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Thread: Jamming Gripper

  1. #31
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    I see no inherent reason Van Rijn's simple idea of using elastic force won't work. My only addition is that this force would be best applied using elastic hoops and/or spring fingers around the "outside" of the gripper rather than throughout the entire gripper's surface.

    Sure, this means that there is no air pressure on the concave portion of the gripper to keep it pressed up against the coffee grinds. So what? The object itself provides the pressure to keep it pressed up against the coffee grinds. And that, ultimately is the point. In any case, there needs to be some excess force pressing the gripper surface against the object, or it can't grip.

  2. #32
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    Quote Originally Posted by IsaacKuo View Post
    I see no inherent reason Van Rijn's simple idea of using elastic force won't work. My only addition is that this force would be best applied using elastic hoops and/or spring fingers around the "outside" of the gripper rather than throughout the entire gripper's surface.
    How much gas does it take to fill a bladder in vacuum to a malleable shape not at the limits of maximum inflation shape while in a relaxed condition (not under tension)?

    Sure, this means that there is no air pressure on the concave portion of the gripper to keep it pressed up against the coffee grinds. So what? The object itself provides the pressure to keep it pressed up against the coffee grinds. And that, ultimately is the point. In any case, there needs to be some excess force pressing the gripper surface against the object, or it can't grip.
    Are you saying that the object (being gripped) exerts a negative pressure, pulling the bladder membrane against itself?

    In the Gripper in the video, ambient air pressure doesn't force the gripper onto the object, it forces the granular material inward against itself from all directions and that friction allows it to lock into a position. This is why coffee grounds in vacuum-pack bricks are so hard (the plastic-foil package is not using elasticity). And I think the thick bladder material's sticky and springy properties allows it to exert force against the object to maintain friction on it (with the packed and locked coffee grains not allowing it to loosen up). Even if gas pressure wasn't used, the act of pulling on the bladder would not pull inward but backward and away from the object surface, causing the part of the bladder that wrapped around something to peel back.

    It's the same mechanism that explains why a rubber surgical glove turns inside-out when pulled off. Now, it might be possible to use granular material to make the pull back stop and pull on what's inside it, but that's because it has a preformed concave cylindrical cavities used on conforming cylindrical shapes, which would be lacking on a spheroidal bladder meant for grabbing onto any shape.
    Et tu BAUT? Quantum mutatus ab illo.

  3. #33
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    Filling the bag with a liquid that freezes may work in certain situations--or would it?

  4. #34
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    Quote Originally Posted by publiusr View Post
    Filling the bag with a liquid that freezes may work in certain situations--or would it?
    Electrorheological fluid.

  5. #35
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    That's right... I was reminded of all the coffee grounds my Mom used to have me throw out in the yard over the years...

  6. #36
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    Quote Originally Posted by publiusr View Post
    Filling the bag with a liquid that freezes may work in certain situations--or would it?
    I dunno, it can get mighty warm in space and take some time/complexity to freeze something quickly enough to be useful for such an application.
    Et tu BAUT? Quantum mutatus ab illo.

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