Gas-Lubricated Vibration-Based Adhesion for Robotics
Controllable adhesion, the ability to selectively attach or detach from a surface, allows animals like geckos to achieve amazing feats like walking up walls and along ceilings. Roboticists have investigated how to endow robotic systems with similar capabilities for tasks like inspection, exploration, and cleaning. However, many previous approaches to achieve both movement and adhesion along a surface require complex robot designs with multiple adhesive pads. In this work, we studied a novel way to achieve controllable adhesion with a simple robot that can stick to a variety of surfaces. We found that when a vibrating flexible disk is placed in close proximity to a smooth surface, it sticks to the surface, but also can slide along the surface while continuously adhering. This is possible as the vibrations induce a net negative pressure in a thin film of air between the disk and the surface. We quantified how the pressure in the thin air film varied from the center of the disk to the outer edge and found that most of the load-bearing capability (i.e. strongest vacuum pressure) was localized at the center of the disk. This means that while larger disks provided larger adhesive forces, smaller disks provided more force per area. We designed and built a mobile robot capable of scaling vertical walls, driving along a curved loop, and supporting a payload approximately x10 the weight of the total robotic system.
Weston-Dawkes W. P., Adibnazari I., Hu Y.-W., Everman M., Gravish N., Tolley M. T. (2021), "Gas-lubricated vibration-based adhesion for robotics", Advanced Intelligent Systems.
The compliance and conformability of soft robots provide inherent advantages when working around delicate objects or in unstructured environments. However, rapid locomotion in soft robotics is challenging due to the slow propagation of motion in compliant structures, particularly underwater. Cephalopods overcome this challenge using jet propulsion and the added mass effect to achieve rapid, efficient propulsion underwater without a skeleton. Taking inspiration from cephalopods, here we present an underwater robot with a compliant body that can achieve repeatable jet propulsion by changing its internal volume and cross-sectional area to take advantage of jet propulsion as well as the added mass effect. The robot achieves a maximum average thrust of 0.19 N and maximum average and peak swimming speeds of 18.4 cm s−1 (0.54 body lengths/s) and 32.1 cm s−1 (0.94 BL/s), respectively. We also demonstrate the use of an onboard camera as a sensor for ocean discovery and environmental monitoring applications.
Christianson C., Cui Y., Ishida M., Bi X., Zhu Q., Pawlak G., Tolley M. T., (2020), "Cephalopod-Inspired Robot Capable of Cyclic Jet Propulsion Through Shape Change", Bioinspiration and Biomimetics, 16, 016014.
Electronics-Free Pneumatic Circuits for Controlling Soft-Legged Robots
Pneumatically actuated soft robots have recently shown promise for their ability to adapt to their environment. Previously, these robots have been controlled with electromechanical components such as valves and pumps that are typically bulky and expensive. In this work, we developed a soft legged walking robot that is controlled and powered by pressurized air. We designed soft valves and pneumatic circuits to control the walking direction of the robot. We used a soft ring oscillator circuit to generate the rhythmic oscillatory movement similar to central pattern generator circuits observed in nature. The robot’s walking pattern was inspired by biological quadrupeds like the African side neck turtle. We demonstrated a control circuit that allowed the robot to select between gaits for omnidirectional locomotion. We also equipped the robot with simple sensors to change its gait in response to interactions with the environment. This work represents a step towards fully autonomous, electronics-free walking robots. Applications include low-cost robotics for entertainment, such as toys, and robots that can operate in environments where electronics cannot function, such as MRI machines or mine shafts.
Drotman D., Jadhav S., Sharp D., Chan C., and Tolley M. T., (2021) "Electronics-Free Pneumatic Circuits For Controlling Soft-Legged Robots", Science Robotics, vol 6, no. 51, 2021, p. eaay2627.
Rajappan, A., Jumet B., and Preston D. J., "Pneumatic Soft Robots Take A Step Toward Autonomy". Science Robotics, vol 6, no. 51, 2021, p. eabg6994.
Variable Stiffness Devices using Fiber Jamming for Application in Soft Robotics and Wearable Haptics
Variable stiffness actuation has applications in a wide range of fields, including wearable haptics, soft robots, and minimally invasive surgical devices. There have been numerous design approaches to control and tune stiffness and rigidity; however, most have relatively low specific load-carrying capacities that restrict their use in small or slender devices. In this research, we present an approach to the design of slender, high flexural stiffness modules based on the principle of fiber jamming. The proposed fiber jamming modules (FJMs) consist of axially packed fibers in an airtight envelope that transition from a flexible to a rigid beam when a vacuum is created inside the envelope. This FJM can provide the flexural stiffness of up to eight times that of a particle jamming module in the rigid state. Unlike layer jamming modules, the design of FJMs further allows them to control stiffness while bending in space. We present an analytical model to guide the parameter choices for the design of fiber jamming devices. Finally, we demonstrate applications of FJMs, including as a versatile tool, as part of kinesthetic force feedback haptic glove, and as a programmable structure.
Jadhav, S., Majit, M. R. A., Shih, B., Schulze, J. P., & Tolley, M. T. (2021). "Variable Stiffness Devices Using Fiber Jamming for Application in Soft Robotics and Wearable Haptics". Soft Robotics 2021. (https://doi.org/10.1089/soro.2019.0203)
Robust capture of unknown objects with a highly under-actuated gripper
Capturing large objects of unknown shape and orientation remains a challenge for most robotic grippers. This problem is especially important for potential satellite servicing missions in space where targets can be large, delicate, and in uncontrolled orbits. Highly under-actuated grippers that can conform to large arbitrarily-shaped objects show promise for this application. However, prior work shows two primary limitations to these highly under-actuated grippers: the grip force of each link tends to decrease as the number of links increases, and the stability of an under-actuated linkage depends on the grasp configuration. In this project we developed a highly under-actuated gripper that addresses these issues. Our approach uses a gecko-inspired adhesive to provide an adhesion-controlled friction that helps stabilize the gripper and improves grasp performance without the need of large normal forces. The under-actuated linkages conform around arbitrary shapes, maintaining performance across disparate target geometries. With these high-friction interfaces, we show highly under-actuated linkages successfully grasp in many configurations without strict stability. The gripper is capable of holding over 30 N and consists of two tendon driven linkages that are each 65 cm long.
Glick P. E., Van Crey N., Tolley M. T., Ruffatto D. (2020), "Robust capture of unknown objects with a highly under-actuated gripper", IEEE International Conference on Robotics and Automation, pp. 3996-4002.
Reversible actuation for self-folding modular machines using liquid crystal elastomer
Robot and mechanism designs inspired by the art of Origami have the potential to generate compact, deployable, lightweight morphing structures, as seen in nature, for potential applications in search-and-rescue, aerospace systems, and medical devices. However, it is challenging to obtain actuation that is easily patternable, reversible, and made with a scalable manufacturing process for origami-inspired self-folding machines. In this work, we describe an approach to design reversible self-folding machines using liquid crystal elastomer (LCE), that contracts when heated, as an artificial muscle. We use a mechanism known as a Sarrus linkage as the basis for a module to enable folding in two directions with a single actuation muscle. We demonstrate this approach with origami-inspired patterns such as a crane and a lily flower. These modules are capable of lifting and holding 13 times and 38 times their weight. Furthermore, we demonstrate that we can achieve distributed actuation of a crawling robot composed of the Sarrus modules with a single layer of LCE. We show that traveling waving gaits generate worm and caterpillar inspired locomotion, and how to use specialized adhesive pads to improve this locomotion.
Minori, A. F., He, Q., Glick, P., Adibnazari, I., Stopol, A., Cai, S., & Tolley, M. T. (2020). " Reversible actuation for self-folding modular machines using liquid crystal elastomer". Smart Materials and Structures.
Minori A., Jadhav S., He Q., Cai S., Tolley M. T. (2017) "Reversible actuation of origami inspired composites using liquid crystal elastomers", ASME Conference on Smart Materials, Adaptive Structures and Intelligent Systems (SMASIS), Snowbird UT, Sept. 2017, V001T08A015. *Best Student Paper Finalist*
Morphing structure for changing hydrodynamic characteristics of a soft robot walking underwater
Existing platforms for underwater exploration and inspection are often limited to traversing open water and must expend large amounts of energy to maintain a position in flow for long periods of time. Many benthic animals overcome these limitations using legged locomotion and have different hydrodynamic profiles dictated by different body morphologies. This work presents an underwater legged robot with soft legs and a soft inflatable morphing body that can change shape to influence drag and lift. When the robot needs to remain stationary in flow, it can increase its resistance to sliding by inflating the body asymmetrically, which reduces lift. When the robot needs to walk in the same direction as flow, it can inflate its body to a large, symmetric shape that is pushed along by the flow. When the robot needs to walk in the opposite direction as flow, it can use the flat, uninflated body shape to resist being pushed backwards. We demonstrate that the robot can detect changes in flow velocity with a commercial flow sensor and respond by morphing into a hydrodynamically preferable shape.
Ishida M., Drotman D., Shih B., Hermes M., Luhar M., and Tolley M. T. (2019), "Morphing structure for changing hydrodynamic characteristics of a soft robot walking underwater", IEEE Robotics and Automation Letters, 4 (4), 4163-4169.
Reversible adhesion inspired by the clingfish
Non-destructive adhesion is difficult to achieve on rough and textured surfaces, both in air and underwater. Ability to reversibly adhere to variable surfaces could lead to improved performance of robotic systems, with specific emphasis on manipulation and locomotion. We turned to nature to investigate and learn from the adhesion strategies of the northern clingfish. Based on the lessons from the clingfish, we designed artificial suction discs that were successful at adhering to irregularly shaped and rough surfaces (such as coarse sand paper, calcareous conch shells, and strawberries) both in air and underwater. We correlated the effect of key bioinspired features (i.e. material composition and body geometry) to adhesion performance using contact visualization techniques and Finite Element Analysis. We have also demonstrated the utility of the discs when applied to robotic manipulators for use on deep sea Remotely Operated Vehicles (ROVs). We envision that this research could provide a soft touch in fields ranging from the packaging industry to underwater archaeological specimen recovery.
Sandoval J.A., Jadhav S., Quan H., Deheyn D.D., Tolley M. T. (2019) "Reversible adhesion to rough surfaces both in and out of water, inspired by the clingfish suction disc", Bioinspiration and Biomimetics, 14, 066016.
3D printed resistive soft sensors
Sensor design for soft robots is a challenging problem because of the wide range of design parameters (e.g. geometry, material, actuation type, etc.) critical to their function. While conventional rigid sensors work effectively for soft robotics in specific situations, sensors that are directly integrated into the bodies of soft robots could help improve both their exteroceptive and interoceptive capabilities. To address this challenge, we designed sensors that can be co-fabricated with soft robot bodies using commercial 3D printers, without additional modification. We describe an approach to the design and fabrication of compliant, resistive soft sensors using a Connex3 Objet350 multimaterial printer and investigated an analytical comparison to sensors of similar geometries. The sensors consist of layers of commercial photopolymers with varying conductivities. We characterized the conductivity of TangoPlus, TangoBlackPlus, VeroClear, and Support705 materials under various conditions and demonstrate applications in which we can take advantage of these embedded sensors.
Shih B., Christianson C., Gillespie K., Lee S., Mayeda J., Huo Z., Tolley M. T. (2019) "Design considerations for 3D printed, soft, multimaterial resistive sensors for soft robotics", Frontiers in Robotics and AI, 6, 30.
Shih B., Mayeda J., Huo Z., Christianson C., and Tolley M. T., "3D printed resistive soft sensors," in 2018 IEEE-RAS International Conference on Soft Robotics (RoboSoft), pp 152-157, Apr 2018. *Best Poster Finalist*
Soft robot perception using embedded soft sensors and recurrent neural networks
Recent work has begun to explore the design of biologically inspired soft robots composed of soft, stretchable materials for applications including the handling of delicate materials and safe interaction with humans. However, the solid-state sensors traditionally used in robotics are unable to capture the high-dimensional deformations of soft systems. Embedded soft resistive sensors have the potential to address this challenge. However, both the soft sensors—and the encasing dynamical system—often exhibit nonlinear time-variant behavior, which makes them difficult to model. In addition, the problems of sensor design, placement, and fabrication require a great deal of human input and previous knowledge. Drawing inspiration from the human perceptive system, we created a synthetic analog. Our synthetic system builds models using a redundant and unstructured sensor topology embedded in a soft actuator, a vision-based motion capture system for ground truth, and a general machine learning approach. This allows us to model an unknown soft actuated system. We demonstrate that the proposed approach is able to model the kinematics of a soft continuum actuator in real time while being robust to sensor nonlinearities and drift. In addition, we show how the same system can estimate the applied forces while interacting with external objects. The role of action in perception is also presented. This approach enables the development of force and deformation models for soft robotic systems, which can be useful for a variety of applications, including human-robot interaction, soft orthotics, and wearable robotics.
Thuruthel T. G.*, Shih B.*, Laschi C., Tolley M. T., (2019) "Soft robot perception using embedded soft sensors and recurrent neural networks", Science Robotics, 4(26), eaav1488.
Translucent Soft Robots Driven by Frameless Fluid Electrode Dielectric Elastomer Actuators
Submersible robots are finding ever-increasing uses in search and rescue, environmental monitoring, and defense applications. Artificial muscles made out of dielectric elastomer actuators (DEAs) provide an attractive choice for driving submersible robotics based on their high energy density, light weight, and efficiency. One challenge for most DEAs is that that they require conductive electrodes that are made out of materials that are challenging to pattern, opaque, and/or add stiffness to the devices. Additionally, many traditional DEAs are based on a pre-stretched elastomer membrane, which requires a rigid or semi-rigid frame to maintain the prestrain thus increasing the overall stiffness of the structure. Our solution is to use water as conductive electrodes and prestrain-free membranes, which simplifies the design of our artificial muscles compared to alternative approaches, allowing us to make lightweight, fully soft, transparent actuators for soft, underwater robots.
Christianson, C., Goldberg, N. N., Deheyn, D., Cai, S., Tolley, M. T., (2018) "Translucent Soft Robots Driven by Frameless Fluid Electrode Dielectric Elastomer Actuators", Science Robotics, 3:17, eaat1893.
Christianson C., Goldberg N. , Cai S., Tolley M. T., (2017) “Fluid electrodes for submersible robotics based on dielectric elastomer actuators,” SPIE Electroactive Polymer Actuators and Devices (EAPAD) XIX, Portland OR, March 2017.
Soft robotic gripper with gecko inspired adhesives
Elastomer actuators, compliant mechanisms for robots that are driven by internal fluid pressure, can be used to create robust and versatile grippers. We apply gecko-inspired adhesives, a micron-scale pattern of wedges that mimics the behavior of gecko’s toes, to extend and enhance this versatility. We show that these grippers made from elastomer actuators and gecko-inspired adhesives are capable of high strength grasps, manipulation of large objects, a wider grasp choice, and fast actuation. We present a novel design, modeling, and manufacturing framework for elastomer actuators to take advantage of the gecko-inspired adhesives. Using this modeling approach we can create a fluidic elastomer actuator that conforms to and evenly distributes pressure across a surface. These developments are applicable to industrial automation and we demonstrate the gripper on a robotic arm lifting 25 lbs. The gripper weighs 48.7 g and uses only $7.25 of raw materials.
Glick, P., Suresh, S.A., Ruffatto III, D., Cutkosky, M., Tolley, M.T., Parness, A., (2018) "A soft robotic gripper with gecko-inspired adhesive" IEEE Robotics and Automation Letters, no. 99, pp. 1-1.
Custom Soft Robotic Gripper Sensor Skins for Haptic Object Visualization
Tactile sensing is an important capability for robots that assist or interact with humans or fragile objects in uncertain environments. An ongoing challenge for soft robots has been incorporating sensors that can recognize complex motions. We present sensor skins that enable haptic object visualization when integrated on a soft robotic gripper that can twist an object. First, we investigate how the design of the actuator modules impact bend angle and motion. Each soft finger is molded using a silicone elastomer, and consists of three pneumatic chambers which can be inflated independently to achieve a range of complex motions. Three fingers are combined to form a soft robotic gripper. Then, we manufacture and attach modular, flexible sensory skins on each finger to measure deformation and contact. These sensor measurements are used in conjunction with an analytical model to construct 2D and 3D tactile object models. Our results are a step towards soft robot grippers capable of a complex range of motions and proprioception, which will help future robots better understand the environments with which they interact, and have the potential to increase physical safety in human-robot interaction.
Shih B., Drotman D., Christianson C., Huo Z., White R., Christensen H. I., Tolley M. T., (2017) "Custom Soft Robotic Gripper Sensor Skins for Haptic Object Visualization", Int. Conf. on Intelligent Robots and Systems (IROS), Vancouver, Sept. 2017.
Differential Pressure Control of 3D Printed Soft Fluidic Actuators
Fluidically actuated soft robots show a great promise for operation in sensitive and unknown environments due to their intrinsic compliance. However, most previous designs use either flow control systems that are noisy, inefficient, sensitive to leaks, and cannot achieve differential pressure (i.e. can only apply either positive or negative pressures with respect to atmospheric), or closed volume control systems that are not adaptable and prohibitively expensive. In this work, we present a modular, low cost volume control system for differential pressure control of soft actuators. We use this system to actuate three-chamber 3D printed soft robotic modules. For this design, we demonstrated improved performance when using differential pressure actuation as compared to the use of only pressure or vacuum. Furthermore, we demonstrate a self-healing capability of the combined system by using vacuum to actuate ruptured modules which were no longer responsive to positive pressure.
Kalisky T., Wang Y., Shih B., Drotman D., Jadhav S., Aronoff-Spencer E., and Tolley M T., (2017) "Differential Pressure Control of 3D Printed Soft Fluidic Actuators", Int. Conf. on Intelligent Robots and Systems (IROS), Vancouver, Sept. 2017.
3D Printed Soft Actuators for a Legged Robot Capable of Navigating Unstructured Terrain
Soft robotics is a rapidly developing field that is changing the way we perceive automated systems. Soft robots deform continuously along their bodies as opposed to at discrete joints like traditional rigid robots. In this work we demonstrated the use of multi-material 3D printing to fabricate a four-legged walking robot with bellowed soft legs. The robot is powered by pressurized air and is able to navigate a variety of terrain. This design is a step towards the development of a mobile soft system for applications including monitoring in hazardous environments and search-and-rescue operations.
Drotman D., Jadhav S., Karimi M., deZonia P., Tolley M. T., (2017) "3D Printed Soft Actuators for a Legged Robot Capable of Navigating Unstructured Terrain", Int. Conf. on Robotics and Automation (ICRA), Singapore, May 2017.
Soft robotic glove for kinesthetic haptic feedback in virtual reality
Current virtual reality technologies rely heavily on visual and audio feedback as a form of sensory feedback. Most existing wearable haptic devices use vibrating motors, which are unable to provide force feedback, or rigid linkage devices which are bulky and inflexible. We address this issue with a wearable soft robotic glove capable of safely applying forces to the fingers of the user. The glove design includes a soft exoskeleton actuated by Mckibben muscles that are controlled using a custom fluidic control board. The result is a haptic glove that is compliant, compact and unintimidating. We demonstrated its application with a virtual reality environment that simulates playing the piano and received positive preliminary feedback from users. This glove represents a step toward developing natural 3D user interfaces by replacing the existing wand controllers.
Jadhav S., Kannanda V., Kang B., Tolley M. T., Schulze J. P., (2017) "Soft robotic glove for kinesthetic haptic feedback in virtual reality environments", IS&T Electronic Imaging: The Engineering Reality for Virtual Reality proceedings, IS&T Springfield VA, 2017.
Soft Robotics - Untethered Quadruped
While robots are traditionally designed to be as rigid as possible so that they can be easily modeled and precisely controlled, nature suggests an alternative approach. Plants and animals exhibit a large range of rigidity, but most are much softer than engineering materials such as steel or injection-molded plastics. Not only does nature tolerate this softness but it embraces it, achieving feats of adaptability and agility unrivaled in engineered systems. The field of Soft Robotics seeks to draw inspiration from natural systems such as cephalopods, to develop a new breed of robots that is more adaptable to unknown environments and safe to work with. The Bioinspired Robotics and Design Lab seeks to develop untethered soft robots with integrated power and control systems. The following video describes a resilient, untethered soft robot developed by Prof. Tolley and collaborators during his Postdoctoral Fellowship at Harvard University.
Fabrication by Folding
Nature frequently employs folding for fabrication. From very small scales where proteins are folded from linear strings of amino acids, to larger scales where organs are folded from sheets of cells and plant leaves and insect wings deploy by folding or unfolding. The ancient Japanese art of origami also uses folding to form three dimensional structures from sheets of material. Inspired by these examples, we seek to develop new approaches to the fabrication of engineered structures and robotic systems, employing folding for assembly or deployment. The following video describes previous work which demonstrates a walking robot fabricated as a flat sheet that deploys itself by folding and is able to immediately begin operation.