Displacement Sensing of an Active String Actuator by an Optical Fiber

We have fabricated a string-shaped actuator called “Active string” that has high contractile displacement/force by accumulating thin pneumatic artificial muscles using the string production process. However, displacement control of the active string is challenging because general bulky and rigid displacement sensors are not suitable for the sensor element of the active string. Therefore, in this report, a flexible optical fiber sensor is combined with the active string to enable sensing of its displacement. As the active string contracts, the radius of curvature of the optical fiber decreases, and light intensity propagating in the optical fiber decreases due to bending loss. The experimental results showed that the optical fiber sensor value changed with corresponding to the displacement of the active string. It shows the possibility that it is possible to make a displacement estimation of the displacement of the active string using an optical fiber sensor.

Development of Li-ion Battery Bulk Force and Expansion Displacement Test-bench

In order to test the bulk force and expansion displacement of lithium-ion batteries, it is planned to develop a corresponding test-bench, which is mainly composed of a measurement-control system and a mechanical system. To improve the accuracy of the test data, the coupled thermal-structure simulation of the test system in the mechanical system of the test-bench is carried out to select an optimal mechanical structure of the test system. At the same time, for safe and convenient testing, a monitoring-testing system software was developed to ensure the reliability and safety of data collection. Finally, through the test-bench, the battery expansion displacement-SOC curve and the battery bulk force-SOC curve under different discharge rates were tested, providing a basis for the development of a battery management system coupling temperature-current-voltage-displacement-force.

The effects of cholesterol accumulation on Achilles tendon biomechanics: A cross-sectional study

Familial hypercholesterolemia, a common genetic metabolic disorder characterized by high cholesterol levels, is involved in the development of atherosclerosis and other preventable diseases. Familial hypercholesterolemia can also cause tendinous abnormalities, such as thickening and xanthoma (tendon lipid accumulation) in the Achilles, which may impede tendon biomechanics. The objective of this study was to investigate the effect of cholesterol accumulation on the biomechanical performance of Achilles tendons, in vivo. 16 participants (10 men, 6 women; 37±6 years) with familial hypercholesterolemia, diagnosed with tendon xanthoma, and 16 controls (10 men, 6 women; 36±7 years) underwent Achilles biomechanical assessment. Achilles biomechanical data was obtained during preferred pace, shod, walking by analysis of lower limb kinematics and kinetics utilizing 3D motion capture and an instrumented treadmill. Gastrocnemius medialis muscle-tendon junction displacement was imaged using ultrasonography. Achilles stiffness, hysteresis, strain and force were calculated from displacement-force data acquired during loading cycles, and tested for statistical differences using one-way ANOVA. Statistical parametric mapping was used to examine group differences in temporal data. Participants with familial hypercholesterolemia displayed lower Achilles stiffness compared to the control group (familial hypercholesterolemia group: 87±20 N/mm; controls: 111±18 N/mm; p = 0.001), which appeared to be linked to Achilles loading rate rather than an increased strain (FH: 5.27±1.2%; controls: 4.95±0.9%; p = 0.413). We found different Achilles loading patterns in the familial hypercholesterolemia group, which were traced to differences in the centre of pressure progression that affected ankle moment. This finding may indicate that individuals with familial hypercholesterolemia use different Achilles loading strategies. Participants with familial hypercholesterolemia also demonstrated significantly greater Achilles hysteresis than the control group (familial hypercholesterolemia: 57.5±7.3%; controls: 43.8±10%; p<0.001), suggesting that walking may require a greater metabolic cost. Our results indicate that cholesterol accumulation could contribute to reduced Achilles function, while potentially increasing the chance of injury.

Theoretical and Experimental Study of a Thermo-Mechanical Model of a Shape Memory Alloy Actuator Considering Minor Hystereses

The paper presents a theoretical and experimental investigation of a thermo-mechanical model of an actuator composed of a shape memory alloy wire arranged in series with a bias spring. The developed mathematical model considers the dynamics of the actuator in the thermal and mechanical domains. The modelling accuracy is increased through the developed algorithm for modelling the minor and sub minor hystereses, thus removing the disadvantages of the classical model. The algorithm improves the accuracy, especially when using pulse-width modulation control, for which minor and sub minor hystereses are likely to occur. Experimental studies show that the system is very sensitive, and there are physical factors whose presence cannot be considered in the mathematical model. The experimental research has shown that setting constant values of the duty cycle is impossible to obtain a stable value of displacement and force. The comparison between the developed mathematical model results and the experimental results shows that the differences are acceptable. The improved modelling serves as a basis for designing such actuators and creating an improved automatic feedback control system to maintain a given displacement (force) or trajectory tracking.

Identification of Bearing Dynamic Parameters and Unbalanced Forces in a Flexible Rotor System Supported by Oil-Film Bearings and Active Magnetic Devices

As the rotational speed of conventional rotor systems supported by oil-film bearings has increased, vibration problems such as oil whip and oil whirl have become apparent. Our group proposed the use of active magnetic bearings (AMBs)/bearingless motors (BELMs) to stabilize these systems. In such a system, measuring the variable stiffness and damping of the oil-film bearings, the current-force and displacement-force parameters of the AMBs/BELMs, and the residual unbalanced force is necessary to satisfy the stability of the rotor system. These parameters are the foundation for the rotor dynamics analysis and optimization of the control strategy. In this paper, we propose a method to simultaneously identify the parameters of the oil-film bearings and AMBs/BELMs along with the residual unbalanced forces during the unbalanced vibration of the rotor. The proposed method requires independent rotor responses and control currents to form a regression equation to estimate all the unknown parameters. Independent rotor responses are realized by changing the PID control parameters of the AMBs/BELMs. Numerical simulation results show that the proposed method is highly accurate and has good robustness to measurement noise. The experimental results show that the unknown parameters identified by the responses generated by different controller parameters are similar. To confirm that the identification results are correct, verification experiments were carried out. The vibration amplitude of the rotor was successfully suppressed by applying a force to the rotor in the opposite direction to the residual unbalanced force. The frequency response characteristics and unbalanced responses of the rotor estimated by the values of the parameters identified show good consistency with the measured results.

Influence of Laying Angles in Reinforcement of Epoxy in Sisal Plain Woven Structures

This study is about microstructure characterization and understanding the flexural properties of plain-woven sisal fabric reinforced epoxy composites. Vibrational Spectroscopy (FTIR) and SEM (Scanning Electron Microscopy) were used to describe the plain-woven sisal fabric and sisal fiber reinforced epoxy composites. Two laying angles were incorporated into the epoxy resin (10 percent), i.e. [0°/90°] and [0°/45°]. To isolate the effect of epoxy type and whether woven sisal fibers were used, an analytical design that is based on [0°/90°] and [0°/45°] orientation used the results. Epoxy treated with woven sisal fibers had a higher tensile (0.62 GPa) and flexural modulus (0.69 GPa) with tensile (17 MPa) and flexural strength (14 MPa) while being applied to a surface that is sloped at 0°/45° and which generates a displacement force of approximately 12 mm and strain 15.8 %. While conventional Weibull failure theory has long been widely used to explain the failure of brittle bulk materials, this new equation integrates that theory with the lay angle effect on flexural strength in plain sisal to calculate flexural strength reinforcement in epoxy. This new method can be applied to any fiber reinforcement, regardless of the type, and in terms of the failure of that reinforcement, which is governed by linear elastic fracture mechanics, and agreement between experimental data sets is excellent. According to our expectations, this theoretical study is going to provide a new method for the advanced strain engineering system to be built using reinforced fibers.

Corrugated Diaphragm Actuator for Soft Robotic and Exoskeleton Applications

Soft robotics is projected to have a significant impact on healthcare, industry, and the military to deliver assistance in rehabilitation, daily living activities, repetitive motion tasks, and human performance augmentation. Many attempts have been made for application-specific robotic joints, robots, and exoskeletons using various actuator types, materials, and designs. The progress of creating soft robotic systems can be accelerated if a set of actuators with defined characteristics were developed, similar to conventional robotic actuators, which can be assembled to create desired systems including exoskeletons and end effectors. This work presents such an attempt by designing a modular corrugated diaphragm actuator that can apply linear displacement, force, and bending motion. This modular actuator approach allows for creating various robotic joints by arranging them into different configurations. Numerical simulation, fabrication, and testing were carried out to evaluate the displacement, force, and bending characteristics of the corrugated diaphragm actuator as a single unit and in multi-unit arrays to understand their applicability for different scenarios. Actuator arrays that are configured in a serial and parallel manner were investigated. The results will be presented in terms of using this modular actuator concept to create single and multi-DOF joints, which will demonstrate the versatility of this modular actuator approach.

Pore-Scale Simulation of Particle Flooding for Enhancing Oil Recovery

The particles, water and oil three-phase flow behaviors at the pore scale is significant to clarify the dynamic mechanism in the particle flooding process. In this work, a newly developed direct numerical simulation techniques, i.e., VOF-FDM-DEM method is employed to perform the simulation of several different particle flooding processes after water flooding, which are carried out with a porous structure obtained by CT scanning of a real rock. The study on the distribution of remaining oil and the displacement process of viscoelastic particles shows that the capillary barrier near the location with the abrupt change of pore radius is the main reason for the formation of remaining oil. There is a dynamic threshold in the process of producing remaining oil. Only when the displacement force exceeds this threshold, the remaining oil can be produced. The flow behavior of particle–oil–water under three different flooding modes, i.e., continuous injection, alternate injection and slug injection, is studied. It is found that the particle size and the injection mode have an important influence on the fluid flow. On this basis, the flow behavior, pressure characteristics and recovery efficiency of the three injection modes are compared. It is found that by injecting two kinds of fluids with different resistance increasing ability into the pores, they can enter into different pore channels, resulting in the imbalance of the force on the remaining oil interface and formation of different resistance between the channels, which can realize the rapid recovery of the remaining oil.

Study on Strength Damage Evolution Regulation of Sandstone under Cyclic Erosion

Owing to salt erosion, the sandstone of Yungang Grottoes has widespread weathering diseases. The soluble salt develops reciprocating crystallization pressure under the action of dry and wet cycles to diminish the sandstone strength. Finally, several pore-like and powder-like weathering phenomena are formed. To explore the change in sandstone strength during this process, the sandstone of Yungang Grottoes was taken as the research object. Herein, the uniaxial compression test, XRD test, and other methods were employed to study the samples under different salt erosion cycles. As the number of salt damage cycles increased, the phenomenon of sand particles on the sandstone surface gradually amplified. The compressive strength, tensile strength, and elastic modulus of sandstone decreased with the increase in erosion cycles. The curve was divided into two stages, and the macroscopic and microscopic damage equations of sandstone after erosion were established. During the entire damage process, erosion damage served as the basis of load damage and was affected by different cycles, impacting the development process of load damage. Through the establishment of numerical simulation meso-parameter evolution equations, the PFC2D particle flow model was used to conduct uniaxial simulation tests, and the simulation results were close to the macroscopic test results. Using the particle flow simulation test parameters under salt erosion, the development of the distribution of “displacement-force chain-crack” was analyzed under different salt erosion cycles. These results further revealed the meso-fracture damage characteristics of the Yungang Grottoes sandstone under the action of salt damage and provided a theoretical basis and a novel method for the protection of Yungang Grottoes against weathering.