| Popis: |
This report describes the results of investigation and analysis by “Subjective Symptoms of Fatigue” to forestry tractor operators, the vibration on the seat of forestry tractor, the position of controls, the frequencies of control operations and operator's head movement. The level of forestry tractor operators' work intensity were allowable, their average complaint rates at “after work” being 11.9%, from the analysis of 167 responses of “Subjective Symptoms of Fatigue” to 31 tractor operators. They had much complaints of pain in some parts of the body. Judging from high complaint rates at “before work”, it can be said that operator always feels fatigue in the shoulder and low back.They operate tractors about 5.7 hours in a day, By means of 1/3 octave band frequency analysis of the vibration on the seat of 8 tractors in 3 directions, the vibration on tractors' seat were alowable, these vibration levels being below the “Fatigue-Decreased Proficiency Boundary” according to the ISO-proposal.Comparing the position of the levers and pedals of 12 kinds of tractors with JIS A 8450-proposal, it found that 9% of levers as the distance from hand to levers and 24% of controls as the direction from Seat Reference Point to control are arranged at unsuitable positions. The percentage of operating time by hand or foot in yarding cycle is 40%, and the state of operating the steering lever, the clutch pedal and the brake pedal appear mostly. The most operating time in links between hand or foot and each controls in yarding cycle appears in the case of operating brake pedal and winch lever, being operator's twisted body posture. Furthermore, operator's head movement was analyzed from the center of phots obtained by eye camera in 3 tractors. In “Driving without load”, the operator “A” of the wheel type tractor often faces the right-rear to direct attention to rear wheel. In “Cable skiddng”, 2 operators “B, C” of crawler type tractor face just to the rear, looking at the winch, but the “A” operator faces to the right-rear, as it stops in the bending position of the back part. As the results of operator's head movement and operating time of tractor in a day, there were much frequencies of operator's twisted body posture in operating tractor, “A” operator being 30.7%, “B” 14.6%, “C” 14.7%.Considering the above results, it can be said that one of the factors causing operator fatigue would be the actuation of the wrong arrangement of controls in operator's twisted body posture. |
