Control of a hybrid robotic system for computer-assisted interventions in dynamic environments

International audiencePurpose Minimally invasive surgery is becoming the standard treatment of care for a variety of procedures. Surgeons need to display a high level of proficiency to overcome the challenges imposed by the minimal access. Especially when operating on a dynamic organ, it becomes very difficult to align instruments reliably and precisely. In this paper, a hybrid ro-botic system and a dedicated robotic control approach are proposed to assist the surgeon performing complex surgical gestures in a dynamic environment. Methods The proposed hybrid robotic system consists of a rigid robot arm on top of which a continuum robot is mounted in series. The continuum robot is locally actuated with McKibben muscles. A control scheme is adopted based on quadratic programming framework. It is shown that this framework allows enforcing a set of constraints on the pose of the tip, as well as of the instrument shaft, which is commanded to slide in and out through the entry point. Results Through simulation and experiments it is shown how the robot tool-tip is able to follow sinus-oidal trajectories of 0.37 Hz and 2 Hz, corresponding to motion due to breathing and heartbeat respectively, while maintaining the instrument shaft pivoting nicely about the entry point. The positioning and tracking accuracy of such system is shown to lie below 3mm in position and 5 • in angle. Herbert De Praetere is with UZ Leuven, Cardiac surgery, Conclusion The results suggest a good potential for applying the proposed technology to assist the surgeon during complex robot-assisted interventions. It is also illustrated that even when using flexible hence relatively safe end-effectors, it is possible to reach acceptable tracking behaviour at relatively high frequencies

Modeling and Constraint-based Control of Continuum Robots. Applications in Robotic Surgery.

A growing interest can be seen in the use of compliant instruments or robots in tasks where interaction with fragile structures in the environment is required. The reason for this interest is that the compliant nature of these devices brings in an inherent level of safety. Flexible robots and instruments would, at least initially, bend away upon contact or impact. These actuated compliant structures are often also referred to as continuum robots. The control of these types of robots is much more involved. The distributed flexibility complicates the derivation of kinematic expressions, as these expressions become a function of the interaction forces that are exchanged with the environment. The work in this thesis treats the problems in the domain of modelling and control of continuum robots. At first instance the modelling principles for the kinematics of the continuum robot are adopted from the Cosserat rod theory. Building upon the Cosserat rod model, a method for calculation of the differential kinematics of continuum robots is developed. This relates to the calculation of the robot Jacobian and compliance matrices which account for the robot actuation but also for the tip applied loads. These Jacobian and compliance matrices are then employed in a constraintbased control framework to allow for concurrent position and force control. Controller synthesis followed hereto the principles of the Task Frame and instantaneous Task Specification using Constraints (iTaSC) formalisms. iTaSC is found particularly suitable due to its ability to express and combine control tasks in a natural way. Control tasks can be formulated as combinations of target positions, velocities or forces expressed in an arbitrary number and type of coordinate frames. In this thesis it has been shown how various artificial constraints can be imposed on the control of the robotic system which features large compliance and undergoes large deformation. Here, force/position control of a robots end-effector is shown to be possible while maintaining a rotational center-of-motion at a more proximal part of the instrument. Especially in Minimal Invasive Surgery this capability is considered highly desirable. In the next stage, a pneumatically driven single-section continuum robot has been designed and developed. Actuated with McKibben muscles, the robot features compliant behaviour in interaction with the environment and possesses two degrees of freedom. The developed continuum robot exhibits large axial and torsional stiffness which allowed for simplification of current state-of-theart kinematic models for antagonistically actuated continuum robots. The shape of the developed continuum robot, when operated in free space, can be described by adopting the constant curvature model. This model, despite its wide popularity, exhibits singularities in case when the robot is straight. In this thesis a singularity-free model for calculation of robot Jacobian has been developed. As a final stage of the thesis, a hybrid rigid/continuum robotic mechanism has been developed by serially combining a pneumatically driven continuum robot and a rigid robot. The motivation for the development of such a robotic system lies in the constraints which arise in the scenarios of minimally invasive surgery. For example, by introducing the instrument through the entry point (trocar), the surgeon is effectively losing two degrees of freedom. Her/his motions are restricted to insertion/retraction, rotation and pivoting about the entry point. By using an instrument which offers two additional degrees of freedom past the trocar point, instrument dexterity can be restored, allowing for complete control over position and orientation of the tool. The performance of the hybrid robotic mechanism was then evaluated for scenarios where following of fast trajectories is required. The envisioned application is here minimally invasive heart surgery. Compensation of the heart-beating motion can allow the surgeon to position and orientate the surgical tools more accurately in presence of a moving environment.status: publishe

Hybrid robotic system featuring a combination of a continuum robot and a rigid robotic arm: static and differential kinematic modeling

This work introduces the forward instantaneous kinematics of a hybrid robotic system consisting of a compact flexible robotic instrument attached to a larger and rigid general-purpose robotic arm. Such hybrid system is expected to be of great use in robotic surgical applications where the robotic arm allows a large workspace and where the flexible robot provides additional dexterity while increasing operational safety [4]. Despite its large application potential few efforts have been conducted to rigorously model the kinematics of such hybrid systems. The emphasis of this paper is therefore on the calculation of the continuum robot's forward and differential kinematics. While the rigid robot follows traditional robotics approaches, the flexible robotic instrument, which is a cable actuated continuum robot, is modeled using the Crosserat rod theory. The proposed modeling approach describes both systems through respective manipulator Jacobian matrices and combines them into a uniform formulation of the hybrid robotic system. The method is exemplified on a rigid robotic arm featuring three rotational degrees of freedom and a flexible instrument actuated by two push-pull cable pairs. The total system thus counts five controlled degrees of freedom.status: publishe

Towards Bilateral Teleoperation of a Standard Electrophysiology Catheter

Robotic catheters have recently made their appearance in cardiac interventions such as RF ablation in treatment of arrhythmic heart fibrillation. Reduced exposure of the surgeon to ionizing radiation, more accurate tip positioning and shorter operation times are some of the claimed benefits. However, procedural outcome is highly dependent on the interaction force between the catheter and the heart tissue during ablation. Severe complications such as perforation of the heart wall occur in case too much force is used. Oppositely, inferior lesion quality and failed treatment results from too weak contacts during ablation. The long-term goal of our research exists in transforming a standard electrophysiological catheter into a bilateral teleoperation controlled one. This article discusses the first steps were a local force control method of a single degree of freedom catheter robot is investigated. The control algorithm introduced here tries to achieve a good force control in the presence of a moving elastic environment representing the beating heart. The algorithm also accounts for the use of sensors with low sampling rates. Simulation results show that the developed controller is able to follow the desired force trajectory and allows to dampen the oscillations in interaction forces compared to the case where no force control is used. Finally, we point at restrictions of the proposed method and indicate directions for further work.status: publishe

Constraint-Based Interaction Control of Robots Featuring Large Compliance and Deformation

© 2004-2012 IEEE. This paper introduces a framework for constraint-based force/position control of robots that exhibit large nonlinear structural compliance and that undergo large deformations. Controller synthesis follows hereto the principles of the Task Frame and instantaneous Task Specification using Constraints (iTaSC) formalisms. iTaSC is found particularly suitable due to its ability to express and combine control tasks in a natural way. Control tasks can be formulated as combinations of target positions, velocities, or forces expressed in an arbitrary number and type of coordinate frames. The proposed framework is applied to a mixed mechatronic system composed of a traditional rigid-link robot whose end-effector is a continuum (flexible) link. A selection of different position/force control tasks is prepared to demonstrate the validity and general nature of the proposed framework.status: publishe

Position Control of Robotic Catheters inside the Vasculature based on a Predictive Minimum Energy Model

© 2016 IEEE. Accurate and precise control of catheters inside a vasculature is a difficult yet important task. Current manual approaches require significant surgical skill. Over the years, surgeons build up a sort of mental kinematic map telling them how to handle the catheter in order to steer the catheter tip safely through the vessel system. The input-output behaviour of the catheter is complex and depends heavily on its configuration within and contacts with the vasculature. This paper introduces an alternative approach to control robotic catheters. The input-output behaviour or so-called differential kinematics are derived from a patient-specific vasculature model, following a minimum-energy argumentation. The validity of the proposed approach is demonstrated experimentally. Whereas the performance of model-based approaches is obviously greatly influenced by the correctness of estimated parameters, within this work we show experimentally how reasonable performance can already be achieved within the setup that was constructed. We expect that there is still ample room for improvement by, e.g., putting more sophisticated identification, modeling and collision detection schemes into place.status: publishe

Hybrid robotic system for applications in robotic surgery

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Manipulability of Robotic Catheters

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Patient-Specific Design of Multi-Component Steerable Catheters

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Control of a hybrid robotic system for computer-assisted interventions in dynamic environments

PURPOSE: Minimally invasive surgery is becoming the standard treatment of care for a variety of procedures. Surgeons need to display a high level of proficiency to overcome the challenges imposed by the minimal access. Especially when operating on a dynamic organ, it becomes very difficult to align instruments reliably and precisely. In this paper, a hybrid rigid/continuum robotic system and a dedicated robotic control approach are proposed to assist the surgeon performing complex surgical gestures in a dynamic environment. METHODS: The proposed robotic system consists of a rigid robot arm on top of which a continuum robot is mounted in series. The continuum robot is locally actuated with McKibben muscles. A control scheme based on quadratic programming framework is adopted. It is shown that the framework allows enforcing a set of constraints on the pose of the tip, as well as of the instrument shaft, which is commanded to slide in and out through the entry point. RESULTS: Through simulation and experiments, it is shown how the robot tool tip is able to follow sinusoidal trajectories of 0.37 and 2 Hz, while maintaining the instrument shaft pivoting along the entry point. The positioning and tracking accuracy of such system are shown to lie below 4.7 mm in position and [Formula: see text] in angle. CONCLUSION: The results suggest a good potential for applying the proposed technology to assist the surgeon during complex robot-assisted interventions. It is also illustrated that even when using flexible hence relatively safe end-effectors, it is possible to reach acceptable tracking behaviour at relatively high frequencies.status: publishe