Patent ID: 7220958

Claim:
An external force detecting device comprising: a support section shaped into a hollow cylinder; an action section disposed centrally inside the support section; and an optical displacement sensor including: a light source which is disposed at the action section on a center axis of the action section, and which emits a light beam in a direction along the center axis; a light branching member which is disposed at the action section on the center axis, and which branches the light beam emitted from the light source into three light beams to progress in respective directions oriented rotation-symmetrically about the center axis at a 120 degree interval; a light reflecting member which is disposed at the action section on the central axis, and which reflects the three light beams in a direction parallel to a plane perpendicular to the center axis; and three light receiving elements which are disposed at the support section in a rotation-symmetric manner at a 120 degree interval such that their light receiving faces look toward the center axis of the action section so as to receive respectively the three light beams reflected at the light reflecting member, the optical displacement sensor detecting displacement of the action section relative to the support section based on a position of each of the three light beams received at the light receiving faces of the light receiving elements, and sending out a signal, based on which an external force applied relatively to the support section and the action section is calculated.