Showing papers by "National Taiwan University of Science and Technology published in 1994"

Control of an inverted pendulum using grey prediction model

Abstract: A system with partial unknown structure, parameters, and characteristics is called a grey system. The grey theory can be employed to improve the control performance of a system without sufficient information or with highly nonlinear property. In this paper, a grey prediction model combined with a proportional plus derivative controller is proposed to balance an inverted pendulum, which is a classic example of an inherently nonlinear unstable system. The control objective is to swing up the pendulum from a stable position to an unstable position and bring its slider back to the origin of the track. The overall control algorithm is decomposed into two separate grey model controllers for swinging up and balancing, respectively, based upon the angular and velocity values of the pendulum. The experimental results show that this grey model controller is able to swing up and balance the inverted pendulum and guide its slider to the center of the track. It also has the robustness to balance the inverted pendulum at an upright position in suffering an external impact acting on the pendulum.

Photo‐electron paramagnetic resonance investigation of the Cr3+ impurity and the (SCl)2− defect in synthetic FeS2 crystals

Abstract: The method of photo‐electron paramagnetic resonance has been used to investigate the photosensitivities of the Cr3+, Ni2+, and (SCl)2− impurities and defects detected by electron paramagnetic resonance (EPR) in synthetic FeS2 crystals grown by the method of chemical vapor transport by using ICl3 as the transport agent. Cr3+ and (SCl)2− are photosensitive, but Ni2+ is not, to IR illumination with photon energy less than the band‐gap energy. A decrease (photoquenching) in the EPR signal of Cr3+ and an increase (photoinduction) in the EPR signal of (SCl)2− were detected at low temperatures. At T≂110 K, the spectral response of the photoquenching of Cr3+ is the largest near λ=1425 nm−1 (0.87 eV), which can be correlated with the 0.90 eV photoconductivity peak and the 0.87 eV IR absorption peak observed at low temperatures in the same batches of crystals. After several cycles of on–off IR illumination, the equilibrium population of Cr3+ is less than that of the virgin state, indicating the presence of hole tra...

Photoconductivity study of synthetic FeS2 single crystals at low temperatures

Abstract: The photoconductivity measurements of synthetic pyrite FeS2 single crystals at low temperatures are used to study the impurity and defect-related photoresponse peaks below the band edge. At temperatures below 100 K, several features on the low-energy side of the photoconductivity spectra are observed. By comparison of the results with those of the absorption and the photo-EPR measurements, the origin of the sharpest peak at 0.866 eV is identified. The nature of other weaker features is discussed. The existence of these features prevents us from determining the band gap of FeS2 by the Moss rule at low temperature. We propose that the energy gap of FeS2 at low temperatures may be determined by adding the thermal ionization energy of the shallow acceptor states to the photo-ionization energy between the (SCl)2- states and the bottom of the conduction band.