Actuation Pressure Research Articles

Redundancy and overactuation in cephalopod-inspired soft robot arms

Current soft robotic arms commonly follow traditional—i.e. hard—robot design conventions. Omnidirectional soft arms most commonly consist of segments that contain three parallel longitudinal actuators, or actuator groups, of which one or two are activated to induce bending. This design uses the minimum number of actuators required for omnidirectional bending, which is consistent with traditional robot design but unnecessarily constrains the soft arm design space. The cephalopods that frequently inspire soft robot arms have tens of bundles of longitudinal muscle fibers, and these bundles are distributed around the limb circumference rather than grouped. This article analyzes fluid-driven soft arm architectures with up to 12 actuators, which mimics the redundant and distributed nature of cephalopod arms and tentacles, in order to investigate the performance implications of an arm morphology closer to nature. Overactuation (i.e. activating more than two actuators) was considered, which is possible because soft robots—unlike traditional robots—can tolerate misaligned or partially opposed actuation without jamming. A previously-developed generalizable model was used to simulate design performance, and a subset of the examined architectures were constructed and tested. Many-actuator soft arms achieve high strokes under equivalent load and equivalent actuation pressures, without sacrificing no-load reach. These arms are also able to achieve quasi-omnidirectionality, as well as to execute near constant-curvature turns using a simple actuation pattern and a single pressure signal. The introduced framework also enables non-circular cross sections that are not possible with minimalist arm designs, allowing the load capacity and reach to be tuned in multiple directions. Several elliptical cross section arms were analyzed to explore the potential of non-circular cross sections. Overactuated, many-actuator arms significantly expand the design space of soft arms, improving performance in some cases and introducing options to tailor behavior that are infeasible in structurally minimal arms.

Volumetric Velocity Measurements of a Three-Dimensional Shock-Wave/Boundary-Layer Interaction with Flow Actuation Using Two-Camera Plenoptic Particle Image Velocimetry

Two-camera plenoptic particle image velocimetry is used to study a three-dimensional (3-D) shock-wave/boundary-layer interaction (SBLI) generated by a single unswept fin. The SBLI considered was the swept interaction induced by a sharp fin at an angle of attack of 15 deg in Mach 2 flow. The fin generates an oblique shock with a wave angle of approximately 45 deg that interacts with the boundary layer on the incident flat plate. As an extension of previous work, these experiments were conducted to examine the effects of momentum-based flow actuation on the 3-D flowfield, as well as reduce the data uncertainty and improve the overall data quality via addition of a second camera. The following three cases are presented for this work: 1) the baseline interaction with the presence of the inactive microjet actuators (physical insert present), 2) the mean SBLI flowfield under the influence of microjet actuation upstream of the oblique shock, and 3) the mean flowfields corresponding to phase-locked images captured at four different phases of the actuator pressure cavity signal. The results show good correlation with the literature of the SBLI with actuation, including a possible shift or rotation of the shock feature during actuation, and an increased velocity deficit and boundary-layer height. The resonance-enhanced microjet actuation also had a notable impact on the low-speed flow region near the fin. This work presents one of the first 3-D measurements of a fin-generated SBLI influenced by flow actuation.

High Energy and Power Density Peptidoglycan Muscles through Super-Viscous Nanoconfined Water.

Water‐responsive (WR) materials that reversibly deform in response to humidity changes show great potential for developing muscle‐like actuators for miniature and biomimetic robotics. Here, it is presented that Bacillus (B.) subtilis’ peptidoglycan (PG) exhibits WR actuation energy and power densities reaching 72.6 MJ m−3 and 9.1 MW m−3, respectively, orders of magnitude higher than those of frequently used actuators, such as piezoelectric actuators and dielectric elastomers. PG can deform as much as 27.2% within 110 ms, and its actuation pressure reaches ≈354.6 MPa. Surprisingly, PG exhibits an energy conversion efficiency of ≈66.8%, which can be attributed to its super‐viscous nanoconfined water that efficiently translates the movement of water molecules to PG's mechanical deformation. Using PG, WR composites that can be integrated into a range of engineering structures are developed, including a robotic gripper and linear actuators, which illustrate the possibilities of using PG as building blocks for high‐efficiency WR actuators.

Fluorescence-coupled micropipette aspiration assay to examine calcium mobilization caused by red blood cell mechanosensing

Mechanical stimuli such as tension, compression, and shear stress play critical roles in the physiological functions of red blood cells (RBCs) and their homeostasis, ATP release, and rheological properties. Intracellular calcium (Ca2+) mobilization reflects RBC mechanosensing as they transverse the complex vasculature. Emerging studies have demonstrated the presence of mechanosensitive Ca2+ permeable ion channels and their function has been implicated in the regulation of RBC volume and deformability. However, how these mechanoreceptors trigger Ca2+ influx and subsequent cellular responses are still unclear. Here, we introduce a fluorescence-coupled micropipette aspiration assay to examine RBC mechanosensing at the single-cell level. To achieve a wide range of cell aspirations, we implemented and compared two negative pressure adjusting apparatuses: a homemade water manometer (− 2.94 to 0 mmH2O) and a pneumatic high-speed pressure clamp (− 25 to 0 mmHg). To visualize Ca2+ influx, RBCs were pre-loaded with an intensiometric probe Cal-520 AM, then imaged under a confocal microscope with concurrent bright-field and fluorescent imaging at acquisition rates of 10 frames per second. Remarkably, we observed the related changes in intracellular Ca2+ levels immediately after aspirating individual RBCs in a pressure-dependent manner. The RBC aspirated by the water manometer only displayed 1.1-fold increase in fluorescence intensity, whereas the RBC aspirated by the pneumatic clamp showed up to threefold increase. These results demonstrated the water manometer as a gentle tool for cell manipulation with minimal pre-activation, while the high-speed pneumatic clamp as a much stronger pressure actuator to examine cell mechanosensing directly. Together, this multimodal platform enables us to precisely control aspiration and membrane tension, and subsequently correlate this with intracellular calcium concentration dynamics in a robust and reproducible manner.

Development of Topology Optimized Bending-Twisting Soft Finger

Abstract This paper proposed a systematic framework to automatically design and fabricate optimized soft robotic fingers. The soft finger is composed of a soft silicone structure with inner air chambers and a harder outer layer, which are fabricated by molding process and 3D printing, respectively. The softer layer is utilized for actuation while the supportive hard structure is used to impose constraints. The framework applies a topology optimization approach based on rational approximation of material properties (RAMP) method to obtain an optimal design of the outer layer of the soft fingers. Two basic motion primitives (bending and twisting) of the soft finger were explored. A multi-segmented soft bending finger and a soft twisting finger were designed and fabricated through the proposed framework. This work also explored the combination of bending and twisting primitives by developing a combined bending-twisting soft finger. The soft fingers were characterized by free and blocked movement tests. The experiments showed that the triple-segmented soft finger can achieve a maximum of 50.5 deg no-load bending under the actuation pressure of 53 kPa. The blocked movement test on the multi-segmented soft actuating finger showed that this finger could generate up to a maximum of 0.63 N force under 57 kPa actuation pressure in 7 s of inflating time. The developed twisting soft finger was shown to achieve tip rotation of up to 219 deg under 29 kPa actuation pressure. Finally, the potential capability of the bending-twisting soft fingers was verified through applications like screwing and object grasping.

Setting the overpressure prevention system for plunger pumps to improve the environmental safety of technological equipment

The relevance of the work is due to the fact that plunger pumps of the PT, PTR, T, TP type, which have found wide application at enterprises of fuel and energy complexes, are mostly operated with an unregulated factory system for preventing pressure overloads due to the lack of technical capability in the production of periodic adjustments built-in safety valve. As a result, the operation of high pressure plunger pumps without a tuned overpressure prevention system significantly reduces the reliability and safety of technological processes. The proposed solutions to this problem are the use of a specially developed adapter of a universal design or a mobile stand, which is a complete system of controlled loading of a safety valve together with a hydraulic unit of a pump with a working fluid, mounted on a mobile frame. As a result, the adapter makes it possible to configure the dismantled valve on a specialized test bench, and the use of a mobile version makes it possible to check the hydraulic system directly at the pump installation site with the ability to adjust the valve actuation pressure.

Design, Computational Modelling and Experimental Characterization of Bistable Hybrid Soft Actuators for a Controllable-Compliance Joint of an Exoskeleton Rehabilitation Robot

This paper presents the mechatronic design of a biorobotic joint with controllable compliance, for innovative applications of “assist-as-needed” robotic rehabilitation mediated by a wearable and soft exoskeleton. The soft actuation of robotic exoskeletons can provide some relevant advantages in terms of controllable compliance, adaptivity and intrinsic safety of the control performance of the robot during the interaction with the patient. Pneumatic Artificial Muscles (PAMs), which belong to the class of soft actuators, can be arranged in antagonistic configuration in order to exploit the variability of their mechanical compliance for the optimal adaptation of the robot performance during therapy. The coupling of an antagonistic configuration of PAMs with a regulation mechanism can achieve, under a customized control strategy, the optimal tuning of the mechanical compliance of the exoskeleton joint over full ranges of actuation pressure and joint rotation. This work presents a novel mechanism, for the optimal regulation of the compliance of the biorobotic joint, which is characterized by a soft and hybrid actuation exploiting the storage/release of the elastic energy by bistable Von Mises elastic trusses. The contribution from elastic Von Mises structure can improve both the mechanical response of the soft pneumatic bellows actuating the regulation mechanism and the intrinsic safety of the whole mechanism. A comprehensive set of design steps is presented here, including the optimization of the geometry of the pneumatic bellows, the fabrication process through 3D printing of the mechanism and some experimental tests devoted to the characterization of the hybrid soft actuation. The experimental tests replicated the main operating conditions of the regulation mechanism; the advantages arising from the bistable hybrid soft actuation were evaluated in terms of static and dynamic performance, e.g., pressure and force transition thresholds of the bistable mechanism, linearity and hysteresis of the actuator response.

Mathematical modelling and virtual decomposition control of heavy-duty parallel–serial hydraulic manipulators

This paper proposes a novel modelling approach for a heavy-duty manipulator with parallel–serial structures connected in series. Each considered parallel–serial structure contains a revolute segment with rigid links connected by a passive revolute joint and actuated by a linear hydraulic actuator, thus forming a closed kinematic loop. In addition, prismatic segments, consisting of prismatic joints driven by hydraulic linear actuators, also are considered. Expressions for actuator forces are derived using the Newton–Euler (N–E) dynamics formulation. The derivation process does not assume massless actuators decoupled from manipulator links, which is common in the Lagrange dynamics formulation. Actuator pressure dynamics are included in the analysis, leading in total to a third-order system of ordinary differential equations (ODEs). With fewer parameters than its predecessors, the proposed model in the N–E framework inspires revision of the virtual decomposition control (VDC) systematic process to formulate a control law based on the new model. The virtual stability of each generic manipulator revolute and prismatic segment is obtained, leading to the Lyapunov stability of the entire robot.

Phase-reduction analysis of periodic thermoacoustic oscillations in a Rijke tube

Phase-reduction analysis captures the linear phase dynamics with respect to a limit cycle subjected to weak external forcing. We apply this technique to study the phase dynamics of the self-sustained oscillations produced by a Rijke tube undergoing thermoacoustic instability. Through the phase-reduction formulation, we are able to reduce these dynamics to a scalar equation for the phase, which allows us to efficiently determine the synchronisation properties of the system. For the thermoacoustic system, we find the conditions for which $m:n$ frequency locking occurs, which sheds light on the mechanisms behind asynchronous and synchronous quenching. We also reveal the optimal placement of pressure actuators that provide the most efficient route to synchronisation.

Biomimetic Artificial Joints Based on Multi-Material Pneumatic Actuators Developed for Soft Robotic Finger Application.

To precisely achieve a series of daily finger bending motions, a soft robotic finger corresponding to the anatomical range of each joint was designed in this study with multi-material pneumatic actuators. The actuator as a biomimetic artificial joint was developed on the basis of two composite materials of different shear modules, and the pneumatic bellows as expansion parts was restricted by frame that made from polydimethylsiloxane (PDMS). A simplified mathematical model was used for the bending mechanism description and provides guidance for the multi-material pneumatic actuator fabrication (e.g., stiffness and thickness) and structural design (e.g., cross length and chamber radius), as well as the control parameter optimization (e.g., the air pressure supply). An actuation pressure of over 70 kPa is required by the developed soft robotic finger to provide a full motion range (MCP = 36°, PIP = 114°, and DIP = 75°) for finger action mimicking. In conclusion, a multi-material pneumatic actuator was designed and developed for soft robotic finger application and theoretically and experimentally demonstrated its feasibility in finger action mimicking. This study explored the mechanical properties of the actuator and could provide evidence-based technical parameters for pneumatic robotic finger design and precise control of its dynamic air pressure dosages in mimicking actions. Thereby, the conclusion was supported by the results theoretically and experimentally, which also aligns with our aim to design and develop a multi-material pneumatic actuator as a biomimetic artificial joint for soft robotic finger application.

A Simple Free-Fold Test to Measure Bending Stiffness of Slender Soft Actuators

A reliable estimate for bending stiffness is critical to many soft robot models when predicting everything from robot-environment contact to buckling resistance. Current methods for predicting actuator bending stiffness rely on highly accurate knowledge of material characteristics, which are not trivial to obtain for composite actuators. Additionally, current models for fluidic actuators often depend on a pressure-independent bending stiffness despite pressure playing a non-negligible role in bending stiffness behavior. Methods to measure actuator stiffness often require costly instrumentation to measure or perturb the motions and forces required to measure actual bending stiffness. We introduce a simple free-fold test to empirically estimate the bending stiffness of slender soft actuators—pressurized or unpressurized and composite or homogeneous—which requires the measurement of one distance from a single image of a specific robot pose. The resulting model also shows that the change in actuator weight per unit length can be used to determine the dependence of bending stiffness on actuation pressure.

Fabrication of titanium bipolar plates for proton exchange membrane fuel cells by uniform pressure electromagnetic forming

Electromagnetic forming (EMF) is a type of noncontact and high-speed forming process that offers several advantages, such as high material formability, low springback, and low die cost. In this study, titanium bipolar plates (BPPs) for proton exchange membrane fuel cells are fabricated by EMF using a uniform pressure actuator that provided a uniform pressure distribution and high efficiency. A three-dimensional coupled electromagnetic-mechanical simulation model is established to optimize the dynamic forming process. Simulation results show that the channel depth is proportional to the impact velocity of the titanium workpiece. A forming window is established as a design guideline. Finally, a titanium BPP with sufficient channel depth (0.4 mm), high aspect ratio (0.67), low thinning rate (not exceeding 15.89%) and high corrosion resistance is successfully fabricated at a velocity of 286 m/s, thereby demonstrating that EMF is a feasible process for fabricating titanium BPPs.

Static Modeling of Soft Reinforced Bending Actuator Considering External Force Constraints.

Soft robots are utilized in various operations such as rehabilitation, manipulation, and locomotion. These robots are sometimes excited by means of rubber based bending actuators, which are highly nonlinear and hyperelastic. In addition, in contrast to robots with rigid links and common actuators, continuous deformation of soft bending actuators in the presence of external forces makes the modeling more complicated. Thus, introducing a proper mathematical framework that accurately describes mechanical behavior of these actuators is still a challenge. In this research study, an analytical static model based on the Neo-Hookean material model is proposed. By resorting to the proposed model, a nonlinear relation between the actuator shape and inlet actuation pressure is extracted. Next, by means of the Euler-Bernoulli beam theory, the effect of external forces on the actuator configuration is investigated. Finally, experimental results are presented to validate the proposed theoretical model. In this regard, first, the actuator nonlinear behavior in a free motion is appropriately verified. Then, the actuator configuration, in the presence of two conventional external forces, called following and fixed direction, is analyzed.

Accessible detection of SARS-CoV-2 through molecular nanostructures and automated microfluidics

Accurate and accessible nucleic acid diagnostics is critical to reducing the spread of COVID-19 and resuming socioeconomic activities. Here, we present an integrated platform for the direct detection of SARS-CoV-2 RNA targets near patients. Termed electrochemical system integrating reconfigurable enzyme-DNA nanostructures (eSIREN), the technology leverages responsive molecular nanostructures and automated microfluidics to seamlessly transduce target-induced molecular activation into an enhanced electrochemical signal. Through responsive enzyme-DNA nanostructures, the technology establishes a molecular circuitry that directly recognizes specific RNA targets and catalytically enhances signaling; only upon target hybridization, the molecular nanostructures activate to liberate strong enzymatic activity and initiate cascading reactions. Through automated microfluidics, the system coordinates and interfaces the molecular circuitry with embedded electronics; its pressure actuation and liquid-guiding structures improve not only analytical performance but also automated implementation. The developed platform establishes a detection limit of 7 copies of RNA target per μl, operates against the complex biological background of native patient samples, and is completed in <20 min at room temperature. When clinically evaluated, the technology demonstrates accurate detection in extracted RNA samples and direct swab lysates to diagnose COVID-19 patients.

Wearable Intracranial Pressure Monitoring Sensor for Infants.

Monitoring of intracranial pressure (ICP) is important for patients at risk of raised ICP, which may indicate developing diseases in brains that can lead to brain damage or even death. Monitoring ICP can be invaluable in the management of patients suffering from brain injury or hydrocephalus. To date, invasive measurements are still the standard method for monitoring ICP; however, these methods can not only cause bleeding or infection but are also very inconvenient to use, particularly for infants. Currently, none of the non-invasive methods can provide sufficient accuracy and ease of use while allowing continuous monitoring in routine clinical use at low cost. Here, we have developed a wearable, non-invasive ICP sensor that can be used like a band-aid. For the fabrication of the ICP sensor, a novel freeze casting method was developed to encapsulate the liquid metal microstructures within thin and flexible polymers. The final thickness of the ICP sensor demonstrated is 500 µm and can be further reduced. Three different designs of ICP sensors were tested under various pressure actuation conditions as well as different temperature environments, where the measured pressure changes were stable with the largest stability coefficient of variation being only CV = 0.0206. In addition, the sensor output values showed an extremely high linear correlation (R2 > 0.9990) with the applied pressures.

Persistent Negative Compressibility Coupled to Optical Modulation in Empty-Perovskite TiOF2

The counterintuitive phenomenon of negative linear compressibility (NLC) has tremendous application potential in the design of ultrasensitive pressure sensors, artificial muscles, and actuators. Ho...

Initial experience with the fourth generation MitraClip™: Outcomes, procedural aspects, and considerations for device selection.

We present our initial experience with the fourth-generation MitraClip™ (G4) system and propose preliminary criteria for device selection. The MitraClip™ G4 system recently underwent a "controlled release" for transcatheter edge-to-edge mitral valve repair. The four new devices include technical improvements such as controlled gripper actuation (independent leaflet capture) and continuous left atrial pressure monitoring. To date, a patient-specific device selection algorithm, and the technology's impact on procedural times and success, have not been described. We present an initial multi-center experience and short-term outcomes with the new system, suggest procedural and imaging considerations, and propose initial guidance for device selection. Sixty-one procedures performed by three operators at two centers between November 2019 and May 2020 were analyzed. At 30-day follow-up, there were three deaths (4.9%), four neurological events (6.6%), and seven re-hospitalizations (11.5%). Fifty-nine patients achieved device and procedural success (96.7%), and there was one device-related technical issue (1.6%). Compared to the same operators utilizing the third generation MitraClip™, the G4 system resulted in a significant reduction in the median number of clips used per patient (1 IQR 1-2 vs. 2 IQR 1-3, p=.023) and a trend toward shorter device times. Based on our initial experience, we found that the MitraClip™ G4 system is associated with high procedural success and fewer devices needed per procedure. The expanded device options may allow a more targeted approach to the myriad of pathologic presentations of mitral regurgitation. This early experience should provide a foundational opportunity for further refinement.

Machine Learning Approach for Constructing Wet Clutch Torque Transfer Function

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;A wet clutch is an established component in a conventional powertrain. It also finds a new role in electrified systems. For example, a wet clutch is utilized to couple or decouple an internal combustion engine from an electrically-driven drivetrain on demand in hybrid electric vehicles. In some electrical vehicle designs, it provides a means for motor speed reduction. Wet clutch control for those new applications may differ significantly from conventional strategy. For example, actuator pressure may be heavily modulated, causing the clutch to exhibit pronounced hysteresis. The clutch may be required to operate at a very high slip speed for unforeseen behaviors. A linear transfer function is commonly utilized for clutch control in automating shifting applications, assuming that clutch torque is proportional to actuator pressure. However, the linear model becomes inadequate for enabling robust control when the clutch behavior becomes highly nonlinear with hysteresis. The use of linear transfer function also leads to errors in powertrain simulation. This paper presents a machine learning approach to construct non-linear clutch torque transfer functions for robust powertrain control and simulation. Several regression methods are evaluated for accuracy and computational efficiency as compared to the conventional linear fitting approach. It is found that Gaussian Process Regression outperforms other approaches for accurately capturing non-linear clutch behavior during training. It also provides a confidence interval for predicted clutch torque. A simulation study is conducted for a hybrid powertrain system to illustrate the impact of the non-linear clutch transfer function on engine restart behavior, as compared to the conventional linear clutch model. The use of machine learning based regression method enables accurate representation of wet clutch behavior for improved simulation and robust control development.&lt;/div&gt;&lt;/div&gt;

Sensing and Control of a Multi-Joint Soft Wearable Robot for Upper-Limb Assistance and Rehabilitation

In the field of wearable robotics, there has been increased interest in the creation of soft wearable robots to provide assistance and rehabilitation for those with physical impairments. Compared to traditional robots, these devices have the potential to be fully portable and lightweight, a flexibility that may allow for increased utilization time as well as enable use outside of a clinical environment. In this letter, we present a textile-based multi-joint soft wearable robot to assist the upper limb, in particular shoulder elevation and elbow extension. Before developing a portable fluidic supply system, we leverage an off-board actuation system for power and control, with the worn components weighting less than half kilogram. We showed that this robot can be mechanically transparent when powered off, not restricting users from performing movements associated with activities of daily living. Three IMUs were placed on the torso, upper arm and forearm to measure the shoulder and elbow kinematics. We found an average RMSE of ~ 5 degrees when compared to an optical motion capture system. We implemented dynamic Gravity Compensation (GC) and Joint Trajectory Tracking (JTT) controllers that actively modulated actuator pressure in response to IMU readings. The controller performances were evaluated in a study with eight healthy individuals. Using the GC controller, subject shoulder muscle activity decreased with increasing magnitude of assistance and for the JTT controller, we obtained low tracking errors (mean ~ 6 degrees RMSE). Future work will evaluate the potential of the robot to assist with activities in post-stroke rehabilitation.

Motion and shape control of soft robots and materials

A continuum-based approach for simultaneously controlling the motion and shape of soft robots and materials (SRM) is proposed. This approach allows for systematically computing the actuation forces for arbitrary desired SRM motion and geometry. In order to control both motion and shape, the position and position gradients of the absolute nodal coordinate formulation (ANCF) are used to formulate rheonomic specified trajectory and shape constraint equations, used in an inverse dynamics procedure to define the actuation control forces. Unlike control of rigid-body systems which requires a number of independent actuation forces equal to the number of the joint coordinates, the SRM motion/shape control leads to generalized control forces which need to be interpreted differently in order to properly define the actuation forces. While the definition of these motion/shape control forces is demonstrated using air pressure actuation commonly used in the SRM control, the proposed procedure can be applied to other SRM actuation types. The approaches for determining the actuation pressure in the two cases of space-dependent and constant pressures are outlined. Effect of the change in the surface geometry on the actuation pressure is accounted for using Nanson’s formula. The obtained numerical results demonstrate that the motion and shape can be simultaneously controlled using the new actuation force definitions.