Development of Three-Fingered End-Effector Using Pneumatic Soft Actuators

In this paper, we propose a three-fingered end-effector driven by pneumatic soft actuators. The proposed end-effector has three thin sticks as the finger, and grips a food with three points to achieve force-closure. Since the sticks have a small diameter, the proposed end-effector will be able to achieve the safely picking from a food basket without breaking the foods. In addition, by using the soft actuator, it is possible to control the gripping force softly. We developed a curved extension type soft actuator for the rotation motion of the proposed end-effector. In addition, we propose a disturbance observer that estimates an external force applied to the stick tip from the food to realize the human-like soft touch. To evaluate the performance of the proposed end-effector, we carried out the three type experiments: an angle control test, an external force estimation, and a food gripping test. As a result, the measured angles sufficiently tracked the given target trajectories, and the proposed external force estimation was effective with its accuracy about 0.1 N. Finally, we confirmed that the proposed end-effector succeeded to grip four different type foods stably.