Large Contraction Ratio Research Articles

2-dimensional impact-damping electrostatic actuators with elastomer-enhanced auxetic structure

Biomimetic robots yearn for compliant actuators that are comparable to biological muscle in both functions and structural properties. For that, electrostatic actuators have been developed to imitate bio-muscle in features of fast response, high power, energy-efficiency, etc. However, those actuators typically lack impact damping performance, making them vulnerable and unstable in real applications. Here, we present auxetic electrostatic actuators that address this issue and demonstrate muscle-like performance by using elastomer-enhanced auxetics and electrostatic zipping mechanism. The proposed actuators contract linearly on applied voltage, producing large actuation strength (15 N) and contraction ratio (59%). Fabricated from readily available materials, our prototypes can quickly attenuate vibrations caused by impacts and absorb shock energy in 0.3 s. Furthermore, leveraging their 2-dimensional working mode and self-locking mechanism, a stiffness-changing muscle for a robotic arm and an active tensegrity device exemplify the potential applications of auxetic electrostatic actuators to a wide range of bionic robots.

Unsteady flow characteristics in an over-under TBCC inlet during mode transition under unthrottled and throttled conditions

The study presents an experimental exploration into the mode transition of an over-under TBCC (Turbine-Based Combined Cycle) inlet, with a specific emphasis on the flow characteristics at off-design transition Mach number. A systematic investigation was undertaken into the mode transition characteristics in both unthrottled and throttled conditions within a high-speed duct, employing high speed Schlieren and dynamic pressure acquisition systems. The results show that the high-speed duct faced flow oscillations primarily dictated by the separation bubble near the duct entrance during the downward rotation of splitter, leading to the duct’s unstart under the unthrottled condition. During the splitter’s reverse rotation, a notable hysteresis of unstart/restart of the high-speed duct was observed. Conversely, hysteresis vanishes when the initial flowfield nears the critical state owing to downstream throttling. Moreover, the oscillatory diversity, a distinctive characteristic of the high-speed duct, was firstly observed during the mode transition induced by throttling. The flow evolution was divided into four stages: an initial instability stage characterized by low-frequency oscillations below 255 Hz induced by shock train self-excitation oscillation and high-frequency oscillations around 1367 Hz caused by the movement of separation bubble. This stage is succeeded by the “big buzz” phase, comprised of pressure accumulation/release within the overflow-free duct and shock motion outside the duct to retain dynamic flow balance. The dominant frequency escalated with the increase of the internal contraction ratio in the range of 280 Hz to 400 Hz. This was followed by a high-frequency oscillation stage around 453 Hz dominated by a large internal contraction ratio with low pulsating energy, accompanied by a continuous supersonic overflow. Lastly, as the splitter gradually intersected the boundary layer of the first-stage compression surface, the capture area and the turbulence intensity of the incoming flow underwent a sudden shift, leading to a more diverse flow oscillation within the duct, manifested as various forms of mixed buzz.

Liquid Crystal Elastomer Hollow Fibers as Artificial Muscles with Large and Rapid Actuation Enabled by Thermal‐Pneumatic Enhanced Effect

AbstractLiquid crystal elastomer (LCE) has large and reversible deformation under stimulation, making it an ideal material for artificial muscles. Currently, multi‐stimulus responsive LCE actually responds to each stimulus independently rather than responding to several stimuli simultaneously. Achieving an enhanced effect from concurrent stimuli is still a challenge, which requires a new stimulus‐response mechanism. This work develops a novel and facile solvent evaporation‐assisted template method to prepare LCE hollow fiber (LCEHF) with axial alignment. Taking advantage of the enhanced effect of heat‐induced phase transition and mechanical force‐induced orientation transition of mesogens, the LCEHF under both heat and pressure can produce a large contraction ratio of ≈50%, which is higher than 42% of thermal stimulation or 27% of pneumatic stimulation. It can also enhance the respective response and recovery speed of LCEHF to 300 and 3700 times of pneumatic actuation. Additionally, the enhanced effect lowers the actuation temperature much below the phase transition temperature, imparting LCEHF with high mechanical performance during actuation. Furthermore, the dual thermal‐pneumatic responsive LCEHF can mimic human biceps and cause large and rapid bending of an artificial arm reversibly. This new actuation methodology sheds new light on improving LCE actuation performance and broadens its application scenarios.

High-Stroke, High-Output-Force, Fabric-Lattice Artificial Muscles for Soft Robots.

Artificial muscles, providing safe and close interaction between humans and machines, are essential in soft robotics. However, their insufficient deformation, output force, or configurability usually limits their applications. Herein, this work presents a class of lightweight fabric-lattice artificial muscles (FAMs) that are pneumatically actuated with large contraction ratios (up to 87.5%) and considerable output forces (up to a load of 20kg, force-to-weight ratio of over 250). The developed FAMs consist of a group of active air chambers that are zigzag connected into a lattice through passive connecting layers. The geometry of these fabric components is programmable to convert the in-plane lattice of FAMs into out-of-plane configurations (e.g., arched and cylindrical) capable of linear/radial contraction. This work further demonstrates that FAMs can be configured for various soft robotic applications, including the powerful robotic elbow with large motion range and high load capability, the well-fitting assistive shoulder exosuit that can reduce muscle activity during abduction, and the adaptive soft gripper that can grasp irregular objects. These results show the unique features and broad potential of FAMs for high-performance soft robots.

Development of a High Flow Rate Soft Pump Driven by Intersected Twisted Artificial Muscles Units

Small soft pumps are extensively explored in medical fields and soft robotics, but the insufficient flow rate constrains their applications. In this article, an intersected twisted artificial muscle unit (ITAMU) is proposed to achieve a large contraction ratio, which is adapted to drive the developed soft pump, and characteristics of high flow rate and no noise pollution are achieved. The configuration and principle of the ITAMU and the soft pump are depicted. Besides, the contraction ratio of ITAMU and the flow rate of the soft pump are calculated theoretically. Then, the prototypes are manufactured and tested. The results indicate that the maximum contraction ratio of ITAMU reaches 41.2%, and the output force is 3.27 N. Ultimately, the experiments on the flow rate and pressure of the soft pump are carried out. The maximum flow rate is 680 mL/min, and the pressure reaches 2.3 kPa. To sum up, the proposed soft pump exhibits a high flow rate, which shows its application prospect in the field like soft exploration robots.

Oscillations in Rectangular Supersonic Inlets with Large Internal Contraction Ratio

Increasing the internal contraction ratio (defined as the area ratio of the duct entrance and throat, denoted as ICR) can improve the operating performance of a variable geometry supersonic inlet, however, excessive ICR typically will bring the inlet into an unstarted state with oscillation. To uncover the underlying mechanism of a large ICR-induced oscillatory-unstarted phenomenon, we employed a high-speed schlieren and dynamic pressure acquisition system, and experimentally examined the flowfields of a rectangular supersonic inlet with different ICRs of 1.5, 2.0, 2.5, and 3.0 in the wind tunnel at a freestream Mach number of 2.9. The inlet stayed unstarted while the ICR ranged from 2.0 to 3.0, and the flowfield had three features. First, the inlet flowfields showed high- and broadband-frequency oscillations, whose dominant frequency and oscillatory amplitude increased with ICR. Second, the inlet flowfields revealed similar oscillatory flow structures, which contained the periodic variation of the ramp-side boundary layer separation, cowl-side flow spillage, and shock train in the internal contraction part. Third, the unstarted flow structure and oscillatory phenomenon mainly occurred upstream of the inlet geometric throat, downstream of which the main flowfield was supersonic. To characterize these three features, we proposed a self-excited oscillatory model consisting of a disturbing source, a disturbing feedback terminal, and a signal feedback loop. Practically, the disturbing source is a scale variation of the entrance separation, the disturbing feedback terminal is an aerodynamic throat near the geometric throat, and the signal feedback loop is composed of communication pathways of shock train motion, acoustic waves, and convection waves. With this model, we explained the underlying mechanism of the high- and broadband-frequency characteristics of the oscillation caused by large ICR, and the ICR’s influence on the flow oscillation.

Ultrafast, High‐Contractile Electrothermal‐Driven Liquid Crystal Elastomer Fibers towards Artificial Muscles

Liquid crystal elastomer (LCE) fibers are capable of large and reversible deformations, making them an ideal artificial muscle. However, limited to stimulating source and structural design, current LCE fibers have not yet achieved both large contraction ratio and fast contraction rate to perform the intense motion. In this work, electrothermal-responsive liquid metal (LM) containing LCE (LM-LCE) fibers is reported. By introducing flexible liquid metal, LM-LCE fibers retain deformability with a large contraction ratio similar to that of pure LCE fibers and are endowed with electrical responsiveness. Applying precisely controlled electrical stimulation, the contraction ratio and rate of LM-LCE fibers can be programmed by adjusting voltage value and pulse time. Under electrical stimulation at 1.25V cm-1 , 0.1 s, LM-LCE fibers can produce over 40% contraction ratio at an ultrafast contraction rate of up to 280% s-1 . Furthermore, LM-LCE fibers mimic human triceps muscle and can conduct precise ball shooting. LM-LCE fibers with excellent contraction ratio and rate extend their functionality as artificial muscles to perform intense movements and are expected to enrich the challenging applications of soft robots.

Armor-Based Stable Force Pneumatic Artificial Muscles for Steady Actuation Properties.

In this article, a novel actuator called armor-based stable force pneumatic artificial muscle (AS-PAM) is presented. AS-PAM has a sealed chamber made of polygonal parts and film, which helps the actuator to be lightweight (∼100 g) and achieve a large contraction ratio (>60%). It has an armor and a constraint to guide its motion, which keeps its force output [6.25 N/(cm2·bar)] stable over its operating range (<10% deviation). An analytical model is presented to predict and control the behavior of the actuator, and various experiments were conducted to show the validity of the model. Afterward, a gripper using the actuators is presented to illustrate how it can be used in real applications. With its characteristics, the actuator shows interesting behaviors that cannot be found in other soft pneumatic actuators, and it would allow AS-PAM to expand the range of applications in which soft robots cooperate with humans.

Development of the Ultralight Hybrid Pneumatic Artificial Muscle: Modelling and optimization.

Pneumatic artificial muscles (PAMs) are one of the key technologies in soft robotics, and they enable actuation in mobile robots, in wearable devices and exoskeletons for assistive and rehabilitative purposes. While they recently showed relevant improvements, they still present quite low payload, limited bandwidth, and lack of repeatability, controllability and robustness. Vacuum-based actuation has been recently demonstrated as a very promising solution, and many challenges are still open, like generating at the same time a large contraction ratio, and a high blocking force with enhanced axial stiffness. In this paper, a novel Ultralight Hybrid PAM (UH-PAM), based on bellow-type elastomeric skin and vacuum actuation, is presented. In particular, open-cell foam is exploited as a structural backbone, together with plastic rings, all embedded in a thin skin. The design and optimization combine numerical, analytical, and experimental data. Both static and dynamic analysis are performed. The weight of the optimized actuator is only 20 g. Nevertheless, a contraction ratio up to 50% and a maximum payload of 3 kg can be achieved. From a dynamic point of view, a rise time of 0.5 s for the contraction phase is observed. Although hysteresis is significant when using the whole contraction span, it can be reduced (down to 11.5%) by tuning both the vacuum range and the operating frequency for cyclic movements. Finally, to demonstrate the potentiality of this soft actuation approach, a 3 DoFs Stewart platform is built. The feasibility of performing smooth movements by exploiting open-loop control is shown through simple and more complex handwriting figures projected on the XY plane.

Restart Processes of Rectangular Hypersonic Inlets with Different Internal Contraction Ratios

In this paper, the restart processes of two generic rectangular hypersonic inlets with different internal contraction ratios have been experimentally studied under a freestream Mach number of 5.0. The experimental results show that without downstream throttling, both inlets start successfully after the flowfield establishment of the wind tunnel. To obtain the restart processes of the two inlets, they are initially set at an unstarted state by a large downstream throttling ratio. Then, the throttling ratio is continuously decreased. For the inlet with a small internal contraction ratio, the restart process undergoes four stages: stable buzz, intermittent buzz, reestablishment of wave system in the inlet, and unthrottled flow; whereas for the inlet with a large contraction ratio, the internal flow cannot be normally reestablished after the intermittent buzz stage because a large-scale separation bubble consistently stands ahead of the inlet. That is, it cannot be restarted. In the stage of the intermittent buzz, there is a probability of the appearance of a quasi-steady flowfield when the pressure in the inlet reaches its maximum value, and the separation shock almost impinges on the cowl lip. For both inlets, the probability of buzz decreases continuously with time, and then it suddenly disappears. Furthermore, for the inlet with a large contraction ratio, two kinds of flowfields (that is, started or unstarted) occur at the same downstream throttling ratio and upstream flow conditions, which indicates that the inlet operates in the dual-solution region and the actual operating state of the inlet significantly depends on the historical flow. Therefore, the evaluation of hypersonic inlet starting capability must be examined carefully.

Flat Inflatable Artificial Muscles With Large Stroke and Adjustable Force– Length Relations

The performance of inflatable artificial muscles depends greatly on their designs and the output shapes resulting from the geometric constraints. Although there have been attempts to apply physical constraints on the air chamber to achieve larger stroke lengths and increased force-length ratios, it has been difficult to achieve the above two goals while maintaining a compact form factor. In this article, we propose flat inflatable artificial muscles that have large contraction ratios (up to 0.5) and show increased forces in wider ranges of contractions by adding an internal geometric constraint. Addition of an external constraint, such as rigid plates, further increased the maximum contraction ratio (up to 0.553) through a synergistic effect. We show that various force-length relations can be achieved by adjusting the height of the plates. Theoretical models based on the geometry and the principle of virtual work are experimentally validated using actuator prototypes made of heat-sealable plastic sheets. Also, compact capacitive sensors are integrated in design for proprioceptive feedback of the proposed actuators, and their feasibility and effectiveness are experimentally evaluated through closed-loop control.

Straight-Fiber-Type Artificial Muscle Deformation Under Pressurization

Currently, researchers are actively conducting studies and experiments on soft robots due to their increasing abilities to cooperate with humans. Particular attention is being paid to pneumatic artificial muscles because of their flexibility and relatively light weight as actuators. Among the multiple types of pneumatic artificial muscles, the straight-fiber-type has a structure, which is typically configured in a cylindrical rubber tube reinforced by fibers in the axial direction. The application of an internal pressure expands the tube in the radial direction, while it contracts in the axial direction. In this study, the deformation of such tubes was theoretically analyzed. First, the differential equation for the cylinder profile was derived, and the solution then obtained in the closed form, when the rubber is relatively soft enough compared to the fiber. Finally, for a large enough inner pressure, the profile of the reinforced rubber cylinder was derived from the incomplete elliptic integral. Moreover, the spring constant, the contraction ratio, and the maximum stress were obtained regarding the cylinder length. The spring constant linearly increased with the initial length of the cylinder. The contraction ratio also increased with the initial cylinder length up to 54.3%. The maximum stress was found to be related to the elastic modulus of the rubber but not to the inner pressure; when the cylinder length was three to five times larger than the initial diameter of the cylinder, the rubber exhibited small a maximum stress and large contraction ratio.

Origami-Based Vacuum Pneumatic Artificial Muscles with Large Contraction Ratios.

A novel linear actuator called origami-based vacuum pneumatic artificial muscle (OV-PAM) is proposed in this study that can produce large forces (>400 N) with a contraction ratio >90% of the active length of the actuator. Moreover, some of the designs presented in this article can lift large loads with large contraction ratios at extremely low vacuum pressure (≈10 kPa). This actuator consists of a sealed origami film chamber connecting a polygonal top and bottom plate with evenly spaced transversal reinforcements that prevent the chamber from contracting laterally at certain points of the actuator under vacuum pressure. As vacuum pressure is applied, both a tension force in the walls and a vertical force on the bottom plate of the actuator generate a large contractile force, and the force on the bottom plate can produce a consistent force throughout the entire motion. A quasistatic analytical model was developed that can accurately predict the behavior of the actuator and that can be used for actuator design. OV-PAMs are lightweight, have large contractile forces throughout their entire motion and large contraction ratios. It can also produce large forces at low pressures with large cross-sectional areas. Their versatility could make them well suited for a wide range of applications. They could take us closer to a future where robots can cooperate with humans to shape a better future.

A Novel Soft Pneumatic Artificial Muscle with High-Contraction Ratio.

There is a growing interest in soft actuators for human-friendly robotic applications. However, it is very challenging for conventional soft actuators to achieve both a large working distance and high force. To address this problem, we present a high-contraction ratio pneumatic artificial muscle (HCRPAM), which has a novel actuation concept. The HCRPAM can contract substantially while generating a large force suitable for a wide range of robotic applications. Our proposed prototyping method allows for an easy and quick fabrication, considering various design variables. We derived a mathematical model using a virtual work principle, and validated the model experimentally. We conducted simulations for the design optimization using this model. Our experimental results show that the HCRPAM has a 183.3% larger contraction ratio and 37.1% higher force output than the conventional pneumatic artificial muscle (McKibben muscle). Furthermore, the actuator has a compatible position tracking performance of 1.0 Hz and relatively low hysteresis error of 4.8%. Finally, we discussed the controllable bending characteristics of the HCRPAM, which uses heterogeneous materials and has an asymmetrical structure to make it comfortable for a human to wear.

Determination method of initial gas desorption law of coal based on flow characteristics of convergent nozzle

The amount of initial gas release after the destruction of coal by ground stress relates closely to the outburst danger. In this paper, the following method was proposed to accurately determine the initial gas desorption law of coal. First, real-time temperature and pressure data of sealed coal sample tank after the sudden exposure of coal that had reached adsorption equilibrium within the tank were collected first via a high-precision, high-frequency response sensor. Then, the mass flow of gas passing through the pneumatic component at different times was calculated according to flow rate characteristics of pneumatic component that communicated with the atmosphere on the tank. In this process, it is determined that a convergent nozzle with a larger contraction ratio should be used as the channel for gas desorption and release. Moreover, in light of the characteristics of the testing process, the existing parameters that characterize the flow characteristics of pneumatic component were optimized and measured. Finally, the initial gas desorption laws of two coal samples with different metamorphic degrees were measured and analyzed under two pressures using three different-sized convergent nozzles.

Coherent structures at different contraction ratios caused by two spill-through abutments

ABSTRACTDetached eddy simulation (DES) at a channel Reynolds number of 45,000 is used to investigate the coherent structures forming around spill-through abutments located at opposite sides of a rectangular channel which contract the flow section. Changes in the coherent structures are investigated for two contraction ratios at two different scour stages. It is observed that at the small contraction ratio the coherent structures forming around the abutments are similar to the ones observed for isolated abutments. However, at the larger contraction ratio there are important changes in these structures. At the beginning of the scour process two counter rotating contraction vortices form close to the bed at the centre of the channel, oriented in the streamwise direction. At this initial scour stage, the upstream part of the main horseshoe vortex is incoherent. On the other hand, at a later stage of scour with the development of the scour hole contraction vortices disappear and the main horseshoe vortex regains its original shape.

Numerical Study on the Effects of Contraction Ratio in a Two-Phase Flow Injection Nozzle

The Euler-Euler numerical method was used to investigate the effects of contraction ratio on twophase flow mixing with mass transfer in the flow injection nozzle. The geometric shape of the nozzle was modified to improve carbonation efficiency. A gas inlet hole was created to increase the flow mixing of CO2 with water. A nozzle throat was also introduced to increase the gas dissolution by increasing flow rates. Various contraction ratios of nozzle throat, inlet gas and liquid velocities, and gas bubble sizes were employed to determine their effects on gas hold-up, gas concentration, and mass transfer coefficient. Results revealed that the flow injection nozzle with high contraction ratios improved carbonation because of high gas hold-up. Gas concentration was directly related to contraction ratio and gas flow velocities. Carbonation reduced when high liquid velocities and large gas bubbles were employed because of inefficient flow mixing. This study indicated that flow injection nozzle with large contraction ratios were suitable for carbonation because of their ability to increase gas hold-up, gas concentration, and mass transfer coefficient.

Dissipation of Alfvén wave pulses propagating along dipole magnetic tubes with reflections at the ionosphere

A ratio of the maximal and minimal cross sections of the magnetic tube (contraction ratio) is a crucial parameter which affects very strongly on reflections of MHD wave pulses propagating along a narrowing magnetic flux tube. In cases of large contraction ratios of magnetospheric magnetic tubes, the wave energy flux at the ionospheric boundary can be rather small. Therefore the dissipation of the wave perturbations can be very weak for each reflection, in spite of a finite conductivity of the planet’s ionosphere. The dissipation is stronger for the pulses with shorter wave scales. Because of that, Alfvén wave pulses with sufficiently long wave scales have a very small energy loss for each reflection at the conducting ionosphere, and thus, they have many reflections without a noticeable decrease of their amplitude. This effect related to converging magnetic lines is dependent very strongly on the polarization of the Alfvén wave. In case of a dipole magnetic field, the effect is most pronounced for wave pulses characterized by velocity and magnetic perturbations in the meridional plane.

Electrochemornechanical deformation in polyaniline and poly( o-methoxyaniline)

pH dependencies of electrochemomechanical deformation (ECMD) and standard redox potential, E 1/2 in poly( omethoxyaniline) (PmAn) have been studied between the states of leucoemeraldine and emeraldine salts. It is found that the magnitude of ECMD is constant of ca. 3% at pH > 2.0 and decreases gradually below the pH 2.O. The result is explained by the redox reactions of anion doping/dedoping process and proton exchange process at pH > 2.0 and pH < 2.0, respectively, taking the pH dependencies of E 1/2 into consideration. A surprisingly large contraction ratio of more than 20% is obtained at the thickness direction of cast films in ECMD of polyaniline/HCl system. This fact is accounted by the anisotropic shrinking of cast film during the dry process.

Effects of turbulence on flame radiation from diffusion flames

Enhancement of heat transfer by flame radiation in furnaces can increase the efficiency and decrease the volume of a furnace. Flame radiation from turbulent diffusion flames, which prevail in furnaces, depends both on the chemistry of soot formation and the turbulent mixing processes of the flow. Previous work has shown that thermochemical effects (i.e. fuel or air preheating, oxygen enhancement, etc.) related to soot formation chemistry and flame radiation can be correlated in turbulent diffusion flames by using smoke-point properties of laminar diffusion flames. This work addresses the other part of the turbulent flame problem which involves the effects of the turbulent flow field on soot formation and radiation for given fuel and thermochemicla conditions. Radiation measurements in turbulent momentum, controleld jet flames were made by using five nozzles (1 mm, 1.5 mm, 2 mm, 3 mm, 4 mm) having a large contraction ratio and burning three fuels: acetylene (C 2 H 2 ), propylene (C 3 H 6 ) and methane (CH 4 ). By employing the relatively well understood flow of a turbulent jet flames, the following fundamental issue was addressed: it soot formation in turbulent diffusion flames determined by the overall residence (macroscale) time or by the straining rate of the small (Kolmogorov) scales wherein combustion occurs? Correlations of the present data obtained by using a simple soot formation and radiation model support the small scale (Kolmogorov) straining rate hypothesis.