Disturbance Force Observer Research Articles

Brake Position Control of Electric Mover Based on the Disturbance Force Observer

Brake Position Control of Electric Mover Based on the Disturbance Force Observer

Modified complementary sliding mode control with disturbance compensation for permanent magnet linear synchronous motor servo system

In this study, a modified complementary sliding mode control (MCSMC) method based on a disturbance force observer with mass identification (DFOB-MI) applicable to the permanent magnet linear synchronous motor is proposed to achieve high-performance servo control fields. MCSMC is an improvement on the complementary sliding mode control (CSMC) method, which incorporates an approach angle into the saturation function. MCSMC allows for asymptotic convergence of the position tracking errors and guarantees the global robustness of the system. In addition, compared to hybrid control strategies combining neural networks with CSMC, the MCSMC method has a simpler structure and faster response. However, in practical applications, the mass variation of the mover has a significant impact on system performance. To achieve better dynamic and static characteristics, a disturbance force observer capable of identifying the mass variation based on model reference adaptive identification theory is proposed. DFOB-MI can identify the mass of the mover and provide information on the disturbance caused by the change of the load. Thus, the compensation current is calculated to reduce the disturbance and realise compensation. The more accurate tracking performance and stronger robustness of the proposed control scheme compared to conventional approaches have been confirmed through comparative experimental studies.

Force compensation for precise positioning in machine tools via state observer design

In machining, cutting force generated is identified as input disturbance to the servo drive systems of the positioning table. In frequency domain, the cutting force magnitudes can be synthesized according to various harmonic components depending on the cutting tool spindle speed rotation. This paper focuses on compensation of high-frequency harmonic components of the cutting force using a state estimator named disturbance force observer (DFO) which explicitly estimates the input disturbance force. The force estimation error and tracking performances of the state estimator and the cascade P/PI positioning controller were analyzed experimentally on a single axis ball screw driven positioning table resembling a milling machine. The cascade P/PI controller was designed using traditional loop shaping frequency domain method while the force observer simultaneously estimated the input disturbance force based on the fundamental frequency dictated by the spindle rotational speeds. In experimental validations, a single, double, and triple harmonic-based force observers were designed at fundamental frequencies of 0.2 Hz, 0.5 Hz, and 0.8 Hz, and at amplitudes of 0.5 mm, 0.3 mm, and 0.2 mm, respectively. In time domain, the tracking performances of the system were analyzed and evaluated using root mean square of the position errors (RMSE) while in frequency domain, fast Fourier transform (FFT) analyses were performed on the tracking error signals. Results of the spectral analyses showed a 99.82% (single harmonic), 99.87% and 98.79% (two harmonics), and 99.83%, 97.13%, and 99.18% (three harmonics) reduction in respective force component magnitudes indicating close to successful estimation of the disturbance force observer. Meanwhile in time domain, numerical results of RMSE values showed reductions of 94.82%, 96.83%, and 94.01% for the three different input disturbance configurations while the experimental result showed reduction of 96.10%, 92.76%, and 92.44%, respectively. The work is to be expanded to include actual measured cutting forces as the input disturbance.

Tool wear estimation method in milling process using air turbine spindle rotation-control system equipped with disturbance force observer

Tool wear estimation method in milling process using air turbine spindle rotation-control system equipped with disturbance force observer

Tool wear estimation method in milling process using air turbine spindle rotation-control system equipped with disturbance force observer

The authors investigate a disturbance-compensating and energy-saving control method for air turbine spindles equipped with a rotation control system designed for use in ultra-precision milling. The controllability and energy-conserving characteristics of the proposed method using the proposed pneumatic regulating device, called a high-precision quick-response pneumatic pressure regulator, were demonstrated experimentally previously. Herein, the proposed rotation-controlled air turbine spindle is first summarised. Subsequently, the proposed rotation-controlled air turbine spindle is set to a milling machine and applied to the milling of an alloy tool steel, to gain data and validate the effectiveness of the in-process tool wear estimation method that have been recently developed and proposed by the authors. Particularly, to evaluate the possibility of applying the proposed estimation method to three-dimensional milling, milling experiments where the air turbine spindle is set at a 45° incline were conducted and the results indicate a high possibility of the proposed method.

Pseudo-magnetic centre identification of an active magnetic bearing for sensorless drive control start-up

A method of identifying runout of an active magnetic bearing at standstill and low speed is presented. The on-line current bias injection method found in literature is improved, but is still found to converge too slowly for sinusoidal tracking. A new method which approximates the deviation from the magnetic centre using a disturbance force observer is presented and tested on an experimental fly-wheel AMB system. The new on-line method is fast enough for real-time tracking of the magnetic centre deviation. The estimated angle derived from the pseudo-magnetic centre was successfully utilized for start-up of the drive’s sensorless vector control.

Vehicle-manipulator system dynamic modeling and control for underwater autonomous manipulation

Underwater autonomous manipulation is a challenging task, which not only includes a complicated multibody dynamic and hydrodynamic process, but also involves the limited observation environment. This study systematically investigates the dynamic modeling and control of the underwater vehicle-manipulator multibody system. The dynamic model of underwater vehicle-manipulator system has been established on the basis of the Newton–Euler recursive algorithm. On the basis of dynamic analysis, a motion planning optimization algorithm has been designed in order to realize the coordinate motions between AUV and manipulator through reducing the restoring forces and saving the electric power. On the other hand, a disturbance force observer including the coupling and restoring forces has been designed. An observer-based dynamic control scheme has been established in combination with kinematic and dynamic controller. Furthermore, from the simulations, although the disturbance forces such as restoring and coupling forces are time varying and great, the observer-based dynamic coordinate controller can maintain the AUV attitude stable during the manipulator swing and pitch motions. During the precise manipulation simulation, the stable AUV attitude and minimization of disturbance forces have been realized through combination of optimal motion planning and the observer-based dynamic coordinate controller.

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.

Proposal of disturbance-compensating and energy-saving control method of air turbine spindle and evaluation of its energy consumption

This paper introduces a disturbance-compensating and energy-saving control method of an air turbine spindle equipped with a rotation control system designed for use in ultra-precision milling. As one of the key components, our proposed pneumatic regulating device, called a high-precision quick-response pneumatic pressure regulator (HPQR), is used to control the air supply pressure of the air turbine spindle precisely and quickly. The rotation feedback control system including the HPQR and a disturbance force observer, which avoids changes of rotation speed due to disturbance forces applied to the air turbine spindle, is explained. In addition, a pneumatic energy assessment method using a device called an “air power meter” is explained. The effectiveness of the proposed method is demonstrated through the experimental results.

Design and Analysis of Disturbance Force Observer for Machine Tools Application

In milling process, the quality of tracking performance is influenced by the characteristics of the cutting forces generated during the material removal process. The undesired frequency harmonics of the cutting force contributes negatively to the positioning accuracy. An effective compensation of these harmonics is desired. This paper presents and discusses a disturbance force observer as an approach to estimate and compensate effect of external disturbance forces on system performance. Knowledge of the properties of the disturbance signal is essential for the design of an observer. A Fast Fourier Transform analysis of the disturbance force reveals the harmonics content of the signal. The frequency harmonics is a function of the spindle rotational speeds. The results show effective compensation of the cutting force with reduced amplitudes of the harmonics frequency content.

Magnetic-Based Motion Control of Paramagnetic Microparticles With Disturbance Compensation

Magnetic systems have the potential to control the motion of microparticles and microrobots during targeted drug delivery. During their manipulation, a nominal magnetic force-current map is usually derived and used as a basis of the control system design. However, the inevitable mismatch between the nominal and actual force-current maps along with external disturbances affects the positioning accuracy of the motion control system. In this paper, we devise a control system that allows for the realization of the nominal magnetic force-current map and the point-to-point positioning of paramagnetic microparticles. This control is accomplished by estimating and rejecting the 2-D disturbance forces using an inner loop based on a disturbance force observer. In addition, an outer loop is utilized to achieve stable dynamics of the overall magnetic system. The control system is implemented on a magnetic system for controlling microparticles of paramagnetic material, which experience magnetic forces that are related to the gradient of the field-squared. We evaluate the performance of our control system by analyzing the transient- and steady-state characteristics of the controlled microparticle for two cases. The first case is done without estimating and rejecting the mismatch and the disturbance forces, whereas the second case is done while compensating for these disturbance forces. We do not only obtain 17% faster response during the transient state, but we are also able to achieve 23% higher positioning accuracy in the steady state for the second case (compensating disturbance forces). Although the focus of this paper is on the wireless magnetic-based control of paramagnetic microparticle, the presented control system is general and can be adapted to control microrobots.

질량추정과 외란추력 관측기를 이용한 자동피킹 시스템 구동용 선형 유도모터의 강인제어 기법

To operate an automatic picking system in distribution center with high precision and high dynamics, this paper presents a robust control scheme of a linear induction motor (LIM) using the mass estimation and disturbance force observer. The force disturbance which gives a direct influence on the control performance of LIM is estimated in real-time through the disturbance observer and compensated by a feedforward manner. To get a satisfactory performance even under the mass variation by reducing the disturbance force due to the mismatched mass during the speed transient such as the acceleration and deceleration periods, a mass estimation algorithm is proposed. A Simulink model for LIM is developed and the validity of the proposed scheme is verified through the comparative simulation studies using Matlab - Simulink.

Design of active vibration control for launcher of multiple launch rocket system

This study deals with analysis and design of active vibration control algorithm for the launcher of multiple launch rocket system (MLRS). The new method proposed is that guidance and control package are equipped on launcher, not rocket, to active control motion of launcher for the first time. It has interesting advantages as follows: (1) active vibration control is more competent, more pliable, and more realizable in engineering compared to passive vibration control. (2) The guidance and control package will not be destroyed. In this study, transfer matrix method of multibody system is used to build the controlled dynamic model of MLRS. This method does not need the global dynamic equations of system and has high computational rate. Independent modal space control method and optimal control theorem are applied to design control law with feedforward and feedback control loops. The modal filters are designed as the state estimator to obtain the modal coordinates and their derivatives. Modal disturbance force observer is designed to obtain modal disturbance force. Pulse-width pulse-frequency (PWPF) modulator is used to modulate the continue control force command into discrete control force in order to avoid high non-linear control action of pulse thruster. The control force provided by pulse thruster and parameters of PWPF are obtained. The numerical results indicate that control law determined by optimal theorem integrated with PWPF modulator achieves good performance in active vibration control of launcher. This study improves the performance of MLRS in resisting impact and provides theoretical support for accurate launch.

Dynamic modeling and H ∞ independent modal space vibration control of laminate plates

In this paper, combining the transfer matrix method and the finite element method, the modified finite element transfer matrix method is presented for high efficient dynamic modeling of laminated plates. Then, by constructing the modal filter and the disturbance force observer, and using the feedback and feedforward approaches, the H ∞ independent modal space control strategy is designed for active vibration control of laminate plates subjected to arbitrary, immeasurable disturbance forces. Compared with ordinary dynamic modeling and control methods of laminated plate structures, the proposed method has the low memory requirement, high computational efficiency and robust control performance. Formulations as well as some numerical examples are given to validate the method and the control performance.

Force Ripple Compensation in Linear Motors Based on Closed-Loop Position-Dependent Identification

Permanent-magnet linear synchronous motors can serve as direct-drive actuators for machine tools and production machines, whenever high dynamic performance are required. Since compliance in transmission elements is eliminated, higher control bandwidths can be achieved, when compared to traditional solutions based on conversion from rotational to linear motion. Like their rotational counterparts, these motors are, however, affected by a ripple, in the form of parasitic and undesired force pulsations. In this paper, a compensation scheme of force ripple is proposed, based on a simple and compact model of the disturbance. The compensation requires a preliminary identification stage that simply consists of a couple of controlled motions at constant and very low velocity. The compensation term is then applied in parallel to the position/velocity controller, as a function of the linear position of the motor. A robustness analysis is performed based on a convenient formulation of the closed-loop system, as well as on a Lyapunov argument. Experiments that demonstrate the effectiveness of the method are reported, even when compared to a traditional force disturbance observer.

Sensorless measurement of pulsatile flow rate using a disturbance force observer in a magnetically levitated centrifugal blood pump during ventricular assistance

Implantable rotary pumps have been developed and used to assist the impaired heart ventricle because of lack of heart donors for transplant. Pulsatile flow rate measurement is important for controlling the flow rate of these rotary pumps. Conventional flow meters are not particularly compact; while the reliability and durability of small flow meters made using micro-electro-mechanical system technology is still uncertain. Several groups have proposed estimating flow rate using the motor power of the centrifugal blood pump (CBP), but none have succeeded in accurately estimating pulsatile flow rate. We have developed an implantable CBP, employing a two degrees-of-freedom radial controlled magnetic bearing (MB) to support the impeller without contact, which decreases the damage to blood cells and increases the durability of the device. The radial thrust acting on the impeller depends on the rotational speed of the impeller and the contractility of the heart ventricle. In this study we present a method to measure pulsatile flow rate during ventricular assistance, using the radial thrust estimated by the radial disturbance force observer of the MB of the CBP. The variable parameters of the dynamic model of the maglev impeller were identified for different flow conditions, assuming the density and viscosity of the water to be constant. The design of the disturbance force observers was based on the linear models obtained for a given rotational speeds. Under non-pulsatile conditions, the relationship between the measured flow rate and the estimated radial thrust was experimentally obtained. Using this relationship, under pulsatile conditions, a high correlation ( r > 0.94 ) between the measured and estimated flow rate was obtained, with a maximum estimation error of 0.3 L/min (15%) for average pulsatile flow rate and 0.5 L/min (7%) for the amplitude of pulsatile flow rate. Also, by observing the amplitude of the pulsatile flow rate, the backflow could be ascertained.

BIO-01 RADIAL HYDRAULIC FORCE ESTIMATION IN A MAGNETICALLY LEVITATED CENTRIFUGAL BLOOD PUMP(Bio-medical Equipments I,Technical Program of Oral Presentations)

In order to solve the problem of lack of heart donors, ventricular assist devices have been developed and used as a bridge to transplant, a bridge to recovery or as destination therapy. Among these devices, maglev rotary pumps have been shown to deliver good clinical results with low blood damage, low risk for blood clot formation and high durability. In order to improve the magnetic bearing design, hydraulic forces acting on the maglev impeller should be precisely evaluated, however direct measurement is impossible due to absence of a rotor shaft. In this study, we propose using disturbance force observer in a two degrees-of-freedom radial controlled maglev centrifugal blood pump to estimate the radial hydraulic force acting on the maglev impeller. The radial dynamic characteristics of the maglev impeller change with flow conditions, so they were evaluated under different rotational speeds and flow resistances, and the radial disturbance force observers were designed based on the linear models obtained for a given rotational speed. Applying these observers at different rotational speeds and flow resistances, under continuous flow, we observed little variation of force direction with respect to rotational speed and proportionality between the force magnitude and the flow rate, being the maximum force 1.3 N for a flow rate of 6.8 L/min at 1700 min^<-1>. Under pulsatile flow, as in ventricular assistance, the estimated hydraulic forces followed the pulsatile flow oscillation at 60, 70 and 80 bpm, and the backflow could also be observed.

Design of a robust force control system for an automatic live-line maintenance robot using a force disturbance observer

Uninterrupted power supply has become indispensable during the maintenance task of high-voltage live lines as a result of today's highly information-oriented society and increasing demand of electric utilities. This maintenance task has the risk of electric shock and needs skilled workers. Therefore it is necessary to realize an autonomous robot system using an electrohydraulic manipulator because hydraulic manipulators have the advantage of electric insulation and high power/mass density. Meanwhile an electrohydraulic manipulator using hydraulic actuators has many non-linear elements, and its parameter fluctuations are greater than those of an electrically driven manipulator. Therefore it is relatively difficult to realize not only stable contact work but also accurate force control for the autonomous assembly tasks using hydraulic manipulators. In this paper, the robust force control of an automatic live-line maintenance robot used in the real maintenance task of an active electric line is examined in detail. A nominal model for the system is obtained from experimental frequency responses of the system, and the deviation of the manipulator system from the nominal model is derived by a multiplicative uncertainty. Robust force disturbance observer is designed using this information in an H∞ framework and implemented on two different set-ups. Experimental results show that highly robust force tracking by the automatic live-line maintenance robot could be achieved even if the stiffness of environment and the shape of wall change.

Design of a robust force control system for an automatic live-line maintenance robot using a force disturbance observer

Uninterrupted power supply has become indispensable during the maintenance task of high-voltage live lines as a result of today's highly information-oriented society and increasing demand of electric utilities. This maintenance task has the risk of electric shock and needs skilled workers. Therefore it is necessary to realize an autonomous robot system using an electrohydraulic manipulator because hydraulic manipulators have the advantage of electric insulation and high power/mass density. Meanwhile an electrohydraulic manipulator using hydraulic actuators has many non-linear elements, and its parameter fluctuations are greater than those of an electrically driven manipulator. Therefore it is relatively difficult to realize not only stable contact work but also accurate force control for the autonomous assembly tasks using hydraulic manipulators. In this paper, the robust force control of an automatic live-line maintenance robot used in the real maintenance task of an active electric line is examined in detail. A nominal model for the system is obtained from experimental frequency responses of the system, and the deviation of the manipulator system from the nominal model is derived by a multiplicative uncertainty. Robust force disturbance observer is designed using this information in an H∞ framework and implemented on two different set-ups. Experimental results show that highly robust force tracking by the automatic live-line maintenance robot could be achieved even if the stiffness of environment and the shape of wall change.

Application of discrete-time variable structure control in the vibration reduction of a flexible structure

This paper studies the application of using the discrete-time variable structure control method to reduce the vibration of the flexible structure. The structure is subjected to arbitrary, unmeasurable disturbance forces. The concept of independent modal space control is adopted, and the system is studied by the discrete-time model. Here, discrete sensors and actuators are used. We choose the modal filters as the state estimator to obtain the modal co-ordinates and modal velocities for the modal space control. A discrete-time variable structure controller with a disturbance force observer is adopted due to its distinguished robustness property of insensitiveness to parameter uncertainties and external disturbances. The included disturbance force observer can observe the unknown disturbance modal forces, which are used in the discrete-time variable structure control law to cancel out the excitations. The upperbound limitations of the unknown disturbances in the variable structure control, therefore, are no longer needed. The switching surface, in the discrete-time variable structure control system, is designed in an optimal sense. That is, along the switching surface, the cost function of the states is minimized. The investigation of this research focuses on the optimal switching surface design and the control performances of the discrete-time variable structure controller. The performance of estimating the disturbance modal forces and the robustness property of the control law are also discussed.