Choong Sik Park

Simplified kinematic calibration for a class of parallel mechanism

Calibration methods and parameter estimation analyses of a class of parallel mechanisms are discussed in order to achieve a nano-modon stage applied in the machining of high quality optical devices. The paper includes mechanical structure of Delta type parallel mechanism, its kinematics analyses for calibration, two calibration methods and their comparisons in the aspects of parameter errors, final achieved accuracy and simple procedure. Exclusion of orientation data will be also discussed for the simplicity of measurements in the calibration procedure.

Fabrication of polymer cantilevers for force-controlled atomic force microscope

We developed the fabrication process of all-plastic cantilever for force controlled atomic force microscope. The force controlled atomic force microscope can prevent damage during the scanning of the soft sample. However it has a drawback in its stability. To stabilize the system the cantilever is required to have small Q factor. The negative photo resist for MEMS (SU-8) has ideal properties, micromachinability and small Q factor, for this purpose. Here we demonstrate the cantilever consists of tip, lever and base with same polyimide. The mold of the probing tip is the pyramidal pit pattern on silicon wafer formed by direct leaser writing and anisotropic etching of silicon. Other elements of the cantilever are formed by contact lithography. The photo mask is also fabricated by direct laser writing. By arranging the dimensions of the cantilever, we can control its spring constant and resonant frequency. For the spring constant of 0.1N/m and the first resonant frequency of 2kHz, the typical dimensions of the cantilever is 1030 x 300 x 7 μm3. The fabrication error in cantilever geometry was 1.5%. The estimated resonant frequency has a good agreement with the designed value.

Measurement by multidirectional interferometers of the position and orientation of a positioning stage

A multidirectional interferometer system is developed to determine the position and orientation of a stage moved in a two-dimensional (2-D) space. In this system four corner-cube prisms are mounted on the moving stage, and four laser beams are incident on the corner cubes in different directions. Moving distances in the observed directions are measured by laser interferometers. The position and orientation of the stage are calculated from the moving distances of the corner cubes. Some experiments are done on the 2-D moving stage with four interferometers, and measurement errors are estimated from redundant data. The estimated accuracy is higher than 0.2 microm for translation and 0.3 x 10(-3) deg for rotation for a measurement range of 0.5 mm and 0.5 deg.

Method for calibrating system parameters of a multidirectional interferometers system

A multidirectional interferometer system has been proposed and developed to measure the position and orientation of a positioning stage. In this method the system parameters, such as positions of the corner-cube reflectors and directions of the rays in the interferometers, must be determined beforehand. However, it is difficult to find ways to determine the system parameters for each different system with necessary accuracy. This paper proposes a systematic method for calibrating the system parameters when the number of the interferometers is larger than the degrees of freedom of the stage. The method is verified for a two-dimensional stage by both simulation and experiment.

Polymer micro cantilevers for force controlled atomic force microscopy 2 - Fabrication of cantilevers

The micro cantilever made of entirely plastic material has been developed. The probing tip, cantilever and base are made of same photo plastic. By arranging the geometry of the cantilever, its spring constant and resonant frequency is controlled. The low Q of the polyimide improves the stability of the force controlled atomic force microscope. The fabrication error in cantilever geometry was 1.5%. The estimated resonant frequency has a good agreement with the designed value.

Development of Three Dimensional Measuring System for Making Precise Patterns on Curved Surface Using Laser Drawing

Abstract A three dimensional measuring system for making precise patterns on curved surface by laser exposure is developed. A interferometer which has been used for two dimensional measurement is improved to measure the position and orientation of the moving stage in three dimensional space. The moving stage with several corner cube arrays can reflect laser beams in the large moving range for interference of the reference laser beam. Processing interference images in the three different directions can realize the three dimensional measurement. Singular value decomposition method is applied to design of parameters for isotropic measuring resolutions. Moreover, error analysis is performed to obtain tolerances of various mechanical errors.

Multilevel Computer Generated Hologram on a Curved Surface for High Power CO2 Laser Beam Shaping

A multilevel computer generated hologram (CGH) on a curved surface was developed for the laser beam shaping of a high-power CO2 laser. The CGH with eight height-levels was fabricated by direct-writing laser-beam lithography and the copper electroplating. The fabricated CGH changes a laser beam profile from a Gaussian distribution to a Rectangle-Gaussian distribution. The measured diffraction efficiency was 68%. When a steel surface was exposed to the shaped laser beam, a uniform melted zone was obtained. We investigated the melted zone with respect to the irradiated conditions experimentally.

Calibration method for parallel mechanism using micro grid pattern

This paper investigates a calibration of a parallel mechanism stage which is set up under the microscope. The calibration method uses the measurement data of the translation movement in the plane of the end-effector and rotation about the axis perpendicular to it using measurement method with the micro grid pattern. This paper discusses its calibration method with experiments for the stage constructed a fixed linear actuated parallel mechanism. The results show that the calibration using limited data is possible and has good performance

Fabrication of Multilevel Copper Computer Generated Hologram for High Power CO2 Laser Beam Shaping

A multilevel computer generated hologram (CGH) was fabricated for shaping a laser beam profile of a high-power CO2 laser. The surface relief has eight height levels with 0.94μm in step heights. A copper surface relief was formed on a flat copper substrate by electroplating with photo-resist masks. Standard deviation of the surface step height was less than 22% of the designed height. The CGH changes a CO2 laser beam of 14mm in diameter to a rectangular beam of 1mm×4mm and its diffraction efficiency was 69.2%. A 200W CO2 laser beam of 14mm in diameter did not damage the CGH surface.