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1. 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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2. 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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3. 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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4. Individual differences impacting skin deformation and tactile discrimination with compliant elastic surfaces

   https://doi.org/10.1109/WHC49131.2021.9517222  

   Li, Bingxu ; Gerling, Gregory J. ( July 2021 , IEEE World Haptics Conference)

   Individual differences in tactile acuity are observed within and between age cohorts. Such differences in acuity may be attributed to various sources, including aspects of nervous system, skin mechanics, finger size, cognitive and behavioral factors, etc. This work considers individual differences, within a younger cohort of participants, in discriminating compliant surfaces. These participants exhibit a range of finger size and stiffness. Interestingly, both their finger size and stiffness well predict their discriminative performance, where softer/smaller fingers outperform stiffer/larger fingers. Stereo imaging captured biomechanical cues in the skin’s deformation, including contact area and penetration depth, and their change rates. In those individuals with stiffer/larger fingers, who perceptually performed worse, we observed less distinguishable contact areas and eccentricities, compared to softer/smaller fingers. These particular cues well predicted individual differences observed in perceptual discrimination. In comparison, with two other cues, curvature and penetration depth, the imaging readily distinguished the compliant surfaces irrespective of finger stiffness/size, not aligned with discrimination. In conclusion, in passive touch, we find that individuals with softer/smaller fingers were better at discriminating compliances, and that certain skin deformation cues predict individual differences in perception. 

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5. A Novel Discrete Variable Stiffness Gripper Based on the Fin Ray Effect

   https://doi.org/10.1007/978-3-031-13835-5_71  

   Fu, J. ; Lin, H. ; Prathyush, I.V.S. ; Huang, X. ; Zheng, L. ; Gan, D. ( August 2022 , Intelligent Robotics and Applications)

   Liu, H. ; Yin, Z. ; Liu, L. ; Jiang, L. ; Gu, G. ; Wu, X. ; Ren, W. (Ed.)

   Variable stiffness grippers can adapt to objects with different shapes and gripping forces. This paper presents a novel variable stiffness gripper (VSG) based on the Fin Ray effect that can adjust stiffness discretely. The main structure of the gripper includes the compliant frame, rotatable ribs, and the position limit components attached to the compliant frame. The stiffness of the gripper can be adjusted by rotating the specific ribs in the frame. There are four configurations for the gripper that were developed in this research: a) all ribs OFF (Flex) mode; b) upper ribs ON and lower ribs OFF (Hold) mode; c) upper ribs OFF and lower ribs ON (Pinch) mode; d) all ribs ON (Clamp) mode. Different configurations can provide various stiffness for the gripper’s finger to adapt the objects with different shapes and weights. To optimize the design, the stiffness analysis under various configurations and force conditions was implemented by finite element analysis (FEA). The 3-D printed prototypes were constructed to verify the feature and performance of the design concept of the VSG compared with the FEA results. The design of the VSG provides a novel idea for industrial robots and collaborative robots on adaptive grasping. 

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