Imperial College London Department of Computing A Snake-Like Articulated Robot for Flexible Access Minimally Invasive Surgery - Modelling, Optimisation and Kinematic Control Valentina Vitiello September 2011 Submitted in part fulfilment of the requirements for the degree of Doctor of Philosophy in Computing of Imperial College London and the Diploma of Imperial College London 1 Declaration I herewith certify that all material in this dissertation which is not my own work has been properly acknowledged. Valentina Vitiello 2 Abstract The integration of robotic technologies in surgical instrumentation has contributed to the further development of Minimally Invasive Surgery (MIS) aimed at reduc- ing the patient trauma and hospitalisation costs. Recent advances in imaging and mechatronics promise to enable the execution of more complex interventions through a single incision or natural orifice access. The main requirement for such proce- dures is the ability to reach the operative target through complex routes and curved anatomical pathways whilst maintaining adequate stability for tissue manipulation. A mechatronically controlled device with a high degree of articulation can poten- tially fulfil these requirements. However, the incorporation of a high number of Degrees-of-Freedom (DoFs) increases the control complexity of the system. The purpose of this thesis is to investigate different methods for reducing the control dimensionality of a hyper-redundant snake-like articulated robot for MIS. The design of the robot is based on a modular, flexible access platform featuring serially connected rigid links and a hybrid micromotor-tendon actuation strategy to construct independently addressable universal joints. A path length compensation scheme for reducing the backlash at the joint is presented, together with experimen- tal evaluation of the joint positioning accuracy when using our proposed kinematic control. The integration of an extra translational DoF along the joint axis allows the performance of a hybrid `inchworm-snake' locomotive scheme for self-propulsion of the device. This `front-drive back-following' approach is implemented by actuating only one module at a time in a serial fashion. Therefore, the operator only needs to steer the distal tip of the device while the body of the robot follows the desired trajectory autonomously. Once the distal tip of the hyper-redundant device has reached the target operative site, the body of the robot has to adapt its shape to the surrounding moving organs while keeping the end-effector stable. A DoF minimisation algorithm is designed to identify the minimum number of joints to be simultaneously actuated to ensure shape conformance whilst simplifying the control complexity of the system. Finally, optimal kinematic configurations of the platform are derived for per- forming two specific single incision procedures. The results, based on workspace requirements estimated through pre-operative imaging of the patients, demonstrate the suitability of the system for such procedures. Results from in vivo experiments on porcine models are also provided to show the potential clinical value of the device. 3 Ai miei genitori e mia sorella 4 Acknowledgements I would like to start by thanking Professor Guang-Zhong Yang, without whom this work would have not been possible. He has always set the example by working very hard and being available to give support and advice whenever needed, even during busy times and especially when most necessary. His attention to details and constant quest for better results has truly helped me towards the completion of the work reported in this thesis. Thanks for believing in me and giving me the possibility to work in such a great and multidisciplinary environment. Thanks to my second supervisor Dr Dan Elson for taking into account my appli- cation and arranging the first interview for the PhD scholarship, which eventually led to an exciting collaboration. I would also like to thank Professor Lord Ara Darzi for supporting this research work in any occasion. Many other people have contributed in different ways to the work presented here, friends and colleagues at the Hamlyn Centre always ready to help and work hard until the last minute before the deadline. Thanks to David Noonan, Ka-Wai Kwok, Jianzhong Shang, Peter Mountney, Christopher Payne, Win Tun Latt, James Clark, Richard Newton, Su-lin Lee for your collaboration and Selen Atasoy, Matina Gian- narou, Marco Visentini Scarzanella, Rachel King for your friendly support. A special thank you must go to George Mylonas, who managed to sweeten the last stressful months during which I was writing this thesis and encouraged me every day to keep working hard. Thanks for finding me when I most needed you. To my dear flatmate and fellow PhD student Laia Querol Cano, thanks for your friendship and for making me feel at home here in London. Thanks for your help during a very difficult period of my life and for your support in the last crazy months. Ai miei genitori e mia sorella dedico questa tesi perche' senza il vostro supporto e amore incondizionato non sarei mai riuscita a trovare tanta forza in me stessa e superare tutte le difficolta’ incontrate lungo il cammino. Nonostante la distanza da casa non mi sono mai sentita sola, anzi vi ho sentito ancora piu' vicino, soprattutto la mia adorata sorellina. Vi amo con tutto il cuore e non smettero' mai di ringraziarvi. 5 `The greatest glory in living lies not in never falling, but in rising every time we fall.' Nelson Mandela 6 Contents Abstract 3 Acknowledgements 5 List of Acronyms and Abbreviations 11 List of Figures 14 List of Tables 23 1 Introduction 25 1.1 Key research challenges and objectives . 27 1.2 Original contributions of the thesis . 30 2 Articulated tools for enhanced dexterity and navigation in robotic- assisted surgery 32 2.1 Introduction . 32 2.2 Robotic-assisted minimally invasive surgery . 34 2.2.1 Introduction . 34 2.2.2 Benefits of robotic integration . 34 2.2.3 Representative robotic systems for MIS . 35 2.2.3.1 CAD/CAM surgical systems . 39 2.2.3.2 Endoscopic camera holders . 44 2.2.3.3 Semi-autonomous robots for soft tissue endoscopy . 46 2.2.3.4 Hand-held mechatronic surgical tools . 48 2.2.3.5 Synergistic control systems . 50 2.2.3.6 Master-slave surgical systems . 52 2.2.4 Open problems and technical challenges . 58 2.3 Articulated robots for MIS . 60 2.3.1 Mechanical designs . 61 2.3.2 Actuation modalities . 70 2.3.3 Human-robot interfaces and control strategies . 71 2.3.4 Current limitations and emerging new directions . 75 2.4 Flexible devices for transluminal and single site surgery . 76 2.4.1 Technical challenges and unmet requirements . 78 7 2.4.2 NOTES and LESS instrumentation . 80 2.4.2.1 Specialised endoscopes . 82 2.4.2.2 Flexible platforms . 85 2.4.2.3 Master-slave systems . 87 2.4.2.4 Bimanual insertable robots . 90 2.4.2.5 Intracorporeal mini-robots . 91 2.4.3 Future perspectives of NOTES and LESS: towards robotic- assisted flexible access surgery . 96 2.5 Articulated robot design for flexible access surgery . 97 2.5.1 System architecture . 97 2.5.1.1 Articulated section . 97 2.5.1.2 Hand-held controller and graphical user interface . 99 2.5.1.3 Motor control box and embedded controller . 100 2.5.1.4 Additional components . 101 2.5.2 System usability and control strategies . 103 2.6 Discussion and conclusions . 104 3 Design optimisation of a hybrid micromotor-tendon joint unit for a modular snake robot 106 3.1 Introduction . 106 3.2 Hybrid micromotor-tendon actuation scheme . 106 3.3 Joint model for backlash quantification and force transmission analysis108 3.3.1 Tendon path length variation . 109 3.3.2 Analysis of torque/force transmission . 112 3.4 Joint design optimisation for backlash minimisation . 114 3.4.1 Algorithm design and force optimisation constraints . 114 3.4.2 Optimisation results . 117 3.4.2.1 Generic joint configuration with α = 0 and r2 = r3 . 117 6 6 3.4.2.2 Joint configuration with α = 0 and r2 = r3 . 120 6 3.4.2.3 Joint configuration with α = 0 and r2 = r3 . 120 6 3.4.2.4 Joint configuration with α = 0 and r2 = r3 . 120 3.5 Optimised joint design and characterisation . 125 3.6 Discussion and conclusions . 131 4 Path following under active constraints 132 4.1 Introduction . 132 4.2 Kinematic modelling of robotic mechanical systems . 133 4.2.1 The Denavit-Hartenberg method . 134 4.2.2 Inverse kinematics resolution . 138 4.2.3 Specialised methods for snake robots modelling . 139 4.3 Hybrid `inchworm-snake' robot kinematic analysis . 140 8 4.3.1 Forward kinematics equations . 143 4.3.2 Inverse kinematics resolution . 145 4.4 Path following under active constraints . 149 4.4.1 Colonoscopy . 150 4.4.1.1 Active constraint model and trajectory definition . 151 4.4.1.2 Accuracy assessment of path following control . 151 4.4.2 Laparoscopic liver biopsy . 155 4.4.2.1 Active constraint model and trajectory definition . 156 4.4.2.2 Accuracy assessment of path following control . 156 4.5 Discussion and conclusions . 160 5 DoF minimisation for optimised shape control under active con- straints 162 5.1 Introduction . 162 5.2 Kinematics of hyper-redundant robots . 163 5.2.1 Task-oriented kinematics resolution using traditional modelling techniques . 164 5.2.1.1 Jacobian-based redundancy resolution . 166 5.2.1.2 Gradient projection approach . 168 5.2.1.3 Redundancy resolution via task augmentation . 169 5.2.1.4 Second-order redundancy resolution . 171 5.2.2 Continuum kinematics resolution using parametrised back- bone curves . 173 5.2.2.1 Rigid-link motion approximation via mode selection and curve fitting .