Backrest Inclination Research Articles

Optimisation design of child seat based on chaos mutation MOPSO

To improve the safety of the children in child seats when a vehicle collision occurs, a finite element model of a child safety seat is established, and LS-DYNA is used for crash simulation. Select backrest inclination, headrest inclination, and seat belt centre height as design variables to establish response surface models. The application of chaotic mutation theory in particle swarm optimisation (PSO) is proposed, and the optimal solution of child seat parameters is obtained by using the chaotic mutation based grouped multi-objective particle swarm optimisation (MOPSO). The optimal solution was used to carry out the simulation experiment again, and compared with the original performance. It turned out that the Head Performance Criterion (HPC) is 47.08% better than the original child seat. Besides, the rib deformation is reduced by 21.30%, the neck shear stress is reduced by 55.74%, and the thigh stress is reduced by 48.55%, which indicate significant improvements. The results suggest that a certain parameter combination of the child seat leads to the optimal overall performance in child injury prevention, which indicates significant improvement in the damage of all parts of the child.

The role of muscle forces in neck comfort for static seating: a pilot study

Aircraft seats play a key role in the competition between aircraft companies seeking to differentiate themselves in terms of passengers’ inflight experience. The seat design process relies on computational and experimental methods based on subjective measures, such as comfort rating questionnaires, and objective comfort indicators of seat-occupant interaction, such as contact pressure distribution and muscle activation. Previous studies around muscle activity for seating comfort assessment have primarily focused on more active scenarios or active systems. As such, there are limited studies about the role of muscle force in normal and relaxed sitting conditions, common in aircraft settings. This paper explores the relationship between activities of the neck muscles, sternocleidomastoid, and upper trapezius, measured from human participants seated sedentarily on conventional business aircraft seats and their perceived comfort with different backrest inclinations. The results show, for normal seating without neck pillow, no significant association is found between the backrest inclination and the neck’s comfort or muscle activation. For general seating across different backrest inclinations, a positive medium correlation between muscle activation and comfort is found in upper trapezius (R = 0.5332, p = 0.0187). This work serves as a pilot study of this new approach of comfort evaluation using muscle feedback in seat designing processes and highlights the posterior’s effect to seating experience in the neck region.

Optimization of the seat position for a personal vehicle equipped with a crankset: pilot study

The aim of the study was to optimize the seat for a personal vehicle equipped with a crankset mechanism, meant for everyday use. The inclination of the seat backrest was selected on the basis of theoretical considerations. Then dynamic tests were carried out on a group of young, healthy men in order to verify the ergonomic aspects of the seat position in relation to the crankset and determine the efficiency of the human-mechanism system with a load of 50 W. The data obtained from the dynamic tests were subject to statistical analysis. Research has shown that higher seat positions result in statistically higher efficiencies. In addition, a holistic analysis of the personal vehicle design problem shows that the upper position of the seat is also the best. The results of the research can be used to optimize personal vehicles using human force as a drive.

A method of aircraft seat dimension design for long-term use by passengers with different body types

To improve the comfort of seat support performance, we proposed a seat dimensions design method. First, an adjustable seat was used to obtain the measurement data of user-selected comfortable seat dimensions. Second, the differences in the measurement data of different body types and riding time variables were analyzed. Third, a compromise treatment method for the different comfort requirements was developed. This method was applied to the design of passenger seats for short-distance flights in China. The lumbar support thickness was significantly different in the time variables, and the seat pan inclination and neck support height were significantly different among body types. We did not find significant differences, however, in seat height, backrest inclination, lumbar support height, or neck support thickness according to time or body type variables. There is one optimal dimension for seat height (430.5 mm), backrest inclination (104.2°), lumbar support height (98.8 mm), and neck support thickness (44.4 mm). However, seat pan inclination (5.8°, 7.2°, and 9.3°), neck support height (582.6 mm and 622.5 mm), and lumbar support thickness (40.6 mm and 48.7 mm) need multiple dimensions to meet passenger comfort requirements. This seat dimension design method provides new ideas to explore the comfort requirements of passengers and addresses the differences in comfortable seat dimension requirements for different body types and different flight durations.

Kinematic response of seated male volunteers in various reclined postures on a sled subjected to a braking pulse

Vehicle occupants expect greater postural flexibility with the introduction of highly automated vehicles, such as reclined postures. Experiments have been conducted with post mortem human subjects to study the risk of injury under impact conditions in reclined postures. However, the influence of the pre-crash phase on the kinematics in reclined postures has not yet been thoroughly studied. The aim of the present study is to investigate human responses under low g braking conditions focusing on different backrest angles in a generic sled environment.Three 50th percentile male volunteers were recruited to participate in a sled experiment. Each of them was subjected to a total of fourteen trials under a braking pulse with a maximum acceleration of 0.7 g for 700 ms. Different sitting postures were investigated: from 23° to 45°, 60° and 75° backrest tilt with respect to the vertical axis. In addition, two different seat pan tilt angles were considered: a 16° tilt angle for 23°, 45° and 60° backrest inclination and a 36° tilt angle for 60° and 75° backrest inclination. Measurements of volunteer kinematics, muscle activation and interaction forces between the volunteers and the sled, among others, were acquired.Initial results show a significant reduction in maximum forward head displacement from the upright to the reclined postures (p < 0.02), with the exception of the 45° reclined posture. However, no significant difference in maximum head displacement was found between the different reclined postures (p > 0.1). Seat pan tilt angle did significantly influence forward head excursion when considering the same seatback inclination (p < 0.01).It is of great importance to investigate occupant kinematics during the pre-crash phase to understand its influence on the potential injuries that may occur with a reclined posture in the event of a collision.

Comfort Study of General Aviation Pilot Seats Based on Improved Particle Swam Algorithm (IPSO) and Support Vector Machine Regression (SVR)

Little work has been carried out to predict the comfort of aircraft seats, a component in close contact with the human body during travel. In order to more accurately predict the nonlinear and complex relationship between subjective and objective evaluations of comfort, this paper proposes a prediction method based on the Improved Particle Swarm Algorithm (IPSO) and optimized Support Vector Machine Regression (SVR). Focusing on the problems of the too-fast convergence and low accuracy of the traditional particle swarm algorithm (PSO), the improved particle swarm algorithm (IPSO) is obtained by linearly decreasing the dynamic adjustments of inertia weight ω, self-learning factor c1, and social factor c2; then, the penalty parameter C and kernel function parameter σ of SVR are optimized by the IPSO algorithm, and the comfort prediction of IPSO-SVR is established. The prediction accuracy of IPSO-SVR was 94.00%, the root mean square error RMSE was 0.37, the mean absolute value error MAE was 0.32, and the goodness of fit R2 was 0.92. The results show that the optimized IPSO-SVR prediction model can more accurately predict seat comfort under different angles and backrest tilt angles and can provide reference and research value for related industries. The results show that the optimized nonlinear prediction model of IPSO-SVR has higher accuracy, and its prediction method is feasible and generalizable, meaning it can provide a reliable basis for the prediction of seat comfort under different angles and backrest inclinations, as well as providing reference and research value for related industries.

Impact of Seat and Back Angle Settings on Seating Furniture Quality: An Experimental Study

Impact of Seat and Back Angle Settings on Seating Furniture Quality: An Experimental Study. The fundamental measure of the quality of seating furniture is seating comfort. Sitting comfort is described in the literature by the discomfort coefficient D, calculated from the pressure values and distribution measured between the human body and a sitting furniture "body support system". The work aims to experimentally verify the influence of selected anthropometric features on sitting comfort. The research was carried out on 12 people using a piezoelectric sensor mat and a model of adjustable sitting furniture. The study investigated how different seat and backrest inclination variants impact pressure distribution. The test results are the values of the contact pressures and discomfort coefficients D for nine combinations of the backrest and seat inclination related to the anthropometric characteristics of the tested group of people. The results indicate that anthropometric factors, such as body mass index (BMI) and user gender, significantly impact objective seating comfort. These findingswill help optimize the seating furniture dimensions at their design stage

Finite element modelling and biodynamic response prediction of the seated human body exposed to whole-body vibration

Biodynamic modelling of seat-occupant systems can assist in seat comfort design. A finite element (FE) model of the seated human body, including detailed modelling of the lumbar spine, was established to reflect the human response to vibration and biodynamic response of the lumbar spine under whole-body vibration (WBV). The lumbar spine model was established and validated against the in-vitro results and calculated data. The posture of the lumbar spine was adjusted according to the radiological research results, and the adjusted model was combined to establish a FE model of the seated human body. The present seated human model with backrest inclination angles of 10, 20, and 30°, validated by comparing the measured apparent mass and seat-to-lumbar spine transmissibility, was used to calculate the biodynamic response of the lumbar spine with three inclined backrests under WBV. The results showed that the model could characterise the apparent mass, seat-to-lumbar spine transmissibility, and the biodynamic response of the lumbar spine. Practitioner summary: Biodynamic models can represent dynamic characteristics of the human body exposed to vibration and assist in seat comfort design. The three-dimensional FE model of the human body can be used to explore the human response to vibration and the biodynamic response of the lumbar spine under WBV.

Adaptation and clinical application of assistive device chair for bedside sitting in acute stroke phase: two case reports

Purpose This report presents the adaptation of an assistive device chair for bedside sitting and its application in two patients with trunk control impairment in the acute stroke phase. Materials and Methods The device was built with polyvinylchloride (PVC) pipes and designed by a team of mechanical engineers and physiotherapists to maintain a prolonged sitting position with less demand from therapists. To test the device, two patients were followed up during the acute phase of stroke. Both patients underwent an early mobilization program (30 min, twice a day, for three days) with an assistive device chair for bedside sitting. Patients were evaluated using the National Institutes of Health Stroke Scale (NIHSS), Trunk Impairment Scale (TIS), and International Classification of Functioning, Disability, and Health (ICF) checklist (b: body function; d: activity and participation). Results The adaptations generated the following equipment: 1) foldable, 2) three levels of backrest inclination, and 3) a safety anterior support or an activity table. Both patients showed clinical improvement after the intervention period, with NIHSS score reduction, TIS improvement, and greater functionality and independence on the ICF framework. Conclusion The equipment with adaptations seems to be functional, easy to handle, and can potentially contribute to clinical and functional improvements in patients with trunk control deficits after stroke.

Lumbar spinal loads and lumbar muscle forces evaluation with various lumbar supports and backrest inclination angles in driving posture.

The low back pain of professional drivers could be linked to excessive lumbar load. This study aims at developing a musculoskeletal model to study the lumbar spinal loads and lumbar muscle forces of the human body in driving posture, so as to contribute to a better understanding of low back pain and to improve the design of vehicle seats. A standing musculoskeletal model, including limbs, head and neck, that can reflect several activities of daily living was established based on the Christophy spine model. The model was then validated by comparing the calculated lumbar loads and muscle forces to the experimental data in the previous studies. Referring to radiology studies, the musculoskeletal model was adjusted into different driving postures with several different lumbar supports (0, 2 and 4cm) and inclinations of the backrest (from 23° to 33°, by 2° intervals). The lumbar biomechanical load with various lumbar supports and backrest inclination angles was calculated. The results showed that the overall lumbar spinal load and lumbar muscle force with 4cm lumbar support were reduced by 11.30 and 26.24%. The lumbar spinal loads and lumbar muscle forces increased first and then decreased with the increase in backrest inclination angles from 23° to 33°. The lumbar biomechanical load varied slightly with the backrest inclination angles from 29° to 33°. There are two findings: (i) the lumbar spinal loads at the L3-L4, L4-L5 and L5-S1, and lumbar muscle forces decreased obviously with the 4cm lumbar support, while the seat cushion inclination angle was set to 10°. (ii) The recommended backrest inclination angles are 29° to 33° with a 10° seat cushion to the horizontal, which can keep a low level of the lumbar spinal loads and lumbar muscle forces. This study could be used to explain the association between drivers' sitting posture and the lumbar load change, and provide a reference for the prevention of low back pain.

Three-Dimensional Biomechanical Modeling for Sitting Contact Stress Analysis.

This paper proposes a three-dimensional biomechanical model of the upper body and analyzes the interaction between the upper body and aircraft seat backrest for different sitting postures and backrest recline angles. The reclined sitting postures of the upper body are defined based on the available spine biomechanical data and the multibody inverse kinematics method. The contact loadings on each contacted spine segment are calculated based on the Newton-Euler dynamic formulation. The backrest contact pressure distribution is simulated using the contact stress theory based on the calculated forces on the backrest. The resultant force and pressure distribution show how the backrest inclination and lateral bending of the trunk affect the backrest loading and contact condition. The simulation results are compared to the experimental measurement for validation, and a good correspondence is found. The parameters, including the average and maximum pressure, and pressure standard deviation based on the pressure distribution, are also compared, and the maximum simulation error is 11.5% on the average pressure. Limitations of the model are discussed. The model proposed in this paper can analyze more posture cases than previous studies that focused on the two-dimensional scenarios. The loading and pressure prediction model can be applied for backrest design evaluation and facilitate seat design optimization.

Effects of backrest and seat-pan inclination of tractor seat on biomechanical characteristics of lumbar, abdomen, leg and spine

Seat is a direct human-machine interaction component between the tractor and driver, and thus its reasonable parameter design is of great significance for preventing occupational diseases and improving driving comfort, safety and operation efficiency. In this study, a biomechanical model of seat-driver system was established with the AnyBody biomechanical software. The activities of the lumbar, abdominal and leg muscles and the load of the spine of the driver were used as indicators for quantitative simulation analysis of the inclination of backrest and seat-pan. The results reveal that the optimal range of backrest inclination angle is 3–15°, which contributes to the lowest muscle activity and spinal load of the driver. As for the seat-pan inclination, the activities of lumbar and abdominal muscles and the spinal load generally show slight fluctuations with increasing inclination angle, but there are complex changes in the activities of leg muscles, and the seat-pan inclination angle of 5–16° was determined as the optimal range for better overall driving comfort.

Modelling and analysis of coupled vibration of human body in the sagittal and coronal planes exposed to vertical, lateral and roll vibrations and the comparison with modal test

To study the coupled vibration of the seated human body in the sagittal plane and coronal plane exposed to lateral, vertical and roll excitations, a seated human body model consisting of abdomen, pelvis, two thighs, upper torso (including the shoulders, thorax, arms), and head (including neck) was proposed. The model was calibrated with the apparent masses measured in 0.5–20 Hz and proved to be applicable for subjects of different weights and heights and different excitation magnitudes in combined lateral, vertical and roll directions. This model was also potentially suitable for different backrest inclinations. Three modes of the human body associated with the resonances in the measured apparent masses were observed by means of modal analysis. The first and second modes with modal frequencies of 1.16 and 2.53 Hz, respectively, featured the vibration of the human body in the coronal plane. The former was dominated by the lateral and roll vibrations of the upper torso and head, while the latter by the lateral whole-body vibration accompanied by roll of the upper torso and head. The third mode with a modal frequency of 5.28 Hz featured the vibration of the human body in the sagittal plane. This mode exhibited a combination of the vertical vibration of the entire body and a bending motion of the upper body arising from the pitch of pelvis. These three modes showed good consistency with those identified in the modal test. The vibration coupling between the sagittal plane and coronal plane associated with these three modes was not significant. This model can be used to calculate the ride vibration and comfort of passengers in rail vehicles.

Dynamic interaction between the human body and the seat during vertical vibration: effect of inclination of the seat pan and the backrest on seat transmissibilities

Seat inclinations at the seat pan and backrest may affect the sitting comfort. This study was designed to quantify the effect of inclination of a seat pan (0°, 10°, and 20°) and backrest (0°, 15°, and 30°), either foamed or rigid, on the transmissibilities measured at the seat pan and backrest. Seat transmissibilities were measured with fifteen subjects exposed to vertical random vibration between 1 and 15 Hz at 0.5 ms−2 r.m.s. It was found the resonance frequencies in transmissibilities measured at the seat pan and backrest increased with increasing the backrest inclination but were not affected by the seat pan angle. Increasing the foamed backrest inclination increased the peak transmissibilities. Inclination of the rigid seat pan or the rigid backrest reduced the transmissibilities measured at the backrest or the seat pan, respectively. Transmissibilities were more significantly affected by the backrest inclination than the seat pan inclination. Practitioner summary: Seat inclinations may alter the human-seat dynamic interaction and hence the riding discomfort. This study was designed to quantify the effect of inclined seats, either foamed or rigid, on the transmissibilities. It was found the backrest angle affected the transmissibilities more strongly than the seat pan angle.

Effect of Seat Backrest Inclination on the Muscular Pattern and Biomechanical Parameters of the Sit-to-Stand.

Objectives: The sit-to-stand (STS) transfer mobilizes an extended part of the kinematic chain throughout a postural phase characterized by a flexion of the trunk and a focal phase consisting of a whole-body extension. The aim of this study was to analyze the variations of the global muscular pattern and the biomechanical parameters in both phases, in relation with seat backrest inclination.Methods: Fifteen participants were asked to stand up from a seat with 5 backrest inclination settings and at 2 execution speeds. The ground reaction forces and the activity levels of fifteen muscles of the trunk and lower limbs were investigated.Results: Backrest-induced modifications were mainly observed in the postural phase: inclining the backrest backward increased the phase duration and the activity level of the sternocleidomastoideus and the rectus abdominis, while it reduced the activity of the tibialis anterior. It also allowed for an increased maximal anteroposterior velocity of the body center of mass. Higher execution speed led to increased and earlier muscular activities of many trunk and lower limbs muscles, predominantly in the postural phase.Discussion: Taken together, these results suggest that a greater backrest inclination increases the demand in the postural phase due to the increase of the upper body gravity torque about the ischial tuberosities, and requires an adaptation of muscular activity levels and timing, but with the same overall pattern. The kinetic energy gained during the longer excursion of the trunk may also require less activation of the lower limbs muscles involved in the generation of propulsive forces of the body.

Mechanism associated with the effect of backrest inclination on biodynamic responses of the human body sitting on a rigid seat exposed to vertical vibration

Drivers and passengers in vehicles usually sit with their backs supported with a backrest. Sitting with a backrest in vehicles can affect the biodynamic responses of the human body and sitting comfort. Understanding the effect of back support on the biodynamic responses can assist in improving vehicle ride comfort. This study was designed to identify the mechanism associated with the effect of backrest inclination on the apparent masses measured at the seat pan and the backrest during vertical whole-body vibration based on experiment and modelling. The apparent masses of 14 subjects sitting on a rigid seat with various backrest inclination angles of 0º, 10º, 20º and 30º during exposure to vertical vibration at 0.5 ms−2 r.m.s. between 0.5 and 20 Hz were measured at the seat pan and the backrest. A biodynamic model previously developed by the authors was updated to include the interaction between the back of the human body and the seat backrest to represent the measured responses for each subject . The effect of backrest inclination on the biodynamic response and on the model parameters were identified. It was found that as the backrest inclination increased, the resonance frequency in the vertical in-line apparent mass measured at the seat pan increased, and the resonance frequency in the fore-and-aft cross-axis apparent mass measured at the seat pan decreased, while the resonance frequency in the normal apparent mass measured at the backrest was not changed. Statistical analysis found that with increasing backrest inclination, the vertical stiffness of the soft tissues at the ischial tuberosities, middle thighs and front thighs, as well as the stiffness at the lumbar joint tended to decrease, while the fore-and-aft stiffness and the damping of the soft tissues at the ischial tuberosities tended to increase. Analysis with the model of the median apparent masses of the 14 subjects disclosed the vibration modes of the body containing the fore-and-aft sliding motion of the pelvis and thighs, the vertical motion of the body on the soft tissue beneath the ischial tuberosities and thighs, and the bending motion of the spine. With the vertical backrest, the fore-and-aft and vertical motions of the pelvis and thighs were coupled together. As the backrest inclination increased, this coupling decreased and the coupling between the vertical motion of the pelvis and the bending of the spine increased.

Sit-to-Stand Muscular Activity for Different Seat Backrest Inclination Levels and Execution Speeds

The sit-to-stand transfer can be separated into a postural phase (trunk flexion) and a focal phase (whole-body extension). The aim of this study was to analyze the as yet little known whole-body muscular activity characterizing each phase of this task and its variations with backrest inclination and execution speed. Fifteen muscles of the trunk and lower limbs of 10 participants were investigated using surface EMG. Results showed that backrest-induced modifications were mostly confined to the postural phase: reclining the backrest increased its duration and the activity level of the sternocleidomastoideus, the rectus and obliquus externus abdominis, and the semitendinosus. Speed-induced variations were also predominant during the postural phase, which was shortened with an increased activity of most muscles at maximal speed.

Musculoskeletal computational analysis on muscle mechanical characteristics of drivers' lumbar vertebras and legs in different sitting postures.

Using computer-aided engineering (CAE) in the concept design stage of automobiles has become a hotspot in human factor engineering research. Based on human musculoskeletal biomechanical computational software, a seated human-body musculoskeletal model was built to describe the natural sitting posture of a driver. The interaction between the driver and car in various combinations of seat-pan/back-rest inclination angles was analyzed using an inverse-dynamics approach. In order to find out the "most comfortable" driving posture of the seat-pan/back-rest, the effect of seat-pan/back-rest inclination angles on the muscle activity degree, and the intradiscal L4-L5 compression force were investigated. The results showed that a much larger back-rest inclination angle, approximately 15°, and a slight backward seat-pan, about 7°, may relieve muscle fatigue and provide more comfort while driving. Subsequently, according to the findings above, a preliminary driving-comfort function was constructed.

Adaptive Automobile Seat Design Based on Ergonomic Principle

In order to improve the comfort of automobile seat, it is necessary to analyse and study the design method of automobile seat. A design method of adaptive automobile seat based on ergonomics principle is proposed. The height, width, depth, backrest, seat inclination and backrest inclination of automobile seat as well as the sitting posture physiology and body pressure distribution of human body are analysed. The frame of automobile seat is designed by using aluminium alloy in PROE software, the size of the energy absorption of headrest, cushion and seat are determined according to national regulations. By analyzing the back force, pillow force, seat belt force and seat belt locking, the force of automobile seat, the strength of back, head pillow and seat cushion of automobile seat are designed and the design of adaptive automobile seat is completed. The experimental results show that the proposed method has high comfort, low processing cost and high production efficiency.

Comfortable leg splay of mid-sized males in automotive seats

Many factors affect the comfort of automotive seats including pressure distribution, vibration, temperature, and backrest inclination. However, one aspect of seating that has not been well studied is leg splay; splay is a rotation at the hips which causes the knees to move outward. The work presented here identified the ranges of “comfortable” splay in different styles of seats and related changes in seating pressure due to leg splay. Sixteen midsized male participants were tested in six seats: a flat control, three mid-sized sedan, a sports car, and a pickup truck. Participants sat with two leg conditions: 1) shoulder width apart and 2) rotating their legs to splay to a self-identified, comfortable position. For each test, the participant placed his left leg on a foot support and right leg on a depressible pedal to mimic a driving position. In each posture, leg angle and seat pan pressures were collected. Of the seats tested, the flat wooden seat had the highest possible splay (24.5°). The three sedan seats had similar splay angles (16.1–18.5°). The lowest splay values were in the sports car seat (8.96°) and truck seat (7.46°). This reduction in splay was attributed to the more aggressive bolsters in the sports car and a higher seat design position in the pickup truck seat. Following participant splay the pressures in the seat bolsters increased while the pressure in the left thigh and left buttocks regions decreased. By determining the comfortable ranges of splay and how pressure distribution is affected, seat designers and automobile manufacturers can use these data when evaluating seat designs and occupant positioning.