A roll sensor 70 is disposed along the roll axis R and a pitch sensor 80 is disposed along the pitch axis P. The pitch and roll axes P, R are provided at angles to one another (i.e., non-parallel axes), preferably right angles. Preferably, the pitch and roll sensors 80, 70 are gyroscopic sensors, such as the microelectromechanical systems (MEMS) gyroscopic pitch and roll sensors, e.g., model IDG-650, available from InvenSense, Inc. or gyro-sensor model XV-3500CB available from Seiko Epson Corporation. When properly oriented along the pitch and roll axes P, R the gyroscopic sensors measure and output the change in angle of the gyroscopic exercise ball 10 over a unit time. By knowing the time necessary to complete a full revolution about each of the pitch and roll axes P, R, the period of revolution of the gyroscopic exercise ball 10 can be determined and multiplied by the angular pitch and roll velocity to determine a range of motion for the gyroscopic exercise ball 10. In one embodiment, either one of the roll sensor 70 and the pitch sensor 80 is provided alone. By using a single gyroscopic sensor to measure either of the pitch and pitch velocity or the roll and roll velocity, the other values can be estimated by assuming that the motion is consistent about each axis. Preferably, both the roll sensor 70 and pitch sensor 80 are provided to obtain a more accurate representation of the motion.
Referring to FIGS. 6 and 7, the relative positions of a plurality of sensors 60, 70, 80, 90 are shown with respect to a rotor 12 of a gyroscopic exercise ball 10, in a plane of pitch axis P and roll axis R at a right angle thereto. The pitch and roll axes P, R are offset from the spin and input axes by 45 degrees.
In an embodiment, in addition to the pitch and roll sensors 80, 70, a third gyroscopic sensor 75 may be disposed at angles, for example, right angles, to the pitch and roll axes P, R. The third gyroscopic sensor 75 may be provided in the embodiments of FIGS. 6 and 7 to measure the rate of movement about a third axis, for example, the yaw axis by positioning the third gyroscopic sensor 75 relative to the third axis of the orthonormal frame of reference, wherein the pitch and roll axes P, R are the first and second axes. In this embodiment, the rotation sensor 60 and gyroscopic sensors 70, 75, 80 may be used to measure the three rotation rates of the gyroscopic exercise ball 10 about the respective yaw, pitch and roll axes.
The monitor 100 is mounted along the output axis 0 (i.e., the precession axis), preferably at the top of the gyroscopic exercise ball 10, and parallel to the plane of the input axis I and the spin axis S. The rotor 12 spins with the integrally formed shaft 14 about the spin axis S and the gimbal ring 24 is freely rotatable about the output axis O. A user of the gyroscopic exercise ball 10 gives the rotor 12 an initial spin, e.g., by pulling a cord attached thereto or by rolling the rotor 12 across a flat surface through the open end 16. Once the rotor 12 is spinning, the user applies a torque by motion of their wrist along the input axis I, thereby causing precession about the output axis O. Through the continuous application of force along the input axis I (i.e., rotational motion of the wrist), the user speeds up the rotor 12 and, of course, exercises their hand and wrist. As the rotor 12 increases in speed, the counter-forces on a user's wrist also increase, thus making the exercise more intense.