Sungbok Kang

A 3 DOF Model for an Electromagnetic Air Mount

A 4 × 4 matrix model with three degrees of freedom is proposed as a means for controlling microvibrations and applied to an electromagnetic isolator. The model was derived from an assumption based on small- and low-frequency vibrations. The coordinates of the 3 DOF was composed of the 4 variables, representing a vertical position, pitch, roll, and a proof term. The coordinates were calculated from the 4 position sensors in the isolator and formulated into a 4 × 4 matrix, which possesses inversive full rank. The electro-magnetic isolator was built for a simulated machine in semiconductor manufacturing and consisted of a heavy surface plate, sensors, amps, a controller, and air springs with electromagnets. The electromagnets are installed in a pneumatic chamber of the individual air spring. The performance of the 3 DOF model was experimented and compared with that of a 1 DOF model in an impact test. The settling time in the result was reduced to 25%.

Automatic focus control for assembly alignment in a lens module process

This study proposes an auto focusing method for multi-focus images in assembling lens modules in digital camera phones. A camera module in a camera phone is composed of a CCD sensor, an IR glass, a lens and a PCB board. The alignment of the components is one of the most important factors in determining the product quality. Auto-focus is essential to adjust the image quality of the IR glass, but there are two focal points in the captured image, due to the thickness of the IR glass. Therefore, the sharpness, probability and scale factor are used to find the desired focus from a multi-focus image. The sharpness is defined as the clarity of the image. The variation of the probability and scale factors are analyzed to find the focus after pattern recognition with a registered image. The presented algorithm was applied to a lens assembly machine which has 5 axes, two vacuum chucks and an inspection system. The desired focus can be determined on the local maximum of the sharpness, the probability and the scale factor in the experiment.

A 3 DOF model for an electro magnetic air mount

A model with three degrees of freedom is proposed as a means for controlling for controlling micro vibrations in semiconductor manufacturing. The model was derived from an assumption based on small and low frequency vibrations. The coordinates of the 3 DOF was composed of a vertical position, pitch, roll and a proof term. The coordinates of the 4 variables can be calculated from the 4 positions in an isolator. This coordinate can be written as a 4 × 4 matrix, which possesses inversive full rank. The proposed algorithm was applied to an electro-magnetic isolator. The active isolator consisted of a heavy surface plate, sensors, electro-magnetic actuators, amps, air springs and a DSP controller. The electro-magnetic actuator was installed in a pneumatic chamber of the individual air spring. The active isolator was experimentally used as a base structure under the semiconductor manufacturing machines. The performance of the 3 DOF model was compared with that of a 1 DOF model in an impact test. The settling time was reduced to 25% in the experiment.

Optical distance control for a multi focus image in camera phone module assembly

Camera phones are very popular these days and mass production is essential for manufacturing the camera modules used in the phones. This study aims at developing a focusing method for use in the camera module assembly process. The camera module is composed of small components and machine vision is necessary to align them before their assembly. The inspected images usually have multiple areas with different focal distances, due to the different thicknesses of the components. Sharpness is the evaluation of focus, calculated by determining its absolute derivative and used for determining the focal point. A dynamic focus region(DFR) is defined to find the object of interest to be focused on. The DFR is built from the edge fragments detected using several narrow ROIs across the vision screen. An assembly machine was constructed to attach lens mounts to a PCB for the experiment. The distance between the lens mount and vision camera was adjusted to find the focus position by means of the sharpness and DFR. The result shows that the desired object is brought into focus and the proposed method can be applied to the camera module assembly process.

The new insertion method of liquid powders using the electrode array for e-paper applications

In this paper, the new particle insertion method was proposed and experimentally demonstrated. In the proposed method, the electrode array was adopted to insert the liquid powders into each cell of the liquid powder display panel. The each electrode pattern size was 140 times 140 mum and the size of the electrode pattern array was fabricated on the glass wafer. The each square cell size of the base panel was 220 times 220 mum and the width of the rib on the panel was 20 mum. The voltage range applied to the electrode array was about from 0 to 600 V DC. To monitor the operation characteristics of the liquid powder under the various applied voltage conditions, the computer vision system was also used. The experimental results showed the strong capability of the noble method to manipulate the charged tiny particles for the mass production applications of the e-paper.

Quick Light-Mixing for Image Inspection Using Simplex Search and Robust Parameter Design

Finding the optimal illumination conditions for industrial machine vision is iterative and time-consuming work. This study discusses simplex search for automatic illumination and the Taguchi method for algorithm tuning. The simplex search could find the illumination inputs to obtain a fine image, but the degree of fineness and processing time varied according to the algorithm parameters. The mechanism from the inputs and the degree of fineness were complex and nonlinear, so it was hard to find the best parameters through conventional experiments. To address these issues, the Taguchi method was applied to the simplex search and used to figure out the best parameter combination with a minimum number of experiments. The targets of Taguchi analysis were finer images and fewer iterations. An L 25(55) orthogonal array was constructed for 5 parameters and 5 levels, and was filled with the experimental results. A new combination of parameters determined by Taguchi analysis was applied to retests. The retest results showed fewer iterations with a fine image that was close to the best case. The Taguchi method can reduce the amount of work required to set parameters for optimal illumination.

A dual wafer prealigner and a multiple level structure

The purpose of this study is to examine the means by which multiple wafers may be aligned in order to reduce wafer handling time in wafer processes. We designed a multilevel structure for a prealigner which can simultaneously handle multiple wafers within a system. The system consists of gripping parts, kinematic parts, vacuum chucks, pneumatic units, hall sensors and a DSP controller. The procedure through which the wafers were aligned consists of two steps: mechanical gripping and notch finding. The first step comprises aligning a wafer along the XY direction using 4-point mechanical contact. The rotational error can be found by detecting a signal in the notch using hall sensors. A dual prealigner was designed for 300mm wafers and constructed for a performance test. The accuracy was monitored by checking the movement of a notch in a machine vision which is separated from the prealigner. The result indicates that the dual prealigner exhibits sufficient performance comparable to existing commercial products.

The Embedded Vision System for Portable Applications

Abstract A simple and cost-effective time switching method is to connect two camera modules into one camera interface port. The suggested embedded vision system is implemented and the image taken as expected. The design requirements for the hardware and the device driver are also considered. The captured image quality proves our suggestion could be a good candidate for two camera interface solutions without using complicated DSPs or FPGAs.

The simple and practical variable optical attenuator using a piezoelectric sheet containing an optical fiber

In this letter, we proposed a new method for a variable optical attenuator (VOA) through controlling a mechanical misalignment between 2 single mode fibers using a piezoelectric sheet. A piezoelectric sheet with 3 electrodes is adopted in our proposed structure. We can change amount of the bend of the PZT sheet by controlling the applied voltage on the inner electrode of the PZT sheet, which causes the optical loss to be dependent on the applied voltage. The numerical analysis about the optical loss related to the various mechanical offsets is also investigated. From our experimental results, the dynamic range of the proposed structure is about from 0 to 56 dB when the applied voltage range is from 0 to 22V DC. In our previous work using the piezoelectric tube, the dynamic range is about from 0 to 25dB when it is from 0 to 600V DC. The required voltage to get the same attenuation is dramatically reduced. It can make it more practical in the optical communication field.

Design and analysis of a rotor type magneto-rheological fluid brake and clutch

This study focuses on the design and analysis of a Rotor type magneto-rheological fluid (MR Fluid) brake and clutch. The brakes braking torque and the clutchs torque output can be easily controlled by adjusting the MR fluid and the configuration of Rotor. Electromagnetic finite element analysis(FEA) is performed, using FEMLAB software of the COMSOL Group, to find out the optimization conditions for the design of the Rotor type MR Fluid clutch and brake. In this paper, the design method of the Rotor type MR Fluid brake and clutch is investigated theoretically. The equation of the torque transmitted by the MR fluid within the Rotor type brake and clutch is derived to provide the theoretical foundation in the rotor design of the brake and clutch. The output torque values are recorded for different input velocities and applied magnetic fields, and the experimental results are compared with the theoretical results. Theoretical and experimental analyses have illustrated that this Rotor type MR fluid brake and clutch can transfer high controllable torques with a very fast time response. It was demonstrated that the Rotor type MR fluid clutch and brake have a strong capability of transmitting and isolating the high torque.