Joint Angle Estimation of a Tendon-Driven Soft Wearable Robot through a Tension and Stroke Measurement.

The size of a device and its adaptability to human properties are important factors in developing a wearable device. In wearable robot research, therefore, soft materials and tendon transmissions have been utilized to make robots compact and adaptable to the human body. However, when used for wearable robots, these methods sometimes cause uncertainties that originate from elongation of the soft material or from undefined human properties. In this research, to consider these uncertainties, we propose a data-driven method that identifies both kinematic and stiffness parameters using tension and wire stroke of the actuators. Through kinematic identification, a method is proposed to find the exact joint position as a function of the joint angle. Through stiffness identification, the relationship between the actuation force and the joint angle is obtained using Gaussian Process Regression (GPR). As a result, by applying the proposed method to a specific robot, the research outlined in this paper verifies how the proposed method can be used in wearable robot applications. This work examines a novel wearable robot named Exo-Index, which assists a human's index finger through the use of three actuators. The proposed identification methods enable control of the wearable robot to result in appropriate postures for grasping objects of different shapes and sizes.

Stretchable and Transparent Kirigami Conductor of Nanowire Percolation Network for Electronic Skin Applications.

Recent research progress of relieving discomfort between electronics and human body involves serpentine designs, ultrathin films, and extraordinary properties of nanomaterials. However, these strategies addressed thus far each face own limitation for achieving desired form of electronic-skin applications. Evenly matched mechanical properties anywhere on the body and imperceptibility of electronics are two essentially required characteristics for future electronic-skin (E-skin) devices. Yet accomplishing these two main properties simultaneously is still very challenging. Hence, we propose a novel fabrication method to introduce kirigami approach to pattern a highly conductive and transparent electrode into diverse shapes of stretchable electronics with multivariable configurability for E-skin applications. These kirigami engineered patterns impart tunable elasticity to the electrodes, which can be designed to intentionally limit strain or grant ultrastretchability depending on applications over the range of 0 to over 400% tensile strain with strain-invariant electrical property and show excellent strain reversibility even after 10 000 cycles stretching while exhibiting high optical transparency (>80%). The versatility of this work is demonstrated by ultrastretchable transparent kirigami heater for personal thermal management and conformal transparent kirigami electrophysiology sensor for continuous health monitoring of human body conditions. Finally, by integrating E-skin sensors with quadrotor drones, we have successfully demonstrated human-machine-interface using our stretchable transparent kirigami electrodes.

Robotic versus conventional primary total knee arthroplasty: clinical and radiological long-term results with a minimum follow-up of ten years.

PURPOSE: The aim of this study was (1) to compare the clinical and radiological outcomes of robotic and conventional total knee arthroplasty with a minimum follow-up of ten years, (2) to evaluate the survival rate, (3) and to estimate the accuracy of the two techniques by analyzing the outliers of the total knee arthroplasty (TKA) patients. METHODS: We evaluated 351 patients (390 knees), 155 patients undergoing robotic TKA, and 196 patients treated with conventional TKA with a mean follow-up of 11.0 years. HSS, KSS, WOMAC, and SF-12 questionnaires were used for clinical evaluation. Mechanical alignment, implant radiological measurements, and outliers were analyzed for radiological results. Kaplan-Meier survival analysis was performed for survival rate. RESULTS: All clinical assessments showed excellent improvements in both groups (all p < 0.05), without any significant difference between the groups (p > 0.05). The conventional TKA group showed a significantly higher number of outliers compared with the robotic TKA group (0 < 0.05). The cumulative survival rate was 98.8% in the robotic TKA group and 98.5% in the conventional TKA group with excellent survival (p = 0.563). CONCLUSION: Our study showed excellent survival with both robotic and conventional TKA and similar clinical outcomes at long-term follow-up. And, in terms of radiological outcome, robotic TKA showed better accuracy and consistency with fewer outliers compared with conventional TKA. With longer follow-up and larger cohort, the accuracy and effectiveness of robotic TKA on implant survival rate can be elucidated in the future.

Fluoroscopic subtraction Eustachian tubography: initial feasibility test in a cadaver model.

OBJECTIVES: To evaluate the technical feasibility of direct Eustachian tube catheterisation and subtraction Eustachian tubography in a cadaver model. METHODS: A total of 12 separate sessions were performed on both sides of the Eustachian tube (ET) in six human cadavers. Cadavers were positioned for the submentovertical view on a fluoroscopy table. Endoscopy-guided ET selection was used in the first three cadavers, whereas fluoroscopy-guided ET selection was used in the remaining three. Eustachian tubography was performed by injecting 2 ml of contrast media through a 5-Fr catheter. We recorded the success of ET selection, number of attempts, procedure time, and tubography quality using native and subtraction images (range, 0-3). RESULTS: Both endoscopy- and fluoroscopy-guided selections were successfully performed in five of six sessions (83.3%). There were no statistically significant differences between the endoscopy- and fluoroscopy-guided procedures in terms of the number of attempts, procedure time, rate of immediate contrast leak to the middle ear cavity, and quality of tubography (p > 0.05). An excellent quality of tubography was obtained in 83.3% (10 of 12 sessions) of subtraction images and in 33.3% (4 of 12 sessions) of native images. The tubography quality score was significantly higher for the subtraction images than for the native images (p = 0.04). CONCLUSION: Subtraction Eustachian tubography using direct catheterisation seems to be technically feasible. The entire ET can be well visualised; thus, this technique can be used as a simple tool for assessment of ET function and anatomy. KEY POINTS: • Direct catheterisation of the Eustachian tube is technically feasible. • The entire Eustachian tube could be well visualised by direct Eustachian tubography. • Subtraction Eustachian tubography images have better image quality than native images. • Subtraction Eustachian tubography can provide objective assessment of ET function and anatomy.

Transnasal Placement of a Balloon-Expandable Metallic Stent: Human Cadaver Study of the Eustachian Tube.

PURPOSE: To investigate the technical feasibility of stent placement in the cartilaginous portion of the Eustachian tube (ET). MATERIALS AND METHODS: Twelve ETs of 6 cadavers were used. Two different-sized stents were placed on either the right (2.5 mm in diameter) or left (3.5 mm in diameter) side of the ET. The procedural feasibility was assessed by subtraction Eustachian tubography, computed tomography before and after the procedure, and fluoroscopic and endoscopic images. The stent location, inner luminal diameter of the stented ET, radiation dose, procedural time, and fluoroscopy time were analyzed. RESULTS: Stent placement was successful in 11 of 12 cadaveric specimens without procedure-related complications. In the 1 specimen, the balloon catheter with crimped stent was passed into the bony canal of the ET without any resistance. The distal end of the stent was located in the middle ear cavity. Stents were located within the cartilaginous portion of the ET (n = 1), the proximal tip bridging the nasopharyngeal orifice of the ET (n = 5), or the proximal end of the stent protruded from the tubal orifice (n = 5). The mean luminal diameter in the outer segment was significantly smaller than in the middle (P < .001) and inner (P < .001) segments. The mean procedure time was 128 ± 37 seconds. The mean radiation dose and fluoroscopy time of each cadaver were 3235.4 ± 864.8 cGy/cm2 and 139 ± 49 seconds, respectively. CONCLUSIONS: Stent placement of the ET under endoscopic and fluoroscopic guidance is technically feasible in a human cadaver model.

Objective quantification of ligament balancing using VERASENSE in measured resection and modified gap balance total knee arthroplasty.

BACKGROUND: Soft tissue balancing which is above all most important factor of total knee arthroplasty, has been performed by subjective methods. Recently objective orthosensor has been developed for compartment pressure measurement. The purpose of this study was: (1) to quantify the compartment pressure of the joint throughout the range of motion during TKA using orthosensor, (2) to determine the usefulness of orthosensor by analyzing correlation between the pressure in both compartment with initial trial and after final implantation, and (3) to evaluate the types and effectiveness of additional ligament balancing procedures to compartment pressure. METHODS: Eighty-four patients underwent total knee arthroplasty (TKA) using VERASENSE Knee System. TKA was performed by measured resection and modified gap balance technique. Compartment pressure was recorded on full extension, 30°, 60°, 90° and full flexion at initial (INI), after each additional procedure, and after final (FIN) implantation. "Balanced" knees were defined as when the compartment pressure difference was less than 15 pounds. RESULTS: Thirty patients (35.7%) showed balanced knee initially and 79 patients (94.0%) showed balance after final implantation. The proportion of balanced knee after initial bony resection, modified gap balancing TKAs showed significantly higher proportion than measured resection TKAs (P = 0.004) On both compartment, the pressure was generally decreased throughout the range of motion. Linear correlation on both compartment showed statistically significant throughout the range on motion, with higher correlation value on the lateral compartment. Total 66 additional ligament balancing procedures were performed. CONCLUSION: Using orthosensor, we could obtain 94% quantified balance knee, consequently. And between the techniques, measured resection TKA showed less balanced knee and also required more additional procedures compared to modified gap balancing TKA. Furthermore, with the acquired quantified data during appropriate ligament balancing, the surgeon could eventually reduce the complications associated with soft tissue imbalance in the future.

Muscle pedicle bone grafting using the anterior one-third of the gluteus medius attached to the greater trochanter for treatment of Association Research Circulation Osseous stage II osteonecrosis of the femoral head.

PURPOSE: The aim of this study was to evaluate the effectiveness of our technique on further collapse of the femoral head in Association Research Circulation Osseous (ARCO) stage II, patient's functional improvements, and analyze the survival rate of the affected hip. METHODS: Between June 2007 and March 2015, 24 hips diagnosed with osteonecrosis of the femoral head (ONFH) were treated with our muscle pedicle bone grafting (MPBG) technique using anterior one-third of gluteus medius attached to the greater trochanter. The group was consisted of 15 men and eight women, mean age of 36 years at the time of surgery. Mean follow-up was 6.2 years. RESULTS: Four hips showed regeneration, 11 hips showed no progression, and nine hips showed slight extent of the lesion. But during the follow-up, three hips underwent total hip arthroplasty at the mean follow-up of 5.8 years after the surgery. The survival rate at the last follow-up was approximately 87.5%. Excluding the three failed cases, the mean total Harris hip score was improved from 57.2 to 82.3 points (p < 0.05). We had no case of complications such as limping, numbness, wound infection, heterotopic ossification, nor intra- and post-operative fracture. CONCLUSION: We showed 87.5% of survival rate by average of 6.2-year follow-up, maximum of 10.1 years. And compared to other reports, our technique showed relatively good results. In the short term, our modified MPBG technique seems to be effective in ARCO stage II ONFH. We, therefore, suggest this technique as one of the promising treatments of choices for patients with ARCO stage II ONFH.

Development and assessment of a hand assist device: GRIPIT.

BACKGROUND: Although various hand assist devices have been commercialized for people with paralysis, they are somewhat limited in terms of tool fixation and device attachment method. Hand exoskeleton robots allow users to grasp a wider range of tools but are heavy, complicated, and bulky owing to the presence of numerous actuators and controllers. The GRIPIT hand assist device overcomes the limitations of both conventional devices and exoskeleton robots by providing improved tool fixation and device attachment in a lightweight and compact device. GRIPIT has been designed to assist tripod grasp for people with spinal cord injury because this grasp posture is frequently used in school and offices for such activities as writing and grasping small objects. METHODS: The main development objective of GRIPIT is to assist users to grasp tools with their own hand using a lightweight, compact assistive device that is manually operated via a single wire. GRIPIT consists of only a glove, a wire, and a small structure that maintains tendon tension to permit a stable grasp. The tendon routing points are designed to apply force to the thumb, index finger, and middle finger to form a tripod grasp. A tension-maintenance structure sustains the grasp posture with appropriate tension. Following device development, four people with spinal cord injury were recruited to verify the writing performance of GRIPIT compared to the performance of a conventional penholder and handwriting. Writing was chosen as the assessment task because it requires a tripod grasp, which is one of the main performance objectives of GRIPIT. RESULTS: New assessment, which includes six different writing tasks, was devised to measure writing ability from various viewpoints including both qualitative and quantitative methods, while most conventional assessments include only qualitative methods or simple time measuring assessments. Appearance, portability, difficulty of wearing, difficulty of grasping the subject, writing sensation, fatigability, and legibility were measured to assess qualitative performance while writing various words and sentences. Results showed that GRIPIT is relatively complicated to wear and use compared to a conventional assist device but has advantages for writing sensation, fatigability, and legibility because it affords sufficient grasp force during writing. Two quantitative performance factors were assessed, accuracy of writing and solidity of writing. To assess accuracy of writing, we asked subjects to draw various figures under given conditions. To assess solidity of writing, pen tip force and the angle variation of the pen were measured. Quantitative evaluation results showed that GRIPIT helps users to write accurately without pen shakes even high force is applied on the pen. CONCLUSIONS: Qualitative and quantitative results were better when subjects used GRIPIT than when they used the conventional penholder, mainly because GRIPIT allowed them to exert a higher grasp force. Grasp force is important because disabled people cannot control their fingers and thus need to move their entire arm to write, while non-disabled people only need to move their fingers to write. The tension-maintenance structure developed for GRIPIT provides appropriate grasp force and moment balance on the user's hand, but the other writing method only fixes the pen using friction force or requires the user's arm to generate a grasp force.

A Novel Low-Cost, Large Curvature Bend Sensor Based on a Bowden-Cable.

Bend sensors have been developed based on conductive ink, optical fiber, and electronic textiles. Each type has advantages and disadvantages in terms of performance, ease of use, and cost. This study proposes a new and low-cost bend sensor that can measure a wide range of accumulated bend angles with large curvatures. This bend sensor utilizes a Bowden-cable, which consists of a coil sheath and an inner wire. Displacement changes of the Bowden-cable's inner wire, when the shape of the sheath changes, have been considered to be a position error in previous studies. However, this study takes advantage of this position error to detect the bend angle of the sheath. The bend angle of the sensor can be calculated from the displacement measurement of the sensing wire using a Hall-effect sensor or a potentiometer. Simulations and experiments have shown that the accumulated bend angle of the sensor is linearly related to the sensor signal, with an R-square value up to 0.9969 and a root mean square error of 2% of the full sensing range. The proposed sensor is not affected by a bend curvature of up to 80.0 m(-1), unlike previous bend sensors. The proposed sensor is expected to be useful for various applications, including motion capture devices, wearable robots, surgical devices, or generally any device that requires an affordable and low-cost bend sensor.

Design of an Optically Controlled MR-Compatible Active Needle.

An active needle is proposed for the development of magnetic resonance imaging (MRI)-guided percutaneous procedures. The needle uses a low-transition-temperature shape memory alloy (LT SMA) wire actuator to produce bending in the distal section of the needle. Actuation is achieved with internal optical heating using laser light transported via optical fibers and side coupled to the LT SMA. A prototype, with a size equivalent to a standard 16-gauge biopsy needle, exhibits significant bending, with a tip deflection of more than 14° in air and 5° in hard tissue. A single-ended optical sensor with a gold-coated tip is developed to measure the curvature independently of temperature. The experimental results in tissue phantoms show that human tissue causes fast heat dissipation from the wire actuator; however, the active needle can compensate for typical targeting errors during prostate biopsy.

3D printing with a 3D printed digital material filament for programming functional gradients.

Additive manufacturing, or 3D printing attracts growing attention as a promising method for creating functionally graded materials. Fused deposition modeling (FDM) is widely available, but due to its simple process, creating spatial gradation of diverse properties using FDM is challenging. Here, we present a 3D printed digital material filament that is structured towards 3D printing of functional gradients, utilizing only a readily available FDM printer and filaments. The DM filament consists of multiple base materials combined with specific concentrations and distributions, which are FDM printed. When the DM filament is supplied to the same printer, its constituent materials are homogeneously blended during extrusion, resulting in the desired properties in the final structure. This enables spatial programming of material properties in extreme variations, including mechanical strength, electrical conductivity, and color, which are otherwise impossible to achieve with traditional FDMs. Our approach can be readily adopted to any standard FDM printer, enabling low-cost production of functional gradients.

Comparison of water and terrestrial jumping in natural and robotic insects.

Jumping requires high actuation power for achieving high speed in a short time. Especially, organisms and robots at the insect scale jump in order to overcome size limits on the speed of locomotion. As small jumpers suffer from intrinsically small power output, efficient jumpers have devised various ingenuous schemes to amplify their power release. Furthermore, semi-aquatic jumpers have adopted specialized techniques to fully exploit the reaction from water. We review jumping mechanisms of natural and robotic insects that jump on the ground and the surface of water, and compare the performance depending on their scale. We find a general trend that jumping creatures maximize jumping speed by unique mechanisms that manage acceleration, force, and takeoff duration under the constraints mainly associated with their size, shape, and substrate.

Effect of anterior translation of the talus on outcomes of three-component total ankle arthroplasty.

BACKGROUND: Ankle osteoarthritis commonly involves sagittal malalignment with anterior translation of the talus relative to the tibia. Total ankle arthroplasty has become an increasingly popular treatment for patients with symptomatic ankle osteoarthritis. However, no comprehensive study has been conducted on the outcomes of total ankle arthroplasty for osteoarthritis with preoperative sagittal malalignment. The purpose of this study was to evaluate the effect of anterior translation of the talus on outcomes of three-component total ankle arthroplasty. METHODS: One hundred and four osteoarthritic ankles in 104 patients who underwent three-component total ankle arthroplasty were included in this study. The 104 ankles were divided into 2 groups: ankles with anteriorly translated talus (50 ankles), and ankles with non-translated talus (54 ankles). Clinical and radiographic outcomes were assessed in both groups. The mean follow-up duration was 42.8 ± 17.9 months (range, 24 to 95 months). RESULTS: Forty-six (92%) of 50 ankles with anterior translation of the talus showed relocation of the talus within the mortise at 6 months, and 48 (96%) ankles were relocated at 12 months after total ankle arthroplasty. But, 2 (4%) ankles were not relocated until the final follow-up. The AOFAS scores, ankle range of motion, and radiographic outcomes showed no significant difference between the two groups at the final follow-up (p > 0.05 for each). CONCLUSIONS: In majority of cases, the anteriorly translated talus in osteoarthritic ankles was restored to an anatomical position within 6 months after successful three-component total ankle arthroplasty. The clinical and radiographic outcomes in the osteoarthritic ankles with anteriorly translated talus group were comparable with those in non-translated talus group.

A Hybrid Anchoring Technology Composed of Reinforced Flexible Shells for a Knee Unloading Exosuit.

Soft robotic wearables have emerged as an ergonomic alternative to rigid robotic wearables, commonly utilizing tension-based actuation systems. However, their soft structure's natural tendency to buckle limits their use for compression bearing applications. This study presents reinforced flexible shell (RFS) anchoring, a compliant, low-profile, ergonomic wearable platform capable of high compression resistance. RFS anchors are fabricated with soft and semirigid materials that typically buckle under compressive loads. Buckling is overcome using the wearer's leg as a support structure, reinforcing the shells with straps, and minimizing the space between the shells and the wearer's skin-enabling force transmission orders of magnitude larger. RFS anchoring performance was evaluated comparatively by examining the shift-deformation profiles of three identically designed braces fabricated with different materials: rigid, strapped RFS, and unstrapped RFS. The unstrapped RFS severely deformed before 200 N of force could be applied. The strapped RFS successfully supported 200 N of force and exhibited a nearly identical transient shift-deformation profile with the rigid brace condition. RFS anchoring technology was applied to a compression-resistant hybrid exosuit, Exo-Unloader, for knee osteoarthritis. Exo-Unloader utilizes a tendon-driven linear sliding actuation system that unloads the medial and lateral compartments of the knee. Exo-Unloader can deliver 200 N of unloading force without deforming, as indicted by its similar transient shift-deformation profile with a rigid unloader baseline. Although rigid braces effectively withstand and transmit high compressive loads, they lack compliance; RFS anchoring technology expands the application of soft and flexible materials to compression-based wearable assistive systems.

Single-Step 3D Printing of Bio-Inspired Printable Joints Applied to a Prosthetic Hand.

Single-step 3D printing, which can manufacture complicated designs without assembly, has the potential to completely change our design perspective, and how 3D printing products, rather than printing static components, ready-to-use movable mechanisms become a reality. Existing 3D printing solutions are challenged by precision limitations, and cannot directly produce tightly mated moving surfaces. Therefore, joints must be designed with a sufficient gap between the components, resulting in joints and other mechanisms with imprecise motion. In this study, we propose a bio-inspired printable joint and apply it to a Single sTep 3D-printed Prosthetic hand (ST3P hand). We simulate the anatomical structure of the human finger joint and implement a cam effect that changed the distance between the contact surfaces through the elastic bending of the ligaments as the joint flexed. This bio-inspired design allows the joint to be single-step 3D printed and provides precise motion. The bio-inspired printable joint makes it possible for the ST3P hand to be designed as a lightweight (∼255 g), low-cost (∼$500) monolithic structure with nine finger joints and manufactured via single-step 3D printing. The ST3P hand takes ∼6 min to assemble, which is approximately one-tenth the assembly time of open-source 3D printed prostheses. The hand can perform basic hand tasks of activities of daily living by providing a pulling force of 48 N and grasp strength of 20 N. The simple manufacturing of the ST3P hand could help us take one step closer to realizing fully customized robotic prosthetic hands at low cost and effort.

Zygote structure enables pluripotent shape-transforming deployable structure.

We propose an algorithmic framework of a pluripotent structure evolving from a simple compact structure into diverse complex 3D structures for designing the shape-transformable, reconfigurable, and deployable structures and robots. Our algorithmic approach suggests a way of transforming a compact structure consisting of uniform building blocks into a large, desired 3D shape. Analogous to a fertilized egg cell that can grow into a preprogrammed shape according to coded information, compactly stacked panels named the zygote structure can evolve into arbitrary 3D structures by programming their connection path. Our stacking algorithm obtains this coded sequence by inversely stacking the voxelized surface of the desired structure into a tree. Applying the connection path obtained by the stacking algorithm, the compactly stacked panels named the zygote structure can be deployed into diverse large 3D structures. We conceptually demonstrated our pluripotent evolving structure by energy-releasing commercial spring hinges and thermally actuated shape memory alloy hinges, respectively. We also show that the proposed concept enables the fabrication of large structures in a significantly smaller workspace.

Body-powered variable impedance: An approach to augmenting humans with a passive device by reshaping lifting posture.

The movement patterns appropriate for exercise and manual labor do not always correspond to what people instinctively choose for better comfort. Without expert guidance, people can even increase the risk of injury by choosing a comfortable posture rather than the appropriate one, notably when lifting objects. Even in situations where squatting is accepted as a desirable lifting strategy, people tend to choose the more comfortable strategy of stooping or semisquatting. The common approach to correcting lifting posture, immobilizing vulnerable joints via fixation, is insufficient for preventing back injuries sustained from repetitive lifting. Instead, when lifting small but heavy objects, the entire kinetic chain should cooperate to achieve a series of squat-lifting patterns. Inspired by the observation that force fields affect the coordination of voluntary human motion, we devised a passive exosuit embedded with a body-powered variable-impedance mechanism. The exosuit adds impedance to the human joints according to how far the wearer's movement is from the squat-lifting trajectories so that it hinders stooping but facilitates squatting. In an experiment that entailed lifting a small 10-kg box, 10 first-time users changed their voluntary lifting motion closer to squatting on average. Simulation results based on recorded kinematic and kinetic data showed that this postural change reduced the compression force, shear force, and moment on the lumbosacral joint. Our work demonstrates the potential of using an exosuit to help people move in a desirable manner without requiring a complicated, bulky mechanical system.

High-load capacity origami transformable wheel.

Composite membrane origami has been an efficient and effective method for constructing transformable mechanisms while considerably simplifying their design, fabrication, and assembly; however, its limited load-bearing capability has restricted its application potential. With respect to wheel design, membrane origami offers unique benefits compared with its conventional counterparts, such as simple fabrication, high weight-to-payload ratio, and large shape variation, enabling softness and flexibility in a kinematic mechanism that neutralizes joint distortion and absorbs shocks from the ground. Here, we report a transformable wheel based on membrane origami capable of bearing more than a 10-kilonewton load. To achieve a high payload, we adopt a thick membrane as an essential element and introduce a wireframe design rule for thick membrane accommodation. An increase in the thickness can cause a geometric conflict for the facet and the membrane, but the excessive strain energy accumulation is unique to the thickness increase of the membrane. Thus, the design rules for accommodating membrane thickness aim to address both geometric and physical characteristics, and these rules are applied to basic origami patterns to obtain the desired wheel shapes and transformation. The capability of the resulting wheel applied to a passenger vehicle and validated through a field test. Our study shows that membrane origami can be used for high-payload applications.

Tendon-Driven Jamming Mechanism for Configurable Variable Stiffness.

Stiffness transition of a soft continuum body is an essential feature for dexterous interaction with an unstructured environment. Softness ensures safe interaction, whereas rigidness generates high force for movement or manipulation. Vacuum-based granular jamming is a widely used technique for on-line stiffness transition because of its high reconfigurability and intuitive driving method. However, vacuum driving method produces limited force levels, and the heavy weight and bulky size are unfavorable for portable applications. In this work, we propose a tendon-driven jamming mechanism for configurable variable stiffness. Compared with a vacuum system, an electric motor-tendon drive system has the benefits of force, bandwidth, size, and weight, but has different force characteristics for distribution, directionality, and transmissibility. In this study, a long snake-like shape is chosen instead of a lump shape for compatibility with tendon-drive characteristics. The snake-like shape is likely to cause buckling under the tendon force as the length increases, making the system extremely unstable. Implanting skeletal disk nodes in the structure is our solution to the buckling phenomenon by maintaining the tendon path in the desired position and for distributing the force evenly, thereby achieving stable stiffness transition capabilities for long free-curved shapes. As a proof of concept, a soft wearable device for wrist support is presented using the proposed variable stiffness mechanism. The weight of the device is 184 g, including the actuators, and it can support 2 kgf. Furthermore, the stiffness transition is completed within 2 s, thus achieving quick responses.

Underwater maneuvering of robotic sheets through buoyancy-mediated active flutter.

Falling leaves flutter from side to side due to passive and intrinsic fluid-body coupling. Exploiting the dynamics of passive fluttering could lead to fresh perspectives for the locomotion and manipulation of thin, planar objects in fluid environments. Here, we show that the time-varying density distribution within a thin, planar body effectively elicits minimal momentum control to reorient the principal flutter axis and propel itself via directional fluttery motions. We validated the principle by developing a swimming leaf with a soft skin that can modulate local buoyancy distributions for active flutter dynamics. To show generality and field applicability, we demonstrated underwater maneuvering and manipulation of adhesive and oil-skimming sheets for environmental remediation. These findings could inspire future intelligent underwater robots and manipulation schemes.