Strategies of Pen Tip Path Estimation and of Workload Comparison for Handwriting Tasks

The magnitude of impulse and work at pen tip, which are related to the fingertip force, may be indicators of fatigue and pain during writing. Previous methods used specially prepared pens for testing which have different sizes and weights from those commercially available; however, they are not suitable for evaluating the operation and workload of ordinary handwriting tasks. This article proposes a data processing method of a six-axis force-torque sensor for determining the contact state of the pen tip and calculating the position and work of the pen tip without adding anything to a commercially available pen. The proposed method consists of kinematic calculation of the pen tip position as the observation and probabilistic determination of the contact state of the pen tip. The performance of the proposed method is presented by applying to the time-series data of force vector and moment vector during handwriting tasks of symbols. The data was measured by a low-resolution high-frequency 6-DoF force-torque sensor. Multiple handwriting tasks with the same or different load at one time were set. It was confirmed statistically whether the work amount with one pen tip can be evaluated appropriately if the work amount is the same or different. The experimental results demonstrate that the proposed method can compare the movement distance and work of the pen tip, depending on the severity of the writing task.