Development of ergo-refined operator’s workplace and biophysically actual cost-benefit analysis of riding type self-propelled machines with special reference for female operators

Abstract

BACKGROUND:

Female agricultural workers contribute to 37% of the total agricultural workforce in India, however, most self-propelled machinery is designed for male agricultural workers.

OBJECTIVE:

The primary objective was to determine the impact of the ergo-refined operator’s workplace on various aspects of operator performance and comfort, including actuating force, posture, and physiological parameters.

METHODS:

Experiments were carried out in real field conditions using a full factorial randomized design. Twelve female operators participated in the study, and measurements were taken for control lever actuating force, operator posture, heart rate, and other relevant parameters.

RESULTS:

The ergo-refined operator’s workplace intervention resulted in significant reductions in actuating force for various control levers, angles of joints, working heart rate (WHR), oxygen consumption rate (OCR), muscle load, and whole-body vibration (WBV) acceleration. These reductions were observed under different operating conditions.

CONCLUSION:

The findings suggest that the ergo-refined operator’s workplace is effective in enhancing operator comfort and reducing physical strain during the operation of riding type self-propelled machines. It contributes to improved safety, comfort, and operational efficiency for operators working in field conditions. ANOVA and MANOVA analyses confirmed the positive impact of operating conditions and engine speed on the measured parameters when using the ergo-refined operator’s workplace.

Keywords

Workplace biophysical cost assessment muscle fatigue working heart rate actuating force and whole body vibration

1 Introduction

Self-propelled machinery is an integral part of agricultural mechanization and plays a crucial role in enhancing productivity. Farming operations like transplantation, crop harvesting, and straw binding involve the use of self-propelled machines such as transplanters, vertical conveyor reapers, mini combine harvesters, and reaper binders. In India, there is an increasing demand for self-propelled machinery, with 5,000 units sold in 2018–2019 [24]. However, the overall farm mechanization level in the country is only 40%, with highly mechanized operations like seedbed preparation accounting for over 50% and less mechanized operations like harvesting and threshing comprising less than 30% for most crops. This level is lower than that of other developing countries [25].

There are two categories of self-propelled machines: walking-behind and riding type. However, the riding type is more popular due to the unacceptability of the walking type. Walking type machines are associated with higher exertion, greater energy consumption, and a higher risk of accidents [5, 48].

Indian female agricultural workers play a significant role in Indian agriculture alongside male workers, being involved in various crop production and post-harvest activities. Female agricultural workers contribute to 37% of the total agricultural workforce [27]. Unfortunately, most self-propelled machinery is designed for male agricultural workers, assuming it is suitable for female agricultural workers [47]. However, these machines are unsuitable for female workers due to gender differences in ergonomic characteristics, such as anthropometry and strength data [45]. Anthropometric dimensions and strength data of female workers are smaller than their male counterparts, and they can only apply around 70% of the muscle strength of male workers [13 , 33]. The unsuitability of the dimensions of the self-propelled machine workplace and control lever locations for female workers forced them to adopt uncomfortable postures during operation [40]. As a result of the repetitive and prolonged operation of such machines, musculoskeletal disorders and bodily pain occur [7, 39].

The application of anthropometry involves the design of workplaces, equipment, tools, and products with the aim of significantly improving work efficiency, productivity, usability, comfort, and safety for all users [7 , 21–23]. Designing workstations that consider the postural relationship between body dimensions and the workplace [15, 11], analyzing strength data and forces/torque involved in controlling or performing physical tasks [8 , 21], and characterizing the anthropometric differences among various occupational and ethnic groups are necessary. The high rate of occupational injuries resulting from inappropriate equipment design has led to the proposal of analyzing anthropometric characteristics and modifying designs to enhance safety and prevent injuries in the workplace [2, 3].

The operation of self-propelled machines can subject operators to vibrations that may cause fatigue, injuries, and vibration-induced disorders, such as white finger disease, leading to significant medical expenses [40]. By installing a piezo-metric based seat suspension system with a custom-designed isolator, the average reduction in tractor seat vibration can reach 40%. Notably, the highest levels of vibration acceleration were experienced in the vertical direction [17, 40]. While operator seats have greatly improved operator comfort, the lack of suitable design and positioning of the operator seat, along with operating controls, safety, and comfort, has been compromised [21]. The most appropriate method for predicting vibration discomfort in an agricultural tractor is the one recommended by ISO 2631. This method utilizes the frequency-weighted root mean square (r.m.s) values of vibration (ranging from 0.5 to 20 Hz) measured on the seat pan in three orthogonal directions. The values from each direction are combined using the square root of their sum, as suggested in Amendment I of ISO 2631 [20]. In the case of hand tractors, suitable isolator materials were tested and identified for effectively reducing vibration [5].

Studies on the exposure of farm equipment drivers to WBV have recommended interventions to reduce the risk of back-related injuries. These interventions include isolating the operators, maintaining seat suspension, and replacing worn or damaged cushions with viscoelastic foam padding tested by the National Institute for Occupational Safety and Health (NIOSH) to help attenuate ride vibrations [28, 39]. In a separate study, the damping characteristics of tractor seat cushion materials were examined to improve operator comfort. It was observed that the equivalent viscous damping coefficient (Ceq) of cushion materials decreased as the frequency and peak-to-peak amplitude of vibration increased. The decrease was particularly pronounced in the lower frequency range, up to 3 Hz. Based on these findings, the present research aims to study the design of the workplace for mini combine harvesters and its vibration characteristics, considering them as representative of riding type self-propelled machinery [39]. It is anticipated that in coming years most of these machines will be operated by female operators, as male operators are migrating to seek better livelihood opportunities in urban areas. Recognizing the importance of women in agriculture, substantial efforts are being given to develop women-friendly tools, equipment, machinery, and workplaces. These endeavors aim to elevate comfort, ensure safety, curtail strenuous tasks, and optimize the overall efficiency of the system. As the self-propelled machines are not ergonomically designed, there is a need for proper evaluation of ergonomic factors to make these machines user-friendly for female workers. To ridicule aforementioned issues a proper quantification of the level of work stress, physiological energy demand, and muscle fatigue including operator’s subjective responses is also needed to design appropriate interventions for the reduction of operating effort, muscle fatigue, and vibration experienced by the female operators. The specific objectives of the study are to design a suitable workplace for self-propelled machines, taking into account female anthropometric data, and to design an ergo-refined seat for comfortable operation and vibration reduction.

2 Materials and methods

2.1 Subjects

The volunteer female subjects were selected from Kharagpur, West Bengal, India, considering their knowledge of driving self-propelled machinery to ensure safe and efficient operation. The twenty mentioned anthropometric dimensions were crucial for the design of the workplace in riding type self-propelled machines. Table 1 presents the mean, range, coefficient of variation, and standard deviation of the body dimensions.

Table 1
Anthropometric dimensions of randomly female agricultural workers

Body dimensions Mean SD^* CV^** Range

Stature 1495.3 44.4 0.028 1403–1580

Weight (kg) 58.70 3.53 0.060 54.5–65.4

Grip diameter (inside) 498.3 41.2 0.083 460–600

Shoulder breadth (Bideltoid) 380.9 18.9 0.050 349–412

Arm reach from wall 699.0 55.9 0.080 624–783

Vertical grip reach 1432.6 66.0 0.046 1320–1540

Foot length 231.2 11.8 0.051 210–253

Sitting eye height 674.3 27.1 0.040 626–694

Sitting shoulder height 529.4 44.9 0.085 440–621

Elbow rest height 562.4 48.2 0.086 450–621

Knee height 464.6 53.7 0.116 388–558

Popliteal height 388.7 34.8 0.090 338–454

Buttock popliteal length 433.3 21.9 0.051 400–471

Bullock knee length‘ 561.8 24.4 0.044 513–585

Functional leg length 891.0 47.0 0.053 850–982

Thigh clearance height (sitting) 137.6 10.1 0.074 120–184

Hip breadth (sitting) 361.5 29.4 0.081 302–406

Shoulder grip length 342.3 23.1 0.067 288–384

Forearm- hand length 368.5 25.1 0.068 323–410

Hand length 175.0 10.5 0.060 160–195

Body dimensions	Mean	SD^*	CV^**	Range
Stature	1495.3	44.4	0.028	1403–1580
Weight (kg)	58.70	3.53	0.060	54.5–65.4
Grip diameter (inside)	498.3	41.2	0.083	460–600
Shoulder breadth (Bideltoid)	380.9	18.9	0.050	349–412
Arm reach from wall	699.0	55.9	0.080	624–783
Vertical grip reach	1432.6	66.0	0.046	1320–1540
Foot length	231.2	11.8	0.051	210–253
Sitting eye height	674.3	27.1	0.040	626–694
Sitting shoulder height	529.4	44.9	0.085	440–621
Elbow rest height	562.4	48.2	0.086	450–621
Knee height	464.6	53.7	0.116	388–558
Popliteal height	388.7	34.8	0.090	338–454
Buttock popliteal length	433.3	21.9	0.051	400–471
Bullock knee length‘	561.8	24.4	0.044	513–585
Functional leg length	891.0	47.0	0.053	850–982
Thigh clearance height (sitting)	137.6	10.1	0.074	120–184
Hip breadth (sitting)	361.5	29.4	0.081	302–406
Shoulder grip length	342.3	23.1	0.067	288–384
Forearm- hand length	368.5	25.1	0.068	323–410
Hand length	175.0	10.5	0.060	160–195

Note: SD^* - standard devation, CV = coffecent of varation and all the dimensions in mm excluding weight.

2.2 Ergo-refined seat

A new seat was designed, taking into account the anthropometric dimensions of Indian male and female agricultural workers, as well as the vibration experienced by operators during operation. Anthropometric body dimensions (5^th percentile female and 95^th percentile male), such as popliteal height, hip breadth, buttock-popliteal length, and sitting acromial height, were considered in the design of the ergo-refined seat [37]. All seat components were fabricated at the workshop of the Agricultural and Food Engineering Department, IIT Kharagpur. The seat parameters and relevant anthropometric measurements used in the design of the ergo-refined seat are presented in Table 2 and Fig. 1 (a). To enhance operator comfort and efficiency, a vibration isolator developed by the International Organization for Standardization [21] was utilized beneath the seat of the riding type self-propelled machine. This isolator, made of piezoelectric material, was embedded between Steryl Butadiene Rubber (SBR) with a damping coefficient adjusted to achieve a critical damping ratio of 0.12. The literature suggests that the use of piezoelectric transduction is the most effective method for converting vibration into electricity and reducing vibration transmission to the operator’s body [7]. Eight isolators were sandwiched between two plates to form the isolator unit, which was then fitted beneath the seat to reduce vibration. Whole-body vibration levels, along with biophysical responses, were measured with and without the incorporation of these selected isolators.

Fig. 1

(a) Ergo-refined seat.

Table 2

Seat parameters and relevant anthropometric measures considered in designing the ergo-refined seat

Seat parameter	Anthropometric measure	Modified dimension of the ergo-refined seat
Seat height (a)	Popliteal height sitting (5^th percentile)	420 mm
Seat backrest	Intersey breadth (95^th percentile)	350 mm
Seat cancavity	–	300 mm
Backrest angle	–	10° inclined from vertical and seat pan was inclined at 5° from the horizontal
Seat width	Hip breadth sitting (95^th percentile)	410 mm
Seat pan	Buttock popliteal length (5^th percentile)	450 mm
seat cushion	–	40 mm thickness.

2.3 Operator’s workplace

The optimal placement of the control lever in the operator’s workplace is crucial for enhancing the efficiency of the man-machine system. To determine the appropriate location for the control lever, it is necessary to understand the operator’s comfortable reach zones. Therefore, hand and leg reach envelopes were developed for the operators, taking into consideration the relevant anthropometric measures and methodology outlined in another study [34]. Based on the reach envelopes, control lever locations were identified that would provide a safe, comfortable, and efficient ride for self-propelled machine operators. These locations were then incorporated into the ergo-refined operator’s workplace. The ergo-refined operator’s workplace, which included the improved seat and isolator, was installed on the riding type self-propelled machine for operation under actual field conditions. There is flexibility to adjust the control lever location as per the operator’s requirements. Figure 1 (b) illustrates the operator’s workplace mounted on the self-propelled machine, featuring the improved seat and isolator.

Fig. 1

(b) Operator’s workplace dimension for self-propelled machine control lever locations.

2.4 Biophysical actual cost-benefit analysis of the ergo-refined operator’s workplace

Preliminary investigations were conducted on the operations of the riding type self-propelled mini combine harvester at the Agricultural and Food Engineering Department, IIT Kharagpur. For the study, an 18 hp self-propelled mini combine harvester machinery was utilized. Experiments were carried out under real field conditions using a full factorial randomized design. All trials were conducted between 9 : 00 AM and 5 : 00 PM, with a duration of 30 minutes each, at engine speeds of 1600 and 2000 rpm. Weather conditions were continuously monitored throughout the trials, and experiments were conducted following standard protocols to minimize environmental influences. The actuating force required for the control levers, including RHC, LHC, HA, MC, and GSL, was measured using S-type load cells. To assess the postural changes of the elbow, hip, knee, and head, bending angles were evaluated during operation by analyzing video captured in still images. The angles of different body parts were determined using Kinovea software [13].

To evaluate the ergonomic assessment of the task, several variables were considered as response indicators: WBV acceleration in m/s², working heart rate (WHR) in beats/min, oxygen consumption rate (OCR) in L/min, body parts discomfort score (BPDS), overall discomfort rating (ODR), and electromyography (EMG) in μV [13, 35]. The treatment variables, also known as independent factors, included the engine speed at two levels (1600 rpm and 2000 rpm) and the operating condition at two levels (existing and modified). The energy cost of operation was assessed using the indirect calorimetric method, following the standard procedure outlined by Astrand and Rodahl [1]. BPDS and ODR were recorded using the Borg CR-10 scales. The participant’s body was divided into 27 regions, and after 30 minutes of operation, they were asked to rate the level of discomfort in each region. This information was used to calculate the BPDS. Participants listed their uncomfortable body parts in order, starting from the most painful, until all body parts were documented. Discomfort severity levels were assigned numerical values, and the sum of the number of body parts and the numerical rating for each category yielded the BPDS. ODR scores were determined by summing each participant’s individual scores for each body part. The mean rating was calculated by averaging the overall discomfort ratings of all participants. For EMG measurements, the EMG LE 230 instrument from Biometrics Ltd, UK, was used. It consisted of wireless sensors with electrodes, Wi-Fi data transfer systems, and Biometrics data LITE software. Adhesive tapes were used to fix the sensors on the skin to reduce electrical impedance between the skin and electrode. Maximal voluntary contraction (MVC) was calculated following the procedure described in previous studies [7 , 22]. Muscle activity was recorded for the flexi carpi radialis (FCR), extensor digitorum (ED), brachio-radialis (BR), and middle deltoid (MD), as these muscles are predominantly involved in operating the machine. The specific procedures outlined in precious studies [24, 30] were followed for recording the EMG activity of each muscle.

In accordance with NIOSH guidelines [7 , 21], the vibration acceleration in the entire body was also measured. To accomplish this, a seat pad accelerometer was utilized. The total root mean square (RMS) vibration experienced by the operator was calculated using Equation (1). $a_{hw} = \sqrt{{K_{x}}^{2} {(a_{hwx})}^{2} + {k_{y}}^{2} {(a_{hwy})}^{2} + {k_{z}}^{2} {(a_{hwz})}^{2}}$ (1) Where,

ahw = total RMS acceleration in the whole body, m/s²; ahwx = the root mean square (RMS) acceleration in longitudinal direction, m/s²; ahwy = the RMS acceleration in lateral direction, m/s²; ahwz = the RMS acceleration in vertical direction, m/s²; kx = multiplying factor for x-axes, 1.4; ky = multiplying factor for y-axes, 1.4; kz = multiplying factor for z-axes, 1.0.

2.5 Statistical analysis

ANOVA and multivariate analysis of variance (MANOVA) were conducted to assess the significance of the influence of the independent parameters (operating condition and engine speeds) on the corresponding WHR, OCR, muscle fatigue, and whole-body vibration in all axes. The statistical analysis was carried out using Design Expert software (version 7.0) and R-Studio. A p-value of less than 0.01 was considered statistically significant for differences among the data.

3 Results

3.1 Actuating forces and angles acquired by body parts

The actuating force required for control levers, including the right-hand clutch (RHC), left-hand clutch (LHC), hand accelerator (HA), main clutch (MC), and gear shifting lever (GSL), was measured to be 124 N, 120 N, 75 N, 190 N, and 180 N, respectively, for the ergo-refined workplace. In contrast, it was found to be 191 N, 175 N, 315 N, 304 N, and 281 N, respectively, for the existing workplace. The use of the ergo-refined operator’s workplace resulted in a significant reduction in actuating force, with percentages of 35%, 31%, 76%, 37.5%, and 35% observed for the LHC, RHC, accelerator, MC, and GSL, respectively, compared to the corresponding values with the existing workplace, as shown in Fig. 2.

Fig. 2

Actuating force required for the different hand control.

The posture adopted during the operation of the mini combine harvester was compared between the ergo-refined operator’s workplace and the existing workplace and seat [13]. The details are presented in Fig. 3 (a and b). The average knee, hip, elbow, and head angles measured in volunteer subjects during the operation were found to be 103°, 104°, 93°, and 15°, respectively, for the ergo-refined workplace, while they were 129°, 104°, 93°, and 22°, respectively, for the existing workplace. Figure 3 (b) shows that females with shorter height tend to exhibit higher torso angles. The ergo-refined workplace enables the operator to adopt a more comfortable posture during the operation of the mini combine harvester. Additionally, the use of the ergo-refined workplace resulted in a significant reduction in the perceived discomfort level, as measured using the Borg Scale. The postural discomfort experienced in the knee, hip, elbow, and head was reduced by 17%, 2%, 2%, and 36%, respectively.

Fig. 3

Body parts angle of the operator during the mini combine operation (a. Existing workplae, b. Ergo-refined workplace).

3.2 Biophysical actual cost-benefit analysis of the subjects

The WHR and OCR of volunteer subjects were recorded during the field operation of the self-propelled machine at two engine speeds for the ergo-refined workplace. These values were compared with the corresponding values for the existing workplace. Figure 4a and 4b show the WHR and OCR values of female subjects during the field operation of the self-propelled machine at both speeds, with and without the ergo-refined workplace.

Fig. 4

Bio-physical cost of volunteer subjects during the operation (a. WHR and b. OCR).

The mean±SD values for WHR and OCR of the volunteer subjects during the operation were lower for the ergo-refined workplace compared to the existing workplace. At 1600 rpm, the WHR and OCR were 91.00±4.49 beats/min and 0.50±0.11 l/min for the ergo-refined workplace, while for the existing workplace, they were 115.00±7.15 beats/min and 0.71±0.08 l/min, respectively. Similarly, at 2000 rpm, the WHR and OCR were 100.00±7.5 beats/min and 0.62±0.09 l/min for the ergo-refined workplace, and 120.00±3.4 beats/min and 0.82±0.07 l/min for the existing workplace, respectively. The WHR and OCR were reduced by 20 to 28% during the field operation at 1600 rpm with the ergo-refined workplace, and by 16 to 25% during the field operation at 2000 rpm with the operator’s workplace, compared to the operation with the existing workplace. The self-propelled machine field operation with the ergo-refined workplace at both 1600 rpm and 2000 rpm fell into the light category with a WHR less than 100 beats/min, whereas the operation with the existing workplace fell into the moderately heavy category with a WHR ranging from 100 to 125 beats/min [32]. The mean±SD values for physiological parameters were 106.76±6.63 beats/min and 0.67±0.09 l/min for WHR and OCR, respectively. The F-values for operating condition were 129.26 and 58.35 for WHR and OCR, respectively, while for engine speed, they were 12.43 and 18.54, respectively. These values indicate that the model is highly significant relative to the noise. The ratios for WHR and OCR were 14.89 and 19.94, respectively, indicating an adequate signal. It can be observed that there is significant variation in WHR and OCR with changes in operating condition and engine speed.

3.3 BPDS and ODR

The maximum body parts discomfort was observed to be at the right foot of the operator during the field operation with an ergo-refined operator’s workplace and seat with isolator, whereas it was observed to be highest in buttock during the field operation with existing seat and workplace (Fig. 5 a). The discomfort level was found to be lower with the use of an ergo-refined operator’s workplace and seat with isolator which helped the operator to maintain the appropriate posture during the operation and prevented the vibration to be transmitted to the operator (Fig. 5 b).

Fig. 5

BPDS and ODR during riding type self-propelled machine operation with existing and ergo-refined operator’s workplace.

3.4 Maximal voluntary contraction (MVC) Muscles fatigue assessment

The FCR, ED, BR, and MD hand muscle responses of twelve subjects during the field operation of the self-propelled machine were recorded in terms of EMG. The overall RMS (mean±SD) values for FCR, ED, BR, and MD hand muscles of all the subjects during the operation at the selected speeds were lower at 1600 rpm with 32.94±8.8, 26.81±6.10, 25.91±7.53, and 25.55±6.48μV, respectively, with the improved workplace compared to the existing workplace. Similarly, at 2000 rpm, these values were found to be 44.16±7.93, 39.53±13.54, 39.99±14.90, and 37.82±9.11μV, respectively, with the ergo-refined workplace and the existing workplace. The percentage load on the selected hand muscles of all the subjects during the field operation with the ergo-refined workplace was calculated using the MVC of the subjects (Fig. 6) and compared with the corresponding values of all the subjects with the existing workplace. The overall % MVC mean for FCR, ED, BR, and MD hand muscles of all the subjects during the operation at both selected speeds was lower at 1600 rpm with 24%, 19%, 16%, and 15%, respectively, with the improved workplace compared to the existing workplace. Similarly, at 2000 rpm, these values were found to be 32%, 29%, 24%, and 22%, respectively, with the ergo-refined workplace and the existing workplace. Since most agricultural tasks are intermittent with frequent interruptions, the endurance times at 20% to 30% of MVC may be within an acceptable range of constant loading for agricultural tasks [33, 50]. The MVC (RMS values) for the improved workplace were found to be below 30%, indicating a comfortable level for the operator. The percentage load on the selected hand muscles was reduced by 57%, 65%, 72%, and 68% at 1600 rpm, and 60%, 65%, 66%, and 66% at 2000 rpm for FCR, ED, BR, and MD, respectively, during the operation of the riding-type self-propelled machine.

Fig. 6

Percentage load on hand muscles during riding type self- propelled machine operation.

The ANOVA analysis revealed that changes in the operating condition and engine speed significantly affected the FCR, ED, BR, and MD hand muscles. The overall % MVC (mean±SD) values for the hand muscles were 66.72±12.07%, 64.41±19.23%, 66.00±20.30%, and 63.02±17.18% for FCR, ED, BR, and MD hand muscles, respectively. The F-values for the operating condition were 261.29, 126.68, 127.17, and 159.87 for FCR, ED, BR, and MD hand muscles, respectively, indicating high significance relative to the noise. Similarly, the F-values for the engine speed were 38.48, 21.46, 17.35, and 17.38, respectively. These results suggest that the model is highly significant in explaining the variance. The probability values of 0.01 for FCR, ED, BR, and MD hand muscles indicate an adequate signal. This model can be utilized for simulating the design space. The variation in FCR, ED, BR, and MD hand muscles is highly significant with respect to the variations in the operating condition and engine speed at a significance level of 1%.

3.5 Total WBV

The total sum of WBV acceleration during field operations at different speeds of operation with an ergo-refined workplace and seat with isolator was calculated and compared to the corresponding values of the existing seat in self-propelled machinery. It was observed that the total WBV was 3.85 m/s² and 6.16 m/s² at the ergo-refined workplace and seat with isolator during self-propelled machinery field operations at 1600 rpm and 2000 rpm, respectively. In contrast, it was 6.16 m/s² and 11.41 m/s² with the existing seat during field operations at 1600 rpm and 2000 rpm, respectively (Fig. 7). Similar trends were reported by [6 , 49]. The use of the ergo-refined workplace resulted in a 38% and 58% reduction in total WBV at the seat pan during actual field operations of the self-propelled machine at 1600 rpm and 2000 rpm, respectively. The mean±SD values for WBV were 3.39±0.35 m/s², 4.47±0.38 m/s², and 5.99±0.58 m/s² for the X, Y, and Z directions, respectively. The F-values for the operating condition were 1521.55, 2548.43, and 1445.18 for WBV in the X, Y, and Z directions, respectively, while they were 313.61, 1085.37, and 1014.84 for ES in the respective directions. The F-values for the interaction were 254.22, 853.21, and 984.25 for WBV in the X, Y, and Z directions, respectively. The individual F-values for the operating condition, engine speed, and their interaction indicate that the model is highly significant in explaining the variance relative to the noise. The probability of such a large F-value occurring due to noise is 0.01%. The variation in WBV in X, Y, and Z directions is highly significant with respect to the variations in the operating condition and engine speed.

Fig. 7

Total WBV acceleration of self-propelled machinery.

3.6 Statistical analysis (MANOVA)

Based on the MANOVA presented in Table 3, it is evident that the test yielded statistically significant results at a p-level of 0.01. MANOVA is a statistical method employed to analyze the effects of various independent variables on the physiological parameters of subjects during field operations at different workplaces and speeds. The analysis revealed that WHR, OCR, muscle fatigue (FCR, ED, BR, and MD), and WBV in the X, Y, and Z directions of the volunteer subjects exhibited high significance at the 0.01 level when comparing operations and different workplaces. The overall response F-values of 452.92, 187.55, and 151.02 for the operating condition, engine speed, and interaction effect, respectively, indicate that the model is significant. P-values lower than 0.001 further confirm the significance of the model terms. These findings demonstrate that the models are highly significant, with only a 0.01 chance of occurrence due to noise. Thus, the mathematical model was deemed statistically significant, with R2 values of 0.74 and 0.63 for WHR and OCR, and 0.87, 0.77, 0.77, and 0.80 for muscle fatigue (FCR, ED, BR, and MD) and WBV in the X, Y, and Z directions, respectively.

Table 3
MAVOVA for responses during the selected operation

DF Pillai Wilks Roy Hotelling F-value

A- Operating condition 1 0.99125 0.0087543 113.229 113.229 452.92 0.000

B- Engine speed 1 0.97912 0.0208818 46.889 46.889 187.55 0.000

A×B 1 0.97420 0.0258037 37.754 37.754 151.02 0.000

Residuals 44

	DF	Pillai	Wilks	Roy	Hotelling	F-value
A- Operating condition	1	0.99125	0.0087543	113.229	113.229	452.92	0.000
B- Engine speed	1	0.97912	0.0208818	46.889	46.889	187.55	0.000
A×B	1	0.97420	0.0258037	37.754	37.754	151.02	0.000
Residuals	44

3.6.1 Effect of operating conditions and engine speed on WHR, OCR muscle fatigue and WBV

Figure 8 illustrates the three-dimensional visualization plot of the hypothesis error (HE) for the main and interaction effects of the operating condition and engine speed on WHR, OCR, and FCR. The plot clearly demonstrates that the operating condition sphere (black) extends significantly beyond the error sphere (red), indicating high significance. Similarly, the engine speed ellipse (magenta) also exhibits significant influence on the respective variable, as it extends farther from the error sphere. Conversely, the interaction effect sphere (blue) was found to be significant but to a lesser degree, as it stretches beyond the error sphere. Figure 9 presents the three-dimensional visualization plot for the ED, BR, and MD hand muscles. The plot reveals that the operating condition ellipse (magenta) extends significantly beyond the error sphere (red), indicating statistical significance. Similarly, the engine speed sphere (blue) demonstrates a significant impact on the respective variable, as its sphere stretches farther from the error sphere. However, the interaction effect sphere (black) was not found to be statistically significant. Figure 10 displays the three-dimensional visualization plot for WBV in the X, Y, and Z directions. The plot demonstrates that the operating condition ellipse (black) extends significantly beyond the error sphere (red), indicating statistical significance. Similarly, the engine speed ellipse (magenta) also exhibits significant influence on the respective variable, as it stretches farther from the error sphere. The interaction effect sphere (blue) was found to be significant, as its ellipses stretch beyond the error sphere.

Fig. 8

HE plot operating condition and engine speed for FCR, ED and BR hand muscles.

Fig. 9

HE plots operating condition and engine speed for MD, WHR and OCR.

Fig. 10

HE plot operating condition and engine speed for WBV in all axes.

Table 4

Biophysically actual cost-benefit analysis of riding type self-propelled machines

Description	Engine speed
Type of seat	Existing	Improved workplace	Exiting	Improved workplace
Engine speed (rpm)	1600		2000
Working heart rate, beats/min	101	93	105	100
oxygen consumption rate, l/min	0.68	0.53	0.74	0.66
Total vibration seat pan	6.14	3.85	11.47	4.84
Total vibration Seat backrest	No backrest	6.56	No backrest	8.13
FCR% load with MVC	53	18	67	25
ED% load with MVC	55	16	86	25
BR% load with MVC	60	16	72	25
MD% load with MVC	52	18	75	26
Grading of work	Moderately heavy	Light	Moderately heavy	Light

4 Discussion

The total recorded WBV acceleration during the actual field operation with the existing seat in riding-type self-propelled machines was found to be higher than the recommended value of 5.2 m/s², with a highly significant effect (P < 0.01) of engine speed. Therefore, it is crucial to minimize the harmful effects of vibration on operators. To address this issue, an improved seat has been developed specifically for Indian female agricultural workers, considering their anthropometry (5^th and 95^th percentiles). The improved seat has dimensions of 450 mm seat pan width, 410 mm seat length, 420 mm seat height, and 350 mm seat backrest width. The improved workplace allows operators to adopt appropriate postures, with body part angles within recommended values, reducing the angles by 2 to 36% compared to the operation with the existing workplace. Physiological parameters such as WHR and OCR were significantly reduced (P < 0.01) by 20%, 28%, and 21%, and 16%, 27%, and 10% during the operation at 1600 and 2000 rpm, respectively, with the use of the improved seat and workplace, compared to the operation with the existing seat. Percentage load on all selected hand muscles was significantly reduced by 57% to 72% and 60% to 66% at 1600 and 2000 rpm, respectively, with the use of the improved seat and workplace. The total reduction in whole-body vibration at the seat pan was 38% and 58% during self-propelled machine operation at 1600 and 2000 rpm, respectively, with the use of the improved seat and isolator. The implementation of a piezoelectric material-based isolator beneath the seat resulted in a significant vibration reduction (P < 0.01), enabling safe and efficient long-duration operation for the operators. Therefore, improved seats with isolators and improved workplaces are valuable assets for riding-type self-propelled machines, providing safety, comfort, and efficient operation for female operators. This design can be successfully adopted by manufacturers to enhance their existing designs, increasing market adaptability among female users due to its comfort and productivity. However, minor modifications may be required for adoption by male users.

5 Conclusions

An improved seat has been developed, considering the anthropometry of Indian female agricultural workers at the 5^th and 95^th percentiles. The seat has dimensions of 450 mm seat pan width, 410 mm seat length, 420 mm seat height, and 350 mm seat backrest width. It has been found to be comfortable for female operators of self-propelled machines. The actuating force required for all hand control levers was observed to be in the range of 175–315 N with the existing workplace. However, with the improved workplace, it was found to be within the range of 75–190 N, significantly improving the controllability of the self-propelled machine during operation. Physiological parameters such as WHR, OCR, and energy expenditure rate (EER) were significantly reduced (P < 0.05) by 20%, 28%, and 21%, and 16%, 27%, and 10% during the operation at 1600 and 2000 rpm, respectively, with the use of the improved workplace and seat compared to the operation with the existing seat. BPDS and ODR were found to be higher during field operations at 2000 rpm due to increased exposure to vibration and higher levels of physical and mental attention. Comparatively, the self-propelled machine operation can be continued comfortably for long durations with the ergo-refined operator’s workplace, following the standard procedure used by Astrand and Rodahl [1] for indirect calorimetric measurement. It was observed that the operator’s workplace successfully reduced the percentage load on the selected hand muscles. Among the muscles, higher percentage loads were observed on the ED, followed by BR, FCR, and MD [22]. The isolator was found to effectively reduce the transmission of vibration to the operator’s body [22, 42]. Therefore, the operation with the operator’s workplace can be comfortably sustained for long durations [30, 41]. The total reduction in whole-body vibration at the seat pan is 38% and 58% during self-propelled machine operation at 1600 and 2000 rpm, respectively, with the use of the improved seat and isolator. Significant vibration reduction (P < 0.01) was observed when using a piezoelectric material-based isolator beneath the seat, enabling safe and efficient long-duration operation for the operator. Consequently, an ergo-refined female operator’s workplace becomes an asset for riding-type self-propelled machines, providing safety, comfort, and efficient operation for female operators.

Ethics statement

The study was approved by the ethics committee of IIT Kharagpur.

Informed consent

Informed consent was obtained from all participants.

Conflict of interest

The authors have no conflict of interest to report.

Footnotes

Acknowledgments

This project was supported by IIT Kharagpur and ICAR, New Delhi. The authors are extremely grateful to the Project Coordinator, AICRP on ESA (ICAR, New Delhi) for advice and financial support for this project.

Funding

Not applicable.

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Development of ergo-refined operator’s workplace and biophysically actual cost-benefit analysis of riding type self-propelled machines with special reference for female operators

Abstract

BACKGROUND:

OBJECTIVE:

METHODS:

RESULTS:

CONCLUSION:

Keywords

1 Introduction

2 Materials and methods

2.1 Subjects

3 Results

3.1 Actuating forces and angles acquired by body parts

Table 3 MAVOVA for responses during the selected operation DF Pillai Wilks Roy Hotelling F-value A- Operating condition 1 0.99125 0.0087543 113.229 113.229 452.92 0.000 B- Engine speed 1 0.97912 0.0208818 46.889 46.889 187.55 0.000 A×B 1 0.97420 0.0258037 37.754 37.754 151.02 0.000 Residuals 44

5 Conclusions

Ethics statement

Informed consent

Conflict of interest

Footnotes

Acknowledgments

Funding

References