Flexible Joint Research Articles

Numerical Analysis of Local Joint Flexibility of K-joints with External Plates Under Axial Loads in Offshore Tubular Structures

Numerical Analysis of Local Joint Flexibility of K-joints with External Plates Under Axial Loads in Offshore Tubular Structures

Cadaver preserving methods – is it possible to do anything better?

Abstract It is impossible to imagine learning anatomy without properly fixating cadavers. Thanks to accurate preservation techniques, students can differentiate anatomical structures by their sight and touch. The formalin method was first described almost 150 years ago, and as such it may seem primitive, however it is effective and easy to use, which is why it is still in use today. Despite formaldehyde’s bactericidal, fungicidal, and insecticidal properties contact with vapors of embalming solutions such as formalin may have a negative health effect. Skin drying, eczema, allergic contact dermatitis and lowered red blood cells (RBCs) and platelets are only a few symptoms that may occur as a result of spending long periods of time in places where cadavers are stored. Due to formalin’s features, other techniques were invented. Thiel’s method is also well known; after liquid application, tissues remain their natural color as the method is non-irritating and almost odorless. With the rise of technology, more modern methods of cadaver preservation were developed as alternative to formalin, such as the use of N-vinyl-2-pyrrolidone (NVP), which is commonly implemented in Japan and Brazil, and the Modified Larssen solution (MLS), which gives the possibility to reduce formalin concentration without losing the effectiveness of tissue preservation. The aim of this work is to develop an integrated approach to cadaver preservation through the analysis of frequently used preservation techniques. This is a considerable issue because first-year students of medicine and related faculties encounter the preserved material while learning anatomy. In comparison to more modern methods, formalin seems to be the worst choice due to worse joint flexibility, tissue colour and structure and, most importantly, its cancerogenic action.

A wrist-inspired suspended tubercle-type tensegrity joint with variable stiffness capacity

In complex and unpredictable environments or in situations of human–robot interaction, a soft and flexible robot performs more safely and is more impact resistant compared to a traditional rigid robot. To enable robots to have bionic features (flexibility, compliance and variable stiffness) similar to human joints, structures involving suspended tubercle tensegrity are researched. The suspended tubercle gives the joint compliance and flexibility by isolating two moving parts. The variable stiffness capacity is achieved by changing the internal stress of tensegrity through the simultaneous contraction or relaxation of the driving tendons. A wrist-inspired tensegrity-based bionic joint is proposed as a case study. It has variable stiffness and two rotations with a total of three degrees of freedom. Through theoretical derivation and simulation calculation in the NASA Tensegrity RobotToolkit (NTRT) simulator, the range of motion, stiffness adjustable capacity, and their interaction are studied. A prototype is built and tested under a motion capture system. The experimental result agrees well with the theoretical simulation. Our experiments show that the suspended tubercle-type tensegrity is flexible, the stiffness is adjustable and easy to control, and it has great potential for bionic joints.

Analysis of load-bearing safety and reliability of solid rocket motor flexible joint structure

Flexible nozzle is the thrust vector control system of a solid rocket engine, and flexible joint is the key component of its load-bearing and changing behavior. It is composed of composite rubber elastic parts with spherical annular structure and metal reinforcing parts with spherical annular structure alternately adhesive. Under the action of complex loads, the flexible nozzle exhibits highly nonlinear mechanical properties. The traditional flexible joint structure with uniform thickness is easily damaged during loading and has large negative mass and short system range. However, the load-bearing swing performance of the system, such as swing center displacement, swing moment, and fatigue life, is difficult to predict, and the safety and reliability of the joint structure cannot be guaranteed. To this end, on the basis of the measured material properties of elastic parts, the Lagrangian structural dynamics algorithm coupling material and geometrically nonlinear, the Design of Experiment multi-objective optimization algorithm and the multi-axial stress fatigue finite element numerical calculation method based on crack propagation combined to design a new lightweight variable-thickness joint. From the mechanical point of view, the failure mechanism and mode of the two joint structures are compared and analyzed, the safety factor is determined, and the load-bearing swing performance of the system is predicted. Results of the ground experiment test of the system prove that variable-thickness flexible joint has better safety and reliability.

Mechanical Properties and Microstructure of Binary In-Sn Alloys for Flexible Low Temperature Electronic Joints

This research evaluates the mechanical properties of a variety of binary In-Sn alloys as potential candidates for low temperature electronic joints. The tensile and hardness tests of as-cast In-5Sn, In-12.5Sn, In-25Sn, In-30Sn, In-35Sn, In-40Sn, In-50Sn, In-60Sn, In-80Sn (wt.%) were assessed at room temperature and compared to those of pure In and Sn. The ultimate tensile strength (UTS) increased from 4.2 MPa to 37.8 MPa with increasing tin content in the alloys under the testing condition of 18 mm/min and the results showed little difference under a lower strain rate (1.8 mm/min). Most compositions showed good ductility in tensile testing with an average of 40% elongation. A melting point range of 119.3 °C to 194.9 °C for tested alloys was measured using differential scanning calorimetry (DSC). The microstructure investigated by scanning electron microscopy (SEM) was discussed with respect to the mechanical properties and it has been found that the presence of the Sn-rich γ-InSn4 phase in the microstructure has a significant impact on mechanical properties. The fundamental data from this study can be used for the development of new low temperature In-Sn alloys.

Research on Dynamic Characteristics of Flap Actuation System Considering Joint Clearance and Flexibility

The flight control effects and flight quality of the aircraft are influenced by the flap actuation system directly. The main motivation of this research is to develop a rigid-flexible model of the flap actuation system with clearance and to explore the coupling effects of clearance joints and flexible bodies on the system’s dynamic characteristics. A modified contact force model is used to a joint with small clearance, heavy load, and large contact area. Then, the effectiveness of an embedded modeling method of this modified model is verified. Based on this method, a rigid-flexible coupling model of the flap actuation system with multi clearance joints is established. Moreover, the influence of system parameters, such as clearance size and clearance joint position, and coupling effects of the flexibility and joint clearance on dynamic responses, are analyzed. The results show that: (1) flexible bodies act as a suspension to reduce negative effects of joint clearance on dynamic responses of a clearance-contained system; (2) one flexible body can reduce the oscillation phenomenon of joint clearances, yet the suspension effect will be gradually weaken with the increase of the clearance joint number; (3) coupling effects of the elastic deformation owing to multi flexible bodies and the collision interaction between multi clearance joints make the system tend to chaos, and the system stability is reduced. This study can contribute to predicting the collision characteristics of the aircraft transmission system and improving the transmission accuracy, response speed, and stability of the aircraft.

An Observer-Based Stiffness Estimation for Space Target Capture by Space Robot with Controllable Damping Mechanism

The space target capturing task using the spacecraft-manipulator system (SMS) has special significance in on-orbit servicing due to its theoretical challenges and practical value. The contact force between the end effector (gripper) and the target exerted by the tumbling motion of the space target destabilizes the spacecraft base. A full-dimensional controllable damping mechanism (FDCDM) with a cross-axis structure was designed to buffer the transient impact force on the end joint. The introduction of a damping mechanism gives the space robot a variable stiffness and damping system, and a stiffness estimation algorithm is proposed to calibrate the system stiffness, as stiffness cannot be measured directly. The full-dimensional controllable damping mechanism (FDCDM) with a cross-axis structure is equivalent to a four-DOF tandem joint, and the whole-body dynamic model of the SMS endowed with a full-dimensional controllable damping mechanism (FDCDM) was established using the Kane equation. Then, an unknown input observer (UIO)-based identification theory is proposed to precisely estimate the internal flexibility torque and the corresponding joint stiffness. A model-based neural learning algorithm is proposed to update the variable parameter matrix of the observer. The simulation experiment results demonstrate that the flexibility torque and joint stiffness could be accurately estimated within the expected error, illustrating the feasibility and effectiveness of the proposed method.

Modelling the performance of immersed tunnel via considering variation of subsoil property

This paper presents a theoretical model to evaluate the time-dependent behaviour of an immersed tube tunnel by considering the changes in soil properties over time. The proposed model simplifies the tunnel as a Timoshenko beam on a Vlasov foundation with a stiffness change. Subsequently, the partial differential equation for calculating the stress and deformation of the immersed tube tunnel was derived. A new approach to solving this partial differential equation is proposed, which is different from the existing solution in the literature. The proposed model can analyse the joint force transmission characteristics of an immersed tube tunnel. This was verified by the field-observed settlement data of the immersed tube tunnel of the Hong Kong-Zhuhai-Macao transportation pass. The results show that the calculated results of the proposed model are consistent with the measured data, and the structural stress of semi-rigid elements can be quantitatively analysed by calculating the settlement of elements caused by flexible and rigid joints and the vertical differential settlement of joints.

Nonlinear dynamic analysis of a multi-link manipulator with flexible links-joints mounted on a mobile platform

The present work theoretically demonstrates the dynamic analysis of a planar multi-link manipulator considering flexible links and joints mounted on a moving base. A nonlinear model of a multi-manipulator (N-links) has been developed accounting for an equivalent bi-directional mobile base. The nonlinear Euler-Bernoulli beam and spring-inertia/mass system have been introduced to demonstrate the flexibilities of links and joints, respectively. Modal analysis followed by trajectory analysis has been performed to investigate the behaviors of manipulator taking into account of accurate boundary conditions. Further, vibration characteristics, steady-state responses, and their stability at resonant situations due to joint motions and inertial coupling have been studied. Results of exploiting geometric and inertial coupling due to flexible arms on stability analysis of steady-state responses have been investigated and have been subsequently verified with the findings by directly solving the governing equations. Steady-state response characteristics to explore the dynamics of the multi-link manipulators under resonant states have been studied with the varying actuator mass, the flexibility of links, lifted payload, and joint parameters. The results thus obtained, deliver a useful insight into the position analysis and long-term behavior of multi-link flexible manipulators under harmonic hub-joint motions that shall further enable its proper vibration attenuation and control.

Neural Networks Application for the Data of LQG Regulator for the Flexible Joint Robot

This paper describes the investigation of a flexible robotic arm with Degree of Freedom (DOF) through Linear Quadratic Gaussian (LQG) regulator under the influence of noise signals with using diagrams below. The derived model is based on the Euler-Lagrange approach while LQG mode is proposed as a modern control method. A flexible robotic arm that is test in the modern regulator is essential for applications. This is even more interesting while these arms have joints that work independently of each other, but they still ensure a tight connection between the joints. Testing the stability characteristics of the system through this regulator helps readers determine the output signals of a system exactly. From here, the author came up with strategies the match the requirements. Although the initial stage of the operating cycle is not stable with the use of LQG regulator, most of later stages of this process of closed systems of robotic systems gradually become stable. In particular, adjusting LQG for flexible joint robot gives satisfactory simulation results. This promises a positive result of other joint robot. Neural networks applied in this paper have proven its effectiveness in information security issues. It is also very useful for tight control of possible situations such as a large scale attack on network systems, automated control systems. The main contributions of this paper have been clearly demonstrated through two strategies that need to be addressed: LQG, neural networks for the data of LQG regulator.The methods described above have not been previously published for this model. Therefore, this article was born to outline the above objectives and the plans have been satisfactorily implemented. These studies are important because they serve as a necessary database in the selection of control strategies according to the requirements. Simulation results are done by Matlab. The purpose of the study of this paper: the author has searched for a stability of the system through the above methods. The applied method is a thorough study of the structure of the system as well as the construction of algorithms to form the regulator. The result ia a reliable simulation of events after the system is controlled by these regulators.

Redesign of a Hydraulic Manifold in Additive Manufacturing for Application in a Cleaning and Inspection Robot

A flexible joint riser inspection and cleaning robot must be small and powerful to perform its mission. Hydraulic units are commonly used in submerged operations for power. We designed a custom hydraulic unit as a robot. As the hydraulic manifold is complex, we developed it to be fabricated by additive manufacturing. The objective was to reduce the volume and mass of the hydraulic power unit. We achieved several computational analyzes and analytical methods to validate the designed concept. As a result, we obtained a more compact and lighter structure at the end of the process.

Vibration Suppression for Flexible Plate with Tunable Magnetically Controlled Joint Stiffness/Damping

Large flexible solar panels have the properties of light weight, low stiffness, and weak damping, which leads to low-frequency and large-amplitude vibrations. The existing vibration control methods of solar panels mainly adopt intelligent piezoelectric structures. However, the disadvantage is that the large stroke drive and control are limited. In the present study, a semi-active vibration control approach is proposed for flexible space solar panels based on magnetically controlled joints. The magnetic stiffness comes from the linear relationship between the joint output torque and rotation angle. The magnetic damping stems from the eddy current damping resulting from the relative motion between the permanent magnet rotor and the stator core of the joint. Firstly, the coupling dynamic modeling of a flexible plate and magnetic joints is established by adopting the Lagrange equation and the assumed mode approach. Secondly, semi-active vibration control simulations of the coupled system are performed. Meanwhile, the influence of the variable joint stiffness on the system frequency-shift effect is studied. Finally, the experimental platform is built, and simultaneously, non-contact permanent magnets and airflow are used to simulate single- and multi- frequency excitations, respectively. The experimental results indicate that, in the range of 0.06–0.343 Hz, magnetic damping is the leading factor with magnetic stiffness being the auxiliary. Additionally, it is also experimentally verified that the dual joint actuation has good synchronization. This study provides a new solution for the low-frequency vibration control of large flexible space structures.

Effect of 8 weeks CrossFit exercises on high school students during a physical fitness program

Purpose: The aim of this study was to assess the effectiveness of CrossFit exercises over a period of 8 weeks in a group of high school students during their physical education sessions at the school. and to mitigate the deficits in fitness caused by COVID-19 prevention measures.
 Material and methods: 94 students subject aged (16– 17) years were randomly allocated into an included 46 students (2nd level:12 men 11 women; 3rd level: 12 men 11 women) and 1 control group included 48 students (2nd level:13 men 11 women; 3rd level: 13 men 12 women Experimental group (EG) that performed the 8 weeks CrossFit exercises and control group (CG). Physical fitness tests were done: lifting straight legs in height (number times); running on the spot with an intensity of 70% of the maximum to severe fatigue (c); "Shuttle" run 4 × 9 m (with); 60 m run (s) and cross twine (cm). Results: there are considering changes, development of the maximum dynamic force endurance, speed abilities, flexibility and mobility in the hip joints of the main groups, In the age aspect, there is mainly the improvement in results with age, both in the main and control groups (p>0,05). Conclusion: the study achieved a significant improvement in the physical condition of the students, also allows to talk about the effectiveness of training, built on the basis of a motivated choice of the target CrossFit high school program.

Effect of 8 weeks CrossFit exercises on high school students during a physical fitness program

Purpose: The aim of this study was to assess the effectiveness of CrossFit exercises over a period of 8 weeks in a group of high school students during their physical education sessions at the school. and to mitigate the deficits in fitness caused by COVID-19 prevention measures.
 Material and methods: 94 students subject aged (16– 17) years were randomly allocated into an included 46 students (2nd level:12 men 11 women; 3rd level: 12 men 11 women) and 1 control group included 48 students (2nd level:13 men 11 women; 3rd level: 13 men 12 women Experimental group (EG) that performed the 8 weeks CrossFit exercises and control group (CG). Physical fitness tests were done: lifting straight legs in height (number times); running on the spot with an intensity of 70% of the maximum to severe fatigue (c); "Shuttle" run 4 × 9 m (with); 60 m run (s) and cross twine (cm). Results: there are considering changes, development of the maximum dynamic force endurance, speed abilities, flexibility and mobility in the hip joints of the main groups, In the age aspect, there is mainly the improvement in results with age, both in the main and control groups (p>0,05). Conclusion: the study achieved a significant improvement in the physical condition of the students, also allows to talk about the effectiveness of training, built on the basis of a motivated choice of the target CrossFit high school program.

The ability of triangular prism drill collar BHA to prevent and correct deviation in drilling

A new bottom hole assembly (BHA) with a triangular prism drill collar and a flexible joint was developed to enhance the BHA’s ability of deviation prevention and correction in drilling. The deformation of the conventional BHA and the triangular prism drill collar BHA under working loads were simulated by finite element method. The result showed that the ability of the triangular prism drill collar BHA to prevent deviation in vertical well was superior to that of the conventional BHA and the triangular prism drill collar BHA had some certain ability to correct deviation in deviated well. The flexible joint length had an effect on the performance of the triangular prism drill collar BHA: when the length of the flexible joint was less than 6 m, the shorter the flexible joint length, the better the deviation prevention ability in vertical well, when the length of the flexible joint was within the range of 9–12 m, the longer the flexible joint length, the better the deviation correction ability in deviated well. Different kinds of BHAs were used in single well and adjacent well for field contrast test. The result showed that in anti-deflection fast drilling, the triangular prism drill collar BHA had excellent deviation prevention ability and it was helpful to get straight and smooth well track.

Glulam Timoshenko–Ehrenfest beams with interlaminar debonding and flexibility of finger joints

Glulam Timoshenko–Ehrenfest beams with interlaminar debonding and flexibility of finger joints

Intelligent algorithms for six degrees of freedom robot trajectory planning considering vibration suppression

The residual vibration of the flexible joint manipulator during and after the movement will seriously affects the positioning accuracy of the manipulator. This paper discusses the trajectory planning method for suppressing the joint vibration. A trajectory optimal model which contains the minimization of both time and jerk was proposed. An optimization method based on comprehensive learning particle swarm optimization (CLPSO) algorithm was utilized for solving the optimal problem. Compared with other optimal solution method, CLPLO has the advantages of avoiding premature convergence. A numerical simulation case shows that the optimal trajectory obtained in this paper generated less joint vibration. The effectiveness of the proposed method was verified to some extent.

Local joint flexibility of tubular K-joints reinforced with external plates under out of plane bending moments

ABSTRACT In this research work, the Local Joint Flexibility (LJF) of steel tubular K-joints reinforced with external plates is investigated. In the first step, a finite element (FE) model was generated and verified. In the next step, a set number of 300 FE analysis was carried out to investigated the effect of the stiffener plate size (η and λ), the angle between brace and chord (θ), the joint geometry (γ, τ, ξ and β) and the loading conditions (balanced and un-balanced OPB moments) on the LJF factor (f LJF) and f LJF ratios (ψ). The results showed that the f LJF of an external plate reinforced K-joint can be down to 26% of the f LJF of the corresponding un-reinforced joint. Also, the gap factor (ξ) has effect on the f LJF. Finally, FE results were used to derive two parametric equations for determining the f LJF in the strengthened K-joints.

Electromagnetic actuator design for distributed stiffness

Origami robots characterized by rigid plates linked together with flexible joints have inherent compliance and large deformations. Their low-profile design and folding mechanical transmissions provide substantial force and torque, especially for wearables and human-interactive devices. The current major limitation in the field is the need for embeddable dynamic actuation systems that produce actuation frequencies similar to human motion. In this study, we propose a novel low-profile printable electromagnetic actuator that can be integrated into thin large robotic surfaces made of rigid panels and into the streamlined pushbutton manufacturing process. We use already existing variable stiffness joints to demonstrate the scalability and distributable properties of the proposed actuation system on a locally controllable variable-stiffness distributed surface.

Determining the hip joint isokinetic muscle strength and range of motion of professional soccer players based on their field position.

BackgroundSoccer players’ physical and physiological demands vary based on their field position. Although the hip joint has an important role in soccer, little information is available about the strength and flexibility of the hip joint based on player positions. Therefore, this study aims to investigate the differences in muscle strength and flexibility of the hip joint of professional soccer players based on their field position.MethodsNinety-six professional soccer players from Saudi Arabia were divided into four groups (goalkeepers, defenders, midfielders, and attackers), with 24 participants in each group based on their field position. The Modified Thomas test was used to measure the hip extension range of motion (ROM), and muscle strength was assessed by an Isokinetic dynamometer.ResultsThere were no statistically significant differences in the isokinetic strength at the hip joint movements between goalkeepers, defenders, midfielders, and attackers (p ≥ 0.05). At the same time, there was a significant difference between groups in the hip extension ROM (p ≤ 0.05). according to different player positions. Post hoc tests reported significant differences between goalkeepers and defenders (p ≤ 0.05), midfielders (p ≤ 0.05), and attackers p ≤ 0.05). At the same time, there were no significant differences between defenders and midfielders (p ≥ 0.05), defenders and attackers (p ≥ 0.05), and midfielders and attackers (p ≥ 0.05).ConclusionEven though there was no significant difference in isokinetic strength, there was a significant difference in hip extension ROM among players based on field position. This study may help coaches and trainers to recognize the strengths and weaknesses of players and design training programs to rectify the weaker components and improve players’ performance in different playing positions.