Sensing Inside the Mill: A Mini-Review of Instrumented Balls for Monitoring and Analysis

Ball mills are energy-intensive units whose performance depends strongly on internal charge dynamics, which are difficult to observe directly. This mini-review analyzes the six studies on instrumented balls identified in our literature search, which was conducted without temporal restrictions. The six identified studies were published between 1978 and 2021. The reviewed works show an evolution from impact-force measurement devices to sensorized grinding media used for dynamic analysis, DEM validation, wet-grinding studies, and mill-load classification. The comparison highlights advances in sensing, mechanical design, data handling, and signal interpretation, while also identifying persistent barriers to industrial use, especially mechanical representativeness, durability, data retrieval, and reliable communication through the mill shell. Future opportunities include wear-state estimation, soft sensing of internal process variables, slurry chemistry sensing, and integration with monitoring and control systems. Overall, instrumented balls are promising tools for improving the understanding, modeling, and supervision of ball mill operation.