For assembly tasks, it is essential to fix target parts firmly and accurately estimate their poses. Several rigid jigs for individual parts are frequently used in assembly factories to achieve a precise and time-efficient product assembly. However, providing customized jigs is time-consuming. In this study, to address the lack of versatility in the shapes for which jigs can be used, we developed a flexible jig with a soft membrane including transparent beads and oil with a tuned refractive index. The bead-based jamming transition was accomplished by discharging only the oil, enabling the part to be firmly fixed. Because the two cameras under the jig can capture membrane shape changes, we proposed a sensing method to estimate the orientation of the part based on the behaviors of markers created on the jig's inner surface. Through estimation experiments, the proposed system can estimate the orientation of a cylindrical object with a diameter larger than 50 mm and an RMSE of less than 3°.

To design a general-purpose assembly robot system that can handle objects of various shapes, we propose a soft jig that fits to the shapes of assembly parts. The functionality of the soft jig is based on a jamming gripper developed in the field of soft robotics. The soft jig has a bag covered with a malleable silicone membrane, which has high friction, elongation, and contraction rates for keeping parts fixed. The bag is filled with glass beads to achieve a jamming transition. We propose a method to configure parts-fixing on the soft jig based on contact relations, reachable directions, and the center of gravity of the parts that are fixed on the jig. The usability of the soft jig was evaluated in terms of the fixing performance and versatility for various shapes and postures of parts.

For a robotic gripper to perform as well as the human hand, the performance of the tactile sensing and grasping of the gripper must be improved. In this study, a parallel gripper with a universal fingertip device that combines both object holding using jamming transition and optical sensing is proposed. By using a transparent material along with the jamming transition, both a tactile sense is achieved via optical sensing and the holding stability is improved by tightly restraining the object. Because the hardness of the contact region of the membrane can be adjusted, the gripper can grasp heavy objects as well as light objects. In this paper, the structure of the developed gripper and its grasping characteristics are described, and the experimental results from grasping and sensing are presented. It is experimentally shown that the proposed gripper is capable of both grasping fragile objects (such as an egg and tofu) by using tactile sensing and grasping dumbbells (with weights between 1-3 kg) by using jamming transition. Additionally, grasping a plastic cup, the proposed gripper demonstrated the potential of combining tactile sensing and more-constrained grasping.

The universal gripper has attracted attention due to its simple structure and advanced grasping ability for irregularly shaped objects. In this research, we propose a novel design for a granular-jamming-based gripper which uses a transparent filling and a semi-transparent membrane to allow optical sensing to detect both deformation of the membrane and the object being grasped. By adjusting the refractive index of an oil mixture to the refractive index of the granular bodies, we produced a fully transparent filling that allows the use of a camera inside the universal gripper. In this paper, we present the materials and development of our prototype, and describe the experimental confirmation of the prototype's performance. We showed that our prototype was able to grasp cylindrical and rectangular objects between 10 to 70 mm length while also tracking the deformation of the gripper.