抄録
A study was conducted to investigate the effects of object weight on the regulation of grip force during holding tasks using a precision grip. In addition, variations in grip force among individuals were examined. Using a force transducer-equipped grip apparatus, grip force, load force and the vertical position of the object were measured continuously while using load weights of 0.98N, 1.96N, and 2.94N under sandpaper grip surface conditions. From the recorded data, peak grip force, average static grip force, slip force, safety margin force (average static grip force-slip force), and time to stabilize the grip force from the peak grip force were evaluated.
It was found that both the slip force and safety margin force increased with object weight. The static friction coefficient, estimated from the slip force and load force, deviated from Amonton's law at a lower load force. The deviation was believed to be due to the influence of the viscoelastic nature of finger skin. An increase in safety margin force with object weight was considered to be related to the psychological reaction to the increased heaviness of the object. Indeed, in trials that included unexpected changes in object weight, the safety margin force was increased, which also seemed to be associated with the psychological reaction to uncertainty about the object's weight. A relatively large inter-subject variation was revealed for both the slip force and safety margin force.
