Department of Electrical Engineering

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In the above-mentioned paper⊥ a variable structure sliding mode controller (VSSM C) design for the tip position control of a flexible one-link manipulator has been presented, where a switching line constructed from the tip position and its derivative was employed for the design. The daim was that if the slope of this line is chosen positive and the system variables are made to stay on this line, they will converge to zero exponentially, thusyielding a stable system in sliding mode (SM). The purpose of this comment is to show that the choice of a positive constant as the slope for this switching line will not guarantee the stability of the system in SM because, in view of the functional relationship of the tip position with the generalized coordinates of the system through the mode shape functions, what is presented asa switching line is in fact a switching hypersurface. Hence, the stability of the system in SM is guaranteed only if the motion on this hyper surface is asymptotically stable. A positive value for the slope of the switching line employed by Qian and Ma will not guarantee this stability because variations in the mode shape functions due to varying payload conditions or other disturbances at the tip will lead to a varying switching surface. These variations can be such that the resulting sliding motion becomes unstable. Also, the varying switching surface implies that the controller will fail to maintain sliding mode motion.

World University root node

IEEE Transactions on Automatic Control

Comments on "a new controller design for a flexible one link manipulator"

A variable structure model following controller (VSMFC) isdesigned for the tip position control of a single flexible link.The design is done for the system model in which only the firsttwo flexible modes are included. Due to the simplicity in choosingsecond order models for the subsystems representing thedynamics of the various flexible modes, the design can be easilyextended to include any desired number of flexible modes. Thetip position response is made to assume a second order stepresponse by suppressing the flexible modes very quickly. Hencethe tip position response can be easily controlled by a suitablechoice of the damping factor and natural frequency of the secondorder model which the rigid body mode of the link is madeto follow. The controller is robust to parameter variations anddisturbances. © 1997 ASME.

Journal of Dynamic Systems, Measurement and Control, Transactions of the ASME

Position control ofsingle link flexible manipulator by variable structure model following control

This brief presents a method of reduction for discrete interval systems using Fade approximation to allow the retention of dominant poles. For a given system, the denominator of the reduced model is formed by retaining the dominant poles of the original system, while the numerator is obtained by matching interval time moments. Two numerical examples illustrate the procedure. © 1997 IEEE.

IEEE Transactions on Circuits and Systems I: Fundamental Theory and Applications

Discrete interval system reduction using fade approximation to allow retention of dominant poles

The paper presents the design of a near optimal linear regulator for controlling xenon-induced spatial oscillations in a large, pressurized heavy water reactor. The nonlinear mathematical model of the reactor including xenon iodine dynamics is characterized by 56 state variables and 14 inputs. This nonlinear model is linearized over rated power of the reactor and then the singularly perturbed structure of the linear model is exploited to decompose it into a fast subsystem of 14th order and a slow subsystem of 42nd order. The slow subsystem regulator problem is formulated as a cheap control problem that entails the solving of regulator problems of a 28th-order submodel and a 14th-order submodel. The fast subsystem regulator problem is also solved. Separately designed regulators are finally combined to obtain the near-optimal composite control for the original 56th-order model. © 1996 IEEE.

IEEE Transactions on Nuclear Science

Spatial control of a large pressurized heavy water reactor

The phenomenon of resist debris (RD) formation in electron beam lithography (EBL) under various conditions of proximity exposure (PE) effect is discussed. It is found that the PE correction at the preferred resist plane together with adequate beam to beam spacing can provide stable and uniformly distributed RD over the exposed pattern area. As an application of such stable and uniformly distributed RD, the fabrication of an array of closely spaced metal dots has been demonstrated. The approach provides the optimum way for achieving high resolution pattern delineation under the given EBL conditions and constraints. Copyright © 1996 Elsevier Science Ltd.

Vacuum

Phenomenon of resist debris formation in electron beam lithography and its possible application

In this paper a sufficient condition for determining controllability and observability of linear symmetric interval systems is proposed, where the transformation matrix is obtained such that the transformed interval system matrix is diagonal. Then the symmetric interval system is said to be controllable if it is controllable in usual sense for each fixed value of uncertain parameters of the interval system. Similarly the symmetric interval system is said to be observable if it is observable in the usual sense for each fixed value of uncertain parameters of the given interval system. Numerical examples illustrate the procedure.

IEEE Conference on Control Applications - Proceedings

Controllability and observability of linear symmetric interval systems

Effects arising from the intercalation of excess oxygen in Bi-O layer has been observed at room temperature using atomic force microscopy. The excess oxygen is incorporated by oxygenating the pure sample. The oxygen is trapped between the alternating Bi-O layers along the b direction. This leads to a change in the local interatomic bond length along the b axis, while the periodicity remained invariant along the a axis. In addition, in-plane atomically resolved structure of single crystal has been imaged at room temperature using AFM. The lattice spacings indicate that the observed structure corresponds to the in-plane bismuth and oxygen positions. Furthermore, high-resolution scanning tunneling spectroscopy measurements show that oxygen doping increases the Bi-O layer density of states near the Fermi level giving rise to metallicity, whereas the pure sample reveals a semiconducting energy gap in the tunneling spectrum.© 1995 American Institute of Physics.

Fulltext

Applied Physics Letters

Observation of intercalation of excess oxygen in Bi2Sr 2CaCu2O8+y single crystal

Surface topography of as-grown films of YBa2Cu3O 7-delta (YBCO) deposited by off-axis RF magnetron sputtering on MgO and SrTiO3 single-crystal (100) substrates, has been investigated by scanning tunnelling microscopy (STM)/scanning tunnelling spectroscopy (STS) operated in air at ambient temperature. Both c-axis- and a-axis-oriented YBCO films have been investigated. In the case of c axis thin films, we have directly observed spiral-shaped growth terraces, which emanate from screw dislocations of this layered superconducting oxide. The growth steps are generally seen to possess a step height close to or multiples of the unit cell height of the YBCO crystalline structure. In the case of a axis growth, the substrate as well as the deposition temperature determines the grain orientation. Furthermore, our STS data revealed that the surface layer of the film is semiconducting and the tunnelling spectrum varies its shape depending on the tip-to-sample distance. A superconducting gap appears clearly in the spectra when the STM tip is placed closer to the surface than the normal position of the scanning mode. This suggests that the semiconducting layer is confined in the topmost surface region of the as-prepared film, while the layer beneath it is superconducting in character.

Superconductor Science and Technology

The effect of sputter deposition conditions on the growth mechanism of YBa2Cu3O7-delta thin films studied by scanning tunnelling microscopy

This paper presents model reduction of linear interval system using Pade approximation method. In the first part a full Pade approximation method for interval system is presented, where as in the second part stable Pade approximation is discussed. A numerical example illustrates the procedure.

Proceedings - IEEE International Symposium on Circuits and Systems

Model reduction of linear interval systems using Pade approximation

This note presents a method of designing the state feedback gain which place the closed-loop poles of a give discrete interval system inside some region. The Levy-Hadamard and Bendixson theorems have been used to derive algebraic relations which set bounds on the real and imaginary parts of the eigenvalues of the closed-loop system matrix. This helps in placing the closed-loop poles in a specified region, either inside a vertical strip, or inside a horizontal strip, or inside a rectangular region. It turns out that the relations are easily computable and the feedback gain can be determined in a very simple way. A numerical example illustrates the proposed procedure.