Active Stiffness Tuning of a Spring-based Continuum Robot for MRI-Guided Neurosurgery

Improving the kinematic accuracy of a collaborative continuum robot by using flexure-hinges

Within various unstructured industrial environments, there is often the requirement to conduct remote engineering tasks, such as sampling the structure for analysis prior to decommissioning. Most existing tools are simply not dexterous enough to fulfil this task, and thus new technology is required. We describe here a simple, lightweight, and water-resistant collaborative dual-arm continuum robot system which can aid in this task. To improve the kinematic accuracy of the system, a class of flexible hinges have been combined with a conventional continuum robot configuration. The thickness and width of said flexible hinges can be adjusted to adapt to various tasks. Kinematic and stiffness models have further been developed, incorporating the influence of these flexible hinges. A set of experiments have been conducted to validate the proposed model and demonstrate the advantages of the platform. It was found that the kinematic accuracy of the continuum robot can be improved by a factor of around 10 with the aid of said hinges.

Comprehensive stiffness regulation on multi-section snake robot with considering the parasite motion and friction effects

Snake robots have been widely used in challenging environments, such as confined spaces. However, most existing snake robots with large length/diameter ratios have low stiffness, and this limits their accuracy and utility. To remedy this, a novel 'macro-micro' structure aided by a new comprehensive stiffness regulation strategy is proposed in this paper. This improves the positional accuracy when operating in deep and confined spaces. Subsequently, a comprehensive strategy for regulating the stiffness of the system is then developed, along with a kinetostatic model for error prediction. The internal friction, variation of cable stiffness as a function of tension, and their effects on the structural stiffness of the snake arm under different configurations have been incorporated into the model to increase the modelling accuracy. Finally, the proposed models were validated experimentally on a physical prototype and control system (error: 4.3% and 2.5% for straight and curved configurations, respectively). The improvement in stiffness due to the adjustment of the tension in the driving cables (i.e. average 183.4%) of the snake arm is shown.

Robotic Instruments Inside the MRI Bore: Key Concepts and Evolving Paradigms in Imaging-enhanced Cranial Neurosurgery

Intraoperative MRI has been increasingly used to robotically deliver electrodes and catheters into the human brain using a linear trajectory with great clinical success. Current cranial MR guided robotics do not allow for continuous real-time imaging during the procedure because most surgical instruments are not MR-conditional. MRI guided robotic cranial surgery can achieve its full potential if all the traditional advantages of robotics (such as tremor-filtering, precision motion scaling, etc.) can be incorporated with the neurosurgeon physically present in the MRI bore or working remotely through controlled robotic arms. The technological limitations of design optimization, choice of sensing, kinematic modeling, physical constraints, and real-time control had hampered early developments in this emerging field, but continued research and development in these areas over time has granted neurosurgeons far greater confidence in using cranial robotic techniques. This article elucidates the role of MR-guided robotic procedures using clinical devices like NeuroBlate and Clearpoint that have several thousands of cases operated in a "linear cranial trajectory" and planned clinical trials, such as LAANTERN for MR guided robotics in cranial neurosurgery using LITT and MR-guided putaminal delivery of AAV2 GDNF in Parkinson's disease. The next logical improvisation would be a steerable curvilinear trajectory in cranial robotics with added DOFs and distal tip dexterity to the neurosurgical tools. Similarly, the novel concept of robotic actuators that are powered, imaged, and controlled by the MRI itself is discussed in this article, with its potential for seamless cranial neurosurgery.

Three-Dimensional Printable Ball Joints with Variable Stiffness for Robotic Applications Based on Soft Pneumatic Elastomer Actuators

This paper contributes to a new design of the three-dimensional printable robotic ball joints capable of creating the controllable stiffness linkage between two robot links through pneumatic actuation. The variable stiffness ball joint consists of a soft pneumatic elastomer actuator, a support platform, an inner ball and a socket. The ball joint structure, including the inner ball and the socket, is three-dimensionally printed using polyamide−12 (PA12) by selective laser sintering (SLS) technology as an integral mechanism without the requirement of assembly. The SLS technology can make the ball joint have the advantages of low weight, simple structure, easy to miniaturize and good MRI compatibility. The support platform is designed as a friction-based braking component to increase the stiffness of the ball joint while withstanding the external loads. The soft pneumatic elastomer actuator is responsible for providing the pushing force for the support platform, thereby modulating the frictional force between the inner ball, the socket and the support platform. The most remarkable feature of the proposed variable stiffness design is that the ball joint has ‘zero’ stiffness when no pressurized air is supplied. In the natural state, the inner ball can be freely rotated and twist inside the socket. The proposed ball joint can be quickly stiffened to lock the current position and orientation of the inner ball relative to the socket when the pressurized air is supplied to the soft pneumatic elastomer actuator. The relationship between the stiffness of the ball joint and the input air pressure is investigated in both rotating and twisting directions. The finite element analysis is conducted to optimize the design of the support platform. The stiffness tests are conducted, demonstrating that a significant stiffness enhancement, up to approximately 508.11 N·mm reaction torque in the rotational direction and 571.93 N·mm reaction torque in the twisting direction at the pressure of 400 kPa, can be obtained. Multiple ball joints can be easily assembled to form a variable stiffness structure, in which each ball joint has a relative position and an independent stiffness. Additionally, the degrees of freedom (DOF) of the ball joint can be readily restricted to build the single-DOF or two-DOFs variable stiffness joints for different robotic applications.

State of the Art and Future Opportunities in MRI-Guided Robot-Assisted Surgery and Interventions

Magnetic resonance imaging (MRI) can provide high-quality 3-D visualization of target anatomy, surrounding tissue, and instrumentation, but there are significant challenges in harnessing it for effectively guiding interventional procedures. Challenges include the strong static magnetic field, rapidly switching magnetic field gradients, high-power radio frequency pulses, sensitivity to electrical noise, and constrained space to operate within the bore of the scanner. MRI has a number of advantages over other medical imaging modalities, including no ionizing radiation, excellent soft-tissue contrast that allows for visualization of tumors and other features that are not readily visible by other modalities, true 3-D imaging capabilities, including the ability to image arbitrary scan plane geometry or perform volumetric imaging, and capability for multimodality sensing, including diffusion, dynamic contrast, blood flow, blood oxygenation, temperature, and tracking of biomarkers. The use of robotic assistants within the MRI bore, alongside the patient during imaging, enables intraoperative MR imaging (iMRI) to guide a surgical intervention in a closed-loop fashion that can include tracking of tissue deformation and target motion, localization of instrumentation, and monitoring of therapy delivery. With the ever-expanding clinical use of MRI, MRI-compatible robotic systems have been heralded as a new approach to assist interventional procedures to allow physicians to treat patients more accurately and effectively. Deploying robotic systems inside the bore synergizes the visual capability of MRI and the manipulation capability of robotic assistance, resulting in a closed-loop surgery architecture. This article details the challenges and history of robotic systems intended to operate in an MRI environment and outlines promising clinical applications and associated state-of-the-art MRI-compatible robotic systems and technology for making this possible.

A Brief Insight on Magnetic Resonance Conditional Neurosurgery Robots

The brain is a delicate organ in the human body that requires extreme care. Brain-related diseases are unavoidable. Perse, neurosurgery is a complicated procedure that demands high precision and accuracy. Developing a surgical robot is a complex task. To date, there are only a handful of neurosurgery robots in the market that distinctly undergo clinical procedures. These robots have exorbitant cost that hinders the utmost care progress in the area as they are unaffordable. This paper looked at the historical perspective and presented insight literature of the magnetic resonance conditional stereotactic neurosurgery robots that find their ways in clinics, abandoning research projects and promising research yet to undergo clinical use. In addition, the study also gives a thorough insight into the advantage of magnetic resonance imaging modalities and magnetic resonance conditional robots and the future challenges in automation use. Image compatibility test data and accuracy results are also examined because they guarantee that these systems work correctly in particular imaging settings. The primary differences between these systems include actuation and control technologies, construction materials, and the degree of freedom. Thus, one system has an advantage over the other.

Current Trends and Prospects in Compliant Continuum Robots: A Survey

Compliant continuum robots (CCRs) have slender and elastic bodies. Compared with a traditional serial robot, they have more degrees of freedom and can deform their flexible bodies to go through a constrained environment. In this paper, we classify CCRs according to basic transmission units. The merits, materials and potential drawbacks of each type of CCR are described. Drive systems depend on the basic transmission units significantly, and their advantages and disadvantages are reviewed and summarized. Variable stiffness and intrinsic sensing are desired characteristics of CCRs, and the methods of obtaining the two characteristics are discussed. Finally, we discuss the friction, buckling, singularity and twisting problems of CCRs, and emphasise the ways to reduce their effects, followed by several proposing perspectives, such as the collaborative CCRs.

Towards Patient-Specific 3D-Printed Robotic Systems for Surgical Interventions

Surgical robots have been extensively researched for a wide range of surgical procedures due to the advantages of improved precision, sensing capabilities, motion scaling, and tremor reduction, to name a few. Though the underlying disease condition or pathology may be the same across patients, the intervention approach to treat the condition can vary significantly across patients. This is especially true for endovascular interventions, where each case brings forth its own challenges. Hence it is critical to develop patient-specific surgical robotic systems to maximize the benefits of robot-assisted surgery. Manufacturing patient-specific robots can be challenging for complex procedures and furthermore the time required to build them can be a challenge. To overcome this challenge, additive manufacturing, namely 3D-printing, is a promising solution. 3D-printing enables fabrication of complex parts precisely and efficiently. Although 3D-printing techniques have been researched for general medical applications, patient-specific surgical robots are currently in their infancy. After reviewing the state-of-the-art in 3D-printed surgical robots, this paper discusses 3D-printing techniques that could potentially satisfy the stringent requirements for surgical interventions. We also present the accomplishments in our group in developing 3D-printed surgical robots for neurosurgical and cardiovascular interventions. Finally, we discuss the challenges in developing 3D-printed surgical robots and provide our perspectives on future research directions.

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.