Adaptive Closed-Loop Micro-Dosing Handwashing System: Minimizing Cleansing-Agent Consumption via Spatial Sensing and Dynamic Feedback

Conventional automatic soap dispensers operate open-loop: they release a fixed, pre-calibratedvolume irrespective of hand size, position or the coverage actually achieved. The result is avoidable soapwaste and a heavier surfactant load on wastewater systems. This paper presents an Adaptive Closed-LoopMicro-Dosing Handwashing System built on a six-stage pipeline: Sense → Estimate → Dose → Wash →Verify → Correct. Time-of-flight (ToF) sensing and a 12-zone micro-nozzle matrix estimate hand area anddirect soap only to occupied zones. After a standardized rubbing phase, UV-A imaging of a fluorescentsurrogate measures liquid coverage, and micro-corrective doses are applied solely to deficient regions. In aprototype evaluation of five operating modes (50 trials, 10 participants), the closed-loop mode consumed 0.72mL of soap per wash against 1.25 mL for a fixed-dose dispenser, a 42.4% reduction. Mean measured coveragerose from 91.2% to 96.4%, and the share of trials reaching C ≥ 95% increased from 62% to 98%.