Handwriting tracking based on coupled μIMU/electromagnetic resonance motion detection

We have recently developed a ubiquitous digital writing instrument system based on a micro inertial measurement unit (mulMU), which consists of MEMS (micro- electro-mechanical system), accelerometers and gyroscopes, to compute the position of a marker through double integration of the acceleration measured, so as to real-time record and recognize human handwriting motion in a large writing area, i.e., a large whiteboard or screen. Owing to the random errors that exist in the MEMS sensors, the accuracy of the position estimate degrades with time. Although Kalman filtering algorithm provides a good navigation tracking solution, its accuracy depends on the amount of position information given about the target. In vehicles, the global positioning system (GPS) can be used to augment an IMU with absolute position information and improve its tracking accuracy. However, due to indoor-usage and a higher accuracy requirement, the GPS is not suitable for updating a mulMU used for hand-motion tracking with absolute position information. In this paper, we propose a novel position estimation method which makes use of an electromagnetic resonance (EMR) motion detection board for position information to improve the tracking accuracy of a mulMU-based digital writing instrument. The EMR board cannot provide high resolution (only 3 cm per grid in our case) position information for a large writing area because of high construction cost and poor tracking performance. However, the combined scheme of using the mulMU and the EMR board can compensate their respective weaknesses. The EMR board can bound the mulMU position estimate error and the mulMU can provide detailed information of the handwriting trajectory for the rough locus obtained from the EMR board. Details of the estimation algorithm will be discussed and experimental results of its implementation are compared with the conventional Kalman filtering without the extra position feedback information.