Safe Joint Research Articles

Identification of formulation parameters that affect the analgesic efficacy of ProGel-Dex – A thermoresponsive polymeric dexamethasone prodrug for chronic arthritis pain relief

The relief of joint pain is one of the main objectives in the clinical management of arthritis. Although significant strides have been made in improving management of rheumatoid and related forms of inflammatory arthritis, there are still major unmet needs for therapies that selectively provide potent, sustained and safe joint pain relief, especially among patients with osteoarthritis (OA), the most common form of arthritis. We have recently developed ProGel-Dex, an N-(2-hydroxypropyl) methacrylamide (HPMA) copolymer-based thermoresponsive dexamethasone (Dex) prodrug, which forms a hydrogel upon intra-articular administration and provides sustained improvement in pain-related behavior and inflammation in rodent models of arthritis. The focus of the present study was to investigate the impact of ProGel-Dex formulation parameters on its physicochemical properties and in vivo efficacy. The results of this study provide essential knowledge for the future design of ProGel-Dex that can provide more effective, sustained and safe relief of joint pain and inflammation.

Reactive mobile manipulation based on dynamic dual-trajectory tracking

The letter presents an online obstacle avoidance strategy for a nonholonomic mobile manipulator, including dual-trajectory generation for the mobile base(MB) and end effector(EE), as well as whole-body reactive obstacle avoidance. The feasible region of the manipulator’s workspace is generated by traversing the path of the MB, and the spatio-temporal trajectory of the EE is generated by quadratically constrained quadratic programming(QCQP) planning, satisfying the physical constraints and obstacle avoidance constraints. The reactive obstacle avoidance strategy is based on quadratic programming(QP), using singularity avoidance and EE trajectory tracking tasks as soft constraints with different priorities. Considering the nonholonomic constraints and motion differences of MB, we employ a dynamic tracking approach to avoid obstacles of MB. Additionally, an adaptive weight method is utilized to adjust the priority of MB path tracking task, effectively preventing joint velocity jitter during the insertion process. Our strategy has been proven to generate obstacle avoidance trajectories for EE in real-time and ensure safe joint velocities for MB and the manipulator through simulation and real-world scenarios.

Pin-bearing mechanical behaviour of composites fabricated via fused filament fabrication as a function of reinforcing, pin diameter and W/D ratio

Additive manufacturing is an advanced technology able to produce parts with different grades of complexity, including its shape, microstructure, functionality and material. Regarding material complexity nowadays, it is possible to produce polymer parts with customized reinforced fibre filling such as carbon, Kevlar or glass. However, their mechanical behaviour is still under investigation and no data are available on the bearing strength for additively manufactured composites. The aim of this work is to provide a contribution on this topic to ensure safe joint design with the current and innovative technologies. In this article the authors present the experimental characterization of polymer filled with Kevlar to pin bearing test. Samples have been designed as a function of filling and geometry parameters. Results have been analysed with statistical methods. Finding highlight similar and different behaviour regarding samples produced with conventional process. The most interesting result is that the authors demonstrate how the pin diameter is significant for the results, particularly for the stiffness keeping constant the bearing strength.

Simulation of a control system for the accident-free flight of three UAVs in the V formation in a heterogeneous environment

Modern methods of creating groups of unmanned aerial vehicles (UAVs) require the use of complex (generalised) criteria, introduced mathematical models in the process of optimising the parameters of the UAV components. Such models should simulate the operation of an unmanned aerial vehicle when performing its task. The study considers strategies for diverging dangerously approaching UAVs using areas of dangerous courses and speeds. First, procedures were performed to establish the dangerous course areas of one UAV and the speeds of the second UAV, taking into account their ratio of speeds and dynamics. The areas for the case of UAV with insignificant transients of changes in courses and speeds, the duration of which can be neglected, is provided. In addition, procedures of the establishment of areas of dangerous courses of one UAV and the speeds of the second UAV with significant inertia are considered. Methods of the establishment of areas in the event of a decrease in the speed of the second UAV by active or passive braking are developed. Examples of choosing a safe manoeuvre in a situation of dangerous convergence of two UAVs are given. A more complex situation of approaching two UAVs in the presence of an interfering third UAV is also considered, and a method for choosing a safe manoeuvre is proposed, taking into account the interfering third UAV. Moreover, for such a situation, two alternative procedures for choosing a safe manoeuvre are proposed. The result of solving this problem was a method for establishing the area of dangerous courses and speeds of UAVs, taking into account the inertia-braking characteristics when determining a safe joint divergence manoeuvre taking into account the presence of a third UAV that provides interference.

Microstructural characteristics of fusion zone in continuous wave fiber laser welded Nb-modified δ-TRIP steel

Welding processes were accomplished by means of a 600 W Continuous Wave (CW) fiber laser instrument in bead on plate manner with 60, 80 and 100 J mm−1 heat inputs. δ-TRIP Steel samples were similar in chemical composition and only contained different Nb (40Nb: 0.040 & 72Nb: 0.072 wt.% Niobium) amounts. Elevation of heat input resulted in changes in microstructure and hardness properties, which are desirable for welders to guarantee safe joints in engineering structures. An increase in the heat input can lead to reduction of the austenite in weld metals of both steel sheets. The reduction of the austenite could be attributed to the increase in δ-ferrite volume fraction which was induced by availability of sufficient time for segregation of aluminum and formation of more dendrite structured δ-ferrite at lower cooling rates. Increase in δ-ferrite content results in decreasing austenite content required for transformation of austenite to martensite. The direct consequence of a decrease in the martensite volume fraction is reduction of hardness. It is shown that an increase in the heat input from 60 to 100 J mm−1 results in reduction of hardness difference between weld and base metals by 40% and 37% for 40Nb and 72Nb steels respectively.

How Dynamic Properties of Inverters Influence Electrode Metal Transfer to the Weld Pool, and Change Structural and Phase Composition of Welded Joints Produced via High Alloyed Electrodes

Covered-electrode arc welding has been currently widely-spread in assembly and maintenance technologies, as soon as it is a reliable tool, which helps get safe permanent joints in critical structural systems applied in Arctic. It is of burning importance to further enhance accuracy in methods which assess the impact of dynamic properties of power supply equipment with various forms of energy conversion on a consumable electrode welding stability and quality. Literature review [1–11] confirms that objectives, aimed at improving critical (in terms of extreme work and low temperatures) metal structures reliability, demand innovative approaches, i.e.:

Evaluation of Tensio n - Shear Stress for zig -zag spot welds by using indirect resistance spot weld technique for fabrication industries

All resistance welding processes are based on the heat that is produced at the interface due to resistance for the flow of electric current through the metal parts being joined. The amount of heat generated basically depends on the magnitude of the current, the duration of current flow and the load transmitted to the inter face. Spot welding is now a very established process in which two sheets to be welded are kept one over the other to get a nugget at the interface. The contact resistance at the interface dictates the quantum of heat that is generated . New concept namely indirect resistance spot welding was developed for applications where the surface appearance on sheet can be critical. In this process outer surface, limiting the extent of electrode indentation is traditionally managed by controlling the heat balance and electrode size. Trials were conducted, for optimum weld parameters for cold rolled carbon steel sheet, for Zig – zag spot weld for the indirect spot welding and also observed the Reduced Tensile stress for the base metal. This research paper reports the results of the trials, under optimum weld parameters. indirect resistance spot welding .The observations on Tension – shear breaking load , nugget diameter ,yield stress, reduced tensile stress, working stress or design stress by considering minimum factor of safety of two, for Tension shear application for indirect resistance spot welding were discussed. Peel test was done to find quantitatively, the formation of nugget and nature of failure. This paper reveals the results for the Zig – zag spot for the indirect spot welding, process were observed more Safe joint specially for tension shear application .Since spot welds during design considerations , for Zig – Zag spots for lap joint for tension shear applications these results will be most useful for optimum design.

Safe Joint Mechanism Using Torsion Springs for Collision Safety and Positioning Accuracy of a Robot Arm

In recent years, the potential for collision between humans and robots has drawn much attention since service robots are increasingly being used in the human environment. A safe robot arm can be achieved using either an active or passive compliance method. A passive compliance system composed of purely mechanical elements often provides faster and more reliable responses to dynamic collision than an active system involving sensors and actuators. Since positioning accuracy and collision safety of a robot arm are equally important, a robot arm should have very low stiffness when subjected to a collision force capable of causing human injury. Otherwise, it should maintain a very high stiffness. To implement these requirements, a novel safe joint mechanism (SJM-IV) consisting of a CAM, rotational links with rollers, and torsion springs is proposed. The SJM-IV has the advantage of nonlinear stiffness, which can be achieved only with passive mechanical elements. Various analyses and experiments on static and dynamic collisions show high stiffness of the SJM-IV against an external torque less than a predetermined threshold torque, with an abrupt drop in stiffness when the external torque exceeds this threshold. The safe joint mechanism enables a robot manipulator to guarantee positioning accuracy and collision safety, and which is simple to install between an actuator and a robot link without a significant change in the robot’s design.

Studies on joint strength and sealing behavior of single and twin-gasketed flange joints

Leakage is the main mode of failure in gasketed flange joints used in nuclear and thermal power plants. The leakage occurs when the joint is not able to withstand the internal fluid pressure. To evaluate the leakage behavior of gasketed flange joint, it is important to incorporate gasket properties and interfacial contact behavior due to friction. However, for safe joint operation, the members also should be structurally sound without exceeding allowable limit of materials. In this study, the joint strength and sealing behavior of gasketed flange joint are investigated through experiments by carrying out leakage test. The joint strength is evaluated based on strains developed in flanges along longitudinal and tangential direction under both pretightening and pressurizing stages. Three-dimensional finite element simulation is also performed under both aforesaid stages, considering the nonlinear properties of gasket along with hysteresis during unloading. The finite element results of joint strength and leakage pressure are compared with experimental values and observed to be conservative. In addition, the performance of twin gaskets (two gaskets concentric to each other) through both experiment and simulation is also evaluated and compared with that of the single gasket. From the experiment and finite element analysis, it is found that the sealability of twin-gasketed joint is higher than that of single-gasketed joint.

Effect of Low Temperature on Tensile Strength and Mode I Fracture Energy of a Room Temperature Vulcanizing Silicone Adhesive

Abstract Aerospace applications have an increasing demand for strong and reliable adhesives, able to withstand large temperature gradients. The variation of the adhesive’s mechanical properties with temperature is therefore one of the factors that must be well understood before safe and reliable adhesive joints can be designed for these applications. The stress–strain curve and the toughness properties of an adhesive show strong dependency with temperature for most adhesives, especially near the glass transition temperature (Tg). In this work, an experimental procedure is undertaken to evaluate the effect of low temperatures on the adhesive strength and mode I fracture toughness of a room temperature vulcanizing silicone (RTV) adhesive. Firstly, the temperature at which the glass transition of the RTV occurs was obtained by means of an in-house developed measurement apparatus. Bulk specimens were manufactured and tested at temperatures above and below the Tg in order to obtain a strength envelope of the adhesive over this large temperature range. Single lap joints were also manufactured with this adhesive to assess the behaviour of the adhesive when assembled in a complete joint. For the determination of pure mode I fracture toughness, double cantilever beam specimens were also tested at negative temperatures near Tg. The results showed that the failure loads of all the tests performed have strong temperature dependence and this must be taken into account during adhesive joint design using this type of adhesives.

Design of a Novel Compliant Safe Robot Joint With Multiple Working States

This paper presents the design and development of a novel compliant safe joint (CSJ). The principle of operation of the CSJ is based on a cam-like transmission mechanism, which we call the bridge. The cam profile on the stationary bridge is designed to have multiple regions, which allow the CSJ to passively achieve multiple working states. The proposed joint behaves as a normal rigid joint when the load is smaller than a preset threshold, shifts into the flexible state when the load exceeds the threshold, and switches into the free state in which the motion cannot be transmitted from the motor to the output shaft. In order to achieve a compact modular assembly, the joint's components are designed to have the shape of a hollow cylinder and to be installed around the motor. We analyze how the key dimension parameters affect the torque threshold and the joint's stiffness. Experiments are conducted to validate the working principle and verify the performance of the joint.

Design of Variable Release Torque-based Compliance Spring-clutch and Torque Estimation

A variable release torque-based compliance spring-clutch (VCSC) is presented. VCSC is a safe joint to reduce the impact of collisions between humans and robots. It is composed of four functional plates, balls, springs to make some functions in compliant movement, release mechanism, gravity compensation during its work. Also, it can estimate torque applied to a joint by using distance sensor and parameters of cam profile. The measured variable torque of prototype is 4.3~7.6 Nm and release torque is 4.3 Nm. In our future studies, a calibration for torque estimation will be conducted.

안전형 비납땜 틀고정 영구 접속형 멀티콘센트 개발에 관한 연구

안전형 비납땜 틀고정 영구 접속형 멀티콘센트 개발에 관한 연구

Design of safe joint with variable threshold torque

This study presents a passively variable threshold torque Spring-Clutch (PVSC). When human beings and robots work together as in the service robot example, physical safety of the former should be guaranteed. A passive mechanism is usually preferred because of its high reliability and fast response to collision. The PVSC comprises the Spring-Clutch mechanism (in that a spring and cam are utilized for generating threshold torque), and an adjuster (an additional cam and lever mechanism to adjust the threshold torque). It functions as a rigid joint between the input and output. However, when the applied torque exceeds the threshold value, the PVSC joint is fully released and becomes freely rotatable to guarantee safety during contact. The threshold torque is passively adjusted according to the gravitational torque and, therefore, a constant releasing torque is maintained for all joint rotation angles. The threshold torque of the PVSC increases (or decreases) in response to the variation in the deflection of the spring (achieved by using the adjuster) according to the rotation angle (or gravitational torque). Experiments were performed and the PVSC was implemented in the second joint of the SS-Arm IV.

Determination of load capacity of a non-gasketed flange joint under combined internal pressure, axial and bending loading for safe strength and sealing

Performance of a bolted flange joint is characterized mainly due to its ‘strength’ and ‘sealing capability’. A number of analytical and experimental studies have been conducted to study these characteristics only under internal pressure loading. A very limited work is found in literature under combined internal pressure and bending loading. Due to the ignorance of external loads i.e. bending and axial in addition to the internal pressure loading, an optimized performance of the bolted flange joint can not be achieved. The present design codes do not address the effects of combined loading on the structural integrity and sealing ability. To investigate joint strength and sealing capability under combined loading, an extensive comparative experimental and numerical study of a non-gasketed flange joint with two different taper angles on the flange surface and with different load combinations is carried out and overall joint performance and behavior is discussed. Actual joint load capacity is determined under both the design and proof test pressures with maximum additional external loading (axial and bending) that can be applied for safe joint performance.

Proposal for a stress modification factor for the fatigue design of flange thickness transitions in welded girders

Thickness steps or transitions are often used in flanges of bridge girders in order to adapt the bending resistance of the cross-sections to variable bending moment distributions. The sudden change of the stiffness distribution within the cross-section at these details causes additional local forces and stresses, which cannot be properly taken into account by classical beam-theoretical calculations, and which lead to a deterioration of the fatigue performance of the welded details at and around the transition. A modification of nominal stresses – e.g. by the use of an appropriate stress concentration factor kf – is therefore required in order to obtain safe joint designs with respect to fatigue.The stress-raising effects at flange thickness transitions are of a similar nature as the ones caused by plate or angular misalignments, for which kf-factors are provided in the literature. However, the specific configuration of flanges in – often quite deep – bridge girders causes additional (beneficial or detrimental) effects that have not been sufficiently studied before, and which are currently not correctly considered in common design practice.This paper discusses the characteristic local load-carrying behaviour and stress distribution in flange thickness transitions of welded I-section bridge girders, which were studied by numerical, experimental and analytical means. The paper furthermore introduces a new, accurate and mechanically coherent analytical formulation of kf-factors for the modification of nominal longitudinal stresses in bridge girder flanges; these new kf-factors could be used for practical fatigue design verifications. The possibility of including further amendments to the proposed formulation in order to take into account for the effects of additional unintentional misalignment or dimensional tolerances at the butt weld were also discussed. Finally, an outlook is given on the need to also consider additional stress concentration factors for shear in the fillet welds in the areas surrounding a thickness transition.

Service Robot Passive Safety Impedance Mechanism Design and Dynamics Analysis

The wide application of service robot caused security problems between humans and robots. Through the theoretical analysis and mathematical formula based on the calculation. Designing a novel safe impedance joint mechanism consisting of an inclined link, a slider with rollers, and linear springs is proposed. Analysis the institutions of different friction between rollers and tilt links in the form of organization function at the same time. Using solidworks software to mechanism of 3D modeling, the design of two different partial CAM model, importing ADAMS software and analysis the function, Comparison between simulation data and experimental data consistency, for later used in robot mechanical arm to provide a theoretical basis.

Development of an Experimentally Validated Analytical Model for Modular Bridge Expansion Joint Behavior

Modular bridge expansion joints (MBEJ) are large-capacity systems placed between two superstructure segments designed to provide safe joint crossing based on anticipated bridge movements. Locations of discontinuity in bridges are often recognized as weak links and therefore characterizing the behavior of expansion systems installed at deck joints under various excitations is critical to support the forecasting of bridge functionality. This paper presents the development of an analytical model representative of a common modular bridge expansion joint including its critical components, such as friction elements, equidistant devices, support bars, and center beams. The model is then validated through full-scale experimental testing of the joint. The results of this study offer a predictive model for the longitudinal motion of bridge joints excited through anticipated service or extreme events, which can be used to help determine local and global failure within the joint and make inferences as to how a bridge system could be affected. Such models provide a key step toward aiding design efforts, enabling more accurate specification of MBEJs, and supporting functionality-based risk assessment for bridges.

A safe robot arm with safe joints and gravity compensator

This study presents a robot arm equipped with safe joints and multi DOFs gravity compensators. The safe joint, also referred to as “Spring-clutch”, is simple passive mechanism that consist of a spring, a cam, and a joint torque sensor. When the torque applied is lower than a pre-set threshold, the Spring-clutch serves as a rigid joint between the input and output. When the applied torque exceeds the threshold, the Spring-clutch is released and is free to rotate like a revolute joint, which significantly reduces the collision force to avoid damage to the robot, as well as to humans. In addition, a compact joint torque sensor is installed in the Spring-clutch to measure the torque at the joint. Also, the analysis of energy and torque shows that the proposed mechanism can function as a gravity compensator capable of static balancing. Since joint torques vary in accordance with the pose of a manipulator (i.e., rotation angles), a Spring-clutch with a constant threshold torque cannot always guarantee the maximum collision torque in some poses of a manipulator. To overcome this limitation, a gravity compensator is adopted to eliminate the gravitational torque. In this research a bevel gravity compensator is applied which can perform static balancing completely. This paper describes the design principles and fabrication of the safety mechanisms and the robot arm.

Safe joint module for safe robot arm based on passive and active compliance method

In recent years, collision safety between humans and robots has drawn much attention as service robots are being increasingly used in human environments. Since various types of collisions can occur during a robot’s operation, multiple safety methods should be implemented to ensure human safety. The most common and practical solutions are the active and passive compliance methods and each has its own merits and disadvantages. To combine the active and passive compliance methods to achieve higher reliability, we propose a novel safe joint module composed of a speed reducer, a torque sensor and a safety mechanism. The torque sensor embedded in the safe joint module can be used to detect a collision; then the actuator appropriately reacts to minimize the impact. However, if the collision detection by the embedded joint torque sensor and the subsequent reaction fail due to the limited bandwidth of the sensor, the safety mechanism composed of purely mechanical elements such as springs and a cam follower absorbs the collision force. With the proposed safety joint module, the combined active and passive compliance method can ensure collision safety. Moreover, the embedded torque sensor can be used for force control. The embedded harmonic drive can achieve high gear reduction and low backlash. Several experiments on static and dynamic collisions showed that the proposed module can guarantee safety while maintaining good performance.