Studies on the Bush Cutter Equipped with a Fixed Blade (Final). Evaluation of the Weight-Reduced Fixed Blade Related to the Operators Physical Strain.:Evaluation of the Weight-Reduced Fixed Blade Related to the Opertors Physical Strain
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The major disadvantage of the new grass cutting system equipped with a fixed blade is due to the weight of the cutting unit. To overcome this disadvantage, we designed a perforated fixed blade, weighing about 315g, as against the conventional fixed blade of about 385g. The perforated blade was used for cutting the grass in different density to measure the operators heartbeat rate, O2 consumption and mowing efficiency. Thereby, an increase in the heartbeat rate, heartbeat rate and O2 consumption per mowing area were obtained. The experimental data, thus obtained, were compared with the data obtained while operating the conventional fixed blade and an ordinary blade, to check the degree of physical strain on the operator. The major results are summarized as follows.1) On the testing site (1) (Lolium Multiflorum Lam, : weighing about 1.4kg live), the site (2) (Sorghum Vulgare Per. and Digitari Adscendens Henr. mixed, : about 2.9kg) and the site (3) (Lolium Multiflorum Lam.: about 5.5kg), the heartbeat rate and the increase in the heartbeat rate while operating the perforated fixed blade were lower than those of the conventional blade.2) The ratio of heartbeat increase while operating the perforated fixed blade was 0.94 on the testing site (1), 0.99 on the testing site (2), and 0.97 on the testing site (3). There was little difference between the three. On the testing site (2) and (3), cut grasses left on the blade had to be removed with extra labor, undermining the effect of the blade to lower the physical strain on the operator. On the testing site (1), removal of the grass off the blade was not necessary. The difference in the weight of the cutting unit affected the physical strain on the operator. In other words, the perforated fixed blade works effectively to reduce the physical strain in cutting the grasses in low density.3) In making a comparison of degrees of the physical strains caused by using the blades of different working efficiency, on the different testing sites with the grass of different density, we judged it appropriate to use the ratio (physiological working efficiency) of the average heartbeat rate per minute in cutting operation against the cutting area per minute (working efficiency: m2/min.). We obtained the ratio of the physiological working efficiency of the perforated fixed blade against that of the conventional fixed blade. The ratio was about 8% on the testing site (1), about 10% on the site (2) and about 3% on the site (3). The results shows that perforated fixed blade worked positively to reduce the physical strain on the operator.4) Ordinary cutting blade, regardless of the kind of grass to be mowed and the weight of the blade, had a larger physiological working efficiency than the perforated fixed blade because of large gyroscopic couple. Increased gyroscopic couple made it difficulty to operate the machine and increased physical strain on the operator.
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