Effect of Presenting Stiffness of Robot Hand to Human on Human-Robot Handovers

In this study, we examine the object handover task as a key example of collaborative work between a human and a robot. To achieve a seamless handover between the two agents, mutual communication is essential for understanding each other's intentions. However, previous research has not addressed the critical moments during handovers when a robot takes an object from a human's grasp or when a robot hands an object to the human. It is important to note that performance during these phases is critical to the success or failure of the task because slight changes in the kinematics of the relationship between hands or fingers and the object can lead to significant changes in the grasping status: the human might forcibly pull the object out while the robot is gripping it or might drop the object. Therefore, this study aims to achieve a smooth handover between a human and a robot by focusing on the moment of object transfer. To accomplish this, the paper proposes presenting the stiffness of the robot's hand to the human. We conducted experiments to investigate the effect of this method on human-robot interaction. The experimental results indicate that this presentation method allows the worker to perceive the robot's stiffness, which is difficult to visually identify, thereby reducing workload and enabling the worker to respond seamlessly to changes in the robot's stiffness.