Active Torque Research Articles

Integrated Active Control of Electric Vehicles

This work describes how it is possible to integrate active chassis control actions in an electric vehicle. A vehicle with Active Front Steering (AFS) is considered, which imposes an incremental steer angle to the front wheels. Using Permanent Magnet Synchronous Motors (PMSMs) as powertrain, fitting on the left/right wheel axle shafts, it is possible to impose not only a desired longitudinal traction, but also an appropriate active yaw torque, so mimicking a classic Rear Torque Vectoring (RTV). The AFS, along with the RTV, allow imposing a desired behavior for the active chassis control of the vehicle, so improving its safety.

Design of Human Knee Smart Prosthesis with Active Torque Control

Design of Human Knee Smart Prosthesis with Active Torque Control

Optimal Control of a Differentially Flat Two-Dimensional Spring-Loaded Inverted Pendulum Model

This letter considers the optimal control problem of an extended spring-loaded inverted pendulum (SLIP) model with two additional actuators for active leg length and hip torque modulation. These additional features arise naturally in practice, allowing for consideration of swing leg kinematics during flight and active control over stance dynamics. On the other hand, nonlinearity and the hybrid nature of the overall SLIP dynamics introduce challenges in the analysis and control of the model. In this letter, we first show that the stance dynamics of the considered SLIP model are differentially flat, which has a strong implication regarding controllability of the stance dynamics. Leveraging this powerful property, a tractable optimal control strategy is developed. This strategy enables online solution while also treating the hybrid nature of the SLIP dynamics. Together with the optimal control strategy, the extended SLIP model grants active disturbance rejection capability at any point during the gait. Performance of the proposed control strategy is demonstrated via numerical tests and shows significant advantage over existing methods.

An Axial Flux Focusing Magnetically Geared Generator for Low Input Speed Applications

An axial-flux magnetic gear (MG) is integrated into a radial field stator to construct a unique magnetically geared generator for low input speed applications. The high-speed rotor of the axial-flux MG uses a flux-focusing typology. This article presents the stator design and experimental testing of this unique proof-of-principle axial-flux focusing MG generator. The peak torque and active region torque density were measured to be 473 N m and 94.4 N m/L, respectively. The stator of the proposed machine shares the high-speed rotor with the axial-flux MG. Therefore, there is no need for a separate rotor. It is shown that the stator can also be used to provide additional flux into the MG in order to boost torque during transient overshoots.

Optimizing Neuromuscular Electrical Stimulation Pulse Width and Amplitude to Promote Central Activation in Individuals With Severe Spinal Cord Injury.

Neuromuscular electrical stimulation (NMES) is one of the most effective treatments for counteracting the deleterious skeletal muscle adaptations that occur after spinal cord injury (SCI). Additionally, previous findings suggest that NMES can activate motor units via both peripheral and central mechanisms; however, this NMES-promoted central activation is not well understood. In this study, we aimed at investigating the effects of NMES on central activation in 10 individuals with motor complete SCI, focusing on understanding how to optimize NMES pulse width and amplitude for promoting central activation in this population. To this end, we used NMES to generate isometric contractions of the knee extensors and ankle plantarflexors while electromyographic (EMG) activity was recorded from the vastus lateralis and gastrocnemius medialis, respectively. We used EMG activity that persisted after the termination of NMES delivery (post-NMES) as a neurophysiological marker to assess central activation and explored differences in post-NMES EMG activity promoted by 500 and 1,000 μs pulse width NMES. Additionally, we explored the relationships between post-NMES EMG amplitude, torque output, and stimulation amplitude. Our results show that the higher pulse width (1,000 μs) demonstrated a greater effect on central activation as quantified by more frequent occurrences of post-NMES EMG activity (p = 0.002) and a 3.551 μV higher EMG amplitude (p = 0.003) when controlling for the torque output generated by 500 and 1,000 μs pulse width NMES. Importantly, we also found that the interplay among central activation, stimulation amplitude, and muscle torque output differs across SCI individuals, conceivably because of the individual-specific characteristics of the cord lesion and following plasticity of the spinal circuitry. These results suggest that NMES can be optimized to promote central activation, which may lead to novel opportunities for motor function recovery after SCI.

Novel Constrained Nonlinear Control of Vehicle Dynamics Using Integrated Active Torque Vectoring and Electronic Stability Control

This study deals with a new integrated control sys-tem using active torque vectoring (ATV) and electronic stability control (ESC) for enhancement of vehicle directional stability and steerability. In this system, the stabilizing yaw moment is calculated using a novel constrained nonlinear controller with both input and state constraints. The proposed controller is designed using the prediction of continuous nonlinear vehicle model. It guarantees the vehicle directional stability by restricting the side slip angle in the admissible range when the yaw rate tracks its desired response for improved steerability. The calculated yaw moment is generated as driving and braking forces by integrated ATV and ESC systems. According to the integration policy, the required yaw moment is initially generated by ATV in the rear wheels to keep the vehicle driving performance. Because of limitation of ATV, if more yaw moment is required, the ESC system applies asymmetric braking pressure to front wheels to compensate the scarcity of ATV. By the proposed strategy, the small reduction of vehicle velocity is achieved and the vehicle drivability performance is maintained. In order to determine the full capacity of ATV, the active differential dynamics is considered in this paper. Simulation studies are conducted to evaluate the efficiency of proposed constrained controller in comparing with the unconstrained controller and a conventional nonlinear model predictive controller (NMPC) developed in the recent papers using 14-DOF vehicle model. By analyzing the results, it is clear that the proposed controller is much faster and easy to solution and implementation.

Simulation of Pedestrian Rotation Dynamics Near Crowded Exits

Pedestrian evacuation simulation is vital for urban civil engineers. Although there exist many works addressing the issue of emergency evacuation, only a few study the phenomenon of people actively squeezing to pass through an exit. To model this behavior, a three-circle model is adopted to represent the shape of pedestrians. Active rotation torque (ART) is proposed to model the active rotation behavior of pedestrians turning their torsos in the desired direction. This torque occurs either when a pedestrian is not facing his velocity direction, or when he wants to pass through a bottleneck. The equation of ART is designed and regressed with real pedestrian experiments, in which a gyroscope was used to measure the angle of torso rotation. The proposed torque model is then applied to manifold scenarios with various door widths and different safety separation belt settings. Then, both microscopic and macroscopic indexes, including evacuation time, rotation angle, and crowd density, are obtained to show that the proposed model can simulate both non-competitive and competitive pedestrian behaviors near exit bottlenecks more accurately than the circular social force model. Thus, the evacuation time of the exit can be predicted more precisely, which helps to design optimal multi-exit assignment strategies.

Mitigation of Resonance Vibration Effects in Marine Propulsion

Electric propulsion has become the solution for large marine vessels over conventional combustion engine propulsion. An azimuth thruster is the primary propulsion unit in such electrified ships, and it has become prevalent recently. However, the mechanical failures among bevel gear, coupling, and bearing in the thruster are reported commonly, and it may be attributed to the dynamic mismatch and torsional oscillations between the motor drive and mechanical drivetrain systems. One main advantage of using electric propulsion is its flexible and instant torque control that can reduce the torsional stress in the drivetrain. In this paper, a new speed difference-based active torque compensating method is proposed. A detailed model for the azimuth propulsion system is developed, and a power electronics-based controller is used to manage the excessive drivetrain torque caused by a sudden load change. The proposed controller can change the damping ratio by introducing virtual material damping in the system, which decreases the resonant torque amplitude in the driveline. The resonant torque attenuating effects are validated both by simulation and experiment with a multi-inertia model operating at rapid ventilation.

Associations between Subtalar Muscle Strength and Balance Performance in Healthy Young and Old Adults

Background: Associations between lower limb muscle strength and balance performance in adults have previously been reported. However, the function of the foot muscles for postural control has not been understood, yet. Objective: The purpose of the present study was to investigate associations between pronator and supinator muscle strength, subtalar range of motion (ROM) and postural stability while standing under various conditions in young versus old adults. Methods: Using a custom-built apparatus equipped with a force transducer and an electrogoniometer, maximum voluntary isometric subtalar pronator and supinator strength as well as ROM tests were administered to 30 young (mean age: 25.1 years) and 30 old (mean age: 65.2 years) volunteers. Total active subtalar ROM, peak pronator and peak supinator torques were measured. While standing on a force plate, limits of stability (LOS) were determined during anterior–posterior (AP) and medio-lateral (ML) leaning tasks. Furthermore, sway distance and velocity during single-legged standing were measured. Correlation and regression analyses were conducted. Results: In both age groups, subtalar pronator muscle strength was related to AP-LOS (young: r = 0.36; old: r = 0.49). In young adults, subtalar supinator muscle strength was associated with ML-LOS (r = 0.41). The regression analyses revealed that summed subtalar muscle strength predicts 13 and 20% of the variance of AP-LOS in young and old adults, respectively. Summed subtalar muscle strength was found to predict 18% of the variance in ML-LOS in young but not in old adults. There were no correlations and no predictors found concerning subtalar muscle strength and postural sway during single-legged standing for both age groups. Conclusions: Longitudinal studies have to proof whether pronator muscle strength training might positively affect balance performance during AP leaning, specifically in old adults.

Position Based Impedance Control Strategy for a Lower Limb Rehabilitation Robot.

Active rehabilitation training can improve patients' neural engagement and the rehabilitation effects. A position based impedance control strategy is proposed for implement of active training in this paper. Firstly, it is necessary to accurately estimate patients' active torques during the training process, which can be calculated by using the human-robot dynamic model. A novel friction model is designed, where the influence of the joint coupling factor and viscosity is considered to improve the model accuracy. In order to prevent sudden changes of the interaction force, a virtual tunnel around the reference trajectory is established to limit the motion range to ensure patient safety in case of emergency, such as muscle spasm. Then, a position based impedance control strategy designed in the joint space is used to convert human torques into the required movement. The strategy is implemented by a double closed loop control structure, the outer loop of which converts the interaction force into angular, angular velocity, and angular acceleration deviations by the inverse impedance equation. The regulated trajectory will be used as reference for the inner position control loop. The experimental results show that the proposed system dynamic model can be used to accurately estimate the patients' active torques, and the proposed control strategy can be used to design a compliant human-robot interaction interface, so that patients can complete the training task comfortably and naturally, and also safety of the training can be ensured.

Off-road motorcycle tyre force estimation

To improve the performance of off-road motorcycles, tyre contact forces need to be estimated. Differently to on-road motorcycle contact force estimators where the rider can be considered attached to the chassis, an off-road motorcycles estimator needs to model the rider dynamics, since driving in standing position provides significant isolation from motorcycle motion. In this article, we use a novel simple rider model to approximate the interaction with the motorcycle when no sensing on him is possible. In particular, the novelty is to keep the pitch angle of the rider constant by means of an active torque on the hip. A tyre force estimator is built using this rider model coupled to a five degree-of-freedom motorcycle, which is verified with a virtual experiment performed on Working Model 2D, showing promising results.

A Neuromuscular-Model Based Control Strategy to Minimize Muscle Effort in Assistive Exoskeletons.

In literature, much attention has been devoted to the design of control strategies of exoskeletons for assistive purposes. While several control schemes were presented, their performance still has limitations in minimizing muscle effort. According to this principle, we propose a novel approach to solve the problem of generating an assistive torque that minimizes muscle activation under stability guarantees. First, we perform a linear observability and controllability analysis of the human neuromuscular dynamic system. Based on the states that can be regulated with the available measurements and taking advantage of knowledge of the muscle model, we then solve an LQR problem in which a weighted sum of muscle activation and actuation torque is minimized to systematically synthesize a controller for an assistive exoskeleton.We evaluate the performance of the developed controller with a realistic non-linear human neuromusculoskeletal model. Simulation results show better performance in comparison with a well known controller in the literature, in the sense of closed loop system stability and regulation to zero of muscle effort.

A Strategy to Eliminate Instantaneous Active Power Oscillations and Reduce High Currents in the DFIG During Asymmetric Voltage Sags

Wind turbines are widespread around the globe, and the number of windfarms connected to the grid is continually increasing. The Doubly-Fed Induction Generator (DFIG) plays an important role, since it is one of the most used configurations for wind power generation. DFIG-based wind plants, however, are very sensitive to grid disturbances, specially to voltage sags, as these machines have their stator circuit directly connected to the grid. Voltage sags can result in oscillations in active power, torque and DC link voltage, as well as damage the machine and the back-to-back converter due to high currents that arise in such type of contingency. This work proposes a control strategy applied to the rotor-side converter (RSC) of the DFIG, in order to protect the machine and the back-to-back converter during voltage sags. The aim of the control strategy is to reduce the machine currents and also to remove the oscillating active power caused by unbalanced voltage sags.

Dynamics analysis of novel parallel manipulator with one central rotational actuator and four translational actuators

A dynamics analysis of a novel parallel manipulator with one central rotational actuator and four translational actuators is conducted. A 3D model of the parallel manipulator is constructed and its characteristics and DoF are analyzed. The kinematics formulae are derived for solving the displacement, velocity and acceleration of the moving links. The dynamics formulae are derived for solving the inertial wrench of the moving links, the dynamic active forces along the active limbs, the dynamic active torque applied on a central active leg, and the dynamic constrained force exerted on the central active leg. A theoretical numerical example is given to solve the kinematics and dynamics solutions, and the theoretical solutions are verified by the simulation mechanism in Matlab. Finally, a reachable workspace of the novel parallel manipulator is constructed using CAD variation geometry.

DLMPCS‐based improved yaw stability control strategy for DDEV

The yaw stability of distributed drive electric vehicle (DDEV) can be guaranteed by the active steering and torque distribution systems. Conventional yaw stability control strategy mainly focuses on the study of yaw moment, while the tyre lateral saturation and excessive longitudinal skid problems are difficult to be solved efficiently. This may lead to the unstable yaw phenomenon of the vehicle such as the sideslip or tail flick. To improve the yaw stability of DDEV under the tyre lateral saturation and excessive longitudinal skid situations, a double-layer model predictive control system (DLMPCS) is presented in this work. The proposed DLMPCS consists of an anti-saturation yaw stability controller (AYSC) and an anti-slip torque distribution controller (ATDC). The AYSC is designed to guarantee the vehicle yaw stability under the tyre lateral saturation situation, through the active steering and yaw moment. The ATDC is designed to realise the torque distribution and keep the longitudinal slip ratio within the stable zone; then, the vehicle can be prevented from the excessive skid phenomenon. The simulation results confirm the improved yaw performance of the DLMPCS for DDEV under different situations.

Improving traction and active safety of the wheeled vehicle by the distribution of the driving torque between its axles

One method to improve dynamic qualities, stability and cross-country ability of wheeled vehicles is to use Active Torque Transfer Systems (ATTS). An operating algorithm for the ATTS that ensures improved traction and dynamic properties, road-holding and trajectory stability of a two-axle wheeled vehicle has been suggested. Efficiency and feasibility of the suggested algorithm have been proved through simulation modeling. Lines of future research have been defined.

Dietary Nitrate Supplementation Improves Exercise Tolerance by Reducing Muscle Fatigue and Perceptual Responses.

The present study was designed to provide further insight into the mechanistic basis for the improved exercise tolerance following dietary nitrate supplementation. In a randomized, double-blind, crossover design, twelve recreationally active males completed a dynamic time-to-exhaustion test of the knee extensors after 5 days of consuming both nitrate-rich (NITRATE) and nitrate-depleted beetroot juice (PLACEBO). Participants who improved their time-to-exhaustion following NITRATE performed a time-matched trial corresponding to the PLACEBO exercise duration with another 5 days of dietary nitrate supplementation. This procedure was performed to obtain time-matched exercise trials with (NITRATEtm) and without dietary nitrate supplementation (PLACEBO). Neuromuscular tests were performed before and after each time-matched condition. Muscle fatigue was quantified as percentage change in maximal voluntary torque from pre- to post-exercise (ΔMVT). Changes in voluntary activation (ΔVA) and quadriceps twitch torque (ΔPS100) were used to quantify central and peripheral factors of muscle fatigue, respectively. Muscle oxygen saturation, quadriceps muscle activity as well as perceptual data (i.e., perception of effort and leg muscle pain) were recorded during exercise. Time-to-exhaustion was improved with NITRATE (12:41 ± 07:18 min) compared to PLACEBO (09:03 ± 04:18 min; P = 0.010). NITRATEtm resulted in both lower ΔMVT and ΔPS100 compared to PLACEBO (P = 0.002; P = 0.001, respectively). ΔVA was not different between conditions (P = 0.308). NITRATEtm resulted in reduced perception of effort and leg muscle pain. Our findings extend the mechanistic basis for the improved exercise tolerance by showing that dietary nitrate supplementation (i) attenuated the development of muscle fatigue by reducing the exercise-induced impairments in contractile muscle function; and (ii) lowered the perception of both effort and leg muscle pain during exercise.

A Practical and Adaptive Method to Achieve EMG-Based Torque Estimation for a Robotic Exoskeleton

To improve the efficacy of robotic exoskeleton-based rehabilitation training, active joint torque of subjects should be detected. This paper presents a practical and adaptive method to estimate active joint torque using electromyography (EMG) signals for a custom lower limb robotic exoskeleton with two degrees of freedom (DOFs). This estimator, constructed of radial basis function neural networks (RBFNNs), was used to form an extended Slotine-Li controller. This extended controller eliminated the need for the calibration for EMG-torque model. The adaptive control of exoskeleton and adaptive estimation of active joint torque were performed within the same framework. By introducing a two-step learning strategy into the controller, the estimator can continuously adapt to changes in the EMG-torque model, and overcome the problems due to the time-varying property of EMG signals. Simulation and experimental results show that the presented estimator can predict the active joint torque of subjects in a practical and adaptive manner. Additionally, the accurate movement control of exoskeleton is also guaranteed. At present, the experiments are conducted only for the swing phase due to the lack of the force plate sensors.

Smooth Fault-Tolerant Control of Induction Motor Drives With Sensor Failures

A smooth fault-tolerant control (FTC) of induction motor drives with sensor failures is presented in this paper. The drive uses concurrently active direct torque control (DTC), indirect field-oriented control (IFOC), and volts-per-hertz (V/f) controllers as replacements of each other in the case of sensor failure or recovery. Speed encoder, current, and voltage sensors are considered. The DTC and IFOC controllers are properly modified and integrated with the V/f controller in synchronous frame, which allows switching between dc-type voltage commands of different controllers. Therefore, difficult synchronization of different controllers is avoided, and a simple rate limiter is able to achieve smooth handoff transition of different controllers. Details of the DTC, IFOC, and V/f controllers, as well as their integration are presented. Simulation and experimental verification of the proposed FTC are given, where normal abc-frame switching and the proposed synchronous-frame switching of controllers are compared with different switching schemes and at different machine operation conditions. Simulation and experimental results show significantly smoother handoff transients.

High Torque Density Macro-scale Electrostatic Rotating Machines: Electrical Design, Generalized <inline-formula> <tex-math notation="LaTeX">$d-q$</tex-math> </inline-formula> Framework, and Demonstration

The use of advanced dielectric liquids and manufacturing techniques for enhanced surface area per unit volume, along with other multiplicative gains, is enabling macro-scale electrostatic machines with competitive torque densities. This emergence prompts the need for circuit modeling—that guides machine design and drive controls—rooted in the canon of well-established electromagnetic machinery practices. In this study, prior dielectric and manufacturing innovations are combined with a newly developed unified electrostatic machine $d-q$ -axis framework to form a machine that demonstrates industrial utility. Design, equivalent circuits, and performance are validated by an experimental prototype intended for low-speed direct-drive servo actuators. A prototype electrostatic machine was constructed entirely of aluminum and printed circuit boards, and possesses active material torque densities ≥1.4 N⋅m/kg and ≥2.65 N⋅m/L without the need for forced air or liquid cooling. Additional features include near zero loss at stall and low torque ripple.