Abstract -- 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.

Abstract -- 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 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 mobile soft systems for applications including monitoring in hazardous environments and search-and-rescue operations.

D. Drotman, S. Jadhav, M. Karimi, P. deZonia, and M. T. Tolley, “3D Printed Soft Actuators for a Legged Robot Capable of Navigating Unstructured Terrain,” in 2017 IEEE International Conference on Robotics and Automation, Soft Robotics Workshop, IEEE, 2017

Abstract -- Soft robots are flexible and adaptable allowing them to conform to objects of different shapes and sizes. However, the flexibility of soft robots leads to challenges in designing and fabricating them to satisfy application-specific requirements. In this paper, we presented a class of 3D printable three-chambered actuators, along with analytical models to predict actuation behavior based on a set of design parameters related to the bellows. The actuators were designed parametrically and fabricated on a commercial 3D printer, which improves the speed, accessibility, and repeatability of fabrication. The approach presented here provides a framework for tailoring actuators to specific soft robotic applications. This process relates actuation characteristics (e.g., bend angle and blocked force) to a small set of design parameters with the goal of reducing the design-fabrication cycle time.

D. Drotman, M. Ishida, S. Jadhav and M. T. Tolley, "Application-Driven Design of Soft, 3-D Printed, Pneumatic Actuators With Bellows," in IEEE/ASME Transactions on Mechatronics, vol. 24, no. 1, pp. 78-87, Feb. 2019, doi: 10.1109/TMECH.2018.2879299.

Abstract -- 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 presented 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., “Differential Pressure Control of 3D Printed Soft Fluidic Actuators,” in 2017 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), pp. 6207–6213, Sept 2017.

Abstract -- Many benthic animals 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 demonstrated that the robot can detect changes in flow velocity with a commercial flow sensor and respond by morphing into a hydrodynamically preferable shape.

M. Ishida, D. Drotman, B. Shih, M. Hermes, M. Luhar and M. T. Tolley, "Morphing Structure for Changing Hydrodynamic Characteristics of a Soft Underwater Walking Robot," in IEEE Robotics and Automation Letters, vol. 4, no. 4, pp. 4163-4169, Oct. 2019, doi: 10.1109/LRA.2019.2931263.

Abstract -- We developed a low-cost, three-degree-of-freedom (3- DOF) prismatic-spherical-revolute (PSR) parallel mechanism used as a testing platform for an unmanned aerial vehicle UAV) tethered to an unmanned surface vehicle (USV). The mechanism had three actuated linear rails kinematically linked to a platform that replicated boat motion up to 2.5 m vertical heave (sea state 4, Douglas Sea Scale). A lookup table relating relative slider heights to platform roll and pitch was developed numerically leveraging geometric constraints. A design parameter study optimized the arm length, platform size, and ball joint mounting angle relative to the overall radius to maximize the workspace. For this design, a maximum roll and pitch range from -32 to 32 and -25 to 35, respectively, is achievable. A prototype was manufactured to carry the tethered UAV winch payload. Experimental testing confirmed the workspace and demonstrated boat motion replication, validated using an inertial measurement unit (IMU).

K. Talke, D. Drotman, N. Stroumtsos, M. de Oliveira and T. Bewley, "Design and Parameter Optimization of a 3-PSR Parallel Mechanism for Replicating Wave and Boat Motion," 2019 International Conference on Robotics and Automation (ICRA), Montreal, QC, Canada, 2019, pp. 7955-7961, doi: 10.1109/ICRA.2019.8793473.

Abstract -- Robots are becoming increasingly prevalent in our society in forms where they are assisting or interacting with humans in a variety of environments, and thus they must have the ability to sense and detect objects by touch. An ongoing challenge for soft robots has been incorporating flexible sensors that can recognize complex motions and close the loop for tactile sensing. 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 has the potential to increase physical safety in human-robot interaction. Please see the accompanying video for additional details.

Shih B., Drotman D., Christianson C., Huo Z., White R., Christensen H. I., and Tolley M. T., “Custom Soft Robotic Gripper Sensor Skins for Haptic Object Visualization,” in 2017 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS) , pp. 494–501, Sept 2017.