Force Amplification Research Articles

Geometric Optimization of the Five-Point Double-Toggle System for the Clamping Unit of an Injection Molding Machine with the Response Surface Method

Injection molding is one of the most used processes for the manufacture of plastic products with high-volume capacity. The five-point double toggle mechanism is frequently employed in the clamping unit to augment the force generated by a linear actuator, thereby achieving the requisite clamping force. This is a crucial aspect that determines the productivity and quality of the finished product in the injection molding process. Nevertheless, the geometrical synthesis of this type of mechanism has not been sufficiently addressed with regard to its integration into the mold design and the opening/closing stroke. This paper presents a novel approach for analyzing and evaluating the impact of parameters pertaining to mechanism posture on its force amplification, employing the Taguchi method. The relationship between force amplification ratio and the most influential parameters is simplified with the Face-Centered Central Composite Design (FCCCD) method, thereby allowing the optimal posture of the mechanism at the mold-closing stage to be determined. With these optimal parameters, once the mold height and desired opening/closing stroke have been selected, the dimensions of the links in the mechanism can be calculated. The results demonstrate that there are numerous combinations of these parameters that can yield a high force amplification ratio, thus providing the designer with a range of options for the design of a clamping unit. The proposed method can be employed at the initial stage of the design process to obtain a preliminary design, thus preparing for the dynamic analysis or further optimization problems of the mechanism.

Effects of Soil–Structure Interaction on the Seismic Response of RC Frame–Shear Wall Building Structures Under Far-Field Long-Period Ground Motions

This paper focuses on the effect of soil–structure interaction (SSI) on the seismic response of high-rise RC frame–shear wall structures under far-field long-period ground motions. Elastic–plastic time–history analyses were performed using ABAQUS. The effects of the ground motion type, soil type, and structural frequency on the seismic response are analyzed and quantitatively evaluated. On this basis, the influence mechanism of SSI on the seismic response under far-field long-period ground motions is discussed and revealed through a ground motion spectrum analysis. The results show that the consideration of the SSI effect leads to an increase in the displacement response and a decrease in the shear response. The SSI coefficient of the base shear is all less than 1, ranging from 0.5 to 1. The SSI effect under far-field long-period ground motions is more pronounced than that under ordinary ground motions. The shear force reduction in the current code may not be applicable to the structural design considering the SSI effect under far-field long-period ground motions. The displacement response amplification of the SSI effect on loess soil (Site 2) is more remarkable than that on sand soil (Site 1). The SSI effect can reduce the structural frequency, especially for the structures with fewer floors on the softer soil site. The “bimodal characteristic” of the acceleration response spectrum for far-field long-period ground motions may lead to shear force amplification when SSI is considered.

A piezoelectric human motion energy harvester with stress amplification mechanism

The kinetic energy is rich in human walking, which may be exploited to provide sustainable energy for portable and miniaturized devices by properly design of the energy harvester. In order to effectively amplify the actual force on the piezoelectric material upon the external load, a beam-shaped piezoelectric energy harvester (PEH) is designed. The PEH is prepared by embedding poly(vinylidene fluoride) (PVDF) piezoelectric strips into the compression zone of the beam. The underlying mechanism is discussed via mechanical theoretical modeling and finite element simulation. It is demonstrated that the actual integrated force on the piezoelectric film of PVDF is about 31.7 times that of the external force applied on the beam’s mid-span. The study would pave the way for force amplification mechanism in designing PEHs and holds promises for portable device applications.

Mechanical drivers of intrinsic foot muscle for maximum toe flexor strength in upright standing across different body size

This study aimed to evaluate maximum toe flexor strength, foot arch height, intrinsic toe flexor muscle size and foot arch stiffness among individuals with different body sizes, and to compare these variables between sitting and standing positions. Maximum toe flexor strength in sitting and standing, and intrinsic foot muscle thicknesses (flexor hallucis brevis: FHB, flexor digitorum brevis: FDB, abductor hallucis: AH and quadratus plantae: QP), were measured using a toe grip dynamometer and a B-mode ultrasound in healthy young men. FHB was thicker than AH, FDB and QP, AH was thicker than FDB and QP, and no significant difference was found between FDB and QP. Toe flexor strength was correlated with FHB and AH, and foot arch height was correlated with FHB. Toe flexor strength was greater in standing than in sitting. Stepwise multiple regression analysis identified FHB and AH as determinants of toe flexor strength in standing, and the relative muscle strength values per body weight in standing were determined by QP, foot arch index and foot arch stiffness. Overweight individuals had a decreased rate of increase in relative toe flexor strength compared to normal individuals. These results suggest that a large muscle thickness of intrinsic foot muscle a key contributor to toe flexor strength. Moreover, toe flexor muscle in upright standing could have the potential to generate force independently of intrinsic foot muscle size, but obese individuals who chronically put weight on their feet might impair the force amplification mechanism in upright standing.

Blast impact on the density-based tri-layered polyurethane foam

Cellular solids are interesting materials for blast energy absorption because of their high porosity, cell structure, and unique mechanical properties. Also, it will undergo graded compression over the same foam density. Hence, in this study, an experimental investigation of blast pressure impact on the trilayered sequences made of three different polyurethane (PU) foam densities of equal thickness, such as D1-29.201 kg/m3, D2-59.692 kg/m3, and D3-107.720 kg/m3 is carried out. The force transmitted (FT) on the reaction plate and incident force on the blast impact face are recorded. The maximum force amplification (Famp) of the 63.79% was observed in the S5 and the minimum of 6.19% in S4. Thus the reduction in Famp in S4 compared to S5 is 90.3%. Similarly, the energy absorbed (Eabs) by the trilayer is a maximum of 24.80 J in S2 and a minimum of 3.60 J in S3. The Eabs increased to 85.48% in S2 solely by altering the layer sequences in S3. Hence, the location of the density in the layer sequences plays a key role in effective blast mitigation on different response measures.

Fluid viscous dampers in tackle-damper configuration: An experimental study

This study presents dynamic test results on a recently developed damper placement known as the tackle-damper configuration. This innovative setup integrates a viscous damper alongside two inclined tackles, each comprising multiple turns of wire ropes threaded between upper and lower sheaves. This configuration has the ability to amplify damper deformations and forces based on the mechanical advantage of the tackle. Four specimens of tackle-damper configurations are tested under different dynamic harmonic and seismic loadings. Obtained results indicated that tackle-damper configuration changes pure viscous behaviour of the fluid viscous damper to an amplified viscoelastic behaviour. It is verified that energy dissipation in the tackle-damper configuration arises from two sources, i.e. fluid viscous damper and capstan friction between the wire ropes and the sheaves. Ideally, deformation and force amplification factors in the tackle-damper configuration should depend solely on the number of wire ropes and the inclination angle of the tackle. However, it has been found that true force amplification factor is much larger than the ideal value due to the capstan friction. Moreover, true deformation amplification factor can also be much smaller than the ideal value. This is attributed to the elastic stretching of individual wire ropes within the tackles. Therefore, both friction and wire rope elongation substantially affect the true amplification capabilities of the tackle-damper configuration.

Bulk and fracture process zone contribution to the rate-dependent adhesion amplification in viscoelastic broad-band materials

The contact between a rigid Hertzian indenter and an adhesive broad-band viscoelastic substrate is considered. The material behavior is described by a modified power law model, which is characterized by only four parameters, the glassy and rubbery elastic moduli, a characteristic exponent n and a timescale τ0. The maximum adherence force that can be reached while unloading the rigid indenter from a relaxed viscoelastic half-space is studied by means of a numerical implementation based on the boundary element method, as a function of the unloading velocity, preload and by varying the broadness of the viscoelastic material spectrum. Through a comprehensive numerical analysis we have determined the minimum contact radius that is needed to achieve the maximum amplification of the pull-off force at a specified unloading rate and for different material exponents n. The numerical results are then compared with the prediction of Persson and Brener viscoelastic crack propagation theory, providing excellent agreement. However, comparison against experimental tests for a glass lens indenting a PDMS substrate shows data can be fitted with the linear theory only up to an unloading rate of about 100μm/s showing the fracture process zone rate-dependent contribution to the energy enhancement is of the same order of the bulk dissipation contribution. Hence, the limitations of the current numerical and theoretical models for viscoelastic adhesion are discussed in light of the most recent literature results.

Insights into the swelling force in commercial LiFePO4 prismatic cell

Lithium-ion batteries undergo reversible and irreversible swelling force during cycling. The mechanical behavior and swelling force of lithium-ion batteries are important in practical applications. In this study, the variation and the aging mechanism of swelling force, and the growth pattern under different cycling conditions have been studied with commercial cells. The findings reveal distinct dynamic stress peaks corresponding to the state of charge (SOC) increase, indicative of notable lattice expansions in both cathode and anode. This expansion intensifies over cycles, with the most significant escalation observed at 30 % SOC, gradually assuming a pivotal role in battery expansion dynamics. Post-mortem analysis, coupled with stress-strain evaluations, attributes this phenomenon primarily to moduli variations across SOC during the aging process. Moreover, the trajectory of swelling force amplification varies across aging paths, with high-temperature cycling demonstrating accelerated growth. This accelerated growth stems from the broadened expansion of battery components beyond solid electrolyte interphase (SEI) formation induced by high-temperature aging.

Geometrically nonlinear design of a rhombus-nested compliant amplification mechanism for use in precision actuators and sensors

A rhombus-nested compliant amplification mechanism is proposed for versatile usages of precision actuators and force sensors with an easy tuning of stiffness. Such a monolithically planar rhombus-nested compliant mechanism has the dual functions of two-stage displacement or force amplification by changing the input and output ports. It features a large ratio of inter-stage stiffness, thus resulting in an enhanced amplification ratio, load capacity and dynamic bandwidth. The geometrically nonlinear analytical equations of displacement amplification ratio and input stiffness are derived in the presence of pronounced axially-loaded stiffening and kinematic-arching effects based on the beam constraint model. It allows an insightful evaluation of geometrically nonlinear deformation behaviors sensitive to structural dimensions in a parametric way. Insights into geometrically nonlinear behaviors in the case of large-stroke and axially-loaded motions are discussed as well. A proof-of-concept prototype with embedded piezoelectric stacks is fabricated with the dimensions of 74mm × 60mm × 10 mm. The dual functions of precision actuator with amplified motion strokes and force sensor with enhanced sensitivity are experimentally demonstrated.

A Series-Parallel Hybrid Pelvic Fracture Reduction Surgical Robotic System Based on Novel 6-DOF Force Amplification Mechanism

A Series-Parallel Hybrid Pelvic Fracture Reduction Surgical Robotic System Based on Novel 6-DOF Force Amplification Mechanism

A purely centered and non-redundant piezoelectric stick-slip rotary stage with force amplification

This paper proposes a purely center-rotation and non-redundant piezoelectric stick–slip rotary stage with force magnification. A bridge driving mechanism with centrosymmetric actuation feet is proposed, and its tilt angle can be adjusted to regulate the clamping force amplification characteristics, thus improving load capacities. Meanwhile, only a single piezoelectric actuator is used, and the driving mechanism is built in the circular slider, hence achieving non-redundant, purely centered rotation and improving the structural compactness. Theoretical calculations and simulation analyses of single-step rotation angles and force amplification of the rotary stage are carried out. In addition, a system dynamics model with electromechanical, rigid-flexible, and friction coupling properties is established. Finally, a prototype is fabricated, and various experiments are conducted. The designed bridge driving mechanism amplifies the piezoelectric actuation force by 2.8 times, and the stick–slip rotary stage has a maximum load of up to 9 kg. Also, the stage can rotate more than 360°, and the angular resolution is 0.1265 μrad, demonstrating superior performances of the non-redundant center-rotation stage.

Surrogate multi-objective optimization of missile RCS performance in hypersonic rarefied flow of the near space

This study focuses on optimizing the lateral jet efficiency of THAAD-like (Terminal High Altitude Area Defense) missiles operating under hypersonic rarefied flow conditions. We employ the DSMC-QK algorithm to simulate the three-dimensional lateral jet flow field, accounting for thermochemical non-equilibrium effects. The analysis investigates how the force/momentum amplification coefficient varies with the angle of attack, jet pressure ratio, jet Mach number, and jet gas composition. Subsequently, we develop an artificial neural network (ANN) proxy model using the pyrenn toolbox, achieving an average prediction error of 0.866% and a maximum error of 1.60%. Utilizing this ANN model, we perform single- and multi-objective optimizations with a genetic algorithm to determine the optimal jet parameters. The results reveal that in multi-objective optimization, the proportion of helium in the jet gas composition increases, leading to a slight reduction in the force amplification coefficient but a substantial 61.4% decrease in the mass flow rate. This demonstrates that a judicious selection of jet gas composition can significantly reduce mass flow while maintaining high jet efficiency, thus achieving efficient lateral jet control.

A design of tuned mass damper with piezoelectric stack energy harvester and two-stage force amplification frame

The paper deals with a novel tuned mass damper (TMD) with an energy harvester consisting of a combination of piezo stacks and two-stage force amplification frames connected in series with TMD springs (TMD-2sPSFAFs). The governing equations of 2sPSFAF are established first, followed by those of TMD-2sPSFAF. It will be demonstrated that the reduced order model of the series combination of 2sPSFAF and TMD spring is an equivalent piezo stack energy harvester. Using the optimal results according to the fixed point theory, the conditions for selecting stiffnesses of piezo stacks and TMD spring are obtained. Next, a numerical examination of the electromechanical system reveals that the voltage amplitude curve has a fixed point independent of TMD spring stiffness. Furthermore, an effective stiffness of the TMD spring would be found to ensure that the peaks of mechanical magnification and voltage amplitude curves are of equal heights.

Design and experiment of electromagnetic-hydraulic-rubber integrated vibration isolator

Low-frequency radiated noise, characterized by a distinctive “acoustic fingerprint” is generated when vibrations from marine machinery propagate through a ship’s hull into the ocean. This type of noise travels long distances with concentrated and stable energy, posing a significant threat to a ship’s acoustic stealth capabilities. Active-passive hybrid isolation is the primary method for reducing low-frequency radiated noise from ships; however, technical challenges remain, such as effectively integrating active and passive components, achieving high output force in a compact design, and addressing the poor linearity of actuator output at low frequencies. To address these issues, this paper presented an innovative electromagnetic-hydraulic-rubber integrated vibration isolator. Firstly, the study analyzed the dynamic characteristics of a two-degree-of-freedom isolation system and investigated the influence of active-passive hybrid vibration isolator parameters on control force and vibration reduction performance. Secondly, it was established that the magnetic circuit model and magnetic field strength expressions for the electromagnetic actuator using magnetic circuit analysis derive the analytical relationship between electromagnetic force, current amplitude, and frequency using the energy method. Subsequently, a mathematical model was developed for the rubber-hydraulic suspension component to examine its dynamic characteristics, hydraulic damping, and hydraulic force amplification transmission laws. Lastly, we organically combine the electromagnetic actuator with the rubber-hydraulic suspension and conduct a multi-physics joint simulation of the integrated vibration isolator using Comsol software to verify the effectiveness of the optimized design and vibration isolation control. Experimental research was carried out on the dynamic characteristics, output force properties, and fatigue characteristics of the integrated vibration isolator prototype. Results indicated that the established models and methods can achieve over 90% accuracy in predicting the performance of the electromagnetic actuator’s output force and exhibit good linearity within the 5–400 Hz range. The rubber-hydraulic suspension can achieve an amplification factor of up to 1.5 for the electromagnetic force while reducing the transmission of vibrations to the base. The research findings can enhance the low-frequency vibration isolation performance of marine machinery equipment and improve their acoustic stealth capabilities.

Parameters Influencing the Effectiveness of Reaction Control Jets on the Basic Finner

Reaction control jets provide a practical option to increase the acceleration rates of high-performance aerodynamic vehicles. Unfortunately, a designer or system engineer incorporating reaction control jets into a design cannot simply add the jet as a point force because it does not account for the change in force due to the modifications of the flowfield caused by the jet. The changes made to the flowfield can impact the forces and moments, enhancing, mitigating, or even reversing the desired force or moment, depending on a complex set of factors. This study examines the influence of different jet configurations, modifications to freestream parameters, and the presence of control surfaces on the body. It is shown that the proximity of the jet to the control surfaces has the most significant impact on the resulting force amplification. The emphasis is placed on differentiating between how the jet interacts with the body and fins. Ultimately, this shows that the interaction with the fuselage is consistent and self-similar, whereas the fins are primarily influenced by the jet blocking the flow and generating a shock that imparts high pressure on the control surface, increasing the force in the direction of the jet.

Shape Effect of Rockfall Impacting Sandy Soil Cushion Layer–Reinforced Concrete Slab Composite Structure

The impact effects of falling rocks on sand–reinforced concrete slab composite protective structures involve several factors. Among them, the existing codes are unable to consider the effect of rockfall shape and the angle of contact between the rockfall and the object on the impact force as well as the depth of penetration. Based on extensive field investigation, this paper proposes a shape factor to simplify the rockfall into an ellipsoid and determines the shape and dimensions of the rockfall by three-dimensional axis length. Besides, a coupled SPH-FEM numerical calculation model is established and validated through comparison with a large-scale outdoor test of a rockfall impact protection structure. Finally, the effects of rockfall shape and impact angle on the symbolic parameters including impact force, impulse and energy in the impact process are revealed. The findings indicate that the maximum force and displacement of the midpoint of the bottom of the reinforced concrete slab have relative errors within 5.0 % when compared to the model test, confirming the precision of the models discussed in this paper. For the same rockfall, the peak force decreases with the impact angle increasing; taking the same volume of spherical rockfall as the reference, under the same rockfall pattern, the peak impact force and impulse amplification factor decreases with the increase in contact attitude angle. Additionally, the scaling effect becomes more pronounced when the shape factor of the rockfall is smaller; under the same shape factor, the impact depth of the cushion layer is the smallest when the attitude angle is 45°, and the maximum when the impact angle is 90°; the SPH-FEM coupling algorithm could reasonably reproduce the pit-forming process of sand and soil, and it is very effective in simulating the flow effect of soil particles under impact.

Comparison in terms of Material Quantity Between Non-Seismic and Seismic Design for Selected Buildings in Malaysia

Almost all buildings in Malaysia were previously designed for non-seismic loading. As such, the need to consider seismic load poses challenges for the engineers and project owners. In order to enlighten the stakeholders on the effect of adopting seismic design, the impact on building material cost and quantities must be investigated in advance. Although many studies have been conducted, the use of hypothetical building models and not considering the actual soil factors in Malaysia may yield unrealistic results. As such, this study is conducted with the aim to evaluate the change in the material quantities of the main frame members using six existing building models subjected to peak ground acceleration of 0.16g and situated on soil type D. The analysis, design and taking-off were conducted with the aid of Tekla Structural Designer software. The results showed significant increase in terms of the material quantity required for the main frame members when seismic design was considered. The increase in the concrete volume and reinforcement tonnage was calculated to be in the range of 6.92% to 404.86% and 3.23% to 563.94%, respectively. The development of high base shear force, the amplification of the seismic force by the soft soil, and relatively stringent detailing in DCM were identified as the contributing factors. With a broader spectrum of results, the stakeholder can anticipate the increase in the material cost for adopting seismic design that can be useful for design submission and project cost estimation.

Understanding the ant’s unique biting system can improve surgical needle holders

Mechanical grasping and holding devices depend upon a firm and controlled grip. The possibility to improve this gripping performance is severely limited by the need for miniaturization in many applications, such as robotics, microassembly, or surgery. In this paper, we show how this gripping can be improved in one application (the endoscopic needle holder) by understanding and imitating the design principles that evolution has selected to make the mandibles of an ant a powerful natural gripping device. State-of-the-art kinematic, morphological, and engineering approaches show that the ant, in contrast to other insects, has considerable movement within the articulation and the jaw´s rotational axis. We derived three major evolutionary design principles from the ant's biting apparatus: 1) a mobile joint axis, 2) a tilted orientation of the mandibular axis, and 3) force transmission of the adductor muscle to the tip of the mandible. Application of these three principles to a commercially available endoscopic needle holder resulted in calculated force amplification up to 296% and an experimentally measured one up to 433%. This reduced the amount of translations and rotations of the needle, compared to the needle's original design, while retaining its size or outer shape. This study serves as just one example showing how bioengineers might find elegant solutions to their design problems by closely observing the natural world.

Design and analysis of magnetostrictive two-dimensional kinetic energy harvester

Conventional energy harvesters often require high ambient vibration frequencies and can only capture vibration energy in a single direction. To address these issues, this paper designs a magnetostrictive two-dimensional kinetic energy harvester placed under the floor and capable of capturing energy in both vertical and horizontal directions. In order to achieve higher electrical power output at low-frequency input forces, a two-stage force amplification mechanism is designed to amplify the walking kinetic energy of pedestrians and the main parameters of this structure are analyzed and optimized. On the other hand, by constructing different forms of bias magnetic field, the influence of bias magnetic field on the deflection and motion of the internal magnetic domain of Terfenol-D is systematically studied, and the best bias form that can make the material shows the strongest magnetization characteristics is determined. Next, a prototype harvester was built, and an experimental vibration system was set up to test and analyze the output characteristics of the harvester comprehensively. The experimental results show that the harvester produces 21.2 mW of peak output power under sinusoidal excitation at an operating frequency of 4 Hz. Under random excitation, a peak output voltage of 2.64 V and 170 mW peak power was obtained. Under actual pedestrian walking tests, 17.62 mW peak output power is obtained to power low-power devices. The study’s results provide preliminary evidence that the designed magnetostrictive energy harvester can stably harvest kinetic energy from pedestrian walking.

Wave motion in a narrow gap coupling with the roll motion of a vessel next to an offshore terminal

Concerning the scenario of a vessel operating alongside an offshore terminal, the vessel being the floating body and the offshore terminal bottom-mounted. The closeness of the two bodies leads to the formation of a long narrow gap, within which the large amplification of the water-surface elevation could occur. The coupling effect between the roll motion of the vessel and the water-surface motion within the gap is primarily concerned. Under the assumption that the quay wall of the terminal is infinitely long and fully reflective, the imaging principle and a modified Green's function have been developed to investigate such an effect. Numerical models are developed based on the two proposed approaches, respectively, in conjunction with a higher-order boundary element method. For a small gap width, the p = 1 resonant mode of water-surface motion in the gap can apparently enhance the roll motion of the vessel. The radiation wave owing to the enhanced roll motion can in turn disturb the water-surface motion, increasing the frequency of the dominant peak while decreasing its amplitude. As the gap width increases, the water-surface elevation around the resonant frequency of roll motion gets more and more noticeable, gradually becoming the dominant peak. The effect of the mooring stiffness is also discussed, revealing the existence of a ꞌnon-resonance regionꞌ where no resonance occurs in this specific frequency region. It is also noted that the resonant water-surface motion of p = 1 mode can cause a remarkable amplification of the negative horizontal mean wave drift force, pushing the vessel away from the terminal.