Maximum Stiffness Research Articles

High-Stiffness Control of Series Elastic Actuators Using a Noise Reduction Disturbance Observer

Rendering a high impedance on a series elastic actuator (SEA) can improve motion control performance while retaining collision safety by a lower physical stiffness. The safe impedance range can be increased with high-gain velocity feedback control, but, in practice, this is limited by noise. This article applies the noise reduction disturbance observer to inner-loop velocity control of an SEA, attenuating noise and allowing higher safe rendered stiffness compared with standard torque and torque/velocity hierarchical control. Closed-form expressions for maximum passive stiffness and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$Z$</tex-math></inline-formula> -region are found, shown to depend strongly on the high-frequency noise gain, and used to optimize the control gains. Performance is experimentally verified on a reaction-force SEA, validating the passivity of the high-stiffness control in impact (free space and stiff environment) while rendering a safe stiffness 3.0 times the intrinsic stiffness.

Additively manufactured foamed polylactic acid for lightweight structures

PurposeThis study aims to make foamed polylactic acid (PLA) structures with different densities by varying deposition temperatures using the material extrusion (MEX) additive manufacturing process.Design/methodology/approachThe extrusion multiplier (EM) was calibrated for each deposition temperature to control foaming expansion. Material density was determined using extruded cubes with the optimal EM value for each deposition temperature. The influence of deposition temperature on the tensile, compression and flexure characteristics of the foamable filament was studied experimentally.FindingsThe foaming expansion ratio, the consistency of the raster width and the raster gap significantly affect the surface roughness of the printed samples. Regardless of the loading conditions, the maximum stiffness and yield strength were achieved at a deposition temperature of 200°C when the PLA specimens had no foam. When the maximum foaming occurred (220°C deposition temperature), the stiffness and yield strength of the PLA specimens were significantly reduced.Practical implicationsThe obvious benefit of using foamed materials is that they are lighter and consume less material than bulky polymers. Injection or compression moulding is the most commonly used method for creating foamed products. However, these technologies require tooling to fabricate complicated parts, which may be costly and time-consuming. Conversely, the MEX process can produce extremely complex parts with less tooling expense, reduction in energy use and optimised material consumption.Originality/valueThis study investigates the possibility of stiff, lightweight structures with low fractions of interconnected porosity using foamable filament.

Design and Analysis of a Novel Variable Stiffness Continuum Robot With Built-in Winding-Styled Ropes

Continuum robots driven by rods have a wide range of applications, such as detection and maintenance tasks in unstructured environments. However, their inherent nature of flexibility also limits their function. Thus, variable stiffness mechanisms for continuum robots have consistently attracted the attention of researchers in recent years. In this letter, a winding-styled rope inspired by snakes’ behavior is first built into the constraint disk of a rod-driven continuum robot. Combined with shape memory alloy (SMA) spring, the winding ropes perform a variable stiffness or ‘lock’ function by adjusting the friction between the ropes and rods. A maximum static friction is up to 2 times the spring tension according to the test results. Based on the fitting relationship between SMA spring tension and friction, the established kinetostatics model can predict the manipulator configuration. Furthermore, comparative experiments proved that the stiffness change is mainly caused by the proposed mechanism. By controlling the temperature of SMA, the variable stiffness of the manipulator is achieved. The C-shape has a maximum stiffness of 0.03505 N/mm and that this shape has a maximum stiffness increase of 300%.

Effect of secretory leucocyte protease inhibitor on early tendon-to-bone healing after anterior cruciate ligament reconstruction in a rat model

AimsTo verify whether secretory leucocyte protease inhibitor (SLPI) can promote early tendon-to-bone healing after anterior cruciate ligament (ACL) reconstruction.MethodsIn vitro: the mobility of the rat bone mesenchymal stem cells (BMSCs) treated with SLPI was evaluated by scratch assay. Then the expression levels of osteogenic differentiation-related genes were analyzed by real-time quantitative PCR (qPCR) to determine the osteogenic effect of SLPI on BMSCs. In vivo: a rat model of ACL reconstruction was used to verify the effect of SLPI on tendon-to-bone healing. All the animals of the SLPI group and the negative control (NC) group were euthanized for histological evaluation, micro-CT scanning, and biomechanical testing.ResultsSLPI improved the migration ability of BMSCs and upregulated the expression of genes related to osteogenic differentiation of BMSCs in vitro. In vivo, the SLPI group had higher histological scores at the tendon-bone interface by histological evaluation. Micro-CT showed more new bone formation and bone ingrowth around the grafted tendon in the SLPI group. Evaluation of the healing strength of the tendon-bone connection showed that the SLPI group had a higher maximum failure force and stiffness.ConclusionSLPI can effectively promote early tendon-to-bone healing after ACL reconstruction via enhancing the migration and osteogenic differentiation of BMSCs.Cite this article: Bone Joint Res 2022;11(7):503–512.

Experimental Study on The Effect of Aspect Ratio on Flexural Behavior of Aluminum Sandwich Composite

Sandwich composites are one such kind of light-weight composites developed for structural and vehicle body buildings etc. Due to their remarkable features such as high specific strength, high toughness and resistance to inter laminar shear strength. In this study, commercially available aluminium sandwich composite (ASC) laminate was considered for investigating its flexural behavior and buckling behavior as it was mostly used for various structural applications. Flexural analysis was done for different aspect ratios in order to analyze the influence of cross section of the specimen and support span on the flexural capability of the sandwich beam. The composite specimens prepared for flexural test consist of length 150 mm and widths 15, 12 and 10 mm. The flexural test was done for support span of 90, 110 and 130 mm respectively. The performance measures of flexural test are maximum bending load, deflection, flexural stiffness and inter-laminar shear stress. The flexural analysis revealed the fact that the aspect ratio appreciably affected the flexural capacity of the sandwich composite laminates. Maximum flexural capacity with bending load around 3.5 to 4 kN and flexural stiffness around 2.5 to 4.7 kN/mm respectively was observed for the sandwich specuimen for the aspect ratios L/t = 30 and b/t = 5. Being a anisotropic structure, the flexural behavior of this sandwich composite exposed as a combination of bending and shear failure. The soft core material and ductile skin face sheets resulted in a combined failure against flexural load in static condition.

A Novel Jamming Structure With Interlocking Mechanism Towards Applications in Wearable Robots

The adoption of variable stiffness actuators allows robots to take advantages of both rigid and soft structures. Jamming based variable stiffness structures are receiving increased attentions due to advantages of light weight, easy fabrication, and so on. However, the maximum bending stiffness and stiffness variation ratio achieved by most existing jamming structures are relatively small and unable to provide sufficient assistance to human joints when used in wearable robots. In this study, we proposed a novel jamming structure called gear jamming. Be different from most existing jamming structures that adopt frictional effects between internal components for resistance generation, the proposed jamming structure relies on an interlocking mechanism consisting of a series of gear-shape components and two layers distributed with teeth. A geometrical model was built to provide guidance for structure design, and experiments were performed to investigate effects of different factors on bending stiffness. A stiffness variation ratio up to 29.09 folds was achieved with the structure when the vacuum pressure increased from 0 to 90 kPa. To evaluate its performance for human joint assistance, a 64-g prototype was worn on subject's wrist to assist static holding of a 3-kg weight under a low vacuum pressure (30 kPa). Muscular activities of three representative muscles on the forearm reduced by 74.31±5.24%, 39.31±11.03%, and 71.48±3.00% in average over five subjects when compared to the condition without wearing the gear jamming prototype, which implied the promise of applying the proposed gear jamming structure in wearable robots.

Combined Medial Plate and Intramedullary Nailing for the Fixation of Extra-Articular Proximal Tibial Fractures: a Biomechanics Study.

Purpose: The extra-articular proximal tibial fractures continue to have high malunion rates despite development in intramedullary nailing (IMN) technology. Combined plate and IMN fixation can increase mechanical stability. The purpose of this study was to investigate combined plate and IMN for the treatment of extra-articular proximal tibial fracture using a biomechanical model. Methods: A 10-mm defective osteotomy was created in the fourth-generation composite tibia to simulate extra-articular proximal tibial fractures (AO/OTA 41A2). The fractures were stabilized with IMN alone (IMN group), IMN with supplementary medial plate (M-IMN group), and IMN with supplementary lateral plate (L-IMN group). The biomechanical properties of each specimen were tested under axial compression loading, bending stress, and cyclic loading. The maximum displacement of the fragments and implant-bone construct failure was recorded. Results: The maximum displacement of the M-IMN group was significantly less than either the L-IMN or IMN group in both axial compression loading and bending stress (p < 0.05 for both comparisons). All specimens in the three groups survived in 10,000 cyclic loading without hardware deformation. The maximum stiffness of failure was similar between the M-IMN and L-IMN groups, but the IMN group was statistically lower than either the L-IMN or the IMN group (p < 0.05). Conclusion: The results indicated that combined medial plate and IMN fixation could effectively increase the mechanical stability of proximal tibial fractures.

Deformation characteristics and mechanical properties tuning of a non-rigid square-twist origami structure with rotational symmetry

Non-rigid origami patterns could provide more versatile performance than their rigid counterparts in the design of mechanical metamaterials owing to the simultaneous deformation of facets and creases, but their complex deformation modes make quantitative characterization and tuneability of mechanical properties a challenging task. Here, we investigated the tensile behavior of a non-rigid square-twist origami structure with rotational symmetry by combining biaxial tension experiments and finite element modeling. A three-stage deformation process, including tightening, unlocking, and flattening, of the structure was unveiled through a detailed analysis of facet distortion and crease rotation, and the relationship between structure deformation and several key features in the energy, force, and stiffness curve was obtained. Based on the analysis, an empirical model was built to correlate the geometric and material parameters of the structure and its deformation energy, initial peak force, and maximum stiffness, which were further validated through experiments. Using the model, the mechanical properties of the structure can be accurately predicted and tuned based on specific engineering requirements, thereby serving the development of new tuneable mechanical metamaterials based on the family of square-twist origami.

Damage mechanism of U-shaped ribs stiffened steel flat plates subjected to close-in explosion

The U-shaped ribs stiffened plates are widely used in civil and marine engineering structures for their high bending resistance performance. Moreover, these structures may be exposed to blast scenario especially terrorist and accidental explosions. Based on this background, this investigation carried out a study on the damage modes and the damage mechanisms of the U-shaped ribs stiffened plates subjected to close-in blast loads. The work used both field experimental and numerical methodologies. In this investigation, field blast tests were conducted on two flat plates and a stiffened plate. Furthermore, a fine numerical model was developed on the LS-DYNA platform and validated by the experimental results. Numerical analysis was conducted follow the validated model, and three typical damage modes (five detailed damage modes) of the single U-shaped stiffener stiffened plates subjected to blast loads were revealed through the numerical calculation of 40 specimens. Furthermore, a new damage number (Φ) was proposed for the classification of the damage modes. Meanwhile, maximum incident angle (α) and relative stiffness (κ) were put forward for further identification of the damage modes. It is proven that the damage modes of the single U-shaped stiffener can be well identified by the combination of damage number, maximum incident angle, and relative stiffness. Damage mode I occurred when Φ is less than Φ1 (0.042). And while the Φ is more than Φ2 (0.071), the stiffened plates exhibited mode IIIb damage. For Φ is between Φ1 and Φ2, the damage modes can be classified as mode IIa (κ < 0.0032) and IIb (κ≥ 0.0032) when α is less than 45°. While α is greater than 45°, the damage modes can be classified as mode IIa (κ < 0.001), IIIa (0.001 ≤κ < 0.0032) and IIIb (κ≥ 0.0032).

Potential value of tumor stiffness and sE-cadherin in predicting the response to neoadjuvant therapy in HER2-positive breast cancers

Background: This prospective study compared the diagnostic value of tumor stiffness and serum soluble E-cadherin (sE-cadherin) expression for predicting response to neoadjuvant therapy in HER2-positive breast cancers. Methods: 112 patients with early or locally advanced HER2-positive breast cancer were enrolled. Maximum stiffness (Emax), mean stiffness (Emean) and their relative changes were assessed at t0 and t2. sE-cadherin levels were analyzed using ELISA. Pathological complete response was defined as no invasive disease in the breast and axilla (ypT0/is, ypN0) after surgery. The ability of tumor stiffness, sE-cadherin and the combination of ΔEmean (the relative change in Emean after the second cycle of neoadjuvant therapy) and sE-cadherin in predicting tumor responses was assessed using receiver operating characteristic curves and the Z-test. Results: Tumor stiffness and sE-cadherin decreased during neoadjuvant therapy. ΔEmean and sE-cadherin revealed the best predictive performance, with areas under the curve (AUCs) of 0.843 and 0.857, respectively. No significant differences in AUCs were reported between ΔEmean and sE-cadherin (p=0.795). The combined use of ΔEmean and sE-cadherin showed the highest sensitivity and specificity (93.22 and 90.57%, respectively), with an AUC of 0.937. Conclusion: The combination of ΔEmean and sE-cadherin may improve the predictive power of each single factor. Although further verification is required, this study may promote noninvasive prediction of neoadjuvant therapy responses and help personalize the treatment regimen.

Optimal Design of a Leaf Flexure Compliant Mechanism Based on 2-DOF Tuned Mass Damping Stage Analysis.

This study proposed an innovative design of a leaf flexural-based 2-DOF tuned mass damping stage that can be integrated into a micro-electromechanical system precision positioning stage to reduce the displacement response of the precision positioning stage excited by a specific vibration frequency and to achieve the damping effect and vibration reduction without adding viscous damping materials. A prototype that conforms to dual-axis decoupling and has 2-DOF translation capability was designed using parallel and vertical arrangements of a leaf flexure. The Taguchi design method and the finite element method were used on the relevant design parameters of the primary mass stage to determine the best size configuration for the maximum off-axial stiffness ratio and the parameters of the tuned mass damper closest to the natural frequency of the primary mass stage with the minimum deflection. In addition, an optimization module, based on a genetic algorithm (GA), was used to optimize the design of the flexure size of the tuned mass damper. Finally, experiments were conducted, the vibration displacement response of the primary mass stage was observed, and the effect with or without the addition of tuned mass damping on the system vibration response was compared. The results indicate that the tuned mass damper can effectively reduce the response amplitude of the stage, where the maximum reduction rate in the experiment was 63.0442%, and the mass of the damper was highly positively correlated with the amplitude reduction.

Design of thrust bearing for hydrogen liquefaction turbine

With rapid development of hydrogen energy industry, liquid hydrogen, as a carrier with the highest energy storage density, is an effective way to ensure the large-scale application of hydrogen energy. Thrust bearing, which is the core component of hydrogen liquefaction turbine expander, has always been difficult to design. In this paper, the stress characteristics of the thrust bearing for hydrogen liquefaction are analyzed, and the analysis for designed prototype is performed. The numerical simulation results are compared with the design method. Results show the optimum clearance of thrust bearing and clearance of closed bearing has obvious influence on the peak value and position of stiffness caused by eccentricity. Numerical simulation results reflect the internal flow structures in bearing clearance, while the maximum stiffness is relatively conservative compared to analysis of radius ratio.

Adding composite truss to improve mechanical properties of reinforced concrete T-girder bridge

To solve the problem of insufficient transverse connection of T-girder bridges, this paper investigated the strengthening method of two composite trusses symmetrically installed in mid-span. The composite truss included two top plates, four diagonal braces, and one horizontal brace. An experimental investigation was carried out to study the mechanical properties of reinforced concrete T-girder using single-point loading method under four load cases. The experimental results showed that the maximum transverse stiffness of T-girder specimens strengthened with composite trusses improved by 12.4% compared with control beams. Simultaneously, it had an excellent restraining effect on the cracks development. The maximum percentage decrease in the deflection corresponding to the maximum load when the reinforced concrete T-girder strengthened with composite trusses over the control beam of up to 39.7 was observed. In addition, the load transverse distribution coefficient was investigated according to rigid-jointed slab (girder) method. The composite trusses were chosen as intermediate diaphragm to calculate moment of inertia. The analytical model was in an accurate with the experimental result under the same loading condition. The optimize spacing of composite trusses was given from 600 mm ( L/10) to 1200 mm ( L/5), and thickness of top plate was 30 mm when the load transverse distribution coefficient was homogeneously distributed. Finally, a three-dimensional finite element model was used to evaluate the effectiveness of composite trusses.

Finite Element Modeling of a stretched automotive conductor response under bending curvature

The present contribution deals with a based FE model treating helically wrapped automotive conductor subjected to pretension force and bending curvature. It is shown that even with low pre-tension force generated by the fixing conditions of the automotive conductor, the bending stiffness varies between two bounds: maximum stiffness for small curvature then from a critical curvature it starts to decrease until reaching a minimum bound independently of friction coefficient and tension force. It can be also, underlined that in addition to the consideration of the inter-layer contact, this elaborated FE model takes into account the friction contact between the same layer wires allowing to the conductor more rigidity. As it can be noticed, this contact mode was neglected in previous literature models.

Using the Dynamic Shear Rheometer for Low-Temperature Grading of Asphalt Binders

Abstract The Superpave Performance Grading (PG) framework or a variation of this framework is often used as a purchase specification in the United States and as a tool to evaluate the expected performance of modified and unmodified asphalt binders in many countries around the world. A cornerstone of the PG framework is the low-temperature grade of the asphalt binder that is assessed using a bending beam rheometer (BBR) using maximum stiffness and a minimum rate of deformation as criteria. Several previous studies from other researchers have demonstrated the feasibility of using the dynamic shear rheometer (DSR) with a 4-mm parallel plate geometry to measure the rheological properties of asphalt binders at low temperatures. This article builds on these studies to evaluate the feasibility of using a DSR to replace the use of a BBR for low-temperature grading of the asphalt binder using two different approaches. The first approach was to measure complex shear modulus of different asphalt binders using the DSR, convert these measurements to BBR equivalent stiffness and m-value using principles of linear viscoelasticity, and compare the two pairs of parameters from each method. The second approach was to use the complex shear modulus and phase angle measured using the DSR in lieu of using the stiffness and m-value measured using the BBR. Although the results from both methods show feasibility of using the 4-mm plate with the DSR to estimate low-temperature properties, the second approach of measuring and using the DSR-based complex shear moduli and phase angle is a more viable alternative for routine use.

Influence of cooling temperature on load-carrying performance of a radial HTS magnetic bearing

High temperature superconducting (HTS) magnetic bearing can operate in the harsh environment of low temperature and negative pressure with low loss and self-stability. Therefore, it has been gradually applied in flywheel energy storage, cryogenic liquid pump, cold compressor and some other cryogenic rotating machinery. The load-carrying performance of HTS magnetic bearing is affected by the cooling temperature of HTS directly. In this paper, the linear model is used to modify the temperature dependence to evaluate the influence of cooling temperature on load-carrying performance quantitatively, and the results are analyzed and displayed from the aspects of maximum levitation force, levitation stiffness and hysteresis effect. The research results of this paper have practical significance for the design and safe operation of HTS levitation system.

Design and analysis of 5 kW helium turbine for EAST cryoplant

The helium turbine is an important core component in the refrigerator, which provides support and guarantee for the stable operation of the cryogenic system. This paper refers to the parameters of one of the four helium turbines in EAST, designs a 5 kW helium turbine. The overall structure of the turbine has been described, and the design and analysis of the impeller and bearing have been carried out. Through CFD analysis, the internal pressure and temperature change law of the flow is analyzed. The variable-condition operating characteristics of the turbine are predicted, and it is found that the turbine can maintain efficient operation within a wide range of mass flow changes. The bearing performance is calculated by solving the Reynolds equation. After determining the optimal bearing clearance 28 μm based on the principle of maximum stiffness, bearing performance parameters of load capacity and stiffness can be further calculated.

Optimal design of vibro-impact resistant fiber reinforced composite plates with polyurea coating

This paper studies on optimal design of vibro-impact resistant fiber reinforced composite plates (FRCPs) with polyurea coating. Initially, a theoretical model for the coated FRCP structures under elastic boundary conditions is proposed, through which dynamic stiffness and impact damage area are predicted. Here, based on the first-order shear deformation theory and the Rayleigh-Ritz method, the dynamic stiffness of coated FRCP structures is calculated, which is taken as an index of vibration suppression performance. Regarded as an index of anti-vibration performance, the impact damage area is identified by employing the Hertz contact law and the predefined delamination threshold load. After validation of the proposed model against a series of experiments on coated and uncoated FRCP specimens, optimization analysis is then conducted based on the Non-dominated Sorting Genetic Algorithm, where the maximum dynamic stiffness, the minimum impact damage area and structural mass are defined as objective functions, and thickness ratio, elastic modulus ratio and ply orientation angle are taken as design variables. It has been found that to possess the desired vibration and impact resistant capabilities together with maintaining lightweight property, it is recommended to choose design variables associated with the turning point of Pareto-optimal solutions as the final optimal results.

An experimental study on reinforced concrete beam with continuous spiral stirrups under pure torsion

This research investigated continuous rectangular spiral shear reinforcement as transverse reinforcement under pure torsion and compared it with conventional concrete beams. This present study tested three different continuous rectangular spiral stirrup (80°, 75°, and 45°) and one with traditional type stirrup (90°). M30 grade concrete and Fe 415 steel were used. The Test results indicate that the maximum ultimate torque at 75° is 32 kNm. Also, the maximum percentage increase in ductility is 19%. The maximum stiffness was observed at 80° stirrups is 2104 kN.m/radians.

Concentric Push–Pull Robots: Planar Modeling and Design

Concentric push–pull robots (CPPR) combine the simplicity, miniaturization potential, and open lumen of concentric-tube robots with the kinematic advantages and stability of push–pull multibackbone designs. A CPPR segment is made from a pair concentric tubes with notches asymmetrically cut into their sides in opposing directions. The two tubes are attached to one another at their tips, and push–pull translation of the tube bases relative to each other changes the curvature along the length of the combined tube pair. Custom, variable-curvature shapes are possible by varying the notch parameters along the tubes. In this article, we present a planar, variable-curvature mechanics model for the actuated segment shape and a method for designing the notch pattern to achieve a desired planar, variable-curvature shape with maximal stiffness within specified strain limits. Experiments validate accuracy for various shapes, materials, and cross sections, showing that the design method achieves a variety of desired shapes. We also demonstrate a multisegment robot made from multiple tube pairs that can independently rotate and actuate, increasing the robot DOF.