• Journal of Advanced Navigation Technology
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• v.22 no.3
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• pp.228-232
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• 2018

Dealing with quntization error in a control system properly becomes much more important as many devices are connected through network and controlled. Thus, in this paper, we study a data rate condition on quantizer to achieve practical stability in a discrete time linear time invariant system with state feedback control. First, required data rate is shown to depend on eigenvalue of the closed loop system, the size of the initial state vector, the magnitude of initial quantization error, and control gain in the absence of process noise. It additionally depends on the maximum magnitude of process noise when noise is not zero. Asymptotic analysis shows that a new design method may be needed to reduce the date rate for a networked control in the presence of quantization error and noise.. We provide a simple numerical evaluation of uniform quantizer and logarithmic qunatizer to assess their characteristics of practical stability depending on data rate in the presence of noise.

• Journal of the Korean Magnetics Society
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• v.14 no.6
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• pp.207-212
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• 2004

Eddy current (EC) testing methods are widely used in a variety of applications including the inspection of steam generator tubes in nuclear power plants, aircraft parts and airframes. A key factor that affects the EC signal is lift-off which means the physical distance between a sensor and a specimen in the testing. In practice, it is difficult to keep track of the actual value of the lift -off during a specific experiment, simulation or testing in the field, which is essential for accurate interpretation of the signal to be used in the following steps. Hence it is necessary to have a scheme to render the EC signal invariant to the effects of lift-off in spite of the changes in the real world. This paper describes a new method for compensating EC signals for variations in lift-off by acquiring an invariance feature using a homomorphic operator and neural network techniques. The signals from various lift-offs are transformed to obtain a zero lift-off equivalent signal that can be subsequently used for defect characterization in the next step.

• Korean Journal of Remote Sensing
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• v.30 no.5
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• pp.547-557
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• 2014

This paper presents a method for designing circular template used in similarity measurement for image registration. Circular template has translation and rotation invariant property, which results in correct matching of control points for image registration under the condition of translation and rotation between reference and sensed images. Circular template consisting of the pixels located on the multiple circumferences of the circles whose radii vary from zero to a certain distance, is converted to two-dimensional Discrete Polar Coordinate Matrix (DPCM), whose elements are the pixels of the circular template. For sensed image, the same type of circular template and DPCM are created by rotating the circular template repeatedly by a certain degree in the range between 0 and 360 degrees and then similarity is calculated using mutual information of the two DPCMs. The best match is determined when the mutual information for each rotation angle at each pixel in search area is maximum. The proposed algorithm was tested using KOMPSAT-2 images acquired at two different times and the results indicate high accurate matching performance under image rotation.