Torque Reversal Research Articles

Influence of Continuous Rotation and Optimal Torque Reverse Kinematics on the Cyclic Fatigue Strength of Endodontic NiTi Clockwise Cutting Rotary Instruments.

Objectives: The objective of the present study was to evaluate the cyclic fatigue strength of clockwise cutting rotary endodontic instruments when subjected to two different kinematics: continuous clockwise rotation and clockwise reciprocation movement under optimum torque reverse (OTR) motion. Methods: New ProTaper Next X1 (n = 20) and X2 (n = 20) instruments were randomly divided into two subgroups (n = 10) based on kinematics (continuous rotation or OTR). The specimens were tested using a custom-made device with a non-tapered stainless-steel artificial canal measuring 19 mm in length, featuring a 6 mm radius and an 86-degree curvature. All instruments were tested with a lubricant at room temperature until a fracture occurred. The time to fracture and the length of the separated fragment were recorded. Subsequently, the fractured instruments were inspected under a scanning electron microscope for signs of cyclic fatigue failure, plastic deformation, and/or crack propagation. The subgroup comparisons for time to fracture and instrument length were performed using the independent samples t-test, with the level of statistical significance set at 0.05. Results: When using OTR movement, the ProTaper Next X1 increased the time to fracture from 52.9 to 125.8 s (p < 0.001), while the ProTaper Next X2 increased from 45.4 to 66.0 s (p < 0.001). No subgroup exhibited plastic deformations, but both showed dimpling marks indicative of cyclic fatigue as the primary mode of failure. Additionally, OTR movement resulted in more metal alloy microcracks. Conclusions: The use of OTR motion extended the lifespan of the tested instruments and resulted in a higher number of metal microcracks. This suggests that OTR motion helped to distribute the mechanical stress more evenly across the instrument, thereby relieving localized tension. As a result, it delayed the formation of a single catastrophic crack, enhancing the overall performance of the instruments during the experimental procedures.

Development of a Jumping Mechanism Inspired by Leg Synchronization of Planthopper

Abstract We developed a small jumping mechanism inspired by planthopper. The planthopper jump is characterized by two functions of the hind legs; the leg synchronization using physical contact of the trochanter head and the power amplification using a torque reversal latch. The proposed jump mechanism adopts the unique leg synchronization strategy of the planthopper, and the nymphal and adult models of the hind legs are designed. However, the power amplification is modified to incorporate two torque reversal structures in a single-motion axis. The mechanisms were fabricated by 3D printer with polylactic acid (PLA) material and equipped with extension springs. They weighed 26 g and performed 260 cm vertical jump within one rotation in the frontal plane. The jump height is over 40 times greater than the body length. The experimental findings indicate that the precise synchronization of the rapid leg movement is an effective approach for the design of a jumping mechanism.

Time Required for Root Canal Retreatment Using Continuous Rotation, Reciprocation, and Optimum Torque Reverse Motions: An In-Vitro Study.

Objective This study aims to evaluate the time required for canal preparation using three different movement kinematics during retreatment: continuous rotational motion, reciprocating motion, and optimum torque reverse (OTR) motion. Materials and methods The sample comprised 45 single-canal mandibular first premolars. The crowns were sectioned to standardize the root length to 16 mm. The root canals were prepared using the AF Gold mechanical preparation system (25/06). The roots were obturated using the lateral condensation technique and kept at 100% humidity at 37°C for seven days. The sample was randomly divided based on the movement pattern used during retreatment into three groups (N = 15): group 1 is continuous rotational motion using the ProTaper Universal Retreatment system; group 2 is reciprocating motion using the WaveOne Gold system; and group 3 is OTR motion using the ProTaper Universal Retreatment system. The retreatment time was measured in seconds by summing two times: T1 (time to reach the apex) and T2 (time to achieve adequate cleaning). The data were statistically analyzed using a one-way ANOVA with a significance level of α = 0.05. Results The results showed that the time required for canal preparation during retreatment with WaveOne Gold files using reciprocating motion was significantly longer than the time needed with ProTaper Universal Retreatment files using continuous rotary motion or OTR motion (P < 0.05). Conclusions The use of OTR motion did not affect the canal preparation time when used with files designed for continuous rotary motion retreatment. The use of WaveOne Gold files for canal preparation during retreatment was associated with a longer working time than ProTaper Universal Retreatment files.

Abnormal sign reversal of the fieldlike spin-orbit torque in Pt/Ni/Py with an ultrathin Ni spacer

Abnormal sign reversal of the fieldlike spin-orbit torque in Pt/Ni/Py with an ultrathin Ni spacer

Probing the weak limit of magnetocrystalline anisotropy through a spin‒flop transition in the van der Waals antiferromagnet CrPS4

The influence of magnetocrystalline anisotropy (MCA) on antiferromagnetism is elucidated through the characterization of the spin‒flop transition. However, due to a lack of suitable candidates for investigation, a detailed understanding of the preservation of the spin‒flop transition in the presence of low MCA energy remains elusive. In this study, we introduce CrPS4, which is a two-dimensional van der Waals antiferromagnet, as an ideal system to explore the exceedingly weak limit of the thermally-evolved MCA energy. By employing a uniaxially anisotropic spin model and fitting it to the experimental magnetic properties, we quantify the MCA energy and identify the discernible spin configurations in different magnetic phases. Notably, even at the limit of extremely weak MCA, with a mere 0.12% of the interlayer antiferromagnetic exchange interaction at T = 33 K, which is slightly below the Néel temperature (TN) of 38 K, the spin‒flop transition remains intact. We further establish a direct correlation between the visualized spin arrangements and the progressive reversal of magnetic torque induced by rotating magnetic fields. This analysis reveals the essential role of MCA in antiferromagnetism, thus extending our understanding to previously undetected limits and providing valuable insights for the development of spin-processing functionalities based on van der Waals magnets.

A Comprehensive Comparison of Spin-up and Spin-down Episodes of 4U 1538-522 Observed with NuSTAR

4U 1538-522 is a persistent high-mass X-ray binary that exhibits secular spin evolution. In 2019, it underwent a torque reversal from spinning up to spinning down. We performed an extensive study using four NuSTAR observations to compare temporal and spectral properties during different states. We observed no abrupt change in luminosity associated with the torque reversal. In addition, the pulse profile, the spectral shape, and the power spectrum remained unchanged before and after the torque reversal. The orbital and superorbital modulation profiles also showed no significant changes. We discuss possible mechanisms for the torque reversal and conclude that it is unlikely to be caused by interactions between the accretion disk and the magnetosphere. Instead, the transition of accretion modes in spherical accretion may be a plausible explanation.

Brain (Yakovlevian) torque direction is associated with volume asymmetry of the intracranial transverse sinuses: evidence from situs inversus totalis.

Previous research reported reversal of the prototypical brain torque in individuals with mirrored visceral topology (situs inversus totalis, SIT). Here, we investigate if typical asymmetry of the posterior intracranial venous system is also reversed in SIT and whether the direction and magnitude of this asymmetry is related to the direction and magnitude of the brain torque. Brain structural MRI images of 38 participants with SIT were compared with those of 38 matched control participants. Occipital and frontal petalia and bending were measured using a standardized procedure. In addition, representative sections of the left and right transverse sinuses were segmented, and their respective volumes determined. Participants with SIT showed general reversal of occipital and frontal petalia and occipital bending, as well as reversal of typical transverse sinus asymmetry. Transverse sinus volume was significantly correlated with several torque measures, such that the smaller transverse sinus was associated with a larger ipsilateral occipital petalia, contralateral occipital bending, and ipsilateral frontal bending. We propose an anatomical mechanism to explain occipital petalia and bending, and conclude that anatomical constraints imposed by the asymmetry of the posterior venous system provide and additional account to elucidate the formation of the human brain torque.

On the lack of X-ray pulsation in most neutron star low-mass X-ray binaries

ABSTRACT We have investigated whether the lack of X-ray pulsations from most neutron star (NS) low-mass X-ray binaries (LMXBs) could be due to the extension of their inner disc to the NS surface. To estimate the inner disc radii, we have employed the model, recently proposed to account for the torque reversals of LMXBs. In this model, the inner disc radius depends on the spin period as well as the dipole moment and the mass inflow rate of the disc. Our model results indicate that most LMXBs have mass accretion rates above the minimum critical rates required for the inner disc to reach down to the NS surface and thereby quench the pulsed X-ray emission. For most sources X-ray pulsations are allowed when the period decreases below a certain critical value. For the same parameters, the model is also consistent with the observed X-ray luminosity ranges of the individual accreting millisecond X-ray pulsars (AMXPs). The paucity of AMXPs compared to the majority population of non-pulsing LMXBs is explained, as well as the fact that AMXPs are transient sources.

Low-luminosity accretion of Be/X-ray pulsar MAXI J1409−619

ABSTRACT This paper used Nuclear Spectroscopic Telescope Array observations to examine the temporal and spectral features of the Be/X-ray binary pulsar MAXI J1409−619. The timing analysis of the light curve finds the pulsation of the source at $(501.23\,\,\pm \,\,0.01)$ s. The pulse profile of the source in various energy bands was analysed and showed weak dependence on energy exhibiting asymmetric character and generally suggests a source accretion in the subcritical regime. The variation of pulse fraction with photon energy in general shows an increasing trend. Assuming a distance of 14.5 kpc, we calculated the 3–30 keV source luminosity to be $\sim 6.13\,\,\times \,\,10^{34}\,\,$ erg s$^{-1}$. The long-term spin evolution of the source was carried out, where the source underwent torque reversal.

Design and control of jumping microrobots with torque reversal latches

Jumping microrobots and insects power their impressive leaps through systems of springs and latches. Using springs and latches, rather than motors or muscles, as actuators to power jumps imposes new challenges on controlling the performance of the jump. In this paper, we show how tuning the motor and spring relative to one another in a torque reversal latch can lead to an ability to control jump output, producing either tuneable (variable) or stereotyped jumps. We develop and utilize a simple mathematical model to explore the underlying design, dynamics, and control of a torque reversal mechanism, provides the opportunity to achieve different outcomes through the interaction between geometry, spring properties, and motor voltage. We relate system design and control parameters to performance to guide the design of torque reversal mechanisms for either variable or stereotyped jump performance. We then build a small (356 mg) microrobot and characterize the constituent components (e.g. motor and spring). Through tuning the actuator and spring relative to the geometry of the torque reversal mechanism, we demonstrate that we can achieve jumping microrobots that both jump with different take-off velocities given the actuator input (variable jumping), and those that jump with nearly the same take-off velocity with actuator input (stereotyped jumping). The coupling between spring characteristics and geometry in this system has benefits for resource-limited microrobots, and our work highlights design combinations that have synergistic impacts on output, compared to others that constrain it. This work will guide new design principles for enabling control in resource-limited jumping microrobots.

The ongoing spin-down episode of 4U 1626-67

Abstract We report the X-ray characteristics of the persistent X-ray pulsar 4U 1626-67 using simultaneous NuSTAR and NICER observations. The X-ray pulsar 4U 1626-67 has just encountered a torque reversal in 2023 and is presently in the spin-down state. We have examined the temporal and spectral characteristics of the source during its ongoing spin-down episode. The pulse profiles of the source are characterized by multiple substructures at lower energies and a wide asymmetric single-peaked structure at higher energies. The pulse fraction follows an overall increasing trend with energy. We confirm the existence of mHz quasi-periodic oscillation (QPO) exclusively during the current spin-down phase in all the observations. The source is spinning down at 0.00045(4) s yr−1. The broadband spectrum during this phase is described by empirical NPEX model and a soft blackbody component with kT ∼ 0.25 keV. In addition to the iron emission line, we also confirm the presence of cyclotron line at ∼ 36 keV. The source flux continues to decrease during the current spin-down phase, and the corresponding luminosity ∼ (3.3–4.9) × 1036 ergs s−1 lies in the intermediate range of accreting X-ray pulsars that may be associated with a hybrid accretion geometry. The magnetic field strengths estimated using the cyclotron line measurements and QPO frequency are consistent. The evolution of the spectral parameters relative to the pulsed phase is examined using phase-resolved spectroscopy.

Torque-dependent orbital modulation of X-ray pulsar Cen X-3

ABSTRACT Cen X-3 shows alternate spin-up/spin-down episodes lasting for tens of days. We study the orbital profiles and spectra of Cen X-3 during these spin-up/spin-down intervals, using long-term data monitored by Fermi/Gamma-ray Burst Monitor (GBM), Swift/Burst Alert Telescope (BAT), and Monitor of All-sky X-ray Image (MAXI)/Gas Slit Camera (GSC). In spin-up intervals, its orbital profile in 2–10 keV is symmetrically peaked around orbital phase 0.42, while in spin-down intervals of similar fluxes and similar magnitudes of spin change rate, its profile reaches a peak around orbital phase 0.22 and then declines gradually. Such a distinct orbital difference between spin-up and spin-down states of similar flux is hard to explain in the standard disc model and indicates that its torque reversals are related to processes on the orbital scale. The durations of continuous spin-up/spin-down trend (tens of days) also point to a superorbital variation. One possible scenario is the irradiation-driven warping disc instability, which may produce a flipped inner disc for tens of days.

Induction motor performance improvement using a five-level inverter topology and sliding mode controllers

This research intends to establish a robust vector control (VC) of a 3-ϕ induction motor (IM). The classical 2-level inverter is displaced by a 5-level neutral-pointclamped (NPC) inverter. The 2-level inverter may only supply 8 voltage vectors, while the 5-level NPC inverter can furnish 125 voltage vectors. The objective is to bring about a command voltage vector that converges to the reference voltage vector as closely as possible; hence, guaranteeing a quick response on one hand and improving the dynamic performance on the other hand. A robust sliding mode controller (SMC) structure is used in all regulation loops. Satisfactory results are obtained for various speed zones. The quality and robustness of the global system are tested under resistive torque disturbance, reversal, high, and low-speed ranges in order to prove system stability. All the simulations have been performed under MATLAB/Simulink.

Long-term evolution of cyclotron line energy in an eclipsing pulsar 4U 1538−522

ABSTRACT We present the timing and spectral analysis of the high-mass X-ray binary source 4U 1538−522 using Nuclear Spectroscopic Telescope Array (NuSTAR) observations. One of the observations partially covers the X-ray eclipse of the source along with eclipse ingress. The source is found to spin down at the rate of 0.163 ± 0.002 s yr−1 between ∼54973 and 58603 MJD. It is evident that at time ∼58620 MJD, a torque reversal occurred; thereafter, the source exhibited a spin-up trend at the rate −(0.305 ± 0.018) s yr−1 until 59275 MJD. A recent NuSTAR observation finds the pulse period of the source: (526.2341 ± 0.0041) s. The pulse profile exhibits a transition from double-peaked to single-peaked nature above ∼30 keV. We analysed the overall trend of the temporal evolution of fundamental cyclotron resonance scattering feature, Ecyc, incorporating recent NuSTAR measurements. Initially, during the time span ∼50452.16–55270.8 MJD, the cyclotron line energy is found to increase at a rate of 0.11 ± 0.03 keV yr−1, which is further followed by a decrease at a rate −0.14 ± 0.01 keV yr−1 between 55270.8 and 59267 MJD. The combined measurements in the time span 50452.16–59267 MJD reveal that the cyclotron line energy is increasing linearly at a rate of 0.08 ± 0.02 keV yr−1.

Development of an impulsive motion generator inspired by cocking slip joint of snapping shrimp.

We propose an impulsive motion generator inspired by snapping shrimp. The proposed device mimics the geometrical arrangement of a unique claw joint calledcocking slip jointand integrates it with an artificial rack-pinion actuator mechanism rather than adopting the musculoskeletal system as it is. The design approach allows the proposed device to reproduce the impulsive slip motion through the torque reversal and unlatching mechanism of the underlying unique joint by using a single servo motor. Static and dynamic analyses revealed that the actuator force required to store and release elastic energy was remarkably small compared with the resulting acceleration force and rotation/tip speed. Through simulations and experiments, we validated the mechanical analyses and confirmed that the resulting ultrafast slip motion was comparable with the claw closure of snapping shrimp based on the cocking slip joint. Moreover, from an engineering perspective, the motion profiles are modifiable through design parameters, and the repeatability of the impulsive slip motion is satisfactory.

4U 1626−67 returns to spin-down: timing features toe the line

ABSTRACT We present a comprehensive analysis of X-ray pulsar 4U 1626−67 during its current spin-down (2SD) state, following a recent torque reversal. Since its discovery, this ultra-compact binary has experienced multiple torque states, transitioning from spin-up (1SU) during 1977–1990 to spin-down (1SD) during 1990–2008, and again spin-up (2SU) until 2023. From Nuclear Spectroscopic Telescope ARray observation of May 2023, we have investigated the timing and spectral properties of this pulsar during its 2SD phase, while also comparing them with previous spin-up-down states. For energies up to 8 keV, a distinct bi-horned pulse profile was observed during the spin-up phase, while several substructures emerged during spin-down. Beyond 8 keV, a broad asymmetric peak was consistently observed across all torque states. The pulse fraction during the 2SD phase was higher than that during 2SU phase. A prominent ∼46.8 mHz quasi-periodic oscillation has been exclusively detected during the spin-down phase. The broad-band spectrum during the 2SD phase is described by empirical Negative and Positive power-law with Exponential cutoff model, cyclotron absorption feature and its first harmonic. The spectrum during 2SU phase requires an additional blackbody component and asymmetry in the cyclotron absorption line. A significant flux drop by a factor of ∼3 in the 2SD was observed.

Large damping-like torque and efficient current-induced magnetization reversal in Ti/Tb–Co/Cr structures

Seeking the magnetic heterostructures with large current-induced torque efficiency is currently one of the core hotspots in spintronics. In this work, we report the large and composition-dependent damping-like (DL) torque in the structure consisting of light metal Cr and Ti layers and a ferrimagnetic Tb–Co layer. The DL torque efficiency in the structures reaches a maximum (around −0.55) as the Tb content in the Tb–Co layer is in the range of 0.15–0.18. This composition-dependent behavior is different from that observed in the usual heavy-metal/ferrimagnetic structures. We also demonstrated the efficient current-induced magnetization reversal in these structures with a low threshold current density down to 8×1010 A/m2. In comparison, only very low efficiency values of −0.06 and −0.086 are obtained in the Ti/Co/Cr and Ti/Tb–Co/SiN control samples, respectively, suggesting that the large DL torque in the Ti/Tb–Co/Cr structures may originate from the orbital Hall effect in the Cr metal. By fitting the Cr layer thickness dependence of the torque efficiency with a simple orbital current diffusion model, we obtained an effective orbital Hall angle of −0.57±0.02 for the Ti/Tb0.85Co0.15/Cr samples. This work demonstrated the possibility to enhance the orbital torque effect by using the magnetic layer containing the element with strong spin–orbit coupling.

Mitigation of transient torque reversals in indirect drive wind turbine drivetrains

AbstractBearing failure in wind turbine gearboxes is one of the significant sources of downtime. While it is well‐known that bearing failures cause the largest downtime, the failure cause(s) is often elusive. The bearings are designed to satisfy their rolling contact fatigue (RCF) life. However, they often undergo sudden and rapid failure within a few years of operation. It is well‐known that these premature failures are attributed to surface damages such as white surface flaking (WSF), white etching cracks (WECs) and axial cracks. In that regard, transient torque reversals (TTRs) in the drivetrain have emerged as one of the primary triggers of surface damage, as explained in this paper. The risk associated with TTRs motivates the need to mitigate TTRs arising in the drivetrain due to various transient events. This paper investigates three TTR mitigation methods. First, two existing devices, namely, the torsional tuned mass damper and the asymmetric torque limiter, are studied to demonstrate their TTR mitigation capabilities. Then, a novel idea of open‐loop high‐speed shaft mechanical brake control is proposed. The results presented here show that while the torsional tuned mass damper and the asymmetric torque limiter can improve the torsional vibration characteristics of the drivetrain, they cannot mitigate TTRs in terms of eliminating the bearing slip risk associated with TTRs. However, the novel approach proposed here can mitigate TTRs both in terms of improving the torque characteristic in the high‐speed shaft and reducing the risk of bearing slip by actuating the high‐speed shaft brake at the onset of the transient event. Furthermore, the control method is capable of mitigating TTRs with the mechanical limitations of a pneumatic actuator in terms of bandwidth and initial dead time applied to it. This novel approach allows the wind turbines to protect the gearbox bearings from TTRs using the existing hardware on the turbine.

Torque reversal and cyclotron absorption feature in HMXB 4U 1538−522

ABSTRACT We present a comprehensive timing and spectral analysis of the HMXB 4U 1538−522 by using the Nuclear Spectroscopic Telescope Array (NuSTAR) observatory data. Using three archived observations made between 2019 and 2021, we have detected ∼ 526 s coherent pulsations up to 60 keV. We have found an instantaneous spin-down rate of $\dot{P} = 6.6_{-6.0}^{+2.4} \times 10^{-6}$ s s−1 during the first observation. The pulse profiles had a double peaked structure consisting of a broad primary peak and an energy dependent, weak secondary peak. We have also analysed the long-term spin period evolution of 4U 1538−522 from data spanning more than four decades, including the data from Fermi/GBM. Based on the recent spin trends, we have found that the third torque reversal in 4U 1538−522 happened around MJD 58800. The source is currently spinning up with $\dot{P} = -1.9(1) \times 10^{-9}$ s s−1. We also report a periodic fluctuation in the spin period of 4U 1538−522. The broad-band persistent spectra can be described with a blackbody component and either power law or Comptonization component along with a Fe Kα line at 6.4 keV and a cyclotron absorption feature around 22 keV. We have also found a relatively weak absorption feature around 27 keV in the persistent spectra of 4U 1538−522 in all three observations. We have estimated a magnetic field strength of $1.84_{-0.06}^{+0.04} (1+z) \times 10^{12}$ and $2.33_{-0.24}^{+0.15} (1+z) \times 10^{12}$ G for the two features, respectively.

Transient torque reversals in indirect drive wind turbines

AbstractThe adverse effect of transient torque reversals (TTRs) on wind turbine gearboxes can be severe due to their magnitude and rapid occurrence compared with other equipment. The primary damage is caused to the bearings as the bearing loaded zone rapidly changes its direction. Other components are also affected by TTRs (such as gear tooth); however, its impact on bearings is the largest. While the occurrence and severity of TTRs are acknowledged in the industry, there is a lack of academic literature on their initiation, propagation and the associated risk of damage. Furthermore, in the wide range of operation modes of a wind turbine, it is not known which modes can lead to TTRs. Further, the interdependence of TTRs on environmental loading like the wind is also not reported. This paper aims to address these unknowns by expanding on the understanding of TTRs using a high‐fidelity numerical model of an indirect drive wind turbine with a doubly fed induction generator (DFIG). To this end, a multibody model of the drivetrain is developed in SIMPACK. The model of the drivetrain is explicitly coupled to state‐of‐the‐art wind turbine simulator OpenFAST and a grid‐connected DFIG developed in MATLAB®'s Simulink® allowing a coupled analysis of the electromechanical system. A metric termed slip risk duration is proposed in this paper to quantify the risk associated with the TTRs. The paper first investigates a wide range of IEC design load cases to uncover which load cases can lead to TTRs. It was found that emergency stops and symmetric grid voltage drops can lead to TTRs. Next, the dependence of the TTRs on inflow wind parameters is investigated using a sensitivity analysis. It was found that the instantaneous wind speed at the onset of the grid fault or emergency shutdown was the most influential factor in the slip risk duration. The investigation enables the designer to predict the occurrence of TTRs and quantify the associated risk of damage. The paper concludes with recommendations for utility‐scale wind turbines and directions for future research.