Torque Observer Research Articles

Speed tracking control of a permanent-magnet synchronous motor with state and load torque observer

This paper is concerned with the speed tracking control problem for a permanent-magnet synchronous motor (PMSM) in the presence of an unknown load torque disturbance. After a brief review of the mathematical model of the PMSM, a speed tracking control law using the exact linearization methodology is introduced. The tracking control algorithm is completed by adding an extended observer which provides, on the one hand, the motor speed and acceleration and, on the other hand, estimates the unknown load torque. The stability of the closed-loop system composed of a nonlinear speed tracking controller and an observer is studied by the way of Lyapunov theory. Furthermore, the decoupling of the state observer and the load torque observer is discussed. Finally, a real-time implementation and the experimental results of the proposed control strategy are presented.

Design of the speed controller for sensorless electric drives based on AI techniques: a comparative study

The paper investigates applicability of different artificial intelligence (AI) techniques in the design of a speed controller for electric drives. A speed-sensorless drive system is considered. A controller structure consisting of a load torque observer, a speed estimator and a speed predictor is developed. Next, different AI based approaches to speed controller design are investigated. The speed controllers based on (1) feed-forward neural network, (2) neuro-fuzzy network, and (3) self-organising Takagi–Sugeno (TS) rule based model are designed. A comparative analysis of the drive behaviour with these three types of AI based speed controllers is performed. In addition, a comparison is made with respect to the drive performance obtained with a conventional optimised PI controller. A detailed simulation study of a number of transients indicates that the best performance, in terms of accuracy and computational complexity, is offered by the self-organising Takagi–Sugeno controller. The controllers are developed and tested for a plant comprising a variable-speed separately excited DC motor.

Design of a torque observer for detecting abnormal load

In manufacturing processes, human error and abnormal operation often result in excessive loads on the servomechanisms. To prevent the abnormal load from damaging the work piece or tool, it is important to find a means to detect the abnormal load so that an appropriate response can be performed. To estimate the load on the servomechanism, two types of torque observer structures are presented in this study. Based on the information obtained from the torque observer, criteria are proposed to determine whether the servomechanism is under the abnormal load, while the Wavelet analysis is employed to enhance the ability of abnormal load detection. Experimental results indicate that the presented observer structures are able to estimate the external torque accurately. In addition, the structure combined with Wavelet analysis is capable of identifying abnormal load events in servomechanisms.

Nonlinear MIMO Speed Sensorless Controller for DC Motor Field Weakening

This paper addresses speed control of a separately excited DC motor (SEDCM) in nonlinear field weakening region. Input output linearization (IOL) technique is used to deal with the motor system with considerable nonlinearity, and a nonlinear multi-input multi-output (MIMO) speed tracking controller is developed for constant power field weakening. The effects of decoupling and linearization permit the controller to be implemented and operated at any desired field weakening point of operation. The control scheme combining this controller with nonlinear speed/load torque observer is, in particular, proposed for speed sensorless operation. Computer simulations are presented to show speed tracking performance of the proposed overall scheme.

Speed Control of 2-Inertia System with Gear Backlash based on Gear Torque Compensation

In this paper, we propose a novel speed control method for 2-inertia system with gear backlash based on the gear torque compensator. The compensator consists of two elements: the gear torque observer and a feedback gain to be adjusted. The ideal gear torque compensation makes the characteristic from motor torque to motor speed to that of 1-inertia system. However, such a direct usage of the compensator causes harmful vibration due to the torsional shaft. To make a compromise, we introduce a feedback gain and adjust it. By combining this method with a usual PID controller, we realized superior performances in vibration suppression and disturbance rejection. Its effectiveness is shown by simulations and experiments.

Speed control of two-inertia system with gear backlash based on gear torque compensation

In this paper, we propose a novel speed control method for a two-inertia system with gear backlash based on the gear torque compensator. The compensator consists of two elements: the gear torque observer and a feedback gain to be adjusted. The ideal gear torque compensation makes the characteristic from motor torque to motor speed to that of one-inertia system. However, such a direct usage of the compensator causes harmful vibration due to the torsional shaft. To compromise, we introduce a feedback gain and adjust it. Combining this method with a typical PID controller, we realized superior performances in vibration suppression and disturbance rejection. Its effectiveness is shown by simulations and experiments. © 2000 Scripta Technica, Electr Eng Jpn, 134(2): 36–43, 2001

Shaft Sensorless Vector Controlled PMSM Servo Drive using Reduced Order Speed Observer

The application of vector control techniques in variable speed ac drives demands accurate position and velocity feed back information for the current and speed control loops. A novel method for shaft sensor elimination of the high performance PMSM servo drives is presented in this paper. A reduced order state observer is proposed to be used as a software transducer, which reconstructs the speed and position of the sinusoidal backemf PMSM from the stator current and voltage measurements. The observer is developed from the d-q model of the machine. The state estimation technique used to achieve global stability of the speed observer is discussed along with the design considerations. Since this method totally eliminates the gain scheduling, which is the major difficulty in implementing any conventional observer based scheme, the implementation of the proposed scheme is very simple and easy. The performance of the observer depends on the accuracy of the parameters in the motor model. To take into account these parameter uncertainties along with the load torque variations, a local disturbance torque observer is used. Simulation results using realistic measurement disturbances and drive parameter uncertainties are also presented to investigate the stability and accuracy of the proposed observer. The simulation results show that the proposed scheme gives good results even at near zero speeds.

Servo Control of Unstable-wheeled System by Using Virtual Disturbance Torque Observer and its Feedback Compensation.

In this paper, we are concerned with the servo control for a unstable-wheeled system by using virtual disturbance torque observer and its feedback compensation. We consider that unstable behavior of the monowheeled system because of one supported point body is caused by the virtual disturbance torque. For this purpose, this paper proposes a design method of disturbance observer for such virtual disturbance torque in feedback loop and evaluates its effectiveness by experiment. In disturbance observer, ordinary 2nd-order low pass filter for noise attenuation is insufficient to stabilize the whole wheeled system, so more high order filter is designed by H ∞ loop shaping method in view point of the regulator specifications. And the servo controller for the closed loop system including such H ∞ high order filter is also designed by satisfying an H ∞ norm condition.

Self-tuning control of induction motor drive using neural network identifier

This study presents a new self-tuning PI speed controller with load torque observer and feedforward compensation based on neural network identification for an induction motor. A two-layer neural estimator is also used to provide a real-time adaptive estimation of the unknown motor dynamics. The widely used projection algorithm is used as the learning algorithm for this network, to minimize the difference between the motor's actual response and that predicted by the neural estimator. The proposed neural estimator uses this learning to adjust PI speed controller with a load torque observer to generate the control signal online, thereby bringing the motor output to a desired reference trajectory. The theoretical analysis, simulation and experimental results demonstrate the proposed scheme's effectiveness.

A load torque compensation scheme under the speed measurement delay

The average speed detection method involves a measurement delay, which can cause a serious instability problem to the unknown load torque observer. The instability can be cured by inserting an artificial delay into the torque-filtering path of the observer. Also, by utilizing the concept of the phase lead compensator, we propose a method of designing an arbitrary high-order low-pass filter (Q filter). Through the results of simulation and experiments, we show that our proposed method yields more robust and improved results than the conventional load torque observer.

Asymptotically stable adaptive load torque observer for precision position control of BLDC motor

A new control method for the precision robust position control of a brushless DC (BLDC) motor using the asymptotically stable adaptive load torque observer is presented. A precision position control is obtained for the BLDC motor system approximately linearised using the field-orientation method. DC motors have been gradually replaced by the BLDC motor, since the industry applications require more powerful actuators in small sizes. Many of these motor systems have BLDC motors to obtain high power rates. On the other hand, the disadvantages are the high cost and more complex controller caused by the complex driving principle of BLDC motors, and the load torque disturbance is directly affected to a motor shaft. The application of the load torque observer using fixed gain has been published (Ko et al, 1993). However, the flux linkage is not exactly known for a load torque observer. There is a problem of uncertainty of obtaining very high precision position control. Therefore, a model reference adaptive observer was considered to overcome the problem of the unknown parameter and torque disturbance (Ko et al, 1994), but this is a case of BIBO stability. A new model reference adaptive observer is considered and stability analysis is carried out using the Lyapunov stability theorem. As a result, asymptotically stable observer gain can be obtained without affecting the overall system response. The load disturbance detected by the asymptotically stable adaptive observer is compensated by feed-forwarding the equivalent current having the fast response.

Real-time IP position controller design with torque feedforward control for PM synchronous motor

A digital signal processor (DSP)-based permanent magnet (PM) synchronous motor (SM) drive with a proposed recursive least-square (RLS) estimator and real-time integral-proportional (IP) position controller is introduced in this study. First, the rotor inertia constant, the damping constant, and the disturbed load torque of the synchronous motor are estimated by the proposed RLS estimator, which is composed of an RLS estimator and a torque observer. Next, the IP position controller is real-time designed according to the estimated rotor parameters, to match the time-domain command tracking specifications. Then, the observed disturbance torque is fed forward, to increase the robustness of the synchronous motor drive.

Walking Control of a Biped Robot by Impedance Control

In this paper, a robust impedance control scheme is used to control a biped locomotion in saggital plane. In particular, the torque observer is introduced and external-force feedback is achieved without force sensor. By the reaction force feedback, the stability of the biped robot increase at the contact of the swing leg and the arbitral impedance control is realized without force sensor. The walking trajectory reference is created from the virtual inverse pendulum model. Simulation and experimental results also show that the effect of the collision between biped leg and the ground is eased and by the proposed control method, the biped robot recover more quickly than the traditional robust position control.

A high-performance induction motor drive with on-line rotor time-constant estimation

A high-performance induction motor (IM) speed drive with online adaptive rotor time-constant estimation and a proposed recursive least square (RLS) estimator is introduced in this paper. The estimation of the rotor time-constant is on the basis of the model reference adaptive system (MRAS) theory; and the rotor inertia constant, the damping constant and the disturbed load torque of the IM are estimated by the proposed RLS estimator, which is composed of an RLS estimator and a torque observer. Moreover, an integral proportional (IP) speed controller is designed online according to the estimated rotor parameters; and the observed disturbance torque is fed forward to increase the robustness of the induction motor speed drive.

Special Issue on Control Systems in Mechatronics

The special issue on Control Systems in Mechatronics is a significant and timely issue since many robotics and mechatronics engineers now pay attention to the research field of motion control and control theory. In Japan, advanced motion control technology is a key technics to improving the performance of robot systems and/or mechanical automation equipment. The definition of motion control in this issue is the control of mechanical systems driven by electrical actuators such as a do servo motor or an ac servo motor. The means or strategy of motion control has so far been of interest only to electrical engineers and mechanical engineers; it has not been as familiar to robotics engineers. Recently, a control system has been developed with industry applications. Advanced motor control technology in Japan is based on the robust control system, such as the disturbance observer, the H00 control system, the two-degrees-of-freedom control system and so on. The disturbance observer has a simple structure, and it is quite valid for disturbance torque rejection. The robust control system based on the disturbance observer is now widely used in robot and mechanical systems in Japan. The disturbance observer is the original Japanese technology designed by two electrical engineers, Prof. Ohnishi and myself, from the viewpoint of the electrical actuator but control theory. Ho control is linear control technics popular around the world. It can make the desired loop shaping of frequency characteristics for a plant system such as the actuator of a mechanical system. The robust control system based on the mixed sensitivity problem of H00 control theory has good frequency characteristics. Moreover, the availability of large amounts of computational power has enabled us to use complex control theory, and actuators for robotics applications are now mainly electrical ones because of the remarkable progress in power electronics. This change in the control of mechanical systems is a new and attractive one. Motion control is becoming a field of interest to control, electrical, and mechanical engineers who work in robotics. In this issue, the eight papers and the two news reports have been selected to show the current topics concerned with control systems in mechatronics. The first paper is a review paper titled ""robust motion control by the disturbance observer"". Prof. Ohnishi describes the physical meaning of motion control and the purpose of robust control. This review paper also shows the effectiveness of motion control based on the disturbance observer. Four papers in this issue deal with robot motion control systems using the disturbance observer. Mr. Oda explains the decoupling force control method of redundant robot manipulation by workspace disturbance observer which is not a joint space disturbance observer such as an ordinary disturbance observer. Dr. Komada explains the hybrid position/force control method based on second derivatives of position and force, which uses the force-based disturbance observer. Dr. Shimada explains the servo system considering a robot of low stiffness, which is based on the disturbance and velocity observer. This observer is mounted with each joint. Prof. Kuroe explains the decoupling control method of robot manipulation using a variable structure disturbance observer which is not an ordinary linear disturbance observer. The other three papers in this issue deal with robot motion control using the other advanced control system. Prof. Ohishi, myself explains the hybrid position/force control method without a force sensor, which is based on H00 acceleration controller and torque observer. This torque observer is the same observer as the ordinary disturbance observer. Mr. Fujimoto explains the three dimensional digital simulation of legged robots for advanced motion control. Mr. Kang explains the state estimation for mobile robots using a partially observable Markov decision process. This method can estimate the mobile robot state precisely and robustly. The two news reports in this issue deal with control and robot laboratory news from Japanese universities such as news generated by Prof. Hori of the University of Tokyo and Prof. Hori of Mie University. Both Prof. Horis are famous and active researchers in advanced motion control. This issue scans only one aspect of control systems, not the whole. Adaptive control, learning control, and other advanced control methods such as the LMI method are not mentioned. The subject of control systems in mechatronics is now expanding and developing. I greatly appreciate the efforts of the reviewers and authors in producing this issue, and I thank the Chief-Editor, Prof. Toshio Fukuda, for encouraging us to prepare it.

Hybrid Position and Force Control Without Force Sensor

Generally, hybrid control is realized by sensor signal feedback of position and force. However, some robot manipulators do not have a force sensor due to the environment. Moreover, a precise force sensor is very expensive. In order to overcome these problems, we propose the estimation system of reaction force without using a force sensor. This system consists of the torque observer and the inverse dynamics calculation. Using both this force estimation system and <I>H</I>∞ acceleration controller which is based on <I>H</I>∞ control theory, it takes into account the frequency characteristics of both sensor noise effect and disturbance rejection. The experimental results in this paper illustrate the fine hybrid control of the three tested degrees-of-freedom DD robot manipulator without force sensor.

MRAC load torque observer for position control of a brushless DC motor

MRAC load torque observer for position control of a brushless DC motor

Robust speed-controlled induction-motor drive using EKF and RLS estimators

An induction-motor (IM) speed drive, with the application of an extended Kalman filter (EKF) and a proposed recursive least-square (RLS) estimator, is introduced. The rotor resistance of the IM is identified by the EKF, and the rotor inertia constant, the damping constant and the disturbed load torque of the IM are estimated by the proposed RLS estimator, which is composed of an RLS estimator and a torque observer. The integral proportional (IP) speed controller is on-line, designed according to the estimated rotor parameters. Then the observed disturbance torque is fed forward to increase the robustness of the induction-motor speed drive.

等価外乱トルクオブザーバの推定誤差をファジィ推論により同定したDCサーボモータのロバスト位置制御

等価外乱トルクオブザーバの推定誤差をファジィ推論により同定したDCサーボモータのロバスト位置制御

Direct torque control of brushless DC motor with nonideal trapezoidal back EMF

In this paper a method of the torque control attenuating the undesired torque pulsation for brushless DC motor with nonideal trapezoidal back EMF is presented. It is the direct torque control method in which the applied output voltage is calculated from the reference torque and the torque of the previous step in the two-phase conducting period and in the commutation period considering the back EMF waveform. The time delay due to the calculation is compensated by the one step ahead current prediction. To measure the instantaneous torque ripple, a torque observer is constructed using a high precision encoder of 50000 pulse per revolution. The simulation and experimental results show that the proposed method reduces the torque ripple significantly and that it keeps the torque control dynamics as well. >