Calibration in 2 m membranes informed a 5 m-span sprayed prototype. Process videos and substrate comparisons also document sagging, overspray, and access limits. View evidence ↓
Inside-out robotic spraying (left) and the illuminated enclosure (right). Variations in internal coating thickness change light transmission through the smooth outer membrane.
Projected deposition at 5 m span
The 5 m-span prototype transferred the calibration and sequencing approach to a membrane that the arm could not surface-follow. In many regions, polyurethane traveled more than 2 m before reaching the membrane. Nozzle direction and robot speed shaped the impact zone; membrane curvature, surface condition, and reaction state influenced how the material accumulated.
Overspray created secondary deposits, wet-material accumulation caused local sagging, and hose drag constrained wrist motion. Operators adjusted nozzle direction, dwell time, and band sequence as membrane deformation and curing conditions changed. The prototype demonstrates architectural-scale deposition from a compact internal robot and identifies projection control, band overlap, and hose management as requirements for a more repeatable process.
Robot placement and access constraints in the 5 m enclosure (left); inspection of deposited bands during an early spraying test (right).
Minimum Device, Maximum Space investigates how a compact fabrication device can materialize an architectural enclosure larger than its reach. Inflation establishes the volume, projected polyurethane bridges the distance between nozzle and membrane, and staged curing converts the deposited material into a stiffened coating.
Inflation defines the fabrication volume
The inflated PVC membrane establishes the enclosure’s geometry before rigid material is added. A compact arm positioned inside directs a polyurethane jet across the interior air volume. The membrane receives and temporarily supports the wet material as it foams, adheres, and cures. Fabrication access therefore depends on robot posture, nozzle orientation, projection distance, and the membrane’s ability to retain the deposit.
Calibrating reach and material retention
Tests in 2 m spherical membranes established the relationship between nozzle clearance and deposited band width. Six standoff settings from 20–70 cm produced paths approximately 12–24 cm wide, providing a basis for planning coverage and overlap. Substrate trials compared PVC, Oxford cloth, and carbon-fiber membrane. The documented Oxford-cloth test showed dripping and gaps between passes; textured PVC retained wet polyurethane more effectively and supported a more continuous coating. These tests connected usable spray reach to both geometry and receiving-surface behavior.
Small-membrane reach calibration (left); deposited PU on Oxford cloth and PVC (right). Nozzle distance and substrate retention informed the larger prototype.
Curing time organizes the sequence
Spraying began near the lower perimeter and progressed upward in staged bands. Lower regions gained stiffness before subsequent passes added material above them, while the crown avoided early accumulation of wet polyurethane. The sequence coordinated deposition with foaming, adhesion, and curing to limit sagging of the compliant membrane.
Related publications
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Project manuscript
Minimum Device, Maximum Space: Reach-Aware Robotic Spray Fabrication of Inflatable Architectural Enclosures
