Comfort improvement and kinetosis reduction by the use of a pendulum type child travel seat

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The current study analyses the effect of using a pendulum type tilting child seat on the comfort improvement and the reduction of kinetosis (motion sickness) among children traveling in an automobile.

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Nội dung Text: Comfort improvement and kinetosis reduction by the use of a pendulum type child travel seat

International Journal of Mechanical Engineering and Technology (IJMET) Volume 10, Issue 03, March 2019, pp. 178-187. Article ID: IJMET_10_03_018 Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=10&IType=3 ISSN Print: 0976-6340 and ISSN Online: 0976-6359 © IAEME Publication Scopus Indexed COMFORT IMPROVEMENT AND KINETOSIS REDUCTION BY THE USE OF A PENDULUM TYPE CHILD TRAVEL SEAT N. L. Pavlov Department of Combustion Engines, Automobile Engineering and Transport, Faculty of Transport, Technical University of Sofia, 8 Kliment Ohridski Blvd., 1000 Sofia, Bulgaria E. E. Sokolov Department of Combustion Engines, Automobile Engineering and Transport, Faculty of Transport, Technical University of Sofia, 8 Kliment Ohridski Blvd., 1000 Sofia, Bulgaria M. H. Peychev Department of Combustion Engines, Automobile Engineering and Transport, Faculty of Transport, Technical University of Sofia, 8 Kliment Ohridski Blvd., 1000 Sofia, Bulgaria D. I. Dacova Department of Combustion Engines, Automobile Engineering and Transport, Faculty of Transport, Technical University of Sofia, 8 Kliment Ohridski Blvd., 1000 Sofia, Bulgaria L. P. Kunchev Department of Combustion Engines, Automobile Engineering and Transport, Faculty of Transport, Technical University of Sofia, 8 Kliment Ohridski Blvd., 1000 Sofia, Bulgaria ABSTRACT The current study analyses the effect of using a pendulum type tilting child seat on the comfort improvement and the reduction of kinetosis (motion sickness) among children traveling in an automobile. Road tests with registration of the accelerations for a conventional child seat and a pendulum type tilting child seat are performed. Results for the spectral densities of the linear accelerations along the orthogonal axes are presented. The quadratic means of accelerations acting on both seats are calculated and compared. Results for the motion sickness dose value are obtained. A http://www.iaeme.com/IJMET/index.asp 178 editor@iaeme.com
N. L. Pavlov, E. E. Sokolov, M. H. Peychev, D. I. Dacova and L. P. Kunchev calculation for the percent of people who can vomit is made and the results for both seats – conventional and tilting, are compared. Keywords: Child seat, kinetosis, comfort, acceleration and road testing. Cite this Article: N. L. Pavlov, E. E. Sokolov, M. H. Peychev, D. I. Dacova and L. P. Kunchev, Comfort Improvement and Kinetosis Reduction by the Use of a Pendulum Type Child Travel Seat, International Journal of Mechanical Engineering and Technology, 10(3), 2019, pp. 178-187. http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=10&IType=3 1. INTRODUCTION When travelling with different types of transport symptoms like nausea vomiting, headache etc. can sometimes occur among passengers. These are typical symptoms of kinetosis, also known as motion sickness. It is caused by a number of factors more or less convenient for measurement and evaluation [1]. One of these factors is the value of acceleration acting on the human organism, mainly in the lower frequencies of external impacts. While estimating the impact of vibrations on kinetosis generation wide attention is paid to the ones with frequencies from 0.1 to 4 Hz and especially to the ones with frequencies under 0.5 Hz [1, 2]. Car suspensions are designed to damp vibration in vertical direction. With frequent speed changes and cornering horizontal vibrations which depend mainly on the traffic situation, the road plan and the vehicle speed appear. In order to reduce the corners harmful impact on human organism tilting car body is used in railway transport for curve motion. No such practice is present in automobiles. It is easier to tilt only the seats or only the head of the passenger [3, 4]. This however is related to certain problems concerning the seats positioning and the passengers cosiness. It is well known that children are more susceptible to the irritations causing kinetosis [5]. That is why the authors propose a special design of a pendulum type tilting child seat. It is a passive one, i.e. it tilts under the impact of centrifugal force, generated during cornering. The aim of this article is to study the indicators of comfort for a child travelling on a conventional seat and on a pendulum type tilting seat. Motion sickness dose value and the percent of people who may vomit will be determined. The results obtained for both seats will be compared. 2. METHODOLOGY AND EQUIPMENT The experiments are conducted on a typical mountain road with a large number of turns. The chosen route from Sofia to Mezdra is shown on fig. 1. http://www.iaeme.com/IJMET/index.asp 179 editor@iaeme.com
Comfort Improvement and Kinetosis Reduction by The Use of a Pendulum Type Child Travel Seat Figure 1 Testing route The designed pendulum type tilting seat, shown in fig. 2, is mounted on the rear seat of a road vehicle (fig. 3). A conventional child seat is also mounted in the vehicle. Test dummies with mass and geometric parameters equal to the mass and geometric parameters of children are mounted on both seats. Three axial accelerometers are mounted on the seating surfaces bellow the dummies. Data collection is done through a data acquisition device (DAQ). The DAQ converts analog signals from accelerometers to digital and submits them to a mobile computer. So, the data is recorded on the hard disc drive of the computer. Figure 2 Pendulum type tilting child travel seat [6] http://www.iaeme.com/IJMET/index.asp 180 editor@iaeme.com
N. L. Pavlov, E. E. Sokolov, M. H. Peychev, D. I. Dacova and L. P. Kunchev Figure 3 Positioning of the conventional and the tilting seat in vehicle 3. RESULTS The accelerations registered for the conventional and for the tilting seat along the x, y and z axes are shown in fig.4-9. Figure 4 Longitudinal acceleration measured on conventional child seat http://www.iaeme.com/IJMET/index.asp 181 editor@iaeme.com
Comfort Improvement and Kinetosis Reduction by The Use of a Pendulum Type Child Travel Seat Figure 5 Longitudinal acceleration measured on tilting child seat Figure 6 Lateral acceleration measured on conventional child seat Figure 7 Lateral acceleration measured on tilting child seat http://www.iaeme.com/IJMET/index.asp 182 editor@iaeme.com
N. L. Pavlov, E. E. Sokolov, M. H. Peychev, D. I. Dacova and L. P. Kunchev Figure 8 Vertical acceleration measured on conventional child seat Figure 9 Vertical acceleration measured on tilting child seat The accelerations power spectral densities (PSD), determined from the recorded acceleration values, are shown in fig. 10-12. Figure 10 Power spectral densities of the longitudinal accelerations on conventional (red solid line) and on tilting seat (black dashed line) http://www.iaeme.com/IJMET/index.asp 183 editor@iaeme.com
Comfort Improvement and Kinetosis Reduction by The Use of a Pendulum Type Child Travel Seat Figure 11 Power spectral densities of the lateral accelerations on conventional (red solid line) and on tilting seat (black dashed line) Figure 12 Power spectral densities of the vertical accelerations on conventional (red solid line) and on tilting seat (black dashed line) The results analysis for the accelerations power spectral densities shows that they are almost equal for the x axis (Sax). That is easy to explain as the vibrations for both seats are determined by the vehicle acceleration and deceleration. The minor differences noticeable in the power spectral densities and the differences in the acceleration recordings (fig. 4 and 5) are due to clearance in the tilting seat cylindrical joint and the different mount of both seats. The accelerations power spectral densities along the y (Say) and the z (Saz) axes differ significantly. This is a result from the tilt of the pendulum seat due to the centrifugal force generated during cornering. As a result of the tilt the lateral accelerations drop but the ones acting on the child vertical axis increase. The biggest change is noticed in the lower frequencies which are the main reason for kinetosis (motion sickness). Root mean square (r.m.s.) acceleration is the most common index for the evaluation of the vibration intensity. Mathematically, r.m.s. acceleration can be expressed as [2]: http://www.iaeme.com/IJMET/index.asp 184 editor@iaeme.com
N. L. Pavlov, E. E. Sokolov, M. H. Peychev, D. I. Dacova and L. P. Kunchev 1 1 T  2 a w    a w2 t dt  T 0  (1) where T is the duration of the measurement in seconds, a w t  is the weighted acceleration as a function of time (time history), meters per second squared (m/s2) for translational vibration [2]. The vibration total value of weighted r.m.s. acceleration, determined from vibration in orthogonal coordinates is [2, 7]:   1 av  a wx 2  a wy 2  a wz 2 2 (2) where a v is the root sum of squares; a wx , a wy , a wz are the weighted r.m.s. accelerations in the x-axis, y-axis and z-axis, respectively. The comfort criterion is assessed accordingly to the following guidelines acceleration [2, 8]: Table 1 Comfort/discomfort ranges [2 and 8] r.m.s. acceleration [m/s2] Reaction less than 0.315 not uncomfortable between 0.315 and 0.63 a little uncomfortable between 0.5 and 1.0 fairly uncomfortable between 0.8 and 1.6 uncomfortable between 1.25 and 2.5 very uncomfortable greater than 2 extremely uncomfortable It is noticeable that the ranges overlap. It comes from the subjective perception of comfort. The assessment analysis should be from the down top on the table, for example a value of r.m.s.=1.3 would be assessed as “very uncomfortable” and not as “uncomfortable” [8]. Results for measured r.m.s. accelerations are shown in Table 2. Table 2 Comparison of results of r.m.s. r.m.s. Child travel seat Acceleration [m/s2] Reaction conventional 0.6027 fairly uncomfortable a wx tilting 0.6996 fairly uncomfortable conventional 0.9093 uncomfortable awy tilting 0.7048 fairly uncomfortable conventional 0.5884 fairly uncomfortable a wz tilting 0.6407 fairly uncomfortable conventional 1.2395 uncomfortable av tilting 1.1818 uncomfortable It is visible that the conventional seat accelerations measured along the x and z axes are fairly uncomfortable. Along the y axis the r.m.s. acceleration value causes an uncomfortable reaction. With the tilting seat values matching the fairly uncomfortable reaction of traveling children are measured for the three directions. http://www.iaeme.com/IJMET/index.asp 185 editor@iaeme.com
Comfort Improvement and Kinetosis Reduction by The Use of a Pendulum Type Child Travel Seat According to [2] the motion sickness dose value (MSDV) may be calculated by: 1 MSDV  a wT 2 (3) In the international standard ISO [2] recommends only the evaluation of the vertical vibration effect on motion sickness, but some authors apply the method for the horizontal (lateral and longitudinal) directions also [7, 9]. The percentage of people who may vomit in meters per second on 1.5 degree (m/s1.5) is approximately [2]: 1 %vomiting  MSDV (4) 3 The results of the MSDV and the percentage of persons who my vomit, are shown in Table 3. Table 3 Comparison of results of MSDV and %vomiting MSDV Child travel seat Dose value [m/s1.5] People who may vomit conventional 45.11 15.03 % x tilting 52.45 17.45 % y conventional 68.05 22.68 % tilting 52.75 17.58 % conventional 44.04 14.68 % z tilting 47.95 15.98 % The highest percent of people who may vomit is calculated for the y axis of the conventional seat. A reduction from 22.68% to 17.58% is observed with the use of a tilting seat. At first sight this looks modest, however the reduction from 22.68 to 17.58 is a significant drop of 22.7%. Along the other axis lower values of 17.58% are observed. This means that the total percent of people who may vomit drops with the same motion sickness value as the y axis percent. 4. CONCLUSION The gathered results of the experiments show that the use of a pendulum type tilting child seat aids for the decrease of the spectral densities of lateral accelerations acting on the travelling child. As a result, the spectral density of the vertical accelerations increases, however it is widely known that they are much easier for the human organism to withstand as it is used to them in its everyday activities. The r.m.s. acceleration analysis marks a drop of the lateral (along the y axis) acceleration so that from values causing uncomfortable reaction in the conventional seat it drops to values causing a fairly uncomfortable reaction in the travelling child. The percent of people who may vomit drops from 22.68% to 17.58%. During the conduction of the experiment a forced vehicle speed reduction was necessary in some road sectors with a lot of corners due to the presence of heavy trucks causing car columns. This gives us a reason to think that during movement with higher speeds the efficiency of the solution proposed will be higher. That’s why in our future work a research on the influence of the vehicle speed on the potential of comfort improvement and kinetosis reduction with the use of a pendulum type child travel seat will be done. ACKNOWLEDGMENTS This work was supported by the National Science Fund of the Ministry of Education and Science of the Republic of Bulgaria [Grant No. ДМ 07/8 (December 17, 2016)]. http://www.iaeme.com/IJMET/index.asp 186 editor@iaeme.com
N. L. Pavlov, E. E. Sokolov, M. H. Peychev, D. I. Dacova and L. P. Kunchev REFERENCES [1] Tjärnbro, H. and Karlsson, N. Motion sickness in cars - Physiological and psychological influences on motion sickness. Bachelor of Science Thesis on behalf of Volvo Cars, Gothenburg: Chalmers University of Technology, 2012. [2] ISO 2631-1 Mechanical vibration and shock – evaluation of human exposure to whole body vibration – part 1: General requirement. International Organization for Standardization, 1997. [3] Mauer, M., Gerdes, J. C., Lenz, B. and Winner, H. Autonomous driving. Berlin: Springer, 2016, pp. 706. [4] Wada, T., Fujisawa, S., Imaizumi, K., Kamiji, N. and Doi, S. Effect of Driver's Head Tilt Strategy on Motion Sickness Incidence. Proceedings 11th IFAC/IFIP/IFORS/IEA Symposium on Analysis, Design, and Evaluation of Human-Machine Systems, Valenciennes, 2010, pp. 192-197. [5] Reason, J. T. Relations between motion sickness susceptibility, the spiral aftereffect and loudness estimation. British Journal of Psychology, 59(4), 1968, pp. 385-393. [6] Pavlov, N., Sokolov, E., Peychev, M. and Dacova, D. Design and test of a tilting seat for improving children’s comfort during traveling. Proceedings of the 2nd International Scientific Conference on IT, Tourism, Economics, Management and Agriculture, ITEMA, Graz, 2018, to be published. [7] Mansfield, N. Human Response to Vibration. New York: CRC Press, 2005, pp. 256. [8] Donegan, M. How Do I Measure Whole Body Vibration? 2015. http://blog.prosig.com/2015/03/20/how-do-i-measure-whole-body-vibration/ [9] Förstberg, J. Ride comfort and motion sickness in tilting trains - Human responses to motion environments in train and simulator experiments. Ph. D. Thesis, Stockholm: Royal institute of technology, 2000. http://www.iaeme.com/IJMET/index.asp 187 editor@iaeme.com