DEVELOPMENT AND EVALUATION OF INSTRUMENTED RIG FOR CASSAVA HARVESTING DATA ACQUISITION

Abstract

In the development of a cassava harvesting tool, there is the need to know the actual weight of materials (soil and cassava tuber plant) that the soil working tool would be working against. The cassava lifting coefficient, k, was theoretically expressed as a function of lifting force, lifting speed, weight of tuber and soil above the tuber as well as the time taken to uproot the cassava tuber. However, the volume of soil displaced during cassava harvesting is cumbersome and difficult to determine. Therefore, an experiment to estimate the volume of soil displaced during cassava tuber lifting was carried out on a loamy sand soil at the National Centre for Agricultural Mechanization, Ilorin in the 2012 farming season using lofting modelling. The lofting modelling, an important method for three dimensional (3D) object creation was employed to model the full shape of the cassava tuber. This feature estimates the volume of tuber and soil displaced accurately despite the irregular shape of the cassava tuber and the soil above the tuber having known the failure pattern. The analysis of field data using least square regression method generated a model equation with which the volume of the soil displaced, by a known volume of tuber, could be estimated having known the soil bulk density, soil moisture content and soil shear strength. The cassava lifting coefficient, k, was empirically determined for loamy sand soil by conducting an experiment using a developed and instrumented rig (incorporated with load sensor and speed selector) in a statistically designed experiment having lifting speed of 8, 11, 13, 16 and 20 mm/s and soil moisture content of 1.27, 5.13, 6.76, 9.84 and 11.96 % db respectively, as the treatment factors. The work revealed that as the soil moisture decreases, the lifting coefficient increases; a unit increase in moisture content results in marginal decrease of 21,230,848.56 mm3 in volume of soil displaced at 10% significance level; a unit increase in volume of cassava results in 42.97 mm3 marginal increase in volume of soil displaced at 1% significance level; a unit increase in soil bulk density leads to a marginal increase of 203,215,193,128.61 mm3 of soil displaced; a unit increase in cone index leads to 111,684,611.87 mm3 marginal decrease in volume of soil displaced and a unit increase in soil shear strength results in 361,798,352 mm3 marginal increase in volume of soil displaced. The maximum lifting force of 367 N was obtained at a lifting coefficient of 539,255.6 for loamy sand soil at the soil moisture content of 1.271 %, lifting speed of 8 mm/s and cassava tuber and soil weight of 1.7 kg. The lifting coefficient reduces as the speed of lifting increases; weight of cassava tuber is proportionally correlated to the volume of soil displaced during the cassava tuber lifting. At the moisture content of 1.271%, the average cassava tubers and soil excavated is 23.26 kg thus the force required to overcome while harvesting/uprooting cassava tubers that would ensure effective harvesting is 5 kN for loamy sand soil. However, the work is recommended to be repeated in other soil types and also the application of in situ apparatus is recommended for easier and faster field measurement.