Ki-hwan Kwon

Development of a coordinate measuring machine (CMM) touch probe using a multi-axis force sensor

Traditional touch trigger probes are widely used on most commercial coordinate measuring machines (CMMs). However, the CMMs with these probes have a systematic error due to the shape of the probe tip and elastic deformation of the stylus resulting from contact pressure with the specimen. In this paper, a new touch probe with a three degrees-of-freedom force sensor is proposed. From relationships between an obtained contact force vector and the geometric shape of the probe, it is possible to calculate the coordinates of the exact probe–specimen contact points. An empirical model of the probe is applied to calculate the coordinates of the contact points and the amount of pretravel. With the proposed probing system, the measuring error induced by the indeterminateness of the probe–specimen contact point and the pretravel can be estimated and compensated for successfully.

Development of a precision indentation and scratching system with a tool force and displacement control module

This article presents a tip-based micropatterning system with a precision device for measuring the machine force and the tool path. The machine force is obtained by a tool control module with a leaf spring and a capacitive displacement sensor. It is controlled to provide a force that ranges from 80 microN to 8 N. The force sensing unit, which is part of the module, is mounted on a PZT (PbZrTi) driven in-feed motion stage with a resolution of 1 nm. The work piece is set on an X-Y motion stage, and the position can be controlled with a tool path accuracy of 5 nm. Micropatterning and precision indentation experiments were performed, while the machined surfaces were examined by atomic force microscopy. From these results, the feasibility of the system for precise force-displacement control was verified for application in tip-based precision machining.

A highly sensitive multi-dimensional motion measurement system using a spherical reflector

A new measurement system is proposed that can detect three-degree-of-freedom (three-DOF) translational motions of an object with high sensitivity. Its measurement method is based on an optical lever technique using a spherical reflector. The spherical reflector is mounted on an object whose motion is to be measured. It reflects each laser beam, generated from two laser sources, in two different directions, depending on the motion of the object of interest. The reflected beam is then detected by two PSDs. Since each PSD is a two-dimensional sensor, the information on the 3D position of the spherical reflector can be acquired, thus enabling us to measure the three-DOF translational motions of the object. The relationship between the 3D position of the spherical reflector and the outputs of two PSDs is modelled through ray tracing. To verify the principle and effectiveness of the proposed method, a series of experiments were performed and the performance indices were evaluated, such as sensitivity, resolution, measurement error and crosstalk. In experiments, the resolution of each sensing direction is approximately 0.16 µm and the measurement error and crosstalk between sensing channels are within ±0.1 µm. The experimental results show that the proposed system can be an effective means of measuring three-DOF translational motions of arbitrary objects with high sensitivity.

Chip-On-ACB (Anodized Circuit Board) Package for High Power Light-Emitting Diode

A new light-emitting diode (LED) package module based on anodized circuit board (ACB) is developed in this study. ACB represents the selectively anodized aluminum board, in which the aluminum oxide layer, formed by anodizing process, serves as a dielectric layer and the electric signal lines are formed on it. LED chips can be directly attached to the metal pads on the aluminum core of ACB, which acts as p-electrode and at the same time easily spreads out the heat generated from the chips. The use of ACB in LED packaging has the benefit that ACB provides an excellent heat dissipation path from junction to board. This characteristic cannot be obtained from metal-core printed circuit board (MC-PCB), because it inevitably has a dielectric layer for electrical insulation of signal lines from metal base, which acts as a blocking layer in the heat path. By using the thermal transient method, the thermal resistance of the LED package (from junction to board) is measured to be about 4 °C/W. Also, we have performed...