This brief presents a novel control strategy for a powered prosthetic ankle based on a biomimetic virtual constraint. We first derive a kinematic constraint for the “effective shape” of the human ankle-foot complex during locomotion. This shape characterizes ankle motion as a function of the center of pressure (COP)-the point on the foot sole where the resultant ground reaction force is imparted. Since the COP moves monotonically from heel to toe during steady walking, we adopt the COP as a mechanical representation of the gait cycle phase in an autonomous feedback controller. We show that our kinematic constraint can be enforced as a virtual constraint by an output linearizing controller that uses only feedback available to sensors onboard a prosthetic leg. Using simulations of a passive walking model with feet, we show that this novel controller enforces exactly the desired effective shape, whereas a standard impedance (i.e., proportional-derivative) controller cannot. This brief provides a single, biomimetic control law for the entire single-support period during robot-assisted locomotion.

中文翻译：

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走向假肢动力假肢虚拟约束控制

本简介介绍了一种基于仿生虚拟约束的动力假肢踝关节的新型控制策略。我们首先得出运动过程中人类踝足复合体“有效形状”的运动学约束。这种形状将脚踝运动表征为压力中心（COP）的函数-脚底上施加合成地面反作用力的点。由于COP在稳定的步行过程中从脚后跟到脚趾单调移动，因此我们将COP用作自主反馈控制器中步态周期阶段的机械表示。我们表明，运动线性约束可以通过输出线性化控制器强制执行为虚拟约束，该输出线性化控制器仅使用对假肢上的传感器可用的反馈。使用带脚的被动行走模型的模拟，我们表明，这种新颖的控制器可以精确地实现所需的有效形状，而标准阻抗（即比例微分）控制器则不能。该摘要为机器人辅助运动期间的整个单支撑周期提供了一个单一的仿生控制律。