Robust three-dimensional non-contacting angular motion sensor

For devices based on a sphere rotating in a cradle, the axis of rotation of the sphere is arbitrary and can change instantaneously. Consequently, a non-contact means of velocity sensing is desirable. For the ball wheel mechanism, which serves as the drive train for a class of onmidirectional mobile robots, most existing methods are not feasible, such as optical techniques based on surface-pattern distinction. Thus, in this paper, a robust, three-dimensional angular velocity sensor based on magnetometry is presented that tracks the orientation of ferromagnet embedded in the sphere. An algorithm based on vector orthogonality is used to approximate the angular velocity vector of the sphere from the sampled orientation data.