Recent Advances in Design and Actuation of Continuum Robots for Medical Applications

Chorda Dorsalis System as a Paragon for Soft Medical Robots to Design Echocardiography Probes with a New SOM-Based Steering Control

Continuum robots play the role of end effectors in various surgical robots and endoscopic devices. While soft continuum robots (SCRs) have proven advantages such as safety and compliance, more research and development are required to enhance their capability for specific medical scenarios. This research aims at designing a soft robot, considering the concepts of geometric and kinematic similarities. The chosen application is a semi-invasive medical application known as transesophageal echocardiography (TEE). The feasibility of fabrication of a soft endoscopic device derived from the Chorda dorsalis paragon was shown empirically by producing a three-segment pneumatic SCR. The main novelties include bioinspired design, modeling, and a navigation control strategy presented as a novel algorithm to maintain a kinematic similarity between the soft robot and the rigid counterpart. The kinematic model was derived based on the method of transformation matrices, and an algorithm based on a self-organizing map (SOM) network was developed and applied to realize kinematic similarity. The simulation results indicate that the control method forces the soft robot tip to follow the path of the rigid probe within the prescribed distance error (5 mm). The solution provides a soft robot that can surrogate and succeed the traditional rigid counterpart owing to size, workspace, and kinematics.

Modeling and experimental analysis of wire-driven continuum surgical robot

A new configuration of continuum surgical robot is proposed, whose skeleton is composed of inner and outer layers. The outer layer is composed of miniature rotating modules connected in series and connected by orthogonal hinges, which can ensure the ability to resist unconventional torsion without losing the degree of freedom. The inner layer is a central support column with superelasticity. When bending, its superelasticity can make the overall configuration biased toward constant curvature bending, which is convenient for motion control and according to the new configuration, this paper establishes the kinematics model of the robot. Finally, the motion control experiment of the continuum robot is carried out. After the experiment, the average positioning error of the robot is 2.674 mm, and the average repetitive positioning error is 2.625 mm. Both are less than 2 % of the robot length, verifying the accuracy of the model.

Design and Development of a Continuum Robot with Switching-Stiffness

Continuum robots have the advantages of agility and adaptability. However, existing continuum robots have limitations of low stiffness and complex motion modes, and the existing variable stiffness methods cannot achieve a wide range of stiffness changes and fast switching stiffness simultaneously. A continuum robot structure, switching stiffness method, and motion principle are proposed in this article. The continuum robot is made up of three segments connected in series. Each segment comprises multiple spherical joints connected in series, and the joints can be locked by their respective airbag. A valve controls each airbag, quickly switching the segment between rigidity and flexibility. The motion of the segments is driven by three cables that run through the robot. The segment steers only when it is unlocked. When a segment becomes locked, it acts as a rigid body. As a result, by locking and unlocking each segment in sequence, the cables can alternately drive all the segments. The stiffness variation and movement of the continuum robot were tested. The segment's stiffness varies from 36.89 to 1300.95 N/m and the stiffness switching time is 0.25-0.48 s. The time-sharing control mode of segment stiffness and motion is validated by establishing a specific test platform and a mathematical model. The continuum robot's flexibility is demonstrated by controlling the fast bending of different segments sequentially.

Research on Self-Stiffness Adjustment of Growth-Controllable Continuum Robot (GCCR) Based on Elastic Force Transmission

Continuum robots have good adaptability in unstructured and complex environments. However, affected by their inherent nature of flexibility and slender structure, there are challenges in high-precision motion and load. Thus, stiffness adjustment for continuum robots has consistently attracted the attention of researchers. In this paper, a stiffness adjustment mechanism (SAM) is proposed and built in a growth-controllable continuum robot (GCCR) to improve the motion accuracy in variable scale motion. The self-stiffness adjustment is realized by antagonism through cable force transmission during the length change of the continuum robot. With a simple structure, the mechanism has a scarce impact on the weight and mass distribution of the robot and required no independent actuators for stiffness adjustment. Following this, a static model considering gravity and end load is established. The presented theoretical static model is applicable to predict the shape deformations of robots under different loads. The experimental validations showed that the maximum error ratio is within 5.65%. The stiffness of the robot can be enhanced by nearly 79.6%.

Bioinspiration and Biomimetic Art in Robotic Grippers

The autonomous manipulation of objects by robotic grippers has made significant strides in enhancing both human daily life and various industries. Within a brief span, a multitude of research endeavours and gripper designs have emerged, drawing inspiration primarily from biological mechanisms. It is within this context that our study takes centre stage, with the aim of conducting a meticulous review of bioinspired grippers. This exploration involved a nuanced classification framework encompassing a range of parameters, including operating principles, material compositions, actuation methods, design intricacies, fabrication techniques, and the multifaceted applications into which these grippers seamlessly integrate. Our comprehensive investigation unveiled gripper designs that brim with a depth of intricacy, rendering them indispensable across a spectrum of real-world scenarios. These bioinspired grippers with a predominant emphasis on animal-inspired solutions have become pivotal tools that not only mirror nature's genius but also significantly enrich various domains through their versatility.

Design of a Novel Haptic Joystick for the Teleoperation of Continuum-Mechanism-Based Medical Robots

Continuum robots are increasingly used in medical applications and the master–slave-based architectures are still the most important mode of operation in human–machine interaction. However, the existing master control devices are not fully suitable for either the mechanical mechanism or the control method. This study proposes a brand-new, four-degree-of-freedom haptic joystick whose main control stick could rotate around a fixed point. The rotational inertia is reduced by mounting all powertrain components on the base plane. Based on the design, kinematic and static models are proposed for position perception and force output analysis, while at the same time gravity compensation is also performed to calibrate the system. Using a continuum-mechanism-based trans-esophageal ultrasound robot as the test platform, a master–slave teleoperation scheme with position–velocity mapping and variable impedance control is proposed to integrate the speed regulation on the master side and the force perception on the slave side. The experimental results show that the main accuracy of the design is within 1.6°. The workspace of the control sticks is −60° to 110° in pitch angle, −40° to 40° in yaw angle, −180° to 180° in roll angle, and −90° to 90° in translation angle. The standard deviation of force output is within 8% of the full range, and the mean absolute error is 1.36°/s for speed control and 0.055 N for force feedback. Based on this evidence, it is believed that the proposed haptic joystick is a good addition to the existing work in the field with well-developed and effective features to enable the teleoperation of continuum robots for medical applications.

Flexible Needle Steering with Tethered and Untethered Actuation: Current States, Targeting Errors, Challenges and Opportunities

Accurate needle targeting is critical for many clinical procedures, such as transcutaneous biopsy or radiofrequency ablation of tumors. However, targeting errors may arise, limiting the widespread adoption of these procedures. Advances in flexible needle (FN) steering are emerging to mitigate these errors. This review summarizes the state-of-the-art developments of FNs and addresses possible targeting errors that can be overcome with steering actuation techniques. FN steering techniques can be classified as passive and active. Passive steering directly results from the needle-tissue interaction forces, whereas active steering requires additional forces to be applied at the needle tip, which enhances needle steerability. Therefore, the corresponding targeting errors of most passive FNs and active FNs are between 1 and 2 mm, and less than 1 mm, respectively. However, the diameters of active FNs range from 1.42 to 12 mm, which is larger than the passive steering needle varying from 0.5 to 1.4 mm. Therefore, the development of active FNs is an area of active research. These active FNs can be steered using tethered internal direct actuation or untethered external actuation. Examples of tethered internal direct actuation include tendon-driven, longitudinal segment transmission and concentric tube transmission. Tendon-driven FNs have various structures, and longitudinal segment transmission needles could be adapted to reduce tissue damage. Additionally, concentric tube needles have immediate advantages and clinical applications in natural orifice surgery. Magnetic actuation enables active FN steering with untethered external actuation and facilitates miniaturization. The challenges faced in the fabrication, sensing, and actuation methods of FN are analyzed. Finally, bio-inspired FNs may offer solutions to address the challenges faced in FN active steering mechanisms.

Collaborative Continuum Robots for Remote Engineering Operations

In situ repair and maintenance of high-value industrial equipment is critical if they are to maintain the ability to continue vital operations. Conventional single-arm continuum robots have been proven numerous times to be successful tools for use in repair operations. However, often more than one arm is needed to ensure successful operation within several scenarios; thus, the collaborative operation of multiple arms is required. Here, we present the design and operating principles of a dual-arm continuum robot system designed to perform critical tasks within industrial settings. Here, presented are the design principle of the robotic system, the optimization-based inverse kinematic calculation of the 6-DoF continuum arms, and the collaborative operation strategy. The collaborative principle and algorithms used have been evaluated by a set of experiments to demonstrate the ability of the system to perform in situ machining operations. With the developed prototype and controller, the average error between planned and real toolpaths can be within 2.5 mm.

Progress in Control-Actuation Robotic System for Gastrointestinal NOTES Development

Purpose

Natural orifice transluminal endoscopic surgery (NOTES) is a minimally invasive surgical procedure that reduces patient trauma, infection probability, and rehabilitation time. This paper reviews the progress made in the control-actuation robotic systems for gastrointestinal NOTES development. Material and Methods. A survey on both existing and state-of-the-art control-actuation robotic systems for gastrointestinal NOTES was conducted in December 2021.

Results

Nine control-actuation robotic systems for gastrointestinal NOTES were identified. The structures and specifications of these robotic systems were reported. The technical parameters were also discussed. Special attention was directed to systems using a control-actuation structure and tendon-driven mechanism. The control-actuation robotic systems typically deploy a control-actuation structure and tendon-driven mechanism. Control-actuation robotic systems for gastrointestinal NOTES show great ability to improve operational accuracy and flexibility and flatten the learning curve of procedures. These characteristics suggest that the use of control-actuation robotic systems is worth exploring in future development.

Aerial Continuum Manipulation: A New Platform for Compliant Aerial Manipulation

Traditional aerial manipulation systems were usually composed of rigid-link manipulators attached to an aerial platform, arising several rigidity-related issues such as difficulties of reach, compliant motion, adaptability to object’s shape and pose uncertainties, and safety of human-manipulator interactions, especially in unstructured and confined environments. To address these issues, partially compliant manipulators, composed of rigid links and compliant/flexible joints, were proposed; however, they still suffer from insufficient dexterity and maneuverability. In this article, a new set of compliant aerial manipulators is suggested. For this purpose, the concept of aerial continuum manipulation system (ACMS) is introduced, several conceptual configurations are proposed, and the functionalities of ACMSs for different applications are discussed. Then, the performances of proposed aerial manipulators are compared with conventional aerial manipulators by implementing available benchmarks in the literature. To enhance the comparison, new features with related benchmarks are presented and used for evaluation purposes. In this study, the advantages of ACMSs over their rigid-link counterparts are illustrated and the potential applications of ACMSs are suggested. The open problems such as those related to dynamic coupling and control of ACMSs are also highlighted.

Optimal locomotion for limbless crawlers

Limbless crawling is ubiquitous in biology, from cells to organisms. We develop and analyze a model for the dynamics of one-dimensional elastic crawlers, subject to active stress and deformation-dependent friction with the substrate. We find that the optimal active stress distribution that maximizes the crawler's center-of-mass displacement given a fixed amount of energy input is a traveling wave. This theoretical optimum corresponds to peristalsislike extension-contraction waves observed in biological organisms, possibly explaining the prevalence of peristalsis as a convergent gait across species. Our theory elucidates key observations in biological systems connecting the anchoring phase of a crawler to the retrograde and prograde distinction seen in peristaltic waves among various organisms. Using our optimal gait solution, we derive a scaling relation between the crawling speed and body mass, explaining experiments on earthworms with three orders of magnitude body mass variations. Our results offer insights and tools for optimal bioinspired crawling robots design with finite battery capacity.

A Survey on Design, Actuation, Modeling, and Control of Continuum Robot

In this paper, we describe the advances in the design, actuation, modeling, and control field of continuum robots. After decades of pioneering research, many innovative structural design and actuation methods have arisen. Untethered magnetic robots are a good example; its external actuation characteristic allows for miniaturization, and they have gotten a lot of interest from academics. Furthermore, continuum robots with proprioceptive abilities are also studied. In modeling, modeling approaches based on continuum mechanics and geometric shaping hypothesis have made significant progress after years of research. Geometric exact continuum mechanics yields apparent computing efficiency via discrete modeling when combined with numerical analytic methods such that many effective model-based control methods have been realized. In the control, closed-loop and hybrid control methods offer great accuracy and resilience of motion control when combined with sensor feedback information. On the other hand, the advancement of machine learning has made modeling and control of continuum robots easier. The data-driven modeling technique simplifies modeling and improves anti-interference and generalization abilities. This paper discusses the current development and challenges of continuum robots in the above fields and provides prospects for the future.

3D Printing in Combined Cartesian and Curvilinear Coordinates

A 3D printing technology that facilitates continuous printing along a combination of cartesian and curvilinear coordinates, designed for in vivo and in situ bioprinting is introduced. The combined cartesian/curvilinear printing head motion is accomplished by attaching a biomimetic, flexible, "tendon cable" soft robot arm to a conventional cartesian three axis 3D printing carousel. This allows printing along a combination of cartesian and curvilinear coordinates using five independent stepper motors controlled by an Arduino Uno with each motor requiring a microstep driver powered via a 12V power supply. Three of the independent motors control the printing head motion along conventional cartesian coordinates while two of the independent motors control the length of each pair of the four "tendon cables" which in turn controls the radius of curvature and the angle displacement of the soft printer head along two orthogonal planes. This combination imparts motion along six independent degrees of freedom in cartesian and curvilinear coordinates. The design of the system is described together with experimental results which demonstrate that this design can print continuously along curved and inclined surfaces while avoiding the "staircase" effect, which is typical of conventional three axis 3D printing along curvilinear surfaces.

Systematic Design of a 3-DOF Dual-Segment Continuum Robot for In Situ Maintenance in Nuclear Power Plants

In situ maintenance works for nuclear power plants are highly beneficial as they can significantly reduce the current maintenance cycle and cost. However, removing absorber balls in a constrained environment through an inspection port is fairly challenging. In this article, a 3-DOF dual-segment continuum robot system is proposed which is equipped with an end-effector to remove absorber balls by pneumatic conveying. Then, according to the symmetrical layout of actuation ropes, the kinematics of the single-segment continuum robot are extended, and the kinematics equation which is universal to the continuum robot with the dual segment is summarized. In addition, some special kinematics solutions can be obtained according to opposite-bending and feeding characteristics. Finally, the functions of the device are verified by tests. The results show that the continuum robot can smoothly pass through the divider plug and reach any position at the bottom of a ball-storage tank where absorber balls are located with only two segments. In a gas environment, the efficiency of absorber ball removal can reach 58.96 kg/h with a lift of 7.5 m and 48.54 kg/h with a lift of 10 m. This result undoubtedly paves the way for the in-service maintenance of nuclear power plants.

Visual servoing of continuum robots: Methods, challenges, and prospects

BACKGROUND

Recent advancements in continuum robotics have accentuated developing efficient and stable controllers to handle shape deformation and compliance. The control of continuum robots (CRs) using physical sensors attached to the robot, particularly in confined spaces, is difficult due to their limited accuracy in three-dimensional deflections and challenging localisation. Therefore, using non-contact imaging sensors finds noticeable importance, particularly in medical scenarios. Accordingly, given the need for direct control of the robot tip and notable uncertainties in the kinematics and dynamics of CRs, many papers have focussed on the visual servoing (VS) of CRs in recent years.

METHODS

The significance of this research towards safe human-robot interaction has fuelled our survey on the previous methods, current challenges, and future opportunities.

RESULTS

Beginning with actuation modalities and modelling approaches, the paper investigates VS methods in medical and non-medical scenarios.

CONCLUSIONS

Finally, challenges and prospects of VS for CRs are discussed, followed by concluding remarks.

Shape Reconstruction Processes for Interventional Application Devices: State of the Art, Progress, and Future Directions

Soft and continuum robots are transforming medical interventions thanks to their flexibility, miniaturization, and multidirectional movement abilities. Although flexibility enables reaching targets in unstructured and dynamic environments, it also creates challenges for control, especially due to interactions with the anatomy. Thus, in recent years lots of efforts have been devoted for the development of shape reconstruction methods, with the advancement of different kinematic models, sensors, and imaging techniques. These methods can increase the performance of the control action as well as provide the tip position of robotic manipulators relative to the anatomy. Each method, however, has its advantages and disadvantages and can be worthwhile in different situations. For example, electromagnetic (EM) and Fiber Bragg Grating (FBG) sensor-based shape reconstruction methods can be used in small-scale robots due to their advantages thanks to miniaturization, fast response, and high sensitivity. Yet, the problem of electromagnetic interference in the case of EM sensors, and poor response to high strains in the case of FBG sensors need to be considered. To help the reader make a suitable choice, this paper presents a review of recent progress on shape reconstruction methods, based on a systematic literature search, excluding pure kinematic models. Methods are classified into two categories. First, sensor-based techniques are presented that discuss the use of various sensors such as FBG, EM, and passive stretchable sensors for reconstructing the shape of the robots. Second, imaging-based methods are discussed that utilize images from different imaging systems such as fluoroscopy, endoscopy cameras, and ultrasound for the shape reconstruction process. The applicability, benefits, and limitations of each method are discussed. Finally, the paper draws some future promising directions for the enhancement of the shape reconstruction methods by discussing open questions and alternative methods.

Micro and nanorobot-based drug delivery: an overview

Progress in the drug delivery system in the last few decades has led to many advancements for efficient drug delivery. Both micro and nanorobots, are regarded as superior drug delivery systems to deliver drugs efficiently by altering other forms of energy into propulsion and movements. Furthermore, it can be advantageous as it is directed to targeted sites beneath physiological environments and conditions. They have been validated to possess the capability to encapsulate, transport, and supply therapeutic contents directly to the disease sites, thus enhancing the therapeutic efficiency and decreasing systemic side effects of the toxic drugs. This review discusses about the microand nanorobots for the diagnostics and management of diseases, types of micro, and nanorobots, role of robots in drug delivery, and its biomedical applications.