ASSIST DEVICE

1 . An assist device comprising:

a first body-worn unit that is worn at least on hips of a user;

second body-worn units that are worn on thighs of right and left legs of the user;

an actuator that includes driving units mounted on the first body-worn unit so as to be located on right and left sides of the hips of the user, the actuator being configured to generate assist torque that assists the user in moving the hips of the user relatively to the thighs of the user and moving the thighs of the user relatively to the hips of the user;

a controller configured to obtain an assist parameter that determines the assist torque to be generated, and perform control to operate the actuator at an output based on the assist parameter; and

a tilt angle detection part configured to obtain tilt angle information on a tilt angle of an upper body of the user,

wherein the actuator includes:

arms each of which has a leading end mounted on a corresponding one of the second body-worn units and a base end mounted on a corresponding one of the driving units, each of the arms being configured to swing back and forth around the base end; and

swing angle detection parts configured to obtain swing angle information on swing angles of the arms that represent angles formed by the upper body and the thighs of the user, and

wherein the controller is configured to obtain the assist parameter based on the swing angle information and the tilt angle information.

2 . The assist device according to claim 1 , wherein the controller is configured to obtain a provisional assist parameter based on the swing angle information, obtain a correction gain based on the tilt angle information, and obtain the assist parameter using the provisional assist parameter and the correction gain.

3 . The assist device according to claim 2 , wherein a value of the correction gain obtained by the controller is a value that makes the assist parameter larger when the tilt angle is large than when the tilt angle is small.

4 . The assist device according to claim 2 , wherein the controller is configured to, when the tilt angle is small, obtain the correction gain for causing the assist parameter to approach zero, based on the tilt angle information on the tilt angle.

5 . The assist device according to claim 2 , wherein the controller includes:

a counting part configured to obtain a lifting duration time indicating an elapsed time since the user starts to lift a load;

a storage part configured to store first correspondence information that indicates a relation between the tilt angle information and the correction gain and second correspondence information that indicates a relation between the lifting duration time and the provisional assist parameter;

a first processing part configured to obtain the correction gain based on the obtained tilt angle information and the first correspondence information; and

a second processing part configured to obtain the provisional assist parameter based on the obtained lifting duration time and the second correspondence information.

6 . The assist device according to claim 1 , wherein the controller is configured to obtain, as the assist parameter, a sum of a value that is obtained by applying a rigidity term gain to the obtained tilt angle information and a value that is obtained by applying a viscosity term gain to the obtained swing angle information.

7 . The assist device according to claim 2 , wherein:

a process in which the controller obtains the assist parameter using the correction gain is a process for lifting;

a process in which the controller obtains, as the assist parameter, a sum of a value that is obtained by applying a rigidity term gain to the obtained tilt angle information and a value that is obtained by applying a viscosity term gain to the obtained swing angle information is a process for a bowing action; and

the controller is configured to select and perform one of the process for lifting and the process for the bowing action.

8 . The assist device according to claim 1 , wherein:

the tilt angle detection part is a sensor configured to produce an output that varies according to a posture of the upper body of the user; and

the swing angle detection parts are detectors configured to detect rotation angles of rotating members provided in the actuator to swing the arms.