Projection-based Stereolithography Research Articles

Combined 3D printing technologies and material for fabrication of tactile sensors

Recently, 3D printing technology has taken the spotlight internationally with the recognition of the importance of the manufacturing industry. Currently, there are many mature 3D printing processes and materials. However, an absence of fabrication capability of smart structures such as sensors and actuators remains. In this research, we present a hybrid manufacturing process including directprint/cure (DPC) and projection-based stereolithography, along with printable materials for stretchable tactile sensors. The suggested DPC system consists of a robotically controlled micro-dispensing head, and a light curing module combined with projection stereolithography (PSL) retrofitted from a commercial projector. The materials developed in this research are based on a photocurable and stretchable liquid resin filled with multi-walled carbon nanotubes (MWNTs); this polymer/nanocomposite exhibits the piezoresistive property used in tactile sensing. We also used another hybrid process to develop a tactile sensor using a commercial machine to build the sensor body while a dispensing system was used to create the sensing elements. We have characterized the fabricated sensors with several experiments to detect the locations where forces are applied to the surfaces of the sensors. It is concluded that the suggested processes and materials are promising in developing accurate and reliable stretchable tactile sensors.

Mask Image Planning for Deformation Control in Projection-Based Stereolithography Process

The mask-image-projection-based stereolithography process (MIP-SL) using a digital micromirror device (DMD) is an area-processing-based additive manufacturing (AM) process. In the MIP-SL process, a set of mask images are dynamically projected onto a resin surface to selectively cure liquid resin into layers of an object. Consequently, the MIP-SL process can be faster with a lower cost than the laser-based stereolithography apparatus (SLA) process. Currently an increasing number of companies are developing low-cost 3D printers based on the MIP-SL process. However, current commercially available MIP-SL systems are mostly based on Acrylate resins, which have larger shrinkages when compared to epoxy resins used in the laser-based SLA process. Consequently, controlling the shrinkage-related shape deformation in the MIP-SL process is challenging. In this research, we evaluate different mask image exposing strategies for building part layers and their effects on the deformation control in the MIP-SL process. Accordingly, a mask image planning method and related algorithms have been developed for a given computer-aided design (CAD) model. The planned mask images have been tested by using a commercial MIP-SL machine. The experimental results illustrate that our method can effectively reduce the deformation by as much as 32%. A discussion on the advantages and disadvantages of the mask image planning method and future research directions are also presented.

Scanning-projection based stereolithography: Method and structure

Projection-based stereolithography (PSL) is an efficient way for rapid fabrication of 3D structures. However, it is suitable for small parts requiring high resolution. The scanning-based SL (SSL) covers a larger area with a lower resolution. Fabrication time in PSL is intrinsically less than SSL due to exposing an entire image field in a single shot. This study introduces a new scanning-projection based stereolithography (SPSL) to include the advantages of both former methods. SPSL takes advantage of a digital micromirror device (DMD) and a moving stage to combine the projection and scanning methods. The DMD moves continuously over the medium while the projected pattern is continuously updated to allow the fabrication of large layers.After modeling the approach, an experimental setup is assembled to produce real parts. An economical ultra violet light-emitting diode (UV-LED) is used as a light source for curing. Seven 3D models with defined geometry consisted of circular, rectangular, complex and overhanging parts are selected. Five copies of each model are built. The experimental results show that the method is feasible and versatile. The achieved standard deviation is lower than 32μm.

규제액면기법의 전사방식 광조형 시스템을 위한 이형력 감소

Projection-based stereolithography is divided into constrained-surface and free-surface type according to controlling liquid layer. The constrained-surface type has a uniform layer thickness due to the use of a projection window, which covers the pattern generator such as liquid crystal display. However, the adhered resin on the projection window causes trouble and requires great separation force when the cured layer is separated from the window. To minimize the separation force, we developed a system to measure the separation force. The influence of material covering the pattern generator and the resin temperature is investigated in the system. Several structures according to the resin temperature and the velocity of z-axis elevation are compared. As a result, the fabrication condition to minimize the separation force reduces the process time.

A pixel based solidification model for projection based stereolithography technology

Projection-based stereolithography (pSL) is a powerful technique for fabricating three-dimensional (3-D) freeform structures. This study developed a new pixel-based solidification model for pSL to predict the patterning results. pSL technology makes it possible to create a two-dimensional (2-D) pattern in a single exposure, using a dynamic mask capable of generating 2-D images with micro-resolution. Then, a 3-D structure can be fabricated by stacking the 2-D patterns. Therefore, pixel-based modeling is crucial for predicting the patterning results because the pixel is the fundamental component of the illuminated 2-D images in the patterning process. This study constructed a mathematical model to describe the intensity distribution of an illuminated image. The model was used to predict solidified shapes by calculating the exposure energy and compared with patterning results. The findings showed that our model is quite useful for estimating fabrication results obtained using pSL technology.