PART B: SYSTEM AND ERGONOMIC ANALYSIS
5. SYSTEM ANALYSIS
5.3 Methodology
Measurements were taken during the 2005 and 2006 harvesting season. The 2005 results were taken from harvesting on Isonti farm, Umzinto and the 2006 results were taken off Esperanza farm, Umzinto. The results obtained in 2005 were not favourable due to teething problems, a steep learning curve and the operators training and practice. The system was adapted slightly in 2006 and showed a marked improvement. The system development followed an incremental change approach. The human body knows its limitations and how to find the easiest and most efficient method of performing a task. The operators where, therefore, given guidelines on an operation, but were allowed freedom to change the system as seen fit. The biggest issue was to ensure that the safety standards were not jeopardised. Proper supervision helped to alleviate this issue. The final system developed is explained below.
5.3.1 System Description
Two fully trained operators operated one machine at a time, while two unskilled workers conducted the sorting, topping and stacking. The tasks for harvesting using the ISH were split
into two task components: (i) Cutting with the machine harnessed and (ii) pulling with a staff implement or crook. Figure 5.2 illustrates these two tasks.
Figure 5.2 System of harvesting using two operators, the puller uses a staff for pulling the cane over into a windrow (red) and the cutter (yellow) cuts the cane using the Illovo sugarcane harvester
The cutter has the machine securely harnessed around his shoulders ensuring that the clip to connect the machine onto himself is positioned a hands length below the hip bone. The machine needs to be balanced on the harness to alleviate excessive arm strain. The cutting motion was from right to left and the front right leg was placed in front of the left and used as leverage. The machine was then swung back by twisting the torso. One motion cuts approximately 5 stalks, but this depends on the thickness and density. Care was taken to not hit excess dirt and stones, but at the same time to cut as low as possible. Two dominant motions are used: (i) a gentle push through the cane where it cuts gradually and (ii) a faster swipe that uses the machines momentum. The faster swipe motion cut quicker, but was less accurate leaving more butts behind and the blades were more susceptible to damage. According to STIHL SA both motions are acceptable and do not damage the machine and it is purely personal preference which motion should be used.
The staff implement used for pulling the cane over was similar to a shepherds crock. It was 1.5 m long with a 400 mm radius half circle at one end and an enclosed handle at the other. It was made out of 12 mm re-enforcing rod and was used to ensure that the cane falls in one direction forming a windrow. The puller stands alongside, to the left of the cutter to pull cane. The puller needs to
pull the cane from above the centre of gravity to ensure no cane sticks fall in the opposite direction and obstruct the cutter. A force must be exerted in the correct direction (left) before the cane is cut to ensure the sticks fall in the correct direction and to help the cutting process. It helps the cutting process by pulling the sticks away and by applying a side force that helps cut the stems. The puller's efficiency was the determining factor with regard to the speed of operation.
The puller needs to lay the cane down and gather the next group of stalks to be cut before the cutter pulls the machine back. The cutter was usually forced to wait, but by applying the correct pulling technique this delay can be minimised. The correct technique uses the left wrist and the staff was held loosely with the right hand. The staff was inserted perpendicularly into the line ahead of the cutter, the wrist then twisted and gathered the cane to be cut. This was followed by pulling and applying a side force to aid the cutter as shown in Figure 5.3. When inserting the staff perpendicular before twisting care must be taken to not hit the rotating blade. The puller's other responsibility was to move rocks that obstruct cutting and cause damage to the blade. The rest of the team comprised of two unskilled workers who sorted the cane, topped and stacked the cane for loading.
Figure 5.3 The twisting motion using the left wrist followed by pulling the cane with the staff to aid the cutting
The sorters, toppers and stackers followed the machine while cutting and combined approximately three cut lines into a single windrow. They ensured that the tops were aligned and the line was clear so that the operators had a clear pathway for harvesting. Figure 5.4 shows the sorters who pushed the cut windrow (circled in yellow) into a manageable small bundle with their
feet and then transfer it to a combined windrow (circled in red). This was then topped and stacked to fit into the current system shown in Figure 5.1.
Figure 5.4 Sorters organising the cut windrow (yellow) and placing it into a combined windrow (red) for subsequent topping and stacking
The Illovo cutter was only able to cut from right to left due to the machine configuration. Cutting in this fashion means that the operators had to cut a row, then walk back and start the next row, this wastes time and energy. Figure 5.5 depicts this, where the green lines are rows of cane, the black arrows show the direction of cutting and the red dashed lines represent walking back to the start of a new line for cutting.
Figure 5.5 Direction of cutting (black arrow) the cane (green lines) and where the operators have to walk back to the start of the next line (red dashed arrow) using System 1
Figure 5.5 depicts System 1 and is used on short lines (< 20m) and on steep slopes (>75%). To save the extra walking (red dashed arrows) a block harvesting system was introduced (System 2).
System 2 cuts in blocks that become smaller and smaller and illustrated in Figure 5.6. This was used if the lengths of lines were greater than 20m (optimally 50m) in length. The total number of lines that were cut per block was approximately 15. This would yield an area of 0.075 hectares and at a yield of 60 tons.ha "l, there would be sufficient cane to stack a 4.5 ton bundle.
The systems were analysed by performing time and motion studies using the sheets seen in Appendix C. The time and motion studies indicate where time was being wasted (e.g. walking with machine to the start of new line). The system was also analysed using the performance and output per hour that was achieved.
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Figure 5.6 Direction of cutting (black arrow) the cane (green lines) and where the operators have to walk (red dashed arrow) using the block method (System 2). This saves time and energy
5.3.2 Safety
The system had to be analysed from a safety perspective. This was achieved by supplying the operators with safety equipment recommended by the suppliers of the machines (goggles, ear-
muffs and long pants with safety boots) and observing where problems might arise. An ergonomic study by a team from Rhodes University, Grahamstown was also carried out. Any problems or injuries where also recorded on sheets provided (Appendix C).
5.3.3 Measurements
A foreman was employed to record and take measurements. He was required to fill in the sheets seen in Appendix C. The type of cane and the conditions of the field (stones, slope, and lodging), the time spent in the field, the total time spent operating, fuel consumption and any problems incurred with the machine while harvesting were recorded. From this, it was possible to obtain the harvesting rate during operation and harvesting rate while in-field with respect to tons cut and area cut per hour. Problem areas could also be identified.
From these results it was possible to obtain the productivity and cost of operating under various conditions. This was compared to current manual harvesting systems and recommendations could be made as to whether it was a viable solution for harvesting sugarcane.
The machine had to be observed for its durability and estimate its life to determine the cost of the system. This was done by regularly returning the machines to a recognised dealer who stripped and tested the machines for wear in the rings, loss of compression caused by dust, damage to the gearbox and drive shaft, and wear in the clutch.