A Design Procedure of Dipole Arrangement and Inversion Algorithm for Magnetic Motion Capture Systems

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  • ATODA Oichi
    Graduaate School of Bio-Applications and Systems Engineering (BASE), Tokyo University of Agriculture and Technology
  • NAKAMURA Yuichi
    Graduaate School of Bio-Applications and Systems Engineering (BASE), Tokyo University of Agriculture and Technology
  • TOMISAWA Masaki
    Faculty of Engineering, Maebashi Institure of Technology
  • YOKOYAMA Kazuya
    Human-Environment System Department, National Institute of Bioscience and Human technology, Agency of Industrial Science and Technology, MITI
  • IMADA Tadahiro
    Graduaate School of Bio-Applications and Systems Engineering (BASE), Tokyo University of Agriculture and Technology

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Other Title
  • 磁気式モーションキャプチャ装置における双極子配置と座標逆算アルゴリズムの一設計法
  • ジキシキ モーションキャプチャ ソウチ ニ オケル ソウキョクシ ハイチ ト

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Abstract

Magnetic motion capture is an instrument which acquires three dimensional position and orientation of magnetic sensors through several time-shared magnetic field vectors from differently exited transmitter coils. Many small sensors could be attached to pin-points of a moving object including human body to record its motion. Tracking problem in pictorial motion picture will be avoided. Apart from Polhemus's which inherently depends on three orthogonal concentric transmitter coils, various coil arrangements could be devised according to the shape and dimension of required sensing volume. We define design of that instrument as an inversion-based problem and discuss on a solving procedure in which arrangement of coils and excitation pattern could be determined heuristically and almost independently of inversion algorithm since proposed algorithm is rather general to various field distributions. The algorithm starts from selected rotation-invariant quantities derived from sensed field vector components such as vector modulus or pattern-by-pattern angular difference of vector directions, and inverts classical dipole equation by Newton-Raphson's method to obtain xyz position of the magnetic sensor. Then the orientation of the sensor is determined by simple comparison of absolute and sensed vector directions. A simplest but very practical solution named point-scan system is presented in which four to nine solenoids aligned in a plane and excited one by one cover the box-shaped sensing volume below them. Its experimental result with newly designed hardware is also shown which covers 0.75 by 0.75 by 1m volume with resolution and stability of 1 to 3mm.

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