Guang Shen Xu

Investigation of UV Light Intensity Distribution of Integral Micro-Stereolithography System

The non-uniformity distribution of UV light intensity in the imaging plane of integral micro-Stereolithography (µSL) System will induces serious distortion of object in building process, and the building accuracy of the SL system can not be assured. To obtain uniformity distribution of UV light intensity, experimental investigations were performed to research the relationship of UV light intensity with position (x,y) in the imaging plane and gray-scale z of the pattern in the integral µSL System. Based on the experiment results, the model of UV light intensity was established with least squares method. According to the model, for a given point in the imaging plane of the µSL system, the UV light intensity can be changed with varying the gray-scale of the pattern. As a result, Uniformity UV light intensity distribution is obtained in the imaging plane, and the difference between maximum and minimum value of UV light intensity is 0.06µW/cm2. The uniformity UV light intensity distribution provides a foundation for building accurate microstructures with the µSL system.

Research of Micro-Stereolithography System with Dynamic Pattern Generator

In order to fabricate micro/meso structures, a novel micro-stereolithography (SL) system with dynamic pattern generator using digital micro-mirror device (DMD) has been investigated. The micro-stereolithography system solidifies photo-sensitive resin with image mask generated by dynamic pattern generator. The micro-stereolithography system is made up of dynamic pattern generator, recoating system and control system. The dynamic pattern generator consists of parabolic concentrator, UV lamp, collimating lens, shutter, DMD and its control, lens and computer. UV light intensity distribution in the imaging plane is investigated. Uniformity UV light intensity distribution is obtained in the imaging plane with changing small area’s gray-scale, and the difference between maximum and minimum value of UV light intensity is 0.4µW/cm2. Small size parts with intricate microstructures have been fabricated with the novel SL system. Compared with laser scanning SL system, the advantage of the novel micro-SL system is that the new SL system can build small objects having micro-structures with low cost in shorter time. The novel micro-SL system provides a solution to the problem that has hampered the progress of SL process into high resolution with low cost.

Research of the Liquid Level Detection System for Integral Stereolithography System

To improve the dimension accuracy of integral stereolithography (SL) system, the resin liquid level in SL system need controlled. Based on the measuring principle of laser triangulation, a laser liquid level detection system for SL system has been developed. The laser liquid level detection system consists of light source, Position Sensitive Detectors (PSD), PSD signal processing circuit and data acquisition system. According to the principle that electrical signal of PSD changes when resin liquid level vary, a PSD is employed to detect the liquid level height in the liquid level detection system. Confirmation experiment is conduct to test the accuracy of the detection system, and the experiment results indicated that deviation is 0.34% in the range of 6mm, and satisfy the accuracy requirement of integral SL system.

Optimizing Build Parameters for Integral Stereolithography System

To improve the dimension accuracy, an experimental investigation has been conducted to determine the optimum build parameters of integral stereolithography (SL) system with Taguchi method. The build parameters include shrinkage compensation factor of resin (factor A), liquid surface waiting time (factor B), exposure time (factor C) and light intensity (factor D). It was found that factor A, factor B, factor D and the interaction between factor A and factor D significantly affect the dimension accuracy, and the interaction between factor A and factor B, the interaction between factor A and factor D also have effects on the dimension accuracy. The optimum factors combination of the integral SL system is concluded by using ANOVA. With the optimum factors combination, an error of ±10μm has been reached using the integral SL system. Confirmation experiment results indicated that the dimension accuracy has been significantly improved with the optimum factors combination

Research of Mask Image’s Generation Based on STL Model for Integral Stereolithography System

To solve the problem that generation of mask image based on STL model for integral Stereolithography System, a novel method that can generate mask image based on STL model for integral Stereolithography System is proposed. Firstly, contour data is obtained with STL model slicing software; then properties of contour loop’s internal and external are determined; and then the order of contour loop’s filling is determined; Lastly, the contour loop is filled with the order, and mask image based on STL model can be produced. Generation of mask image is implemented with VC++6.0. The verification result indicates that this method can fill multiple nested contour loops correctly and generate correct mask image for integral Stereolithography System.

Applied Technology in Generation of Image Mask for Integral Stereolithography with Scanning Line Algorithm

To resolve the problem of low scanning conversion efficiency when great data of nested cross-section contours is processed for implement of mask image in integral stereolithography (SL), a novel method for implement of the mask image with improved scanning line algorithm is proposed in this paper. The improved scanning line algorithm processes the scan conversion only in an Edge Table (ET), and the singularity problem also can be solved with the improved algorithm. The novel algorithm can process nested contour loops and generate correct mask image for integral SL system. The new method of implement of the mask image provides a new solution for integral SL system to build objects with high accuracy.

Distortion Correction of Image in Integral Stereolithography System

There is geometric distortion of image in integral Stereolithography (SL) system, and the geometric distortion will influence the building accuracy of the SL system. To improve the building accuracy of the SL system, researches of distortion correction of image in the SL system are carried out. The distortion model of binary cubic polynomial interpolation is established with least-square method. The gray scale rebuilding is implemented with space-variable linear interpolation by using VC++6.0. The experimental results indicate that the geometric distortion of the image in integral SL system has been eliminated remarkably, and the radial RMS error is 0.96 pixels. The research lays a foundation for improving building accuracy of the integral SL System.

Investigation of Solidification Characteristics of Resin for Integral Stereolithography System

Photo-curable resin’s solidification under beam exposure in integral stereolithography (SL) is a dynamic process. Firstly, the up-part in photo-curable resin solidifies after absorbing enough energy; and then with the beam exposure, after the beam penetrates the solidified resin, the liquid resin under solidified resin have the opportunity to be cured. But the model which describes the solidification characteristics for photo-curable resin in SL process does not reflect the dynamic characteristics, and obvious predicting error will be introduced. In this paper, a solidification characteristics model of the photo-curable resin UV-2230, which describes the resin’s dynamic characteristics in solidifying process, is established with least square method in experiments. By using the model, critical exposure of the resin, penetration depth of the liquid resin and penetration depth of the solid resin are obtained. The research provides a base for improving the building accuracy for integral SL system.

Research of Matching Character of Light Source in Integral Stereolithography System with Photo-Curable Resin

In order to choose right photo-curable resin for integral stereolithography (SL) system, researches have been carried out to find the matching of light source of integral SL System and the photo-curable resin. Spectrum distribution of light source is investigated with raster spectrum meter. The research result shows that main light power of the light source distributes in the span of 400-650nm, and there is few light power distributing in other span. Absorption spectrum of several photo-curable resin is measured with grating spectrometer, and measure results indicates that sample 1 (ad2230) has good absorption in the span of 0-650nm, and the average absorption ratio is above 80%. Other resins (ad2210, jd01, jd02) have only good UV absorption, the average absorption ratio is almost 100% particularly under 300nm, and the absorption band is under 350nm. As a result, ad2230 is the right photo-curable resin for integral SL system, and three-dimensional parts are fabricated by the integral SL System with the resin (ad2230). The research results lay a foundation for building objects with photo-curable resin by using integral SL System.

Research of Deformation in Integral Stereolithography System

There is more reaction heat of layer curing during fabrication process, so the integral SL System has shrinkage deformation. To improve the building accuracy of integral SL System, the deformation of integral SL is analyzed, a little deflection temperature stress bending differential equation, which describe the relationship of deformation with other parameters in integral SL System, is established with elastic mechanics. The relationship of distortion deformation with layer thickness, contract rate of resin, temperature difference and locations is obtained through the equation. The deformation of a bridge model is simulated with ANSYS software in different building condition. In the simulation process, curing units are activated layer by layer with the method of elements birth and death. The simulation results are in good agreement with the equation. The research results lay a foundation for building high accuracy objects with integral SL System.