Slow resonance ratio control for vibration suppression anddisturbance rejection in torsional system

In the resonance ratio control, which the authors proposed for vibration suppression and disturbance rejection in a torsional system, the estimation speed of the disturbance observer should have been much faster than the resonance frequency of the controlled system. However, too fast a disturbance observer sometimes causes an implementation problem. In this paper, the authors give the optimal speed of the disturbance observer and propose a novel technique named “slow resonance ratio control”. It does not have any fast part in the controller. It also enables us to design the speed control and the vibration suppression control almost completely independently     

Continuous variable structure controller for BLDDSM positioncontrol with prescribed tracking performance

The continuous, accurate, and robust sliding mode tracking controller based on a disturbance observer for a brushless direct drive servo motor (BLDDSM) is presented. Although the conventional sliding mode control (SMC) or variable structure control (VSC) can give the desired tracking performance, there exists an inevitable chattering problem in control which is undesirable for a direct drive system. With the proposed algorithm, not only are the chattering problems removed, but also the prescribed tracking performance can be obtained by using the efficient compensation of the disturbance observer. The design of the sliding mode tracking controller for the prescribed, accurate, and robust tracking performance without the chattering problem is given based on the results of the detailed stability analysis. The usefulness of the proposed algorithm is demonstrated through the computer simulations for a BLDDSM under load variations     

Active damping of drive train oscillations for an electrically driven vehicle

A problem encountered with electrically driven vehicles are resonances in the drive train caused by elasticity and gear play. Disadvantageous effects caused by this are noticeable vibrations and high mechanical stresses due to torque oscillations. The oscillations can be damped using a control structure consisting of a nonlinear observer to estimate the torque in the gear and a controller, which computes a damping torque signal that is added to the driver's demand. The control algorithm was implemented in the existing motor control unit without any additional hardware cost. The controller was successfully tested in a test vehicle. The resonances can essentially be eliminated. The controller copes satisfactorily with the backlash problem.     

Vibration Suppression Using Single Neuron-Based PI Fuzzy Controller and Fractional-Order Disturbance Observer

An approach is proposed for vibration suppression in a two-inertia system using an integration of a fractional-order disturbance observer and a single neuron-based PI fuzzy controller. The former is used to obtain disturbance estimate and generate compensation signal, and the latter is utilized to realize outer loop control. Fractional-order disturbance observer has a wider range to select a suitable tradeoff between robustness and vibration suppression, because introduction of fractional calculus makes universe of relative degree of Q-filter is expanded from integer domain to real-number domain. For the single neuron-based PI fuzzy controller, a single neuron makes up a PI controller and such a controller is embedded in each cell of the fuzzy control table. Thus, the fuzzy control table is changed into a controller matrix and it constructs a nonlinear adaptive controller with parameter self-tuning property. Experimental results illustrate that the integration of fractional-order disturbance observer and single neuron-based PI fuzzy controller can improve the performance of disturbance attenuation and system robustness     

Intelligent optimal control of single-link flexible robot arm

This paper addresses the design and properties of an intelligent optimal control for a nonlinear flexible robot arm that is driven by a permanent-magnet synchronous servo motor. First, the dynamic model of a flexible robot arm system with a tip mass is introduced. When the tip mass of the flexible robot arm is a rigid body, not only bending vibration but also torsional vibration are occurred. In this paper, the vibration states of the nonlinear system are assumed to he unmeasurable, i.e., only the actuator position can be acquired to feed into a suitable control system for stabilizing the vibration states indirectly. Then, an intelligent optimal control system is proposed to control the motor-mechanism coupling system for periodic motion. In the intelligent optimal control system a fuzzy neural network controller is used to learn a nonlinear function in the optimal control law, and a robust controller is designed to compensate the approximation error. Moreover, a simple adaptive algorithm is proposed to adjust the uncertain bound in the robust controller avoiding the chattering phenomena. The control laws of the intelligent optimal control system are derived in the sense of optimal control technique and Lyapunov stability analysis, so that system-tracking stability can be guaranteed in the closed-loop system. In addition, numerical simulation and experimental results are given to verify the effectiveness of the proposed control scheme.     

Effects of muscle fatigue on the ground reaction force and soft-tissue vibrations during running: a model study

A modeling approach is used in this paper to study the effects of fatigue on the ground reaction force (GRF) and the vibrations of the lower extremity soft tissues. A recently developed multiple degrees-of-freedom mass-spring-damper model of the human body during running is used for this purpose. The model is capable of taking the muscle activity into account by using a nonlinear controller that tunes the mechanical properties of the soft-tissue package based on two physiological hypotheses, namely, "constant force" and "constant vibration." In this study, muscle fatigue is implemented in the model as the gradual reduction of the ability of the controller to tune the mechanical properties of the lower body soft-tissue package. Simulations are carried out for various types of footwear in both pre- and postfatigue conditions. The simulation results show that the vibration amplitude of the lower body soft-tissue package may considerably increase (up to 20%) with muscle fatigue, while the effects of fatigue on the GRF are negligible. The results of this modeling study are in line with the experimental studies that found muscle fatigue does not significantly change the GRF peaks, but may increase the level of soft-tissue vibrations (particularly for hard shoes). A major contribution of the current study is the formulation of a hypothesis about how the central nervous system tunes the muscle properties after fatigue.     

Vibration reduction of seat suspension using observer based terminal sliding mode control with acceleration data fusion

In this work, a disturbance observer and state observer based terminal sliding mode (TSM) controller with acceleration data fusion is proposed for the active control of a seat suspension. In practical applications, the driver's body and the friction forces are difficult to be accurately described with a mathematical model; for this reason, the proposed controller is designed based on a model simplified from a 6-degree-of-freedom (6-DOF) seat-driver model with nonlinear friction. The disturbance observer and state observer are designed together with Linear Matrix Inequality (LMI) method. For improving the observer's performance, a complementary filter is applied to fuse the estimation of the seat suspension velocity from the acceleration measurement and the state observer. The proposed controller is validated using simulations with various bump excitations applied, and the conventional state feedback TSM controller is implemented for comparison. The proposed controller is also implemented in a practical active seat suspension prototype, and a well-tuned commercial heavy duty vehicle seat suspension is applied for comparison. The power spectral density (PSD) value and ISO 2631–1 standard are used to evaluate the active seat suspension system's performance under random vibration. Both the simulation and the experimental results indicate that with the proposed controller, the vibration magnitude caused by a rough road can be greatly reduced, and the driver ride comfort is greatly improved.     

Backstepping boundary control of flexible-link electrically drivengantry robots

Gantry robots are used for precision manufacturing and material handling in the electronics, nuclear, and automotive industries. Light, flexible links require less power, but may vibrate excessively. An implementable boundary controller is developed to damp out undesirable vibrations in a flexible-link gantry robot driven by a brushed DC motor. Hamilton's principle produces the governing equations of motion and boundary conditions for the flexible link. The electrical subsystem dynamics for a permanent magnet brushed DC motor couple with the link dynamics to form a hybrid system of partial and ordinary differential equations. A boundary voltage control law is developed based on Lyapunov theory for distributed parameter systems. Through an embedded desired-current control law, the integrator backstepping controller generates the desired control force on the mechanical subsystem. A velocity observer estimates the gantry velocity, eliminating one feedback sensor. Modal analysis and Galerkin's method generate the closed-loop modal dynamics. Numerical simulations demonstrate the improved vibration damping characteristics provided by the backstepping boundary control law. Experimental results confirm the theoretical predictions, showing the high performance of backstepping boundary control     

Static shape and vibration control of flexible payloads with applications to robotic assembly

This paper addresses the simultaneous control of vibration and static shape deformation of arbitrarily shaped thin-walled flexible payloads. During robotic assembly of these thin-walled parts, gravity and inertial forces acting on the parts may induce both static shape deformation and vibrations in the part sufficiently large that accurate and high speed assembly of these parts is hindered. Static deformations, which arise due to deformation of the part caused by its own weight under the influence of gravity, lead to misalignment of mating points of the parts. Unwanted vibrations, arising from inertial forces acting on the thin-walled parts as they are positioned for assembly, must damp out before parts can be mated, further hindering the process. In this work, a smart gripper with actuated contact points to grasp the flexible thin-walled parts is proposed to solve this problem. The smart gripper is capable of both part reshaping and active damping of unwanted vibrations of the part. It is fixed to a robotic manipulator and is comprised of multiple linearly actuated fingers with laser-based noncontact proximity sensors, and associated signal processing and controllers. In this paper, a simultaneous vibration and static shape controller is developed. The proposed controller is a composite modal controller in conjunction with a quasi-static modal filter and a bias Kalman filter, which is synthesized based on the reduced-order dynamic model of the flexible payload. A near industrial practice demonstration of the feasibility of the proposed approach is carried out using a proof-of-concept smart gripper to manipulate an automotive fender. Experimental results indicate that unwanted vibrations are successfully damped out, allowing faster cycle times for an assembly process, and static shape deformations are corrected, allowing accurate positioning of parts for assembly.     

Integrated design of speed-sensorless and adaptive speed controller for a brushless DC motor

The study develops a design of an integrated new speed-sensorless approach that involves a torque observer and an adaptive speed controller for a brushless dc motor (BLDCM). The system is based on the vector control drive strategy. The speed-sensorless approach first employs a load observer to estimate the disturbed load torque, and then the estimated load torque is substituted into the mechanical dynamic equation to determine the rotor speed, and thus develop a speed-sensorless algorithm. Additionally, the mechanical rotor inertia constant and the friction coefficient, which are the inputs of the load observer, are estimated using the recursive least-square rule. Therefore, the proposed speed-sensorless approach is unaffected by the time-variant motor parameters nor is affected by the integrator drift problem. It also has a simpler computing algorithm than the extended Kalman filter for estimating the speed. The modified model reference adaptive system algorithm, an adaptive control algorithm, is adopted as a speed controller of the BLDCM to improve the performance of the speed-sensorless approach. Simulation and experimental results confirm that the performance of the design of a new integrated speed-sensorless approach and the adaptive speed controller is good.     

Observer-Based Ripple Force Compensation for Linear Hybrid Stepping Motor Drives

This paper describes our research on a force ripple compensation and closed-loop position control scheme using linear hybrid stepping motors (LHSMs) with significant thrust vibrations. In order to estimate unobservable force ripple components, we propose the Jacobian linearization observer that guarantees the convergence of state estimates into true states. For the precise control of velocity and position, an input-output feedback linearization controller is derived from a nonlinear position-dependent model of the LHSM based on elaborate reluctance network analysis. In addition, we discuss the separation principle used to separate the observer design from the controller design. Common problems associated with the force ripple, such as the positioning error, mechanical stress, and acoustic noise, are efficiently handled using the proposed active damping control scheme. Experimental results show that the positioning accuracy is significantly improved through a closed-loop control while restraining the thrust ripple.     

Frequency-adaptive cancellation of harmonic disturbances at non-measurable positions of steel strips

The active rejection of harmonic disturbances is of great importance in many industrial applications. For instance, transverse vibrations of steel strips in hot-dip galvanizing lines entail an inhomogeneous zinc coating of the final product. Controlling the vibrations of these steel strips is particularly complicated because their direct measurement at the relevant location is not available. More specifically, the disturbance input, the displacement measurement, the electromagnetic actuator which acts as control input, and the system output to be controlled are all located at different positions along the steel strip. The control scheme proposed in this work minimizes the harmonic steady-state response of the system output to be controlled. In contrast to a state–space approach, the method does not utilize a high-dimensional state observer, and requires only modest computational resources during online operation. Furthermore, negative effects in the closed-loop system due to observation or control spillover are effectively avoided. The developed harmonic disturbance rejection scheme is validated by experiments conducted on a test rig that mimics the conditions from an industrial hot-dip galvanizing line.     

基于压电陶瓷作用的气体主轴抑振研究

针对空气静压主轴气膜刚度不高,在工作中易受自身及外部激励的影响,从而产生不平衡振动的现象,设计了一种基于压电陶瓷的可控空气静压径向轴承,研究了压电陶瓷的相关特性。结合气体主轴建立了轴承转子压电陶瓷的耦合模型,并在此基础上建立了基于扩张观测器的滑模控制器,同时将压电陶瓷综合控制器串联其中,在限制条件内利用控制器使压电陶瓷挤压气膜为主轴提供有效的主动控制力,从而抑制空气静压主轴的振动。研究结果表明,利用压电陶瓷对空气静压主轴系统的振动进行抑制取得了良好的效果,对于主要控制点可使其振动位移减小99.17%,对于次要控制点均有不同程度的减振效果,最多可减少94.36%。     

Vertical-vibration control of elevator using estimated caracceleration feedback compensation

In this paper, a vibration suppression strategy is proposed for improving the riding comfort of an elevator, using car acceleration feedback compensation. The vertical vibration of a lift car is mainly caused by the resonance of elastic ropes between the car and the sheave, and the resonant frequency of the system is dependent upon both passenger load and lift position. To suppress the vibration of a lift car, the car velocity or acceleration is needed, but only a sheave velocity is measurable in a practical situation. The proposed method applies an extended full-order observer for the simultaneous estimation of car acceleration and the identification of mechanical parameters. Acceleration feedback compensation is used for the vibration suppression control. Experimental evaluation has been performed with a 30 kVA insulated gate bipolar transistor inverter and a medium-speed elevator system in an elevator test tower. Computer simulated and experimental results prove the feasibility of the proposed vertical-vibration controller     

Adaptive robust control of fully-constrained cable driven parallel robots

In this paper, adaptive robust control (ARC) of fully-constrained cable driven parallel robots is studied in detail. Since kinematic and dynamic models of the robot are partly structurally unknown in practice, in this paper an adaptive robust sliding mode controller is proposed based on the adaptation of the upper bound of the uncertainties. This approach does not require pre-knowledge of the uncertainties upper bounds and linear regression form of kinematic and dynamic models. Moreover, to ensure that all cables remain in tension, proposed control algorithm benefit the internal force concept in its structure. The proposed controller not only keeps all cables under tension for the whole workspace of the robot, it is chattering-free, computationally simple and it does not require measurement of the end-effector acceleration. The stability of the closed-loop system with proposed control algorithm is analyzed through Lyapunov second method and it is shown that the tracking error will remain uniformly ultimately bounded (UUB). Finally, the effectiveness of the proposed control algorithm is examined through some experiments on a planar cable driven parallel robot and it is shown that the proposed controller is able to provide suitable tracking performance in practice.     

基于扰动观测器的机载云台扰动复合补偿方法

针对多旋翼无人机(mUAV)机载云台的扰动补 偿需求,提出一种基于改进的扰动观测器(IDO,improved disturbance observer)的伺服控 制器与减振装 置相结合的复合补偿方法。深入分析了IDO的扰动补偿能力和鲁棒性,构建 了基于IDO的云 台伺服控制结构;依据mUAV机载云台的振动特性,设计出减振装置的结构参数 及安装位置。飞行实验表明, 引入复合补偿方法后,视轴(LOS)指向误差减小到了0.03°,振动隔 离度提高了约15dB。复合补偿方法有效地补偿了机载云 台的扰动,完全满足了mUAV机载云台扰动补偿的需求。     

Robust Fault Estimation and Accommodation for a Class of T–S Fuzzy Systems with Local Nonlinear Models

This paper focuses on the problems of fault estimation and accommodation for a class of T–S fuzzy systems with local nonlinear models and having an external disturbance and sensor and actuator faults, simultaneously. A fuzzy robust fault estimation observer is designed to estimate the system state and sensor and actuator faults. Compared with existing results, the observer not only is robust to the disturbance but also has a wider application range and more freedom for design. To compensate for the effect of faults and to stabilize the closed-loop system, an observer-based fault-tolerant controller is proposed. The separate design of the observer and controller avoids coupling between them. Finally, a simulation is conducted to demonstrate the effectiveness of the proposed method.     

H∞ loop shaping for the torque-vectoring control of electric vehicles: Theoretical design and experimental assessment

This paper presents an H_∞ torque-vectoring control formulation for a fully electric vehicle with four individually controlled electric motor drives. The design of the controller based on loop shaping and a state observer configuration is discussed, considering the effect of actuation dynamics. A gain scheduling of the controller parameters as a function of vehicle speed is implemented. The increased robustness of the H_∞ controller with respect to a Proportional Integral controller is analyzed, including simulations with different tire parameters and vehicle inertial properties. Experimental results on a four-wheel-drive electric vehicle demonstrator with on-board electric drivetrains show that this control formulation does not need a feedforward contribution for providing the required cornering response in steady-state and transient conditions.     

Sensorless Sine‐Wave Controller IC for PM Brushless Motor Employing Automatic Lead‐Angle Compensation

This paper presents an advanced sensorless permanent magnet (PM) brushless motor controller integrated circuit (IC) employing an automatic lead‐angle compensator. The proposed IC is composed of not only a sensorless sine‐wave motor controller but also an isolated gate‐driver and current self‐sensing circuit. The fabricated IC operates in sensorless mode using a position estimator based on a sliding mode observer and an open‐loop start‐up. For high efficiency PM brushless motor driving, an automatic lead‐angle control algorithm is employed, which improves the efficiency of a PM brushless motor system by tracking the minimum copper loss under various load and speed conditions. The fabricated IC is evaluated experimentally using a commercial 200 W PM brushless motor and power switches. The proposed IC is successfully operated without any additional sensors, and the proposed algorithm maintains the minimum current and maximum system efficiency under 0 N·m to 0.8 N·m load conditions. The proposed IC is a feasible sensorless speed controller for various applications with a wide range of load and speed conditions.     

Vibration Absorption Control of Industrial Robots by Acceleration Feedback

This paper describes an electrical control method of absorbing arm vibrations of industrial robots. Arm vibration problems are divided into two categories: resonance vibration phenomenon depending on actuator velocity and transient oscillations caused by acceleration change of actuators. Because resonance frequency of an industrial robot changes more than double due to the arm posture, mechanical vibration absorbing methods may not be easily utilized. The method applied in this paper is to compose dampers as electric manners by utilizing arm acceleration feedback to actuators of an industrial robot. Acceleration sensors are attached on three axes which construct a robot arm. Acceleration signals are fed back to the corresponding actuators passed through phase compensation circuits. By experiments applied to an industrial robot, this method has been proved to be effective in eliminating both resonance and transient vibrations. According to this control, a smart motion industrial robot which does not have resonance characteristics and operates speedily and smoothly has been realized.