Passive Joint Problem

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Dear all, I want to simulate the passive joint(sping-damper) using in my model. But what i found in the joint setting is just <damping> tag, without stiffness tag as expected. Any suggest to that idea? Thank so much!

Here my joint:

<joint type='revolute' name='Joint'>
 <pose>0 0.0 0.0 0 0.0 0</pose>
 <child>LowerSg</child>
 <parent>UpperSg</parent>
 <axis>
  <xyz>0 1 0</xyz>
      <dynamics>
       <damping>0.0000</damping>
       <friction>0.0000</friction>
      </dynamics>
 </axis>
</joint>