How to interprete urdf file to deformable object

Omniverse Isaac Sim
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How to interprete urdf file to deformable object in Isaac Lab

I’m trying to use my own urdf file to create a deformable object in Isaac Lab.
My URDF file is defined as:

<?xml version="1.0" encoding="utf-8"?>    
    
    <robot name="box_0">
        <link name="box_0">    
            <fem>
                <origin rpy="0.0 0.0 0.0" xyz="0 0 0" />
                <density value="100" />
                <youngs value="1005"/>
                <poissons value="0.3"/>
                <damping value="0.0" /> 
                <attachDistance value="0.0"/>
                <tetmesh filename="../../meshes/multi_box_1kPa/box_0.tet"/>
                <scale value="1.0"/>
            </fem>
        </link>
    </robot>

I used convert_urdf.py --make-instanceable to convert the urdf file to USD file.
I also tried convert_mesh.py --make-instanceable --collision-approximation convexDecomposition --mass 1.0.

Then I initialize the deformable object by

deformable = DeformableObjectCfg(
        prim_path="{ENV_REGEX_NS}/Deformable",
        spawn=sim_utils.UsdFileCfg(
            usd_path=box_usd,
        ),
        init_state=DeformableObjectCfg.InitialStateCfg(pos=(0.0, 0.5, 1.0)),
    )

The tutorial and demo provided in the documentation are all use MeshCfgto generate deformable object, which can specify the deformable parameters inside

deformable_props=sim_utils.DeformableBodyPropertiesCfg(rest_offset=0.0, contact_offset=0.0),
visual_material=sim_utils.PreviewSurfaceCfg(diffuse_color=(0.5, 0.1, 0.0)),
physics_material=sim_utils.DeformableBodyMaterialCfg(density=100, poissons_ratio=0.3, youngs_modulus=1005),

Thus I can not successfully create the deformable object
RuntimeError: Failed to find a deformable body when resolving '/World/envs/env_.*/Deformable'. Please ensure that the prim has 'PhysxSchema.PhysxDeformableBodyAPI' applied.

So what is the correct way to generate deformable objects using urdf/mesh file? Is my urdf file wrong?

3

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