Hi there,
This is Bogdan from Romania.
I'm a mechanical engineer, specialized in the industrial robotics, 3D modeler and designer.
I have over 15 years work experience, designing, prototyping and launching different devices/systems across multiple industries.
I could help with your project.
1 - i will need some details: which is the initial opening of the balloon and how much do you expect to open?
2 - there are more dimensions?
3 - in order to achieve all your requirements, in the solution I am thinking (a kind of iris - like in the camera's objective) it will be necessary around 10-12 pieces
4 - is not possible that the opening to remain circular - who's telling you this is laying. because the circumference of the circle will vary, the ring should be split into several segments
5 - i will deliver you all the files required for manufacturing, several views, screen shots during designing process, 3d model and a simple animation of the device working
For any other questions, you may open a chat room here and we'll discuss about the details.
Regards
Bogdan