Flexible Joint Research Articles

Maximum likelihood FIR filter for systems with Bernoulli distributed random delays and measurement failures

A new solution for the state estimation problems for the state-space model with random time delay and measurement failures is proposed, and the batch and iterative versions of the finite impulse response (FIR) filter are constructed based on the theorem of maximum likelihood in this paper. First, the state model is addressed with the maximum likelihood in the situation of random delays and measurement failures. Then the state-space model is expressed as a linear probability function following a random Bernoulli distribution. Finally, the proposed algorithm is compared to an adaptive Kalman filter and the UFIR filter using a drifting stochastic resonator and rotary flexible joint simulation analysis. It shows that the proposed maximum likelihood FIR method has improved estimation performance and robustness in coping with random delays and measurement failures compared to some commonly used algorithms.

Biomechanical analysis of the effect of finger joint configuration on hand grasping performance: rigid vs flexible.

Human finger joints are conventionally simplified as rigid joints in robotic hand design and biomechanical hand modelling, due to their anatomic and morphologic complexity. However, our understanding of the effect of the finger joint configuration on the resulting hand performance is still primitive. In this study, we systematically investigate the grasping performance of the hands with the conventional rigid joints and the biomechanical flexible joints based on a computational human hand model. The measured muscle electromyography (EMG) and hand kinematic data during grasping are used as inputs for the grasping simulations. The results show that the rigid joint configuration currently used in most robotic hands leads to large reductions in hand contact force, contact pressure and contact area, compared to the flexible joint configuration. The grasping quality could be reduced up to 40% and 36% by the rigid joint configuration in terms of algebraic properties of grasping matrix and finger force limit respectively. Further investigation reveals that these reductions are caused by the weak rotational stiffness of the rigid joint configuration. This study implies that robotic/prosthetic hand performance could be improved by exploiting flexible finger joint design. Hand contact parameters and grasping performance may be underestimated by the rigid joint simplification in human hand modelling.

IMPACTOS DA TÉCNICA PNF SOBRE FLEXIBILIDADE E FORÇA EM ATLETAS DE ARTES MARCIAIS

ABSTRACT Introduction: Joint flexibility and muscle strength play a vital role in the training process of martial arts athletes. The proprioceptive neuromuscular facilitation (PNF) technique encourages the neural receptors, through the application of manual resistances, in the gain of functional range of motion and stability to its patients. It is believed that this technique can be adapted to the sports environment. Objective: Evaluate the impact of stretching using the PNF technique on martial arts athletes’ flexibility and muscle strength. Methods: Through a controlled experiment, 100 martial arts athletes, without significant differences, were selected as experimental subjects, and randomly divided into two groups for a 4-week experiment. The experimental group added a protocol with PNF stretching exercises in the training, while the control group performed the usual training without interventions. Indicators of flexibility, functional activities, and strength were measured before and after the intervention, compared, and statistically analyzed. Results: Joint flexibility with the shoulder rotation test evolved from 21.88±5.71 to 19.22±5.94, and the left and right division was from 16.90±5.36 to 10.57±3.75; as for muscle strength, the flexor peak moment elevated from 210.36±51.18 to 251.37± 45.72, and flexor power had a gain from 111.76±30.63 to 135.20±2,.42. The extensor peak moment also showed expressive evolutions from 179.47±43.96 to 221.52±33.60. Conclusion: The PNF stretching exercise technique effectively optimizes martial arts athletes’ joint flexibility and muscle strength. Level of evidence II; Therapeutic studies - investigation of treatment outcomes.

Nonlinear extended state observer based control for the teleoperation of robotic systems with flexible joints.

The control of robot manipulator pose is significantly complicated by the uncertainties arising from flexible joints, presenting substantial challenges in incorporating practical operational constraints. These challenges are further exacerbated in teleoperation scenarios, where factors such as synchronization and external disturbances further amplify the difficulties. At the core of this research is the introduction of a pioneering teleoperation controller, ingeniously integrating a nonlinear extended state observer (ESO) with the barrier Lyapunov function (BLF) while effectively accommodating a steady time delay. The controller in our study demonstrates exceptional proficiency in accurately estimating uncertainties arising from both flexible joints and external disturbances using the nonlinear ESO. Refined estimates, in conjunction with operational constraints of the system, are integrated into our BLF-based controller. Consequently, a synchronized control mechanism for teleoperation is achieved, exhibiting promising performance. Importantly, our experimental findings provide substantial evidence that our proposed approach effectively reduces the tracking error of the teleoperation system to within 0.02 rad. This advancement highlights the potential of our controller in significantly enhancing the precision and reliability of teleoperated robot manipulators.

On Tracking Control of Robot Manipulator with Flexible Joints in Operational Space

In this paper, an adaptive control framework and a command-filtered control framework are proposed for flexible joint robot manipulators to track a desired trajectory in the workspace. First, we present an adaptive control algorithm which ensures that the output (the end-effector) of the uncertain manipulator with flexible joints tracks a desired trajectory in the operational space. Subsequently, a control algorithm is synthesized with the command-filtered technique to eliminate the requirements of the joint-jerk feedback and the third-order derivative of system models. The advantages of the proposed control frameworks are guaranteeing the tracking performance in the workspace and scaling down the complexity of the controller. Therefore, the proposed approaches can be applied to heterogeneous robotic systems and are easier to implement. The stability and convergence of the closed-loop systems are analyzed based on Lyapunov technique. Simulation results are provided to show the efficiency of the proposed control frameworks.

Dual Arm Impact-Aware Grasping through Time-Invariant Reference Spreading Control

With the goal of increasing the speed and efficiency in robotic dual arm manipulation, a novel control approach is presented that utilizes intentional simultaneous impacts to rapidly grasp objects. This approach uses the time-invariant reference spreading framework, in which partly-overlapping ante and post-impact reference vector fields are used. These vector fields are coupled via the impact dynamics in proximity of the expected impact area, minimizing the otherwise large velocity errors after the impact and the corresponding large control efforts. A purely spatial task is introduced to strongly encourage the synchronization of impact times of the two arms. An interim-impact control phase provides robustness in the execution against the inevitable lack of exact impact simultaneity and the corresponding unreliable velocity error. In this interim phase, a position feedback signal is derived from the ante-impact velocity reference, which is used to enforce sustained contact in all contact points without using velocity error feedback. With an eye towards real-life implementation, the approach is formulated using a QP control framework, and is validated using numerical simulations on a realistic robot model with flexible joints and low-level torque control.

The stress state analysis of lattice tower support for 330 kV overhead line using the “USL” software package

In conditions of market economy, overhead power transmission line (OPTL) support structures must be low-cost and of guaranteed quality, the manufacture of which will require a minimum amount of steel. Therefore, it is necessary to improve overhead line supports, which is possible by clarifying the forces in the support elements and when designing using numerical methods. In this article, a mode of deformation of a corner dead-end support of OPTL is analysed, which is considered a spatially multiple indeterminate open system with flexible joints. Attention is given to the basic problems that can occur in setting initial parameters and constructing design models for such structures. There are a number of problems connected with a refined specification of internal longitudinal stresses in the components of an OPTL structure. In designing, the joint operation of the lattice components of the support spatial pattern model is analysed, and the inclusion of stiffening diaphragms and diagonal element members in the operation on all four faces is taken into account. On the basis of the design and the extension of the results, the internal forces obtained and the ones specified in the components of the pattern OPTL support on the similar values of loads were thoroughly compared. When calculating the spatial model of an anchor-corner support as a result of the joint work of lattice elements, a decrease in internal forces in the elements of the spatial model is observed on average by 6.8%, compared to the forces determined in a typical overhead line support from the same load values. It has been established that it is quite acceptable to calculate overhead line lattice structures in the USL software package since the error in determining the forces in the rods is within 2% and the computer time consumption is less than in other software packages.

A semi-fluid multi-functional binder for a high-performance silicon anode of lithium-ion batteries.

Currently, a variety of binders are developed to inhibit the rapid capacity fading of Si. The Si anodes are mainly enhanced by the chemical bonding effect on the surface of conventional solid-state binders. However, with a huge volume change of silicon, solid binders are easily deactivated. Herein, a semi-fluid binder termed GPC is designed based on a viscoelastic crosslinking network with abundant active sites and self-healing performance. The backbone of the binder network is in situ synthesized using guar gum (GG), polyacrylic acid (PAA), and citric acid (CA). Serving as the flexible joints and the plasticizer of the network, CA small molecules remarkably improve the viscoelasticity of the binder to tolerate the volume change of Si via rearranging particles in the network during cycling. Moreover, CA can form a layer of surface coating on Si to stabilize the SEI for long-term electrochemical performance. As a result, the Si@GPC electrode shows excellent cycling stability and exhibits a superb capacity of 1292 mA h g-1 after 1000 cycles at 2 A g-1. This work illustrates the advantages and prospects of designing semi-fluid binders for high-performance batteries.

IMPACTOS DO ALONGAMENTO PNF SOBRE A FLEXIBILIDADE ARTICULAR EM ATLETAS DE VÔLEI

ABSTRACT Introduction: It is believed that the stretching method by Proprioceptive Neuromuscular Facilitation (PNF) can improve functional joint flexibility through neural stimuli, resulting in more precise movements for volleyball players. Objective: Study the effect of PNF stretching exercise on shoulder joint flexibility in volleyball athletes. Methods: A total of 30 members of a university volleyball team were randomly divided into experimental and control groups. The traditional stretching method was used in the control group, while the PNF stretching method was employed in the experimental group. Data regarding the range of motion and functional quality were collected before and after the intervention for statistical analysis. Results: After eight weeks of the experiment, the left anterior flexion functional score on the shoulder flexibility index of the experimental group increased from 147.05 ± 4.95 to 160.99 ± 4.56; the right frontal flexion score increased from 150.27 ± 5.93 to 162.16 ± 4.46. Shoulder joint stability was gradually stabilized from 88.33 to 101.17. The pass functional score increased from 4.17 ± 1.93 to 18.96 ± 1.77; the overall functional performance score increased from 9.02 ± 4.04 to 23.07 ± 3.96. The control group had an increase without statistical significance. Conclusion: PNF stretching exercises can improve the shoulder joint flexibility of volleyball players. Level of evidence II; Therapeutic studies - investigation of treatment outcomes.

Observer-Based Control for a Cable-Driven Aerial Manipulator under Lumped Disturbances

With the increasing demand for interactive aerial operations, the application of aerial manipulators is becoming more promising. However, there are a few critical problems on how to improve the energetic efficiency and pose control of the aerial manipulator for practical application. In this paper, a novel cable-driven aerial manipulator used for remote water sampling is proposed and then its rigid-flexible coupling dynamics model is constructed which takes joint flexibility into account. To achieve high precision joint position tracking under lumped disturbances, a newly controller, which consists of three parts: linear extended state observer, adaptive super-twisting strategy, and fractional-order nonsingular terminal sliding mode control, is proposed. The linear extended state observer is adopted to approximate unmeasured states and unknown lumped disturbances and achieve model-free control structure. The adaptive super-twisting strategy and fractional-order nonsingular terminal sliding mode control are combined together to achieve good control performance and counteract chattering problem. The Lyapunov method is utilized to prove the overall stability and convergence of the system. Lastly, various visualization simulations and ground experiments are conducted, verifying the effectiveness of our strategy, and all outcomes demonstrate its superiorities over the existing control strategies.

Characteristics of Ruptured Anterior Cruciate Ligament (ACL) Patients at Hasan Sadikin Hospital Bandung

Background: ACL injury is the most common injury in sports knee injuries. An ACL injury can be a stretch to the ligament or it can be completely torn. The ACL ligament is one of the main ligaments in the knee region. Discussions about ligaments in the knee joint are still rarely heard, especially in Indonesia. So there is little knowledge for the community. The discussion of literature originating from Indonesia is still small and makes it difficult for the public to obtain information related to this ligament rupture. Cases in Indonesia are quite numerous and varied, so a better understanding of ACL rupture injuries is needed. In the last 5 years, 187 cases were found at Hasan Sadikin Hospital, Bandung, with a variety of cases and different treatments, especially using the arthroscopy method. Methods: This study was conducted to determine the characteristics of ACL injured patients at Hasan Sadikin Hospital, Bandung Period January 2017 to December 2021. The inclusion criteria in this study were all patients with ACL injuries from January 2017 to December 2021 with complete medical record data. Results: The results of this study showed that the age range of ACL patients was 14-64 years, with an average age of 24.5 years. male to female is 4.67:1. There were 10 patients who were athletes. The type of ACL injury was partial, there were 39 patients and the total was 148 patients. Other comorbidities Hoffa syndrome 18 patients. Plica syndrome 30 patients. Joint flexibility 19 people, who do not have joint flexibility 168 patients. Management of patients with remnant resurface as many as 163 patients and 23 patients who underwent augmentation. Other problems after ACL surgery were 18 patients underwent menisectomy and 6 patients underwent meniscus repair Conclusion: From the results of this study, the characteristics of patients with ACL rupture were found to be on average at the age of 24.5 years, male gender, college students. 10 professional athletes suffered ACL ruptures. More patients suffered total rupture than partial. Treatment for ACL patients is more often with remnant surfaces. After ACL treatment, complications such as menisectomy could occur as many as 38 patients and 16 patients underwent meniscus repair

Streaming Variational Monte Carlo.

Nonlinear state-space models are powerful tools to describe dynamical structures in complex time series. In a streaming setting where data are processed one sample at a time, simultaneous inference of the state and its nonlinear dynamics has posed significant challenges in practice. We develop a novel online learning framework, leveraging variational inference and sequential Monte Carlo, which enables flexible and accurate Bayesian joint filtering. Our method provides an approximation of the filtering posterior which can be made arbitrarily close to the true filtering distribution for a wide class of dynamics models and observation models. Specifically, the proposed framework can efficiently approximate a posterior over the dynamics using sparse Gaussian processes, allowing for an interpretable model of the latent dynamics. Constant time complexity per sample makes our approach amenable to online learning scenarios and suitable for real-time applications.

AWOT and CWOT for genotype and genotype by treatment interaction joint analysis in pharmacogenetics GWAS.

Pharmacogenomics (PGx) research holds the promise for detecting association between genetic variants and drug responses in randomized clinical trials, but it is limited by small populations and thus has low power to detect signals. It is critical to increase the power of PGx genome-wide association studies (GWAS) with small sample sizes so that variant-drug-response association discoveries are not limited to common variants with extremely large effect. In this paper, we first discuss the challenges of PGx GWAS studies and then propose the adaptively weighted joint test (AWOT) and Cauchy weighted joint test (CWOT), which are two flexible and robust joint tests of the single nucleotide polymorphism (SNP) main effect and genotype-by-treatment interaction effect for continuous and binary endpoints. Two analytic procedures are proposed to accurately calculate the joint test p-value. We evaluate AWOT and CWOT through extensive simulations under various scenarios. The results show that the proposed AWOT and CWOT control type I error well and outperform existing methods in detecting the most interesting signal patterns in PGx settings (i.e., with strong genotype-by-treatment interaction effects, but weak genotype main effects). We demonstrate the value of AWOT and CWOT by applying them to the PGx GWAS from the Bezlotoxumab Clostridium difficile MODIFY I/II phase 3 trials. The R package COWT is publicly available on CRAN https://cran.r-project.org/web/packages/cwot/index.html. Supplementary data are available at Bioinformatics online.

A tactile force/Angle perception method for flexible humanoid finger joints

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Design of Earthquake-Resistant Buildings by Using Reinforced Concrete or Steel Flexible Corner Joints

Design of Earthquake-Resistant Buildings by Using Reinforced Concrete or Steel Flexible Corner Joints

EFEITOS DOS EXERCÍCIOS DE FLEXIBILIDADE PARA PREVENÇÃO EM LESÕES DO JOELHO NOS TENISTAS

ABSTRACT Introduction: Despite the intrinsic benefits of sports practice, the adherence to tennis by a large part of the population without the due physical preparation apparently resulted in a high rate of knee joint injuries in tennis players, either in daily training or competitions. Objective: Prevent tennis players’ knee joint injuries by exploring ways to improve lower limb joint stability. Methods: This paper selected 50 national second-level professional tennis players and divided them into two groups. Both groups had daily tennis training, but the experimental group experienced additional lower limb flexibility exercises. Results: The tennis players in the experimental group increased their seated forward flexion from 22.19 cm to 26.96 cm, the knee joint extensor muscle strength index increased from 142.69 to 176.23, and the knee joint flexor muscle strength index increased from 93.21 to 149.28, P<0.05, with significant differences. The general stability index was changed from 0.23 to 0.20, the internal and external indices varied from 0.13 to 0.08, and the frontal and posterior indices changed from 0.13 to 0.08. Conclusion: Knee joint injuries in tennis players can be effectively combated by adding lower limb flexibility exercise protocol to daily training. Level of evidence II; Therapeutic studies - investigation of treatment outcomes.

Q-learning based model-free input-output feedback linearization control method⋆

Input-output feedback linearization is a nonlinear control method that relies on a precise dynamical model. Combining Q-learning techniques, an input-output feedback linearization correction framework is presented to accomplish model-free feedback linearization of affine nonlinear systems in order to tackle the problem caused by the unknown dynamics model. This framework formulates a model reference tracking control problem that guides the input-output relationship of the nonlinear system into a linear relationship. Due to the two Lie derivative terms present in the feedback linearized controller, the controller is designed as a dual network structure. To overcome the issue of coupling in the dual-network controller, a model-free Q-learning method is presented to solve the unknown controller network weights. The proposed method is experimentally validated on a single-link flexible joint manipulator system, and the resultant linearized system exhibits dynamics similar to the desired linear system in a new tracking task, proving the effectiveness of the proposed method.

Throughput Maximization for UAV-Enabled Integrated Periodic Sensing and Communication

Driven by unmanned aerial vehicle (UAV)’s advantages of flexible observation and enhanced communication capability, it is expected to revolutionize the existing integrated sensing and communication (ISAC) system and promise a more flexible joint design. Nevertheless, the existing works on ISAC mainly focus on exploring the performance of both functionalities simultaneously during the entire considered period, which may ignore the practical asymmetric sensing and communication requirements. In particular, always forcing sensing along with communication may make it is harder to balance between these two functionalities due to shared spectrum resources and limited transmit power. To address this issue, we propose a new integrated periodic sensing and communication (IPSAC) mechanism for the UAV-enabled ISAC system to provide a more flexible trade-off between two integrated functionalities. Specifically, the system achievable rate is maximized via jointly optimizing UAV trajectory, user association, target sensing selection, and transmit beamforming, while meeting the sensing frequency and beam pattern gain requirement for the given targets. Despite that this problem is highly non-convex and involves closely coupled integer variables, we derive the closed-form optimal beamforming vector to dramatically reduce the complexity of beamforming design, and present a tight lower bound of the achievable rate to facilitate UAV trajectory design. Based on the above results, we propose a two-layer penalty-based algorithm to efficiently solve the considered problem. To draw more important insights, the optimal achievable rate and the optimal UAV location are analyzed under a special case of infinity number of antennas. Furthermore, we prove the structural symmetry between the optimal solutions in different ISAC frames without location constraints in our considered UAV-enabled ISAC system. Based on this, we propose an efficient algorithm for solving the problem with location constraints. Numerical results validate the effectiveness of our proposed designs and also unveil a more flexible trade-off in ISAC systems over benchmark schemes.

PUFJ (PolyUrethane Flexible Joints) as an innovative polyurethane system for structural and non-structural bonding of timber elements

PolyUrethane Flexible Joints (PUFJ) as an innovative adhesive system has been developed by a team of researchers from the Cracow University of Technology (CUT) for several years. Initially, the research focused mainly on joining masonry and reinforced concrete elements. Due to environmental concerns and climate changes, further advancement of the PUFJ system was focused on the technology development based on connecting natural materials such as wood and wood-based materials. In 2019, the cooperation of the CUT with a private company resulted in the implementation of the PUFJ system for the construction of innovative connections in a prefabricated timber frame construction of a family house near Cracow. Currently, further research are carried out focused on the complex understanding of behaviour of adhesive bond used in structural and non-structural timber bonding, taking into account different species of wood (pine, spruce, beech, douglas fir) and a different thickness of the flexible adhesive layer (from 1 mm to 30 mm). The article contains the properties of the PUFJ system, describes variants of the available applications (wet application in form of liquid substance curing in time or dry application as a prefabricated bonding layers glued to the elements with a thin adhesive layer). Examples of double-lap shear connections and laminated beams made of douglas fir wood of C24 class and Sika®PS polyurethane flexible layer are presented. All specimens were constructed with three various flexible adhesive thicknesses of 1, 2 and 4 mm. The influence of elevated temperature on the load capacity of the connection and on the final deflection was tested. The tests were conducted at four temperature levels (20, 40, 60 and 80°C).

The Rotary Flexible Joint – A Holistic View from Modeling and Control to Observer Design and Experiments

A two degrees of freedom (2DOF) control for a lab-scale vertically-mounted rotary flexible joint is addressed to realize a benchmark example for nonlinear control education and experimentation. To this end, the mathematical model is derived based on the Euler-Lagrange equations. Further insight into the model is given by addressing the relationship between the two translational springs and their approximation as a single torsion spring. The model is known to be differentially flat, which facilitates a feedforward control design by means of the flat parameterization. Furthermore, a state-feedback controller is introduced to stabilize the desired trajectory. State information is reconstructed using a Luenberger-type observer. Both the state-feedback controller and the Luenberger-type observer are designed based on a linear time-varying (LTV) approximation obtained using a linearization around the flat state parameterization of the system. The 2DOF design is illustrated using experimental results.