Joint Bending Research Articles

Flexural and vibration behaviours of novel covered CFRP composite joints with an MWCNT-modified adhesive

Abstract Co-curing bonding is more efficient than co-bonding and secondary bonding for structural component assembly. This work used novel covered laminas with co-cured joining techniques (CL-CCT) to create carbon fibre-reinforced polymer (CFRP) composite adhesive-bonded joints. Additionally, the researchers evaluated how multi-walled carbon nanotubes (MWCNTs) affect the bending and dynamic properties of CFRP composite joints. The researchers added various weights of MWCNTs to the covered laminas along with co-cured CFRP adhesive-bonded joints. The study revealed that epoxy and 0.25 wt% MWCNT adhesive produced the strongest and most flexible joints. These joints were 118 and 15% stronger than joints made from pure epoxy CL-CC CFRP, respectively. Compared to pure epoxy CC-CFRP composite joints, the strength of CL-CC CFRP composite joints with 0.25 wt% MWCNTs increased by 374 and 109%, respectively. Interestingly, MWCNTs with a wt% of 1.25 had the greatest natural frequency in all three vibration modes, which are 19, 19, and 13% higher than that of the pure epoxy CL-CC CFRP composite joint. There are 28, 30, and 24% more natural frequencies in 1.25 wt% MWCNT-based CL-CC CFRP composite joints than those in pure epoxy-based joints in all three modes. Analysis of variance was employed for statistical investigation. Optimization and prediction were done using an artificial neural network and the Levenberg–Marquardt technique.

Ultrasensitive and Stretchable Strain Sensors Based on Laser-Induced Graphene With ZnO Nanoparticles.

Laser-induced graphene (LIG) has attracted considerable attention for its use in flexible and stretchable sensors, owing to its electrical/mechanical properties and scalable fabrication processes. Although laser scanning facilitates the formation of LIG and its strain sensor, the strain-sensing sensitivity enhancement of LIG remains limited by the material's properties and structural design. In this study, we demonstrate a substantial improvement in sensitivity that was achieved by fabricating a LIG using ZnO nanoparticle (NP)-assisted photothermal enhancement. The results show that ZnO NPs selectively reduce the threshold fluence needed to convert polyimide (PI) into LIG. By transferring the LIG formed on PI to poly(dimethylsiloxane), we fabricate a stretchable strain sensor with ultrahigh sensitivity and a gauge factor of 1214 at 10% strain, which is approximately 60 times higher than the gauge factor without ZnO NPs. Using the selective graphenization properties of LIG, a flexible, dual-sided integrated sensor sheet that is equipped with flexible strain and ultraviolet (UV) sensors is demonstrated. This sheet enables simultaneous monitoring of UV intensity and joint bending angles of sports wearable devices. We validated the developed sensors by attaching them to a runner's body to monitor and simulate forefoot and heel strikes, demonstrating the sensor's ultrahigh sensitivity and long-term stability without the need for a camera. These findings highlight the potential of the proposed method for developing multifunctional sensor applications with ultrahigh sensitivity and stability.

Preparation and application of organic hydrogels incorporating polyacrylamide/sodium alginate/DMSO for enhanced anti-drying, anti-freezing, and self-healing properties

The double-network hydrogel comprises two asymmetrically structured cross-linked networks, demonstrating exceptional mechanical properties and possessing significant potential for application in the field of flexible sensors. However, conventional hydrogels primarily disperse in water as a medium and continuously lose moisture in natural environments, rendering them incapable of retaining hydration over extended periods and unsuitable for utilization under low-temperature conditions. In this study, we devised an organic hydrogel based on polyacrylamide (PAM), sodium alginate (SA), and dimethyl sulfoxide (DMSO). Through hydrogen bonding interactions among DMSO molecules, polyacrylamide, and sodium alginate, this organic hydrogel not only exhibits anti-drying and anti-freezing properties but also demonstrates self-healing characteristics. Moreover, the organic hydrogel showcases remarkable mechanical properties and conductivity capabilities that render it suitable for constructing flexible strain sensors to monitor human movements such as finger bending, elbow flexion, knee joint bending, and ankle extension. Additionally, the sensor exhibits excellent stability and durability.

Influence of Joint Stiffness on Three-dimensional Deformation Mechanisms of Pipelines under Tunnel Active Face Instability

Although extensive research has been conducted in literature to investigate tunnelling effects on pipelines, the performance of existing jointed pipelines subjected to excessive tunnel movement has not been investigated. This study sets out to examine the effects of tunnel active instability on three-dimensional deformation patterns of existing pipelines using physical model tests. Tunnelling induced ground / pipeline settlement, joint rotation, and bending strain under various horizontal tunnel face movements are systematically explored. Results show that the tunnel face pressure at the active limit state is practically independent of tunnel cover to diameter ratio (C/D). Existing pipelines that fall within a range of 0.1 D ~ 0.5 D ahead of the tunnel face experience excessive settlements, significant bending strains and joint rotation. The measured peak settlement of pipelines at 0.3 D in front of the tunnel face exceeds the allowable limit, and the maximum settlements in the jointed pipeline are up to 2.67 times those observed in the continuous pipeline. Meanwhile, the joint rotation angle and settlement induced in the jointed pipeline are greatly affected by the C/D ratio and decrease by up to 55.5% and 22.0% with an increasing C/D ratio from 1.0 to 1.5.

Self-Adhesive Electronic Skin with Bio-Inspired 3D Architecture for Mechanical Stimuli Monitoring and Human-Machine Interactions.

Recent development of wearable devices is revolutionizing the way of artificial electronic skins (E-skin), physiological health monitoring and human-machine interactions (HMI). However, challenge remains to fit flexible electronic devices to the human skin with conformal deformation and identifiable electrical feedback according to the mechanical stimuli. Herein, an adhesive E-skin is developed that can firmly attach on the human skin for mechanical stimuli perception. The laser-induced adhesive layer serves as the essential component to ensure the conformal attachment of E-skin on curved surface, which ensures the accurate conversion from mechanical deformation to precise electrical readouts. Especially, the 3D architecture facilitates the non-overlapping outputs that bi-directional joint bending and distinguishes strain/pressure. The optimized E-skin with bio-inspired micro-cilia exhibited significantly improved sensing performances with sensitivity of 0.652 kPa-1 in 0-4kPa and gauge factor of 8.13 for strain (0-15%) with robustness. Furthermore, the adhesive E-skin can distinguish inward/outward joint bending in non-overlapping behaviors, allowing the establishment of ternary system to expand communication capacity for logic outputs such as effective Morse code and intelligent control. It expects that the adhesive E-skin can serve as a functional bridge between human and electrical terminals for applications from daily mechanical monitoring to efficient HMI.

Lignin sulfonate induced ultrafast fabrication of polypyrrole-based conductive organohydrogel for high performance flexible strain and temperature sensor

The ultrafast preparation of electrically conductive hydrogels to endow high sensing performance and temperature tolerance remains a critical challenge. Herein, lignosulfonate sodium-templated polypyrrole (LS-PPy) nanofillers were rapidly introduced into polyacrylic acid (PAA) hydrogel through ultrafast free radical polymerization in a glycerol/water binary solvent system. The resultant LS-PPy/PAA electrically conductive organohydrogel possesses satisfactory mechanical performance (strength of 56 kPa at a tensile strain of 800 %), strong adhesion, and a desirable low freezing point (−35 °C). Furthermore, this organohydrogel exhibits high strain sensitivity (gauge factor = 2.65), fast response time (~160 ms), low signal hysteresis, and excellent cyclic stability (over 1200 cycles). And the wearable LS-PPy/PAA organohydrogel sensor could accurately and real-time monitor various intense or subtle human movements, such as joint bending, facial expression and hand writing. Besides, the developed LS-PPy/PAA temperature sensor can respond to environmental temperature variations over a wide range of −20–100 °C. High resolution of 0.5 °C with remarkable sensitivity (−0.80 %/°C and linearity of R2 = 0.99) and repeatability were achieved within 36.5–40 °C, which makes it suitable for human body temperature monitoring. All these results demonstrate the substantial prospective value of the LS-PPy/PAA hydrogel in wearable sensors and other associated fields.

Strain measurement of CFRP-Steel bonded joints using distributed optical fibre sensors

ABSTRACT Externally bonded carbon fibre reinforced polymer (CFRP) is widely employed for strengthening steel structures. The CFRP-steel bond behaviour is typically conducted using the single-lap joint (SLJ) and double-lap joint (DLJ) shear tests. This study utilizes advanced distributed optical fibre sensors (DOFS) to measure strains in CFRP-steel SLJs and DLJs, with a specific focus on examining the bending effect. An experimental investigation was conducted to verify the appropriate adhesive and fibre coating materials, achieving synergistic deformation between optical fibre sensors and adherends. The strain results reveal that PI-coated fibres bonded with epoxy resin enhance deformation compatibility. The CFRP strain distributions within the joints are accurately measured by DOFS, enabling the calculation of bending strain to assess joint bending effects. The observed strain aligns well with the finite element (FE) predictions. A more significant bending effect is observed in SLJs compared to DLJs, predominantly concentrated at the loaded end. It can be inferred that the SLJs are subjected to mixed-mode I/II loading in shear tests, and the DLJs appears to be mainly influenced by mode II loading. Additionally, the verified FE model demonstrates that the shear strain across the thickness of the adhesive layer exhibits significant variation at the bond ends.

Flexible Tactile Sensors with Gradient Conformal Dome Structures.

The trade-off between high sensitivity and wide detection range remains a challenge for flexible capacitive pressure sensors. Gradient structure can provide continuous deformation and lead to a wide sensing range. However, it simultaneously augments the distance between two electrodes, which diminishes the variation in the relative distance and results in a decreased sensitivity. Herein, a conformal design is introduced into the gradient structure to construct a flexible capacitive pressure sensor. The gradient conformal dome structure is fabricated by a simple reverse dome adsorption process. Taking advantage of the progressive deformation behavior of the gradient dielectric, and the significant improvement of relative distance variation between two electrodes from the conformal design, the sensor achieves a sensitivity of 0.214 kPa-1 in an ultrabroad linear range up to 200 kPa. It maintains high-pressure resolution under the preload of 10 and 100 kPa. Benefiting from the rapid response and excellent repeatability, the sensor can be used for physiological monitor and human motion detection, including arterial pulse, joint bending, and motion state. The gradient conformal design strategy may pave a promising avenue to develop pressure sensors with high sensitivity and wide linear range.

Fabrication of Flexible Wearable Mechanosensors Utilizing Piezoelectric Hydrogels Mechanically Enhanced by Dipole-Dipole Interactions.

Conductive hydrogels have been increasingly employed to construct wearable mechanosensors due to their excellent mechanical flexibility close to that of soft tissues. In this work, piezoelectric hydrogels are prepared through free radical copolymerization of acrylamide (AM) and acrylonitrile (AN) and further utilized in assembling flexible wearable mechanosensors. Introduction of the polyacrylonitrile (PAN) component in the copolymers endows the hydrogels with excellent piezoelectric properties. Meanwhile, significant enhancement of mechanical properties has been accessed by forming dipole-dipole interactions, which results in a tensile strength of 0.51 MPa. Flexible wearable mechanosensors are fabricated by utilizing piezoelectric hydrogels as key signal converting materials. Self-powered piezoelectric pressure sensors are assembled with a sensitivity (S) of 0.2 V kPa-1. Additionally, resistive strain sensors (gauge factor (GF): 0.84, strain range: 0-250%) and capacitive pressure sensors (S: 0.23 kPa-1, pressure range: 0-8 kPa) are fabricated by utilizing such hydrogels. These flexible wearable mechanosensors can monitor diverse body movements such as joint bending, walking, running, and stair climbing. This work is anticipated to offer promising soft materials for efficient mechanical-to-electrical signal conversion and provides new insights into the development of various wearable mechanosensors.

High-Performance Stretchable Strain Sensors Based on Auxetic Fabrics for Human Motion Detection.

Wearable strain sensors play a pivotal role in real-time human motion detection and health monitoring. Traditional fabric-based strain sensors, typically with a positive Poisson's ratio, face challenges in maintaining sensitivity and comfort during human motion due to conflicting resistance changes in different strain directions. In this work, high-performance stretchable strain sensors are developed based on graphene-modified auxetic fabrics (GMAF) for human motion detection in smart wearable devices. The proposed GMAF sensors, with a negative Poisson's ratio achieved through commercially available warp-knitting technology, exhibit an 8-fold improvement in sensitivity compared to conventional plain fabric sensors. The unique auxetic fabric structure enhances sensitivity by synchronizing resistance changes in both wale and course directions. The GMAF sensors demonstrate excellent washability, showing only slight degradation in auxeticity and an acceptable increase in resistance after 10 standard wash cycles. The GMAF sensors maintain stability under different strain levels and various motion frequencies, emphasizing their dynamic performance. The sensors exhibit superior conformability to joint movements, which effectively monitor a full range of motions, including joint bending, sports activities, and subtle actions like coughing and swallowing. The research underscores a promising approach to achieve industrial-scale production of wearable sensors with improved performance and comfort through fabric structure design.

Bending of fusion-bonded thermoplastic single lap joints

The assembly of thermoplastic composites is one of the most important issues for their reliable use in the aerospace and automotive industries. Assembly through co-curing is a process that enables simultaneous bonding and curing of adherends and is a preferable option for these industries. This paper presents a study of fusion-bonded, co-cured single lap joints with thermoplastic adherends that were subjected to four-point bending. Processing of the joint created a 45° notch at one edge of the overlap. The effect of this notch on the strength of the joint was assessed in tension and compression by flipping the joint. Compared to samples without such notches, experiments indicated that the tensile stresses in the vicinity of the notch decreased the maximum load and applied displacements at failure initiation by about 30 % and 33 %, respectively. In order to better understand this behavior, the joints were also analyzed using finite element simulations. The initial failure was predicted using the Maximum Stress Theory. Both experimental and numerical results were consistent up to the initial failure. The analysis did not account for the subsequently observed interlaminar delamination in the adherends. This type of failure would most likely be approached using measured interlaminar traction-separation relations in a cohesive zone modelling approach.

A flexible sensor based on ionogel/knitted coil prepared by a simple method for accurate monitoring of human physiological signals

Flexible sensors have received increasing attention due to their various applications in health monitoring, artificial intelligence, and other fields. The simple fabrication of flexible sensing devices with high performances has been a research hotpot. In this work, an ionogel composite sensor combined with elastic knitted coil (EIC) is proposed as a wearable device to monitor human movement and related feature information. This sensor can be fabricated in a simple and easy protocol, which can work as a clothing accessary to track the wellness status parameters in daily life. After washing, the redundant gel originally embedded between the fibers was removed, improving the sensitivity of the sensor, which can provide accurate information about human joint movements and other physiological activities. The EIC sensor is in high sensitivity with superior working durability, which can provide continuous piezoresistive signals in detection mode. Other than the common joint bending movements (wrist, knee, elbow and finger) of human body, this sensor can also accurately output monitoring data on periocular, oral, and pharyngeal movements, providing information about human health status. Besides, a Morse codes transmission system can be constructed based on the piezoresistive outputs of this EIC sensor under different tapping modes, providing a new working platform in other related applications.

Thin, flexible hybrid-structured piezoelectric sensor array with enhanced resolution and sensitivity

Wearable piezoelectric electronics have garnered significant interest in healthcare and human-machine interfaces due to their unique ability to convert mechanical stimuli into electrical signals. However, current wearable piezoelectric sensors struggle with low spatial resolution, limited sensitivity, and insufficient mechanical flexibility. Here, we report materials and designs of a thin, flexible piezoelectric sensor array with a balanced performance that could be used for spatiotemporal pressure mapping on human skin. The device with a soft-rigid hybrid structure integrates small-pixel, highly sensitive piezoceramic thick films into a conformally adaptable format that achieves satisfactory spatial resolution (6 mm), high sensitivity (15.08 mV/kPa) and optimal flexibility (bending radius of 4.23 mm). Theoretical analysis indicates that the thickness of substrate presents a trade-off between output performance and mechanical flexibility. To demonstrate the capabilities of the device, it has been employed to monitor joint bending, human gait, and throat sounds. Furthermore, it incorporates a convolutional neural network (CNN-2D) for voice recognition, achieving an impressive accuracy of 98.18 %. These capabilities underscore the potential of the device in advanced wearable applications, offering a robust platform for real-time, high-resolution physiological monitoring.

Multifunctional chitosan-based composite hydrogels engineered for sensing applications

Chitosan-based hydrogels, as natural high-molecular-weight flexible materials, are widely utilized due to their outstanding properties. In this research, we developed a one-pot method for synthesizing a novel PVA/CS@PPy-PDAx% conductive hydrogel and explored the internal bonding patterns through molecular dynamics simulations. By adding PPy-PDA nanoparticles into a hydrogel matrix, an interpenetrating conductive network established successfully. The uniform distribution of PPy-PDA nanoparticles endowed the hydrogel with good electrical conductivity (0.171 S/m), significantly enhanced mechanical properties, and strain sensing (S = 5.04), as well as near-infrared photothermal responsiveness (temperature increase of 41.9 °C within 30 s). Additionally, due to the hydrogel's significant photothermal conversion efficiency under near-infrared radiation, it exhibits rapid elimination of Escherichia coli with an antibacterial efficiency exceeding 90 %. The unique hydrogen-bonded crosslinked structure provides the hydrogel with excellent re-healing properties, allowing for restoration through a freeze-thaw process after damage. The conductivity remains nearly unchanged after re-healing, maintaining the material's integrity and functionality. The flexible sensor based on this hydrogel has a response time of 100 ms and can sensitively detect large-scale deformations (e.g., joint bending at various angles), different gravitational forces, and recognize human handwriting. These characteristics make this hydrogel a promising candidate for advancing intelligent wearable technologies and human-machine interaction systems.

Flexible sensor based on conformable, sticky, transparent elastomers for electronic skin

As 5G technology advances and enhances the interconnection of science and technology, the demand for advanced sensors has increased. Conventional rigid sensors are inadequate to meet these new requirements, thus sparking significant interest in flexible sensors. However, taking into account the biocompatibility, skin compliance, sensing performance, mechanical properties and optical properties of flexible sensors is still the direction of efforts. Therefore, in this study, the flexible sensor with a sandwich structure was prepared using AgNWs as a conductive filler and P32-PDMS elastomer as a flexible substrate. The PDMS elastomer is modified by blending PEG-PPG-PEG and PDMS, giving the P32-PDMS elastomer low Young’s modulus (32.35 kPa), high elongation at break (over 450 %) and good adhesion (18.94 N/m), and the P32-PDMS elastomer still retains a certain light transmittance (82.22 %) and biocompatibility (RGR=89.524). These properties simultaneously endow the flexible sensor with good sensitivity (GF=17.27), wide detection range (0–100 % strain), and excellent cycling stability (5000 cycles). When the flexible sensor is used as e-skin to monitor human body movements, stable signals are generated regardless of the low-strain movements of the human body (pulse and sound) or the high-strain movements of the human body (pressing and joint bending). Therefore, the prepared flexible sensor has great potential as e-skin in many fields such as personal health monitoring, human motion detection, human–computer interaction, flexible display, etc.

Joints mechanical characteristics of prefabricated subway station considering bending stiffness difference

In prefabricated subway stations, the presence of joints leads to an uneven circumferential distribution of structural stiffness. However, there has been limited research focusing on the variability in bending stiffness of joints so far. Therefore, this paper proposes a theoretical framework to study deformation characteristics considering the differences in bending stiffness. This study aim to analyze the deformation characteristics of prefabricated structures, with a specific focus on the impact of variations in bending stiffness on the overall structural behavior. The research scope includes the calculation methods for the bending stiffness of joints, predicting maximum settlement of the top plate, and analyzing the influence of key parameters such as joint positions, geometric shapes, and dimensions, overburden density γ, lateral earth pressure coefficient λ, overburden thickness hf, and concrete density ρ on the joint bending stiffness. Results validate the reliability of the proposed method for calculating joint bending stiffness and demonstrate the key factors contributing to differences in bending stiffness.

Lignin-Stabilized Tough, Sticky, and Recyclable Liquid Metal/Protein Organogels for Multifunctional Epidermal Smart Materials.

Biomass-encapsulated liquid metals (LMs) composite gels have aroused tremendous attention as epidermal smart materials due to their biocompatibility and sustainability. However, they can still not simultaneously possess toughness, adhesion, and recoverability. In this work, the tough, sticky, and recyclable protein-encapsulated LMs organogels (GLMx) are fabricated through the micro-interfacial stabilization of LMs by lignin and the following preparation of food-making inspired gels. With the help of lignin modification, the LMs micro-drops demonstrated uniform dispersion in the protein matrix, as well as dense non-covalent interactions (e.g., H─bond and hydrophobic interaction) with amino acid residues in peptide chains, which endowed the GLMx with high conductivity (≈5.4Sm-1), toughness (≈738.2kJm-3), self-adhesiveness (a maximal lap-shear strength of ≈58.3kPa), and recoverability. By tightly adhering onto human skin, the GLMx can act as epidermal sensors to detect drastic (e.g., joint bending) and subtle body movements (e.g., swallowing) and even recognize handwriting and speaking in real-time. Moreover, the organogels can also harvest solar energy and convert it into heat and electricity, which is promising in self-powered intelligent devices. Thus, this work paves a facile way to prepare protein/LMs composite organogels that are suitable for multiple applications like healthcare, human-robot interactions, and solar energy conversion.

Bio-Inspired Photoelectric Dual-Mode Sensor Based on Photonic Crystals for Human Motion Sensing and Monitoring.

Photoelectric dual-mode sensors, which respond to strain signal through photoelectric dual-signals, hold great promise as wearable sensors in human motion monitoring. In this work, a photoelectric dual-mode sensor based on photonic crystals hydrogel was developed for human joint motion detection. The optical signal of the sensor originated from the structural color of photonic crystals, which was achieved by tuning the polymethyl methacrylate (PMMA) microspheres diameter. The reflective peak of the sensor, based on 250 nm PMMA PCs, shifted from 623 nm to 492 nm with 100% strain. Graphene was employed to enhance the electrical signal of the sensor, resulting in a conductivity increase from 9.33 × 10-4 S/m to 2 × 10-3 S/m with an increase in graphene from 0 to 8 mg·mL-1. Concurrently, the resistance of the hydrogel with 8 mg·mL-1 graphene increased from 160 kΩ to 485 kΩ with a gauge factor (GF) = 0.02 under 100% strain, while maintaining a good cyclic stability. The results of the sensing and monitoring of finger joint bending revealed a significant shift in the reflective peak of the photoelectric dual-mode sensor from 624 nm to 526 nm. Additionally, its resistance change rate was measured at 1.72 with a 90° bending angle. These findings suggest that the photoelectric dual-mode sensor had the capability to detect the strain signal with photoelectric dual-mode signals, and indicates its great potential for the sensing and monitoring of joint motion.

Highly compressive aerogel-elastomer hybrid porous material with redistributed strain for high-sensitive soft pressure sensors

Owing to the good sensitivity and simple fabrication process, flexible piezoresistive pressure sensors based on aerogels shows great applications in soft robotics, bioelectronics and so on. However, the poor compressibility and stability of the aerogel is still challenging the development of aerogel based flexible piezoresistive pressure sensors, simultaneously, it is urgent to pave a way to enhance the sensitivity of these sensors. Here, for the first time, we propose a universal strategy to prepare aerogel skeleton-elastomer shell hybrid porous material with enhanced compressibility for high-sensitive and stable flexible pressure sensors. We found that the elastomer shell disperses the strain in the aerogel skeleton and enhances the compressibility of the aerogel, which improve the stability of the sensor (10000 cycles of compression). More importantly, there are elastomer micro-blocks formed in the hybrid material, these micro-blocks redistribute the strain in the material which contributes to the high sensitivity (10.25 kPa−1) of the sensors. Furthermore, the sensors are successful in monitoring both of the large joint bending and subtle skin vibration, as well as remote controlling toy car and artificial hand. This work provides an effective and universal strategy to enhance the sensitivity and stability of the aerogel based flexible pressure sensors and promotes their development towards practical applications.

Design and Control of a Tendon-Driven Robotic Finger Based on Grasping Task Analysis.

To analyze the structural characteristics of a human hand, data collection gloves were worn for typical grasping tasks. The hand manipulation characteristics, finger end pressure, and finger joint bending angle were obtained via an experiment based on the Feix grasping spectrum. Twelve types of tendon rope transmission paths were designed under the N + 1 type tendon drive mode, and the motion performance of these 12 types of paths applied to tendon-driven fingers was evaluated based on the evaluation metric. The experiment shows that the designed tendon path (d) has a good control effect on the fluctuations of tendon tension (within 0.25 N), the tendon path (e) has the best control effect on the joint angle of the tendon-driven finger, and the tendon path (l) has the best effect on reducing the friction between the tendon and the pulley. The obtained tendon-driven finger motion performance model based on 12 types of tendon paths is a good reference value for subsequent tendon-driven finger structure design and control strategies.