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1. Contact-less Manipulation of Millimeter-scale Objects via Ultrasonic Levitation

   https://doi.org/10.1109/BioRob49111.2020.9224384  

   Nakahara, Jared ; Yang, Boling ; Smith, Joshua R. ( November 2020 , 2020 8th IEEE RAS/EMBS International Conference for Biomedical Robotics and Biomechatronics (BioRob))

   Although general purpose robotic manipulators are becoming more capable at manipulating various objects, their ability to manipulate millimeter-scale objects are usually limited. On the other hand, ultrasonic levitation devices have been shown to levitate a large range of small objects, from polystyrene balls to living organisms. By controlling the acoustic force fields, ultrasonic levitation devices can compensate for robot manipulator positioning uncertainty and control the grasping force exerted on the target object. The material agnostic nature of acoustic levitation devices and their ability to dexterously manipulate millimeter-scale objects make them appealing as a grasping mode for general purpose robots. In this work, we present an ultrasonic, contact-less manipulation device that can be attached to or picked up by any general purpose robotic arm, enabling millimeter-scale manipulation with little to no modification to the robot itself. This device is capable of performing the very first phase-controlled picking action on acoustically reflective surfaces. With the manipulator placed around the target object, the manipulator can grasp objects smaller in size than the robot's positioning uncertainty, trap the object to resist air currents during robot movement, and dexterously hold a small and fragile object, like a flower bud. Due to the contact-less nature ofmore »the ultrasound-based gripper, a camera positioned to look into the cylinder can inspect the object without occlusion, facilitating accurate visual feature extraction.« less
2. A Mechanically Intelligent and Passive Gripper for Aerial Perching and Grasping

   https://doi.org/10.1109/TMECH.2022.3175649  

   Hsiao, HaoTse ; Sun, Jiefeng ; Zhang, Haijie ; Zhao, Jianguo ( January 2022 , IEEE/ASME Transactions on Mechatronics)

   Perching onto an object (e.g., tree branches) has recently been leveraged for addressing the limited flight time for flying robots. Successful perching needs a mechanical mechanism to damp out the impact and robustly grasp the object. Generally, such a mechanism requires actuation for grasping. In this article, we present a fully passive mechanism without using any actuator: a mechanically intelligent and passive (MIP) gripper that can be used for either aerial perching or grasping. Initially open, the gripper can be closed by the impact force during perching. After closure, if a sufficient mass (e.g., the robot’s mass) is applied, the gripper can switch to a holding state and maintain that state to hold the mass. Once the mass is removed, the gripper can automatically open. We establish static models for the gripper to predict the required forces for successful state transitions. Based on the models, we develop design guidelines for the gripper so that it can be used for different flying robots with different weights. Experiments are conducted to validate the models. Attaching the gripper onto a quadcopter, we demonstrated aerial perching onto rods and aerial grasping rod-like objects. Because the MIP gripper is lightweight (can reach a mass ratiomore »of 0.75% between the gripper and the grasped object for static grasping), we expect it would be well suited for aerial perching or grasping due to the limited payload capability for flying robots.« less
3. Modeling of Soft Robotic Grippers Integrated With Fluidic Prestressed Composite Actuators

   https://doi.org/10.1115/1.4052699  

   Zhou, Yitong ; Headings, Leon M. ; Dapino, Marcelo J. ( June 2022 , Journal of Mechanisms and Robotics)

   Abstract Soft robotic grippers can gently grasp and maneuver objects. However, they are difficult to model and control due to their highly deformable fingers and complex integration with robotic systems. This paper investigates the design requirements as well as the grasping capabilities and performance of a soft gripper system based on fluidic prestressed composite (FPC) fingers. An analytical model is constructed as follows: each finger is modeled using the chained composite model (CCM); strain energy and work done by pressure and loads are computed using polynomials with unknown coefficients; net energy is minimized using the Rayleigh–Ritz method to calculate the deflected equilibrium shapes of the finger as a function of pressure and loads; and coordinate transformation and gripper geometries are combined to analyze the grasping performance. The effects of prestrain, integration angle, and finger overlap on the grasping performance are examined through a parametric study. We also analyze gripping performance for cuboidal and spherical objects and show how the grasping force can be controlled by varying fluidic pressure. The quasi-static responses of fabricated actuators are measured under pressures and loads. It is shown that the actuators’ modeled responses agree with the experimental results. This work provides a framework for themore »theoretical analysis of soft robotic grippers and the methods presented can be extended to model grippers with different types of actuation.« less
4. An untethered isoperimetric soft robot

   https://doi.org/10.1126/scirobotics.aaz0492  

   Usevitch, Nathan S. ; Hammond, Zachary M. ; Schwager, Mac ; Okamura, Allison M. ; Hawkes, Elliot W. ; Follmer, Sean ( March 2020 , Science Robotics)

   For robots to be useful for real-world applications, they must be safe around humans, be adaptable to their environment, and operate in an untethered manner. Soft robots could potentially meet these requirements; however, existing soft robotic architectures are limited by their ability to scale to human sizes and operate at these scales without a tether to transmit power or pressurized air from an external source. Here, we report an untethered, inflated robotic truss, composed of thin-walled inflatable tubes, capable of shape change by continuously relocating its joints, while its total edge length remains constant. Specifically, a set of identical roller modules each pinch the tube to create an effective joint that separates two edges, and modules can be connected to form complex structures. Driving a roller module along a tube changes the overall shape, lengthening one edge and shortening another, while the total edge length and hence fluid volume remain constant. This isoperimetric behavior allows the robot to operate without compressing air or requiring a tether. Our concept brings together advantages from three distinct types of robots—soft, collective, and truss-based—while overcoming certain limitations of each. Our robots are robust and safe, like soft robots, but not limited by a tether;more »are modular, like collective robots, but not limited by complex subunits; and are shape-changing, like truss robots, but not limited by rigid linear actuators. We demonstrate two-dimensional (2D) robots capable of shape change and a human-scale 3D robot capable of punctuated rolling locomotion and manipulation, all constructed with the same modular rollers and operating without a tether.« less
5. Performance Is Not Everything: Audio Feedback Preferred Over Visual Feedback for Grasping Task in Virtual Reality

   https://doi.org/10.1145/3424636.3426897  

   Canales, Ryan ; Jörg, Sophie ( October 2020 , Motion, Interaction and Games)

   In this work, we investigate the influence that audio and visual feedback have on a manipulation task in virtual reality (VR). Without the tactile feedback of a controller, grasping virtual objects using one’s hands can result in slower interactions because it may be unclear to the user that a grasp has occurred. Providing alternative feedback, such as visual or audio cues, may lead to faster and more precise interactions, but might also affect user preference and perceived ownership of the virtual hands. In this study, we test four feedback conditions for virtual grasping. Three of the conditions provide feedback for when a grasp or release occurs, either visual, audio, or both, and one provides no feedback for these occurrences. We analyze the effect each feedback condition has on interaction performance, measure their effect on the perceived ownership of the virtual hands, and gauge user preference. In an experiment, users perform a pick-and-place task with each feedback condition. We found that audio feedback for grasping is preferred over visual feedback even though it seems to decrease grasping performance, and found that there were little to no differences in ownership between our conditions.