Variable Structure System Observer Research Articles

Digital Position Control Strategy of Traveling-wave Ultrasonic Motors

Since a conventional controller is continuous one, control period is normally set for a long time. When applying that controller for a travelling-wave ultrasonic motor whose parameters and performance are time-varying as a result of increasing temperature and operating condition, it is consequently resulted in degradation of the control performance. In this paper, a digital control algorithm is proposed for position control of the motors to shorten the long control period to maintain the stability of the motor performance. The proposed controller is digitally implemented by a SH7125 microcomputer utilizing a high-performance embedded workshop. The state quantities such as acceleration, speed and position, which are necessary for digital implementation, are provided by a rotary encoder. However, the optical encoder causes quantization errors in the speed information. To overcome the problem, a digital Variable Structure System (VSS) observer is also included to estimate the state quantities. The control input will be calculated after comparing the measured values and the estimated values given by the VSS observer. In short, a small, low cost and fast responsive digital controller is designed, based on a digital VSS observer, by using the SH7125 microcomputer. Effectiveness and reliability of the proposed digital controller are experimentally verified.

Digital Position Control Strategy of Traveling-wave Ultrasonic Motors

Since a conventional controller is continuous one, control period is normally set for a long time. When applying that controller for a travelling-wave ultrasonic motor whose parameters and performance are time-varying as a result of increasing temperature and operating condition, it is consequently resulted in degradation of the control performance. In this paper, a digital control algorithm is proposed for position control of the motors to shorten the long control period to maintain the stability of the motor performance. The proposed controller is digitally implemented by a SH7125 microcomputer utilizing a high-performance embedded workshop. The state quantities such as acceleration, speed and position, which are necessary for digital implementation, are provided by a rotary encoder. However, the optical encoder causes quantization errors in the speed information. To overcome the problem, a digital Variable Structure System (VSS) observer is also included to estimate the state quantities. The control input will be calculated after comparing the measured values and the estimated values given by the VSS observer. In short, a small, low cost and fast responsive digital controller is designed, based on a digital VSS observer, by using the SH7125 microcomputer. Effectiveness and reliability of the proposed digital controller are experimentally verified.

Nonlinear Adaptive Control of Ultrasonic Motors Considering Dead-Zone

When applying a load torque to an ultrasonic motor, a dead-zone occurs in the control input. A nonlinear adaptive control, which considers dead-zones, is consequently proposed for the motor. To implement the proposed control strategy, a microcomputer and an embedded system are employed. The state quantities, such as acceleration, speed, and position, are required to apply digital implementation. However, a rotary encoder, which is used to get feedback, causes quantization errors in the speed information. To overcome these problems, a variable structure system observer with the possibility of decreasing quantization error is also presented. In other words, a small, low-cost, and fast responsive microcomputer-based nonlinear adaptive controller is designed and assembled. Effectiveness and reliability of the proposed method is experimentally verified.

Robust Position Control for Ultrasonic Motor Using Variable Structure System Observer in Non-linear Observer

The intrinsic properties of an ultrasonic motor (high torque for low speed, high static torque, compact in size, no electromagnetic interference, etc.) offer great advantages for industrial applications. However, when load torque is applied, a dead-zone occurs in control input. Therefore, a sliding-mode controller, which is a non-linear controller, is adopted for the ultrasonic motor. The state quantities, such as acceleration, speed, and position, are needed to apply the sliding-mode controller for position control. However, a rotary encoder causes quantization errors in the speed information. This article presents a robust position control method for an ultrasonic motor by using a variable structure system observer. The state variables for the sliding-mode controller are estimated by the variable structure system observer. A small, low-cost, and good response sliding-mode controller is designed in this work by using a microcomputer that is essential in an embedded system for the development of industrial equipment. The effectiveness of the proposed method is verified by experimental results.

空気圧制動系における非線形粘着状態観測器

This paper shows that the VSS observer has the possibility to estimate adhesion force using wheel slip simulation and wheel slip experiments. It has been shown that the disturbance observer was effectives in estimation of adhesion force. To apply a strain gauge to the brake caliper in order to measure the braking torque is difficult, because the delicate parts on bogies are to be avoided at the train depot. When all the axles of vehicles slip, the wheel slip prevention cannot work sufficiently. Moreover, the brake systems of railway vehicles possess strong nonlinear characteristics with variable parameters, such as adhesion force and friction coefficient of brake materials. It is important that the estimation method has robustness against such disturbance and parameter changes, and it is known that the Variable Structure System (VSS) observer has robustness against parameter change, disturbance input and so on. However, there have been no research reports about a Variable Structure System (VSS) observer for the brake system or wheel slip preventing methods in a railway vehicle. In order to compare the theoretical value of adhesion force with estimated value by a VSS observer, wheel slip simulation was preformed. Simulation results show that the VSS observer can estimate the adhesion force efficiently. Moreover, estimation experiments of adhesion force using VSS observer were performed, and it has been clarified that the VSS observer can efficiently estimate the tangential force coefficient from the experimental results.

Active suspension design of one-wheel car models using an improved sliding mode control with the VSS observer

This paper is concerned with the active suspension design of one-wheel car models subject to excitation from a road profile using an improved sliding mode control with the variable structure system (VSS) observer. The active control is composed of the equivalent and the switching controls. The active control force for the suspension system is obtained by operating a pneumatic actuator due to the control signal that is generated by the measurement of the state variables, and the estimate of the excitation from the road profile. The experimental result indicates that the proposed active suspension system is relatively effective in the vibration suppression of the car model.

Discrete Time Predictive Sliding Mode Control of Hot Strip Mill. Application of Linear Reaching Law.

Sliding Mode Control (SMC) as a Variable Structure System (VSS) and a nonlinear control theory, has been widely used in various engineering fields, and carried out excellent performances in practical use. The purpose of this study is to attempt to utilize SMC for hot strip hishing mill and present the details of design procedure of discrete time sliding mode servo-controller. The plant is described as a MIMO system and the thickness measuring dead-time is added into state space equation as a series of delay elements. The influence of this dead-time can be nullified by the use of an augmented VSS observer. A state predictor is also used to compensate for the time delay caused in calculation and transmission of process control computers. A new approach of discrete sliding mode control which can remove the chattering phenomenon entirely, is proposed with the use of linear reaching law. The usefulness and robustness of the SMC are demonstrated through computer simulations under plant perturbation and external disturbances, and compared with a conventional optimal servo-controller.

Discrete Silding Mode Control of Hot Strip Mill

Sliding Mode Control(SMC) as a Variable Structure System(VSS) and a nonlinear control theory, has been widely used in various engineering fields, and carried out excellent performances in practical use. The purpose of this study is to make a try of utilizing SMC for hot strip finishing mill. The plant is described as a MIMO system and The influence of thickness measurement dead-time is canceled with the use of an augmented VSS observer. A state predictor is also used to compensate the time delay caused in calculation and transmission of process computers. A new approach of discrete SMC which can remove the chattering phenomenon entirely, is proposed with the use of linear reaching function. The usefulness and robustness of the SMC are demonstrated through computer simulations under plant perturbation and external disturbances, and compared with a conventional optimal controller.

Robust Control of a Spindle-Magnetic Bearing System Using Sliding-Mode Control and Variable Structure System Disturbance Observer

This paper is concerned with the design and control of flexible rotor magnetic bearing systems using the discrete time sliding-mode control method. The plant dynamics, consisting of actuator dynamics and flexible rotor dynamics, are described in detail. A variable structure system (VSS) disturbance observer, with which the state vector and disturbance can be estimated simultaneously, is investigated to compensate the mismatched disturbance load on the rotor. A new discrete time sliding-mode servocontroller that can attenuate the chattering phenomenon is proposed using the VSS observer. The usefulness of the proposed controller is demonstrated through computer simulations and experiments for a spindle-magnetic bearing system under external disturbances and modeling uncertainties.

Discrete Predictor and Sliding Mode Control of Hot Strip Fimishing Mill.

Sliding Mode Control (SMC) as a Variable Structure System (VSS) and a nonlinear robust control theory, has been widely used in various engineering fields today, and carried out excellent performances in practical use. The purpose of this study is to make a try of utilizing SMC for hot strip finishing mill and present the datails of design procedure of discrete time sliding mode servocontroller. The plant is described as a MIMO system and the thickness measured dead-time is added into state space as a series of delay elements. The influence of this dead-time can be cancelled with the use of an augmented VSS observer. A state predictor also is used to compensate the time delay caused in calculation and transmission of control computers. A new approach of discrete sliding mode control which can remove the chattering phenomenon entirely, is proposed with the use of linear reaching law. The usefulness and robustness of the SMC are demonstrated through computer simulations under plant perturbation and external disturbances, and compared with a conventional optimal serve-controller.

Sliding Mode Servo Controller Design for Sensorless Flexible Rotor-Magnetic Bearing Systems with VSS Disturbance Observer

This paper is concerned with the design of discrete time sliding mode controller to sensorless flexible rotor-magnetic bearing systems (SFR-MBS). The plant dynamics, consisting of actuator dynamics and flexible rotor dynamics, are described. A variable structure system (VSS) disturbance observer, with which the state vector and disturbance can be estimated simultaneously, is investigated to compensate the mismatched disturbance. A new discrete time sliding mode servo controller, which can attenuate the chattering phenomenon, is proposed by using this VSS observer. The usefulness of the proposed controller is demonstrated through the computer simulations for a sensorless flexible rotor-magnetic bearing system under external disturbances and modeling uncertainties.

Sliding mode control and a variable structure system observer as a dual problem for systems with non-linear uncertainties

Sliding mode control is described for continuous-time systems with uncertain nonlinear elements, in which the euclidean norm of the unknown element is bounded by a known value. For a case of complete state information, we first consider a sliding mode controller consisting of three parts: a linear state feedback control, an equivalent input and a min-max control. It is then shown that the present attractiveness condition is simpler than that for a case without using the concept of equivalent input. We next derive a variable structure system (VSS) observer as a completely dual form to the sliding mode controller. The attractiveness condition is also simpler than that for a case an equivalent term is not used, but a more severe assumption is required to solve such a VSS observer. Finally, we discuss a case of incomplete state information by applying the VSS observer.