05-23-1984: Yoji Marutani filed a patent application for the "optical forming method"
This was yet another version of stereolithography
On May 23, 1984 Japanese Yoji Marutani from the Osaka Prefectural Industrial Research Institute (OPIRI) developed and demonstrated his own stereolithography process. His patent document titled "Optical Forming Method" (JPS60247515A) details many of the key elements of stereolithography such as using a photocurable liquid material, focusing rays of light onto the surface of the liquid resin, and applying a fresh layer of material on top of the cured layer.
This is an interesting event because it is three months ahead of the submission of a patent application by Charles Hull, considered the creator of stereolithography and 3D printing in general.
It is unclear whether Marutani's work was related to the work of Hideo Kodama, who first developed the foundations of stereolithography technology in 1980, although it can be assumed that he studied Kodama's patent application and technical documents from October 1980 and November 1981. Doubtful is instead that Marutani knew about the work Charles Hull and Alan Herbert were carrying out at the same time.
Marutani continued to research the development of stereolithography until at least mid-1987. In an article dated August 7, 1987, Takashi Nakai and Yoji Marutani announced that they had developed a new type of system for producing three-dimensional objects using a UV laser and liquid polymer. However, instead of describing the development of a new type of system, the article focused on improvements to already known processes that increased speed and dimensional accuracy.