Degree Type

Dissertation

Date of Award

2020

Degree Name

Doctor of Philosophy

Department

Agricultural and Biosystems Engineering

Major

Agricultur al and Biosystems Engineering

First Advisor

Brian L Steward

Abstract

Mechanical cultivation is common weed control method for organic farming. A wide variety of mechanical tool designs exist for mechanical cultivation applicable for inter-row and intra-row weeds. Some of the tool designs for intra-row weeding require active control in the row and sometimes between the rows. For these tools, the knowledge of soil disturbance and forces at different operational settings could help achieve desired weeding performance from the tools. Information on soil disturbance could help when making operational decision that focus on damaging weeds without harming the crops. Understanding soil reaction forces on a weeding tool could be valuable for achieving desired movement of the tool required for higher weeding efficacy. Soil disturbance and forces are two important aspects which could be explored using soil-tool interaction study to optimize settings and design of a weeding tool to achieve higher weed control. In this research, interactions between soil and tines of an intra-row weeder prototype were investigated for effective weeding. The prototype consisted of vertical rotating tines for weeding which were intended to move in and out of the crop row by an actuator.

The first objective of this research was to develop a method to investigate the effects of soil and tool interaction on weeding performance for different settings in a controlled environment. Specifically, the effects of tines on small wooden cylinders, used as simulated weeds, were investigated through soil disturbance at different settings. Experiments for the study were conducted using a single cylindrical tine and a rotating tine mechanism in a loam soil. The total width of the soil disturbance and potential weeding rate were evaluated for the single cylindrical tine at different tine diameters (6.35 mm, 7.94 mm and 9.53 mm), working soil depths (25.4 mm, 50.8 mm and 76.2 mm) and two tine speeds (0.23 m/s and 0.45 m/s). The width of soil disturbance increased with increasing test levels of depth and diameters, while there was no significant evidence that tine speeds affected the width of soil disturbance. Potential weeding rate for a single tine was found to be affected by tine diameter, working depths and tine speeds. Particularly, the potential weeding rates increased with increasing levels of the three parameters. For the rotating tine mechanism, potential weeding rate was analyzed at different working soil depths (25.4 mm and 76.2 mm) and rotational speeds (25, 50 and 100 rpm). The potential weeding rate for the mechanism was found to increase for higher levels of working soil depths and rotational speeds. A simulation was developed to estimate area of soil disturbance caused by rotating tine mechanism at the same settings used in the experiment for the mechanism. The simulation results showed the percentage of disturbed soil area matched the patterns of the percentage of disturbed simulated weeds in the experiment.

For the second objective of the research, models were developed to estimate soil forces on a vertical tine of a rotating tine mechanism operating at different linear and rotational velocities. Separate models were developed for longitudinal and tangential forces which relate to horizontal draft force and torque on the tine, respectively. The models used longitudinal velocity and speed ratio as kinematic parameters associated with linear and rotational velocities. Longitudinal velocity was the forward traveling velocity of the rotating tine mechanism across the soil bin length. Speed ratio was the ratio of longitudinal velocity to peripheral velocity of the tines due to rotation of the mechanism. The models also accounted for shearing and inertial forces on the tine and associated coefficients were acquired empirically. Two sets of soil bin experiments were conducted using artificial soil: (i) with one tine to estimate the coefficient values and (ii) with two tines 180o apart to evaluate model performance. A working soil depth of 70 mm and tine diameter of 6.35 mm were used for both experiments. In the experiments, horizontal draft force and torque were measured across variation of two experimental factors: longitudinal velocity and speed ratio. Three levels of longitudinal velocity were 0.09 m/s, 0.29 m/s and 0.5 m/s, and three levels of speed ratio were 1, 1.5 and 2. The coefficients estimated by curve fitting experimental data using nonlinear least squares method yielded values of KS ranging from 2.96 to 37.5 N and KI ¬ranging from 16.6 to 528 N-s2-m-2 for the treatments. The different values of the coefficients captured the variation in shearing and inertial forces on the tine due to difference in patterns of soil failure among the treatments. The means of longitudinal and tangential forces predicted using the model for two tines 180o apart had trends similar to those of means of respective measured forces for different treatments. However, the model underestimated the predicted forces because it did not account for the reduced force on a tine due to soil disturbance created by the other tine.

In the research, the third objective was to study the effects of linear and rotational velocities on horizontal draft force and torque on the rotating tine mechanism operating in the soil. Experiments were conducted using the rotating tine mechanism consisting of four vertical cylindrical tines 6.35 mm in diameter in a soil bin with loam soil. The working soil depth of 70 mm was used throughout the experiment, and draft force and torque were investigated across different levels of longitudinal velocity and speed ratio. In the study, three levels of longitudinal velocity (0.09 m/s, 0.29 m/s, 0.5 m/s) were used for both draft force and torque. Four levels of the speed ratio (0, 1, 1.5 and 2) were used for investigating draft force and torque. Analysis of Variance (ANOVA) was conducted using significance level of 5%. The result showed the draft force, in general, decreased with increasing levels of speed ratio for the three levels of longitudinal velocity. The torque for different longitudinal velocity was found to increase, for most cases, as the speed ratio increased. These relationships were non-linear and exhibited large variability likely due to complex physical process that occurred during dynamic interaction between soil aggregates and tines of the mechanism. The results suggest that linear travel and rotational velocities can be optimized to manipulate draft force and torque of the rotating tine mechanism while targeting for desired weeding performance.

DOI

https://doi.org/10.31274/etd-20200902-80

Copyright Owner

Safal Kshetri

Language

en

File Format

application/pdf

File Size

120 pages

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