Fully Fabric-Based Triboelectric Nanogenerators as Self-Powered Human–Machine Interactive Keyboards

Combination flexible and stretchable textiles with self-powered sensors bring a novel insight into wearable functional electronics and cyber security in the era of Internet of Things. This work presents a highly flexible and self-powered fully fabric-based triboelectric nanogenerator (F-TENG) with sandwiched structure for biomechanical energy harvesting and real-time biometric authentication. The prepared F-TENG can power a digital watch by low-frequency motion and respond to the pressure change by the fall of leaves. A self-powered wearable keyboard (SPWK) is also fabricated by integrating large-area F-TENG sensor arrays, which not only can trace and record electrophysiological signals, but also can identify individuals' typing characteristics by means of the Haar wavelet. Based on these merits, the SPWK has promising applications in the realm of wearable electronics, self-powered sensors, cyber security, and artificial intelligences.

Variable Admittance Control Based on Human–Robot Collaboration Observer Using Frequency Analysis for Sensitive and Safe Interaction

A collaborative robot should be sensitive to the user intention while maintaining safe interaction during tasks such as hand guiding. Observers based on the discrete Fourier transform have been studied to distinguish between the low-frequency motion elicited by the operator and high-frequency behavior resulting from system instability and disturbances. However, the discrete Fourier transform requires an excessively long sampling time. We propose a human–robot collaboration observer based on an infinite impulse response filter to increase the intention recognition speed. By using this observer, we also propose a variable admittance controller to ensure safe collaboration. The recognition speed of the human–robot collaboration observer is 0.29 s, being 3.5 times faster than frequency analysis based on the discrete Fourier transform. The performance of the variable admittance controller and its improved recognition speed are experimentally verified on a two-degrees-of-freedom manipulator. We confirm that the improved recognition speed of the proposed human–robot collaboration observer allows us to timely recover from unsafe to safe collaboration.

The violent ground motion before the Jiuzhaigou earthquake Ms7.0

An Ms7.0 earthquake occurred in Jiuzhaigou, Sichuan Province, China, on August 8, 2017. In this study, we used the vertical component data from 31 seismic stations near the epicenter from May 1 to August 20, 2017, to calculate the amplitude spectrum hourly using the fast Fourier transform method. Furthermore, the spectral area of the low frequency band (0.02–1 Hz), which represents the energy of low frequency motion, was calculated. In this way, the temporal and spatial variations in the vertical ground motion in this region were determined. Four high-value processes occurred in mid-June, mid-July, late July, and early August (the last three are discussed in this article). Based on a comparison with the local meteorological data, the meteorological factors had no influence, local geological factors did not affect the results, and typhoon factors did not show obvious correlation. Combined with the results of previous studies, we believe that the increase in the spectral area reflects the intense movement of deep material in the region related to the Jiuzhaigou earthquake. The spatial distribution of the spectral area (energy) reveals that the deep material moved eastward rapidly, was obstructed by the Sichuan Basin, and expanded to the northwest in a U-shaped channel, which may be the main dynamic factor for the formation or triggering of the earthquake.

Rudder Roll Stabilization Based on Arc Tangent Nonlinear Feedback for Ships

The rudder is used for damping the roll motion of a ship. Study of this motion is the essence of this paper. The responses of yaw and roll motions are different as the rudder angle varies. The low frequency motion of the rudder mainly affects the ship’s yaw motion, whereas the high frequency motion of the rudder mainly affects the roll motion. As long as the controller is well designed, the characteristic of the rudder can be used to reduce the roll motion. In order to save energy and reduce steer frequency, a nonlinear feedback controller is proposed based on the arc tangent function processing feedback error to save energy consumption. In addition, a ZOH component is applied in the system to reduce the steer frequency. In heavy sea state, simulation results illustrate that controllers based on pole assignment with and without nonlinear feedback can reduce roll motion by 32.1% and 30.3%, respectively, when the rudder turn rate is limited within 7°/s. Furthermore, the former reduces the amplitude of rudder angle by 23.3% compared with the latter, which means the nonlinear feedback control consumes less energy. Consequently, the ZOH can lower steer frequency to once every 1 s, which protects steering gear from abrasion.

All-fiber tribo-ferroelectric synergistic electronics with high thermal-moisture stability and comfortability

Developing fabric-based electronics with good wearability is undoubtedly an urgent demand for wearable technologies. Although the state-of-the-art fabric-based wearable devices have shown unique advantages in the field of e-textiles, further efforts should be made before achieving “electronic clothing” due to the hard challenge of optimally unifying both promising electrical performance and comfortability in single device. Here, we report an all-fiber tribo-ferroelectric synergistic e-textile with outstanding thermal-moisture comfortability. Owing to a tribo-ferroelectric synergistic effect introduced by ferroelectric polymer nanofibers, the maximum peak power density of the e-textile reaches 5.2 W m−2 under low frequency motion, which is 7 times that of the state-of-the-art breathable triboelectric textiles. Electronic nanofiber materials form hierarchical networks in the e-textile hence lead to moisture wicking, which contributes to outstanding thermal-moisture comfortability of the e-textile. The all-fiber electronics is reliable in complicated real-life situation. Therefore, it is an idea prototypical example for electronic clothing.

Generation of disturbances in the boundary layer of a flat plate by periodic low-frequency motion of the surface section

The development of localized disturbances, generated by periodic impulse lifting of three-dimensional surface in the flat plate boundary layer at Reδ1 > 400 is experimentally investigated. It is shown that a large amplitude surface lifting leads simultaneously to the formation of two types of perturbations in the boundary layer: longitudinal localized structures and two wave packets. Spatial development of oscillations at the central frequency of the wave packets is consistent with the linear theory of hydrodynamic stability.

Research on the Influence of Backlash on Mesh Stiffness and the Nonlinear Dynamics of Spur Gears

In light of ignoring the effect of backlash on mesh stiffness in existing gear dynamic theory, a precise profile equation was established based on the generating processing principle. An improved potential energy method was proposed to calculate the mesh stiffness. The calculation result showed that when compared with the case of ignoring backlash, the mesh stiffness with backlash had an obvious decrease in a mesh cycle and the rate of decline had a trend of decreasing first and then increasing, so a stiffness coefficient was introduced to observe the effect of backlash. The Fourier series expansion was employed to fit the mesh stiffness rather than time-varying mesh stiffness, and the stiffness coefficient was fitted with the same method. The time-varying mesh stiffness was presented in terms of the piecewise function. The single degree of freedom model was employed, and the fourth order Runge–Kutta method was utilized to investigate the effect of backlash on the nonlinear dynamic characteristics with reference to the time history chart, phase diagram, Poincare map, and Fast Fourier Transformation (FFT) spectrogram. The numerical results revealed that the gear system primarily performs a non-harmonic-single-periodic motion. The partially enlarged views indicate that the system also exhibits small-amplitude and low-frequency motion. For different cases of backlash, the low-frequency motion sometimes shows excellent periodicity and stability and sometimes shows chaos. It is of practical guiding significance to know the mechanisms of some unusual noises as well as the design and manufacture of gear backlash.

Validation of Applicability of Low Frequency Motion Analysis Theory Using Observation Data of Floating Offshore Substation

In recent years, the social demands for the introduction of renewable energy are increasing, demonstration projects of floating offshore wind power generation are being implemented and planned around the world. In Japan, a demonstration project named Fukushima FORWARD (Fukushima Floating Offshore Wind Farm Demonstration Project) has been conducted since 2011. Fukushima FORWARD is carried out by the Ministry of Economy, Trade and Industry. The project is the world’s first floating offshore windfarm with a total capacity of 14 MW, including three floating offshore wind facilities and one floating offshore substation. In Fukushima FORWARD, Japan Marine United Corporation is in charge of floater part EPCI (Engineering, Procurement, Construction and Installation) of one floating offshore wind facility and one floating offshore substation. This floating offshore substation is installed in order to observe meteorological and oceanographic data and motion data as well as boosting the generated electric power. Since the installation in 2013 it continues to record various kinds of continuous data. The substation is an advanced spar type floater moored by four spread catenary mooring lines. In the design of the mooring system for offshore structure, the motion of the structure under environmental external force is very important. The motion of the moored floating structure is divided into wave frequency motion, which is a motion of a relatively short period, and low frequency motion caused by mooring restoring force and variable external force, both of which are important elements in the design. Among them, wave frequency motion is known to be accurately estimated by potential theory as a result of research on various types of structures. On the other hand, in addition to the existence of various calculation methods including time domain analysis, its statistical characteristic and applicability are entirely depending on the target structure. Also, observation data of low frequency motion have been very few. In this paper, long-term data observed at the floating offshore substation in Fukushima FORWARD was analyzed with focusing on low frequency motion and its statistical properties were clarified. Furthermore, we analyzed the low frequency wave force spectrum and motion by conventional low frequency motion theory using the wave drifting force calculated by the potential theory. And, we compared the calculated value with the analysis result of the observation data and validated the applicability of the simplified low frequency motion theory.

On the extraction technique of the single-coil self-feedback signal on a standard vibration table

In the process of calibration on vibration and shock transducers, it is necessary for the vibration table to generate a small sine-function form distortion as the excitation signal, and the closed-loop servo feedback technology is one of the proven effective ways to reduce low-frequency motion signal distortion of the vibration table. In this paper, we report a method based on the principle of closed-loop servo feedback that can directly extract induction electromotive force of the vibrator coil. This method solves the problems caused by using sensors in the process of getting the vibration signals. Furthermore, this device has some advantages such as small size, light weight, low cost and simple maintenance. In this article, the system components and technical indexes and analyzis of the control method of the vibration table are described. Next, we compare the wave distortion obtained using monocoil signal extraction technology and that obtained using relative speed sensor. Finally, the error analysis of monocoil signal extraction technology is carried out, and the experiment is finished to prove this analysis.