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A parallel continuum manipulator (PCM) is a mechanism of closed-loop morphology with flexible elements such that their deformation contributes to its mobility. Flexible hexapods are six-degrees-of-freedom (DoF) fully parallel continuum mechanisms already presented in the literature. Devices of reduced mobility, i.e., lower mobility than six DoF, have not been studied so far. An essential characteristic of lower mobility mechanisms is that reduced mobility is due to kinematic constraints generated by mechanical arrangements and passive joints. In rigid-link parallel manipulators, those constraints are expressed as a set of equations relating to the parameters representing the end effector’s pose. As a consequence, independent output pose variables are controllable with the position equations, while dependent output variables undergo parasitic motions. In this paper, the performance of a tripod-type parallel continuum manipulator, 3PF̲S, is compared with the operation of its rigid counterpart 3P̲RS. We will show that in PCMs there are no such geometric constraints expressible with algebraic equations, but it is difficult to perform some types of motion in the end effector with the input torques. Another goal of this paper is to evaluate such limitation of motion in a tripod-like PCM and compare it with the constraints of the rigid 3P̲RS. Finally, the paper shows that there are strong similarities in the reduced mobility of both mechanisms.

The magnetic field has unique advantages in manipulating miniature robots working inside the human body, such as high transparency to biological tissue and good controllability for field generation. Generally, the actuated magnetic robot can be classified into two categories: tethered devices like intravascular microcatheters and untethered devices like helical swimmers. Among these, the tethered devices have a long history and good clinical application prospects, considering their high‐dose delivery and easy removal after the procedure. As an evolution of traditional continuum medical devices, the integration with magnetic actuation provides them with better scalability and improved dexterity. Although rapidly developed in the last two decades, the field of tethered magnetic robots requires further advancements in terms of design, fabrication, modeling, and control, especially for clinical applications. Herein, the recent progress of magnetically actuated continuum medical robots is focused on, intending to offer readers a comprehensive survey of the state‐of‐the‐art technologies and an information collection for future system design. Magnetically actuated continuum robots (MCRs) have been widely developed due to their miniature size and flexible manipulability, and viewed as the tethered category of magnetic robots or the evolution of traditional continuum devices. This review focuses on the recent progress of MCRs, intending to offer a comprehensive survey of the state‐of‐the‐art technologies and an information collection for future robot design.

Continuum manipulators, despite their prominent flexibility and compliance, possess relatively low inherent stiffness and weak load capacity. Realizing simultaneous curvature tracking control and joint stiffness regulation for continuum manipulators would further broaden their application possibilities. In this paper, we propose a concurrent robot shape and stiffness control framework for a class of tendon-driven continuum manipulators (TDCMs). Firstly, by employing an efficient lumped-parameter dynamics model, the feedforward control term is computed offline along the desired reference trajectory. Integrating this term with our designed nonsmooth proportional-derivative robust controller leads to rapid convergence of the curvature tracking errors. Secondly, to further enhance the robustness of the control scheme, a lightweight recurrent neural network observer is designed to estimate the disturbances. Finally, the joint stiffness model of the TDCMs is derived. Based on the redundant-driven characteristics of the flexible segments and considering tendon tension constraints, we achieve simultaneous adjustment of joint stiffness and positions through tendon tension redistribution using the null-space control term. Global uniform asymptotic stability is established by the designed Lyapunov function. Simulation experiments validate the effectiveness of the proposed control scheme.

Aerial manipulators have seen a rapid uptake for multiple applications, including inspection tasks and aerial robot–human interaction in building and construction. Whilst single degree of freedom (DoF) and multiple DoF rigid link manipulators (RLMs) have been extensively discussed in the aerial manipulation literature, continuum manipulators (CMs), often referred to as continuum robots (CRs), have not received the same attention. This survey seeks to summarise the existing works on continuum manipulator-based aerial manipulation research and the most prevalent designs of continuous backbone tendon-driven continuum robots (TDCRs) and multi-link backbone TDCRs, thereby providing a structured set of guidelines for fabricating continuum robots for aerial manipulation. With a history spanning over three decades, dominated by medical applications, CRs are now increasingly being used in other domains like industrial machinery and system inspection, also gaining popularity in aerial manipulation. Fuelled by diverse applications and their associated challenges, researchers have proposed a plethora of design solutions, primarily falling within the realms of concentric tube (CT) designs or tendon-driven designs. Leveraging research works published in the past decade, we place emphasis on the preparation of backbones, support structures, tendons, stiffness control, test procedures, and error considerations. We also present our perspectives and recommendations addressing essential design and fabrication aspects of TDCRs in the context of aerial manipulation, and provide valuable guidance for future research and development endeavours in this dynamic field.

Forward kinematics is essential in robot control. Its resolution remains a challenge for continuum manipulators because of their inherent flexibility. Learning-based approaches allow obtaining accurate models. However, they suffer from the explosion of the learning database that wears down the manipulator during data collection. This paper proposes an approach that combines the model and learning-based approaches. The learning database is derived from analytical equations to prevent the robot from operating for long periods. The database obtained is handled using Deep Neural Networks (DNNs). The Compact Bionic Handling robot serves as an experimental platform. The comparison with existing approaches gives satisfaction.

Continuum manipulators have found several applications in surgical interventions like endoscopy, laparoscopy, and as end‐effectors for surgical robots. Continuum manipulators coupled with magnetic actuation can be precisely maneuvered inside the human body. Recently, variable stiffness manipulators (VSMs) have been introduced for enhanced dexterity and safe navigation. This study presents a new design of a magnetically actuated VSM based on shape memory polymer (SMP) springs. The VSM has a silicone backbone enclosed within a spring made of SMP that can change in length with stiffness change that is triggered by Joule heating. The stiffness and thermal characteristics of the VSM are studied using analytical models and experiments. Subsequently, a one‐segment VSM and a two‐segment VSM having outer diameters of 9 and 10 mm and lengths of 15 and 25 mm, respectively, capable of extending to four times their length are designed. The VSM can be deployed in a compact form and extended to achieve variable bending curvatures in soft and rigid states, which can facilitate instrument insertion and reduce operation invasiveness. Potential clinical applications are demonstrated by incorporating miniature camera, biopsy tool, and laser optical fiber in the working channel of the VSM and coupled with robotic magnetic actuation. This work presents a new deployable variable stiffness manipulator (VSM) based on shape memory polymer (SMP) springs. The VSM exhibits variable stiffness and variable bending curvatures at variable working lengths. The shape locking ability of the VSM is coupled with magnetic actuation to facilitate instrument insertion, stably deploy surgical tools, and enhance maneuverability to reach difficult‐to‐access surgical sites safely.

The steerable catheter refers to the catheter that is manipulated by a mechanism which may be driven by operators or by actuators. The steerable catheter for minimally invasive surgery has rapidly become a rich and diverse area of research. Many important achievements in design, application and analysis of the steerable catheter have been made in the past decade. This paper aims to provide an overview of the state of arts of steerable catheters. Steerable catheters are classified into four main groups based on the actuation principle: (1) tendon driven catheters, (2) magnetic navigation catheters, (3) soft material driven catheters (shape memory effect catheters, steerable needles, concentric tubes, conducting polymer driven catheters and hydraulic pressure driven catheters), and (4) hybrid actuation catheters. The advantages and limitations of each of them are commented and discussed in this paper. The future directions of research are summarized.

Aiming at the challenge of trajectory planning for a continuum manipulator in the confined spaces of gas-insulated switchgear (GIS) chambers during intelligent operation and maintenance of power equipment, this paper proposes a configuration space (C-space) obstacle-avoidance planning method based on an improved RRT-Connect algorithm. By constructing a virtual joint-space obstacle map, the collision-avoidance problem in Cartesian space is transformed into a joint-space path search problem, significantly reducing the computational burden of frequent inverse kinematics solutions inherent in traditional methods. Compared to the RRT-Connect algorithm, improvements in node expansion strategies and greedy optimization mechanisms effectively minimize redundant nodes and enhance path generation efficiency: the number of iterations is reduced by 68% and convergence speed is improved by 35%. Combined with polynomial-driven trajectory planning, the method successfully resolves and smoothens driving cable length variations, achieving efficient and stable control for both the end-effector and arm configuration of a dual-segment continuum manipulator. Simulation and experimental results demonstrate that the proposed algorithm rapidly generates collision-free arm configuration trajectories with high trajectory coincidence in typical GIS chamber scenarios, verifying its comprehensive advantages in real-time performance, safety, and motion smoothness. This work provides theoretical support for the application of continuum manipulator in precision operation and maintenance of power equipment.

Multisegment continuum manipulators exhibit broad application prospects for complex tasks in confined spaces due to their inherent compliance and dexterity. However, the dynamic behaviors of these manipulators are highly nonlinear, bringing great challenges to their obstacle-avoidance motion planning. In this paper, a combined kinodynamic motion planning method is proposed for cable-driven multisegment continuum manipulators in confined spaces. The kinodynamic motion planning problem for these manipulators is first transformed into a nonlinear optimization problem (NOP) with both obstacle-avoidance constraints and input limitation constraints. The workspace of the continuum manipulator is then divided into a safe subspace and a warning subspace. By introducing parameters, the transformed NOP for motion planning in the safe subspace is further reformulated as a mixed complementarity problem to solve, which can rapidly generate paths while strictly satisfying system constraints. In addition, based on normal distribution and adaptive parameters, an improved particle swarm optimization algorithm with great search performance is developed to address the motion planning problem in the warning subspace. The proposed path optimization framework can effectively address the highly nonlinear kinodynamic motion planning problem for multisegment continuum manipulators. Numerical simulations for obstacle-avoidance motion planning of multisegment continuum manipulators are conducted to illustrate the effectiveness and advantages of the proposed method.

In rigid lower-mobility parallel manipulators the motion of the end-effector is partially constrained due to a combination of passive kinematic pairs and rigid components. Translational mechanisms, such as the Delta manipulator, are the most common ones among this type of mechanisms. When flexible elements are introduced, as in Parallel Continuum Manipulators, the constraint is no longer rigid, and new challenges arise in performing certain motions depending on the degree of compliance. Mobility analysis shifts from being purely a geometric issue to one that heavily relies on force distribution within the mechanism. Simply converting classical lower-mobility rigid parallel mechanisms into Parallel Continuum Mechanisms may yield unexpected outcomes. This work, making use of a planar parallel continuum Delta manipulator, on the one hand, presents two different approaches to solve the Forward Kinematics of planar continuum manipulators, and, on the other hand, explores some challenges and issues in assessing the resultant workspace for different design alternatives of this kind of flexible manipulators.