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Experiments on physical continuum robot are the gold standard for evaluations. Currently, as no commercial continuum robot platform is available, a large variety of early-stage prototypes exists. These prototypes are developed by individual research groups and are often used for a single publication. Thus, a significant amount of time is devoted to creating proprietary hardware and software hindering the development of a common platform, and shifting away scarce time and efforts from the main research challenges. We address this problem by proposing an open-source actuation module, which can be used to build different types of continuum robots. It consists of a high-torque brushless electric motor, a high resolution optical encoder, and a low-gear-ratio transmission. For this article, we create three different types of continuum robots. In addition, we illustrate, for the first time, that continuum robots built with our actuation module can proprioceptively detect external forces. Consequently, our approach opens untapped and under-investigated research directions related to the dynamics and advanced control of continuum robots, where sensing the generalized flow and effort is mandatory. Besides that, we democratize continuum robots research by providing open-source software and hardware with our initiative called the Open Continuum Robotics Project, to increase the accessibility and reproducibility of advanced methods., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision., (Copyright © 2024 Grassmann, Shentu, Hamoda, Dewi and Burgner-Kahrs.)

This paper presents the singularity analysis of 3-DOF planar parallel continuum robots (PCR) with three identical legs. Each of the legs contains two passive conventional rigid 1-DOF joints and one actuated planar continuum link, which bends with a constant curvature. All possible PCR architectures featuring such legs are enumerated and the kinematic velocity equations are provided for each of them. Afterwards, a singularity analysis is conducted based on the obtained Jacobian matrices, providing a geometrical understanding of singularity occurences. It is shown that while loci and occurrences of type II singularities are mostly analogous to conventional parallel kinematic mechanisms (PKM), type I singularity occurences for the PCR studied in this work are quite different from conventional PKM and less geometrically intuitive. The study provided in this paper can promote further investigations on planar parallel continuum robots, such as structural design and control., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Lilge, Wen and Burgner-Kahrs.)

We propose a segment design that combines two distinct characteristics of tendon-driven continuum robots, i.e. variable length and non-straight tendon routing, into a single segment by enabling rotation of its backbone. As a result, this segment can vary its helical tendon routing and has four degrees-of-freedom, while maintaining a small-scale design with an overall outer diameter of 7 mm thanks to an extrinsic actuation principle. In simulation and on prototypes, we observe improved motion capabilities, as evidenced by position redundancy and follow-the-leader deployment along spatially tortuous paths. To demonstrate the latter on a physical prototype, a simple, yet effective area-based error measure for follow-the-leader deployment is proposed to evaluate the performance. Furthermore, we derive a static model which is used to underpin the observed motion capabilities. In summary, our segment design extends previous designs with minimal hardware overhead, while either archiving similar accuracy in position errors and planar follow-the-leader deployment, or exhibiting superior motion capabilities due to position redundancy and spatial follow-the-leader deployment., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Grassmann, Rao, Peyron and Burgner-Kahrs.)

Tendon actuation is one of the most prominent actuation principles for continuum robots. To date, a wide variety of modelling approaches has been derived to describe the deformations of tendon-driven continuum robots. Motivated by the need for a comprehensive overview of existing methodologies, this work summarizes and outlines state-of-the-art modelling approaches. In particular, the most relevant models are classified based on backbone representations and kinematic as well as static assumptions. Numerical case studies are conducted to compare the performance of representative modelling approaches from the current state-of-the-art, considering varying robot parameters and scenarios. The approaches show different performances in terms of accuracy and computation time. Guidelines for the selection of the most suitable approach for given designs of tendon-driven continuum robots and applications are deduced from these results., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Rao, Peyron, Lilge and Burgner-Kahrs.)

Purpose: Laser-induced thermotherapy in the brain is a minimally invasive procedure to denature tumor tissue. However, irregularly shaped brain tumors cannot be treated using existing commercial systems. Thus, we present a new concept for laser-induced thermotherapy using a concentric tube robotic system. The planning procedure is complex and consists of the optimal distribution of thermal laser ablations within a volume as well as design and configuration parameter optimization of the concentric tube robot., Methods: We propose a novel computer-assisted planning procedure that decomposes the problem into task- and robot-specific planning and uses a multi-objective particle swarm optimization algorithm with variable length., Results: The algorithm determines a Pareto-front of optimal ablation distributions for three patient datasets. It considers multiple objectives and determines optimal robot parameters for multiple trajectories to access the tumor volume., Conclusions: We prove the effectiveness of our planning procedure to enable the treatment of irregularly shaped brain tumors. Multiple trajectories further increase the applicability of the procedure.

Added to their high dexterity and ability to conform to complex shapes, continuum robots can be further improved to provide safer interaction with their environment. Indeed, controlling their stiffness is one of the most challenging yet promising research topics. We propose a tubular stiffening sheath as a replaceable cover for small-diameter continuum robots to temporarily increase the stiffness in a certain configuration. In this article, we assess and compare performances of two different stiffening modalities: granular and layer jamming, provide arguments for material selection and experimental results for stiffness with respect to lateral and axial applied forces. Furthermore, we detected empirically additional effects relating sheath stiffness to material parameters and added to recent investigations in the state of the art, which are based exclusively on material roughness. Finally, we integrated the selected layer jamming material in a miniaturized sheath (13 mm outer diameter, 2.5 mm wall thickness) and covered a tendon-actuated continuum robot with it. Experimental characterization of the behavior with respect to applied external forces was performed via stiffness measurements and proved that the initial tendon-actuated continuum robot stiffness can be improved by a factor up to 24.

This paper presents a miniature wrist that can be integrated into needle-sized surgical instruments. The wrist consists of a nitinol tube with asymmetric cutouts that is actuated by a single tendon to provide high distal curvature. We derive and experimentally validate kinematic and static models for the wrist and describe several prototype wrists, illustrating the straightforward fabrication and scalability of the design. We experimentally investigate fatigue life, the concept of tip-first bending, and practical use of the wrist with a concentric tube robot in an endonasal surgical scenario.

Purpose: Organ-level registration is critical to image-guided therapy in soft tissue. This is especially important in organs such as the kidney which can freely move. We have developed a method for registration that combines three-dimensional locations from a holographic conoscope with an endoscopically obtained textured surface. By combining these data sources clear decisions as to the tissue from which the points arise can be made., Methods: By localizing the conoscope's laser dot in the endoscopic space, we register the textured surface to the cloud of conoscopic points. This allows the cloud of points to be filtered for only those arising from the kidney surface. Once a valid cloud is obtained we can use standard surface registration techniques to perform the image-space to physical-space registration. Since our methods use two distinct data sources we test for spatial accuracy and characterize temporal effects in phantoms, ex vivo porcine and human kidneys. In addition we use an industrial robot to provide controlled motion and positioning for characterizing temporal effects., Results: Our initial surface acquisitions are hand-held. This means that we take approximately 55 s to acquire a surface. At that rate we see no temporal effects due to acquisition synchronization or probe speed. Our surface registrations were able to find applied targets with submillimeter target registration errors., Conclusion: The results showed that the textured surfaces could be reconstructed with submillimetric mean registration errors. While this paper focuses on kidney applications, this method could be applied to any anatomical structures where a line of sight can be created via open or minimally invasive surgical techniques.