Power tiller: Vibration magnitudes and intervention development for vibration reduction

Applied Ergonomics 43 (2012) 891e901

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Power tiller: Vibration magnitudes and intervention development for vibration reduction Varun Chaturvedi, Adarsh Kumar*, J.K. Singh Division of Agricultural Engineering, Indian Agricultural Research Institute, PUSA, New Delhi 110012, India

a r t i c l e i n f o

a b s t r a c t

Article history: Received 25 November 2009 Accepted 30 December 2011

The operators of power tiller are exposed to a high level of vibration originating from the dynamic interaction between the soil and the machine. The vibration from the power tiller is transmitted from the handle to hands, arms and shoulders. In the present study, experiments were conducted in three operational conditions i.e. transportation on farm roads, tilling with cultivator and rota-tilling with rotavator. The highest vibration values were observed in x-direction in all the experiments. The maximum vibration rms values for x-direction were 5.96, 6.81 and 8.00 ms
2 in tilling with cultivator, transportation and rota-tilling respectively. Three materials were used for intervention development to reduce vibration magnitude. The maximum reduction of 25.30, 31.21 and 30.45% in transportation; 23.50, 30.64 and 20.86% in tilling with cultivator and 24.03, 29.18 and 25.52% in rota-tilling were achieved with polyurethane (PU), rubber and combination of PU and rubber intervention. It was found that the maximum vibration reductions were achieved with the rubber in all three operational conditions. The average exposure time for occurrence of white finger syndrome increased by 28e50% with incorporation of intervention in different operations. Physiological and postural parameters also improved with incorporation of interventions. Ó 2012 Elsevier Ltd and The Ergonomics Society. All rights reserved.

Keywords: Power tiller Hand-arm vibration Intervention Rubber Polyurethane India

1. Introduction In India, small and medium farmers use power tillers for growing crops such as rice, potato and wheat. With increasing pressure on limited land resources and increasing up-keep cost of draught animal, the power tillers is emerging as viable alternative for farmers with small land holdings. Furthermore, the crucial need for timely completion of various farm operations may increase their demand in future. One of the major apprehension and safety concern of power tiller user had been the adverse effect of exposure to a high intensity of hand-arm vibrations. Hand-transmitted vibration of a power tiller is very severe as the handle grip is a cantilever beam, and the power is generated by a single cylinder diesel engine (Ying et al., 1998). The handle vibration is transmitted to the hands, arms and shoulders resulting in discomfort and early fatigue to the operator. Such fatigue experienced over a period of months and years may cause physical, physiological and musculoskeletal disorders (Waersted and Westgaard, 1991; Buckle, 1997). Exposure to hand-transmitted vibration may cause a decrease in skin

* Corresponding author. Tel.: þ91 9312375100; fax: þ91 11 26858703. E-mail address: [email protected] (A. Kumar).

temperature (Iwata, 1974) associated with a reduced blood supply to the fingers as well as an increases in plasma norepinephrine and epinephrine concentration (Krasavina et al., 1977 and Miyashita et al., 1981). Researchers have reported different sources for hand-arm vibration in power tiller operation. Araya (1986) reported that handle vibration in hand operated tilling machines was mainly due to the reciprocating motion of the main moving parts. Jiao et al. (1989) reported that the major excitations of the handtransmitted vibration of a walking tractor are the unbalanced inertia force of the engine and the unevenness of road surface. Dong (1996) concluded that the main cause of vibration was engine and the vibrations in the handle were very strong and seriously affects walking tractor operator’s health. Based on the magnitude of vibrations, researchers had quantified the permissible exposure in power tiller operation. The time taken for vibration-induced white finger (VWF) to appear (latent interval) depends on the level of exposure for the individual. Researchers have quantified magnitude of vibrations and compared them with ISO standards. Mehta et al. (1996) studied the vibrations on a 7.5 kW rotary power tiller. It was reported that the exposure time for the power tiller operator should not exceed 2.5 h during rota-tilling and 4 h during rota-puddling (churning of the soil by attached rotating implement in the standing water condition); increasing the exposure time may cause severe discomfort, pain

0003-6870/$ e see front matter Ó 2012 Elsevier Ltd and The Ergonomics Society. All rights reserved. doi:10.1016/j.apergo.2011.12.012

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and injury. Ragni et al. (1999) reported that if hand tractors are used at least for 4 h per day, the time expected for the appearance of the VWF disorders was 3 years, for 10% of the operators. Goglia et al. (2003) presented research results of the vibration transmitted from the steering wheel of the small tractor with a 4-wheel drive to the driver’s hands. Based on the measurement the vibration acceleration level transmitted from the steering wheel to the driver’s hands will produce finger blanching in 10% of exposed persons in less than 2 years. In another study, Goglia et al. (2006) concluded that the 10% workers are exposed to a risk of vibration-induced white finger in relatively short periods (3 or 4 years), if the hand tractor is used 8 h per day in soil tillage and transportation at full load. Kathirvel and Binisam (2006) studied the characteristics of both walking and riding type power tillers. They concluded that the hand-arm system was most sensitive in the frequency range of 6.3e16 Hz and a seated man was most sensitive in the frequency range of 4e8 Hz. The walking type power tiller showed higher hand arm transmitted vibrations (HTV) than the riding type during rota-tilling, whereas the riding type power tiller exhibited higher hand-transmitted and whole body vibrations during the transport mode. The latent periods for 10% of an exposed population for VWF varied from 4 to 8 years during rota-tilling and 6e13 years during transport at different speeds. In other farm equipment also, the vibration levels are significant. Cakmak et al. (2011) measured the vibration of different harvesters at both idling and full load conditions. The results indicated that in 10% of the exposed population, traumatic vasospastic disease (TVD) appeared after 0.7e7.1 years for the left hand, 1.0e4.7 years for the right hand of the operator in continuous use of these harvesters, under usual working conditions. Mallick (2010) studied, the influence of several operating parameters (length of nylon cutting thread, engine speed and handle material) in a grass trimming machine on HAV. It was reported that the proper selection of the operating parameters can attenuate the HAV level to a magnitude of 2.76 ms
2, which is 36.40% lower than base line value 4.34 ms
2. Researchers have also studied the operator discomfort in power tillers operations. Dewangan and Tewari (2008) reported that work related body pain (WRBP) was highest at the wrist during rotatilling (4.9) and rota-puddling (3.7) whereas it was the highest at the hand (3.5) during transportation using Borg CR-10 scale. There are very few studies, which have focused on intervention development to reduce vibrations. Researchers had made the provision for seat to make the operator comfortable and reduce hand-arm vibrations, but at the cost of exposure to whole body vibrations. Keeping in view the above operational difficulties, the present study was undertaken with the specific objectives: to quantify vibration at the hand-handle interface, assess energy consumption and postural discomfort of operator due to the above level of vibration and to develop and evaluate interventions for vibration reduction to improve comfort and performance of man-machine system. 2. Materials and methods 2.1. Power tiller A commercially available and commonly used power tiller manufactured in India was selected for the study. The power tiller weighing 130 kg was powered with a single cylinder, four stroke, water cooled 13 HP horizontal diesel engine. The power tiller had provision for two attachments namely rota-vator and cultivator. There were two driving wheels in the machine and a small gauge wheel (Fig. 1b) to facilitate the transportation. The cultivator

Fig. 1. Power tiller attachment for tilling (a) with cultivator (b) with rota-vator.

(Fig. 1a) had a width of 570 mm with five stationary tynes with reversible shovel The rota-vator (Fig. 1b) attachment had a 600 mm wide rotating element with 18 C-type tilling tynes blades fitted on the shaft of the rotor. 2.2. Tasks Three male subjects were used to operate the power tiller and perform three operations, namely transportation on farm road (T), tilling with cultivator (C) and rota-tilling with rota-vator (R) on an untilled field (mustard harvested field having stubbles, soil texture - sandy loam, soil structure - granular) condition. In all the three modes the operators has to walk behind the machine. The mean values of temperature and humidity were 35  C and 44 percent, respectively. Transportation was done to carry the machine to the field and back on a leveled field road with no slope. During transportation the gauge wheel was kept at lower height so that the blades of rotating element does not touch the ground. In the rotatilling mode the field was tilled by attaching the rotating implement i.e. rota-vator. In this case the gauge wheel was kept in such a way so that the rotating element touched the ground and gave the required depth of operation. The power tiller was operated at three different speeds (1.0, 1.5 and 2.0 kmh
1) during all the three operations (T1, T2, T3 during transport, C1, C2, C3 during cultivator, and R1, R2 and R3 during rota-vator). All the three speeds were achieved in second gear position and at the different accelerator lever positions. The rota-tiller was operated in first gear position for all the three operational speeds. The experiments were conducted for 20 min duration. 2.3. Instrumentation An adapter was used for attachment of transducer to measure the vibration intensity of hand-arm system. The adapter was made

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up of the aluminum alloy. A lightweight tri-axial accelerometer was fixed by a stud in the adapter for measurement of vibration acceleration. The design of the adapter was such that the accelerometer fixed in between the index and middle finger (Fig. 2). The total weight of the adapter including the accelerometer was 22.5 g. The adapter was mounted according to the ISO-5349 (2001) on the handle bar of the tractor with the help of the metal straps. After mounting, the adapter acted as an integral part of the power tiller, so that it can sense the actual vibration levels as of the handle of the power tiller and there is no vibration dampening in between the adapter and the handle. The adapter was mounted on the right hand handle bar of the power tiller. To measure the vibration magnitude, one tri-axial ICP accelerometer (manufacturer-PCB PIEZOTRONICS) of size 14.0 mm  20.3 mm  14.0 mm and weight 7.4 gm was mounted on the adapter with the help of a stud. The position of hand on the handle bar (Fig. 2) was such that it followed the directions according to the ISO standard. A portable digital, sound and vibration meter (AIDA Vibra., Italy) was used for data acquisition. BNC and LEMO port consists four acquisition channels for simultaneously performing both vibration and sound with 24 bit, 48 kHz converters, being able to monitor and record signals from 0.01 Hz to 22 kHz. It has a low-consumption processor with real time analysis in terms of 1/3 octave (according to IEC 61260, 1995) on the whole band 0.63 Hz to 22 kHz for every acquisition channel. The acquisition system has two measuring ranges i.e. 56.2 ms
2 and 1000 ms
2. A four-pin cable is used for connecting accelerometer with data analyzing system. The signal was pre-amplified before recording by a four channel dataacquisition system. The data stored in the data-acquisition system was downloaded on a personal computer at the end of the experiment for further analysis. 2.4. Design of the experiment The experiments were designed in two phases. In first phase, measurements were taken without interventions and in the second phase, all the experiments were repeated incorporating the developed interventions. The vibration measurements and analysis were carried out as outlined in the Fig. 3. The subjects were asked to take rest initially and then operate the power tiller. For a pre-

Fig. 2. Accelerometer with handgrip.

Operator with power tiller

893

Transducer and signal conditioner

Results in the form of graph

Data analysis software

Data acquisition system

Personal computer

Fig. 3. Schematic diagram of the experimental set-up for measuring vibration acceleration in the hand-arm system.

selected gear setting and type of operation, the rms vibration accelerations were recorded. 2.5. Interventions development The strategies to reduce the vibration magnitude at the handhandle interface were focused on to place the damper in between the handle bar and the chassis or to put them in between engine and the chassis or at both interfaces. Different studies had been conducted to reduce the hand-transmitted vibration. Researchers have suggested addition of seat to make a power tiller riding type. In this approach the hand-transmitted vibration were reduced but at the same time the operator were exposed to whole body vibration. There are few studies on isolation of engine vibrations with the help of isolators, dampening sleeves on the handle bar and splitting handle arm to reduce vibrations. But the invasive technique of splitting handle bar and incorporating damping member in between may reduce the structural strength of handle. In the present study, the interventions were designed to be placed at the interface of handle bar and chassis. In power tillers the handle bar and the chassis have metallic surface-to-surface contact and are secured through bolts and nuts. Therefore to break the contact between two metallic surfaces, so that vibration transmission is reduced between the surfaces. Vibration reduction interventions had two components; one is bush with collar to hold nut and bolts and another one is flat sheet of the damping material to separate direct contact between two metallic surfaces (Fig. 4). The materials for development of interventions were selected for their mechanical strength, vibration damping properties, durability and availability in the market. Synthetic rubber (I1), polyurethane (I2) and combination of rubber and polyurethane (I3) were used to develop the interventions. Characteristics of damping materials are given in the Table 1. The solid rods of materials were used to make bushes with collar and the sheets were used to separate the direct contact between flat surfaces. These materials were also cost effective (4, 6 and 10 $ for I1, I2 and I3 intervention) and are abundantly available in local market. They also have has good elastic reversibility; flexibility, impermeability, machinability and excellent vibration damping qualities which make them a good intervention material. The design and dimensions of different interventions are shown in Figs. 4 and 5 respectively. The developed interventions were placed at contact point of chassis and handle bar (Fig. 6). The developed interventions breaks the direct contact between the two metallic surfaces without compromising on structural strength/ rigidity, so that maneuverability to operate the power tiller in the different operational conditions is not adversely effected.

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Fig. 4. Different vibration reduction intervention: bush and sheet.

2.6. Vibration measurement 2.6.1. Direction of vibration The vibrations from all three directions are transmitted to the hand of the operator. Therefore to measure the quantum of vibration received by operator shall be measured simultaneously for all three directions. In practice, measurements are usually obtained with respect to a basicentric coordinate system centered on (or adjacent to) the vibrating surface (Griffin, 1996). Fig. 7 illustrates an anatomical and basicentric coordinate system for measurement of hand-arm vibration exposure as defined in ISO 5349-1(2001). In anatomical (Biodynamic) coordinate system; z-axis, is defined as the longitudinal axis of the third metacarpal bone and is oriented positively towards the distal end of the finger; the x-axis passes through the origin and is perpendicular to the z-axis, and is positive in the forward direction when the hand is in the normal anatomical position (palm facing forwards); the y-axis is perpendicular to the other two axes and is positive in the direction towards the fifth finger (thumb). In practice the basicentric coordinate system is used. The system is generally rotated in the yez plane so that the yaxis is parallel to the handle axis.

Table 1 Characteristics of the damping materials. Material

Chemical Content

Hardness

Elongation (%)

Melting point ( C)

Rubber

Styrene-butadiene rubber Aliphatic polyurethane

40e80 A

450e500

120

70e90 A

5e55

Polyurethane

177e232

2.6.2. Magnitude of vibration Human response to vibration is dependent on the frequency of the vibration. According to ISO 5349 (2001) recommendations, the most important quantity used to describe the magnitude of vibration transmitted to the operator’s hands is root mean square (rms) frequency-weighted acceleration in ms
2 expressed as

2

ahw

31=2 n  2 X Wh ahj 5 ¼ 4

(1)

j¼1

Where ahw - root mean square (rms) frequency weighted acceleration Wh - weighting factor for the jth one third octave ahj - rms acceleration measured in one third octave bands used in ms
2 n - number of frequencies used in the octave band The weighted value should be determined over the eight octave bands (i.e., n ¼ 8) from 8 to 1000 Hz or over the 24 one-third octave bands (i.e., n ¼ 24) from 6.3 to 1250 Hz. The sensitivity of human body to different frequencies is not uniform, therefore, weighting factor for different frequency bands are defined in ISO 5349-1 (2001). The hand-arm system is more sensitive to the frequency range of 6.3e31.5 Hz. The evaluation of vibration exposure in accordance with ISO 5349-1 (2001) is based on a quantity that combines all three axes. This, value ahv (vector sum) is defined as the rms sum of the three component values. The vector sum of vibration intensity is virtually independent of the orientation of the coordinate system.

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895

Fig. 5. Dimensions of intervention (A) Bush (B) Sheet. All dimensions in mm.

ahv ¼

qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi  2  2  2 ahwx þ ahwy þ ahwz

(2)

Where ahv - total rms acceleration at the handle in ms ahwx - rms acceleration in the x-axis in ms
2 ahwy - rms acceleration in the y-axis in ms
2 ahwz - rms acceleration in the z-axis in ms
2

Dy ¼ 31:8½Að8Þ
1:06
2

(4)

Where A(8) - daily vibration exposure (8-h energy-equivalent vibration total value at a surface in contact with the hand) in ms
2 Dy - the group mean total (lifetime) exposure duration, in years.

The daily vibration exposure in terms of 8-h energy equivalent was derived from the magnitude of the vibration (vibration total value) and daily exposure duration. In order to facilitate comparisons between daily exposures of different durations, the daily vibration exposure were expressed in terms of 8-h energyequivalent frequency-weighted vibration total value, ahv(eq,8 h), as shown in the equation (3). For convenience, ahv(eq,8 h) is denoted as DA(8).

sffiffiffiffiffi T Að8Þ ¼ ahv To

The following formula is used to estimate exposure duration for finger blanching in 10% of exposed persons as given in ISO 5349 (2001).

(3)

Where A(8) - vibration exposure in terms of 8-h energy equivalent T - total daily duration of exposure to the vibration ahv (h or sec) ahv - vibration total value in ms
2 T0 - reference duration of 8 h (28,800 s).

2.7. Ergonomic parameters evaluation during different selected operational conditions 2.7.1. Calibration of subjects In the present study three subjects were selected for the experiments. It was ensured that subjects were physically fit; not suffering from any illness (Seidal et al., 1980). Calibration of subjects was done with, heart rate monitor, Oxylog2 and bicycle ergometer. The calibration process was conducted for 5e7 min. During this process, the subject was instructed to run bicycle ergometer vigorously up to heart rate sub maximal level. Ambient condition was recorded during experiment for making necessary correction in the observation. After completion of calibration process, the stored data of heart rate and oxygen consumption rate were transferred to computer for determining the relationship between heart rate and oxygen consumption. A linear relationship between heart rate and oxygen consumption rate was obtained.

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Fig. 6. Installation of interventions.

2.7.2. Measurement of operator’s physiological parameters Heart rate and oxygen consumption rate were taken as the physiological parameters. The mean values of heart rate, the corresponding values of oxygen consumption (VO2) of subject had linear relationship and this relationship was used to compute oxygen consumption in experiments. The energy expenditure during the experiments was computed by multiplying the oxygen consumption (VO2) with the calorific value of oxygen, which is equal to 20.88 k J min
1 (Nag et al., 1980) for all the subjects. 2.7.3. Determination of postural discomfort The body part discomfort score and the overall discomfort score were taken as the postural parameters and the subjective evaluation of discomforts were done by recording the discomfort levels in

different body part and overall discomfort experienced by the subjects. To measure localized discomfort, Corlett and Bishop (1976) technique was used. In this method, the body of subject is divided into 27 regions. Each body region was numbered differently to avoid a subject marking on particular numbered body region only. The subject was asked to mention all body parts with discomfort, starting with the most painful and so on in descending order till all the body parts experiencing discomfort had been recorded. The number of different groups of body parts, which were identified from extreme discomfort to no discomfort, represented the intensity levels of discomfort experienced. The maximum number of intensity levels of discomfort experienced during the experiment was categorized. The ratings were assigned to these categories in an arithmetical order. The body part discomfort score

V. Chaturvedi et al. / Applied Ergonomics 43 (2012) 891e901

897

2.0 kmh
1 speed which is higher than the transportation and tilling with cultivator. In y-direction hand arm transmitted vibrations were highest, 2.72 and 2.86 ms
2 at 1.0 and 1.5 kmh
1. But at 2.0 kmh
1 speeds the vibration magnitude was 1.18 ms
2, which was lower than the rota-tilling and transportation operation. The trend of vibration magnitude in z-direction was similar as in the case of y-direction. 3.1.2. With intervention With the application of interventions the vibration magnitudes (rms acceleration) were reduced in all the directions. However, the vibration magnitudes showed the similar trends, as x-direction vibrations were higher than the other two directions even with the application of interventions. The rms acceleration values for individual direction are given in the Table 3.

3.2. Hand-transmitted total rms vibration acceleration value

Fig. 7. Coordinate system for the hand.

assigned by subject was multiplied by the number of body parts corresponding to each category. The total body part score for a subject was sum of all individual scores of all the body parts assigned by the subject. The body part discomfort score of all the subjects was added and averaged to obtain mean score. The same procedure was repeated for all the experiments. At the end of experiment, subject was asked to mention their overall discomfort rating. The overall discomfort ratings of all the subjects were added and averaged to get the mean rating. 3. Results Magnitudes of vibration were measured without intervention and with intervention to ascertain magnitude severity and effectiveness of interventions. 3.1. Frequency weighted rms acceleration in different directions 3.1.1. Without intervention The hand-transmitted vibration for all the three axes as defined in ISO 5349 (2001) was measured and recorded (Equation (1)) in different field operations viz transportation, tilling with cultivator and rota-tilling for x, y and z direction (Table 2). It is evident from the Table 2 that in all the operations, vibration magnitudes were higher in the x-direction. In rota-tilling, the magnitudes in x-direction varied from 6.01 to 8.00 ms
2 at 1.0 to

Table 2 Frequency weighted rms acceleration values of hand-transmitted vibration at handle without intervention. Operational conditionsa

Table 3 Frequency weighted rms acceleration values of hand-transmitted vibration at handle with intervention. Operational conditions

Speed Vibration magnitudes in rms acceleration (kmh
1) (ms
2) x-axis

y-axis

z-axis

T1 T2 T3

1.0 1.5 2.0

6.15 5.99 6.81

1.33 1.35 1.49

2.23 2.43 2.82

Tilling with cultivator

C1 C2 C3

1.0 1.5 2.0

4.84 5.23 5.96

2.72 2.86 1.18

3.52 3.94 1.91

Rota-tilling

R1 R2 R3

1.0 1.5 2.0

6.01 6.62 8.00

1.46 1.47 1.68

2.24 2.43 2.67

Transportation

The total rms acceleration and percentage reduction with interventions were calculated as shown in Table 4 and Fig. 8, respectively. The total vibration values were calculated as shown in Equation (2). The values were maximum at 2.0 kmh
1 for transportation (T3) and rota-tilling (R3) but it was maximum at 1.5 kmh
1 for tilling with cultivator (C2). In transportation mode the maximum vibration total values varied from 6.67 to 7.51 ms
2. The maximum total vibration value in rota-tilling varied from 6.58 ms
2 to 8.43 ms
2. In cultivator, the total vibration values varied from 6.37 to 7.14 ms
2, lower than the other two operations. With application of intervention the maximum reduction was achieved with rubber (I1) followed by rubber þ PU (I3) and PU (I2). With (I1) interventions the total vibration values reduced significantly from 4.54 to 5.56 ms
2 in case of transportation, 4.37e4.84 ms
2 in case of cultivator operation and 4.58e6.01 ms
2 in case of rota-tilling (F ¼ 18.06, CD ¼ 0.147). In transportation mode the vibration reductions were in the range of 24e31% (Fig. 8). The maximum reduction of 31.21%, 25.30%, and 30.45% were achieved with, I1, I2 and I3 at 1.5 kmh
1 speed. In tilling with cultivator, the average reductions in total vibration value were 30.64, 23.50 and 20.86% with the application of I1, I2 and I3 interventions. The vibration intervention also resulted in reduction of 29.18, 24.03 and 25.52% in rota-tilling with I1, I2 and I3 interventions. The vibration reduction with I1, was maximum in all the three operational conditions. This was due to the fact that rubber has better elastically recoverable as compare to PU. The PU has a very

a T1, T2, T3, C1, C2, C3, R1, R2 and R3 are transportation, cultivator and rota-vator operation at 1.0, 1.5 and 2.0 kmh
1 respectively.

Vibration magnitudes in rms acceleration (ms
2) x-axis

y-axis

z-axis

Intervention I1 Transportation

I2

I3

I1

I2

I3

I1

I2

I3

T1 4.30 4.73 4.54 0.98 1.02 1.01 2.33 1.52 1.60 T2 4.23 4.54 4.15 1.01 1.05 1.03 1.28 1.60 1.67 T3 5.08 5.21 5.13 1.11 1.15 1.13 1.95 1.94 2.02

Tilling with cultivator C1 3.42 3.79 3.71 2.07 2.06 2.10 2.49 2.53 2.52 C2 3.68 4.06 3.83 1.46 2.24 2.18 2.79 2.70 2.86 C3 4.07 4.74 5.40 0.84 0.84 0.89 1.34 1.29 1.37 Rota-tilling

R1 4.15 4.57 4.48 1.12 1.15 1.14 1.59 1.27 1.59 R2 4.69 4.94 4.89 1.09 1.15 1.12 1.84 1.80 1.78 R3 5.54 6.31 5.94 1.25 1.23 1.13 1.95 1.77 1.93

I1 ¼ Rubber intervention, I2 ¼ PU Intervention, I3 ¼ Rubber þ PU intervention.

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Table 4 Hand-transmitted total rms vibration acceleration value. Total rms vibration acceleration value (ms
2)

Operational condition

Without intervention

Intervention I1

I2

I3

Transportation

T1 T2 T3

6.67 6.60 7.51

4.67 4.54 5.56

5.07 4.93 5.68

4.92 4.59 5.63

Tilling with cultivator

C1 C2 C3

6.57 7.14 6.37

4.71 4.84 4.37

5.00 5.37 4.98

4.95 5.25 5.25

Rota-tilling

R1 R2 R3

6.58 7.21 8.43

4.58 5.16 6.01

4.88 5.38 6.67

4.89 5.32 6.35

I1 ¼ Rubber intervention, I2 ¼ PU Intervention, I3 ¼ Rubber þ PU intervention.

high fatigue strength, which will have a higher life, but lower elastic recoverability. To make an effective intervention for vibration reduction and to overcome cyclic fatigue a combination of PU and rubber was used, which gave better result than PU alone but lower reduction as compared to rubber alone. 3.3. Assessment of exposure time for white finger syndrome ISO 5439 (2001)

PU (I1)

Rubber (I2)

Combination of PU and rubber (I3)

35 30

% reduction

Fig. 9. Mean total (lifetime) exposure duration for predicted 10% prevalence of vibration-induced white finger (ISO 5439, 2001) without and with rubber interventions in (a) transportation (b) tilling with cultivator and (c) rota-tilling.

reduced to 4.58e6.01 ms
2 and corresponding lifetime exposure increased to 6.32 to 4.75 years (Fig. 9c). With incorporation of different intervention, there was significant increase in permissible exposure duration. The average exposure time for occurrence of white finger syndrome increased by 37.6, 50.7 and 43.37% with I1 intervention, 34.67, 35.35 and 28.31% with I2 intervention, and 35.73, 38.38 and 34.94% with I3 intervention in transportation, tilling with cultivator and rotatilling operation respectively for 8 h daily exposure (Fig. 10). The

25 20 15 10

Rubber (I1)

60

Percent increase in exposure time

As evident from Table 4, in transportation mode, the maximum values of total vibration varied from 6.67 to 7.51 ms
2. The corresponding value of exposure limit for 10% of operators as prescribed in ISO 5439 (2001) to have white finger syndrome (Equation (4)) were 4.25 and 3.75 years for 8 h of daily vibration exposure. After application of the rubber interventions (I1), which is found to be most effective intervention, the total vibration values were in the range of 4.67e5.56 ms
2 which corresponds to lifetime exposure of 5.16e6.21 years (Fig. 9a). In cultivator the total vibration values were less than the other two operations, but . total vibration values varied from 6.37 to 7.14 ms
2, and the lifetime exposure limit computed to be in the range of 4.47 to 3.96 years. With I1, interventions the total vibration values were reduced to 4.37e4.84 ms
2 and corresponding lifetime exposure increased to 6.66 to 5.98 years (Fig. 9b). The maximum total vibration value in rota-tilling varied from 6.58 ms
2e8.43 ms
2. The corresponding exposure duration (years) for this magnitude of vibration were 4.32 to 3.32 years for 8 h daily exposure for 10% operators to have white finger syndrome. With I1, interventions the total vibration values were

PU (I2)

PU+Rubber (I3)

50

40

30

20

10

5 0

0 T1

T2

T3

C1

C2

C3

R1

R2

Operational condition Fig. 8. Effect of interventions on total rms vibration acceleration value.

R3

T1

C2

R3

Operational condition Fig. 10. Effect of interventions on exposure duration.

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increase in exposure limit was maximum with the I1 intervention for all the operational conditions. 3.4. One third octave band analysis Frequency spectra were obtained for all three axes for all the operational condition for one third octave band analysis. The vibration magnitudes concentrated over a frequency range of 0e200 Hz. Fig. 11 shows the frequency spectrum of x-direction, which had higher values compare to y and z-direction. One peak of vibration was found between 25 and 31.5 Hz, second at 50 Hz and third around 125 Hz. 3.5. Ergonomic parameters evaluation during selected operating conditions The heart rates (HR) were recorded with heart rate monitor during the experiments conducted in all operating conditions for selected subjects A, B and C. The corresponding values of oxygen consumption (VO2) of subjects were estimated from calibration chart. The relationship between the heart rate and oxygen consumption of subjects was found to be linear. The other anthropometric data (Table 5) was also recorded at the time of study. The mean values of heart rate from 6th to 15th minute of experiment of all subjects for all operational conditions with and without interventions are shown in Table 6. It is evident from the observation that the working heart rate was higher for rota-tilling than the tilling with cultivator and transportation. The maximum value of working heart rate for rota-tilling was 141.15 beats min
1 without interventions. With the help of interventions the working heart rate reduced to 131.56 beats min
1, which is significant reduction. The maximum value of oxygen consumption was 1.15 l min
1 in rota-tilling. The energy consumption varied from 22.55 to 24.01 kJ min
1 in rota-tilling for all the subjects, which can be categorized in moderately heavy work class. Based on the Corlett and Bishop (1976) technique, the body part discomfort score (BPDS) of all subjects for all the experiments was determined. The body part discomfort score were highest in the rota-tilling followed by cultivator and transportation. With the application of interventions the BPDS reduced for all operational conditions. The maximum reduction of BPDS was 10.74 in transportation with the application of rubber interventions. The overall discomfort scores (ODS) of the subjects for all operational conditions at the speed with maximum vibrations were calculated as explained at 2.7.3. The maximum overall discomfort was in the rota-tilling operation. The lowest overall discomfort was in transportation. The reduction in ODS was not significant (F ¼ 168.68,

Fig. 11. Frequency spectrum of x-direction vibrations.

899

Table 5 Anthropometric data of subjects. Subject

Age (years)

Height (cm)

Weight (kg)

A B C

46 30 42

166 164 162

76 62 74

CD ¼ 0.113) after the application of vibration interventions because ODS is effected by other factors i.e. walking with the power tiller in different farm conditions, controlling the movement of power tiller and other environment conditions also.

4. Discussion The hand-transmitted vibration for all the three axis as defined in ISO 5349 (2001) were measured and recorded in different field operations. The magnitudes of vibrations were higher in x-direction in all the operations at all the speeds, indicating that the xdirection was the major contributor in the total vibration value. In cultivator operation, there was significant reduction in magnitudes of vibration in y and z-directions with increase in speed up to 2.0 kmh
1. It might be due to downward pull exerted by cultivator and requirement of higher draft force during tillage, which reduced side movement of power tiller. The interaction of cultivator tines with soil also helped in damping of vibration. The vibration magnitudes in rota-tilling were higher in x-direction than tilling with cultivator and transportation mode. The hitching arrangement for rota-vator is rigid due to rotary power transmission to tines, which make it behave like a single integrated unit. The interactions of rotary tines with soil also generate additional vibration. These results were similar to results reported by Ragni et al. (1999) showing that lowest value of vibration was in y direction for single axle tractor with rotary cultivator. In transportation, the maximum acceleration value appeared around 50 Hz Goglia et al. (2006) also reported the similar range of frequency for peak accelerations. In transportation and soil tillage, y-direction maximum acceleration appeared at 63 Hz. In transportation the vibrations in z-direction acceleration were maximum at 25 and 50 Hz. In tilling with cultivator one peak of vibration appeared at 31.5 Hz which may causes more detrimental effect due to resonance. As Dewangan and Tewari (2008) reported that the peak transmissibility at metacarpal was at 31.5 Hz during rota-puddling, rota-tilling and transportation, which was also the dominant frequency of vibration of hand tractor. They suggested that this may be due to resonance of the skin at metacarpal. The resonance frequency of the hand reported by Reynolds and Angevine (1977), Gurram et al. (1994), Cherian et al. (1996) and Sorensson and Burstrom (1997) were at 63, 63e100, 20e30 and 40e100 Hz respectively. Reynolds and Soedel (1974) reported resonance at 50 Hz frequency in cutaneous, subcutaneous and muscle tissues of hand. In the present study another higher peak acceleration appears at 125 Hz, but this may not have a detrimental effect as weighting has roll-off rate at higher frequencies (Mansfield, 2004). In rota-tilling the peak value in x-direction was found at 50 Hz and around 160 Hz. The vibration magnitudes were concentrating over a frequency range of 0e200 Hz. Ying et al. (1998) reported the similar trends. They found that most vibration was concentrated in the frequency range of 0e200 Hz and the most serious vibration occurs in x-direction. Three types of interventions were developed and installed on the power tiller for conducting experiments. The observations were recorded in the similar operating conditions as mentioned above.

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V. Chaturvedi et al. / Applied Ergonomics 43 (2012) 891e901

Table 6 Ergonomic parameters during power tiller operation. Mode

Without intervention

Operational conditions

Transportation (2.0 kmh
1)

Tiller with cultivator (1.5 kmh
1) Rota-tilling (2.0 kmh
1)

Rubber intervention (I1)

Transportation (2.0 kmh
1)

Tiller with cultivator (1.5 kmh
1) Rota-tilling (2.0 kmh
1)

PU intervention (I2)

Transportation (2.0 kmh
1)

Tiller with cultivator (1.5 kmh
1) Rota-tilling (2.0 kmh
1)

Combination of PU and rubber intervention (I3)

Transportation (2.0 kmh
1)

Tiller with cultivator (1.5 kmh
1) Rota-tilling (2.0 kmh
1)

Physiological parameters

Postural parameters

Subject

Working heart rate (beats min
1)

Oxygen consumption (l min
1)

Energy consumption (kJ min
1)

BPDS

ODS

A B C A B C A B C

116.31 117.22 119.63 123.15 130.52 126.76 137.88 141.15 138.16

0.85 0.71 0.93 0.94 0.91 1.02 1.13 1.08 1.15

17.75 14.82 19.42 19.63 19.00 21.30 23.59 22.55 24.01

33.01 36.06 32.26 39.11 41.33 38.15 51.18 53.89 52.48

1.00 1.50 1.00 2.83 3.50 2.67 3.83 4.00 3.83

A B C A B C A B C

98.49 99.40 101.27 112.57 119.94 105.57 128.29 131.56 128.25

0.63 0.44 0.72 0.81 0.75 0.77 1.01 0.93 1.04

13.15 09.19 15.03 16.91 15.66 16.08 21.09 19.42 21.72

22.27 30.27 24.15 30.30 32.38 28.94 44.74 47.52 46.58

1.00 1.50 1.00 2.67 3.50 2.67 3.50 3.83 3.50

A B C A B C A B C

108.12 109.03 110.43 116.16 123.53 118.46 131.69 134.96 131.74

0.75 0.58 0.83 0.85 0.81 0.92 1.05 0.98 1.08

15.66 12.11 17.33 17.75 16.91 19.21 21.92 20.46 22.55

27.76 32.70 29.48 32.93 35.98 32.57 47.24 50.78 48.54

1.00 1.50 1.00 2.67 3.50 2.67 3.83 4.00 3.83

A B C A B C A B C

107.93 108.84 106.42 110.65 118.02 111.94 129.72 132.99 129.24

0.75 0.58 0.78 0.78 0.72 0.84 1.02 0.95 1.05

15.66 12.11 16.29 16.29 15.03 17.54 21.30 19.84 21.92

25.27 31.73 25.45 32.33 34.40 33.12 46.30 48.30 48.67

1.00 1.50 1.00 2.67 3.50 2.67 3.83 3.83 3.83

The total vibration values and percentage reduction in total vibration value were calculated with different interventions. In transportation mode the vibration reductions were in the range of 24e31%. The maximum reduction of 25.30%, 31.21% and 30.45% with I2, I1 and I3 were achieved at 1.5 kmh
1 speeds. The vibration reduction with the I1 was highest in all three operational conditions. The total vibration values were maximum at 2.0 kmh
1 for transportation and rota-tilling but it was maximum at 1.5 kmh
1 for tilling with cultivator. As per ISO 5439 (2001) the exposure limit for 8-h daily use of power tiller was 3.32e3.75 years, which was close to value suggested by Goglia et al. (2006). They reported that 10% of workers were exposed to vibration-induced white finger after relatively short period (3e4 years) if the tractor was used at 8-h per day at full load in transportation and soil tillage. The average exposure time for occurrence of white finger syndrome increased by 28e50% with the use of intervention in different operations. The increase in permissible exposure time with the intervention I1 was maximum for all the three operational conditions due to higher reduction in vibration. The relationship between the heart rate and oxygen consumption of subjects was found to be linear for all subjects, which was in close agreement with results reported by Rodahl (1989), Sanders and McCormic (1993) and Bridger (1995). This linearity of relationship differed from one individual to another due to difference in subject age, weight and stature (Kroemer et al., 1997). The

maximum value of working heart rate for rota-tilling was 141.15 beats min
1 without interventions. Pawar and Pathak (1980) have reported heart rate values varying from 105 to 114 beats min
1 at forward speed from 0.18 to 0.52 ms
1 during rota-tilling. With the help of interventions the working heart rate reduced significantly. The trend for oxygen consumption was same as for the working heart rate. The oxygen consumption was higher for subject A in rota-tilling. The energy consumption varied from 18 to 24 kJ min
1 in the rota-tilling for all subjects. Pawar (1978) concluded that the energy consumption of power tiller varied between 24.7 and 34.6 kJ min
1, which is classified as moderately heavy similar to present study. The body part discomfort score were highest in the rota-tilling than cultivator and transportation. The maximum reduction of BPDS was 10.74 in transportation with the application of interventions I1, indicating that vibrations are major contributing factor for the discomfort score. With the application of interventions the BPDS also reduced for each operating condition. The maximum overall discomfort was in the rota-tilling operation. The lowest overall discomfort was observed in transportation. In rota-tilling, rotary blades impact the soil, which in turn produce vibration. The operator also has to apply the force to maneuver power tiller and to maintain the uniformity of tillage depth. Moreover, rotating blades create elevated dust concentration in the breathing zone of operator, which could also induce feeling of fatigue.

V. Chaturvedi et al. / Applied Ergonomics 43 (2012) 891e901

In case of cultivator a dead weight (24 kg) was added for maintaining the depth of operation. The measured vibration levels were lower in cultivator operation, which resulted in lower discomfort and tiredness. During transportation the discomfort and tiredness were lowest, as the machine was supported on three wheels i.e. two transport wheels and gauge wheel and efforts required by operator was lower. Similar observations were also reported by Dewangan and Tewari (2008). They reported the lower work related body pain in transportation mode as machine was balanced and operator efforts were limited to actuating the hand clutch. 5. Conclusions The maximum vibration values were observed in x-direction for all the conditions. The x-direction vibrations were 5.96, 6.81 and 8.00 ms
2 in tilling with cultivator, transportation and rota-tilling respectively. Higher values of x-direction vibration were major contributor in the total vibration value. Maximum vibration reductions in all three operating conditions were achieved with intervention ‘I1’. In transportation mode maximum reduction achieved was 31.21%, 25.30% and 30.45% with intervention I1, I3 and I2. Total vibration reduction of 30.64, 23.50 and 20.86% in tilling with cultivator was achieved with intervention I1, I3 and I2. In rota-tilling with the intervention I1, I2 and I3, the vibration reduced by 29.18, 24.03, and 25.52% respectively. The average exposure time for occurrence of white finger syndrome increased by 37.6, 50.7 and 43.37% with I1 intervention, 34.67, 35.35 and 28.31% with I2 intervention, and 35.73, 38.38 and 34.94% with I3 intervention in transportation, tilling with cultivator and rota-tilling operation respectively for 8 h daily exposure. With the help of interventions the working heart rate reduced significantly in the case of I1 intervention. However there was less reduction in ODS with the application of vibration interventions.

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