• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.6
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• pp.667-673
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• 2010

This paper proposes a control method based on a pseudo-impedance model to control the motion of biped robots walking on an uneven surface. The pseudo-impedance model simulates the action of the ankle of a foot landing on the ground when a human walks. When the foot is in contact with the ground, the human ankle goes through two different phases. In the first phase, the human exerts little or no effort and applies no torque on the ankle so that the orientation of the foot is effortlessly and passively adjusted with respect to the ground. In the second phase of landing, the ankle generates a significant amount of torque in order to rotate and move the main part of the human body forward and to support the weight of the human; this phase is called the weight acceptance phase. Computer simulations of a 12-DOF biped robot with a 6-DOF environment model were performed to determine the effectiveness of the proposed pseudo-impedance control. The simulation results show that stable locomotion can be achieved on an irregular surface by using the proposed model.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.7
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• pp.537-548
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• 2014

In this paper, horn loudspeaker modeling was suggested, investigated and verified through comparison of test results and simulation ones based on input electrical impedance curves and acoustic sensitivity ones. First, Thiele Small parameters of horn driver were identified by using pseudo loudspeaker model concept and verified in case of both closed and open horndriver. Second, cone-shaped horn models were investigated and compared with input acoustic impedance curves for real horn(cone angle $6.6^{\circ}$) and short horn(cone angle $27.9^{\circ}$). It showed that Leach model for cone horn was well described to test results, which were electrical impedance and acoustic sensitivity, compared to Lemaitre one. To represent horn system model good approximation in wide frequency range, mass correction filter and lowpass filter were adopted and consequently showed good fitted to test results.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.11
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• pp.1112-1118
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• 2007

It was discussed to identify Thiele Small Parameters for Pseudo loudspeaker within 10mm grade microspeaker attached to closed-box using known dynamic mass of moving parts. Also, enhanced circuit model for vented-box micro speaker system was used to more accurately simulate electrical impedance curves for real vented-box microspeaker system and compared to test results. Consequently, it showed that micro speaker could be modeled by pseudo loudspeaker TS parameters similar to general loudspeaker. Vented-box microspeaker model with pseudo loudspeaker TS parameters was well suited to describe real microspeaker. Also, it was proposed to estimate volume of rear closed-box of microspeaker without design specifications.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.10
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• pp.983-992
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• 2007

It was proposed to identify Thiele Small Parameters for loudspeaker attached to closed-box using known dynamic mass of moving parts. Also, enhanced PSPICE circuit model for closed-box loudspeaker system was proposed to more accurately simulate real closed-box loudspeaker system. Frequency dependent parameters were used to model voice coil inductor. Acoustic pressure response curves and electrical impedance curves were simulated and investigated by PSPICE circuit model according to compensation filter's parameters. Finally, proposed method is expected to be utilized for identification of pseudo Thiele Small parameters of microspeaker.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.7
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• pp.525-536
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• 2014

In this paper, GUI program for microspeaker system simulation program was developed and verified through closed box, vent box and 6th order bandpass enclosure system. By using the pseudo loudspeaker model concept, TS parameters and rear volume of microspeaker were identified. Their suitabilities were proved by comparing test results with simulations of electrical impedance and sound pressure response curves for the three box types; closed box, vent box and 6th order bandpass box. Also, MSSP was found to be effective regardless of the microspeaker's shape, either circular or rectangular shape. MSSP can be used for the microspeaker system simulation, and can give a general prediction of such as; sound pressure level curve, electrical impedance, diaphragm velocity and displacement curve according to multiple design parameters; diaphragm mass, compliance, force factor, front and rear volume, front and rear port's diameter and length.

• Earthquakes and Structures
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• v.3 no.2
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• pp.97-115
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• 2012

The energy-transmitting boundary, which is used in the well-known finite element method (FEM) program FLUSH, is quite efficient for the earthquake response analysis of buildings considering soil-structure interaction. However, it is applicable only in the frequency domain. The author proposed methods for transforming frequency dependent impedance into the time domain, and studied the time domain transform of the boundary. In this paper, first, the estimation methods for both the halfspace condition under the bottom of the soil model and the pseudo three-dimensional effect were studied with the time domain transmitting boundary. Next, response behavior when using the boundary was studied in detail using a practical soil and building model. The response accuracy was compared with those using viscous boundary, and the boundary that considers the excavation force. Through these studies, the accuracy and efficiency of the proposed time domain transmitting boundary were confirmed.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.10
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• pp.803-806
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• 2011

1 mol% $Li_2O$ excess $0.9(Na_{0.52}K_{0.48})NbO_3-0.1LiTaO_3$ lead-free piezoelectric multilayer ceramic actuators were investigated to determine their aging properties. To reduce the thermal aging behavior, we applied a rectified unipolar electric field of 5 kV/mm to the specimen to accelerate the electric aging behavior. By employing a rectified unipolar electric field for the piezoelectric actuators, we could remove undesirable heating from the relaxation current in the motion of the ferroelectric domain. To accelerate the aging test, the applied electric fields had a frequency of 900 Hz. To have enough time for charging and discharging, we employed an accurate time constant to design the equivalent circuit model for the aging tester. To extract exact aging behavior, we measured the pseudo-piezoelectric coefficient before and after the aging process. We also measured the electro-mechanical coupling coefficient, the frequency-dependent dielectric permittivity, and the impedance to compare with fresh and aged specimen.