Architectural-Scale Artistic Brush Painting with a Hybrid Cable Robot

TL;DR

This work addresses the challenge of architectural-scale brush painting by integrating a four-cable planar CDPR with a 4-DoF serial arm to paint a large mural. The authors develop a software stack featuring iLQG-based CDPR control, a three-state arm controller with a stabilizing end-effector, and a two-stage proprioceptive-exteroceptive calibration framework that includes piecewise homography warping to align canvas sections. They validate the system experimentally through cable routing studies, a brush-stabilization assessment, calibration ablations, and a full mural execution, achieving significant reductions in trajectory error from initial proprioceptive-only calibration to piecewise-homography-guided control. The results demonstrate a practical, public-facing approach to immersive robot art, offering actionable hardware, control, and calibration strategies for architectural-scale robotic painting.

Abstract

Robot art presents an opportunity to both showcase and advance state-of-the-art robotics through the challenging task of creating art. Creating large-scale artworks in particular engages the public in a way that small-scale works cannot, and the distinct qualities of brush strokes contribute to an organic and human-like quality. Combining the large scale of murals with the strokes of the brush medium presents an especially impactful result, but also introduces unique challenges in maintaining precise, dextrous motion control of the brush across such a large workspace. In this work, we present the first robot to our knowledge that can paint architectural-scale murals with a brush. We create a hybrid robot consisting of a cable-driven parallel robot and 4 degree of freedom (DoF) serial manipulator to paint a 27m by 3.7m mural on windows spanning 2-stories of a building. We discuss our approach to achieving both the scale and accuracy required for brush-painting a mural through a combination of novel mechanical design elements, coordinated planning and control, and on-site calibration algorithms with experimental validations.

Figures (11)

• Figure 1: Polycentric Truthes [sic] is a 27m by 3.7m mural painted on the windows of the Price Gilbert Library in Atlanta for the Library's Artist-in-Residence program with an audience of thousands of visitors. The mural was designed by Tristan Al-Haddad and painted by our hybrid cable-driven robot over the course of 7 days across 3 weeks.
• Figure 2: Our 4-cable planar CDPR is 5.8m wide by 3.7m tall.
• Figure 3: The 4-cable planar CDPR uses platform-mounted pulleys on the top two cables to achieve a 2:1 mechanical force advantage. We perform an analysis showing we do not lose estimation accuracy with this approach compared to halving the winch radius.
• Figure 4: The serial manipulator is mounted on the CDPR's moving platform (Left) controlled by 4 cables routed through pulleys rigidly mounted to the window mullions with wooden clamps (Right).
• Figure 5: The brush stabilizer's self-centering mates are engaged when the brush is in the painting position.