Design of a variable-stiffness robotic hand using pneumatic soft rubber actuators

In recent years, Japanese society has been ageing, engendering a labor shortage of young workers. Robots are therefore expected to be useful in performing tasks such as day-to-day support for elderly people. In particular, robots that are intended for use in the field of medical care and welfare are expected to be safe when operating in a human environment because they often come into contact with people. Furthermore, robots must perform various tasks such as regrasping, grasping of soft objects, and tasks using frictional force. Given these demands and circumstances, a tendon-driven robot hand with a stiffness changing finger has been developed. The finger surface stiffness can be altered by adjusting the input pressure depending on the task. Additionally, the coefficient of static friction can be altered by changing the surface stiffness merely by adjusting the input air pressure. This report describes the basic structure, driving mechanism, and basic properties of the proposed robot hand

Compliant actuators that mimic biological muscle performance with applications in a highly biomimetic robotic arm

This paper endeavours to bridge the existing gap in muscular actuator design for ligament-skeletal-inspired robots, thereby fostering the evolution of these robotic systems. We introduce two novel compliant actuators, namely the Internal Torsion Spring Compliant Actuator (ICA) and the External Spring Compliant Actuator (ECA), and present a comparative analysis against the previously conceived Magnet Integrated Soft Actuator (MISA) through computational and experimental results. These actuators, employing a motor-tendon system, emulate biological muscle-like forms, enhancing artificial muscle technology. A robotic arm application inspired by the skeletal ligament system is presented. Experiments demonstrate satisfactory power in tasks like lifting dumbbells (peak power: 36W), playing table tennis (end-effector speed: 3.2 m/s), and door opening, without compromising biomimetic aesthetics. Compared to other linear stiffness serial elastic actuators (SEAs), ECA and ICA exhibit high power-to-volume (361 x 10^3 W/m) and power-to-mass (111.6 W/kg) ratios respectively, endorsing the biomimetic design's promise in robotic development

Design, implementation, and evaluation of a variable stiffness transradial hand prosthesis

We present the design, implementation, and experimental evaluation of a low-cost, customizable, easy-to-use transradial hand prosthesis capable of adapting its compliance. Variable stiffness actuation (VSA) of the prosthesis is based on antagonistically arranged tendons coupled to nonlinear springs driven through a Bowden cable based power transmission. Bowden cable based antagonistic VSA can, not only regulate the stiffness and the position of the prosthetic hand but also enables a light-weight and low-cost design, by the opportunistic placement of motors, batteries, and controllers on any convenient location on the human body, while nonlinear springs are conveniently integrated inside the forearm. The transradial hand prosthesis also features tendon driven underactuated compliant fingers that allow natural adaption of the hand shape to wrap around a wide variety of object geometries, while the modulation of the stiffness of their drive tendons enables the prosthesis to perform various tasks with high dexterity. The compliant fingers of the prosthesis add inherent robustness and flexibility, even under impacts. The control of the variable stiffness transradial hand prosthesis is achieved by an sEMG based natural human-machine interface

Variable stiffness robotic hand for stable grasp and flexible handling

Robotic grasping is a challenging area in the field of robotics. When interacting with an object, the dynamic properties of the object will play an important role where a gripper (as a system), which has been shown to be stable as per appropriate stability criteria, can become unstable when coupled to an object. However, including a sufficiently compliant element within the actuation system of the robotic hand can increase the stability of the grasp in the presence of uncertainties. This paper deals with an innovative robotic variable stiffness hand design, VSH1, for industrial applications. The main objective of this work is to realise an affordable, as well as durable, adaptable, and compliant gripper for industrial environments with a larger interval of stiffness variability than similar existing systems. The driving system for the proposed hand consists of two servo motors and one linear spring arranged in a relatively simple fashion. Having just a single spring in the actuation system helps us to achieve a very small hysteresis band and represents a means by which to rapidly control the stiffness. We prove, both mathematically and experimentally, that the proposed model is characterised by a broad range of stiffness. To control the grasp, a first-order sliding mode controller (SMC) is designed and presented. The experimental results provided will show how, despite the relatively simple implementation of our first prototype, the hand performs extremely well in terms of both stiffness variability and force controllability

A Bioinspired Bidirectional Stiffening Soft Actuator for Multimodal, Compliant, and Robust Grasping

The stiffness modulation mechanism for soft robotics has gained considerable attention to improve deformability, controllability, and stability. However, for the existing stiffness soft actuator, high lateral stiffness and a wide range of bending stiffness are hard to be provided at the same time. This paper presents a bioinspired bidirectional stiffening soft actuator (BISA) combining the air-tendon hybrid actuation (ATA) and a bone-like structure (BLS). The ATA is the main actuation of the BISA, and the bending stiffness can be modulated with a maximum stiffness of about 0.7 N/mm and a maximum magnification of 3 times when the bending angle is 45 deg. Inspired by the morphological structure of the phalanx, the lateral stiffness can be modulated by changing the pulling force of the BLS. The lateral stiffness can be modulated by changing the pulling force to it. The actuator with BLSs can improve the lateral stiffness about 3.9 times compared to the one without BLSs. The maximum lateral stiffness can reach 0.46 N/mm. And the lateral stiffness can be modulated decoupling about 1.3 times (e.g., from 0.35 N/mm to 0.46 when the bending angle is 45 deg). The test results show the influence of the rigid structures on bending is small with about 1.5 mm maximum position errors of the distal point of actuator bending in different pulling forces. The advantages brought by the proposed method enable a soft four-finger gripper to operate in three modes: normal grasping, inverse grasping, and horizontal lifting. The performance of this gripper is further characterized and versatile grasping on various objects is conducted, proving the robust performance and potential application of the proposed design method

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

Designing a robotic port system for laparo-endoscopic single-site surgery

Current research and development in the field of surgical interventions aim to reduce the invasiveness by using few incisions or natural orifices in the body to access the surgical site. Considering surgeries in the abdominal cavity, the Laparo-Endoscopic Single-site Surgery (LESS) can be performed through a single incision in the navel, reducing blood loss, post-operative trauma, and improving the cosmetic outcome. However, LESS results in less intuitive instrument control, impaired ergonomic, loss of depth and haptic perception, and restriction of instrument positioning by a single incision. Robot-assisted surgery addresses these shortcomings, by introducing highly articulated, flexible robotic instruments, ergonomic control consoles with 3D visualization, and intuitive instrument control algorithms. The flexible robotic instruments are usually introduced into the abdomen via a rigid straight port, such that the positioning of the tools and therefore the accessibility of anatomical structures is still constrained by the incision location. To address this limitation, articulated ports for LESS are proposed by recent research works. However, they focus on only a few aspects, which are relevant to the surgery, such that a design considering all requirements for LESS has not been proposed yet. This partially originates in the lack of anatomical data of specific applications. Further, no general design guidelines exist and only a few evaluation metrics are proposed. To target these challenges, this thesis focuses on the design of an articulated robotic port for LESS partial nephrectomy. A novel approach is introduced, acquiring the available abdominal workspace, integrated into the surgical workflow. Based on several generated patient datasets and developed metrics, design parameter optimization is conducted. Analyzing the surgical procedure, a comprehensive requirement list is established and applied to design a robotic system, proposing a tendon-driven continuum robot as the articulated port structure. Especially, the aspects of stiffening and sterile design are addressed. In various experimental evaluations, the reachability, the stiffness, and the overall design are evaluated. The findings identify layer jamming as the superior stiffening method. Further, the articulated port is proven to enhance the accessibility of anatomical structures and offer a patient and incision location independent design

Redundant Unilaterally Actuated Kinematic Chains: Modeling and Analysis

Unilaterally Actuated Robots (UAR)s are a class of robots defined by an actuation that is constrained to a single sign. Cable robots, grasping, fixturing and tensegrity systems are certain applications of UARs. In recent years, there has been increasing interest in robotic and other mechanical systems actuated or constrained by cables. In such systems, an individual constraint is applied to a body of the mechanism in the form of a pure force which can change its magnitude but cannot reverse its direction. This uni-directional actuation complicates the design of cable-driven robots and can result in limited performance. Cable Driven Parallel Robot (CDPR)s are a class of parallel mechanisms where the actuating legs are replaced by cables. CDPRs benefit from the higher payload to weight ratio and increased rigidity. There is growing interest in the cable actuation of multibody systems. There are potential applications for such mechanisms where low moving inertia is required. Cable-driven serial kinematic chain (CDSKC) are mechanisms where the rigid links form a serial kinematic chain and the cables are arranged in a parallel configuration. CDSKC benefits from the dexterity of the serial mechanisms and the actuation advantages of cable-driven manipulators. Firstly, the kinematic modeling of CDSKC is presented, with a focus on different types of cable routings. A geometric approach based on convex cones is utilized to develop novel cable actuation schemes. The cable routing scheme and architecture have a significant effect on the performance of the robot resulting in a limited workspace and high cable forces required to perform a desired task. A novel cable routing scheme is proposed to reduce the number of actuating cables. The internal routing scheme is where, in addition to being externally routed, the cable can be re-routed internally within the link. This type of routing can be considered as the most generalized form of the multi-segment pass-through routing scheme where a cable segment can be attached within the same link. Secondly, the analysis for CDSKCs require extensions from single link CDPRs to consider different routings. The conditions to satisfy wrench-closure and the workspace analysis of different multi-link unilateral manipulators are investigated. Due to redundant and constrained actuation, it is possible for a motion to be either infeasible or the desired motion can be produced by an infinite number of different actuation profiles. The motion generation of the CDSKCs with a minimal number of actuating cables is studied. The static stiffness evaluation of CDSKCs with different routing topologies and isotropic stiffness conditions were investigated. The dexterity and wrench-based metrics were evaluated throughout the mechanism's workspace. Through this thesis, the fundamental tools required in studying cable-driven serial kinematic chains have been presented. The results of this work highlight the potential of using CDSKCs in bio-inspired systems and tensegrity robots