• Journal of the Korean Society for Precision Engineering
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• v.27 no.6
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• pp.7-16
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• 2010

Physical fundamentals of ultrashort femtosecond lasers are addressed along with emerging applications for precision manufacturing and metrology. Femtosecond lasers emit short pulses whose temporal width is in the range of less than a picosecond to a few femtoseconds, thereby enabling extremely high peak-power machining with less thermal damages. Besides, the broad spectral bandwidth of femtosecond lasers constructed in the form of frequency comb permits absolute distance measurements leading to ultraprecision positioning control and dimensional metrology.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.3
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• pp.323-329
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• 2011

Certified reference materials (CRMs) have been used to calibrate surface profilers for reliable measurements. In this paper, we present a newly designed step height CRM which has a step height pattern with two different widths and various special patterns for checking radial magnification, distortion of optical viewing systems, etc. Especially, it could be useful for multi-probe inspection instruments in the manufacturing lines. The fabrication was done by conventional optical lithography and dry etching process with optimized conditions. To verify the step height values, a white-light scanning interferometer was used with objective lenses having magnification of $10{\times}$ and $100{\times}$. CRMs with nominal step heights of $0.5\;{\mu}m$, $1\;{\mu}m$, $3\;{\mu}m$, $5\;{\mu}m$, $7\;{\mu}m$, and $10\;{\mu}m$ were fabricated and the uniformity of these CRMs was evaluated to be less than 3 nm ($1{\sigma}$).

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.10a
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• pp.541-542
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• 2006

• International Journal of Precision Engineering and Manufacturing
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• v.9 no.4
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• pp.32-38
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• 2008

This paper describes a fast tool control (FTC)-based diamond turning process for fabricating large-area high-quality micro-lens arrays. The developed FTC unit has a stroke of $48{\mu}m$ and a resonance frequency of 4.9 kHz. Micro-lens arrays were fabricated using a micro-cutting tool with a nose radius of $50{\mu}m$. The FTC unit was integrated with a force sensor so that the initial position of the micro-cutting tool with respect to the workpiece surface could be detected through monitoring the contacting force. The length and depth of the designed parabolic micro-lens profile were $190{\mu}m$ and $20{\mu}m$, respectively. A micro-lens array was fabricated on a cylinder surface over an area of ${\phi}55 mm{\times}40 mm$.

• Journal of the Korean Society for Precision Engineering
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• v.24 no.6
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• pp.96-104
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• 2007

Calibration of the spring constants of atomic force microscopy (AFM) cantilevers is one of the issues in biomechanics and nanomechanies for quantified force metrology at pieo- or nano Newton level. In this paper, we present an AFM cantilever calibration system: the Nano Force Calibrator (NFC), which consists of a precision balance and a one-dimensional stage. Three types of AFM cantilevers (contact and tapping mode) with different shapes (beam and V) and spring constants (42, 1, 0.06 N $m^{-1}$) are investigated using the NFC. The calibration results show that the NFC can calibrate the micro cantilevers ranging from 0.01 ${\sim}$ 100 N $m^{-1}$ with relative uncertainties of less than 2%.

• Journal of the Korean Society for Precision Engineering
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• v.32 no.2
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• pp.185-190
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• 2015

This paper presents a new method to determine sensitivity coefficients of temperature and humidity of torque transducers by using a natural and seasonal variation of ambient conditions at the laboratory. We had measured the sensitivities of the torque transducers over almost one year using the KRISS 2 kN m torque standard machine. The sensitivity data acquired at various ambient conditions were processed using our measurement model to extract the sensitivity coefficients of temperature and humidity simultaneously with high precision. A comparison with a previous method using an environmental control chamber was carried out to test the feasibility of using our new method. Two results agreed within the uncertainty. We revealed that the torque measuring errors could be 8 times higher than the measurement and calibration capability of KRISS torque standard machine if the sensitivity changes due to the temperature and humidity are not properly corrected during a calibration.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2013.05a
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• pp.1075-1076
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• 2013

• Journal of the Korean Society for Precision Engineering
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• v.18 no.1
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• pp.9-11
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• 2001

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.674-677
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• 2003

This work presents a method of point-to-surface assignment for 3D inspection of solder pastes on PCB. A bounding box enclosing the solder paste tightly on all sides is introduced to avoid incorrect point-to-surface assignment. The shape of bounding box for solder paste brick is variable according to geometry of measured points. The surface geometry of the bounding box is obtained by using five peaks selected from the histogram of normalized gradient vectors for measured points. By using the bounding box enclosing the solder paste. the task of point-to-surface assignment is successfully executed. Subsequently, the geometrical features are obtained via surface fitting.

• Journal of Positioning, Navigation, and Timing
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• v.5 no.2
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• pp.67-74
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• 2016

In this paper, time comparison is performed with standardization institution in Japan using a Two-Way Satellite Time and Frequency Transfer (TWSTFT) technique as one of the methods for high precision time comparison. To analyze the performance of time comparison in the TWSTFT method, time comparison results via the Global Positioning System (GPS) code and carrier wave are analyzed. Through the time comparison performance, frequency stability is analyzed using modified Allan deviation and by this result, characteristics of time comparison of the TWSTFT that is utilized in international time comparison are presented.