Retrieving a file binder from a bookshelf using pseudo-curved trajectory generation for a foldable robotic hand.

Human-assistive robots need to perform trajectory making for and control of a robotic hand along the many rotating mechanisms in our living spaces. If such trajectory control can be performed without high-cost sensors, certainly a significant cost reduction in building the robot will be achieved. This paper describes a method of retrieving a file binder by generating a pseudo-curved trajectory for tilting it using a simple system. A simple claw mechanism with a switch sensor to grasp an object was designed and 3D-printed, and it was attached to a 6-DOF foldable robotic hand developed by the authors. A method for generating a pseudo-curved trajectory using the switch sensor was developed, and the robotic hand was successfully moved along this trajectory to tilt and grasp a file binder to retrieve it from a bookshelf. Experiments to clarify the success rate were also conducted, and it was found that the results depend on the rotational speed of manipulator links and the vibration of the claw mechanism link. A rubber sponge was added to give flexibility to the claw mechanism, which significantly improved the success rate. Furthermore, a control system to recover from tilting failure was constructed, and its effectiveness was validated by experiments.

Transformation of foldable robotic hand to scissor-like shape for pinching based on human hand movement.

Increasing the number of degrees of freedom for multi-finger robotic hands is necessary to achieve high performance. However, this increases structural complexity and the obtained improvement may be small. Humans change the shape of their hands by extending or bending the fingers to apply force to an object through contact with a wide surface or two or more fingers. In some cases, continuous finger movements are not necessary or some fingers do not make contact with the object. A robotic hand with a small number of degrees of freedom could effectively use its fingers to perform many tasks by properly arranging the fingers, increasing the movable range of joints, and utilizing the back and sides of the fingers. This paper proposes a hand system and conducts a theoretical analysis of the transformation of the hand shape into a scissor-like motion to handle a cylindrical object. It is found that the scissor-like motion is unsuitable for cylindrical objects that exceed a certain size. Experiments show the effectiveness of the proposed hand system. The correlation between the contact position of a finger with an object and the success ratio of pinching is demonstrated. Furthermore, a control system that can switch from pinching to grasping when the robot judges that pinching is difficult is developed and experimentally validated.