• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.16 no.2
• /
• pp.88-93
• /
• 2017

Due to the requirement of the development of the precision manufacturing industry, the accuracy of machine tools has become a key issue in this field. A critical factor that affects the accuracy of machine tools is the feed system, which is generally driven by a ball screw. Basically, to improve the performance of the feed drive system, which will be thermally extended lengthwise by continuous usage, a thermal error compensation system that is highly dependent on the feedback temperature or positioning data is employed in the machine tool system. Due to the overdependence on measuring technology, the cost of the compensation system and low productivity level are inevitable problems in the machine tool industry. This paper presents a novel feed drive thermal error compensation system method that could compensate for thermal error without positioning or temperature feedback. Regarding this thermal error compensation system, the heat generation of components, principal of compensation, thermal model, mathematic model, and calculation method are discussed. As a result, the test data confirm the correctness of the developed feed drive thermal error compensation system very well.

• International Journal of Precision Engineering and Manufacturing
• /
• v.4 no.3
• /
• pp.20-27
• /
• 2003

Compensation of probe radius is required for accurate measurement in metal working industry. Compensation involves correctly measuring data on the surface in the amount of radius of the touch probe with a Coordinate Measuring Machine (CMM). Mechanical parts with free-formed curves and surfaces are complex enough so that accurate measurement and compensation are indispensable. This paper presents necessary algorithms involved in the compensation of the probe radius for free-formed curves and surfaces. Application of pillar curve is the focus for the compensation.

• KIPS Transactions on Software and Data Engineering
• /
• v.6 no.6
• /
• pp.321-328
• /
• 2017

We have implemented a technique to correct the brightness, saturation, and contrast of an image according to the degree of light, and further compensate the backlight. Backlight compensation can be done automatically or manually. For manual backlight compensation, we have to select the region of interest (ROI). ROI can be selected by connecting the outline of the desired object. We make users select the region delicately with the new magnetic lasso tool. The previous lasso tool has a disadvantage that the start point and the end point must be connected. However, the proposed lasso tool has the advantage of selecting the region of interest without connecting the start point and the end point. We can automatically obtain various results of backlight compensation by adjusting the number of k-means clusters for texture extraction and the threshold value for binarization.

• Journal of Broadcast Engineering
• /
• v.13 no.3
• /
• pp.401-410
• /
• 2008

Multiview Video Coding contains a macroblock-based illumination compensation tool which can compensate the variations of illuminations according to view or temporal directions. Thanks to illumination compensation tool, the coding efficiency of Multiview Video Coding has been enhanced. However illumination compensation tool also generates additional subjective drawbacks of the blocking artifacts due to macroblock-based compensations of mean values. A deblocking filtering method for Multiview Video Coding which is the same as in H.264/AVC does not consider illumination difference between the illumination compensated blocks, thus it can not effectively eliminate the blocking artifacts. Therefore, this paper analyzes the phenomena of blocking artifacts caused by illumination compensation and proposes a method which can effectively eliminate the blocking artifacts with the minimum changes of the H.264 deblockding filtering method. In the simulation results, it can be easily found the blocking artifacts are clearly eliminated in the subjective comparisons, and the average bit-rate reduction is up to 1.44%.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1997.04a
• /
• pp.297-302
• /
• 1997

Linear displacement accuracy is one of the most important factors that determine machine tool accuracy. The laser interferometer has been usually recommended for the measurement of linear displacement accuracy. In this paper, microcomputer aided measurement and compensation system has been developed forthe pitch error in a CNC machine tool. For accurate pitch error calculation, the analysis code for the pitch error has been also implemented according to the international standards(ISO). The PC based automatic compensation system for the pitch error is also implemented. A new algorithm for calculating optimum value for pitch error compensation is proposed, minimizing the deviation at each target points. The development system has been applied to a practical CNC maching center and the performance has been demonstrated.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 1998.03a
• /
• pp.148-153
• /
• 1998

In order to control thermal deformation of machine origin of machine tools due to internal and external heat sources, the real-time compensation system has been developed. First, GMDH models were constructed to estimate thermal deformation of machine origin for a vertical machining center through the measurement of deformation data and temperature data of specific points on the machine tool. Thermocouples and gap sensors are used respectively for measurement. These models are nonlinear equations with high-order polynomials and implemented in a multilayered perceptron type network structure. Secondly, work origin shift method were developed by implementing digital I/O interface board between CNC controller and IBM-PC. The work origin shift method is to shift the work origin by the compensation amounts which is calculated by pre-established GMDH model. From the experimental result, thermal deformation of machine origin was reduced to below $\pm$5${\mu}{\textrm}{m}$.

• Journal of the Semiconductor & Display Technology
• /
• v.20 no.4
• /
• pp.141-145
• /
• 2021

The brightness of the Organic Light Emitting Diode (OLED) display is controlled by thin-film transistors (TFTs). Regardless of the materials and the structures of TFTs, an OLED suffers from the instable threshold voltage (V_th) of a TFT during operation. When designing an OLED pixel with circuit simulation tool such as SPICE, a designer needs to take V_th shift into account to improve the reliability of the circuit and various compensation methods have been proposed. In this paper, the effect of the compensation circuits from two typical OLED pixel circuits proposed in the literature are studied by the transient simulation with a SPICE tool in which the stretched-exponential time dependent V_th shift function is implemented. The simulation results show that the compensation circuits improve the reliability at the beginning of each frame, but V_th shifts from all TFTs in a pixel need to be considered to improve long-time reliability.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2010.11a
• /
• pp.115-116
• /
• 2010

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 2002.10a
• /
• pp.417-422
• /
• 2002

One of the major limitations of productivity and quality in metal cutting is the machining accuracy of machine tools. The machining accuracy is affected by geometric errors, thermally-induced errors, and the deterioration of the machine tools. Geometric and thermal errors of machine tools should be measured and compensated to manufacture high quality products. In metal cutting, the machining accuracy is more affected by thermal errors than by geometric errors. In this study, the compensation device and temperature-based algorithm have been implemented on the machining center in order to compensate thermal error of machine tools under the real-time. The thermal errors are predicted using the neural network and multi-regression modeling methods. In order to compensate thermal characteristics under several operating conditions, experiments performed with five gap sensors and manufactured compensation device on the horizontal machining center.

• Journal of Electrical Engineering and Technology
• /
• v.6 no.2
• /
• pp.147-153
• /
• 2011

This paper proposes a methodology using a tool based on the branch-parameter continuation power flow (BCPF) in order to restore the power flow solvability in unsolvable contingencies. A specified contingency from a set of transmission line contingencies is modeled, considering the transient analysis and practice in the Korean power system. This tool traces a solution path that satisfies the power flow equations with respect to the variation of the branch parameter. At a critical point, in which the branch parameter can move on to a maximum value, a sensitivity analysis with a normal vector is performed to identify the most effective compensation. With the sensitivity information, the location of the reactive power compensation is determined and the effectiveness of the sensitivity information is verified to restore the solvability. In the simulation, the proposed framework is then applied to the Korean power system.