Patent ID: 7032465

Claim:
A rotational angle detecting device for a wave gear device that includes a ring-shaped rigid internal gear, a flexible external gear, and a wave generator with an elliptical shape for flexing the flexible external gear into an elliptical shape so as to partially engage the rigid internal gear and for moving engagement positions of the two gears in a circumferential direction, comprising: first, second, and third strain detecting elements that are disposed at intervals of 120° in the circumferential direction on one of the rigid internal gear and the flexible external gear; signal component extracting means that extracts, from outputs of the first to third strain detecting elements, signal components that appear as two cycles of a sine wave per rotation of the wave generator and are synchronous with a rotational angle of the wave generator; signal processing means that generates two-phase sinusoidal signals that are 90° out of phase by carrying out a coordinate transformation on the three-phase sinusoidal signals that are 120° out of phase and have been extracted from the outputs of the first to third strain detecting elements; and angle calculating means that calculates a rotational angle of the wave generator based on the two-phase sinusoidal signals.