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1. A Novel Variable Stiffness Soft Robotic Gripper

   https://doi.org/10.1109/CASE49439.2021.9551616  

   Arachchige, Dimuthu D.K.; Chen, Yue; Walker, Ian D.; Godage, Isuru S. (August 2021, IEEE International Conference on Automation Science and Engineering (CASE))

   Compliant grasping is crucial for secure handling objects not only vary in shapes but also in mechanical properties. We propose a novel soft robotic gripper with decoupled stiffness and shape control capability for performing adaptive grasping with minimum system complexity. The proposed soft fingers conform to object shapes facilitating the handling of objects of different types, shapes, and sizes. Each soft gripper finger has a length constraining mechanism (an articulable rigid backbone) and is powered by pneumatic muscle actuators. We derive the kinematic model of the gripper and use an empirical approach to simultaneously map input pressures to stiffness control and bending deformation of fingers. We use these mappings to demonstrate decoupled stiffness and shape (bending) control of various grasping configurations. We conduct tests to quantify the grip quality when holding objects as the gripper changes orientation, the ability to maintain the grip as the gripper is subjected to translational and rotational movements, and the external force perturbations required to release the object from the gripper under various stiffness and shape (bending) settings. The results validate the proposed gripper's performance and show how the decoupled stiffness and shape control can improve the grasping quality in soft robotic grippers. 

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2. A Novel Variable Stiffness Soft Robotic Gripper

   Arachchige, D.K.; Chen, Y.; Walker, I.D.; Godage, I.S. (August 2021, IEEE International Conference on Automation Science and Engineering CASE)

   null (Ed.)

   Compliant grasping is crucial for secure handling objects not only vary in shapes but also in mechanical properties. We propose a novel soft robotic gripper with decoupled stiffness and shape control capability for performing adaptive grasping with minimum system complexity. The proposed soft fingers conform to object shapes facilitating the handling of objects of different types, shapes, and sizes. Each soft gripper finger has a length constraining mechanism (an articulable rigid backbone) and is powered by pneumatic muscle actuators. We derive the kinematic model of the gripper and use an empirical approach to simultaneously map input pressures to stiffness control and bending deformation of fingers. We use these mappings to demonstrate decoupled stiffness and shape (bending) control of various grasping configurations. We conduct tests to quantify the grip quality when holding objects as the gripper changes orientation, the ability to maintain the grip as the gripper is subjected to translational and rotational movements, and the external force perturbations required to release the object from the gripper under various stiffness and shape (bending) settings. The results validate the proposed gripper’s performance and show how the decoupled stiffness and shape control can improve the grasping quality in soft robotic grippers. 

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3. A Novel Variable Stiffness Compliant Robotic Link Based on Discrete Variable Stiffness Units for Safe Human-Robot Interaction

   https://doi.org/10.1115/DETC2022-89825  

   Fu, Jiaming; Lin, Han; Xu, Wei; Gan, Dongming (August 2022, ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference)

   Abstract Variable stiffness manipulators balance the trade-off between manipulation performance needing high stiffness and safe human-robot interaction desiring low stiffness. Variable stiffness compliant links provide a solution to enable this flexible manipulation function in human-robot co-working scenarios. In this paper, we propose a novel variable stiffness link based on discrete variable stiffness units (DSUs). A DSU is a parallel guided beam that can adjust stiffness discretely by changing the cross-sectional area properties of the hollow beam segments. The variable stiffness link (named Tri-DSU) consists of three tandem DSUs to achieve eight stiffness modes and a maximum stiffness change ratio of 31. To optimize the design, stiffness analysis of the DSU and Tri-DSU under various configurations and forces was performed by a derived theoretical model compared with finite element analysis (FEA). The analytical stiffness model is derived using the approach of serially connected beams and superposition combinations. It works not only for thin-walled flexure beams but also for general thick beam models. 3-D printed prototypes were built to verify the feature and performance of the Tri-DSU in comparison with the FEA and analytical model results. It’s demonstrated that our analytical model can accurately predict the stiffnesses of the DSU and Tri-DSU within a certain range of parameters. The developed variable stiffness link method and analytical model are extendable to multiple DSUs with different sizes and parameter configurations to achieve modularization and customization. The advantages of the stiffness change mechanism are rapid actuation, simple structure, and compact layout. These methods and results provide a new conceptual and theoretical basis for the development of new reconfigurable cobot manipulators, variable stiffness structures, and compliant mechanisms. 

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4. A Novel Variable Stiffness Compliant Robotic Gripper Based on Layer Jamming

   https://doi.org/10.1115/1.4047156  

   Gao, Yuan; Huang, Xiguang; Mann, Ishan Singh; Su, Hai-Jun (October 2020, Journal of Mechanisms and Robotics)

   Abstract In this paper, we present a novel compliant robotic gripper with three variable stiffness fingers. While the shape morphing of the fingers is cable-driven, the stiffness variation is enabled by layer jamming. The inherent flexibility makes compliant gripper suitable for tasks such as grasping soft and irregular objects. However, their relatively low load capacity due to intrinsic compliance limits their applications. Variable stiffness robotic grippers have the potential to address this challenge as their stiffness can be tuned on demand of tasks. In our design, the compliant backbone of finger is made of 3D-printed PLA materials sandwiched between thin film materials. The workflow of the robotic gripper follows two basic steps. First, the compliant skeleton is driven by a servo motor via a tension cable and bend to a desired shape. Second, upon application of a negative pressure, the finger is stiffened up because friction between contact surfaces of layers that prevents their relative movement increases. As a result, their load capacity will be increased proportionally. Tests for stiffness of individual finger and load capacity of the robotic gripper are conducted to validate capability of the design. The results showed a 180-fold increase in stiffness of individual finger and a 30-fold increase in gripper’s load capacity. 

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5. A Low-Cost Compliant Gripper Using Cooperative Mini-Delta Robots for Dexterous Manipulation

   Mannam, P.; Rudich, A.; Zhang, Kevin L.; Veloso, M.; Kroemer, O.; Temel, Z. (July 2021, Robotics science and systems)

   null (Ed.)

   Traditional parallel-jaw grippers are insufficient for delicate object manipulation due to their stiffness and lack of dexterity. Other dexterous robotic hands often have bulky fingers, rely on complex time-varying cable drives, or are prohibitively expensive. In this paper, we introduce a novel low-cost compliant gripper with two centimeter-scaled 3-DOF delta robots using off-the-shelf linear actuators and 3D-printed soft materials. To model the kinematics of delta robots with soft compliant links, which diverge from typical rigid links, we train neural networks using a perception system. Furthermore, we analyze the delta robot’s force profile by varying the starting position in its workspace and measuring the resulting force from a push action. Finally, we demonstrate the compliance and dexterity of our gripper through six dexterous manipulation tasks involving small and delicate objects. Thus, we present the groundwork for creating modular multi-fingered hands that can execute precise and low-inertia manipulations. 

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