Papers by Author: Byung Oh Choi

Abstract: This paper shows the performance analysis of a sealless cylinder with a conical type piston and one of three types of rod bearings. The piston without seal is composed of cylindrical and conical portions in the axial direction. The 2D Reynolds equation is solved with a finite difference method for the performance analysis. The relationship between self-centering force and leakage flow rate are investigated. The sealless cylinder fabricated with the proposed optimum design values was tested with three different types of rod bearings having four, five and six pockets respectively. Leakage flow rate tests were conducted to evaluate the performance of the proposed sealless cylinder.

Abstract: This paper presents a computer-based tracking control approach for a piezoelectric actuator based on incorporating a feedforward loop with a PID feedback controller. The purpose of this paper is to improve the hysteresis characteristics of a stack type piezoelectric actuator using the hysteresis nonlinearity compensator. The system proposed in this study prints by spraying the molten metal, and consists of a nozzle, heating furnace, operating actuator, and an XYZ 3-axis stage. As an operating system, the piezoelectric(PZT) method has very valuable uses. The PZT actuator, however, has a hysteresis nonlinearity due to the ferroelectric characteristics of the PZT element. This causes problems in the system position control characteristics and deteriorates the performance of the system. This study proposed a inverse hysteresis model, a mathematic modeling method that can express the geometric relationship between voltage and displacement, in order to reduce the hysteresis of the PZT actuator. In addition, system identification and PID control methods were examined. Also, it was confirmed that the proposed control strategy gives good tracking performance.

Abstract: This paper presents the design, fabrication, and performance test of a gap adjustable piezoelectrically-actuated DoD(drop-on-demand) molten metal injector for application to the 3D microstructure manufacturing or printed electronics. In the design process, we propose the gap adjustable mechanism of the piezoelectrically-actuated inkjet system to control the volume and velocity of the ejected molten metal droplets. In the experimental process, we fabricate the DoD metal injector and measure the volumes and velocities of the ejected droplets for molten metal as well as pure water to compare the ejecting performance for the different viscosity of ink and the operating temperature of the system.

Abstract: In order to develop more elaborate and speedy system for large objects than existing selective laser sintering (SLS), this study applies a new selective dual-laser sintering process. It contains a 3-axis dynamic focusing scanner system for scanning large area instead of the existing fθ lens. As sintering parameters, the sintering temperature, the laser beam power and the layer thickness have a great influence on sintering of the polymer and metal powder. This paper will address the development of a solid freeform fabrication (SFF) system employing the dual laser system. Experiments were performed to evaluate the effect of a scanning path and to fabricate the large-sized object.