A subjective framework for seat comfort based on a heuristic multi criteria decision making technique and anthropometry

Consumer expectations for automobile seat comfort continue to rise. With this said, it is evident that the current automobile seat comfort development process, which is only sporadically successful, needs to change. In this context, there has been growing recognition of the need for establishing theoretical and methodological automobile seat comfort. On the other hand, seat producer need to know the costumer’s required comfort to produce based on their interests. The current research methodologies apply qualitative approaches due to anthropometric specifications. The most significant weakness of these approaches is the inexact extracted inferences. Despite the qualitative nature of the consumer’s preferences there are some methods to transform the qualitative parameters into numerical value which could help seat producer to improve or enhance their products. Nonetheless this approach would help the automobile manufacturer to provide their seats from the best producer regarding to the consumers idea. In this paper, a heuristic multi criteria decision making technique is applied to make consumers preferences in the numeric value. This Technique is combination of Analytical Hierarchy Procedure (AHP), Entropy method, and Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS). A case study is conducted to illustrate the applicability and the effectiveness of the proposed heuristic approach.     

A conceptual framework proposed to formalize the scientific investigation of automobile seat comfort

Consumer expectations for automobile seat comfort continue to rise. With this said, it is evident that the current automobile seat comfort development process, which is only sporadically successful, needs to change. In this context, there has been growing recognition of the need for automobile seat comfort researchers to establish a theoretical and methodological foundation. Only in this way can automobile seat comfort achieve recognition as a true scientific discipline and enable its further development. The present contribution hopes to stimulate and lead researchers to focus on a framework through which this recognition and development can take place. This paper describes the current automobile seat comfort development process and details the associated limitations. The limitations were the catalysts for the creation of a systematized framework intended to direct the investigative process associated with seat comfort research. The framework is expected to produce theories and methods that can explain, guide, and further legitimize the discipline of automobile seat comfort.     

Some observations regarding the vibrational environment in child safety seats

A growing issue in the area of vehicular ride comfort is that of child safety seats. Postural, thermal and vibrational comfort considerations are finding their way into child seat design. This paper makes some observations regarding the current state of child safety seat design, then goes on to present the results of vibration tests performed over two road surfaces using two child seats and two children. The vibration levels measured at the interfaces between the children and their seats were found to be higher than the vibration levels between the driver and the driver's seat. Calculated power spectral densities and acceleration transmissibility functions showed that the vibration transmission characteristics of the coupled system consisting of the automobile seat, child seat and child were different from those of the driver/seat system. Whereas, automobile seats normally reduce vibrational disturbances at most frequencies, the child seats tested amplified vibration at most frequencies up to 60 Hz.     

Evaluation of an intelligent seat system

This study was conducted to evaluate the effect of an intelligent seat system, a microprocessor-based interactive seat that automatically adjusts itself to fit a seated individual by making pressure-sensitive adjustments on its own. First, a standard American automobile seat ('baseline' seat) was assessed for comfort. Subjective ratings of comfort, pressure distribution and seated anthropometric measurements were recorded for 20 test subjects. These measurements were recorded while the subjects maintained a simulated driving position in a seat buck. The comfort scale was based on a rating of 1 to 10, with 1 corresponding to 'very poor' and 10 corresponding to 'very good.' Based on a nonlinear, multiple regression model that had been previously developed, the comfort rating of the seat was predicted based on the subjective ratings and the recorded values of 450 pressure measurements from 20 subjects. The predicted comfort value was 7.46 for the baseline seat. Following the baseline assessment, the intelligent seat system was installed into the standard American automobile seat. The objective and subjective assessments were then repeated for 17 subjects and the new predicted comfort rating was 8.06. A t-test performed on the subjective and objective measures indicated that this was a significant improvement in seat comfort. Overall, subjects felt the self-adjusting seat was more customized and more comfortable, providing a better fit.     

An ergonomics investigation into human thermal comfort using an automobile seat heated with encapsulated carbonized fabric (ECF).

This report presents the results of an ergonomics investigation into human thermal comfort using an automobile seat heated with an encapsulated carbonized fabric (ECF). Subjective and objective thermal comfort data were recorded while participants sat for 90 min in a heated and a non-heated automobile seat in an environmental chamber. Eight male participants each completed eight experimental sessions in a balanced order repeated measures experimental design. The conditions in the chamber were representative of a range of cool vehicle thermal environments (5, 10, 15 and 20 degrees C; in the 20 degrees C trial participants sat beside a 5 degrees C 'cold wall'). Participants in the heated seat condition used the heating controller with separate temperature control over the back of the seat (squab) and bottom of the seat (cushion) in an effort to maintain their thermal comfort while wearing the provided clothing, which had an estimated insulation value of 0.9 Clo. The trials showed that participants' overall sensations remained higher than 'slightly cool' in the heated seat at all temperatures. Participants' overall discomfort remained lower (i.e. more comfortable) than 'slightly uncomfortable' at temperatures ranging down to nearly 5 degrees C in the heated seat. Hand and foot comfort, sensation and temperature were similar in both seats. Asymmetric torso and thigh skin temperatures were higher in the heated seat although no significant discomfort was found in the front and back of the torso and thigh in either seat. Participants reported no significant difference in alertness between the control and heated seat.     

Technical note: spine loading in automotive seating

For car manufacturers, seat comfort is becoming more important in distinguishing themselves from their competitors. Therefore, many studies on participative seat comfort are carried out. In this paper, an objective assessment approach is reported which evaluates the concept of "optimal load distribution", based on the identification of a close relationship between the pressure on the seat and the discomfort felt by the person sitting. An in vivo measurement of the pressure in the spinal disc, which is an indicator of the load in the spine, was performed. For this research, a pressure sensor was implanted with a canula in the middle of the disc intervertebralis of a participant. The local pressure on the disc was established for the participant in an automobile seat set in various seat positions. The results indicate that in the seat position with the pressure distribution corresponding to the most comfortable posture the pressure in the intervertebral disc is lowest. The pressure in this position is 0.5 bar, while in the upright seated position the pressure is 1.6 bar.     

Factors affecting static seat cushion comfort

To improve the understanding of factors affecting automobile seat cushion comfort in static conditions (i.e. without vibration), relationships between the static physical characteristics of a seat cushion and seat comfort have been investigated. The static seat comfort of four automobile cushions, with the same foam hardness but diOEerent foam compositions, was investigated using Scheffe?s method of paired comparisons. The comfort judgements were correlated with sample stiOEness, given by the gradient of a force-deflection curve at 490 N (= 50 kgf). Samples with lower stiffness were judged to be more comfortable than samples with greater stiffness. A similar comfort evaluation was conducted using five rectangular foam samples of the same composition but different foam hardness (and a wider range than in the first experiment). There was no linear relationship between the sample stiffness and seat comfort for these samples. Static seat cushion comfort seemed to be affected by two factors, a ‘bottoming feeling’ and a ‘foam hardness feeling’. The bottoming feeling was reflected in the sample stiffness when loaded to 490 N, while the foam hardness feeling was reflected in foam characteristics at relatively low forces. The pressures underneath the buttocks of subjects were compared with the comfort judgements. The total pressure over a 4 cm × cm area beneath the ischial bones was correlated with static seat comfort, even when the differences among samples were great; samples with less total pressure in this area were judged to be more comfortable than samples with greater total pressure. It is concluded that the pressure beneath the ischial bones may reflect both comfort factors: the bottoming feeling and the foam hardness feeling.     

Modeling of human model for static pressure distribution prediction

Vehicle comfort, the key factor that influences the purchase of automobile products, is becoming increasingly important. However, the processes of traditional empirical and experimental approaches to design a new, more comfortable seat is complicated, time consuming and costly. The finite element method could facilitate, accelerate and economize this process. In the present work, a complete human FE model is established based on the Hybrid III dummy, the appropriate element size of 10 mm was ascertained. The body segment mass was verified by comparing segment mass percentages obtained from this model with previous data. The further validation study of the human model was achieved via the human pressure distribution experiments over human-rigid seat interaction under three postures, the validation reveals that the simulation results agree well with the experimental data. On this basis, the human model was applied to predict the interactions between human body and an automobile seat, then the contact pressure distribution, additional information about the contact shear stresses distribution and stress distribution within the soft tissue were obtained through simulation. The human model presented in this paper can reflect the interaction between human body and automobile seat precisely.Relevance to industryThe results deduced that the model is capable of realistically predicting pressure distribution, the present model allows the evaluation of seating comforts in a virtual phase of seat development, and the study can be taken as reference for vehicle seat design and biomechanical evaluation.     

Review of anthropometric considerations for tractor seat design

Tractor driving imposes a lot of physical and mental stress upon the operator. If the operator's seat is not comfortable, his work performance may be poor and there is also a possibility of accidents. The optimal design of tractor seat may be achieved by integrating anthropometric data with other technical features of the design. This paper reviews the existing information on the tractor seat design that considers anthropometry and biomechanical factors and gives an approach for seat design based on anthropometric data. The anthropometric dimensions, i.e. popliteal height sitting (5th percentile), hip breadth sitting (95th percentile), buttock popliteal length (5th percentile), interscye breadth (5th and 95th percentile) and sitting acromion height (5th percentile) of agricultural workers need to be taken into consideration for design of seat height, seat pan width, seat pan length, seat backrest width and seat backrest height, respectively, of a tractor. The seat dimensions recommended for tractor operator's comfort based on anthropometric data of 5434 Indian male agricultural workers were as follows: seat height of 380 mm, seat pan width of 420–450 mm, seat backrest width of 380–400 mm (bottom) and 270–290 mm (top), seat pan length of 370±10 mm, seat pan tilt of 5–7° backward and seat backrest height of 350 mm.

Relevance to industry

The approach presented in this paper for tractor seat design based on anthropometric considerations will help the tractor seat designers to develop and introduce seats suiting to the requirements of the user population. This will not only enhance the comfort of the tractor operators but may also help to reduce the occupational health problems of tractor operators.     

Factors affecting static seat cushion comfort.

To improve the understanding of factors affecting automobile seat cushion comfort in static conditions (i.e. without vibration), relationships between the static physical characteristics of a seat cushion and seat comfort have been investigated. The static seat comfort of four automobile cushions, with the same foam hardness but different foam compositions, was investigated using Scheffe's method of paired comparisons. The comfort judgements were correlated with sample stiffness, given by the gradient of a force-deflection curve at 490 N (= 50 kgf). Samples with lower stiffness were judged to be more comfortable than samples with greater stiffness. A similar comfort evaluation was conducted using five rectangular foam samples of the same composition but different foam hardness (and a wider range than in the first experiment). There was no linear relationship between the sample stiffness and seat comfort for these samples. Static seat cushion comfort seemed to be affected by two factors, a 'bottoming feeling' and a 'foam hardness feeling'. The bottoming feeling was reflected in the sample stiffness when loaded to 490 N, while the foam hardness feeling was reflected in foam characteristics at relatively low forces. The pressures underneath the buttocks of subjects were compared with the comfort judgements. The total pressure over a 4 cm x 4 cm area beneath the ischial bones was correlated with static seat comfort, even when the differences among samples were great; samples with less total pressure in this area were judged to be more comfortable than samples with greater total pressure. It is concluded that the pressure beneath the ischial bones may reflect both comfort factors: the bottoming feeling and the foam hardness feeling.     

Automobile seat comfort prediction: statistical model vs. artificial neural network

The current automobile seat comfort development process, which is executed in a trial and error fashion, is expensive and outdated. The prevailing thought is that process improvements are contingent upon the implementation of empirical/prediction models. In this context, seat-interface pressure measures, anthropometric characteristics, demographic information, and perceptions of seat appearance were related to an overall comfort index (which was a single score derived from a previously published 10-item survey with demonstrated levels of reliability and validity) using two distinct modeling approaches-stepwise, linear regression and artificial neural network. The purpose of this paper was to compare and contrast the resulting models. While both models could be used to adequately predict subjective perceptions of comfort, the neural network was deemed superior because it produced higher r2 values (0.832 vs. 0.713) and lower average error values (1.192 vs. 1.779).     

Coach design for the Korean high-speed train: a systematic approach to passenger seat design and layout

Proper ergonomic design of a passenger seat and coach layout for a high-speed train is an essential component that is directly related to passenger comfort. In this research, a systematic approach to the design of passenger seats was described and the coach layout which reflected the tradeoff between transportation capacity and passenger comfort was investigated for the Korean high-speed train. As a result, design recommendations and specifications of the passenger seat and its layout were suggested. The whole design process is composed of four stages. A survey and analysis of design requirement was first conducted, which formed the base for designing the first and second class passenger seats. Prototypes were made and evaluated iteratively, and seat arrangement and coach layout were finally obtained. The systematic approach and recommendations suggested in this study are expected to be applicable to the seat design for public transportations and to help modify and redesign existing vehicular seats.     

The application of SEAT values for predicting how compliant seats with backrests influence vibration discomfort

The extent to which a seat can provide useful attenuation of vehicle vibration depends on three factors: the characteristics of the vehicle motion, the vibration transmissibility of the seat, and the sensitivity of the body to vibration. The ‘seat effective amplitude transmissibility’ (i.e., SEAT value) reflects how these three factors vary with the frequency and the direction of vibration so as to predict the vibration isolation efficiency of a seat. The SEAT value is mostly used to select seat cushions or seat suspensions based on the transmission of vertical vibration to the principal supporting surface of a seat. This study investigated the accuracy of SEAT values in predicting how seats with backrests influence the discomfort caused by multiple-input vibration. Twelve male subjects participated in a four-part experiment to determine equivalent comfort contours, the relative discomfort, the location of discomfort, and seat transmissibility with three foam seats and a rigid reference seat at 14 frequencies of vibration in the range 1–20 Hz at magnitudes of vibration from 0.2 to 1.6 ms⁻² r.m.s. The ‘measured seat dynamic discomfort’ (MSDD) was calculated for each foam seat from the ratio of the vibration acceleration required to cause similar discomfort with the foam seat and with the rigid reference seat. Using the frequency weightings in current standards, the SEAT values of each seat were calculated from the ratio of overall ride values with the foam seat to the overall ride values with the rigid reference seat, and compared to the corresponding MSDD at each frequency. The SEAT values provided good predictions of how the foam seats increased vibration discomfort at frequencies around the 4-Hz resonance but reduced vibration discomfort at frequencies greater than about 6.3 Hz, with discrepancies explained by a known limitation of the frequency weightings.     

Effect of lumbar support on seating comfort predicted by a whole human body-seat model

Automobile seat greatly affects the ride comfort of drivers in a prolonged driving. Not only the layout parameters of automobile seats, such as seat height, cushion inclination angle, backrest inclination angle, etc, but also the backrest surface related with lumbar support all affect the seating comfort. The human body-seat system includes the three-dimensional data of body based on anatomy and anthropometry, three-dimensional data of seat and adjustable assembly interaction between body and seat based on human body kinematics. Body height and driving posture are adjusted in POSER software, then the solid model of human skin, skeleton and muscle are created in ANSA software, and the integrated model of body-seat system is created in ABAQUS software. The adjustment of the lumbar support parameters is achieved by setting boundary condition of lumbar support region of seats. The finite element model of human body-seat system is validated by comparison to available literature results. At last the finite element model is applied to analyze the effect of lumbar support parameters of seats on the interaction between body and seat under the action of gravity. The pressure value and distribution, contact area, total force of backrest and intervertebral disc stress are obtained. The result shows that the optimal thickness of seat's lumbar support size for the seating comfort is 10 mm after comprehensive comparison and evaluation.Relevance to industry: This study investigated the effects of lumbar support on seating comfort, and can be used to protect the lumbar health. The modeling and simulation method can be applied for the optimization design of vehicle seats.     

Ergonomics modelling and evaluation of automobile seat comfort

Automobile seats are developed in an iterative manner because subjective feedback, which is usually of questionable quality, drives the design. The time and cost associated with iteration could be justified if the process was guaranteed to produce a comfortable seat. Unfortunately, this is not the case. Current practices are based on the premise that seat system design teams need objective, measurable laboratory standards, which can be linked to subjective perceptions of comfort. Only in this way can predictions be made regarding whether or not a particular design will be viewed by the consumer as comfortable. This type of forecasting ability would effectively improve the efficiency with which automobile seats are designed. In this context, the research reported, developed, and validated a stepwise, multiple linear regression model relating seat interface pressure characteristics, occupant anthropometry, occupant demographics, and perceptions of seat appearance to an overall, subjective comfort index derived from a survey with proven levels of reliability and validity. The model performance statistics were: adjusted r ²?=?0.668, standard error of estimate?=?2.308, F (6, 38)?=?15.728, p?=?0.000, and cross-validated r (15)?=?0.952, p?=?0.000. From the model, human criteria for seat interface pressure measures were established. These findings could not have been attained without first demonstrating that (1) the data collection protocol for seat interface pressure measurement was repeatable and (2) seat interface pressure measurements can be used to distinguish between seats.     

Automobile seat comfort: occupant preferences vs. anthropometric accommodation

Automobile seat design specifications cannot be established without considering the comfort expectations of the target population. This contention is supported by published literature, which suggests that ergonomics criteria, particularly those related to physiology, do not satisfy consumer comfort. The objective of this paper is to challenge ergonomics criteria related to anthropometry in the same way. In this context, 12 subjects, representing a broad range of body sizes, evaluated five different compact car seats during a short-term seating session. Portions of a reliable and valid survey were used for this purpose. The contour and geometry characteristics of the five seats were quantified and compared to the survey information. Discrepancies were discovered between published anthropometric accommodation criteria and subject-preferred lumbar height, seatback width, cushion length, and cushion width. Based on this finding, it was concluded that automobile seat comfort is a unique science. Ergonomics criteria, while serving as the basis for this science, cannot be applied blindly for they do not ensure comfortable automobile seats.     

Ergonomics modelling and evaluation of automobile seat comfort

Automobile seats are developed in an iterative manner because subjective feedback, which is usually of questionable quality, drives the design. The time and cost associated with iteration could be justified if the process was guaranteed to produce a comfortable seat. Unfortunately, this is not the case. Current practices are based on the premise that seat system design teams need objective, measurable laboratory standards, which can be linked to subjective perceptions of comfort. Only in this way can predictions be made regarding whether or not a particular design will be viewed by the consumer as comfortable. This type of forecasting ability would effectively improve the efficiency with which automobile seats are designed. In this context, the research reported, developed, and validated a stepwise, multiple linear regression model relating seat interface pressure characteristics, occupant anthropometry, occupant demographics, and perceptions of seat appearance to an overall, subjective comfort index derived from a survey with proven levels of reliability and validity. The model performance statistics were: adjusted r(2)=0.668, standard error of estimate=2.308, F (6, 38)=15.728, p=0.000, and cross-validated r (15)=0.952, p=0.000. From the model, human criteria for seat interface pressure measures were established. These findings could not have been attained without first demonstrating that (1) the data collection protocol for seat interface pressure measurement was repeatable and (2) seat interface pressure measurements can be used to distinguish between seats.     

A method to support a reflective derivation of business components from conceptual models

To successfully compete in today’s volatile business environments, enterprises need to consolidate, flexibly adapt, and extend their information systems (IS) with new functionality. Component-based development approaches can help solving these challenges as they support the structuring of IS landscapes into business components with a loosely coupled business functionality. However, the structuring process continues to pose research challenges and is not adequately supported yet. Current approaches to support the structuring process typically rely on procedures that cannot be customized to the designer’s situational preferences. Furthermore, they do not allow the designer to identify and reflect emerging conflicts during the structuring. In this paper, we therefore propose a new method that introduces a rational, reflective procedure to systematically derive an optimized structuring according to situational preferences. Using a design science approach, we show (i) how the derivation of business components can be formulated as a customizable multi-criteria decision making problem and (ii) how conceptual models can be used to derive business components with an optimized functional scope. To evaluate the feasibility of the proposed method, we describe its application in a complex case that was taken from a German DAX-30 automobile manufacturer.     

In-vehicle vibration study of child safety seats

This paper reports experimental measurements of the in-vehicle vibrational behaviour of stage 0&1 child safety seats. Road tests were performed for eight combinations of child, child seat and automobile. Four accelerometers were installed in the vehicles and orientated to measure as closely as possible in the vertical direction; two were attached to the floor and two located at the human interfaces. An SAE pad was placed under the ischial tuberosities of the driver at the seat cushion and a child pad, designed for the purpose of this study, was placed under the child. Four test runs were made over a pave’ (cobblestone) surface for the driver's seat and four for the child seat at both 20?km?h^?1 and 40?km?h^?1. Power spectral densities were determined for all measurement points and acceleration transmissibility functions (ATFs) were estimated from the floor of the vehicle to the human interfaces. The system composed of automobile seat, child seat and child was found to transmit greater vibration than the system composed of automobile seat and driver. The ensemble mean transmissibility in the frequency range from 1 to 60 Hz was found to be 77% for the child seats systems as opposed to 61% for the driver's seats. The acceleration transmissibility for the child seat system was found to be higher than that of the driver's seat at most frequencies above 10 Hz for all eight systems tested. The measured ATFs suggest that the principal whole-body vibration resonance of the children occurred at a mean frequency of 8.5, rather than the 3.5 to 5.0 Hz typically found in the case of seated adults. It can be concluded that current belt-fastened child seats are less effective than the vehicle primary seating systems in attenuating vibrational disturbances. The results also suggest the potential inability of evaluating child comfort by means of existing whole-body vibration standards.     

Aspects to improve cabin comfort of wheel loaders and excavators according to operators

Comfort plays an increasingly important role in interior design of earth moving equipment. Although research has been conducted on vehicle interiors of wheel loaders and excavators, hardly any information is known about the operator's opinion. In this study a questionnaire was completed by machine operators to get their opinion about aspects which need to be improved in order to design a more comfortable vehicle interior. The results show that almost half of the operators rate the comfort of their cabin "average" or "poor". According to the operators, cab comfort of wheel loaders can be increased by improving seat comfort. Besides improving seat comfort, cabin comfort of excavators can be improved by changing the cab design (including dimensions, ingress/egress), view, reliability, and climate control.