Tendon Actuation Research Articles

Anatomically-Inspired Robotic Finger with SMA Tendon Actuation for Enhanced Biomimetic Functionality.

This research introduces an advanced robotic finger designed for future generalist robots, closely mimicking the natural structure of the human finger. The incorporation of rarely discussed anatomical structures, including tendon sheath, ligaments, and palmar plates, combined with the usage of anatomically proven 3D models of the finger, give rise to the highly accurate replication of human-like soft mechanical fingers. Benefiting from the accurate anatomy of muscle insertions with the utilization of Shape Memory Alloy (SMA) wires' muscle-like actuation properties, the bonding in-between the flexor tendons and extensor tendons allows for the realization of the central and lateral band of the finger anatomy. Evaluated using the computer vision method, the proposed robotic finger demonstrates a range of motion (ROM) equivalent to 113%, 87% and 88% of the human dynamic ROM for the DIP, PIP and MCP joints, respectively. The proposed finger possesses a soft nature when relaxed and becomes firm when activated, pioneering a new approach in biomimetic robot design and offering a unique contribution to the future of generalist humanoid robots.

Bioinspired Bidirectional Stiffening Soft Actuators Enable Versatile and Robust Grasping.

The bending stiffness modulation mechanism for soft grippers has gained considerable attention to improve grasping versatility, capacity, and stability. However, lateral stability is usually ignored or hard to achieve at the same time with good bending stiffness modulation performance. Therefore, this article presents a bioinspired bidirectional stiffening soft actuator (BISA), enabling compliant and stable performance. BISA combines the air tendon 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 three times when the bending angle is 45°. Inspired by the morphological structure of the phalanx, the lateral stiffness can be modulated by changing the pulling force of the BLS. The actuator with BLSs can improve the lateral stiffness by 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 by decoupling about 1.3 times (e.g., from 0.35 to 0.46 N/mm when the bending angle is 45°). The test results show that the influence of the rigid structures on bending is small with about 1.5 mm maximum position errors of the distal point of the actuator in different pulling forces. The advantages brought by the proposed method enable versatile four-finger grasping. The performance of this gripper is characterized and demonstrated on multiscale, multiweight, and multimodal grasping tasks.

Design and analyses of tendon-driven continuum robots for minimally invasive surgery

Continuum robots have great potential to be used for many special applications due to their flexible kinematic structure. The perspective area of utilization is minimally invasive surgery (MIS). One of the main actuation principle of continuum robots is tendon actuation. The paper introduces the developed MISBOT robot for the purposes of MIS monitoring. The paper also presents mechanical design of universal actuation subsystem for tendon-driven continuum robots based on three segmental tendon system. The paper investigates three different mechanical structures of continuum robots from the view of their basic motion properties. The results of the experimental analyses show the better results for continuum robot with elastic structure in comparison with rigid structures, especially from the view of motion repeatability.

Design and performance of a slender soft continuum manipulator for tall structure inspection

PurposeThe current methods for inspecting tall or deep structures such as towers, chimneys, silos, and wells suffer from certain constraints. Manual and assisted inspection methods including humans, drones, wall climbing robots, and others are either costly, have a limited operation time, or affected by field conditions, such as temperature and radiation. This study aims to overcome the presented challenges through a teleoperated soft continuum manipulator capable of inspecting tall or deep structures with high resolution, an unlimited operation time and the ability to use different arms of the manipulator for different environments and structure sizes.Design/methodology/approachThe teleoperated manipulator uses one rotary and two tendon actuators to reach and inspect the interior of a tall (or deep) structure. A sliding part along the manipulator’s body (arm constrainer and tendon router) induces a variable-length bending segment, allowing an inspection camera to be placed at different distances from the desired location.FindingsThe experiments confirmed the manipulator’s ability to inspect different locations in the structure’s interior. The manipulator also demonstrated a submillimeter motion resolution vertically and a 2.5 mm per step horizontally. The inspection time of the full structure was 48.53 min in the step-by-step mode and was calculated to be 4.23 min in the continuous mode.Originality/valueThe presented manipulator offers several design novelties: the arm’s thin-wide cross-section, the variable-length bending segment in a fixed-length body, the external rolling tendon routing and the ability to easily replace the arm with another of different material or dimensions to suite different structures and environments.

Soft Robotic Glove with Sensing and Force Feedback for Rehabilitation in Virtual Reality.

Many diseases, such as stroke, arthritis, and spinal cord injury, can cause severe hand impairment. Treatment options for these patients are limited by expensive hand rehabilitation devices and dull treatment procedures. In this study, we present an inexpensive soft robotic glove for hand rehabilitation in virtual reality (VR). Fifteen inertial measurement units are placed on the glove for finger motion tracking, and a motor-tendon actuation system is mounted onto the arm and exerts forces on fingertips via finger-anchoring points, providing force feedback to fingers so that the users can feel the force of a virtual object. A static threshold correction and complementary filter are used to calculate the finger attitude angles, hence computing the postures of five fingers simultaneously. Both static and dynamic tests are performed to validate the accuracy of the finger-motion-tracking algorithm. A field-oriented-control-based angular closed-loop torque control algorithm is adopted to control the force applied to the fingers. It is found that each motor can provide a maximum force of 3.14 N within the tested current limit. Finally, we present an application of the haptic glove in a Unity-based VR interface to provide the operator with haptic feedback while squeezing a soft virtual ball.

Pneumatic and tendon actuation coupled muti-mode actuators for soft robots with broad force and speed range

Pneumatic and tendon actuation coupled muti-mode actuators for soft robots with broad force and speed range

Development of a Series Elastic Tendon Actuator (SETA) Based on Gait Analysis for a Knee Assistive Exosuit

An exosuit is a wearable robot that assists the muscular strength of a human that wears it by using multiple wires with similar functions to human muscles. This study focuses on the development of a series elastic tendon actuator (SETA) for the actuation of an exosuit. A gait analysis was performed for walking on stairs to deduce the design requirements of SETA, and the necessary performances were then determined based on these requirements. The SETA is designed to assign compliance to rigid wires using linear springs. The deformation in linear springs generated during tension was measured through an encoder to calculate the human robot interaction (HRI) force. By utilizing the HRI force as feedback of an admittance controller, the SETA was capable of providing wire tensions required by an exosuit. The performance of the SETA was verified through series elastic component (SEC) deformation and force control experiments. The SEC deformation increased from 0 to 3.86 mm when the wire tension increased from 0 to 100 N. This force controller demonstrated a slight vibration owing to the mechanical properties of the springs constituting the SEC during the step input; however, the value gradually converged to 100 N. The developed SETA was applied to an exosuit system for supporting knee strength of the elderly when walking on stairs.

The GummiArm Project: A Replicable and Variable-Stiffness Robot Arm for Experiments on Embodied AI.

Robots used in research on Embodied AI often need to physically explore the world, to fail in the process, and to develop from such experiences. Most research robots are unfortunately too stiff to safely absorb impacts, too expensive to repair if broken repeatedly, and are never operated without the red kill-switch prominently displayed. The GummiArm Project was intended to be an open-source “soft” robot arm with human-inspired tendon actuation, sufficient dexterity for simple manipulation tasks, and with an eye on enabling easy replication of robotics experiments. The arm offers variable-stiffness and damped actuation, which lowers the potential for damage, and which enables new research opportunities in Embodied AI. The arm structure is printable on hobby-grade 3D printers for ease of manufacture, exploits stretchable composite tendons for robustness to impacts, and has a repair-cycle of minutes when something does break. The material cost of the arm is less than $6000, while the full set of structural parts, the ones most likely to break, can be printed with less than $20 worth of plastic filament. All this promotes a concurrent approach to the design of “brain” and “body,” and can help increase productivity and reproducibility in Embodied AI research. In this work we describe the motivation for, and the development and application of, this 6 year project.

Design and Experimental Validation of a Miniaturized Robotic Tendon-Driven Articulated Surgical Drill for Enhancing Distal Dexterity in Minimally Invasive Spine Fusion

Steerable drills have the potential to minimize the required dimensions of incisions in minimally invasive spine fusion (MISF). Existing steerable drills mostly rely on flexible continuum mechanisms to create distal tip steerability. However, due to their inherent compliance and underactuation, high stiffness and dexterity cannot be achieved at the same time, which limits their application. In this article, we present a ømm robotic steerable surgical drill offering high stiffness, strength, and dexterity, simultaneously. Contrary to existing flexible-transmission-based approaches, we use nonflexible transmissions (tendon-driven articulated joints and universal joints) to provide two distal degrees of freedom. To evaluate its performance, we integrated it with a customized tendon actuation platform for mechanical performance tests and the da Vinci Research Kit, as an exchangeable instrument, for robotic steerable drilling tests. The results of these tests showed that our drill had high strength, stiffness, accuracy, and drilling stability while preserving high steerability and was sufficient to complete hole drilling in confined space in MISF.

Soft Origami Gripper with Variable Effective Length

Nature has evolved to shape morphing to adapt to complex environments while engaging with the surroundings. Inspired by this capability, robots are expected to be endowed with the ability to perform shape‐changing, thus interacting with complex environments. Herein, a soft origami actuator with variable effective length (VEL) is proposed to adapt to different objects. The actuator's VEL is realized by an origami structure and actuated by hybrid actuation of tendons and pneumatic pressure. The soft actuator yields motion combining both elongation and bending generated by the asymmetric Yorshimura origami structure. Then an adaptive gripper composed of four origami actuators with programmable effective length is fabricated and its effect on grasping performance is evaluated through both simulations and experiments. Results show that the gripper can grip objects of different shapes, weights, sizes, and textures. This research may shed light on a new soft gripper design using origami structure for the environment's self‐adaptability.

A Dual-Mode Actuator for Soft Robotic Hand

Fluidic and tendon driven actuators are widely applied in soft robotic hand design. Fluidic actuated soft robotic hands are highly compliant and can adapt to various objects. Tendon driven soft robotic hands are easier to control and have high dexterity and large force output, however, they are less compliant than fluidic actuated ones. Most robotic hands are designed with only one actuation method. Combining both actuation methods can tap the advantages and make up each other's limitations but at the expense of more complicated design and control. In this research, we propose a simple dual-mode actuator that provides both fluidic and tendon actuation. The two actuation modes are achieved simultaneously by twisting an elastic tube filled with gas, liquid, or even a combination. The soft robotic finger, designed as a fluidic elastomer actuator (FEA), is actuated by the fluid displaced from tube twisting, as well as by the tendon due to tube contraction in twisting. The tendon drives a compliant metacarpophalangeal (MCP) joint of the finger in order to provide a large bending angle and bending force to finger. Compared to an FEA soft finger, the proposed design can effectively increase the bending angle up to 150% (from 170 degrees to 260 degrees), and the blocking force up to 134% (from 3.2N to 4.3N). A soft robotic hand prototype with dual-mode actuators design is made for various grasping demonstrations.

How to Model Tendon-Driven Continuum Robots and Benchmark Modelling Performance.

Tendon actuation is one of the most prominent actuation principles for continuum robots. To date, a wide variety of modelling approaches has been derived to describe the deformations of tendon-driven continuum robots. Motivated by the need for a comprehensive overview of existing methodologies, this work summarizes and outlines state-of-the-art modelling approaches. In particular, the most relevant models are classified based on backbone representations and kinematic as well as static assumptions. Numerical case studies are conducted to compare the performance of representative modelling approaches from the current state-of-the-art, considering varying robot parameters and scenarios. The approaches show different performances in terms of accuracy and computation time. Guidelines for the selection of the most suitable approach for given designs of tendon-driven continuum robots and applications are deduced from these results.

Influence of Foot Orthotics and Intrinsic Factors on Strain Measurements in the Fifth Metatarsal

Category:Midfoot/Forefoot; SportsIntroduction/Purpose:Fractures of the fifth metatarsal occur in young, athletic populations and often result in sub-optimal clinical outcomes, even after surgical fixation. With such a high demand for decreased return to play in athletic populations, the development of intervention strategies which mitigate intrinsic and extrinsic risk factors of initial injury is important. Foot orthotics have been shown to decrease strain in the 2nd metatarsal. However, limited research has investigated the influence of intrinsic risk factors and the use of foot orthotics on fifth metatarsal strain. Therefore, the purpose of our study was to investigate the effect of foot orthotics and intrinsic risk factors on fifth metatarsal strain during cadaveric simulation.Methods:Ten specimens were loaded to simulate the stance phase of normal gait using a validated 6-degree of freedom robot with tendon actuators. Strain gauges were placed at the metaphyseal - diaphyseal junction (Zone II), and the proximal diaphysis (Zone III) to measure principal strain. Specimens were tested in a sneaker-only control condition and ten orthotic conditions, which include combinations of a commercial orthotic insole, three plates, and two foam wedges (Figure 1A). The average peak strain from three simulations were recorded for each orthotic condition. Relevant intrinsic factors were recorded from reconstructions of axially loaded computed tomography scans. A two-way repeated measures ANOVA was conducted to determine the effect of orthotic conditions on fifth metatarsal strains, with significantly correlated intrinsic factors included as covariates. Tukey-Kramer post-hoc analysis with a Bonferroni correction was used to analyze differences between individual orthotic conditions and main effects of components.Results:Metatarsus adductus angle, 4-5 intermetatarsal angle, and Meary’s angle (R2= 0.944; p<0.001) were included as covariates in analysis of Zone III strain. Significant (p<0.05) differences in Zone III strain were found for the both the main effect of a plate and individual orthotic conditions with statistical adjustment for previously stated intrinsic measurements. However, post- hoc testing revealed no significant differences between non-plate conditions and full plate conditions(p=0.23), lateral plate conditions (p=0.025), or lateral cut plate conditions (p=0.026). Additionally, the Full Plate with Lateral Wedge condition reduced strains by 285 µΕ relative to the sneaker condition, no significant differences (p = 0.07) were found in post-hoc analysis. No significant differences were found in Zone II with the models considered.Conclusion:Zone III strains were shown to be significantly correlated with intrinsic factors in the current analysis. Plate conditions demonstrated a trend towards significant reduction of Zone III strain relative to the sneaker condition, despite failing to achieve statistical significance in conservative post-hoc analysis. However, these results may be clinically significant as the reduction of strain in plate conditions exceeded previously reported significant decreases in the 2nd metatarsal. Correlations found between intrinsic risk factors and strain in this study corroborate with previous studies. This indicates that the effectiveness of foot orthotics to reduce strain is strongly influenced by individual foot structure.

3D Electromagnetic Reconfiguration Enabled by Soft Continuum Robots

The properties of radio frequency electromagnetic systems can be manipulated by changing the 3D geometry of the system. Most reconfiguration schemes specify different conductive pathways using electrical switches in mechanically static systems, or they actuate and reshape a continuous metallic structure. Here, we demonstrate a novel strategy that utilizes soft continuum robots to both dynamically assemble electrical pathways and mechanically reconfigure 3D electromagnetic devices. Our concept consists of using soft robotic actuation to conductively connect multiple subwavelength-scale metallic building blocks, which form into electromagnetic structures when joined together. Soft robots offer an exciting avenue for electromagnetic device construction because they can form complex, high curvature shapes from low-loss dielectric materials using straightforward manufacturing methods. As a proof of concept, we experimentally implement a helical antenna that can switch chirality through tendon actuation of a soft pneumatic continuum robot. Our work introduces a new paradigm for electromagnetic reconfiguration using soft robotic platforms.

Patient-Specific, Voice-Controlled, Robotic FLEXotendon Glove-II System for Spinal Cord Injury

Reduced hand function in spinal cord injury (SCI) patients is commonly associated with a lower quality of life and limits the autonomy of the patient because he/she cannot perform most tasks independently. Robotic rehabilitation exoskeletons have been introduced as a method for assisting in hand function restoration. In this article, we propose a voice-controlled, tendon-actuated soft exoskeleton for improving hand function rehabilitation. The exoskeleton is constructed from soft materials to conform to the user's hand for improved fit and flexibility. A partially biomimetic tendon routing strategy independently actuates the index finger, middle finger, and thumb for a total of 4 degrees-of-freedom of the overall system. Nitinol wires are used for passive finger extension and screw-guided twisted tendon actuators are used for active finger flexion to create a compact, lightweight actuation mechanism. A continuous voice control strategy is implemented to provide a hands-free control interface and a simplified user interface experience while retaining distinct user intention. The exoskeleton was evaluated in a case study with a spinal cord injury patient. The patient used the exoskeleton and completed range-of-motion measurement as well as hand function tests, including the Box and Block Test and Jebsen-Taylor Hand Function Test.

Design and Control of Foam Hands for Dexterous Manipulation

There has been great progress in soft robot design, manufacture, and control in recent years, and soft robots are a tool of choice for safe and robust handling of objects in conditions of uncertainty. Still, dexterous in-hand manipulation using soft robots remains a challenge. This paper introduces foam robot hands actuated by tendons sewn through a fabric glove. The flexibility of tendon actuation allows for high competence in utilizing deformation for robust in-hand manipulation. We discuss manufacturing, control, and design optimization for foam robots and demonstrate robust grasping and in-hand manipulation on a variety of different physical hand prototypes.

EMG control of a 3D printed myo electric prosthetic hand

Recent technological advances have enabled the prosthetic developers to derive an ideal replacement for the human arm in near future. This research presents design of a 3D Printed Myo Electric Prosthetic Hand that grasp symmetrical objects through Electromyographic signals and is intended for people suffering from Trans-radial Amputation. In the current study, a set of data about three motions that include hand open, close and rest position was been acquired from forearm muscles of a human arm. The computer aided model of the prosthetic hand was developed in SolidWorks® which was later 3D printed using Poly Lactic Acid (PLA).The proposed design was based closely on tendon actuation, related to human hand functionality. Signal acquisition and processing has been done using Myo Armband. Different features were selected such that they can be passed through classification process in order to control the hand motions. Using the Bluetooth transmitter, the filtered data was sent and saved in Arduino Uno® controller. Later, the Support Vector Machine (SVM) was been evaluated as a classifier. The classification accuracy obtained from SVM was 96.7%. The results were found significant (p<0.01) for twelve able bodied subjects. EMG based grasp control was implemented with successful testing of designed prosthetic hand for three different motions. The practical effectiveness of the Myoelectric Hand was demonstrated by grasping household objects such battery charger, wallet and water bottle.

Modeling and inverse control of a compliant single-tendon-sheath artificial tendon actuator with bending angle compensation

Artificial tendon is a kind of bionic actuation system capable of imitating the transmission characteristics of skeleton tendon. This paper presents a new compliant single-tendon-sheath artificial tendon actuator inspired by Hill-type muscle model. The proposed artificial tendon can perform variable compliance properties with two linear springs applying onto the tendon-sheath element. Detailed development and modeling of the actuation system is given, and transmission characteristics are analyzed and validated via simulations and experiments. Then, a bending angle measurement method is developed to compensate the variation of tendon-sheath configuration during transmission process. A model-based inverse control strategy with bending angle compensation is developed for displacement and force control without distal feedback. Trajectory tracking experiments are conducted to verify the effectiveness of the proposed control strategy. Experimental results indicate that the control errors of displacement and force control without distal feedback could be limited within 7.07% and 13.62%, respectively.

Design of a Series Elastic Tendon Actuator Based on Gait Analysis for a Walking Assistance Exosuit

Exosuits are wearable robots that enhance a person’s muscular strength from outside the body. Many exosuits use tendon actuators with multiple wires that work similarly to human muscles to minimize user unfamil-iarity caused by the discrepancy between the human body’s degree of freedom and the influence of the mass of the exoskeleton. This paper describes the design of a series elastic tendon actuator (SETA) to be used in exosuits. The SETA performs the agonist and antagonist functions of human muscles using two internal wires as well as elastic elements (springs) to measure the human-robot interaction force and overcome differences in variations occurring between the wires. We defined design objectives and selected the main components based on biomechanical gait analysis to design a small SETA. Moreover, we conducted an experiment to verify the basic performance of our SETA design.

Effect of Radial Lengthening on Distal Forearm Loading Following Simulated In Vitro Radial Shortening During Simulated Dynamic Wrist Motion

To evaluate the effect of radial length change on distal forearm loading during simulated dynamic wrist motion. A custom-built adjustable radial implant was used to simulate up to 4 mm of distal radius shortening (-4 mm) and 3 mm of lengthening (+3 mm). Load cells were placed in the distal radius and ulna in cadavers to measure their respective axial loads. The specimens were mounted on a wrist motion simulator that produced active wrist motion via tendon actuation. To simulate radial lengthening osteotomy following radial shortening from malunion, the radius was sequentially lengthened by 1-mm intervals from -4 mm to+3 mm. Radial and ulnar loads were measured during simulated wrist flexion, ulnar deviation (UD), and flexion dart throw (DT) at each interval of radial lengthening up to+3 mm. During wrist flexion and UD, for each millimeter of radial lengthening from -4 mm to the native length, there was a significant increase in distal radial loads. No significant change in radial load was observed beyond the native length during flexion and UD. There was no change in distal radial loads during DT for each interval of radial lengthening from -4 mm to+3 mm. A sequential decrease in ulnar loads was observed as the radius was lengthened from -4 mm to+3 mm for all wrist motions evaluated. Radial lengthening beyond the native length was not detrimental to radial loading and further reduced distal ulnar loading; achieving at least native ulnar variance seems to be appropriate to restore normal biomechanical loading based on this invitro study. Lengthening of the radius beyond native variance in the setting of ulnar impaction syndrome, distal radius malunion, or distal radioulnar instability may not result in excessive loading of the distal radius and further reduces loading on the distal ulna. Surgeons should obtain contralateral wrist x-rays to serve as a template when performing distal radius osteotomies.