• 제어로봇시스템학회:학술대회논문집
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• 1995.10a
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• pp.154-157
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• 1995

A magnetic levitation control system is nonlinear and very unstable. Thus there should be a stabilizing compensation network and a feedback path. Due to the levitation control a noncontact photoresistor sensor is generally used. One photocell provides a certain amount of variation in length by the ball shadow casted on the cell surface. Furthermore at the boundary of the cell, the linearity of sensitivity deteriorates severely. To overcome the constraints of the length and linearity, an efficient sensor array is deviced and applied in the feedback path of a large-gap magnetic levitation control system. A number of CdS photocells and a summing circuit of the sensor output signals are used for a sensor array. The levitation length of a ball and the transient performances are main objectives of the large-gap suspension system using the sensor array.

• Journal of Sensor Science and Technology
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• v.26 no.2
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• pp.85-90
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• 2017

A wide dynamic range (WDR) CMOS image sensor (CIS) was developed with a specialized readout architecture for realizing high-sensitivity (HS) and low-sensitivity (LS) reading modes. The proposed pixel is basically a three-transistor (3T) active pixel sensor (APS) structure with an additional transistor. In the developed WDR CIS, only one mode between the HS mode for relatively weak light intensity and the LS mode for the strong light intensity is activated by an external controlling signal, and then the selected signal is read through each column-parallel readout circuit. The LS mode is implemented with the column capacitors and a feedback structure for adjusting column capacitor size. In particular, the feedback circuit makes it possible to change the column node capacitance automatically by using the incident light intensity. As a result, the proposed CIS achieved a wide dynamic range of 94 dB by synthesizing output signals from both modes. The prototype CIS is implemented with $0.18-{\mu}m$ 1-poly 6-metal (1P6M) standard CMOS technology, and the number of effective pixels is 176 (H) ${\times}$ 144 (V).

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.109-114
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• 2004

This paper presents a theoretical and experimental study of a non-collocated pair of piezopolymer PVDF sensor and piezoceramic PZT actuator, which are bonded on a cantilever beam, in order to suppress unwanted vibration at the tip of the beam. The PZT actuator patch was bonded near the clamped part and the PVDF sensor, which was triangularly shaped, was bonded on the other part of the beam. This is because the triangular PVDF sensor is known that it can detect the tip velocity of a cantilever beam. Because the arrangement of the sensor and actuator pair is not collocated and overlapped each other, the pair can avoid so called 'the in-plane coupling'. The test beam is made of aluminum with the dimension of $200\times20\times2mm$, and the two PZT5H actuators are both $20\times20\times1mm$ and bonded on the beam out-of-phase, and the PVDF sensor is $178mm\times6mm\times52{\mu}m$. Before control, the sensor-actuator frequency response function is confirmed to have a nice phase response without accumulation in a reasonable frequency range of up to 5000 Hz. Both the DVFB and displacement feedback strategies made the error signal from the tip velocity (or displacement) sensor is transmitted to a power amplifier to operate the PZT actuator (secondary source). Both the control methods attenuate the magnitude of the first two resonances in the error spectrum of about 6-7 dB.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1458-1463
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• 2003

This paper presents an improved identification algorithm of active magnetic bearing rotor systems considering sensor and actuator dynamics. An AMB rotor system has both real and complex poles so that it is very hard to identify them together. In previous research, a linear transformation through a fictitious proportional feedback was used in order to shift the real poles close to the imaginary axis. However, the identification result highly depends on the fictitious feedback gain, and it is not easy to identify the additional dynamics including sensor and actuators at the same time. First, this paper discusses the necessity and a selection criterion of the fictitious feedback gain. An appropriate feedback gain minimizes dominant SVD(Singular Value Decomposition) error through maximizing rank deficiency. Second, more improvement in the identification is achieved through separating the common additional dynamics in all elements of frequency response matrix. The feasibility of the proposed identification algorithm is proved with two theoretical AMB rotor models. Finally, the proposed scheme is compared with previous identification methods using experimental data, and a great improvement in model quality and large amount of time saving can be achieved with the proposed method.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.5 s.98
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• pp.186-193
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• 1999

Sensor feedback for process control is one of the essential elements is an automated deburring procedure. This paper presents the implementation of acoustic emission (AE), which has been developed as a feedback sensing technique for precision (mechanical) deburring, in a precision laser deburring process. AE signals were sampled for laser machining/deburring under various experimental conditions and analyzed using several signal-processing methods including AErms and spectral analysis. The results, such as the sensitivity of AE signals for different laser cutting depths, edge detection capability and the frequency analysis show a clear correlation between physical process parameters and the AE signals. A subsequent control strategy for deburring automation is also briefly discussed.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.10
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• pp.1007-1014
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• 2004

This paper presents a study of low frequencies volume velocity vibration control of a smart panel in order to reduce sound transmission. A distributed piezoelectric quadratically shaped polyvinylidene fluoride (PVDF) polymer film is used as a uniform force actuator and an array of $4\;{\times}\;4$ accelerometer is used as a volume velocity sensor for the implementation of a single-input single-output control system. The theoretical and experimental study of sensor-.actuator frequency response function shows that this sensor-actuator arrangement provides a required strictly positive real frequency response function below about 900 Hz. Direct velocity feedback could therefore be implemented with a limited gain which gives reductions of about 15 dB in vibration level and about 8 dB in acoustic power level at the (1,1) mode of the smart panel. It has been also shown that the shaping error of PVDF actuator could limit the stability and performance of the control system.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.11
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• pp.1185-1191
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• 2008

This paper presents an approach to define an optimal piezoactuator length to actively control structural vibration. The optimal ratio of the piezoactuator length against the beam length when a pair of piezoceramic actuator and accelerometer is used to suppress unwanted vibration with direct velocity feedback(DVFB) control strategy is not clearly defined so far. It is well known that DVFB control can be very useful when a pair of sensor and actuator is collocated on structures with a high gain and excellent stability. It is considered that three different collocated Pairs of piezoelectric actuators (20, 50 and 100 mm long) and accelerometers installed on three identical clamped-clamped beams($30{\times}20{\times}1mm$). The response of each sensor-actuator pair requires strictly positive real(SPR) property to apply a high feedback gain. However the length of the piezoactuator affects the SPR property of the sensor-actuator response. Intensive simulation and experiment show the effect of the actuator length variation is strongly related with the frequency range of the SPR property. Thus an optimal length ratio was suggested to obtain relevant performance with a good stability under the DVFB strategy.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.2
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• pp.48-58
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• 1995

A micro positioning system using piezoelectric actuators have very wide application region such as ultra-precision machine tool, optical device, measurement systen. In order ro keep a high precision displacement resolution, they use a position sensor and feedback the error. From the practical point of view, a high-resolution displacement sensor system are very expensive and difficult to guarantee such sensitive sensors work properly in the hard opera- tion environment of industry. In this study, a micro-positioning grinding table which does not require position sensor but uses piezoelectric voltage feedback, has been developed. It is driven by hystersis-considering reference input voltage which calculated from computer and then uses actuator/sensor characteristics of piezoelectric materials. From the result of experiments we proved a fast and stable response of micro-positioning system and suggested efficient technique to control the piezoelectric actuator. And through grinding experiments, it is revealed that a characteristics of ground surfaces transient to plastic deformation as extremely small depth of grinding.

• The Journal of the Korea institute of electronic communication sciences
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• v.11 no.3
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• pp.277-282
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• 2016

Effect of spectral drift in coherent fiber laser was investigated by injecting optical feedback to Fabry-Perot resonance loop. Er+3 doped fiber laser having unilateral optical feedback loop in Fabry-Perot configuration using two FBGs was fabricated. The optical feedback was found to be effective in linewidth reduction of fiber laser compared to the case without any optical feedback. The linewidth of three fiber lasers using above configuration were measured to be within 3kHz which is resolution-limited performance of self-heterodyne linewidth measurement set-up. The frequency drift measurement using Mach-Zehnder measurement set-up having 200m optical delay-line in one arm showed that the frequency drift rate of optical feedback fiber laser was measured as 300kHz/sec which was better than the case without optical feedback.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.3
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• pp.253-263
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• 2004

The problem considered in this paper is about the collocation of sensor and actuator for the active control of sound and vibration. It is well-known that a point collocated sensor-actuator pair offers an unconditional stability with very high performance when it is used with a direct velocity feedback (DVFB) control, because the pair has strictly positive real (SPR) property. In order to utilize this SPR characteristics, a matched piezoelectric sensor and actuator pair is considered. but this pair suffers from the in-plane motion coupling problem with the out-of-plane motion due to the piezo sensor and actuator interaction. This coupling phnomenon limits the stability and performance of the matched pair with DVFBcontrol. As a new alternative, a point sensor and distributed piezoelectric actuator pair is also considered, which provides SPR property in all frequency range when the pair is implemented on a clamped-clapmed beam. The use of this sensor-actuator pair is highly expected for the applications to more practical active control of sound and vibration systems with the DVFB control strategy.