To address the tracking control problem for
n
-DOF parallel robots in presence of the lumped disturbance, including modeling errors, friction and external disturbance, a finite-time stable robust ...sliding mode dynamic control (FRSMDC) for parallel robots is explored. From the implementation condition of the FRSMDC for parallel robots, the limitation on the change rate of the lumped disturbance is relaxed for easy realization. From the results of the FRSMDC for parallel robots, the finite-time stability of the sliding variable is proved and the settling time is derived; the switching gain required is only larger than the upper bound of the disturbance estimation error, instead of the upper bound of the disturbance, due to the feed-forward compensation to the lumped disturbance via a disturbance observer. Consequently, the system robustness is improved and the chattering of FRSMDC is alleviated. The finite-time stability of the closed-loop system is confirmed with Lyapunov theory. Besides, the application of the proposed method is extended to a general multi-input multi-output nonlinear system with the relative degree
m
by analogy. Finally, the case of the dynamic control of a 6-DOF parallel robot for automobile electro-coating conveying is studied for simulation and experiment, so as to attest the validity of the FRSMDC for parallel robots.
Understanding the mechanism of the stability and decay of surface electrostatic charges in different liquid environments is critical for the reliability of devices based on electrostatic functions or ...preventing the damage from electrostatic charge accumulation. In this work, the influences of surface electrostatic charges in polar and protic (Ethanol and Water), polar and aprotic (Tetrahydrofuran and Chloroform), and non-polar and aprotic (Benzene and Hexane) liquids have been investigated. Results prove that ionization in liquid or polarity of the liquid molecules can determine the electrostatic charges neutralization, and adding small amount of matter (1% Vol) that can ionize in non-polar and aprotic liquids can avoid the electrostatic charges accumulation. Moreover, air-bubble-structured electret is designed to improve the water-against ability for surface electrostatic charges.
This work provides strategies for improving the durability of electrostatic-based devices in liquids and preventing the risk caused by electrostatic charges accumulation. Display omitted
•Ionization and polarity of the liquid molecule are two key parameters that lead to the neutralization of electrostatic charges.•Adding small amount of matter that can ionize in non-polar and aprotic liquid can speed up the decay of charges.•Air-bubble-structured electret is designed and can recover the surface charges after water wet-dry process.
While electrochemical supercapacitors often show high power density and long operation lifetimes, they are plagued by limited energy density. Pseudocapacitive materials, in contrast, operate by fast ...surface redox reactions and are shown to enhance energy storage of supercapacitors. Furthermore, several reported systems exhibit high capacitance but restricted electrochemical voltage windows, usually no more than 1 V in aqueous electrolytes. Here, it is demonstrated that vertically aligned carbon nanotubes (VACNTs) with uniformly coated, pseudocapacitive titanium disulfide (TiS2) composite electrodes can extend the stable working range to over 3 V to achieve a high capacitance of 195 F g−1 in an Li‐rich electrolyte. A symmetric cell demonstrates an energy density of 60.9 Wh kg−1—the highest among symmetric pseudocapacitors using metal oxides, conducting polymers, 2D transition metal carbides (MXene), and other transition metal dichalcogenides. Nanostructures prepared by an atomic layer deposition/sulfurization process facilitate ion transportation and surface reactions to result in a high power density of 1250 W kg−1 with stable operation over 10 000 cycles. A flexible solid‐state supercapacitor prepared by transferring the TiS2–VACNT composite film onto Kapton tape is demonstrated to power a 2.2 V light emitting diode (LED) for 1 min.
TiS2 is coated coaxially onto vertically aligned carbon nanotubes (VACNTs) via an atomic layer deposition sulfurization process, providing an exceptionally high capacitance of 195 F g‐1 and working voltage window up to 3 V in a Li+ ion rich (21 m) electrolyte. The energy density of a supercapacitor based on TiS2–VACNT electrodes is enhanced to 60.9 Wh kg‐1, which outperforms many other pseudocapacitors.
Developing eco-friendly and low-cost electronics is an effective strategy to address the electronic waste issue. In this study, transparent cellulose nanopaper (T-paper) and polylactic acid (PLA) ...electret were used to construct a biodegradable and transparent paper-based electret nanogenerator. The nanogenerator could be assembled with paper products to form a self-powered smart packaging system without impairing the appearance, due to the high transparency and desirable output performance. Furthermore, the self-degradation property in the natural soil of the nanogenerator is demonstrated, indicating that the nanogenerator is recycled and will not pollute the environment. We anticipate that this study will provide new insights to develop eco-friendly power source and paper-based electronics.
Different coating technological requirements of automobile electro-coating control system have different desired trajectories. For a dual parallel robot used for automobile electro-coating conveying ...(DPRAEC), an intelligent tracking smooth sliding mode synchronization control method (ITSSMSC) is proposed to achieve better tracking control performance with high synchronization and flexibility for the system under different desired trajectories. According to the dual parallel and symmetrical structure of the robot, the sliding surface is designed based on a composite error. A deep neural network with multi-hidden layer is trained by deep learning algorithms. Then, any given trajectories caused by different coating technological requirements could be tracked without tuning additional parameters and the synchronous performance could be guaranteed. The convergence of the network training process and the stability of the ITSSMSC are proved theoretically. Compared with the synchronization proportion-derivative control, the sliding mode control based on constant velocity reaching law without synchronization control and the smooth sliding mode synchronization control without training, simulation and experimental results demonstrate the effectiveness of the proposed approach. Compared with synchronization proportion-derivative control, the maximum tracking errors of constant velocity reaching law without synchronization control among each active joint are, respectively, reduced 92.2%, 94.7%, 98.8%. The maximum tracking errors of smooth sliding mode synchronization control and ITSSMSC in
z
direction are, respectively, 9.06×10−5m and 1.01×10−9m. The maximum tracking errors of smooth sliding mode synchronization control and ITSSMSC in
β
angle are, respectively, 4.50×10−3rad and 1.45×10−4rad. Therefore, the proposed control method could improve the tracking control performance and synchronization performance simultaneously under different desired trajectories.
Monitoring the breath information from two nostrils can detect breath-related health problems. In this work, we introduce a wearable hot-film/calorimetric breath sensing system composed of a hot-film ...senor in the center and two calorimetric sensors on two sides. This design has the advantages of low power consumption of 60 mW and good sensitivity to simultaneously measure the mix breath velocity and individual breath airflow signals from the two nostrils. In prototype demonstrations, abnormal breath conditions (apnea, hypopnea, polypnea) and the asymmetric breath conditions between the right and left nostril have been recorded and analyzed for potential usages in the diagnosis of specific breath-related diseases.
•We introduce a wearable hot-film/calorimetric sensing system composed of a hot-film sensor and two calorimetric sensors.•The sensing system has advantages of low power consumption and good responding time.•The sensing system could quantificationally characterize the asymmetric breath condition between right and left nostril.
For the trajectory tracking control of uncertain hybrid robot with fluid resistance, the matched and mismatched uncertain problem is a challenge. The matched uncertainties include joint friction, ...modeling error and so on. And the fluid resistance may cause the time-varying discontinuous mismatched uncertainty. Thus, the unmeasured auxiliary variables-based second-order sliding mode control with time-varying gain extended state observer for the hybrid robot is proposed. By defining unmeasured auxiliary state variables, the dynamic equation of hybrid robot with mismatched uncertainty of fluid resistance is reconstructed into a state equation with only matched uncertainty structure. To observe and compensate the lumped uncertainty including matched uncertainties, fluid resistance uncertainty and unmeasured auxiliary state variables of hybrid robot, an extended state observer is designed, which only needs the condition of bounded uncertainty change rate. Moreover, by devising the continuous adjustment rule for observer gain’s transient process, the observed error converges quickly and the initial peaking value of system state observation is reduced. To suppress the residual error of uncertainty compensation, the unmeasured auxiliary variables-based super-twisting sliding mode control algorithm is combined with the time-varying gain extended state observer, which could enhance system robustness and weaken chattering of the sliding mode control. The stability of the closed-loop system is proved by Lyapunov stability theorem. Finally, taking the hybrid robot for automobile electro-coating conveying as an example, simulations and experiments are conducted on the prototype system to demonstrate the effectiveness of the proposed control method.
The cellular piezoelectret generator (CPG) has drawn considerable attention as an emerging flexible energy harvester because of its advantages of a simple structure, easy assembly, a low cost, and ...eco‐friendliness. To facilitate practical applications, an initial theoretical study of CPGs is presented in this work, in which the output characteristics of CPGs can be optimized through an appropriate choice of parameters, including the electret dielectric permittivity, device structure, polarization process, and external load. A good agreement with experimental results is achieved, verifying the validity of the theoretical study. The reported theory offers a complete interpretation of the dynamic working mechanism of CPGs and provides significant guidance for the design of a CPG with enhanced yield.
A theoretical study of cellular piezoelectret generators (CPGs) is presented, focusing on the enhancement of their dynamic performance. An effective means to optimize the output characteristics of CPGs is found. This discovery will enhance performance and application range of future devices.
In the practical application of sarcopenia screening, there is a need for faster, time-saving, and community-friendly detection methods. The primary purpose of this study was to perform sarcopenia ...screening in community-dwelling older adults and investigate whether surface electromyogram (sEMG) from hand grip could potentially be used to detect sarcopenia using machine learning (ML) methods with reasonable features extracted from sEMG signals. The secondary aim was to provide the interpretability of the obtained ML models using a novel feature importance estimation method.
A total of 158 community-dwelling older residents (≥ 60 years old) were recruited. After screening through the diagnostic criteria of the Asian Working Group for Sarcopenia in 2019 (AWGS 2019) and data quality check, participants were assigned to the healthy group (n = 45) and the sarcopenic group (n = 48). sEMG signals from six forearm muscles were recorded during the hand grip task at 20% maximal voluntary contraction (MVC) and 50% MVC. After filtering recorded signals, nine representative features were extracted, including six time-domain features plus three time-frequency domain features. Then, a voting classifier ensembled by a support vector machine (SVM), a random forest (RF), and a gradient boosting machine (GBM) was implemented to classify healthy versus sarcopenic participants. Finally, the SHapley Additive exPlanations (SHAP) method was utilized to investigate feature importance during classification.
Seven out of the nine features exhibited statistically significant differences between healthy and sarcopenic participants in both 20% and 50% MVC tests. Using these features, the voting classifier achieved 80% sensitivity and 73% accuracy through a five-fold cross-validation. Such performance was better than each of the SVM, RF, and GBM models alone. Lastly, SHAP results revealed that the wavelength (WL) and the kurtosis of continuous wavelet transform coefficients (CWT_kurtosis) had the highest feature impact scores.
This study proposed a method for community-based sarcopenia screening using sEMG signals of forearm muscles. Using a voting classifier with nine representative features, the accuracy exceeds 70% and the sensitivity exceeds 75%, indicating moderate classification performance. Interpretable results obtained from the SHAP model suggest that motor unit (MU) activation mode may be a key factor affecting sarcopenia.
Wearable active sensors have extensive applications in mobile biosensing and human–machine interaction but require good flexibility, high sensitivity, excellent stability, and self-powered feature. ...In this work, cellular polypropylene (PP) piezoelectret was chosen as the core material of a sensitivity-enhanced wearable active voiceprint sensor (SWAVS) to realize voiceprint recognition. By virtue of the dipole orientation control method, the air layers in the piezoelectret were efficiently utilized, and the current sensitivity was enhanced (from 1.98 pA/Hz to 5.81 pA/Hz at 115 dB). The SWAVS exhibited the superiorities of high sensitivity, accurate frequency response, and excellent stability. The voiceprint recognition system could make correct reactions to human voices by judging both the password and speaker. This study presented a voiceprint sensor with potential applications in noncontact biometric recognition and safety guarantee systems, promoting the progress of wearable sensor networks.
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