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CHEMICAL ENGINEERING TRANSACTIONS
VOL. 58, 2017
A publication of
The Italian Association
of Chemical Engineering
Online at www.aidic.it/cet
Guest Editors: Remigio Berruto, Pietro Catania, Mariangela Vallone
Copyright © 2017, AIDIC Servizi S.r.l.
ISBN 978-88-95608-52-5; ISSN 2283-9216
A Study of a Barometric Methodology for Assessing the
Agricultural and Forestry Machine’s Seat Comfort
Marco Pirozzia, Venerando Rapisardab, Marco Ferric, Aldo Calcantec, Roberto
Obertic, Elio Romanod
aINAIL – Dipartimento Innovazioni Tecnologiche e Sicurezza degli Impianti, Prodotti ed Insediamenti Antropici –
Laboratorio II – Macchine e attrezzature di lavoro - Via Fontana Candida 1 -00040 - Monte Porzio Catone (RM) ;
bUniversity of Catania - Occupational Medicine; Via Santa Sofia 78, 95123 Catania, Italy
cDipartimento di Scienze Agrarie e Ambientali - Produzione, Territorio, Agroenergia – Università di Milano.
dConsiglio per la ricerca in agricoltura e l’analisi dell’economia agraria (CREA)– Unità di Ricerca per l’Ingegneria Agraria
(CREA-ING); Laboratorio di Treviglio, via Milano 43, 24047 Treviglio (BG), Italy
m.pirozzi@inail.it
The agricultural operations carried out with machines, require the operator spends a substantial amount of
hours in a seated position on a seats often not properly padded therefore the parts of the body in contact with
the seat are subject to considerable stresses. In addition, the operator must not only control the task he has
done but he must also continually monitor actively with a significant commitment to operate levers, buttons
and steering.
Therefore, the operator's body is subject to various twists carried out in dynamic conditions according to the
crop processing to perform. The parts of the body in contact with the seat, in particular the buttocks and the
back, receive continuously, at irregular intervals, and with different intensity, different mechanical stresses that
are translated immediately in pressure to the them tissues.
Often these compressions occur in a concentrated manner, especially if the body is skinny and therefore the
pressures could immediately affect the comfort perceived by the operator and at a later time, if repeated by
the same operator and with the same machine, they could degenerate into occupational diseases because of
the possible an incidence on blood flow.
The purpose of this paper is to propose a new methodology based on barometric mapping, to investigate how
forces are applied to the back and buttocks while driving a tractor, under standardized test conditions.
In particular, the experimental tests have been conducted on a smooth surface free of roughness which is the
simplest movement a vehicle can do along a road, such as transporting a trailer.
The data were collected through an acquisition system based on a carpet with small pressure sensors. It has
been used a carpet of 1024 cells for the sitting and one for the backrest.
Acquisitions between the two sides of the seat were synchronized and the tests were repeated five times in
order to develop an adequate analysis.
Statistical analysis was mainly aimed at verifying the variability among datasets in order to study the effect of
the seat on the value recorded.
The statistical analysis was mainly aimed at verifying the variability between the data sets to study the effect of
the seat on the pressure value recorded.
The results showed, for the observed correlations, this method based on pressure between the seat and the
body is a good tool to help the valuation judgment of a seat.
1. Introduction
In all field operations conducted with agricultural machines, the tractor driver is exposed to vibrations. Many of
these exposures may exceed regulatory limits so as to consider an increased risk of injury to workers from
these operations. The vibrations occur along three translations and three axes of rotation (6-DOF), and can
afflict the driver’s body at any point of contact with a vibrating surface (Griffin et al., 1990).
DOI: 10.3303/CET1758027
Please cite this article as: Pirozzi M., Rapisarda V., Ferri M., Calcante A., Oberti R., Romano E., 2017, A study of a barometric methodology for
assessing the agricultural and forestry machine’s seat comfort, Chemical Engineering Transactions, 58, 157-162 DOI: 10.3303/CET1758027
157
The vibration comes, in the operator's body working seated, from the feet resting on the floor, from the seat
and from the controls managed by the operator's hands (Mansfield et al., 2005).
The main device of transmission of vibrations from the vehicle frame to the operator is the seat. The
manufacturer can implement the type of seat already fitted for a cabin model, with a better one, to prepare a
more comfortable cabin. The WBV (whole body vibration) exposure generate discomfort and has been linked
to the pain behind the back (Bernard et al., 1997; Lings et al. 1999), and the neck (Rehn et al., 2002). The
daily exposure to vibration may compromise the health of the driver, as demonstrated by medical studies
(Kumar et al., 2001). In particular, excessive exposure to WBV and awkward working postures are considered
the main stress factors that contribute to the development of musculoskeletal disorders among professional
drivers (Bovenzi et al., 1994).
So the replacement of the seat as a function of the operations to be performed, as well as the duration and the
conditions of the working, could be a very useful option to improve the operator's working conditions. Other
factors can affect the attenuation of vibrations, such as tires (Sherwin et al., 2004), wheel suspension (Donati,
2002), driving speed (Malchaire et al., 1996; Rehn et al., 2005) and terrain (Piette et al. 1992).
Modern tractors normally have components capable to reduce vibration, such as new kind of tires; in particular
the modern low pressure tires can transmit less vibration (Sam et al. 2006; Schrottmaier et al., 2000). Even
the seat suspension system is one of the most effective solutions (Dufner et al. 2002; Melemez et al. 2013).
However, even if several advances have been developed, some authors (Scarlett et al. 2007) found in their
experiments with modern tractors that the limits established by law (EEC Directive 2002/44/EC) were
exceeded when the analyzes were developed in the time intervals corresponding to the actual use of the
agricultural machine.
In the automotive industry is used, since the 90s, for the verification of the comfort of the seat, a system based
on the reading of the pressure between the tissues of the human body and the seat, called barometric
mapping.
Barometric maps have been used in order to study the effects of vibration magnitude and frequency
transmitted to the operator as well as the pressure distribution in the ischial areas (Wu et al, 1999). The
instrumentation is based on the matrices of pressure sensors that express in real time the pressure variation
and the persistence of the pressure in certain areas of the body. Several studies have shown assessments
isobars curve distribution of the pressure exerted by operators sitting on a horizontal plane (Schoberth, 1962;
Pheasant et al., 1991 e Gross et al., 1994).
The aim of the article is the study of a method able to read the pressure between the operator and the
agricultural and forestry machines seat. In particular, the study has focused on the ability of a barometric
sensor array to sense differences between seats with anatomical conformations which define different levels
of comfort.
2. Material and methods
Tests were conducted at the CREA-ING (Consiglio per la ricerca in agricoltura e l’analisi dell’economia
agraria) of Treviglio (Bergamo, Italy). Data were recorded on 500 m of standardized asphalt (ISO 2631-
1:1997) test track (Figure 1), developing five repetitions for each condition.
Figure 1: The test track of the Laboratory of Treviglio
158
2.1 Seats and tractors features
The tests have been carried out with the use of three different commercial seats. The three seats were
distinguished by the following characteristics: area of the seating surface, the presence of headrest,
adjustment options (mechanical, pneumatic) of the seat, size and padding (table 1).
The three seats had the following characteristics: seat A: seat "low range" with reduced (about -10% of the
seat B, and about -20% of the seat C) seating surface (measured as a projection on a flat surface), poor
cushioning, lack of restraint and poorly adjustable; seat B: seat of "middle range" with a medium seating
surface, good padding (about +10% of the seat A), the presence of head restraints and adjustable
mechanically; seat C) seat "high-end" with headrest and pneumatic adjustment, wide and adjustable seat, with
possible adjustments also in the lower back, in the armrests and head restraints. In the latter case the seat
was also able to perform self-calibration according to the operator's weight, while maintaining the possibility of
further manual adjustments.
Table 1: Seats’ characteristics
Seat A Seat B Seat C
Sitting area (cm2) 2.068 2.288 2.499
Backrest area (cm2) 1.634 1.665 2.021
Thickness seat (cm) 4.5 5.0 6.0
Thickness backrest (cm) 4.0 4.0 6.0
Head rest (Y/N) N Y Y
Breathable fabric (Y/N) N N Y
Height adjustment (Y/N) N Y Y
Lumbar adjustment (Y/N) Y N Y
Suspension type Mechanic Pneumatic Pneumatic/Auto
Y= presence; N=absence
2.2 Subjects
The tests were carried out by five subjects, volunteers, healthy, with experience in conducting agricultural
machinery. The age range was between 22-50 years old, the mass between 62-106 kg and height between
172-187 cm. All of them were right handed.
2.3 Pressure measurement system
The sensors applied in the tests consisted of a carpet of resistive sensors (32x32) (Figure.2) that instantly
generates a matrix of values 1024 (Figure 3). In particular, the instrumental chain constituted of two acquirers
Evolution Handle (Tekscan Pressure Measurement System, 1998-2012, South Boston) data with the scanning
frequency of 100 Hz.
Figure 2 – The acquisition system Figure 3 – An array of the pressure (g cm-2) produced from an
instantaneous acquisition.
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
5 0 5 57 18 23 17 17 28 20 0 4 0 0 0 0 0 27 44 16 31 22 0 0 0 0 0 0 0 0 0
0 75 48 114 140 153 123 179 172 104 31 0 0 0 0 0 66 187 163 89 94 74 126 41 27 51 8 0 0 0 0
0 49 71 92 129 147 70 214 150 113 67 6 0 0 0 5 80 43 98 83 98 107 72 41 31 68 6 0 0 0 0
0 83 186 175 159 169 89 130 184 101 90 13 0 0 0 0 150 119 85 99 90 85 90 59 37 21 0 0 0 0 0
0 73 54 73 159 128 107 195 165 63 99 10 9 0 0 15 54 79 44 59 63 81 69 76 98 61 9 0 0 0 0
0 71 99 175 109 108 103 119 119 121 103 47 0 8 5 17 29 69 55 93 59 71 41 48 111 43 0 0 0 0 0
0 62 70 27 37 79 28 57 58 63 70 39 7 0 6 16 35 30 43 55 57 38 41 55 35 30 11 0 0 0 0
0 66 93 87 100 53 120 72 99 109 67 71 11 8 0 15 41 54 20 50 45 55 75 48 17 78 25 0 0 0 0
0 33 58 85 95 160 18 95 61 78 42 24 10 12 5 25 27 40 37 45 37 31 45 71 41 69 23 0 0 0 0
0 22 37 36 63 50 59 59 44 63 27 11 31 0 0 13 44 20 33 23 44 26 33 23 29 87 36 0 0 0 0
0 13 26 40 63 47 25 43 27 18 20 21 9 0 0 4 38 22 19 35 59 23 23 26 19 28 23 0 0 0 0
0 8 31 54 21 44 43 32 70 30 23 47 19 0 0 17 38 31 27 24 27 19 21 39 26 37 16 0 0 0 0
0 7 55 43 49 31 33 37 24 39 20 33 22 9 6 21 31 38 20 34 28 34 11 21 30 129 13 0 0 0 0
0 0 31 36 43 67 29 33 47 67 46 37 35 8 0 53 60 72 86 75 36 40 44 95 46 98 0 0 0 0 0
0 0 21 28 43 42 35 46 48 71 54 50 35 10 0 36 48 72 74 65 45 52 58 67 75 82 0 0 0 0 0
0 0 11 21 44 17 41 60 50 75 62 63 36 12 0 19 36 73 62 55 55 65 72 40 104 65 0 0 0 0 0
0 0 42 40 45 60 61 41 128 61 35 62 22 11 9 7 51 67 39 79 88 107 79 51 37 57 0 0 0 0 0
0 0 4 10 49 58 25 63 109 67 69 35 37 21 0 31 54 115 70 71 117 75 47 126 96 100 0 0 0 0 0
0 0 9 52 27 53 47 79 101 164 153 50 46 22 0 62 58 79 62 215 58 58 110 78 75 73 0 0 0 0 0
0 0 9 16 23 38 101 106 127 105 130 55 46 69 0 53 80 203 145 120 43 70 79 88 136 68 0 0 0 0 0
0 0 0 17 26 54 46 115 129 169 87 57 37 43 0 42 68 155 196 152 121 60 49 107 95 51 0 0 0 0 0
0 0 0 26 48 35 30 88 154 140 67 44 39 45 0 55 84 86 117 172 101 45 38 50 88 11 0 0 0 0 0
0 0 0 0 45 33 39 130 78 111 66 76 56 83 11 67 66 103 168 132 82 67 45 41 41 0 0 0 0 0 0
0 0 0 0 26 13 40 46 51 49 83 48 39 45 51 47 108 76 56 102 46 35 38 32 21 0 0 0 0 0 0
0 0 0 0 0 8 25 12 23 99 142 61 76 99 93 68 103 65 56 122 32 12 4 19 0 0 0 0 0 0 0
0 0 0 0 0 0 0 10 19 67 95 34 62 49 64 52 55 78 14 6 40 98 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 9 34 165 20 20 69 94 58 73 72 133 11 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 11 0 16 0 12 20 13 0 26 0 53 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 36 0 6 0 38 4 15 22 0 0 24 0 24 4 4 35 37 0 16 11 45 0 8 0 0 0 0 0
159
Each sensor is 0.64 mm thick and is able to measure a pressure range between 0 and 1000 g cm-2. From
each array, the maximum and mean value can be calculated on 600 frames.
The software used for the reading of the data retrieved by the sensor array is CONFORMat Research ver.
7.60-21C (Tekscan Pressure Measurement System, 1998-2012, South Boston).
The software is also able to provide graphs about: the pressure, the contact area and the distribution of
pressures through time. The software can execute the dynamic playback function of two or more signals
simultaneously; the system could export data in ASCII.
The acquisition, of variable lenght in function of the speed of travel, was cut away of the entrance phase to the
track and the exit phase from the track, characterized by an indicator signal (a bump). From every single test
the maximum peak pressure (PMAX) and the average pressure value (PAVG) were obtained.
2.4 Statistical Analysis
The statistical analysis was conducted through the software Comprehensive R Archive Network (CRAN),
developed by the Institute for Statistics and Mathematics (Wien-Umgebung, Austria).
The data were reported as means and standard deviations from the mean, and after the first checks the
normality of their distribution with the Shapiro Wilk test and their homogeneity of variance test with Fisher's
exact test, were subjected to ANOVA variance analysis to obtain an assessment of the factors in the study,
constituting the independent variables, with respect to the response selected values representing the
dependent variable (PMAX, PAVG).
In addition to the information generated from the analysis of variance were developed post-hoc test for
discrimination in classes of the observed variations.
3. Results and discussion
The dataset of the values collected between all compared conditions showed the highest value PAVG of 136.04
g cm-2 and the highest value PMAX of 691.00 g cm-2 recorded with the use of the seat A.
The summary of the dataset, grouped by seat, is shown in Table 2.
Table 2: PAVG (g cm-2) e PMAX(g cm-2) recorded in the three seats
PAVG mean sd IQR min Max
Seat A 136.04*° 36.93 69.56 82.00 184.75
Seat B 122.01 30.07 41.13 84.25 194.38
Seat C 101.39 23.27 27.13 72.75 154.00
PMAX mean sd IQR min Max
Seat A 335.80*° 172.29 225.5 143.00 691.00
Seat B 271.20 92.05 91.5 160.00 500.00
Seat C 159.60 57.70 60.0 102.00 303.00
Number of value=75
Duncan’s test significance: *seat A vs. B; °seat A vs. C
The Shapiro-Wilk test, conducted both on PAVG and PMAX, showed normality of the data distribution.
Levene’s test for homogeneity of variance was positive. So it was possible to carry out the analysis of variance
(ANOVA) for the effect evaluation of the operator and the seat, on the registered values. The seat type has
shown statistically significant influence on the value of PMAX and PAVG with p-value <0.01.
Of the two response values, only PAVG was statistically influenced (p-value <0.05) by the operator sitting on
the seat. Instead the PMAX was not significantly influenced by the operator. Both response values showed no
statistically significant differences that depend on the repetitions performed, showing a statistically verified
repeatability.
Therefore, for the response values dependent on the type of seat has been performed post-hoc Duncan test
for the search of the homogeneous medium and the verification of the difference between the seats and the
results are reported in table 2, while the distribution of values, grouped by the seat, it is shown in the box plot
of Figure 4 and 5.
The same test developed for the research of the difference among the five averages obtained by the operators
showed that the PMAX and PAVG were statistically influenced by the operator 1 who had a body mass index
(BMI=weight height-2) different from the others (Duncan’s test at confidence level=0.95). The correlations
between BMI and PMAX and PAVG values were positive and significant (p-value<0.05), respectively of 0.68 and
160
0.72. The correlations between the height of seat padding and the values of PMAX and PAVG were negative and
significant (p-value<0.05), respectively of -0.56 and -0.64.
Figure 4 – Median line boxplot of PAVG values (g cm-2). Figure 5 – Median line boxplot of PMAX values (g cm-2).
4. Conclusion
The reading ability of an instrument equipped with sensors has been evaluated for the assessment of the
pressures which occur between the seat and the operator ride on seated in an agricultural or forestry machine.
The experimental plan was designed to test the differences detected by the barometric instruments with three
different types of seats on the market. It was chosen an area of standardized asphalt to avoid the variability
coming from the driving surface.
Among the five operators that drove the tractor, only one, the one whose combination of height and body
weight has generated a different BMI from the group, has had an effect, together with the type of seat, on the
average pressure values (PAVG) registered, probably due to the manifested correlation of BMI with PMAX and
PAVG.
The maximum peak values (PMAX) recorded were influenced only by the type of the seat. Further studies
should evaluate if the BMI and operators’ anthropometric measurements could and how have effect on the
reading ability of the proposed methodology. In addition, the investigated method, should be verified during
cultivation operations in the field.
This research allows to conclude the methodology applied in this study could be used to describe and
compare seats of agricultural and forestry vehicles, with the main objective to highlight the degree of comfort
available, assessing the minimum and maximum pressures obtainable in the dynamic situations where the
operator can be in the working hours.
The hope is therefore to use the experience gained as a tool for comparing new materials and design and
implementation technologies and in the evaluations to improve the quality of the operator's work environment.
Acknowledgments
The authors would like to thank the INAIL (National Institute for Insurance against Accidents at Work) which
funded the ERGSEAT project that allowed the useful experiments in this research and they would like to thank
also Elia Premoli (CREA-ING Treviglio, Bergamo, Italy), for his technical support in fitting out the sensor array
and collecting the experimental data.
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