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Design and control of patient- and surgery- specific multi-arm concentric tube robots

Project ID: 2019_D17

1st Supervisor: Christos Bergeles, King’s College London
2nd Supervisor: Lyndon da Cruz, Moorfields Eye Hospital

Concentric tube robots are a representative of continuum robots, i.e. robots that can flexibly control their shape. Such robots are envisioned as minimally invasive instruments that can navigate natural pathways to reach deep seated pathologies for intervention and surgery. For example, concentric tube robots have been proposed for neurosurgery, where they navigate through the sinuses; for cardiac surgery, where they navigate through the jugular vein; for prostate surgery, by entering through the urethra; renal surgery etc.

Several teams have approached the patient-specific design of those robots, aiming to tune their mechanical properties to make them safe for introduction through the anatomy. No team, however, has attempted to design multi-arm concentric tube robots, nor has their interaction with the anatomy being factored in yet.

Therefore, this project aims at developing the design interface for multi-arm robots, modelling their interaction with the anatomy through their deployment, and develop robot control sequences that account for the patient-specific simulations during actual robot use.

The student will be part of an ERC funded project to design a sub-centimetre multi-arm flexible robot for peri-ocular navigation and optic nerve interventions.

Existing ophthalmic surgical robots reduce hand-tremor, scale-down the clinician’s motions, and provide a certain degree of force feedback and haptic guidance to the clinician. However, no surgical system has been designed to enable interventions in the optic nerve area. According to clinical practice, accessing the optic nerve requires multiple incisions to detach the eye muscles, and disclocations of the eye. This is an invasive and long procedure that could be facilitated with a endoscope-like robotic system that navigates around the muscles to reach the posterior part of the eye, within the orbit.

Our robot, termed Pioneer, will be one of the first multi-arm redundant miniature flexible robots. It will have 6 degrees-of-freedom (DoF) at the tip via its shape-controllable shaft, and multiple arms. Three tools, each with 2DoF, will be housed within the flexible functionalised robot sheath. The first will hold a 1.0×1.0x1.7mm 0.6MPixels NanEye camera (Awaiba, Gmbh) for visualisation, the second a forceps for vessel or tissue holding, and the third a hollow needle, also serving as the illumination trocar; therapeutics could be introduced through the needle, since illumination can be retracted after the robot reaches its destination.

Pioneer will be based on concentric telescoping pre-curved super elastic (usually NiTi – nickel/titanium) tubes. Tubes are the preferred flexible robot technology due to their increased capacity to exhibit large curvatures as their diameter decreases, as well as their tuneable application-specific stiffness. Concentric tube robots are rigid but compliant and can navigate natural pathways. As the tubes rotate and translate with respect to each other they deform elastically controlling the robot’s tip pose. The tubes’ lumen can deliver a tool at the pathology location. The important but underexplored topic tackled within this project is force-inclusive design, and hybrid force/position control.

To date, despite work on the effect of external forces on, all robot design algorithms have considered simplified static environments. The computational complexity of such design algorithms precluded the inclusion of tissue-and-robot interactions in the design. With novel distributed computation approaches, however, this project will include tissue-specific properties in robot design. This is critical for microsurgical robots in general, and for Pioneer specifically, as even small forces can cause surgically relevant anatomy deformations. Pioneer’s novel design process will be founded on Finite Element Modelling (FEM) of coupled robot-and-tissue systems, with MRI volumes providing the robot design constraints and tissue properties. Established robot kinematics models, developed within the group, and extensively used FEM-frameworks, such as SOFA, will lead to a new type of design methodology with wide applications in surgical robotics.

In parallel, work on embedded force sensing for surgical robots will be coupled with the developed models to enable hybrid force/position control, first in a simulated environment, and afterwards by application to the multi-arm robot under development within our group.

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