Sci Robot

Robotic leg prostheses promise to improve the mobility and quality of life of millions of individuals with lower-limb amputations by imitating the biomechanics of the missing biological leg. Unfortunately, existing powered prostheses are much heavier and bigger and have shorter battery life than conventional passive prostheses, severely limiting their clinical viability and utility in the daily life of amputees. Here, we present a robotic leg prosthesis that replicates the key biomechanical functions of the biological knee, ankle, and toe in the sagittal plane while matching the weight, size, and battery life of conventional microprocessor-controlled prostheses. The powered knee joint uses a unique torque-sensitive mechanism combining the benefits of elastic actuators with that of variable transmissions. A single actuator powers the ankle and toe joints through a compliant, underactuated mechanism. Because the biological toe dissipates energy while the biological ankle injects energy into the gait cycle, this underactuated system regenerates substantial mechanical energy and replicates the key biomechanical functions of the ankle/foot complex during walking. A compact prosthesis frame encloses all mechanical and electrical components for increased robustness and efficiency. Preclinical tests with three individuals with above-knee amputation show that the proposed robotic leg prosthesis allows for common ambulation activities with close to normative kinematics and kinetics. Using an optional passive mode, users can walk on level ground indefinitely without charging the battery, which has not been shown with any other powered or microprocessor-controlled prostheses. A prosthesis with these characteristics has the potential to improve real-world mobility in individuals with above-knee amputation.R01 HD098154/HD/NICHD NIH HHSUnited States/T42 OH008414/OH/NIOSH CDC HHSUnited States

사람 근골격 특성을 반영한 로봇 손가락 설계

학위논문(박사) -- 서울대학교대학원 : 융합과학기술대학원 융합과학부(지능형융합시스템전공), 2023. 2. 박재흥.What the manipulator can perform is determined by what the end-effectors, including the robotic hand, can do because it is the gateway that directly interacts with the surrounding environment or objects. In order for robots to have human-level task performance in a human-centered environment, the robotic hand with human-hand-level capabilities is essential. Here, the human-hand-level capabilities include not only force-speed, and dexterity, but also size and weight. However, to our knowledge, no robotic hand exists that simultaneously realizes the weight, size, force, and dexterity of the human hand and continues to remain a challenge. In this thesis, to improve the performance of the robotic hand, the modular robotic finger design with three novel mechanisms based on the musculoskeletal characteristics of the human hand was proposed. First, the tendon-driven robotic finger with intrinsic/extrinsic actuator arrangement like the muscle arrangement of the human hand was proposed and analyzed. The robotic finger consists of five different tendons and ligaments. By analyzing the fingertip speed while a human is performing various object grasping motions, the actuators of the robotic finger were separated into intrinsic actuators responsible for slow motion and an extrinsic actuator that performs the motions requiring both large force and high speed. Second, elastomeric continuously variable transmission (ElaCVT), a new concept relating to continuously variable transmission (CVT), was designed to improve the performance of the electric motors remaining weight and size and applied as an extrinsic actuator of the robotic finger. The primary purpose of ElaCVT is to expand the operating region of a twisted string actuator (TSA) and duplicate the force-velocity curve of the muscles by passively changing the reduction ratio according to the external load applied to the end of the TSA. A combination of ElaCVT and TSA (ElaCVT-TSA) is proposed as a linear actuator. With ElaCVT-TSA, an expansion of the operating region of electric motors to the operating region of the muscles was experimentally demonstrated. Finally, as the flexion/extension joints of the robotic finger, anthropomorphic rolling contact joint, which mimicked the structures of the human finger joint like tongue-and-groove, and collateral ligaments, was proposed. As compliant joints not only compensate for the lack of actuated degrees of freedom of an under-actuated system and improve grasp stability but also prevent system failure from unexpected contacts, various types of compliant joints have been applied to end-effectors. Although joint compliance increases the success rate of power grasping, when the finger wraps around large objects, it can reduce the grasping success rate in pinch gripping when dealing with small objects using the fingertips. To overcome this drawback, anthropomorphic rolling contact joint is designed to passively adjust the torsional stiffness according to the joint angle without additional weight and space. With the anthropomorphic rolling contact joint, the stability of pinch grasping improved.엔드이팩터는 로봇과 주변 환경이 상호작용하는 통로로 매니퓰레이터가 수행할 수 있는 작업은 엔드이펙터의 성능에 제한된다. 사람 중심의 환경에 로봇이 적용되어 사람 수준의 다양한 작업을 수행하기 위해서는 사람 손 수준의 성능을 갖는 로봇 손이 필수적이며 사람 손 수준의 성능은 단순히 힘-속도, 자유도만을 포함하는 것이 아닌 크기와 무게 그리고 물체 조작에 도움을 주는 여러 손 특성도 포함한다. 그러나 현재까지 사람 손 수준의 무게, 크기, 힘 그리고 자유도를 모두 만족시키는 로봇 손은 개발되지 않았으며 여전히 도전적인 과제로 남아있다. 본 논문에서는 로봇 손가락의 성능을 향상하기 위하여 사람의 근골격 특성을 반영한 세 가지의 새로운 메커니즘을 제안하고 이를 통합한 모듈형 로봇 손가락 구조를 보인다. 첫 번째로, 사람의 손 근육 배치와 유사한 내재/외재 구동기 배치를 적용한 힘줄 구동 로봇 손가락 구조를 제안하고 분석한다. 로봇 손가락은 다섯 개의 서로 다른 힘줄과 인대로 구성된다. 사람 손동작 분석에 기반하여 로봇 손가락의 구동기는 느린 속도를 담당하는 내재 구동기와 빠르고 큰 힘이 모두 요구되는 외재 구동기로 구분된다. 두 번째로, 구동기의 크기와 무게를 유지하며 성능을 향상하기 위하여 새로운 개념의 무단 변속기 Elastomeric Continuously Variable Transmission (ElaCVT) 을 제안하고 이를 로봇 손가락의 외재 구동기에 적용하였다. ElaCVT는 선형 구동기의 작동 영역을 확장하고 출력단에 가해지는 외부 하중에 따라 감속비를 수동적으로 변경하여 근육의 힘-속도 곡선을 모사할 수 있다. 본 연구에서는 근육의 특성을 모사하기 위해 선형 액추에이터로 ElaCVT에 줄 꼬임 메커니즘을 적용한 ElaCVT-TSA를 제안, 근육의 동작 영역을 모사할 수 있음을 보였다. 마지막으로 로봇 손가락의 모든 굽힘/펼침 관절에 적용된 사람의 관절구조를 모사한 유연 구름 접촉 관절 (Anthropomorphic Rolling Contact joint)을 제안한다. Anthropomorphic rolling contact joint는 사람 관절의 tongue-and-groove 형상과 collateral ligament를 모사하여 관절의 안정성을 향상시켰다. 기존의 유연 관절과 달리 관절이 펴진 상태에서는 유연한 상태를 유지하며 굽혀진 상태에서는 강성이 증가한다는 특징을 갖는다. 특히, 강성 변화에 별도의 구동기가 요구되지 않아 기존의 관절에서 무게, 크기 증가 없이 해당 특징 구현이 가능하다. 이는 로봇 손가락에 적용되어 손가락을 펴고 물체를 탐색하는 과정에서는 충격을 흡수하여 안정적인 접촉을 구현할 수 있으며 물체를 파지하는 과정에서는 손가락을 굽혀 강인하게 물체를 파지할 수 있게 한다. Anthropomorphic rolling contact joint를 적용한 그립퍼를 이용하여 제안하는 가변 강성 유연 관절이 pinch grasping의 파지 안정성을 높임을 보였다.1 INTRODUCTION 1 1.1 MOTIVATION: ROBOTIC HANDS 1 1.2 CONTRIBUTIONS OF THESIS 10 1.2.1 Intrinsic/Extrinsic Actuator arrangement 11 1.2.2 Linear actuator mimicking human muscle properties 11 1.2.3 Flexible rolling contact joint 12 2 ROBOTIC FINGER STRUCTURE WITH HUMAN-LIKE ACTUATOR ARRANGEMENT 13 2.1 ANALYSIS OF HUMAN FINGERTIP VELOCITY 14 2.2 THE ROBOTIC FINGER WITH INTRINSIC/EXTRINSIC ACTUATORS 18 2.2.1 The structure of proposed robotic finger 18 2.2.2 Kinematics of the robotic finger 20 2.2.3 Tendons and Ligaments of the proposed robotic finger 26 2.2.4 Decoupled fingertip motion in the sagittal plane 28 3 ELASTOMERIC CONTINUOUSLY VARIABLE TRANSMISSION COMBINED WITH TWISTED STRING ACTUATOR 35 3.1 BACKGROUND & RELATED WORKS 35 3.2 COMPARISON OF OPERATING REGIONS 40 3.3 DESIGN OF THE ELASTOMERIC CONTINUOUSLY VARIABLE TRANSMISSION 42 3.3.1 Structure of ElaCVT 42 3.3.2 Design of Elastomer and Lateral Disc 43 3.3.3 Advantages of ElaCVT 48 3.4 PERFORMANCE EVALUATION 50 3.4.1 Experimental Setup 50 3.4.2 Contraction with Fixed external load 50 3.4.3 Contraction with Variable external load 55 3.4.4 Performance variation of ElaCVT over long term usage 55 3.4.5 Specifications and Limitations of ElaCVT-TSA 59 4 ANTHROPOMORPHIC ROLLING CONTACT JOINT 61 4.1 INTRODUCTION: COMPLIANT JOINT 61 4.2 RELATED WORKS: ROLLING CONTACT JOINT 65 4.3 ANTHROPOMORPHIC ROLLING CONTACT JOINT 67 4.3.1 Fundamental Components of ARC joint 69 4.3.2 Advantages of ARC joint 73 4.4 TORSIONAL STIFFNESS EVALUATION 75 4.4.1 Experimental Setup 75 4.4.2 Design and Manufacturing of ARC joints 77 4.4.3 Torsional Stiffness Change according to Joint Angle and Twist Angle 79 4.5 TORSIONAL STIFFNESS WITH JOINT COMPRESSION FORCE DUE TO TNESION OF TENDONS 80 4.6 TORSIONAL STIFFNESS WITH LUBRICATION STRUCTURE 82 4.7 GRASPING PERFORMANCE COMPARISON OF GRIPPERS WITH DIFFERENT ARC JOINTS 86 5 CONCLUSIONS 92 Abstract (In Korean) 107박

An anthropomorphic robotic finger with innate human-finger-like biomechanical advantages part II : flexible tendon sheath and grasping demonstration

The human hand has a fantastic ability to interact with various objects in the dynamic unstructured environment of our daily activities. We believe that this outstanding performance benefits a lot from the unique biological features of the hand musculoskeletal system. In Part I of this article, a bio-inspired anthropomorphic robotic finger was developed, based on which two human-finger-like biomechanical advantages were elaborately investigated, including the anisotropic variable stiffness associated with the ligamentous joints and the enlarged feasible force space associated with the reticular extensor mechanisms. In Part II, the fingertip force-velocity characteristics resulting from the flexible tendon sheath are studied. It indicates that the fingertip force–velocity workspace can be greatly augmented owing to the self-adaptive morphing of the flexible tendon sheaths, showing the average improvement of 41.2% theoretically and 117.5% experimentally compared with the results of 2 mm, 4 mm, and 6 mm size rigid tendon sheaths. Grasping tests and comparisons are then conducted with four three-fingered robotic hands (one with the robotic finger proposed in Part I, one with hinge joints, one with linear extensors, and one with rigid tendon sheaths) and the human hands of six subjects to handle various objects on flat, rough, and soft surfaces. The results show that the novel bio-inspired design in this research could improve the grasping success rates of the robotic hand. Compared with the grasping test results from the robotic hand with the bio-inspired robotic finger proposed in Part I, the overall grasping performance of a robotic hand with hinge joints, linear extensors, and rigid tendon sheaths decreases by 10%, 6%, and 17%, respectively. The results have also shown that with the embedded biomechanical advantages, even without complex control and sensory systems, the robotic fingers can achieve very comparable performance to human fingers in the grasping demonstrations presented, indicating average 94% of the success rate achieved by the human fingers. Successfully demonstrating 14 of 16 grasp types in the Cutkoskey taxonomy further shows the human-finger-like grasping capability of the proposed robotic fingers

Functional Soft Robotic Actuators Based on Dielectric Elastomers

Dielectric elastomer actuators (DEAs) are a promising soft actuator technology for robotics. Adding robotic functionalities--folding, variable stiffness, and adhesion--into their actuator design is a novel method to create functionalized robots with simplified actuator configurations. We first propose a foldable actuator that has a simple antagonistic DEA configuration allowing bidirectional actuation and passive folding. To prove the concept, a foldable elevon actuator with outline size of 70 mm × 130 mm is developed with a performance specification matched to a 400 mm wingspan micro air vehicle (MAV) of mass 130 g. The developed actuator exhibits actuation angles up to ± 26 ° and a torque of 2720 mN·mm in good agreement with a prediction model. During a flight, two of these integrated elevon actuators well controlled the MAV, as proven by a strong correlation of 0.7 between the control signal and the MAV motion. We next propose a variable stiffness actuator consisting of a pre-stretched DEA bonded on a low-melting-point alloy (LMPA) embedded silicone substrate. The phase of the LMPA changes between liquid and solid enabling variable stiffness of the structure, between soft and rigid states, while the DEA generates a bending actuation. A proof-of-concept actuator with dimension 40 mm length × 10mm width × 1mm thickness and a mass of 1 g is fabricated and characterized. Actuation is observed up to 47.5 ° angle and yielding up to 2.4 mN of force in the soft state. The stiffness in the rigid state is ~90 × larger than an actuator without LMPA. We develop a two-finger gripper in which the actuators act as the fingers. The rigid state allows picking up an object mass of 11 g (108 mN), to be picked up even though the actuated grasping force is only 2.4 mN. We finally propose an electroadhesion actuator that has a DEA design simultaneously maximizing electroadhesion and electrostatic actuation, while allowing self-sensing by employing an interdigitated electrode geometry. The concept is validated through development of a two-finger soft gripper, and experimental samples are characterized to address an optimal design. We observe that the proposed DEA design generates 10 × larger electroadhesion force compared to a conventional DEA design, equating to a gripper with a high holding force (3.5 N shear force for 1 cm^2) yet a low grasping force (1 mN). These features make the developed simple gripper to handle a wide range of challenging objects such as highly-deformable water balloons (35.6 g), flat paper (0.8 g), and a raw chicken egg (60.9 g), with its lightweight (1.5 g) and fast movement (100 ms to close fingers). The results in this thesis address the creation of the functionalized robots and expanding the use of DEAs in robotics

Distributed Sensing and Stimulation Systems Towards Sense of Touch Restoration in Prosthetics

Modern prostheses aim at restoring the functional and aesthetic characteristics of the lost limb. To foster prosthesis embodiment and functionality, it is necessary to restitute both volitional control and sensory feedback. Contemporary feedback interfaces presented in research use few sensors and stimulation units to feedback at most two discrete feedback variables (e.g. grasping force and aperture), whereas the human sense of touch relies on a distributed network of mechanoreceptors providing high-fidelity spatial information. To provide this type of feedback in prosthetics, it is necessary to sense tactile information from artificial skin placed on the prosthesis and transmit tactile feedback above the amputation in order to map the interaction between the prosthesis and the environment. This thesis proposes the integration of distributed sensing systems (e-skin) to acquire tactile sensation, and non-invasive multichannel electrotactile feedback and virtual reality to deliver high-bandwidth information to the user. Its core focus addresses the development and testing of close-loop sensory feedback human-machine interface, based on the latest distributed sensing and stimulation techniques for restoring the sense of touch in prosthetics. To this end, the thesis is comprised of two introductory chapters that describe the state of art in the field, the objectives and the used methodology and contributions; as well as three studies distributed over stimulation system level and sensing system level. The first study presents the development of close-loop compensatory tracking system to evaluate the usability and effectiveness of electrotactile sensory feedback in enabling real-time close-loop control in prosthetics. It examines and compares the subject\u2019s adaptive performance and tolerance to random latencies while performing the dynamic control task (i.e. position control) and simultaneously receiving either visual feedback or electrotactile feedback for communicating the momentary tracking error. Moreover, it reported the minimum time delay needed for an abrupt impairment of users\u2019 performance. The experimental results have shown that electrotactile feedback performance is less prone to changes with longer delays. However, visual feedback drops faster than electrotactile with increased time delays. This is a good indication for the effectiveness of electrotactile feedback in enabling close- loop control in prosthetics, since some delays are inevitable. The second study describes the development of a novel non-invasive compact multichannel interface for electrotactile feedback, containing 24 pads electrode matrix, with fully programmable stimulation unit, that investigates the ability of able-bodied human subjects to localize the electrotactile stimulus delivered through the electrode matrix. Furthermore, it designed a novel dual parameter -modulation (interleaved frequency and intensity) and compared it to conventional stimulation (same frequency for all pads). In addition and for the first time, it compared the electrotactile stimulation to mechanical stimulation. More, it exposes the integration of virtual prosthesis with the developed system in order to achieve better user experience and object manipulation through mapping the acquired real-time collected tactile data and feedback it simultaneously to the user. The experimental results demonstrated that the proposed interleaved coding substantially improved the spatial localization compared to same-frequency stimulation. Furthermore, it showed that same-frequency stimulation was equivalent to mechanical stimulation, whereas the performance with dual-parameter modulation was significantly better. The third study presents the realization of a novel, flexible, screen- printed e-skin based on P(VDF-TrFE) piezoelectric polymers, that would cover the fingertips and the palm of the prosthetic hand (particularly the Michelangelo hand by Ottobock) and an assistive sensorized glove for stroke patients. Moreover, it developed a new validation methodology to examine the sensors behavior while being solicited. The characterization results showed compatibility between the expected (modeled) behavior of the electrical response of each sensor to measured mechanical (normal) force at the skin surface, which in turn proved the combination of both fabrication and assembly processes was successful. This paves the way to define a practical, simplified and reproducible characterization protocol for e-skin patches In conclusion, by adopting innovative methodologies in sensing and stimulation systems, this thesis advances the overall development of close-loop sensory feedback human-machine interface used for restoration of sense of touch in prosthetics. Moreover, this research could lead to high-bandwidth high-fidelity transmission of tactile information for modern dexterous prostheses that could ameliorate the end user experience and facilitate it acceptance in the daily life

A Perspective on Cephalopods Mimicry and Bioinspired Technologies toward Proprioceptive Autonomous Soft Robots

Octopus skin is an amazing source of inspiration for bioinspired sensors, actuators and control solutions in soft robotics. Soft organic materials, biomacromolecules and protein ingredients in octopus skin combined with a distributed intelligence, result in adaptive displays that can control emerging optical behavior, and 3D surface textures with rough geometries, with a remarkably high control speed (≈ms). To be able to replicate deformable and compliant materials capable of translating mechanical perturbations in molecular and structural chromogenic outputs, could be a glorious achievement in materials science and in the technological field. Soft robots are suitable platforms for soft multi-responsive materials, which can provide them with improved mechanical proprioception and related smarter behaviors. Indeed, a system provided with a “learning and recognition” functions, and a constitutive “mechanical” and “material intelligence” can result in an improved morphological adaptation in multi-variate environments responding to external and internal stimuli. This review aims to explore challenges and opportunities related to smart and chromogenic responsive materials for adaptive displays, reconfigurable and programmable soft skin, proprioceptive sensing system, and synthetic nervous control units for data processing, toward autonomous soft robots able to communicate and interact with users in open-world scenarios

3D printed muscle-powered bio-bots

Complex biological systems sense, process, and respond to a range of environmental signals in real-time. The ability of such systems to adapt their functional response to dynamic external signals motivates the use of biological materials in other engineering applications. Recent advances in 3D printing have enabled the manufacture of complex structures from biological materials. We have developed a projection stereolithographic 3D printing apparatus capable of patterning cells and biocompatible polymers at physiologically relevant length scales, on the order of single cells. This enables reverse engineering in vitro model systems that recreate the structure and function of native tissue for applications ranging from high-throughput drug testing to regenerative medicine. While reverse engineering native tissues and organs has important implications in biomedical engineering, the ability to “build with biology” presents the next generation of engineers with both a unique design challenge and opportunity. Specifically, we now have the ability to forward engineer bio-hybrid machines and robots (bio-bots) that harness the adaptive functionalities of biological materials to achieve more complex functional behaviors than machines composed of synthetic materials alone. Perhaps the most intuitive demonstration of a “living machine” is a system that can generate force and produce motion. To that end, we have designed and 3D printed locomotive bio-bots, powered by external electrical and optical stimuli. In addition to being the first demonstrations of untethered locomotion in skeletal musclepowered soft robots, these bio-hybrid machines have served as meso-scale models for studying tissue self-assembly, maturation, damage, remodeling, and healing in vitro. Bio-hybrid machines that can dynamically sense and adaptively respond to a range of environmental signals have broad applicability in healthcare applications such as dynamic implants or targeted drug delivery. Advanced research in exoskeletons and hyper-natural functionality could even extend the useful application of such machines to national defense and environmental cleanup. We have developed a modular skeletal muscle bioactuator that can serve as a fundamental building block for such machines, setting the stage for future generations of bio-hybrid machines that can self-assemble, self-heal, and perhaps even self-replicate to target grand engineering challenges. Furthermore, we present a robust optimized protocol for manufacturing 3D printed muscle-powered biological machines, and a mechanism to incorporate biological “building blocks” into the toolbox of the next generation of engineers and scientists