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Implementation of restoring method for reading bar code
Kadlčík, Libor ; Bartušek, Karel (referee) ; Mikulka, Jan (advisor)
Bar code stores information in the form of series of bars and gaps with various widths, and therefore can be considered as an example of bilevel (square) signal. Magnetic bar codes are created by applying slightly ferromagnetic material to a substrate. Sensing is done by reading oscillator, whose frequency is modulated by presence of the mentioned ferromagnetic material. Signal from the oscillator is then subjected to frequency demodulation. Due to temperature drift of the reading oscillator, the demodulated signal is accompanied by DC drift. Method for removal of the drift is introduced. Also, drift-insensitive detection of presence of a bar code is described. Reading bar codes is complicated by convolutional distortion, which is result of spatially dispersed sensitivity of the sensor. Effect of the convolutional distortion is analogous to low-pass filtering, causing edges to be smoothed and overlapped, and making their detection difficult. Characteristics of convolutional distortion can be summarized into point-spread function (PSF). In case of magnetic bar codes, the shape of the PSF can be known in advance, but not its width of DC transfer. Methods for estimation of these parameters are discussed. The signal needs to be reconstructed (into original bilevel form) before decoding can take place. Variational methods provide effective way. Their core idea is to reformulate reconstruction as an optimization problem of functional minimization. The functional can be extended by other functionals (regularizations) in order to considerably improve results of reconstruction. Principle of variational methods will be shown, including examples of use of various regularizations. All algorithm and methods (including frequency demodulation of signal from reading oscillator) are digital. They are implemented as a program for a microcontroller from the PIC32 family, which offers high computing power, so that even blind deconvolution (when the real PSF also needs to be found) can be finished in a few seconds. The microcontroller is part of magnetic bar code reader, whose hardware allows the read information to be transferred to personal computer via the PS/2 interface or USB (by emulating key presses on virtual keyboard), or shown on display.
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Design of magnetic bar-code read head
Kadlčík, Libor ; Drexler, Petr (referee) ; Mikulka, Jan (advisor)
Magnetic bar-code is composed from ferromagnetic bars printed on a substrate. The amount of ferromagnetic material is low, therefore reading magnetic barcode requires sensitive methods. Principle of methods of sensing both low-intensity magnetic field (fluxgates) and detecting low concentration of ferromagnetic material (resonant circuit, differential sensor) will be described. There are sensors producing frequency-modulated signal, therefore we focus on frequency demodulators as well. Signal acquired by sensor suffers from convolution distortion, reconstruction methods will be introduced. The assembled device consists of sensing oscillator, frequency demodulator, amplifier and reconstructing circuit. Frequency demodulation is done by phase-locked loop or differential demodulator. Reconstruction is based on detection of inflection points, producing square signal (representing bars of barcode). Design of these blocks is described. The device is able to read magnetic barcodes and reconstruct convolutionary distorted acquired signal. The differential demodulator exhibits low noise and low temperature drift (contrary to phase-locked loop). Signal produced by reading 2 mm wide bars is reconstructed without any problems, bars of width less than 1 mm cause troubles in certain cases (due to high degree of convolution distortion).
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Mountain Pass Theorem and its applications
Příhoda, Vojtěch ; Černý, Robert (advisor) ; Vlasák, Václav (referee)
Cílem této práce je formulovat a dokázat Větu o horském sedle a ukázat příklady její aplikace tak, aby student třetího ročníku matematiky nebo fy- ziky, jenž absolvoval alespoň úvodní kurs funkcionální analýzy, byl schopen práci porozumět. D·kaz Věty o horském sedle provedeme s pomocí Ekelan- dova variačního principu, který si rovněž formulujeme a dokážeme. Následně si ukážeme dva příklady její aplikace na d·kaz existence netriviálního sla- bého řešení eliptické parciální diferenciální rovnice obsahující nelinearitu se subkritickým r·stem. 1
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Mountain Pass Theorem and its applications
Příhoda, Vojtěch ; Černý, Robert (advisor) ; Vlasák, Václav (referee)
Cílem této práce je formulovat a dokázat Větu o horském sedle a ukázat příklady její aplikace tak, aby student třetího ročníku matematiky nebo fy- ziky, jenž absolvoval alespoň úvodní kurs funkcionální analýzy, byl schopen práci porozumět. D·kaz Věty o horském sedle provedeme s pomocí Ekelan- dova variačního principu, který si rovněž formulujeme a dokážeme. Následně si ukážeme dva příklady její aplikace na d·kaz existence netriviálního sla- bého řešení eliptické parciální diferenciální rovnice obsahující nelinearitu se subkritickým r·stem. 1
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Design of magnetic bar-code read head
Kadlčík, Libor ; Drexler, Petr (referee) ; Mikulka, Jan (advisor)
Magnetic bar-code is composed from ferromagnetic bars printed on a substrate. The amount of ferromagnetic material is low, therefore reading magnetic barcode requires sensitive methods. Principle of methods of sensing both low-intensity magnetic field (fluxgates) and detecting low concentration of ferromagnetic material (resonant circuit, differential sensor) will be described. There are sensors producing frequency-modulated signal, therefore we focus on frequency demodulators as well. Signal acquired by sensor suffers from convolution distortion, reconstruction methods will be introduced. The assembled device consists of sensing oscillator, frequency demodulator, amplifier and reconstructing circuit. Frequency demodulation is done by phase-locked loop or differential demodulator. Reconstruction is based on detection of inflection points, producing square signal (representing bars of barcode). Design of these blocks is described. The device is able to read magnetic barcodes and reconstruct convolutionary distorted acquired signal. The differential demodulator exhibits low noise and low temperature drift (contrary to phase-locked loop). Signal produced by reading 2 mm wide bars is reconstructed without any problems, bars of width less than 1 mm cause troubles in certain cases (due to high degree of convolution distortion).
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Implementation of restoring method for reading bar code
Kadlčík, Libor ; Bartušek, Karel (referee) ; Mikulka, Jan (advisor)
Bar code stores information in the form of series of bars and gaps with various widths, and therefore can be considered as an example of bilevel (square) signal. Magnetic bar codes are created by applying slightly ferromagnetic material to a substrate. Sensing is done by reading oscillator, whose frequency is modulated by presence of the mentioned ferromagnetic material. Signal from the oscillator is then subjected to frequency demodulation. Due to temperature drift of the reading oscillator, the demodulated signal is accompanied by DC drift. Method for removal of the drift is introduced. Also, drift-insensitive detection of presence of a bar code is described. Reading bar codes is complicated by convolutional distortion, which is result of spatially dispersed sensitivity of the sensor. Effect of the convolutional distortion is analogous to low-pass filtering, causing edges to be smoothed and overlapped, and making their detection difficult. Characteristics of convolutional distortion can be summarized into point-spread function (PSF). In case of magnetic bar codes, the shape of the PSF can be known in advance, but not its width of DC transfer. Methods for estimation of these parameters are discussed. The signal needs to be reconstructed (into original bilevel form) before decoding can take place. Variational methods provide effective way. Their core idea is to reformulate reconstruction as an optimization problem of functional minimization. The functional can be extended by other functionals (regularizations) in order to considerably improve results of reconstruction. Principle of variational methods will be shown, including examples of use of various regularizations. All algorithm and methods (including frequency demodulation of signal from reading oscillator) are digital. They are implemented as a program for a microcontroller from the PIC32 family, which offers high computing power, so that even blind deconvolution (when the real PSF also needs to be found) can be finished in a few seconds. The microcontroller is part of magnetic bar code reader, whose hardware allows the read information to be transferred to personal computer via the PS/2 interface or USB (by emulating key presses on virtual keyboard), or shown on display.
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