A Structure for Fast Stiffness-Variation and Omnidirectional-Steering Continuum Manipulator

Continuum robots, owing to their inherent compliance, have become essential in endoscopic surgical procedures, such as mucosal ablation. However, the prevalent design of endoscopic manipulators, which typically features only a single active bending segment, often results in limited dexterity and accessibility. Additionally, the incorporation of variable stiffness in these robots has attracted significant interest, with the aim to improve manipulation capabilities in confined spaces. In the paper, we propose a novel variable-length continuum robot with variable stiffness for endoscopic surgery. The robot’s stiffness can be altered either by modifying the catheter’s length or solid-liquid transition of low-melting-point alloy (LMPA). The design and fabrication methods of the robot are meticulously detailed. Additionally, a quasi-static stiffness model along with a learning-based stiffness compensation approach for accurate stiffness estimation are proposed. Leveraging this model, a contact force controller is designed for ablation procedure. The experimental results show that our robot possesses good flexibility and accessibility, making it highly adept at manipulating in confined spaces. Its variable stiffness feature significantly enhances its ability to counteract external disturbance and prevent tip deformation (with a average position change of 1.1mm). Finally, through force control experiments and a surgical demonstration in a gastrointestinal model, we have further validated the robot’s applicability in surgical contexts. Note to Practitioners—This paper proposed a variable-length continuum robot with variable stiffness for endoscopic surgery. The robot can achieve axial elongation and omnidirectional bending motion, having better dexterity and accessibility than traditional medical continuum robots with one active bending segment. The robot’s stiffness can be adjusted by the length changes or solid-liquid transition of low-melting-point alloy (LMPA). Besides, an accurate stiffness model and a contact force controller are proposed for endoscopic ablation surgery. By experimental results, the robot shows high flexibility and accessibility, allowing access to confined spaces for manipulation, and good control accuracy and variable stiffness capability for endoscopic surgery.

Rigid instruments with limited flexibility utilized in the traditional endoscopic sinus surgery maybe damage the tissue when surgeon operates in the narrow space of nose specific area. Flexible continuum manipulator would solve this issue. However, current manipulators may not be able to address the intricate and varied surgical demands effectively, and they may not meet the surgical requirements adequately in terms of the flexibility, precision, and stiffness. This article introduced a novel modular continuum manipulator designed to offer exceptional adaptability, precision, and adjustable stiffness. The various sizes of the manipulators could be optimized according to different surgical scenario while taking its flexibility into account. Moreover, the model-based estimation and feedforward compensation control were applied to enhance its precision, taking into account the coupling effect of two sections and friction loss. Additionally, this study introduced a theoretical analysis on the feasibility of implementing variable stiffness for the manipulator, and the coupling was also lessened via increasing the stiffness of the first section. The experiments demonstrated that the maximum average deviation observed was 3.43 mm, which is equivalent to just 2.5% of the total length of the manipulator. Furthermore, the stiffness could be enhanced by up to 75%. Therefore, the proposed flexible manipulator has a potential for the nasal minimally invasive surgery.

There is an increasingly popularity for the continuum robot in minimally invasive surgery(MIS), because of the compliance and dexterity. In the first place, a variable stiffness manipulator can resolve the two contradictions of the demands for predominant flexibility and strong payload capacity. In the second place, to control the continuum robot more precisely and avoid the collision between robot and human body, real-time tracking of the shape of the continuum robot is of great significance. A new type of flexible manipulator with variable stiffness is proposed which can track the bending shape timely. The low-melting-point-alloy (LMPA) is used to realize the variable stiffness and shape detection for the flexible manipulator. The concept design for a single module is put forward. Then the stiffness control method and finite element simulation, the method of shape detection are presented. Moreover, the presented method of shape detection is evaluated by experiments.

Soft robots have advantages such as low weight and compact size compared to rigid robots. Variable stiffness is one of the key methods of improving the performance of a soft robot. The soft gripper grasps objects of various shapes or sizes based on the variable stiffness. In a previous study, we validated the variable stiffness mechanism where flexible and rigid segments were connected alternately in series. This paper presents a soft variable stiffness gripper that can be used to control the stiffness by pulling tendons. The soft gripper has three variable stiffness structures acting as fingers and the stiffness can be controlled using two motors by winding tendons. To understand the tendency of the stiffness variation and determine the design parameters, a compliant mechanism was developed using a pseudo-rigid-body model (PRBM). The experimental results show that the difference between the lowest and highest stiffness values of the fabricated variable stiffness gripper was 5.6 times the original. Similarly, the difference in the gripping weight was 19 times. Using the experimental results, the variable stiffness gripper can be designed and manufactured based on the required stiffness and used to grip various types of objects.

Snake-like manipulators can navigate and perform manipulation in confined spaces. Their recent implementations in surgical robots attracted a lot of attentions. These slender manipulators usually possess either a hyper-redundant articulated vertebrate structure or a continuum one. Primary design considerations usually converge to a balance between proper workspace and acceptable stiffness. Efforts have hence been constantly made to achieve higher or adjustable stiffness for a manipulator to widen its applications. This paper presents a simple continuum manipulator design with variable stiffness based on redundantly arranged elastic backbones and continuously constrained bending curvature. The design concepts, kinematics, a preliminary formulation for stiffness adjustment, system construction and experimental characterizations are elaborated. The results showed that the manipulator's stiffness can be increased up to 4.71 times of the value without the curvature constraining rod, indicating the efficacy of the proposed idea.

Switchable adhesion with a high tuning ratio achieved on polymer surfaces with embedded low-melting-point alloy

Shape memory alloys (SMAs) or shape memory polymers (SMPs) enable soft actuators to achieve advanced adaptabilities applied in soft robotics. However, actuators that combine multiple shape memory materials struggle to achieve complex deformation effects and stiffness variations with effective control strategies. To achieve controllable, shape adaptation, and programmed deforming behavior, this study proposes an integrated control strategy for an SMA-SMP based programmable morphing structure used as an actuator in soft robotics. To achieve precise control over programming deformations and stiffness variation, a multi-target thermal sensing method (MTTSM) was proposed, integrated into an interaction-driven control framework. Based on MTTSM, the coordinated actuation between the SMA springs and the SMP structure is realized, enabling standby of preheating, stepping with programmed deformations, and dynamic stiffness changes. In addition, to achieve dynamic monitoring of deformed states, the co-training-based monitoring system is developed for collaboration, enabling the use of multisensor fusion for position estimation in the absence of end-effectors that can directly measure the deformed structure of the flexible body. In conclusion, the proposed integration strategy of MTTSM and the cotraining monitoring system offers a control solution for integrating multiple shape memory materials into morphing structures as smart actuators applied to soft robotic applications.

The soft robot is a kind of continuum robot, which is mainly made of soft elastic material or malleable material. It can be continuously deformed in a limited space, and can obtain energy in large bending or high curvature distortion. It has obvious advantages such as high security of human-computer interaction, strong adaptability of unstructured environment, high driving efficiency, low maintenance cost, etc. It has wide application prospects in the fields of industrial production, defense military, medical rehabilitation, exploration, and so on. From the perspective of the bionic mechanism, this paper introduces the soft robots corresponding to insect crawling, snake crawling, fish swimming, elephant trunk, arm, etc. According to different driving modes, the soft robots can be classified into pneumatic-hydraulic driven, intelligent material driven, chemical reaction driven, and so on. The mechanical modeling, control strategy, material, and manufacturing methods of soft robot are summarized, and the application fields of soft robot are introduced. This paper analyzes the main challenges faced by the research on the key technologies of soft robots, summarizes and analyzes them, and puts forward the prospects for the future research of soft robots. The development trend of the future is to develop the soft robot with the characteristics of micro-scale, rigid-flexible coupling, variable stiffness, multi-functional, high integration, and intelligence of driving sensor control.

The main objective of this paper is to evaluate the capabilities of the non-destructive impact-response method in detecting the existence of defects in piles with high slenderness ratio. The impact-echo technique was developed many years ago for non-destructive detection of defects in piles and structures. However, it is recognised that this method could be applied confidently for piles with length/diameter relationship up to 20. In the last years, with the development of hardware in computers and sensors, it is now possible to use this method for piles with high slenderness ratio. In this paper, piles of length/diameter relationship of about 40 are studied. A numerical-experimental study was carried out. It was shown that the results of the experiment were in agreement with those of the numerical studies and the accuracy of the impact-echo method was influenced by the type, size and location of the defects. Taking into account the uncertainties related to the studied problem, the obtained results preliminarily allow consider this NDT methodology as a promissory alternative to detect defects in piles with high slenderness ratio.

Soft robots have become increasingly prevalent in today's AI era due to their ability to meet the specialized needs and technological advancements that rigid robots cannot. Soft robots are characterized by their flexibility, deformability, and variable stiffness, which greatly compensate for the limitations of rigid robots in specialized environments. This chapter aims to provide extensive examples of how soft robots are being applied in various areas including underwater exploration, agriculture, medicine, industry and space. The chapter will discuss the types of soft robots, their movement characteristics, driving methods, and the advantages they bring to different applications. By showcasing the vast potential and research value of soft robots, this chapter underscores their significant role in promoting technological innovation and societal progress.

Inspired by the physiological structure of the hand capable of realizing the continuous change in finger stiffness when grasping objects of different masses, a self-locking soft continuum robot with a large variable-stiffness range based on particle jamming and fibre jamming is proposed in this paper to meet the requirements of it in practical application. In this paper, a variable stiffness range is derived due to the good fluidity and rigidity of the spherical particles and the low elasticity and high toughness of the fibres. Then, an analysis model is established to deduce its self-locking condition, and the deflection angle of self-locking under the influence of external force is about 0.17 rad. The maximum stiffness of the experimental prototype can reach 1223.58 N m−1 due to the limitation of the experimental materials, despite the fact that the theoretical stiffness can be increased infinitely after self-locking. To explain the adaptability of the robot, the adaptive conditions of the soft continuum robot with variable stiffness are deduced. A new evaluation index, the adaptive intensity of the soft continuum robot, is introduced and the adaptability experiments are carried out. In adaptability experiments, the maximum bending angle of the continuum robot reaches 108°. Finally, the adaptability of the soft continuum robot to different geometries is discussed.

Variable stiffness mechanisms as Jamming Transition draw huge attention recently in Soft Robotics. This paper proposes a comprehensive design methodology for developing variable stiffness devices based on layer jamming. Starting from pre-existing modelling, we highlight the design parameters that should be considered, extracting them from literature and our direct experience with the phenomenon. Then we validated the methodology applying the design process to previous layer jamming cases presented in literature. The comparison between the results obtained from our methodology and those presented in the analyzed previous works highlights a good predictive capability, demonstrating that this methodology can be used as a valid tool to design variable stiffness devices based on layer jamming transition. Finally, in order to provide the scientific community with an easily usable tool to design variable stiffness structures based on layer jamming transition, we have elaborated a Matlab script that guides the user through the main design parameters implementing the proposed methodology in an interactive process.

Grippers based on fluid elastomer actuators have shown their ability to manipulate fragile and delicate objects. However, they cannot resist large external force due to their soft material and compliant structure, leading to an unstable or even failed grasp. Low stiffness has limited their applicability. In this paper, we propose a soft robotic finger based on multimaterial 3D printing and layer jamming to achieve varied finger bending motion and variable stiffness. The proposed finger has two DoF, including two pneumatic actuators (top actuator and bottom actuator) and each with an integrated layer jamming unit. A prototype of the proposed finger is directly printed out by an Object350Connex 3D printer without requiring an additional casting process. The finger’s bending angle and stiffness can be controlled due to the novel actuator design. Experiments were carried out to exam the finger’s bending angles. Four finger motion can be achieved and the stiffness of the finger is increased with the aid of the layer jamming mechanism. Multi-material 3D printing technique can provide flexibility to the design of soft robotics, shorten the fabrication process and offer a range of materials to achieve desired mechanical properties.

In this paper, the design and testing of a novel valve for the intuitive spatial control of soft or continuum manipulators are presented. The design of the valve is based on the style of a hydraulic flapper valve, but with simultaneous control of three pressure feed points, which can be used to drive three antagonistically arranged hydraulic actuators for positioning soft robots. The variable control orifices are arranged in a rotationally symmetric radial pattern to allow for an inline mounting configuration of the valve within the body of a manipulator. Positioning the valve ring at various 3D configurations results in different pressurizations of the actuators and corresponding spatial configurations of the manipulator. The design of the valve is suitable for miniaturization and use in applications with size constraints such as small soft manipulators and surgical robotics. Experimental validation showed that the performance of the valve can be reasonably modeled and can effectively drive an antagonistic arrangement of three actuators for soft manipulator control.

Smart material based variable internal connectivity has the potential to overcome the inherent conflicting requirements of lightweight shape adaptable structures by reducing the actuation force required for shape adaptation, and, consequently, volume and mass of the actuation system, by increasing the compliance of the structure temporarily. In this paper, we consider shape adaptable sandwich panels with a truss core and implement smart material based variable connections, called mechanical switches, in the trusses of the core. We present three concepts of mechanical switches based on electro-bonded laminates, dielectric elastomer actuators and shape memory alloys, and evaluate their performance in terms of variation in stiffness and in maximum transferable force. Based on these results, we show how the implementation of variable connections in the core trusses can be used to reduce the actuation force by different orders of magnitude for three simple types of deformation of the panel: change in thickness, in transverse shear angle and bending. Further, considering the influence of the mechanical switches on the out-of-plane stiffness of the core, we demonstrate that this approach can be used to obtain changes in thickness of the panel, a kind of deformation that is not possible to obtain with other approaches found in literature. Moreover, we show that mechanical switches can be used to selectively vary the shear stiffness of the panel in the desired direction. Finally, we analyze the limitations of this technology in terms of mechanical properties in order to identify possible applications.