Torque Source Research Articles

Parity-controlled spin-wave excitations in synthetic antiferromagnets

We report in this study the current-induced-torque excitation of acoustic and optical modes in Ta/NiFe/Ru/NiFe/Ta synthetic antiferromagnet stacks grown on SiO2/Si substrates. The two Ta layers serve as spin torque sources with the opposite polarizations in both spin currents and Oersted fields acting on their adjacent NiFe layers. This can create the odd symmetry of spatial spin torque distribution across the growth direction, allowing us to observe different spin-wave excitation efficiency from synthetic antiferromagnets excited by homogeneous torques. We analyze the torque symmetry by the in-plane angular dependence of symmetric and anti-symmetric line shape amplitudes for their resonance and confirm the parallel (perpendicular) pumping nature for the acoustic (optical) modes in our devices, which is in stark contrast to the modes excited by spatially homogeneous torques. We also present our macrospin model for this particular spin-torque excitation geometry, which excellently supports our experimental observation. Our results offer capability of controlling spin-wave excitations by local spin-torque sources, and we can explore further spin-wave control schemes based on this concept.

Spin-orbit torques originating from the bulk and interface in Pt-based structures

We investigated spin-orbit torques in prototypical Pt-based spintronic devices. We found that, in Pt/Ni and Pt/Fe bilayers, the damping-like torque efficiency depends on the thickness of the Pt layer. We also found that the damping-like torque efficiency is almost identical in the Pt/Ni and Pt/Fe bilayers despite the stronger spin memory loss at the Pt/Fe interface. These results suggest that although the dominant source of the damping-like torque is the bulk spin Hall effect in the Pt layer, a sizable damping-like torque is generated by the interface in the Pt/Fe bilayer due to the stronger interfacial spin-orbit coupling. In contrast to the damping-like torque, whose magnitude and sign are almost identical in the Pt/Ni and Pt/Fe bilayers, the field-like torque strongly depends on the choice of the ferromagnetic layer. The sign of the field-like torque originating from the bulk spin Hall effect in the Pt layer is opposite between the Pt/Ni and Pt/Fe bilayers, which can be attributed to the opposite sign of the imaginary part of the spin-mixing conductance. These results demonstrate that the spin-orbit torques are quite sensitive to the electronic structure of the FM layer.

Large Spin-Orbit-Torque Efficiency Generated by Spin Hall Effect in Paramagnetic Co - Ni - B Alloys

The spin Hall effect is a major source of spin-orbit torques (SOTs), which allow efficient electrical manipulation of magnetization. So far, the spin Hall effect has been investigated using materials with strong spin-orbit coupling, such as 5d transition metals, and the spin Hall effect in light elements, which results in weak spin-orbit coupling, is often considered to be negligible. Here, we report an efficient spin Hall material that can be realized using 3d transition metals, namely, an amorphous $\mathrm{Co}$-$\mathrm{Ni}$-$\mathrm{B}$ alloy under a paramagnetic state. Despite no heavy elements being used in this material, we estimate the spin Hall angle of $\mathrm{Co}$-$\mathrm{Ni}$-$\mathrm{B}$ alloys to be about 0.10 via harmonic Hall measurements, which is comparable to that of 5d transition metals. A highly efficient spin Hall angle originates from the high-spin Hall conductivity of paramagnetic $\mathrm{Ni}$. We also demonstrate SOT-induced magnetization switching using the spin Hall effect on the $\mathrm{Co}$-$\mathrm{Ni}$-$\mathrm{B}$ alloy with comparable switching current density using a heavy-metal spin Hall material. Our findings provide an approach to realize the coexistence between highly efficient and heavy-element-free SOT-based devices.

Theory of Current-Induced Angular Momentum Transfer Dynamics in Spin-Orbit Coupled Systems.

Motivated by the importance of understanding various competing mechanisms to the current-induced spin-orbit torque on magnetization in complex magnets, we develop a theory of current-induced spin-orbital coupled dynamics in magnetic heterostructures. The theory describes angular momentum transfer between different degrees of freedom in solids, e.g., the electron orbital and spin, the crystal lattice, and the magnetic order parameter. Based on the continuity equations for the spin and orbital angular momenta, we derive equations of motion that relate spin and orbital current fluxes and torques describing the transfer of angular momentum between different degrees of freedom, achieved in a steady state under an applied external electric field. We then propose a classification scheme for the mechanisms of the current-induced torque in magnetic bilayers. We evaluate the sources of torque using density functional theory, effectively capturing the impact of the electronic structure on these quantities. We apply our formalism to two different magnetic bilayers, Fe/W(110) and Ni/W(110), which are chosen such that the orbital and spin Hall effects in W have opposite sign and the resulting spin- and orbital-mediated torques can compete with each other. We find that while the spin torque arising from the spin Hall effect of W is the dominant mechanism of the current-induced torque in Fe/W(110), the dominant mechanism in Ni/W(110) is the orbital torque originating in the orbital Hall effect of the non-magnetic substrate. Thus the effective spin Hall angles for the total torque are negative and positive in the two systems. Our prediction can be experimentally identified in moderately clean samples, where intrinsic contributions dominate. This clearly demonstrates that our formalism is ideal for studying the angular momentum transfer dynamics in spin-orbit coupled systems as it goes beyond the "spin current picture" by naturally incorporating the spin and orbital degrees of freedom on an equal footing. Our calculations reveal that, in addition to the spin and orbital torque, other contributions such as the interfacial torque and self-induced anomalous torque within the ferromagnet are not negligible in both material systems.

A field study, laboratory test and cost estimation of solid and liquid lubricants in directional wells to reduce friction coefficient and improve ROP

Drilling fluid is being used to facilitate drilling operation from the surface to a target formation. Due to the complexity of well geometry in directional drilling operations and high torque and drag forces, minimizing the coefficient of friction (CoF) is important. Excessive torque and axial drag cause mechanical erosion on the drill string, which ultimately leads to fatigue, wash out and twist off. Field data for 9 wells in one of the Iranian oilfields showed that slide drilling was practically impossible beyond 4000 m due to the unexpected high torque and drag during directional drilling despite the presence of liquid lubricants in drilling fluid at concentrations up to 5 vol% as per drilling program. Based on the results, the primary source of torque and drag in the wells with proper hole conditioning is sliding friction. Using different types of lubricant in drilling fluid system is the most practical methods to reduce the drag force (sliding friction) caused by the contact between drillstring and well casing or borehole. This paper investigates the effect of solid and liquid lubricants on the CoF in laboratory and field applications. Based on the successful implementation, a specific instruction was designed for the use of glass bead as a solid lubricant in drilling fluid to reduce the CoF. Cost estimation indicates that compared to the liquid lubricants, solid lubricants can reduce drilling fluid costs significantly. Moreover, based on Experimental results, no more than 5–6 percent of liquid lubricants can be used to reduce friction coefficient. This limitation, along with the issue of lubrication regimes, leads us to use solid lubricants. Laboratory and field test results showed that addition of glass bead as a solid lubricant can improve the performance of water-based drilling fluids as evidenced by improvement in ROP up to 240% (average ROP: 160%).

Einstein–de Haas effect at radio frequencies in and near magnetic equilibrium

The Einstein-de Haas (EdH) effect and its reciprocal the Barnett effect are fundamental to magnetism and uniquely yield measures of the ratio of magnetic moment to total angular momentum. These effects, small and generally difficult to observe, are enjoying a resurgence of interest as contemporary techniques enable new approaches to their study. The high mechanical resonance frequencies in nanomechanical systems offer a tremendous advantage for the observation of EdH torques in particular. At radio frequencies, the EdH effect can become comparable to or even exceed in magnitude conventional cross-product magnetic torques. In addition, the RF-EdH torque is expected to be phase-shifted by 90 degrees relative to cross-product torques, provided the magnetic system remains in quasi-static equilibrium, enabling separation in quadratures when both sources of torque are operative. Radio frequency EdH measurements are demonstrated through the full hysteresis range of micrometer scale, monocrystalline yttrium iron garnet (YIG) disks. Equilibrium behavior is observed in the vortex state at low bias field. Barkhausen-like features emerge in the in-plane EdH torque at higher fields in the vortex state, revealing magnetic disorder too weak to be visible through the in-plane cross-product torque. Beyond vortex annihilation, peaks arise in the EdH torque versus bias field, and these together with their phase signatures indicate additional utility of the Einstein-de Haas effect for the study of RF-driven spin dynamics.

Unconventional spin-orbit torque in transition metal dichalcogenide/ferromagnet bilayers from first-principles calculations.

Motivated by recent observations of unconventional out-of-plane dampinglike torque in WTe2/Permalloy bilayer systems, we calculate the spin-orbit torque generated in two-dimensional transition metal dichalcogenide (TMD)/ferromagnet heterostructures using first-principles methods and linear response theory. Our numerical calculation of spin-orbit torques in WTe2/Co and MoTe2/Co heterostructures shows both conventional and novel dampinglike torkances (torque per electric field) with comparable magnitude, around one hundred ℏ/2e (Ω · cm)-1, for an electric-field applied perpendicular to the mirror plane of the TMD layer. To gain further insight into the source of dampinglike torque, we compute the spin current flux between the TMD and Co layers and find good agreement between the two quantities. This indicates that the conventional picture of dampinglike spin-orbit torque, whereby the torque results from the spin Hall effect plus spin transfer torque, largely applies to TMD/Co bilayer systems.

Muscles Reduce Neuronal Information Load: Quantification of Control Effort in Biological vs. Robotic Pointing and Walking.

It is hypothesized that the nonlinear muscle characteristic of biomechanical systems simplify control in the sense that the information the nervous system has to process is reduced through off-loading computation to the morphological structure. It has been proposed to quantify the required information with an information-entropy based approach, which evaluates the minimally required information to control a desired movement, i.e., control effort. The key idea is to compare the same movement but generated by different actuators, e.g., muscles and torque actuators, and determine which of the two morphologies requires less information to generate the same movement. In this work, for the first time, we apply this measure to numerical simulations of more complex human movements: point-to-point arm movements and walking. These models consider up to 24 control signals rendering the brute force approach of the previous implementation to search for the minimally required information futile. We therefore propose a novel algorithm based on the pattern search approach specifically designed to solve this constraint optimization problem. We apply this algorithm to numerical models, which include Hill-type muscle-tendon actuation as well as ideal torque sources acting directly on the joints. The controller for the point-to-point movements was obtained by deep reinforcement learning for muscle and torque actuators. Walking was controlled by proprioceptive neural feedback in the muscular system and a PD controller in the torque model. Results show that the neuromuscular models consistently require less information to successfully generate the movement than the torque-driven counterparts. These findings were consistent for all investigated controllers in our experiments, implying that this is a system property, not a controller property. The proposed algorithm to determine the control effort is more efficient than other standard optimization techniques and provided as open source.

A Differential Electric Drive for Electric Vehicles with an Independent Power Supply

In this paper, we consider the effectiveness of using a twin-engine electric drive from the point of view of acceleration dynamics and energy efficiency. To take into account the acceleration time of the electric vehicle and the energy consumed during the transition process, evaluation criterion G was introduced. By a “twin-engine system” is meant a system of electric drive of a wheel pair through two independent mechanical channels: the first is a “high-torque” channel implemented through the use of a gearbox with a high gear ratio, and the second is a “high-speed” channel implemented through the use of a gearbox with a low gear ratio or without a gearbox at all. The summation of power is carried out by means of a differential gear. We performed mathematical modeling of the operation of such a system. Asynchronous electric drives with vector control, which operate in the torque source mode, are used as electromechanical converters. An algorithm and a system for distributing torque between two channels are developed. The gear ratio of the “high-torque” channel gearbox was optimized by the criterion of G minimum. A quantitative comparison and analysis of transient acceleration processes in single- and twin-engine systems were performed based on the example of a 30-kW electric race car. It is concluded that it is effective to use a twin engine system for specific types of electric vehicles.

An LQR Approach of Automatic Transmission Upshift Control Including Use of Off-Going Clutch within Inertia Phase

<div class="section abstract"><div class="htmlview paragraph">This paper considers using linear quadratic regulation (LQR) for multi-input control of the Automatic Transmission (AT) upshift inertia phase. The considered control inputs include the transmission input/engine torque, oncoming clutch torque, and traditionally not used off-going clutch torque. Use of the off-going clutch has been motivated by discussed Control Trajectory Optimization (CTO) results demonstrating that employing the off-going clutch during the inertia phase along with the main, oncoming clutch can improve the upshift control performance in terms of the shift duration and/or comfort by trading off the transmission efficiency and control simplicity to some extent. The proposed LQR approach provides setting an optimal trade-off between the conflicting criteria related to driving comfort and clutches thermal energy loss. It ensures tracking a linear-like profile of oncoming clutch slip speed reference, which was found to be nearly optimal based on control trajectory optimization results. A special attention is given on proper implementation of nonlinear energy loss term through LQR cost function cross term and using a clipped optimal control approach to provide that the clutches (described as torque source elements) can only dissipate energy. The LQR approach was applied to a fifth-order powertrain model and different upshift control scenarios ranging from the use of single clutch towards using both clutches and transmission input/engine torque reduction. It is shown that the LQR approach can reproduce Pareto frontiers obtained by multi-objective control parameter optimization demonstrating that apart from being used in closed loop controls, the proposed LQR approach can also be exploited for computationally efficient (off-line) optimization purposes.</div></div>

Design and Research of a Model of a Pair Active Aircraft Control Sidesticks Operation in MATLAB

Development of an aircraft active sidestick control is an actual direction in modern flight control systems which allows to increase safety, to improve cabin ergonomics and to reduce the mass and weight of control levers. The article devoted to simulation modeling of a pair active sidesticks based on electromechanical actuators coupled by a frameless kinematic scheme, providing identical dynamic characteristics for the pitch and roll channels. MATLAB, Simulink, Simscape, with SimMechanics and SimPowerSystems libraries was used to create the mathematical model. Parameters such as moments of inertia was count based on the 3D model of the active sidestick. The complex model includes two active sidesticks units, three blocks as the input source ("Autopilot", blocks of the 1st and 2nd pilots), a block that compute a loading characteristic for the manual control mode and a block with logic for switching from automatic to manual mode. The model of each active sidestick unit consists of three main blocks: a regulator, an electric motor with a control system, and a block of mechanics. The regulator block includes a PID regulator and a PWM modulator. The electric motor unit includes a power source, a three-phase bridge inverter, a model of a brushless three-phase electric motor from the SimPowerSystems library and a power switch control unit. The mechanics block includes a planetary gearbox, hinge mechanism, handle, moments of inertia, a position sensor, a torsion rod equal to tension springs which are used in device, a nonlinear speed damper and a torque source unit, depending on the force applied by the pilot. Developed model makes it possible to get static and dynamic characteristics of the actuators, to check control algorithms to simulate operating modes in automatic and manual control, including piloting by both pilots at the same time and the interruption in automatic control mode. Including in model a " hold position block" allowed to simulate situation when in manual control mode the 1st pilot tries to hold the handle in a position that he considers correct, despite the intervention of the 2nd pilot. The simulation results showed that developed device meets specified requirements for the aircraft active sidesticks.

Operating Performance Enhancing Method for Doubly Salient Electromagnetic Machine Under Light Load Condition

Nowadays, more and more electric machines are demanded to operate under wide ranges of speed and load conditions. This paper deals with the operating performance enhancing method for doubly salient electromagnetic machine (DSEM) under light load condition. With the finding that the power loss can be decreased with reduced field current, and there's regulated space for the distribution of field current and armature current under light load condition. A novel control method with field current inner loop and speed outer loop is proposed for DSEM, the system driving efficiency is desired to be improved. Meanwhile, the cogging torque which is a main ripple source of DSEM torque can be decreased with the reduced filed current, so the output torque performance can be enhanced as well. In addition, the armature reaction of the proposed control method is researched, and the influence on the filed current control during commutation process is theoretically analyzed. The experiments on a 12/8-pole DSEM validate the correctness and flexibility of the proposed control method.

Tutorial: Source simulation for 3D poroelastic wave equations

The choice of seismic sources is an important issue in numerical simulation. To demonstrate the importance of the seismic source and investigate the wavefields of different seismic sources in a poroelastic medium, we have developed representations of the seismic sources: the force-density source and moment-density source. In the numerical simulation, we use the staggered-grid finite-difference method to discretize the spatial and temporal derivatives. We compare the numerical results of different spatial functions of a seismic source including the delta function and the Gaussian function, and we find that the numerical dispersion can be suppressed by the Gaussian function compared to the delta function. We compare and evaluate the numerical results for the explosion source, torque source, and force-density source for a 3D homogeneous poroelastic model, which demonstrates that the different seismic sources generate completely different wavefields. In addition, the three seismic sources are used to generate the response of a 3D-layered poroelastic model to investigate the reflected waves at the interface. Our numerical results indicate that the fast P-wave, the slow P-wave, and the S-wave give rise to each other at an interface.

Study on Drag Torque Characteristics of Corrugated Joint for Spacesuit under Human-Induced Loads

The mobility of spacesuit joints is the key factor affecting the ability of the lower-torso space service, and the drag torque of joint is an important indicator which represents the mobility of joint. Drag torque is affected by many factors, such as contact with garment, gas pressure and materials of spacesuit, which cause difficulties in theoretical calculation. A finite element simulation on drag torque characteristics of corrugated joint of spacesuit with human body is carried out. And a detailed finite element model is established which reflects the characteristics of fabric material and the actual structure of corrugated joint. Based on this model, the dynamic simulation of joint rotation in two ways of external driving and human body driving is carried out. The cause of drag torque is analyzed. Then the influence of spacing and arc length of bellows on characteristics of drag torque is studied. The results show that the sources of drag torque during rotation are the structural elastic deformation and the work to compress gas. The drag torque of joint which is in the way of human body driving is greater than by external driving, which is because the elastic deformation and work to compress gas of the former are both larger than the latter. And methods, reducing the spacing and increasing the arc length of bellows, could reduce the drag torque of joint.

Decoupled Torque Control of Series Elastic Actuator With Adaptive Robust Compensation of Time-Varying Load-Side Dynamics

Modern robots are increasingly being designed to collaborate with human, and the safety of human-robot interaction has become more significant than ever. Series elastic actuator (SEA) is a potential actuator system in force control for various robotic applications with inherent safe property. However, achieving the good performances of SEA torque control especially with unknown load-side dynamics is still challenging. In this article, a high performance decoupled torque controller is proposed to control the SEA as an ideal torque source that is suitable for various application scenarios. A more general decoupled dynamics of the SEA system is first established to fit the various scenarios by considering the large parametric uncertainties, nonlinearities, and unmodeled uncertainties. The adaptive robust control algorithm with an effective compensation mechanism is then developed to attenuate the uncertainties. Theoretically, the proposed approach guarantees the stability and high performance of the SEA system. Comparative experiments are carried out on a SEA testbed, and the experimental results demonstrate that the proposed approach has significant performance improvements over previous approaches.

Understanding the driving forces for crystal growth by oriented attachment through theory and simulations

Abstract

Modelling and analysis of gradient effect on the dynamic performance of three-wheeled vehicle system using Simscape

In India, three-wheeled electric vehicles are one of the important modes of public transport in congested areas. The gradient is an important factor that affects the dynamic performance of the vehicle. The proposed work presents an extensive analysis of the gradient effects on the dynamic performance of a three-wheeled solar electric vehicle. Firstly, we have designed the physical vehicle model of three-wheeled using Simscape® environment tool. The generated torque from “ideal torque source” block is transferred to the input drive shaft of the “differential” mechanism. The output drive shafts of “sun gears” or “differential” block are connected to the rear left as well as to the right wheels respectively. The “ideal translational motion sensor” subsystem block measures the speed and distance of the vehicle. Next, to examine the gradient effects and accuracy of the Simscape model, we have designed the longitudinal vehicle model of a three-wheeled electric vehicle. Undertaken a comparative analysis of the Simscape® models’ results from the longitudinal vehicle model for three different road gradient condition having a slope of zero degrees (0°), six degrees (6°) and twelve degrees (12°) respectively.

Deformation due to a torque source in layered orthotropic elastic medium in welded contact with another orthotropic elastic medium

Deformation due to a torque source in layered orthotropic elastic medium in welded contact with another orthotropic elastic medium

Dynamic modeling and controller design for SEA joints

PurposeThe purpose of this paper is to study the dynamic modeling and controller design for the series element actuator (SEA) joints. The robot equipped with SEA joints is a strong coupling, nonlinear, highly flexible system, which can prevent itself from damaging by the accidental impact and the people to be injured by the robot.Design/methodology/approachBased on the torque source model, the authors built a dynamic model for the SEA joint. To improve the accuracy of this model, the authors designed an elastic element into the joint and implemented the vector control for the joint motor. A control method of combined PD controller and back-stepping was proposed. Moreover, the torque control could be transformed into position control by stiffness transformation.FindingsThe established model and the proposed method are verified by the position and torque control experiments. The experimental results show that the dynamic model of the SEA joint is accurate and the proposed control strategies for the SEA joint are reasonable and feasible.Originality/valueThe main contribution of the paper is as follows: designing an elastic element with high linearity to improve the model accuracy of the SEA joint. The control strategy-based back-stepping method for the SEA joint is proposed to increase the robustness of the controller.

Coupling magneto-elastic Lagrangians to spin transfer torque sources

The consequences of coupling magnetic and elastic degrees of freedom, where spins and deformations are carried by point-like objects subject to local interactions, are studied, theoretically and by detailed numerical simulations. From the constrained Lagrangians we derive consistent equations of motion for the coupled dynamical variables. In order to probe the dynamics of such a system, we consider external perturbations, such as spin transfer torques for the magnetic part, and homogeneous stresses for the elastic part, associated to their corresponding damping. This approach is applied to the study of ultrafast switching processes in anti-ferromagnetic systems, which have recently attracted attention as candidates for anti-ferromagnetic spintronic devices. Our strategy is then checked in simple, but instructive, situations. We carried out numerical experiments to study, in particular, how the magnetostrictive coupling and external stresses affect the nature of the switching processes in a prototype anti-ferromagnetic material.