Bending Angle Research Articles

Deflection of Light by a Reissner-Nordström Black Hole and Painlevé VI equation

Abstract We consider the bending angle of the trajectory of a photon incident from and deflected to infinity around a Reissner-Nordström black hole. We treat the bending angle as a function of the squared reciprocal of the impact parameter and the squared electric charge of the background normalized by the mass of the black hole. It is shown that the bending angle satisfies a system of two inhomogeneous linear partial differential equations with polynomial coefficients. This system can be understood as an isomonodromic deformation of the inhomogeneous Picard-Fuchs equation satisfied by the bending angle in the Schwarzschild spacetime, where the deformation parameter is identified as the background electric charge. Furthermore, the integrability condition for these equations is found to be a specific type of the Painlevé VI equation that allows an algebraic solution. We solve the differential equations both at the weak and strong deflection limits. In the weak deflection limit, the bending angle is expressed as a power series expansion in terms of the squared reciprocal of the impact parameter and we obtain the explicit full-order expression for the coefficients. In the strong deflection limit, we obtain the asymptotic form of the bending angle that consists of the divergent logarithmic term and the finite O(1) term supplemented by linear recurrence relations which enable us to straightforwardly derive higher order coefficients. In deriving these results, the isomonodromic property of the differential equations plays an important role. Lastly, we briefly discuss the applicability of our method to other types of spacetimes such as a spinning black hole.

Numerical investigation on dynamic characteristics of oil-water annular flow-induced vibration in curved pipes

To improve the stability of water-lubricated transportation and reliability of pipes in service, the fluid–structure interaction numerical model has been established to investigate the dynamic characteristics of oil-water annular flow-induced vibration in curved pipes and the effect of main parameters in this study. The results illustrate that a single vibration mode of curved pipes is excited by oil-water annular flow, and there exists no multi-modality due to the limited pulsation of pressure and interface of two-phase flow. The change of velocities and oil-water ratios leads to change of flow pattern, making the dynamic response severer. When the oil-water ratio is larger than 2.035, its effect is greater than velocity. The physical properties of oil have a significant effect on the dynamic response. The root-mean-square dimensionless displacement AY,RMS/D and maximum dimensionless displacement AY,MAX/D of fuel oil-water annular flow-induced vibration decrease to 75.6% and 76.5% respectively, which means that the increase of dynamic viscosity reduces the fluid force and suppresses the vibration. AY,RMS/D and AY,MAX/D increases by 1.62 times when the bending angle θ increases from 30° to 90°, indicating that the increase of bending angles also leads to the severer dynamic response.

An Ergonomic Flexible Multi-Fire Clip Applier With Multiple Degrees-of-Freedom for Minimally Invasive Surgery to Improve Hemostatic Efficiency

Abstract Hemorrhage can lead to shock and even death of patients, making one of the main risks in surgical procedures. Most traditional clip appliers are rigid, have limited flexibility, and can only fire a single clip within each insertion, which cannot meet the needs of surgeons to efficiently and flexibly control bleeding vessels. In this study, a novel hand-held Hem-o-lok clip applier is proposed, which is designed to have a high flexibility and allow multiple fires of clips. The wrist at the end effector consists of discrete joints and a flexible shaft, allowing bending in two directions. The tong head at the end effector enables multiple fires of hemostats and can be delivered to different positions for clamping blood vessels and human tissues. It also can be driven to rotate by the flexible shaft. Additionally, an ergonomic handle is designed to control the multiple degrees-of-freedom (DOFs) movements of the instrument tip. Finally, the effectiveness of the entire system is evaluated through performance experiments. The bending angle of end effector was about ±70 deg in both directions (yaw and pitch), and the rotation angle was ±160 deg. The measured gripping forces of the applier ranged from 16.70 N to 24.93 N, and the average time to complete three consecutive clamping was 8.67 s. The proposed clip applier could improve the hemostatic efficiency and allow an intuitive and flexible operation in the meantime.

Study on ultimate capacity and design method of cold-formed steel equal lipped angle components under axial compression

This study focuses on evaluating the load-bearing capacity of cold-formed steel (CFS) equal lipped angle components. It delves into the structural behavior and design methods, taking into account various edge conditions and buckling modes. By considering the key parameters, which are component length, component thickness, total lip length, and lip bending angle, a total of 555 numerical models are developed for a systematic analysis on the components with two types of cross-sectional shapes. Since the coefficients within the direct strength method (DSM) inadequately capture the ultimate load-bearing capacity of lipped angle components, we introduce a design methodology rooted in the DSM framework to address global and global-local coupling buckling modes while imposing constraints to prevent local-distortion coupling buckling modes. The machine learning models (XGBoost, BPNN, and 1D-CNN) are adopted to predict the structural behavior of the two types of lipped angle components. These models can integrate the analysis of the components with two types of cross-section shapes in predictions of ultimate load capacity, axial deformation, and buckling modes. Meanwhile, the prediction accuracy of the machine learning models surpasses that of the analytical design methodology, offering more accurate prediction for ultimate load capacity, axial deformation and buckling modes.

Multifunctional composite flexible films of hydroxypropyl cellulose and silver nanowires

Flexible wearable devices have aroused attentions since the booming flexible electronic technologies, as well as the requirements for improved comfortableness and real-time monitoring for complex motion state of human body. Developing a flexible integrated wearable device with multi functions provides a promising route for next-generation wearable devices. Meanwhile, transparency and biocompatibility are also considered a lot. Herein, hydroxypropyl cellulose/silver nanowires (HPC/AgNWs) flexible composite films were fabricated with a facile two-step method. The fabricated composite films exhibited sufficient transparency and mechanical strength. More importantly, the HPC/AgNWs composite films afforded good motion sensing performances with current sensitivity as high as 350 %. It can accurately identify different bending angles and frequencies, and remained stable for more than 1000 bending cycles. Apart from being employed as motion sensors, the fabricated HPC/AgNWs could be also used for electrical heating and electromagnetic shielding. The films could be heated to more than 60°C at 3.0 V in 57 seconds, and the electromagnetic shielding efficiency reached more than 99.9 %. This study contributed a feasible strategy for the preparation of multifunctional flexible films which are expected to be further applicated in the field of wearable devices.

Lateral Pelvis and Lumbar Motion in Seated and Standing Office Work and Their Association With Transient Low Back Pain.

To assess frontal plane motion of the pelvis and lumbar spine during 2 h of seated and standing office work and evaluate associations with transient low back pain. Although bending and twisting motions are cited as risk factors for low back injuries in occupational tasks, few studies have assessed frontal plane motion during sedentary exposures. Twenty-one participants completed 2 h of seated and standing office work while pelvic obliquity, lumbar lateral bending angles, and ratings of perceived low back pain were recorded. Mean absolute angles were compared across 15-min blocks, amplitude probability distribution functions were calculated, and associations between lateral postures and low back pain were evaluated. Mean pelvic obliquity (sit = 4.0 ± 2.8°, stand = 3.5 ± 1.7°) and lumbar lateral bending (sit = 4.5 ± 2.5°, stand = 4.1 ± 1.6°) were consistently asymmetrical. Pelvic obliquity range of motion was 4.7° larger in standing (13.6 ± 7.5°) than sitting (8.9 ± 8.7°). In sitting, 52% (pelvis) and 71% (lumbar) of participants, and in standing, 71% (pelvis and lumbar) of participants, were considered asymmetric for >90% of the protocol. Lateral postures displayed weak to low correlations with peak low back pain (R ≤ 0.388). The majority of participants displayed lateral asymmetries for the pelvis and lumbar spine within 5° of their upright standing posture. In short-term sedentary exposures, associations between lateral postures and pain indicated that as the range in lateral postures increases there may be an increased possibility of pain.

A comprehensive review of experimental studies on shear behavior of bolted rock joints with varying rock joint and bolt parameters and normal stress

AbstractThe shear characteristics of bolted rock joints are crucial for the stability of tunneling and mining, particularly in deep underground engineering, where rock bolt materials are exposed to high stress, water pressure, and engineering disturbance. However, due to the complex interaction between bolted rock joints and various geological contexts, many challenges and unsolved problems arise. Therefore, more investigation is needed to understand the shear performance of bolted joints in the field of deep underground engineering. This study presents a comprehensive review of research findings on the responses of bolted joints subjected to shearing under different conditions. As is revealed, the average shear strength of bolted rock joints increases linearly with the normal stress and increases with the compressive strength of rock until it reaches a stable value. The joint roughness coefficient (JRC) affects the contact area, friction force, shear strength, bending angle, and axial force of bolted rock joints. A mathematical function is proposed to model the relationship between JRC, normal load, and shear strength. The normal stress level also influences the deformation model, load‐carrying capacity, and energy absorption ratio of bolts within bolted rock joints, and can be effectively characterized by a two‐phase exponential equation. Additionally, the angle of the bolts affects the ratio of tensile and shear strength of the bolts, as well as the mechanical behavior of both bolted rock joints and surrounding rock, which favors smaller angles. This comprehensive review of experimental data on the shear behavior of bolted rock joints offers valuable theoretical insights for the development of advanced shear devices and further pertinent investigations.

Design Optimization of Printed Multi-Layered Electroactive Actuators Used for Steerable Guidewire in Micro-Invasive Surgery.

To treat cardiovascular diseases (i.e., a major cause of mortality after cancers), endovascular-technique-based guidewire has been employed for intra-arterial navigation. To date, most commercially available guidewires (e.g., Terumo, Abbott, Cordis, etc.) are non-steerable, which is poorly suited to the human arterial system with numerous bifurcations and angulations. To reach a target artery, surgeons frequently opt for several tools (guidewires with different size integrated into angulated catheters) that might provoke arterial complications such as perforation or dissection. Steerable guidewires would, therefore, be of high interest to reduce surgical morbidity and mortality for patients as well as to simplify procedure for surgeons, thereby saving time and health costs. Regarding these reasons, our research involves the development of a smart steerable guidewire using electroactive polymer (EAP) capable of bending when subjected to an input voltage. The actuation performance of the developed device is assessed through the curvature behavior (i.e., the displacement and the angle of the bending) of a cantilever beam structure, consisting of single- or multi-stack EAP printed on a substrate. Compared to the single-stack architecture, the multi-stack gives rise to a significant increase in curvature, even when subjected to a moderate control voltage. As suggested by the design framework, the intrinsic physical properties (dielectric, electrical, and mechanical) of the EAP layer, together with the nature and thickness of all materials (EAP and substrate), do have strong effect on the bending response of the device. The analyses propose a comprehensive guideline to optimize the actuator performance based on an adequate selection of the relevant materials and geometric parameters. An analytical model together with a finite element model (FEM) are investigated to validate the experimental tests. Finally, the design guideline leads to an innovative structure (composed of a 10-stack active layer screen-printed on a thin substrate) capable of generating a large range of bending angle (up to 190°) under an acceptable input level of 550 V, which perfectly matches the standard of medical tools used for cardiovascular surgery.

Unraveling lithium-ion intercalation in lead-free bismuth-based vacancy ordered halide perovskites supercapacitors

Halide perovskites have recently gained a lot of attention in energy storage applications because of their unique properties. The difficulty in getting high-performance supercapacitors requires the significant development and customization of electrode materials. This study explores vacancy-ordered lead-free halide perovskites with chemical formula A3B2X9 as electrode material for supercapacitors. Furthermore, we have tuned the X site (X = Br−, Cl−, I−) to see the effect of halide ions on supercapacitor performance. Due to high ionic mobility and BET surface area, Cs3Bi2I9 has a specific capacitance of ∼242 F/g and energy density of ∼140 Wh/kg; however, power density variation is almost the same for all samples, measured in three-electrode systems. We have performed the ex-situ XRD and FTIR to understand the structural changes before and after charging. XPS measurement shows the peak shifting before and after measurement in Lithium-based electrolytes. Further, we have fabricated double perovskite-based symmetric devices with gel electrolyte as a separator. The Cs3Bi2I9 device shows an areal energy density of ∼23 μWh/cm2, the highest among all halide perovskite-based supercapacitor devices reported to date. The flexible device on the S.S. substrate shows 79% and 82% capacitance retention up to 180° bending angle and 200 bending cycles, respectively.

Multi-sensor-based process monitoring and quality assessment during laser forming of novel titanium foam to prevent cellular structure damage

Titanium foam finds its application in different fields like battery electrodes, heat exchangers, biological prosthetics, and lightweight structures for aeronautical parts. However, the inherent property of the foam to fail during mechanical loading conditions poses a challenge in providing final shape to these materials for practical applications. The present work investigates forming of Titanium foam (Ti Foam) using inline process monitoring for achieving controlled foam deformation while maintaining its quality without failure. Infrared (IR) pyrometer and laser-based displacement sensor were used to monitor the foam deformation behavior and thermal signature. The monitoring data were used to understand the process mechanism of laser forming. The bending mechanism within the foam was analysed with respect to solid sheet bending process. The correlation of the achieved bending angles, was attempted with the process parameters for surface, microstructural, elemental, and phase transformation. A critical analysis of Ti foam behavior, like surface melting, in situ oxidation, phase transformation, and formation of nano-structures on foam surface was addressed based on process parameter combinations. Micro-computed tomography (μCT) was carried out to investigate the pore deformation mechanism. Metallurgical characterisations for foam surface and phase analysis were carried out using X-ray photoelectron spectroscopy (XPS) and tunneling electron microscopy (TEM) to determine the chemical and crystallographic states of the laser-formed surface.

Liquid crystal elastomer-based all-printed actuator and sensing array systems

Liquid crystal elastomers (LCEs) are valuable in soft actuators, sensors and other emerging fields. However, it is still a huge challenge to build high-performance LCE-based functional devices in a simple and fast way to achieve the orderly and patterned integration of multiple functional layers and LCE. Herein, screen-printing technology is used to realize the multi-layer pattern deposition of silver fractal dendrites conductive ink (with excellent Joule heating effect and strain-sensing function) and carbon black conductive ink (with photothermal conversion ability) on the surface of LCE. A series of LCE-based electronic devices are prepared through customized printing patterns. The as-obtained actuator possesses excellent electric actuating performance (bending angle of 102° at 200 mA) and self-sensing function (maximum relative resistance changes of −55.0 %), and also exhibits NIR light-driven self-sensing bending actuation behavior (bending angle of 81° at 1.43 W/cm2), which can be used to control the robotic arm. The as-printed NIR light sensing array system can accurately sense the intensity, spot size and position of NIR light, showing good application potential in the field of unmanned aerial vehicle flight safety. This work provides a new strategy for the efficient preparation of LCEs-based flexible electronics.

Laser Printing of Large‐Area Conformal 3D photonic Circuits in Glass

AbstractPhotonic integrated circuits (PICs) are iterating on electronic ones to enable higher‐speed parallel computing while meeting the growing demands for energy efficiency in big‐data processing. However, manufacturing multi‐layered and 3D PICs remains challenging based on conventional planar lithography. Here, a rapid prototyping technique is delineated to configure large‐area and 3D PIC in glass based on laser‐direct written optical waveguides by employing femtosecond cylindrically polarized vortex laser beams. The vortex laser beam is mathematically rotationally invariant and capable of conformally transforming waveguide cross‐sections at arbitrary bending angles of 0–90° and across a large depth change. Based on this approach, a one‐layer 12‐core waveguide circuit with a variable cross‐section (diameter 5–11.5 µm) while maintaining a high mode ellipticity >0.974, as well as a more complex three‐layer 36‐core connector in which the waveguide dives continuously from 50 µm to 550 µm with a small loss difference of <0.1 dB is demonstrated. This work offers a pathway for 3D imprinting of large‐area photonic circuits in glass and other transparent materials, which has potential applications in high‐efficiency photonic computing, multidimensional quantum networks, and 3D optics topology.

Research on optimization of basic rail top bending prediction model

Since the basic rail of the switch needs to have a certain bending angle when the train changes direction, top bending is an important link in the production process of the basic rail. The three-point pressure top bending method is simple, flexible and widely used. In this study, the traditional three-point pressure bending is optimized, the influence of the pick width in the model is considered, a corresponding rebound model is established, and the model is applied to the pressure bending process of the basic rail. The bilinear strengthening model of the material was used to construct the bending moment expressions at different positions during the top bending process, and the relationship between the load and bending deflection in the elastic stage and elastic-plastic stage was obtained. The final top bending prediction model was obtained by combining the load-deflection model in the bending stage and the rebound stage. The correctness of the theoretical mathematical model was verified by establishing finite element simulations, and the theoretical calculation results were compared with the experimental results. The results showed that the top bend prediction optimization model established in this study had high feasibility and met the machining accuracy requirements.

Understanding Ionospheric and Geomagnetic Effects on Residual Biases in Radio Occultation Data for Stratospheric Climate Monitoring

AbstractHigher‐order residual ionospheric errors in Global Navigation Satellite System (GNSS) radio occultation (RO) data can induce a systematic residual ionospheric bias (RIB) in RO bending angles, which can impact stratospheric climate monitoring. The main RIB causes are the ray path splitting of dual‐frequency GNSS signals, the electron density distribution along the ray path and at the RO receiver location, and the geomagnetic field. In this study, we investigate the ionospheric and geomagnetic effects on RO‐retrieved stratospheric bending angle and temperature profiles by inspecting the kappa and bi‐local RIB correction methods, the current state‐of‐the‐art methods, using multiple RO satellite mission data in different ionospheric and geomagnetic conditions. We find that, globally, the layer mean/median RIBs of the kappa and bi‐local correction methods exhibit similar behaviors for different RO missions: the estimated bending angle RIBs reach about −0.025/−0.01 and −0.024/−0.008 μrad in the upper (40–45 km) and lower (30–35 km) stratosphere, respectively, while the temperature RIBs reach about −1.0/−0.3 and −0.2/−0.1 K in these layers. However, in the equatorial day time region, the RIB statistics of the mission results diverge. Both the kappa and bi‐local RIBs increase in magnitude with increasing ionization and geomagnetic field strength but show no increase with an increasing degree of ionospheric asymmetry. Overall, the more refined bi‐local method has higher capacity than the comparatively simple kappa method to represent the variability of the ionospheric and geomagnetic conditions that affect RO events. This is important for regional‐scale studies, where the geomagnetic term can be of key relevance.

Deformation behavior and scale effects in microchannel hydroforming in ultra-thin TA1/CFRP fuel cell bipolar plates

Microchannels of fuel cell bipolar plates have complex shapes and dimensions at the microscale level, posing significant challenges for manufacturing. Additionally, for traditional bipolar plate materials, mainly based on graphite composites and metals, make it difficult to meet the increasing performance requirements. As the latest fourth-generation fiber-reinforced metal composites, Ti/CFRP laminates exhibit high impact resistance and stiffness after solidification and are electrically conductive, presenting broad prospects for application in bipolar plates. In this study, the metallic layer of the traditional Ti /CFRP laminate was miniaturized to microscale, and a new method for ultra-thin TA1/CFRP laminate low-constraint hydro-microforming was proposed. By combining theoretical modeling, numerical simulation, and process experiments, the deformation behavior and scale effects of the laminate, during the microchannel hydroforming process, were investigated under different process and structural parameters. A single-channel deformation mode was used to study the forming process and examine the impact of hydraulic pressure loading paths and temperature. Additionally, multi-channel and curved channel deformation modes were employed to elucidate the influence of section inclination, channel width, ridge width, and bending angle on the forming process. By varying the laminate thickness, grain size and friction status, the geometric, grain and friction scale effects, as well as the microscale mechanisms of ultra-thin TA1/CFRP laminates in microchannel forming, were explored. This study explores new avenues for the precise microforming of lightweight laminate structures and their application in fuel cell bipolar plates. It provides a theoretical foundation to address the challenges in the microchannel forming of laminates and improve forming accuracy and performance quality.

Model-Based Design of Variable Stiffness Soft Gripper Actuated by Smart Hydrogels.

Soft grippers have shown their ability to grasp fragile and irregularly shaped objects, but they often require external mechanisms for actuation, limiting their use in large-scale situations. Their limited capacity to handle loads and deformations also restricts their customized grasping capabilities. To address these issues, a model-based soft gripper with adaptable stiffness was proposed. The proposed actuator comprises a silicone chamber with separate units containing hydrogel spheres. These spheres exhibit temperature-triggered swelling and shrinking behaviors. In addition, variable stiffness strips embedded in the units are introduced as the stiffness variation method. The validated finite element method model was used as the model-based design approach to describe the hydrogel behaviors and explore the affected factors on the bending performance. The results demonstrate that the actuator can be programmed to respond in a desired way, and the stiffness variation method enhances bending stiffness significantly. Specifically, a direct correlation exists between the bending angle and hydrogel sphere layers, with a maximum of 128° achieved. In addition, incorporating gap configurations into the chamber membrane results in a maximum threefold increase in the bending angle. Besides, the membrane type minimally impacts the bending angle from 21.3° to 24.6°. In addition, the embedded variable stiffness strips substantially increase stiffness, resulting in a 30-fold rise in bending stiffness. In conclusion, the novel soft gripper actuator enables substantial bending and stiffness control through active actuation, showcasing the potential for enhancing soft gripper performance in complex and multiscale grasping scenarios.

Growth of CQD/PPy on cotton cloth as a binder-free high-performance flexible electrode for symmetric supercapacitor

Benefited from the continuous development of nanomaterials, wearable microelectronics with flexible and miniaturized features are booming, and smart textiles are attracting more attentions because of their superior flexibility and perfect safety. The combination of conductive polymers and flexible substrates has created a new field for flexible supercapacitors. Herein, cotton cloth (CC), which is commonly used in daily life, was selected as the flexible substrate and a layer of CQDs was uniformly grown on the CC fibers, and then pyrrole was directly grown on CC by in-situ polymerization under Fe3+ initiation to realize the tight bonding between the conductive polymer and the flexible substrate. The electrochemical properties of the composite electrode could be controlled by changing the amount of CQD. The obtained CC@CQD@PPy electrode has a high specific capacitance (C) of 537.9 F/g at 0.5 A/g. The assembled symmetric CC@CQD@PPy supercapacitor exhibits an excellent energy density (E) of 18.7 Wh/kg at a power density (P) of 125.0 W/kg, and a supreme cycling stability with a capacitance retention of 77.9 % after 10,000 cycles. In addition, the CC@CQD@PPy supercapacitor has excellent flexibility, with almost unchanged electrochemical performance under different bending angles, and the assembled all-solid-state supercapacitor has good electrochemical properties.

Design and optimization of soft colonoscopy robot with variable cross section

Background Colonoscopy is the best choice for detecting bowel cancer; its effectiveness and early screening can significantly reduce the incidence rate of bowel cancer. However, the existing colonoscopy procedure is very technically demanding for doctors and painful for patients due to the difficult maneuver of long and slender colonoscope inside human colon. This paper will be focused on designing flexible robots with high dexterity to improve the performance of current colonoscopy. Methods This article optimizes and simulates the shape and layout of the driving cavity of the soft robot, as well as the multi-stage structure. This paper presents a design scheme of the soft robot with variable cross-section. The robot comprises two cross-sections in serial connection, with the outer diameter of the upper section 14mm and the outer diameter of the lower part 16mm. The bending angle and direction of the soft robot can be controlled by adjusting the pressure of the cavity. The soft robot is placed at the end of the traditional colonoscopy, replacing the standard manual operation for guidance during colonoscopy surgery. The relationship between the end position of the actuator and air pressure is calculated by the piecewise constant curvature (PCC) method and verified by subsequent experiments. At the same time, the motion trajectory of the soft robot is further simulated by finite element analysis. Results Experimental verification shows that the bending performance of the newly designed soft robot has significantly improved compared to the old design. Conclusion An improvement was made to address the design shortcomings of traditional actuators, and a new actuator was obtained. The performance of the latest and old actuators was compared through experiments, and it was ultimately known that the new actuator had significantly improved performance compared to the old actuator.

Development of new improved plastic collapse moment equations of pressurized different angled pipe bends under bending moments

In a piping system, pipe bends are more flexible than straight pipes because of their curved geometry, supplemented by higher stress and strain concentration, leading to one of the crucial components in piping industries. Therefore, safe design of pipe bends is essential for smooth running of the piping system, and plastic collapse moment is one of its criteria. This paper utilizes three-dimensional finite element analyses to model empirical solutions for the plastic collapse moment for different angled pipe bends subjected to combined pressure and in-plane closing, in-plane opening, and out-of-plane bending moments. Plastic collapse moments for 30∘ to 180∘ pipe bends are determined for elastic perfectly plastic and strain hardening materials, employing large geometry change option and internal pressure effect. It is observed from results that pressure effect is more prominent in thinner pipe bends of larger bend angle under all bending cases. For in-plane opening and out-of-plane bending moments, collapse moment increases and then decreases with increase in pressure intensity for all sizes of pipe bend. However, for in-plane opening bending moment, collapse moments keep on decreasing for thicker ([Formula: see text] = 11.33) pipe bends. Finally, the study presents new improved plastic collapse moment solutions for different angled pipe bends under bending moment and internal pressure, derived from the finite element results of elastic perfectly plastic and strain hardening material models.

Learning control for body caudal undulation with soft sensory feedback

Soft bio-mimetic robotics is a growing field of research that seeks to close the gap with animal robustness and adaptability where conventional robots fall short. The embedding of sensors with the capability to discriminate between different body deformation modes is a key technological challenge in soft robotics to enhance robot control–a difficult task for this type of systems with high degrees of freedom. The recently conceived Linear Repetitive Learning Estimation Scheme (LRLES)–to be included in the traditional Proportional–integral–derivative (PID) control–is proposed here as a way to compensate for uncertain dynamics on a soft swimming robot, which is actuated with soft pneumatic actuators and equipped with soft sensors providing proprioceptive information pertaining to lateral body caudal bending akin to a goniometer. The proposed controller is derived in detail and experimentally validated, with the experiment consisting of tracking a desired trajectory for the bending angle envelope while continuously oscillating with a constant frequency. The results are compared vis a vis those achieved with the traditional PID controller, finding that the PID endowed with the LRLES outperforms the PID controller (though the latter has been separately tuned) and experimentally validating the novel controller’s effectiveness, accuracy, and matching speed.