Accelerometer vibration analysis in finding out velocities of pen input device

The pen input devices have become a popular input method with personal digital assistants and communication devices. The development of microelectromechanical systems (MEMS) technology has made it possible to put accelerometers-acceleration sensors — inside the pen. The acceleration information can be utilised in order to find out the movements of the pen. This makes it possible to manufacture pen input devices that do not need touch sensitive surfaces. However, due to the complex nature of the acceleration data, i.e. a mixture of movement and gravity data, it is not easy to extract the essential information. This paper presents an idea how the acceleration data could be utilised in finding out the instantaneous velocity of the pen tip. The idea is based on the vibration caused by the friction between the accelerometer pen and the textured surface, on which the pen is drawn. The properties of the vibration relate to the direction and the speed of the pen movement.