Optimization of Geometrical Parameters of Weeding Tool in Soilbin using Response Surface Methodology

Optimization of Geometrical Parameters of Weeding Tool in Soilbin using Response Surface Methodology

Sunil Shirwal^1* , M. Veerangouda¹ , Vijayakumar Palled¹ , Sushilendra¹ , Arunkumar Hosamani² , Krishnamurthy D³

¹Department of Farm Machinery and Power Engineering, College of Agricultural Engineering, UAS, Raichur – 584104, India

²Department of Entomology, Main Agricultural Research Station, UAS, Raichur – 584104, India

³Department of Agronomy, Agricultural Research Station Hagri, UAS Raichur, India

Corresponding Author Email: sunilsshirwal@gmail.com

DOI : http://dx.doi.org/10.53709/ CHE.2020.v01i01.014

Abstract

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Introduction

Soil mechanical manipulation aims to control weeds, organic matter incorporation into soil and improvement of soil structure. Optimizing the tillage tool geometry and working conditions also minimizes the number of subsequent tillage operations required. So, the total energy input for a given tillage system decreases. To reduce the tillage operations and energy requirement, it is essential to know the draft requirements for different tillage tool geometry [1]. Primary and secondary soil manipulation is the basic operation required for cultivation of any kind of crop. Soil manipulating tools should withstand the adverse field conditions, such as the presence of a hardpan, small rocky formations, stumps and stubble, during soil engagement without failure [2].

Agricultural tools have for a long time been designed on trial and error basis as soil-tool interactions have not been well defined and quantified. Accurate knowledge of draft and energy requirement of tillage implements is essential for proper design of the implements, appropriate matching of the implements with their power sources, and selecting the optimum operation conditions [3]. The most convenient method to estimate a given implement’s energy requirement is to measure the draft required to pull the implement under desired operating soil conditions. More research needs to be conducted to clearly understand soil mechanics under the influence of agricultural tillage tools [4]. The type and degree of soil disturbance is the prime factor when selecting tillage implements but this must be considered together with the draft and penetration force requirements for efficient operation [5]. Wings or sweeps attached to the foot of the tine modify the type of soil disturbance by doubling the disturbed area for an increase in draft force of 30% [6]. This significantly increases the effectiveness of the operation, by reducing the specific resistance (draft/disturbed area) by 30%.

There have been intensive research efforts to obtain a better understanding of the soil- tool interaction due to the complex problems of interaction between the various devices (tillage tools, wheel, etc.) and various type conditions of soil surfaces [7]. Tractive performance of tractors has been a challenging problem for many engineers. The soil- tool tests usually are determined using experimental methods. The tests are conducted either on soil bin found in indoor testing facilities or by performing accurate field testing. Usually, the soil parameters in soil bins such as variation of cone index and soil compaction level are more constant. Generally, a soil bin facility consists of soil bin, tool carriage, drive system, instrumentation and data acquisition systems. Soil bins are grouped into two design classes. One class of soil bin consists of straight or circular rails, movable soil bin in which the tested tool remains stationary. Another class involves fixed soil bin with a carriage that travels over the soil.

Mechanical weeding can be performed by many soil-engaging tools viz. hand hoes, rotary hoes, brushes, tine harrows, and sweeps [8]. Harrow-type weeders uproot weeds, whereas hoe-type weeders bury and kill weeds [9]. A tine harrow and a powered brush hoe were used for intra-row weeding, and sweeps were used for inter-row weeding [10]. The effectiveness of mechanical weeding can be affected by several factors. Besides the efficacy of weed kill, soil disturbance is one of the essential performance indicators. Soil disturbance determined the burying and uprooting kills of weeds and also related to crop damage. Generally, a weeding tool has the best performance when it cultivates most of the inter-row area without damaging the crop [11]. Limited research has been conducted on tool geometry role on weeding tool performance. Hence, a study was conducted to determine the influence of geometric parameters and optimize draft and soil disturbance performance indicators.

Materials and Methods

Designing soil-cutting tools for agricultural purposes is by far one of the most complex engineering problems because of the variability of soil conditions and the fact that soil is non-homogeneous and anisotropic. However, the design of tillage tools is based on an assumption of soil homogeneity. The aim of the soil bin study was to optimize the geometric parameters for the ‘V’sweeps, which will be used for the intercultural operations. The geometric parameters considered were apex angle (θ), rake angle (γ) and lift angle (δ) (Fig. 1). The apex angle is the included angle formed between the two cutting edges. It was varied from 90° to 140°. Rake angle is the angle subtended between the tool profile axis to the horizontal plane with respect to the direction of travel. The rake angle was varied from 15° to 35°.  Lift angle is the angle formed between the tool cutting edge and horizontal plane measured perpendicular to the direction of travel. It was varied between 0° to 15°.

A laboratory soil bin with artificial soil was employed for the investigation. The soil was processed to provide minimum variation in soil properties with depth. This was achieved by loosening the soil with a rotary tiller and levelling it with a roller to compact the soil for each test. The experiments were conducted for varying tool geometric parameters.  The test performance parameters measured were draft, uprooting width, burial width, and draft efficiency. First the tool was attached to a single shank, and this shank was attached to the tool carriage through octagonal ring transducer. A constant travel speed of 0.7 ms^-1 and a constant working depth of 50 mm were selected for all tests within the typical ranges of travel speeds and working depths for mechanical weeding for row-crops (Fig 2).

Draft

Draft is very important parameter for measuring and evaluating performance of soil cutting tools. Draft depends on blade geometry, moisture content, soil structure, soil texture, soil compaction. The draft was directly measured with the help of EORT (Extended Octagonal Ring Transducer) by recording horizontal force. The data was recorded continuously at 50 Hz data logging software “CATMAN EASY” AND “SPIDER 8” signals processor, the average draft volume was recorded and obtained in MS-EXCEL format.

Uprooting width and burial width

The disturbed soil cross-section after sweep tool passage was characterised using two variables associated with mechanical weed control: uprooting width (W_u), and burial width (W_b) [11], as illustrated in Fig. 3. Within the tool working width (W_t), weeds would be mechanically cut off if they were sown deeper than the working depth of the sweep; otherwise, they may be potentially uprooted by the sweep. The potential uprooting zone could be laterally expanded up to uprooting width, which was equal to the width of the maximum soil disturbance. Within uprooting width, soil was disturbed and weeds in this zone could be either cut or potentially uprooted. The loose soil was thrown further from the centre of the sweep path, which would potentially bury the weeds. Thus, a burial width, W_b, was defined as the maximum lateral distance covered by the loose soil. The uprooting width and burial width values were measured after each test at seven random locations within the constant velocity section of the soil bin.

Draft efficiency

The draft efficiency is defined as the ratio of area of soil cut or disturbed to the total draft required by the tool [12].

Design and analysis of experiment using response surface methodology

Response surface methodology was used with central composite rotatable experiment design (CCRD) for optimization of geometric parameters and to fit a second order polynomial equation [13] [14] and [15]. Three independent parameters viz. apex angle (θ), rake angle (γ) and lift angle (δ) were considered for optimization based on the four dependent parameters viz. draft, uprooting width, burial width and draft efficiency. Based on selected range of independent variables, 5 different levels of coded values (+1.682, +1, 0, -1 and -1.682) were selected [13]. The independent variables in their coded and actual value levels were obtained through following equations.

Get the equation here…

The X_i is the actual value of the i^th variable, x_i is the coded variable of the i^th variable, X_max is the maximum value of independent variable, X_min is the minimum value of the independent variable and a_m is the extreme coded value.

            A nonlinear second-order regression equations were developed for controlled parameters in coded values to optimize draft, uprooting width, burial width and draft efficiency with following general form of equation (5). The goodness of fit of the developed nonlinear second-ordered equation was tested by F-value for lack of fit (F_lof).

Get the equation here…

The Y is predicted response, b₀ is constant, b_i is linear regression constant, b_ii is quadratic regression coefficient, b_ij is interaction regression coefficient, N is total number of experiments, Y_ai is the experimental value of i^th response, Y_ci is calculated value of the i^th response, Y_av is the average actual value of responses and n_c is number of central experiments. A total number of 20 experiments were conducted as per CCRD at 5 levels of independent variables (Table 1).The results of the response parameters were substantiated by ANOVA – analysis of variance, root mean square error, correlation coefficient (R²), coefficient of variations, adequate precision and model graphs.

Results and Discussions

            The effect of geometrical parameters on the performance of weeding tool was studied in the soilbin. The performance was evaluated in random order as per the CCRD experimental design and noted in Table 2.The response surface methodology was used for numerical optimization of the data. The effect of geometrical parameters were on selected performance parameters were studied individually.

Influence of apex angle (θ), rake angle (γ) and lift angle (δ) on draft

The draft on the weeding tool was measured using octagonal ring transducer. The maximum draft was observed to be about 278 N when the tool was operated having apex angle of 140º, rake angle of 25º and 7º lift angle. The tool having apex angle of 90º, rake angle of 25º and 7º lift angle has developed a minimum draft of 118 N. The effect of apex angle, rake angle and lift angle on draft was represented in Fig. 4. It was observed that there was a substantial increase in the draft value as the apex angle was increased. This was observed because, as the apex angle was increased due to more extensive area of contact, larger cutting edge of the tool, and soil abrasion [2]. Due to this larger area of contact and more speed the frictional force between the tool and soil increases, results in larger force requirement to break the soil [16] and [17].

It was also been observed that as the rake angle was increased, draft was also increased at considerable rate. Even the lift angle also had similar effect as that of rake angle. As the rake angle was increased more amount of soil will be handled by the tool, this increases the draft on the tool. In case of increase in lift angle, it increases the amount of soil disturbance and toll will be working on more amount of soil. This might have caused significant increase in draft on tool [18] and [4]. Apex angle, rake angle and lift angle were influencing the draft on the weeding tool significantly at 1 per cent level of significance. The geometric parameter interactions also affected the draft significantly (Table 3). The mean draft was about 186.6 N with a standard deviation of 1.25 (Table 4). The coefficient of determination (R²) was found to be 0.9995, which was a very good fit. The predicted R² of 0.9998 was in reasonable agreement with the adjusted R² of 0.9999. The adequate precision was about 726.644, which measures signal to noise ratio, the value indicates the signal was adequate and can be used to navigate in the design space. The quadratic model equation (7) was developed to know the relationship between the geometric parameters and response variable i.e. draft (D).

D = 77.72 – 1.86 θ + 1.59 γ + 0.44 δ – (9.35 θγ x 10^-3) + 3.58 θδ – 6.95 γδ +0.02 θ² – (1.74 γ² x 10^-3) – (3.24 δ² x 1^-3)                                                                                                          … (7)

Influence of apex angle (θ), rake angle (γ) and lift angle (δ) on uprooting width

The width of soil actually cut by the tool was represented by the uprooting width of cutting tool. The maximum uprooting width was observed to be about 351 mm when the apex angle was 140º, rake angle was 25º and 7º lift angle. The uprooting width was recorded to be minimum of 300 mm at tool apex angle of 90º, rake angle of 25º and 7º lift angle. The influence of apex angle, rake angle and lift angle on uprooting width was portrayed in Fig. 5. It can be depicted that, as the apex angle was increased, a significant increase in the uprooting width was also observed. This might be due to wider width of cut was achieved as apex angle was increased. Thereby disturbed a larger cross-section area; consequently, it should favor a higher soil disturbance [1]. The rake angle also had a direct effect on the uprooting width, as the rake angle increased; it improves the tool penetration into the soil and further increase the uprooting width of the tool. The lift angle has shown a remarkable effect on the uprooting width of the tool. As the lift angle was increased, more soil was disturbed because the rise of angle will be perpendicular to soil cut by the tool. Also it improves the penetration of tool into soil which further increases the soil disturbance. Both rake angle and lift angle increases the uprooting width upto certain limit, further increase will not yield any improvement in the uprooting width. The results were in agreement with the [19] [5] and[6].

Apex angle, rake angle and lift angle had a significant effect on the uprooting width of the tool at 1 per cent level of significance (Table 3). Whereas its interaction effect has a significant effect at 5 per cent level of significance. The mean uprooting width was obtained to be about 322.1 mm with a standard deviation of 0.84 and the coefficient of variation among the observed values was 0.26 per cent. The R² value for the quadratic model was obtained to be 0.9977 and the predicted R² value of 0.9934 was in reasonable agreement with adjusted R² of 0.9957. The signal to noise ratio was 84.90, which was more than 4, and the signal was adequate. For the estimation of the uprooting width (W_u) of the tool with respect to tool geometry considered is given below.

W_u = 267.15 – 0.35 θ + 0.94 γ + 0.42 δ – (4.24 θγ x 10^-3) + (1.88 θδ x 10^-3) – (4.71 γδ x 10^-3) + (6.39 θ² x 10^-3) – (5.05 γ ² x 10^-3) – 0.01 δ ²                                                                        … (8)

Influence of apex angle (θ), rake angle (γ) and lift angle (δ) on burial width

Burial width of the tool is the total width of soil disturbed including the width of soil inversion. It was recorded that the maximum burial width of 427 mm was obtained at 140º apex angle, 25º rake angle and 7º lift angle. It was also noted that at apex angle of 90º, rake angle of 25º and 7º lift angle the minimum burial width was observed to be about 324 mm. The burial width of the tool is important as it incorporates the weeds into the soil effectively. In Fig. 6 illustrates burial width as a function of apex angle, rake angle and lift angle. It was cleanly depicted that, the apex angle has a considerable amount of effect on the burial width. As the apex angle was increased, burial width was also increased. This was due to increase in the cutting width of the tool as the apex angle was increased. Increased cutting width also increases the soil disturbance, which in turn increase the burial width. Burial width was also increased with increase in the rake angle, this was due to, at higher rake angle the weeding tool and more soil will handle more soil volume will be inverted, which results into maximum burial width of tool. The lift angle was also had a considerable effect on the burial width than rake angle. This was due increase in lift angle more amount of soil mass will be thrown out on sideways increasing soil inversion and burial width. The lift angle of the weeding tool, helps to get a deeper cut and pushes the soil outwards.

Apex angle, rake angle and lift angle had significant effect on burial width at 1 percent level of significance. The interaction effects of selected geometric parameters of weeding tool were also affected burial width significantly. The mean burial width of the tool was obtained to be about 368.25 with a standard deviation of 0.78. The R² value of the selected quadratic model was determined to be 0.9995, the predicted R² of 0.9977 was in reasonable agreement with the adjusted R² of 0.9991. The adequate precision was found to be about 183.05, which indicates that there was adequate signal. The quadratic model equation was developed for relation between burial width (W_b) and geometrical parameters of tool was given below.

W_b = 302.11 – 1.23 θ + 0.95 γ + 0.25 δ – 7.07 θγ + (1.88 θδ x 10^-3) – (4.71γδx10^-3) + 0.01 θ ² + 3.10 γ ² + 5.51 δ ²                                                                                                                    … (9)

Influence of apex angle (θ), rake angle (γ) and lift angle (δ) on draft efficiency 

The draft efficiency of the weeding tool represents the area of soil disturbed per unit draft. It was found that the draft efficiency was maximum of 1.08 cm² N^-1when the weeding tool having a apex angle of 90º, rake angle of 25º and 7º lift angle. It was also observed that, at 140º apex angle, 25º rake angle and 7º lift angle, the minimum draft efficiency of 0.51 cm² N^-1 was observed. The effect of apex angle, rake angle and lift angle on draft efficiency was shown in Fig. 7. It was found that as the apex angle was increased, draft efficiency was decreased. This was due to increase in the amount of draft developed as apex angle was increased. It means that more draft is required for considerable amount of increase in soil disturbance. Even the rake angle also has inverse effect on the draft efficiency. It was observed that draft efficiency was decreased as the rake angle was increased, this was due to more draft was developed with increase in the rake angle. Lift angle was also has the same effect against the draft efficiency. In all the cases, it was observed that more amount of draft was required for getting considerable amount of soil disturbance.

All geometric parameters were significantly effecting the draft efficiency at 1 per cent level of significance. Even the interactions of the selected geometric parameters were significantly effecting draft efficiency. The mean of the draft efficiency was obtained to be about 0.74 with standard deviation of 0.006. The R² value for the selected quadratic model was determined to be 0.9991 and the predicted R² value of 0.9951 was in reasonable agreement with the adjusted R² of 0.9983. The adequate precision was obtained to be 134.06, which indicates that the signal was adequate and that the model can be used to navigate the design space. The functional relationship of draft efficiency (D_e) with respect to apex angle, rake angle and lift angle was given by following equation (10).

D_e = 3.92 – 0.04 θ – 0.01 γ – (5.0 δ x 10^-3) + (8.48 θγ x 10^-5) + (3.77 θδ x 10^-5) + γδ + (1.18 θ² x 10^-4) – (1.13 γ ² x 10^-5) – (2.01 δ ² x 10^-5)                                                    … (10)

Optimization of the geometrical parameters of weeding tool in soil bin

Numerical optimization technique was adopted to obtain the optimum treatment combinations of experiment and with applied constraints. The performance parameters considered for optimization were draft, uprooting width, burial width and draft efficiency. The constraints applied to the performance parameters were minimization for draft, maximization for uprooting width, burial width and draft efficiency. After optimizing the geometrical parameters of the weeding tool, based upon the performance parameters, the optimum values were found to be apex angle of 114.95°, rake angle of 30.37° and lift angle of 9.99° and their corresponding predicted performance parameters were draft of 186.62 N, uprooting width of 322.67 mm, burial width of 368.33 and draft efficiency of 0.71 cm² N^-1 with a desirability level of 0.84 (Table 5). The experiment was again conducted in the soil bin at optimized geometric parameters and the performance parameters were measured and compared with predicted values.  The percentage variation in between actual and predicted values of draft was 2.35 percent, uprooting width was 1.45 per cent, burial width was 1.00 per cent and draft efficiency was 2.82 per cent (Table 6).

Conclusions

Geometric parameters of the weeding tool were optimized based on the performance parameters viz. draft, uprooting width, burial width and draft efficiency using response surface methodology in soil bin. It was found that all selected geometric parameters significantly affected the performance parameters of the weeding tool. The optimized geometric parameters were viz. apex angle, rake angle and lift angle were about 115°, 30° and 10°, respectively with predicted performance parameters viz. draft, uprooting width, burial width and draft efficiency were 186.62 N, 322.67 mm, 368.33 mm and 0.71 cm² N^-1, repectively. The predicted performance of the weeding tool was validated at optimized geometric parameters and the variation was found to be less than 3 per cent.

Get the all tables and images here…

REFERENCES

1. Marakoglu T; Carman K. 2009. Effects of design parameters of cultivator share on draft force and soil loosening in soil bin. J. of Agron., 8(1), 21-26.
2.  Gupta A K; Jesudas D M; Das P K; Basu K. 2004. Performance evaluation of different types of steel for duck foot sweep application. Biosyst. Eng., 88 (1), 63–74.
3.  Ademosun O C. 1990. The design and operation of soil tillage dynamics equipment. The Nig. Eng., 25 (1), 51–57.
4.  Makanga J T; Salokhe V M; Gee-Clough D. 1997. Effects of tine rake angle and aspect ratio on soil reactions in dry loam soil. J. of Terramech.,34, 250-235.
5.  Goodwin R J. 2007. A review of the effect of implement geometry on soil failure and implement forces. Soil & Til. Res., 97, 331-340.
6.  Spoor G; Godwin R J. 1978. Experimental Investigation into the deep loosening of soil by rigid tines. J. of Agric. Eng. Res., 23 (3), 243–258.
7.  Mardani A; Shahidi K; Rahmani A; Mashoofi B; Karimmaslak H. 2010. Studies on a long soil bin for soil-tool interaction. Cercetări Agronomice în Moldova. 43(2), 5-10.
8.  Young S L; Pierce F J. 2014. Automation: The Future of Weed Control in Cropping Systems. Springer, New York.
9.  Cirujeda A; Melander B; Rasmussen K; Rasmussen I A. 2003. Relationship between speed, soil movement into the cereal row and intra-row weed control efficacy by weed harrowing. Weed Res., 43, 285–296.
10. Johnson W C; Boudreau M A; Davis J W. 2012. Implements and cultivation frequency to improve in-row weed control in organic peanut production. Weed Technol., 26 (2), 334–340.
11.  Zhang  X; Chen Y. 2017. Soil disturbance and cutting forces of four different sweeps for mechanical weeding. Soil & Til. Res.,168, 167-175.
12.  Mckyes E; Maswaure J. 1997. Effect of design parameters of flat tillage tools on loosening of a clay soil. Soil & Till. Res., 43, 195-204.
13.  Myers R H; Montgomery D C; Anderson-Cook C. 2009. Response surface methodology: process and product optimization using designed experiments, 3rd edn. Wiley, New York.
14.  Singh K P; Pardeshi I L; Kumar M; Srinivas K; Srivastva A K. 2008. Optimization of machine parameters of a pedal-operated paddy thresher using RSM. Biosyst. Eng. 100(4), 591–600.
15.  Powar R V; Aware V V;  Shahare P U. 2019. Optimizing operational parameters of finger millet threshing drum using RSM. J Food Sci Technol.,56(7), 3481–3491.
16.  Gopal U S; Badgujar P; Shyam D; Kajale R. 2011. Experimental analyses of tillage tool shovel geometry on soil disruption by speed and depth of operation. International conference on Environmental and agricultural engineering, 15-28.
17.  Al-Janobi A; Eldin A M. 1997. Development of a soil bin test facility for soil tillage tool interaction studies. Res. Bul. Agric. Res. Center, King Saud University, 72, 5- 26.
18.  Al-Suhaibani S A; Al-Janobi A A. 1997. Draught requirements of tillage implements operating on sandy loam soil. J.  Agric. Eng. Res.,66, 177-182.
19.  Manuwa S I. 2009. Performance evaluation of tillage tines operating under different depths in a sandy soil. Soil &Til. Res., 103, 399-405.