# An Approach to Improve the Resolution of DLP 3D Printing by Parallel Mechanism
## 4 Experiments and Discussion
### Small Feature Forming Contrast Experiment  
In order to test the feasibility of this printing scheme, we designed and printed the flowers with small cylindrical features called stamens. It can clearly illustrates our verification method. The model is shown in Figure 11a, and the printed models are shown in Figure 11b,d. The original dimensions of both models are the same, the difference is in how the features are molded. Specifically, Figure 11b adopts the common molding method, that is, parts and features are printed with fixed projection distance and fixed projection resolution. Figure 11d adopts the molding scheme proposed in the paper, that is, when printing features, the projection distance is shortened and a small format is used for printing. The original size of small features is designed to be 0.85 mm.  
Using an industrial microscope BC4800 (Bocheng Electronics, Dongguan, China) to photograph features and the results are shown in Figure 11c,e. The maximum diameter of the cylindrical feature was obtained using the measurement function in the microscope, and the results are shown in Table 5. We characterize the change in molding resolution by comparing the feature size under the two methods. The sizes of features 1-5 at a fixed resolution are 0.8689 mm, 0.8477 mm, 0.8543 mm, 0.8792 mm and 0.8278 mm, respectively,  
Figure 11: Features comparison test: (**a**) Test model: flowers with cylindrical small features (**b**) Test model printed at fixed resolution; (**c**) Small features printed at a fixed resolution, photographed with an industrial microscope; (**d**) Test model printed at adjustable resolution; (**e**) Small features printed with increased resolution during printing, photographed with an industrial microscope.  
where the RSE ranges from 0.51% to 3.41%. The sizes of features 1-5 using a small format molding are 0.6689 mm, 0.649 mm, 0.6495 mm, 0.6814 mm, and 0.6358 mm, respectively, and the respective sizes are reduced by about 1.3, 1.31, 1.31, 1.29, and 1.3 times. Overall, the size of the features printed in both ways is proportionally reduced. And the average size is 0.8556 mm and 0.6569 mm, which is about 1.3 times smaller. In addition, the features size printed in the small format are lower than 0.7 mm, which is not within the large format forming capability. Therefore, the features' resolution is improved by about 1.3 times.  
It can also be seen from Figure 11c,e that the position of the features modeled with adjusted resolution changes slightly compared to the features modeled with fixed resolution. The reason is believed to be that in the process of adjusting the resolution, due to the assembly and motion errors of the prototype, the position of the adjusted dynamic mask projected on the liquid surface is slightly misaligned. In addition, it is also an important research content to conduct analysis experiments on the strength and other mechanical properties of the parts. Articles [39; 40] provide valuable references for mechanical property analysis and experimental methods. However, in the current experiment, the proposed method is mainly verified from the perspective of size, and the analysis of mechanical properties such as the strength of the printed parts needs further research, which will be reported in future work.