Aerosp Med Hum Perform. 2022 Aug 1;93(8):643-648. doi: 10.3357/AMHP.5961.2022.
Heel-lift is a subjectively reported fit issue in planetary spacesuit boot prototypes that has not yet been quantified. Inertial measurement units (IMUs) could quantify heel-lift but are susceptible to integration drift. This work evaluates the use of IMUs and drift-correction algorithms, such as zero-velocity (ZVUs) and zero-position updates (ZPUs), to quantify heel-lift during spacesuited gait. Data was originally collected by Fineman et al. in 2018 to assess lower body relative coordination in the spacesuit. IMUs were mounted on the spacesuit lower legs (SLLs) and spacesuit operator's shank as three operators walked on a level walkway in three spacesuit padding conditions. Discrete wavelet transforms were used to identify foot-flat phase and heel-off for each step. Differences in heel-off timepoints were calculated in each step as a potential indicator of heel-lift, with spacesuit-delayed heel-off suggesting heel-lift. Average drift rates were estimated prior to and after applying ZVUs and ZPUs. Heel-off timepoint differences showed instances of spacesuit-delayed heel-off and instances of operator-delayed heel-off. Drift rates after applying ZVUs and ZPUs suggested an upper time bound of 0.03 s past heel-off to measure heel-lift magnitude with an accuracy of 1 cm. Results suggest that IMUs may not be appropriate for quantifying the presence and magnitude of heel lift. Operator-delayed heel-off suggests that the SLL may be expanding prior to heel-off, creating a false vertical acceleration signal interpreted by this study to be spacesuit heel-off. Quantifying heel-off will therefore require improvements in IMU mounting to mitigate the effects of SLL, or alternative sensor technologies.
脚跟提升是行星航天服靴原型中一个主观报告的适配问题，尚未进行量化。惯性测量单元（IMU）可以量化脚跟提升，但容易受到积分漂移的影响。这项工作评估了使用 IMU 和漂移校正算法（如零速度（ZVU）和零位置更新（ZPU））来量化航天服步态中的脚跟提升。数据最初是由 Fineman 等人于 2018 年收集的，用于评估航天服中下肢的相对协调性。IMU 安装在航天服小腿（SLL）和航天服操作员的小腿上，三名操作员在三种航天服衬垫条件下在水平人行道上行走。离散小波变换用于识别每个步骤的足平相和脚跟离地。在每个步骤中计算脚跟离地时间点的差异，作为脚跟提升的潜在指标，航天服延迟脚跟离地表明脚跟提升。在应用 ZVU 和 ZPU 之前和之后估计平均漂移率。脚跟离地时间点的差异显示了航天服延迟脚跟离地和操作员延迟脚跟离地的实例。应用 ZVU 和 ZPU 后的漂移率表明，在测量脚跟提升幅度的准确性为 1 厘米的情况下，0.03 秒过去的脚跟离地时间点是一个上限。结果表明，IMU 可能不适合量化脚跟提升的存在和幅度。操作员延迟的脚跟离地表明，SLL 可能在脚跟离地之前扩张，从而产生了本研究解释为航天服脚跟离地的虚假垂直加速度信号。因此，要量化脚跟离地，需要改进 IMU 安装，以减轻 SLL 的影响，或采用替代传感器技术。
