Rigid Joints Research Articles

Simultaneous Optimization of Discrete and Continuous Parameters Defining a Robot Morphology and Controller.

The morphology and controller design of robots is often a labor-intensive task performed by experienced and intuitive engineers. Automatic robot design using machine learning is attracting increasing attention in the hope that it will reduce the design workload and result in better-performing robots. Most robots are created by joining several rigid parts and then mounting actuators and their controllers. Many studies limit the possible types of rigid parts to a finite set to reduce the computational burden. However, this not only limits the search space, but also prohibits the use of powerful optimization techniques. To find a robot closer to the global optimal design, a method that explores a richer set of robots is desirable. In this article, we propose a novel method to efficiently search for various robot designs. The method combines three different optimization methods with different characteristics. We apply proximal policy optimization (PPO) or soft actor-critic (SAC) as the controller, the REINFORCE algorithm to determine the lengths and other numerical parameters of the rigid parts, and a newly proposed method to determine the number and layout of the rigid parts and joints. Experiments with physical simulations confirm that when this method is used to handle two types of tasks-walking and manipulation-it performs better than simple combinations of existing methods. The source code and videos of our experiments are available online (https://github.com/r-koike/eagent).

Experimental and numerical investigation of the load-bearing capacity of bolt-fastened wedge active joints for prestressed internal bracing in subway excavations

The present study develops a novel type of active joint node-bolt fasten wedge (BFW) active joints, aiming to investigate the load-bearing capacity of a BFW joint in a quantitative way and put forward precise formulas for its yield load and compression rigidity. To achieve this, indoor axial loading tests were conducted on two BFW joints, accompanied by a set of numerical simulations with the finite element approach (FEA) implemented in ABAQUS. Parametric research was then conducted to assess the impact of various factors on the yield load and initial compression rigidity of BFW joints, leading to the derivation of precise calculation formulas for accurate prediction of these parameters. The key findings indicate that enhancing the bolt strength from 10.9 to 12.9 significantly improves mechanical performance. Under axial compression, the final bearing force, yield load, and initial compression rigidity increase by 0.86, 1.06, and 0.15 times, respectively. Numerical models accurately predict joint behavior under axial force, confirming their reliability. Parameter studies reveal that increasing web and eaves thickness, bolt strength, and diameter improves bearing capacity, while splint thickness has little effect. The fitting formulas introduced can precisely estimate yield load and rigidity, providing practical value for engineering applications.

Vertical diaphragms for moment connection of thin-walled CFT column to steel beam

A vertical diaphragm scheme is proposed to connect the concrete-filled thin-walled steel tube (thin-walled CFT) column and steel beam, as an alternative to horizontal diaphragm connections: dual vertical diaphragms are installed inside the steel tube, considering poor out-of-plane resistance of the thin tube wall. For verification of the moment connection, two experimental programs were carried out. In the first experiment, an ultimate tension test was conducted for flange-to-column connections, to identify the fundamental behavior of the proposed connection (i.e., strength, failure mode, and out-of-plane deformation). The design parameters, such as the thickness, number, and continuity of the vertical diaphragms, were considered. All the test specimens exceeded the design strengths based on a yield line model (i.e., the tensile capacity-to-demand ratios ranged Tu/TYL = 1.11–1.31), without early fracture of welded joints. In particular, at the design strengths, the tube out-of-plane deformations were more limited with the heavier diaphragms. In the second experiment, beam-to-column connections using prototype I-section steel were tested under cyclic flexure, to verify the joint flexural strength and rigidity as well as the seismic performance. The beam-to-column connections failed by the beam flexural mechanism, whereas damage was marginal at the joint wall (i.e., the flexural capacity-to-demand ratios ranged Mu/Mj = 0.87–1.09). Overall, the dual diaphragms were effective in achieving rigid (full-strength) connections with satisfactory plastic rotation of the beam. On the basis of the test results, design considerations were recommended for the vertical diaphragm connections.

Use of computer-assisted hexapod external fixators for complex foot and ankle reconstructions – An analysis of functional outcomes and complications

IntroductionFoot and ankle pathology can often require complex surgical reconstruction. Until recently, circular external fixators such as the Ilizarov frame have proven to be useful, yet they fall short when progressive, precise corrections are required. Computer-assisted hexapod external fixators seek to address many of the shortfalls of traditional circular fixators. However, evidence for their use is scarce. The objective of this work was to evaluate the functional and quality of life outcomes and post-operative complications of patients treated with computer-assisted hexapod external fixation. MethodsA retrospective, observational study was conducted. All cases were treated with either a TrueLok hex (TL-HEX) or a Taylor Spatial Frame (TSF) fixator. Primary outcomes were post-operative improvement in 12-Item Short Form Survey (SF12) and American Orthopaedic Foot and Ankle Score (AOFAS) scores, and complications following Paley’s classification. ResultsA total of 59 patients with complex foot and ankle conditions using 64 external fixation frames were included. The median sum of both SF12 score domains improved from a preoperative score of 63.6 to 91.3 at last follow-up (p < 0.001). Median AOFAS improved from a preoperative score of 35 to 75.5 at last follow up (p < 0.001). Functional improvement was not affected by the choice of external fixator. Complications occurred in 49 cases (77 %). The most common post-operative complications included pin tract complications in 37 (58 %) cases, joint rigidity in 24 (38 %) and axial deviation in 9 (14 %). ConclusionsComputer-assisted hexapod external fixation is an effective technique to correct complex foot and ankle deformities and leads to a marked improvement in post-operative functional and quality-of-life outcomes with a high minor complication rate.

Examining characteristics of those who receive pedorthic services: A clinical audit.

Diabetes-related foot complications, including neuropathic plantar forefoot ulcers, are a significant contributor to morbidity and increased healthcare costs. This retrospective clinical audit examines the characteristics of people accessing pedorthics services who are at risk of neuropathic plantar forefoot ulcer (re)occurrence and the pathways and funding models used to access these services. A clinical record audit was conducted on all patients accessing a pedorthics service who had diabetes and neuropathy with a history of plantar forefoot ulceration. The data included demographics, diabetes and neuropathy duration, main forefoot pathology and other comorbidity, footwear and insole interventions, and health fund access status. A total of 70 patient records were accessed, and relevant data was extracted. The mean age of participants was 64.69 (standard deviation (SD) 11.78) years; 61% were male and 39% female. Duration of diabetes ranged from one to 35 years, with a mean of 14.09 years (SD 6.58). The mean duration of neuropathy was 8.56 (SD 4.16) years. The most common forefoot conditions were bony prominences at 71% (n = 50), rigid flat foot and limited joint mobility (53%, n = 37), and hallux abductovalgus at 47% (n = 33). All participants had hyperkeratosis; 34% (n = 24) had forefoot amputation, and around 34% (n = 24) had a history of digital amputation. Various publicly funded packages and private health insurance were accessed. This study investigates the sociodemographic and medical profiles of individuals with diabetes-related foot complexities prone to neuropathic plantar forefoot ulcers. It is the first to examine patients receiving pedorthic services, informing practitioner surveys and preventive care strategies. Understanding patient characteristics aids in optimising multidisciplinary care and reducing ulcer incidence. Further studies are warranted to explore the field to establish an effective multidisciplinary care approach between medical professionals, podiatrists and pedorthists to optimise patient outcomes.

Functions of Epimedin C in a zebrafish model of glucocorticoid-induced osteoporosis.

Epimedium is thought to enhance the integrity of tendons and bones, ease joint discomfort and rigidity and enhance kidney function. Although glucocorticoids are commonly used in clinical practice, the mechanism by which the active compound Epimedin C (EC) alleviates glucocorticoid-induced osteoporosis (GIOP) is not well understood. The therapeutic potential of EC in treating GIOP was evaluated using alizarin red S staining, calcein immersion and fluorescence imaging, and bone mineralization, bone mass accumulation and bone density in zebrafish larvae were determined. Using the Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, the key signalling pathways related to bone development were identified. A protein-protein interaction network (PPIN) was constructed to identify osteoclast characteristic genes and the findings were verified using real-time quantitative PCR (RT-qPCR). The bone tissue damage caused by prednisolone was reduced by EC. It also altered physiological processes, improved bone density, boosted mineralization and increased bone mass and activity. Subsequent empirical investigations showed that EC impacted the major signalling pathways involved in bone development, such as osteoclast differentiation, oestrogen, MAPK, insulin resistance, PPAR and AMPK signalling pathways. It also decreased the expression of genes typical of osteoclasts. The results of our study uncover a previously unknown function of EC in controlling bone formation and emphasize the potential of EC as a therapeutic target. The osteoprotective effect of EC indicates its potential as a cost-effective strategy for treating GIOP.

Research on coupling dynamics modeling and composite control of the multi-flexible space robot

Space robots can assist astronauts in accomplishing a variety of space missions in high-risk environments. As spacecraft become increasingly lightweight, large-scale, and integrated, space robots are a type of large-scale robots with flexible links and flexible joints. However, the flexibility of the components complicates robot modeling and controller design. Therefore, to address the issue of stable trajectory tracking for multi-flexible space robots, a dynamics model of space robots with multiple flexibilities is established, and a composite controller is designed to enhance control stability. In modeling, comprehensively considering the rigid joints, joint flexibility and link flexibility, the kinematics is consistently described by using the component deformation matrix and recursive method. An accurate dynamics model is established by Lagrange’s equations. In control, using fuzzy neural network sliding mode control, a rigid subsystem controller is designed to suppress the system jitter caused by sudden parameter changes. And it implements the robust tracking of the robot trajectory. Meanwhile, the weighted average fuzzy controller is designed to control the link deformation. The regulation of the flexible joint by the fast feedback controller is implemented using the virtual torque feedback control. Finally, the validity of the dynamics and control models is verified using Matlab and Adams. Compared with previous studies, this study considers multiple flexibility factors more fully. The vibration of multiple flexible components is suppressed during the stable trajectory tracking of the robot.

Deformation ability of steel inner sleeve T-joint in modular gymnasia based on 3D-DIC method

Substantial loads the roofs bear exert stringent performance standards on connecting joints in movable modular gymnasiums. Previously, we introduced a novel joint design, utilizing internal sleeves and bolts to integrate the upper and lower columns of modular units. To explore the actual deformation behavior and force distribution of this joint, this study employed a three-dimensional digital image correlation (3D-DIC) measurement method to visualize its full-field displacement and strain distribution. The reliability of the 3D-DIC results was confirmed through comparison with traditional measurement methods. Building upon this solid foundation, this study proceeds to assess the static performance of this innovative joint in two distinct directions, successfully revealing micro-deformation and local buckling phenomena undetectable to the naked eye. Notably, the quality of the welds connecting the beams and columns plays a pivotal role in ensuring the overall structural integrity of the joint. Under lateral loading conditions, the destructive behavior of the joints is primarily governed by material strength. Moment-rotation curves were plotted to delve further into the mechanical characteristics of the joint, revealing that the inner-sleeve T-joint exhibits the attributes of a rigid joint. Moreover, the primary damage modes observed in the specimens were fractures at the beam root or buckling of the column, with the joint area remaining intact. Consequently, this joint qualifies as a full-strength connection. These findings will deepen knowledge and understanding of this novel joint for designers.

Learning the Appropriate Local Averaging Length for Traffic Speed Deflectometer Deflection Velocity Measurements: Application to the Analysis of Rigid Pavement Joint Responses

Learning the Appropriate Local Averaging Length for Traffic Speed Deflectometer Deflection Velocity Measurements: Application to the Analysis of Rigid Pavement Joint Responses

Attenuation of osteoarthritis progression via locoregional delivery of Klotho-expressing plasmid DNA and Tanshinon IIA through a stem cell-homing hydrogel

BackgroundOsteoarthritis (OA) is an aging-related degenerative joint disorder marked by joint discomfort and rigidity. Senescent chondrocytes release pro-inflammatory cytokines and extracellular matrix-degrading proteins, creating an inflammatory microenvironment that hinders chondrogenesis and accelerates matrix degradation. Targeting of senescent chondrocytes may be a promising approach for the treatment of OA. Herein, we describe the engineering of an injectable peptide-hydrogel conjugating a stem cell–homing peptide PFSSTKT for carrying plasmid DNA-laden nanoparticles and Tanshinon IIA (pPNP + TIIA@PFS) that was designed to attenuate OA progression by improving the senescent microenvironment and fostering cartilage regeneration.ResultsSpecifically, pPNP + TIIA@PFS elevates the concentration of the anti-aging protein Klotho and blocks the transmission of senescence signals to adjacent healthy chondrocytes, significantly mitigating chondrocyte senescence and enhancing cartilage integrity. Additionally, pPNP + TIIA@PFS recruit bone mesenchymal stem cells and directs their subsequent differentiation into chondrocytes, achieving satisfactory chondrogenesis. In surgically induced OA model rats, the application of pPNP + TIIA@PFS results in reduced osteophyte formation and attenuation of articular cartilage degeneration.ConclusionsOverall, this study introduces a novel approach for the alleviation of OA progression, offering a foundation for potential clinical translation in OA therapy.

FUNCTIONAL OUTCOMES OF DORSAL BRIDGE PLATING FOR LISFRANC INJURIES WITH ROUTINE METALWORK RETENTION: A MAJOR TRAUMA CENTRE EXPERIENCE

BackgroundAnatomical reduction of unstable Lisfranc injuries is crucial. Evidence as to the best methods of surgical stabilization remains sparse, with small patient numbers a particular issue. Dorsal bridge plating offers rigid stability and joint preservation.The primary aim of this study was to assess the medium-term functional outcomes for patients treated with this technique at our centre. Additionally, we review for risk factors that influence outcomes.Methods85 patients who underwent open reduction and dorsal bridge plate fixation of unstable Lisfranc injuries between January 2014 and January 2019 were identified. Metalwork was not routinely removed. A retrospective review of case notes was conducted. The Manchester-Oxford Foot Questionnaire summary index (MOXFQ-Index) was the primary outcome measure, collected at final follow-up, with a minimum follow-up of 24 months. The American Orthopedic Foot and Ankle Society (AOFAS) midfoot scale, complications, and all-cause re-operation rates were secondary outcome measures. Univariate and multivariate analyses were used to identify risk factors associated with poorer outcomes.ResultsMean follow-up 40.8 months (24–72). Mean MOXFQ-Index 27.0 (SD 7.1). Mean AOFAS score 72.6 (SD 11.6). 48/85 patients had injury patterns that included an intra-articular fracture and this was associated with poorer outcomes, with worse MOXFQ and AOFAS scores (both p &lt; 0.001). 18 patients (21%) required the removal of metalwork for either prominence or stiffness. Female patients were more likely to require metalwork removal (OR 3.89, 95% CI 1.27 to 12.0, p = 0.02). Eight patients (9%) required secondary arthrodesis.ConclusionsThis is the largest series of Lisfranc injuries treated with dorsal bridge plate fixation reported to date and the only to routinely retain metalwork. The technique is safe and effective. The presence of an intraarticular fracture is a poor prognostic indicator. Metalwork removal is more likely to be needed in female patients but routine removal may not be essential.

Design, performance analysis and applications of pneumatic bellows actuator for building block soft robots

Currently, there are some new challenges for pneumatic soft robots brought by complex application environments and variable task objectives. To address these challenges, inspired by the building blocks, we develop a novel pneumatic soft actuator named pneumatic bellows actuator (PBA) that can generate bidirectional deformation, and propose a building block design concept for the soft robots based on the developed PBA. The PBA consists of three parts: a soft rubber layer (SRL), a fiber-reinforced layer (FRL) and some rigid joints. We design the SRL as a bellows-like shape so the PBA can generate bidirectional deformation, and weave an FRL as the coating of the SRL to prevent the significant radial expansion of the SRL that may affect the application of the PBA. The rigid joints include sealing glands and connectors. The sealing glands are used to seal the SRL, while the connectors having interfaces on their five surfaces are used to connect the PBAs through the customized plugs corresponding to these interfaces. Moreover, the experimental results indicate that the PBA can generate large deformation and driving force, while it has the advantages of good repeatability and approximate rate-independent under low frequency. Based on the building block design concept for the soft robots, we construct three PBA-based soft robots: a soft crawling robot, a soft gripper, and a soft manipulator, to demonstrate that we can easily use the PBAs to construct various soft robots.

Digital twin model of a large scale hot molten metal ladle pouring system

In steel-making processes, large quantities (frequently exceeding 300 t) of liquid metal are transferred between vessels. In Basic Oxygen Steel (BOS) making process, metal is poured from Hot Metal (HM) ladles, utilising overhead gantry cranes, into furnaces for further processing. Due to the large quantities of liquid metal poured, this operation poses significant safety concerns associated with metal spillage and releases of heat emissions. This can further lead to damage being caused to surrounding infrastructure. Pouring automation can reduce the likelihood of metal spillage, optimising ladle movement for reduction in heat emission releases. Given the hazardous nature of this operation, robust testing and evaluation of automated crane pouring movements is required prior to their application. A digital twin (DT) model of an overhead gantry crane/HM ladle system is presented here, intended to provide a safe testing environment for controlled pouring movement and serve as a testbed for control system design studies. Accurate crane movement is achieved using multi-body dynamics, solving for non-linearities present due to rigid joint frictional components. The flow rate of HM is estimated through the application of a dynamic model, allowing the modelling of system dynamics due to differences in HM pouring weights. The devised DT model is evaluated by simulating real crane movement and making a comparison on the resultant changing HM weight inside the ladle. The devised DT removes the need for construction of a physical model or performing tests directly on the HM pouring system.

Experimental study of self-tightening high-strength single-side bolted joints under low cyclic loading

Single-side bolts can be installed on one operating surface and are very suitable for closed cross-section connections. Based on the forming mechanism of materials, a new type of self-tightening high-strength single-side bolt, named SHSB-PRO (Progressed version), was developed herein. The SHSB-PRO was successfully applied to the assembled steel structure joints, with a range of low cyclic loading tests executed. In this test, three assembled steel structure joints were designed. Two of them were connected using SHSB-PRO, while the third was connected using traditional torsional shear high-strength bolt. Different bolt types and axial compression ratios of the steel column were examined to explore their impact on the seismic behavior of the joints. Through the low cyclic loading test, data such as hysteresis curves, skeleton curves, and strain in key parts of the joints were obtained. The mechanical properties, energy dissipation characteristics, failure mechanisms, and seismic performance of these assembled joints were elucidated. The test results indicate that the forming quality of the SHSB-PRO is stable within the joint, and a fine stress condition is maintained. The joints connected by the SHSB-PRO exhibit seismic performance comparable to those with torshear high-strength bolted connection. All joints failed due to the formation of the plastic hinge of the steel beam above the stiffener, and the joints connected by SHSB-PRO belong to the rigid joint. The influence of the axial compression ratio on the load-bearing capacity, ductility, and stiffness of the joints connected using SHSB-PRO is virtually minimal when the ratio is no more than 0.2. The finite element model was rigorously validated against the experimental results, demonstrating its accuracy and reliability in capturing the behavior of SHSB-PRO joints. The research herein lays a foundation for the design and improvement of SHSB-PRO, and promotes its wide application in civil engineering.

Influence of joint types on rigidity of Chebyshev elastic gridshells: A parametric analysis

Elastic gridshells (EGS) have many applications in the field of architecture. Built according to Chebyshev net geometry, the Chebyshev EGS (CGES) is a famous kind of EGS; since an arbitrary three-dimensional CEGS can be transformed into a planar state without any stretching strain. Due to its tremendous potential application in novelly deployed structures, the rigidity of CEGS is an important mechanical property to be investigated.In this study, using the analytical and finite element methods, the influence of joint types and gridshell parameters on the rigidity of CEGS subjected to point loads is studied in detail. The joint types are classified as pin joints, semi-rigidity joints, and rigid joints. A robust relation between rigidity and gridshell parameters is proposed, including Young's modulus, rod diameter, size of CEGS, joint stiffness, and rod numbers. Further, the above relation is nondimensionalized. The dimensionless rigidity is only related to the two dimensionless parameters, which are dimensionless joint stiffness and rod number. The rigidities of CEGS on four types of surfaces are calculated to verify the above relation, and satisfactory agreement is obtained. Therefore, the proposed relationship of rigidity is confirmed to be accurate and efficient for a wide range of parameters.

Model free sliding mode control for serial robot manipulator: rigid and elastic joint robot

Model free sliding mode control for serial robot manipulator: rigid and elastic joint robot

Tailored rehabilitation for interphalangeal joint rigidity: a case report on novel noninvasive techniques

Tailored rehabilitation for interphalangeal joint rigidity: a case report on novel noninvasive techniques

Straw movement and flow field in a crushing device based on CFD-DEM coupling with flexible hollow straw model

To accurately predict and evaluate the performance of the crushing device of no-till planter, it is strongly necessary to establish an accurate interaction model of the straw-crushing device coupling system. The traditional model has low prediction accuracy and cannot simulate the fracture characteristics of the straw during the operation of the crushing device due to the straw being usually regarded as a rigid body or a combination of rigid ball joints. In this paper, a breakable and flexible hollow straw model is first proposed and a CFD-DEM coupling model of the straw group-crushing device considering the effect of gas-solid two phase is also established. Afterwards, the corresponding verification experiments are conducted and the effect of working and structural parameters on the straw-throwing weight and crushing length is also analysed. It is demonstrated that the relative error between the simulation results and the experimental results for the straw crushing length is 7.7%, and the relative error for the straw-throwing weight is 7.1%, thereby verifying the correctness of the CFD-DEM model. Finally, the response surface method is also used to determine the optimal working and structural parameters of the crushing device and corresponding field tests verification is also conducted. Results indicate that the optimal parameter combination is as: the rotational speed of the crushing spindle is 2400 rpm, the inlet clearance is 30 mm and the starting point angle is 45°. Moreover, the crushing length after optimisation is 6.6% smaller than before optimisation, and the straw-throwing weight is increased by 11.5%.

Studying the Impact of Soil Stabilization Techniques on Rigid Pavement Joints Across Various Axle Loads

Rigid pavement slabs are erected on a prepared subgrade or foundation layer, providing a hard and continuous surface. Transverse joints made of dowel bars connect them, and longitudinal joints made of tie bars join them longitudinally. This study is an investigation of the impact of soil strength and concrete parameters on the effectiveness of dowel bars in rigid pavements. Moreover, three parameters were examined; California Bearing Ratio (CBR), concrete compressive strength and slab thickness. The analysis was conducted using the Ever FE program and focused on several axle configurations applied to the joint. The results indicate inverse association between the pavement slab thickness and the concrete strength, under the assumption of consistent soil strength. Moreover, an assortment of reduced shear forces on the dowel bars is seen when the soil strength values increase. It indicates that soil strength has a greater impact on the shear load of dowel bars compared to the qualities of concrete. Additionally, the type of axles used and the magnitude of soil strength were shown to have a significant effect on the shear load.

Experimental study on edge cell partially-replaced joint for I-beam to multi-celled CFST walls under cyclic loading

The multi-celled concreted-filled steel tubular walls (MCCFSTWs) are widely used in practice, especially in apartment constructions. The use of thin steel tubes in MCCFSTWs makes it weak at the joint zone, therefore the connections between the MCCFSTWs and steel beams become an important issue for the application of MCCFSTWs. A novel joint for the connection between the MCCFSTWs and I-beams is proposed in this study. The main feature of the proposed joint is that the edge cell of the MCCFSTW is partially replaced using a welded C-section, where two partial internal diaphragms are set to transfer the bending moment from the I-beam. With this treatment, the edge cell of MCCFSTWs near the joint zone can be significantly strengthened to satisfy the requirements of the seismic design, while the compactness of concrete at the joint zone can be guaranteed by using the partial internal diaphragms. The design philosophy of the proposed joint is first introduced in this study. Three specimens are then designed and tested under the cyclic lateral loading. Subsequently, the behaviors of the proposed joints are discussed based on the test results, including the failure mode, the hysteresis curve, the ductility, the ultimate load and the initial stiffness. The stress states at the joint zone obtained from tests are also analyzed and compared with those using simplified analytical model. According to Eurocode 3, all tested specimens can be classified as rigid and full-strength joints. Moreover, the rotation capacity of this novel joint meets the requirements of GB50011. The investigation of this paper is believed to be meaningful for the application of the novel joints in the practice.