Ergonomical evaluation of 9 hp self-propelled multi-purpose planter cum sprayer

Introduction

Ergonomic assessment of agricultural machinery is essential to ensure operator safety, comfort, and sustained field performance, particularly in small-scale mechanization systems. In this study, the self-propelled multipurpose machine was evaluated in planter-cum-sprayer mode to determine the ergonomic implications of two key operational parameters: hand grip (S₁) and forward speed (S₂). These parameters play a critical role in influencing operator exposure to hand-arm vibrations, physiological workload, and overall discomfort during planting operations. To systematically quantify these effects, experiments were conducted using the Central Composite Rotatable Design (CCRD), enabling efficient exploration of the design space and identification of nonlinear interactions. The collected data were analysed using Response Surface Methodology (RSM) in Design Expert 13.5 software, through which second-order polynomial models were developed for key ergonomic responses-hand-arm vibration (HAV), heart rate, body part discomfort score (BPDS), overall discomfort rating (ODR), and sound level. Model adequacy was evaluated using analysis of variance (ANOVA) at a 5% significance level, while response surface and contour plots were generated to interpret the combined influence of S₁ and S₂ on operator ergonomics.

Material and Methods

The ergonomic performance of the self-propelled multipurpose machine in planter-cum-sprayer mode was evaluated by systematically varying two independent operational parameters: hand grip (S₁) at three levels (No Grip, General Grip, Soft Grip) and forward speed (S₂) at three levels (1.2, 1.5, and 1.8 km h⁻¹). A Central Composite Rotatable Design (CCRD) was employed to plan the experiments efficiently and to capture nonlinear and interaction effects between the variables. This design generated a total of 13 experimental combinations consisting of factorial, axial, and canters points. Ergonomic responses measured during each trial included hand-arm vibration (HAV), heart rate, body part discomfort score (BPDS), overall discomfort rating (ODR), and sound level. Heart rate was recorded using a digital heart rate monitor, while HAV and sound levels were measured using calibrated vibration and sound meters.

BPDS and ODR were obtained through standard ergonomic rating scales immediately after each experimental run. The collected data were analysed using Response Surface Methodology (RSM) in Design Expert 13.5 software. Secondorder polynomial models were developed for each response variable to describe the relationship between the independent factors and ergonomic outcomes. Model adequacy was examined using analysis of variance (ANOVA) at a 5% significance level. Diagnostic tests including lack-of-fit, coefficient of determination (R²), adjusted R², predicted R² and adequate precision were used to confirm the reliability of the developed models. Response surface and contour plots were generated to visualize the combined influence of S₁ and S₂ on the ergonomic parameters and to determine optimal operating conditions. The independent parameters and corresponding response variables used for ergonomic evaluation are summarized in Table 2.1, forming the basis for subsequent analysis and optimization. Where, S1 = Hand grip, S2 = Forward Speed.

The ANOVA results clearly show that the developed model is statistically significant in explaining the variations in hand-arm vibration (HAV) for the self-propelled multipurpose plantercum-sprayer. The model F-value of 23.30 with a p-value of 0.003 indicates a strong overall influence of the selected parameters on vibration levels. Among the individual factors, the linear terms A-HG and B-FS, their interaction (AB), and the quadratic components A² and B² were all significant at the 5% level, demonstrating that both direct and nonlinear effects of handle grip and forward speed play an important role in determining HAV. The non-significant lack-of-fit confirms that the model adequately represents the experimental data without systematic deviations. Overall, the analysis validates that the chosen operational parameters are critical contributors to vibration behaviour and that the fitted model is reliable for prediction and optimization.

The statistical summary indicates that the developed model provides a strong and reliable fit for predicting hand-arm vibration responses. The low standard deviation and coefficient of variation reflect good precision and consistency in the experimental data. Although the predicted R² is somewhat lower, it remains within an acceptable range, showing reasonable predictive capability. Additionally, the adequacy precision value is well above the recommended minimum, indicating a strong signal-to-noise ratio and confirming that the model is suitable for effective navigation of the experimental design space.

3.2: Effect of Hand grip and Forward Speed on percent Heart Rate (beats per min) of self-propelled multipurpose machine for Planter cum sprayer

The evaluation of operator heart rate for the self-propelled multipurpose planter demonstrated that the independent parameters exerted a significant influence on the physiological workload of the operator. The average heart rate of 101.08 bpm reflected a moderate physiological load during machine operation, suggesting that although the machine is ergonomically manageable, certain combinations of operating parameters can increase physical stress. Similar range reported by P. A. Munde (2020) [8] . Where, S1 = Hand grip, S2 = Forward Speed.

A high coefficient of determination (R² = 0.95) was obtained for the responses, indicating that the developed model for Heart Rate (beats per min) effectively explained 95.00% of the total variation. The magnitude of the linear term coefficients revealed that the effect was most pronounced on Heart Rate (beats per min), followed by hand grip (S₁) and forward speed (S₂). The positive coefficient of the first-order term for hand grip (S₁) suggested that Heart Rate (beats per min) increased with an increase in this parameter, whereas the negative coefficients of forward speed (S₂) and its quadratic terms indicated that an excessive rise in these parameters resulted in a reduction of Heart Rate (beats per min). The developed statistical model was found to be highly reliable, with strong coefficients of determination (R² = 0.9505 and adjusted R² = 0.9151), indicating that the major portion of variability in heart rate was effectively explained by the selected factors. The predicted R² (0.7406) also remained in reasonable agreement, confirming the model's suitability for prediction within the experimental domain. The linear terms of S₁ and S₂, the quadratic terms of S₁² and S₂², and the interaction term S₁S₂ were found to be significant at the 5% level of significance. Table 3.4 showed that the model F-value was significant, while the lack-of-fit F-value was not significant for the obtained model. Therefore, the developed model was considered suitable for navigating the design space effectively. The study effectively demonstrates the interaction and nonlinear effect of machine operational parameters (Forward Speed and Hand grip) on the operator's physiological response (Heart Rate). For optimizing the design and operation of this selfpropelled machine for Planter cum sprayer, the settings should be adjusted to operate around the identified optimum zone of B: FS 10.50-11.00 kmph to minimize operator fatigue and improve long-term productivity and safety. The negative linear coefficient of forward speed (S₂) suggests that a slight increase in speed may initially reduce discomfort, likely due to smoother machine movement and reduced muscular holding time. However, the positive quadratic term for speed indicates that excessively high operating speeds eventually lead to an increase in BPDS. The ANOVA results further revealed that the linear terms of S₁ and S₂, the quadratic terms of S₁² and S₂², and the interaction term S₁S₂ were all significant at the 5% level. The model F-value presented in Table 5.14 confirmed the overall significance of the regression model, whereas the lack-of-fit F-value was not significant, indicating that the model adequately fitted the experimental data. The predicted R² value of 0.94 was in close agreement with the adjusted R² value of 0.90, with a difference of less than 0.2. This demonstrates good model reliability and confirms that non-significant terms were appropriately excluded during model refinement. Consequently, the final model is considered suitable for effectively navigating the experimental design space and predicting BPDS across the tested operating conditions. The Overall Discomfort Rating (ODR) of the operator while performing planting operations using the self-propelled multipurpose machine was evaluated under different combinations of hand grip (S₁) and forward speed (S₂). A second-order response surface model was developed to quantify the relationship between ODR and the two independent parameters. The fitted polynomial equation is: ODR = 38.5111-2.2691 S1 -6.4196 S2 + 0.1779 S1S2 + 0.4644S1 2 + 0.2976S2 2 (R 2 = 0.9474) ….. (5.4) Where, S1 = Hand grip, S2 = Forward Speed The sound pressure level data for various levels of independent parameters were presented in Table 5.13, and the analysis of variance is given in Table 5.5.

The SPL values with respect to the forward speed of the planter were plotted in Fig. 5.19. The mean SPL values ranged from 73 to 90.84 dB for the straight blade and from 76 to 95 dB for the rotary blade at speeds of 1.2 to 1.8 km/h, and the differences were statistically significant at the 5% level. Similar trends were reported by Dewangan et al. (2005), Dixit (2006), Chhuneja (2011), and Gagandeep (2016) [15, 16, 17, 18] .

Where, Sound Level (db), Forward Speed (KMPH)

The analysis of variance confirmed that the developed model was statistically significant, as indicated by the model F-value of 33.69 (p<0.0001). The linear effects of hand grip (A) and forward speed (B) were significant, with HG showing a stronger influence (F = 50.05; p = 0.0002) than speed (F = 7.17; p = 0.0317). The interaction term AB was also significant (F = 8.95; p = 0.0202), demonstrating that the combined influence of both factors differed from their individual effects. The quadratic components A² (F = 47.85; p = 0.0002) and B² (F = 17.52; p = 0.0041) were significant as well, confirming curvature and a nonlinear response pattern. Similarly, the linear terms (S₁, S₂), quadratic terms (S₁², S₂²), and interaction term (S₁S₂) remained significant at the 5% level, while the model F-value presented in Table 5.64 was significant and the lack-of-fit was non-significant, indicating an adequate model fit. The predicted R² (0.96) closely matched the adjusted R² (0.90), remaining well within the acceptable difference of less than 0.2. Overall, the statistical evidence demonstrated that the model was robust, reliable, and suitable for accurately representing the system behaviour within the design space. This 3D surface plot, Fig 3 .5, illustrates the Effect of Hand grip (HG) and Forward Speed (FS) on the Sound Level (SL) of the self-propelled multipurpose machine. The plot shows that the Sound Level, measured in dB, is generally minimized in the central region of the surface. Specifically, a minimum sound level is achieved when the Forward Speed is around 11.00 to 11.50 km/hr and the Hand Grip factor is near 0.00 (General HG).

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