Passive Human Grasp Control of an Active Instrumented Object

An active instrumented object was built to investigate the human ability to grasp and hold the object against gravity during rapid contractions of the object. Initial grasp force was shown to be the dominant variable that determined whether the object was held or dropped. Other factors such as the friction of the interface or the contraction velocities used (130 mm/s or higher) were not found to have a significant effect. A third order lumped parameter model of the finger was proposed and the parameters of the model corresponding to the stiffness and damping of the fingerpad and muscle together with finger mass were identified using the recorded force and displacement data. This model of the finger was shown to predict the experimental data quite well, indicating that the subjects’ fingers are effectively passive during rapid haptic events that occur within 60 to 80 ms.