Phase variables are continuous real-valued functions which parameterize the gait cycle. As such, they can be used to estimate a powered prosthesis user's walking state. It is common to represent the phase variable as a function of the thigh angle. This approach assumes the thigh angle profile and its integral to be sinusoids. However, this assumption does not hold at lower walking speeds which leads to inaccurate heel-strike detection. In this study, we show that the thigh angle and its integral are phase-shifted from the ideal sinusoids by analyzing both able-bodied and amputee subject walking data. We then propose a novel phase variable incorporating phase-shift that is accurate even at lower walking speeds. We tested two variants of the proposed phase-shifted phase variable on a transfemoral prosthesis in an emulator study. Results show that phase-shifting improves heel-strike detection. Additionally, phase-shifting improves the linearity of the phase variable over the gait cycle. Analysis of the knee and ankle phase portraits showed that phase-shifting results in less deviations from the limit cycle.

中文翻译：

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基于相移的动力型股骨假体步态相位估计

相位变量是连续的实值函数，可对步态周期进行参数化。这样，它们可以用于估计动力假体使用者的行走状态。通常将相位变量表示为大腿角度的函数。该方法假定大腿角度轮廓及其积分为正弦曲线。但是，该假设在较低的步行速度下不成立，这会导致不正确的后跟打击检测。在这项研究中，我们通过分析身体健全和被截肢者的步行数据，表明大腿角度及其积分与理想正弦曲线相移。然后，我们提出了一种新的相位变量，该变量结合了相移，即使在较低的步行速度下也很精确。在仿真器研究中，我们在经股假体上测试了提出的相移相位变量的两个变体。结果表明，相移可改善后跟打击的检测。另外，相移改善了步态周期内相位变量的线性。对膝盖和脚踝相画像的分析表明，相移导致与极限循环的偏差较小。