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.

Related Publications:

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.

Related Publications:

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.

Related Publications:

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.

Related Publication:

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.

Related Publication:

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.

Related Publication:

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.

Related Publication:

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.

Related Publication:

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.

Related Publication:

Tolley M. T., Shepherd R. F., Mosadegh B., Galloway K. C., Wehner M., Karpelson M., Wood R. J., Whitesides G. M. (2014) “A Resilient, Untethered Soft Robot”, Soft Robotics, 1:3, pp. 213-223.

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.

Related Publication:

Felton S. M., Tolley M. T., Demaine E., Rus D., Wood R. J. (2014) “A Method for Building Self-Folding Machines”, Science, 345:6197, pp. 644-646.