• Proceedings of the Korean Society of Medical Physics Conference
• /
• 2002.09a
• /
• pp.74-82
• /
• 2002

In Intensity Modulated Radiotherapy (IMRT), radiation is delivered in a multiple of Multileaf Collimator (MLC) subfields. A subfield with a small leaf-to-leaf opening is highly sensitive to a leaf-positional error. We introduce a method of identifying and rejecting IMRT plans that are highly sensitive to a systematic MLC gap error (sensitivity to possible random leaf-positional errors is not addressed here). There are two sources of a systematic MLC gap error: Centerline Mechanical Offset (CMO) and, in the case of a rounded end MLC, Radiation Field Offset (RFO). In IMRT planning system, using an incorrect value of RFO introduces a systematic error ΔRFO that results in all leaf-to-leaf gaps that are either too large or too small by (2ㆍΔRFO), whereas assuming that CMO is zero introduces systematic error ΔCMO that results in all gaps that are too large by ΔCMO = CMO. We introduce a concept of the Average Leaf Pair Opening (ALPO) that can be calculated from a dynamic MLC delivery file. We derive an analytic formula for a fractional average fluence error resulting from a systematic gap error of Δ$\chi$ and show that it is inversely proportional to ALPO; explicitly it is equal to, (equation omitted) in which $\varepsilon$ is generally of the order of 1 mm and Δx=2ㆍΔRFO+CMO. This analytic relationship is verified with independent numerical calculations.

• 제어로봇시스템학회:학술대회논문집
• /
• 1997.10a
• /
• pp.375-378
• /
• 1997

This research deals with a problem of reconstructing 3D surface structures from their 2D projections, which is an important research topic in computer vision. In order to provide robust reconstruction algorithm, that is reliable even in the presence of uncertainty in the range images, we first present a detailed model and analysis of several error sources and their effects on measuring three-dimensional surface properties using the space encoded range imaging technique. Our approach has two key elements. The first is the error modeling for the space encoding range sensor and its propagation to the 3D surface reconstruction problem. The second key element in our approach is the algorithm for removing outliers in the range image. Such analyses, to our knowledge, have never attempted before. Experimental results show that our approach is significantly reliable.

• International Journal of Control, Automation, and Systems
• /
• v.3 no.3
• /
• pp.469-476
• /
• 2005

Performance of a force-torque sensor is affected significantly by an error signal that is included in the sensor signal. The error sources may be classified mainly into two categories: one is a structural error due to inaccuracy of sensor body, and the other is a noise signal existing in sensed information. This paper presents a principle of 6-axis force-torque sensor briefly, a double-hole structure to be able to improve a structural error, and then a signal conditioning to reduce the effect of a noise signal. The validity of the proposed method is investigated through experimental study, which shows that SIN ratio is improved significantly in our experimental setup, and the sensor can be implemented cheaply with reasonable performance.

• Journal of Institute of Control, Robotics and Systems
• /
• v.7 no.11
• /
• pp.953-957
• /
• 2001

This paper is concerned with a transfer alignment method for the SDINS under ship motions. Major error sources of transfer alignment are data transfer time-delay, lever-arm velocity and ship body flexure. Specifically, to reduce alignment errors induced by measurement time-delay effects, the error compensation method through delay state augmentation is suggested. A linearized error model for the velocity and attitude matching transfer alignment system is first derived by linearizing the nonliner measurement equation with respect to its time delay and augmenting the delay state into the conventional linear state equations. And then it is shown via observability analysis and computer simulations that the delay state can be estimated and compensated during ship motions resulting in considerably less alignment errors.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.11 no.3
• /
• pp.48-54
• /
• 2012

This paper introduces the kinematic calibration method to improve the positioning accuracy of a parallel mechanism. Since all the actuators in the parallel mechanism are controlled simultaneously toward the target position, the volumetric errors originated from each motion element are too complicated. Therefore, the exact evaluation of the error sources of each motion element and its calibration is very important in terms of volumetric errors. In the calibration processes, the measurement of the errors between commands and trajectories is necessary in advance. To do this, a digitizer was used for the data acquisition in 3 dimensional space rather than arbitrary planar error data. After that, the optimization process that was used for reducing the motion errors were followed. Consequently, Levenberg-Marquart algorithm as well as the error data acquisition method turned out effective for the purpose of the calibration of the parallel mechanism.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2001.11a
• /
• pp.73-78
• /
• 2001

Main sources of the vibration of a gear-pair system are backlash and transmission error. This paper investigates the dynamics of a gear-pair system involving backlash and transmission error. This paper presented 4 types of gear motions due to the existence of a backlash. The solutions are calculated using a multiple-time scale method and numerically. The results shows the existence of 4 type motions, jump phenomenon, and chaotic motion consequently the design of gear driving system with low vibration and noise requires the study on the effects of transmission error and backlash, i.e. nonlinearities in gear driving system.

• Proceedings of the KSME Conference
• /
• 2000.04a
• /
• pp.411-414
• /
• 2000

Optical Triangulation Probes (OTPs) are widely used for their simple structure. high resolution, and long operating range. However, errors originating from speckle, inclination of the object, source power fluctuation, ambient light, and noise of the detector limit their usability. In this paper, we propose new design criteria for an error-reduced OTP. The light source module for the system consists of an incoherent light source and a multimode optical fiber for eliminating speckle and shaping a Gaussian beam Intensity profile. A diffuse-reflective white copy paper, which is attached to the object, makes the light intensity distribution on the change-coupled device(CCD). Since the peak positions of the intensity distribution are not related to the various error sources, a sub-pixel resolution signal processing algorithm that can detect the peak position makes it possible to construct an error-reduced OTP system

• 제어로봇시스템학회:학술대회논문집
• /
• 2000.10a
• /
• pp.486-486
• /
• 2000

This paper is concerned with a transfer alignment method for the SDINS(StrapDown Inertial Navigation System) under ship motions. Major error sources of transfer alignment are data transfer time-delay, lever-arm velocity and ship body flexure. Specifically, to reduce alignment errors induced by measurement time-delay effects, the error compensation method through delay state augmentation is suggested. A linearized error model for the velocity and attitude matching transfer alignment system is first derived by linearizing the nonlinear measurement equation with respect to its time delay and augmenting the delay state into the conventional linear state equations. And then it is shown via observability analysis and computer simulations that the delay state can be estimated and compensated during ship motions resulting in considerably less alignment errors.

• Journal of Aerospace System Engineering
• /
• v.10 no.1
• /
• pp.95-102
• /
• 2016

There are many possible disturbance sources on such a spacecraft, but reaction wheel assembly (RWA) which is generally used for spacecraft attitude control is anticipated to be the largest. These effects on degradation of performance of spacecraft such as attitude stability. In reaction wheel, disturbance caused by imbalance and speed error. It is hard to emulate speed error disturbance because it is not coincide with wheel frequency. This paper concentrates on emulating and analyzing the speed error disturbance. Firstly, classify the causes that lead to speed error disturbance which generate RPM fluctuation. Secondly, simulated with disturbance driver module and reaction wheel assembly which are developed by Spacecraft Control Lab. Experimental investigations have been carried out to test the disturbance emulator module as a disturbance generator for RWA. Measurements and test have been conducted on various fault. Frequency analysis of test data show that speed error disturbance effects on wheel settling wheel speed or fluctuation type.

• Journal of the Optical Society of Korea
• /
• v.15 no.3
• /
• pp.222-226
• /
• 2011

We demonstrated the feasibility of an amplified wavelength-division multiplexed passive optical network (WDM-PON) architecture based on broadband light source (BLS) seeded optical sources and a novel bidirectional reach extender. Our bidirectional reach extender could provide an amplification of both downstream and upstream signals as well as a BLS output for the upstream WDM signal generation. An error-free 1.25 Gb/s signal transmission over a 100-km long single-mode fiber was achieved in a bidirectional WDM-PON using BLS seeded reflective semiconductor optical amplifier (RSOA) sources.