Torque Observer Research Articles

Application of torque observer based on belief rule base to power redistribution process

When navigating in ice zones, broken ice can be drawn into the propeller by the wake current, significantly altering the propeller load and causing severe fluctuations in the power grid of electrical propulsion ship. To address this issue, this paper presents two kinds of power redistribution control (PRC) strategies, which utilises the dynamic feedback from the ship's generator sets to the electric propulsion system to improve the frequency control. The PRC strategy #2, which receives feedback from generator's torque deviation, has better control effect than PRC strategy #1 with feedback from speed deviation. Since the accuracy of the estimated mechanical torque directly affects the control effect of strategy #2, this paper designs a torque observer based on the Belief Rule Base (BRB) by matching the PRC strategy to regulate the grid frequency in real-time. Given the power grid's fluctuations primarily caused by aft propellers, the power will be partly redistributed to the bow thruster to stabilise the ship's grid. Experiments show that this method can maintain the stability of the grid frequency by quickly correcting the power distribution during the process of sudden shedding propeller load.

Anti‐Interference Sliding Mode Control of PMSM Based on Improved Salp Swarm Algorithm

AbstractAiming at the problem that the control performance of permanent magnet synchronous motor is easily affected by load disturbance during operation, a fractional‐order sliding mode control method combining fractal‐order sliding mode controller (FOSMC) and fractional‐order sliding mode load torque observer (FOSMO) is proposed. The parameters of this method are tuned using the improved salp swarm algorithm (ISSA). Initially, the fractional‐order sliding mode controller is designed by applying fractional‐order calculus theory to enhance the system's response speed. Subsequently, a fractional‐order sliding mode load torque observer is developed to improve the system's anti‐interference capability and robustness due to the slow response and low identification accuracy of traditional load torque observers. Lastly, the control parameters are self‐tuned using the improved salp swarm algorithm due to the difficulty of adjusting them manually. Simulation and experimental results demonstrate that the proposed control method exhibits good convergence, no overshoot, minimal buffeting, and strong robustness against uncertain factors like load disturbances. © 2024 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.

The study of forced oscillations in the non-linear system of an individual traction drive

BACKGROUND: The processes taking place in the ‘traction electric drive – wheel – road’ system during acceleration and braking cause increased dynamic loads on drive components, which may lead to a breakdown. Therefore, it is important to control the drive in a way to minimize and to suppress the given processes. To make it possible, the control system is to be equipped with a resistance torque observer at the electric motor shaft. In addition, in any system, there is a heighten interest in study of arise of resonances, which come with abrupt increase of oscillations amplitudes. Therefore, the features of oscillation phenomena in the given non-linear system are to be studied. AIM: Identification of the peculiarities of oscillatory processes, resonance phenomena in the systems of electromechanical drive of vehicles, which are nonlinear technical systems. METHODS: The study of features of the oscillating processes and the study of capabilities of arise of resonant phenomena were conducted using analysis of the differential equations system describing the operation of the non-linear system. RESULTS: The features of the oscillating phenomena in non-linear systems of interaction between an elastic wheel and road as well as capabilities of arise of resonant phenomena were considered. It is defined that arise of the resonant phenomena in the considered systems is not possible due to breakdown of them. The behavior of modes of interaction between an elastic wheel and road during intensive acceleration and braking was analyzed. The abrupt shock behavior of change rate of wheel torque and current consumed by a drive as well as features of lowering of them when using the self-oscillating phenomena suppression were found. CONCLUSION: The practical value of the study lies in ability of using the proposed conclusions at development of units of a traction electric drive and at synthesis of vehicle motion control systems.

Load torque estimation for cable failure detection in cable-driven parallel robots: a machine learning approach

AbstractThis paper proposes a method for cable failure detection in cable-driven parallel robots (CDPRs) with arbitrary architecture, which is based on the estimates of the motor load torques, together with machine learning algorithms. By just exploiting the dynamic model of each actuator in the conditions of no load, an open-loop load torque observer is designed for each motor to estimate the presence of a load coupled through a cable. Since such a load instantaneously goes to zero for the motor with a broken cable, a simple but effective and robust signature of failure can be inferred to provide reliable detection even in the case of various model mismatches. Additionally, the load torque observer is not computationally demanding since just motor measurements are required, thus avoiding any direct measurement (and a dynamic model as well) on the end-effector. The detection of a failure is made through supervised classification algorithms based on artificial intelligence. The training of the machine learning algorithm is based on a “hybrid” approach: the dataset includes several failure cases, which are numerically generated through a system digital twin developed through the multibody system theory, together with measurements of the real system in nonfailing conditions. Different classification algorithms are considered, together with different sets of input variables to be fed to the classifier. Four numerical examples are proposed by showing the method capability in handling both fully actuated and redundantly actuated CDPRs under cable failure, both rigid and flexible cables, and also evaluating the response in the presence of cable slackness.

Regenerative braking fault compensation control of distributed electric vehicle considering random wheel fault degree

Distributed drive electric vehicles can reduce range anxiety through regenerative braking. However, if the wheel motor torque output fails, it will form an additional yaw moment to the vehicle, causing instability, or deviation and threatening its safety. To solve this problem, the research object is an electric vehicle driven by a four-wheel hub motor. A braking force compensation distribution strategy for front and rear axles is proposed, which combines electronic hydraulic braking (EHB) system compensation control and deviation auxiliary control. Firstly, a fault detection module is established, and the motor’s output torque is estimated by designing a torque observer to obtain the fault degree information of the motor. Secondly, to fully use the motor’s regenerative braking force, the fault-free and faulty electro-hydraulic braking force distribution strategies are designed in the coordinated distribution layer of the electro-hydraulic braking system. The corresponding electro-hydraulic braking force compensation method is selected according to the fault degree of the regenerative braking function, the position of the faulty wheel, and the braking strength. Then, a deviation auxiliary controller is designed based on the model predictive control, and the intervention time of the auxiliary controller is determined according to the vehicle’s state. Finally, the control method is verified based on CarSim/Simulink co-simulation and hardware-in-the-loop (HIL) platform. The test results show that the designed control method can effectively compensate for the regenerative braking failure of random wheel and ensure the braking safety of the vehicle.

Flexible control and trajectory planning of medical two-arm surgical robot.

This paper introduces the flexible control and trajectory planning medical two-arm surgical robots, and employs effective collision detection methods to ensure the safety and precision during tasks. Firstly, the DH method is employed to establish relative rotation matrices between coordinate systems, determining the relative relationships of each joint link. A neural network based on a multilayer perceptron is proposed to solve FKP problem in real time. Secondly, a universal interpolator based on Non-Uniform Rational B-Splines (NURBS) is developed, capable of handling any geometric shape to ensure smooth and flexible motion trajectories. Finally, we developed a generalized momentum observer to detect external collisions, eliminating the need for external sensors and thereby reducing mechanical complexity and cost. The experiments verify the effectiveness of the kinematics solution and trajectory planning, demonstrating that the improved momentum torque observer can significantly reduce system overshoot, enabling the two-arm surgical robot to perform precise and safe surgical tasks under algorithmic guidance.

Load torque observation and compensation for permanent magnet synchronous motor based on sliding mode observer

Background Permanent magnet synchronous motors (PMSM) are widely used in various industries. However, in practical applications, the time-varying nature of load torque may lead to speed fluctuations, negatively impacting the motor's control performance and stability. To mitigate these issues, this paper proposes a load torque observation method for PMSMs based on a sliding mode observer. Methods The sliding mode observer is designed to estimate the load torque and convert it into a current, which is fed back as a feedforward compensation to the q-axis current in the current closed-loop control system. The observer's dynamic performance is optimized using a genetic algorithm to minimize the Integral of Time-weighted Absolute Error (ITAE) between the observer and the actual system state. Experimental tests are conducted on a motor torque testing platform. After stabilizing the motor at 800rpm, a sudden torque of 0.5Nm is applied. Results Compared to the situation without load torque compensation, the motor speed fluctuations are reduced by approximately 60% after adding load torque compensation. Conclusions This enhancement improves the system's speed control performance during torque variations and increases the system's robustness and disturbance rejection capability.

Sliding Mode Speed Control for PMSM Based on Model Predictive Current

To enhance the dynamic performance and disturbance rejection capability of the permanent magnet synchronous motor speed control system, a novel speed control method based on a novel sliding mode control (NSMC) and load torque observer is proposed on the basis of model predictive current control (MPCC) with a sliding mode disturbance observer. First, on the basis of MPCC, the influence of parameters such as resistance, inductance, and flux linkage on MPCC is analyzed. To address the aggregated disturbance caused by parameter mismatches, a piecewise square-root switching function sliding mode disturbance observer (SMDO) is designed to enhance the robustness of the parameters. To address the poor dynamic performance and inadequate robustness resulting from the proportional-integral-controller (PI) velocity loop control in the MPCC, a novel NSMC velocity control method is proposed. This method utilizes the hyperbolic sine function and fractional-order integral sliding mode surface, resolving the dilemma faced by traditional slide mode controllers (SMC) in balancing fast response and reduced vibration. Additionally, to enhance the system’s disturbance rejection capability, a sliding mode torque observer (SMTO) is designed to continuously update the observed load torque value into the NSMC controller, achieving speed compensation control. Finally, through comparative experiments among the proportional integral controller (PI), SMC, NSMC, and NSMC + SMTO, the results indicate that the proposed NSMC + SMTO exhibits the best speed response, steady-state characteristics, and disturbance rejection capability.

Adaptive-neural command filtered synchronization control of tele-robotic systems using disturbance observer with safety enhancement

Due to the nature of the tele-robotic systems, some main problems are imposed, such as external disturbances, time-varying delays and external torques. However, some applications such as tele-surgery systems, require high precision, safety and accurate transmission of information between the leader and follower robots. In order to facilitate the imposed restrictions and to guarantee transient-state, and even steady-state performances in the presence of external disturbances and system uncertainties, the time-varying full state constrained control is employed by applying the Barrier Lyapunov function (BLF). In this regard, a new adaptive neural network torque observer is proposed to make the system independent from the force sensors. Moreover, the independence of the proposed algorithm from perfect knowledge of the manipulator dynamics and time-delay’s derivative of communication channels are advantages of this paper. Furthermore, the key idea of this paper is to lessen the computational complexity in the backstepping-based adaptive neural controller by means of the command filter strategy and the BLF approach is combined to converge the synchronization error signals into a predefined constraint. In order to consider practical limitations, time-varying delays in the communication channel and input saturation constraint are also considered in the design mechanism. Finally, the stability analysis of the observer and controller together is conducted and the evaluation of the performance of the proposed method is performed through a series of various scenarios and comparisons.

Direct observation of current-induced nonlinear spin torque in Pt-Py bilayers

Direct observation of current-induced nonlinear spin torque in Pt-Py bilayers

Load torque composite synchronous control of dual‐driven systems

AbstractFor enhancing the load torque synchronization performance of dual‐driven systems, the inherent coupling effect between the parallel axes is analyzed first and could be described as two distinct components of the synchronous error. Thus, the feedforward‐feedback composite synchronous control scheme is proposed in this paper to eliminate these desynchronization factors. Secondly, the selection of synchronization objectives such as speeds, positions or currents of parallel axes is analyzed, which may not accurately reflect the actual load desynchronization due to mismatch dynamics. To overcome this drawback, the synchronous feedback controller is modified by incorporating a load torque observer, which can provide good adaptation to modelling errors, disturbances and eliminate the load desynchronization effectively. Simulation and experimental results demonstrate significant improvement in load torque synchronization performance achieved by the proposed control scheme.

Observation of Long-Range Current-Induced Torque in Ni/Pt Bilayers.

The generation of current-induced torques through the spin Hall effect in Pt has been key to the development of spintronics. In prototypical ferromagnetic-metal/Pt devices, the characteristic length of the torque generation is known to be about 1 nm due to the short spin diffusion length of Pt. Here, we report the observation of a long-range current-induced torque in Ni/Pt bilayers. We demonstrate that when Ni is used as the ferromagnetic layer, the torque efficiency increases with the Pt thickness, even when it exceeds 10 nm. The torque efficiency is also enhanced by increasing the Ni thickness, providing evidence that the observed torque cannot be attributed to the spin Hall effect in the Pt layer. These findings, coupled with our semirealistic tight-binding calculations of the current-induced torque, suggest the possibility that the observed long-range torque is dominated by the orbital Hall effect in the Pt layer.

Force Compensation Control for Electro-Hydraulic Servo System with Pump–Valve Compound Drive via QFT–DTOC

Each joint of a hydraulic-driven legged robot adopts a highly integrated hydraulic drive unit (HDU), which features a high power–weight ratio. However, most HDUs are throttling-valve-controlled cylinder systems, which exhibit high energy losses. By contrast, pump control systems offer a high efficiency. Nevertheless, their response ability is unsatisfactory. To fully utilize the advantages of pump and valve control systems, in this study, a new type of pump–valve compound drive system (PCDS) is designed, which can not only effectively reduce the energy loss, but can also ensure the response speed and response accuracy of the HDUs in robot joints to satisfy the performance requirements of robots. Herein, considering the force control requirements of energy conservation, high precision, and fast response of the robot joint HDU, a nonlinear mathematical model of the PCDS force control system is first introduced. In addition, pressure–flow nonlinearity, friction nonlinearity, load complexity and variability, and other factors affecting the system are considered, and a novel force control method based on quantitative feedback theory (QFT) and a disturbance torque observer (DTO) is designed, which is denoted as QFT–DTOC herein. This method improves the control accuracy and robustness of the force control system, reduces the effect of the disturbance torque on the control performance of the servo motor, and improves the overall force control performance of the system. Finally, experimental verification is performed using the PCDS performance test platform. The experimental results and quantitative data show that the QFT–DTOC proposed herein can significantly improve the force control performance of the PCDS. The relevant force control method can be used as a bottom-control method for the hydraulic servo system to provide a foundation for implementing the top-level trajectory planning of the robot.

Dynamic coordinated control strategy of a dual-motor hybrid electric vehicle based on clutch friction torque observer

The hybrid power system with dual motors and multiple clutches experiences significant torque fluctuation during mode switching process due to the different torque response characteristics of the motor and engine. To address this issue, this paper focuses on the estimation of clutch friction torque and the development of dynamic coordinated control strategies for the components. Firstly, based on the dynamic model of the novel dual-motor hybrid electric vehicle, a torque observer based on the Kalman filter algorithm is developed to predict the friction torque generated in the clutch sliding friction stage. Secondly, the control strategies are developed for the mode switching process from single-motor to dual-motor and from dual-motor to parallel drive on a co-simulation platform. Thirdly, a power level Hardware-In-the-Loop test platform is built, and the performance of the designed control strategies is verified by the HIL platform. The results show that for the mode switching process from dual-motor to parallel drive, compared with the control strategy using the engine target speed, the control strategy based on engine idle speed proposed in this paper reduces the clutch sliding friction work and the maximum longitudinal jerk of the vehicle by 42.5% and 25.4%, respectively.

A Review of the State of the Art of Torque Ripple Minimization Techniques for Permanent Magnet Synchronous Motors

Industrial applications such as automation, robots, and electric vehicles are widely employing permanent magnet synchronous motors (PMSM) due to inherent characteristics such as high torque to power ratio, low maintenance, high efficiency, and wide operating range. However, PMSM drives can suffer from unwanted torque ripples caused by periodic disturbances of the electromagnetic effect. First, this paper analyses the sources of torque ripple in PMSMs. Second, the torque measurement techniques of the PMSM including torque sensors, torque observers, and indirect measurement methods are discussed to highlight their shortcomings. Third, this paper categorizes and summarizes advanced control-based torque ripple minimization (CB-TRM) techniques for the PMSM by critically evaluating their impacts. These CB-TRM techniques actively control the current waveforms to ensure smooth torque generation and mitigate the effects of torque ripples. Finally, the paper concludes by discussing remaining research questions and opportunities for future research on TRM techniques for PMSMs.

Limiting Control and Accurate Observation of Transmission Torque and Its Jerk in Elastic Servo Systems

Limiting Control and Accurate Observation of Transmission Torque and Its Jerk in Elastic Servo Systems

Dynamic characterization and control of a back-support exoskeleton 3D-printed cycloidal actuator

The safety, health, and well-being of human workers are crucial for socially sustainable production systems, especially in Industry 5.0. Occupational exoskeletons, particularly back-support devices, are increasingly being adopted to reduce musculoskeletal disorders and human fatigue. To reduce costs and weight, optimized exoskeleton design is being explored. A 3D-printed cycloidal reduction stage for the actuation unit is proposed, focusing on an interaction torque observer and an impedance-based controller for human-robot interaction. The device's dynamic characterization and control are analyzed to evaluate its applicability to a sensorless back-support occupational exoskeleton.

Assist-As-Needed rehabilitation using velocity field for upper limb exoskeleton

Assist-As-Needed (AAN) rehabilitation in related works typically limits subjects to perform rehabilitation tasks with particular time instants. This paper proposes a velocity field based on an active-assistive control system to solve this issue. The active intention of motion of the subjects are extracted via a Kalman filter constructed on the basis of an interactive torque observer. Then, given a task motion pattern devised to provide subjects the time-decoupled assistance, our system can first automatically produce a position-coupled velocity field. Afterwards, a method is proposed to integrate the active and assistive motion based on the subjects’ performance and involvement so that eventually they will actively perform the task in a more accurate manner. The stability of the proposed system is verified by Lyapunov analysis. The experiment results show that the execution time and the subjects’ exertion are reduced when performing given tasks compared with the related work. To sum up, the hereby developed system not only can maintain the subjects’ active intention but also can assist them to run the task accurately.

Application of External Torque Observer and Virtual Force Sensor for a 6-DOF Robot

Application of External Torque Observer and Virtual Force Sensor for a 6-DOF Robot

Research on improved sliding mode control of permanent magnet synchronous motor with disturbance compensation

In order to address the shortcomings of traditional sliding mode variable structure control in permanent magnet synchronous motor vector control, such as the state quantity’s inability to converge to 0 in limited time, too large chattering, too large load disturbance, poor dynamic performance, a non-singular fast terminal sliding mode control algorithm in speed loop is proposed. At the same time, a new approach rate is designed by comparing the advantages and disadvantages of different approach rates, which can restrain the natural chattering of sliding mode and improve the approach rate. On this basis, in order to increase response time, lessen chattering, and enhance the observer’s capacity for adaptation, a load torque observer is constructed, load disturbance is added to the speed loop as feedforward compensation, and a new approach rate is added to the observer. The simulation results manifest that the design successfully tracks load torque, enhances the system’s dynamic performance, and lessens the impact of sliding mode chattering.