• 제어로봇시스템학회:학술대회논문집
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• 1996.10b
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• pp.948-951
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• 1996

High-speed/high-accuracy control of robot manipulator becomes more and more stringent because of the external disturbance and nonlinear characteristics. To meet this ends, lots of control strategies were proposed in the past such as the computed torque control, the nonlinear decoupled feedback control, and adaptive control. These control methods need computations of the inverse dynamics and require much computational effort. Recently, a disturbance observer with unmodeled robot dynamics and simple algorithms to motion control have been widely studied. This paper proposes a motor control strategy based on the disturbance observer which estimate the disturbance of each joint from input-output relationship of the actuator and eliminate the estimated disturbance including the torque due to modeling errors, coupling force, nonlinear friction, and so on. To apply the disturbance observer to closedloop system like velocity servo pack, the modified control structure was constructed and shown that it is equivalent to a disturbance observer in open-loop system. Finally, using the proposed approach, simulation and experiments were carried out for a two-degree-of-freedom SCARA type direct drive robot, and show some results to verify the effectiveness of the proposed algorithms.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.48 no.6
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• pp.773-780
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• 1999

A digital tracking controller is proposed for micro electrostatic actuator with input nonlinearity, where disturbance observer is utilized in cooperation with inverse function. Generally the disturbance observer is announced to be robust to modeling uncertainty, and external disturbance. But, when the nonlinearity exists in the systems, the disturbance observer may not directly be applied to that system, because the nonlinearity may destabilize the overall system. Therefore, first, we linearize the nonlinear input characteristics of micro electrostatic actuator by the use of inverse function. Secondly, we apply disturbance observer to approximately linearized system for eliminating the residuals of nonlinearity and the modeling uncertainty. Then, we get the good properties of the disturbance rejection as well as the robustness due to the own nature of disturbance observer. In this case, we propose a sufficient condition for the robust stability of overall systems. Furthermore, we discuss the problem that may be exposed when disturbance observer is applied to the internally stable system with saturation, and analyze two methods to overcome input saturation problem in the sense of internal stability. Simulations have been carried out to show the effectiveness of the proposed controller.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.6
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• pp.431-441
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• 2020

In this paper, we propose a new method using a feedforward disturbance observer that guarantees stability and robustness about the effects of external disturbance and model uncertainty. The method is consist of a disturbance observer, a feedforward controller, and an overshoot detecting logic. It has an advantage of reducing the excessive overshoot by external disturbance and model uncertainty. Also, it is easy to adjust the control gain due to a simple structure. In order to verify the effectiveness of a new method, simulation results are given for longitudinal model of F-16 aircraft. By reflecting a various of model uncertainties, the stability and the robustness are guaranteed. Finally, the stability and the robustness of the proposed method are verified using root locus plot and bode plot.

• 제어로봇시스템학회:학술대회논문집
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• 1996.10a
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• pp.99-102
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• 1996

A novel iterative learning control scheme comprising a unique feedforward learning controller and a disturbance observer is proposed. Disturbance observer compensates disturbance due to parameter variations, mechanical nonlinearities, unmodeled dynamics and external disturbances. The convergence and robustness of the proposed controller is proved by the method based on Lyapunov stability theorem. The results of numerical simulation are shown to verify the effectiveness of the proposed control scheme.

• Journal of Institute of Control, Robotics and Systems
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• v.10 no.5
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• pp.385-394
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• 2004

This paper proposes the generalized structure of a model-based disturbance rejection controller called a Robust Internal-loop Compensator (RIC). The framework consists of the RIC in the internal-loop to eliminate disturbances and a feedback controller in the external-loop to achieve nominal control performance. As the main contribution of this paper, we redefine the design problem of the RIC as a regulation control problem, then show that this new definition with the RIC structure provides more design flexibility and less implementation constraints. This is verified through a comparative structural analysis with Disturbance Observer (DOB) and Adaptive Robust Control (ARC). Two design examples of the RIC are given, along with practical issues that should be considered in the design procedure. The proposed framework is demonstrated by simulations of a rotary-type motor and experiments with a linear-type motor system.

• The Journal of Korea Robotics Society
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• v.13 no.3
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• pp.157-163
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• 2018

This paper deals with the development and application of control algorithms for series elastic relief robots for rescue operations in harsh environment like disasters or battlefield. The joint controller applied in this paper has a cascade structure combining inner loop for torque control and outer loop for position control. The torque loop contains feedforward and feedback controller and disturbance observer for independent, decentralized joint control. The effect of the elastic component and motor dynamics are treated as the nonlinear disturbance and compensated with the disturbance observer of torque controller. For the collision detection, Band Designed Disturbance Observer is configured to recognize/respond to external disturbance robustly in the continuously changing environment. The controller is applied to a 7-dof series elastic manipulator to evaluate the torque tracking and collision detection/response performance.

• Proceedings of the KIEE Conference
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• 2004.11c
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• pp.738-740
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• 2004

The disturbance observer is effective in enhancing the performance of position control in high speed optical disk drive systems(ODDS). It is known that error based modified disturbance observer (EM-DOB) is more effective structure than general DOB. It has a simple structure and realization, but it loses robustness. We propose a dual modified disturbance observer(Dual mDOB). It consists of internal loop EM-DOB and external loop DOB. Those loops are designed for different objects. We see that the dual mDOB is an effective method for tracking performance.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.4
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• pp.666-671
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• 2017

A disturbance-observer-based adaptive neural tracker design problem is investigated for a class of perturbed uncertain non-affine nonlinear systems with unknown control direction. A nonlinear disturbance observer (NDO) design methodology using neural networks is presented to construct a tracking control scheme with the attenuation effect of an external disturbance. Compared with previous control results using NDO for nonlinear systems in non-affine form, the major contribution of this paper is to design a NDO-based adaptive tracker without the sign information of the control coefficient. The stability of the closed-loop system is analyzed in the sense of Lyapunov stability.

• Proceedings of the KIEE Conference
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• 2003.11c
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• pp.372-375
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• 2003

Using disturbance observer is effective to enhance tracking performance of system in the presence of disturbances. Various types of disturbance observers have been proposed to improve sensitivity of systems, but they tend to bring poor transient response due to cross coupling of inter-loops. In this paper, we propose dual disturbance observer(Dual DOB) which is designed to reduce the cross coupling. Dual DOB is consist of an internal DOB and an external DOB, that are designed for different object. The Dual DOB is applied to Optical Disk Drive tracking system. It is shown that the Dual DOB has improved performance over conventional DOB via experimental result. There is good agreement between simulation and experimental results.

• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.87.4-87
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• 2001

In this paper, a design guideline of disturbance observer(DOB) for track-following controller is presented. In the track-following control system(TFCS) of optical disk drive(ODD), disturbance rejection is the key issue for the overall performance. DOB gives an excellent advantage of disturbance rejection within its bandwidth determined by a low-pass filter. In general, design of DOB requires a tradeoff between performance and stability, which should be based on quantitative analysis. The external disturbance is well-defined in the frequency domain, which provides the base of the analysis. In addition to a DOB, a proper feedback controller is utilized for guaranteeing overall stability. Some computer simulations and experiments are conducted and some of the results are presented.