Rigid Joints Research Articles

Моделирование динамического воздействия авиационного двигателя на крыло самолета при отрыве лопатки вентилятора

One of the requirements for a projected aircraft is the ability to continue flying and land in the event of a breakdown of one of the engines. One of the calculated cases of engine breakdown is a fan blade breakaway. This phenomenon causes large vibrations of both the engine itself and the aircraft structure.Design model and method for studying engine vibrations with damage in the form of blade breakaway have been developed; numerical studies of unsteady vibrations of an engine suspended on a pylon have been carried out. Herewith, the following load options are considered: engine operation with fan imbalance before shutdown, which is performed by the pilot; sharp braking and jamming of the fan rotor as a result of breakage of the front elastic support of the rotor, which can occur when the blade breaks off; braking the rotor after turning off the engine.The front bearing of the rotor is ball the bearing installed in elastic elements "squirrel wheel". The ball bearing is modeled as a rigid joint. Outside the elastic element, there are two thin-walled shells, which are intermediate load-bearing elements. With an increase in the imbalance of the fan rotor, the gap in the oil damper closes, the damper housing sits on the shells, switching on their rigidity to work. Thus, the stiffness characteristic of the support is bilinear. The stiffness coefficients of the elastic element "squirrel wheel" and the front support shells are determined by the method of numerical simulation. The fan rotor is modeled as a solid body on bearing supports. The stator of the engine is modeled by a rigid body on an elastic suspension. The pylon and the elastic engine mount elements are modeled by beams of variable cross-section operating simultaneously in tension, torsion and bending.A numerical analysis of the transient vibration processes of the D-436-148FM engine on the pylon of the An-178 airplane is carried out. The most dangerous case of damage as the breakdown of the bearing support after the fan blade breakaway is investigated. The results of the calculations are the graphs of the forces in the bearing arrangements and in the hinges of the engine mounting depended on time.

Rigid and Flexible Double Shear Lap Adhesive Joint at Elevated Temperature-An Experimental Study.

Double lap adhesive connections made of Sika® PS and Monolith EP2579-1 were studied experimentally in shear tests. The destructive shear tests were conducted under a quasi-static load at 20 °C and 80 °C. The aim was to study the impact of elevated temperature on the load capacity of the joint and make a comparative analysis of the results for two types of adhesives: polyurethane Sika® PS (flexible) and epoxy Monolit EP 2579-1 (rigid). The impact of adhesive layer thickness (t = 1, 2 and 4 mm) on the structural response of the joint was tested in two temperature ranges. A distinct impact of the temperature on the joint deformability was noticed. A visual assessment of the joint failure was performed and the initiation and form of failure was described. At 20 °C, the ultimate loading for epoxy adhesive joint depending on the joint thickness (t) was greater than for the polyurethane joint by, respectively, 282% for t = 1 mm, 88% for t = 2 mm and 279% for t = 4 mm. It was proved that the temperature increases to 80 °C in case of both adhesives reduces the mean destructive force in comparison with the measurements made at 20 °C. For the Sika® PS (PUR two-component polyurethane) adhesive, the greatest load capacity decrease was measured for the joint of thickness t = 2 mm (55%), and in case of the epoxy adhesive for the joint of thickness t = 4 mm (89%). It was found that after reaching the destructive force the flexible joints retain a partial load capacity contrary to the rigid joints.

Effect of electroacupuncture on articular morphological changes and serum inflammatory factors and synovial MMPs in collagen-induced arthritis rats

To observe the effect of electroacupuncture (EA) of "Zusanli"(ST36) and "Sanyinjiao"(SP6) on serum TNF-α, IL-1β, and IL-6 and expression of synovial matrimetalloproteinases (MMPs) and articular morphology in collagen-induced arthritis (CIA) rats, so as to explore its mechanisms underlying relief of arthritis. Thirty male SD rats were randomly divided into normal control, CIA model and EA groups (n=10 rats per group). The arthritis model was induced by multi-point intradermal injection of bovine type Ⅱ collagen emulsion. EA (2 Hz/100 Hz, 1 mA) was applied to bilateral ST36 and SP6 for 30 min, once a day for 28 days. The hind-limb paw volume was measured and the arthritis index (AI) score given according to the swelling degree, rigidity and deformity of the ankle joint (0-4 points). After EA intervention, the morphological damage of the affected ankle joints was revealed by H.E. staining, safranin O-fast green staining, and tartrate-resistant acid phosphatase (TRAP) staining, separately. The levels of serum TNF-α, IL-1β, and IL-6 were measured by ELISA, and the expression levels of MMP-1, MMP-3, MMP-13, and receptor activator of nuclear factor Kappa B ligand (RANKL) in the synovial tissue were detected by Western blot. Compared with the normal control group, the paw volume, AI score, TRAP-revealed number of osteoclasts, contents of serum TNF-α, IL-1β and IL-6, and expression levels of MMP-1, MMP-3, MMP-13 and RANKL proteins were significantly increased in the model group (P<0.01, P<0.05). Following the intervention, the paw volume, AI score, number of osteoclasts, contents of serum TNF- α, IL-1β and IL-6, and expression levels of MMP-1, MMP-3, MMP-13 and RANKL proteins were significantly decreased in the EA group (P<0.05, P<0.01) in contrast to the model group. H.E. and safranin O-fast green staining showed rough articular cartilage surface with thinned cartilage layer, obvious hyperplasia of the synovial tissue with many inflammatory cells, and serious damage and degradation of the cartilage matrix in the model group, these situations were relatively milder in the EA group. EA of ST36 and SP6 can reduce the articular damage in collagen-induced arthritis rats, which is associated with its function in reducing inflammatory response and down-regulating the expression of synovial MMP-1, MMP-3, MMP-13 and RANKL proteins.

A new joint-slippage model for galvanized steel bolted joints with slippage

This paper presents a new joint-slippage model for determining the behavior of galvanized steel bolted joints with slippage based on the joint test results. The influence of the slip coefficient of the friction surface is considered in the new model. Validation of the new joint-slippage model is performed in terms of test results of full-size galvanized latticed steel girders. In addition, by comparison with the conventional rigid joint model and the most representative joint-slippage model – Ungkurupanian’s joint-slippage model, the new joint-slippage model exhibits the best performance according to predicted structural deflection, stiffness and ultimate bearing capacity. The effect of slip coefficient on the behavior of the new joint-slippage model and Ungkurupanian’s joint-slippage model is further discussed through structural response. The new model can be easily embedded into finite element analysis software and has the potential to be used in the design stage for accurately assessing the safety and reliability of galvanized steel structures.

Modelling and Control of a 2-DOF Robot Arm with Elastic Joints for Safe Human-Robot Interaction.

Collaborative robots (or cobots) are robots that can safely work together or interact with humans in a common space. They gradually become noticeable nowadays. Compliant actuators are very relevant for the design of cobots. This type of actuation scheme mitigates the damage caused by unexpected collision. Therefore, elastic joints are considered to outperform rigid joints when operating in a dynamic environment. However, most of the available elastic robots are relatively costly or difficult to construct. To give researchers a solution that is inexpensive, easily customisable, and fast to fabricate, a newly-designed low-cost, and open-source design of an elastic joint is presented in this work. Based on the newly design elastic joint, a highly-compliant multi-purpose 2-DOF robot arm for safe human-robot interaction is also introduced. The mechanical design of the robot and a position control algorithm are presented. The mechanical prototype is 3D-printed. The control algorithm is a two loops control scheme. In particular, the inner control loop is designed as a model reference adaptive controller (MRAC) to deal with uncertainties in the system parameters, while the outer control loop utilises a fuzzy proportional-integral controller to reduce the effect of external disturbances on the load. The control algorithm is first validated in simulation. Then the effectiveness of the controller is also proven by experiments on the mechanical prototype.

Dynamic modeling of closed-chain robotic manipulators in the presence of frictional dynamic forces: A planar case

In this paper, the phenomenon of impact-contact in a closed-loop robotic chain has been dynamically modeled. The motion of this system, which comprises rigid links and ideal joints, has two phases. In the flight phase, the system is suspended in the air and moves only under the effect of Earth’s gravity. And in the impact phase, the mentioned robotic mechanism collides with a rough surface. We first present the direct form of dynamic equations for an open chain robotic system in the suspension phase. Then by applying the constraints that originate from the closed topology of the examined kinematic chain, the differential equations of the closed-loop system are obtained for the flight phase. In the impact phase, the contact force model is employed for modeling the impact-contact phenomenon. Although this method of impact modeling is more realistic, it leads to the stiffening of motion equations. In order to solve these equations, a special computational algorithm has been developed in this paper. To achieve more realistic results, the force of friction has also been considered in the collision of system joints with the ground. The dynamic formulations of friction have been used to obtain the friction force. In these models, an additional state variable is added to system variables in order to simulate some of the existing friction phenomena. Another objective of this paper is to present a criterion for selecting the most suitable model for simulating the motion of closed-loop robotic systems in the presence of friction. In this regard, the four dynamic friction force models of Dahl, reset integrator, LuGre, and elasto-plastic have been compared with the two static models of Coulomb and Bengisu & Akay. Although the developed algorithm is able to simulate any closed-loop robotic system that comes into contact with an uneven surface, the simulation of a 5-rigid-link closed-loop mechanism in collision with a rough surface of sinusoidal profile has been presented in this paper.

A study on the effect of the deformations in flexiblocks on the behavior of the vehicle axle suspension mechanisms

This work deals with a study on the effect of the deformations in flexiblocks (bushings) on the behavior of the vehicle axle suspension mechanisms. The mechanism in study is a representatiove one for the structural group/class of mono-mobile axle suspension systems, namely the guiding mechanism by five points - on five spheres (so called 5SS). In a previous work, it was established that the rigid joint model for this class of mechanisms does not provide results close to the real flexible bushing model, reason for which the research in this paper is directed towards the identification of a theoretical model of joint which, at a lower complexity than that of the real model, would still provide viable results, in terms of axle guidance accuracy in the spatial movement relative to car body. In this regard, static and kinematic models were developed and analyzed by using the MBS (Multi-Body Systems) software solution ADAMS.

Research of changes in the parameters that affect the rigidness of the column-foundation joints

Introduction. The existing types of connection assignment in the design scheme — hinged and absolutely rigid joints — do not reflect the actual operation of the connection. The lack of calculation of the actual rigidness of joint and its failure to take into account in the design of the frame can lead to a different distribution of efforts from the calculated one and an increase in the movement of the frame elements. The purpose of this work is to researching the influence of the change size of the elements forming the column base on its rotational rigidity. Materials and methods. The calculation of the transverse frame was performed in the Dlubal RFEM software package. The calculated efforts acting in the lower section of the column were transferred to the calculated models of the column base, made in the IDEA StatiCa software package, in which the further calculation of the joint rigidness was performed. Results. The rotational rigidness of the joints with different structural solutions of the column base is determined. The change in the rigidness of the connection between the column and the foundation with an increase in the thickness and height of the support ribs is analyzed. Based on the calculations, graphs of the identified dependencies are constructed. As an example of strengthening the base of the column, the introduction of a traverse was proposed. The article considers six variants of the traverse device, and variants with three support ribs and with traverses, but without support ribs. The calculated rigidness of the column bases is summarized in graphs, where it can be seen that the metal adding is effective only up to a certain point. Variants of the arrangement of column bases with additional transverse ribs are considered. Conclusions. The greatest contribution to the increase in the rotational rigidness of the joint is made by the addition of a traverse. By increasing the thickness or height of the introduced traverse, it is impossible to achieve absolutely rigid fixing, it is necessary to change several parameters in a complex way. The introduction of additional ribs located outside the plane of action of the moment practically does not affect the rigidity of the joint.

Joint modeling for the analytical estimation of dynamic behaviors of beam-coupled structures

In this study, analytical method is applied for the estimation of dynamic behaviors of beam-coupled structures. Mathematical expressions are given with terms of shape factors, material information and assembly angles of each sub-component. Based on Euler-Bernoulli beam theory, entire formulation is built with compatibility of system dynamics. The coupled structures are divided into two types, point coupling and mass coupling, related with the properties of coupling points. Point coupling is commonly used assumption that two sub-components are combined with lumped spring or damping, and mass coupling has undeformable rigid joint which has mass and inertia like welded structures. Dynamic properties of coupled structures are predicted in forms of frequency response functions and spectral responses about given forces. The verification process is conducted for assessing the accuracy of the estimation formula by using modal frequencies and mode shapes of beam-coupled structures. Extracted modal parameters from experimental modal analysis and finite element method are adopted as reference values for verification.

Mode-II fracture behavior evaluation for adhesively bonded pultruded GFRP/steel joint using four-point bending test

The pure mode-II fracture behavior of an adhesively bonded glass fiber reinforced polymer (GFRP)/steel joint was experimentally investigated using a four-point end-notched flexure (4ENF) test. Cracking of the 4ENF specimen initiated and propagated in the adhesive-steel surface. The dominant failure mode observed in all specimens was adhesive-steel interface failure. The compliance of the 4ENF specimen was determined with the rigid joint model and finite element method. The extended global method was employed to obtain a simple analytical solution of the mode-II energy release rate, and the corresponding results were compared with that determined by the virtual crack closure technique (VCCT). The full R-curve for the pure mode-II fracture behavior of an adhesively bonded pultruded GFRP/steel joint was obtained. Then, the VCCT was used to determine the load–displacement curves of the 4ENF specimens for validating the accuracy and applicability of the pure mode-II fracture criteria of the adhesively bonded pultruded GFRP/steel joint.

Effect of inter-module connections on progressive collapse behaviour of MiC structures

Modular integrated Construction (MiC) is a game changing construction approach which could significantly increase construction efficiency, quality, and sustainability. For steel MiC structures, modules are manufactured in the factories and assembled at the construction sites through inter-module connections. The concern of the vulnerability of these connections under abnormal hazards leading to disproportionate progressive collapse will impede industrial applications of MiC structures in the construction community. This study investigates the structural robustness of corner-supported modular steel buildings with the focus on different inter-module connections. A sub-structure extracted from a five-storey modular building is analysed by high fidelity finite element analysis under a corner column removal scenario. The load redistribution mechanism and failure modes are investigated thoroughly, based on which the simplified macro model is proposed where connections are modelled with rotational springs. Good consistence is found for the simplified model and the detailed FE analysis in terms of the pushdown curve. It is also found that the inter-module connection types will affect the beam-column joint properties which dominate the progressive collapse resistance of MiC structures. Therefore, attention should be paid when selecting different inter-module connections. The current rigid beam-column joint connection may lead to nonconservative evaluation.

Design and numerical evaluation of two innovative moment-free beam-gusset-column connections for BRBFs

Buckling-restrained braces (BRBs) are strong, ductile members used in structural steel frames, called BRBFs, for resisting lateral seismic loads. However, in previous experiments on BRBFs, typical beam-gusset-column (BGC) joints underwent premature fractures, even under cyclic lateral-loadings equivalent to design-basis-earthquakes. The damages were related to the presence of thick gusset-plates, connecting BRB to beam-and-column, which caused unintended joint rigidities and so stress concentrations around gusset-tips. In this paper, two innovative BGC connections are developed to accommodate high story-drifts, by releasing their beam-column fixities. For this purpose, work-point is displaced and the following connection-components are utilized: (1) two bolted flexible wide-plates (WPs) placed on spacer plates, transferring shear forces from beam-web and gusset-plate to column, and a double plate in the middle, carrying horizontal forces; or (2) a few square pins with one vertically and some horizontally slotted holes, connecting only gusset-plate to column. Finite-element models of the connections situated in BRBFs are constructed and their validities are verified against four comparable experiments. Therefore, the cyclic performances of the simulated connections are investigated under cyclic loadings up to 4% drifts. The results demonstrate that the introduced connections possess high rotation capacities and can withstand maximum considered earthquakes (MCEs) without suffering from low-cycle-fatigue. In addition, the important parameters of bolt-pretensioning, bolt-hole clearance, column-section orientation, BRB-strength, bolt-gage, WP-extension, WP-fracture, WP-to-column connection, pin-section, pin-hole arrangement, and work-point location are investigated; and comparisons are made with previous BGC connections incorporating single flexible-plate or double-angles

On the steady motions control of viscoelastic joined robotic manipulators

In this paper, the control problem of the serial multi-link robotic manipulators with rigid and viscoelastic joints is considered. The manipulators structure is such that only the rigid joints are controlled by DC motors. It is shown that such robotic manipulators can make so called stationary motions wherein the part of the generalized coordinates does’t change in time and the others change according to a linear law. The robust output feedback controllers are obtained for the robotic manipulators such that the stationary motion is locally, semi-globally, and globally asymptotically stable.

Analysis of Numerical Method on Inverse Kinematics of Robotic Arm Welding with Artificial Intelligence

The key component of versatile production processes is robots. They are found in diverse systems where it is possible to bypass and optimize human function. I simulated a remote-control trickster in MATLAB with 6 degrees of freedom in this research. A robot is used in numerous applications, such as decoration, carpentry and equipment testing. In hardware verification labs, robotic arms are used to hold passive and power rail probes that connect from instruments like scopes and power supplies to PCB boards to protect the PCB layout from rip off due to sudden movement of the probes. Robot kinematics uses the geometry (position and orientation) of rigid bodies (links) and joints to control the movement of the robot. In this project, to control its movement, I have illustrated either forward or reverse enzyme kinetics of a device. Through Kinematics uses the positions of a joint to measure the end-effector position of the robot. The angles of the joints with the end-effector position are determined by inverse kinematics as the reference. There are several methods to calculate the forward and inverse kinematics such as analytical methods, numerical hit and trial, and iterative methods.

Design, Modeling, and Control of an Autonomous Legged-Wheeled Hybrid Robotic Vehicle with Non-Rigid Joints

This paper presents a legged-wheeled hybrid robotic vehicle that uses a combination of rigid and non-rigid joints, allowing it to be more impact-tolerant. The robot has four legs, each one with three degrees of freedom. Each leg has two non-rigid rotational joints with completely passive components for damping and accumulation of kinetic energy, one rigid rotational joint, and a driving wheel. Each leg uses three independent DC motors—one for each joint, as well as a fourth one for driving the wheel. The four legs have the same position configuration, except for the upper hip joint. The vehicle was designed to be modular, low-cost, and its parts to be interchangeable. Beyond this, the vehicle has multiple operation modes, including a low-power mode. Across this article, the design, modeling, and control stages are presented, as well as the communication strategy. A prototype platform was built to serve as a test bed, which is described throughout the article. The mechanical design and applied hardware for each leg have been improved, and these changes are described. The mechanical and hardware structure of the complete robot is also presented, as well as the software and communication approaches. Moreover, a realistic simulation is introduced, along with the obtained results.

V-Shape Pneumatic Torsional Actuator: A Building Block for Soft Grasper and Manipulator.

Robotic joints are fundamental components in artificial graspers and manipulators, and they are designed to achieve high dexterity to carry out various tasks. Traditional robotic hands are often driven by rigid joints, such as tendons and electric motors, resulting in bulky and complex designs. Soft robotics, composed of flexible and compliant materials, offers promising solutions to mimic the human hands and handle delicate objects safely. In this article, we propose a simple yet effective V-shape pneumatic torsional actuator (V-PTA) as the building blocks of soft grasper and manipulators. The proposed actuator is capable of producing large angular changes and twisting torque, responding fast to pneumatic changes, and scaling to appropriate dimensions easily. Because the design is generic and modular in nature, these lightweight actuators could also be assembled to form a variety of patterns of structures to suit the needs of individual tasks. We further fabricated robotic graspers and manipulators based on multiple V-PTA and demonstrated that our design could offer solutions to execute daily laboratory operations that interact with small and irregular components. Experimental data confirmed that the V-PTA building block structure could potentially pave the path forward for miniature robotic automation in laboratory or industrial settings.

The in-plane elastic-plastic response of an incompressible, filled hexagonal honeycomb

Exact solutions are derived for the small-strain, in-plane, elasto-plastic response of a hexagonal honeycomb using slender beam theory; incompressibility of the honeycomb is enforced by filling its voids with an incompressible, inviscid fluid. The honeycomb has sides of equal length, but its inclined struts subtend an angle that can deviate from 120° with respect to the vertical side walls. The relative density is sufficiently small that the struts are slender and can be treated as Euler-Bernoulli beams. Exact solutions are obtained for the elastic moduli and macroscopic yield surface of the rigid, ideally plastic lattice under general in-plane loading: the solutions satisfy equilibrium, compatibility and the constitutive response of each elastic, ideally plastic beam. Prior to conducting an elastic analysis, and a rigid, ideally plastic analysis, initial insight is gained by exploring the vector space of inextensional collapse mechanisms of the pin-jointed, compressible version of the hexagonal truss. Two inextensional collapse mechanisms of the compressible honeycomb are identified from the null space of the kinematic matrix. The presence of an incompressible, inviscid fluid in the voids of the honeycomb locks-up one mechanism but the other mechanism survives and generates macroscopic shear strain. Consequently, the incompressible hexagonal honeycomb with rigid joints has a high shear compliance and a low shear strength, with values equal to that of the unfilled, compressible honeycomb. In contrast, macroscopic tensile straining of the incompressible honeycomb requires the stretching of bars in addition to bar-bending, and the tensile modulus and strength of the incompressible honeycomb are thereby elevated. Explicit analytical formulae are derived for the macroscopic tensile modulus and strength of the incompressible honeycomb.

Form-finding of aluminum alloy reticulated structures considering joint rigidity

This paper proposes a form-finding method of free-form aluminum alloy reticulated structures with semi-rigid gusset joints. The vertical coordinates of the control points of the B-spline surface are selected to be the design variables adjusting the shape of the structure. The joint gap index, which is proposed for characterizing the manufacturing and assembling convenience of aluminum alloy structures, the strain energy, and the safety factor under short-term snow load, are chosen as the objective functions of the multi-objective optimization problem. The Pareto optimal solutions of the numerical example indicate that slight differences in the structural shape can result in quite different mechanical behavior, and the NSGA-II algorithm is effective in providing a wide range of optimal structures as compromise solutions of the multi-objective problem. Finally, the same optimization problem is solved for rigid jointed structures to study the influence of the joint rigidity on the form-finding result. By comparison of the internal force distribution, it is found that the joint semi-rigidity will influence the optimal structural shape due to the difference in the load-bearing mechanism. Therefore, it is suggested that the actual joint rigidity should be considered in the structural optimization process of reticulated structures.

Pier Luigi Nervi’s design process of hangars

AbstractThe objectives of this paper are to report the construction process of hangars in Orvieto and Orbetello by the construction company of Nervi and Bartoli, and to analyze the formation process of the design philosophy proposed by Nervi through a model experiment conducted on both hangars. Nervi initially attempted to design a hangar with pin joints. This indicates that although Nervi was initially uncertain of the structural safety of a vault roof with rigid joints, he eventually understood its structural safety through experiments. In conclusion, Nervi arrived at a hyperstatic structure of the diagonal rib vault which consisted of crossing each arch in the design process of the hangar in three phases. Furthermore, the joint between the roof composed of them and the pillar is ultimately rigidly joined instead of pin junctions after sketching the relevant plans. Nervi’s design philosophy is to connect each member with a rigid joint, a solid monolithic structure, that is, to constitute a hyperstatic structure, which was seen in the design process of the airplane hangar.

Joint Equivalence Design and Analysis of a Tensegrity Joint

Abstract We propose a method to design a tensegrity joint, making its elastic deformation an accurate joint-like motion, such as a rotation around the designed rotational center. The tensegrity joint can be a revolute, universal, and ball joint through this method. Axis drift is presented as a design criterion to describe the rotational center’s deviation degree with respect to the compliance center since the rotational center is not fixed to one point for different positions of the tensegrity joint. The axis drift is designed to be in a prescribed range so that the tensegrity joint is approximately equivalent to a rigid joint. In other words, the tensegrity joint’s elastic response under external torque and force becomes precise rigid joint-like kinematics and can replace rigid joints to transfer motion, force, and energy. A large-size tensegrity rotational joint is developed to verify the joint equivalence experimentally. The experimental results show that the tensegrity joint achieved maximum dimensionless axis drift of less than 2%, which indicates an excellent joint equivalence. The tensegrity joints’ ability to replace rigid joints as modular joints to construct a hyper redundant serial structure is demonstrated using a tensegrity robotic arm. The proposed compliant tensegrity joint has notable benefits of tensegrity structure, such as high mechanical efficiency, modularity, and scalability. It can be extended to many robotic applications, such as large-size serial robotic arms and snake-like robots.