Walking assistance device

A walking assistance device, comprising:

• a load transmit portion adapted to transmit load for supporting a part of the weight of a user to a body trunk of the user;
• a foot-worn portion adapted to be attached to a foot of the user;
• a leg link which connects the foot-worn portion to the load transmit portion, the leg link comprising an upper link member extended from the load transmit portion via a first joint, a lower link member extended from the foot-worn portion via a second joint, and a third joint which bendably connects the upper link member and the lower link member;
• and
• a drive mechanism for driving the third joint,
• wherein the drive mechanism has a crank arm fixed to the lower link member and a linear-motion actuator which has a linear-motion output shaft, one end thereof being connected to the crank arm, and which is mounted on the upper link member such that the linear-motion actuator is swingable about an axial center of a swing shaft parallel to a joint axis of the third joint, and the drive mechanism is constructed to convert a translational force output from the linear-motion output shaft of the linear-motion actuator into a rotational driving force for the third joint through an intermediary of the crank arm,
• a relationship between a first angle and a flexion degree of the leg link at the third joint is set such that the first angle, which is an angle formed by a first straight line connecting a joint axis and a connecting portion of the linear-motion output shaft relative to the crank arm, and a second straight line which passes the connecting portion and which is oriented in a direction parallel to an axial center of the linear-motion output shaft, changes from a substantially straight angle when the flexion degree of the leg link at the third joint is the flexion degree associated with an upright posture state of the user, toward a substantially right angle as the flexion degree of the leg link at the third joint increases from that associated with the upright posture state as the lower link member bends relative to the upper link member at the third joint,
• the linear-motion actuator has the linear-motion output shaft functioning as a screw shaft with thread grooves formed in an outer peripheral surface thereof, a nut member which retains, in an inner peripheral portion thereof, a plurality of balls engaged with the thread grooves of the linear-motion output shaft and which is concentrically threaded to the linear-motion output shaft through an intermediary of the plurality of balls, an enclosure which rotatably accommodates the nut member therein and which is supported by the upper link member such that the enclosure may swing about the axial center of the swing shaft together with the nut member and the linear-motion output shaft, and a rotational actuator which has a rotational output shaft for imparting a rotational driving force to the nut member and which is installed to the enclosure such that the rotational actuator may swing about the axial center of the swing shaft together with the enclosure, the swing shaft being provided such that the axial center thereof is orthogonal to the axial center of the nut member at inside the nut member, and
• the nut member is rotatably supported by the enclosure through an intermediary of a pair of angular bearings inserted in an outer periphery of the nut member with an interval provided in the direction of the axial center of the nut member, a side wall of the enclosure has an opening in a place within the interval between the pair of angular bearings, and the swing shaft is inserted in a bearing member attached to the enclosure such that the bearing member is accommodated in the opening between the pair of angular bearings.