Snake Robots for Surgical Applications: A Review

Although substantial advancements have been achieved in robot-assisted surgery, the blueprint to existing snake robotics predominantly focuses on the preliminary structural design, control, and human–robot interfaces, with features which have not been particularly explored in the literature. This paper aims to conduct a review of planning and operation concepts of hyper-redundant serpentine robots for surgical use, as well as any future challenges and solutions for better manipulation. Current researchers in the field of the manufacture and navigation of snake robots have faced issues, such as a low dexterity of the end-effectors around delicate organs, state estimation and the lack of depth perception on two-dimensional screens. A wide range of robots have been analysed, such as the i2Snake robot, inspiring the use of force and position feedback, visual servoing and augmented reality (AR). We present the types of actuation methods, robot kinematics, dynamics, sensing, and prospects of AR integration in snake robots, whilst addressing their shortcomings to facilitate the surgeon’s task. For a smoother gait control, validation and optimization algorithms such as deep learning databases are examined to mitigate redundancy in module linkage backlash and accidental self-collision. In essence, we aim to provide an outlook on robot configurations during motion by enhancing their material compositions within anatomical biocompatibility standards

형태적응형 이력현상 모형을 이용한 유연구동 메커니즘의 모델링

학위논문 (박사) -- 서울대학교 대학원 : 공과대학 기계항공공학부, 2020. 8. 김종원.Flexible surgical robots and instruments are slowly paving its way into the modern surgical arena. Compared to conventional laparoscopic surgical systems, flexible systems have some distinct advantages in that it can approach surgical targets that were unreachable before, leaves less scar and therefore reducing recovery time for patients. In order to drive the articulated surgical instruments joints, flexible instruments require a tendon-sheath mechanism (TSM). Utilization of TSM brings about a different attribute in a position control standpoint, compared to the rather simple cable-pulley system found in conventional robotic surgical instruments. In this research, a tendon-sheath mechanism was configured, taking into account the actual size constraint of a robotic surgical instrument and the material characteristics of the components. An experiment hardware was designed to measure the input signal and the corresponding output response while varying the shape configuration parameters of TSM. Twenty four distinct experiments with different shape configuration parameters were carried out to identify how the shape affects the performance and the hysteresis curve of the TSM. For modeling the hysteretic behavior of the TSM, a composite model consisting of elementary hysteresis operators is proposed. Such a composite models parameters are empirically identified with least-squares optimization, for every shape configurations defined. The model processes the input to produce an estimated output for a certain shape, and this was verified with various types of input signals. Lastly, for compensating TSMs hysteretic behavior, a recursive algorithm producing inverse control signal from the empirical model is proposed, with a guaranteed real-time performance. The inverse algorithms position control effectiveness was verified under various shape configurations and input signal types.본 연구에서는 유연한 로봇 수술도구를 구현하기 위해 사용되는 Tendon-Sheath Mechanism (TSM)이 형상에 따른 이력현상의 변화가 발생하는 것을 실험적으로 확인하였으며, 이러한 이력현상을 표현하기 위한 모형을 제안하고 이를 이용하여 이력현상을 보상할 수 있는 알고리즘을 제안하였다. 첫 단계로 TSM을 구성하는 부품인 Tendon과 Sheath를 선정하는데 있어, 이력현상에 일조 하는 비선형적 특성을 최소화하는 재료와 공정 및 후처리 방법을 고려하여 적용하였다. 다음으로 TSM의 형상 변수를 정의하고 이를 다양한 형상하에서 이력현상의 변화를 관찰하는 실험장치를 설계하여 실험 데이터를 수집하였다. 이를 토대로 입력에 대한 출력의 관계를 Preisach type 연산자를 이용하여 표현하였고 실험 데이터에 기반한 연산자의 변수들을 최소자승 최적화를 통해 탐색하였으며, 모델의 적합성을 다양한 형상하에서, 각기 다른 종류의 입력 신호에 대한 출력을 모델을 통해 생성되는 출력 추정치와의 오차 분석으로 검증하였다. 이러한 모델로 이력현상을 보상하기 위해서 Set-Point 출력에 대한 Inverse Control 신호를 생성하는 재귀적 알고리즘을 제안하였으며, 이러한 알고리즘이 다양한 Set-point 출력의 형태에 대해서 실시간성이 보장되는 빠른 연산이 가능하다는 점을 보였다. 이력현상이 보상된 실험데이터와 기존의 보상전 실험데이터의 비교를 통해 보상전략이 효과적이라는 것을 보였으며, 다양한 형태에서도 적용이 가능함을 검증하였다.Table of Contents Chapter 1. Introduction 1 1.1 Background 1 1.1.1 Evolution of surgical robots 1 1.1.2 Flexible robotic systems 3 1.2 Tendon-sheath mechanism 6 1.2.1 Application of TSM in flexible surgical instruments 6 1.2.2 Effects on motion transfer characteristics 8 1.3 Previous studies 10 1.4 Research objectives 12 Chapter 2. Configuration and fabrication of TSM 14 2.1 Sheath 17 2.2 Tendon 19 2.2.1 Cable 19 2.2.2 Fitting 23 Chapter 3. Hysteretic behavior of TSM 25 3.1 Experiment setup 26 3.1.1 Experiment design 26 3.1.2 Hardware design 28 3.2 Experiment results 34 3.2.1 Effect of curve angle variation 34 3.2.2 Effect of radius of curvature variation 39 3.2.3 Summary of results of hysteretic behavior 46 Chapter 4. Modeling Hysteresis of TSM 49 4.1 Preisach model and Hysterons 50 4.2 Mechanical play operator 53 4.3 Complex hysteresis operator: 56 4.4 Parameter identification for complex hysteresis operator 59 4.5 Result of experimental verification of complex hysteresis operator 60 4.5.1 Result of reference input profile sinusoidal excitation 63 4.5.2 Result of validation input profile triangular excitation 65 4.5.3 Result of reference input profile trapezoidal excitation 67 4.5.4 Obtained weights for all shape configurations and summary 69 4.6 Inverse operator formulation 60 4.7 Experimental verification of hysteresis compensation with the inverse operator: 77 4.7.1 Experiment setup 77 4.7.2 Result of hysteresis compensation for shape =90,r=30mm 79 4.7.3 Result of hysteresis compensation for shape =60,r=60mm 82 4.7.4 Error statistic and result analysis 85 Chapter 6. Conclusion 87 Bibliography 88 Abstract in Korean 92Docto

A Methodology Towards Comprehensive Evaluation of Shape Memory Alloy Actuators for Prosthetic Finger Design

Presently, DC motors are the actuator of choice within intelligent upper limb prostheses. However, the weight and dimensions associated with suitable DC motors are not always compatible with the geometric restrictions of a prosthetic hand; reducing available degrees of freedom and ultimately rendering the prosthesis uncomfortable for the end-user. As a result, the search is on-going to find a more appropriate actuation solution that is lightweight, noiseless, strong and cheap. Shape memory alloy (SMA) actuators offer the potential to meet these requirements. To date, no viable upper limb prosthesis using SMA actuators has been developed. The primary reasons lie in low force generation as a result of unsuitable actuator designs, and significant difficulties in control owing to the highly nonlinear response of SMAs when subjected to joule heating. This work presents a novel and comprehensive methodology to facilitate evaluation of SMA bundle actuators for prosthetic finger design. SMA bundle actuators feature multiple SMA wires in parallel. This allows for increased force generation without compromising on dynamic performance. The SMA bundle actuator is tasked with reproducing the typical forces and contractions associated with the human finger in a prosthetic finger design, whilst maintaining a high degree of energy efficiency. A novel approach to SMA control is employed, whereby an adaptive controller is developed and tuned using the underlying thermo-mechanical principles of operation of SMA wires. A mathematical simulation of the kinematics and dynamics of motion provides a platform for designing, optimizing and evaluating suitable SMA bundle actuators offline. This significantly reduces the time and cost involved in implementing an appropriate actuation solution. Experimental results show iii that the performance of SMA bundle actuators is favourable for prosthesis applications. Phalangeal tip forces are shown to improve significantly through bundling of SMA wire actuators, while dynamic performance is maintained owing to the design and implementation of the selected control strategy. The work is intended to serve as a roadmap for fellow researchers seeking to design, implement and control SMA bundle actuators in a prosthesis design. Furthermore, the methodology can also be adopted to serve as a guide in the evaluation of other non-conventional actuation technologies in alternative applications

Modeling and Control for a Class of Tendon-Driven Continuum Mechanisms

This thesis contributes to the emerging field of soft material robots and treats modeling, state estimation and control for a special class of continuum mechanisms. The overall outcome of is a novel treatment of a continuum in robotics research. At first a description of the overall system as a tendon-driven multi-body system modeled by a nonlinear rigid-body dynamics is proposed. In combination with the introduced real-time pose and velocity estimation, nonlinear model-based control in real-time is possible. Furthermore, the structural properties of the model allow employing modern control methods for underactuated mechanical systems which are adapted to provide set point control for the upper platform. The developed methods in modeling, state estimation and control presented in this work are experimentally validated on a humanoid robot. Due to their promising results, this thesis lays the foundation for the use of tendon-driven continuum mechanisms as generic joint modules for modular robotic systems which may mark the beginning of a new generation of light-weight robots

Aeroelastic model and analysis of an active camber morphing wing

Morphing aircraft structures usually introduce greater compliance into aerodynamic sections, and therefore will affect the aeroelasticity with the potential risk of increased flutter. A low-fidelity model of an active camber morphing wing and its aeroelastic model are developed in order to investigate the potential critical speed by exploiting its chord-wise dimension and flexibility. Such a model may be used for conceptual design, where low fidelity models are used to explore and optimise a wide range of configurations. The morphing camber concept is implemented using a continuous representation of a two-segment structure with a rigid segment and a deformable part. The aeroelastic model is developed based on both steady and unsteady aerodynamic models, so that different parameters can be easily modified to examine changes in the flutter solutions. Of particular interest are the ratio of the morphing segment length to the chord, and its relative stiffness, as such morphing camber is potential operated using the deformable part as a flap. By comparing the results of the quasi-steady and unsteady aerodynamic models, it is shown that the quasi-steady aerodynamic model gives a more conservative prediction of the flutter speed. In addition, responses in phase space are simulated to show the fundamental aeroelastic behaviour of the morphing camber wing. It is also shown that the active compliant segment can be used to stabilise the morphing aircraft by using feedback control. This paper provides a system-level insight through mathematical modelling, parameter analysis and feedback control into dynamics applications of morphing camber

Reduction of dimensionality of a cellular actuator array for driving a robotic hand

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.Includes bibliographical references (p. 89-93).In an attempt to explore an alternative to today's robot actuators, a new approach to artificial muscle actuator design and control is presented. The objective of this research is to coordinate the multitude of artificial muscle actuator axes for a large DOF (degree of freedom) robotic system based on dimensionality reduction. An array of SMA actuators is segmented into many independently controlled, spatially discrete volumes, each contributing a small displacement to create a large motion. Segmented Binary Control is proposed where each segment is controlled in an on-off manner, creating a stepper-motor like actuator. This overcomes hysteresis and other nonlinearities of the actuator material. The segmented cellular architecture of SMA wires is extended to a multi-axis actuator array by arranging the segments in a two-dimensional array. The multi-axis control is streamlined and coordinated using a grouping of segments called C-segments in order to activate multiple links of a robot mechanism in a coordinated manner. This allows control of large DOF with a small number of controls. The proposed approach is inspired by the segmented architecture of biological muscles and synergies, a strategy of grouping output variables to simplify the control of large number of muscles. Data from various hand postures are collected using data glove and used in creating the C-segment design that is capable of performing the given postures. A lightweight Robotic Hand with 16 DOF is built using shape memory alloy actuators. This hand weighs less than 1kg including 32 SMA actuators and control circuitry. Eight C-segments that are ON-off controlled are used to create sixteen given postures. In the future, this approach can be applied to applications where the control signal is inherently limited due to limited amount of information that can be extracted or transferred to the robot, such as brain machine interface and tele-operation.by Kyu-Jin Cho.Ph.D

Robotic Exoskeleton Hand with Pneumatic Actuators

With modern developments of smart portable devices and miniaturization of technologies, society has been provided with computerized assistance for almost every daily activity but the physical aspects have been frequently ne-glected. It is currently possible to make robots that process information thru neural networks, that identify and mimic facial expressions and that replace manual labour in assembly plants, getting ever closer to skills associated to human beings. In spite of these technological advances being kept close to they remain separate of humans, replacing or providing assistance with other pe-ripheral tasks, not generally adopting a direct physical symbiotic user assis-tance path. In this dissertation a robotic exoskeleton hand will be described that al-lows for human-machine bidirectional interaction making it possible to provide physical activities with the electromechanical assistance similarly. This system is designed to mimic the human hands functionalities and biomechanical struc-ture, as well sensing and controlling systems. A partial prototype was also built, using components easily acquired in the market, as a proof of concept

Muscular Properties and Balance Control in Older Adults

The goal of this dissertation was to understand the role of age-related changes in muscle mechanical properties in the control of upright posture in humans. First, a methodology for estimating subject-specific muscle properties in healthy young and older individuals was developed. Magnetic resonance and ultrasound imaging were used in conjunction with dynamometer experiments, musculoskeletal modeling, and numerical optimization to estimate the properties of the dorsiflexor and individual plantarflexor (gastrocnemius and soleus) muscles for 12 young and 12 older adults (balanced for gender). With aging there were declines in maximal isometric strength and increases in series-elastic stiffness in the male subjects, but no differences in the female subjects. Regardless of gender, there were age-related changes in the shape of the force-velocity relation, such that the older subjects produced less relative force during both concentric and eccentric muscle contractions. The second study tested the balance abilities of the same subjects under a variety of static (quiet stance, leaning forward/backward) and dynamic (swaying at preferred/imposed frequencies, maximal reaching, external perturbation) conditions. The older adults performed more poorly on most of the balance tasks. While maximal isometric force made a smaller than expected contribution to predicting balancing ability, the force-length, force-velocity and force-extension properties of the muscles were all predictive of the age-related declines in balance control, explaining ~40% of the variance as independent predictors and ~50% when these factors were combined. Finally, a feedback-driven inverted pendulum model of postural control was developed, which incorporated realistic representations of young and old dorsiflexor and individual plantarflexor muscles using the previously estimated mechanical properties. A sensitivity analysis was performed by manipulating the properties of the plantarflexor muscles. The balancing ability of the model was most influenced by the optimal length of the contractile component and the slack length of the series elastic component of the plantarflexor muscle models. The quiet stance model highlighted the importance of the force-length relation of muscle to the stabilization of upright posture. This dissertation demonstrated that there are age-related changes in the dorsi- and plantarflexor mechanical properties, and these changes are associated with the declines in postural control that accompany aging

On the role of stability in animal morphology and neural control

Mechanical stability is vital for the fitness and survival of animals and is a crucial aspect of robot design and control. Stability depends on multiple factors, including the body\u27s intrinsic mechanical response and feedback control. But feedback control is more fragile than the body\u27s innate mechanical response or open-loop control strategies because of sensory noise and time-delays in feedback. This thesis examines the overarching hypothesis that stability demands have played a crucial role in how animal form and function arise through natural selection and motor learning. In two examples, finger contact and overall body stability, we investigated the relationship between morphology, open-loop control, and stability. By studying the stability of the internal degrees of freedom of a finger when pushing on a hard surface, we find that stability limits the force that we can produce and is a dominant aspect of the neural control of the finger\u27s muscles. In our study on whole body lateral stability during locomotion in terrestrial animals, we find that the overall body aspect ratio has evolved to ensure passive lateral stability on the uneven terrain of natural environments. Precisely gripping an object with the fingertips is a hallmark of human hand dexterity. In Chapter 2, we show how human fingers are intrinsically prone to a buckling-type postural instability and how humans use careful neural orchestration of our muscles so that the elastic response of our muscles can suppress the intrinsic instability. In Chapter 3, we extend these findings further to examine the nature of neuromuscular variability and how the nervous system deals with the need for muscle-induced stability. We find that there is structure to neuromuscular variability so that most of the variability lies within the subspace that does not affect stability. Inspired by the open-loop stable control of our index fingers, in Chapter 4, we derive open-loop stability conditions for a general mechanical linkage with arbitrary joint torques subjected to holonomic constraints. The solution that we derive is physically realizable as cable-driven active mechanical linkages. With a user-prescribed cable layout, we pose the problem of actuating the system to maintain stability while subject to goals like energy minimization as a convex optimization problem. We are thus able to use efficient optimization methods available for convex problems and demonstrate numerical solutions in examples inspired by the finger. Chapter 5 presents a general formulation of the stability criteria for active mechanical linkages subject to Pfaffian holonomic and non-holonomic constraints. Active mechanical linkages subject to multiple constraints represent the mechanics of systems spanning many domains and length scales, such as limbs and digits in animals and robots, and elastic networks like actin meshes in microscopic systems. We show that a constrained mechanical linkage with regular stiffness and damping, and circulation-free feedback, can only destabilize by static buckling when subject to holonomic constraints. In contrast, the same mechanical linkage, subject to a non-holonomic constraint, such as a skate contact, can exhibit either static buckling or flutter instability. Chapter 6 moves away from neural control and studies the shape of animal bodies and their relationship to stability in locomotion. We investigate why small land animals tend to have a crouched or sprawled posture, whereas larger animals are generally more upright. We propose a new hypothesis that the scaling of body aspect ratio with size is driven by the scale-dependent unevenness of natural terrain. We show that the scaling law arising from the need for stability on rough natural terrain correctly predicts the frontal aspect ratio scaling law across 335 terrestrial vertebrates and invertebrates, spanning eight orders of magnitude in mass so that smaller animals have a wider aspect ratio. We also carry out statistical analyses that consider the phylogenetic relationship among the species in our dataset to show that the scaling is not due to gradual changes of the traits over time. Thus, stability demands on natural terrain may have driven the macroevolution of body aspect ratio across terrestrial animals. Interrogating unstable and marginally stable behaviors has helped us identify the morphological and control features that allow animals to perform robustly in noisy environments where perfect sensory feedback cannot be assumed. Although the thesis identifies the `what\u27 and `why,\u27 further studies are needed to understand `how\u27 mechanics and development intertwine to give rise to control and form in growing and adapting biological organisms