How could I create a Flat Pack Box using 4 Revolute Joints?

[JohnJoeKelly]

Hi,

I am a student who is doing a final year project.
I have attached a screenshot of the scene where I tried creating a box:



There are no imported meshes in the box components.

I am using the box in a simulation where I grab the box at the edges with the larger diameter revolute joints using a 3 finger gripper attached to an LBR iiwa 14.
I then move this box linear until it meets an L-angle piece upon which I then press the box against said L-angle (which is at an angle of 45 degrees to the box) so that it will pop open at joints "InnerJoint(1_2)" and "InnerJoint(3_4)".

I am currently simulating the box in the scene using 2 linked dummies ("Dummy3" and "Dummy4") with a link type of Dynamics, overlap constraint between Cuboids 3 and 4. However, this linkage does not hold well when the box is pressed against the L-angle in comparison with the other 3 corners which are revolute joints.

I have a limited knowledge of the software so my question would be is there a method (or is it possible) to incorporate ""InnerJoint(3_4)" within the "Cuboid1" hierarchy so that I can join "Cuboid3" and "Cuboid4" with a revolute joint as I have done so in the other 3 corner cases?

Here is a screenshot of the box open against the L-angle with the linked dummies not aligned:


Any help on the matter is greatly appreciated!

[coppelia]

Hello John,

if I understood your explanations correctly, you are trying to model a cardboard box that you can pop open by squeezing it? i.e. from a flat configuration to a squared configuration?

If this is the case, then you are missing one joint: you have 4 edges that can fold/unfold. Two linked dummies with the overlap constraint are only needed for loop closing, but they do not introduce a degree of freedom. So I would add another joint right after Cuboid3:

Cuboid3 --> joint --> Dummy3

The position of that joint should be on the edge where the two dummies are. The point is that two overlapping dummies should ideally always stay overlapped for a perfect loop closure. But with 3 joints this is not possible.

Cheers

[JohnJoeKelly]

Hi there,

Yes, you understood it correctly!

I see what you mean about the degree of freedom being missing when only using the linked dummies.
I have inserted the joint into the box as you suggested after Cuboid3 and it is working very well now!

Thank you very much for your help, it is much appreciated!!

Kind regards,
John Joe