ranges of motion (control, 21.1 degrees +/- 3.0 and 33.9 degrees +/- 7.1 respectively) increased (p < 0.05) with load (LAW, 25.5 degrees +/- 2.3 and 37.8 degrees +/- 1.5 respectively). The trunk flexed significantly further forward, confirming results from previous studies. In addition, the craniovertebral angle decreased (p < 0.001) indicating a more forward position of the head with load. It is concluded that the head functions in concert with the trunk to counterbalance load. The higher muscular tensions necessary to sustain these changes have been associated with injury, muscle strain and joint problems.

Impedance methods (apparent mass, driving point mechanical impedance and absorbed power) for assessment of the biomechanical response of the seated person to whole-body vibration.

Exposure to whole-body vibration is a risk factor for the development of low back pain. In order to develop a fuller understanding of the response of the seated person to vibration, experiments have been conducted in the laboratory investigating the biomechanics of the seated person. Some of these methods are based on the driving force and acceleration at the seat and are reported in the literature as apparent mass, driving point mechanical impedance or absorbed power. This paper introduces the background behind such impedance methods, the theory and application of the methods. It presents example data showing typical responses of the seated human to whole-body vibration in the vertical, fore-and-aft and lateral directions. It also highlights problems that researchers might encounter in performing, analysing and interpreting human impedance data.