Blocking Force Research Articles

Dynamics modeling and experiment validation for piezoelectric-transmission-wing system

Aiming at the challenge of predicting the dynamic behavior of the flapping wing in the piezoelectric-transmission-wing (PTW) wingbeat system, a lumped-parameter model coupling piezoelectric structural mechanics and flapping-wing aerodynamics is proposed to address the challenge caused by the fluid-structure interaction (FSI). Firstly, a model describing the piezoelectric mechanical response is established, which has the ability to better predict the mechanical response of the piezoelectric actuator under high electric field and low-frequency driving conditions. In order to verify the validity and accuracy, tip deflection, stiffness and blocking force experiments as well as data comparisons are performed to substantiate the findings. Secondly, a comprehensive and reasonable lumped-parameter dynamic model is constructed based on the analysis of the transmission mechanics based on pseudo-rigid-body theory and the improved aerodynamic modeling of the wing, along with the aforementioned piezoelectric mechanical modeling. Thirdly, simulation and dynamic response experiments of the wingbeat system are carried out. Results show that the simulation data are in good agreement with the experimental values, which indicates the accuracy of the model in predicting the dynamic behavior of the flapping wing powered by the piezoelectric actuator. Moreover, some interesting phenomena such as the pitch oscillation of the wing and the dependence of the flapping motion on the driving frequency have been demonstrated in the simulation and the wingbeat experiment, respectively. The research findings of this article offer three types of assistance: (1) providing a parameter design method for piezoelectric actuators to achieve the desired mechanical response; (2) predicting and explaining the dynamic behavior of the PTW wingbeat system; and (3) providing a theoretical foundation for the parameter design and optimization of the wing-actuator pairing in the flapping wing system.

Organically modified mesoporous silica as a performance additive in tubular quenched polypropylene films

Mesoporous silica nanoparticles were synthesized by base-catalyzed hydrolysis of tetraethyl orthosilicate in the water-acetone medium. For surface modification of mesoporous silica, commercially available silane, 3-(trimethoxysilyl)propyl methacrylate was reacted with mono-thioglycerol via 2,2,6,6-tetramethylpiperidin-1-yl)oxidanyl (TEMPO) aided thiol-ene reaction, and the obtained silane was incorporated on the surface of neat mesoporous silica to graft extended alkyl chains terminating in hydroxyl groups. The prepared MSNs were characterized by thermal gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), nitrogen adsorption-desorption analysis, scanning electron microscopy, and dynamic light scattering. These MSNs were compared to conventionally used commercial silica as an additive in tubular quenched polypropylene films (TQPP) for their anti-blocking, thermal, mechanical, optical, and barrier properties. Organic modification of MSNs decreased the blocking force in TQPP films. The mechanical properties including % elongation and tensile strength increased for TQPP films with mesoporous silica, while it decreased for films containing commercial silica. Both modified and unmodified MSNs decreased haze and enhanced gloss in TQPP films, showing improved optical properties as compared to commercial silica particles. In TQPP film with modified MSNs, a reduced value of the water contact angle was obtained, indicating better wettability of the surface of the TQPP film.

Design and identification of a double-acting piezoelectric-hydraulic hybrid actuator

Traditional single-acting piezoelectric-hydraulic hybrid actuators usually have the problem of inertial force caused by flow pulsation of the liquid, which degrades their output performance. To suppress or solve the associated inertial force and enhance its output capabilities, this paper proposes a new type of double-acting piezoelectric-hydraulic hybrid actuator with four check valves acting as mechanical diodes. The new hybrid actuator was fabricated and its output performance was tested. When the voltage is 700 Vp-p and the bias pressure is 2 MPa, the pulsation rates δ of the new actuator at 400 Hz, 500 Hz and 600 Hz are 2.29, 2.08 and 1.78, respectively, while δ of the single-acting hybrid actuator under the same conditions are 10.98, 11.05 and 17.12. Therefore, the liquid pulsation rate of the new hybrid actuator is significantly reduced, which is beneficial for improving the flow uniformity and weakening the influence of inertial force on the hybrid actuator. This strategy ultimately leads to a maximum no-load velocity of 168.1 mm/s at 600 Hz and a maximum blocking force of 141 N at 450 Hz for the new hybrid actuator. In addition, this strategy has the potential to be used in other electrohydrostatic actuators to improve their performance.

Large-scale impacts of small-scale ocean topography

While large-scale seafloor features (e.g. continental slopes, mid-ocean ridges) help shape the broad patterns of ocean circulation, small-scale rough topography (e.g. seamounts, abyssal hills) can also impact the large-scale dynamics in two significant ways. First, they impact the momentum budget through flow steering, flow blocking and drag force, non-local momentum transfer via the generation of radiating internal waves and momentum dissipation by topographically induced turbulence. Second, they impact the density budget. Turbulence induced by flow–topography interactions facilitates ocean overturning circulation by upwelling dense, deep waters which form in polar oceans and sink to the abyss. Rough topography and its associated dynamics are of subgrid scale in Earth systems models (ESMs) and need parameterization for the foreseeable future. A parameterization of the intertwined impacts of flow–topography interactions on momentum and density budgets is currently non-existent, although its importance is well established. Radko (J. Fluid Mech., vol. 961, 2023, A24) provides a novel analytical model for representing the impact of rough seafloor on larger-scale flows, spanning slow to fast flow-speed regimes in homogeneous and multilayer models. The proposed ‘closure’ is in remarkable agreement with high-resolution numerical simulations and provides a crucial step forward in parameterizing the impact of rough topography in coarse-resolution ocean models. Extending the model to the full Navier–Stokes equations, linking it to the density budget and considering more realistic ocean topography are three critical future steps towards implementing Radko's theory in operational ESMs.

穴盘苗基质块仿真粘结参数标定与试验

To accurately simulate the interactions between the plug seedlings and the planter during the planting process and explore the damage mechanism of the plug seedling substrate block, the bonding parameters of plug seedlings substrate block were calibrated by the discrete element method. The physical puncture test showed that the average of maximum force of the cone indenter on substrate block measured by texture analyzer was 4.633 N. A Hertz-Mindlin with the bonding model was established for the substrate block in EDEM software. A virtual calibration experiment was designed with the puncture force of substrate block as the evaluation index. The two-level factorial test and the steepest climbing test were used to screen out the significant parameters and the optimal interval. Then, the Box-Behnken test and the optimization solution were used to obtain the optimal bonding parameter combination of the substrate block particles. Finally, the optimal parameter combination was simulated and verified. The relative error of the maximum puncture force between the simulated value and the measured value was 1.88 %, which indicated that the bonding parameters of the substrate block obtained by calibration were accurate and reliable.

Dynamic characteristics analysis of a novel vibrating screen based on electromechanical coupling simulation

The vibrating screen with statically indeterminate mesh beam structure (VSSIMBS) is a novel type of large vibrating screen, which is widely used in coal preparation plants due to its high strength and processing capacity. In this study, the VSSIMBS motion differential equations were obtained via on Lagrange equation, and the dynamic vibration system model was established. The eccentric block force conditions during the operation were analyzed, and the stable vibrating screen operational conditions were obtained. The electromechanical coupling simulation model of VSSIMBS was built in Simulink, allowing frequency control and vibration synchronization experiments. Experimental frequency control results have shown that when the output characteristics of both motors are either the same or similar, synchronous movement can be achieved. Regarding vibration synchronization, experiment results have shown that when two motors are in synchronous motion, and the power supply of one motor is cut off, they still can operate synchronously. Thus, the experimental results obtained in this study provide a theoretical reference for improving the motion stability of large vibrating screens.

Active Textile Fabrics from Weaving Liquid Crystalline Elastomer Filaments.

Active fabrics, responding autonomously to environmental changes, are the "Holy Grail" of the development of smart textiles. Liquid crystal elastomers (LCEs) promise to be the base materials for large-stroke reversible actuation. The mechanical behavior of LCEs matches almost exactly the human muscle. Yet, it has not beenpossible to produce filaments from LCEs that will be suitable for standard textile production methods, such as weaving. Based on the recent development of LCE fibers, here, the crafting of active fabrics incorporating LCE yarn, woven on a standard loom, giving control over the weave density and structure, is presented. Two types of LCE yarns (soft and stiff) and their incorporation into several weaving patterns are tested, and the "champions" identified: the twill pattern with stiffer LCE yarn that shows the greatest blocking force of 1-2Ncm-1 , and the weft rib pattern with over 10% reversible actuation strain on repeated heating cycles. Reversible 3D shape changes of active fabric utilize the circular weaving patterns that lead to cone shapes upon heating. The seamless combination of active LCE yarns into the rich portfolio of existing passive yarns can be transformative in creating new stimuli-responsive actuating textiles.

Electroactive trilayer actuators taking advantage of the ionic conductivity and self-adhesion of ionic liquid plasticized starch

Ionic liquid (IL) plasticized potato starch and pure amylose films are used as Ionically Conductive Polymers (ICP) for manufacturing electroactive polymer trilayer films able to change of shape upon electrical stimulus, and to work as motion sensors. This promising alternative to fossil fuel based ICPs takes advantage of the water solubility of the starch/IL mixture and its stickiness after casting as films, allowing the design of a solvent free, origami inspired process for its assembly with PEDOT:PSS electrodes.Electroactive free bending motions with an amplitude of deformation Δε of 0.45% are observed upon ± 2 V electrical stimulus for all EAPs, with a 7-fold higher blocking force for the pure amylose based system making it able to lift more than 180 times its weight.Conversely, when tested as sensors, a 4-fold higher sensitivity is observed for the potato starch based EAP, which was comparable to that of fossil-fuel based polymers systems.

Improved ionic and mechanical properties of ion-exchange membrane with an ionic silica network for high-performance ionic polymer-metal composites

Ion-exchange membranes considerably affect the actuation of ionic polymer–metal composites (IPMCs) through ion movement under an applied voltage. To enhance the performances of IPMCs, previous studies have increased the ionic content of the ion-exchange membrane, thereby improving its ionic conductivity and water uptake. Although this increased ionic content enhances IPMC displacement, the increased water uptake diminishes IPMC stiffness, resulting in decreased IPMC blocking force. Therefore, a new approach is needed to resolve the trade-off between displacement and force. Here, we reinforced the Nafion membrane by forming a sulfonated polysilsesquioxane structure inside. The incorporation of this ionic silica network increased the total ion content of the membrane and included silica as a mechanically reinforcing filler. The force of the IPMC can be enhanced despite increased water uptake by the membrane. Therefore, IPMCs were obtained with improvements in displacement and blocking force. Comparison of the IPMCs with commercial Nafion films revealed similar displacement and superior force, demonstrating their applicability. These findings represent a breakthrough in enhancing the actuation of IPMCs while resolving the trade-off between displacement and force.

Improvement of Precision Grasping Performance by Interaction Between Soft Finger Pulp and Hard Nail.

In this study, we investigated the effect of the presence or absence of fingernails on precision grasping using artificial anthropomimetic fingers. We hypothesized that fingernails improve precision grasping performance by increasing the friction coefficient while suppressing fingertip deformation. To test our hypothesis, we developed artificial fingertips, each composed of bone, nail, skin, and soft tissue, and fabricated three types of artificial fingers with different skin softness grades and artificial fingers without nails as the control condition. Pullout experiments of cylindrical objects and T-shaped blocks were conducted using the developed artificial fingertips with and without nails, and the magnitude of the holding force was compared. The nail contributed to object grasping stability because the magnitude of the holding force was significantly increased by the presence of the nail in the artificial fingertip with soft skin. The rate of increase in the magnitude of the holding force of the T-shaped block was more significant (3.10 times maximum) compared with the cylindrical object (1.08 times maximum) because the finger pulp deformation was suppressed by the nail, and the form closure, that is, geometric constraint, was formed for the grasping object. The results of this study show that soft fingertips and hard nails can significantly improve the grasping performance of soft robotic hands. And these results suggest that the human nail improves precision grasping performance by forming geometric constraints on the grasped object, suppressing finger pulp deformation.

The Inexpensive Starting Block Force Plate for Sprinters

The Inexpensive Starting Block Force Plate for Sprinters

Graphene Oxide–Doped PVDF/PSSA/PVP Polymer Blend Polymer Thin Film for Actuation Application

AbstractPVDF/PSSA/PVP blend membrane in the blend ratio of 60/15/25 and 50/30/20 are prepared by solution cast technique. The actuating performance of PVSD/PSSA/PVP 60/15/25 and water uptake (WUP) of blend membrane is found to be higher than blend ratio of 50/30/20. PVDF/PSSA/PVP 60/15/25 characterized by different techniques such as XRD, SEM, FTIR, and electrical conductivity is determined at different frequencies. Ionic–polymer composite (IPC) actuator displays continuously large actuation displacement without back relaxation and with large blocking force at direct current (DC) voltage (1–30 V). In this membrane, PSSA is the polyelectrolyte, PVP is the hydrophilic basic polymer, and PVDF is the hydrophobic polymer.

Photocured Liquid-Crystalline Polymer Electrolytes with 3D Ion Transport Pathways for Electromechanical Actuators

Self-assembly of ionic molecules into hierarchical ordered structures is a promising route to new types of solid electrolytes with enhanced ion transport. Herein, we report a liquid-crystalline polymer electrolyte membrane that contains three-dimensionally (3D) interconnected ionic pathways. To build this membrane, we used wedge-shaped amphiphilic molecules that have two ionic heads and a lipophilic tail. These molecules were combined with a low content of ionic liquid (5.6 wt %) to form a hexagonal columnar phase, where the self-assembled lipophilic cylinders were surrounded by the ionic shell. Photopolymerization of this phase produced flexible nanostructured films with 3D ionic pathways, which can serve as an electrolyte layer in soft robotic actuators. Ionic transport in the 3D pathways leads to shape memory capability as well as durable bending actuation with a voltage-controllable blocking force. Furthermore, we find a significant enhancement of actuation for the nanostructured electrolyte compared with the corresponding amorphous electrolyte.

Ionic electroactive PEDOT:PSS/liquid-crystalline polymer electrolyte actuators: photopolymerization of zwitterionic columnar liquid crystals complexed with a protic ionic liquid

Ionic electroactive polymer actuators based on photopolymerizable zwitterionic columnar liquid crystals complexed with a protic ionic liquid provided a high bending strain and a large blocking force under a voltage of 2 V.

Design and experimental analysis of a high force piezoelectric linear motor

In this paper, the design and experimental analysis of a piezo-motor for applications requiring compact size, high blocking and driving forces are presented. Mechanical design addresses difficulties associated with high integration flexibility and high blocking force for the motor. The technology is inspired from a real inchworm motion and is based on Piezoelectric Actuators (PAs). The proposed Inchworm Motor (IM) consists of an extending mechanism (EM) and two doubled clamping mechanisms (CMs). Theoretically and by using Finite Element Analysis (FEA), the CM is designed in order to obtain high clamping forces between rotor and stator (2500N), while the EM is designed for large displacement (free stroke of 0.01mm) and high force (500N) using PAs. Practically and by using a preliminary low power supply (80V, 1Hz), the working principle of the motor is validated under testing conditions of 300N as a clamping force and 5N as a driving force. The fabricated IM achieves speed of 2.25μm/s. Experimental methods for verifying the theoretical force, calibrating the pre-stressing force and measuring the friction coefficient between the stator and the rotor are proposed. A motor with a weight of 78g and dimensions of 100mm×16mm×7mm ensures full clamping ability when not electrically activated.

Analytical modeling of Ni–Co based multilayer bimorph actuators involving dual insulation layers

This paper proposes a new design of multilayered bimorph electrothermal actuators based on a Ni and Co alloy (Ni–Co) substrate and analytical models to estimate their performance. The proposed bimorph actuator consists of a flexible Ni–Co substrate having high coefficient of thermal expansion (CTE) along with two insulation (low-CTE materials) and Pt heater layers. A multilayered thermo-mechanical model to estimate the tip deflection was derived based on Timoshenko’s classical model for metal bilayers. An analytical model based on the Euler–Bernoulli beam theory was also derived to calculate the blocking force of the multilayered actuators. An appropriate layer composition of the low-CTE layers was derived based on the analytical models and lattice parameters of the adjacent layers: the performance of the bimorph actuator was significantly improved when the low-CTE layers are composed of a dual layer instead of a single layer of SiO2. The analytical solutions of the simplified 3D models were then compared with finite element analysis (FEA) and experimental results. In the comparison of the tip deflection, the analytical solution of the three-layer actuator omitting the Pt heater was similar to the FEA result and the experimental result compensating for the initial dead zone. In the comparison of the blocking force, the analytical solution was also similar to the FEA results, though there was a deviation from the experimental results. Abnormal behavior of the actuator was observed in the experimental result of the blocking force, and the cause was investigated in this study.

Design of multi-stimuli responsive hybrid pneumatic – magnetic soft actuator with novel channel integration

Smart polymeric materials based soft actuators are flexible, lightweight, and can deliver a wide range of actuations. Thus, they are ideal for applications requiring delicate and unconventional motions, such as biomedical and soft robotics. This paper reports a novel multi-stimulus responsive soft actuator that combines the advantages of pneumatic and magnetic systems to achieve multi-plane actuation behavior with high blocking forces at low power input. This novel pneumatic – magnetic (HPM) soft actuator is designed through geometric, nanoparticle alignment, and mechanical criterions. By utilizing 3D printed wires and the compliant matrix, unique micro air channels were manufactured. These distinct internal tubular structures created localized and distinctive bending paths beyond the traditional circular trajectory. Addition of Fe3O4 nanoparticles under a magnetic field exhibited a decrease in stiffness of the elastomer matrix by 85%, increasing the blocking force by 3500%, and decreasing the air pressure input to achieve same degree of actuation. Furthermore, it was observed that the magnetic nanoparticles alignment within the samples enhanced the magnetic deflection and susceptibility. The HPM soft actuator demonstrated its practicability through a gripper system to lift objects greater than its initial width and 3.4 times its own mass. Multi-plane actuation was also demonstrated to complete a circuit and light up an LED. A 5 legged “star” shaped HPM soft actuator was also fabricated to exhibit the multi-stimuli response, reacting to both pneumatic and magnetic stimuli in both air and water environments. Using the advantage of the multi-plane pneumatic/magnetic actuation, such hybrid soft actuator has the capability to be utilized in biomimicking and unconventional applications where unique maneuverability is required.

Modeling of projectile penetrating fiber-reinforced concrete via the continuum discontinuum element method

In this paper, the projectile penetrating fiber-reinforced concrete (FRC) is modeled and simulated by the continuum discontinuum element method (CDEM) and a fiber-block interpolation coupling algorithm. The Mohr–Coulomb constitutive model is applied to the blocks to calculate the block forces, and the Mohr–Coulomb criterion and the maximum tensile criterion are applied to estimate the failure of contact surfaces. Numerical simulations of projectiles penetrating plain concrete and FRC with 1 to 3 vol% are performed. We verify the validity of the model by predicting the crack morphology and penetration depth for plain concrete and FRC, which are in agreement with experimental results. Detailed images of crack surfaces in the concrete blocks caused by projectile penetration are included. The effects of fiber content on crack width are analyzed. The results indicate that the normalized widths of the cracks approximately satisfy the Weibull distribution. Compared with plain concrete, the addition of fibers results in a reduction in both the expectation and variance of crack widths. However, the degree of reduction weakens as fiber content increased.

Double-Acting Soft Actuator for Soft Robotic Hand: A Bellow Pumping and Contraction Approach.

When compressing a soft bellow, the bellow will contract and pump out the fluid inside the bellow. Utilizing this property, we propose a novel actuation method called compressing bellow actuation (CBA), which can output fluidic power and tendon-driven force simultaneously. Based on the CBA method, a double-acting soft actuator (DASA) combining fluidic elastomer actuator (FEA) and tendon-driven metacarpophalangeal (MCP) joint is proposed for robotic finger design. The proposed DASA exhibits both compliance and adaptiveness of FEAs, and controllability and large output force of the tendon-driven methods. The fluid in the bellow can be either air or water or even integration of the two, thus constituting three different actuation modes. Mathematical modeling of the relationship between bellow compression displacement and DASA’s bending angle is developed. Furthermore, experimental characterizations of DASA’s bending angle and blocking force are conducted at different actuation modes. The double-acting method can availably promote the bending angle of an FEA by up to 155%, and the blocking force by up to 132% when the FEA is water-filled. A soft robotic hand with a forearm prototype based on the DASA fingers is fabricated for the demonstration of finger motion and gripping applications.

Fabrication and performance analysis of high-performance cylindrical ionic polymer-metal composite actuators with various diameters

Ionic polymer-metal composites (IPMCs) are electroactive polymer actuators that have been used as artificial muscles and have broad application prospects. In order to further improve the actuation performance of cylindrical IPMCs, Nafion rods with different diameters were prepared by extrusion process, and cylindrical IPMCs with high-quality Pt electrode layers were prepared by electroless plating in this study. The electrochemical properties and actuation performance of cylindrical IPMCs with various diameters were investigated. The tests show that the prepared cylindrical IPMCs have excellent electromechanical properties. As diameter increases, the blocking force and counter back-relaxation ability both increase significantly. Furthermore, the IPMCs with diameter of 3.0 mm under a DC voltage exhibits a superior blocking force (323.9 mN) and excellent power density (up to 139.41 W m−3). Moreover, the thick cylindrical IPMC can lift objects 400 times its weight, demonstrating exceptional load capacity, which shows great prospect of realizing artificial muscles.