Abstract
In order to investigate the effects of hand-arm posture, grip force, push force, and vibration excitation intensity on the mechanical impedance of human hand-arm system, a test system with a self-developed vibration handle has been prepared. Based on the testing system, the mechanical impedance of the hand-arm system of seven Chinese adult males were tested and calculated under the random vibration excitation with the frequency of 10–1000 Hz. The results reveal that when the frequency is lower (<40 Hz), the hand-arm system with an elbow angle of 180o produces a higher mechanical impedance; when the frequency ranges from 40 Hz to 100 Hz, the hand-arm system with an elbow angle of 90o generates a higher mechanical impedance; while when the frequency is higher (>100 Hz), the hand-arm posture seems to have no obvious effect on the mechanical impedance. Higher grip or push force would increase the frequency corresponding to the peak value of the mechanical impedance and often correspond to a higher mechanical impedance in a specific frequency range (30–200 Hz). When the frequency is lower (<140 Hz), vibration intensity has certain effects on the mechanical impedance of the hand-arm system. In conclusion, vibration intensity does not directly affect the mechanical impedance, but an increase in grip or push force often causes an increase in mechanical impedance and a higher frequency that corresponds to the peak of mechanical impedance.
Highlights
When the agricultural machinery and equipment are working in the field, strong vibrations are inevitably produced due to the low levelness of the farmland, large motion range of the working device, high running speed of the transmission system and its own structural characteristics, and the vibrations will be passed to the body of the operator through the seat, steering wheel, handrails, and pedals
Matlab software was used to calculate the mechanical impedance amplitude of the human hand-arm system, and the results were expressed at the center frequency point of 1/3 octave in the frequency range of 10–1000 Hz
Observations showed that, under two different handarm postures, the amplitude of mechanical impedance of the hand-arm system was only different among individual subjects at low vibration frequencies (
Summary
When the agricultural machinery and equipment are working in the field, strong vibrations are inevitably produced due to the low levelness of the farmland, large motion range of the working device, high running speed of the transmission system and its own structural characteristics, and the vibrations will be passed to the body of the operator through the seat, steering wheel, handrails, and pedals. According to different body parts that are influenced by the transmitted vibrations, the vibrations can be divided into whole body vibration and local vibration. E workers who manipulate this kind of tools or machines for a long time may feel tingling and numbness in their hands, the severity of which usually increases with stronger vibration intensity of the tool. In severe cases, it may cause physical discomfort and loss of control of the tool [3]. Prolonged exposure to such high-intensity hand-transmitted vibrations can cause a series of diseases in the blood vessels, sensory nerves, and musculoskeletal parts of the human hand-arm system. Prolonged exposure to such high-intensity hand-transmitted vibrations can cause a series of diseases in the blood vessels, sensory nerves, and musculoskeletal parts of the human hand-arm system. ese diseases are
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