# HKUST (Guangzhou) prints 1.6 μm gear clearances with 2 μm pixels in projection stereolithography

- Published: 2026-11-06 06:23 UTC
- Section: Machines & Making › Manufacturing
- Tags: projection stereolithography, sub-pixel resolution, grayscale mask compensation, segmented exposure, planetary gearset, alumina suspension, continuous 3D printing, Huachen Cui, HKUST Guangzhou
- URL: https://realtech.media/news/rt-b876d6f4b2bf5c05aff399fe_hkust_guangzhou_prints/

**Researchers modelled photopolymerization and adjusted exposure timing, printing gap features smaller than the projector pixel in resin and alumina–resin suspensions in a lab setting.**

![HKUST (Guangzhou) prints 1.6 μm gear clearances with 2 μm pixels in projection stereolithography](https://sgzwpqqelzmajkcubgkl.supabase.co/storage/v1/object/public/rt-media/2026/11/6d9d87e3b5cd5821.jpg)
*dw_ross from Springfield, VA, USA, Wikimedia Commons, CC BY 2.0*

A team led by Prof. Huachen Cui at the Hong Kong University of Science and Technology (Guangzhou) has reported a way to print features smaller than the projected pixel in projection stereolithography. The work was published on 15 September 2026 in the International Journal of Extreme Manufacturing. On a system with a native pixel pitch of 2 μm, the researchers printed a planetary gearset with a 50 μm gear module and a clearance of 1.6 μm, equal to 0.8 of the pixel pitch [1].

## Why the pixel limits resolution

In projection stereolithography, a digital mask projects cross-sections of a part into liquid photocurable resin. Light from each pixel follows a Gaussian profile rather than a sharp edge, so energy reaches regions meant to stay dark. Ceramic nanoparticles, added to give a part heat or wear resistance, scatter light sideways. Radicals formed by the light also diffuse across the liquid–solid boundary and cure unintended areas, which tends to fuse fine moving joints and narrow channels [1].

The authors built a reaction–diffusion–scattering model that predicts and visualizes the photopolymerization reaction with sub-pixel spatial resolution. It covers both photosensitive resin and resin–ceramic composites [1].

## Segmented exposure and grayscale compensation

Based on the model, the team combined grayscale mask compensation, which trims excess light at fine edges, with a segmented exposure strategy. The segmentation draws on the four-color map theorem: a single slice is split into sub-masks so that adjacent zones are never exposed together. Non-touching sections are exposed in turn, and, according to the authors, a quick recoating sweep of resin between exposures flushes drifting radicals away before they can bridge open gaps [1].

In a suspension with 40% alumina by volume, the method formed open fluid channels 27.2 μm wide on an optical system whose native pixel was 40 μm [1]. In a separate demonstration, the team achieved continuous printing on a standard top-down projection system under ambient conditions, by matching exposure rates to the continuous downward motion of the platform [1]. The paper names pillar bumps, gearsets and microfluidic channels as example structures [1].

The authors note the remaining limits: thicker, stacked ceramic parts, where accumulated light exposure is harder to balance, and micro-seams formed between segmented exposure zones. The team plans to adapt the exposure algorithms to a wider range of commercial resins and to integrate the controls into factory slicing software.

## Sources

1. [International Journal of Extreme Manufacturing](https://doi.org/10.1088/2631-7990/aea0b1)
2. [EurekAlert](https://www.eurekalert.org/news-releases/1150575)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-b876d6f4b2bf5c05aff399fe_hkust_guangzhou_prints/