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Thread: Clutch Mechanism for Ankle Exoskeleton

  1. #1
    Associate Engineer
    Join Date
    Jul 2022

    Clutch Mechanism for Ankle Exoskeleton

    I am designing a passive ankle exoskeleton with a spring in parallel with the calf ****** to provide a torque assist during walk. A clutch mechanism is needed to engage and disengage the spring during the different phases of gait, to be able to time the release of energy at the end of the stance phase and at the same time allow free rotation of the ankle during the swing phase (disengaged position).

    The mechanism is a two tier pawl (orange part) with a ratchet gear (blue part) with is attached to the foot plate (dark green part). An Engagement Arm (bright green part), when moved by two timing screws (represented by the 2 gray cylinders), pushes the pawl back to disengage the mechanism. The pawl is constantly pushed against the ratchet gear thanks to a spring.

    I'm struggling to keep the engagement arm up so that the mechanism stays in the disengaged position, allowing free rotation of the ankle, until the other timing screw pushes the Engagement Arm down.

    Should I modify the whole thing to place a detent pin? or is there a simpler solution?

    Thank you in advance for any help/insight.

    If any precision is needed, let me know.
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  2. #2
    Principle Engineer
    Join Date
    May 2015
    can you attach the cylinder/screws directly to the pawl thereby eliminating the engagement arm?

  3. #3
    Associate Engineer
    Join Date
    Jul 2022
    Sadly no, the bottom timing screw disengages the pawl, that needs to stay in this position until the Blue part (whose rotation is dictated by the ankle of the subject) goes into an enough counter-clockwise rotation so that the top timing screw (top gray cylinder) pushes down the engagement arm and thereby tuning into the engaged position (which allows a rotation of the blue part in one way but not the other)
    These timing screws are adapted differently to each participant since their ankle range of motion for dorsi and plantar flexion is different.

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