Vacuum gripper does not work

By referring to the links above, we are implementing the suction function of the vacuum gripper. I tried to implement a vacuum gripper with one gripper link, but the vacuum force is too low, so they say that multiple grippers are used. So, I tried to pull the object using 10 grippers, but I confirmed that the plug-in was running, but the force did not work properly. I don’t know what could be causing this. I’ll attach the package file I’m working on, so can you take a look at where the problem is…?

The files I mainly work with in the link above are grippertest.urdf(gazebo).xacro , climbbot_grippertest.py , and test.launch files.