The main objective of the investigation was to investigate the new CANETHUMPER® method of cutting sugar cane in the Oribi and Harding regions of Kwazulul Natal. A further objective was to compare the responses to a previous project which investigated the manual method of cutting sugar cane.
2. Task description
The nature of the task was to have a ‘team’ of workers consisting of a driver and 5-8 sorters, with the goal of cutting and sorting sugar cane. The driver was responsible for manoeuvring the CANETHUMPER® to cut the sugar cane at the base (Figure 1). Evident in Figure 1 is that the sorters were required to manually bundle sugar cane and pull it toward them (to prevent contact with the blade of the CANETHUMPER®) so that bundles of sugar cane could then be cut by the driver and placed on the adjacent ground by the sorter. The workers then kept rotating as the driver moved forward on each line.
Four workers were assessed each day (one driver and three sorters) in each of the regions. In the first area all the workers were male while in the second area only the driver was male and the other workers were female. Spinal kinematics were assessed using an exoskeleton, the lumbar motion monitor (Figure 2). Physiological cost was assessed using continuous monitoring of heart rate during the work shift and a progressive step test following work when heart rate and oxygen uptake (using an ergospirometer, see Figure 2) were continuously assessed. The heart rate-oxygen uptake relationship was then used to calculate predicted oxygen uptake and energy expenditure using the working heart rate responses.
Referring to Table I, average lateral velocity for the driver has reduced from a mean of 18.00, during manual cutting, to a mean of 6.63 degrees per second with the new CANETHUMPER® method of cutting cane. Mean saggital velocity has also reduced from 11.0 to 6.7 degrees per second.
The CANETHUMPER® method of cutting cane shows a mean heart rate of 109 bt.min-1 compared to 122 bt.min-1 (Table 2) which was the mean working heart rate when cutting cane manually. Therefore, whereas the manual cutters average heart rate exceeds the recommended limit of 110 bt.min-1 for an 8-hour shift, those of the workers using the new CANETHUMPER® method are within the recommended ergonomics limits for heart rate.
Energy expenditure should not exceed 20.98kJ.min-1 over an 8-hour shift. As can be seen in Table 2 manual cutting (mean energy cost of 26.83 kJ.min-1) exceeds the recommended energy expenditure (20.98kJ.min-1) for an 8-h shift. Using the CANETHUMPER® does not surpass this recommended limit (19.71 kJ.min-1) and therefore does not pose any immediate threat to the workers. With respect to the energy expended per shift (Table 2), the mean cost of the CANETHUMPER® method was 8806 kJ.shift-1 which was 27% less than the manual method of cutting which is performed by one worker. Manual cutters expend 1157kJ in order to get one ton of sugar cane off the land, while mechanical operators (CANETHUMPER®) only expend 904.01 kJ in order to remove the same amount of cane. Therefore the energy cost per worker per ton, is reduced by 22%.
Overall it is evident that the new CANETHUMPER® method of cutting cane is superior to manual sugar cane cutting – this was biomechanically, physiologically and perceptually.