Being the  third instalment of an inaugural lecture delivered  by Lawson Olabosipo Adekoya, Professor of Mechanical Engineering,  at Oduduwa Hall, Obafemi Awolowo University, Ile Ife

INTENDED cylinders separate grains based on differences in shape while inclined drapers effect separation on the basis of differences in surface textures of the particles. In contrast, the electromagnetic separator effects separation based on differences in the electrical properties of the grains and the foreign matter.

All the above previous methods have limited successes in removing stones from grains. However, the specific gravity table has been reported to achieve efficient separation of stones from grains (Henderson and Perry, 1976).

In order to domesticate the principle for the cleaning of local grains, such a machine will have to be specifically designed and made adjustable for varieties of local food grains such as maize, rice and cowpea.

Prof. Lawson Olabosipo Adekoya

As a first step in meeting this goal, Koya and Adekoya (1994) determined some physical, mechanical and aerodynamic properties relevant in mechanically-removing stones from some local food grains. The relevant properties were physical (size, shape, mass and density), mechanical (coefficient of static friction) and aerodynamic (suspension velocity). The properties were determined for two varieties of maize (Farz7 and TZSR-W), two varieties of rice (Faro II and BG 90/2), and three varieties of cowpea (Ife Brown, TVX 3236 and IT84E-124). Relevant properties of rock and mineral particles (often referred to as stone) that usually constitute impurities in grains were compiled from Telford et al (1976).

Using the above data and basic design principles, a machine for removing stones from local grains was designed and fabricated (Adekoya and Koya, 1998). The machine consisted of an oscillating table, the transmission, the fan and air chamber, and the power source. The oscillating table was an inclined perforated plane made from expanded metal with an overlay of mosquito netting. The oscillatory motion of the table was imparted through a crank-rocker mechanism driven by an electric motor (Plate 8).

Separation by specific gravity separator is based on two conditions. (1) the lifting or floating effect produced by the upward motion of air through the perforations in the oscillatory table, and (ii) pure-slip conveyance of granular materials on an oscillating conveyor within a certain range of frequencies. Test results showed that for varieties of the same grain, the optimum values of the parameters that affected the machine operation were basically the same but were different for different grains.

The machine successfully separated up to 94%, 90% and 74% of the stones present in rice, cowpea and maize varieties respectively in the first pass of the grains.

•Oil Palm Harvesting on Plantations: The oil palm (Elaeis guineensis Jacq.) is a tree without branches but with many wide leaves (or fronds) at its top (or crown). Bunches, each of which contains over a thousand fruits, are held in the axils of the leaves and are arranged in a rosette around the crown. The oil palm is a native of tropical Africa growing wild in many parts of West Africa and the Congo basin.

The oil palm is a very important economic tree. The two most important products of the oil palm are palm oil and palm kernels, both of which are obtained from the fruits. Palm oil is used primarily for human consumption, but a substantial amount is also used in the manufacture of margarine, soaps, etc, while the oil from the kernel is used mostly for pomades, oil paints, etc.

Mechanical harvesting

Generally, for fruit crops, the majority of mechanical harvesting systems utilized today are shake-and-catch methods (Futch et al, 2006). The oil palm defies this harvesting method because the fruits are compactly packed in bunches which are hidden in leaf axils in the crowns.

Also, the trunk of the oil palm is not compliant enough to create the required vibration phase difference between it and the fruits (as is found between the tomato fruits and vines for example). Additionally, the bunches have very thick and strong stalks and could be at heights of over 9 m.

Work done by Bevan and Gray (1969) in Malaysia showed that for palms aged between 9 and 16 years, 43.5% of the total man-hours for annual production was expended on harvesting. The corresponding value for palms aged between 17 and 25 years was 45.4%. According to Hartley (1977), booms mounted on tracks or high floatation wheeled tractors were tried in Honduras and Costa Rica. The booms took the harvesters to the crowns of palms up to 12m in height, and the bunches were cut and they fell into a trailer drawn behind the tractor. The method was cumbersome because it was difficult to manoeuvre the tractors around the tree trunks and also ensure that the bunches fell into the trailer.

Locally, the oil palm is currently being manually harvested using simple implements such as cutlasses, axes, chisels and the Malaysian knife. The method used depends largely on the height of the tree. The methods currently being used in Nigeria are: the chisel method (for plants less than 2.5m in height or within arm-reach), the ladder and cutlass/ladder and axe method (for moderately-tall trees beyond arm-reach), the knife and bamboo pole method (for trees from moderately-tall up to 9 m in height), and the rope and cutlass/rope and axe method (for trees beyond the reach of the knife and pole method).

Adekoya and Makinde (1990) carried out preliminary investigations to obtain data on oil palm and oil palm harvesting on plantations in Nigeria in order to facilitate the mechanisation of the process. The research was carried out on the oil palm plantations of the Nigerian Institute for Oil Palm Research (NIFOR) in Benin-City. The data sought were the following:

i. base circumference of the oil palm measured at a height of 30 cm from the ground surface,

ii. trunk circumferences measured at a height of 2 m from the ground surface and at intervals of 1 m,

iii. bunch stalk circumference,

iv. force required to cut a palm frond,

v. force required to cut a palm bunch,

vi. number of bunches on a tree, and

vii. mass of a ripe bunch.

Further work by Adetan and Adekoya (1995) showed that harvesting of the oil palm can be broken down into five separate activities which can be classified as:

i. locating, reaching and cutting of the ripe fruit bunches and underlying fronds,

ii. stacking of the cut fronds along the row,

iii. searching for and collecting the cut fruit bunches and the scattered loose fruits from the ground,

iv. transporting the fruit bunches and the loose fruits to the collection centres in the field, and

v. loading the fruit bunches and the loose fruits into vehicles for transportation to the processing plant.

Additionally, a time and motion study was carried out on the two methods used for harvesting tall trees: the bamboo pole and knife (BPK), and the single rope and cutlass (SRC) methods, in order to determine where intervention was most urgently needed (Adetan and Adekoya, 1995). Data was collected on the times used for carrying out the first four activities described in the previous paragraph.

The research showed that:

i. With the BPK method, the greater mass and length of the harvesting pole made harvesting very uncomfortable.

ii. Transportation of the long and heavy harvesting pole to, from, and on the field was very onerous. There was the risk of injuring other field workers with the Malaysian knife on the long pole.

iii. Severe damages were inflicted on the fruits from tall trees as they impacted the ground. This was likely to substantially raise the free fatty acid level of the oil produced from them, which would lead to a lower quality of oil.

iv. There were the risks of accidental falls and snake and insect bites in the SRC method.

v. In either method, the search for, and the collection of the detached and scattered fruits were never fully accomplished because it was impossible to know how many fruits were detached from the bunches, and hence when the search and collection should be terminated. Therefore, there is always the probability of leaving an appreciable proportion of the detached fruits uncollected especially in high-yielding but weedy plots.

vi. The fruit collector always complained of waist pains, and because of this problem, there was a tendency for an incomplete search and collection of detached loose fruits. The preceding and current observations informed us that there could be resultant high cumulative losses in the collection activity.

Based on the facts that the climbing before cutting substantially reduced harvesting rate, and that much risk was involved in climbing, it was decided that further research should be done to make the BPK method more suitable for harvesting tall trees. This was effected through an improved pole-and-knife method of harvesting the oil palm (Adetan et al, 2007).

Basically, the research consisted of the design and fabrication of a  telescoping mechanical pole that was easier to carry, was easier in engaging fronds and bunch stalks, and was able to harvest both short and tall trees. By treating the pole as a cantilever, deflection analysis was carried out (Juvinall, 1967) on various lengths and diameters of locally-available aluminium poles to determine the sizes to procure for the construction. The  telescoping was achieved by using three sections of aluminium pipes of different diameters with the Malaysian knife attached to the topmost section.

To complement the telescoping pole, a catchment platform was designed and fabricated from high density foam sandwiched between a tough polyethylene tetraphalate tarpaulin material on top and a fairly tough nylon (polyamide) material at the bottom. The foam made the spreading and folding of the platform easy and also helped to absorb some of the kinetic energy of the falling bunches.

Field tests showed that the combination of telescoping pole and catchment platform significantly reduced the detachment of the fruits from the bunches and also ensured that the few detached fruits do not possess enough kinetic energy to be dispersed from the catchment platform. These actions reduced the severe damages inflicted on the fruits as they impacted the ground. The telescoping harvesting pole was easily disassembled and packed together for easier transportation to the fields, was much lighter than the bamboo pole, and was easily used to harvest trees of different heights (Plate 9). Of course, it also had a longer life than the bamboo pole.

Successful commercialisation

Mr. Vice-Chancellor, I am happy (or is it sad?) to inform you that the telescoping harvesting pole is presently being manufactured in Malaysia and exported to many oil palm producing countries including Nigeria. The telescoping harvesting pole (without a catchment platform) has been sighted in service at the Araromi Oil Palm Plantation, Araromi-Obu, Ondo State and Swanlux Farms, Coker Village (near Osogbo), Osun State. My sadness is due to the fact that there is no royalty accruing to the University or the researchers from the commercialisation of the idea!

With the “successful” commercialization of the telescoping harvesting pole, as it were, attention was shifted back to the improvement of the traditional climbing rope. The traditional climbing rope is made from vines or some other vegetative material. The major problem of the traditional climbing rope is failures due to rope breakages. These failures resulted in falls that were either minor or fatal. On some occasions, the climber is attacked by snakes or insects.

In an attempt to strike the snake and /or drive away the insects, the climber sometimes loses his balance and is cut by the cutlass or bruised by the tree. In this climbing method, it is impracticable for both legs of the planter to leave the tree at the same time. If done, the climber either gets bruised during the impaction of his body on the tree or he is completely immobilised by the rope pinning his body to the tree.

Simple solution

A simple solution to these problems was to design an engineered rope with a device that enabled the climber to free his hands and legs from the rope and the oil palm tree without falling down or impacting his body on the tree. Thus he can use his hands, cutlass and legs to defend himself in the case of an attack by either a snake or insects.

The engineered rope was made up of two parts: the body brace  belt and the rope. The body brace belt consists of a belt part made of canvas and a brace part made of gauge 16 sheet metal strip padded with rubber foam. The gauge 16 sheet metal strip carried two locks for attaching the rope part. The rope part was also made of two parts: a safety arm made of aluminium and the rope made from 6 mm-thick canvas lined with a stainless strip, punched so that the surface was rough enough to grip the oil palm tree (Plates 10 and 11). The safety arm was constructed of aluminium and weighed a only 2.5 kg. Accelerated testing showed that the engineered climbing rope had a life of at least five years while the traditional climbing rope had a life of a few months (usually a harvesting season).

Peeling of Cassava Tubers

The cassava root is a tuber. It is the main economically-useful part of the plant. Apart from its use as a source of food for humans, the cassava tuber has many non-food uses. These include its use as industrial starch in the textile industry and as cassava flour used for blending wheat flour in processing of biscuits, bread, etc.

Several attempts have been made to mechanise the peeling of cassava prior to our work. Chemical peeling using a hot solution of sodium hydroxide (which has been successful in peeling potatoes) were shown to be unsuitable for cassava tubers (Igbeka, 1985).

Abrasion has had limited success mainly because the process reduced the tubers to uniform cylinders before all peels could be removed (Ezekwe, 1976). Additionally, before the big tubers are adequately peeled, the small tubers would have been literally grated.