Gripper modeling

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This topic contains 5 replies, has 4 voices, and was last updated by eme eme 2 months, 3 weeks ago.

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  • #6807

    lalaland
    Participant

    We are trying to model a gripper that we found from grabcad based on a gripper that is already in the models in visual components in terms of linking and movement of different parts. (The image of the gripper as well as its disclosed version is attached to the post )

    We tried copying some of the behaviours and linking relations from an already existing gripper but it did not work out the way we planned. The joints do not rotate sensibly we need any help we can get.

    Thank you in advance.

     

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    #6812
    zesty
    zesty
    Moderator

    Where are the pivot points? Also, do you understand the expressions for the joints in the component? Sometimes it is easier to focus on one jaw, make it work, and then make the other jaw a “follower” of its counter-part’s joint.

    Someone should definitely be able to help you, my friend.

    #6822
    eme
    eme
    Participant

    You can model those kinematics with the trigonometric helper functions in the expression language. Commonly referred as sasa-functions. It gets a bit tricky as you need to measure the current state of the mechanism after import and take those angles and link lengths into account. However it is quite straight forward, but it is not super easy or fast on the first try. That’s why we are working on an addon that would do the math automatically for you, but it is not quite ready yet and I noticed the current addon wouldn’t support the structure you are referring to. Need to add it in the addon.

    Anyways, this is how you can solve that one.

    I modeled dummy shapes to represent similar kinematics. Find the model attached. Here’s a picture showing the key elements in the mechanism. We want to drive the angle “a” which will be driven by the joint “J1”. Go to reference doc and find sasasa functions for quadrilaterals. Help > Reference Guide > Expressions > Functions

     

    basically d we can calculate with sasssa1(B,a,A,D,C) but we need to take into account that the sasas use radians instead of degrees and we need to take into account the angles the mechanism is after cad importing. So e.g. “a” in the mechanism in the sate shown in the picture is 87.3 even though the joint J1 in that state is at zero. After taking those into account we can calc the d and c like this:

    d = degree(sasssa1(115, radian(-J3+87.3), 29.55, 100, 43.5))-99.2

    c = degree(sasssa2(115, radian(-J3+87.3), 29.55, 100, 43.5))-102.6

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    #6828

    lalaland
    Participant

    Hi,

    First off, thank you very much for your explanation.  We tried to do everything that you explained and failed miserably.

    If you ever have the time and resources could you possibly give it a try? It would mean so much to us as we have been working on it for days now. We attached the document in vcmx format.

    Thank you again for your help.

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    #6877

    JobW
    Participant

    Gripper #2

    link to a follow-up thread.

     

    #6894
    eme
    eme
    Participant

    Sorry for the over engineering. The kinematics of your model was a lot simpler than what I described. When those links on the opposing sides of the rectangle are same lengths, it makes it a lot simpler. That also forces the pads to be parallel to each other at all joint values.

    Sorry for the confusion. Maybe that solution for the complex quadrilateral comes handy some day later.

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