A Coal Loading Height Monitoring and Blockage Warning Method for Scraper Conveyors Based on Multi-Point State and Time Confirmation

INTRODUCTION: Accurate monitoring of coal loading height in scraper conveyors is important for maintaining continuous and safe operation in fully mechanized mining faces. In practical underground operation, a short-time rise in coal height may be caused by vibration, coal impact, or equipment passage, whereas continuous accumulation at adjacent positions may develop into blockage. Conventional fixed monitoring devices are easily affected by shearer passage, large coal impacts, and repeated mechanical disturbance. Meanwhile, warning methods based on single-point instantaneous thresholds may produce false alarms or missed alarms, which reduces the reliability of scraper conveyor monitoring. OBJECTIVES: To improve monitoring stability and blockage warning reliability, this study proposes a coal loading height monitoring and blockage warning method for scraper conveyors based on multi-point state and time confirmation. METHODS: An adjustable contact-type monitoring device was developed by combining a self-adaptive rotating mechanism with a quick-positioning detachable base. The device can yield under external mechanical interference and return to the preset monitoring position after the disturbance is removed. Each monitoring node converts the contact state caused by over-limit coal accumulation into a binary switching signal for PLC acquisition. Instead of using a single instantaneous signal as the warning condition, the PLC evaluates whether abnormal states appear in adjacent monitoring nodes and whether these states remain for a preset confirmation time. Isolated or short-duration abnormal signals are treated as possible interference, while continuous abnormal states in adjacent nodes are identified as potential blockage. A laboratory-scale scraper conveyor test platform was constructed to evaluate the monitoring response and warning performance of the proposed method. RESULTS: Experimental results showed that the proposed system could distinguish normal, critical, and excessive coal loading states under the tested laboratory conditions. The response time for over-limit coal accumulation was less than 0.5 s. The observed false alarm rate and missed alarm rate were 1.22% and 0.82%, respectively. The adaptive monitoring structure reduces mechanical interference during the equipment's operation and still has the ability to recover after being disturbed. Compared with the traditional single-point threshold strategy, the multi-point state and time confirmation logic proposed in this paper reduces the unstable warning outputs caused by instantaneous impacts and local fluctuations. CONCLUSION: The proposed method provides a laboratory-scale proof of concept for coal loading height monitoring and blockage warning in scraper conveyors. Under the tested conditions, the combination of adaptive contact sensing, spatial consistency assessment, and temporal persistence confirmation reduced unstable warning outputs caused by isolated and short-duration disturbances. The mechanical sensing device is specifically designed for scraper conveyors, whereas the associated decision logic can be interpreted as a potentially transferable spatio-temporal robust event detection pattern. Nevertheless, the 1:2-scale platform did not reproduce full-scale underground vibration spectra, long-term coal-dust deposition, electromagnetic interference, or mechanical degradation. Therefore, the reported response time, false alarm rate, and missed alarm rate should not be generalized to field operation until full-scale underground validation has been completed.