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1. 3D Printing of Concrete with a Continuum Robot Hose Using Variable Curvature Kinematics

   https://doi.org/10.1109/ICRA46639.2022.9812123  

   Srivastava, M.; Ammons, J.; Peerzada, A.B.; Krovi, V.N.; Rangaraju, P.; Walker, I.D. (May 2022, IEEE International Conference on Robotics and Automation)

   We present a novel application of continuum robots acting as concrete hoses to support 3D printing of cementitious materials. An industrial concrete hose was fitted with a cable harness and remotely actuated via tendons. The resulting continuum hose robot exhibited non constant curvature. In order to account for this, a new geometric approach to modeling variable curvature inverse kinematics using Euler curves is introduced herein. The new closed form model does not impose any additional computational cost compared to the constant curvature model and results in a marked improvement in the observed performance. Experiments involving 3D printing with cementitious mortar using a continuum hose robot were also conducted. 

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2. Dynamically Reconfigurable Discrete Distributed Stiffness for Inflated Beam Robots

   https://doi.org/10.1109/ICRA40945.2020.9197237  

   Do, Brian H.; Banashek, Valory; Okamura, Allison M. (May 2020, IEEE International Conference on Robotics and Automation (ICRA))

   null (Ed.)

   Inflated continuum robots are promising for a variety of navigation tasks, but controlling their motion with a small number of actuators is challenging. These inflated beam robots tend to buckle under compressive loads, producing extremely tight local curvature at difficult-to-control buckle point locations. In this paper, we present an inflated beam robot that uses distributed stiffness changing sections enabled by positive pressure layer jamming to control or prevent buckling. Passive valves are actuated by an electromagnet carried by an electromechanical device that travels inside the main inflated beam robot body. The valves themselves require no external connections or wiring, allowing the distributed stiffness control to be scaled to long beam lengths. Multiple layer jamming elements are stiffened simultaneously to achieve global stiffening, allowing the robot to support greater cantilevered loads and longer unsupported lengths. Local stiffening, achieved by leaving certain layer jamming elements unstiffened, allows the robot to produce "virtual joints" that dynamically change the robot kinematics. Implementing these stiffening strategies is compatible with growth through tip eversion and tendon steering, and enables a number of new capabilities for inflated beam robots and tip-everting robots. 

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3. Helical actuation on a soft inflated robot body

   https://doi.org/10.1109/ROBOSOFT.2018.8404927  

   Blumenschein, Laura H.; Usevitch, Nathan S.; Do, Brian H.; Hawkes, Elliot W.; Okamura, Allison M. (April 2018, IEEE International Conference on Soft Robotics (RoboSoft))

   Continuum and soft robots can leverage routed actuation schemes to take on useful shapes with few actuated degrees of freedom. The addition of vine-like growth to soft continuum robots opens up possibilities for creating deployable structures from compact packages and allowing manipulation and grasping of objects in cluttered or difficult-to-navigate environments. Helical shapes, with constant curvature and torsion, provide a starting point for the shapes and actuation strategies required for such applications. Building on the geometric and static solutions for continuum robot kinematics given constant curvature assumptions, we develop a static model of helical actuation and present the implementation and validation of this model. We also discuss the forces applied by the soft robot when wrapped around an object that deforms the static shape, allowing a quantification of grasping capabilities. 

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4. Modeling Variable Curvature Parallel Continuum Robots Using Euler Curves

   https://doi.org/10.1109/ICRA.2019.8794238  

   Gonthina, Phanideep S.; Kapadia, Apoorva D.; Godage, Isuru S.; Walker, Ian. D. (May 2019, 2019 International Conference on Robotics and Automation (ICRA))

   In this paper, we propose and investigate a new approach to modeling variable curvature continuum robot sections, based on Euler spirals. Euler spirals, also termed Clothoids, or Cornu spirals, are those curves in which the curvature increases linearly with their arc length. In this work, Euler spirals are applied to the kinematic modeling of continuum robots for the first time. The approach was evaluated using the sections of numerous continuum robots, including two novel parallel continuum robots. Each robot consists of three parallel sections, each with three thin, long McKibben actuators. These sections are poorly modeled by the widely used constant curvature kinematic model. The constant curvature and Euler spiral models were compared and the Euler spiral method was seen to be a significantly better match for a wide range of configurations of the robot hardware. 

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5. Encoder-less Robot Control for Space Operations with Continuum Robots

   Frazaelle, C.G.; Walker, I.D.; AlAttar, A.; Kormushev, P. (March 2021, IEEE Aerospace Conference)

   null (Ed.)

   Continuum robots have strong potential for application in Space environments. However, their modeling is challenging in comparison with traditional rigid-link robots. The Kinematic-Model-Free (KMF) robot control method has been shown to be extremely effective in permitting a rigid-link robot to learn approximations of local kinematics and dynamics (“kinodynamics”) at various points in the robot’s task space. These approximations enable the robot to follow various trajectories and even adapt to changes in the robot’s kinematic structure. In this paper, we present the adaptation of the KMF method to a three-section, nine degrees-of-freedom continuum manipulator for both planar and spatial task spaces. Using only an external 3D camera, we show that the KMF method allows the continuum robot to converge to various desired set points in the robot’s task space, avoiding the complexities inherent in solving this problem using traditional inverse kinematics. The success of the method shows that a continuum robot can “learn” enough information from an external camera to reach and track desired points and trajectories, without needing knowledge of exact shape or position of the robot. We similarly apply the method in a simulated example of a continuum robot performing an inspection task on board the ISS. 

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