The role of the tactile sense of human fingers when handling a pin to insert it into a hole or extract it from the hole was studied. First, the accuracy of the tactile sense in discriminating the orientation of a small bar which was pressed to the index finger was investigated. Secondly, the ability to discriminate the direction of motion was measured when the bar was moved in various directions with constant angular velocity. Thirdly, the ability to discriminate the movement in various directions of a small pin held between a thumb and an index finger was determined.
The directional difference limen was found to decrease dramatically when the bar or the pin moved on the fingers in a certain range of speeds. The minimum difference limen of 0.25 degrees was obtained at an angular velocity of 2.8 degrees.
These experimental results motivated us to design a force vector sensor. Our sensor model can calculate the force direction as well as the force itself. The detection accuracy for force direction was found to be about 0.27 degrees, which is similar to that of the human tactile sense.