Patent ID: 7860562

Claim:
An external force control method for controlling an external force applied to a first living body portion of an animal through an orthosis attached to the first living body portion of the animal that makes a movement along with the activities of animal muscle fibers, the method comprising: a myoelectric potential measurement step of measuring a myoelectric potential x that occurs in a second living body portion of the animal; an external force setting step of setting a value of an external force f applied to the first living body portion of the animal through the orthosis according to an external force function f(x) with the myoelectric potential x as a variable on the basis of the measured value of the myoelectric potential x; a motion variable measurement step of measuring a motion variable y varying with the motion of the animal under the condition of the external force applied through the orthosis; a factor setting step of setting a value of a factor γ according to a factor function γ(f, y) with the external force f and the motion variable y as variables on the basis of the set value of the external force f and the measured value of the motion variable y; a determination step of determining whether a deviation δ between the set value of the factor γ and target value γ t thereof is less than a reference value ε; and an external force function setting step of setting a new external force function f(x) in such a way that the set value of the factor γ approaches the target value γ t if the deviation δ is determined to be equal to or greater than the reference value ε in the determination step, wherein the motion variable measurement step comprises measuring the resultant force of an internal force, which is a force exerted on the orthosis by the first living body portion caused by activities of animal muscle fibers in at least the second living body portion of the animal, and an external force, caused by a motion of an actuator and applied through the orthosis to the first living body portion of the animal, as the motion variable y; and the factor setting step comprises setting the ratio of the external force f to the resultant force of the internal force and the external force of the animal as the factor γ(0≦γ<1).