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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  

   M. Srivastava, J. Ammons (April 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. 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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3. Evaluation of Durability of 3D-Printed Cementitious Materials for Potential Applications in Structures Exposed to Marine Environments.

   Rodriguez, Fabian; Lopez, Cristian; Wang, Yu; Olek, Jan; Zavattieri, Pablo; Youngblood, Jeffrey; Falzone, Gabriel; Cotrell, Jason. (June 2022, Third RILEM International Conference on Concrete and Digital Fabrication. DC 2022.)

   The rising interest in 3D-printing of concrete structures for use in marine environments requires development of concrete mixtures with adequate mechanical and durability characteristics. The incorporation of alternative cementitious materials, combined with careful selection of printing parameters has emerged as an effective way of controlling not only the fresh properties and printability of mixtures, but also their mechanical and durability properties. This paper presents the results of various durability related tests performed on 3D-printed mortars, including density, porosity, rate of water absorption and resistance to chloride penetration. Results of these tests indicate that the performance of mortar elements 3D-printed using controlled overlap process was similar to the performance of conventionally cast mortar elements with the same composition. Moreover, the results of the chloride transport related tests obtained from all specimens evaluated during the course of the study indicate low chloride ion penetrability, thus re-affirming that combination of the proposed material and 3D-printing method of fabrication have a potential for producing structural elements for applications in marine environments. 

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4. 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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5. Series pneumatic artificial muscles (sPAMs) and application to a soft continuum robot

   https://doi.org/10.1109/ICRA.2017.7989648  

   Greer, Joseph D.; Morimoto, Tania K.; Okamura, Allison M.; Hawkes, Elliot W. (May 2017, IEEE International Conference on Robotics and Automation)

   We describe a new series pneumatic artificial muscle (sPAM) and its application as an actuator for a soft continuum robot. The robot consists of three sPAMs arranged radially around a tubular pneumatic backbone. Analogous to tendons, the sPAMs exert a tension force on the robot’s pneu- matic backbone, causing bending that is approximately constant curvature. Unlike a traditional tendon driven continuum robot, the robot is entirely soft and contains no hard components, making it safer for human interaction. Models of both the sPAM and soft continuum robot kinematics are presented and experimentally verified. We found a mean position accuracy of 5.5 cm for predicting the end-effector position of a 42 cm long robot with the kinematic model. Finally, closed-loop control is demonstrated using an eye-in-hand visual servo control law which provides a simple interface for operation by a human. The soft continuum robot with closed-loop control was found to have a step-response rise time and settling time of less than two seconds. 

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