Model-based Disturbance Observer Research Articles

Comparison of Direct and Inverse Model-based Disturbance Observer for a Servo Drive System

Comparison of Direct and Inverse Model-based Disturbance Observer for a Servo Drive System

Inversed Model-Based Disturbance Observer Base on Adaptive Fast Convergent Sliding Mode Control and Fixed-Time State Observer for Slotless Self-Bearing Motor

The slotless self-bearing motor (SSBM) is a motor with its self-bearing function. The mechanical structure of the motor is six symmetrical hexagonal shapes. The main control problem for this motor is disturbance and uncertainty rejection. Therefore, this paper proposes a new disturbance observer (DOB) based on an optimal fixed-time state observer (OFTSOB) and adaptive sliding mode control (SMC) for the motor. Firstly, the optimal state observer was used to construct to obtain the information of the states of the bearing-less motor system. Second, a new disturbance observer base on the fast speed reaching law is proposed for estimating the unknown dynamics and unpredicted uncertainty of the motor system. Third, the adaptive fast-reaching law-sliding mode control is designed to control the positions and rotational speed. Fourth, the proposed control system is proved via the Lyapunov theorem. Finally, the corrections of proposed method once again tested by using MATLAB simulation. The obtained results figured out that the proposed method is good at rejection disturbance and uncertainty and precision in control the movement and rotation. The novelties of the proposed method are that the gains of fixed-time observer were met by the support of optimal pole placement method, the disturbances were mostly rejected by a new reaching law of unknown input observer.

Control Design of Observer-Based Virtual Soft Boundary for a Power-Assist System with Limited Operating Range

Control design of power-assist systems has been widely applied to human-robot interactive systems such as wearable exoskeleton systems, of which the range of motion limitation of human joints in the power-assist systems is essential. This paper presents a virtual soft boundary design for a human-robot cooperation system with a limited operating range. The proposed virtual soft boundary is realized by impedance control and integrated into the power-assist robot arm system; meanwhile, power-assist robot arm systems are typical human-in-the-loop systems, and the control of the power-assist system in performing in accordance with a human’s perception is a significant issue. Therefore, a model-based disturbance observer with a pseudo-derivative feedback feedforward (PDFF) compensator is designed to effectively estimate the human’s torque for an appropriate motor torque command. Experimental results show that the proposed control method can estimate the human torque exerted on the robot arm system to achieve a power-assist system, and the virtual soft boundary can be realized by the impedance control and integrated into the power-assist robot arm system.

Model Predictive Control for Steering System of Water-Jet Propulsion

Water-jet propulsion is a widely applied ship propulsion technology. Its steering control system has an important impact on manoeuvre performance. In this paper, transfer function model is firstly established on the basis of mechanism analysis of water-jet steering system. Then, by considering the variability of model parameters and input constraints in practical operation, a model predictive controller is designed for steering system control. Subsequently, model based disturbance observer is employed in an attempt to reject environmental disturbances. The performance of the proposed model predictive control (MPC) scheme for a particular steering system is compared with that of conventional proportional integral derivative (PID) control strategy. Simulation results demonstrate that the proposed model predictive controller outperforms conventional PID controller, particularly in robustness, response delay and tracking accuracy.

Internal Model-Based Disturbance Observer With Application to CVCF PWM Inverter

In constant-voltage constant-frequency (CVCF) pulsewidth modulation (PWM) dc–ac inverters, the lumped disturbance, including the parameter uncertainties, unmodeled dynamics, and nonlinear loads, will deteriorate the performance and cause high harmonic distortions, or even result in instability. Conventional disturbance observer (CDOB), in which a low-pass $Q$ filter is adopted to estimate the lumped disturbance, cannot completely eliminate the harmonics. While the conventional repetitive control (CRC) can attenuate the harmonics by using the error signal of previous period(s), that may result in slow transient response due to nonperiodic components in the tracking error during the transient state. In this paper, an internal model-based disturbance observer (IM-DOB) is proposed and has been applied in a CVCF PWM inverter to improve the control performance. In IM-DOB, a novel IM-based disturbance estimation observer is proposed to estimate the disturbance both in the low-frequency region and at harmonic frequencies, while compensation filters are introduced to enhance the robustness and stability. The IM-DOB scheme, which fuses the merit of CDOB and CRC, is actually a two-degree-of-freedom scheme. The stability analysis and a design case are also given. Comparative experiments are conducted to demonstrate the effectiveness of the proposed scheme.

Experimental investigation of a compound force tracking control strategy for electro-hydraulic hybrid testing system with suppression of vibration disturbances

Electro-hydraulic hybrid testing, which imposes the desired acceleration and force on the specimen in parallel, is a novel structural testing method for structures or facilities and is extensively applied in civil and seismic engineering. To efficiently suppress the surplus force resulted from the acceleration motion of the specimen during the force control process, a compound force tracking control strategy comprised of a force and voltage feedforward controller (FVFC) and feedforward inverse with disturbance observer (FIDOB) controller is presented in this research. The FVFC controller as an inner loop feedforward component is first constituted by the generated force feedback signal and the real-time control voltage signal of the acceleration actuator so as to compensate for the acceleration motion of the specimen for a better disturbance rejection performance, and the FVFC controller requires little information of the system dynamic structure or parameters. The FIDOB controller composed by a feedforward inverse controller and an inverse model-based disturbance observer is then combined with the FVFC controller as an outer loop to further deal with the remaining disturbances for the FVFC-controlled electro-hydraulic hybrid testing system. The inverse model applied in the FIDOB controller is obtained with the frequency domain complex curve fitting and zero magnitude error tracking technology with respect to the proportional–integral controlled static loading system. Hence, the proposed controller integrates the advantages of the FVFC controller and FIDOB controller in terms of easy implementation and high tracking performance. Finally, comparative experiments are carried out on an uniaxial electro-hydraulic hybrid testing test rig with the xPC rapid prototyping technology and experimental results demonstrate the effectiveness of the proposed control strategy.

미지의 상수 오프셋을 갖는 삼각함수 외란 추정을 위한 모델기반 저차 외란 관측기 설계

In practical control systems differences between nominal and real systems arise from internal uncertainties and/or external disturbances. This paper presents a model-based low-order disturbance observer for a sinusoidal disturbance with unknown constant offset. By using the disturbance model of a biased harmonic signal, the proposed method can successfully estimate the biased sinusoidal disturbance with unknown amplitude and phase but known frequency. At the first stage of the observer design, a model-based disturbance observer is designed when all the system states are measurable. Next, a sufficient condition is presented for the proposed observer to estimate the sinusoidal disturbance with a minimal-order additional dynamics using only output measurement. Comparative computer simulations are performed to test the performance of the proposed method. The simulation results show the enhanced performance of the proposed disturbance observer.

Sustainable Cutting Process for Milling Operation Using Disturbance Observer

This paper focuses on design of disturbance force observer for sustainable machining process in milling application. In milling process, cutting force acts directly on work surfaces thus producing external impact on the drives system of the positioning table. This effect must be compensated in order to preserve accuracy and quality of the final product, thus creating a sustainable machining process. Disturbance force observer (DFO) is a type of estimator that estimates precisely the disturbance force with prior knowledge of the cutting force harmonics frequencies. This paper presents both numerical and experimental results of DFO performed on an XYZ positioning milling table using measured cutting force. Four control configurations were considered; PID, cascade P/PI, PID with inverse model based disturbance observer, and PID with DFO. The FFT tracking error analysis showed that a near complete compensation of the disturbance force at identified harmonics frequencies was achieved.

내부 모델 기반 외란 관측기를 이용한 수직 1축 머니퓰레이터의 속도 제어기 설계

This paper deals with a robust speed control problem of a vertical one-link manipulator in the presence of parameter uncertainties and unknown input disturbance. Uncertain load weight causes an additional sinusoidal disturbance in the rotation of the link. In order to improve the robustness against parameter uncertainties and external input disturbances, this paper employs an internal model-based disturbance observer approach. Comparative computer simulations are performed to test the performance of the proposed controller. The simulation results show the enhanced performance of the proposed method.

Precise Positioning Control Using Auto-Tuned Fuzzy Logic Controller

Nonlinear friction, resonant vibration modes, in addition to dead time of a positioning mechanism deteriorate the control performance in the microscopic displacement range. A control scheme composed of two types of control methodology is proposed in this paper in order to obtain high speed and high precision positioning of a ball-screw-driven mechanism: a feedforward compensator, based on coprime factorization of the positioning mechanism with dead time compensator, and a feedback compensator, an auto-tuned PDFLC (Proportional plus Derivative Fuzzy Logic Controller) based on real coded genetic algorithm as an optimization technique, with nonlinear friction compensation by using inverse model-based disturbance observer. Experimental results verified the effectiveness and robustness of the proposed control system against the difference of the nonlinear friction accompanied with the repetitive motion.

An Improvement of Speed Control Performances of a Two-Mass System using a Universal Approximator

A new control scheme using a universal approximator based on a radial basis function network (RBFN) is proposed and investigated for improving the control characteristics of the high-performance motion control system. This control method presents better performance in the corresponding speed vibration response, compared with the inverse model-based disturbance observer. The proposed RBFN-universal approximator keeps the self-learning capability, whereas the inverse model-based disturbance observer with the low-pass filter should adjust the time constant of the filter according to the resonance frequency determined by varying the system parameters. The simulation results show the validity of the proposed control scheme.

모델 기반 외란 관측기와 Waterfall 해석을 이용한 광 디스크 외란 분석

A novel disturbance measurement method, model based disturbance observer (MBDO) for optical disk drives (ODDs), is proposed and the disturbance analysis using the proposed method is performed under various conditions. In ODDs, the quantitative and qualitative analysis for the generated disturbance during normal operation is very important to successful servo loop design. However, the disturbance measurement is difficult, and high precision measurement is necessary. Furthermore, the conventional disturbance measurement method using a LDV (laser Doppler vibrometer) has many difficulties in eccentricity direction due to the vertical movement of an optical disk. To solve this problem, the MBDO is proposed. First, the relationship between the servo loop for ODDs and the generated disturbance are briefly reviewed. Second, the principle of the MBDO is introduced, and the disturbance measurement results, which are measured by the MBDO and a LDV, are compared. In these experiments, test DVD-ROM disks are used to generate quantitative/qualitative disturbance. Then, the disturbance analysis under various conditions is performed using waterfall technique. This technique clearly shows the disturbance trend from the inner part of an optical disk to the outer part of it. Finally, the various disturbances measurement results are summarized and some remarks for it are commented.