Pinch Mode Research Articles

True pinch mode of magnetorheological fluids

Abstract Magnetorheological (MR) fluids are representatives of smart materials. They react to magnetic fields by developing a yield stress. The effect has been employed in real-world applications such as automotive chassis systems or optical finishing. By convention, MR devices can be operated in at least one of the fundamental modes: flow, shear, squeeze, gradient pinch of which the former has been the least studied and understood. In pinch mode, the material in the flow channel is exposed to non-uniform magnetic fields in the direction parallel to fluid flow. As a result, only the volume of MR fluid near the channel walls are energized to modify the particular material property (yield stress). The result is the channel’s effective diameter change. The behavior of the material in pinch mode is unique and unseen in the other controllable fluids. To study the material’s characteristics in the specific mode, the authors developed a novel circuit concept for energizing the material in an effort to achieve the ’true-zero’ pinch mode magnetic behavior. Contrary to the existing pinch mode valve concepts, the concept valve allows to achieve zero magnetic flux density in the center of the flow channel regardless of the current level. To test the hypothesis a prototype valve was modeled, manufactured and tested across a range of external (flow rate, current/magnetic flux) stimuli. The obtained results yield sufficient evidence proven by results of magnetic simulations to support the underlying hypothesis. The experimental results illustrate the pinch mode type behaviour, i.e. the slope change in the pressure vs flow rate characteristics.

Novel Hydro-Pneumatic Interconnected Suspension Integrating Pipe-Connected Magnetorheological Valve Designed Based on Magnetic Gradient Pinch Mode—Experimental Study and Modelling

Novel Hydro-Pneumatic Interconnected Suspension Integrating Pipe-Connected Magnetorheological Valve Designed Based on Magnetic Gradient Pinch Mode—Experimental Study and Modelling

Theoretical analyses and experimental study on the factors influencing the pressure resistance of the magnetorheological grease seal with pinch mode pole piece

This paper mainly focuses on experimental research and theoretical analysis on the pressure resistance capability of magnetorheological grease rotary shaft sealing with pinch mode pole piece structure. Combining magnetorheological grease and pinch mode pole piece structure, the using of permanent magnet as magnetic source is aiming to reduce the lag of yield stress establishment and release. Herein, the micro-nano composite magnetorheological grease was prepared. Right after the synthesis process, its magnetization properties and rheological properties were scientifically and systematically characterized. The influence of different gaps and tooth widths on the magnetic induction intensity is analyzed by finite element method. Based on the theoretical method, the pressure resistance capacity induced by magnetic force is calculated. By comparing the theoretical calculation and experimental results of the pressure resistance, the cause of error and failure is analyzed.

Grasping the behavior of magnetorheological fluids in gradient pinch mode via microscopic imaging

Magnetorheological (MR) fluids are suspensions of micrometer-sized ferromagnetic particles in a carrier fluid, which react to magnetic fields. The fluids can be operated in several fundamental modes. Contrary to the other modes, the rheology and microstructure formation of the MR fluid in the gradient pinch mode have been studied to a far lesser extent. The magnetic field distribution in the flow channel is intentionally made non-uniform. It is hypothesized that the Venturi-like contraction is achieved via fluid property changes, leading to a unique behavior and the presence of a pseudo-orifice. The main goal is to investigate the presence of the Venturi-like contraction effect in the fluid by means of optical imaging and hydraulic measurements. To accomplish the goal, a unique test rig has been developed including a fluorescence microscope and MR valve prototype. The Venturi-like contraction hypothesis was confirmed. The results indicate that the effective flow channel size decreases by 92% at the maximum magnetic flux applied. This has a direct impact on the flow characteristics of the MR valve. The variation of the pressure–flow rate curve slope with magnetic field was demonstrated. The results provide valuable information for understanding the rheology and microstructure formation mechanism in MR fluids in the pinch mode.

Assessment of the Dynamic Range of Magnetorheological Gradient Pinch-Mode Prototype Valves

Magnetorheological (MR) fluids have been known to react to magnetic fields of sufficient magnitudes. While in the presence of the field, the material develops a yield stress. The tunable property has made it attractive in, e.g., semi-active damper applications in the vibration control domain in particular. Within the context of a given application, MR fluids can be exploited in at least one of the fundamental operating modes (flow, shear, squeeze, or gradient pinch mode) of which the gradient pinch mode has been the least explored. Contrary to the other operating modes, the MR fluid volume in the flow channel is exposed to a non-uniform magnetic field in such a way that a Venturi-like contraction is developed in a flow channel solely by means of a solidified material in the regions near the walls rather than the mechanically driven changes in the channel’s geometry. The pinch-mode rheology of the material has made it a potential candidate for developing a new category of MR valves. By convention, a pinch-mode valve features a single flow channel with poles over which a non-uniform magnetic field is induced. In this study, the authors examine ways of extending the dynamic range of pinch-mode valves by employing a number of such arrangements (stages) in series. To accomplish this, the authors developed a prototype of a multi-stage (three-stage) valve, and then compared its performance against that of a single-stage valve across a wide range of hydraulic and magnetic stimuli. To summarize, improvements of the pinch-mode valve dynamic range are evident; however, at the same time, it is hampered by the presence of serial air gaps in the flow channel.

Magnetorheological fluids subjected to non-uniform magnetic fields: experimental characterization

Magnetorheological (MR) fluids are suspensions of fine, low-coercivity, high-magnetizable particles in a continuous liquid phase. When subjected to magnetic field, the material exhibits a rapid change in the apparent viscosity of several orders of magnitude. This unique capability has been successfully exploited in automotive semi-active suspensions systems or systems for manufacturing high quality optics. In a majority of the existing systems, the rheology of MR fluids is controlled by an external uniform field oriented perpendicularly to the fluid flow direction. In general, it is an inherent feature of MR systems operating in flow, shear or squeeze modes, respectively. There is an experimental evidence that the behavior of MR fluids in the so-called pinch-mode (in which the fluid is subjected to non-uniform magnetic field distributions) clearly stands out against the remaining three operating modes. With the predecessors, the flow through the channel occurs once a pressure across it exceeds the field-dependent threshold pressure. For comparison, in pinch mode valves the magnetic flux energizes mostly the layers of the materials near the channel walls. The outcome is a change in the channel’s effective diameter achieved solely via material means without changing its geometry. To study the fluid’s unique behaviour in the pinch mode, the authors designed a prototype valve assembly and examined several fluid formulations of various particle concentration levels across a wide range of external (velocity, magnetic field density) stimuli in an organized effort to further comprehend the phenomenon. The obtained data indicate that the magnitude of the particular effect does not only depend on the magnitudes of the magnetic stimuli but also on the particle concentration; the smaller the concentration of particles the more pronounced the pinch mode like behavior is. In general, the authors believe that the study may provide guidelines as to the selection of fluid formulations for developing novel valveless actuators utilizing MR fluids operating in pinch mode.

Kinetic Simulations of Instabilities and Particle Acceleration in Cylindrical Magnetized Relativistic Jets

Relativistic magnetized jets, such as those from AGN, GRBs, and XRBs, are susceptible to current- and pressure-driven MHD instabilities that can lead to particle acceleration and nonthermal radiation. Here, we investigate the development of these instabilities through 3D kinetic simulations of cylindrically symmetric equilibria involving toroidal magnetic fields with electron–positron pair plasma. Generalizing recent treatments by Alves et al. and Davelaar et al., we consider a range of initial structures in which the force due to toroidal magnetic field is balanced by a combination of forces due to axial magnetic field and gas pressure. We argue that the particle energy limit identified by Alves et al. is due to the finite duration of the fast magnetic dissipation phase. We find a rather minor role of electric fields parallel to the local magnetic fields in particle acceleration. In all investigated cases, a kink mode arises in the central core region with a growth timescale consistent with the predictions of linearized MHD models. In the case of a gas-pressure-balanced (Z-pinch) profile, we identify a weak local pinch mode well outside the jet core. We argue that pressure-driven modes are important for relativistic jets, in regions where sufficient gas pressure is produced by other dissipation mechanisms.

Eccentric High-Force Soft Pneumatic Bending Actuator for Finger-Type Soft Grippers

Abstract Soft pneumatic actuators (SPAs) play an important role in leading the development of soft robotics. However, due to the inherent characteristics of soft materials, the low driving force limits the application of SPAs. This study presents a high-force soft pneumatic bending actuator (SPBA) that consists of a spring, an eccentric silicone cylinder, and a limiting fiber. Based on the Neo-Hookean model, a theoretical model is established to predict the relationship between the bending angle and the pressure of SPBA. Furthermore, we characterize the performance of SPBA in terms of the bending capability, tip force, as well as response time. The results demonstrate the effectiveness of the theoretical model, as well as the high tip force (10.2 N) and fast response capability of SPBA. Finally, SPBAs are used to construct a three-finger soft gripper. The load capacity of the gripper is proofed, which indicates that the gripping force of the gripper increases with the pressure of the fingers and the diameter of the object. The gripping test of the gripper is performed. The result shows that the gripper with the pinching mode can grip objects of various sizes and shapes in the air and underwater, and the gripper with enveloping mode can grip objects with weight up to 1.25 kg.

Stability and tip streaming of a surfactant-loaded drop in an extensional flow. Influence of surface viscosity

We study numerically the nonlinear stationary states of a droplet covered with an insoluble surfactant in a uniaxial extensional flow. We calculate both the eigenfunctions to reveal the instability mechanism and the time-dependent states resulting from it, which provides a coherent picture of the phenomenon. The transition is of the saddle-node type, both with and without surfactant. The flow becomes unstable under stationary linear perturbations. Surfactant considerably reduces the interval of stable capillary numbers. Inertia increases the droplet deformation and decreases the critical capillary number. In the presence of the surfactant monolayer, neither the droplet deformation nor the stability is significantly affected by the droplet viscosity. The transient state resulting from instability is fundamentally different for drops with and without surfactant. Tip streaming occurs only in the presence of surfactants. The critical eigenmode leading to tip streaming is qualitatively the same as that yielding the central pinching mode for a clean interface, which indicates that the small local scale characterizing tip streaming is set during the nonlinear droplet deformation. The viscous surface stress does not significantly affect the droplet deformation and the critical capillary number. However, the damping rate of the dominant mode considerably decreases for viscous surfactants. Interestingly, shear viscous surface stress considerably alters the tip streaming arising in the supercritical regime, even for very small surface viscosities. The viscous surface stresses alter the balance of normal interfacial stresses and affect the surfactant transport over the stretched interface.

Optomechanical crystals for spatial sensing of submicron sized particles

Optomechanical crystal cavities (OMC) have rich perspectives for detecting and indirectly analysing biological particles, such as proteins, bacteria and viruses. In this work we demonstrate the working principle of OMCs operating under ambient conditions as a sensor of submicrometer particles by optically monitoring the frequency shift of thermally activated mechanical modes. The resonator has been specifically designed so that the cavity region supports a particular family of low modal-volume mechanical modes, commonly known as -pinch modes-. These involve the oscillation of only a couple of adjacent cavity cells that are relatively insensitive to perturbations in other parts of the resonator. The eigenfrequency of these modes decreases as the deformation is localized closer to the centre of the resonator. Thus, by identifying specific modes that undergo a frequency shift that amply exceeds the mechanical linewidth, it is possible to infer if there are particles deposited on the resonator, how many are there and their approximate position within the cavity region. OMCs have rich perspectives for detecting and indirectly analysing biological particles, such as proteins, viruses and bacteria.

A Review on Structural Configurations of Magnetorheological Fluid Based Devices Reported in 2018–2020

Magnetorheological fluid (MRF) is a kind of smart materials with rheological behavior change by means of external magnetic field application, which has been widely adopted in many complex systems of different technical fields. In this work, the state-of-the-art MRF based devices are reviewed according to structural configurations reported from 2018 to 2020. Based on the rheological characteristic, the MRF has a variety of operational modes, such as flow mode, shear mode, squeeze mode and pinch mode, and has unique advantages in some special practical applications. With reference to these operational modes, improved engineering mechanical devices with MRF are summarized, including brakes, clutches, dampers, and mounts proposed over these 3 years. Furthermore, some new medical devices using the MRF are also investigated, such as surgical assistive devices and artificial limbs. In particular, some outstanding advances on the structural innovations and application superiority of these devices are introduced in detail. Finally, an overview of the significant issues that occur in the MRF based devices is reported, and the developing trends for the devices using the MRF are discussed.

Operation Capability Analysis and Experiments of Underactuated Compliant Multi-Fingered Hands

In this paper, operation capabilities of underactuated compliant robot hands have been investigated based on the shape stability analysis of underactuated compliant fingers and operation modes analysis of human hands. It is shown that the operation modes of robot hands can be classified into two major classes, namely, enveloping grasp mode and pinch mode. For the two operation modes, two principles are respectively presented with regard to the mechanical design issues of the underactuated robot hands. According to the principles presented in this paper, a robot hand prototype with four underactuated compliant fingers has been fabricated. On the robot hand prototype, enveloping grasp capability of underactuated compliant robot hands has been verified by many experiments. For precision operations, a proposition is presented and it is shown that the prototype should be further improved.

What is the significance of the traditional pinching mode of holding chopsticks?

BackgroundThe purpose of this study was to clarify the influence of manipulation mode of chopsticks on the learning process, using assessment of task performance and electromyography, and to understand the significance of the traditional manipulation mode from the viewpoint of physiological anthropology. Previous studies have described two modes of manipulating chopsticks, the traditional pincers-pinching mode and the scissors-pinching mode.MethodsWe conducted experiments with two conditions of holding chopsticks: scissors mode and pincers mode. Eight subjects participated and were assigned to these modes, and they learned handling tasks in their assigned mode for 5 days with the non-dominant hand. We measured task execution times and conducted electromyography of the following muscles: first dorsalis interosseus, flexor pollicis brevis, flexor digiti minimi brevis, flexor digitorum superficialis, and extensor digitorum.ResultsThe training effects were found in each mode. The pincers mode showed significantly shorter task performance times than did scissors mode. On electromyography, significant increases in activity of flexor digiti minimi brevis and tended an increase in flexor digitorum superficialis and a decrease in extensor digitorum occurred in pincers mode but not in scissors mode.ConclusionsThe traditional mode of holding chopsticks was associated with not only high task performance but also an advantage in terms of learning motor control.

Portable compact suction pad unit for parallel grippers

This paper proposes a portable compact suction pad unit for the parallel grippers of a mobile manipulation robot to place items for product display. In addition, this paper includes verification of the unit’s mechanism. Given that robots have to hold various items, we propose an operation method by which the parallel gripper holding the compact suction pad unit switches between a pinching mode and a vacuum suction mode depending on the item being placed. The compact suction pad unit is self-contained, with all the devices necessary for the suction operation inside the unit. The suction operation is switched on and off wirelessly by an external host system controller. The compact suction pad unit produced a suction force of about 5.6 N at an allowable inclination angle of 15°. We demonstrated in a competition that our proposed operation method of the compact suction pad unit is useful by having it place a beverage in a cup with lid and a boxed lunch.

A quasi-static model for the pinch mode analysis of a magnetorheological fluid flow with an experimental validation

Abstract The flow behaviors of a magnetorheological fluid (MR fluid) can be divided into four operating modes: flow, shear, squeeze and pinch mode. Despite many research works on the first three modes, the study on the pinch mode is relatively few. This study proposes a new mathematical model of the pinch mode flow motion of MR fluid and its fidelity is verified through a comparison with experimental results. In order to achieve this goal, the flow configuration of the pinch mode is provided followed by the magnetic analysis to design an appropriate magnetic circuit and to obtain the relationship between the magnetic intensity and applied current. Then, a mathematical model for predicting the pinch mode flow motion is formulated based on the quasi-static flow associated with several different conditions of the flow velocity. It is shown from a comparative work between the simulation results from the proposed mathematical model and experimental test results of the pinch mode MR damper that the proposed model fairly well predicts the field-dependent damping force in a low flow volume domain.

A magnetorheological fluid shaft seal with low friction torque

This paper deals with the design and tests of a magnetorheological fluid seal (MRFs) using the innovative concept of the magnetic circuit, which allows the achievement of a promising trade-off between burst pressure and friction of the seal. Low friction torque and low burst pressure are typical for a ferrofluid seal (FFs). Replacement of the ferrofluid by magnetorheological fluid increases the burst pressure of the seal but the friction torque of the seal increases too. The optimum for sealing application is low friction torque and high burst pressure. The presented design is based on the pinch mode of magnetorheological fluid. The geometry of the seal was determined by a magnetostatic model. Subsequently, the chosen concept of the seal was manufactured and tested. Pinch MRFs achieved lower friction torque than common (standard) MRFs and a higher burst pressure than any FFs.

Soft under-actuated hand with fin-ray structure

When the traditional under-actuated hands pinch the small objects, they tend to be unstable. To solve this problem, a new soft under-actuated hand is designed in this paper, which combines the soft fin-ray structure and the parallel under-actuated linkage mechanism. Compared with the traditional hands, the new design not only has the adaptive grasping mode, but also has the soft pinching mode, and through the pinching mode the small objects can be pinched stably. For tractable analysis, the design of the new hand is fully presented in this paper. Moreover, the force analysis and simulation are provided simultaneously. Finally, the experiments are conducted to verify the performance of the new design. The results indicate that the new hand could pinch small objects stably.

Registration of over-accelerated electrons in a high-current picoseconds accelerator

A high-voltage (U = 280 keV) high-current (I = 5 kA) electron accelerator with a beam duration of 200 ps was investigated. The luminescent method showed that the beam diameter in the uniform pinching mode is about a micrometer, therewith the beam contains electrons with an energy exceeding 400 keV.

Collective “overacceleration” of electrons in a pinched picosecond electron beam

The extreme operating mode of a high-voltage (U = 280 keV) high-current (I = 5 kA) electron accelerator with a beam duration of 200 ps is investigated. The luminescent method shows that the beam diameter in the uniform pinching mode is about a micrometer, and the beam contains electrons with an energy exceeding 400 keV. The analysis of the bremsstrahlung X-ray spectrum of the beam electrons shows that in this mode, a significant part of the spectrum lies in the energy range >300 keV, with the energy of quanta in the “tail” of the spectrum exceeding 500 keV.

Separation of Liquid Mixtures and the Minimum Steam Rectification Stream

In this paper, we compare various estimates of the abilities of liquid mixtures to be separated by distillation. The minimum specific heat consumption in rectification is shown to be proportional to the fraction of the upper product and the minimum reflux ratio. The conditions for energetically favorable application of different schemes of separation of three-component mixtures are determined. We also calculated the minimum reflux number for real binary mixtures with the possibility of forming pinch regimes. In the presence of a pinch mode in the strengthening part of the column, the value of the minimum reflux ratio is proved to be independent of the aggregate state of the initial mixture. For this case, we derived a formula for calculating the minimum reflux ratio taking the energy level of the initial mixture into account.