How to Prevent My Articulation Joints from Bending Easily Under External Forces?

[strn18]

Hello,

I am trying to perform object grasping using a Shadow Hand.

However, I am facing the following issue: when the hand approaches the object, the fingers sometimes sweep across the object surface before achieving stable contact. During this process, the contact force from the object causes the finger joints to bend undesirably, as shown in the attached image.

To prevent this, I believe I need to make the finger joints more resistant to external forces.

For example, suppose currently a force of 10 can bend a joint by 5. What I would like is to configure the system so that it requires a force of 50 to bend the joint by the same amount. In other words, I want to increase the joint stiffness or resistance to external disturbance.

Is there a way to configure this in IsaacLab? For example, through joint stiffness, damping, drive strength, or other articulation parameters?

In my ArticulationCfg, I configured the actuators as follows:

actuators={
    "fingers": ImplicitActuatorCfg(
        joint_names_expr=["robot0_(FF|MF|RF|LF|TH)J(3|2|1)", "robot0_(LF|TH)J4", "robot0_THJ0"],
        effort_limit_sim={
            "robot0_(FF|MF|RF|LF)J1": 100,
            "robot0_FFJ(3|2)": 100,
            "robot0_MFJ(3|2)": 100,
            "robot0_RFJ(3|2)": 100,
            "robot0_LFJ(4|3|2)": 100,
            "robot0_THJ4": 100,
            "robot0_THJ3": 100,
            "robot0_THJ(2|1)": 100,
            "robot0_THJ0": 100,
        },
        stiffness={
            "robot0_(FF|MF|RF|LF|TH)J(3|2|1)": 1.0,
            "robot0_(LF|TH)J4": 1.0,
            "robot0_THJ0": 1.0,
        },
        damping={
            "robot0_(FF|MF|RF|LF|TH)J(3|2|1)": 0.2,
            "robot0_(LF|TH)J4": 0.2,
            "robot0_THJ0": 0.2,
        },
    ),
},

I tried to set the stiffness of a last fingertip joint, for example robot0_LFJ0, to 1.0. However, this caused an error.

It seems that LFJ0 is not directly actuated by the action space. Instead, it moves indirectly through a tendon mechanism when other joints (e.g., LFJ1) move. So I assume this is why I cannot configure stiffness/damping for that joint using ImplicitActuatorCfg.

Is this understanding correct? If so, what would be the proper way to make joints more resistant to external forces?

Thank you very much for your help.