Dynamic Capture Using a Traplike Soft Gripper With Stiffness Anisotropy

Dynamic capture is a common skill that humans have practiced extensively but is a challenging task for robots in which sensing, planning, and actuation must be tightly coordinated to deal with targets of diverse shapes, sizes, and velocity. In particular, the impact force may cause serious damage to a rigid gripper and even its carrier, e.g., a robotic arm. Existing soft grippers suffer from low speed and force to actively respond to capturing dynamic targets. In this article, we propose a soft gripper capable of efficient capture of dynamic targets, taking inspiration from the biological structures of multitentacled animals or plants. The presented gripper uses a cluster of tentacles to achieve an omnidirectional envelope and high tolerance to dynamic target during the capturing process. In addition, a stiffness anisotropy property is implemented to the tentacle structure to form a “trap” making it easy for the targets to enter yet difficult to escape. We also present an analytical model for the tentacle structure to describe its deformation during the collision with a target. In experiments, we construct a robotic prototype and demonstrate its ability to capture dynamic targets

Design and Modeling of Parallel Two-degree-of-freedom Variable Stiffness Actuator

Abstract In this paper, a new 2-DOF variable stiffness actuator based on a 2-DOF spherical wrist parallel mechanism is proposed. A 2-DOF VSA based on a parallel ball wrist mechanism and a parallel arrangement of leaf spring sets is used. Control its stiffness adjustment, analysis its variable stiffness principle and actuator mechanical structure. The parallel arrangement of the leaf spring groups reduces the mass and volume of the joints, enabling simultaneous adjustment of the stiffness. The analytical formula of the rotational stiffness of the actuator is established according to the geometric nonlinearity of the large deflection of the leaf spring

A tendon-driven actuator with cantilever initiated variable stiffness used for robotic fingers

Variable stiffness actuators (VSAs) have emerged as a key actuation technology known for their bionic performance and task adaptability. However, current VSAs often exhibit relatively large sizes, making them possible for use in robotic arms and legs but less convenient for integrations into robotic hands. This paper introduces a compact design of a tendon-driven variable stiffness actuator (TVSA) based on an adjustable cantilever mechanism, which can be embedded into a robotic finger. This implementation endows the robotic finger with the independent regulation of joint position and stiffness. A concise and computationally efficient stiffness mapping model from the TVSA to the finger joints is then established, providing a theoretical foundation for the stiffness regulation of the tendon-driven fingers. A prototype of a robotic hand equipped with the presented TVSA demonstrates safe interactions with various objects of diverse shapes, weights and stiffness