Assistance for positioning of human by using the passive joint of robot arm

The present study proposes a robot arm that can support precise positioning in operation by a human. The robot arm has passive and actuated joints. The passive joint is not mechanically constrained and can move passively with the motion of the output point of the robot arm. Therefore, a human can move the output point of the robot arm by his will. When a human tries to move the output point along an object path, the displacement of the passive joint is determined passively. Then, if the actuated joint is controlled so that the output point may be on the object path, the human can achieve precise positioning. Namely, using the proposed robot arm, the human can adjust the velocity, acceleration, applied force and so on by his will, while the position is preciously compensated by the actuated joint. This paper describes a mechanical form of such robot arm for drawing of planar figures and shows that the robot arm has specific singularity condition. In order to avoid the singularity condition, the proposed robot arm interchanges the actuated joint and the passive one situationally. The study fabricated the two degrees of freedom robot arm for positioning assistance and described its control method. Furthermore, its availability is confirmed by drawing some figures.