Predictive Energy Stability Margin: Prediction of Heavy Machine Overturning Considering Rotation and Translation

Fatal accidents caused by the overturning of heavy machines still happen, so the prediction and prevention of overturns are urgently needed. Indicators to evaluate overturn, such as the energy stability margin (ESM), have been proposed but are limited to a non-slip ground surface. Even if ESM is above zero, the machine may overturn due to additional manipulator operation or hitting an obstacle while sliding down a slope. This study thus proposes a predictive energy stability margin, ${\bm{p}}$-ESM, that focuses on kinetic energy in the translational and rotational directions for overturn prediction. Rotational kinetic energy ${{{\bm{E}}}_{\bm{R}}}$ accelerates overturning, and the translational kinetic energy ${{{\bm{E}}}_{\bm{T}}}$ in the slope direction is converted to ${{{\bm{E}}}_{\bm{R}}}$. Both are calculated from the mass and the position and acceleration of the center of gravity (COG) for each part of the machine. ESM ${\bm{U}}$ is defined as the difference between the height of COG just before overturn and the current height of the COG. Thus, ${\bm{p}}$-ESM is defined as ${\bm{U}}$ minus the sum of ${{{\bm{E}}}_{\bm{R}}}$ and ${{{\bm{E}}}_{\bm{T}}}$. We also developed an operation support system to limit the manipulator operation by using ${\bm{p}}$-ESM. The results of experiments using a hydraulically driven scale model (1/14) with different combinations of operations, loading weights, and ground surfaces confirmed that ${\bm{p}}$-ESM can predict overturns early and accurately, which conventional ESM cannot do. We also found that the support system using ${\bm{p}}$-ESM can prevent inappropriate operations and avoid overturns.