높은 강성을 갖는 소형 뼈 천공 로봇 시스템

뼈 천공, 영상 기반 네비게이션, 원격 중심 움직임 메커니즘, 천공 메커니즘One of the most important and difficult tasks during the bone drilling is to guide the orientation of the drill-ing axis for the target and to maintain the orientation against the reaction force of drilling during the procedure. To assist the drilling task, a remote center of motion (RCM) mechanism is proper for aligning the orientation without changing the entry point. However, existing RCM mechanisms do not provide sufficient resolution and rigidity to deal with hard tissues. We proposed a new type of RCM mechanism which uses two pairs of lin-ear actuators and gearless-arc guide. For the drilling motion, we designed a single motor-based 2-axis control mechanism based on the rolling friction. In addition, a release mechanism for instant stopping of the drilling motion as requested was added. For the automatic control of guiding and drilling, a CT based navigation sys-tem with an optical tracking system was incorporated. The effectiveness of the integrated robotic system was demonstrated in a series of experiments and ex-vivo drilling test on swine femurs. The proposed robotic system withstood an external force of up to 51 N to maintain the joint angle, and an average targeting error was less than 1.2 mm.openI. INTRODUCTION 1 1.1 Introduction of Bone Drilling 1 1.2 Reported Bone Drilling Robotic Systems 2 1.3 Challenges of the Reported Robotic Systems 4 1.4 Contribution and Research Contents 6 Ⅱ. ROLLING FRCTION BASED DRILLING MECHANISM 7 2.1 Introduction of Drilling Mechanism 7 2.2 Mechanisms of Robotic System 10 2.2.1 Rolling Friction Based Drilling Mechanism 10 2.2.2 Release Mechanism 14 2.2.3 Orientation Mechanism 15 2.3 Navigation System 20 2.3.1 Robot and Drill Calibration 21 2.3.2 Frame Matching between the Robot and CT Image 21 2.3.3 Navigation Algorithm 22 2.4 Experiments and Results 24 2.4.1 Drilling Mechanism 24 2.4.2 Orientation Mechanism 27 2.4.3 Ex Vivo Drilling Test 30 2.5 Discussion 35 2.6 Conclusion 38 Ⅲ. REMOTE CENTER OF MOTION BASED GUIDING MECHANISM 39 3.1 Introduction of Guiding Mechanism 39 3.2 Design of the Proposed RCM Mechanisms 41 3.2.1 Design Consideration 41 3.2.2 Structure and Workspace of the RCM Mechanism 42 3.3 Navigation System 47 3.3.1 System Configuration 47 3.3.2 Frame Matching between the Robot and CT Image 48 3.3.3 Tracking Algorithm 49 3.4 Experiments and Results 51 3.4.1 Existence of an RCM 51 3.4.2 Rigidity Test about Tilting Motion 53 3.4.3 Targeting Test 55 3.5 Discussion 59 3.6 Conclusion 61 Ⅳ. INTEGRATED ROBOTIC SYSTEM FOR BONE DRILLING 62 4.1 Dual Trigonometric Ratio based RCM Mechanism 62 4.1.1 Design Consideration 62 4.1.2 Structure and Workspace of the DT-RCM 63 4.1.3 Static Analysis of Resolution and Force 65 4.2 Single Moter based Drilling Mechanism 68 4.2.1 Design of the Proposed Drilling Mechanism 68 4.2.2 Release Mechanism 70 4.3 Navigation System 72 4.3.1 System Sonfiguration 72 4.3.2 Registration between the Robot and CT Image Frame 73 4.3.3 Tracking Algorithm 74 V. EXPERIMENTS AND RESULTS 76 5.1 Accuracy Test for RCM 76 5.2 Rigidity Test for Yaw and Pitch Axes 78 5.3 Targeting Accuracy and Resolution 80 5.4 Ex Vivo Drilling Test on Swine Femurs 82 Ⅵ. DISCUSSION 86 Ⅶ. CONCLUTION AND FUTURE WORKS 88본 연구에서 뼈 천공 수술을 위한 천공 메커니즘, 가이드 메커니즘, 그리고 네비게이션 시스템을 개발하였다. 이전에 제안되었던 직선과 회전 모터를 따로 사용하는 천공 메커니즘들과 달리 회전모터만을 사용하는 마찰력 기반의 천공 메커니즘을 제안하였다. 이로써 직선 가이드 없이도 천공 운동을 구현 할 수 있기 때문에 로봇의 크기를 줄 일 수 있었으며, 로봇과 드릴의 기계적인 채결이 필요 없기 때문에 위급상황 시에 간단하게 드릴의 움직임을 중단하고 제거할 수 있게 되었다. 또한, 볼 나사 기반의 직선 엑추에이터 기반의 RCM (Remote Center of Motion) 메커니즘을 개발하였다. 뼈 천공 수술에서 가장 중요하고 어려운 작업 중 하나는 목표 지점까지 드릴의 방향을 가이드해주고 천공 중에 발생할 수 있는 반력에 삽입 방향을 유지하는 것이다. 천공의 방향을 가이드해주기 위해 초기 삽입 지점을 유지하면서 방향을 목표 지점에 정렬해 줄 수 있는 RCM 메커니즘이 적합하다. 그러나 기존의 RCM 메커니즘은 단단한 조직을 다루기에 충분한 정밀도나 강성을 제공하지 않는다. 우리는 직선 엑추에이터 만을 사용하는 새로운 형태의 RCM 메커니즘을 개발하여 높은 정밀도와 강성을 달성하였다. 목표 위치로의 천공 및 방향 가이드를 위해 CT 영상 기반의 네비게이션 시스템을 개발 및 통합하였다. 팬텀을 통한 일련의 기초 실험과 돼지 대퇴골을 통한 생검 실험을 통해 통합 로봇 시스템의 효과가 입증되었다. 제안된 로봇 시스템은 실제 천공에 필요한 강성의 3배인 51 N까지의 외력을 버티며 삽입 각도를 유지하였고, 생검 실험의 평균 천공 오차는 1.2 mm 미만이었다.DoctordCollectio

Wave-shaped Notched Compliant Joint with High Rigidity

Notched compliant joints (NCJs) have been widely used in orthopedic surgeries requiring large curvatures for a minimally invasive approach to lesions and high rigidity for cutting hard tissues. With current NCJ designs, there is a trade-off between maximizing rigidity and maximizing curvature for a specified constrained size. Considering notch geometry, larger sizes of notch gaps lead to greater curvatures, however, smaller spacing between notches decreases rigidity. Herein, we propose an NCJ with a novel notch shape, such that the gap of the spacer can be increased without changing that of the notch. Furthermore, we determined the best design parameters for achieving the maximum rigidity for a given driving force. The higher rigidity of the proposed NCJ compared with that of general NCJs is shown through a simulation and experiments. The difference in rigidities between the proposed and general NCJs was 66% with the p-value of $5.68 \times {10}^{ - 9}$ in a 95% confidence interval which was found to be a statistically significant improvement. In a cutting test, while keeping the curvature, the proposed NCJ increased the cutting amount compared with general NCJs. We verified that the proposed NCJ can achieve both high rigidity and large curvature. The main feature of this study is the development of an NCJ in which both the gap of the spacer and the gap of the notch can be independently changed without affecting each other. The proposed NCJ achieves improved rigidity without loss of curvature. IEEEFALS

Analysis of Twist Deformation in Wire-driven Continuum Surgical Robot

Wire-driven continuum surgical robots are attracting significant interest in minimally invasive surgeries owing to their high dexterity level and miniaturization. However, twist deformation due to the external force at the end effector decreases the accuracy and controllability of these robots. In this study, we analyze the two factors responsible for twist deformation and propose models incorporating these factors. In our analyses, we first consider twist deformation due to the elastic deformation of the wire; when a tensioned wire is subjected to normal force, a sag effect occurs, which results in twist deformation in the robot. We analyze this sag effect statically considering the material properties of the wire. We also analyze the twist deformation due to the clearance between the wire and hole boundary in the spacer of the robot. Clearance is required in a wire-driven continuum robot to realize bending motion; however, this is considered one of the main causes of twist deformation and is referred to as the clearance effect. Subsequently, we propose sag and clearance effect models that quantitatively predict the twist deformation. The results of the experiments conducted to verify the accuracy of the proposed models, including a payload test using a conventional continuum robot comprising spherical joints, indicate that the accuracy of the proposed models is 95%. © 2019, ICROS, KIEE and Springer.FALS

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. © 2019, CARS.1

Compact Bone Surgery Robot With a High-Resolution and High-Rigidity Remote Center of Motion Mechanism

Objective: Two important and difficult tasks during a bone drilling procedure are guiding the orientation of the drilling axis toward the target and maintaining the orientation against the drilling force. To accomplish these tasks, a remote center of motion (RCM) mechanism is adopted to align the orientation of the drilling axis without changing the entry point. However, existing RCM mechanisms do not provide sufficient resolution and rigidity to address hard tissue cases. Methods: We propose a new type of RCM mechanism that uses two sets of linear actuators and a gearless-arc guide to have a high resolution and rigidity. In addition, we designed a single motor-based drilling mechanism based on rolling friction. To achieve automatic control of the guiding and drilling process, we incorporated a computer-tomography-based navigation system that was equipped with an optical tracking system. Results: The effectiveness of the integrated robotic system was demonstrated through a series of experiments and ex vivo drilling tests on swine femurs. The proposed robotic system withstood a maximum external force of 51 N to maintain the joint angle, and the average drilling error was less than 1.2 mm. Conclusion: This study confirms the feasibility of the proposed bone drilling robotic system with a high-resolution and high-rigidity RCM mechanism. Significance: This drilling system is the first successful trial based on an RCM mechanism and a single motor-based drilling mechanism, reducing the footprint and required motors with respect to previous bone surgical robots. © 1964-2012 IEEE.1

Simultaneous Optimization of Patient-Image Registration and Hand-Eye Calibration for Accurate Augmented Reality in Surgery

Objective: Augmented reality (AR) navigation using a position sensor in endoscopic surgeries relies on the quality of patient-image registration and hand-eye calibration. Conventional methods collect the necessary data to compute two output transformation matrices separately. However, the AR display setting during surgery generally differs from that during preoperative processes. Although conventional methods can identify optimal solutions under initial conditions, AR display errors are unavoidable during surgery owing to the inherent computational complexity of AR processes, such as error accumulation over successive matrix multiplications, and tracking errors of position sensor. Methods: We propose the simultaneous optimization of patient-image registration and hand-eye calibration in an AR environment before surgery. The relationship between the endoscope and a virtual object to overlay is first calculated using an endoscopic image, which also functions as a reference during optimization. After including the tracking information from the position sensor, patient-image registration and hand-eye calibration are optimized in terms of least-squares. Results: Experiments with synthetic data verify that the proposed method is less sensitive to computation and tracking errors. A phantom experiment with a position sensor is also conducted. The accuracy of the proposed method is significantly higher than that of the conventional method. Conclusion: The AR accuracy of the proposed method is compared with those of the conventional ones, and the superiority of the proposed method is verified. Significance: This study demonstrates that the proposed method exhibits substantial potential for improving AR navigation accuracy. © 1964-2012 IEEE.1

Vision Guided Robotic System for Bone Drilling Based on Rolling Friction

Drilling procedures to the bone are frequently conducted with CT in the various surgical fields. The proposed vision guided robotic system provides orientation alignment of the drill-tip and automatic drilling to the target. The feasibility of the proposed robotic system was demonstrated by ex-vivo drilling tests on swine femur