441 research outputs found

    Anthropomorphic Twisted String-Actuated Soft Robotic Gripper with Tendon-Based Stiffening

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    Realizing high-performance soft robotic grippers is challenging because of the inherent limitations of the soft actuators and artificial muscles that drive them, including low force output, small actuation range, and poor compactness. Despite advances in this area, realizing compact soft grippers with high dexterity and force output is still challenging. This paper explores twisted string actuators (TSAs) to drive a soft robotic gripper. TSAs have been used in numerous robotic applications, but their inclusion in soft robots has been limited. The proposed design of the gripper was inspired by the human hand. Tunable stiffness was implemented in the fingers with antagonistic TSAs. The fingers' bending angles, actuation speed, blocked force output, and stiffness tuning were experimentally characterized. The gripper achieved a score of 6 on the Kapandji test and recreated 31 of the 33 grasps of the Feix GRASP taxonomy. It exhibited a maximum grasping force of 72 N, which was almost 13 times its own weight. A comparison study revealed that the proposed gripper exhibited equivalent or superior performance compared to other similar soft grippers.Comment: 19 pages, 15 figure

    Compliant, Large-Strain, and Self-Sensing Twisted String Actuators with Applications to Soft Robots

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    The twisted string actuator (TSA) is a rotary-to-linear transmission system that has been implemented in robots for high force output and efficiency. The basic components of a TSA are a motor, strings, and a load (to keep the strings in tension). The twisting of the strings shortens their length to generate linear contraction. Due to their high force output, energy efficiency, and compact form factor, TSAs hold the potential to improve the performance of soft robots. Currently, it is challenging to realize high-performance soft robots because many existing soft or compliant actuators exhibit limitations such as fabrication complexity, high power consumption, slow actuation, or low force generation. The applications of TSAs in soft robots have hitherto been limited, mainly for two reasons. Firstly, the conventional strings of TSAs are stiff and strong, but not compliant. Secondly, precise control of TSAs predominantly relies on external position or force sensors. For these reasons, TSA-driven robots are often rigid or bulky.To make TSAs more suitable for actuating soft robots, compliant, large-strain, and self-sensing TSAs are developed and applied to various soft robots in this work. The design was realized by replacing conventional inelastic strings with compliant, thermally-activated, and conductive supercoiled polymer (SCP) strings. Self-sensing was realized by correlating the electrical resistance of the strings with their length. Large strains are realized by heating the strings in addition to twisting them. The quasi-static actuation and self-sensing properties are accurately captured by Preisach hysteresis operators. Next, a data-driven mathematical model was proposed and experimentally validated to capture the transient decay, creep, and hysteretic effects in the electrical resistance. This model was then used to predict the length of the TSA, given its resistance. Furthermore, three TSA-driven soft robots were designed and fabricated: a three-fingered gripper, a soft manipulator, and an anthropomorphic gripper. For the three-fingered gripper, its fingers were compliant and designed to exploit the Fin Ray Effect for improved grasping. The soft manipulator was driven by three TSAs that allowed it to bend with arbitrary magnitude and direction. A physics-based modeling strategy was developed to predict this multi-degree-of-freedom motion. The proposed modeling approaches were experimentally verified to be effective. For example, the proposed model predicted bending angle and bending velocity with mean errors of 1.58 degrees (2.63%) and 0.405 degrees/sec (4.31%), respectively. The anthropomorphic gripper contained 11 TSAs; two TSAs were embedded in each of the four fingers and three TSAs were embedded in the thumb. Furthermore, the anthropomorphic gripper achieved tunable stiffness and a wide range of grasps

    Design, characterisation and validation of a haptic interface based on twisted string actuation.

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    This paper presents the design and experimental characterisation of a wrist haptic interface based on a twisted string actuator. The interface is designed for controlled actuation of wrist flexion/extension and is capable of rendering torque feedback through a rotary handle driven by the twisted string actuator and spring-loaded cable mechanisms. The interface was characterised to obtain its static and dynamic haptic feedback rendering capabilities. Compliance in the spring and actuation mechanism makes the interface suitable for smooth rendering of haptic feedback of large magnitudes due to the high motion transmission ratio of the twisted strings. Haptic virtual wall rendering capabilities are demonstrated

    Design, Fabrication, and Control of an Upper Arm Exoskeleton Assistive Robot

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    Stroke is the primary cause of permanent impairment and neurological damage in the United States and Europe. Annually, about fifteen million individuals worldwide suffer from stroke, which kills about one third of them. For many years, it was believed that major recovery can be achieved only in the first six months after a stroke. More recent research has demonstrated that even many years after a stroke, significant improvement is not out of reach. However, economic pressures, the aging population, and lack of specialists and available human resources can interrupt therapy, which impedes full recovery of patients after being discharged from hospital following initial rehabilitation. Robotic devices, and in particular portable robots that provide rehabilitation therapy at home and in clinics, are a novel way not only to optimize the cost of therapy but also to let more patients benefit from rehabilitation for a longer time. Robots used for such purposes should be smaller, lighter and more affordable than the robots currently used in clinics and hospitals. The common human-machine interaction design criteria such as work envelopes, safety, comfort, adaptability, space limitations, and weight-to-force ratio must still be taken into consideration.;In this work a light, wearable, affordable assistive robot was designed and a controller to assist with an activity of daily life (ADL) was developed. The mechanical design targeted the most vulnerable group of the society to stroke, based on the average size and age of the patients, with adjustability to accommodate a variety of individuals. The novel mechanical design avoids motion singularities and provides a large workspace for various ADLs. Unlike similar exoskeleton robots, the actuators are placed on the patient\u27s torso and the force is transmitted through a Bowden cable mechanism. Since the actuators\u27 mass does not affect the motion of the upper extremities, the robot can be more agile and more powerful. A compact novel actuation method with high power-to-weight ratio called the twisted string actuation method was used. Part of the research involved selection and testing of several string compositions and configurations to compare their suitability and to characterize their performance. Feedback sensor count and type have been carefully considered to keep the cost of the system as low as possible. A master-slave controller was designed and its performance in tracking the targeted ADL trajectory was evaluated for one degree of freedom (DOF). An outline for proposed future research will be presented

    ์‚ฌ๋žŒ ๊ทผ๊ณจ๊ฒฉ ํŠน์„ฑ์„ ๋ฐ˜์˜ํ•œ ๋กœ๋ด‡ ์†๊ฐ€๋ฝ ์„ค๊ณ„

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    ํ•™์œ„๋…ผ๋ฌธ(๋ฐ•์‚ฌ) -- ์„œ์šธ๋Œ€ํ•™๊ต๋Œ€ํ•™์› : ์œตํ•ฉ๊ณผํ•™๊ธฐ์ˆ ๋Œ€ํ•™์› ์œตํ•ฉ๊ณผํ•™๋ถ€(์ง€๋Šฅํ˜•์œตํ•ฉ์‹œ์Šคํ…œ์ „๊ณต), 2023. 2. ๋ฐ•์žฌํฅ.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.์—”๋“œ์ดํŒฉํ„ฐ๋Š” ๋กœ๋ด‡๊ณผ ์ฃผ๋ณ€ ํ™˜๊ฒฝ์ด ์ƒํ˜ธ์ž‘์šฉํ•˜๋Š” ํ†ต๋กœ๋กœ ๋งค๋‹ˆํ“ฐ๋ ˆ์ดํ„ฐ๊ฐ€ ์ˆ˜ํ–‰ํ•  ์ˆ˜ ์žˆ๋Š” ์ž‘์—…์€ ์—”๋“œ์ดํŽ™ํ„ฐ์˜ ์„ฑ๋Šฅ์— ์ œํ•œ๋œ๋‹ค. ์‚ฌ๋žŒ ์ค‘์‹ฌ์˜ ํ™˜๊ฒฝ์— ๋กœ๋ด‡์ด ์ ์šฉ๋˜์–ด ์‚ฌ๋žŒ ์ˆ˜์ค€์˜ ๋‹ค์–‘ํ•œ ์ž‘์—…์„ ์ˆ˜ํ–‰ํ•˜๊ธฐ ์œ„ํ•ด์„œ๋Š” ์‚ฌ๋žŒ ์† ์ˆ˜์ค€์˜ ์„ฑ๋Šฅ์„ ๊ฐ–๋Š” ๋กœ๋ด‡ ์†์ด ํ•„์ˆ˜์ ์ด๋ฉฐ ์‚ฌ๋žŒ ์† ์ˆ˜์ค€์˜ ์„ฑ๋Šฅ์€ ๋‹จ์ˆœํžˆ ํž˜-์†๋„, ์ž์œ ๋„๋งŒ์„ ํฌํ•จํ•˜๋Š” ๊ฒƒ์ด ์•„๋‹Œ ํฌ๊ธฐ์™€ ๋ฌด๊ฒŒ ๊ทธ๋ฆฌ๊ณ  ๋ฌผ์ฒด ์กฐ์ž‘์— ๋„์›€์„ ์ฃผ๋Š” ์—ฌ๋Ÿฌ ์† ํŠน์„ฑ๋„ ํฌํ•จํ•œ๋‹ค. ๊ทธ๋Ÿฌ๋‚˜ ํ˜„์žฌ๊นŒ์ง€ ์‚ฌ๋žŒ ์† ์ˆ˜์ค€์˜ ๋ฌด๊ฒŒ, ํฌ๊ธฐ, ํž˜ ๊ทธ๋ฆฌ๊ณ  ์ž์œ ๋„๋ฅผ ๋ชจ๋‘ ๋งŒ์กฑ์‹œํ‚ค๋Š” ๋กœ๋ด‡ ์†์€ ๊ฐœ๋ฐœ๋˜์ง€ ์•Š์•˜์œผ๋ฉฐ ์—ฌ์ „ํžˆ ๋„์ „์ ์ธ ๊ณผ์ œ๋กœ ๋‚จ์•„์žˆ๋‹ค. ๋ณธ ๋…ผ๋ฌธ์—์„œ๋Š” ๋กœ๋ด‡ ์†๊ฐ€๋ฝ์˜ ์„ฑ๋Šฅ์„ ํ–ฅ์ƒํ•˜๊ธฐ ์œ„ํ•˜์—ฌ ์‚ฌ๋žŒ์˜ ๊ทผ๊ณจ๊ฒฉ ํŠน์„ฑ์„ ๋ฐ˜์˜ํ•œ ์„ธ ๊ฐ€์ง€์˜ ์ƒˆ๋กœ์šด ๋ฉ”์ปค๋‹ˆ์ฆ˜์„ ์ œ์•ˆํ•˜๊ณ  ์ด๋ฅผ ํ†ตํ•ฉํ•œ ๋ชจ๋“ˆํ˜• ๋กœ๋ด‡ ์†๊ฐ€๋ฝ ๊ตฌ์กฐ๋ฅผ ๋ณด์ธ๋‹ค. ์ฒซ ๋ฒˆ์งธ๋กœ, ์‚ฌ๋žŒ์˜ ์† ๊ทผ์œก ๋ฐฐ์น˜์™€ ์œ ์‚ฌํ•œ ๋‚ด์žฌ/์™ธ์žฌ ๊ตฌ๋™๊ธฐ ๋ฐฐ์น˜๋ฅผ ์ ์šฉํ•œ ํž˜์ค„ ๊ตฌ๋™ ๋กœ๋ด‡ ์†๊ฐ€๋ฝ ๊ตฌ์กฐ๋ฅผ ์ œ์•ˆํ•˜๊ณ  ๋ถ„์„ํ•œ๋‹ค. ๋กœ๋ด‡ ์†๊ฐ€๋ฝ์€ ๋‹ค์„ฏ ๊ฐœ์˜ ์„œ๋กœ ๋‹ค๋ฅธ ํž˜์ค„๊ณผ ์ธ๋Œ€๋กœ ๊ตฌ์„ฑ๋œ๋‹ค. ์‚ฌ๋žŒ ์†๋™์ž‘ ๋ถ„์„์— ๊ธฐ๋ฐ˜ํ•˜์—ฌ ๋กœ๋ด‡ ์†๊ฐ€๋ฝ์˜ ๊ตฌ๋™๊ธฐ๋Š” ๋Š๋ฆฐ ์†๋„๋ฅผ ๋‹ด๋‹นํ•˜๋Š” ๋‚ด์žฌ ๊ตฌ๋™๊ธฐ์™€ ๋น ๋ฅด๊ณ  ํฐ ํž˜์ด ๋ชจ๋‘ ์š”๊ตฌ๋˜๋Š” ์™ธ์žฌ ๊ตฌ๋™๊ธฐ๋กœ ๊ตฌ๋ถ„๋œ๋‹ค. ๋‘ ๋ฒˆ์งธ๋กœ, ๊ตฌ๋™๊ธฐ์˜ ํฌ๊ธฐ์™€ ๋ฌด๊ฒŒ๋ฅผ ์œ ์ง€ํ•˜๋ฉฐ ์„ฑ๋Šฅ์„ ํ–ฅ์ƒํ•˜๊ธฐ ์œ„ํ•˜์—ฌ ์ƒˆ๋กœ์šด ๊ฐœ๋…์˜ ๋ฌด๋‹จ ๋ณ€์†๊ธฐ Elastomeric Continuously Variable Transmission (ElaCVT) ์„ ์ œ์•ˆํ•˜๊ณ  ์ด๋ฅผ ๋กœ๋ด‡ ์†๊ฐ€๋ฝ์˜ ์™ธ์žฌ ๊ตฌ๋™๊ธฐ์— ์ ์šฉํ•˜์˜€๋‹ค. ElaCVT๋Š” ์„ ํ˜• ๊ตฌ๋™๊ธฐ์˜ ์ž‘๋™ ์˜์—ญ์„ ํ™•์žฅํ•˜๊ณ  ์ถœ๋ ฅ๋‹จ์— ๊ฐ€ํ•ด์ง€๋Š” ์™ธ๋ถ€ ํ•˜์ค‘์— ๋”ฐ๋ผ ๊ฐ์†๋น„๋ฅผ ์ˆ˜๋™์ ์œผ๋กœ ๋ณ€๊ฒฝํ•˜์—ฌ ๊ทผ์œก์˜ ํž˜-์†๋„ ๊ณก์„ ์„ ๋ชจ์‚ฌํ•  ์ˆ˜ ์žˆ๋‹ค. ๋ณธ ์—ฐ๊ตฌ์—์„œ๋Š” ๊ทผ์œก์˜ ํŠน์„ฑ์„ ๋ชจ์‚ฌํ•˜๊ธฐ ์œ„ํ•ด ์„ ํ˜• ์•ก์ถ”์—์ดํ„ฐ๋กœ ElaCVT์— ์ค„ ๊ผฌ์ž„ ๋ฉ”์ปค๋‹ˆ์ฆ˜์„ ์ ์šฉํ•œ ElaCVT-TSA๋ฅผ ์ œ์•ˆ, ๊ทผ์œก์˜ ๋™์ž‘ ์˜์—ญ์„ ๋ชจ์‚ฌํ•  ์ˆ˜ ์žˆ์Œ์„ ๋ณด์˜€๋‹ค. ๋งˆ์ง€๋ง‰์œผ๋กœ ๋กœ๋ด‡ ์†๊ฐ€๋ฝ์˜ ๋ชจ๋“  ๊ตฝํž˜/ํŽผ์นจ ๊ด€์ ˆ์— ์ ์šฉ๋œ ์‚ฌ๋žŒ์˜ ๊ด€์ ˆ๊ตฌ์กฐ๋ฅผ ๋ชจ์‚ฌํ•œ ์œ ์—ฐ ๊ตฌ๋ฆ„ ์ ‘์ด‰ ๊ด€์ ˆ (Anthropomorphic Rolling Contact joint)์„ ์ œ์•ˆํ•œ๋‹ค. Anthropomorphic rolling contact joint๋Š” ์‚ฌ๋žŒ ๊ด€์ ˆ์˜ tongue-and-groove ํ˜•์ƒ๊ณผ collateral ligament๋ฅผ ๋ชจ์‚ฌํ•˜์—ฌ ๊ด€์ ˆ์˜ ์•ˆ์ •์„ฑ์„ ํ–ฅ์ƒ์‹œ์ผฐ๋‹ค. ๊ธฐ์กด์˜ ์œ ์—ฐ ๊ด€์ ˆ๊ณผ ๋‹ฌ๋ฆฌ ๊ด€์ ˆ์ด ํŽด์ง„ ์ƒํƒœ์—์„œ๋Š” ์œ ์—ฐํ•œ ์ƒํƒœ๋ฅผ ์œ ์ง€ํ•˜๋ฉฐ ๊ตฝํ˜€์ง„ ์ƒํƒœ์—์„œ๋Š” ๊ฐ•์„ฑ์ด ์ฆ๊ฐ€ํ•œ๋‹ค๋Š” ํŠน์ง•์„ ๊ฐ–๋Š”๋‹ค. ํŠนํžˆ, ๊ฐ•์„ฑ ๋ณ€ํ™”์— ๋ณ„๋„์˜ ๊ตฌ๋™๊ธฐ๊ฐ€ ์š”๊ตฌ๋˜์ง€ ์•Š์•„ ๊ธฐ์กด์˜ ๊ด€์ ˆ์—์„œ ๋ฌด๊ฒŒ, ํฌ๊ธฐ ์ฆ๊ฐ€ ์—†์ด ํ•ด๋‹น ํŠน์ง• ๊ตฌํ˜„์ด ๊ฐ€๋Šฅํ•˜๋‹ค. ์ด๋Š” ๋กœ๋ด‡ ์†๊ฐ€๋ฝ์— ์ ์šฉ๋˜์–ด ์†๊ฐ€๋ฝ์„ ํŽด๊ณ  ๋ฌผ์ฒด๋ฅผ ํƒ์ƒ‰ํ•˜๋Š” ๊ณผ์ •์—์„œ๋Š” ์ถฉ๊ฒฉ์„ ํก์ˆ˜ํ•˜์—ฌ ์•ˆ์ •์ ์ธ ์ ‘์ด‰์„ ๊ตฌํ˜„ํ•  ์ˆ˜ ์žˆ์œผ๋ฉฐ ๋ฌผ์ฒด๋ฅผ ํŒŒ์ง€ํ•˜๋Š” ๊ณผ์ •์—์„œ๋Š” ์†๊ฐ€๋ฝ์„ ๊ตฝํ˜€ ๊ฐ•์ธํ•˜๊ฒŒ ๋ฌผ์ฒด๋ฅผ ํŒŒ์ง€ํ•  ์ˆ˜ ์žˆ๊ฒŒ ํ•œ๋‹ค. Anthropomorphic rolling contact joint๋ฅผ ์ ์šฉํ•œ ๊ทธ๋ฆฝํผ๋ฅผ ์ด์šฉํ•˜์—ฌ ์ œ์•ˆํ•˜๋Š” ๊ฐ€๋ณ€ ๊ฐ•์„ฑ ์œ ์—ฐ ๊ด€์ ˆ์ด pinch grasping์˜ ํŒŒ์ง€ ์•ˆ์ •์„ฑ์„ ๋†’์ž„์„ ๋ณด์˜€๋‹ค.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) 107๋ฐ•

    Overtwisting and Coiling Highly Enhances Strain Generation of Twisted String Actuators

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    Twisted string actuators (TSAs) have exhibited great promise in robotic applications by generating high translational force with low input torque. To further facilitate their robotic applications, it is strongly desirable but challenging to enhance their consistent strain generation while maintaining compliance. Existing studies predominantly considered overtwisting and coiling after the regular twisting stage to be undesirable non-uniform and unpredictable knots, entanglements, and coils formed to create an unstable and failure-prone structure. Overtwisting would work well for TSAs when uniform coils can be consistently formed. In this study, we realize uniform and consistent coil formation in overtwisted TSAs, which greatly increases their strain. Furthermore, we investigate methods for enabling uniform coil formation upon overtwisting the strings in a TSA and present a procedure to systematically "train" the strings. To the authors' best knowledge, this is the first study to experimentally investigate overtwisting for TSAs with different stiffnesses and realize consistent uniform coil formation. Ultra-high molecular-weight polyethylene (UHMWPE) strings form the stiff TSAs whereas compliant TSAs are realized with stretchable and conductive supercoiled polymer (SCP) strings. The strain, force, velocity, and torque of each overtwisted TSA was studied. Overtwisting and coiling resulted in approximately 70% strain in stiff TSAs and approximately 60% strain in compliant TSAs. This is more than twice the strain achieved through regular twisting. Lastly, the overtwisted TSA was successfully demonstrated in a robotic bicep

    Impedance Controlled Twisted String Actuators for Tensegrity Robots

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    We are developing impedance controlled twisted string actuators (TSA) for use in tensegrity robots, as an alternative to traditional spooled cable actuation. Tensegrity robots are composed of continuous tension and discontinuous compression elements, with no rigid joints between elements, which give them unique force distribution properties. The use of tensegrity robots is strongly motivated by biological examples, and they are capable of locomotion and manipulation by changing lengths of their continuous network of tensional elements, which is also the primary pathways for load transfer through the structure. TSA show the potential to address some of the unique engineering challenges faced by tensegrity structures, and provide unique qualities well suited to an actively controlled tension system, such as compact, light-weight mechanical structures, inherent compliance, variable gearing'', and the ability to transmit high forces with a very low input torque. The inherent variable compliance of impedance control is essential for tensegrity robots to move through and manipulate the environment, and is a natural match to the unique qualities of TSA. This paper briefly introduces the tensegrity robots in the NASA Ames Intelligent Robotics Group and an overview of their future application to space planetary exploration. Then the effectiveness and robustness of TSA are verified through the performance of impedance control modes

    Design and Development of a Twisted String Exoskeleton Robot for the Upper Limb

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    High-intensity and task-specific upper-limb treatment of active, highly repetitive movements are the effective approaches for patients with motor disorders. However, with the severe shortage of medical service in the United States and the fact that post-stroke survivors can continue to incur significant financial costs, patients often choose not to return to the hospital or clinic for complete recovery. Therefore, robot-assisted therapy can be considered as an alternative rehabilitation approach because the similar or better results as the patients who receive intensive conventional therapy offered by professional physicians.;The primary objective of this study was to design and fabricate an effective mobile assistive robotic system that can provide stroke patients shoulder and elbow assistance. To reduce the size of actuators and to minimize the weight that needs to be carried by users, two sets of dual twisted-string actuators, each with 7 strands (1 neutral and 6 effective) were used to extend/contract the adopted strings to drive the rotational movements of shoulder and elbow joints through a Bowden cable mechanism. Furthermore, movements of non-disabled people were captured as templates of training trajectories to provide effective rehabilitation.;The specific aims of this study included the development of a two-degree-of-freedom prototype for the elbow and shoulder joints, an adaptive robust control algorithm with cross-coupling dynamics that can compensate for both nonlinear factors of the system and asynchronization between individual actuators as well as an approach for extracting the reference trajectories for the assistive robotic from non-disabled people based on Microsoft Kinect sensor and Dynamic time warping algorithm. Finally, the data acquisition and control system of the robot was implemented by Intel Galileo and XILINX FPGA embedded system

    Design and Implementation of Innovative Robotic Devices Using Twisted String Actuation (TSA) System

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    The twisted string actuation system is particularly suitable for very compact, low-cost and light-weight robotic devices, like artificial limbs and exoskeletons, since it allows the implementation of powerful tendon-based driving systems, based on small-size DC motors characterized by high speed, low torque and very limited inertia. The following activities has been done using the Twisted String Actuation System: - The basic properties of the twisted string actuation system. - An ongoing work for verifying the behavior of a twisted string actuator in contact with a sliding surface or guided through a sheath. - The implementation of a variable stiffness joint actuated by a couple of twisted string actuators in antagonistic configuration. - The design and the implementation of a force sensor based on a commercial optoelectronic component called light fork and characterized by the simple construction process. - A twisted string actuation module with an integrated force sensor based on optoelectronic components. - The preliminary experimental study toward the implementation of an arm rehabilitation device based on a twisted string actuation module. - A 6 DoF cable-driven haptic interface for applications in various robotic scenarios. - A wearable hand haptic interface driven by a couple of twisted string actuators

    Controller Synthesis of Multi-Axial Robotic System Used for Wearable Devices

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    Wearable devices are commonly used in different fields to help improving performance of movements for different groups of users. The long-term goal of this study is to develop a low-cost assistive robotic device that allows patients to perform rehabilitation activities independently and reproduces natural movement to help stroke patients and elderly adults in their daily activities while moving their arms. In the past few decades, various types of wearable robotic devices have been developed to assist different physical movements. Among different types of actuators, the twisted-string actuation system is one of those that has advantages of light-weight, low cost, and great portability. In this study, a dual twisted-string actuator is used to drive the joints of the prototype assistive robotic device. To compensate the asynchronous movement caused by nonlinear factors, a hybrid controller that combines fuzzy logic rules and linear PID control algorithm was adopted to compensate for both tracking and synchronization of the two actuators.;In order to validate the performance of proposed controllers, the robotic device was driven by an xPC Target machine with additional embedded controllers for different data acquisition tasks. The controllers were fine tuned to eliminate the inaccuracy of tracking and synchronization caused by disturbance and asynchronous movements of both actuators. As a result, the synthesized controller can provide a high precision when tracking simple actual human movements
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