Tendon-driven continuum robot for neuroendoscopy: validation of extended kinematic mapping for hysteresis operation

A Fast Soft Continuum Catheter Robot Manufacturing Strategy Based on Heterogeneous Modular Magnetic Units

Developing small-scale continuum catheter robots with inherent soft bodies and high adaptability to different environments holds great promise for biomedical engineering applications. However, current reports indicate that these robots meet challenges when it comes to quick and flexible fabrication with simpler processing components. Herein, we report a millimeter-scale magnetic-polymer-based modular continuum catheter robot (MMCCR) that is capable of performing multifarious bending through a fast and general modular fabrication strategy. By preprogramming the magnetization directions of two types of simple magnetic units, the assembled MMCCR with three discrete magnetic sections could be transformed from a single curvature pose with a large tender angle to a multicurvature S shape in the applied magnetic field. Through static and dynamic deformation analyses for MMCCRs, high adaptability to varied confined spaces can be predicted. By employing a bronchial tree phantom, the proposed MMCCRs demonstrated their capability to adaptively access different channels, even those with challenging geometries that require large bending angles and unique S-shaped contours. The proposed MMCCRs and the fabrication strategy shine new light on the design and development of magnetic continuum robots with versatile deformation styles, which would further enrich broad potential applications in biomedical engineering.

A Survey of Transoral Robotic Mechanisms: Distal Dexterity, Variable Stiffness, and Triangulation

Robot-assisted technologies are being investigated to overcome the limitations of the current solutions for transoral surgeries, which suffer from constrained insertion ports, lengthy and indirect passageways, and narrow anatomical structures. This paper reviews distal dexterity mechanisms, variable stiffness mechanisms, and triangulation mechanisms, which are closely related to the specific technical challenges of transoral robotic surgery (TORS). According to the structure features in moving and orienting end effectors, the distal dexterity designs can be classified into 4 categories: serial mechanism, continuum mechanism, parallel mechanism, and hybrid mechanism. To ensure adequate adaptability, conformability, and safety, surgical robots must have high flexibility, which can be achieved by varying the stiffness. Variable stiffness (VS) mechanisms based on their working principles in TORS include phase-transition-based VS mechanism, jamming-based VS mechanism, and structure-based VS mechanism. Triangulations aim to obtain enough workspace and create adequate traction and counter traction for various operations, including visualization, retraction, dissection, and suturing, with independently controllable manipulators. The merits and demerits of these designs are discussed to provide a reference for developing new surgical robotic systems (SRSs) capable of overcoming the limitations of existing systems and addressing challenges imposed by TORS procedures.

Modeling and control of cable-driven continuum robot used for minimally invasive surgery

Continuum robot has great advantages in minimally invasive surgery (MIS) due to the slenderness and dexterity. But the friction and backlash result in the low trajectory tracking accuracy. This paper aims to study the transmission process of the driving force and the error compensation method. The statics is performed considering the frictional transmission process, and the variation of friction force with driving force is revealed by the model. The hysteresis effect of the tip trajectory is revealed. Then the relationship between the load history and the robot shape is studied, next, the deflection of the robot subject to the different loading forces can be predicted. The correctness of the mechanical model is verified by numerical simulation and experiments. Furthermore, the control methods according to the cable length and the driving force are compared respectively, and a method of error compensation according to the cable length is worked out considering the mechanical model. The rationality of the compensation method is validated by experiment. The results show that the compensation method based on cable length greatly improves the control accuracy, and the maximum deviation is 1.08 mm. The established model and compensation method create conditions for clinical application of the proposed continuum robot.

Design and kinematics of a tube-shaped multidirectional bending robotic device using slackened SMA wires for transurethral ureterolithotripsy

PURPOSE

The complex and elaborate structure of the urinary system presents surgeons with difficulty in using a ureteroscope with a fixed optical fiber to reach the targeted calculus. To address this challenge, a robotic device is required to control the direction of laser irradiation position independently in ureteroscopes.

METHOD

A continuum robotic device was designed and fabricated. The device is constructed with three slackened shape memory alloy (SMA) wires to control the laser irradiation position of the optical fiber combined with the view of the camera on the tip of the ureteroscope. Kinematics analysis and experimental evaluation reveal the capability of the device.

RESULTS

The structure of the device is the same as a single-joint continuum robot. This device is unique because of the tiny diameter of 1.1 mm which can be used inside the ureteroscope through a Ø1.2 mm inner channel into the kidney for transurethral ureterolithotripsy. Kinematic analysis revealed the relationship among space coordinates, angles of bending, and direction and SMA wires length. The maximum bending angle was around 25° when the current value was 350 mA on a single SMA wire. The device could achieve multi-directional bending by allocating the values of current on SMA wires, separately.

CONCLUSION

This device offers a major advancement in small size and dexterity in medical robotics. Combined with a proper control system, this device could simplify the operation and improve the efficiency of the transurethral ureterolithotripsy.

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.

Equilibrium Conformation of a Novel Cable-Driven Snake-Arm Robot under External Loads

Based on the anti-parallelogram mechanism, an approximate cylindrical rolling joint is proposed to develop a novel cable-driven snake-arm robot with multiple degrees of freedom (DOF). Furthermore, the kinematics of the cable-driven snake-arm robot are established, and the mapping between actuator space and joint space is simplified by bending decoupling motion in the multiple segments. The workspace and bending configurations of the robot are obtained. The static model is established by the principle of minimum potential energy. Furthermore, the simplified cable constraints in the static model are proposed through Taylor expansion, which facilitates the equilibrium conformation analysis of the robot under different external forces. The cable-driven snake-arm robot prototype is developed to verify the feasibility of the robot design and the availability of the static model through the experiments of the free bending motion and the external load on the robot.

Snake Robots for Surgical Applications: A Review

Although substantial advancements have been achieved in robot-assisted surgery, the blueprint to existing snake robotics predominantly focuses on the preliminary structural design, control, and human–robot interfaces, with features which have not been particularly explored in the literature. This paper aims to conduct a review of planning and operation concepts of hyper-redundant serpentine robots for surgical use, as well as any future challenges and solutions for better manipulation. Current researchers in the field of the manufacture and navigation of snake robots have faced issues, such as a low dexterity of the end-effectors around delicate organs, state estimation and the lack of depth perception on two-dimensional screens. A wide range of robots have been analysed, such as the i²Snake robot, inspiring the use of force and position feedback, visual servoing and augmented reality (AR). We present the types of actuation methods, robot kinematics, dynamics, sensing, and prospects of AR integration in snake robots, whilst addressing their shortcomings to facilitate the surgeon’s task. For a smoother gait control, validation and optimization algorithms such as deep learning databases are examined to mitigate redundancy in module linkage backlash and accidental self-collision. In essence, we aim to provide an outlook on robot configurations during motion by enhancing their material compositions within anatomical biocompatibility standards.

Impact of Generic Tendon Routing on Tension Loss of Tendon-Driven Continuum Manipulators with Planar Deformation

We present a novel physically-intuitive mathematical formulation to investigate the effects of a fully-constrained generic tendon routing (GTR) on the correlation between tension loss and deformation behavior of a variable-curvature tendon-driven continuum manipulator (TD-CM). The proposed model can account for distributed friction forces/moments along a GTR path that have been typically ignored in the previous approaches (e.g., the well-known frictionless Cosserat rod model). For the first time, the internal distributed forces on a GTR are expressed using three physically-intuitive generic functions. Solely relying on the known actuation input(s), the proposed mathematical formulation can also solve the entangled and unknown correlation between GTR, internal distributed forces, tension loss and deformation behavior of TD-CMs. To evaluate the performance of the proposed approach, we performed various simulation studies using eight different GTR paths. Additionally, we fabricated two different types of TD-CMs with different GTRs to experimentally evaluate the efficacy and performance of the proposed mathematical framework. The results demonstrate the proposed model can successfully and accurately (i.e., about <10% error) capture the trends of substantial tension loss (e.g., about <50%) on fully constrained GTRs, which reveals the importance of considering tension loss in modeling these TD-CMs.

Design and Validation of a Novel Cable-Driven Hyper-Redundant Robot Based on Decoupled Joints

In most of the prior designs of conventional cable-driven hyper-redundant robots, the multiple degree-of-freedom (DOF) bending motion usually has bending coupling effects. It means that the rotation output of each DOF is controlled by multiple pairs of cable inputs. The bending coupling effect will increase the complexity of the driving mechanism and the risk of slack in the driving cables. To address these problems, a novel 2-DOF decoupled joint is proposed by adjusting the axes distribution of the universal joints. Based on the decoupled joint, a 4-DOF hyper-redundant robot with two segments is developed. The kinematic model of the robot is established, and the workspace is analyzed. To simplify the driving mechanism, a kinematic fitting approach is presented for both proximal and distal segments and the mapping between the actuator space and the joint space is significantly simplified. It also leads to the simplification of the driving mechanism and the control system. Furthermore, the cable-driven hyper-redundant robot prototype with multiple decoupled joints is established. The experiments on the robot prototype verify the advantages of the design.

Investigation of Micro-motion Kinematics of Continuum Robots for Volumetric OCT and OCT-guided Visual Servoing

Continuum robots (CR) have been recently shown capable of micron-scale motion resolutions. Such motions are achieved through equilibrium modulation using indirect actuation for altering either internal preload forces or changing the cross-sectional stiffness along the length of a continuum robot. Previously reported, but unexplained, turning point behavior is modeled using two approaches. An energy minimization approach is first used to explain the source of this behavior. Subsequently, a kinematic model using internal constraints in multi-backbone CRs is used to replicate this turning point behavior. An approach for modeling the micro-motion differential kinematics is presented using experimental data based on the solution of a system of linear matrix equations. This approach provides a closed-form approximation of the empirical micro-motion kinematics and could be easily used for real-time control. A motivating application of image-based biopsy using 3D optical coherence tomography (OCT) is envisioned and demonstrated in this paper. A system integration for generating OCT volumes by sweeping a custom B-mode OCT probe is presented. Results showing high accuracy in obtaining 3D OCT measurements are shown using a commercial OCT probe. Qualitative results using a miniature probe integrated within the robot are also shown. Finally, closed-loop visual servoing using OCT data is demonstrated for guiding a needle into an agar channel. Results of this paper present what we believe is the first embodiment of a continuum robot capable of micro and macro motion control for 3D OCT imaging. This approach can support the development of new technologies for CRs capable of surgical intervention and micro-motion for ultra-precision tasks.

Design and analysis of a continuum robot for transnasal skull base surgery

BACKGROUND

The traditional surgical instruments for transnasal endoscopic skull base surgery have poor flexibility and continuum robot has attracted extensive attention for its high dexterity and safety.

METHODS

A new type of micro continuum surgical robot is designed. On the basis of kinematic analysis, a superposition method is proposed to analyse the reachable configuration space of the system, and the workspace is analysed. The results obtained by superposition method can provide reference for the selection of joint parameters. At last, the static model of the system is established considering friction and coupling between two segments.

RESULTS

The simulation results show that the workspace can meet the requirements of surgery. And the validity of the static model is verified by numerical simulation and experiment, which lays a foundation for the establishment of the driving force transmission system and precise control of the robot.

CONCLUSIONS

The research results of this study contribute to the real-time control and movement of robot. The proposed continuum robot provides convenient conditions for the clinical application.

Miniature Flexible Instrument with Fibre Bragg Grating-Based Triaxial Force Sensing for Intraoperative Gastric Endomicroscopy

Optical biopsy methods, such as probe-based endomicroscopy, can be used to identify early-stage gastric cancer in vivo. However, it is difficult to scan a large area of the gastric mucosa for mosaicking during endoscopy. In this work, we propose a miniaturised flexible instrument based on contact-aided compliant mechanisms and fibre Bragg grating (FBG) sensing for intraoperative gastric endomicroscopy. The instrument has a compact design with an outer diameter of 2.7 mm, incorporating a central channel with a diameter of 1.9 mm for the endomicroscopic probe to pass through. Experimental results show that the instrument can achieve raster trajectory scanning over a large tissue surface with a positioning accuracy of 0.5 mm. The tip force sensor provides a 4.6 mN resolution for the axial force and 2.8 mN for transverse forces. Validation with random samples shows that the force sensor can provide consistent and accurate three-axis force detection. Endomicroscopic imaging experiments were conducted, and the flexible instrument performed no gap scanning (mosaicking area more than 3 mm²) and contact force monitoring during scanning, demonstrating the potential of the system in clinical applications.

How to Model Tendon-Driven Continuum Robots and Benchmark Modelling Performance

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.

Millimeter-Scale Soft Continuum Robots for Large-Angle and High-Precision Manipulation by Hybrid Actuation

Developing small-scale soft continuum robots with large-angle steering capacity and high-precision manipulation offers broad opportunities in various biomedical settings. However, existing continuum robots reach the bottleneck in actuation on account of the contradiction among small size, compliance actuation, large tender range, high precision, and small dynamic error. Herein, a 3D-printed millimeter-scale soft continuum robot with an ultrathin hollow skeleton wall (300 μm) and a large inner-to-outer ratio (0.8) is reported. After coating a thin ferromagnetic elastomer layer (≈100-150 μm), the proposed soft continuum robot equipped with hybrid actuation (tendon- and magnetic-driven mode) achieves large-angle (up to 100°) steering and high-precision (low to 2 μm for static positioning) micromanipulation simultaneously. Specifically, the robot implements an ultralow dynamic tracking error of ≈10 μm, which is ≈30-fold improved than the state of art. Combined with a microneedle/knife or nasopharyngeal swab, the robot reveals the potential for versatile biomedical applications, such as drug injection on the target tissue, diseased tissue ablation, and COVID-19 nasopharyngeal sampling. The proposed millimeter-scale soft continuum robot presents remarkable advances in large-range and high-precise actuation, which provides a new method for miniature continuum robot design and finds broad applications in biomedical engineering.

Surgical Robot for Intraluminal Access: An Ex Vivo Feasibility Study

Early-stage gastrointestinal cancer is often treated by endoscopic submucosal dissection (ESD) using a flexible endoscope. Compared with conventional percutaneous surgery, ESD is much less invasive and provides a high quality of life for the patient because it does not require a skin incision, and the organ is preserved. However, the operator must be highly skilled because ESD requires using a flexible endoscope with energy devices, which have limited degrees of freedom. To facilitate easier manipulation of these flexible devices, we developed a surgical robot comprising a flexible endoscope and two articulating instruments. The robotic system is based on a conventional flexible endoscope, and an extrapolated motor unit moves the endoscope in all its degrees of freedom. The instruments are thin enough to allow insertion of two instruments into the endoscope channel, and each instrument has a bending section that allows for up–down, right–left, and forward–backward motion. In this study, we performed an ex vivo feasibility evaluation using the proposed robotic system for ESD in a porcine stomach. The procedure was successfully performed by five novice operators without complications. Our findings demonstrated the feasibility of the proposed robotic system and, furthermore, suggest that even operators with limited experience can use this system to perform ESD.

Toward Task Autonomy in Robotic Cardiac Ablation: Learning-Based Kinematic Control of Soft Tendon-Driven Catheters

The goal of this study was to propose and validate a control framework with level-2 autonomy (task autonomy) for the control of flexible ablation catheters. To this end, a kinematic model for the flexible portion of typical ablation catheters was developed and a 40-mm-long spring-loaded flexible catheter was fabricated. The feasible space of the catheter was obtained experimentally. Furthermore, a robotic catheter intervention system was prototyped for controlling the length of the catheter tendons. The proposed control framework used a support vector machine classifier to determine the tendons to be driven, and a fully connected neural network regressor to determine the length of the tendons. The classifier and regressors were trained with the data from the feasible space. The control system was implemented in parallel at user-interface and firmware and exhibited a 0.4-s lag in following the input. The validation studies were four trajectory tracking and four target reaching experiments. The system was capable of tracking trajectories with an error of 0.49 ± 0.32 and 0.62 ± 0.36 mm in slow and fast trajectories, respectively. Also, it exhibited submillimeter accuracy in reaching three preplanned targets and ruling out one nonfeasible target autonomously. The results showed improved accuracy and repeatability of the position control compared with the recent literature. The proposed learning-based approach could be used in enabling task autonomy for catheter-based ablation therapies.

Positioning and stiffening of an articulated/continuum manipulator for implant delivery in minimally invasive surgery

BACKGROUND

Hollow, bendable manipulators can advance implant delivery in minimally invasive surgery, by circumventing the drawbacks of straight-line delivery and fostering single-port approaches. Variable stiffness manipulators are sought to be safe and effective.

METHODS

We designed and experimentally assessed a cable-driven articulated/continuum manipulator, devised for cardiac valve delivery. Positioning and stiffening were teleoperated, based on cable shortening. Stiffening was parameterized by using the leading tension (LT, ie, tension of the cables driving bending). We assessed positioning (repeatability/reversibility along eight/two bending directions) and stiffening (eight bent configurations).

RESULTS

We achieved good repeatability and reversibility (mean errors <1% and 1.5%, respectively, of the workspace characteristic length). Stiffening was effective (up to 9-fold increase, depending on pose). Stiffening was linearly correlated (R² = 0.92) with LT for all the considered configurations.

CONCLUSION

We accurately positioned and effectively stiffened the manipulator in several bent configurations. The proposed stiffness modulation strategy can be extended to other manipulators.

Continuum Robot With Follow-the-Leader Motion for Endoscopic Third Ventriculostomy and Tumor Biopsy

BACKGROUND

In a combined endoscopic third ventriculostomy (ETV) and endoscopic tumor biopsy (ETB) procedure, an optimal tool trajectory is mandatory to minimize trauma to surrounding cerebral tissue.

OBJECTIVE

This paper presents wire-driven multi-section robot with push-pull wire. The robot is tested to attain follow-the-leader (FTL) motion to place surgical instruments through narrow passages while minimizing the trauma to tissues.

METHODS

A wire-driven continuum robot with six sub-sections was developed and its kinematic model was proposed to achieve FTL motion. An accuracy test to assess the robot's ability to attain FTL motion along a set of elementary curved trajectory was performed. We also used hydrocephalus ventricular model created from human subject data to generate five ETV/ETB trajectories and conducted a study assessing the accuracy of the FTL motion along these clinically desirable trajectories.

RESULTS

In the test with elementary curved paths, the maximal deviation of the robot was increased from 0.47 mm at 30 ° turn to 1.78 mm at 180 ° in a simple C-shaped curve. S-shaped FTL motion had lesser deviation ranging from 0.16 to 0.18 mm. In the phantom study, the greatest tip deviation was 1.45 mm, and the greatest path deviation was 1.23 mm.

CONCLUSION

We present the application of a continuum robot with FTL motion to perform a combined ETV/ETB procedure. The validation study using human subject data indicated that the accuracy of FTL motion is relatively high. The study indicated that FTL motion may be useful tool for combined ETV and ETB.

Nitinol actuated soft structures towards transnasal drug delivery: a pilot cadaver study

Sudden hearing loss can be treated noninvasively by administering drugs to the middle ear (≈1 ml) via the eustachian tube. The nasopharyngeal cavity requires high dexterity manipulation as it is restricted by the nasal vestibule, and precise drug delivery through the small cavity can allow previously unreachable areas to be reconsidered for localized delivery. Nitinol has shape memory capabilities and can be used for distal actuation accessed from small lumen and a tortuous path. The drug delivery device (DDD) is a soft and needle-sized (2 mm) and comprises of Nitinol, ribbon spring, and a drug delivery tube. By controlling the input voltage to the Nitinol, bending of the device at different angles could be achieved, and the ribbon spring works antagonistically to the Nitinol to revert to the initial position once deactivated. The actuation of the device and its corresponding bending are calculated in vitro and found to have a bending angle ranging between 36.2 and 66.8° for applied voltages of 1.2-2.0 V, with surface temperature of 45.6-154 °C. The DDD is able to actuate 200 cycles with ≈91-76% retention of bending performance, with a temperature increase of ≈8.5-9% when 1.2-2.0 V is applied. Addition of soft insulating material shows ≈34-62% reduction in the surface temperature in the first cycle and ≈37-59% over 200 cycles when actuated at 1.2-2.0 V. The active steering and navigation capabilities of the DDD are demonstrated in simulated environments (based on the eustachian tube dimensions of adult and infant). Preclinical testing in human cadavers is demonstrated and suggests the developed DDD controlled by varying the input voltages for bending, and mechanically varied drug delivery may be a feasible option for localized drug delivery in eustachian tube. Graphical abstract.

Wire-driven flexible manipulator with constrained spherical joints for minimally invasive surgery

PURPOSE

One of the main factors that affect the rigidity of flexible robots is the twist deformation because of the external force exerted on the end effector. Another important factor that affects accuracy is the fact that such robots do not have a constant curvature. The conventional kinematic model assumes that the curvature is constant; however, in reality, it is not. To improve the rigidity and accuracy of flexible robots used in minimally invasive surgery via preventing the twist deformation while ensuring a constant curvature, we propose a novel flexible manipulator with ball-constrained spherical (BCS) joints and a spring.

METHODS

The BCS joints are used to prevent the twist deformation in the flexible robot. The joints have two degrees of freedom (DOFs), which limit the rotation about the axial direction. The rotation is limited because the ball that is inserted into a BCS joint can move only along the ball guide. To obtain a constant curvature, springs are installed among the BCS joints. The springs receive the uniform compression force generated among the joints, thus achieving a constant curvature. The proposed BCS joint is designed based on the diameter of the forceps, desired workspace, and desired bending angle.

RESULTS

To evaluate the proposed mechanism, three experiments were performed using a 20-mm-diameter prototype consisting of 13 BCS joints with a two-DOF motion. The experimental results showed that the prototype can realize a constant curvature with a mean error of 0.21°, which can support up to 5 N with no apparent twist deformation.

CONCLUSIONS

We developed a flexible manipulator with BCS joints for minimally invasive surgery. The proposed mechanism is anticipated to help prevent the twist deformation of the robot and realize a constant curvature. Accordingly, it is expected that rigidity is improved to ensure accuracy.