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1. Characterization of Compliant Parallelogram Links for 3D-Printed Delta Manipulators

   https://doi.org/10.1007/978-3-030-71151-1_7  

   Mannam, P.; Kroemer, O.; Temel, F. Z. (March 2021, International Symposium on Experimental Robotics)

   Siciliano, B.; Laschi, C.; Khatib, O. (Ed.)

   We design a compliant delta manipulator using 3D-printing and soft materials. Our design is different from the traditionally rigid delta robots as it is more accessible through low-cost 3D-printing, and can interact safely with its surroundings due to compliance. This work focuses on parallelogram links which are a key component of the delta robot design. We characterize these links over twelve dimensional parameters, such as beam and hinge thickness, and two material stiffness settings by displacing them, and observing the resulting forces and rotation angles. The parallelogram links are then integrated into a delta robot structure to test for delta mechanism behavior, which keeps the end-effector parallel to the base of the robot. We observed that using compliant hinges resulted in near-delta behavior, laying the groundwork for fabricating and utilizing 3D-printed compliant delta manipulators. 

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2. Configurable Tendon Routing in a 3D-printed Soft Actuator for Improved Locomotion in a Multi-Legged Robot

   Jose Barreiros, Kevin W. (April 2019, IEEE International Conference on Soft Robotics)

   Soft robots struggle with terrestrial locomotion due to their inherent lack of rigidity, specifically along axes not in line with the direction of actuation (side loads). We present a method for improved stiffness in a 3D printed, tendon-driven soft actuator. We show, both mathematically and experimentally, that our method leads to improved stiffness to these side loads. Additionally, we demonstrate the use of complex tendon routing schemes to achieve various trajectories with a single actuator morphology. Finally, we demonstrate that these two tendon routing strategies lead to improved locomotion speed and gait efficiency in a 3- legged, 3D printed, soft robot. 

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3. Extensible High Force Manipulator For Complex Exploration

   https://doi.org/10.1109/RoboSoft48309.2020.9116024  

   Hughes, Josie; Santina, Cosmio Della; Rus, Daniela (May 2020, IEEE Conference on Soft Robotics (RoboSoft))

   The development of compliant robotic manipulators which can show length change, compliance and dexterity could assist many challenging applications. Potential applications range from dexterous manipulation, robotic surgery or exploration of challenging environments. Despite significant developments in both fabrication and control approaches for continuum body manipulators, there have been few demonstrations of continuum body systems which display all these properties. We present a method for fabricating a continuum manipulation which shows extension, high force movements and a range of dexterous position. This approach uses 3D printing to create a flexible rack and pinion system. These high torque mechanisms are mounted at points along the 3D printed tracks to allow complex shape control of the continuum system. A controller has been also been developed based on a Piecewise Constant Curvature approximation to allow the position of the tip of the manipulator to be controlled, and motion paths to be followed. In this work, we show the force capabilities of this manipulator and demonstrate how multiple segments can be created for more complex movements. 

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4. Semi-Physical Modeling of Soft Pneumatic Actuators With Stiffness Tuning

   https://doi.org/10.1115/1.4064090  

   Fairchild, Preston; Shephard, Noah; Mei, Yu; Tan, Xiaobo (October 2023, ASME Letters in Dynamic Systems and Control)

   Abstract The inherent low stiffness in soft robots makes them preferable for working in close proximity to humans. However, having this low stiffness creates challenges when operating in terms of control and sensitivity to disturbances. To alleviate this issue, soft robots often have built-in stiffness tuning mechanisms that allow for controlled increases in stiffness. Additionally, redundant pneumatic manipulators can utilize antagonistic pressure to achieve identical positions under increased stiffness. In this paper, we develop a model to predict the stiffness and configuration of a pneumatic soft manipulator under different pressure inputs and external forces. The model is developed based on the physical characteristics of a soft manipulator while enabling efficient parameter estimation and computation. The efficacy of the modeling approach is supported via experimental results. 

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5. Validation of an Extensible Rod Model for Soft continuum Manipulators

   https://doi.org/10.1109/ROBOSOFT.2019.8722721  

   Gilbert, Hunter B.; Godage, Isuru S. (April 2019, 2019 2nd IEEE International Conference on Soft Robotics (RoboSoft))

   Numerous soft and continuum robotic manipulators have demonstrated their potential for compliant operation in highly unstructured environments or near people. Despite their recent popularity, modeling of their smooth bending deformation remains a challenge. For soft continuum manipulators, the widespread, constant curvature approach to modeling is inadequate for modeling some deformations that occur in practice, such as combined bending and twisting deformations. In this paper, we extend the classical Cosserat rod approach to model a variable-length, pneumatic soft continuum arm. We model the deformation of a pneumatically driven soft continuum manipulator, and the model is then compared against experimental data collected from a three degree of freedom, pneumatically actuated, soft continuum manipulator. The model shows good agreement in capturing the overall behavior of the bending deformation, with mean Euclidean error at the tip of the robot of 2.48 cm for a 22 cm long robot. In addition, the model shows good numerical stability for simulating long duration computations. 

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