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second row of a vehicle
Xuguang Wang, Thomas Robert, Jian Wan, Ksenia Kozak, Nanxin Wang
To cite this version:
Xuguang Wang, Thomas Robert, Jian Wan, Ksenia Kozak, Nanxin Wang. Dynamic motion analysis
when getting in and out of the second row of a vehicle. 3rd International Symposium on digital human
modelling, May 2014, TOKYO, Japan. 7 p, �10.13140/2.1.3700.2564�. �hal-01743663�
Dynamic motion analysis when getting in and out of the
second row of a vehicle
Wang X.†, Robert T.†, Wan J. ‡, Kozak K. ‡, Wang N. ‡
† Université de Lyon, F-69622, Lyon, France, IFSTTAR, UMR_T9406, LBMC, Université Lyon1 ‡ FORD, Dearborn, Michigan, USA
Abstract
The 2nd row ingress and egress motions were analyzed from the data collected by FORD R&A for a better understanding of perceived discomfort. Fourteen females and males participated in the experiment for testing seven different 2nd row configurations. A detailed description of motion sequences and contacts between participant and vehicle was provided. The effects of participant group (three groups by stature and two by BMI) and test configuration (seven configurations) on discomfort, maximum joint torques developed at the lower limbs were analyzed. Our findings support the general requirement that the occupants should be able to enter and exit from the vehicle quickly and comfortably without any awkward postures, high physical efforts and hitting of body parts on the vehicle components. Particular attention should be paid to the seat height to ground so that it is not too high for short occupants and too low for tall occupants to avoid high physical efforts when sitting down and standing up. The longitudinal distance of the frontal seat back to the seat is also a critical parameter. It should be long enough to avoid knee collision especially for tall occupants.
Keywords: 2nd row, ingress, egress, motion analysis, dynamics, discomfort.
1. Introduction
The ease of getting in and out of a vehicle either for drivers or for passengers is one of the ergonomics issues that catch the attention of many automotive manufacturers. It represents the first physical contact of the customer with the vehicle. It is important to ensure a pleasant perception while interacting with the vehicle. Understanding and being able to assess vehicle ingress/egress performance early in a design process is therefore critical to a successful vehicle program development.
Many studies focused on driver’s ingress and egress motions but few on the vehicle accessibility of other occupants than drivers. For instance, Ait El Menceur et al. (2009) presented a panorama of ingress/egress movement strategies adopted by young and elderly drivers with and without prosthesis (es) within a national French research project named Handiman. Within the same project, Chateauroux (2009) focused more on the analysis of the interactions between drivers and car for identifying the geometric constraints imposed on the body for both ingress and egress motions (see also Chateauroux and Wang 2010). Andreoni et al. (2004) investigated the kinematics of the driver’s
head and the trunk when getting in and out of a medium-sized car. Recently, Causse et al (2012) performed a parametric study of the effects of roof height and sill width on the driver’s ingress and egress movements. They focused the analysis of body positions at some keyframes. Robert et al (2013) extended to the analysis of the joint torques at the lower limb from the motion data collected in Causse et al. However, only very few investigations were performed for ingress and egress of passengers. Petzäll (1995) tried to find suitable dimensions of entrance of taxis for elderly and disabled passengers using a multi-adjustable mock-up. Giacomin and Quattrocolo (1997) performed a parametric study of passengers when entering and exiting the rear seat of an automobile. They found that the roof rail and front seat were the two troublesome elements. Though motions were captured, detailed motion analysis was not performed. Effects of participants’ anthropometry were not analyzed.
In this paper, the movements of the 2nd row ingress and egress were analyzed with help of a digital human model (RPx, a motion reconstruction and simulation tool developed at IFSTTAR, Monnier et al, 2009) from the data collected by Ford R&A.
2 Both kinematic and dynamic characteristics of
motions will be presented.
2. Materials and Methods 2.1.Participants
7 males and 7 females participated in the experiment. Participants were Ford Motor Company employees. Subjects were excluded if they had any medical conditions that affected their motion. According to stature, three groups are defined:
• 5 short persons with stature<1620 mm (S)
• 4 averaged-height persons with 1620 mm <=stature<=1760 mm (A)
• 5 tall persons with stature>1750 mm (T)
Two groups are defined according to body mass index (BMI):
• 8 normal persons with BMI<25 kg/m²
• 6 over-weighted persons with BMI>=25 kg/m²
2.2.Experimental conditions
A multi-adjustable 2nd row mock-up was used, simulating seven different test configurations, covering a large range of 2nd row seat designs. Their main characteristics are summarized in Table 1.
Table 1: Test configurations. SgRP* -Ground Height (mm) SgRP -Floor Height (mm) SgRP-Roof Height (mm) Cushion – FSB** Distance (mm) C01 721 399 817 372 C02 566 332 772 156 C03 787 396 822 228 C04 778 319 793 316 C05 554 305 781 265 C06 730 349 785 217 C07 636 323 767 272
*SgRP, seat reference point, ** FSB denotes frontal seat back
A Vicon T40 motion capture system with 14 cameras was used for motion capture at 100 Hz. External contact forces were measured at 1000 Hz by three AMTI force plates placed on the ground, the floor and under the seat. One strain gauge was placed at the mounting structure of the frontal seat, allowing an estimation of contact between body and frontal seat back (FSB).
Trial order of test configurations was randomized for avoiding order effect. For each configuration, participants were instructed to get in and out naturally. After practicing two times, the full motion of getting in and out was recorded on the 3rd time for each test configuration. Afterwards, they were asked to rate each test configuration in terms of perceived discomfort using the category partition scale CP50 (Shen and Pearson, 1997).
2.3.Data processing
The motions were reconstructed kinematically by Ford and dynamically by RPx, a Matlab-based motion reconstruction and simulation software package developed at IFSTTAR. Both motion capture and force contact measurements were re-sampled at 50 Hz. An inverse dynamics procedure was used to compute the net joint torques developed during these motions. The procedure is based on a Newton-Euler recursive approach using the homogeneous (4x4) matrices formalism (Doriot and Chèze, 2004). 3-D inertial parameters of the 16 rigid bodies considered were estimated from regressions (Dumas et al., 2007).
For the sake of comparison between trials and subjects, motor torques were normalized by Body Height × Body Weight and time normalized over 101 frames (0 to 100 % of the motion). Then, in order to facilitate data interpretation and to compare them across degrees of freedom, motor torques were expressed as a percentage of the maximal torque that can be developed for the considered degree of freedom. See Robert et al. (2014) for more details.
2.4.Statistical analysis
Discomfort scores, motion durations, peak joint torques were analysed using a two-way ANOVA for investigating effects of test configuration and subject group. As three participant groups could be formed according to gender, stature and BMI, three separate ANOVAs were performed for each response to be analysed.
3. Results
3.1.Discomfort ratings
The effects of gender/stature group and test configuration and their interactions were analyzed. No significant difference in rating was observed between males and females and between three stature groups and between two BMI groups, suggesting that perceived discomfort was not very much affected by anthropometry. As expected, there were significant differences between test configurations (Figure 1). In particular, C01 and C02 were significantly different from the five others. C01 had the lowest discomfort and C02 the highest. If we take C01 as the reference configuration, the following preliminary observations can be made based on the main differences in package dimensions:
• C02 had the highest discomfort rating probably due to its short distance between frontal seat back (FSB) and seat and to low seat height. C02 had the shortest longitudinal distances (in x) between seat cushion and FSB. It also had quite a low seat height to ground. There is a high probability of collision between occupants’ lower legs and FSB.
• C03 and C04 were rated right behind C02 in terms of discomfort. Their seat heights to ground are much higher than others.
• C05 had quite similar discomfort score with respect to C03 and C04. It had the lowest seat height. Compared to C02, its space in x was much larger.
• C06 was quite narrow, but had a high seat height.
• C07 had the lowest roof. But it seems to have no effect on discomfort.
Possible effects of the interaction between seat height and distance cushion-FSB may exist. A narrow longitudinal space with a low seat height is probably worse than a narrow longitudinal space with a high seat height. A low seat height requires more space for the legs.
The interactions between test configuration and participant group by stature or by BMI were also investigated. Only a significant effect of the interaction between stature group and test configuration was found. From Figure 5, one can see that the short participants (S) were clearly different from tall (T) and average height (A) groups for C03, C04 and C05. C03 and C04 had the highest seat height to ground whereas C05 had the lowest seat height.
Figure 1: Means and Fisher LSD intervals of the CP-50 ratings by test configuration.
Figure 2: Effects of interaction between test configuration and stature group on CP-50 ratings
3.2.Motion description
With help of the recorded external contact forces by the three force plates (floor, ground and seat) and the velocity profiles of the left and right feet and the head, different key frames mainly corresponding to the instants of contacts between body and different components of the mock-up were identified. From visual inspection on the reconstructed motions, similar ingress and egress motion sequences were observed for most of trials, as illustrated in Figure 3. For a very few number of trials, the typical motion sequence for both ingress and egress was not respected. For example, for one trial, a participant pressed on the seat cushion before raising the right foot. For another trial, a participant got into the vehicle (two feet on the floor) before sitting down.
Motion durations for ingress and egress are defined as the time from RFLeavingGrd (right foot leaving from the ground) to LFArrivingFl (left foot arriving at the floor) and from LFLeavingFl (left foot leaving from the floor) to RFArrivingGr (Right foot arriving at the ground) respectively. Ingress and egress motion durations were highly positively correlated with a Pearson’s correlation coefficient r=0.75. Their means are respectively 2.758 and 3.282 seconds. Egress motion was significantly longer than ingress. A two way ANOVA was performed for testing possible effects of participant group and test configuration. Only test configuration was found to affect both ingress and egress motion durations. C2 had the longest ingress and egress duration.
RF leaving the ground (RFLeavingGrd)
RF getting in contact with the floor (StartFlContact)
Start of seat contact (StartStCont)
LF leaving the ground (EndGrdCont)
LF arriving at the floor (LFArrivingFL)
Seated
C01 C02 C03 C04 C05 C06 C07 Means and 95.0 Percent LSD Intervals
Config 0 10 20 30 40 R a ti n g s Interaction Plot Config 0 10 20 30 40 R a ti n g s C01 C02 C03 C04 C05 C06 C07 Group A S T
4
LF leaving the floor (LFLeavingFL)
LF getting in contact with the ground (StartGrCont2)
End of seat contact (EndStCont)
RF leaving the floor (EndFlCont))
RF arriving at the ground (RFArrivingGrd)
Figure 3: Typical ingress and egress motion sequences
3.3.Contacts with vehicle
Apart from the contacts between the body and vehicle required for ingress and egress, such as contacts between the feet and floor, between the buttock and the seat, a high variety of hand and other body vehicle contacts were observed from a visual inspection of reconstructed motions and with help of the strain gauge mounted on the frontal seat back:
• No hand contact
• One hand, both hands, one then another hand contact with the frontal seat back (FSB), seat (cushion, back) and door
• Knee hitting on the frontal seat back
• Etc…
The FSB strain gauge was intended to give an indication of contact force between the body and FSB. Its maximum measurement reached to 186N during ingress and to 216 N during egress. Using the threshold of the maximum FSB force Fmax_FSB > 70 N during motion for effective contacts, 40 out of 98 trials were observed for having contact during ingress whereas only 28 for egress, showing that more FSB contacts occurred during ingress than during egress. Four participants had a FSB contact force over 70N for more than 6 test configurations during ingress: three short females with a stature less than 1620mm and a tall and overweight male with a BMI > 30. During egress, five participants had a FSB contact force over 70N for more than 4 test configurations, among them two were tall (stature > 179 cm) and two over-weighted with BMI>27.5. It seems that FSB contact occurred more frequently for tall and
heavy persons with a high BMI during egress and short participants during ingress. This is confirmed by the contingency table (Table 2 and Table 3) crossing participant groups according to BMI and Stature. 52.4% of the trials by the over-weighted participants had a FSB contact force over 70N during egress and 57.1% for the short participants during ingress.
Table 2: Contingency table crossing participant groups and test configuration for Fmax_FSB > 70N during ingress Grp C01 C02 C03 C04 C05 C06 C07 All (%) N 3 6 3 3 2 3 2 22 (39.3) O 1 5 3 2 3 1 3 18 (42.9) S 3 4 3 3 2 3 2 20 (57.1) A 0 4 1 1 2 0 2 10 (35.7) T 1 3 2 1 1 1 1 10 (28.6) All 4 11 6 5 5 4 5 40 (40.8)
Table 3: Contingency table crossing participant groups and test configuration for Fmax_FSB > 70N during egress Grp C01 C02 C03 C04 C05 C06 C09 All (%) N 1 2 1 1 0 1 0 6 (10.7) O 1 4 5 2 4 3 3 22 (52.4) S 1 1 1 1 0 0 0 4 (11.4) A 0 2 3 0 2 1 2 10 (35.7) T 1 3 2 2 2 3 1 14 (40) All 2 6 6 3 4 4 3 28 (28.6) 3.4.Joint torque
Thanks to the external contact forces measured by the ground and floor force plates, the joint torques of both right and left low limbs could be estimated from RFLeavingGrd (Right foot leaving the ground) to LFArrivingFL (Left foot arriving at the floor) during ingress and from LFLeavingFL (Left foot leaving the floor) to RFArrivingGrd (Right foot arriving at the ground) during egress. Joint torque profile is quite similar to what we observed for drivers’ ingress and egress motions of the 1st row (Robert et al, 2013). To illustrate physical effort required for getting in and out, left knee extension torque is selected as a high extension torque may be involved during both ingress and egress. Figure 4 shows the left knee flexion
extension torque profile for the group of four average height subjects for C01. Peak knee extension torque appeared at about 40% of normalized time for ingress and at about 60% for egress.
(a) (b)
Figure 4: Mean (thick line) ± one standard deviation (shaded area) of the normalized left knee flexion-extension torques (in %) across the four average height subjects for C01 during ingress (a) and egress (b)
Peak knee extension torque was significantly affected by test configuration for both ingress and egress. C02 and C05 required significantly higher efforts than others (see Figure 5), knowing that C02 and C05 are the two configurations which had the lowest seat height. It was also significantly affected by stature group. As expected, tall participants exerted higher knee extension torque.
Figure 5: Means and Fisher’s LSD (Least Significant Difference) intervals of the normalized peak left knee extension torque in absolute during ingress according to test configuration and stature group
Figure 6: Interaction between participant group by BMI (Normal versus Over-weighted) and test configuration for the normalized peak left knee extension torque during egress
As joint torques are normalized with weight*stature, effects of anthropometric dimensions are much reduced, in particular the body weight. Slight but significant effect of BMI group was observed. Interestingly, a significant interaction between BMI group and test configuration was also observed during egress (Figure 6). Much higher knee extension torque was developed for C02 and C05, the two lowest seat height configurations.
4. Discussion
In this study, the 2nd row ingress and egress motions were analyzed for a better understanding of perceived discomfort. The main observations are listed as follows:
• There were significant differences in perceived discomfort between test configurations. In particular, C01 and C02 were significantly different from the others. C01 had the lowest discomfort and C02 the highest. C02 had the narrowest space between the 2nd row seat and frontal seat back. No significant differences in discomfort rating between three stature groups and between two BMI groups were observed. Contrary to the findings by Giacomin and Quattrocolo (1997), the roof height was not found critical in this study as the configuration with the lowest SgRP-roof height C07 was not badly rated. One possible explaination could be that the the roof of the test configurations in this study were not low enough, because they all had a roof heigher than the base configuration tested by Giacomin and Quattrocolo with a SgRP-roof height of 764mm.
• Almost same motion sequences were observed in terms of feet and buttock contacts with vehicle irrespective of participant groups and test configurations. Ingress and egress motion durations were respectively 2.758 and 3.282 seconds on average. They were not affected by
Ingress C01 C02 C03 C04 C05 C06 C07 Config 29 39 49 59 69 L e ft K n e e _ fl e x A S T Ingress Group_S 37 41 45 49 53 57 61 L e ft K n e e _ fl e x Interaction Plot Config 22 32 42 52 62 72 L e ft K n e e _ fle x C01 C02 C03 C04 C05 C06 C07 Group_BMI N O
6 participant group but only by test
configuration. C02 had the longest duration for both ingress and egress.
• A high variety of hand contacts with frontal seat back and seat were observed. Proportionally, more short persons tended to touch the FSB when getting in, whereas when getting out, more over-weighted persons needed to get in contact with FSB. Hand contacts could be used for reducing joint torques at the lower limb.
• Significant differences in joint torque between seven test configurations were found mainly on the left side of hip and knee joint axes during ingress and egress. Higher joint torque was developed for the low seat configurations C02 and C05. Taller participants developed higher joint torque than those in the two other stature groups.
One of main motivations was to understand possible causes of discomfort with help of motion analysis. Basically, our findings support the general requirement (Bhise, 2012) that the occupants should be able to enter and exit from the vehicle quickly and comfortably without any awkward postures, high physical efforts and hitting of body parts on the vehicle components. Table 4 gives the coefficients of correlation between discomfort rating, ingress motion time (TimeIng), egress motion time (TimeEgr), normalized peak left knee flexion extension torque during ingress (LKFlexIng) and egress (LKflexEgr). Interestingly, discomfort rating is strongly correlated with ingress and egress motion durations. The longer the motion duration is, the higher the discomfort. Rating is also significantly correlated with peak left knee joint torques. The higher joint torque is, the higher the discomfort.
Table 4: Coefficients of correlation between discomfort rating, ingress motion time (TimeIng), egress motion time (TimeEgr), normalized peak left knee flexion extension torque during ingress (LKFlexIng) and egress (LKflexEgr)
TimeIng TimeEgr LKflexIng LKflexEgr
Ratings 0.3696 0.4438 0.2418 0.4172
TimeIng 0.7493 0.2057 0.3481
TimeEgr 0.1224 0.3776
LkflexIng 0.5323
In the present study, only 14 subjects participated in the experiment. Due to high variability in discomfort ratings, it is certainly difficult to generalize the findings on the effects of subject group. In addition to the small sample of participants in this study, there are also some limitations we would like to point out. The first is
related to the classical inverse dynamic method use in this study. In particular, it requires the measurement of all contact loads between the subject and its environment. It implies a large experimental effort to equip as many mock-up parts as possible with load sensors. However, one cannot handle all possible contact situations. Specifically in this study, the hand contact forces with FSB and seat were not fully measured, limiting our investigation of joint torque only on the lower limbs. For the same reason, the interpretation of the role of hand contacts was difficult. The second is that it is difficult to compare physical efforts between participants with different physical capacity. In this study, only a constant static joint strength from an average male was used to normalize joint torque developed during motion. The third limitation is that only seven configurations were compared without a systematic parametric study. In order to know the effect of critical design parameters and their interaction, a parametric study is needed.
5. Conclusion
The ingress and egress movements of the 2nd row were analyzed from the data collected at Ford R&A for a better understanding of discomfort. Our findings support the general requirement (Bhise, 2012) that the occupants should be able to enter and exit from the vehicle quickly and comfortably without any awkward postures, high physical efforts and hitting of body parts on the vehicle components. Particular attention should be paid to the seat height so that it is not too high for short occupants and too low for tall occupants to avoid high physical efforts when sitting down and standing up. The longitudinal distance of the frontal seat back to the seat is also a critical parameter. It should be long enough to avoid knee collision especially for tall occupants.
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