• Journal of Power Electronics
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• v.19 no.5
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• pp.1224-1234
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• 2019

Hybrid rotor position estimation methods that integrate a fundamental model and high frequency (HF) signal injection are widely used for the wide speed-range sensorless control of interior permanent-magnet synchronous machines (IPMSMs). However, the direct transition of two different schemes may lead to system fluctuations or system instability since two estimated rotor positions based on two different schemes are always unequal due to the effects of parameter variations, system delays and inverter nonlinearities. In order to avoid these problems, a seamless transition strategy to define and construct a virtual q-axis inductance is proposed in this paper. With the proposed seamless transition strategy, an estimated rotor position based on a fundamental model is forced to track that based on HF signal injection before the transition by adjusting the constructed virtual q-axis inductance. Meanwhile, considering that the virtual q-axis inductance changes with rotor position estimation errors, a new observer with a two-phase phase-locked loop (TP-PLL) is developed to accurately obtain the virtual q-axis inductance online. Furthermore, IPMSM sensorless control with maximum torque per ampere (MTPA) operations can be tracked automatically by selecting the proper virtual q-axis inductance. Finally, experimental results obtained from an IPMSM demonstrate the feasibility of the proposed seamless transition strategy.

• Journal of the Semiconductor & Display Technology
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• v.23 no.2
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• pp.33-37
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• 2024

Recently, wearable virtual reality devices are widely used. These instruments include a 3-axis accelerometer. User's heart rate information in virtual reality contents can be useful for measuring user experience. In this paper, we propose a method to measure the heart rate through a 3-axis accelerometer based on the principle of ballistocardiography without additional sensors. The angular velocity was successively measured in a time series by the 3-axis accelerometer mounted to the head. The frequency of the maximum magnitude is determined as the heart rate through frequency transform and band pass filtering of the time series signal. For verification, the heart rate calculated from photoplethysmography sensors acquired at the same time was compared as ground-truth. In the virtual reality, the user's heart rate information can be extracted without additional heart rate sensor, and the emotional state and fatigue can be measured.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.2
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• pp.227-233
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• 2015

In this study, an indoor test environment was developed for studying the vision stabilizer of an unmanned vehicle, using a virtual environment and a 6-axis motion simulator. The real driving environment was replaced by a virtual environment based on the Aberdeen Proving Ground bump test course for military tank testing. The vehicle motion was reproduced by a 6-axis motion simulator. Virtual reality driving courses were displayed in front of the vision stabilizer, which was located on the top of the motion simulator. The performance of the stabilizer was investigated by checking the image of the camera, and the pitch and roll angles of the stabilizer captured by the IMU sensor of the camera.

• Current Optics and Photonics
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• v.5 no.6
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• pp.660-671
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• 2021

We present a novel optical system for an augmented reality head-up display (AR HUD) with two virtual images at different conjugates by employing a confocal off-axis two-mirror and introducing the horopter circle. For a far virtual image with large asymmetrical aberrations, we initially obtain an off-axis two-mirror system corrected for these aberrations and compensated for the down angle by configuring its parameters to satisfy the confocal and Scheimpflug conditions, respectively. In addition, this system is designed to reduce the biocular parallax by matching Petzval surface into the longitudinal horopter circle in a near virtual image. This design approach enables us to easily balance the residual aberrations and biocular parallax when configuring the optical system with two different conjugates, which results in an AR HUD available for near and far virtual images together.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.05a
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• pp.263-264
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• 2012

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2010.05a
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• pp.75-76
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• 2010

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.6
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• pp.703-713
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• 2011

In this study, to minimize trial and error in the design and manufacturing processes of a high-precision large-surface micro-grooving machine which is able to fabricate the molds for 42 inch LCD light guide panels, the effects of the structural deformation of the micro-grooving machine according to the positions of the X-axis, Y-axis and Z-axis feed systems were examined on the tool tip displacement errors associated with the machining accuracy. The virtual prototype (finite element model) of the micro-grooving machine was constructed to include the joint stiffnesses of the hydrostatic bearings, hydrostatic guideways and linear motors, and then the tool tip displacement errors were measured from the virtual prototype. Especially, to establish the prediction model of the tool tip displacement errors, which was constructed using the positions of the X-axis, Y-axis and Z-axis feed systems as independent variables, the response surface method based on the central composite design was introduced. The reliability of the prediction model was verified by the fact that the tool tip displacement errors obtained from the prediction model coincided well those measured from the virtual prototype. And the causes of the tool tip displacement errors were identified through the analysis of interactions between the positions of the X-axis, Y-axis and Z-axis feed systems.

• Current Optics and Photonics
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• v.5 no.4
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• pp.402-408
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• 2021

An off-axis system refers to an optical system in which the optical axis and normal vector at the vertex of each surface do not match. The most important specification in an optical system is its focal length. Among the various methods for measuring the focal length, the most suitable method for the off-axis system is the method that adopts magnification. However, head-mounted display (HMD) optics must be measured while considering the virtual image distance, which is not infinity owing to product characteristics. For the virtual image distance, a camera with a focusing function was used. By measuring HMD optics via this magnification method, the error generated in this measurement was 0.68% of the HMD's focal length, which is within the 1%-3% range of the conventionally permitted design error for the focal length allowed at the optical design stage. Therefore, it can be verified that the measurement accuracy of the method proposed in this study is sufficiently feasible in practice.

• 제어로봇시스템학회:학술대회논문집
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• 2000.10a
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• pp.556-556
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• 2000

In the multi-purpose lathe, the design of tilting turret slide system has an important and critical role to enhance the accuracy of the machining process. Tilting turret unit is traveled by 3-axis slide systems. There is a need to design this part very carefully. In this research, the 3-axis slide system with tilting turret unit is researched with two approaches; The first is that 3-axis slide system is modeled and simulated using ADAMS software. The dynamic behavior of this system is visualized by data graphs and dynamic animations. The second is that the slide system is analyzed with the aspect of stress distribution. The slide system is modeled and displayed by PATRAN and analyzed by NASTRAN. The analysis of strain and stress distribution in the each node is prompted and visualized in the computer. The first step of virtual prototype which makes it possible to design economically and effectively is developed.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.10
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• pp.172-179
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• 1998

To quickly determine the effect of the substitute component on the machine's performance is very important in the design and manufacturing processes. And minimizing machine cost and maximizing machine quality mandate predictability of machine accuracy. In this study, in order to evaluate the effects of the component's geometric errors and dimensions on the machining accuracy of gantry-type 5-axis machining centers, a geometric error analysis and virtual manufacturing system are developed based on the mathematical model for the shape generation motion of machine tool considering the component's geometric errors and dimensions, the solid modeling techniques and so on.