biosystems engineering xxx (xxxx) xxx
Available online at www.sciencedirect.com
ScienceDirect
journal homepage: www.elsevier.com/locate/issn/15375110
Special Issue: Agri Machinery Safety
Research Paper
Assessment of a ride comfort number for
agricultural tractors: A simplified approach
Maurizio Cutini*, Massimo Brambilla, Carlo Bisaglia
CREA Research Centre for Engineering and Agro-Food Processing, via Milano 43, 24047, Treviglio (BG), Italy
article info
Farming activities cause operators to experience whole body vibration (WBV), which may
Article history:
result in back injuries. Studies have shown that despite a wide variability when operating a
Published online xxx
tractor, the accelerations arising from “ground input” have similar spectral trends making
it possible to simplify and standardise the driver comfort testing procedures. Based on the
Keywords:
Safety
recommendations of three standards on WBV measurement, a single scalar value (Ride
Number e RN) has been defined and used to characterise the vibration comfort of agricultural tractors. The operation of ten tractors equipped with different damping systems on a
Comfort
Test track
Whole-body vibration
standard test track (ISO 5008:2002) at three speeds (10, 12, 14 km h 1) has resulted in the
acquisition of accelerations along the x, y and z axes at the seat. The RN was calculated by
averaging the overall total values of vibration (aw) calculated for each speed. Data processing has shown that machine settings (tyre size and pressure, tractor mass) significantly
affect the RN so as to achieve the recommendations for proper tractor settings. It has been
observed that at each speed, the relative contribution of the components (aw10, aw12 and
aw14) ranged from
12% to þ11.5% showing that obtaining the RN by averaging them
arithmetically was a suitable procedure. According to principal component analysis, great
part of the accounted variance can be explained by accelerations acquired on the y and z
axes, distinguishing between tractors with and without suspension. Thus the RN obtained
can be used to compare a given tractor when provided with different equipment.
© 2019 IAgrE. Published by Elsevier Ltd. All rights reserved.
1.
Introduction
Work injury statistics have shown the considerable hazard
related to agricultural tasks: the fatality rate in agriculture is
six times higher than that of all other industrial activities (EC,
2004; HSA, 2013). Work-related exposure to vibration is one of
the most significant contributors to the onset of chronic diseases whose outcomes, even if not resulting in premature
mortality, may lead to substantial disability, with significant
costs from both the human and socio-economic standpoints
(Litchfield, 1999; Hoy, Brooks, Blyth, and Buchbinder, 2010; EUOSHA and European Agency for Safety and Health at Work,
2005). The exposure of operators during agricultural tasks
(both whole-body and hand-arm) has been already studied in
depth by Cutini et al., 2017 (Cutini, Brambilla and Bisaglia,
2017). Nevertheless, the basic concepts are re-examined
here, since operator exposure requires more attention.
* Corresponding author. CREA Research Centre for Engineering and Agro-Food Processing, via Milano 43, 24047, Treviglio (BG), Italy.
E-mail address: maurizio.cutini@crea.gov.it (M. Cutini).
https://doi.org/10.1016/j.biosystemseng.2019.02.015
1537-5110/© 2019 IAgrE. Published by Elsevier Ltd. All rights reserved.
Please cite this article as: Cutini, M et al., Assessment of a ride comfort number for agricultural tractors: A simplified approach, Biosystems Engineering, https://doi.org/10.1016/j.biosystemseng.2019.02.015
2
biosystems engineering xxx (xxxx) xxx
Nomenclature
LBP
LBPD
WBV
EAV
ELV
ANOVA
PCA
RMS
aw
Wi
ai
Lower back pain
Lower back pain disease
Whole body vibration
Exposure action values
Exposure limit values
Analysis of variance
Principal component analysis
Root mean square
Frequency weighted acceleration
Weighting factor ith one third octave band
Root-mean-square acceleration for the ith one
third octave band
kx, ky, kz Multiplying factors that account for the
different sensitivity of the body for vibration on
each axis
Ride number
RN
Currently, there are many standards focusing the assessment of vibration exposure on the adoption of a frequencyweighting factor to take into considerations the different
risk of damage occurring from different frequencies (Els, 2005;
VDI, 2017; BS, 1987; Leatherwood & Barker, 1984; ISO, 1997).
ISO 2631-1:1997 is one of the most widely adopted: it defines
how to calculate the value for the assessment of periodic,
random and transient vibration by considering human responses such as health and comfort. As the human sensitivity
to vibration is highly frequency dependent, different frequency weightings are required for the different axes of the
body. The effect of frequency is reflected in weightings that
are labelled Wk, Wd, Wf, Wc, We and Wj. According to the
standard, vibration assessment follows the calculation of the
weighted root-mean-square (RMS) acceleration (aw, m s 2)
along the longitudinal (x), lateral (y) and vertical (z) axes (Eq.
(1))
awðx;y;zÞ ¼
Tractor driving is significantly linked to an increased risk of
lower back symptoms. Furthermore, the total vibration and
awkward postures experienced at work were found to be the
most predictive occupational factors for the occurrence of
lower back pain (LBP) among tractor drivers (Bovenzi & Betta,
1994; Lings & Leboeuf-Yde, 2000). Correlating LBP with professional lower back pain diseases (LBPD) is somehow difficult, because of the various approaches that different
countries have adopted for the definition of LBPD (Hulshof,
Van der Laan, and Braam, 2002). From the regulation standpoint, European countries consider LBPD from overload and
WBV differently. Despite this, the manual handling of materials, the frequent bending or twisting of the trunk and whole
body vibration (WBV) exposure are important factors for the
et al., 2015; Lo
€ tters, Burdorf,
LBPD diagnosis (Lastovkova
Kuiper, & Miedema, 2003).
Whole-body vibration (WBV) is defined as “the mechanical
vibration that, when transmitted to the whole body, entails
risks to the health and safety of workers, in particular, lowerback morbidity and trauma of the spine” (EC, 2004). To protect
workers exposed during their work to risks arising from vibration, ‘exposure action values’ (EAVs) and ‘exposure limit
values’ (ELVs) have been established together with obligations
and preventative actions (EC, 2004) such that any employer,
who requires tasks to be carried out that involve vibration
exposure risks, must implement a series of protection measures before and during the work.
The use of agricultural machinery exposes operators to
risks arising from vibration (HSE, 2013; EU, 2006) and therefore
manufacturers are continuously improving tractor comfort
with active seats, suspended front axles and specially
designed cab suspension systems. These efforts, on the one
hand reduce operator exposure to vibrations, but on the other
they suffer from the lack of a specific approach in defining
tractor vibration comfort. There is no reference data that can
make it possible to characterise the vibrational comfort of
tractors, despite the European regulatory assessment
requiring the implementation of appropriate actions to reduce
the risk of mechanical vibration exposure.
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
n
X
ðWi $ai Þ2
(1)
i¼1
where aw(x,y,z) (m s 2) is the frequency weighted acceleration;
Wi (dimensionless) is a weighting factor i-th one third octave
band as given in ISO 2631:1997 and ai (m s 2) is the root-meansquare acceleration for the i-th one third octave band.
Therefore, aw values can subsequently define WBV risk conditions in compliance with the European Directive/44/EC
(2002).
Many studies have quantified WBV emission and estimated the exposure levels of operators under controlled
conditions while carrying out various tasks (i.e. crossing ISO
ride vibration test tracks or performing selected agricultural
operations) as well as while carrying out identical tasks in
different environments (e.g. on paved and unpaved surfaces).
Yet, despite the wide variability characterising agricultural
surfaces, the accelerations resulting from the ground input
has shown similar spectral trends, which were found to be
relevant at frequencies of less than 12 Hz (Oude Vrielink, 2012;
Scarlett, Price, & Stayner, 2007; Anthonis, Vaes, Engelen,
Ramon, & Swevers, 2007; Cutini et al., 2013) pointing out that
the outcome of the forces exchanged between soil profile and
agricultural tires doesn't follow a random pattern (Cutini,
Costa, & Bisaglia, 2016; Mattetti, Molari, & Vertua, 2015).
When a tractor runs over a cleat, the response of the hub
acceleration to the effect of the cleat is to produce a sine
function characterised by the same resonance frequency as
that of the tyre (Jianmin, 2001; Pacejka, 2010) irrespective of the
forward speed of the tractor or the randomness of the track
profile (Cutini, Deboli, Calvo, Preti, Brambilla et al., 2017). These
considerations confirm the need for an index in the range of
frequencies of interest along the three orthogonal axes.
Given the impossibility to define a “typical” scenario, help
in overcoming such limit comes from the European Norm EN
13059:, 2002 þ A1:2008(E) standard (EN, 2002), which recommends to manufacturers the essential safety requirements in
compliance with the Machinery Directive (EU, 2006). It makes
it possible to compare industrial trucks of the same category
or a given truck in different configurations: nevertheless, this
standard cannot be used to assess the daily vibration exposure of operators in field conditions.
Please cite this article as: Cutini, M et al., Assessment of a ride comfort number for agricultural tractors: A simplified approach, Biosystems Engineering, https://doi.org/10.1016/j.biosystemseng.2019.02.015
3
biosystems engineering xxx (xxxx) xxx
Information provided by the work equipment manufacturers in accordance with the relevant Community
Directives;
The existence of replacement equipment designed to
reduce the levels of exposure to mechanical vibration.
However, as mentioned earlier, it cannot be used to
determine the daily exposure of the operator to vibration in
field conditions.
2.2.
When running the tractor, the operator typically sat in the
vehicle and the vibrations were measured only at the seat
(health method in ISO 2631) along the three mutually
perpendicular axes:
Fig. 1 e The ISO 5008 100 m test track at the CREA Research
Centre, Treviglio, Italy (the agricultural tractor shown is
merely an example).
x-direction: back to chest;
y-direction: right side to left side;
z-direction: buttocks to head.
The focus of this work is the definition and the calculation
of a simplified index (hereafter the Ride Number e RN, Heissing,
Ersoy, 2011, pp. 421e448) enabling the association of a vibrational comfort level for a given machine with different
equipment (i.e. seats, suspensions, tyres). Results concerning
the approach used, and the machine settings to be used are
provided and discussed.
2.
Material and methods
2.1.
The standard test track
Ride number definition
The value used to describe the magnitude of vibration is
the frequency-weighted acceleration in m s 2, expressed as
root-mean-square (RMS) value in compliance with ISO 2631
and ISO 5008. The operator chosen to perform the test
weighed 75 kg, in compliance with the ISO 5008 standard that
recommends the body mass of the worker to be in the range
75 ± 5 kg and with the EN 13059 standard.
The ISO 2631:1997 sets out the method for representing
vehicle comfort in a single value; when assessing the effects
on comfort, it recommends that all the relevant vibration directions shall be considered to obtain the overall total value of
vibration (aw, Eq. (2)):
The International Standards Organization (ISO) has issued the
ISO 5008:, 2002 standard: “Agricultural wheeled tractors and
field machinerydMeasurement of whole-body vibration of
the operator” (ISO, 2002) to specify the instruments, measurement procedures, measurement site characteristics and
frequency weighting that allow the WBV intensity of agricultural wheeled tractors and field machinery to be assessed. The
standard defines two standard test tracks together with the
relevant operating conditions. The standard test tracks are
100 m (smooth track) and 35 m long, consisting of two
different parallel, non-deformable lanes (left and right) made
of wooden beams (80 mm wide and with 80 mm spacing in the
smooth track, without spaces in the 35 m track) of a different
standardised height to induce vibrations (Fig. 1).
This approach complies with the following requirements
of Directive/44/EC (2002):
12
2
2
2
aw ¼ kx $a2wx þ ky $a2wy þ kz $a2wz
(2)
where awx, awy, awz are the weighted RMS accelerations along
the x, y, z-axes respectively; and kx, ky, kz are the multiplying
factors that account for the different sensitivity to vibration of
the body on each axis. In this specific case, in compliance with
Table 2 e Values of averaged weighted RMS accelerations
(m s¡2) for each forward speed obtained for a give tractor.
Speed (km h 1)
awx
awy
awz
aw
10
12
14
0.53
0.75
0.85
1.01
1.11
1.15
0.59
0.70
0.85
1.29
1.51
1.66
Table 1 e Complete dataset of the accelerations acquired running a tractor on an ISO 5008 smooth track (numbers from 1 to
5 represent the repetitions).
Weighted RMS accelerations (m s 2)
Parameters
awx
Track
ISO 5008 (smooth)
Speed (km h 1)
10
12
14
1
0.53
0.77
0.86
2
0.53
0.75
0.85
3
0.54
0.73
0.85
awy
4
0.53
0.75
0.85
5
0.54
0.75
0.86
1
1.03
1.09
1.14
2
1.02
1.13
1.15
3
1.02
1.11
1.16
awz
4
0.99
1.12
1.14
5
1.01
1.08
1.17
1
0.6
0.7
0.86
2
0.6
0.71
0.83
3
0.58
0.69
0.84
4
0.57
0.71
0.84
5
0.58
0.7
0.86
Please cite this article as: Cutini, M et al., Assessment of a ride comfort number for agricultural tractors: A simplified approach, Biosystems Engineering, https://doi.org/10.1016/j.biosystemseng.2019.02.015
4
biosystems engineering xxx (xxxx) xxx
y and z-axes. For each speed five runs were carried out and the
obtained database is hereafter reported in Table 1.
For each axis the mathematical average of the five acquisitions for each speed was calculated and the value was
therefore used to assess the total value of vibration for each
forward speed (aw10, aw12, aw14) in compliance with Eq. (2) (e.g.
pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
aw10 ¼ 2 0:532 þ 1:012 þ 0:592 ¼ 1.29 m s 2). Table 2 reports all
these values.
Entering the aw values in Eq (3) allowed assessing for each
tractor the related ride number (RN). An example follows:
Table 3 e The main elastic setting of the tested tractor.
Tractor
Suspension
T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
Seat,
Seat,
Seat,
Seat,
Seat,
Seat,
Seat
Seat
Seat
Seat
cab, front axle
cab, front axle
cab, front axle
cab, front axle
front axle
front axle
RN ¼ ð1:29 þ 1:51 þ 1:66Þ=3 ¼ 1:49 m s
2.3.
the standard's recommendations (ISO 2631:1997, comfort
chapter), kx, ky, kz are all equal to 1.
The frequency-weightings to be used are Wd and Wk (ISO
2631:1997): the former for x and y-axis, the latter for the z one.
Vibration measurements should be made when the tractor is
driven at speeds of 10 km h 1, 12 km h 1 and 14 km h 1 over
the 100 m smoother track (ISO 5008). The effects of vibration
on the comfort of a person exposed to periodic, random or
transient vibration are assessed in the frequency range
0.5e80 Hz.
The output of the test initially results in nine values of
weighted accelerations: three speeds for three axes (awx10;
awx12; …; awz14), then applying Eq. (2) it will be combined to one
value for each speed (aw10; aw12; aw14). The arithmetic mean is
the Ride number value (Eq. (3)):
RN ¼
awx þ awy þ awz
3
(3)
An example follows.
Running a tractor on the ISO 5008 smooth track at 10, 12
and 14 km h 1 has resulted in obtaining the accelerations on x,
2
(4)
The tested tractors
The experimental plan envisaged testing ten tractors, hereafter labelled T1 to T10 and all the tractors had cabs. Usually
cabs are provided with equipment (rubber mounts, air springs
etc.) preventing them from being in contact with the frame: in
the dataset, suspended cabs are defined as only such when
they are equipped with air springs. Table 3 reports the suspension systems characterising the ten tested tractors.
The nominal power of the tested tractors ranged from 60 to
250 kW (median value 86.5 kW): two of them (T9 and T10) had
a nominal power lower than 76.5 kW; three were between 76.5
and 86.5 kW (T3, T5 and T7); two had a nominal power between 86.5 and 126 kW (T6 and T8) while the remaining three
had a nominal power in the range 126e250 kW (T1, T2 and T4).
The masses of the tractors were in the 3600e12,900 kg range.
Table 4 reports a more detailed description of the features of
the tractors when tested.
In the first phase of the research some tractors were tested
with tyres at the nominal pressure of 160 kPa to point out what
was happening in the worst-case scenario with reference to
tyre stiffness. Table 4 provides a more detailed description of
tractor characteristics.
Table 4 e Basic information on tractors characteristics and settings during the testing.
Tractor label
T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
Mass (kg)
12,710
7710
4720
7830
4475
7000
3665
5075
3720
5750
Front
Rear
Tyre size
Pressure (kPa)
Tyre size
Pressure (kPa)
650/65/34
650/65/28
440/65/28
540/65/30
380/70/24
540/65/28
360/70/24
420/85/24
7.5/20
420/65/28
160
130
130
130
130
160
160
160
130
130
710/75/42
710/70/38
540/65/38
650/65/42
480/70/34
650/65/38
480/70/34
460/85/38
13.6 R38
540/65/38
160
130
130
130
130
160
160
160
130
130
Table 5 e The apparatus and equipment used.
Instrument/material
Data logger
Speed wheel
Cushion triaxial accelerometer
Make/model
Test type
Rogadaq 16 (ROGA Instruments, Nentershausen, Germany)
€ benzell, Germany)
Peiseler (Peiseler gmbh, Gro
PCB 356 B 40 (PCB Group, Depew, NY, USA)
Comfort
Forward speed measurement
Comfort
Please cite this article as: Cutini, M et al., Assessment of a ride comfort number for agricultural tractors: A simplified approach, Biosystems Engineering, https://doi.org/10.1016/j.biosystemseng.2019.02.015
biosystems engineering xxx (xxxx) xxx
Table 6 e The effect of adopting different tyres on the ride
number.
Run
Label
Tyre sizes
T1_W1
T1_W2
T1_W3
T2_W4
T2_W5
T2_W6
Front
Rear
650/65R34
650/65R34
650/65R34
600/60R30
600/65R28
540/65R28
710/75R42
800/70R42
900/60R42
710/60R42
710/70R38
650/65R42
RN (m s 2)
Grouping
(p < 0.05)
1.43
1.44
1.54
1.39
1.45
1.46
b
b
a
b
a
a
Table 7 e The effect of ballasting on the comfort value.
Run Label
T3_B1
T3_B2
T4_B3
T4_B4
T8_B5
T8_B6
Tractor mass (kg)
RN
Grouping (p < 0.05)
4720
6290
7830
10545
5075
6310
1.47
1.52
1.32
1.02
1.91
1.76
a
a
a
b
a
b
Table 8 e The effect of different tyre pressure on the
comfort value.
Run Label
T2_P13
T2_P20
T8_P08
T8_P16
2.4.
Inflation
pressure (kPa)
RN
Grouping
(p < 0.05)
130
200
80
160
1.46
1.54
1.47
1.91
b
a
b
a
Instrumentation
Acceleration acquisitions were performed using the apparatus and equipment briefly listed in Table 5.
5
Five repetitions were carried out at the three standard
speeds and the acceleration at the three axes were acquired
with an acquisition frequency of 1250 Hz.
2.5.
Defining machine operating condition
The scientific literature reports that tyre pressure, tractor
mass and its distribution between front and rear axles affects
operator comfort (Cutini, Deboli, Calvo, Preti, Brambilla et al.,
2017; Nguyen & Inaba, 2011; Sherwin, Owende, Kanali, Lyons,
& Ward, 2004). Given the aim of defining an index that summarises all the effects arising from different factors (i.e.
ballast, tyre pressure, size and model), there is the need to
define which of these factors are important for the RN calculation. Tractors were therefore tested to verify the effect of
each factor on the RN running by them on the ISO 5008 test
track.
In detail, three sets of tests were performed:
T1 and T2 were tested differing in tyre size (six samples
labelled W1 to W6)
T3, T4 and T8 ran the test track in two mass settings:
without ballast (Table 4) and with the mass increased
respectively of 1,570, 2715 and 1235 kg
T2 and T8 were tested with tyres with different inflating
pressure (130 and 200 kPa for T2; 80 and 160 kPa for T8)
In each test, the tractors ran on the ISO 5008 track at three
speeds (10, 12 and 14 km h 1); five repetitions for each speed
were performed (see section 3.4); by means of Pearson coefficient of correlation and one way analysis of variance
(ANOVA) followed by post hoc comparison (Tukey test,
p < 0.05) using the MINITAB 17.0 statistical software (Minitab,
2010). With the same software, to increase the knowledge
attained from the variables under consideration and, according to them, try to make out as many differences as possible,
the RMS resulting from the accelerations acquired at the
tractor seat were processed by means of principal component
Fig. 2 e The results of the RN assessment.
Please cite this article as: Cutini, M et al., Assessment of a ride comfort number for agricultural tractors: A simplified approach, Biosystems Engineering, https://doi.org/10.1016/j.biosystemseng.2019.02.015
6
biosystems engineering xxx (xxxx) xxx
Table 9 e Loadings of the 9 factors on PC1 and PC2 on the
whole dataset.
Factor
awx10
awx12
awx14
awy10
awy12
awy14
awz10
awz12
awz14
Loadings
PC1
PC2
0.083
0.099
0.078
0.065
0.118
0.07
0.137
0.564
0.786
0.002
0.403
0.34
0.3
0.085
0.585
0.35
0.244
0.317
analysis (PCA) using the covariance matrix. PCA is a linear,
unsupervised pattern-recognition technique that analyses,
classifies, and reduces the dimensionality of numerical datasets in multivariate problems (Todeschini, 1998); it makes it
possible to extract target information from the dataset, carry
out an analysis of its structure and obtain a global correlation
of the variables. Correlations between the considered factors
were also explored in depth.
3.
Results
3.1.
Definition of the machine's operating condition
Data processing pointed out that ballast, tyre pressure and
tyre model affect the resulting RN: Tables 6e8 provide evidence of this.
In detail, Table 6 shows that the tyre size can affect the RN
significantly with variations of the ride number of þ7% and
þ4% for T1 and T2.
The same can be noticed for changes in tractor mass: in
this case in two out of the three tested tractors, an increase of
Fig. 3 e Loading plot (top) and biplot (bottom) of the PCA representing the distribution of the tested tractors (labelled T1 to
T10) based on the accelerations acquired at 10, 12 and 14 km h¡1 on x, y and z axes.
Please cite this article as: Cutini, M et al., Assessment of a ride comfort number for agricultural tractors: A simplified approach, Biosystems Engineering, https://doi.org/10.1016/j.biosystemseng.2019.02.015
biosystems engineering xxx (xxxx) xxx
the mass resulted in a significant reduction of the RN ( 22%
and 8% for T4 and T8).
The effect of tyre pressure on the ride number is reported
in Table 8: changes in tire pressure results in significant variations of the ride number (from þ5% to þ29%) which reflect
changes in operator comfort as well.
Following these preliminary results, it has been established that, to achieve the aim of the research, and in
compliance with ISO 5008 recommendations, when performing tractor runs:
Mass setting: Tractors shall be run without ballast, with
full fuel tank and radiator and any mounted
implements.
Tyre size setting: The model used shall be declared.
Tyre pressure setting: Tyre pressures shall be set at the
arithmetic mean of the ranges manufactures
recommend.
3.2.
7
Ride number assessment
The RN resulting from the described procedure of the ten
tested vehicles is reported in Fig. 2 for each tractor. It must be
strictly fitted on the tested model tractor and setting as
different mass, cab or frame adoption, suspended cab supports, front suspension and tyres size, all affect the results
significantly.
It can be noticed that the RN tends to increase when the
tractors' suspension devices are limited to the seat meaning
that tractors with suspended cab and front axle provide better
operator comfort (ride numbers from 1.32 to 1.47 m s 2).
Following the application of Eq. (3), RN results from averaging the values of aw10, aw12 and aw14. Going deeper in this RN
assessment pointed out that, with respect to the mean, the
relative contribution of the three components to the resulting
RN is 12.5% for aw10, þ1% for aw12 and þ11.5% aw14. This
makes it possible to consider the arithmetic mean as valid.
Fig. 4 e Loading plot (top) and biplot (bottom) of the PCA representing the distribution of the suspended tractors only
(labelled T1 to T6) based on the accelerations acquired at 10, 12 and 14 km h¡1 on x, y and z axes.
Please cite this article as: Cutini, M et al., Assessment of a ride comfort number for agricultural tractors: A simplified approach, Biosystems Engineering, https://doi.org/10.1016/j.biosystemseng.2019.02.015
8
biosystems engineering xxx (xxxx) xxx
Moreover, to better highlight the influence these factors have
on the index, figures representing the results of the PCA, turn
out to be more useful. PCA was performed using the RMS of
the accelerations acquired on the three axes at the three
speeds (Table 9 and Fig. 3). According to this multivariate
processing, the 1st principal component (PC 1) represents
82.7% and the 2nd principal component (PC 2) represents
11.3% of the total variance. Overall, both components account
for 94.0%.
The analysis of the loadings (Table 9) pointed out that awz14,
awz12, awz10 and awy12 are the factors acting the most on PC1,
splitting the observations into two groups: unsuspended
tractors (T7 to T10, in the right part of the biplot) and suspended ones (Fig. 3, below). This underlines the role vertical
acceleration has on the comfort level experienced by operators running unsuspended tractors: adopting a damping system on the front axle and the cab, if on the one hand helped
reduce the discomfort originating from vertical accelerations,
on the other resulted in some issues related to the effect of
lateral accelerations (along the y axis).
Concerning PC2, the factors distinguish between two
clusters of observations. T3 and T6 result in a single group
and, following the analysis of the loadings this can be ascribed
to two phenomena:
Stresses occurring on the z axis at 10 and 12 km h 1 and
on the x axis at 12 km h 1 which are higher than those
measured on the other tractors.
Stresses occurring on the y axis at 14 km h 1, which for
these two tractors are lower.
To better point out the role that suspension devices have
on the vibrations perceived by operators, a further PCA analysis was performed on the data related to suspended tractors
only (T1 to T6). This resulted in the biplot hereafter reported in
Fig. 4 and in the loadings of Table 10. Overall the two components model accounted for 96.4% of the explained variance
(89.9% on PC1 and 6.5% on PC2). Here the main factors
affecting PC1 are accelerations acquired on the y and z axes
highlighting how the different directions of the vibrations
discriminate among observations. It is interesting to note that,
for suspended tractors, the weight of awz10 and awz12 is higher
than awz14. This can be related to the suspension damping
effect that is higher at 14 km h 1. PC2 points out that
Table 10 e Loading of the 9 factors on PC1 and PC2 on the
suspended tractors' dataset.
Factor
awx10
awx12
awx14
awy10
awy12
awy14
awz10
awz12
awz14
Loadings
PC1
PC2
0.07
0.34
0.21
0.27
0.04
0.49
0.36
0.54
0.32
0.006
0.52
0.156
0.058
0.49
0.22
0.04
0.27
0.576
accelerations at 12 and 14 km h 1 can discriminate among
observations: anyway, this accounts for a small part of
explained variance meaning that acceleration directions
retain great part of it.
The analysis of the Pearson correlation coefficient pointed
out that, as already shown in other studies (Cutini et al., 2016),
a positive correlation exists between accelerations on x and z
axis. Surprisingly, this analysis resulted also in a significant
negative correlation between accelerations occurring on the x
and z axes and those on the y axis.
4.
Conclusions and recommendations
The continuous restructuring of the agricultural machinery
industry and the increasing complexity of agricultural and
forestry tractors needs new standards for product development and testing.
The research has combined the purpose of the EN13059
with the technical document for measuring vibration ISO 2631
and the specific standard for tractors ISO 5008 resulting in the
definition of a simplified measurement protocol with the aim
of obtaining an indication of tractor comfort with a single
scalar number (ride number - RN).
The index proved to be extremely sensitive to any setting
modification and this, on the one hand, is an advantage of the
procedure but, on the other, it is its main limitation as results
may be closely linked to the tested model and related settings,
leading to difficulties in considering the ride number as a
value of homologation since every tractor has a wide range of
possible settings. Moreover, this ride number cannot be used
to assess the daily vibration exposure of operators in field
conditions.
Nevertheless, this index makes it possible to compare the
adoption of different technical solutions: it can provide an
evaluation of the effect technical improvements have on the
operator's comfort. Concerning operators, further work aimed
at pointing out significant perceived comfort levels due to
variations in the index still needs to be carried out.
The analysis carried out on the nine components of the
index indicates that the efforts of manufacturers in equipping
tractors with suspension systems has resulted in an effective
reduction of the stresses occurring on the vertical axis, highlighting the role of lateral stresses in suspended tractors.
Following this, the research has also pointed out the
importance of considering the stresses occurring along the
three orthogonal axes at different speeds: as a matter of fact:
this can account for the different dynamic responses that
vehicles have when varying the technical solution for vibration control they are equipped with. The introduced RN summarises all these issues.
Conflicts of interest
The authors declare to have no conflict of interest. The
funding sponsors had no role in the design of the study; in
the collection, analyses, or interpretation of data; in the
writing of the manuscript, or in the decision to publish the
results.
Please cite this article as: Cutini, M et al., Assessment of a ride comfort number for agricultural tractors: A simplified approach, Biosystems Engineering, https://doi.org/10.1016/j.biosystemseng.2019.02.015
biosystems engineering xxx (xxxx) xxx
Acknowledgments
This study was performed within the INTRAC project (D.M. n.
12488/7303/11 of 09/06/2011) “Integrazione tra gli aspetti ergonomici e di sicurezza nei trattori agricoli”, funded by the Italian
Ministry of Agricultural, Food and Forestry Policies, (MiPAAF).
The Organisation for Economic Co-operation and Development (OECD) Tractor Codes Program provided further funding
that made it possible further development of the study. The
opinions expressed and the arguments are solely those of the
authors and do not necessarily reflect the official views of the
OECD or of its member countries. The authors are grateful to
OECD delegates for the fruitful discussions during the OECD
meetings. The authors are also grateful to Mr. Gianluigi Rozzoni and Mr. Alex Filisetti for the valuable help provided in
accelerations acquisition and machinery set up.
references
Anthonis, J., Vaes, D., Engelen, K., Ramon, H., & Swevers, J. (2007).
Feedback approach for reproduction of field measurements on
a hydraulic four poster. Biosystems Engineering, 96, 435e445.
https://doi.org/10.1016/j.biosystemseng.2006.11.015.
Bovenzi, M., & Betta, A. (1994). Low-back disorders in agricultural
tractor drivers exposed to whole-body vibration and postural
stress. Applied Ergonomics, 25, 231e241. https://doi.org/10.1016/
0003-6870(94)90004-3.
BS 6841:1987. (1987). Guide to measurement and evaluation of human
exposure to whole-body mechanical vibration and repeated shock.
London, UK: The British Standards Institution.
Cutini, M., Brambilla, M., & Bisaglia, C. (2017b). Whole-body
vibration in farming: Background document for creating a
simplified procedure to determine agricultural tractor
vibration comfort. Agriculture, 7(10), 1e20. https://doi.org/
10.3390/agriculture7100084. MDPI, Open Access Journal.
Cutini, M., Costa, C., & Bisaglia, C. (2016). Development of a
simplified method for evaluating agricultural tractor's
operator whole body vibration. Journal of Terramechanics, 63,
23e32. https://doi.org/10.1016/j.jterra.2015.11.001.
Cutini, M., Deboli, R., Calvo, A., Preti, C., Brambilla, M., &
Bisaglia, C. (2017a). Ground soil input characteristics
determining agricultural tractor dynamics. Applied Engineering
in Agriculture, 33. https://doi.org/10.13031/aea.11979.
Cutini, M., Deboli, R., Calvo, A., Preti, C., Inserillo, M., & Bisaglia, C.
(2013). Spectral analysis of a standard test track profile during
passage of an agricultural tractor. Journal of Agricultural
Engineering, 44(Suppl. 1), 719e723.
Directive/44/EC of the European Parliament and of the Council of 25
June 2002 on the minimum health and safety requirements
regarding the exposure of workers to the risks arising from physical
agents (vibration).(2002).
EC, European Commission. (2004). The magnitude and spectrum of
farm injuries in the European Union countries. Athens, Greece.
Els, P. S. (2005). The applicability of ride comfort standards to offroad vehicles. Journal of Terramechanics, 42, 47e64. https://doi.
org/10.1016/j.jterra.2004.08.001.
ENdEuropean Standard. (2002). EN 13059:2002þA1:2008. Safety of
industrial trucksdtest methods for measuring vibration.
EU, European Union. (2006). Guide to good practice on whole-body
vibration. Brussel, Belgium.
EU-OSHA, & European Agency for Safety and Health at Work..
(2005). Expert forecast on Emerging physical risks related to
9
occupational safety and health. European Agency for Safety and
Health at Work: Bilbao, Espana. ISBN 92-9191-165-8.
Heissing, B., & Ersoy, M. (2011). Ride Comfort and NHV, chassis
handbook. Springer. https://doi.org/10.1007/978-3-8348-97893_5.
Hoy, D., Brooks, P., Blyth, F., & Buchbinder, R. (2010). The
Epidemiology of low back pain. Best Practice & Research Clinical
Rheumatology, 24, 769e781. https://doi.org/10.1016/
j.berh.2010.10.002.
HSA, Health and Safety Authority. (2013). Farm safety action plan
2013e2015. Dublin: The Metropolitan Building 2013. ISBN 9781-84496-186-3.
HSE, Health and Safety Executive. (2013). Whole-body vibration in
agriculture, agriculture information sheet No 20 (revision 2).
Liverpool, UK www.hse.gov.uk/pubns, pubns/ais20.htm.
Hulshof, C. T. J., Van der Laan, G., Braam, I. T. J., &
Verbeek, J. H. A. M. (2002). The fate of Mrs Robinson: Criteria
for recognition of whole body vibration injury as an
occupational disease. Journal of Sound and Vibration, 253,
185e194. https://doi.org/10.1006/jsvi.2001.4255.
ISOdInternational Standard Organization. (1997). Standard ISO
2631-1:1997. Mechanical vibration and shockdevaluation of human
exposure to whole-body vibrationdPart 1: General requirements.
ISOdInternational Standard Organization. (2002). Standard ISO
5008:2002. Agricultural wheeled tractors and field
machinerydmeasurement of whole-body vibration of the operator.
Jianmin, G., Gall, R., & Zuomin, W. (2001). Dynamic damping and
stiffness characteristics of the rolling tire. Tire Science and
Technology, 29, 258e268. https://doi.org/10.2346/1.2135243.
, A., Nakla
dalova
, M., Fenclova
, Z., Urban, P.,
La
stovkova
Gad’ourek, P., Lebeda, T., et al. (2015). Low-back pain disorders
as occupational diseases in the Czech Republic and 22
European Countries: Comparison of national systems, related
diagnoses and evaluation criteria. Central European Journal of
Public Health, 23, 244e251. https://doi.org/10.21101/
cejph.a4185.
Leatherwood, J. D., & Barker, L. M. (1984). A user oriented and
computerised model for estimating vehicle ride quality. NASA
Technical Paper 2299.
Lings, S., & Leboeuf-Yde, C. (2000). Whole body vibration and low
back pain: A systematic, critical review of the epidemiological
literature 1992e1999. International Archives of Occupational and
Environmental Health, 73, 290e297. https://doi.org/10.1007/
s004200000118.
Litchfield, M. H. (1999). Agricultural work related injury and illhealth and the economic cost. Environmental Science and
Pollution Research International, 6, 175e182. https://doi.org/10.
1007/BF02987623.
€ tters, F., Burdorf, A., Kuiper, J., & Miedema, H. (2003). Model for
Lo
the work relatedness of low-back pain. Scandinavian Journal of
Work, Environment & Health, 29, 431e440.
Mattetti, M., Molari, G., & Vertua, A. (2015). New methodology for
accelerating the four-post testing of tractors using wheel hub
displacement. Biosystems Engineering, 129, 307e314. https://
doi.org/10.1016/j.biosystemseng.2014.10.009.
Minitab. (2010). Minitab 17 statistical software. State College, PA:
Minitab.
Nguyen, V. N., & Inaba, S. (2011). Effects of tire inflation pressure
and tractor velocity on dynamic wheel load and rear axle
vibrations. Journal of Terramechanics, 48, 3e16.
Oude Vrielink, H. H. E. (2012). Comparison of high power agricultural
tractors: Effect on whole body vibration exposure during a
standardised test in practice. The Netherland: Ergolab Research
B.V.: Bennekom.
Pacejka, H. B. (2010). Tyre and vehicle dynamics (2nd ed.). Oxford,
UK: Butterworth Heinemann.
Scarlett, A. J., Price, J. S., & Stayner, R. M. (2007). Whole body
vibration: Evaluation of emissions and exposure levels arising
Please cite this article as: Cutini, M et al., Assessment of a ride comfort number for agricultural tractors: A simplified approach, Biosystems Engineering, https://doi.org/10.1016/j.biosystemseng.2019.02.015
10
biosystems engineering xxx (xxxx) xxx
from agricultural tractors. Journal of Terramechanics, 44, 65e73.
https://doi.org/10.1016/j.jterra.2006.01.006.
Sherwin, L. M., Owende, P. M. O., Kanali, C. L., Lyons, J., &
Ward, S. M. (2004). Influence of tyre inflation pressure on
whole-body vibrations transmitted to the operator in a cut-tolength timber. Applied Ergonomics, 35(3), 235e261.
Todeschini, R. (1998). Introduzione alla chemiometria. Naples, Italy:
EdiSES.
VDI 2057-1:2017-08. (2017). Human exposure to mechanical
vibrationsdWhole-body vibration. Beuth, Berlin, Germany.
Please cite this article as: Cutini, M et al., Assessment of a ride comfort number for agricultural tractors: A simplified approach, Biosystems Engineering, https://doi.org/10.1016/j.biosystemseng.2019.02.015