The <collision> do not work when I import STL file as link

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I am trying to simulate a forklift in gazebo. And I use a Fusion360 plugin to export URDF file and STL files as meshes. But when I want to use the fork to raise up some object, it does not work like the picture below. And I have added the <collision> tag.

Here is my description code: desvription And the controller code: controller

I can find where is the problem. So I was wondering is STL file doesn't support collision? Please help me :(