With the maturity of surgical robotic systems based on traditional rigid-link principles, the rate of progress slowed as limits of size and controllable degrees of freedom were reached. Continuum robots came with the potential to deliver a step change in the next generation of medical devices, by providing better access, safer interactions and making new procedures possible. Over the last few years, several continuum robotic systems have been launched commercially and have been increasingly adopted in hospitals. Despite the clear progress achieved, continuum robots still suffer from design complexity hindering their dexterity and scalability. Recent advances in actuation methods have looked to address this issue, offering alternatives to commonly employed approaches. Additionally, continuum structures introduce significant complexity in modelling, sensing, control and fabrication; topics which are of particular focus in the robotics community. It is, therefore, the aim of the presented work to highlight the pertinent areas of active research and to discuss the challenges to be addressed before the potential of continuum robots as medical devices may be fully realised.
Despite increasing interest in minimally invasive surgical techniques and related developments in flexible endoscopes and catheters, follow-the-leader motion remains elusive. Following the path of least resistance through a tortuous and potentially delicate environment without relying on interaction with the surrounding anatomy requires the control of many degrees of freedom. This typically results in large-diameter instruments. One viable solution to obtain dexterity without increasing size is via multiple-point magnetic actuation over the length of the catheter. The main challenge of this approach is planning magnetic interaction to allow the catheter to adapt to the surrounding anatomy during navigation. We design and manufacture a fully shape-forming, soft magnetic catheter of 80 mm length and 2 mm diameter, capable of navigating a human anatomy in a follow-the-leader fashion. Although this system could be exploited for a range of endoscopic or intravascular applications, here we demonstrate its efficacy for navigational bronchoscopy. From a patient-specific preoperative scan, we optimize the catheters’ magnetization profiles and the shape-forming actuating field. To generate the required transient magnetic fields, a dual-robot arm system is employed. We fabricate three separate prototypes to demonstrate minimal contact navigation through a three-dimensional bronchial tree phantom under precomputed robotic control. We also compare a further four separate optimally designed catheters against mechanically equivalent designs with axial magnetization profiles along their length and only at the tip. Using our follow-the-leader approach, we demonstrate up to 50% more accurate tracking, 50% reduction in obstacle contact time during navigation over the state of the art, and an improvement in targeting error of 90%.
In the present work we discuss a novel dynamic control approach for magnetically actuated robots, by proposing an adaptive control technique, robust towards parametric uncertainties and unknown bounded disturbances. The former generally arise due to partial knowledge of the robots' dynamic parameters, such as inertial factors, the latter are the outcome of unpredictable interaction with unstructured environments. In order to show the application of the proposed approach, we consider controlling the Magnetic Flexible Endoscope (MFE) which is composed of a soft-tethered Internal Permanent Magnet (IPM), actuated with a single External Permanent Magnet (EPM). We provide with experimental analysis to show the possibility of levitating the MFE-one of the most difficult tasks with this platform-in case of partial knowledge of the IPM's dynamics and no knowledge of the tether's behaviour. Experiments in an acrylic tube show a reduction of contact of the 32% compared to non-levitating techniques and 1.75 times faster task completion with respect to previously proposed levitating techniques. More realistic experiments, performed in a colon phantom, show that levitating the capsule achieves faster and smoother exploration and that the minimum time for completing the task is attained by the proposed approach.
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