Precision plasma sterilization system integrating machine vision and Z-axis closed-loop distance control

To mitigate active-species flux attenuation and localized treatment blind spots caused by variations in jet-to-surface distance during atmospheric-pressure low-temperature plasma treatment of three-dimensional nonplanar targets, we developed a precision plasma-treatment system integrating machine vision, field-programmable gate array-based trajectory planning, and Z-axis closed-loop laser distance control. The field-programmable gate array handled target-boundary extraction and scan-trajectory generation, while a tilted laser displacement sensor, a spatial geometric compensation model, and a segmented-velocity closed-loop strategy corrected Z-axis deviations in real time and maintained a 10 mm standoff distance. Static tests showed a Z-axis distance-control error of ±0.04 mm, and dynamic step-response tests converged within 500 ms. In a representative scan with repeated ±0.5 mm step disturbances, the measured standoff distance was 10.00 ± 0.18 mm, with an instantaneous range of 9.49–10.52 mm, and the system returned to within ±0.1 mm in approximately 400 ms after each disturbance. Starch-potassium iodide visualization indicated a distance-dependent spatial distribution of plasma-induced oxidative effects. In three independent biological replicates, Escherichia coli plate experiments showed pronounced distance-dependent attenuation in the conventional fixed-height mode, whereas Z-axis closed-loop scanning maintained 99.4%–100.0% sterilization efficiency across all tested regions and geometries. The corresponding log-reduction values, including detection-limit lower bounds for plates with no recovered colonies, were consistent with these results. These findings show that real-time standoff-distance compensation improves treatment uniformity on nonplanar model surfaces and supports the system as a precision plasma-treatment engineering platform for future plasma-medicine studies.