Flexible Joint Research Articles

An Optimal Weighted Spectral Difference Method for Faulty Vibration Separation in Flexible Joint Robot

An Optimal Weighted Spectral Difference Method for Faulty Vibration Separation in Flexible Joint Robot

Influence of Column–Base Connections on Seismic Behavior of Single-Story Steel Buildings

This study focuses on assessing the seismic performance of existing single-story steel buildings used as industrial buildings. This research aims to provide a systematic procedure for evaluating the seismic response of a single-story strategic building and properly accounting for the behavior of the column–base joints. Through meticulous data collection, advanced numerical modeling, and pushover analyses, this study highlights the significant impact of column–base joint behavior on the overall seismic performance of industrial buildings. The findings reveal that while single-story steel buildings show a satisfactory seismic performance in terms of lateral resistance and stiffness in the longitudinal direction, deficiencies in the joint design can strongly impact the performance in the transversal direction. This study emphasizes the necessity of incorporating joint flexibility into numerical analyses to accurately assess structural behavior. In conclusion, a precise assessment of the base joints provides insights for informing retrofitting strategies.

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.

Morphy: A Compliant and Morphologically Aware Flying Robot

This study introduces a novel compliant and morphologically aware aerial robot called Morphy. The system is small (primary dimension 25.2 cm), lightweight (260 g), and agile (thrust‐to‐weight ratio of 3.3) while simultaneously integrating sensorized flexible joints in its arms. These elastic joints unlock the potential of experiencing flexible deformations, thus enabling the robot to resiliently withstand collisions at high speeds and squeeze through openings more narrow than its nominal dimensions. Extensive analysis of the flexible joints’ behavior under static loads and in free flight is conducted. Driven by the deformations that the robot can experience, adaptive control allocation exploiting real‐time angle deflection feedback from Hall‐effect sensors embedded in the joints is proposed and combined with fixed‐gain control. To demonstrate Morphy's performance, multiple experiments are conducted, including free flight trajectory tracking, impacts with the environment, and flying through narrow passages. As shown, the system can withstand collisions up to 7.6 m s−1 in drop tests and 3 m s−1 midflight while recovering back to hover. Finally, Morphy's capability to passively change its shape and squeeze through openings smaller than its nominal size is showcased both in the horizontal and in the vertical directions.

Faulting by the 2023 great earthquakes of Türkiye and associated stress field and its effects on built environment

Abstract Background Faulting induced by earthquakes and its analysis are of great importance for areas with high probability of earthquakes. However, there has been no particularly effective methods to evaluate the damage and applicable solutions for recovery. In this paper, the damage from Türkiye earthquakes is investigated by authors, which has important theoretical significance and practical value. On 6 February, 2023, two successive earthquakes with magnitudes (Mw) of 7.8 (called Pazarcık earthquake) and 7.6 (Ekinözü earthquake) occurred in the south-eastern part of Türkiye. The total length of the surface ruptures was more than 500 km long and resulted in striations reflecting the sinistral faulting and extensive ground deformations. In this study, the authors present the outcomes of the investigations on the surface ruptures, their characteristics, stress field associated with both earthquakes, shear strength property of fault segments and the damaging effects on various structures and made some recommendations with the purpose of how to build structures in active fault zones and decrease the negative effects of faulting on structures. Results Besides summarizing the main characteristics of the world-shaking Kahramanmaraş earthquake doublet in southeast Türkiye in 2023, this study described the main features of the surface ruptures, their relation to the inferred crustal stresses in Türkiye, and the damaging effects on the major engineering structures. The observations and inferences are of great significance for understanding the causes of earthquakes and future seismic risk assessment. Various laboratory experiments were performed on the samples of fault gouge gathered from the sites of surface ruptures and these experimental results provided very valuable quantitative information on the constitutive models of the fault zones. The observations clearly showed that it is almost impossible to prevent damage on structures due to surface ruptures, if certain engineering principles such as increasing higher ductility, lowering gravitational center and/or the implementations of raft foundations are followed. Conclusions The stress state inferences obtained from the striation of the fault surface ruptures as well as from the focal plane solutions are expected to be useful to evaluate the regional stress state of the earthquake region. Assessments indicated that the stress states in Arabian plate and Anadolu platelet are different from each other. However, in-situ direct stress measurement techniques would be quite useful to validate the stress state inferred in this study. The laboratory experiments on samples gathered from the fault outcrops of the earthquakes using direct shear tests, stick-slip tests as well as conventional tensile, compressive and triaxial tests provided the quantitative values for the parameters of constitutive laws for fault zones, which can be utilized in the numerical simulation of earthquakes. If a fault break happens to be just passing underneath the structures, it is almost impossible for mankind to prevent the damage to structures. However, the authors made some recommendations to reduce the negative effects of fault ruptures on structures. These recommendations are such that the structures should be built as ductile and redundant structures with lower center of gravity and raft foundations. Dam construction should be on active faults should be avoided. If they are to be built for whatever reason, they should be of rock-fill type. As tubular structures and tunnels would be generally subjected forced displacement field, it is recommended to utilize flexible joints, segmented and enlargement to deal such displacement fields.

Research on innovative design of intelligent wearable products based on human machine engineering and bionics

Designing intelligent wearable products entails integrating human factors, engineering, and bionics to develop ergonomic, efficient and convenient products. Human-machine engineering is a discipline that addresses the integration between the user wearing a particular system and improving the relationship between the user and the system. At the same time, bionics is an approach that aims to mimic biological systems and structures to enhance the performance of a particular product. This research explores the possibility of integrating these specializations to design new and enhanced wearable technology products with improved usability, convenience, and flexibility for practical usage. A detailed analysis of human biomechanics and ergonomic requirements established design parameters to ensure that wearable devices could be seamlessly integrated into daily life without hindering user movement. Bionic principles, such as the flexibility of animal joints and the energy-efficient movements of natural organisms, were applied to optimize the mechanical and structural aspects of the devices. This approach enabled the creation of products that mimic the natural dynamics of the human body, offering improved responsiveness and functionality. Prototypes were developed based on human-centred design principles and evaluated using simulation and testing environments. Wearables such as exoskeletons, bright clothing, and health-monitoring devices were examined for their ability to adapt to various physical conditions and environmental changes. Results demonstrate a significant increase in user comfort, reduction in mechanical strain, and enhanced performance, validating the effectiveness of integrating human-machine engineering and bionics in wearable design.

Impact of various training programs on lower limb biomechanics in adolescent Latin dancers

Latin dance attracts many young dancers globally. While these adolescents exhibit flexibility and imitation skills, their muscular strength and neuromuscular control often fall short, making complex movements challenging. Thus, incorporating functional training methods is essential for enhancing performance and reducing injury risk. This study, a total of 30 adolescent female Latin dancers aged 12–14 years with at least one year of training and competition experience were recruited for this study and randomly divided into two groups: One group of 15 students (average height 154.37 ± 3.82 cm, average weight 45.31 ± 5.29 kg) received traditional Latin dance training, and the other group of 15 students (15 students average height 154.73 ± 4.28 cm, average weight 44.63 ± 4.37 kg) received traditional Latin dance training and based on traditional Latin dance training, functional exercise was carried out for 12 weeks. A Vicon motion capture system, force platform, and electromyography were used to collect biomechanical data. Paired samples t-tests assessed significant differences between groups pre- and post-intervention. The experimental group showed significant improvements post-intervention: in the sagittal plane, ankle joint angles improved by 14.01% to 52.21% (p < 0.001); in the coronal plane, knee joint angles increased by 0% to 31.21% (p < 0.001) and 66.67% to 100% (p < 0.001); in the horizontal plane, hip joint angles improved by 4.99% to 76.00% (p < 0.001). Muscle activation showed significant increases in gastrocnemius lateral (p = 0.016), gluteus maximus (p = 0.001), tibialis anterior (p = 0.014), and rectus femoris (p < 0.001). Functional training enhances joint flexibility, muscle activation, balance, and overall performance in adolescent Latin dancers. Integrating functional training into regular routines can improve athletic performance and lower injury risk, informing the development of targeted training programs.

Bionic ankle-assisted rehabilitation training system based on biomechanical evaluation

In modern society, people’s life rhythm is getting faster and faster. Ankle injury would significantly reduce the frequency of people’s activities, which has a great impact on people’s normal work and life. As a new medical method, the bionic ankle rehabilitation training system is used to assist rehabilitation doctors to help patients complete joint flexibility and recovery training. In the research method of ankle biomechanical characteristics, the detection of ankle joint patient’s motion is particularly important. The purpose of this paper is to study how to design a bionic ankle assisted rehabilitation training system based on image processing. Therefore, this paper proposes an image-based moving target detection method, which has the advantages of high reliability and simple operation, and can improve the recognition rate of the ankle joint movement. The experimental results of this paper showed that the system can realize the predetermined trajectory movement and run the system stably. In terms of patient following error, it was kept within 0.03cm. The following error of the ankle joint trajectory was up to 0.03cm and the lowest was 0.01cm, which was almost negligible. In terms of accuracy, the accuracy of the system was also very high, and it can respond and determine the patient’s actions quickly, thereby helping patients to better perform rehabilitation training.

Design and Implementation of Bionic Robot Structure Based on Flexible Joints

Design and Implementation of Bionic Robot Structure Based on Flexible Joints

Neural Network Adaptive Inverse Control of Flexible Joint Space Manipulator Considering the Influence of Gravity.

With the aim of correcting the problem of trajectory tracking control of a flexible joint space manipulator in environments with different gravity, a neural network adaptive inverse control algorithm based on singular perturbation theory is proposed to resist the disturbance caused by system uncertainty. Firstly, the dynamic model of a flexible joint space manipulator with the influence of gravity is established, and then the system is divided into a fast subsystem and a slow subsystem using singular perturbation theory. The velocity feedback control rate is designed for the fast subsystem to suppress the elastic vibration caused by the joint flexibility. For the slow subsystem, the uncertain term and known term are separated by the inverse control algorithm, where the uncertain term is approximated online by the RBF neural network, and the robust control rate is designed to compensate for the approximation error. The simulation results show that the control method can not only effectively reduce the high-frequency vibration caused by the flexible joint but also resist the system disturbance so that a good track control effect is achieved.

Free vibration of flexible two links manipulator with variable cross-sectional areas

This paper demonstrated the free vibration of a planar two-link flexible manipulator with harmonic drivers and non-uniformity in the cross-section of links. A dynamic model has been developed that incorporates flexibilities in both link and joint experiencing harmonic vibration, with joint flexibility modeled as torsional spring-inertia components combination. Two links were modeled based on Von Karman’s nonlinear strain relations and theory of the Euler-Bernoulli beam. The nonlinear governing equations were derived using the extended Hamilton’s principle for planar two-link flexible manipulators with variable cross-sections for each link. The coefficients of the obtained partial differential equations were as a function of spatial coordinates and were reduced to the ordinary differential equations for a family of cross-section geometries with exponentially varying widths of rectangular sections of each link. The frequency equation was obtained and analytical solutions of the vibration were achieved for different exponential shapes of each link (widening and narrowing beam for each link). Natural frequencies and mode shapes were presented for varying cross-section areas of the links. The effects of the end masses, payload, beam mass density, flexural rigidity ratio, and joint frequency were investigated on the mode shapes and natural frequencies when the power of the exponential function of the cross-sectional areas of two links was varied. The numerical results were verified with experimental results.

Analytical modeling and computational optimization for a 1-DOF compliant mechanism

The first natural frequency directly affects the operational conditions of compliant mechanisms in precision engineering systems. To address this challenge, a computational method based on the surface response method is proposed to optimize the frequency of a new one degree of freedom (DOF) compliant mechanism. Initially, a 1-DOF 3D model of a compliant mechanism is built. The dynamic equation and the frequency response are formulated via equivalent stiffness and the Lagrange method. Subsequently, a series of numerical simulations are conducted to find the fundamental frequency of the mechanism. The initial dimensions of the flexible joints are determined, and the initial frequency is analyzed by using finite element analysis. Next, the flexible joints in the designed mechanism are optimized by a variant of the genetic algorithm. The optimized dimensions of the mechanism are found with the thickness of the circular joint of 1.10 mm, the thickness of the leaf joint of 1.19 mm, and the length of the leaf joint of 54.50 mm. The optimized result showed that there is a significant improvement in the frequency of the mechanism, increasing from an initial design of 53.218 Hz to an optimal design of 75.927 Hz with an improvement of 42.6%. This study provides important reference materials for future research on compliant mechanisms.

LJF of thin-walled gapped uni-planar K-type tubular steel joints with collar under brace balanced axial loads

This paper investigates the efficacy of the collar plate in improving the Local Joint Flexibility (LJF) of thin-walled circular hollow section (CHS) K-joints under axial loads. Initially, a finite element model (FEM) was created and verified against data from 14 available experimental tests. Subsequently, an extensive series of 136 unreinforced and reinforced K-joints was simulated to analyze the influence of parameters such as collar plate dimensions (η and λ), brace angle (θ), and joint geometry (β, ξ, and γ) on the LJF factor (fLJF) and the fLJF ratio (χ). The FEMs incorporated plate-to-member contact and weld modeling. Findings indicate that the utilization of the plate reduces the fLJF by 73 %. Additionally, it was observed that plate length significantly affects the fLJF compared to plate thickness. While the impact of γ, θ, and ξ on χ is marginal, β, η and λ emerge as a noteworthy determinant of χ. Despite the pivotal role of fLJF in joint behavior, there exists a gap in studies and equations specifically addressing fLJF in collar-plate reinforced K-joints under axial loads. To address this gap, leveraging the FE results, a design equation is proposed. This equation is subsequently validated with high coefficients of determination and standards set by the UK Department of Energy.

Transforming rehabilitation: A narrative review on reversible knee flexor contracture assistive devices

Abstract: Joint contracture, marked by restricted joint movement due to connective tissue and muscle shortening, is a common complication in chronic musculoskeletal conditions such as osteoarthritis, osteonecrosis, rheumatoid arthritis, healed septic joint, and postsurgical complications. This limitation adversely impacts joint mobility and flexibility, increasing the likelihood of physical constraints. Contractures elevate the risk of impaired self-care, limited physical mobility, and hindered social activities, emphasizing the critical need to manage such contractures. The study aims to find the most appropriate, effective, user-friendly mechanical device to treat reversible knee flexor contracture. Method of a literature review was conducted utilizing PubMed, Google Scholar, and the physiotherapy evidence database (PEDro) up to April 2023. The inclusion criteria comprised studies related to flexion contracture (FC), written in English languages were included. The literature searched using the terms “flexion contracture, hamstring contracture, knee flexor contracture, burn contracture, knee joint hypomobility, and devices for flexion contracture.” Result after applying the selection criteria, the initial screening of literature gives 35,400 results on Google Scholar, PubMed, and PEDro. Subsequently, 128 articles underwent screening based on abstract and full-text availability in the English language. Following this, seven articles were selected and thoroughly reviewed, which included randomized control trials, systematic reviews, and exploratory studies. The study concluded the use of conventional physiotherapy interventions, coupled with assistive devices, diminishes the burden on physiotherapists and provides effective improvements to patients with FCs.

Effects of Fatigue on Ankle Flexor Activity and Ground Reaction Forces in Elite Table Tennis Players.

Fatigue specifically affects the force production capacity of the working muscle, leading to a decline in athletes' performance. This study investigated the impact of fatigue on ankle flexor muscle activity and ground reaction forces (GRFs) in elite table tennis players, with a focus on the implications for performance and injury risk. Twelve elite male table tennis athletes participated in this study, undergoing a fatigue protocol that simulated intense gameplay conditions. Muscle activity of the soleus (SOL) and gastrocnemius lateralis (GL) muscles, heel height, and GRFs were measured using a combination of wireless electromyography (EMG), motion capture, and force plate systems. Results showed a significant decrease in muscle activity in both legs post-fatigue, with a more pronounced decline in the right leg. This decrease in muscle activity negatively affected ankle joint flexibility, limiting heel lift-off. Interestingly, the maximal anteroposterior GRF generated by the left leg increased in the post-fatigue phase, suggesting the use of compensatory strategies to maintain balance and performance. These findings underscore the importance of managing fatigue, addressing muscle imbalances, and improving ankle flexibility and strength to optimize performance and reduce the risk of injuries.

An Assessment of the Impact of Protective Lifeline Safety Systems on Formwork Systems

Work related to the installation of formwork and the pouring of concrete involves the need to move on the formwork walls. There is a high risk of falling off the wall and falling during work. It is therefore necessary to use systems that allow for safe work at heights, but also the safety of the formwork systems themselves. This article presents the results of tests under real conditions of a person falling from the formwork. Two safety systems were tested: one based on a pole–rope system with a flexible joint and one based on climbing arrester hooks. The test results showed that the additional forces occurring in the system do not exceed 6.4 kN and that the stresses reach the highest value only at the site of installation of the system and do not exceed the yield strength of the steel used in the formwork structure. The results obtained indicate that during a fall, the fall energy is absorbed so much that there is no damage to the formwork elements, and the highest effort is observed for the formwork arrester hook and reaches 87% of the structure effort. In the case of systems with flexible posts, the maximum load values do not exceed 30% of the structure. The presented results may be useful in designing and planning assembly works and using formwork systems in concrete pouring conditions.

Experimental study on mechanical behavior and countermeasures of mountain tunnels under strike-slip fault movement

In the seismic mountainous regions such as western China, it is usuallly inevitable to construct tunnels near active fault zones. Those fault-crossing tunnel structures can be extremely vulnerable during earthquakes. Extensive experimental studies have been conducted on the response of continuous mountain tunnels under reverse and normal fault movements, limited experimental investigations are available in the literatures on mountain tunnels with special structural measures crossing strike-slip faults. In this study, a new experimental facility for simulating the movement of strike-slip fault was developed, accounting for the spatial deformation characteristics of large active fault zones. Two groups of sandbox experiment were performed on the scaled tunnel models to investigate the evolution of ground deformation and surface rupture subjected to strike-slip fault motion and its impact on a water conveyance tunnel. The nonlinear response and damage mechanism of continuous tunnels and tunnels incorporated with specially designed articulated system were examined. The test results show that most of slip between stationary block and moving block occurred within the fault core, and significant surface ruptures are observed along the fault strike direction at the fault damage zone. The continuous tunnel undergoes significant shrinkage deformation and diagonal-shear failure near the slip surface and resulted in localized collapse of tunnel lining. The segments of articulated system tunnel suffer a significant horizontal deflection of about 5°, which results in opening and misalignment at the flexible joint. The width of the damaged zone of the articulated system tunnel is about 0.44 to 0.57 times that of the continuous tunnel. Compared to continuous tunnels, the articulated design significantly reduces the axial strain response of the tunnel lining, but increases the circumferential tensile strain at the tunnel crown and invert. It is concluded that articulated design provides an effective measure to reduce the extent of damage in mountain tunnel.

Dynamic modelling and a model-based control strategy of joint servo system for power transmission line inspection robot

Abstract The time-varying load inertia is one of the important dynamic characteristics of the power transmission line inspection robots (PTLIRs) in joint space, which can heavily affect the stability of the robot in the inspection process. In this paper, with considering the time-varying characteristics of load inertia, a method for modelling and control of the flexible joint servo system of the PTLIR is studied. First, the control system of the PTLIR is established based on the two inertia system. In order to calculate the load inertia, a dynamic model of the inspection robot is established. Then, the model-based notch filter is designed to improve dynamic performance of the robot, and suppress the vibration amplitude change which caused by the time-varying load inertia. Finally, the comparison of the control performance between the traditional control strategy and the model-based control strategy with notch filter are compared. The simulation results show that the paper can provide an effective tool for modelling and improving the stability of the PTLIR.

Multi-Behavior Recommendation with Personalized Directed Acyclic Behavior Graphs

A well-developed recommendation system can not only leverage multi-typed interactions (such as page view, add-to-cart, and purchase) to better identify user preferences, but also demonstrate high performance, low complexity, and strong interpretability. However, many existing solutions for multi-behavior recommendation fall short of intuitive modeling of real-world scenarios, leading to overly complex models with massive parameters and cumbersome components. In particular, they share two critical limitations: (1) Some pioneering models are built upon the strict assumption of cascade effects across behaviors, which contradicts multifarious behavior paths in practical applications. (2) Existing approaches fail to explicitly capture the unique idiosyncrasies of users and even neglect the inherent nature of items involved in the multi-behavior interactions. To this end, we propose a novel Directed Acyclic Graph Convolutional Network (DA-GCN) for the multi-behavior recommendation task. Specifically, we pinpoint the partial order relations within the monotonic behavior chain and extend it to personalized directed acyclic behavior graphs to exploit behavior dependencies. Then, a GCN-based directed edge encoder is employed to distill rich collaborative signals embodied by each directed edge. In light of the information flows over the directed acyclic structure, we propose an attentive aggregation module to gather messages from all potential antecedent behaviors, representing distinct perspectives to understand the terminated behavior. Thus, we obtain comprehensive representations for the follow-up behavior through learnable distributions over its preceding behaviors, explicitly reflecting personalized interactive patterns of users and underlying properties of items simultaneously. Finally, we design a customized multi-task learning objective for flexible joint optimization. Extensive experiments on public benchmarking datasets fully demonstrate the superiority of DA-GCN with significant performance improvement and computational efficiency over a wide range of state-of-the-art methods. Our code is available at https://github.com/xizhu1022/DA-GCN .

Understanding medicine related adverse events in people with multiple long-term conditions and polypharmacy

Background and ObjectivesPolypharmacy is increasingly common in people living with multiple long-term conditions (MLTC), but clinical evidence often does not consider medicine interactions beyond two or three treatments at a time. The aim of this research is to develop statistical models to better understand interactions between treatments leading to adverse events for people living with MLTC. ApproachWe will develop models of risk of adverse events in people with MLTC and polypharmacy using data in the Secure Anonymised Information Linkage (SAIL) Databank - a trusted research environment with linked electronic health record data at the individual-level for the population of Wales, UK. Taking a flexible Bayesian joint modelling approach, where the posterior risk is the product of several sub-models, will enable the characterisation of this complex system in a way that is interpretable for healthcare decision-makers, leading to improved understanding of risk factors for adverse events. ResultsThe Welsh Multimorbidity e-Cohort (WMC) includes 2.9 million people alive and living in Wales on 1st Jan 2000 with follow-up for 20 years. Individuals in the cohort have 932,552,061 medication items prescribed and 277,279 coded adverse events recorded in primary care data. Modelling approaches will focus on feasibility of fitting models to population-level datasets, and the interpretability of the model results for healthcare decision-making. Conclusions and ImplicationsResults have the potential to inform healthcare policy and practice for the management of people living with MLTC and polypharmacy, thus improving patient outcomes and making the best use of limited healthcare resources.