Skill-Assist Arm Using Passive Joints to Aid Spatial Movement of Human Limbs

Robots that assist with limb movement in rehabilitation or training have been studied to effectively recover the motor function of hemiplegic limbs or to effectively train manual tasks. However, because many of these robots use force control, they are unsuitable for precise positioning. Therefore, this study proposes a translational three-degrees-of-freedom (3-DOF) robot arm using position control with passive joints and its control method to assist in the precise positioning of a human limb. This assistive robot arm can set a trajectory or surface in three-dimensional (3-D) space as a target. An operator can input a movement to the arm by rotating the passive joints. After inputting the movement, the output point is positioned on the target by position control using actuated joints. We refer to an arm using such a method as a skill-assist arm. Experiments were conducted using a prototype of the fabricated 3-DOF arm. Straight lines, circles, and planes oriented in various directions were set as targets. The experimental results showed that the output point was accurately positioned along the target trajectories or planes in 3-D space according to the operator's input motion. As a result, the feasibility of the proposed arm and its method was clarified.