Adaptive magnetorheological energy absorber control method for drop-induced shock mitigation

This paper presents a minimum duration deceleration exposure (MDDE) control method for drop-induced shock mitigation system using a magnetorheological energy absorber (MREA) at high sink rates. The key MDDE control goal is that the payload should come to rest after fully using the available MREA stroke, that is, to accomplish a soft landing, without exceeding the maximum allowable deceleration and simultaneously minimizing the duration of exposure to the maximum allowable deceleration. The MDDE control algorithm is developed as follows for a given available stroke. The payload deceleration is initially set to the maximum allowable value and held constant until the remaining damper stroke and payload velocity are such that the Bingham number control can be used for the terminal trajectory to ensure a soft landing. The sink rate range of the MDDE control is calculated and the results show that the MDDE control can be utilized at high sink rates, whereas prior Bingham number control can be used only at sufficiently low sink rates without violating the maximum allowable deceleration constraint. An optimal criterion to switch from the BN control method to MDDE control method is developed. Finally, the optimal control method is applied for a helicopter seat suspension system by optimal selection criterion to automatically accommodate varying sink rate (drop velocity) and occupant weight.