Wearable assistive robots have been studied widely to reduce the physical burden of tasks such as lifting and caregiving. Most existing systems, however, control only the joint torque. Even though wearable robots transmit actuator forces through direct contact with the body, these systems do not focus on managing the contact force generated at the human–robot interface. Our previous study developed wearable assistive robots capable of measuring and controlling the contact-force distribution. We verified the feasibility of evaluating safety and control performance using a single-joint arm-mounted robot and a multi-joint whole-body robot. However, the influence of force distribution on assist performance was not been sufficiently examined for multi-joint robots under assist conditions. The current study aimed to experimentally verify the effectiveness of using contact-force distribution information in a torso-mounted multi-joint robot (through experiments involving seven participants). The results showed that whereas the actual motor torque tracked the commanded torque under conventional torque-based control, the contact-force distribution experienced by the wearer varied across participants. This finding indicates that for wearable robots with complex joint structures, assessments of wearing states and assist effectiveness require an evaluation of the contact-force distribution in addition to the torque.

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