[Bug Report] Merge fixed joints parameters doesn't work

[gcfy63821]

[Bug]

Merge fixed joints parameters doesn't work

I am trying to convert URDF to USD by IsaacLab/script/tools/convert_urdf.py with the command:

python convert_urdf.py g1_29dof_rev_1_0.urdf g1 --merge-joints

in which g1_29dof_rev_1_0.urdf is from unitree ros

However, the converted USD is showed that some links like head_link,logo_link still exist which should be merge.

I think it is a problem with UrdfConvert because I also tried isaaclab.sim.UrdfFileCfg following BeyondMimic, in which merge_fixed_joints parameter doesn't work.

Steps to reproduce

You can just try with the command above and see the converted USD in IsaacSim GUI, then check whether there is some links like 'logo_link' which should be merged.

System Info

Describe the characteristic of your environment:

• Commit: [3c6e67b (HEAD -> release/2.3.0, tag: v2.3.0)]
• Isaac Sim Version: [5.1]
• OS: [Ubuntu 24.04]
• GPU: [RTX 5090]
• CUDA: [12.8]
• GPU Driver: [580.95.05]

Additional context

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Checklist

• I have checked that there is no similar issue in the repo (required)
• I have checked that the issue is not in running Isaac Sim itself and is related to the repo

Acceptance Criteria

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• With merged fixed joints, the number of body links should be 30 instead of 39 without merging fixed joints

[xiaohu-art]

The same issue here.

[fan-ziqi]

+1