Biomechanical models of the hand-arm system to predict the hand gripping forces and transmitted vibration

With the rapid development of logistics, forklifts are increasingly used in warehouses and other industrial sites. Drivers of the forklifts experience vibration and noise affecting the ride comfort during work. Focusing on the hand and arm vibration, this paper proposed a hybrid hand-arm model to represent the vibration transmitted from the steering wheel of a forklift to the hand and arm with different grasping forces. The model consisted of the shoulder, upper arm, forearm, and hand connected by joints with stiffness and damping. The hand model included the palm and five fingers, with each finger being modelled with the distal, middle, and proximal segments interconnected via revolute joints. Surface-to-surface contact was adopted between the hand and handle, and self-contact was defined for the hand. Moments were applied to finger joints to simulate the active muscle forces when gripping the handle. The material properties of the skin, bones, and subcutaneous tissues were determined based on published literatures. The parameters were further adjusted to match the contact pressures and vibrations of the hand and arms when griping a vibrating handle reported in literatures. The calibrated model was then used to predict the vibration transmissibility of the hand-arm system from the steering wheel of a working forklift and reasonably good results were obtained. The results showed that the developed model accounting for the grasping force and the contact conditions between the hand and handle is capable of predicting the vibration transmission of the hand-arm system of vehicle drivers.