Bong Keun Kim

Advanced disturbance observer design for mechanical positioning systems

Disturbance-observer (DOB)-based controller design is one of the most popular methods in the field of motion control. In this paper, the generalized disturbance compensation framework, named the robust internal-loop compensator (RIC) is introduced and an advanced design method of a DOB is proposed based on the RIC. The mixed sensitivity optimization problem, which is the main issue of DOB design, is also solved through the parametrization of the DOB in the RIC framework. Differently from conventional methods, the Q-filter is separated from the mixed sensitivity optimization problem and a systematic design law for the DOB is proposed. This guarantees the robustness and optimality of the DOB and enables the design for unstable plants.

Analysis and Design of Robust Motion Controllers in the Unified Framework

Model based disturbance compensating methods such as disturbance observer, robust control with adaptive algorithm, enhanced internal model control are well known control structures for robust motion controller which can satisfy desired performance and robustness of high-speed/high-accuracy positioning systems. In this paper, these are analyzed in the unified framework and their design method is proposed. To do this, a generalized disturbance attenuation framework named RIC (robust internal-loop compensator) structure is introduced. Through parameterization based on RIC, it is shown that there are inherent equivalences in their structures and the proposed RIC gives a general design framework for the model based disturbance compensating methods. Through simulation, the proposed method is verified.

Design and Performance Tuning of Sliding-Mode Controller for High-Speed and High-Accuracy Positioning Systems in Disturbance Observer Framework

The tuning method of controllers can be used for effectively determining the overall performance of positioning systems. In particular, this method is highly effective in the case of high-speed and high-accuracy positioning systems. In this paper, a sliding-mode controller that uses one of the well-known approaches of robust control methodology is designed for high-speed positioning systems that require a high-accuracy performance. A performance-tuning method based on a disturbance observer (DOB) structure is also proposed. First, a generalized disturbance attenuation framework named robust internal-loop compensator (RIC) is introduced, and a sliding-mode controller based on a Lyapunov redesign is analyzed in the RIC framework. Then, the DOB properties of the sliding-mode controller are presented, and it is shown that the performance of the closed-loop system with a sliding-mode controller can be tuned up by using the structural characteristics of the DOB. These results make the design of an enhanced sliding-mode controller possible. Finally, the proposed algorithm is experimentally verified and discussed with two positioning systems. Experimental results show the effectiveness and the robustness of the proposed scheme.

Web Services Based Robot Control Platform for Ubiquitous Functions

In this paper, we employ Web services, programmable application logic accessible using standard Internet protocol, to enable a robot to access the distributed application logic based on the recent network technologies like XML, SOAP, WSDL, UDDI. Applications can communicate with each other in a platform and programming language independent manner. We first discuss a ubiquitous control platform based on ubiquitous functions to allow a robot the infinitive freedom of movement and knowledge acquirement. We then explain the fundamental ubiquitous functions management framework for a robot. In this framework, the applications are constructed from multiple Web services that work together to provide data and services for the application. Finally, the proposed scheme is applied to the control of the knowledge distributed robot system.

Ubiquitous Localization and Mapping for Robots with Ambient Intelligence

In this paper, a novel approach of knowledge management for the space/location perceiving capacity of robots is proposed. First, the ubiquitous function services composed of smart object, smart logic, and smart discovery service are proposed in order to distribute knowledge flexibly and reliably to changing environment and also for a robot to invoke and merge the distributed knowledge more freely. Next, physical and virtual spaces are merged by RFID tags. Through this, it is shown that ambient intelligence is realized and the space localization and mapping problem of robots can be more easily solved. Finally, the experiment based on an example scenario is carried out to verify the proposed method in the informative space named u-RT space which has two kinds of RFID tags, a virtual space with ubiquitous function services realized by Web services, and a networked robot system which works in these spaces

Performance tuning of robust motion controllers for high-accuracy positioning systems

This paper presents a structural design method of robust motion controllers for high-accuracy positioning systems, which makes it possible to tune the performance of the whole closed-loop system systematically. First, a stabilizing control input is designed based on Lyapunov redesign for the system in the presence of uncertainty and disturbance. And adopting the internal model following control, robust internal-loop compensator (RIC) is proposed. By using the structural characteristics of the RIC, disturbance attenuation properties and the performance of the closed-loop system determined by the variation of controller gains are analyzed. Next, in order to design a robust motion controller for a high performance positioning system, dual RIC structure is proposed and it is shown that if the synthesis of the robust motion control law is performed in the RIC framework, the robust property of RIC can be naturally implanted in the feedback controller. The proposed structural design of robust motion controller provides a systematic approach to the problem of robust stability and performance requirement in the face of uncertainty. Furthermore, by allowing the tradeoffs between robust stability and performance to be quantified in a simple fashion, it can illuminate systematic design procedure of the robust motion controllers. Finally, the proposed method is verified through simulation and the performance is evaluated by experiments using a high-accuracy positioning system.

Robust controller design for PTP motion of vertical XY positioning systems with a flexible beam

This paper presents a point-to-point (PTP) motion control method for accurate positioning and vibration suppression of a vertical XY positioning system with a flexible beam. The proposed method is composed of a feedforward and feedback controller. The input preshaping based on the analytic modeling and frequency equation of the system is proposed as a feedforward controller to produce the desired responses. The feedback controller based on a robust internal-loop compensator is designed to meet the specified performance and to stabilize the whole system in the presence of uncertainties and disturbances. By integrating the input preshaping controller and feedback controller, it is shown that the system is stable and the vibration of the flexible beam is suppressed. The proposed algorithm is demonstrated experimentally on an XY positioning system which consists of a base cart, elastic beam and moving mass.

Robust time optimal controller design for hard disk drives

Robust time optimal control algorithm based on internal loop compensator is proposed. Internal loop compensator effectively isolates the hard disk system from the uncertain disturbances including modeling error, external disturbance, shock, and control torque saturation. We use the H/spl infin/ mixed sensitivity method for the optimization of internal loop compensator and proximate time optimal controller as a feedback controller to provide a time optimal property. The performance of the proposed controller is verified via simulation.

Design of Robust High-Speed Motion Controller for a Plant With Actuator Saturation

A robust high-speed motion controller is proposed. The proposed controller consists of the proximate time optimal servomechanisms (PTOS) for high-speed motion, disturbance observer (DOB) for robustness, friction compensator, and saturation handling element. In the proposed controller, DOB basically provides the chance to apply PTOS to nondouble integrator systems by drastically reducing disturbances as well as unwanted signals due to difference between real system and the double integrator model. But, in DOB-based systems, if control input is saturated due to control input of PTOS and/or DOB, overall system stability cannot be guaranteed, which is first found and analyzed in this paper. To solve this problem, robust stability and internal stability conditions of DOB-based system are derived. It is also shown that DOB could violate the internal stability, when the control input is saturated. Eventually, a simple saturation handling element is inserted to maintain internal stability of overall system. Also, we explain that our two saturation handling methods, i.e., Additional Saturation Element (ASE) and Self Adjusting Saturation (SAS) are the equivalent solutions of saturation problem to maintain internal stability. The stability and performances of the proposed controller are verified through numerical simulations and experiments using a precision linear motor system.

Unified analysis and design of robust disturbance attenuation algorithms using inherent structural equivalence

Model based disturbance compensating methods such as disturbance observer, adaptive robust controller, etc. are well known control structures for robust motion controller which can satisfy desired performance and robustness of high-accuracy positioning systems. In this paper, these are shown to be the same with different parameterizations. To do this, a general framework, called as RIC (robust internal-loop compensator) structure is proposed and the analysis of the conventional schemes is performed in the RIC framework. Through this analysis, it can be shown that there are inherent similarities between the schemes and advantages of the RIC in the viewpoint of controller design. This is verified through simulation works.