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Purpose: For suppressing the vibration excitation transmission from the robot to the elastic component during robotic handling, a new type of quasi-zero-stiffness flexible connection device (QZSCD) is designed. Methods: By introducing the tilt linkage on the basis of the traditional quasi-zero-stiffness isolator with three oblique springs, the configuration of the QZSCD is confirmed, which can actively adapt to varying load conditions. According to the static equilibrium relationship, the conditions that the QZSCD has zero-stiffness at the equilibrium position are obtained. Then, the optimal structure parameters of the QZSCD are determined based on maximizing the system quasi-zero-stiffness interval. And the quantitative relationship between the tilt angle of the tilt linkage and the load mass is investigated. Furthermore, a unified dynamic equation of the QZSCD under varying load conditions is established. The influences of the structural parameters, the tilt linkage angle, and the load mass on the vibration response and displacement transmission characteristics of the QZSCD are analyzed. Results: Simulation and experimental results indicate that by actively adjusting the tilt angle of the tilt linkage, the QZSCD can ensure good vibration transmission suppression performance under varying load conditions during the robotic handling of the elastic component. Conclusions: This study provides a new solution for suppressing the system vibration excitation transmission of the robotic handling system of the elastic component. [ABSTRACT FROM AUTHOR]

The current work presents a theoretical framework to analyze the nonlocal thermoelastic model with a general kernel function for memory-based derivatives by incorporating two-time delays. The introduced model aims at studying the thermomechanical response of rotating size-dependent nanobeams. The nonlocal elasticity theory and the generalized heat conduction model with phase delays are utilized to formulate the problem. In the proposed model, the thermal conductivity is expected to vary linearly with temperature and the system is excited by a variable harmonic heat source by considering the time-dependent exponential decaying load. To this end, the semi-analytical solutions for the transverse and axial displacements, thermodynamic temperature and bending moment are examined using the Laplace transform method. The effects of the nonlocal parameter and various loading conditions are also investigated and discussed. Finally, it is demonstrated that how the linear variation of thermal conductivity could affect the performance of the considered system. [ABSTRACT FROM AUTHOR]

The objectives of this article are to present a mathematical model that uses Eringen's nonlocal elasticity theory to describe the free vibratory motion of rotating nanoscale beams. The Euler–Bernoulli beam theory, Eringen's nonlocal elasticity theory, and generalized thermoelasticity with phase-lags are used to derive the system of equations for rotating thermoelastic nanobeams. The studied nanobeam is subjected to ramp-type heating and to a significantly exponentially decaying load. The analytical solution was derived using the Laplace transform method, and the transformation of the converted fields was performed by applying the residue calculus. The numerical results of the physical fields under investigation are collected and displayed graphically. The impacts of nonlocal parameters, different types of loads, and ramping-time parameters in addition to rotation were studied and analyzed. [ABSTRACT FROM AUTHOR]

In this article, the influence of thermal conductivity on the dynamics of a rotating nanobeam is established in the context of nonlocal thermoelasticity theory. To this end, the governing equations are derived using generalized heat conduction including phase lags on the basis of the Euler-Bernoulli beam theory. The thermal conductivity of the proposed model linearly changes with temperature and the considered nanobeam is excited with a variable harmonic heat source and exposed to a time-dependent load with exponential decay. The analytic solutions for bending moment, deflection and temperature of rotating nonlocal nanobeams are achieved by means of the Laplace transform procedure. A qualitative study is conducted to justify the soundness of the present analysis while the impact of nonlocal parameter and varying heat source are discussed in detail. It also shows the way in which the variations of physical properties due to temperature changes affect the static and dynamic behavior of rotating nanobeams. It is found that the physical fields strongly depend on the nonlocal parameter, the change of the thermal conductivity, rotation speed and the mechanical loads and, therefore, it is not possible to neglect their effects on the manufacturing process of precise/intelligent machines and devices. [ABSTRACT FROM AUTHOR]

Quadrotors are highly maneuverable drones, which are susceptible to the parameter uncertainties such as the mass, drag coefficients, and moment of inertia. Whose nonlinearities, aerodynamic disturbances, and higher coupling between the rotational and the translational dynamics stand for a problem that demands a robust controller. In the present paper, a fractional order (FO) improved super twisting proportional-integral-derivative sliding-mode control (STPIDSMC) is proposed for the quadrotor system. To improve the speed tracking performance, a FOPIDSM surface is designed. Moreover, the proposed FO control approach ensures fast convergence, high precision, good robustness against stochastic perturbations and uncertainties. Finally, the performance of the FOSTPIDSMC is investigated under different scenarios. The simulation results clearly show the high control performance, efficiency and high disturbance rejection capacity of the controller strategy proposed in this work in comparison with the nonlinear internal model control (NLIMC) and FO backstepping sliding mode control (FOBSMC) strategies. [ABSTRACT FROM AUTHOR]

Abstract Due to their high maneuverability, quadrotors are very suitable vehicles for displacement of loads. Even so, loads can cause overweight that acts as a disturbance in momentums of inertia of quadrotor. As a result, the performance of quadrotor in path tracking will be negatively affected. In this paper, a fractional order sliding mode controller based on back-stepping method is designed to attenuate wind disturbance and effects of variations in load and momentums of inertia. The amount of load is estimated by considering an adaptive correcting coefficient in mass parameter of quadrotor, to allow the quadrotor to track the ideal path in the presence of such disturbances. Then, by using numerical simulation, the robustness of the proposed controller is shown in face of the disturbances. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The present paper produces a new nonlocal model for thermoelastic nanobeams of temperature-dependent thermal conductivity. A nanobeam excited by harmonically varying heat and subjected to an exponential decaying time varying load. The analytical solution has been gotten by means of Laplace’s transform method in time domain and its inversion has been preceded by using calculus of residues. Effects of nonlocal parameter, variable thermal conductivity, varying load and angular frequency of thermal vibration on the field quantities of nanobeam are investigated and discussed. [ABSTRACT FROM AUTHOR]

This paper presents an experimental characterization of a two-stage planetary gearbox (TSPG) designed at the Laboratory of Robot Mechatronics (LARM2) in the University of Rome Tor Vergata. The TSPG operates differentially as function of the attached load and the internal friction forces caused for the contact between gears. Experiments under varying load conditions are developed in order to analyze the usefulness of the gearbox to avoid excessive torques on its internal elements. The analysis of the dynamic torques is presented as an indicator of stability in the gearbox operation. The results show that the actuation of the second operation stage reduces the torques 57% in the output shaft and 65% in the input shaft. The efficiency of the gearbox is estimated as 40% in presence of high internal friction forces.

This work produces a new model of nonlocal thermoelastic nanobeams of temperature-dependent physical properties. A nanobeam is excited by harmonically varying heat and subjected to an exponential decaying time varying load. The analytical solution is obtained by means of Laplace transform method in time domain. Inversions of transformed solutions have been preceded by using calculus of residues. Effects of nonlocal parameter, variability thermal conductivity, varying load and angular frequency of thermal vibration on studied fields of nanobeam are investigated and discussed. [ABSTRACT FROM AUTHOR]

In this paper, an active disturbance rejection control approach is proposed for a pneumatic muscle actuator mechanism to achieve angle tracking precisely under varying load conditions. The varying load conditions are treated as external disturbances which are estimated by a linear extended state observer. An active disturbance rejection controller is presented to compensate negative impacts induced by the varying loads. Moreover, stabilization of the closed-loop system are performed for the pneumatic muscle actuator mechanism. Finally, experimental results show the effectiveness of the developed technique in this paper. [ABSTRACT FROM AUTHOR]

The existing lumped parameter model was commonly used to analyze the non-linear dynamics of gear systems, in which stiffness excitation and error excitation due to eccentricity were major considerations, while time-varying backlash caused by gear eccentricity and varying load were rarely concerned. In this paper, theoretical formulas of no load transmission error (NLTE) and time-varying backlash are presented, which are suitable for the double gear eccentricities system whose contact ratio is random. The finite element model is developed and confirmed by the results of dynamic transmission error (DTE) without gear eccentricity, furthermore, the DTE can be predicted by this model in consideration of gear eccentricities and varying load. Under three different cases (no backlash, constant backlash and time-varying backlash), the influence of backlash on DTE is investigated with the gear pairs suffering from sinusoidal varying loads. It turns out that the DTE curve jumps as the load direction changes, and the discontinuity value is just equal to the backlash size at that time. What is more, if the frequency of load change is high enough (here, mesh frequency is chosen), the DTE curve distributes in a certain region, whose lower outline is approximately (transmission error caused by tooth deformations is taken into account as well) consistent with the NLTE curve and the upper outline is approximately consistent with the curve of NLTE plus backlash. [ABSTRACT FROM AUTHOR]

• Integrating static and ultrasonic structural health monitoring. • Combination of FBG strain arrays and PSFBG acoustic emission sensors. • Structural health monitoring of full-size aerospace multi-function capsule. • Alerting the unhealthy status of aerospace structures before catastrophic failure. In this study, we developed an integrated static and ultrasonic structural health monitoring (SHM), that was achieved using fiber Bragg grating (FBG) arrays and phase-shifted FBG (PSFBG) sensors, to monitor a full-size aerospace multi-function capsule under varying load. The FBG and PSFBG were bonded using direct and remote adhesive methods, respectively, to ensure the performance of the integrated SHM. The static strain measured by FBG accurately followed the loading curve during the initial 15 min of the test, and subsequently exhibited an irregular trend due to damage. Acoustic emission signals induced by damage were first detected by PSFBG at 15 min 11 sec. Following the detectable irregular strain and AE signals, the failure of the capsule manifested as a wrinkling ultimately occurred at 18 min. The FBG arrays and PSFBG sensors performed well for the integrated SHM and demonstrated that the newly proposed method can alert the unhealthy status of a large-scale aerospace structure before catastrophic failure. [ABSTRACT FROM AUTHOR]

Abstract: This study proposes a sensor-less adaptive fuel concentration control (SAFCC) algorithm to maintain methanol concentration consistency for direct methanol fuel cells (DMFC). Methanol concentration has a dominant effect on fuel cell performance, however varying load poses a problem to maintain consistent concentration. The transient response for varying load is influenced by a series of interactively complex factors. Here, we introduce the SAFCC algorithm by measuring the present voltage and checking the decrease from a reference voltage. Compared to existing literature on sensor-less control methods, the delicate but simple algorithm can avoid complex mathematical derivation while maintaining quick decision to inject fuel. This algorithm can be used under both of steady and dynamic loading conditions and has the adaptive capability suitable for degraded fuel cells. Practical experiments for several scenarios are carried out with satisfactory results. [Copyright &y& Elsevier]

Gearboxes usually run under fluctuating load conditions during service, however most of papers available in the literature describe models of gearboxes under stationary load conditions. Main task of published papers is fault modeling for their detection. Considering real situation from industry, the assumption of stationarity of load conditions cannot be longer kept. Vibration signals issued from monitoring in maintenance operations differ from mentioned models (due to load non-stationarity) and may be difficult to analyze which lead to erroneous diagnosis of the system. The objective of this paper is to study the influence of time varying load conditions on a gearbox dynamic behavior. To investigate this, a simple spur gear system without defects is modeled. It is subjected to a time varying load. The speed-torque characteristic of the driving motor is considered. The load variation induces speed variation, which causes a variation in the gearmesh stiffness period. Computer simulation shows deep amplitude modulations with sidebands that don't differ from those obtained when there is a defective tooth. In order to put in evidence the time varying load effects, Short Time Fourier Transform and then Smoothed Wigner-Ville distribution are used. Results show that the last one is well suited for the studied case. The experimental validation presented at the end of the paper confirms the obtained results. Such results offer useful information when diagnosing gear transmissions by avoiding confusing conclusions from vibration signals. [ABSTRACT FROM AUTHOR]

In this paper, an intelligent technique for detecting the turn fault and supply voltage unbalances in an induction machine is proposed under varying load conditions. The proposed probabilistic neural network (PNN) technique is based on well-established statistical principles rather than heuristic approaches that are adopted in the multi-layer perceptrons. The PNN is derived from the Bayes decision strategy and nonparametric kernel-based estimators of probability density functions. The machine model is developed for inter-turn short circuit fault and it is compared with its a priori models for its robustness in detecting the fault at incipient stages under various operating conditions of the machine. This algorithm is proposed for first time and training, testing, and validation results using the method appear promising and easily realizable in the industries. [ABSTRACT FROM AUTHOR]

Leakages and valve faults are among the most common faults in hydraulic systems. This paper studies the real-time detection and isolation of certain leakage and valve faults based on the results obtained in part one. In the first part, the mathematical model of a hydraulic test bed was analysed with Global Sensitivity Analysis to facilitate a systematic and verified approach to model-based condition monitoring. In this paper, an Unscented Kalman Filter-based Fault Detection and Isolation scheme for leakage and valve faults of a generic servo valve-controlled hydraulic cylinder is devised. Compared to existing literature, the leakage and valve faults are decoupled from cylinder static and dynamic loading which makes the results generic and applicable to any servo valve-controlled hydraulic cylinder. Moreover, a more comprehensive set of fault patterns for the detection and isolation of leakages and valve faults with experimental and simulation results are presented. We show that detecting an external leakage of as small as 0.17 l/min is possible in some cases, but the accuracy of the method varies considerably. We also report why the isolation of valve faults from leakages is very difficult. [ABSTRACT FROM AUTHOR]

Abstract: Crack propagation behavior of SCM440H low-alloy steel enhanced by absorbed hydrogen is investigated. Six materials tempered at different temperatures are used. Effects of stress ratio, loading frequency, hold time and material hardness on the crack propagation rate are examined under long-term varying load. Tests have been performed under continuous hydrogen charging, in which the crack tip has been isolated from the electrolyte and kept dry. An acceleration of crack propagation rate about six times compared to the uncharged material is found in all materials. In addition to this, however, an unexpected acceleration of crack propagation up to 1000 times is experienced under certain conditions. In materials with Vickers hardness higher than 280 tested at low frequency, the above marked acceleration is experienced. The crack surface morphology is quasi-cleavage. This critical hardness (HV =280) is a little lower than the usually accepted critical hardness for delayed failure (HV =350). In material with Vickers hardness lower than 268, however, such a marked acceleration is not experienced. [Copyright &y& Elsevier]

Brushless dc (BLDC) machines are finding increasing use in applications that demand high and rugged performance. Automotive and aerospace are some such areas where these machines may be used. In this context, condition monitoring of these machines would provide added value. This paper investigates the effect of several potential rotor faults on the current spectrum of BLDC motors with a view to develop an effective condition-monitoring scheme. The effect of load unbalances, misalignments, and varying load torques on the diagnosis of such machines is investigated. A method to estimate the strength of the rotor magnets is also provided. Simulation and experimental results are presented to substantiate that current signature analysis could be a viable tool for diagnosing the condition of BLDC machines. [ABSTRACT FROM AUTHOR]

Pin-on-disk type wear tests of mild steel in contact with itself were conducted under unlubricated conditions in moist air to investigate the effect of changes in load on the transition behavior between severe and mild wear. Machines in operation are usually subjected to varying loads. In this study, two contact load levels were used as a simple varying load condition. The load was changed in a step-wise manner between the low and high levels either once or twice during certain tests.Severe wear appears at the high load levels and mild wear at the low load levels in wear tests under constant loading. After oxidized, work-hardened wear surfaces have been formed under mild wear at the low load during the first stage, the wear mode changes to “quasi-mild wear” having a low rate at the high load in the final stage. The load range, where the low wear rate can be maintained under quasi-mild wear, extends to the higher load level after the change(s) in load. Once the quasi-mild wear surface has been generated, the wear mode can be maintained even at the high load for a very long sliding distance. [Copyright &y& Elsevier]

• Acoustic Emission (AE) and acceleration signals are evaluated for monitoring and failure detection. • Low speed (15–20 rpm) gear transmission is employed, setting an incorrect alignment of a shaft as a fault. • Signal parameters in time domain and frequency domain has been assessed in order to discuss its appliance. The most common condition monitoring method applied to rotating machines is vibration measurement, although recently it has been proposed that acoustic emission (AE) offers additional advantages in early fault detection and low speed rotation systems. Capturing the AE signals is conditioned by the severe attenuation with distance and the presence of material discontinuities between source and sensor, therefore measurement device placement is more important than in traditional accelerometry. In this study AE signals are measured in gearboxes at misalignment conditions for the revision of signal characteristics from the generated signal due to the interaction of shafts, bearings and gears. For this purpose, several tests are performed using combinations of speed and varying load, considering the effect of lubricating oil temperature. Fixed measurements are taken over the bench supports, and on-board, where the sensors are rotating with the shafts. In parallel to acoustic emission a vibration analysis is done in order to contrast and analyze differences between both technologies at different operation states. Acquired data is processed to obtain statistical parameters from measurements in order to verify the values and tendencies due to transient phenomena related to changes in speed and load. AE provides better results than vibration employing the same time domain condition indicators. On the contrary, vibration recognizes clearly the fault through frequency analysis. [ABSTRACT FROM AUTHOR]

This paper presents an experimental characterization of a two-stage planetary gearbox (TSPG) designed at the Laboratory of Robot Mechatronics (LARM2) in the University of Rome Tor Vergata. The TSPG operates differentially as function of the attached load and the internal friction forces caused for the contact between gears. Experiments under varying load conditions are developed in order to analyze the usefulness of the gearbox to avoid excessive torques on its internal elements. The analysis of the dynamic torques is presented as an indicator of stability in the gearbox operation. The results show that the actuation of the second operation stage reduces the torques 57% in the output shaft and 65% in the input shaft. The efficiency of the gearbox is estimated as 40% in presence of high internal friction forces. [ABSTRACT FROM AUTHOR]