Our proposed mechanism has one link attached to the ground (foot) with a slider-crank that provides resistive feedback to prevent an excessive shank angle and a set of linkages dedicated to provide visual feedback to the user when their thigh is parallel to the ground. , one on the knee and the other on the thigh. As the person performing the motion progresses through the exercise the link attached to the will slide up and eventually 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). There may be further updates to our design which configure the device in a brace mechanism reducing the need to limit the locomotion of object. Additionally, another key part of the exercise stems from upward and downward motion of the torso once the optimal position is met, therefore we are working to create a mechanism which allows the user to be notified on the thigh when they have reached the bottom of their motion.
The kinematic challenges involved with our mechanism include:
1) Determining where the spring must be positioned to provide the 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
For the slider crank mechanism attached to the shank, the slider position p can be calculated as a function of the ankle joint angle θ. First, the ankle joint angle of the optimal posture θopt will be acquired by geometric positional analysis based on the user’s anthropometric data when the knee and toe are in line (Figure 4 (b)). Since the position of the slider p must be calculated as a function of the ankle joint angle θ, the slider position of the optimal posture popt will be calculated from the determined ankle joint angle θopt. In the same manner, pmin and pmax will determine what to set as the travel distance (dtravel ), the safe range of motion to minimize risk of injury. However, popt and dtravel are different between individuals since θopt varies depending on the user’s body segment length. Since differences in popt and dtravel vary between individuals, device calibration is necessary before using such as changing spring position and the range of motion. Changing spring position is not just the stretch distance of the spring. Changing spring position means adjusting the threshold and changing the range of motion adjusting physical restriction of back and forth motion at knee motion. The ideal design would account for the spring length to not change. To avoid potential additional adjustments for different sized bodies, popt and dtravel will require additional positional analysis based off different shank length to foot ratios to investigate whether the travel distance changes drastically between different sized people. If the optimal position and travel distance varies a negligible amount, then a fixed universal spring placement and range of motion will be calculated to give any user some flexibility in motion. If the optimal angle varies a non-negligible amount, then more detailed positional analysis is required to calibrate device.
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.
Figure 1: Kinematic analysis overview
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