Our proposed mechanism has two main parts. First, it includes one link attached to the ground (foot) with a slider-crank that provides resistive feedback at an optimal position to prevent an excessive shank angle where the anterior knee exceeds the big toe (Figure 1). Second, it includes a set of linkages dedicated to provide visual feedback to the user when their anterior thigh is parallel to the ground.
As the person performing the motion progresses through the lunge, the link (c) attached to the shank will slide up and hit the optimal position; any motion forward following that will result in the spring deflecting, providing a resistance to the knee (making sure too much over flexion does not occur).
The kinematic challenges involved with our mechanism include:
1) Determining where the spring must be positioned to optimally provide resistive force against further motion such that the knee does not move past the user's big toe.
2) Determining the optimal linkage lengths for the
Figure 1: Kinematic analysis overview
To address the first kinematic challenge, the slider position can be calculated as a function of the ankle joint angle θ2 (Figure 2). The optimal angle θ2 can be determined by geometric positional analysis based on the user’s anthropometric data when the knee and big toe are in line. Using the vector loop method, we can then solve for θ4, the angle of the linkage arm attached to the slider, and b, the distance the slider must travel. These equations allow us to calculate how long our shank links to be and where the spring should be placed to hinder further motion.
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The second kinematic problem involves the slider moving above the thigh link. We must calculate the angle gamma such that a button (blue dot) is clicked when the thigh is parallel to the ground. This requires a more difficult kinematic analysis because the thigh mechanism is coupled to the shank link; it will involve determining relative positions between the thigh and shank linkages.
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