Assist device

1. An assist device comprising:

a first worn component worn on at least one of a shoulder and a chest of a user;

a second worn component worn on one of a hip and a pair of right and left legs of the user;

a band-shaped belt member provided along a back side of the user that provides a variable tension force between the first worn component and the second worn component;

an actuator provided on one of the first worn component and the second worn component, the actuator being configured to wind up part of the belt member and configured to let out part of the band-shaped belt member, the actuator being configured to apply assisting force to the user by applying a force to the band-shaped belt member in a direction to wind up the belt member;

a position detection unit configured to obtain a position parameter indicating a position of the user; and

a controller configured to obtain a required output in the direction to wind up the band-shaped belt member from the actuator based on the position parameter and configured to control operation of the actuator.

2. The assist device according to claim 1 , wherein the controller is configured to cause the actuator to operate at a predetermined output in a standby state where the assisting force is not applied to the user, the predetermined output is an output in the direction to wind up the belt member and weaker than an output when the assisting force is applied to the user.

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

the position detection unit is configured to obtain a rate of change in position when the user changes from an upright position to a forward-leaning position; and

the controller is configured to obtain the required output according to the rate of change.

4. The assist device according to claim 3 , wherein the controller is configured to, when the required output obtained according to the rate of change is lower than a lower limit set value, obtain the lower limit set value or a value exceeding the lower limit set value as the required output of the actuator.

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

the position detection unit is configured to obtain a rate of change in position when the user changes from a forward-leaning position to an upright position; and

the controller is configured to obtain the required output according to the rate of change.

6. The assist device according to claim 5 , wherein the controller is configured to, when the required output obtained according to the rate of change is higher than an upper limit set value, obtain the upper limit set value or a value lower than the upper limit set value as the required output of the actuator.

7. The assist device according to claim 1 , wherein the position detection unit includes a detector configured to detect an operation amount of the actuator when the belt member is wound up or let out as a result of a change in position of the user, and a position estimation unit configured to obtain the position parameter based on correspondence information representing a relation between the operation amount and the position parameter.

8. The assist device according to claim 1 , wherein the position detection unit includes a sensor provided on one of the first worn component and the second worn component and configured to output a signal corresponding to a position of the user, and a position estimation unit configured to obtain the position parameter based on an output of the sensor.