HAVS and HAV-nots: Investigating Resonance in the Human Arm Caused by Contact with Machinery

International audienceMechanical vibration is a vast field composed of thousands of studies and experiments regarding individual systems and structures' vibrations and oscillations. In this paper a special and complex case regarding hand-arm vibration will be studied and analyzed mathematically. The human hand-arm system is affected by vibrations caused by contact with vibrating objects. In order to understand the effect on the hand-arm system, a mathematical model of the system as two viscoelastic rods connected by a hinge was derived. Using this model, it was possible to derive the propagation of both the longitudinal and bending vibrations of the arm, and find the resonance frequencies of the system from the elbow to the shoulder. The harmful effect of these frequencies is discussed with regards to Hand-Arm Vibration Syndrome, a disease stemming from repeated contact with vibrating objects. Hand-Arm Vibration Syndrome is found to be a pervasive issue among physical laborers who use vibrating machinery. A sample set of construction tools is analyzed and compared with the modeled resonance frequencies of the arm. Considering the resonance frequencies of the arm is significant for tools manufacturers. Research on the frequencies at which tools function may be overly dangerous to workers who are required to handle such tools frequently. Introduction. Vibration is a common byproduct of mechanical technology. Construction and contract workers typically are in contact with such technology on a daily basis. This interaction has been found to lead to a disease known as Hand-Arm Vibration Syndrome (HAVS). The disease causes intensive damage to the hand and arm and can be debilitating. Individual machines emit vibration at a specific frequency, and if it is at the natural frequency of the material in the human arm or hand, can cause devastating damage and more quickly lead to the development of HAVS. Therefore it is important to know accurately the resonance frequencies in the arm and compare them to the individual frequencies emitted by construction technology. Due to the extreme difficulty of gathering data on the human arm from a living subject, models of the arm are a practical solution to the resonance problem. An investigation of the arm modeled and analyzed as two viscoelastic rods is conducted below. Resonance. Resonance is the phenomenon at which an externally forced frequency coincides with the natural frequency, defined by a ratio close to one between the two frequencies. When damping is present, pseudo resonance will occur with the maximum amplitude of the vibrating object. In general, amplitude is not linearly dependent on frequency. An important case of resonance, including the hand-arm system, relates amplitude í µí°´o the square of the frequency í µí¼” [1]. The case of resonance in the hand-arm system will be examined later