Actuation Pressure Research Articles

Fabrication and characterization of thin-film silicon resonators on 10 m-thick polyimide substrates

MEMS fabricated on polymer substrates can allow for a range of new applications that require bending or lightweight, unbreakable substrates. The surface micromachining of hydrogenated amorphous silicon resonators on 10 µm-thick flexible polyimide substrates is presented. Clamped-clamped (bridges) and clamped-free (cantilevers) resonators are fabricated and characterized, exhibiting quality factors as high as 2.0 × 103 and natural resonance frequencies in the 104–106 Hz range. The deflection of an 80 µm long bridge was measured to be over 100 pm, using laser Doppler vibrometry. The electrical addressing of the devices was demonstrated to be reliable when bent to radii of curvature larger than 10 mm. The resonators on ultra-thin polymer are characterized using different actuation voltages and pressures, showing comparable performance to resonators on rigid (glass) substrates. However, the flexible substrate allows the relaxation of the residual stress of the structural film in clamped-clamped structures, lowering the resonance frequency. Resonators on PI were found to be suitable for mass-sensing applications, achieving a minimum frequency shift detectable Δfmin = 30 Hz which results in a calculated mass sensitivity of 25 pg in vacuum. Ultimately, the reliable performance of the resonators developed in this work make them good candidates for applications that require mass-sensing on ultra-thin, flexible substrates.

A Pneumatic/Cable-driven Hybrid Linear Actuator with Combined Structure of Origami Chambers and Deployable Mechanism

Pneumatic actuators have been widely used in robotics due to their inherent compliance and relatively high strength. In this letter, the authors report on the design, analysis and experimental validation of a novel pneumatic/cable-driven hybrid linear actuator whose structure is a combination of origami chambers and passive deployable mechanism. Under the joint actuation of the cable and compressed air, the proposed actuator can generate bidirectional motion; meanwhile, both thrust and tensile force can be produced. The combined structure of the rigid deployable mechanism and the axially soft origami chambers possesses high radial stiffness and an extension ratio up to 200% without radial expansion. The position can be controlled at whole motion range through a simple strategy and the actuation pressure can be as low as 2 kPa at no load. The kinematic as well as the quasi-static model is developed to accurately predict the behavior of the actuator and design the control strategy. A prototype is built based on a new fabrication method, on which the validation experiments are conducted. The experimental results prove the effectiveness of the model and show that the prototype possesses acceptable positioning accuracy, even when an external load is exerted on its moving plate.

Design and Automatic Fabrication of Novel Bio-Inspired Soft Smart Robotic Hands

Soft material robots are developing rapidly benefited from their inherent flexibility, adaptability and safety compared to rigid-bodied robots. However, most soft robots are unable to offer high force/strength due to the low rigidity of soft materials that they are composed of. Absence of position feedback is another problem for soft robots. In this research, we aim to address these two challenges in a novel designed soft smart robotic hand. The design of this soft hand is also delicately considered to make it 3D printable, which shortens the design cycle and reduces the fabrication time. This hand consists of five fingers and a palm, all of which can be actuated independently. The finger is designed with two chambers: one air-tight active chamber which can be actuated by compressed air, one passive chamber filled with loosely arranged particles. During bending actuation, particles inside the passive chamber are squeezed by pressurized air, which causes passive jamming. As a result, the stiffness of the finger is strengthened during bending, which endows the hand with larger force output and load-holding capability. Furthermore, position feedback modules made of conductive elastomers are integrated and co-printed with the finger during fabrication. In this research, a hand prototype is manufactured and several experiments regarding to its characteristics and performance are conducted for evaluation. From experimental results, the soft hand achieves maximum holding weight of 1.452kg with particles and 0.8425kg without particles at same actuation pressure of 450kPa.

Optimizing Aerosolization Using Computational Fluid Dynamics in a Pediatric Air-Jet Dry Powder Inhaler.

The objective of this study was to optimize the performance of a high-efficiency pediatric inhaler, referred to as the pediatric air-jet DPI, using computational fluid dynamics (CFD) simulations with supporting experimental analysis of aerosol formation. The pediatric air-jet DPI forms an internal flow pathway consisting of an inlet jet of high-speed air, capsule chamber containing a powder formulation, and outlet orifice. Instead of simulating full breakup of the powder bed to an aerosol in this complex flow system, which is computationally expensive, flow-field-based dispersion parameters were sought that correlated with experimentally determined aerosolization metrics. For the pediatric air-jet DPI configuration that was considered, mass median aerodynamic diameter (MMAD) directly correlated with input turbulent kinetic energy normalized by actuation pressure and flow kinetic energy. Emitted dose (ED) correlated best with input flow rate multiplied by the ratio of capillary diameters. Based on these dispersion parameters, an automated CFD process was used over multiple iterations of over 100 designs to identify optimal inlet and outlet capillary diameters, which affected system performance in complex and unexpected ways. Experimental verification of the optimized designs indicated an MMAD < 1.6μm and an ED > 90% of loaded dose. While extrathoracic depositional loss will be determined in future studies, at an operating flow rate of 15L/min, it is expected that pediatric mouth-throat or even nose-throat aerosol deposition fractions will be below 10% and potentially less than 5% representing a significant improvement in the delivery efficiency of dry powder pharmaceutical aerosols to children.

Discrete Layer Jamming for Variable Stiffness Co-Robot Arms

Abstract Continuous layer jamming is an effective tunable stiffness mechanism that utilizes vacuum to vary friction between laminates enclosed in a membrane. In this paper, we present a discrete layer jamming mechanism that is composed of a multilayered beam and multiple variable pressure clamps placed discretely along the beam; system stiffness can be varied by changing the pressure applied by the clamps. In comparison to continuous layer jamming, discrete layer jamming is simpler as it can be implemented with dynamic variable pressure actuators for faster control, better portability, and no sealing issues due to no need for an air supply. Design and experiments show that discrete layer jamming can be used for a variable stiffness co-robot arm. The concept is validated by quasi-static cantilever bending experiments. The measurements show that clamping 10% of the beam area with two clamps increases the bending stiffness by around 17 times when increasing the clamping pressure from 0 to 3 MPa. Computational case studies using finite element analysis for the five key parameters are presented, including clamp location, clamp width, number of laminates, friction coefficient, and number of clamps. Clamp location, number of clamps, and number of laminates are found to be most useful for optimizing a discrete layer jamming design. Actuation requirements for a variable pressure clamp are presented based on results from laminate beam compression tests.

Designing Fiber-Reinforced Soft Actuators for Planar Curvilinear Shape Matching.

Fiber-reinforced soft pneumatic actuators can generate a wide variety of deformation behavior, making them popular in the field of soft robotics. Designing an actuator to meet a specified deformed shape is an important step toward the design of soft robots. We present a two-step methodology to design an actuator that matches a given planar curve on pressurization. In the first step, the curve is divided into a series of constant curvature (CC) segments that best approximate its shape. The second step involves designing a bending actuator by determining its fiber orientations for each CC segment. Further, this two-step method is extended to match two curves: a final deformed curve and an intermediate curve at a lower actuation pressure. On combining all the CC segments, the resulting actuator lies along a straight line unpressurized, and on pressurization deforms to trace the desired final curve through a preset intermediate curve. To demonstrate the method, we show different examples: an omega curve for an inchworm robot, an acronym SoRo for the Soft Robotics Journal, and a two-stage bending actuator.

Experimental testing of pneumatically forced actuated compressor-expander valves

The possibility of forced actuation of valves enables new operation modes for existing reciprocating compressors, e.g. capacity control or reverse operation as expander. A pneumatically forced actuated valve was tested within a reciprocating compressor and a quite complex behaviour was found, as shown in previous publications. A test rig outside of the compressor was set up for a better understanding of the system. Two measurement techniques were used to observe the sealing element motion over the time at varying operating conditions, like applied pressure levels and actuation time. The dependency of the valve motion to those operation conditions is evaluated and discussed. Improvements to the test bench and measurement techniques are also proposed to achieve more accurate results.

Novel monolithic “Slightly-Open doormat” (SOD) valve enables efficient fabrication of highly-scalable microfluidic gas-on-gas multiplexer

The use of monolithic normally-closed (NC) valves within microfluidic systems is currently limited by the poor scalability of mitigation strategies developed to prevent the formation of a permanent bond between the valve ‘seat’ and elastomeric membrane during fabrication. Herein we report the highly-scalable design and characterization of a slightly-open doormat (SOD) valve that exhibits properties traditionally associated with NC valves including operability at low actuation pressures, and the capacity to produce a complete seal. In addition, these valves are comparable in their scalability and in responsiveness, and exhibit a capacity to eliminate resting channel resistance that is absent in their NC counterparts. We demonstrate the utility of this novel valve design through the design and operation of a gas-on-gas multiplexer containing 32 device valves controlled by a multiplexer containing 160 SOD valves using only 10 external solenoid valves and a single common pressure source.

Paper-Based Mechanical Sensors Enabled by Folding and Stacking.

Electronics based on paper substrates can be foldable, inexpensive, and biodegradable, making such systems promising for low-cost sensors, smart packaging, and medical diagnostics. In this work, we saturate tissue paper with poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) by using a simple and scalable process and construct pressure sensors that exhibit an enhanced response when the active material is folded or stacked. Nanoscale pressure actuation and current mapping reveals a sensing mechanism that takes advantage of the fibrous microstructure of the paper and relies on the formation and expansion of electrical contacts between fibers in adjacent paper layers as pressure is applied. The resulting paper-based pressure sensors respond to an impulse within 20 ms and are robust, showing only a 4.6% decrease in the operating current after 30 000 load/unload cycles. Pressure distribution mapping was achieved by using a sensor array with a stacked architecture, whereas folding was used to demonstrate multistate switching and to detect conformational change in a three-dimensional origami system. These strategies of folding and layering paper saturated with functional materials open up new avenues for building multifunctional paper electronics.

Modeling the Bending Behavior of Fiber-Reinforced Pneumatic Actuators Using a Pseudo-Rigid-Body Model

Abstract Fiber reinforced elastomeric enclosures (FREEs) are soft pneumatic representative elements that can form the basis for building soft self-actuating structures/mechanisms. When placed in different configurations, they exhibit unique stroke amplification characteristics that can be leveraged to create interesting deformation patterns. Such deformations occur as a combination of axial and bending deflection due to internal pressurization and external forces. This paper presents a lumped reduced-order model that enables quick and accurate analysis of mechanisms made from FREEs grouped as a system. The model proposed is a modified four-spring pseudo-rigid-body (PRB) model that effectively captures the axial and bending stiffnesses of contracting FREEs. Parametric estimation of the model is performed using a multistart optimization routine to fit the PRB model with results from experiments and finite element analysis (FEA). The model is also generalized and statistically verified for FREEs with different fiber angles, length-to-diameter ratios, and different actuation pressures. Finally, efficacy of the approach is validated through three case studies that involve a planar arrangement of FREEs at different orientations.

Selective droplet splitting using single layer microfluidic valves

Droplet microfluidics, with its small scale isolated samples, offers huge potential in the further miniaturisation of high throughput screening. The challenge is to deliver multiple samples in a manner such that reactions can be performed in numerous permutations. The present study investigates the use of single layer valves to break up individual droplets selectively. This splitting of large droplets, allows the main sample volume to navigate around the chip, with smaller daughter droplets being removed at desired locations. As such, the mother droplet is no longer an isolated sample akin to an on-chip test tube, but rather a mobile sample delivery system akin to an on-chip pipette. The partitioning takes place at the entrance to a bypass loop of the main channel. Under normal operating conditions the droplet passes the entrance intact, however, when a valve located at the entrance to the bypass loop is actuated, the geometry changes causes the droplet to split. We analyse this transition in behaviour for a range of oil and water inlets, and valve actuation pressures, showing that the valve can be actuated such that the next droplet to pass the bypass loop will be split, but subsequent droplets will not be.

Adaptive eyeglasses for presbyopia correction: an original variable-focus technology.

We propose an original variable-focus technology specially designed for presbyopia-correcting adaptive eyeglasses. It has been thought through to offer vision comfort without cutting on aesthetics. It relies on a fluid-filled variable-focus lens (presenting 2 liquids and 1 ultra-thin membrane) assisted by a low-power, high-volume microfluidic actuator. It also features a distance-sensing system to provide automatic focusing. We demonstrate the qualities of this novel technology on our first prototype. Our prototype achieves the necessary 3-diopter-high power variation on a 20-millimeter-wide variable zone with low actuation pressures (~200 Pa at most), and the preliminary optical quality analysis shows the spatial resolution is much better than the one specified by classic eye charts. We discuss further improvements in terms of optics, aesthetics and portability. In particular, we point out that this variable technology is compatible with standard base curves, and we highlight an optimal configuration where the power consumption of our opto-fluidic engine is about 25 mW peak.

Review on solar sail technology

This paper reviews solar sail trajectory design and dynamics, attitude control, and structural dynamics. Within the area of orbital dynamics, methods relevant to transfer trajectory design and non-Keplerian orbit generation are discussed. Within the area of attitude control, different control strategies, including utilisation of solar radiation pressure and conventional actuators, are discussed. Finally, the methods of modelling structural dynamics during and after deployment are discussed, before considering possible future trends in developing of solar sailing missions.

Finite-Element Modeling and Design of a Pneumatic Braided Muscle Actuator With Multifunctional Capabilities

This paper reports the concept, design, and development of a pneumatic braided muscle actuator, able to produce bidirectional force and motion. Such a capability can simplify the design and enhance the capabilities of robotic/automation systems using pneumatic muscles as actuators. Finite-element modeling is utilized as a design tool in order to study the feasibility of the concept, where a single braid structure is deformed to produce both contraction and elongation. A three-dimensional finite-element model of the actuator is developed and a number of nonlinear quasi-static simulations are performed using the explicit dynamic solver LS-Dyna to measure the blocked force and free displacement of the actuator. The effect of varying the end-fittings diameter and the length of the inner chamber on the mechanical characteristics of the actuator is also analyzed. The simulation results are validated through mechanical experimentation performed on the functional prototype. With an actuation pressure of 1 bar, the actuator is able to produce a contraction force of around 80 N, extension force of around 40 N, and an overall stroke of >40% of the total length of the actuator. Moreover, the novel actuator has been utilized as a main driver for a one degree of freedom variable stiffness joint, as a case study, to demonstrate the usability of the actuator.

Negative area compressibility of a hydrogen-bonded two-dimensional material.

Very few materials expand two-dimensionally under pressure, and this extremely rare phenomenon, namely negative area compressibility (NAC), is highly desirable for technological applications in pressure sensors and actuators. Hitherto, the few known NAC materials have dominantly been limited to 2D crystals bonded via coordination interactions while other 2D systems have not been explored yet. Here, we report the large NAC of a hydrogen-bonded 2D supramolecular coordination complex, Zn(CH3COO)2·2H2O, with a synergistic microscopic mechanism. Our findings reveal that such an unusual phenomenon, over a wide pressure range of 0.15-4.44 GPa without the occurrence of any phase transitions, arises from the complex cooperation of intra-layer coordination and hydrogen-bonding interactions, and inter-layer van der Waals forces. In addition, we propose that these NAC crystals could have important applications as pressure-converting materials in ultrasensitive pressure sensing devices.

Importance of electrical and physical contact in electromagnetic forming simulations

Abstract In both industry and academia, researchers often use numerical simulations to reduce the number of trial-and-error iterations required in experiments to reduce costs. However, this can be difficult in the EMF process where electricity is flowing with relative motion between the workpiece and conductor. Thus, a coupled electromagnetism (EM)-structural analysis, which also includes EM contact, has to be conducted. In this paper, in order to further understand the science behind the EMF process and benefits of a coupled numerical analysis, a numerical model was created in a commercial software package, LS-DYNA, for a coil design called a uniform pressure actuator (UPA). Numerically predicted workpiece velocities and displacements were compared with those in experimental tests measured using a Photon Doppler Velocimetry (PDV) and Coordinate Measurement Machine (CMM). Simulations of idealized electrical conditions without material draw-in as well as more physically accurate simulations where EM contact allowed material draw-in were conducted. The inclusion of material draw-in allowed more accurate predictions of experimental displacements and velocities. In addition, the fact that shear stresses in the formed wall cause the inverse saddle geometry of components produced with a UPA is shown.

Investigation of the State Transition and Moving Boundary in a Pneumatic–Hydraulic Coupled Dielectric Elastomer Actuator

Compared to robots and devices made of rigid components, soft robots and flexible devices driven by soft active materials possess various advantages including high adaptability under extreme environment and compatibility with a human. Dielectric elastomer (DE) membrane, which is commonly used in building soft actuators, can achieve large actuation by the combined loadings of voltage-induced Maxwell stress and fluidic pressures (pneumatic and hydraulic pressure). This paper proposes a pneumatic–hydraulic coupled electromechanical actuator (PHCEA), which exhibits strong coupling effect of electromechanical actuation (the Maxwell stress on DE membrane), pneumatic and hydraulic pressures. Considering the moving boundary and state transition, a computational model has been developed to investigate the coupling behaviors of the PHCEA. The numerical result by this model is in accordance with the experimental measurements. The combination of experimental data and the theoretical result indicates that the state transition and moving boundary separate the potential region of electrical breakdown and mechanical damage. This model can be utilized as a practical method to characterize the performance and guide the design of soft devices. The experimental setup and computational method of the PHCEA bring new insights into the fabrication and characterization of soft robots, adaptive optics, and flexible bio-medical devices. The PHCEA possesses wide applications in underwater robots, soft muscles, and microfluidics systems. It can serve as the gas bladder of soft swimming robots, the soft actuator of hydraulic–pneumatic coupling systems, and the gas–liquid valve of flexible microfluidics systems.

Design and Development of a Topology-Optimized Three-Dimensional Printed Soft Gripper.

In the past decade, a rich repertoire of soft robots, designed from biomimetic and intuitive approaches, has been developed to overcome challenges faced by their rigid-bodied counterparts. However, these design approaches are greatly limited by the designers' experience and inspiration. In this article, the structural design problem is mathematically modeled under the framework of topology optimization, and solved by a new implementation tool that combines Abaqus/CAE and Matlab coding. Herein, a pneumatic soft gripper with two identical fingers was developed as a practical application. To fulfill the grasping task, each gripper finger is optimized to achieve its maximal bending deformation. The optimized gripper fingers are in high consistence with human fingers as indicated by pseudo-joints. Thereafter, the optimized gripper fingers are directly fabricated by three-dimensional printing technique with unprecedented fidelity regardless of high geometric complexity. Experimental results show that the gripper can grasp an elastic balloon, and each gripper finger is able to undergo a [Formula: see text] free travel bending and exert 0.23 N grasping force upon 0.06 MPa actuation pressure. The proposed approach is freely extendable to develop other types of soft robots and this represents an important step toward the goal of designing and fabricating soft robots automatically.

Experimental investigations of lightweight structures with fluidically actuated Compressible Constrained Layer Damping

Since strength, stiffness and damping are coupled design variables of fibre reinforced plastics, the lightweight-focused design often leads to a problematic vibration susceptibility of the developed components. This article presents an experimental proof-of-concept of fluidically controlled Compressible Constrained Layer Damping, a novel, semi-active, lightweight-compatible solution for vibration mitigation without explicit actuators.The proposed actuating principle is based on structural cavities generating forces and slight structural deformations when supplied with fluid. The cavities encapsulate compressible, low profile viscoelastic layers operating according to the principle of the Constrained Layer Damping. The intended actuation mechanism controls the thickness of the viscoelastic layers and thus the material properties and the amount of the vibration-induced shear deformation.The described actuating principle is experimentally investigated on a sample composite structure which was excited using an electrodynamic shaker while the vibration response was measured using a laser scanning vibrometer. The obtained results for monofrequent excitation revealed that the compression-driven adjustment allows mobility changes in the range up to 15.8 dB and the mobility can be decreased up to 24.3 dB compared to the untreated base structure due to a shift of the resonance peaks frequency. A second indicator – the adaptive dissipative power – was analysed showing a complex dependency upon the negative actuation pressure and offering a wide adjustment capability.

Friction Compensation in Pneumatic Control Valves Through Feedback Linearization

Control valves are very important actuators in the process industry. Due to friction in the stem, they present a nonlinear behavior, which can generate errors in the stem position and oscillations in control loops. This paper presents five control algorithms based on feedback linearization technique, to deal with pneumatic control valves affected by high friction in their stems. These control algorithms measure the valve position and manipulate the actuator pressure, acting as a valve positioner. The paper also shows practical results with a control valve operating in a real flow control loop.