Development of the gyro-free handwriting input device based on inertial navigation system (INS) theory

This study presents a simple attitude estimation technique for the gyro-free handwriting input device that uses inertial navigation system (INS) theory. Generally, three acceleration signals and three angular rate signals have been used to apply INS technique for estimating the trajectory of a pen-tip. We, however, propose the gyro-free INS technique for a pen system which uses acceleration information only to estimate the trajectory of a pen-tip. It was examined from the experimental study that the Euler angles of the pen did not change so much in the motion of handwriting. Based on this observation, we made a simple linear approximation method that used acceleration signals of the pen system to estimate its Euler angles. The experimental results show the proposed method is useful for gyro-free handwriting input devices using acceleration information only.